Electroactive polymers (EAPs) are also known as artificial muscles because they expand and contract when voltage is applied. Researchers have been working on them for decades, and, until recently, their main use would probably be limited to moving robotic limbs such as the one shown in the video below.
Now, The Economist reports, “a team led by Iain Anderson [link is ours], the head of the Auckland Bioengineering Institute’s Biomimetics Lab in New Zealand, has built an entire menagerie of muscle-powered motors” and opened up the design possibilities.
According to The Economist:
Artificial muscles seem unlikely ever to be able to compete with hydraulic actuators for strength, or combustion engines for speed and torque. But in some applications, it seems, they could give the venerable electric motor a run for its money. And although they may yet find uses in Mars rovers and space telescopes, in the short term they would appear to have more potential inside mobile phones, cameras, game controllers and other consumer-electronics products.
The two main types of EAPs are ionic and dielectric. Ionic EAPs are comprised of a spongy polymer soaked in electrolyte solution and positioned between two electrodes. Applying a voltage causes the polymer to swell up on one side and shrink on the other, resulting in a bending motion good, for example, for windshield wipers.
Dielectric EAPs are considered easier to work with, partly because there is no solution that dries out. Made of flexible polymer sandwiched between two electrodes, they are better suited for tiny, precise push-and-pull motions, such as autofocus mechanisms on a smartphone. The polymer contracts in one direction and expands in another when voltage is applied.
Yoseph Bar-Cohen, a physicist and pioneer in the field at NASA’s Jet Propulsion Laboratory in Pasadena, California, told The Economist:
A stack of several dielectric EAPs can generate substantial forces using little power. They are also light, which is one reason why America’s space agency, NASA, is so interested in them.
Among their machines, Anderson’s team used dielectric electroactive polymers to turn a wheel. Researchers have used muscles to turn wheels before, but Anderson’s team did it without a ratcheting mechanism, bearings, or gears. Anderson said, “The breakthrough idea was to grip the shaft from both sides, which made bearings redundant,” according to The Economist.
Here is how the wheel, which resembles a spoked bicycle wheel, operates:
With at least six per motor, working as opposing pairs, these muscles are positioned between the outer rim and the central driveshaft. To make the shaft turn, the muscles work in concert, rhythmically contracting, one pair after another. As they do so, each pair applies pressure to a soft ring around the driveshaft. The pulsating muscles collectively and continuously pinch the shaft and apply a rotational force, causing it to turn.
Anderson concedes that the muscle motors probably won’t power cars or trains because they have few revolutions per minute. “But it has opened up a new design space,” he told The Economist.
Source: “Muscling in on motors,” The Economist, 9/3/11
Source: “Electroactive Polymer Artificial Muscle (EPAM) Hexapod Robot,” YouTube
Rachel Petkewich is a freelance science writer and editor. She has worked as a research scientist in the chemical industry and spent eight years as a staff writer and editor at various science journals and magazines, including Chemical & Engineering News.