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Visual Servoing of a Conventional CNC Machine Using an External Axis Controller.doc

Visual Servoing of a Convention…

上传者: 绯色琉璃真人 2018-04-30 评分 0 0 0 0 0 0 暂无简介 简介 举报

简介:本文档为《Visual Servoing of a Conventional CNC Machine Using an External Axis Controllerdoc》,可适用于高等教育领域,主题内容包含VisualServoingofaConventionalCNCMachineUsinganExternalAxisControllerVisual符等。

VisualServoingofaConventionalCNCMachineUsinganExternalAxisControllerVisualServoingofaConventionalCNCMachineUsinganExternalAxisControllerDanielHana,,GuyRodnay,MichalTordonandJayanthaKatupitiyaSchoolofMechanicalandManufacturingEngineeringUniversityofNewSouthWalesSydneyNSWAustraliajkatupitiyaunsweduauAbstractAnumberofstudieshavebeencarriedoutintherecentyearsinanattempttobringtheCNCmachinesunderlowlevelcontrol,TheworkdescribedThispaperpresentstheimplementationofanexternalaxiscontrolsystemonaconventionalCNCmainreportstheuseofaPCbasedcontrollerforachinesothatthemachinecanbeactivelycontrolledCNCmachineByusingtheexternalPCtogenerinresponsetosensorssuchasvisionandforceTheateactuatingsignals,theyretainthemonitoringandcontrollerthatrunsonanexternalcomputerhasdisafetyaspectsoftheCNCmachineWhereastheworkrectaccesstotheCNCcontrollerformachineposidescribedinisaimedatoptimizingdrillingusingantionsensingThecontrolsignalstothemachineareexternalPCTheworkpresentedinisabletoconsentthroughpurposebuiltcircuitryviathemachine’strolfeedrateofaCNCmachineTheirworkdetectsthetoolworkpiececontactonlineandadjustthefeedmanualpulsegenerator(MPG)inputsTodemonratefromrapidtraversewhen’notcutting’tocuttingstratetheaccuracyandperformanceofthecontrolfeedrateswhenthetoolisincontactwiththeworksystem,itwasusedtovisuallytrackthepro,leofamandrelusedforshearspinningTheimplementedpieceTheirworkhoweverdoesnotactivelycontrolsystemeliminatestheparallaxerrorandtheneedtothetoolpathuseanaccuratepixelresolutionTherawtrackingThemethodpresentedinthispaperusestrainsofdataisprocessedbyacurvaturedetectionalgorithmpulsesgeneratedbyanexternalcontrollertoactuatethatdetectslinearandcircularsegmentsandsegmenttheaxesofthemachineThesepulsesreplacethetransitionsTheresultsshowthatthevisualtrackingpulsesgeneratedbyMPGsToclosethepositionfeedsystemprovidesaccuratetrackingresultsthatarewellbacklooptheexternalcontrollerrequiresthemachinewithinthetolerancesusedintheindustrypositionMostCNCmachineshavesomemeansofKeyword:Visualpro,letracking,activecontrol,readingtheircurrentpositionIfsuchasystemisnotshearspinningreadilyavailable,themachineencodersorresolverscanbeaccesseddirectlyfromoutsideAspecialpurposeHighSpeedSerialBus(HSSB)wasavailabletothemachineusedinthisstudytoreadthemachinepoIntroductionsitionTheexternalaxiscontrolleristhenconvertedintoanactiveaxiscontrolsystembyclosingavisualFirst,thispaperpresentsthedesignandimplemenfeedbackloopUsingtheactivecontrolsystem,acamtationofanaxiscontrolsystemthatallowstherealeramountedinthetoolmagazineistraversedinantimecontrolofacommercialCNCmachineThenitautomatedfashiontotrackapro,ledemonstratesitsusebyvisuallyservoingoneaxisoftheCNCmachinesothatapro,leisautomaticallyTheabilitytoaccuratelydetecttheedgesoftheacscannedTheaxiscontrolsystempresentedenablesquiredimagesplaysaveryimportantroleThereareathemachinetobeactivelycontrolledAnactivesysnumberofmethodspresentedinliteratureAmethodtemhastheabilitytorespondtoinputsfromsenofenhancingobjectresolutionanddetectingedgecursorssuchasforceandvisionACNCmachinethatvaturesbyobservinggradualchangesofgreylevelsofisequippedwithanactiveaxiscontrolsystemcanbeapixelispresentedinImprovingtheimageconutilizedtocarryoutvarioustaskssuchasforcecontrasthasmadeedgedetectionmoreresilientIntrolandvisualpro,letrackingCommercially,CNCotherstudiespresentsastatisticalmethodtoenmachinesarenotequippedwithactiveaxiscontrolhancetheluminanceofgreylevelsofpixelsaroundsystemsTheyutilizepartprogramswhicharerunintheedgeThecomparisonofperformancesofedgeblockexecutionmodePartprogramsdonotresponddetectorsandcriteriaforoptimizingedgedetectorstosensorsignalsarepresentedinManyotheredgedetectiontechSYSTEMICS,CYBERNETICSANDINFORMATICSVOLUMENUMBEREXTERNALEPGniquesareavailable,howevertheuseofdi,erentialCONTROLLERoperator,isofparticularinterestTheedgedetectiontechniquepresentedinintroducesa,lterAnalogoPhasevoltageVFShiftercalledIn,niteSymmetricalExponentialFilter(ISEF)Inthisstudy,themethoddescribedinisusedtoStartCountingaccuratelydetecttheedgesAoutputbitcounterMagnitudeBbitclkThedevisedsystemwasusedtotrackthepro,leofloadoutputComparatorDesiredcountsamandrelmountedonaCNClatheforshearspindatadataningTwosetsofexperimentalresultsarepresentedDirectionDirectionOpmodethe,rstshowingthetrackingaccuracyandthesecModeondshowingthedimensionalaccuracyofspuncomponentsFigure:TheEPGsystemSystemComponentsActiveAxisControlSystemThepurposeoftheactiveaxiscontrolsystemistoauareusedtointerfacetheactuatingsignalstothematomaticallytrackthecontourofapro,leThetrackchineCustombuiltelectronichardwarecalledtheingsystemmustoperateinsuchamannerthattheelectronicpulsegenerators(EPGs)areusedtogeneraxisofthecameraisabletoaccuratelyfollowtheproatequadraturesignalsthataremultiplexedwiththe,leTheactiveaxiscontrolsystemconsistsofaposiexistingMPGsignalsWhiletheMPGsaremanuallytionsensingsystem,amachineactuatingsystemandoperated,theEPGsarecommandedbythecontrolthecontrollerscomputerWhenEPGsarechosenasthequadraturesignalsource,themachinemovesinresponsetothePositionsensingsystemcommandsfromthecontrolcomputerThemultiplexingoftheMPGsandEPGsareshowninFigureFIBREOPTICLINK(MACHINEPOSITION)AblockdiagramoftheEPGsystemisgiveninFigMPGAPGSELECTHSSBPCEndureTheEPGcircuitreceivesthreeprimarycomHSSBmandsfromthecontrolcomputerFirst,itreceivesZPositionAPGananalogvoltageInresponse,theEPGgeneratesSYSTEMZAxisMACHINEtrainsofquadraturepulsesThefrequencyoftheCONTROLLERpulsetrainsareproportionaltotheappliedanalogXAxisCONTROLvoltageThefeedrateofaparticularaxisdependsCOMPUTERXPositiononthefrequencyofpulsesThereforethefeedrateisZMPGXMPGproportionaltotheanalogvoltageappliedThusinacontouringoperation,itisnecessarytoappropriatelyFigure:SchematicoftheexternalaxiscontrolsysadjusttheanalogvoltagesappliedtobothaxesofthetemmachineNexttheEPGcircuitreceivesadirectioncommandThissignaldetermineswhetheraparticularaxismustmoveforwardorreverseFinally,itreTheHSSBshowninFigure,linkingtheCNCmaceivestheexactnumberofpulsestobeissuedtoeachchineandthecomputerthatrunstheexternalaxisaxisApartfromtheseprimarysignals,italsoreceivescontroller,readsthemachinepositionThesemachineasecondarysignalThissignalcontrolsthemodeofpositionsareusedasthefeedbacksignalsfortheexoperationTheEPGcircuitoperatesintwomodesternalaxiscontrollerTheHSSBinterfaceisalsoablethefreerunningmodeandthecontrolmodeWhentoprovideotherinformationsuchasthespeedofeachthetotalnumberofcountsbywhichthemachineaxisaxisandthemodesofoperationofthemachinemustmoveisgreaterthanthemaximumpulsespermissiblewithinthesamplinginterval,theEPGconMachineactuatingsystemstantlyoutputpulsestothemachineattheratedeterminedbytheappliedanalogvoltageThismodeTheCNCmachineshavemanualpulsegenerators(MPGs)toenabletheoperatortomanuallymoveiscalledfreerunningWhenthenumberofpulsesthetooltoadesiredpositionThesignalsgenerfallbelowthemaximumpermissibleforthenextsamatedbytheMPGsofthelathemachineareidenplingtime,theEPGswitchestocontrolledmodeAtticaltoquadraturesignalsgeneratedbyopticalintheendoftheappropriatenumberofpulses,theEPGwillstopissuingpulsescrementalencodersInthisstudy,theMPGinputsSYSTEMICS,CYBERNETICSANDINFORMATICSVOLUMENUMBERTheControllersVisualTrackingSystemThevisualscanningsystemmustnotbesusceptibletoImageExternalparallaxerrorWhenimagesofobjectsofsigni,cantPositionAxisEPGControllerControllerdepthareacquired,parallaxerrormaycausetheacquiredimagetobeinaccurateThisisespeciallytrueVFvoltsGCI(z)GCM(z)whenimagingcylindricalobjectsoflargediametersThesurfaceofthecylinderitselfwillcovertheareaDesiredpositionofthecylinderthatactuallyshowsitsfulldiameterImagecoordinatesThereforeasingleimageoftheentireobjectwillnotImageHSSBdeliverthedesiredresultFurthermore,theprocessingGM(z)camerawillbeimagebasedInsuchasituation,itisnecessaryprofiletotransformtheimagecoordinatesintomachinecoorMachinedinatesInaddition,duetothesphericalabberationofthelens,theimageresolutionchangesasafuncFigure:TheactiveaxiscontrolsystemtionofthepixellocationwithrespecttothelineofsightofthecameraThisrequiresthemaintenanceofaprecalibratedaccuratesetofpixelresolutiondataAsshowninFiguretheactivecontrolsystemconHowever,thesedataaresusceptibletoerrorsinthesistsofanumberofcontrollersTheyaretheexternaldistancebetweenthecameraandtheobjectEvenaxiscontrollersandtheimagepositioncontrollerTowhenthesphericalabberationhasbeeneliminated,proceedwiththedesignofthecontroller,thetransfertheparallaxerrorcannotbeavoidedThereforethefunctionofthemachineaxesmustbeidenti,edExonlyimageinformationthatcanbetrustedisattheperimentalsystemidenti,cationwasusedtoobtaincenteroftheimageplaneThescanningmethodsugthesetransferfunctionsgestedinthispaperavoidsparallaxerror,sphericalThetransferfunctionofthemachineaxescontrolabberationandtransformationfromimagecoordinatesystemmustrelatethepulseinput(fromEPGs)tosystemtomachinecoordinatesystemthemachinepositionThetransferfunctionsofthemachineaxessysteminZandXaxesareasfollowZ(z)=z()GMzX(z)=z()GMzNotethattheDCgainoftheabovetransferfunctionsisThisagreeswiththefactthateachMPGinputrequirescountstoproduceµmmotionThecontrollersforthetwomachineaxes,designedusingdirectanalyticaldesignmethod,aregiveninEqandEqGCMZ(z)=Figure:Toolmagazinemountedcamera(zzz)zzz()Toimplementthevisualscanningsystem,showninFigurethecamerawasmountedonthetoolmagazineOfthetwoaxesZandX,onlytheXaxisGCMZ(x)=wasactivelycontrolledwithvisualfeedbackTheZaxiswasincrementallymoveduntiltheentirepro,le(zzz)isscannedThevisualfeedbacksignalfortheXaxiszzzzwasgeneratedasfollows()Usingbacklight,animageofthesilhouetteofthepro,leis,rstacquiredTheareaimagedisspeci,Tomaintainsimplicity,theimagepositioncontrollerchoseninthisstudyisaproportionalcontrollercallychosensothatthepro,lewillbewithintheimThepixelresolutionofcountspixelisusedastheageSinceonlythecenteroftheimageplanecontainscontrollerconstanttrustedinformation,onlythecenterverticallineofSYSTEMICS,CYBERNETICSANDINFORMATICSVOLUMENUMBERpixelsareanalyzedThemethoddescribedinisasthediscontinuityofthederivativeatthetransitionthenimplementedThedi,erentialoperatorisappointwillgeneratehighcurvatureForallsegmentspliedtwicetothe,lteredgreylevelstoobtainthewithnonzerocurvatures,radiiwillbeworkedoutsosubpixelcoordinateofthepro,leedgeThissubthatifnecessary,theycanbeusedintheCNCpropixelvalueisusedasthevisualfeedbacksignalforgramEndpointsofanysegmentplayanimportanttheactivecontrolsystemroleastheymaintaincontinuitybetweensegmentsThedesiredsubpixelvalueiszero,ietheactiveTherefore,despitethepossibilityofbeinga,ectedbyaxiscontrolsystemrequiresthecameratobeactivelynoise,allrawboundarypointsofeachsegmentaremovedintheverticaldirectionuntiltheimageofthekeptKnowingtheradiiandboundarypoints,forpro,leedgepassesthroughthecameracenterWheneachsegmentaCNCpartprogramcanbegeneratedthishasbeenachieved,thepossibilityofparallaxerThemaximumallowabledeviationofcurvatureisroriscompletelyeliminatedAtthismoment,themadenotebyεInitially,seti=tobetheindexofthechinepositionisalsorecordedTheimageresolution,rstpointofthesegmentandj=itobetheindexwasusedonlyasaconstantintheactivecontrollerofthelastsegmentThen,jisrepeatedlyincrementedandassuchneednotbeknownaccuratelyItonlyafuntilfectsthestabilityandspeedofresponseoftheactiveminmaxκki<k<jκk>εcontrolsystemAlsonotethatthemachinepositioni<k<jAtthisstagetheendpointsofthesegmentaredeterwasdirectlyrecordedandthereforethetransformaminedtobe(iz,xi)and(jz,xj)Ifthesegmenttionfromimageplanetotherealworldcoordinatesishasonlytwopoints,ieji=,orifnotnecessaryκ=averageκki<k<jCurvatureDetectionAlgorithmTheshapesofthepro,lesusedinthisstudycontainedislessthenR,whereRisthemaximumallowableonlystraightlineandcirclesegmentsThecurvatureradiusforasegment,thenthesegmentisapproxidetectionalgorithmdescribedinthissectioncanbematedbyastraightlineOtherwisethesegmentisusedtoidentifystraightlinesegments,circlesegments|κ|circularwithradiusequaltoandinterpolationisandtransitionpointsinthesetofrawdataobtainedclockwiseifκ<orcounterclockwiseifκ>AtbyrecordingthemachinepositionduringscanningthisstageiisassignedthevalueofjandtheprocessThealgorithmisdescribedbelowisrepeatedforthenextsegmentByassemblingallFirst,aseriesofcurvaturesalongtheextractedproextractedsegmentssequentially,acompleteCNCpart,leiscalculatedusingnarrowbandsoftolerancesReprogramcanbegeneratedcallthatthecurvatureofacurvex=x(z)isx(z)ExperimentalSetupκ(z)=(x(z))TheCNCmachineusedinthisstudyisaColchesterTornadoAlatheItisequippedwithtwosimultaInthiscasex(z)isrepresentedinadiscretewayneouslycontrollableMPGsThemachinehasaminbytheorderedsetofscannedvalues{xi=x(iz)}imumincrementalmotionofµmAsdescribedearwithinThecentral,rstderivativelier,anHSSBisavailableforanexternalcomputerto=()()andbackwardsecondderivaxxzitivex=(xixi)zwereusedtocalculatethereadthemachinepositioniixThevisionsystemconsistsofaDataTranslationseriesofcurvaturesiDTFrameGrabberandaPulnixTMCNcam(xxixi)eraInordertoenhancethecontrastbetweentheiκi=,backgroundandforeground,backlightingwasusedz(z(xixi))ThebacklightingwillprovideanimageofthesilhouwhereinetteofthemandrelwithuniformlowgreylevelsinallThecurvaturesarethengroupedintosetsofapcoveredareasproximateconstantcurvaturesAmongthese,zerocurvaturesrepresentstraightlinesandnonzerocurvaturesrepresentcircularsegmentsClockwiseandResultsanticlockwisecircularinterpolatedregionscanbedeterminedusingthesignofthecurvatureAtransitionTheresultspresentedbelowrelatestoashearspinningbetweencircularsegmentsisdetectedbyachangeinexerciseShearspinningrequiresamandrelacurvatureThismethodwillalsoidentifyatransitionthickchunkofsteelofacertainshape,mountedonbetweentwosegmentswithidenticalcurvatures(forthelatheThevisualtrackingsystemdevelopedwasusedtoscanthepro,leofthemandrelThe,rstsetexampletwostraightsegmentswithdi,erentslopes),SYSTEMICS,CYBERNETICSANDINFORMATICSVOLUMENUMBERofresultsdemonstratethevisualtrackingaccuracytheactualmandrelpro,leTheactualmandrelpro,leThesecondsetofresultsdemonstratethedimensionalwasobtainedfromtheCNCprogramusedtomachineaccuracyofacomponentspunusingdataobtainedthemandrelTheerrorplotofFigureisshowninthroughvisualtrackingFigureNotethatintheerrorplot,thehorizontalaxisshowsthelengthalongthemandrelpro,leTheverticalaxisshowsthenormalpro,leerrorwithrespecttotheexactpro,leDimensionalAccuracyThreecomponentswerespunusingthethreesetsofdatadescribedinthelastsectionThespuncomponentisshowninFigureAhardenedsteeltoolofnoseradiusmmwasusedtospinthecomponentsoutofmmthickannealedaluminumdiscsIneachcasetheedgeofthecomponentwaspartedo,usingexactmandrelprofilerawdatamandrelprofilethesametoolatthesamemachinepositiontoavoidsegmentextractedmandrelprofileanyadjustmentsduringmeasurementusingDcoordinatemeasuringmachineZinmmFigure:Actual,rawdataandsegmentextractedmandrelpro,lessegextractedmandrelprofilerawdatamandrelprofileFigure:SpuncomponentexactprofilerawdataprofileMandrelprofilelength(mm)segmentextractedprofileFigure:ErrorplotofFigureVisualTrackingResultsTheresultsobtainedbyvisuallytrackingthemandrelpro,leisshowninFigureThreesetsofdataareplottedTherawtrackingdatawereobtainedbyrecordingthemachinepositionduringactivevisualtrackingEachrecordedpointwasjoinedbyastraightlinetoitsadjacentpointsThesegmentexZ(mm)tracteddatawereobtainedbyfurtherprocessingtherawdatabyapplyingthesegmentextractionalgoFigure:Comparisonofspunpro,lesrithmTherefore,itcontainsstraightlineandcirclesegmentsThesetwosetsofdataarecomparedwithSYSTEMICS,CYBERNETICSANDINFORMATICSVOLUMENUMBERwithaforcesensorusingsegextractionusingrawdataReferencesSJRoberandYCShin,”ModelingandcontrolofCNCmachinesusingaPCBasedopenarchitecturecontroller”,Mechatronics,vol,No,pp,GCOnwubolu,SAborhey,RSingh,HReddy,MPrasad,SKumarandSSingh,”DevelopmentofaPCBasedcomputernumericalcontroldrillingmachine”,ProcInstnMechEngrs,vol,PartB:JEngineeringManufacture,Componentprofilelength(mm)GVNenovandTSzecsi,”IncreasingCNCmaFigure:ErrorplotofFigurechinetoolproductivitybyusingtoolparttouchcontrol”,RoboticsandComputerIntegratedManufacturing,vol,pp,TheresultsfromDcoordinatemeasuringmachineJShenandSCastan,”AnoptimallinearoperisshowninFigureTheexactpro,lecorrespondsatorforstepedgedetection”,GraphModelsandtothecomponentspunusingthesamepartprogramImageProcess,vol,no,pp,MarusedtomachinethemandrelAppropriatetoolo,setswereusedtoaccountforthematerialthicknessandthetoolnoseradiusWhenusingrawdatatoDHana,,MTordonandJKatupitiya,”Enspinthecomponent,linearinterpolationwasusedtohancingobjectpro,leresolutionwhenusinglowmovefromonepointtoanotherInsegmentextractedresolutionmachinevisionforshearspinning”,pro,le,dependingonwhetherthesegmentwasacirProceedingofThethWorldMulticonferenceoncleorastraightline,circularandlinearinterpolationSystemics,CyberneticsandImformatics,volIII,wasusedAnerrorplotofFigureisshowninFigpp,JulyureInFigureitisclearlyshownthattheerrorofthecomponentproducedusingsegmentextractedJCanny,”Acomputationalapproachtoedgedepro,leismaintainedbelowµmAsigni,cantfactection”,IEEETransactionsonPatternAnalytorthata,ectsthedimensionsofthespuncomponentsisandMachineIntelligence,PAMI(),ppis’springback’e,ectduetoelasticityThespring,backissigni,cantlya,ectedbythetoolpathHowABeghdadiandALeNegrate,”Contrasteneverthereisnotenoughdataavailableonthespringhancementtechniquebasedonlocaldetectionofbacke,ectsofshearspinningedges”,ComputerVision,GraphicsandImageProcessing,vol,pp,ConclusionFKammounandJPAstruc,”Optimumedgedetectionforobjectbackgroundpicture”,ThisstudydemonstratedamethodtoimplementanCVGIP:GraphicalModelsandImageProcessing,externalaxiscontrolsystemthatcanbeusedinanvol,No,pp,JanuaryactivesenseinrealtimeThedevelopedsystemwasMHFWilkinson,”Optimizingedgedetectorsusedtovisuallytrackapro,lemountedonaCNCforrobustautomaticthresholdselection:copinglathemachineThescanningmethodeliminatesthewithedgecurvatureandnoise”,GraphicalModelsparallaxerrorbyactivelyaligningthelineofsightofandImageProcessing,vol,pp,thecamerawiththepointofinterestTheinaccuraciesofimageresolutiondoesnota,ecttheaccuracyofSKalpakcioglu,”AstudyofshearspinnabilitythedataobtainedthroughvisualtrackingAlthoughofmetals”,JournalofEngineeringforIndustry,visualfeedbackisused,thesystempredominantlyoppp,NovembereratesinthemachinecoordinatesystemThusthescanningdataisdirectlyavailableinmachinecoordinatesnotinimagecoordinatesTheaxiscontrolsystemcanbeusednotonlyforvisualscanning,butalsofortactilescanningbyreplacingthevisionsystemSYSTEMICS,CYBERNETICSANDINFORMATICSVOLUMENUMBER

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