Study on Stiffness Modeling and Performance of Spatial Rotation 4-SPS-S Parallel Robot Mechanism

The paper focuses on a spatial rotation three Degree of Freedom (DOF) 4-SPS-S parallel robot mechanism, which has four SPS Active Legs and one passive constraining leg. The geometric model of the parallel robot mechanism is introduced, and then velocity mapping equation and Jacobian matrix for the robot mechanism are developed. Based on principle of virtual work and sub-structure synthesis method, taking into full consideration the compliancy of driving pairs and transferring components, flexibility of constraining chains and minute deformation of joints, stiffness matrix model is established for the mechanism. And then the square root of eigenvalues of K^T K matrix is defined as stiffness performance indexes, and take it as a criteria to judge stiffness performance of the manipulator. With a case study, Simulation analysis is conducted to explore distribution rules of how stiffness changes are linked with pose changes in workspace. Results show that the proposed robot mechanism has good stiffness and significant implication in engineering application. This paper provides theoretical foundations for engineering design and application for this class of parallel robot mechanism.