1、附录 Article 1: 英文文献译文 Application and development Of case based reasoning in fixture design Abstract: Based on the case based designing (CBD) methodology, the fixture similarity is in two respects: the function and the structure information. Then, the computer aided fixture design system is created o
2、n case based reasoning (CBR),in which the attributes of the main features of workpiece and structure of fixture as case index code are designed for the retrieve of the similar cases, and the structure and hierarchical relation of case library are set up for store. Meanwhile, the algorithm based on t
3、he knowledge guided in the retrieve of the similar cases, the strategy of case adapt at ion and case storage in which the case ident if cat ion number is used to distinguish from similar cases are presented. The application of the system in some projects improves the design efficiency and gets a goo
4、d result . Keywords: case based reasoning ；fixture design； computer aided design(CAD) Fixtures are devices that serve as the purpose of holding the workpiece securely and accurately, and maintaining a consistent relationship with respect to the tools while machining. Because the fixture structure de
5、pends on the feature of the product and the status of the process planning in the enterprise, its design is the bottleneck during manufacturing, which restrains to improve the efficiency and leadtime. And fixture design is a complicated process, based on experience that needs comprehensive qualitati
6、ve knowledge about a number of design issues including workpiece configuration, manufacturing processes involved, and machining environment. This is also a very time consuming work when using traditional CAD tools (such as Unigraphics, CATIA or Pro/E), which are good at performing detailed design ta
7、sks, but provide few benefits for taking advantage of the previous design experience and resources, which are precisely the key factors in improving the efficiency. The methodology of case based reasoning (CBR) adapts the solution of a previously solved case to build a solution for a new problem wit
8、h the following four steps: retrieve, reuse, revise, and retain 1. This is a more useful method than the use of an expert system to simulate human thought because proposing a similar case and applying a few modifications seems to be self explanatory and more intuitive to humans .So various case base
9、d design support tools have been developed for numerous areas2-4, such as in injection molding and design, architectural design, die casting die design, process planning, and also in fixture design. Sun used six digitals to compose the index code that included workpiece shape, machine portion, bushi
10、ng, the 1st locating device, the 2nd locating device and clamping device5. But the system cannot be used for other fixture types except for drill fixtures, and cannot solve the problem of storage of the same index code that needs to be retained, which is very important in CBR6. 1 Construction of a C
11、ase Index and Case Library 1.1 Case index The case index should be composed of all features of the workpiece, which are distinguished from different fixtures. Using all of them would make the operation in convenient. Because the forms of the parts are diverse, and the technology requirements of manu
12、facture in the enterprise also develop continuously, lots of features used as the case index will make the search rate slow, and the main feature unimportant, for the reason that the relative weight which is allotted to every feature must diminish. And on the other hand, it is hard to include all th
13、e 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 workpiece and the structure of fixture. The case index code is made up of 16 digits: 13 digits for case features and 3 digits for case identific
14、ation number. The first 13 digits represent 13 features. Each digit is corresponding to an attribute of the feature, which may be one of“*”, “？ ”, “1”, “2”,“A”,“B”, “Z”, etc. In which, “*” means anyone, “?” uncertain, “0” nothing. The system rules: fixture type, workpiece shape, locating model canno
15、t be “*”or“?”. When the system is designed, the attribute information of the three items does not have these options, which means the certain attribute must be selected. The last three digits are the case identification number, which means the 13 digits of the case feature are the same, and the numb
16、er of these three digits is used for distinguishing them. The system also rules: “000” is a prototype case, which is used for retrieval, and other cases are “001”,“002”, which are used f or reference cases to be searched by designers. If occasionally one of them needs to be changed as the prototype
17、case, first it must be required to apply to change the one to “000”, and the former is changed to referential case automatically. The construction of the case index code is shown in Fig.1. 1.2 Case library The case library consists of lots of predefined cases. Case representation is one of the most
18、important issues in case based reasoning. So compounding with the index code,. 1.3 Hierarchical form of Case The structure similarity of the fixture is represented as the whole fixture similarity, components similarity and component similarity. So the whole fixture case library, components case libr
19、ary, component case library of fixture are formed correspondingly. Usually design information of the whole fixture is composed of workpiece information and workpiece procedure information, which represent the fixture satisfying the specifically designing function demand. The whole fixture case is ma
20、de up of function components, which are described by the function components names and numbers. The components case represents the members. (function component and other structure components， main driven parameter, the number, and their constrain relations.) The component case (the lowest layer of t
21、he fixture) is the structure of function component and other components. In the modern fixture design there are lots of parametric standard parts and common non standard parts. So the component case library should record the specification parameter and the way in which it keeps them. 2 Strategy of C
22、ase Retrieval In the case based design of fixtures ,the most important thing is the retrieval of the similarity, which can help to obtain the most similar case, and to cut down the time of adaptation. According to the requirement of fixture design, the strategy of case retrieval combines the way of the nearest neighbor and knowledge guided. That is, first search on depth, then on breadth； the knowledge
