Robust Non-Singular Fast Terminal Sliding Mode Gait Tracking Control of a Pediatric Exoskeleton

This study investigates a robust control strategy for a lower-limb exoskeleton system in a passive-assist mode that assists motion and restores gait for the pediatric age group of 8-12 years. The system’s complexities, i.e., uncertainties and external disturbances, make it challenging to design a real-time gait tracking control for such exoskeletons. The study introduces the experimental setup and real-time control architecture, followed by the dynamic analysis of the exoskeleton. A non-singular fast terminal sliding mode control (NFTSMC) is proposed to bring the error variables close to equilibrium within a finite time, and Lyapunov’s theory is used to verify the rapid convergence of the system states. The proposed NFTSMC scheme is implemented for a 12-year-old child coupled with the exoskeleton in passive-assist gait tracking. The results are compared to sliding mode control with exponent-based reaching law (SMC-ERL). The proposed robust control approach offers fast and effective gait tracking in a finite-time and minimizes chattering compared to the SMC-ERL scheme.