hu‐motor integrated hammering mechanism

8/12/2019 Humotor Integrated Hammering Mechanism

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HumotorIntegratedHammeringMechanism

TeamA

KothaBharathKumarReddyED11B021

PaboluSahithipriyaED11B025

ShrutiPandeyED11B035

DiyyalaChaitanyakumarED11B045

SaneethSriramojuED11B053


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Appendix

SINo Topic PageNo

1) Problemstatement 3

2) Motivation 35

3) TargetSpecification 5

4) Assumptions 6

5) TargetCustomers 6

6) Challengesanddifficulties 6

7) Somepossiblesolutionsandtheir

evaluation

712

8) Calculations 1315

9)

Constraints

on

design 15

16

10) Partsandmaterial 16

11) Partsandfinaldimensions 1718

12) CompleteCADmodel 18

13) Scopeofimprovement 19

14) Suggestionsandcritics 19

15) References 19


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ProblemStatement:

Todesignamechanismwhichcanreplacethetraditionalhammering

mechanismto

crush

the

stones,

and

to

improve

the

efficiency

of

worker

and

reduceeffortwhilehammeringthestones.Alsomechanismisdesignedto

integrateitwithHumotor(amechanismdevelopedtoutilizeworkerstimeand

energyinanefficientway)

Motivation:

Themainmotivationistodevelopanalternativehammeringmechanismto

reduceworkereffect.MechanismisdesignedtobeintegratedwithHumotorto

furtherincrease

the

efficiency

of

the

worker.

Intraditionalways,aheavyweighthammerisusedtocrushthestones.

Hammerheadhastobeliftedabovetheshoulderlevelandshouldbedroppedon

thestonestocrushthestones.Liftingheavyweightsrepeatedlyisnotagoodidea

inperspectiveofergonomics.Soifwecancomeupwithaway,sothatworker

willberelaxedtolifttheweights,thenwecanreducemusclefatigue.

Figure1:Atraditionalsledgehammer.


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Imagesource:http://www.blackrocktools.com/media/catalog/product/cache/1/image/9df78eab33525d08d6e5fb8d27136e95/3/1/3103_3

lb._sledge_hammer_tekton_2_.jpg

Figure2:Workerusingsledgehammer

Humotorisamechanismwhichisdevelopedtoreducetheeffortof

workerwhileliftingheavyloads.Insteadofliftingheavyloadsworkerhastodo

pedalingmotiontolifttheheavyloadsusingHumotor.Soifwecanintegrate

hammeringtoHumotorwecangreatlyreducehumaneffort.


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Figure3:

Schematic

of

Hu

motor

Thesolutionsalreadyexisting includecrushingplants.Generallytheseare

heavydutystonecrushingplantsandcantbemovestonewplaces.Theseplants

use a lot of electricity. Cost of these plants is too high and a normal building

constructor cant afford to spend so much. So we want to design a mechanism

which dont use electricity, cheap, not so heavy and uses human energy

efficiently.

TargetSpecifications:

o Atleastasmuchproductivityaswithmanualhammering(eachhitinevery1.75sec)

o Amomentumtransferof35KgN/mpereachhit.o Costbelow10,000/ INR.


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o Longlifeofproduct.Assumptions:

Wemadesomeassumptionsduringtheanalysisanddesignofmechanism

whichsimplifies

the

process.

Assumptions

are

mentions

below.

o Time of impact is same regardless of the mass of hammer head. Time ofimpactmayvaryfromhittohitbutbyassumingthatitisconstant,wejust

needtoworryaboutmomentumtransfer.Whentimeofimpactissame,it

isenoughtotransfersameamountoflinearmomentum.

o Afterhittingtherock,hammerheadmomentarilycomestorest(i.e.,allthemomentumistransfertorock)

o The momentum that needs to be transferred is calculated using a videowhich

is

taken

while

aworker

is

actually

using

hammer.

We

assumed

that

it

isenoughifourmechanismgivesthismuchfinalmomentum.

o Productivityrate isalsocalculatedfromavideo.Althoughproductionratemayvaryfromworkertoworker,weassumedittobeourtargetvalueand

designedmechanismaccordingly.

TargetCustomer:

1. Constructionworkers.2. Mines3. Otherplaceswherestonesneedtobecrushed.

We went and met workers in constructions sites of our institute (near

SharavathihostelandSaraswathihostel).Fromoutinteractionwecametoknow

that, it isveryhardtousesledgehammer for longtimes.Liftingthehammer to

suchheightisadifficulttaskandtheysaidalternativemechanismwillbehelpful.

Wetookavideowhileworkerisusingsledgehammertoanalyzethehammering

process.

ChallengesandDifficulties:

o Liftingthehammerheadupto2metersheight.o Repetitivemotionofhammero Jerkproducedwhenhammerheadhitstherock.o Protectingworkerandcomponentsfromjerk.


