A hierarchical approach to generating precedence graphs for assembly planning

This paper presents a hierarchical approach to generating precedence graphs for assembly planning. The basic idea of the approach is to identify constraint direction sets for all components of an assembly, hierarchically abstract out precedence relations for them, then obtain and evaluate all precedence graphs for each layer. The input to the approach consists of the mating relation graph (MRG), and hierarchical relation graph (HRG), which is deduced from MRG through geometric reasoning and knowledge. According to the MRG of an assembly, a revised algorithm to generate the non-directional blocking graph (NDBG) is proposed. Using the stored constraint direction sets and HRG of an assembly, all feasible precedence graphs for each layer are generated by another algorithm. In terms of operation replacement and graph transformation, the number of possible sequences allowed by a precedence graph is computed, from which an optimal precedence graph in a certain layer is selected. To verify the validity and efficiency of the approach, a variety of assemblies including some complicated products from industry are tested, and the corresponding results are also presented. (C) 2003 Elsevier Ltd. All rights reserved.