JPH10239036A - Three-dimensional measuring optical device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce speckle contrast without moving an object and also without significantly reducing the resolution in the X, Y directions by minutely scanning spots within the exposure time of a reflected light detector. SOLUTION: A galvanometer 11b(1) can change the inclination of a parallel plane 11a at high speed by the driving signal of a controller 11b(2). Since the inclination of the parallel plane 11a that has been inserted into an optical path becomes the parallel displacement of the whole spots, the scanning of the whole spots can be possible by changing the angle of the parallel plane 11a. The galvanometer 11b(1) is suitable for the control of angular change. By driving the galvanometer 11b(1) by the controller 11b(2) so as to synchronize with the exposing timing of a two-dimensional detector 10, minute scanning of spots can be achieved within the exposure time of the two-dimensional detector 10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical apparatus used for performing three-dimensional measurement of an object, and more particularly to an apparatus for detecting a position of an object in an optical axis direction using focus information.

[0002]

2. Description of the Related Art When a confocal optical system is used, it is possible to accurately measure a position (hereinafter, referred to as a height) of an object in an optical axis direction (hereinafter, referred to as a Z direction). Prior to the description of the prior art, the principle of height measurement using a confocal optical system will be described. FIG. 11 shows the basic configuration of the confocal optical system. Light emitted from the point light source 101 is condensed by the objective lens 103 and projected on an object. The light reflected from the object and incident on the objective lens 103 again enters the pinhole 104 located at the same optical position as the point light source 101 via the half mirror 102, and the amount of light passing through the pinhole 104 is detected by the detector. Measured by 105. This is the basic structure of the confocal optical system. With such an optical system, the height of a point on the surface of an object can be measured as follows. When the object surface is at a position conjugate to the point light source 101, the reflected light converges on the pinhole 104 surface, which is also at the conjugate position, and a large amount of reflected light
Pass through 04. However, when the object surface moves away from the position conjugate to the point light source, the amount of light passing through the pinhole 104 decreases rapidly. From this, if the distance between the object and the objective lens 103 is changed and the detector 105 finds a point showing the maximum output, the height of the object surface can be known. The above is the principle of height measurement by the confocal optical system.

[0003] The confocal optical system basically targets only one point on the surface of an object, but three-dimensional measurement requires planar measurement. In order to obtain a two-dimensional image (hereinafter referred to as a confocal image) using a confocal optical system, it is necessary to have some kind of scanning means or to make the confocal optical system parallel. A typical optical system for performing the latter parallelization is 2
There is a dimensional array type confocal optical system. The two-dimensional array type confocal optical system has a feature that extremely high-speed measurement is possible because each point of a two-dimensional image can be simultaneously exposed in parallel by the confocal optical system. As an apparatus having a two-dimensional array type confocal optical system, there is Japanese Patent Application No. 8-94682 already filed by the present inventors. This apparatus will be described with reference to FIG. 10 as a representative example of a two-dimensional array type confocal optical system.

[0004] Illumination light emitted from the light source 1 is collimated by the illumination pinhole 2 and the collimator lens 3 and is incident on the beam splitter 4. The illumination light that has passed down the beam splitter 4 is
At the focal position of each lens of the microlens array 5. The focal plane of the microlens array 5 is a pinhole array 6, and each pinhole is coaxial with each lens of the microlens array 5. Therefore, most of the illumination light passes through the pinhole array 6. The illumination light emitted from the pinhole array 6 is equivalent to the point light sources being arranged in parallel. The two-sided telecentric objective lens 7 composed of the lenses 7a and 7b and the aperture 8 serves as the pinhole array 7.
(That is, a large number of minute spots) are projected onto the object A. The reflected light from the object A is collected by the objective lens 7 near the pinhole array 6. The pinhole array 6 has a role of a pinhole in front of a detector of a point measurement type confocal optical system, and if there is an object surface at a focal position (convergence position) of each minute spot projected on the object A, Although a large amount of reflected light passes through the corresponding pinhole, when the surface of the object A deviates from the focal position, the amount of reflected light passing through the pinhole decreases. The reflected light that has passed through the pinhole array 6 is emitted as a parallel beam from each lens by the microlens array 5, deflected by the beam splitter 4, reduced in beam diameter by the reduction lens 9, and reduced by the two-dimensional detector 10. Its intensity is detected.

