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Control Actuators

1 proportional pressure-limi ting valveto set maximum force.

1 pneumatic valve to actuate the metalsheet feeding

1 on/off valve within the water coolingsystem for oil temperature control.

1 analog 4-port directional/proportionalvalve for commanding the change of thespeed of the ram mounted on the top ofthe cylinder

Hardware and Software ToolsThe data acquisition and control system isbased on an Apple Macintosh IIfx runningLabVIEW, equipped with an NB-MIO-16

multifunction DAQ board, an NB-DIO-32Fdigital I/O board, and an NB-DMA-2800DMA controller board from NationalInstruments. LabVIEW provides state-of-the-art graphical software tools forinstrumentation programming andgraphical user interface development.

The National Instruments products arealigned perfectly for the construction ofvirtual instrumentation systems, whichrely heavily on the personal computer as

Automated System for Educational Trainingon Punching Process Characterization

by Maria Teresa Restivo and JoaquimGabriel Mendes, Mechanical Department,

University of Porto, Portugal

The Challenge: Efficiently studyingthe mechanical characteristics of solidmaterials during the punching process.The Solution: Developing aMacintosh-based measurement systemusing analog and digital DAQ boardscontrolled by LabVIEW.

IntroductionAutomation of both test and measurementand process monitoring and control is

significant to university laboratories.Flexibili ty in the selection of parameters tobe measured and a user-friendly interfaceare both important goals for experimentalmeasurements. These aspects are essentialin R&D activities where postgraduatestudents play an important role. Someof the work also can be adapted to trainundergraduate students. LabVIEW graphi-cal software is an important key in usingpersonal computers to achieve our goal ofintegrating hardware into easy-to-usesystems for the experimental study ofscientific and engineering phenomena.

Experimental OverviewFor our experiments with the punchingprocess, we used a prototype hydraulicpress with a C-shaped frame and anominal range of 35 kN. It was equippedwith a variety of transducers, detectors,and control actuators. With specialcontrol strategies, i t was possible to reacha cutting frequency of 11 Hz. The maininstrumentation and control actuatorsare summarized as follows:

Transducers and Detectors

3 absolute pressure transducers that alsomeasure temperature one in eachcylinder chamber and the third in thehydraulic power unit

1 accelerometer and charge amplifiermeasuring the effect on the pressstructure during the cutting process

1 load cell designed and built to fit theparticular needs of this press and its loadrange, used for a direct measurement offorce (special care was taken in anautomatic sensing of its supply valueand autocompensation actions areimplemented)

1 LVDT displacement transducer for

structure deformation measurements 1 incremental encoder for tool position

measurement 1 Hall-effect sensor for fine tool posit ion

measurements 1 optical sensor (red beam) for metal

sheet detection on the pneumatic metalsheet-feeder

3 digital Hall-effect sensors as top,bottom, and middle dead center detectors

Educati on/Mechani cal Engineeri ngs DAQs LabVIEW

LabVIEW graphical software is animportant key in using personal

computers to achieve our goal of

integrating hardware into easy-to-use

systems for the experimental study of

scientifi c and engineering phenomena.

Front Panel of the VI for Punching Process Studies

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the host platform. We think of virtualinstrumentation as a layer of software andhardware added to a general-purposecomputer so that users can interact withthe computer as though it were their owncustom-designed traditional electronic

instrument. The main point is that eachuser can construct his or her own instru-ment, as simple or as complex as needed,establishing simultaneously the specificityof the measurement methodology required.

Virtual instrumentation is ideal foruniversity laboratories. Unlike industrialapplications, where traditional turnkeysolutions are often used, a university labneeds an open-architecture developmentenvironment to foster new creativeapproaches. We believe it is important atthe educational level to allow students to

be creative in building a measurementsystem to probe the phenomena understudy, given that proper safety proceduresare in place.

The VI for Punching StudiesThe virtual instrument (VI) for studyingthe punching process characterizes thecutting force pattern evolution in termsof tool position and time (during thepunching process). We have acquired alarge amount of data for later correlationstudies by introducing changes inparameters such as punching speed,hydraulic pressure, type and thickness of

material, and di fferent tool parameters.

friendly system. In this approach, thestudent is an active participant instead of atraditional passive observer. We believe thisapproach is an important goal in experi-mental science and engineering education.

The flexibility in choosing testparameters offers a wide variety of possibleexperiments. Students report their resultsafter they are analyzed based on the syllabusof a mechanical engineering course. Thisprocedure introduces students to the tradi-tional methodology of R&D activities.1

For more details, contact M aria Teresa Resti vo

or Joaquim Gabriel Mendes, Mechanical

Department, Facult y of Engineering, Uni versit y

of Porto, Rua dos Bragas, 4099 Porto Codex,

Portugal, tel 351 (02) 204 1701,

fax 351 (02) 207 4241, e-mail ,

tresti vo@fe.up.pt or jgabriel@fe.up.pt

USER SOLUTION

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Copyright 1998 National Instruments Corporation. Al l rights reserved. Product and company names listed are trademarks or trade names of their respective companies. 361318A-01

Block Di agram of the Punching Process Studies VI

From the front panel, you can defineparameters such as cutting speed, numberof samples acquired, tool position triggerpoint, hydraulic pressure, gain selection(for the different transducers), width ofthe windows to be recorded, and the dataformat. The front panel displays a graphof the cutting force and the average timebetween samples. We can also selectadditional mechanical measurementquantities such as press structure defor-mation, hydraulic pressure evolution, andmachine vibration level from the frontpanel of this VI.

SummaryThis type of experimental training, usingintegrated teaching of experimentaltechniques and LabVIEW graphicalsoftware, gives students excellent training

through an open, interactive, flexible, and

This type of experimental training,using integrated teaching of experimen-

tal techniques and LabVIEW graphical

software, gives the student excellent

training through an open, interactive,

flexible and friendly system.