夹具类外文翻译-基于事例推理的夹具设计研究与应用【中文4050字】【PDF+中文WORD】

夹具类外文翻译-基于事例推理的夹具设计研究与应用【中文4050字】【PDF+中文WORD】,中文4050字,PDF+中文WORD,夹具,外文,翻译,基于,事例,推理,设计,研究,应用,中文,4050,PDF,WORD Journal of Southeast University(English Edition)Vol.20 No.2 June 2004 ISSN 1003)7985Application and developmentof case-based reasoning in fixture designWang Qi1,2 Liao Wenhe1(1College of Mechanical and Electrical Engineering,Nanjing University of Aeronautics and Astronautics,Nanjing 210016,China)(2Department of Mechanical Engineering,Yancheng Institute of Technology,Yancheng 224002,China)Abstract:Based on the case-based designing(CBD)methodology,the fixture similarity is in two respects:thefunction and the structure information.Then,the computer-aided fixture design system is created on case-based reasoning(CBR),in which the attributes of the main features of workpiece and structure of fixture ascase index code are designed for the retrieve of the similar cases,and the structure and hierarchical relation ofcase library are set up for store.Meanwhile,thealgorithm based on the knowledge-guided in theretrieve of thesimilar cases,the strategy of case adaptation and case storage in which the case identification number is used todistinguish from similar cases are presented.The application of thesystem in some projects improves the designefficiency and gets a good result.Key words:case-based reasoning;fixture design;computer aided design(CAD)Received 2003-10-22.Foundation items:The National High TechnologyResearch andDevelopmentProgramofChina(863Program)(No.2002AA411030),the Natural Scientific Research Program College ofUniversity of Jiangsu Province(No.03KJD520246).Biographies:Wang Qi(1962),male,doctor,associate professor,wqi003 ;Liao Wenhe(corresponding author),male,doctor,professor,cnwho .Fixtures are devices that serve as the purpose ofholding the workpiece securely and accurately,andmaintaining a consistent relationship with respect tothe tools while machining.Because the fixturestructure depends on the feature of the product andthe status of the process planning in the enterprise,its design is the bottleneck during manufacturing,which restrains to improve the efficiency and lead-time.And fixture design is a complicated process,basedonexperiencethatneedscomprehensivequalitative knowledge about a number of design issuesincludingworkpiececonfiguration,manufacturingprocesses involved,and machining environment.Thisis also a very time-consuming work when usingtraditional CAD tools(such as Unigraphics,CATIAor Pro/E),which are good at performing detaileddesign tasks,but provide few benefits for takingadvantage of the previous design experience andresources,which are precisely the key factors inimproving the efficiency.T he methodology of case-based reasoning(CBR)adapts the solution of apreviously solved case to build a solution for a newproblem with the following four steps:retrieve,reuse,revise,and retain1.This is a more usefulmethod than the use of an expert system to simulatehuman thought because proposing a similar case andapplying a fewmodifications seems to be sel-fexplanatory and more intuitive to humans.So variouscase-based design support tools have been developedfor numerous areas 2-4,such as in injection moldingand design,architectural design,die-casting diedesign,process planning,and also in fixture design.Sun used six digitals to compose the index code thatincluded workpiece shape,machine portion,bushing,the 1st locating device,the 2nd locating device andclamping device 5.But the system cannot be used forother fixture types except for drill fixtures,andcannot solve the problem of storage of the same indexcode that needs to be retained,whichis veryimportant in CBR 6.1 Construction of a Case Index and CaseLibrary1.1 Case index The case index should be composed of all featuresof the workpiece,which are distinguished from dif-ferent fixtures.Using all of them would make the op-eration in convenient.Because the forms of the partsare diverse,and the technology requirements of man-ufacture in the enterprise also develop continuously,lots of features used as the case index will make thesearch rate slow,and the main feature unimportant,for the reason that the relative weight which is allot-ted to every feature must diminish.And on the otherhand,it is hard to include all the features in the caseindex.Therefore,considering the practicality and thedemand of rapid design,the case index includes boththe major feature of the workpiece and the structureof fixture.The case index code is made up of 16 dig-its:13 digits for case features and 3 digits for case-identification number.T he first 13 digits represent 13 features.Eachdigit is corresponding to an attribute of the feature,which may be one of/*0,/?0,/10,/20,/A0,/B0,/Z0,etc.In which,/*0 meansanyone,/?0 uncertain,/00 nothing.T he systemrules:fixture type,workpieceshape,locating model cannot be/*0 or/?0.Whenthe system is designed,the attribute information ofthe three items does not have these options,whichmeans the certain attribute must be selected.And thedefault of the otherattributes of the feature isworkpiece material as/30(middle carbon steel),batch size as/20(middle batch),workpiece scale/30(medium),workpiece weight/30(middle),workpiece toughness/10(much stiffer),machiningcontent/90(relative),process property/30(finishedmachining),clampingmethod/?0(uncertain),and others(They are degree,profilemodeling,etc.)