Robot ankles mean quick strides for amputees - Marine Corps News | News from Afghanistan & Iraq - Marine Corps Times

Robot ankles mean quick strides for amputees

PROVIDENCE, R.I. — Garth Stewart lost his left leg four years ago when a bomb ripped through it in Baghdad. The leg had to be amputated below the knee, but the young Army gunner was determined to get moving again. He refused to spend more than three weeks at a stateside hospital and quickly got an artificial foot — then qualified as a martial arts instructor.

Despite his fitness and four years of practice, Stewart said walking without an ankle still means a slower stride and lower back pain.

Stewart and others like him hope that will change with a new kind of robotic ankle that uses a battery-powered engine and springs to propel the leg forward, uphill or over stairs, just as the human foot naturally gives a push from the toes. On Monday, the 24-year-old veteran paced on stage to demonstrate the PowerFoot, one of at least three such ankles in development.

“Once you get used to it, it feels like you have your leg back,” Stewart said.

About the size of a boot, the PowerFoot was developed during a $7 million research effort run by the Center for Restorative and Regenerative Medicine, a collaboration between the Massachusetts Institute of Technology, Brown University and the Providence Veterans Affairs Medical Center.

Its researchers share a long-term goal of attaching a robotic limb directly onto human bone and controlling it with brain waves.

Created by Hugh Herr, a double amputee and MIT researcher, the PowerFoot appears to be the robotic ankle system closest to commercial production, said Thomas Sugar, a researcher at Arizona State University’s Polytechnic Campus, who is developing a competing product.

Traditional prosthetic feet use springs to give an amputee some bounce, Herr said. Because they lack ankles, studies show amputees expend up to 30 percent more energy than nonamputees in using their hips to power through strides. That can cause an irregular, hunched walk, pain and chronic back problems.

“By the end of the day, your lower back is pretty sore,” Stewart said. “This device pretty much eliminates that.”

The PowerFoot also can add resistance, simulating an ankle’s braking function.

Miniaturization proved one of the key obstacles. Unlike an arm, ankles are small but specialized joints capable of providing enormous power and withstanding a body’s pressure.

“We have to package all of the robot into a very small space,” Herr said.

Using existing technology, Herr’s team crammed a lithium-ion battery, gears, springs, nine sensors, joints and a tendonlike strip of carbon fiber into a package that can mostly fit into a shoe. The metal components sit on a carbon and rubber sole, almost like a silver foot in a black sandal.

The rechargeable battery provides enough energy for 10,000 steps, a rigorous day’s walk.

Herr describes transitioning from his normal prosthesis to the robotic ankle as similar to stepping onto a motorized walkway at an airport.

“It’s like the hand of God pushing me,” Herr said. “It’s really cool.”

Stewart has spent hours pacing in the PowerFoot and will participate in another clinical study this fall. iWalk, a Cambridge, Mass., company, has licensed MIT’s patent and tentatively plans to produce a commercial test version of the PowerFoot by next summer, said John Stephens, the company’s vice president of research and development.

Stephens said the PowerFoot will cost several thousand dollars, but the final price tag hasn’t been set.