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】
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【中文4050字】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 3 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，w i表示每个特性的重量，si ( f a i f b ji )表示事例库中特性f a i和相关夹具的特性f b ji 的相似尺寸。同时，0s i ( f ai , f b ji )1 ，数值计算如下： 其中f a i表示第i 个特征的索引特性值，f b ji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 型单里相似尺寸的最大值。 3 事例的修改和存储 3.1 事例的修改 夹具设计中相似事例的修改包括以下三个阶段： 1） 成分的替代 2） 保持形式不变，调整成分的特性 3） 模型重新设计 如果夹具的成分是普通的物品，它们能通过使用工具被修改，代替以及删 除，这些已经被设计好了。3.2 事例的存储 在将一个新的事例保存到事例库之前，设计者必须考虑保存是否有价值。如 果这个事例不能增加系统的知识，就没有必要把它保存到事例库里。如果它有 价值的话，设计者在保存之前必须分析一下，看看这个事例是否作为标准事例 或参考事例被存储了。一个标准事例是一个描述同族事例主要特征的标准。一 个同族事例是有事例库中索引码前 13 位相同而最后三位不同的那些事例组成 的。一个标准事例的最后三位通常是“000”。一个参考事例属于同族标准事例， 5 最后三位用不同数字区分。 从被解释的概念中，可采用以下方法： 1）如果一个新的事例和任何一个存在的事例族一致，和一个存在的标准 事例的前13 位数相同，那么这个事例就不能存储因为已经这种标准事例了。或 者只能作为一个参考事例保存（最后三位不是“000”，而且和其它的不一样） 在事例库中。 2）如果一个新的事例和任何一个存在的事例族一致，并且被认为代替这 个事例族要比以前的标准事例好，那么这个标准事例就被这个新的事例代替， 以前的标准事例作为一个参考事例保存。 3）如果一个新的事例和任何一个存在的事例族不一致，一个新的事例族 将会自动产生，并作为标准事例保存到事例库中。 4 夹具设计中基于事例推理的过程 根据夹具设计的特性，夹具设计的基本信息，例如夹具的名字，零件，生 产和设计者等等，必须先输入。然后，输入或设计工件的模型。输入有关工件 的细节信息，建立事例索引码，然后CBR 开始依靠相似尺寸查找相似事例，选 出最相似的事例。如果需要的话，事例要满足通用性设计，再存储到事例库中。 程序流程图如图2 所示 图2 基于事例推理的夹具设计流程图 6 5 基于事例推理的夹具设计说明 这是一个工件如图3 所示。材料是45 钢，底座，形状为块状，生产批量 为中批等。需要设计成一个用来旋转孔的旋转夹具。 图3 需要设计夹具的一个工件 （最大尺寸80mmx49mmx22mm） 工件的特征值，属性值，事例索引码和重量在表1 中列出。 表1 工件的事例索引码和重量 特征名称特性值索引码重量夹具类型车床夹具1100工件形状块状990工件材料中碳钢370批量中批260工件比例小560工件重量轻560工件刚度硬度强160加工内容孔380程序要求完成加工370定位方法三个平面1100夹紧方法不确定？90夹具体复合480其他没有060通 过 查 找 和 计 算 相 似 点 ， 最 相 似 的 事 例 的 事 例 索 引 码 是 19325513321402000，细节信息在表2 中列出。 表2 最相似事例的事例索引码 特征名称特性值索引码夹具类型车床夹具1工件形状块状9工件材料中碳钢3批量中批2工件比例小5工件重量轻5工件刚度硬度强1加工内容孔3程序要求完成加工3定位方法三个平面1夹紧方法不确定？夹具体复合4其他没有0相似点的计算如下：所以夹具的相似尺寸值是0.806，这是在事例库中用于设计的最相似的事 例，最相似的事例的结构如图4 所示 图4 最相似的夹具 当成分替代，修改定位模型和夹紧模型，以及调节相关尺寸之后，新的夹 具被设计出来，图形如图5 所示 图5 需要设计的新夹具 因为在事例库中没有相似夹具，新夹具被储存到事例库中。事例索引码是 19325523311402000。 6 结论 基于事例推理，作为一个问题解决的方法，是一个比模仿人类思想的专业系 统更有效的方法，已经在很多难获取知识的领域里得到发展。基于事例推理的 优点如下：它和人类的思想很相似；一个事例库通过保存新事例获得自学能力， 它比有惯例库更快更容易，它可以更好的传递和解释新的知识，这和惯例库有 9 很大的不同。基于事例推理中提出的一个夹具设计的框架已经被实行了，使用 的是支持基础数据的VC+，UG 电脑绘图软件。这个框架也已经和普通成分库 和典型夹具库结合起来。这个发展的标准系统，用于航空项目，帮助夹具设计 者提高设计效率和重新使用先前的设计资源。Journal of Southeast University ( English Edition)Vol. 20No. 2June2004ISSN 1003 ) 7985Application and developmentof case-based reasoning in fixture designWang Qi1, 2Liao Wenhe1( 1College of M echanical and Electrical Engineering , N anjing U niversity of A er onautics and Astronautics, Nanjing 210016, China) ( 2 Department of M echanical Eng ineering, Y ancheng Institute of T echnology , Yancheng 224002, China)Abstract: Based on the case-based designing ( CBD) methodology, the fixture similarity is in two respects: the funct ion and the structure information. T hen, the computer-aided fixture design system is created on case- based reasoning ( CBR) , in which the att ribut es of the main features of workpiece and struct ure of fixture as case index code are designed for the ret rieve of the similar cases, and the structure and hierarchical relation of case library are set up for st ore. M eanw hile, the algorithm based on the knowledge- guided in the retrieve of the similar cases, the strategy of case adaptation and case storage in which the case identificat ion number is used to dist inguish from similar cases are presented. The applicat ion of the system in some projects improves the design efficiency and gets a good result.Key words: case-based reasoning; f ixture design; computer aided design ( CAD)Fix tures are dev ices that serve as the purpose of holding the w orkpiece securely and accurately, and maintaining a consistent relationship w ith respect to the tools w hile machining. Because the fixture structure depends on the feature of the product and the status of the process planning in the enterprise, it s design is the bottleneck during m anufacturing, w hich restrains to im prove the ef ficiency and lead- time. And fixture design is a com plicated process, based on ex perience that needs comprehensive qualitative know ledg e about