Development of a Hip Abduction-Adduction Exoskeleton for Mediolateral Assistance

Abstract

Lower limb exoskeletons are gaining prevalence to augment mobility of people with gait impairments. However, current exoskeletons using serial elastic actuators do not have the torque and bandwidth capabilities to assist in balance control in daily activities. Considering the critical role of mediolateral stability in balance control of individuals affected by neurological and age-related gait impairments, we propose an abduction-adduction exoskeleton for mediolateral assistance. The exoskeleton utilizes harmonic gear driven actuators with active torque feedback to ensure high bandwidth and admittance control capabilities, designed as an assistive device for enhanced balance. The exoskeleton is developed to be able to provide assistance up to a bandwidth of 5 Hz at the hip to individuals weighing up to 90 Kgs. Benchtop testing of the exoskeleton showed closed loop velocity bandwidth of more than 5 Hz while under loading with a user weighing 85 Kgs. Further, analysis of admittance controller using both static and dynamic testing showed that the developed controller can simulate stiffnesses up to 95 Nm/rad with an R 2 of over 99%. Pilot human testing individuals showed that the exoskeleton can modulate step width behavior of individuals while ensuring compliance with the users, facilitating seamless human robot interaction. The implication of the developed exoskeleton for balance control in elderly and neurologically impaired populations, and future avenues of research are discussed.