JPH06102194A - Surface flaw inspection device - Google Patents

Abstract

PURPOSE:To detect a flaw with high S/N ratio by providing a detector in optical arrangement so that the reflection intensity of white light source cast from a light source becomes a specific intensity of the light intensity of normal reflection direction for the part without flaw. CONSTITUTION:The white light source cast from a rod shape light source supplied electricity from a power source 3 on an inspected matter 1 is scattered by the inspected matter and a part of it is introduced and photographed with a one-dimensional photographing device 4. At that moment, noize component due to radiation energy from the high temperature surface of the inspected matter 1 is cut by an optical filter 5. If a flaw is on the inspected matter 1, by placing the device 4 in an optical arrangement so as to be below 30% intensity of the normal reflection direction intensity, the light intensity from the position with flaw becomes stronger than that without flaw and thus, the detected signal intensity drastically changes. And the flaw with low reflectivity generated on the inspected matter 1 can not be detected with the device 4 and thus, is detected with the photographing device 10. The detected signal is A/D converted 6 in the devices 4 and 10, processed 7 for the signal, processed for the image with an image processing device, the kind of the flaw and the grade are defined and displayed on a display 9.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface defect inspection apparatus for optically inspecting surface defects of a strip-shaped inspected material such as a hot rolled steel sheet which moves at high speed.

[0002]

2. Description of the Related Art FIG. 7 shows the structure of a typical conventional surface defect inspection apparatus. A strip-shaped inspected material 1 such as a steel plate is continuously conveyed in the direction of the arrow, and the light source 14 arranged above the inspected material 1 illuminates the surface of the inspected material 1, and the surface image is used by a one-dimensional CCD or the like. The line sensor camera 15 is used to take an image, and the video signal from the camera 15 is processed to extract the surface defect of the inspected material.

[0003]

In such a conventional technique, the optical arrangement such as the irradiation angle of the light source and the light receiving angle of the detector has not been clarified. The only option was to adjust and determine the optical configuration. However, it is extremely difficult to determine such an optical arrangement in an actual line due to a bad environment or the like, and sufficient examination cannot be performed. Furthermore, since it changes with a certain width depending on the conditions of the line at that time, such as the temperature of the running steel plate and the type of steel plate,
Preliminary determination of the optical arrangement in a laboratory is extremely important when determining the optical arrangement corresponding to the actual line.

Further, when the defect portion, such as a hot-rolled steel sheet, has a lower reflectance than the peripheral portion having no defect, and there are both a dark-looking defect and a bright-looking defect which is not so, one type of optical arrangement is used. It is impossible to detect both types of defects efficiently and with high S / N, and an optical arrangement capable of coping with such defects has not been clarified so far.

In order to solve the above problems, the present invention provides
An object of the present invention is to provide a surface defect inspection apparatus capable of inspecting a surface defect generated in a hot-rolled steel sheet with high sensitivity.

[0006]

Means for Solving the Problems The inventors of the present invention investigated the surface condition of a hot-rolled steel sheet and the reflection of light by the surface in order to solve the above conventional problems. Is a wide variety of roughness parameters,
The state of reflection of light by the surface cannot be accurately stated. Further, there are many types of surface defects that occur on the surface of the hot rolled steel sheet, and the shape cannot be generally stated.

However, when white light is projected onto the surface of the hot-rolled steel sheet, a portion having no surface defect has a strong intensity in the specular reflection direction as shown in FIG. It is known that the reflection distribution has a certain value. on the other hand,
When white light is projected on a defective part, the reflection state changes greatly depending on the shape of the defect, and the reflection state greatly depends on the shape of the defect. As a result, the diffused state is diffused as a whole, and even on the surface with no defects, even in the direction of low reflected intensity,
As shown in (b), a relatively high reflection intensity is obtained.

From the above knowledge, the present invention is characterized in that the detector is installed in such an optical arrangement that the light intensity is less than 30% of the light intensity in the specular reflection direction in the defect-free portion. It is an inspection device. According to this apparatus, the light intensity from the diffusely reflected light from the defect portion becomes higher than the light intensity which becomes a noise component from the surface without defects, and a high S / N can be obtained. In the case of a steel sheet, oxide scale adheres to the surface, and in particular, when a defect occurs at a high temperature, the oxide scale may adhere to the defect part thickly. The reflectance may be significantly reduced, and even if white light is projected from the light source, the defective portion may become dark. Further, even in a defect such as a red scale, which is generally called a scale defect, the reflectance of the defect surface is also lowered, and the defect portion becomes dark. In such a case, the detector is installed in an optical arrangement such that the light intensity is 30% to 90% of the light intensity in the specular reflection direction. According to this device, the strength of the peripheral portion having no defect is high, and the strength of the defective portion is low.
With N, it becomes possible to detect the darkening defect as described above.

