Design of a compact hydraulic actuation mechanism for active ankle-foot prostheses

Ankle-foot prostheses (AFPs) are devices commonly used for transtibial amputees to recover their mobility. In order to emulate the characteristics of human ankle joints, various materials are utilized to impose necessary elasticity and viscosity in most of the AFPs. Also, the characteristics of the artificial ankle joint are important to guarantee gait stability and energy efficiency during walking. Therefore, there are a number of options in the artificial joint materials for adapting various ground conditions (e.g., incline, decline, steps, etc.), and the materials are usually classified by their elasticity and viscosity (or impedance). Although the adjusted impedance of AFPs may improve the environment-adaptability and gait stability of amputees, the users may still feel discomfort and need extra efforts to walk when the impedance is not adaptively changed according to the motion phases. To this end, a novel hydraulic actuation mechanism, which can integrate the advantages of various actuation systems, is proposed to meet the required impedance characteristics of AFPs in this paper. The proposed actuator can switch actuation modes according to the motion phases and thus improve the efficiency while achieving a compact size and light weight.