a number of desig n issues including w orkpiece conf iguration, manufacturing processes involved, and machining environment. This is also a very t ime- consum ing w ork w hen using traditional CAD tools ( such as Unigraphics, CATIA or Pro/ E ) , which are good at perform ing detailed design tasks, but prov ide f ew benefits for taking advantage of the prev ious design ex perience and resources, w hich are precisely the key factors in improving the efficiency. T he m ethodology of case- based reasoning ( CBR) adapts the solution of a previously solved case to build a solution for a new problem w ith the f ollow ing four steps: retrieve, reuse, revise, and retain 1 . This is a more useful method than the use of an expert system to simulate hum an thought because proposing a similar case and applying a few modifications seems to be sel-fReceived 2003-10-22.Foundation items: The Nat ional H igh Technology Research an d Development Programof C hina( 863Program )( No. 2002AA 411030) , the Natural S cientific Research Program College of University of Jiangsu Province ( No. 03KJD520246) .Biographies: Wang Qi ( 1962 ) ) , male, doctor, associate prof essor, w qi003 sohu. com; Liao W enhe ( corresponding author) , male, doctor, professor, cnw ho nuaa. edu. cn.ex planatory and more intuitive to humans. So various case- based design support tools have been developed for numerous areas 2- 4 , such as in injection molding and design,architectural design,die- casting die design, process planning, and also in f ix ture design. Sun used six digitals to compose the index code that included w orkpiece shape, machine portion, bushing, the 1st locating dev ice, the 2nd locating device andclamping device 5 . But the system cannot be used for other f ixture types except for drill fixtures, and cannot solve the problem of storage of the same index code that needs to be retained, w hich is very important in CBR 6 .1 Construction of a Case Index and Case Library1. 1 Case indexThe case index should be composed of all f eatures of the w orkpiece, which are distinguished f rom dif- ferent f ix tures. Using all of them would make the op- eration in convenient. Because the f orms of the parts are diverse, and the technology requirements of m an- ufacture in the enterprise also develop continuously, lots of features used as the case index w ill m ake the search rate slow , and the main feature unimportant, for the reason that the relative weig ht w hich is allot- ted to every feature must diminish. And on the other hand, it is hard to include all the features in the case index.Therefore, considering the practicality and the demand of rapid design, the case index includes both the major feature of the w orkpiece and the structure of fixture. The case index code is m ade up of 16 dig-Application and development of case- based reasoning in fixture design175its: 13 digits for case features and 3 dig it s for case -i dentification number.T he first 13 digits represent 13 features. Each dig it is corresponding to an at t ribute of the feature, w hich m ay be one of / * 0, / ?0, / 10, / 20, ,/ A0, / B0, , / Z0, , etc. In w hich, / * 0 means anyone, / ?0 uncertain, / 00 nothing.T he system rules: fixture type, w orkpiece shape, locating model cannot be / * 0 or / ?0. When the system is designed, the at tribute information of the three it ems does not have these options, w hich means the certain at t ribute must be selected. And the default of the other at tributes of the feature is w orkpiece material as / 30 ( m iddle carbon steel) , batch size as / 20 ( middle batch ) , w orkpiece scale/ 30 ( medium ) , workpiece w eight / 30 ( m iddle ) , w orkpiece toughness / 10 ( much stiff er) , machining content / 9 0 ( relative ) , process property / 3 0 ( finished machining ) , clamping method / ?0 ( uncertain) , and others ( They are degree, profile modeling, etc. ) / 00 ( nothing ) . And the default v alues can be changed by the system administrator. For / * 0 and / ?0, w hen in retrial, / * 0 means matching anyone, / ?0 means matching