Stiffness Evaluation and Dimensional Synthesis of a 5-DOF Parallel-Serial Robot

This article focuses on the stiffness analysis and dimensional synthesis of a parallel-serial robot with five degrees of freedom (DOFs). The robot includes a 3-DOF redundantly actuated planar parallel mechanism, whose stiffness affects the stiffness of the entire robot. Two geometrical parameters of this mechanism are selected as variables for solving the dimensional synthesis problem. First, we establish the stiffness model and define the stiffness matrix of the mechanism. Next, we analyze two components of this matrix and the inverse of its condition number to evaluate the mechanism stiffness. We perform this procedure for various combinations of geometrical parameters and derive workspaces and stiffness maps for each combination. The chord method provides a computationally fast procedure to obtain the workspaces. Finally, we determine the average values of the stiffness indices and use them for dimensional synthesis. The results of numerical simulations show that the lateral stiffness has increased by 67.4% compared to the initial design.