Saturated PD Control of Compliant Robot Arms Using Position Measurements Only

As control input saturation may severely affect control performance, we should pay more attention to control input saturation for compliant robots owing to the limited output range of the compliant actuators compared to rigid-link robots. This paper proposes a saturated PD (proportional-derivative) regulation control algorithm for robot arms driven by series elastic actuators (SEAs) with control input saturation using position measurements only. The designed controller, composed of a hyperbolic tangent function-based saturated PD control term and a gravity compensation term guarantees the control constraint satisfaction by using the hyperbolic tangent function and the boundedness of the gravity compensation term. The saturated PD control term guarantees the control stability and the static gravity compensation ensures the stabilization towards the desired position. According to the Krasovskii-LaSalle theorem, we prove asymptotical control stability. We validate the saturated PD control by taking simulations on a compliant manipulator and experiments on a one-joint SEA-driven robot arm.