Active Disturbance Rejection with Fast Terminal Sliding Mode Control for a Lower Limb Exoskeleton in Swing Phase

In this paper, a control strategy is proposed to improve the tracking performance of the lower limb exoskeleton (LLE). The proposed active disturbance rejection control (ADRC) with fast terminal sliding mode control (FTSMC) can not only alleviate the disturbance but also converge to a bounded region fast. Based on the robotics analysis, a dynamic model for the LLE was established. To achieve decoupling control for a coupled system, the virtual control input was introduced, where the system uncertainty and external disturbances were regarded as lumped disturbances. To validate the feasibility of the proposed control strategy, the simulations and experiments were both carried out. The numerical simulation results were shown that the proposed control strategy and ADRC can remarkably reduce the chattering phenomena, which is owing to the estimation ability of extended state observer (ESO). Both the simulations and the experiments results were shown that this strategy was better than the conventional proportional-integral-derivative (PID) and ADRC in terms of tracking performance. With the proposed ADRC-FTSMC, the LLE system can achieve higher tracking precision and faster response.