JPH0815177A - Method and apparatus for imaging surface defect - Google Patents

Abstract

PURPOSE:To preferably image a surface defect having directionality, to early discover a product failure and to improve a yield in the next step in a method for optically imaging to detect the defect of a surface to be inspected. CONSTITUTION:The surface of a lens 3 and the detecting surface of a one- dimensional CCD 4 are disposed in parallel with the surface 2 to be inspected of a steel plate. A main axis 7 for connecting the center of the CCD 4 to that of the lens 3 is disposed at a position inclined with respect to the normal 8 of the surface 2 to be inspected. The image of the entire visual field is focused on the detecting surface of the CCD 4 without unsharpness in the image.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an imaging method and an imaging apparatus for detecting a surface defect of a material to be inspected, such as a steel plate or a steel piece.

[0002]

2. Description of the Related Art Conventionally, in the case of optically inspecting surface defects, a one-dimensional scanner is used as disclosed in Japanese Patent Laid-Open No. 63-40843, or Japanese Patent Laid-Open No. 1807/1993.
As disclosed in Japanese Patent Publication No. 81-81, the surface of a material to be inspected is imaged using a television camera, and the accuracy of surface defect detection is improved by advanced signal processing from the obtained image signal.

[0003]

However, JP-A-63-4
In the one-dimensional scanner and television camera used in Japanese Patent Publication No. 0843 and Japanese Unexamined Patent Publication No. 5-180781, the center of the photodetector is arranged on the optical axis of the lens, so that the installation position is restricted. There is also a problem that it is difficult to detect directional surface defects.

FIG. 6 is an elevational view showing the installation positional relationship of the image pickup device when a conventional television camera is used, for example. FIG. 6 is a view of the surface defects 12 of the surface 2 to be inspected of the steel sheet shown in FIGS. 7, 8 and 9 as seen from the longitudinal direction of the steel sheet as an example. FIG. 7 is a plan view of the surface 2 to be inspected, showing the steel plate longitudinal direction 20 and the steel plate width direction 21. 8 is an elevation view of FIG. 7, and FIG. 9 is a side view of FIG. As shown in FIG. 6, in the conventional television camera, in order to obtain a detailed image of the surface 2 to be inspected, the image forming surface 11 is made to coincide with the surface of the photodetector 4, and the center of the photodetector 4 is aligned. There is a constraint that the main axis 7 connecting the centers of the lenses 3 must exist in a plane perpendicular to the surface 2 to be inspected.

If there is such a restriction on the installation position relationship of the image pickup apparatus, for example, as shown in FIGS. 7, 8 and 9, one is steeply inclined with respect to the surface to be inspected and the other is steeply inclined. It is difficult to detect the surface defect 12 with a defect as a surface defect by signal processing. This is because the image is picked up from the upper direction in FIG. 8, and the surface inclination of the surface defect is small unless a part of the right end is directed toward the surface defect 12, so that an image signal with a small change in brightness is obtained. .

On the other hand, as shown in FIG. 10, when a surface defect is imaged from a direction inclined with respect to the normal line 8 of the surface to be inspected, the main axis 7 connecting the center of the photodetector 4 and the center of the lens 3 is picked up. The surface defect existing in the vicinity of the intersection of the inspection surface 2 and the surface 2 to be inspected is imaged on the surface of the photodetector 4, so an image with a large change in brightness is obtained, but the surface defect existing in the other parts. The image is blurred and a clear image cannot be obtained.

Therefore, even if the surface defect 12 as shown in FIG. 8 exists at most of the positions, a clear image cannot be obtained, so that the surface defect cannot be detected by the subsequent signal processing. Therefore, the present invention is to propose an imaging method and an imaging apparatus that have no restriction on the installation positional relationship of the imaging apparatus and can favorably detect directional surface defects.

[0008]

According to the present invention, in an optical imaging method for detecting a surface defect on a surface to be inspected, a main axis connecting a center of a lens and a center of a photodetector is defined as a normal line of the surface to be inspected. The surface defect imaging method is characterized in that the surface to be inspected, the lens surface, and the photodetector surface are arranged in parallel with each other and imaged.

