JPH0875665A - Method and apparatus for inspecting surface using reverse reflection screen - Google Patents

Abstract

PURPOSE: To enhance the detecting sensitivity of the defect of a surface under inspection in a surface inspecting apparatus using a reverse reflection screen. CONSTITUTION: Two light sources 1a and 1b are arranged at positions holding a camera 2 at the upper and lower sides with respect to the surface of a material under inspection 10. A light source switching device 4, which changes the irradiations of the light sources 1a and 1b, in provided. The images of the light sources 1a and 1b are picked up which the camera 2. The differential image is formed from two images and processed with an image processor 6. Thus, the sensitivity is doubled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inspection apparatus using a retroreflective screen for the surface of automobile steel plates, plastics, glass and the like. In particular, the present invention relates to a surface inspection method and an apparatus therefor capable of obtaining an image with high contrast and enhancing false detection when emphasizing uneven surface defects as a bright and dark image using a retroreflective screen.

[0002]

2. Description of the Prior Art For the principle of detecting irregularities on the surface using a retro-reflective screen, see Theory.
and applications of a sur
face inspection technique
using double-pass controller
effect (Optical Engine)
ring, September 1993, vo
l. 32 No. 9), and a technique for applying such a device to the surface inspection of automobile outer panels, plastics, etc. is disclosed in JP-A-6-26844, JP-A-6-34349, and JP-A-6-34349. It is disclosed in JP-A-6-74913 and JP-A-6-148082.

FIG. 9 is a diagram showing the basic structure of a surface inspection apparatus using a retroreflective screen. 3 is a schematic view of the YZ cross section of FIG. 9 when the surface to be inspected is flat. This device comprises a retroreflective screen 13, a light source 11 and a camera 12 arranged near the upper part of the light source 11. Light source 1
The material 10 to be inspected is arranged between 1 and the retroreflective screen 13, and the light from the light source 11 is arranged to be reflected by the surface of the material 10 to be inspected and directed toward the retroreflective screen 13. Since the bead-shaped reflecting spheres having a diameter of about 60 μm are spread over the surface of the retroreflective screen, the retroreflective screen has the property of reflecting light incident on the retroreflective screen in substantially the same direction as the incident optical axis.

The light from the light source 11 is reflected on the surface of the material 10 to be inspected, enters the bead-shaped reflecting sphere of the retroreflective screen 13, and then is reflected in substantially the same direction as the incident optical axis. The light is reflected by the surface at substantially the same position and is captured by the camera 12 arranged near the upper portion of the light source 11. With this configuration, since the variation of the unevenness on the surface of the inspection target material 10 is optically emphasized, it is possible to easily detect the unevenness defect from the image captured by the camera 12.

Next, the principle of optically emphasizing unevenness defects by a surface inspection device using a retroreflective screen is shown in FIG.
Will be described with reference to. It is assumed that there is a recess between points B and C on the surface of the material to be inspected and points A and D are flat. The bead-shaped reflecting spheres 21 spread over the retro-reflecting screen 13 have a directional reflected light intensity distribution 2 as shown in the figure for incident light.
2

A camera 12 (not shown) arranged near the top of the light source captures the light reflected from the retroreflective screen and re-reflected on the surface of the material to be inspected. When viewed from the camera direction, flat points A and D of the material to be inspected are irradiated with light of intermediate intensity which is reflected at an angle α in the counterclockwise direction with respect to the incident optical axis of each reflecting sphere of the retroreflective screen. Therefore, the image of the camera has intermediate brightness.

On the other hand, when viewed from the camera direction, at point B (downhill when viewed from the camera), light with a strong reflection angle β is emitted,
At point C (uphill as seen from the camera), the reflected light with a weak reflection angle γ is emitted. Therefore, the image of the camera 12 is brighter at the point B on the downhill as viewed from the camera and darker at the point C on the uphill as viewed from the camera, as compared with the flat points A and D.

