JPH0875666A - Surface inspection device using retro-reflective screen - Google Patents

Abstract

(57) [Summary] [Objective] In a surface inspection device using a retro-reflective screen, a clear image with less focus shift can be obtained even if the imaging angle θ of the camera 12 is increased, and defect detection sensitivity is increased. To do. [Structure] The line sensor camera 4 captures the reflected light reflected from the cold-rolled steel sheet 1 through a retro-reflection screen 3. The scanning cycle of the line sensor camera 4 is controlled by the moving speed signal of the cold-rolled steel sheet 1 from the speedometer 5 to generate a two-dimensional image while correcting the intensity of the image pickup signal. Image blur does not occur even if the imaging angle θ is large.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for detecting uneven surface defects by using a retroreflective screen, and more particularly to a sheet-shaped object in a manufacturing line such as a cold rolled steel sheet manufacturing process. The present invention relates to a device for inspecting an inspection surface in-process.

[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 the present invention to an automobile outer panel, plastic, etc., is disclosed in JP-A-6-26844 and JP-A-6-34.
349, JP 6-74913, and JP 6
It is disclosed in Japanese Patent No. 148082.

FIG. 7 is a diagram showing the basic construction of a surface inspection apparatus using a retroreflective screen. 2 is a schematic view of the YZ cross section of FIG. 7 when the surface to be inspected is flat. The surface inspection apparatus using the retroreflective screen is composed of the retroreflective screen 3, the light source 2, and the camera 12 arranged near the upper portion of the light source 2. The material 11 to be inspected is arranged between the light source 2 and the retroreflective screen 3, and the light of the light source 2 is arranged to be reflected by the surface of the material 11 to be inspected and directed toward the retroreflective screen 3. The retro-reflective screen has bead-shaped reflective spheres having a diameter of about 60 μm spread on the surface thereof, and therefore has a characteristic of reflecting the light incident on the retro-reflective screen 3 in substantially the same direction as the incident optical axis.

The light from the light source 2 is reflected on the surface of the material 11 to be inspected, enters the bead-shaped reflecting sphere of the retro-reflection screen 3, and then is reflected in substantially the same direction as the incident optical axis, and the material 1 to be inspected again.
It is reflected by the surface of the light source 1 at substantially the same position and is captured by the camera 12 placed near the upper portion of the light source 2. With this configuration, since the change in the unevenness on the surface of the inspection target material 11 is optically emphasized, the unevenness defect can be easily detected from the image captured by the camera 12.

Next, the principle of optically emphasizing unevenness defects by a surface inspection apparatus using a retroreflective screen will be described with reference to FIG. This is a case where there is a recess between points B and C on the surface of the material 11 to be inspected and points A and D are flat. The bead-shaped reflecting spheres 21 spread over the retro-reflecting screen 13 are scattered as incident light 31 as reflected light having directivity as shown in the figure and have an intensity distribution 22.

A camera (not shown) arranged near the upper part of the light source in the direction of the arrow 33 captures the light 32 reflected from the retroreflective screen 13 and re-reflected on the surface of the material 11 to be inspected. When viewed from the camera direction, the flat point A of the inspected material,
At point D, since the light of intermediate intensity is reflected at an angle α in the counterclockwise direction with respect to the incident optical axis of each bead-shaped reflecting sphere of the retroreflective screen 13, the image of the camera has an intermediate brightness. It becomes

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 on the downhill as seen from the camera at the point B and darker on the uphill as seen from the camera at the point C, as compared with the flat points A and D.

As described above, in the surface inspection apparatus using the retroreflective screen, the surface irregularities and the defects can be picked up as an image in which they are optically emphasized, so that the defects of the inspection object 11 can be detected. .