Further, a luminous flux from a light source is projected on the surface of a running steel strip, and the reflected light is detected by a one-dimensional image pickup device,
In a device for detecting a surface defect of a material to be inspected, at least one or more detectors are installed in a first optical arrangement where the light intensity is less than 30% of the light intensity in the regular reflection direction of a light source to be projected, and projection is performed. 30% or more of the light intensity in the regular reflection direction of the light source
At least one or more detectors are installed in the second optical arrangement where the light intensity is 0% or less. In this way, by installing the second detector installed in the second optical arrangement and the second detector installed in the first optical arrangement together, all kinds of defects with high S / N can be achieved. It becomes possible to detect.

[0010]

The present inventors examined the surface condition of the hot rolled steel sheet and the reflection of light by the surface. Specifically, detectors were installed in optical arrangements with various light intensities, images of defects were taken, and the S / N of the signal intensity of the defect was examined. Also,
When the S / N of the signal intensity of the defective portion was examined for various samples, it was found that the larger the defect size, the higher the S / N of the signal intensity of the defective portion. Therefore, if the smallest defect can be detected, the larger defect can be detected under the same condition.

FIG. 3A shows 20% of the light intensity in the regular reflection direction.
The signal (upper figure) when the one-dimensional imaging device is installed in the optical arrangement that gives the light intensity of (1) and the image of the defect is taken, and the signal obtained by applying the digital filter to that signal (lower figure) is there. The S / N was obtained from the digitally filtered signal. The S / N was about 3 in this optical arrangement. FIG. 3B is a view similar to FIG. 3A when the defect is imaged by installing the one-dimensional imaging device in an optical arrangement in which the light intensity is about 60% of the light intensity in the regular reflection direction. is there. In this optical arrangement, the signal intensity from the defect is buried in the surrounding noise and is completely invisible, making it impossible to identify the defective portion.

Such an imaging experiment was repeated with respect to the sample of the smallest size in various optical arrangements to examine the S / N, and the results shown in FIG. 4 were obtained. In FIG. 4, the S / N is set to 1 in the case of the optical arrangement in which the signal of the defective portion cannot be discriminated. It can be seen that there is reflection intensity from the defective portion even when there is almost no reflection intensity in the defect-free portion compared to the light intensity in the regular reflection direction. It was found that the light intensity was less than 30% in the specular reflection direction when the detectable S / N was set to 1.5 or more as a reference for determining the optical arrangement that enables the defect detection.

Therefore, according to the present invention, the detector is arranged in such an optical arrangement that the reflection intensity of the white light source projected from the light source becomes less than 30% of the light intensity in the specular reflection direction in the defect-free portion. With the installation, the intensity of the reflected light from the defective portion becomes higher than the intensity of the reflected light from the portion having no defect that becomes a noise component, and the defect can be detected with a high S / N.

Further, with respect to the defect in which the scale is thickly attached to the surface of the defect portion and the reflectance of the defect portion is low, various optical arrangements were examined. FIG. 5A shows a signal (upper diagram) when a one-dimensional image pickup device is installed in an optical arrangement such that the light intensity is 80% of the light intensity in the regular reflection direction and an image of a defect is shown, It is a signal (lower figure) obtained by applying a digital filter to the signal. FIG. 5C is a similar diagram of a signal in the one-dimensional image pickup device arranged in the optical arrangement in which the light intensity is 20% in the regular reflection direction.

As can be seen from the figure, when the image is picked up at a position where the light intensity is 80%, the signal intensity due to the defect appears clearly lower than the signal intensity of the peripheral part, and the defect part is clearly visible. It appears that 95%, 20%
When the image is picked up at the optical arrangement position, the signal intensity from the defect is not so different from the noise in the peripheral portion, and the defect cannot be clearly seen. The determination of S / N is the same as in the case of FIG. 3, but in the case of such a defect, the signal of the defective portion becomes lower than the signals of the surroundings, so that the signal with a digital filter has a negative intensity. S
/ N was determined. At 80%, the S / N is 4.7. 9
At 5% and 20%, the defective portion cannot be identified.

