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

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IntJAdvManufTechnol199713658-6651997Springer-VerlagLondonLimitedTheInternationalJournalofRdvancedmanufacturinglechnologgDevelopingaPostprocessorforThreeTypesofFive-AxisMachineToolsR.-S.LeeandC.-H.SheDepartmentofMechanicalEngineering,NationalChengKungUniversity,Tainan,Taiwan,RepublicofChinaThispaperpresentsapostprocessorcapableofconvertingcutterlocationCLdamtomachinecontroldataforthreetypicalfive-axismachinetoolstoestablishaninterfacebetweencomputer-aidedmanufacturingCAMsystemsandnumericallycontrolledNCmachines,TheanalyticalequationsforNCdataareobtainedusingthehomogeneouscoordinatetrans-formationmatrixandinversekinematics.Inaddition,thedevelopedpostprocessormethodisimplemenwdthroughatrial-cutonafive-axismachineandverifiedonthecoordinatemeasurementmachine.Experimentalresultsconfirmedtheeffectivenessoftheproposedpostprocessormethodwhichcanbeusedtointegratethevariousfive-axismachinetoolsemployedinmanufacturingsystems.KeywordsCoordinatetransformationmatrix;Cutterlocationdata;Five-axismachines;NCprogramming;Postprocessor1.IntroductionFreeformsurfacesorsculpturedsurfaceshavefoundextensiveindustrialapplications,suchasinautomobilebodies,shiphullsandaerospaceparts.ThemouldorstampingdieusedtocreatesuchapartisusuallymachinedusingnumericallycontrolledNCmachinetools.Theconventionalwayofmachiningfree-formsurfacesisbyusingathree-axismachinetoolwithaballend-mill.Three-axismachinetoolscannotchangethetoolorientation,soafive-axismachinetoolisintroducedtosetthecuttingtoolinanappropriateorientationforefficientmachin-ing.Withtherapidlyadvancingcomputertechnology,commer-cialCAD/CAMsystemscandesignfreeformsurfacesandgenerateeitherthethree-axisorfive-axistoolpath.ThecutterlocationCLdata,composedofcuttertippositionandthetoolorientation,canthenbedirectlyobtainedfromaCADmodelofaproductdesigncreatedintheCAD/CAMsystems.However,difficultyfrequentlyarisesincommunicationbetweentheCAMsystemsandtheNCmachinetools,especiallywhenCorrespondenceandoffprintrequeststoProfessorRong-SheanLee,DepartmentofMechanicalEngineering,NationalChengKungUniver-sity,Tainan,Taiwan70101,RepublicofChina.variousmachinetoolsareemployed.TheinterfacethatlinkstheCAMsystemsandNCmachinesiscalledthepostprocessoranditconvertsCLdatatomachinecode.Essentially,differentcombinationsofmachinetoolandcontrolunitrequiredifferentpostprocessors.Consequently,amanufacturingsystemwithavarietyofmachinetoolsrequiresseveralpostprocessors.Variousstudieshaveaddressedtheissueofdevelopingpostprocessorsformachinetools.BediandVickers[1]developedapostprocessorprogramforFANUC6MBmachinetool.Balaji[2]presentedthedevelopmentandimplementationofapostprocessorbyconvertingAPTsourcecodestoamachinecodeformat.LinandChu[3]derivedtheNCdataformachinetoolstomanufacturecamswithfiat-facefollowersusingamodifiedDenavit-HartenbergD-Hnotation.However,theaboveworksareonlyrelatedtothree-axismachining.Inaddition,sincethetoolaxisorientationisfixedforathree-axismachinetool,thetransformationfromCLdatatoNCdataisstraightforwardandnoadditionalcoordinatetransformationtechniqueisnecessaU.Tofulfiltheindustrialdemandforgeometricvarietyandhighprecision,theuseofmulti-axismachininghasincreased,especiallyformachiningsculpturedsurfaces.SuhandLee[4]developedafour-axisCAMsystemincludingCLdatagenerationandpostprocessing.Vickersetal.[5]usedaG-surfmethodtodefineandmachinecompoundcurvaturesurfacesonthree-,four-andfive-axismachinetool.TakeuchiandWatanabe[6]proposedafive-axiscontrolcollision-freetoolpathandpostprocessormethodfortwotypesofmachineconfiguration.SakamotoandInasaki[7]classifiedtheconfigurationoffive-axismachinetoolsintothreetypes.However,theanalyticalNCdataexpressionisnotavailableintheaboveworks.LinandTsai[8]recentlyusedtheD-HnotationtogenerateanNCdataequationformachiningaspatialcamonafour-axismachinetool.Furthermore,Warkentinetal.