基于虛擬儀器的應(yīng)變測試系統(tǒng)外文文獻

StrainTestSystemBasedonVirtualInstrumentTechnology

BY：TomafridFrom:SCIENCEOFNEWJERSEYDAILY2010.1

ComputerScienceDepartment

collegeofnewjerseyInstituteoftechnology

USA.

Email:

Tomafrid@

Abstract

Straintestisoneofthemostwidelyappliedtechnologiesinmechanicalengineering.Nowadays,theconventionalstraintesttechnologygraduallycan’tkeepupwiththestepofmoderntesttechnology’sdevelopment.VirtualInstrument,whosecoreiscomputer,isbecomingthemaintrendoftesttechnologyinsteadofconventionalinstruments.ButthesoftwaredevelopmentofvirtualInstrumentisrathercomplicate,itlimitstheapplicationanddevelopmentofvirtualinstrumenttechnologyinstraintestfield.Inordertosolvetheproblemmentionedabove,astraintestsoftwaresystemwasdevelopedinLabVIEW8.0.First,functionalmoduledesignmethodwasadoptedtoconstructthesoftwaresystembasedonstudyingthetestmethodusingtraditionalinstruments.Intheprocessofrealizingfunctionalmodule,“event-loop-statemachine”modelwasdesigned.Second,therunningprocedureofsoftwaresystemwasdesignedbasedonstudyingtheconventionaltestprocess.Third,basedonthestraintesthardwaresystemconsistingofNISCXI-1520etc.,themodulesincludingparameterinitialization,bridgebalance,shuntcalibration,filter,stressandloaddisplay,timedomainanalysis,frequencydomainanalysis,datastorage,signalreplay,experimentreportgenerationandstaticcalibrationofsystemweredevelopedtoimplementthetestandcontrolassignment.Finally,someexperimentsweredonetovalidatethesystem’sreliability.Theuserwascapableofcarryingoutthestraintestandanalysistaskusingthecorrespondingsoftwaretestsystemconstructedonlythroughclickingthefunctionalbuttonsonthesystem’smainboardaccordingtothetestrequirement.Itmakesuserfarawayfromthecomplicatesoftwaredevelopment.

LabVIEW(shortforLaboratoryVirtualInstrumentationEngineeringWorkbench)isaplatformanddevelopmentenvironmentforavisualprogramminglanguagefromNationalInstruments.Thegraphicallanguageisnamed"G".OriginallyreleasedfortheAppleMacintoshin1986,LabVIEWiscommonlyusedfordataacquisition,instrumentcontrol,andindustrialautomationonavarietyofplatformsincludingMicrosoftWindows,variousversionsofUNIX,Linux,andMacOSX.ThelatestversionofLabVIEWisversionLabVIEW2010,releasedinAugust2010.

Dataflowprogramming

TheprogramminglanguageusedinLabVIEW,alsoreferredtoasG,isadataflowprogramminglanguage.Executionisdeterminedbythestructureofagraphicalblockdiagram(theLV-sourcecode)onwhichtheprogrammerconnectsdifferentfunction-nodesbydrawingwires.Thesewirespropagatevariablesandanynodecanexecuteassoonasallitsinputdatabecomeavailable.Sincethismightbethecaseformultiplenodessimultaneously,Gisinherentlycapableofparallelexecution.Multi-processingandmulti-threadinghardwareisautomaticallyexploitedbythebuilt-inscheduler,whichmultiplexesmultipleOSthreadsoverthenodesreadyforexecution

Graphicalprogramming

LabVIEWtiesthecreationofuserinterfaces(calledfrontpanels)intothedevelopmentcycle.LabVIEWprograms/subroutinesarecalledvirtualinstruments(VIs).EachVIhasthreecomponents:ablockdiagram,afrontpanel,andaconnectorpanel.ThelastisusedtorepresenttheVIintheblockdiagramsofother,callingVIs.Controlsandindicatorsonthefrontpanelallowanoperatortoinputdataintoorextractdatafromarunningvirtualinstrument.However,thefrontpanelcanalsoserveasaprogrammaticinterface.Thusavirtualinstrumentcaneitherberunasaprogram,withthefrontpanelservingasauserinterface,or,whendroppedasanodeontotheblockdiagram,thefrontpaneldefinestheinputsandoutputsforthegivennodethroughtheconnectorpane.ThisimplieseachVIcanbeeasilytestedbeforebeingembeddedasasubroutineintoalargerprogram.

