JPH04340447A - Method and device for inspecting surface by retro-reflection screen - Google Patents

Abstract

PURPOSE:To enable a capability for detecting a pseudo image at a defective portion to be improved by allowing a luminous position of a light source to be moved to a plurality of locations and an image which is captured by a camera to be subjected to addition by an image-processing device for each movement of the luminous position. CONSTITUTION:Light sources 3a, 3b,... and 3n are placed at relative positions where light of the light sources hits against an object 5 to be inspected, is reflected, and then travels toward a retro-reflection screen 1. The light sources 3a-3n are successively lit up by a light source switcher 6, one light at a time. A timing of lighting is synchronized to a timing signal generator 12 and a timing signal simultaneously allows an image pickup timing of a camera 2 to be synchronized. When the light source 3a-3n are lit successively, the luminous positions are moved. Therefore, an image which is captured by the camera 2 for each luminescence of light sources 3a-3n is subjected to addition by an image processing device 8 and a traveling pseudo image becomes ambiguous when it is observed by a monitor 9. However. since the defective image is fixed, the image is highlighted, thus preventing the pseudo image from being regarded as the defective portion by mistake.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a surface inspection method for automobile exterior panels, plastic surfaces, etc., and more specifically, the present invention relates to a method for inspecting surfaces such as automobile exterior panels and plastic surfaces. This invention relates to a surface inspection method for detecting parts.

0002

2. Description of the Related Art A surface inspection method using a retroreflective screen is disclosed in Japanese Patent Laid-Open No. 62-502358, the gist of which is as follows. The inspection device used in this inspection method consists of a retroreflective screen 3 as shown in Figure 8.
0, camera 31, and light source 32. The surface of the object to be inspected 33 is placed between the retroreflective screen 30 and the light source 32, and placed in a relative position such that the light from the light source 32 hits the surface of the object to be inspected 33 and is reflected toward the retroreflective screen 30. do. The light reflected by the inspection object 33 and entering the retroreflection screen 30 is reflected in almost the same direction as the incident optical axis, and is reflected again from the surface of the inspection object 33, and is placed slightly above the light source 32. Captured by camera 31. This allows the camera 31 to capture an image in which changes in unevenness on the surface of the inspection object 33 are optically emphasized, making it possible to easily find defective locations on the surface, which should be smooth.

The principle of this detection will be explained using FIGS. 9 and 10. FIG. 9 shows a case where there is no defect on the surface of the inspection object 33, and FIG. 10 shows a case where there is a defect. The retroreflective screen 30 has bead-shaped reflective spheres 34 closely attached to its surface, and each reflective sphere 34 has a directional reflection pattern for incident light as shown. As shown in FIG. 9, when there is no defect on the surface, the light coming from the direction of the light source is reflected in the direction of the retroreflection screen 30 on the surface of the inspection object 33. The camera installed near the light source and slightly above the light source faces the surface of the inspection object 33 from the camera viewing direction in the figure, and the reflected light from the retroreflective screen 30 is re-reflected by the inspection object 33. It captures the light. Now, when we look at points A, B, and C on the surface of the inspection object 33 from the camera, on a flat surface with no defects, we see the same intensity of light reflected at the angle α of each reflection sphere 34 of the retroreflection screen 30. Therefore, the camera captures it as a surface with intermediate brightness without any change in shading. On the other hand, if there is a defect on the surface of the inspection object 33 as shown in FIG.
At point B (downhill when viewed from the camera side), light from the angle α of the reflective sphere of the retroreflection screen 30 is captured as before, but at point C (downhill when viewed from the camera side), light with a strong reflection angle γ is captured, and at point C (camera When viewed from the side (uphill), weak light at angle β will be captured. Therefore, it will appear bright on a downhill slope at point B, and dark on an uphill slope at point C. The width of the directivity of the reflection pattern of the reflective spheres 34 of the retroreflective screen 30 is as sharp as about ±1 degree, so even if the defect is slightly tilted, the amount of change in brightness is large and the unevenness of the defect is observed to be emphasized. It turns out.

0004

[Problem to be Solved by the Invention] In the conventional device described above, considering the optical path in which the light from the light source 32 directly hits the defective part, if the defective part is a recess, the light reflected from the recess will be reversed. When the camera 31 captures the light that is reflected from the reflective screen 30 and returned to the inspection object 33, the concave portion acts like a concave mirror, and as a result, a bright and dark image of the defective portion appears, due to the influence of the defective concave portion. A bright false image occurs. Further, when the defective portion is a convex portion, the convex portion acts like a convex mirror, and a dark false image is generated at the same position. A false image appears in a place where there is no defect, as if there were a defect there, so that during defect inspection, the position where the false image occurs is mistakenly recognized as having a defect.

