A comparison study of three degree-of-freedom parallel robotic machine tools with/without actuation redundancy

This article presents a comparison study of two unique parallel robotic machine tools (PRMTs): a three degrees of freedom (DOF) PRMT and a 3-DOF PRMT with actuation redundancy. The 3-DOF PRMT has three driving units with linear motion, while the 3-DOF PRMT with actuator redundancy has four of these units. For both designs, the linear motion driving units are identical and both machines have the same passive constraining link in the middle of the structure. The manipulator with actuator redundancy is designed to prevent singularity and to improve stiffness. The inverse kinematics and Jacobian matrix of these two PRMTs are analysed. The stiffness properties are determined and global stiffness is optimised using genetic algorithm. The finite-element analysis is conducted to find the maximum and minimum stress points of each link and the moving platform. The dynamic simulations are implemented to analyse the velocity and acceleration of both structures. A comparison of the global stiffness indicates that the 3-DOF PRMT with actuator redundancy outperforms the one without actuator redundancy.