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Infrared Sensor Works Better than Coffee

Photonics Spectra
Mar 1998
Kevin Robinson

A helmet-mounted infrared sensor promises to reduce heavy-truck accidents caused by sleepy drivers. According to South Africa's Council for Scientific and Industrial Research, mining companies suffer substantial losses each year when drivers fall asleep while operating the ore-filled trucks. Using light-emitting diodes (LEDs) for illumination and an infrared sensor, researchers have developed the Deadman's Switch to monitor drivers' eyes and alert them if they fall asleep.
The unit is mounted on the brim of a driver's hard hat. The only part of the device that hangs below the brim is a shield in front of the driver's eyes. The shield is 90 percent transparent to visible light, but the inside coating reflects 85 percent of infrared light. Siemens LEDs bounce 15 spots of low-power, 0.95-µm light off the shield and into the driver's eye. The 6- to 7-mm spots are illuminated in a series much like a raster pattern. LED light reflected off the surface of the eye or off the eyelid returns to the shield, which in turn reflects it up to a Siemens photodiode on the helmet.

Don't fall asleep
The eye itself absorbs IR light more heavily than the eyelid, which is more reflective. The sensor detects differences in the reflectance from an open vs. a closed eye. When an eye closes for more than two seconds, the sensor triggers an alarm that shouts, "Wake Up! Wake Up!"
The Deadman's Switch is hooked via a cable to its power supply and communications unit, which are mounted in the truck. The communications unit provides the voice alarm and a radio link to alert a dispatcher when a driver nods off.
At the beginning of a shift, the driver dons a helmet and plugs in the communications cable. Following voice prompts from the unit, the driver adjusts the hard hat so that the four red alignment dots fall into the center of his or her view. Still following the voice prompts, the driv-
er calibrates the instrument by pushing a button with eyes closed and again with eyes open. After this, the device operates with no more input.
According to Valery Kononov of the research council, one of the sensor's developers, the device should last about four years, depending on how roughly it is handled. The prototype already has been tested in open pit mines.



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