WO2008075905A1 - Apparatus for detecting surface defect on slab - Google Patents

Apparatus for detecting surface defect on slab Download PDF

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Publication number
WO2008075905A1
WO2008075905A1 PCT/KR2007/006677 KR2007006677W WO2008075905A1 WO 2008075905 A1 WO2008075905 A1 WO 2008075905A1 KR 2007006677 W KR2007006677 W KR 2007006677W WO 2008075905 A1 WO2008075905 A1 WO 2008075905A1
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WO
WIPO (PCT)
Prior art keywords
slab
image
defect
light source
light
Prior art date
Application number
PCT/KR2007/006677
Other languages
French (fr)
Inventor
Ki Won Kim
Ho Mun Bae
Original Assignee
Posco
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Posco filed Critical Posco
Publication of WO2008075905A1 publication Critical patent/WO2008075905A1/en

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/84—Systems specially adapted for particular applications
    • G01N21/88—Investigating the presence of flaws or contamination
    • G01N21/89—Investigating the presence of flaws or contamination in moving material, e.g. running paper or textiles
    • G01N21/8914—Investigating the presence of flaws or contamination in moving material, e.g. running paper or textiles characterised by the material examined
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B38/00—Methods or devices for measuring, detecting or monitoring specially adapted for metal-rolling mills, e.g. position detection, inspection of the product
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/84—Systems specially adapted for particular applications
    • G01N21/88—Investigating the presence of flaws or contamination
    • G01N21/8806—Specially adapted optical and illumination features
    • G01N2021/8822—Dark field detection
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/84—Systems specially adapted for particular applications
    • G01N21/88—Investigating the presence of flaws or contamination
    • G01N21/89—Investigating the presence of flaws or contamination in moving material, e.g. running paper or textiles
    • G01N21/8914—Investigating the presence of flaws or contamination in moving material, e.g. running paper or textiles characterised by the material examined
    • G01N2021/8918—Metal
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/84—Systems specially adapted for particular applications
    • G01N21/88—Investigating the presence of flaws or contamination
    • G01N21/89—Investigating the presence of flaws or contamination in moving material, e.g. running paper or textiles
    • G01N21/892—Investigating the presence of flaws or contamination in moving material, e.g. running paper or textiles characterised by the flaw, defect or object feature examined
    • G01N2021/8925—Inclusions

