翻译1

(function component and other structure components， main driven parameter, the number, and their constrain relations.) The component case (the lowest layer of the 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 Case 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 guided strategy means to search on the knowledge rule from root to the object, which is firstly searched by the fixture type, then by the shape of the workpiece, thirdly by the locating method. For example, if the case index code includes the milling fixture of fixture type, the search is just for all milling fixtures, then for 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 the upper layer, and retrieves all the relative cases on breadth.

Retrieval algorithms:

1)According to the case index information of fixture case library, search the relevant case library;

2)Match the case index code with the code of each case of the case library, and

5

calculate the value of the similarity measure;

3)Sort the order of similarity measure, the biggest value, which is the most analogical case.

Similarity between two cases is based on the similarity between the two cases. features. The calculation of similarity measure depends on the type of the feature. The value of similarity can be calculated for numerical values, for example, compareWorkpiece with the weight of 50kg and 20kg. The value can also be calculated between non numerical values, for example, now the first 13 digits index code is all non numerical values. The similarity measure of a fixture is calculated as follows:

where S is the similarity measure of current fixture, n is the number of the index feature,

is the weight of each feature,

is the similarity

of relative

,

measure of the attribute of the i2th feature with the attribute

feature of the j-th case in the case library. At the same time, the value counts as follows:

6

.

Where

is the value of the index attribute of the i-th feature, and

is the

value of attribute of the relative i-th feature 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 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 3.1 Case adaptation

The modification of the analogical case in the fixture design includes the following three cases:

1) The substitution of components and the component;

2) Adjusting the dimension of components and the component while the form

7

remains;

3) The redesign of the model.

If the components and component of the fixture are common objects, they can be edited, substituted and deleted with tools, which have been designed.

3.2 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

8