外文翻译--机器人控制和装配结合的机密机械手.doc

COMBINATIONOFROBOTCONTROLANDASSEMBLYPLANNINGFORAPRECISIONMANIPULATOORAbstractThispaperresearcheshowtorealizetheautomaticassemblyoperationonatwo-fingerprecisionmanipulator.Amulti-layerassemblysupportsystemisproposed.Atthetask-planninglayer,basedonthecomputer-aideddesign(CAD)model,theassemblysequenceisfirstgenerated,andtheinformationnecessaryforskilldecompositionisalsoderived.Then,theassemblysequenceisdecomposedintorobotskillsattheskill-decompositionlayer.Thesegeneratedskillsaremanagedandexecutedattherobotcontrollayer.Experimentalresulteshowthefeasibilityandefficiencyoftheproposedsystem.Keywords：ManipulatorAssemblyplanningSkilldecompositionAutomatedassembly1IntroductionOwingtothemicro-electro-mechanicalsystems(MEMS)techniques,manyproductsarebecomingverysmallandcomplex,suchasmicrophones,micro-opticalcomponents,andmicrofluidicbiomedicaldevices,whichcreatesincreasingneedsfortechnologiesandsystemsfortheautomatedassemblyhavebeenfocusedonmicroassemblytechnologies.However,microassemblytechniquesofhighflexibility,efficiency,andreliabilityskillopentofurtherresearch.Thispaperresearchestohowtorealizetheautomaticassemblyoperationonatwo-fingermicromanipulator.Amuli-layerassemblysupportsystemisproposed.Automaticassemblyisacomplexproblemwhichmayinvolvemanydifferentissues,suchastaskplanning,assemblysequencesgeneration,execution,andcontrol,etc.Itcanbesimplydividedintotwophases,theassemblyplanningandtherobotcontrol.Attheassembly-planningphase,theinformationnecessaryforassemblyoperation,suchastheassemblysequence,isgenerated.Attherobotcontrolphase,therobotisdrivenbasedontheinformationgeneratedattheassembly-planningphase,andtheassemblyoperationsareconducted.Skillprimitivescanworkastheinterfaceofassemblyplanningtorobotcontrol.Severalrobotsystemsbasedonskillprimitiveshavebeenreported.Thebasicideabehindthesesystemsistherobotprogramming.Robotmovementsarespecifiedasskillprimitives,basedonwhichtheassemblytaskismanuallycodedintoprograms.Withtheprograms,therobotiscontroltoassemblytasksautomatically.Askill-basedmicromanipulationsystemhasbeendevelopedintheauthorslab,anditcanrealizemanymicromanipulationoperations.Inthesystem,theassemblytaskismanuallydiscomposedintoskillsequencesandcompliedintoafile.Afterimportingthefileintothesystem,thesystemcanautomaticallyexecutetheassemblytask.Thispaperattemptstoexploreauser-friendly,andatthesametimeeasy,sequence-generationmethod,torelievetheburdenofmanuallyprogrammingtheskillsequence.Itisaneffectivemethodtodeterminetheassemblysequencefromgeometriccomputer-aideddesign(CAD)models.Manyapproacheshavebeenproposed.Thispaperappliesasimpleapproachtogeneratetheassemblysequence.Itisnotinvolvedwiththelow-leveldatastructureoftheCADmodel,andcanberealizedwiththeapplicationprogramminginterface(API)functionsgraphamongdifferentcomponentsisfirstconstructedbyanalyzingtheassemblymodel,andthen,possiblesequencesaresearched,basedonthegraph.Accordingtocertaincriterion,theoptimalsequenceisfinallyobtained.Todecomposetheassemblysequenceintorobotskillsequences,someworkshavebeenreported.InNnajietal.work,theassemblytaskcommandsareexpandedtomoredetailedcommands,whichcanbeasrobotskills,accordingtoapredefinedformat.ThedecompositionapproachofMosemannandwahlisbasedontheanalysisofhyperarcsofAND/ORgraphsrepresentingtheautomaticallygeneratedassemblyplans.Thispaperproposesamethodtoguidetheskilldecomposition.Theassemblyprocessesofpartsaregroupedintodifferentstartatateandtargetoftheworkflow,theskillgeneratorcreatesaseriesofskillsthatcanpromotetheparttoitstargetstate.Thehierarchyofthesystemproposedhere,theassemblyinformationonhowtoassembleaproductistransferredtotherobotthroughmultiplelayers.Tetoplayerisfortheassembly-taskplanning.TheinformationneededforthetaskplanningandskillgenerationareextractedfromtheCADmodelandaresavedinthedatabase.BaseontheCADmodel,theassemblytasksquencesaregenerated.Attheskill-decompositionlayer,tasksaredecomposedintoskillsequences.Thegeneratedskillsaremanagedandexecutedattherobotcontrollayer.2TaskplanningSkillsarenotuseddirectlyattheassembly-planningphase,theconceptofataskisused.Ataskcanfulfillaseriesofassemblyoperations,forexample,fromlocatingapart,throughmovingthepart,tofixingitwithanotherpart.Inotherwords,onetaskincludesmanyfunctionsthatmaybefulfilledbyseveraldifferentskills.Ataskisdefinedas:T=(BasePart；AssemblyPart；Operation)Based-partandAssembly-Partaretwopartsthatareassembledtogether.Base-partisfixedontheworktable,whileAssembly-Partishandledbyrobotsend-effectorandassembledontotheBase-Part.OperationdescribeshowtheAssembly-PartisassembledwiththeBase-Part；Operation=Intertion-T,serew-T,align-T,.Thestructureofmicropartsisusuallyuncomplicated,andtheycanbemodeledbytheconstructivesolidgeometry(CAG)method.Currently,manycommercialCADsoftwarepackagescansupport3DCSGmodeling.Theassemblymodelisrepresentedasanobjectthatconsistsoftwopartswithcertainassemblyrelationsthatdefinehowthepartsaretobeassembled.IntheCADmodel,therelationsaredefinedbygeometricconstraints.Thegeometricinformationcannotbeuseddirectlytoguidetheassemblyoperation-wehavetoderivetheinformationnecessaryforassemblyoperationsfromtheCADmodel.Throughsearchingtheassemblytreeandgeometricrelations(matesrelations)definedintheassemblysCADmodel,wecangeneratearelationgraphamongparts,forexample,Inthegraph,thenodesrepresenttheparts.Ifnodesareconnected,itmeansthatthereareassemblyrelationsamongtheseconnectednodes(parts).2.1MatingdirectionInCSG,therelationsoftwoparts,geometricconstraints,arefinallyrepresentedasrelationsbetweenplanesandlines,suchascollinear,coplanar,tangential,perpendicular,etc.Forexample,ashaftisassembledinahole.TheassemblyrelationsbetweenthetwopartsmayconsistofsuchtwoconstraintsascollinearbetweenthecenterlineofshaftLc-shaftandthecenterlineofholeLc-holeandcoplanarbetweentheP-ShaftandtheplaneP-Hole.Thematingdirectionisakeyissue,foranassemblyoperation.Thispaperappliesthefollowingapproachtocomputethepossiblematingdirectionbasedonthegeometricconstraints(theshaft-in-holeoperationofFig.3istakenasanexample):Forapartintherelationgraph,calculateitsremainingdegreesoffreedom,alsocalleddegreesofseparation,ofeachgeometricconstraint.Fortheconplanarconstraint,theremainingdegreesoffreedomareR1=x,y,Rotz.Forthecollinearconstraint,theremainingdegreesoffreedomareR2=z,Rotz.R1andR2canalsoberepresentedasR1=1,1,0,0,0,1andR20,0,1,0,0,1.Here,1meansthatthereisadegreeofseparationbetweenthetwoparts.R1R2=0,0,0,0,1,andso,thedegreeoffreedomaroundthezaxiswillbeignoredinthefollowingsteps.Intheeasethatthereisloopintherelationgraph,suchaspartsPart5,Part6,andPart7inFig.2,theloophastobebrokenbeforethematingdirectioniscalculated.UndertheassumptionthatallpartsintheCADmodelarefullyconstrainedandnotover-constrained,thefollowingsimpleapproachisadopted.Fortheparttintheloop,calculatethenumberofisinNin=Ri1Ri2.Rin；whereRistheremainingdegreesoffreedomofconstraintkbyparti.Forexample,inFig.2,giventhatthenumberof1sinUislargerthanU,thenitcanberegardedthatthepositionofpart7isdeterminedbyconstraintsbetweenpart5andpart6,whilePart5andPart6canbefullyconstrainedbyconstraintsbetweenPart5andPart6.wecanunitePart5andPart6asonenodewillberegardedasasingle,butitisobviousthatthecompositenodeimpliesanassemblysequence.Calculatematingdirectionsforallnodesintherelationgraph.Again,beginningatthestatethattheshaftandtheholeareassembled,separatethepartinonedegreeofseparationbyacertaindistance(largerthanthemaximumtolerance),andthancheckifinterferenceoccurs.Separationinboth±xaxisand±yaxisofR1causestheinterferencebetweentheshaftandthehole.Separationinthe+zdirectionraisesoninterference.Then,selectthe+zdirectionasthematingdirection,whichisrepresentedasavectorMmeasuredinthecoordinatesystemoftheassembly.Itshouldbenotedthat,insomecase,theremaybeseveralpossiblematingdirectionsforapart.Theconditionforassemblyoperationinthematingdirectionattheassembledstate,whichcanbecheckedsimplywithgeometricconstraints,theendconditionismeasuredbyforcesensoryinformation,whereaspositioninformationisusedasanendcondition.Calculatethegraspingposition.Inthispaper,partsarehandledandmanipulatedwithtwoseparateprobes,whichwillbediscussedintheSect.4,andplanesoredgesareconsideredforgrasping.Inthecasethatthereareseveralmatingdirections,thegraspingplansareselectedasG1G2Gi,whereGiispossiblegraspingplane/edgesetfortheithmatingdirectionwhenthepartisatitsfreestate.Forexample,inFig.4,thepairplanesP1/P1,P2/P2,andP3/P3canserveaspossiblegraspingplanes,andthenthegraspingplanesareP1/P1,P2/P2,P3/P3/P1/P1,P3/P3/P1/P1,P2/P2=P1/P1Theapproachingdirectionoftheend-effectorisselectedasthenormalvectorofthegraspingplanes.Itisobviousthatnotallpointsonthegraspingplanecanbegrsped.Thefollowingmethodisusedtodeterminethegraspingarea.Theend-effector,whichismodeledasacuboid,isfirstaddedintheCADmodel,withtheconstraintofcoplanarortangentialwiththegraspingplane.BeginningattheedgethatisfarawayfromtheBae-Partinthematingdirection,movetheend-effectorinthematingdirectionalongthegraspingplaneuntiltheend-effectorisfullyincontactwiththepart,thegraspingplaneisfullyincontactwiththeend-effector,oracollisionoccurs.Recordtheedgeandthedistance,bothofwhicharemeasuredinthepartscoordinatesystem.Separategraduallythetwopartsalongthematingdirection,whichcheckinginterferenceintheotherdegreesofseparation,untilnointerferenceoccursinalloftheotherdegreesofseparation.Thereisobviouslyaseparationdistancethatassuresinterferencenottooccurineverydegreeofseparation.Itiscalledthesafelengthinthatdirection.Thislengthisusedforthecollision-freepathcalculation,whichwillbediscussedinthefollowingsection.2.2AssemblysequenceSomecriteriacanbeusedtosearchtheoptimalassemblysequence,suchasthemechanicalstabilityofsubassemblies,thedegreeofparallelexecution,typesoffixtures,etc.Butformicroassembly,weshouldpaymoreattentiontooneofitsmostimportantfeatures,thelimitedworkspace,whenselectingtheassemblysequence.Microassemblyoperationsareusuallyconductedandmonitoredundermicroscopy,andtheworkspaceformicroassemblyisverysmall.Theassemblysequencebringsmuchinfluenceontheassemblyefficiency.Forexample,asimpleassemblywiththreeparts.Insequencea,partAisfirstfixedontopartB.InthecasethatpartCcannotbemountedintheworkspaceatthesametimewithcomponentABbecauseofthesmallworkspace,inordertoassemblepartCwithAB,componentABhastounmountedfromtheworkspace.Then,componentCistransportedandfixedintotheworkspace.Afterthat,component