Design and analysis of a re-configurable parallel

Designandanalysisofare-configurableparallelrobotFengfengXia,*,YounanXub,GuoliangXiongbaDepartmentofAerospaceEngineering,RyersonUniversity,Toronto,ON,CanadabSchoolofMechatronicsEngineering,EastChinaJiaotongUniversity,Nanchang,PRChinaReceived2June2004;receivedinrevisedform12April2005;accepted26April2005Availableonline5July2005AbstractInthispaperare-configurableparallelrobotispresentedwhichconsistsoftwobasetripods.Thefirsttripodismadeofthreeprismaticjointswiththefixed-leglength,calledslidetripod.Thesecondtripodismadeofthreerevolutejoints,calledswingtripod.Whiletheslidetripodisfixedtothemovingplatform,thebranchesoftheswingtripodaredesignedtobedetachablefromthemovingplatform.Bydetachingoneortwoorthreebranchesoftheswingtripodseparately,thisparallelrobotcanbere-configuredfrom6degrees-of-freedomto5or4or3degrees-of-freedom,respectively.Inaddition,thedetachedbranchescanbeusedtoperformcollaborativeworkwiththeparallelrobot.Todescribethisdesign,first,designmeth-odologyispresented.Thenaparametricmodelisdevelopedtomodeltheconstraintequationsresultingfromre-configuration.Basedonthismodelaunifiedmethodisdevelopedtosolvetheconstraintequations.Furthermore,aunifiedmethodispresentedtosolvetheinversekinematicsconsideringvaryingconfigura-tionsincluding3,4,5and6DOFs.Finally,anapplicationcaseispresentedtoshowthattheproposedre-configurableparallelrobotcanbere-configuredtoperformtasksthatwouldotherwiserequiretworobots.
2005ElsevierLtd.Allrightsreserved.1.IntroductionRe-configurablesystemsperhapsaretheultimateintelligentsystemsthathumanbeingcanpos-siblydreamof.Ideally,suchsystemswouldautonomouslychangetheirconfigurationsinorderto0094-114X/$-seefrontmatter
2005ElsevierLtd.Allrightsreserved.doi:10.1016/j.mechmachtheory.2005.04.007*Correspondingauthor.Tel.:[phone];fax:[phone].E-mailaddress:[e-mail](F.Xi).(2006)191–211MechanismandMachineTheoryadapttoenvironmentandtaskchanges.Theadvantagesofdevelopingre-configurablesystemsincludeadaptability,reusability,convertibility,compactness,fault-toleranceandemergencybehavior[1].Researchintore-configurablesystemsisprimarilyactiveinrobotics.Themainideaofdevelopingre-configurablesystemsisbasedontheuseofmodularcomponentsasbuildingblocks[2].Intheroboticsarea,severalinterestingmodularre-configurablerobotshavebeenproposed,andtheymaybeclassifiedintothreecategories:self-assembly,self-configuringandmanual-config-uring.Self-assemblyrobotsaretherobotswiththehighestlevelofre-configurabilitybecausetheycandetachfromandattachintoaroboticsystemautomatically.Forexample,Tomitaetal.[3]developedaself-assemblyroboticsystemthatuseselectro-magneticdisksasthebasicunitsthatcanattractandrepeleachotherthroughcomputercontrolforautomaticre-configuration.Self-configuringrobotscannotperformself-assembly.However,theycanperformre-configura-tionafteraroboticsystemisassembledwithsomeformofmanualassistance.Michael[4]devel-opedwhathecalledthefractalshapechangingrobotbasedonroboticcubes.Thesecubesarebuiltwiththeembeddedactivedrivingmechanisms.Onceattachedmanually,thesecubescanslideoneachother
sfacesforre-configuration.Sincethecubesaremadeindifferentsizesandcanbecombinedtogether,therobotiscalledthefractalshapechangingrobot.Manual-configuringrobotsareinfactmodularrobots.Theycanonlybere-configuredwithsomeformofmanualassistance.Themodularunitsareusuallybuiltwiththeembeddedcontrol-lersandthehostcomputerhasthecapabilitytoquicklyrecognizenewconfigurationsandauto-maticallygeneratethekinematicanddynamicequationsforcontrol.ExamplesincludetheworkatStanford[5],CarnegieMellonUniversity(CMU)[6]andUniversityofToronto[7].Morere-cently,Chen[8]developedare-configurablemanufacturingcellbasedonmodularroboticcom-ponents.Hisresearchteamdemonstratedthatbyusingmodularcomponentstheywereabletoquicklyconstructaparallelkinematicmachineformachiningandseveralserialrobotsformate-rialhandling.Re-configurablesystemsforspaceapplicationshavealsobeenexplored.Onodaetal.[9]pro-posedatwo-dimensionalfoldablehexapodtrussforspacedeployment.HamlinandSanderson[10]designedamodularparallelrobot,calledTETROBOT,basedontetrahedronmodulesthatcanbere-configuredfordifferentapplications.Variablegeometrytrussmanipulators(VGTM)havebeenstudiedasre-configurablesupportstructuresforspaceapplication[11].Re-configurablemobilerobotshavebeenresearchedbyaresearchteamfromMIT,JPLandCMU[12].AlightweightmodularrobotwasrecentlyproposedbyHafezetal.fromMIT[13].Theworkreportedinthispaperisonthedevelopmentofare-configurableparallelrobot.Themainideaistoutilizethemodularityinherentintheparallelrobots,whichwasoverlookedinthepast.Sinceparallelrobotsaremadeoftheidenticalkinematicchainsarrangedinparallelfashion,allthecomponents(mechanicalandelectrical)usedineachindividualkinematicchain,calledbranch,arethesame.Thisprovidesanaturalbaseforthedevelopmentofre-configurablesystems.Theproposedre-configurableparallelrobotisconstructedbytwobasetripods,eachbeingathreedegrees-of-freedomparallelrobot.Thefirsttripodismadeofthreeprismaticjointswiththefixed-leglength.Thesecondtripodismadeofrevolut