[0009]

In the surface inspection apparatus using the retroreflective screen, it is better to make the image pickup angle of the camera 12 as large as possible in order to increase the defect detection sensitivity. That is, the imaging angle shown in FIG. 2, that is, the angle θ formed by the normal line of the surface of the inspection target material 11 and the imaging light is increased, and the camera 12 images the inspection target material 11 obliquely, so that the inspection target material 11 is detected. This is because the effect of increasing the directivity of the reflected light on the surface of is obtained. FIG. 4 shows the sensitivity of a defect image when the imaging angle θ of the camera 12 is changed with respect to a concave defect and a convex defect. here,
The detectability of defects was evaluated using the luminance ratio of defect signals as shown in FIG. As is clear from FIG. 4, as the imaging angle θ becomes larger, the luminance ratio of the defect signal becomes higher and the detectability of the defect becomes better. However, if the imaging angle θ becomes too large, the defect detectability becomes poor. I also know that. This is because the camera 1 increases as the imaging angle θ increases.
This is because the angle formed by the focal plane of the second imaging lens and the surface of the material 11 to be inspected becomes large and only a part of the material 11 to be inspected can be focused.

The present invention provides a means for obtaining a clear image with little defocus even if the image pickup angle of the camera 12 is increased and increasing the defect detection sensitivity.

[0011]

According to the present invention, a retroreflective screen and a light source are arranged at a relative position where light from the light source is reflected by the surface of the material to be inspected and is directed to the retroreflective screen, By reflecting the reflected light when the surface of the material is irradiated with the light source to the surface of the material to be inspected by the retro-reflection screen, and by imaging the light re-reflected on the surface of the material to be inspected by the camera arranged near the light source The present invention relates to an improvement of a surface inspection apparatus using a retroreflective screen that obtains a bright and dark image in which unevenness of a defect portion on the surface of an inspection object is emphasized. An image pickup means arranged side by side, a speed detection means for detecting a moving speed of the material to be inspected or a transport speed of the material to be inspected, and an image processing apparatus for processing an image pickup signal imaged by the image pickup means by a signal from the speed detection means Equipped with It is intended to provide a surface inspection apparatus using the retroreflective screen, characterized in.

[0012]

According to the present invention, the image signal can be obtained by the line sensor camera only in the width direction of the material to be inspected, that is, in the direction parallel to the retroreflective screen. This image signal is a signal in which the lens is in focus and has no blur regardless of the imaging angle θ of the camera. When the material to be inspected is a sheet and in-process inspection is performed on the manufacturing line, the operation timing of the line sensor camera is controlled according to the line speed, and the imaging signal is always provided at regular intervals in the longitudinal direction of the material to be inspected. A two-dimensional image is obtained by taking in and superimposing. The two-dimensional image of the material to be inspected thus obtained is an image that is not out of focus, as if the camera were to image it from the direction normal to the surface of the material to be constructed. Therefore, by providing the image processing device that controls the line sensor camera by using the moving speed of the inspected material, it is possible to detect the uneven defect of the inspected material according to the defect detection principle by the retroreflective screen. . Further, for example, in an example of inspecting automobile outer panels in batches after press molding,
The material to be inspected is moved on the transport table, and the movement signal is received by the image processing apparatus, so that the same effect as the in-process inspection can be obtained.

[0013]

1 is a diagram showing the construction of an embodiment of a surface inspection apparatus using a retroreflective screen according to the present invention, which is applied to an in-line inspection in a cold rolled steel sheet manufacturing process. In FIG. 1, a cold-rolled steel sheet 1 as a material to be inspected
The light emitted from the light source 2 is reflected on the surface of, and the surface of the cold-rolled steel sheet 1 is irradiated again by the retroreflective screen 3. As shown in FIG. 3, the irradiated light has a scattering intensity distribution 22 as shown in FIG. 3 due to the bead-shaped reflecting spheres on the surface of the retroreflective screen 3, and is re-applied on the surface of the cold-rolled steel sheet 1. The reflected light is captured by the line sensor camera 4. As described above, the image pickup signal of the line sensor camera 4 is a signal in which unevenness is optically emphasized.

