Continuous finite-time control approach for series elastic actuator

In this paper, a practical control approach is suggested for series elastic actuators(SEAs) to generate the desired torque. Firstly, based on the analysis of a nonlinear SEA, the generic dynamics for a class of SEAs is summarized. Then the dynamic equations are transformed into a novel state-space form which is convenient for controller design. Finally, based on the recently developed finite-time control technique, a finite time disturbance observer and a continuous terminal sliding-mode control scheme are introduced to synthesize the control law. The finite-time stability of the proposed controller is theoretically ensured by Lyapunov analysis. Compared with most existing methods, the contribution of the paper is two-fold: (i) The proposed controller is suitable for not only linear, but also a class of nonlinear SEAs, which means that it is a more generic method for SEA torque control; (ii) It achieves faster convergence rate and works well even in the presence of unknown payload parameters and external disturbances. A series of experiments are carried out on the self-built SEA testbed to demonstrate the superior performance of the proposed controller by comparing it with the cascade-PID controller.