Photography – With exposure objective focusing means – focusing aid – or... – Having auxiliary illumination
Reexamination Certificate
1999-10-19
2001-02-27
Perkey, W. B. (Department: 2851)
Photography
With exposure objective focusing means, focusing aid, or...
Having auxiliary illumination
C396S120000, C356S003040
Reexamination Certificate
active
06195510
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention n 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. In general, since errors may occur when the distance is measured upon a single light-projecting operation, light is projected a plurality of times so as to obtain a plurality of distance information items, which are then integrated by an integrating circuit so as to be averaged.
SUMMARY OF THE INVENTION
However, there still exist cases where errors occur in distance measurement results even in the above-mentioned rangefinder apparatus.
For example, light is projected to the object a plurality of times at the timings indicated by the line
201
of
FIG. 1
(light being projected when pulses are HIGH), and a capacitor charged with a reference voltage V
REF
is sequentially discharged in response to the distance information with respect to the object obtained by each light emission as indicated by the line
202
of
FIG. 1
(first integration). Then, after a predetermined number of light emissions, the capacitor is charged with a constant current by a constant current source (second integration), and the time required for the second integration is measured. Such a distance measuring operation may continuously be carried out a plurality of times, and the distance to the object may be determined according to the results of individual distance measuring operations.
In this case, in view of the fact that the second integration time varies depending on the distance to the object, after a lapse of the maximum second integration time from the completion of the first integration time, the next distance measuring operation may be started. In this case, if the actual second integration time is shorter, it will take a longer time until the next distance measuring operation is started. As a consequence, the charging voltage may drop due to dielectric absorption in the capacitor, whereby the second integration time may elongate by &Dgr;t
1
, &Dgr;t
2
due to the drops in charging voltage &Dgr;V
1
, &Dgr;V
2
, thus yielding errors in measurement.
In order to overcome such a technical problem, it is an object of the present invention to provide a rangefinder apparatus which can reduce errors in distance measurement.
For achieving such a problem, 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 signal outputted from the arithmetic means so as to integrate the 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 detecting the distance to the object according to the signal outputted from the integrating means; the rangefinder apparatus further comprising control means for causing the light-projecting means to restart projecting light after a lapse of a predetermined time from when the outputting of the comparison result signal from the integrating means is completed, so as to cause the integrating means to output a plurality of comparison result signals with respect to the same object, and causing the detecting means to detect the distance according to the plurality of comparison result signals.
In accordance with the present invention, when a plurality of distance measuring operations are carried out so as to determine the distance to the object to be measured, after a lapse of a predetermined time from the time when the second integration in one distance measuring operation is completed, the next distance measuring operation is started, whereby errors in measurement can be reduced, and the accuracy in distance measurement can be improved. Also, as the next distance measuring operation is started after a lapse of a predetermined time from the completion of the second integration in one distance measuring operation, the distance measuring time required for a plurality of distance measuring operations can be shortened.
The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus 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 become 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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