Force-Motion Coupled Mechanism Synthesis Method of Heavy Load Parallel Kinematic Mechanism for Multi-DoF Forming Process

At present, the design of parallel kinematic mechanism (PKM) generally starts from type synthesis based on the motion pattern and then the dimensions are synthesized based on performance requirements. The synthesized type of PKM with optimal load-bearing capacity is hard to determine because the above type synthesis is just based on the motion pattern and the number of synthesized types of PKM is huge. Therefore, this paper aims to investigate a force-motion coupled mechanism synthesis method for heavy-load PKM with optimal motion performance and load-bearing capacity. First, the optimal load-bearing conditions for PKM are derived, namely, the wrench screw of a limb is parallel to the external force acting on the moving platform and is reciprocal with the wrench of the actuator. Furthermore, a novel force-motion coupled type synthesis method is proposed, in which the wrench of the limb is added to the constrained screw system. In this situation, the synthesized PKM is singular. Therefore, dimension synthesis is carried out based on the workspace, and a near-singular 6-PHSS PKM is then synthesized. Finally, a novel multi-DoF forming machine with a forming force of 6000 kN is developed. Compared with the Stewart platform (6-UPS PKM), the maximum forces of the actuator and limb of the new near-singular 6-PHSS PKM were reduced by 80% and 10%, respectively, validating the proposed force-motion coupled synthesis method for heavy-load PKM.