moreS.TAuc,University10(CNC)STEP-NCmachinetools.ThedatamodelrepresentsacommonstandardspecificallyaimedattheintelligentCNCmanufacturingworkstation,makingtheComputersinIndustry57(2006)goalofastandardisedCNCcontrollerandNCcodegenerationfacilityareality.ItisbelievedthatCNCmachinesimplementingSTEP-NCwillbethebasisforamoreopenandadaptablearchitecture.ThispaperoutlinesafuturisticviewofSTEP-NCtosupportdistributedinteroperableintelligentmanufacturingthroughglobalnetworkingwithautonomousmanufacturingworkstationswithSTEPcompliantdatainterpretation,intelligentpartprogramgeneration,diagnosticsandmaintenance,monitoringandjobproductionscheduling.#2005ElsevierB.V.Allrightsreserved.Keywords:CNC；Interoperability；STEP；STEP-NC1.IntroductionFromthestartofcraftproductioninthe1800stothepioneeringmassproductionoftheearly1900stherehavebeenanumberofrevolutionarychangestomanufacturingsystemsconfigurations.Themostrecognisedtraditionalconfigurationofmanufacturingsystemswasthededicatedtransfer(machine)line,whichenabledmassproductionathighefficiencyandlowcost.Withtheneedofthe1970sand1980stoproduceawiderrangeofparts,flexiblemanufacturingwasdevelopedtomeettheseneedsfortheproductionofsmallerbatchesofdifferentparts.Thesesystemsusedgroupsofcomputernumericallycontrolled(CNC)machinesthatcouldbereprogrammedtomakedifferentpartscombinedwithautomatedtransportsystemsandstorage.TheseCNCmachinesbecamethecentralelementsinthesystemssuchasflexibletransferlines,flexiblemanufacturingsystems(FMS)andflexiblemanufacturingcells(FMC).However,theamountofflexibilityexistinginthesesystemswasstillbelievedtobelimited.Inordertopreparemanufacturingcompaniestofaceincreasinglyfrequentandunpredictablemarketchangeswithconfidence,interoperableandmoreopenmanufacturingsystemsareneeded.Intheprocessofdesigningandoperatinginteroperableandopenmanufacturingsystemsthereisaneedtodistinguishfromamongsystem-levelissues,component-level(i.e.machineandcontrol)issues,andramp-uptimereductionissues1,2.Mostoftheresearchefforthasbeensparedontheissuesatthesystemlevel,someatthecomponentlevelandlittleontheramp-uptimereductionissues.Atthecomponentlevel,researchworkhasprimarilycentredaroundthecontrolissuesconcerningmachinetools,withtheaimtoprovideenablingCNCtechnologiesformodularandopen-architecturecontrol3,4.CNCmachinetoolsarethemaincomponentsinanymanufacturingsystem.Therearedemandsandnewopportu-nitiestoempowerthecurrentCNCmachineswiththemuch-neededfeaturessuchasinteroperability,adaptability,agilityandreconfigurability.Tothisend,therearetwomajorissuesthatneedtobeaddressednamelyproductdatacompatibility/*Correspondingauthor.Tel.:+6493737599x84527；fax:+6493737479.E-mailaddress:x.xuauckland.ac.nz(X.W.Xu).0166-3615/$seefrontmatter#2005ElsevierB.V.Allrightsreserved.doi:10.1016/pind.2005.06.002MakingCNCmachinetoolsintelligentareviewX.W.Xua,*,aDepartmentofMechanicalEngineering,SchoolPrivateBag92019,bDepartmentofMechanicalEngineeringReceived30August2004；AvailableonlineAbstractTheaimofthenextgenerationofcomputernumericallycontrolledyears,G-codes(ISO6983)havebeenextensivelyusedbytheCNCmachinedevelopingnextgenerationofCNCmachines.Anewstandardknownasopen,interoperableandofthetechnologies.NewmanbofEngineering,TheUniversityofAuckland,kland,NewZealandofBath,Bath,BA27AY,UKaccepted7June2005October2005machinesistobeportable,interoperableandadaptable.OverthetoolsforpartprogrammingandarenowconsideredasabottleneckforisbeingdevelopedasthedatamodelforanewbreedofCNC/locate/compind141152rsinteroperabilityandadaptableCNCmachines.Uptillnowlittleresearchhasbeencarriedoutinthisfield,butduetothedevelopmentsofthenewCNCdatamodelknownasSTEP-NC,therehasbeenasurgeofresearchactivitiesintryingtoaddresstheabove-mentionedissues.Thispaperreportsontheseresearchactivitiesandtriestoaddresstheissuesofinteroper-abilityandadaptabilityforCNCmachinetools.2.ImpedimentsofcurrentCNCtechnologiesTodaysCNCmachinedesignsarewelldevelopedwithcapabilitiessuchasmulti-axiscontrol,errorcompensationandmulti-processmanufacture(binedmill/turn/laserandgrindingmachines).Inthemeantime,thesecapabilitieshavemadetheprogrammingtaskincreasinglymoredifficultandmachinetoolsthemselveslessadaptable.Someefforthasbeenmadetoalleviatethisproblem,inparticularlythetrendtowardsopenarchitecturecontrol,basedonOSACA5andopenmodulararchitecturecontroller(OMAC)6,wherethirdpartysoftwarecanbeusedatthecontrollerworkingwithinastandardwindowsoperatingsystem.Onefurtherrecognisableindustrialdevelopmentistheapplicationofsoftwarecontrollers,wherePLClogiciscapturedinsoftwareratherthaninhardware.AlthoughthesedevelopmentshaveimprovedsoftwaretoolsandthearchitectureofCNCsystems,vendorsandusersarestillseekingacommonlanguageforCAD,CAPP,CAM,andCNC,whichintegratesandtranslatestheknowledgeofeachstagewithnoinformationloss.ThoughtherearemanyCAMtoolssupportingNCmanufacture,theproblemofadaptabilityandinteroperabilityfromsystemtosystemwasandisstillseenasoneofthekeyissuesinlimitingthewideruseofthesetools.2.1.ProductdatacompatibilityandinteroperabilityCNCmachinetoolscompletetheproductdesignandmanufacturinglifecycle,andmoreoftenthannottheyhavetocommunicatewithupstreamsub-systems,suchasCAD,CAPPandCAM.Inthecasewhenneutraldataexchangeprotocols,suchasSET,VDA,andinitialgraphicsexchangespecification(IGES)areused,informationexchangecanhappenbetweenheterogeneousCADand/orCAMsystems.ThisishoweveronlypartiallysuccessfulsincetheseprotocolsaremainlydesignedtoexchangegeometricalinformationandnottotallysuitabletoalltheneedsoftheCAD/CAPP/CAMindustry.Thus,theinternationalcommunitydevelopedtheISO103037setofstandards,wellknownasSTEP.ByimplementingSTEPAP-2038andSTEPAP-2149withinCADsystems,thedataexchangebarrierisremoved.Yet,dataexchangeproblemsbetweenCAD/CAMandCNCsystemsremainunsolved.CADsystemsaredesignedtodescribethegeometryofapartprecisely,whereasCAMsystemsfocusonusingcomputersystemstogenerateplansandcontrolthemanufacturingoperationsaccordingtothegeometricalinformationpresentinaCADmodelandtheexistingresourcesontheshop-floor.ThefinalresultfromaCAMsystemisasetofCNCprogramsthatcanbeexecutedonaCNCmachine.STEPX.W.Xu,S.T.Newman/Compute142AP-203andSTEPAP-214onlyunifytheinputdataforaCAMsystem.OntheoutputsideofaCAMsystem,a50-year-oldinternationalstandardISO6983(knownasG-CodeorRS274D)10stilldominatesthecontrolsystemsofmostCNCmachines.Outdatedyetstillwidelyused,ISO6983onlysupportsone-wayinformationflowfromdesigntomanufactur-ing.TheCADdataarenotutilisedatamachinetool.Instead,theyareprocessedbyapost-processoronlytoobtainasetoflow-level,incompletedatathatmakesmodification,verifica-tionsandsimulationdifficult.Thechangesmadeattheshop-floorcannotbedirectlyfedbacktothedesigner.Hence,invaluableexperiencesontheshop-floorcannotbepreservedandre-utilised.2.2.InflexibleCNCcontrolregimeTheISO6983standardfocusesonprogrammingthepathofthecuttercentrelocation(CL)withrespecttothemachineaxes,ratherthanthemachiningtaskswithrespecttothepart.Thus,ISO6983definesthesyntaxofprogramstatements,butinmostcasesleavesthesemanticsambiguous,togetherwithlow-levellimitedcontroloverprogramexecution.Theseprograms,whenprocessedinaCAMsystembyamachine-specificpost-processor,becomemachine-dependent.InordertoenhancethecapabilityofaCNCmachine,CNCcontrollervendorshavealsodevelopedtheirowntailoredcontrolcommandsetstoaddmorefeaturestotheirCNCcontrollerstoextendISO6983.Thesecommandsetsonceagainvaryfromvendortovendorresultinginfurtherincompatibledataamongthemachinetools.ThecurrentinflexibleCNCcontrolregimemeansthattheoutputfromaCAMsystemhasnoadaptability,whichinturndeniestheCNCmachinetoolsofhavinganyinteroperability.ThemainreasonisthataG-codebasedpartprogramonlycontainslow-levelinformationthatcanbedescribedashow-to-doinformation.TheCNCmachinetools,nomatterhowcapabletheyare,candonothingbutfaithfullyfollowtheG-codeprogram.Itisimpossibletoperformintelligentcontrolnormachiningoptimization.3.TheSTEP-NCstandardTodayanewstandardnamelyISO146491116recognisedinformallyasSTEP-NCisbeingdevelopedbyvendors,usersandacademicinstitutesworldwidetoprovideadatamodelforanewbreedofintelligentCNCs.ThedatamodelrepresentsacommonstandardspecificallyaimedatNCprogramming,makingthegoalofastandardisedCNCcontrollerandNCcodegenerationfacilityareality.CurrentlytwoversionsofSTEP-NCarebeingdevelopedbyISO.ThefirstistheApplicationReferenceModel(ARM)(i.e.ISO14649)andtheotherApplicationInterpretedModel(AIM)ofISO14649(i.e.ISO10303AP-23817).Formoreinformationontheuseanddifferencesbetweenthemreadersarereferredto18,19.ContrarytothecurrentNCprogrammingstandard(ISO6983),ISO14649isnotamethodforpartprogramminganddoesnotnormallydescribethetoolmovementsforaCNCinIndustry57(2006)141152machine.Instead,itprovidesanobjectorienteddatamodelforCNCswithadetailedandstructureddatainterfacethatincorporatesfeature-basedprogrammingwherearangeofinformationisrepresentedsuchasthefeaturestobemachined,tooltypesused,theoperationstoperform,andthesequenceofoperationstofollow.ThoughitispossibletocloselydefinethemachinetooltrajectoryusingSTEP-NC,theaimofthestandardistoallowthesedecisionstobemadeatalatterstagebyanewbreedofintelligentcontrollerSTEP-NCcontroller.ItistheaimthatSTEP-NCpartprogramsmaybewrittenonceandusedonmanydifferenttypesofmachinetoolcontrollerprovidingthemachinehastherequiredprocesscapabilities.Indoingthis,bothCNCmachinetoolsandtheircontrolprogramsaremadeadaptableandinteroperable.Fig.1illustratesthatbothgeometricandmachininginformationcannowbebi-directionallytransferredbetweenaCAD/CAMsystemandaSTEP-NCcontroller20.OnecriticalissueisthatthetoolpathmovementinformationisoptionalandideallyshouldbegeneratedatthemachinebytheSTEP-NCcontroller.Geometricinformationisdefinedbymachiningfeatures(similartoAP-22422)withmachiningoperationstermedWorkingstepsperformedononeormorefeatures.TheseC15STEP-NCprovidesacompleteandstructureddatamodel,linkedwithgeometricalandtechnologicalinformation,sothatnoinformationislostbetweenthedifferentstagesoftheproductdevelopmentprocess.C15ItsdataelementsareadequateenoughtodescribetaskorientedNCdata.C15Thedatamodelisextendabletofurthertechnologiesandscalable(withconformanceclasses)tomatchtheabilitiesofaspecificCAM,SFPorNC.C15MachiningtimeforsmalltomediumsizedjoblotscanbereducedbecauseintelligentoptimisationcanbebuiltintotheSTEP-NCcontrollers.C15Post-processormechanismwillbeeliminated,astheinter-facedoesnotrequiremachine-specificinformation.C15MachinetoolsaresaferandmoreadaptablebecauseSTEP-NCisindependentfrommachinetoolvendors.C15Modificationattheshop-floorcanbesavedandfedbacktothedesigndepartmenthencebi-directionalinformationflowfromCAD/CAMtoCNCmachinescanbeachieved.C15XMLfilescanbeusedasaninformationcarrierhenceenableWeb-baseddistributedmanufacturing.X.W.Xu,S.T.Newman/ComputersinIndustry57(2006)141152143WorkingstepsprovidethebasisofaWorkplantomanu-facturethecomponent.Fig.2illustratesanactualextractofsuchdataforapartwithaWorkplanconsistingofWorkingstepsforslotting,drillingandpocketing.OneimportantpointtonoteisthatthiscodeistheSTEP-NCtransfer(physical)file,whichisimported/exportedintoandoutofaSTEP-NCintelligentcontroller.Thisfilewouldbeinterpretedbythecontroller,enablingCNCoperatorstointeractataWorkingstep(i.e.machiningoperation)levelviaanintelligentmanualdatainterface(MDI)orCAD/CAMsystematthecontroller.SomeofthebenefitswithusingSTEP-NCareasfollows23.Fig.1.Bi-directionalinformationAdetaileddiscussiononvaluepropositionforSTEP-NCcanbefoundinareportproducedbytheOMACSTEP-NCWorkingGroup24andotherpublications20,23,25.4.STEP-NCinternationalcommunityInthesecondhalfofthe1990s,aneffortfromtheinternationalcommunitybackedbyISOstartedthemajorchangeintheconceptofNCprogramming,throughaninternationalintelligentmanufacturingsystems(IMS)pro-gramme26.Theprogrammewasco-ordinatedacrossfourflowwithSTEP-NC21.rsX.W.Xu,S.T.Newman/Compute144worldwideregionseachwithindividualprojectsnamelyEurope,Korea,SwitzerlandandtheUSA.Themajorco-ordinatorsoftheprogrammeareSiemens(EU),CADCAMa-tion(Switzerland),STEPTools(USA)andERC-ACI(Korea).STEP-NCEuropeisresponsibleformilling,turningandinspectionoftheISO14649standard.Ithas15partners,ledbySiemens,withuserssuchasDaimlerChrysler,Volvo,andthesupportofresearchinstitutessuchasWZLRWTH-AachenandISWStuttgartUniversity.TheSwissareleadingthedevelop-mentofthestanda