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外文翻译--机器人控制和装配结合的机密机械手.doc

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外文翻译--机器人控制和装配结合的机密机械手.doc

COMBINATIONOFROBOTCONTROLANDASSEMBLYPLANNINGFORAPRECISIONMANIPULATOORAbstractThispaperresearcheshowtorealizetheautomaticassemblyoperationonatwofingerprecisionmanipulator.Amultilayerassemblysupportsystemisproposed.Atthetaskplanninglayer,basedonthecomputeraideddesignCADmodel,theassemblysequenceisfirstgenerated,andtheinformationnecessaryforskilldecompositionisalsoderived.Then,theassemblysequenceisdecomposedintorobotskillsattheskilldecompositionlayer.Thesegeneratedskillsaremanagedandexecutedattherobotcontrollayer.Experimentalresulteshowthefeasibilityandefficiencyoftheproposedsystem.KeywordsManipulatorAssemblyplanningSkilldecompositionAutomatedassembly1IntroductionOwingtothemicroelectromechanicalsystemsMEMStechniques,manyproductsarebecomingverysmallandcomplex,suchasmicrophones,microopticalcomponents,andmicrofluidicbiomedicaldevices,whichcreatesincreasingneedsfortechnologiesandsystemsfortheautomatedassemblyhavebeenfocusedonmicroassemblytechnologies.However,microassemblytechniquesofhighflexibility,efficiency,andreliabilityskillopentofurtherresearch.Thispaperresearchestohowtorealizetheautomaticassemblyoperationonatwofingermicromanipulator.Amulilayerassemblysupportsystemisproposed.Automaticassemblyisacomplexproblemwhichmayinvolvemanydifferentissues,suchastaskplanning,assemblysequencesgeneration,execution,andcontrol,etc.Itcanbesimplydividedintotwophases,theassemblyplanningandtherobotcontrol.Attheassemblyplanningphase,theinformationnecessaryforassemblyoperation,suchastheassemblysequence,isgenerated.Attherobotcontrolphase,therobotisdrivenbasedontheinformationgeneratedattheassemblyplanningphase,andtheassemblyoperationsareconducted.Skillprimitivescanworkastheinterfaceofassemblyplanningtorobotcontrol.Severalrobotsystemsbasedonskillprimitiveshavebeenreported.Thebasicideabehindthesesystemsistherobotprogramming..Robotmovementsarespecifiedasskillprimitives,basedonwhichtheassemblytaskismanuallycodedintoprograms.Withtheprograms,therobotiscontroltoassemblytasksautomatically.Askillbasedmicromanipulationsystemhasbeendevelopedintheauthorslab,anditcanrealizemanymicromanipulationoperations.Inthesystem,theassemblytaskismanuallydiscomposedintoskillsequencesandcompliedintoafile.Afterimportingthefileintothesystem,thesystemcanautomaticallyexecutetheassemblytask.Thispaperattemptstoexploreauserfriendly,andatthesametimeeasy,sequencegenerationmethod,torelievetheburdenofmanuallyprogrammingtheskillsequence.ItisaneffectivemethodtodeterminetheassemblysequencefromgeometriccomputeraideddesignCADmodels.Manyapproacheshavebeenproposed.Thispaperappliesasimpleapproachtogeneratetheassemblysequence.ItisnotinvolvedwiththelowleveldatastructureoftheCADmodel,andcanberealizedwiththeapplicationprogramminginterfaceAPIfunctionsgraphamongdifferentcomponentsisfirstconstructedbyanalyzingtheassemblymodel,andthen,possiblesequencesaresearched,basedonthegraph.Accordingtocertaincriterion,theoptimalsequenceisfinallyobtained.Todecomposetheassemblysequenceintorobotskillsequences,someworkshavebeenreported.InNnajietal.work,theassemblytaskcommandsareexpandedtomoredetailedcommands,whichcanbeasrobotskills,accordingtoapredefinedformat.ThedecompositionapproachofMosemannandwahlisbasedontheanalysisofhyperarcsofAND/ORgraphsrepresentingtheautomaticallygeneratedassemblyplans.Thispaperproposesamethodtoguidetheskilldecomposition.Theassemblyprocessesofpartsaregroupedintodifferentstartatateandtargetoftheworkflow,theskillgeneratorcreatesaseriesofskillsthatcanpromotetheparttoitstargetstate.Thehierarchyofthesystemproposedhere,theassemblyinformationonhowtoassembleaproductistransferredtotherobotthroughmultiplelayers.Tetoplayerisfortheassemblytaskplanning.TheinformationneededforthetaskplanningandskillgenerationareextractedfromtheCADmodelandaresavedinthedatabase.BaseontheCADmodel,theassemblytasksquencesaregenerated.Attheskilldecompositionlayer,tasksaredecomposedintoskillsequences.Thegeneratedskillsaremanagedandexecutedattherobotcontrollayer.2TaskplanningSkillsarenotuseddirectlyattheassemblyplanningphase,theconceptofataskisused.Ataskcanfulfillaseriesofassemblyoperations,forexample,fromlocatingapart,throughmovingthepart,tofixingitwithanotherpart.Inotherwords,onetaskincludesmanyfunctionsthatmaybefulfilledbyseveraldifferentskills.AtaskisdefinedasTBasePartAssemblyPartOperationBasedpartandAssemblyPartaretwopartsthatareassembledtogether.Basepartisfixedontheworktable,whileAssemblyPartishandledbyrobotsendeffectorandassembledontotheBasePart.OperationdescribeshowtheAssemblyPartisassembledwiththeBasePartOperation{IntertionT,serewT,alignT,}.Thestructureofmicropartsisusuallyuncomplicated,andtheycanbemodeledbytheconstructivesolidgeometryCAGmethod.Currently,manycommercialCADsoftwarepackagescansupport3DCSGmodeling.Theassemblymodelisrepresentedasanobjectthatconsistsoftwopartswithcertainassemblyrelationsthatdefinehowthepartsaretobeassembled.IntheCADmodel,therelationsaredefinedbygeometricconstraints.ThegeometricinformationcannotbeuseddirectlytoguidetheassemblyoperationwehavetoderivetheinformationnecessaryforassemblyoperationsfromtheCADmodel.ThroughsearchingtheassemblytreeandgeometricrelationsmatesrelationsdefinedintheassemblysCADmodel,wecangeneratearelationgraphamongparts,forexample,Inthegraph,thenodesrepresenttheparts.Ifnodesareconnected,itmeansthatthereareassemblyrelationsamongtheseconnectednodesparts.2.1MatingdirectionInCSG,therelationsoftwoparts,geometricconstraints,arefinallyrepresentedasrelationsbetweenplanesandlines,suchascollinear,coplanar,tangential,perpendicular,etc.Forexample,ashaftisassembledinahole.TheassemblyrelationsbetweenthetwopartsmayconsistofsuchtwoconstraintsascollinearbetweenthecenterlineofshaftLcshaftandthecenterlineofholeLcholeandcoplanarbetweenthePShaftandtheplanePHole.Thematingdirectionisakeyissue,foranassemblyoperation.ThispaperappliesthefollowingapproachtocomputethepossiblematingdirectionbasedonthegeometricconstraintstheshaftinholeoperationofFig.3istakenasanexampleForapartintherelationgraph,calculateitsremainingdegreesoffreedom,alsocalleddegreesofseparation,ofeachgeometricconstraint.Fortheconplanarconstraint,theremainingdegreesoffreedomareR1{x,y,Rotz}.Forthecollinearconstraint,theremainingdegreesoffreedomareR2{z,Rotz}.R1andR2canalsoberepresentedasR1{1,1,0,0,0,1}andR2{0,0,1,0,0,1}.Here,1meansthatthereisadegreeofseparationbetweenthetwoparts.R1R2{0,0,0,0,1},andso,thedegreeoffreedomaroundthezaxiswillbeignoredinthefollowingsteps.Intheeasethatthereisloopintherelationgraph,suchaspartsPart5,Part6,andPart7inFig.2,theloophastobebrokenbeforethematingdirectioniscalculated.UndertheassumptionthatallpartsintheCADmodelarefullyconstrainedandnotoverconstrained,thefollowingsimpleapproachisadopted.Fortheparttintheloop,calculatethenumberofisinNinRi1Ri2...RinwhereRistheremainingdegreesoffreedomofconstraintkbyparti.Forexample,inFig.2,giventhatthenumberof1sinUislargerthanU,thenitcanberegardedthatthepositionofpart7isdeterminedbyconstraintsbetweenpart5andpart6,whilePart5andPart6canbefullyconstrainedbyconstraintsbetweenPart5andPart6.wecanunitePart5andPart6asonenodewillberegardedasasingle,butitisobviousthatthecompositenodeimpliesanassemblysequence.Calculatematingdirectionsforallnodesintherelationgraph.Again,beginningatthestatethattheshaftandtheholeareassembled,separatethepartinonedegreeofseparationbyacertaindistancelargerthanthemaximumtolerance,andthancheckifinterferenceoccurs.Separationinboth±xaxisand±yaxisofR1causestheinterferencebetweentheshaftandthehole.Separationinthezdirectionraisesoninterference.Then,selectthezdirectionasthematingdirection,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,andthenthegraspingplanesare{P1/P1,P2/P2,P3/P3}/{P1/P1,P3/P3}/{P1/P1,P2/P2}{P1/P1}Theapproachingdirectionoftheendeffectorisselectedasthenormalvectorofthegraspingplanes.Itisobviousthatnotallpointsonthegraspingplanecanbegrsped.Thefollowingmethodisusedtodeterminethegraspingarea.Theendeffector,whichismodeledasacuboid,isfirstaddedintheCADmodel,withtheconstraintofcoplanarortangentialwiththegraspingplane.BeginningattheedgethatisfarawayfromtheBaePartinthematingdirection,movetheendeffectorinthematingdirectionalongthegraspingplaneuntiltheendeffectorisfullyincontactwiththepart,thegraspingplaneisfullyincontactwiththeendeffector,oracollisionoccurs.Recordtheedgeandthedistance,bothofwhicharemeasuredinthepartscoordinatesystem.Separategraduallythetwopartsalongthematingdirection,whichcheckinginterferenceintheotherdegreesofseparation,untilnointerferenceoccursinalloftheotherdegreesofseparation.Thereisobviouslyaseparationdistancethatassuresinterferencenottooccurineverydegreeofseparation.Itiscalledthesafelengthinthatdirection.Thislengthisusedforthecollisionfreepathcalculation,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

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