[0005]

[Means for Solving the Problems] The present invention aims to solve the above problems by connecting a retroreflective screen having bead-shaped reflective balls tightly arranged on its surface, a light source, and an object to be inspected with light from the light source. is placed at a relative position such that the light hits the object to be inspected and is reflected and faces the retroreflective screen, and the reflected light when the surface of the object to be inspected is irradiated with a light source is returned to the object to be inspected by the retroreflector screen. By capturing the light re-reflected on the surface of the object to be inspected with a camera placed near the light source, a retroreflective screen is used to obtain an image that emphasizes changes in brightness and darkness of the unevenness of the defective area on the surface of the object to be inspected. A surface inspection method using a retroreflective screen, characterized in that the light source has a plurality of light emission positions, and images captured by the camera for each light source generation position are summed by an image processing device. Further, the inspection device for realizing the above surface inspection method includes a light emitting position moving means for moving the light emitting position of the light source to multiple positions near the camera, and an addition process for images captured by the camera at each light source generation position. The apparatus is characterized in that it includes an image processing means.

[0006]

[Operation] According to the surface inspection method described above, the position where the pseudo image appears accompanying the defect image caused by the surface defect of the object to be inspected moves when the generation position of the light source is moved. On the other hand, the defect image always remains at the defective position even if the light emitting position of the light source is changed. This is because a false image is a virtual image that appears due to a deviation in the optical path due to the camera and light source not being in the same position, and a defective image is a real image that appears at a defective position regardless of the light emitting position of the light source.

[0007] Therefore, if the light emitting position of the light source is moved over multiple positions and the image captured by the camera is added up by the image processing device each time, the false image whose appearance position changes will gradually fade, and conversely, the false image whose appearance position will not change will fade. Since the image appears emphasized, the more the light emitting position of the light source is moved, the greater the contrast ratio between the false image and the defective image becomes, and the detection ability of the false image can be improved. In addition, the inspection device for realizing the above-mentioned surface inspection method is a light emitting device in which a plurality of light sources are arranged in a row in the moving direction and are turned on sequentially, or
It is composed of a light source moving means such as a light emitting device that slides one light source step by step in the movement direction, and an image processing means that adds and processes images captured by a camera each time the light emitting position of the light source is moved.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of an apparatus for carrying out the surface inspection method using a retroreflective screen according to the present invention. A camera 2 and a light source 3a are located opposite to the retroreflective screen 1.
3b...3n are arranged, and the inspection object 5 is placed between them. At this time, the light sources 3a to 3n are arranged at relative positions such that the light from the light sources 3a to 3n hits the object 5 to be inspected and is reflected toward the retroreflective screen 1. The light sources 3a to 3n are sequentially turned on one by one by a light source switch 6, and the switching timing for sequential lighting is determined by a timing signal generator 12.
The timing signal simultaneously operates to synchronize the imaging timing of the camera 2.

First, the light source 3a is turned on and the object to be inspected 5 is exposed.
When irradiated with , the light reflected by the inspection object 5 heads toward the retroreflection screen 1, and the light is reflected by the reflection sphere 7 closely mounted on the surface of the retroreflection screen 1 and returns to the inspection object 5 and is re-reflected. Therefore, the re-reflected light is captured by camera 2. The re-reflected light from the inspection object 5 captured by the camera 2 at this time has an optical path as shown in FIG. Since the reflective sphere 7 of the retroreflective screen 1 has a reflective pattern with the directionality shown in the figure for the incident light beam, the image captured by the camera 2 will be bright and dark if there is no defect on the surface of the inspection object 5. Capture it as a surface with intermediate brightness that does not change. When there is a concave defect on the surface of the inspection object 5, as shown in FIG.
Based on the reflected light at the defective part, point C (
On the downhill slope (as seen from the camera side), it receives strong light from the reflecting sphere 7 at an angle γ and becomes brighter than point A, which is also the defective part B.
At the point (uphill as seen from the camera side), the angle β of the reflecting sphere 7
The defective part becomes easier to detect because it receives weaker light and becomes darker than point A. At this time, the concentrated light from the light source 3 is reflected by the defective part acting like a concave mirror, and as shown in FIG.
When viewed from the camera 2, a brighter image appears at the Y point of the inspection object 5 than at the A point, creating a false image as if there is also a defect at the Y point. The image captured by the camera 2 of the above state is as shown in FIG. 3, with a defect image D whose brightness changes in the center and a pseudo image Q displayed above it. At this time, if the defective part is a convex part instead of a concave part, the defective part acts like a convex mirror, so the pseudo image Q' is round, as the light does not return, as shown in Figure 4. It appears as a dark side.

