Stiffness modeling approach for a 3-DOF parallel manipulator with consideration of nonlinear joint stiffness

Considering the nonlinear characteristics of joint, this paper proposes a new comprehensive stiffness analysis method by combining finite element analysis and matrix structural analysis. Based on the force/moment equilibrium equations of a 3-DOF over-constrained parallel manipulator, a method for solving the internal forces of the joints is proposed. By calculating the stiffness of the bearing under the action of joint internal forces, the stiffness matrix of the revolute joint and the composite spherical joint can be derived. The FEA-based identification method for the stiffness matrix of multi-node components is proposed by importing the structural model into the finite element software for virtual experiments. Then, integrating the stiffness matrices of components and joints, the stiffness matrix of the whole manipulator can be derived and the theoretical stiffness computed from the stiffness model is mapped in the workspace. Finally, the stiffness analysis method is verified by experiments in the physical prototype.