JP2008151744A - Steel sheet defect inspection device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a steel sheet defect inspection device capable of identifying the kinds of defects generated on a surface and in a surface layer, a defect generated in an inside, and a hole defect. <P>SOLUTION: This steel sheet defect inspection device is provided with a surface magnetic sensor 2 comprising an array type magnetic sensor 2a and an array type magnetic sensor 2b disposed separately with different distances from a surface side of a thin steel sheet 1, a reverse face magnetic sensor 3 comprising an array type magnetic sensor 3a and an array type magnetic sensor 3b disposed along a width direction separately with a prescribed distance from the surface magnetic sensor 2, and separately with different distances from a reverse face side of the thin steel sheet 1, a defect determination part 4 for comparing output signals from the array type magnetic sensors 2a-3b with a preset determination level to determine the presence of the defect, and a defect kind determination part 5 for determining a detection pattern of a determined defect signal by a defect kind determination algorithm. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a steel sheet defect inspection apparatus, and more particularly to a steel sheet defect inspection apparatus using an array type magnetic sensor that detects a leakage magnetic flux generated by a defective portion of a thin steel sheet.

  Conventionally, as a device for detecting the surface layer of a thin steel plate (also called a strip) such as a tin plate, which is a material for food cans, and the minute defects existing inside, the leakage magnetic flux generated by the defective portion is detected to determine the presence or absence of a defect. There is a magnetic flaw detection apparatus (see, for example, Patent Document 1).

  In this magnetic flaw detector, since it is necessary to shorten the relative distance (lift-off) between the strip and the leakage magnetic flux detection sensor in order to detect a minute defect, there is a problem that contact between the magnetic flaw detector and the thin steel plate is unavoidable. there were.

  Therefore, this array is used in a magnetic flaw detector which magnetizes a thin steel plate in the traveling direction and detects a leakage magnetic flux generated by a defect portion in the thin steel plate and in a surface layer by arranging a plurality of leakage magnetic sensors in the width direction of the thin steel plate. As for the type of magnetic leakage sensor, a technique is disclosed in which even if there is a contact between the magnetic flaw detector and the thin steel plate, the thin steel plate is not wrinkled or the magnetic flaw detector is broken. For example, see Patent Document 2.)

  This array-type magnetic flaw detector has a magnetic element that detects a leakage magnetic flux leaked from a minute defect portion in close proximity to a thin steel plate, and has one end face portion in close contact with the magnetic sensing surface of the magnetic element, and the other Provided at the back of the magnetic sensing surface of the magnetic element, and a magnetic fiber concentrator made of magnetic fibers having soft magnetic properties that are provided with the end face portion facing the surface of the thin steel plate and concentrating the leakage magnetic flux on the magnetic sensing surface. And a soft magnetic plate.

  By the way, there are defects that occur on the surface and the surface layer, defects that occur inside, and hole defects, etc. in the form of minute defects in the thin steel sheet. These defects are identified and detected, and quality control of the thin steel sheet There is a demand to improve.

  However, since the conventional magnetic flaw detection apparatus as described above detects a change in leakage magnetic flux on the surface of a thin steel plate, there is a problem that it is impossible to identify which type of defect it is.

Techniques to improve the accuracy of determining the type of minute defects include optical sensors that irradiate light on a thin steel plate and obtain a signal corresponding to the reflected light from the surface, and magnetic flux applied to the thin steel plate to leak its magnetic flux A sensor unit having a magneto-optical sensor that obtains a signal obtained by optically detecting a pattern, an image processing unit that independently develops each signal obtained from the sensor unit into a two-dimensional image, and extracts a feature amount of the eyelid, There is a wrinkle determination device characterized by including a wrinkle determination unit that determines the type and grade of a defect from a feature amount of the extracted wrinkle according to a specific algorithm (for example, see Patent Document 3).
JP 2002-195984 A (FIG. 1, page 1) Japanese Patent Application No. 2006-150561 (FIG. 1, page 1) JP-A-6-273349 (FIG. 1, page 1)

  The magnetic flaw detector disclosed in Patent Document 2 has a small lift-off, and even if there is contact between the magnetic flaw detector and the thin steel plate, the thin steel plate is not wrinkled or the magnetic flaw detector is broken. Techniques for doing so are disclosed.

  However, the detected signal is only proportional to the magnitude of the leakage magnetic flux, and there is no detection element that captures the form of defects such as defects generated on the surface and surface layer, defects generated inside, and hole defects. There is a problem that the type of can not be identified.

