Image analysis – Applications – 3-d or stereo imaging analysis
Reexamination Certificate
2000-04-20
2002-04-16
Mancuso, Joseph (Department: 2623)
Image analysis
Applications
3-d or stereo imaging analysis
Reexamination Certificate
active
06373978
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a three-dimensional shape measuring apparatus, and particularly to a three-dimensional shape measuring apparatus using a confocal imaging system.
2. Discussion of the Background
A three-dimensional shape measuring apparatus using a confocal imaging system is used for automatic inspections of minute products on production lines.
The basic configuration of the confocal imaging system is shown in FIG.
1
. Light emitted from a pinhole
1
passes through a half mirror
2
. The light from the half mirror
2
is then converged by an objective lens
3
toward an object. The light which strikes the surface of the object is reflected. Of the reflected light, the light which enters the objective lens
3
is caused to converge by the objective lens
3
, and is then deflected by the half mirror
2
toward the pinhole
4
which is disposed at the same position optically as the pinhole
1
. The quantity (intensity) of the light passing through the pinhole
4
is measured by a detector
5
. This is the basic configuration of the confocal imaging system. The position of a point on the surface of an object in the Z direction (the direction of the optical axis of the objective lens
3
) can be measured using this confocal imaging system as follows.
When a point P on the surface of an object is at a position where the light converges, the light reflected from the point P is focused on the pinhole
1
if the half mirror
2
does not exist. The reflected light deflected by the half mirror
2
therefore converges on the pinhole
4
which is located at the same position optically as the pinhole
1
, and most of this light passes through the pinhole
4
. However, as the point P moves away from the converging position of the illuminating light in the direction of the optical axis of the objective lens
3
(the Z direction), the position at which the reflected light converges also shifts away from the pinhole
4
and the amount of light which passes through the pinhole
4
abruptly decreases.
Therefore, the height of the point P on the surface of the object can be calculated by measuring the intensity of the reflected light which passes through the pinhole
4
using the detector
5
at differing distances while changing the distance between the object and the objective lens
3
by moving the object stage in the Z direction (or by moving the confocal imaging system), and then by determining the position where the intensity of the reflected light reaches the maximum. The position of an object point at which the intensity of the light reflected from that point becomes maximum is herein called the object-position-in-focus. As described above, the object-position-in-focus is the same position as the converging position of the light.
Further, a three-dimensional shape of an object can be measured by moving the object stage in the direction at right angles to the optical axis of the objective lens
3
(XY direction) to position points on the surface of the object on the optical axis in turn and repeating the above Z-position measurement. This method, however, requires moving the object stage in the Z direction for each of a large number of points to be measured, and therefore takes a long time for measurement.
For this reason, instead of moving the object stage in the Z direction for each point to be measured on the surface of the object, the three-dimensional shape is measured by moving the object stage stepwise in the Z direction and in the XY direction so that the object is scanned by the optical axis of the objective lens
3
at each stop position of the object stage, sampling the intensity of the reflected light to obtain a two-dimensional image corresponding to the intensity of the light reflected from each measuring point on the surface of the object (this two-dimensional image is called a confocal image), and finding a confocal image for each pixel in which the intensity of light of the pixel is maximum among the thus-obtained confocal images. Accordingly, the height of the point on the surface of the object corresponding to the pixel from the Z position of the confocal image can be calculated. In this method, the object stage has to be moved in the Z direction only once, and therefore the measuring speed is improved in comparison with the above described method which is more faithful to the principle of measurement of the three-dimensional shape of an object.
However, since scanning in the XY direction by moving the object stage in the XY direction takes a long time, a method for scanning a laser beam using a light-deflecting means such as an AO element, an EO element, a galvano-mirror, or a polygon mirror, and scanning by rotating at high speed a disk (Nipkow disk) containing a number of pinholes spirally arranged, is used to further increase the measuring speed. The apparatus using these scanning methods is called a three-dimensional shape measuring apparatus using a scanning confocal imaging system. This type of apparatus has the following problems. Since the apparatus cannot simultaneously detect the reflected light from all points for measuring an object, the Z positions for various points gradually shift, one after another, by a small distance if acquisition of a confocal image is performed continuously moving the object stage in the Z direction. This slight shifting in the Z position causes errors. For this reason, the object stage must be moved by steps in the Z direction, and moving the object stage by steps takes a much longer time than moving it continuously. In addition, deviations in scanning and sampling timing cause errors in the XY positions of the measured points of a confocal image.
To acquire more accurate confocal images at a higher speed and to simplify the structure of the apparatus, Japanese Patent Applications Laid-open (JPA) No. 265918/1982 and No. 181023/1995 disclose three-dimensional shape measuring apparatuses which acquire confocal images without optical scanning by arranging confocal imaging systems in parallel (hereinafter referred to as an arrayed confocal imaging system).
The apparatus of JPA No. 265918/1982 is shown in
FIG. 2
, in which light emitted from a white-light source
6
is refracted into parallel light rays by a collimating lens
7
and directed onto a pinhole array
8
. The pinhole array
8
consists of a large number of pinholes arranged on the same plane. Each pinhole of the pinhole array
8
can be regarded as a point light source, and therefore the pinhole array
8
is equivalent to an array of point light sources. The light which passes through the pinholes of the pinhole array
8
then passes through a half mirror
2
, and the light emitted from the half mirror
2
is directed onto an object O by an objective lens
3
consisting of lenses
10
and
11
and a telecentric diaphragm
12
placed between the lenses
10
and
11
. The reflected light from the object O is converged through the objective lens
3
and is deflected by the half mirror
2
. It then enters a CCD sensor
9
. This configuration is equivalent to a plurality of confocal imaging systems arranged in parallel. Although confocal imaging systems generally must be disposed apart from one another by a distance five to ten times the diameter of the pinhole in order to provide a plurality of confocal imaging systems in parallel, the size of this apparatus is reduced to a reasonable size by using pinholes of a very small diameter and thereby disposing the confocal imaging systems more close together. In addition, by using a CCD sensor with a small aperture ratio (i.e. the ratio of the size of the photoelectric elements of a CCD to the pixels is very small), this apparatus eliminates the use of pinholes which are necessary on the detection side in the conventional configuration.
Next, the apparatus disclosed in JPA No. 181023/1995 is shown in FIG.
3
. The light source
6
of this apparatus is a laser beam source, and a beam expander
2
is used to obtain parallel light rays of a large diameter. The light
Bali Vikkram
Mancuso Joseph
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Takaoka Electric Mtg. Co., Ltd.
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