[0005] With such a structure, all points of the confocal image are detected simultaneously and in parallel. By moving in the z-axis direction to obtain a plurality of confocal images having different focal positions and finding an image having the maximum intensity at each point of the image, the surface shape of the object A can be measured.

The two-dimensional array type confocal optical system is suitable for industrial use because it can be exposed at a high speed because all points of an image can be exposed at the same time, has no moving parts, and can use a shutter.

[0007]

The problem with the optical system occurs when the object has a rough surface. The spot projected on the object A is basically light having a high coherence emitted from a point light source. If there are irregularities on the object surface in the spot, these reflected lights are converted into a pinhole array 6 which is an image plane. It causes interference in the vicinity. That is, speckle occurs. The occurrence of speckle has a significant adverse effect on the height measurement result. The speckle has higher contrast (hereinafter referred to as speckle contrast) as the light has higher coherence, and the higher the speckle contrast, the greater the influence on the height measurement.

Although it is possible to reduce speckle contrast by performing neighborhood smoothing processing by image processing and improve the accuracy of height measurement, the resolution in the X and Y directions is significantly reduced.

Although smoothing can be performed by vibrating an object, high-frequency vibration is not possible depending on the damage to the object due to high-frequency vibration and the weight and size of the object, and the two-dimensional array type cannot be used. The high speed of the focusing optical system may be lost, which is not desirable.

Accordingly, an object of the present invention is to provide an optical device for three-dimensional measurement capable of reducing speckle contrast without moving an object and without significantly reducing resolution in the XY directions.

[0011]

Prior to the description of the means, the basis thereof will be described. Since speckles are generated by irregularities on the object surface in the spot, if the irregularities are random (rough surfaces are generally random), scanning the spot will change the state of the irregularities and the speckle contrast will be random. change. By superimposing a speckle contrast that changes randomly by scanning, the speckle contrast can be reduced by the effect of smoothing. In general, if the speckle contrast is superimposed by scanning, the resolution in the X and Y directions is reduced. However, the two-dimensional array type confocal optical system is within one pixel for the following reason, that is, X
Speckle contrast can be reduced by scanning within a range in which the resolution in the Y direction does not decrease.

The two-dimensional array type confocal optical system projects a spot (an image of a pinhole array) on an object, and the spot pitch is 5 to 10 with respect to the spot diameter as shown in FIG.
Need to double. This is to prevent blurred light from an adjacent pinhole from entering a certain pinhole. Under these conditions, the pixel aperture ratio (spot area / 1 pixel area) of each point of the two-dimensional array type confocal optical system is extremely low. The large pixel size with respect to the spot diameter as described above allows the surface of the object included in the spot to sufficiently change even in a minute scan that scans the spot within one pixel. Means to appear enough. If this minute scanning is performed within the exposure time of the two-dimensional detector, the change in the speckle contrast is temporally superimposed and smoothed. As described above, the two-dimensional array type confocal optical system can reduce the speckle contrast without lowering the resolution in the XY directions by performing a minute scan of about one pixel within the exposure time of the two-dimensional detector. . The above-described theory is configured as an optical device for three-dimensional measurement as follows.

According to the first aspect of the present invention, one or more minute spots are projected onto an object through at least one objective lens, reflected light from the object is collected by the same objective lens, and the collected reflected light is detected. The optical device for measuring the surface position of the object from the focus information of the reflected light is provided with a micro-scanning means for micro-scanning the spot within the exposure time of the reflected light detector.

According to a second aspect of the present invention, the minute scanning means comprises a parallel plane disposed between the objective lens and the object, and an angle changing means for changing an angle of the parallel plane with respect to the optical axis. And

According to a third aspect of the present invention, the minute scanning means is constituted by a parallel plane disposed between the objective lens and the object at an angle to the optical axis, and a rotating means for rotating the parallel plane. Features.

According to a fourth aspect of the present invention, the micro-scanning means is constituted by a deflecting mirror disposed at the aperture stop position of the objective lens and an angle changing means for changing the angle of the deflecting mirror. .