Next, with reference to FIG. 5, an image when the camera 15 is arranged near the lower side of the light source 14 and imaged will be described. FIG. 5 is a schematic diagram showing a device configuration of a surface inspection device in which the camera 15 is arranged below the light source 14, and is a cross-sectional view when the surface to be inspected is flat. The angles α ₃₁ and α ₃₂ formed by the incident light and the reflected light on the retroreflective screen shown in FIGS. 3 and 5 may be the same or different.

FIG. 6 shows a camera 15 (not shown) as a light source 1.
4 is a diagram for explaining the principle that the unevenness of the surface is optically emphasized by arranging it near the lower side of FIG. This is a case where there is a recess between points B and C on the surface of the material to be inspected and points A and D are flat.
A camera 15 (not shown) arranged near the lower part of the light source captures the light reflected from the retroreflective screen and re-reflected on the surface of the material to be inspected. When viewed from the camera direction, at flat points A and D of the material to be inspected, it is reflected by light of intermediate intensity which is reflected at an angle α in the clockwise direction with respect to the incident optical axis of each reflecting sphere of the retroreflective screen. Therefore, the image of the camera has an intermediate brightness. On the other hand, when viewed from the camera direction, light is emitted with a weak reflection angle γ at point B (downhill as seen from the camera) and light with strong reflection angle β at point C (uphill as seen from the camera). There is. Therefore, the image of the camera 12 is
Compared to the flat points A and D, the point B on the downhill as seen from the camera is darker and the point C on the uphill as seen from one camera is brighter.

As described above, it is known that the lightness and darkness due to the inclination of the defect are reversed in the image taken by the camera arranged near the upper part of the light source and the image taken by the camera arranged near the lower part of the light source. ing.

[0011]

As described above, the surface inspection device using the retro-reflective screen is a device that optically emphasizes the inclination angle of the surface. Even if there is, it should be detectable. However, in reality, there are limits to the uneven defects that can be detected due to the influence of the size of the bead-shaped reflecting sphere, the sensitivity of the imaging camera, the resolution, the surface roughness component of the material to be inspected, and the like. Therefore, in order to extract smaller defects, it is necessary to improve the optical sensitivity for enhancing the inclination.

On a metal surface such as a cold-rolled steel sheet, it is difficult to detect defects on the surface as it is due to the influence of surface roughness, and a thin oil must be applied to the surface. FIG. 7 (a) is an enlarged cross-sectional view of the vicinity of the metal surface of such a material 10 to be inspected, and FIG. 7 (b) shows the surface coated with oil. As shown in FIG. 7A, if there is no oil film, the incident light 31 becomes scattered reflected light, but by applying the oil film 34, as shown in FIG. 7B, it corresponds to the surface roughness. The incident light 31 can be reflected as reflected light 32 without being scattered by the oil film surface.
In this case, the surface of the oil film 34 has to accurately simulate the unevenness of the surface of the material to be inspected 10. However, basically, the oil flows into the concave portion and the oil flows out from the convex portion. Is smaller than the surface inclination angle of the material to be inspected. Therefore, the detection device needs to have higher sensitivity.

Further, the texture of the surface of the material to be inspected, dust adhering to the surface, oil bubbles, etc. are erroneously detected as minute defects, so that the defect detection sensitivity can be increased and at the same time the erroneous detection can be reduced. Is desired. SUMMARY OF THE INVENTION It is an object of the present invention to solve the above problems and provide a surface inspection and method using a retroreflective screen which is capable of detecting microscopic defects and has high sensitivity and no false detection, and an apparatus therefor.

In the surface inspection method using the retroreflective screen, the retroreflective screen and the light source are arranged at a relative position where the light from the light source is reflected by the surface of the material to be inspected and is directed to the retroreflective screen, By returning the reflected light when the surface of the inspection material is irradiated by the light source to the surface of the inspection material with a retro-reflective screen, and capturing the light re-reflected on the surface of the inspection material with a camera arranged near the light source. A surface inspection method for obtaining a bright and dark image in which the unevenness of the defect portion on the surface of the material to be inspected is emphasized.

