JP2001275042A - Image pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image pickup device which is free of restriction of device constitution and can make shading correction without deteriorating an image having been corrected. SOLUTION: This image pickup device is provided with the line camera 15 which is equipped with a line CCD array sensor 15a arranged in a line and picks up an image of a sample, a lighting optical system (light source 11, optical fiber bundle 12, and line-type optical fiber luminaire 10) which has a projection surface extending in the array direction of the image pickup elements of the line camera 15 and illuminates the sample, an image formation optical system (lens 16) which focuses the reflected light from the sample on the line CCD array sensor 15a, and a projection intensity control means (transmissivity distribution type diffusion film 13) which is provided on the projection surface of the lighting optical system and controls a lighting luminance distribution on a sample surface so that the luminance of an sample image inputted from the line camera 15 is inputted with a flat gain in the image pickup direction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an imaging device.

[0002]

2. Description of the Related Art There has been conventionally known a technique of performing inspection and measurement by inputting an image of an inspection object by an imaging device having an illumination optical system, an imaging optical system, and a line camera.

[0003] In such an image pickup apparatus, the lens of the imaging optical system has the property that the amount of light decreases in principle as it deviates from the center of the optical axis, and such a phenomenon is called a shading phenomenon. This shading phenomenon is inconvenient for image processing. For example, processing to cut out a specific part at the same luminance threshold in the field of view is the most basic function for image processing.However, if there is shading in the image, appropriate thresholds will be set at the center and the periphery in the image. Because of the difference, a problem occurs that a desired image cannot be cut out properly.

As a method of correcting such a shading phenomenon, the following countermeasures have conventionally been taken.

[0005] First, the effective field of view of the imaging optical system is designed to be enlarged. The imaging optical system may be designed so that shading does not substantially cause a problem in the effective field of view.

The second is shading correction by digital processing. After the image information is converted into electronic information by a CCD camera or the like, shading is corrected by multiplying the electric signal by a coefficient corresponding to the position. An example is disclosed in JP-A-08-254499.

A third method is to correct shading by inserting a correction plate in the middle of an image pickup optical system as disclosed in Japanese Patent Application Laid-Open No. 6-291945.

[0008]

When the above-described first method is used as a means for correcting shading caused by the imaging lens, the diameter of the optical lens becomes large as a result. Restrictions arise. Further, the above-described second method is excellent in that flexible correction can be performed. However, since the luminance of the peripheral region having a small gain is originally raised, the S / S is higher in the corrected region than in the central portion.
There is a problem that N is deteriorated and the image quality of the corrected image is deteriorated.

In the third method, it is necessary to additionally provide a diffusing plate for defocusing in order to overcome a problem when a correcting plate is provided in the middle of the image pickup optical system.

On the other hand, a line camera is useful for the need to input a high-definition or wide-field image. In other words, assuming that an image having an extremely large number of pixels such as 2000 × 2000 pixels or 4000 × 4000 pixels is input, an area camera equipped with a two-dimensional CCD array sensor is expensive and has a low pixel transfer clock. Although there is a problem, if a method of moving the stage or camera in parallel using a line camera equipped with a one-dimensional CCD array sensor is used, an inexpensive camera can be used with a width of 400
Even a two-dimensional image having 0 or more pixels can be input relatively easily.

However, in spite of the convenience of such a line sensor, in view of inputting an image with a line camera, there is a proposal for realizing shading correction by controlling an illumination method of an illumination optical system. Not previously done.

The present invention has been made in view of such a problem, and an object of the present invention is to solve the above-mentioned drawbacks of the conventional shading correction in an image pickup apparatus using a line camera. It is to provide an imaging device.

[0013]

In order to achieve the above object, a first aspect of the present invention is an imaging apparatus, comprising an imaging device arranged in a line, and a line camera for imaging a sample; An illumination optical system having an emission surface extending in an arrangement direction of an image sensor of the camera and illuminating the sample, an image forming optical system for imaging reflected light from the sample on the image sensor, and the illumination An emission intensity control means provided on the emission surface of the optical system and controlling an illumination brightness distribution on the sample surface so that the brightness of the sample image input by the line camera is input with a flat gain in the imaging direction; Is provided.

