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英文原文ApplicationanddevelopmentOfcasebasedreasoninginfixturedesignAbstract:Basedonthecasebaseddesigning(CBD)methodology,thefixturesimilarityisintworespects:thefunctionandthestructureinformation.Then,thecomputeraidedfixturedesignsystemiscreatedoncasebasedreasoning(CBR),inwhichtheattributesofthemainfeaturesofworkpieceandstructureoffixtureascaseindexcodearedesignedfortheretrieveofthesimilarcases,andthestructureandhierarchicalrelationofcaselibraryaresetupforstore.Meanwhile,thealgorithmbasedontheknowledgeguidedintheretrieveofthesimilarcases,thestrategyofcaseadaptationandcasestorageinwhichthecaseidentifcationnumberisusedtodistinguishfromsimilarcasesarepresented.Theapplicationofthesysteminsomeprojectsimprovesthedesignefficiencyandgetsagoodresult.Keywords:casebasedreasoning；fixturedesign；computeraideddesign(CAD)Fixturesaredevicesthatserveasthepurposeofholdingtheworkpiecesecurelyandaccurately,andmaintainingaconsistentrelationshipwithrespecttothetoolswhilemachining.Becausethefixturestructuredependsonthefeatureoftheproductandthestatusoftheprocessplanningintheenterprise,itsdesignisthebottleneckduringmanufacturing,whichrestrainstoimprovetheefficiencyandleadtime.Andfixturedesignisacomplicatedprocess,basedonexperiencethatneedscomprehensivequalitativeknowledgeaboutanumberofdesignissuesincludingworkpiececonfiguration,manufacturingprocessesinvolved,andmachiningenvironment.ThisisalsoaverytimeconsumingworkwhenusingtraditionalCADtools(suchasUnigraphics,CATIAorPro/E),whicharegoodatperformingdetaileddesigntasks,butprovidefewbenefitsfortakingadvantageofthepreviousdesignexperienceandresources,whicharepreciselythekeyfactorsinimprovingtheefficiency.Themethodologyofcasebasedreasoning(CBR)adaptsthesolutionofapreviouslysolvedcasetobuildasolutionforanewproblemwiththefollowingfoursteps:retrieve,reuse,revise,andretain1.Thisisamoreusefulmethodthantheuseofanexpertsystemtosimulatehumanthoughtbecauseproposingasimilarcaseandapplyingafewmodificationsseemstobeselfexplanatoryandmoreintuitivetohumans.Sovariouscasebaseddesignsupporttoolshavebeendevelopedfornumerousareas2-4,suchasininjectionmoldinganddesign,architecturaldesign,diecastingdiedesign,processplanning,andalsoinfixturedesign.Sunusedsixdigitalstocomposetheindexcodethatincludedworkpieceshape,machineportion,bushing,the1stlocatingdevice,the2ndlocatingdeviceandclampingdevice5.Butthesystemcannotbeusedforotherfixturetypesexceptfordrillfixtures,andcannotsolvetheproblemofstorageofthesameindexcodethatneedstoberetained,whichisveryimportantinCBR6.1ConstructionofaCaseIndexandCaseLibrary1.1CaseindexThecaseindexshouldbecomposedofallfeaturesoftheworkpiece,whicharedistinguishedfromdifferentfixtures.Usingallofthemwouldmaketheoperationinconvenient.Becausetheformsofthepartsarediverse,andthetechnologyrequirementsofmanufactureintheenterprisealsodevelopcontinuously,lotsoffeaturesusedasthecaseindexwillmakethesearchrateslow,andthemainfeatureunimportant,forthereasonthattherelativeweightwhichisallottedtoeveryfeaturemustdiminish.Andontheotherhand,itishardtoincludeallthefeaturesinthecaseindex.Therefore,consideringthepracticalityandthedemandofrapiddesign,thecaseindexincludesboththemajorfeatureoftheworkpieceandthestructureoffixture.Thecaseindexcodeismadeupof16digits:13digitsforcasefeaturesand3digitsforcaseidentificationnumber.Thefirst13digitsrepresent13features.Eachdigitiscorrespondingtoanattributeofthefeature,whichmaybeoneof“*”,“？”,“1”,“2”,“A”,“B”,“Z”,etc.Inwhich,“*”meansanyone,“?”uncertain,“0”nothing.Thesystemrules:fixturetype,workpieceshape,locatingmodelcannotbe“*”or“?”.Whenthesystemisdesigned,theattributeinformationofthethreeitemsdoesnothavetheseoptions,whichmeansthecertainattributemustbeselected.Thelastthreedigitsarethecaseidentificationnumber,whichmeansthe13digitsofthecasefeaturearethesame,andthenumberofthesethreedigitsisusedfordistinguishingthem.Thesystemalsorules:“000”isaprototypecase,whichisusedforretrieval,andothercasesare“001”,“002”,whichareusedforreferencecasestobesearchedbydesigners.Ifoccasionallyoneofthemneedstobechangedastheprototypecase,firstitmustberequiredtoapplytochangetheoneto“000”,andtheformerischangedtoreferentialcaseautomatically.TheconstructionofthecaseindexcodeisshowninFig.1.1.2CaselibraryThecaselibraryconsistsoflotsofpredefinedcases.Caserepresentationisoneofthemostimportantissuesincasebasedreasoning.Socompoundingwiththeindexcode,.1.3HierarchicalformofCaseThestructuresimilarityofthefixtureisrepresentedasthewholefixturesimilarity,componentssimilarityandcomponentsimilarity.Sothewholefixturecaselibrary,componentscaselibrary,componentcaselibraryoffixtureareformedcorrespondingly.Usuallydesigninformationofthewholefixtureiscomposedofworkpieceinformationandworkpieceprocedureinformation,whichrepresentthefixturesatisfyingthespecificallydesigningfunctiondemand.Thewholefixturecaseismadeupoffunctioncomponents,whicharedescribedbythefunctioncomponentsnamesandnumbers.Thecomponentscaserepresentsthemembers.