基于事例推理的夹具设计研究与应用Application机械类外文翻译.docx

基于事例推理的夹具设计研究与应用Application机械类外文翻译.docx

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基于事例推理的夹具设计研究与应用Application机械类外文翻译

Applicationanddevelopment

Ofcasebasedreasoninginfixturedesign

Abstract:

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,andretain[1].Thisisamoreusefulmethodthantheuseofanexpertsystemtosimulatehumanthoughtbecauseproposingasimilarcaseandapplyingafewmodificationsseemstobeselfexplanatoryandmoreintuitivetohumans.Sovariouscasebaseddesignsupporttoolshavebeendevelopedfornumerousareas[2-4],suchasininjectionmoldinganddesign,architecturaldesign,diecastingdiedesign,processplanning,andalsoinfixturedesign.Sunusedsixdigitalstocomposetheindexcodethatincludedworkpieceshape,machineportion,bushing,the1stlocatingdevice,the2ndlocatingdeviceandclampingdevice[5].Butthesystemcannotbeusedforotherfixturetypesexceptfordrillfixtures,andcannotsolvetheproblemofstorageofthesameindexcodethatneedstoberetained,whichisveryimportantinCBR[6].

1ConstructionofaCaseIndexandCaseLibrary

1.1Caseindex

Thecaseindexshouldbecomposedofallfeaturesoftheworkpiece,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.

1.2Caselibrary

Thecaselibraryconsistsoflotsofpredefinedcases.Caserepresentationisoneofthemostimportantissuesincasebasedreasoning.Socompoundingwiththeindexcode,.

1.3HierarchicalformofCase

Thestructuresimilarityofthefixtureisrepresentedasthewholefixturesimilarity,componentssimilarityandcomponentsimilarity.Sothewholefixturecaselibrary,componentscaselibrary,componentcaselibraryoffixtureareformedcorrespondingly.Usuallydesigninformationofthewholefixtureiscomposedofworkpieceinformationandworkpieceprocedureinformation,whichrepresentthefixturesatisfyingthespecificallydesigningfunctiondemand.Thewholefixturecaseismadeupoffunctioncomponents,whicharedescribedbythefunctioncomponents’namesandnumbers.Thecomponentscaserepresentsthemembers.（functioncomponentandotherstructurecomponents，maindrivenparameter,thenumber,andtheirconstrainrelations.）Thecomponentcase（thelowestlayerofthefixture）isthestructureoffunctioncomponentandothercomponents.Inthemodernfixturedesigntherearelotsofparametricstandardpartsandcommonnonstandardparts.Sothecomponentcaselibraryshouldrecordthespecificationparameterandthewayinwhichitkeepsthem.

2StrategyofCaseRetrieval

Inthecasebaseddesignoffixtures,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,

isthesimilaritymeasureoftheattribute

ofthei2thfeaturewiththeattribute

ofrelativefeatureofthej-thcaseinthecaselibrary.Atthesametime,

thevaluecountsasfollows:

.

Where

isthevalueoftheindexattributeofthei-thfeature,and

isthevalueofattributeoftherelativei-thfeatureofthej-thcaseincaselibrary.

Sotherearetwomethodstoselecttheanalogicalfixture.Oneistosetthevalue.Ifthevaluesofsimilaritymeasureofcurrentcaseswerelessthanagivenvalue,thosecaseswouldnotbeselectedasanalogicalcases.Whenthecaselibraryisinitiallysetup,andthereareonlyafewcases,thevaluecanbesetsmaller.Iftherearelotsofanalogicalcases,thevalueshouldgetlarger.Theotherisjusttosetthenumberoftheanalogicalcases（suchas10）,whichisthelargestvalueofsimilaritymeasurefromthesortedorder.

3CaseadaptationandCaseStorage

3.1Caseadaptation

Themodificationoftheanalogicalcaseinthefixturedesignincludesthefollowingthreecases:

1）Thesubstitutionofcomponentsandthecomponent。

2）Adjustingthedimensionofcomponentsandthecomponentwhiletheformremains。

3）Theredesignofthemodel.

Ifthecomponentsandcomponentofthefixturearecommonobjects,theycanbeedited,substitutedanddeletedwithtools,whichhavebeendesigned.

3.2Casestorage

Beforesavinganewfixturecaseinthecaselibrary,thedesignermustconsiderwhetherthesavingisvaluable.Ifthecasedoesnotincreasetheknowledgeofthesystem,itisnotnecessarytostoreitinthecaselibrary.Ifitisvaluable,thenthedesignermustanalyzeitbeforesavingittoseewhetherthecas