| 摘要 |
PROBLEM TO BE SOLVED: To accurately measure the distance to an optical axis irrespective of the angle and irregularity of a target surface. SOLUTION: Three counter circuits 8, 9, 10 start counting action after counted values are all reset at the timing of emission of a laser beam, and the timing of reception of the laser beam reflected from a target is detected by three CFD(constant fraction discriminator) circuits 5, 6, 7 having different characteristics. Then the counting action is stopped and distance measurement data are output. Interval detection circuits 11, 12 and determining circuits 13, 14 calculate (variation in timing of reception)/(variation in delay time) from the delay time set in CFD circuits 8, 9, 10 and the timing of reception of the output, determine the CFD circuit that outputs the optimum timing of reception, and control a selecting circuit 15 to output the optimum distance data from among the counter circuits 8, 9, 10.
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