Dynamics and Control of an Anthropomorphic Compliant Arm Equipped With Friction Clutches

Robots powered by intrinsic compliant actuation systems have been developed in the past years to provide improved mechanical robustness and physical interaction performance. Despite these benefits, the incorporation of passive elasticity in the actuation system can however generate unwanted oscillations complicating the control of these systems. An approach to address this issue proposes the addition of physical damping in the transmission system of the compliant joints. A particular embodiment of this physical damping can be based on clutch mechanisms integrated in parallel to the physical elasticity. This paper studies a class of variable impedance robotic arms driven by compliant actuation systems equipped with a clutch mechanism in parallel to the passive compliant transmission element. The dynamics of these systems is derived and a novel control scheme extracted from the dynamic model of the robot is proposed. The control scheme modulates the friction torque applied by the clutch to effectively operate the robot arm at a stiff mode with high precision or disengage the clutch when physical interactions occur and detected through a sensor-less scheme. Extended simulation and experimental results are presented to demonstrate the performance of the proposed controller.