Laser Rangefinder

At the heart of our range acquisition system is a commercial laser rangefinder, the AccuRange 4000-LIR from Acuity Research, Inc. in Palo Alto, CA. It modulates the laser for time-of-flight measurements to accurately measure distances from less than 1 inch to 50 feet (15m). It weighs less than 4 lbs, and is reasonably compact. It can take measurements at speeds up to 50 kHz, but we usually run it between 8-25 kHz to improve quality. We purchased the infrared model (the 4000-LIR) because of higher powered laser (8mW vs. 5mW) that gives better readings at long range and in sunlight. The high-speed interface card is required to obtain data at rates higher than 1 kHz, which requires a computer with an available ISA slot. More information is available at http://www.GoodEnuf.com/client/Acuity/.

The high-speed interface returns an 8-byte sample for each range reading. The information contained includes 19 bits of range information, 8 bits of signal strength (laser light reflected), 8 bits of ambient light, 8 bits indicating motor position, and a few flag bits indicating such things as buffer overflow and scanning motor zero.

The laser is not eye-safe, due to its power, invisibility, and lack of hardware interlocks. When in operation, the nominal hazard zone is only a few meters in diameter. Precautions are taken when the laser is in operation, we currently use it in closed environments where all occupants are wearing eye protection (we are hoping to relax this restriction with our safety officers).