Metal strip surface inspection device, surface inspection method, and metal strip manufacturing method

Abstract

To provide a surface defect detection device capable of accurately detecting defects in a metal band.SOLUTION: A surface inspection device of a metal band includes: an imaging unit having a plurality of light-emitting elements whose optical axes are directed toward the metal band that is transported in one direction and a plurality of image sensors with optical axes arranged toward the metal band, which are provided to be paired with the plurality of light-emitting elements; and a determination unit for determining a defect in the metal band based on imaging data generated by the imaging unit. Each of the plurality of light-emitting elements is provided so that it emits emitted light having a mutually distinguishable wavelength, and an irradiation range of the emitted light includes a width direction of the metal band. An imaging range of each of the plurality of image sensors is set to include the irradiation range of the paired light-emitting elements. Each of the imaging ranges has a line shape along the width direction of the metal band, and is provided at different angles with respect to the one direction.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a metal strip surface inspection device and method for inspecting surface defects of a metal strip, and a metal strip manufacturing method. [Background technology]

[0002] Metal strips, such as thin steel sheets, are manufactured through various processes. For example, in the manufacturing process of metal strips, a slab is first cast in a steelmaking process. The slab is then turned into a hot-rolled metal strip in a hot-rolling process. Oxides on the surface of the hot-rolled metal strip are removed in a pickling process. The hot-rolled metal strip from which the oxides have been removed is then cold-rolled to a predetermined thickness in a cold-rolling process. The metal strip hardened in these processing processes is then softened in an annealing process. The metal strip that has undergone the annealing process is then subjected to multiple treatments, such as plating and temper rolling.

[0003] Between these processes, the metal strip is inspected for defects. If a defect is detected, measures are taken depending on the severity of the defect. For example, if the defect is serious, measures such as marking or removing the defect are taken. If the defect is minor, the worker is notified that a minor defect has been detected. Furthermore, if the defect is very minor, settings are made so that it is not detected as a defect.

[0004] In the manufacturing process of metal strips, when a defect is detected, its level of importance is also determined. For example, when a flaw caused by a roll or the like is transferred to the metal strip, a concave-convex defect occurs, which causes unevenness on the surface. Such concave-convex defects are transferred to the metal strip with each rotation of the roll, and therefore have a significant impact on quality. For this reason, a higher level of importance is set for concave-convex defects compared to other types of defects. Various efforts are being made to detect such concave-convex defects with high accuracy.

[0005] For example, in Patent Document 1, light beams having different wavelengths from three or more line light sources are emitted in parallel from different directions, and the irradiated lines are scanned with a line scan camera. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2019-39798 Summary of the Invention [Problem to be solved by the invention]

[0007] In Patent Document 1, scanning is performed using one line scan camera. That is, since inspection is performed using only the image information from the scan camera, it is difficult to obtain the fine shape of uneven defects. This causes a problem that the detection accuracy decreases for uneven defects with gentle slopes, for example.

[0008] The present invention has been made in consideration of the above-mentioned problems, and aims to provide a metal strip surface inspection device, a metal strip surface inspection method, and a metal strip manufacturing method that are capable of accurately detecting uneven defects formed on the surface of a metal strip. [Means for solving the problem]

[0009] In order to solve the above problems, the present invention has the following features.

[0010] [1] an imaging unit having a plurality of light-emitting elements whose optical axes are directed toward a metal strip conveyed in one direction, and a plurality of imaging elements whose optical axes are directed toward the metal strip and which are provided so as to be paired with the plurality of light-emitting elements; a determination unit that determines defects in the metal strip based on the imaging data generated by the imaging unit, each of the plurality of light-emitting elements emits light having a wavelength that can be distinguished from one another, and is provided such that an irradiation range of the emitted light includes the width direction of the metal strip; an imaging range of each of the plurality of imaging elements is set so as to include the illumination range of the pair of light-emitting elements; A metal strip surface inspection device, wherein each of the imaging ranges is linear along the width direction of the metal strip and is arranged so that the angles they form with the one direction are different from each other. [2] The metal strip surface inspection device according to [1], wherein the angle formed by the optical axes of the pair of imaging elements in the one direction is equal to the angle formed by the optical axes of the pair of light-emitting elements in the one direction. [3] The metal strip surface inspection device according to [1], wherein the angle formed by the optical axes of the pair of imaging elements in the one direction is different from the angle formed by the optical axes of the pair of light-emitting elements in the one direction. [4] the determination unit includes an angle correction unit that corrects image data captured by the image sensor so that an angle of the image capture range with respect to the one direction approaches a reference angle; The metal strip surface inspection device according to any one of [1] to [3], wherein the determination unit determines defects in the metal strip based on the imaging data corrected by the angle correction unit. [5] the determination unit includes a position correction unit that selects, from the plurality of imaging data, imaging data in which a portion of the metal band included in one of the imaging data matches the portion of the metal band included in another of the imaging data, and The metal strip surface inspection device according to [4], wherein the determination unit determines defects in the metal strip based on the imaging data selected by the position correction unit. [6] The metal strip surface inspection device according to any one of [1] to [5], wherein each of the imaging elements is arranged so that at least two of the imaging ranges intersect at one point. [7] The metal strip surface inspection device according to any one of [1] to [6], wherein the imaging range of at least one of the imaging elements extends in the width direction of the metal strip. [8] a conveying step of conveying the metal strip in one direction; an irradiation step of irradiating a plurality of emission lights having mutually distinguishable wavelengths toward a plurality of irradiation ranges set along the width direction of the metal strip; a setting step of setting a plurality of linear imaging ranges that are set to be paired with the illumination range and extend along the width direction of the metal strip so as to form different angles with respect to the one direction; an imaging data generating step of generating imaging data of the metal strip, the imaging data being captured so as to include the irradiation range paired with the imaging range, in accordance with the imaging range set in the setting step; and a determining step of determining defects in the metal strip based on the plurality of pieces of imaging data. [9] The determining step an angle information acquisition step of acquiring angles formed by each of the imaging ranges in the one direction; and an angle correction step of correcting the imaging data so that the angle acquired in the angle information acquisition step approaches a reference angle.

