Rubbery muscle motors to make robots more lifelike

It wobbles like a jelly, but could make robots more flexible than ever before. Soft artificial muscles have been used to make a motor with only a few parts, and no gears, bearings or cogs.

The motor (watch a video of it here) signals a new dawn for artificial muscles, says Iain Anderson, head of the Auckland Bioengineering Institute's Biomimetics Lab in New Zealand, where it was created.

The muscles themselves are electroactive structures consisting of two layers of conducting carbon grease separated by an extremely stretchy insulating polymer film, says Anderson. "It can stretch by more than 300 per cent."

When a voltage is applied, the configuration behaves like a capacitor, with positive and negative charges accumulating on either side of the insulator. As the opposite charges attract one another the insulator is squashed between them and flattens and stretches. Turn the voltage off and it contracts again to its original size.

The motor looks rather like a bicycle wheel, with the elastic muscles stretched between the edge of the wheel and the centre, like flat spokes. To turn a shaft, six of the muscles work in concert, contracting one after the other. Although the device looks as if it is wobbling like jelly, the spokes are connected to a foam ring wrapped tightly around the central shaft, and this arrangement exerts a continuous rotational force.

This is not the first time electroactive polymers (EAPs) have been used to create rotary motion, says Anderson. But previous efforts used a sort of ratcheting mechanism instead of the foam ring. Anderson's design removes the need for bearings, gears or anything else that is rigid.

"There's huge potential for this kind of actuator," says Chris Melhuish, director of the Bristol Robotics Lab in the UK. "We are going to have a different class of robot." Robots made of artificial muscle would feel soft and flesh-like and would be able to mimic the dexterity and mobility of living creatures, without the need for rigid mechanical components.

These kinds of EAPs are extremely strong, says Yosef Bar-Cohen, who specialises in electroactive materials at NASA's Jet Propulsion Laboratory in Pasadena, California - many times stronger than their biological counterparts. The simplified motor that Anderson has built opens up a whole new range of uses for artificial muscles, he says.

For example, they could be used to make instruments for keyhole surgery that are soft enough to be squeezed through tiny incisions but still able to perform the jobs of more rigid mechanical devices.

A company called Artificial Muscle in Sunnyvale, California, is developing EAP-based motors designed to behave like haptic displays, which respond when they are touched. They provide tactile feedback for cellphones, computer mice and touchscreens, producing a range of different feelings beneath a user's fingertips. They can produce the satisfying "click" sensation of a real button when typing on a touchscreen, for example.

The first of these, designed for the iPhone, will become available in May. It will replace the traditional vibrate function, and its diaphragm-like design allows it to respond much faster than the motors currently used in cellphones and produce a broader range of frequencies, says Andy Chen of Artificial Muscle.

Anderson's design will be presented at the Electroactive Polymer Actuators and Devices conference in San Diego, California, this week, along with the iPhone device. Also on display will be EAPs capable of generating electricity by a reverse process, creating a current when physically pumped, as well as robots that can harvest their own power and muscles that provide sensory feedback.

"I'd like to think that the future is soft," says Anderson.

This post originally appeared on New Scientist. Image of the Telenoid via Yoshikazu Tsuno/AFP/Getty.