Further, in the surface inspection apparatus using the retroreflective screen, the retroreflective screen and the light source are arranged at relative positions where the light from the light source is reflected on the surface of the material to be inspected and is directed to the retroreflective screen. The reflected light when the surface of the material to be inspected is irradiated with the light source is returned to the surface of the material to be inspected by a retro-reflection screen, and the light re-reflected on the surface of the material to be inspected is imaged by a camera arranged near the light source. Thus, the surface inspection apparatus obtains a bright and dark image in which the unevenness change of the defective portion on the surface of the inspection target material is emphasized.

[0016]

A first aspect of the method of the present invention is a surface inspection method using a retroreflective screen,
It is characterized in that images of two reflected lights at the same position on the surface of the material to be inspected irradiated with two different incident angles are respectively captured, a differential image of the two captured images is created, and the differential image is processed. It is a surface inspection method using a retroreflective screen.

A second invention of the method of the present invention is a surface inspection method using a retro-reflective screen, wherein images of reflected light at the same place on the surface of the material to be inspected are imaged at two different reflection angles, respectively. A surface inspection method using a retroreflective screen, which is characterized in that a differential image of two images is created and the differential image is processed. The first device of the present invention capable of suitably carrying out the above-mentioned method of the present invention is
In a surface inspection device using a retro-reflective screen, two light sources arranged so that one camera is vertically sandwiched with respect to the surface of the material to be inspected, a light source switching device for switching the light source for irradiation, and a light source for irradiation are switched. A surface inspection apparatus using a retro-reflective screen, comprising: an image processing apparatus that creates a difference image from two images captured by the image processing apparatus and processes the difference image. The second apparatus of the present invention creates two difference images from images captured by these two cameras and two cameras arranged at positions where one light source is vertically sandwiched with respect to the surface of the material to be inspected. It is a surface inspection apparatus using a retroreflective screen, which is equipped with an image processing apparatus for processing a differential image.

[0018]

According to the principle that the concave and convex defects are emphasized by the retro-reflective screen, the camera installed above the light source and the camera installed below the light source have a The light and dark are reversed. The detailed mechanism is as described with reference to FIGS. That is, in the camera installed above the light source, the downward slope is brighter than the flat portion when viewed from the camera, and the upward slope is darker than the flat portion when viewed from the camera. On the contrary, in the camera installed below the light source, the downward slope is darker than the flat portion when viewed from the camera, and the upward slope is brighter than the flat portion when viewed from the camera. Therefore, images are taken under the condition that the relative positions of the light source and the camera are opposite to each other, and the difference image obtained by subtracting the respective images has unevenness compared to the images taken under only one of the conditions. The lightness and darkness of the image due to the tilt is almost doubled. on the other hand,
The texture of the surface that does not depend on the inclination of the surface of the material to be inspected, the brightness of the air bubbles of dust, oil, etc. does not occur under any condition, and therefore, the inversion of the brightness does not occur. Therefore, in the image after the difference, only the portion due to the inclination of the defect is left as the light and dark image. The image processing apparatus has a function of generating and processing such a difference image, and an image with good contrast is obtained even for a minute defect, so that the defect can be easily detected.

Further, in the difference image, the texture of the surface of the material to be inspected, the dust and oil bubbles adhering to the surface are canceled by the difference, and therefore these are not detected as defects. As a result, it is possible to realize a surface defect device using a retroreflective screen with high defect detection sensitivity and less false detection.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram showing the configuration of a first embodiment device according to the present invention. FIG. 1 shows a retroreflective screen 3 and a light source 1.
a and 1b are arranged at relative positions where the incident light 31 from the light sources 1a and 1b is reflected on the surface of the inspected material 10 toward the retro-reflective screen 3, and the surface of the inspected material 10 is changed by the light source. The reflected light 32 when irradiated is returned to the surface of the inspected material 10 by the retro-reflective screen 3, and the light re-reflected on the surface of the inspected material 10 is imaged by the camera 2 arranged near the light source, thereby inspecting A surface inspection apparatus using a retroreflective screen 3 that obtains a bright and dark image in which unevenness of a defect portion on the surface of the material 10 is emphasized, and its characteristic configuration is the retroreflective screen 3 and one camera 2 It is composed of two light sources 1a and 1b arranged at the upper and lower positions with respect to the camera 2, shutters 5a and 5b, a light source selection device 4, and an image processing device 6.

