ThispapertobepublishedintheProceedingsofthe1996IEEEInternationalConferenceonRoboticsandAutomationFormoreinformation,contact:RogerQuinn,AssociateProfessor-MechanicalEngineeringCaseWesternReserveUniversity,216-368-3222DesignofanAgileManufacturingWorkcellforLightMechanicalApplicationsRogerD.Quinn,GregC.CauseyDepartmentofMechanicalandAerospaceEngineeringFrankL.Merat,DavidM.Sargent,NicholasA.BarendtWyattS.Newman,VirgilioB.VelascoJr.DepartmentofElectricalEngineeringandAppliedPhysicsAndyPodgurski,Ju-yeonJoLeonS.Sterling,YoohwanKimDepartmentofComputerEngineeringandScienceCaseWesternReserveUniversity(CWRU)ClevelandOhio,44106AbstractThispaperintroducesadesignforagilemanufacturingworkcellsintendedforlightmechanicalassemblyofproductsmadefromsimilarcomponents(i.e.partsfamilies).Wedefineagilemanufacturingastheabilitytoaccomplishrapidchangeoverfromtheassemblyofoneproducttotheassemblyofanotherproduct.Rapidhardwarechangeoverismadepossiblethroughtheuseofrobots,flexiblepartfeeders,modulargrippersandmodularassemblyhardware.Theflexiblefeedersrelyonbeltfeedingandbinarycomputervisionforposeestimation.Thishasadistinctadvantageovernon-flexiblefeedingschemessuchasbowlfeederswhichrequireconsiderableadjustmenttochangeoverfromoneparttoanother.Rapidsoftwarechangeoverisbeingfacilitatedbytheuseofareal-time,object-orientedsoftwareenvironment,modularsoftware,graphicalsimulationsforoff-linesoftwaredevelopment,andaninnovativedualVMEbuscontrollerarchitecture.Theseagilefeaturespermitnewproductstobeintroducedwithminimaldowntimeandsystemreconfiguration.1.Introduction1.1WhatisAgileManufacturing?Agilemanufacturingisatermthathasseenincreaseduseinindustryoverthepastseveralyears.Thedefinitionof“agile”,however,isnotclear,norisitconsistent:“Agility:Themeasureofamanufacturersabilitytoreacttosudden,unpredictablechangeincustomerdemandforitsproductsandservicesandmakeaprofit”1.“Todayfactoriesarecomingonlinethatareagileattailoringgoodstoacustomersrequirements,withouthaltingproduction.”2.“Agilemanufacturingassimilatesthefullrangeofflexibleproductiontechnologies,alongwiththelessonslearnedfromtotalqualitymanagement,just-in-timeproductionandleanproduction”3.Theonlycommonthreadamongthevariousdefinitionsistheabilitytomanufactureavarietyofsimilarproductsbasedonwhatmayberapidlychangingcustomerneeds.Inthepast,productionwasgearedtowardhigh-volumeproductionofasingleproduct.Intodaysmarket,however,theemphasisismovingtowardsmalllotsizesfromanever-changing,customer-drivenproductline.Figure1:AgileWorkcellAdefinitionof“agile”manufacturinghasbeenadoptedwhichappliestolightmechanicalassemblyofproducts:Agilemanufacturingistheabilitytoaccomplishrapidchangeoverbetweenthemanufactureofdifferentassembliesutilizingessentiallythesameworkcell.Rapidchangeover(measuredinhours),further,isdefinedastheabilitytomovefromtheassemblyofoneproducttotheThispapertobepublishedintheProceedingsofthe1996IEEEInternationalConferenceonRoboticsandAutomationFormoreinformation,contact:RogerQuinn,AssociateProfessor-MechanicalEngineeringCaseWesternReserveUniversity,216-368-3222assemblyofanotherproductwithaminimumofchangeintoolingandsoftware.Rapidchangeoverenablestheproductionofsmalllotsizes,allowingforjust-in-timeproduction.Acentralthemeofourdefinitionof“agile”manufacturingistheabilitytorapidlyintroduce(measuredinweeks)newassembliesandcomponentsintothesystem.Inthissystem,rapidchangeoverisaccomplishedthroughtheuseofreusablesoftware,quickchangegrippersfortheroboticmanipulators,modularworktables,andpartsfeederswhichareflexibleenoughtohandleseveraltypesofpartswithoutneedingmechanicaladjustment.Thesefeedersusevision,inplaceofhardfixturing,todeterminethepositionandorientationofparts.Generic,reusablevisionroutinespermitnewpartstobeaddedtothesystemwithaminimumofeffort.Atestbedimplementationofanagilemanufacturingworkcellhasbeendeveloped(Figure1).Thisincludesmechanicalmanipulators,flexiblepartfeeders,avisionsystem(cameras,framegrabber,andalibraryofimageprocessingroutines),aswellasalimitednumberofdedicatedsensorsandactuatorsneededtocompleteagivenassembly.Thecentralfeatureofsuchaworkcellisacontrollercapableofcontrollingeachoftheaforementionedcomponents.1.2RelevanceofCWRUWorkSeveralcompanieshaveimplementedwhatmaybeconsidered“agile”manufacturing.Motorolahasdevelopedanautomatedfactorywiththeabilitytoproducephysicallydifferentpagersonthesameproductionline4.AtPanasonic,acombinationofflexiblemanufacturingandjust-in-timeprocessingisbeingusedtomanufacturebicyclesfromcombinationsofagroupofcoreparts5.Againstthebackdropofsuchwork,theCWRUworkcellisinnovativeinseveralways.Theuseofvision-guided,flexiblepartsfeedersisoneexample.Anotheristhedevelopmentofsoftwaredesignpatternsforagilemanufacturing.Theover-archingdesignphilosophyofquick-changeover,however,iswhatmakesthisworkcellparticularlynovel.TheCWRUworkcellhasbeendesignedtobeaversatileproductionfacility,amenabletoawiderangeofapplicationsandanenablingtechnologyforfactorywideagilemanufacturing.2.WorkcellHardwareTheagileworkcelldevelopedatCWRUconsistsofaBoschflexibleautomationsystem,multipleAdeptSCARArobots,asmanyasfourflexiblepartsfeedersperrobot,andanAdeptMVcontroller.Animportantfeatureoftheworkcellisthecentralconveyorsystem,whichwasimplementedusingstandardBoschhardware.ItisresponsiblefortransferringpartiallycompletedassembliesbetweentherobotsandforcarryingfinishedunitstoanunloadingrobotTherobotsaremountedonpedestalsneartheconveyorsystem.Palletswithspecializedpartsfixturesareusedtocarryassembliesthroughoutthesystem,afterwhichthefinishedassembliesareremovedfromthepalletbytheunloadingrobot.Finally,asafetycageenclosestheentireworkcell,servingtoprotecttheoperatoraswellasprovidingastructureformountingoverheadcameras.2.1ConveyorSystemTheconveyorsystemusedintheCWRUworkcellisamodelT2manufacturedbyBosch.Palletsarecirculatedontwomainconveyorlines.Theselinesareparalleltoeachotherandoperateinoppositedirections.PalletsaretransferredbetweenthesetwosectionsbymeansofLiftTransferUnits(LTUs).Theseallowforthecirculationofpalletsaroundtheconveyorsystemandthecapabilitytore-orderthepallets.Eachofthepalletsinthesystemisgivenauniqueidentificationnumber,allowingthesystemtotrackanddirectitsprogress.Stopsaremountedatcriticalpointsontheconveyortocontroltheflowofthepallets.Aninnovativeuseofthisconveyorsystemistheuseofshort“spurlines”.Aspur(Figure2)issimplyanextensionoftheconveyor,perpendiculartothemainline(analogoustoarailroadspur).Thisallowstheflowofthemainconveyorlinetobemaintainedwhilearobotperformsanassemblyatthespur.Palletsenteringaspurareregisteredintherobotsworldcoordinateframebyanarm-mountedcamera,allowingtherobottoplaceorremovepartsonthepalletandavoidingtheexpenseofmechanicalregistration.2.2AssemblyStationsSeveralassemblystationlayoutswereanalyzedinchoosingthefinallayout.Afterevaluatingseveralfeaturesofeachlayout,including:placementoftherobotsrelativetotheconveyor,impactoffeederplacementrelativetotherobotworkenvelope,andtherobotmotionsnecessaryforagenericassembly,itwasdeterminedthatthelayoutinFigure2wouldbestsuittheneedsoftheworkcell.Eachassemblyrobotissurroundedbytwomodular,removableworktablesandtwofixedfeedingtables(Figure2).Themodulartablesareeasilyexchangeable,allowingforspecializedassemblyhardwaretobeplacedwithintherobotsworkenvelope.ThemodulartablescontainpneumaticactuatorsandThispapertobepublishedintheProceedingsofthe1996IEEEInternationalConferenceonRoboticsandAutomationFormoreinformation,contact:RogerQuinn,AssociateProfessor-MechanicalEngineeringCaseWesternReserveUniversity,216-368-3222electricalsensorswhichcanbeconnectedquickly,allowingtherapidchangeofanyspecializedtoolingrequiredforagivenassembly.Bydesigningthesetablestobemodularandeasilyexchanged,differentassemblyhardwarecanbequicklyaccommodated.Toachieverapidchangeover,themodularworktablesareregisteredintherobotsworldcoordinatesysteminthesamemannerasthepallets(i.e.usinganarm-mountedcamera).Thefeedingtablesarefixed,andthehorizontal,parts-feedingconveyorsaremountedtothem.Figure2:WorkstationLayoutOnedrawbackoftheconveyor/spursystem,asoutlinedabove,isthetimerequiredtoexchangeafullpalletforanemptyone.Duringthistime(approximately15seconds)therobotwouldconceivablybeinactive.Asimplesolutiontothisproblemisamini-warehouse:afixtureislocatedontheexchangeableportionoftheworktabletoholdafewcompletedassemblies.Duringapalletswap,therobotcancontinuetheassemblyoperationworkingwhiletheincomingpalletarrives,placingthecompletedassembliesinthemini-warehouse.Aftertheincomingpalletistransferredtothespur,thevisionsystemregistersthepallet.Therobotplacesthecurrentassembly(stillinitsgripper)onthepalletandthenproceedstomovethecompletedassembliesfromthemini-warehousetothepallet.2.3FlexiblePartsFeedersEachfeederconsistsofthreeconveyors(Figure3).Thefirstconveyorisinclinedandliftspartsfromabulkhopper.Thesecondconveyorishorizontal,withatranslucentbelt.Ittransportsthepartstotherobot,presentingthematanunderlitsectionneartherobot.Thethirdconveyorreturnsunusedorunfavorablyorientedpartstothebulkhopper.Properfunctioningofthefeedersdependsonthepartsbeingliftedfromthebulkhopperinaquasi-singulatedmanner.Manyfactorsinfluencetheeffectivenessoftheinclinedconveyor:theangleoftheconveyorwithrespecttothehorizontal,thebeltproperties(e.g.coefficientoffriction),thetypeofbelt(cleated,magnetic,vacuum),andthelinearspeedofthebelt,forexample.Figure3:FlexibleFeedingSystemSchematicWhendifferentpartsaretobefed,thebulkhopperisemptiedandfilledwiththenewparts.Ifthepartsareofasimilargeometry,nochangestothefeedingsystemaretypicallyneeded.Someparts,suchascircularorcylindricalones(i.e.onesthatwouldrollbackdowntheincline)mayneedadifferentbeltsurface,suchasacleatedone,oradifferentangleofinclination.Overheadcamerasareusedtolocatepartsonthehorizontalconveyors.Anarrayofcompactfluorescentlightsisinstalledwithineachofthehorizontalconveyors.Theselightstogetherwithatranslucentconveyorbeltprovideanunderlitareainwhichpartscanbepresentedtothevisionsystem.Usingbinaryvisiontools(currentlyprovidedbyanAdeptvisionsystem)partsonthefeederbeltsareexamined.First,thevisionsystemlookstoseeifapartisgraspable(i.e.thepartisinarecognized,stablepose(positionandorientation)andenoughclearanceexistsbetweenthepartanditsneighborstograspitwithagripper).Second,theposeofthepartintherobotsworldcoordinatesisdetermined.Thispose,andthemotionsassociatedwithacquiringthepart,arecheckedtomakesurethattheyarewithintheworkenvelopeoftherobot.2.4VisionSystemOneessentialfunctionofthevisionsystemistodeterminetheposeofcomponentsforflexiblepartsfeeding.Poseestimationisperformedusingbuilt-infunctionsoftheAdeptVisionsoftware,andmustbefastenoughnottointerferewiththeassemblycycle-time.Asecondaryfunctionofthevisionsystemistoregisterpalletsandmodularworktablestoarobotsworldcoordinatesystem,avoidingtheneedforalignmenthardware.Stillanotherusemaybeerrorrecovery,ThispapertobepublishedintheProceedingsofthe1996IEEEInternationalConferenceonRoboticsandAutomationFormoreinformation,contact:RogerQuinn,AssociateProfessor-MechanicalEngineeringCaseWesternReserveUniversity,216-368-3222whereinthecamerascanbeusedtoinspectcriticalpointsinthesystem,orin-processassemblies.ThevisionsystemusesanumberofstandardCCDcameras,mountedeitherabovetheflexiblepartsfeedersorontherobotarms.SincethenumberofcamerainputstotheAdeptVisionsystemislimitedtofour,alow-cost,customvideomultiplexerwasdeveloped,utilizingamonolithicvideo-switcherintegratedcircuit.Thisallowsuptofourcamerastobeattachedtoeachvideoinputonthevideohardware.Inkeepingwiththequick-changeoverphilosophy,thevisionroutinesaredesignedtobereusable；thatisagivenroutinemaybeusedtolocateseveraldifferentbutsimilarparts(i.e.similarasymmetries,topology,etc.).Thisapproachhasmanyadvantages,includingminimizingthenumberofsoftwareroutines.Inaddition,thisreusabilityallowsforsoftwaremodularityand“agility6.”Forexample,byparameterizingthecharacteristicsthataroutinesearchesfor,itcanbeappliedtopartsthathaveasimilarprofilebutareofadifferentsize.Thismeansthatpartswithsimilargeometriestothoseinthepartslibrarycanbeaddedtothesystembysimplymodifyingtheinspectionproceduresthatcalltheselower-level,reusableroutines.2.5IntroductionofNewPartsAddinganewparttothesysteminvolvesafewwelldefinedtasks.Avisionroutinewhichdeterminestheposeofthepartisdeveloped,utilizingthelibraryofreusablevisionroutines.Ifthenewparthascharacteristicsthatappearnowhereelseinthepartslibrary,newroutinesmayneedtobeaddedtothesoftwarelibrary.Also,iftheparthasnotbeendesignedforuseonthegenericpartsfeeders(e.g.ithasnostableposes,likeacylinder),thefeedersmayrequireabeltchangeorachangeintheangleofinclination.Agrippermustalsobedesignedtomanipulatethenewpart.Inordertominimizethespecializedhardwareandavoidtoolchangesduringassembly,thegripperdesignshouldbeperformedconcurrentlywiththegripperdesignsforotherpartstobeassembledatagivenrobot.Forinstance,ifagivenoperationrequiresbothanAwidgetandaBwidgettobeassembledatthefirstrobot,thegripperdesignershouldtakethisintoaccount.Ingeneral,itisbesttodesignthepartsandtheassociatedhardwareconcurrently.Thiswillallowmaximumreuseofsoftware,minimalchangetotheflexiblefeedingsetupandthedesignofarobustassemblysequencewhichwillenhanceunattendedoperation.ThisapproachisknownasDesignforManufacturingandAssembly7,orsimplyDFMA.3.ComputerHardware/ControllerDesignThecurrentsoftwarehasbeendevelopedentirelyintheV+8programminglanguageandoperatingsystem,onAdeptsMVcontroller.Formostindustrialapplications,thispro