/00(nothing).And the defaultvalues can be changed by the system administrator.For/*0 and/?0,when in retrial,/*0 meansmatching anyone,/?0means matching none ofthem,and when saved,the certain means of/*0and/?0 must be given.The last three digits are the case identificationnumber,which means the 13 digits of the casefeature are the same,and the number of these threedigits is used for distinguishing them,and savingthem in the same case family if needed.The system also rules:/0000 is a prototypecase,which is used for retrieval,and other cases are/0010,/0020,which are used for reference casesto be searched by designers.If occasionally one ofthem needs to be changed as the prototype case,firstit must be required to apply to change the one to/0000,and the former is changed to referential caseautomatically.The construction of the case index code is shownin Fig.1.1.2 Case libraryThe case library consists of lots of predefinedcases.Caserepresentationisone ofthe mostimportantissuesincase-basedreasoning.Socompounding with the index code,the structure ofcase library is shown in Tab.1.Fig.1 Construction of case index codeTab.1 Structure of case libraryField nameData typeDescriptionCase IDAuto numberSpecify the case.s place in case libraryCase indexVercharCase index code:*-*Fixture typeVerchar1)Lathe fixture;2)Drilling jig;3)Milling fixture;4)Boring fixture;,Workpiece shapeVerchar1)Box;2)Shaft;3)Round;4)Sheath;5)Seat;6)Piston rod;7)Frame;8)Plate-shell;9)Block;A)Compound;,Workpiece materialVerchar*)Anyone;1)Cast iron;2)Low carbon steel;3)Middle carbon steel;4)Alloy steel;5)Middle hardness aluminum;,Batch sizeVerchar*)Random;1)Large batch;2)Middle batch;3)Low batch;4)FewWorkpiece scaleVerchar1)Much bigger;2)Bigger;3)Medium;4)Less bigger;5)SmallWorkpiece weightVerchar1)Much heavier;2)Heavier;3)Middle;4)Less heavy;5)LightWorkpiece toughnessVerchar?)Uncertain;1)Much stiffer;2)Stiffer;3)Middle;4)Less stiffer;5)WeakMachining contentVerchar1)Cylinder;2)End face;3)Hole;4)Plane;5)Step plane;6)Slot;7)Pocket;8)Hole of dril-l ream;9)Relative;A)CompoundingProcess propertyVerchar1)Blank;2)Unfinishing machining;3)Finish machiningLocating methodVerchar1)3plane;2)1plane+2pin;3)Big plane+short pin;4)Long V+plane;5)Double V+plane;6)Long pin+little plane;7)Small taper shaft;8)centredClamping methodVerchar?)Uncertain;0)Nothing;1)T op clamping;2)T op+side clamping;3)Side clamping;4)Tiltedclamping;5)Mult-i point top clamping;6)Compounded clamping;7)Centred clamping;8)Vacuum clamping;,Fixture bodyVerchar?)Uncertain;1)Plane;2)Casting;3)Welding;4)CompoundingOthersVerchar?)Uncertain;0)Nothing;1)Horizon-move-divided degree;2)Horizon-round-divided degree;3)Radia-l round-divided degree;4)Profile modeling;,Case identification numberVercharCase identification number:000;001;,Case mappingVercharT he location of case modeling stored in hard disk of computer171Application and development of case-based reasoning in fixture design1.3 Hierarchical form of CaseT hestructuresimilarityofthefixtureisrepresentedasthewholefixturesimilarity,components similarity and component similarity.Sothe whole fixture case library,components caselibrary,component case library of fixture are formedcorrespondingly.Usually design information of thewhole fixture is composed of workpiece informationandworkpieceprocedureinformation,whichrepresentthefixturesatisfyingthespecificallydesigning function demand.The whole fixture case ismade up of function components,which are describedby the function components.names,numbers,andrelationship to object-workpiece which are the body ofthe knowledge.The components case represents themembers.