Wednesday, October 21, 2009

Scientists Develop New Material For Robot Muscles

A group of researchers at the University of Texas have made a breakthrough in their quest to find a stronger, more effective material for use in making artificial muscles for robots. They’ve found a way to create tangled nanotube ribbons that are, relative to weight, stronger than steel and stiffer than diamond.

The ribbons have the remarkable ability to expand in width by 220% when a voltage is applied. When the voltage is removed, the ribbons return to their normal state. The shift in state occurs over mere milliseconds. Additionally, the nanotube ribbons retain their properties in an extreme range of temperature: between -196 °C and 1538 °C.

The scientists construct the nanotube ribbons into an aerogel, which contains primarily air. A cubic centimeter of the stuff weighs just 1.5 milligrams; one gram could cover a space of 30 square meters. Researchers are still experimenting with ribbon lengths. So far, the team has produced ribbons that are 1/50th of a millimeter thick, 16 centimeters wide and several meters long. Larger sheets are in the works.

Besides serving as material for artificial muscles, the nanotube ribbons could be used to create sturdy, lightweight structures in space.

Hydrogen muscle silences the domestic robot

IF ROBOTS are ever going to be welcome in the home they will need to become a lot quieter. Building them with artificial muscles that run on hydrogen, instead of noisy compressed-air pumps or electric motors, could be the answer.

Kwang Kim, a materials engineer at the University of Nevada in Reno, came up with the idea after realising that hydrogen can be supplied silently by metal hydride compounds.

Metal hydrides can undergo a process called reversible chemisorption, allowing them to store and release extra hydrogen held by weak chemical bonds. It's this property that has led to the motor industry investigating metal hydrides as hydrogen "tanks" for fuel cells.

To make a silent artificial muscle, Kim and his colleague Alexandra Vanderhoff first compressed a copper and nickel-based metal hydride powder into peanut-sized pellets. They then secured them in a reactor vessel and pumped in hydrogen to "charge" the pellets with the gas. A heater coil surrounded the vessel, as heat breaks the weak chemical bonds and releases the stored hydrogen.

The next step was to connect the vessel to an off-the-shelf artificial muscle, which comprises an inflatable rubber tube surrounded by Kevlar fibre braiding. Two of these placed either side of a robotic joint can mimic the push/pull action of muscles by being alternately inflated and deflated (see diagram).

Turning the heater on and off controls the flow of hydrogen into the rubber tube, causing the muscle to move silently. Even better, the pair say, the muscle performs as well as those that run on compressed air systems (Smart Materials and Structures, DOI: 10.1088/0964-1726/18/12/125014). Importantly, the gas didn't leak.

"The system has biological muscle-like properties for humanoid robots that need high power, large limb strokes - and no noise," says Kim.

Yoseph Bar-Cohen, an engineer specialising in artificial muscle technology at NASA's Jet Propulsion Lab in Pasadena, California, says this is "a novel approach" for controlling artificial muscles. "It is an important contribution and increases the arsenal of potential actuators that may become available in the future," he says.

iRobot Unveils Morphing Blob Robot

iRobot's latest robot is unique on many levels. The doughy blob moves by inflating and deflating - a new technique its developers call "jamming."

As the researchers explain in the video below, the jamming mechanism enables the robot to transition from a liquid-like to a solid-like state.

Earlier this week, researchers from iRobot and the University of Chicago presented the new "blob bot" at the IEEE/RSJ International Conference on Intelligent Robots and Systems.

As a new kind of chemical robot (or chembot), the blob bot has stretchy silicone skin, which is composed of multiple cellular compartments that each contain a "jammable slurry."

When some of these cells are unjammed, and an actuator in the center of the robot is inflated, the robot inflates in the areas of the unjammed cells. By controlling which cells are unjammed, the researchers can change the shape of the robot and make it roll in a specific direction.

The new robot is being funded by DARPA, which gave iRobot $3.3 million to work on the chembot last year. The goal is to build a robot that can squeeze through tiny openings smaller than its own dimensions, which could be valuable in a variety of missions.

The video shows the robot from about one year ago, and since then the researchers have been working on adding sensors and connecting multiple blob bots together.