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CONTENTS

Preface

1.AUTOMATIONIntroductionDefinitionofAutomationMechanizationvsAutomationAdvantagesofAutomationGoalsofAutomationSocialIssuesofAutomationLowCostAutomationTypesofAutomationCurrentEmphasisinAutomationReasonsforAutomationReasonsforNoAutomationIssuesforAutomationinFactoryOperationsStrategiesforAutomationExercises

2.BASICLAWSANDPRINCIPLESFluidPropertiesExercises

3.BASICPNEUMATICANDHYDRAULICSYSTEMSIntroductiontoFluidPowerBasicElementsofFluidPowerSystemAdvantagesandDisadvantagesofFluidPowerApplicationsofFluidPowerPneumaticsvs.HydraulicsAdvantagesandDisadvantagesofPneumaticsAdvantagesandDisadvantagesofHydraulics

ApplicationsofPneumaticsApplicationsofHydraulicsBasicPneumaticSystemBasicHydraulicSystemHydraulicSystemDesignFluidsUsedinHydraulicsExercises

4.PUMPSANDCOMPRESSORSIntroductionPumpsvs.CompressorsPositiveDisplacementvs.NonPositiveDisplacementDevicesClassificationofHydraulicPumpsPositiveDisplacementPumpsRotaryPumpsReciprocatingPumpsMeteringPumpDynamic/NonPositiveDisplacementPumpsCentrifugalPumpsPumpSelectionParametersComparisonofPositiveandNonPositiveDisplacementPumpsAirCompressorsTypesofAirCompressorsPositiveDisplacementCompressorsRotaryCompressorsReciprocatingCompressorsPistonCompressorsDiaphragmCompressorDynamicCompressorsComparisonofDifferentCompressorsSpecificationsofCompressorsExercises

5.FLUIDACCESSORIESIntroductionAirReceiverAftercooler

AirDryerAirFilterPressureRegulatorAirLubricatorAirServiceUnit(F.R.L.)PipelineLayoutSealsHydraulicFluidsHydraulicReservoirHydraulicFilterPressureGaugesandVolumeMetersHydraulicAccumulatorIntensifierLinesFittingsandConnectorsHydraulicSealsExercises

6.CYLINDERSANDMOTORSIntroductionCylindersClassificationofCylindersClassificationofCylindersontheBasisofConstructionSingle-ActingCylinderDouble-ActingCylinderTypesofSingle-ActingCylindersTypesofDouble-ActingCylindersOtherTypesofCylindersClassificationofCylindersontheBasisofWorkingMediumHydraulicCylindersPneumaticCylindersApplicationsofCylindersCylinderCushioningCylinderMountingsCylinderSizingCylinderSpecificationIntroductiontoMotorsMotorRatings

HydraulicandPneumaticMotorsSymbolofMotorsClassificationofFluidMotorsGearMotorsVaneMotorsPistonMotorsApplicationofMotorsExercises

7.CONTROLVALVESIntroductionClassificationofValvesDirectionControlValvesSymbolandDesignationofDirectionControl(DC)ValveClassificationofDCValvesClassificationofDCValvesontheBasisofMethodsofValveActuationSymbolsforValveActuatorsExamplesofDCValvesWithActuatorsClassificationofDCValvesontheBasisofConstruction2/2DCValves3/2DCValves4/2DCValvesCenterConditionsin4WayDCValvesCheckValvePilotOperatedCheckValvePressureControlValvesPressureReliefValvePressureReducingValveSequenceValveCounterbalanceValveFlowControlValvesNonReturnFlowControlValveQuickExhaustValveTimeDelayValve/AirTimerPneumaticLogicValvesTwinPressureValveShuttleValveServoValves

TorqueMotorandArmatureAssemblyClassificationofServoValvesSingle-StageServoValveMultistageServoValveServoSystemExampleofaServoControlSystemHydraulicandPneumaticSymbolsExercises

8.CIRCUITSIntroductionBuildinguptheCircuitDiagramDesignationofComponentsinaCircuitDiagramPneumaticCircuitsPneumaticCircuitforControlofSingle-ActingCylinderPneumaticCircuitforControlofDouble-ActingCylinderApplicationof2/2and3/2DCValvesCircuitwithMechanicalFeedbackSpeedControlCircuitsUseofFlowControlValvetoControlSingle-ActingCylinderUseofQuickExhaustValveinPneumaticCircuitsTimeDelayCircuitCircuitswithNecessaryConditionsApplicationoftheTwinPressureValveApplicationoftheShuttleValveHydraulicCircuitsHydraulicCircuitforControlofSingle-ActingCylinderHydraulicCircuitforControlofDouble-ActingCylinderCircuitsUsing3PositionValvesSpeedControlinHydraulicCircuitsBleedoffCircuitRegenerativeCircuitCircuitShowingApplicationofCounterBalanceValveSequencingCircuitPressureReductionCircuitProblemsinCircuitDesignExercises

9.PNEUMATICLOGICCIRCUITSIntroductionControlSystemOpenLoopControlSystemClosedLoopControlSystemCircuitDesignMethodsMotionSequenceRepresentationMotionDiagramsControlDiagramCascadeDesignStepsInvolvedinCascadeDesignSignConventionsSequencingExamplesExercises

10.FLUIDICSIntroductionBooleanAlgebraLawsofBooleanAlgebraTruthTableLogicGatesOriginandDevelopmentofFluidicsCoanda’sEffectTesla’sValvularConduitFluidicDevicesFluidicLogicDevicesFluidicSensorsFluidicAmplifierAdvantagesandDisadvantagesofFluidicsExercises

11.ELECTRICALANDELECTRONICCONTROLSIntroductiontoSensorsandTransducersSensorTerminologySelectionofaTransducerClassificationofSensors

ClassificationofTransducersTemperatureSensorsLightSensorsPositionSensorsPiezoelectricSensorsPressureSensorsStrainGaugesMicroprocessorMicrocontrollerProgrammableLogicController(PLC)Exercises

12.TRANSFERDEVICESANDFEEDERSIntroductionFundamentalsofProductionLinesTypesofAssemblyLinesReasonsforUsingAutomatedAssemblyLinesTransferSystemsinAssemblyLinesAutomaticMachinesTransferDevices/MachinesSelectionofTransferDevicesTransferMechanisminTransferDevicesLinearTransferMechanismRotaryTransferMechanismClassificationofTransferDevicesAdvantagesandDisadvantagesofTransferMachinesConveyorSystemsUsedinTransferDevicesFeedersClassificationofFeedersCriteriaforFeederSelectionPartsFeedingDevicesTypesofFeedersApronFeedersReciprocatingFeeders(PlateFeeders)Reciprocating-TubeHopperFeederReciprocatingPlateFeederVibratoryBowlFeederScrewFeeders

BeltFeedersRotaryPlowFeedersRotaryTableFeedersCentrifugalHopperFeederCenterboardHopperFeederFlexibleFeedersExercises

13.ROBOTICSIntroductionHistoryofRobotsDefinitionofaRobotIndustrialRobotLawsofRoboticsMotivatingFactorsAdvantagesandDisadvantagesofRobotsCharacteristicsofanIndustrialRobotComponentsofanIndustrialRobotComparisonoftheHumanandRobotManipulatorRobotWristandEndofArmToolsRobotTerminologyRoboticJointsClassificationofRobotsRobotClassificationontheBasisofCo-OrdinateSystemsRobotClassificationontheBasisofPowerSourceRobotClassificationontheBasisofMethodofControlRobotClassificationontheBasisofProgrammingMethodRobotSelectionRobotWorkcellMachineVisionRoboticsandMachineVisionRoboticAccidentsRoboticsandSafetyRobotsMaintenanceRobotsInstallationExercises

14.ROBOTICSENSORS

IntroductionTypesofSensorsinRobotsExteroceptorsorExternalSensorsTactileSensorsProximitySensors(PositionSensors)RangeSensorsMachineVisionSensorsVelocitySensorsProprioceptorsorInternalSensorsRobotwithSensorsExercises

15.ROBOTENDEFFECTORSIntroductionEndEffectorClassificationofEndEffectorsGrippersSelectionofGripperGrippingMechanismsToolsTypesofToolsCharacteristicsofEnd-of-ArmToolingElementsofEnd-of-ArmToolingTypesofGrippersFingerGrippersMechanicalGrippersVacuum/SuctionGrippersMagneticGrippersExercises

16.ROBOTPROGRAMMINGIntroductionRobotProgrammingRobotProgrammingTechniquesOnlineProgrammingLead-ThroughProgrammingWalk-ThroughProgrammingorTeaching

OfflineProgrammingTaskLevelProgrammingMotionProgrammingOverviewofRobotProgrammingLanguagesRequirementsforaStandardRobotLanguageRobotLanguagesTypesofRobotLanguagesExampleofaRobotProgramUsingVALReviewExercises

17.APPLICATIONSOFROBOTSIntroductionRobotCapabilitiesApplicationsofRobotsManufacturingApplicationsMaterialHandlingApplicationsCleanroomRobotsExercises

18.ROBOTSUSINGREAL-TIMEEMBEDDEDSYSTEMSIntroductiontoRobotsUsingReal-TimeEmbeddedSystemsRoboticArmActuationEndEffectorPathSensingTaskingAutomationandAutonomyExercises

INDEX

PREFACE

The purpose of this book is to present an introduction to themultidisciplinary field of automation and robotics for industrialapplications.Thebookinitiallycoverstheimportantconceptsofhydraulicsand pneumatics and how they are used for automation in an industrialsetting. It then moves to a discussion of circuits and using them inhydraulic,pneumatic,andfluidicdesign.The latterpartof thebookdealswith electric and electronic controls in automation and final chapters aredevoted to robotics, robotic programming, and applications of robotics inindustry.Acompaniondiscisincludedwithapplicationsandvideos.

CompanionFiles

Companion files (videos, lab projects, and figures from the book) forthistitleareavailableonthecompaniondiscorbycontactingthepublisheratinfo@merclearning.com.

Acknowledgments

ThematerialinChapter18andthevideosonthecompaniondiscappearin and were adapted fromReal-Time Embedded Components and Systemswith Linux and RTOS by S. Siewert and J. Pratt. Mercury Learning andInformation, 2016. ISBN: 978-1-942270-04-1. I would like to thank JenBlaneyofMercuryLearningforherprofessionalandpatientassistancewiththis product, SeanWestcott for his input and support, and to dedicate thisprojecttothetruestfriend,Sandy.

JeanRiescherWestcottOctober2016

CHAPTER1

AUTOMATION

INTRODUCTIONThe word automation comes from the Greek word “automatos,”

meaningself-acting.Thewordautomationwascoined in themid-1940sbythe U.S. automobile industry to indicate the automatic handling of partsbetween productionmachines, togetherwith their continuous processing atthemachines.Theadvancesincomputersandcontrolsystemshaveextendedthedefinitionofautomation.Bythemiddleofthe20thcentury,automationhad existed formany years on a small scale, usingmechanical devices toautomatetheproductionofsimplyshapeditems.Howevertheconceptonlybecame truly practicalwith the additionof the computer,whose flexibilityallowedittodrivealmostanysortoftask.

DEFINITIONOFAUTOMATIONAutomation can generally be defined as the process of following a

predetermined sequence of operationswith little or no human labor, usingspecialized equipment and devices that perform and controlmanufacturingprocesses. Automation in its full sense, is achieved through the use of avariety of devices, sensors, actuators, techniques, and equipment that arecapable of observing the manufacturing process, making decisionsconcerning the changes that need to be made in the operation, andcontrollingallaspectsofit.

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Automation is the process in industry where various productionoperations are converted from a manual process, to an automated ormechanizedprocess.

Example: Let’s assume that aworker is operating ametal lathe. Theworkercollectsthestock,alreadycuttosize,fromabin.Hethenplacesitinthelathechuck,andmovesthevarioushand-wheelsonthemachinetocreateacomponent;aboltcouldbesuchanitem.Whenfinishedtheworkerbeginstheprocessagaintomakeanotheritem.Thiswouldbeamanualprocess.Ifthisprocesswereautomated,theworkerwouldplacelonglengthsofbarintothe feedmechanismof an automatic lathe.The lathemechanisms feed thematerialintothechuck,turnthepiecetothecorrectshapeandsize,andcutitoff the bar before beginning another item. This is an example of anautomatedmachineinamanufacturingprocess.

Automationisastepbeyondmechanization,wherehumanoperatorsareprovidedwithmachinery to help them in their jobs. Industrial robotics aresaidtobethemostvisiblepartofautomation.Modernautomatedprocessesaremostly controlled by computer programs, which through the action ofsensorsandactuators,monitorprogressandcontrolthesequencesofeventsuntil the process is complete.Decisionsmadeby the computer ensure thattheprocessiscompletedaccuratelyandquickly.

Many people fear that automation will result in layoffs andunemployment;theybelievethatitsevilsconsiderablyoutweighitsbenefits.Basically, automation does take over jobs performed by workers; butautomation does not need to bring about unemployment, as some peoplefear,forthreeverypositivereasons:

First,intermsofthenumbersofworkersrequiredtoproduceaproduct,the reduction is a temporary displacement which can be offset by thedemandsofabroadeningmarket,aswellasthecreationofnewindustries.Itstill takes many workers to build, service, and operate any automaticmachine.

Second, automation does not happen overnight; it is an evolutionaryprocess. Manual, direct-labor work will be progressively transformed intowork,whichwillbecleaner,easier,safer,andmorerewardingtotheworker,who, through theprocessof automation itself,will be trained for themoreskillfulaccomplishmentsrequiredinthebetterjobsofthefuture.

Third, and most important, automation is the necessary solution to apredictedshortageoflabor.Itisdesignedtodotheworkofpeoplewhoarenotthere;itisasolutiontoaproblem,notacause.

Automation is a technology dealing with the application ofmechatronics and computers for production of goods and services.Manufacturingautomationdealswiththeproductionofgoods.Itincludes:

Automaticmachinetoolstoprocessparts.Automaticassemblymachines.Industrialrobots.Automaticmaterialhandling.Automatedstorageandretrievalsystems.Automaticinspectionsystems.Feedbackcontrolsystems.Computersystemsforautomaticallytransformingdesignsintoparts.Computer systems for planning and decision making to supportmanufacturing.

The decision to automate a new or existing facility requires thefollowingconsiderationstobetakenintoaccount:

Typeofproductmanufactured.Quantityandtherateofproductionrequired.Particularphaseofthemanufacturingoperationtobeautomated.Levelofskillintheavailableworkforce.Reliability and maintenance problems that may be associated withautomatedsystems.Economics.

MECHANIZATIONVSAUTOMATIONMechanizationreferstotheuseofpoweredmachinerytohelpahuman

operator insometask.Theuseofhand-poweredtools isnotanexampleofmechanization. The term is most often used in industry. The addition ofpowered machine tools; such as the steam powered lathe dramaticallyreducedtheamountoftimeneededtocarryoutvarioustasks,andimproves

productivity. Today very little construction of any sort is carried out withhand tools. Automation and mechanization are often confused with eachother, though it should not be too hard to keep them apart.Mechanizationsaves the use of human muscles; automation saves the use of humanjudgment. Mechanization displaces physical labor, whereas automationdisplacesmentallabor.

Mechanization is thereplacementofhumanpowerbymachinepower.Mechanizationoftenreplacescraftworkandcreatesjobsforunskilledlabor.It also only affects one or two industries at a time.Mechanizationmovesslowly and the job displacement is short-term. Mechanization is whatoccurredduring the industrial revolution.Automation is the replacementofhuman thinkingwith computers andmachines.Automation tends to createjobsforskilledworkersattheexpenseofunskilledandsemi-skilledworkers.It affectsmany industries at the same time,moving rapidly. It also createslonger-term job displacement and has been more characteristic since the1950s.

ADVANTAGESOFAUTOMATIONManufacturing companies in virtually every industry are achieving

rapid increases in productivity by taking advantage of automationtechnologies. When one thinks of automation in manufacturing, robotsusually come to mind. The automotive industry was the early adopter ofrobotics,using theseautomatedmachines formaterialhandling,processingoperations, and assembly and inspection. Automation can be applied tomanufacturingofalltypes.Theadvantagesofautomationare:Increasein

productivity.Reductioninproductioncosts.Minimizationofhumanfatigue.Lessfloorarearequired.Reducedmaintenancerequirements.Betterworkingconditionsforworkers.Effectivecontroloverproductionprocess.Improvementinqualityofproducts.Reductioninaccidentsandhencesafetyforworkers.Uniformcomponentsareproduced.

GOALSOFAUTOMATIONAutomationhascertainprimarygoalsaslistedbelow:

Integratevarious aspects ofmanufacturingoperations so as to improvetheproductqualityanduniformity,minimizecycletimesandeffort,andthusreducelaborcosts.Improve productivity by reducing manufacturing costs through bettercontrolofproduction.Partsare loaded, fed,andunloadedonmachinesmoreefficiently.Machinesareusedmoreeffectivelyandproduction isorganizedmoreefficiently.Improvequalitybyemployingmorerepeatableprocesses.Reducehumaninvolvement,boredom,andpossibilityofhumanerror.Reduceworkpiecedamagecausedbymanualhandlingofparts.Raise the level of safety for personnel, especially under hazardousworkingconditions.Economize on floor space in themanufacturing plant by arranging themachines,materialmovement,andrelatedequipmentmoreefficiently.

SOCIALISSUESOFAUTOMATIONAutomation has contributed to modern industry in many ways.

Automation raises several important social issues. Among them isautomation’s impact on employment/unemployment. Automation leads tofuller employment. When automation was first introduced, it causedwidespreadfear.Itwasthoughtthatthedisplacementofhumanworkersbycomputerizedsystemswouldleadtounemployment(thisalsohappenedwithmechanization,centuriesearlier).Infacttheoppositewastrue,thefreeingupofthelaborforceallowedmorepeopletoenterinformationjobs,whicharetypically higher paying.One odd side effect of this shift is that “unskilledlabor” now pays very well in most industrialized nations, because fewerpeopleareavailabletofillsuchjobsleadingtosupplyanddemandissues.

Somearguethereverse,atleastinthelongterm.First,automationhasonly just begun and short-termconditionsmight partially obscure its long-term impact. For instancemanymanufacturing jobs left the United Statesduringtheearly1990s,butamassiveupscalingofITjobsatthesametime

offsetthisasawhole.Currently,formanufacturingcompanies,thepurposeofautomationhasshiftedfromincreasingproductivityandreducingcoststoincreasingqualityandflexibilityinthemanufacturingprocess.

Another important social issue of automation is better workingconditions. The automated plants needs controlled temperature, humidity,and dust free environment for proper functioning of automated machines.Thustheworkersgetaverygoodenvironmenttoworkin.

Automationleads tosafetyofworkers.Byautomatingthe loadingandunloadingoperations,thechancesofaccidentstotheworkersgetreduced.

Workers expect an increase in standard of living with the help ofautomation.Standardsoflivinggoupwiththeincreaseinproductivity,andautomation is thesuremethodof increasingproductivity.ThecostofcolorTVs, washing machines, and stereos has declined, thus enabling a largenumberofhouseholdstobuytheseproducts.

LOWCOSTAUTOMATIONLowcostautomation(LCA)isatechnologythatcreatessomedegreeof

automation around the existing equipment, tools, methods, people, etc. byusingstandardcomponentsavailable in themarketwith lowinvestment,sothatthepaybackperiodisshort.

Thebenefitsoflowcostautomationarenumerous.Itnotonlysimplifiestheprocess,butalsoreducesthemanualcontentwithoutchangingthebasicset up. Major advantages of low cost automation are low investment,increased labor productivity, smaller batch size, better utilization of thematerial,andprocessconsistencyleadingtolessrejections.

A wide range of activities such as loading, feeding, clamping,machining, welding, forming, gauging, assembly, and packing can besubjected to low cost automation systems adoption. Besides, low costautomation can be very useful for process industries manufacturingchemicals, oils, or pharmaceuticals. Many operations in food processingindustries, which need to be carried out under totally hygienic conditions,canalsoberenderedeasythroughlowcostautomationsystems.

Awidevarietyofsystems(mechanical,hydraulic,pneumatic,electrical,and electronics) are available for deployment in LCA systems. However,

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each has its own advantages as well as limitations. For uncomplicatedsituations, one can build a simple LCA device using any of the abovesystems, througha rapid techno-economicevaluation.However, inmostofthepracticalapplications,hybridsystemsareusedbecausethatcanallowuseof the advantages of different devices, while simultaneously minimizingindividualdisadvantages.

IssuesinLowCostAutomationAssessmentoftheCurrentProductivityLevel:Therearesomesimpleproceduresforthis.Worksampling(activitysampling)isoneofthem.Itneeds no equipment and little time to collect the data. If the data isprocessed, considerable information will come out about the currentproductivitylevel.PMTS:PredeterminedMotionandTimeStudiesisaveryusefultooltocheck whether an existing manual operation is correctly pasted. If thetime taken ismore thandesirable,PMTSwillhelp in identifying itandimprovingit.Design for Automation and Assembly: When components are madeandassembledmanuallyonemaynothavethoughtaboutthecomplexityofautomation.Forexample,puttingtogetherhalfadozennutsandboltsis very easy in amanual assembly but very complex for an automaticsystem.

TYPESOFAUTOMATIONFixedAutomation(HardAutomation)

Fixed automation refers to the use of special purpose equipment toautomate a fixed sequence of processing or assembly operations. It istypicallyassociatedwithhighproductionratesanditisrelativelydifficulttoaccommodate changes in the product design. This is also called hardautomation. For example, GE manufactures approximately 2 billion lightbulbsperyearandusesfairlyspecialized,high-speedautomationequipment.Fixed automation makes sense only when product designs are stable andproductlifecyclesarelong.Machinesusedinhard-automationapplicationsare usually built on the building block, or modular principle. They are

generally called transfermachines, and consist of the following twomajorcomponents:powerheadproductionunitsandtransfermechanisms.

Advantages

Maximumefficiency.Lowunitcost.Automatedmaterialhandling—fastandefficientmovementofparts.Verylittlewasteinproduction.

Disadvantages

Largeinitialinvestment.Inflexibleinaccommodatingproductvariety.

ProgrammableAutomationIn programmable automation, the equipment is designed to

accommodate a specific class of product changes and the processing orassemblyoperationscanbechangedbymodifyingthecontrolprogram.Itisparticularlysuitedto“batchproduction,”orthemanufactureofaproductinmediumlotsizes(generallyatregularintervals).Theexampleofthiskindofautomation is the CNC lathe that produces a specific product in a certainproduct class according to the “input program.” In programmableautomation, reconfiguring the system for anewproduct is timeconsumingbecause it involves reprogramming and set up for the machines, and newfixtures and tools. Examples include numerically controlled machines,industrialrobots,etc.

Advantages

Flexibilitytodealwithvariationsandchangesinproduct.Lowunitcostforlargebatches.

Disadvantages

Newproductrequireslongsetuptime.Highunitcostrelativetofixedautomation.

FlexibleAutomation(SoftAutomation)

In flexible automation, the equipment is designed to manufacture avarietyofproductsorpartsandverylittletimeisspentonchangingfromoneproduct to another. Thus, a flexible manufacturing system can be used tomanufacture various combinations of products according to any specifiedschedule. With a flexible automation system, it is possible to quicklyincorporatechangesintheproduct(whichmayberedesignedinreactiontochanging market conditions and to consumer feedback) or to quicklyintroduce a newproduct line. For example,Honda iswidely creditedwithusingflexibleautomationtechnologytointroduce113changestoitslineofmotorcycle products in the 1970s. Flexible automation gives themanufacturer the ability to produce multiple products cheaply incombinationthanseparately.

Advantages

Flexibilitytodealwithproductdesignvariations.Customizedproducts.

Disadvantages

Largeinitialinvestment.Highunitcostrelativetofixedorprogrammableautomation.

CURRENTEMPHASISINAUTOMATIONCurrently,formanufacturingcompanies,thepurposeofautomationhas

shifted from increasing productivity and reducing costs, to broader issues,suchas increasingqualityandflexibility in themanufacturingprocess.Theold focus on using automation simply to increase productivity and reducecosts was short-sighted, because it is also necessary to provide a skilledworkforcewhocanmakerepairsandmanagethemachinery.Moreover,theinitialcostsofautomationwerehighandoftencouldnotberecoveredbythetimeentirelynewmanufacturingprocessesreplacedtheold.(Japan’s“robotjunkyards” were once world famous in the manufacturing industry.)Automation is now often applied primarily to increase quality in themanufacturingprocess,whereautomationcanincreasequalitysubstantially.Forexample,automobileandtruckpistonsusedtobeinstalledintoenginesmanually. This is rapidly being transitioned to automated machineinstallation, because the error rate for manual installment was around 1–

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1.5%,but is 0.00001%with automation.Hazardousoperations, such asoilrefining, themanufacturing of industrial chemicals, and all forms ofmetalworking,werealwaysearlycontendersforautomation.

Another major shift in automation is the increased emphasis onflexibilityandconvertibilityinthemanufacturingprocess.Manufacturersareincreasinglydemandingtheabilitytoeasilyswitchfromonemanufacturingproducttootherwithouthavingtocompletelyrebuildtheproductionlines.

REASONSFORAUTOMATIONShortageoflaborHighcostoflaborIncreased productivity: Higher production output per hour of laborinput is possible with automation than with manual operations.Productivityisthesinglemostimportantfactorindetermininganation’sstandard of living. If the value of output per hour goes up, the overallincomelevelsgoup.Competition: The ultimate goal of a company is to increase profits.However, there are other goals that are harder tomeasure.Automationmayresultinlowerprices,superiorproducts,betterlaborrelations,andabettercompanyimage.Safety: Automation allows the employee to assume a supervisory roleinstead of being directly involved in the manufacturing task. Forexample,diecastingishotanddangerousandtheworkpiecesareoftenveryheavy.Welding,spraypainting,andotheroperationscanbeahealthhazard.Machines can do these jobsmore precisely and achieve betterqualityproducts.Reducing manufacturing lead-time: Automation allows themanufacturer to respond quickly to the consumers needs. Second,flexible automation also allows companies to handle frequent designmodifications.Lowercosts:Inadditiontocuttinglaborcosts,automationmaydecreasethescrap rateand thus reduce thecostof rawmaterials. Italsoenablesjust-in-time manufacturing which in turn allows the manufacturer toreduce the in-process inventory. It ispossible to improve thequalityoftheproductatlowercost.

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REASONSFORNOAUTOMATIONLaborresistance:People lookat robotsandmanufacturingautomationas a cause of unemployment. In reality, the use of robots increasesproductivity,makes the firmmorecompetitive, andpreserves jobs.Butsome jobs are lost. For example, Fiat reduced its work force from138,000 to 72,000 in nine years by investing in robots. GM’s highlyautomatedplantbuiltincollaborationwithToyotainFremont,Californiaemploys 3,100workers in contrast to 5,100 at a comparable olderGMplant.Costofupgradedlabor:Theroutinemonotonoustasksaretheeasiesttoautomate. The tasks that are difficult to automate are ones that requireskill.Thus,manufacturinglabormustbeupgraded.Initialinvestment:Cashflowconsiderationsmaymakeaninvestmentinautomationdifficulteveniftheestimatedrateofreturnishigh.

ISSUESFORAUTOMATIONINFACTORYOPERATIONS

Taskistoodifficulttoautomate.Shortproductlifecycle.Customizedproduct.Fluctuatingdemand.Reduceriskofproductfailure.Cheapmanuallabor.

STRATEGIESFORAUTOMATIONSpecializationofoperations.Combinedoperations.Simultaneousoperations.Integrationofoperations.Increasedflexibility.Improvedmaterialhandlingandstorage.

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6.7.8.9.10.11.12.13.

On-lineinspection.Processcontrolandoptimization.Plantoperationscontrol.ComputerIntegratedManufacturing.

EXERCISESDifferentiatebetweenmechanizationandautomation.Identifysomeofthemajorreasonsforautomation.Listthelevelsofautomation.Discuss the concept of low cost automation with the help of suitableexamples.What are the types of automation that can be used in a productionsystem?Comparethemfortheirfeaturesanddrawbacks.Discussthevariouslevelsofautomation.Writeshortnoteson“lowcostautomation.”Identifymajorsocio-economicconsiderationsfavoringautomation.Statetheadvantagesofautomatingproductionoperations.Listthestrategiesforautomation.Comparehardautomationwithsoftautomation.Listtheadvantagesofflexibleautomation.Listatleastfourreasonswhyautomationisrequiredinindustry.

CHAPTER2

BASICLAWSANDPRINCIPLES

FLUIDPROPERTIES

ForceAforceisapushorapull,ormoregenerallyanythingthatcanchange

anobject’sspeedordirectionofmotion.TheInternationalSystemofUnits(SI)unitusedtomeasureforceistheNewton(symbolN).

F=ma

where F stands for force in Newton,m stands formass in Kg and arepresentsaccelerationexpressedasmetersdividedbysecondssquaredm/s2.

PressurePressureistheratioofforcetotheareaoverwhichtheforceacts.

Mathematically,itcanbeexpressedas:

where p is pressure, F is force, and A represents area. Pressure isusuallyexpressed inNewtonper squaremeter,given thenamePascal, andtraditionally,itwasexpressedinpoundsforcepersquareinch(PSI).

AtmosphericPressure

Atmosphericpressureisdefinedasthepressureduetotheweightoftheatmosphere (air and water vapor) on the earth’s surface. Atmosphericpressure is determined by a mercury column barometer, that is why it issometimescalledasbarometricpressure.Theaverageatmosphericpressureatsea levelhasbeendefinedas1.01325bars,or14.696poundspersquareinchabsolute(PSIA).

FIGURE2.1PressureRelationship.

AbsolutePressureAbsolute pressure can be given as gauge pressure plus barometric or

atmosphericpressure.Absolutepressure is referencedagainstabsolutezeropressure,oracompletevacuum.Theunitsofabsolutepressurearefollowedbysuffix“a,”suchaspsia.Ifweholdanabsolutepressureinstrumentintheopenair, the readingshouldbewellabovezero, in the rangeof14.7 to12psia.

GaugeandVacuumPressureGauge pressure is referenced against the atmospheric pressure at the

measurementpoint.Theunitsofgaugepressurearefollowedbya“g,”suchaspsig.Agaugepressureinstrumentshouldalwaysreadzerowhenexposedto atmospheric pressure. Similarly, when the pressure falls belowatmospheric, it is called vacuum pressure, sometimes it is also callednegativegaugepressure.

Based upon the above discussions, the following equations can bederived:

Where

ConversionofvariousunitsofpressureinPascal

Unit Symbol No.ofpascals

Bar bar 1×105Pa

Millibar mbar 100Pa

Hectopascal hPa 100Pa

conventionalmmofHg mmHg 133.322Pa

conventionalinchofHg inHg 3,386.39…Pa

Torr torr 101325/760≈133.322Pa

pound-forcepersquareinch lbf/in2 6,894.76≈6895Pa

Pascal’sLawBlaisePascalformulatedthisbasiclawinthemid-17thcentury.Hislaw

states thatpressureinaconfinedfluidis transmittedundiminishedineverydirection and acts with equal force on equal areas and at right angles tocontainerwalls.Hydraulicbrakes,lifts,presses,syringepistons,etc.workontheprincipleofPascal’slaw.

According to Pascal’s law, inside the pipes of a confined systempressureisuniformatallpoints.Mathematically,

FIGURE2.2Pascal’sLawIllustrated

From the above expression, P1 = P2, therefore F2 is greater than F1becauseA2 isgreater thanA1.Thismeansthat, inorder toobtainagreateroutputforce,itisenoughtohavesuitablysizedsurfacesavailable.

FlowandFlowRateThevolumeofasubstancepassingapointperunittimeiscalledflow

andthevolumeofwater,apumporacompressorcanmoveduringagivenamountoftimeiscalled,“flowrate.”

VolumetricFlowRate

It is the volume of the fluid flowing through a cross section per unittime.Airrelatedflowsareusuallyexpressedincubicfeetperminute(CFM)andforliquid-basedfluids,theyareexpressedaslitersorgallonsperminute(LPMorGPM)orcubicmeterspersecond,etc.

VolumetricFlowRate=Area×Velocity

MassFlowRate

Volumetric flowrate timesdensity, i.e.,poundsperhourorkilogramsperminute.

MassFlowRate=Area×Velocity×Density

MassFlowRate=Area×Velocity×Density

Conversionofvariousflowrateunitsintom3/s

Unit Symbol No.ofm3/s

Liters/second l/s 10−3m3/s

Gallons/second gps 0.003788m3/s

cubicfeet/min cfm 4.719×10−4m3/s

Bernoulli’sEquationItstatesthat,foranon-viscous,incompressiblefluidinsteadyflow,the

sumofpressure,potential,andkineticenergiesperunitvolumeisconstantatanypoint.Mathematically,itcanbeexpressedas:

Where

Bernoulli’s principle states that in fluid flow, an increase in velocityoccurs simultaneously with a decrease in pressure. It is named for theDutch/Swissmathematician/scientistDanielBernoulli;thisphenomenoncanbeseeninairplanelift,acarburetor,theflowofairaroundtheball,etc.

VenturiEffectA fluid passing through smoothly varying constrictions is subject to

changes in velocity and pressure, as described byBernoulli’s principle. Incaseof fluidorairflowthrougha tubeorpipewithaconstriction in it, thefluidmustspeedupintherestriction,reducingitspressure,andproducingapartialvacuum.

AsshownintheFig.2.3fluiddensity=(ρ),area=(A),andvelocity=(V).Let the properties of fluid at entrance and exit be (ρ1,A1,V1) and at

(a)

constrictionbe(ρ2,A2,V2).Thereisadropinpressureattheconstrictionasshownbytheheightof thecolumnandit isduetoconservationofenergy.The fluid experiences a gain in kinetic energy and a drop inpressure as itenters the constriction; this effect is calledVenturi effect, it is namedaftertheItalianphysicistGiovanniBattistaVenturi.

FIGURE2.3Venturi’sLawIllustrated.

ContinuityEquationIt issimplyamathematicalexpressionoftheprincipleofconservation

ofmass.Mass isneither creatednordestroyed.For a steady flow, it states

that:

The “continuity equation” is a direct consequence of the rather trivialfact that what goes into the pipe must come out. This has the importantconsequencethatas theareaof theholedecreases, thevelocityof thefluidmustincrease,inordertokeeptheflowrateconstant.

SpecificWeight,Density,andSpecificGravitySpecificWeightorWeightDensity

(b)

(c)

Theweightperunit volumeof a substance.Usually it is expressed inN/m3orlbs/ft3.Mathematically,

Where

Density

Density isdefinedas the ratioof themassofanobject to itsvolume;usuallyitisexpressedinkg/m3org/cm3.Mathematically,

Where

SpecificGravity

Theratioofthedensity(orspecificweight)ofasubstancetothedensity(orspecificweight)ofastandardfluidiscalledSpecificgravityorRelativedensity.Theusualstandardofcomparisonforsolidsandliquids iswaterat4°C at atmospheric pressure. Gases are commonly compared to dry air,understandardconditions(0°Candatmosphericpressure).

Specific gravity is not expressed in units, as it is purely a ratio.Mathematically,

Where

CompressibilityandBulkModulusCompressibilityisthemeasureofchangeinvolumeofsubstancewhen

pressure is exerted on it. Liquids are incompressible fluids. For each

atmosphere increase in pressure, the volumeofwaterwould decrease 46.4partspermillion.Thehydraulicbrakesystemsusedinmostcarsoperateontheprinciple that there is essentiallynochange in thevolumeof thebrakefluidwhenpressureisappliedtothisliquid.

Ontheotherhand, thevolumeof thegasescanbereadilychangedbyexerting an external pressure on the gas. An internal combustion engineprovidesagoodexampleoftheeasewithwhichgasescanbecompressed.

The compressibility is the reciprocal of the bulk modulus.

Compressibilityisdenotedby“k”andisexpressedmathematicallyas:

WhereBiscalledthebulksmodulusofelasticityandisdefinedastheratio of change inpressure to volumetric strain (change involume/originalvolume)overafluidelement.Itisexpressedasfollows:

Where

ViscosityandViscosityIndexViscosity is the measure of the internal friction of a fluid or its

resistancetoflow.Ahydraulicfluidthatistooviscoususuallycauseshigh-pressure drop, sluggish operation, low-mechanical efficiency, and high-power consumption. Low-viscosity fluids permit efficient low-dragoperation, but tend to increase wear, reduce volumetric efficiency, andpromoteleakage.

Viscosityindexisanarbitraryscale,whichindicateshowtheviscosityofafluidvarieswithchangesintemperature.Thehighertheviscosityindex,the lower theviscositychangeswith respect to temperatureandviceversa.Ideally,thefluidshouldhavethesameviscosityatverylowtemperaturesaswellasathightemperatures.Inreality,thiscannotbeachieved.Thischangeis common to all fluids. Heating tend to make fluids thinner and coolingmakesthemthicker.

(a)

(b)

(c)

GasLawsBoyle’sLaw

EnglishscientistRobertBoyleinvestigatedtherelationshipbetweenthevolume of a dry ideal gas and its pressure. It states that at constanttemperature,thepressureisinverselyproportionaltothevolumeofadefiniteamountofgas.Mathematically,

thereforeWhere

Charle’sLaw

FrenchscientistJacquesCharlesexperimentedwithgasunderconstantpressureandhisobservationshavebeenformalizedintoCharle’slaw.

Thevolumeofagasatconstantpressureisdirectlyproportionaltotheabsolutetemperature.Mathematically,itcanbeexpressedas:

thereforeWhere

Gay-Lussac’sLaw

French scientist Joseph Gay-Lussac investigated the relationshipbetweenthepressureofagasanditstemperature.Itstatesthatthepressureof a gas at constant volume is directly proportional to the absolutetemperature.Themathematicalstatementisasfollows:

(d)

(a)

(i)

(ii)

(iii)

thereforeWhere

CombinedGasLaws

AnytwoofthethreegaslawsofBoyle,Charles,orGay-Lussaccanbecombined,hence thename, combinedgas law. In short, this combinedgaslaw is used when it is difficult to keep either the temperature or pressureconstant:P1V1T2=P2V2T1

This relationship can be used to predict pressure, volume, andtemperaturerelationshipswhereanyfiveofthesixvariablesareknown.

MoistureintheAirHumidity

Humidity is the concentration of water vapor in the air. Theconcentration can be expressed as specific humidity, absolute humidity, orrelativehumidity.Adeviceusedtomeasurehumidityiscalledahygrometer.

Specifichumidity.Isdefinedasmassofwatervaporpresentperkgofdryair.Itisexpresseding/kgofdryair.Humidityismeasuredbymeansofahygrometer.Absolute humidity. Is expressed as the mass of water vaporcontainedinagivenvolumeofair.Thehottertheairis,themorewater itcancontain.Itmaybemeasuredingramsofvapor/cubicmeter of air. Absolute humidity finds greatest application inventilationandair-conditioningproblems.Relative humidity. Is defined as the ratio (usually expressed as apercentage) of themass ofwater in a given volume ofmoist airdivided by themaximummass ofwater that can be held by thatsamevolumeofair(saturatedair)atagiventemperature.Wecancomparehowmuchwatervaporispresentintheairtohowmuchwatervaporwouldbeintheairiftheairweresaturated.Areadingof 100 percent relative humidity means that the air is totallysaturatedwithwatervaporandcannotholdanymore.

(b)

(c)

(d)

Example: If20gramsofwatervaporwerepresent ineachm3ofdryair,andtheairwouldbesaturatedwith30gramsofwatervaporperm3ofdryair,therelativehumiditywouldbe20/30=66.66%.

Practically,“relativehumidity”istheamountofmoistureintheairatacertaintemperature.Itiscalled“relative”becauseitisbeingcomparedtothemaximum amount of moisture that could be in the air at the sametemperature.

DewPointTemperatureandHoldingCapacityofAir

Airpresentatcertaintemperaturescouldconsumeacertainquantityofwater in it, likewise when this temperature is attained, air becomescompletely saturated. If the air is further cooled then water will startcondensing out of it. Dew point is the temperature at which water vaporbegins tocondenseoutof theair.Dewpointscanbedefinedandspecifiedfor ambient air or for compressed air.Dew point normally occurswhen amass of air has a relative humidity of 100%. This temperature can berecordedbyathermometer.

AtmosphericDewPoint

Atmospheric dew point is the value of the temperature at whichmoisturepresentintheairbeginstocondenseatatmosphericpressure,i.e.,at1.01325bar.Atmosphericdewpoint isnotatall important forpneumatics,aspressureisalwaysmorethanatmosphericpressureinapneumaticline.

PressureDewPoint

Pressure dew point is the value of the temperature atwhichmoisturepresentintheairbeginstocondenseatpressuresmorethantheatmosphericpressure. As pressures encountered in pneumatics are generallymore thanatmosphericsoitisofgreatimportance.Obviously,athigherpressures,thewater present in air condenses at higher temperatures in comparison toatmosphericpressure,sodewpointshouldbekeptverylowsoastoensuretheleastamountofmoistureinthepneumaticline(asmoistureisthebiggestenemyinpneumatics).

Energy,Work,andPower

(i)(ii)(iii)

Energyistheabilitytodoworkandisexpressedinfootpound(ftlb)orNewtonmeter (Nm). The three forms of energy are potential, kinetic, andheat.Workmeasuresaccomplishments;itrequiresmotiontomakeaforcedowork.Poweristherateofdoingworkortherateofenergytransfer.

PotentialEnergy

Potential energy is energy due to position. An object has potentialenergy in proportion to its vertical distance above the earth’s surface. Forexample,waterheldbackbyadamrepresentspotentialenergybecauseuntilit is released, thewaterdoesnotwork. Inhydraulics, potential energy is astaticfactor.Whenforceisappliedtoaconfinedliquid,potentialenergyispresent because of the static pressure of the liquid. Potential energy of amovingliquidcanbereducedbytheheatenergyreleased.Potentialenergycan also be reduced in a moving liquid when it transforms into kineticenergy.Amovingliquidcan,therefore,performworkasaresultofitsstaticpressureanditsmomentum.

KineticEnergy

Kinetic energy is the energy a body possesses because of itsmotion.Thegreaterthespeed,thegreaterthekineticenergy.Whenwaterisreleasedfromadam,itrushesoutatahighvelocityjet,representingenergyofmotion—kineticenergy.Theamountofkineticenergyinamovingliquidisdirectlyproportionaltothesquareofitsvelocity.Pressurecausedbykineticenergymaybecalledvelocitypressure.

HeatEnergyandFriction

Heatenergyistheenergyabodypossessesbecauseofitsheat.Kineticenergyandheatenergyaredynamic factors.Pascal’sLawdealtwith staticpressureanddidnot include the frictionfactor.Friction is the resistance torelative motion between two bodies. When liquid flows in a hydrauliccircuit,frictionproducesheat.Thiscausessomeofthekineticenergytobelost in the form of heat energy. Although friction cannot be eliminatedentirely, it can be controlled to some extent. The three main causes ofexcessivefrictioninhydraulicsystemsare:Extremelylonglines.

Numerousbendsandfittingsorimproperbends.Excessivevelocityfromusingundersizedlines.

1.2.

3.4.5.6.7.8.9.

10.11.12.13.

14.

EXERCISESWhatarethedifferencesbetweenaliquidandagas?Whatdoyoumeanbypressuredewpoint?Doesithaveanyimportanceinpneumatics?Statetheimportanceofgaslaws.Definethetermsspecificweight,density,andspecificgravity.Whatistheeffectoftemperatureonviscosityoffluids?Statecontinuityequation.Differentiatebetweenthetermsviscosityandviscosityindex.Whatisthedifferencebetweenpressureandforce?Explainventurieffect.Givethenameofimportantpneumaticequipment,whichusesthisprinciple.StateBernoulli’sequation.Whatismeantbythetermbulkmodulus?StateandprovePascal’slaw.What is the relationship between atmospheric, absolute, and vacuumpressure?Differentiatebetweenabsoluteandrelativehumidity.

CHAPTRE3

BASICPNEUMATICANDHYDRAULICSYSTEMS

INTRODUCTIONTOFLUIDPOWERAfluidpowersystemtransmitsandcontrolsenergythroughtheuseof

pressurized fluid. The term fluid power applies to both hydraulics andpneumatics.Withhydraulics,thatfluidisaliquidsuchasoilorwater.Withpneumatics,thefluidistypicallycompressedairorinertgas.Hydraulicsusesoil or liquid as the medium that cannot be compressed and pneumatics,whichinvolvesgases,usesairorgasasthemediumthatcanbecompressed.It is a term, which was created to collect the generation, control, andapplication of smooth, effective power of pumped or compressed fluids(eitherliquidsorgases).Thispowerisusedtoprovideforceandmotiontovariousmechanisms.Thisforceandmotionmaybeintheformofpush,pull,rotate,regulate,ordrive.

Fluid power is one of three commonly used methods of transmittingpower in an industry; the others are electrical and mechanical powertransmission. Electric power transmission uses an electric current flowingthroughawiretotransmitpower.Mechanicalpowertransmissionusesgears,pulleys, chains, etc. to transmit power. Fluid power’smotive force comesfrom the principle that pressure applied to a confined fluid is transferreduniformlyandundiminishedtoeveryportionofthefluidandtothewallsofthe container that holds the fluid.A surface such as a cylinder pistonwillmoveifthedifferenceinforceacrossthepistonislargerthanthetotalloadplus frictional forces. The resulting net force can then accelerate the loadproportionatelytotheratiooftheforcedividedbythemass.

Fluidpowerencompassesmostapplicationsthatuseliquidsorgasestotransmitpowerintheformofmechanicalwork,pressure,and/orvolumeinthe system. This definition includes all systems that rely on pumps andcompressors to transmit specific volumes andpressuresof liquidsor gaseswithin a closed system. Fluid power is used in the steering, brake system,andautomatictransmissionsofcarsandtrucks.Inadditiontotheautomotiveindustry, fluid power is used to control airplanes and spacecraft, harvestcrops,minecoal,drivemachinetools,andprocessfood.Fluidpowercanbeeffectively combined with other technologies through the use of sensors,transducers,andmicroprocessors.

BASICELEMENTSOFFLUIDPOWERSYSTEMThebasicelementsoffluidpowersystemare:

Powerdevice:PumporCompressorControlvalvesActuators:CylindersorMotors

Figure3.1showsthebasicelementsofafluidpowersystemconnectedbyfluidpowerlines.Theseelementsarediscussedindetailinnextchapters.

FIGURE3.1ElementsofFluidPowerSystem.

ADVANTAGESANDDISADVANTAGESOFFLUIDPOWER

Advantages

There are fewadvantages,whichmake fluidpower sopopular.Thesearelistedbelow:

No need of intermediate equipment: They eliminate the need forcomplicated systems of gears, cams, and levers. Motion can betransmittedwithouttheslackinherentintheuseofsolidmachineparts.Lesswearandtear:Thefluidsusedarenotsubjecttobreakageasaremechanicalparts,andthemechanismsarenotsubjectedtogreatwear.Multi-functioncontrol:Asinglehydraulicpumporaircompressorcanprovidepowerandcontrolfornumerousmachinesormachinefunctionswhencombinedwithfluidpowermanifoldsandvalves.Constantforceortorque:Thisisauniquefluidpowerattribute.Flexibility: Hydraulic components can be located with considerableflexibility. Pipes and hoses instead of mechanical elements virtuallyeliminatelocationproblems.Comparatively small pressure losses: The different parts of a fluidpower system can be conveniently located at widely separated points,because the forces generated are rapidly transmitted over considerabledistanceswithsmallloss.Theseforcescanbeconveyedupanddownoraround corners with small loss in efficiency and without complicatedmechanisms.Multiplication and variation of force: Very large forces can becontrolled by much smaller ones and can be transmitted throughcomparatively small lines and orifices. Linear or rotary force can bemultipliedfromafractionofanouncetoseveralhundredtonsofoutput.Accurateandeasytocontrol:Wecanstart,stop,accelerate,decelerate,reverse,orpositionlargeforceswithgreataccuracy.Highhorsepowerandlowweight:Pneumaticcomponentsarecompactandlightweight.Smoothness:Fluidsystemsaresmoothinoperation.Vibrationiskepttoaminimum.Overload protection: In case of an overload, an automatic release ofpressurecanbeguaranteed;automaticvalvesguardthesystemagainstabreakdown from overloading so that the system is protected againstbreakdownorstrain.Wide variety of motions: Fluid power systems can provide widelyvariablemotionsinbothrotaryandstraight-linetransmissionofpower.

Lowspeedtorque:Unlikeelectricmotors,airorhydraulicmotorscanproducelargeamountsoftorque(twistingforce)whileoperatingatlowspeeds.Somehydraulicandairmotorscanevenmaintaintorqueatzerospeedwithoutoverheating.Less human intervention: The need for control by hand can beminimized.Low operating costs: Fluid power systems are economical to operatetheir high efficiency with minimum friction loss keeps the cost of apowertransmissionataminimum.Safetyinhazardousenvironments:Fluidpowercanbeusedinmines,chemicalplants,nearexplosives,and inpaintapplicationsbecause it isinherentlyspark-freeandcantoleratehightemperatures.Better force control: Force control ismuch easierwith fluid systemsthan for electricmotors.Fluidactuators, eitherhydraulicorpneumatic,arewellsuitedtowalkingrobotsbecausetheyarehighforce,lowspeedactuators. They provide much higher force densities than electricsystems.Simpler design: Inmost cases, a few pre-engineered componentswillreplacecomplicatedmechanicallinkages.

Disadvantages

Themain disadvantage of a fluid system ismaintaining the precisionparts when they are exposed to bad climates and dirty atmospheres.Protection against rust, corrosion, dirt, oil deterioration, and other adverseenvironmentalconditionsisveryimportant.

APPLICATIONSOFFLUIDPOWERMobile

Fluidpowerisusedtotransport,excavate,andliftmaterials,aswellascontrolorpowermobileequipment.Enduseindustriesincludeconstruction,agriculture,marine,andthemilitary.Applicationsincludebackhoes,graders,tractors,truckbrakesandsuspensions,spreaders,andhighwaymaintenancevehicles.

Industrial

Fluidpowerisusedtoprovidepowertransmissionandmotioncontrolforthemachinesofindustry.Enduseindustriesrangefromplasticstopaperproduction. Applications include metal working equipment, controllers,automatedmanipulators,materialhandling,andassemblyequipment.

AerospaceFluid power is used for both commercial and military aircraft,

spacecraft,andrelatedsupportequipment.Applicationsincludelandinggear,brakes,flightcontrols,motorcontrols,andcargoloadingequipment.

PNEUMATICSVS.HYDRAULICSFluid power can be broadly divided into two fields: pneumatics and

hydraulics.Bothpneumaticsandhydraulicsareapplicationsoffluidpower.

Pneumatic systems use compressed gas such as air or nitrogen toperformwork processeswhereas hydraulic systems use liquids such as oilandwatertoperformworkprocesses.Pneumaticsystemsareopensystems,exhaustingthecompressedairtotheatmosphereafterusewhereashydraulicsystemsareclosedsystems,recirculatingtheoilorwaterafteruse.

A fluid power system uses hydraulics or pneumatics to deliverextremely powerful pushing and pulling forces tomachinery.Much of thefactory equipment used to lift andmove large components is powered byhydraulics. For example, forklift trucks, opencast mining equipment, andmulti-purpose agricultural spraying equipment all use hydraulic systems tooperate their lifting arms. Pneumatics, on the other hand, are used for avarietyofpurposesthatincludedeliveringpowertotoolslikejackhammers,air guns, and complex industrial equipment for conveying, separating, andairhandlinggoods.

The extensive use of hydraulics and pneumatics to transmit power isdue to the fact that properly constructed fluid power systems possess anumberoffavorablecharacteristics.Theyeliminatetheneedforcomplicatedsystems of gears, cams, and levers. The fluids used are not subject tobreakageasaremechanicalparts,and themechanismsarenot subjected togreatwear.

Some points of difference between hydraulics and pneumatics areshowninTable3.1.

TABLE3.1DifferencebetweenHydraulicsandPneumatics.

Pneumatics Hydraulics

Pressurelevel 5–10bar Upto200bar

Actuatingforces Pneumatic actuators can produce onlylowormediumsizeforces.

Hydraulicactuatorsaresuitableforveryhighloads.

Elementcost Pneumatic elements such as cylindersandvalvesarelesscostlyascomparedtohydraulicelements.

Hydraulic elements can cost from 5 to10 times more than similar sizepneumaticelements.

Transmissionlines Transmission lines in pneumatics aremade up of inexpensive flexible plastictubing. Only single line is needed inpneumaticstosimplyexhausttheairintoatmosphere.

Transmission lines in hydraulics aremadeupofmetaltubingwithexpensivefittings to withstand high workingpressureand toavoid leaks.Also returnlines are needed in hydraulics to returnthe oil from each cylinder back toreservoir.

Stability Low stability because air iscompressible.

High stability because oil isincompressible.

Speedcontrol Difficult to control the speed ofpneumaticcylindersormotors.

Easytocontrolthespeed.

ADVANTAGESANDDISADVANTAGESOFPNEUMATICS

Advantages

Pneumatic systems are clean because they use compressed air. If apneumaticsystemdevelopsaleak,itwillbeairthatescapesandnotoil.Pneumaticsystemsarecheapertorunthanothersystems.Inherentlymodulatingactuatorsandsensors.Explosionproofcomponents.Highefficiency,example,a relativelysmallcompressorcan filla largestoragetanktomeetintermittenthighdemandsforcompressedair.Easeofdesignandimplementation.Highreliability,mainlybecauseoffewermovingparts.

Compressed gas can be stored, allowing the use of machines whenelectricalpowerislost.Easyinstallationandmaintenance.

Disadvantages

Lowaccuracyandcontrollimitationbecauseofcompressibility.Noisepollution.Leakageofaircanbeofconcern.Needforacompressorproducingcleananddryair.Costofairpiping.Needforregularcomponentcalibration.

ADVANTAGESANDDISADVANTAGESOFHYDRAULICS

Advantages

Through the use of simple devices, an operator can readily start, stop,speed up, slow down, and control large forces with very close andprecisetolerance.Highpoweroutputfromacompactactuator.Hydraulicpowersystemscanmultiplyforcessimplyandefficientlyfromafractionofanouncetoseveralhundredtonsofoutput.Force canbe transmittedover distances and around cornerswith smalllossesofefficiency.Thereisnoneedforcomplexsystemsofgears,cams,orleverstoobtainalargemechanicaladvantage.Extremeflexibilityofapproachandcontrol.Controlofawiderangeofspeedandforcesiseasilypossible.Safetyandreliability.Hydraulicsystemsaresmoothandquietinoperation.Vibrationiskepttoaminimum.

Disadvantages

Hydraulicsystemsareexpensive.

System componentsmust be engineered tominimize or preclude fluidleakage.Protection against rust, corrosion, dirt, oil deterioration, and otheradverseenvironmentisveryimportant.Maintenance of precision partswhen they are exposed to bad climatesanddirtyatmospheres.Firehazardifleakoccurs.Adequateoilfiltrationmustbemaintained.

APPLICATIONSOFPNEUMATICSOperationofheavyorhotdoorsLiftingandmovinginslabmouldingmachinesSpraypaintingBottlingandfillingmachinesComponentandmaterialconveyortransferUnloadingofhoppersinbuilding,mining,andchemicalindustryAirseparationandvacuumliftingofthinsheetsDentaldrills

APPLICATIONSOFHYDRAULICSMachinetoolindustryPlasticprocessingmachinesHydraulicpressesConstructionmachineryLiftingandtransportingAgriculturalmachinery

BASICPNEUMATICSYSTEMPneumatic systems use pressurized air tomake thingsmove. A basic

pneumatic system consists of an air generating unit and an air-consuming

1.2.3.4.5.6.7.8.9.10.11.12.13.

unit.Aircompressedinacompressorisnotreadyforuse.Theairhastobefiltered, the moisture present in air has to be dried, and, for differentapplications in theplant, thepressureofairhas tobevaried.Severalothertreatmentsaregiventotheairbeforeitreachesfinallytotheactuator.Figure3.2 gives an overview of a basic pneumatic system. Some accessories areaddedforeconomicalandefficientoperationofsystem.

FIGURE3.2BasicPneumaticSystem.

Atypicalpneumaticpowersystemincludesthefollowingcomponents:

CompressorElectricmotorAirreceiverPressureswitchSafetyvalveAutodrainCheckvlvePressuregaugeAirdryerAfterfilterAirserviceunitDirectioncontrolvalvePneumaticactuator

1.

2.3.

4.

5.

6.

7.

8.

9.

10.

11.

Compressor:Adevice,which convertsmechanical force andmotionintopneumaticfluidpower,iscalledacompressor.Everycompressed-airsystembeginswithacompressor,asitisthesourceofairflowforallthedownstreamequipmentandprocesses.ElectricMotor:Anelectricmotorisusedtodrivethecompressor.AirReceiver:Anairreceiverisacontainerinwhichairisstoredunderpressure.Pressure Switch:A pressure switch is used tomaintain the requiredpressure in the receiver. It adjusts the high pressure limit and lowpressure limit in the receiver.Thecompressor isautomatically turnedoffwhen the pressure is about to exceed the high limit and it is alsoautomatically turned onwhen the pressure is about to fall below thelowlimit.Safety Valve: The function of the safety valve is to release extrapressure if the pressure inside the receiver tends to exceed the safepressurelimitofthereceiver.Auto Drain: Air condenses to give out water in the receiver and adevicecalledautodraindirectsthiswaterout.CheckValve:Thevalveenablesflowinonedirectionandblocksflowinacounterdirectioniscalledcheckvalve.Oncecompressedairentersthereceiverviacheckvalve,itisnotallowedtogobackevenwhenthecompressorisstopped.PressureGauge: The pressure gauge tells us the pressure inside thecompressorreceiver.AirDryer:Adeviceforreducingthemoisturecontentoftheworkingcompressedair.AfterFilter:Afilterthatfollowsthecompressedairdryerandusuallyusedfortheprotectionofdownstreamequipmentfromdesiccantdust,etc. is called an after filter. The name filter refers to a devicewhoseprimaryfunctionistheremovalofinsolublecontaminantsfromaliquidoragaswiththehelpofporousmedia.Air Service Unit: Filter, regulator, and lubricator combined in onedevice is popularly known as an air service unit or F.R.L unit. Itspurpose is tosupplyair toothersuccessiveapplications in the line. Itprovidescleanairattherequiredpressurewithlubricantaddedtoittoincreasethelifeofequipment.

12.

13.

1.2.3.4.5.6.7.8.9.

DirectionControlValve:Directional-controlvalvesaredevicesusedto change the flow direction of fluid within a pneumatic/hydrauliccircuit.Theycontrolcompressed-airflowtocylinders,rotaryactuators,grippers,andothermechanismsinpackaging,handling,assembly,andcountless other applications. These valves can be actuated eithermanuallyorelectrically.PneumaticActuator:Adeviceinwhichpoweristransferredfromonepressurized medium to another without intensification. Pneumaticactuators are normally used to control processes requiring quick andaccurate response, as they do not require a large amount of motiveforce.Theymaybereciprocatingcylinders,rotatingmotors,ormayberobotendeffectors.

Afewmorecomponentscanbeaddedtothesystem;first,anairintakefilterandsecond,anairintercooler(ifamultistagecompressorisused).Thefunctionof theformer is toprevent theentryofvastquantitiesofdustanddirtalongwithairandthelatteristocooltheairagaintoroomtemperatureafteritisdischargedfromthelow-pressurecompressor.

BASICHYDRAULICSYSTEMFigure3.3givesanoverviewofabasichydraulicsystem.

Atypicalhydraulicpowersystemincludesthefollowingcomponents:ElectricmotorHydraulicpumpStrainersandfiltersPressuregaugePressurereliefvalvesCheckvalveDirectioncontrolvalveHydraulicactuatorReservoir

1.2.

3.

FIGURE3.3BasicHydraulicSystem.

ElectricMotor:Anelectricmotorisusedtodrivethepump.HydraulicPump:Hydraulicpumps convertmechanical energy fromaprimemover(engineorelectricmotor)intohydraulic(pressure)energy.Thepressureenergyisusedthentooperateanactuator.Pumpspushonahydraulicfluidandcreateflow.Strainers and Filters: To keep hydraulic components performingcorrectly,thehydraulicliquidmustbekeptascleanaspossible.Foreignmatterandtinymetalparticlesfromnormalwearofvalves,pumps,andother components are going to enter a system. Strainers, filters, andmagnetic plugs are used to remove foreign particles from a hydraulicliquidandareeffectiveassafeguardsagainstcontamination.

Strainers:Astraineristheprimaryfilteringsystemthatremoveslargeparticlesofforeignmatterfromahydraulicliquid.Eventhoughitsscreeningactionisnotasgoodasafilter’s,astrainerofferslessresistancetoflow.

Filters:Afilterremovessmallforeignparticlesfromahydraulicfluidandismosteffectiveasasafeguardagainstcontaminates.Theyareclassifiedasfullfloworproportionalflow:

(a)Full-Flow Filter: In a full-flow filter, all the fluid entering a unitpassesthroughafilteringelement.Althoughafull-flowtypeprovidesamore

4.

5.

6.

7.

positivefilteringaction,itoffersgreaterresistancetoflow,particularlywhenitbecomesdirty.

(b) Proportional-Flow Filters: This filter operates on the venturiprinciple in which a tube has a narrowing throat (venturi) to increase thevelocityof fluid flowing through it.Flowthroughaventuri throatcausesapressuredropatthenarrowestpoint.Thispressuredecreasecausesasuckingaction that draws a portion of a liquid down around a cartridge through afilterelementandupintoaventurithroat.

PressureGauge:Apressure gauge tells us the pressureof fluid goingintothevalve.Pressure Relief Valves: Relief valves are the most common type ofpressure-controlvalves.Thereliefvalvesfunctionmayvary,dependingon a system’s needs. They can provide overload protection for circuitcomponents or limit the force or torque exerted by a linear actuator orrotary motor. The internal design of all relief valves is similar. Thevalvesconsistoftwosections:abodysectioncontainingapistonthatisretainedonitsseatbyaspring(s),dependingonthemodel,andacoveror pilot-valve section that hydraulically controls a body piston’smovement.Theadjustingscrewadjusts thiscontrolwithin the rangeofthe valves. Valves that provide emergency overload protection do notoperateasoftenbecauseothervalvetypesareusedtoloadandunloadapump.However, relief valves should be cleaned regularly by reducingtheirpressureadjustments toflushoutanypossiblesludgedeposits thatmayaccumulate.Operatingunderreducedpressurewillcleanoutsludgedepositsandensurethatthevalvesoperateproperlyafterthepressureisadjustedtoitsprescribedsetting.Check Valve: Check valves are the most commonly used in fluid-poweredsystems.Theyallowflowinonedirectionandpreventflowintheotherdirection.Theymaybeinstalledindependentlyinaline,ortheymaybeincorporatedasanintegralpartofasequence,counterbalance,orpressure-reducingvalve.Thevalveelementmaybeasleeve,cone,ball,poppet,piston, spool,ordisc.Forceof themoving fluidopensacheckvalve;backflow,aspring,orgravityclosesthevalve.DirectionControlValve:Directional-controlvalvesaredevicesusedtochange the flowdirectionof fluidwithin apneumatic/hydraulic circuit.Theycontrolcompressed-airflowtocylinders,rotaryactuators,grippers,

8.

9.

andothermechanisms in packaging, handling, assembly, and countlessotherapplications.HydraulicActuator:Ahydraulicactuatorreceivespressureenergyandconvertsittomechanicalforceandmotion.Anactuatorcanbelinearorrotary.Alinearactuatorgivesforceandmotionoutputsinastraightline.It ismore commonly called a cylinderbut is also referred to as a ram,reciprocatingmotor, or linearmotor.A rotary actuator produces torqueand rotatingmotion. It ismore commonly called a hydraulicmotor ormotor.Reservoir: A reservoir stores a liquid that is not being used in ahydraulicsystem.Ithasmanyotherimportantfunctionsaswell.

It also allows gases to expel and foreign matter to settle out from aliquid.Itfunctionsasacooler.Itfunctionsasa“coarsestrainer,”providingsedimentationofimpurities.Itfunctionsasanairandwaterseparator.Itfunctionsasafoundationforpumps,etc.

Aproperlyconstructed reservoir shouldbeable todissipateheat fromtheoil,separateairfromtheoil,andsettleoutcontaminatesthatareinit.Itshould be high and narrow rather than shallow and broad. The oil levelshould be as high as possible above the opening to a pump’s suction line.This prevents the vacuum at the line opening from causing a vortex orwhirlpooleffect,whichwouldmeanthatasystemisprobablytakinginair.Mostmobileequipmentreservoirsarelocatedabovethepumps.Thiscreatesa flooded-pump-inlet condition. This condition reduces the possibility ofpumpcavitation;aconditionwhereall theavailable space isnot filledandoftenmetalpartswillerode.Mostreservoirsareventedtotheatmosphere.Aventopeningallowsairtoleaveorenterthespaceabovetheoilasthelevelof theoilgoesupordown.Thismaintainsaconstantatmosphericpressureabovetheoil.

HYDRAULICSYSTEMDESIGNEach component in the systemmust be compatiblewith and form an

integralpartofthesystem.Example,aninadequatesizefilterontheinletof

a pump can cause cavitation and subsequent damage to the pump. Eachcomponent in the systemhas amaximum rated speed, torque, or pressure.Loading the system beyond the specifications increases the possibility offailure.

All lines must be of proper size and free of restrictive bends. Anundersizedorrestrictedlineresultsinapressuredropinthelineitself.Somecomponents must be mounted in a specific position with respect to othercomponents or lines. The housing of an in-line pump, for example, mustremainfilledwithfluidtoprovidelubrication.

Systemsshouldbedesignedforcorrectoperatingpressures.Thecorrectoperating pressure is the lowest pressure, which will allow adequateperformance of the system function and still remain below the maximumratingofthecomponentsandmachine.Alwayssetandcheckpressureswithagauge.

FLUIDSUSEDINHYDRAULICSTheoil in ahydraulic systemmust first and foremost transfer energy,

butthemovingpartsincomponentsmustalsobelubricatedtoreducefrictionandconsequentheatgeneration.Additionally,theoilmustleaddirtparticlesand friction heat away from the system and protect against corrosion. Oilrequirementsinclude:

Goodlubricatingproperties.Goodwearproperties.Suitableviscosity.Goodcorrosioninhibitor.Goodanti-aerationproperties.Reliableairseparation.Goodwaterseparationmotoroil.

Liquids beingused includemineral oil,water, phosphate ester,water-based ethylene glycol compounds, and silicone fluids. The three mostcommon types of hydraulic liquids are petroleum-based, synthetic fire-resistant,andwater-basedfire-resistant.

Petroleum-BasedFluids

1.2.3.

4.5.6.

Petroleum-BasedFluidsThemost commonhydraulic fluidsusedare thepetroleum-basedoils.

These fluids contain additives to protect the fluid from oxidation(antioxidant), to protect system metals from corrosion (anticorrosion), toreduce tendency of the fluid to foam (foam suppressant), and to improveviscosity.

SyntheticFire-ResistantFluidsPetroleum based oils contain most of the desired properties of a

hydraulicliquid.However,theyareflammableundernormalconditionsandcan become explosive when subjected to high pressures and a source offlame or high temperatures. Nonflammable synthetic liquids have beendevelopedforuseinhydraulicsystemswherefirehazardsexist.

Water-BasedFire-ResistantFluidsThemostwidelyusedwater-basedhydraulicfluidsmaybeclassifiedas

water-glycolmixtures andwater-synthetic basemixtures. Thewater-glycolmixture contains additives to protect it from oxidation, corrosion, andbiologicalgrowthand toenhance its load-carryingcapacity.Fire resistanceof the water mixture fluids depends on the vaporization and smotheringeffectofsteamgeneratedfromthewater.Thewaterinwater-basedfluidsisconstantlybeingdrivenoffwhilethesystemisoperating.Thereforefrequentcheckstomaintainthecorrectratioofwaterareimportant.

EXERCISESDefinefluidpower.Whatarethedifferentfluidpowerelements?Discuss.What is the difference between fluid power and hydraulics andpneumatics?Discussthebasicelementsofanautomatedsystem.Whataretheadvantagesanddisadvantagesoffluidpower?Distinguishbetweenhydraulicandpneumaticsystems.

7.

8.9.10.

11.12.13.14.15.

What are the properties of pneumatic energy thatmake it a fit for theengineeringapplications?Whataretheadvantagesofhydraulicsoverpneumatics?Discusstheapplicationofhydraulicsinautomation.Compare the different features of a hydraulic system with those of apneumaticsystem.Drawasketchofahydraulicsystemandexplainitscomponents.Drawasketchofapneumaticsystemandexplainitscomponents.Listtheapplicationsofhydraulicsandpneumatics.Discussthevarioustypesoffluidusedinhydraulics.Whatarethereasonsforpressuredropinhydraulics?

CHAPTER4

PUMPSANDCOMPRESSORS

INTRODUCTIONThe power source is the key element in a fluid-power system. In a

pneumatic system, the power source is an air compressor, while in ahydraulic system, it is a pump. These normally are driven by an electricmotor or internal combustion engine. Storage devices are used alongwithmostsystemssothattheycanbemadetoworkmoreefficiently.Inhydraulicsystems,thestoragedeviceisanaccumulator; inpneumaticsystems,it isatankorreceiver.However,mostpneumaticsystemsareusedwithareceiver.One may define the fluid power generator as a means of converting themechanicalenergyofamotororengineintopotentialenergyofthefluid.

Apump is theheartof thehydraulicsystem.It isamechanicaldeviceusedtomoveliquidsunderpressureortoraisethemfromalowerleveltoahigherlevel.Thisisdonebycreatingsuctionattheinletandhighpressureatthe outlet. Pumps are used throughout the plant to move fluids from oneplacetoanother.Everysystemfromfueloiltowaterusepumps.Theyplayavital role in supplying fluids at the correct flow rate and pressure tocomponentsdownstreamofthepumps.Theselectionofthepumpclassandtype foracertainapplication is influencedbysystemrequirements, systemlayout, fluid characteristics, intended life, energy cost, code requirements,andmaterialsofconstruction.

Acompressor isadevice that takes inairatatmosphericpressureanddelivers it at a pressure higher than atmospheric. Every compressed airsystembeginswithacompressor,whichisacontinuoussourceofairflowforallthedownstreamequipmentandprocesses.Themainparametersofanyair

compressor are capacity and its pressure; capacity does the work and thepressureaffectstherateatwhichworkisdone.

PUMPSVS.COMPRESSORSThe purpose of both the compressor and the pump is to raise the

pressureoffluid.Themaindifferencebetweenapumpandacompressoristhat the fluid delivered by compressor, i.e., air, is compressed and underpressure at the time it is delivered, even if there is no loadon the system.Mostdevicesused tocompressairareverysimilar inconceptandperhapseven in hardware to hydraulic pumps, and selection considerations aresimilar.Theonlyothersubstantivedifferenceisthatmosthydraulicsystemsarepoweredbyasinglepumpthatisactuallyapartofthesystem,whereasmostpneumaticsystemsareoftenpoweredbyasinglecompressor,whichisalmostautility in theplant likewaterorelectric service.Hydraulicpumpsdeliver high-pressure fluid flow to the pump outlet. Hydraulic pumps arepowered by mechanical energy sources to pressurize fluid. A hydraulicpump,whenpoweredbypressurizedfluid,canrotate ina reversedirectionandactasamotor.

POSITIVEDISPLACEMENTVS.NONPOSITIVEDISPLACEMENTDEVICES

Positive displacement devices are also called hydrostatic devices. Apositivedisplacementdeviceisonethatdisplaces(delivers)thesameamountof fluid for each rotating cycle of the pumping element.Constant deliveryduringeachcycle ispossiblebecauseof theclose tolerancefitbetweenthepumpingelementandthepumpcase.Theyuseamechanismthatsealsfluidinachamberandforcesitoutbyreducingthevolumeofthechamber.Thisactionincreasesthefluid’spressure.Positivedisplacementdevicescanbeofeither fixed or variable displacement. The output of a fixed displacementdevice remains constant during each pumping cycle and at a given pumpspeed. The output of a variable displacement device can be changed byalteringthegeometryofthedisplacementchamber.Generally,thesedevicesareusedforlowvolumeandhighlift.

Nonpositivedisplacementdevicesarethosewherefluidiscompressedbythedynamicactionofrotatingvanesorimpellersimpartingvelocityandpressure to the fluids. These devices are also called as Rotodynamic orhydrodynamicdevices.

CLASSIFICATIONOFHYDRAULICPUMPSAll pumps may be classified as either positive displacement or non

positivedisplacementpumps.

Most pumps used in hydraulic systems are positive displacement.Figure4.1showstheclassificationofpumps.

FIGURE4.1ClassificationofPumps.

POSITIVEDISPLACEMENTPUMPSTheworddisplacementreferstohowmuchfluidapumpcanmoveina

single rotation. Positive displacement pumps displace a known quantity ofliquid with each revolution of the pumping elements. This is done bytrapping fluid between the pumping elements and a stationary casing.Pumping element designs include gears, lobes, rotary pistons, vanes, andscrews. Positive displacement pumps are found in a wide range ofapplications such as chemical processing, liquid delivery, marine,

pharmaceutical, as well as food, dairy, and beverage processing. Thesepumps are usedwhen higher head increases are required. Their versatilityand popularity are due to their relatively compact design, high-viscosityperformance,continuousflowregardlessofdifferentialpressure,andabilityto handle high differential pressure. Positive displacement pumps can beclassifiedas:

Rotarypumps.Reciprocatingpumps.Meteringpumps.

ROTARYPUMPSRotary pumps operate in a circular motion and displace a constant

amountof liquidwitheachrevolutionof thepumpshaft. Ingeneral, this isaccomplished by pumping elements (e.g., gears, lobes, vanes, screws)moving in such a way as to expand volumes to allow liquid to enter thepump. These volumes are then contained by the pump geometry until thepumpingelementsmove insuchawayas to reduce thevolumesandforceliquidoutof thepump.Flowfromrotarypumpsisrelativelyunaffectedbydifferentialpressureandissmoothandcontinuous.Rotarypumpshaveverytightinternalclearanceswhichminimizetheamountofliquidthatslipsbackfromdischargetothesuctionsideofthepump.Becauseofthis,theyareveryefficient. These pumps work well with a wide range of viscosities,particularlyhighviscosities.Theycanhandlealmostanyliquidthatdoesnotcontainhardandabrasivesolids,includingviscousliquids.Afewimportantdesignsofrotarypumpsarelistedandexplainedbelow:

GearpumpLobepumpVanepumpPeristalticpumpScrewpumpPistonpumpFlexibleimpellerpump

GearPump

1.2.

Agearpumpworksontheprinciplethatwhenapairofgearsisbeingdrivenbyanexternalmeans,fluidmovingintothepumpasapartialvacuumisformedandthendischargedthoughtheoutletbythemeshingofthegears.Theyareoneofthemostcommontypesofpumpsforhydraulicfluidpowerapplications. Gear pumps are fixed displacement, meaning they pump aconstantamountoffluidforeachrevolution.Gearpumpsarebuilttooperateinthemostpunishingapplications,particularlythosewithlargeamountsofdebris and extremelyhigh temperatures, such as steelmills, foundries, andminingoperations.Therearetwomainvariationsofgearpumps:

ExternalgearpumpsInternalgearpumps

External gear pumps use two external spur gears and internal gearpumpsuseanexternalandaninternalspurgear.

ExternalGearPumpA typical external-gear pump is shown in Figure 4.2. These pumps

comewith a straight spur, helical, or herringbonegear.Straight spurgearsareeasiesttocutandarethemostwidelyused.

FIGURE4.2ExternalGearPump.

Helicalandherringbonegearsrunmorequietly,butcostmore.

External gear pumps are similar in pumping action to internal gearpumps in that two gears come into and out ofmesh to produce flow.Thegear pumpconsists of pumphousing that contains a pair ofmeshedgears.

Theexternalgearpumpusestwoidenticalgearsrotatingagainsteachother,onegearisdrivenbyamotorcalleddrivegearanditinturndrivestheothergearcalleddrivengear.Eachgear issupportedbyashaftwithbearingsonbothsidesofthegear.

Figure4.3showstheworkingofanexternalgearpump.Thegearpumpworksbycreatingapartialvacuumatthepumpinlet.Asthegearsmesh,apartialvacuumiscreatedatthepumpinletasshowninFigure4.3(a).Thisallowstheatmosphericpressuretopushoilfromthereservoirintothepump.The oil is carried into the cavity and is trapped by the gear teeth as theyrotate. (Refer to Figure 4.3 (b).)As the gears come out of themesh, theycreateexpandingvolumeontheinletsideofthepump.Finally,themeshingof the gears forces oil through the outlet port under pressure as shown inFigure4.3(c).

FIGURE4.3WorkingofExternalGearPump.

Advantages

HighspeedHighpressureNooverhungbearingloadsRelativelyquietoperationDesignaccommodatesawidevarietyofmaterials

Disadvantages

NosolidsallowedFixedendclearances

Applications

Variousfueloilsandlubeoils.Chemicaladditiveandpolymermetering.Chemicalmixingandblending(doublepump).Industrialandmobilehydraulicapplications(logsplitters,lifts,etc.).Acidsandcaustic(stainlesssteelorcompositeconstruction).Lowvolumetransferorapplication.

InternalGearPumpTheworkingprincipleoftheinternalgearpumpissimilartothatofthe

externalgearpump.Figure4.4showsaninternalgearpump.Hereaninnergearmeshes onto the inside of a larger gear. This is unlikely the externalgearpumpwherebothgearsmeshontheiroutersurface.Pumpingchambersare formedbetween the innergear teethand theoutergear teethandoil isforcedoutofpumpoutletwhere the teethmesh.Thecrescent seal ensurestheseparationof the inletandoutletport.Thecrescentsealprevents liquidfromflowingbackwardsfromtheoutlet.

FIGURE4.4InternalGearPump.

Therotationof the internalgearbyashaftcauses theexternalgear torotate,becausethetwoareinmesh.Everythinginthechamberrotatesexceptthecrescent,causingaliquidtobetrappedinthegearspacesastheypassthecrescent.Fluidiscarriedfromaninlettothedischarge,whereitisforcedoutofapumpbythegearsmeshing.Asfluidiscarriedawayfromtheinletside

ofapump,thepressureisdiminished,andfluidisforcedinfromthesupplysource.Thesizeofthecrescentthatseparatestheinternalandexternalgearsdeterminesthevolumedeliveryofthispump.Asmallcrescentallowsmorevolumeofafluidperrevolutionthanalargercrescent.

Advantages

OnlytwomovingpartsExcellentforhigh-viscosityliquidsConstantandevendischargeregardlessofpressureconditionsOperateswellineitherdirectionEasytomaintainFlexibledesignoffersapplicationcustomization

Disadvantages

UsuallyrequiresmoderatespeedsMediumpressurelimitationsOnebearingrunsintheproductpumpedOverhungloadonshaftbearingExpensivetomanufactureandmaintain

Applications

Commoninternalgearpumpapplicationsinclude,butarenotlimitedto:

Allvarietiesoffueloilandlubeoil.Resinsandpolymers.Alcoholsandsolvents.Asphalt,bitumen,andtar.Foodproductssuchascornsyrup,chocolate,andpeanutbutter.Paint,inks,andpigments.Soapsandsurfactants.

Gerotor Pump. Gerotor pump is one of the most common types ofinternal gear pumps. (Refer to Figure 4.5.) It consists of an internal gearinsideanexternalgear.Theinternalgeariskeyedtothedriveshaftandhasone fewer tooth than an external gear. During rotation each tooth of theinternalgear is inconstantcontactwith theexternalgear.Due to theextra

tooth, the outer gear rotates slowly. Space between the rotating teethincreases during the first half of each turn thus taking fluid in. In the lasthalf,thespacedecreasesthusforcingfluidoutthroughtheoutletport.

FIGURE4.5GerotorPump.

LobePumpThelobepumpissimilartoanexternalgearpumpinoperation,i.e.,the

fluidflowsaroundtheinteriorofthecasing.Itdiffersfromtheexternalgearpump in theway thegearsaredriven. Inagearpump,onegeardrives theother; in a lobe pump, both rotors are driven through suitable drive gearsoutsideofthepumpcasingchamber.Gearsarereplacedbyimpellerswhichhavetwoorthreelobeshapedteeth.Theseteetharewiderandmoreroundedthan the teeth of a regular gear pump.As a result, displacement is higher.Unlike external gear pumps, the pumping gear elements or lobes do notmake contact. Figure 4.6 illustrates a three-lobe pumpwith two impellers.Thenumberoflobeswilldeterminetheamountofpulsationfromthepumpoutput.Thegreater thenumberof lobes, themoreconstant is thedischargefromthepump.

FIGURE4.6LobePumpwithTwoImpellers.

As the rotors start to rotate, an expanding cavity is formed by therotationofthelobes,whichcreatesavacuumattheinletport,drawingfluidinthepumpingchamber.Fluidtravelsaroundtheinteriorofthecasinginthepocketsbetweenthelobesandthecasing.Itdoesnotpassbetweenthelobes.Finally, the fluid is forcedorpressedoutofdischargeportof thepump incontinuoussmoothflowandpressureisgeneratedbythemeshingoftheloberotors.The lobed impellersareeasier to replaceand tend towear lesswithabrasivesthanthegearsinthegearpump.

Advantages

PassmediumsolidsNometal-to-metalcontactLong-termdryrun(withlubricationtoseals)Non-pulsatingdischarge

Disadvantages

RequirestiminggearsCostlyRequirestwosealsReducedliftwiththinliquids

Applications

Commonrotarylobepumpapplicationsinclude,butarenotlimitedto:

PolymersPapercoatingsSoapsandsurfactantsPaintsanddyesRubberandadhesivesPharmaceuticalsFoodapplications

Theyarepopular in thesediverse industriesbecause theyoffer superbsanitaryqualities,highefficiency,reliability,corrosionresistance,andgoodcleanin-placecharacteristics.

VanePumpA rotary vane pump is a positive displacement pump that consists of

vanes mounted to a rotor that rotates inside of a cavity. Vane pumps areavailable in a number of vane configurations including sliding vane (left),flexiblevane,swingingvane, rollingvane,andexternalvane.Each typeofvanepumpoffersuniqueadvantages.Forexample,externalvanepumpscanhandlelargesolids.Flexiblevanepumps,ontheotherhand,canonlyhandlesmall solids but create good vacuum. Sliding vane pumps can run dry forshortperiodsoftimeandhandlesmallamountsofvapor.

Slidingvanepumpsoperatequitedifferentlyfromgearandlobetypes.The most simple vane pump consists of a circular rotor rotating inside alarger circular cam ring. (Refer to Figure 4.7). The centers of these twocircles are offset, causing eccentricity. The vanes are fitted into the rotorslotsandtherotorismountedonthedriveshaft.Therotorrotatesinsidethecamringbyaprimemover.Thevanesforcedoutoftheirslotscontactandfollow the inner surface of the housing.This occurs due to the centrifugalforce which pushes the vanes out of their slots and holds them in placecreatingasealagainstthecamring.Thereisanincreaseinvolumefromthepointwherethecamringsurfaceisclosesttotherotor.Duetoanincreaseinvolume,apartialvacuumiscreatedandoilispushedintotheinletfromthereservoir. As the fluid crosses the rotor centerline, the chambers becomeprogressivelysmallerasthecamringforcesthevanesintotheirslots.Asthevolumedecreases,fluidisforcedoutofthepumpoutlet.

FIGURE4.7VanePump.

Advantages

SimpleinconstructionHighefficiencyandlowcostHandlesthinliquidsatrelativelyhigherpressuresSometimespreferredforsolvents,LPGCanrundryforshortperiodsDevelopsgoodvacuum

Disadvantages

ComplexhousingandmanypartsNotsuitableforhighpressuresNotsuitableforhighviscosityNotgoodwithabrasives

Applications

AerosolandPropellants.AviationService-FuelTransfer,Deicing.AutoIndustry-Fuels,Lubes,RefrigerationCoolants.BulkTransferofLPGandNH3.LPGCylinderFilling.Usedinspraypaintingequipment.

PeristalticPump

PeristalticPumpA peristaltic pump is a type of positive displacement pump used for

pumpingavarietyoffluids.(RefertoFigure4.8.)Thispumpisbasedonanelectrometric tube throughwhich thefluid is forced.Aflexible tubepassesthrough the fixed casing of the pump. A rotor with rollers attached to itmoves and presses against the flexible tube. The tube is compressed at anumberofpointsincontactwiththerollers.Thissqueezingactionproducesanevenflowoffluid.Thefluidismovedthroughthetubewitheachrotatingmotion.Forproperaction,itisimportantthatthetubingisflexibleenoughtoallowtherollerstosqueezeituntilitiscompletelyclosed.Thepumpedfluidis completely isolated from the moving parts, which permits pumping ofcorrosive substances. The flow rate of the pump is related directly to thediameterofthetubeandthespeedofrotationofthedrive.

FIGURE4.8PeristalticPump.

Advantages

Hydraulicallyoperatedspeedvariationstomeetalljobdemands.Enablespumpingofheavy,fibered,thick,andabrasivematerialsathighvolumes.The pump’smechanicalmaintenance is limited to hosewear. Pumpedmaterialdoesnotcomeincontactwithanymovingparts.Easytosterilizeandcleantheinsidesurfacesofthepump.Replacementofthehoseisquickandeasy.Dryrunningcanoccurwithoutcausingdamagetothepump.Lowcostofmaintenance.Inexpensivetomanufacturebecausetherearenomovingpartsincontactwiththefluid.

Applications

Some common applications include pumping aggressive chemicals,high solid slurries, andothermaterialswhere isolationof theproduct fromtheenvironment,andtheenvironmentfromtheproduct,arecritical.

ScrewPumpScrewpumpsareauniquetypeofrotarypositivedisplacementpumpin

which the flow through the pumping element is truly axial. Screw pumpsconsist of helical screws which revolve in a fixed casing. As the screwrotates in the casing, a cavity created between the screw and the casingprogressestowardsthedischargesideofthepump.Thismovementcreatesapartialvacuumwhichdrawsliquidintothepump.Theshapeofthecasingatthe discharge end is such that the cavity becomes closed. Screw pumpsproduce a constant discharge with negligible pulsation. They have anexceptionally long life expectancy. Significant disadvantages of screwpumps are that they are bulky and heavy. Application of screw pumps inagricultureislimitedtofoodprocessingandhydraulicsystemsformachinetools.Screwpumpscanbeoftwinscrewormultiplescrewtypes.

Twin-ScrewPumpsIn twin-screw pumps, timing gears are used to control the relative

motionofthescrews.Inpumpswithmorethantwoscrews,asinglecentralscrewcausesthecomplimentaryrotationoftheadjacentscrews.Twin-screwpumpshavethefollowingcharacteristics:

Applicableforalltypesofliquid,fromlowtohighviscosity,chemicallyneutraloraggressive.Screws do not touch. Therefore low shear rate, low emulsion, lowfriction/lesstorque.Highreliabilityandefficiency.Quietoperation.Highself-primingproperty.Lowpulsationflow.Compactandspace-savingdesign.Longlife.

Multi-ScrewPumps

Multi-ScrewPumpsIn multi-screw pumps, the fluid is transferred under the action of a

numberofscrewsmeshedtogetherinacasingprovidedwithchannelstosuitthescrews.Thesepumpsareusedinthechemicalprocessindustryandintheoilindustryforapplicationsonoilrigs.Theyareusedforpumpingfueloil,lubrication oil, seawater, paints, etc. Multiple screw pumps have thefollowingcharacteristics:

Outputissmooth.Produceaconstantdischargewithnegligiblepulsation.Awiderangeoffluidviscositiescanbehandled.Thepumpisself-primingespeciallywhenthescrewsarewetted.Thevolumetricandmechanicalefficiencyisgood.Thepumpsarequietoperating.Thepumpshaveahighlevelofreliability.

PistonPumpsArotarypistonpumphasarotarymotionratherthanabackandforth

motionasinthereciprocatingpistonpumps.Therearetwobasicdesignsofrotarypistonpumpsavailable:

RadialpistonpumpAxialpistonpump

In a radial design, the number of pistons and cylinders are arrangedradiallyaroundtherotorhub,whileintheaxialdesigntheyarelocatedinaparallelpositionwithrespecttotherotorshaft.

Pistonpumpsoperateathigherefficiencies thangearandvanepumpsandareusedforhigh-pressureapplicationswithhydraulicoilorfire-resistantfluids.Thepistonpumpsareextensivelyusedforpowertransferapplicationsintheoff-shorepowertransmission,agricultural,aerospace,andconstructionindustries,etc.

Construction

Thepumpconsistsofablockwithanumberofsymmetricallyarrangedcylindricalpistonsaroundacommoncenter line.Thepistonsarecaused toreciprocate inandoutunder theactionofa separate fixedor rotatingplate

(axial pistons) or an eccentric bearing ring (radial pump). Each piston isinterfacedwith the inlet andoutletportvia a specialvalve arrangement sothatasitmovesoutofitscylinder,itdrawsfluidinandasitmovesback,itpushesthefluidout.

Rotarypistonpumpsincludeanumberofvariationswhichworksonasimilarprinciple:

RadialpistonpumpSwashplatepistonpumpWobbleplatepumpBentaxispistonpump

RadialPistonPumpA radial piston pump shown inFigure 4.9 is the simplest design of a

piston pump. It consists of a rotating cylinder containing equally spacedradial pistons arranged radial around the cylinder center line. A springpushes thepistonsagainst the innersurfaceofanencirclingstationary ringmounted eccentric to the cylinder. The pistons draw in fluid during half arevolution and drive fluid out during the other half. The greater the ringeccentricity,thelongerthepistonsstrokeandthemorefluidtheytransfer.

FIGURE4.9RadialPistonPump.

SwashPlatePumpSwash plate pumps shown in Figure 4.10 have a rotating cylinder

containingparallelpistonsarrangedradiallyaroundthecylindercenterline.Aspringpushes thepistonsagainst a stationary swashplate locatedatone

endofthecylinder,whichsitsatanangletothecylinder.Thepistonsdrawinfluidduringhalfarevolutionanddrivefluidoutduringtheotherhalf.Thegreater theswashplateangle relative to thecylindercenter line, the longerthepistonsstrokeandthemorefluidtheytransfer.

FIGURE4.10SwashPlatePump.

WobblePlatePumpThis pump includes a stationary piston block containing a number

parallel pistons arranged radially around the block center (at least five).(Refer to Figure 4.11.)The end of each piston is forced against a rotatingwobblevplatebysprings.Thewobbleplateisshapedwithvaryingthicknessaround its center line and thus, as it rotates, it causes the pistons toreciprocateatafixedstroke.Thepistonsdrawinfluidfromthecavityduringhalfarevolutionanddrivefluidoutattherearofthepumpduringtheotherhalf.Thefluidflowiscontrolledusingnon-returnvalvesforeachpiston.

FIGURE4.11WobblePlatePump.

BentAxisPump

Anotherdesignofpistonpumpsisthebentaxispistonpump.Itconsistsofacylinderblockplacedatanangleoffsetfromthedriveshaft.Thepistonrods are attached to the shaft flange by ball joints. (Refer to Figure 4.12.)Thecylinderblockissplinedtotheshaftandthisshaftisjoinedtothedriveshaft by a universal link. This link ensures that the drive shaft and thecylinderblockarealignedproperlyandrotatetogether.Whenthedriveshaftrotates,thepistonsareforcedinandoutoftheirboresbecausethedistancebetween the cylinder block and the shaft flange varies. Due to thereciprocating action of the pistons, the fluid is pushed in through the inletportbyatmosphericpressureanddischargefromtheoutletport.

FIGURE4.12BentAxisPump.

FlexibleImpellerPumpFlexibleimpellerpumpsconsistofflexiblebladedimpellerswhichare

placedeccentrically incasings.Theimpellerbladesunfoldas theypass thesuctionport,creatingapartialvacuumwhichcauses liquidtoflowintothepump.Astherotormoves,thebladesbendduetotheeccentricplacementoftherotor,resultinginasqueezingactionontheliquidandincreasedpressure.(RefertoFigure4.13.)

FIGURE4.13FlexibleImpellerPump.

BenefitsofImpellerPumpsFlexible impeller pumps are used in a wide range of applications in

mosttypesofindustries.Someoftheuniquefeaturesofthesepumpsare:

Inexpensiveandsimpledesign.Easytoselect,service,anduse.Extremelygoodself-primingcapacitydisplacesairandgaspositivelyoraeratedproducts.Smoothoperatingprinciple.Hard/softsolidstransportedthroughthepumpwithoutdamagetopumporproduct.

RECIPROCATINGPUMPSThe term reciprocating is defined as a back and forthmotion. In the

reciprocatingpump,itisthisbackandforthmotionofthepistoninsidethecylinder that provides the flow of fluid. Reciprocating pumps, like rotarypumps,operateonthepositiveprinciple,i.e.,eachstrokedeliversadefinitevolume of fluid to the system. Reciprocating pumps are generally veryefficientandaresuitableforveryhighheadsatlowflows.

