Power-Harvesting Prosthetic Uses Every Footstep to Power the Next

Energy-Recycling Foot

Easier walking for amputeesUniversity of Michigan

Prosthetic users typically spend more energy walking on their artificial feet than most people, because the devices cannot replicate the force of a living ankle pushing off the ground. Now researchers have created a new prosthetic foot that recaptures the mechanical energy between steps.

Test subjects who used a conventional prosthetic foot spent 23 percent more metabolic energy, as opposed to when they walked on two normal feet. One engineer likened the experience to walking with an extra 30 pounds weighing him down.

But the new prosthetic device manages to cut down the energy usage to just 14 percent more than normal. Keep in mind that these prosthetic feet are for everyday use, as opposed to the specialized devices used by athletes.

"We know there's an energy penalty in using an artificial foot," said Art Kuo, a biomedical and mechanical engineer at the University of Michigan. "We're almost cutting that penalty in half."

The energy-recycling foot captures dissipated energy naturally. A microcontroller then tells the foot precisely when to apply the energy so that it enhances the power of the ankle push-off for the next step. The saved energy means that the prosthetic device only uses less than 1 Watt of electricity provided by a small portable battery.

Other prosthetic feet store and return mechanical energy, but don't allow for the precise timing that applies the recycled energy to the ankle push-off. Devices that try to provide a boost push-off also typically require motors and large batteries.

The University of Michigan team has already begun testing the foot on amputees at the Seattle Veterans Affairs Medical Center, and hope to commercialize the device for more widespread use among military veterans returning from Iraq and Afghanistan. We're looking forward to this and future prosthetics that not only recycle mechanical energy, but also harvest it as electrical energy to power our iPads.