Geometric tolerances reasoning and its specification verification based on polychromatic sets theory

To avoid improper assignment of datum reference frames, tolerance types and tolerance symbols to geometric tolerances on 3D model of parts, a reasoning and specification verification method based on polychromatic sets theory was proposed. A reasoning hierarchy structure of tolerance specifications was established and modeled with polychromatic sets based on geometric tolerance ontology model. According to the new generation Geometric Product Specification(GPS), the mapping relationships between information from different layers of the hierarchy structure was extracted, and the contour matrixes were formed. On this basis, the datum redundancy and sequence inconsistency problems were distinguished through analyzing the Degree Of Freedom (DOF) of datum constraints, and the specification of datum system was also verified. Meanwhile, reasoning algorithms of tolerance specifications were presented to extract suitable tolerance types and symbols to validate designed geometric tolerances by two steps. A software module was developed based on above models and algorithms to demonstrate the feasibility and efficiency of the proposed method.