Unknown System Dynamics Estimator-Based Composite Anti-Saturation Control Method for Series Elastic Actuators

This article investigates the torque tracking problem of series elastic actuators (SEAs) that are affected by nonlinear uncertainty and actuator saturation. An unknown system dynamics estimator (USDE), which has only one parameter to be turned, is designed to provide an estimation of the nonlinear uncertainty. Then, based on the estimation, a composite proportional-derivative with sliding-mode control (PD-SMC) method is proposed to solve the problem. It has a simple PD-like structure and can achieve an antisaturation property. In addition, with the USDE and the SMC, the robustness of the SEA system under the proposed method is obtained, while the chattering phenomenon of SMC is greatly attenuated due to the uncertainty estimation of USDE. The Lyapunov function-based theoretical analysis is present to demonstrate the stability of the closed-loop control system. Experiments are carried out to verify the effectiveness and superiority of the proposed control method.