(function component and other structurecomponents)main-driven parameter,the number,and their constrain relations.The component case(the lowest layer of the fixture)is the structure offunction component and other components.In themodern fixture design there are lots of parametricstandard parts and common non-standard parts.Sothecomponentcaselibraryshouldrecordthespecification parameter and the way in which it keepsthem.The hierarchical form of the fixture caselibrary is shown in Fig.2.Fig.2 Hierarchical form of fixture case library2 Strategy of Case RetrievalIn the case-based design of fixtures,the mostimportant thing is the retrieval of the similarity,which can help to obtain the most similar case,and tocut down the time of adaptation.According to therequirement of fixture design,the strategy of caseretrieval combines the way of the nearest neighborand knowledge-guided.Thatis,first search ondepth,thenonbreadth;the knowledge-guidedstrategy means to search on the knowledge rule fromroot to the object,which is firstly searched by thefixture type,then by the shape of the workpiece,thirdly by the locating method.For example,if thecase index code includes the milling fixture of fixturetype,the search is just for all milling fixtures,thenfor box of workpiece shape,the third for 1plane+2pine of locating method.If there is no match of it,then the search stops on depth,and returns to theupper layer,and retrieves all the relative cases onbreadth.Retrieval algorithms:According to the case index information offixture case library,search the relevant case library;Match the case index code with the code ofeach case of the case library,and calculate the valueof the similarity measure;Sort the order of similarity measure,thebiggest value,which is the most analogical case.Similarity between two cases is based on thesimilarity between the two cases.features.T hecalculation of similarity measure depends on the typeof the feature.The value of similarity can becalculated for numerical values,for example,compareworkpiece with the weight of 50 kg and 20 kg.T hevalue can also be calculated between non-numericalvalues,for example,now the first 13 digits indexcode is all non-numerical values.It is important that aCBR systemsupportsa multitudeofsimilaritymeasure,and,ideally,allows the definition of newtypes.Thesimilaritymeasure ofa fixtureiscalculated as follows:S=Eni=1(wisi(f ai,f bji)Eni=1wi i=1,2,nwhere S is the similarity measure of current fixture,n is the number of the index feature,wiis theweight of each feature,si(f ai,f bji)is the similaritymeasure of the attribute f aiof the i-th feature withthe attribute f bj iof relative feature of the j-th case inthe case library.At the same time,0 si(f ai,f bji)1,the value counts as follows:If(f aiand f bjiare non-numerical values)If(f ai=f bji)si(f ai,f bji)=1;Else172Wang Qi,and Liao Wenhesi(f ai,f bj i)=0;If(f aiand f bj iare numerical values)si(f ai,f bj i)=1-f ai-f bj imax(f ai,f bj i).where f aiis the value of the index attribute of the i-th feature,and f bj iis the value of attribute of therelative i-th feature of the j-th case in case library.So there are two methods to select the analogicalfixture.One is to set the value.If the values of similaritymeasure of current cases were less than a given value,those cases would not be selected as analogical cases.When the case library is initially set up,and there areonly a few cases,the value can be set smaller.If there arelots of analogical cases,the value should get larger.Theother is just to set the number of the analogical cases(such as 10),which is the largest value of similaritymeasure from the sorted order.3 Case Adaptation and Case Storage3.1 Case adaptation The modification of the analogical case in thefixture design includes the following three cases:1)T he substitution of components and thecomponent;2)Adjusting the dimension of components andthe component while the form remains;3)T he redesign of the model.If the components and component of the fixtureare common objects,they can be edited,substitutedand deleted with tools,which have been designed.3.2 Case storageBefore saving a new fixture case in the caselibrary,the designermust consider whetherthesaving is valuable.If the case does not increase theknowledge of the system,it is not necessary to storeit in the case library.If it is valuable,then thedesigner must analyze it before saving it to seewhether the case is stored as a prototype case or asreference case.A prototype case is a representationthat can describe the main features of a case family.Acase family consists of those cases whose index codeshave the same first 13 digits and different last threedigits in the case library.The last three digits of aprototype case are always/0000.A reference casebelongs to the same family as the prototype case andis distinguished by the different last three digits.From the concept that has been explained,thefollowing strategies are adopted:1)If a new case matches any existing case family,ithas the same first 13 digits as an existing prototype case,so the case is not saved because it is represented well bythe