Boundary models for assembly knowledge representation

This paper presents a boundary graph representation to handle geometric information for assembly. Boundary graphs represent the faces or surfaces of an assembly part. We show that assembly operations joining two parts together may be modeled simply as the splicing of two boundary graphs representing the two assembly parts. Subgraphs which become detached during the graph splicing process represent surfaces which become inaccessible as a consequence of an assembly operation. These subgraphs are therefore discarded. An added bonus of this approach is that in some instances the feasibility of an assembly operation can be evaluated very quickly by simply scanning the boundary graph for certain geometrical features such as radii of specific surfaces. The modeling of assembly operations and feasibility testing based on boundary graph models advocated here form the basis of a direct or forward assembly planner