Radiant energy – Photocells; circuits and apparatus – With circuit for evaluating a web – strand – strip – or sheet
Reexamination Certificate
2001-12-11
2004-03-09
Pyo, Kevin (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
With circuit for evaluating a web, strand, strip, or sheet
C250S559220, C356S601000
Reexamination Certificate
active
06703634
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to 3D-shape measurement apparatuses and, more particularly, to a 3D-shape measurement apparatus which can suppress a reduction in measurement accuracy due to deformation of a scanning optical system, and variations in height accuracy depending on scanning positions, when the apparatus measures the 3D-shape of an object by linearly scanning the object with a laser beam or the like, employing a polarization/scanning/convergence means such as a polygon mirror and a f&thgr; lens, and then measuring the reflected light of the scanning light on the basis of the principle of triangulation.
BACKGROUND OF THE INVENTION
Conventional methods for geometric-optically measuring a 3D-shape are roughly classified into two methods as follows: a method of projecting various kinds of lights to an object, and measuring the reflected lights with a photodetector, and a method of measuring an object with cameras from multiple directions under natural light or normal lighting, and obtaining the 3D-shape of the object according to the correlation between plural images.
The former method is further classified into various methods according to the method of light projection, the type of the photodetector, and the positional relationship between a light source and the photodetector.
FIG. 14
is a schematic diagram illustrating a conventional 3D-shape measurement apparatus which is widely used for industrial equipment.
With reference to
FIG. 14
, a light beam emitted from a light source
1
is polarized with a rotating mirror
2
such as a polygon mirror, and a scanning light beam
4
is converged by a convergence/scanning lens
3
such as a f&thgr; lens to form a spot light
6
a
on a target
5
to be measured. With rotation of the rotating mirror
2
, the spot light
6
a
scans the target
5
along a straight line (hereinafter referred to as a scanning line
7
) up to a spot
6
b.
Among light beams irregularly reflected at the surface of the target
5
, a reflected beam
8
traveling in the direction different from the direction of the scanning beam
4
is focused to form an image on a position detector
10
such as a PSD or CCD camera through a photoreceptive optical system
9
, and height data of a point irradiated with the spot light
6
is obtained by triangulation from position data of the image, which is obtained by converting the reflected light
8
into an electric signal.
The spot light
6
scans the target
5
along the scanning line
7
, and the target
5
moves in synchronization with rotation of the rotating mirror
2
, in the direction (sub scanning direction
12
) perpendicular to a plane which is formed by the direction of the scanning line
7
(main scanning direction
11
) and the direction
40
along which the scanning light
4
travels, whereby the spot light
6
scans the target
5
two-dimensionally, and the stereoscopic 3D shape of the target
5
is measured by storing and arranging the height data at the respective scanning positions on a memory.
FIGS.
15
(
a
)-
15
(
c
) are diagrams for explaining problems of the height measurement by triangulation, in the conventional 3D-shape measurement apparatus.
Since, in the height measurement by triangulation, the reflected light is measured from the direction different from the direction of the scanning light
4
, it is affected by the shape of the target
5
or the distribution of reflectivity. Accordingly, a blind spot occurs as shown in FIG.
15
(
a
), or a height measurement error due to multiple reflection occurs as shown in FIG.
15
(
b
).
FIG.
15
(
c
) shows the case where the reflected light is measured from plural directions.
In FIG.
15
(
c
), when the shape of the target
5
is complicated or the luminance change is considerable, reflected light beams
8
a
(a blind spot occurs),
8
b
(double-reflection occurs),
8
c
(no influence by the target
5
), . . . are measured, and a height output value obtained from the reflected light beam
8
c
which is measured in the direction where no blind spot and no multiple reflection occur, must be selected.
FIG. 16
is a cross-sectional view illustrating the relationship between the scanning position and the image position of received light in the conventional 3D-shape measurement apparatus, for explaining the problems of triangulation in the case where the spot light
6
scans on the scanning line
7
.
With reference to
FIG. 16
, in the conventional 3D-shape measurement apparatus, when the reflected light
8
from the target
5
is guided to the position detector
10
through a photoreceptive optical system
9
which is independent of the scanning optical system comprising the rotating mirror
2
and the convergence/scanning lens
3
, the image position on the position detector
10
moves according to the scanning position, resulting in a height change H. Therefore, a position detector wider than the height measurement range is required, leading to degradation in performance, such as a reduction in measurement accuracy or a reduction in processing speed.
FIG. 17
is a perspective view illustrating the structure of the conventional 3D-shape measurement apparatus wherein the scanning optical system is included in the photoreceptive optical system.
With reference to
FIG. 17
, the photoreceptive optical system
9
shown in
FIG. 14
is divided into a photoreceptive optical system
9
a
and a photoreceptive optical system
9
b
, and the scanning optical system is placed between the photoreceptive optical system
9
a
and the photoreceptive optical system
9
b.
The reflected light
8
reaches the position detector
10
through the scanning optical system, and a movement of the reflected light
8
according to the scanning position is canceled by the scanning optical system. Then, a movement of the image on the position detector
10
is mainly caused by a height change of the target
5
, whereby the height measurement accuracy is increased, resulting in improved performance.
Furthermore, there is a 3D-shape measurement apparatus which solves the problems of triangulation shown in FIG.
15
(
c
) by providing plural sets of the photoreceptive optical system
9
a
, the photoreceptive optical system
9
b
, and the position detector
10
shown in
FIG. 17
, and measuring the reflected light
8
from the target
5
from multiple directions.
The conventional 3D-shape measurement apparatuses are constructed as described above.
FIGS.
18
(
a
) and
18
(
b
) are diagrams for explaining a positional deviation of spot light, and a height error.
In the case where the conventional 3D-shape measurement apparatus measures the reflected light from multiple directions by straight-line scanning employing the scanning optical system to perform 3D-shape measurement by triangulation, when the photoreceptive optical system
9
which measures the reflected light
8
does not change and only the position of the spot light
6
on the target
5
changes from point A to point B as shown in FIG.
18
(
a
), the image position on the position detector
10
changes from A′ to B′, whereby the height of the target
5
cannot be measured accurately.
Especially when the spot light
6
is guided to the target
5
through the scanning optical system which comprises the polarization means by the rotating mirror such as a polygon mirror or a galvano mirror, and the convergence/scanning lens such as a f&thgr; lens, deterioration of the rotating part of the rotating mirror or deformation of the f&thgr; lens holder causes a deviation in the angle or position of the optical axis of the scanning light
4
with a change in environment such as temperature or with the passage of time, whereby the position of the spot light
6
changes, resulting in a difficulty in performing accurate height measurement.
Furthermore, in the case where the reflected light
8
is measured from multiple directions to accurately measure the height of the target
5
having a complicated shape as shown in FIG.
15
(
c
), when the position of the spot light
6
changes from point A to point B
Pyo Kevin
Wenderoth , Lind & Ponack, L.L.P.
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