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.
Energy to Restore Impaired Ankle Function during Human Walking