According to a second aspect of the present invention, in the imaging apparatus according to the first aspect, the emission intensity control means is constituted by a member capable of fixedly controlling the illumination luminance distribution.

According to a third aspect of the present invention, in the imaging apparatus according to the second aspect, the emission intensity control means is constituted by a diffusion film having a distribution such that the light transmittance gradually varies.

According to a fourth aspect of the present invention, in the imaging apparatus according to the second aspect, the emission intensity control means is configured by combining a plurality of diffusion films having different transmittances.

According to a fifth aspect of the present invention, in the imaging apparatus according to the first aspect, the emission intensity control means has a member capable of adaptively controlling the illumination luminance distribution.

According to a sixth aspect of the present invention, in the imaging apparatus according to the fifth aspect, the emission intensity control means adaptively controls the illumination luminance distribution according to a change in illumination conditions of the illumination optical system.

According to a seventh aspect of the present invention, in the imaging apparatus according to the fifth aspect, the emission intensity control means is configured by combining a member capable of adaptively controlling the illumination luminance distribution and a diffusion film.

The eighth invention is directed to any one of the fifth to seventh aspects.
In one embodiment, the member capable of adaptively controlling the illumination luminance distribution is a micromirror array device.

The ninth invention is directed to any one of the fifth to seventh aspects.
In one, the member capable of adaptively controlling the illumination luminance distribution is a liquid crystal panel.

According to a tenth aspect, in the imaging apparatus according to the first aspect, the illumination optical system includes a plurality of illuminators having different illumination conditions, and each of the plurality of illuminators has the emission intensity control. Means is provided for controlling the illumination brightness distribution on the sample surface obtained when the illumination light from the plurality of illuminators is simultaneously illuminated, so that the sample image is input with the flat gain. .

According to an eleventh aspect, in the imaging apparatus according to the tenth aspect, the illumination optical system includes two line-type illuminators, and the line directions of the two line-type illuminators are the same as the line direction. The object plane that is parallel to the array direction of the imaging device of the camera, and that the line camera images,
Illuminate from the left and right directions at the same illumination angle.

According to a twelfth aspect, in the imaging apparatus according to the tenth aspect, the illumination optical system includes two or more even-numbered line illuminators, and the two or more even-numbered line illuminators. Is parallel to the arrangement direction of the imaging elements of the line camera, and the two line-type illuminators forming a pair on the left and right are arranged in the right and left directions at the same illumination angle on the object plane imaged by the line camera. , And a plurality of pairs of the two line-type illuminators are arranged at different illumination angles.

[0025]

Embodiments of the present invention will be described below in detail with reference to the drawings. First, the principle of shading correction will be described with reference to FIG.

The "original image" of FIG. 1A is an example of a multi-valued image in which a plurality of circular pads having the same material and shape are arranged. In order to extract all pad images from the multi-valued image, binarization is performed with an appropriate threshold value, and image processing for generating an “appropriate binary image” is assumed. Assuming that an image is input by a line camera using an image forming lens having "shading by image formation" as shown in (B), shading occurs in the luminance distribution in the horizontal direction (C). If this "image with shading" is directly subjected to binarization processing,
An “inappropriate binary image” in which the center pad image swells and the peripheral portion is reduced is output (D).

Therefore, when the image is corrected by a "shading correction curve" (E) having an inverse gain to the "shading by image formation" characteristic, "shading is corrected" as shown in (F). Image "is obtained, and when this image is again subjected to binarization processing,
An “appropriate binary image” (G) is obtained.

(First Embodiment) FIG. 2A is an overall configuration diagram of an image input system to which an imaging device according to a first embodiment of the present invention is applied. 2A, the illumination optical system includes a pair of left and right light sources 11-1 and 11-2, optical fiber bundles 12-1 and 12-2, and line-type optical fiber illuminators 10-1 and 10-2. It consists of. These illuminators have the same specifications, and are arranged so as to illuminate a linear object surface of the sample 17 from left and right illumination directions having the same illumination angle. The imaging optical system includes a lens 16. The imaging system is configured by combining the line cameras 15.

