Elastostatic Stiffness Modeling and Performance Evaluation of a 2UPR–2PRU Redundantly Actuated Parallel Manipulator

Redundantly actuated parallel manipulators (PMs) have attracted a great deal of attention since they generally have better stiffness than non-redundantly actuated ones. This paper presents an analytical elastostatic stiffness modeling and performance study of a 2UPR–2PRU PM with actuation redundancy, which has two rotational and one translational degrees of freedom (U: universal joint; P: prismatic joint; R: revolute joint). First, the inverse displacement is reviewed and verified briefly. Second, the stiffness matrices of UPR and PRU limbs are deduced by using the principle of strain energy, followed by the overall stiffness matrix of the 2UPR–2PRU PM. Combined with the ANSYS software, the finite element analysis method is then used to verify the correctness and universality of the stiffness models by calculating the deformations of four selected configurations. Finally, the stiffness index based on the virtual work is used to evaluate the performance of the 2UPR–2PRU PM, and the influence of different external loads and operational heights on the stiffness performance is discussed. The relationship between singular configurations and the stiffness index is also presented. The stiffness models and performance distributions of the 2UPR–2PRU PM with actuation redundancy can provide references for the actual applications.