Method and apparatus for detecting defects on end faces of wound coil, and method for manufacturing steel sheet using the detection method

Abstract

To provide a defect detection technique for a coil end face of a steel strip and a method for manufacturing a steel sheet, in which the detection accuracy of a minute defect is improved by irradiating the end face of the coil with light and photographing it with a camera.SOLUTION: A method for detecting a defect appearing on an end face of a coil around which a steel strip is wound, the method comprising the steps of: irradiating the end face of the coil with light having a predetermined illuminance; acquiring a captured image having a number of pixels of 640 million or more per 1 / 4 field of view of the end face of the coil; and comparing a luminance value of each pixel of a steel strip portion in the acquired captured image with a predetermined value to determine a defect portion. The method for manufacturing the steel sheet includes a hot rolling process of a steel strip using the method for detecting the defect of the end face of the wound coil, and a process for coping with the detected defect.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an inspection method for a hot-rolled steel sheet in a hot strip mill, a method for detecting defects on the end surface of a winding coil of a steel strip, an apparatus for detecting defects on the end surface of a winding coil of a steel strip, and a method for manufacturing a steel sheet using the detection method. [Background technology]

[0002] After being rolled in a continuous hot rolling mill, the hot-rolled steel strip is transported on a hot run table and wound up on a coiler after leaving the final finishing mill. The wound coil is transported by crane or cart, and the presence and number of defects on the end surface are visually inspected at the finishing line to determine whether they exist or not.

[0003] Therefore, in order to solve the problem of defects on the end surface of the wound coil, a coil end surface inspection technique has been proposed. Patent Document 1 discloses a technology in which defects such as scratches, tears, and breaks on the coil end surface that occur when the end surface of the steel strip comes into contact with a guide or is squeezed during the rolling process are photographed using a camera, the location of the defects in the longitudinal direction of the hot-rolled steel strip is identified, and the leveling of a specified stand of a finishing rolling mill is set.

[0004] Furthermore, Patent Document 2 discloses a method for inspecting the winding shape of a hot-rolled steel sheet coil after hot rolling by measuring the distance from a scanning distance meter to the end face of the coil.

[0005] Furthermore, Patent Document 3 discloses a method for inspecting defects on the front and back surfaces of a steel plate using a camera.

[0006] Furthermore, Patent Document 4 discloses that there are cases in which the tip of a steel strip becomes bent into two pieces when being wound onto a winding device, and a method is disclosed in which the end surface of the coil is photographed with a CCD camera to inspect this condition. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-221259 [Patent Document 2] Japanese Patent Application Laid-Open No. 2003-97923 [Patent Document 3] Japanese Patent Application Publication No. 2-89514 [Patent Document 4] Japanese Patent Application Publication No. 10-213550 Summary of the Invention [Problem to be solved by the invention]

[0008] However, when the above-mentioned conventional technology is applied to the inspection of defects on the coil end surface, the following problems arise.

[0009] Prior Patent Documents 1 to 4 describe methods for photographing the end face of a coil with a camera to detect defects on the end face, such as scratches, tears, and bends, which are several tens to several centimeters in size. However, there is no technology for using a camera to photograph smaller defects on the end face, such as chipped or rough edges, which are approximately 1 to 5 mm in size. Therefore, it was difficult to clearly photograph the defect due to differences in contrast caused by irregularities in the coil winding shape and the small size of the defect itself.

[0010] The present invention was developed in consideration of the above-mentioned problems of the prior art, and its object is to provide a defect detection technology for the end surface of a wound coil of a steel strip, which improves the accuracy of detecting minute defects by irradiating the end surface of the coil with light and photographing it with a camera. Another object is to provide a steel sheet manufacturing method using this detection technology. [Means for solving the problem]

[0011] The gist of the present invention, which advantageously solves the above problems, is as follows.

