Position-Based Impedance Control Design for a Hydraulically Actuated Series Elastic Actuator

Series elastic actuators (SEAs) have become a common actuation method in torque-controlled electric lightweight arm applications that physically interact with the environment in assembly tasks. Compared to traditional actuators, SEAs can provide high force fidelity, shock tolerance, and force sensing for interaction control. Considering inherent system dynamics and the variable stiffness of the fluid, the control design for hydraulic SEAs (HSEAs) that lead into fifth-order system is a challenging task. As a novelty, a full state feedback controller design for the developed fifth-order HSEA system is presented to serve as an inner-loop controller to handle highly nonlinear dynamics behavior. In addition, as an outer-loop impedance controller for HSEAs in heavy-duty applications, the position-based impedance controller is designed to handle control of the HSEA system during the contact motion. Experimental results with a one-degree-of-freedom real-size experimental setup with a payload of 200 kilos demonstrates the effectiveness of the proposed HSEA control methods both in the free-space motion and in a contact impedance motion.