Optics: measuring and testing – Range or remote distance finding – Triangulation ranging to a point with one projected beam
Reexamination Certificate
1999-11-24
2001-09-25
Buczinski, Stephen C. (Department: 3662)
Optics: measuring and testing
Range or remote distance finding
Triangulation ranging to a point with one projected beam
C250S201600, C396S106000, C396S109000
Reexamination Certificate
active
06295124
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, a light-projecting section projects a beam toward an object to be measured (object to be photographed), the part of beam reflected by the object is received by a position sensitive detector (PSD) in a light-receiving section, and the distance to the object is measured (range-finding is effected) according to a signal outputted from the PSD.
FIG. 1
is a view showing an arrangement of the front face of a camera. As depicted, a finder
9
and a lens mount
8
A holding a taking lens
8
are disposed in the front face portion of the camera body. As a rangefinder apparatus, a light-projecting device
4
and a PSD
5
are disposed in alignment with the sidewise direction, i.e., base-length direction
50
, on the upper side of the lens mount
8
A.
FIGS. 2A and 2B
are explanatory views of range-finding by the light-projecting device
4
and PSD
5
. As shown in FIG.
2
A, when the object to be measured is located at position P
1
, then the reflected light of the beam projected to the object from the light-projecting device
4
is received, by way of a light-receiving lens
5
A, at position p
1
on the PSD
5
. When the object is located at position P
2
, then the reflected light of the beam projected to the object from the light-projecting device
4
is received, by way of the light-receiving lens
5
A, at position p
2
on the PSD
5
. Then, as shown in
FIG. 2B
, the center-of-gravity position
400
of the beam
300
received by the PSD
5
is detected, and the distance to the object is detected according to thus detected center-of-gravity position
400
.
SUMMARY OF THE INVENTION
However, the inventor has found that the above-mentioned conventional rangefinder apparatus has the following problems. Namely, if the beam projected from the light-projecting device
4
toward the object to be measured does not completely impinge on the object, then a beam eclipse will occur in the reflected beam received by the PSD
5
. The center-of-gravity position
401
of the beam
301
received by the PSD
5
when the beam eclipse occurs differs from the center-of-gravity position
400
of the beam
300
received by the PSD
5
when no beam eclipse occurs. Therefore, the distance to the object detected when the beam eclipse occurs becomes erroneous.
Also, as long as the beam received by the PSD
5
has a constant size, the shorter is the distance between the light-projecting device
4
and the light-receiving lens
5
A in the base-length direction
50
, the greater becomes the difference occurring in the measured distance value, whereby fluctuations in the center-of-gravity position caused by beam eclipses yield greater range-finding errors.
In order to overcome the above-mentioned problems, it is an object of the present invention to provide a rangefinder apparatus which can carry out accurate range-finding even when a beam eclipse occurs.
The rangefinder apparatus in accordance with the present invention comprises: (1) a light-projecting section for successively projecting toward an object to be measured a reference beam, a first correction beam, and a second correction beam having an identical emission center-of-gravity position with respect to a base-length direction and respective emission light intensity distributions different from each other; (2) a light-receiving section for receiving reflected light of the beam projected to the object from the light-projecting section at a light-receiving position corresponding to a distance to the object, and outputting distance information corresponding to the light-receiving position; and (3) correcting means which determines a correction value by correcting a beam eclipse with reference to a correction expression according to respective distance information items outputted from the light-receiving section when the beam projected from the light-projecting section is the reference beam, the first correction beam, and the second correction beam, and adds the correction value to the distance information outputted from the light-receiving section when the projected beam is the reference beam, so as to determine the distance to the object.
According to this rangefinder apparatus, the reference beam, the first correction beam, and the second correction beam having an identical emission center-of-gravity position with respect to the base-length direction and respective emission light intensity distributions different from each other are successively projected from the light-projecting section toward the object to be measured. The reflected light of each beam projected to the object by the light-projecting section is received by the light-receiving section at the light-receiving position corresponding to the distance to the object, and distance information corresponding to the light-receiving position is outputted therefrom. Then, the correcting means determines a correction value by correcting the beam eclipse with reference to a correction expression according to respective distance information items outputted from the light-receiving section when the beam projected from the light-projecting section is the reference beam, the first correction beam, and the second correction beam, and adds the correction value to the distance information outputted from the light-receiving section when the projected beam is the reference beam, so as to determine the distance to the object.
In particular, it is preferred that the emission light intensity distribution of at least one of the reference beam, the first correction beam, and the second correction beam with respect to the base-length direction be asymmetrical about the emission center-of-gravity position. In this case, the angular range where the beam eclipse correction is appropriately carried out can be widened in a laterally symmetrical manner.
In the rangefinder apparatus in accordance with the present invention, the correction expression may be determined beforehand according to a correlation value (e.g. difference) among distance information items outputted from the light-receiving section with respect to respective light-projecting angles of the reference beam, first correction beam, and second correction beam projected from the light-projecting section. In this case, the beam eclipse correction is appropriately effected in the correcting means. In particular, the correction expression may comprise a plurality of expressions different from each other in respective partial ranges into which a range available by the correlation value is divided. Also, the correcting means may select one of a plurality of expressions different from each other in respective partial ranges with reference to switching standards different from each other according to whether the beam eclipse is generated on the right side or left side. In these cases, an accurate beam eclipse correction is possible.
In the rangefinder apparatus in accordance with the present invention, the correcting means may correct the beam eclipse only if the difference between respective distance information items outputted from the light-receiving section when the beam projected from the light-projecting section is the reference beam, the first correction beam, and the second correction beam is not smaller than a first reference value. In this case, unnecessary corrections are not effected, whereby the processing time is shortened, or the range-finding error would not increase upon carrying out corrections. A weighted-averaging means may further be provided so as to weight, if the above-mentioned difference is smaller than the first reference value, two or more distance information items among respective distance information items outputted from the light-receiving section when the beam projected from the light-projecting se
Buczinski Stephen C.
Fuji Photo Optical Co., Ltd.
Leydig , Voit & Mayer, Ltd.
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