Fine touch.
Using four "whiskers," a robot can reproduce the contours of face (right).

Mitra Hartmann and Joseph Solomon

Robots That Feel Like Rats

With their dismal vision, rats rely on their whiskers to navigate the junkyards and sewers they call home. Now, a pair of mechanical engineers has devised a mathematical model that tries to mimic how animals use their whiskers to build a mental picture of their environment, and they've built a robot that works on the same principles. Such "biomimetic" whiskers might one day enhance the navigation of robotic vehicles used to explore other planets and underwater environments here on Earth.

Animals use their whiskers for more than just avoiding major obstacles. In lab experiments, rats can distinguish shapes and make extremely fine distinctions between textures. And seals use their whiskers to follow the wakes of tasty fish (ScienceNOW, 5 July 2001). But exactly how animals size up the world with their whiskers isn't clear, says Mitra Hartmann, a mechanical engineer at Northwestern University in Evanston, Illinois.

In a paper published in the 5 October Nature, Hartmann and her graduate student Joseph Solomon propose an answer in the form of a mathematical model. What sets their model apart from previous whisker models is that it considers the torque generated in two dimensions at the base of a whisker (where it attaches to the face) when the whisker hits an object. Torque depends on both the force at the point of contact and the distance of that point from the base.

By tracking torque as a whisker makes multiple sweeps across an object, Hartmann and Solomon's model computes the distance between the whisker base and different points on the object's surface. These distances, in turn, reveal cavities, protrusions, and other contours. The researchers tested their model by building a simple robot--a rotating rod with a row of four whiskers, each equipped with strain gauges at the base to measure torque. When they swept the whiskers across a clay Chia Pet head and fed data from the gauges into their model, it recreated a recognizable likeness of the Chia's face.

The work nicely demonstrates a simple principle for using whiskers to detect distances at close range, says David Kleinfeld, a physicist who studies rat whiskers at the University of California, San Diego. Although experiments with live animals will be needed to determine whether rats actually use this strategy to extract shapes, Kleinfeld thinks the research could have practical applications either way. For example, he says, whiskers on the underside of planetary rovers could monitor the terrain and help the vehicles avoid getting stuck. Such a system would probably require far less computation than current methods, thereby helping to conserve a rover's precious battery power, Kleinfeld says.

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