Robust Sliding Mode Control with Reaching Laws for a Pediatric Lower-Limb Exoskeleton System

The precise control of an exoskeleton, especially for pediatric subjects, is a challenging task due to the presence of parametric perturbations and external disturbances (PPED). The sliding mode control is a well-known robust control scheme to address such dynamic uncertainties. Therefore, in this work, a robust sliding mode control (RSMC) with is proposed for a pediatric lower-limb exoskeleton system during passive-assist therapy mode. The performance of different reaching laws (constant, power, exponential, and general) used in proposed control are compared with each other. Lyapunov stability analysis is carried out to ensure the asymptotic convergence of the gait tracking error. It is noted from the simulation runs that the proposed RSMC with exponential reaching law outperforms the different controllers for the less tracking error in passive-assist gait rehabilitation. However, chattering is found to be less with constant reaching law.