Photography – With exposure objective focusing means – focusing aid – or... – Having auxiliary illumination
Reexamination Certificate
1999-10-19
2001-02-20
Perkey, W. B. (Department: 2851)
Photography
With exposure objective focusing means, focusing aid, or...
Having auxiliary illumination
C396S120000, C356S003040
Reexamination Certificate
active
06192199
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a rangefinder apparatus for measuring the distance to an object, and, in particular, to an active type rangefinder apparatus suitably used in a camera or the like.
2. Related Background Art
In active type rangefinder apparatus used in cameras and the like, an infrared light-emitting diode (IRED) projects a luminous flux toward an object to be measured, the reflected light of thus projected luminous flux is received by a position sensitive detector (PSD), a signal outputted from the PSD is arithmetically processed by a signal processing circuit and an arithmetic circuit and then is outputted as distance information, and the distance to the object is detected by a CPU. Namely, an integrating capacitor charged with a reference voltage V
REF
is discharged by a voltage value corresponding to the distance information signal. As a consequence, the voltage of the integrating capacitor decreases stepwise (C
INT
in FIG.
1
: first integration) as the distance information signal is inputted every time the IRED emits light (when the INT signal in
FIG. 1
is HIGH). Thereafter, the integrating capacitor is charged at a constant rate determined by the rating of a constant current source (C
INT
in FIG.
1
: second integration). Then, the time required for the second integration is measured, and the distance to the object is detected according to thus measured time.
SUMMARY OF THE INVENTION
Meanwhile, in the above-mentioned rangefinder apparatus, a comparator compares the voltage of the integrating capacitor and the reference voltage V
REF
during the period of the second integration. If it is determined that they coincide with each other, the comparator outputs the S
OUT
signal (the S
OUT
signal is made HIGH), so as to stop charging the integrating capacitor and terminate the measurement of the time required for the second integration.
If a wrong S
OUT
signal is outputted due to chattering and the like, however, then the integrating capacitor will not be charged with the reference voltage V
REF
but with a voltage lower than that by &Dgr;V. As a consequence, the time required for the second integration will be measured shorter, whereby errors will occur in detection of the distance to the object.
It is an object of the present invention to provide a rangefinder apparatus which can reduce errors in distance measurement.
The rangefinder apparatus in accordance with the present invention comprises: light-projecting means for projecting a luminous flux toward an object to be measured; light-receiving means for receiving reflected light of the luminous flux projected to the object at a light-receiving position on a position sensitive detector corresponding to a distance to the object, and outputting a signal corresponding to the light-receiving position; arithmetic means for carrying out an arithmetic operation according to the signal outputted from the light-receiving means, so as to output a distance signal corresponding to the distance to the object; integrating means, having an integrating capacitor, for carrying out first integration by discharging or charging the integrating capacitor according to the distance signal outputted from the arithmetic means so as to integrate the distance signal outputted from the arithmetic means, then carrying out second integration by charging or discharging the integrating capacitor with a constant current, and comparing the voltage of the integrating capacitor and a reference voltage with each other upon the second integration, so as to output a comparison result signal corresponding to the result of comparison; and detecting means for measuring the time of the second integration according to the comparison result signal outputted from the integrating means, and detecting the distance to the object according to the result of measurement; the rangefinder apparatus further comprising: comparison result signal detecting means for detecting, when the comparison result signal is outputted by the integrating means, whether or not there is an output of the comparison result signal after a lapse of a predetermined time from the outputting of the comparison result signal; and measurement terminating means for terminating the measurement of the time of the second integration when it is determined by the comparison result signal detecting means that there is an output of the comparison result signal.
In the rangefinder apparatus in accordance with the present invention, after a lapse of a predetermined time from the outputting of the comparison result signal by the integrating means, the comparison result signal detecting means detects whether or not there is an output of the comparison result signal. If it is determined that there is an output of the comparison result signal, then the measurement of the time of the second integration is terminated by the measurement terminating means. As a consequence, even when an output of the comparison result signal is generated due to chattering and the like, the time of the second integration can be measured accurately, whereby errors in distance measurement can be prevented from occurring.
The present invention will be more fully understood from the detailed description given hereinbelow and the accompanying drawings, which are given by way of illustration only and are not to be considered as limiting the present invention.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will be apparent to those skilled in the art from this detailed description.
REFERENCES:
patent: 5337116 (1994-08-01), Nonaka et al.
patent: 5659387 (1997-08-01), Yoshida
patent: 7-181038 (1995-07-01), None
Fuji Photo Optical Co., Ltd.
Leydig , Voit & Mayer, Ltd.
Perkey W. B.
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