MCB工业的机械手巴雷特机械手爪外文文献翻译中英文翻译可编程式可弯曲部分的搬运和组装外文翻译.docx
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MCB工业的机械手巴雷特机械手爪外文文献翻译中英文翻译可编程式可弯曲部分的搬运和组装外文翻译.docx
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MCB工业的机械手巴雷特机械手爪外文文献翻译中英文翻译可编程式可弯曲部分的搬运和组装外文翻译
附录A
MCB–IndustrialRobotFeatureArticle
TheBarrettHandgrasper–programmableflexibleparthandlingandassembly
Abstract
ThispaperdetailsthedesignandoperationoftheBarrettHandBH8-250,anintelligent,highlyflexibleeight-axisgripperthatreconfiguresitselfinrealtimetoconformsecurelytoawidevarietyofpartshapeswithouttool-changeinterruptions.Thegrasperbringsenormousvaluetofactoryautomationbecauseit:
reducestherequirednumberandsizeofroboticworkcells(whichaverageUS$90,000each–notincludingthehighcostoffootprint)whileboostingfactorythroughput;consolidatesthehodgepodgeproliferationofcustomizedgripper-jawshapesontoacommonprogrammableplatform;andenablesincrementalprocessimprovementandaccommodatesfrequentnew-productintroductions,capabilitiesdeployedinstantlyviasoftwareacrossinternationalnetworksoffactories.
Introduction
Thispaperintroducesanewapproachtomaterialhandling,partsorting,andcomponentassemblycalled“grasping”,inwhichasinglereconfigurablegrasperwithembeddedintelligencereplacesanentirebankofunique,fixed-shapegrippersandtoolchangers.ToappreciatethemotivationsthatguidedthedesignofBarrett’sgrasper,wemustexplorewhatiswrongwithroboticstoday,theenormouspotentialforroboticsinthefuture,andthedead-endlegacyofgrippersolutions.
Forthebenefitsofaroboticsolutiontoberealized,programmableflexibilityisrequiredalongtheentirelengthoftherobot,fromitsbase,allthewaytothetargetworkpiece.Arobotarmenablesprogrammableflexibilityfromthebaseonlyuptothetoolplate,afewcentimetersshortofthetargetworkpiece.Buttheselastfewcentimetersofarobotmustadapttothecomplexitiesofsecuringanewobjectoneachrobotcycle,capabilitieswhereembeddedintelligenceandsoftwareexcel.Liketheweakestlinkinaserialchain,aninflexiblegripperlimitstheproductivityoftheentirerobotworkcell.
Grippershaveindividually-customized,butfixedjawshapes.Thetrial-and-errorcustomizationprocessisdesignintensive,generallydrivescostandschedule,andisdifficulttoscopeinadvance.Ingeneral,eachanticipatedvariationinshape,orientation,androbotapproachanglerequiresanothercustom-but-fixedgripper,aplacetostoretheadditionalgripper,andamechanismtoexchangegrippers.Anunanticipatedvariationorincrementalimprovementissimplynotallowable.
Bycontrast,themechanicalstructureofBarrett’spatentedgrasper,illustratedinFigure1,isautomaticallyreconfigurableandhighlyprogrammable,matchingthefunctionalityofvirtuallyanygrippershapeorfixturefunctioninlessthanasecondwithoutpausingtheworkcellthroughputtoexchangegrippers.
Fortasksrequiringahighdegreeofflexibilitysuchashandlingvariablyshapedpayloadspresentedinmultipleorientations,agrasperismoresecure,quickertoinstall,andmorecosteffectivethananentirebankofcustom-machinedgripperswithtoolchangersandstorageracks.
Foruninterruptedoperation,justoneortwosparegrasperscanserveasemergencybackupsforseveralworkcells,whereasoneortwosparegrippersarerequiredforeachgrippervariation–potentiallydozensperworkcell.And,it’scatastrophicifbothgripperbackupsfailinagrippersystem,sinceitmaybedaysbeforereplacementscanbeidentified,customshapedfromscratch,shipped,andphysicallyreplacedtobringtheaffectedlinebackintooperation.Bycontrast,sincegraspersarephysicallyidentical,theyarealwaysavailableinunlimitedquantity,withallcustomizationprovidedinstantlyinsoftware.
Gripperlegacy
Mostoftoday’sroboticparthandlingandassemblingisdonewithgrippers.Ifsurfaceconditionsallow,vacuumsuctionandelectromagnetscanalsobeused,forexampleinhandlingautomobilewindshieldsandbodypanels.Aspartsizesbegintoexceedtheorderof100gms,agripper’sjawsarecustomshapedtoensureasecurehold.Asthedurablemainstayofhandlingandassembly,thesetoolshavechangedlittlesincethebeginningofroboticsthreedecadesago.
Grippers,whichactassimplepincers,havetwoorthreeunarticulatedfingers,called“jaws”,whicheitherpivotorremainparallelduringopen/closemotionsasillustratedinFigure2.Wellorganizedcatalogsareavailablefrommanufacturersthatguidetheintegratororcustomerinmatchingvariousgrippercomponents(exceptnaturallyforthecustomjawshape)tothetaskandpartparameters.
