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THISPAPERTOBEPUBLISHEDINTHEPROCEEDINGSOFTHE1996IEEEINTERNATIONALCONFERENCEONROBOTICSANDAUTOMATIONFORMOREINFORMATION,CONTACTROGERQUINN,ASSOCIATEPROFESSORMECHANICALENGINEERINGCASEWESTERNRESERVEUNIVERSITY,2163683222DESIGNOFANAGILEMANUFACTURINGWORKCELLFORLIGHTMECHANICALAPPLICATIONSROGERDQUINN,GREGCCAUSEYDEPARTMENTOFMECHANICALANDAEROSPACEENGINEERINGFRANKLMERAT,DAVIDMSARGENT,NICHOLASABARENDTWYATTSNEWMAN,VIRGILIOBVELASCOJRDEPARTMENTOFELECTRICALENGINEERINGANDAPPLIEDPHYSICSANDYPODGURSKI,JUYEONJOLEONSSTERLING,YOOHWANKIMDEPARTMENTOFCOMPUTERENGINEERINGANDSCIENCECASEWESTERNRESERVEUNIVERSITYCWRUCLEVELANDOHIO,44106ABSTRACTTHISPAPERINTRODUCESADESIGNFORAGILEMANUFACTURINGWORKCELLSINTENDEDFORLIGHTMECHANICALASSEMBLYOFPRODUCTSMADEFROMSIMILARCOMPONENTSIEPARTSFAMILIESWEDEFINEAGILEMANUFACTURINGASTHEABILITYTOACCOMPLISHRAPIDCHANGEOVERFROMTHEASSEMBLYOFONEPRODUCTTOTHEASSEMBLYOFANOTHERPRODUCTRAPIDHARDWARECHANGEOVERISMADEPOSSIBLETHROUGHTHEUSEOFROBOTS,FLEXIBLEPARTFEEDERS,MODULARGRIPPERSANDMODULARASSEMBLYHARDWARETHEFLEXIBLEFEEDERSRELYONBELTFEEDINGANDBINARYCOMPUTERVISIONFORPOSEESTIMATIONTHISHASADISTINCTADVANTAGEOVERNONFLEXIBLEFEEDINGSCHEMESSUCHASBOWLFEEDERSWHICHREQUIRECONSIDERABLEADJUSTMENTTOCHANGEOVERFROMONEPARTTOANOTHERRAPIDSOFTWARECHANGEOVERISBEINGFACILITATEDBYTHEUSEOFAREALTIME,OBJECTORIENTEDSOFTWAREENVIRONMENT,MODULARSOFTWARE,GRAPHICALSIMULATIONSFOROFFLINESOFTWAREDEVELOPMENT,ANDANINNOVATIVEDUALVMEBUSCONTROLLERARCHITECTURETHESEAGILEFEATURESPERMITNEWPRODUCTSTOBEINTRODUCEDWITHMINIMALDOWNTIMEANDSYSTEMRECONFIGURATION1INTRODUCTION11WHATISAGILEMANUFACTURINGAGILEMANUFACTURINGISATERMTHATHASSEENINCREASEDUSEININDUSTRYOVERTHEPASTSEVERALYEARSTHEDEFINITIONOF“AGILE”,HOWEVER,ISNOTCLEAR,NORISITCONSISTENT“AGILITYTHEMEASUREOFAMANUFACTURERSABILITYTOREACTTOSUDDEN,UNPREDICTABLECHANGEINCUSTOMERDEMANDFORITSPRODUCTSANDSERVICESANDMAKEAPROFIT”1“TODAYFACTORIESARECOMINGONLINETHATAREAGILEATTAILORINGGOODSTOACUSTOMERSREQUIREMENTS,WITHOUTHALTINGPRODUCTION”2“AGILEMANUFACTURINGASSIMILATESTHEFULLRANGEOFFLEXIBLEPRODUCTIONTECHNOLOGIES,ALONGWITHTHELESSONSLEARNEDFROMTOTALQUALITYMANAGEMENT,JUSTINTIMEPRODUCTIONANDLEANPRODUCTION”3THEONLYCOMMONTHREADAMONGTHEVARIOUSDEFINITIONSISTHEABILITYTOMANUFACTUREAVARIETYOFSIMILARPRODUCTSBASEDONWHATMAYBERAPIDLYCHANGINGCUSTOMERNEEDSINTHEPAST,PRODUCTIONWASGEAREDTOWARDHIGHVOLUMEPRODUCTIONOFASINGLEPRODUCTINTODAYSMARKET,HOWEVER,THEEMPHASISISMOVINGTOWARDSMALLLOTSIZESFROMANEVERCHANGING,CUSTOMERDRIVENPRODUCTLINEFIGURE1AGILEWORKCELLADEFINITIONOF“AGILE”MANUFACTURINGHASBEENADOPTEDWHICHAPPLIESTOLIGHTMECHANICALASSEMBLYOFPRODUCTSAGILEMANUFACTURINGISTHEABILITYTOACCOMPLISHRAPIDCHANGEOVERBETWEENTHEMANUFACTUREOFDIFFERENTASSEMBLIESUTILIZINGESSENTIALLYTHESAMEWORKCELLRAPIDCHANGEOVERMEASUREDINHOURS,FURTHER,ISDEFINEDASTHEABILITYTOMOVEFROMTHEASSEMBLYOFONEPRODUCTTOTHETHISPAPERTOBEPUBLISHEDINTHEPROCEEDINGSOFTHE1996IEEEINTERNATIONALCONFERENCEONROBOTICSANDAUTOMATIONFORMOREINFORMATION,CONTACTROGERQUINN,ASSOCIATEPROFESSORMECHANICALENGINEERINGCASEWESTERNRESERVEUNIVERSITY,2163683222ASSEMBLYOFANOTHERPRODUCTWITHAMINIMUMOFCHANGEINTOOLINGANDSOFTWARERAPIDCHANGEOVERENABLESTHEPRODUCTIONOFSMALLLOTSIZES,ALLOWINGFORJUSTINTIMEPRODUCTIONACENTRALTHEMEOFOURDEFINITIONOF“AGILE”MANUFACTURINGISTHEABILITYTORAPIDLYINTRODUCEMEASUREDINWEEKSNEWASSEMBLIESANDCOMPONENTSINTOTHESYSTEMINTHISSYSTEM,RAPIDCHANGEOVERISACCOMPLISHEDTHROUGHTHEUSEOFREUSABLESOFTWARE,QUICKCHANGEGRIPPERSFORTHEROBOTICMANIPULATORS,MODULARWORKTABLES,ANDPARTSFEEDERSWHICHAREFLEXIBLEENOUGHTOHANDLESEVERALTYPESOFPARTSWITHOUTNEEDINGMECHANICALADJUSTMENTTHESEFEEDERSUSEVISION,INPLACEOFHARDFIXTURING,TODETERMINETHEPOSITIONANDORIENTATIONOFPARTSGENERIC,REUSABLEVISIONROUTINESPERMITNEWPARTSTOBEADDEDTOTHESYSTEMWITHAMINIMUMOFEFFORTATESTBEDIMPLEMENTATIONOFANAGILEMANUFACTURINGWORKCELLHASBEENDEVELOPEDFIGURE1THISINCLUDESMECHANICALMANIPULATORS,FLEXIBLEPARTFEEDERS,AVISIONSYSTEMCAMERAS,FRAMEGRABBER,ANDALIBRARYOFIMAGEPROCESSINGROUTINES,ASWELLASALIMITEDNUMBEROFDEDICATEDSENSORSANDACTUATORSNEEDEDTOCOMPLETEAGIVENASSEMBLYTHECENTRALFEATUREOFSUCHAWORKCELLISACONTROLLERCAPABLEOFCONTROLLINGEACHOFTHEAFOREMENTIONEDCOMPONENTS12RELEVANCEOFCWRUWORKSEVERALCOMPANIESHAVEIMPLEMENTEDWHATMAYBECONSIDERED“AGILE”MANUFACTURINGMOTOROLAHASDEVELOPEDANAUTOMATEDFACTORYWITHTHEABILITYTOPRODUCEPHYSICALLYDIFFERENTPAGERSONTHESAMEPRODUCTIONLINE4ATPANASONIC,ACOMBINATIONOFFLEXIBLEMANUFACTURINGANDJUSTINTIMEPROCESSINGISBEINGUSEDTOMANUFACTUREBICYCLESFROMCOMBINATIONSOFAGROUPOFCOREPARTS5AGAINSTTHEBACKDROPOFSUCHWORK,THECWRUWORKCELLISINNOVATIVEINSEVERALWAYSTHEUSEOFVISIONGUIDED,FLEXIBLEPARTSFEEDERSISONEEXAMPLEANOTHERISTHEDEVELOPMENTOFSOFTWAREDESIGNPATTERNSFORAGILEMANUFACTURINGTHEOVERARCHINGDESIGNPHILOSOPHYOFQUICKCHANGEOVER,HOWEVER,ISWHATMAKESTHISWORKCELLPARTICULARLYNOVELTHECWRUWORKCELLHASBEENDESIGNEDTOBEAVERSATILEPRODUCTIONFACILITY,AMENABLETOAWIDERANGEOFAPPLICATIONSANDANENABLINGTECHNOLOGYFORFACTORYWIDEAGILEMANUFACTURING2WORKCELLHARDWARETHEAGILEWORKCELLDEVELOPEDATCWRUCONSISTSOFABOSCHFLEXIBLEAUTOMATIONSYSTEM,MULTIPLEADEPTSCARAROBOTS,ASMANYASFOURFLEXIBLEPARTSFEEDERSPERROBOT,ANDANADEPTMVCONTROLLERANIMPORTANTFEATUREOFTHEWORKCELLISTHECENTRALCONVEYORSYSTEM,WHICHWASIMPLEMENTEDUSINGSTANDARDBOSCHHARDWAREITISRESPONSIBLEFORTRANSFERRINGPARTIALLYCOMPLETEDASSEMBLIESBETWEENTHEROBOTSANDFORCARRYINGFINISHEDUNITSTOANUNLOADINGROBOTTHEROBOTSAREMOUNTEDONPEDESTALSNEARTHECONVEYORSYSTEMPALLETSWITHSPECIALIZEDPARTSFIXTURESAREUSEDTOCARRYASSEMBLIESTHROUGHOUTTHESYSTEM,AFTERWHICHTHEFINISHEDASSEMBLIESAREREMOVEDFROMTHEPALLETBYTHEUNLOADINGROBOTFINALLY,ASAFETYCAGEENCLOSESTHEENTIREWORKCELL,SERVINGTOPROTECTTHEOPERATORASWELLASPROVIDINGASTRUCTUREFORMOUNTINGOVERHEADCAMERAS21CONVEYORSYSTEMTHECONVEYORSYSTEMUSEDINTHECWRUWORKCELLISAMODELT2MANUFACTUREDBYBOSCHPALLETSARECIRCULATEDONTWOMAINCONVEYORLINESTHESELINESAREPARALLELTOEACHOTHERANDOPERATEINOPPOSITEDIRECTIONSPALLETSARETRANSFERREDBETWEENTHESETWOSECTIONSBYMEANSOFLIFTTRANSFERUNITSLTUSTHESEALLOWFORTHECIRCULATIONOFPALLETSAROUNDTHECONVEYORSYSTEMANDTHECAPABILITYTOREORDERTHEPALLETSEACHOFTHEPALLETSINTHESYSTEMISGIVENAUNIQUEIDENTIFICATIONNUMBER,ALLOWINGTHESYSTEMTOTRACKANDDIRECTITSPROGRESSSTOPSAREMOUNTEDATCRITICALPOINTSONTHECONVEYORTOCONTROLTHEFLOWOFTHEPALLETSANINNOVATIVEUSEOFTHISCONVEYORSYSTEMISTHEUSEOFSHORT“SPURLINES”ASPURFIGURE2ISSIMPLYANEXTENSIONOFTHECONVEYOR,PERPENDICULARTOTHEMAINLINEANALOGOUSTOARAILROADSPURTHISALLOWSTHEFLOWOFTHEMAINCONVEYORLINETOBEMAINTAINEDWHILEAROBOTPERFORMSANASSEMBLYATTHESPURPALLETSENTERINGASPURAREREGISTEREDINTHEROBOTSWORLDCOORDINATEFRAMEBYANARMMOUNTEDCAMERA,ALLOWINGTHEROBOTTOPLACEORREMOVEPARTSONTHEPALLETANDAVOIDINGTHEEXPENSEOFMECHANICALREGISTRATION22ASSEMBLYSTATIONSSEVERALASSEMBLYSTATIONLAYOUTSWEREANALYZEDINCHOOSINGTHEFINALLAYOUTAFTEREVALUATINGSEVERALFEATURESOFEACHLAYOUT,INCLUDINGPLACEMENTOFTHEROBOTSRELATIVETOTHECONVEYOR,IMPACTOFFEEDERPLACEMENTRELATIVETOTHEROBOTWORKENVELOPE,ANDTHEROBOTMOTIONSNECESSARYFORAGENERICASSEMBLY,ITWASDETERMINEDTHATTHELAYOUTINFIGURE2WOULDBESTSUITTHENEEDSOFTHEWORKCELLEACHASSEMBLYROBOTISSURROUNDEDBYTWOMODULAR,REMOVABLEWORKTABLESANDTWOFIXEDFEEDINGTABLESFIGURE2THEMODULARTABLESAREEASILYEXCHANGEABLE,ALLOWINGFORSPECIALIZEDASSEMBLYHARDWARETOBEPLACEDWITHINTHEROBOTSWORKENVELOPETHEMODULARTABLESCONTAINPNEUMATICACTUATORSANDTHISPAPERTOBEPUBLISHEDINTHEPROCEEDINGSOFTHE1996IEEEINTERNATIONALCONFERENCEONROBOTICSANDAUTOMATIONFORMOREINFORMATION,CONTACTROGERQUINN,ASSOCIATEPROFESSORMECHANICALENGINEERINGCASEWESTERNRESERVEUNIVERSITY,2163683222ELECTRICALSENSORSWHICHCANBECONNECTEDQUICKLY,ALLOWINGTHERAPIDCHANGEOFANYSPECIALIZEDTOOLINGREQUIREDFORAGIVENASSEMBLYBYDESIGNINGTHESETABLESTOBEMODULARANDEASILYEXCHANGED,DIFFERENTASSEMBLYHARDWARECANBEQUICKLYACCOMMODATEDTOACHIEVERAPIDCHANGEOVER,THEMODULARWORKTABLESAREREGISTEREDINTHEROBOTSWORLDCOORDINATESYSTEMINTHESAMEMANNERASTHEPALLETSIEUSINGANARMMOUNTEDCAMERATHEFEEDINGTABLESAREFIXED,ANDTHEHORIZONTAL,PARTSFEEDINGCONVEYORSAREMOUNTEDTOTHEMFIGURE2WORKSTATIONLAYOUTONEDRAWBACKOFTHECONVEYOR/SPURSYSTEM,ASOUTLINEDABOVE,ISTHETIMEREQUIREDTOEXCHANGEAFULLPALLETFORANEMPTYONEDURINGTHISTIMEAPPROXIMATELY15SECONDSTHEROBOTWOULDCONCEIVABLYBEINACTIVEASIMPLESOLUTIONTOTHISPROBLEMISAMINIWAREHOUSEAFIXTUREISLOCATEDONTHEEXCHANGEABLEPORTIONOFTHEWORKTABLETOHOLDAFEWCOMPLETEDASSEMBLIESDURINGAPALLETSWAP,THEROBOTCANCONTINUETHEASSEMBLYOPERATIONWORKINGWHILETHEINCOMINGPALLETARRIVES,PLACINGTHECOMPLETEDASSEMBLIESINTHEMINIWAREHOUSEAFTERTHEINCOMINGPALLETISTRANSFERREDTOTHESPUR,THEVISIONSYSTEMREGISTERSTHEPALLETTHEROBOTPLACESTHECURRENTASSEMBLYSTILLINITSGRIPPERONTHEPALLETANDTHENPROCEEDSTOMOVETHECOMPLETEDASSEMBLIESFROMTHEMINIWAREHOUSETOTHEPALLET23FLEXIBLEPARTSFEEDERSEACHFEEDERCONSISTSOFTHREECONVEYORSFIGURE3THEFIRSTCONVEYORISINCLINEDANDLIFTSPARTSFROMABULKHOPPERTHESECONDCONVEYORISHORIZONTAL,WITHATRANSLUCENTBELTITTRANSPORTSTHEPARTSTOTHEROBOT,PRESENTINGTHEMATANUNDERLITSECTIONNEARTHEROBOTTHETHIRDCONVEYORRETURNSUNUSEDORUNFAVORABLYORIENTEDPARTSTOTHEBULKHOPPERPROPERFUNCTIONINGOFTHEFEEDERSDEPENDSONTHEPARTSBEINGLIFTEDFROMTHEBULKHOPPERINAQUASISINGULATEDMANNERMANYFACTORSINFLUENCETHEEFFECTIVENESSOFTHEINCLINEDCONVEYORTHEANGLEOFTHECONVEYORWITHRESPECTTOTHEHORIZONTAL,THEBELTPROPERTIESEGCOEFFICIENTOFFRICTION,THETYPEOFBELTCLEATED,MAGNETIC,VACUUM,ANDTHELINEARSPEEDOFTHEBELT,FOREXAMPLEFIGURE3FLEXIBLEFEEDINGSYSTEMSCHEMATICWHENDIFFERENTPARTSARETOBEFED,THEBULKHOPPERISEMPTIEDANDFILLEDWITHTHENEWPARTSIFTHEPARTSAREOFASIMILARGEOMETRY,NOCHANGESTOTHEFEEDINGSYSTEMARETYPICALLYNEEDEDSOMEPARTS,SUCHASCIRCULARORCYLINDRICALONESIEONESTHATWOULDROLLBACKDOWNTHEINCLINEMAYNEEDADIFFERENTBELTSURFACE,SUCHASACLEATEDONE,ORADIFFERENTANGLEOFINCLINATIONOVERHEADCAMERASAREUSEDTOLOCATEPARTSONTHEHORIZONTALCONVEYORSANARRAYOFCOMPACTFLUORESCENTLIGHTSISINSTALLEDWITHINEACHOFTHEHORIZONTALCONVEYORSTHESELIGHTSTOGETHERWITHATRANSLUCENTCONVEYORBELTPROVIDEANUNDERLITAREAINWHICHPARTSCANBEPRESENTEDTOTHEVISIONSYSTEMUSINGBINARYVISIONTOOLSCURRENTLYPROVIDEDBYANADEPTVISIONSYSTEMPARTSONTHEFEEDERBELTSAREEXAMINEDFIRST,THEVISIONSYSTEMLOOKSTOSEEIFAPARTISGRASPABLEIETHEPARTISINARECOGNIZED,STABLEPOSEPOSITIONANDORIENTATIONANDENOUGHCLEARANCEEXISTSBETWEENTHEPARTANDITSNEIGHBORSTOGRASPITWITHAGRIPPERSECOND,THEPOSEOFTHEPARTINTHEROBOTSWORLDCOORDINATESISDETERMINEDTHISPOSE,ANDTHEMOTIONSASSOCIATEDWITHACQUIRINGTHEPART,ARECHECKEDTOMAKESURETHATTHEYAREWITHINTHEWORKENVELOPEOFTHEROBOT24VISIONSYSTEMONEESSENTIALFUNCTIONOFTHEVISIONSYSTEMISTODETERMINETHEPOSEOFCOMPONENTSFORFLEXIBLEPARTSFEEDINGPOSEESTIMATIONISPERFORMEDUSINGBUILTINFUNCTIONSOFTHEADEPTVISIONSOFTWARE,ANDMUSTBEFASTENOUGHNOTTOINTERFEREWITHTHEASSEMBLYCYCLETIMEASECONDARYFUNCTIONOFTHEVISIONSYSTEMISTOREGISTERPALLETSANDMODULARWORKTABLESTOAROBOTSWORLDCOORDINATESYSTEM,AVOIDINGTHENEEDFORALIGNMENTHARDWARESTILLANOTHERUSEMAYBEERRORRECOVERY,THISPAPERTOBEPUBLISHEDINTHEPROCEEDINGSOFTHE1996IEEEINTERNATIONALCONFERENCEONROBOTICSANDAUTOMATIONFORMOREINFORMATION,CONTACTROGERQUINN,ASSOCIATEPROFESSORMECHANICALENGINEERINGCASEWESTERNRESERVEUNIVERSITY,2163683222WHEREINTHECAMERASCANBEUSEDTOINSPECTCRITICALPOINTSINTHESYSTEM,ORINPROCESSASSEMBLIESTHEVISIONSYSTEMUSESANUMBEROFSTANDARDCCDCAMERAS,MOUNTEDEITHERABOVETHEFLEXIBLEPARTSFEEDERSORONTHEROBOTARMSSINCETHENUMBEROFCAMERAINPUTSTOTHEADEPTVISIONSYSTEMISLIMITEDTOFOUR,ALOWCOST,CUSTOMVIDEOMULTIPLEXERWASDEVELOPED,UTILIZINGAMONOLITHICVIDEOSWITCHERINTEGRATEDCIRCUITTHISALLOWSUPTOFOURCAMERASTOBEATTACHEDTOEACHVIDEOINPUTONTHEVIDEOHARDWAREINKEEPINGWITHTHEQUICKCHANGEOVERPHILOSOPHY,THEVISIONROUTINESAREDESIGNEDTOBEREUSABLETHATISAGIVENROUTINEMAYBEUSEDTOLOCATESEVERALDIFFERENTBUTSIMILARPARTSIESIMILARASYMMETRIES,TOPOLOGY,ETCTHISAPPROACHHASMANYADVANTAGES,INCLUDINGMINIMIZINGTHENUMBEROFSOFTWAREROUTINESINADDITION,THISREUSABILITYALLOWSFORSOFTWAREMODULARITYAND“AGILITY6”FOREXAMPLE,BYPARAMETERIZINGTHECHARACTERISTICSTHATAROUTINESEARCHESFOR,ITCANBEAPPLIEDTOPARTSTHATHAVEASIMILARPROFILEBUTAREOFADIFFERENTSIZETHISMEANSTHATPARTSWITHSIMILARGEOMETRIESTOTHOSEINTHEPARTSLIBRARYCANBEADDEDTOTHESYSTEMBYSIMPLYMODIFYINGTHEINSPECTIONPROCEDURESTHATCALLTHESELOWERLEVEL,REUSABLEROUTINES25INTRODUCTIONOFNEWPARTSADDINGANEWPARTTOTHESYSTEMINVOLVESAFEWWELLDEFINEDTASKSAVISIONROUTINEWHICHDETERMINESTHEPOSEOFTHEPARTISDEVELOPED,UTILIZINGTHELIBRARYOFREUSABLEVISIONROUTINESIFTHENEWPARTHASCHARACTERISTICSTHATAPPEARNOWHEREELSEINTHEPARTSLIBRARY,NEWROUTINESMAYNEEDTOBEADDEDTOTHESOFTWARELIBRARYALSO,IFTHEPARTHASNOTBEENDESIGNEDFORUSEONTHEGENERICPARTSFEEDERSEGITHASNOSTABLEPOSES,LIKEACYLINDER,THEFEEDERSMAYREQUIREABELTCHANGEORACHANGEINTHEANGLEOFINCLINATIONAGRIPPERMUSTALSOBEDESIGNEDTOMANIPULATETHENEWPARTINORDERTOMINIMIZETHESPECIALIZEDHARDWAREANDAVOIDTOOLCHANGESDURINGASSEMBLY,THEGRIPPERDESIGNSHOULDBEPERFORMEDCONCURRENTLYWITHTHEGRIPPERDESIGNSFOROTHERPARTSTOBEASSEMBLEDATAGIVENROBOTFORINSTANCE,IFAGIVENOPERATIONREQUIRESBOTHANAWIDGETANDABWIDGETTOBEASSEMBLEDATTHEFIRSTROBOT,THEGRIPPERDESIGNERSHOULDTAKETHISINTOACCOUNTINGENERAL,ITISBESTTODESIGNTHEPARTSANDTHEASSOCIATEDHARDWARECONCURRENTLYTHISWILLALLOWMAXIMUMREUSEOFSOFTWARE,MINIMALCHANGETOTHEFLEXIBLEFEEDINGSETUPANDTHEDESIGNOFAROBUSTASSEMBLYSEQUENCEWHICHWILLENHANCEUNATTENDEDOPERATIONTHISAPPROACHISKNOWNASDESIGNFORMANUFACTURINGANDASSEMBLY7,ORSIMPLYDFMA3COMPUTERHARDWARE/CONTROLLERDESIGNTHECURRENTSOFTWAREHASBEENDEVELOPEDENTIRELYINTHEV8PROGRAMMINGLANGUAGEANDOPERATINGSYSTEM,ONADEPTSMVCONTROLLERFORMOSTINDUSTRIALAPPLICATIONS,THISPROGRAMMINGENVIRONMENTWOULDBESUFFICIENTHOWEVER,ITLACKSTHEPOWERANDFLEXIBILITYNEEDEDTOSUPPORTRAPIDSOFTWAREDEVELOPMENTANDCHANGEOVERTHISISLARGELYBECAUSEVLACKSFEATURESWHICHARESTANDARDINOTHERLANGUAGESANDOPERATINGSYSTEMS,SUCHASUSERDEFINEDFUNCTIONS,STANDARDDATASTRUCTURESANDSHELLSCRIPTEXECUTIONTOCIRCUMVENTTHESELIMITATIONS,AMOREEXTENSIVECONTROLLERINTERFACEDESIGNISUNDERDEVELOPMENTITWILLALLOWTHESYSTEMTOSUPPORTCANDC,ANDPROVIDEAFRIENDLIERANDMOREFLEXIBLEUSERINTERFACEINADDITION,ITWILLALLOWTHEUSEOFAREALTIMEOPERATINGSYSTEM,THUSSIMPLIFYINGSOFTWAREDEVELOPMENTANDIMPROVINGPERFORMANCEI/OREFLECTIVEMEMORYNETWORKETHERNETADEPTMVCONTROLLERAGILEWORKCELLNONADEPTVMECAGEWORKSTATIONFIGURE4SYSTEMARCHITECTUREINTHISDESIGN,THESYSTEMSCAPABILITIESAREEXPANDEDBYUSINGASECONDVMEBUSINADDITIONTOTHEMVCONTROLLERVMEBUSFIGURE4THISSECONDVMEBUSHOUSESI/OBOARDSANDDEDICATEDSINGLEBOARDCOMPUTERSSBCS,ONWHICHAREALTIMEOPERATINGSYSTEMEXECUTESCANDCPROGRAMSRUNNINGONTHESBCSARERESPONSIBLEFORALLHIGHLEVELCONTROLANDROBOTMOTIONSEGCONVEYORCONTROL,PNEUMATICOPERATIONS,SPECIFYINGROBOTDESTINATIONS,WHILETHEMVCONTROLLERISUSEDEXCLUSIVELYFORLOWLEVELROBOTMOTIONSEGSERVOCONTROLANDTRAJECTORYGENERATIONANDSOMEMACHINEVISIONROUTINESINLATERIMPLEMENTATIONS,AVISIONPROCESSINGBOARDCANALSOBEUSEDONTHESECONDVMEBUS,THEREBYAUGMENTINGTHEADEPTVISIONSYSTEMTHETWOBUSESARECONNECTEDBYAREFLECTIVEMEMORYNETWORKTHISCONSISTSOFTWOMEMORYCARDS,ONEONEACHBUS,WHICHCANBECONNECTEDBYEITHERACABLEORAFIBEROPTICLINKCHANGESMADETOMEMORYONTHISPAPERTOBEPUBLISHEDINTHEPROCEEDINGSOFTHE1996IEEEINTERNATIONALCONFERENCEONROBOTICSANDAUTOMATIONFORMOREINFORMATION,CONTACTROGERQUINN,ASSOCIATEPROFESSORMECHANICALENGINEERINGCASEWESTERNRESERVEUNIVERSITY,2163683222ONEBOARDAREAUTOMATICALLYREFLECTEDONTHEOTHER,THUSALLOWINGCOMMANDSANDDATATOBETRANSMITTEDBETWEENTHETWOBUSES9THESBCSCANTHUSPLACEROBOTANDVISIONCOMMANDSONTHEREFLECTIVEMEMORYNETWORKTHESEAREREADBYASETOFCOMMANDSERVERSRUNNINGONTHEMVCONTROLLERTHESERVERSEXECUTETHECOMMANDSAND,WHEREAPPLICABLE,RETURNTHERESULTSVIATHESAMENETWORK4WORKCELLSOFTWARESOFTWAREISANOTHERKEYTOTHEFLEXIBILITYOFANAGILEMANUFACTURINGWORKCELLHOWEVER,THISFLEXIBILITYDOESNOTCOMEWITHOUTCAREFULDESIGNALTHOUGHSOFTWAREISINHERENTLYEASIERTOCHANGETHANHARDWARE,THESTRUCTUREOFASOFTWARESYSTEMCANDEGRADEAFTERREPEATEDMODIFICATION,LEADINGTOPOORRELIABILITYANDINCREASEDMAINTENANCECOSTSINDESIGNINGTHEWORKCELLCONTROLSOFTWARE,WEHAVEEMPLOYEDSOFTWAREENGINEERINGMETHODSANDTOOLSTHATSUPPORTTHEPRINCIPLEOFDESIGNFORCHANGEINPARTICULAR,OURLATESTDESIGNISOBJECTORIENTEDOO,THATIS,ITISBASEDUPONIDENTIFYINGTHEOBJECTSOFTHESYSTEM,WHICHARETHOSEENTITIESHAVINGASTATEANDABEHAVIORPHYSICALDEVICES,ABSTRACTDATASTRUCTURES,ANDENTIRESUBSYSTEMSAREMODELEDASOBJECTSTHATPROVIDEAWELLDEFINEDSETOFSERVICESWHOSEIMPLEMENTATIONISENCAPSULATEDANDHIDDENEMPHASISONOOSOFTWAREDESIGNREDUCESTHEAMOUNTOFEFFORTREQUIREDTOINTRODUCENEWPRODUCTSINTOTHEWORKCELLTHROUGHREUSABLECODETHEABILITYTORAPIDLYINTRODUCENEWPRODUCTSINTOTHEWORKCELLISCRUCIALTOANAGILESYSTEMOBJECTTYPESORCLASSESAREDEFINEDUSINGTHECCLASSCONSTRUCT,WHEREINSERVICESCORRESPONDTOMEMBERFUNCTIONCALLSNEWCLASSESAREDERIVEDFROMEXISTINGONESBYADDINGSERVICESORBYOVERRIDINGTHEIMPLEMENTATIONSOFEXISTINGSERVICESOBJECTORIENTATIONFACILITATESMAINTENANCEBECAUSETHEIMPLEMENTATIONOFACLASSCANBECHANGEDWITHOUTAFFECTINGCLIENTCODE,WHICHUSESTHECLASSSSERVICES,ANDBECAUSEADERIVEDCLASSCANBEUSEDWHEREVERITSPARENTCLASSCANBEINADDITIONTOSATISFYINGTHEREQUIREMENTSOFOURPARTICULARMANUFACTURINGAPPLICATION,WEWISHTOSPECIFYSOFTWAREDESIGNCOMPONENTSTHATMIGHTPROVEUSEFULINAVARIETYOFAGILEMANUFACTURINGAPPLICATIONSHENCE,WEHAVESOUGHTTOIDENTIFYDESIGNPATTERNSFORAGILEMANUFACTURINGADESIGNPATTERNISAGROUPOFCOMMUNICATINGOBJECTSORCLASSESWHICHTOGETHERREPRESENTAREUSABLEDESIGNELEMENTTHATISAPPLICABLE,AFTERSOMESPECIALIZATION,TOAVARIETYOFSYSTEMS10SOFAR,WEHAVEIDENTIFIEDDESIGNPATTERNSFORSUCHACTIVITIESASOVERALLSYSTEMCONTROL,COMMUNICATIONBETWEENSYSTEMCOMPONENTS,PROVISIONOFPARTSANDASSEMBLIES,SCHEDULINGOFSYSTEMTASKS,ANDERRORHANDLING41OPERATINGSYSTEMTHEINITIALVERSIONSOFTHEWORKCELLCONTROLSOFTWAREWEREIMPLEMENTEDWITHTHEVOPERATINGSYSTEMANDPROGRAMMINGLANGUAGEPROVIDEDWITHTHEADEPTMVCONTROLLERALTHOUGHVPROVIDESADEQUATEFACILITIESFORMANYROBOTICAPPLICATIONS,WEDETERMINEDTHATAMOREADVANCEDOPERATINGSYSTEMANDPROGRAMMINGLANGUAGEWOULDBETTERSUPPORTOURSOFTWAREDESIGNPHILOSOPHYANDTHEGOALSOFAGILEMANUFACTURINGINGENERAL,WORKCELLCONTROLINVOLVESTHEMANAGEMENTOFANUMBEROFCONCURRENTTASKSWITHREALTIMECONSTRAINTSHENCE,AREALTIMEOPERATINGSYSTEMRTOSWITHSUFFICIENTANDRELIABLEFACILITIESFORTASKSCHEDULING,COMMUNICATION,ANDSYNCHRONIZATIONISDESIRABLE42SOFTWAREARCHITECTURETHEWORKCELLCONTROLSOFTWAREISDESIGNEDASAHIERARCHYOFSERVERSATTHEHIGHESTLEVEL,THEWORKCELLCONTROLLERSERVICESREQUESTSFROMTHEHUMANOPERATORFORCRATESOFFINISHEDASSEMBLIESINDOINGSO,ITCOMMUNICATESWITHSUBORDINATESERVERSITMAKESREQUESTSTOTHEPALLETSERVERTOMOVEPALLETSALONGTHECONVEYORBETWEENSPURSTHEPALLETSERVERTRACKSTHEMOVEMENTOFEACHPALLET,BUTTHEWORKCELLCONTROLLERISRESPONSIBLEFORKNOWINGPALLETCONTENTSTHEWORKCELLCONTROLLERMAKESREQUESTSTOASSEMBLYSERVERS,WHICHAREASSOCIATEDWITHROBOTS,TOFILLPAL