none ofthem, and w hen saved, the certain means of / * 0and / ?0 must be g iven.The last three digits are the case identif ication number, w hich means the 13 digits of the case feature are the same, and the number of these three digits is used for distinguishing them, and saving them in the same case family if needed.The system also rules: / 0000 is a prototype case, which is used for retrieval, and other cases are/ 0010, / 0020, , which are used for reference cases to be searched by designers. If occasionally one of them needs to be changed as the prototype case, f irst it must be required to apply to change the one to/ 0000, and the former is changed to referential case automatically.The construction of the case index code is show n in Fig. 1.1. 2 Case libraryThe case library consists of lots of predefined cases. Case representation is one of the most important issues in case- based reasoning . So compounding w ith the index code, the structure of case library is show n 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 l ibraryCase indexVercharCase index code: * * * * * * * * * * * * * - * * *Fixture typeVerchar1) Lathe f ixt ure; 2) Drilling jig; 3) M illing fixture; 4) Boring fixture; ,Workpiece shapeVerchar1) Box; 2) Shaft; 3) Round; 4) Sheat h; 5) Seat ; 6) Piston rod; 7) Frame; 8) Plate-shel; 9) Block; A) Compound; ,5) M iddle hardness aluminum; ,Batch sizeVerchar* ) Random; 1) Large batch; 2) M iddle batch; 3) Low batch; 4) FewWorkpiece scaleVerchar1) M uch bigger; 2) Bigger; 3) M edium; 4) Less bigger; 5) SmallWorkpiece w eightVerchar1) M uch heavier; 2) Heavier; 3) M iddle; 4) Less heavy; 5) LightWorkpiece toughnessVerchar?) Uncertain ; 1) M uch stif fer; 2) Stiff er; 3) M iddle; 4) Les st iff er; 5) W eakM achining content Process propertyVerchar Verchar1) Cylinder; 2) End face; 3) H ole; 4) Plane; 5) Step plane; 6) Slot; 7) Pocket; 8) Hole of dril-l ream; 9) Relative; A) Compounding1) Blank; 2) Unfinishing machining; 3) Finish machiningWorkpiece materialVerchar* ) Anyone; 1) Cast iron; 2) Low carbon steel; 3) M iddle carbon steel; 4) Alloy steel;Locating 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) centred?) Uncertain ; 0) Nothing; 1) T op clamping; 2) T op+ side clamping; 3) S ide clamping; 4) TiltedClamping methodVercharclamping; 5 ) M ult-i point top clamping; 6) Compounded clam ping; 7 ) Centred clamping; 8 ) Vacuum clamping; ,Fixture bodyVerchar?) Uncertain; 1) Plan e; 2) Cast ing; 3) W elding; 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 identificat ion number: 000; 001; ,Case mappingVercharT he location of case modeling stored in hard disk of com puter1. 3 H ierarchical f orm of CaseT he structure similarity of the f ix ture is represented as the w hole fixture similarity, components sim ilarity and component similarity . So the w hole f ix ture case library, com ponents case library, component case library of f ix ture are f ormed corresponding ly. Usually design information of the w hole fix ture is composed of workpiece information and w orkpiece procedure information, w hich represent the fixture satisfying the specifically designing function demand. The w hole f ix ture case is made up of function components, w hich are described by the function components. names, numbers, and relationship to object- workpiece which are the body of the knowledge. The com ponents case represents the members. ( function component and other structure components) main- driven parameter, the number, and their constrain relations. The component case ( the low est layer of the f ixture) is the structure of function component and other components. In the modern f ix ture design there are lots of parametric standard parts and common non- standard parts. So the component case library should record the specif ication parameter and the w ay in w hich it keeps them. The hierarchical form of the f ix ture case library is show n in Fig. 2.cut dow n the t im e of adaptation. According to the requirement of fixture design, the strategy of case retrieval combines the w ay of the