[0012] [1] A method for detecting defects that appear on the end surface of a coil wound from a steel strip, which involves irradiating the end surface of the coil with light of a predetermined illuminance, obtaining an image of the end surface of the coil with 64 million or more pixels per 1 / 4 field of view, and comparing the brightness value of each pixel of the steel strip portion of the obtained image with a predetermined value to determine the defective portion. [2] In the above [1], the light irradiated onto the end surface of the coil is 7000 lx or more, and the pixels of the steel band part and the pixels between the coil are distinguished from the connection of pixels of similar brightness values, and for the pixels corresponding to the steel band part, the difference from the representative value of the brightness value is 100 cd / m 2 This is a method for detecting defects on the end surface of a wound coil, in which the pixel portions described above are determined to be defective. [3] The method for detecting defects in a wound coil end surface according to the above [1] or [2], wherein the size of the defect is 1 to 8 mm in the length in the major axis direction. [4] A device for detecting defects that appear on the end surface of a coil wound with a steel strip, comprising: a light projection means for irradiating the end surface of the coil with light of a predetermined illuminance; an imaging means for acquiring an image of the coil end surface with 64 million or more pixels per 1 / 4 field of view; and a determination means for comparing the brightness value of each pixel of the steel strip portion of the acquired image with a predetermined value to determine the defective portion. [5] In the above item [4], the light projecting means has a light projecting section with an illuminance of 7000 lx or more, and the determining means distinguishes between pixels in the steel band section and pixels between the coils based on the connection of pixels with similar luminance values, and determines whether the pixels corresponding to the steel band section have a difference of 100 cd / m from the representative value of the luminance value. 2 The defect detection device for the end surface of the winding coil has a determination unit that determines the pixel portion as a defective portion. [6] The defect detection device for a wound coil end surface according to the above [4] or [5], wherein the size of the defect is 1 to 8 mm. [7] A method for manufacturing a steel sheet, comprising: a hot rolling step of a steel strip using the method for detecting defects on the end surface of a wound coil according to any one of [1] to [3] above; and a step of dealing with the detected defects. [Effects of the Invention]

[0013] According to the present invention, the contrast variation in the end face portion due to misalignment of the coil winding or the like is reduced by using appropriate photographing conditions, so that it is possible to detect defects occurring in the coil end face portion in the photographed image. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a schematic diagram of an apparatus suitable for use in a method for detecting defects in a coil end surface according to an embodiment of the present invention. [Figure 2] (a) is a schematic diagram of an image of the coil end surface when light is irradiated by a projector, and (b) is a schematic diagram of an image of the coil end surface when light is not irradiated by a projector. [Figure 3] (a) is an example of an image of a coil end surface photographed by irradiating it with light, and (b) and (c) are magnified images of the defective portion of the coil end surface, respectively. DETAILED DESCRIPTION OF THE INVENTION

[0015] An outline of the technique for detecting defects on the end surface of a winding coil according to this embodiment will be described. In this embodiment, light is irradiated onto the coil end surface to highlight defective areas, making it possible to capture images that make it easy to distinguish between normal and defective areas. Furthermore, by rotating the coil itself or by rotating a camera to capture images of the entire coil end surface, and then setting a brightness threshold between normal and defective areas, it becomes possible to quantitatively and automatically determine the number and size of defects.

[0016] First, the defect detection device for a wound coil end surface according to this embodiment will be described with reference to FIG. <Defect detection device> The defect detection device for wound coil end faces according to this embodiment comprises a light projecting means 3, an imaging means 2, and a determination means 6. The light projecting means 3 can project light at a predetermined illuminance onto the end face of the coil 1. The imaging means 2 can capture an image with 64 million or more pixels per 1 / 4 field of view of the end face of the coil 1. The "1 / 4 field of view of the end face of the coil 1" refers to a range with a central angle of 90° on the approximately concentric circular coil end face. The determination means compares the brightness value of each pixel of the steel band portion of the captured image with a predetermined value to determine whether there are any defects.

[0017] Each part of the detection device according to this embodiment is not limited to a specific component, and may be any component that has the function of implementing the present invention.

[0018] [Imaging means 2 and light projection means 3] As shown in Figure 1, a camera 2 serving as an imaging means and a projector 3 serving as a light-projecting means are arranged facing the end face of the coil 1. The light projection direction is preferably set with the optical axis of the projector 3 tilted relative to the central axis of the coil 1. If the optical axis of the projector 3 is set parallel to the central axis or close to parallel to the end face of the coil 1, the contrast between the sound end face of the steel strip and the defective part may not be clear in the captured image. Furthermore, the projector 3 preferably has a function to ensure that the illuminance on the coil end face by light irradiation is 7000 lx or more. Conversely, excessive illuminance may cause saturation in the captured image and result in insufficient contrast, so a value of around 10000 lx is preferable.

