Hirsute machines

Rats may be feared and loathed, but they have one feature that some humans are eager to replicate — whiskers. These long, stiff hairs, known as vibrissae, tell the rodents a lot about their surroundings and now man-made copies are being attached to robots to improve their senses.

Whiskers are a particularly efficient method of encoding tactile information. ‘Tactile sensing serves as a natural complement to vision as it can operate in the dark, underground, in fog, in the very near field of view or when reflections and glare prevent accurate visual assessment,’ said Mitra Hartmann of Northwestern University, Illinois.

So her laboratory has developed inexpensive arrays of artificial whiskers modelled after vibrissal systems that can be used either in active ‘whisking’ mode or in passive ‘dragging’ mode.

‘The artificial vibrissae can determine obstacle distance, perform 3D extraction of object shape, and determine the velocity of a fluid flow,’ said Hartmann. Studies reveal that rats make about eight sweeps a second with their whiskers, while mice whisk at up to 12Hz. Different lengths and diameters of whiskers gather different information about surface texture, proximity and solidity.

Hartmann’s team is investigating how the knowledge of natural whiskers can be applied to artificial versions and used to improve the sensory capabilities of autonomous robots.

For example, future Mars Rovers may sprout whiskers. ‘Such arrays could be used to map terrain features, determine ground and surface texture, provide an estimate of rover speed, and identify “slip” of the rover wheels,’ said Hartmann. NASA’s Jet Propulsion Lab likes the idea so much it has helped fund the research.

Whiskers can be just as useful in water. Walruses and manatees use theirs to detect subtle current changes, and seals can detect water waves 0.001mm (one thousandth of a millimetre) across, the width of the wake left by a goldfish.

With this in mind, Hartmann’s team is looking to apply artificial whiskers to autonomous submarine craft. ‘On an underwater vehicle, vibrissal arrays might be used to track wakes and characterise fluid flow,’ she said.

The Northwestern lab is studying whisker dimension and geometry to discover which configurations are best suited to which applications. Yet the ability of vibrissae to acquire information that is hard work, or downright impossible, for other sensors to gather and interpret makes it likely that some robots will evolve into hirsute machines.