nearest neighbor and know ledge- guided.That is,first search on depth,then on breadth;the knowledge- guided strategy means to search on the know ledge rule f rom root to the object, w hich is f irst ly searched by the f ix ture type, then by the shape of the workpiece, thirdly by the locating method. For ex ample, if the case index code includes the m illing fixture of f ix ture type, the search is just for all milling fixtures, then for box of w orkpiece shape, the third f or 1plane+ 2pine of locating method. If there is no match of it, then the search stops on depth, and returns to the upper layer, and retrieves all the relative cases on breadth.Retrieval algorithms: According to the case index information of f ix ture case library, search the relevant case library; M atch the case index code w ith the code of each case of the case library, and calculate the valueof the sim ilarity measure; Sort the order of similarity measure, the biggest value, w hich is the most analogical case.Sim ilarity betw een two cases is based on the similarity between the two cases . features. T he calculation of similarity measure depends on the type of the feature. The value of similarity can be calculated for num erical values, for example, compare w orkpiece with the w eight of 50 kg and 20 kg . T he value can also be calculated betw een non- numerical values, for example, now the first 13 digits index code is all non- numerical values. It is important that a CBR system supports a multitude of sim ilarity measure, and, ideally, allows the definition of new types. The sim ilarity measure of a f ix ture is calculated as follow s:nE ( w i si ( f ai , f bji ) )i= 1S =nE w ii= 1i = 1, 2, , nFig. 2 Hierarchical form of fix ture case library2 Strategy of Case RetrievalIn the case- based desig n of fixtures, the most important thing is the retrieval of the similarity, w hich can help to obtain the most sim ilar case, and tow here S is the similarity measure of current fixture, n is the number of the index feature, w i is the w eight of each f eature, si ( f ai , f bji ) is the sim ilarity measure of the at tribute f ai of the i- th feature w ith the attribute f bj i of relative feature of the j- th case in the case library . At the same t ime, 0 si ( f ai , f bji ) 1, the value counts as follows:If ( f ai and f bji are non- numerical values) If ( f ai = f bji )si ( f ai , f bji ) = 1;Elsesi ( f ai , f bj i ) = 0;If ( f ai and f bj i are numerical values) f ai - f bj iso the case is not saved because it is represented well by the prototype case. Or is just saved as a reference case ( the last 3 digits are not / 0000, and not the same withsi ( f ai , f bj i ) = 1-max( f ai , f bj i ) .others) in the case library.w here f ai is the value of the index at t ribute of the i- th feature, and f bj i is the value of at tribute of the relative i- th f eature of the j- th case in case library.So there are two methods to select the analogical fixture. One is to set the value. If the values of similarity measure of current cases were less than a given value, those cases would not be selected as analogical cases. When the case library is init ially set up, and there are only a few cases, the value can be set smaller. If there are lots of analogical cases, the value should get larger. The other is just to set the number of the analogical cases ( such as 10) , which is the largest value of similarity measure from the sorted order.3 Case Adaptat ion and Case Storage3. 1 Case adaptationThe modification of the analog ical case in the fixture design includes the f ollowing three cases:1) T he substitution of components and the component;2) Adjusting the dimension of components andthe component w hile the form rem ains;3) T he redesig n of the model.If the components and component of the fixture are com mon objects, they can be edited, substituted and deleted with tools, w hich have been designed.3. 