Design and verification of the compact cable-driven series elastic actuator module in ankle assistance soft wearable robot

Abstract

In this paper, the design and verification process of the compact actuator module of soft wearable robots for daily walking assistance is introduced. To assist in the daily walking of the elderly or patients who suffer from abnormality in walking due to hemiplegia, wearable robots consisting of soft materials such as bowden-cable are being actively developed and are at the initial commercialization phase. The main advantage of those types of robots is the relatively ideal inertia of the combined distal body parts with the robot, which is essential for stabilizing the gait balance. However, a flexible power transmission system has the disadvantage in that it cannot directly measure the tension applied to the patients. Therefore, a tension sensor on the assisting point is required for precise assistance of the patients. However, adding the sensor is challenging since it increases the complexity and inertia. Thus, a methodology for designing and controlling of the reaction force-based Series Elastic Actuator (SEA) is proposed to generate the precise assistance force while minimizing the overall weight. The mechanical elements of the SEA are designed with the optimal specifications required for stroke patient assistance. The compactness and weight reduction are also guaranteed by designing the mechanical elements with optimal specifications, so assisting the patients with minimal gravitational load is attainable. In addition, 6-Minute Walk Tests, which mimic the walking of stroke patients, are conducted on non-disabled people. Therefore, improving the robustness for stabilizing the patient's gait is evaluated and verified by measuring the metabolic cost and ankle rotation of motion.