Definitions

  • the present invention relates to an apparatus for detecting surface defect on a slab apparatus, and more particularly, to a non-contact defect detection apparatus for automatically detecting a defect on a surface of a slab manufactured in a continuous casting process.
  • defect of the surface of the slab is capable of being detected before being charged into a heating furnace or after out of the heating furnace.
  • an oxide layer such as a scale is formed on the surface to cover the defect of the surface in the hot rolling process, it is impossible to accurately detect the defect.
  • magnetic methods and optical methods have been proposed.
  • FIG. 1 is a diagram illustrating a defect detection apparatus provided to solve the problem.
  • a charge-coupled device (CCD) camera 3 is disposed in the center and lightings 2 are installed in a longitudinal direction of a slab 1 and facing each other to brightly illuminate a portion of the slab 1 to be detected.
  • CCD charge-coupled device
  • Japanese Laid-open Patent Publication No. 2006-177746 discloses a method of detecting a defect on a steel sheet by installing CCD cameras in two channels such as a specular reflection area and a diffused reflection area in a location opposite to emitted light for accurate optical detection.
  • CCD cameras since this is a technology required to measure minute defects and micro uneven portions on a surface, a refinement may act as noise when a slab has a surface that is not clean.
  • An aspect of the present invention provides a non-contact defect detection apparatus automatically detecting a defect on a surface of a slab manufactured in a continuous casting process.
  • a defect detection apparatus including: a light source emitting light to a surface of a slab; a charge- coupled device (CCD) camera located in an outer area of directly reflective light emitted from the light source and reflected on the surface of the slab, imaging the surface of the slab to which the light is emitted, and providing an image of the surface of the slab; and an image processor detecting a defect formed on the surface of the slab from the image provided by the CCD camera.
  • CCD charge- coupled device
  • FIG. 1 is a configuration diagram illustrating a conventional apparatus for detecting a defect on a surface of a slab
  • FIG. 2 is a diagram illustrating images imaged by a conventional apparatus for detecting a defect on a surface of a slab
  • FIG. 3 is a configuration diagram illustrating an apparatus for detecting a defect on a surface of a slab, according to an exemplary embodiment of the present invention
  • FIGS. 4(a) and 4(b) illustrate images of defects on a surface of a slab and an image of the surface of the slab, imaged using the apparatus according to an exemplary embodiment of the present invention
  • FIG. 5 is a diagram illustrating a pixel image of a surface of a slab, obtained by the apparatus according to an exemplary embodiment of the present invention.
  • the apparatus includes a light source 110, a charge-coupled device (CCD) camera 120, and an image processor 130.
  • the light source 110 emits light a to a surface of a slab.
  • the light source 110 is inclined in a longitudinal direction of the slab to form reflected light b reflected on a surface of the slab.
  • the light source 110 may be a direct current (DC) light source uniformly emitting the light a according to time.
  • DC direct current
  • the CCD camera 120 is located facing the light source 110 in a longitudinal direction of the slab and asymmetrical to the light source to be away of the reflected light bgenerated by the light source 110. [39] When installed symmetrical to the light source 110 and the surface of the slab is imaged within a range of an angle of reflection, unnecessary small changes on the surface of the slab 1 may be read in addition to the defect on the surface of the slab. Accordingly, the CCD camera 120 is installed out of the range of angle of reflection. Therefore, the CCD camera 120 removes all changes on the surface of the slab excluding the defect on the surface of the slab and allows the defect to be revealed as a dark shape.
  • the image processor 130 receives an image signal from the CCD camera 120, forms an entire image of the surface of the slab by composing image information of the surface of the slab included in the image signal, and detects a defect in the formed image of the surface of the slab.
  • the image processor 130 may include an image collector 131 composing the image information of the surface of the slab included in the image signal.
  • FIGS. 4(a) and 4(b) illustrate images of defects on a surface of a slab and an image of the surface of the slab, imaged using the apparatus according to an exemplary embodiment of the present invention.
  • FIG. 5 is a diagram illustrating a pixel image of the surface of a slab, obtained by the apparatus according to an exemplary embodiment of the present invention.
  • the images of the surface of the slab, composed by the image processor 130, is processed in such a way that only defects on the surface of the slab is processed to be black.
  • the light source 110 is installed in one side in the longitudinal direction of the slab and emits a DC light to the surface of the slab and the CCD camera 120 is installed another side opposite to the one side in the longitudinal direction of the slab to be asymmetrical to the light source 110 and images the surface of the slab.
  • the DC light should be emitted from the light source 110 to the surface of the slab, imaged by the CCD camera 120. Accordingly, an actual imaged area for each pixel is previously set by using a length of an area imaged by the CCD camera 120 and a number of pixels of the CCD camera 120. As shown in FIG. 3, the CCD camera 120 is located above an area into which light from the light source 110 is reflected.
  • the slab to be detected is transferred at a certain speed.
  • the transfer speed is synchronized with a imaging speed of the CCD camera 120, thereby preventing a distortion in which a length of an image is more extended or contracted than that of a real image.
  • the image signal obtained from the CCD camera 130 is inputted to the image collector 131 of the image processor 130 and images included in the image signal are composed to form an entire image.
  • the formed image is shown in FIG. 4B. Comparing with a real image of the surface, shown in FIG. 4(a), all of images of the surface excluding a defect are processed to be bright.
  • the image processor 130 designates a defect area in the entire image formed by the image collector 131, calculates a size of the defect to remove the defect, and connects to a slab surface processor in a next process to remove the defect.
  • levels of brightness of the image formed as shown in FIG. 5 are sequentially read from a left top to right bottom, a certain level is determined as a threshold, and each pixel area is divided into a dark portion and a bright portion.

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  • Engineering & Computer Science (AREA)
  • Textile Engineering (AREA)
  • Physics & Mathematics (AREA)
  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Biochemistry (AREA)
  • General Health & Medical Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Immunology (AREA)
  • Pathology (AREA)
  • Mechanical Engineering (AREA)
  • Investigating Materials By The Use Of Optical Means Adapted For Particular Applications (AREA)

Abstract

There is provided a non-contact defect detection apparatus for automatically detecting a defect on a surface of a slab manufactured in a continuous casting process. The apparatus includes: a light source emitting light to a surface of a slab; a charge-coupled device (CCD) camera located in an outer area of directly reflective light emitted from the light source and reflected on the surface of the slab, imaging the surface of the slab to which the light is emitted, and providing an image of the surface of the slab; and an image processor detecting a defect formed on the surface of the slab from the image provided by the CCD camera.