Thegraphicalapproachalsoallowsnon-programmerstobuildprogramsbydragginganddroppingvirtualrepresentationsoflabequipmentwithwhichtheyarealreadyfamiliar.TheLabVIEWprogrammingenvironment,withtheincludedexamplesandthedocumentation,makesitsimpletocreatesmallapplications.Thisisabenefitononeside,butthereisalsoacertaindangerofunderestimatingtheexpertiseneededforgoodquality"G"programming.Forcomplexalgorithmsorlarge-scalecode,itisimportantthattheprogrammerpossessanextensiveknowledgeofthespecialLabVIEWsyntaxandthetopologyofitsmemorymanagement.ThemostadvancedLabVIEWdevelopmentsystemsofferthepossibilityofbuildingstand-aloneapplications.Furthermore,itispossibletocreatedistributedapplications,whichcommunicatebyaclient/serverscheme,andarethereforeeasiertoimplementduetotheinherentlyparallelnatureofG-code.

Benefits

OnebenefitofLabVIEWoverotherdevelopmentenvironmentsistheextensivesupportforaccessinginstrumentationhardware.Driversandabstractionlayersformanydifferenttypesofinstrumentsandbusesareincludedorareavailableforinclusion.Thesepresentthemselvesasgraphicalnodes.Theabstractionlayersofferstandardsoftwareinterfacestocommunicatewithhardwaredevices.Theprovideddriverinterfacessaveprogramdevelopmenttime.ThesalespitchofNationalInstrumentsis,therefore,thatevenpeoplewithlimitedcodingexperiencecanwriteprogramsanddeploytestsolutionsinareducedtimeframewhencomparedtomoreconventionalorcompetingsystems.Anewhardwaredrivertopology(DAQmxBase),whichconsistsmainlyofG-codedcomponentswithonlyafewregistercallsthroughNIMeasurementHardwareDDK(DriverDevelopmentKit)functions,providesplatformindependenthardwareaccesstonumerousdataacquisitionandinstrumentationdevices.TheDAQmxBasedriverisavailableforLabVIEWonWindows,MacOSXandLinuxplatforms.

Intermsofperformance,LabVIEWincludesacompilerthatproducesnativecodefortheCPUplatform.Thegraphicalcodeistranslatedintoexecutablemachinecodebyinterpretingthesyntaxandbycompilation.TheLabVIEWsyntaxisstrictlyenforcedduringtheeditingprocessandcompiledintotheexecutablemachinecodewhenrequestedtorunoruponsaving.Inthelattercase,theexecutableandthesourcecodearemergedintoasinglefile.TheexecutablerunswiththehelpoftheLabVIEWrun-timeengine,whichcontainssomeprecompiledcodetoperformcommontasksthataredefinedbytheGlanguage.Therun-timeenginereducescompiletimeandalsoprovidesaconsistentinterfacetovariousoperatingsystems,graphicsystems,hardwarecomponents,etc.Therun-timeenvironmentmakesthecodeportableacrossplatforms.Generally,LVcodecanbeslowerthanequivalentcompiledCcode,althoughthedifferencesoftenliemorewithprogramoptimizationthaninherentexecutionspeed.

Manylibrarieswithalargenumberoffunctionsfordataacquisition,signalgeneration,mathematics,statistics,signalconditioning,analysis,etc.,alongwithnumerousgraphicalinterfaceelementsareprovidedinseveralLabVIEWpackageoptions.Thenumberofadvancedmathematicblocksforfunctionssuchasintegration,filters,andotherspecializedcapabilitiesusuallyassociatedwithdatacapturefromhardwaresensorsisimmense.Inaddition,LabVIEWincludesatext-basedprogrammingcomponentcalledMathScriptwithadditionalfunctionalityforsignalprocessing,analysisandmathematics.MathScriptcanbeintegratedwithgraphicalprogrammingusing"scriptnodes"andusesasyntaxthatisgenerallycompatiblewithMATLAB[citationneeded].

ThefullymodularcharacterofLabVIEWcodeallowscodereusewithoutmodifications:aslongasthedatatypesofinputandoutputareconsistent,twosubVIsareinterchangeable.

TheLabVIEWProfessionalDevelopmentSystemallowscreatingstand-aloneexecutablesandtheresultantexecutablecanbedistributedanunlimitednumberoftimes.Therun-timeengineanditslibrariescanbeprovidedfreelyalongwiththeexecutable.

AbenefitoftheLabVIEWenvironmentistheplatformindependentnatureoftheGcode,whichis(withtheexceptionofafewplatform-specificfunctions)portablebetweenthedifferentLabVIEWsystemsfordifferentoperatingsystems(Windows,MacOSXandLinux).NationalInstrumentsisincreasinglyfocusingonthecapabilityofdeployingLabVIEWcodeontoanincreasingnumberoftargetsincludingdeviceslikePharLaporVxWorksOSbasedLabVIEWReal-Timecontrollers,FPGAs,PocketPCs,PDAs,andWirelesssensornetworknodes.