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o Minimizingtheenergylossesduetofrictionetc.o Longlifeofproduct.o Lowcost.

Somepossible

solutions

and

their

evaluation:

Weconsideredsomepossiblemechanismstotheproblem.Theyare listed

below.

Mechanism1:

Figure4:Schematicofsolutionusingcams

We considered using two cams and attaching hammer head to one cam

usinginextensiblerope.Herewehaveproblemsoffriction.Surfacedamagemay

occur because of the friction between two cams.And also cams may have very

highinertia.


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Mechanism2:

Figure5:Schematicofsolutionusingfourbarmechanism

Anothersolutionistousefourbarmechanismandattachinghammerhead

tooneofthefourlinks.Butherewewillhavetheproblemofjerk.Linkinfourbar

mechanism cant sustain thejerk produced when hammer head hits rock. As a

resultlinkswillbedamagedeasilyandlifetimeofproductwillbeveryless.

Mechanism3:In thismechanism,aroller is attached to a rotating link. One endof long

stringis

attached

to

afixed

point

and

to

the

other

end

hammer

head

is

attached.

While rotating, roller which is attached to the link will lift the string and so

hammer head rises. After some time hammer head reaches its maximum point

and start to fall on to rock. Here the main problems is that, to create same

momentumnecessarylinkhastorotatewithhighvelocityforsometimeandfor

while lifting the hammer it need to move slowly so as to reduce human effort.

Thoseveryhighvelocitiesareabigtroublewiththismechanism.


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Figure6:Schematicofsolutionusingpulleysandrotatinglink.

Mechanism4:

Figure7:Aschematicusingpulleysandcams.

Becauseofthefrictionbetweenpulleyandsemicircleshapedcam,when

camrotateshammerheadwillraise.Andwewillhavefreefallwhencamleaves

contactwithpulley.Eventhoughsolutionseemstobeworking,wemayface


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problemswhileimplementingthismechanism.Weneedaninterferencefit

betweencamandpulley,becauseoftheneedofhighfrictionbetweenthese.So

whenevercamstartstocomeintocontactwithpulley,theseinterferencewill

causealotoftroubles.Andalsowhenhammerheadfallsonstones,jerk

developedwill

cause

damage

to

the

rope.

Mechanism5:

Figure8:Schematicusingpulley,rollersandlinks.

Thisisanothermechanismusingcams.Rollerisusedtoeliminatefriction

between

cam

and

links.

Mechanism

is

protected

from

jerk

by

the

design

of

cam.

Whenhammerheadmakescontactwithstone,therewontbeanycontact

betweenrollerandcam.Alsothecenterofrotationofhammerheadiscenterof

percussionaboutwhichtherewontbeanynetmomentortorque.


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Belowprosandconsofmechanismsconsideredabovearetabulated.

Mechanism Pros Cons

Mechanism1

Easyto

design

Jerkwontaffectcamsand

otherparts

Surfacefailure

Frictionatsurface

Difficulttofabricatecams

Mechanism2 Veryaccuraterepeated

movement

Welldeveloped

mathematical

solutions

Easytofabricate

Cantaccommodatejerk

developed

Lesslife

time.

Mechanism3 Easytofabricate

Lowcost

Partscanbereplacedeasily

Difficulttogetenoughimpact

Ropemightneedtobechanged

frequently.

Mechanism4

Easyto

manufacture.

Highproductivitycanbe

obtained.

Difficultto

generate

friction

betweenpulleyandcam

Failureofropeduetoimpact

Mechanism5 Uniformliftofhammerhead.

Verylessfriction

Jerkswont

affect

the

system

Difficulttomanufacture

Table1:Comparingadvantagesanddisadvantagesofdifferentmechanisms


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Intheabovemodels,firstfourarehavingsomeproblemswhichcause

troublestofunctioningofmechanism.Eventhoughfifthmechanismseemstobe

workingwell,itisverydifficulttomanufacturesuchacam.Butwehave

advantageofconstantliftofhammerheadwiththiscam.Wedecidetochange

theshape

of

cam,

so

that

manufacturing

will

be

easy,

at

the

cost

of

constant

force

toliftthehammerhead.

Figure9:Initialdesignofcam Figure10:Redesignedcam

Herewecomparedthesetwocamsintermsoffunctionality.

Initiallydesignedcam Redesignedcam

Difficulttomanufacture Comparativelyeasytomanufacture

Almostconstantforcesareinvolved

whileliftingthehammerhead

Varyingforcesareinvolvedwhilelifting

thehammerhead

Nonconvexshapedperimeter Convexshapedperimeter

Table2:Comparingfunctionalitiesoftwocams

Fortheabovereasonswedecidedtogowiththeredesigncameventhough

forcesinvolvedarenotconstantthroughoutthemechanism.


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Calculations:

Tocalculateimpulseneededtobreakthestonewevisitedaconstructionsite,

wherewe

took

the

video

of

the

worker

working

with

the

hammer.