The light source selection device 4 is linked to the image processing device 6, and is connected to the shutters 5a, 5a installed in front of the light sources 1a, 1b.
The opening and closing of 5b is controlled to switch the light source for irradiating the surface of the inspection material 10. The camera 2 includes the surface of the inspection object 10 irradiated by the light source 1a and the inspection object 1 irradiated by the light source 1b.
The surface of 0 is imaged. The image processing device 6 generates a difference image from the image of the surface of the inspection material 10 irradiated by the light source 1a and the image of the surface of the inspection material 10 irradiated by the light source 1b, detects a defect, and detects the defect. The grade, type, etc. of
The inspection result is transmitted to an output device (not shown).

The surface inspection method by the apparatus of FIG. 1 is as follows. First, the shutter 5a is opened and the shutter 5b is closed by the light source selection device 4, and the surface of the inspected material 10 is irradiated with the first light source 1a installed above the camera 2. The light emitted from the first light source 1a installed above the camera 2 is reflected on the surface of the inspected material 10 toward the retroreflective screen 3, and is reflected by the retroreflective screen 3 to be the surface of the inspected material 10. And is reflected again on the surface of the material 10 to be inspected and captured by the camera 2. This image captured by the camera 2 is stored in the image processing device 6.

Next, the shutter 5 is operated by the light source selection device 4.
A is closed and the shutter 5b is opened, and the surface of the inspected material 10 is irradiated with the second light source 1b installed below the camera 2. The light from the first light source 1a installed above the camera 2 is blocked by the shutter, and the light emitted from the second light source 1b installed below the camera 2 passes through the same path,
Captured by camera 2. The image captured by the camera 2 is stored in the image processing device 6. Next, the image processing apparatus 6 generates a difference image from the image of the surface of the inspection material 10 irradiated by the light source 1a and the image of the surface of the inspection material 10 irradiated by the light source 1b, detects a defect, and detects the defect. The grade of
The type etc. are judged and the inspection result is transmitted to an output device (not shown).

In the above embodiment, the light source is switched by opening and closing the shutter by the light source selecting device 4, but the light source selecting device 4 may be turned on and off. In FIG. 1, the angles α ₁₁ and α ₁₂ formed by the incident light and the reflected light when the lights from the two light sources are reflected by the retroreflective screen 3 may be the same or different.

FIG. 2 is a diagram showing the configuration of a second embodiment showing a surface inspection method and apparatus using a retroreflective screen according to the present invention. In FIG. 2, the light emitted from the light source 1 is reflected on the surface of the material 10 to be inspected, and the light is irradiated onto the surface of the material 10 to be inspected again by the retroreflective screen 3. The light re-reflected on the surface of the material 10 to be inspected is captured by the camera 2 a installed above the light source 1 and the camera 2 b installed below the light source 1. Cameras 2a, 2b
Is installed so that the same point on the surface of the material 10 to be inspected is in focus, and is θ with respect to the normal line of the material 10 to be inspected.
The imaging angle is set to ₁ and θ ₂ . Image processing device 7
For each of the images of the cameras 2a and 2b, the distortion caused by the difference in the imaging angle is corrected to make the scale of the images the same, and then a difference image between the image of the camera 2a and the image of the camera 2b is generated. Furthermore, defect detection for the difference image,
Apply processing logic required for recognition. In the present embodiment, the image processing device 7 corrects the image distortion, but it is also possible to use the cameras 2a and 2b in which the arrangement of the light receiving devices is adjusted in advance so that the distortion does not occur. In FIG. 2, the angle α ₂₁ between the incident light on the retro-reflective screen and the reflected light is
It may be equal to or different from ₂₂ .

