Design of a soft ankle-foot orthosis exosuit for foot drop assistance

This paper presents the design of a soft ankle-foot orthosis (AFO) exosuit to aid natural gait restoration for individuals suffering from foot drop. The sock-like AFO is comprised of soft actuators made from fabric-based, thermally-bonded nylon and designed to be worn over the users shoes. The system assists dorsiflexion during swing phase of the gait cycle utilizing a contracting soft actuator, and provides ankle joint proprioception during stance with a variable stiffness soft actuator. A computational model is developed using finite element analysis to optimize the performance characteristics of the fabric actuators prior to fabrication, maximize contraction, and minimize overall volume. The dorsiflexion actuator is able to achieve a linear tensile force of 197 N at 200 kPa. The variable stiffness actuator generates up to 1. 2 Nm of torque at the same pressure. The computational model and soft AFO are experimentally validated and with a healthy participant through kinematic and electromyography studies. When active the AFO is capable of reducing by 13.3% the activity of the muscle responsible for ankle dorsiflexion during the swing phase.