[10] [9] The surface inspection method according to [9], wherein the determination step includes a position correction step of selecting, from the plurality of imaging data, imaging data in which the portion of the metal strip included in one of the imaging data matches the portion of the metal strip included in another of the imaging data.

[11] A method for manufacturing a metal strip using the metal strip surface inspection device according to any one of [1] to [6]. [Effects of the Invention]

[0011] The metal strip surface inspection device according to the present invention can determine the presence or absence of defects using a plurality of pieces of image data of an object to be inspected, the image data being different from one another in the angle that the imaging range forms with respect to one direction, and irradiated with emitted light of mutually distinguishable wavelengths. This allows the surface inspection device to obtain detailed data on the shape of uneven defects, thereby enabling accurate detection of uneven defects on metal strips. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is an explanatory diagram showing the configuration of a metal strip surface inspection device. [Figure 2] FIG. 2 is a block diagram of a defect detection unit in FIG. [Figure 3] 3 is an explanatory diagram showing the positional relationship between a first light-emitting element and a first imaging element in FIG. 2. FIG. [Figure 4] 3 is an explanatory diagram showing another arrangement relationship between the first light emitting element and the first imaging element in FIG. 2. FIG. [Figure 5] 4 is an explanatory diagram showing another arrangement relationship between the first light emitting element and the first imaging element in FIG. 3. FIG. [Figure 6] 10 is an explanatory diagram showing the arrangement of a first light-emitting element and a first imaging element as viewed from above the metal band. FIG. [Figure 7] 3 is an explanatory diagram showing an example of the arrangement of first to third light emitting elements and first to third imaging elements. FIG. [Figure 8] 10A to 10C are explanatory diagrams showing various aspects of the irradiation range on the metal strip. [Figure 9] 10A and 10B are explanatory diagrams showing other aspects of each of the irradiation ranges on the metal strip. [Figure 10] 10A and 10B are explanatory diagrams showing other aspects of each of the irradiation ranges on the metal strip. [Figure 11] FIG. 1 is a flow diagram of a surface inspection of a metal strip. [Figure 12] FIG. 12 is a flowchart showing a subroutine of the determination step in FIG. [Figure 13] 10 is a schematic diagram in which imaging data generated by a first imaging element over a predetermined period of time is associated with the position on the surface of the metal strip. [Figure 14] 10 is a schematic diagram in which imaging data generated by a first imaging element over a predetermined period of time is associated with the position on the surface of the metal strip. [Figure 15] This is an example in which imaging data acquired at a predetermined time is associated with the position of the metal strip. [Figure 16] 10A and 10B are explanatory diagrams showing examples of angle correction by an angle correction unit. [Figure 17] FIG. 13 is a flowchart showing a subroutine of the position correction step of FIG. [Figure 18] 10 shows how the position corrector corrects the position of a plurality of correction data. [Figure 19] FIG. 2 is a cross-sectional view of a metal strip showing an aspect of uneven defects. [Figure 20] 20 is an example of image data of the uneven defect in FIG. 19. [Figure 21] FIG. 10 is an explanatory diagram showing how specularly reflected light is received at a flat portion of a metal strip. [Figure 22] FIG. 10 is an explanatory diagram showing how specularly reflected light is reflected at a negatively inclined portion of a metal strip. [Figure 23] FIG. 10 is an explanatory diagram showing how specularly reflected light is reflected at a positively inclined portion of a metal strip. [Figure 24] 20 is an explanatory diagram showing an example of imaging data obtained by capturing an image of specularly reflected light from the uneven defect in FIG. 19. FIG. [Figure 25] FIG. 10 is an explanatory diagram showing a state in which diffusely reflected light is received at a flat portion of a metal strip. [Figure 26] FIG. 10 is an explanatory diagram showing how diffusely reflected light is reflected at a negatively inclined portion of a metal strip. [Figure 27] FIG. 10 is an explanatory diagram showing how diffusely reflected light is reflected at a positively inclined portion of a metal band. [Figure 28] 20 is an explanatory diagram showing an example of imaging data obtained by capturing an image of diffusely reflected light from the uneven defect in FIG. 19. FIG. [Figure 29] FIG. 2 is a cross-sectional view of a metal strip showing an aspect of uneven defects. [Figure 30] 30 is an example of image data of the uneven defect in FIG. 29. [Figure 31] FIG. 10 is an explanatory diagram showing composite data obtained by combining three pieces of imaging data. [Figure 32] 10 is another example of image data of a concave-convex defect. [Figure 33] FIG. 10 is an explanatory diagram showing another piece of composite data obtained by combining three pieces of imaging data. DETAILED DESCRIPTION OF THE INVENTION

[0013] Fig. 1 shows the configuration of a metal strip surface inspection device. A metal strip 10 is transported in one direction D, which is the direction of the arrow shown in Fig. 1. The metal strip 10 is transported, for example, by a transport unit 20 provided on a production line for the metal strip 10. The surface inspection device 100 detects defects in the metal strip 10 transported in one direction D in this manner.

[0014] The conveying unit 20 is a conveying roller provided in a production line for the metal strip 10. In this embodiment, the conveying unit 20 is configured by two conveying rollers provided along one direction D.

[0015] The surface inspection device 100 can be used to detect defects on the surface of a metal strip 10 that has undergone any manufacturing process. Specifically, the surface inspection device 100 can be used for a metal strip 10 that has undergone any of the manufacturing processes of a hot rolling process, a pickling process, a cold rolling process, an annealing process, a plating process, and a temper rolling process, as well as a final inspection process for quality assurance of the metal strip. The surface inspection device 100 can be installed at any position from the entry side to the exit side of the equipment for these processes.

