Modularity in design of products and systems
IEEE Transactions on Systems, Man, and Cybernetics, Part A: Systems and Humans
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We extend traditional directed graphs to generalized directed graphs, making them capable of representing function structures as graphs. In a generalized directed graph, vectors are used to denote the edges, which are pairs of sub-function vertices connected by a relationship, and elements of the vectors indicate different types of flow (i.e., material, energy, or signal) on which sub-functions operate. Based on these definitions, we formalize the three heuristics proposed by Stone et al. into rules to identify functional modules in function structures: (1) sequential flow rule, (2) parallel flow rule and (3) flow transformation rule. The arithmetic for identifying functional modules based on these formalized rules is developed, and a computer-aided software tool is created to facilitate this process. Finally, the proposed approach is applied to a function structure for a power screwdriver, and the results compare favorably to those obtained using the three heuristics.