Passivity-Based Robust Compliance Control of Electro-Hydraulic Robot Manipulators With Joint Angle Limit

This paper presents a robust compliance control scheme for an electro-hydraulic robot manipulator with an electrohydraulic torque actuators (EHTAs) and joint torque sensors. The EHTA, a torque-sourced hydraulic actuator, consists of electrohydraulic backdrivable servovalve and a rotary hydraulic vane actuator and it allows us to design controllers similar to those for robot manipulators with electric motors. However, unlike in electric motors, the EHTA has a limited rotational angle and this may lead to instability when using a non-passive robust controller that generates the energy. As a solution to this problem, this paper proposes a robust two-loop control structure that has a passivity-based disturbance observer as an inner-loop controller and a nominal state feedback compliance controller as an outer-loop controller. The proposed control method was evaluated through single-degreeof-freedom experiments.