Experimental verification of antagonistic stiffness planning for a planar parallel mechanism with 2-DOF force redundancy

In this paper, an experimental verification of antagonistic stiffness planning is presented for a 2-DOF parallel mechanism with four actuators. With 2-DOF force redundancy, the magnitude and direction of the stiffness enhancement can be controlled by the additional actuators, where the internal torques of the mechanism exist on the two-dimensional null space. In the experiments, the passive and active stiffness are measured, respectively, during endowing the external force at the end-effector. Two stiffness assignment methods for a given pathway are suggested and are verified by the experiments.