  In addition, in the wrinkle determination device combining the optical sensor and the magneto-optical sensor disclosed in Patent Document 3, although the signal components for identifying the surface and internal signals are included, the detection position and resolution of different sensors are increased. There is a problem that the configuration of the apparatus is complicated and expensive, such as matching with accuracy.

  Furthermore, in order to identify the type of defect by associating the characteristics of the wrinkle image collected by detecting the actual wrinkles with the actual wrinkles, it is necessary to collect and learn a large amount of data. There is a problem that this learning takes time.

  The present invention has been made to solve the above problems, and it is possible to identify the types of defects generated on the surface and surface layer, defects generated inside, and hole defects using an array type magnetic sensor. An object of the present invention is to provide a steel sheet defect inspection apparatus.

  In order to achieve the above object, a steel sheet defect inspection apparatus according to the present invention magnetizes a thin steel sheet in the running direction, and causes a plurality of magnetic sensing elements in the width direction of the thin steel sheet to generate leakage magnetic flux generated by the defective portion of the thin steel sheet. A steel plate defect inspection apparatus for detecting a defect type of the thin steel sheet by detecting an array type magnetic sensor arranged in an array, wherein the first steel sheet is provided in the width direction at a different distance from the surface side of the thin steel sheet. A surface magnetic sensor provided on the surface side of the thin steel plate composed of the array type magnetic sensor and the second array type magnetic sensor, and separated from the surface magnetic sensor in a moving direction of the thin steel plate by a predetermined distance; A back surface magnet provided on the back surface side of the thin steel plate comprising a third array type magnetic sensor and a fourth array type magnetic sensor which are provided in the width direction at different distances from the back surface side of the thin steel plate. A defect determination unit that determines the presence or absence of a defect by comparing a sensor, an output signal from the first array type magnetic sensor to the fourth array type magnetic sensor with a predetermined determination level, and the defect determination The detection patterns of the four defect signals of the first array type magnetic sensor to the fourth array type magnetic sensor detected by the section are determined by a preset defect type determination algorithm to determine the type of defect. A defect type determination unit, wherein the defect signal detected by the defect determination unit is determined to be any of an internal defect, a surface defect, a back surface defect, or a hole defect of the thin steel sheet. And

  In order to achieve the above object, a steel sheet defect inspection apparatus according to the present invention is the first array type magnetic sensor to the fourth array type magnetic sensor according to claim 1, wherein each of the magnetic elements corresponding in the width direction corresponds. The detection elements are arranged in advance so that the positions of the detection elements coincide with each other, and the output of the defect determination unit is output in units of the magnetic detection elements, and the first array type magnetic sensor and the third array type magnetic sensor are connected. The first and second array type magnetic detection sensors are arranged to be spaced apart from each other by a preset first distance with respect to the front surface side and the rear surface side of the thin steel plate. A speed detector for detecting the moving speed of the thin steel sheet, and the first array type in the moving direction of the thin steel sheet. Magnetic sensor through the first A delay circuit unit that corrects a deviation of the detection position of each defect signal due to a difference in the installation position of the array type magnetic sensor with a speed signal of the speed detector; and a storage unit that stores an output signal of the delay circuit unit; A defect type determination unit configured to determine a detection pattern of the defect signal for each magnetic detection element stored in the storage unit in advance using a defect type determination algorithm stored in the storage unit, and The type of defect is determined from the detection pattern of the defect signal for each detection element.

  In order to achieve the above object, a steel sheet defect inspection apparatus according to the present invention is the determination level setting according to claim 1, wherein the defect determination unit has determination levels for determining a defect signal into three types of large, small, and none. A defect signal from the first array type magnetic sensor to the fourth array type magnetic sensor is identified and detected as three types of large, small, and none, and the defect type determination algorithm includes three types The presence / absence of a defect is determined at the determination level, and the type of defect is determined from the detected defect detection pattern.

  As described above, according to the present invention, two array-type magnetic sensors are provided at different distances from the surface of the thin steel plate on the front surface side and the back surface side in the traveling direction of the thin steel plate. On the other hand, the detection sensitivity differs depending on the occurrence position in the thickness direction, and the detection pattern of the leakage magnetic flux is judged by a plurality of front and back array type magnetic sensors to identify the type of defect. Therefore, it is possible to provide a steel sheet defect inspection apparatus capable of identifying the types of defects generated on the surface and surface layer of thin steel sheets, defects generated inside, and hole defects.

  Embodiments of the present invention will be described below with reference to FIGS. FIG. 1 is a configuration diagram of a steel sheet defect inspection apparatus according to the present invention, and shows a layout as viewed from a side surface in a traveling direction indicated by an arrow of a thin steel sheet 1.

  In FIG. 1, the steel plate defect inspection apparatus includes a front surface magnetic sensor 2 provided on the front surface side of the thin steel plate 1, a back surface magnetic sensor 3 provided on the back surface side of the thin steel plate 1, a front surface magnetic sensor 2 and a back surface magnetic sensor 3. The defect determination unit 4 determines whether or not there is a defect from the detected signal, and the defect type determination unit 5 determines the type of defect from the output of the defect determination unit 4.

  The surface magnetic sensor 2 and the back magnetic sensor 3 of the steel plate defect inspection apparatus are in a state in which there is no vertical movement of the thin steel plate 1 on the surface of the nonmagnetic roll 11a provided at a predetermined distance in the traveling direction of the thin steel plate 1. It is installed in the place of.

  The surface magnetic sensor 2 includes a C-type magnetizing yoke 2c wound with a magnetizing coil for magnetizing the thin steel plate 1 wound around the non-magnetic roll 11a and traveling in the direction of the arrow, and both ends of the C-type magnetizing yoke 2c. It consists of an array type magnetic sensor 2a and an array type magnetic sensor 2b provided at the center of the surface portion.

  Similarly, the back magnetic sensor 3 includes a C-type magnetizing yoke 3c wound with a magnetizing coil for magnetizing the thin steel plate 1 wound around a large-diameter nonmagnetic roll 11a and traveling in the direction of the arrow, and the C-type magnet yoke 3c. The magnetic yoke 3c includes an array type magnetic sensor 3a and an array type magnetic sensor 3b provided at the center of both end portions.

  Both end portions of the C-shaped magnetization yoke 2c are spaced a predetermined distance in the traveling direction of the thin steel plate 1 and a predetermined distance from the surface of the thin steel plate 1 so that the thin steel plate 1 is magnetized at a predetermined magnetic flux density or more. Placed close together.

  When a predetermined direct current is passed through the magnetizing coil, the thin steel plate 1 is magnetized by the magnetizing yoke 2c, and if there are inclusions or surface flaws inside the thin steel plate 1, a leakage magnetic flux is generated in this portion. The leakage magnetic flux is detected by the front magnetic sensor 2 and the rear magnetic sensor 3 made of the magnetic detection element 21 to determine the presence or absence of a defect.

  Next, the setting of the front surface magnetic sensor 2 and the back surface magnetic sensor 3 will be described with reference to FIG. FIG. 2A is an external perspective view of the surface magnetic sensor 2, and each of the array type magnetic sensor 2a and the array type magnetic sensor 2b is formed by arranging the same magnetic detection elements 21 in a plurality of width directions.

  The array type magnetic sensor 2a and the array type magnetic sensor 2b are set at different distances ΔL1 and ΔL2 from the thin steel plate 1 as shown in FIG.

  Similarly, the back surface magnetic sensor 3 includes an array type magnetic sensor 3a and an array type magnetic sensor 3b, and is set at different distances ΔL1 and ΔL2 from the thin steel plate 1 as shown in FIG. 2B.

  Further, the front surface magnetic sensor 2 and the back surface magnetic sensor 3 are disposed at a linear distance L with respect to the moving direction of the thin steel plate 1 in which the magnetization yoke 2c and the magnetization yoke 3c are horizontally disposed.

  The array type magnetic sensor 2a to the array type magnetic sensor 3b are arranged in advance so that the detection positions of the respective magnetic detection elements 21 are aligned in the width direction.

  The distance ΔL1 and the distance ΔL2 from the surface of the thin steel plate 1 are obtained by conducting a sample test in advance on the surface and internal defects generated in the thin steel plate 1 detected by the magnetic detection element 21, and in the thickness direction. The detection sensitivity is set to be different for defects occurring at different positions.

  That is, the defect of the thin steel plate 1 is different from the size of the defect or the spatial distribution of the leakage magnetic flux between the surface and the surface layer of the steel plate and the internal central portion of the steel plate. The magnetic detection elements 21 are placed at different distances to make a determination.

  Therefore, the setting of this distance is statistically carefully determined in advance by a sample test by increasing the number of defective samples of the thin steel sheet 1 to be detected.

  Next, signal processing for determining the type of defect from the detection signals from the surface magnetic sensor 2 and the surface magnetic sensor 3 set as described above will be described with reference to FIG.

