JPH06129995A - Optical inspection device for surface defect - Google Patents

Abstract

PURPOSE:To reduce the deterioration of a contrast caused by the ruggedness or irregular color of the surface of a slab so as to inexpensively inspect the slab surface for defects with high sensitivity by providing a lighting device, diffusing device, image pickup device, and picture displaying device. CONSTITUTION:The irradiating light made incident upon a diffusing plate 4 is radially spread at an emitting point and, since a lighting device 3 provided as a light source has a rod-like shape, the incident angle and intensity of the incident light are diversified and the light transmitted through the plate 4 (diffused light) becomes uniform and has a uniform directivity. In addition, since the line of sight of a camera 5 is extended and a point source is necessary provided in the direction in which the irradiating light is regularly reflected, a uniform and bright picture can be obtained. Therefore, the generation of parts from which regularly reflected light is obtained and no regularly reflected light is obtained due to the ruggedness of the slab surface. In addition, when the lighting device 3 and camera 5 are deviated from optically symmetrical positions, the quantity of regularly reflected light from the slab surface decreases and the contrast between a defect 2 and defectless defectless part disappears. In order to perform optimum defect detection, therefore, the device 3 and camera 5 are positioned at optically symmetrical positions with respect to a normal to the slab 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical surface defect inspection apparatus for detecting defects on the surface of a slab, for example.

[0002]

2. Description of the Related Art For example, slab cracks and pinholes remain as surface defects of products even after rolling, so it is desirable to detect and remove them at the slab stage. For this reason, many automatic defect inspection techniques have been developed in this field in the past.

For example, Japanese Patent Application Laid-Open No. 59-52735 discloses a method of irradiating a hot slab with visible light and detecting defects on the surface of the slab from an image of self-emission from the slab and reflected light of illumination. ing. Also, JP-A-59-154312
The publication discloses a hot slab surface flaw detection illuminator that illuminates the surface of a hot continuous casting slab and is composed of a halogen lamp, an elliptical reflecting mirror, and a cooling device. Further, JP-A-63-18255 and JP-A-2
Japanese Patent Publication No. 163645 discloses a detection method for detecting a surface flaw from an image of the slab surface at the time of scarfing.

As described above, although various slab surface defect methods and detecting devices have been devised conventionally,
Since the technology for detecting micro defects has not been established yet, the current situation is that it depends exclusively on visual inspection after scarfing the entire slab.

[0005]

SUMMARY OF THE INVENTION The present inventors have taken an image of a slab surface with a TV camera using normal illumination and attempted automatic detection by processing an image signal (image processing). A defect image of a possible level could not be obtained. As a result of examining this cause, the slab surface after the scarf has a smooth uneven surface due to the flow of the cutting gas, and the oxide film covers the surface, resulting in a black glossy surface. With normal diffuse illumination, the amount of light scattered in the shooting direction of the camera is small, so no contrast of the defect image can be obtained on the shot image, while with the conventional specular reflection arrangement, the contrast that allows partial defect discrimination. However, it was found that regular reflection was only partially obtained due to the unevenness of the surface.

As disclosed in Japanese Patent Laid-Open No. 59-52735, a method of irradiating a hot slab with visible light and detecting defects on the surface of the slab from an image of self-emission from the slab and reflected light of the illumination If the uniformity of light and the ratio of the intensity of self-emission to the intensity of reflected light are not optimal, a clear defect image cannot be obtained, and it is difficult to detect a defect even if optimal imaging is performed.

Further, the surface of the slab after the scarfing described above has a smooth uneven surface due to the flow of the ablation gas, and the color thereof has silver white or black unevenness due to the uneven color of the oxide layer. . Therefore, in the case of oblique illumination light, the smooth shadow of the convex portion and the uneven color of the oxide layer cause uneven brightness of the reflected light, which is a major obstacle to defect detection.

In the hot slab surface defect detection illuminating device disclosed in Japanese Patent Laid-Open No. 59-154312, the reflecting plate reflects the illumination to illuminate parallel light, but the slab surface reflects the illumination. Shading occurs because light and direct light are applied. Further, the above-mentioned JP-A-59-5273.
As in the case of Japanese Patent Laid-Open No. 5, in the illumination from an oblique direction, smooth unevenness of the slab surface after scarfing and color unevenness of the oxide layer are factors that cause shade of illumination light and brightness unevenness of reflected light. This is a major obstacle to defect detection.