According to a fifth aspect of the present invention, the minute scanning means is constituted by a deflecting prism disposed at the position of the aperture stop of the objective lens for deflecting a light beam and a rotating means for rotating the deflecting prism.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a first example of an embodiment of the present invention. S is a two-dimensional array type confocal optical system described in the related art. As the two-dimensional detector 10, the most common CCD television camera at present is used. A minute scanning means 11 is inserted between the objective lens 7 and the object A. The minute scanning means 11 includes a parallel plane 11a and a parallel plane 11
It comprises angle changing means 11b for changing the angle of a. The angle changing means 11b is a galvanometer 11b
(1) and the controller 11b (2). The controller 11b (2) is a galvanometer 11b
This is a part for controlling (1), and generates a drive signal for the galvanometer 11b (1). The controller 11b (2) is a galvanometer 11b.
A shutter timing signal is also issued to the two-dimensional detector 10 in synchronization with the drive signal for (1).

With such a configuration, fine scanning of the spot is realized as follows. Galvanometer 11b
(1) The controller 11b calculates the inclination of the parallel plane 11a.
It can be changed at high speed by the drive signal of (2). Parallel plane 11a inserted in the optical path as shown in FIG.
Is the parallel movement of the entire spot, so the parallel plane 1
By changing the angle of 1a, it is possible to scan the entire spot. For example, a parallel plane 11 having a thickness of about 2 mm
By changing a by ± 1 degree, a minute scan of about ± 10 μm is possible. The galvanometer 11b (1) is suitable for controlling such an angle change. By driving the galvanometer 11b (1) in accordance with the exposure timing of the two-dimensional detector 10 by the controller 11b (2), minute scanning of the spot within the exposure time of the two-dimensional detector 10 can be achieved.

In this example, one-dimensional minute scanning is performed.
Two-dimensional minute scanning is also possible using two parallel planes 11a. Further, the angle changing means 11b includes a parallel plane 11a.
If the angle can be changed, the galvanometer 11b (1) is not necessarily required, and for example, a resonance type scanner or a tuning fork may be used. In addition, it is not always necessary to control the exposure timing of the two-dimensional detector 10, and it is considered that more accurate measurement can be performed by controlling the exposure timing. Therefore, only the control is performed in this example.

FIG. 3 shows a second embodiment of the present invention. Except for the structure of the micro-scanning means 13, it is the same as the first example. In this example, instead of changing the angle of the parallel plane as in the first example, fine scanning is realized by changing the direction in which the parallel plane is inclined. FIG. 4 shows the fine scanning means 13 of the second example in detail. The rotating means 13b for rotating the parallel plane 13a is a ring type ultrasonic motor 13b
It is composed of (1) and a controller 13b (2), and a parallel plane 13a is attached to the hollow portion of the ring type ultrasonic motor 13b (1) at a slight angle. The controller 13b (2) outputs a drive signal for the ring-type ultrasonic motor 13b (1) and an exposure timing signal to the two-dimensional detector as in the first example. When the rotation axis of the ring-type ultrasonic motor 13b (1) is made to coincide with the optical axis of the objective lens 7 and the ring-type ultrasonic motor 13b (1) is rotated, the parallel plane 13a is rotated accordingly, and the parallel plane 1 is rotated.
The direction in which 3a is inclined changes. Parallel plane 1
Since the inclination of 3a has the effect of parallel movement of the entire spot as described in the first example, if the direction of inclination changes, the direction of parallel movement will change, and the ring-type ultrasonic motor 13b (1) The rotation results in a circular scan of the spot.

Of course, the motor of the rotating means 11b does not need to be the ring-type ultrasonic motor 13b (1), but may be a general motor having a central axis to rotate the parallel plane 13a using gears or belts. . A similar effect can be obtained by inserting a large parallel plane circumferential portion into the optical path of the objective lens 7 as shown in FIG.

FIG. 6 shows a third embodiment of the present invention. The two-dimensional confocal optical system is basically the same as that of the first and second examples, except that the optical path of the objective lens 7 is bent 90 degrees at the position of the stop. At the position of the stop, a deflecting mirror 14a and an angle changing means 14b for changing the angle between the deflecting mirror 14a are attached, and the deflecting mirror 14a has an angle of 45 degrees with respect to the optical axis. The configuration of the angle changing means 14b is the same as that of the first example, except that the galvanometer 14b (1) and the controller 14b are used.
The role of the controller 14b (2) is the same as that of the first example. When the angle of the deflecting mirror 14a changes, the directions of all the principal rays change, and as a result, the entire spot moves in parallel. That is, scanning can be performed by changing the angle of the deflecting mirror 14a by the angle changing means 14b. This scanning mechanism is the same as the scanning mechanism of a general laser scanning microscope. The only difference is that in the case of laser scanning, one spot is scanned, whereas in this example, all spots are scanned simultaneously.

