October 4, 2006 | David F. Coppedge

Whiskers Inspire Technology

The latest gadget on robots or Mars rovers could be whiskers.  These tactile sensors provide ways to see in 3D, says a report on National Geographic News.  Information about latitude, longitude and elevation can be gleaned from whiskers.  Rodents continually rotate their whiskers to gather information, but seals and sea lions let the ocean currents flow around them.
    Joseph H. Solomon and Mitra J. Hartmann, engineers at Northwestern University, devised robotic whiskers and tested their sensitivity.  Writing in the Oct. 5 issue of Nature, they said,

Several species of terrestrial and marine mammals with whiskers (vibrissae) use them to sense and navigate in their environment – for example, rats use their whiskers to discern the features of objects, and seals rely on theirs to track the hydrodynamic trails of their prey.  Here we show that the bending moment – sometimes referred to as torque – at the whisker base can be used to generate three-dimensional spatial representations of the environment, and we use this principle to construct robotic whisker arrays that extract precise information about object shape and fluid flow.

They believe this knowledge could help improve robotic engineering.  “Our results on biomimetically engineered whiskers may find application in land-based robots and autonomous underwater vehicles, in which a capability for tactile perception could broaden and enhance performance.”  Sean Markey began his National Geographic article with a speculation about a future generation of Mars explorers: “Armed with high-resolution cameras and infrared sensors, the Mars rovers have been collecting data from the red planet in unprecedented detail…. But, some researchers say, the robotic space explorers could boost their performance if they added another powerful tool to their arsenal: whiskers.”  See also the writeup on LiveScience.

1Joseph H. Solomon and Mitra J. Hartmann, “Biomechanics: Robotic whiskers used to sense features,” Nature 443, 525(5 October 2006), doi:10.1038/443525a.

It’s clear that the interpretation of whisker movements must come from the base, since the protein fiber that makes up a whisker contains no nerve endings.  This means an elaborate sensory apparatus must inhabit the tiny follicle of each whisker.
    Car drivers used to install curb whiskers to sense the car position during parallel parking, but the transduced information was useful not to the car, but to the driver, who through auditory input could respond accordingly.  Imagine what it would take to engineer a car to parallel park itself based on one curb whisker’s tactile response.  Sensors would have to be mounted orthogonally at the base, and computer software would have to be written, complete with feedback to the steering and brakes.
    In the mammal body, whether of a rat, cat, seal or otter, sensing the conical movements of a whisker must require multiple nerve endings in each hair follicle.  The timing and strength of each nerve response must be coordinated with brain software to draw the 3D image, and the reaction time must be nearly instantaneous to do the animal any good.  This is all complicated by the large number of individual whiskers (nearly 20 per side on the face of this Weddell seal).  All this technology can fit on the tiny head of a mouse or weasel, allowing the animal to gain a continuous image of its dark surroundings.
    Based on the observed performance, design-theoretic researchers could probably expect to find even more engineering behind this one tactile sense.  Undoubtedly similar responses occur in hair follicles since we are aware of temperature and touch with those smaller antennae also – another reason not to shave, men, especially if you like cave exploring or crawling under the house.

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