已阅读5页,还剩10页未读, 继续免费阅读
版权说明:本文档由用户提供并上传,收益归属内容提供方,若内容存在侵权,请进行举报或认领
文档简介
MCBIndustrialRobotFeatureArticleTheBarrettHandgrasperprogrammableflexibleparthandlingandassemblyAbstractThispaperdetailsthedesignandoperationoftheBarrettHandBH8-250,anintelligent,highlyflexibleeight-axisgripperthatreconfiguresitselfinrealtimetoconformsecurelytoawidevarietyofpartshapeswithouttool-changeinterruptions.Thegrasperbringsenormousvaluetofactoryautomationbecauseit:reducestherequirednumberandsizeofroboticworkcells(whichaverageUS$90,000eachnotincludingthehighcostoffootprint)whileboostingfactorythroughput;consolidatesthehodgepodgeproliferationofcustomizedgripper-jawshapesontoacommonprogrammableplatform;andenablesincrementalprocessimprovementandaccommodatesfrequentnew-productintroductions,capabilitiesdeployedinstantlyviasoftwareacrossinternationalnetworksoffactories.IntroductionThispaperintroducesanewapproachtomaterialhandling,partsorting,andcomponentassemblycalled“grasping”,inwhichasinglereconfigurablegrasperwithembeddedintelligencereplacesanentirebankofunique,fixed-shapegrippersandtoolchangers.ToappreciatethemotivationsthatguidedthedesignofBarrettsgrasper,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,themechanicalstructureofBarrettspatentedgrasper,illustratedinFigure1,isautomaticallyreconfigurableandhighlyprogrammable,matchingthefunctionalityofvirtuallyanygrippershapeorfixturefunctioninlessthanasecondwithoutpausingtheworkcellthroughputtoexchangegrippers.Fortasksrequiringahighdegreeofflexibilitysuchashandlingvariablyshapedpayloadspresentedinmultipleorientations,agrasperismoresecure,quickertoinstall,andmorecosteffectivethananentirebankofcustom-machinedgripperswithtoolchangersandstorageracks.Foruninterruptedoperation,justoneortwosparegrasperscanserveasemergencybackupsforseveralworkcells,whereasoneortwosparegrippersarerequiredforeachgrippervariationpotentiallydozensperworkcell.And,itscatastrophicifbothgripperbackupsfailinagrippersystem,sinceitmaybedaysbeforereplacementscanbeidentified,customshapedfromscratch,shipped,andphysicallyreplacedtobringtheaffectedlinebackintooperation.Bycontrast,sincegraspersarephysicallyidentical,theyarealwaysavailableinunlimitedquantity,withallcustomizationprovidedinstantlyinsoftware.GripperlegacyMostoftodaysroboticparthandlingandassemblingisdonewithgrippers.Ifsurfaceconditionsallow,vacuumsuctionandelectromagnetscanalsobeused,forexampleinhandlingautomobilewindshieldsandbodypanels.Aspartsizesbegintoexceedtheorderof100gms,agrippersjawsarecustomshapedtoensureasecurehold.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,arobottooldesignermustcustomizetheshapeofeverysetofgripperjawsatime-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,thenonlyadayslaboriswasted.Ifthesystemsucceeds,thentherearenotanyhiddenexpensesfollowingtheoriginalpurchaseorder.Beyondcost,thephysicalweightoftoolchangermechanisms,locatedattheextremeouterendofaserial-linkroboticarm,limitstheusefulpayloadanddynamicresponseoftheentiresystem.Theadditionallengthofthetoolchangerincreasesthecriticaldistancebetweenthewristcenterandpayloadcenter,degradingkinematicflexibility,dynamicresponse,andsafety.DescriptionoftheBarrettHandFlexibilityanddurabilityinacompactpackageTheflexibilityoftheBarrettHandisbasedonthearticulationoftheeightjointaxesidentifiedinFigure3.OnlyfourbrushlessDCservomotors,showninFigure4,areneededtocontrolalleightjoints,augmentedbyintelligentmechanicalcoupling.Theresulting1.18kggrasperiscompletelyself-containedwithonlyan8mmdiameterumbilicalcablesupplyingDCpowerandestablishingatwo-wayserialcommunicationlinktothemainrobotcontrolleroftheworkcell.Thegrasperscommunicationselectronics,fivemicroprocessors,sensors,signalprocessingelectronics,electroniccommutation,currentamplifiers,andbrushlessservomotorsareallpackedneatlyinsidethepalmbodyofthegrasper.TheBarrettHandhasthreearticulatedfingersandapalmasillustratedinFigure5whichactinconcerttotrapthetargetobjectfirmlyandsecurelywithinagraspconsistingofsevencoordinatedcontactvectorsonefromthepalmplateandonefromeachlinkofeachfinger.EachoftheBarrettHandsthreefingersisindependentlycontrolledbyoneofthreeservomotorsasshowninFigure6.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.Thesequenceofcontactsissorapidthatyoucannotvisualizetheprocesswithouttheaidofhigh-speedphotography.Afterthegrasperreleasestheobject,itsetstheTorqueSwitchthresholdtorqueforeachfingerinanticipationofthenextgraspbyopeningeachfingeragainstitsmechanicalstopwithacontrolledtorque.Thehighertheopeningtorque,thehigherthesubsequentthresholdtorque.Inthisway,thegraspercanaccommodateawiderangeofobjectsfromdelicate,tocompliant,toheavy.Thefingerarticulations,notavailableonconventionalgrippers,alloweachdigittoconformuniquelyandsecurelytotheshapeoftheobjectsurfacewithtwoindependentcontactpointsperfinger.Theposition,velocity,acceleration,andeventorquecanallbeprocessorcontrolledoverthefullrangeof17,500encoderpositions.Atmaximumvelocityandaccelerationsettings,eachfingercantravelfullrangeineitherdirectioninlessthanonesecond.Themaximumforcethatcanbeactivelyproducedis2kg,measuredatthetipofeachfinger.Oncethegraspissecure,thelinksautomaticallylockinplaceallowingthemotorcurrentstobeswitchedofftoconservepoweruntilcommandedtoreadjustorreleasetheirgrasp.Whiletheinnerandouterfinger-linkmotionscurlanthropomorphically,thespreadmotionofFigure10isdistinctlynon-anthropomorphic.Thespreadmotionisclosestinfunctiontoaprimatesopposable(thumb)finger,butinsteadofoneopposablefinger,theBarrettHandhastwin,symmetricallyopposablefingerscenteredonparalleljointaxesrotating180degreesaroundtheentirepalmtoformalimitlessvarietyofgripper-shapesandfixturefunctions.Thespreadcanbecontrolledtoanyof3,000positionsoveritsfullrangeineitherdirectionwithin1/2second.Unlikethemechanicallylockablefinger-curlmotions,thespreadmotionisfullybackdrivable,allowingitsservostoprovideactivestiffnesscontrolinadditiontocontroloverposition,velocity,acceleration,andtorque.Byallowingthespreadmotiontobecompliantwhilethefingersclosearounda
温馨提示
- 1. 本站所有资源如无特殊说明,都需要本地电脑安装OFFICE2007和PDF阅读器。图纸软件为CAD,CAXA,PROE,UG,SolidWorks等.压缩文件请下载最新的WinRAR软件解压。
- 2. 本站的文档不包含任何第三方提供的附件图纸等,如果需要附件,请联系上传者。文件的所有权益归上传用户所有。
- 3. 本站RAR压缩包中若带图纸,网页内容里面会有图纸预览,若没有图纸预览就没有图纸。
- 4. 未经权益所有人同意不得将文件中的内容挪作商业或盈利用途。
- 5. 人人文库网仅提供信息存储空间,仅对用户上传内容的表现方式做保护处理,对用户上传分享的文档内容本身不做任何修改或编辑,并不能对任何下载内容负责。
- 6. 下载文件中如有侵权或不适当内容,请与我们联系,我们立即纠正。
- 7. 本站不保证下载资源的准确性、安全性和完整性, 同时也不承担用户因使用这些下载资源对自己和他人造成任何形式的伤害或损失。
最新文档
- 财产秘密保护的离婚协议
- 财产与子女抚养权的离婚协议
- 离婚协议的签订及生效条件
- 离婚协议的基本原则
- 离婚协议的财产产权和继承
- 离婚协议的内容和要点
- 离婚协议共同财产协商
- 离婚协议的签署程序及注意事项
- 离婚协议对资产分配的约定
- 2024年云南住院医师-云南住院医师神经内科笔试参考题库含答案
- 洗衣店转让协议书模板
- 无人机驾驶培训班合作协议
- 完形填空12篇(15空题)-2022-2023学年八年级英语下学期期中复习练习(人教版)
- 游杜甫草堂(共10篇)
- 单排防护架施工方案
- 教育城乡义务教育均衡发展的思考与建议
- 读书点亮人生(主题班会用)课件
- 通信基站维护承包协议书
- 沪科版七年级上册数学全册教学课件
- 中铁公司招聘笔试题目答案
- 昆明保障性租赁住房房源确定合同签订怎么办理
评论
0/150
提交评论