Optimal Design and Analysis of a Powered Ankle-Foot Prosthesis with Adjustable Actuation Stiffness

In past decades, the technology of ankle-foot prosthesis is rapidly developing for lower-limb amputees to restore the lost function of the human ankle. Several powered ankle-foot prostheses are proposed with good performance on lever-ground walking at normal speed. However, compared with prosthesis focusing on a specific speed, the adaptability of different walking speeds is still a big challenge for current powered ankle-foot prosthesis. In this paper, the authors present the optimal design and analysis of a novel powered ankle-foot prosthesis by combining the typical SEA actuator with a length-adjustable lever arm. The prosthesis can adjust the system stiffness by changing the length of the lever arm. After the optimization of the length of the lever arm, the novel prosthesis can provide amputee good performance on torque mimicking at low speed, high energy efficiency at normal speed and reduction of peak power at high speed. This paper also gives insight to the benefit of adjustable mechanical system on the performance of the prosthesis to the future design of the powered ankle-foot prosthesis at different walking speeds.