Description

Description
APPARATUS FOR DETECTING SURFACE DEFECT ON SLAB
Technical Field
[I] The present invention relates to an apparatus for detecting surface defect on a slab apparatus, and more particularly, to a non-contact defect detection apparatus for automatically detecting a defect on a surface of a slab manufactured in a continuous casting process.
[2]
Background Art [3] In a slab manufactured in a continuous casting process, impurities in molten steel form an inclusion. Accordingly, in a solidification process, the inclusion has a different composition from general steel. [4] [5] Since the binding force of the inclusion with the adjacent general steel is weak, such inclusion is easily separated from the slab and forms a hole in the form of a groove when present on a surface and an external force is applied during a scarfing process.
When the defect is rolled as it is in a hot rolling process, the defect is transferred to a next process and shown as a surface defect of a steel sheet. [6] [7] Such defect of the surface of the slab is capable of being detected before being charged into a heating furnace or after out of the heating furnace. However, since an oxide layer such as a scale is formed on the surface to cover the defect of the surface in the hot rolling process, it is impossible to accurately detect the defect. [8] [9] To solve the problem, magnetic methods and optical methods have been proposed.
As optical methods, there are provided a triangulation method and a plane imaging by a strobescope beam. However, there is still a problem that a defect on a surface of a slab is not distinguished from other remnants. [10]
[I I] FIG. 1 is a diagram illustrating a defect detection apparatus provided to solve the problem.
[12] Referring to FIG. 1, to detect with the naked eye, a charge-coupled device (CCD) camera 3 is disposed in the center and lightings 2 are installed in a longitudinal direction of a slab 1 and facing each other to brightly illuminate a portion of the slab 1 to be detected. According to this method, since it is impossible to distinguish a difference between an image from a defect on a surface of the slab 1 and an interlaced image from a color difference on the surface, it is not suitable to detect a defect.
[13]
[14] Referring to FIG. 2, since an AC light source whose strength varies according to time is used (refer to (a) of FIG. 2), when an image obtained by imaging a slab 1 is composed (refer to (b) of FIG. 2), a light and dark phenomenon between images occurs. Accordingly, an image finally obtained by composing is unclear.
[15]
[16] On the other hand, in addition to the described conventional defect detection apparatuses, ACERALIA Spain provides a defect detection method with a type of line scanning based on Conoscopic Holography (1998, Association of Iron and Steel Engineers). However, in this method, since an apparatus thereof is very complicated and an image processing algorithm thereof is very complicated, it is difficult to apply this method to a rolling process in which defect detection information should be quickly transferred to a next process.
[17]
[18] Also, Japanese Laid-open Patent Publication No. 2006-177746 discloses a method of detecting a defect on a steel sheet by installing CCD cameras in two channels such as a specular reflection area and a diffused reflection area in a location opposite to emitted light for accurate optical detection. However, since this is a technology required to measure minute defects and micro uneven portions on a surface, a refinement may act as noise when a slab has a surface that is not clean.
[19]
[20] That is, to detect a defect present in a state in which a surface of a slab is uneven due to a remnant after a defect removal process, there is required a system less sensitive to other minute surface remnants excluding defects on the surface of the slab.
[21]
Disclosure of Invention Technical Problem
[22] An aspect of the present invention provides a non-contact defect detection apparatus automatically detecting a defect on a surface of a slab manufactured in a continuous casting process.
[23]
Technical Solution
[24] According to an aspect of the present invention, there is provided a defect detection apparatus including: a light source emitting light to a surface of a slab; a charge- coupled device (CCD) camera located in an outer area of directly reflective light emitted from the light source and reflected on the surface of the slab, imaging the surface of the slab to which the light is emitted, and providing an image of the surface of the slab; and an image processor detecting a defect formed on the surface of the slab from the image provided by the CCD camera. [25]
Advantageous Effects
[26] As described above, according to the present invention, there is an effect of accurately detecting a defect on a surface of a slab by asymmetrically installing a light source and a CCD camera and brightly imaging unnecessary information excluding the defect on the surface of the slab. [27]
Brief Description of the Drawings [28] FIG. 1 is a configuration diagram illustrating a conventional apparatus for detecting a defect on a surface of a slab; [29] FIG. 2 is a diagram illustrating images imaged by a conventional apparatus for detecting a defect on a surface of a slab; [30] FIG. 3 is a configuration diagram illustrating an apparatus for detecting a defect on a surface of a slab, according to an exemplary embodiment of the present invention; [31] FIGS. 4(a) and 4(b) illustrate images of defects on a surface of a slab and an image of the surface of the slab, imaged using the apparatus according to an exemplary embodiment of the present invention; and [32] FIG. 5 is a diagram illustrating a pixel image of a surface of a slab, obtained by the apparatus according to an exemplary embodiment of the present invention. [33]
