机械毕业设计英文外文翻译基于事例推理的夹具设计研究与应用.docx
《机械毕业设计英文外文翻译基于事例推理的夹具设计研究与应用.docx》由会员分享,可在线阅读,更多相关《机械毕业设计英文外文翻译基于事例推理的夹具设计研究与应用.docx(19页珍藏版)》请在冰豆网上搜索。
机械毕业设计英文外文翻译基于事例推理的夹具设计研究与应用
附录1英文原文
ApplicationanddevelopmentOfcasebasedreasoninginfixturedesign
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,thenthedesignermustanalyzeitbeforesavingitto