TypesofReciprocatingPumpsReciprocatingpumpsareclassifiedas:

Pistonpump/plungerpumpDiaphragmpump

Thisclassificationisbasedonthetypeofreciprocatingelementusedtotransfer energy to the fluid. These types of pumps operate by using areciprocatingpistonordiaphragm.Theliquidentersapumpingchamberviaaninletvalveandispushedoutviaanoutletvalvebytheactionofthepistonordiaphragm.Reciprocatingpumpsoperatewithhighefficiencies.Thesearesuitableforveryhighheadsatlowflowsandcanhandlevaryingpressuresataconstantspeed.

PistonPump/PlungerPumpPistonpumps/plungerpumpsarereciprocatingpumpsthatuseaplunger

or piston tomove fluid through a cylindrical chamber. In piston pumps, apiston, which is attached to a mechanical linkage, transforms the rotarymotionofadrivewheelintothereciprocatingmotionofthepiston.

A single-acting piston pump is shown in Figure 4.14.During suctionstroke, as shown in Figure 4.14 (a), liquid enters the cylinder through thesuctioncheckvalve.Duringcompressionstroke,asshowninFigure4.14(b),theliquidisforcedintothedischargelinethroughthedischargecheckvalve.This action is similar to the action of a piston in the cylinder of anautomobileengine.

FIGURE4.14Single-ActingPistonPump.

Theflowrateofasimplepistonpumpisnotconstantbecausethereisnoflowontheintakestrokeandtheflowvariesfromzerotothemaximumand back to zero on each compression stroke. Pulsation of flow can bereduced by using a double-action piston pump as shown in Figure 4.15,wherethevolumeonbothsidesofthepistonisusedforpumpingliquid.In

this case, each suction stroke is a companion compression stroke for theoppositesideofthepumpandtheliquidispumpedonbothstrokes.

FIGURE4.15Double-ActingPistonPump.

CharacteristicsofPistonPumps

Thesepumpscancreatehighpressures.Theydeliveraconstantflowrateindependentofthedischargepressure.Theycanrundry.Theyhavealonglife.Thesepumpsarebulkyandheavy.

DiaphragmPumpDiaphragm pumps are common industrial pumps that use positive

displacementprincipletomoveliquids.Sometimesthistypeofpumpisalsocalled a membrane pump. These devices typically include a singlediaphragm and chamber, aswell as suction and discharge check valves toprevent backflow. Pistons are either coupled to the diaphragm, or used toforce hydraulic oil to drive the diaphragm. The operation of a diaphragmpumpissimilartothatofapistonpump.Thepulsatingmotionistransmittedtothediaphragmthroughafluidoramechanicaldrive,andthenthroughthediaphragmtothepumpedliquid.AschematicofthistypeofpumpisshowninFigure4.16.

FIGURE4.16DiaphragmPump.

CharacteristicsofDiaphragmPump

Thepumpedliquiddoesnotcomeintocontactwithmostoftheworkingparts of the pump. Hence, diaphragm pumps are suitable for pumpingcorrosiveliquids.Diaphragm pumps can run dry for extended periods of time withoutdamage.Mostdiaphragmpumpscanbeadjustedforcalibrationwhenrunning.Diaphragmpumpsarehighlyreliable.These pumps can handle abrasive materials such as acids, chemicals,concrete,coolants,combustibleorcorrosivematerials,andeffluents.Disadvantagesof thesepumps include limitedheadandcapacityrange,andthenecessityofcheckvalvesinthesuctionanddischargingnozzles.These pumps are used in a variety of industries such as aerospace ordefense, agriculture or horticulture, automotive, brewery or distillery,construction, cryogenic, dairy, or flood control applications, medical,

pharmaceutical, and biotechnology applications; power generation; thepulpandpaperindustries.

METERINGPUMPAmeteringpumpisused topumpliquidsatadjustableflowrates that

areprecisewhenaveragedovertime.Deliveryoffluidsinpreciseadjustableflowratesissometimescalledmetering.Thetermmeteringpumpisbasedontheapplicationoruseratherthantheexactkindofpumpused.Theyarealsocalledproportioningorcontrolled-volumepumps.

Meteringpumpsareavailable ineitheradiaphragmorpiston/plunger,andaredesignedforcleanserviceasdirtyliquidcaneasilyclogthevalvesand nozzle connections.A piston/plunger typemetering pump is shown inFigure 4.17. Many metering pumps are piston-driven. Piston pumps arepositivedisplacementpumpswhichcanbedesigned topumpatpracticallyconstant flow rates. In piston driven metering pumps, there is apiston/plunger,whichgoesinandoutofacorrespondinglyshapedchamberinthepumphead.Theinletandoutletlinesarejoinedtothepistonchamber.Therearetwocheckvalvesattachedtothepumphead,oneat theinletandtheotherattheoutlet.Theinletvalveallowsflowfromtheinletlinetothepistonchamber,butnotinthereversedirection.Theoutletvalveallowsflowfromthechambertotheoutletline,butnotinreverse.Themotorrepeatedlymovesthepistonintoandoutofthepistonchamber,causingthevolumeofthe chamber to repeatedly become smaller and larger. When the pistonmovesout,avacuumiscreated.Lowpressureinthechambercausesliquidto enter and fill the chamber through the inlet check valve, but higherpressureat theoutletcauses theoutletvalve toshut.Thenwhen thepistonmoves in, it pressurizes the liquid in the chamber. High pressure in thechamber causes the inlet valve to shut and forces theoutlet valve toopen,forcingliquidoutattheoutlet.

FIGURE4.17PlungerTypeMeteringPump.

DYNAMIC/NONPOSITIVEDISPLACEMENTPUMPS

Hydrodynamic or non positive displacement pumps are low pressure,high volume pumps. These pumps operate by developing a high liquidvelocityandconvertingthevelocitytopressureinadiffusingflowpassage.Dynamicpumpsusuallyhave lowerefficiencies thanpositivedisplacementpumps,butalsohavelowermaintenancerequirements.Dynamicpumpsarealso able to operate at fairly high speeds and high fluid flow rates. Thesepumpsarelargeinsize.Dynamicpumpsareclassifiedas:

CentrifugalpumpsAxialpumps

CENTRIFUGALPUMPSCentrifugalpumpsdifferfromrotarypumpsinthattheyrelyonkinetic

energyratherthanmechanicalmeanstomovefluid.Acentrifugalpumpisarotodynamicpumpthatusesarotatingimpellertoincreasethevelocityofafluid. Fluid enters the pump at the center of a rotating impeller and gainsenergyasitmovestotheouterdiameteroftheimpeller.Fluidisforcedoutofthepumpbytheenergyitobtainsfromtherotatingimpeller.Typicallythevoluteshapeofthepumpcasing(increasinginvolume),orthediffuservanes(whichservetoslowthefluid,convertingtokineticenergyintoflowwork)areresponsiblefor theenergyconversion.Theenergyconversionresults inan increased pressure on the downstream side of the pump, causing flow.

Centrifugal pumps can transfer large volumes of liquid but efficiency andflowdecreaserapidlyaspressureand/orviscosityincreases.

There are several kinds of centrifugal pumps.Every centrifugal pumphas two characteristics that are same; each has an impeller that forces theliquid being pumped into a rotary motion, and each has a casing, whichdirects the liquid to the impeller. The liquid leaves the impeller as theimpellerrotates.Theliquidleaveswithahighervelocityandpressurethanithad when it entered. There is a conversion of some of the velocity topressure that takes place before the liquid leaves the pump; this partialconversiontakesplaceinthepumpcasing.AcentrifugalpumpisshowninFigure4.18.

FIGURE4.18CentrifugalPump.

Centrifugalpumpsareclassifiedintothreegeneralcategories:

Radial flow: a centrifugal pump in which the pressure is developedwhollybycentrifugalforce.

Mixed flow: a centrifugal pump in which the pressure is developedpartlybycentrifugalforceandpartlybytheliftofthevanesoftheimpellerontheliquid.

Axial flow: acentrifugalpump inwhich thepressure isdevelopedbythepropellingorliftingactionofthevanesoftheimpellerontheliquid.

Advantages

Someoftheadvantagesofcentrifugalpumpsaresmoothflowthroughthe pump and uniform pressure in the discharge pipe, low cost, and anoperating speed that allows for a direct connection to steam turbines andelectricmotors.Theyarewidelyusedinchemicalprocessingplantsandoilrefineries.

Disadvantages

Primary disadvantages are higher cost and limited flow at higherpressure.

PUMPSELECTIONPARAMETERSThe process involved in the selection of a suitable pump for a given

applicationdependsonmanyparameters.Thesefactorsinclude:

CostPressurerippleandnoiseSuctionperformanceContaminantsensitivitySpeedWeightFixedorvariabledisplacementMaximumpressureandflow,orpowerFluidtype.

COMPARISONOFPOSITIVEANDNONPOSITIVEDISPLACEMENTPUMPS

Parameter CentrifugalPumps ReciprocatingPumps RotaryPumps

OptimumFlowandPressureApplications

Medium/HighCapacity,Low/MediumPressure

LowCapacity,HighPressure

Low/MediumCapacity,Low/MediumPressure

MaximumFlowRate 6,300+l/s 630+l/s 630+l/s

LowFlowRateCapability

No Yes Yes

MaximumPressure 400+bar 6,500+bar 270+bar

RequiresReliefValve No Yes Yes

SmoothorPulsatingFlow

Smooth Pulsating Smooth

VariableorConstantFlow

Variable Constant Constant

Self-priming No Yes Yes

SpaceConsiderations RequiresLessSpace RequiresMoreSpace RequiresLessSpace

LowerInitial,Lower HigherInitial,Higher LowerInitial,Lower

Costs LowerInitial,LowerMaintenance,HigherPower

HigherInitial,HigherMaintenance,LowerPower

LowerInitial,LowerMaintenance,LowerPower

FluidHandling Suitableforawiderangeincludingclean,clear,non-abrasivefluidstofluidswithabrasive,high-solidcontent.Notsuitableforhighviscosityfluids.Lowertoleranceforentrainedgases.

Suitableforclean,clear,non-abrasivefluids.Speciallyfittedpumpssuitableforabrasive-slurryservice.Suitableforhighviscosityfluids.Highertoleranceforentrainedgases.

Requiresclean,clear,non-abrasivefluidduetoclosetolerances.Optimumperformancewithhighviscosityfluids.Highertoleranceforentrainedgases.

AIRCOMPRESSORSEvery compressed air systembeginswith a compressor, the sourceof

airflowforalltheequipmentandprocesses.Aircompressorsareutilizedtoraise the pressure of a volume of air. Air compressors are versatilemechanical tools thatuseoneornumerouspistons topumpcompressedairintoadefinedspace.Anaircompressorisdefinedasacomponentthattakesinairatatmosphericpressureanddeliversitatahigherpressure.

CompressedAir

Compressed air is widely used throughout industry and is consideredoneof themostusefulandclean industrialutilities. It is simple touse,butcomplicatedandcostlytocreate.Compressedairisairthatiscondensedandcontainedatapressurethatisgreaterthantheatmosphere.Theprocesstakesagivenmassofair,whichoccupiesagivenvolumeofspace,andreducesitinto a smaller space. In that space, greater air mass produces greaterpressure. Compressed air is used in many different manufacturingoperations.

ApplicationsofCompressedAir

Compressed air is used in almost every industry like automotive,construction,universities,hospitals,mining,agriculture,foodandbeverage,consumergoods,pharmaceutical,electronics,andmore.

Formaintenancework, plants can use air-operated drills, screwdrivers,andwrenches.Paintingcanbedoneusingpaint-sprayingsystems.

Sprinklersystemsarecontrolledbyairpressure,whichkeepswaterfromenteringthepipesuntilheatbreaksthesealandreleasesthepressure.Pneumatictoolsareusedonaproductionline.Used in the foundry for cleaning large castings, and to remove weldscale,rust,andpaintinotherindustries.Grinding,wire brushing, polishing, sanding, shot blasting, and buffingareperformedefficientlywithcompressedairintheautomotive,aircraft,railcar, locomotive,vesselshops,shipbuilding,otherheavymachinery,andotherindustries.

TYPESOFAIRCOMPRESSORSAircompressorsareoftwotypes:

PositivedisplacementaircompressorsNonpositive/dynamicaircompressors

In the positive displacement type, a given quantity of air or gas istrapped in a compression chamber and the volume it occupies ismechanically reduced, causing a corresponding rise in pressure prior todischarge.Atconstantspeed, theair flowremainsessentiallyconstantwithvariationsindischargepressure.

Dynamic compressors impart velocity energy to continuously flowingairorgasbymeansof impellers rotatingatveryhighspeeds.Thevelocityenergy is changed into pressure energy both by the impellers and thedischargevolutesordiffusers.

ThecompressorsarefurthersegmentedintoseveralcompressortypesasshowninFigure4.19.

FIGURE4.19ClassificationofCompressors.

Thefunctionofallof themis todraw inair fromtheatmosphereandproduceairatsubstantiallyhigherpressures.

POSITIVEDISPLACEMENTCOMPRESSORSPositive displacement compressors decrease the volume and increase

thepressureofaquantityofairbymechanicalmeans.Theseareclassifiedas:

RotarycompressorsReciprocatingcompressors

ROTARYCOMPRESSORSRotary air compressors arepositive displacement compressors.Rotary

compressors have rotors that give a continuous pulsation free discharge.Theyoperateathighspeeds.Theircapitalcostsarelow.Theyarecompactinsize,havelowweight,andareeasytomaintain.Theseunitsarebasicallyoilcooled (withaircooledorwatercooledoilcoolers)where theoil seals theinternal clearances. Because the cooling takes place right inside thecompressor, the working parts never experience extreme operatingtemperatures.Rotarycompressorsareclassifiedintothreegeneralgroups:

ScrewcompressorLobecompressor

Vanecompressor

ScrewCompressorRotary screw compressors are positive displacement compressors.

Compressionisachievedviathemeshingoftwohelicallycutrotorprofiles.One rotor iscutasamaleprofile,and theotherasa femaleprofile.Thesetworotors spin inoppositedirections.The rotaryscrewcompressorcanbesinglescrewortwinscrew.

Asingle-screwcompressorusesasinglemainscrewrotormeshingwithtwogaterotorswithmatchingteeth.Themainscrewisdrivenbytheprimemover,typicallyanelectricmotor.(RefertoFigure4.20.)

FIGURE4.20Single-ScrewCompressor.

Atwin-screwcompressorconsistsoftwointermeshingscrewsorrotors,whichtrapgasbetweentherotorsandthecompressorcase.(RefertoFigure4.21.)Themotordrivesthemalerotor,whichinturndrivesthefemalerotor.Bothrotorsareencasedinahousingprovidedwithairinletandoutletports.Airisdrawnthroughtheinletportintothevoidsbetweentherotors.Astherotors move, the volume of trapped air is successively reduced andcompressedbytherotorscomingintomesh.

FIGURE4.21Twin-Screwcompressor.

Thesecompressorsareavailableasdryorwet(oil-flooded)screwtypes.Inthedry-screwtype,therotorsruninsideofastatorwithoutalubricant(orcoolant). The heat of compression is removed outside of the compressor,limiting it to a single-stage operation. In the oil-flooded screw typecompressor, the lubricant is injected into theair,whichis trappedinsideofthe stator. In this case, the lubricant is used for cooling, sealing, andlubrication.Theairisremovedfromthecompressedgas-lubricantmixtureinaseparator.

Because of simple design and few wearing parts, rotary screw aircompressors are easy to maintain, operate, and provide great installationflexibility. Advantages of the rotary screw compressor include smooth,pulse-freeairoutputinacompactsizewithhighoutputvolumeoveralonglife.

LobeCompressorAschematicdiagramforarotarylobecompressorisprovidedinFigure

4.22.Inthistypeofcompressor,therotorsdonottouchandacertainamountof slip exists. The slip increases as the output pressure increases. Theprinciple of operation is analogous to the rotary screw compressor, exceptthatwith the lobecompressor, themating lobesarenot typically lubricatedforairservice.Asthelobeimpellersrotate,gasistrappedbetweenthelobeimpellersandthecompressorcase,wherethegasispressurizedthroughtherotation of lobes and then discharged. The bearings and timing gears arelubricatedusingapressurizedlubricatingsystemorsump.

FIGURE4.22LobeCompressors.

VaneCompressorA rotary vane compressor is schematically illustrated in Figure 4.23.

Rotary vane compressors consist of a rotor which is mounted offset in alargerhousingwhichcanbeofcircularoramorecomplexshape.Therotorhas slots along its length, each slot contains a vane.Thevanes are thrownoutwardsbycentrifugalforcewhenthecompressorisrunningandthevanesmoveinandoutoftheslotbecausetherotoriseccentrictothecasing.Thevanes sweep thecylinder, suckingair inonone sideandejecting iton theother.

FIGURE4.23VaneCompressor.

RECIPROCATINGCOMPRESSORS

Reciprocatingcompressorswerethefirstofthemodernaircompressordesigns.Reciprocating air compressors arepositive displacementmachinesinwhichpistons aredrivenbya crankshaft.Thismeans theyare taking insuccessive volumes of air that is confined within a closed space andelevating this air to a higher pressure. The reciprocating air compressoraccomplishesthisbyusingapistonwithinacylinderasthecompressinganddisplacingelement.As thepistonenters thedownstroke, air isdrawn intothecylinder from theatmosphere throughanair inletvalve.During theupstroke,thepistoncompressestheairandforcesitthroughadischargecontrolvalve and out of the compressor. These are available in single-acting anddouble-actingconfigurations.Thereciprocatingaircompressorisconsideredsingleactingwhenthecompressingisaccomplishedusingonlyonesideofthepiston.Acompressorusingbothsidesofthepistonisconsidereddoubleacting.Reciprocatingcompressorsareoftwotypes:

PistoncompressorsDiaphragmcompressors

Advantages

Goodforsmallapplications.Cheapandsimpletooperate.Operatesoverawiderangeofpressures.

Disadvantages

Noisy.Maintenanceproblems.Notgoodforsmallapplications.Oilfreeairunitsareexpensive.

PISTONCOMPRESSORSPistoncompressorsareoftwotypes:

Single-StagePistonCompressorThe single-stage reciprocating compressor has a piston that moves

downward during the suction stroke, expanding the air in the cylinder as

shown inFigure4.24.Theexpandingaircausespressure in thecylinder todrop.Whenthepressurefallsbelowthepressureontheothersideoftheinletvalve, thevalveopensandallowsair inuntil thepressureequalizes acrosstheinletvalve.Thepistonbottomsoutandthenbeginsacompressionstroke.The upward movement of the piston compresses the air in the cylinder,causingthepressureacrosstheinletvalvetoequalizeandtheinletvalvetoreset. The piston continues to compress air during the remainder of theupward stroke until the cylinder pressure is great enough to open thedischargevalveagainst thevalvespringpressure.Oncethedischargevalveis open, the air compressed in the cylinder is discharged until the pistoncompletesthestroke.

FIGURE4.24Single-StagePistonCompressor.

Two-StagePistonCompressorToavoidanexcessive rise in temperature,multistagecompressorsare

provided with intercoolers. These heat exchangers remove the heat ofcompression from the gas and reduce its temperature to approximately thetemperature existing at the compressor intake. Such cooling reduces thevolume of gas going to the high pressure cylinders, reduces the powerrequired for compression, and keeps the temperaturewithin safe operatinglimits.

These compressors can generate high pressures than single-stagecompressors. The most common type is two-stage or double-acting

compressors. This style of reciprocating air compressor utilizes a double-acting piston (compression takes place on both sides of the piston), pistonrod, crosshead, connecting rod and crankshaft. (Refer to Figure 4.25.)Double-acting compressors are available in single-and multi-cylinder andsingle-andmultistageconfigurations.Mostdouble-actingaircompressorsareavailable either water-cooled or air-cooled. Lubrication of double-actingcompressors is accomplished with a positive pressure oil pump. The oilrequiredtobothlubricateandprotectthecompressoriscirculatedviatheoilpump to the cylinders and the crankshaft bearings. Discharge airtemperatures in these machines may often exceed 300°C in some of theapplications. On the whole, the reciprocating compressors run hotter thanothertypesofcompressors.

FIGURE4.25Two-StageReciprocatingCompressor.

The compressed air from the first cylinder enters the second-stagecylinderatgreatlyreducedtemperatureafterpassingthroughtheintercooler,thusimprovingefficiencyascomparedtothatofasingle-stageunit.

Advantages

Highestefficiency.Longestservicelife.Fieldserviceability.

Disadvantages

Highestinitialcost.Highinstallationcost.Highmaintenancecost

DIAPHRAGMCOMPRESSORAdiaphragmcompressor(alsoknownasamembranecompressor)isa

variant of the conventional reciprocating compressor. The compression ofgas occurs by themovement of a flexiblemembrane, instead of an intakeelement.Thebackandforthmovementofthemembraneisdrivenbyarodandacrankshaftmechanism.(RefertoFigure4.26.)Onlythemembraneandthe compressor box come in touch with the gas being compressed.Diaphragmcompressorsareused forhydrogenandcompressednaturalgas(CNG)aswellasinanumberofotherapplications.

FIGURE4.26DiaphragmCompressor.

Theoilpressurerequiredtobendthediaphragmisgeneratedbyacrankdrivewithareciprocatingpiston.Duringthecompressionstroke,thepistonpushesoilfromthecylinderintothediaphragmheadwhereitflowsthroughtheperforatedplatetothebacksideofthediaphragm.Thediaphragmisthusforcedtobendintotheconcavediaphragmheadcoversurface.Asthepistonmoves back, it pulls the diaphragm against the surface of the perforatedplate,which isalsoconcave.So theoscillationfrequencyof thediaphragmcorrespondstothecompressorspeed.

DYNAMICCOMPRESSORSThesecompressorsraisethepressureofairorgasbyimpartingvelocity,

energy,andconvertingittopressureenergy.First,rapidlyrotatingimpellers(similartofans)acceleratetheair.Then,thefastflowingairpassesthroughadiffuser section that converts its velocity head intopressure bydirecting itinto a volute. Dynamic compressors include centrifugal and axial types.These typesofcompressorsarewidelyused in thechemicalandpetroleumrefineryindustriesforspecificservices.Theyarealsousedinotherindustriessuchas the ironandsteel industry,etc.Compared topositivedisplacementtype compressors, dynamic compressors are much smaller in size andproducemuchlessvibration.

Centrifugal/AxialCompressorsTheresultsaccomplishedbycentrifugalcompressorsarethesameasby

previously explained compressor types, but the centrifugal compressors goabout it in an entirely different way. Whereas reciprocating and screwcompressors compress air by squeezing the air froma large volume into asmaller one, centrifugal compressors raise pressure by increasing the air’svelocity.Forthisreason,centrifugalcompressorsarereferredtoasdynamiccompressors.

Centrifugalcompressorsraisethepressureofairbyimpartingvelocity,using a rotating impeller, and converting it to pressure. Each stage ofcompression in a centrifugal compressor consists of an impeller whichrotatesandastationaryinletanddischargesection.Theairenterstheeyeoftheimpeller,designatedDasshowninFigure4.27.Astheimpellerrotates,air is thrown against the casing of the compressor. The air becomescompressedasmoreandmoreairisthrownouttothecasingbytheimpellerblades.TheairispushedalongthepathdesignatedA,B,andC.Thepressureoftheairisincreasedasitispushedalongthispath.

FIGURE4.27CentrifugalCompressor.

Centrifugalcompressorsproducehigh-pressuredischargebyconvertingangular momentum imparted by the rotating impeller (dynamicdisplacement).Inordertodothisefficiently,centrifugalcompressorsrotateat higher speeds than the other types of compressors. These types ofcompressorsarealsodesignedforhighercapacitybecauseflowthroughthecompressoriscontinuous.Comparetoothertypeofcompressors,axialflowcompressorsaremainlyusedforapplicationswheretheheadrequiredislow.

Advantages

High-qualityair.Moderateefficiency.Longerservicelife.

Disadvantages

Higherinitialcost.Mustbewater-cooled.Airflowissensitivetochangesinambientconditions.

AxialFlowCompressorTheaxialflowtypeaircompressorisessentiallyalargecapacity,high

speed machine with characteristics quite different from the centrifugal aircompressor.Axialflowcompressorsareusedmainlyascompressorsforgasturbines.Thecomponentofanaxialflowcompressorconsistsoftherotatingelement that constructs from a single drum to which are attached several

rowsofdecreasingheightbladeshavingairfoilcrosssections.Betweeneachrotatingbladerowisastationarybladerow.Allbladeanglesandareasaredesigned precisely for a given performance and high efficiency. Theefficiency in an axial flow compressor is higher than the centrifugalcompressor.Theoperationoftheaxialflowcompressorisafunctionoftherotational speedof thebladesand the turningof the flow in the rotor.Thestationaryblades(stator)areusedtodiffusetheflowandconvertthevelocityincreasedintherotortoapressureincrease.Onerotorandonestatormakeupastageinacompressor.

COMPARISONOFDIFFERENTCOMPRESSORS

Iterm Reciprocating RotaryVane RotaryScrew Centrifugal

Efficiencyatfullload

High Medium-high High High

Efficiencyatpartload

Highduetotostaging

Poor:below60%offullload

Poor:below60%offullload

Poor:below60%offullload

Efficiencyatnoload(poweras%offullload)

High(10%–25%) Medium(30%–40%)

High-Poor(25%–60%)

High-Medium(20%–30%)

Noiselevel Noisy Quiet Quiet-ifenclosed Quiet

Size Large Compact Compact Compact

Oilcarryover Moderate Low-medium Low Low

Vibration High Almostnone Almostnone Almostnone

Maintenance Manywearingparts

Fewwearingparts Veryfewwearingparts

Sensitivetodustinair

Capacity Low-high Low-medium Low-high Medium-high

Pressure Medium-veryhigh

Low-medium Medium-high Medium-high

SPECIFICATIONSOFCOMPRESSORSFollowing parameters are taken into account while selecting a

compressor:

Pressurerange(psi)

1.2.

3.

4.5.6.7.8.

9.10.

11.

12.13.14.15.16.17.

18.

FlowrateReceiversize(gallons)Powersupply(maybeelectricormechanical)SizeofinstallationNumberofstages(incaseofreciprocating)

EXERCISESClassifyvarioustypesofpumpsandcompressors.Differentiate between fixed displacement and variable displacementpumps.Stateatleastfourpointsofdifferencesbetweenpositiveandnonpositivedisplacementdevices.Listthetypesofrotarypumps.Listthecharacteristicsofgearandvanepumps.Namethetwobasictypesofrotarypumps.Withthehelpofasketch,explainhowavanepumpworks.Sketch constructional details of a variable capacity axial piston pump,label its components, and explain how it works. Give the standardgraphicalsymbolforsuchadevice.Differentiatebetweenthescrewandlobecompressors.Differentiatebetweenexternalandinternalgearpumpswiththehelpofasketch.With the help of a sketch, explain the construction and working of aperistalticpump.Comparedifferenttypesofcompressors.Discusstheconstructionofacompressor.Howcanreciprocatingcompressorsbeclassified?Whatarethepropertiesofadouble-actingcompressor?Whatismeantbydynamiccompressors?What are the various methods of varying the flow rate of a pump?Illustratewiththehelpofsketches.Listthevariousparametersforselectingvariouspumpsandcompressors.

19.20.21.

22.

23.

Whatarethefactorstobeconsideredwhilesizingacompressor?Nameanyfiveapplicationsofcompressedair.Define screw pump. Explain how it works, the types, and thecharacteristics.Draw the cross sectional diagram of a two-stage compressor with anintercooler.Sketchexplanatorydiagramsofanyonetypeofaircompressor.

CHAPTER5

FLUIDACCESSORIES

INTRODUCTIONFluidAccessoriesaredividedinto:

PneumaticAccessoriesHydraulicAccessories.

Thesearediscussedseparatelyinthefollowingparagraphs.

PNEUMATICACCESSORIES

AIRRECEIVERAir receivers are tanks used for compressed air storage and are

recommendedforallcompressedairsystems.Usingairreceiversofunsoundor questionable construction can be very dangerous. The vessel should befittedwith a safety valve, pressure gauge, drain, and inspection covers forcheckingorcleaninginside.Airreceiversserveseveralimportantpurposes:

Eliminatepulsationsfromthedischargeline.Separate some of the moisture; oil and solid particles that might bepresent from the air as it comes from the compressor or that may becarriedoverfromtheaftercooler.Helpreducedewpointandtemperaturespikesthatfollowregeneration.

1.2.

Offer additional storage capacity made to compensate for surges incompressedairusage.Contribute to reduce energy costs by minimizing electric demandcharges.

Airreceiversareoftwotypes:

WetAirReceiversDryAirReceivers

1. Wet Air Receivers: Wet receivers provide additional storagecapacityandreducemoisture.Thelargesurfaceareaoftheairreceiveractsasafreecooler,whichremovesthemoisture.Becausethemoistureisbeingreduced at this point in the system, the load on filters and dryers will bereduced.

2.DryAirReceivers:When sudden largeairdemandsoccur,dryairreceivers should have adequate capacity tominimize a drop in system airpressure.If thesepressuredropswerenotminimizedhere, theperformanceofairdryersandfilterswouldbereducedbecausetheywouldnolongerbeoperatingwithintheiroriginaldesignparameters.

AFTERCOOLERWhen free air is drawn into a compressor, all the moisture and dirt

floatingaroundinthefreeairisalsodrawnintothecompressor.Onceinside,the air, moisture, and dirt are compressed. The process of compressiongenerates heat because air molecules collide more frequently in a smallerspace.Heat andmoisture are undesirable in a compressed air system.Theaftercoolerandtheairdryerworktocooltheairandremovemoisture.

Compressed air discharges from the compressor and enters theaftercooler.Aftercoolersareheatexchangersthatcoolairtowithin5-20°Fofambient air temperature immediately after it is discharged from thecompressor.Theaftercoolerisadevicecontainingaseriesoftubesandfins,whichusesambientairtocondenseoutmoistureinthecompressedair.Thiscondensationprocessalsoworkstocooltheair.Condensedwatershouldberemoved from the aftercooler using drain traps. The aftercooler removesapproximately80%ofthemoisture.However,theremaining20%isstillnot

1.2.

acceptableairqualityinamanufacturingenvironment.Alargeportionoftheremaining20%moistureisremovedbyanairdryeroraseriesofairdryers.

Almost all industrial systems require aftercooling. In some systems,aftercoolers are an integral part of the compressor package,while in othersystemstheaftercoolerisaseparatepieceofequipment.Somesystemshaveboth.Theaftercoolershouldbelocatedascloseaspossibletothedischargeofthecompressor.Functionsofcompressedairaftercoolerare:

Coolairdischargefromaircompressorsviatheheatexchanger.Reduceriskoffire(hotcompressedairpipescanbeasourceofignition).Reducecompressedairmoisturelevel.Increasesystemcapacity.Protectdownstreamequipmentfromexcessiveheat.

TypesofAftercoolersTherearetwobasictypesofairaftercoolers:

Air-cooledWater-cooled

1.Air-CooledAftercooler

Air-cooledaftercoolersuseambientair tocool thehotcompressedair(Refer toFigure5.1).Thecompressedair enters theair-cooledaftercooler.The compressed air travels through either finned tubes or corrugatedaluminum sheets of the aftercooler while ambient air is forced over thecoolerbyamotor-drivenfan.Thecooler,ambientairremovesheatfromthecompressedair.

FIGURE5.1AirCooledAftercooler.

2.Water-CooledPipeLineAftercooler

Refer toFigure5.2.Thepipelineaftercoolerconsistsofashellwithabundleoftubesfittedinside.Typicallythecompressedairflowsthroughthetubes in one direction as water flows on the shell side in the oppositedirection. Heat from the compressed air is transferred to thewater.Watervapor forms as the compressed air cools. Themoisture is removed by themoistureseparatoranddrainvalve.Amodulatingvalveisrecommendedtomaintain a consistent temperature and reduce water consumption. Thedisadvantages of a water-cooled aftercooler include high water usage anddifficult heat recovery. Advantages of using a water-cooled aftercoolerincludebetterheattransferandnorequirementofelectricity.

1.2.3.

FIGURE5.2Water-CooledAftercooler.

AIRDRYERWatervaporiscontainedinhigh-pressureair.Invaporform,thewater

does little damage in most components. But if the water is allowed tocondenseinthesystem,itcancausegreatdamage.Dryingofcompressedairis achievedbypassing it throughdryers.Compressedairdryers reduce thequantityofwatervapor, liquidwater,hydrocarbon,andhydrocarbonvaporincompressedair.Moistureincompressedairisharmful.Waterdamagesacompressedairsysteminseveralways:

Erosion: Water mist erodes piping, valves, and other systemcomponents.Corrosion:Mistcondensesandcombineswithsaltsandacidswithinthesystemforminghighlycorrosivesolutions.Microbial Contamination: Moisture supplies a growth medium forbacteria and mold, which produce acidic waste and can be a healththreat.Freezing:Water can freeze in compressed air lines shutting down thesystem.

The result is lower productivity, increased maintenance, and higheroperatingcosts.Compressedair isdried toprotect the system’spipingandprocess equipment. Dry air also protects against lost product. Mostpneumaticequipmenthasarecommendedoperatingpressure,drynesslevel,andamaximumoperatingtemperature.

TypesofCompressedAirDryersThemostcommontypesofairdryersare:

RefrigeratedAirDryerDesiccantAirDryerDeliquescentAirDryer

1.RefrigeratedAirDryers

Refrigeratedairdryersarethemosteconomicaltypesofdryerthatcoolair to 35-50°F, condense, mechanically separate, and discharge the water,and then reheat the air. These utilize amechanical refrigeration system tocool the compressed air and condense water and hydrocarbon vapor. Thesaturated, moist air entering is precooled by the exiting cooled air in theprecooler/reheater. Further cooling is provided by refrigerant in the air-to-refrigerantheatexchanger.Theseparatorremovescondensedwaterdroplets,oil, and solid particles from the air stream. Condensate is automaticallydischarged by a condensate drain trap. The compressed air, now free ofliquidmoisture,isreheatedintheair-to-airprecooler/reheateranddischargedintothecompressedairsystem.

2.DesiccantAirDryers

Desiccant dryers utilize chemicals beads, called desiccant, to absorbwatervaporfromcompressedair(RefertoFigure5.3).Silicagel,activatedalumina,andmolecularsievearethemostcommondesiccantsused.(Silicagel or activated aluminas are the preferred desiccants for compressed airdryers.) A desiccant dries air by absorbing moisture on its surface andholding the water as a mono or bimolecular film. The method ofregeneration,theprocessofremovingabsorbedwaterfromthedesiccant,isthe primary distinguishing feature among the various types of desiccantdryers.Most regenerative desiccant dryers are dual-chamber systems withone chamber on-stream drying the compressed air while the other is off-stream being regenerated. There are three ways to regenerate a desiccant:withair,internalorexternalheaters,oraheatpump.

FIGURE5.3DesiccantAirDryer.

3.DeliquescentAirDryer

Deliquescent dryers are simply large pressure vessels filled with achemicalhavinganaffinity forwater (Refer toFigure5.4).Salt, urea, andcalcium chloride are the common chemicals used. As the compressed airpassesthroughthevessel, thesaltdissolvesin thewatervaporanddrips tothebottomof the tankwhere it isdrained.Thedriedair is thendischargedthroughtheoutletportatthesametemperatureatwhichitentered.

FIGURE5.4DeliquescentAirDryer.

Thesearetheleastexpensivedryers topurchaseandmaintainbecausethey have no moving parts and require no power to run, however, theyrequire that the saltbe replenished regularly. Inaddition, thecorrosive saltsolutioncancausedraintrapstoclog.

AIRFILTERIt is inevitable that impurities will make their way into the air

distribution lines in any system.Pipe scale, rust,moisture, compressor oil,pipecompound,anddirtaresomeofthecontaminantsthatcandamagevalvepartsandotherclosefittingpartsofdownstreamdevices.Inthecompressedairsystem,hardparticlesassaultequipmentandpiping.Theresultisdamagetothesystem.Particlesinacompressedairsystemcan:

Plugorificesofsensitivepneumaticinstrumentation.Wearoutseals.Erodesystemcomponents.Decreaseairdryercapacity.Foulheattransfersurfaces.Reduceairtoolefficiency.Damagefinishedproducts.

Compressed air contaminants combine inside the air system formingsludge. Sludge clogs pipes and valves causing valves to jam.A filterwillremoveallforeignmatterandallowcleandryairtoflowfreely.Clean,dryairprotectstheairsystem,reducesmaintenancecosts,andincreasesfinishedproductyields. It shouldbe installed in the lineupstreamfromallworkingdevices and in such away that it cannot be bypassed to avoid damage tothose devices. The filter capacity should be large enough to handle therequired flow of air. In order to properly size a filter for a particularapplication,themaximumallowablepressuredropthatcanbecausedbythefiltershouldbeestablished.

ConstructionandWorkingofPneumaticFilter(RefertoFigure5.5.)Constructionofairfilterisshownalongwithits

majorparts.Airentersfromaninletportandisdirectedtoinsidethefilter.Thecompressedairhastopassthroughthefilterelement,asthereisnootherwaytopassout.Inthiscourseofairpassage,theaircomesincontactwiththeelementof thefilterandfinallyafterremovalofall theimpuritiesfromair, the compressed air is directed outside by means of an outlet port.Moisture present in the air is blocked by the filter and it can bemanuallydrainedoutbysimplyoperatingthemanuallyoperateddrainplug.

FIGURE5.5PneumaticFilter.

TypesofAirFilters1.General-PurposeFilters

General-purpose filters remove harmful water condensate, pipe scale,dirt, and rust from your compressed air system. This prevents corrosivedamage to compressed air equipment and finished products. Typically,general-purpose filtersare installedupstreamof regulators topreventvalvefailure. They are also used as pre-filters to oil removing and coalescingfilterstoensurehighefficiencyandlongelementlifeinapplicationssuchaspaintspraying,instrumentation,andpharmaceutical.

2.CompressorIntakeFilter

Thefirst lineofdefenseis theintakeairfilter,whichreducesthebulkcontaminantloadprotectingthecompressorfromdirtandsolids.

3.CoarseCoalesceFilter

Acoarsecoalescingfilterseparateslargewaterandoildropletsfromthecompressedairstreambeforethecoalescingfilter.Thecoarsecoalesceralsoremoveslargesolids.

4.CoalescingFilter

Coalescing filters function in a different way from general-purposefilters. Air flows from inside to outside through a coalescing media.Coalescing by definition means “to come together.” It is a continuousprocessbywhichsmallaerosolscomeincontactwiththefibersinthefiltermedia uniting with other collected aerosols and growing to emerge as adroplet on the downstream surface of the media which by its weight isgravitationally drained away. For maximum performance and efficiency,coalescingfiltersshouldbeprecededbyageneral-purposefilter.

5.VaporFilter(CharcoalFilter)

Avaporfilterremovesorganicsfromtheairstream.Organicsliketasteand odor need to be removed from breathing air systems. In general,industrialapplicationsofvaporcompressedairfiltersremovehydrocarbonsand other organic chemical vapors from the air system.Depending on theairflow,vapor filtersneed tobe replacedevery fewmonthsbecauseof theeffectivenessoftheactivatedcarbondegradesasitabsorbs.

PRESSUREREGULATORPneumatic equipment is designed to operate properly at a certain

pressure. Although most equipment will run at pressure higher thanrecommended. The excess force, torque, and wear can shorten theequipment’s life and waste compressed air. A regulator will provide aconstant set flow of air pressure at its outlet, thus assessing optimumoperation and life of the downstream equipment. An airline regulator is aspecializedcontrolvalve,whichreducesupstreamsupplypressureleveltoaspecified constant downstream pressure. The size of the regulator isdeterminedbythedownstreamflowandpressurerequirements.

ThediagramofapressureregulatorisshowninFigure5.6.Itworksontheprincipleofpressuredifferences.Thereare twoopposingforces,whichmaintain a constant output pressure at outlet. Spring force applyingdownward pressure and the upward force due to fluid pressure act on thedownsideofdiaphragm.

FIGURE5.6PressureRegulator.

Air at fluctuating pressures is allowed to enter the inlet port. Air isentered to a spacious chamber by applying force against a spring-loadeddiaphragmandpoppetassembly.Thespringforceisadjustedwith thehelpofanadjustingscrew,dependingonhowmuchpressureisrequiredatoutlet.

If thepressure in thechamber isalreadyhigh, theenteringairhas toapplymoreandmorepressureon thepoppetanddiaphragm,against the forceofthespring.Ontheotherhand,ifthepressureinthechamberislessthanthespringforce,theairfromaninletportentersfreelyandquicklywithoutanyresistance and maintains the required pressure at which the spring isadjusted. It is important to add to a pneumatic systemapressure regulatorthat:

Suppliesairatconstantpressureregardlessofflowvariationorupstreampressure.Helpsoperatethesystemmoreeconomicallybyminimizingtheamountofpressurizedairthatiswasted.(Thishappenswhenthesystemoperatesatpressureshigherthanneededforthejob.)Helpspromotesafetybyoperatingtheactuatoratreducedpressure.Extendscomponent lifebecauseoperatingathigher-than-recommendedpressuresincreaseswearrateandreducesequipmentlife.Producesreadilycontrolledvariableairpressureswhereneeded.Increasesoperatingefficiency.

AIRLUBRICATORMostpneumaticsystemcomponentsandairtoolsrequireoillubrication

forproperoperationandlongservicelife.Toolittleoilcancauseexcessivewearandprematurefailure.Toomuchoil iswastefulandcancontaminate,particularly when carried over with the air exhaust. Pneumatic equipmentcanbelubricatedbytheuseofanairlinelubricator.Filteredandregulatedairentersthelubricatorandismixedwithoilinanaerosolmist.Theairisthenroutedtotheoperatingsystem.

Theworkingofthelubricatorisbasedontheprincipleofventurieffect,asshowninFigure5.7.Thecompressedairfromthecompressor,filter,andregulatorispassedthroughtheinletportoflubricator.Thishigh-pressureairhastopassthroughaconverginganddivergingpassage.Whilepassingfromtheconvergingportion,pressureheadgoesondecreasingandvelocityheadgoes on increasing. When the air reaches the middle portion of nozzle,velocity becomes comparatively very high, due to which suction head iscreatedinthesuctionpipeandoilissuckedupandmixedintheairpassingathighvelocity.

FIGURE5.7AirLubricator.

AIRSERVICEUNIT(F.R.L.)FRL stands for filter, regulator, and lubricator. Filters, regulators, and

lubricatorscanbecombined toensureoptimumcompressedairpreparationforaspecificpneumaticsystemasshowninFigure5.8.Theyformaunitthatwill prepare the condition of compressed air before delivering it topneumaticequipmentormachinery.Thisensurestheairsupplyiscleananddry,thepressureisatthecorrectlevel,andfineparticlesofoilarecarriedintheairtolubricatethewearingpartsbetweenthevalves,cylinder,andtools.

FIGURE5.8AirServiceUnit(F.R.L.).

PIPELINELAYOUTThepurposeofthecompressorpipingsystemistodelivercompressed

air to the points of usage. The compressed air needs to be deliveredwithenough volume, appropriate quality, and pressure to properly power thecomponents that use the compressed air. Compressed air is costly tomanufacture.Apoorlydesignedcompressedairsystemcanincreaseenergycosts, promote equipment failure, reduce production efficiencies, andincreasemaintenance requirements. It is generally considered true that anyadditionalcostsspentimprovingthecompressedairpipingsystemwillpay.Dischargepipingfromacompressorwithoutanintegralaftercoolercanhaveveryhightemperatures.Thepipethatisinstalledheremustbeabletohandlethesetemperatures.Thehightemperaturescanalsocausethermalexpansionofthepipe,whichcanaddstresstothepipe.

Thelayoutof thesystemcanalsoaffect thecompressedairsystem.Averyefficientcompressedairpipingsystemdesignisaloopdesign.Theloopdesign allows airflow in two directions to a point of use.This can cut theoverall pipe length to a point in half that reduces pressure drop. Inmanycases,abalancelineisalsorecommendedwhichprovidesanothersourceofair.Reducing thevelocityof theairflowthrough thecompressedairpipingsystemisanotherbenefitoftheloopdesign.Incaseswherethereisalargevolumeuser,anauxiliaryreceivercanbeinstalled.Thisreducesthevelocity,

whichreducesthefrictionagainstthepipewallsandreducespressuredrop.Receiversshouldbepositionedclosetothefarendsoratpointsofinfrequentheavyuseof longdistribution lines.Manypeakdemands for air are short-lived,andstoragecapacitynearthesepointshelpsavoidexcessive.

Figure5.9 shows the layout of compressed air pipeline in an industrywhere compressed air is used in almost all the operations starting fromrunning the various types of tools like pneumatic drills or pneumatichammerstospecialpurposeautomaticmachines.

FIGURE5.9PipelineLayout.

CondensateControlCondensationcontrolmustbeconsideredwheninstallingacompressed

air piping system. Drip legs should be installed at all low points in thesystem.Adriplegisanextensionofpipebelowtheairline,whichisusedtocollect condensation in the pipe. At the end of the drip leg, a drain trapshouldbeinstalled.Preferablyanautomaticdrainwillbeused.

To eliminate oil,condensate, or cooling water (if the water-cooledaftercoolerleaks),alowpointdrainshouldbeinstalledinthedischargepipebefore the aftercooler. Be sure to connect the aftercooler outlet to theseparator inlet when connecting the aftercooler and themoisture separator

together.Iftheyarenotconnectedproperly,itwillresultineitherpooraftercoolingorpoorseparation.Anothermethodofcontrollingthecondensationistotakeallbranchconnectionsfromthetopoftheairline.Thiseliminatescondensation from entering the branch connection and allows thecondensationtocontinuetothelowpointsinthesystem.

PressureDropPressuredrop in acompressedair system is a critical factor.Pressure

dropiscausedbyfrictionofthecompressedairflowingagainsttheinsideofthepipeand throughvalves, tees,elbows,andothercomponents thatmakeupacompletecompressedairpipingsystem.Pressuredropcanbeaffectedbypipesize, typeofpipesused, thenumberand typeofvalves,couplings,and bends in the system. Each header or main should be furnished withoutletsascloseaspossibletothepointofapplication.Thisavoidssignificantpressuredropsthroughthehoseandallowsshorterhoselengthstobeused.Toavoidcarryoverofcondensedmoisture to tools,outletsshouldbe takenfromthetopofthepipeline.Largerpipesizes,shorterpipeandhoselengths,smoothwall pipe, long radius swept tees, and long radius elbows all helpreducepressuredropwithinacompressedairpipingsystem.

PressuredropcanbegivenbyDarcy’sequationwhichcanbeexpressedmathematicallyas:

wherethepressurelossduetofrictionΔpisafunctionof:

thecoefficientoflaminar,orturbulentflow,λ

theratioofthelengthtodiameterofthepipe,L/D

thedensityofthefluid,ρ

thevelocityoftheflow,V

PipingMaterialCommon piping materials used in a compressed air system include

copper, aluminum, stainless steel, and carbon steel.Compressed air pipingsystems that are 2” or smaller utilize copper, aluminum, or stainless steel.Pipeand fittingconnectionsare typically threaded.Piping systems that are

4” or larger utilize carbon or stainless steelwith flanged pipe and fittings.Plastic piping may be used on compressed air systems; however cautionmust be used because many plastic materials are not compatible with allcompressor lubricants. Ultraviolet light (sun light) may also reduce theuseful service life of some plastic materials. Installation must follow themanufacturer’sinstructions.

It is always better to oversize the compressed air piping system youchoosetoinstall.Thisreducespressuredrop,whichwillpayforitself,anditallows for expansion of the system. Corrosion-resistant piping should beusedwith any compressed air piping systemusingoil-free compressors.Anon-lubricated system will experience corrosion from the moisture in thewarmair,contaminatingproducts,andcontrolsystems,ifthistypeofpipingisnotused.

SEALSAseal isaring-shapedcomponent that isdesignedtoprohibitor limit

the leakage of fluid from a device. Various types of seals are used inapplicationsthathaveconstantlymovingequipment,suchastherotatingorreciprocatingshaftsandcylindersthatareanessentialpartofhydraulicandpneumaticsystems.

ClassificationofSealsSealsareclassifiedas:

BasedondesignrequirementsBasedonmediuminwhichsealisusedBasedonmaterialusedBasedonshapes.

1.BasedonDesignRequirements

(a)StaticSeals:Staticsealsareplacedbetweensurfaces,whichdonotmove. Some form of pressure must be exerted to squeeze the surfacestogether and force the seal material into the small imperfections in thesurfaces.Someofthestaticsealsare:

(a)(b)

Gaskets: Gaskets are cut out of thin sheets of material and placedbetweenmatingsurfaces,whicharethensqueezedtogetherbyscrewsorbolts. The materials used are paper, copper, brass, rubber, and so on.Typical applications are between flanges on pipes and flanges on thefluidportofapumpormotor.Rings:Ringsareplacedingroovesbetweenthematingsurfacessothatthey are squeezedwhen the surfaces are pulled together.The rings areusually circular in section and are then called O-rings. The materialsused are natural or synthetic rubbers. Typical applications includeflanges,cylinderendcaps,andmotorbodies.

(b) Sliding Seals: Sliding seals are mainly used with cylinders topreventfluidescapingaroundapistonrodorfrompassingfromonesideofapistontotheother.Allslidingsealsareringsbutmanydifferenttypesexist.ThesemaybesolidringssuchasO-ringsorringswithrectangularsections.

(c)RotarySeals:Rotarysealsareusedonpumpsandmotorstopreventfluid leaking out through the gap between the shaft and the shaft bearing.Theyaredesignedwitha spring-loaded lip,whichpresses to the shaft.Oilleakingintothespacebehindthesealwillforcethelipeventighterbutthisspace should be drained to prevent the seal from being blown out bypressure.

2.BasedonMediuminwhichSealisUsed

HydraulicSealsPneumaticSeals

3.BasedonMaterialUsed

Thematerials seals aremade from generally include rubber ormetal,andinsomecases,leatherorfelt.Someoftherubbermaterialsusedtocreateseals include nitrile, silicone, natural rubber, butyl, and styrene butadiene.Additionally,quiteafewmanufacturersusetheirownuniquematerialsthatthey have specially developed for their products. Common sealsmaterialscan be categorized as: leather, metal, polymers, elastomers and plastics,asbestos,nylon,etc.

4.BasedonShapes

Variousvarietiesofgeometricshapesorconfigurationsofsealsare:

1.2.3.4.5.6.

1.

O-ringsealQuad-ringsealT-ringsealV-ringsealV-cupringHatring

PneumaticSealsThe purpose of a pneumatic seal is to contain theworking fluid (air)

withinthepneumaticunitandtokeepexternalcontaminationout.Sealsforpneumatic cylinders and valves are required to withstand lower pressuresthan hydraulic seals. Pneumatic seals are used at higher temperatures thanhydraulic seals. The term “pneumatic seals” actually describes a class ofsealsthatareusedinapplicationswitheitherrotaryorreciprocatingmotions.Pneumatic seals areexposed toairwithaminimumamountof lubrication.Theyareoftenused inpneumatic cylinders andvalves andusually arenotunder high pressure. However, pneumatic seals may be exposed to highoperating speeds. Rod seals, piston seals, u-cups, vee-cups, and flangepackingarejustsomeofthesealingdesignsthatcanbeusedforapneumaticseal.Asinthecaseofhydraulicsealssometimesacompositesealisusedasapneumaticseal.Rotaryapplicationsneedonlyonepneumaticseal (singleacting) because it can seal in the one axial direction the application ismoving.However,areciprocatingapplicationwillneedtwopneumaticseals(doubleacting)oneforeachofthedirections.

HYDRAULICACCESSORIES

HYDRAULICFLUIDSThe term hydraulic fluid generally refers to a liquid used as a power

transmitting medium. Choosing a correct fluid for a hydraulic system isimportant.Inahydraulicsystemfluidhasfourbasicfunctions:

Power transmission:Theprimarypurposeof anyhydraulic fluid is totransmitpowermechanicallythroughoutahydraulicpowersystem.

2.

3.

4.

Lubrication: Hydraulic fluids must provide the lubricatingcharacteristics and qualities necessary to protect all hydraulic systemcomponents against friction and wear, rust, oxidation, corrosion, anddemulsibility.Theseprotectivequalitiesareusuallyprovidedthroughtheuseofadditives.Sealing: Many hydraulic system components, such as control valves,operate with tight clearances where seals are not provided. In theseapplications, hydraulic fluids must provide the seal between the low-pressure and high-pressure side of valve ports. The amount of leakagewilldependontheclosenessorthetolerancesbetweenadjacentsurfacesandthefluidviscosity.Cooling: The circulating hydraulic fluidmust be capable of removingheatgeneratedthroughoutthesystem.

PropertiesofHydraulicFluidsAgoodhydraulicfluidcomprisesof:

Good Lubricity: A hydraulic system has various components thatcontain surfaces that are in close contact andmove in relation to eachother.Agoodhydraulicfluidmustprotectagainstwearandseparateandlubricatesuchsurfaces.Stable Viscosity: Viscosity is a vital fluid property that varies withtemperatureandpressure.Fluidshavinglargechangesofviscositywithtemperature are commonly referred as low viscosity index fluids andthosehavingsmallchangesofviscositywith temperatureareknownashighviscosityindexfluids.ChemicalandPhysicalStability:Thecharacteristicsofa fluidshouldremainunchangedduringanextendedusefullife.Becausemanyaspectsofstabilityarechemicalinnature,thetemperaturetowhichthefluidwillbeexposedisanimportantcriterionintheselectionofahydraulicfluid.SystemCompatibility:Thehydraulicfluidshouldbeinerttomaterialsusedinornearthehydraulicequipment.Ifthefluidinanywayattacks,destroys,dissolves,orchangespartsofthehydraulicsystem,thesystemmayloseitsfunctionalefficiencyandmaystartmalfunctioning.Good Heat Dissipation: Pressure drops, mechanical friction, fluidfriction, leakages, all generateheat.The fluidmust carry thegenerated

1.

2.

(a)

(b)

heatawayandreadilydissipateittotheatmosphereorcoolers.Flash Point: The flash point of hydraulic oil is defined as thetemperature atwhich flasheswill begeneratedwhen theoil is broughtintocontactwithanyheatedmatter.Prevent Rust Formation:Moisture and oxygen cause rusting of ironpartsinthesystemthatcanleadtoabrasivewearofsystemcomponentsand also act as a catalyst to increase the rate of oxidationof the fluid.Fluidswithrustinhibitorsminimizerustformationinthesystem.Demulsibility: Demulsibility is the ability of a fluid to separate outwater. Excessive water in the oil promotes the collection ofcontaminants,causestickyvalves,andacceleratedwear.

TypesofHydraulicFluidsHydraulic fluids are a large group of liquidsmade ofmany kinds of

chemicals.Theyareusedinautomobileautomatictransmissions,brakes,andpower steering; fork lift trucks; tractors; bulldozers; industrial machinery;andairplanes.Waterwasthefirsthydraulicfluidusedduringtheearlystagesof the industrial revolution. The common types of fluid used in hydraulicsystemsare:

Petroleum:Petroleum-basedoilsarethemostcommonlyusedstockforhydraulicapplicationswherethereisnodangeroffire,nopossibilityofleakage that may cause contamination of other products, no widetemperaturefluctuations,andnoenvironmentalimpact.Fire resistant: In applications where fire hazards or environmentalpollution are a concern, water-based or aqueous fluids offer distinctadvantages. The fluids consist of water-glycols and water-in-oil fluidswithemulsifiers,stabilizers,andadditives.

Water-glycol:Water-glycolfluidscontainfrom35to60percentwatertoprovidethefireresistance,plusaglycolantifreezesuchasethylene,diethylene, or propylene which is nontoxic and biodegradable, and athickener such as polyglycol to provide the required viscosity. Thesefluids alsoprovide all the important additives suchas antiwear, foam,rust,andcorrosioninhibitors.

Water-oilemulsions:Theseareoftwotypes:

(i)

(ii)

(c)

1.

2.

3.

Oil-in-water. These fluids consist of very small oil dropletsdispersed in a continuous water phase. These fluids have lowviscosities, excellent fire-resistance, and good cooling capabilitydue to the large proportion of water. Additives must be used toimprovetheirinherentlypoorlubricityandtoprotectagainstrust.

Water-in-oil. The water content of water-in-oil fluids may beapproximately40percent.Thesefluidsconsistofverysmallwaterdroplets dispersed in a continuous oil phase. The oil phaseprovides good to excellent lubricity while the water contentprovidesthedesiredleveloffire-resistanceandenhancesthefluidcooling capability. Emulsifiers are added to improve stability.Additivesareincludedtominimizerustandtoimprovelubricityasnecessary.Thesefluidsarecompatiblewithmostsealsandmetalscommontohydraulicfluidapplications.

Synthetic fire-resistant fluids: These fluids are usually a blend thatconsists of phosphate esters, chlorinated hydrocarbons, andhydrocarbonbasedfluids.Thesefluidsdonotcontainwaterorvolatilematerials,and theyprovidesatisfactoryoperationathigh temperatureswithout loss of essential elements (in contrast to water-based fluids).Thefluidsarealsosuitableforhigh-pressureapplications.

HYDRAULICRESERVOIRHydraulic systems need a finite amount of liquid fluid that must be

stored and reused continually as the system works. This finite amount ofliquidfluidisstoredinatankorreservoir.Areservoirisastorageareafromwhere the hydraulic fluid is supplied to the system. Hydraulic reservoirperformsseveralfunctionssuchas:

Heatdissipation:Thehydraulicfluidabsorbstheheatgeneratedbythehydraulicsystems.Hydraulicreservoirdissipatesandtransfersheatfromthefluidbyradiationandconvection.Settling basin: Hydraulic reservoir acts as a settling basin as thecontaminantsinthefluidsettledown.Reserve for operation: A reservoir should be able to hold the entiresystem fluid together with the reserve fluid for the operation. The

4.reservoircapacityshouldbetwotothreetimesthepumpdelivery.Accessorymounting:Thereservoirsurfacecanbeusedasamountingplatformtosupportthepump,motor,andothersystemcomponents.Thissavesfloorspace.

Hydraulic reservoirs are usually rectangular, cylindrical, T-shaped, orL-shapedandmadeofsteel,stainlesssteel,aluminum,orplastic.Hydraulicreservoirs vary in terms of capacity, but need to be large enough toaccommodatethethermalexpansionoffluidsandchangesinfluidlevelduetonormalsystemoperation.Largehydraulicreservoirsprovidecoolingandreducerecirculation.Somereservoirsincludestationaryorremovablebafflestodirectfluidflowandensurepropercirculation.

HYDRAULICFILTERFilters are components used in hydraulic systems for contamination

control.Filterconsistsofporousmaterial,whichtrapscontaminantsaboveaparticular size in the system fluid. Hydraulic filters are available in amultitude of shapes, sizes, micron ratings, and construction materials.Hydraulic filters provide inbuilt protection andminimize hydraulic systembreakdownsthatarequiteoftencausedbycontamination.Efficientfiltrationhelpspreventsystemfailureandmakesasignificantcontributiontolowcostof ownership. These are fitted for both low-and high-pressure hydraulicapplications. The filter used in a hydraulic system should be subjected toperiodic and routine cleaning and maintenance. The life of a filter in ahydraulic system depends primarily on the system pressures, level ofcontamination,andnatureofcontaminants.

ConstructionandWorkingofHydraulicFilterConstructionofatypicalhydraulicfilterisshowninFigure5.10along

with its importantparts. Itworks thesameasapneumatic filter.Hydraulicfluidenteringfromaninletportisenteredintothefilterbodyandboundtopass out only from the filter element. After passing out from the filterelement, all the impurities which were present in the hydraulic fluid getstrappedinthefilterelementandcleanhydraulicfluidisobtainedatoutletofthehydraulicfilter.Hydraulicfiltersaredesignedtotoleratehigherpressures

1.

2.

1.

thenincaseofpneumatics,i.e.,whytheyaresometimescalledasheavydutyfilters.

FIGURE5.10HydraulicFilter.

TypesofFiltersIn a hydraulic system, there are two main types of filters that are

frequentlyused.Theseare:

Surface filters: These are simple screens used to clean oil passingthrough thepores.Thedirtyunwantedparticlesarecollectedat the topsurfaceofthescreenswhentheoilispassed.Depthfilters:Theseare thickwalled filterelements throughwhich theoil is made to pass retaining the undesirable foreign particles. Thecapacityofdepthfiltersismuchhigherthansurfacefiltersasmuchfinermaterialshaveachanceofbeingarrestedbythesefilters.

Filterscanalsobeclassifiedas:

Full-flow filter: In a hydraulic system it is necessary that all the flowmust be through the filter element. So, the oil must enter the filterelementatitsinletsideandgetsentoutthroughtheoutletaftercrossingthefilterelementfully.Incaseoffullflowfiltration,thefilterissizedtoaccommodatetheentireoilflowatthatpartofthecircuit.

2.

1.

2.

By-passfilter:Attimes,theentirevolumeofoilneednotbefilteredandthus,only aportionof theoil ispassed through the filter element.Themain portion is directly passed without filtration through a restrictedpassage.

FilterLocationThelocationofafilterinthehydraulicsystemisofmuchsignificance.

Variouslocationsareusedtoarrangeafiltereitherinthereturnlineorinthepressureline.Afiltermaybeusedeitherintheintakesideofthepumporintheoutletsideofthepump.Generally,forafilter,thepreferredlocationsare:

Returnlinefilter:Itmayreducetheamountofdirtingestedthroughthecylinderandsealsfromreachingthetank.Intakefilter:Thesearefittedbeforethepumpsothattheycanpreventrandom entry of contaminants like large chips into the pump and thuspreventdamagetoit.Pressurefilter:Apressurefilterisusedsometimesatthepumpoutlettoprevent entry of contaminants generated in the pump, into othercomponentslikevalves,etc.andthushelpinavoidingthespreadofsuchundesirable elements into the whole system. This will thus protectvalves,cylinders,etc.Final control filter:Tokeep the large debris out of a component thatcan cause the component to fail through inbuilt arrangement or byadditionalprotectivedesign.

FilteringMaterialandElementsThe general classes of filter materials are mechanical, absorbent

inactive,andabsorbentactive.

Mechanical filters contain closely wovenmetal screens or discs. Theygenerallyremoveonlyfairlycoarseparticles.Absorbent inactive filters, such as cotton, wood pulp, yarn, cloth, orresin, remove much smaller particles; some remove water and water-solublecontaminants.Theelementsoftenaretreatedtomakethemstickytoattractthecontaminantsfoundinhydraulicoil.

3. Absorbentactivematerials,suchascharcoalandfuller’searth(aclaylikematerial of very fine particles used in the purification of mineral orvegetable-baseoils),arenotrecommendedforhydraulicsystems.

PRESSUREGAUGESANDVOLUMEMETERSPressuregaugesareusedinliquid-poweredsystemstomeasurepressure

tomaintainefficientandsafeoperating levels.Pressure ismeasured inpsi.Flowmeasurementmaybeexpressedintermsof totalquantity—gallonsorcubicfeet.

PressureGauges

Figure5.11showsasimplepressuregauge.Gaugereadingsindicatethefluidpressure setupbyoppositionof forceswithina system.Atmosphericpressureisnegligiblebecauseitsactionatoneplaceisbalancedbyitsequalactionatanotherplaceinasystem.

FIGURE5.11PressureGauge.

FlowMeters

Measuringflowdependsonthequantities,flowrates,andthetypesofliquidinvolved.Allliquidmeters(flowmeters)aremadetomeasurespecificliquids andmust be used only for the purpose forwhich theyweremade.Eachmeteristestedandcalibrated.

HYDRAULICACCUMULATOR

1.2.3.

An accumulator is essentially a pressure storage reservoir in which anoncompressiblehydraulicfluidisretainedunderpressurefromanexternalsource. Like an electrical storage battery, a hydraulic accumulator storespotentialpower,inthiscaseliquidunderpressure,forfutureconversionintouseful work. That external source can be a spring, a raised weight, or acompressedgas.Becauseoftheirabilitytostoreexcessenergyandreleaseitwhenneeded,accumulatorsareusefultoolsindevelopingefficienthydraulicsystems.Incertaincircuitdesigns,theaccumulatorwillpermitapumpmotorto be completely shut down for an extended period of time while theaccumulator supplies the necessary fluid to the circuit. Accumulators areusedinconjunctionwithhydraulicsystemsonlargehydraulicpresses,farmmachinery,dieselenginestarters,powerbreaksonairplanes,lifttrucks,etc.

Applications/FunctionsofanAccumulatorHydraulicaccumulatorsareusedinhydraulicsystemsas:

Compensationforlargeflowvariation:Duringoperationofhydraulicinstallation, if requirementsofsupplyof largevolumetricflowsappear,thentheserequirementscanbesuppliedbyanaccumulator.To smooth out pressure surges: Pressure surges are caused in ahydraulicsystemwhenfluidflowissuddenlychanged.Thehighinertiaof themoving fluid sets up shockwaves in the pipes causing hammerand vibration. Accumulators will absorb the energy and dampen outthesesurgesthusreducingvibrationsandshock.To provide emergency power source: The fluid energy stored in anaccumulatormaybesufficient togiveanemergencysupply in thecaseofmajorelectricalfailurecausingthepumpstostop.

TypesofAccumulatorsTherearethreemaintypesofaccumulatorsusedinhydraulicsystems:

Weight-loadedAccumulatorsSpring-loadedAccumulatorsGaschargedAccumulators

1.Weight-LoadedAccumulator

The weight-loaded accumulator consists of a vertical cylindercontaining fluid connected to the hydraulic system (Refer to Figure 5.12).Thecylinder is closedbyapistononwhicha seriesofweights areplacedthatexertsadownwardforceonthepistonandtherebyenergizesthefluidinthe cylinder. The weight may be of some heavy material such as iron,concreteblock,pigorscrapiron,etc.Thepressureonthefluiddependsontheweighton thepistonand thesizeof thepiston,andcanbechangedbyaddingorremovingweightsfromthepiston.

FIGURE5.12WeightLoadedAccumulator.

2.Spring-LoadedAccumulator

A spring-loaded accumulator works on the same principle as theweight-loaded accumulator. A spring-loaded accumulator consists of acylinderbody,amovablepiston,andaspring.Thespringappliesforcetothepiston. As fluid is pumped to it, the pressure in the accumulator isdeterminedbythecompressionrateofthespring.Thespringforceincreasesasitiscompressedbymorefluidenteringthechamber.

The advantages of these accumulators are that these are usually lessexpensive than the deadweight type andmounting is easy. They are builtdirectlyintothepowerunit.Thedisadvantageisthatthespringforceandtheresultingpressurerangecannotbeeasilyadjusted.Thisaccumulator isalsonotsuitableforapplications,whichrequirelargevolumeoffluids.

3.GasChargedAccumulators

1.2.

1.

2.

Gaschargedorcompressedgasaccumulatorsconsistofacylinderwithtwo chambers that are separated by an elastic diaphragm or by a floatingpiston. One chamber contains hydraulic fluid and is connected to thehydraulic line. The other side contains an inert gas under pressure thatprovides the compressive force on the hydraulic fluid. Inert gas is usedbecauseoxygenandoilcanformanexplosivemixturewhencombinedunderhighpressure.Asthevolumeofthecompressedgaschangesthepressureofthe gas, and the pressure on the fluid, changes inversely. Gas chargedaccumulatorsareoftwotypes:

PistontypeBladdertype

FIGURE5.13SpringTypeAccumulator.

Piston type: These have an outer cylinder tube, end caps, a pistonelement,andsealingsystem.Thecylinderholdsfluidpressureandguidesthe piston, which forms the separating element between gas and fluid.Chargingthegassideforcesthepistonagainsttheendcoveratthefluidend. As system pressure exceeds the minimum operating level for theaccumulator,thepistonmovesandcompressesgasinthecylinder.Bladdertype:Itconsistsofapressurevesselandaninternalelastomericbladderthatcontainsthegas.Thebladderischargedthroughagasvalveatthetopoftheaccumulator,whileapoppetvalveatthebottompreventsthe bladder from being ejected with the outflowing fluid. The poppetvalveissizedsothatmaximumvolumetricflowcannotbeexceeded.Tooperate, thebladder is chargedwithnitrogen toapressure specifiedbythe manufacturer according to the operating conditions. When systempressureexceedsgasprechargepressureof theaccumulator, thepoppet

1.

2.

1.2.3.

valve opens and hydraulic fluid enters the accumulator. The change ingas volume in the bladder betweenminimum andmaximum operatingpressuredeterminestheusefulfluidcapacity.

INTENSIFIERIntensifiers, also known as boosters, use a large quantity of low-

pressurefluidtoproduceasmallerquantityofhigher-pressurefluid.Theunithasapiston,whichreciprocatesautomatically.Thelargepistonisexposedtotheforcedeliveredbythelow-pressurepumpandthispistonmovesthelargepistonbackandforthasthevalvestemshifts.Thesmallareapistononeachendofthelargepistonforcesoilintothesystemunderhighpressure.Therearethreeclassesofintensifiers:air-to-oil,oil-to-oil,andair-to-air.Hydraulicboosters can develop andmaintain high pressure for long periods of timewithoutusingpowerorgeneratingheatinthecircuit.Theydeliverfluidonlywhenthecylinderdemandsit.Becausealltheoilfromtheboosterisdirectedto the cylinder, there are no relief-valve losses.Generally, boosters can beused as a hydraulic power source only in single cylinder applications. Abooster can drivemore than one cylinder if the cylinderswork in unison.However, to sequence two or more cylinders, additional boosters arerequired.Threemajorstepsareinvolvedinselectingtherightboosterforanapplication.

Booster size: If a cylinder requires high-pressure deliverythroughoutthestroke,asingle-pressureboostercircuitisneeded.Adouble-headed booster can be used if the number of cycles perminuteislow,andautomaticbleedingandfillingarenotimportant.Atriple-headedtypemustbeusedwhererapidcyclingisrequired.

Tank size: The air-oil tanks in booster circuits perform threegeneralfunctions:

Makeupforleakage.Actaspressuresourcestotraverseorreturncylinder.Provideoutletsforentrainedair.

Whenthe tankfunctionsasareservoir, itssizedependsonhowmuchthesystemleaks.However,tanksarealsooutletsforentrainedair.Here,thetankisnotpressurizedandactsprimarilyasareservoir.

When functioning as a pressure source, tanks must have a volumeslightly greater than the displaced volume of the cylinder. Volume of thetankshouldbeenoughtoprecludeoillevelreachingtheuppertankbaffleatthe high-level point. When at the low-level point, the lower tank baffleshouldnotbeexposedtoairpressure.

Pressurizedtanksmustalsoserveasanoutletforentrainedair.

3. Cylinder speed: If rapid cylinder action is required, the hydrauliccylindershouldbesizedsothatthereactionforce(forcerequiredtodowork)is50to60%ofavailablecylinderforceatcalculatedpressure.Considerbothhigh-pressureandlow-pressureworkreactions.

LINESPipes and fittings, with their necessary seals, make up a circulatory

systemofliquidpoweredequipment.Properlyselectingandinstallingthesecomponentsareveryimportant.Ifimproperlyselectedorinstalled,theresultwouldbeseriouspowerlossorharmfulliquidcontamination.Thefollowingisalistofsomeofthebasicrequirementsofacirculatorysystem:

Lines must be strong enough to contain liquid at a desired workingpressureandthesurgesinpressurethatmaydevelopinthesystem.Linesmustbestrongenoughtosupportthecomponentsthataremountedonthem.Terminal fittingsmustbeatall junctionswherepartsmustbe removedforrepairorreplacement.Linesupportsmustbecapableofdampingtheshockcausedbypressuresurges.Linesshouldhavesmoothinteriorstoreduceturbulentflow.Linesmusthavethecorrectsizefortherequiredliquidflow.Linesmustbekeptcleanbyregularflushingorpurging.Sourcesofcontaminantsmustbeeliminated.

Thecontrolandapplicationoffluidpowerwouldbeimpossiblewithoutsuitable means of transferring the fluid between the reservoir, the powersource,andthepointsofapplication.Fluidlinesareusedtotransferthefluidtothepointsofapplication.

1.

2.

3.

The threecommon typesof lines in liquid-powered systemsarepipes,tubing,andflexiblehose,whicharealsoreferredtoasrigid,semirigid,andflexibleline.

Piping: The piping can be used that can be threaded with screwedfittingswithdiameters up to 1 1/4 inches andpressures of up to 1,000psi.Where pressureswill exceed 1,000 psi and required diameters areover11/4 inches,pipingwithwelded, flangedconnectionsandsocket-welded size are specified by nominal inside diameter (ID) dimensions.The thread remains thesame foranygivenpipesize regardlessofwallthickness.Pipingisusedeconomicallyinlarger-sizedhydraulicsystemswhere largeflowiscarried. It isparticularlysuitedfor long,permanentstraightlines.Tubing:The two typesof tubingused forhydraulic lines are seamlessand electricwelded. Both are suitable for hydraulic systems. Seamlesstubing is made in larger sizes than tubing that is electric welded.Seamless tubing is flared and fittedwith threadedcompression fittings.Tubing bends easily, so fewer pieces and fittings are required. Unlikepipe,tubingcanbecutandflaredandfittedinthefield.Generally,tubingmakes aneater, less costly, lower-maintenance systemwith fewer flowrestrictionsandlesschancesofleakage.Flexible Hosing: When flexibility is necessary in liquid-poweredsystems,hoseisused.Exampleswouldbeconnectionstounitsthatmovewhile in operation to units that are attached to a hinged portion of theequipment or are in locations that are subjected to severe vibration.Flexible hose is usually used to connect a pump to a system. Flexiblehose should not be twistedwhile installing it.Doing so reduces its liftandmaycauseitsfittingstoloosen.Flexiblehoseshouldbeinstalledsothatitwillbesubjectedtoaminimumofflexingduringoperation.Hoseshouldnotbestretchedtightlybetweentwofittings.

Thelinesshouldbekeptasshortandfreeofbendsaspossible.Allthelines should be installed so that it can be removed without dismantling acircuit’s componentsorwithout bendingor springing them to abad angle.Supports should be added to the lines at frequent intervals to minimizevibrationormovement.

1.

2.

FITTINGSANDCONNECTORSFittings are used to connect the units of a fluid-powered system,

including the individual sections of a circulatory system. Many differenttypesofconnectorsareavailable for fluid-poweredsystems.The typeuseddependsonthetypeofcirculatorysystem(pipe,tubing,orflexiblehose),thefluidmedium,andthemaximumoperatingpressureofasystem.Someofthemostcommontypesofconnectorsaredescribedbelow:

Threaded Connectors: Threaded connectors are used in some low-pressureliquid-poweredsystems.Theyareusuallymadeofsteel,copper,orbrass, in avarietyofdesigns (Refer toFigure5.14).Theconnectorsaremadewithstandard female threadingcuton the insidesurface.Theend of the pipe is threadedwith outside (male) threads for connecting.Standardpipethreadsaretaperedslightlytoensuretightconnections.

FIGURE5.14ThreadedConnectors.

(Socket, Tee, Elbow, Reducer, Hexagonal nipple, Reducing bush,Reducingthreadednipple,90°bend)

Flared Connectors: The common connectors used in circulatorysystems consist of tube lines. These connectors provide safe, strong,dependable connections without having to thread, weld, or solder thetubing.A connector consists of a fitting, a sleeve, and a nut. (Refer toFigure5.15.)

3.

(a)

(b)

FIGURE5.15FlaredConnectors.

Hose Couplings: A hydraulic hose consists of an inner tube throughwhich the fluid is conveyed and comes into direct contact with thehydraulicfluid.Therubberorothersyntheticmaterialusedforthisneedstobecompatibleandabletowithstandtherangeofworkingtemperaturewithout losing its chemical and physical stability. The hydraulic hosescanbemadeusingavarietyofmaterials,dependingonthefactorsofoilcompatibility,abrasionresistance,etc.Theseinclude:

Plastic:Theplasticmaterialscompriseof:Nylon,Braidednylonhose,Polyvinylchloride,Textilebraidedhoses,Thermoplasts,Teflon,Chlorosulfonatedpolyethylene(Hypalon),Ethylenepropylenediene(EPDM),Chlorinatedpolyethylene,etc.

HomogeneousSyntheticRubber:Thiscategoryincludeshosematerialslike:BunaN,Neoprene,Naturalrubber,Butyl,etc.

Thehydraulichoseisanimportantelementinthesystemthatneedstobecheckedforitsreliabilityanddurabilityduringthemanufactureprocess.Inmanyhydraulicsystems,itisnecessarytomovethedriveunitalongwiththeoillines.Here,syntheticrubberissuitedasthematerialforthehydraulichoses.Plastictuningsarealsousedinhydraulicsystemstoconveythefluid.

HYDRAULICSEALS

Seals are packing materials used to prevent leaks in liquid-poweredsystems. A seal is any gasket, packing, seal ring, or other part designedspecificallyforsealing.Sealingkeeps thehydraulicoil flowinginpassagestoholdpressureandkeep foreignmaterials fromgetting into thehydraulicpassages. To prevent leakage, a positive sealing method should be used,whichinvolvesusingactualsealingpartsormaterials.Thestrengthofanoilfilmthatthepartsslideagainstprovidesaneffectiveseal.

Hydraulicsealsareexposedtohydraulicfluidssuchashydrocarbonandphosphate ester and are designed for high-pressure dynamic applicationssuch as hydraulic cylinders. Hydraulic seals usually need to be higherfriction seals thanpneumatic sealsbutoftenoperateunder loweroperatingspeeds.Rodseals,pistonseals,u-cups,vee-cups,andflangepackingarejustsomeofthesealingdesignsthatcanbeusedforahydraulicseal.Sometimesacompositeseal isusedasahydraulicseal.Acompositeseal isaproduct,whichhastwoorthreematerialsmanufacturedintooneseal.OftentherewillbeanelastomerringandaPTFEringgivingthesealtheadvantagesofbothmaterials.

The lifeofhydraulicseals isdependentonmanyfactors including themaximum operating speed, maximum operating temperature, maximumoperating pressure, and the vacuum rating.When ordering hydraulic sealsonemustknowtheshaftouterdiameterorsealinnerdiameter,housingborediameterorsealouterdiameter, theaxialcrosssection,andtheradialcrosssection.

FIGURE5.16Seals.

EXERCISES

1.2.3.4.5.

6.

7.8.9.

10.11.

12.

13.14.15.16.17.18.19.20.21.

22.23.

Whyisareceiverusedinapneumaticsystem?Discussthevariouskindsofairreceiver.Listthevariousbenefitsofintercooling.Classifythevariousintercoolersandgiveatleasttwoadvantagesofeach.Explain the construction andworking of pneumatic filter alongwith aneatsketch.What is the function of an accumulator? How is it different from areservoir?Whatarethepropertiesofhydraulicfluids?Writeashortnoteonsealsusedinhydraulicsandpneumatics.Explaintheconstructionandworkingofhydraulicfilteralongwithaneatsketch.WhatisaFRLunitinpneumaticsystems?What are deliquescent and desiccant air dryers?Why are they used inindustries?Withthehelpofaneatsketch,explain theconstructionandworkingofairlubricator.Differentiatebetweenthehydraulicandpneumaticfilter.Stateatleasttwodifferencesbetweenpressureandflowregulator.Differentiatebetweendeadweightandspring-loadedaccumulators.Whyareaccumulatorsusedinpneumaticandhydraulicsystems?Differentiatebetweenstrainersandfilters.Differentiatebetweenfullflowandbypassfilters.Whatarethepropertiesoffluidusedinhydraulics?Distinguishbetweensafetyandreliefvalves.What is the function of the seal? Briefly explain the various types ofsealsusedinthefluidpowersystem.Whatisthefunctionofintercoolerinpneumatics?Listthereasonsforusingfiltersinhydraulicsandpneumatics.

CHAPTER6

CYLINDERSANDMOTORS

INTRODUCTIONAn actuator is an essential component in all fluid power systems.

Actuator is last in a fluid power system. The purpose of all downstreamequipmentistoconvertthefluidpowerintomechanicalpowerbymeansofanactuator.Theoutputofthefluidpowersystemisthroughanactuator.Theoutputcanbeintheformoflinearorrotarymotion.Actuatorsthatproducelinearoutputarecalledcylindersandactuators thatproducearotaryoutputarecalledmotors.Figure6.1showsasystemhavingtwoactuators.

FIGURE6.1SystemShowingTwoActuators.

Cylinders can be classified as hydraulic and pneumatic based on theworkingfluidused,similarlycylinderscanbesingleactingordoubleactingdependingupontheconstructionalfeatures.Thesearegenerallyspecifiedbyboreandstroke;theycanalsohaveoptionslikecushionsinstalled.Cushionsslowdownthecylinderattheendofthestroketopreventslamming.

Afluidmotorisadevicethatconvertsenergyoffluidtorotarymotion.Fluid motors are used for power transmission in various pneumatic andhydraulic devices in industry. Fluid motors may be classified asunidirectional and bi-directional motors. The motors that can rotate theoutputshaftinonedirectiononlyarecalledunidirectionalmotorsandthosecanrotatetheoutputshaftineitherdirectionarecalledbi-directionalmotors.Furtherthefluidmotorscanbeclassifiedasfixedandvariabledisplacementmotors. Fixed displacement motors deliver constant torque and variablespeeds.Variablespeedscanonlybeachievedbycontrolling theamountofflow input.On the other hand in variable displacementmotors the relativeposition of internal and external parts can be changed to obtain differenttorquespeedcombinations.

CYLINDERSAcylinderisoneofthesimplestcomponentsusedinhydraulicsystems.

Cylinders are linear actuators, which convert fluid power into mechanicalpower. The linear motion and high force produced by cylinders are bigreasonswhydesignersspecifyhydraulicandpneumaticsystemsin thefirstplace. One of the most basic of fluid power components, cylinders haveevolved into an almost endless array of configurations, sizes, and specialdesigns. This versatility not onlymakesmore innovative designs possible,but also makes many applications a reality that would not be practical orpossiblewithoutcylinders.Acylinderconsistsofacylinderbodyandarodandpistonassembly thatmoves inside itasshown inFigure6.2.Thefluidforceactingonthepistoncausesthemovementofthepistonassembly.

FIGURE6.2ACylinderwithRodandPistonAssembly.

1.2.

Acylinderisoneofthedevicesthatcreatemovement.Whenpressureisapplied to aport it causes that sideof the cylinder to fillwith fluid. If thefluid pressure and area of the cylinder are greater than the load that isattached, then the loadwillmove. If thepressure remainsconstanta largerdiametercylinderwillprovidemoreforcebecause ithasmoresurfaceareaforthepressuretoacton.Cylindersaresometimescalledlinearactuatorsorlinearmotors.

CLASSIFICATIONOFCYLINDERSTherearemanywaysofclassifyingcylindersbut,broadly,cylindersor

linearactuatorscanbeclassifiedonthebasisof:

ConstructionWorkingfluid

CLASSIFICATIONOFCYLINDERSONTHEBASISOFCONSTRUCTION

Dependingontheconstruction,cylinderscanbeclassifiedas:

Single-ActingCylindersDouble-ActingCylinders

The basic difference between the two single cylinders is that singleacting cylinders can be pressurized from one end,while the double actingcylinderscanbepressurizedfrombothends.

SINGLE-ACTINGCYLINDERAsingle-actingcylinderisshowninFigure6.3(a).Thecylinderisonly

powered in one direction and needs another force to return it such as anexternal load or a spring. This cylinder only has a head-end port and isoperated hydraulically/pneumatically in one direction. When pressurizedfluidissendintoaport,itpushestheplunger/pistonrodthusextendingit.Toreturnor retract a cylinder, fluidmustbe exhaustedout.Aplunger returns

eitherbecauseoftheweightofaloadorfromsomemechanicalforcesuchasaspring. Inmobileequipment, flowtoandfromasingle-actingcylinder iscontrolledbyareversingdirectionalvalveofasingle-actingtype.Thistypeofcylinderiscommonlyusedforjacksandlifts.Figure6.3(b)showsthecutsectionviewofaspringreturnedpneumaticsingle-actingcylinder.

FIGURE6.3(a)Single-ActingCylinder.

FIGURE6.3(b)CutsectionviewofaPneumaticSingle-ActingCylinder(SpringReturned).

DOUBLE-ACTINGCYLINDERDouble-acting cylinders are the most commonly used cylinders in

hydraulicandpneumaticapplications.Inthisdesign,pressurecanbeappliedtoeithersideof thecylinder.Thesymbolfordouble-actingcylindershowstwoportswhere fluidpressurecanbeappliedas shown inFigure6.4.Theextensionandretractionofcylinderisduetohydraulic/pneumaticpressure.

1.2.3.4.5.6.7.8.9.10.

FIGURE6.4SymbolofDouble-ActingCylinder.

ConstructionofaDouble-ActingCylinderConstructionofadouble-actingcylinderisshowninFigure6.5.

Adouble-actingcylinderismadeupoffollowingcomponents:

CylindertubePistonPistonrodCylinderendCylinderheadPistonsealPistonrodsealPistonrodwiperCylinderport(capend)Cylinderport(rodend).

1.2.

FIGURE6.5Double-ActingCylinder.

Acylinderisconstructedofabarrelortube,apistonandrod(orram),twoendcaps,andsuitableoilseals.Abarrelisusuallyseamlesssteeltubing,orcast,andtheinteriorisfinishedverytrueandsmoothly.Themovingpartinside the cylinder body is highly polished; chromeplated steel piston rodand the solid cast iron piston assembly. The body and the heads are heldtogetherbysteeltierodsandnuts.Theheadsoneitherendcontainportsforfluid flow. It is supported in the end cap by a polished surface. Seals andwipersareinstalledintherod’sendcaptokeeptherodcleanandtopreventexternalleakagearoundtherod.Otherpointswheresealsareusedareattheendcapand jointsandbetween thepistonandbarrel.Mountingprovisionsoftenaremadeintheendcaps,includingflangesforstationarymountingorclevises for swinging mounts. Internal leakage should not occur past apiston.Itwastesenergyandcanstopaloadbyahydrostaticlock(oiltrappedbehindapiston).

Figure 6.6 shows the cut section view of a double-acting hydrauliccylinder.

FIGURE6.6CutSectionViewofDouble-ActingHydraulicCylinder.

TYPESOFSINGLE-ACTINGCYLINDERSThere are three types of single-acting cylinders,which are commonly

available:

RamtypecylinderTelescopiccylinder

3. Springreturncylinder

RamTypeCylinderThe ram type of cylinder is the simplest type of cylinder used in

hydraulicsystems.Itconsistsofafluidchamberandfluidinlet.Theramismounted vertically and is pushed up by hydraulic pressure as shown inFigure 6.7.When the pressure is removed, it retracts back due to force ofgravity. Ram type cylinders are used in applicationswhere a single-actingforceisrequiredusually inverticaldirection.Thesecancarryaheavyloadandhavealargestabilityonheavyload.Thesearemostlyusedinelevators,jacks,andautomobilehoists.

FIGURE6.7RamTypeCylinder.

TelescopingCylinderTelescopingcylindersareusedinapplications,whichrequirealengthy

operation.Theseconsistofaseriesofnestedcylinderscalledsleeves(RefertoFigure6.8).Thesesleevesareprogressivelysmallerindiameterandeachonecanfit into thenext largersleeve.All thesleevescancollapse into thesleeveof largerdiameter,whichgives itaverycompactsize.Thecylindercanachievealongstrokewhenallthesleevesareextended.Intheextendedposition, theforceontheloaddependsonthesmallestsleeveinuse.Forceoutputvarieswithrodextension:highestat thebeginning,whenfullpistonareaisused;lowestattheendofthestroke,whenonlytheareaofthefinalstage canbeused to transmit force.Telescoping cylinders arewidelyusedforvehicleapplicationssuchasforklifttrucksanddumptrucks.

1.

FIGURE6.8TelescopingCylinder.

SpringReturnCylinderSpringreturncylinder isanothervariationofsingle-actingcylinder, in

whichpressure is appliedonone end. It consists of a piston inside a fluidchamber,which iskept inoneextremepositionby spring (Refer toFigure6.9).Whenpressure is applied to the piston, it extends by overcoming thespringforce.Thepistonretractsbackduetospringforcewhenthepressureappliedonthepistonisremoved.

FIGURE6.9SpringReturnCylinder.

TYPESOFDOUBLE-ACTINGCYLINDERSThecommonlyavailabletypesofdouble-actingcylindersare:

Doublerodcylinder

2. Tandemcylinder

DoubleRod/ThroughRodCylinderIt consists of rods on both end of the piston. Due to this, the area

exposedtothefluidonbothsidesofthepistonisidentical.Therefore,thesecylinders produce equal force and equal speed in either direction, whileperformingtwooperationswithonestroke.ItcontainstwopressureportsasshowninFigure6.10.Doublerodcylindersareavailablewithahollowrod,sothatfluidoranothermachineelementcanbepassedthroughthecylinder.Thesecylindersareusedinapplicationswheretwoloadshavetobemovedthroughequaldistance.

FIGURE6.10DoubleRodCylinder.

TandemCylinderAtandemcylinderconsistsoftwocylinders,whichhaveacommonrod

as shown in Figure 6.11. Thismeans that two cylinders are being used intandemwithacommonrod.Withthesetypesofcylinders,higherforcecanbedevelopedwiththesameboresizeandfluidpressure.Thisisbecausethefluidpressureactsondouble theareaat thesametimethatare joinedwithoneanothertoworkassingleunit.

FIGURE6.11TandemCylinder.

OTHERTYPESOFCYLINDERS

Tie-RodCylinderTie-rodcylindersare theoldestandmostcommonlyusedcylinders in

industrial jobs.Thecylinderbody isheld togetherbyfourormore tie rodsthat extend the full length of the body and pass through the end caps ormountingplate.Inoperation,theymayperformanyofthecommoncylinderfunctionsexcepttelescoping.(RefertoFigure6.12.)

FIGURE6.12Tie-RodCylinders.

One-PieceCylinderThese aremost often usedonmobile equipment and farmmachinery.

Thebodyiseithercastintegrally,orheadandbodymaybeweldedtogether.Thisistheleastexpensivetypeofcylinder.Itiscompactandsimple.Butitcannotberepairedwhendamagedorworn.(RefertoFigure6.13.)

FIGURE6.13Single-ActingandDouble-ActingOne-PieceCylinders.

ThreadedHeadCylinderThese typesofcylindersofferacompromisebetween tie-rodandone-

pieceunits.Threadedunits are relativelycompact and streamlined,yet canbe disassembled for repair by unthreading either or both ends from thecylinderbody.

DiaphragmCylinderTheseareusedineitherhydraulicorpneumaticserviceforapplications

thatrequirelowfriction,noleakageacrossthepiston,orextremelysensitiveresponse to small pressure variations. In diaphragm type of cylinders, thepistonisattachedtoadiaphragm,whichisattachedtotheendcapasshowninFigure6.14.Becausethereisnofrictionbetweenthecylinderpistonandthecylinderbarrelascompressedairenters thecylinder, thepistonandtherodstarttomovealmostinstantly.Movementisfree,almostfrictionless.Asthepistontravelsthelengthofthecylinderbarrel, thediaphragmunrollstoallowthepistonto travel.Uponthereturnstroke, thediaphragmre-rolls toits former shape. This type of cylinder requires no external lubricationsource. They are frequently used as pneumatic actuators in food and drugindustries because they require no lubrication and do not emit acontaminatingoilmist.

FIGURE6.14DiaphragmCylinder.

RotatingCylinderThe rotatingcylinder shown inFigure6.15 imparts linearmotion toa

rotating device. They are often used to actuate rotating chucks on turretlathes.Fluidisportedtotherotatingcylinderthroughastationarydistributor.Rotatingcylindersareavailablebothwithsolidandhollowpistons.

FIGURE6.15RotatingCylinder.

Non-RotatingCylinderNon-rotating cylinders are used in applications that demand both

accurate linear position andprecise angular orientation.Special guides canbe added to standard cylinders to prevent rod rotation, but this is oftenexpensive and unwieldy.More often, twin-rod or rectangular cylinders areused.Sometimesitisalsopreferabletouseauniquesquarepistonrodwithroundedcornersthatpreventsrotationbetterthanotherrodconfigurations.

DuplexCylinderDuplexcylindersalsohavetwoormorecylindersconnectedinline,but

thepistonsofaduplexcylinderarenotphysicallyconnected(RefertoFigure6.16).Therodofonecylinderprotrudesintothenon-rodendofthesecond,and so forth. A duplex cylinder may consist of more than two in-linecylinders and the stroke lengthsof the individual cylindersmayvary.This

1.2.

makesthemusefulforachievinganumberofdifferentfixedstrokelengths,dependingonwhichindividualpistonsareactuated.

FIGURE6.16DuplexCylinder.

CLASSIFICATIONOFCYLINDERSONTHEBASISOFWORKINGMEDIUM

Dependingonworkingmediumcylinderscanbeclassifiedas:

HydraulicCylindersPneumaticCylinders.

