PROBLEM: Can prosthetic devices be engineered to feel natural?
Lonnie Love's robotics group traditionally has worked on robotic applications for big things—really big things, like industrial-scale manipulators and mobile robots. In predictable scientific fashion, one of his colleagues posed the question, "What if we reversed our thinking, scaled the process down and, instead of designing huge robots, started making very small robotic devices?" Some two years later, the answer has materialized in the form of a surge of research in the relatively new field of mesofluidics.
Mesofluidics is the application of millimeter- to centimeter-sized hydraulics to problems that require substantial amounts of power to be generated and applied in a limited space. "One of the first things we demonstrated in this relatively new area of research was an artificial finger powered by mesofluidics," says Love. The unique thing about this accomplishment was that all the control valves and other equipment required to operate the finger were small enough to fit inside the finger. Despite their miniature size, the hydraulics in the finger provide about 20 pounds of pinch force—about twice the force generated by a human finger.
Packing that level of performance into such a small space required some innovation on the part of the mesofluidics team. Love credits the group's development of two "enabling" technologies for much of the progress they have made. The first is a small but powerful pump. About a cubic inch in volume, the pump operates at 200 psi and generates about 30 watts of hydraulic power. The other new technology is the specialized valves that control motion in the system. "We cannot buy control valves off the shelf that provide this level of performance at this small scale," says Love. "Because no one makes the kind of high-pressure, low-flow valves needed for mesofluidic applications, we were forced to make them ourselves."
The design of a hydraulic finger led, perhaps predictably, to the group's current effort to design and control a mesofluidic hand. In addition to the obvious prosthetic applications, the ORNL team believes the hand also could serve as a remotely controlled device used for disposing of explosives. "If we can make a hand that has the same dexterity as the human hand," says Love, "we could use the device not only for prosthetics but also for remotely disarming weapons, handling IEDs, and thereby removing humans from the risk zone."
One of the first challenges that confronted the project was developing the ability to control a device of such complexity. " A joystick for every joint in the hand is not practical," says Love. "We needed something more natural." To find the balance of complexity and natural function, Love's team is designing a glove with a mesofluidic exoskeleton. They hope to enable the position of each finger joint to be measured and transmitted to the remote hand. Similarly, the exoskeleton would be able to measure the forces occurring remotely and use mesofluidics to provide force feedback, so the user can 'feel' what the remote hand is doing.
As is often the case with scientific exploration, the enabling technologies developed by Love and his colleagues are leading to a broader understanding that wearable robotics can be applied in a number of areas. The team is currently working with Orthocare, one of the leading American manufacturers of prosthetic limbs, on a system to strengthen weakened joints such as elbows or knees. 'If you have a weak knee," Love says, " it would be nice if you could wear a device that would give that joint a little extra power—not to make you a superman, but to restore the strength that you've lost."
Several companies have expressed an interest in applying mesofluidic technology to other prosthetic applications, as well as the production of small-scale, unmanned aerial vehicles with almost bird-like agility. Not surprisingly, Love is enthusiastic about the future of this line of research. "Our initial discoveries have opened a variety of opportunities," he says. "Our challenge now is to find even more unique applications."
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