(functioncomponentandotherstructurecomponents，maindrivenparameter,thenumber,andtheirconstrainrelations.)Thecomponentcase(thelowestlayerofthefixture)isthestructureoffunctioncomponentandothercomponents.Inthemodernfixturedesigntherearelotsofparametricstandardpartsandcommonnonstandardparts.Sothecomponentcaselibraryshouldrecordthespecificationparameterandthewayinwhichitkeepsthem.2StrategyofCaseRetrievalInthecasebaseddesignoffixtures,themostimportantthingistheretrievalofthesimilarity,whichcanhelptoobtainthemostsimilarcase,andtocutdownthetimeofadaptation.Accordingtotherequirementoffixturedesign,thestrategyofcaseretrievalcombinesthewayofthenearestneighborandknowledgeguided.Thatis,firstsearchondepth,thenonbreadth；theknowledgeguidedstrategymeanstosearchontheknowledgerulefromroottotheobject,whichisfirstlysearchedbythefixturetype,thenbytheshapeoftheworkpiece,thirdlybythelocatingmethod.Forexample,ifthecaseindexcodeincludesthemillingfixtureoffixturetype,thesearchisjustforallmillingfixtures,thenforboxofworkpieceshape,thethirdfor1plane+2pineoflocatingmethod.Ifthereisnomatchofit,thenthesearchstopsondepth,andreturnstotheupperlayer,andretrievesalltherelativecasesonbreadth.Retrievalalgorithms:1)Accordingtothecaseindexinformationoffixturecaselibrary,searchtherelevantcaselibrary；2)Matchthecaseindexcodewiththecodeofeachcaseofthecaselibrary,andcalculatethevalueofthesimilaritymeasure；3)Sorttheorderofsimilaritymeasure,thebiggestvalue,whichisthemostanalogicalcase.Similaritybetweentwocasesisbasedonthesimilaritybetweenthetwocases.features.Thecalculationofsimilaritymeasuredependsonthetypeofthefeature.Thevalueofsimilaritycanbecalculatedfornumericalvalues,forexample,compareWorkpiecewiththeweightof50kgand20kg.Thevaluecanalsobecalculatedbetweennonnumericalvalues,forexample,nowthefirst13digitsindexcodeisallnonnumericalvalues.Thesimilaritymeasureofafixtureiscalculatedasfollows:whereSisthesimilaritymeasureofcurrentfixture,nisthenumberoftheindexfeature,istheweightofeachfeature,isthesimilaritymeasureoftheattributeofthei2thfeaturewiththeattributeofrelativefeatureofthej-thcaseinthecaselibrary.Atthesametime,thevaluecountsasfollows:.Whereisthevalueoftheindexattributeofthei-thfeature,andisthevalueofattributeoftherelativei-thfeatureofthej-thcaseincaselibrary.Sotherearetwomethodstoselecttheanalogicalfixture.Oneistosetthevalue.Ifthevaluesofsimilaritymeasureofcurrentcaseswerelessthanagivenvalue,thosecaseswouldnotbeselectedasanalogicalcases.Whenthecaselibraryisinitiallysetup,andthereareonlyafewcases,thevaluecanbesetsmaller.Iftherearelotsofanalogicalcases,thevalueshouldgetlarger.Theotherisjusttosetthenumberoftheanalogicalcases(suchas10),whichisthelargestvalueofsimilaritymeasurefromthesortedorder.3CaseadaptationandCaseStorage3.1CaseadaptationThemodificationoftheanalogicalcaseinthefixturedesignincludesthefollowingthreecases:1)Thesubstitutionofcomponentsandthecomponent；2)Adjustingthedimensionofcomponentsandthecomponentwhiletheformremains；3)Theredesignofthemodel.Ifthecomponentsandcomponentofthefixturearecommonobjects,theycanbeedited,substitutedanddeletedwithtools,whichhavebeendesigned.3.2CasestorageBeforesavinganewfixturecaseinthecaselibrary,thedesignermustconsiderwhetherthesavingisvaluable.Ifthecasedoesnotincreasetheknowledgeofthesystem,itisnotnecessarytostoreitinthecaselibrary.Ifitisvaluable,thenthedesignermustanalyzeitbeforesavingittoseewhetherthecaseisstoredasaprototypecaseorasreferencecase.Aprototypecaseisarepresentationthatcandescribethemainfeaturesofacasefamily.Acasefamilyconsistsofthosecaseswhoseindexcodeshavethesamefirst13digitsanddifferentlastthreedigitsinthecaselibrary.Thelastthreedigitsofaprototypecasearealways“000”.Areferencecasebelongstothesamefamilyastheprototypecaseandisdistinguishedbythedifferentlastthreedigits.Fromtheconceptthathasbeenexplained,thefollowingstrategiesareadopted:1)Ifanewcasematchesanyexistingcasefamily,ithasthesamefirst13digitsasanexistingprototypecase,sothecaseisnotsavedbecauseitisrepresentedwellbytheprototypecase.Orisjustsavedasareferencecase(thelast3digitsarenot“000”,andnotthesamewithothers