HYDRAULICCYLINDERSHydrauliccylindersarelinearhydraulicmotorsthatturnthehydrostatic

powerofa fluid intomechanicalpower.Thehydraulic fluidutilized in thecylinder is oil, most commonly used in industrial applications. Hydrauliccylindersconsistofaplungerorpistoninsideacylindricalhousing.Theboreofthecylindermustbeperfectlycylindricaltopreventanyobstructionofthepiston.Piston sealsprevent internal leakage from thehigh-pressure sideofthehydrauliccylindertothelowside.Rodsealsareusedtopreventexternalleakage.Pistonrods,whichmoveinandoutofthecylinder,areusuallyhardchrome plated to provide protection from corrosion and wear resistance.Mosthydrauliccylindersaremadeoutofsteel,stainlesssteel,oraluminum.

Hydraulic cylinders can be single acting or double acting. A single-acting hydraulic cylinder is configured for motion in only one direction,eitherpullinginorpushingout.Aninternalspringisusedtoprovideplungerreturn when the hydraulic pressure is removed. In single-action hydrauliccylinders, less valving and plumbing is needed than in double-actingcylinders.Themorecomplexdouble-actingcylinderispressurizedtomoveinbothdirectionsalongtheverticalorhorizontalplaneoranyotherplaneasneeded.Thesecylindersprovidehigherspeedoperationsandtightercontrolthan single-acting cylinders and are less sensitive to system backpressuresthat can occur due to long tube lengths.A typical hydraulic double-actingcylinderalongwithall thepartsisshowninFigure6.17andthepart list isgiveninTable6.1.

FIGURE6.17PartsofDouble-ActingHydraulicCylinder.

TABLE6.1BillofMaterial. S.No. Nameofcomponent Quantity 1 Headscrew 4 2 Head 1 3 Retainingring 1 4 Rodbearing 1 5 Rodwiper 1

6 Rodseal 1

6 Rodseal 1

7 Cushionkitwithneedlevalve 2 8 TubesealO-ring 2 9 Pistonrodseal 1 10 Pistonseal 2 11 Pistonwearstrip 1 12 Pistonmagnet 1 13 Pistonfollower 2 14 Retainingnutforpiston&rod 1 15 Pistonrod 2 16 Mainstudforretainingnut 1 17 Tube,cylinderbody 1 18 Cap 1 19 Capscrew 4

PNEUMATICCYLINDERSPneumatic cylinders are the final component in a pneumatic or

compressed air control or power system. Air or pneumatic cylinders aredevices that convert compressed air power into mechanical energy. Thismechanical energy produces linear or rotary motion. In this way, the aircylinder functions as the actuator in the pneumatic system, so it is alsoknown as a pneumatic linear actuator. Main components of a pneumaticcylinder consist of steel or stainless steel piston, a piston rod, a cylinderbarrel,andendcovers.Pneumaticcylinderscanbeusedforpressurerangesbetween5barsand20bars.Consequentlytheyareconstructedfromlightermaterials such as aluminum and brass. Because gas is a compressiblesubstance, themotion of a pneumatic cylinder is hard to control precisely.Thebasictheoryofhydraulicandpneumaticcylindersisotherwisethesame.Pneumaticcylindersareaprovenwaytoprovidequick,clean,reliable,andinexpensive linearmotion,andamultitudeofavailabledesigns,styles,andoptionscansuitmostanyconceivableapplication.InFigure6.18,a typical

pneumaticdouble-actingcylinder is shownalongwith itsall theparts.TheassemblypartslistisgiveninTable6.2.

FIGURE6.18ISOStandardDouble-ActingPneumaticCylinder.

TABLE6.2BillofMaterial. S.No. Nameofcomponent Quantity 1 Locknut 1 2 Retainingring 1 3 Rodseal 1 4 Rodbearing 1 5 Dustseal 1 6 Retainercushionscrew 1 7 Cushionscrew 1 8 O-ring 1 9 Shockabsorber 1 10 Cushionseal 1 11 Cushionspear 1 12 Pistonseal 2 13 Pistonwearstrip 1 14 Barrelseal 2 15 Pistonretainingnut 2 16 Pistonrod 1

17 Rodendcover 1

17 Rodendcover 1

18 Piston 1 19 Magnet 1 20 O-ring 1 21 Coverbolt 4 22 Headendcover 1 23 Barrel 1

APPLICATIONSOFCYLINDERSCylinders found their applications in food processing equipment,

chemical and pharmaceutical machinery, power plants, waste-to-steamgeneratingplants,valveactuators,marineuseindamsandpollutioncontrol,printing machinery, medical and surgical tables, packaging machinery,damper controls, earth moving machinery, mining industry, constructionmachinery, plant engineering, defense technology, automotive engineering,mechanical engineering, textile industries, railways, power plants,agriculturalmachinery,etc.

CYLINDERCUSHIONINGCylinders (pneumatic/hydraulic) are widely used for mechanical

handling systems. Pneumatic cylinders operate at much higher speed thanhydraulic cylinders. Due to this, there is a tendency of the piston to ramagainst the end covers as the piston approaches the ends at high velocity.Often,theimpactoccursatthebothendpointsofcylinderandgeneratesthedestructiveshockwithinthestructuraloperatingmembersofthemachineorequipment.Someformofcushioningisnormallyrequiredtoreducetherateoftravelofacylinderbeforethepistonstrikestheendcover.Reducingthepiston velocity at the end of its travel lowers the stresses on the cylinderwhile reducing vibration in the structure ofwhich it is a part. To slow anaction and prevent shock at the end of a piston stroke, some actuatingcylindersareconstructedwithacushioningdeviceateitherorbothendsofacylinder.Thiscushionisaflowcontrolvalvethatdoesnotoperateuntilthecylinder piston reaches a certain point in the cylinder. Then, the cushion

restrictsairflowtoslowthecylindermovement.Thisallowsittomovetotheendofitstravelataslowerspeed.Thisadjustmentisnormallyontheendofthe cylinder head. Cushioning of cylinders at one or both ends of pistonstroke is used to reduce the shock and vibration. All the double-actingcylinders except for small sizes are providedwith end position cushioningarrangement.

WorkingofCushionsTheworkingofcushionsisexplainedwiththehelpofadouble-acting

cylinderwithcushionsatbothends(RefertoFigure6.19).

FIGURE6.19Double-ActingCushionedCylinderwithCushionsatBothEnds.

Thepistonmoving in thecylinderhascushionnoses installedonboththe sides. These cushion noses are designed such that they mate with thecavity made in cap end, which is called as cushion chamber. Cushionassembly consists of a needle valve mechanism. Needle valve adjusts thecushioningeffect,i.e.,byrotatingneedleoftheneedlevalve;theintensityofshockcanbedecreasedorincreased.Whenthepistonismovingbackwards,i.e.,itisproceedinginthedirectionofendcapshowninfigure,thecushionnoseentersinsidethecushionchamber.Thelockedupfluidjustbeforethecapendisallowedtopassthroughacarefullydesignedflowresistancepath.Thisproducesthebackuppressurehenceopposingmovementofpistonandpiston rod. This force decelerates the motion and result in a smoothoperation.

1.

Nowwhen the process is over and cushion nose fully enters into thecushionchamberthentheforwardstrokewill taketimetostartbecausetheareaofnoseisgreat,whereastheentrancefromwherefluidiscominginisintentionally kept small. In order to overcome this problem sometimes acheck valve gallery is provided below the cushion chamber to initiate theprocesswithoutconsumingmuchtime.

IdealCushioningmeansthat thereisnoendofstrokebounce, i.e., thedirectionoftravelofthepistonisthesamethroughouttheentirecushioningsequence,andthatitsvelocityisexactlyzerowhenitreachestheendofitstravel.Thesoundofendcovercontactisnegligibleandthetotalcycletimeisminimized.Cushioningisanimportantaspectofcylinderlife.Cushioningnotonlyensuressmoothoperationbutalsoextends the lifeofcylindersbypreventingshocks.InFigure6.20,apneumaticcylinderisshownwhichhasbothconventionalpneumaticandelasticcushions.

FIGURE6.20APneumaticCylinder.

CYLINDERMOUNTINGSCylindersaremanufactured in innumerablecombinationsofbore, rod,

and stroke sizes with various standard-mounting styles. There is a directrelationship between the cylinder mounting style and the effects of theoperatingpressureupon theunit.Standardmounting styles for fluidpowercylinders are divided into two general classifications based upon thecombined effects of force direction and mounting conditions. Thoseclassificationsareasfollows:

Cylinderswhichproducea straight-line transfer of force:Thisclass consists of models having fixed mounting styles that aresecured in a rigid condition. Cylinder mountings of this type aredivided into two groups: thosemodels,which absorb force on the

2.

cylinder centerline and those styles,whichdonot absorb force onthecenterlineoftheunit.

Pivoted cylinders which transfer force along a variable path:Thisgroupconsistsofmountingstyles,whichpivotaroundafixedpinandareabletocompensateforalignmentchangesinoneplaneduringoperation.

Theway inwhich a cylinder ismounted is critical to its performanceandservicelife.Impropermountingcanresultindamagetothecylinderaswellastotheequipmentonwhichitisbeingused.Inaccurateinstallation,ortheuseofaninappropriatemountingstylemayresultinmisalignment,whichcauses harmful side loading and bending. Some of the common ways inwhichcylinderscanbemountedare:

Extendedtie-rodsmountedcylindersFlange-mountedcylindersSideorlugmountedcylindersPivotmountedcylindersTrunnionmountedcylinders

ExtendedTie-RodsMountingExtended tie-rod cylinders are suitable for straight-line force transfer

andattheplaceswherethespaceforinstallationislimited.ThearrangementisshowninFigure6.21.Forpullapplications(wheretensileforcessetupinpistonrod)headendtie-rodmountsaresuitablesolution,ontheotherhandforpushapplications(wherecompressiveforcessetupinpistonrod)capendtie-rodmountsarepreferred.Thismountingstyleprovidesastablemeansofhandlingthrustloadsandmaybeusedwheneveravailableclearancespermitthe installation of this model. Consideration should be given to providingadded support to the cylinder body on horizontally mounted units havinglongstrokelengths.

FIGURE6.21ExtendedTie-RodMounting.

Mounting styles recommended by NFPA (National Fluid PowerAssociation)fortie-rodmountedcylindersareshowninFigure6.22.

FIGURE6.22PreferredMountingStylesUsingTieRods.

Flange-MountedCylindersFlange-mountedcylindersarealsosuitableforuseonstraight-lineforce

transfer applications. The flangemount is one of the strongest,most rigidmethodsofmounting(RefertoFigure6.23).Withthistypeofmountthereislittleallowanceformisalignment,thoughwhenlongstrokesarerequired,thefree end of the mounting should be supported to prevent sagging andpossible binding of the cylinder. The best use of a cap end flange is in athrust load application (rod in compression). Head end flange mounts arebestusedintensionapplications.Properselectionofaflangemountingstyledepends upon whether the primary work direction results in tension orcompression loadsbeingcarriedby thecylinder rod.Front flange-mountedunits are preferred for “pull type” applications where the rod is held intension. “Push type” applications, which subject the cylinder rod tocompressionloads,arebestsuitedforrearflangestylemountings.

FIGURE6.23FlangeMounting.

Mounting styles recommended by NFPA (National Fluid PowerAssociation)forflange-mountedcylindersareshowninFigure6.24.

FIGURE6.24PreferredMountingStylesUsingFlanges.

SideorLugMountedCylindersSide or Lug lug mounted cylinders do not absorb force on their

centerlines; due to this the movement of the cylinder applies a turningmoment,which tends to rotate thecylinderabout itsbolts.The sideor lugmountedcylinderprovidesafairlyrigidmount.Thesetypesofcylinderscantolerateaslightamountofmisalignmentwhenthecylinderisatfullstroke,butasthepistonmovestowardthecapend,thetoleranceformisalignmentdecreases.Itisimportanttonotethatifthecylinderisusedproperly(withoutmisalignment), the mounting bolts are either in simple shear or tensionwithoutanycompoundstresses.(RefertoFigure6.25.)

FIGURE6.25SideLugMounting.

Mounting styles recommended by NFPA (National Fluid PowerAssociation)forcylindersusinglugsareshowninFigure6.26.

FIGURE6.26PreferredMountingStylesUsingLugs.

FIGURE6.27PivotMounting.

Pivot-MountedCylindersAllpivotedcylindersneedaprovisiononbothendsforpivoting.These

types of cylinders are designed to carry shear loads. Long-stroke, pivot-mountedcylinderswillunavoidablyhavehigh-sideloadsbecauseoftherodweight. In these applications, a stop tubeordualpistonbecomesessential.Both spread the distance between the rod bearing and piston, reducing theeffectiveloadatthesetwopoints.

Mounting styles recommended by NFPA (National Fluid PowerAssociation)forpivot-mountedcylindersareshowninFigure6.28.

FIGURE6.28PreferredMountingStylesUsingPins.

Trunnion-MountedCylindersThesecylindersaredesignedtoabsorbforceontheircenterlines(Refer

to Figure 6.29). They are suitable for both push (compression) and pull(tension)applications.Theymayalsobeusedwherethemachinemembertobemovedfollowsacurvedpath.Thetrunnionpivotpinsshouldbecoveredbybearingsthatarerigidlyheldandcloselyfittedfortheentirelengthofthepin.On trunnion-mounted cylinders, it is necessary to fit pillow blocks ormated bearings as close to the cylinder head as possible, to minimizebending stresses in the heads. Spherical-bearing pillow blocks on trunnionmountsshouldbeavoidedbecausetheyintroducebendingstresses.

FIGURE6.29TrunnionMounting.

Mounting styles recommended by NFPA (National Fluid PowerAssociation)fortrunnion-mountedcylindersareshowninFigure6.30.

FIGURE6.30PreferredMountingStylesUsingTrunnions.

CYLINDERSIZINGTo determine the cylinder size that is needed for a particular system,

certainparametersmustbeknown.Firstofall,atotalevaluationoftheloadmustbemade.Thistotalloadisnotonlythebasicloadthatmustbemoved,but also includes any friction and the force needed to accelerate the load.Alsoincludedmustbetheforceneededtoexhausttheairfromtheotherendof the cylinder through the attached lines, control valves, etc. Any otherforcethatmustbeovercomemustalsobeconsideredaspartofthetotalload.Once the loadand required forcecharacteristics aredetermined, aworkingpressureshouldbeassumed.Thisworkingpressurethatisselectedmustbethepressureseenat thecylinder’spistonwhenmotion is takingplace. It isobvious that cylinder’s working pressure is less than the actual systempressure due to the flow losses in lines and valves. With the total load(includingfriction)andworkingpressuredetermined,thecylindersizemaybecalculatedusingPascal’sLaw.Forceisequaltopressurebeingappliedtoaparticulararea.Theformuladescribingthisactionis:

Force=PressurenArea

AreaofaCylinderThereare two typeofareas inonecylinder, i.e., areaon rod sideand

areaonnon-rodsideofthecylinder.Boththeforceandspeedofacylinderaredependentonknowingtheareaofthecylinder.Itisimportanttoaddherethattheareaontherodendofacylinderisdifferentthanthatofthenon-rodend.Area on non-rod side of piston is equal to the area of bore it can begivenmathematically(insquareinches)as:

Thesameformulacanbeusedtofindouttheareaofrodandthustheareaontherodsideofpistoncanbegivenas:

Area(rodend)=AreaofPiston−Areaoftheroditself

It can be added here that when pressure is applied to the rod end ofcylinderitwillmovefasterandhavelessforceascomparedtorodlesssideofcylinder.

ForcesofaCylinderAcylinderusuallyhas two forces.When fluidat the samepressure is

enteredinbothinputandoutputports,theforceactingontheside“withouttherod”ofthepistonismorebecausetheareaismoreinthatcase.P1andP2arethepressuresactingontwosidesofthepistonwiththeconditionthatP1=P2.LetusassumethatA1andF1aretheareaandforceactingonthepistonon“without therod”siderespectivelyandsimilarlyA2andF2are theareaandforceactingontherodsideofpiston.Mathematically:

Therefore,fromtheaboveexpression,itisclearthatforceF1onthesideofthepiston“withouttherod”ismorethantheforceF2onthe“rod”sideofpiston.

CYLINDERSPECIFICATIONCylinderscanbespecifiedonthebasisoffollowing:

CylinderborePistonroddiameterStrokelengthPressurerangeForceoutputatmaxpressureMountingstylesRodendsCushions(atoneendorbothends)Standardoperatingtemperature

INTRODUCTIONTOMOTORSA fluid power motor is a device that converts fluid power energy to

rotarymotion and force.Pressure is converted into torque and flow rate isconvertedintospeed.Thefunctionofhydraulicmotorisoppositetothatofapump. However, the design and operation of fluid powermotors are verysimilar topumps.Thedifferencebeing, insteadofpushing the fluid as thepump does in a hydraulic motor, the rotating elements, i.e., vanes, gears,pistons,etc.arepushedbytheoilpressuretoenablethemotorshafttorotateand thus develop the necessary turning torque and continuous rotatingmotion.Figure6.31showstheworkingprincipleoffluidmotor.

FIGURE6.31WorkingPrincipleofFluidMotor.

Fluid motors may be either fixed or variable displacement. Fixeddisplacementmotorsprovideconstanttorqueandvariablespeed.Thespeedis varied by controlling the amount of input flow. Variable displacementmotorsareconstructedsothattheworkingrelationshipoftheinternalpartscan be varied to change displacement.With the input flow and operatingpressure remaining constant, varying the displacement can vary the ratiobetween torque and speed to suit the load requirements. The majority ofmotors used in fluid power systems are fixed displacement type; however,variabledisplacementpistonmotorsareinusemainlyinhydrostaticdrives.

Although most fluid power motors are capable of providing rotarymotion in either direction, some applications require rotation in only onedirection. In these applications, one port of the motor is connected to the

systempressurelineandtheotherporttothereturnlineorexhaustedtotheatmosphere.The flowof fluid to themotor is controlledby a flowcontrolvalve, a two-waydirectional control valve, or by starting and stopping thepowersupply.Thespeedofthemotormaybecontrolledbyvaryingtherateof fluid flow to it. In most fluid power systems, the motor is required toprovide actuationpower in either direction. In these applications, theportsare referred to as working ports, alternating as inlet and outlet ports. Theflow to the motor is usually controlled by either a four-way directionalcontrolvalveoravariable-displacementpump.

MOTORRATINGSHydraulicmotorsareratedaccordingtothefollowingparameters:

Torque:Torqueistheturningforcedevelopedatthemotorshaftduetoitsrotation.The torqueincreaseswithan increase inoperatingpressureanddecreaseswithadecreaseinoperatingpressure.Pressure: The pressure required by a motor depends on the torquerequirement and its displacement.Amotorwith a higher displacementrequires lower pressure to generate a specific torque as compared to amotoroflowerdisplacement.Displacement:Displacementisdefinedastheamountoffluidrequiredtoturnthemotorshaftonerevolution.Itisexpressedincubicinchesperrevolution, the sameaspumpdisplacement.Hydraulicmotorscanbeafixedorvariabledisplacementtype.Afixeddisplacementmotorgivesaconstantspeedandtorquewithafixedflowrateandoperatingpressure.A variable displacementmotor gives a variable speed and torque evenwithconstantflowrateandoperatingpressure.Speed:Speedofamotoristhefunctionofitsdisplacementandtheinputflowrate.Themaximumspeedofamotoristhespeeditcansustainforaspecified timewithout damage. Theminimum speed of amotor is theslowestspeedatwhichamotorrotatessmoothlyandcontinuously.Thetorqueoutputofmotorisindependentofitsspeed.

HYDRAULICANDPNEUMATICMOTORS

Hydraulicmotorsconverthydraulicenergy intomechanicalenergy. Inindustrialhydrauliccircuits,pumpsandmotorsarenormallycombinedwithpropervalvesandpipingtoformahydraulicpoweredtransmission.Apump,whichismechanicallylinkedtoaprimemover,drawsfluidfromareservoirandforcesittoamotor.Usually,apumpisconnectedviaacarrierlinetoamotor,whichthendrawsfluidfromareservoirandforcesitintothemotor.Thefluidforcesthemovablecomponentsofthemotorintomotion,whichinturnrotatestheattachedshaft.Theshaft,whichismechanicallylinkedtotheworkload,providesrotarymechanicalmotion.Finally,thefluidisdischargedatlowpressureandtransferredbacktothepump.Hydraulicmotorsarepartof hydrostatic power transmission systems. Depending upon specificapplications, these motors prove more efficient, suitable, and economicalovertheirelectricalorpneumaticcounterparts.

Figure6.32showsthebasicoperationsofahydraulicmotor.

FIGURE6.32HydraulicMotor.

AdvantagesofHydraulicMotorsThe torque of the hydraulic motor is independent of the speed of themotor.Thus,aconstant torquecanbeobtainedfromahydraulicmotorevenwithchangingspeeds.Ahydraulicmotor isprotectedagainstanydamagedue tooverloading.Allhydraulicsystemsareequippedwithreliefvalves,whichopenwhenthesystempressurerisestoohighduetooverloading.

Pneumatic/Air Motors are used to produce continuous rotary powerfromacompressedairsystem.Thesemotorsaresimilarinconstructionandfunction to hydraulic motors. Pneumatic motors are used in applicationswhere low to moderate torque is required. Advantages of air motors overelectricmotors:

Theydonotrequireelectricalpower;airmotorscanbeusedinvolatileatmospheres.Theygenerallyhaveahigherpowerdensity,soasmallerairmotorcandeliverthesamepowerasitselectriccounterpart.Unlikeelectricmotors,manyairmotorscanoperatewithouttheneedforauxiliaryspeedreducers.Air motor speed can be regulated through simple flow-control valvesinsteadofexpensiveandcomplicatedelectronicspeedcontrols.Airmotortorquecanbevariedsimplybyregulatingpressure.Airmotorsgeneratemuchlessheatthanelectricmotors.

SYMBOLOFMOTORSFigure6.33showsthesymbolsforhydraulicandpneumaticmotors.

FIGURE6.33SymbolsforHydraulicandPneumaticMotors.

CLASSIFICATIONOFFLUIDMOTORSTherearethreebasicdesignsofrotarypumpsorcompressors;thegear

pump, the vane pump, and various designs of piston pumpor compressor,whichhavealreadybeenexplainedinChapter4.Thesecanalsobeusedasthe basis of rotary actuators. The principles of hydraulic and pneumatic

motorsareverysimilarbuthydraulicmotorsgivelargeavailabletorquesandpowers despite lower rotational speeds because of high pressures. Fluidmotorsareusuallyclassifiedaccordingtothetypeofinternalelement,whichisdirectlyactuatedbytheflow.Themostcommontypesofelementsarethegear,thevane,andthepiston.Sothefluidmotorsareclassifiedas:

GearmotorsVanemotorsPistonmotors

Eachof thesetypescanbeproducedbymotormanufacturersaseitherunidirectionalorreversible,althoughmostmotorsusedinmobileequipmentarethereversible.

GEARMOTORSGearmotorsare themostcommonhydraulicunits.Theoperationofa

gearmotorisshowninFigure6.34.Theseconsistofapairofmatchedspurorhelicalgearsenclosedinacase.Bothgearsaredrivengears,butonlyoneis connected to theoutput shaft.Operationof gearmotor is essentially thereverseofthatofagearpump.Flowfromthepumpenterstheinletportandflowsineitherdirectionaroundtheinsidesurfaceofthecasing,forcingthegearstorotateasindicated.Thisrotarymotionisthenavailableforworkattheoutput shaft.Like thegearpump, thegears inagearmotorarecloselyfittedinthehousingend,andforthisreason,flowoffluidthroughthemotorfromtheinlettotheoutletcanoccuronlywhenthegearsrotate.Gearmotorsareoffixeddisplacementtypewhichmeansthattheoutputshaftspeedvariesonly when the flow rate through the motor changes. These motors aregenerally two directional, the motor being reversed by direction of fluidthroughthemotorintheoppositedirection.

FIGURE6.34Gear-TypeMotor.

ThemotorshowninFigure6.34isoperatinginonedirection;however,thegear-typemotoriscapableofprovidingrotarymotionineitherdirection.Toreversethedirectionofrotation,theportsmaybealternatedasinletandoutlet.Whenfluidisdirectedthroughtheoutletport,thegearsrotateintheoppositedirection.Gearmotorsaretheleastexpensivebutthenoisiestofthehydraulicmotors.Thesehavetheabilitytooperateathighspeeds;however,theyareinefficientatlowspeeds.

VANEMOTORSA typical vane-type motor is shown in Figure 6.35. This particular

motorprovides rotation inonlyonedirection.Whenpressureoilenters theinlet port, the unequal area of the vanes results in the development of atorqueinthemotorshaft.Thelargertheexposedareaofthevane,orhigherthe pressure, the more torque is developed, which makes the shaft rotate.Because no centrifugal force exists until themotor begins to rotate, somemethod must be provided to initially hold the vanes against the casingcontour. Springs are often used for this purpose.However, springs usuallyarenotnecessaryinvane-typepumpsbecauseadriveshaftinitiallysuppliescentrifugal force to ensure vane to casing contact. Vane motors rotate ineitherdirectionbuttheydosoonlywhentheflowratethroughthemotoris

reversed.Hydraulicvanemotorsarethemostpopulargeneralpurposemotor,but they are limited by their tolerance to high pressure systems and thehigherpercentageof slippageor internal leakage relative to the lower totalfluidflowatlowspeeds.

FIGURE6.35VaneMotor.

PISTONMOTORSPistonmotorsarethemostcommonlyusedinhydraulicsystems.They

are basically the same as hydraulic pumps except they are used to converthydraulicenergyintomechanical(rotary)energy.Themostcommonlyusedhydraulic motor is the fixed displacement piston type. These motors arepositivedisplacementmotors thatcandevelopanoutput torqueat theshaftby allowing oil pressure to act on the pistons. Some equipment uses avariable displacement piston motor where very wide speed ranges aredesired. Hydraulic piston motors can be either axial or radial and aregenerallythemostexpensiveofthehydraulicmotors.Theyhaveadvantagesovertheothermotors,however,inthatpistonmotorsarefarmoreadaptabletohightorque,lowspeedoperationandhighersystempressureapplications.

Therearethreetypesofpistonmotors:

Swashplatein-line-axispiston-typemotorsSwashplatebentaxispistontypemotorsRadial-pistonmotors

SwashPlateIn-Line-AxisPiston-TypeMotorsThe axial pistonmotor is of the swash plate type and has a bank of

cylindersarranged inacircle (360degrees)parallel toeachother (Refer toFigure6.36).Eachcylinderhasapiston,whichreciprocateswithoneendofthepistonpushingagainstaneccentricswash-platelocatedatoneendofthebank of cylinders. There is a mechanical arrangement through which theeccentricplateisconnectedtoanoutputshaftthatisaxiallyalignedwiththecylinders.Duringmotoroperation,thecylindersarefilledwithhigh-pressurehydraulicfluidinaparticularsequencemakingthepistonsmoveoutwardstopushsequentiallyagainst theswash-platecausingit torotate.Onthereturnstroke of the piston, the fluid is swept back at low pressure to return to areservoir.Theoperationimpartsrotationalmovementtotheoutputshaft,ofwhichoneendisconnectedtotheswash-plateandtheothertotheworkload.Thisisadesignthatcaterstoaverycompactcylindricalhydraulicmotor.

FIGURE6.36SwashPlateIn-Line-AxisMotors.

Axial-piston motors have high volumetric efficiency, combined withexcellentoperationatbothhighandlowspeeds.

SwashPlateBentAxisPistonTypeMotorsThesemotorsarealmost identical to thepumps.Theyareavailable in

fixed-and variable-displacement models in several sizes (Refer to Figure6.37). Variable-displacementmotors can be controlledmechanically or bypressure compensation. These motors operate similarly to in-line motors

exceptthatpistonthrustisagainstadrive-shaftflange.Aparallelcomponentof thrust causes a flange to turn. Torque is maximum at maximumdisplacement; speed is at aminimum.This design of pistonmotor is veryheavyandbulky,particularly thevariable-displacementmotor.Using thesemotorsonmobile equipment is limited.Although somepiston typemotorsare controlled by directional-control valves, they are often used incombination with variable-displacement pumps. This pump-motorcombination(hydraulictransmission)isusedtoprovideatransferofpowerbetweenadrivingelement,suchasanelectricmotor,andadrivenelement.Hydraulic transmissions may be used for applications such as a speedreducer, variable speed drive, constant speed or constant torque drive, andtorqueconverter.

FIGURE6.37SwashPlateBentAxisMotors.

Radial-PistonMotorsRadial-piston motors produce very high torque at low speed. These

motorshaveacylinderbarrelattachedtoadrivenshaft.Thebarrelcontainsanumber of pistons that reciprocate in radial bores. The radial-pistonmotoroperates in reverseof the radial-pistonpump. In the radial-pistonpump,asthecylinderblockrotates,thepistonspressagainsttherotorandareforcedinandoutof thecylinders, therebyreceivingfluidandpushingitout into thesystem.Intheradialmotor,fluidisforcedintothecylindersanddrivesthepistons outward. The pistons pushing against the rotor cause the cylinderblock to rotate.Figure6.38 showsadesignwith radial cylinders each in aseparate block. The pistons are connected to the shaft by a crank or someother mechanism. Suitable valve designs allow the oil into cylinders and

1.

forcethepistonstoreciprocateandturntheshaft.Theseproducehighpowerandtorque.

FIGURE6.38Radial-PistonMotors.

APPLICATIONOFMOTORSHydraulic motors provide solutions in applications involving infinite

speed control, stalling under full torque, high power-to-weight ratio, andsmall size. Their characteristics make them useful in a wide variety ofindustries.Someoftheapplicationsofmotorsare:

Intheaerospaceindustry.Inthefoodprocessingindustry.Inconstructionandagriculturalequipment.Inheavyearthmovingequipmentlikeexcavators,skids,forklifts,heavydumptrucks,bulldozers,etc.

Cost-wise,piston typehydraulicmotors are the costliestwhereasgeartypemotorsare the leastexpensive.However,eachhas itsownadvantagesdependingonhowitisused.

EXERCISESWhatisanactuator?

2.3.4.

5.

6.7.

8.

9.10.

11.12.

13.

14.15.16.17.18.19.20.

21.22.23.

Classifyvarioustypesofactuators.Classifyvarioustypesofcylinders.Explain the construction and working principle of a single-actinghydrauliccylinderwithaneatsketch.Explainwithaneatsketchtheconstructionandworkingofdouble-actingcylinder.Drawthesymbolfordouble-actingcylinder.With the aid of sketches, explain the constructional features of ahydrauliccylinder.Differentiatebetweendouble-actinghydrauliccylinderanddouble-actingpneumaticcylinder.Explaintheworkingofthedouble-actingpneumaticcylinder.Discussvariousconfigurationsinsingle-actingcylinders.List various differences between single-acting and double-actingcylinders.Howisthehydrauliccylinderdifferentfromthepneumaticcylinder?With thehelpofaneatsketch,showthevariouspartsofhydraulicandpneumaticdouble-actingcylinders.Explain the construction, working, design, and mounting of hydraulicandpneumaticcylinderswiththehelpofneatsketches.Whatarethefunctionsoftheramtypeandtelescopingcylinders?Whatisatandemcylinder?Listthevariousstandardmountingstylesbeingusedinindustry.Whataretheapplicationsofthetandemandduplexcylinders?Whatisacylindercushion?Statethepurposeofcushioningincylinders.Listvariousmaterialsbeingusedforthemanufacturingofacylinder.Sketch a double-acting cushioned hydraulic cylinder and label thecomponents.Brieflydiscussthetypesofmotors.Listtheparametersformotorratings.Withthehelpofaneatsketch,explain theconstructionandworkingofgearandvanemotors.

24. Sketchthestandardsymbolforapneumaticmotor.

CHAPTER7

CONTROLVALVES

INTRODUCTIONInapneumaticorhydraulicsystem,theobjectiveisgenerallytosupply

power from a compressor or pump to the fluid actuator (i.e., motor orcylinder).But theproblemisnotalwaysthesame,example,sometimesthestrokeofthecylindermovesveryfastwhereassometimesitisextendsveryslowly. The solution to these fluid problems can be obtained by using acombinationofvalves.

In almost every fluid system, valves are required to control thedirection, flow, pressure, or quantity of fluid. Based on the application,valves can be divided into four categories: direction control valves, flowcontrol valves, pressure control valves, and special valves. Valves can beclassified according to their construction, i.e., poppet valves and spoolvalves.Wecanalsoclassifythevalvesonthebasisofmodeofactuation,i.e.,theycanbeactuatedmanually,electrically,electromagnetically,orwiththehelp of fluids. This chapter concentrates on explaining identification,function, construction, and location of valves in relation to hydraulic andpneumaticcircuits.

Hydraulicsystemsarehigh-pressuresystemsandpneumaticsystemsarelow-pressure systems.Hydraulic valves aremade of strongmaterials (e.g.,steel) and are precision manufactured. Pneumatic valves are made fromcheaper materials (e.g., aluminum and polymer) and are cheaper tomanufacture.

CLASSIFICATIONOFVALVES

1.

Valvesareclassifiedas:

DirectioncontrolvalveFlowcontrolvalvePressurecontrolvalveCheckvalveDirectioncontrolvalvesaremostimportantamongallothervalvesbecause of their frequent use in a fluid power system. As the nameimplies,theyareusedtodirecttheflowoffluidinadesireddirection.

Flow control valves are those in which the flow of fluid is variedaccording to requirements. They are of fixed and adjustable flow controltype.

Pressurecontrolvalvesareusedforregulatingthepressureoffluidsinafluidsystem.Pressurereliefvalve,regulatingvalve,etc.comesunderthiscategory.

Allothervalvesinwhichthefreeflowoffluidisallowedonlyinonedirection come under the category of check valves, e.g., non return valve,quickexhaustvalve,twinpressurevalve,nonreturnflowcontrolvalve,etc.

Someoftheimportantvalvesarediscussesbelow.

DIRECTIONCONTROLVALVESDirectioncontrolvalvesaredesignedtodirect theflowoffluid,at the

desired time, to the point in a fluid power systemwhere it will do work.Direction control valves are intermediators,which supply pressurized fluidfrom component or pump to an actuator (cylinder or motor) as per itsrequirements.Itstarts,stops,andregulatesthedirectionoffluidanddirectsthe fluid in the line in which it is required. Direction control valves arespecifiedbythenumberofportsandthenumberofitspossiblepositions.

SYMBOLANDDESIGNATIONOFDIRECTIONCONTROL(DC)VALVE

ADCvalveisspecifiedbythenumberoffluidportsandthenumberofpositions a valve can take. The number before the slash identifies thenumberofports,andthesecondnumberreferstonumberofpositionsavalvecantake,e.g.,a3/2DCvalveisa3portand2positiondirection

2.

3.

4.

controlvalve,4/3DCvalve isa4portand3positiondirectioncontrolvalve,etc.ThesymbolforaDCvalveisbuiltaroundaseriesofboxesorrectangles,one box for each usable position of the valve.The number of adjacentboxesindicateswhetheravalveisatwoorthreepositionvalve.(RefertoFigure7.1.)

FIGURE7.1Symbolsfor2-Positionand3-PositionValves.

Ports are ways or openings in the DC valve from where fluid underpressure enters and exits. Usually a DC valve may have 2, 3, 4, or 5ports. Each valve port should be shown on the symbol. The ports areshownon only one of the boxes, the box that represents the flowpaththatexistsat thestartofthecycle.SomeexamplesareshowninFigure7.2.

FIGURE7.2Symbolsfor3TypesofValves.

ADCvalvemaytakeamaximumof3positions.TheyareON,OFF,orNeutral (1, 2, or 0) and each position of the valve are shown by aseparatebox.(RefertoFigure7.3.)

5.

6.

FIGURE7.3SymbolsforValveswithPositionsShown.

The naming of ports is standardized, i.e., it is followed all over and isgivenbelow:

P Pressureport/supplyport.

R,T Exhaustports,RforpneumaticsandTforhydraulics.

A,B,orC Workingports,whichsupplypressuretoactuators(cylinderormotors).

L Leakageport.(Onlyinhydraulics)

X,Y,Z Pilotsupplies.(Shownbydottedlines)

Arrowsusedforhydraulicsarefilledones.

Lines and arrows are used to represent the flow and direction of fluidacross thevalves.Eachboxcontainsagroupof lines that represent theflow paths the valve provides when it is in that position. If a port isblocked,itisshownbythesymbolasshowninFigure7.4.Iftwoportsareconnectedandfluidcanflow,thisisshownbyalinedrawnbetweenthe two ports. The direction in which fluid flows during a normaloperatingcycle is shownbyputtingarrowheadsat theendsof the flowpathsnexttotheportsfromwherethefluidwillcomeout.Theabovecanbeexplainedwiththehelpofa2/2DCvalve,whichisshowninFigure7.4.

FIGURE7.42/2DCValve.

In theabove figure, the leftboxshows theconditions thatexistat thestartofthecycle.PortPisblocked,andportAisblocked.Whenthevalveisshifted,theflowconditionshownintherighthandboxexists,i.e.,portPisopentoportA.

7.

1.

(a)

The normal position of a valve is that position atwhich the naming isdone.InthevalvesymbolshowninFigure7.5,right-sidepositionisthenormalpositionofthevalve.XandYarethepilotsupplies.

FIGURE7.53/2PilotOperatedNormallyClosedDCValve.

CLASSIFICATIONOFDCVALVESDCvalvesareclassified:

Onthebasisofmethodofvalveactuation.Onthebasisofconstruction.

CLASSIFICATIONOFDCVALVESONTHEBASISOFMETHODSOFVALVEACTUATION

TheflowoffluidsiscontrolledbychangingthepositionofDCvalves.Knowledgeofthesecontrolmethodsisveryimportantbecauseactuationofvalves is always subject to the application of valves. The actuators aredevicesormethodsthatcausethevalvetoshiftfromonepositiontoanother.Valve actuators are selected based upon a number of factors such as thetorquenecessary tooperate thevalveand theneedforautomaticactuation.Therearedifferentmethodsofactuation,whichcanbeused toactuateDC

valves.Thedifferenttypesofactuatorsavailableare:ManualActuation:Itmeanswhenthedesignedsystemisnotfullyautomaticandnorelationshipcan be defined between operation of valves and time lag between twoconsecutiveoperations.Manualactuatorsarecapableofplacingthevalveinanypositionbutdonotpermitautomaticactuation.Therearefour typesof

manualactuations:PushButton:Abuttonispusheduntil thepressureisrequired toflowfromthatvalve is reachedand then thebutton is released;the valve again attains its previous position under the action of a spring(becauseaspringisusedincombinationontheothersideofthevalve).

(b)

(c)(d)

2.

(a)

FIGURE7.6DCValvewithPushButton.

Push/PullButton: Inthiscase,springreturnisnotprovidedontheothersideofthevalvehencetheoperatorhastopullthevalveagainwhenthepositionhastobechanged.Pedal:Valvescanbeactuatedbypressingafootpedal.Lever: Valves can be actuated by pulling the lever backward andpushingitforward.

Mechanical Actuation: This category includes all the mechanicalcomponents, which are operated by an external force. Types ofmechanicalactuationsare:Roller:Forchangingthepositionofthevalve,aspringreturnleverisused.Theforceofpushisappliedontheleverandthepositionofthevalveischanged.Inordertomakefrictionfreecontactoftheleverandforceapplyingmember,arollerismountedonthelever.The external force-applying member may be the piston rod of thecylinder when the piston is extending or it may be a cam, whichcontinuouslyprovidesmotiontotheleverviatheroller.(RefertoFigure7.7.)

(b)(c)

3.

4.

FIGURE7.7RollerOperatedDCValve.

PlungerSpring:Aspring isused inmostdirectionalcontrolvalves toholdtheflow-directingelementinneutralposition.Springholdsthenonactuatedvalveinonepositionuntilanactuatingforcegreatenoughtocompressthespringshiftsthevalve.Whentheactuatingforceisremoved,thespringreturnsthevalvetoitsoriginalposition.

PilotOperation/Actuation:Whenthepressurizedfluidisusedtooperatethe valves in addition to extending and retracting of the cylinder, it iscalledpilotactuationorpilotoperationandtheadditionalvalvesusedforthis purpose are called pilot valves. Pilot-operated valves (Refer toFigure7.8)canbemountedatanypositiontowhichpressurizedfluidcanbepiped.Dependinguponthetypeoffluidused,pilotactuationcanbeoftwotypes:hydraulic,pneumatic.

FIGURE7.8Pilot-OperatedDCValve.

Hydraulicactuatorsuseoilunderpressureforitsoperation.Becausethepressurizedfluidneeds tobecontrolledbyaDCvalve,suchvalvescannot be used alone. Pneumatic actuators use compressed air for itsoperation.

Detent: Detent are locks that hold a valve in its last position after theactuating force is removed until a stronger force is applied to shift thevalve to another position. The detentmay then hold this new positionaftertheactuatingforceisagainremoved.(RefertoFigure7.9.)

5.

6.

FIGURE7.9DCValvewithDetent.

Electromagnets: Electromagnets are commonly known as solenoids.Solenoidactuatedvalvesarepopularfor industrialmachinesbecauseofreadyavailabilityofelectricalpowerinindustries.Asolenoidconsistsofacoilandanarmature.Whenthecoilisenergizedbyanelectriccurrent,amagneticfieldiscreatedaroundit,whichattractsthearmature.Whenthearmaturemoves,itpushesthespool.(RefertoFigure7.10.)

FIGURE7.10Solenoid.

Electromagnets are nothing but temporary magnets. They behavelikemagnetswhenacurrentispassedthroughthem.Inthesamewayaplunger ismade tomoveupanddown ina framebyenergizing it, thismotionisusedtoactuatevalves.

Pilot Solenoid Operation: When pilot valves and solenoid valves areusedincombination,itiscalledpilotsolenoidoperation.Forexample,a3/2pilotoperatedDCvalve (pneumaticorhydraulic),which isused tooperatethemain5/2DCvalve,isitselfoperatedbyasolenoidvalve.

SYMBOLSFORVALVEACTUATORS

Thesymbolsforvalveactuatorsaredrawnnexttotheendofthevalveboxes.Therearestandardsymbols forvalveactuators.Thesesymbolsmaybe drawn on either end of the valve without altering their meaning. ThesymbolsforvalveactuatorsareshowninTable7.1.

TABLE7.1SymbolsforValveActuators.

EXAMPLESOFDCVALVESWITHACTUATORSFigure 7.11 shows a 4/2 solenoid-operated spring-returnedDC valve.

Theruleisthateachvalveactuatorisdrawnnexttotheboxthatexistswhenthatactuatorisincommand.

FIGURE7.114/2Solenoid-OperatedSpring-ReturnDCValve.

Intheabovefigure,whenthespringhascontrolofthevalve,theflowpathsintheleft-handboxexist.Whenthesolenoid(theright-handactuator)isincommand,theflowpathsintheright-handboxexist.

AtypicalDCvalveismadeupofthreeparts.(RefertoFigure7.12.)

FIGURE7.12ASampleDCValve.

SomeofthecommonDCvalveswithactuatorsareshowninTable7.2.

1.2.3.

1.

TABLE7.2DCValveswithActuators.

NameofDCValve Symbol

2/2pushbuttonoperatedspringreturnedDCvalve

3/2pushbuttonoperatedspringreturnedDCvalve

3/2rolleroperatedspringreturnedDCvalve

3/2leveroperatedspringreturnedDCvalve

3/2airpilotoperatedspringreturnedDCvalve

4/2pilotoperatedDCvalve

4/2pushbuttonoperatedspringreturnedDCvalve

4/2solenoidairoperatedspringreturnedDCvalve

4/3solenoidoperatedspringreturnedDCvalve

CLASSIFICATIONOFDCVALVESONTHEBASISOFCONSTRUCTION

Valvesmaybeclassifiedon thebasisofconstruction into three types:RotaryvalvesPoppet/seatvalvesSpool/slidingvalves

Rotary Valves:A rotary valve consists of a rotary spool that is placedinsideavalvebody.A rotary spoolhaspassages for fluid to flow.Thespoolcanberotatedmanuallyormechanically.Whenthespoolrotates,iteither blocks the valve port or connects them to the passages. Theworking of rotary valves is explained in Figure 7.13 by taking all thepositionsofvalves.

2.

InitiallypressureportPisconnectedtoworkingportAandportBisconnected to the tank as shown in Figure 7.13 (a). All the ports areblockedintheintermediateposition,whenthevalverotatesasshowninFigure7.13(b).Intheextremeposition,whenthevalvespoolisrotated,theflowfrompressureportPgoestoportBandflowfromportAgoestotankasshowninFigure7.13(c).Rotaryvalvesarecompact,simple,andmainlyusedforhandoperationinpneumaticsystems.

FIGURE7.13WorkingofRotaryValve.

PoppetValves: Poppet or seat valveshave a ball or a piston cone as aseatingelement,whichisnormallykeptclosedbyalightspring.Inthesevalves, the poppet is forced off its seat allowing flow in only onedirection.Noflowisallowedintheoppositedirection.Figure7.14showsa simple poppet valve.When the push button is pressed, as shown inFigure7.14(b),theballliftsoffitsseatandallowsfluidtoflow.Whenthepushbuttonisreleased,thespringforcestheballupagainclosingthevalve. (Refer to Figure 7.14 (a).) Seat valves have the advantage ofperfectsealingoverspoolvalves.

3.

FIGURE7.14WorkingofPoppetValve.

SpoolValves:Aspooltypeofdirectionalvalveisthemostcommontypeofvalveusedinahydraulicsystem.Aspoolvalveconsistsofaspoolandvalvehousing.Differentportsarecutinthevalvehousingandthespoolis constrained tomove axially inside the housing.Fluid is routed to orfrom thework ports as the spool slides between passages to open andcloseflowpaths,dependingonthespoolposition.Spoolvalvesarecheapandeasytomanufacture.Theyrequirelessfinishingascomparedtoseatvalves. Spool valves are compatible with all the methods of valveactuation,whereas this isnot thecaseof seatvalves.Perfect sealing inspool valves cannot be achieved because of their specific construction.Thesevalvesarewidelyusedbecausetheycanbeshiftedto2,3,ormorepositions formoving fluid between different combinations of inlet andoutletports.

Figure 7.15 shows the typical directional control valve, whichconsists of a valve body with internal flow passages within the valvebody and a sliding spool. When the spool is in position as shown inFigure7.15(a),theflowpathisopen,i.e.,pressureportPisconnectedtoworkingportA.Whenthespoolisshiftedoneitherside,theflowpathisclosedasshowninFigure7.15(b).

FIGURE7.15WorkingofSpoolValve.

CONSTRUCTIONOF2/2,3/2,AND4/2DIRECTIONCONTROLVALVES

2/2DCVALVESA2/2DCvalveisa2portand2positiondirectioncontrolvalve.A2/2

DCvalveconsistsoftwoportsconnectedtoeachotherwithpassages,whichareconnectedordisconnected.A2/2DCvalvecanbeof two types:2/2spooltypeDCvalve2/2seattypeDCValve

2/2SpoolTypeDCValveThe 2/2 spool valve is explained with the help of the diagram given

below.InitiallyinFigure7.16(a),the2/2DCvalveisatitsnormallyclosedposition, i.e.,pressureportP isnotconnectedwithworkingportA.As thespoolmovesbackandforth, iteitherallowsorprevents fluid flowthroughthevalve. InFigure7.16 (b),when themanual pushbutton is pressed, thespoolmovesinsideandthusconnectspressureportPwithworkingportA.Positionsareshownwithsymbolicrepresentation.

FIGURE7.162/2SpoolTypeDCValve.

Symbol

Figure7.17showsthesymbolofa2/2DCvalve.

FIGURE7.172/2PushButtonOperatedSpringReturnedDCValve.

2/2SeatTypeDCValveTounderstandthe2/2seattypevalverefertoFigure7.18(a)and(b).In

this typeof construction, a poppet valvewith its valve seat is restingon aspring.Amanualpushbuttonisprovidedtochangethepositionofthevalve.InFigure7.18(a),thevalveisinitsnormallyclosedpositionasportPandport A are not connected, so fluid cannot pass through this valve. Thisrepresentsthe‘OFF’positionofthevalveandwhenthemanualpushbuttonis pressed as shown in Figure 7.18 (b), the valvemoves downward hencemakingwayforfluidtopass,andinthiswaythe‘ON’positionofthevalvecanbeattained.

FIGURE7.182/2SeatTypeDCValve.

3/2DCVALVESA3/2DCvalveisa3portand2positiondirectioncontrolvalve.A3/2

DC valve consists of three ports connected to each other with passages,whichareconnectedordisconnected.3/2DCvalvecanbeof two types:3/2spooltypeDCvalve3/2seattypeDCvalve

3/2SpoolTypeDCValveConstructionofa3/2DCspoolvalveissimilartoa2/2DCspoolvalve

withasmalldifferencethatoutletportRorT(RforpneumaticsandTforhydraulics) is added. Again the position of the spool is shifted for theextendingandretractingofacylinder.(RefertoFigure7.19.)

FIGURE7.193/2SpoolTypeDCValve.

Symbol

Figure7.20showsthesymbolofa3/2DCvalve.

FIGURE7.203/2PushButtonOperatedSpringReturnedDCValve.

3/2SeatTypeDCValveThegeneralarrangementofa3/2seattypeDCvalveisshowninFigure

7.21.Aleverisusedasameansofactuation.Whentheleverispulled,theleft-sidepressureportPgetsconnectedwithworkingportAandfluidfromthetankorsourceissuppliedtotheactuatorandsimilarlywhenthisleverispushed, the right-side port P is closed andworking portA gets connectedwithexhaustportRorTandfluidfromthecylinderisexhausted.

FIGURE7.213/2SeatTypeDCValve.

Symbol

Figure7.22showsthesymbolofa3/2DCvalve.

FIGURE7.223/2LeverOperatedSpringReturnedDCValve.

4/2DCVALVESA4/2DCvalveisa4portand2positiondirectioncontrolvalve.A4/2

directional valve consists of four ports connected to each other withpassages,whichareconnectedordisconnected.Four-wayvalvesareusedtocontrolthedirectionoffluidflowinahydraulic/pneumaticcircuit.A4/2DC

valve can be of two types: 4/2 spool typeDC valve 4/2 seat typeDCvalve

4/2SpoolTypeDCValveA4/2spooltypeDCvalveisverycommonanditsmainapplicationis

in thecontrolofadoubleactingcylinder.Thisvalveconsistsof fourportsandtwopositionsasshowninFigure7.23.Theworkingofa4/2DCvalveisexplained by taking all positions of valve. In the figure shown below, thespoolisactuatedbymeansofpilotsuppliesfrombothsides.

FIGURE7.234/2SpoolTypeDCValve.

AsshowninFigure7.23(a),whenthespoolisinapositionwherethesupply pressure P is connected to port A and port B is connected to theexhaust port, the cylinder will extend. As the spool moves to the otherextremeposition,i.e.,left,thepressureportPisconnectedtoportBandportA is connected to the exhaust port (Refer to Figure 7.23 (b)), now the

cylinderretracts.Withadirectionalcontrolvalveinacircuit,thecylinder’spistonrodcanbeextendedorretractedandworkisperformed.

Symbol

Figure7.24showsthesymbolofa4/2DCvalve.

FIGURE7.244/2PilotOperatedDCValve.

4/2SeatTypeDCValveA4/2seatvalveisshowninFigure7.25.Ithasfourports(namelyP,R,

A,andB)and twopositions.Apushbuttonwithaspringreturn isused tocontroltheverticalmovementoftheseatvalvesinsidetheguides.Theportsare alternately connected and departed by moving the seat valves up anddown.Initiallywhenthebuttonisnotpressed, thecompressedaircanpassfrom pressure port P to theworking port B from the passage between thevalve seats and compressed air may exhaust out from working port A toexhaustportRonotherside.Whenthepushbuttonispressed,pressureportPisjoinedwithworkingportAandworkingportBgetslinkedwithexhaustportRbymeansofinternalgalleries.

FIGURE7.254/2SeatTypeDCValve.

Symbol

Figure7.26showsthesymbolofa4/2DCvalve.

FIGURE7.264/2PushButtonOperatedSpringReturnedDCValve.

CENTERCONDITIONSIN4WAYDCVALVESThedefaultpositionofaspoolina4way(4ports)DCvalveiscalled

itscenterposition.Thecenterpositionofthespooldeterminestheoperationof thedirectioncontrolvalve.Thedifferentcenterconditions inDCvalves

are: Open center Closed center Tandem center Float centerOpenCenterCondition: In the open center condition, all ports (namelyA,B, P,and T) are interconnected to each other as shown in Figure 7.27. In thiscondition,theactuatorisnotheldunderpressureandthepumpflowgoestothetankatlowpressure.Thesymbolfortheopencenterconditionshowsallthefourportsconnectedtoeachother.Thistypeofcenterconditionisused

when the pump flow is supposed to perform a single operation only. Thiscondition is suitable for applications where the actuator is not held underpressure.Thisspoolhelpstominimizeshockswhilebeingmovedfromonepositiontoother.

FIGURE7.27OpenCenterConditionina4WayDCValve.

ClosedCenterCondition: In the closed center condition, all ports areblockedasshowninFigure7.28.Inthiscondition,thefluidcannotpassthroughthevalveandcanbeusedforanyotheroperation.Thevalveswith closed center condition are used when a single pump performsmorethanoneoperationandwheretheremustbenopressureloss.Thesymbolforclosedcenterconditionshowsallthefourportsblocked.Thedisadvantageofclosedcenterconditionisthatthepumpflowcannotgotothetankunderthisconditionandthereispossibilityofleakage.

FIGURE7.28ClosedCenterConditionina4WayDCValve.

TandemCenterCondition:Inthetandemcentercondition,thepressureportisconnectedtothetankportandboththeactuatorportsareblockedasshowninFigure7.29.Inthiscondition,thepumpflowgoestotankatlowpressure.Thiscenterconditionisusedinapplicationswheretwoormoreactuatorsareinserieswiththesamepowersource.ThesymbolofatandemcenterconditionshowsactuatorportsAandBblockedandpressureportPconnectedtothetankportT.

FIGURE7.29TandemCenterconditionina4WayDCValve.

FloatCenterCondition:Inthefloatcentercondition,thepressureportis blocked and the actuator ports are connected to the tank port asshown in Figure 7.30. In this condition, pressure ismaintained in thepressure port and removed from the actuator port to the tank. Thiscenterconditionisusedinapplicationsusingpilotoperateddirectionalvalves.ThesymbolofafloatcenterconditionshowstheactuatorportsAandBconnectedtotankportTandpressureportPisblocked.

FIGURE7.30ClosedCenterConditionina4WayDCValve.

1.

CHECKVALVECheckvalveisaone-waydirectionalvalve.Itsfunctionistoallowthe

flow in one direction only. It does not permit the flow in the oppositedirection.(RefertoFigure7.31.)Forthisreason,theyarealsoknownasnon-return valves. In order to avoid any leakage, these valves are always ofpoppettypeconstruction.Theyconsistofaballorapoppet,whichiskeptinitsnormallyclosedpositionbyaspring.Whenthefluidpressureovercomesthe spring force, the poppet is forced off its seat, allowing flow in thatdirection.Flow isnotpossible in theoppositedirection.Thisvalve isusedfrequently in hydraulic and pneumatic circuits because of its number ofapplications.

FIGURE7.31CheckValve.

ApplicationsofCheckValve

Toprevent return flow inhydraulics:Checkvalvesareused topreventreturnflowoffluidfromthehydraulicsystem.Itsapplicationisshowninthebasichydraulic circuit diagram for controlof single acting cylinder(Refer to Chapter 8). Like the pressure relief valve, a check valve isrequiredineveryhydraulicsystem.

2.

3.

Speedcontrol:Thesevalves canalsobeused to control the speedof apneumatic or hydraulic cylinder. This application is shown in speedcontrolincircuits(RefertoChapter8).

Speedinpneumaticandhydrauliccircuitscanalsobecontrolledbyusing a check valve rectifier.Working of check valve rectifiers can beunderstoodbystudyingtheexamplegiveninFigure7.32.Thiscircuitisdrawntoobtaintheslowforwardandbackwardmotiontotheram.Whenpressurizedfluid(eitherhydraulicsorpneumatics)isfedtopressureportP,itescapesoutoftheDCvalveviaworkingportAandgotherectifier.In this, check valves are so arranged that fluid have to pass throughvariable speed controlwhen flowing from the pump/compressor to thecylinder. As a result the speed is reduced, i.e., the pistonmoves slowduringforwardstroke.

FIGURE7.32CheckValveRectifier.

WhenthepositionoftheDCvalveischanged,thepressurizedfluidstartsflowingthroughtherodsideofthecylinderandisdischargedfromthe other side of the cylinder. The pressurized fluid coming out of thecylinder has to pass through check valves and variable restrictors.Thisresultsintheloweringofspeedofthepistonduringthebackwardstroke.Hence, speedof thecylindercanbe reducedby theuseof flowcontrolvalves.

Tobypass theblocked lines inhydraulics:SometimescheckvalvesarealsousedtobypasstheflowfromblockedlinesasshowninFigure7.33.

FIGURE7.33ACheckValveCanbeusedtoBypassaCloggedFilter.

PILOTOPERATEDCHECKVALVEThistypeofcheckvalveallowsflowinonedirectionbutpreventsflow

in the opposite direction unless pilot pressure is applied. A pilot operatedcheckvalvecomprisesofamovablepoppetandapiston,whichactsonthepoppet based upon the pilot pressure. It consists of pilot portX, one inletport,andoneoutletport.(RefertoFigure7.34.)AsshowninFigure7.34(a),whenfluidpressureisappliedthroughtheinletport,itcausesthepoppettoshift, allowing flow in that direction. No flow is possible in the oppositedirection.The reverse flow ispossibleonlywhenpilotpressure is applied.AsshowninFigure7.34(b),aspilotpressureisappliedthroughpilotportX,the fluid pressure forces the piston to shift the poppet allowing flow inreversedirection.

FIGURE7.34PilotOperatedCheckValve.

Symbol

ThesymbolofapilotoperatedcheckvalveisshowninFigure7.35.Apilotpressurelineisshownactinginadirection,whichopensthevalve.

FIGURE7.35SymbolforPilotOperatedCheckValve.

PRESSURECONTROLVALVESPressurecontrolvalvesarefoundineveryhydraulicsystem,wherethey

act as safety devices. These valves assist in a variety of functions, fromkeepingsystempressuressafelybelowadesiredupperlimittomaintainingaset pressure in the part of a circuit. Most pressure control valves areclassifiedasnormallyclosed.Thismeansthatflowtoavalve’sinletportisblocked from an outlet port until there is enough pressure to cause anunbalanced operation.Valves that come under this category include relief,reducing, sequence, counterbalance, andunloadingvalves.Pressure controlvalvescanbedesignedeitherasapoppet/seattypeorspooltypevalve.Spooltypevalveshavetheadvantageofshortstrokeandthereforerapidresponse.Seattypevalveshavetheadvantageofbeingtotallyleakproof.Ontheotherhand,spooltypepressurecontrolvalvesprovideprecisioncontrol.

PRESSURERELIEFVALVEPressure relief valves are themost common types of pressure control

valvesusedinhydraulics.Itisalwaysrequiredthatpressureinthehydraulicline should not increase the design limit of components in a hydraulicsystem.A pressure relief valve is required in a hydraulic line to limit thepressureinlineandtoensuresafetyofthecomponentsofahydraulicsystemfromthedangerofoverloadandbursting.Itisgenerallyconnectedbetweenthepump lineand the tank line soasnot toobstruct the fluidpassageandcomes under action when required. This valve is also called a maximumpressurevalveorsafetyvalveduetoitsfunction.

The pressure relief valve shown in Figure 7.36 consists of a bodysectioncontainingapiston/plunger that is retainedbya springandacoversection that controls the piston body movement. It is set at a particularpressurebyadjustinga springcompressionprovided in thevalve. Initially,valve isshown in its restposition.Whenpressure in the line increases, the

fluid pressure overcomes the set pressure and the piston/plunger (springloaded)isforcedtomoveinsidebymakingwayforfluidtoenterthevalve.The fluid is exhausted out via another port directly to the tank, therebysaving the system components from the danger of bursting. When thepressureinthehydraulicsystemnormalizesagain, i.e.,pressureoutsidethevalveislessthanpressureinsidethevalve,theplungeragaincomesbacktoitsinitialpositionandpassageisblocked.

FIGURE7.36PressureReliefValve.

Symbol

Symbol of a pressure relief valve is shown in Figure 7.37. A boxrepresentsthesymbolofareliefvalvewithaspringononeside.Thismeansthat the valve is spring operated.The arrowon the springmeans that it isadjustable.

FIGURE7.37SymbolforPressureReliefValve.

CrackingPressureandPressureOverride

Crackingpressure:Itisdefinedasthepressureatwhichthereliefvalveopensfirstandallowsfluidtopassthroughit.Fullflowpressure:Itisdefinedasthepressureatwhichmaximumfluidispassingthroughthevalve.Pressure Override: The difference between full flow pressure andcrackingpressureisknownaspressureoverride.

PRESSUREREDUCINGVALVEPressurereducingvalvesareusedtoattainlowpressuresinahydraulic

systemwhererequired.Heretheemphasisisontheprecisecontroloffluid.Forexample,if inahydraulicsystem,thebranchcircuitpressureislimitedto250psi,butthemaincircuitisoperatingat750psi,apressurereliefvalveisadjustedinamaincircuittoasettingabove750psitomeetmaincircuit’srequirements.However,itwouldsurpassabranchcircuitpressureof250psi.Therefore, besides a pressure relief valve in the main circuit, a pressure-reducingvalvemustbeinstalledinabranchcircuitandsetat250psi.

Apressurereducingvalve isshowninFigure7.38.Thebranchcircuitpressure is set by adjusting the spring’s compression. The fluid from themain circuit enters through the inlet port and enters the branch circuitthrough the outlet port. (Refer to Figure 7.38 (a).) The pressure of fluidpassingfromthevalveisalmostequivalenttopressureexertedbythespringfromupwards.Hence,thespringmovementisnegligible.InFigure7.38(b),pressureoffluidpassingfromthevalveisveryhighascomparedtosystempressure,i.e.,pressuresetbythespring.Hence,fluidpressurewillbeexertedonthebottomofthespool.Asaresult,thespoolwillmoveupward,therebyreducingthepassageofhigh-pressurefluidattheinletport.Thiswilllowerdownthepressureattheoutletport.

FIGURE7.38PressureReducingValve.

SEQUENCEVALVE

Sequence valves used in hydraulic systems are also pressure controlvalves. A sequence valve is used to control various operations in asequence/order.Forexample,asequencevalveisusedforsequencingoftwocylinders to perform a drill operation. One cylinder clamps theworkpieceand theothercylinderperforms thedrillingoperation.Asequencevalve inprinciple and in operation is very similar to a pressure relief valve. In apressurereliefvalve,oncethesetpressureisreached,thereliefvalvedrainsthefluidbacktothetank,whereasinasequencevalve,oncethesetpressureis reached, the pressurized fluid is made available for the next operation.Sequence valves are normally closed 2-way valves. They regulate thesequenceinwhichvariousfunctionsoccurinacircuit.

The operation of a typical pressure-controlled sequence valve isillustratedinFigure7.39.Theopeningpressureisobtainedbyadjustingthetension of the spring that normally holds the piston in the closed position.The top part of the piston has a larger diameter than the lower part. Fluidentersthevalvethroughtheinletport,flowsfreelyaroundthelowerpartofthepiston,andexitsthroughtheoutletporttoperformtherequiredoperationintheprimaryunitasshowninFigure7.39(a).Thisfluidpressurealsoactsagainstthelowersurfaceofthepiston.

FIGURE7.39SequenceValve.

Whentheprimaryactuatingunitcompletesitsoperation,pressureinthelineincreasessufficientlytoovercometheforceofthespring,andthepistonrises.Thevalveisthenintheopenposition,asshowninFigure7.39(b).Thefluid entering the valve takes the path of least resistance and flows to thesecondaryunit.Adrainpassage isprovided toallowanyfluid leakingpastthepistontoflowfromthetop.

Symbol

SymbolofasequencevalveisshowninFigure7.40.

FIGURE7.40SymbolforSequenceValve.

COUNTERBALANCEVALVEA counterbalance valve is a pressure control valve that maintains

control of a vertical cylinder to prevent it from falling freely because ofgravity or due to a load attached to it.A counterbalance valve allows freeflowof fluid inonedirectionandmaintainsa resistance to flowinanotherdirectionuntilacertainpressureisreached.Thisvalveisnormallylocatedina line between a directional-control valve and an outlet of a verticallymounted actuating cylinder, which supports weight or must be held inposition for a period of time. A counterbalance valve is set at a higherpressure than the system load pressure. If the cylinder has to extend, thepressure has to rise above the set pressure and open the counterbalancevalve.Acounterbalancevalveservesasahydraulicresistancetoanactuatingcylinder. Themain difference between the pilot operated check valve andcounterbalancevalveisthattheopeningpressureofthepilotoperatedcheckvalvedependsonthepressurebehindthevalveandtheopeningpressureofcounterbalance valve depends on the spring pressure behind the valve.Figure7.41showsacounterbalancevalve.

FIGURE7.41CounterbalanceValve.

Intheinitialposition,thecounterbalancevalveisinaclosedpositionasshowninFigure7.41(a).ThepressurizedfluidcomingfromtheDCvalveenters through port P. In the closed position, the spool valve blocks thedischargeportAandthefluidcannotflowthroughthevalve.Thefluidwillgotothedischargeportthroughthecheckvalveandliftthecylinder.Itisthetendency of the cylinder to fall because of the load attached to it or bygravity.Becauseof thehigher-pressuresettingof thecounterbalancevalve,thecylinderremainsintheupwardposition.

During reverse flow, the fluid from the cylinder enters thecounterbalance valve as shown in Figure 7.41 (b). The pressurized fluidcannot pass to the DC valve because of the closed position of the valve.Whenthereisanincreaseinpressureduetoresistancetoflowintheline,theflowisdivertedthroughthepilotline.Theforceexertedbythepressurizedfluid acts at the bottom of the piston. The fluid pressure overcomes thepressure setting of the valve and forces the spool to move in an upwarddirection. Itopensandallowsfreeflowaroundtheshaftof thespoolvalveandfluidescapesoutfrominletportP.

Acounterbalancevalveisusedinsomehydraulicallyoperatedforklifts.Itoffersa resistance to the flow fromanactuatingcylinderwhena fork islowered.Italsohelpssupportaforkintheupposition.

Symbol

Figure7.42showsthesymbolofacounterbalancevalve.

FIGURE7.42SymbolforCounterBalanceValve.

FLOWCONTROLVALVESAs the major application of flow control valves in hydraulics and

pneumatics is tocontrol thespeedof thecylinderandfluidmotor,sotheseare also known as speed control valves. Flow control valves control thespeedofanactuatorbyregulatingtheflowrate.Therearetwotypesofflow

control valves: Fixed throttle Adjustable throttle Constant flow rate isrequired if constant speed is required.Fixed throttle valves areusedwheresome reduction in flow is required.As shown in Figure 7.43, fluid has topassthroughareservoir,whichisintheformofalongcylinder.Thistypeofdesign is appreciable in case of pneumatics because of increased viscosityinfluence.Thiswouldresultinlossesduetointernalfrictionandgenerationofheat.

FIGURE7.43VaryingSectionResistanceIllustrated.

Arrangement shown inFigure 7.44 is amodification over the former.Withthis,influenceofviscosityisreducedandresultsinlessergenerationofheat.

FIGURE7.44ContinuousSectionRestrictionIllustrated.

Adjustable throttle valves are used where there is a need of infinitespeeds of cylinders and motors or where a cylinder or motor is to run atconstant speed under changing loads. In case of adjustable throttle valves,usuallyanadjustableneedleisusedtovaryflowconfigurationincomparisontorequirements.GeneralarrangementisshownwiththehelpofFigure7.45.

FIGURE7.45AdjustableThrottleFlowControlValve.

NONRETURNFLOWCONTROLVALVEThisisacombinationofvariableflowcontrolandacheckvalve.This

arrangementisusedtocontroltheflowinonedirectiononly,thatdirectiondepends on the position and direction of the check valve.As illustrated inFigure 7.46, therewill be no restriction on flow controlwhen fluid has toflowfromalowerport toahigherportbutfluidflowiscontrolledwhenithastoflowfromupperporttolowerport.

FIGURE7.46NonReturnFlowControlValve.

SymbolFigure7.47showsthesymbolofanonreturnflowcontrolvalve.

FIGURE7.47SymbolforNonReturnFlowControlValve.

ApplicationofNonReturnFlowControlValve forSpeedControl inaCylinder

Speed of a cylinder can be reduced by either entering the pressurizedfluid at slow speed or by exhausting it at a slow speed. This task can beaccomplishedby employing a non return flowcontrol valve at the inlet orexitofthecylinder,respectively.ThistopiciscoveredindetailinChapter8undertheheading“ThrottleInandThrottleOutCircuit.”Asthespeedofthecylindercanbesloweddownbyprovidingaflowcontrolvalve,thespeedofthecylindercanalsobeincreasedbytheuseofaquickexhaustvalveincaseofpneumatics.

QUICKEXHAUSTVALVEQuick exhaust valve is used to exhaust pressurized fluid from the

cylinderatafasterrateinpneumatics.Thisisdonebypreventingtheexhaust

airfromthecylindertopassthroughtheDCvalve.AquickexhaustvalveisshowninFigure7.48.

FIGURE7.48QuickExhaustValve.

ItconsistsofpressureportP fromwhere the fluid iscomingfromthemainline,theworkingportAfromwherethefluidgoestothecylinder,andexhaustportR.Whenthepressurizedfluid(air)isenteredintothecylinder,i.e.,when pressurized fluid goes fromport P to portA (frommain line tocylinder), it simplyallows thefluid topassas itcomesasshowninFigure7.48(a).Whenthefluidfromthecylinderistobereturned,thentheelasticelementisdisplacedbythefluid(air)pressureitselfasshowninFigure7.48(b).ThefluidgetsexhaustedthroughportRwithoutpassingthroughportPas shown in Figure 7.48 (c). Hence, the speed of the cylinder can beincreasedbytheuseofthequickexhaustvalve.Thisvalveislimitedforitsuseincompressedairapplicationsbecauseoneneednotrecollecttheairinthesystem.

SymbolFigure7.49showsthesymbolofaquickexhaustvalve.

FIGURE7.49QuickExhaustValve.

TIMEDELAYVALVE/AIRTIMERThisvalveispopularlyknownasairtimerbecausethetimeofdelaying

asignalcanbeadjustedby5–15secwiththisvalve.Timedelayvalvesarepilot-operated valves in which the pilot air is supplied through a variable

restrictorsothatittakestimefortheoperatingpressuretobuildup.Thetimedelay is adjusted by adjusting the variable restrictor. A time delay valveconsists of a 3/2 pilot operated spring return DC valve, an inbuilt airreservoir,andanonreturnflowcontrolvalveasshowninFigure7.50.

FIGURE7.50TimeDelayValve.

To send a signal (in the form of pressurized fluid) to some otheractuatorinthesystem,thevalvespoolhastobeshifted.TheshiftingdependsonpressureinpilotlineX.Thepilotlineisconnectedwithanonreturnflowcontrol valve and an air receiver. Air starts accumulating in the receiver.Whenthepressurerequiredtoshiftthespoolisbuiltupinthereceiver,thespool of the DC valve shifts and the pressure port P gets connected toworking portA.The size of the receiver and the setting of the non returnflow control valve decides the time required to shift the spool of the DCvalve.Thistimeistheamountofdelaytimeofferedbythetimedelayvalve.

SymbolFigure7.51showsthesymbolofatimedelayvalve.

FIGURE7.51SymbolforTimeDelayValve.

PNEUMATICLOGICVALVESPneumaticsisalwayspreferredoverhydraulicswhereprecisecontrolis

required. Pneumatic valves are capable of performing logic functions asrequired in various applications of industry. A machine can be fullyautomatedbyusingelectronic logicgates, timers, switches,etc.andfinallyprogrammingtheirPLCs.Thenthatmachineisboundtodothesameworkagain and again. Similarly, pneumatic logic elements can be used as anartificialbraintostart,stop,check,warnatemergencies.Allthegates(NOT,YES, AND, OR, NOR, NAND, MEMORY) are derived from four basiclogic functions, i.e., NOT, AND, OR, and MEMORY. Whereas frompneumaticvalves,twinpressurevalvesandshuttlevalvesareimportantfromthesubjectpointofview.Theyaredescribedbelow.

TWINPRESSUREVALVEItconsistsofavalvebodyhaving3portsandamovablespoolasshown

inFigure7.52.ThisvalveisalsocalledanANDgatebecauseitrequirestwoequalinputstodeliverasignal.OutputattheCportisattainedifinputfromportsAandBisfedandisequalinstrength.ThentherewillonlybeflowatC. If there is input fromA port only then the spoolwill shift towards theright andblock thepassage fromA toCand similarly, if there is an inputfrom B port only then the spool will shift to the left side and close flowpassagefromBtoC.

FIGURE7.52TwinPressureValve.

SymbolFigure7.53showsthesymbolofatwinpressurevalve.

FIGURE7.53SymbolforTwinPressureValve.

SHUTTLEVALVEIt consists of a valve bodyhaving 3 ports (A,B, andC) as shown in

Figure7.54.ThisvalveisalsocalledanORgatebecauseitrequiresasingleinputortwoequalinputstodeliverasignal.AandBareinputportsandCisanoutputportandacontrolelementintheformofaball.Here,atleast,oneinputisrequiredtoattainanoutputattheCport.IfairisblownthroughportA,aballclosesportBandairescapestoportC,andifairisblownthroughport B, again the spherical element moves and closes port A and air willescape throughportC.And if theair isblownfrombothAandBportsatsametime,eventhentherewillbeflowtoCport,i.e.,eitherfromAorfromBorfromboth.

FIGURE7.54ShuttleValve.

SymbolFigure7.55showsthesymbolofashuttlevalve.

FIGURE7.55ShuttleValve.

SERVOVALVESServovalvesaregenerallyusedforprovidingapressureresponsetoan

electrical or electronic control signal. They can be infinitely positioned tocontrol the amount, pressure, anddirectionof fluid flow.Servo control bydefinition is the process of controlling greater energies by using smallerenergies.

Ingeneral,servovalveshaveapilotvalveandaslavevalve.Thispilotvalveuseelectricaltorquemotorsorforcemotorsasamodeofitsactuation.Apilot valve sends the amplified signal to the slavevalve (also called themainvalve) in the formofpressurized fluid.Feedback is alsoprovidedbysome means to see whether the spool of the main valve has acquired itsdesiredpositionornot.Thiskindofvalve,whichperforms the functionofcontrolling fluid in a certain direction, is called a two-stage servo valve.Servovalvesareavailableinone,two,orthreestagedesigns.Asinglestageisadirectlyoperatedvalve.Twovalvestagesarecomprisedofapilotstageand final/main stage. Three stage valves are similar, except that the pilotitself is a two-stage servo valve. Three-stage servo valves are used insituationswhereveryhighflowisanticipated.

The term servo valve was traditionally understood as mechanicalfeedbackvalves,whereatorquemotorisconnectedtothemainvalvespoolbyaspringelement(feedbackwire).Spooldisplacementcausesthewiretoimpartatorqueontothepilotvalvemotor.Thespoolwillholdpositionwhentorque from the feedback wire’s deflection equals the torque from anelectromagnetic field inducedby the current through themotor coil.Thesetwo-stagevalvescontainapilotstagecontrolledbytorquemotor,andamainorsecondstagecontrolledby fluiddischarging from the first stage.Useofservovalvesinindustryisincreasingdaybydaybecauseoftheircapacitytocontrollargeamountoffluids.

TORQUEMOTORANDARMATUREASSEMBLYTorque motor and armature assembly is shown in Figure 7.56. The

torquemotorconsistsofanarmaturemountedatthecenterintheairgapofmagneticfieldproducedbyasetofpermanentmagnetsasshowninFigure7.56 (a). By passing a current from the armature coils, the armature endsbecomepolarizedandareattractedtoonemagnetpolepieceandrepelledby

the other. This sets up the torque in the armature assembly,which rotatesaboutthefixturesleeveasshowninFigure7.56(b).Theupwardmovementofthearmatureassemblyistransmittedtothemainvalvespoolintheformof linear motion with the help of a linkage whether it is a jet pipe or aflapper.

FIGURE7.56TorqueMotorandArmatureAssembly.

CLASSIFICATIONOFSERVOVALVESServovalvescanbebroadlyclassifiedas:

Single-stageservovalve.Multistageservovalve.

SINGLE-STAGESERVOVALVEA valve is said to be a single-stage servo valve when the electrical

signal isdirectlyapplied to thecontrolmainvalvepositionand there isnofurther intermediator required. Single-stage servo valves consist of amainvalve(whichistobecontrolled)andatorquemotor.Thearmatureortorquemotor is connected with the spool of the main valve via a mechanicallinkage.ThearmatureispivotedalongitscenterasshowninFigure7.57andissurroundedbythecoilsofthetorquemotor.Dependingupontheelectricalsignal,whetherthesignalislow,medium,orhigh,thearmatureisdeflectedinwardsoroutwards.Thesameistrueforthemainspoolvalve.

1.2.

FIGURE7.57SingleStageServoValve.

(S-Dischargeport,A-Workingport,P-Pressureport,B-workingport,T-Dischargeport)With a lowelectrical signal or a practically zero electricalsignal,pressureportPwillbeconnectedtoworkingportAandworkingportBwillbeconnectedtodischargeportT.Whentheelectricalsignalis50%,thearmaturebecomesstraightandthisresemblestheclosedcenterpositionof themainvalve.At that time,allof theports remaindeparted fromeachotherasshowninFigure7.57.Inthethirdcase,whenthesignalis100%,thepressure port P connects the working port B and working port A getsconnectedtothedischargeportS.

Forheavyloadoperation,two-stageservovalvesaregenerallypreferredoversingle-stageservovalvesbecausetheforcesrequiredtomovethespoolarehigherforhigherflowsoffluidfromthemainvalve.Furtherthesesingle-

stageservovalvescanbeoftwotypes:FlapperjetservovalvePipejetservovalve

FlapperJetServoValveThegeneralarrangementofaflapperjetservovalveisshowninFigure

7.58. Itconsistsofamainvalve, torquemotor,a flapper, thepipelinewithorifice,andnozzleswherethearmatureisplacedbetweenthetorquemotorcoils. The coils, by means of an electric signal, deflect the flapper in thedesired direction. The other end of the flapper is used to control the pilotpressureinthemainvalve.

Aslongastheflapperremainsstraight,thepilotpressureonbothsidesofthemainvalveremainsthesameandthevalveremainsinthepositionasshown in Figure 7.58 (a). But with a change in the electrical signal, theflapper changes the position thereby increasing pressure in one side anddecreasingpressureontheotherside.TheotherpositionofthemainvalveisattainedbydispositioningoftheflapperisshowninFigure7.58(b).

FIGURE7.58FlapperJetServoValve.

PipeJetServoValveA jet pipe servo valve also uses an electrical signal to change the

positionof themainvalve.Thevalveconsistsofa torquemotor,armature,nozzles,jetpipes,andmainvalvewithspooltypeconstructionasshowninFigure7.59.Forobtainingrestpositionofthisvalve(positionthatisshowninFigure7.59,whenalltheportsareclosedtoeachother),only50%ofthecontrolsignalisapplied.Withthis,thearmatureremainsstraightandthereisanequalamountofflowinbothpilotlinesofthemainvalve.

FIGURE7.59PipeJetServoValve.

Inordertochangethepositionoftheservovalve,thecontrolsignalischanged and that deflects the armature therebydirectingmore fluid in onepilot line and less fluid in other pilot line. The bottom free end of thearmature isconnectedwith the spoolof themainvalve.This isdoneso toensurethat,whetherthespoolhasattainedtherequiredpositionornot,andalsoafter reaching thedesiredposition, furthermovementof thespoolandarmaturecancelsouttheelectricsignalautomatically.

MULTISTAGESERVOVALVEAll of the aforementioned designs can be used to design amultistage

hydraulicservovalve.Theideaforeachdesignisspecifictotheapplicationrequirements.Usually,mostdesignsdonotexceedthreestages.Mountinganozzle flapper, jet pipe, or direct-driven valve onto a larger main stagesatisfiesmost requirements fordynamicsandflow.Sometimes, the jet-pipevalveisusedinamultistageconfigurationwherethemechanicalfeedbackofatraditionaljetpipeisreplacedwithelectronicfeedback.Thisservojetstylehasthepilotcharacteristicsofatypicaljetpipe.

SERVOSYSTEMThe servo system as shown in Figure 7.60 consists of an amplifier,

whichamplifies thesignal,so that it is tobeusedasasignal for theservovalve.Therearenow two inputs to thenextcomponentof thesystem, i.e.,servovalve.Thefirstinputispressurizedfluidfromthepump,thatistobedirectedbytheservovalvetotheactuatorandthesecondinputisacontrolsignalbyanamplifierorpilotvalve.Theservovalvedirectstheflowoffluidtotheactuator,i.e.,adouble-actinghydrauliccylinder.Themovementofthedouble-acting cylinder takes place, and this movement is measuredelectronically. Actual value is compared with the desired value and therelevanterrorsignalisprovided.

FIGURE7.60BlockDiagramofServoControlSystem.

EXAMPLEOFASERVOCONTROLSYSTEMFigure7.61showsanexampleofahydraulicservosysteminwhichan

axialpistonpumpisbeingusedasasourceofenergy,whichisdrivenbyanelectricmotor.Hydraulicfluidistakenfromaservicetankviathehydraulicfilter.Thepressurizedfluidisfedtoactuatorbyusingaservovalve,whichprovides certain amplification and directs it in right direction. Anaccumulator can also be provided depending upon the pressure-flowcharacteristicsofthepump.Thisfluidunderpressureisthenusedtodisplacetheworktableinsomemachinery.

FIGURE7.61ShowsUseofServoSysteminDisplacingWorktable.

HYDRAULICANDPNEUMATICSYMBOLSPumpsandCompressorsHydraulicPumps

Unidirectional(Fixed-displacementtype)

Bi-directional(Fixed-displacementtype)

Unidirectional(Variable-displacementtype)

Bi-directional(Variable-displacementtype)

AirCompressorsCylinders

Singleacting(returnedbyexternalforce)

Singleacting(returnedbyspringforce)

Double-actingcylinder

Doubleacting(doubleendedpistonrod)

Singlefixedcushion

Doublefixedcushion

Unidirectional

Vacuumpump

HydraulicandPneumaticActuatorsHydraulicmotors

Unidirectional(Fixed-displacementtype)

Bi-directional(Fixed-displacementtype)

Unidirectional(Variable-displacementtype)

Bi-directional(Variable-displacementtype)

Oscillatingmotor

PneumaticMotors

Unidirectional

Bi-directional

Unidirectional(Variable-displacementtype)

Bi-directional(Variable-displacementtype)

Oscillatingmotor

CheckValves

Check/nonreturnvalve

Pilotoperatedcheckvalve(Pilottoclose)

Pilotoperatedcheckvalve(Pilottoopen)

Shuttlevalve

Singleadjustablecushion

Doubleadjustablecushion

Doubleactingtelescopiccylinder

HydraulicandPneumaticValvesDirectionControlValves

2/2directioncontrolvalve(Normallyclosed)

2/2directioncontrolvalve(Normallyopen)

3/2directioncontrolvalve(Normallyclosed)

3/2directioncontrolvalve(Normallyopen)

4/2directioncontrolvalve

4/3directioncontrolvalve(Closedcenter)

5/2directioncontrolvalve

5/3directioncontrolvalve(Closedcenter)

MethodsofActuationManualControl

Manualcontrol(Generalsymbol)

Pushbutton

Lever

Quickexhaustvalve

Shutoffvalve

FlowControlValves

Fixedorifice

Adjustablethrottlevalve

Flowcontrolvalve(Withfixedoutput)

Flowcontrolvalve(Withvariableoutput)

Nonreturnflowcontrolvalve

Pressurecompensated

Pressure&temperaturecompensated

Flowdividingvalve

PressureControlValves

Pressurereliefvalve(Normallyclosed)

Pilotoperatedpressurereliefvalve

Proportionalpressurereliefvalve

Pressurereducingvalve

Sequencevalve

CombinedOperation

Pilotvalveactuatedbysolenoid

Anyonecanindependentlyactuate

Footpedal

MechanicalControl

Plunger

Plunger

Spring

Roller

Roller(Onedirectiononly)

ElectricalControl

Solenoid(Singlewinding)

Solenoid(Doublewinding)

Solenoid(Doublewindingvariablecontrol)

Electricmotor

PilotOperation

Pneumatic

Hydraulic

Workingline

Pilotline

Drainline

Flexiblehose

FluidAccessories

Filterorstrainer

Watertrapwithmanualdrain

Watertrapwithautomaticdrain

Filter&watertrapwithmanualdrain

Filter&watertrapwithautomaticdrain

Airdryer

Airlubricator

FRLunit(Compoundsymbol)

FRLunit(Simplifiedsymbol)

HeatexchangerAirsilencer

Accumulator

EnergyTransmission

Pressuresource(General)

Pressuresource(Hydraulic)

Pressuresource(Pneumatic)

Exhaustport(Pneumatic)

Hydraulicreservoir

Pivotingdevice

Quickreleasecouplingswithoutcheckvalves

Coiledtubingfortorsionloads

Electricline

Permanentjoint

Re-connectablejoint

Lineconnection

Crossinglines

Rotary/swiveljunction(Oneconnection)

Rotary/swiveljunction(Threeconnections)

Bleederfitting(Temporary)

Bleederfitting(Permanent)

1.

Directionofflow

PilotOperation

Directionofflow

Powertakeoff/pluggedconnection

Shaft(Unidirectionalrotation)

Shaft(Bi-directionalrotation)

Overcenterdevicetoavoidstoppingatcenter

Quickreleasecouplingswithcheckvalves

MeasuringInstruments

Pressuregauge

Differentialpressuregauge

Thermometer

Liquidlevelindicator

Flowindicator

Flowmeter

Tachometer

Torquemeter

EXERCISESWhataredirectionalcontrolvalves?

2.

3.

4.5.6.

7.8.

9.10.11.12.13.14.15.16.

17.

18.

19.

20.21.22.

23.

Identify the different types of pneumatic valves used in pneumaticcircuits.Whatisthefunctionofadirectionalcontrolvalve?Identifythetypesofdirectionalcontrolvalves.Whatisaservosystem?Whatisapressuresequencevalve?Describe theworking principle of a pneumatic flow control valvewiththehelpofasketch.Whatisa5/2pilotoperateddirectioncontrolvalve?Sketchany4/2directioncontrolsolenoidoperatedvalveandapneumaticpressureregulatorvalve.Whatisafourwaydirectionalcontrolvalve?Whatdoyoumeanbya5/2DCvalve?Whatisatimedelayvalve?Whatisasolenoid?Howdoesitwork?Whatisaservovalve?Sketchashuttlevalve.Namethethreetypesofservovalves.What type of DC valve will you use for controlling a double-actingpneumaticactuator?WhattypeofDCvalvewillyouuseforcontrollingasingle-actingspringreturnpneumaticactuator?Explaintheconstructionandworkingprincipleofpneumaticdirectionalcontrolvalveswiththehelpofasketch.Whatisthedifferencebetweenanopencenterandaclosedcentertypeofdirectionalcontrolvalve?Withthehelpofasketch,explainhowacheckvalveworks.WhatarethealternatenamesgiventoanANDgateandanORgate?Drawthestandardsymbol foranonreturn type flowcontrolvalveandtwinpressurevalve.Draw the standard graphical symbol for a 4-way pilot operated springcentereddirectionalcontrolvalve.

24.

25.

26.27.28.29.30.

31.

32.33.34.35.

36.37.38.39.40.41.42.

43.44.45.46.

47.

Draw the cross section of any position control spool valve and poppetvalve.Identifythestandardgraphicsymbolsapplicabletofluidpowercontrol.(PTU,Dec.2002)Explainhowapressurecontrolvalveworkswiththehelpofasketch.Howdoesapilotcheckvalvedifferfromasimplecheckvalve?DrawasketchofpneumaticANDvalve.Whatisthefunctionofaquickexhaustvalveinpneumatics?Whatareservovalves?Explaintheconstructionandworkingofvarioustypesofservovalveswiththehelpofsketches.What are the differences between servo-controlled valves and pilotoperatedvalves?Drawthestandardgraphicalsymbolofanytypeofservovalve.Explainhowthehydraulicflowcontrolvalveworks.HowareDCvalvesclassified?Discuss the various types of valves used for pressure control and flowcontrolinfluidpowersystems.Differentiatebetweenspoolandseatvalves.Withthehelpofasketch,explainhowarotaryvalveworks.WhatarethedifferentcenterconditionsinDCvalves?Explainhowacounterbalancevalveworkswiththehelpofasketch.ExplainthedifferentmethodsofactuationofDCvalves.DrawasketchofapneumaticORvalve.Differentiate between pressure and flow control valves. Explain theworkingofanytwo-pressurecontrolvalveswiththehelpofasketch.Whatisthefunctionof5/2-wayvalve?Whatisasequencevalveanditspurpose?Whatisaquickexhaustvalve?Explain the twin pressure valve and shuttle valve with the help of asketch.Explaintheconstructionandworkingofpipejetservovalve.

48.

49.50.51.

52.

53.54.

55.

What is the function of a check valve in hydraulics and pneumatics?Discusstheapplicationsofthecheckvalve.Whatiscrackingpressureandpressureoverride?Whatisaservovalve?Howdoesitwork?Check valve is used to control the speed of hydraulic and pneumaticcylinder.Explain.Draw the symbols of (i) check valve, (ii) sequence valve, (iii)counterbalancevalve,(iv)timedelayvalve,(v)twinpressurevalve,and(vi)shuttlevalve.Distinguishbetweenpressurereliefandpressurereducingvalves.What are the differences between servo-controlled valves and pilotoperatedvalves?Withthehelpofasketch,explaintheworkingofapneumaticcylinderofdoubleactingtypecontrolledbyappropriateflowregulatingandcontrolvalves.

CHAPTER8

CIRCUITS

INTRODUCTIONApneumaticorhydraulicsystemisdesignedtoperformaparticularjob

anditconsistsoflargenumberofequipmentlikeapowerunit,aserviceunit,accessories, valves, actuators, etc. These componentswhen combined in alogical sequence to get desired output in the form of the motion of theactuatorsandshowndiagrammaticallybyusingcertainstandardsymbolsofcomponents,constitutesafluidcircuit.Fluidengineersdesignfluidcircuits.It isvery important toremember thestandardsymbolsofeverycomponentalongwith the function of that component in order to draw a fluid circuitdiagram.This chapter focuseson illustrating standard fluid symbols asperISO(InternationalOrganizationforStandardization)standardsandexplainsthemethodologytodrawacircuitbytakingsuitableexamples.

ThefluidsymbolsaredrawninChapter7(ControlValves).

There isnotmuchdifferencebetweenpneumaticandhydrauliccircuitdiagrams.Someofthecommondifferencesare:

Inpneumaticcircuitdiagrams, thereturn line isnotnecessaryas in thecase of hydraulic circuit diagrams because in pneumatics, the used airfromthecylindercanbedirectlyexhaustedtoatmosphere.Inpneumaticcircuitdiagrams,Rrepresentstheexhaustportwhereasinhydraulics,Trepresentsit.

Namesofthepressureandworkingportsremainthesameinpneumaticandhydrauliccircuits.

Basic circuits, which are important from a subject point of view, aregiveninthischapter.Pneumaticsandhydraulicsareexplainedseparatelyfortheeaseofthereaders.

BUILDINGUPTHECIRCUITDIAGRAMAny circuit diagram, whether hydraulics or pneumatics, consists of

certainelements,whichcanbedividedintothreecategories:

DrivingelementsControllingelementsEnergyconsumingmembers

Driving elements consist of pumps/compressors, filters, regulators,pressuregauges,serviceunits,pressurereliefvalves,etc.

Controllingelementscomprisealltypesofvalves,i.e.,directioncontrolvalves,flowcontrolvalves,pressurecontrolvalves,signalingelements,etc.

Hydraulic and pneumatic actuators come under energy consumingmembers.

Someelementsaremonostableorbistableelements.

Amonostableelementhasonestablepositionandautomaticallyreturnstoitwhentheswitchingsignalisremoved.Examplesofthesearedirectionalvalveswithaspringreturn,pressureswitches,proximitydetectors,andlogicvalves.

A bistable element has two stable positions and requires a switchingsignal to change it from one state to the other. Examples of these aredirectionalcontrolvalveswithnospringreturnsuchaspilot-pilotoperation,solenoid-solenoidoperation,valveswithdetents,andswitcheswithnospringreturn.

Figure 8.1 represents the control chain flowchart showing how thesignal flows through various elements from bottom to top in apneumatic/hydraulic circuit. All elements required for the energy supplyshouldbedrawnatthebottomandtheenergyshouldbedistributedfromthebottom to the top. This flowchart means that the circuit diagrammust bedrawnwithoutconsideringtheactualphysicallocationsoftheelementsand

(a)

(b)

it isrecommendedthatall thecylindersanddirectionalcontrolvalvesmustbedrawnhorizontally.

