This paper addresses the prescribed performance tracking control problem of knee rehabilitation exoskeleton systems, contending with output constraints, uncertain dynamics, time-varying external disturbances, and potential actuator faults. Firstly, a fuzzy logic system (FLS) is introduced to estimate uncertainties in knee rehabilitation exoskeleton systems. Then, a prescribed performance controller with fixed-time convergence is devised to meet the performance criteria encompassing output constraints and tracking error, accounting for the potential occurrence of actuator faults. Furthermore, the effects of unknown control gains and upper bounds of external disturbances can be eliminated by the robust term with dynamic gain. In addition, theoretical analysis establishes that the proposed approach ensures both prescribed accuracy and adherence to output constraints even in the presence of actuator faults. Finally, preliminary experimental results of the knee rehabilitation exoskeleton (KREXO) are presented, demonstrating the potential effectiveness and safety of the proposed method in rehabilitation.
Jia et al. (Sun,) studied this question.