Imitating Sound Ankle Behavior with a Powered Below-Knee Prosthesis and Validation of its Mechanical Performance

Lower extremity amputation constitute high percentage of limb amputation which significantly reduce the motion ability of the amputees. Therefore the most important goal in the design of prosthesis is to restore function of the limb. Most of the commercially ankle-foot prostheses are passive and thus cause many gait pathologies for below knee amputees. Several powered prosthetic devices have been designed to improve amputee’s walking experience by exploiting active elements. However, most of them include heavy and bulky actuators which is used to produce the power of propulsion. The main purpose of the present design is to store energy during stance period and release it at push off using a combination of springs as well as a low power actuator. Therefore, this prosthesis can provide high mechanical power and torque observed in natural human walking, by employing a small and light actuator. Moreover, in the designed mechanism, the ankle stiffness is mimicked properly in each phase of walking based on the characteristics of a sound ankle. The performance of the proposed prosthesis, was verified by MATLAB/SimMechanics simulation. The results indicate that the ankle-foot prosthesis is capable of following the torque-angle and the power-percent gait cycle characteristics of a normal ankle, sufficiently.