Published online 8 June 2006 | Nature | doi:10.1038/news060605-12

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Robot sensors go touchy-feely

Touch-sensitive 'skin' will give robots the sense they lack

Could robots become well acquainted with the touch of a velvet hand?Could robots become well acquainted with the touch of a velvet hand?© Getty

Robots are one step closer to having a human sense of touch, thanks to a thin, flexible film that mimics the sensitivity of a human finger. The device may become useful in the next generation of robots and in automated tools used for microsurgery.

Touch is one of the first senses that humans develop, but because of its complexity it has been one of the last to be tackled by robotics. Touch has to relay information about the surface of an object, and also the amount of pressure needed in order to grasp it.

Previous touch sensors have had big problems with rigidity and durability. When constructed out of hard materials such as silicon, they were not able to contour to the robotic 'hand', while the daily wear and tear of touching also tended to bend and scratch the delicate materials. Robots clearly need something "more like human skin," says chemical engineer Ravi Saraf from the University of Nebraska, Lincoln. "And we're getting there."

Saraf and his colleague Vivek Maheshwari unveil their new sensor film in this week's Science1.

Thin film

The film is about 100 nanometres (100 x 10-9 metres) thick, roughly 1,000 times thinner than standard office paper. It is built like a sandwich of alternating layers of gold and cadmium sulphide nanoparticles, each separated by insulating polymer sheets just 2 or 3 nanometres thick.

The whole device is hooked up to electrodes that allow a current to flow through the film. When pressed onto a surface, the stress distorts the layers so that electrons can more easily hop across the insulating polymer layers and hit the cadmium sulphide particles. This makes the particles glow — the greater the stress, the more light they emit. A camera then measures the strength of the glow, which relates directly to the pressure felt by different parts of the film.

The sensor can detect tiny surface details with a pressure of 9 kilopascals, equivalent to a one-pound (half-kilogram) bag of sugar resting on a postage stamp. The pressure is similar to that used by human fingers to feel things and pick them up.

The nanofilm can sense letters and shapes on a penny (below), as compared with a conventional microscope image (above).The nanofilm can sense letters and shapes on a penny (below), as compared with a conventional microscope image (above).© Science

It can also distinguish a feature as small as 40 micrometres wide (40 x 10-6 metres) on a surface, just like a human finger can. Previous sensors could only detect in the millimetre range.

To illustrate this phenomenon, the team pressed a US penny against the sensor. The image from the camera shows astonishing detail, including the folds of President Lincoln's clothing and the letters 'TY' in 'LIBERTY'.

Clever combination

The sensor is an ingenious combination of materials already known to nanotechnology, says Edwin Thomas, head of material sciences and engineering at the Massachusetts Institute of Technology, Cambridge. "It's clever what they've done," he comments. "You could kick yourself and say 'hey, I could have done that'."

Saraf's main research area is materials science rather than robotics. He explains that it was the loss of a close friend to breast cancer that spurred him try to invent a sensor that could detect small, malignant growths. Currently, with the best monitoring devices, cancers can only be detected when they are a couple centimetres in length, which in some cases is too late.

This poor resolution disappointed Saraf. "We can get to the Moon and we're on our way to Mars but we can't look at a small ball," he says.

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It may be some time before such sensors are used in the clinic, but for now, robotics researchers are surprised and excited about the device. "It's another tool in the armoury" of robotics research, says electronic engineer Richard Crowder of the University of Southampton, UK2. "And it came out of left-field."

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  • References

    1. SarafR.F.& MaheshwariV. . Science, 312. 1501 - 1504 (2006).
    2. [author]CrowderR.[/author]. Science, 312. 1478 - 1479 (2006).