Abstract: With the Stewart platform as an example, a new method is proposed to analyze stiffness of parallel kinematic machines(PKM) based on analytical and finite element analysis(FEA) means. In this method, FEA software is used to simulate the nonlinear contact deformation inside spherical joints at first. A feature parameter is extracted from the FEA model and considered in the stiffness matrix of the mechanism. This method solves the problem of inability to treat joint stiffness in the analytical model and its reliability is verified using FEA software. If joint deformation is ignored in the analytical process to compute the mechanism stiffness, the overall stiffness results will produce rather large error. Based on the above analysis, quantitative study on improving stiffness by active redundant leg is carried out with the proposed method. The results show that in certain range of the workspace, active redundant leg can increase stiffness of PKM significantly.

Key words: Finite element analysis(FEA), Parallel kinematic machines(PKM), Spherical joint, Static stiffness