[0016] The metal strip 10 is not particularly limited, but for example, a thin steel sheet can be used. More specifically, the metal strip 10 to be inspected can be a thin steel sheet that has been subjected to any process after the hot rolling process, such as a pickling process, a cold rolling process, an annealing process, a plating process, a temper rolling process, and a final inspection process. Note that after the hot rolling process, the thin steel sheet as the metal strip 10 is wound into a coil and subjected to the above processes.

[0017] The metal strip 10 is not limited to a coiled thin steel plate, but may be, for example, a sheet-like steel plate or the like on which the above-described steps are performed. Furthermore, the metal strip 10 is not limited to a steel material, but may be a metal material containing aluminum, copper, or the like.

[0018] The surface inspection device 100 for the metal strip 10 includes an imaging unit 31 that images the surface of the metal strip 10, and a determination section 32 that determines defects based on the image data captured by the imaging unit 31.

[0019] The determination unit 32 can determine uneven defects that are formed by, for example, concaves, convexities, or a combination of these. Examples of uneven defects include defects whose uneven shapes can be recognized visually.

[0020] Specifically, the inspection target can be a circular, elliptical, streak-like, or irregularly shaped irregular defect having a diameter of about 0.1 to 1.0 mm when viewed from a direction perpendicular to the surface of the metal strip 10. In addition, the inspection target can be a irregular defect having a depth (or height) of about 5 to 1000 μm from the surface, for example.

[0021] Incidentally, uneven defects are conventionally classified into more detailed categories, such as dents, dull baldness, compression marks, and scratches. Dents are concave defects that occur when some kind of hard foreign matter gets caught in the metal strip 10 while it is being threaded along the line.

[0022] Dull baldness is a defect in the area where the irregularities (dull marks) of the rolling rolls that have been subjected to dulling are not transferred to the metal strip 10 during the rolling process (cold rolling process or temper rolling process) using the rolling rolls. Dull baldness occurs due to wear of the rolling rolls or adhesion of foreign matter to the rolling rolls.

[0023] A pressure bond defect is a defect that occurs when a part of the bonded layers of the metal strip 10 is peeled off during batch annealing of the coiled metal strip 10. A scratch defect is a defect that occurs as a sliding mark on the surface of the metal strip 10 when the metal strip 10 comes into contact with a foreign object such as an equipment part.

[0024] As described above, uneven defects occurring on the surface of the metal strip 10 have a variety of shapes depending on the cause of occurrence. For this reason, it is important to determine the shape of the uneven defect using the determination unit 32 in order to take appropriate measures corresponding to the cause of occurrence.

[0025] 2 shows the configuration of the surface inspection device 100 for the metal strip 10. As shown in FIG. 2, the imaging unit 31 has a first light emitting element 311, a second light emitting element 312, and a third light emitting element 313.

[0026] The first light-emitting element 311, the second light-emitting element 312, and the third light-emitting element 313 can emit light of wavelengths that can be distinguished from one another. More specifically, the first light-emitting element 311, the second light-emitting element 312, and the third light-emitting element 313 can emit light of, for example, different color tones from one another.

[0027] In this embodiment, the first light-emitting element 311 can emit light having a wavelength whose peak is in a band of, for example, 435 to 500 nm, i.e., blue light. The second light-emitting element 312 can emit light having a wavelength whose peak is in a band of, for example, 600 to 800 nm, i.e., red light. The third light-emitting element 313 can emit light having a wavelength whose peak is in a band of, for example, 500 to 580 nm, i.e., green light.

[0028] It should be noted that each of the emitted lights may be in any form that can be distinguished by an imaging element, which will be described later. For example, even if each of the first light-emitting element 311 to the third light-emitting element 313 emits light of approximately the same color tone, it is sufficient that the peak bands of each of the emitted lights are different and that each of the bands can be separated by a BPF (Band Pass Filter). This is because the imaging element, which will be described later, can distinguish each of the emitted lights.

[0029] For example, LEDs arranged in a row along a predetermined direction can be used as each of the first light-emitting element 311, the second light-emitting element 312, and the third light-emitting element 313. For example, LEDs arranged in a row along the width direction of the metal strip 10 when viewed from one direction D can be used as each of the first light-emitting element 311, the second light-emitting element 312, and the third light-emitting element 313.

[0030] The imaging unit 31 has a first imaging element 314, a second imaging element 315, and a third imaging element 316. Each of the imaging elements 314-316 is provided so as to be paired with each of the light emitting elements 311-313.

[0031] Specifically, the first imaging element 314 is provided to be paired with the first light-emitting element 311. The first imaging element 314 can selectively receive the light emitted from the first light-emitting element 311. The first imaging element 314 can selectively receive the light emitted from the first light-emitting element 311 by, for example, a BPF that passes a band corresponding to the emitted light.

[0032] The second imaging element 315 is provided to be paired with the second light-emitting element 312. The second imaging element 315 can selectively receive the light emitted from the second light-emitting element 312. The second imaging element 315 can selectively receive the light emitted from the second light-emitting element 312 by, for example, a BPF that passes a band corresponding to the emitted light.

[0033] The third imaging element 316 is provided to form a pair with the third light-emitting element 313. The third imaging element 316 can selectively receive the light emitted from the third light-emitting element 313. The third imaging element 316 can selectively receive the light emitted from the third light-emitting element 313 by, for example, a BPF that passes a band corresponding to the emitted light.

[0034] Each of the first to third imaging elements 314 to 316 may be, for example, a line scan camera equipped with a CCD imaging sensor element or a CMOS imaging element.