ThereisalowcostLabVIEWStudentEditionaimedateducationalinstitutionsforlearningpurposes.ThereisalsoanactivecommunityofLabVIEWuserswhocommunicatethroughseverale-mailgroupsandInternetforums.

Criticism

LabVIEWisaproprietaryproductofNationalInstruments.UnlikecommonprogramminglanguagessuchasCorFORTRAN,LabVIEWisnotmanagedorspecifiedbyathirdpartystandardscommitteesuchasANSI.

Asofversion8,allLabVIEWinstallationsonWindowscomputersrequirecustomerstocontactNationalInstrumentsbyInternetorphoneto"activate"theproduct.MacintoshandLinuxusersarenotsubjecttothisrequirement.

Buildingastand-aloneapplicationwithLabVIEWrequirestheApplicationBuildercomponentwhichisincludedwiththeProfessionalDevelopmentSystembutrequiresaseparatepurchaseifusingtheBasePackageorFullDevelopmentSystem.CompiledexecutablesproducedbytheApplicationBuilderarenottrulystandaloneinthattheyalsorequirethattheLabVIEWrun-timeenginebeinstalledonanytargetcomputeronwhichusersruntheapplication.TheuseofstandardcontrolsrequiresaruntimelibraryforanylanguageandallmajoroperatingsystemsupplierssupplytherequiredlibrariesforcommonlanguagessuchasC.However,theruntimerequiredforLabVIEWisnotsuppliedwithanyoperatingsystemandisrequiredtobespecificallyinstalledbytheadministratororuser.Thisrequirementcancauseproblemsifanapplicationisdistributedtoauserwhomaybepreparedtoruntheapplicationbutdoesnothavetheinclinationorpermissiontoinstalladditionalfilesonthehostsystempriortorunningtheexecutable.

AccordingtotheNationalInstrumentslicenseagreementanexecutablebuiltwithLabVIEWshouldcontainanotethatthesoftwareiswritteninLabVIEW.

ThereissomedebateastowhetherLabVIEWisreallyageneralpurposeprogramminglanguage(orinsomecaseswhetheritisreallyaprogramminglanguageatall)asopposedtoanapplication-specificdevelopmentenvironmentformeasurementandautomation.Criticspointtoalackoffeatures,commoninmostotherprogramminglanguages,suchas,untilversion2009,nativerecursionand,untilversion8.20,nativeobjectorientedfeatures.

Also,foranenvironmentheavilytargetedfortest,LabVIEWincludesnobuilt-infunctionsforformallytestinglimits,readingalimitsfile,andconvenientlytrackingthepassingorfailingresults.CompaniestendtobuildtheirownproprietaryfunctionsforthisbasicfeatureiftheychoosenottouseTestStand.

TimingSystem

LabVIEWusestheJanuary1,1904Epoch(referencedate)asits"zero"time.OtherprogramsthatusetheJanuary1,1904epochareAppleInc.'sMacOSthroughversion9,PalmOS,MP4,andMicrosoftExcel

Labviewisabove，nowletusdisussthestrain.Duetoexternalobjects(stress,humidity,temperaturechanges,etc)anddeformation,theobjectbetweenthepartsproducedwithintheinternalinteractiontoresisttheexternalcauserole,andtriedtomaketheobjectfromthedeformationafterpositionreverttodeformationpreviousposition.Inthesectionsomeinvestigationonunitareaofinternalforcecalledstress.Withsectionofverticalcallednormalstressormethodtostress,withsectiontangentcalledshearstressorshearstress.Stressincreaseswiththeexternalgrowth,withaparticularkindofmaterial,thebuild-upofstressislimited,exceedthisalimit,materialwillbedestroyed.Foracertainmaterialsfor,stresscanbereachedthisplateaucalledthematerialsofultimatestress.Ultimatestressvaluethroughthematerialmechanicstesttodetermine.Willdeterminethelimitshouldbereduced,setthemasterpieceofappropriatematerialscansafeworkstress,thisisthemaximumallowablestress.Materialstothesafeuse,whenuseinsidethestressshouldbelessthanitsultimatestress,otherwisematerialswilloccurwhenusedestruction.Engineeringcomponents,mostcases,internalforceisnotevenlydistributed,usually"destruction"or"failure"tendtobeagedfrominternalforcesetde