[9]presentedatechniqueformachiningsphericalsurfaces.Intheirwork,thedesiredNCdataisderivedforonlyoneconfigurationoffive-axismachine.Meanwhile,Raoetal.[10]developedtheprincipal-axismethodtomachinecomplexsurfacesontwoconfigurationsoffive-axismachines.Nevertheless,onlyrotationalmovementsweredetermined.Translationalmove-mentsforthemachinetoolwerenotinvestigated.Sincetheremaybeaconsiderablenumberofcombinationsoffive-axisDevelopingaPostprocessorfirFive-AxisMachineTools659machinetoolconfiguration,thepostprocessorwillinevitablybedevelopedindividually[6].However,accordingtotheclassificationproposedbySakamotoandInasaki[7],thestructureofthefive-axismachinetoolcanbedividedintothreebasictypes.NoneoftheabovestudieshasderivedthecompleteanalyticalequationsforNCdatawhichcontainthreelinearmotionsandtworotarymotions.Thisworkaimstodevelopapostprocessorforthreekindsoffive-axismachinetools,basedonthehomogeneouscoordinatetransformationmatrix.TheanalyticalequationsforNCdatacanbeobtainedbyequatingtheform-shapingfunctionmatrixandtheknownCLdataandsolvingthesimultaneousalgebraicequations.Moreover,themachinetoolsettingprocedureandthecharacteristicsfordifferentconfigurationsarediscussed.Toverifythevalidityandeffectivenessofthedevelopedpostprocessor,adesignedBeziersurfaceismachinedwithmodelmaterialonatypicalfive-axismachiningcentreandthenmeasuredonthecoordinatemeasurementmachineCMM.2.KinematicsModelMachinetoolsarearticulatedopenchainsofseriallyconnectedlinkswithjoints.Thejointsmayeitherberevoluteorprismatic.Actuationofarevolutejointrotatesthelinkaboutthejointaxis,whileactuationofaprismaticjointtranslatesthelinkalongthejointaxis.Toadequatelycontrolthepositionandorientationofthecuttingtoolandthemachinetool,akinemat-icsmodelestablishingthemathematicaldescriptionofthegeometryandmotionofamachinetoolisrequired.DenavitandHartenberg[11]firstintroducedthespatialtransformationbetweentwosuccessivelinkcoordinatesystemsusinga4x4homogeneouscoordinatetransformationmatrix,whichwaslateradoptedbyPaul[12].Itisaconventionalmodellingtechniqueusedformechanisms,robotics,erroranalysisandcomputervisions.Inthispaper,fourfundamentaltransformationmatricesusingPaul snotationareintroduced.TheycanbeexpressedasfollowsTransa,b,cii10RotX,0000RotY,0-SO0SORotZ,Oi110010000]CO-SOSOCO00OSO0l000CO0001-SO00CO000100011234Transa,b,cimpliesatranslationgivenbythevectoraibjck,andRotX,0,RotY,0,RotZ,0implyrotationsof0abouttheX,YandZcoordinateaxis,respectively;andCandSrefertocosineandsinefunctions,respectively.Thespatialtransformationfromonecoordinatesystemtoanothercoordinatesystemcanthereforebedecomposedbycombiningthefundamentaltransformationmatrices.3.DefinitionofCLDataforFive-AxisMachiningThecutterlocationdataforfive-axismillingconsistsofthepositionandorientationofthecutterwithrespecttotheworkpiececoordinatesystem,asshowninFig.1.Inthispaper,thepointvectoriswrittenas[QQyQ1]T,andvectorsoftheform[KxK,KzO]Tareusedtorepresentdirectionsforhomogeneouscoordinatenotation;thesuperscriptTdenotesthetransposedmatrix.Itisworthmentioningthatthesignificantcutterpositionisdefinedasthecuttercentretipandnotthecuttercontactpoint.Foragivenparametricdesignsurfacetobemachinedusingfive-axismillingwithageneralisedcuttingtooldefinedaccordingtoDIN66215whereanypointofthecuttingtoolcanbedefinedasthecontactpoint,theappropriateCLdatacanbedetermined[13]bydifferentialgeometryandthehomogeneouscoordinatetransformationmatrix.4.PostprocessorforFive-AxisMachiningTheCLfile,onceobtained,shouldbetransformedintofivereferenceinputsi.e.threelinearmotionsplustworotationalmotionsusingtheinversekinematicstransformationforcon-trollersofthefive-axismachine.ThistranslationisknownaspostprocessingandthetranslatingsoftwareiscalledtheZwThetoolaxisvector[KKyKzo]gTheworkpiecesurfaceThecuttertipcentre[QxeyQz1]TowFig.1.GeometricdefinitionofCLdata.Yw660R.-S.LeeandC.