JPH07286968A - Surface defect inspecting device - Google Patents

Abstract

PURPOSE:To prevent that the defects other than a recess form defect and a scratch form defect are detected in error as a defect, by comparing with a high threshold value, as well as detecting the recess form defect and the scratch form defect securely from the image signals of CCD cameras at an excellent S/N. CONSTITUTION:A projection means 1 to emit a slit light 29; two CCD cameras 21 and 22 set at specific receiving solid angles respectively in order to receive the reflected light 26 from a heat stretched steel plate 11; a half mirror 25 to lead the reflected light 26 to the cameras 21 and 22; and a signal processing means 28 to process the image signals 21a and 22a from the CCD cameras 21 and 22; are provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for inspecting surface defects, and more specifically, for detecting concave defects, scratch defects, etc. on the surface of a hot-rolled steel sheet which is conveyed at high speed on a roller. The present invention relates to a surface defect inspection device used for this purpose.

[0002]

2. Description of the Related Art FIG. 4 is a block diagram schematically showing a conventional surface defect inspection apparatus for detecting a surface defect of an object to be inspected which is being conveyed at a high speed on a conveying line. Reference numeral 11 denotes a steel plate as an inspection object. Steel plate 11
Is conveyed on the roller 12 in the direction of arrow A at a high speed, and a light projecting means 13 for irradiating the surface of the steel plate 11 with light is arranged at a predetermined position above the steel plate 11. Further, one predetermined one-dimensional CCD as a light receiving means is provided at a predetermined position above the steel plate 11.
(Charge Coupled Device) The camera 14 is arranged and fixed, and the light receiving diaphragm mechanism of the CCD camera 14 (not shown)
Is set and held in a predetermined aperture state. The irradiation light 13a from the light projecting means 13 is reflected by the steel plate surface 11a to become reflected light 14a, and a part of the reflected light 14a is received by the CCD camera 14 through the light receiving diaphragm mechanism. Further, a signal processing means 15 is connected to the CCD camera 14, and the signal processing means 15 includes a differential processing (filtering) circuit 15a, a comparison circuit 15b, a microcomputer 15c and the like.

When detecting a surface defect using the surface defect inspection apparatus having the above-described structure, first, the CCD camera 14 is used.
The steel plate surface 11a is imaged. Then, the image signal 14b output for each scanning of the one-dimensional CCD camera 14 is transmitted to the signal processing means 15, is converted into the differential signal 15d by the differential processing circuit 15a, and the noise signal is removed. Next, the differentiated signal 15d is transmitted to the comparison circuit 15b, where it is compared with a preset threshold value, and the microcomputer 15c performs determination processing to detect a defect. The noise signal includes flapping of the steel plate 11 that occurs when the roller 12 moves, and the steel plate surface 11
This includes the light reception unevenness of the CCD 14 camera caused by the difference in the surface roughness of a. Therefore, the signal-to-noize ratio (S / N ratio) is increased due to the removal of the noise signal during the differentiation process, preventing a defect that is not detected or a defect other than the defect is detected as a defect. To be done.

[0004]

There are many types of surface defects on the steel sheet 11, such as concave defects and scratch defects. For example, the concave defect has a concave shape or a convex shape, and a flaw generated on the rolling roll is transferred to the surface of the steel sheet 11 during rolling. In addition, the scratch-like defects have gloss,
The scale with a thickness of several μm adhered to the surface of the steel plate 11 peeled off
The trace is a defect.

In the above-mentioned surface defect inspection apparatus, 1
The image signal 14b picked up by each CCD camera 14 is signal-processed by the signal processing means 15, so that the defect is detected. However, while this signal processing alone detects a concave defect, it is difficult to detect a scratch defect, or a scratch defect is detected but it is difficult to detect a concave defect. There was a problem that occurs.

The present invention has been made in view of the above problems, and an object thereof is to provide a surface defect inspection apparatus capable of surely detecting many kinds of surface defects.

[0007]

In order to achieve the above object, a surface defect inspection apparatus according to the present invention irradiates an object to be inspected with light, and the object to be inspected is based on the amount of light reflected from the object to be inspected. In the surface defect inspection apparatus for detecting the surface defect, the light projecting means for irradiating the object to be inspected with light, and the predetermined light receiving solid angle for receiving the reflected light from the object to be inspected are set. A plurality of light receiving means, a light guiding means for guiding the reflected light to each of the light receiving means, and a signal processing means for processing a signal from the light receiving means are provided.