Here, the line type optical fiber illuminators are arranged so that the longitudinal direction of the line type optical fiber illuminator and the arrangement direction of the imaging elements of the line camera are parallel to each other.

The one-axis automatic stage 14 is driven by the stage controller 22 in the direction indicated by the arrow to convert the image of the sample 17 input by the line camera 15 into a two-dimensional image. A personal computer (PC) 23 is connected to the stage controller 22 to control the operation of the one-axis automatic stage 14, and is connected to the line camera 15 to perform image input and two-dimensional reconstruction.

As shown in FIG. 2B, the line camera 15
Has a configuration in which the line CCD array sensor 15a is arranged at the center of the image plane.

Line type optical fiber illuminators 10-1 and 10
-2, transmittance distribution type diffusion films 13-1 and 13-2 as emission intensity control means are mounted on each emission surface. Such a transmittance distribution type diffusion film 13-1, 1
Attaching 3-2 has the following meaning. For example, diffuse illumination is effective for inputting an image suitable for performing an appearance inspection on a metal plating surface of a printed circuit board. In other words, fine irregularities are given to the metal surface by a polishing process so that the subsequent processes such as soldering and wire bonding are performed steadily. Illumination conditions with high diffusivity are advantageous for inputting such a metal surface as a homogeneous image.

When an optical fiber illuminator is used, diffusion is obtained by the spread of the illumination light from the exit end face of the optical fiber exposed on the exit surface. In this embodiment, the diffusion of the illumination light on such an exit surface is achieved. As means for realizing optical shading correction without losing the performance, the transmittance distribution type diffusion films 13-1 and 13-2 are mounted on the exit surfaces of the line type optical fiber illuminators 10-1 and 10-2. ing. Further, the transmittance distribution type diffusion films 13-1, 13-
There is also a secondary effect that the illumination brightness unevenness between the fibers can be absorbed by attaching 2.

FIGS. 3A, 3B, and 3C are a detailed configuration and an explanatory diagram of the illumination optical system described with reference to FIG. Here, one of the components shown as a pair in FIG. 2 is shown as a representative.

The line type optical fiber illuminator 10 is shown in FIG.
As shown in (B), it is configured such that a uniform illuminance distribution is realized on the sample surface 17a. However, shading depending on the lens 16 occurs in an image input through the system of FIG. Therefore, in the present embodiment, the transmittance distribution type diffusion film 13 is mounted on the emission surface 30 of the line type optical fiber illuminator 10 to thereby obtain the configuration shown in FIG.
An illuminance distribution as shown in FIG.

This illuminance distribution corresponds to the “shading correction curve” shown in FIG. 1E, and the sample image is input with a flat gain by canceling out the illuminance distribution and the shading of the lens 16. Become. In other words, by mounting the transmittance distribution type diffusion film 13 of the present embodiment, an illumination brightness distribution opposite to the shading profile of the imaging optical system is generated on the sample surface, whereby the sample input by the line camera 15 is generated. The luminance distribution of the image is canceled out and becomes flat.

The transmittance distribution type diffusion film 13 here
Are made of a diffusion film having a distribution in which diffusion conditions are the same and light transmittances are gradually different (a diffusion film in which different transmittances are distributed seamlessly). In this case, the illumination luminance distribution is fixed.

The illumination optical system according to the present embodiment is composed of two line-type optical fiber illuminators 10-1 and 10 having a pair of right and left.
The shading correction is set for an illumination luminance distribution generated by combining the illumination light from the two illuminators 10-1 and 10-2 on the object plane.
That is, according to the simple model, the two illuminators 10-1,
Since the illumination luminance distribution according to 10-2 is represented by the addition of the illumination luminance distributions of the respective illuminators, it is not necessary to perform shading correction independently for each illuminator, but rather the two illuminators 10-1 and 10-10. The transmittance distribution of the diffusion film mounted on each illuminator is designed so that the illumination luminance distribution generated by combining the illumination light according to -2 provides an appropriate shading correction effect.

