Patent ID: 6421115
Filing Date: 2002-07-16
Classification: G01S,G02B

Abstract:
A distance measuring apparatus comprising:light projecting means for projecting light toward an object at a distance to be measured; light detecting means for detecting reflected light of the light projected toward the object, at a reception position on a position sensitive device according to the distance to the object, and for outputting a far signal, which increases with an increase in the distance if quantity of detected light is constant, and a near signal, which increases with a decrease in the distance if the quantity of detected light is constant; clamping means receiving the far signal and comparing the far signal with a level of a clamp signal, wherein said clamping means outputs the far signal if the far signal is not less than the level of the clamp signal, and otherwise outputs the clamp signal; arithmetic means for calculating a ratio of the near signal and a signal output from said clamping means to output an output ratio signal; integrating means for cumulatively integrating the output ratio signal and outputting an integral signal according to the integrating; and control means for controlling each of projection of the light by said light projecting means, the level of the clamp signal in said clamping means, and total integrating time for the output ratio signal in said integrating means, and for detecting a distance value, based on the integral signal output from said integrating means, wherein said control means: (a) sets the clamp signal to a first level, and detects a first distance value, based on the integral signal output from said integrating means when the total integrating time for the output ratio signal in said integrating means is a first time; (b) when the first distance value is larger than a first set distance, sets the clamp signal to a second level smaller than the first level, and detects a second distance value, based on the integral signal output from said integrating means when the total integrating time for the output ratio signal in said integrating means is a second time; (c) when the second distance value is smaller than a second set distance, or, when the second distance value is not smaller than the second set distance and a difference between the second distance value and the first distance value is smaller than a first set value, sets the clamp signal to the first level, detects a third distance value, based on the integral signal output from said integrating means when the total integrating time for the output ratio signal in said integrating means is a third time, and calculates the distance to the object, based on a sum of the first distance value and the third distance value; and (d) when the second distance value is not smaller than the second set distance and when the difference between the second distance value and the first distance value is not smaller than the first set value, sets the clamp signal to the second level, detects the third distance value, based on the integral signal output from said integrating means when the total integrating time of the output ratio signal in said integrating means is the third time, and calculates the distance to the object, based on a sum of said second distance value and said third distance value.