Dean Kamen’s “Luke arm”—a prosthesis named for the remarkably lifelike prosthetic worn by Luke Skywalker in Star Wars—came to the end of its two-year funding last month. Its fate now rests in the hands of the Defense Advanced Research Projects Agency (DARPA), which funded the project.
If DARPA gives the project the green light—and some greenbacks—the state-of-the-art bionic arm will go into clinical trials. If all goes well, and the U.S. Food and Drug Administration gives its approval, returning veterans could be wearing the new artificial limb by next year.
When DARPA director Tony Tether and Revolutionizing Prosthetics program manager Colonel Geoffrey Ling approached him in 2005, Kamen says he thought they were crazy—“in the good kind of way,” he says. There was no financial incentive to create a next-generation prosthetic arm. The research and development costs were enormous. Unless funded by DARPA, no private company would take such a risk for such a comparatively small market (in the Americas, about 6000 people require arm prostheses each year). Kamen spent a few weeks traveling around the country interviewing patients, doctors, and researchers to get an idea of the current technology—and soon saw the deficit in available arm prosthetics. He was swayed by the discrepancy between the current state of leg prostheses and that of arm prostheses. “Prosthetic legs are in the 21st century,” he says. “With prosthetic arms, we’re in the Flintstones.”
So he set out to reinvent the prosthesis that has been pretty much the same since the U.S. Civil War. Until now, a state-of-the-art prosthetic arm has meant having up to three powered joints. However, since this type of arm is frustrating to control and doesn’t provide that much functionality, most users still opt for the hook-and-cable device which has been around for over a century. In either case, these prosthetics only have three degrees of freedom—a user can move the elbow, the wrist, and open and close some variant of a hook.
The timing was good: microprocessors had gotten small enough, and power consumption efficient enough, to make it possible to cram the control electronics, lithium batteries, motors, and wiring into a package the size, shape, and weight of a human arm—about 3.6 kilograms. Still, the engineering was tough, says program manager Ling. “You’re asking an engineer to build an arm that can do what your arm can do, but they’re confined to a package the size of—an arm. In addition to being the right size and weight, it also has to look like an arm!”
In order to make a better arm, Kamen first had to figure out what was wrong with the old one. Part of the reason the technology was still in “the Flintstones” was a lack of agility: a human arm has 22 degrees of freedom, not three. The Luke Arm prosthetic is agile because of the fine motor control imparted by the enormous amount of circuitry inside the arm, which enables 18 degrees of freedom. The engineers fought for space inside the arm and created workarounds when they couldn’t have the space they needed, such as using rigid-to-flex circuit boards folded into origami-like shapes inside the tiny spaces, which are connected by a dense thicket of wiring.
The arm has motor control fine enough for test subjects to pluck chocolate-covered coffee beans one by one, pick up a power drill, unlock a door, and shake a hand. Six preconfigured grip settings make this possible, with names like chuck grip, key grip, and power grip. The different grips are shortcuts for the main operations humans perform daily.