New reasoning algorithm for assembly tolerance specifications and corresponding tolerance zone types

When designing a mechanical product, how to determine its assembly tolerance specifications (ATS) and tolerance zone types (TZT) is a complex design problem, in which designers need to consider comprehensively the functional requirement, geometric feature, tolerance principle, and so on. Therefore, it has high requirements for designers. Meanwhile, the design and development of a complex assembly need to be done jointly by designers. This will cause difficulties for the overall coordination of tolerance design, which affects the quality and efficiency of product development. In order to reduce the uncertainty of ATS and TZT design, and to adapt to the requirements of digital design, a new reasoning algorithm for the automatic generation of ATS and TZT is presented. Polychromatic sets theory (PST) can provide a more formal approach to describe research objects and the relationships among them. Based on PST, this method establishes reasoning relation matrices to represent the relations among research objects, such as assembly feature, assembly constraint type, datum reference frame and tolerance zone type. Therefore, it can use a unified formal mathematical model to describe the whole reasoning process from assembly to ATS and TZT. This method realizes the systematization and computerization of ATS and TZT design, which can help designers to achieve the coordination and coherence of tolerance design. This method facilitates knowledge management and improves reasoning quality and efficiency. ATSs and TZTs generated by this method meet the functional requirements of product and are in accord with the tolerance standards in ISO/ASME. Furthermore, the method only requires a little geometric information and is consistent with the designers' way of thinking, which shows good applicability for the practical design of ATS and TZT. Finally, the reasoning steps of ATSs and TZTs are demonstrated by means of an example.