关于机械手的中英文翻译.docx
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关于机械手的中英文翻译
外文翻译
COMBINATIONOFROBOTCONTROLANDASSEMBLYPLANNINGFORAPRECISIONMANIPULATOOR
Abstract
Thispaperresearcheshowtorealizetheautomaticassemblyoperationonatwo-fingerprecisionmanipulator.Amulti-layerassemblysupportsystemisproposed.Atthetask-planninglayer,basedonthecomputer-aideddesign(CAD)model,theassemblysequenceisfirstgenerated,andtheinformationnecessaryforskilldecompositionisalsoderived.Then,theassemblysequenceisdecomposedintorobotskillsattheskill-decompositionlayer.Thesegeneratedskillsaremanagedandexecutedattherobotcontrollayer.Experimentalresultsshowthefeasibilityandefficiencyoftheproposedsystem.
KeywordsManipulatorAssemblyplanningSkilldecompositionAutomatedassembly
1Introduction
Owingtothemicro-electro-mechanicalsystems(MEMS)techniques,manyproductsarebecomingverysmallandcomplex,suchasmicrophones,micro-opticalcomponents,andmicrofluidicbiomedicaldevices,whichcreatesincreasingneedsfortechnologiesandsystemsfortheautomatedprecisionassemblyofminiatureparts.Manyeffortsaimingatsemi-automatedorautomatedassemblyhavebeenfocusedonmicroassemblytechnologies.However,microassemblytechniquesofhighflexibility,efficiency,andreliabilitystillopentofurtherresearch.Thispaperresearcheshowtorealizetheautomaticassemblyoperationonatwo-fingermicromanipulator.Amulti-layerassemblysupportsystemisproposed.
Automaticassemblyisacomplexproblemwhichmayinvolvemanydifferentissues,suchastaskplanning,assemblysequencesgeneration,execution,andcontrol,etc.Itcanbesimplydividedintotwophases;theassemblyplanningandtherobotcontrol.Attheassembly-planningphase,theinformationnecessaryforassemblyoperations,suchastheassemblysequence,isgenerated.Attherobotcontrolphase,therobotisdrivenbasedontheinformationgeneratedattheassembly-planningphase,andtheassemblyoperationsareconducted.Skillprimitivescanworkastheinterfaceofassemblyplanningtorobotcontrol.Severalrobotsystemsbasedonskillprimitiveshavebeenreported.Thebasicideabehindthesesystemsistherobotprogramming.Robotmovementsarespecifiedasskillprimitives,basedonwhichtheassemblytaskismanuallycodedintoprograms.Withtheprograms,therobotiscontrolledtofulfillassemblytasksautomatically.
Askill-basedmicromanipulationsystemhasbeendevelopedintheauthors’lab,anditcanrealizemanymicromanipulationoperations.Inthesystem,theassemblytaskismanuallydiscomposedintoskillsequencesandcompiledintoafile.Afterimportingthefileintothesystem,thesystemcanautomaticallyexecutetheassemblytask.Thispaperattemptstoexploreauser-friendly,andatthesametimeeasy,sequence-generationmethod,torelievetheburdenofmanuallyprogrammingtheskill
sequence.
Itisaneffectivemethodtodeterminetheassemblysequencefromgeometriccomputer-aideddesign(CAD)models.Manyapproacheshavebeenproposed.Thispaperappliesasimpleapproachtogeneratetheassemblysequence.Itisnotinvolvedwiththelow-leveldatastructureoftheCADmodel,andcanberealizedwiththeapplicationprogramminginterface(API)functionsthatmanycommercialCADsoftwarepackagesprovide.Intheproposedapproach,arelationsgraphamongdifferentcomponentsisfirstconstructedbyanalyzingtheassemblymodel,andthen,possiblesequencesaresearched,basedonthegraph.Accordingtocertaincriterion,theoptimalsequenceisfinallyobtained.
Todecomposetheassemblysequenceintorobotskillsequences,someworkshavebeenreported.InNnajietal.’swork,theassemblytaskcommandsareexpandedtomoredetailedcommands,whichcanbeseenasrobotskills,accordingtoapredefinedformat.ThedecompositionapproachofMosemannandWahlisbasedontheanalysisofhyperarcsofAND/ORgraphsrepresentingtheautomaticallygeneratedassemblyplans.Thispaperproposesamethodtoguidetheskilldecomposition.Theassemblyprocessesofpartsaregroupedintodifferentphases,andpartsareatdifferentstates.Specificworkflowspushforwardpartsfromonestatetoanotherstate.Eachworkflowisassociatedwithaskillgenerator.Accordingtothedifferentstartstateandtargetstateoftheworkflow,theskillgeneratorcreatesaseriesofskillsthatcanpromotetheparttoitstargetstate.
Thehierarchyofthesystemproposedhere,theassemblyinformationonhowtoassembleaproductistransferredtotherobotthroughmultiplelayers.Thetoplayerisfortheassembly-taskplanning.TheinformationneededforthetaskplanningandskillgenerationareextractedfromtheCADmodelandaresavedinthedatabase.BasedontheCADmodel,theassemblytasksequencesaregenerated.Attheskill-decompositionlayer,tasksaredecomposedintoskillsequences.Thegeneratedskillsaremanagedandexecutedattherobotcontrollayer.
