Robotic ankle only steps away from daily use

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Two years ago, George Wolf was injured in a hang-gliding accident. His left leg was amputated below the knee.

He now has an artificial limb, but he longs to walk with fluid movement.

When he heard that fellow Arizona State University professor Thomas Sugar was looking for candidates to test a new spring-loaded robotic ankle that his team was developing, Wolf couldn’t wait to volunteer.

“I dream about running and walking normally,” said Wolf, a 54-year-old chemistry professor. “I walk pretty well with my prosthetic, but what I noticed when I got on (the device) was how smooth the gait was, just a flow, with no hint of a limp or any asymmetry.”

Sugar and his ASU team have been working with the Military Amputee Research Program at Walter Reed Army Medical Center to develop a technology called Spring Ankle with Regenerative Kinetics, nicknamed SPARKy after the ASU Sun Devil mascot.

They believe they are close to perfecting it.

Sugar says the device is one of a kind because it uses lightweight energy-storing springs to provide a flex that traditional devices just can’t give.

“About 1,000 servicemen and women have had below-the-knee-amputations in the wars in Afghanistan and Iraq, and every year about 100,000 diabetics have the same amputation,” said Sugar, an engineering professor based at ASU’s Polytechnic campus in Mesa. “We believe this device could mean a different life for many of those people.”

The shortcomings of current prosthetics are numerous because the mechanics are “largely passive,” Sugar said.

Amputees use 20 to 30 percent more energy than able-bodied people just to walk. Their gait is uneven because they must swing their hips to propel their prosthetics. When they’re climbing stairs or even walking backward, the challenges increase.

But SPARKy’s technology is radically different because it relies on a “robotic tendon” that stretches with each step, generating energy stored in a small motor in the ankle.

The motor in turn moves uniquely tuned springs as the upper leg moves over the ankle. The springs in turn propel the artificial leg forward with each step.

The result: a fluid gait that looks and feels no different from a real leg.

SPARKy is the culmination of Sugar’s research that began in the 1990s during his doctoral research in rehabilitative robotics at the University of Pennsylvania.

He said once he could show that he could store energy in the springs and use it to propel the artificial leg, he attracted the attention of the Department of Defense about three years ago.

Eager to see Sugar’s idea lead to a better prosthetic for maimed soldiers, the department gave him and his team a $680,000 grant to build the technology.

His team includes Jeff Ward and Matt Holgate, who recently received their doctorates in engineering, and engineer Thierry Flaven.

Now, Sugar believes SPARKy has great promise as a marketable product.

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