Couple Approach to Fixture Design Based on Maximum Common Subgraph Mining and Fixturing Performance Analysis

A numerous of fixture cases, which accumulate reusable experience and knowledge, can supply the theoretical basis and decision criterion for fixture design of a new workpiece. However, the accurate search of similar fixtures from fixture cases is key to the achievement of fixture design, in addition that the searched fixtures can successfully grasp the new workpiece. Therefore, based on the entity B-Rep (i.e., Boundary Representation) model of a workpiece, the labeled graph of a workpiece is constructed according to the geometrical and topological relationships between features. In combination with the linear sequence of labeled graph, the principles of the DFS dictionary sequence, which can calibrate the index value for an arbitrary feature, are proposed to traversal the minimum DFS code. Again, based on the minimum DFS code, the mining method of maximum common subgraph is suggested for workpieces according to the feature value, performance value and link relationship between features. Furthermore, two concepts on the workpiece similarity and library similarity are defined to formulize the decision factor for the sequence of the searched fixtures. The final step is to formulize the locating determination and the fixturing stability so that the searched fixtures are one by one evaluated the fixturing performance for a new workpiece. the design process of fixture is over when and only when a fixture achieves the good fixturing performance. In fact, the minimum DFS code and a workpiece can hold a unique one to one relationship. The search method of DFS code, which is classic algorithm in graph theory, can be easily realized by the recursion method. On other hand, the fixturing performance evaluation only concern on the coordinates and the corresponding normal vectors. It belongs to the programmed discretization problem. So the presented "it is crucial for the searched fixture to satisfy the fixturing performance" method is not only well enrich the theory of computer aided fixture design, but greatly accelerate its practicability.