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Knee Power ““ The New Energy Source

February 8, 2008

Researchers in the United States and Canada have unveiled a new accessory for your knees that can generate energy and may offer a green alternative to power portable devices of the future.

Max Donelan, director of the Simon Fraser University Locomotion Laboratory in Burnaby, Canada, and his colleagues have created a modified knee brace with a drive train that converts the mechanical energy into electricity.

The knee brace works by collecting energy lost when a person brakes the knee after swinging the leg forward to take a step, the researchers said told Reuters.

Arthur Kuo, a University of Michigan mechanical engineer who worked on the device, said it works similarly to the way that regenerative braking charges a battery in hybrid cars.

“There is power to be harvested from various places in the body, and you can use that to generate electricity. The knee is probably the best place,” Kuo said in a statement. “During walking, you dissipate energy in various places, when your foot hits the ground, for example. You have to make up for this by performing work with your muscles. We believe that when you’re slowing down the knee at the end of swinging the leg, most of that energy normally is just wasted.”

One minute of using the device can produce enough power to charge up 10 cell phones at once, the researchers report in the journal Science.

Researchers looked at six volunteers who wore the device while walking on treadmills. Sensors detected the angle and velocity of their legs, switching the device on only during the braking phase of each swing.

The modified knee brace weighs 1.6 kg, or 3.5 pounds. Donelan said users do burn energy while wearing the device, but after they remove it, they also miss the extra braking power that it provides.

Previous devices aimed at harnessing human energy include a shoe-mounted device that was lighter but didn’t collect enough energy. Also, Lawrence C. Rome of the University of Pennsylvania had developed a backpack device that generated power as a person walked. Although the backpack created a lot of electricity, it was too bulky and heavy for normal use.

By generating decent amounts of power while still being relatively light, the new energy-capturing knee brace seems to find a happy medium its inventors said.

Rome called the development “extremely clever.”

Other people have thought of rotational devices around joints, Rome said, “but what’s really clever is these guys only turn on resistance when person trying to brake, so it helps you.”

The first practical use for the generator is likely to be in producing power for artificial limbs, said Donelan, who with his co-authors has founded a company to develop the device commercially.

Other possible uses for the device in the future include powering a portable GPS locator or implanted drug pumps.

Kuo said that the prototype is bulky, but the energy generation part itself has very little effect on the wearer.

“We hope to improve the device so that it is easier to carry, and to retain the energy-harvesting capabilities,” he told Associated Press.

The research was funded by the National Sciences and Engineering Research Council of Canada, Michael Smith Foundation for Health Research and the Canadian Institute of Health Research.

Photo Caption: An undated image shows a biomechanical energy harvester mounted on a customized orthopedic knee brace. Scientists in the United States and Canada said on Thursday they have developed a unique device that can be strapped on the knee that exploits the mechanics of human walking to generate a usable supply of electricity. (Greg Ehlers/Simon Fraser University)

On the Net:

Science

More on the biomechanics of muscles

Biomechanical shoes

More about neural prostheses




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