Electric wheelchairs are a real boon to people with disabilities, but they lack something that every automobile has: a way to adjust the power to the wheels, making them less useful when the terrain gets rough.

Emmanuel Collins, professor of mechanical engineering at Florida State University, decided to solve that problem. He used a system that was originally designed for military vehicles. The device is called a laser line striper, and it is a combination of laser beam and infrared camera that takes a picture of the terrain ahead.

The picture - really a slice of an image - is sent to a computer that adjusts the amount of power to the wheels in a way similar to how a person switches gears in a car. Since the motors in wheelchairs are electric, there isn't a change of gears, rather the system would alter the response of the joystick used to control the hair.

On a slippery surface, you wouldn't want to accelerate or decelerate too fast, he said. In the case of a slippery surface, the computer would adjust the acceleration and deceleration and the sensitivity of the joystick.

Automatic terrain-sensing controls are already used for military robotic vehicles, and several four-wheel-drive cars and trucks now on the market include such controls for better safety. So Collins decided to adapt it to wheelchairs.

The trick is in the signal processing and software. A computer has to basically be able to extrapolate a lot of information from a very narrow slice of the surroundings. A scanning-type technology - like a radar dish swinging back and forth - would get a much better picture. But that would also be a lot more expensive and require even more sophisticated hardware, Collins said. The key with new technologies like this is to make them cheap enough for more or less everyday use.

Collins cautions that he hasn't got a prototype yet - right now the modeling is experimental. But he is confident that with some work eventually wheelchairs will also be equipped with these control systems, perhaps in the next five years.

The technology is being developed in partnership with the U.S. Army Medical Research and Materiel Command's Telemedicine and Advanced Technology Research Center, which has provided funding.

The partnership started when Collins heard a presentation by Professor Rory Cooper, chairman of the University of Pittsburgh's rehabilitation science and technology department. Cooper has used a wheelchair since suffering a spinal cord injury in 1980 during his service in the Army.

In his presentation, Cooper mentioned the need for terrain-dependent, electric-powered wheelchair assistance. Collins approached him about working together, and the two of them began developing ideas with other collaborators at the National Science Foundation-sponsored Quality of Life Technology Center, an engineering research center affiliated with the Human Engineering Research Laboratories that Cooper co-directs.