Experimental verification of antagonistic stiffness planning for a 2-DOF planar parallel manipulator

In this paper, two torque assignment methods of the antagonistic stiffness for a 2-DOF planar parallel manipulator are presented and verified by experiments. The first method is equalizing the magnitude of the stiffness in all directions at a desired position. The second method is maximizing the active stiffness in one direction at a given path. A 2-DOF parallel mechanism with four actuators is used for verification tests, where the internal torque of the mechanism exists on the two dimensional null space. In the experiment, passive and active stiffness are tested when endowing the external force at the moving platform and compared with the estimated results.