Optics: measuring and testing – Range or remote distance finding – Triangulation ranging to a point with one projected beam
Reexamination Certificate
2000-11-30
2001-12-25
Tarcza, Thomas H. (Department: 3662)
Optics: measuring and testing
Range or remote distance finding
Triangulation ranging to a point with one projected beam
C396S106000, C396S120000, C250S201400, C250S201600
Reexamination Certificate
active
06333782
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a distance measuring apparatus for measuring the distance to an object and, more particularly, to a distance measuring apparatus of an active type used in cameras and the like.
2. Related Background Art
The distance measuring apparatus of the active type used in the cameras and the like is normally constructed to detect the distance to the object in the following manner. First, an infrared emitting diode (hereinafter referred to as “IRED”) projects a light beam toward the object and a position sensitive detector (hereinafter referred to as “PSD”) detects reflected light of the thus projected beam. Output signals from this PSD are processed by signal processing circuits and a computing circuit and the computing circuit outputs the result of computation as distance data to a CPU. Then the CPU detects the distance to the object, based on this distance data.
Since there is the possibility of causing an error in distance measurement (ranging) based on only one light projection, it is conventional practice to employ a method of carrying out the light projection multiple times to generate a plurality of distance computation values and integrating the plurality of distance computation values with an integrating circuit provided with an integrating capacitor to effect averaging, as in the distance measuring apparatus described in Japanese Patent Application Laid-Open No. H10-281758. Then the CPU detects the distance to the object, based on distance data corresponding to the integration result of the integrating circuit.
The distance measuring apparatus constructed to integrate the distance computation values by use of the integrating capacitor, including the distance measuring apparatus described in the above Japanese application, however, had the following problem. Since the capacitor changes its capacitance with a change in ambient temperature, it posed the problem of ranging error. In addition, a capacitor has such characteristics as to change its capacitance with a lapse of time even in storage without being used, which was also the cause of the ranging error.
SUMMARY OF THE INVENTION
The present invention has been accomplished under such circumstances and an object of the invention is to provide a distance measuring apparatus that can reduce the ranging error due to the variation in the capacitance of the integrating capacitor.
(1) In order to achieve the above object, a distance measuring apparatus according to the present invention is an apparatus comprising light projecting means for projecting a beam toward an object to be measured; light receiving means for receiving reflected light of the beam projected toward the object, at a reception position according to a distance to the object and outputting a position signal according to the reception position; computing means for carrying out a predetermined operation based on the position signal from the light receiving means to generate a distance computation value according to the distance to the object; integrating means comprising an integrating capacitor, the integrating means charging or discharging the integrating capacitor according to the distance computation value generated by the computing means to integrate the distance computation value; detecting means for detecting the distance to the object, based on distance data corresponding to the result of integral in the integrating means; charging means for charging the integrating capacitor by letting a constant current flow for a predetermined time; and voltage calculating means for calculating a voltage of the integrating capacitor charged by the charging means, wherein the detecting means detects the distance to the object, based on a correction voltage being the voltage calculated by the voltage calculating means in a ranging routine, a reference voltage of the integrating capacitor preliminary calculated before the ranging routine, and the distance data.
In the distance measuring apparatus according to the present invention, the charging means charges the integrating capacitor by letting the constant current flow for the predetermined time in the ranging routine and the voltage calculating means calculates the correction voltage being the voltage of the integrating capacitor thus charged. The detecting means calculates the distance to the object, based on (1) this correction voltage, (2) the reference voltage of the integrating capacitor preliminarily calculated before the ranging routine, e.g., immediately after manufacturing of the distance measuring apparatus, and (3) the distance data corresponding to the integral result in the integrating means. The voltage after the flow of the constant current for the constant time in the integrating capacitor is related to the capacitance of the capacitor. Namely, the ranging error due to change in the capacitance of the integrating capacitor can be reduced, because the distance to the object is calculated with also considering the reference voltage, e.g., the voltage immediately after manufacturing and the correction voltage in actual ranging, in addition to the distance data.
It is preferable that the detecting means detect the distance to the object, based on corrected distance data Ra given by Ra=(&agr;1/&bgr;1)×D (where D is the distance data, &agr;1 the reference voltage, and &bgr;1 the correction voltage).
In this case, the detecting means detects the distance to the object, based on the corrected distance data Ra obtained by converting the distance data to data upon calculation of the reference voltage, for example, upon manufacturing of the distance measuring apparatus, which can reduce the ranging error due to the change in the capacitance of the integrating capacitor.
In the distance measuring apparatus according to the present invention, it is also preferable that the detecting means detect the distance to the object, based on corrected distance data Rb given by Rb=[&agr;1/{(&bgr;1−&agr;1)×A+&agr;1}]×D+(&bgr;1−&agr;1)×B (where D is the distance data, &agr;1 the reference voltage, &bgr;1 the correction voltage, and A and B correction coefficients).
The various members and housing constituting the distance measuring apparatus sometimes undergo distortion with change in ambient temperature. The distortion of the housing etc. will cause distortion of the optical system of the distance measuring apparatus, which can be the cause of degradation of ranging accuracy. In such cases, it is difficult to improve the ranging accuracy by simply making use of the value of the ratio of the reference voltage to the correction voltage. It thus becomes feasible to improve the ranging accuracy by employing such a configuration that the correction coefficient A and correction coefficient B of the distance measuring apparatus are preliminarily calculated and the detecting means detects the distance to the object, based on the above corrected distance data Rb.
Further, in the distance measuring apparatus according to the present invention, it is preferable that the detecting means detect the distance to the object, based on corrected distance data Ra given by Ra=(&agr;1/&bgr;1)×D (where D is the distance data, &agr;1 the reference voltage, and &bgr;1 the correction voltage), when a difference between the correction voltage and the reference voltage is smaller than a predetermined value and that the detecting means detect the distance to the object, based on corrected distance data Rb given by Rb=[&agr;1/{(&bgr;1−&agr;1)×A+&agr;1}]×D+(&bgr;1−&agr;1)×B (where D is the distance data, &agr;1 the reference voltage, &bgr;1 the correction voltage, and A and B correction coefficients), when the difference between the correction voltage and the reference voltage is not less than the predetermined value.
In this case, when the difference between the correction voltage and the reference voltage is smaller th
Andrea Brian
Fuji Photo Optical Co., Ltd.
Leydig , Voit & Mayer, Ltd.
Tarcza Thomas H.
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