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VR Interfaces: Ann Arbor Energy Recycling Foot


Overview of Ann Arbor Energy Recycling Foot

Developed by Ann Arbor engineers at the University of Michigan, a new (as of 2010) method of building prosthetic feet is being developed, in which the foot is able to reabsorb much of the energy of each impact. This is then transferred into power for the next step, in much the same way as the human ankle does. It looks likely that this approach may be the first such to successfully recreate the mechanics of the organic ankle.

In natural human motion, every time the heel impacts with the ground, energy is lost, transferred into the ground. Yet, the springy action of the ankle reclaims some of that energy every time the foot lifts off that ground. This is what prosthetics have typically been missing.

You can compensate for the effect of course, with powered ankles. Delivering additional power to motors on the joint, reclaims lost energy, giving the foot an extra oomph of push-off that comes close to replicating the effect of normal walking. Of course, to do that, requires a battery power source, and motor components in the foot itself, which adds to the bulk and weight of the foot, and thus making it harder to walk with them. In addition, adding such components multiplies manufacturing costs, taking such prosthesis out of budget range for many.

To replicate the natural way of handling the situation, would be to create a much lighter foot, much cheaper and simpler to manufacture, that lends itself well to natural walking rhythms.

It's not ideal yet of course. Based on measurements of changes in metabolic rate of test subjects, the Ann Arbor foot required 14% more energy per step than a natural foot would use. That sounds like significant wastage, until you factor in that the best we've been able to achieve previously was 23% more energy - even with a powered ankle.

To test it a prosthesis simulator was used, rather than finding individuals missing a foot.

A prosthesis simulator basically artificially immobilises the ankle and foot muscles via a rigid boot, with the prosthesis strapped below it. One of the disadvantages of this method is that it is significantly more difficult to obtain a natural gait when so encumbered, and that was factored into the results.

This is not a functional prosthetic of course - thus it's lack of name. The foot that has been developed is still at the proof of concept stage, and is being developed further, in the hope of being included in future prosthetic - and robotic - foot designs.

Further Reading

Recycling Energy to Restore Impaired Ankle Function during Human Walking

Design Schematics

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