Synthesis of asymmetric parallel mechanism with multiple 3-DOF motion modes

Abstract

A method for designing asymmetric multi-mode parallel mechanism is proposed. Parallel mechanisms with 2R1T and 2T1R motion modes are synthesized by using displacement manifold theory. Based on the parallel mechanism, a kind of mechanism with hybrid variable DOF kinematic chain is proposed. The DOF characteristics of the mechanism in the process of motion mode transformation are analyzed by using screw theory, and the rationality of the selection of driving pairs in different motion modes is verified. The results show that the mechanism with hybrid variable DOF kinematic chain has 3R, 2T1R, and 2R1T motion modes. When the mechanism is in the general configuration of the four motion modes mentioned above, three driving pairs can control the mechanism. When the mechanism is in the transformation configuration having 2R2T or 3R1T instantaneous DOF, an additional auxiliary driving pair is needed to control the mechanism. The mechanism can realize multiple motion modes by using fewer driving pairs. It does not need to reassemble the mechanism when the motion mode is changed.