A Singularity-Free Terminal Sliding Mode Control of an Uncertain Paediatric Exoskeleton System

The coupled human-exoskeleton design holds the problem of uncertain model parameters and disturbances, which vary for different age groups and related gait pathological levels. These uncertainties become more dominant in the case of pediatric subjects. Therefore, in this work, a robust singularity-free terminal sliding mode (SFTSM) control is proposed for an uncertain pediatric exoskeleton system in passive-assist mode. At first, the dynamic model is presented using Lagrangian principle. Thereafter, the non-singular sliding surface is considered to derive the required control law. The boundary layer approach is considered to avoid chattering behavior. The novelty of this work lies in the Lyapunov stability analysis with upper-bound criterion to ensure the finite-time convergence of the gait tracking error. Finally, it is observed from the simulation runs that the proposed SFTSM control outperforms different contrast control schemes for the passive-assist gait rehabilitation.