From

the

video

wecalculatedImpulse,Numberofhitspersecond,Angularvelocityandrelevant

parameters.

Hammerarmlength=90cms

Timetakenforeachhit=1.75seconds

Angularvelocity=7.85rad/seconds

Impulse

calculated

=

32.325

kg

m/sec

Assume

the

link

1(1

)

makes

an

equal

angle

on

both

sides

of

the

horizontal

axis

LettheHeightthroughwhichitmovesbe

Sofromthefigure

sin

21


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Impulsemomentumtheorem

Energyconservationprinciple

2 2

Fromaboveequationsweget

19.6

Tosetthevaluesofmass,lengthsangleaCcodewithconsiderationslike

o Torqueshouldbeuniformandtorquevariationshouldbeminimum(


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Mass(M) Height(H) Length(l1) Angle(rad) Torque(Nm) Torque

variation

13 0.414 0.607 0.348 77.357 4.64

14.2 0.347 0.373 0.483 51.99 5.95

15.1

0.307 0.453 0.3454 67.1 3.9617.2 0.236 0.518 0.23 87.37 2.30

Highlightedvaluesarethesetofselectedvalues.

Aslink1andlink2aretworigidpartsofalink,when1rotatesthelink2alsorotatesbysameangle.

Timetakentodropthehammerhead

2

Thisturnsouttobe0.25seconds.So,ittakes1.750.25secondstomovethe

hammerup.Matchingtheangletotheriseofthehammerwecangetbase

dimensionsofcam,angularaccelerationandtorque.

ConstraintsonDesign:

1) Ifmassofthehammerisincreased,thenwedontneedtoliftittothesame

height

to

create

same

impulse,

so

we

can

have

smaller

link

lengths.

Butatthesametime,wewillbehavingproblemsforfeedingtherockin

andalsoinputtorqueincreases.

2)Ifweincreasethelengthofthelink1,wedontneedtoturnittoomuch

aboutpivottoraiseittothesameheight,butatthesametimeweneedto

applymoretorquetorotatethemass.Linklengthandtorquearelinearly

related.

3)Ifwechangethepivotposition,alltheassemblywillgetaffected.

Hammermay

not

rise

to

the

complete

height

required

or

it

may

rise

more

thanrequired,somecomponentsmaygetstuckwhilemoving.Soweneed

exactpositionforpivotforgoodimpulsegeneration.

4)Rotationangleatpivotisalsoveryimportant.Ifitistoolarge,camsize

willincreasedramaticallyandtherewillbealotoftorquevariationswhile


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rotatingcam.Ifitistoosmall,weneedtohavelargelinksthusby

increasingtorques.

5)Iflengthofsecondlink(onewhichisincontactwithcam)ismore,we

willneedlargercamandifitistoosmalllargerforceswillbegeneratedat

camand

link

contact

which

damages

components.

6)Ifcambaseradiusistoosmall,pressureanglewillbehigh,whichcauses

morestressatcambearingcontact.Ifitistoolargewewillneedalotof

materialwhichincreasesthecostofassembly.Alsoifwehavelargemass,

wewillneedtoputinmoreenergytostartorstopthemechanism(Itacts

likeflywheel)

MassVs.

Torque

variation

*dissameas

PartsandMaterials:

PART MATERIAL

Cam Ductilecastiron

Links Hotrolledplaincarbonsteel

Supportshafts

Ductile

cast

iron

Hammerhead Mediumcarbonsteel

CamsupportandLinksupport Ductilecastiron


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PartsandfinalDimensions:

CAM LINKS

CAMSUPPORT

LINK

SUPPORT

LINK

SUPPORTSHAFT


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BASE CAMSUPPORTSHAFTHAMMERHEAD

CompleteCADmodeloftheMechanism(IncludingFeedingmechanism):


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SCOPEOFIMPROVEMENT:

o DesignofCam:Improveddesignofcamtomaketheforcesinvolvedinliftingthehammerheadconstant

oProductivity:

Productivity

can

be

increased

by

increasing

the

size

of

product

sothatitcanaccommodatemorenumberofcamsandhammerheadsto

increasethenumberofstonescrushingataninstant

o FeedingMechanism:Implementingthefeedingmechanism(AsshowninCADmodel)

SUGGESTIONSANDCRITICS:

o Multipleuseofproductwithmodificationindesignbyreplacinghammerwithaxeforwoodcutting.

o Manufacturingcouldhavebeendoneinbetterway.o AttachmentofCamtoshaftcouldhavebeendonethroughakeyrather

thanwelding.

o IntegrationwithHumotorandincorporatingfeedingmechanism.

REFERENCES:

1. https://www.youtube.com/watch?v=gD6d4hyLNNs2. MachineDesignbyRobertL.Norton3. http://www.efunda.com/materials/alloys/alloy_home/steels_properties.cf

m

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