According to the first embodiment, when an image is input by the line camera, the illuminance distribution of the illumination optical system is controlled as a means for correcting shading caused by the imaging lens. Is obtained.

1. Since there is no need to enlarge the effective range of the imaging lens, it is possible to reduce restrictions in designing optical systems and devices.

2. Since this is not a correction process for an electronically converted image signal, the S / N ratio of the peripheral portion is larger than that of the central portion.
And the memory required for processing increases when the image size is large.

3. It is not necessary to provide a diffusing plate for defocusing.

FIG. 4 is a diagram for explaining a modification of the first embodiment of the present invention. Here, instead of using a diffusion film with the same diffusion conditions and a light transmittance that is gradually different as the transmittance distribution type film, multiple diffusion films with the same diffusion conditions and different transmittances are attached. Use the one configured together. The light transmittance of each diffusion film is uniform. In FIG. 4, three types of diffusion films 13 having transmittances of 95%, 80%, and 60% are shown as examples.
By laminating a, 13b, and 13c, an illumination optical system for approximately achieving appropriate shading correction is realized.

In this case, 95% × 8 at the center of the object plane.
0% × 60% = 46% illumination luminance is obtained, 95% × 80% = 76% in the periphery, and 95% illumination luminance in the most peripheral area. Further, the configuration in which the diffusion film is mounted on the exit surface enhances the diffusivity of the illumination light, and has an effect of smoothly changing the three-level illumination luminance distribution.

According to this modification, the same effect as that of the first embodiment can be obtained by simple and inexpensive means.

(Second Embodiment) FIG. 5 is an overall configuration diagram of an image input system to which an imaging device according to a second embodiment of the present invention is applied. The difference from the first embodiment is the following two points.

1. The illuminator has illuminator arrangement driving units 50-1 and 50-2 and illuminator arrangement controllers 52-1 and 52-2 for changing illumination conditions of the illuminator. The height and direction of 10-2 can be changed. With such a configuration, the illumination conditions such as the illumination angle can be set to appropriate ones according to the material and structure of the target object. In addition, since the figure becomes complicated, PC
A connection line between the optical fiber 23 and the reflected light distribution control adapter 54-1 is omitted.

2. A reflected light distribution control adapter 54 composed of a micromirror array device for adaptively changing an illuminance distribution (illumination luminance distribution) in accordance with a change in illumination conditions.
-1, 54-2 are line type optical fiber illuminators 10-1,
10-2.

That is, 1. When the illumination conditions are changed due to the configuration of the illuminator, the illuminance distribution on the sample surface changes, so that in accordance with the change of the height and angle of the illuminator, the transmission is performed to realize the illuminance distribution that always performs appropriate shading correction. It is necessary to control the rate distribution. Therefore, here, a reflected light distribution control adapter 54- having a micro mirror array device and adaptively realizing illumination conditions having the same diffusion conditions and different transmittance distributions under the control of the PC 23 is adopted.
1, 54-2 are provided. In addition, as a device constituting the reflected light distribution control adapters 54-1 and 54-2, a reflective liquid crystal panel may be used instead of the micro mirror array device.

FIG. 6 is a diagram showing a specific configuration of the line type optical fiber illuminator 10 and the reflected light distribution control adapter 54 shown in FIG. Here, one of the components shown as a pair in FIG. 5 is shown as a representative.

The operation when the micromirror array device 54a is used as a device constituting the reflected light distribution control adapter 54 will be described below. The illumination light emitted from the emission surface 10a of the line type optical fiber illuminator 10 is transmitted to the micromirror array device 5 in the reflected light distribution control adapter 54.
The light is reflected by 4a, passes through a diffusion film having a uniform transmittance distribution, and irradiates the sample surface.

In the micro mirror array device 54a, for example, micro mirrors made of a metal having a high reflectivity are integrated in a grid on the reflection surface, and each mirror is held so as to rotate about two diagonal lines. Has a structure supported by posts. By controlling the rotation of each of these micromirrors, the amount of reflection of light from the light source can be controlled. The rotation of the micromirror is controlled by a command from the PC 23 in the following manner.

