Disturbance-Observer-Based Compliance Control of Electro-Hydraulic Actuators With Backdrivability

Abstract

This letter proposes an intrinsically backdrivable electro-hydraulic torque actuator (EHTA) and associated control algorithms that could lead to the design of a high-performance interactive robot system. The EHTA consists of (electro-hydraulic) backdrivable servovalves and double vane rotary hydraulic actuators. It is represented as a flexible actuator model considering servovalve dynamics and fluid dynamics. In the flexible actuator structure, the interaction stability is not guaranteed because the EHTA is a noncollocated system. However, due to the use of backdrivable servovalves, the EHTA is rigidly represented in the finite frequency region that a robot operates in daily life; it has the property of finite frequency passivity. Based on this property, a disturbance observer was designed to compensate for friction effects and model uncertainties. Then, the compliance control was applied to the friction-free actuator. Consequently, we achieved the actuator with a torque sensitivity of 0.1 Nm and a maximum torque output of approximately 100 Nm. The proposed actuators and controllers were evaluated through experiments.