FIGURE8.1

DESIGNATIONOFCOMPONENTSINACIRCUITDIAGRAM

Circuit diagrams are prepared by arranging various components of apneumatic/hydraulic system into a sequence according to their functions.Sometimesthesefluidcircuitsaresocomplexthatitisdifficulttounderstandwhere it starts and where it ends. In order to deal with this difficulty, asystemfordesignatingcomponentsisused.Therearetwotypesofsystemsfordesignatingcomponentsinacircuitdiagram:

SystemusingdigitsSystemusingalphabets

SystemUsingDigitsOnemethod is to allot serial, e.g., 1, 2, 3, etc., to components of thecircuit. Thismethod avoids confusion and is best for use in complexcircuits.

Second method is to divide one pneumatic circuit into a number ofsmall groups and there by allotting serial number to groups like 1, 2,

3….,etc.,andthenfurthergivenaserialnumberwithinthegroup.Thecomplete designation consists of group numbers and serial numberswithinagroup,e.g.,2.4meansGroup–2,Componentnumber–4.

Allocationofgroupnumbers

Group0Group1,2,3,4

AllitemsinvolvedinsupplyofenergyOnegroupallocatedtoonecylinderanditssubcomponents

Serialnumbersareusedbyprefixingthegroupnumberbeforethem.

.1.01,.02.2,.4(evennumbers).3,.5(oddnumbers)

ControlcomponentsComponentsbetweenmovingandcontrolcomponentslikeflowcontrol,pressurecontrol,orcheckvalves.Allcomponentsinfluencingforwardstroke.Allcomponentsinfluencingbackwardstroke.

The above said terminology is shown with the help of followingexample:

The circuit shown in Figure 8.2 is drawn for a special punchingoperation using a double-acting cylinder as ram, which starts punchingoperationwhen safety cover is secured and operator pushes the button. Acylinderextendsfastandpunchesaholeandreturnsbackslowlytoitsinitialposition.

Theabovedrawncircuitisdividedinto2groups:

Group0—EnergysupplyGroup1—Double-actingcylinderasworkingelement

InthepneumaticcircuitdiagramshowninFigure8.2,compressedairissupplied fromacommonsource suchas a centralizedcompressorwith thehelp of pipelines to FRL/service unit (0.1). Then this air is supplied to 3signalelements(3/2DCvalves)namely1.2,1.3,1.4andacontrolelement(4/2 DC valve) namely 1.1. Serial number 1.02 denotes the twin pressurevalve. Manual push button of 1.2 signal element is pressed but supplypressure cannot pass through the 1.02 twin pressure valve until the signalelement1.4isoperated.Signalelement1.4isoperatedwhenthesafetycoveronaworkpieceissecuredproperly.Whenthesetwoconditionsarefulfilled,i.e.,thefirstmanualpushbuttonispressedandthesecondcoveronthework

pieceissecured,thenonlypressurizedfluid,i.e.,airpassesfromvalve1.02andenterspilotlineX,therebypushingthecontrolelementandchangingitsposition.When this piston rod starts extending outside at a normal speedbecause of the flow control valve in line and after reaching the extremeforward position, the piston returns back automatically and with acomparativelylowerspeed.

FIGURE8.2CircuitShowingDesignationofVariousComponents.

PNEUMATICCIRCUITSPneumatic circuits can be defined as a graphic representation of the

elements of a pneumatic system where these elements are represented bytheircorrespondingsymbolsandthesesymbolsaresequentiallyarrangedinaspecificmannerdependinguponthenatureofoutputrequired.Someofthebasicpneumaticcircuitsareexplainedbelow.

PNEUMATICCIRCUITFORCONTROLOFSINGLE-ACTINGCYLINDER

The basic pneumatic circuit for control of a single-acting cylinder isshowninFigure8.3.

Here a single-acting cylinder (1.0) is being controlled by a 3/2 pushbutton operated, spring return direction control (DC) valve (1.1) as thecontrol element. The compressed air is supplied from a main compressorplacedanywhereintheplanttoFRLunit(servingunit),whereairisfiltered,lubricated, and regulated to the desired pressure and directed to the 1.1control element. In the initialposition, as shown inFigure8.3 (a), 1.1DCvalveisinanormallyclosedpositionandthecylinderisinafullyretractedposition.When the push button of the control element 1.1 is pressed, thepressure port P gets connected to he working port A and the pressurizedfluid,i.e.,airstartsmovingfroma1.1DCvalvetoacylinderinletcausingitto move forward. Figure 8.3 (b) shows the fully extended position of thecylinder.Ascylinder1.0isspringreturned,thecylinderattainsitspreviouspositionwhenthepushbuttonof1.1controlelementisreleased.

FIGURE8.3PneumaticCircuitforControlofSingle-ActingCylinder.

PNEUMATICCIRCUITFORCONTROLOFDOUBLE-ACTINGCYLINDER

The basic pneumatic circuit for control of a double-acting cylinder isshowninFigure8.4.Hereadouble-actingcylinder(1.0)isbeingcontrolledby a 4/2 push button operated, spring return direction control (DC) valve(1.1).Thecircuitshowsthemanualcontrolover theforwardandbackward

motionofthecylinder.Inthecircuitshownbelow,thereisnoreturnspringin the double-acting cylinder for the retraction of the piston rod, so bothforwardandbackwardmotionsofthecylinderarecontrolledbypressurizedfluid,i.e.,airandDCvalve.

FIGURE8.4PneumaticCircuitforControlofDouble-ActingCylinder.

Initially the cylinder 1.0 is in a fully retracted position as shown inFigure8.4(a).PressureportPisconnectedtoworkingportBandportAisconnectedtoexhaustportR.Whenthepushbuttonofcontrolelement1.1ispressed, the position of the DC valve changes. The pressure port P getsconnected to the working port A and the pressurized fluid, i.e., air startsmovingfrom1.1DCvalve to thecylindercausing it tomove ina forwarddirection.Figure8.4(b)showsthefullyextendedpositionofthecylinder.Tocause thebackwardmotionof cylinder 1.0, thepushbuttonof the1.1DCvalveisreleased.Becauseoftheactionofthespring,1.1DCvalveattainsitspreviouspositionasshowninFigure8.4(a).

APPLICATIONOF2/2AND3/2DCVALVES2/2DCvalvecanbeusedonlytorunthosedevicesinwhichthereisno

returnflowoffluid,example,incaseofpneumaticmotors,airescapesoutintheatmosphereafter rotating the rotor.Figure8.5 shows theapplicationofthe2/2and3/2DCvalves.

FIGURE8.5CircuitShowingApplicationof2/2and3/2DCValves.

Figure8.5showstheapplicationof2/2and3/2DCvalves.Here,boththeDCvalves,1.1and1.2,areinthenormallyclosedpositionasshowninFigure8.5(a).Whenthepushbuttonof1.2DCvalveispressed,thepressureport P gets connected to the working port A and compressed air startsflowingfromthepressureportPtotheworkingportAof1.2DCvalve.Thecompressed air then enters the pilot lineX of the control element 1.1 andactuatesthe1.1DCvalveasshowninFigure8.5(b).Whenthepositionofthe1.1DCvalveischanged,portPgetsconnectedtoportAandcompressedairreachestheinletportofthepneumaticmotor.Noreturnlineisrequiredinthecaseofairmotorsasairisexhausteddirectlyfromtheoutletportofthemotor.Nowinordertostoptherotationofmotors,thepushbuttonof1.2DCvalve is released and both valves return back to their normally closedpositionbyactionofspringforce.

CIRCUITWITHMECHANICALFEEDBACKRefertoFigure8.6.Thiscircuitisdesignedfortheconditionthatwhen

themanualpushbuttonof1.2DCvalve ispressed, thepiston rodextendsfrompositionA topositionBand then it retracts automaticallyback to itsstartposition.

Initially the cylinder 1.0 is in a fully retracted position as shown inFigure 8.6.As the operator pushes themanual push button of the 1.2DCvalve,thesupplyofcompressedairgoestothepilotlineXandchangesthepositionofthe1.1DCvalve.Withthechangeofposition,thecompressedair

enters the cylinder 1.0 and the piston rod of cylinder 1.0 starts extendingfrompositionA.Themoment it reachespositionB,a roller tripof1.3DCvalve isactuatedwhichresults in inducingcompressedair intopilot lineYandfurther results inchanging thepositionof the1.1DCvalve.With this,the compressed air enters the cylinder and results in the retraction of thecylinder.

FIGURE8.6CircuitwithMechanicalFeedback.

SPEEDCONTROLCIRCUITSFlowcontrolvalves are also called speedcontrollersbecause theyare

used in pneumatic circuits to slow down the speed of the cylinder. Nonreturnadjustablethrottlevalvesarecommonlyusedinapneumaticsystem,astheycanbeadjustedtogivedesiredoutput.Acheckvalveisalwaysusedinconjunctionwithaflowcontrolvalve.Dependingonthearrangementofthe flow control valves, speed control circuits for a double-acting cylindercanbeoftwotypes:

Infeedthrottling/ThrottleincircuitOutfeedthrottling/Throttleoutcircuit

InfeedthrottlingInfeed throttlingmaybedefinedasamethod to reduce thespeedofa

pneumaticcylinderinwhichfluidattheentrancetoadouble-actingcylinderis passed through control restrictors so as to slow down the speed of thepistoninthecylinderwhereasnorestrictionisappliedtoairexhaustingfromthecylinder.

OutfeedthrottlingOutfeedthrottlingmaybedefinedasamethodtoreducethespeedofa

pneumaticcylinder inwhich fluidat theexitofadouble-actingcylinder ispassedthroughcontrolrestrictorssoastoslowdownthespeedofthepistoninthecylinderwhereasnorestrictionisappliedtoairenteringthecylinder.

Thesemethodsare furtherexplained indetailswith thehelpofcircuitdiagramsasshownbelow:

1.Throttleincircuit

Throttle in circuit is shown in Figure 8.7. The circuit consists of aserviceunit0.1,a4/2DCvalveasthecontrolelement(1.1),twononreturnflow control valves (1.01), and (1.02) respectively, and a double-actingcylinder(1.0).

FIGURE8.7ThrottleInCircuit.

Consider thevalve isat itsnormalposition,which is shown inFigure8.7. The pressure port P is connected to working port A and port B isconnectedtoexhaustportR.Thecompressedairfromthecompressorpassesthroughcontrolelement1.1andfurtherreachesthenonreturnflowcontrolvalve1.02.Hereairwillhavetopassfromthevariablerestrictorbecauseacheckvalveismountedonthebypassline.Thisresultsinareductionofflowofcompressedairat theentranceof thecylinder (1.0).Hence, thecylinderextends smoothly towards the forward direction. At the same time,compressed air in the rod side of the cylinder is to be exhausted out. Thecompressed air is bound to pass through thenon return flowcontrol valve(1.01).But this timeair isventedout from thecheckvalve through thebypass without any restriction. When the manual push button of controlelement1.1ispressed,thepositionofthe1.1DCvalvechanges.Thistimeairisenteredthroughthenonreturnflowcontrolvalve(1.01).Again,attheentrance air has to pass through the variable restrictor because of the “noflow”positionofthecheckvalveinthatdirectionwhichresultsintheslowmotionofthepistoninabackwarddirection.Airatothersideofthepistonisvented out again through the check valve 1.02 and no resistance isencounteredwhileexhaustingthroughthecylinder.

2.Throttleoutcircuit

ThrottleoutcircuitisshowninFigure8.8.Constructionofthiscircuitisthesameasthatofthethrottleinthecircuit.Theonlydifferenceisthatthedirectionofthecheckvalveischangedinthiscircuitforprovidingrestrictiontoairattheoutlet.

Consider thevalve isat itsnormalposition,which is shown inFigure8.8. The pressure port P is connected to working port A and port B isconnectedtoexhaustportR.Thecompressedairfromthecompressorpassesthroughcontrolelement1.1andfurtherreachesnonreturnflowcontrolvalve1.02.No restriction is offered in valve 1.02 as the check valve allows theflowofairthroughit.Airfinallyentersthecylinderandpushesthepistoninaforwarddirection.Atthesametime,airhastobeexhaustedfromtherodsideofthecylinderandthistimeairhastopassthroughthenonreturnflowcontrolvalve (1.01).This time thecheckvalvedoesnotallowair to freelypass from it and air passes through restriction. Hence, speed of piston issloweddownasairescapesslowlyoutoftherestrictor.Aftercompletionof

theforwardstroke,themanualpushbuttononcontrolelement1.1ispushedand the circuit proceeds in the samemanner as explained in the case of aforwardstroke.

FIGURE8.8ThrottleOutCircuit.

In pneumatic circuits, generally outfeed throttling is preferred overinfeedthrottlingbecausebettercontrolcanbeattainedintheformercase.Itis also important to add here that flow control valves can be fitted at theexhaustalsowith5/2DCvalvesascontrolelementsinline.(RefertoFigure8.9.)

FIGURE8.9

USEOFFLOWCONTROLVALVETOCONTROLSINGLE-ACTINGCYLINDER

The flow control valves can also be used to control the single-actingcylinder.ThecircuitshowninFigure8.10describesthemannerinwhichthespeed is controlled in a single-acting cylinder during both forward andbackwardstrokesbyusingtheflowcontrolvalve.

FIGURE8.10ControlofSingle-ActingCylinderUsingFlowControlValve.

Here,twononreturnflowcontrolvalves1.02and1.04areusedintheseriesas shown inFigure8.10. Initially, cylinder1.0 is ina fully retractedposition as shown in the figure.When the push button of 1.1DCvalve ispressed, the pressure port P gets connected to working port A andpressurized fluid, i.e., air enters the cylinder through two non return flowcontrol valves 1.02 and 1.04. The restriction to air is offered by the flowcontrolvalve1.02duringtheforwardstrokeofthecylinder.Whenthepushbuttonof1.1DCvalveisreleased,thebackwardstrokeofthecylindertakesplaceandduringthebackwardstroketherestrictiontoair isofferedbytheflow control valve 1.04. So the speed is reduced in both the forward andreturnstrokeofthecylinder.

USEOFQUICKEXHAUSTVALVEINPNEUMATICCIRCUITS

Flow control valves are used to slow the speed of the pneumaticcylinder.Similarly,thequickexhaustvalveisusedtoexhausttheairoutofthecylinderata faster ratewithoutpassing it through thedirectioncontrolvalvetherebyincreasingthespeedofthecylinder.Thecircuitsgivenbelow

showhow the accelerationof thepiston in single-acting anddouble-actingcylinderisachievedusingaquickexhaustvalve.

UseofaQuickExhaustValveinSingle-ActingCylinderThe circuit (refer to Figure 8.11) shows the control of a single-acting

cylinder(1.0)byusinga3/2manuallyoperatedspringreturnDCvalve(1.1)andquickexhaustvalve(1.01).

FIGURE8.11ControlofSingle-ActingCylinderUsingQuickExhaustValve.

Initially,thecylinderisinafullyretractedpositionasshowninFigure8.11(a).PortAisconnectedtoexhaustportR.Whenthepushbuttonofthe1.1DCvalveispressed,thepressureportPgetsconnectedtoworkingportAandthepressurizedfluid,i.e.,airstartsmovingfromthe1.1DCvalvetothecylinder1.0throughthequickexhaustvalve1.01causingittomoveinaforwarddirection.Figure8.11 (b) shows the fullyextendedpositionof thecylinder.Tohave thebackwardmotionof the cylinder, thepushbuttonof1.1 DC valve is released. When the push button of the 1.1 DC valve isreleased, the cylinder startsmoving backward because of the action of thespring forceand thecompressedair escapes to theatmosphere through thequick exhaust valve 1.01 without getting exhausted through the 1.1 DCvalve.Hence,thespeedofthecylinderisincreasedbyexhaustingairoutofthe cylinder at a faster rate.A silencer is installed at the outlet of a quickexhaustvalvetoreducethenoiseoftheairgoingouttotheatmosphere.

UseofaQuickExhaustValveinaDouble-ActingCylinderThecircuit (refer toFigure8.12)shows thecontrolofadouble-acting

cylinder(1.0)byusinga4/2manuallyoperatedspringreturnDCvalveasthecontrolelement(1.1)andquickexhaustvalve(1.01).

FIGURE8.12ControlofDouble-ActingCylinderusingQuickExhaustValve.

Initially, the cylinder 1.0 is in a fully retracted position as shown inFigure8.12(a).PressureportPisconnectedtoworkingportBandportAisconnected to exhaust port R. The pressurized fluid, i.e., air starts movingfromcontrolelement1.1tothecylinder1.0throughthequickexhaustvalve1.01.Whenthepushbuttonofthe1.1DCvalveispressed,thepressureportPgetsconnectedtoworkingportAandthepressurizedfluid, i.e.,airstartsmovingfromcontrolelement1.1tocylinder1.0causingtheforwardmotionof the cylinder. Figure 8.12 (b) shows the fully extended position of thecylinder.Atexhaust,aquickexhaustvalve1.01ispresentwhichletstheairescapefromitself.Soairdoesnotgobacktothecontrolelement1.1forthepurposeofexhausting.Asilencerisinstalledattheoutletofaquickexhaustvalve for reduction in noise of the air going out to the atmosphere. Thisresultsinextendingthecylinderatafasterrate.It isimportanttonoteherethat the quick exhaust valve does not play any role during the backwardmotion(retraction)ofthepiston.

TIMEDELAYCIRCUITThe time delay circuit as shown in Figure 8.13 is used to delay an

already started signal. The circuit consists of a double-acting cylinder 1.0,4/2pilotoperatedDCvalve (1.1), timedelayvalve (1.01), two3/2manualoperated and roller button operated spring returnDCvalves (1.2 and 1.3),FRLunit(0.1),andacompressor.

FIGURE8.13TimeDelayCircuit.

Initially,supplyisgivenfrompressureportPtoworkingportBofa1.1DCvalveandcylinder1.0isinafullyretractedpositionasshowninFigure8.13.Whenthemanualpushbuttonofthesignalingelement1.2ispressed,theairflowisstarted in thecircuit.Controlelement1.1 isactuatedbypilotlineX.Withthis,airentersthecylindersandpushesthepistoninaforwarddirection.Whenthepistonrodiscompletelyextended,itactuatesthesignalvalveelement1.3.Withthis,thecompressedairisdirectedtothetimedelayvalve 1.01.The time delay valve can delay the signal for 5 to 15 secondsdepending on the requirement. The signal from the time delay valve 1.01actuatesthepilotlineYofcontrolelement1.1,therebychangingthepositionoftheDCvalveandallowsfluidtoentertherodsideofthecylinderandtodischargefromtheotherside.Timedelayvalvesareusedincertainspecialapplications.Forexample,thetasktobepreformedbyusingadouble-actingcylinderisbondingofthetwoworkpiecesbyfillingadhesivebetweenthem

(a)(b)

andapplyingheatandpressureonitforsometime.Applicationofpressurefor sometime on thework pieces can be achieved by the above discussedcircuit. The cylinder will stop and apply pressure for sometime (5 to 15seconds depending upon specification of the time delay valve) afterextendingcompletely.

CIRCUITSWITHNECESSARYCONDITIONSThese typesof circuits aredrawn to fulfill a particular condition.The

circuitsthatcomeunderthiscategoryare:

CircuitshowingapplicationofthetwinpressurevalveCircuitusingapplicationoftheshuttlevalve

APPLICATIONOFTHETWINPRESSUREVALVE

Figure8.14showstheapplicationofthetwinpressurevalve.Thisvalverequires two equal inputs to give one output. Twin pressure valve is alsotermedas“pneumaticANDelement”becauseithasthebasiclogicfunctionofANDgate,i.e.,asignalisgivenattheoutputonlyifbothinletsignalsarepresent.Thecircuitdiagramisdrawnbytakingsomeconditioninmindthatthedouble-actingcylinderwillstartextendingonlywhentwojobsaredone.Theseare:

Unloadingofprocessedcomponent,andLoadingoffreshcomponentthatistobeprocessed.

The circuit shown in Figure 8.14 consists of a double-acting cylinder(1.0)astheactuator,a4/2pilotoperatedspringreturnDCvalve(1.1),twinpressure valve (1.01), and two 3/2 push button operated spring returnDCvalves(1.2and1.4).

FIGURE8.14CircuitShowingApplicationofTwinPressureValve.

Intheinitialpositionasshowninthefigure,thesupplyofcompressedair isgiventocontrolelement1.1.PressureportPisconnectedtoworkingportBandportAisconnectedtoexhaustportR.Thecylinderisinafullyretracted position. When the two above said conditions are filled, thesignalingelements1.2and1.4areoperatedbythemachineoperatorandthesignal is sent to the pilot line X of control element 1.1 via twin pressurevalve1.01resulting inaforwardmotionof thecylinder. It is interesting tonote here that until these two switches (1.2 and 1.4) are not pressed,operationofcylinder(onwhichtoolismounted)cannotbestarted.

APPLICATIONOFTHESHUTTLEVALVEFigure8.15showstheapplicationoftheshuttlevalve.Theshuttlevalve

alwaysgivesoneoutputirrespectiveofthenumberofinputswhether1or2,as shown in the circuit diagram. The shuttle valve is also termed as“pneumaticORelement”becauseithasthebasiclogicfunctionofORgate,i.e.,asignalisgivenattheoutputifasignalispresentateitheroneinputortheotheror atboth inputs.Thecircuit consistsof adouble-actingcylinder(1.0)asanactuator,a4/2pilotoperatedspringreturnedDCvalveascontrol

element(1.1),shuttlevalve(1.01),andtwo3/2pushbuttonoperatedspringreturnDCvalves(1.2and1.4).

FIGURE8.15CircuitShowingApplicationoftheShuttleValve.

Intheinitialpositionasshowninthefigure,thesupplyofcompressedair isgiventocontrolelement1.1.PressureportPisconnectedtoworkingportBandportAisconnectedtoexhaustportR.Thecylinderisinafullyretractedposition.Theinputsignalingelements1.2and1.4performthesamefunction.Bothsignalingelementsareusedtogiveinputtoshuttlevalve1.01.Bypushinganyswitchoutof1.2and1.4,thecompressedairisenteredintolineandismadetoflowthroughtheshuttlevalve.FromtheshuttlevalvethecompressedairentersthepilotlineXofcontrolelement1.1andchangesitsposition. This results in forward motion of the cylinder. These types ofcircuits are used to provide a solution to all problems in which ‘if’ isinvolved.

HYDRAULICCIRCUITSHydraulic circuits can be defined as graphic representation of the

elementsofahydraulicsystemwheretheseelementsarerepresentedbytheircorresponding symbols and these symbols are sequentially arranged in aspecific manner depending upon the nature of output required. Themajor

difference between hydraulic and pneumatic circuits is that hydraulicelementsaredesignedforhighpressure(20–400bar)andpneumaticcircuitsaredesignedforlowpressure(5–20bar).

Hydraulic circuits are similar to pneumatic circuits because most ofcomponentsusedinhydraulicandpneumaticsystemsaresimilar.Thereareafewspecificrequirementsofhydrauliccircuitswhicharefrequentlyusedinhydraulic systems (example, pressure relief valves, check valves, pressuregauges,etc).Themethodologyisexplainedwiththehelpofsimplecircuitsgivenbelow.

HYDRAULICCIRCUITFORCONTROLOFSINGLE-ACTINGCYLINDERHydraulicCircuitforControlofSingle-ActingCylinderusinga2/2DCValve

In the circuit shown in Figure 8.16, a single-acting cylinder (1.0) isbeingcontrolledwitha2/2manuallyoperatedspringreturnDCvalve(1.1).Therequiredpressureinthelineismaintainedwiththehelpofapumpandmotor assembly. Pressure gauge (0.1) and pressure relief valve (0.3) areprovided in the lineof the fluid flow.Now, if thepressure rises above thedesign limit, thepressurereliefvalveexhausts theexcessfluidandensuresthe safety of the system. Afterwards, a check valve (0.2) is provided topreventtheflowoffluidintothecylinder.Theoilisreturnedtotheoiltankby passing it through a hydraulic filter (0.4), which removes any dirtparticlespresent in theoil. In thegivencircuit, a2/2DCvalve isused forcontrolling a single-acting cylinder.Generally, a 3/2DC valve is used forthispurposebutthepositionofthecheckvalvehasmadeitpossiblehere.

FIGURE8.16ControlofSingle-ActingCylinderusing2/2DCValve.

Initially,thecylinderisinaretractedpositionasshowninFigure8.16(a). Pressure port P is not connected toworking port A. Pressurized fluidcannotenter into thecylindereither throughthecheckvalveor the1.1DCvalve.Whenthepushbuttonofcontrolelement1.1ispressed,thepressureportPgets connected toworkingportAas shown inFigure8.16 (b).Thepressurizedfluidstartsflowingintothecylinderthroughcontrolelement1.1,which results in forward motion of the cylinder. As the push button isreleased, the DC valve comes back to its original position because of thespringaction.Pressurizedfluidfromthecylinderwillpassthoughthecheckvalveintothetankcausingitsbackwardmotion.

HydraulicCircuitforControlofSingle-ActingCylinderusing3/2DCValve

In the circuit shown in Figure 8.17, a single=acting cylinder (1.0) isbeingcontrolledwitha3/2manuallyoperatedspringreturnDCvalve(1.1).Therequiredpressureinthelineismaintainedwiththehelpofapumpandmotor assembly. Pressure gauge (0.1) and pressure relief valve (0.3) areprovidedinthelineoffluidflow.Now,ifthepressurerisesabovethedesignlimit, the pressure relief valve exhausts the excess fluid and ensures thesafetyofthesystem.Afterwards,acheckvalve(0.2)isprovidedtopreventthe flow of fluid into the cylinder. The oil is returned to the oil tank bypassing it throughahydraulic filter (0.4),which removesanydirtparticlespresentintheoil.

FIGURE8.17ControlofSingle-ActingCylinderusing3/2DCValve.

Initially,thecylinderisinaretractedpositionasshowninFigure8.17(a).WorkingportAisconnectedtoexhaustportT.Pressurizedfluidcannotenter thecylinder.When thepushbuttonofcontrolelement1.1 ispressed,thepressureportPgetsconnectedtoworkingportAasshowninFigure8.17(b). The pressurized fluid starts flowing into the cylinder through controlelement1.1,whichresultsintheforwardmotionofthecylinder.Asthepushbuttonisreleased,thecyclerepeatsagain.

HYDRAULICCIRCUITFORCONTROLOFDOUBLE-ACTINGCYLINDER

The basic hydraulic circuit for control of a double-acting cylinder isshowninFigure8.18.Double-actingcylindersarethoseinwhichmovementofthepistonandpistonrodisobtainedbyfluidenteringfromoneportandsimultaneouslyexhausting it fromanotherport.For thispurpose,a4/2DCvalve is at least required. Here a double-acting cylinder (1.0) is beingcontrolled by a 4/2 push button operated, spring returnDC valve (1.1).Afixeddisplacementpumpdeliverspressurizedfluidtocontrolelement1.1viacheckvalve(0.2)andpressurereliefvalve(0.3).Theoilisreturnedtotheoiltankbypassingitthroughahydraulicfilter,whichremovesanydirtparticlespresentintheoil.Thecircuitshowsthemanualcontrolovertheforwardandbackward motion of the cylinder. In the circuit shown below, there is no

returnspringinthecylinderforretractionofthepistonrod,sobothforwardandbackwardmotionsofthecylinderarecontrolledbypressurizedfluidanda1.1DCvalve.

FIGURE8.18ControlofDouble-ActingCylinderusing3/2DCValve.

Initially, the cylinder 1.0 is in a fully retracted position as shown inFigure8.18(a).PressureportPisconnectedtoworkingportBandportAisconnected toexhaustportT.When thepushbuttonof the1.1DCvalve ispressed,thepositionofthe1.1DCvalvechanges.ThepressureportPgetsconnectedtoworkingportAandthepressurizedfluidstartsflowingfromthe1.1DCvalvetothecylindercausingittomoveinaforwarddirection.Figure8.18 (b) shows the fully extended position of the cylinder. To have thebackward motion of the cylinder, the push button of the 4/2 DC valve isreleased. Because of the action of the spring, the DC valve attains itspreviousposition.Thecyclerepeatsagain.

In thiscircuitdiagram, themotionof thepistonandpistonrodcanbestoppedonlyattwoextremepositionsofthecylinderbutitisalsopossibletostop thepistonandpistonrodatanyextremeposition in thecylinder.Thiscanbeachievedbyusing3positionDCvalves.Thesevalvesnotonlyservetheabovesaidpurposebutalsohaveuniquecharacteristicsthatarediscussedinthefollowingparagraphs.

CIRCUITSUSING3POSITIONVALVES

ClosedCenterCircuitThiscircuitiscalledaclosedcentercircuitbecauseaclosecentered4/3

DCvalveisusedasacontrolelement.Byclosedcenter,itmeansthatalltheportsatneutralpositionof thevalvearedeparted fromeachother (refer toFigure 8.19). When the valve is brought to its neutral position, thepressurizedfluidsent to thedouble-actingcylinder isunable tocomeback.Whenthispositionisattained,thepressurizedfluidgetsblockedontherodside and other side of the cylinder. Due to this, the piston immediatelybecomes motionless. For example, let’s assume initially that the piston isextendingorretracting.ButoncetheDCvalveisbroughttoaneutralclosedcenterposition,thepistonwillstopimmediately.

FIGURE8.19ClosedCenterCircuit.

OpenCenterCircuitAnopencircuitisoneinwhichtheopencenterDCvalveisusedasthe

controlelement.Thiscircuit(refertoFigure8.20)hasanadvantagethatthecenterpositionoftheDCvalveallowsfluid(inthecylinder)toescapefromthecylinderatalowpressureensuringlesserheatgeneration.Inthiscircuit,

fluid is raised with the help of a hydraulic pump and is sent to controlelements(4/3solenoidoperatedspringreturnDCvalves).Thetwoextremepositionofvalves,i.e.,onandoffareresponsibleforretractionandextensionofthecylinderandtheneutralpositionresultsinconnectingpressureportPwithworkingportAandexhaustportTwithworkingportB.Thus,thefluidfrom both sides of the cylinder escapes back to the tank. This position isbrought only when the pump is switched off and there must be a low-pressureregionsetinthehydraulicline.

FIGURE8.20OpenCenterCircuit.

There are two drawbacks associated with this circuit. First, all thecylindershavetostartandstopat thesametimeastheportsareconnectedall the timeduring center position.Secondly, the load cannot be locked inneutralposition.Thismayleadtoanaccident.

TandemCenterCircuitInatandemcentercircuitasshowninFigure8.21,atandemcenter4/3

DC valve is used as a controlling element. In this circuit, a pump is notrequiredtobeswitchedoff.Also,themovementofadouble-actingcylindercan be stopped at any position between two extreme positions of thecylinders. But this valve enjoys an advantage over a closed center circuit,

that thepressurized fluid fromportP isdirectlysupplied toportT therebyensuring the flow fromone subsystem to anotherwhereas in closed centercircuitflowisdividedintotwolines.Pressurelossesandheatgenerationarealsoless.Thefluidthathadgonetobothsidesofadouble-actingcylinderisblockedthereonly,therebylockingthepistonandpistonrodatthatposition.Thepressurizedfluidblocked in thecylindermaycause theproblemofoilspillage.

FIGURE8.21TandemCenterCircuit.

SPEEDCONTROLINHYDRAULICCIRCUITSSpeedofhydraulicactuatorsiscontrolledbychangingflowrates.These

flowratescanbevariedeitherbyfixedrestrictorsorflowcontrolvalves.Incaseoffixedrestrictorsororifices,flowrateisdependentontheresistanceofferedbyload,i.e.,thespeedcouldn’tbeaccuratelycontrolled.Ifaconstantspeedisrequiredirrespectiveoftheresistance,thantheflowcontrolvalvesare to be used. Flow control valves have further two configurations. Thesimpleadjustablethrottlevalveprovidesspeedregulationinbothreturnandforwardstrokesofdouble-actingcylinderwhereasadjustablethrottlevalveswithabypasscheckvalve provides speed regulationonly inonedirectionandtheyarecallednonreturnflowcontrolvalves.

Figure 8.22 shows the location of an adjustable throttle valve in ahydraulic circuit. The throttle valve (0.6) is mounted at the inlet of DCvalves.Asaresult,thepressurerisesintheinletlinethatisexhaustedfromthe pressure relief valve. In thisway, the double-acting cylinder get lesserfluidonthecapendsideofthecylinder.Therefore,thepistonwillextendataslowerrate.Thesameprocessisrepeatedinthereturnstroke.

FIGURE8.22UseofAdjustableThrottleValve.

Although the use of adjustable throttle valves are not recommended,this is common practice in hydraulics. The flow control valve is alwaysaccompaniedbyabypasscheckvalve.Thedirectionofthecheckvalveinahydraulic linedecides the flow tobe regulatedatwhat timewhetherat theinletorat theexhaustportfromthecylinders.Speedcontrolcircuitsareoftwotypes:

MeterincircuitMeteroutcircuit

MeterInCircuitInmeterincircuit,thefluidhastopassthroughtheflowcontrolvalve

before entering the cylinder, i.e., speed of fluid is reducedwhen it has to

enter the cylinder. Figure 8.23 shows the details of meter in circuit. Thecircuitconsistsofa4/2DCvalveasthecontrolelement(1.1),twononreturnflow control valves (1.01) and (1.02), respectively, and a double-actingcylinder(1.0).

FIGURE8.23MeterInCircuit.

Pressurized fluid from the pump is entered in the non return flowcontrolvalve1.02throughcontrolelement1.1.Astheflowcontrolvalveisplacedintheprimarylineandthecheckvalveisclosedinthisdirection,sothefluidhastopassthroughrestriction,whichresultsintheloweringspeedoftheactuatorduringtheextension/forwardstroke.Thefluidtobeexhaustedout of the cylinder is bound to pass through the flow control valve 1.01without any restriction. When the push button of control element 1.1 ispressed, itspositionchanges.This timepressurizedfluidisenteredthroughthenonreturnflowcontrolvalve(1.01).Again,attheinlet,thefluidhastopassthroughthevariablerestrictorbecauseofthe“noflow”positionofthecheckvalveinthatdirectionwhichresultsintheslowmotionofthepistoninabackwarddirection.

Meter incircuit isnotrecommended,except infewcases,because thepressureofhydraulicfluidwhichwasbuiltupinordertopushthepistonofthe cylinder is reduced before even entering the hydraulic cylinder. This

arrangementissuitableforpreciseandlow-pressuresystemsbecauseabetterspeedcontrolcanbeattained.

MeterOutCircuitInthemeteroutcircuit,thefluidhastopassthroughthenonreturnflow

controlvalveafterescapingfromthecylinder,i.e.,speedoffluidisreducedwhenit iscomingoutofthecylinder.ConstructionofthiscircuitshowninFigure8.24isthesameasthatofmeterincircuit.Theonlydifferenceisthatthe direction of the check valve is changed in this circuit for providingrestrictiontofluidattheoutlet.

FIGURE8.24MeterOutCircuit.

Consider the valve at its normal position, which is shown in Figure8.24. The pressure port P is connected to working port A and port B isconnected to exhaust port T. The pressurized fluid passing from controlelement1.1reachesthenonreturnflowcontrolvalve1.02.Norestrictionisofferedinvalve1.02asthecheckvalveallowstheflowoffluidthroughit.Thefluidentersthecylinderandpushesthepistoninaforwarddirection.Atthesametime,thefluidhastobeexhaustedfromtherodsideofthecylinderandthistimethefluidhastopassthroughthenonreturnflowcontrolvalve(1.01).Thistimecheckvalvedoesnotallowfluidtopassfreelyfromitand

fluidpassesthroughrestriction.Hence,thespeedofthepistonisslowedasthefluidescapesslowlyoutoftherestrictor.Aftercompletionoftheforwardstroke, the manual push button on control element 1.1 is pressed and thecircuitproceedsinthesamemannerasexplainedinthecaseoftheforwardstroke.

Meter out circuit is preferred in hydraulics because the pressure ofenteringfluid isnotreducedhereas isdonein thecaseofmeter incircuit.Thewholepressureenergy isconverted intomechanicalenergy.Meteroutcircuits can also be used to control speed in the case of hydraulicmotorswhereasmeter incircuitsarenotsuitable toperformthis task.Inmeteroutcircuit, heat generation due to the flow control valve does not affect thesystem, i.e., actuator,because fluidapproaches the flowcontrolvalveaftertheactuator.

BLEEDOFFCIRCUITIn this circuit, a small quantity of pressurized fluid from the pump is

sentdirectlytothetank.Thisisdoneinordertoslowdownthespeedofthecylinder inbothdirections, i.e.,duringtheforwardandbackwardstroke.Aflowcontrolvalveisusedinthebypasslineforregulatingtheflow.Thesecircuits areusedonly to slowdown the speedof thecylinder.As the flowcontrol valve is placed before the DC valve in the circuit, speed can bereducedonlytosomelimitedvalue.

Bleedoffcircuitisexplainedwiththehelpofasimplecircuitdiagramshown in Figure 8.25 for controlling a double-acting cylinder. For ease ofreaders,thecircuitisexplainedinthreestepstakingallpositionsoftheDCvalve. Here, a double-acting cylinder (1.0) is being controlled by a 4/3solenoid operated spring return DC valve as control element (1.1). Therequiredpressureinthelineismaintainedwiththehelpofamotorandpumpassembly.Apressurereliefvalve(0.3)isalsoprovided.Flowcontrolvalve(0.2)isusedinbypasslineforregulatingtheflow.

Step1:OFForneutralpositionofcircuit

Initially, as shown in Figure 8.25 (a), the control element is in itsnormallyclosedposition.Alltheports,P,A,B,andT,areblockedtoeachother.DuringOFFpositionwhenthecircuitisnotinuseallthecoils,i.e.,X

andYarede-energized.Atthisstage,pressureinbothsidesofthecylinder,i.e.,capendandrodendsidesareequal.

FIGURE8.25BleedOffCircuit.

Step2:Forwardstoke

Theforwardmotionof thecylindercanbeachievedbyenergizingthesolenoid X.When the solenoid X gets energized, the control element 1.1changes itsposition.PressureportPgetsconnected toworkingportAandportBgetsconnectedtoportTasshowninFigure8.25(b).Asmallquantityofpressurizedfluid,whichisgoingfromPtoA,issenttothetankthroughflowcontrolvalve0.2.Thisslowsdownthespeedofthecylinderduringtheforwardstroke.Thesolenoidgetsde-energized,thenduetotheactionofthespring force, the 1.1 DC valve comes back to its original position, i.e.,normallyclosedposition.

Step3:Backwardstroke

Now,when the solenoidY isenergized, the1.1DCvalvechanges itsposition.PressureportPgetsconnected toworkingportBandportAgetsconnected to port T as shown in Figure 8.25 (c). This results in slowingdown the speed of the cylinder during the backward stroke as a smallquantityofpressurizedfluid,whichisgoingfromPtoB,issenttothetankthroughflowcontrolvalve0.2.Thesolenoidgetsde-energized,thenduetothe actionof the spring force, the1.1DCvalve comesback to its originalposition,i.e.,normallyclosedposition.

REGENERATIVECIRCUITRegenerative circuit is used when there is a requirement of rapid

extensionof thecylinderagainst load.This requirementof forwardmotionwithpushforcecanbeachievedbyusingaregenerativecircuit.RegenerativecircuitisexplainedwiththehelpofasimplecircuitdiagramshowninFigure8.26foracontrollingdouble-actingcylinder.Here,adouble-actingcylinder(1.0)isbeingcontrolledbya4/3solenoidoperatedspringreturnDCvalveascontrolelement(1.1).A3/2solenoidoperatedspringreturnDCvalve(1.3)is placed in between the cylinder and control element 1.1. The requiredpressure in the line is maintained with the help of a motor and pumpassembly. A pressure relief valve (0.3) is also provided. For the ease ofreaders, this circuit is explained in three steps taking all positions of DCvalve.

FIGURE8.26RegenerativeCircuit.

Step1:OFForneutralpositionofcircuit

Initially, as shown in Figure 8.26 (a), the control element is in itsnormallyclosedposition.Alltheports,P,A,B,andT,areblockedtoeachother.DuringtheOFFpositionwhenthecircuitisnotinuseallthecoils,i.e.,X, Y and Z, are de-energized. At this stage, pressure in both sides of thecylinder,i.e.,capendandrodendsideareequal.

Step2:Forwardstroke

Theforwardmotionof thecylindercanbeachievedbyenergizingthesolenoidX.Whenthesolenoidgetsenergized,the1.1DCvalvechangesits

position.PressureportPgetsconnected toworkingportAandportBgetsconnected to port T as shown in Figure 8.26 (b). The pressurized fluidcoming out of cylinder 1.0 is passed through 1.3 DC valve where it getsmixedwith the fluid coming from the pump. The fluid from the pump aswellasfromtherodsideofthecylinderisdirectedtothecapendsideofthecylinder.Thisinducesafastforwardmotioninthepistonandpistonrodendassembly.

Step3:Backwardstroke

During thebackward strokeof thecylinder, the regenerativecircuit isnotrequiredbecauserapidmovementofcylinderisonlyrequiredduringtheforward stroke. So, solenoids Y and Z are energized to deactivate theregenerative circuit and to change the position of control element,respectively.WhensolenoidsYandZareenergized,thepressureportPgetsconnectedtoworkingportBandthepressurizedfluidenterstherodsideofthecylinderthrougha1.3DCvalve,whichresultsinthebackwardmotionofthe cylinder as shown in Figure 8.26 (c). The backward motion of thecylinderwill be at normal speed because fluid coming out of the cylinderduringthebackwardstrokeisnotsentbacktothepressureline.

CIRCUITSHOWINGAPPLICATIONOFCOUNTERBALANCEVALVE

Thecounterbalancevalveisusedtopreventthefreefallofthecylinderunderitsownweightorduetotheloadattachedtoit.Theapplicationofthecounterbalancevalveisexplainedwiththehelpofasimplecircuitdiagramas shown inFigure8.27 for thecontrollingdouble-actingcylinder.Here, adouble-acting cylinder (1.0) is being controlled by a 4/3 solenoid operatedspringreturnDCvalveascontrolelement(1.1).Thecounterbalancevalve(1.01) is placed in between the cylinder and control element.The requiredpressure in the line is maintained with the help of a motor and pumpassembly.Apressurereliefvalve(0.3)isalsoprovided.Foreaseofreaders,thecircuitisexplainedinthreestepstakingallpositionsoftheDCvalve.

FIGURE8.27ApplicationofCounterBalanceValve.

Step1:OFForneutralpositionofcircuit

Initially, as shown in Figure 8.27 (a), the control element is in itsnormallyclosedposition.Alltheports,P,A,B,andT,areblockedtoeachother.DuringtheOFFposition,whenthecircuit isnot inuse,all thecoils,i.e.,X andY are de-energized.At this stage, pressure in both sides of thecylinder,i.e.,capendandrodendsidesareequal.

Step2:Upwardstrokeofcylinder

Theupwardmotionof thecylindercanbeachievedbyenergizing thesolenoid X. When the solenoid X gets energized, pressure port P getsconnectedtoworkingportAandportBgetsconnectedtoportTasshowninFigure 8.27 (b). Because the counter balance valve 1.01 is in its closedposition,thepressurizedfluidgoingfromportPtoportApassesthroughthecheckvalveandliftsthepistoninanupwarddirection.Itisthetendencyofthepistontofallbecauseoftheloadattachedtoit.Herecomestheuseofthecounterbalance valve. The pressure setting of the counter balance valve isdone at higher limits as compared to the pressure exerted by the loadattachedtothepistononthefluid.Sobecauseofahigherpressuresettinginthecounterbalancevalve,thepistonremainsheldinverticalposition.

Step3:Downwardstrokeofcylinder

WhenthesolenoidYgetsenergized,pressureportPgetsconnectedtoworkingportBandportAgetsconnectedtoportTasshowninFigure8.27(c). The pressurized fluid going from port P to port B exerts force on thepistonwhichovercomesthepressuresettingofthecounterbalancevalve,so

thecounterbalancevalvegetsopenandthepistonstartsmovingdownwardasshowninFigure8.27(c).

SEQUENCINGCIRCUITSequencingmeans control of more than one cylinder to move in the

desired sequence during forward and return strokes. Sequencing circuit isexplainedbytakingasimplesequenceoftwocylinders.Forexample,thereare two cylinders, 1 and 2, and it is required thatwhen the start button ispressed, thepistonofcylinder1extendsandwhen it is fullyextended, thepiston of cylinder 2 extends.When both the cylinders are in an extendedposition, it is required that the piston of cylinder 1 retracts, andwhen thepistonofcylinder1 is ina fully retractedposition, thepistonofcylinder2retracts.The sequencing circuit for the above sequence is shown inFigure8.28.

FIGURE8.28SequenceControlCircuit.

1.2.3.4.

The circuit is divided into groups based on the number of actuators.First actuator 1.0 is driven by a double pilot operated 4/2DCvalve (1.1).Two roller-operated spring returned DC valves 2.2 and 2.3 are placed atinner and outer extreme position of cylinder 2.0, respectively. One roller-operated spring returned3/2DCvalve (2.4) is placed at theouter extremepositionofcylinder1.0.

Initially,boththecylindersareinafullyretractedpositionasshowninthe figure. The 2.2 DC valve is initially in an actuated position. Thepressurized fluid coming from2.2DCvalve actuates the pilot signalX ofcontrol element 1.1. The pressurized fluid enters the cylinder 1.0. Thiscausestheforwardmotionofcylinder1.0.Thisforwardmotionleadstotheactuation of a 2.4 DC valve. The position of control element 2.1 changeswith theactuationof the2.4DCvalve.Thepressurized fluidcoming fromcontrolelement2.1enters thecylinder2.0.Thiscauses theforwardmotionof cylinder 2.0. The forwardmotion leads to the actuation of the 2.3 DCvalve.

The actuation of the 2.3 DC valve changes the position of controlelement 1.1,which leads to the backwardmotion of cylinder 1.0.Becausethe 2.1 DC valve is spring returned, it causes the backward motion ofcylinder2.0.Thiscompletestherequiredsequenceoftwocylinders.

ExampleofSequencingCircuitThecircuit(refertoFigure8.29)showsthesequencingoftwocylinders

toperformthedrilloperationonaworkpiece.Thesequenceofcylinderstobeaccomplishedisasgivenbelow:

Cylinder1clampstheworkpiece.Cylinder2performsdrillingoperationonworkpiece.Cylinder2returnsback.Cylinder1unclampstheworkpiece.

Initially both cylinders 1.0 and 2.0 are in a fully retracted position asshown inFigure 8.29. Pressurized fluid from the pump enters the cylinder1.0through1.1DCvalve.Thiscausesforwardmotionofcylinder1.0,whichresultsintheclampingoperation.Thepressurizedfluidgetsexhaustedfromcylinder 1.0 through the check valve of 1.01 sequence valve. The fully

extendedpositionofcylinder1.0resultsinopeningofsequencevalve2.01.Nowpressurizedfluidstartsflowingintocylinder2.0throughthesequencevalve 2.01, which results in the drilling operation. When the solenoid isenergized, the pressurized fluid starts flowing directly into cylinder 2.0resulting in its backward motion, which further results in retraction ofcylinder1.0.Hence,theabovesequenceisachieved.

FIGURE8.29

PRESSUREREDUCTIONCIRCUITA pressure reducing valve is used in a supply line joining two

subsystems.Suppose the supply from thepump takenat10-barpressure issent directly to the actuator (1.0) via the DC valve. In order to drive theactuator(2.0) ina low-pressurecircuit,fluidhastopassthroughapressurereducing valve where its pressure is reduced to 5-bar and then sent toactuator2.0viatheDCvalve.(RefertoFigure8.30.)

FIGURE8.30PressureReductionCircuit.

PROBLEMSINCIRCUITDESIGNProblem 1:Design a pneumatic system having cylinder flow control

valves,pressureregulatingvalves,FRLunit,etc. foroperatingthecylinderoncein100secondswithadwelltimeof15secondsintheretractedaswellasextendedextremes.

Solution:(RefertoFigure8.31.)Forsatisfyingtheconditionsgivenintheaboveproblem,nonreturnflowcontrolvalves(1.01and1.02)andtimedelayvalves(1.2and1.3)areusedinthecircuit.Inthiscircuit,compressedairfromthesourceissenttothe2/2solenoidoperatedDCvalvethroughaFRL unit.When the solenoid of the 2/2DC valve is energized, the valveopensandthepressurizedfluid,i.e.,airissenttotherestofthesystem.Limitswitches (3/2 DC valves) 1.4 and 1.5 are placed at both extremes of thecylinder.Limitswitchesareactuatedautomaticallyasthepistonrodmovesbetween two extreme positions and pilot signals X and Y are sentalternatively via the time delay valves. Limit switch (1.5) and time delayvalve(1.3)areresponsibleforthebackwardstrokeofthecylinderandlimitswitch (1.4) and the timedelayvalve (1.2) are responsible for the forwardstrokeof thepiston.Timedelayvalvesare fora timedelayof15seconds.

Further,flowcontrolvalves1.01and1.02areprovidedsothatforwardandbackwardmovementisobtainedin100seconds.

FIGURE8.31

Problem2:Asteeldoorisinstalledinanauditorium.ThisdoormaybeopenedorclosedbyONandOFFswitchesoperatedeitherfromoutsideorinside as shown inFigure 8.32.Design a pneumatic circuit and explain itworks.

FIGURE8.32

Solution:(RefertoFigure8.33.)Inthisproblem,twoswitcheshavetobeprovidedforopeningthedoorandtwoforclosingthedoor,i.e.,oneONandoneOFFswitchonbothsidesofthewall.ForthesetwoORgates/shuttlevalves (1.01, 1.02) are used. Valve 1.01 is connected with two 3/2 pushbuttonDCvalves (1.3 and 1.5).These two valves perform the function ofmanually operated OFF switches. Similarly, valve 1.02 is connected withtwo3/2pushbuttonDCvalves (1.2and1.4) and thesevalvesperform thefunctionofmanuallyoperatedONswitches.

FIGURE8.33

TherewillbeoneshuttlevalveforeachsetofONswitchesandanotherforeachsetofOFFswitches.Thewholedoorassemblyissurmountedonathrough rod double-acting cylinder with a fixed rod (1.0). In this type ofcylinder,therodisfixedbetweentwoendsandthecylinderbodyisfreetomove forwardandbackwardbyenteringandexhaustingcompressedair intwo ends alternately. The double-acting cylinder is driven by means ofcompressedairandthe4/3closedcenterDCvalve(1.1)isusedinthesystemtocontrol thedirectionof the fluid.The twoshuttlevalves (1.01,1.02),asdiscussed above, provide the pilot signal (depending on which switch ispressed)tothe4/3DCvalve(1.1)andthedoorwillmoveinthatparticulardirection.

Problem3:Componentsaretobesuppliedfromagravitymagazinetoworkstation by using a double-acting cylinder as shown in Figure 8.34.Feeding starts when the push button is pressed. The piston returnsautomaticallytostarttheprocessagain.Designapneumaticcircuitfortheaboveproblemandexplainitsconstructionandhowitworks.

FIGURE8.34

Solution:AsshowninFigure8.35forwardandbackwardmotionofthecylinderisobtainedbychangingthepositionofthe4/2DCvalve(1.1).Thesystemstartsbyoperatingthe1.2DCvalve.Whenthemanualpushbuttonof the1.2DCvalve ispressed, the supplyof compressedair is sent to thepilotsignalXofcontrolelement1.1,whichresultsintheforwardmotionofcylinder1.0.Onreachingtheextremeoutwardend,thepistonrodpushestheroller switch operated (3/2) DC valve (1.3) and due to which the pistonreturnsautomatically.

FIGURE8.35

Problem 4: Design a hydraulic circuit to control the motion of adouble-acting cylinder in such a way that the forward movement of thepiston rod can be possible with three different speeds (lower than normal

speed)but thepistoncomesbackwith itsnormal speed.Thepistoncanbestoppedatanypositionbetweentwoextremepositionstoo.

Solution: (Refer to Figure 8.36.) Fluid is made to pass through thehydraulicfilterandcheckvalvetothe4/3DCvalve(closedcenter).AandBaretheworkingportsofthecontrolvalve(1.1).WorkingportAisconnectedtoahydraulicsubsystemconsistingofthree2/2DCvalves(1.01,1.02,1.03),allof themhavingaseparatevariable flowcontrolvalve (1.05,1.06,1.07)which is responsible for changing the velocity of fluid to a particular setlevelforwhichitisdesigned.Also,thereisacheckvalve(1.04)inthelinewhose function is to by pass the discharged fluid from the cylinder to thereservoirduringreturnstroke.

FIGURE8.36

Theoutputfromthissubsystemdependsonvalves1.01,1.02,and1.03thataresolenoidoperated.Therequiredspeedisobtainedbyenergizingandde-energizing the respective solenoids of valves (1.01, 1.02, and 1.03).During the return stroke, there is no such arrangement provided after

workingportBandthecylindercomeswithafasterspeed.Inordertosatisfythe condition of stopping the piston of the double-acting cylinder at anyposition between two extremes,we use the 4/3 closed centerDC valve. Itsatisfiestheabove-mentionedcondition.

Problem5: In somemanufacturingoperations, it is required that themovement of the ram of a machine tool should be fast but sometimes itshould be slow, both during forward and backward stroke. In case ofelectricity failure, the reciprocating motion of the ram becomes free andoperationcanbecarriedoutmanually.Designahydraulic circuit keepingtheaboveconditionsinmind.

(Note:Aconstantspeedpumpisusedinthissystem.)

Solution: (Refer to Figure 8.37.) A 4/3 float-centered valve (1.1) isusedtocontrolthemotionofthedouble-actingcylinder.TheworkingportsAandBareconnectedtoexhaustportTinaneutralpositionthatdischargesallthefluidtothetankandthepistonisfreetomoveinthecylinder.

FIGURE8.37

1.

2.

3.4.

5.6.

7.

8.

9.10.11.

12.

13.

Two non return flow control valves (1.01 and 1.02) are used to slowdownthespeedofthecylinderbutwhenitisnotrequiredtoslowdownthespeed, the fluid is bypasseddirectly from the 2/2DCvalves namely1.03and 1.04 by simply energizing the electromagnets of valve 1.03. Thiswilldirectlyflushthedischargedfluidtothetank,hencecausingnorestrictiontothe forward and backward movement of the ram. Throttle out non returnflowcontrolvalveisusedbecauseitispreferredwithconstantspeedpumps.

EXERCISESWhatare thebasicdifferencesbetweenpneumaticandhydrauliccircuitdiagrams?Explain the method of designating components in a hydraulic orpneumaticcircuitwiththehelpofasketch.Listthebasictypesofhydrauliccircuits.Explain the construction, working, and performance characteristics offluidicelements.Identifythebasicelementsusedinahydrauliccircuit.Differentiatebetweenthrottleinandthrottleoutspeedcontrolcircuitsinpneumaticswiththehelpofasketch.Draw a basic block of a circuit showing the reservoir, accessories,pressurereliefvalve,andthepumpandtanklines.Drawapneumaticcircuittoachievethecontinuousreciprocatingmotionofasingle-actingspringreturnpneumaticactuator.Explainthefunctionofthequickexhaustvalvewiththehelpofasketch.Differentiatebetweenanopencenterandclosedcentercircuit.Draw a circuit diagram to control the hydraulic double-acting cylinderwiththeconditionthatthecylindercanbestoppedanywherebetweentheextremepositions.Drawapneumaticcircuit tooperateadouble-actingpneumaticactuatorsuch that the forward and backward motions of the actuator can beaffectedwithvaryingspeeds.Why is speed control less accurate and also difficult to obtain theintermediate positioning of the cylinder in the case of a pneumaticsystemdesign?

14.15.16.

17.

18.19.20.

21.22.

Sketchableed-offcircuit.Whyisitnecessarytousethepressurereliefvalveinhydrauliccircuits?Drawadouble-handedpneumaticsafetycircuitforaclampingoperationand explain itworks.Compare this circuitwith a single-handed circuitforthesamepurpose.Draw and discuss the pneumatic circuit for speed control of a double-actingcylinderbothinforwardaswellasinbackwardmotion.Whatarethepressuresrangesinhydraulicandpneumaticcircuits?Drawpressurereductioncircuitandexplainhowitworks.Draw the schematic of a hydraulic circuit for the following sequence:Extendacylinder,provideadwell,andthenretractthecylinder.Explainthesequencecontrolcircuitwiththehelpofasketch.Drawthepneumaticcircuitsforthefollowing:

Tocontrolthemotionofasingle-actingcylinder.Tocontrolthemotionofadouble-actingcylinder.Tocontrolthemotionofamotor.

1.2.

CHAPTER9

PNEUMATICLOGICCIRCUITS

INTRODUCTIONPneumatic systems arewell suited to process automation, as they not

only provide the necessary force to accomplish the task but also performcontrol functions. Pneumatic self-contained circuits are possible by whichthe process can be completely automated. This can be achieved by usingsimple fluidic elements in a logical manner. The use of special purposeelectronicequipmentispopularbecausetheseareconsideredthebestmediatoprovidecontrolonpneumaticpower.Itsmainfunctionsaretogenerateasignal, stop and start a process, and provide feedback, etc., but nowadayspneumaticcontrolshasdevelopedtosuchanextentthatitcanperformallthecontrol related functions alone.Because the problems related to pneumaticcontrols are sometimes complex, certain techniques are developed to solvethe problems of circuit design that add simplicity to the process of circuitdiagram.Thesetechniquesareexplainedinthischapterwithsomeexamples.

CONTROLSYSTEMControlsystemcanbedefinedasamechanismbyvirtueofwhichany

quantityofinterestinequipmentcanbemaintainedoralteredinaccordanceto one’s desire. Pneumatic systems as discussed already can be a controlsystemwhen air is used as controllingmedia. Like other control systems,pneumaticcontrolsystemscanbeclassifiedas:

OpenloopcontrolsystemsClosedloopcontrolsystems

OPENLOOPCONTROLSYSTEMIn an open loop control system, control function is independent of

output.

FIGURE9.1OpenLoopControlSystem.

ApneumaticopenloopcontrolsystemisshowninFigure9.1inwhichcompressedairistakenastheinputtothesystem.ADCvalveisusedasthecontrol element, which changes its position after fixed time intervals. Theflowofairisdirectedtothepneumaticcylinderandasanoutputthedouble-actingpneumaticcylinderextendsoutward.Hereonecannotdeterminewhenend position of cylinder will be reached and also for backward stroke ofcylinderoperatorhastopushanotherbutton.Openloopcontrolsystemsaresimple systems, not troubled with problems of instability. Their ability toprovidedesireandaccurateoutputdependsonthestability,calibration,andqualityofthecontrolelement.Outputoncegeneratedcannotbealteredagaininthesesystems.

CLOSEDLOOPCONTROLSYSTEMClosed loop control systems, on the other hand, are called feedback

systems.Inthesesystems,controlfunctionisdependentonoutput(RefertoFigure9.2).

FIGURE9.2ClosedLoopControlSystem.

In the above pneumatic control system, a pilot operated DC valve isusedasthecontrolelementwhichdirectstheflowofcompressedairtotheappropriatesideofthedouble-actingcylinder(workingelement)and,asanoutput,thedouble-actingcylinderextendsforward.Atthemomentthepistonrodreachesextremeposition,ithitsthetripvalveplacedthereandactuatesapilotsignal,whichchangesthepositionoftheDCvalve.Hence,theprocessis controlled, i.e., air is allowed to enter one side of the cylinder until thepistonreachesitsextremepositionand,afterthat,thesameairisdirectedtothe other side of the piston. This ensures the automatic forward andbackwardmotionofthepiston.Closedloopcontrolsystemsarecomplexandcostly but their output is accurate. Pneumatic closed loop systems areconsiderably cheaper because of the low cost of pneumatic equipment aswellastheirreliableoperation.

CIRCUITDESIGNMETHODSTherearetwoprimarymethodsofcircuitdesign:

TrailanderrorMethodologicaldesign

TrialandErrorMethodsTrialanderrormethodsarealsocalledintuitivemethodsbecausethese

methodsdonothaveanymethodologicalapproachbuttheyaredependentonpast experience and knowledge of the designer. Trial and error methodsrequiremoretimefordesigningcomplexcircuits.Onecaneasilyrealizethattherecanbeanumberofsolutionstoonedesignproblem.Itisalsoimportanttonotethatdesignwiththismethodisdependentonpersonal influencesofthe designer such as ability, mood, knowledge of pneumatic systems, etc.and it also relies onwhether onegivesmoreweight to the least expensivesolutionorthemorereliablesolution.

MethodologicalDesignOntheotherhand,methodologicaldesignfollowsacertainsetofrules

andinstructionstoarriveat theoptimalsolution.Thismethodconsistsofapreciselydefinedmethodandthedesigner’sinfluenceisless,whereassometheoreticalknowledgeaboutthetechniquethatisbeingfollowedisrequired.

A methodological circuit design takes lesser time and provides a reliablesolution.Becauseofthesereasonsthesemethodsarebeingusedinindustry.Control isalways independentofpersonal influencesofdesigner. It isalsoworth noting thatmore components are requiredwhile designing a circuitdiagram by using these techniques than in circuits designed by intuitivemethods.The additional cost of the components is compensated by savingtimeincompletingaprojectaswellasreducedmaintenancecosts.

At this stage,when both themethods have their own advantages anddisadvantages,itisdifficulttodecidewhichmethodistobeused.Again,itisworthnotingthatregardlessof themethodor techniqueusedtodesignacircuitdiagram,oneshouldhaveacquiredsoundknowledgeaboutpneumaticvalves,switches,fluidicelements,andmeansofactuation.

Some of the commonly used techniques under heading ofmethodologicaldesignare:

Cascade design Algebric method (using Boolean Algebra)Graphicalmethod(K-mapping)

MOTIONSEQUENCEREPRESENTATIONAn automatic system constitutes working elements and control

elements. It is required that the motion schedule and the start and stopconditions of the elements in a system must be known and interpretedclearly.Understandingwhatistobedoneisveryimportantforfinalresults.So it becomes important to show the sequence of operation of variouselementsinapneumaticsystemintheformofagraph.Therearetwotypesof diagrams, which are used to represent functional sequences: Motiondiagrams Control diagrams Motion diagrams are the graphical

representationofalltheconditionsofworkingelements(elementswhichdonot take part in controlling). Similarly, control diagrams are those whichprovideinformationaboutcontrolelementsonly.Theseareexplainedbelow.

MOTIONDIAGRAMSMotiondiagramsareoffollowingtypes:

1.2.

PositionstepdiagramPositiontimediagram

PositionStepDiagramThe position step diagram shown in Figure 9.3 is drawn only by

consideringthetwopositionsofadouble-actingpneumaticcylinder.

FIGURE9.3PositionStepDiagram.

Position A is retracted or the rear position of the piston rod and position Brepresentstheextendedorforwardpositionofthepistonrod.Positionisplottedagainststeps(changeinpositionofanycomponent).StepsareplottedontheX-axis and position is plotted on the Y-axis. On actuating or operating anyparticularswitch/elementinthesystem,therearetwopossibilities.Thepositionof thepiston rodeitherchanges (forexample fromextreme inward toextremeoutward) or remains the same. Only these two cases can be shown with thisdiagram. Position step diagram for cylinder 1 is shown in Figure 9.3 and isexplainedinTable9.1. TABLE9.1 Step CylinderPosition 0-1 Retracted 1-2 Extended 2-3 Extended 3-4 Extended 4-5 Retracted

Example:Draw the position step diagram for the example shown inFigure9.4forwhichtheseriesofoperationstobecarriedoutare:

CylinderAclampstheworkpiece.Machineoperationisperformedonworkpiece.

3.4.

CylinderAproceedsbackward.CylinderBproceedsforward.Afterpushingtheworkpieceontheconveyor,cylinderBtravelsback.

FIGURE9.4

Solution:

SequenceofOperations:Thesequenceofoperationsof twocylindersfortheabovesaidexampleisshowninTable9.2.

TABLE9.2 Step CylinderA CylinderB 0-1 Extends —— 1-2 —— —— 2-3 Retract —— 3-4 —— Extends 4-5 —— Retract

Position Step Diagram: The position step diagram for the aboveexampleisshowninFigure9.5.

FIGURE9.5PositionStepDiagram

PositionTimeDiagramApositiontimediagramissimilartoofthepositionstepdiagram.Here,

cylinder positions are plotted with respect to time. The displacement stepdiagramissimpletounderstandanddraw,onotherhand, thepositiontimediagram overlaps and operating speeds can be better shown. The positiontimediagramfortheaboveexampleisshowninFigure9.6.

FIGURE9.6PositionTimeDiagram.

CONTROLDIAGRAM

Control diagrams are drawn for a particular control element. Theysimply display the sequence of actions conducted by a particular controlelement.Itmaybecalledaconditionstepdiagram.

ThediagramshowninFigure9.7isdrawnforanelectromagnetwhichconstitutes a spoolvalve.The flowof fluid is startedwhenelectromagnetsareenergizedandtheflowoffluidstopswhenthecoilisde-energized.

FIGURE9.7ControlDiagram.

CASCADEDESIGNCascading is amethodological approach to the problem of pneumatic

circuitdesign.Asalreadydiscussed,intuitivetechniquesofcircuitdesignarenot suitable for complex circuits. This technique not only reduces thecomplexity in design but also reduce the size and number of componentsusedincircuits.

Cascadingmeans“inseries.”Inthismethod,thesequenceofpneumaticcylinders is controlledbyusingvarious typesof signaling elements.Thesesignaling elements are, of course, driven by the forward and backwardstrokesofthecylindersbuttheairsupplytopilotlinesisdeliveredthroughacascadesystem.Inacascadesystem,theforwardandbackwardmotionsofthe pneumatic cylinders are classified into various groups. Then, thoseparticular groups of movements are controlled with components in thecascade system.The cascade system consists of group selector valves, busbarlines,andpilotlines.Busbarlinesarebasicallypneumaticenergylines,which pass from plant. These are used to supply pneumatic energy topneumaticsystems.

STEPSINVOLVEDINCASCADEDESIGN

1.2.

3.

4.5.

6.

7.

8.

9.

10.

The steps involved in drawing a circuit using the cascademethod arethefollowing:

CylindersarenamedasA,B,C,etc.dependingontheirnumber.Cylinder advancedmovement is designated by “+” sign and cylinderbackwardmovementisdesignatedby“−”sign.SotheforwardmotionofcylinderAisdenotedbythesignA+andbackwardmotionbyA−.Thegivensequence iswrittenwith“+”and“−”signdependingupontheproblem.Thesteppositiondiagramforthegivensequenceisdrawn.The given sequence of cylinders is divided into groups. Groups areformedbyensuring that the lettersAorB should comeonlyonce inonegroupregardlessofthesign,i.e.,itmaybe+veor−ve.Each group is assigned “bus bars” or “compressed air lines.” Thenumberofbusbarlinesisequaltothenumberofgroupsformed.Thebus bar line is responsible for the supply of compressed air in onegrouponly.Each cylinder is provided with a 4/2 pilot operated DC valve. ThenumberofDCvalvesisequaltothenumberofcylinders.Limitswitches/valvesarepositionedateitherendandareactuatedbypistonrod.Theseidentifytheextensionandretractionofthecylinders.Limitswitchesconsistofmechanicallyactuatedelectricalcontacts.Thecontacts open or close when some machine component reaches acertainposition(i.e.,limit)andactuatestheswitch.Thelimitswitchesaredenotedbysuffix“o”and“1.”Suffix“o”meansthereturnstrokeofthe cylinder and suffix “1”means the forward stroke of the cylinder.For each cylinder, there are two limit switches. Each bus bar linesupplies compressedair to the limit switcheswithin thegroup.Thesearenormally3/2DCvalves.Group selector valves act as an energy source for the limit switchesused for controlling the motion of cylinders. These are 4/2 pilotoperatedDC valves.As a rule of thumb, group selector switches arealways equal to “the number of bus bar lines or number of groupsminus1.”Thecircuitisdrawnbykeepingthegivensequenceinmind.Toknowand learn how the cascade system is drawn for a particular problem,

onemustbefamiliarwiththecomponentsofthecascadesystem.Inthefollowingparagraphs,themethodofcascadingisexplainedstepbystepby showing various examples. Various components of the cascadesystemarealsoexplained.

SIGNCONVENTIONSCertain sign conventions have to be adopted to denote forward and

backwardmotionsofcylinders.Thesearegivenbelow:

Signconventions

Cylinderadvancedmovementisdesignatedby:+ve(positive)sign

Cylinderbackwardmovementisdesignatedby:−ve(negative)sign

Cylinders can be named A, B, C, D, etc. ……. depending on theirnumber

SowecandenotetheforwardmotionofcylinderAbythesignA+andbackwardmotionbyA−.

SEQUENCINGSequencingmaybedefinedastheprocessofputtingthingsintheright

order. It is the prime step in circuit design depending on the problemassigned. One can arrange the forward and backward motions of all thecylinders in the circuit. Position step diagrams can further show thissequencegraphically.

EXAMPLESExample 1: Design a pneumatic logic circuit by using the cascade

method for the following sequence of cylinders: In a two cylinder circuit,cylinderAextendsinthefirststep,Bextendsinthesecondstep,cylinderAretractsinthethirdstep,andcylinderBretractsinthefourthstep.

Solution:

Drawingapneumaticcircuitbyusingthecascademethodinvolvesthefollowingsteps:

Step1.SequenceofMotions

Thesequenceofmotionsfortheaboveproblemis

A+B+A−B−

Themotion that occurs in the same steps can bewritten in the samecolumn.

Step2.PositionStepDiagram

For the above sequence of movements, the position step diagram isshowninFigure9.8.

FIGURE9.8PositionStepDiagram.

Step3.Grouping

Thenextstepistodividethesequenceofcylindermotionsintogroups.GroupsareformedbyensuringthatthelettersAorBshouldcomeonlyonceinonegroupregardlessofthesign,i.e.,itmaybe+veor−ve.Forexample,

groupingforthesequencewrittenaboveis:

GroupsaredenotedbyletterG.So,thegroupsareG1andG2.

Step4.BusBarLines

The next step is to draw the cascade system. For this “bus bars” or“compressedairlines”aredrawn.Thenumberofbusbarlinesareequaltothe number of groups formed. This is because each bus bar line isresponsible for the supply of compressed air in one group only. For theaboveexample,theselinesaredrawnasshowninFigure9.9.

FIGURE9.9BusBarLines.

Step5.GroupSelectorSwitches

Groupselectorswitchesarebasically4/2DCvalves(pilotoperated).Asaruleofthumb,groupselectorswitchesarealwaysequalto“thenumberofbusbarlines−1.”

Ormathematically: ifB1,B2,B3,…….. ,Bn impliesbusbar lines inacascadesystem,Numberofgroupselectorswitchesincascadesystem=n-1

For above example, the arrangement of the group selector valves isshowninFigure9.10.

FIGURE9.10

Group selector valves act as an energy source for the limit switchesused for controlling themotionof the cylinders.Group selector valves areplacedinacascadesystembykeepinginmindthatonlyonebusbarlineisgivencompressedairsupplyatatimetoensuretheproperfunctioningofthecircuit.

Currently, the supply is being given to bus bar line B1 as shown inFigure9.10andrestofthelinesareempty.WhentherequirementinlineB1isover,pilotsignalS2isgeneratedwhichchangesthepositionofGS1.Now,

airsupplyisdirectedtobusbarlineB2.Atlast,whentheaboveprocessistobe repeated, i.e., when the air supply is required at bus bar B1, the pilotsignalS1 isgiventoGS1.Nowagain thesupply isrestoredtobusbar lineB1.Theabovecycleisrepeatedagain.

Step6.DrawingaCircuit

Afterdrawing thecascadesystemforacircuit,all theelementsof thecircuit are drawn according to the requirements. The number of cylinders,controlling elements, limit switches, pressure control valves, flow controlvalves, etc. are determined from the given problem. All the requiredelementsofthecircuitforaboveexampleareshowninFigure9.11.

FIGURE9.11

Thenextstepistomakethecylindermoveinasequenceasdeterminedabove.Foreaseofreaders,thecircuitisdrawnin3steps:Step1:Inthefirststep,onlythefirstgroupistakingcompressedairfrombusbarlineB1.The

sequenceofthemotionforthefirstgroupis:

The pneumatic circuit for the sequence of the first group is shown inFigure9.12.

FIGURE9.12

In this figure, group selector valve GS1 is at its initial position bysupplyingcompressedairtobusbarB1.Thecompressedairwillbesuppliedtothecontrolelementsinsuchawaythatthesequenceofmotionsofgroup1shouldbeaccomplished.Theairafteractivatingtherespectivepilotlinealsorushes to limit switches (3/2 DC valves). These signaling elements onlyallow the air to pass, when the piston rod reaches the extreme desiredposition. For example, 1.1 DC valve is actuated by the pilot line. Thecylinder 1.0 starts moving forward. When outer extreme position A+ isreached,onlythenthelimitswitcha1isactuatedandairissenttothenextvalve for completion ofmotion sequence B+. Thus, the sequenceA+B+ isachieved.

Step2:Instep2,thesignalcomingfromlimitswitchb1ofstep1actsasapilot signalS2 forGS1.Nowbusbar lineB2 is selected.Sequenceof

motionforgroup2is

The pneumatic circuit for the sequence of second group is shown inFigure9.13.

FIGURE9.13

Compressed air taken from bus bar line B2 is used to apply pilotpressure in attainingA− position. The cylinderA startsmoving backward.When the extreme positionA− is reached only then the limit switch ao isactuatedandairissentto2.1DCvalveforcompletionofB−sequence.Thus,thesequenceA−B−isachieved.

Step3:Inthisstep,thecircuitsofstep1and2arecombinedtogether.ThefinalcircuitisshowninFigure9.14.

FIGURE9.14

Thebackwardmotionofcylinder2.0, i.e.,B− leadstotheactuationofbo.NowthecompressedairfromlimitswitchbowillactasapilotsignalS1forGS1andresetsittoitsoriginalpositionwhichagainselectsbusbarlineB1.Thus, the sequenceA+B+A−B− is achieved.Now, the cycle is againreadytostart.

Note: The circuit shown in Figure 9.14will not stop at anymomentonce it gets activated. It keeps running continuously. Tomake the circuitcontrol,apushbuttonoperatedspringreturned3/2DCvalveisadded.ThismakesthecircuitmanuallycontrolledwhichisshowninFigure9.15.

1.2.3.4.

FIGURE9.15

Example2:Thedrillingoperationistobeperformedonaworkpiece.Thesequenceofmotionofthecylindersare:

Cylinder1clampstheworkpiece.Cylinder2performsadrillingoperationontheworkpiece.Cylinder2returnsback.Cylinder1unclampstheworkpiece.

Fortheabovesaidsequence,drawapneumaticcircuit.

Solution:

Thesequenceofmotionfortheaboveexampleis

A+B+B−A−

ThepneumaticcircuitfortheabovesequenceisshowninFigure9.16.

FIGURE9.16

Initially, both the cylinders are in the retracting position as shown inFigure 9.16. When the push button of the 1.2 DC valve is pressed, thecompressedairstartsflowingintocylinder1.0throughcontrolelement1.1.This results in the forward motion of cylinder 1.0, which leads to theactuationof the2.2DCvalve.Now, thecompressedair starts flowing intocylinder2.0throughcontrolelement2.1,whichleadstotheforwardmotionofcylinder2.0.Thisforwardmotionofcylinder2.0leadstotheactuationofthe 2.3 DC valve. The 2.3 DC valve sends a pilot signal to the controlelement2.1.Asthepilotsignalisalsocomingfromthepreviousoperation,i.e.,B+,soboththepilotsignals(onefromthe2.2DCvalveandsecondfromthe2.3DCvalve)areavailabletocontrolelement2.1.Theextendedpositionof cylinder A is actuating the 2.2 DC valve and, on the other side, theextended position of cylinder B is actuating the 2.3DC valve. Both theseleadstolockingofthesystem.Thisiscalledasignaloverlappingproblemasthe signal is coming from both sides. To overcome the problem ofoverlapping,cascadingisused.

Useofcascadingfortheaboveexample

Thesteps involvedindrawingthecircuitbycascadingmethodfor theaboveexampleare:

Step1.SequenceofMotions

Thesequenceofmotionsfortheabovesaidproblemis

A+B+B−A−

Themotionthatoccursinsamestepscanbewritteninsamecolumn.

Step2.PositionStepDiagram

For the above sequence of movements, the position step diagram isshowninFigure9.17.

FIGURE9.17

Step3.Grouping

The next step is to divide the sequence of the cylinder motions intogroups.GroupsareformedbyensuringthatthelettersAorBshouldcomeonly once in one group regardless of the, i.e., it may be +ve or −ve. For

example,groupingforthesequencewrittenaboveis:

GroupsaredenotedbyletterG.So,thegroupsareG1andG2.

Step4.BusBarLines

The next step is to draw the cascade system. For this “bus bars” or“compressedairlines”aredrawn.Thenumberofbusbarlinesareequaltothe number of groups formed. This is because each bus bar line isresponsible for the supply of compressed air in one group only. For theaboveexample,theselinesaredrawnasshowninFigure9.18.

FIGURE9.18

Step5.GroupSelectorSwitches

Groupselectorswitchesarebasically4/2DCvalves(pilotoperated).Asaruleofthumb,groupselectorswitchesarealwaysequalto“thenumberofbusbarlines−1.”

Ormathematically: ifB1,B2,B3,……..,Bn implies bus bar lines in acascadesystem,Numberofgroupselectorswitchesincascadesystem=n−1

For the above example, the arrangement of group selector valves isshowninFigure9.19.

FIGURE9.19

Groupselectorvalvesactasanenergysourceforlimitswitchesusedforcontrollingthemotionofcylinders.Groupselectorvalvesareplacedin thecascade systembykeeping inmind that onlyonebusbar line at a time isgivencompressedairsupplytoensureproperfunctioningofcircuit.

RefertoFigure9.19.Currently,thesupplyisbeinggiventothebusbarlineB1andalltherestofthelinesareempty.WhentherequirementinlineB1 isover,pilot signalS2 isgeneratedwhichchanges thepositionofGS1.NowairsupplyisdirectedtobusbarlineB2.Atlast,whentheaboveprocessistoberepeated,i.e.,whentheairsupplyisrequiredatbusbarB1,thepilotsignalS1isgiventoGS1.NowagainthesupplyisrestoredtobusbarlineB1.Theabovecycleisrepeatedagain.

Step6.DrawingaCircuit

Afterdrawing thecascadesystemforacircuit,all theelementsof thecircuitaredrawnaccordingtotheserequirements.Thenumberofcylinders,controlling elements, limit switches, pressure control valves, flow controlvalves, etc. are determined from the problem given. All the requiredelementsofthecircuitfortheaboveexampleareshowninFigure9.20.

FIGURE9.20

Thenextstepistomakethecylindermoveinasequenceasdeterminedabove.Foreaseofreaders,thecircuitisdrawnin3steps:Step1:Inthefirststep,onlythefirstgroupistakingcompressedairfrombusbarlineB1.The

sequenceofthemotionforfirstgroupis:

The pneumatic circuit for the sequence of the first group is shown inFigure9.21.

FIGURE9.21

In this figure, group selector valve GS1 is at its initial position bysupplyingcompressedairtobusbarB1.Thecompressedairwillbesuppliedtothecontrolelementsinsuchawaythatthesequenceofmotionsofgroup1shouldbeaccomplished.Theairafteractivatingtherespectivepilotlinealsorushestothelimitswitches(3/2DCvalves).Thesesignalingelementsonlyallow the air to pass, when the piston rod reaches the extreme desiredposition. For example, the 1.1DC valve is actuated by the pilot line. Thecylinder 1.0 starts moving forward. When outer extreme position A+ isreached,onlythenthelimitswitcha1isactuatedandairissenttothenextvalve for completion ofmotion sequence B+. Thus, the sequenceA+B+ isachieved.

Step2:Instep2,thesignalcomingfromthelimitswitchb1ofstep1actsasapilotsignalS2forGS1.NowbusbarlineB2isselected.Sequence

ofmotionforgroup2is

ThepneumaticcircuitforthesequenceofthesecondgroupisshowninFigure9.22.

FIGURE9.22

Compressed air taken from bus bar line B2 is used to apply pilotpressure in attaining B− position. The cylinder B startsmoving backward.When the extreme positionB− is reached, only then the limit switch bo isactuated and air is sent to the 1.1 DC valve for completion of the A−

sequence.Thus,thesequenceB−A−isachieved.

Step3:Inthisstep,thecircuitsofstep1and2arecombinedtogether.ThefinalcircuitisshowninFigure9.23.

FIGURE9.23

Thebackwardmotionofcylinder1.0, i.e.,A− leads toactuationofao.Nowthecompressedair fromlimit switchaowillactaspilot signalS1 forGS1andresetsittoitsoriginalposition,whichagainselectsbusbarlineB1.Now the cycle is again ready to start.Thus, the sequenceA+B+B−A− isachieved. Hence, with the use of cascading, the problem of signaloverlappingisavoided.

Example 3: Movement diagram for a 3 cylinder (A, B, and C)pneumatic system is given in Figure 9.24. Draw the pneumatic circuitdiagramfortheabove.

FIGURE9.24

Solution: The steps involved in drawing the circuit by the cascadingmethodfortheabovesaidexampleare:Step1.SequenceofMotions

Thesequenceforthegivenpositionstepdiagramis:

Step2.Grouping

Thenextstepistodividethesequenceofcylindermotionsintogroups.GroupsareformedbyensuringthatthelettersA,B,orCshouldcomeonlyonce in one group regardless of the sign, i.e., it may be +ve or −ve. For

example,groupingforthesequencewrittenaboveis:

GroupsaredenotedbyletterG.SothegroupsareG1andG2.

Step3.BusBarLines

The next step is to draw the cascade system. For this “bus bars” or“compressed air lines” are drawn.Thenumberof busbar lines is equal tonumberofgroupsformed.Thisisbecauseeachbusbarlineisresponsibleforthe supply of compressed air in one group only. For the above example,theselinesaredrawnasshowninFigure9.25.

FIGURE9.25

Step4.GroupSelectorSwitches

Groupselectorswitchesarebasically4/2DCvalves(pilotoperated).Asaruleofthumb,groupselectorswitchesarealwaysequalto“thenumberofbusbarlines−1.”

Ormathematically: ifB1,B2,B3,…….. ,Bn impliesbusbar lines inacascadesystemNumberofgroupselectorswitchesincascadesystem=n-1

Fortheaboveexample,thearrangementofthegroupselectorswitchesvalvesisshowninFigure9.26.

FIGURE9.26

Group selector valves act as the energy source for the limit switchesused for controlling themotionof the cylinders.Group selector valves areplacedinthecascadesystembykeepinginmindthatonlyonebusbarlineisgivencompressedairsupplyatatimetoensureproperfunctioningofcircuit.

RefertoFigure9.26.Currently,thesupplyisbeinggiventobusbarlineB1andtherestofallthelinesareempty.Whentherequirementinline‘B1’isover,pilotsignalS2isgeneratedwhichchangesthepositionofGS1.Now,airsupplyisdirectedtobusbarlineB2.Atlast,whentheaboveprocessistoberepeated,i.e.,theairsupplyisrequiredatbusbarB1,thepilotsignalS1isgiventoGS1.NowagainthesupplyisrestoredtobusbarlineB1.Theabovecycleisrepeatedagain.

Step5.DrawingaCircuit

Afterdrawing thecascadesystemforacircuit,all theelementsof thecircuitaredrawnaccordingtotheserequirements.Thenumberofcylinders,controlling elements, limit switches, pressure control valves, flow controlvalves, etc. are determined from the problem given. All the requiredelementsofthecircuitfortheexampleareshowninFigure9.27.

FIGURE9.27

Thenextstepistomakethecylindermoveinasequenceasdeterminedabove.Foreaseofreaders,thecircuitisdrawnin3steps:Step1:Inthefirststep,onlythefirstgroupistakingcompressedairfrombusbarlineB1.The

sequenceofthemotionforthefirstgroupis:

The pneumatic circuit for the sequence of the first group is shown inFigure9.28.

FIGURE9.28

Inthisfigure,groupselectorvalveisatitsinitialpositionbysupplyingcompressedairtobusbarlineB1.Thecompressedairwillbesuppliedtothecontrol elements in such a way that the sequence of motions of group 1

shouldbeaccomplished.Theairafteractivatingtherespectivepilotlinealsorushestothelimitswitches(3/2DCvalves).Thesesignalingelementsonlyallow the air to pass, when the piston rod reaches the extreme desiredposition. For example, the 1.1DC valve is actuated by the pilot line. Thecylinder1.0 startsmoving forward.When theouterextremepositionA+ isreached,onlythenthelimitswitcha1isactuatedandairisplacedtothenextvalveforthecompletionofmotionsequence.Thus,thesequenceA+B+C+

isachieved.

Step2: Instep2, thesignalcomingfromthelimitswitchc1ofstep1acts as a pilot signal S2 for GS1. Now, bus bar line B2 is selected. The

sequenceofmotionforgroup2is

The pneumatic circuit for the sequence of second group is shown inFigure9.29.

FIGURE9.29

CompressedairsupplytakenfrombusbarlineB2isusedtoapplypilotpressure in attainingA−B−C− simultaneously.The sequenceA−B−C− istaking place in a single step, i.e., backwardmotion of all the cylinders is

taking place simultaneously in step 2. The group selector switchGS1willchangeitspositiononlyafterthecompletionofA−B−C−inasinglestep.

Whenthecylinders1.0and2.0areinafullyretractedposition,boththelimit switches ao and bo gets actuated.Their supply is routed to two inputportsofANDgateI,i.e.,atwinpressurevalve.TheoutputofANDgateIisroutedtotheinputofANDgateII.Theotherinput,whichisgiventoANDgateIIiscomingfromlimitswitchco,whichgetsactuatedaftercompletionofC−, i.e., thebackwardstrokeofcylinder3.0.TheoutputofANDgateIIactsasapilotsignalS1forGS1.

Step3:Inthisstepthecircuitsofstep1and2arecombinedtogether.ThefinalcircuitisshowninFigure9.30.TheoutputofANDgateIIactsasapilot signal S1. the group selector switch GS1 resets GS1 to its originalpositionandthecycleisrepeatedgain.

FIGURE9.30

Example4:Ina4cylindercircuit,cylinderAextendsinthefirststep,cylinderB extends in the second step, cylinderC extends in the third stepandcylinderA retracts in the fourth stepandat the same timecylinderDextendsinthefourthstep.Similarly,cylinderDandcylinderBretractsinthenextstepandcylinderCretractsinthesixthstep.Fortheabovesequenceofcylinders,designapneumaticcircuitbyusingcascading.

Solution: Drawing a pneumatic circuit by using cascade methodinvolvesthefollowingsteps.

Step1.SequenceofMotions

Thesequenceofmotionsfortheabovesaidproblemis

Step2.PositionStepDiagram

For the above sequence of movements, the position step diagram isshowninFigure9.31.

FIGURE9.31

Step3.Grouping

Thenextstepistodividethesequenceofcylindermotionsintogroups.GroupsareformedbyensuringthatthelettersABCorDshouldcomeonlyonce in one group regardless of the sign, i.e., it may be +ve or −ve. For

example,groupingforthesequencewrittenaboveis:

GroupsaredenotedbyletterG,sothegroupsareG1,G2,andG3.

Step4.BusBarLines

Thenextstepistodrawthe“busbars”or“compressedairlines.”Thenumbersofbusbarlinesareequaltothenumberofgroupsformed.Thisisbecause thebusbar line is responsible for the supplyof compressedair inonegrouponly.For theaboveexample, these linesaredrawnas shown inFigure9.32.

FIGURE9.32

Step5.GroupSelectorSwitches

Groupselectorswitchesarebasically4/2DCvalves(pilotoperated).Asaruleofthumb,groupselectorswitchesarealwaysequalto“thenumberofbusbarlines-1”

Ormathematically:ifB1,B2,B3,……..,BnimpliesthebusbarlinesinacascadesystemGroupselectorswitches=n−1

Fortheaboveexample,thearrangementofthegroupselectorvalvesisshowninFigure9.33.

FIGURE9.33

RefertoFigure9.33.Currently,thesupplyisbeinggiventobusbarlineB1andtherestofthelinesareempty.Whentherequirementinline‘B1’isover,pilot signalS1 isgeneratedwhichchanges thepositionofGS1.NowtheairsupplyisdirectedtothebusbarlineB2.Similarly,whenitisrequiredtoactivatethelineB3,thepilotsignalS2willbegeneratedandcompressed

airgoestobusbarlineB3therebyemptyingalltheotherlines.Atlast,whentheaboveprocessistoberepeated,i.e.,theairsupplyisrequiredatthebusbarlineB1,thepilotsignalS3isgiventoGS2withoutchangingthepositionof GS1 and the supply is restored to bus bar line B1. The above cycle isrepeatedagain.

Step6.DrawingaCircuit

Afterdrawingthecascadesystemforacircuit,alloftheelementsofthecircuitaredrawnaccordingtotheserequirements.Thenumberofcylinders,controlling elements, limit switches, pressure control valves, flow controlvalves, etc. are determined from the problem given. All of the requiredelementsofthecircuitfortheaboveexampleareshowninFigure9.34.

FIGURE9.34

Thenextstepistomakethecylindermoveinasequenceasdeterminedabove.Foreaseofthereaders,thecircuitisdrawnin3steps:Step1:Inthefirststep,onlythefirstgroupistakingcompressedairfrombusbarlineB1.

Thesequenceofthemotionforthefirstgroupis:

The pneumatic circuit for the sequence of the first group is shown inFigure9.35.

FIGURE9.35

In this figure, the group selector valve is at its initial position bysupplying the compressed air to bus bar B1. The compressed air will besuppliedtothecontrolelementsinsuchawaythatthesequenceofmotionsof group 1 should be accomplished. The air after activating the respectivepilotlinealsorushestothelimitswitches(3/2DCvalves).Thesesignalingelementsonlyallowtheairtopass,whenthepistonrodreachestheextremedesiredposition.Forexample,1.1DCvalveisactuatedbythepilotline.Thecylinder1.0 startsmoving forward.When theouterextremepositionA+ isreached,onlythenthetripvalvea1 isactuatedandair issent tonextvalveforcompletionofmotionsequenceB+.WhentheouterextremepositionB+isreached,onlythenthetripvalveb1 isactuatedandairissenttothenextvalve for the completion ofmotion sequenceC+.When the outer extremepositionC+isreached,onlythenthetripvalvec1isactuatedandairissenttothegroupselectorswitchGS1whichactsasapilotsignalS1andselectsthebusbarlineB2.

Step2:Instep2,thesignalcomingfromlimitswitchc1ofstep1actsasapilotsignalS1forGS1.NowbusbarlineB2isselected.Thesequenceof

motionforgroup2is

ThepneumaticcircuitforthesequenceofthesecondgroupisshowninFigure9.36.

FIGURE9.36

Compressed air taken from bus bar line B2 is used to apply pilotpressureinattainingA−andD+position.ItisrequiredthatthegroupselectorswitchGS2 is actuatedby thepilot signalS2 onlywhenbothpositionsA−

andD+areattained.For this, theoutputs fromlimitswitchesa0andd1aregiven to twin pressure valve I and the common output is used as a pilotsignalS2forGS2,sothatbothtasksshouldbeaccomplishedbeforestartingthenewtask.

Step3:Inthethirdstep,GS2isactuatedasinlaststep,i.e.,step2,pilotsignalS2haschanged thepositionofgroupselectorswitchGS2.Supply istakenfrombusbarlineB3andthefollowingmotionsareaccomplished.

Compressed air taken from bus bar line B3 is used to apply pilotpressure in attaining D−, B−, and C− positions, where D− and B− areaccomplished simultaneously and C− is started after finishing the formermotions.ThepneumaticcircuitforthesequenceofthethirdgroupisshowninFigure9.37.

FIGURE9.37

Again,thetwinpressurevalveisusedinthiscase.CylinderDandBareretracted back by inducing pressure in the respective pilot line. Then, theoutputsfromtripvalvesd0andb0aredirectedtotwinpressurevalveII,soastoensuretheaccomplishmentofthesemotionsbeforethestartingofmotionC−.Finally,outputfromtwinpressurevalveIIisdirectedtothepilotlineof3.1DCvalvetoattaintheC−positionandoutputofthetripvalveC0issentto thepilot lineS3ofgroupselectorswitchGS2.Thepilot signalS3 againresetsthevalvesGS1andGS2totheirpreviouspositionsandcycleisagainreadytostart.

Figure 9.38 shows the accomplishment of all the motionssimultaneously.

1.2.

3.4.5.

6.7.8.9.10.11.

12.13.14.

FIGURE9.38

EXERCISESDefinepneumaticlogiccontrolcircuits.Givethestep-by-stepprocedureforthedesignofpneumaticlogiccontrolcircuits.Listthevariouscomponentsofpneumaticlogiccontrolcircuits.Differentiatebetweentheopenandclosedloopcontrolsystem.Whatarethemethodsofcircuitdesign?Discuss the step-wise procedure for the design of the pneumatic logiccircuit for the given sequence of operation. Illustrate the procedure bytakinganysimpleexample.Whatistheneedofpneumaticlogiccircuits?Whatisanopenloopcontrolsystem?Givetwoexamples.Whatisthefunctionofusingcascade?Whatisaclosedloopcontrolsystem?Givetwoexamples.Explainthefunctionoftripvalve?Whatrulesaretobefollowedwhiledecidingthenumberofbusbarlinesandgroupselectorswitchesincascading?Differentiatebetweenthemotionandcontroldiagram.Explaintheimportanceofthepositionstepdiagram.Listtheadvantagesofcascadingoverintuitivemethod.

