Elastostatic stiffness modeling and performance evaluation of a 2RPU-UPU parallel mechanism with two operation modes.

This article presents a parallel mechanism (PM) that is consists of a UPU and two RPU limbs (U, P, R denote universal joint, prismatic joint, and revolute joint, respectively). It can switch into two different configurations with three degrees of freedom (DOFs), in which one configuration outputs two rotations and one translation, and the other outputs two translations and one rotation. Four joints should be actuated to fully control the PM. Inverse position analysis is carried out. Taking the compliances of links into consideration, wrench analysis of the RU chain is conducted by using screw theory. Stiffness matrix and compliance matrix of the limb are derived through the strain energy method. The PM's overall stiffness matrix is then obtained according to the deformation compatibility equations. The theoretical results are compared with simulation results obtained in ANSYS, which shows a maximum deviation less than 0.6%. Static stiffness performance evaluation is carried out using the virtual work stiffness index. Performance distributions of the PM in two operation modes under external loads are obtained. The proposed stiffness modeling and performance evaluation could be helpful for optimal design and application investigation of the PM. [ABSTRACT FROM AUTHOR]