An Active Disturbance Rejection controller design for the robust position control of Series Elastic Actuators

Abstract

Series Elastic Actuators (SEAs) have several superiorities over conventional stiff and non-back-drivable actuators in force control, e.g., lower reflected inertia, low cost force measurement, high force fidelity, safety, and so on. However, their position control applications significantly suffer from low performance and disturbances due to insufficient controller designs. In this paper, a new Active Disturbance Rejection (ADR) controller is proposed for the robust position control problem of SEAs by combining Differential Flatness (DF) and Disturbance Observer (DOb) in state space. The trajectory of the actuator is generated by using DF and is tracked by using a conventional state feed-back controller. The state and control input references of a DF-based trajectory tracking controller are modified by using estimated disturbances so that the robustness is achieved. The proposed controller provides high performance position control for SEAs when they suffer from plant uncertainties and external disturbances such as inertia variation, backlash, friction and external load. Experimental results are given to validate the proposal.