15.

16.

17.

A pneumatic circuit is to be designed for the following sequence:Campingajobandmaintainingitspositionwhileclamping.

Movingthetoolformachining.Returningthetool.Unclampingthejob.

Sketchthemovementdiagramandexplainthecompletecircuit.DesignapneumaticvalvecircuittogivethesequenceA-followedbyB+andthensimultaneouslyfollowedbyA-andB-.If themovement diagram for a 2 cylinder (A&B) pneumatic system isgiveninfigure,drawthepneumaticcircuitdiagramforthesame.

CHAPTER10

FLUIDICS

INTRODUCTIONFluidics,abranchofengineeringandtechnology,isconcernedwiththe

development of equivalents of various electronic circuits usingmovementsoffluidratherthanmovementsofelectriccharge.Thebasicdevicesusedinfluidics are specially designed valves that can be arranged to act asamplifiers and logic circuits. The principal advantage of fluidic systems isthat they can be designed to tolerate conditions under which electronicsystems could not possibly operate. For example, a fluidic system couldoperate in the exhaust of a rocket, using the exhaust as its working fluid.Fluidic systems are also advantageouswhere the system output is to be aflowoffluid,asinanautomobilecarburetor.

BOOLEANALGEBRABoolean algebra is a mathematical system for formulating logical

statements with symbols so that problems can be solved in a manner toordinary algebra. In short, Boolean algebra is the mathematics of digitalsystems.

ThemostobviouswaytosimplifyBooleanexpressionsistomanipulatethem in the samewaynormal algebraic expressions aremanipulated.Withregards to logic relations in digital forms, a set of rules for symbolicmanipulation is needed in order to solve for the unknowns.A set of rulesformulated by the Englishmathematician,GeorgeBoole, describes certainpropositionswhose outcomewould be either true or false.With regard to

1.

(a)

(b)

2.

(a)

(b)

3.

(a)

(b)

4.

(a)

digital logic, these rules are used to describe circuits whose state can beeither, 1 (true) or 0 (false). The basic rules for Boolean addition andmultiplicationareshownbelow:

AdditionRules MultiplicationRules 0+0=0 0.0=0 0+0=1 0.1=0 1+0=1 1.0=0 1+1=1 1.1=1

LAWSOFBOOLEANALGEBRAJust like in regular algebra, Boolean algebra has postulates and

identities.These lawscanbeused toreduceexpressionsorputexpressionsinto a more desirable form. Using just the basic postulates such asCommutative laws,Distributive laws, IdentityandInverse laws,everythingelse can be derived.Note that every law has two expressions, (a) and (b).Someofthebasiclawsare:

CommutativeLaw

A+B=B+A

A·B=B·A

DistributiveLaw

A·(B+C)=A·B+A.C

A+(B·C)=(A+B)·(A+C)

IdentityLaw

A+0=A

A·1=A

InverseLaw

Ā+A=1

(b)

5.

(a)

(b)

6.

(a)

(b)

7.

(a)(b)

Ā·A=0

Otheridentitiescanbederivedfromthebasicpostulatessuchas:

LawsofOnesandZeros

A+1=1LawofOnes

A·0=0LawofZeros

AssociativeLaws

A+(B+C)=(A+B)+C

A·(B·C)=(A·B)·C

Demorgan’sTheorem

TRUTHTABLEThe truth table is a type of mathematical table used in logic to

determinewhetheranexpressionis trueorvalid.Truthtablesaremeansofrepresenting the results of a logic function using a table. They areconstructedbydefiningallpossiblecombinationsoftheinputstoafunction,andthencalculatingtheoutputforeachcombinationinturn.Truthtablesarewidelyusedbecauseofthefollowingreasons:Theyarerelativelyeasyto

understand,as theydonot involveanyformulas,yetcanpreciselydescribetheresultofanyBooleanformula.

In the abbreviated form, they are succinct descriptions ofBooleanoperations,andarewidelyusedinthedatasheetsofelectroniclogicdevicesforthisreason.Difficult operations, such as simplifyingBoolean expressions, canreadily be performed by manipulating truth tables, and theabbreviation technique given here is a large part of suchsimplification.Theycanbeusedtodefinealogicalformula,withoutthatformulabeingknown,andtheformulacanthenbedeterminedfromthetruth

1.

table.

ConstructionofaTruthTable

EveryBoolean function can be specified as a table. Suppose that thefunctionhasnarguments,andthenaseachhastwopossiblevalues,thereareonly2npossibleargumentcombinations,whichcanbelistedinfull.Foreachlistentry,thefunctionvaluecanthenbeadded,formingthetruthtableofthefunction. The truth table is a complete and unambiguous definition of thefunction,becauseitgivesthefunctionvalueineverypossiblecase.Itshowstheoutputstatesforeverypossiblecombinationofinputstates.Thesymbols0(false)and1(true)areusuallyusedintruthtables.

LOGICGATESA logic gate is a device (whether it is electrical, electronic, or

mechanical is irrelevant),whichhas inputsandoutputs.The logicstatesoftheinputsdeterminethelogicstatesoftheoutputs.Thewayinwhichthisisdonecanbe(completely)describedusingtruthtables.Allthelogicdeviceswill takeinputsandproduceoutputs,whichareeitherONorOFF.Alogicgate is an elementary building block of a digital circuit.Most logic gateshavetwoinputsandoneoutput.Atanygivenmoment,everyterminalisinoneofthetwobinaryconditionslow(0)orhigh(1),representedbydifferentvoltage levels. There are seven basic logic gates: AND, OR, XOR, NOT,NAND,NOR,andXNOR.

TheANDgateissonamedbecause,if0iscalled“false”and1iscalled“true,”thegateacts inthesamewayasthelogical“and”operator.Thefollowing illustration and table show the circuit symbol and logiccombinationsforanANDgate.(Inthesymbol,theinputterminalsareattheleftandtheoutputterminalisattheright.)Theoutputis“true”whenbothinputsare“true.”Otherwise,theoutputis“false.”

Input1 Input2 Output

0 0 0

2.

3.

0 0 0

0 1 0 1 0 0 1 1 1

TheORgategetsitsnamefromthefactthatitbehavesafterthefashionofthelogicalinclusive“or.”Theoutputis“true”ifeitherorbothoftheinputsare“true.”Ifbothinputsare“false,”thentheoutputis“false.”

Input1 Input2 Output 0 0 0 0 1 1 1 0 1 1 1 1

The XOR (exclusive-OR) gate acts in the same way as the logical“either/or.”Theoutputis“true”ifeither,butnotboth,oftheinputsare“true.”Theoutputis“false”ifbothinputsare“false”orifbothinputsare“true.”Anotherwayoflookingatthiscircuitistoobservethattheoutputis1iftheinputsaredifferent,but0iftheinputsarethesame.

Input1 Input2 Output 0 0 0 0 1 1 1 0 1 1 1 0

4.

5.

6.

Alogicalinverter,sometimescalledaNOTgate todifferentiateitfromothertypesofelectronicinverterdevices,hasonlyoneinput.Itreversesthelogicstate.

Input Output 1 0 0 1

TheNANDgate operates as anANDgate followed by aNOTgate. Itacts in themannerof the logicaloperation“and”followedbynegation.Theoutput is “false” ifboth inputs are “true.”Otherwise, theoutput is“true.”

Input1 Input2 Output 0 0 1 0 1 1 1 0 1 1 1 0

TheNOR gate is a combination OR gate followed by an inverter. Itsoutput is “true” if both inputs are “false.” Otherwise, the output is“false.”

Input1 Input2 Output

0 0 1

7.

0 0 1

0 1 0 1 0 0 1 1 0

TheXNOR(exclusive-NOR)gateisacombinationXORgatefollowedbyaninverter.Itsoutputis“true”if theinputsarethesame,and“false”iftheinputsaredifferent.

Input1 Input2 Output 0 0 1 0 1 0 1 0 0 1 1 1

ORIGINANDDEVELOPMENTOFFLUIDICSFluidics (also known as Fluidic Logic) is the use of a fluid or

compressiblemediumtoperformanalogordigitaloperationssimilartothoseperformedwithelectronics.Thephysicalbasisoffluidicsispneumaticsandhydraulics,basedonthetheoreticalfoundationoffluiddynamics.Thetermfluidicsisnormallyusedwhenthedeviceshavenomovingparts,soordinaryhydrauliccomponents suchashydrauliccylindersand spoolvalvesarenotreferredtoasfluidicdevices.

Fluidicstechnologieshavegrowntosuchanextentthatfluidsarebeingusedforcalculationanddatatransferpurposes.Butinthepreviousphasesofdevelopment of fluidics, the electronics systems were predominant in thefieldof control engineering.Thebasicdevelopment in the fieldof fluidicsstartedtakingplacefrom1904,whenL.PrandtlaGermanaircraftengineersuggested the solution for a problem of flow separation in diffuser.According to him, by applying suction to the boundary layer, the flow

separation can be prevented by applying suction to boundary layer on thediffuser.PrandtlhimselfdevisedthefirstNOTgate.Furtherin1916,NicolaTeslahasclaimedtobetheinventoroffirstfluidicdiode.Hehasdevisedavalvularconduit.Thepatentwasgrantedin1980.Thistubehasmovingpartsbut the tube offers resistance to the motion of fluid in one direction andallowsthefreeflowintheouterdirection.

Then,in1938HenriCoanda,aRussianengineerdiscoveredthetheoryof ‘wall attachment,’ Coanda’s theory of wall attachment was a majorstepping-stoneinthedevelopmentofthisfield.Later,thiseffectwasusedforthe development of fluidic logic components. Further in 1962, RayAugerdiscoveredafluidiclogicelementcalledturbulenceamplifier.

Developmentsinthepreviousyearhaveledtosignificantgrowthinthisparticular field. Fluid logic elements have gained popularity over last fewyears as they replaced electronic equipments in the tolerant workingenvironment.

COANDA’SEFFECTThe Coanda Effect was discovered in 1930 by the Romanian

aerodynamicistHenriMarieCoanda(1885–1972). It states that theCoandaEffectisthephenomenainwhichajetflowattachesitselftoanearbysurfaceandremainsattachedevenwhenthesurfacecurvesawayfromtheinitialjetdirection.Heobservedthatasteamofair(orfluid)emergingfromanozzletends to follow a nearby curved surface, if the curvature of the surface oranglethesurfacemakeswiththestreamisnottoosharp.

Itiseasilydemonstratedbyholdingthebackofaspoonverticallyundera thin streamofwater froma faucet. If oneholds the spoon so that it canswing, onewill feel it being pulled towards the stream ofwater (Refer toFigure10.1).Theeffecthaslimits: ifoneusesasphereinsteadofaspoon,one will find that the water will only follow a part of the way around.Further,ifthesurfaceistoosharplycurved,thewaterwillnotfollowbutwilljustbendabitandbreakawayfromthesurface.

FIGURE10.1

PrincipleofCoanda’sEffectCoanda effect or wall-attachment effect, is the tendency of amoving

fluid,eitherliquidorgas,toattachitselftoasurfaceandflowalongit.Asafluid moves across a surface, a certain amount of friction (called “skinfriction”)occursbetweenthefluidandthesurface,whichtendstoslowthemovingfluid.Thisresistancetotheflowofthefluidpullsthefluidtowardsthesurface,causingittosticktothesurface.Thus,afluidemergingfromanozzletendstofollowanearbycurvedsurfaceeventothepointofbendingaroundcornersifthecurvatureofthesurfaceortheanglethesurfacemakeswith the stream is not too sharp. This phenomenon has many practicalapplications in fluidics and aerodynamics. It has important applications invarioushigh-liftdevicesonaircraft,whereairmovingoverthewingcanbe“bentdown”towardsthegroundusingflaps.

Coanda’sExperimentsCoanda’s experiments (Refer to Figure 10.2) showed that a sheet of

fluiddischargedthroughaslitontoanextendedandroundedlipwouldattachitself to the curved surface and follow its contour. He discovered that ashouldermadeofaseriesofshortflatsurfaces,eachataspecifiedangletotheonebeforeandeachwithacertainlengthwouldmakeitpossibletobenda jet stream around an 180° arc. Further, he found that the deflected air-streamsuckedupairfromthesurroundings.Hefoundthatasthejetflowedaroundtheshoulder,itentraineduptotwentytimestheamountofairintheoriginaljet.

FIGURE10.2Coanda’sExperiment.

TESLA’SVALVULARCONDUITTeslaclaimed that thevalvularconduit (Refer toFigure10.3)devised

byhimcomposedofaclosedpassagehavingrecessesinitswallssoformedas topermita fluid topass freely from it in thedirectionof flowbut fluidwillbesubjectedtoarapidreversalofdirectionwhenenteredfromanotheroroppositedirection,therebyinterposingfrictionandmassresistance.

Thisdeviceresemblesthetoday’scheckvalvebutthiskindofconduithasnomovingparts.This iswhyTesla’s tubehasbeengiven thenameoffluiddiodeof1916.

FIGURE10.3Tesla’sValvularConduit.

FLUIDICDEVICESFluidiccomponentsarethesimplecomponentsdevisedonthebasisof

somewell-knownprinciplesandphenomenon.Fluidicdevicesaresimpleto

design, repair, and use, and one can intend them as a substitute forelectronics for their use in fluid control systems. Fluidic devices can be

classified as: Digital fluidic devices Analog fluidic devices Digitalfluidic devices are those which has two outputs. There will be flow fromeitheroneoutputortheotheroutput.Theflowneversplitsintwooutputs.Indigital fluidic devices, there is no question ofmore output or less output,they justgive signal in the formof “Output”or “Nooutput.”Examplesofsuchdevicesarebi-stableflipflops,logic,etc.

Analogfluidicdevicesarethose,whichcanvarytheoutputfromlowtohigh.Heretheoutputwillincreaseordecreaseasafunctionofcontrolinput.Examples of such devices are fluidic position sensors, fluidic vortexamplifier,wall-attachmentamplifier,fluidicoscillator,etc.

Fluidicdevicescanbefurtherdividedintothreecategories:

FluidiclogicdevicesFluidicsensorsFluidicamplifiers

FLUIDICLOGICDEVICESGenerally, all fluidic devices are based on Coanda’s theory of wall

attachment. This phenomenon has already been explained earlier in thischapter.Basedonthetheories,afewsimpledeviceshavebeenpatentedbyvarious agencies in last few decades.Most popular amongst these are bi-stable flip-flop, AND gate, OR-NOR gate, etc. Some of these importantfluidiclogicdevicesareexplainedinthefollowingtext.

Bi-stableFlipFlopBi-stable flip flop is a most common fluidic logic element (Refer to

Figure 10.4). It works on the principle of Coanda effect. Its generalconfigurationconsistsoffiveportsoutofwhichoneisthesupplyport;twocontroljetportsandtwooutputports.Supplyisalwayspresentontheinputport whereas output is dependent on the control jets, i.e., when fluid ispassedfromcontroljetC1therewillbeanoutputatO1and,similarly,whenthereissupplyatcontroljetC2theoutputwillbeatO2.

It is also important to know here the difference betweenmono-stableandbi-stable.

FIGURE10.4Bi-stableFlipFlop.

DifferencebetweenMono-stableandBi-stableElements

Mono-stable means when the device has one stable state, i.e., in theabsence of signal it will always remain in that particular state only. Thesecondstatecanonlybeachieved in thepresenceofanapplied signal, forexample, a3/2manuallyoperated spring returnDCvalve is amono-stabledevice.

Ontheotherhand,bi-stablemeansadeviceisstableinanyonepositionout of its two possible positions; whether the signal is applied or not, forexample,a4/2pilotoperatedDCvalveisabi-stabledevice.

Inthisway,byusingthetwocontroljetsalternatively,thisfluidiclogicelement can be used to performmemory functions. The output from a bi-stableflip-flopcanbeusedasapilotsignalforactuatingvariousvalveswithalowpressureactuatingelement.

FluidicANDGateFigure 10.5 shows a fluidicANDgate. SupplyA and supplyB show

inputports fromwherefluid isentered.Further, there isoneoutputventYandtwodrainventsnamed1and2.If thefluidstreamispresent insupplyportAandabsentinsupplyportB,thefluidisdrainedoutfromdrainvent2.Similarly,ifthefluidstreamispresentinsupplyportBbutabsentinsupply

portA, fluid is drained through drain vent 1. Thismeans therewill be nooutputorzerooutputintheabovetwocases.

TheonlyconditionfortheoutputatYisthepresenceoffluidstreamsofequal strength at the two supply ports. Operation of this fluid logiccomponentalsodependsonCoanda’swall-attachmenttheory.

FIGURE10.5FluidicANDGate.

FluidicOR-NORGateFigure10.6showsafluidicOR-NORgate.Thisfluidicdeviceconsists

of supply portA fromwhich fluid is supplied all the time. There are twocontrol ports, ‘a’ and ‘b’ and two output ports, Y and Y1. Y outputrepresents the OR gate and Y1 output represents the NOR gate. In theabsenceofboththecontroljets‘a’and‘b,’supplyAispassedoutthroughthe gate via outputY1. It implies thatwhen there is no input (‘a’ or ‘b’),thereisanoutput.ThisisthelogiccharacteristicoftheNORgateandY1isconsidered as a NOR output. On the other hand, when a fluid stream ispresentateithercontroljet‘a’or‘b’oratboth‘a’and‘b,’therewillbeanoutputatY.Itimpliesthatevenwithoneinputthereisanoutput.ThisisthelogiccharacteristicoftheORgateandYoutputisconsideredanORoutput.ThiscompletedeviceiscalledanOR-NORfluidicgate.

FLUIDICSENSORSFluidicsensorsareprimarilyusedfordetectingthepresenceofobjects.

These sensors are designed to provide a signal in the form of fluid jet toannounce the presence of an object. Fluidic sensors are generally of verysmall size. This is to reduce the air consumption. Similarly, their otherdesign aspects like the diameter of nozzles producing jets and the size ofinlet. Outlet orifices are also important from the view of minimizing air

consumption.Theoutputoffluidicsensorscanbedirectlyusedasacontrolsignal for pneumatic logic circuits. But fluidic control signals requireamplification when used in such pneumatic and hydraulic devices. A fewimportantfluidicsensorsareexplainedinthefollowingtext.

FIGURE10.6FluidicOR-NorGate.

ConeJetSensorFigure10.7showsaconejetsensor.Aconejetsensorisusedtosense

thepositionsof anobject evenwhen theobject isplacedat a considerabledistance from it.A cone jet sensor has two supplynozzles connectedwithsupplyport‘A’and‘B,’respectively,fromwhichfluidisprojectedontotheobjecttobelocatedandbetweenthetwonozzlesthereiscylindricalpassage.Thiscylindricalpassageisconnectedwithoutputorifice.Fluid,whichcomesbackafterhittingtheobject,isdirectedtothecylindricalpassageandfurther,passedfromoutputorifice‘Y.’Whentheobjectisatsomedistancefromthecone jet sensor, there is low pressure output at ‘Y,’ whereas if the objectcomescloser to thecone jetsensor, thehighpressureoutput isobservedatoutputorifice‘Y.’Thus,outputpressureisindicativeofthecurrentpositionoftheobject.

FIGURE10.7ConeJetSensor.

InterruptibleJetSensorTheprincipleofinterruptiblejetsensoristhesameasdiscussedabove

for thecone jetsensor.Figure10.8showsan interruptible jetsensor.Low-pressureairflowinginlaminarmodeissuppliedfromthenozzle.Theairhastopassacrossagapbetweentheissuingnozzleandthecollector.Thejetofair passes uninterrupted if the object does not obstruct the path. Aninterruptible jet sensor consists of a nozzle and a collector. There is aconsiderable gap between both. From the nozzle, fluid is supplied and isdirectedtothecollector.IfthepathbetweenAandYisnotblockedbytheobject or component, then the laminar flow remains continuous and thestreamofairissuingfromthenozzleprovidesasignaltothecollectorintheformofoutputY.Ontheotherhand,iftheobjectblocksthesupplyairjetA,then the flowwillbecome turbulent andoutputYwill bevery small.This

decreased output can be sufficiently used to actuate a gate, which isincorporatedinthedevice.

FIGURE10.8InterruptibleJetSensor.

BackPressureSensorAbackpressuresensor,asthenameimplies,worksontheprincipleof

back pressure. The supply of fluid is provided from supply orifice ‘A.’Figure10.9showstheworkingofabackpressuresensor.

When theobjectwhoseposition is tobe locatedat someconsiderabledistance from the back pressure sensor, air escapes out on the other sidefollowingthesamestraighthorizontalpath.Asaresult,thereishighoutputat outlet orificeY and low output at output orificeX.On the other hand,whentheobjectisbroughtclosertooutputportYofbackpressuresensor,insuch away that objects block thepassageof fluid to pass from theoutputorifice.ThentheflowofairwillbedirectedtooutputorificeX.Asaresult,therewillbenooutputatYandhighoutputatX.Thissensorisusedtofindthe locationofobjectswhen thedistancebetween thebackpressuresensorandobjectisnottoolarge.

FIGURE10.9BackPressureSensor.

FLUIDICAMPLIFIERFluidicamplifiersaredeviceswhichhavenomovingpartsanduseagas

or liquid as the working medium. A high energy stream of fluid isacceleratedinanozzleintheamplifiertocreateapowerjet.Lowerenergycontroljetsaresuppliedtransversetothepowerjetflowtoproduceachangein direction of the power jet and a corresponding change of the flow invariousoutput ports in thedevice.Hence, an amplificationof the signal isobtained. This amplification process is similar to that occurring in anelectronictube.Afewofthemareexplainedbelow.

VortexAmplifierAvortexamplifierisafluidicdeviceusedtoregulatetheflowoffluid

by utilizing properties of a vortex. A vortex amplifier consists of acylindrical, disc-like container, which is divided by cylindrical porouselementsintotwochambers,namely,anouterchamberandavortexchamberasshowninFigure10.10.

Supply port A is provided for the inlet of fluid in a cylindrical disc.Fluidentersalongtheouterperipheryoftheporouselementfromthesupplyport. There is a control jet, which is provided to generate a vortex in thevortex chamber. Several control jets along the circumference can beprovided depending upon capacity, which throws streams of fluid intangential direction and generate the vortexmotion in fluid.At the center,thereisanoutputportYfromwherethesignalistransmitted.

In order to understand theworking of the vortex amplifier, onemustknow what the possible outputs of this device are. This fluidic deviceprovideseitheran‘amplifiedsignal’or‘nosignal’asanoutput.Thesetwoconditionsofthevortexamplifierareexplainedbelow:

FIGURE10.10VortexAmplifier.

Case1:Amplifiedsignal

Fluid is entered from the supplyport inside thecylindricaldisc.Fluidpassesfromtheporouselementandmovestowardstheoutputportundertheeffectofgravity.Themoment fluidenters thevortexchamber, it comes incontactwithcontroljet‘a.’Duetopressureanddirection,thesecontroljetsarealreadymovingwiththevortexmotion.Now,thefluidfromsupplyport‘A’ follows this tangential component and approaches the output port.Becauseofthis,someangularvelocityisimpartedtoitasitleavesthevortexchamber.Thereasonbehindtheincreaseinangularvelocityisbecauseofthedrop inpressure and the increase invelocityof the fluiddue to thevortexmotion. In order to conserve angularmomentum, angular velocity of fluidmust increaseas it approaches theoutputport.Similarly, radialvelocityofthe fluid also increases while flowing upwards to downwards or from thesupply port to the output port, respectively. Thus, there are two kinds ofsignalamplificationsinavortexamplifier,i.e.,(1)riseinradialvelocity,(2)riseinangularvelocity.Inthewayexplainedabove,theamplifiedsignalistransmittedfromtheoutputport.

Case2:Nosignal

The second condition of ‘no signal’ can be attained by regulating thesupplyatsupplyportA.Withthis,centrifugaleffectsinthevortexchamberbecomesprominentduetocentrifugalforce.Ahigh-pressureregionisbuiltup and the supply at output port Y is almost stopped. In fact, due to thispressurerise,flowtosupplyportAisslightlyreversed.However,theremaystillbesomeflowatoutletportY.Itissolelyduetotheflowofcontroljets.Itisimportanttonoteherethatforcertainsupply,pressureatleastequivalentto a control jet is required. Control pressure should not be less than thesupplypressureinanycase.

TurbulenceAmplifierA turbulence amplifier is a logic device based on fluid dynamic

phenomenon, which was described by Lord Rayleigh in 19th century.According toRayleigh,a jetof fluid flowingwithaReynoldsnumber lessthan 1500 in laminar mode becomes turbulent when interrupted by atransverse control jet.Refer toFigure 10.11.Typical turbulence amplifiersthatareusedinindustryconsistofathinsupplyandoutputtubeshaving15–20mm gap between them. Supply/output tubes are housed in anothercylindrical pipe perfectly closed at ends, having a base size equal tomore

than 25 times the supply/output tubes. Control jets and drain vent areprovidedinthisouterpipe.

Thesupplyoffluidfromthesupplytubeisdirectedtotheoutputtube,intheabsenceofcontroljets.Thefluidwillbecollectedbyanoutputtube.However,ifanyoneofthecontroljetsisactiveatthattime,thelaminarflowbecomes turbulent and therewill be no fluid in the outlet pipe. In normalarrangements, 4–6 control jets can be used in one turbulence amplifier.However,itisimportanttonotethatanyoneofthecontroljetscanturntheamplifier‘OFF.’

Thepowerrequiredtoturnofftheamplifierismuchlessthanthepowerinoutputline.Itworksonlowoperatingpressure.Thepressureintheoutputtube is approximately 10 cm of water, to turn off the signal pressure isapproximately1cmofwater,andthesupplypressureisoftheorderaround25 cm of water. The time needed to turn ON and OFF the turbulenceamplifieris2–3millisecondsand5–7milliseconds,respectively.Turbulenceamplifiers are based on laminar/turbulent flows as well as concept of jetdestruction, so they are also called laminar-turbulent flow devices or jetdestructiondevices.

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FIGURE10.11TurbulenceAmplifier.

ADVANTAGESANDDISADVANTAGESOFFLUIDICS

Advantages

Fluidic devices are reliable: Fluidic devices have no moving parts.These are robust systems, i.e. , they have practically no effect ofelectromagneticandnuclearradiation.Thesesystemsarepreferredoverelectronicdeviceswherethereisaquestionofhightemperatureservice.These systemsarehowever sensitive todirtof fluidmedium.Butonecaneasilycopeusinggoodqualityfiltersforairorliquidspriortotheirentry.Fluidicdevicesarenoisefree:Practically,therearenomovingpartsinfluidicdevices,sotheydonotproduceanynoise.Fluidicdevicesarecompact:Fluidicdevicesarecompactincomparisonwith pneumatic, hydraulic, electro pneumatic devices. But this

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statement is not correct in context with microelectronics becauseelectronic gates and other components are still several times morecompactthanfluidicsystems.Fluidicdevicesaresimpleindesign:Fluidicdevicesarebasedonfewbasic operating principles. These principles are easy to understand.Oncetheseareunderstooditiseasyforanindividualtodesign,modify,and repair these fluidicdevices.Nospecializedknowledge is requiredforthispurpose.Fluidic devices are hazard free: These devices are preferred inhazardousareaswhereelectroniccomponentsfailtoperform.

DisadvantagesLimiteddevelopmentofthefield:Asdiscussedearlier,fluidicsisbasedonafewsimpleprinciples,whicharescientificallyapproved,butsomephenomenon, for example, the Coanda effect is still not clearlyunderstood.Fluidic devices have slow speeds and low power outputs: Fluidicdevicesgenerallyuseairasamediumandoperateonpressurelessthan0.1 bar because the use of such a low pressure, fluidic devices sufferfromrelativelyslowspeedsandlowpoweroutput.Actuationofpower-operatedequipmentisnotdirectlypossible;somemodeofamplificationis required. Further, these kind of additional components increase theoverallexpenseofafluidicsystem.Fluidic devices are not suitable for incompressible fluids: At low-pressureoperation,incompressibleliquidslikeoilsarenoteconomical.Theiruseislimitedinafluidicsystem.Complex fluidic systems are impracticable: Because of size and costlimitations, a maximum 1,000 logic functions in one system is anextreme limit for a fluidic system.A fluidicmicrocomputer is neitherpracticablenordesirable.Anotherreasonbehindthisstatementisspeed.Simple fluidic systems are comparatively slower, further whencomplexityisaddedtothefluidicsystemitbecomestooslow.Fluidic devices are not suitable for intermittent operation controlsystems: In control systems where operation is intermittent and cycletime is long, fluidic devices are not desirable because of continuouspowerconsumption.

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Fluidicdevicesareinefficient:Thepowerofcontrollingmedium(e.g.,air) is generally lost by traveling long distances in transmission lines.Further,fluidicdeviceswhichworkontheprincipleofwallattachmentrecover about 15% of the power passing through them and a vortexamplifierrecoversasmuchas40%ofsuppliedpower.Afluidicsignalover long distances presents problems both in phase shift and signaldegradation.

EXERCISESIdentifythevariouslawsofBooleanalgebra.Identify three logic elements of Boolean algebra. How are theyexpressed?Explain the construction, working, and performance characteristics offluidicelements.ExplainNANDgateandNORgate.Usingatruthtable,showthatCompletetheBooleanexpression.WhatistheCoandaeffect?Describewithadiagram.Whatisatruthtable?Write the truth table forORgateanddraw thesymbol for representingORgate.DrawthediagramforNORgateandbi-stableflip-flop.Also,statetheirworkingalongwithconstructionaldetails.Definefluidicbi-stableswitch.ExplainthefluidicNORgatewithasketch.Describetheworkingofanyfluidicdevice.Explain the working of a fluidic diode and prepare a truth table for afluidicbi-stableswitch.Sketchanyfluidicdeviceandexplainitsoperation.Stateitsapplications.Whataretheadvantagesanddisadvantagesoffluidics?Howcanfluidicdevicesbeclassified?

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Whatarefluidicsensors?Explaintheworkingofanyonesensorwiththehelpofsketch.Isthereanysimilaritybetweenfluidicsandelectronics?Discuss the construction and working of the following fluidiccomponent:(i)OR/NOR.(ii)Proximitydetector(anyonetype).What are the major advantages of fluidic systems over traditionalsystems?Differentiatebetweenanaloganddigitaldevices.Howareconejetandbackpressuresensorsdifferentfrominterruptiblejetsensors?WritethetruthtableforANDgateanddrawthesymbolforthesame.

CHAPTER11

ELECTRICALANDELECTRONICCONTROLS

INTRODUCTIONTOSENSORSANDTRANSDUCERS

A transducercanbedefinedasadevicecapableofconvertingenergyfromone form intoanother.Transducerscanbe foundbothat the inputaswell as at the output stage of ameasuring system.The input transducer iscalled the sensor, because it senses the desired physical quantity andconverts it into another energy form. The output transducer is called theactuator, because it converts the energy into a form to which anotherindependentsystemcanreact,whetheritisabiologicalsystemoratechnicalsystem.So,forabiologicalsystem,theactuatorcanbeanumericaldisplayoraloudspeakertowhichthevisualorauralsensesreactrespectively.Foratechnicalsystem,theactuatorcouldbearecorderoralaser,producingholesinaceramicmaterial.Humanscaninterprettheresults.

Asensorisadevicethatproducesasignalforpurposesofdetectingormeasuringaproperty,suchasposition,force,torque,pressure,temperature,humidity,speed,vibration,etc.Sensortechnologyhasbecomeanimportantcomponent of manufacturing processes and systems, because they convertonequantitytoanother.Sensorsarealsoreferredastransducers.Asensorisa physical device or biological organ that detects, or senses, a signal orphysical condition and chemical compounds. Sensors are devices thatprovide an interface between electronic equipment and the physicalworld.Oftentheactiveelementofasensorisreferredtoasatransducer.

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SENSORTERMINOLOGY

Sensitivity:Sensitivityofasensorisdefinedasthechangeinoutputofthe sensor per unit change in the parameter being measured. Thefactormaybeconstantovertherangeofthesensor(linear),oritmayvary(nonlinear).

Range:Everysensorisdesignedtoworkoveraspecifiedrange.Thedesignrangesareusuallyfixed,and,ifexceeded,resultinpermanentdamagetoordestructionofasensor.Rangeisthedifferencebetweenmaximumandminimumvaluesof theappliedparameter thatcanbemeasured.

Precision: Precision is the degree of reproducibility of themeasurements.

Resolution:Resolution is defined as the smallest change that canbedetected by a sensor. In other words, it is the response of themeasuringinstrumentforsmallvariationsintheinputparameter.

Accuracy: A very important characteristic of a sensor is accuracy,which reallymeans inaccuracy. Inaccuracy ismeasuredasa ratioofthehighestdeviationofavaluerepresentedbythesensortotheidealvalue.Itmayberepresentedintermsofmeasuredvalue.

Hysteresis:Hysteresisisthedifferenceinresponseforincreasinganddecreasingvaluesoftheappliedparameter.

Responsetime:Thetimetakenbyasensortoapproachitstrueoutputwhensubjectedtoastepinputissometimesreferredtoasitsresponsetime.

Offset:Offsetisthesensoroutputthatexistswhenitshouldbezero.

Linearityerror: It isdefinedasanexpressionof theextent towhichthemeasuredcurvedepartsfromtheidealtheoreticalcurve.

Span:Spanisdefinedastherangeofmeasuredvariableforwhichaninstrumentisdesignedtomeasurewithfulllinearity.

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Calibration: It isdefinedas thecomparisonofspecificvaluesof theinput and output of an instrument with the corresponding referencestandardvalues.

SELECTIONOFATRANSDUCERThe following factors should be kept in mind while selecting a

transducer.Thetransducershould:

Recognizeandsensethedesiredinputsignalandshouldbesensitivetoothersignals.Havegoodaccuracy.Havegoodprecision.Haveamplitudelinearity.Have environmental compatibility, i.e., corrosive fluids, pressure,shocks,size,etc.

CLASSIFICATIONOFSENSORSSensorscanbeclassifiedaccordingtothetypeofenergytheydetect:Thermal energy. For measuring temperature, flux, conductivity, andspecificheat.

Temperaturesensors:thermometers,thermocouples,thermistorsHeatsensors:calorimeter

Electromagnetic sensors. For measuring voltage, current, charge,magneticfield,flux,andpermeability.

Electricalresistancesensors:ohmmeter,multimeterElectricalcurrentsensors:galvanometer,ammeterElectricalvoltagesensors:voltmeterElectricalpowersensors:watt-hourmetersMagnetism sensors:magnetic compass,magnetometer, Hall effectdevice

Mechanical sensors.Formeasuringquantities suchasposition, shape,velocity,force,torque,pressure,strain,andmass.

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Pressure sensors: barometer, barograph, pressure gauge, air speedindicator.Gas and liquid flow sensors: flow sensor, flowmeter, gasmeter,watermeter.Straingauge

ChemicalsensorsIon-selectiveelectrodes,pHglasselectrodes.

OpticalandradiationsensorsBubblechamber,dosimeter.Photocells,photodiodes,phototransistors,photoelectrictubes.

AcousticsensorsSoundsensors:microphones,hydrophones,seismometers.

CLASSIFICATIONOFTRANSDUCERSTransducerscanbeclassifiedindifferentways:

Self-generating and non–self-generating transducers. Self-generatingtransducersarethosewhichproducetheirownelectricalsignal (either current or voltage). For example, thermocouple,thermopile, moving coil generator, piezoelectric pick up,photovoltaiccell,etc.

Non–self-generatingtypetransducersarethosewhicharenotcapableofgenerating theirownsignals.Thesewillnotproduceanelectrical signaloftheir own but show some variations of resistance, capacitance, andinductance. For example, thermistor, linear variable differential transducer,capacitivepickup,straingauge,resistancetemperaturedetector,etc.

Inputandoutputtransducers.Inputtransducersarethosethathaveelectronic output and another form of energy as input, i.e., inputtransducersconvertaquantitytoanelectricalsignal(voltage)ortoresistance (which can be converted to voltage). Examples: Lightdependent resistor (LDR) converts brightness (of light) toresistance, thermistor converts temperature to resistance,

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microphone converts sound to voltage, variable resistor convertsposition(angle)toresistance,etc.

Outputtransducersarethosethathaveelectronicinputandanotherformof energy for output. Examples: lamp converts electricity to light, LEDconvertselectricitytolight,loudspeakerconvertselectricitytosound,motorconvertselectricitytomotion,heaterconvertselectricitytoheat,etc.

Analog and digital transducers. Analog transducer converts inputsignal into output signal, which is a continuous function of timesuchasthermistor,straingauge,thermocouple,LVDT,etc.

Adigital transducerconverts the input signal into theoutput signaloftheformofpulsethatgivesdiscreteoutput.

Transducersarealsoclassifiedas:

Temperaturetransducers,flowtransducers,magnetictransducers,etc.Forceandpressuretransducers.Displacementtransducers.

TEMPERATURESENSORSThe measurement of temperature is important in many industrial

applications. These applications require temperature sensors of differentphysicalconstructionandoften-differenttechnology.Severalfactorsmustbeconsidered when selecting the type of sensor to be used in a specificapplication: temperature range, accuracy, response time, stability, linearity,and sensitivity. The commonly used sensors for temperaturemeasurementare:

ResistanceTemperatureDetector(RTD)ThermocoupleThermistorFiberOpticTemperatureSensors

ResistanceTemperatureDetector(RTD)

A resistance temperature detector (RTD) is a temperature sensor thatsensestemperaturebymeansofchangesinthemagnitudeofcurrentthrough,or voltage across an element whose electrical resistance varies withtemperature. These types of sensors provide a change in resistanceproportional to a change in temperature. Resistance temperature detectorshavebeenusedformakingaccuratetemperaturemeasurements.Theyutilizearesistanceelementwhoseresistancechangeswiththeambienttemperatureinapreciseandknownmanner.Theresistancetemperaturedetectormaybeconnectedinabridgecircuit,whichdrivesadisplay,calibratedtoshowthetemperatureoftheresistanceelement.Mostmetalsbecomemoreresistanttothepassageofanelectricalcurrentasthemetalincreasesintemperature.Theincrease in resistance is generally proportional to the rise in temperature.Thus, a constant current passed through a metal of varying resistanceproduces a variation in voltage that is proportional to the temperaturechange.

ThebasicconstructionofanRTDisquitesimple.Itconsistsofalengthoffine-coiledwirewrappedaroundaceramicorglasscore.Theelementisusuallyquitefragile,soitisoftenplacedinsideasheathedprobetoprotectit.(RefertoFigure11.1.)

FIGURE11.1ResistanceTemperatureDetector.

Common resistance materials for RTDs are platinum, nickel, andcopper. Platinum is the most commonly used metal for RTDs due to itsstability and nearly linear temperature. It can measure temperatures up to800°C. The resistance of the RTD changes as a function of absolutetemperature,soitiscategorizedasoneoftheabsolutetemperaturedevices.(In contrast, the thermocouple cannotmeasure absolute temperature; it canonlymeasurerelativetemperature.)

Advantages

Stableandaccurate.Morelinearthanthermocouples.

Disadvantages

Moreexpensive.Selfheating.Requiresacurrentsource.Responsetimemaynotbefastenoughforsomeapplications.

ThermocoupleWhentwodissimilarmetalconductorsareconnectedtogethertoforma

closed circuit and the two junctions are kept in different temperatures,thermal electromotive force (EMF) is generated in the circuit (Seebeck’seffect). Thermocouples make use of this so-called Peltier-Seebeck effect.Thus,whenoneend(coldjunction)iskeptconstantatacertaintemperature,normally at 0°C, and the other end (measuring junction) is exposed to anunknown temperature, the temperature at latter end can be determined bymeasurement of EMF so generated. This combination of two dissimilarmetalconductorsiscalled“thermocouple”.

Thermocouple is an active transducer,which is used tomeasure veryhightemperaturesoffurnacesinindustrialplants.Thermocoupleconsistsofapairofdissimilarmetals/wiresjoinedtogethertoformajunctionasshowninFigure 11.2.One end of the junction is the sensing end,which is to beimmersed in the medium of temperature. This is called hot junction. Theother end of the junction is called cold or reference junction, which ismaintained at a constant reference temperature. When the hot junction isbeingheatedbykeepingthesensingendofthethermocoupleinthemediumwhose temperature is to be measured, a temperature difference existsbetween the hot and reference junctions. This produces an EMF, whichcauses a current in the circuit and can be measured with the help ofvoltmeter.

FIGURE11.2Thermocouple.

AthermoelectriccircuitcontainingtwojunctionsisillustratedinFigure11.3. Two wires of metals A and B form junctions at two differenttemperaturesT1andT2,resultinginapotentialVthatcanbemeasured.

FIGURE11.3ThermoelectricCircuit.

The thermocouple voltage is directly proportional to the junctiontemperaturedifference:

V=α(T1–T2)

whereαisSeebackcoefficient.

Advantages

Selfpoweredrequiringnoexternalpowersupply.Simple,rugged,inexpensive,andcommonlyavailable.Canwithstandharshenvironments.

Disadvantages

Nonlinearandrequireacoldjunctioncompensationforlinearization.NotasaccurateasRTDsorthermistors.Lowvoltage,leaststable,andsensitive.

ThermistorLike RTD, thermistor is also a temperature sensitive resistor. A

thermistor is an electronic component that exhibits a large change inresistance with a change in body temperature. Thermistors are highlysensitive to temperature variation; hence, they are also called temperaturesensitive resistors. Thermistors are manufactured from metal oxidesemiconductor material, which is encapsulated in a glass or epoxy bead.Thermistorsalsohavealowthermalmassthatresultsinfastresponsetimes,but are limited by a small temperature range. Some of different types ofthermistorsareshowninFigure11.4.

FIGURE11.4Thermistors.

Thermistors are divided into negative temperature coefficient (NTC)and positive temperature coefficient (PTC) types. The temperaturecoefficient of a material can be defined as change in resistance of thematerial for a unit degree change in temperature. Although positivetemperature coefficients units are available,most thermistors have aNTC,i.e.,theirresistancedecreaseswithincreasingtemperature.TheNTCcanbeaslargeasseveralpercentperdegreeCelsius,allowingthethermistorcircuit

todetectminutechanges in temperature,whichcouldnotbeobservedwithanRTD,orthermocouplecircuit.

Iftherelationshipbetweenresistanceandtemperatureisassumedtobelinear,then:

where

Ifkispositive,theresistanceincreaseswithincreasingtemperature,andthedeviceiscalledaPTCthermistor,posistororsensistor.Ifkisnegative,theresistancedecreaseswithincreasingtemperature,andthedeviceiscalledaNTCthermistor.

Advantages

Inexpensive,rugged,andreliable.Respondquickly.

Disadvantages

Smallertemperaturerange.Signalisnotlinear.Self-heating.

FiberOpticTemperatureSensorsOptical-based temperature sensors provide accurate and stable remote

measurement of online temperatures in hazardous environments and inenvironments having high ambient electromagnetic fieldswithout the needforcalibrationofindividualprobesandsensors.

Opticaltemperaturesensorsystemsmeasuretemperaturesfrom-200°Cto600°Csafelyandaccuratelyeveninextremelyhazardous,corrosive,andhigh electromagnetic field environments. They are ideal for use in theseconditions because their glass-based technology is inherently immune toelectricalinterferenceandcorrosion.Becausethereisnoneedtorecalibrateindividualsensors,operatorandtechniciansafetyisgreatlyenhancedastheneedfortheirrepeatedexposuretofieldconditionsiseliminated.Probesaremade from largely nonconducting and low thermal conductance material,

resulting in high stability and low susceptibility to interference, and inincreased operator safety. Optical cables also have a much higherinformation-carrying capacity and are far less subject to interference thanelectricalconductors.

ApplicationsofTemperatureSensorsTheseinclude:

HVAC—room,duct,andrefrigerantequipmentMotors—overloadprotectionElectroniccircuits—semiconductorprotectionElectronic assemblies — thermal management, temperaturecompensationProcesscontrol—temperatureregulationAutomotive—airandoiltemperatureAppliances—heatingandcoolingtemperature

LIGHTSENSORSWhen light strikes special types of materials, a voltage may be

generated,achange inelectrical resistancemayoccur,orelectronsmaybeejected from the material surface. As long as the light is present, theconditioncontinues.Itceaseswhenthelightisturnedoff.Anyoftheaboveconditionsmaybeusedtochangetheflowofthecurrentorthevoltageinanexternalcircuitand, thus,maybeused tomonitor thepresenceof the lightand tomeasure its intensity.Someof thecommonlyused light sensors arediscussedbelow:

PhotoresistorsPhotoresistors,astheirnamesuggests,areresistorswhoseresistanceis

a function of the amount of light falling on them.Their resistance is veryhigh when no light is present and significantly lower when they areilluminated. These are also often called light-dependent resistors (LDRs)(refertoFigure11.5).Photoresistorscanbeusedaslightsensors,whichcan

enablerobotbehaviorssuchashidinginthedark,movingtowardabeacon,etc.

FIGURE11.5TypicalPhotoresistors.

PhotodiodeAphotodiodeisatypeofphotodetectorcapableofconvertinglightinto

either current or voltage, depending upon the mode of operation.Photodiodesareusedbothtodetectthepresenceoflightandtomeasurelightintensity.Mostphotodiodesconsistofsemiconductorpnjunctionshousedina container designed to collect and focus the ambient light close to thejunction.Theyarenormallybiasedinthereverse,orblockingdirection;thecurrent,therefore,isquitesmallinthedark.Whentheyareilluminated,thecurrentisproportionaltotheamountoflightfallingonthephotodiode.

PhototransistorAsecondoptoelectronicdevicethatconductscurrentwhenexposedto

light is the phototransistor. A phototransistor, however, is much moresensitivetolightandproducesmoreoutputcurrentforagivenlightintensitythatdoesaphotodiode.

POSITIONSENSORSA position, or linear displacement sensor, is a device whose output

signalrepresentsthedistanceanobjecthastraveledfromareferencepoint.Typesofposition/displacementsensorsare:

Inductivesensors

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CapacitivedisplacementsensorsMagnetostrictivesensors

InductiveSensorsThesesensorsmeasureinductancevariationscausedbymovementofa

flux-concentrating element. They are probably the most versatile of allposition sensors, with a wide range of operating characteristics. Inductivesensorsarecontact-free, inherentlyrobust,andhaveinfiniteresolutionwithhigh repeatability. They are often used where long-term reliability isimportant, particularly in harsh and hostile environments. There are twobasictypesofinductivesensors:

Linearvariabledifferentialtransducer(LVDT)Rotaryvariabledifferentialtransducer(RVDT)

Linear Variable Differential Transducer (LVDT): Linear variabledifferentialtransducer(LVDT)isacommontypeofelectromechanicaltransducerthatcanconverttherectilinearmotionofanobjecttowhichit is coupledmechanically into a corresponding electrical signal. ThebasicLVDTdesignshowninFigure11.6consistsofthreeelements:

OneprimarywindingTwoidenticalsecondarywindingsAmovablemagneticarmatureor“core”

FIGURE11.6DesignofLVDT.

Withexcitationoftheprimarycoil,inducedvoltageswillappearinthesecondary coils. Because of the symmetry of magnetic coupling to the

(b)

primary,thesesecondaryinducedvoltagesareequalwhenthecoreisinthecentral (“null” or “electric zero”) position. When the secondary coils areconnected in series opposition, as shown in the figure, the secondaryvoltageswillcanceland(ideally)therewillbenonetoutputvoltage.

If,however,thecoreisdisplacedfromnullposition,ineitherdirection,onesecondaryvoltagewill increase,whiletheotherdecreases.Becausethetwo voltages no longer cancel, a net output voltage will now result. Thedifference in induced voltages produces an output that is linearlyproportionalinmagnitudetothedisplacementofthecore.

Advantages

Relativelowcostduetoitspopularity.Solidandrobust,capableofworkinginawidevarietyofenvironments.No friction resistance, because the iron core does not touch thetransformercoils,resultinginanverylongservicelife.Shortresponsetime,onlylimitedbytheinertiaoftheironcoreandtherisetimeoftheamplifiers.No permanent damage to the LVDT if measurements exceed thedesignedrange.

Disadvantages

Thecoremustcontactdirectlyor indirectlywith themeasured surface,which is not always possible or desirable. However, a non-contactthickness gage can be achieved by including a pneumatic servo tomaintaintheairgapbetweenthenozzleandtheworkpiece.

Rotary Variable Differential Transducer (RVDT): The rotationalvariable differential transducer (RVDT) is used to measure rotationalangles and operates under the same principles as the LVDT sensor.WhereastheLVDTusesacylindricalironcore,theRVDTusesarotaryferromagneticcore.ItissimilartotheLVDTexceptthatitscoreiscamshapedandmayberotatedbetweenthewindingsbymeansofashaft.(RefertoFigure11.7.)

FIGURE11.7RVDT.

CapacitiveDisplacementSensorsCapacitive sensors detect virtually any material (paper, cardboard,

plastic,etc.)atanoperatingdistanceofupto10mm.Theyarealsosuitablefor thedetectionofmetallicor fluidobjects.Theyofferhighspeedandnocontact sensing at an extremely long life. Capacitive sensors detect anextremely wide variety of materials, primarily non-metallic materials, atcloserange.

Capacitiveproximitysensorsaredesigned tooperatebygeneratinganelectrostatic field and detecting changes in this field causedwhen a targetapproaches the sensing face. The sensor’s internal workings consist of acapacitiveprobe,anoscillator,asignalrectifier,afiltercircuit,andanoutputcircuitasshowninFigure11.8.

FIGURE11.8

In the absence of a target, the oscillator is inactive. As a targetapproaches, it raises the capacitance of the probe system. When thecapacitance reaches a specified threshold, the oscillator is activatedwhich

triggerstheoutputcircuittochangebetween“on”and“off.”Thecapacitanceof the probe system is determined by the target’s size, dielectric constant,anddistancefromtheprobe.Thelargerthesizeanddielectricconstantofatarget, themore it increases capacitance. The shorter the distance betweentargetandprobe,themorethetargetincreasescapacitance.

MagnetostrictiveSensorThemagnetostrictiveeffectisthechangeoftheresistivityofamaterial

due to a magnetic field. Magnetostriction is a property of ferromagneticmaterialssuchasiron,nickel,andcobalt.Whenplacedinamagneticfield,thesematerialschangesizeand/orshape.Magnetostrictivematerialsconvertmagneticenergytomechanicalenergyandviceversa.Asamagnetostrictivematerial ismagnetized, it strains; that is, it exhibits a change in lengthperunitlength.Magnetostrictivetransducersconsistofalargenumberofnickel(orothermagnetostrictivematerial)platesorlaminationsarrangedinparallelwithoneedgeofeachlaminateattachedto thebottomofaprocess tankorother surface to be vibrated. A coil of wire is placed around themagnetostrictive material. When a flow of electrical current is suppliedthrough the coil of wire, a magnetic field is created. This magnetic fieldcauses the magnetostrictive material to contract or elongate therebyintroducingasoundintothesurfacetobevibrated.

MagneticSensorsorHall-EffectSensorsTheseproduceoutputvoltagesproportionaltothestrengthofanearby

magnetic field generated by a moving magnet. They have relatively poortemperatureperformance,butcanbeeffectivelyusedforshort-rangepositionsensingwherecost ismost important and temperature isnot an issue.Hallsensorsworkbestwhenmovementsarelessthananinch(25mm).

PIEZOELECTRICSENSORSPiezoelectric sensors are considered to be a versatile tool for the

measurementofvariousprocesses.Thesesensorsareusedtomeasurestrainorforcebyconvertingthemtoanelectricalsignal.Theyareusedforqualityassurance, process control, and process development in many differentindustries.Piezoelectric sensors relyon thepiezoelectric effect,whichwas

discoveredbytheCuriebrothersinthelate19thcentury.Whileinvestigatinga number of naturally occurring materials such as tourmaline and quartz,Curie brothers realized that these materials had the ability to transformenergy of a mechanical input into an electrical output. More specifically,whenapressureisappliedtoapiezoelectricmaterial,itcausesamechanicaldeformation and a displacement of charges. Those charges are highlyproportionaltotheappliedpressure.

Piezoelectricsensorsareusedtosensemovementorvibrationsinmanyapplications.Apiezoelectricsensorcomprisesapiezoelectriccrystal,whichis typicallymechanically coupled to an object that produces amechanicalmovement. In piezoelectric materials, an applied electric field results inelongationsorcontractionsofthematerial.Thesesensorsareabletoconvertelectricenergydirectlyintomechanicalenergyandofferseveraladvantages,such as high actuating resolution, high actuating power, and very shortresponse times,while their size is small. Piezoelectric sensors are used astransducers because a potential difference is generated when the sensor issubjecttoapressurechange.Thecommonusesofpiezoelectricdevicesare“buzzers,”which produce a buzzing noisewhen a voltage is applied. Thesingledisadvantageofpiezoelectric sensors is that theycannotbeused fortruestaticmeasurements.

PRESSURESENSORSA pressure transducer is a transducer that converts pressure into an

analog electrical signal. Although there are various types of pressuretransducers, one of the most common is the strain-gauge base transducer.The conversion of pressure into an electrical signal is achieved by thephysicaldeformationofstraingauges,whicharebondedintothediaphragmofthepressuretransducerandwiredintoawheatstonebridgeconfiguration.Pressure applied to the pressure transducer produces a deflection of thediaphragm,whichintroducesstraintothegauges.Thestrainwillproduceanelectricalresistancechangeproportionaltothepressure.

STRAINGAUGES

There are several methods of measuring strain; the most common iswithastraingauge.Thestraingaugehasbeeninuseformanyyearsandisthe fundamental sensing element for many types of sensors, includingpressuresensors,loadcells,torquesensors,positionsensors,etc.Theuseofstraingaugesisbasedonthefactthattheresistanceofaconductorchangeswhentheconductorissubjectedtostrain.Whenexternalforcesareappliedtoastationaryobject,stressandstrainaretheresult.Stressisdefinedastheobject’s internal resisting forces, and strain is defined as the displacementanddeformation that occur.The strain gauge is one of themost importanttoolsoftheelectricalmeasurementtechniqueappliedtothemeasurementofmechanical quantities. Strain consists of tensile and compressive strain,distinguishedbyapositiveornegativesign.AstraingaugeisathinpieceofconductingmaterialthatmaylooklikeasshowninFigure11.9.

FIGURE11.9StrainGauge.

TheoryofOperationTheoperationof the resistance straingauge is basedon theprinciple,

thattheelectricalresistanceofaconductorchangeswhenitissubjectedtoamechanicaldeformation,sincetheresistivitychangeswithachangeinlengthandarea.Figure11.10showsaresistancewireinitsoriginalstate,andafterthat subjected to a strain.The stretchedwire has higher resistance, as it islongerandthinner.

FIGURE11.10

Theresistanceofaconductorcanbeexpressedas:

where,

Ristheresistance,

ρisthematerialresistivity,

Listhelengthoftheconductor,and

Aisthecross-sectionalareaoftheconductor.

TypesofStrainGaugesStrain gauges can be classified as mechanical, optical, or electrical

dependingupontheprincipleofoperationandtheirconstructionalfeatures.Of these, electrical straingaugesare themostpopular.Theprincipleof anelectrical strain gauge is based upon the measurement of the changes inresistance, capacitance, or inductance that is proportional to the straintransferred from the object to the basic gauge element. Some of thecommonlyusedstraingaugesarediscussedbelow:

1.ResistanceStrainGauges

The resistance of an electrically conductive material changes withdimensional changes, which take place when the conductor is deformedelastically.Whensuchamaterialisstretched,theconductorsbecomelongerandnarrower,whichcauses an increase in resistance.Awheatstonebridgethenconvertsthischangeinresistancetoanabsolutevoltage.Theresultingvalueislinearlyrelatedtostrainbyaconstantcalledthegaugefactor.

2.CapacitanceStrainGauges

Capacitancedevices,whichdependongeometricfeatures,canbeusedto measure strain. The capacitance of a simple parallel plate capacitor isproportionalto:

where,Cisthecapacitance,aistheplatearea,

kisthedielectricconstant,andtistheseparationbetweenplants.

Thecapacitancecanbevariedbychangingtheplatearea,a,orthegapt. The electrical properties of thematerials used to form the capacitor arerelativelyunimportant, socapacitancestraingaugematerialscanbechosento meet the mechanical requirements. This allows the gauges to be morerugged,providingasignificantadvantageoverresistancestraingauges.

3.PhotoelectricStrainGauges

Anextensometer (anapparatuswithmechanical levers attached to thespecimen)isusedtoamplifythemovementofaspecimen.Abeamoflightispassedthroughavariableslit,actuatedbytheextensometer,anddirectedtoaphotoelectriccell.Asthegapopeningchanges,theamountoflightreachingthe cell varies, causing a varying intensity in the current generated by thecell.

4.SemiconductorStrainGauges

In piezoelectric materials, such as crystalline quartz, a change in theelectronicchargeacrossthefacesofthecrystaloccurswhenthematerialismechanically stressed.Thepiezoresistiveeffect isdefinedas thechange inresistance of a material due to an applied stress and this term is usedcommonlyinconnectionwithsemiconductingmaterials.Theresistivityofasemiconductor is inversely proportional to the product of the electroniccharge,thenumberofchargecarriers,andtheiraveragemobility.Theeffectofappliedstress is tochangeboth thenumberandaveragemobilityof thechargecarriers.

FeaturesofaGoodStrainGauge

SmallsizeandmassEaseofproductionoverarangeofsizesRobustnessGoodstability,repeatability,andlinearityoverlargestrainrangeGoodsensitivityFreedom from (or ability to compensate for) temperature effects andotherenvironmentalconditionsSuitabilityforstaticanddynamicmeasurementsandremoterecording

Lowcost

MICROPROCESSORMicroprocessors are regardedasoneof themost importantdevices in

oureverydaymachinescalledcomputers.Amicroprocessor(abbreviatedasμP or uP) is a computer electronic component made from miniaturizedtransistorsonasinglesemiconductorintegratedcircuit(IC).

OR

Microprocessor is an electronic circuit that functions as the centralprocessingunit(CPU)ofacomputer,providingcomputationalcontrol.

Themicroprocessorcommunicatesandoperates in thebinarynumbers0and1,calledbits.Eachmicroprocessorhasafixedsetofinstructionsintheform of binary patterns called amachine language.Amicroprocessor is asingle-integrated circuit. The integrated circuit is a complex collection ofvery small electronic components organized into a circuit that controls the‘on’ and ‘off’ switches of the computer. The circuit is referred to asintegrated because all of the components that need to work together areetched intoasinglesiliconchip.Themicroprocessorprocesses instructionsandcommunicateswithoutsidedevices,controllingmostoftheoperationofthecomputer.Themicroprocessorusuallyhasalargeheatsinkattachedtoit.Somemicroprocessorscomeinapackagewithaheatsinkandafanincludedas a part of the package.Microprocessors are also used in other advancedelectronicsystems,suchascomputerprinters,automobiles,andjetairliners.

Microprocessorsareclassifiedbythesemiconductortechnologyoftheirdesign (TTL, transistor-transistor logic;CMOS, complementarymetal-oxidesemiconductor; or ECL, emitter-coupled logic), by the width of the dataformat (4-bit, 8-bit, 16-bit, 32-bit, or 64-bit) they process; and by theirinstructionset (CISC,complex-instruction-setcomputer,orRISC, reduced-instruction-set computer). TTL technology is most commonly used, whileCMOSisfavoredforportablecomputersandotherbattery-powereddevicesbecauseof its lowpowerconsumption.ECLisusedwhere theneed for itsgreaterspeedoffsetsthefactthatitconsumesthemostpower.Figure11.11showsthePentium4microprocessor.

FIGURE11.11Pentium-4Microprocessor.

HistoryofMicroprocessorsThefirstdigitalcomputerswerebuiltinthe1940susingbulkyrelayand

vacuum-tube switches. Relays had mechanical speed limitations. Vacuumtubes required considerablepower, dissipated a significant amountof heat,and suffered high failure rates. In 1947, Bell Laboratories invented thetransistor,whichrapidlyreplacedthevacuumtubeasacomputerswitchforseveralreasons,includingsmallersize,fasterswitchingspeeds,lowerpowerconsumption and dissipation, and higher reliability. In the 1960s, TexasInstrumentsinventedtheintegratedcircuit,allowingasinglesiliconchiptocontainseveraltransistorsaswellastheirinterconnections.

The first microprocessor was the Intel 4004, produced in 1971.Originally developed for a calculator, and revolutionary for its time, itcontained2,300transistorsona4-bitmicroprocessorthatcouldperformonly60,000 operations per second. The first 8-bitmicroprocessorwas the Intel8008, developed in 1972 to run computer terminals. The Intel 8008contained3,300 transistors.The first trulygeneral-purposemicroprocessor,developed in 1974, was the 8-bit Intel 8080, which contained 4,500transistorsandcouldexecute200,000instructionspersecond.By1989,32-bit microprocessors containing 1.2 million transistors and capable ofexecuting20millioninstructionspersecondhadbeenintroduced.

Developedduringthe1970s,themicroprocessorbecamemostvisibleasthecentralprocessorofthepersonalcomputer.

LayoutofaMicroprocessorSystemThe microprocessor system consists of three main components as

showninFigure11.12.Centralprocessingunit(CPU)Memory

(a)

(b)

Input/Output

FIGURE11.12LayoutofMicroprocessor.

Thesethreecomponentswillworktogetheror interactwitheachotherto perform a given task. Different buses are used to interconnect thesecomponents.

1.CentralProcessingUnit(CPU)

TheCPUiscalledthebrainofthemicroprocessors.TheCPUconsistsof:

ArithmeticlogicunitControlunitRegisters

Arithmetic Logic Unit: The ALU performs basic arithmeticalcalculations(addition,subtraction,multiplication,anddivision)andlogicfunctions(AND,OR,EXCLUSIVEOR,etc.).TheALUisafundamental building block of the CPU of a computer. TheALUcarriesouttheseoperationsinthefollowingmanner:

StoresdatafetchedfrommemoryorI/Ointheregisters.Sendthisdataeithertoitsarithmeticcircuitryorlogicalcircuitry,wherethenecessaryarithmeticorlogicaloperationsarecarriedout.Sendresultsofitsarithmeticorlogicaloperationtorelevantaccumulator,tothememory,ortotheI/Ointerfaces.

ControlUnit:Thecontrolunitisthepartofthemicrocomputerthatcontrols its basic operations. It is made up of the control signalgeneratingcircuitry(clock)andthecommand(instruction)decoder.The control section fetches pre-programmed instructions from

(c)

memory as needed and temporarily stores them in the commandregister(alsoknownasinstructionregister[IR]).Theseinstructionsare then decoded by the operation decoder, which sends controlsignals to the relevant parts of themicrocomputer system (via thesystem busses) to cause them to carry out the required operation.The clock determines the timingwith which these control signalsaregenerated.Registers: When the processor executes instructions, data istemporarilystoredinregisters.Dependingonthetypeofprocessor,the overall number of registers can vary from about ten to manyhundred.Theseregistersareusedtostoredatatemporarily,either8-bit data or 16-bit data according to their size. Registers are givennames,normallyanalphabet,suchasA,B,C,D,E,H,Landeachcapableofstoringan8-bitdata.Theseregisterscanalsoworkasapair,suchasBC,DE,andHLandcapableofstoring16-bitdata.

Forall8-bitoperations,registerAisusedastheaccumulator,wheretheresult after anALUoperationwill be storedautomaticallyhere.For16-bitoperations,registerpairHLwillbeusedtostoretheresult.RegisterFisan8-bitregisterusedtostorethestatusoftheCPU,suchascarry,zero,parity,overflow,etc.Theothersare16-bitregisters,whichisusedtostorememoryaddresses.Averysimplemicroprocessormayhavethefollowingregisters:

Accumulator register,which stores the resultsof arithmetic and logicaloperations.Program counter, which determines in which sequence the programinstructions,aretobeexecuted.Instruction register, which hold the last instruction, fetched frommemory.Memory data register,which holds the data thatwas last read fromorwrittentomemory.Memory address register, which holds the address of the data or theinstructioncurrentlybeingaccessed.

2.Memory

Allmicroprocessor systems have somememory.Memory is the termforvariousstoragedevices,whichareusedtostoretheprogramsanddataforthemicroprocessor.Thereare2typesofmemory:

(a)

(b)

Readonlymemory(ROM)Randomaccessmemory(RAM)

Read onlymemory (ROM): It is used to store programs and data thatdon’tneedtobealtered,i.e.,permanentstorage.TheCPUcanonlyreadprogramsanddata stored inROMs.Themonitorprogram isnormallystoredintheROM.

Randomaccessmemory (RAM): It is used to store user programs anddata, and can be altered at any time, i.e., temporary storage. TheinformationstoredinRAMcanbeeasilyreadandalteredbytheCPU.The contents (data or programs) stored is lost if power supply to thischipisturnedoff.Therearedifferentkindsofrandom-accessmemory.Static RAM (SRAM) holds information as long as power is turned onandisusuallyusedascachememorybecauseitoperatesveryquickly.Anothertypeofmemory,dynamicRAM(DRAM),isslowerthanSRAMandmustbeperiodicallyrefreshedwithelectricityortheinformationitholdsislost.DRAMismoreeconomicalthanSRAMandservesasthemainmemoryelementinmostcomputers.

3.Input/Output

The input/output unit allows themicroprocessor to communicatewiththe outsideworld, either to receive or to send data.Most of the time, theinput/outputunitwillalsoactasaninterfaceforthemicroprocessor,i.e.,toconvertthedataintoasuitableformatforthemicroprocessor.Inputdevicesare devices that input data or senddata to the computer. Input devices aresuch as keyboards, punched card readers, sensors, switches, etc. Outputdevicesaredevicesthatoutputdataorperformvariousoperationsunderthecontrol of theCPU.Output devices areLEDs, display unit, speaker,CRT,printer,etc.

4.Buses

The interconnectionsareknownasbusesbecause theycontaina largenumberofparallelconnectingwires.Thebusesareofthreetypes:

DatabusAddressbusControlbus

Thedata bus can senddata tomemoryor receivedata frommemory.Theaddressbuscarriesmemoryaddresses.Thecontrolbusisusedtomakesure everything works in the correct sequence by sending and receivingtimingsignals.

ClassificationofMicroprocessorsThe different types of microprocessors used most frequently are as

follows:

Microprocessors

Amicroprocessorisasingleintegratedcircuit(IC)whichcomprisesallof the functionsofCPU.Beforemicroprocessors,computerswould requiremultiplecircuitboardswithmanyICs.EarlyIntelmicroprocessorswerethe4000series (the4004wasdeveloped in1972byBusicomof Japan)whichhad a four-chip set and the 8000 series (1972-1979) which increasedcomputingpowerbyafactorof20.Thefirstmodernmicroprocessorwasthe80286in1982,whichcamewith16MBofaddressablememoryand1GBofvirtual memory, this 16-bit chip is referred to as the first “modern”microprocessor.

Modern personal computers use multi-core microprocessors whichwhile still a single IC but with multiple processing units operatingindependentlybutinterconnectedly.

ApplicationsofMicroprocessorsMicroprocessorsareutilizedincomputersystemsrangingfrompersonal

computers, tosmartphonesandtabletstosupercomputer-classworkstations.Programs ranges from simple word processing, email, Internet browsing,spreadsheets, animation, graphics, and database processing.Owing to theirlowcostandflexibility,microprocessorsappearinmanyeverydayhouseholdappliances.Allmodern cars incorporatemicroprocessor controlled ignitionandemissionsystemstoimproveengineoperation,increasingfueleconomywhilereducingpollution.

MICROCONTROLLER

Microcontroller(orMCU)isacomputeronachip.Microsuggeststhatthe device is small, and controller tells that the device might be used tocontrol objects, processes, or events. Another term to describe amicrocontroller is embeddedcontroller,because themicrocontrollerand itssupportcircuitsareoftenbuiltinto,orembeddedin,thedevicestheycontrol.It is a type of microprocessor emphasizing self-sufficiency and cost-effectiveness, in contrast to amicroprocessor. In addition to all arithmeticand logic elements of a microprocessor, the microcontroller usually alsointegratesadditionalelementssuchasread-onlyandread-writememory,andinput/outputinterfaces.

Microcontrollers are frequently used in automatically controlledproducts and devices, such as automobile engine control systems, officemachines,appliances,powertools,andtoys.Byreducingthesize,cost,andpowerconsumptioncompared toadesignusinga separatemicroprocessor,memory, and input/output devices,microcontrollersmake it economical toelectronicallycontrolmanymoreprocesses.

Microcontrollerdiffersfromamicroprocessorinmanyways.Firstandthemost important is its functionality. In order for amicroprocessor to beused, other components such asmemory, or components for receiving andsending data must be added to it. On the other hand, microcontroller isdesigned tobeallof that inone.Nootherexternalcomponentsareneededforitsapplicationbecauseallnecessaryperipheralsarealreadybuiltintoit.Thus, the time and space needed to construct devices is saved. Amicrocontrollerisaspecializedformofmicroprocessorthatisdesignedtobeself-sufficient and cost-effective, whereas a microprocessor is typicallydesignedtobegeneralpurpose(thekindusedinaPC).

FeaturesofaMicrocontroller

Microcontrollers are embedded inside some other device (often aconsumerproduct)sothattheycancontrolthefeaturesoractionsoftheproduct.Microcontrollerarealsocalledembeddedcontroller.Microcontrollersarededicatedtoonetaskandrunonespecificprogram.Theprogram is stored inROM(read-onlymemory)andgenerallydoesnotchange.Microcontrollersareoftenlow-powerdevices.

Amicrocontrollerhasadedicatedinputdeviceandoften(butnotalways)hasasmallLEDorLCDdisplayforoutput.Amicrocontrolleralsotakesinputfromthedeviceitiscontrollingandcontrolsthedevicebysendingsignalstodifferentcomponentsinthedevice.

ApplicationsofMicrocontrollerMicrocontrollersarefoundinallkindsofthingsthesedays.Anydevice

that measures, stores, controls, calculates, or displays information is acandidate for putting a microcontroller inside. Some of the commonapplicationsare:

In automobiles: Just about every car manufactured today includes atleast onemicrocontroller for engine control, and oftenmore to controladditionalsystemsinthecar.In desktop computers: Microcontrollers are found inside keyboards,modems,printers,andotherperipherals.Intestequipment:Microcontrollersmakeiteasytoaddfeaturessuchastheabilitytostoremeasurements,tocreateandstoreuserroutines,andtodisplaymessagesandwaveforms.

PROGRAMMABLELOGICCONTROLLER(PLC)In digital electronic systems, there are three basic kinds of devices:

memory, microprocessors, and logic. Memory devices store randominformation such as the contents of a spreadsheet or database.Microprocessorsexecutesoftwareinstructionstoperformawidevarietyoftasks such as running a word processing program or video game. Logicdevices provide specific functions, including device-to-device interfacing,data communication, signal processing, data display, timing and controloperations,andalmosteveryotherfunctionasystemmustperform.

Theadventof thePLCbegan in the1970s, andhasbecome themostcommon choice for manufacturing controls. A programmable logiccontroller,alsocalledaPLCorprogrammablecontroller,isacomputer-typedevice used to control equipment in an industrial facility. The kinds ofequipmentthatPLCscancontrolincludeconveyorsystems,foodprocessingmachinery, auto assembly lines etc. PLCs are often defined as miniature

industrial computers that contain hardware and software used to performcontrol functions. Unlike general-purpose computers, the PLC is designedformultiple inputs and output arrangements, extended temperature ranges,immunitytoelectricalnoise,andresistancetovibrationandimpact.

NationalElectricalManufacturersAssociation has definedPLC as “adigitallyoperatingelectronicapparatuswhichusesaprogrammablememoryfor the internal storage of instructions for implementing specific functionssuchaslogic,sequencing,timing,countingandarithmetictocontrol,throughdigital or analog input/output modules, various types of machines orprocesses.”

Ina traditional industrial control system,all controldevicesarewireddirectlytoeachotheraccordingtohowthesystemissupposedtooperate.InaPLCsystem,however, thePLC replaces thewiringbetween thedevices.Thisisshowninfigure11.13.Thus,insteadofbeingwireddirectlytoeachother, all equipment iswired to thePLC.Then, thecontrolprogram insidethePLCprovidesthe“wiring”connectionbetweenthedevices.ThecontrolprogramisthecomputerprogramstoredinthePLC’smemorythattellsthePLCwhat’s supposed to be going on in the system. The use of a PLC toprovidethewiringconnectionsbetweensystemdevicesiscalledsoftwiring.

FIGURE11.13

Forexample, letsassumethatapushbuttonissupposedtocontrol theoperationofamotor.Inatraditionalcontrolsystem,thepushbuttonwouldbe wired directly to themotor. In a PLC system, however, both the pushbuttonand themotorwouldbewired to thePLC instead.Then, thePLC’s

control program would complete the electrical circuit between the two,allowingthebuttontocontrolthemotor.

ComponentsofPLCAPLCconsistsoftwobasicsections:thecentralprocessingunit(CPU)

and the input/output interface system. The CPU, which controls all PLCactivity,canfurtherbebrokendownintotheprocessorandmemorysystem.The input/output system is physically connected to field devices (e.g.,switches,sensors,etc.)andprovidestheinterfacebetweentheCPUandtheinformationproviders(inputs)andcontrollabledevices(outputs).Tooperate,theCPU“reads”inputdatafromconnectedfielddevicesthroughtheuseofitsinputinterfaces,andthen“executes”orperformsthecontrolprogramthathas been stored in its memory system. Programs are typically created inladder logic, a language that closely resembles a relay-based wiringschematic, and are entered into the CPU’s memory prior to operation.Finally,basedon theprogram, thePLC“writes”orupdatesoutputdevicesvia the output interfaces. This process, also known as scanning, typicallycontinuesinthesamesequencewithoutinterruption,andchangesonlywhenachangeismadetothecontrolprogram.

The schematic diagram of PLC is shown in Figure 11.14. The basiccomponentsofPLCare:

InputmoduleOutputmoduleProcessorMemoryPowersupplyProgrammingdevice

FIGURE11.14BlockDiagramshowingComponentsofProgrammableLogicController.

1.TheInput/OutputModule

The input/output (I/O) module is the connections to the industrialprocessesthataretobecontrolled.IftheCPUcanbethoughtofasthebrainofaPLC, thentheI/Osystemcanbe thoughtofas thearmsandlegs.TheI/O system is what actually physically carries out the control commandsfromtheprogramstored in thePLC’smemory.TheI/Osystemconsistsoftwomainparts:

TherackI/Omodules

TherackisanenclosurewithslotsinitthatisconnectedtotheCPU.

Input/OutputunitsaretheinterfacesbetweentheinternalPLCsystemsand theexternalprocesses tobemonitoredandcontrolled.I/Omodulesaredeviceswithconnectionterminalstowhichthefielddevicesarewired.

Together,therackandtheI/Omodulesformtheinterfacebetweenthefielddevicesand thePLC.Whensetupproperly, each I/Omodule isbothsecurelywiredtoitscorrespondingfielddevicesandsecurelyinstalledinaslot in the rack. This creates the physical connection between the fieldequipmentandthePLC.

AllofthefielddevicesconnectedtoaPLCcanbeclassifiedinoneoftwocategories:

InputsOutputs

Inputsaredevicesthatsupplyasignal/datatoaPLC.Typicalexamplesofinputsarepushbuttons,limitsensors,switches,andmeasurementdevices.

Outputs are devices that await a signal/data from thePLC to performtheircontrolfunctions.

Lights, horns, motors, and valves are all good examples of outputdevices.

For example, a bulb and its corresponding wall switch are goodexamplesofeverydayinputsandoutputs.Thewallswitchisaninput,whichprovidesasignalforthelighttoturnon.Thebulbisanoutput,whichwaitsuntiltheswitchsendsasignalbeforeitturnson.Let’sassumeabulb/switchcircuitthatcontainsaPLC.Inthissituation,boththeswitchandthebulbwillbewiredtothePLCinsteadoftoeachother.Thus,whentheswitchisturnon,theswitchwillsendits“turnon”signaltothePLCinsteadoftothebulb.ThePLCwillthenrelaythissignaltothebulb,whichwillthenturnon.

2.TheCentralProcessingUnit

The central processing unit (CPU) is the part of a programmablecontroller that retrieves, decodes, stores, and processes information. It alsoexecutes the control program stored in thePLC’smemory. In essence, theCPU is the “brains” of a programmable controller. It functions much thesameway theCPUof a regular computer does, except that it uses specialinstructionsandcodingtoperformitsfunctions.TheCPUhasthreeparts:

TheprocessorThememorysystemThepowersupply

The processor is the section of the CPU that codes, decodes, andcomputesdata.

The memory system is the section of the CPU that stores both thecontrol program and data from the equipment connected to the PLC.Memory in a PLC system is divided into the program memory, which isusually stored in EPROM/ROM, and the operating memory. The RAMmemory is necessary for the operation of the program and the temporarystorageofinputandoutputdata.

ThepowersupplyisthesectionthatprovidesthePLCwiththevoltageandcurrentitneedstooperate.

3.ProgrammingDevice

The PLC is programmed by means of a programming device. Theprogramming device is usually detachable from the PLC cabinet so that itcanbesharedbetweendifferentcontrollers.

WorkingofPLCAPLCworks by continually scanning a program. It consists of three

stepsasshowninFigure11.15.

CheckinputstatusExecuteprogramUpdateoutputstatus

FIGURE11.15

1.CheckInputStatus

FirstthePLCtakeslookateachinputtodetermineifitisonoroff.Inotherwords, is the sensor connected to the first input on?How about thesecondinput?Howaboutthethird.Itrecordsthisdataintoitmemorytobeusedduringnextstep.

2.ExecuteProgram

Next,thePLCexecutesprogram,i.e.,oneinstructionatatime.Maybetheprogramsays that if first the input ison then it should turnon the first

output.Becauseitalreadyknowswhichinputsareon/offfromthepreviousstep, itwill be able to decidewhether the first output shouldbe turnedonbasedonthestateofthefirstinput.Itwillstoretheexecutionresultstouselaterduringthenextstep.

3.UpdateOutputStatus

FinallythePLCupdatesthestatusoftheoutputs.Itupdatestheoutputsbased on which inputs were on during the first step and the results ofexecutingyourprogramduringthesecondstep.Basedontheexampleinthestep2,itwouldnowturnonthefirstoutput.

PLCProgrammingPLC programming is done with the help of special programming

languages.Thefunctionofallprogramminglanguagesistoallowtheusertocommunicate with the programmable controller (PC) via a programmingdevice. They all convey to the system, by means of instructions, a basiccontrolplan.

Ladderdiagrams,functionblocks,andthesequentialfunctionchartarethe most common types of languages encountered in programmablecontroller system design. Ladder diagrams form the basic PC languages,whilefunctionblocksandthesequentialfunctionchartingarecategorizedashigh-level languages.Thebasicprogrammable controller languages consistof a setof instructions thatwill perform themost common typeof controlfunctionslikerelayreplacement,timing,counting,sequencing,andlogic.

LadderLogic

Ladder logic is the main programming method used for PLCs. Theladder logic diagram has been found to be very convenient for shoppersonnelwhoarefamiliarwithcircuitdiagramsbecauseitdoesnotrequirethemtolearnanentirelynewprogramminglanguage.ModernPLCscanbeprogrammed in ladder logic or inmore traditional programming languagessuchasC.

Theladderdiagramlanguageisasymbolicinstructionsetthatisusedtocreate a programmable controller program. The aim of ladder diagramprogramistocontroloutputsbasedoninputconditions.Ladderrungisusedforthecontrol.Controlrung,ingeneral,consistsofasetofinputconditions

representedbyrelaycontact-typeinstructionsandanoutputinstructionattheendoftherungrepresentedbythecoilsymbol.

An example of ladder logic can be seen inFigure 11.16.To interpretthisdiagram,imaginethatthepowerisontheverticallineontheleft=handside,wecallthisthehotrail.Ontherighthandsideistheneutralrail.Inthefigure, there are two rungs, and on each rung there are combinations ofinputs (twovertical lines)andoutputs (circles). If the inputsareopenedorclosedintherightcombinationthepowercanflowfromthehotrail,throughtheinputs,topowertheoutputs,andfinallytotheneutralrail.Aninputcancomefromasensor,switch,oranyother typeofsensor.Anoutputwillbesome device outside the PLC that is switched on or off, such as lights ormotors.Inthetoprung,thecontactsarenormallyopenandnormallyclosed.Which means if input A is on and input B is off, then power will flowthrough the output and activate it. Any other combination of input valueswillresultintheoutputXbeingoff.

FIGURE11.16ASimpleLadderLogicDiagram.

AdvantagesandDisadvantagesofPLCAdvantages

There are significant advantages in using a programmable logiccontroller rather than conventional relays, timers, counters, and otherhardwareelements.Theseadvantagesinclude:

ProgrammingthePLCiseasierthanwiringtherelaycontrolpanel.

Highreliability.ThePLCcanbereprogrammed.Conventionalcontrolsmustberewiredandareoftenscrappedinstead.PLCstakelessfloorspacethenrelaycontrolpanels.Littlemaintenanceduetonomovingparts.Nospecialprogrammingskillsrequiredbymaintenancepersonnel.Computingcapabilities.Reducedcosts.Abilitytowithstandharshenvironments.Expandability.Highspeedofoperation.

Disadvantages

Although the PLC systems have many advantages, there are alsodisadvantages.Theseinclude:

Fault finding, as PLC systems are oftenmuchmore complex than thehardwiredrelaysystems.FailureofthePLCmaycompletelystopthecontrolledprocess,whereasafaultinaconventionalcontrolsystemwouldonlydisrupttheprocess.ExternalelectricalinterferencemaydisruptthePLCmemory.

ApplicationsofPLCPLCshavenowbecomeaveryconvenienttoolforflexibleautomation.

ApplicationsofPLCinclude:

Controlofelectricalmotorsinindustrialdrives.CNCmachines.Robotcontrol.Homeandmedicalequipment.Operationofliftsinbuildings.Controloftrafficsignals.Safetycontrolofpresses.

1.2.3.

4.5.

6.

7.

8.

9.10.11.12.13.

14.15.

16.

17.

18.19.20.

EXERCISESWriteshortnoteson“transducertypes.”Distinguishbetweenatransducerandasensor.Discuss the various types of sensors used for position or displacementmeasurement.NameanyfouradvantagesofPLCoverconventionalcontrolsystems.Describe the construction and working principle of a microprocessorwiththehelpofaschematicdiagram.Identify the various types of integrating devices used to integratemechanical systemswith computer systems. Describe any two of suchdevicesindetailgivingtheirapplications.Identify the desirable features of a good transducer. Describe theconstructionandworkingprincipleofLVDTwiththehelpofasketch.DiscusstheconstructionofPLCandmicroprocessorsanddescribetheiruseinindustrialapplicationswiththehelpofsuitableexamples.Defineaprogrammablelogiccontroller(PLC).Whatisasensor?Identifydesirablefeaturesoftransducers.Bymeansofasketch,describetheworkingofanypiezoelectricsensor.Whataremicroprocessors?IdentifythevariouscomponentsofaPLC.DescribeaPLCwiththehelpofaschematicdiagram.WherearePLCemployed?Nameanythreepartsrequiredforintegrationofmechanicalsystemwithelectricalsystem.Discuss the advantages and limitations of microprocessor basedcontrollers.Mention two significant differences between a microprocessor and aprogrammablelogiccontroller.Whatarethefactorstobeconsideredinselectionofatransducer?WhatarethemainfunctionsoftheAregisterinamicroprocessor?What are ports in a microprocessor system? Explain the differencebetweenaccessingportsandmemory.

21.22.23.

24.25.

26.27.28.29.30.

31.

32.33.

34.

Writeashortparagraphonthermocouple.Whatarethemainregistersandtheirfunctionsinamicroprocessor?What are programmable logic controllers?Discuss the applications forwhich these are used. Discuss three significant advantages anddisadvantages.Whatisamicrocontroller?Explainthearchitectureofaprogrammablelogiccontrollerwiththehelpofasketch.DistinguishbetweenLVDTandRVDT.WhataretheapplicationofmicroprocessorsandPLC?WhywereladderdiagramsusedforprogrammingPLCsystems?Howcantransducersbeclassified?List the various electric and electronic control elements used inautomation.Discuss the advantages and limitations of microprocessor-basedcontrollers.ExplaintheconstructionalfeaturesofaPLC.List the various electric and electronic control elements used inautomation.Explaintheconstructionalfeaturesofamicrocontroller.

CHAPTER12

TRANSFERDEVICESANDFEEDERS

INTRODUCTIONSince thebeginningof thenineteenth century, the increasingneed for

finished goods in large quantities has led engineers to search for and todevelop new methods of manufacturing or production. As a result ofdevelopment in the variousmanufacturing processes, it is now possible tomass-produce high-quality durable goods at low cost. One of the mostimportantmanufacturingprocesses is the assemblyprocess that is requiredwhentwoormorecomponentspartsaretobesecuredtogether.Thehistoryof assembly process development is closely related to the history of thedevelopmentofmass-productionmethods.Thepioneersofmassproductionare also the pioneers of modern assembly techniques. Their ideas andconcepts have brought significant improvement in the assembly methodsemployedinhighvolumeproduction.

However, many aspects of manufacturing engineering, especially theparts fabrication process, have been revolutionized by the application ofautomation,thetechnologyofthebasicassemblyprocesshasfailedtokeeppace. Although, during the last few decades, efforts have been made toreduceassemblycostsbytheapplicationofhighspeedautomationandmorerecentlyby theuseof assembly robots, successhasbeenquite limited andmany assembly workers are still using the same basic tools as thoseemployed at the time of the industrial revolution. So, in these days, it isnecessary that manufacturing engineers and designers must learn about

automatic assembly. This in turn provides means to improve design,productivity,andcompetitiveness.

FUNDAMENTALSOFPRODUCTIONLINESAproduction lineconsistsofa seriesofworkstationsarrangedso that

the product moves from one station to the next, and at each location, aportionofthetotalworkisperformedonit.Productionlinesareassociatedwithmassproduction.Ifquantitiesoftheproductareveryhighandtheworkcan be divided into separate tasks that can be assigned to individualworkstations, then a production line is themost appropriatemanufacturingsystem. In terms of the capacity of a production line to cope with modelvariations,threetypesoflinecanbedistinguished:

Single-modellineproducesonlyonemodelandthereisnovariationinthemodel.The tasksperformedateachstationare thesameonallproductunits.

Batch-modellineproduceseachmodelinbatches.Theworkstationsaresetuptoproducethedesiredquantityofthefirstmodel,andthenthestationsare reconfigured toproduce thedesiredquantityof thenextmodel, and soon.

Mixed-model linealsoproducesmultiplemodels;however, themodelsareintermixedonthesamelineratherthanbeingproducedinbatches.Whilea particularmodel is beingworked on at one station, a differentmodel isbeingprocessedatthenextstation.

TYPESOFASSEMBLYLINESTherearetwotypesofassemblylines:

ManualassemblylinesAutomatedassemblylines

ManualAssemblyLinesA manual assembly line consists of multiple workstations arranged

sequentially,atwhichassemblyoperationsareperformedbyhumanworkers.

Because all of theoperations are in the control of theworker, so the toolsrequired are simple and less expensive than those used in automatedassembly.Manualassemblysystemsarebestsuitedforlowvolumeproductsthathavehighproductvariety.Processesaccomplishedonmanualassemblylinesincludemechanicalfasteningoperations,spotwelding,handsoldering,andadhesivejoining.

AutomatedAssemblyLinesThe term automated assembly refers to the use of mechanized and

automateddevicestoperformthevariousassemblytasksinanassemblyline.Mostautomatedassemblysystemsaredesignedtoperformafixedsequenceofassemblystepsonaspecificproduct.Anautomatedassemblylineconsistsof automated workstations connected by a parts transfers system whoseactuationiscoordinatedwiththestations.Inanidealline,nohumanworkersareontheline,excepttoperformauxiliaryfunctionssuchastoolchanging,loadingandunloadingparts,andrepairandmaintenanceactivities.Modernautomated lines are integrated systems operating under computer control.Automatedproduction linesareapplied inprocessingoperationsaswellasassembly.

An automated assembly system performs a sequence of automatedassembly operations to combine multiple components into a single entity.Thesingleentitycanbeafinalproductorasubassemblyinalargerproduct.Inmany cases, the assembled entity consists of a basepart towhichothercomponentsareattached.Thecomponentsarejoinedoneatatime(usually),so the assembly is completedprogressively.A typical automated assemblysystemconsistsofthefollowingsubsystems:

Oneormoreworkstationsatwhichtheassemblystepsareaccomplished.Parts feeding devices that deliver the individual components to theworkstations.Aworkhandlingsystemfortheassembledentity.

REASONSFORUSINGAUTOMATEDASSEMBLYLINES

(a)

(b)

Automated assembly technology should be considered when thefollowingconditionsexist:

High product demand: Automated assembly systems should beconsideredforproductsmadeinlargequantity(inmillions).Stable product design: In general, any change in the product designmeans a change in workstation tooling and possibly the sequence ofassemblyoperations.Suchchangescanbeverycostly.Theassemblyconsistsofnomorethanalimitednumberofcomponents.

Automatedproductionlinescanbedividedintotwobasicscategories:

Transfer lines, which consist of a sequence of workstations thatperformsprocessingoperations,withtheautomatictransferofworkunits between stations.Transfer lines are usually expensive piecesofequipment; theyaredesignedfora jobrequiringhighquantitiesofparts.

Dial indexing machine, is a device used to convey parts forassembly,machining,packaging, finishing,orothermanufacturingoperations. In a dial indexing machine, the workstations arearrangedaroundacircularworktablecalledadial.Theworktableisactuatedbyamechanism thatprovidespartial rotationof the tableoneachworkcycle.

TRANSFERSYSTEMSINASSEMBLYLINESThefourmaintypesoftransfersystemsare:

ContinuoustransfersystemIntermittent/synchronoustransfersystemAsynchronoustransfersystemStationarytransfersystem

In continuous transfer systems, the work carriers are moving at aconstantspeedwhiletheworkheadindexmovesbackandforth.Assemblyoperationsarecarriedoutduringtheperiodwhentheworkheadsaremovingforward, keeping pace with the work carriers. Examples of continuous

transfersystemscanbeseeninbottlingoperations,manualassemblywheretheworkercanmovewiththemovingline.

In intermittent transfer, theworkcarriersare transferred intermittentlyandtheworkheadsremainstationary.Allthepartsaremovedatsametime,hence,thetermsynchronoustransfersystem,whichisalsousedtodescribethis method of workpiece transport. For example, intermittent transfersystems are used in machining operations, press-working operations, etc.Thissystemisstressfultohumanworkers,butgoodinautomatedoperations.

Theasynchronoustransfersystemallowseachworkparttoadvancetothenextstationwhenprocessingat thecurrentstationhasbeencompleted.Eachpartmoves independentof theotherparts, increasing flexibility.Thistypeofsystemisgoodforbothmanualandautomatedoperations.

Inthestationarysystem, thepart isplacedinafixedlocationwhereitremains during the entire assembly process. This system is usedwhen theassembledproductisbulkyordifficulttohandle,e.g.,airplanes,ships,etc.

AUTOMATICMACHINESAutomaticmachines are thosemachines inwhich both theworkpiece

handling and the metal cutting operations are performed automatically.Thesemachineshaveplayedan important role in increasing theproductionrateandhavebeen inuse for long time. Inautomaticmachines,operationsfrom feeding of stock to clamping,machining, and even inspection of theworkpiecearecarriedoutautomatically.

TRANSFERDEVICES/MACHINESA transfer machine is an automatic machine capable of performing

manyoperations.Itconsistsofmanymachinetoolsproperlylinkedtogether.Thesearespecialpurposemachineswherethecomponentsareautomaticallytransferred fromonemachininghead to another.Operations are performedsequentially. Each machining head carries out one operation until thecomponentreachestheendofthelineandallthenecessaryoperationshavebeen performed. Transfer of the workpiece and its fixture from station tostation is done automatically. Each station could be considered as simple

workheadwithitsownmotormountedonabase.Itcouldalsobedefinedasacombinedmaterialprocessingandmaterial-handlingmachine.

Transfer machines perform a variety of machining, inspecting, andquality control functions. They drill, mill, grind, as well as, control andinspect the operations. Transfer machines range from comparatively smallunits having only two to threeworkstations to long straight-linemachineswith more than 100 workstations. These machines are used primarily inautomobile industry. A wide variety of transfer machines with differentmodels, designs, and sizes are available in themarketwith salient featureslike automatic reset timer, sliding headstock, increased platen clampingspeed,pressureadjustmentsystem,andmanymore.Someofthesemachinesareflexible,precise,fast,andsomeareusedforhighproductionjobs.Theyare used in many industrial sectors. There are different types of transfermachines available in the market like the CNC rotary transfer machine,economy precision transfer machine, rotary transfer machines for brassgoods,automatic transfer linemachine, transfermachinesforproductionofvalve bodies, six-station dial rotary transfer machines, and many moresuitingdifferentindustrialpurposes.

SELECTIONOFTRANSFERDEVICESSelection of a particular transfer device is based upon the following

factors:

Accuracyrequiredincomponents.Variousforcesactingatstationsonthecomponents.Physicalsizeofpartsandproductionrate.Numberofoperationstobeperformed.Type of drive required, i.e., pneumatic, hydraulic, electric, or acombinationofthese.

TRANSFERMECHANISMINTRANSFERDEVICES

Transfermechanismsareusedtomovetheworkpiecefromonestationtoanotherinthemachineorfromonemachinetoanothertoenablevariousoperations to be performed on the part. Sensors and other devices usuallycontroltransfersofpartsfromstationtostation.Toolsontransfermachinescanbechangedeasilyusingtoolholderswithquick-changefeatures.Thesemachinesmay be equippedwith various automatic gauging and inspectionsystems. These systems are utilized between operations to ensure that thedimensionsofapartproducedinonestationarewithinacceptabletolerancesbefore that part is transferred to the next station. The two transfermechanismsusedtheare:

LineartransfermechanismRotarytransfermechanism

Thegoal is thesameforboth—putablank,bar,casting,orforginginthefirststationandgetacompletelymachinedpartattheotherend.

LINEARTRANSFERMECHANISMLineartransfersystemsprovidealinearmotionforworkparttransferin

automated production systems. Linear transfer mechanisms are used forinline machines. Some of the commonly used linear transfer mechanismsare:

WalkingBeamSystemIn this type of linear transfer mechanism (refer to Figure 12.1), the

workpantsareliftedupfromtheirworkstationlocationsbyatransferbarandmovedonepositionahead to thenext station.The transferbar then lowersthe parts into nests that position them for processing at their stations. Thebeamthenretractstomakereadyforthenexttransfercycle.Awalkingbeamtransfer system is used in transferring cylindrical parts, motor shafts,camshafts, crankshafts, tubing, and piping of all types. The advantages ofwalkingbeammachinesincludealowermachinechassiscostandsignificantreductionsinfixturingcosts.Thissystemlendsitselfwelltoveryhigh-speedmachines.

FIGURE12.1WalkingBeamSystem.

PoweredRollerConveyorSystemThis type of system (refer to Figure 12.2) is used in automated flow

lines.Theconveyorcanbeused tomovepartsorpallets.Rollerconveyorsareflexible,robust,andhighlyefficient.

FIGURE12.2PoweredRollerConveyorSystem.

ChainDriveConveyorSystemAchainor steel belt is used to transport thework carriers.The chain

drive conveyor system shown in Figure 12.3 can be used for continuous,intermittent,ornon-synchronousmovementofworkparts.

FIGURE12.3ChainDriveConveyorSystem.

ROTARYTRANSFERMECHANISMIn rotary transfer system, the workpieces are held in fixtures on a

continuousrotatingtable.Therearevariousmethodsusedtoindexacirculartableordialatvariousequalangularpositionscorrespondingtoworkstationlocations.Someofthemethodsaredescribedbelow:

RackandPinionTherackandpinionmechanismisnotsuitedforhigh-speedoperation

oftenassociatedwith indexingmachines.Thedeviceusesapiston todrivetherack,whichcausesthepiniongearandattachedindexingtabletorotate.

RatchetandPawlAratchetmechanismisbasedonawheelthathasteethcutoutofitand

apawlthatfollowsasthewheelturns.LookingatFigure12.4,astheratchetwheelturns,thepawlfallsintothedipbetweentheteeth.Theratchetwheelcan only turn in one direction (in this case anticlockwise). Its operation issimplebutsomewhat reliable,owing towearandstickingofseveralof thecomponents.

FIGURE12.4RatchetandPawlSystem.

GenevaMechanismTheGeneva-typemechanismhasmoregeneralapplicationinassembly

machines but its cost is higher than the mechanisms described earlier. AGeneva mechanism as shown in Figure 12.5 is used to provide anintermittent rotational motion of the driven part while the driver wheelrotatescontinuously.Ifthedrivenmemberhaseightslotsforaneight-stationdialindexingmachine,eachturnofthedriverwillcausethetabletoadvanceone-eighthofaturn.Thedriveronlycausesmovementofthetablethroughaportionofitsrotation.

FIGURE12.5GenevaMechanism.

Because the driven wheel in a Geneva motion is always under fullcontrolofthedriver,thereisnoproblemwithoverrunning.Impactisstillaproblem unless the slots of the driven wheel are accuratelymade and thedrivingpinenterstheseslotsattheproperangle.Themaincharacteristicofthe Geneva mechanism is its restriction on the number of stops perrevolution. The smaller the number of stops, the greater the adversemechanical advantage between the driver and the driven members. Thisresultsinahighindexingvelocityatthecenteroftheindexingmovement.

CLASSIFICATIONOFTRANSFERDEVICESTransferdevices/machinescanbeclassifiedas:

Inlinetransfermachines

Rotarytransfermachines

Thegoalisthesameforall,i.e.,putablank,bar,casting,orforginginthefirststationandgetacompletelymachinedpartattheotherend.

InlineTransferMachinesThe inline assembly machine consists of a series of automatic

workstations located along an inline transfer system (refer toFigure 12.6).Inlinetransfermachineshavealoadstationatoneendandanunloadstationattheotherend.Thepartsfeeders,workstations,andinspectionstationsarearrangedalongtheworkflow.Thecomponentsaretransferredautomaticallyfromonemachiningstation toanothereitherbypullingsupportingrailsbymeansofanendlesschainconveyororbypushingalongthecontinuousrailsby air or hydraulic pressure. The components are loaded manually orautomatically onto the central bed. All types of machining operations arecarried out at various stations and the chips produced are removed so thatthesedonotfoultheworkingparts.

FIGURE12.6InlineTransferMachine.

These machines are generally suitable for operations involving largeworkpieces and for those in which large workstations are required. Inlinemachineshave theadvantagesofanunlimitednumberofworkstationsandefficient operator loading. In comparison with rotary transfer systems, themanufacturing costs of linear transfer systems are generally 10 to 20%

higheraccordingtotype.Spacerequirementsaregreaterascomparedtotherotarytransfersystem.

Inlinetransfermachinescanbebroadlyclassifiedas:

PallettypetransfermachinesPlaintypetransfermachines

In pallet type transfer machines, the workpieces are transferred fromstations by holding them in fixtures called pallets. In plain type transfermachines, the parts move in an unclamped position. Pallet type transfermachines are used for producing components requiring a high degree ofaccuracy.

RotaryTransferMachinesInrotarytransfermachines,theworkpiecesarelocatedandclampedin

pallet type fixtures that are indexed in a circular path as shown in Figure12.7. The table rotates about a vertical axis and its movement could becontinuous or intermittent. Rotary transfer machines automatically feedmultiple workstations from a rotating turret. This combines an automatedpartfeedwithmultiplesimultaneousoperations,streamliningthemachiningprocess significantly. The rotary transfer technology indexes a workpiecefromstationtostationviaarotarytable,withoperationsperformedateachstation. The number of stations allow for easier balance between long andshort operation cycles. Because the tools rather than the workpiece arerotating, it is possible to insertmachine stock of virtually any shape. Thistypeofmachiningmethodpermitstheworkpiecetobeloadedandunloadedatasinglelocationwithoutinterruptingthemachining.

FIGURE12.7RotaryTransferMachine.

Machining operations are typically hole-making operations (drilling,cross drilling, tapping, boring, counter boring, etc.) but can also includemilling,turning,cutoff,broaching,crimping,threading,tapping,broachving,andothersecondarymachiningandassemblyoperations.Althoughtherotarytransfermachineisbestsuitedformulti-millionpartruns,itsflexibilityalsomakes it effective for familyofpartsproduction.Thesemachines areusedwhen few machining stations need to be employed. Rotary arrangementsavesfloorspaceandpresentsamorecompactarrangement.

RotaryIndexTableRotaryindexingtablesareusedtoindex/transferpartsandcomponents

in defined, angular increments so that they can be machined, worked, orassembledinmultipleoperations.Tablesconsistofacircularsteelplate,oneormorespindles,adrivesystem,andpinsthatholdpartsandcomponentsinplace.A rotary indexing table as shown in Figure 12.8 has either fixed oradjustable indexing angles. During each revolution, the table stops for aspecified period of time so that an operation can be performed at eachstation. Rotary indexing tables are powered by pneumatic and electricmotors, hydraulic drives, andmanual actuation. Drivemechanisms can belocatedabove,below,behind,ortothesideofthetablesurface.Pneumaticrotary indexingtablesaresuitableforsmallandmediumloads.Electricallypowered tables aregenerally faster thanpneumaticdevices andcanhandleheavierloads.Tablesthatarepoweredbyhydraulicdrivesuseapressurized

fluid that transfers rotational kinetic energy. Manually actuated rotaryindexing tables often include a hand crank or are loosened, turned, andadjustedbyhand.

FIGURE12.8RotaryIndexingTable.

Besides boosting output, indexing tables improve safety. Hazardousoperationscanbeplacedontheoppositesideofthetablefromtheoperator.A light curtainor safetyglass installedabove the table, along itsdiameter,willensure that thehazardousoperationand theoperator remainseparated.Applications for rotary indexing tables include assembly and equipmentpositioning as well as various automation, inspection, and machiningapplications.

ADVANTAGESANDDISADVANTAGESOFTRANSFERMACHINES

Advantages

Transfermachinesofferanumberofadvantages:

Complexshapedcomponentscanbeeasilymachined.Optimumutilizationoffloorspacewiththesemachines.Increasedproductivity.Componentsproducedareofhighquality,accurate,andcheap.Eliminationofworker’sfatigue.Loadingandunloadingtimeiseliminated.

Disadvantages

(a)

Highinitialinvestment.Thesemachinesarelimitedtohighproductionindustries.Abreakdownofonemachinemeansstoppageofwholeproductionline.Overhaulingandmaintenancecostsarehigh.

CONVEYORSYSTEMSUSEDINTRANSFERDEVICES

Aconveyorsystemisacommonpieceofmaterialhandlingequipmentthatmovesmaterialsfromonelocationtoanother.Conveyorsworkbytwomethods: throughmanual operation or through a power source.Conveyorsareespeciallyusefulinapplicationsinvolvingthetransportationofheavyorbulkymaterials.Conveyor systemsallowquickandefficient transportationfor a wide variety of materials, which makes them very popular in thematerial handling and packaging industries. Many kinds of conveyingsystems are available, and are used according to the various needs ofdifferent industries. By laying the conveyors along the line of productionmachines, the integration of material movement with the productionprocessesisfacilitated.Thevarioustypesofconveyorsusedare:

RollerconveyorWheelconveyorChuteconveyorBeltconveyorChainconveyorMagneticbeltconveyorBucketconveyor

Roller Conveyor: Roller conveyors form an important means ofconveying unit material in the industry. Usually, the load shouldpossess a flat base, or should be mounted on a flat-bottomedpallet/container, so that it can roll on top of straight cylindricalrollers.Thesemaybepowered(orlive)ornon-powered(orgravity)rollerconveyors.Gravityconveyorsdonotrequireamotor,butusewheels, rollers, and the pull of gravity tomovematerials along aconveyor. Power conveyors, unlike gravity conveyors, require a

(b)

(c)

pneumaticoranelectricalpowersource.Poweristransmittedfromthe drive system to a drive pulley, which is fastened to the driveshaft. The drive pulley then transmits the power to the conveyorbelt,whichmovestheconveyorbed,uponwhichthematerialsrest.RollerconveyorsareshowninFigure12.9.

FIGURE12.9RollerConveyor.

Wheel Conveyor: The wheel conveyor as shown in Figure 12.10usesaseriesofskatewheelsmountedonashaft(oraxle),wherethespacing of thewheels is dependent on the load being transported.Slope for gravity movement depends on load weight. These aremoreeconomicalthantherollerconveyor.

FIGURE12.10WheelConveyor.

ChuteConveyor:Aninexpensivechuteconveyorisusedtolinktwohandling devices. These are used to provide accumulation inshipping areas and to convey items between floors. These areinexpensivebuthavethelimitationofdifficulty tocontrolpositionoftheitems.(RefertoFigure12.11.)

(d)

(e)

FIGURE12.11ChuteConveyor.

BeltConveyor:Belt conveyors as shown inFigure 12.12 are usedfor thecontrolledmovementofa largevarietyofboth regularandirregular shaped products. They can move light, fragile to heavy,ruggedunit loadsonahorizontal, inclined,ordeclinedpathwithinthe limits of product stability and the conveyor componentcapacities.Theitemsbeingconveyedarecarriedbythetopsurfaceofthebelt.

FIGURE12.12BeltConveyor.

Chain Conveyor: These conveyors offer high flexibility of layoutandconditionsofwork.(RefertoFigure12.13.)

(f)

(g)

FIGURE12.13ChainConveyor.

Magnetic Belt Conveyor: A magnetic belt conveyor is used totransport ferrous materials vertically, upside down, and aroundcorners.(RefertoFigure12.14.)

FIGURE12.14MagneticConveyor.

Bucket Conveyor: Bucket conveyors are used to move bulkmaterials in a vertical or inclined path. Buckets are attached to acable,chain,orbelt.Bucketsareautomaticallyunloadedattheendoftheconveyorrun.(RefertoFigure12.15.)

FIGURE12.15BucketConveyor.

FEEDERSAfeederisanextremelyimportantelementinabulkmaterialhandling

system, because it is the means by which the rate of solids flow from ahopperorbin iscontrolled.Whena feederstops, solids flowshouldcease.Whenafeeder is turnedon, thereshouldbeaclosecorrelationbetweenitsspeedofoperationandtherateofdischargeof thebulksolid.Feedersfeedmaterialtoconveyors,processors,andotherequipmentatacontrolledratetomaximize efficiency and production. In essence, they are short conveyorsthat come inmultiple shapes and sizes. Feeders are also used in recyclingapplications.

Feeders differ from conveyors in that the latter are only capable oftransportingmaterial, notmodulating the rate of flow.Dischargers are notfeeders.Suchdevicesaresometimesusedtoencouragematerialtoflowfromabin,buttheycannotcontroltherateatwhichmaterialflows.Thisrequiresafeeder.

CLASSIFICATIONOFFEEDERSTherearetwobasictypesoffeedersusedinindustrialplants:

VolumetricfeedersGravimetricfeeders

As the name implies, a volumetric feeder modulates and controls thevolumetric rate of discharge from a bin (e.g., cu.ft./hr.). The four most

common types of such feeders are screw, belt, rotary valve, and vibratingpan.

Agravimetricfeeder,ontheotherhand,modulatesthemassflowrate.Thiscanbedoneeitheronacontinuousbasis(thefeedermodulatesthemassper unit time ofmaterial discharge) or on a batch basis (a certainmass ofmaterialisdischargedandthenthefeedershutsoff).Thetwomostcommontypesofgravimetricfeedersareloss-in-weightandweightbelt.Gravimetricfeedersshouldbeusedwheneverthereisarequirementforclosecontrolofmaterialdischarge.Agravimetricfeedershouldalsobeusedwhenthebulkdensityofthematerialvaries.

CRITERIAFORFEEDERSELECTIONThefeederused(whethervolumetricorgravimetric)shouldprovidethe

following:

Reliableanduninterruptedflowofmaterialfromsomeupstreamdevice(typicallyabinorhopper).Thedesireddegreeofcontrolofdischargerateoverthenecessaryrange.Uniform withdrawal of material through the outlet of the upstreamdevice.Interfacewith the upstream device such that load acting on the feederfromtheupstreamdeviceisminimal.Thisminimizesthepowerrequiredtooperate the feeder,particle attrition, andabrasivewearof the feedercomponents.

PARTSFEEDINGDEVICESParts feeding devices are the devices that deliver the individual

components to the workstations. Some of these parts feeding devices areexplainedasfollows:

HopperChuteMagazinesSeparator

(a)

PartsfeederFeedtrackEscapementandplacementdeviceSelectorsandorientorEjectorsandpushersReelCradleBowlsPallets

Hopper: Hoppers are receptacles for the temporary storage ofmaterial.Theyaredesignedso thatstoredmaterialcanbedumpedeasily.Thismeans that theparts are initially randomlyoriented inthe hopper. Hoppers can be made out of aluminum or steel forheavy-dutyuse,andplasticforlight-dutyapplications.Hoppersaregenerally one of two types, bottom or tilt. Bottom hoppers aredesignedsothatstoredmaterialcanbedumpedfromthebottomofthehopper.Livebottomhoppershavehydraulicallyormechanicallydrivenscrewstoaidindischargingthematerial.Theyaretypicallyusedtoaidinthedischargeofsluggishorviscousmaterials.Somehoppers have a base that allows them to be lifted by forklifts fordumping.

Importantparameterstoconsiderwhenspecifyinghoppersarethe weight capacity, volume capacity, height, and weight of thehopperwhen empty. Theweight capacity is themaximumweightthe hopper is designed to hold. The volume capacity is themaximumvolumeofmaterial the hopper is designed to hold.Theheightofthehopperisnecessarytoconsiderforapplicationswhereoverheadspaceislimited.

Common features for hoppers includeagitation,perforations,self-dumping, side dumping, stackable, andwheels. A hopperwilluse agitation to dislodge material while dumping. Hoppers withagitationmay alsobe calledvibratoryhoppers.Perforations in thehopper allow for the drainage of water or other liquids. Self-dumpinghoppershaveamechanismtoallowthemtoself-dumpthematerial.Sidedumpinghoppersdump their contents from the siderather than the front.Stackablehoppersallowforgreatereconomy

(b)

(c)

(d)

(e)

ofspace,mostareonlytobestackedwhenempty,notwhenloaded.Somehopperswillcomeequippedwithwheelsforeasymoving.Chute: Chutes are smooth surfaced, inclined troughs that allowmaterialstomovedownthechuteundertheforceofgravity.Chutescan bemade of steel, plastic, orwood.Chutesmay be straight orspiral.Chutesaredesigned tomovematerialswithoutdamageandconveyobjectsfromhigh-to-lowlevelsundertheforceofgravity.Magazines:Magazinesareloadingdevicesadoptedtoholdapileofwork of various shapes and sizes, for further loading into themachine.Magazinescanbesubdividedintoflat(palettes)andchutemagazines.ThreedifferenttypesofmagazinesareshowninFigure12.16.Figure12.16Ashowsaflatmagazine.Figure12.16Bshowsachutemagazineinzigzagformforthemagaziningofsymmetricalcylindricalparts.Figure12.16Cshowsachutemagazineforplateparts.

FIGURE12.16TypesofMagazines.

Separator:Manytimesworkpiecesaretobefedintothemachineatsetintervalsoftime.Soworkpiecesareseparatedbyinterruptingtheflow of parts to machine. This can be done with the help ofseparators.PartsFeeders:Itisverycostlytomaintainpartorderthroughoutthemanufacturecycle.Forexample,insteadofkeepingpartsinpallets,theyareoftendeliveredinbagsorboxes,wheretheymustbepickedout and sorted.Aparts feeder is amachine thatorients suchpartsbefore they are fed to an assembly station (refer toFigure 12.17).

(f)

(g)

Themostcommontypeofpartsfeederisthevibratorybowlfeeder,where parts in a bowl are vibrated using a rotarymotion, so thattheyclimbahelicaltrack.Astheyclimb,asequenceofbafflesandcutoutsinthetrackcreateamechanical“filter”thatcausespartsinallbutoneorientationtofallbackintothebowlforanotherattemptat running the gauntlet. Other common devices use centrifugalforces, reciprocating forks, or belts to push parts through filters.Thesedeviceshavethedisadvantagethatdesignandsetupfornewpartsrequiresmanualtrialanderror,whichisslowanderror-prone.Parts feeders provide a cost-effective alternative to manual labor,savingmanufacturers valuable time and labor costs. One operatorcan oversee a number of automatedmachines, as opposed to oneworkerhandloadingonemachine.Handselectingandinspectingisalso time consuming and labor intensive. The tediousness of theprocesscansubjecttheworkerstorepetitivemotioninjuries.Usingvibratoryfeederstypicallyresultsinabetterproduct,aswell.Whenselectingapartsfeeder,severalfactorsmustbetakenintoaccount,includingtheindustry,application,materialproperties,andproductvolume.

FIGURE12.17APartsFeederOrientsPartsasTheyArriveontheLeft-handConveyorBelt.

FeedTrack:A feed track is used to transfer the components fromthe hopper and part feeder to the exact location of the assemblyworkhead, maintaining proper orientation of the parts during thetransfer.Feedtrackscanbepoweredorgravitytype.EscapementandPlacementDevices:Thepurposeofanescapementdevice is to remove components from the feed track at timedintervals that are consistent with the cycle time of the assemblyworkhead. The placement device physically places the componentinthecorrectlocationattheworkstationsfortheassemblyoperationbytheworker.(RefertoFigure12.18.)

(h)

FIGURE12.18EscapementDevice.

SelectorandOrientor:Thepurposeoftheselectorand/ororientoristo establish the proper orientation of the components for theassemblyworkhead.Aselectorisadevicethatactsasafilter,whichallows only those parts to pass through which are in correctorientation. Improperlyorientedcomponentsare rejectedback intothe hopper. An orientor is a device that allows properly orientedpartstopassthroughbutprovidesareorientationofcomponentsthatarenotproperlyorientedinitially.(RefertoFigure12.19.)

FIGURE12.19SelectorandOrientor.

TYPESOFFEEDERSApronfeedersBeltfeedersVibratoryfeedersRotaryfeedersReciprocatingfeedersDiscfeedersScrewfeeders

CentrifugalfeedersFlexiblefeeders

Someofthecommonlyusedfeedersaredescribedbelow:

APRONFEEDERSApronfeedersareusefulforfeedinglargetonnagesofbulksolidsbeing

particularly relevant to heavy, abrasive, ore-type bulk solids andmaterialsrequiring feeding at elevated temperatures. They are also able to sustainextremeimpactloading.Apronfeedersconsistofacontinuoussteelbeltthatismadeupofoverlappingflightsorpansthatareconnectedtoandsupportedby steel chains or bars. The underside of these flights is reinforced anddesigned towithstand impact andpressure.Anendless conveyor travellingoverrollersiscreated.Somefeedersaremadeofextra-heavystructuralsteeland are particularly suited to handling coarse, abrasive material. Apronfeedersprovideapositivematerial flowandwithvariablespeeddrivescanprovideclosecontrolofthefeedratetothecrusher.Thesefeedershavethelimitationofhighcostandlimitedlength.(RefertoFigure12.20.)

FIGURE12.20ApronFeeders.

RECIPROCATINGFEEDERS(PLATEFEEDERS)Plate feeders, also known as reciprocating feeders (refer to Figure

12.21), are in widespread use, usually at the tail end of a conveyor orelevatortorelievepressureanddrag.Designedforfeedingatafixedrate,aplateisdrivenreciprocallyunderaheadofbulkmaterial.Sizevariesandthe

feed rate can be controlled easily. These feeders use rollers to support thebelt and are engineered formaximum uptime. They often are used inwetapplications,andproductsrangingfromsandandgraveltocrushedstonethatpassoverbeltfeeders.

FIGURE12.21ReciprocatingFeeders.

Advantages

Lowcost.Abilitytohandleawiderangeofmiscellaneousmaterials.

Disadvantages

Notself-cleaning.Notrecommendedforhighlyabrasivematerials.

RECIPROCATING-TUBEHOPPERFEEDERAreciprocating-tubehopperfeeder(refertoFigure12.22)consistsofa

conical hopper with a hole in the center through which the delivery tubepasses.Relativeverticalmotionbetweenthehopperandthetubeisachievedby reciprocating either the tubeor thehopper.During theperiodwhen thetop of the tube is below the level of parts, some parts will fall into thedeliverytube.

FIGURE12.22ReciprocatingTubeHopperFeeder.

RECIPROCATINGPLATEFEEDERAreciprocatingplatefeederconsistsofaplatemountedonfourwheels

andformsthebottomofthehopper.(RefertoFigure12.23.)Whentheplateismovedforward,itcarriesthematerialwithit;whenmovedback,theplateiswithdrawnfromunderthematerial,allowingittofallintothechute.Theplateismovedbyconnectingrodsfromcranksoreccentrics.Thelengthandnumber of strokes, width of plate, and location of the adjustable gatedeterminethecapacityofthisfeeder.

FIGURE12.23ReciprocatingPlateFeeder.

VIBRATORYBOWLFEEDER

(a)

(b)

(c)

(d)

(e)

Vibratorypartsfeedingisatechnologyusedtoorient(properposition),singulate (properquantity), anddifferentiate (separate/sort) andmovepartstoadesiredlocation.Vibratorybowlfeedersareusedforfeedinginorientedform,awide rangeof components suchas steelballs,nuts,belts,washers,rivets, nails, caps, plugs, spoons droppers, rings, and various othercomponentshavingveryoddshapes.Thevibratorybowlfeederistheoldestand still most common approach to the automated feeding (orienting) ofindustrial parts. These feeders are very useful for automatic feeding ofcomponents to variousmachines and on automatic assembly lines such aspresses, grinders, threading machines, wadding machines, knurlingmachines, etc. The size of the feeders varies from 200 mm–1000 mmdiametersdependinguponsize,shape,andweightofcomponents.Therearenomovingparts in theequipmentand thusnowearand tearandneedsnomaintenance.

VibratoryFeederTerminology

Hopper (Storage Hopper): The storage hopper is the storage areaprovided tobacklogbulkpartsprior to entering the feederbowl.Thishoppereliminatesoverloadingorinsufficientloadsofparts,causingthebowlnottofunctionasrequired.Feedratefromthehoppertoabowlismeteredbyalevelcontrolswitch.

BasicBowl:Basicbowlsarenotoff-the-shelfstandarditems.Theyareindividuallydesignedandcanbesuppliedforanyprofileofpartuptoapproximately5”long.

FeederBowl:Thefeederbowlistheactualorientingandfeedingdevicethatorientsthepartaccordingtomachinerequirementsandistheheartof the system. The feeder bowl is always custom tooled to a specificpart configuration. Feeder bowls are almost always round andconstructedofstainlesssteelforlonglife.

Rate(orFeedRate):Feedrateisthenumberofpartsperminute,orperhour,whichmeetstheproductionrequirements.

Selector:Anareaofthesystemdesignedandcustomfittoprofileonlytheproperlypositionedpart.Partsenteringaselector,whicharenotintheproperposition,aredivertedoutofthefeedline.

(f)

(g)

(h)

(i)

Confinement: The fabrication installed to ensure 100% control of thepartafteraselectorejectsimproperlypositionedparts.

ReturnPan:Anextrapan-likeareawelded to theoutsideof thebowl,whichcatchesexcessandrejectedpartsfallingfromthetrack.Thepanguidesthesepartsbackintotheinteriorofthebowlforrecirculation.

Dischargeof theFeederBowl:This is the last sectionof thebowl. Inmost cases, it is a straight exit that confines the parts after they areoriented.

Track Switch: A switch of any type, which turns the feeder offwhenever, the tracking to themachinebecomes full.The track switchalso helps to eliminate wear, noise, and jams within the feeder. Air,photoelectric,proximity,andelectro-mechanical trackswitchescanbeused.

ConstructionandWorkingofVibratoryBowlFeedersVibratory bowl feeders are commonly used for aligning and feeding

smallparts.Atypicalvibratorybowlfeederconsistsofabowlmountedonabasebythreeorfourinclinedleafsprings.Thespringsconstrainthebowlsothat,asittravelsvertically,italsotwistsaboutaverticalaxis.Aspartsmoveupaninclinedtrackalongtheedgeofthebowl,toolinginthebowlorientspartsintotheproperorientationorrejectsmisalignedpartsintothecenterofthebowlwheretheybegintheirtravelupthetrackagain.Anelectromagnet,mounted between the base and the bowl, generates the force to drive thebowlfeeder.Thefeederbaserestsonrubberfeet,whichservetoisolatethevibrationofthefeederfromthesurroundingenvironment.

Thedriveunit, equippedwithavariable-amplitudecontroller,vibratesthebowl,forcingthepartstomoveupacircular,inclinedtrack.Thetrackisdesigned to sort and orient the parts in consistent, repeatable positions,accordingtocertainrequirements.Thelength,width,anddepthofthebedofthevibratoryfeedercanbeadjusted,andspecialbedlinerscanbeinstalledifthe material to be handled is abrasive. Dust-proof outlet covers can beattached to the inlet and discharged to reduce dusting caused by dustymaterial.

Apartfeedertakesinastreamofidenticalpartsinarbitraryorientationsandoutputs them inauniformorientation. It consistsofabowl filledwithparts surrounded by a helicalmetal track. The bowl and track undergo anasymmetrichelical vibration that causesparts tomoveup the track,wherethey encounter a sequence of mechanical devices such as wiper blades,grooves, and traps. Most of these devices are filters, that serve to reject(forcebacktothebottomofthebowl)partsinallorientationsexceptforthedesired one. Thus, a stream of oriented parts emerges at the top aftersuccessfullyrunningthegauntlet.

A picture of a section of the vibratory bowl feeder track is given inFigure12.24.Thepartsmovefromtheright to the lefton thefeeder track.Parts in undesired orientations fall back into the bowl, other orientationsremainsupported.

FIGURE12.24VibratoryBowlFeederTrack.

Figure12.25 showsa typicalvibratorybowl feederused to sort smallpartsforanautomatedassemblysystem.Largenumbersofunorientedpartsareplacedintothedeviceandmoveupthespiraltrackonthebowl’sinteriorbymeansofvibratorymotion.Partsreachthetopofthetrackinsinglefileinoneofafinitenumberofstableorientationswheretheyinteractwithaseriesoffeaturesbuiltintothetrackandbowlwall.

FIGURE12.25VibratoryBowlFeeder.

ControlsforVibratoryFeedersThere are a variety of controls available for the different types of

vibratoryfeeders.Pneumaticfeedercontrolsincludeaquick-actingvalve,anairlinefilter,apressureregulatorgauge,alubricator,andalongairhose.Atransformer-type device, available for electromagnetic vibratory feeders,adjusts the intensity of vibration by varying the applied voltage.Electromechanical feedershaveawall-mountedcontrolboxwithanon/offbutton or switch and overload protection. Special controls for remoteoperation include twospeed,maximum-to-minimummaterial flowcontrolsforbatchweighing,andpanelboardcontrolsformultiplefeederinstallation.Anaccelerometercanbeattachedtothedriveunittomonitortheamplitudeandtoapplyacorrectiontothefeeder,whichtendstovibratemorequicklyasthematerialleveldrops.

ApplicationsofVibratoryFeedersVibratory feeders are utilized in the pharmaceutical, automotive,

chemical, and mining industries. Other industries include steel, glass,foundry, concrete, recycling, bakery, railroad unloading, and plastics.Chemical plants typically use vibratory feeders to control the flow ofingredients to the mixing tanks. Foundries use them to add binders andcarbons to sand reprocessing systems. The pulp and paper industry usesvibratory feeders for chemical additive feeding in the bleaching process,while themetalworking industryuses themfor feedingmetalparts tobeattreating furnaces. Water and sewage treatment plants also use vibratory

feedersinchemicaladditivehandling.Othermaterialsthatareseparatedbyvibratoryfeedersincludepowder,plasticpellets,drychemicals,coal,metals,ore,minerals,aluminum,miningandaggregates,grains,seed,drydetergents,ceramics,textiles,rubber,fibers,woodchips,salt,sugar,andmanymore.

SCREWFEEDERSScrew feeders are among the most widely used types of bulk-solids-

handlingequipment in thechemical industry.Thesearewell suited forusewithbinshavingelongatedoutlets.AscrewfeederisshowninFigure12.26.Screwfeederscanbeusedtodeliverbulksolidsattremendousrangeoffeedrates. Bulk solid materials are usually metered into production processesfrom storage containers, such as hoppers and bins. These feeders have anadvantageoverbeltfeedersthatinthesefeedersthereisnoreturnelementtospillsolids.Becauseascrewis totallyenclosed, it isexcellent forusewithfine, dusty materials. Screw feeders require less maintenance than beltfeeders.Allscrewfeedersarevolumetricdevices.Thismeans that theyareintended to deliver a certain volumeof bulkmaterial per revolutionof thescrew.Thevolumedelivereddependsonthescrewoutsideandinside(shaft)diameterandthepitchofthescrew.Commercialfeedersoftenuseavarietyof agitation devices to ensure that the solids enter the screw in a highlyflowablestate.Thesedevicesmaystir,massage,orvibratethesolidsinordertofillthescrewsascompletely,oratleastasuniformly,aspossible.

FIGURE12.26ScrewFeeder.

BELTFEEDERS

Belt feeders are used to provide a controlled volumetric flow of bulksolids from storage bins and bunkers (refer to Figure 12.27). Like screwfeeders,beltfeederscanbeanexcellentchoicewhenthereisaneedtofeedmaterialfromanelongatedhopperoutlet.Beltfeedersgenerallycanhandleahigher flow rate than screw feeders. They generally consist of a flat beltsupportedbycloselyspacedidlersanddrivenbyendpulleys.Thesetypesoffeeders have more moving parts and, therefore, generally require moreattention and maintenance than a well-designed screw or vibrating bowlfeeder.Theyusuallyalsorequiremoreinstallationspacethanscrewfeeders.

Someparticularfeaturesofbeltfeedersinclude:

Suitable for withdrawal of material along slotted hopper outlets whencorrectlydesigned.Cansustainhigh-impactloadsfromlargeparticles.Flat belt surfaces can be cleaned quite readily allowing the feeding ofcohesivematerials.Suitableforabrasivebulksolids.Capableofprovidingalowinitialcostfeeder.

FIGURE12.27BeltFeeder.

ROTARYPLOWFEEDERSRotary plow feeders are often used under large stockpiles because of

lower capital and operating costs, as well as greater ease of maintenance.This system can be used to move minerals ranging from coal to iron ore

storedatminesites,processingfacilities,andpowerplants.Themechanismbywhicharotaryplowmovesmaterialisasfollows:

When a rotary plow begins operating, it loosensmaterial in a narrowverticalchannelaboveit.Iftwinplowsareusedandbothareoperating,twochannelswillformindependentofeachother.Thepressuresexertedonthematerial adjacent to the channels aregenerally lowandproportional to thesizeoftheflowchannel.Ifaplowdoesnottraverseunderthestockpile,andif the material has sufficient cohesive strength, the channel eventuallyempties out, forming a rat hole.However, as a plow traverses, the narrowplow channel lengthens. Whether material on either side of it remainsstationaryorslidesdependsonthewallfrictionanglealongtheslopingwall,thewallangle,andtheheadofthematerial.

Ifthematerialslides,itdoessoforonlyashortdistance,because,asthematerial in the flow channel is compressed, the pressure it exerts on theadjacentmaterial increases, resulting in a stablemass. If the sidematerialdoesnotslide, the levelofmaterial in the flowchanneldropsandmaterialsloughsoffthetopsurface.

ROTARYTABLEFEEDERSThe rotary table feeder canbe considered as an inverseof theplough

feeder.Itconsistsofapower-drivencircularplaterotatingdirectlybelowthebinopening,combinedwithanadjustable feedcollarwhichdetermines thevolumeofbulkmaterialtobedelivered.Theaimistopermitequalquantitiesofbulkmaterialtoflowfromthecompletebinoutletandspreadoutevenlyover the table as it revolves.Thematerial is thenploughedoff in a steadystreamintoadischargechute.This feeder issuitable forhandlingcohesivematerials, which require large hopper outlets, at flow rates between 5 and125metric tons per hour. Feed rates to some extent are dependent on thedegreetowhichthematerialwillspreadoutoverthetable.Thisisinfluencedby theangleof reposeof thematerial,whichvarieswithmoisturecontent,size distribution, and consolidation. These variations prevent high feedaccuracy from being obtained. Rotary table feeders are suitable for binoutletsupto2.5mindiameter;thetablediameterisusually50to60%largerthan the hopper outlet diameter. With some materials, a significant deadregion canbuild up at the center of the table.This can sometimesbe keptfrombecomingexcessivebyincorporatingascrapingbaracrossthehopper

outlet. It is important to ensure that thebulkmaterial doesnot skidon thesurface of the plate, severely curtailing or preventing removal of the bulkmaterial.

CENTRIFUGALHOPPERFEEDERAcentrifugalhopperfeedershowninFigure12.28 isafeedersystem,

with a central flat or conical turntable,whichdrives theworkingmaterialsvia a rotary action. The resulting centrifugal force causes workpieces toseparateoutoftheheapandmovetowardstheedgeofthedrum.Here,theymeet thedeliveryringandslideonto theramp.Thespeedsof the turntableand thedelivery ring canbe adjusted separately.Separatedoutworkpiecescanbealignedbyorientingdevicesand, thus,proceed to thepick-uppointcorrectly orientated. Incorrectly orientated workpieces pass back into thehopper.Complexworkpiecescanbefedbymeansofaconveyorbelt.Anyexcessconveyedworkpiecesfallbackintotheheapinthehopper.

FIGURE12.28CentrifugalHopperFeeder.

CENTERBOARDHOPPERFEEDERIn this feeder, a blade made of hardened steel, with a shaped top is

oscillated up and down (by a crankmechanism) through a mass of parts.Properly oriented parts are picked by the blade and discharged by gravityinto the track.This typeof feeder is suitable forpartshavingsimpleshapelike balls, cylinders, nuts and bolts, rivets, etc. These are very robust andhavealongworkinglife.Thecapacityofacenterboardhopperislarge.Thedisadvantageoftheseisthattheycannotbeusedforfragilecomponentsandthedegreetowhichtheycanorientisratherlimited.

FIGURE12.29CenterboardHopperFeeder.

FLEXIBLEFEEDERSA crucial component of any assembly system is the parts feeders.

Unfortunately,partsfeedersarealsooneofthemostspecializedcomponentsofsuchsystems.Whileamodularapproachcouldbeemployedwhichwouldallowspecializedfeederstobequicklybroughtintotheworkcell,thereareseveral difficulties, which present themselves using this approach. First, afeeding system tends to be large and bulky in comparison to otherspecialized components, such as a robot’s gripper. Size alone couldmakestoring all the specialized feeders difficult. Second, a feeding system isgenerally more expensive than other specialized components. It might bedifficult to economically justifybuilding severalnew feeders for eachnewproduct being assembled. Third, the lead-time to build and adjust mostcurrent feeding systems is rather long. This diminishes the ability of theworkcell toberapidlyadapted tonewproducts.Therefore,simplyplacing

current feeding technology behind a generic, modular interface is not afeasiblesolution.

A typical robotic mechanical assembly work cell may have severalfeeders that are tooled specifically for particular parts. Any change to thedesign of a part requires that the feeder be either re-tooled or completelyreplaced.Withtoday’sproductlifecyclesasshortasafewmonthsformanyconsumer products, this is no longer acceptable. The need for greaterflexibility,lowercostofautomation,andfasterproductchangeovertimehasbrought about a new approach to parts feeding, termed flexible feeding.Flexible feeding is an emerging alternative to traditional part feedingmethods.Thisalternativegreatlyenhancestheversatilityofamanufacturingworkcell by using a robot manipulator and sophisticated sensing devicessuchasmachinevision; therebysignificantlyreducingbothcostandsetuptime.

Flexible feeding combines several different technologies into asubsystem including servo controlled conveyors that canbe reprogrammedfordifferentspeedandmotionprofiles,mechanicaltransferdevicessuchashoppersandbucketsusedtore-circulateparts,machinevisionandlighting,andarobotmanipulator.

While vibratory bowl feeders are “hard tooled” tomanipulate the fedpart into a single orientation, flexible feeders take advantage of the visionsystem’s capability to determinepart position andorientation.The flexiblepartfeederneedonlyde-bulk,disentangle,andre-circulateparts,whichisamuch simpler task. Conversely, because the bowl feeder is morecomplicated, itmaybecomejammed,therebycausingexpensivedowntime.Incaseswhererobotandmachinevisionsystemsarealreadyrequiredfortheassembly task itself, it becomes very cost effective to use the sameequipmentintheupstreampartsfeedingprocess.Insomecases,itispossibleto feed multiple parts in the same feeder and use the vision system todetermine the part type, thus reducing the number of feeders, and savingmoneyandfloorspace.

This system shown in Figure 12.30 is composed of three conveyorsworkingtogether.

FIGURE12.30

Thefirstconveyor,underservocontrol,ismountedataninclinedangleandisusedtoliftpartsfromabulkhopper.Partsslidedownarampat theend of the inclined conveyor and onto the horizontal conveyor. Overheadcameras are used to locate parts on the horizontal conveyors. An array ofcompact fluorescent lights is installed within each of the horizontalconveyors.Theselightstogetherwithatranslucentconveyorbeltprovideanunder lit area inwhich parts can be presented to the vision system.Usingbinaryvision toolspartson the feederbelts are examined.First, thevisionsystem looks to see if a part is graspable (i.e., the part is in a recognized,stable, and enough clearance exists between the part and its neighbors tograsp itwith a gripper). Second, the pose of the part in the robot’sworldcoordinates is determined. This pose, and the motion associated withacquiring the part, is checked tomake sure that they are within the workenvelope of the robot. Parts, which are not in useful orientations or areoverlapping, aredropped from the endof thehorizontal conveyoronto thereturn conveyor.The return conveyor transports the parts back to the bulkhopperforre-feeding.

FlexibleFeederSubsystemFlexiblefeedersaredividedintothreedistinctsubsystems,whichwork

together to feed parts. They are the parts presentation subsystem, the partpose determination subsystem, and the part retrieval subsystem, discussedbelow.

1.PartsPresentation

The firstmajor component of any flexible feeding system is the partspresentation subsystem. This is the component of the feeder, which is

responsibleforremovingpartsfromthebulksupplyandpresentingtheminaquasi-singulated fashion to the rest of the system. There are two majormodesofoperation,whichmaybeidentifiedforthissubsystem:incrementalandcontinuous.Intheincrementalmode,ahigher-levelobjectrequeststhatthesubsystemmovemorepartsintotherangeofthesensingelement.Whenthesubsystemhasaccomplishedthistask,itsignalsthecallingobjectthatithasfinished.Thesecondmodeofoperationiscontinuous,inwhichpartsarecontinuouslymovedpastthesensor.Inthecontinuousmode,ahigher-levelobjectfirstrequeststhatthesubsystembeginoperation,andthenwaitsforasignalthatanadditionalbatchofpartshasmovedintorange.Aslongasthesubsystemisoperating,additionalnewparts-in-rangesignalsaregenerated.

2.PartPoseDetermination

The second major component of any flexible feeder is the part posedeterminationsubsystem.Thisisthecomponentofthefeederresponsibleforexaminingtheparts,whicharewithinsensingrange,anddeterminingwhichofthosepartsareadvantageoustoretrievalandassembly.Thissubsystemismostoftenconstructedusinganindustrialvisionsystem.Ingeneral,avisionsystemplacestheleastamountofrestrictiononthetypesofpartsthatcanbesensed. The part pose determination subsystem can also operate in twomodes.Thefirstistofindasingleretrievablepartinthesensingareaandthesecondistofindallretrievablepartsinthesensingarea.

3.PartRetrieval

The final component of any flexible feeder is the part retrievalsubsystem. This is the component, which is responsible for actuallyretrievingtheparts,whichhavebeenidentifiedbythepartposesubsystem.While this component of the feeder is most often an industrial robot, thefundamental requirement is amechanism capable of reaching any locationand orientationwithin a certain space. Industrial robots are generally usedbecause they are well understood, well accepted, and often come with aprogrammable controller, which can save substantial time in systemdevelopment.

AdvantagesofFlexibleFeedingSomeof the advantagesof the flexible feedingconceptof automation

are:

1.

2.3.4.5.

6.

7.

8.9.

10.11.

Toolingissoft:Thetoolingisthevisionandrobotsoftware.Nolongleadtimestofabricatetooling.Tooling is flexible: Simultaneous product and tooling development canoccur with flexible feeding. Flexible feeding easily accommodatesdesignchangesthatoccurinproductdevelopment.Theabilitytoquicklyproducenewproductsatproductionvolumes isacompetitiveadvantage.Avoidstheexpenseofbuildingprototypeandmanualassemblytooling.Can automate with lower production volumes through combining ofproductsonsameflexfeedingcell.Simultaneous quality vision inspection using the vision system thatguidesrobot.Majority of tooling capital expense is reusable if new product is notsuccessfulinthemarketplace.

EXERCISESHoware transferdevicesclassified?Describe theconstruction,workingprinciple,andimportantapplicationsofanytwotypesoftransferdevices.Whatisatransfermachine?Whataretheadvantagesanddisadvantagesoftransfermachines?Defineautomatedmaterialhandling.What are automated assembly lines? What are the reasons for usingautomatedassemblylines?What is amaterial transport system?List the various types ofmaterialtransportequipment.Briefly explain the various types of transfer systems used in assemblylines.Namethreelinearandthreerotarytransfersystems.Namesomeimportantapplicationsoftransferdevicesandfeedersintheindustry.Statetheroleoftransferdevicesinassemblyoperations.List various transfer devices available formovement of components inindustry.

12.13.

14.15.

16.17.18.19.

20.21.22.

23.24.25.26.27.28.29.

30.31.32.

33.

34.35.

Differentiatebetweeninlineandrotarytransferofworkparts.Identifythevarioustypesoftransferdevices.Explaintheworkingofanyonetypeoftransferdevicewithasketch.Describeanyonetypeofjobrotatingdevice.Identify the main elements of a parts feeding system at an assemblyworkstation.Whatarethevariousdevicesusedforalignmentofjobsforassembly?Listthefactorstobeconsideredintheselectionoftransferdevices.Whatisthefunctionoffeedersinmaterialhandling?Describetheconstructionandworkingprincipleofanytwotypesofjoborienting devices used in automatic feeding systems with the help ofsketches.Classifythevariousfeeders.Comparetransferdeviceswithfeeders.Discuss the various types of conveyors used in automated materialhandling.Listthevariouspartsfeedingdevices.Differentiatebetweenmanualandautomatedassemblylines.WriteashortnoteonGenevamechanism.Listtheadvantagesanddisadvantagesoftransfermachines.Whatisagravityconveyor?Differentiatebetweenvolumetricandgravimetrictypefeeders.Explaintheconstructionandworkingofavibratorybowlfeederwiththehelpofasketch.Whataretheadvantagesofflexiblepartsfeeding?Differentiatebetweenflexibleandvibratorybowlfeeders.Whatistheuseofanescapementandplacementdeviceinapartfeedingsystem?With the help of a sketch, explain the construction and working ofreciprocatingtubehopperfeeder.Whatarethevariousdevicesusedforalignmentofjobsforassembly?Describeanyonetypeofjobrotatingdevices.

CHAPTER13

ROBOTICS

INTRODUCTIONThe subject of robotics coversmanydifferent areas.Robots alone are

hardly ever useful. They are used togetherwith other devices, peripherals,andmanufacturingmachines. They are generally integrated into a system,whichasawholeisdesignedtoperformataskortodoanoperation.Robotsare very powerful elements of today’s industry. They are capable ofperformingmanydifferenttasksandoperationspreciselyanddonotrequirecommonsafetyandcomfortelementsthathumansneeds.However,ittakesmucheffortandmanyresourcestomakearobotfunctionproperly.Aswithhumans, robotscandocertain things,butnotother things.As longas theyaredesignedproperlyfortheintendedpurpose,theyareveryusefulandwillcontinuetobeused.Roboticsistheart,knowledgebase,andtheknow-howof designing, applying, and using robots in human endeavors. Roboticsystemsconsistofnotjustrobots,butalsootherdevicesandsystemsthatareusedtogetherwiththerobotstoperformthenecessarytasks.

HISTORYOFROBOTSThe word robot always refers to an automated multifunctional

manipulator thatworksbyenergy, toperformavarietyof tasks.Thewordrobot was introduced in 1920 in a play byKarel Capek called R.U.R., orRossum’s Universal Robots. Robot comes from the Czech word robota,meaning forced labor or drudgery. In the play, human-like mechanicalcreaturesproduced inRossum’sfactoryaredocileslaves.Because theyarejustmachines,therobotsarebadlytreatedbyhumans.Onedayamisguided

scientist gives them emotions, and the robots revolt, kill nearly all thehumans, and take over the world. However, because they are unable toreproduce themselves, the robots are doomed to die. However, the solesurviving human creates a male and a female robot to perpetuate theirspecies.

Oneofthefirsttypesofrobotswasafeedback(self-correcting)controlmechanism. It was a watering trough that used a float to sense the waterlevel.Whenthewatergetstolow,thefloatdrops,opensavalve,andmorewaterdumps into the trough.As thewater rises, sodoes the float.Once itreachesacertainheight,thevalveisclosedandthewaterisshutoff.In1954,the American inventor George Devol, Jr. developed a primitive arm thatcould be programmed to perform specific tasks. In 1975, the Americanmechanical engineer Victor Scheinman developed a truly flexiblemultipurpose manipulator known as the Programmable UniversalManipulationArm (PUMA).PUMAwas capable ofmoving anobject andplacingitwithanyorientationinadesiredlocation.Beforethe1960s,robotusuallymeantamanlikemechanicaldevice(mechanicalmanorhumanoid)capableofperforminghumantasksorbehavinginahumanmanner.Todayrobots come in all shapes and sizes, including small robots and largerwheeled robots that play footballwith a full-size ball. In 1995, therewereabout700,000 robotsoperating in theworld.Amajoruserof robots is theautomobile industry.GeneralMotors uses approximately 16,000 robots fortasks such as spot welding, painting, machine loading, parts transfer, andassembly.

DEFINITIONOFAROBOTArobotisacomputer-controlledmachinethatisprogrammedtomove,

manipulate objects, and accomplish work while interacting with itsenvironment.AccordingtotheRobotInstituteofAmerica(1979),arobotisdefined as “a reprogrammable, multifunctional manipulator designed tomove material, parts, tools, or specialized devices through variousprogrammedmotionsfortheperformanceofavarietyoftasks.”

Or

Industrial robot is defined as “a number of rigid links connected byjointsofdifferenttypesthatarecontrolledandmonitoredbycomputer.”

Onefeatureofarobotistheabilitytooperateautomatically,onitsown.This means that there must be in-built intelligence, or a programmablememory,orsimplyanarrangementofadjustablemechanismsthatcommandmanipulation.

INDUSTRIALROBOTIndustrial robots are advanced automation systems, mainly controlled

by a computer. Today computers form an important part of industrialautomation. They supervise production lines and control manufacturingsystems (e.g.,machine tools,welders, laser cuttingdevices, etc.).Thenewgeneration of robots executes various tasks in industrial systems and theyparticipate in the full automation of factories. Japanese defined industrialrobots in four levels:Manualmanipulators: perform fixed or preset task

sequences.Playbacks:repeatpre-programmedfixedinstructions.NCrobot:carryouttasksthroughnumericallyloadedinformation.Intelligentrobots:performthroughtheirownrecognitioncapabilities.

Arobotandacraneareverysimilarinthewaytheyoperateandintheway theyaredesigned.Bothpossessanumberof linksattachedserially toeachotherwithjoints,wheresometypeofactuatorcanmoveeachjoint.Inboth systems, the hand of themanipulator can bemoved in space and beplacedinanydesiredlocationwithintheworkspaceofthesystem,eachonecan carry a certain amount of load and eachone is controlledby a centralcontrollerwhichcontrols theactuators.However,one iscalleda robotandtheothermanipulator(or,inthiscase,acrane).Thefundamentaldifferencebetweenthetwoisthatinthecaseofacrane,ahumanoperatesandcontrolsthe actuators, whereas a computer that runs a program controls the robotmanipulator.Thisdifferencebetweenthetwodetermineswhetheradeviceisasimplemanipulatororarobot.Ingeneral,robotsaredesignedandmeanttobecontrolledbyacomputerorsimilardevice.Themotionsoftherobotarecontrolledthroughacontrollerthatisunderthesupervisionofthecomputer,which itself is running some type of a program. Thus, if the program ischanged, the actions of the robot is changed accordingly. The robot isdesigned to be able to perform any task that can be programmed (within

1.2.3.

(a)

(b)(c)(d)

limit, of course) simply by changing the program.The simplemanipulator(orcrane)cannotdothiswithoutanoperatorrunningitallthetime.

LAWSOFROBOTICSIsaac Asimov proposed three laws of robotics and he later added a

“zerothlaw.”

LawOne:Arobotmaynotinjureahumanbeing,or,throughinaction,allow a human being to come to harm, unless thiswould violate a higherorderlaw.

LawTwo:Arobotmustobeyordersgiventoitbyhumanbeings,exceptwheresuchorderswouldconflictwithahigherorderlaw.

Law Three: A robot must protect its own existence as long as suchprotectiondoesnotconflictwithahigherorderlaw.

LawZero:Arobotmaynotinjurehumanity,or,throughinaction,allowhumanitytocometoharm.

MOTIVATINGFACTORSForroboticssystemstobeintroducedtotheindustrialworld,theymust

have positive factors that would make a difference in using them. Themotivatingfactorscanbecategorizedas:Technicalfactors

EconomicfactorsSocialfactors

TechnicalFactorsRobotscandoincomparabletasksthathumanscan’tdo.Itisgenerally

considered that humans can’tmatch the speed, quality, reliability, and theendurance of a robotic system. In that they offer: High flexibility of

producttypeandvariation.Lowerpreparationtimethanhardautomation.Betterqualityofproducts.Fewerrejectsandlesswastethanlaborintensiveproduction.

(a)(b)(c)(d)

EconomicFactorsTheneedstoincreaseproductionratestoremaincompetitive.Pressurefromthemarketplacetoimprovequality.Increasingcosts.Shortageofskilledlabor.

SocialFactorsSome people think that the use of robotized systems increases the

unemploymentofworkers andpreventsmanypeople fromamain income.But the usage of robots causes a reduction of workload on workers andpreventsdangerousworkingconditions as robots canbeused inhazardousenvironments.

ADVANTAGESANDDISADVANTAGESOFROBOTS

Robots offer specific benefits toworkers, industries, and countries. Ifintroduced correctly, industrial robots can improve the quality of life byfreeing workers from dirty, boring, dangerous, and heavy labor. It can besaid, therefore, that robots give the possibility to humans to occupy withjobs, that they can execute better. It is true that robots can causeunemploymentbyreplacinghumanworkersbutrobotsalsocreatejobssuchasrobottechnicians,salesmen,engineers,programmers,andsupervisors.

Theadvantagesofrobotsare:

Increase in productivity, safety, efficiency, quality, and consistency ofproductswiththeuseofrobots.Robots can work in hazardous environments without the need for lifesupport,comfort,orconcernaboutsafety.Robotsneednoenvironmentalcomfortsuchaslighting,airconditioning,ventilation,andnoiseprotection.Robotscanworkcontinuouslywithoutexperiencingfatigueorboredom,donothavehangovers,andneednomedicalinsuranceorvacation.Robotshaverepeatableprecisionatalltimes,unlesssomethinghappenstothemorunlesstheywearout.

Robotscanbemuchmoreaccuratethanhumans.

Thedisadvantagesofrobotsare:

Robotsreplacehumanworkerscreatingeconomicproblems,suchaslostsalaries, and social problems such as dissatisfaction and resentmentamongworkers.Robotslackcapabilitytorespondinemergencies,unlessthesituationispredictedandtheresponseisincludedinthesystem.Safetymeasuresareneededtoensurethattheydonotinjureoperatorsandmachinesworkingwiththem.Robotsarecostlyduetoinitialcostofequipment,installationcosts,needfortraining,andneedforprogramming.

CHARACTERISTICSOFANINDUSTRIALROBOT

An industrial robot has a hand, wrist, arm, base, lifting power,repeatability,manualcontrol,automaticcontrol,memory,programs,safetyinterlock, speed of operation, computer interface, reliability, and easymaintenance.

Thehandofarobotisknownasagripperorendeffectororend-of-armtooling. It is the driven mechanical device(s) attached to the end of themanipulator.

Thewristof therobot isusedtoaimthehandatanypartof theworkpiece.Thewristmayhavethreemotions:pitch(up-and-downmotion),yaw(side-to-sidemotion),androll(rotatingmotion).

Thearmisusedtomovethehandwithinreachofapartorworkpiece.Itcanpivotatitselbowandatitsshoulderjoint.

The waist, or base, of the robot supports the arm and is called theshoulder.Thearmcanrotateabouttheshoulder.

Repeatability is the replication of motion within some specifiedprecisionortolerance.

AnRCCorremotecentercompliancedevicehelpspullthehandortoolintotherequiredpositionbyactingasamulti-axisfloat.

Amanual control device is used to teach the robot how to do a newtask.

Anautomaticcontrolsystemisusedtocarryouttheinstructionsstoredintherobot’smemory.

The robot’smemory holds a library of programs to use in executingdifferenttasks.

Safetyinterlockspreventtherobotfrominsertingahandintoamachineandcausingdamagetotherobotandmachine.

Therobot’sspeedofoperation inperforminga taskshouldbeat leastequaltothatofthehumanworkeritisreplacing.

Therobot’scomputerinterfaceenablestherobottousethecomputer’slargermemory to holdmore task programs and to synchronize its actionswithacompleteproductionlineofrobotsandothermachines.

COMPONENTSOFANINDUSTRIALROBOTIndustrial robotsystemsconsistof fourmajorsubsystemsasshown in

Figure13.1.

MechanicalunitDriveControlsystemTooling

FIGURE13.1ComponentsofanIndustrialRobot.

Ashortdescriptionofeachisgivenbelow:

MechanicalUnit.Themechanicalunitreferstotherobot’smanipulativearmanditsbase.Toolingsuchasendeffectors,toolchangers,andgrippersareattachedtothewrist-toolinginterface.Themechanicalunitconsistsofafabricatedstructuralframewithprovisionsforsupportingmechanicallinkageand joints, guides, actuators, control valves, limiting devices, and sensors.Thephysicaldimensions,design,andloadingcapabilityoftherobotdependsupontheapplicationrequirements.

Drive.An important component of the robot is the drive system.Thedrivesystemsuppliesthepower,whichenablestherobottomove.Driveforarobotmaybehydraulic,pneumatic,orelectric.Hydraulicdriveshavebeenused for heavier lift systems. Pneumatic drives have been used for highspeed, non-servo robots and are often used for powering tooling such asgrippers. Electric drive systems can provide both lift and/or precision,dependingon themotor and servo system selection anddesign.AnACorDC powered motor may be used depending on the system design andapplications.

Control System. Controller is the brain of the robot. Controller is acommunicationand information-processingdevice that initiates, terminates,andcoordinatesthemotionsandsequencesofarobot.Mostindustrialrobotsincorporate computer or microprocessor based controllers. These perform

computational functions and interface with sensors, grippers, tooling, andotherperipheralequipment.

Controller programmingmaybe doneon-line or fromoff-line controlstations. Programsmaybe on cassettes, floppy disks, internal drives, or inmemory;andmaybeloadedordownloadedbycassettes,disks,ortelephonemodem. Some robot controllers have sufficient computational ability,memorycapacity,andinput/outputcapabilitytoserveassystemcontrollersforotherequipmentandprocesses.

Tooling.Tooling ismanipulatedby the robot toperform the functionsrequired for the application. Depending on the application, the robot mayhaveonefunctionalcapability,suchasmakingspotweldsorspray-painting.Thesecapabilitiesmaybeintegratedwiththerobot’smechanicalsystemormaybeattachedattherobot’swrist-endeffectorinterface.Alternatively,therobotmayusemultipletoolsthatmaybechangedmanually(aspartofset-upforanewprogram)orautomaticallyduringaworkcycle.

Tooling and objects that may be carried by a robot’s gripper cansignificantly increase the envelope in which objects or humans may bestruck.Toolingmanipulatedby the industrial robot andcarriedobjects cancausemoresignificanthazardsthanmotionofthebareroboticsystem.Thehazards added by the tooling should be addressed as part of the riskassessment.

Sensors.Sensorsareusedtocollectinformationabouttheinternalstateoftherobotortocommunicatewiththeoutsideenvironment.Asinhumans,therobotcontrollerneedstoknowwhereeachlinkoftherobotis,inordertoknowtherobot’sconfiguration.Thestateof thehumanbodyisdeterminedbecause feedback sensors in human’s central nervous system embedded intheir muscle tendons send information to the brain. The brain uses thisinformation todetermine the lengthof theirmuscles, and thus, the stateoftheirarms,legs,etc.Thesameistrueforrobots;sensorsintegratedintotherobot send information about each joint or link to the controller, whichdetermines the configuration of the robot. Robots are often equippedwithexternalsensorydevicessuchasavisionsystem, touchand tactilesensors,speech synthesizers, etc.,which enable the robot to communicatewith theoutsideworld.

Figure 13.2 given below compares the physical parts of the humanbeingandthoseoftheindustrialrobot.

FIGURE13.2ComparisonofPartsofRobotandHumanBeing.

COMPARISONOFTHEHUMANANDROBOTMANIPULATOR

The parts of a robot’smanipulator are named after similar parts in ahuman’s chief manipulators, i.e., the arm and the hand. (Refer to Figure13.3.)

FIGURE13.3ComparisonofHumanandRobotManipulator.

ROBOTWRISTANDENDOFARMTOOLSSix axis coordinates are required by a robot in order to completely

specify the location and orientation of an object. Three coordinates canlocate the center of gravity of an object (e.g., x, y, and z coordinates-in arectangular coordinate system). Three other coordinates are normallyachievedbyaddingwristandhandmovementswiththeendofarmtooling.Therearethreebasictypesofwristmotions:Pitch-Rotationalorbending

movementinaverticalplane.Yaw-Rotationalortwistingmovementinahorizontalplane.Roll-Rotationalorswivelmovement.

Additionally, the wrist (refer to Figure 13.4) serves as the mountingpoint for a variety of devices. These end effectors are either hand, orgrippingdevices,orjobspecifictools.

FIGURE13.4RoboticWrist.

Figure13.5showsthevariousarmsandwristmotionsofarobot.

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FIGURE13.5ArmandWristMotionsofaRobot.

EndEffector.Theendeffectoristhedeviceattheendoftherobotarm.Theendeffectorattachedto therobotwrist isshowninFigure13.6.Therearetwomaintypesofendeffectors:grippersandtools.

Grippers: Grippers are devices,which can be used for holding orgripping an object. These includemechanical hands and anythinglike hooks, magnets, and suction devices, which can be used forholdingorgripping.Tools:Toolsaredevices,whichrobotsusetoperformoperationsonan object, e.g., drills, paint sprays, grinders, welding torches, andanyothertoolwhichgetaspecificjobdone.

FIGURE13.6EndEffectorAttachedtoRobotWrist.

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ROBOTTERMINOLOGYThereisasetofbasicterminologyandconceptscommontoallrobots.

Thesetermsfollowwithbriefexplanationsofeach.

LinksandJoints:Linksarethesolidstructuralmembersofarobot,andjointsarethemovablecouplingsbetweenthem.Degree of Freedom (dof): Degree of freedom is the number ofindependentmovementsarobotcanrealizewithrespecttoitsbase.Thenumberofaxesisnormallythesameasthenumberofdegreesoffreedomoftherobot.Eachjointontherobotintroducesadegreeoffreedom.Eachdegreeoffreedomcanbeaslider,rotary,orothertype of actuator. Robots typically have five or six degrees offreedomasshowninFigure13.7.Threeof thedegreesoffreedomallowpositioningin3Dspace,whiletheothertwoorthreeareusedfor orientation of the end effector. Six degrees of freedom areenoughtoallowtherobot toreachallpositionsandorientationsin3D space. Six degrees of freedom are commonly available witharticulated arm and gantry robots. Four degrees of freedom aretypicalwiththeselectivecomplianceassemblyrobotarm(SCARA)configuration. Seven or more axes are used for some specialapplications.

FIGURE13.7RobotwithSixDegreesofFreedom.

RobotwithSevenDegreesofFreedom

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Figure 13.8 shows an industrial robot with three basic degrees offreedomplusthreedegreesoffreedominthewristandaseventhinitsabilitytomovebackandforthalongthefloor.

FIGURE13.8RobotwithSevenDegreesofFreedom.

OrientationAxis:Basically,ifthetoolisheldatafixedposition,theorientation determines which direction it can be pointed in. Roll,pitch, and yaw are the common orientation axes used. (Refer toFigure13.9.)

FIGURE13.9Orientations.

PositionAxis:Thetool,regardlessoforientation,canbemovedtoanumberofpositionsinspace.ToolCenterPoint(TCP):Thetoolcenterpointislocatedeitherontherobot,orthetoolasshowninFigure13.10.Typically,theTCPis usedwhen referring to the robots position, aswell as the focalpoint of the tool (e.g., the TCP could be at the tip of a welding

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torch).TheTCPcanbespecifiedinCartesian,cylindrical,spherical,etc.,coordinatesdependingontherobot.Astoolsarechanged,oneoftenreprogramstherobotfortheTCP.

FIGURE13.10ToolCenterPoint.

Accuracy: Accuracy specification describes how close the armwillbewhenitmovestothedesiredpoint.Precision (validity): Precision is defined as how accurately aspecifiedpointcanbereached.Thisisafunctionoftheresolutionoftheactuators,aswellasitsfeedbackdevices.Repeatability (variability): Repeatability is how accurately thesamepositioncanbereachedifthemotionisrepeatedmanytimes(RefertoFigure13.11).Supposethatarobotisdriventothesamepoint100times.Becausemanyfactorsmayaffecttheaccuracyoftheposition, the robotmaynot reach the samepoint every time,but will be within a certain radius from the desired point. Theradiusofacircle that isformedbythisrepeatedmotioniscalledrepeatability.Repeatabilityismuchmoreimportantthanprecision.Ifarobotisnotprecise,itwillgenerallyshowaconsistenterror,whichcanbepredictedandthus,correctedthroughprogramming.

FIGURE13.11AccuracyversusRepeatability.

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Work envelope/Workspace:A robot can onlywork in the area inwhich it can move. This area is called the work envelope. Theworkenvelopeisdeterminedbyhowfartherobot’sarmcanreachand how flexible the robot is. The more reach and flexibility arobot has, the larger the work envelopewill be. It is one of themost important characteristics to be considered in selecting asuitable robot. Various robot configurations have different workenvelopes. For a Cartesian configuration, the reach is arectangular-typespace.Foracylindricalconfiguration,thereachisahollowcylindricalspace.Forapolarconfiguration, thereach ispart of a hollow spherical shape. Robot reach for a jointed-armconfigurationdoesnothaveaspecificshape.Figure13.12showstheworkenvelopeofarobot.

FIGURE13.12WorkEnvelopeofaRobot.

Stability.Stabilityreferstorobotmotionwiththeleastamountofoscillation.Agoodrobotisonethatisfastenoughbutatthesametimehasgoodstability.Speed. Speed refers either to the maximum velocity that isachievable by the Tool Center Point (TCP), or by individualjoints.Thisnumberisnotaccurateinmostrobots,andwillvaryover the workspace as the geometry of the robot changes (andhence the dynamic effects). The number will often reflect themaximumsafestspeedpossible.Somerobotsallowthemaximumratedspeed(100%)tobepassed,butitshouldbedonewithgreatcare.Payload.Payloadistheweightarobotcancarryandstillremainwithin its specifications. For example, a robot’smaximum loadcapacitymaybemuchlargerthanitsspecifiedpayload,butatthe

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maximumlevel,itmaybecomelessaccurate,maynotfollowitsintendedpathaccurately,ormayhaveexcessivedeflections.Thepayloadofrobotscomparedwiththeirownweightisusuallyverysmall.Reach.Reachis themaximumdistancearobotcanreachwithinitsworkenvelope.SettlingTime.During amovement, the robotmoves fast, but astherobotapproachesthefinalpositionitslowsdown,andslowlyapproachesatfinalposition.Thesettlingtimeisthetimerequiredfortherobottobewithinagivendistancefromthefinalposition.

ROBOTICJOINTSArobot joint is amechanism thatpermits relativemovementbetween

partsofarobotarm.Thejointsofarobotaredesignedtoenabletherobottomove itsend-effectoralongapath fromoneposition toanotherasdesired.Thebasicmovementsrequiredforadesiredmotionofmostindustrialrobotsare:Rotationalmovement:This enables the robot toplace its arm in any

directiononahorizontalplane.Radial movement: This enables the robot to move its end-effectorradiallytoreachdistantpoints.Vertical movement: This enables the robot to take its end-effector todifferentheights.

Degrees of freedom, independently or in combination with others,define the complete motion of the end-effector. These motions areaccomplishedbymovementsofindividualjointsoftherobotarm.Thejointmovements are basically the same as relative motion of adjoining links.

Dependingonthenatureofthisrelativemotion,thejointsareclassifiedasPrismaticjoints

Revolutejoints

Prismatic joints are also known as sliding as well as linearjoints.Theyarecalledprismaticbecausethecrosssectionofthejoint isconsideredasageneralizedprism.Theypermit linkstomakea lineardisplacement alonga fixedaxis. Inotherwords,

2.

onelinkslidesontheotheralongastraightline.Thesejointsareusedingantry,cylindrical,orsimilarjointconfigurations.

Revolutejoints,thesecondtypeofjointisarevolutejointwhereapairoflinksrotatesaboutafixedaxis.

Figure13.13showstheprismaticandrevolutejoint.

FIGURE13.13

ThevariationsofrevolutejointsshowninFigure13.14include:

Rotationaljoint(R)Twistingjoint(T)Revolvingjoint(V)

FIGURE13.14RevoluteJoints.

Arotationaljoint(R)isidentifiedbyitsmotion,rotationaboutanaxisperpendiculartotheadjoininglinks.Here,thelengthsofadjoininglinksdonotchangebuttherelativepositionofthelinkswithrespecttooneanotherchangesastherotationtakesplace.

A twisting joint (T) is also a rotational joint,where the rotation takesplaceaboutanaxisthatisparalleltobothadjoininglinks.

1.

Arevolvingjoint(V)isanotherrotationaljoint,wheretherotationtakesplaceaboutanaxisthatisparalleltooneoftheadjoininglinks.Usually,thelinks are aligned perpendicular to one another at this kind of joint. Therotationinvolvesrevolutionofonelinkaboutanother.

CLASSIFICATIONOFROBOTSRobotscanbeclassifiedbyfourfundamentalelementsofoperation:

CoordinatesystemsPowersourceMethodofcontrolProgrammingmethod

ROBOTCLASSIFICATIONONTHEBASISOFCOORDINATESYSTEMS

Structurally, robots are classified according to the wrist’s coordinatesystemasfollows:

Cartesian/RectilinearRobot:Theaxisordimensionsoftheserobotsare 3 intersecting straight lines (x-y-z) as shown in Figure 13.15.TheCartesiancoordinaterobotisonethatconsistsofacolumnandanarm.Itissometimescalledanx-y-zrobot,indicatingtheaxisofmotion. The x-axis is lateral motion, the y-axis is longitudinalmotion, and thez-axis isverticalmotion.Thus, thearmcanmoveupanddownonthez-axis;thearmcanslidealongitsbaseonthex-axis;andthenitcantelescopetomovetoandfromtheworkareaonthey-axis.ThefeaturesofaCartesianrobot(electronicequipment,control program) are same as those of CNC machine tools.Cartesian robots are not preferred in the industry because they donothavemechanical flexibility (i.e., theycannot reachobjects thatlieonthefloororthatarenotvisiblefromtheirbase).Also,speedof operation on a horizontal plane is usually less than thecorrespondingspeedofrobotswitharevolutebase.

2.

FIGURE13.15CartesianRobot.

Applications

Thesetypesofrobotsareusedfor:

PickandplaceworkApplicationofsealantAssemblyoperationsHandlingmachinetoolsArcwelding

Advantages

AbilitytodostraightlineinsertionsintofurnacesEasycomputationandprogrammingMostrigidstructureforgivenlengthDisadvantages

RequireslargeoperatingvolumeExposed guiding surfaces require covering in corrosive or dustyenvironmentsCanonlyreachfrontofitselfAxishardtoseal

Cylindrical Robot: Cylindrical robots have one angular dimensionand 2 linear dimensions as shown in Figure 13.16. The rigidstructureofthissystemoffersthemthecapabilitytoliftheavyloadsthrougha largeworkingenvelope.Themainbodyof sucha robotconsists of a horizontal arm mounted on a vertical column. Thecolumn ismounted on a rotating base. The horizontal armmovesforwardandbackwardonthedirectionofthelongitudinalaxisandit also moves up and down on the column. Column and arm arerotating on the base around the vertical axis. Resolution of a

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cylindrical robot is not constant, but depends on the distancebetweenthecolumnandthetoolalongthehorizontalarm.

FIGURE13.16CylindricalRobot.

Applications

Thesetypesofrobotsareusedfor:

AssemblyoperationsHandlingmachinetoolsSpot-weldingHandlingdie-castingmachines

Advantages

CanreachallarounditselfRotationalaxiseasytosealRelativelyeasyprogrammingRigidenoughtohandleheavyloadsthroughlargeworkingspaceGoodaccessintocavitiesandmachineopeningsDisadvantages

Can’treachaboveitselfWon’treacharoundobstaclesExposeddrivesaredifficulttocoverfromdustandliquidsLinearaxesishardtoseal

Spherical (Polar) Robot: Robots of this type consist of a rotatingbase,aliftingpart,andatelescopicarm,whichmovesinwardsandoutwards (refer to Figure 13.17). The 2 dimensions of spherical

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robotsareanglesandthethirdisalineardistancefromthepointoforigin.Theserobotsoperateaccordingtosphericalcoordinatesandoffergreaterflexibility.Thisdesignisusedwhereasmallnumberofverticalactionsareadequate.

FIGURE13.17SphericalRobot.

Applications

Thesetypesofrobotsareusedfor:

HandlingsatdiecastingorfettlingmachinesHandlingmachinetoolsArc/spotwelding

Advantages

LargeworkingenvelopeTworotarydrivesareeasilysealedagainstliquids/dustDisadvantages

Complex coordinates more difficult to visualize, control, and programExposedlineardriveLowaccuracy

ArticulatedRobot:Articulatedrobotsconsistofthreeconstantparts(links) that are joined with revolute joints and are placed on arotating base as shown in Figure 13.18. The kinematics layout issimilartoahumanarm.Thetool(gripper)issimilartoapalmandisadjusted to the lowerpartof thearmthroughthewrist.Theelbowconnects the lower and upper part of the arm and the shoulderconnects the upper part of the armwith the base.Many times theshoulder joint has a rotationalmotion in the horizontal plane.The

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articulated robot has all three axes revolute, so the positionresolutioniscompletelydependentonthearm’sposition.Thetotalaccuracy of an articulated robot is small, because joint errors areaccumulatedattheendofthearm,whichisatthewristposition.

FIGURE13.18ArticulatedRobot.

Applications

Thesetypesofrobotsareusedfor:

AssemblyoperationsDiecastingFettlingmachinesGasweldingArcweldingSpray-painting

Advantages

HighmechanicalflexibilityThey canmovewithhigh speed at threedegreesof freedomAll jointscanbesealedfromtheenvironmentDisadvantages

Extremelydifficulttovisualize,control,andprogramRestrictedvolumecoverageLowaccuracy

SCARA Robot: One style of robot that has recently become quitepopular isacombinationof thearticulatedarmand thecylindrical

robot.ThisrobothasmorethanthreeaxesandiscalledaSCARArobot (refer to Figure 13.19). It is used widely in electronicassembly. The rotary axes are mounted vertically rather thanhorizontally. This configuration minimizes the robot’s deflectionwhenitcarriesanobjectwhilemovingataprogrammedspeed.TheacronymSCARAstands forSelectiveComplianceAssemblyRobotArm,aparticulardesigndevelopedinthelate1970s.

FIGURE13.19SCARARobot.

Applications

SCARArobotsarecommonlyusedfor:

PickandplaceworkAssemblyoperationsApplicationofsealantHandlingmachinetools

Advantages

HighspeedExcellentrepeatabilityGoodpayloadcapacityLargeworkareaforfloorspaceModeratelyeasytoprogram

Disadvantages

Limitedapplications

TwowaystoreachpointDifficulttoprogramoff-lineHighlycomplexarm

ROBOTCLASSIFICATIONONTHEBASISOFPOWERSOURCE

Actuators drive the mechanical linkages and joints of a manipulator,which can be various types of motors and valves. The energy for theseactuatorsisprovidedbysomepowersourcesuchashydraulic,pneumatic,orelectric.Therearethreemajortypesofdrivesystemsforindustrialrobots:

HydraulicdrivesystemPneumaticdrivesystemElectricdrivesystem

1.HydraulicDriveSystem

Themostpopularformofthedrivesystemisthehydraulicdrivesystembecause hydraulic cylinders and motors are compact and allow for highlevelsofforceandpower,togetherwithaccuratecontrol.Thesesystemsaredrivenbyafluidthatispumpedthroughmotors,cylinders,orotherhydraulicactuator mechanisms. A hydraulic actuator converts forces from highpressurehydraulicfluid into themechanicalshaft rotationor linearmotion.Hydraulic robotsarepreferred inenvironments inwhich theuseofelectricdriverobotsmaycausefirehazards,forexample,inspraypainting.

Advantages

Ahydraulicdevicecanproduceanenormousrangeofforceswithouttheneed for gears, simply by controlling the flow of fluid Preferred formovingheavypartsPreferredtobeusedinexplosiveenvironmentsSelf-lubricationandself-coolingSmoothoperationatlowspeedsThereisneedforreturnline

Disadvantages

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OccupylargespaceareaThereisadangerofoilleaktotheshopfloor

2.PneumaticDriveSystem

Pneumatic drive systems are found in approximately 30 percent oftoday’s robots. These systems use compressed air to power the robots.Becausemachineshopstypicallyhavecompressedairlinesintheirworkingareas, the pneumatically driven robots are very popular. These robotsgenerallyhavefeweraxisofmovementandcancarryoutsimplepick-and-place material-handling operations, such as picking up an object at onelocation and placing it at another location. These operations are generallysimple and have short cycle times. The pneumatic power can be used forslidingorrotationaljoints.

Advantages

Less expensive than electric or hydraulic robots Suitable for relativelyless degrees of freedomdesignDo not pollutework areawith oilsNoreturnlinerequiredPneumaticdevicesarefastertorespondascomparedtoahydraulicsystemasairislighterthanfluidDisadvantages

Compressibility of air limits control and accuracy aspects NoisepollutionfromexhaustsLeakageofaircanbeofconcern

3.ElectricDriveSystem

Electricaldrivesystemsareusedinabout20percentoftoday’srobots.These systems are servomotors, steppingmotors, and pulsemotors. Thesemotorsconvertelectricalenergyintomechanicalenergytopowertherobot.Comparedwithahydraulicsystem,anelectricsystemprovidesarobotwithless speed and strength. Electric drive systems are adopted for smallerrobots.Electricallydrivenrobotsarethemostcommonlyavailableandusedindustrialrobots.Therearethreemajortypesofelectricdrivethathavebeenusedforrobots:

Stepper Motors: These are used mainly for simple pick and placemechanismswherecostismoreimportantthanpowerorcontrollability.DCServos:For theearlyelectricrobots, theDCservodrivewasusedextensively.Itgavegoodpoweroutputwithahighdegreeofcontrolof

(c)bothspeedandposition.ACServos: In recentyears, theACservohas takenover fromtheDCservo as the standard drive. Thesemodernmotors give higher poweroutputandarealmostsilentinoperation.Astheyhavenobrushes,theyareveryreliableandrequirealmostnomaintenanceinoperation.

Advantages

GoodforsmallandmediumsizerobotsBetterpositioningaccuracyandrepeatabilityLessmaintenanceandreliabilityproblemsDisadvantages

Provides less speed and strength than hydraulic robotsNot all electricmotors are suited for use as actuators in robots Require moresophisticatedelectroniccontrolsandcanfailinhightemperature,wet,ordustyenvironments

ROBOTCLASSIFICATIONONTHEBASISOFMETHODOFCONTROL

Themotionsofarobotarecontrolledbyacombinationofsoftwareandhardware that is programmedby the user.Robots are classified by controlmethodintoservoandnon-servorobots.

1.Non-ServoControlledRobots

Non-servo control is a purely mechanical system of stops and limitswitches,whicharepre-programmedforspecificrepetitivemovements.Thiscanprovideaccuratecontrolforsimplemotionsatlowcost.Themotionsofnon-servo controlled robots are controlled only at their endpoints, notthroughout their paths.Non-servo robots are often referred as “endpoint,”“pick and place,” or “limited sequence” robots. These robots are usedprimarilyformaterialstransfer.

Characteristicsofnon-servorobotsinclude:

Relatively high speed possible due to smaller size of the manipulatorTheserobotsarelowcostandsimpletooperate,program,andmaintainThese robots have limited flexibility in terms of program capacity andpositioningcapability

2.ServoControlledRobots

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2.ServoControlledRobots

Servocontrolsystemiscapableofcontrollingthevelocity,acceleration,and path of motion, from the beginning to the end of the path. It usescomplex control programs. These systems use programmable logiccontrollers (PLCs) and sensors to control themotions of robots. They aremore flexible than non-servo systems, and they can control complicatedmotions smoothly. Sensors are used in servo-control systems to track thepositionofeachof theaxisofmotionof themanipulator.Servocontrolledrobotsareclassifiedaccordingtothemethodthatthecontrollerusestoguide

the end-effector. These are: Point-to-point (PTP) control robotContinuous-path(CP)controlrobotControlled-pathrobot

Point-to-PointControlRobot(PTP)

Apoint-to-pointrobotiscapableofmovingfromonediscretepointtoanother within its working envelope. During point-to-point operation therobotmoves toaposition,which isnumericallydefined,and itstops there.Theendeffectorperformsthedesiredtask,whiletherobotishalted.Whentaskiscompleted,therobotmovestothenextpointandthecycleisrepeated.Suchrobotsareusually taughtaseriesofpointswitha teachpendant.Thepointsarethenstoredandplayedback.

Applications:Point-to-point robots are severely limited in their rangeofapplications.Commonapplicationsinclude:ComponentinsertionSpot-weldingHoledrillingMachineloadingandunloadingAssemblyoperations

An example of a typical point-to-point system is found in a spotweldingrobot. In thiscase, therobotmovesuntil thepoint tobewelded ispositionedbetweenthetwoelectrodesoftheweldingpistol,andweldingisperformed.Then, therobotmoves toanotherpoint,which isagainwelded.Thisprocedureisrepeateduntilallnecessarypointsarewelded.

Continuous-path(CP)ControlRobot

In acontinuous-path robot, the toolperforms its task,while the robot(its axes) is inmotion, like in the case of arcwelding,where theweldingpistol is driven along the programmed path. All axes of continuous path

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robots move simultaneously, each with a different speed. The computercoordinatesthespeedssothattherequiredpathisfollowed.Therobot’spathis controlled by storing a large number of spatial points in the robot’smemoryduringtheteachsequence.Duringteaching,andwhiletherobotisbeing moved, the coordinate points in space of each axis are continuallymonitoredandplacedintothecontrolsystem’scomputermemory.Thesearethe most advanced robots and require the most sophisticated computercontrollersandsoftwaredevelopment.

Applications:Typicalapplicationsinclude:

SpraypaintingFinishingGluingArcweldingoperationsCleaningofmetalarticlesComplexassemblyprocesses

Controlled-pathRobot

In controlled-path robots, the robot is moved along a computer-generated, predictable path as the robot travels from point to point. Thecomputer-generatedpathmaybeastraightlinewithend-effectororientationor it may involve curved paths through successive points and/or gradualorientationchanges.Goodaccuracycanbeobtainedat anypoint along thespecified path. Only the start and finish points and the path definitionfunctionmustbestoredintherobot’scontrolmemory.Therobotmovementsaremoreprecisethanwithpoint-to-pointprogrammingandarelesslikelytopresentahazardtopersonnelandequipment.

ROBOTCLASSIFICATIONONTHEBASISOFPROGRAMMINGMETHOD

Robotscanbeclassifiedaccordingtotheprogrammingmethodsuchas:

ManualprogrammingLead-throughprogramming

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Walk-throughprogramming

These methods are discussed in detail in chapter of RobotProgramming.

ROBOTSELECTIONOncetheapplicationisselected,asuitablerobotshouldbechosenfrom

themanycommercial robotsavailable in themarket.Thecharacteristicsofrobotsgenerallyconsideredinaselectionprocessinclude:SizeofclassDegreesoffreedomVelocityDrivetypeControlmodeRepeatabilityLiftcapacityRight-left,Up-down,andIn-outtraverseYaw,pitch,androllWeightoftherobot

Size of class: The size of the robot is given by the maximumdimension(x)oftherobotworkenvelope.

Micro(x<1m)Small(1m<x<2m)Medium(2m<x<5m)Large(x>5m)

Degreesoffreedom:Thecostoftherobotincreaseswiththenumberofdegreesoffreedom.Sixdegreesoffreedomissuitableformostworks.

Velocity: Velocity consideration is effected by the robot’s armstructure.

RectangularCylindricalSphericalArticulated

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Drivetype:HydraulicElectricPneumatic

Controlmode:Point-to-pointcontrol(PTP)Continuouspathcontrol(CP)Controlledpathcontrol

Liftcapacity:0–5kg5–20kg20–40kgandsoforth

ROBOTWORKCELLIndustrialapplicationsof robotsalmostalways involveotherpiecesof

equipment, such as machine tools, conveyors, sensors, and fixtures, inadditiontotherobotitself.Eachpieceofequipmentperformssomefunctioninthecell,andforthecelltoperformproperly,allofthesefunctionsmustbesequenced and coordinated with the actions of the robot. The function ofworkcell control is to provide this sequencing and coordination of the cellcomponents.RobotworkcellisshowninFigure13.20.

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FIGURE13.20RobotWorkcell.

A control unit called the workcell controller accomplishes workcellcontrol. Inmost applications, the robot’s controller serves as theworkcellcontroller.Anumberofinputandoutputportsareincludedonthebackpaneloftherobotcontrollertopermitelectricalconnectionstobeestablishedwiththe other cell components.Control commands, interlocks, sensor data, andothersimilarsignalsenterandleavethecontrollerthroughtheseinput/outputports.The sequencingandcoordinationof the signals isdonebymeansofthe robot program. In some robot applications, the robot controller isinadequateastheworkcellcontrolunit.Theseapplicationsincludesituationswhere the robot lacks sufficient input/output capacity to deal with thenumberofinput/outputsignalsthatmustbecoordinated,orwheretherearemultiplerobotsinthecell(e.g.,arobotspotweldinglineforcarbodies).Inthese cases, a programmable controller or small computer is used as theworkcell controller.These control units download commands to the robots(toactivateportionsoftherobotprograms)andothercomponentsinthecellinordertoaccomplishtheworkcellcontrolfunction.

The workcell controller performs several important functions in therobot installation. The functions can be divided into three categories:

SequencecontrolOperatorinterfaceSafetymonitoring

SequenceControl:Sequencecontrolisthebasicfunctionoftheworkcellcontroller.Itisconcernedwithregulatingthesequenceofactivitiesinthecell.Thesequenceisdeterminednotonlybycontrolling the activities as a function of time; it is alsodeterminedbyusinginterlockstoensurethatcertainelementsoftheworkcyclearecompletedbeforeotherelementsarestarted.For example, consider a robotmachine loading and unloadingapplication.Input/outputinterlocksinsequencecontrolareusedforpurposessuchasthefollowing:Makingsurethatthepartisatthepickuplocationbeforetherobotattemptstograspit.

Ensuring that the part is properly loaded into the machine before theprocessingcyclebegins.Indicatingtotherobotthatthemachinecycleiscompletedandthepartisreadforunloading.

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OperatorInterface:Ameansfortheoperatortointeractwiththerobot cell must be provided. Reasons for establishing theoperatorinterfaceincludethefollowing:Programmingtherobot.

Participation in theworkcyclebyahumanoperator.Thehumanbeingandtheroboteachperformaportionoftheworkinthecell.Thehumanbeing typically accomplishes tasks that require judgment or sensorycapabilitiesthattherobotdoesnotpossess.Certainassemblyoperationsfitthiscategory.Data entry by the human operator. The datamight simply be the partidentificationso that the robotcanuse thecorrectworkcycle. Inothercases,alphanumericdata(e.g.,partdimensions)mustbeprovided.Emergencystoppingofthecellactivities.

There are a number of ways to provide the operator interface: teachpendant, control panel of the robot controller, alphanumeric keyboard andCRTmonitor, and emergency stopbuttons located in the cell.Alternativesthatmightbeconsideredincludeautomaticbarcodereadersandvoiceinputofdata.Anotherimportantreasonforoperatorinteractionwiththerobotcellisforstoppingtheworkcycleduetoemergencyconditions.Theemergencymightresultfromamalfunctionoftherobot(orotherequipmentinthecell),or fromahumanworker inadvertently intruding into the cell space.Underthese circumstances, itwould be desirable to stop the action in the cell topreventharmtoeitherequipmentorpeople.Anemergencystopbuttonintheworkcellisprovidedforthispurpose.

SafetyControl:Emergencystoppingoftherobotcyclerequiresan alert operator to notice the emergency and take positiveactiontointerruptthecycle.Safetyemergenciesarenotalwaysso convenient as to occurwhen an alert operator is present.Amore automatic and reliable means of protecting the cellequipmentandpeoplewhomightwanderintotheworkzoneiscalled safety monitoring. Safety monitoring (the term hazardmonitoring is also sometimes used) is a workcell controlfunction in which sensors are used to monitor the status andactivities of the cell and to detect the unsafe or potentiallyunsafeconditions.Varioussensorscanbeused to implementasafetymonitoringsysteminarobotcell.Thesesensors includesimple limit switches that detect whether the movement of a

particular component has occurred correctly, temperaturesensors, pressure sensitive floor mats, light beams combinedwithphotosensitivesensors,andmachinevisionsystems.

Thesafetymonitoringsystemisprogrammedtorespondtothevarioushazard conditions in differentways.These responsesmight include one ormoreofthefollowing:completestoppageofthecellactivity,slowingdownthe robot speed to a safe level (when human beings are present), warningbuzzers to alert maintenance personnel of a safety hazard in the cell, andspecially programmed subroutines to permit the robot to recover from aparticularunsafeevent.Thislastresponseisanexampleofprogrammingforautomatedsystemsthatiscallederrordetectionandrecovery.

MACHINEVISIONTheuseofmachinevisiontechnologyisgrowingveryrapidly,spurred

bytheneedofmanufacturersforincreasinglyfinecontroloverthequalityofmanufactured parts. Machine vision (MV) is the application of computervision to industry and manufacturing.Whereas computer vision is mainlyfocused on machine-based image processing, machine vision most oftenrequiresalsodigital input/outputdevicesandcomputernetworks tocontrolother manufacturing equipment such as robotic arms. Machine visiontechnologyusesanimagingsystemandacomputertoanalyzeanimageandto make decisions based on that analysis. There are two basic types ofmachine vision applications—inspection and control. In inspectionapplications, the machine vision optics and imaging system enable theprocessor to “see” objects precisely and, thus,make valid decisions aboutwhichpartspassandwhichpartsmustbescrapped.Incontrolapplications,sophisticated optics and software are used to direct the manufacturingprocess.Machine vision-guided assembly can eliminate any operator errorthat might result from doing difficult, tedious, or boring tasks; can allowprocessequipmenttobeutilized24hoursaday;andcanimprovetheoveralllevelofquality.

Machinevision systemsareprogrammed toperformnarrowlydefinedtasks such as counting objects on a conveyor, reading serial numbers, andsearching for surface defects.Manufacturers favormachine vision systemsfor visual inspections that require high-speed, high-magnification, 24-hour

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operation, and repeatability of measurements. Machine vision systemstypically are fast enough to inspect 100% of the product being processedwithoutslowingupthemanufacturingline.Machinevisionsystemsaremoreadaptable than traditional optical or mechanical sensors. They offer theversatilityand flexibilityofa robot.Whenalterations to themanufacturingprocessarerequired, thesesystemsareeasilyreconfigured,oftenwithonlyminorsoftwarechanges.

The following process steps are common to all machine visionapplications:

Image acquisition: An optical system gathers an image, which isthenconvertedtoadigitalformatandstoredintocomputermemory.

Imageprocessing:Acomputerprocessorusesvariousalgorithmstoenhanceelementsoftheimagethatareofspecificimportancetotheprocess.

Feature extraction: The processor identifies and quantifies criticalfeaturesintheimage(e.g.,thepositionofholesonaprintedcircuitboard, the number of pins in a connector, the orientation of acomponentonaconveyor)andsendsthedatatoacontrolprogram.

Decision and control: The processor’s control program makesdecisionsbaseduponthedata.Aretheholeswithinspecification?Isapinmissing?Howmustarobotmovetopickupthecomponent?Machine vision technology is used extensively in the automotive,agricultural,consumerproduct,semiconductor,pharmaceutical,andpackaging industries, tonamebut a few.Someof thehundredsofapplications include vision-guided circuit board assembly, andgauging of components, razor blades, bottles and cans, andpharmaceuticals.

ComponentsofaMachineVisionSystemAsimplemachinevisionsystemwillconsistofthefollowing:

AnopticalsensorAblack-and-whitecameraLightingCamerainterfacecardforcomputer,knownas“framegrabber”

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Computer software to process images Digital signal hardware or anetworkconnectiontoreportresults.