[0035] Line scan cameras have a higher scan rate than other imaging sensors, allowing them to quickly capture images of light reflected by the metal strip 10. For example, the scan rate of a line scan camera is preferably 10 MHz or higher for a metal strip production line, and more preferably 50 MHz or higher. The upper limit of the scan rate of a line scan camera is preferably about 640 MHz. With this setting, sufficient image data can be obtained to identify defects in the metal strip 10.

[0036] The surface inspection device 100 for the metal strip 10 has a determination unit 32 that determines defects in the metal strip 10 based on the imaging data generated by the imaging unit 31.

[0037] The determination unit 32 has an input unit 321 which is an interface that receives input of imaging data from the imaging unit 31 .

[0038] The determination unit 32 has a storage unit 322 that stores the imaging data transmitted from the imaging unit 31. The storage unit 322 is not particularly limited, but may be, for example, a non-volatile memory such as a hard disk drive (HDD) or a solid state drive (SSD).

[0039] The determination unit 32 has an output unit 323 which is an interface that outputs display data to the display unit 33 that displays the determination result.

[0040] The determination unit 32 has a control unit 324 that controls the entire surface inspection device 100 for the metal strip 10. The control unit 324 is configured by a computer including a CPU, ROM, and RAM (not shown). The control unit 324 has an angle correction unit 324a that corrects the imaging data input from the input unit 321. The control unit 324 has a position correction unit 324b that selects imaging data suitable for processing from multiple imaging data. The control unit 324 has a defect discrimination unit 324c that discriminates defects based on the imaging data. The angle correction unit 324a, the position correction unit 324b, and the defect discrimination unit 324c are executed by the CPU reading out software stored in the ROM.

[0041] The angle correction unit 324a corrects the imaging data captured by each of the first to third imaging elements 314 to 316. Specifically, the angle correction unit 324a identifies an imaging range determined by the arrangement of each of the first to third imaging elements 314 to 316, and corrects the imaging data so that the angle that each of the imaging ranges forms with respect to one direction D becomes a predetermined reference angle.

[0042] The position correction unit 324b selects, from among the plurality of pieces of imaging data, imaging data in which a portion of the metal band included in one piece of imaging data matches a portion of the metal band included in another piece of imaging data. More specifically, the position correction unit 324b selects, from the plurality of pieces of imaging data, data that includes a specific portion of the metal band 10. For example, the position correction unit 324b can perform position correction on the plurality of angle-corrected imaging data to match the position of the specific portion of the metal band 10 included in one piece of imaging data with the position of the specific portion on the imaging data of the other piece of imaging data.

[0043] This allows the imaging data acquired by the imaging unit to be associated with data for the same position on the surface of the metal strip, making it possible to acquire information on the reflected light when light of different wavelengths is irradiated at different angles relative to the transport direction of the metal strip to the same position on the surface of the metal strip.

[0044] The surface inspection device 100, by including the position correction unit 324b, does not need to adjust the positional relationship to align the irradiation ranges of the first to third light emitting elements 311 to 313. In other words, it is possible to use image data of the same portion of the metal strip 10 for judgment without adjusting the imaging ranges of the first to third imaging elements 314 to 316.

[0045] Therefore, by providing the position correction unit 324b, the surface inspection apparatus 100 can increase the degree of freedom in arranging the first light-emitting element 311 to the third light-emitting element 313 and the first image pickup element 314 to the third image pickup element 316 that are paired with these elements.

[0046] The defect determination unit 324c determines whether or not a concave-convex defect has been formed on the inspection object based on the imaging data. For example, the defect determination unit 324c can determine that a concave-convex defect has been formed on the inspection object when a contrast equal to or greater than a predetermined threshold is detected.

[0047] The display unit 33 displays the determination result output from the determination unit 32. The display unit 33 may be, for example, a display such as a liquid crystal display. The display unit 33 may also have a speaker that outputs audio. That is, the display unit 33 may notify the operator of the determination result by audio corresponding to the received determination result.

[0048] 3 to 5 show the positional relationship between the first light-emitting element 311 and the first imaging element 314. Specifically, the first imaging element 314 is disposed at a position where it can capture an image of light that is emitted from the first light-emitting element 311 and reflected on the surface of the metal strip 10.

[0049] As shown in Fig. 3, the first imaging element 314 and the first light-emitting element 311 are disposed so as to face each other when viewed from above the transport section 20. The optical axis AX1 of the first light-emitting element 311 forms an angle β1 with an axis AX2 perpendicular to the surface of the metal strip 10. The optical axis AX3 of the first imaging element 314 forms an angle β2 with the axis AX2 perpendicular to the surface of the metal strip 10. In the example shown in Fig. 3, the angle β1 is approximately the same as the angle β2.

[0050] In other words, the first light-emitting element 311 is disposed at a position where the angle formed by the optical axis AX1 of the paired first light-emitting element 311 in the one direction D is approximately the same as the angle formed by the optical axis AX3 of the paired first image capturing element 314 in the one direction D. By arranging the first image capturing element 314 in this manner, it is possible to capture a clear image of uneven defects on the metal strip 10.

[0051] In this way, the first imaging element 314 can be disposed at a position where it can capture the specularly reflected light of the first light emitting element 311. In other words, in the example shown in Fig. 3, the imaging range of the first imaging element 314 is set so as to be able to capture the specularly reflected light.

[0052] In the example shown in FIG. 4, the angle β1 between the optical axis AX1 of the first light emitting element 311 and the axis AX2 is smaller than the angle β2 between the optical axis AX3 of the first imaging element 314 and the axis AX2.

[0053] In other words, the angle formed by the optical axis AX1 of the paired first light-emitting element 311 in the one direction D and the angle formed by the optical axis AX3 of the paired first image capturing element 314 in the one direction D may be arranged at different positions. By arranging the first image capturing element 314 in this way, it is possible to capture a clear image of uneven defects on the metal strip 10.

