Robotic Whiskers Inspired by Rats Can "See" in 3-D

Sean Markey
for National Geographic News
October 4, 2006
Armed with high-resolution cameras and infrared sensors, the Mars rovers have been collecting data from the red planet in unprecedented detail (see images taken by the Mars rovers).

But, some researchers say, the robotic space explorers could boost their performance if they added another powerful tool to their arsenal: whiskers.

Whiskered animals such as rats can detect an object's size, shape, texture, and orientation with just a few sweeps of their body bristles.

So how do the animals sense this 3-D data with what are basically overgrown hairs? Scientists have been puzzling over the features for nearly a century.

Now, in a report appearing in tomorrow's issue of the journal Nature, researchers in Illinois say they may have solved the mystery.

What's more, the team has already applied their insights to building robotic whiskers that may one day appear in everything from assembly lines to space and deep-sea rovers.

By a Whisker

Using their whiskers, rats gather three coordinates—similar to latitude, longitude, and elevation—to discern an object's contours, such as the features of a human face.

Scientists believe that the height of each whisker and its angle from nose to tail supply the equivalents of longitude and elevation.

"The mysterious coordinate [latitude] has been … how far out along the length of the whisker the rat touched something," said study co-author Mitra Hartmann, a mechanical and biomechanical engineer at Northwestern University in Evanston, Illinois.

"Without knowing that distance, the rat can't tell how far away is an object, and it can't figure out three-dimensional properties," she added, noting that whiskers lack nerves that could relay the information to the brain.

Hartmann and colleague Joseph Solomon suspect that rats instinctively determine the distance based on the torque—a turning or twisting force—felt in their whisker follicles.

More precisely, the researchers believe that rat neurons process the change in torque over time as a whisker encounters an object, allowing the animal to record the object's exact location.

While the pair hasn't performed behavioral studies on rats to test their hypothesis, they have applied their ideas to build robotic whiskers that mimic the supersensing powers of rats and seals.

In one experiment the researchers connected four steel-wire whiskers to strain gauges, which in turn were tied to a computer.

Brushed repeatedly against a mock human head, the whiskers fed data points into the computer. When connected by smooth curves, the coordinates accurately reproduced the face in three dimensions.

The team also built a similar array of eight plastic whiskers that could detect shifts in air currents, much the same way that seals' whiskers help the marine mammals track the wakes of underwater prey (related photo: the whiskers on a Weddell seal's face).

From Mars to Factories

The researchers say they envision many uses for their new technology, from checking the positions of spare parts on assembly lines to helping robots scour oil pipelines for blockages (related news: "Alaska Oil Pipeline Faces Big Scrutiny After Small Spill" [August 2006]).

Other potential applications could see the whiskers installed on underwater remotely operated vehicles (ROVs) to help the bots operate in dark, muddy, dusty, or high-glare conditions.

"The early part of this work was actually funded by NASA, because they were interested in perhaps putting whiskers on a Mars rover to figure out terrain properties," Hartmann said.

Unlike electromagnetic sensors such as cameras or infrared eyes, whiskers are passive devices that require very little power, an advantage for remote space missions.

Hartmann says that whiskers could also tell a rover when it is stuck or sliding.

"Sometimes if the rover is in sand, for example, the wheels are turning. So the optical encoders on the wheels tell the machine that it's going somewhere, but it's actually not," she said.

By simply feeling the ground, a whisker could tell the rover what's really happening. The same is true for a rover sliding down a hill with its wheels locked.

Insect Antenna

Noah Cowan, an assistant professor at Johns Hopkins University in Baltimore, Maryland, has helped develop robot antennae inspired by cockroaches.

(Read "Cockroaches Inspire Robot Antenna Design" [April 2005].)

He praised the new work by the Illinois team, writing in an email that "it shows the critical role of mechanics in decoding sensory signals, which is something that neuroscientists often neglect."

He adds that building tactile probes like the robotic whiskers is a "great idea," but notes that Mother Nature offers other design inspirations, too.

Real insect antennae "have thousands of sensors for touch, smell, temperature, and pressure all along the mechanical probe itself, not just at the base" like whiskers do, he said.

The feature, he says, may be one of the reasons insects are so abundant and widespread.

"Find a bug without a pair antennae—it is not easy," he said.

Meanwhile, study co-author Hartmann says that her research has important implications for neuroscience as well.

"There are probably 500 papers published every year on the rat whisker system," which, she said, serves as a model for how animals process and transmit information from outside their bodies to the highest levels of the brain.

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