Blind Cave Fish Inspires New Robot Sensory System

Charles Q. Choi

Date: 07 April 2010 Time: 08:08 AM ET

Robot subs with sensory systems inspired by blind cave fish could help make the droids more autonomous.

Although robots can handle corrosive and toxic gases, moisture, dirt and germs all right, they can typically only do their jobs if each step is precisely programmed beforehand. Autonomous robots, on the other hand, could react somewhat intelligently to their surroundings, and perform their tasks largely independently — or at least that's the hope.

One key to autonomy is the development of sensory systems that allow robots to recognize the situations they are in to fulfill their tasks. Harsh environments can overwhelm conventional senses with dust or fumes, so new senses might be called for, including ones people lack but that are found elsewhere in the animal kingdom.

One favorite creature of researchers at the University of Technology Munich in Germany is the blind Mexican cave fish, a subspecies of Astyanax mexicanus. This subterranean creature has no need for sight in the darkness, and as it matures its eyes degenerate.

Regardless, it has no difficulty navigating its pitch-black habitat with its lateral line, an organ that is also found in sharks, other fish, and some aquatic amphibians.

The lateral line

The lateral line, which is non-existent in land animals, extends along both sides of the body. It is composed of hundreds to thousands of fine sensory hairs located on the scales or in tiny ducts beneath the skin.

They help creatures perceive minute variations in water flow and pressure, generating very detailed pictures of their immediate surroundings, even in murky water, and at a range of about the length of their body. The lateral line system can be used to reveal where obstacles lie, where dangers lurk and where prey is to be found.

In terms of precision, the lateral line is comparable with the human inner ear, where hundreds of thousands of fine sensory hairs enable us to distinguish between sounds. For example, the African clawed frog Xenopus laevis can use its lateral line to distinguish edible and inedible insects on the basis of water-borne vibrations.

Artificial lateral lines could prove especially helpful for robot submarines, as visibility underwater is often limited to a few inches. The infrared detectors that land robots commonly use alongside cameras to identify their surroundings also work poorly underwater, and any wireless communication that robots might use to get help from people travels poorly underwater.

"An underwater robot is as much on its own as a vehicle on Mars," said researcher Stefan Sosnowski, an electrical engineer at the University of Technology Munich.

Snookie

Now researchers have developed an experimental underwater robot dubbed "Snookie" — named after a species of perch with a distinctive lateral line — that can orient itself in murky waters with an artificial sensory organ inspired by the lateral line.

The robot, made of plastic and aluminum, is roughly 32 inches long and 12 inches wide. It has six propellers to help drive and position it and guiding sensors packed into its rounded yellow nose.

"Snookie had to be designed small enough such that it can be handled easily and that it can operate in small spaces but large enough that all the electronics and power supply fit into it," said researcher J. Leo van Hemmen, a theoretical biophysicist at the University of Technology Munich

Biophysicist Jan-Moritz Franosch, also at the University of Technology Munich, and his students helped develop an artificial lateral line for Snookie, enabling it to detect obstacles and movements in the water a hand's breadth in front of its nose and on either side. At intervals of a tenth of a second and using only a tiny amount of electrical energy, the electronic sensors in the system can detect velocity fluctuations of less than one percent.

"There are no velocity sensors commercially available that fit our needs," Franosch said. "Therefore we are still constructing the sensors, although prototypes meanwhile exist."

However, the complicated part of this system doesn't involve sensing the environment, but processing these signals to create a complete picture of the surrounding area, the researchers explained. Differences in pressure are much harder to accurately pin down than waves of light. Van Hemmen and his colleagues are researching the algorithms animals are wired with to analyze their environment and developing hardware and software to enable robots to imitate them.

From sea to sewers

The research on Snookie could lead to autonomous underwater robots for a wide range of operations. In the deep sea, they could investigate shipwrecks and locate flight recorders after air disasters. More mundanely, they could also inspect tanks and sewer pipes.

"Snookies could also accompany divers as partners for safety — carrying spare compressed air bottles, or supporting divers through extra equipment," van Hemmen said.

Even more sensitive lateral lines could even find uses on land, offering a cheaper alternative to laser scanners land robots currently use to feel their way around their immediate surroundings, van Hemmen noted.

Unlike laser scanners, lateral lines won't blind other robots. As a result, "a lot of small Snookies could operate in a swarm and autonomously explore their environment in a joint effort," van Hemmen said.