[0054] The attenuation behavior of the light reflected by the inclined surface of the uneven defect changes depending on the difference between the angles β1 and β2. Therefore, the determination unit 32 can obtain detailed information including the contour shape of the inclined portion of the uneven defect, and can identify the uneven defect in detail. Note that, in order to ensure that the first image sensor 314 receives a sufficient amount of reflected light, the difference between the angles β1 and β2 is preferably 15 to 45 degrees.

[0055] In this way, the first imaging element 314 may be arranged at a position where it can capture an image of forward scattered light among the diffusely reflected light of the first light emitting element 311. In other words, the imaging range of the first imaging element 314 may be set so as to be able to capture an image of forward scattered light among the diffusely reflected light.

[0056] Furthermore, in the example shown in Figure 5, the angle β1 between the optical axis AX1 of the first light-emitting element 311 and the axis AX2 is smaller than the angle β2 between the optical axis AX3 of the first imaging element 314 and the axis AX2, and is smaller than the angle β1 in the example shown in Figure 4.

[0057] In this way, the first imaging element 314 may be disposed in a position where it can capture, for example, backscattered light among the diffusely reflected light of the first light emitting element 311. In other words, the imaging range of the first imaging element 314 may be set so as to be able to capture backscattered light among the diffusely reflected light.

[0058] By positioning the first imaging element 314 in this way, it is possible to receive reflected light in a manner different from the example shown in Figure 4, making it possible to obtain information on uneven defects in the metal strip 10 from multiple angles.

[0059] The second light-emitting element 312 and the second imaging element 315 may be arranged in the same manner as the first light-emitting element 311 and the first imaging element 314, or in a different manner. The third light-emitting element 313 and the third imaging element 316 may be arranged in the same manner as the first light-emitting element 311 and the second light-emitting element 312, and the first imaging element 314 and the second imaging element 315, or in a different manner. That is, each of the first light-emitting element 311, the second light-emitting element 312, and the third light-emitting element 313 may be provided such that its optical axis is directed toward the transport unit 20 and the angles formed by each optical axis and a given direction are different from each other.

[0060] 6 shows the arrangement of the first light-emitting element 311 and the first image sensor 314 as viewed from above the conveying unit 20. As shown in FIG. 6, when viewed from above the conveying unit 20, the light emitted from the first light-emitting element 311 is irradiated onto the metal strip 10 in a manner that includes the width direction of the metal strip 10. In this embodiment, the light emitted from the first light-emitting element 311 is irradiated across the entire width direction of the metal strip 10.

[0061] That is, in this embodiment, when viewed from above the conveying section 20, an irradiation range AR1 of the emitted light is formed on the surface of the metal strip 10 across its width. Specifically, the irradiation range AR1 of the emitted light is formed in a line extending along the width direction of the metal strip 10. The irradiation range AR1 of the emitted light forms an angle α with one direction D. It is preferable to set the angle α in advance. Furthermore, the positional relationship between the first light-emitting element 311 and the first image sensor 314 can be determined based on the angle α, angle β1, and angle β2.

[0062] The first image sensor 314 is installed so that the imaging range includes the irradiation range AR1 of the emitted light. Therefore, the first image sensor 314 is installed so that it can receive light reflected in the irradiation range AR1. In this embodiment, the irradiation range AR1 and the imaging range are the same, so they will be described below with the same reference numerals.

[0063] The second light-emitting element 312 and the second imaging element 315, as well as the third light-emitting element 313 and the third imaging element 316, can be arranged in the same manner as the first light-emitting element 311 and the first imaging element 314.

[0064] Fig. 7 shows an example of the arrangement of the first light-emitting element 311 to the third light-emitting element 313 and the first image capturing element 314 to the third image capturing element 316. In Fig. 7, an illumination range AR1 of the first light-emitting element 311 is shown. An illumination range AR2 of the second light-emitting element 312 is shown. An illumination range AR3 of the third light-emitting element 313 is shown.

[0065] The first to third light-emitting elements 311 to 313 and the first to third image capturing elements 314 to 316 are preferably arranged such that, for example, at least two of the irradiation ranges AR1 to AR3 intersect with each other. In other words, the first to third light-emitting elements 311 to 313 are preferably arranged such that at least two irradiation ranges of emitted light intersect at one point.

[0066] It is more preferable that the first to third light emitting elements 311 to 313 are arranged so that the irradiation ranges of the three emitted lights intersect at one point, as shown in Fig. 7. In Fig. 7, the irradiation ranges AR1 to AR3 intersect with each other at the center in the width direction of the metal strip 10 when viewed from one direction D.

[0067] The first light emitting element 311 to the third light emitting element 313 and the first image capturing element 314 to the third image capturing element 316 can be freely provided depending on the embodiment.

[0068] 8 to 10 show the respective irradiation ranges AR1 to AR3 on the metal strip 10. For example, as shown in Fig. 8, the first to third light emitting elements 311 to 313 may be arranged so that the respective irradiation ranges AR1 to AR3 do not intersect with each other.

[0069] Furthermore, for example, each of the irradiation areas AR1 to AR3 may have one intersection point, as shown in Fig. 9. In Fig. 9, the irradiation areas AR2 and AR3 intersect with each other at the center in the width direction of the metal strip 10 when viewed from one direction D.

[0070] Furthermore, as shown in Fig. 10, each of the irradiation areas AR1 to AR3 may have two intersections. In Fig. 10, the irradiation areas AR1 and AR3 intersect with each other at one end side in the width direction of the metal strip 10 when viewed from the one direction D. Furthermore, the irradiation areas AR2 and AR3 intersect with each other at the other end side in the width direction of the metal strip 10 when viewed from the one direction D. The intersection of the irradiation areas AR1 and AR3 is located upstream in the one direction D from the intersection of the irradiation areas AR2 and AR3.

