Powered ankle-foot prosthesis

S. K. Au, and H. M. Herr. Powered ankle-foot prosthesis, IEEE Robotics & Automation Magazine, vol. 15, no. 3, pp. 52-59, 2008.


The loss of a limb is a major disability. Unfortunately, today’s prosthetic technology is a long way from realizing fully functioning artificial limb replacements. Although lower-extremity prostheses are currently better able to provide assistance than their upper-extremity counterparts, very basic locomotory problems still remain. For example, compared with intact persons, walking amputees require 10–60% more metabolic energy depending on walking speed, physical fitness level, cause of amputation, amputation level, and prosthetic intervention characteristics. Additionally, amputees walk at 11–40% slower selfselected gait speeds than do persons with intact limbs [1]–[7]. Such clinical problems may, in part, be attributed to today’s prosthetic ankle-foot designs. Commercially available prostheses comprise spring structures that store and release elastic energy throughout each walking stance period [8], [9]. Because of their passive nature, such prostheses cannot generate more mechanical energy than is stored during each walking step. In distinction, the human ankle performs positive net work and has a greater peak power over the stance period, especially at moderate to fast walking speeds [10]–[14].

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