Such an imaging experiment was repeated for various samples in various optical arrangements for the smallest sample, and the S / N was examined. The results shown in FIG. 6 were obtained. The S / N from which defects can be extracted is 1.5 as in the case of FIG.
As a result, 30% or more of the light intensity in the specular reflection direction 9
It has been found that detection can be performed by installing the detector in an optical arrangement in which the light intensity is 0% or less.

Therefore, a defect having a surface reflectance lower than that of a defect-free portion, such as a defect in which scale is attached to the surface of the defect portion or a defect called scale flaw such as red scale, is different. The detectors are installed in two optical arrangements, and at least one or more detectors have a light intensity of less than 30% of the light intensity in the specular reflection direction.
And the second optical arrangement that provides a light intensity of 30% or more and 90% or less of the light intensity in the specular reflection direction.
It is possible to detect such a darkening defect with a high S / N by taking a high intensity in the defect-free peripheral portion and a low intensity in the defect portion. Therefore, it becomes possible to detect all kinds of defects with high S / N.

[0018]

EXAMPLES The results of applying the examples of the present invention to hot-rolled steel sheets will be described. FIG. 1 is a block diagram showing an embodiment of the present invention in which two detectors are installed. In the figure, the bar-shaped light source 2 is irradiated onto the surface of the hot-rolled steel sheet that is the material 1 to be inspected. Continuous irradiation is possible. The rod-shaped light source 2 is arranged at an angle of about 30 degrees from the direction perpendicular to the inspected material 1. The light source power source 3 supplies electric power to the rod-shaped light source. The one-dimensional image pickup device 4 such as a CCD line sensor camera for picking up an image of the surface of the material 1 to be inspected also has a function of transmitting the obtained detection signal. The one-dimensional imaging device 4 is installed in a direction substantially perpendicular to the inspected material 1, and when the inspected material 1 is a hot rolled steel sheet, the light intensity in the specular reflection direction is 5 to 10% in this direction. .

The second one-dimensional image pickup device 10 is installed in an optical arrangement in which the light intensity is in the range of 30% to 90% of the light intensity in the specular reflection direction. In this embodiment, it is perpendicular to the material 1 to be inspected. It is installed at an angle of 20 degrees on the side opposite to the light source from the direction, and at this angle, a light intensity of about 70% of the light intensity in the specular reflection direction is obtained. The heat ray-cutting optical filter 5 reduces the influence of self-luminous light from the hot-rolled steel sheet that is the inspection target material 1. A
The / D conversion device 6 performs A / D conversion on the detection signals transmitted from the one-dimensional imaging devices 4 and 11. The signal processing device 7 performs signal processing on the detection signal transmitted from the one-dimensional imaging device to extract defects. The image processing device 8 outputs the defects extracted by the signal processing and performs image processing. Reference numeral 9 is a display device for the operator.

A rod-shaped light source 2 which is supplied with power from a power source 3.
The white light source applied to the inspection material 1 from the above is scattered by the surface of the inspection material, and a part of the light source is incident on the first one-dimensional imaging device 4 and is imaged. At that time, the material to be inspected 1 having a high temperature surface
The noise component due to the radiant energy from is cut by the optical filter 5. If there is a defect on the surface of the material 1 to be inspected, the one-dimensional image pickup device 4 is set to a light intensity of 30 in the regular reflection direction.
If the optical arrangement is such that the light intensity is less than%, the light intensity from the defective portion becomes higher than the light intensity from the defect-free portion, and the intensity of the obtained detection signal greatly changes.

[0021] Further, a low-reflectance generated on the hot-rolled steel sheet to be inspected, for example, an uneven scale defect generated in the early rolling stage when the temperature is extremely high and oxide scale adheres to the surface, or red. What is called a scale flaw such as a scale cannot be detected by the first one-dimensional imaging device 4 and is detected by the second one-dimensional imaging device 10. Then, the detection signal is A / D converted by the A / D conversion device 6 from the one-dimensional imaging devices 4 and 10 and transmitted to the signal processing device 7, where the defect is extracted by signal processing. Furthermore, if there is a defect, the detection signal from which the defect signal has been extracted is transmitted to the image processing device 8, where image processing is performed to determine the defect type and grade, and the display device 9 displays the defect type, The grade is displayed.

