Fake Skin Gives Robots Sense of Touch

Stu Hutson
for National Geographic News
August 17, 2005
About 20 square feet (1.9 square meters) of skin covers the average adult. In that epidermis, there are nearly 4 million nerves that detect touch and more than 16,000 that detect temperature.

Robots, by comparison, are pretty numb creatures. Except for small clusters of sensors specifically embedded for certain tasks, the machines don't "feel" the objects around them.

"Most robots today interact with their environment almost entirely through visual cues. But that's often a pretty dumb way to go about it," said Gill Pratt, a specialist in robotic sensor systems at Olin College in Needham, Massachusetts.

As Pratt notes, our own tactile sense is far more sophisticated. "You can feel that you're about to crush something in your hand, but you can't see it."

Now researchers at the University of Tokyo say they have put robots in touch with the world. A team lead by Takao Someya has developed what he calls E-skin.

The meshwork of sensors laced onto a thin plastic film resembles thickly threaded fishnet stockings. When stretched over an object, such as a robotic hand, E-skin can detect pressure and temperature.

What's more, the meshwork can bend with a robot hand or other object, however it moves. Experts say this type of all-encompassing sensor system could be a big step toward developing fully functioning, humanoid robots.

Thin Skinned

Scientists overcame a major technological hurdle to develop the electronic epidermis: finding a sensor network pliant enough to fold into the joints—even the wrinkles—that might appear on a robot's face.

Silicon-based detectors, which are most commonly used in robots today, would snap under the strain of crow's feet, for example.

The Japanese researchers instead used carbon-based organic transistors—similar to those being developed for "paper" television screens that can be rolled into a tube.

Organic transistors are basically lightweight, flexible computer circuits made from a chemical ink of organic compounds. The ink can be placed onto a backing material using methods akin to paper printing.

After some tweaking, Someya and his colleagues built a system that enables the sensors to bend with a radius as small as two-hundredths of an inch (half a millimeter), flexible enough for any move a humanoid finger can make.

E-skin still doesn't compare to the real thing, though. You'd have to stack 30 pennies on the mesh before it could detect the pressure.

Additionally, the "robot skin" can sense only hot temperatures between 86° and 176°F (30° and 80°C).

Someya said that it will be fairly simple to improve these sensitivities; his team simply chose to develop flexibility before tweaking E-skin's sensitivity.

That flexibility comes at a price, however. Organic transistors aren't as tough as their metal counterparts. E-skin run roughshod through the Australian outback probably wouldn't last a week. In home use, however, the electronic epidermis would probably remain stable for years.

On the upside, the relatively low production cost of organic transistors, which can be "ink-jetted" onto a material backing, would make E-skin fairly cheap to replace—only a few hundred dollars (U.S.) a square foot.

Crime-Fighting Carpets?

E-skin researchers plan to apply their mesh sensor system to devices other than robots.

For example, Someya points to home security products. "If a pressure carpet is spread onto the floor in your house, the sensors could distinguish the family members and strangers just from footprints."

Other potential applications include running tracks that might monitor an athlete's stride and self-molding sofa cushions that could improve an armchair quarterback's comfort.

In general, E-skin-like sensors could make many objects a little smarter. The technology has already garnered interest from toymakers, automobile manufacturers, sports equipment companies, and security providers.

Scientists add that E-skin won't be limited to detecting temperature and pressure since the product's mesh structure makes it easy to include additional sensors. The team is working to integrate the ability to detect sound, humidity, and light.

"I have confidence that the Six Million Dollar Man should definitely want to buy our superhuman E-skins," Someya joked. Although the researcher admits that he won't be marketing the most basic types of E-skin for several years.

Someya and colleagues describe their research in the current issue of the academic journal Proceedings of the National Academy of Sciences.

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