Hierarchical tolerance representation model based on polychromatic sets theory

The tolerance plays an important role in the selection of manufacturing processes and assembly strategies. In order to achieve the requirements for tolerance representation, tolerance validation, tolerance analysis and tolerance inspection in computer, the appropriate tolerance representation model must be firstly built. This paper presents a hierarchical tolerance representation model based on feature which combines the different types of tolerance with the corresponding geometric entities and metric relations. The hierarchical rock-bottom frame based on the features of this hierarchical tolerance representation model is proposed as the carrier of the tolerance. The hierarchical structure of the rock-bottom frame and the relations between the tiers are discussed. For the purpose of programming to realize the hierarchical rock-bottom frame in computer, polychromatic sets are used to represent the hierarchical structure and the relations between the tiers. In the end, an example is given to verify the correctness of the techniques and approaches proposed in this paper.