Assist-As-Needed Control of Soft Ankle Orthosis for Walking in Patients with Foot Drop

This article investigates a soft robotic ankle-foot orthosis that aims to enhance gait rehabilitation and reduce foot drop. The orthosis is lightweight, entirely untethered, and operated by a bi-directional tendon-driven actuator that facilitates both dorsiflexion and plantar flexion. It incorporates an adaptive Assist-As-Needed (AAN) controller that customizes assistance based on user capabilities through a need index, which integrates interaction force and positional tracking errors. The orthosis utilizes soft materials and a cable-driven mechanism to enhance flexibility and comfort for the user, allowing free ankle movement while maintaining structural integrity. Real-time gait sensing, implemented through a smart insole with force-sensitive resistors, enables accurate control in accordance with the user's biomechanics. Experimental results demonstrate that the orthosis maintained the ankle within the desired gait trajectory for almost 93 % of the gait cycle, with improvements in gait propulsion and foot-drop prevention. Additionally, the time of each gait phase closely matched the desired one, with the swing phase lasting 0.158 seconds longer than expected. This technology, which integrates a highly responsive gait detection system and a cable-driven robotic mechanism, is a viable method for rehabilitation with minimal intervention.