Robotizing Double-Bar Ankle-Foot Orthosis

Abstract

This paper introduces an approach that robotizes an ankle-foot orthosis (AFO). In particular, toward post-stroke gait rehabilitation, we robotize a double-bar AFO, which is widely used in rehabilitation facilities, by newly designing a modular joint, a pneumatic actuator, and a Bowden cable force-transmission system. Our modular joint system, called the Modular Exoskeletal Joint (MEJ), has a hollow shaft for simple attachment to an AFO's pivot. We designed MEJ to compactly house an encoder that is built in a bearing in a pulley. We adopted Bowden cables to transmit contraction forces from an actuator to the MEJ. As an actuation scheme, we developed the Nested-cylinder Pneumatic Artificial Muscle (NcPAM) system. Even though PAMs are mechanically compliant and lightweight, they can still generate a large force. Therefore, they can provide an ideal actuation system for exoskeletal robots. The nested-cylinder in NcPAM houses a cable-tensioning spring to properly maintain small cable tension for passive movements and a cable stopper to connect the PAM and the cable for properly transmitting the large force generated by PAM. We show the ankle-joint trajectory tracking performances of this integrated system using iterative learning control.