Rangefinder

Details Rangefinder Rangefinder

2000-03-17

2002-08-27

Tarcza, Thomas H. (Department: 3662)

Optics: measuring and testing

Range or remote distance finding

With photodetection

C356S005040, C356S004060, C359S032000, C348S131000, C348S132000

Reexamination Certificate

active

06441888

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a rangefinder for measuring the three-dimensional (3D) shape or obtaining range information of an object.
FIG. 24
illustrates an exemplary configuration for a prior art rangefinder. The rangefinder shown in
FIG. 24
captures a set of images of an object by projecting light onto the object, thereby measuring the 3D shape of the object based on the principle of triangulation. The rangefinder shown in
FIG. 24
was designed to operate in real time.
As shown in
FIG. 24
, the rangefinder includes laser light sources
101
A and
101
B, half mirror
102
, light source controller
103
, rotating mirror
104
, rotation controller
105
, lens
107
, wavelength separating filters
108
A and
108
B, CCD's
109
A,
109
B,
109
C, signal processors
110
A,
110
B,
111
, distance calculator
112
and controller
113
. The wavelengths of laser beams emitted from the light sources
101
A and
101
B are slightly different from each other. The laser beams outgoing from the light sources
100
A and
101
B are combined with each other at the half mirror
102
. The intensities of the beams emitted from the light sources
101
A and
101
B are controlled by the light source controller
103
. The rotating mirror
104
is provided to scan the combined laser radiation and the rotation thereof is controlled by the rotation controller
105
. The laser radiation, which has been projected onto an object
106
and reflected therefrom, is condensed by the lens
107
, selectively passed through the wavelength separating filters
108
A and
108
B and then incident on the CCD's
109
A,
109
B and
109
C. The filters
108
A and
108
B separate parts of the reflected radiation with the same wavelengths as those of the light sources
101
A and
101
B, respectively. The CCD's
109
A and
109
B capture monochromatic images of the object
106
, while the other CCD
109
C captures a color image of the object
106
. The signal processors
110
A,
110
B and
111
are provided for these CCD's
109
A,
109
B and
109
C, respectively. The distance calculator
112
obtains, by computation, information about the distance or shape of the object
106
based on the intensities of the beams incident on the CCD's
109
A and
109
B. And the controller
113
synchronizes or controls the overall operating timing of this rangefinder.
Hereinafter, it will be described how the rangefinder shown in
FIG. 24
operates.
The laser light sources
101
A and
101
B emit laser beams with slightly different wavelengths. These laser beams are in the shape of a slit with an optical cross section crossing the scanning direction of the rotating mirror
104
at right angles. That is to say, if the rotating mirror
104
scans the laser beams horizontally, then the slitlike beams extend vertically.
FIG. 25
illustrates how the intensities of the laser beams projected from these two light sources
101
A and
101
B change with wavelength. As can be seen from
FIG. 25
, the beams emitted from these light sources
101
A and
101
B have close wavelengths. This is because the reflectance of the object
106
is less dependent on the wavelength in such a case. As described above, the laser beams emitted from the laser light sources
101
A and
101
B are combined into a single beam at the half mirror
102
. Then, the combined beam is scanned at the rotating mirror
104
toward the object
106
.
The rotation controller
105
drives the rotating mirror
104
on a field-by-field basis, thereby scanning the laser beams that have been projected from the light sources
101
A and
101
B. In this case, the light source controller
103
changes the intensities of the beams emitted from these light sources
101
A and
101
B as shown in FIG.
26
(
a
) within the cycle time of one field. That is to say, the intensities of the laser beams are changed while the rotating mirror is driven.
The laser radiation that has been reflected from the object
106
is condensed by the lens
107
toward the CCD's
109
A,
109
B and
109
C. The wavelength separating filter
108
A selectively transmits only a part of the laser radiation with the same wavelength as that of the beam emitted from the light source
101
A but reflects the remaining parts of the radiation with other wavelengths. On the other hand, the wavelength separating filter
108
B selectively transmits only a part of the laser radiation with the same wavelength as that of the beam emitted from the light source
101
B but reflects the remaining parts of the radiation with other wavelengths. As a result, respective parts of the laser beams that have been projected from the light sources
101
A and
101
B onto the object
106
and then reflected therefrom are incident on the CCD's
109
A and
109
B, respectively. And the rest of the laser radiation with other wavelengths is incident onto, and captured as a color image by, the CCD
109
C.
The signal processors
110
A and
1108
perform signal processing on the outputs of the CCD's
109
A and
109
B as is done for an ordinary monochromatic camera. On the other hand, the signal processor
111
performs signal processing on the output of the CCD
109
C as is done for an ordinary color camera.
The distance calculator
112
obtains distances for respective pixels based on the outputs of the CCD's
109
A and
109
B, the baseline length and the coordinates of the pixels.
Specifically, based on the outputs of the CCD's
109
A and
20
109
B, the distance calculator
112
calculates an intensity ratio of the reflected parts of the laser radiation. The relationship between the intensity ratio and the scanning time is known. Accordingly, if an intensity ratio is given, then a specific point in time during one scan period can be estimated automatically. And the angel &phgr; of rotation of the rotating mirror
104
can be derived from the specific point in time. For example, as shown in FIG.
26
(
b
), supposing the intensity ratio is Iao/Ibo, then the scanning time is estimated to be t
0
, from which the angle &phgr; of rotation of the rotating mirror
104
is known. This angle &phgr; corresponds to the angle formed by a visual axis, which extends from the light source to the object, with the X-axis.
The relationship between the scanning time t and the angle &phgr; of rotation of the rotating mirror
104
is already known, too. Thus, a characteristic table representing the relationship between the intensity ratio Ia/Ib and the angle &phgr; of rotation may be prepared by substituting the angle &phgr; of rotation for the axis of abscissas of the graph shown in FIG.
26
(
b
). In such a case, the angle &phgr; of rotation can be derived directly from the given intensity ratio without using the scanning time t.
FIG. 27
diagrammatically illustrates how the distance calculator
112
derives the distance. In
FIG. 27
, O is the center of the lens
107
, P is a point of incidence on the object
106
and Q is a point at which the axis of rotation of the rotating mirror
104
is located. For the illustrative purposes, the CCD
109
is illustrated as being located closer to the object
106
. The distance between the CCD
109
and the center O of the lens
107
is identified by f. Supposing the baseline length between the points O and Q is L, the angle formed by a visual axis QP with the X-axis within the XZ plane is &phgr;, the angle formed by another visual axis OP with the X-axis within the XZ plane is &thgr; and the angle formed by still another visual axis OP with the Z-axis within the YZ plane is &ohgr;, the three-dimensional coordinates (X, Y, Z) of the point P are given by the following equations:
X=L
·tan &phgr;/(tan &thgr;+tan &phgr;)
Y=L
·tan &thgr;·tan &phgr;·tan &ohgr;/(tan &thgr;+tan &phgr;)
Z=L
·tan &thgr;·tan &phgr;/(tan &thgr;+tan &phgr;)
In these equations, the angle &phgr; can be derived from the intensity ratio of the reflected beams that are being monitored by the CCD's
109
A and
109
B as described above. On the other hand, t

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