An apparatus of the present invention capable of suitably implementing the above method is a light source for illuminating a surface to be inspected, a lens for collecting scattered light scattered on the surface to be inspected, and a scattering light condensed by the lens. In an imaging device including a photodetector installed at a position where light is imaged, a main axis connecting a center of a lens and a center of the photodetector has an inclination with respect to a normal line of a surface to be inspected, and The surface defect imaging device is characterized in that a lens surface and a photodetector surface are arranged parallel to the surface. In this case, the light source is slit-shaped, the photodetector is a one-dimensional CCD,
Moreover, it is preferable that the centers of the light source, the photodetector and the lens are arranged in a plane perpendicular to the surface to be inspected.

[0010]

In the present invention, the surface of the lens that collects the scattered light scattered on the surface to be inspected and the surface of the photodetector that detects the scattered light collected by the lens are parallel to the surface to be inspected. Since the main axis connecting the center of the lens and the center of the photodetector is arranged at, even if it has an inclination with respect to the normal to the surface to be inspected,
An image of the entire visual field on the surface to be inspected is clearly formed on the photodetector surface. Therefore, there is no limitation on the imaging angle as in the conventional case, and directional surface defects can be satisfactorily submitted. The inclination of the main axis connecting the center of the lens and the center of the photodetector with respect to the normal to the surface to be inspected may be appropriately determined according to the surface to be inspected and its surroundings, and the imaging device, but is not limited, but an actual device. Then, 30 ° to 60 ° is preferable.

Further, the light source is slit-shaped, the photodetector is a one-dimensional CCD, and the center of the light source, the lens and the photodetector are in the normal to the surface to be inspected in the same plane perpendicular to the surface to be inspected. If it is arranged so as to be inclined with respect to the material to be inspected that moves at a high speed, a sufficient amount of light can be secured and a clear image can be obtained, so that the accuracy of surface defect detection is improved. .

[0012]

EXAMPLES As examples of the present invention, a slit-shaped light source, 1
A one-dimensional image pickup device including a three-dimensional CCD and a lens will be described as an example. 1 to 3 show a surface defect imaging device in which the surface 2 to be inspected is the surface of a steel plate during traveling, FIG. 1 is an elevation view seen from the longitudinal direction of the steel plate, and FIGS. 2 and 3 are seen from the steel plate width direction. It is a side view.

In FIG. 1, the slit-shaped light source 1 is an illumination light 5
To illuminate the surface 2 to be inspected of the steel sheet. The scattered light 6 scattered at each point on the surface 2 to be inspected of the illuminated steel plate is condensed in the width direction by the lens 3, and the one-dimensional CC installed at the image forming position.
Detected by D4. At this time, the surface of the lens 3 and 1
The detection surface of the dimensional CCD 4 is arranged parallel to the steel plate surface 2 to be inspected. Therefore, even if the main axis 7 connecting the center of the one-dimensional CCD 4 and the center of the lens 3 is tilted with respect to the normal line 8 of the steel plate inspected surface 2, the image of the entire visual field on the steel plate inspected surface 2 is one-dimensional CCD 4 It is possible to form an image on the detection surface of 1 without causing the image to be blurred. Therefore, directional surface defects can also be detected satisfactorily.

FIG. 2 shows the case where the main axis 7 connecting the centers of the light source 1 and the one-dimensional CCD 4 and the center of the lens 3 exists in a plane perpendicular to the length direction of the steel sheet, but the light source 1 is not always located at this position. You don't have to. Further, as shown in FIG. 3, the main axis 7 connecting the center of the one-dimensional CCD 4 and the center of the lens 3 may be inclined from a plane perpendicular to the length direction of the steel sheet. Although FIG. 3 shows the case where the light source 1 exists on the surface perpendicular to the length direction of the steel sheet, it does not necessarily have to be at this position as long as it is on the side of the surface to be inspected.

