JPH06137845A - Device for inspecting uneven streak on surface of steel plate - Google Patents

Abstract

PURPOSE:To provide a surface uneven streak-inspection device for inspecting chatter mark (lateral streak) which is produced on the surface of a steel plate due to vibration of rolls. CONSTITUTION:A device for inspecting uneven streak on the surface of a steel plate is provided with an illuminating means having a light source 1 and an optical system 2 capable of collecting light from the light source 1 to obtain a roughly parallel light, a light receiving means comprising a semi-transparent screen 3 on which a reflected light reflected on the surface of a steel plate 10 is projected and an image sensing means to sense a projected image on the semi-transparent screen 3 by a camera 4 to obtain an image signal, and an inspection means to inspect unevenness on the surface of the steel plate from the image signal from the image sensing means. In the light receiving means, the semi-transparent screen 3 is used as a screen on which a reflected light reflected on the surface of the steel plate is projected, and the camera 4 is positioned at the rear of the semi-transparent screen 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sheet-like object surface unevenness inspection apparatus for inspecting minute unevenness on the surface of a sheet-like object such as a surface-treated steel plate or a stainless steel plate with high sensitivity and high speed.

[0002]

2. Description of the Related Art As a means for inspecting the surface irregularities of a sheet-like object having a relatively high reflectance such as surface-treated steel plate, stainless steel plate, plastic, etc. during traveling, Japanese Patent Laid-Open No. 62-62.
There is No. 205. FIG. 4 is a block diagram of a conventional surface unevenness fringe inspection apparatus for a sheet-like object using a reflection method. In FIG. 4, the light from the slit-shaped light source 20 is applied to the steel plate 10 as the inspection object. The light reflected by the steel plate 10 is projected on the reflection type screen 13, and unevenness in the intensity distribution of the reflected light is generated according to the surface unevenness of the steel plate 10. This is imaged by the camera 4 and input to the image processing unit, The quality of the inspection target is determined.

[0003]

In the conventional surface unevenness fringe inspection apparatus as described above, it is caused by the unevenness of the intensity distribution (of the reflected light corresponding to the surface unevenness of the sheet-like object to be inspected) projected on the screen. The camera should be installed at a position where the strongest scattered light can be detected, but in the method of observing the screen surface side, if the camera is placed in front of the screen,
There is a problem that it obstructs the field of view and makes it difficult. In addition, since the image is distorted due to the opposing angle between the screen and the camera, there is a problem that the image processing becomes complicated to correct the distortion.

The present invention has been made to solve the above problems, and the distribution of scattered light generated on the screen by the reflected light from the object to be inspected can be detected most strongly, and the surface uneven fringes are less affected by external light. The purpose is to provide an inspection device.

[0005]

In order to achieve the above object, the present invention according to claim 1 comprises a light source and an illuminating means having an optical system for condensing light from the light source to obtain substantially parallel light. A screen on which the reflected light reflected by the surface of the steel sheet, which is irradiated from the illumination means to the sheet-shaped steel sheet, is projected; and a light-receiving means comprising an imaging means for capturing a projected image on the screen to obtain an image signal; And a means for inspecting the unevenness of the steel sheet surface from the image signal, wherein the light receiving means is a screen on which the reflected light reflected by the steel sheet surface is projected, and a projected image on the screen behind the screen. An image pickup means for picking up an image is provided, and in the second aspect, the light receiving means is a hood that blocks outside light around the screen onto which the reflected light reflected by the steel plate surface is projected. It is obtained by the configuration Tsu, by further forming a black coating film for anti-reflection on the inner surface of the hood, greater than its advantages.

[0006]

With the structure of the present invention, the camera can capture a projected image from the back of the screen,
No image distortion, no influence of extraneous light,
The strongest scattered light can be detected.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the configuration of an embodiment of the surface unevenness fringe inspection apparatus for sheet-like objects of the present invention.

The surface unevenness fringe inspection apparatus of this embodiment comprises a light source 1,
A lens 2 for obtaining parallel light, a semitransparent screen 3 onto which reflected light from the steel plate 10 is projected, a two-dimensional CCD camera 4 for picking up an image on the semitransparent screen 3, and a shielding member for covering the front surface of the camera 4. It includes a hood 5, an image processing unit 6, a calculation unit 7, a memory 8 for temporarily storing image signals, and a display unit 9. The image processing unit 6 performs binarization, noise removal, density conversion, moment search, and the like. The calculation unit 7 is a device for performing processing such as fast Fourier transform (FFT) and affine transform at high speed. Further, the semi-transparent screen 3 is made of a semi-transparent plate such as a frosted glass and a diffusion plate to form a projected image of the light reflected by the steel plate 10. Further, the hood 5 blocks external light and prevents reflection. The inside is painted black. The illumination device including the light source 1 and the lens 2 is a steel plate 10
Of the translucent screens 3 and 2 which are arranged upstream in the transport direction of
The light-receiving portion including the dimensional CCD camera 4 is arranged downstream. The arrangement of the lighting device and the light receiving portion may be reversed.

The light from the light source 1 is converted into parallel light by the lens 2 and then radiated to the steel plate 10 as an inspection object.
At this time, when a point light source is used as the light source 1, the lens 2
The distance between the steel plate and the lens 2 is selected so that the size of the irradiation spot of 1 is sufficiently larger than the pitch of the chatter mark. When the width of the steel plate is 1 meter, the lens spot diameter is set to be large enough to inscribe a square of 500 mm × 500 mm, and two adjacent light sources 1 in the width direction of the steel plate 1
Was set up. The two-dimensional CCD camera 4 has a CCD of 512 × 512 pixels, and a 500 mm × 500 mm square is set as an imaging range. When a rod-shaped light source is used as the light source 1,
Cylindrical lens is used for lens 2, 500 mm x 1
A cylindrical lens was arranged at a position that realized a spot range of 000 mm. Also in this case, two two-dimensional CCD cameras 4 are arranged adjacent to each other in the steel plate width direction.

The light reflected by the steel plate 10 is projected on the semi-transparent screen 3 on the front surface of the hood 5, and on the semi-transparent screen 3, there is unevenness in the intensity distribution of the reflected light according to the surface irregularities of the steel plate 10, as shown in FIG. Occur. The recessed portion of the steel plate 10 acts as a concave mirror and collects incident light, so that it becomes bright on the semitransparent screen 3. On the contrary, the convex portion acts as a convex mirror and disperses the incident light, so that it becomes dark on the semitransparent screen 3. This is a two-dimensional CCD camera 4
Then, the image is picked up and is input to the image processing unit 6 as digital data of 512 × 512 pixels.

The image processing unit 6 performs a process such as binarization, and the binarized data is Fourier-transformed using the arithmetic unit 7. A power spectrum is obtained from the result of the Fourier transform and its peak power is obtained. In addition, the inverse Fourier transform is performed leaving only specific frequency components, and the length and
Find the area. The peak power of the power spectrum and the length and area of the time series data are the strength of the uneven stripes. The quality of the inspection target is determined according to the strength of the uneven stripes, and the result is displayed on the display unit 9.

Further, without performing the analysis up to this point, the presence or absence of a bright portion (recessed portion) above the A% increase level of the image data with reference to the overall brightness average value, and conversely below the B% decrease It is also possible to determine only the presence or absence of a dark part (convex part). Here, A and B are constants predetermined according to the inspection target.

[0013]

As described above, according to the present invention, since the semi-transparent screen is shielded by the hood, the strongest scattered light on the steel plate surface can be detected without being affected by external light. It is possible to detect finer uneven fringes than before, and the S / N ratio of the obtained image signal is also improved.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention.

FIG. 2 is an explanatory view showing a waviness state of a steel plate.

FIG. 3 is an explanatory diagram showing a generation state of chatter marks.

FIG. 4 is a configuration diagram of a conventional inspection device using a reflection screen method.

[Explanation of symbols]

 1 light source 2 lens 3 semi-transparent screen 4 two-dimensional CCD camera 5 hood 6 image processing unit 7 computing unit 9 display unit 10 steel plate 13 screen

Claims (4)

[Claims] 1. A lighting unit having a light source and an optical system that collects light from the light source to obtain substantially parallel light, and reflected light that is irradiated from the lighting unit onto a sheet-shaped steel plate and reflected on the surface of the steel plate. The light receiving means includes a light receiving means including a projected screen and an image pickup means for picking up a projected image on the screen to obtain an image signal, and an inspection means for inspecting the unevenness of the steel plate surface from the image signal from the image pickup means. Is a semi-transparent screen on which the reflected light reflected by the surface of the steel plate is projected, and an image pickup means for picking up a projected image on the screen is provided behind the screen, and a device for inspecting unevenness in the surface of a steel plate. . 2. The steel sheet surface irregularity stripe inspection apparatus according to claim 1, wherein the light receiving means is covered with a hood that blocks outside light around the screen onto which the reflected light reflected by the steel plate surface is projected. An apparatus for inspecting surface unevenness of steel plates, which is characterized by 3. The surface unevenness fringe inspection device for a steel sheet having the light receiving means according to claim 2, wherein a black coating film for preventing reflection is formed on the inner surface of the hood. . 4. The steel sheet surface unevenness fringe inspection device according to claim 1, wherein a slit is provided in front of the illumination means.