Wide-Angle Optical Ranging System

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Abstract
A relatively simple and inexpensive near-infrared (IR) ranging system is being developed for mobile robot navigation and collision avoidance. Active triangulation ranging is employed with about 5 degree spatial resolution over a nominal field-of-regard of 100° in azimuth and 30° in elevation. Under typical indoor conditions, fairly accurate target detection and range measurements are obtained to about 8 meters in the dark and about 5 meters in the light. No mechanical scanning is employed, and the entire field-of-regard can be scanned in 0.1 to 1 second, depending upon the required accuracy, allowing range measurements to be taken in real-time while the robot is in motion. The transmitter consists of a number of high-power near-IR light-emitting diodes (LEDs) arranged in a partial spherical array behind a spherical lens, so as to produce a corresponding number of narrow, evenly spaced beams that interrogate the field-of-regard. The LEDs in the array are sequentially activated at a particular repetition rate, and a synchronous receiver detects reflected energy from targets within its field-of-view (FOV). The receiver consists of two identical units, each covering a FOV of about 50° by 50°. Each unit contains a Fresnel lens, an optical bandpass filter, a lateral-effect position-sensing detector, and the associated electronics to process and digitize the analog signals. The location of the centroid of reflected energy focused on the position-sensing detector is a function of the particular beam that is active and the range to the target being illuminated by that beam. The position signals from the detector (resulting from the sequential activation of LEDs in the transmitter) are collectively processed by a dedicated microcomputer to determine the ranges to valid targets throughout the sensor's FOV. Target azimuth and elevation are a function of the LED position in the transmitter array that is active at the time of detection. A look-up table derived from calibration data is used to perform the position-to-range conversions and to compensate for receiver nonuniformities. Detected-target ranges can be compared to a previously stored range-map of the area under surveillance for use in navigational or collision-avoidance algorithms.

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