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ThispapertobepublishedintheProceedingsofthe1996IEEEInternationalConferenceonRoboticsandAutomationFormoreinformation,contactRogerQuinn,AssociateProfessorMechanicalEngineeringCaseWesternReserveUniversity,2163683222DesignofanAgileManufacturingWorkcellforLightMechanicalApplicationsRogerD.Quinn,GregC.CauseyDepartmentofMechanicalandAerospaceEngineeringFrankL.Merat,DavidM.Sargent,NicholasA.BarendtWyattS.Newman,VirgilioB.VelascoJr.DepartmentofElectricalEngineeringandAppliedPhysicsAndyPodgurski,JuyeonJoLeonS.Sterling,YoohwanKimDepartmentofComputerEngineeringandScienceCaseWesternReserveUniversityCWRUClevelandOhio,44106AbstractThispaperintroducesadesignforagilemanufacturingworkcellsintendedforlightmechanicalassemblyofproductsmadefromsimilarcomponentsi.e.partsfamilies.Wedefineagilemanufacturingastheabilitytoaccomplishrapidchangeoverfromtheassemblyofoneproducttotheassemblyofanotherproduct.Rapidhardwarechangeoverismadepossiblethroughtheuseofrobots,flexiblepartfeeders,modulargrippersandmodularassemblyhardware.Theflexiblefeedersrelyonbeltfeedingandbinarycomputervisionforposeestimation.Thishasadistinctadvantageovernonflexiblefeedingschemessuchasbowlfeederswhichrequireconsiderableadjustmenttochangeoverfromoneparttoanother.Rapidsoftwarechangeoverisbeingfacilitatedbytheuseofarealtime,objectorientedsoftwareenvironment,modularsoftware,graphicalsimulationsforofflinesoftwaredevelopment,andaninnovativedualVMEbuscontrollerarchitecture.Theseagilefeaturespermitnewproductstobeintroducedwithminimaldowntimeandsystemreconfiguration.1.Introduction1.1WhatisAgileManufacturingAgilemanufacturingisatermthathasseenincreaseduseinindustryoverthepastseveralyears.Thedefinitionofagile,however,isnotclear,norisitconsistentAgilityThemeasureofamanufacturersabilitytoreacttosudden,unpredictablechangeincustomerdemandforitsproductsandservicesandmakeaprofit1.Todayfactoriesarecomingonlinethatareagileattailoringgoodstoacustomersrequirements,withouthaltingproduction...2.Agilemanufacturingassimilatesthefullrangeofflexibleproductiontechnologies,alongwiththelessonslearnedfromtotalqualitymanagement,justintimeproductionandleanproduction3.Theonlycommonthreadamongthevariousdefinitionsistheabilitytomanufactureavarietyofsimilarproductsbasedonwhatmayberapidlychangingcustomerneeds.Inthepast,productionwasgearedtowardhighvolumeproductionofasingleproduct.Intodaysmarket,however,theemphasisismovingtowardsmalllotsizesfromaneverchanging,customerdrivenproductline.Figure1AgileWorkcellAdefinitionofagilemanufacturinghasbeenadoptedwhichappliestolightmechanicalassemblyofproductsAgilemanufacturingistheabilitytoaccomplishrapidchangeoverbetweenthemanufactureofdifferentassembliesutilizingessentiallythesameworkcell.Rapidchangeovermeasuredinhours,further,isdefinedastheabilitytomovefromtheassemblyofoneproducttotheThispapertobepublishedintheProceedingsofthe1996IEEEInternationalConferenceonRoboticsandAutomationFormoreinformation,contactRogerQuinn,AssociateProfessorMechanicalEngineeringCaseWesternReserveUniversity,2163683222assemblyofanotherproductwithaminimumofchangeintoolingandsoftware.Rapidchangeoverenablestheproductionofsmalllotsizes,allowingforjustintimeproduction.Acentralthemeofourdefinitionofagilemanufacturingistheabilitytorapidlyintroducemeasuredinweeksnewassembliesandcomponentsintothesystem.Inthissystem,rapidchangeoverisaccomplishedthroughtheuseofreusablesoftware,quickchangegrippersfortheroboticmanipulators,modularworktables,andpartsfeederswhichareflexibleenoughtohandleseveraltypesofpartswithoutneedingmechanicaladjustment.Thesefeedersusevision,inplaceofhardfixturing,todeterminethepositionandorientationofparts.Generic,reusablevisionroutinespermitnewpartstobeaddedtothesystemwithaminimumofeffort.AtestbedimplementationofanagilemanufacturingworkcellhasbeendevelopedFigure1.Thisincludesmechanicalmanipulators,flexiblepartfeeders,avisionsystemcameras,framegrabber,andalibraryofimageprocessingroutines,aswellasalimitednumberofdedicatedsensorsandactuatorsneededtocompleteagivenassembly.Thecentralfeatureofsuchaworkcellisacontrollercapableofcontrollingeachoftheaforementionedcomponents.1.2RelevanceofCWRUWorkSeveralcompanieshaveimplementedwhatmaybeconsideredagilemanufacturing.Motorolahasdevelopedanautomatedfactorywiththeabilitytoproducephysicallydifferentpagersonthesameproductionline4.AtPanasonic,acombinationofflexiblemanufacturingandjustintimeprocessingisbeingusedtomanufacturebicyclesfromcombinationsofagroupofcoreparts5.Againstthebackdropofsuchwork,theCWRUworkcellisinnovativeinseveralways.Theuseofvisionguided,flexiblepartsfeedersisoneexample.Anotheristhedevelopmentofsoftwaredesignpatternsforagilemanufacturing.Theoverarchingdesignphilosophyofquickchangeover,however,iswhatmakesthisworkcellparticularlynovel.TheCWRUworkcellhasbeendesignedtobeaversatileproductionfacility,amenabletoawiderangeofapplicationsandanenablingtechnologyforfactorywideagilemanufacturing.2.WorkcellHardwareTheagileworkcelldevelopedatCWRUconsistsofaBoschflexibleautomationsystem,multipleAdeptSCARArobots,asmanyasfourflexiblepartsfeedersperrobot,andanAdeptMVcontroller.Animportantfeatureoftheworkcellisthecentralconveyorsystem,whichwasimplementedusingstandardBoschhardware.ItisresponsiblefortransferringpartiallycompletedassembliesbetweentherobotsandforcarryingfinishedunitstoanunloadingrobotTherobotsaremountedonpedestalsneartheconveyorsystem.Palletswithspecializedpartsfixturesareusedtocarryassembliesthroughoutthesystem,afterwhichthefinishedassembliesareremovedfromthepalletbytheunloadingrobot.Finally,asafetycageenclosestheentireworkcell,servingtoprotecttheoperatoraswellasprovidingastructureformountingoverheadcameras.2.1ConveyorSystemTheconveyorsystemusedintheCWRUworkcellisamodelT2manufacturedbyBosch.Palletsarecirculatedontwomainconveyorlines.Theselinesareparalleltoeachotherandoperateinoppositedirections.PalletsaretransferredbetweenthesetwosectionsbymeansofLiftTransferUnitsLTUs.Theseallowforthecirculationofpalletsaroundtheconveyorsystemandthecapabilitytoreorderthepallets.Eachofthepalletsinthesystemisgivenauniqueidentificationnumber,allowingthesystemtotrackanddirectitsprogress.Stopsaremountedatcriticalpointsontheconveyortocontroltheflowofthepallets.Aninnovativeuseofthisconveyorsystemistheuseofshortspurlines.AspurFigure2issimplyanextensionoftheconveyor,perpendiculartothemainlineanalogoustoarailroadspur.Thisallowstheflowofthemainconveyorlinetobemaintainedwhilearobotperformsanassemblyatthespur.Palletsenteringaspurareregisteredintherobotsworldcoordinateframebyanarmmountedcamera,allowingtherobottoplaceorremovepartsonthepalletandavoidingtheexpenseofmechanicalregistration.2.2AssemblyStationsSeveralassemblystationlayoutswereanalyzedinchoosingthefinallayout.Afterevaluatingseveralfeaturesofeachlayout,includingplacementoftherobotsrelativetotheconveyor,impactoffeederplacementrelativetotherobotworkenvelope,andtherobotmotionsnecessaryforagenericassembly,itwasdeterminedthatthelayoutinFigure2wouldbestsuittheneedsoftheworkcell.Eachassemblyrobotissurroundedbytwomodular,removableworktablesandtwofixedfeedingtablesFigure2.Themodulartablesareeasilyexchangeable,allowingforspecializedassemblyhardwaretobeplacedwithintherobotsworkenvelope.ThemodulartablescontainpneumaticactuatorsandThispapertobepublishedintheProceedingsofthe1996IEEEInternationalConferenceonRoboticsandAutomationFormoreinformation,contactRogerQuinn,AssociateProfessorMechanicalEngineeringCaseWesternReserveUniversity,2163683222electricalsensorswhichcanbeconnectedquickly,allowingtherapidchangeofanyspecializedtoolingrequiredforagivenassembly.Bydesigningthesetablestobemodularandeasilyexchanged,differentassemblyhardwarecanbequicklyaccommodated.Toachieverapidchangeover,themodularworktablesareregisteredintherobotsworldcoordinatesysteminthesamemannerasthepalletsi.e.usinganarmmountedcamera.Thefeedingtablesarefixed,andthehorizontal,partsfeedingconveyorsaremountedtothem.Figure2WorkstationLayoutOnedrawbackoftheconveyor/spursystem,asoutlinedabove,isthetimerequiredtoexchangeafullpalletforanemptyone.Duringthistimeapproximately15secondstherobotwouldconceivablybeinactive.Asimplesolutiontothisproblemisaminiwarehouseafixtureislocatedontheexchangeableportionoftheworktabletoholdafewcompletedassemblies.Duringapalletswap,therobotcancontinuetheassemblyoperationworkingwhiletheincomingpalletarrives,placingthecompletedassembliesintheminiwarehouse.Aftertheincomingpalletistransferredtothespur,thevisionsystemregistersthepallet.Therobotplacesthecurrentassemblystillinitsgripperonthepalletandthenproceedstomovethecompletedassembliesfromtheminiwarehousetothepallet.2.3FlexiblePartsFeedersEachfeederconsistsofthreeconveyorsFigure3.Thefirstconveyorisinclinedandliftspartsfromabulkhopper.Thesecondconveyorishorizontal,withatranslucentbelt.Ittransportsthepartstotherobot,presentingthematanunderlitsectionneartherobot.Thethirdconveyorreturnsunusedorunfavorablyorientedpartstothebulkhopper.Properfunctioningofthefeedersdependsonthepartsbeingliftedfromthebulkhopperinaquasisingulatedmanner.Manyfactorsinfluencetheeffectivenessoftheinclinedconveyortheangleoftheconveyorwithrespecttothehorizontal,thebeltpropertiese.g.coefficientoffriction,thetypeofbeltcleated,magnetic,vacuum,andthelinearspeedofthebelt,forexample.Figure3FlexibleFeedingSystemSchematicWhendifferentpartsaretobefed,thebulkhopperisemptiedandfilledwiththenewparts.Ifthepartsareofasimilargeometry,nochangestothefeedingsystemaretypicallyneeded.Someparts,suchascircularorcylindricalonesi.e.onesthatwouldrollbackdowntheinclinemayneedadifferentbeltsurface,suchasacleatedone,oradifferentangleofinclination.Overheadcamerasareusedtolocatepartsonthehorizontalconveyors.Anarrayofcompactfluorescentlightsisinstalledwithineachofthehorizontalconveyors.Theselightstogetherwithatranslucentconveyorbeltprovideanunderlitareainwhichpartscanbepresentedtothevisionsystem.UsingbinaryvisiontoolscurrentlyprovidedbyanAdeptvisionsystempartsonthefeederbeltsareexamined.First,thevisionsystemlookstoseeifapartisgraspablei.e.thepartisinarecognized,stableposepositionandorientationandenoughclearanceexistsbetweenthepartanditsneighborstograspitwithagripper.Second,theposeofthepartintherobotsworldcoordinatesisdetermined.Thispose,andthemotionsassociatedwithacquiringthepart,arecheckedtomakesurethattheyarewithintheworkenvelopeoftherobot.2.4VisionSystemOneessentialfunctionofthevisionsystemistodeterminetheposeofcomponentsforflexiblepartsfeeding.PoseestimationisperformedusingbuiltinfunctionsoftheAdeptVisionsoftware,andmustbefastenoughnottointerferewiththeassemblycycletime.Asecondaryfunctionofthevisionsystemistoregisterpalletsandmodularworktablestoarobotsworldcoordinatesystem,avoidingtheneedforalignmenthardware.Stillanotherusemaybeerrorrecovery,ThispapertobepublishedintheProceedingsofthe1996IEEEInternationalConferenceonRoboticsandAutomationFormoreinformation,contactRogerQuinn,AssociateProfessorMechanicalEngineeringCaseWesternReserveUniversity,2163683222whereinthecamerascanbeusedtoinspectcriticalpointsinthesystem,orinprocessassemblies.ThevisionsystemusesanumberofstandardCCDcameras,mountedeitherabovetheflexiblepartsfeedersorontherobotarms.SincethenumberofcamerainputstotheAdeptVisionsystemislimitedtofour,alowcost,customvideomultiplexerwasdeveloped,utilizingamonolithicvideoswitcherintegratedcircuit.Thisallowsuptofourcamerastobeattachedtoeachvideoinputonthevideohardware.Inkeepingwiththequickchangeoverphilosophy,thevisionroutinesaredesignedtobereusablethatisagivenroutinemaybeusedtolocateseveraldifferentbutsimilarpartsi.e.similarasymmetries,topology,etc..Thisapproachhasmanyadvantages,includingminimizingthenumberofsoftwareroutines.Inaddition,thisreusabilityallowsforsoftwaremodularityandagility6.Forexample,byparameterizingthecharacteristicsthataroutinesearchesfor,itcanbeappliedtopartsthathaveasimilarprofilebutareofadifferentsize.Thismeansthatpartswithsimilargeometriestothoseinthepartslibrarycanbeaddedtothesystembysimplymodifyingtheinspectionproceduresthatcalltheselowerlevel,reusableroutines.2.5IntroductionofNewPartsAddinganewparttothesysteminvolvesafewwelldefinedtasks.Avisionroutinewhichdeterminestheposeofthepartisdeveloped,utilizingthelibraryofreusablevisionroutines.Ifthenewparthascharacteristicsthatappearnowhereelseinthepartslibrary,newroutinesmayneedtobeaddedtothesoftwarelibrary.Also,iftheparthasnotbeendesignedforuseonthegenericpartsfeederse.g.ithasnostableposes,likeacylinder,thefeedersmayrequireabeltchangeorachangeintheangleofinclination.Agrippermustalsobedesignedtomanipulatethenewpart.Inordertominimizethespecializedhardwareandavoidtoolchangesduringassembly,thegripperdesignshouldbeperformedconcurrentlywiththegripperdesignsforotherpartstobeassembledatagivenrobot.Forinstance,ifagivenoperationrequiresbothanAwidgetandaBwidgettobeassembledatthefirstrobot,thegripperdesignershouldtakethisintoaccount.Ingeneral,itisbesttodesignthepartsandtheassociatedhardwareconcurrently.Thiswillallowmaximumreuseofsoftware,minimalchangetotheflexiblefeedingsetupandthedesignofarobustassemblysequencewhichwillenhanceunattendedoperation.ThisapproachisknownasDesignforManufacturingandAssembly7,orsimplyDFMA.3.ComputerHardware/ControllerDesignThecurrentsoftwarehasbeendevelopedentirelyintheV8programminglanguageandoperatingsystem,onAdeptsMVcontroller.Formostindustrialapplications,thisprogrammingenvironmentwouldbesufficienthowever,itlacksthepowerandflexibilityneededtosupportrapidsoftwaredevelopmentandchangeover.ThisislargelybecauseVlacksfeatureswhicharestandardinotherlanguagesandoperatingsystems,suchasuserdefinedfunctions,standarddatastructuresandshellscriptexecution.Tocircumventtheselimitations,amoreextensivecontrollerinterfacedesignisunderdevelopment.ItwillallowthesystemtosupportCandC,andprovideafriendlierandmoreflexibleuserinterface.Inaddition,itwillallowtheuseofarealtimeoperatingsystem,thussimplifyingsoftwaredevelopmentandimprovingperformance.I/OReflectiveMemoryNetworkEthernetAdeptMVControllerAgileWorkcellNonAdeptVMECageWorkstationFigure4SystemArchitectureInthisdesign,thesystemscapabilitiesareexpandedbyusingasecondVMEbusinadditiontotheMVcontrollerVMEbusFigure4.ThissecondVMEbushousesI/OboardsanddedicatedsingleboardcomputersSBCs,onwhicharealtimeoperatingsystemexecutes.CandCprogramsrunningontheSBCsareresponsibleforallhighlevelcontrolandrobotmotionse.g.conveyorcontrol,pneumaticoperations,specifyingrobotdestinations,whiletheMVcontrollerisusedexclusivelyforlowlevelrobotmotionse.g.servocontrolandtrajectorygenerationandsomemachinevisionroutines.Inlaterimplementations,avisionprocessingboardcanalsobeusedonthesecondVMEbus,therebyaugmentingtheAdeptVisionsystem.Thetwobusesareconnectedbyareflectivememorynetwork.Thisconsistsoftwomemorycards,oneoneachbus,whichcanbeconnectedbyeitheracableorafiberopticlink.Changesmadetomemoryon
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