Abstract: An optimization scheme is presented in mechanism path-synthesis using B-spline curve matching, and four-bar mechanism is used as example to illustrate the approach. A space model of the relative link-length types of four bar linkage is used to confine all possible combinations of the four link-lengths of the four bar mechanism within a closed region in the three dimensional space. Therefore all the related couple curver of the four bar mechanism can be derived from the above data model. The targeted curve for which the mechanism is to be designed can be represented by non-uniform nonrational cubic B-spline. The matching of the targeted curve and the coupler curve can be converted into the matching of polygons generated by either the control points or the interpolation points of B-spline curves. The maximum corresponding angle deviation of polygons is used as the object function and it can guarantee that the curve matching is independent of movement, rotation, an scale transform. An algorithm for searching the optimum solution in solution space is developed which simulates the trial-and error practical design process and can bedescribed as first-rough-then-refined. In the first rough searching, the shole space is browsed through to search for the area for optimum point, and the exact optimum point can be derived by the refined searching. The searching method presented includes the random effect of point selection in order to enhance the reliability of global optimum.

Key words: Curves match, Four-bar linkage, Linkage curves, Optimum