Payloadsizesrangefromgramsfortinypneumaticgrippersto100+kilogramsformassivehydraulicgrippers.Thepowersourceistypicallypneumaticorhydraulicwithsimpleon/offvalvecontrolswitchingbetweenfull-openandfull-closestates.Thejawstypicallymove1cmfromfull-opentofull-close.Thesehandshavetwoorthreefingers,called“jaws”.Thepartofthejawthatcontactsthetargetpartismadeofaremovableandmachineablysoftsteeloraluminum,calleda“softjaw”.
Basedontheuniquecircumstances,anexperttooldesignerdeterminesthecustomshapestobemachinedintotherectangularsoft-jawpieces.Oncemachinedtoshape,thesoft-jawsetsareattachedtotheirrespectivegripperbodiesandtested.Thisprocesscantakeanynumberofiterationsandadjustmentsuntilthesystemworksproperly.Tooldesignersrepeattheentireprocesseachtimeanewshapeisintroduced.
Asconsumersdemandawidervarietyofproductchoicesandevermorefrequentproductintroductions,theneedforflexibleautomationhasneverbeengreater.However,ratherthanmakegrippersmoreversatile,theroboticsindustryoverthepastfewyearshasfollowedtheexampleoftheautomatictoolexchangetechniqueusedtoexchangeCNC-millcuttingtools.
Butapplyingthetool-changermodeltoserial-linkrobotsisprovingexpensiveandineffective.Unlikethestandardizedoff-the-shelfcuttingtoolsusedbymillingmachines,arobottooldesignermustcustomizetheshapeofeverysetofgripperjaws—atime-consuming,expensive,anddifficult-to-scopetask.AlthoughgrippersmayseemcheapatonlyUS$500each,thelabor-intensiveefforttoshapethesoftjawsmaycostseveraltimesthat.Ifyoumultiplythatcosttimesadozengrippersasintheexampleaboveandthrowinatoolchangerandtool-storagerackforanadditionalUS$10,000,therealcostofthe“few-hundred-dollar”grippersolutionballoonstoUS$20,000toUS$60,000.
Toaggravatematters,unknownsinthecustomizationprocessconfoundaccuratecostprojections.Sothecustomermustcommitapurchaseordertotheinitialinstallationfeeonatimeandmaterialsbasiswithoutguaranteeofsuccessoracostceiling.WhilepricedatUS$30,000,intelligentgraspersarenotcheap.However,onecan“customize”andvalidatetheprocessinsoftwareinamatterofhoursatthefactoryinasingleday.Ifthesystemdoesnotmeetperformancetargets,thenonlyaday’slaboriswasted.Ifthesystemsucceeds,thentherearenotanyhiddenexpensesfollowingtheoriginalpurchaseorder.
Beyondcost,thephysicalweightoftoolchangermechanisms,locatedattheextremeouterendofaserial-linkroboticarm,limitstheusefulpayloadanddynamicresponseof
theentiresystem.Theadditionallengthofthetoolchangerincreasesthecriticaldistancebetweenthewristcenterandpayloadcenter,degradingkinematicflexibility,dynamicresponse,andsafety.
DescriptionoftheBarrettHand
Flexibilityanddurabilityinacompactpackage
TheflexibilityoftheBarrettHandisbasedonthearticulationoftheeightjointaxesidentifiedinFigure3.OnlyfourbrushlessDCservomotors,showninFigure4,areneededtocontrolalleightjoints,augmentedbyintelligentmechanicalcoupling.Theresulting1.18kggrasperiscompletelyself-containedwithonlyan8mmdiameterumbilicalcablesupplyingDCpowerandestablishingatwo-wayserialcommunicationlinktothemainrobotcontrolleroftheworkcell.Thegrasper’scommunicationselectronics,fivemicroprocessors,sensors,signalprocessingelectronics,electroniccommutation,currentamplifiers,andbrushlessservomotorsareallpackedneatlyinsidethepalmbodyofthegrasper.
TheBarrettHandhasthreearticulatedfingersandapalmasillustratedinFigure5whichactinconcerttotrapthetargetobjectfirmlyandsecurelywithinagraspconsistingofsevencoordinatedcontactvectors—onefromthepalmplateandonefromeachlinkofeachfinger.
EachoftheBarrettHand’sthreefingersisindependentlycontrolledbyoneofthreeservomotorsasshowninFigure6.ExceptforthespreadactionoffingersFlandF2,whichisdrivenbythefourthandlastservomotor,thethreefingers,Fl,F2,andF3,haveinnerandouterarticulatedlinkswithidenticalmechanicalstructure.
Eachofthethreefingermotorsmustdrivetwojointaxes.Thetorqueischanneledtothesejointsthroughapatented,TorqueSwitchmechanism(Figure7),whosefunctionisoptimizedformaximumgraspsecurity.Whenafingertip,nottheinnerlink,makesfirstcontactwithanobjectasillustratedinFigure8,itsimplyreachesitsrequiredtorque,locksbothjoints,switchesoffmotorcurrents,andawaitsfurtherinstructionsfromthemicroprocessorsinsidethehandoracommandarrivingacrossthecommunicationslink.
Butwhentheinnerlink,asillustratedinFigure9,makesfirstcontactwithanobjectforasecuregrasp,theTorqueSwitch,reachesapresetthresholdtorque,locksthatjointagainsttheobjectwithashallow-pitchworm,andredirectsalltorquetothefingertiptomakeasecond,enclosingcontactagainsttheobjectwithinmillisecondsofthefirstcontact.Thesequenceofcontactsissorapidthatyoucannotvisualizetheproce
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