Stiffness estimation for the 4-DOF hybrid module of a novel reconfigurable robot

In this paper a novel reconfigurable robot is introduced, which is composed of a 4-DOF hybrid module and a 2-DOF rotating head. Compared with the well-known Tricept robot, an active prismatic limb is properly connected to the constrained passive limb of the 3-DOF spherical-coordinate parallel module so as to enlarge the workspace/volume ratio. To ensure better performance of the virtual prototype designed, an analytical approach is presented for time-effectively evaluation of the stiffness distribution throughout the workspace. The 4-DOF module is firstly decomposed into two subsystems and the Jacobian matrix of the parallel subsystem is derived by means of the screw theory. The stiffness model of each subsystem is developed respectively by assuming the other one be rigid. The stiffness model of the entire system is then achieved with resort to the linear superposition principle, whose validity is further proved by FEA software. Finally the stiffness distribution of the 4-DOF module is investigated and the contributions of component compliances to those of the entire system are discussed.