The Application of Series Elastic Actuators in the Hydraulic Ankle-Foot Orthosis

Advances in ankle-foot orthosis (AFO) technology have been trending toward more powerful and lightweight devices. A hydraulic series elastic actuator (HSEA) was explored to design a lightweight powered AFO that meets the high peak power demand of ankle gait. With its excellent power density and its ability to separate the power supply from the actuator using a hose, hydraulic power was used, combined with an SEA that takes advantage of the high-peak and low-average power profile of ankle gait to store energy and release it during the push-off stage of gait. The parameters required for the SEA were determined and validated using simulation. A gait pattern that would require 235W of motor power was able to be tracked using a motor rated at 95W. The actuator weight of the hydraulic ankle-foot orthosis (HAFO) at the ankle was 0.35, which is 43% of an equivalent electromechanical system. A novel design of an HSEA with a clutch capability is proposed for future HAFO applications.