[0071] The illumination ranges AR1 to AR3 can be set, for example, to have different angles with respect to one direction D. The angles that the illumination ranges AR1 to AR3 form with respect to one direction D may be set in advance and stored in the storage unit 322.

[0072] As described above, in this embodiment, the imaging ranges of the first to third imaging elements 314 to 316 coincide with the irradiation ranges AR1 to AR3. Therefore, the imaging ranges of the first to third imaging elements 314 to 316 will be described using the same reference numerals as the irradiation ranges AR1 to AR3. The angles that each of the imaging ranges AR1 to AR3 makes with respect to the one direction D may be set in advance and stored in the storage unit 322.

[0073] 7, the angle that the illumination range AR1 forms with respect to the one direction D is 90°. The angle that the illumination range AR2 forms with respect to the one direction D is 135°. The angle that the illumination range AR3 forms with respect to the one direction D is 45°. In other words, the illumination range AR1 of the first light-emitting element 311 is in the shape of a line extending in the width direction of the metal strip 10 when viewed from the one direction D.

[0074] It should be noted that any of the first light emitting element 311 to the third light emitting element 313 and the first image capturing element 314 to the third image capturing element 316 may be located on the upstream side in the one direction D.

[0075] The first light emitting element 311 to the third light emitting element 313 emit, for example, light selected from different wavelength bands of RGB in a line shape. In this embodiment, the first light emitting element 311 emits light in the blue wavelength band.

[0076] The first imaging element 314 captures an image of light in the blue wavelength band emitted from the first light-emitting element 311. The second light-emitting element 312 emits light in the red wavelength band. The second imaging element 315 captures an image of light in the red wavelength band emitted from the second light-emitting element 312. The third light-emitting element 313 emits light in the green wavelength band. The third imaging element 316 captures an image of light in the green wavelength band emitted from the third light-emitting element 313.

[0077] As described above, according to the surface inspection device 100 for the metal strip 10 of this embodiment, the imaging range is set to include the irradiation range of emitted light of mutually distinguishable wavelengths, making it possible to inspect defects in the metal strip 10 from multiple perspectives.

[0078] Furthermore, by having at least one of the angle correction unit 324a and the position correction unit 324b, the surface inspection device 100 for the metal strip 10 can process each piece of image data as if it were data from the same position on the surface of the metal strip 10. This allows the defect discrimination unit 324c to discriminate uneven defects using more detailed data.

[0079] The surface inspection device 100 for the metal strip 10 is preferably used after at least one step has been completed in the manufacturing process for the metal strip 10, which comprises multiple steps. In other words, the metal strip 10 is preferably manufactured using the surface inspection device 100 for the metal strip 10.

[0080] The manufacturing process of the metal strip 10 may include, for example, a steelmaking process in which a slab is cast, a hot rolling process in which the slab is turned into a hot-rolled metal strip, a pickling process in which oxides are removed from the surface of the hot-rolled metal strip, and a cold rolling process in which the hot-rolled metal strip from which the oxides have been removed is cold-rolled to a predetermined thickness. In addition to these processes, the manufacturing process may also include a plurality of processes such as an annealing process in which the metal strip 10 is softened, plating, and temper rolling.

[0081] A method for inspecting the surface of a metal strip 10 using the above-described surface inspection device 100 for the metal strip 10 will now be described. Fig. 11 is a flow diagram of the surface inspection of the metal strip 10. Routine R1 of the method for inspecting the surface of the metal strip 10 is started, for example, when the start of the conveying section 20 is detected as a trigger.

[0082] As shown in FIG. 11, when the routine R1 of the method for inspecting the surface of the metal strip 10 is started, the control unit 324 operates the transport unit 20 to transport the metal strip 10 in one direction D (step S101).

[0083] After the transport step of step S101 is performed, the control unit 324 causes the first to third light emitting elements 311 to 313 to irradiate the metal strip 10 with light emitted therefrom at wavelengths that can be distinguished from one another (step S102).

[0084] In the irradiation step of step S102, the control unit 324 causes each of the emitted light beams to be emitted toward irradiation ranges AR1 to AR3 set along the width direction of the metal strip 10. For example, the control unit 324 causes the first light-emitting element 311 to emit blue emitted light. The control unit 324 causes the second light-emitting element 312 to emit red emitted light. The control unit 324 causes the third light-emitting element 313 to emit green emitted light.

[0085] The control unit 324 sets a plurality of linear imaging ranges AR1 to AR3 that are set to form pairs with the irradiation ranges AR1 to AR3 and extend along the width direction of the metal strip 10 so as to form different angles from each other with respect to one direction D (step S103).

[0086] The setting step of step S103 may be performed in advance before the routine R1 of the surface inspection method is started. The control unit 324 may set the imaging ranges AR1 to AR3 by, for example, reading out the imaging ranges AR1 to AR3 stored in the storage unit 322.

[0087] The first to third imaging elements 314 to 316 generate imaging data using the received light in the specific bands (step S104). Specifically, the first imaging element 314 generates imaging data of the metal strip 10 imaged to include an illumination range AR1 that pairs with the imaging range AR1. The second imaging element 315 generates imaging data of the metal strip 10 imaged to include an illumination range AR2 that pairs with the imaging range AR2. The third imaging element 316 generates imaging data of the metal strip 10 imaged to include an illumination range AR3 that pairs with the imaging range AR3. The imaging unit 31 transmits each of the imaging data generated in the imaging data generation step of step S103 to the determination unit 32.

[0088] Upon receiving the imaging data, the control unit 324 stores the imaging data in chronological order in the storage unit 322. The control unit 324 determines defects in the metal strip 10 based on the received imaging data (step S105).