prototype case.Or is just saved as a reference case(the last 3 digits are not/0000,and not the same withothers)in the case library.2)If a new case matches any existing case familyand is thought to be better at representing this case familythan the previous prototype case,then the prototype caseis substitutedby thisnew case,andthe previous prototypecase is saved as a reference case.3)If a new case does not match any existing casefamily,anewcasefamilywillbegeneratedautomatically and the case is stored as the prototypecase in the case library.4 Process of CBR in Fixture DesignAccordingtothecharacteristicsoffixturedesign,the basic information of the fixture designsuch as the name of fixture,part,product and thedesigner,etc.must be input first.T hen the fixturefile is set up automatically,in which all componentsof the fixture are put together.Then the model of theworkpieceisinputordesigned.Thedetailedinformation about the workpiece is input,the caseindex code is set up,and then the CBR begins tosearch the analogical cases,relying on the similaritymeasure,and the most analogical case is selected out.If needed,the case is adapted to satisfy the currentdesign,and restored into the case library.T heflowchart of the process is shown in Fig.3.Fig.3 Flowchart of case-based reasoning for fixture deign5 Illustrating for Fixture Design by CBRThis is a workpiece(see Fig.4).Its material is45#steel.Its name is seat.Its shape is block,andthe product batch size is middle,etc.A fixture isturning fixture that serves to turn the hole,whichneeds to be designed.The value of feature,attribute,case index code173Application and development of case-based reasoning in fixture designand weight of the workpiece is shown in Tab.2.Fig.4 A workpiece requested to design a fixture(Maximum size is 80 mm 49 mm 22 mm)Tab.2 The case index code and weight of workpieceFeature nameAttribute valueIndex codeWeightFixture typeLathe fixture1100Workpiece shapeBlock990Workpiece materialMiddle carbon steel370BatchsizeMiddle260Workpiece scaleSmall560Workpiece weightLight560Workpiece toughnessMuch stiffer160Machining contentHole380Process propertyFinish machining370Locating method3plane1100Clamping methodUncertain?90Fixture bodyCompounding480OthersNothing060 T hroughsearching,andcalculatingthesimilarity,the case index code of the most similarcaseis1932551332140-000,andthedetailedinformation is shown in Tab.3.Tab.3 Case index code of the most similar caseFeature nameAttribute valueIndex codeFixture typeLathe fixture1Workpiece shapeBlock9Workpiece materialM iddle carbon steel3Batch sizeM iddle2Workpiece scaleSmall5Workpiece weightLight5Workpiece toughnessMuch stiffer1M achining contentHole3Process propertyFinish machining3Locating method3plane2Clamping methodUncertain1Fixture bodyCompounding4OthersNothing0The similarity is calculated as follows:S=1 100+1 90+2 1 70+5 1 60+2 1 80+0 100+0 90100+90+70+60+60+60+60+80+70+100+90+80+60=790980=0.806So the value of similarity measure of the fixturewhich needs to be designed with the most analogicalcase in case library is 0.806,and the structure of themost analogical case is shown in Fig.5.Fig.5 Most analogical fixtureAfter having been substituted the component,modified the locating model and clamp model,andadjusted the relative dimension,the new fixture isdesigned,and the figure is shown in Fig.6.Fig.6 New fixture that needs to be designedAs there is not the analogical fixture in the caselibrary,the new fixture is restored into the caselibrary.The case index code is 1932551331140-000.6 ConclusionCBR,as a problem-solving methodology,is amore efficient method than an expert system tosimulate human thought,and has been developed inmanydomainswhere knowledge isdifficulttoacquire.T he advantages of the CBR are as follows:it174Wang Qi,and Liao Wenheresembles human thought more closely;the buildingof a case library which has sel-f learning ability bysaving new cases is easier and faster than the buildingof a rule library;and it supports a better transfer andexplanation of new knowledge that is more differentthan the rule library.A proposed fixture designframework on the CBR has been implemented byusing Visual C+,UG/Open API in Ungraphicswith Oracle as database support,which also has beenintegratedwiththe3-Dparametriccommoncomponent library,common components library andtypicalfixturelibrary.T heprototypesystem,developed here,is used for the aviation project,andaids the fixture designers to improve the designefficiency and reuse previous design resources.References 1Watson I,Perera S.Case based design:a review andanalysis of building design application J.Artif icialIntelligenceforEngineeringDesign,A 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