JP2008145373A - Apparatus and method for inspecting surface defect on stainless steel plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inspection apparatus and an inspection method for accurately detecting a surface defect on a stainless steel plate whose scale is removed by hot rolling, annealing and acid washing. <P>SOLUTION: An incident light is irradiated from a light emitting apparatus for scanning a light in the width direction of the stainless steel plate at an angle α to a traveling direction of the stainless steel plate. A regular reflection light is reflected from the surface of the stainless steel plate at the angle α, and received by a regular reflection CCD camera. An irregular reflection light is reflected from the surface of the stainless steel plate at the angle β, and received by an irregular reflection CCD camera. An input signal as regular reflection data and irregular reflection data obtained by the regular reflection CCD camera and the irregular reflection CCD camera is transmitted to a calculation apparatus. The calculation apparatus calculates and processes the regular reflection data and the irregular reflection data regarding the same surface defect. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an inspection apparatus and an inspection method for detecting a surface defect of a stainless steel plate that has been subjected to hot rolling and subsequent annealing, and further pickled to remove scale.

A stainless steel plate subjected to hot rolling and further annealed has a scale (thickness of 10 μm) formed on its surface. Various products manufactured by processing stainless steel sheets are required to have a specific surface gloss. Therefore, it is necessary to remove the scale in the manufacturing process of the stainless steel plate before feeding the stainless steel plate to the machining process.
In order to remove scale, pickling is widely used. Prior to pickling, descaling may be performed by brush grinding. If a defect (for example, a scratch or a dent) occurs on the surface of the stainless steel plate not only by hot rolling but also by brush grinding, the defect remains even if the subsequent cold rolling is performed, leading to a decrease in yield of the stainless steel plate. In addition, defects caused by inclusions mixed in the steel making process (for example, heges) also cause a decrease in yield of the stainless steel plate.

On the other hand, the yield of stainless steel sheets can be improved by detecting defects (hereinafter referred to as surface defects) after removing scales (that is, pickling) and then detecting such defects such as slits, dents, and baldness. it can. This is because the surface defects are eliminated by performing cold rolling after polishing the stainless steel plate in which the surface defects are detected.
Therefore, various techniques for detecting surface defects of a stainless steel plate that has been subjected to hot rolling and annealing and then pickled to remove scale have been studied.

  For example, conventionally, a technique for detecting surface defects by irradiating a stainless steel plate with laser light is known. This technology uses the phenomenon that laser light irradiated on a clean surface (ie flat and smooth flat surface) is reflected at the same angle as the incident angle, whereas laser light irradiated on surface defects is diffusely reflected. This technology detects surface defects. That is, the reflected light reflected at the same angle as the incident angle is received, and the surface defect is determined based on the signal waveform. However, since laser light is easily diffusely reflected even on a clean surface, the surface defect detection accuracy is low.

In the following description, the reflected incident light reflected at the same angle as the incident angle is referred to as regular reflection, and is distinguished from irregular reflection (that is, reflection having a different incident angle and reflection angle).
Patent Document 1 discloses a technique for detecting defects by irradiating a plate-like inspection object (ie, a steel plate, an aluminum plate, paper, etc.) with white light to receive regular reflection light and irregular reflection light. . In this technique, a defect having a large size is detected by a regular reflection light receiver, and a small defect is detected by a diffuse reflection light receiver. That is, in Patent Document 1, since one defect is detected by only one of regular reflection light and irregular reflection light, it is easily affected by noise, and the defect detection accuracy is low.

Therefore, in Patent Document 1, in order to improve the S / N ratio, a regular reflection light receiver is set so as to identify only two points having an interval larger than the average interval of unevenness on the surface of the object to be inspected. However, the diffusely reflected light receiver has not been improved in the S / N ratio, and a significant improvement in detection accuracy cannot be expected.
JP-A-9-89800

  An object of this invention is to provide the inspection apparatus and inspection method which detect the surface defect of the stainless steel plate which performed hot rolling and subsequent annealing, and also pickled and removed the scale with high precision.

