Predefined Performance Torque Control for a Series Elastic Actuator Based on State Observer and Disturbance Observer

In this paper, a predefined performance torque tracking control scheme is developed based on state observer and disturbance observer for a series elastic actuator (SEA) with disturbance. Firstly, the dynamic model of SEA is transformed into a system in the form of differential equation with lumped disturbance by defining auxiliary variables. Moreover, a state observer is designed to estimate unmeasurable states in the system. A nonlinear disturbance observer is presented to observe lumped disturbances in the system. By combining predefined performance control (PPC) technology and the backstepping method, the proposed control scheme can ensure that all signals in the closed-loop system are bounded and the torque tracking errors can converge to an arbitrarily small predefined set of residuals. Finally, the effectiveness of the proposed control scheme is verified by a simulation example.