Theopticalsensordetermineswhenapartmovingonaconveyorisinposition to be inspected. The optical sensor triggers the camera to take apictureofthepartasitpassesbeneaththecameraandlighting.Thelightingused to illuminate the part is designed to highlight features of interest andobscureorminimizetheappearanceoffeaturesthatarenotofinterest.

Thecamera’s image iscapturedby the framegrabber.Aframegrabberis a computer card that converts theoutputof the camera todigital formatandplacestheimageincomputermemorysothatitmaybeprocessedbythemachinevisionsoftware.

Thesoftwarewilltypicallytakeseveralstepstoprocessanimage.Oftentheimageisfirstmanipulatedtoreducenoiseortoconvertmanyshadesofgray to a simple combination of black and white. Following the initialsimplification, the softwarewill count,measure, and/or identify objects intheimage.Asafinalstep,thesoftwarepassesorfailsthepartaccordingtoprogrammed criteria. If a part fails, the softwaremay signal amechanicaldevicetorejectthepart;alternately,thesystemmaystoptheproductionlineandwarnahumanworkertofixtheproblemthatcausedthefailure.

Thoughmostmachinevisionsystemsrelyonblack-and-whitecameras,theuseofcolorcamerasisbecomingmorecommon.It isalsoincreasinglycommonformachinevisionsystemstoincludedigitalcameraequipmentfordirectconnectionratherthanacameraandseparateframegrabber.

AdvantagesofMachineVisionAmachinevisionsystemthathasbeencarefullyengineered tomeeta

well-definedsetofrequirementswillperformwellandbeverycosteffective.Specific advantages of such a system include the following:Precision:

Thewell-designedvisionsystemiscapableofmeasuringdimensionstoonepart in a thousand or better. Because these measurements do not requirecontact,thereisnowearordangertodelicatecomponents.

Consistency: Because vision systems are not prone to the fatiguesuffered by human operators, operational variability is eliminated.Furthermore, multiple systems can be configured to produceidenticalresults.

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Costeffectiveness:Withthepriceofcomputerprocessingdroppingrapidly, machine vision systems are becoming increasingly costeffective.A$10,000visionsystemcaneasily replace threehumaninspectorswho each earn $20,000 per year ormore. Furthermore,theoperatingandmaintenancecostsofvisionsystemsarelow.

Flexibility: Vision systems can make a wide variety ofmeasurements. When applications change, the software can beeasilymodifiedorupgradedtoaccommodatenewrequirements.

ApplicationsofMachineVisionTheapplicationsofMVinclude:

Large-scaleindustrialmanufactureShort-rununiqueobjectmanufactureSafety systems in industrial environments Inspection of pre-manufacturedobjects (e.g.,qualitycontrol, failure investigation)Visualstockcontrolandmanagementsystems(counting,barcodereading,storeinterfaces for digital systems) Control of automated guided vehicles(AGVs) Automated monitoring of sites for security and safetyMonitoringofagriculturalproductionQualitycontrolandrefinementoffoodproductsRetailautomationConsumerequipmentcontrolMedical imaging processes (e.g., interventional radiology) Medicalremoteexaminationandprocedures

ROBOTICSANDMACHINEVISIONThemachine vision systemprovides robotswith eyes. The intelligent

sensing system can be used to detect locations, identify items, and evenmeasurethedimensionsofprocessabletargets.Theneedforstandardrobotprogramminginrobotweldingapplicationsisreducedandaccurate3DCADinformationisnolongerrequired.Machinevisionenablesrobotstonavigateorchards and battlefields or to follow precisely the contours of a fighteraircraft. Imageanalysisandpattern recognitionalgorithms locate tumors inthebody,identifycustomersatbankautomatictellermachines(ATMs),anddetecthiddencracksinmachinedparts.

Here is an example ofmachine vision used together with robotics toperformataskbetterthanahumancan.

“Amanufacturerofanti-lockbrakesensorsexperiencedrecallproblemsdue to the high failure rate of components.Themain cause of the failureswasthewirestothesensors,whichweredamaged.Thecauseofthedamagewasthefatigueoftheworker,whotuckedthewiresaroundthebodyofthesensor.Amachinevisionsystemwas installedandconnected toa robot. Itwas able to perform the task using a three-dimensional machine visionsystem,whichcontrolledtherobot.Thefailureratehasbeenreducedtozeroand the systemworks three shifts a day without breaks. The solution haseliminateda tediousandrepetitive task,whichoften leads toanunpleasantworkingenvironment.”

ReasonsforIncreasedAdoptionofVision-guidedRobotics

Productiondemandsforhigherspeedandhigherflexibility.Increased use of vision guided robots has become a standard part ofproduction equipment and are designed into the application from thebeginning.Theneedformoreflexibility.Theneedforhigherautomationtosavelaborcosts.Theneedforhigheraccuracyinproduction.Theincreasingacceptanceofthetechnology.Decreasinginvestmentforsimpleapplications.MoreuserfriendlyMMI.

ApplicationsofVision-guidedRobotsIndustries of all types are embracing vision-guided robots because of

thebenefitsthetechnologiesprovide:lowercosts,flexibility,reliability,andsafety, just to name a few. Every industry with high production costs orcriticalproductionstepsarepotentially interested invision-guidedrobotics.Some of the industries using vision-guided robots are: Automotive,

automotive suppliers: part handling, assembly, gauging, robot-guidedinspection,andlogisticsElectronics:pick&placePackaging:pick&place

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Machining: loading & unloading Press shops: loading & unloadingAerospace:rivet-robotCeramics:parthandlingConsumergoodsPackagingofconsumergoodsWarehouselogisticsandobjecthandling

MachineVisionTechnologies

ImageprocessingSceneanalysisPatternrecognitionModel-basedvisionSensorfusionMotionanalysisInfraredimageanalysisDimensionalinspectionIndustrialinspectionandprocesscontrol

ROBOTICACCIDENTSRobot accidents occur during programming, program touchup,

maintenance, repair, testing, setup, or adjustment rather than under normaloperating conditions.Theoperator, programmer, or correctivemaintenanceworker may temporarily be within the robot’s working envelope where

unintended operations can result in injury. For example:A robot’s armfunctioned erratically during a programming sequence and struck theoperator.

A materials-handling-robot operator entered a robot’s workenvelopeduringoperationsandwaspinnedbetweenthebackendoftherobotandasafetypole.

A fellow employee accidentally tripped the power switchwhile amaintenanceworkerwas servicing an assembly robot.The robot’sarmstruckthemaintenanceworker’shand.

CausesofRobotAccidents

CausesofRobotAccidentsUnsafeActs

Placingoneselfinhazardouspositionswhileprogrammingorperformingmaintenancewithintherobot’sworkenvelope.Inadvertently entering the envelope because of unfamiliarity with thesafeguardsinplaceornotknowingiftheyareactivated.Making errors in programming, interfacing peripheral equipment, andconnectinginput/outputsensors.

UnsafeConditions

Mechanicalfailure.Safeguardsdeactivated.Hazards from pneumatic, hydraulic, or electrical power that can resultfrom malfunction of control or transmission elements of the robot’spower system such as control valves, voltage variations, or voltagetransients disrupting the electrical signals to the control and/or powersupplylines.Electricalshockandreleaseofstoredenergyfromaccumulatingdevicesthatcanresultininjurytopersonnel.

PreventionofAccidentsSystemcomponentsmustbedesigned,installed,andsecuredsothatthe

hazardsassociatedwith storedenergyareminimized.Adequate roommustbeprovidedforarobot’smovementaswellasforworkers.Theremustbeameansforcontrollingthereleaseofstoredenergyinalltheroboticsystemsand for shuttingoffpower fromoutside the restrictedenvelope.Adetailedrisk assessment should be performed to ensure the safety of workers whooperate,service,andmaintaintheroboticssystem.

ROBOTICSANDSAFETYSafetyiseveryone’sresponsibility.Thepresent-dayindustrialrobotisa

dumb, senseless idiot. Therefore, safety in robotics must be managed byhumans.Inmattersofrobotsafety, thesafetyofhumansshouldcomefirst,thenthesafetyoftherobot,andfinallythesafetyofotherrelatedequipment.

Topreventhazardstothesystem,therobotsystemsoperatorshouldensurethat all appropriate safeguards are established for all robot operations.Themostdangeroussituationinwhichahumanmustworkwitharobotiswhenrepairingit.Thenextmostdangeroussituationinwhichahumanmustworkwith a robot is during the robot’s training or programming. The leastdangeroussituation inwhichhumansmustworkwitha robot isduring therobot’s normal operation. Both workers and visitors need to be protectedfrom robots.Robots can injurepeople inmanyways either throughbodilyimpactorbypinningthehumanagainstsomestructure.Allworkersshouldbeeducatedaboutthesafetyissuesinvolvedinworkingwithrobotsorotherequipment.Whenarc-weldingrobotsareused,shieldsorcurtainsshouldbeplacedaround theweldingarea toprotectpasserby fromthebright lightofthe arc. Whenever repair personnel works with a live robot, they shouldknowthelocationofnearestemergencystopbutton.

SafeguardingDevicesPersonnel should be safeguarded from hazards associated with the

restricted envelope (space) through the use of one or more safeguardingdevices:Mechanicallimitingdevices;Nonmechanicallimitingdevices;Presence-sensing safeguarding devices; Fixed barriers (which preventcontactwithmovingparts);andInterlockedbarrierguards.

ROBOTSMAINTENANCEThe user of a robot or robot system should establish a regular and

periodic inspection and maintenance program to ensure safe equipmentoperations. This program should include, but not be limited to, therecommendationsof therobotmanufacturerand themanufacturersofotherassociated robot system equipment such as conveyer mechanisms, partfeeders, tooling, gages, and sensors. These recommended maintenanceprograms are essential for minimizing the hazards that can result fromcomponentmalfunction,breakage,andunpredictedmovementsoractionsofthe robot or other system equipment. To ensure that robots are safely andadequately maintained, it is recommended that periodic maintenance beconducted and documented, including the names of the personnel whoperformmaintenanceandthenamesoftheindependentverifiers.

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ROBOTSINSTALLATIONArobotorrobotsystemshouldbeinstalledbytheusersinaccordance

withthemanufacturer’srecommendationsandinconformancetoacceptableindustrystandards.Temporarysafeguardingdevicesandpracticesshouldbeused to minimize the hazards associated with the installation of newequipment. The facilities, peripheral equipment, and operating conditionsthatshouldbeconsideredare:Installationspecifications;Physicalfacilities;Electricalfacilities;Actionofperipheralequipment integratedwith the robot; Identificationrequirements;Control and emergency stop requirements; andSpecial robot operatingproceduresorconditions.

EXERCISESHowarerobotsclassifiedbasedongeometry?Identifyvarioustypesofrobotcontrol.Distinguish between point-to-point and continuous path motion of arobot.Whatisaworkenvelopeofarobot?Defineaccuracy.Defineprecision.Whatistheimportanceoftheworkenvelopeofarobot?Classifyrobotsbasedontheirgeometry.Distinguishbetweenaccuracyandrepeatabilityofarobot.Classifyrobotsonthebasisofpathmovement.Bymeansofasketch,explaintheconstructionofapolartyperobot.List the parameters used for selection of a robot for a particularapplication.State themajor subsystems of a robot and their functions. Show thesesubsystemsonasketch.Describebrieflythevarioustypesofmotioncontrolspossibleinrobots.

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Definemachinevision.Whatarethecomponentsofmachinevision?Nametwomethodsbywhichpathiscontrolledbyarobotcontroller.Explaintheanatomyofarobotmanipulatorindetail?Distinguishbetweenaccuracyandrepeatability.Whatdoyouunderstandbydegreeoffreedomofrobot?Definespeedofresponse.Whatarethecharacteristicsofanindustrialrobot?Classify robots based on their geometry. Explain the applicationpertainingtoeachclass.Withthehelpofsketches,discussthecommonrobotconfigurations.Brieflyexplain thevariouscomponentsofan industrial robot.State themainfunctionofeachofthecomponents.Definearobot.Listtheadvantagesanddisadvantagesofrobots.Explain the following termswith reference toa robot: repeatabilityandaccuracy.Explainbrieflynon-servocontrolledandservocontrolledrobots.Listthevarioustypesofjointsusedinrobots.Sketchtherevolvingjointandshowtherelativejointmotions.Whatarethelawsofrobotics?Whatarethetypesofwristmotions?What is a robotic joint? Distinguish between prismatic and revolutejoints.Whatarethevarioustechnologiesofmachinevision?Howisroboticvisionsensed?Whatarethecomponentsystemsusedinmostcommonvisionbasedapplications?What are the causes of robotic accidents? How can accidents beprevented?Drawasketchshowingallthesubsystemsofanarticulatedtypeofrobot.Discusstheanatomyofarobotandexplaintheimportantpartsofarobotwithasketch.Explainthefollowingterms:

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AccuracyDegreeoffreedomRepeatabilitySpeed

Sketchanarticulatedarmtyperobotandlabelitsparts.Differentiate the four common types of robot configurations with thehelpofsketches.

CHAPTER14

ROBOTICSENSORS

INTRODUCTIONSensors serve as a robot’s sight, hearing, touch, taste, and smell.

Without sensors, a robotic device would not be able to discern anythingaboutcurrentsurroundings.AsignalisreturnedfromthesensortotherobotCPU and is applied to the current situation or saved for later analysis.Withoutsensors,arobotisjustamachine.Sensorsprovidefeedbacktothecontrol systemsandgive the robotsmore flexibility.As robots areused inhazardous areas and industrial processes, they are fitted with sensors togather information about the nearby environment and objects around, tocome outwith precise results of thework.Robots need sensors to deducewhat is happening in their world and to be able to react to changingsituations. Sensors are used to gain information about theworld,which isuseful for guiding a robot to achieve a particular goal. The control of amanipulator or industrial robot is based on the correct interpretation ofsensory information. This information can be obtained from a robot eitherinternally(forexample,jointpositionsandmotortorque)orexternallyusingawiderangeofsensors.

Foraroboticdevicetobeuseful,itneedstohavesomeinformationofwhat is currently happening in the environment around it. Whether thisinformationisthetemperatureoftheair,thedistancefromanobject,orhowmuchpressurearoboticarmisapplying,thesensoristhepieceofequipmentprovidingthisinformation.Dependingonthejobrequirementsoftherobot,sensorsareneededtoprovideextremelyaccurateinformation.Aswithmostthings,higherperformancecomesatacost.Arobotbuiltbyahobbyistmay

employ sensors costing less thanadollar,while a robotbuilt for industrialusemayutilizesensorscostinghundredsofdollars.

TYPESOFSENSORSINROBOTSThebasicfunctionofasensoristomeasuresomefeatureoftheworld,

such as light, sound, or pressure and convert that measurement into anelectrical signal, usually a voltage or current. Typical sensors respond tostimulibychangingtheirresistance(photocells),changingtheircurrentflow(phototransistors), or changing their voltage output (the sharp IR sensor).The electrical output of a given sensor can easily be converted into otherelectricalrepresentations.Thecontrolof themanipulatoror industrialrobotis based on correct interpretation of sensory information. Sensing includesactivities such as seeing, hearing, touching, smelling, and measuringdistance.Awidevarietyofdevicesareusedbyrobotstoobtaininformation.They include not only transducers for physical quantities such asmicrophones for sounds, but also data processing input devices such askeyboard for textual informationandspecializedsensors.Sensors in robotscanbeclassifiedas:

Exteroceptors or External Sensors (for the measurement of robot’senvironmentalparameters).Proprioceptors or Internal Sensors (for the measurement of robotsinternalparameters).

EXTEROCEPTORSOREXTERNALSENSORSExteroceptors are sensors that measure the positional or force-type

interaction of the robot with its environment. These sensors are added torobots to perceive the world in which they operate and interact with theenvironmentoutsidetherobot.Externalsensorscanbecategorizedas:

ContactsensorsNoncontactsensors

ContactSensors

Contact sensing is one of the most basic requirements for anymanipulatorinteractingphysicallywiththeenvironmentinanon-structuredmanner.Itistheabilityoftherobottodeterminetheshape,size,weight,oreventhesurfacetextureofanobjectbytouchingit.Thecontactsensorsaresituated in thedesignof thegripper of the robot to provide the robotwithinformationabouttheforcesinthewristorthejointoftherobotandalsointheobjectsthataretobehandled.Itisveryimportantforrobotstodeterminethis information especially in fettling and grinding operations and inassembly operations. The functions of contact sensors in controllingmanipulation may be classified into the following basic material handlingandassemblyoperations:

Searching—detecting a part by sensitive touch sensors on the handexteriorwithoutmovingthepart.Recognition—determining the identity, position, and orientation of apart, again without moving it, by sensitive touch sensors with highspatialresolution.Grasping—acquiring the part by deformable, roundish fingers, withsensorsmountedontheirsurfaces.Moving—placing, joining, or inserting a part with the aid of forcesensors.

Mostimportanttypesofroboticsensorsofcontacttypeare:TactilesensorsForcesensors

NoncontactSensorsThesesensorsareusedtogivetherobotinformationabouttheprocess

or theenvironmentwithout theuseofphysicalcontact.Noncontactsensorsinclude:

Pneumaticsensors,whichdetectpartpresencebyair,flowdisturbance.Ultrasonicsensorsthatanalyzesoundwavesreflectedfromapart.Proximitysensorsthatregistertheapproach,arrival,orremovalofparts.Optical sensors utilizing interrupted light beams across the path of anincomingpart.

Machinevisionsystems thatusevisual sensors,usuallyvideocameras,to provide data that allows the robot to make intelligent decisionsregardingparts.

TACTILESENSORSFor a robot to accomplish light, delicate tasks, the end effector must

possesshumanhandlikequalities.Itmusthaveasenseoftouch.Touchisofparticular importance for close-up assembly work and for providingfeedbacknecessarytogripdelicateobjectsfirmly,withoutcausingdamage.Tactile sensors are used to identify and to control directly the interactionbetweentherobotendeffectorandtheenvironment.Theinteractionwiththeobject may occur by direct contact. These sensors either detect when thehand touches something, or they measure some combination of force andtorque components that the hand is exerting on an object. These sensorssensetheexternalconditionofanobject,theroughnessorsmoothnessofitssurface, its slipperiness, its elasticity, etc. This sort of information isnecessary in order to position the robot manipulators on an object and tocomputetheforceandpressurethatmustbeapplied,saytograspandlifttheobject.Tactile sensors find theiruse invarious locationsofa robot systemincludingjointsbetweentherobotlinks,wristbetweenarmandendeffector,thefingerpointsandthefingertip.Tactilesensorsareimportantforassemblyandforquality.Sensorsuseful in theseareas includepressuresensorsusedfor part orientation and gripping force control, piezoelectric sensors forcontinuouspressure,etc.Tactilesensorscanbeclassifiedinto:

TouchsensorsStresssensors

TouchSensorsTouchsensorsproduceabinaryoutputsignal,dependinguponwhether

ornottheyareincontactwithsomething.Touchsensorsmaybemountedontheouterandinnersurfacesofeachfinger.Theoutersensorsmaybeusedtosearch for an object and possibly determine its identity, position, andorientation. The innermounted sensorsmay be used to obtain informationaboutanobjectbeforeitisacquiredandaboutgraspingforcesandworkpieceslippage during acquisition. The simplest kind of touch sensors require no

specific sensor device at all if the objects they are going to touch areelectricallyconductive.Microswitchsarethemostcommonlyusedandleastexpensive kind of touch sensor which either turns on or off as contact ismade.AmicroswitchisshowninFigure14.1.

FIGURE14.1ATypicalMicroswitch.

Often,theswitchissimplymountedonarobotsothatwhentherobotrunsintosomething,theswitchispressed,andthemicroprocessorcandetectthattherobothasmadecontactwithsomeobjectandtakeappropriateaction.ThebumperskirtontherobotshowninFigure14.2isanexampleofatouchsensor.Whentherobotrunsintoawall,thebumperskirthitsamicroswitchwhichletstherobotcontrollerknowthattherobotisupagainstawall.Othertypesoftouchsensorsareusedinternallytolettherobotknowwhenanarmisextendedtoofaranditshouldberetracted.

FIGURE14.2RoboticPlatformEmployingBumperCoupledtoTouchSensor.

Touchsensorscanalsoserveaslimitswitchestodeterminewhensomemovablepartoftherobothasreachedthedesiredposition.Forexample,ifamotor drives a robot arm, perhaps using a gear rack, touch switches coulddetectwhenthearmreachedthelimitoftravelontherackineachdirection.

Force/TorqueSensors

Force/TorqueSensorsForce/torquesensorsmeasuretheamountofforceandtorqueexertedby

themechanicalhand.Thesesensorsarenormallyusedtomeasuretheroboticsystem’s forces as it performs various operations. Forces,which the robotuses in manipulation and assembly, are usually of great importance. Themajor parts of these devices are transducers, which measure force/torque.The interaction forces and torques, which appear during mechanicalassembly operations at the robot hand level, can be measured by sensorsmountedonthejointsoronthemanipulatorwrist.Individualstresssensorsusually respond only to force in one direction on them. However, thecombinationof twoormorecan report forces aswell as torques in twoorthree directions. Strain gauges are used to make force sensors, torquesensors,andsensorsthatcanmeasurebothkindsofstresssimultaneously.

Thesimplesttypeoftactilesensorisagripperthatisequippedwithanarrayofminiaturemicroswitches.Thistypecanonlydeterminethepresenceor absence of an object at a particular point or array of points. A moreadvancedtypeoftactilesensorusesarraysofpressure-sensitivepiezoelectricmaterial. This material conducts an electrical current when stressed. Themore pressure applied to the material, the more electrical current isproduced. This aspect allows the sensor to perceive changes in force andpressure.Thetactilesensorcanalsobeusedinforcefeedbackapplications.Thisisessentialwherethegripperishandlingdelicate,fragileobjectssothattherobotwillnotapplytoomuchforceandcrushtheobjectitisholding.Fortactilesensingtobetrulyusefulinadaptiveassemblytasks,thesensormustbe capable of sensing physical quantities like the human hand. Thesequalities include pressure, direction of forces, temperature, vibration, andtexture.

PROXIMITYSENSORS(POSITIONSENSORS)Aproximitysensorisadevicethatsensesandindicatesthepresenceor

absence of an object without requiring physical contact. This helps theworkstationcontrollertosafelymovetheendeffectorsquicklytowardsthatobject even if its position is not precisely known. The signal from theproximity detector would give the workstation controller the warning itwould need in order to slow down and avoid a collision.Most proximitysensors indicate only the presence or absence of an object within their

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(b)

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(d)

sensing region but some can give some information about the distancebetween theobject and the sensor aswell.Proximity sensors are classifiedaccording to their operating principle: inductive, Hall effect, capacitive,ultrasonic,andoptical.Thesenoncontactsensorshavewidespreaduse,suchas for high speed counting, protection of workers, indication of motion,sensing presence of ferrous materials, level control, and noncontact limitswitches.Someofthecommonproximitysensorsareexplainedbelow:

Opticalproximitysensorsoperateoneithervisibleorinvisiblelight.Thesesensorsmeasuretheamountoflightreflectedfromanobject.

A photoelectric proximity sensor uses a light-beam generator, aphotodetector, a special amplifier, andamicroprocessor.The lightbeamreflectsfromanobjectandispickedupbythephotodetector.The light beam is modulated at a specific frequency, and thedetector has a frequency sensitive amplifier that responds only tolightmodulatedat that frequency.Thisprevents false imaging thatmight otherwise be caused by lamps or sunlight. If the robot isapproachingalight-reflectingobject,itsmicroprocessorsensesthatthereflectedbeamisgettingstronger.Therobotcanthensteerclearoftheobject.

Anacousticproximitysensorworksonthesameprincipleassonar.An oscillator generates a pulsed signal, having a frequencysomewhatabovetherangeofhumanhearing.Thissignalisfedtoatransducer that emits ultrasound pulses at various frequencies in acoded sequence. These pulses reflect from nearby objects and arereturned toanother transducer,whichconverts theultrasoundbackintohigh-frequencypulses.Thereturnpulsesareamplifiedandsentto the robot controller. The delay between the transmitted andreceived pulses is timed, and this will give an indication of thedistancetotheobstruction.

A capacitive proximity sensor uses a radio-frequency oscillator, afrequency detector, and ametal plate connected into the oscillatorcircuit.Theoscillatorisdesignedsothatachangeinthecapacitanceof theplate,with respect to theenvironment,causes the frequencytochange.Thischange is sensedby the frequencydetector,whichsendsasignaltotheapparatusthatcontrolstherobot.Inthisway,arobotcanavoidbumpingintothings.Objectsthatconductelectricity

(e)

tosomeextent,suchashousewiring,animals,cars,orrefrigerators,aresensedmoreeasilybycapacitivetransducersthanarethingsthatdonotconduct,likewood-framebedsanddrymasonrywalls.

Magnetic field sensors are excellent proximity sensors. Inductivesensorsarebasedonthechangeofinductanceduetothepresenceofmetallicobjects.Halleffectsensorsarebasedontherelation,whichexists between the voltage in a semiconductor material and themagneticfieldacrossthatmaterial.InductiveandHalleffectsensorsdetectonlytheproximityofferromagneticobjects.

RANGESENSORSArangesensorisadevicethatcanprovideprecisemeasurementofthe

distancefromthesensortoanobject.Rangesensorsareusefulforlocatingobjectswithintheworkstationareaandforcontrollingamanipulator.Rangesensingisaccomplishedbymeansoftelevisioncamerasorsonartransmittersandreceivers.Theyareusedforrobotnavigation,obstacleavoidance,ortorecover the third dimension for monocular vision. The main goal of anyranging system is to repeatedly obtain accurate range information ofsurroundings. Ranging systems are usually used in automated guidedvehiclesorwhere the robothas a largeworkspace.Range-imaging sensorshave been applied primarily to object recognition. However, they are alsovery suitable for other tasks, such as finding a factory floor or a road,detecting obstacles and pits, and inspecting the completeness ofsubassemblies.

Range sensors arebasedononeof these twoprinciples: time-of-flightandtriangulation.Time-of-flightsensorsestimatetherangebymeasuringthetime elapsed between the transmission and return of a pulse. Laser rangefinders and sonar are the best-known sensors of this type. Triangulationsensorsmeasurerangebydetectingagivenpointontheobjectsurfacefromtwodifferentpointsofviewataknowndistancefromeachother.Knowingthisdistanceandthetwoviewanglesfromtherespectivepointstotheaimedsurface point, a simple geometrical operation yields the range. The rangesensorsareclassifiedintotwocategories:

Passivedevices,suchasstereoscopicvisionsystemsand,Activedevices,suchasultrasonicrangingsystems.

(a)

(b)

Stereoscopic vision system: the main problem with range sensingoccurs when the transmitter does not sense all objects in theworkspace.The use of additional transmitters helps to reduce, butnot eliminate the problem. In the case of a stereoscopic visionsystem,asingleprojectorwithmultiplecamerasisusedtoviewthetargetareafromdifferentangles.Thesystemsensesmoredatathanasingle-camerasystem,butrequiresmorehardware,software,andcomputingtimetowork.Ultrasonicrangingsystems:Ultrasonicrangingsystemsliketheoneusedon the automatic-focusingpolaroid camera havebeenwidelyused to give environmental awareness to a mobile robot. Anultrasonic sensor determines the range by measuring the elapsedtime between the transmission of certain frequencies and theirdetected echoes. Different discrete frequencies are used becausesurface characteristics could cancel a singlewaveform, preventingdetection.

MACHINEVISIONSENSORSRobot vision is a complex sensing process. It involves extracting,

characterizing,andinterpretinginformationfromimagesinordertoidentifyordescribeobjects in theenvironment.Therepeatabilityandaccuracyofavision system, the ability to produce approximately the same resultswhengivenapproximatelythesameinputs,areitsgreatestvirtues.Itcanperformsimple taskssuchasmonitoringand inspection fasterandmore reliably.Avision sensor (camera)converts thevisual information toelectrical signals,which are then sampled and quantized by a special computer interfaceelectronics yielding a digital image. Solid-state CCD image sensors havemany advantages over conventional tube-type sensors as: small size,lightweight, more robust, better electrical parameters, which recommendthem for robotic applications. Virtually all-existent vision sensors aredesigned for television, which is not necessarily best, suited for roboticapplications.Becauseof thereducedresolution,androbothandobstructingthefieldofview,thecommonwisdomapproachofplacingcameraabovetheworkingareaisofquestionablevalueformanyroboticapplications.

Mountingthevisionsensorintherobothandmaybeabettersolution,whicheliminatestheseproblems.Illuminationisaveryimportantcomponent

of the imageacquisition.Controlled illuminationoffersexpedient solutionsto many robotic vision problems. Vision sensors are used extensively ininspectionhandlingandacquisitionofparts, say fromanassemblybelt. Inaddition, vision is used in geometric analysis of shape to determine thepointsofapartthathavetobegraspedbytherobot.

Ageneralvisionsystemconsistsofalightsource,animagesensor,animagedigitizer,asystemcontrolcomputer,andsomeformofoutput.

The image sensorof amachinevision system isdefinedas anelectrooptical device that converts an optical image to a video signal. The imagesensor isusuallyavacuumtubeTVcameraorasolidstate-sensingdevice.Tube-typecameras:Vidiconsarethemostcommontube-typecameras.Theimage is focused on a photosensitive surface where a correspondingelectricalsignalisproducedbyanelectronbeamscanningthephotosensitivesurface.Theelectronbeampasseseasilythroughthephotosensoratahighlyconductivepointcausedbyveryintenselight.Fewerelectronspassthroughthe photo sensor where lower light levels have made it less conductive.Scanning the electron beam carefully across the entire surface produceselectricalinformationabouttheentireimage.

VELOCITYSENSORSTheyareusedtoestimatethespeedwithwhichamanipulatorismoved.

The velocity is an important part of the dynamic performance of themanipulator.TheDCtachometerisoneofthemostcommonlyuseddevicesforfeedbackofvelocityinformation.Thetachometer,whichisessentiallyaDCgenerator,providesanoutputvoltageproportionaltotheangularvelocityof the armature. This information is fed back to the controls for properregulationofthemotion.

PROPRIOCEPTORSORINTERNALSENSORSFrom a mechanical point of view, a robot appears as an articulated

structureconsistingofaseriesoflinksinterconnectedbyjoints.Eachjointisdrivenbyanactuator,whichcanchangetherelativepositionofthetwolinksconnectedbythatjoint.Proprioceptorsaresensorsmeasuringbothkinematicand dynamic parameters of the robot. Based on these measurements, the

controlsystemactivatestheactuatorstoexerttorquessothatthearticulatedmechanical structureperforms thedesiredmotion.Themost common joint(rotary) position transducers are: potentiometers, synchros and resolvers,encoders,RVDT(rotaryvariabledifferentialtransformer),etc.

Encoders are digital position transducers, which are the mostconvenientforcomputerinterfacing.

Incrementalencoders are relative-position transducers,whichgeneratea number of pulses proportionalwith the traveled rotation angle.They arelessexpensiveandofferahigherresolutionthantheabsoluteencoders.Asadisadvantage,incrementalencodershavetobeinitializedbymovingtheminareference(“zero”)positionwhenpowerisrestoredafteranoutage.

Absolute shaft encoders are attractive for joint control applicationsbecausetheirpositionisrecoveredimmediatelyandtheydonotaccumulateerrorsasincrementalencodersmaydo.Absoluteencodershaveadistinctn-bitcode(naturalbinary,Gray,BCD)markedoneachquantizationintervalofa rotating scale.The absolute position is recoveredby reading the specificcode written on the quantization interval that currently faces the encoderreferencemarker.

Joint position sensors are usuallymounted on themotor shaft.Whenmounted directly on the joint, position sensors allow feedback to thecontroller with the joint backlash and drive train compliance parameters.Angular velocity ismeasured (when not calculated by differentiating jointpositions)by tachometer transducers.AtachometergeneratesaDCvoltageproportionaltotheshaftrotationalspeed.Digitaltachometersusingmagneticpickupsensorsare replacing traditional,DCmotor-like tachometers,whicharetoobulkyforroboticapplications.

Straingagesmountedonthemanipulator’slinksaresometimesusedtoestimate the flexibility of the robot’s mechanical structure. Strain gagesmountedonspeciallyprofiled(square,cruciformbeamorradialbeam)shaftsarealsousedtomeasurethejointshafttorques.

ROBOTWITHSENSORSBecausesensorsareanydevicesthatprovideinputofdatatotherobot

controllerawideverityofsensorsexist.Figure14.3showsthesomeofthebasictypesofsensorsusedinrobot.Theseare:

Lightsensors,whichmeasurelightintensity.Heatsensors,whichmeasuretemperature.Touchsensors,whichtelltherobotwhenitbumpsintosomething.Ultrasonicrangers,whichtelltherobothowfarawayobjectsare.Gyroscopes,whichtelltherobotwhichdirectionisup.

FIGURE14.3SensorsinRobots.

LightSensors

Light sensors are used to detect the presence and intensity of light.These can be used to make a light-seeking robot and are often used tosimulateinsectintelligenceinrobots.

HeatSensors

Heatsensorshelprobotsdetermineiftheyareindangerofoverheating.These sensors are often used internally to make sure that the robot’selectronicsdonotbreakdown.

1.

UltraSonicSensors

Ultrasonicsensorsareusedtodeterminehowfararobotisawayfromobject. They are often used by robots that need to navigate complicatedterrainandcannotriskbumpingintoanything.

Gyroscopes

Gyroscopesareusedinrobotsthatneedtomaintainbalanceorarenotinherently stable. Gyroscopes are often coupled with powerful robotcontrollers thathave theprocessingpowernecessary tocalculate thousandsofphysicalsimulationspersecond.

EXERCISESWhatisasensor?

2.3.

4.

5.6.

7.8.9.10.11.

Identifyvarioustypesofsensorsusedinrobots.What is a proximity sensor? Name three techniques for designingproximitysensors.Differentiatebetweencontactandnoncontactsensors inrobotswith thehelpofexamples.Describetheconstructionandworkingprincipleofonecontactandonenoncontacttypeofsensor.Differentiatebetweenaproximityandarangesensor.What are touch sensors? Describe its different types along with theiradvantagesanddisadvantages.Whataremachinevisionsensors?Whataretheclassificationsofproximitysensors?Whatdoyouunderstandbytactilesensors?Definerangesensorsanditstypes.Explaintheprincipleofworkingofthefollowingsensorsusedinrobots:

RangesensorProximitysensorTactilesensorMagneticsensor

CHAPTER15

ROBOTENDEFFECTORS

INTRODUCTIONThefunctionofarobot is to interactwith thesurroundings.Therobot

doesthisbymanipulatingobjectsandtoolstofulfillagiventask.Therobotendeffectorbecomesabridgebetweenthecomputercontrolledarmandtheworldaroundit.Earlierindustrialrobotswereusedasstandalonemachinesfor painting, spot welding, or pick and place work in which parts weremovedfromonelocationtoanotherwithoutmuchattentionpaidtohowthepartswere picked up and put down.Nowadays, robots are put towork inmore challenging applications. The tasks the robot perform may involveassemblingpartsorfittingthemintoclampsandfixtures.Thesetasksplacegreaterdemandsontheaccuracyofthearmandtheendeffector.Theactionsof the robot and the gripper determine whether the assembly will gosmoothlyorthepartswillgetdamagedintheprocess.

ENDEFFECTOROneof themost important areas in thedesignof robot systems is the

designof end effectors.Most of theproblems that occur in production arecausedbybadlydesignedtoolingandnotbyfaultsintherobots.

Inrobotics,anendeffectorisadeviceortoolconnectedtotheendofarobot arm. Basically, it is a tool to grip, hold, and transport objects andposition them in a desired location.End effectors are the devices throughwhicharobotinteractswiththeworldaroundit,graspingandmanipulatingparts, inspectingsurfaces,andworkingonthem.Assuch,endeffectorsare

amongthemostimportantelementsofaroboticapplicationandanintegralcomponent of the overall tooling, fixturing, and sensing strategy. An endeffectorattachedtotheroboticarmisshowninFigure15.1.

FIGURE15.1

Anendeffectorisoftendifferentfromahumanhand.Itcouldbeatoolsuchasagripper,avacuumpump,tweezers,scalpel,blowtorch,etc.orjustaboutanythingthathelpstodothejob.Aroboticend-effectorisanyobjectattachedtotherobotflange(wrist)thatservesafunction.Thiswouldincluderobotic grippers, robotic tool changers, robotic collision sensors, roboticrotary joint, robotic press tooling, compliance device, robotic paint gun,roboticdeburringtool,roboticarcweldinggun,etc.Robotendeffectorsarealsoknownasroboticperipherals,roboticaccessories,robottoolsorrobotictools, end of arm tooling (EOA), or end-of-arm devices. Some robots canchangeend-effectors,andbereprogrammedforadifferentsetoftasks.Iftherobothasmorethanonearm,therecanbemorethanoneend-effectoronthesamerobot,eachsuitedforaspecifictask.

End-of-arm tooling is defined as the subsystem of an industrial robotsystemthatlinksthemechanicaloptionoftherobot(manipulator)totheartbeinghandledorworkedon.Anindustrialrobotisessentiallyamechanicalarmwithaflattoolmountingplateatitsendthatcanbemovedtoanyspatialpointwithinitsreach.End-of-armtoolingintheformofspecializeddevicestopickuppartsorholdtools toworkonparts isphysicallyattachedto therobot’s toolmountingplate to link therobot to theworkpiece.Arobotcanbecomeaproductionmachineonlyifanendeffectorhasbeenattachedtoitsmechanical arm by means of the tool mounting plate as shown in Figure

15.2.Toolmountingplate is for the interfacebetweenendeffectorand thecontroller.

FIGURE15.2

Thestructureofanendeffector,andthenatureoftheprogrammingandhardwarethatdrivesit,dependsontheintendedtask.Ifarobotisdesignedtoset a table and serve a meal, then robotic hands, more commonly calledgrippers,are themostfunctionalendeffectors.Thesameorsimilargrippermightbeused,withgreaterforce,aspliersorawrenchfortighteningnutsorcrimpingwire.

CLASSIFICATIONOFENDEFFECTORSAnendeffectorcoversawiderangeofdifferenttoolsanddevicesthat

canbeclassifiedintotwomaincategories:

GrippersToolsforprocessapplications

GRIPPERSGrippersareendefectorsthatactuallygripapartfortransferoperations

in thework envelope of the robot.Agripper is a component of the robotused to manipulate an object loose from the robot itself. This can be acomponent it needs to pick up, or thewaste it is programmed to find and

1.

2.

3.

4.

disposeof.Grippersincludemechanicalhandsandalsoanythinglikehooks,magnets, and suction devices, which can be used for holding or gripping.Grippers takeadvantageofpoint-to-pointcontrol (exactpath that the robottakes between what it is picking up and where it is placing it). Grippersshouldbedesignedsothatitrequirestheminimumamountofmaneuveringinordertogriptheworkpiece.Grippersareusedinapplicationsformaterialhandling, machine loading, and assembling. In many grippers, themechanismisactivatedthroughapneumaticpistonthatmovesthegripper’sfingers.ArobotgripperisshowninFigure15.3.

FIGURE15.3RobotGripper.

Therearefourmaincategories,whichmakesuseofagripper:

Nogripping:Inthissituation,theworkpieceisheldinajig(aspeciallydesignedpurposebuiltholder)and the robotperformsanactivityon it.Jobs that use no gripping can include spotwelding, flame cutting, anddrilling.Coarse gripping: In this case, the robot holds the workpiece but thegripping does not have to be precise. Jobs that use coarse grippinginclude handling and dipping castings, unloading furnaces, stackingboxes,orsacks.Precisegripping:Arobotholds theworkpiece,whichrequiresaccuratepositioning,forexample,unloadingandloadingmachinetools.Assembly:Therobotisrequiredtoassembleparts,whichrequireaccuratepositioning, and some form of sensory feedback to enable the robot tomonitorandcorrectitsmovements.

(a)

SELECTIONOFGRIPPERTheselectionofgripperisusuallymadebyexaminingthegeometryof

thepart,itsorientation,thespaceavailable,andthemanufacturingtreatmenttobeperformed.Externalgrippingis themostwidelyusedtype,wheretheclosing force isutilized toclench thepart.An internalgripmakesway forunobstructedaccesstotheoutsidesurfaceofthepart,whichisnecessaryforpolishing/buffing, grinding, or painting applications. The opening force ofthe gripper is used to hold the part. There are numerous types of grippersbothinstyleandpowersource.Determiningwhichisthebesttypetouseisan important issue that roboticsusersmust face.Selectionof thegripper isbaseduponanumberoffactorsthatmayneedconsideration:

SourceofpowerGrippingforceGrippingstyleWeightEnvironmentalcapabilitiesSensorcapabilitiesNumberofjawsOtherfactors

SourceofPowerAccording to source of power, grippers are classified as pneumatic,

hydraulic,andelectrical.

Pneumatic grippers have no motors or gears. So it is simple totranslatethepowerofapiston/cylindersystemintoagrippingforce.Mostmanufacturingfacilitiesalreadyhavecompressedair,solittleeffortisrequiredtobringit toagripperinacostefficientmanner.Pneumaticsputoutahighamountofgrippingforceinasmallandlightpackage.Thisiscriticalwhenlimitedspaceisafactor.

There are twomain types of pneumatic grippers: angular andparallel.Themaindifferencebetweenthemishowtheirjawsmove.The jaws of an angular gripper swing open and closed on pivots.Thejawsofaparallelgripperslideopenandclosedintracks.Eitherstyle can have two or three jaws. Jaw movement is usually

(b)

(c)

synchronized, but some models can be modified so the jaws canmove independently. Parallel grippers can grab a part from theoutsideortheinside.Thejawscanbeactuateddirectlybythepistonorindirectlythroughacamorwedgemechanism.Theformerhavelongerstrokelengths,butthelatterproducemoregrippingforce.

Angulargripperscost less thanparallelgrippers,which requiremoreprecisemachiningandmoreexpensivebearingsforthejaws.Theycanonlygrasppartsfromtheoutside.Comparedwithparallelgrippers, angular grippers can’t handle awide range of part sizes,andtheydon’tresistsideloadsaswell.Ontheplusside,thejawsonangulargripperscanswingoutof thewayof incomingparts.Thiscan save time when picking parts off a conveyor, because theactuatordoesnothavetomoveasmuch.Hydraulic grippers are a cost effective alternative to pneumaticgrippers. The primary advantage of a hydraulic actuator is itsgrippingpower.Hydraulicpower isusedwhen there is aneed forextragrippingforce.Becausehydraulic fluid isnotacompressiblemediumasisair,thereismoregrippingpoweravailable.Hydraulicgrippers have disadvantages also. Hydraulic grippers are morecostlyandtheyaregenerallylessaccuratethanpneumaticorelectricgrippers. Hydraulic grippers have the disadvantage of being notsuitedforcleanroomapplications.Pneumaticgrippersarecommonbecause they are clean, especially when compared to hydraulics.Theremight bemore strength in a hydraulic gripper, but they aremessyandmuchmorecostlytomaintain.Electricity is the othermajor optionwhen looking for a source ofpower for robotic grippers. Electric grippers are a fairly newtechnology. They have not been cost effective until recently.Electric grippers are suitable for applications that require highspeedsandforthoserequiringlightormoderategripforces.Electricgrippers are cleaner than either pneumatic or hydraulic grippers.Electricgrippersdonotputoutanydirtorparticulate, so theyaregood for clean room operations. The major advantage of electricpowered grippers is control. Pneumatic grippers are not verycontrollable.Typicallythevalve,whichcontrolsthegripper,isfullyopenedorclosed.Withelectric,itisrelativelyeasytoaddasteppermotortocontrolthegripperastohowfaritopensandcloses.Thisadds flexibility and the capability of varying grip forcewith ease.

Thedisadvantageof electric is the grippers tend to be a bit largerbecauseyouhavetoworkthemotor in,andtheytendtohavelessforcethanpneumatic.

GrippingForceWhenconsideringthegrippingforcerequired,anumberoffactorsmust

beconsidered.Notonlymustthemassoftheobjecttobegrippedbetakeninto account but also the accelerations imposedon it by the robotmust betaken into account.The coefficient of friction between the gripper and theobjectmayalsobeanimportantfactor.Thiscanoftenbeincreasedbyusingoneofthespecialrubberbasedmaterialsthathavebeendeveloped.Theuseof thesematerials can createmaintenance issues, however, as they have afinite life.Oneotherwayof reducing thegripping force required is tousefingersdesignedfortheformofthecomponent.Thisreducestheflexibilityofthegripperbutdramaticallyincreasestheweightcarryingcapacity.

GrippingStyleTheconfigurationsofgrippersincludeparallelandangularstyles,and

those with two or three jaws. Parallel jaws move in a motion parallel inrelation to the gripper body, while angular jaws open and close around acentralpivotpoint,movinginanarcingmotion.Determiningwhichgrippertouseisdependentonthespecificneedsofanapplication.

Anangulargripperisusedwhenoneneedstogetthetoolingoutoftheway.Angulargrippers areusually themost economical.However, becauseof the sweeping action of an angular gripper, it is not always practical forsomeapplications,anditismoredifficulttodesign.

A parallel gripper is used for pulling a part down inside a machinebecausethefingersfitintosmallareasbetter.Spaceconstraintsmightleadtothe use of parallel over angular. Two jaw parallel grippers are the mostwidely used. They are the most popular type because two jaw parallelgrippersareeasiertodesignandprogramasthereisonlyaxisofmotion.

AngularandparallelgrippersareshowninFigure15.4.

FIGURE15.4AngularandParallelGrippers.

Agrippercanalsobeexternalorinternal.Theexternalgripperisusedto grasp the exterior surface of objects with closed fingers, whereas theinternal gripper grips the internal surface of objects with open fingers.ExternalandinternalgrippersareshowninFigure15.5.

FIGURE15.5ExternalandInternalGrippers.

WeightIndustrialrobotshavefixedliftingcapabilitiesandthecombinedweight

of the gripper and gripped component may be important. Even when thisweight iswithin the capability of the robot, itmay cause an unacceptableincrease in thecycle timeof theoperation.Thedistancebetween the robotflangeandthecenterofmassmayalsobeimportantandthisshouldbekepttoaminimum.

EnvironmentalCapabilitiesEndeffectorsareoftenrequiredtoworkinhostileenvironments.High

temperatures, dust, or the presence of chemicals will require special

materialsordesignstobeused.

SensorCapabilitiesFor certain applications, some degree of sensory feedback from the

gripper is necessary. This may be measurement of insertion or grippingforcesormaysimplybeaproximitysensortosayifanythingisbetweenthejawsof thegripper.Some standardgrippers areprovidedwith feedback toshowtheseparationofthejawsbutmostgrippershavenofeedback.

NumberofJaws(TwoorThreeJawGripper)In two jaw units,which come in both parallel and angular styles, the

grasperaffordstwomountingspotsforthefingerstoholdthepart.Thejawsmoveinasimultaneousmotion,openingandclosingtowardthecentralaxisof the gripper body. Three jaws furnish more contact with the part to beclaspedandaremoreaccurateincenteringthanaretwojaws.

OthersOtherfactorstobeconsideredincludethespeedofthegripperjawsand

the range of sizes of the components they can grip. The amount ofmaintenance required is also important though most modern mechanismsrequire little or no maintenance. For some situations, the behavior of thegripperonpowerfailuremaybecritical.Somebutnotalluseeitherspringsto apply the gripping force or non-return valves to ensure that pressure ismaintained.

GRIPPINGMECHANISMSA gripper is specifically end of arm tooling that uses a mechanical

mechanismandactuator tograspapartwithgrippingsurfaces.Fingersaredesignedto:

Physicallymatewiththepartforagoodgrip.Applyenoughforcetotheparttopreventslipping.

Typicalmechanisms

LinkageactuationGearandrackCamScrewRopeandpulleyMiscellaneous,e.g.,bladder,diaphragm

TOOLSToolsaredevices,whichrobotsusetoperformoperationsonanobject,

for example, drills, paint sprays, grinders, welding torches, and any othertool,whichgetaspecificjobdone.Toolstakeadvantageofcontinuouspathcontrol (the path the end effector takes needs to careful, steady andcontinuouslycontrolledateverymoment).Takethecaseofaspraygunasatool.Ifitmovestooquickly,thepaintwillbetoothin.Ontheotherhand,ifitmovestooslowly,thepaintwillbetoothickorinblobs.Anytoolrequiredcanbefittedtotheendoftheroboticarmandcanbeprogrammedtoselectandchangetoolswithouthumanintervention.

TYPESOFTOOLSAt times, a robot is required to manipulate a tool to perform an

operationonaworkpart.Insuchapplications,theend-effectorisusedasagripper that can grasp and handle a variety of tools and the robot hasmultitool handling function.However, inmost robot applications inwhichonlyonetoolistobemanipulated,thetoolisdirectlymountedonthewrist.Here the tool itself acts as the end effector. In such applications, the endeffectorisatoolitself.Someofthetoolsusedare:

Spot-weldingtoolsArc-weldingtoolsSpray-paintingnozzlesRotatingspindlesfordrillingRotatingspindlesforgrindingDeburringtools

1.2.3.4.

Pneumatictools

CHARACTERISTICSOFEND-OF-ARMTOOLINGEnd-of-arm tooling in a robot work cell should have the following

characteristics:

Thetoolingmustbecapableofgripping,lifting,andreleasingthepartorfamilyofpartsrequiredbythemanufacturingprocess.The tooling must sense the presence of a part in the gripper, usingsensors located either on the tooling or at a fixedposition in theworkcell.Toolingweightmustbekept toaminimumbecause it is added topartweighttodeterminemaximumpayload.Containmentofthepartinthegrippermustbeensuredunderconditionsofmaximumaccelerationatthetoolplateandlossofgripperpower.Thesimplestgripper thatmeets thefirst fourcriteriashouldbe theoneimplemented.

ELEMENTSOFEND-OF-ARMTOOLINGEnd-of-arm tooling is commonly made up of four distinct elements,

whichprovidefor:

Attachmentofthehandortooltotherobottoolmountingplate.Powerforactuationoftoolingmotions.Mechanicallinkages.Sensorsintegratedintothetooling.

MountingPlateThemeansofattachingtheend-of-armtoolingtoanindustrialrobotis

providedbyatoolmountinglocatedattheendofthelastaxisofmotiononthe robot. This tool mounting plate contains either threaded or clearanceholesarrangedinapatternforattachingtooling.Forafixedmountingofagripperortool,anadapterplatewithaholepatternmatchingtherobottool

mountingplatecanbeprovided.Theremainderoftheadapterplateprovidesa mounting surface for the gripper or tool at the proper distance andorientation from the robot tool mounting plate. If the task of the robotrequiresittoautomaticallyinterchangehandsortools,acouplingdevicecanbeprovided.Anadapterplateisattachedtoeachofthegrippersortoolstobe used, with a common lock-in position for the pickup by the couplingdevice. The coupling device may also contain the power source for thegrippersortoolsandautomaticallyconnectsthepowerwhenitpicksupthetooling.

PowerPowerforactuationoftoolingmotionscanbepneumatic,hydraulic,or

electrical,or the toolingmaynot requirepower,as in thecaseofhooksorscoops.Generally, pneumatic power is usedwhere possible because of itsease of installation and maintenance, low cost, and light weight. Higher-pressure hydraulic power is used where greater forces are required in thetooling motions. However, contamination of parts due to leakage ofhydraulic fluidoften restricts its application as a power source for tooling.Although it is quieter, electrical power is used less frequently for toolingpower,especiallyinpart-handlingapplications,becauseofitslowerappliedforce.Severallightpayloadassemblyrobotsutilizeelectricaltoolingpowerbecauseofitscontrolcapability.Inmatchingarobottoend-of-armtooling,considerationshouldbegivento thepowersourceprovidedwith therobot.Somerobotshaveonefortoolingpower,especiallyinpart-handlingrobots,anditisaneasytasktotapintothisactuationfortoolingfunctions.

MechanicsToolingforrobotsmaybedesignedwithadirectcouplingbetweenthe

actuatorandworkpiece.Take thecaseofanaircylinder thatmovesadrillthroughaworkpiece,oruseindirectcouplingstogainmechanicaladvantage,as in the case of a pivot-type gripping device. A gripper may also haveprovisions formounting interchangeable fingers to conform tovariouspartconfigurations.Inturn,fingersattachedtogrippersmayhaveprovisionsforinterchangeabletoconformtovariouspartconfigurations.

Sensors

1.2.

1.

2.

Sensors are incorporated in tooling to detect various conditions. Forsafety considerations, sensors are normally designed into tooling to detectworkpieceor tool retentionby the robotduringoperation.Sensorsarealsobuiltintotoolingtomonitortheconditionoftheworkpieceortoolduringanoperation,asinthecaseofatorquesensormountedonadrilltodetectwhenadrillhasbroken.Sensorsarealsousedintoolingtoverifythataprocessiscompleted satisfactorily as wire-feed detectors in arc welding torches andflowmetersindispensingheads.Morerecently,robotsspeciallydesignedforassembly taskscontainforcesensors(straingauges)anddimensionsensorsin the end-of-arm tooling. Tools are the devices that actually perform thetask,e.g.,gluingguns,drills,weldingtorches,arcweldingguns,sprayguns,automaticscrewdrivers.

TYPESOFGRIPPERSRobotic end effectors include everything from simple two-fingered

grippers and vacuum attachments to elaborate multifingered hands. Thegrippersareclassifiedas:

PassivegrippersActivegrippers

PassiveGrippersMostendeffectorsinusetodayarepassive,i.e.,theyemulatethegrasps

thatpeopleuseforholdingaheavyobjectortool,withoutmanipulatingitinthefingers.However,apassiveendeffectormaybeequippedwithsensors,andtheinformationfromthesesensorsmaybeusedincontrollingtherobotarm.Passivegripperscanholdparts,butcannotmanipulatethemoractivelycontrolthegraspforce.Passivegrippersinclude:

Nonprehensileendeffectors

These end effectors are called nonprehensile because they neitherenclose parts nor apply grasp forces across them. These include vacuum,electromagnetic,andBernoulli-effectendeffectors.

Wrapendeffectors

3.

Thesegrippersholdapart inthesamewaythatapersonmightholdaheavyhammer. Insuchapplications,humansusewrapgrasps inwhich thefingersenvelopapart,andmaintainanearlyuniformpressuresothatfrictionisusedtomaximumadvantage.Theseincludebladesandlinkages.

Pinchendeffectors

The next type of the end effector includes common two-fingeredgrippers.Thesegrippersemployastrong“pinch”forcebetweentwofingers,inthesamewaythatapersonmightgraspakeywhenopeningalock.Mostsuchgrippersaresoldwithoutfingertipsbecausetheyarethemostproduct-specificpartof thedesign.Thefingertipsaredesignedtomatchthesizeofcomponents,theshapeofcomponents(e.g.,flatorV-groovedforcylindricalparts), and the material (e.g., rubber or plastic to avoid damaging fragileobjects). Pinch end effectors include 2 or 3 fingers, parallel or angularmotion,fingertipstyleslikeflat,V,etc.Becausetwo-fingeredendeffectorstypically use a single air cylinder or motor that operates both fingers inunison,theywilltendtocenterpartsthattheygrasp.

ActiveGrippersTheseincludeactiveservogrippersanddexterousrobothandsfoundin

research laboratories and teleoperated applications. Here the distinctionsdependlargelyonthenumberoffingersandthenumberofjointsordegreesoffreedomperfinger.Servo-controlledendeffectorsprovideadvantagesforfine-motiontasks.Incomparisontoarobotarm,thefingertipsaresmallandlight,whichmeansthattheycanmovequicklyandprecisely.Thetotalrangeofmotionisalsosmall,whichpermitsfineresolutionpositionandvelocitymeasurements.Whenequippedwithforcesensorssuchasstraingauges,thefingerscanprovideforcesensingandcontrol,typicallywithbetteraccuracythan can be obtained with robot wrist or joint mounted sensors. A servogripper can also be programmed either to control the position of anunconstrainedpartor toaccommodate to thepositionofaconstrainedpart.The sensors of a servo-controlled end effector also provide usefulinformation for robot programming. For example, position sensors can beused to measure the width of a grasped component, thereby providing acheckthatthecorrectcomponenthasbeengrasped.Similarly,forcesensorsareuseful forweighinggraspedobjectsandmonitoring task related forces.Formost industrial applications, the robot’s handor end effectorsmust be

designedtoperformaspecificjob.Therefore,whenarobotchangestasks,itneedsanewgripper.Hereareafewofthemanyavailabletypesofgrippers.

Someofthecommonlyusedgrippersare:FingergrippersMechanicalgripperswhere frictionor thephysical configurationof thegripperretainstheobjectSuctionorvacuumcupsusedforflatobjectsMagnetizedgripperdevicesusedforferrousobjects

FINGERGRIPPERSThe most commonly used grippers are finger grippers. These will

generallyhavetwoopposingfingersorthreefingerslikealathechuck.Thefingersaredriventogethersuchthatoncegripped,anypartiscenteredinthegripper.Thisgivessomeflexibilitytothelocationofcomponentsatthepick-up point. Two finger grippers can be further split into parallel motion orangularmotionfingersasshowninFigure15.6.

FIGURE15.6

Two fingered pneumatic actuated: As the cylinder is actuated, ittranslates to the fingers opening or closing. The extra links help increaseholdingforce.(RefertoFigure15.7.)

FIGURE15.7

Two-finger internal gripper: As the cylinder is actuated, the fingersmoveoutward.(RefertoFigure15.8.)

FIGURE15.8

Othertypesofgripperswithtwo,three,andmultiplefingersareshowninFigure15.9.

FIGURE15.9TypesofGrippers.

MECHANICALGRIPPERSOnecanthinkofamechanicalgripperasarobothand.Themechanical

grippersusemechanicalfingersactuatedbyamechanismtograspanobject.Abasicrobothandwillhaveonlytwoorthreefingers.Amechanicalhandthatwrapsaroundanobjectwillrelyonfrictioninordertosecuretheobjectitisholding.Frictionbetweenthegripperandtheobjectwilldependontwothings, first is the type of surfacewhether it bemetal onmetal, rubber onmetal,smoothsurfaces,orroughsurfacesandthesecondistheforcewhichispressingthesurfacestogether.

There are different types of mechanism: pneumatic, electrical,mechanical,orhydraulic.Somekindsoffingerscanbedetachable.Inmostcases,twofingersareenoughtograspthetargetingoodcondition.Themainproblemoftenconsistsof countering thegravityproblemwhen thegripperhastograspsomething.Thesolutionisgivenbyapplyinganoppositeforcethatoneneedstolift.Thenonecanconsiderthephysicalconstrictionandthefrictionmethods.Thefirstoneisaccomplishedbydesigningthecontactingsurfacesofthefingerstobeintheapproximateshapeofthepartgeometry.In the secondmethod, the fingersapplieda strongenough friction force to

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retainthepartagainstgravity.Thismethodisusuallycheaperbecauseofthedesignofthefingers.

Mechanical grippers are often fitted with some type of pad usuallymadefrompolyurethaneasthisprovidesgreaterfriction.Padsarelesslikelytodamagetheworkpiece.Padsarealsousedsotohaveabettergrip,asthepolyurethanewillmakecontactwithallpartsofthesurfacewhenthegripperis closed. Mechanical grippers can be designed and made for specificpurposesandadjustedaccordingtothesizeoftheobject.Theycanalsohavedualgrippers.Robotsbenefitfromhavingdualgrippersastheycanincreaseproductivity,beusedwithmachinesthathavetwoworkstationswhereonerobotcan load twoparts inasingleoperation,andwhere thecycle timeofthe robot is too slow to keep up with the production of the other. Somemechanical grip devices contain three moving fingers that simultaneouslyclosetograspapartortool.Thesehandsareparticularlyusefulinhandlingcylindrical-shaped parts, as the three-point contact centers around parts ofvaryingdiametersonthecenterlineofthehand.

VACUUM/SUCTIONGRIPPERSSuctiongrippersareoftwotypes:

Devices operated by a vacuum: The vacuum may be provided by avacuumpumporbycompressedair.Deviceswitha flexiblesuctioncup:Thiscuppresseson theworkpiece.Compressedairisblownintothesuctioncuptoreleasetheworkpiece.

Theadvantageofthesuctioncupisthatifthereisapowerfailureitwillstill work, as the workpiece will not fall down. The disadvantage of thesuction cup is that they onlywork on clean, smooth surfaces. The suctioncups aremade of rubber-likematerials (silicone, neoprene).Depending onthe design and the material, suction cups are suitable for workpiecetemperaturesupto200°C.Thenumberofgrippers(cups)determinesthesizeandweightofobjecttobegrasped.Figure15.10showsavacuumgripper.

FIGURE15.10VacuumGrippert.

Advantages

Requiresonlyonesurfaceofaparttograsp.A uniform pressure can be distributed over some area, instead ofconcentratedatapoint.Thegripperislightweight.Manydifferentmaterialscanbeused.Nodangerofcrushingfragileobjects.

Disadvantages

Themaximumforceislimitedbythesizeofsuctioncups.Positioningmaybesomewhatinaccurate.Timemaybeneededforthevacuuminthecuptobuildup.WTherobotsystemmustincludeaformofapumpforairandthelevelofnoisecancauseannoyanceinsomecircumstances.

MAGNETICGRIPPERSMagnetic grippers are considered when the part to be handled is of

ferrouscontent.Theprincipleisthesameasofvacuumgrippersexceptthatmagneticgrippersreplacethecups.Thissystemhastheadvantagethatitcanquickly handle metal parts with holes. For maximum effect, the magnetneedstohavecompletecontactwiththesurfaceofthemetaltobegripped.Any air gapswill reduce the strength of themagnetic force; therefore flatsheetsofmetalarebestsuitedtomagneticgrippers.Ifthemagnetisstrongenough,amagneticgrippercanpickupanirregularshapedobject.Insomecases,theshapeofthemagnetmatchestheshapeoftheobject.AmagneticgripperisshowninFigure15.11.

FIGURE15.11MagneticGripper.

A disadvantage of using magnetic grippers is the temperature.Permanentmagnetstendtobecomedemagnetisedwhenheatedandsothereisthedangerthatprolongedcontactwithahotworkpiecewillweakenthemtothepointwheretheycannolongerbeused.Theeffectofheatwilldependon the time themagnet spends incontactwith thehotpart.Mostmagneticmaterialsarerelativelyunaffectedbytemperaturesuptoaround100degrees.Auniquefeaturethatsets themagneticgripperapartfromothergrippers isthatitleaveslittletonoresidualmagneticchargewhenturnedoff,thereforereleasing thepart instantly.Themagneticgripper isable to release its loadquickly,anddespiteitscompactsize,cansustainenormousholdingpower.

Electromagnetscanbeused insteadandareoperatedbyaDCelectriccurrent.Ifanelectromagnetisused,apowerfailurewillcausetheparttobedropped immediately, which may produce an unsafe condition. Althoughelectromagnetsprovideeasiercontrolandfasterpickupandreleaseofparts,permanent magnets can be used in hazardous environments requiringexplosion-proofelectricalequipmentand losenearlyallof theirmagnetismwhenthepoweristurnedoff.Permanentmagnetsarealsousedinsituationswherethereisanexplosiveatmosphereandsparksfromelectricalequipmentwouldcauseahazard.

Advantages

Variation in part size can be tolerated.The grippers do not have to bedesignedforoneparticularworkpart.Abilitytohandlemetalpartwithholes.Pickuptimesareveryfast.Requiresonlyonesurfaceforgripping.

Disadvantages

Residualmagnetismthatremainsintheworkpiece.

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7.8.9.10.11.12.

(i)(ii)(iii)

13.14.15.16.

17.

Possiblesideslippage.Morethanonesheetwillbeliftedbythemagnetfromastack.

EXERCISESExplaintheworkingprincipleofanendeffectorwiththehelpofasketchandgiveitsimportantapplications.Howaretherobotendeffectorsclassified?Listthedifferentendeffectorsusedonrobots.Whatarethevarioustypesofgrippersusedinrobots?Explain theconstructionofdifferentendeffectorsfordifferent typesofapplications.Identify the different types of end effectors used in robots and theirapplications.Defineendeffectors.Discusstheworkingofanythreetypesofendeffectors.Whatarethecharacteristicsofend-of-armtooling?Brieflyexplaintheelementsofend-of-armtooling.Discussthevariousfactorstobeconsideredinselectingagripper.Showthefollowinggripperswiththehelpofadiagram:

TwofingergripperInternalandexternalgripperAngularandparallelgripper

Distinguishbetweenmagneticandvacuumgrippers.Listtheadvantagesanddisadvantagesofvacuumgrippers.Whataretheadvantagesanddisadvantagesofmagneticgrippers?Explain theconstructionofdifferentendeffectorsfordifferent typesofapplications.Describeasimpleservocontrolsystemforarobot.Explainthefollowingwithasketch:

MagneticgrippersVacuumgrippersMechanicalgrippers

CHAPTER16

ROBOTPROGRAMMING

INTRODUCTIONRobots are becoming more powerful, with more sensors, more

intelligence,andcheapercomponents.Asaresult robotsaremovingoutofcontrolled industrial environments into uncontrolled service environmentssuchashomes,hospitals,andworkplaceswheretheyperformtasksrangingfromdeliveryservicestoentertainment.Itisthisincreaseintheexposureofrobots tounskilledpeople that requiresrobots tobecomeeasier toprogramandmanage.The flexibilityof a robot systemcomes from its ability tobeprogrammed.How the robot isprogrammed is amainconcernof all robotusers.A goodmechanical arm can be underutilized if it is too difficult toprogram. Earlier robot programming was easy because it only requiredguiding the robot through the sequence of desiredmovements. To executecompletetasksofthetypefoundinassembly,robot-programminglanguageshad to be introduced. Although the introduction of robot programminglanguageshas representedan importantbreakthrough in industrial robotics,currently available languages are not easy to use. The programmer mustdefineall themovementsveryprecisely.Programming the robot isnot thesameasprogrammingthecomputer.

ROBOTPROGRAMMINGArobotprogramcanbedefinedasapathinspacetobefollowedbythe

manipulator,combinedwithperipheralactions that support theworkcycle.A robot can perform complex tasks under the control of stored programs,whichcanbemodifiedatwill.Theprocessof robotprogramming includes

1.2.3.4.5.

teaching it the task to be performed, storing the program, executing theprogram, and debugging it. Robotic programming is similar to real-timeprogramminginthattheprogramsmustbeinterruptdrivenandtakeaccountof limited resources. Robot programs can be simple or complex. Simpleprogramswillhavea setofpre-programmed responses to expectedevents.For example, if the robot is hit, it may move in a particular direction.Complex robotprogramsmay includeaway to learn frompast eventsandactionsandpredictwhatwillhappen.Forexample,a robotprogrammed tomove left when it reaches a barrier will always move in this direction.However,arobotmightbeprogrammedtorememberwhichdirectionhasthefewestbarriersandwillmove in thatdirection.Thiselementof learning ismore likely found in robotprograms than real-timeprograms.Examplesofthe peripheral actions include opening and closing the gripper, performinglogicaldecisionmaking,andcommunicatingwithotherpiecesofequipmentintherobotcell.

ROBOTPROGRAMMINGTECHNIQUESA number of different techniques are used to program robots. The

principaltaskofrobotprogrammingistocontrolthemotionsandactionsofthe manipulator. A robot is programmed by entering the programmingcommands into its controller memory. The methods of entering thecommandsare:

OnlineprogrammingLeadthroughprogrammingWalk-throughprogrammingOfflineprogrammingTaskprogramming

ONLINEPROGRAMMINGOnline programming takes place at the site of production itself and

involves theworkcell.Onlineprogramming systems (Refer toFigure16.1)uses a teach pendant to direct the robot’smovementwhich allows trainedpersonneltophysicallyleadtherobotthroughthedesiredsequenceofevents

by activating the appropriate pendant button or switch. Position data andfunctional information are “taught” to the robot, and a new program iswritten.Taughtdataisstoredinthependant’smemorythentransferredtotherobot’s controller. The teach pendant can be the sole source by which aprogramisestablished,or itmaybeused inconjunctionwithanadditionalprogramming console and/or the robot’s controller. When using thistechnique of teaching or programming, the person performing the teachfunction can be within the robot’s working envelope, with operationalsafeguardingdevicesdeactivatedorinoperative.Thereareanumberofteachpendanttypesavailable,dependingonthetypeofapplicationforwhichtheywillbeused.Ifthegoalissimplytomonitorandcontrolaroboticsunit,thenasimplecontrolboxstyleissuitable.Ifadditionalcapabilities,suchasonthesiteprogrammingarerequired,moresophisticatedboxesshouldbeused.

FIGURE16.1OnlineProgramming.

Onlineprogrammingisaconvenientandeasymethodofprogrammingwhentasksaresimpleandrevisionsoradjustmentscanbemadeonthespot.However,theproductionlinemustbestoppedduringtheprogrammingandtherearesafetyissuestoconsider,astheprogrammermustworkwithintherobot’sworkenvelope.

Advantages

Easilyaccessible.

The robot is programmed in concordance with the actual position ofequipmentandpieces.

Disadvantages

Unavailabilityofrobotforproductionduringprogrammingphase.Slowmovementoftherobotwhileprogramming.Timeconsumingprocess.Programlogicandcalculationsarehardtoprogram.Suspensionofproductionwhileprogramming.Costequivalenttoproductionvalue.Inefficientinflexiblemanufacturingsystem.

TheTeachPendant(ManualControlPendant)Theteachpendanthasthefollowingprimaryfunctions:

Serve as the primary point of control for initiating and monitoringoperations.Guidetherobotormotiondevice,whileteachinglocations.Supportapplicationprograms.

The teach pendant as shown in Figure 16.2 is used with a robot ormotion device primarily to teach robot locations for use in applicationprograms. The teach pendant is also used with custom applications thatemploy“teachroutines,” thatpauseexecutionatspecifiedpointsandallowan operator to teach or re-teach the robot locations used by the program.Therearetwostylesofteachpendants:theprogrammer’spendant,whichisdesignedforusewhileanapplicationisbeingwrittenanddebugged,andtheoperator’s pendant, which is designed for use during normal systemoperation.

1.2.

3.

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FIGURE16.2TeachPendant.

Theoperator’spendanthasapalm-activatedswitch,whichisconnectedto the remote emergency stop circuitry of the controller. Whenever thisswitchisreleased,armpowerisremovedfromthemotiondevice.Tooperatetheteachpendant, thelefthandisput throughtheopeningontheleft-handsideofthependantandtheleft thumbisusedtooperatethependantspeedbars.Therighthandisusedforalltheotherfunctionbuttons.

Themajorareasoftheteachpendantare:

Liquidcrystaldisplay(LCD)Data entry buttons: The data entry buttons are used to input data,normallyinresponsetopromptsthatappearonthependantdisplay.Thedata entry buttons include YES/NO, DEL, the numeric buttons, thedecimal point, and the REC/DONE button, which behaves like theReturn orEnter key on a normal keyboard. Inmany cases, applicationprograms have users press the REC/DONE button to signal that theyhavecompletedatask.Emergencystopswitch:Theemergencystopswitchontheteachpendantimmediatelyhaltsprogramexecutionandturnsoffarmpower.UserLED:ThependantisinbackgroundmodewhentheuserLEDisnotlitandnoneofthepredefinedfunctionsarebeingused.TheuserLEDislitwheneveranapplicationprogramismakinguseoftheteachpendant.

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Modecontrolbuttons:Themodecontrolbuttonschange thestatebeingusedtomovetherobot,switchcontrolbetweentheteachpendantandtheapplicationprograms,andenablearmpowerwhennecessary.Manual control buttons: When the teach pendant is in manual mode;thesebuttonsselectwhich robot jointwillmove,or thecoordinateaxisalongwhichtherobotwillmove.ManualstateLEDs:ThemanualstateLEDsindicatesthetypeofmanualmotionthathasbeenselected.Speed bars: The speed bars are used to control the robot’s speed anddirection.Pressingthespeedbarneartheouterendswillmovetherobotfaster,whilepressing thespeedbarnear thecenterwillmove the robotslower.Slow button: The slow button selects between the two different speedrangesofthespeedbars.Predefined function buttons: The predefined function buttons havespecific, system-wide functions assigned to them, like display ofcoordinates,clearerror,etc.Programmablefunctionbuttons:Theprogrammablefunctionbuttonsareused in custom application programs, and their functions will varydependingupontheprogrambeingrun.Soft buttons: The “soft” buttons have different functions depending onthe application program being run, or the selection made from thepredefinedfunctionbuttons.

LEADTHROUGHPROGRAMMINGLeadthroughprogrammingrequirestheoperatortomovetherobotarm

through thedesiredmotionpathduringa teachprocedure, therebyenteringtheprogramintothecontrollermemoryforsubsequentplayback.Therearetwomethodsofperformingtheleadthroughteachprocedure:

PoweredleadthroughManualleadthrough

Thedifferencebetweenthetwoisthemannerinwhichthemanipulatorismovedthroughthemotioncycle.

Powered leadthrough is commonly used as the programmingmethodforplaybackrobotswithpoint-to-pointcontrol.Itinvolvestheuseofateachpendant (hand-held control box) which has toggle switches or contactbuttons for controlling themovement of themanipulator joints. Using thetoggle switches or buttons, the programmer drives the robot arm to thedesired positions, in sequence, and records the positions into memory.During subsequent playback, the robot moves through the sequence ofpositionsunderitsownpower.

Manual leadthrough is convenient for programming playback robotswith continuous path control in which the continuous path is an irregularmotionpatternsuchasinspraypainting.Thisprogrammingmethodrequirestheoperatortophysicallygrasptheend-of-armortoolsattachedtothearmandmanually move through the motion sequence, recording the path intomemory.Becausetherobotarmitselfmayhavesignificantmassandwouldthereforebedifficult tomove,aspecialprogrammingdeviceoftenreplacesthe actual robot for the teach procedure. The programming device has asimilar joint configuration to the robot, and it is equipped with a triggerhandle(orothercontrolswitch),whichisactivatedwhentheoperatorwishesto record motions into memory. The motions are recorded as a series ofcloselyspacedpoints.Duringplayback, thepathisrecreatedbycontrollingtheactualrobotarmthroughthesamesequenceofpoints.

Powered leadthrough is the most common programming method inindustryatthistime.

Advantages

Easytoprogram:shoppersonnelcanreadilylearnitanddoesnotrequiredeeperprogrammingexperience.

Disadvantages

Interruptioninproduction.Teachpendanthave limitations in theamountofdecisionmaking logicthatcanbeincorporatedintheprogram.Nointerfacetoothercomputersubsystemsinthefactory.

WALK-THROUGHPROGRAMMINGOR

TEACHINGInwalk-throughprogramming, theteacherphysicallymoves(“walks”)

therobotthroughthedesiredpositionswithintherobot’sworkingenvelope(RefertoFigure16.3).Duringthistime,therobot’scontrollermayscanandstorecoordinatevaluesonafixed-timeintervalbasis.Thesevaluesandotherfunctionalinformationarereplayedintheautomaticmode.Thismaybeatadifferentspeedthanthatusedinthewalk-through.

FIGURE16.3Walk-throughProgrammingMethod.

This type of walk-through programming uses triggers on manualhandles that move the robot.When the trigger is depressed the controllerremembers the position.The controllerwould thengenerate themovementbetween these points when the program is played. The walk-throughmethods of programming require the teacher to be within the robot’sworking envelope with the robot’s controller energized at least in theposition sensors. This may also require that safeguarding devices bedeactivated.Apersondoingtheteachinghasphysicalcontactwiththerobotarmandactuallygainscontrolandwalkstherobot’sarmthroughthedesiredpositions within the working envelope. With the walk-through method ofprogramming, the person doing the teaching is in a potentially hazardousposition because the operational safeguarding devices are deactivated orinoperative.Thewalk-throughmethodisappropriateforspraypaintingandweldingrobots.

OFFLINEPROGRAMMINGOfflineprogrammingisaccomplishedoncomputerslocatedawayfrom

the robot station (Refer toFigure16.4).Using simulation software, data is

generated and then sent to the robot’s controllerwhere it is translated intoinstructions.Additionally,thesoftwarecontainsmodelingdata,whichassistsselection of the best robot configuration for a particular application. Theadvantage of this programming method is that programming can be donewhile the robot is still in productionon thepreceding job, thusproductiontimeoftherobotisnotlosttodelaysinteachingtherobotanewtask.Thisensureshigherutilizationoftherobot.

FIGURE16.4.OfflineProgramming.

Advantages

Effectiveprogrammingofprogramlogicsandcalculationswithstateoftheartdebuggingfacilities.Locations are built according to models and this can mean thatprogrammerswillhavetofinetuneprogramsonlineorutilizesensors.Effectiveprogrammingoflocations.Verificationofprogramthroughsimulationandvisualization.Welldocumentedthroughsimulationmodelwithappropriateprograms.

ReuseofexistingCADdata.Cost independent of production. Production can continue whileprogramming.Processsupporttools,forinstance,selectionofweldingparameters.

Disadvantages

Demandsinvestmentinanofflineprogrammingsystem.Needsextensivetraining.

TASKLEVELPROGRAMMINGTask level programming requires specifying goals for the position of

objects,ratherthanthemotionsofarobotneededtoachievethosegoals.Atasklevelspecificationismeanttobetotallyrobotindependent,nopositionsorpathsthatdependonrobotgeometryarespecifiedbytheuser.Tasklevelprogramming systems requires complete geometric models of theenvironmentandoftherobotasinput.

Inthetasklevellanguage,robotactionsarespecifiedbytheireffectsonobjects.Forexample,auserwouldspecifythata jobshouldbeplacedinapalletratherthanspecifyingthesequenceofmanipulatormotionsneededtoperform the insertion. A task planner would transfer the task levelspecificationsintorobotlevelspecifications.

MOTIONPROGRAMMINGMotion programming with today’s robot languages requires a

combinationoftextualstatementsandleadthroughtechniques.Accordingly,this method of programming is sometimes referred to as online/offlineprogramming. The textual statements are used to describe themotion, andtheleadthroughmethodsareusedtodefinethepositionandorientationoftherobotduringand/orattheendofthemotion.

The leadthroughmethodsprovideaverynaturalwayofprogrammingmotion commands into the robot controller. In manual leadthrough, theoperator simply moves the arm through the required path to create theprogram.Inpoweredleadthrough,theoperatorusesateachpendanttodrive

themanipulator.Theteachpendantisequippedwithatoggleswitchorapairofcontactbuttonsforeachjoint.Byactivatingtheseswitchesorbuttonsinacoordinated fashion for the various joints, the programmer moves themanipulatortotherequiredpositionsintheworkspace.

Coordinatingtheindividualjointswiththeteachpendantissometimesanawkwardwaytoentermotioncommandstotherobot.Forexample,itisdifficulttocoordinatetheindividualjointsofajointed-armrobottodrivetheend-of-arm in a straight-line motion. Therefore, many of the robots usingpowered leadthrough provide two alternative methods for controllingmovementofthemanipulatorduringprogramming,inadditiontoindividualjointcontrols.With thesemethods, theprogrammercancontrol the robot’swrist end to move in straight-line paths. The names given to thesealternativesare(1)worldcoordinatesystem,and(2)toolcoordinatesystem.Both systems make use of a Cartesian coordinate system. In the worldcoordinatesystem,theoriginandframeofreferencearedefinedwithrespecttosome fixedpositionandalignment relative to the robotbase. In the toolcoordinatesystem,thealignmentoftheaxissystemisdefinedrelativetotheorientationof thewrist faceplate (towhich theendeffector isattached). Inthis way, the programmer can orient the tool in a desired way and thencontroltherobottomakelinearmovesindirectionsparallelorperpendiculartothetool.

Thespeedof the robot iscontrolledbymeansofadialorother inputdevice locatedon the teachpendant and/or themaincontrolpanel.Certainportions of the program should be performed at high speeds (e.g.,movingparts over substantial distances in the workcell), while other parts of theprogramrequirelow-speedoperation(e.g.,movesthatrequirehighprecisioninplacingtheworkpart).Speedcontrolalsopermitsagivenprogramtobetriedoutatasafeslowspeed,andthenforahigherspeedtobeusedduringproduction.

OVERVIEWOFROBOTPROGRAMMINGLANGUAGES

Virtually all robots are programmed with some kind of robotprogramminglanguage.Theseprogramminglanguagesareusedtocommandthe robot tomove tocertain locations, signaloutputs, and read inputs.The

1.

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programminglanguageiswhatgivesarobotitsflexibilityandallowsarobotto react to its environment (through the use of sensors), and to makedecisions.Robotprogramminglanguagesfallintothreebasiccategories:

Specializedrobotlanguages

Theselanguageshavebeendevelopedspecificallyforrobots.Thecommandsfoundintheselanguagesaremostlymotioncommandswithminimal logic statements available.Most of the early robot languageswereofthistype,althoughmanystillexisttoday.VALisanexampleofthis.

Robotlibraryforanewgeneral-purposelanguage

These languages were created by first creating a new general-purpose programming language and then adding robot-specificcommands to it. These languages are generally more capable than aspecialized language, because they tend to have better logic testingcapabilities.KARELlanguageisanexampleofthistype.

Robotlibraryforanexistingcomputerlanguage

These languages are developedby creating extensions to popularcomputer programming languages. Consequently, these languagesclosely resemble traditional computer programming languages, andbenefitfromthepowerofexisting,widelyusedlanguages.Robotscriptisanexampleofthistypeoflanguage.

Generally, all the robot programs have three basic modes ofoperation.Theyare:

Monitormode:Inthismode, theuserdefinesthevariouspositionstobeusedintheprogram.Thesepositionswillbetaughtusingtheteach pendant and stored into the memory to be used in theprogram.Editormode:Thismodeisusedbytheusertowritenewprogramsandedittheexistingones.Inthismode,thesyntaxcheckingwillbedone.Runmode:Thisisthemodeinwhichtherobotisactuallyexecutingthe program. The robot is actually performing the sequence ofmotionsintherunmode.

REQUIREMENTSFORASTANDARDROBOTLANGUAGE

Becauseofthedifferentmethodsofdevelopingrobotlanguages,manydifferent typesof languagesareavailable.Currently, therearenostandardsfor robot languages,andeachrobotmanufacturerhasdeveloped theirown,eachwith theirownsyntaxanddatastructures.Somefactorieshave robotsfrommultiplerobotmanufacturers, thus,multiple languagesarerunningonthese control systems.This requires robot programmers to be proficient inmany languages, or for the robot programmers to specialize in certainlanguages.Theresultofthisvarietyisademandforacommonlanguagethatcan be used on any type of robot. To develop a new robot programminglanguage, the deficiencies of the existing languages, as well as therequirementsofanewlanguage,needtobeidentified.

As robot workcells are becoming more complex, the robot has toperformmorecomplicatedmovesand interactwithmoresensorsandotherperipheraldevices.Robotsoftenhavetodecidewhichpartiscomingdownthe line, and determine the proper program to run. Existing robot-programming languages, especially the specialized languages, often havelimited ability to use subroutines and do logic testing. Some of the earlygenerationcontrollersjustdon’thavethememorycapacitytoholdsuchlargeprograms.

Most robot languages require the user to compile a program beforerunningitontherobotcontroller.Compilingaprogramconvertsthehuman-readablesourcecodeintoamachine-readableform.This isusuallydonetoincreasethespeedoftheprogramexecution,becausetheprogramisalreadyintheeasiestformforthecomputertoread.Interpreters,ontheotherhand,convert the human-readable code to computer-readable code on the fly, asthe program executes. Usually, this results in a significant amount ofcomputerprocessingtimebeingusedtodotheconversion.Intheearlydaysof robotics, compiling was required because the processors were not fastenough to interpret a program. Many robot controllers still require theprogramstobecompiledbeforerunning,eventhoughthereisnowplentyofcomputerpowertointerpretprograms.

ROBOTLANGUAGES

1.2.3.

Alanguageisasystemofcommunication,whichusually isconnectedto human spoken language and which is based on an arbitrary system ofsymbols.Themost important featureofa language is itsability toproducemessages. In a computer, the executable control program is formed of asequence of machine-language commands. A machine-language commandconsistsofanumericalcode,whichcontains the typeof thecommandandthe source and destination addresses of the information. To makeprogramming easier, several high-level programming languages have beendeveloped. Instead of numbers and addresses, the developer can now usewords and names. Before the use of such a high-level control program, itmust be compiled to machine-language code. This is done by compilers,whichhavebeendevelopedforeachlanguage.

Different languages have different aims and are suitable for differentpurposes. For example,MATLAB is a mathematical language, which hasbeendevelopedtosolvemathematicalproblems.Ithasbuilt-infunctionsforpowerfulmathematicalanalysis,butitisnotsuitableforreal-timecontrolofamobile robot.HTML is amarkup language to describe how informationappears in web browsers, but it is not suitable to solve mathematicalproblems.Someofthebasictypesofcommandsinprogramminglanguagesare:

Motionandsensingfunctions(e.g.,MOVE,MONITOR)Computationfunctions(e.g.,ADD,SORT)Programflowcontrolfunctions(e.g.,RETURN,BRANCH)

TYPESOFROBOTLANGUAGESTheearliestmethods for traininga robot likemechanical setup,point-

to-point path recording, and task lead through did not use word-basedlanguages.Someofthehigh-levelcomputerlanguagesnowusedtoprogramrobotsare:Wave,AL,ACL,AML,APT,ARCL,ZDRL,HELP,Karel,CAP1,MML,RIPL,MCL,RAIL,RPL,ARMBASIC,Androtext,VAL,IBL,andLadderLogic.

Wave

Wave was the first high-level language created for programming arobot.StandfordArtificialLaboratorydevelopeditin1973.

AL

The AL (Arm Language) high-level programming language wasdevelopedattheroboticsresearchcenterofStanfordUniversity.

ACL

The Advanced Command Language (ACL) is a robot language thatemploys a user-friendly conversational command environment. Yaskauarobotsuseit.

AML

AML is the programming language used for the control of robotsproduced by IBM. AML is intended to provide a complete interpretedcomputer language along with all of the programming support typicallyassociatedwithhigh-levelprogramminglanguages.

APT

TheAutomatically Programmed Tools (APT) language is a computerlanguage dealing with motion. Electronic Systems Laboratory of MITdevelopeditin1956.

ARCL

ARCL(ARobotControlLanguage)wasbasedonPascal-likesyntax.Itwas a compiled language and the developed cross-compiler required threepassesbeforetheexecutablecodewasreadytobedownloadedandexecutedinarobot.This languagehasaPascal-likesyntaxwithsensory-controlandmotioncontrolcommands.AnexampleofanARCL-languagecommand isMOVA (GRIP, HI, CONT,MED), which opens the gripper on the robot.ARCL emphasized sensory-based programming rather than plannedtrajectorymotionandwasdesignedforeducationalrobot.

ZDRL

ZDRL (Zhe Da Robot Language) was a motion-oriented robotlanguage.Itwasaninterpretativesystemandthelanguagewascomposedofsystemcommandsandprograminstructions.Systemcommandswereusedtoprepare thesystemforexecutionofuser-writtenprograms.ZDRL included32 system commands and 37 program instructions, and it contained

capabilities for program editing, file management, location-data teaching,programexecuting,andprogramdebugging.

HELP

HELP is a high-level programming language developed for use withGeneralElectric’sAllegroassemblyrobot.

Karel

Karel,Karel2,andKarel3are robotcontrol languagesusedbysomeFANUCrobotcontrollers.

CAP1

The Conversational Auto Programming 1 (CAP 1) robot language isusedbytheFANUC32-18-TRobotController.

MML

MMLwasamodel-basedmobilerobotlanguagethatwasdevelopedattheUniversityofCalifornia.Itisahigh-levelofflineprogramminglanguage,which contains functions for high-level sensor functions, geometricmodeldescription and path planning, and others. This language contains animportantconceptofslowandfastfunctions,whicharchitectureisessentialfor real-time control of robots. A slow function is executed sequentially,whileafastfunctionisexecutedimmediately.Thesecondimportantconceptis theseparationof the referenceandcurrentposture,whichmakespreciseandsmoothmotioncontrolanddynamicposturecorrectionpossible.

RIPL

RIPL (Robot Independent Programming Language) is based on anobject-orientedRobot IndependentProgrammingEnvironment [RIPE].TheRIPE computing architecture consists of a hierarchical multiprocessorapproach,whichemploysdistributedgeneralandspecial-purposeprocessors.Thisarchitectureenables thecontrolofdiversecomplexsubsystemsinrealtimewhileco-coordinatingreliablecommunicationsbetweenthem.

MCL

MCLisshortforManufacturingControlLanguageandwasdevelopedbyMcDonnellDouglasfortheU.S.AirForce’sICAMproject.

RAIL

RAIL is a high-level programming language developed byAutomatixforusewithrobotsandvisionsystems.

RPL

RPL is a high-level programming language developed by SRI and isusedtoconfigureautomatedmanufacturingsystems.

ARMBASIC

ARMBASICisanextensionofthehobbyistcomputerlanguageBASIC.ItwasusedwiththeMicrobotMini-Mover5educationalrobot.

Androtext

Androtext isahigh-levelcomputer languagedevelopedbyRobotronicCorporationtomakecommandingapersonalroboteasier.

VAL

VAL stands for Victor’s Assembly Language. VAL is a high-levelprogramming language developed for PUMA lines of robots. Theprogramming language is similar to BASIC. It has a complete set ofvocabularywordsforwritingandeditingrobotprograms.

IBL

IBL (Instruction Based Learning) is a method to train robots usingnatural language instructions. IBL uses unconstrained language with alearningrobotsystem.Arobot isequippedwithasetofprimitivesensory-motorproceduressuchasturnleftorfollowtheroadthatcanberegardedasan execution-level command language. The user’s verbal instructions areconverted into a new procedure and that procedure becomes a part of theknowledgethattherobotcanusetolearnincreasinglycomplexprocedures.With thisprocedure, the robot shouldbe capableof executing increasinglycomplex tasks. Because errors are always possible in human-machinecommunication,IBLverifieswhetherthelearnedsubtaskisexecutable.Ifitisnot,thentheuserisaskedformoreinformation.

LadderLogic

1.2.3.4.5.6.7.8.

•1.2.3.4.5.6.7.

Ladder logic is a programming language designed to be used byelectricians. It closely resembles the relay logic that appears on the insidelidsordoorsofdishwashersandwashingmachines.Theonlyrobotsthatuseladderlogicprogrammingarethosethatcomewithoutacontrollerorwithaprogrammablelogiccontroller.

EXAMPLEOFAROBOTPROGRAMUSINGVALTheVALlanguageisthemostadvancedcommerciallanguagedesigned

for use with Unimation, Inc. industrial robots. VAL stands for Victor’sAssemblyLanguage.Itisbasicallyanofflinelanguageinwhichtheprogramdefiningthemotionsequencecanbedevelopedoffline,butthevariouspointlocations used in the work cycle are most conveniently defined byleadthrough.TodemonstratetheVALlanguage,letusassumethattherobotmustpickupobjectsfromachuteandplacetheminsuccessiveboxes.Onepossiblesequenceofrobotactivityisasfollows:

Movetoalocationabovethepartinthechute.Movetothepart.Closethegripperjaws.Removethepartfromthechute.Carrytheparttoalocationabovethebox.Putthepartintothebox.Openthegripperjaws.Withdrawfromthebox.

ThecorrespondingVALprogramisasfollows:

EDITDEMO.1

PROGRAMDEMO.1?APPROPART,50@?MOVESPART@?CLOSEI@?DEPARTS150@?APPROSBOX,200@?MOVEBOX@?OPENI@

8.

1.2.3.4.5.6.7.8.

1.2.3.4.5.

?DEPART@

Theexactmeaningofeachlineis:Movetoalocation50mmabovethepartinthechute.Movealongastraightlinetothepart.Closethegripperjaws.Withdrawthepart150mmfromthechutealongastraight-linepath.Movealongastraightlinetoalocation200mmabovethebox.Putthepartintothebox.Openthegripperjaws.Withdraw75mmfromthebox.

Whentheprogramisexecuted,itcausestherobottoperformthestepswhichdescribethetask.

Most articulated robots perform by storing a series of positions inmemory, andmoving to them at various times in their programming. Forexample,arobotthatismovingitemsfromoneplacetoanothermighthaveasimpleprogramlikethis:

DefinepointsP1–P5:

Safelyaboveworkpiece20cmabovebinAAtpositiontotakepartfrombinA20cmabovebinBAtpositiontotakepartfrombinB

Defineprogram:

MovetoP1MovetoP2MovetoP3ClosegripperMovetoP4MovetoP5Opengripper

1.2.3.

4.5.6.7.8.9.10.11.12.

13.14.

15.

MovetoP1andfinish

For a given robot, the only parameters necessary to locate the endeffector(gripper,weldingtorch,etc.)oftherobotcompletelyaretheanglesofeachof the joints.However, therearemanydifferentways todefine thepointsfortherobottomoveto,someofwhichcanbemuchmoreefficient,dependingonthetasktobeaccomplished.

