Active Gait Retraining with Lower Limb Exoskeleton Based on Robust Force Control

This article addresses the design of a robust inner and outer loop controller for active gait retraining in individuals with leg motor weakness, using a lower limb exoskeleton with elastic joints. The proposed control algorithm for the inner loop is based on a robust force controller that considers dynamics in the sagittal plane, accounting for human and external perturbations. For the outer loop, a robust controller is proposed to ensure the tracking of the desired trajectories. Lyapunov candidate functions are used to demonstrate the stability of the closed-loop system. To validate the proposed algorithmic approach, numerical simulations and experimental tests are developed. The experimental results show excellent performance, even in the presence of external perturbations and opposing human reactions; the tracking error is minimal (MAE ≤ 0.0661 rad).