Multi-rate operational space control of compliant motion in robotic manipulators

In this paper, we introduce a new multi-rate hybrid motion and force control using operational space framework. Conventional implementation of operational space control (OSC) does not perform well in the presence of model uncertainties. In order to overcome this issue, a two layered hierarchical controller structure is proposed in this paper. In the outer control loop, the control torque from the OSC is applied to the joint space dynamic model of the robot. By integrating the output of this system, reference joint velocities for the next control loop can be obtained. At the inner control loop, the conventional computed-torque control scheme is used to ensure the robot can track the above desired joint velocities. To illustrate the effectiveness of the proposed controller, intensive experiments have been conducted on the Mitsubishi PA10 7-DOF manipulator. Experimental results indicate that there is a significant improvement in comparison to the conventional implementation and the proposed approach is shown to have performed favorably in comparison to the commercial force controller from PushCorp.