Because of a lack of knowledge to support functional reasoning from functional requirements of kinematic compound mechanisms to their constituent basic mechanisms, the conceptual design of kinematic compound mechanisms based on functional synthesis approach is still a challenging task. With the aid of the stratified hierarchical theory, a functional decomposition model in quotient space is proposed. According to the requirements of granularity in the functional decomposition layer, and the close degrees to the purpose functional layer defined in the attribute function, based on fuzzy equivalence relation and the improved breadth-first algorithm, the optimum decomposition scheme of the purpose functional layer are configured. Through refining the decompose process step by step, the functional means tree corresponding to basic operation actions as the minimum functional units is obtained. Traversing all tree branches and leaf nodes in the functional means tree, the topology of the functional directed network is determined. In the quotient space model, the functional decomposition process does not rely on humans' experiments as well as knowledge in the database. Therefore it can be applied to solve the functional decomposition problem of conceptual design for kinematic compound mechanisms, and gives functional decomposition supports in exploring innovative compound mechanisms combined by a number of basic mechanisms ingeniously. Taking a powder tablet pressing mechanism as an example, the algorithm of the functional decomposition and the computerized realization to construct the functional directed network graph are given.
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