Performance estimation of the lower limb exoskeleton for plantarflexion using surface electromyography (sEMG) signals

Abstract

In this paper, we evaluate the performance of the rigid and soft exoskeleton by measuring electromyography (sEMG) signal of human lower limb muscles. sEMG represents the degree of muscle activation and the higher sEMG level can be measured if the greater muscle force generated. We compared the sEMG activation level whether wearing the rigid exoskeleton or soft exoskeleton. First, we manufactured the rigid inspired by ‘Berkeley Lower Extremity Exoskeleton (BLEEX)’ and soft exoskeleton motivated by ‘Exosuit’ respectively. After developed the systems, sEMG signals on VM, HAM, GAS, and TA with the rigid lower limb exoskeleton were measured during walking. As a result, up to 150 % muscle activation level increased and it implies that the resistance occurred between human and the rigid lower limb exoskeleton and the user should make an effort to generate more force. After validate the limitation of the rigid lower limb exoskeleton, we did isometric experiment with the soft lower limb exoskeleton, there was 3.4 % normalized MAV decrease at GAS muscle. From this result, we concluded that developed soft lower limb exoskeleton assisted the subject with lower muscle activation level. In addition, the density of the sEMG signal was lower when the subject was assisted by the developed system. It implies that lower fatigue human can feel to maintain isometric condition. Therefore, soft lower limb exoskeleton can assist human more effective than the rigid lower limb exoskeleton.

Keywords

• surface electromyography (semg)
• rigid lower limb exoskeleton
• soft lower limb exoskeleton
• mean absolute values (mav)
• normalized mav