With the configurations of the first and second embodiments, it is possible to obtain the difference between two images in which the lightness and darkness of the images are reversed according to the inclination direction of the defect on the surface of the material 10 to be inspected. Further, it is possible to cancel the noise component that does not depend on the inclination of the surface of the inspection object 10. FIG. 8 is a difference image obtained by the apparatus according to the embodiment of FIG. 1 and the light source 1a shown in FIG.
FIG. 7 shows a gray level signal of a conventional image captured using only the image. In the figure, in order to normalize the image signal, the average value of the gray levels is set to zero brightness. As is clear from the figure, it can be confirmed that in the difference image according to the present invention, the signal intensity indicating a defect is greatly changed, and the defect detection sensitivity is improved.

According to the embodiment described above, it is possible to realize a surface inspection apparatus using a retroreflective screen which enables detection of minute defects and has few false detections.

[0028]

According to the present invention, in a surface inspection apparatus using a retro-reflective screen, it becomes possible to detect minute defects which cannot be detected by the conventional surface inspection apparatus, and at the same time, it is possible to detect an image that does not depend on the defects. Since the light and dark can be erased, false detection can be reduced. As a result, it is effective for more precise surface inspection.

[Brief description of drawings]

FIG. 1 is a diagram showing a first embodiment of a surface inspection apparatus using a retroreflective screen according to the present invention.

FIG. 2 is a diagram showing a second embodiment of a surface inspection apparatus using a retroreflective screen according to the present invention.

FIG. 3 is a diagram showing a device configuration of a surface inspection device in which a camera is arranged above a light source.

FIG. 4 is a diagram illustrating a principle in which unevenness is emphasized by a retroreflective screen in the optical arrangement of FIG.

FIG. 5 is a diagram showing a device configuration of a surface inspection device in which a camera is arranged below a light source.

FIG. 6 is a diagram illustrating a principle in which unevenness is emphasized by a retroreflective screen in the optical arrangement of FIG.

FIG. 7 is a diagram illustrating light reflection on a surface coated with oil.

FIG. 8 is a diagram showing a comparison between a defect signal according to the present invention and a defect signal according to the related art.

FIG. 9 is a diagram showing a device configuration of a surface inspection device in which a camera is arranged above a light source.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 light source 1a 1st light source 1b 2nd light source 2 camera 2a 1st camera 2b 2nd camera 3 retroreflection screen 4 light source selection device 5a, 5b shutter 6 image processing device 7 image processing device 10 inspected material 11 light source 12 camera 13 retro-reflective screen 14 light source 15 camera 21 beaded reflective sphere 22 reflected light intensity distribution 23 reflected light intensity distribution 31 incident light 32 reflected light 33 camera direction 34 oil film

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location G06T 1/00 7/60 9061-5H G06F 15/70 350 G

Claims (4)

[Claims] 1. A surface inspection method using a retro-reflective screen, wherein images of two reflected lights at the same location on the surface of a material to be inspected irradiated at two different incident angles are respectively captured, and the difference between the two captured images. A surface inspection method using a retroreflective screen, which comprises creating an image and processing the difference image. 2. In a surface inspection method using a retro-reflective screen, two images of reflected light at the same spot on the surface of the material to be inspected are displayed.
A surface inspection method using a retroreflective screen, characterized in that images are picked up at three different reflection angles, a difference image between the two picked-up images is created, and the difference image is processed. 3. A surface inspection apparatus using a retroreflective screen, wherein two light sources are arranged at positions where one camera is vertically sandwiched with respect to the surface of the material to be inspected, and a light source switching device for switching the light source for irradiation. A surface inspection apparatus using a retroreflective screen, comprising: an image processing device that creates a difference image from two images that are picked up by switching the illuminating light source and that processes the difference image. 4. A surface inspection apparatus using a retro-reflective screen, two cameras arranged at positions where one light source is vertically sandwiched with respect to the surface of the material to be inspected, and a difference image from the images captured by the two cameras. And an image processing device for processing the difference image, the surface inspection device using a retroreflective screen.