Spatial reasoning about three-dimensional mechanical assemblies

Abstract

A methodology has been developed to generate selected assembly sequences of three-dimensional, tri-axial mechanical products. A feature-based design system is first introduced and its representation scheme briefly explained. This representation incorporates the abstraction necessary to allow a designer to describe a product using common engineering vocabulary. Parts are initially designed in terms of descriptive form features and the assembled product model is created from inter-part mating information specified interactively by the designer. From the initial product description, a graph of planar contacts between parts is created and transformed uniquely into a new graph, describing an exploded view of the product. The transformation rules combine knowledge of part geometry and assembly process heuristics to infer the relative spatial locations in an exploded layout. The problem of assembly sequence generation is addressed next. Once the exploded view of a product is determined, the task of assembly sequence generation becomes relatively straightforward because of the implicit precedence provided by the exploded view. The assembly planning system selects an assembly operation upon satisfaction of the primary constraints imposed by the exploded view and the part mating conditions. A set of selection criteria is used to eliminate redundant and awkward assembly operations. The strength of this type of constraint-based approach to assembly planning lies in the fact that no search space is generated and the computational power can be directed toward enhanced reasoning about the assembly and its components.