Admittance Shaping-Based Assistive Control of SEA-Driven Robotic Hip Exoskeleton

This paper presents an admittance shaping-based assistive control for a series elastic actuator (SEA) driven robotic hip exoskeleton that can assist individuals with hip muscle weakness to restore normative mobility. The motivation for this paper is to develop a unified controller framework for designing an SEA-driven hip exoskeleton to assist walking and enhance gait stability. The controller design aims to modify the dynamic response of a coupled human-exoskeleton system, i.e., the relationship between the net muscle torque exerted by the human and the resulting angular motion, to ensure strong human-exoskeleton synergy to provide the effective assistance. This controller was preliminarily evaluated on a healthy subject walking on a treadmill at a speed of 1.0 m/s. Results showed that the exoskeleton can effectively provide walking assistance to the human by reducing electromyography (EMG) activation and increasing agility during locomotion. Specifically, EMG was reduced 3.3%-38% when walking with the hip exoskeleton when compared to walking without wearing the hip exoskeleton. In addition, timing of the maximum hip flexion angle increased by 10% (moved from 42% to 32% of gait cycle) when the controller had an inertia compensation of 60%. The faster onset of the maximum flexion angle will allow the wearer to more quickly generate reactive steps when trying to avoid a fall. Future work will aim to apply the hip exoskeleton to persons having hip muscle weakness or other musculoskeletal impairment, to restore hip movement and enough hip force to walk normally.