Analysis and optimization of a novel planar 5R parallel mechanism with variable actuation modes

A closed-loop structure composed of multiple identical branches is a typical feature for parallel mechanisms. The number of joints (including active and passive ones) is much larger than the number of terminal degrees of freedom, and diverse actuation modes (schemes of active joints) are available. Different actuation modes inevitably lead to performance changes. Transformation of actuation modes is a potential way to improve the kinematic performance of parallel mechanisms and deserves further research. In this paper, we propose a novel planar 5R (R denotes revolute joint) parallel mechanism with nine actuation modes. Kinematic performance indices are defined on the basis of matrix orthogonal degree, which possess the advantages of conciseness and clear physical meaning. The performance of the proposed mechanism under different actuation modes is evaluated via the proposed indices. Analysis and simulation results show that the kinematic performance of the parallel mechanism can be significantly improved through reasonable transformations of actuation modes. An optimization method of a variable actuated 5R parallel mechanism is finally established. Optimal dimension and transformation map of optimal actuation modes for the proposed 5R parallel mechanism are obtained. A new approach to improve the kinematic performance of parallel mechanisms by transforming actuation modes is established.