Modified Adaptive Control of an Actuated Ankle Foot Orthosis to assist Paretic Patients

Abstract

In this paper, a model reference adaptive control with saturated proportional derivative (PD) action for an active ankle foot orthosis (AAFO) to assist the gait of paretic patients, is studied. Unlike most classical model-based controllers, the proposed controller does not require any prior estimation of the system's model parameters. The AAFO system is actively driven by the residual human torque delivered by muscles spanning the ankle joint and the AAFO's actuator's torque. The ankle reference trajectory is updated online based on the self-selected walking speed of the wearer. The input-to-state stability of the AAFO-wearer system with respect to a bounded human muscular torque is proved in closed-loop based on a Lyapunov analysis. Experimental results, obtained from one healthy subject and one paretic patient, show satisfactory results in terms of tracking performance and ankle joint assistance throughout the full gait cycle.