[0089] The determination step of step S105 is executed as subroutine R2. Fig. 12 shows the subroutine R2 of the determination step. As shown in Fig. 12, the control unit 324 refers to the storage unit 322 and acquires the angles that the imaging ranges AR1 to AR3 make with respect to one direction D (step S201).

[0090] The angle correction unit 324a corrects the imaging data so that the angle acquired in the angle information acquisition step of step S201 approaches the reference angle (step S202).

[0091] For example, in the example shown in Fig. 6, the first imaging element 314 generates imaging data tilted by an angle α with respect to one direction D. Also, in the example shown in Fig. 7, the first to third imaging elements 314 to 316 each generate imaging data tilted at a different angle with respect to one direction D.

[0092] In step S202, the angle correction step, the angle correction unit 324a corrects the imaging data so that the angles approach a reference angle. For example, the angle correction unit 324a sets the imaging range AR1 as a reference angle and corrects the imaging ranges AR2 and AR3 so that they approach the reference angle.

[0093] 13 is a schematic diagram showing the correspondence between imaging data generated by the first imaging element 314 over a predetermined period of time and positions on the surface of the metal strip 10. For example, imaging data at time t0 is generated with the metal strip 10 at a shifted position in the width direction when viewed from one direction D. Specifically, imaging data is generated at a position where the lower side of FIG. 13 is shifted further in one direction D than the upper side.

[0094] 14 is a schematic diagram showing how the angle correction unit 324a corrects the angle of the detection data at each time. The angle correction unit 324a arranges the imaging data to be processed (in this embodiment, the imaging data of the second imaging element 315 and the third imaging element 316) from among the imaging data generated by the first imaging element 314 to the third imaging element 316 in chronological order. The angle correction unit 324a moves and positions each pixel in the imaging data for each time series so that they are at the same position in the width direction of the metal strip 10 (rearranged data).

[0095] For example, the angle correction unit 324a uses a pixel at the center of the strip width as a reference for the detection data at time t0, and moves the pixel so that it extends from the reference in the width direction of the metal strip 10 (so that it extends in the vertical direction in the figure). In other words, the angle correction unit 324a corrects the imaging data captured by the imaging element so that the angle formed by the imaging ranges AR2 and AR3 with respect to one direction D becomes a reference angle (90°).

[0096] The imaging data is generated at each scan rate preset in the first to third imaging elements 314 to 316. That is, the angle correction unit 324a reads out the scan rate and the conveying speed of the conveying unit 20 from the storage unit 322, thereby making it possible to associate the position of the surface of the metal strip 10 with the imaging data.

[0097] It is also advisable to synchronize the imaging timing of the first to third imaging elements 314 to 316 with the transport speed of the metal strip 10. Specifically, it is advisable to synchronize the timing at which the metal strip 10 reaches each of the imaging ranges AR1 to AR3 with the imaging timing of the first to third imaging elements 314 to 316. By synchronizing these, imaging data is generated at a constant pitch with respect to the surface of the metal strip 10, making it easier to associate the imaging data with the position on the surface of the metal strip 10.

[0098] The angle correction unit 324a preferably performs angle correction on the imaging data acquired from the first imaging element 314 to the third imaging element 316. For example, when the reference angle is set to 90°, the imaging data is converted into data arranged in the plate width direction on the surface of the metal strip 10.

[0099] For example, if the angle that the imaging range AR1 makes with respect to the one direction D is 90°, the imaging data of the imaging ranges AR2 and AR3 may be corrected based on the imaging data of the imaging range AR1.

[0100] 7, 9, and 10, when at least one intersection is provided by each of the imaging ranges AR1 to AR3, the angle correction unit 324a preferably performs angle correction so as to rotate the imaging data around the intersection of the imaging ranges. This eliminates the need for position correction processing, thereby simplifying the correction processing.

[0101] The angle correction unit 324a may perform interpolation processing and rearrange the data depending on the timing of image data generation. FIG. 15 shows an example in which image data acquired at a predetermined time is associated with positions on the surface of the metal strip 10. For example, the angle correction unit 324a uses pixel data a1 at the first position at time t1 as a reference. The angle correction unit 324a moves pixel data b1 at the second position, pixel data c1 at the third position, and pixel data d1 at the fourth position at time t1 to the position of the reference pixel data a1. That is, the angle correction unit 324a moves pixel data b1, c1, and d1 to the position of pixel data a1 in the width direction of the metal strip 10. Image data from the second column onward may be selected so that they overlap adjacent pixels. In this case, the angle correction unit 324a may weight the luminance of adjacent pixels according to the degree to which the pixel positions overlap, and use this weighted luminance value as a new luminance value.

[0102] For example, in the example of Figure 15, if pixel data a1 at the position of the first example is used as a reference, the same position in the board width direction as a1 is a range that spans pixels b1 and b2 in the second column. In this case, the weighting coefficient for pixels b1 and b2 in the second column can be determined from the distance in the board width direction between the pixels in the first column and the pixels in the second column and the angle α of the irradiation range. Therefore, the sum of the values ​​obtained by multiplying pixels b1 and b2 in the second column by the weighting coefficient can be used as the brightness value of the relocated data.

[0103] Fig. 16 shows an example of angle correction by the angle correction unit 324a. Fig. 16 shows an example in which the imaging ranges AR1 to AR3 do not intersect with each other on the metal strip 10, similar to the example shown in Fig. 8.

[0104] In this figure, an example is shown in which the angle correction unit 324a corrects imaging data using 90° as a reference angle. The imaging range AR1 has an angle α of 90° and is a line extending in the plate width direction. The angle correction unit 324a does not perform correction on the imaging data obtained in the imaging range AR1 because correction is not required.

