Optics: measuring and testing – Range or remote distance finding – Triangulation ranging to a point with two or more projected...
Reexamination Certificate
2001-10-15
2003-09-09
Tarcza, Thomas H. (Department: 3662)
Optics: measuring and testing
Range or remote distance finding
Triangulation ranging to a point with two or more projected...
C356S003100, C356S004010, C348S131000, C348S132000
Reexamination Certificate
active
06618123
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a technique regarding a range finder capable of taking three-dimensional information of a subject (namely, a three-dimensional camera capable of measuring a range image).
FIG. 21
is a diagram for showing the structure of a conventional range finder. In
FIG. 21
, a reference numeral
51
denotes a camera, reference numerals
52
a
and
52
b
denote light sources, a reference numeral
55
denotes a light source control unit and a reference numeral
56
denotes a distance calculation unit. The light source control unit
55
makes the light sources
52
a
and
52
b
alternately emit light every field cycle in synchronization with a vertical synchronizing signal of the camera
51
.
At this point, it is assumed that the optical center of the camera lies at the origin with the optical axis direction of the camera set as the Z-axis, the horizontal direction set as the X-axis and the vertical direction set as the Y-axis, that the direction of a viewing point from the light sources is at an angle &phgr; against the X-axis, that the direction of the viewing point from the camera is at an angle &thgr; against the X-axis, and that the light sources are positioned at (0,-D), namely, the base line length is D. The depth value Z of the viewing point P is calculated in accordance with the principle of triangulation calculation as follows:
Z=D
tan &thgr; tan &phgr;/(tan &thgr;−tan &phgr;) (1)
In order to obtain the angle &phgr;, predetermined light patterns are projected by the light sources
52
a
and
52
b.
As the light sources
52
a
and
52
b
, for example, flash light sources
57
and
58
such as a xenon flash lamp are longitudinally disposed with reflector plates
57
and
58
disposed behind to be shifted in the lateral direction as shown in FIG.
22
A.
FIG. 22B
is a plan view of the light sources of FIG.
22
A. The light sources
52
a
and
52
b
radiate light in ranges A and B, respectively.
FIG. 23
is a diagram for showing light patterns radiated from the light sources
52
a
and
52
b
. In
FIG. 23
, the brightness obtained by projecting the light on a virtual screen Y is indicated along a direction of an arrow shown in the drawing. Specifically, the light projected from each of the light sources
52
a
and
52
b
has a characteristic that it is brightest on the center axis and is darker toward the periphery. Such a characteristic is exhibited because the reflector plates
59
and
60
each in the shape of a semi-cylinder are respectively disposed behind the flash light sources
57
and
58
. Also, since the reflector plates
59
and
60
are shifted laterally in their directions, the projection ranges of the light sources
52
a
and
52
b
partially overlap each other.
FIG. 24
is a diagram for showing the relationship between the light projection angle &phgr; in an H direction of FIG.
23
and the light intensity. The H direction accords with the direction of a crossing line between the virtual screen Y and one optional plane S among a plurality of planes each including the light source center and the lens center. In a region &agr; of
FIG. 24
, one of the light patterns projected from the light sources
52
a
and
52
b
is bright relatively on the right hand side and the other is bright relatively on the left hand side, whereas the brightness of the light pattern is varied also along the height direction (Y-axis direction).
FIG. 25
is a graph for showing the relationship between the light intensity ratio between the two kinds of projected light in the region &agr; of FIG.
24
and the light projection angle &phgr;. As shown in
FIG. 25
, the light intensity ratio and the angle &phgr; are in a one-to-one corresponding relationship in the region &agr;.
In order to measure a distance, the two kinds of light patterns are alternately projected on a flat plane vertically provided so as to face the light sources at a predetermined distance and reflected light is taken by the camera
1
, so that data of the relationship between the light intensity ratio and the light projection angle as shown in
FIG. 25
can be previously obtained with respect to each Y-coordinate (corresponding to a Y-coordinate on the CCD). A data with respect to each Y-coordinate means a data with respect to each of the plural planes including the light source center and the lens center. Also, when the light sources
52
a
and
52
b
are disposed so that a line extending between the lens center of the camera
51
and the light sources
52
a
and
52
b
can be parallel to the X-axis of the CCD camera face, a distance can be accurately calculated by using the data of the relationship between the light intensity ratio and the light projection angle determined with respect to each Y-coordinate.
Assuming that a point P of
FIG. 21
is the viewing point, the angle &phgr; of the point P from the light source is measured by using the brightness ratio of the point P obtained images taken with the two kinds of light patterns projected and the relationship as shown in
FIG. 25
corresponding to the Y-coordinate of the point P. Furthermore, the angle &thgr; of the point P from the camera is determined on the basis of the position in the image (namely, the pixel coordinate values of the point P) and camera parameters (such as the focal length and the position of the optical center of the lens system). Then, the distance is calculated in accordance with the equation (1) based on these two angles &phgr; and &thgr; and the distance (base line length) D between the position of the light sources and the position of the optical center of the camera.
In this manner, when the light sources for generating the light patterns that are monotonically increased/decreased in accordance with the projection direction as in the region &agr; of
FIG. 24
are used, the three-dimensional measurement of a subject can be simply carried out.
However, in the conventional structure, the xenon flash lamp, which has a life of merely approximately 5000 stable emissions, is used as the light source. Therefore, when the range finder is used for a long period of time, maintenance such as exchange of the lamp should be frequently conducted. Also, the stability of the quantity of light emitted by the flash lamp is merely several %, and hence, higher measurement accuracy cannot be obtained.
Furthermore, a light source with a long life is, for example, an LED (light emitting diode), but the quantity of light emitted by one LED is small. Therefore, when the LED is singly used, the light quantity is so insufficient that the three-dimensional measurement cannot be stably carried out.
Moreover, since the projected light patterns are determined in accordance with the shapes of the reflector plates in the conventional structure, merely one set of light patterns can be generated in principle.
SUMMARY OF THE INVENTION
An object of the invention is providing a range finder usable for a long period of time and capable of executing stable three-dimensional measurement. Another object is easily generating optional light patterns in the range finder.
Specifically, the range finder of this invention for measuring a three-dimensional position of a subject by projecting light on the subject and receiving reflected light comprises a light source array unit in which a plurality of light sources are arranged; and a light source control unit for allowing at least two kinds of light patterns to be projected from the light source array unit by controlling a light emitting state of each of the plurality of light sources of the light source array unit.
According to this invention, since the light patterns are projected from the plural light sources included in the light source array unit, even when each light source has a small light quantity, a sufficiently large quantity of light can be projected on the subject as a whole, so that stable three-dimensional measurement can carried out. Also, since the light patterns are generated by controlling the light emitting states of the light sources of the
Azuma Takeo
Morimura Atsushi
Uomori Kenya
Wada Joji
Andrea Brian K
Harness & Dickey & Pierce P.L.C.
Matsushita Electric - Industrial Co., Ltd.
Tarcza Thomas H.
LandOfFree
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