The synthesis of three-degree-of-freedom planar parallel mechanisms with revolute joints (3-(R)under-barRR) for an optimal singularity-free workspace

In this paper, a method is presented for the synthesis of 3-RRR planar parallel mechanisms. The method uses a genetic algorithm while considering three different design criteria: the optimization of the mechanism workspace to approach a prescribed workspace, the maximization of the mechanism's dexterity, and the avoidance of singularities inside the mechanism workspace. It is shown that, for a given mechanism, some working modes do not have any corresponding singularity curves located inside the mechanism workspace. Furthermore, a case is presented where, for a given orientation range of the mechanism's end-effector, there are no parallel singularities located inside the workspace. Finally, two methods are described and compared to deal with the nonuniform units of the mechanism's Jacobian matrix during the dexterity computation. (C) 2004 Wiley Periodicals, Inc.