Defense Technology International - October 2007 - (Page 54) LIMBS ROBOTIC GAIT KEEPER Researchers craft life-like ankles for amputees DAVID AXE• WASHINGTON The iWalk is heavy but replicates a biological foot, decreasing back strain while walking. you’re climbing stairs, for instance, until after you’ve taken a couple steps. Herr’s ankle requires a smarter computer brain to detect changes seemingly instantaneously. After months of tinkering, Herr began testing the device in March in his lab at MIT. Stewart was one of his subjects, selected because he lived nearby and because he is heavier, more athletic and more comfortable in a prosthesis than most amputees. Stewart did two daylong sessions at MIT, walking 40 ft. at a time, providing feedback while a technician modified the ankle’s software algorithms in real time. Herr himself also wore two of the experimental ankles to generate more data. In July, confidence in the design was such that MIT and the ankle’s financial backers, Brown University and the Providence (R.I.) V.A. Medical Center, hosted an o cial unveiling. By then the device had a name: iWalk. The iWalk team is building 10 more-robust prototypes for “field testing.” Stewart will wear one to supplement his two prostheses. In time, iWalk will be available to patients at Walter Reed and at the military’s two other amputee wards, helping round out a growing catalog of prosthetic devices—some high-tech, some basic—that can be mixed and matched to provide patients with options. The lower-body amputee rehabilitation center at Walter Reed is a madhouse of activity on a mid-August morning. In one DAVID AXE/DEFENSE TECHNOLOGY INTERNATIONAL WEBB CHAPELL/MIT n Apr. 5, 2003, U.S. Army Pfc. Garth Stewart stepped on a land mine in Baghdad. The explosion blew off his left leg beneath the knee. The injury, Stewart told reporters later, looked like a charred rose. He was evacuated and treated at Walter Reed hospital in Washington, and in 2004 was medically discharged from the service. Today he’s a student at Columbia University in New York, studying ancient history. Like more than 650 military amputees from the Iraq war, Stewart wears a prosthesis to get around, and as long as he’s in blue jeans, you can’t tell it from looking at him. But he sure can tell. Most of today’s prosthetic lower-leg designs are essentially springs attached on one end to a hinged artificial foot and, on the other, to a carbon-fiber socket that fits around the wearer’s stump. They absorb shock, but don’t push back the way a real leg does. That causes back pain and makes walking a chore. But not for long, if one prosthesis designer has his way. Hugh Herr, a professor at the Massachusetts Institute of Technology who lost both legs below the knees in a childhood mountain-climbing accident, has developed many advanced 54 O lower-body prostheses, including the popular “Rheo” knee with an embedded microprocessor. His latest, an intelligent robotic ankle, promises to make walking easier for Stewart and others like him. “Existing designs, when the foot’s on the ground, are passive and only provide as much energy as an amputee puts into them,” Herr says. “The new device puts in energy. It has its own energy source. The device controls its sti ness, damping and resistance as the amputee walks on di erent terrains. An amputee can walk faster and with less energy.” The key, Herr says, is in understanding how legs work with their joints, tendons and muscles, and translating that into plastic, metal and software. What’s the hardest part? “Everything. We’re trying to have a device that has three times the power of conventional prostheses, but is lightweight and small enough to scale down to a woman’s size five.” The software is a challenge, too. There are robotic prostheses in use, but they don’t react quickly to changing terrain. There’s latency: the limb doesn’t know The iWalk will replace such models as this Proprio ankle. DEFENSE TECHNOLOGY INTERNATIONAL OCTOBER 2007 www.aviationweek.com/dti http://www.aviationweek.com/dti
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