  The array type magnetic sensor 2a (2b, 3a, 3b) is composed of n magnetic detection elements 21, and the output of each is determined by the defect determination unit 4 to determine the presence / absence of a defect in comparison with a predetermined determination level. The

  By the way, as shown in FIG. 2B, the signals detected by the defect determining unit 4 as being defective are the array type magnetic sensor 2a and the array type magnetic sensor 2b, and the array type magnetic sensor 3a and the array. The ΔL detection position is shifted in the moving direction of the thin steel plate 1 with the mold magnetic sensor 3b. Further, the front magnetic sensor 2 and the rear magnetic sensor are shifted by a distance L.

  Therefore, a unit distance (Δd) signal having a predetermined correction resolution is generated from the speed detector 7, and the defect signal detected by the defect determination unit 4 is transmitted by the delay circuit unit 6 a to the delay circuit unit 6 c with the following unit distance. The detection position is corrected by delaying by several (n) so that the detection position is aligned with the detection position of the array type magnetic sensor 3b.

The number of corrections for each unit distance is as follows in the delay circuit unit 6a.
Delay in the array type magnetic sensor 2a: n _2a = (L + ΔL) / Δd,
In the delay circuit unit 6b,
Delay in the array type magnetic sensor 2b: n _2b = (L + ΔL)
In the delay circuit unit 6c,
Delay in the array type magnetic sensor 3a: n _3a = ΔL / Δd
It becomes.

  The outputs of the delay circuit unit 6a (6b, 6c) and the array type magnetic sensor 3b are corrected in detection position and stored in the storage unit 5a of the defect type determination unit 5. And the defect signal memorize | stored in the memory | storage part 5a is the defect type memorize | stored in the memory | storage part 5 which is not shown in advance by the detection pattern from the magnetic detection element 21 installed in the front side and back surface side of the thin steel plate 1 at different distances. The determination algorithm is read, and the calculation unit 5b performs a calculation based on the defect type determination algorithm to determine the type of defect.

  In this defect type determination algorithm, not only a combination of determination levels but also an image of a detected signal can be imaged and a determination can be made based on a detected two-dimensional image instead of a detection pattern at a different distance.

  Next, the operation of the thus configured steel plate defect inspection apparatus will be described in the case of detection of a modeled defect shown in FIG. 4, for example.

  FIG. 4 is a model diagram of defect occurrence positions and leakage magnetic fluxes viewed from the thickness direction. The size of the internal defect, surface defect, and hole defect of the thin steel sheet 1 targeted by this steel sheet defect detection apparatus is a large defect of 200 μφ, and a small one of about 20 μφ. The state of the spatial expansion of the leakage magnetic flux from the defective part is shown by a broken line.

  As for the leakage magnetic flux, the internal defect D1 and the surface defect D2 (D3) have a smaller leakage magnetic flux inside. Therefore, the magnetic strength of the thin steel plate 1 and the detection sensitivity of the magnetic detection element 21 are the same as those of the minute internal defect D1b. It is set to be detectable.

  For example, for a thin steel plate 1 having a thickness of 1 mm, this setting is such that the magnetizing current is such that a magnetic flux density of 2 Tesla or more is obtained, and the magnetic detection element 21 is configured by a Hall element, The simulation showed that the required detection sensitivity was obtained when the relative distance (lift-off) to the detection element 21 was about 1 mm to 2 mm.

  FIG. 5 shows a model of large internal defect D1a, small internal defect D1b, large surface defect D2a (D3a), small surface defect D2b (D3b) and hole defect D4 as shown in FIG. The detection pattern in the defect determination part 4 of each magnetic detection element 21 from the provided array type magnetic sensor 2a thru | or the array type magnetic sensor 3b is shown.

  Here, those detected at the higher of the three judgment levels are indicated by “◎”, those detected at the lower of the two judgment levels are indicated by “、”, and those not detected at all are indicated by “x”.

  For example, the small internal defect D1b is detected at any of the lower determination levels of the array type magnetic detection sensor 2a and the array type magnetic detection sensor 2b, and the small surface defect D2b and the small surface defect D3b are close to the generation surface. It is detected by the array type detection elements 2a and 2b and the array type detection elements 3a and 3b.

  If the leakage magnetic flux is a defect of the same size, the surface is larger than the inside. Therefore, in the case of a surface defect, it indicates that the defect was detected from any of the array type magnetic sensors on the side where the defect occurred.

  In this way, the state of the leakage magnetic flux in the vertical direction changes due to the difference in the occurrence position in the thickness direction of the defect, so the detection pattern from the array type magnetic sensor installed at different distances, the defect is an internal defect or a surface defect In addition, it is possible to determine the type of defect by identifying whether the position is the front side or the back side.