  The present invention is an inspection device that detects surface defects of a stainless steel plate that has been subjected to hot rolling and annealing and then pickled to remove scale, and is incident at an angle α along the traveling direction of the stainless steel plate. Projection device for irradiating incident light, regular reflection CCD camera for receiving regular reflection light reflected from the surface of the stainless steel plate at an angle α, and irregular reflection CCD camera for receiving irregular reflection light reflected from the surface of the stainless steel plate at an angle β A light source scanning device that scans the light projecting device in the width direction of the stainless steel plate, an arithmetic device that performs arithmetic processing using the regular reflection data obtained by the regular reflection CCD camera and the irregular reflection data obtained by the irregular reflection CCD camera as input signals, And a display device for displaying an output signal obtained by an arithmetic device.

  Further, the present invention provides an inspection method for detecting surface defects of a stainless steel plate that has been subjected to hot rolling and annealing, and then pickled to remove scale, from a light projection device that scans in the width direction of the stainless steel plate to the stainless steel plate. Irradiate incident light at an angle α along the traveling direction of the light, and receive regular reflection light reflected at an angle α from the surface of the stainless steel plate with a regular reflection CCD camera, and diffuse reflection light reflected at an angle β from the surface of the stainless steel plate. Is received by the irregular reflection CCD camera, the regular reflection data obtained by the regular reflection CCD camera and the irregular reflection data obtained by the irregular reflection CCD camera are transmitted as input signals to the arithmetic unit, and the regular reflection data and irregular reflection on the same surface defect are obtained by the arithmetic unit. Detects surface defects on stainless steel plates that transmit the output signal obtained by computing the data to the display device and displays the output signal on the display device. It is a method.

  In the surface defect inspection apparatus and the surface defect inspection method of the present invention, the light projecting apparatus is preferably a halogen lamp.

  According to the present invention, it is possible to accurately detect surface defects of a stainless steel plate that has been subjected to hot rolling and subsequent annealing, and further pickled to remove scale.

  FIG. 1 is a cross-sectional view schematically showing an example of the arrangement of a light projecting device, a regular reflection CCD camera, a diffuse reflection CCD camera, and a stainless steel plate when detecting surface defects of a stainless steel plate by applying the present invention. An arrow A in FIG. 1 indicates the traveling direction of the stainless steel plate 1. A stainless steel plate 1 shown in FIG. 1 is a stainless steel plate that has been subjected to hot rolling and subsequent annealing and further pickled to remove scale.

  As shown in FIG. 1, the incident light 4 is irradiated along the traveling direction of the stainless steel plate 1 (that is, the direction of the arrow A). An angle formed by the incident light 4 and the stainless steel plate 1 (so-called incident angle) is α (°). The light projecting device 2 that irradiates the incident light 4 is scanned in the width direction of the stainless steel plate 1 by a light source scanning device (not shown). By scanning the light projecting device 2 in the width direction of the stainless steel plate 1, the entire surface of the stainless steel plate 1 can be inspected. The type of the light projecting device 2 is not particularly limited, but a halogen lamp is suitable according to the inventor's research.

1 shows an example in which the traveling direction of the stainless steel plate 1 (that is, the direction of the arrow A) is the same as the direction in which the incident light 4 is irradiated, but the traveling direction of the stainless steel plate 1 and the incident light 4 are irradiated. The present invention can be applied without hindrance even if the direction is reversed.
The incident light 4 thus irradiated is reflected on the surface of the stainless steel plate 1. At this time, if the surface of the stainless steel plate 1 is a clean (that is, flat and smooth) plane, the angle (so-called reflection angle) formed between the reflected light 5a and the stainless steel plate 1 is α (°). That is, the incident angle and the reflection angle are the same angle. Here, the reflected light 5a is referred to as regular reflected light.

In order to receive this regular reflection light 5a, a regular reflection CCD camera 3a is provided.
However, when the incident light 4 is irradiated to the surface defect, not only regular reflection but also irregular reflection occurs. The angle (so-called reflection angle) formed between the reflected light by irregular reflection (that is, irregularly reflected light) and the stainless steel plate 1 is not constant and varies depending on various factors such as the shape and depth of the surface defect. In order to receive the irregular reflection light, an irregular reflection CCD camera 3b is provided. The reflection angle of the irregularly reflected light 5b received by the irregularly reflected CCD camera 3b is assumed to be β (°).

