The effects of a powered ankle exoskeleton for plantarflexion torque assistance for the elderly

It is necessary to develop a rehabilitation robot for the assistance of movement of the ankle joint and the enhancement of ankle muscular activities during walking for the elderly. A powered ankle exoskeleton with an artificial pneumatic muscle has been designed to provide powered assistance in the plantarflexion motion of the ankle joint. The objective of this study was to confirm the effectiveness of the powered ankle exoskeleton for the plantarflexion torque of the ankle joint. Fifteen healthy and fifteen elderly people used a wearable ankle exoskeleton during the plantarflexion motion of the ankle joint. Participants were assessed with three parameters to confirm the effectiveness of the system: a) maximal voluntary isokinetic plantarflexion torque using a Biodexdynamometer, b) muscular activities of the lower limbs, c) correlation of the agonist muscle and plantar torque during plantarflexion motion of the ankle joint. The assistance of the plantarflexion motion of the ankle joint is determined by the plantarflexion torque of the artificial pneumatic muscle of the powered ankle exoskeleton, and the assistant timing was decided the detection of subject’s movement intention that they did plantarflexion motion of the ankle joint. We developed a muscular stiffness force sensor to detect the activation of the soleus muscle for feed-forward control of the ankle exoskeleton. The experimental results show that the muscular stiffness force of the soleus muscle with feed-forward control was decreased, and the plantarflexion torque of the ankle joint while only wearing the ankle exoskeleton was decreased, but the plantarflexion torque with feed-forward control was increased. The amount of increasing with feed-forward control is higher than that of decreasing only wearing the exoskeleton. Based on the effectiveness of the system with the healthy participants, the elderly may have benefited from the plantarflexion motion augmented by the powered ankle exoskeleton.