Automatic Selection of Mechanism Designs from a Three-Dimensional Design Map

Abstract

Often a simple (four-bar linkage) mechanism to trace a desired path is sought. Dimensions of linkages to trace a specified coupler curve exactly are difficult to determine. Precision point techniques do not guarantee that the desired path will be generated. The methodology presented in this paper is based on indirect synthesis approach to select four-bar linkages that trace a given desired path. A practical, computer-aided three-dimensional design chart for the selection of four-bar linkage candidate designs that trace symmetrical paths is presented. It is based on hypothesis that any arbitrary path can be approximated by a symmetrical path at least for the purpose of choosing an initial design. Four-bar linkages that generate symmetrical paths are easier to design and exhibit a definite pattern of changes in their shape as the linkage parameters are varied. General design categories and the corresponding solution subspaces in the 3-D design map are identified to aid in the selection of candidate designs. The automation of the design-selection process requires a satisfactory means to quantitatively compare the “desired” and the “known” coupler curves. This paper addresses the issues involved in quantitative comparison of two arbitrary curves using parameterization and shape evaluation. A design example of automated selection of mechanism designs is also presented.