An approach to the selection of mechanism types in computer-aided conceptual design

The selection of mechanism type is one of the important aspects in conceptual design of machine products. The paper applies the set theory for representing the attribute items of kinematic function to reflect the kinematic state and the function quality to reflect overall performances of the function unit for some complex design task. It gives a set-theory-based mode for the selection of mechanism types, in which precise reasoning by computer is combined with fuzzy appraisement by human. By precise reasoning at first, the computer selects from mechanisms database those mechanisms that can meet the kinematic requirements of the function unit to be solved. And then the function qualities of the selected mechanisms are appraised by human approving, which is actually a process of fuzzy match. This approach avoided the difficulty that the computer cannot yet effectively process fuzzy information and is suitable for the selection of both single-degree-of-freedom (DOF) and many-DOF mechanisms. The selected mechanisms can thus meet the requirements not only of the kinematic function, but also of the function quality. The approach presented in the current paper has been successfully applied to the software development of computer-aided conceptual design of mechanism systems.