Development of an assistive torque generation system for a lower limb exoskeleton

This paper presents a design for generating assistive torque of a lower limb exoskeleton to increase user's strength during walking. It can be used for walking assistance as well as for rehabilitation. Pressure sensors were set under both feet to detect the user's center of pressure(COP). The COP is included in the control loop to improve balance in walking. In the control design, the assist torque from motors consists of three parts, namely the support torque, the gravity compensation torque, and the correction torque. The support torque is generated based on the estimated user's external torque during walking. The gravity compensation torque is calculated by using posture data of the exoskeleton to compensate gravity effect of the mechanism. The correction torque is based on user balance state to allow a user to keep balance when he/she tends to lost body balance. We have designed and constructed a prototype of lower limb exoskeleton adopting a modular design approach. The experimental results verified the effectiveness of proposed control system. The developed exoskeleton can assist to provide suitable torque at the correct time to assist a user to walk and keep balance on a slope surface.