Best Mode for Carrying Out the Invention [34] Hereinafter, embodiments of the present invention will be described with reference to the attached drawings. [35] Referring to FIG. 3, the apparatus includes a light source 110, a charge-coupled device (CCD) camera 120, and an image processor 130. [36] The light source 110 emits light a to a surface of a slab. The light source 110 is inclined in a longitudinal direction of the slab to form reflected light b reflected on a surface of the slab. The light source 110 may be a direct current (DC) light source uniformly emitting the light a according to time. [37] [38] The CCD camera 120 is located facing the light source 110 in a longitudinal direction of the slab and asymmetrical to the light source to be away of the reflected light bgenerated by the light source 110. [39] When installed symmetrical to the light source 110 and the surface of the slab is imaged within a range of an angle of reflection, unnecessary small changes on the surface of the slab 1 may be read in addition to the defect on the surface of the slab. Accordingly, the CCD camera 120 is installed out of the range of angle of reflection. Therefore, the CCD camera 120 removes all changes on the surface of the slab excluding the defect on the surface of the slab and allows the defect to be revealed as a dark shape.
[40]
[41] The image processor 130 receives an image signal from the CCD camera 120, forms an entire image of the surface of the slab by composing image information of the surface of the slab included in the image signal, and detects a defect in the formed image of the surface of the slab.
[42] The image processor 130 may include an image collector 131 composing the image information of the surface of the slab included in the image signal.
[43]
[44] FIGS. 4(a) and 4(b) illustrate images of defects on a surface of a slab and an image of the surface of the slab, imaged using the apparatus according to an exemplary embodiment of the present invention.
[45] Referring to FIGS. 4(a) and 4(b), only the defects on the surface of the slab are imaged to be dark and portions other than the defects are imaged to be bright, thereby accurately detecting the defects of the surface of the slab.
[46]
[47] FIG. 5 is a diagram illustrating a pixel image of the surface of a slab, obtained by the apparatus according to an exemplary embodiment of the present invention.
[48] Referring to FIG. 5, the images of the surface of the slab, composed by the image processor 130, is processed in such a way that only defects on the surface of the slab is processed to be black.
[49] Hereinafter, operations and effects of the present invention will be described in detail with reference to FIGS. 3 to 5.
[50]
[51] Referring to FIGS. 3 to 5, the light source 110 is installed in one side in the longitudinal direction of the slab and emits a DC light to the surface of the slab and the CCD camera 120 is installed another side opposite to the one side in the longitudinal direction of the slab to be asymmetrical to the light source 110 and images the surface of the slab.
[52] In this case, the DC light should be emitted from the light source 110 to the surface of the slab, imaged by the CCD camera 120. Accordingly, an actual imaged area for each pixel is previously set by using a length of an area imaged by the CCD camera 120 and a number of pixels of the CCD camera 120. As shown in FIG. 3, the CCD camera 120 is located above an area into which light from the light source 110 is reflected.
[53]
[54] Unnecessary surface image in addition to defects may be imaged when directly imaging reflected light. Accordingly, the surface of the slab out of the area of the angle of the reflection is imaged to prevent this.
[55] After installing the light source 110 and the CCD camera 120 as described above, the slab to be detected is transferred at a certain speed. In this case, the transfer speed is synchronized with a imaging speed of the CCD camera 120, thereby preventing a distortion in which a length of an image is more extended or contracted than that of a real image.
[56]
[57] After that, the image signal obtained from the CCD camera 130 is inputted to the image collector 131 of the image processor 130 and images included in the image signal are composed to form an entire image. The formed image is shown in FIG. 4B. Comparing with a real image of the surface, shown in FIG. 4(a), all of images of the surface excluding a defect are processed to be bright.
[58] The image processor 130 designates a defect area in the entire image formed by the image collector 131, calculates a size of the defect to remove the defect, and connects to a slab surface processor in a next process to remove the defect.
[59]
[60] That is, levels of brightness of the image formed as shown in FIG. 5 are sequentially read from a left top to right bottom, a certain level is determined as a threshold, and each pixel area is divided into a dark portion and a bright portion.
[61] Coordinates of an area A shown as 0, which indicates the defect, are read, a number of pixels having a value of 0 in the coordinates is calculated, and the size of the defect is calculated by using a real length of one pixel, which is previously set.
[62] The coordinates and size of the defect on the surface of the slab, obtained as described above, are transmitted to a system for managing a defect on a surface continuously cast to connect to operation data, and the coordinates of the area are transmitted to the slab surface processor later to remove the defect of the surface of the slab continuously cast after removing the surface.
[63]
[64] While the present invention has been shown and described in connection with the exemplary embodiments, it will be apparent to those skilled in the art that modificat ions and variations can be made without departing from the spirit and scope of the invention as defined by the appended claims.

