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similarity, components similarity and component similarity. So the whole fixture
case library, components case library, 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 made 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 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 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: