前钢板弹簧吊耳加工工艺及钻2-Φ10.5孔夹具设计参考素材
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1ApplicationApplicationApplicationApplication andandandand developmentdevelopmentdevelopmentdevelopmentOfOfOfOf casecasecasecase basedbasedbasedbasedreasoningreasoningreasoningreasoning ininininfixturefixturefixturefixturedesigndesigndesigndesignAbstract:Abstract:Abstract:Abstract: Based on the case baseddesigning(CBD)methodology,thefixture similarity is in two respects: thefunction and the structure information.Then, the computer aided fixture designsystemiscreatedoncasebasedreasoning (CBR),in which the attributesof the main features of workpiece andstructure of fixture as case index codeare designed for the retrieve of thesimilar cases, and the structure andhierarchical relation of case library aresetupforstore.Meanwhile,thealgorithmbasedontheknowledgeguided in the retrieve of the similarcases, the strategy of case adapt at ionand case storage in which the case identif cat ion number is used to distinguishfrom similar cases are presented. Theapplicationofthesysteminsomeprojects improves the design efficiencyand gets a good result .Keywords:Keywords:Keywords:Keywords:casebasedreasoning;fixturedesign;computeraided design(CAD)Fixtures are devices that serveas the purpose of holding the workpiecesecurelyandaccurately,andmaintaining a consistent relationshipwithrespecttothetoolswhilemachining.Becausethefixturestructure depends on the feature of theproduct and the status of the processplanning in the enterprise, its design isthe bottleneck during manufacturing,whichrestrainstoimprovetheefficiency and leadtime. And fixture2design is a complicated process, basedonexperiencethatneedscomprehensive qualitative knowledgeaboutanumberofdesignissuesincludingworkpiececonfiguration,manufacturing processes involved, andmachining environment. This is also avery time consuming work when usingtraditionalCADtools(suchasUnigraphics, CATIA or Pro/E), whichare good at performing detailed designtasks, but provide few benefits fortaking advantage of the previous designexperience and resources, which areprecisely the key factors in improvingthe efficiency. The methodology of casebasedreasoning(CBR)adaptsthesolution of a previously solved case tobuild a solution for a new problem withthe following four steps: retrieve, reuse,revise, and retain 1. This is a moreuseful method than the use of an expertsystemtosimulatehumanthoughtbecause proposing a similar case andapplying a few modifications seems tobe self explanatory and more intuitivetohumans.Sovariouscasebaseddesignsupporttoolshavebeendevelopedfornumerousareas2-4,such as in injection molding and design,architectural design, die castingdiedesign, process planning, and also infixture design. Sun used six digitals tocompose the index code that includedworkpieceshape,machineportion,bushing, the 1stlocating device, the 2ndlocating device and clamping device5.But the system cannot be used for otherfixture types except for drill fixtures,and cannot solve the problem of storageof the same index code that needs to beretained, which is very important inCBR6.1 Construction of a Case Index and3Case Library1.1 Case indexThecaseindexshouldbecomposedofallfeaturesoftheworkpiece,whicharedistinguishedfrom different fixtures. Using all ofthem wouldmake the operation inconvenient. Because the forms of theparts are diverse, and the technologyrequirementsofmanufacture intheenterprise also develop continuously,lots of features used as the case indexwill make the search rate slow, and themainfeatureunimportant,forthereason that the relative weight which isallotted to every feature must diminish.And on the other hand, it is hard toinclude all the features in the caseindex.Therefore,consideringthepracticality and the demand of rapiddesign, the case index includes both themajor feature of the workpiece and thestructure of fixture. The case index codeis made up of 16 digits: 13 digits forcase features and 3 digits for caseidentification number.The first 13 digits represent 13features. Each digit is corresponding toan attribute of the feature, which maybe one of“*”, “？”