MEETING ABSTRACT Open Access Active control of a powered ankle-foot prosthesis

Amputees suffer a higher metabolic demand on their bodies. Passive prostheses seek to reduce this deficit through elastic distribution of the energy inherently dis-sipated in walking. Yet with no capacity to generate tor-que they lack truly biomimetic function. The active prosthesis is a solution to this and opens up a world of active control in the timing and magnitude of energy return. Being able to also modulate the dynamic charac-ter of the replaced joint, in impedance and position, brings us closer to a true model of the ankle-foot com-plex. And so the ankle-foot complex can be seen to be modelled as a visco-elastic system with loading and unloading phases and active power output. It was identified that the concept of the active auto-mobile suspension system designed by Bose has the capacity to satisfy these functional demands and so was investigated as a viable model for a prosthetic device. In using this model, the ankle joint was modelled as a motor, driven in drive and dynamo modes to convert an elastic system into an electromagnetic system based around a battery. Low power drain derived from signifi-cant power recovery makes this concept particularly interesting. The versatility of this concept is regarded as approaching that of the human beyond those devices that rely on passive or fixed elastic systems. This is active elasticity. A CAD model was generated along with a correspond-ing control scheme. The control system is proposed as a viable and innovative concept for future prosthetics with great potential for development. This proposal makes use of underfoot sensors to deter-mine the displacement of the fore and aft sections of th