Development of an elbow power assist device with a water-hydraulic muscle actuator

Abstract

Robotic technologies for supporting human activities have received much attention in recent years. The purpose of this study is to develop a wearable power assist device with a water-hydraulic artificial muscle actuator. This power assist device aims at helping wearer's elbow-joint movement. Since our power assist device is directly driven by tap water, it does not require pumps or compressors. Therefore, it needs much lower electric power than typical pneumatic and electric actuators. An artificial muscle actuator is used to actuate the power assist device because artificial muscle actuators are lightweight and highly flexible and would not hurt a person even in a collision, as this type of actuator consists of a flexible rubber tube surrounded by a braided-fiber shell. The control system of the power assist device comprises impedance control and amplification control. The impedance control is able to adjust the characteristics of dynamic interaction between the power assist device and a wearer, i.e. inertia, damping, and stiffness. The amplification control enables the power assist device to enhance torque exerted by a wearer. The power assist device developed in this study was worn by subjects and its effectiveness was examined based on surface electromyogram signals which reflect muscle activity. Experimental results demonstrated that our water-hydraulic power assist device leads to a decrease of muscle activity for all the subjects.