Abstract
In this paper, a novel fixed-time convergent sliding mode control method is proposed for the gait trajectory-tracking problem of lower limb rehabilitation exoskeleton robots. Firstly, the dynamic model of a lower limb rehabilitation exoskeleton robot is achieved through mechanism analysis. Then, a novel nonsingular fast terminal sliding surface is designed to achieve fixed-time convergence and effectively enhance the convergence rate. A new sliding mode control strategy for lower limb rehabilitation exoskeleton robots is designed based on this sliding surface, and the stability and global fixed-time convergence characteristics of the control system are proved by using the Lyapunov criterion. Finally, the proposed control method is experimentally validated via a lower limb rehabilitation exoskeleton robot experimental platform. The experimental results show that the control method proposed in this paper can achieve rapid convergence of lower limb exoskeleton trajectory tracking error, with the error converging to about 1? , strong robustness against wearers of different weights (61 kg and 80 kg) and different gait trajectories (with the period of 8 s and 6 s), and has a certain inhibitory effect on chattering phenomenon.