Claims

Claims
[1] A defect detection apparatus comprising: a light source emitting light to a surface of a slab; a charge-coupled device (CCD) camera located in an outer area of directly reflective light emitted from the light source and reflected on the surface of the slab, imaging the surface of the slab to which the light is emitted, and providing an image of the surface of the slab; and an image processor detecting a defect formed on the surface of the slab from the image provided by the CCD camera. [2] The apparatus of claim 1, wherein the light source is a direct current light source emitting a certain amount of light according to time. [3] The apparatus of claim 1, wherein the outer area is an area of diffused reflection light emitted from the light source and reflected on the surface of the slab. [4] The apparatus of claim 1, wherein the light source and the CCD camera are installed to face each other in a longitudinal or lateral direction. [5] The apparatus of claim 1, wherein the image processor comprises an image collector collecting images from the CCD camera and composing an entire image of the surface of the slab, and the image processor detects the defect on the surface of the slab from the entire image from the image collector.
PCT/KR2007/006677 2006-12-20 2007-12-20 Apparatus for detecting surface defect on slab WO2008075905A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
KR10-2006-0131212 2006-12-20
KR1020060131212A KR100928792B1 (en) 2006-12-20 2006-12-20 Flaw Detection Device on Slab Surface

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CN104267040A (en) * 2014-08-29 2015-01-07 莱芜钢铁集团电子有限公司 Method and device for detecting surface crack of continuous cast billet
CN109215009A (en) * 2017-06-29 2019-01-15 上海金艺检测技术有限公司 Continuous casting billet surface image defect inspection method based on depth convolutional neural networks
JP2019171389A (en) * 2018-03-27 2019-10-10 ダイハツ工業株式会社 Inspection method of streak-like pattern on copper plate surface
RU2795303C1 (en) * 2022-08-02 2023-05-02 Общество с ограниченной ответственностью "Объединенная Компания РУСАЛ Инженерно-технологический центр" Method for automatic continuous surface quality control

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KR101027042B1 (en) * 2008-12-09 2011-04-11 주식회사 엔시스 Apparatus for Inspecting Metal Refined With Electrolysis
KR101325458B1 (en) * 2009-12-29 2013-11-04 주식회사 포스코 Slab cleanness measurement apparatus and method
KR101228741B1 (en) * 2010-12-28 2013-02-04 주식회사 포스코 Apparatus for imaging slab surface
KR101977477B1 (en) * 2017-07-12 2019-05-10 한양대학교 산학협력단 Method and apparatus for recognizing concave indication, calssification apparatus of used medicine using the same
KR102161348B1 (en) * 2018-10-16 2020-09-29 주식회사 포스코아이씨티 Apparatus and Method for Determining Descaling Method Based on Image of Slab

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KR970024700A (en) * 1995-10-30 1997-05-30 양승택 Optical time demultiplexer using 2x2 optical switch to correct distortion of optical signal
KR20040057725A (en) * 2002-12-26 2004-07-02 주식회사 포스코 Apparatus for detecting pin-hole at strip edge without edge mask

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN104267040A (en) * 2014-08-29 2015-01-07 莱芜钢铁集团电子有限公司 Method and device for detecting surface crack of continuous cast billet
CN109215009A (en) * 2017-06-29 2019-01-15 上海金艺检测技术有限公司 Continuous casting billet surface image defect inspection method based on depth convolutional neural networks
CN109215009B (en) * 2017-06-29 2023-05-12 上海金艺检测技术有限公司 Continuous casting billet surface image defect detection method based on deep convolution neural network
JP2019171389A (en) * 2018-03-27 2019-10-10 ダイハツ工業株式会社 Inspection method of streak-like pattern on copper plate surface
JP7094749B2 (en) 2018-03-27 2022-07-04 ダイハツ工業株式会社 Inspection method of streak pattern on the surface of steel plate
RU2795303C1 (en) * 2022-08-02 2023-05-02 Общество с ограниченной ответственностью "Объединенная Компания РУСАЛ Инженерно-технологический центр" Method for automatic continuous surface quality control

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