[0019] The function of camera 2 is to photograph the end face of coil 1 with the camera, and the image resolution is preferably 64 million or more pixels in a quarter field of view of the entire coil end face so that the steel band portion and the gap between the coils can be distinguished in the photographed image. Although there is no upper limit, it is preferable to set the upper limit at 100 million pixels from an economical viewpoint. Camera 2 is preferably installed facing the end face of coil 1, at a distance of 50 cm or more from the end face of coil 1, and at the same height as the center of the coil. Although there is no upper limit on the distance of camera 2 from coil 1, it is preferable to set the upper limit at around 100 cm from the viewpoint of ensuring sufficient resolution.

[0020] [Judgment means 6] The determination unit 6, which serves as a determination means, has the function of determining whether a part is defective or normal based on the brightness, or luminance, of the steel band part in the captured image of the coil end surface. In the captured image, the luminance value of each pixel of the steel band part is compared with a representative value. Then, if the difference between the luminance of the pixel in a specific part and the representative value of luminance is less than 100 cd / m 2 If this is the case, it is preferable to determine that specific portion as a defect. It is particularly preferable to define the defect as a portion with a low brightness value. First, the pixels of the steel band portion and the pixels between the coils are distinguished from each other based on the connection of pixels with similar brightness values ​​in the captured image. For example, the steel band portion can be considered a series of bright pixels, i.e., pixels with high brightness values. The areas between the coils can be considered a series of dark pixels, i.e., pixels with low brightness values. It can be assumed that the width of the steel band portion and the width between the coils do not change suddenly in the circumferential direction. The average, median, or mode of the distribution of brightness values ​​of each pixel can be used as a representative value of the brightness of the steel band portion. Furthermore, the entire steel band portion or a specific portion including the target portion can be used to determine the representative value of the brightness of the steel band portion.

[0021] The determination unit 6 can be an image analysis device that can distinguish between defective and normal parts through image analysis based on image data and identify the defective parts. The defect detection device of this embodiment can also detect minute defects on the coil end surface, even those measuring 1 to 8 mm. The size of the defect refers to the circumferential length of the steel strip. Furthermore, an information transmission system can be established to transmit defect detection information to the coil end surface for defect treatment or for the subsequent cold rolling process.

[0022] Next, a method for detecting defects on the end surface of a wound coil according to this embodiment will be described. <Defect detection method> The method for detecting defects in the end surface of a wound coil according to this embodiment involves irradiating the end surface of the coil with light of a predetermined illuminance, obtaining an image of the coil end surface with 64 million or more pixels per 1 / 4 field of view, and comparing the brightness value of each pixel of the steel strip portion of the obtained image with a predetermined value to determine the defective portion.

[0023] First, light is projected from a floodlight 3 onto the end face of coil 1 of the steel strip wound on the coiling machine. To distinguish between the steel strip and the coil gap in the captured image, the illuminance of the light projected onto the end face of coil 1 is preferably 7000 lx or more. Next, camera 2 is pointed at the end face of coil 1 to capture an image. The coil 1 itself is rotated, or camera 2 is rotated to capture the entire end face of coil 1. The captured image may have 64 million or more pixels per 1 / 4 field of view of the entire coil end face, and may also display the steel strip and the gap between the coils on the end face of coil 1.

[0024] By setting a brightness threshold between normal and defective areas, the number, size, or type of defects can be quantitatively and automatically determined. First, the pixels in the steel band and the pixels between the coils are distinguished from each other based on the connection of pixels with similar brightness values ​​in the captured image. For example, the steel band can be represented as a series of bright pixels, i.e., pixels with high brightness values. The areas between the coils can be represented as a series of dark pixels, i.e., pixels with low brightness values. It can also be assumed that the width of the steel band and the width between the coils do not change suddenly in the circumferential direction. The representative value of the brightness of the steel band can be determined by the average, median, or mode of the distribution of brightness values ​​of each pixel. Furthermore, the representative value of the brightness of the steel band can be determined using the entire steel band or a specific portion including the target area. The brightness value of each pixel in the steel band in the captured image is compared with the representative value. If the brightness of the pixel in the specific area is lower than the representative value, the specific area is determined to be a defective area. Here, the difference in brightness between the representative value and the defective area is 100 cd / m 2 It is preferable that the defect level is equal to or higher than this. The judgment result indicating the defect level can be used to perform edge removal, transmit information to the next process, and grade the coil. Furthermore, the defect detection method of this embodiment can detect even minute defects on the coil end surface, even those with a size of 1 to 8 mm. The size of the defect refers to the circumferential length of the steel strip portion. [Example]

[0025] The effects of this embodiment will be specifically described below based on examples, but the present invention is not limited to these examples.