Further, a cold-rolled steel sheet 1 which is a material to be inspected measured by a steel sheet speed meter 5 installed on a production line.
Of the moving speed is transmitted to the image processing device 6. The image processing device 6 controls the scanning cycle of the line sensor camera 4 according to the moving speed of the cold-rolled steel sheet 1, and changes in the exposure time of the image sensor of the line sensor camera 4 caused by controlling the scanning cycle, that is, The image pickup signals are sequentially combined while correcting the intensity of the image pickup signal to generate a two-dimensional image. The two-dimensional image obtained in this manner is used by the line sensor camera 4
Since the focus of is always on the imaging part shown in FIG. 1,
Image blur does not occur even if the image is picked up from an oblique direction. Since the image processing device 6 can perform processing necessary for defect detection from the image thus obtained, the defect detection sensitivity can be increased. Further, by controlling the scanning cycle of the line sensor camera 4, it is possible to capture an image with a constant resolution in the longitudinal direction 1a of the cold rolled steel sheet 1 (in this case, the moving direction of the steel sheet), so it is necessary to correct the size of the captured image. There is no.

FIG. 6 shows the effect of the present invention, and shows a comparative example of the concave defect with the imaging result of the conventional apparatus. In the comparative example of FIG. 6, the imaging resolution per pixel of the line sensor camera is set so as to match the resolution in the width direction of the camera in the conventional device. Also,
While the defective sample, which is the material to be inspected, is moved at a constant speed on the transport table, the scanning cycle of the line sensor camera is controlled in synchronization with the pulse signal of the motor driver that drives the transport table. The imaging resolution of the embodiment of the above and the camera resolution of the conventional apparatus are made to match. As shown in FIG.
It is confirmed that the defect image luminance ratio does not decrease even when the photographing angle θ exceeds 75 degrees, and the defect detection sensitivity is improved.

In the above-described embodiment, the defect detection processing is performed after the two-dimensional image is generated. However, the image pickup signal of the line sensor camera 4 is processed and only the portion where the defect signal is extracted is image-processed. It is also possible to judge the type and grade of the defect. If the material to be inspected does not move continuously, place the material to be inspected on the transport table and move it.
When the image processing device 6 receives the movement signal of the transport table, it can be operated in the same manner as the in-process inspection.

[0017]

According to the present invention, in a surface inspection apparatus using a retroreflective screen, a clear image with less defocus can be obtained even if the image pickup angle of the camera is increased. Can be improved.

[Brief description of drawings]

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

FIG. 2 is a diagram showing a device configuration of a surface inspection device using a conventional retroreflective screen.

FIG. 3 is a diagram illustrating a principle in which unevenness is emphasized by a retroreflective screen.

FIG. 4 is a diagram showing a relationship between an imaging angle of a camera and a sensitivity of a defect image.

FIG. 5 is a diagram illustrating a luminance ratio of a defect signal.

FIG. 6 is a diagram showing an effect of the present invention.

FIG. 7 is a diagram showing a device configuration of a surface inspection apparatus using a conventional retroreflective screen.

[Explanation of symbols]

 1 Cold Rolled Steel Plate 2 Light Source 3 Retro-Reflecting Screen 4 Line Sensor Camera 5 Steel Plate Speedometer 6 Image Processing Device 11 Inspected Material 12 Camera 21 Bead-like Reflecting Sphere 22 Reflected Light Intensity Distribution 31 Incident Light 32 Reflected Light 33 Arrow

─────────────────────────────────────────────────── ─── 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 (1)

[Claims] 1. A surface inspection apparatus using a retro-reflective screen, an image pickup device having image pickup elements arranged in a one-dimensional form, and a speed detection device for detecting a moving speed of a material to be inspected or a transportation speed of the material to be inspected. An image processing device for processing an image pickup signal picked up by the image pickup means by a signal from the speed detecting means, and a surface inspection apparatus using a retroreflective screen.