Study on functional specification scheme on interface based on positioning features

Abstract

This article proposes a scheme for functional specification in accordance with the new generation of geometrical product specification. The scheme is to decompose a geometrical functional requirement on a complex mechanism into geometric specifications defined on key parts. The assembly is analyzed by graph theory. The general geometrical functional requirement is analyzed and decomposed if necessary, with geometrical tolerances specified on ending parts. Then geometric variation model is built according to the invariant degree of freedom of both datum reference system and tolerance zone, which is subsequently used to validate the sufficiency of the datum reference frame on positioning features, thereby inferring joints that perform key roles in affecting function. After a series of topological rules formulated and validation algorithm applied, datum reference system is validated and detailed specifications are generated on joint surfaces. Those specifications on underlying parts or subassemblies are then defined as new geometrical functional requirements and should be further developed. Therefore, the designer can carry out an effective recursive approach capable of realizing each geometric specification on key features while ensuring functional tolerancing of the entire assembly. A case study is given to validate the proposed method.