Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Reexamination Certificate
1999-12-15
2002-06-04
Ham, Seungsook (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
C359S397000
Reexamination Certificate
active
06399942
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical apparatus for capturing confocal images and a method of three-dimensional measurement using the apparatus.
2. Discussion of the Background
By utilizing a confocal optical system, the position (hereinafter referred to as the height) of the object measured in the direction of the optical axis (hereinafter referred to as the z-axis direction) can be measured accurately. Before description of the prior art, the principle of measurement of the height by a confocal optical system is explained. A basic configuration of the confocal optical system is shown in FIG.
10
. Illumination emitted from the point light source
101
passes through the half-mirror
102
and is refracted by the objective lens
103
to converge on the object. The light that is reflected by the object and enters the objective lens
103
again is converged by the objective lens
103
and then diverted by the half-mirror
102
toward the pinhole
104
disposed at the same position optically as the point light source
101
. The amount of light that passes through the pinhole
104
is detected by the photodetector
105
. This is the basic configuration of the confocal optical system. By using this optical system, the height of a point on the surface of the object can be measured in the following manner. When a point on the surface on which light for illumination is shone is at the position conjugate to the point light source
101
, the light reflected from the point focuses on the position of the pinhole
104
, another conjugate position. Therefore, a large amount of light passes through the pinhole
104
. The amount of light passing through the pinhole
104
sharply decreases with the distance from the position conjugate to the point light source to the point on the surface. This makes it possible to calculate the height of the point by moving the object with respect to the object lens
103
(hereinafter referred to as Z scan) and finding the position where the output of the photodetector
105
becomes greatest. This is the principle of measurement of height by a confocal optical system.
Since a confocal optical system of the above basic configuration can measure only one point on the surface of the object, scanning in the X and Y directions is required for three-dimensional measurement. However, a primitive method of three-dimensional measurement whereby the object is moved in the X and Y directions in a systematic pattern with respect to the objective lens at each height of stepwise scanning in the Z direction takes a very long time. Therefore, another method that executes Z scanning stepwise and performs X-Y scanning quickly by means of a laser beam or a rotating disk called a Nipkow disk while stopping Z scanning (keeping the distance between the object and objective lens fixed) at each of consecutive heights is commonly used. More specifically, this method performs image acquisition by repeating the steps of capturing a confocal image and moving the object to the next position in the Z direction. For every pixel position it finds the confocal image (Z position) in which the intensity of the pixel at that pixel position is greatest by comparing the intensities of the pixels at that pixel position for all the confocal images acquired. Finally, it calculates the three-dimensional shape of the object.
The confocal image acquisition system is most important for this measurement. Therefore, the confocal image acquisition system is described below as the prior art. There are two types of confocal image acquisition systems: the X-Y scanning type such as the laser scanning type, Nipkow disk scanning type, and table scanning type and the nonscanning type having a plurality of confocal optical systems arrayed in parallel in the X and Y directions. According to the number of illumination spots projected onto the surface of the object, the confocal image acquisition systems can be divided into two types: single spot and multispot (multibeam). The former includes the laser scanning type and the table scanning type, and the latter, the Nipkow disk scanning type and the nonscanning type. Since the present invention relates to the latter multibeam type, the principle of this type of confocal image acquisition system is described below.
FIG.
11
(
a
) shows the configuration of the Nipkow disk scanning confocal image acquisition system. FIG.
11
(
b
) shows the pinholes of a Nipkow disk. The Nipkow disk
111
is disposed at a focal plane (image-forming plane) of the objective lens
8
consisting of lenses
8
a
and
8
b
and a diaphragm
9
. The Nipkow disk
111
is rotated by the motor
112
. The Nipkow disk
111
has pinholes arranged in a spiral. The images of the pinholes are moved over the surface of the object in a raster pattern by one rotation of the Nipkow disk
111
. The Nipkow disk
111
was originally invented for raster scanning for television.
The Nipkow disk
111
is illuminated from above by the illuminating arrangement consisting of the light source
1
, pinhole
2
, and collimator lens
4
. Illumination that passes through the pinholes of the Nipkow disk
111
is refracted by the objective lens
8
and forms the images of the pinholes (illumination spots) on the surface of the object A. The light that is reflected from each spot and passes through the objective lens
8
is refracted to converge on the corresponding pinhole. The amount of reflected light that passes through the pinhole is greatest when the surface reflecting the light is at the position conjugate to the pinhole and decreases abruptly with the distance from the conjugate position to the surface. This produces the effect of a confocal optical system. The light that passes through the pinholes is diverted by the beam splitter
113
, passes through the image re-forming lens
114
, and forms an image of the pinholes on the detector array
11
. By rotating the Nipkow disk
111
, the light reflected from the illumination spots, which sweep the surface of the object in a raster pattern, moves over the whole detector array
111
and thereby a confocal image is obtained. This confocal image acquisition system using a Nipkow disk is herein called prior art A.
Next, the nonscanning confocal image acquisition system is described below. The nonscanning confocal image acquisition system is not so common, but it is disclosed in Japanese patent application laid-open 265918/1992, 181023/1995, and 257440/1997 and described in a paper written by H. J. Tiziani, et al., “Three-Dimensional Analysis by a Microlens-Array Confocal Arrangement”, Applied Optics, Vol. 33, No. 4, pp. 567-572 (1994). The apparatus disclosed in Japanese patent application laid-open 265918/1992 and the one disclosed in Japanese patent application laid-open 257440/1997, which was invented by the same inventor as the present invention, are described below as examples of the nonscanning confocal image acquisition system.
First, the apparatus disclosed in Japanese patent application laid-open 265918/1992 is described with reference to FIG.
12
. Illumination emitted from the light source
1
is refracted by the collimator lens
4
into parallel-ray light and shone over the pinhole array
7
. The pinhole array
7
consists of a plurality of pinholes arranged on the same plane. Each pinhole of the pinhole array
7
performs the same function as a point light source, and the pinhole array
7
is equivalent to arrayed point light sources. The light passing through the pinholes of the pinhole array
7
passes through the half-mirror
121
. The light is then converged by the objective lens
8
consisting of lenses
8
a
and
8
b
and a telecentric diaphragm
9
and shone on the object A in small spots. The light that is reflected from each spot on the object A enters the objective lens
8
converges on the corresponding pinhole of the pinhole array
7
. The light is then diverted by the half-mirror
121
away from the pinhole array
7
to the detector pinhole array
10
aligned with the pinhole array
7
so
Ham Seungsook
Kanesaka & Takeuchi
Sohn Seung C.
Takaoka Electric Mfg. Co., Ltd.
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