Design of a Powered Lower-Limb Exoskeleton and Control for Gait Assistance in Paraplegics

Abstract

This work describes the design and implementation of a powered lower limb exoskeleton for providing legged mobility to the spinal cord injury (SCI) population. The exoskeleton has a mass of 12.5 kg and provides sagital plane joint torques of up to 65 Nm at the hips and knees to enable walking, sit-to-stand transitions, stand-to-sit transitions, stair ascent, and stair descent. A custom distributed embedded system controls the exoskeleton with power being provided by a lithium polymer battery. The control structure provides an intuitive interface between the user and the exoskeleton for ease of use with a minimal learning curve. In order to demonstrate the ability of the exoskeleton to assist walking and stair ascent/descent, the exoskeleton was experimentally implemented on a paraplegic subject with a T10 complete injury. Data collected during walking indicates a high degree of step-to-step repeatability of hip and knee trajectories (as enforced by the exoskeleton). Experimental data is presented characterizing the joint torque and power required to provide stair ascent and descent functionality to a person with paraplegia. Also described is a functional assessment protocol for assessing the mobility and exertion associated with systems that provide legged mobility assistance for persons with SCI.