Five-axis milling machine tool__ kinematic chain d

InternationalJournalofMachineTools&Manufacture42(2002)505–520Five-axismillingmachinetoolkinematicchaindesignandanalysisE.L.J.Bohez*DepartmentofDesignandManufacturingEngineering,AsianInstituteofTechnology,P.O.Box4,KlongLuang,12120Pathumthani,ThailandReceived23May2000;receivedinrevisedform12September2001;accepted13September2001AbstractFive-axisCNCmachiningcentershavebecomequitecommontoday.ThekinematicsofmostofthemachinesarebasedonarectangularCartesiancoordinatesystem.Thispaperclassifiesthepossibleconceptualdesignsandactualexistingimplementationsbasedonthetheoreticallypossiblecombinationsofthedegreesoffreedom.Someusefulquantitativeparameters,suchastheworkspaceutilizationfactor,machinetoolspaceefficiency,orientationspaceindexandorientationangleindexaredefined.Theadvantagesanddisadvantagesofeachconceptareanalyzed.Criteriaforselectionanddesignofamachineconfigurationaregiven.NewconceptsbasedontheStewartplatformhavebeenintroducedrecentlyinindustryandarealsobrieflydiscussed.2002ElsevierScienceLtd.Allrightsreserved.Keywords:Five-axis;Machinetool;Kinematicchain;Workspace;CNC;Rotaryaxis1.IntroductionThemaindesignspecificationsofamachinetoolcanbededucedfromthefollowingprinciples:
Thekinematicsshouldprovidesufficientflexibilityinorientationandpositionoftoolandpart.
Orientationandpositioningwiththehighestposs-iblespeed.
Orientationandpositioningwiththehighestposs-ibleaccuracy.
Fastchangeoftoolandworkpiece.
Savefortheenvironment.
Highestpossiblematerialremovalrate.Thenumberofaxesofamachinetoolnormallyreferstothenumberofdegreesoffreedomorthenumberofindependentcontrollablemotionsonthemachineslides.TheISOaxesnomenclaturerecommendstheuseofaright-handedcoordinatesystem,withthetoolaxiscorre-spondingtotheZ-axis.Athree-axismillingmachinehasthreelinearslidesX,YandZwhichcanbepositionedeverywherewithinthetravellimitofeachslide.Thetoolaxisdirectionstaysfixedduringmachining.Thislimits*Tel.:[phone];fax:[phone].E-mailaddress:[e-mail](E.L.J.Bohez).0890-6955/02/$-seefrontmatter2002ElsevierScienceLtd.Allrightsreserved.PII:S0890-6955(01)00134-1theflexibilityofthetoolorientationrelativetothework-pieceandresultsinanumberofdifferentsetups.Toincreasetheflexibilityinpossibletoolworkpieceorien-tations,withoutneedofre-setup,moredegreesoffree-dommustbeadded.Foraconventionalthreelinearaxesmachinethiscanbeachievedbyprovidingrotationalslides.Fig.1givesanexampleofafive-axismillingmachine.Fig.1.Five-axismachinetool.506E.L.J.Bohez/InternationalJournalofMachineTools&Manufacture42(2002)505–5202.KinematicchaindiagramToanalyzethemachineitisveryusefultomakeakinematicdiagramofthemachine.Fromthiskinematic(chain)diagramtwogroupsofaxescanimmediatelybedistinguished:theworkpiececarryingaxesandthetoolcarryingaxes.Fig.2givesthekinematicdiagramofthefive-axismachineinFig.1.Ascanbeseenthework-pieceiscarriedbyfouraxesandthetoolonlybyoneaxis.Thefive-axismachineissimilartotwocooperatingrobots,onerobotcarryingtheworkpieceandonerobotcarryingthetool.Fivedegreesoffreedomaretheminimumrequiredtoobtainmaximumflexibilityintoolworkpieceorien-tation,thismeansthatthetoolandworkpiececanbeorientedrelativetoeachotherunderanyangle.Theminimumrequirednumberofaxescanalsobeunder-stoodfromarigidbodykinematicspointofview.Toorienttworigidbodiesinspacerelativetoeachother6degreesoffreedomareneededforeachbody(toolandworkpiece)or12degrees.Howeveranycommontrans-lationandrotationwhichdoesnotchangetherelativeorientationispermittedreducingthenumberofdegreesby6.Thedistancebetweenthebodiesisprescribedbythetoolpathandallowseliminationofanadditionaldegreeoffreedom,resultinginaminimumrequirementof5degrees.3.LiteraturereviewOneoftheearliest(1970)andstillveryusefulintro-ductionstofive-axismillingwasgivenbyBaughman[1]clearlystatingtheapplications.TheAPTlanguagewasthentheonlytooltoprogramfive-axiscontouringappli-cations.TheproblemsinpostprocessingwerealsoFig.2.Kinematicchaindiagram.clearlystatedbySim[2]inthoseearlierdaysofnumeri-calcontrolandmostissuesarestillvalid.BoydinRef.[3]wasalsooneoftheearlyintroductions.Beziers’book[4]isalsostillaveryusefulintroduction.Held[5]givesaverybriefbutenlighteningdefinitionofmulti-axismachininginhisbookonpocketmilling.Arecentpaperapplicabletotheproblemoffive-axismachinework-spacecomputationisthemultiplesweepingusingtheDenawit-HartenbergrepresentationmethoddevelopedbyAbdel-MalekandOthman[6].Manytypesanddesignconceptsofmachinetoolswhichcanbeappliedtofive-axismachinesarediscussedinRef.[7]butnotspecificallyforthefive-axismachine.ThenumberofsetupsandtheoptimalorientationofthepartonthemachinetableisdiscussedinRef.[8].AreviewaboutthestateoftheartandnewrequirementsfortoolpathgenerationisgivenbyB.K.Choietal.[9].GraphicsimulationoftheinteractionofthetoolandworkpieceisalsoaveryactiveareaofresearchandagoodintroductioncanbefoundinRef.[10].4.Classificationoffive-axismachines’kinematicstructureStartingfromRotary(R)andTranslatory(T)axesfourmaingroupscanbedistinguished:(i)threeTaxesandtwoRaxes;(ii)twoTaxesandthreeRaxes;(iii)oneTaxisandfourRaxesand(iv)fiveRaxes.Nearlyallexistingfive-axismachinetools