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October 8th, 2006 at 12:35 am

Designing Robots With Whiskers

Taking tips from both land and sea animals, researchers have crafted arrays of robotic whiskers that can create accurate, 3D images of objects.

The tactile devices could be used to enhance the vision and maneuverability of land-based robots, autonomous underwater vehicles and perhaps robots on Mars.

"Whiskers on planetary rovers might be able to figure out topography and surface texture of the ground, and that’s important to know if a rover is about to get caught in sand," said co-researcher Mitra Hartmann of Northwestern University in Evanston, Illinois.

Rats rely on whiskers to determine everything from the shape and texture of nearby predators to the relative size of an underground burrow. Also called vibrissae, the long hairs dot their cheeks in a square-grid pattern.

A rat constantly whisks these hairs backward and forward, about seven or eight times per second, hitting objects that bend the whiskers to various degrees. By whisker-tapping an object several times at different places, the rat can put together a 3D image in its brain.

Seals sport much larger whiskers, and instead of using a whisking motion they rely on the water pushing against each hair. The seal’s bending whiskers help the animal determine direction of water flow or whether a juicy fish just swam by.

Whiskers of both these creatures lack any sensors along their lengths, so the scientists wondered how the animals decipher where along each whisker an object has brushed.

Using computer simulations and a lab experiment, Hartmann and Joseph Solomon, also of Northwestern University, discovered the animals can calculate how the twisting, or torque force at the base of each whisker changes. If that force increases, it signals the object is close to the whisker base.

So they constructed rat whiskers out of spring-steel wires and seal whiskers from thick plastic strips and equipped each with a gauge at its base to measure torque. Tests of the robotic hairs churned out nearly dead-on images of an object.

"That’s the third dimension that’s been mysterious for almost a century now," Hartmann told LiveScience.


The AMouse robot consists of three basic systems: an omnidirectional camera (A) and its artificial whisker sensors (B) which are mounted on a mobile Khepera platform (C).

In setting up the whisker array (see picture below), the researchers noted that rats can move their whiskers separately in two dimensions, but mostly they move them in synchrony and in a forward/backward sweep. The selected design for the whisker array moves all whiskers synchronously in one dimension, which closely approximates the typical rat whisker motion.

(AMouse whisker array)

Each AMouse whisker is plugged directly into a capacitor microphone at the front of the robot. This capacitor can detect vibrations up to 3000 vibrations per second. The process imitates the way a real mouse uses its whiskers to sense, via the nerves in its nose.

Moving on its caterpillar tracks, the AMouse is programmed to proceed until it senses an obstacle; it then alters direction until it finds its way around it. But the robot can also sense acceleration and ground vibrations using its whiskers. 



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