五轴可重构机床的控制和发展外文文献翻译

外文文献HindawiPublishingCorporationJournalofRoboticsVolume2011,ArticleID583072,9pagesdoi:10.1155/2011/583072ResearchArticleDevelopmentandControlofa5-AxisReconfigurableMachineToolZ.M.BiDepartmentofEngineering,IndianaUniversity—PurdueUniversityFortWayne,FortWayne,IN46805-1499,USACorrespondenceshouldbeaddressedtoZ.M.Bi,biz@Received13January2011;Revised19March2011;Accepted4May2011AcademicEditor:YangminLiThedevelopmentofahybridreconfigurablemachinetoolhasbeenintroduced.Themachinetoolconsistsofatripod-basedparallelkinematicmachine(PKM)modulewiththreedegreesoffreedom(DOF)andaseriallinearX-YtablewithtwoDOF.ThePKMisinstalledonagantrysystemwhichiscapableofreconfiguringitspositionandorientation.Inthedesignoftripod-basedparallelmechanism,apassivelinkisusedtoenhancethestiffnessandincreasetheworkingload.Toavoidthebuildupoftheheatoftheextensiveactuation,threejointsareactuatedviatheactuatorswithaconstantlength.ThegeometriesofthePKMhavebeenoptimizedforthebestandhighestaccuracy.Inthispaper,itscontrolsystemandtheprototypingdevelopmentarefocused.Anopenarchitectureisapplied,thecontrolmethodologiesaredevelopedandvalidated,andthecorrespondingsoftwaretoolshavebeenimplementedforthesoftwarereconfigurationofthecontrolsystem.IntroductionTheglobalizationofthemanufacturingenvironmentbringsuncertaintiesandturbulencesofcustomers’requirementsandmanufacturingresources.Reconfigurablemanufacturingsystem(RMS)paradigmbecomesaneffectivemeanstoincreasethecompetitivenessandadaptabilityofmanufacturingsystems.AnRMSconsistsofmodularcomponentsthatcanbearrangedtomeetthemachiningneeds(recon-figuration)withminimalornonrecurringcost.Theabilitytoreconfiguremachinesallowsaquickramp-upandrobustnesstoadaptvariouschangesinadynamicproductionenviron-ment.Productionmachineryisusuallyspecializedandverycapitalintensive.OtherbenefitsofanRMSisitspotentialtoreducetheunitcostofmachining;thesamesystemcanservefordifferenttasksand,thus,increasetheutilizationofresources,andthemachinemoduleswithacertainvolumemakeitpossibletobefabricatedandassembledinamassproductionmode.Thebasicstrategytomakeasystemreconfigurableisthemodularizationofsystem.Undermodularizedarchitecture,thesystemisformedfromasetofmodules.Thesemodulescanbeconnectedonewithanotherinterchangeably,andvarioussystemconfigurationscanbegeneratedbyusingdifferenttypesofmodules,changingthenumberofmodules,orchangingthetopologyofmoduleconnections.Eachconfigurationcanbespeciallydesignedtomeetthegivenrequirementsoptimally[1].Systemmodlarizationhasbeenwellrecognizedinmachinetoolindustry.Modularmachinetoolshavebeenonthemarketforafewofdecades.Theinternationalstandardsbecameavailabletomachinemod-ulesintheseventies[2].Researchershavemadecontinuouseffortinimprovingmodularmachinetools.Forexample,HannoverUniversityinitializedaprojectcalledModularSynthesisofAdvancedMachineTools(MOSYN)tosupportthedesignofcustomer-specificconfigurationsofmodularmachinetools[3].Nevertheless,itisworthtonotethattheprimaryobjectiveofthemachine-toolbuilderstomodularizetheirproductsistoproducethevariants;onotherhand,machine-toolusersstillpurchasethesystemswithaspecificconfiguration,andthesesystemsarerarelyreconfiguredaftertheirinstallments.Differingfromtraditionalmodularmachinetools,thereconfigurablemachinetoolattheUniversityofMichiganaimsatmodularity,integrability,customization,convertibility,anddiagnosability.Thesystemisdesignedtoreconfigurefrequentlyinadynamicenvironment[4-6].Unfortunately,thedesignconceptwasnotfullyimplemented,andsomeobstaclessloweddowntheirresearchanddevelopment[7].ThereconfigurableParallelKinematicMachine(PKM)isanotheralternativetoreconfiguremachinetools[8-10].Theoretically,PKMshavethepotentialstoachievehigherspeed,higheraccuracy,anddealwithaheavierload.However,thecharacteristicsofthePKMshavenotbeenwellstudied.MostofthecommerciallyavailablePKMsarehigh-costmachinesthatprovideloweraccuracythanconventionalmachinetools[7,11].MorestudiesareondemandtodevelopcompetitivePKMs.Forexample,Zhaoetal.