On the other hand, Japanese Patent Application Laid-Open No. 63-18255 and Japanese Patent Application Laid-Open No. 2-163645 describe a detection method for detecting a surface defect from an image of a slab surface at the time of scarfing. In this image, a clear defect image cannot be obtained, and there is a problem in terms of cost and maintenance to protect the photographing device from high temperature gas, dust, etc. at the time of scarfing.

Therefore, the present invention has been a problem in the prior art, that is, deterioration of a defect image caused by uneven illumination light, for example, smooth unevenness on the slab surface after scarfing, and a surface oxide film having a black gloss. It is an object of the present invention to provide an optical surface defect inspection apparatus which has high sensitivity, is inexpensive, and has good maintainability, which reduces deterioration of contrast between a defective portion and a sound portion on a captured image due to the above.

[0011]

An optical surface defect inspection apparatus of the present invention comprises an illuminating device for illuminating an inspection target material; a diffusing device for diffusing illumination light of the illuminating device; and an illuminated portion of the inspection target material. It is characterized by comprising: a photographing device for photographing; and an image display device for displaying a photographed image or a processed image.

[0012]

Since the diffusing device diffuses the illumination light of the illuminating device,
The material to be inspected is illuminated relatively uniformly, and the defect image becomes clear on the captured image of the image capturing device.

For the diffuser plate, frosted glass, roughly ground glass, or a film is usually used. In principle, diffused light is obtained by surface irregularities or irregular reflection of an opaque material.
However, even with such a diffusing plate, it is possible to obtain uniform illumination to some extent, but if the irradiation light from the light source has uneven illuminance, it is natural that the diffuse light also has uneven illuminance. In order to obtain a more uniform diffused light source, it is possible to stack several diffuser plates. However, this method is not preferable as illumination for defect inspection because the light transmittance of the whole is sharply reduced.

Therefore, in a preferred embodiment of the present invention,
A diffuser plate is used which is a two-dimensional array of minute lens arrays in which a large number of minute lenses are aligned in the same direction and parallel to each other so that the main planes are on the same plane. This diffuser plate is inserted so that the illumination direction and the diffuser plate surface are vertical in the optical path of the inspection surface of the inspection target material with the illumination light source,
Arrange so that the diffused light transmitted through the diffuser plate can illuminate the entire field of view of the imager. Keep the distance between the light source and the diffuser plate at a distance that does not damage the diffuser plate due to heat radiation from the light source, or at a distance where cooling is performed normally if a diffuser plate cooling device is provided, and the shooting field of view of the shooting device. Insert it in a place where the diffusion plate itself does not hang. Further, the distance between the diffusion plate and the material to be inspected is set to be longer than the focal length of the minute diameter lens forming the diffusion plate, and the illumination light illuminates the entire visual field of the photographing device.

Further, the illumination light source and the photographing device are arranged in optical symmetry with respect to the normal line set up on the inspection target material, and the inclination angle thereof is within a range of 60 ° or less with respect to the normal line set up on the inspection target material. Set to.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the device of the present invention will be described below with reference to FIG. In FIG. 1, 1 is a slab which is an inspection object, 2 is a slab surface defect, 3 is an illuminating device, 4 is a diffusion plate, 5 is a camera, 6 is an image processing device and an image display device. As a light source of the lighting device 3, a white light source having a large light emitting area, for example, a rod-shaped halogen lamp is used.