2 Case storageBefore sav ing a new fixture case in the case library, the designer must consider w hether the saving is valuable. If the case does not increase the know ledge of the system, it is not necessary to store it in the case library . If it is valuable, then the designer must analyze it before sav ing it to see w hether the case is stored as a prototy pe case or as reference case. A prototy pe case is a representation that can describe the main features of a case f amily. A case family consists of those cases w hose index codes have the same f irst 13 digits and different last three dig it s in the case library. The last three digits of a prototy pe case are alw ays / 0000. A reference case belongs to the same family as the prototype case and is distinguished by the different last three digits.From the concept that has been ex plained, the follow ing strategies are adopted:1) If a new case mat ches any existing case family, it has the same first 13 digits as an existing prototype case,2) If a new case matches any existing case familyand is thought to be better at representing this case family than the previous prototype case, then the prototype case is substit uted by this new case, and the previous prototype case is saved as a reference case.3) If a new case does not match any existing case f amily, a new case family w ill be generated automatically and the case is stored as the prototype case in the case library.4 Process of CBR in Fixture DesignAccording to thecharacteristics off ix ture design, the basic information of the fixture design such as the name of f ix ture, part, product and the designer, etc. must be input first . T hen the f ix ture f ile is set up autom at ically, in which all components of the fixture are put together. Then the model of the w orkpiece is inputor desig ned.The detailed information about the workpiece is input, the case index code is set up, and then the CBR begins to search the analogical cases, relying on the sim ilarity measure, and the most analog ical case is selected out. If needed, the case is adapted to satisfy the current design,and restored into the case library. T he f low chart of the process is show n 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 is 45# steel. Its name is seat. Its shape is block, and the product batch size is middle, etc. A f ix ture is turning fixture that serves to turn the hole, w hich needs to be designed.The value of f eature, at tribute, case index codeand w eight of the w orkpiece is show n in Tab. 2.The similarity is calculated as follow s:S= 1 100+ 1 90+ 2 1 70+ 5 1 60+ 2 1 80+ 0 100+ 0 90 100+ 90+ 70+ 60+ 60+ 60+ 60+ 80+ 70+ 100+ 90+ 80+ 60=790= 0. 806980Fig. 4 A workpiece requested to design a fix ture ( M aximum size is 80 mm 49 mm 22 mm)Tab. 2 T he case index code and w eight of workpieceFeature nameAt tribut e valueIndex codeWe ig htFix ture ty peLa the fixt ure1100Workpiece shapeBlock990Workpiece ma terialM iddle carbon steel370Bat ch sizeM iddle260Workpiece scaleSmall560Workpiece weightL ig ht560Workpiece toughnessM uch stiffer160Machining contentHole380Pro cess propert yF inish machining370L ocating method3plane1100Clam ping methodUncert ain?90Fixt ure bodyCompounding480OthersNo thing060T hrough searching, and calculating the similarity, the case index code of the most similar case is 1932551332140- 000, and the detailed information is shown in Tab. 3.Feature nameAttribute valueIndex codeFixture typeLathe f ixture1W orkpiece shapeBlock9W orkpiece materialM iddle carbon st eel3Batch sizeM iddle2Workpiece scaleSmall5W orkpiece w eightLight5W orkpiece toughn essM uch st if fer1M achining contentHole3Process propertyFinish machining3Locating method3plane2Clamping m ethodUncertain1Fixture bodyCompounding4OthersNothing0Tab. 3 Case index code of t he most similar caseSo the value of similarity measure of the f ix ture w hich needs to be designed w ith the most analog ical case in case library is 0. 806, and the structure of the most analogical case is show n in Fig. 5.Fig. 5 M ost analogical fixtureAfter having been substituted the com ponent, modified the locating model and clamp model, and
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