EXERCISESNamesomeprogramminglanguagesforrobotprogramming.Explaintheuseofteachpendantforrobotprogramming.Identify any four robot programming languages. Name the importantrequirementofprogramminglanguages.Whatismeantbyteachpendantprogrammingofrobots?Whatisateachpendant?Givethreemethodsforprogrammingarobot.Giveanexampleofarobotprogram.Listthenamesofthreerobot-programminglanguages.Whatdoyoumeanbytasklevelprogramming?Whatarethedifferentclassesofrobotlanguages?Discuss.Compareonlineandofflineprogrammingofrobot.Discuss the lead through programming technique used in robotprogramming.Listatleastfourlanguagesusedforprogrammingofrobots.Write notes on languages available, features required of programminglanguage, and classification of commands in respect of robotprogramminglanguages.Explainthefollowing

ManualprogrammingLeadthroughprogramming

1.

2.

CHAPTER17

APPLICATIONSOFROBOTS

INTRODUCTIONThe present-day applications for robots are much broader than most

people realize. While the emphasis in robot development is on industrialrobots, factories are not the only place where robots are used. Small,medium,andlargecompaniesinjustabouteveryindustryaretakingafreshlook at robots to see how this powerful technology can help them solvemanufacturingchallenges.Inbusinessofficesandelsewhere,robotsserveasmail delivery carts, promotional or show robots, laboratory assistants,hospitalorderlies,andwindowwashers.Ingeneral,industrialrobotsarebestusedforjobsthataredirty,dull,dangerous,ordifficult,thetypesofjobsthathumansdomostpoorly.

Robots are used in a wide range of industrial applications. The firstcommercial application of an industrial robot took place in 1961, when arobotwas installed to load andunload a die-castingmachine.Thiswas anunpleasanttaskforhumanoperators.Manyrobotapplicationstookplaceinareaswhereahighdegreeofhazardordiscomforttohumansexisted,suchasinwelding,painting,andfoundryoperations.Theearliestapplicationswereinmaterialshandling,spotwelding,andspraypainting.Robotswereinitiallyapplied to jobs that were hot, heavy, and hazardous such as die-casting,forging,andspotwelding.Thereasonsforusingrobotsare:

Reduced costs—robots can perform tasks more economically thanhumans.Improved productivity—robots are not only less expensive than humanlabor,butalsohavehigherratesofoutput.Thisincreaseinproductivity

3.

4.

isdue to robot’s slightly fasterworkpacebutmuch is the resultof therobot’sabilitytoworkalmostcontinually,withoutlunchbreaksandrestperiods.Betterquality—robotshaveadistinctadvantageofbeingabletoperformrepetitivetaskswithahigherdegreeofconsistency,whichinturnleadstoimprovedproductquality.Eliminationofhazardoustasks.

ROBOTCAPABILITIESThe three important capabilities of robots that make them useful for

applicationsare:

TransportManipulationSensing

TransportMaterialhandlingisoneofthebasicoperations,whichisperformedon

an object as it passes through the manufacturing process. The object ismoved fromone location to another tobe stored,machined, assembled, orpackaged.Therobot’scapabilitytoacquireanobject,moveitthroughspace,and release itmakes it ideal for transport operations. Simple tasks such aspart transfer from one conveyor to another may only require one-or two-dimensional movements, which are often performed by non-servo robots.Otherpartshandlingoperationssuchasmachineloadingandunloadingandpackaging may be more complicated and require varying degrees ofmanipulativecapability.Servo-controlledrobotsperformtheseoperations.

ManipulationAnother basic operation performed on an object as it is transformed

from raw material to a finished product is processing, which generallyrequiressometypesofmanipulation, i.e.,workpiecesareinserted,oriented,or twisted tobe inproperposition formachining, assembly,or someotheroperation.Arobot’scapabilitytomanipulatebothpartsandtoolingmakeit

very suitable for processing applications. Examples in this regard includespotandarcwelding,andspraypainting.

SensingA robot’s ability to react to its environment by means of sensory

feedback is also important, particularly in applications like assembly andinspection.These sensory inputsmaycome fromavarietyof sensor types,includingproximityswitches,forcesensors,andmachinevisionsystems.

Ineachapplication,oneormoreoftherobot’scapabilitiesoftransport,manipulation,orsensingisemployed.Theseapplicationsmakearobotidealformanyapplicationsnowperformedmanually.

APPLICATIONSOFROBOTS

ManufacturingApplications

Arcandspot-weldingSpraypaintingMachineloadingandunloadingMachiningDiecastingForgingInvestmentcastingPartstransferringPlasticsmoldingFinishingAssemblyInspection

MaterialsHandling

TransportgoodsPickandplacePalletizing

SpaceIndustry

RobotarmsusedasmanipulatortohandlebulkytelescopesMountedonspaceshuttleorrepaircraft

Military

RemotebombdetonationSmartbombs

MedicalApplications

IntelligentwheelchairsRobotarmsusedtomanipulateandhandlepatients

MANUFACTURINGAPPLICATIONSWelding

Perhaps the most popular applications of robots are in industrialwelding.Therepeatability,uniformityquality,andspeedofroboticweldingareunmatched.ArobotperformingaweldingoperationisshowninFigure17.1. The two basic types of welding are spot welding and arc welding,althoughlaserweldingisdone.Someenvironmentalrequirementsshouldbeconsidered for a successful operation. The automotive industry is a majoruser of robotic spot welders. The other major welding task performed byrobots is arc or seam welding. In this application, two adjacent parts arejoinedtogetherbyfusingthem,therebycreatingaseam.

FIGURE17.1RobotPerformingWeldingOperation.

Whyshouldrobotsbeusedforwelding?

Aweldingprocessthatcontainsrepetitivetasksonsimilarpiecesmightbe suitable for automation.Thenumberof itemsof any type tobeweldeddetermines how difficult automating a process will be or not. If partsnormallyneedadjustment tofit togethercorrectly,or if joints tobeweldedare too wide or in different positions from piece to piece, automating theprocedure will be difficult or impossible. Robots work well for repetitivetasksor similarpieces that involvewelds inmore thanoneaxis.Themostprominentadvantagesofautomatedweldingareprecisionandproductivity.Robot welding improves weld repeatability. Once programmed correctly,robotswill giveprecisely the samewelds every timeonworkpiecesof thesamedimensionsandspecifications.

ArcWelding

Arc or fusion welding is considered a major growth area for theapplicationofrobotics(RefertoFigure17.2).Theprocessisveryhostiletothe operator, generating noise, fumes, and intense light. Automationproduceshighqualityweldswithgreaterconsistencyandatafasterrate.Ingeneral, equipment for automatic arcwelding is designed differently fromthatusedformanualarcwelding.Automaticarcweldingnormallyinvolveshigh-dutycycles,andtheweldingequipmentmustbeabletooperateunderthose conditions. In addition, the equipment components must have thenecessaryfeaturesandcontrolstointerfacewiththemaincontrolsystem.

FIGURE17.2RobotsforArcWelding.

Aspecialkindofelectricalpower is required tomakeanarcweld.Aweldingmachine,alsoknownasapowersource,providesthespecialpower.

All arc-welding processes use anarcwelding gun or torch to transmit theweldingcurrentfromaweldingcabletotheelectrode.Theyalsoprovideforshieldingtheweldareafromtheatmosphere.Thenozzleofthetorchiscloseto the arc and will gradually pick up spatter. A torch cleaner (normallyautomatic)isoftenusedinrobotarcweldingsystemstoremovethespatter.Allofthecontinuouselectrodewirearcprocessesrequireanelectrodefeedertofeedtheconsumableelectrodewireintothearc.Theprocessisappliedtoautomobile subassemblies mainly for reasons of strength, low distortion,high-speedapplicationswhereone-sidedaccessisrequired,andsealing.

SpotWelding

Automatic welding imposes specific demands on resistance weldingequipment. Often, equipment must be specially designed and weldingproceduresdevelopedtomeetrobot-weldingrequirements.Thespotweldingrobot(RefertoFigure17.3)isthemostimportantcomponentofarobotizedspotweldinginstallation.Weldingrobotsareavailableinvarioussizes,ratedbypayloadcapacityandreach.Robotsarealsoclassifiedbythenumberofaxes.Spotweldinginvolvesapplyingaweldingtooltosomeobject,suchasa car body, at specified discrete locations. A spot welding gun appliesappropriatepressureandcurrenttothesheetstobewelded.Thisrequirestherobot to move its hand (end effector) to a sequence of positions withsufficientaccuracytoperformthetaskproperly.Itisdesirabletomoveatahigh speed to reduce cycle time, while avoiding collisions and excessivewearordamagetotherobot.

FIGURE17.3Spot-weldingGun.

There are different types of welding guns, used for differentapplications, available. An automatic weld-timer initiates and times theduration of current.A robot can repeatedlymove thewelding gun to each

weld location and position it perpendicular to the weld seam. It can alsoreplay programmedwelding schedules. Amanual-welding operator is lesslikelytoperformaswellbecauseoftheweightofthegunandmonotonyofthetask.Spotweldingrobotsshouldhavesixormoreaxesofmotionandbecapable of approaching points in thework envelope from any angle. Thispermits the robot to be flexible in positioning a welding gun to weld anassembly.Aroboteasilyperformssomemovementsthatareawkwardforanoperator,suchaspositioningtheweldinggunupsidedown.

Typicalcomponentsofanintegratedroboticspotweldingcellare:

SpotweldingrobotSpotweldinggunWeldtimerElectrodetipdresserSpotweldingswivel

ElectronBeamWelding

Electronbeamwelding(EBW)isafusionjoiningprocessthatproducesaweldbyimpingingabeamofhigh-energyelectronstoheattheweldjoint.Electronsareelementaryatomicparticlescharacterizedbyanegativechargeand an extremely small mass. An electron beam-welding gun uses a highintensity electron beam to target aweld joint. Theweld joint converts theelectronbeamtotheheatinputrequiredtomakeafusionweld.Theelectronbeamisalwaysgenerated inahighvacuum.Theuseof speciallydesignedorificesseparatedaseriesofchambersatvarious levelsofvacuumpermitswelding in medium and non-vacuum conditions. Although, high vacuumweldingwillprovidemaximumpurityandhighdepth towidthratiowelds.An electron beam robot welding system benefits the customer with a lowcontaminationvacuum,narrowweldzone,useslowfillermetal,andhaslowdistortion.

MIGWelding

Gas metal arc welding (GMAW) is frequently referred to as MIGwelding. MIG welding is a commonly used high deposition rate weldingprocess.Wire is continuously fed from a spool.MIGwelding is thereforereferred to as a semiautomatic welding process. Robotic systems areintegrated towards MIG welding applications on a consistent basis. With

advancesintechnology,andthebenefitsofaGMAWroboticcell,factoriesandjobshopslargeandsmallareinvestinginarobot.Returnoninvestmentofaroboticsystemispossibleafterjustafewyears.MIGweldingrobots,orGMAWcellshavemanybenefits for customers.Robots are all positioncapable,havehigherdepositratesthanSMAW,needlessoperatorskill,canperform longer welds without stopping, and have minimal post weldcleaning.

TIGWelding

Gas tungsten arc welding (GTAW) is frequently referred to as TIGwelding. TIG welding is a commonly used high-quality welding process.TIGweldinghasbecomeapopularchoiceofweldingprocesseswhenhighquality, precision welding is required. In TIG welding, an arc is formedbetweenanon-consumable tungsten electrode and themetalbeingwelded.Gasisfedthroughthetorchtoshieldtheelectrodeandmoltenweldpool.Iffillerwire is used, it is added to theweld pool separately.ATIGweldingrobotsystemhasmanybenefitstocustomers.Arobotproduceshigh-qualitywelds, welds can be made with or without filler metal, variable precisecontrols,lowdistortion,andfreeofspatter.

SprayPaintingAnother popular and efficient use for robots is in the field of spray

painting.Theconsistencyandrepeatabilityofarobot’smotionhaveenablednear perfect quality while at the same time wasting no paint. The spraypaintingapplicationsseemstoepitomizetheproperapplicationsofrobotics,relieving thehumanoperator fromahazardous,albeit skillful job,whileatthe same time increasing work quality, uniformity, and cutting costs. Inspraying applications, the robotmanipulates a spray gun,which is used toapply some material such as paint, stain, or plastic powder, to either astationary ormoving part. These coatings are applied to awide variety ofparts, including automotive body panels, appliances, and furniture. Thespray-paintingenvironmentconstitutesafirehazardandisalsodangeroustohumanworker’s respiration.An early paint-sprayingmachinewas built byPollard in the 1930s. Today, this machine would be called an industrialrobot. Robots perform painting, coating, and dispensing jobs in manyindustriestoday.Companiesmakingproductssuchasmotorcycles,bicycles,boats, jet skis, and cars are using painting automation to their advantage.Painting robots are generally equipped with six axes, three for the base

1.2.

3.

4.5.

motionsandthreeforapplicatororientation.Someunitsincorporatemachinevisionforguidanceortocheckapplicationquality.Typically,thesepaintingrobots are electrically driven, rather than hydraulically or pneumaticallypowered.Advantagesofusingspray-paintingrobots(Figure17.4)include:

FIGURE17.4RobotsforSprayPainting.

Humansareremovedfromahostileenvironment.Less energy is needed for fresh air requirements and the need forprotectiveclothingisreduced.The quality of the painting is improved, reducing works and warrantycosts.Lesspaintandothermaterialsareused.Directlaborcostsarereduced.

MachineTendingMachine loading and unloading is a more complex application than

basic material handling; for this application, the robot provides bothmanipulativeandtransportcapabilities(RefertoFigure17.5).Robotscanbeused to grasp a workpiece from a supply point (e.g., a conveyor belt),transport it toamachine,orient it,andtheninsert it intothemachineworkholder. This may require that the robot signal the machine tool when theworkpiece is in the correct position, so that the part can be secured in theworkholder.Therobotthenreleasesthepartandwithdrawsthearmsothatmachiningcanbegin.Uponcompletionofthemachining,therobotunloadstheworkpieceandtransfers it toanothermachineorconveyor.Inarobotic

cell, a single robot can service severalmachines.The single robotmay beused to perform other operations while the machines are performing theirprimaryfunctions.Thismayrequirethattherobotbeabletoexchangeend-effectors.Examplesofmachinetendingfunctionsincludethefollowing:

FIGURE17.5MachineTendingOperation.

Exchangingmachinetools,suchaslatheandmachiningcenters.Stampingpressloadingandunloading.Tendingplasticinjectionmoldingmachines.Holdingapartforaspotweldingoperation.Loadinghotbilletsintoforgingpresses.Loadingautopartsforgrinding.LoadinggearsontoCNCmillingmachines.

ForgingRobots have been applied in many different types of forging

applications such as hammer forge operations, upsetter operations, rollforges,hot formingpresses, anddrawbenchapplications. In somecases, arobotactsasaforgingmachineoperatororasaroleofforgehelper.

Forge hammers: Forging hammers are either hydraulic, steamhydraulic,orairdriven.One-halfoftheformingdieisontheanvil,andtheotherhalfofthedieisonaramthatmovesupanddown,eitherunderforceby air, steam, or gravity.Under the control of an operator, the hammer isallowedtostrikethepartthatislyingbetweenthetwodiesacertainnumberoftimes.Dependingontheobservationoftheforgingoperator,theoperator

1.2.3.

4.

determineswhentotakeapartoutofonedieandmovesitintothenext.Thefunctionoftherobotinthisapplicationcanbetoactasaforgehelper.Whenworkingheavierparts,therobotcanbeusedtoloadandunloadfurnacesandprocessthebillets to theforgingbed,wheretheoperatorcantakeoverandprocess the parts through the various forming cycles. The robot then canmaneuverthefinishedproducttoatrimoperation.

DieCastingDie casting involves forcing nonferrous metals into dies under high

pressuretoformpartsofadesiredshape.Atypicaldie-castingtaskinvolvesunloadingapartfromthedie-castingmachine,quenchingthepart,andthendisposingofthepartonaconveyorbeltorintoabin.Apossiblerobottaskcyclesindie-castingcouldincludeanyofthefollowing:

Alternatelyloadingtwoormorediecastingmachines.Unloading,quenching,trimming,anddisposingofthepart.Unloading the die castingmachine and preparing the dye for the nextcastingcycle.(Thiswouldrequireanothergripperorattachmenttospraythedie.)Loadinganinsertintothediecastingmachineandunloadingthefinishedpart.

PlasticMoldingThe plastic molding process is typically used for thermoplastic

materials. The material to be molded is supplied in a granule form andmovedfromahoppertoacylinder,fromwhichaplungerforcesthegranulesthrough a heat chamber into themold.Then, themoldhalf opens, and theproductsarewithdrawn.Manyautomotivepartsareinjectionmoldedtoday,aswellasmanypartsutilizedinhouseholdappliances.Therobotistypicallyemployed toremove thepart fromthemoldeitherbygraspingasprueandrunnerassembly.Arobotis typicallyusedataninjectionmoldingmachineworkcellwherepartsmustnotbedroppedbecauseoffragility,orwhererunsaresoshortthatitisnoteconomictobuildatotallyautomaticmoldtodropthepartthroughthebottomofthemachine.

Assembly

Thisistheprocessofrobotmanipulationofcomponents,resultinginafinishedassembledproduct.Assembly(Refer toFigure17.6) is theprocessoffittingandholdingtogetherpartsandassemblies;generallyperformedbymeans of nuts, bolts, screws, fasteners, or snap-fit joints. Examples ofassemblyoperationsinclude:

FIGURE17.6RobotDoingAssemblyOperation.

Assemblyofcomputerharddrives.Insertionoflampsintoinstrumentpanels.Insertionandplacementofcomponentsontoprintedcircuitboards.Automatedassemblyofsmallelectricmotors.Furnitureassembly.

Sealing/DispensingFordispensingapplications,therobotmanipulatesadispenserorgunto

apply amaterial such as paint, adhesive, sealant, orwashing solution to astationary or moving part. Additional equipment used to complete adispensingsystemmayincludematerialcontainers,pumps,andregulators.Itisveryimportantthat,foroperationsthatinvolvetheapplicationofmaterialthatproducesflammableorexplosivefumes,therobotbesealedandhaveasystemthatpurgestherobot’sinternalcavities.Iftherobotisnotsealedanddoesnothaveapurgingsystem,thepossibilityoftheignitionofflammableor explosive fumes by the arcing of the robot’s internal electricalcomponents(i.e.,motors,electroniccomponents,andelectricalconnections)exists.

Inapplicationswherethepartisonaconveyorline,therobot’smotioniscoordinatedwiththemotionoftheconveyor.Themanipulativecapabilityoftherobotistheprimaryfunctionthatmakesarobotespeciallywellsuitedfordispensingapplications.Themajorbenefitofusingarobot(Figure17.7)for dispensing applications is that a robot provides uniform application ofmaterial (repeatability). Other benefits include a reduction of labor costs,coatingmaterialwaste,andexposureofworkerstohazardousmaterials.

FIGURE17.7RobotPerformingSealingOperation.

Examplesofdispensingapplicationsinclude:

Paintingpartsonanautomatedline.Applicationofadhesiveandsealanttocarbodies.Applicationofthermalmaterialtorockets.Washing.

InspectionandMeasurementWithagrowinginterest inproductquality, thefocushasbeenonzero

defects. However, the human inspection system has somehow failed toachieve its objectives. Robot applications of vision systems have providedservicesinpartlocation,completenessandcorrectnessofassemblyproducts,and collision detection during navigation. Machine vision applicationsrequiretheabilitytocontrolbothpositionandappearanceinordertobecomeaproductivecomponentofanautomatedsystem.

MaterialRemovalRoboticmaterial removal is a new application that hasmany uses in

industrial automation. The robot can grind, roll, and file metal parts toprecision.Theroboticsystemcanremovematerialwithqualityeverysingle

time it is being used. The robot can work long hours and produce morethroughputs.Robotics has becomemore affordable andmany factories arelooking to buy a robotic deburring cell for their operation. With expertengineering, any material removal application can bring your company agood return on investment (ROI). A material removal robot can be verybeneficialtoanoperationbecauseoftherobot’sprecisionandquality.Withamaterial removal robot system technologycanbeaspreciseas removingspots on jewellery. Material removal can be described as a deburringprocess, andcanbe integrated to themostpreciseapplications.Companiescanautomateamaterialremovalprocessandgainmanybenefits.

DeburringRoboticdeburringistheuseofarobottoremoveburrs,sharpedges,or

fins from metal parts. The robot can grind, roll, and file metal parts toprecision(RefertoFigure17.8).Theroboticsystemcanproduceadeburringapplication, i.e., quality every single time it is being used. The robot canworklonghoursandproducemorethroughputs.Roboticshasbecomemoreaffordableandmanyfactoriesarelookingtobuyaroboticdeburringcellfortheiroperation.Aroboticdeburringcellcanworklonghourswithoutfatigueremovingroughedges.Thequalityoftheprocess,aswellasthelonghoursofaroboticcellisunmatched.

FIGURE17.8RobotPerformingDeburringOperation.

Grinding

Manual grinding is tough, dirty, and noisy work. The metal dustproduced by grinding is harmful to employee’s eyes and lungs. Grindingrobots removeexcessmaterial fromthesurfaceofmachinedparts/productsquicklyandefficiently.Arobotcanperformworkwithmoreconsistencyandhigherqualityresults.

DrillingWiththeautomationofadrillingrobotsystem,companiescanimprove

accuracyandrepeatability.Drillingrobotscanwork24hoursadaywithoutworriesorfatiguethusenhancingoperationaloutput.(RefertoFigure17.9.)

FIGURE17.9RobotPerformingDrillingOperation.

MATERIALHANDLINGAPPLICATIONSUsing robots for handling materials are an essential component of

today’sautomatedmanufacturingsystems.Materialhandlingandlogisticsisthe movement, protection, storage, and control of materials and productsthroughout the process of theirmanufacture anddistribution, consumption,anddisposal. It isa repetitiveoperation;carriedoutoftenunderunpleasantand hard working conditions, which requires little skill. This applicationmakesuseoftherobot’scapabilitytotransportobjects.Figure17.10showsarobotdoingmaterialhandlingoperation.

(1)(2)(3)(4)(5)(6)(7)(8)

FIGURE17.10MaterialHandlingRobot.

The term “material handling” covers a lot of ground in the world ofrobotics:tinyworkpiecesthatpeoplecan’thandleverywell,ifatall;large,heavypartslikeengineblocksandwheels;bulkyitemslikebagsandboxes;delicateandexpensiveelectroniccomponents;medicalequipment.Thelistisextensive. Robotic material-handling applications range from tendinginjection-moldingmachinesandmachinetools,toreorientingpartsbetweenprocesses,topackagingandpalletizing.

Byfittingtherobotwithanappropriateend-effector(e.g.,gripper),therobot can grasp the object that needs to be moved. The robot may bemountedeitherstationaryonthefloororonatraversingunit,enablingittomove from one workstation to another. The robot can also be ceilingmounted. The primary benefits of using robots for material handling arereductionofdirectlaborcostsandremovalofhumansfromtasksthatmaybehazardous, tedious,or fatiguing.Also, theuseof robots formoving fragileobjectsresultsinlessdamagetopartsduringhandling.Robotsthatareusedformaterial handling can interfacewithothermaterial handling equipmentsuch as containers, conveyors, guided vehicles, monorails, and automatedstorage/retrievalsystems.Ahandlingprocessconsistsofeightsequences:

TransferoftherobotarmuptheworkpieceFinemotionapproachingtheworkpieceGraspingFinemotionuprisingtheworkpieceTransfertheworkpiecetothedesiredpositionFinemotiondowntothedestinationpositionReleasetheworkpieceFinemotionupward

The gripping sequence is themore delicate part of handlingmaterial.Thegripper’sandtherobot’spositionshavetobecheckedforcollisionwithotherobjectsintheenvironment.Thelimitationoftherobot’sworkspacecanalsobeaproblemforallotherplanningsequencesofthehandling.

Thefollowingareexamplesofmaterialhandlingapplications:

Transferringpartsfromoneconveyortoanother.Transferringpartsfromaprocessinglinetoaconveyor.Loadingbinsandfixturesforsubsequentprocessing.Movingpartsfromawarehousetoamachine.Transportingexplosivedevices.Transferofpartsfromamachinetoanoverheadconveyor.

PartsTransferringPartstransferringrefertoremovingpartsfrompalletsandplacingthem

inbinsoronconveyorbelts,orremovingpartsfrombinsandconveyorbeltsandplacingthemonpallets.Parttransferapplicationsaregenerallyreferredtoasmaterialhandlingrobotapplications.Withtheadvancementsinend-of-arm tooling, and technology companies are taking a closer look into parttransfer robotics. As robots become more affordable, and competitionbecomes fierce, many companies will look into a part transfer robot toautomate their press operation. An integrated part transfer robot (Refer toFigure 17.11) system is easy to install and brings many benefits to ourcustomers. A robot moves a part in and out of a press, with ease and nofatigue.Therobotcantransferapart24hoursaday,givingmoreflexibilitytothecompany.

FIGURE17.11RobotusedforPartsTransferring.

Palletizing

Palletizing is the act of loading or unloadingmaterial onto pallets.Aroboticpalletizingsystem(RefertoFigure17.12)allowsmoreflexibilitytorunmoreproductsforlongerperiodsoftime.Withtheadvancementsinend-of-arm tooling, robot-palletizing workcells have been integrated in manyfactories. The use of robots in palletizing is a popular material-handlingoperation, particularly where more than one type of packaging is beinghandled.Thenewspaperindustryhasbeenparticularlyhardhitbyincreasedlabor costs. Part of the solution to this problem was to use robots likeCincinnatiMilacronRobot being used to palletize advertising inserts for anewspaper. Robotic palletizing technology can help with productivity andprofitability. The robotic workcells can be integrated towards any project.The savings of using a robot for longer hourswithout fatigue is always aconsideration for plantmanagers. Robots have becomemore affordable inrecent years and can be paid off in just a fewyearsworth ofwork.Manyfactories,foodprocessingplants,andpalletizingplantshaveautomatedtheirapplicationwithapalletizingrobot.

FIGURE17.12RobotsPerformingPalletizingOperation.

PickandPlaceOperationsIndustrial robots also perform what are referred to as pick and place

operations.Pickandplaceis thenamecommonlygivento theoperationofpicking up a part and placing it appropriately for subsequent operations.Pick-and-place operations have some requirements. The part must not bedropped.Itmustbeheldsecurelyenoughtoprevent it fromslippingin thegripperbutgentlyenoughtoavoiddamage.Inaddition,caremustbetakentoavoiddisturbingthepartduringapproachanddeparture.Apickandplacerobot is a material handling robot that can work 24 hours a day withoutworries or fatigue. The consistent output of a robotic system along withqualityandrepeatabilityareunmatched.Amongthemostcommonofthese

operations is loading and unloading pallets, used across a broad range ofindustries.Thisrequiresrelativelycomplexprogramming,astherobotmustsensehowfullapalletisandadjustitsplacementsorremovalsaccordingly.Robotshavebeenvitalinpickandplaceoperationsinthecastingofmetalsandplastics.Inthediecastingofmetals,forinstance,productivityusingthesame die-casting machinery has increased up to three times, the result ofrobot’sgreaterspeed,strength,andabilitytowithstandheatinpartsremovaloperations.

Pickandplaceroboticcellsarebeing integrated intofactoryfloorsallover the world. They are a more favorable solution to production linesbecause they move at faster speeds and have more flexibility than everbefore.Managersare realizing the long-termsavingswithapickandplacerobotic workcell rather than the operation they are currently doing. Anincrease in output with a material handling robotic system has savedfactories money. With the advancements in technology, and roboticsbecomingmoreaffordablepickandplaceroboticcellsarebeinginstalledformanydifferentpickandplaceautomationapplications.

MachineToolLoadingandUnloadingMachineloadingandunloadingapplicationsaregenerallyreferredtoas

material handling. With the advancements in end-of-arm tooling, andtechnology,companiesaretakingacloserlookintothebenefitsofmachineloading robotics. As robots become more affordable, and competitionbecomesfierce,manycompanieswilllookintomachineloadingroboticstoautomatetheiroperation.Arobotcanbegivenalongerreachthanahumanworker andmight be able to load and unloadmore then onemachine.Anintegratedmachine-loadingrobotiseasytoinstallandbringsmanybenefitsto our customers. A robot loads a part into the press, with ease and nofatigue.Therobotcan loadparts24hoursaday,givingmoreflexibility tothecompany.

OrderPickingArobotorderpickingsystemcanbeprogrammedtodomultipletasks.

Withtheadvancementsinend-of-armtooling,order-pickingapplicationcanbeusedinmostcompanies.Aroboticsystembenefitsafirmwithflexibility,repetitivequalityandnofatigue.Arobotorderpickingprocesswouldmostlikelybeassociatedwithmaterialhandling.

1.2.

3.4.5.

6.7.

8.9.10.11.12.

CLEANROOMROBOTSCleanroomrobotsarespecificallysealedandisolatedfromdustorany

kindofairparticlestoperformtasksinanisolatedatmosphere.Mostlyusedinmedicalor labapplication tohandleparts, tendmachinery,anddispensedrugs. A robot is a valuable tool in a clean room setting because it canprovide the samequality resultswithout error for a longperiodof time.Arobotic systemallows laboratories andother clean room robot applicationsmuchflexibility.(RefertoFigure17.13.)

FIGURE17.13CleanRoomRobotCell.

EXERCISESNamesomeindustrialapplicationsofrobots.What are the reasons for successful application of robots inmanufacturingindustries?Identifysometypicalapplicationsofrobotsintheindustry.Writeanexplanatorynoteontheindustrialapplicationsofrobots.Explaintheuseofarobotforindustrialmaterialhandlingwiththehelpofsomeexamples.Explaintheuseofrobotformachineloading/unloading.Preparealistofanyfourindustrialoperationsthatcanbeperformedbyrobot.Listvarioustypesofassemblytasks,whichcanbeperformedbyrobots.Whatarethereasonsforusingrobotsinindustries?Listthecapabilitiesofarobot.Discussthematerialhandlingapplicationofrobots.Whatismachinetendinginindustrialrobots?

13.14.15.

Writeashortnoteonsealing/dispensingapplicationofrobots.Writeanessayontherobotsusedinspraypaintingapplications.Writeashortnoteonthefollowing:

Materialhandling.Weldingoperation.

CHAPTER18

ROBOTSUSINGREAL-TIMEEMBEDDEDSYSTEMS

(The material in this chapter appears and was adapted from Real-TimeEmbeddedComponentsandSystemswithLinuxandRTOSbyS.SiewertandJ.Pratt.MercuryLearningandInformation,2016.ISBN:978-1-942270-04-1.)

INTRODUCTIONTOROBOTSUSINGREAL-TIMEEMBEDDEDSYSTEMS

Modern robotic applications can be operated as real-time embeddedsystems.Real-timesystemsarecomputersystemsthatcanmonitor,respondto, or control their environment making decisions without active humancontrol. A robot as part of a real-time embedded system can use sensors,actuatorsandotherinputsandoutputstoaffectobjectsintherealworldandmust do so within the real-time physical constraints of environments thathumans often operate in as well. This chapter reviews basic conceptsimportant to the design and implementation of basic real-time roboticsystems.

Real-time applications also might have deadlines that are beyondhuman ability. A real-time system must simply operate within anenvironment tomonitorand/orcontrolaphysicalprocessata rate requiredby the physics of the process. In the case of robotics, this is a distinctadvantagethatroboticshasoverhumanlabor, theability tokeepupwithaprocess that requires faster response and more accuracy than is humanlypossible. Furthermore, robots can perform repetitive tasks for long hourswithouttiring.Figure18.1showsanindustrialroboticassemblyline.

FIGURE18.1IndustrialRobotsonanAssemblyLine.

It is important to note that robotics is often deployed in controlledenvironments such as assembly lines rather than in uncontrolledenvironmentswherehumansoftenoperatebetter,atleastpresently.

ROBOTICARMThe robotic arm approximates the dexterity of the human armwith a

minimum of five degrees of rotational freedom including: base rotation,shoulder, elbow,wrist, andagripper.Thegripper canbea simpleclaworhavethedexterityofahumanhand.Ingeneral,thegripperisoftencalledanend effector to describe the broad range of devices that might be used tomanipulateobjectsortools.Thesebasicarmsareavailableaslowcosthobbykits and canbe fitwith customcontrollers and sensors for fairly advancedroboticsprojects.Themainlimitationoflow-costhobbyarmsisthattheyareunable to grip and move any significant mass, offer less accurate andrepeatable positioning, and are less dexterous than industrial or researchrobotic arms. Most industrial or research robotic arms have six or more

degreesoffreedom(additionalwristmotionandcomplexendeffectors)andcanmanipulatemassesfromonetohundredsofkilograms.Roboticarmsareoftencombinedwithmachinevision,withcameraseitherfixedinthearmorwithviewsofthearmfromfixedlocations.Abasicfivedegreeoffreedomarm with end effector vision can be used to implement interesting tasksincludingsearch,targetrecognition,grappling,andtargetrelocation.Figure18.2 shows the OWI-7 robotic trainer arm with a reference coordinatesystem.

FIGURE18.2RoboticArmCoordinatesandHomePosition.

Withareferencecoordinatesystemwithanoriginatthefixedbaseforthe arm, the reach-ability of an arm can be defined based upon the armmechanical design and kinematics. Figure 18.2 shows the OWI arm withelbowrotationsuch that the forearm isheldparallel to thebasesurface. Inthisposition,thebasecanberotatedtomovetheendeffectoroveracirculartraceonthesurface.

The five degree of freedom arm is capable of tracing out reachablecirclesarounditsbase.Figure18.4showstheinnermostringofreach-abilityfortheOWIarm.

FIGURE18.3RoboticElbowRotationOnly.

FIGURE18.4InnermostSurfaceRingReach-ability.

CombinedrotationoftheshoulderandelbowallowstheOWIarmendeffector to reach locationsoncircular arcs around thebase atvarious radiifrom the innermost ring. Figure 18.5 shows an intermediate ring of reach-ability.

FIGURE18.5IntermediateSurfaceRingReach-ability.

Finally,theoutermostringofreach-abilityfortheOWIarmisdefinedbyarmlengthwithnoelbowrotationandshoulderrotationsuchthattheendeffectorreachesthesurface.Figure18.6showsthelimitofoutermostreach-ability.

FIGURE18.6OutermostSurfaceRingReach-ability.

Thisbasicanalysisonlyconsidersthesurfacereach-abilityoftheOWIarm on its X, Y base plane.More sophisticated tasks might require threedimensional reach-ability analysis. Once the kinematics (the mathematicalrepresentation of the mechanics of objects in motion) and reach-abilityanalysishasbeencompletedsothatthejointrotationsareknownformovingtheendeffector toand fromdesired target locations,nowanactuationandcontrolinterfacemustbedesigned.

ACTUATIONActuationandendeffectorcontrolisgreatlysimplifiedwhenthetarget

objectmassesthattheendeffectormustworkwitharenegligible.Significanttargetmassrequiresmorecomplexactivejointmotortorquecontrol.Movingsignificant mass requires motor controllers with DAC output (Digital toAnalog)andsteppermotorswithactive feedbackcontrolchannels foreachdegree of freedom. For the OWI arm and negligible payload mass, theactuation can be designed using relays or simpleH-bridge types ofmotorcontrollers.Themotorsmustbereversible.Thesimplestcircuitforreversingamotorcanbeimplementedwithswitchestochangethepolarityacrossthemotor leads as shown inFigure18.7.With changingpolarity, themotor iscontrolledinforwardandreversedirections.

FIGURE18.7ThreeSwitchReversibleMotor.

Each switch state of “on” or “off” combine to result in one of threetypes of operation: 1) nomotion or “off”; 2) forward; and 3) reverse.Thepossibleswitchstatesandtheoperationthatresults,knownastheactuation,areenumeratedinTable18.1.

TABLE18.13SwitchReversibleMotorControl.

SW-A SW-B SW-C MOTOR

Off X Off Off

Off On On Forward

On Off On Reverse

Setting three switches is not very practical since this would requirethree relays and therefore fifteen total for a five degree of freedom arm.Figure18.8showshowtworelayscanbeusedtoimplementthethreeswitchreversiblemotorcircuitbymakinguseofrelaysthatincludenormallyopenandnormallyclosedpoles.

FIGURE18.8TwoRelayReversibleMotor.

This simplifies the relay reversible motor actuation to ten relaysrequiredforafivedegreeoffreedomarm.Table18.2summarizesthemotoractuationasafunctionoftherelaysettingforthisdesign.

TABLE18.22RelayReversibleMotorControl. RLY-A RLY-B MOTOR

Off Off Off

Off On Forward

On Off off

On On Reverse

This is scaled to actuate a five degree of freedom arm as shown inFigure18.9.

FIGURE18.9FiveDegreeofFreedomRoboticArmRelayCircuit.

Actuation of a robotic arm can lead to mechanical arm failure if themotors are allowed to over drive the joint rotations based upon the armmechanical limits of rotation for each joint. To avoid gear damage amechanicalclutchorslipsystemcanbeemployed,afeatureoftheOWIarm,however reliance upon a clutch or slip system is still not ideal. Jointsdesignedwithmechanical slipor clutches can slipunder theweight of thearmandcausepositioningerrorsiftooloose,andiftootight,overdrivingajointwillstillcausegeardamage.Abetterapproachistointegratehardandsoft limit switches so that electrical and software protection mechanismspreventoverrotationofjoints.Figure18.10showsacircuitdesignforhardlimitswitches.

FIGURE18.10UseofHardLimitSwitchesforArmJointMotorControl.

ThelimitswitchesshowninFigure18.10mustbemountedonthearmsuch that the joints cause the switch to be activated at each limit ofmechanicalmotion.Thedownsidetothiscircuitisthatthearmjointwhichhitsalimitremainsinoperableuntilitismanuallyreset.

A better approach is to use soft limits monitoring with a softwareservice that periodically or on an interrupt basis samples the output of aswitched circuit through an A/D (Analog to Digital) converter so thatsoftwarecandisablemotorsthathitalimit.ThisdesignisshowninFigure18.11.

FIGURE18.11UseofSoftLimitSwitchesforMotorControlSafing.

Eachof thesoft limitswitchescanbemechanically integratedso theywilltriggerbeforethehardlimitswitches,allowingsoftwaretosafe(disable)apotentiallyoverrotatedjoint,decidewhetheralimitover-rideforrecoveryis feasible, and then recover by commanding rotation back to the operablerange.Ifsoftwarelimitsmonitoringfailsorthesoftwarecontrollerfails,thehardware limits will continue to protect the arm from damage. The relayactuation design with hard and soft limit switches provides basic armactuation,butonlywithbinaryon/offmotorcontrol.

TheconceptofreversiblemotorpolescanbegeneralizedusingrelaysinanH-bridge,providingmoremotorcontrolstatesthanthetworelaydesign.TheH-bridgerelaycircuitisshowninFigure18.12.

FIGURE18.12RelayH-BridgeMotorControl.

Inspection of the relay H-bridge states shows that the H-bridge alsoprovidesadditionalcontrolfeatures.

ThebrakingfeaturesofanH-bridgecanprovidethebasisfortorqueandovershootcontrolsothatthemotorcontrollercanrampuptorqueandrampitdownwhilepositioning.Theramp-upcanbeprovidedbyaDAC(DigitaltoAnalogConverter) and the ramp-down braking can be provided by theH-bridgebraking states.The short-circuit states of theH-bridge, “fuse tests,”mustspecificallybeavoidedbyH-bridgecontrollerlogic.

Relayactuationprovidesonlyonandoffmotorcontrolandrequirestheuse of electro-mechanical relay coils which are create noise, dissipatesignificant power, and take up significant space even for compact reedrelays. Figure 18.13 shows the same H-bridge controller design as Figure18.12,butusing solid stateMOSFETs (MetalOxideSubstrateFieldEffectTransistors).

FIGURE18.13MOSFETH-BridgeMotorControl.

TABLE18.3RelayH-BridgeMotorControlStates. A B C D MOTOR

0 0 0 0 off

0 0 1 1 Brake

0 1 0 1 FuseTest

0 1 1 0 Reverse

1 0 0 1 Forward

1 0 1 0 FuseTest

1 1 0 0 Brake

1.

2.3.

TheMOSFETdesignprovides the samestatesandcontrolas the fourrelay H-bridge, but much more efficiently with less power requiredcomparedtoelectromagneticcoilactuation.

ENDEFFECTORPATHThe ability to actuate an arm still does not provide the ability to

navigatethearm’sendeffectortoandfromspecificreachablelocations.Thismustbedonebypathplanningsoftwareandbyendeffectorguidance.Thesimplestpathplanningandendeffectorguidance function implements armmotiondead-reckoningandsingle joint rotationsequences.Dead-reckoningsimplyturnsonajointmotorforaperiodoftimebaseduponarotationratethat is assumed constant, perhaps calibrated during an arm initializationsequence between joint limits.Using a dead-reckoning estimation for jointrotation will lead to significant positioning error, but can work forpositioning taskswheresignificanterror is tolerable.Movingone jointatatime is also tolerable for paths which do not need to optimize the time,energy,ordistanceforthemotionbetweentwotargets.Muchmoreoptimalpathsbetweentwotargetscanbeimplementedusingpositionfeedbackandmultiple concurrent joint rotation.Concurrent joint rotation is simple todowith a relay orH-bridge controller, although the kinematics describing thepath taken are more complex. Motion feedback requires active sensingduringjointrotation.

SENSINGJointrotationsensingcanbeprovidedbyjointpositionencodersand/or

machinevisionfeedback.Positionencodersinclude:Electrical(multi-turnpotentiometer)

Optical (LED and photodiode with light-path occlusion and counting)Mechanicalswitch(withamomentaryswitchcounter)

Positionencodersprovidedirectfeedbackduringarmpositioning.Thisfeedbackcanbeusedtodrivethefeedbackinacontrolloopwhenthearmismovedtoadesiredtargetposition.Thisassumesthedesiredtargetisknown,eitherpre-programmedorknownthroughadditionalsensingsuchasmachinevision.Figure18.14showsthebasicfeedbackcontroldesignforaposition

encoded controlled process to move an arm from one target position toanother.

Figure 18.14 can be further refined to specifically show an actuationwith feedback design using relays and a potentiometer position encoderfeedbackchannel.Themaindisturbancetoconstantrotationwillcomefromstick/slip friction in the joint rotation and motor ramp up and downcharacteristics in the motor/arm plant. Figure 18.15 shows this specificfeedbackcontroldesign.

FIGURE18.14BasicFeedbackControlArmPositioning.

FIGURE18.15RelayControlwithPositionEncoderFeedbackThroughandA/DConverter.

CloserinspectionofthedesigninFigure18.15revealsthatthecontrolloophasananalogandadigitaldomainasshowninFigure18.16.

FIGURE18.16ArmPositioningwithFeedbackDigitalandAnalogDomains.

Thismixedsignalcontrolloopdesignrequiressamplingofthefeedbacksensors and a digital control law.The control law can be implemented foreach joint on an individual basis as a basic PID (Proportional, Integral,Differential) process controlproblem.For thePIDapproachaproportionalgain,anintegralgain,andadifferentialgainareusedinthecontroltransfer

functionwhichis:

The transfer function defined by aLaplace transform is depicted as acontrolloopblockdiagrambyFigure18.17.

FIGURE18.17PIDControlLoop.

The Laplace transform for the PID control law makes traditionalstability analysis simple, but to implement a PID control law on a digitalcomputer,astatespaceortimedomainformulationforthePIDcontrollawmustbeunderstood.Furthermore,arelationshipbetweenthemeasurederrorandthecontrolfunctionoutputmustbeknownintermsofdiscretesamples.

Thistimedomainrelationshipis:

Thisequationcanthenbeusedtodesignthecontrol loopasshowninFigure18.8.

FIGURE18.18PIDDigitalControlLoop.

The numerical integration can be done using an algorithm such asforwardintegration,trapezoidal,orRunge-Kuttaoverseriesoftimesamples.Likewise,differentiationovertimesamplescanbeapproximatedasasimpledifference. The proportional, integral, and differential gains must then beapplied to the integratedanddifferentiated functions and summedwith theproportionalforthenextcontroloutput.Applyingthesethreecomponentsofthe digital control law with appropriately tuned gains leads to quick risetime,minimumovershoot,andquicksettlingtimeasshowninFigure18.19.

FIGURE18.19PIDTimeResponse.

Figure 18.19 shows proportional control alone, proportional withintegral,andfinallythefullPID.TuningthegainsforaPIDcontrollawcanbeaccomplishedassummarizedbyTable14.4.

TABLE18.4PIDGainTuningRules. Parameter RiseTime Overshoot SettlingTime

Kpgainincrease Decreases Increases SmallChange

Kigainincrease Decreases Increases Increases

Kdgainincrease SmallChange Decreases Decreases

The PID controller provides a framework basic single-input, singleoutput control law development. More advanced control can be designedusing the modern control state space methods for multiple-inputs andoutputs. State space control provides a generalizedmethod to analyze anddesign a control function for a set of differential equationsbasedupon thekinematicsandmechanicsofaroboticsystem.

Figure 18.20 shows the feedback control block diagram for thegeneralizedsetofstatespacecontrolsystemofdifferentialequations.

FIGURE18.20StateSpaceFeedbackControl.

Adetailedcoverageofstatespacecontrolanalysisanddesignmethodsisbeyondthescopeofthisbook,butmanyexcellentresourcesareavailableforfurtherstudy.

TASKINGThe robotic armmust be commanded and controlled at a higher level

thanactuationandfeedbackcontrolinordertoprovidethebasiccapabilities

1.2.3.4.

of:Searching,identifyingandacquiringavisualtargetforpickupPathplanningandexecutiontopickupatargetObjectgrapplingandgrapplefeedbackCarrypathplanningandexecutiontorelocatetheobjecttoanewtargetlocationThesefourtaskscomposethelargertaskofpickandplace.TheOWI arm command and control software and hardware actuation andfeedback control system can be designed so that a single high levelcommand can initiate pick andplace taskswithin the arm reach-abilityspace. The target search, identification, and acquisition task is afundamental machine vision task. It requires an overhead, side, orfront/backfixedcamerasystemorasimplerembeddedcameraintheendeffector.Withanembeddedcamera,thearmcanstartasearchsequencetosweepthecamerafieldofviewovertheconcentricreach-abilityringsinFigures18.4,18.5,and18.6.Whilethecameraisbeingsweptovertherings, frame acquisition of NTSC frames at 30 frames/sec or less canformat the digital camera data into a digital frame stream. The digitalframestreamimagescanbeprocessedsothateachframeisenhancedtobetterdefineedgesandtosegmentobjectsforcomparisonmatchingwitha target object description. The target object description can includetarget geometry and color (invariants) as well as target size (variant).Oncethetargetisseen(matchedwithasegmentedobjectinthefieldofview)thenthearmcanstarttotrackandcloseinonthetarget.

Closing in on a visual target in the reach-ability space of the OWIrequires constant video visual object centering based upon computation oftheobject’scentroidinthefieldofview.Thearmcanusethecentroidvisualfeedback to rotate thebase tocontrolXYplaneerrors inorder tokeep theobjectcenteredasthearmisloweredtowardtheXYplane.Thekinematicsrequirethatthearmshoulderandelbowbeloweredtoapproachatargetonthe XY plane and to control the X translation of the end effector andembedded camera. Simultaneously the base rotation can be controlled tocoordinate the targetYtranslation tokeep the targetcenteredas thearmislowered.This basic task requires actuation and control of three degrees offreedomataminimum.TheOWIwristonlyhasasingledegreeoffreedomwhich rotates about the forearm. More sophisticated robotic arms alsoinclude rotation about the other two axes of the wrist joint. So, a fixedcameraembeddedintheOWIarmmayneedindependenttilt/pancontrolsothatthecameraanglecanbemaintainedperpendiculartotheXYplaneasthe

arm is lowered. More sophisticated wrist degrees of freedom would alsoprovidethisfinecamerapointing.

Targetpickuprequires thearmtousepositionandlimitsfeedbacksothat the armknowswhen it has intersected theXYplane andacquired theXYplane located target object. Furthermore, the grappler shouldbe in thefullyopenpositionatthistime.Oncethisreadytograpplepositionhasbeenachievedwithfeedbackmachinevisionandpositioning,thegrapplercanbeclosed around the target object. Positive indication of successful targetgrappling can be provided by sensing switches built into the end effectorfingers.Mostoftenbrasscontactsseparatedbyasemi-conductingfoam(ICpackingfoam)ormicro-switcheswithinterfaceplatesoneachfingerprovidegoodfeedbackforgrappling.

Oncethetargethasbeensuccessfullygrappled,thearmcannowswitchtoacarrypathplanningtasktoguideittothedropofftargetlocation.Thisdropoffpathplanningmightonceagaininvolvesearchorapre-determinedtargetpositionatarelativeoffsetfromthetargetacquisitionlocation.Eitherway this is essentially identical to the acquirepathplanningand executionexceptthatthearmisraisedtoacarryheightatadesiredreach-abilityring,then carried with base translation. The raise and carry sequence can beconcurrent for amoreoptimal path in termsof time anddistance traveled.The arm is again lowered to the drop-off target and the target object isreleased using the grappler feedback to ensure that the fingers no longersenseagripontheobject.

Thisoverallsequenceisahighlevelautomationusingtasking.Itisstillcommanded by the operator, but the robotic arm performs the sub-taskscomposingtheoveralltaskautonomously.Twomajorarchitecturalconceptsin thefieldof roboticshaveemergedwhichprovidea frameworkfor robottaskingandplanning interfaced to lower levelcontrolsandwithorwithouthumaninteraction.Thesearesharedcontrolandthedegreeofautonomythata robotic system has along with the subsumption architecture. In the nextsection,thesearchitecturalconceptsarebrieflyintroduced.

AUTOMATIONANDAUTONOMYFigure 18.21 shows command and control loops for a robotic system

thatrangefromfullyautonomoustotelerobotic.

FIGURE18.21TeleoperatedandFullyAutonomousRoboticTaskControlLoops.

An intermediate level of control between fully autonomous andteleroboticiscalledsharedcontrol.Insharedcontrolsomeaspectsofrobotictaskingareautonomous,somearetelerobotic,andothersareautomated,butrequire operator concurrence to approve action ormust be initiated by theoperator.TheconceptofsharedcontrolisshowninFigure18.22.

1.2.

3.4.5.

FIGURE18.22SharedControlofaRoboticSystem.

Telerobotic systemsmay still have closed-loop digital control, but alltasking and decisionmaking comes from the operator, and in the extremecase, literally every movement of the robot is an extension of the user’smovements and no actuation is initiated autonomously. Once the roboticaction is commandedby theuser controlledmotionmaybemaintainedbyclosed-loopdigitalcontrol.Thisissimilartoconceptsinvirtualrealitywherea user input is directly replicated in the virtual model and the concept ofremotely piloting aircraft. For example, it would be possible to set up anOWI interface so that theOWI arm attempts tomatch themovement andpositionofthehumanarmbaseduponarmflexuremeasurements.

Robotics requires a hierarchy of automation, the subsumptionarchitecture,wherelowlevelcomponentactuationandsensingisinterfacedtohigherlevelsub-systemcontrol.Sub-systemsinturnaretaskedwithgoalsandconfiguredwithbehaviors.Forexample,a rollingrobotmaybe taskedwith exploring and mapping a room, but configured to have a collisionavoidancebehavior.Thiscontrol,behavior,andtaskingmustbecoordinatedby an intelligent human operator or by artificially intelligent goal-basedplanning. This chapter provides an introduction to robotic systemarchitecture and design from a bottom-up viewpoint providing practicalexamplesforhowtocontrolandtaskafivedegreeoffreedomroboticarm.As the reader can see, building upon these concepts will allow a roboticssystem that can operate in real-time through the use of feedback fromsensingandinstructionsprogrammedintotherobot’sArtificialIntelligence.

EXERCISESWhatisaReal-TimeEmbeddedSystem?Witha referencecoordinate systemwithanoriginat the fixedbase forthearm, the______________ofanarmcanbedefinedbaseduponthearmmechanicaldesignandkinematics.Whyaresoftandhardlimitswitchesusedinroboticembeddedsystems?Dead-reckoning control of a joint motor requires calibration of the_________, Motion feedback requires active sensing during jointrotation:giveanexampleofonemethodofprovidingthisfeedback?

6.

7.

8.

Providethefourtasksnecessaryforarobottoperforminpickandplaceoperation.An intermediate level of control between fully autonomous andteleroboticiscalled______control.Definesubsumptionarchitecture.

INDEX

2/2DCvalves,171–172applicationof,213–214constructionof2/2seattypevalve,171–1722/2spooltypevalve,171

3/2DCvalves,172–173applicationof,213–214constructionof3/2seattype,173,1743/2spooltype,172–173

4/2DCvalves,173–176constructionof4/2seattype,175–1764/2spooltype,174–175

AAbsolutehumidity,22Absolutepressure,14Absoluteshaftencoders,451Absorbentactivematerials,108Absorbentinactivefilters,108Accumulator,109Accumulatorregister,343Accuracy,322Accuracy,ofrobot,411vs.repeatability,411

ACL(AdvancedCommandLanguage),490Acousticproximitysensor,447Acousticsensors,324Activegrippers,468Actuation,524–530fivedegreeoffreedomarm,526H-bridgerelaycircuit,528limitswitches,527MOSFETH-bridgemotorcontrol,529threeswitchreversiblemotor,524tworelayreversiblemotor,525

Actuator,121,321linear,123

systemwith,122Adjustablethrottlevalves,188–189Afterfilter,36Aftercoolers,86–88functionsof,87typesofair-cooled,87–88water-cooled,88,89

Aircompressors,69–70defined,69–70typesof,70–82nonpositive/dynamic,79–82positivedisplacement,71–79

Air-cooledaftercoolers,87–88Airdryers,36,88–91typesofdeliquescent,91desiccant,90–91refrigerated,90

Airfilters,92constructionandworkingof,92typesof,93–94coalescing,94coarsecoalesce,93compressorintake,93general-purpose,93vapor(charcoal),94

Airlubricator,96Airmotors,149–150advantagesoverelectricmotors,150

Airreceivers,35,86purposesof,86typesdry,86wet,86

Airserviceunit(F.R.L.),36,97Airtimer,191–192AL(ArmLanguage),490AML,490–491Analogfluidicdevices,307Analogtransducers,325ANDgate,300–301Androtext,492Angulargrippers,460,462Apronfeeders,379,380APT(AutomaticallyProgrammedTools),491Arcwelding,robotsfor,501–502ARCL(ARobotControlLanguage),491ARMBASIC,492Articulatedrobots,418–419

advantagesanddisadvantagesof,419applicationsof,419

Assembly,507–508examplesof,508robotsfor,507–508

Assemblylines,358–359transfersystemsin,360–361typesofautomated,359manual,359

Associativelaws,299Asynchronoustransfersystem,361Atmosphericdewpoint,23Atmosphericpressure,14Autodrain,36Automatedassembly,359Automatedassemblylines,359reasonsforusing,359–360typesof,360

Automaticmachines,361Automatictellermachines(ATMs),433Automationadvantagesof,4–5andautonomy,537–538considerationsfor,3currentemphasisin,9definitionof,2–3exampleof,2goalsof,5issuesinfactoryoperations,11lowcost,6–7manufacturing,3mechanizationvs.,4originofword,1reasonsfor,2–3,10,10reasonsfornon,10–11socialissuesof,5–6strategiesfor,11typesof,7–9fixed,7–8flexible,8–9programmable,8

Axialflowcentrifugalpumps,68Axialflowcompressors,81Axialpistonpump,57–58

BBackpressuresensor,312–313Barometricpressure,14Basicbowls,382

Basichydraulicsystem,componentsof,37–40Batch-modelline,358Beltconveyors,371–372Beltfeeders,387–388Bentaxispumps,60,61Bernoulli,Daniel,17Bernoulli’sequation,17Bernoulli’sprinciple,17Betterworkingconditions,6Bi-directionalmotors,122Bistableflipflop,307–308Bistableelement,209Bladdertypeaccumulator,112Bleedoffcircuit,236–237Booleanalgebra,298lawsof,298–299

Boosters,112–113Boyle’slaw,21Bucketconveyors,373Buildingblock,7Bulkmodulus,19–20Busbarlines,263,266Buses,typesofaddressbus,344controlbus,344databus,344

By-passfilter,107

CCalibration,323CAP1(ConversationalAutoProgramming1),491Capacitancestraingauges,338–339Capacitivedisplacementsensors,334–335Capacitiveproximitysensor,447–448Cartesianrobots,415–416advantagesanddisadvantagesof,416applicationsof,415–416featuresof,415

Cascadedesign,262–264stepsin,263–264

Cascading,262–263Centerconditionsin4WayDCvalvesclosedcenter,177floatcenter,178opencenter,176–177tandemcenter,178

Centerboardhopperfeeders,390Centralprocessingunit(CPU),340,350–351arithmeticlogicunit,342controlunit,342–343

memorysystem,351powersupply,351processor,351registers,343

Centrifugal/axialcompressors,79–81.SeealsoDynamiccompressorsadvantagesanddisadvantagesof,80–81

Centrifugalhopperfeeders,389–390Centrifugalpumps,66–68advantagesanddisadvantagesof,68characteristicsof,67classificationof,67axialflow,68mixedflow,67radialflow,67

Chainconveyors,372Chaindriveconveyorsystem,364Charcoalfilter,94Charle’slaw,21Checkvalve(s),36,39,160,179–180applicationsof,179–180pilotoperated,180–181rectifier,180

Chemicalsensors,324Chuteconveyors,371Chutes,376Circuitdesignmethods,257–258methodologicaldesign,257trailanderror,257

Circuitdiagrams,208–209controllingelements,208designationofcomponentsin,209–211drivingelements,208energyconsumingmembers,208

Circuitsapplicationofcounterbalancevalve,239–241applicationofshuttlevalve,225–226applicationoftwinpressurevalve,223–225design,problemsin,246–252withmechanicalfeedback,214–215

Cleanroomrobots,516Closedcentercircuit,230Closedloopcontrolsystems,257Coalescingfilters,94Coanda,HenriMarie,304Coanda’seffect,304–305principleof,305

Coanda’sexperiments,305–306Coanda’stheoryofwallattachment,304Coarsecoalescefilters,93Combinedgaslaws,22

Commutativelaw,298Complementarymetal-oxidesemiconductor(CMOS),340Complex-instruction-setcomputer(CISC),340Compositeseal,117Compressedair,70applicationsof,70pipelinelayout,97–99

Compressedgasaccumulators,111–112Compressibility,19–20Compressorintakefilters,93Compressors,35classificationof,71comparisonofdifferent,81–82defined,44pumpsvs.,44purposeof,44specificationsof,82

Condensationcontrol,99Conditionstepdiagram,262Conejetsensor,310–311Confinement,383Connectors,115–117typesofflared,116hosecouplings,116–117threaded,115,116

Contactsensing,443Contactsensors,443functionsof,443typesof,443force/torquesensors,446tactilesensors,444–446

Continuityequation,18Continuous-path(CP)robots,425Continuoustransfersystems,360Controldiagrams,259,262Controlmethod,ofrobotclassificationnon-servocontrolledrobots,423servocontrolledrobots,423

Controlsystemdefined,256types,256closedloop,257openloop,256

Controlsystem,404Controllingelements,208Conveyorsystems,intransferdevices,369–373typesofbelt,371–372bucket,373

chain,372chute,371magnetic,372–373roller,370wheel,371

Counterbalancevalve,186–187,239–241initialposition,187reverseflow,187symbolof,187

Crackingpressure,183Cylindercushioning,136–139double-acting,138idealcushioning,139pneumaticcylinder,139workingofcushions,138–139

Cylindermountings,139–144classificationsof,139–140extendedtie-rod,140–141flange-mounted,141–142pivot,143sideorlug,142–143trunnion,143–144

Cylindersizing,145–146areaofcylinder,145forcesofcylinder,145–146

Cylinder(s),121,122–123applicationsof,136classificationonbasisofconstruction,123–124diaphragm,131–132double-acting,125–127,129–130duplex,133non-rotating,132–133one-piece,131rotating,132single-acting,124–125,127–129threadedhead,131tie-rod,130–131

classificationonbasisofworkingmedium,133–136hydraulic,133–135pneumatic,135–136

cushioning,136–139(SeealsoCylindercushioning)mountings,139–144(SeealsoCylindermountings)sizing,145–146(SeealsoCylindersizing)specifications,146

Cylindricalrobots,416–417advantagesanddisadvantagesof,417applicationsof,417

DDCvalves.SeeDirectioncontrolvalvesDeburring,robotsfor,510Degreeoffreedom,ofrobot,408–409,413

seven,409six,409

Deliquescentairdryers,91Demorgan’stheorem,299Density,19Depthfilters,107Desiccantairdryers,90–91Detent,165,166Dewpointtemperatureandholdingcapacityofair,23Dewpoints,23Dialindexingmachine,360Diaphragmcompressor,78–79Diaphragmcylinders,131–132Diaphragmpumps,64–65characteristicsof,65operationof,64

Diecasting,robotsfor,507Digitalfluidicdevices,307DigitaltoAnalog(DAC)SeealsoActuation,524Digitaltransducers,325Directioncontrol(DC),212Directioncontrolvalves(DCvalves),36,39,160–161withactuators,examplesof,167–1684/2solenoid-operatedspring-returnedDCvalve,168DCvalve,168

centerconditions,176–178closed,177float,178open,176–177tandem,178

classificationonbasisofconstruction,169–170poppetvalves,169rotaryvalves,169spoolvalves,169

classificationonbasisofvalveactuationmethod,163–167detent,165electromagnets,166manualactuation,164mechanicalactuation,164–165pilotoperation/actuation,165pilotsolenoidoperation,166

constructionof2/2DCvalves,171–1723/2DCvalves,172–1734/2DCvalves,173–176

symbolanddesignationof,161–163Dischargeoffeederbowl,383Distributivelaw,298Double-actingcylinders,125–127componentsof,125–126

constructionof,125–126sectionviewof,127symbolof,125typesofdoublerod/throughrod,129,130tandem,129–130

Double-actingpistonpump,63Doublerodcylinder,129,130Drillingrobot,511Drivingelements,208Dryairreceivers,86Duplexcylinders,133Dynamiccompressors,79–81axialflow,81centrifugal/axial,79–81

Dynamic/nonpositivedisplacementpumps,66axial,66centrifugal,66–68

DynamicRAM(DRAM),344

EElectricdrivesystemadvantagesanddisadvantagesof,422types,422ACservos,422DCservos,422steppermotors,422

Electricgrippers,461Electricmotor,35,37Electricpowertransmission,28Electricalcurrentsensors,323Electricalpowersensors,323Electricalresistancesensors,323Electricalvoltagesensors,323Electromagneticsensors,323Electromagnets,166Electronbeamwelding(EBW),robotsfor,503Embeddedcontroller,345Emitter-coupledlogic(ECL),340Encoders,451Endeffector,456Endeffectorpath,530Endeffectors,typesof,406,407–408,456.SeealsoRobotendeffectorsEnd-of-armdevices,457End-of-armtoolingcharacteristicsof,465defined,457elementsof,465–467

Energy,23–24Energyconsumingmembers,208Escapementdevice,378

Extendedtie-rodsmountedcylinders,140–141Externalgearpump,47–49advantagesanddisadvantagesof,49applications,49workingof,48

Externalgrippers,462Externalsensors,443–445Externalvanepumps,53Exteroceptors,443–445

FFeedrate,382Feedtrack,377–378Feederbowl,382Feeders,373–374classificationofgravimetric,374volumetric,374

selectioncriteria,374–375typesofapron,379,380belt,379centrifugal,379disc,379flexible,379reciprocating,379–380reciprocatingplate,381,382reciprocating-tubehopper,381rotary,379screw,379vibratory,379

Fiberoptictemperaturesensors,330Filter,regulator,andlubricator(FRL),97Filters,38Fingergrippers,470–471Fireresistantfluids,104Fittings,115Fixedautomation,7–8advantagesanddisadvantagesof,8

Fixeddisplacementmotors,122Fixedthrottlevalves,188Flange-mountedcylinders,141–142Flapperjetservovalve,197.SeealsoServovalvesFlaredconnectors,116Flexibleautomation,8–9advantagesanddisadvantages,9

Flexiblefeedersadvantagesof,394conveyors,392sub-systems,393–394

Flexiblefeeding,391

Flexibleimpellerpumps,60–61benefitsof,62

Flexiblevanepumps,53Flow,16Flowcontrolvalves,160,187–189,215,220applicationof,187continuoussectionrestriction,188controlofsingle-actingcylinder,219–220typesof,188varyingsectionrestriction,188

Flowmeters,109Flowrate,16conversionof,17mass,16volumetric,16

Fluidaccessorieshydraulic,102–118pneumatic,86–102

Fluidlines.SeeLinesFluidmotors,122,147.SeealsoMotorsbi-directional,122fixeddisplacement,122typesof,150–156gear,151–152piston,153–156vane,152–153

unidirectional,122variabledisplacement,122workingprincipleof,147

Fluidpowermotor,146Fluidpowersystem,27–28advantagesof,28–30applicationsof,30–31aerospace,31industrial,31mobile,30–31

disadvantagesof,30elementsof,28,29pneumaticsvs.hydraulics,31–32

Fluidproperties,13–24Fluidicamplifiers,313–317turbulence,315–317turbulenceamplifier,315–317vortex,313–315

FluidicANDgate,308–309Fluidicdevices,303,306–307advantagesanddisadvantagesof,317–318amplifiers,313–317analog,307digital,307logic,307–309

sensors,309–313Fluidiclogic,303Fluidiclogicdevices,307–309bi-stableflipflop,307–308ANDgate,308–309OR-NORgate,309

Fluidicor-norgate,309FluidicOR-NORgate,309,310Fluidicsensors,309–310backpressuresensor,312–313conejetsensor,310–311interruptiblejetsensor,311–312

Fluidics,297,303advantagesanddisadvantagesof,317–318originanddevelopmentof,303–304

Force,13Forcesensors,446Forgehammers,506–507Forging,robotsfor,506–507Framegrabber,431Friction,24FRL.SeeFilter,regulator,andlubricator(FRL)Full-flowfilter,38,107Fullflowpressure,183Fundamentalsofproductionlines,358

GGasandliquidflowsensors,324Gaschargedaccumulators,111–112typesof,111–112bladdertype,112pistontype,112

Gaslaws,21–22Gasmetalarcwelding(GMAW).SeeMIGweldingGastungstenarcwelding(GTAW).SeeTIGweldingGaskets,101Gaugepressure,15Gay-Lussac’slaw,21–22Gearmotors,151–152operationof,151

Gearpumps,47external,47–49internal,49–51

General-purposefilters,93Genevamechanism,364–365Gerotorpump,51Gravimetricfeeders,374Grindingrobots,511Grippers,407,457,458–459.Seealsospecificgrippersactive,468

applications,458categoriesof,459assembly,459coarsegripping,459nogripping,459precisegripping,459

commonlyusedfingergrippers,470–471magneticgrippers,473–474mechanicalgrippers,471–472vacuum/suctiongrippers,472–473

defined,458external,462internal,462mechanisms,464passive,467–468robot,458selectionof,459–463

Grippingmechanisms,464Grippingstyleconfiguration,461angular,461parallel,461

Groupselectorswitches,266–267Groupselectorvalves,279Gyroscopes,451,453

HHall-effectsensors,335Hardautomation,7–8Heatenergy,24Heatsensors,323,451,452Heavydutyfilters.SeeHydraulicfiltersHELP,491Holdingcapacityofair,23Hopper,375–376,382featuresof,376self-dumping,376stackable,376vibratory,376

Hosecouplings,116–117homogeneoussyntheticrubber,117plastic,117

HTML,490Humanvs.robotmanipulator,406Humanoid,398Humidity,22–23Hydraulicaccessories,102–118Hydraulicaccumulator,109–112applications/functionsof,110

typesof,110–112gascharged,111–112spring-loaded,110–111weight-loaded,110

Hydraulicactuator,39,165,421,460Hydrauliccircuits,226controlofdouble-actingcylinder,228–229controlofsingle-actingcylinder,226–228defined,226speedcontrol,232–236adjustablethrottlevalveand,233types,234meterincircuit,234–235meteroutcircuit,234,235–236

Hydrauliccylinders,133–135assemblyparts,135double-acting,134single-acting,134

Hydraulicdrivesystem,421Hydraulicfilters,106–108constructionandworkingof,106filteringmaterialandelements,108locationof,108typesof,107by-pass,107depth,107full-flow,107surface,107

Hydraulicfluids,102–105functions,102–103propertiesof,103–104typesof,104–105

Hydraulicgrippers,460–461Hydraulicmotors,148–150,149advantagesof,149–150applicationof,156operationsof,149

Hydraulicpumps,37–38classificationof,45

Hydraulicreservoir,105–106functionsof,105–106

Hydraulicseals,117–118.SeealsoSealslifeof,118Hydraulicsymbols,200–203Hydraulics,27advantagesof,33applicationsof,34basicsystem,37–40disadvantagesof,33–34fluidsusedin,40–41petroleum-based,41

syntheticfire-resistant,41water-basedfire-resistant,41

pneumaticsvs.,31–32pressuredropin,40systemdesign,40

Hydrodynamicdevices,45Hydrodynamicpumps,66Hydrostaticdevices,44Hygrometer,22Hysteresis,322

IIBL(InstructionBasedLearning),493Idealcushioning,139Identitylaw,299Incrementalencoders,451Inductivesensors,332–334Industrialroboticassemblyline,520Industrialrobots,399–400characteristicsof,402–403componentsof,403–405controlsystem,404drive,404mechanicalunit,403–404tooling,404

cranevs.,399–400defined,399humanbeingvs.,405sensorsand,405

Infeedthrottling,216Inlinetransfermachines,366–367pallettype,367plaintype,367

Inputdevices,344Input/outputunit,344Inputtransducers,324Inputs,350Inspectionandmeasurement,robotsfor,509Instructionregister,343Intensifiers,112–113classesof,113selectionparameters,113

Intermittenttransfersystems,360Internalgearpump,49–51advantagesanddisadvantagesof,50applications,50–51workingprincipleof,49

Internalgrippers,462Internalsensors,450–451Internationalorganizationforstandardization(ISO),207

Interruptiblejetsensor,311–312Intuitivemethods,258Inverselaw,299

JJointpositionsensors,451Joints,robot,413–414prismatic,413revolute,413–414

KKarel,491Kinematics,523Kineticenergy,24

LLadderlogic,352–353,493,493exampleof,352–353

LawsofBooleanalgebra,298–299Lawsofonesandzeros,299Lawsofrobotics,400LCA.SeeLowcostautomation(LCA)Lead-throughprogramming,482–483methodsof,483manual,483powered,483

Light-dependentresistors(LDRs),324,331Lightsensors,331–,332,451,452,451photodiode,331photoresistors,331phototransistor,332

Linearactuators,122Lineardisplacementsensors,332Lineartransfermechanism,362–364chaindriveconveyorsystem,364poweredrollerconveyorsystem,363walkingbeamsystem,363

Linearvariabledifferentialtransducer(LVDT),332–333advantagesanddisadvantagesof,333designof,333

Linearityerror,323Lines,114–115typesofflexiblehosing,115piping,114tubing,114–115

Linksandjoints,ofrobot,408Lobecompressor,rotary,74Lobepump,51–53advantagesanddisadvantagesof,52–53

applications,53Logicgates,300–303Logicalinverter,302Lowcostautomation(LCA),6–7advantagesof,6infoodprocessing,6issuesin,7

MMachineloadingandunloadingrobot,515Machinetendingrobot,505–506examplesof,506

Machinevisionsensors,449–450Machinevisionsystem,429–432advantagesof,431–432applicationsof,432componentsof,431processsteps,430–431robotics,433–434applicationsof,434reasonsfor,433technologies,434

typesof,430Magazines,376typesof,376

Magneticbeltconveyors,372–373Magneticfieldsensors,448Magneticgrippers,473–474advantagesanddisadvantagesof,474

Magneticsensors,335Magnetismsensors,323Magnetostriction,335Magnetostrictiveeffect,335Magnetostrictivesensors,335Magnetostrictivetransducers,335Manualactuation,164lever,164pedal,164pushbutton,164push/pullbutton,164

Manualassemblylines,359Manuallead-through,483Manufacturingapplications,ofrobots,499–511assembly,507–508deburring,510diecasting,507drilling,511forging,506–507grinding,511inspectionandmeasurement,509

machinetending,505–506materialremoval,509–510plasticmolding,507sealing/dispensing,508–509spraypainting,504–505welding,499–504

Massflowrate,16Materialhandlingapplications,ofrobots,511–516examplesof,513machineloadingandunloading,515orderpicking,515–516palletizing,513–514partstransferring,513,514pickandplaceoperations,514–515sequencesof,512–513

Materialremoval,robotsfor,509–510MATLAB,490Maximumpressurevalve,182–183MCL(ManufacturingControlLanguage),492Mechanicalactuationplunger,165roller,164–165spring,165

Mechanicalfilters,108Mechanicalgrippers,471–472Mechanicalpowertransmission,28Mechanicalsensors,324Mechanization,4automationand,4

Membranecompressor,78Membranepump,64Memory,343–344Memoryaddressregister,343Memorydataregister,343Memorysystem,351Metaloxidesubstratefieldeffecttransistors(MOSFET),529Meterincircuit,234–235Meteroutcircuit,235–236Metering,65Meteringpumps,65–66diaphragm,65piston/plungertype,65,66

Microcontroller,345–347applicationsof,346–347featuresof,346vs.microprocessor,346

Microprocessorsysteminput/output,341memory,341

Microprocessors,340–345

applicationsof,345classificationof,345defined,340historyof,340–341layoutof,341–344registers,343

MIGweldingrobots,503–504Mixedflowcentrifugalpumps,67Mixed-modelline,358MML,492Modularprinciple,7Moistureinair,22–23Monostableelement,208vs.bi-stableelements,308

Motiondiagrams,259–262typesof,259positionstepdiagram,259–261positiontimediagram,261–262

Motionprogramming,486–487Motionsequencerepresentation,259Motorratings,148Motor(s),121,146–148applicationof,156fixeddisplacement,147hydraulic,148–150(SeealsoHydraulicmotors)ratings,148symbolof,150variabledisplacement,147workingprincipleof,147

Multi-screwpumps,57Multistageservovalve,198.SeealsoServovalvesMV.SeeMachinevision(MV)

NNANDgate,302NationalFluidPowerAssociation(NFPA),141Negativegaugepressure,15Negativetemperaturecoefficient(NTC),329NFPA.SeeNationalFluidPowerAssociation(NFPA)Non-contactsensors,443–444Nonpositivedisplacementdevices,45positivedisplacementvs.,44–45

Nonpositivedisplacementpumps,66Nonpositive/dynamicaircompressors,70Nonreturnflowcontrolvalve,189–190applicationof,190symbolof,190

Non-returnvalves,179Non-rotatingcylinders,132–133Non-self-generatingtransducers,324Non-servorobots,423,498Nonprehensileendeffectors,467

NOTgate,302

OOfflineprogramming,484–486advantagesanddisadvantages,485–486

Offset,322One-piececylinders,131Online/offlineprogramming,486Onlineprogramming,479–482advantagesanddisadvantagesof,480teachpendantand,480–482

Opencentercircuit,230–231Openloopcontrolsystems,256Operator’spendant,480–481Opticalproximitysensors,447Opticalsensors,324,444ORgate,301Orderpickingrobot,515–516Orientationaxis,ofrobot,410Outfeedthrottling,216Outputdevices,344Outputtransducers,325Outputs,350

PPalletizingrobot,513–514Parallelgrippers,460,462Partsfeeders,377Partsfeedingdevicesbowls,375chute,376cradle,375ejectorsandpushers,375escapementandplacementdevice,378feedtrack,377–378hopper,375–376magazines,376pallets,375partsfeeder,377reel,375selectorsandorientor,378separator,377

Partstransferringrobot,513,514Pascal’slaw,15–16Passivegrippers,467–468pinchendeffectors,467–468,468wrapendeffectors,467–468

Payload,ofrobot,412Peltier-Seebeckeffect,327Pentium-4microprocessor,341

Peristalticpumps,55–56advantagesof,56applications,56

Petroleum,104Photodiode,331Photoelectricproximitysensor,447Photoelectricstraingauges,339Photoresistors,331Phototransistor,332Pickandplacerobot,514–515PID(proportional,integral,differential),531Piezoelectricsensors,336Pilotoperatedcheckvalves,180–181symbolof,181

Pilotoperation/actuation,165,166Pilotsolenoidoperation,166Pinchendeffectors,468Pipejetservovalve,197–198.SeealsoServovalvesPipelinelayout,97–99condensationcontrol,99pipingmaterials,100pressuredrop,99–100

Pipingmaterials,100Pistoncompressors,76–78single-stage,76–77two-stage,77–78

Pistonmotors,153–156typesofradial,155–156swashplatebentaxis,154,155swashplatein-line-axis,153–154

Piston/plungertypemeteringpump,65,66Pistonpumps,57–58,62–64bentaxis,60,61characteristicsof,64constructionof,58double-acting,63radial,58,59single-acting,63swashplate,58,59wobbleplate,59–60

Pistontypeaccumulator,112Pivot-mountedcylinders,143Placementdevice,378Plasticmolding,robotsfor,507Pneumaticaccessories,86–102Pneumaticactuator,36Pneumaticcircuitdiagrams,208Pneumaticcircuitsdefined,211double-actingcylinder,212–213

outfeedthrottling,218quickexhaustvalvein,220–222single-actingcylinder,212

Pneumaticcylinders,135–136assemblyparts,137double-acting,136

Pneumaticdrivesystems,421–422Pneumaticfilter,93constructionandworkingof,92

Pneumaticgrippers,460typesofangular,460parallel,460

Pneumaticlogicvalves,192Pneumaticmotors,149–150Pneumaticseals,102.SeealsoSealsPneumaticself-containedcircuits,255Pneumaticsensors,443Pneumaticsymbols,200–203Pneumaticvs.hydrauliccircuitdiagrams,208Pneumaticsadvantagesof,32–33applicationsof,34basicsystem,34–37componentsof,35–36disadvantagesof,33vs.hydraulics,31–32

Point-to-pointcontrol(PTP)robots,423–424Polarrobots,417–418Poppetvalves,169workingof,170

Positionaxis,ofrobot,410Positionsensors,332–335capacitivedisplacement,332inductive,332magnetostrictive,332

Positionsensors,446–448Positionstepdiagram,259–261Positiontimediagram,261–262Positivedisplacementaircompressors,71–76classificationof,71reciprocating,75–79rotary,72–75

Positivedisplacementdevicesfixeddisplacement,45variabledisplacement,45vs.nonpositivedisplacementdevices,44–45

Positivedisplacementpumps,46classificationof,46meteringpumps,65–66reciprocatingpumps,62–65

rotarypumps,46–62nonpositivedisplacementpumpsvs.,68–69

Positivetemperaturecoefficient(PTC),329Positivevs.nonpositivedisplacementpumps,68–69Potentialenergy,24Power,24Powersource,502Powersupply,351Poweredlead-through,483Poweredrollerconveyorsystem,363Powerheadproductionunits,7Prandtl,L.,304Precision,322Precision(validity),ofrobot,411PredeterminedMotionandTimeStudies(PMTS),7Pressure,14Pressurecontrolvalves,160,182Pressuredewpoint,23Pressuredrop,99–100Pressuregauges,36,38,108–109Pressureoverride,183Pressurereducingvalves,183–,184,245Pressurereductioncircuit,245Pressureregulator,94–95Pressurerelationship,14Pressurereliefvalves,38–39,182–183symbolof,183

Pressuresensors,324,336Pressureswitch,35Pressuretransducer,336Prismaticjoints,413Processor,351Productionlinesfundamentalsof,358typesof,358

Programcounter,343Programmableautomation,8advantagesanddisadvantagesof,8examples,8

Programmablelogiccontroller(PLC),347–355advantagesanddisadvantagesof,354applicationsof,354–355componentsof,348–351input/outputmodule,349–350memory,351powersupply,351processor,351programmingdevice,351

programming,352–353workingof,351–352

ProgrammableUniversalManipulationArm(PUMA),398Programmer’spendant,480Programmingdevice,351Programmingmethod,ofrobotclassification,425Proprioceptors,450–451Proximitysensors,446–448typesacoustic,447capacitive,447–448magneticfield,448optical,447photoelectric,447

Pumps,44classificationof,45defined,44purposeof,44selectionparameters,68vs.compressors,44

QQuickexhaustvalve,190–191pneumaticcircuits,220–222indouble-actingcylinder,221–222insingle-actingcylinder,220–221

symbolof,191

RRackandpinionmechanism,364Radialflowcentrifugalpumps,67Radialmovement,ofrobot,413Radial-pistonmotors,155–156Radialpistonpumps,58,59Radiationsensors,324RAIL,492Ramtypecylinders,127,128Randomaccessmemory(RAM),344Range,322Rangesensors,448–449principlesof,448typesofstereoscopicvisionsystems,449ultrasonicrangingsystems,449

Ratchetandpawlmechanism,364,365Rate,382Reach,ofrobot,412Readonlymemory(ROM),344Real-timeembeddedsystems,519–520Reciprocating,defined,62Reciprocatingcompressors,75–79advantagesanddisadvantagesof,75–76

types,75diaphragm,78–79piston,76–78

Reciprocatingfeeders,379–380Reciprocatingplatefeeder,381,382Reciprocatingpumps,62–65typesofdiaphragm,64–65piston/plunger,62–64

Reciprocating-tubehopperfeeder,381Rectilinearrobots,415–416Reduced-instruction-setcomputer(RISC),340Refrigeratedairdryers,90Regenerativecircuit,237–239Relativedensity,19Relativehumidity,22–23Repeatability(variability),ofrobot,411Reservoir,39–40Resistancestraingauges,338Resistancetemperaturedetector(RTD),325–326advantagesanddisadvantages,326constructionof,326

Resolution,322Responsetime,322Returnoninvestment(ROI),510Returnpan,383Revolutejoints,413variationsof,413

Revolvingjoint,414Rings,101RIPL(RobotIndependentProgrammingLanguage),492Robotapplications,499–500capabilitiesof,498manipulation,499sensing,499transport,498–499

cleanroomrobots,516manufacturing,499–511materialhandling,511–516medicalapplications,500military,500reasonsfor,498spaceindustry,500

Robotclassificationcoordinatesystems,415–420controlmethod,423–425powersource,420–422programmingmethod,425

Robotendeffectors,456–458classificationof,458

grippers,458–464(SeealsoGrippers)toolsforprocessapplications,464–465RobotInstituteofAmerica,399Robotprogram,478Robotprogramming,478techniques,478–479lead-through,482–483motion,486–487offline,484–486online,479–482tasklevel,486walk-through,484

Robotprogramminglanguages,487–488,489–490categoriesof,487–488exampleof,usingVAL,493–495modesofoperation,488standard,requirementsfor,488–489typesof,490–493

Robotselection,425–426controlmode,426degreesoffreedom,426drivetype,426liftcapacity,426repeatability,425sizeofclass,425–426velocity,426

Robotvision,449Robotworkcellfunctionsof,427–429operatorinterface,428–429safetymonitoring,429sequencecontrol,427–428

Roboticaccidents,434–435causesof,435preventionof,435

Roboticarms,521–523elbowrotation,522innermostringofreach-ability,522intermediateringofreach-ability,523outermostreach-ability,523referencecoordinatesystem,521

Roboticjoints,413–414prismatic,413,414revolute,413,414

Roboticsensorstypesof,442exteroceptors/externalsensors,443–444proprioceptors/internalsensors,450–451

Robotics,397–398lawsof,400machinevision,433–434

applicationsof,434reasonsfor,433technologies,434

motivatingfactors,400–401economic,401social,401technical,400–401

safety,436Robot(s)advantages,401–402classificationof,414–425(SeealsoRobotclassification)definitionof,399disadvantages,402featureof,399historyof,398installation,437joints(SeealsoRoboticjoints)maintenance,436–437selection,425–426terminology,408–412typesofsensorsin,451–453wristandendofarmtools,406–408

Rollerconveyors,370Rotaryaircompressors,72–75lobecompressor,74screwcompressor,72–74vanecompressor,74–75

Rotaryindexingtables,368–369Rotarypistonpumps,57–58constructionof,58designsof,57–58variations,58

Rotaryplowfeeders,388Rotarypumps,46–62typesflexibleimpeller,60–62gear,47–51lobe,51–53peristaltic,55–56piston,57–60screw,56–57vane,53–55

Rotaryseals,101Rotarytablefeeders,388–389Rotarytransfermechanisms,364–365geneva,364–365rackandpinion,364ratchetandpawl,364,365

Rotaryvalves,169Rotaryvanepumps,53Rotaryvariabledifferentialtransducer(RVDT),334,450

Rotatingcylinders,132Rotationaljoints,413–414Rotationalmovement,ofrobot,413Rotodynamicdevices,45RPL,492Rrotarytransfermachines,367–368RVDT.SeeRotaryvariabledifferentialtransducer(RVDT)

SSafetyofworkers,6Safetyvalve,35,182–183SCARA.SeeSelectiveComplianceAssemblyRobotArm(SCARA)SCARArobots,419–420advantagesanddisadvantagesof,420applicationsof,420

Screwcompressors,rotary,72–74advantagesof,74single-screw,72,73twin-screw,73

Screwfeeders,386–387Screwpumps,56multi-screw,57twin-screw,56–57

Sealing/dispensing,robotsfor,508–509examplesof,509

Seals,100,117designrequirements,basedon,101rotary,101sliding,101static,101

materials,basedon,101–102medium,basedon,101pneumatic,102shapes,basedon,102

Seatvalves,169workingof,170

SelectiveComplianceAssemblyRobotArm(SCARA),420Selector,383Selectorandorientor,378Self-generatingtransducers,324Semiconductorstraingauges,339Sensing,530–534armpositioningwithfeedbackdigitalandanalogdomains,532basicfeedbackcontrolarmpositioning,531PIDcontrolloop,532PIDdigitalcontrolloop,533PIDgaintuningrules,534PIDtimeresponse,533positionencoderselectrical,530

mechanicalswitch,530optical,530

positionencodersand,532relaycontrolwithpositionencoderfeedback,531statespacefeedbackcontrol,534

Sensitivity,322Sensors,321,322,405,441–442.Seealsospecificsensors;specificsensorsclassificationof,323–324

acoustic,324chemical,324electromagnetic,323mechanical,324optical,324radiation,324thermalenergy,323

inrobot,451–453Separators,377Sequencevalves,184–186operationof,185symbolof,185–186

Sequencing,241defined,264examplesof,265–293

Sequencingcircuit,241–245exampleof,244–245

Servocontroldefinitionof,194

Servo-controlledrobots,423–425,499continuous-pathrobot,424controlled-pathrobots,425point-to-point,423–424

Servosystem,198–199blockdiagramof,199exampleof,199

Servovalves,194–195multistage,198single-stage,194,195–198three-stage,194two-stage,194useof,195

Settlingtime,ofrobot,412Sharedcontrol,536,537Shuttlevalves,193–194applicationof,225–226symbolof,194

Sideorlugmountedcylinders,142–143Signconventions,264Single-actingcylinders,124–125forjacksandlifts,125sectionviewof,124typesof

ramtype,127,128springreturn,129telescoping,127–128

Single-actingpistonpump,63Single-modelline,358Single-stagepistoncompressor,76–77Single-stageservovalves,195–198flapperjet,197pipejet,197–198

Slidingseals,101Slidingvanepumps,53Softautomation,8–9Softwiring,348Solenoids,166,167Soundsensors,324Span,323Specificgravity,19Specifichumidity,22Specificweight,18–19Speed,ofrobot,412Speedcontrolcircuits,215–218infeedthrottling,216outfeedthrottling,216throttleincircuit,216–217throttleoutcircuit,217–218

Speedcontrolvalves,187–189Speedcontroller,215Sphericalrobots,417–418advantagesanddisadvantagesof,418applications,418

Spoolvalves,169Spotweldingrobot,502–503Spraypaintingrobots,504–505Spring-loadedaccumulators,110–111,112Springreturncylinders,129Stability,ofrobot,412Standardofliving,6StaticRAM(SRAM),344Staticseals,101Stationarytransfersystem,361Stereoscopicvisionsystems,449Storagehopper,382Strain,defined,337Straingauges,337,451featuresof,339typesof,338–339

Strainers,38Stress,defined,337Stresssensors,446Subsumptionarchitecture,538

Suctiongrippers,472–473advantagesanddisadvantagesof,472–473typesof,472

Surfacefilters,107Swashplatebentaxispistontypemotors,154–155Swashplatein-line-axispiston-typemotors,153–154Swashplatepumps,58–59Synchronoustransfersystem,360Syntheticfire-resistantfluids,105Systemusingdigits,211

TTactilesensors,444typesof,444–446

Tandemcentercircuit,232Tandemcylinder,129–130Tasklevelprogramming,486Tasking,535–536TCP.SeeToolcenterpoint(TCP)Teachpendant,480–482functionsof,480majorareasof,481–482stylesof,480

Telescopingcylinders,127–128Temperaturesensors,323,325–330applicationsof,330fiberoptic,330resistancetemperaturedetector,325–326thermistor,328–330thermocouple,327–328

Tesla,Nicola,304Tesla’svalvularconduit,306Thermistor,328–330advantagesanddisadvantagesof,330negativetemperaturecoefficient,329positivetemperaturecoefficient,329

Thermocouple,327–328advantagesanddisadvantagesof,328thermoelectriccircuit,328

Threadedconnectors,115,116Threadedheadcylinders,131Throttleincircuit,216–217Throttleoutcircuit,217–218Throughrodcylinder,129,130Tie-rodcylinders,130–131TIGweldingrobots,504Timedelaycircuit,222–223Timedelayvalves,191–192symbolof,192

Time-of-flightsensors,448

Toolcenterpoint(TCP),ofrobot,410Tools,464typesof,464–465

Torquemotorandarmatureassembly,195Torquesensors,446Touchsensors,444–446,451exampleof,445aslimitswitches,446microswitch,445

Trackswitch,383Transducersclassificationof,324–325analoganddigitaltransducers,325inputandoutputtransducers,324–325self-generatingandnon-self-generating,324

defined,321selectionof,323

Transferdevices,361–362advantagesanddisadvantagesof,369classificationof,366–369conveyorsystemsin,369–373mechanisms,362linear,362–364rotary,364–365

selectionof,362Transferlines,360Transfermachines,7,361–362Transfermechanisms,7,362Transfersystems,typesof,360–361asynchronous,361continuous,360intermittent/synchronous,360stationarysystem,361

Transistor-transistorlogic(TTL),340Trialanderrormethods,258Triangulationsensors,448Trunnionmountedcylinders,143–144mountingstyles,144

Truthtables,299–300constructionof,300reasonsforusing,299–300

Tube-typecameras,450Turbulenceamplifier,304,315–317Twinpressurevalve,applicationof,223–225Twinpressurevalves,192–193symbolof,193

Twin-screwpumps,56–57characteristicsof,57

Twistingjoint,414Two-fingerinternalgripper,471

Twofingeredpneumaticactuated,471Two-stagepistoncompressor,77–78advantagesanddisadvantagesof,78

UUltrasonicrangingsystems,449Ultrasonicsensors,444,451,453Unidirectionalmotors,122

VVacuumgrippers,472–473advantagesanddisadvantages,472–473typesof,472

Vacuumpressure,15VAL(Victor’sAssemblyLanguage),493exampleofrobotprogramusing,493–495

Valveactuation,ofDCvalvesdetent,165,166electromagnets,166manual,164mechanical,164–165pilotoperation,165,166pilotsolenoidoperation,166–167

Valveactuators,163Valves,159.Seealsospecificvalvesclassificationof,160

Vanecompressor,rotary,74–75Vanemotors,152–153Vanepumps,53–55advantagesanddisadvantagesof,54–55applications,55typesexternal,53flexible,53sliding,53

Vaporfilters,94Variabledisplacementmotors,122Velocitypressure,24Velocitysensors,450Venturi,GiovanniBattista,17Venturieffect,17Venturi’slaw,18Verticalmovement,ofrobot,413Vibratorybowlfeedertrack,384Vibratorybowlfeeders,377,381–386applicationsof,385–386constructionandworkingof,383controlsfor,385terminology,382–383

Victor’sassemblylanguageSeealsoVAL,493

Viscosity,20Viscosityindex,20Viscosityoffluids,effectoftemperatureon,20Visualsensors,444Volumetricfeeders,374Volumetricflowrate,16Vortexamplifier,313–315amplifiedsignal,315nosignal,315

WWalk-throughprogramming,484Walkingbeamsystem,363Water-cooledaftercoolers,88,89Water-glycol,104Water-oilemulsionsoil-in-water,105water-in-oil,105

Wave,490Weightdensity,18–19Weight-loadedaccumulators,110,111Welding,robotsfor,500–504arc,501–502electronbeam,503MIG,503–504reasonsforusingrobots,500–501spot,502–503TIG,504

Wetairreceivers,86Wheelconveyors,371Wobbleplatepumps,59–60Work,24Workenvelope/workspace,ofrobot,411,412Wrapendeffectors,467–468Wristmotions,typesof,406,407

XX-y-zrobots,415XNOR(exclusive-NOR)gate,303XOR(exclusive-OR)gate,301–302

ZZDRL(ZheDaRobotLanguage),491