The reflection angle β of the irregular reflection light 5b is different from the reflection angle α of the regular reflection light 5a. Although FIG. 1 shows an example of α <β, the present invention can be applied without any trouble even when α> β.
Since the light projecting device 2 is scanned in the width direction of the stainless steel plate 1, the light receiving device having the regular reflection CCD camera 3 a and the irregular reflection CCD camera 3 b is scanned in synchronization with the light projecting device 2. Alternatively, a plurality of light receiving devices may be fixed and installed in the width direction of the stainless steel plate 1.

The regular reflection data obtained by the regular reflection CCD camera 3a that receives the regular reflection light 5a and the irregular reflection data obtained by the irregular reflection CCD camera 3b that receives the irregular reflection light 5b are transmitted to the arithmetic unit 6. That is, regular reflection data and irregular reflection data are input signals to the arithmetic unit 6.
In the arithmetic unit 6, the specular reflection data and irregular reflection data related to the same surface defect are arithmetically processed to determine the shape and depth of the surface defect. The calculation processing method is appropriately set according to the nature (namely, shape, depth, etc.) of the surface defect to be detected and the surrounding environment (namely, temperature, brightness, etc.). Hereinafter, as an example, a detection technique based on the aspect ratio and color tone of a surface defect will be described with reference to FIG. 2A and 2B are images obtained by photographing the same surface defect with the regular reflection CCD camera 3a and the irregular reflection CCD camera 3b. FIG. 2A is an image of the regular reflection CCD camera 3a, and FIG. 2B is an image of the irregular reflection CCD camera 3b.

The image of the regular reflection CCD camera 3a is analyzed, and the maximum length L ₁ (mm) in the vertical direction and the maximum length L ₂ (mm) in the horizontal direction of the surface defect 8 are measured. Next, the aspect ratio is calculated using the measured values of L ₁ and L ₂ . The aspect ratio is a value calculated by the following equation (1).
Aspect ratio (%) = 100 × L ₁ / L ₂ (1)
Further, the image of the irregular reflection CCD camera 3b is analyzed, and the difference (so-called gray scale) between the color tone of the surface defect 8 and the color tone of the surrounding stainless steel plate 1 is measured.

Based on the aspect ratio and gray scale obtained in this way, the presence or absence of surface defects is detected, and the type and properties (ie, shape, depth, etc.) are further determined. This becomes an output signal of the arithmetic unit 6.
The arithmetic processing performed by the arithmetic device 6 is not limited to the analysis relating to the aspect ratio and gray scale, and determination based on other factors (for example, the wavelength and amplitude of received regular reflection light or irregular reflection light) is also possible. Also in this case, the presence / absence, type, and properties of surface defects are output signals of the arithmetic unit 6.

  The output signal of the arithmetic device 6 is transmitted to the display device 7 and displayed. The configuration of the display device 7 is not particularly limited. For example, there are various display devices such as blinking a lamp when a specific surface defect is detected, sounding an alarm when a specific surface defect is detected, and displaying the detected surface defect on a screen. Can be used.

  A surface defect of the stainless steel plate was inspected in a stainless steel plate conveying line that was subjected to hot rolling and subsequent annealing, and further pickled to remove scale. As shown in FIG. 1, a projector 2, a regular reflection CCD camera 3a, and an irregular reflection CCD camera 3b are provided. The incident angle α of the incident light 4 and the reflection angle α of the regular reflection light 5a are both 80 °, and the reflection angle β of the irregular reflection light 5b is 60 °. The light projector 2 used a halogen lamp and scanned in the width direction of the stainless steel plate 1. Three light receiving devices including the regular reflection CCD camera 3a and the irregular reflection CCD camera 3b were installed in the width direction of the stainless steel plate 1.