, “1”, “2”,“A” , “B” , “Z” , etc. In which,“*” means anyone, “?” uncertain,“0” nothing.The system rules: fixture type,workpiece shape, locating model cannotbe “*”or“?”. When the system isdesigned, the attribute information ofthe three items does not have theseoptions,whichmeansthecertainattribute must be selected.The last three digits are the caseidentification number, which means the13 digits of the case feature are the4same, and the number of these threedigits is used for distinguishing them.The system also rules: “000”is aprototypecase,whichisusedforretrieval, and other cases are “001”,“ 002 ” ,which are used forreferencecasestobesearchedbydesigners. If occasionally one of themneeds to be changed as the prototypecase, first it must be required to applyto change the one to “000”, and theformer is changed to referential caseautomatically.The construction of the case indexcode is shown in Fig.1.1.2 Case libraryThe case library consists of lots ofpredefined cases. Case representation isone of the most important issues in casebased reasoning. So compounding withthe index code,.1.3 Hierarchical form of CaseThestructuresimilarityofthefixture is representedas the wholefixture similarity, components similarityand component similarity. So the wholefixture case library, components caselibrary,componentcaselibraryoffixtureareformedcorrespondingly.Usuallydesigninformationofthewhole fixture is composed of workpieceinformation and workpiece procedureinformation, which represent the fixturesatisfyingthespecificallydesigningfunction demand. The whole fixturecase is made up of function components,which are described by the functioncomponentsnames and numbers. Thecomponentscaserepresentsthemembers.(functioncomponentand5other structure components ，maindriven parameter, the number, and theirconstrain relations.)The componentcase (the lowest layer of the fixture) isthe structure of function component andothercomponents.Inthemodernfixturedesigntherearelotsofparametric standard parts and commonnon standard parts. So the componentcaselibraryshouldrecordthespecification parameter and the way inwhich it keeps them.2 Strategy of Case RetrievalInthecasebaseddesignoffixtures ,the most important thing is theretrieval of the similarity, which canhelp to obtain the most similar case, andto cut down the time of adaptation.According to the requirement of fixturedesign, the strategy of case retrievalcombinesthewayofthenearestneighbor and knowledge guided. That is,first search on depth, then on breadth;the knowledge guided strategy means tosearch on the knowledge rule from rootto the object, which is firstly searchedby the fixture type, then by the shape ofthe workpiece, thirdly by the locatingmethod. For example, if the case indexcode includes the milling fixture offixture type, the search is just for allmillingfixtures,thenforboxofworkpiece shape, the third for 1plane+2pine of locating method. If there is nomatch of it, then the search stops ondepth, and returns to the upper layer,and retrieves all the relative cases onbreadth.Retrieval algorithms:1)Accordingtothecaseindexinformationoffixturecaselibrary,search the relevant case library;2)Match the case index code withthe code of each case of the case library,6and calculate the value of the similaritymeasure;3)Sorttheorderofsimilaritymeasure, the biggest value, which is themost analogical case.Similarity between two cases isbased on the similarity between the twocases.features.Thecalculationofsimilarity measure depends on the typeof the feature. The value of similaritycan be calculated for numerical values,for example, compareWorkpiece withthe weight of 50kg and 20kg. The valuecan also be calculated between nonnumerical values, for example, now thefirst 13 digits index code is all nonnumericalvalues.Thesimilaritymeasure of a fixture is calculated asfollows:where S is the similarity measureof current fixture, n is the number of theindex feature,is the weight of eachfeature,is the