Abstract: The main advantage of polychromatic sets based tolerance representation model is that the number of feature types to be processed is larger. Because polychromatic sets cannot deal with the information of degrees of freedom, the number of recommended assembly tolerance types generated by the model is somewhat large. The model cannot be directly applied to tolerance analysis and synthesis. Aiming at this problem, a tolerance representation model based on feature surfaces and spatial relations is constructed by adding the mappings from spatial relations to assembly tolerance types to the mappings from feature surfaces to assembly tolerance types. Through the mappings from spatial relations to assembly tolerance types, the number of the recommended assembly tolerance types generated by the constraint relations between feature surfaces is further reduced. The information of degrees of freedom needed in tolerance analysis and synthesis is generated when the recommended assembly tolerance types are generated by spatial relations. Thus the constructed model can be directly applied to tolerance analysis and synthesis. The effectiveness of the constructed model is demonstrated through an automatic generation algorithm of assembly tolerance types and a practical example.

Key words: Assembly tolerance types, Feature surfaces, Representation model, Spatial relations