[0008]

FIG. 3 is a curve diagram showing the results of a comparative examination of the relationship between the amount of light reflected from these defect areas or normal areas and the scattering angle, and (a) is a concave defect. In the case of the portion (curve A) and the normal portion (curve C), (b) shows the case of the scratch-like defect portion (curve B) and the normal portion (curve C). As is clear from this result, the light quantity ratio between the concave defect portion and the normal portion in the range where the scattering angle is within α is 7:10.
And the light amount ratio in the range where the scattering angle is within β is 6: 7 (a). On the other hand, the light quantity ratio between the scratched defect portion and the normal area is 5: 4 in the scattering angle range of α or less, and the light quantity ratio is 5: 3 in the scattering angle range of β or less.
(B). Thus, it can be seen that the reflection pattern differs depending on the type of defect. Therefore, in the case of a concave defect, if the reflected light having a scattering angle within the range of α is imaged, the S / N ratio is increased, and the concave defect can be reliably detected. Further, in the case of the scratch-like defect, if the reflected light having a scattering angle within the range of β is imaged, the S / N ratio is increased, and the scratch-like defect can be reliably detected.

Further, in order for the CCD camera to receive light within a predetermined scattering angle, it is necessary to adjust the light receiving solid angle of the CCD camera. This light receiving solid angle is the distance between the CCD camera and the object to be inspected. Alternatively, it can be changed depending on the degree of aperture of incident light in the CCD camera.

According to the surface defect inspection apparatus of the present invention,
A light projecting means for irradiating the object to be inspected with light, a plurality of light receiving means set to a predetermined light receiving solid angle for receiving the reflected light from the object to be inspected, and the reflection to each of the light receiving means. Since the light guide means for guiding the light and the signal processing means for processing the signal from the light receiving means are provided, a plurality of light receiving means can be obtained by selecting the light receiving solid angle suitable for the reflection pattern of each defect type. Each of the defect types can be reliably detected from the image signal of 1. with an excellent S / N ratio and can be compared with a high threshold value, so that a defect other than the defect types is prevented from being erroneously detected as a defect. Will be done.

[0011]

EXAMPLES AND COMPARATIVE EXAMPLES Examples of the surface defect inspection apparatus according to the present invention will be described below with reference to the drawings. It should be noted that components having the same functions as those of the conventional example are designated by the same reference numerals. FIG. 1 is a block diagram schematically showing an embodiment of a surface defect inspection apparatus according to the present invention, in which reference numeral 11 denotes a hot rolled steel sheet as an inspection object. The hot-rolled steel sheet 11 is conveyed on a plurality of rollers 12 in the direction of arrow A at a high speed, and a light projecting means 13 is arranged at a predetermined position above the hot-rolled steel sheet 11. The light projecting means 13 is composed of a DC-lit metal halide light source 13b and a condenser lens 13c. Light emitted from the metal halide light source 13b passes through the condenser lens 13c to become slit light 29, which is applied to the steel plate surface 11a. It is supposed to be done. On the other hand, a one-dimensional CCD camera 21 as a first light receiving means is arranged at a predetermined position on the reflected light 26 line symmetrical to the slit light 29 with respect to the normal 11b on the steel plate surface 11a. Also, the steel plate surface 11a and CC on the 26th line of the reflected light
A half mirror 25 as a light guide is disposed at a predetermined position between the D camera 21 and the D camera 21. Further, a one-dimensional CCD camera 22 as a second light receiving means is arranged at a predetermined position behind the half mirror 25, and the half mirror 25 causes the reflected light 26 from the steel plate surface 11a to be reflected by the CCD.
The cameras 21 and 22 are separated from each other. While the CCD cameras 21 and 22 have the same optical resolution, for example, the light receiving solid angle of the CCD camera 21 is set to a relatively large α, and the concave defect is easily detected. The light-receiving solid angle is set to a relatively small β, and the scratch-like defect is easily detected. A light-shielding filter 24 is arranged in front of the CCD camera 21 and is corrected so that the light receiving amounts of the CCD cameras 21 and 22 are the same even if the light receiving solid angles are different, and a common threshold value is used. The comparison circuit 28b can perform comparison processing. A heat ray absorbing filter 23 is mounted in front of each of the CCD camera 22 and the light shielding filter 24. The heat ray absorbing filter 23 blocks the radiant heat from the steel plate 11, and the radiant heat damages the CCD cameras 21 and 22. Are prevented.

A controller 27 is connected to the CCD cameras 21 and 22, and the charge storage time is adjusted by the controller 27 so that the CCD cameras 21 and 22 are scanned at high speed at the same timing. A signal processing means 28 is connected to the CCD cameras 21 and 22, and the signal processing means 28 is an A / D converter 28.
a, a comparison circuit 28b, a microcomputer 28c, and the like.

When detecting a surface defect using the surface defect inspection apparatus having the above structure, the CCD cameras 21 and 2 are used.
The same steel plate surface 11a is imaged by 2. Then, the image signals 21a and 22a output for each scanning of the one-dimensional CCD cameras 21 and 22 are transmitted to the signal processing means 28. The image signal 21a includes a concave defect signal, and the image signal 22a includes a scratch-shaped defect signal. The image signals 21a and 22a are converted into digital signals 28d by the A / D converter 28a and then transmitted to the comparison circuit 28b. Then, it is compared with a preset threshold value, a logical sum of signals exceeding the threshold value is output, and a determination process is performed by the microcomputer 28c to perform a concave defect,
Scratch-like defects are detected.

