Assembly feature tutor and recognition algorithms based on mating face Pairs

Assembly features encode geometric and functional relationships between parts in an assembly. They can be used in assembly design by features, kinematic and structural analyses, assembly planning and assemblability evaluation. Explicit definition of assembly features and archival in libraries can be used to assist in design and analysis of mechanical assemblies. This paper builds on our past work in neutral definition of generic assembly features to provide a mechanism for user-defined custom assembly features using an interactive system, called the assembly feature tutor. The user teaches the system interactively by examples and the tutor outputs an assembly definition file that is written in EXPRESS like language. Central to the definition are pairs of mating part faces and includes algebraic, geometric and parametric relations. Twist and wrench matrices can be extracted from face pair relations. The definition is implementation independent and provides a uniform way to define assembly features. The paper also describes the implementation of an automatic recognition system for user defined assembly features. The algorithm is based on contact pairs which is found to be more efficient than those based on pre-recognition of part features, as the issue of feature interaction is avoided.