similaritymeasure of the attributeof the i2thfeature with the attributeof relativefeature of the j-th case in the caselibrary.Atthesametime, the value countsas follows:.Whereis the value of the indexattribute of the i-th feature, andis7the value of attribute of the relative i-thfeature of the j-th case in case library.So there are two methods to selectthe analogical fixture. One is to set thevalue.Ifthevaluesofsimilaritymeasure of current cases were less thana given value, those cases would not beselected as analogical cases. When thecase library is initially set up, and thereare only a few cases, the value can besetsmaller.Iftherearelotsofanalogical cases, the value should getlarger. The other is just to set thenumber of the analogical cases (suchas10), which is the largest value ofsimilaritymeasurefromthesortedorder.3CaseadaptationandCaseStorage3.1 Case adaptationThemodificationoftheanalogical case in the fixture designincludes the following three cases:1) The substitution of componentsand the component;2) Adjustingthedimensionofcomponents and the component whilethe form remains;3) The redesign of the model.If the components and componentof the fixture are common objects, theycan be edited, substituted and deletedwith tools, which have been designed.3.2 Case storageBefore saving a new fixture case inthecase library, the designermustconsider whether the saving is valuable.Ifthecasedoesnotincreasetheknowledge of the system, it is notnecessary to store it in the case library.If it is valuable, then the designer mustanalyzeitbefore savingittoseewhetherthecaseisstoredasaprototype case or as reference case. A8prototype case is a representation thatcan describe the main features of a casefamily. A case family consists of thosecases whose index codes have the samefirst 13 digits and different last threedigits in the case library. The last threedigits of a prototype case are always“000” . A reference case belongs to thesame family as the prototype case andis distinguished by the different lastthree digits.From the concept that has beenexplained, the following strategies areadopted:1) If a new case matches anyexisting case family, it has the samefirst 13 digits as an existing prototypecase, so the case is not saved because itis represented well by the prototypecase. Or is just saved as a referencecase (the last 3 digits are not “000”,and not the same with others) in thecase library.2) If a new case matches anyexisting case family and is thought tobebetteratrepresentingthiscasefamily than the previous prototype case,then the prototype case is substituted bythisnewcase,andthepreviousprototype case is saved as a referencecase.3) If a new case does not matchany existing case family, a new casefamily will be generated automaticallyand the case is stored as the prototypecase in the case library.4ProcessofCBRinFixtureDesignAccording to the characteristics offixture design, the basic information ofthe fixture design such as the name offixture, part, product and the designer,etc. must be input first. Then the fixturefile is set up automatically, in which all9componentsofthefixtureareputtogether.Thenthemodeloftheworkpiece is input or designed. Thedetailedinformationabouttheworkpiece is input, the case index codeis set up, and then the CBR begins tosearch the analogical cases, relying onthe similarity measure, and the mostanalogicalcaseisselectedout.Ifneeded, the case is adapted to satisfythe current design, and restored into thecaselibrary.Theflowchartoftheprocess is shown in Fig.3.5 Illustrating for Fixture Design byCBRThis is a workpiece (seeFig.4). Itsmaterial is 45# steel. Its name is seat.Its shape is block, and the product batchsize is middle, etc.Afixture is turningfixture that serves to turn the hole,which needs to be designed.The value of feature, attribute,case index code and weight of theworkpiece is show n in Tab.2.10Through searching, and calculatingthe similarity, the case index code of themostsimilarcaseis19325513321402000, and the detailedinformation is show n in Tab. 3.The similarity is