Design, Optimization and Energetic Evaluation of an Efficient Fully Powered Ankle-Foot Prosthesis With a Series Elastic Actuator

Dianbiao Dong,Tom Verstraten,Yuanxi Sun,Bram Vanderborght,Wenjie Ge,Bryan Convens

doi:10.1109/access.2020.2983518

Abstract

The use of powered ankle-foot prostheses for below-knee amputees leads to challenges like the peak power of the applied actuator and biomechanical features of the prosthesis foot. This paper proposes an efficient powered ankle-foot prosthesis with a series elastic actuator. By combining the geared five-bar spring (GFBS) mechanism and the traditional series elastic actuator (SEA), a series elastic with geared five-bar (SGFB) actuator is built. The new SGFB actuator has the benefits of both the GFBS and the SEA on mimicking biomechanics of the human ankle and reducing the peak power of the motor. The healthy walking gait in the experiment results indicates that the optimized SGFB prosthesis foot including a 150W Maxon DC motor can provide a 70kg subject enough net positive energy with an energy efficiency of 35.3% during normal speed walking in the treadmill trials. The experiment of the SGFB prosthesis foot in semi-active mode shows the advantage on closely mimicking the human biomechanics during the control dorsiflexion phase and the importance of injecting positive energy during the powered plantarflexion phase. The experiment results also show that the optimization of different parameters within the electromechanical model considering the efficiency of the whole drive train can effectively reduce the motor's peak power to 132 W by making the motor more effective in high-power conditions.

Highlights

Below-knee amputation is one of the major amputations due to increasing number of peripheral vascular diseases and traffic accidents [1]
Based on the biomechanics data from Winter’s research [2], we presented a powered anklefoot prosthesis with a directly driven geared-five bar spring (GFBS) mechanism [44] to better mimic the biomechanics of human ankle during control dorsiflexion phase at normal walking speed in our previous research [45]
TWO CONTROL STRATEGIES WITH FINITE STATE MACHINE To evaluate the performance of the series elastic with geared five-bar (SGFB) prosthesis foot on the torque angle relationships during the Controlled dorsiflexion (CD) phase and the energetic features of the actuator during the Powered plantarflexion (PP) phase, two modes with different control strategies are implemented on the SGFB prosthesis: Semi-active mode and active mode

Summary

INTRODUCTION

Below-knee amputation is one of the major amputations due to increasing number of peripheral vascular diseases and traffic accidents [1]. Based on the biomechanics data from Winter’s research [2], we presented a powered anklefoot prosthesis with a directly driven geared-five bar spring (GFBS) mechanism [44] to better mimic the biomechanics of human ankle during control dorsiflexion phase at normal walking speed in our previous research [45]. Considering the biomechanics of the ablebodied human ankle and the efficiency of the whole prosthesis, the parameters of the actuator system and other parts are optimized to closely mimic the torque-angle profile of a human ankle and reduce the high demand of the motor power. The torque produced by the SGFB actuator need to mimic the torque angle profile of the human ankle during CP, PP and SW phases To achieve these two goals, the optimization function is built by discretizing the whole walking gait data into 1000 points, D. The optimization variable x is replaced by a, b, c:

OPTIMIZATION AND SIMULATION RESULTS

EXPERIMENTAL TEST AND EVALUATION

Findings

CONCLUSION