In other words, each micromirror is recognized on the PC 23 as a digital pixel forming the reflection surface of the micromirror array device 54a, and the PC23 controls the reflected light intensity of each pixel to a desired value. Is performed. Therefore, in practice, rotation control is performed to set the micro mirror corresponding to each pixel in a desired direction.

When a reflection type liquid crystal panel is used instead of the micro mirror array device 54a, it is realized by a substantially similar configuration. The reflection type liquid crystal panel is configured by arranging pixels whose reflectance can be controlled in accordance with the intensity of the applied voltage in a square grid pattern.
The desired reflectance is set based on the control from.

According to the above-described second embodiment, in addition to the effect of the first embodiment by realizing shading correction by the illumination optical system, flexible and adaptive processing can be realized according to the properties of the object. This has the effect.

(Third Embodiment) FIG. 7 is an overall configuration diagram of an image input system to which an imaging device according to a third embodiment of the present invention is applied. In FIG. 7, illustration of PCs and the like is omitted to avoid complicating the figure. Here, the illumination optical system is constituted by a two-stage line type optical fiber illuminator. In other words, focusing on the illumination system on the left side of the figure,
A line-type optical fiber illuminator 10-1A for illuminating the sample from a high angle disposed above and a line-type optical fiber illuminator 10-1B for illuminating the sample from a shallow angle provided at a low position are provided. ing. The transmittance distribution type diffusion films 13-1A and 13-1 are respectively provided on the exit surfaces of the line type optical fiber illuminators 10-1A and 10-1B.
B are mounted, and shading correction is realized according to the principle described in the first embodiment. 11-1A, 1
1-1B is a light source, and 12-1A and 12-1B are optical fiber bundles.

Similarly, the illumination system on the right side is also configured to be mirror-symmetrical to the configuration on the left side.
Then, a two-stage line type optical fiber illuminator 10-1A,
Each transmittance distribution such that the illumination luminance distribution on the sample surface of the sample 17 realized by all the illuminations from 10-1B and 10-2A and 10-2B results in an appropriate shading correction effect. Mold diffusion film 13-1A,
The transmittance distributions of 13-1B, 13-2A, and 13-2B are set.

In this embodiment, the reason why the illumination optical system is constituted by a two-stage line type optical fiber illuminator is as follows, for example.

1. An image with better uniformity can be obtained by illuminating from a wide angle direction due to the optical characteristics of the sample surface.

2. In the case of detecting foreign matter mixed in a translucent material such as a solder resist on a printed circuit board as a defect, appropriate lighting conditions differ depending on whether the foreign matter adheres to the surface or exists inside. In order to detect both, illumination optical systems having different illumination angles may be required at the same time.

According to the third embodiment described above, in addition to the effects of the first embodiment, shading correction can be realized by a simple method even when multi-stage illumination is required.

[0062]

According to the present invention, the following effects can be obtained.

1. Since there is no need to enlarge the effective range of the imaging optical system, it is possible to reduce restrictions on the design of the optical system and the device.

2. Since this is not a correction process for an electronically converted image signal, the S / N ratio of the peripheral portion is larger than that of the central portion.
And the memory required for processing increases when the image size is large.

3. It is not necessary to provide a diffusing plate for defocusing.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining the principle of shading correction.

FIG. 2A is an overall configuration diagram of an image input system to which an imaging device according to a first embodiment of the present invention is applied;
(B) is a diagram showing a configuration of a line camera.

FIG. 3 is a detailed configuration of an illumination optical system and an explanatory diagram thereof.

FIG. 4 is a diagram for explaining a modification of the first embodiment of the present invention.

FIG. 5 is an overall configuration diagram of an image input system to which an imaging device according to a second embodiment of the present invention is applied.

6 is a diagram showing a specific configuration of the line-type optical fiber illuminator 10 and the reflected light distribution control adapter 54 shown in FIG.