[0010] Since these pseudo images Q and Q' appear as if there were a defect at a position where there is no defect, there is a high possibility that the position of the pseudo images Q and Q' may be mistakenly recognized as having a defect as well. . Since these pseudo images Q and Q' are unnecessary during inspection, it is required to eliminate them. The method and means for erasing the pseudo images Q and Q' is to move the light emitting position of the light source. As shown in Fig. 1, the light source 3 has a plurality of (n) lamps arranged in a row in the moving direction, so if the light sources 3a to 3n are turned on in sequence, the light emitting position of the light source 3 will be moved. Therefore,
Images captured by the camera 2 each time the light sources 3a to 3n emit light are summed by the image processing device 8, and when viewed on the monitor 9, a pseudo image Q whose generation position moves on the image is shown in FIG.
, Q' are faded, and conversely, since the defect images D and D' remain unchanged, their images are emphasized. Therefore, when images corresponding to the number of times the light emitting position is moved from the light source 3a to the light source 3n are added, the brightness ratio of the defective images D, D' and the pseudo images Q, Q' will change as the light emitting position of the light source is moved more. This makes it possible to prevent false images Q and Q' from being mistaken as defective parts.

The means for moving the light emitting position of the light source 3 is not a method of sequentially lighting up a plurality of light sources 3a to 3n as described above, but a method of moving one light source 3 step by step in the moving direction as shown in FIG. The driving device 10 is attached to the sliding plate 11 to
It can also be moved by Alternatively, as shown in FIG. 7, the light source 3 can be moved by installing a liquid crystal shutter 15 in front of the light source 3 and sequentially shutting it off in the moving direction by the control device 13. . In either method shown in FIGS. 6 and 7, the movement timing of the light source 3 is synchronized with the imaging timing of the camera 2 using a timing signal from the timing signal generator 12 described above. Note that the same effect as described above can be obtained by moving the light source position not only in the vertical direction as described above but also in the horizontal direction.

0012

Effects of the Invention As explained above, according to the surface inspection method and device using a retroreflective screen of the present invention, the generation of false images due to the influence of defective parts, which was a problem with conventional methods, can be avoided by changing the light emitting position of the light source. This problem can be solved by moving the light emitting position and adding the images captured by the camera each time the light emitting position is moved. This has the effect of making the surface inspection method and device using a retroreflective screen more perfect.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of an inspection device using a retroreflective screen according to an embodiment of the present invention.

FIG. 2 is an optical path diagram illustrating the generation of defect images and pseudo images.

FIG. 3 is an image captured by a camera when the defective part is a recess.

FIG. 4 is an image captured by a camera when the defective portion is a convex portion.

FIG. 5 is an image diagram when image processing is performed by moving the light source.

FIG. 6 is a conceptual diagram showing an embodiment of a light emitting position moving means of a light source.

FIG. 7 is a conceptual diagram showing another embodiment of the light emitting position moving means of the light source.

FIG. 8 is a conceptual diagram of an inspection device that implements a conventional surface inspection method.

FIG. 9 is an explanatory diagram of an optical path when there is no defective part in a conventional inspection method.

FIG. 10 is an explanatory diagram of an optical path when there is a defective part in a conventional inspection method.

[Explanation of symbols]

1...Retroreflective screen 2...Camera 3 (3a, 3b...3n)...Light source (light emitting position moving means) 5...Inspection object 7...Reflecting ball 8...Image processing device (image processing means)

Claims (2)

[Claims] 1. A retroreflective screen having bead-like reflective balls closely arranged on its surface, a light source, and an object to be inspected; light from the light source hits and reflects the object to be inspected, and the retroreflective screen When the surface of the object to be inspected is irradiated with a light source, the reflected light is returned to the object to be inspected using a retroreflective screen, and the light re-reflected from the surface of the object to be inspected is reflected by the light source. In a surface inspection method using a retroreflective screen, in which changes in unevenness of a defective portion on a surface of an object to be inspected are captured as an image with emphasis on changes in brightness and darkness by capturing with a camera placed nearby, the light source is emitted at a plurality of positions, The image captured by the camera for each light emitting position of the light source is
A surface inspection method using a retroreflective screen, characterized in that addition processing is performed by an image processing device. 2. A retroreflective screen, a light source, and an object to be inspected are arranged in relative positions such that light from the light source is reflected by the object to be inspected and directed toward the retroreflective screen, A surface using a retro-reflective screen in which the reflected light when the surface of the object is irradiated with a light source is returned to the object to be inspected using a retro-reflective screen, and a camera is placed near the light source to capture the light that is re-reflected from the surface of the object to be inspected. The inspection device is characterized by comprising a light emitting position moving means for moving the light emitting position of the light source to a plurality of positions near the camera, and an image processing means for performing addition processing on images captured by the camera for each light emitting position of the light source. A surface inspection device using a retro-reflective screen.