Abstract: To study the functional tolerance specification methods consistent with the new generation of geometrical product specification (GPS), the class of positioning joints of part assembling and the principle of determining its priority are studied on the basis of definition of invariance class of GPS. The existing assembly oriented graph (AOG) is reformed and the expression of assembly positioning constraint is added in AOG. The methods of representing and decomposing of functional geometrical requirement are studied. And, the tolerance specification technology of interface between part-part based on the improved AOG is studied. A new functional tolerancing method from geometrical functional requirement to geometrical specification is presented. Tolerance specification example of an assembly is adopted to verify the feasibility of the proposed method.

Key words: Assembly positioning constraint, Functional tolerance, Tolerance specification design