Artificial Muscles [Preview]

Novel motion-producing devices--actuators, motors, generators--based on polymers that change shape when stimulated electrically are reaching commercialization.

It's only a $100 toy—an aquarium of swimming robotic fish developed by the Eamex Corporation in Osaka, Japan. What makes it remarkable is that the brightly colored plastic fish propelling themselves through the water in a fair imitation of life do not contain mechanical parts: no motors, no driveshafts, no gears, not even a battery. Instead the fish swim because their plastic innards flex back and forth, seemingly of their own volition. They are the first commercial products based on a new generation of improved electroactive polymers (EAPs), plastics that move in response to electricity.

For decades, engineers who build actuators, or motion-generating devices, have sought an artificial equivalent of muscle. Simply by changing their length in response to nerve stimulation, muscles can exert controlled amounts of force sufficient to blink an eyelid or hoist a barbell. Muscles also exhibit the property of scale invariance: their mechanism works equally efficiently at all sizes, which is why fundamentally the same muscle tissue powers both insects and elephants. Something like muscle might therefore be useful in driving devices for which building tiny electric motors is not easily accomplished.

EAPs hold promise for becoming the artificial muscles of the future. Investigators are already ambitiously working on EAP-based alternatives to many of today's technologies. And they aren’t afraid to pit their creations against nature's. A few years ago several individuals, including Yoseph Bar-Cohen, a senior research scientist at the Jet Propulsion Laboratory (JPL) in Pasadena, Calif., posted a challenge to the electroactive polymer research community to drum up interest in the field: a race to build the first EAP-driven robotic arm that could beat a human arm wrestler one on one. Later, they began searching for sponsors to subsidize a cash prize for the winner. The first such contest was held in March 2005, and the outcome was disappointing for robot designers: a 17-year-old girl easily defeated her three mechanized opponents, each demonstrating a different type of artificial muscle.

Research continued despite this result, and perhaps the most promising of the current EAP efforts is being conducted by SRI International, a nonprofit contract-research laboratory based in Menlo Park, Calif. Another pioneer in the field of EAPs is Micromuscle AB, a company based in Linköping, Sweden, that focuses on medical device applications in the areas of cardiovascular treatment and drug delivery.

In 2003 SRI launched a spin-off company, Artificial Muscle, Inc. (AMI), to commercialize the EAP technology it had patented. AMI now manufactures actuators and transducers (touch sensors) that employ its electroactive polymer artificial-muscle technology. These solid-state devices are intended for use in audio speakers, power generators, motors, pumps, valves, sensors and actuators. The company's Universal Muscle Actuator is the first high-production-volume platform that can serve as a fundamental building block for advanced linear actuator designs. AMI recently introduced, for example, the DLP-95 autofocus lens positioner, a compact device that adjusts lenses for focusing and zooming.

The firm's long-term goal? Only to replace a substantial number of the myriad electric motors we use regularly, not to mention many other common motion-generating mechanisms, with smaller, lighter, cheaper products using SRI's novel actuators. “We believe this technology has a good chance to revolutionize the field of mechanical actuation,” states Philip von Guggenberg, the lab's director of business development. “We’d like to make the technology ubiquitous, the kind of thing you could pick up in hardware stores.”

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