calculated asfollows:So the value of similarity measureofthefixturewhichneedstobedesigned with the most analogical caseincaselibraryis0.806,andthestructure of the most analogical case isshown in Fig.5.After having been substituted thecomponent,modifiedthelocatingmodel and clamp model, and adjustedthe relative dimension, the new fixtureis designed, and the figure is show n in11Fig.6.As there is not the analogicalfixture in the case library, the newfixture is restored in to the case library.Thecaseindexcodeis19325513311402000.6 ConclusionCBR,asaproblemsolvingmethodology,isamoreefficientmethodthananexpertsystemtosimulate human thought, and has beendevelopedinmanydomainswhereknowledge is difficult to acquire. Theadvantages of the CBR are as follows:itresembleshumanthoughtmoreclosely; the building of a case librarywhichhasselflearningabilitybysaving new cases is easier and fasterthan the building of a rule library; and itsupportsabettertransferandexplanation of new knowledge that ismore different than the rule library.Aproposed fixture design framework onthe CBR has been implemented byusing Visual C +, UG/Open API in Un graphics with Oracle as databasesupport, which also has been integratedwiththe32Dparametriccommoncomponentlibrary,commoncomponents library and typical fixturelibrary.Theprototypesystem,developed here, is used for the aviationproject, and aids the fixture designers toimprove the design efficiency and reuseprevious design resources.附录1 外文翻译基于事例推理的夹具设计研究与应用摘要:根据基于事例的设计方法,提出采用工序件的特征信息和夹具的结构特征信息来描述夹具的相似性,并建立了包括这2方面主要特征信息为基础的事例索引码,设计了事例库的结构形式,创建了层次化的事例组织方式;同时,提出了基于知识引导的夹具事例检索算法,以及事例的修改和采用同族事例码进行相似事例的存贮,形成了基于事例推理的夹具设计.所开发的原型系统在型号工程夹具设计等项目的设计过程中得到了应用,并取得了令人满意的使用效果.关键词: 基于事例的推理 夹具设计 CAD夹具是以确定工件安全定位准确为目的的装置，并在加工过程中保持工件与刀具或机床的位置一致不变。因为夹具的结构依赖于产品的特点和在企业规划中加工工序的地位,所以它的设计是制造过程中的瓶颈,制约着效率的提高. 夹具设计是一个复杂的过程,需要有从大量的设计论文中了解质量知识的经验，这些设计论文包括工件的结构设计、涉及加工工艺，和加工环境。当用这些擅长绘制详细设计图的传统的CAD工具（如Unigraphics、CATIA、Pro/E)时,这仍然是一项非常耗时的工作，但是利用以往的设计经验和资源也不能提供一些益处,而这正是提高效率的关键因素. 基于事例推理 (CBR) 的方法适应以往个案解决的办法,建立一个新问题的方法,主要有以下四步骤:检索、利用、修改,并保留.这是一个比用专业系统模仿人类思维有用的使用方法，因为提出一个类似的情况,和采用一些修改,似乎不言自明,而且比人类更直观.所以支持不同事例的设计工具已经在诸多领域中发展起来，如在注射成型及设计、建筑设计、模具设计投死, 规划过程中,还有夹具设计. 孙用六个数字组成代码参数,包括工件的形状、机械部分、轴衬,第一定位装置,第二定位装置和夹紧装置. 但这个系统不能用于除钻床夹具外的其他夹具类型,不能解决储存需要保留的同一参数代码的问题,这在CBR中是非常重要的. 1事例参数和事例图书馆的建立1.1事例参数事例参数应该由工件的所有的特征组成，来区别不同的夹具. 使用他们能够使操作方便. 因为零件的形状是多种多样的, 在生产企业中制造的技术要求也不断发展,许多特征作被用做事例参数将会使搜索速度降低,其主要特征是不重要的,因为分配给每个特征的比重必须减少. 另一方面,事例参数包含所有的特征是困难的。 因此,考虑到实际和快速设计的需求,事例参数要包含工件的主要特征和夹具的结构。事例参数代码由16位数组成：13位数是事例特征 3位数是事例识别数字。 前13位数代表13个特征。 每个数字与特征的一个属性相一致,这可能是*、？、1、2，A、B,，Z，等其中的一个。其中，*是指任何一个,?代表不确定,0代表没有。 系统规定:夹具的类型，工件的形状，位置模式不能是*和?。在设计系统时,三个项目的属性信息没有这些选择,这就意味着必须选择确定的属性。最后三位数是事例识别号码,如果事例特征的13位数是一样的,这三个数字就用来区别他们。该系统还规定:000是用于修正的一个典型事例,其他事例001、002、,这些是用于设计师查找参考事例的. 如果其中一个偶尔需要改变成典型事例,首先它必须要求改成000,前面的自动变成参考事例. 事例索引码的结构如图1所示。 1夹具类型； 6工件重量； 11夹紧模型； 2工件形状； 7工件刚度； 12夹具体； 3工件材料； 8加工内容； 13其他； 4批 量； 9过程所有物； 14到16事例识别码； 5工件比例； 10定位模型； 图1 事例索引码的结构1.2事例库事例库由许多预定义的事例组成。事例的描述是基于事例推理的最重要的问题之一。所以由索引码复合。1.3 事例的层次化夹具的结构相似被认为是整个夹具，成分和内容相似。所以，整个夹具事例库，成分事例库，夹具的成分事例库形成相同。整个夹具的设计资料通常是由工件资料和工件加工资料组成,这就意味着夹具的设计应满足特别功能的需求.全部夹具事例是由功能成分组成，它是用功能成分的名字和数字来进行描述的。成分事例代表成员（成分功能和其他结构成分，主要驱动参数，数字，和它们的约束关系）。成分事例（夹具的最低层）是功能成分和和其他成分的结构。在现代夹具设计中有很多参数化准件和普通非标准件。所以成分事例图书馆应记录特殊参数和保持它们的方法。2事例修改的策略在基于事例的夹具设计中，最重要的是相似点的修改，这样能有助于获得最相似的事例，以及缩短适应时间。根据夹具设计的需求，事例修改的策略使最接近的事例方法和知识指导结合起来。首先在深度上查找，然后在宽度上；知识指导策略意味着在来自客观事物根源的知识规则上查找，这就要首先查找固定类型，然后查找工件的形状，第三查找定位方法。例如，如果事例索引码包括夹具类型的磨削夹具，就只查找所有的磨削夹具，然后查找工件形状的盒子，第三查找一个平面两个销的定位方法。如果没有合适的，就查找深度标点，然后回到最上层，然后再找所有与宽度相关的事例。 修改方法：1） 根据夹具事例库的事例索引信息，查找有关事例库。2） 将事例索引码与事例库的每个事例码匹配，然后计算相似尺寸的价值。3） 整理相似尺寸的次序，最大的架子是最类似的事例。两个事例之间的相似点是基于两个事例特征之间的相似点。相似点尺寸的计算依靠特征的类型。相似点的价值可以通过数字化的价值来计算，例如比较重量分别是50kg 和 20kg的工件。非数字化的价值也能计算，例如，现在前13位索引码都是非数字化的价值。一个夹具的相似尺寸的计算公式如下：其中S表示通用夹具的相似尺寸，n表示索引特性数，表示每个特性的重量，表示事例库中特性和相关夹具的特性的相似尺寸。同时， ，数值计算如下： 其中表示第i个特征的索引特性值，表示事例库中第j个事例的第i个特征的特性值。 所以有两种方法选择相似夹具。一个方法是建立数值。如果通用事例的相似尺寸值比给定的数值小，这些事例就不能选来作相似事例。事例库最初建立的时候，只有一些事例，数值可以建小一点。如果有大量的相似事例，数值就应该建的大一些。另外一个方法是只建立相似事例的数字（例如10），这是类型单里相
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