  However, the actual defect is not defined uniquely associated with the above model because the material of the thin steel plate 1 and the shape of the defect are variously changed. However, the lift-off of the magnetic detection element 21 is selected in advance. It is possible to improve the judgment system of internal defects or surface defects.

  Note that the present invention is not limited to the above-described embodiments, and the defect determination level is not limited to three, but multilevel processing, and other optical systems are used to improve the defect identification system. It is possible to make an appropriate adjustment within a range not departing from the gist of the present invention, such as identifying the occurrence position in the thickness direction of the defect in combination with the defect detection device.

The block diagram of the steel plate defect inspection apparatus of this invention. 1 is a layout view of an array type magnetic sensor of the present invention. The signal processing system diagram of the steel plate defect inspection apparatus of the present invention. Model of defect type and leakage flux. The example of the defect determination output of the array type magnetic sensor corresponding to the kind of defect.

Explanation of symbols

1 Thin steel plate (strip)
2 Surface magnetic sensor 2a Array type magnetic sensor 2b Array type magnetic sensor 2c Magnetization yoke 3 Surface magnetic sensor 3a Array type magnetic sensor 3b Array type magnetic sensor 3c Magnetization yoke 4 Defect determination unit 5 Defect type determination unit 5a Storage unit 5b Operation unit 6a , 6b, 6c, 6d Delay circuit section 7 Speed detector 11a, 11b Nonmagnetic roll 12 Array type magnetic sensor 12c Magnetizing yoke 21 Magnetic detecting element

Claims (3)

Magnetic flux is magnetized in the running direction of the thin steel plate, and leakage magnetic flux generated by the defective portion of the thin steel plate is detected by an array type magnetic sensor in which a plurality of magnetic detection elements are arranged in the width direction of the thin steel plate. A steel sheet defect inspection apparatus for determining the type of
A surface magnetic sensor provided on the surface side of the thin steel plate, comprising a first array type magnetic sensor and a second array type magnetic sensor provided in the width direction at different distances from the surface side of the thin steel plate;
A third array type magnetic sensor and a fourth array that are spaced apart from the surface magnetic sensor by a predetermined distance in the moving direction of the thin steel plate and spaced apart from the rear surface side of the thin steel plate by a different distance. A back surface magnetic sensor provided on the back surface side of the thin steel plate composed of a mold type magnetic sensor;
A defect determination unit that determines the presence or absence of a defect by comparing output signals from the first array type magnetic sensor to the fourth array type magnetic sensor with a predetermined determination level;
Four defect signal detection patterns of the first array type magnetic sensor to the fourth array type magnetic sensor detected by the defect determination unit are determined by a preset defect type determination algorithm, and the type of defect is determined. A defect type determination unit for determining
A steel plate defect inspection apparatus, wherein the defect signal detected by the defect determination unit is determined to be any of an internal defect, a surface defect, a back surface defect, or a hole defect of the thin steel plate. The first array type magnetic sensor to the fourth array type magnetic sensor are arranged in advance so that the positions of the corresponding magnetic detection elements in the width direction coincide with each other,
The output of the defect determination unit is output in units of the magnetic detection element,
The first array type magnetic sensor and the third array type magnetic sensor are set apart from each other at a first distance set in advance with respect to the front surface side and the back surface side of the thin steel plate,
Installing the second array type magnetic detection sensor and the fourth array type magnetic detection sensor apart from each other by a preset second distance longer than the first distance;
A speed detector for detecting the moving speed of the steel sheet;
In the moving direction of the thin steel plate, the displacement of the detection position of each defect signal due to the difference in the installation position of the first array type magnetic sensor to the fourth array type magnetic sensor is a speed signal of the speed detector. The delay circuit section to be corrected by
A storage unit for storing an output signal of the delay circuit unit;
A defect type determination unit for determining a detection pattern of the defect signal for each of the magnetic detection elements stored in the storage unit, which is set in advance using a defect type determination algorithm stored in the storage unit;
The steel sheet defect inspection apparatus according to claim 1, wherein a defect type is determined from a detection pattern of a defect signal for each magnetic detection element. The defect determination unit includes a determination level setting unit having determination levels for determining a defect signal into three types, large, small, and none, from the first array type magnetic sensor to the fourth array type magnetic sensor. Detect and detect three types of defect signals, large, small, and none,
2. The steel sheet according to claim 1, wherein the defect type determination algorithm determines the presence / absence of a defect at the three types of determination levels, and determines the type of defect from the determined defect detection pattern. Defect inspection equipment.

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