-H.ShexIxFig.2.Configurationforthreekindsoffive-axismachiningcentres.aTable-tiltingtype.bSpindle-tiltingtype.cTable/spindle-tiltingtype.postprocessor.Theinversekinematicstransformationdependsonthegeometricstructureofthefive-axismachinetoolused.Theoretically,therearenumerouscombinationstoyieldthefive-axismachinetoolconfiguration.However,inpractice,theconfigurationcanbeclassifiedintothreebasictypesaccordingtothedistributionofthetworotationalmovementunits[6,7]1.Table-tiltingwithtworotationsonthetable.2.Spindle-tiltingwithtworotationsonthespindle.3.Table/spindle-tiltingwithonerotationeachonthetableandspindle.Thepostprocessorforfive-axismachiningpresentedinthispaperisappliedtotheabovethreetypes.Moreover,thekinematicstructuresinFigs2ato2c,areselectedtodemon-stratethederivationprocedure.Inaddition,thetworotaryaxesareassumedtobecontinuouslyintersectedwitheachotherfortable-tiltingtypeandspindle-tiltingtypeofconfigurationstosimplifytheformulations.Generallyspeaking,tomachineaworkpieceonaCNCmachineaccordingtoapartprogram,acoordinatesystemandanaxisdesignationsystemmustfirstbeestablished.InadditiontothreelinearperpendicularaxesX,Y,Z,CNCmachinetoolsmayinvolverotarymotionaroundtherotationalaxes,whicharedesignatedbythecharactersA,B,andCtoindicatetherotarymotionsaroundtheX,Y,andZaxes,respectively.Therefore,thefive-axismachinetoolconfigurationinFigs2ato2ccanbecharacterisedbyX,Y,Z,A,CandX,Y,Z,A,B.Allthemovementsshouldbereferredtotheprogramcoordinatesystem,e.g.theG54-G59codeisusedtodefinetheprogramcoordinatesystemintheFANUCcontroller.Inmostcases,theprogramcoordinatesystemiscoincidentwiththeworkpiececoordinatesystemandisthusappliedinthispaper.4.1Table-TiltingTypeRegardingthetable-tiltingtype,Fig,3depictsrelevantcoordi-natesytems.CoordinatesystemsOwXwYwZwandOtXtY,Z,areattachedtotheworkpieceandthecuttingtool,repsectively.DevelopingaPostprocessorforFive-AxisMachine7bols661Cuttingtool\tOtiZwWorkpieceAOffsetvector-/Lse.v;Lzkq,pivotont,Fig.3.Coordinatesystemsoftable-tiltingtypeconfiguration.ThepivotpointRistheintersectionofthetworotaryaxes.TheoffsetvectorLxiLjLkasdeterminedfromoriginOwtopointRisrequiredforthecoordinatetransformation.Sincethestructuralelementsofthemachinetoolconsistofarotarytable,lineartable,machinebed,spindleandthecuttingtool,thegeneratingmotionofthemachinetool,whichdeterminesthedesignedcharacteristicsformachinetoolandisreferredtoastheform-shapingfunction[14],canbecharacterisedsequen-tiallystartingfromtheworkpieceandendingatthecuttingtool.ForthemachinetoolconfigurationshowninFig.2a,theconsecutivestructuralelementscanbedescribedaccordingtoFig.4.Consequently,therelativeorientationandpositionofthecuttingtoolwithrespecttotheworkpiececoordinatesystemcanbedeterminedbymultiplyingthecorrespondingfundamen-taltransformationmatricesinseries,andshouldbeequaltotheknownCLdata,[KKyKz0]Tand[QxQyQz1]T,respect-ively.Themathematicalexpressionisdescribedasfollows[KKyKz0]TTransLx,Ly,LzRotZ,-cRotX,-ATransP,p.,P[o01o]T5[QxQyQz1]TTransLx,Le,L0RotZ,-cRotX,--ATransP,,P[0001]T6wheredpaand4caretherotationanglesabouttheX,andZaxes,respectively,andpositiverotationisinthedirectiontoadvancearight-handscrewintheXandZaxisdirections.P,Py,ParetherelativetranslationdistancesoftheX,Y,andZtables,respectively.Multiplyingequations5and6,yieldsStructuralelementsWorkpiece[IPrimaryrotationonfixturetable[C-axisIISecondaryrotationonfixturetableA-axisXtable[ZtableIIMachinebedIIIIoogtooIFig.4.Relationshipofstructuralelementsoftable-tiltingtypecon-figuration.ixILxexClcl-PyCtASbcqyezSASc-ilLz-PySqb;PzCdAILy-PxsqbcPrcqbACqbcPzS SACc8Fromtheaboveequations,therotationanglesa,candtherelativetranslationdistancesPx,Py,Pzcanbesolved.Ontheotherhand,theX,Y,ZvaluesoftheNCdatainprogram-mingareobtainedusingequation6undertheconditionAqbc0,and[QxQyQz1]T[XYZ1]Tsincetheprogramcoordinatesystemiscoincidentwiththeworkpiececoordinatesystem.Thisleadsto[XYZl]T[LxP,LA-PyLzP1]T9Thus,thedesiredequationsforNCdataofthisconfigurationcanbeexpressedasfollowsabaarccosKs0--qbA--7010C6carctan2Kx,Ky-w--qbc--r11XLxP.Qx-L.Cqbc-Qy-LySdcLx12
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