ELECTRO-OPTICAL RANGING SYSTEM FOR DISTANCE MEASUREMENTS TO MOVING TARGETS

摘要

ELECTRO-OPTICAL RANGING SYSTEM FOR DISTANCE MEASUREMENTS TO MOVING TARGETS An electro-optical ranging system for measuring the distance to a moving target object. A transceiver illuminates a small portion of the target object with a narrow beam of light modulated by a reference R-F signal. Reflected light is received and focused upon a photodetector for demodulation to generate a detected R-F signal. A preliminary measurement of the relative phase of the reference and detected signals is made by adjusting the relative phase using a digitally-controlled phase shifter until the output of a comparator circuit is as nearly null as possible without exceeding a digital input word corresponding to a distance less than or equal to the target object. The average amplitude of the comparator output corresponding to the aforementioned preliminary digital word is determined, and the average comparator output corresponding to that word as modified by the addition of one bit thereto is next determined. The actual distance to the surface of the target object is then calculated by interpolating between the two resulting words to find an equivalent word corresponding to a null phase-comparator output. Errors due to changes in the D-C offset of the comparator output are eliminated by A-C coupling the comparator's input and output utilizing a chopper stabilization circuit.