White light emitted from the light source enters the diffusion plate 4. The incident angle of the incident light incident on the diffusion plate 4 is different at each point on the diffusion plate. For example, when the illumination light emitted from the center of the rod-shaped light source in the longitudinal direction is incident on the center of the diffusion plate,
The angle of incidence is vertical. When the illumination light emitted from the longitudinal center of the rod-shaped light source is incident on the end of the diffuser plate, the incident angle is determined by the angle formed by the exit point, the incident point, and the diffuser plate surface. Also,
Since the illumination light incident on the diffuser plate 4 spreads radially at the exit point, its intensity varies depending on the difference in the distance between the exit point and the incident point on the diffuser plate. Furthermore, since the light source is a rod-shaped light source, the emission point of the illumination is over the entire light emitting surface of the tube of the light source,
The incident angle and the intensity of the above-mentioned incident light become more diverse, and the transmitted light (diffused light) of the diffusion plate 4 becomes uniform and has a uniform directivity. When the illumination light is made incident on the diffusion plate 4 to obtain uniform illumination, it is preferable that the incident light on the diffusion plate 4 has various incident angles and illuminances. It can be seen that the light source has a good rod shape.

The diffuser plate 4 is not a diffuse reflection diffuser due to surface irregularities such as frosted glass, but is a diffuser plate that diffuses light by diverging light when passing through a two-dimensional array plate of a large number of minute lenses. The illumination light incident on the diffusion plate 4 has various directions and intensities as described above, and is incident on each minute lens. Light is condensed by refraction in a minute lens, goes straight through the focal point and diverges. Therefore, when the focal length is longer than the focal length, each optical lens itself becomes a point diffusion light source having the same size as the lens diameter. The point diffusion light sources are gathered in an array to form a surface light source in which the point light sources are gathered, and have a good diffusion ability. Further, since the diffuser plate 4 is made of a transparent material, the diffuser plate 4 has a high transmittance and the decrease in illuminance can be minimized. Since the light source uses a rod-shaped light source, illumination with various incident angles and intensities enters the microlens array as described above, and the diffusing ability of the diffusion plate 4 using the microlens array is further enhanced. .

The illumination light that has passed through the diffusion plate 4 is the inspection target material 1
Is irradiated. In the conventional slab lighting, the reflected light from the slab surface that enters the camera has some areas where regular reflection light is obtained and other areas where it is not, due to the smooth unevenness of the slab surface, resulting in strong shading. Therefore, it is difficult to visually check and automatically detect the defect. However, in the present embodiment, as shown in FIG. 1, the line of sight of the camera 5 is extended and the point light source is always present in the direction of regular reflection, so that a uniform bright image can be obtained.

On the other hand, in a defective portion such as a crack or a pinhole,
Since the shadow of the concave portion is formed, the defective portion becomes a black image. For this reason, the defect can be extracted only by a simple binarization process. Even if the surface is rusted or dirty, the amount of received light is reduced, but it is brighter than the defective portion, and it is possible to discriminate only by the level.

The illumination device 3 having a rod-shaped halogen lamp as a light source is an image pickup device which is set within a range of 60 ° or less with respect to the normal line standing on the inspection target material 1 and illuminates the inspection target material 1 obliquely from above. The camera 5 is arranged so as to receive the specularly reflected light.
The diffuser plate 4 consisting of a two-dimensional array of minute lenses is inserted between the halogen lamp and the material to be inspected, and the center of the optical path passes through the center of the diffuser plate 4 so that the illumination passing through the diffuser plate 4 can illuminate the maximum area. And insert so that the optical path direction and the surface of the diffuser plate are perpendicular.

Here, when the illuminating device 3 is at an angle of 60 ° or more with respect to the normal line to the inspection target material 1, a slab surface image illuminated from obliquely above the inspection target material 1 is photographed by the camera 5 under specular reflection conditions. Then, even if the above-mentioned diffusion plate 4 is used, the convex portions of the smooth unevenness on the surface of the slab can be shaded, which is not preferable for defect detection.

When the distance between the diffusing plate 4 and the surface of the slab is made closer than the focal length of the minute lens forming the diffusing plate 4, a condensing effect of the lens occurs, and the illuminated surface is a condensing portion and the non-condensing portion. However, it is not preferable for defect detection because uniform illumination cannot be performed.

When the illuminating device 3 and the photographing device 5 deviate from the optically symmetrical positions, the specularly reflected light from the slab surface gradually decreases, and the contrast between the defect 2 and the sound part becomes sharp and disappears. Therefore, in order to detect a defect under the optimum condition, it is desirable that the illumination device 3 and the imaging device 5 are arranged in optical symmetry with the normal line set to the inspection target material 1 as an axis.
The image capturing device 5 captures an image of the slab surface illuminated by the illumination device 3 and the diffusing plate 4, and the image processing device and the display device 6 perform image processing and display the image on a CRT display or the like. Although not shown in the drawing, the image photographed by the photographing device 5 may be subjected to image processing in the device 6 such as sharpening of a defect image to extract a defective portion.