[0026] The wound coil end surface was photographed and minute defects were identified using a wound coil end surface defect detection device with the configuration shown in Figure 1. A wound coil 1 of hot-rolled steel sheet was prepared, and a 64-megapixel high-definition camera 2 and a floodlight 3 with an illuminance of 10,000 lx were installed at the same height, facing the coil, 1 m away from the end face of the coil. The angle of the camera was adjusted so that the coil's inner diameter and outer diameter were included in a field of view 4 of 180 cm x 180 cm. The photographs were taken while illuminating the field of view of the camera using a floodlight 3.

[0027] Figure 2(a) shows a schematic diagram of an image of the coil end surface when light is irradiated. Figure 2(b) shows a schematic diagram of an image of the coil end surface when light is not irradiated. It can be seen that the defect 5 can be clearly observed when light is irradiated. Furthermore, Figure 3(a) shows a quarter-field photograph of the coil end surface taken when light is irradiated, and Figures 3(b) and (c) show enlarged photographs of the defect. The illuminance at the coil end surface was 7000 lx. The optical axis of the projector 3 was positioned on the central axis of the coil, and it was irradiated at an angle to the coil end surface. Camera 2 was installed 100 cm away from the coil end surface, at the height of the coil center. In the enlarged photograph, the lined gray areas are the steel band parts, the lined black lines are the spaces between the coils and are surrounded by the gray areas, and the black parts wider than the black lines are defects (selvage). Image analysis revealed that the luminance of the black parts was 6 cd / m 2 The brightness of the gray area of ​​the steel band is 126 cd / m 2 The black part has a brightness of 120 cd / m 2 Because the black part was small, it was determined to be a defect. By shining light on it and taking a photo, it was possible to clearly distinguish between the normal part of the coil end surface and the minute defect part 5, which was only a few millimeters in length. [Explanation of symbols]

[0028] 1 coil 2. Camera (imaging means) 3. Floodlight (light projection means) 4 Camera field of view 5. Defects 6 Judgment unit (judgment means)

Claims

1. A method for detecting defects appearing on the end surface of a coil wound from a steel strip, comprising: Irradiating the end surface of the coil with light of a predetermined illuminance; Acquires a photographic image of over 64 million pixels per quarter field of view of the coil end surface, In the obtained photographed image, the brightness value of each pixel of the steel band portion is compared with a predetermined value to determine the defective portion. A method for detecting defects on the end surface of a wound coil.

2. The light irradiated onto the end surface of the coil is 7000 lx or more, The pixels in the steel band section and the pixels between the coils are distinguished from the way pixels with similar brightness values ​​are connected. For the pixels corresponding to the steel band portion, the difference from the representative value of the luminance value is 100 cd / m ２ 2. The method for detecting defects in a wound coil end surface according to claim 1, wherein the pixel portion is determined to be a defective portion.

3. 3. The method for detecting defects in a wound coil end surface according to claim 1, wherein the size of the defect portion is 1 to 8 mm in length in the major axis direction.

4. A device for detecting defects that appear on the end surface of a coil wound from a steel strip, a light projecting means for projecting light of a predetermined illuminance onto the end surface of the coil; an imaging means for acquiring an image of the coil end surface with 64 million or more pixels per quarter field of view; a determination means for determining a defective portion by comparing the brightness value of each pixel of the steel band portion in the obtained photographed image with a predetermined value; A defect detection device for a wound coil end surface, comprising:

5. the light projecting means has a light projecting unit that emits light with an illuminance of 7000 lx or more, The determining means determines whether the pixel is a steel band part or a pixel between the coils based on the connection of pixels with similar brightness values, and determines whether the pixel corresponding to the steel band part has a brightness value that is less than 100 cd / m from the representative value. ２ 5. The defect detection device for a wound coil end surface according to claim 4, further comprising a determination unit for determining the pixel portion as a defective portion.

6. 6. The defect detection device for a wound coil end surface according to claim 4, wherein the size of the defect is 1 to 8 mm.

7. a hot rolling process of a steel strip using the method for detecting defects on a wound coil end surface according to claim 1 or 2; A process for dealing with detected defects; A method for manufacturing a steel plate, comprising:

Images