  In this way, the same surface defect is photographed by the regular reflection CCD camera 3a and the irregular reflection CCD camera 3b, and the image is analyzed by the arithmetic unit 6 to obtain the aspect ratio and the gray scale, and compared with the respective threshold values. Thus, the type of surface defect was determined. The determination criteria are shown in Table 1. The threshold value is a preset value, the threshold value of the aspect ratio is 50%, and the threshold value of the gray scale is 200.

The indentations in Table 1 are those in which foreign objects (for example, scales) are pushed in and dropped out during hot rolling, resulting in depressions. , The spear is a foreign material sprinkled and rolled during hot rolling, and each has a different shape, size and depth.
Thus, the presence or absence of surface defects was determined and displayed on the display device 7 of the liquid crystal screen. This is an invention example.

On the other hand, conventionally, the light projecting device 2 receives only specular reflection light using a laser transmitter, and determines the presence or absence of a surface defect based on the light reception signal waveform. This is a conventional example.
The stainless steel plates in which surface defects were detected in the inventive example and the conventional example were visually observed to investigate the wrinkle coincidence rate. The wrinkle coincidence rate is a value calculated by the following equation (2).
疵 Match rate (%) = 100 × N ₂ / N ₁ (2)
N ₁ : Total number of wrinkles visually confirmed N ₂ : Number of surface defects inspection device and visually confirmed wrinkles As a result, the wrinkle agreement rate of the inventive example was 77.6%, The wrinkle agreement rate of the conventional example was 60.1%.

  Thus, it was confirmed that the accuracy of detection of surface defects was improved by applying the present invention.

It is sectional drawing which shows typically the example of arrangement | positioning of the light projector at the time of applying this invention, a regular reflection CCD camera, a diffuse reflection CCD camera, and a stainless steel plate. It is an example of the image which image | photographed the surface defect, (a) is an image of the regular reflection CCD camera 3a, (b) is an image of the irregular reflection CCD camera 3b.

Explanation of symbols

1 Stainless steel plate 2 Floodlight device
3a Regular reflection CCD camera
3b Diffuse reflection CCD camera 4 Incident light
5a Regular reflection
5b Diffuse reflected light 6 Arithmetic device 7 Display device 8 Surface defect

Claims (4)

  An inspection device for detecting surface defects of a stainless steel plate that has been subjected to hot rolling and annealing and then pickled to remove scale, and incident light incident at an angle α along the traveling direction of the stainless steel plate A projecting device for irradiating; a regular reflection CCD camera that receives regular reflection light reflected from the surface of the stainless steel plate at an angle α; and a diffuse reflection CCD camera that receives irregular reflection light reflected from the surface of the stainless steel plate at an angle β; A light source scanning device for scanning the light projecting device in the width direction of the stainless steel plate, and an arithmetic device for performing arithmetic processing using the regular reflection data obtained by the regular reflection CCD camera and the irregular reflection data obtained by the irregular reflection CCD camera as input signals And a display device for displaying an output signal obtained by the arithmetic device.   The surface defect inspection apparatus for a stainless steel plate according to claim 1, wherein the light projecting apparatus is a halogen lamp.   In an inspection method for detecting surface defects of a stainless steel plate that has been subjected to hot rolling and annealing and then pickled to remove scale, the traveling direction of the stainless steel plate from a light projection device that scans in the width direction of the stainless steel plate Is irradiated with incident light at an angle α, and regular reflection light reflected at an angle α from the surface of the stainless steel plate is received by a regular reflection CCD camera, and irregular reflection light reflected at an angle β from the surface of the stainless steel plate is received. The regular reflection data received by the irregular reflection CCD camera, the regular reflection data obtained by the regular reflection CCD camera and the irregular reflection data obtained by the irregular reflection CCD camera are transmitted as input signals to the arithmetic unit, and the regular reflection data relating to the same surface defect is obtained by the arithmetic unit. And output the output signal obtained by computing the diffuse reflection data to the display device, and display the output signal on the display device Surface defect inspection method of a stainless steel sheet characterized.   4. The surface defect inspection method for a stainless steel plate according to claim 3, wherein the light projecting device is a halogen lamp.

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