The results of imaging the concave defects and the scratch defects by using the surface defect inspection apparatus according to the embodiment will be described below. The CCD camera 21 has a light receiving solid angle α of about 1 × 10 ⁻³ str, and the CCD camera 22 has a light receiving solid angle β.
Was set to about 2 × 10 ⁻⁴ str. As a comparative example, a defect was imaged using a device set to a light receiving solid angle different from the light receiving solid angle.

FIG. 2 is a curve diagram showing the results of investigating the relationship between the S / N ratio and the light receiving solid angle. In the figure, curve A shows a concave defect, and curve B shows a scratch defect. As is clear from this result, the S / N ratio of the CCD camera 21 (image signal 21a) set to the light receiving solid angle of about 1 × 10 ⁻³ str.
As for the ratio, the concave defect shows a peak, while the scratch-like defect is below the detection limit (S / N ratio 3). Also about 2 × 1
CCD camera 22 set to a light receiving solid angle of 0 ^-4 str
Regarding the S / N ratio of (image signal 22a), the scratch-like defects show a peak, while the concave defects are below the detection limit (S / N ratio 3). Therefore, in the case of the device according to the embodiment, C
The concave defect and the scratch defect are clearly discriminated from the image signals of the CD cameras 21 and 22, respectively. On the other hand, in the case of the apparatus of the comparative example provided with only one of the CCD cameras 21 and 22, it was difficult to determine whether the defect was a concave defect or a picked defect. Furthermore, in the case of the apparatus of the comparative example, which is greatly deviated from the scattering angles α and β, for example, the light receiving solid angle is set to 5 × 10 ⁻⁴ str, it is difficult to discriminate both the concave defect and the picked defect.

As is clear from this result, in the surface defect inspection apparatus according to the embodiment, the slit light 2 is applied to the hot-rolled steel sheet 11.
9 for projecting light, two CCD cameras 21, 22 set to predetermined light receiving solid angles α, β for receiving the reflected light 26 from the hot rolled steel plate 11, and CC
Half mirror 2 that guides the reflected light 26 to the D cameras 21 and 22
5 and the image signals 21a from the CCD cameras 21 and 22,
22a, the signal processing means 28 for processing the image signals 21a of the CCD cameras 21, 22 is selected by selecting the light receiving solid angles α, β that respectively match the reflection patterns of the concave defect and the scratch defect. It is possible to reliably detect two types of concave defects and scratch-like defects with an S / N ratio of 22a or more. In addition, the S / N ratio is large,
Since the comparison process can be performed at a high threshold value, it is possible to prevent detection of defects other than the concave defect and the scratch-like defect as defects.

In the above embodiment, the device provided with the two CCD cameras 21 and 22 as the light receiving means has been described, but three or more CCD cameras may be used when there are many kinds of defects.

[0018]

As described in detail above, in the surface defect inspection apparatus according to the present invention, the light projecting means for irradiating the object to be inspected with light and the light reflected from the object to be inspected are received. Since a plurality of light receiving means set to a predetermined light receiving solid angle, light guiding means for guiding the reflected light to the respective light receiving means, and signal processing means for processing a signal from the light receiving means are provided. By selecting the light receiving solid angle that matches the reflection pattern of each defect type, it is possible to reliably detect each defect type with an excellent S / N ratio from the image signals of the plurality of light receiving means. Since the comparison can be performed with a high threshold value, it is possible to prevent erroneous detection of a defect other than the defect type as a defect.

[Brief description of drawings]

FIG. 1 is a block diagram schematically showing an embodiment of a surface defect inspection apparatus according to the present invention.

FIG. 2 is a curve diagram showing the results of investigating the relationship between the S / N ratio and the light-receiving solid angle using the devices of Examples and Comparative Examples,
In the figure, A indicates a concave defect, and B indicates a scratch defect.

FIG. 3 is a curve diagram showing the results of investigating the relationship between the light amount of light reflected from the defective portion or the normal portion and the scattering angle, and (a) is a concave defect (curve A). ), In the case of a normal part (curve C), (b) shows the case of a scratch-like defect (curve B) and a normal part (curve C).

FIG. 4 is a block diagram schematically showing a conventional surface defect inspection apparatus for detecting a surface defect of an object to be inspected conveyed at a high speed on a conveying line.

[Explanation of symbols]

 11 Hot Rolled Steel Plate 13 Projection Means 21, 22 CCD Cameras 21a, 22a Image Signal 25 Half Mirror 26 Reflected Light 28 Signal Processing Means 29 Slit Light

Claims (1)

[Claims] 1. A surface defect inspection apparatus for irradiating an object to be inspected with light and detecting a surface defect of the object to be inspected on the basis of the amount of light reflected from the object to be inspected. Projecting means for irradiating, a plurality of light receiving means set to a predetermined light receiving solid angle for receiving reflected light from the object to be inspected, and light guiding means for guiding the reflected light to the respective light receiving means. And a signal processing means for processing a signal from the light receiving means.