Next, a concrete description will be given. The light source of the illuminating device 3 uses a rod-shaped halogen lamp 1000W, and the length of the lamp tube is 250 mm. The diffuser 4 has a sheet size of 203 × 254 mm, the diameter of the constituent lenses is 2.2 mm,
The focal length is 3 mm, and the number of lenses per square inch is 134. Distance between light source and slab surface is 1000m
The distance between the light source and the diffuser plate 4 is 600 mm.

A two-dimensional CCD camera is used as the photographing device 5, and its field of view is adjusted to the illuminated portion of the slab surface. The mounting position is set in optical symmetry with the illumination light source with a vertical line standing on the slab surface as an axis, and the distance between the slab surface and the CCD camera 5 is 700 m. The illuminating angle and the shooting angle are 30 ° with respect to the vertical line standing on the surface of the slab and are arranged in optical symmetry.

As a result of photographing the image of the slab surface defect in this embodiment, only the defect portion is shown in black as compared with the image of the slab surface defect photographed by another photographing device, and the shading due to the smooth unevenness on the surface of the slab is shown. It was possible to obtain a good image which was hardly affected by the presence of the above or the shade of the color of the surface oxide layer.

[0028]

[Effect] For example, the inspection and maintenance work of cold slabs was one of the hot and humid adverse environment works. However, since many strict materials are inspected and it is necessary to detect microscopic defects, the slab itself is used exclusively. Although this was done by human visual inspection, the application of the device of the present invention enables remote detection by visual inspection on the display or by image processing, which enables automation remote control.

The present invention has a possibility of being applicable to the inspection of a thin plate, and it is possible to detect even a defect which cannot be detected by the conventional optical surface defect detector with high accuracy by suppressing the interference of the surface roughness. Have.

[Brief description of drawings]

FIG. 1 is a side view showing an outline of the configuration of an embodiment of the present invention.

[Explanation of symbols]

1: Slab (material to be inspected) 2: Defect 3: Lighting device 4: Diffuser (diffuser) 5: Camera (imaging device) 6: Image processing and display device (image display device)

Front page continued (72) Inventor Satoshi Nakamura 1-1, Tobata-cho, Tobata-ku, Kitakyushu City Inside Nippon Steel Yawata Works (72) Inventor Toru Takagi 1-1-1 Tobata-cho, Tobata-ku, Kitakyushu City Nippon Steel Yawata Works Co., Ltd.

Claims (4)

[Claims] 1. An illuminating device for illuminating an inspection target material; a diffusing device for diffusing illumination light of the illuminating device; a photographing device for photographing an illuminated portion of the inspection target material; and displaying a photographed image or a processed image. An optical surface defect inspection device comprising an image display device. 2. A diffusing device is a diffusing plate in which a large number of minute lenses are arranged in a two-dimensional array with their optical planes aligned in the same direction and parallel to each other so that their main planes are on the same plane. The optical surface defect inspection apparatus according to claim 1. 3. The diffusion plate is such that the direction of illumination is perpendicular to the surface of the diffusion plate, and the distance between the light source and the diffusion plate is such that the diffusion plate is not damaged by heat radiation from the light source or a diffusion plate cooling device is provided. At a distance where cooling can be performed normally, and outside the field of view of the image capturing device, the inspection target material is separated by a distance equal to or more than the focal length of a small-diameter lens that forms a diffuser plate, and the transmitted light has a field of view of the image capturing device. The optical surface defect inspection apparatus according to claim 2, which is inserted into an optical path of an illumination light source and an inspection surface of an inspection target material so as to illuminate the entire surface. 4. The illumination angle of the illuminating device is within a range of 60 ° with respect to a normal line set up on the inspection target material, and the photographing direction of the photographing device is about the normal line set up on the inspection target material as an axis. The optical surface defect inspection apparatus according to claim 1, 2 or 3, which is optically symmetrical with the illumination direction of the illumination device.