FIG. 7 shows a fourth embodiment of the present invention. The two-dimensional array type confocal optical system is basically the same as those of the first and second examples. At the position of the stop of the objective lens 7, a minute scanning means 15 is arranged. Micro scanning means 15
Comprises a deflecting prism 15a and a rotating means 15b for the deflecting prism 15a as shown in FIG.
a is a wedge shaped ring type ultrasonic motor 15b
It is attached to the hollow part of (1). The role of the controller 15b (2) is the same as in the second example. Since the deflecting prism 15b changes the direction of all the light beams including the chief light beam, the entire spot is translated in the same manner as the mirror in the third example is inclined. When the deflecting prism 15b is rotated by the rotating means 15b, the direction of parallel movement changes, so that a circular scan is performed.

Although the above example is directed to a two-dimensional array type confocal optical system, it goes without saying that a one-dimensional array type confocal optical system is a point measurement type confocal optical system. Is also good. Basically, a measurement optical system that projects a minute spot on an object through an objective lens, collects reflected light through the same objective lens, and evaluates defocus and blur amount,
Even if the illumination light is not a laser light (even a white light), it is considered that a speckle problem occurs if the object surface in the spot has irregularities. The present invention is applicable to all such measurement optical systems.

According to the present invention, the scanning of a minute distance of about one pixel is performed within the exposure time of the detector by using an actuator capable of high-speed operation such as a motor or a galvanometer. It is possible to reduce the speckle contrast with respect to an object having a rough surface without substantially reducing the resolution and the resolution in the X and Y directions, and high-speed and high-accuracy three-dimensional measurement can be realized.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first example of an embodiment of the present invention.

FIG. 2 is a diagram for explaining a minute scanning unit according to the first embodiment of the present invention;

FIG. 3 is a diagram showing a second example of the embodiment of the present invention.

FIG. 4 is a diagram for explaining a micro-scanning unit according to a second example of the embodiment of the present invention;

FIG. 5 is a diagram for explaining another method for realizing the micro-scanning means of the second example of the embodiment of the present invention.

FIG. 6 is a diagram showing a third example of the embodiment of the present invention.

FIG. 7 is a diagram showing a fourth example of an embodiment of the present invention.

FIG. 8 is a diagram for explaining a minute scanning unit according to a fourth example of the embodiment of the present invention;

FIG. 9 is a diagram for explaining a relationship between a pinhole diameter and a pinhole pitch.

FIG. 10 is a diagram for explaining the prior art of the present invention.

FIG. 11 is a diagram for explaining a confocal optical system.

[Explanation of symbols]

 A Object 1 Light source unit 2 Illumination pinhole 3 Collimator lens 4 Polarization beam splitter 5 Microlens array 6 Pinhole array 7 Objective lens 8 Aperture 9 Reduction lens 10 2D detector 11 Microscanning means 13 Microscanning means 14 Microscanning means 15 Micro scanning means

Claims (5)

[Claims] At least one minute spot is projected onto an object through at least one objective lens, reflected light from the object is collected by the same objective lens, the collected reflected light is detected, and reflected light is detected. An optical device for measuring a surface position of an object from focusing information, comprising: a micro-scanning means for micro-scanning the spot within an exposure time of a reflected light detector. 2. The micro-scanning means according to claim 1, wherein the micro-scanning means comprises a parallel plane disposed between the objective lens and the object, and angle changing means for changing an angle of the parallel plane with respect to the optical axis. Item 3. The optical device for three-dimensional measurement according to Item 1. 3. The micro-scanning means comprises a parallel plane disposed between the objective lens and the object at an angle to the optical axis, and a rotating means for rotating the parallel plane. The optical device for three-dimensional measurement according to claim 1. 4. The micro-scanning means according to claim 1, wherein said micro-scanning means comprises a deflecting mirror disposed at an aperture stop position of said objective lens and an angle changing means for changing an angle of said deflecting mirror. The optical device for three-dimensional measurement according to claim 1. 5. The micro-scanning means according to claim 1, wherein said micro-scanning means comprises a deflecting prism disposed at an aperture stop position of said objective lens for deflecting a light beam, and a rotating means for rotating said deflecting prism. Optical device for three-dimensional measurement.