[12]introducedanewparallelsimulatorwithsixdegreesoffreedom(DOF);thisnewPKMadoptsredundantactuationstoincreasethecapacitytoresistexternalloadandprolongtheactuators’lifetime.Redundancyofinversekinematicsforaredundantrobotisoftenaddressedbythepseudoinversemethod;Wangetal.expandedthismethodasaresolutionfortheredundantrelationsatvelocityandaccelerationlevels,socalledclosed-loopinversekinematicsalgorithmwasproposedtocontrola7-DOFredundantPKM[13].YunandLidevelopedthestiffnessmodelsfortheflexurehinges[14];theirworkhasitssignificanceinpredictingthedeflectionsandimprovingtheprecisionofPKMs.Researchershavecontinuedinmakingprogressonreconfigurableroboticsystems.Forexample,atypeofsquare-cubic-cellmodulehasbeendesignedasthebasicelementtobuildvariousroboticconfigurationsfordifferentapplication.Thetargetedconfigurationscanbeopenloop,closedloop,oracombinationofboth[15].Todevelopacost-effectivePKMmachinetool,thetripod-basedPKMisfocusedduetoitstwosignificantmerits,thatis,theversatilityandthebenefitsofaclosed-loopmechanism.Tripod-basedPKMsarethemostversatileoneamongtheexistingPKMs.Atripod-basedPKMtypicallypossessesthreeDOF.Dependingonitsstructure,itcanproduceanend-effectormotionwiththepurerotation,thepuretranslation,oracombinationofrotationandtranslation.Tripod-basedPKMscanperformmanydifferentmachiningoperationssincethemajorityofthemachiningoperationsrequireamotionwithfiveorlessDOF[9].Atripod-basedPKMcanbeusedasastandalonemachineoramoduleinasystem.Asastand-alonemachine,itcanbeasubstitutionofatraditionalmachinetoolwiththreeorlessDOF.Asasystemmodule,itcanbecombinedwithotheractuatedmodulesorsubsystems.Anewtripod-basedmachinewithapassiveleghasbeenproposedbytheauthor,andthedetailsofdesignmethodologiesandassistivedesigntoolboxhavebeenreported[16,17].Inthispaper,thecontrolmethodandimplementationofthismachinetoolwillbefocused.Theremainderofthepaperisorganizedasfollows.InSection2,thehybridmachinestructureisintroduced,theparallelstructureforpositioningisspeciallyexamined,anditskinematicmodelisoverviewed.InSections3and4,therequirementsofsystemcontrolarediscussed,andcontrolarchitectureisproposedaccordingly.Thecontrolmodelisdevelopedforthemachinetool,andtheimplementationofsystemcontrolisdiscussed.InSection5,acalibrationapproachforsystemreconfigurationisintroduced.FinallyinSection6,theresearchworkspresentedinthispaperaresummarized.StructureofFive-DOFReconfigurableMachineToolFigures1(a)and1(b)haveillustratedthevirtualmodelandphysicalmodelofthenewhybridreconfigurablemachinetool,respectively.Thismachinetoolconsistsofthreemodules:atripodtool,anX-Ytable,andareconfigurablearch.Thismachinetoolishybrid,thepositioningstructureisatripod-basedPKMwiththreeDOF,andtheorientingstructureisaserialwristwithtwoDOF.Thetripod-basedPKMisthemostimportantmodule.Themodularizedtripod-basedPKMincludesthreelinearactuators;theseactuatorscanbereconfiguredandintegratedwiththecustomisablebaseandend-effectorplatforms.Thegeometriesofthebaseandend-effectorplatformscanchangethebehavioursoftheparallelstructuresignificantly.Thetripod-basedPKMstructureisexpectedtoprovidetherotationsaboutXaxisandYaxisandthetranslationalongheZaxis.ReconfigurabilityofthemachinetoolcanbefurtherenhancedbytheadjustmentsoftheX-Ytableandreconfigurablearch.Bothofthemarereconfigurable.TheX-YtableprovidesvariousmotionrangesoftranslationalongXandYaxes,anditsheightalongtheZaxiscanbereconfiguredoffline.Thearchisanassemblyofthreecomponents:twoverticalcolumnsandahorizontalbeam.Theorientationofthehorizontalbeamcanbereconfiguredtoaccommodatethechangesoflocationandorientationoftheworkingvolume.Thevariationsofthereconfigurablemachinetoolarefromsomecustomerizedmodulesinthesystem.Thedimensionsofthesemodulessuchasbinarylegsandtheplatformscanbecustomizedbasedonthegiventask.Theadjustablearchandthex-ytableallowformanyconfigurationstomeetdifferentmanufacturingrequirements,forexample,changingfromaverticalconfigurationatvariousdiscreteanglestowardsahorizontalconfiguration,ifrequired.Systemcontrolsoftwareisalsoreconfigurabletorepresentacorrectkinematicbehaviourofthereconfiguredmachinetool.Thekeytothisreconfigurationisthequickverificationofthenewmachinegeometry.Insteadoflengthycalibrationofthemachine,onlyaquickmeasurementofafewreferencepointsisrequired,andthecalibrationofthemachineisaccomplishedinthecontrollerinternally.3.Tripod-BasedPKMThetripod-basedPKMofthemachinetoolisparameterizedinFigure2.Therearethreeplatforms:baseplatform,middleplatform,andend-effectorplat-form.Thebaseplatformisfixedontheground.Themiddleplatformistosupportguide-wayofactiveleg.Theend-effectorplatformistomountatoolorgripper.Apassivelinkisinstalledbetweenthemiddleplatformandtheend-effector.Activelegisconnectedtotheend-effectorplatformbyasphericaljointat,andtotheslideoftheactiveprismaticjointbyauniversaljointatD.Thepassivelegisfixedonthemiddleplatformatoneend,andconnectedtotheend-effectorplatformbyauniversaljointattheotherend.Theparametersforthedescriptionofthetripodmachinetoolareasfollows:theangleαi(i=1,2,3)betweenOBandx,theangle(i=1,2,3)betweenandx,theradiusofthebaseplatform,theradiusoftheend-effectorplatform,thedirectionofaguide-way,andthelengthofanactiveleg.TheDOFofthetripod-basedPKMcanbecalculatedasf=6×(n−1)−×=3,(1)wheref:DOFofthemechanism,n:thenumberofrigidbodiesincludingthebase,ji:thenumberofjointswithi-DOF.Notethatthetripod-basedPKMhas8rigidbodies,3prismaticjoints,3rotationaljoints,and3sphericaljoints.Thecompletedescriptionofthemotionofarigidbodyrequiresthreerotationalparameters(θx,θy,θz)andthreetranslationalparameters(x,y,z).However,x-andy-translationsandz-rotationareeliminatedbecauseofthepassivelink.Therefore,themotionoftheendeffectorcanbefullydescribedbythreeindependentvariablesθx,θy,andz,whereθxandθyaretherotationsaboutxandy,andzisthetranslationalongz.Thepostureoftheendeffectortoolisrepresentedby,(2)whereTisthepostureoftheend-effectorwithrespectto{O—xyz}.,(3)istherotationalmatrixoftheendeffector.Pe=[00z]isthecentralpositionOoftheendeffector.Whentherequiredpositionoftheend-effectortoolisspecified,inversekinematicsistofindthejointdisplacements.Assumethatthejointdisplacementofactiveprismaticjointiisu,itcanbederivedbasedonthefactthatthelengthofanactivelinkisfixed,thus,,(4)where,(5)Notethatthesolutionofufrom(4)shouldbeexaminedtoensurenoneofactiveorthepassivejointsexceedsitsmotionlimit.3.1.TaskandJointWorkspace.WorkspaceisanimportantcharacteristictodescribetheperformanceofaPKM.Workspaceisusuallydefinedasthesetofreachablepointsofthetoolcenterpoint(TCP)intheCartesiancoordinatesystem.Itcanbedeterminedbytheinversekinematicsolvernumerically,anexampleoftaskworkspacehasbeenillustratedinFigure3(a)forthismachinetool.Motionrangesofjointshaveusuallybeengivenforthereconfigurablemachinetool.However,whetherornotajointcouldbemovedfreelyoveritsmotionrangedependsonthestructureofthePKMandtheconfigurationofthePKMatacertainposition.ThePKMistotransferjointmotionsintothemotionofTCP.Anewconceptcalledjointworkspaceisproposedtomeasuretheefficiencyofthistransformation[18].ThesolvertoforwardkinematicsisneededtoacquirethejointworkspaceofaPKM.Wehaveformulatedtheforwardkinematicproblemasapolynomialequationwhosecoefficientscanbedeterminedautomatically.AsshowninFigure3(b),anexampleofthejointworkspacehasbeenillustratedfortheprototypedPKM.3.2.DeflectionunderExternalLoads.DeflectionoftherigidbodiesunderaninternalorexternalloadcausespositionalandorientationalerrorsoftheTCP.StiffnessisdefinedtomeasurethecapabilityofaPKMtoresistthedeflection.SystemstiffnessalongallofthesixCartesianmotionaxesisevaluatedbasedonakinetostaticmodel.Figure4showsanexampleofthestiffnessdistributionalongallofthesixmotionaxes,respectively,foracross-sectionwherealloftheactivejointsareinthemiddleoftheirmotionranges.3.3.EstimationofDrivingForces.SincealloftheexistingPKMsusekinematiccontrol,adynamicmodelofaPKMbecomeslessimportant.However,atypicalrobotictasknotonlyhastherequirementsofagivenmotiontrajectorybutalsotherequirementsofaworkingload.Adynamicmodelwillbeneededtodeterminehowanexternalloadiscarriedoutbythedrivingforcesattheactuators.Atanextremecasewhentheexternalloadbecomescritical,thedynamicmodelisrequiredtoestimateifanactuatedjointhasthesufficientdrivingforcetoresisttheexternalload.AdynamicmodelbasedonNewton-Eulerapproachhasbeendeveloped.Themodelingprocedureisasfollows:(i)thedisplacements,velocities,andaccelerationsofthejointmotionsareobtainedfromaninversekinematicmodelunderthegivenend-effectormotion;(ii)thevelocitiesandaccelerationsofthejointsandmasscentersofallbodiesarederivedsequentially;(iii)theNewton’slawandEuler’sequationareappliedtocalculateinertiaforces/moments,andtheequilibriumequationsaredefinedforeachofbodies;(iv)thedynamicmodelofthesystemisassembledfromtheequilibriumequationsofthebodies;(v)thedynamicmodelissolvedtogettheforces/torquesofjoints.Thedrivingforcesoftheactuatedjoints,aswellasthereactionforcesonanyofpassivejoint(s),canbeanalyzed.Figure5hasshownanexampleofthedrivingforcescorrespondingtoagivenTCPmotion.ControlArchitectureandModelAftersystemreconfiguration,themachiningoperationneedstocontrolthecomponentsincludingthreelinearactuators,thespindleontheend-effectortool,andtwolinearactuatorsontheX-Ytable.Sincethereconfigurablemachineisahybrid,themotionsofthesecomponentsarecoupledwhenthemotionofthetaskisgiven.ThecontrolarchitectureforthereconfigurablemachinetoolisshowninFigure6.Themotionofthetripod-basedPKMlinksallofthecontrolexpectationsofthesystemcomponentsincludingthetripodtool,thespindle,andtheX-Ytable.ThedeterminationofthefeeddepthisbasedontheZtranslationsofbothfromthespindleandthetripodtool.ThecoordinatesoftheX-YtablemustcompensatetheXandYdisplacementscausedbytherotationofthespindleaboutXandY.Whenthemachineissetattheverticaltoolorientation,themachineanditscontrolbehavelikearegular5-axismachinewithatiltingandpivotingtoolhead.ThetoolpathisgeneratedintheCartesianspace,andpostprocessedwithagenericCAMpackagefora5-axismachine.Theoperation,programming,andcontrolofthetripodmodulearetransparenttotheuser.Thelastthreecomponentsofamachinepositioningcommand,Z,A,andBareusedtorepresentthedisplacementsofthreeactuatedjointsfromtheinversekinematics.WhenthemachineisconfigureddifferentlyfromtheVerticaltoolaxis,additionaltransformationshavetobecarriedout.Forthecalculationsofgeneraltransformations,thehomogeneouscoordinatesareused,whichwereoriginallydevelopedforrobotmanipulatorcontrol[18].Notethatanofflinesimulationofmachiningprocessishelpful.Whentheheadangleisgettingclosertothehorizontal,theworkingenvelopeisdegenerating.Inthehorizontalposition,themachine“looses”adegreeoffreedom,theZtoolaxismovementisintheTable’sX-Yplane.References[1]Z.M.BiandW.J.Zhang,“Modularitytechnologyinmanufacturing:taxonomyandissues,”InternationalJournalofAdvancedManufacturingTechnology,vol.18,no.5,pp.381–390,2001.[2]Z.M.Bi,S.Y.T.Lang,W.M.Shen,andL.Wang,“Reconfigurablemanufacturingsystems:thestateoftheart,”InternationalJournalofProductionResearch,vol.46,no.4,pp.967–992,2008.[3]D.Sniegulska-Gradzka,M.Klasztorny,andM.Szefarczyk,“Anapproximatemethodfordeterminingstaticanddynamicstiffnessofmachinetoolswithrollingguideways,”ArchivesofCivilandMechanicalEngineering,vol.4,no.2,2004.[4]Y.Koren,“Willindust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