Coordinated human-exoskeleton locomotion emerges from regulating virtual energy

Abstract

Lower-limb exoskeletons showed great potential for the gait rehabilitation of individuals with motor impairments; however, maintaining human-exoskeleton coordination is still a challenge. Human-exoskeleton coordination problem, referred to as any mismatch or asynchrony between the users intended trajectories and exoskeleton desired trajectories, results in sub-optimal gait performance, particularly for the individuals with residual motor ability. Here, we investigate the virtual energy regulator (VER)s ability to generate coordinated locomotion in lower limb exoskeleton in a study on nine individuals. A comprehensive analysis of metrics obtained at three different speeds demonstrates the emergence of natural and coordinated locomotion as a result of a shared control between human and exoskeleton maintained with the VER. We also introduce a metric to measure the users contribution to gait and demonstrated that the resultant locomotion limit cycle is a linear combination of human-intended limit cycle and the VERs limit cycle. This results may have implications about how central nervous system controls our locomotion.