In order to inspect the surface defects along the longitudinal direction of the surface 2 to be inspected, the apparatus is installed in a process in which the surface to be inspected is moving in the longitudinal direction, or the apparatus is moved in the longitudinal direction. This is done by moving along. As another embodiment of the present invention, a two-dimensional image pickup apparatus using a planar light source 1, a two-dimensional CCD 4 and a cylindrical lens 3 is shown in FIGS. The elevation view seen from the longitudinal direction of the steel plate has the same arrangement as in FIG. In FIG. 4, the main shaft 7 connecting the center of the two-dimensional CCD 4 and the center of the cylindrical lens 3 is perpendicular to the longitudinal direction of the steel plate, but as shown in FIG. 5, the main shaft 7 is arranged so as to be inclined in the longitudinal direction of the steel plate. I don't mind.

The optical arrangement is shown in FIGS.
In the embodiment of FIG. 5, the width direction and the longitudinal direction may be opposite. Further, although the embodiment shown in FIGS. 1 to 5 shows the image picked up from only one direction, the present invention is not limited to this, and the image may be picked up from a plurality of directions. Further, in the above embodiment, the imaging of the surface defects of the steel plate was described, but the invention may be applied to the imaging of the surface to be inspected of various materials by using a metal plate such as a steel plate or an aluminum plate or a non-metal such as a polyethylene film. Can be used.

[0017]

According to the image pickup method and the image pickup apparatus of the present invention, there is no restriction on the installation positional relationship and directional surface defects can be satisfactorily imaged, so that the surface defect which has conventionally been missed can be detected. Moreover, the effects of early detection of product defects and improvement of yield in the next process were obtained.

[Brief description of drawings]

FIG. 1 is an elevational view showing the configuration and arrangement of a one-dimensional image pickup apparatus according to an embodiment of the present invention.

FIG. 2 is a side view showing the configuration and arrangement of the one-dimensional image pickup apparatus according to the embodiment of the present invention.

FIG. 3 is a side view showing the configuration and arrangement of a one-dimensional image pickup apparatus according to another embodiment of the present invention.

FIG. 4 is a side view showing the configuration and arrangement of the two-dimensional imaging device according to the embodiment of the present invention.

FIG. 5 is a side view showing the configuration and arrangement of a two-dimensional image pickup apparatus according to another embodiment of the present invention.

FIG. 6 is an elevational view showing a method of installing a conventional television camera.

FIG. 7 is a plan view showing directional surface defects.

FIG. 8 is an elevational view showing directional surface defects.

FIG. 9 is a side view showing directional surface defects.

FIG. 10 is a front view when a conventional television camera tries to capture an image of a directional surface defect.

[Explanation of symbols]

1 Light source 2 Surface to be inspected 3 Lens 4 Photodetector (CCD) 5 Illumination light 6 Scattered light 7 Main axis 8 Normal line 11 Image plane 12 Surface defect 20 Steel plate longitudinal direction 21 Steel plate width direction

Claims (3)

[Claims] 1. An optical imaging method for detecting surface defects on a surface to be inspected, wherein a main axis connecting a center of a lens and a center of a photodetector is tilted with respect to a normal line of the surface to be inspected. Surface, a lens surface, and a photodetector surface are arranged in parallel to each other and imaged. 2. A light source that illuminates the surface to be inspected, a lens that collects the scattered light scattered by the surface to be inspected, and a photodetector installed at a position where the scattered light collected by the lens is imaged. In the imaging device consisting of, the main axis connecting the center of the lens and the center of the photodetector is inclined with respect to the normal to the surface to be inspected, and the lens surface and the photodetector surface are arranged parallel to the surface to be inspected. A surface defect imaging device characterized by the above. 3. The light source is slit-shaped, and the photodetector is 1
3. The surface defect imaging device according to claim 2, wherein the imaging device is a three-dimensional CCD, and the centers of the light source, the photodetector and the lens are arranged in a plane perpendicular to the surface to be inspected.