Adaptive Control of an Actuated Ankle Foot Orthosis for Foot-Drop Correction

Abstract This paper deals with the control of an actuated-ankle-foot-orthosis (AAFO) intended to help foot-drop patients. The foot-AAFO system is driven by the human torque delivered by the muscles spanning the ankle joint and by the AAFO’s actuator’s torque. A model reference adaptive control is proposed to dorsiflex the foot during the swing phase. Unlike most classical model-based controllers, the proposed one does not require any prior estimation of the system’s (foot-AAFO) parameters. The ankle reference trajectory was extracted during gait activities of healthy subjects in a clinical environment. The input-to-state stability of the foot-AAFO system with respect to a bounded human muscular torque is proved in closed-loop based on Lyapunov analysis. Preliminary experimental results show satisfactory tracking performances of the reference trajectory within few steps. Furthermore, the muscular activities for the tibialis anterior (TA) and gastrocnemius (GA) muscles when wearing the AAFO were reduced by 30% and 12% respectively.