FIG. 7 is an overall configuration diagram of an image input system to which an imaging device according to a third embodiment of the present invention is applied.

[Explanation of symbols]

10 (10-1, 10-2) Line type optical fiber illuminator 10a Emission surface 11 (11-1, 11-2) Light source 12 (12-1, 12-2) Optical fiber bundle 13 (13-1, 13) -2) Transmittance distribution type diffusion film 14 Single axis automatic stage 15 Line camera 15a Line CCD array sensor 16 Lens 17 Sample 22 Stage controller 23 PC 30 Emission surface 50 (50-1, 50-2) Illuminator arrangement drive unit 52 (52-1, 52-2) Illuminator arrangement controller 54 (54-1, 54-2) Reflected light distribution control adapter 54a Micro mirror array device or reflective liquid crystal panel 55 Diffusion film

Continued on the front page (72) Inventor: Satoshi Arai 2-43-2, Hatagaya, Shibuya-ku, Tokyo F-term in Olympus Optical Co., Ltd. 5C022 AA03 AB15 AB51 AC26 AC42 AC54 AC55 AC69 AC74 AC77 CA00 5C024 AX02 CX35 EX42 EX51 GY01

Claims (12)

[Claims] 1. An imaging device comprising: an imaging device arranged in a line;
A line camera for imaging the sample, an illumination optical system having an emission surface extending in the arrangement direction of the image sensor of the line camera, and illuminating the sample; and connecting reflected light from the sample to the image sensor. An imaging optical system for imaging, and an illumination on the sample surface provided on the exit surface of the illumination optical system, such that the luminance of the sample image input by the line camera is input with a flat gain in the imaging direction. An imaging device comprising: emission intensity control means for controlling a luminance distribution. 2. An imaging apparatus according to claim 1, wherein said emission intensity control means is constituted by a member capable of fixedly controlling said illumination luminance distribution. 3. An imaging apparatus according to claim 2, wherein said emission intensity control means is constituted by a diffusion film having a distribution in which light transmittances are gradually different. 4. The imaging apparatus according to claim 2, wherein said emission intensity control means is configured by combining a plurality of diffusion films having different transmittances. 5. The imaging apparatus according to claim 1, wherein said emission intensity control means has a member capable of adaptively controlling said illumination luminance distribution. 6. The imaging apparatus according to claim 5, wherein said emission intensity control means adaptively controls said illumination luminance distribution according to a change in illumination conditions of said illumination optical system. 7. The imaging apparatus according to claim 5, wherein the emission intensity control means is configured by combining a member capable of adaptively controlling the illumination luminance distribution and a diffusion film. 8. The imaging apparatus according to claim 5, wherein the member capable of adaptively controlling the illumination luminance distribution is a micro mirror array device. 9. The liquid crystal panel according to claim 5, wherein the member capable of adaptively controlling the illumination luminance distribution is a liquid crystal panel.
8. The imaging device according to any one of 7. 10. The illumination optical system is composed of a plurality of illuminators having different illumination conditions, each of the plurality of illuminators is provided with the emission intensity control means, and receives illumination light from the plurality of illuminators. 2. The imaging apparatus according to claim 1, wherein an input of the sample image with the flat gain is performed by controlling an illumination luminance distribution on the sample surface obtained when the irradiation is performed simultaneously. 11. The illumination optical system includes two line-type illuminators, and the line directions of the two line-type illuminators are parallel to the arrangement direction of the imaging elements of the line camera, and 11. The imaging apparatus according to claim 10, wherein the object surface imaged by the line camera is illuminated from right and left directions at an equal illumination angle. 12. The illumination optical system includes two or more even-numbered line-type illuminators, and the line direction of the two or more even-numbered line-type illuminators is relative to the arrangement direction of the imaging elements of the line camera. The two line-type illuminators, which are parallel to each other and form a pair on the left and right, are configured to illuminate the object plane imaged by the line camera from the left and right directions at the same illumination angle, and The imaging device according to claim 10, wherein a plurality of pairs of the two line illuminators are arranged at different illumination angles.