【文章內(nèi)容簡(jiǎn)介】 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 initially 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 as10), which is the largest value of similarity measure from the sorted order. 3 Case adaptation and Case Storage Case adaptation The modification of the analogical case in the fixture design includes the following three cases: 1) The substitution of ponents and the ponent。 2) Adjusting the dimension of ponents and the ponent while the form 8 remains。 3) The redesign of the model. If the ponents and ponent of the fixture are mon objects, they can be edited, substituted and deleted with tools, which have been designed. Case storage Before saving a new fixture case in the case library, the designer must consider whether the saving is valuable. If the case does not increase the knowledge 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 saving it to see whether the case is stored as a prototype case or as reference case. A prototype case is a representation that can describe the main features of a case family. A case family consists of those cases whose index codes have the same first 13 digits and different last three digits in the case library. The last three digits of a prototype case are always “ 000” . 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 explained, the following strategies are adopted: 1) If a new case matches any existing case family, it has the same first 13 digits as an existing prototype case, so 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 “ 000” , and not the same with others) in the case library. 2) If a new case matches any existing case family and is thought to be better at representing this case family than the previous prototype case, then the prototype 9 case is substituted 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 family, a new case family will be generated automatically and the case is stored as the prototype case in the case library. 4 Process of CBR in Fixture Design According to the characteristics of fixture design, the basic information of the fixture design such as the name of fixture, part, product and the designer, etc. must be input first. Then the fixture file is set up automatically, in which all ponents of the fixture are put together. Then the model of the workpiece is input or designed. 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 similarity measure, and the most analogical case is selected out. If needed, the case is adapted to satisfy the current design, and restored into the case library. The flowchart of the process is shown in . 10 5 Illustrating for Fixture Design by CBR This is a workpiece (). Its material is 45 steel. Its name is seat. Its shape is block, and the product batch size is middle, etc. A fixture is turning fixture that serves to turn the hole, which needs to be designed. The value of feature, attribute, case index code and weight of the workpiece 11 is show n in . Through searching, and calculating the similarity, the case index code of the most similar case is 193255133214020xx, and the detailed information is show n in Tab. 3. The similarity is calculated as follows: 12 So the value of similarity measure of the fixture which needs to be designed with the most analogical case in case library is , and the structure of the most analogical case is shown in . After having been substituted the ponent, modified the locating model and clamp model, and adjusted the relative dimension, the new fixture is designed, and the figure i