2Taskplanning
Skillsarenotuseddirectlyattheassembly-planningphase.Instead,theconceptofataskisused.Ataskcanfulfillaseriesofassemblyoperations,forexample,fromlocatingapart,throughmovingthepart,tofixingitwithanotherpart.Inotherwords,onetaskincludesmanyfunctionsthatmaybefulfilledbyseveraldifferentskills.Ataskisdefinedas:
T=(BasePart;AssemblyPart;Operation)
Base_PartandAssembly_Partaretwopartsthatareassembledtogether.Base_Partisfixedontheworktable,whileAssembly_Partishandledbyrobot’send-effectorandassembledontotheBase_Part.OperationdescribeshowtheAssembly_PartisassembledwiththeBase_Part;Operation∈{Insertion_T,screw_T,align_T,...}.
Thestructureofmicropartsisusuallyuncomplicated,andtheycanbemodeledbytheconstructivesolidgeometry(CSG)method.Currently,manycommercialCADsoftwarepackagescansupport3DCSGmodeling.Theassemblymodelisrepresentedasanobjectthatconsistsoftwopartswithcertainassemblyrelationsthatdefinehow
thepartsaretobeassembled.IntheCADmodel,therelationsaredefinedbygeometricconstraints.Thegeometricinformationcannotbeuseddirectlytoguidetheassemblyoperation—wehavetoderivetheinformationnecessaryforassemblyoperationsfromtheCADmodel.
Throughsearchingtheassemblytreeandgeometricrelations(mates’relations)definedintheassembly’sCADmodel,wecangeneratearelationgraphamongparts,forexample,Inthegraph,thenodesrepresenttheparts.Ifnodesareconnected,itmeansthatthereareassemblyrelationsamongtheseconnectednodes(parts).
2.1Matingdirection
InCSG,therelationsoftwoparts,geometricconstraints,arefinallyrepresentedasrelationsbetweenplanesandlines,suchascollinear,coplanar,tangential,perpendicular,etc.Forexample,ashaftisassembledinahole.TheassemblyrelationsbetweenthetwopartsmayconsistofsuchtwoconstraintsascollinearbetweenthecenterlineofshaftLc_shaftandthecenterlineofholeLc_holeandcoplanarbetweentheplaneP_ShaftandtheplaneP_Hole.Thematingdirectionisakeyissueforanassemblyoperation.Thispaperappliesthefollowingapproachtocomputethepossiblematingdirectionbasedonthegeometricconstraints(theshaft-in-holeoperationofFig.3istakenasanexample):
1.Forapartintherelationgraph,calculateitsremainingdegreesoffreedom,alsocalleddegreesofseparation,ofeachgeometricconstraint.
Forthecoplanarconstraint,theremainingdegreesoffreedomare
.Forthecollinearconstraint,theremainingdegreesoffreedomare
.
and
canalsoberepresentedas
and
.Here,1meansthatthereisadegreeofseparationbetweenthetwoparts.
andso,thedegreeoffreedomaroundthezaxiswillbeignoredinthefollowingsteps.
Inthecasethatthereisaloopintherelationgraph,suchaspartsPart5,Part6,andPart7inFig.2,theloophastobebrokenbeforethematingdirectioniscalculated.UndertheassumptionthatallpartsintheCADmodelarefullyconstrainedandnotover-constrained,thefollowingsimpleapproachisadopted.Fortheparttintheloop,calculatethenumberof1sin
;where
istheremainingdegreesoffreedomofconstraintkbyparti.Forexample,inFig.2,giventhatthenumberof1sin
and
islargerthan
and
respectively,thenitcanberegardedthatthepositionofPart7isdeterminedbyconstraintswithbothPart5andPart6,whilePart5andPart6canbefullyconstrainedbyconstraintsbetweenPart5andPart6.WecanunitePart5andPart6asonenodeintherelationgraph,alsocalledacompositenode,asshowninFig.2b.Thecompositenodewillberegardedasasinglepart,butitisobviousthatthecompositenodeimpliesanassemblysequence.
2.Calculatematingdirectionsforallnodesintherelationgraph.Again,beginningatthestatethattheshaftandtheholeareassembled,separatethepartinonedegreeofseparationbyacertaindistance(largerthanthemaximumtolerance),andthencheckifinterferenceoccurs.Separationinboth±xaxisand±yaxisofR1causestheinterferencebetweentheshaftandthehole.Separationinthe+zdirectionraisesnointerference.Then,selectthe+zdirectionasthematingdirection,whichisrepresentedasavectorMmeasuredinthecoordinatesystemofthe
assembly.Itshouldbenotedthat,insomecases,theremaybeseveralpossiblematingdirectionsforapart.Theconditionforassemblyoperationinthematingdirectiontobeendedshouldbegiven.Whencontactoccursbetweenpartsinthematingdirectionattheassembledstate,whichcanbecheckedsimplywithgeometricconstraints,theendconditionismeasuredbyforcesensoryinformation,whereaspositioninformationisusedasanendconditi