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外文资料--Developing a Postprocessor for Three Types of Five-Axis Machine Tools.pdf

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外文资料--Developing a Postprocessor for Three Types of Five-Axis Machine Tools.pdf

IntJAdvManufTechnol199713658665©1997SpringerVerlagLondonLimitedTheInternationalJournalofRdvancedmanufacturinglechnologgDevelopingaPostprocessorforThreeTypesofFiveAxisMachineToolsR.S.LeeandC.H.SheDepartmentofMechanicalEngineering,NationalChengKungUniversity,Tainan,Taiwan,RepublicofChinaThispaperpresentsapostprocessorcapableofconvertingcutterlocationCLdamtomachinecontroldataforthreetypicalfiveaxismachinetoolstoestablishaninterfacebetweencomputeraidedmanufacturingCAMsystemsandnumericallycontrolledNCmachines,TheanalyticalequationsforNCdataareobtainedusingthehomogeneouscoordinatetransformationmatrixandinversekinematics.Inaddition,thedevelopedpostprocessormethodisimplemenwdthroughatrialcutonafiveaxismachineandverifiedonthecoordinatemeasurementmachine.Experimentalresultsconfirmedtheeffectivenessoftheproposedpostprocessormethodwhichcanbeusedtointegratethevariousfiveaxismachinetoolsemployedinmanufacturingsystems.KeywordsCoordinatetransformationmatrixCutterlocationdataFiveaxismachinesNCprogrammingPostprocessor1.IntroductionFreeformsurfacesorsculpturedsurfaceshavefoundextensiveindustrialapplications,suchasinautomobilebodies,shiphullsandaerospaceparts.ThemouldorstampingdieusedtocreatesuchapartisusuallymachinedusingnumericallycontrolledNCmachinetools.Theconventionalwayofmachiningfreeformsurfacesisbyusingathreeaxismachinetoolwithaballendmill.Threeaxismachinetoolscannotchangethetoolorientation,soafiveaxismachinetoolisintroducedtosetthecuttingtoolinanappropriateorientationforefficientmachining.Withtherapidlyadvancingcomputertechnology,commercialCAD/CAMsystemscandesignfreeformsurfacesandgenerateeitherthethreeaxisorfiveaxistoolpath.ThecutterlocationCLdata,composedofcuttertippositionandthetoolorientation,canthenbedirectlyobtainedfromaCADmodelofaproductdesigncreatedintheCAD/CAMsystems.However,difficultyfrequentlyarisesincommunicationbetweentheCAMsystemsandtheNCmachinetools,especiallywhenCorrespondenceandoffprintrequeststoProfessorRongSheanLee,DepartmentofMechanicalEngineering,NationalChengKungUniversity,Tainan,Taiwan70101,RepublicofChina.variousmachinetoolsareemployed.TheinterfacethatlinkstheCAMsystemsandNCmachinesiscalledthepostprocessoranditconvertsCLdatatomachinecode.Essentially,differentcombinationsofmachinetoolandcontrolunitrequiredifferentpostprocessors.Consequently,amanufacturingsystemwithavarietyofmachinetoolsrequiresseveralpostprocessors.Variousstudieshaveaddressedtheissueofdevelopingpostprocessorsformachinetools.BediandVickers1developedapostprocessorprogramforFANUC6MBmachinetool.Balaji2presentedthedevelopmentandimplementationofapostprocessorbyconvertingAPTsourcecodestoamachinecodeformat.LinandChu3derivedtheNCdataformachinetoolstomanufacturecamswithfiatfacefollowersusingamodifiedDenavitHartenbergDHnotation.However,theaboveworksareonlyrelatedtothreeaxismachining.Inaddition,sincethetoolaxisorientationisfixedforathreeaxismachinetool,thetransformationfromCLdatatoNCdataisstraightforwardandnoadditionalcoordinatetransformationtechniqueisnecessaU.Tofulfiltheindustrialdemandforgeometricvarietyandhighprecision,theuseofmultiaxismachininghasincreased,especiallyformachiningsculpturedsurfaces.SuhandLee4developedafouraxisCAMsystemincludingCLdatagenerationandpostprocessing.Vickersetal.5usedaGsurfmethodtodefineandmachinecompoundcurvaturesurfacesonthree,fourandfiveaxismachinetool.TakeuchiandWatanabe6proposedafiveaxiscontrolcollisionfreetoolpathandpostprocessormethodfortwotypesofmachineconfiguration.SakamotoandInasaki7classifiedtheconfigurationoffiveaxismachinetoolsintothreetypes.However,theanalyticalNCdataexpressionisnotavailableintheaboveworks.LinandTsai8recentlyusedtheDHnotationtogenerateanNCdataequationformachiningaspatialcamonafouraxismachinetool.Furthermore,Warkentinetal.9presentedatechniqueformachiningsphericalsurfaces.Intheirwork,thedesiredNCdataisderivedforonlyoneconfigurationoffiveaxismachine.Meanwhile,Raoetal.10developedtheprincipalaxismethodtomachinecomplexsurfacesontwoconfigurationsoffiveaxismachines.Nevertheless,onlyrotationalmovementsweredetermined.Translationalmovementsforthemachinetoolwerenotinvestigated.SincetheremaybeaconsiderablenumberofcombinationsoffiveaxisDevelopingaPostprocessorfirFiveAxisMachineTools659machinetoolconfiguration,thepostprocessorwillinevitablybedevelopedindividually6.However,accordingtotheclassificationproposedbySakamotoandInasaki7,thestructureofthefiveaxismachinetoolcanbedividedintothreebasictypes.NoneoftheabovestudieshasderivedthecompleteanalyticalequationsforNCdatawhichcontainthreelinearmotionsandtworotarymotions.Thisworkaimstodevelopapostprocessorforthreekindsoffiveaxismachinetools,basedonthehomogeneouscoordinatetransformationmatrix.TheanalyticalequationsforNCdatacanbeobtainedbyequatingtheformshapingfunctionmatrixandtheknownCLdataandsolvingthesimultaneousalgebraicequations.Moreover,themachinetoolsettingprocedureandthecharacteristicsfordifferentconfigurationsarediscussed.Toverifythevalidityandeffectivenessofthedevelopedpostprocessor,adesignedBeziersurfaceismachinedwithmodelmaterialonatypicalfiveaxismachiningcentreandthenmeasuredonthecoordinatemeasurementmachineCMM.2.KinematicsModelMachinetoolsarearticulatedopenchainsofseriallyconnectedlinkswithjoints.Thejointsmayeitherberevoluteorprismatic.Actuationofarevolutejointrotatesthelinkaboutthejointaxis,whileactuationofaprismaticjointtranslatesthelinkalongthejointaxis.Toadequatelycontrolthepositionandorientationofthecuttingtoolandthemachinetool,akinematicsmodelestablishingthemathematicaldescriptionofthegeometryandmotionofamachinetoolisrequired.DenavitandHartenberg11firstintroducedthespatialtransformationbetweentwosuccessivelinkcoordinatesystemsusinga4x4homogeneouscoordinatetransformationmatrix,whichwaslateradoptedbyPaul12.Itisaconventionalmodellingtechniqueusedformechanisms,robotics,erroranalysisandcomputervisions.Inthispaper,fourfundamentaltransformationmatricesusingPaulsnotationareintroduced.TheycanbeexpressedasfollowsTransa,b,cii10RotX,0000RotY,0SO0SORotZ,O°°i110010000COSOSOCO00OSO0l000CO0001SO00CO000100011234Transa,b,cimpliesatranslationgivenbythevectoraibjck,andRotX,0,RotY,0,RotZ,0implyrotationsof0abouttheX,YandZcoordinateaxis,respectivelyandCandSrefertocosineandsinefunctions,respectively.Thespatialtransformationfromonecoordinatesystemtoanothercoordinatesystemcanthereforebedecomposedbycombiningthefundamentaltransformationmatrices.3.DefinitionofCLDataforFiveAxisMachiningThecutterlocationdataforfiveaxismillingconsistsofthepositionandorientationofthecutterwithrespecttotheworkpiececoordinatesystem,asshowninFig.1.Inthispaper,thepointvectoriswrittenasQQyQ1T,andvectorsoftheformKxK,KzOTareusedtorepresentdirectionsforhomogeneouscoordinatenotationthesuperscriptTdenotesthetransposedmatrix.Itisworthmentioningthatthesignificantcutterpositionisdefinedasthecuttercentretipandnotthecuttercontactpoint.ForagivenparametricdesignsurfacetobemachinedusingfiveaxismillingwithageneralisedcuttingtooldefinedaccordingtoDIN66215whereanypointofthecuttingtoolcanbedefinedasthecontactpoint,theappropriateCLdatacanbedetermined13bydifferentialgeometryandthehomogeneouscoordinatetransformationmatrix.4.PostprocessorforFiveAxisMachiningTheCLfile,onceobtained,shouldbetransformedintofivereferenceinputsi.e.threelinearmotionsplustworotationalmotionsusingtheinversekinematicstransformationforcontrollersofthefiveaxismachine.ThistranslationisknownaspostprocessingandthetranslatingsoftwareiscalledtheZwThetoolaxisvectorKKyKzogTheworkpiecesurfaceThecuttertipcentreQxeyQz1TowFig.1.GeometricdefinitionofCLdata.Yw660R.S.LeeandC.H.ShexIxFig.2.Configurationforthreekindsoffiveaxismachiningcentres.aTabletiltingtype.bSpindletiltingtype.cTable/spindletiltingtype.postprocessor.Theinversekinematicstransformationdependsonthegeometricstructureofthefiveaxismachinetoolused.Theoretically,therearenumerouscombinationstoyieldthefiveaxismachinetoolconfiguration.However,inpractice,theconfigurationcanbeclassifiedintothreebasictypesaccordingtothedistributionofthetworotationalmovementunits6,71.Tabletiltingwithtworotationsonthetable.2.Spindletiltingwithtworotationsonthespindle.3.Table/spindletiltingwithonerotationeachonthetableandspindle.Thepostprocessorforfiveaxismachiningpresentedinthispaperisappliedtotheabovethreetypes.Moreover,thekinematicstructuresinFigs2ato2c,areselectedtodemonstratethederivationprocedure.Inaddition,thetworotaryaxesareassumedtobecontinuouslyintersectedwitheachotherfortabletiltingtypeandspindletiltingtypeofconfigurationstosimplifytheformulations.Generallyspeaking,tomachineaworkpieceonaCNCmachineaccordingtoapartprogram,acoordinatesystemandanaxisdesignationsystemmustfirstbeestablished.InadditiontothreelinearperpendicularaxesX,Y,Z,CNCmachinetoolsmayinvolverotarymotionaroundtherotationalaxes,whicharedesignatedbythecharactersA,B,andCtoindicatetherotarymotionsaroundtheX,Y,andZaxes,respectively.Therefore,thefiveaxismachinetoolconfigurationinFigs2ato2ccanbecharacterisedbyX,Y,Z,A,CandX,Y,Z,A,B.Allthemovementsshouldbereferredtotheprogramcoordinatesystem,e.g.theG54G59codeisusedtodefinetheprogramcoordinatesystemintheFANUCcontroller.Inmostcases,theprogramcoordinatesystemiscoincidentwiththeworkpiececoordinatesystemandisthusappliedinthispaper.4.1TableTiltingTypeRegardingthetabletiltingtype,Fig,3depictsrelevantcoordinatesytems.CoordinatesystemsOwXwYwZwandOtXtY,Z,areattachedtotheworkpieceandthecuttingtool,repsectively.DevelopingaPostprocessorforFiveAxisMachine7bols661Cuttingtool\tOtiZwWorkpieceAOffsetvector/L°se.vLzkq,pivotont,Fig.3.Coordinatesystemsoftabletiltingtypeconfiguration.ThepivotpointRistheintersectionofthetworotaryaxes.TheoffsetvectorLxiLjLkasdeterminedfromoriginOwtopointRisrequiredforthecoordinatetransformation.Sincethestructuralelementsofthemachinetoolconsistofarotarytable,lineartable,machinebed,spindleandthecuttingtool,thegeneratingmotionofthemachinetool,whichdeterminesthedesignedcharacteristicsformachinetoolandisreferredtoastheformshapingfunction14,canbecharacterisedsequentiallystartingfromtheworkpieceandendingatthecuttingtool.ForthemachinetoolconfigurationshowninFig.2a,theconsecutivestructuralelementscanbedescribedaccordingtoFig.4.Consequently,therelativeorientationandpositionofthecuttingtoolwithrespecttotheworkpiececoordinatesystemcanbedeterminedbymultiplyingthecorrespondingfundamentaltransformationmatricesinseries,andshouldbeequaltotheknownCLdata,KKyKz0TandQxQyQz1T,respectively.ThemathematicalexpressionisdescribedasfollowsKKyKz0TTransLx,Ly,LzRotZ,cRotX,ATransP,p.,Po01oT5QxQyQz1TTransLx,Le,L0RotZ,cRotX,ATransP,,P0001T6wheredpaand4caretherotationanglesabouttheX,andZaxes,respectively,andpositiverotationisinthedirectiontoadvancearighthandscrewintheXandZaxisdirections.P,Py,ParetherelativetranslationdistancesoftheX,Y,andZtables,respectively.Multiplyingequations5and6,yieldsStructuralelementsWorkpieceIPrimaryrotationonfixturetableCaxisIISecondaryrotationonfixturetableAaxisXtableZtableIIMachinebedIIIIoogtooIFig.4.Relationshipofstructuralelementsoftabletiltingtypeconfiguration.ixILxexClclPyCtASbcqyezSAScilLzPySqbPzCdAILyPxsqbcPrcqbACqbcPzSSACc8Fromtheaboveequations,therotationanglesa,candtherelativetranslationdistancesPx,Py,Pzcanbesolved.Ontheotherhand,theX,Y,ZvaluesoftheNCdatainprogrammingareobtainedusingequation6undertheconditionAqbc0,andQxQyQz1TXYZ1Tsincetheprogramcoordinatesystemiscoincidentwiththeworkpiececoordinatesystem.ThisleadstoXYZlTLxP,LAPyLzP1T9Thus,thedesiredequationsforNCdataofthisconfigurationcanbeexpressedasfollowsabaarccosKs0qbA7010C6carctan2Kx,Kywqbcr11XLxP.QxL.CqbcQyLySdcLx12

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