An Autonomous Exoskeleton for Ankle Plantarflexion Assistance

Lower-limb exoskeletons are of great interest in the robotics community because of their various applications in enhancement and rehabilitation. In this paper we present an autonomous exoskeleton platform for ankle plantarflexion assistance. The untethered exoskeleton has a high efficiency transmission system with reduction ratio of 27.4:1. This allows relocating the actuator to the wearer's hip, which reduces device inertia. A feed-forward controller based on field oriented control was implemented to control the brushless DC motor on the exoskeleton. Through various performance tests, the exoskeleton was shown to provide a torque control bandwidth of 17.5Hz and can effectively track biological torque profiles. The augmentation factor (AF) of the exoskeleton is 64.7W, implying potential to reduce walking metabolic cost. This exoskeleton establishes an autonomous platform for experiments involving ankle assistance.