The S / N at the time of detection for each defect type is as follows.

[0023]

[Table 1] ──────────────────────────────────── Type of defects Scratches S / N 1. 9-4.6 Hacks 3.5-5.1 Biting flaws 2.1-3.6 Crimping flaws 2.3-3.5 Heading flaws 1.7-2.2 Push flaws 3.1-4 .8 Scratch defect 3.3 to 5.6 Red scale 1.6 to 1.9 ─────────────────────────────── ──────

[0024]

According to the present invention, the detector is arranged in such an optical arrangement that the luminous flux is projected from the light source to the defect-free portion of the surface of the material to be inspected and the reflected light intensity is less than 30%. By installing, it becomes possible to lower the reflected light intensity of a portion having no defect, which becomes a noise component, as compared with the reflected light intensity of the defective portion, and it becomes possible to detect a defect with a high S / N. Further, the detectors are installed in two different optical arrangements, and the second detector is set to 30% to 90% of the light intensity in the specular reflection direction.
By installing in an optical arrangement that gives a light intensity of%,
It becomes possible to detect a darkening defect having a low reflectance at a high S / N ratio by increasing the intensity of the defect-free peripheral portion and decreasing the intensity of the defect portion. Therefore,
It is possible to detect not only unevenness defects called surface defects but also non-concave defects called scale defects with high S / N.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a surface defect inspection apparatus.

FIG. 2 is a diagram showing a reflection state of white light incident on a material to be inspected.

FIG. 3 shows an example of a signal obtained when an image of a defect on a material to be inspected is picked up by an optical arrangement in which the light intensity is 20% and 60% of the light intensity in the regular reflection direction, and a signal obtained by filtering the signal. It is a figure.

FIG. 4 is a diagram showing a correlation between reflection intensity and S / N when a signal of a defective portion is brightly imaged and detected.

FIG. 5: 80%, 95% and 20% of the light intensity in the direction of regular reflection
FIG. 5 is a diagram showing an example of a signal when an image of a defect having a small reflectance on an inspection object is picked up by an optical arrangement having the light intensity of and a signal obtained by filtering the signal.

FIG. 6 is a diagram showing a correlation between reflection intensity and S / N when a signal of a defect portion is darkly imaged and detected.

FIG. 7 is a configuration diagram of a conventional surface defect inspection apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Inspected material 2 Rod-shaped light source 3 Power source for light source 4 One-dimensional imaging device 5 Heat ray cut filter 6 A / D conversion device 7 Signal processing device 8 Image processing device 9 Display device 10 One-dimensional imaging device 11 Light source 12 Inspected material 13 Defect 14 light source 15 camera

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masakazu Yokoo 1 Kawasaki-cho, Chuo-ku, Chiba City Kawasaki Steel Co., Ltd. Technical Research Headquarters (72) Inventor Satoshi Maruyama 1 Kawasaki-cho, Chuo-ku, Chiba Kawasaki Steel Co., Ltd. Technical Research Headquarters (72) Inventor Susumu Moriya 1 Kawasaki-cho, Chuo-ku, Chiba City Kawasaki Steel Co., Ltd. Technical Research Headquarters

Claims (3)

[Claims] 1. A device for projecting a light beam from a light source onto the surface of a traveling steel strip, detecting the reflected light with a one-dimensional image pickup device, and detecting a surface defect of a material to be inspected, the specular reflection of the light source being projected. A surface defect inspection apparatus characterized in that a detector is installed in an optical arrangement in which the light intensity is less than 30% of the light intensity in the direction. 2. A device for projecting a light beam from a light source onto the surface of a running steel strip, detecting the reflected light with a one-dimensional image pickup device, and detecting a surface defect of a material to be inspected, the specular reflection of the light source being projected. A surface defect inspection apparatus characterized in that a detector is installed in an optical arrangement in which the light intensity is 30% or more and 90% or less of the directional light intensity. 3. A device for projecting a light flux from a light source onto the surface of a running steel strip, detecting the reflected light with a one-dimensional image pickup device, and detecting a surface defect of a material to be inspected, the specular reflection of the light source being projected. 30% or more and 90% or less of the light intensity in the specular reflection direction of the light source for projection, in which at least one detector is installed in the first optical arrangement having a light intensity of less than 30% of the light intensity in the direction A surface defect inspection apparatus characterized in that at least one or more detectors are installed in a second optical arrangement having a high intensity.