[0105] The angle correction unit 324a corrects the imaging range AR2 so that the angle it forms with respect to one direction D becomes 90°, thereby generating a virtual imaging range AR21. The angle correction unit 324a corrects the imaging range AR3 so that the angle it forms with respect to one direction D becomes 90°, thereby generating a virtual imaging range AR31.

[0106] By performing angle correction in this manner, the pixel values ​​of the image data can be arranged in the width direction on the surface of the metal strip 10. This makes it possible to generate multiple image data at the same position in the longitudinal direction of the metal strip 10.

[0107] The position corrector 324b selects, for example, from the plurality of pieces of imaging data corrected by the angle corrector 324a, imaging data in which a portion of the metal band 10 included in one piece of imaging data matches the corresponding portion of the metal band included in the other piece of imaging data (step S203). The position correcting step of step S203 is executed as subroutine R3.

[0108] Fig. 17 shows a subroutine R3 of the position correction step of step S203. As shown in Fig. 17, the position correction unit 324b acquires corrected data, which is the imaging data corrected in the angle correction step of step S202 (step S301).

[0109] When the correction data acquisition step of step S301 is executed, the position correction unit 324b selects imaging data including a specific portion of the metal band 10 from the plurality of acquired correction data (step S302).

[0110] 18 shows how the position corrector 324b corrects the positions of a plurality of correction data items. As shown in FIG. 18, the imaging range AR1 and the virtual imaging ranges AR21 and AR31 form an angle of 90° with respect to one direction D.

[0111] The imaging range AR1 and the virtual imaging ranges AR21 and AR31 are arranged to be shifted from each other in one direction D. That is, the correction data for the virtual imaging ranges AR21 and AR31 is data at a position shifted in one direction D from the imaging data for the imaging range AR1 generated at the same time.

[0112] The position corrector 324b selects imaging data including a specific portion of the metal strip 10 imaged within the imaging range AR1 from the imaging data within the virtual imaging range AR21. Similarly, the position corrector 324b selects imaging data including a specific portion of the metal strip 10 imaged within the imaging range AR1 from the imaging data within the virtual imaging range AR31. This allows all imaging data to be arranged in the width direction on the surface of the metal strip 10, and a set of imaging data at the same position in the longitudinal direction of the metal strip can be generated.

[0113] Furthermore, the position correction unit 324b can perform position correction by, for example, storing the distances between the imaging range AR1, virtual imaging range AR21, 31 and the reference position in the memory unit 322 in advance, and referring to the distances and the conveying speed of the conveying unit 20.

[0114] FIG. 19 is a cross-sectional view of a metal strip 10 showing an example of a concave-convex defect. As shown in FIG. 19, the metal strip 10 has a concave-convex defect 11 formed by being recessed from the surface. FIG. 20 shows an example of imaging data of the concave-convex defect 11 in FIG. 19. As shown in FIG. 20, the area having the concave-convex defect has a deeper (darker) color than the surrounding area.

[0115] The defect determination unit 324c determines whether or not a concave-convex defect 11 is formed on the metal strip 10, for example, based on the imaging data corrected by the position correction unit 324b. Hereinafter, a case will be described in which the metal strip 10 shown in FIG. 19 has a circular concave-convex defect 11.

[0116] 21 to 23 show an example in which the imaging range of the first imaging element 314 is set to a position where it can capture the specularly reflected light of the first light emitting element 311. Fig. 24 shows an example of imaging data of the uneven defect of Figs. 21 to 23.

[0117] In a flat area where no irregular defects are formed as shown in FIG. 21, image data with uniform brightness is obtained as shown in FIG. 24(a).

[0118] 22, when the inclination of the uneven defect 11 is along the optical axis of the first light-emitting element 311 (negative inclination: inclination in the direction in which the depression deepens relative to the conveyance direction of the metal strip 10), the reflected light is scattered according to the inclination of the uneven defect 11. For this reason, as shown in (b) in FIG. 24, the amount of reflected light received by the first imaging element 314 is lower than that of light reflected from a flat portion.

[0119] 23, when the slope of the uneven defect 11 is not aligned with the optical axis of the first light-emitting element 311 (positive slope: slope in the direction in which the recess becomes shallower relative to the conveyance direction of the metal strip), the reflected light is scattered according to the slope of the uneven defect 11. For this reason, as shown in (c) in FIG. 24, the amount of reflected light received by the first imaging element 314 is lower than that of light reflected from a flat portion.

[0120] 24, the defect discriminator 324c discriminates the presence or absence of a concave-convex defect based on imaging data in which the contrast between the area corresponding to the concave-convex defect and its surrounding area is increased, thereby enabling the defect discriminator 324c to clearly detect the concave-convex defect.

[0121] 25 to 27 show an example in which the imaging range of the first imaging element 314 is set to a position capable of capturing an image of diffusely reflected light from the first light emitting element 311. Fig. 28 shows an example of imaging data of the uneven defect of Figs. 25 to 27.

[0122] In a flat area where no irregular defects are formed as shown in FIG. 25, image data with uniform brightness is obtained as shown in FIG. 28(a).

[0123] 26, when the inclination of the uneven defect 11 is along the optical axis of the first light-emitting element 311 (negative inclination: inclination in the direction in which the recess becomes deeper relative to the conveyance direction of the metal strip 10), the reflected light is scattered according to the inclination of the uneven defect 11. For this reason, as shown in (b) in FIG. 28, the amount of reflected light received by the first imaging element 314 is lower than that of light reflected from a flat portion, and the image becomes darker.

[0124] 27, when the slope of the uneven defect 11 is not aligned with the optical axis of the first light-emitting element 311 (positive slope: slope in the direction in which the recess becomes shallower relative to the conveyance direction of the metal strip), the reflected light is scattered according to the slope of the uneven defect 11. Specifically, the direction of the reflected light is reflected so as to approach the optical axis of the diffusely reflected light, and therefore, as shown in (c) in FIG. 28, the amount of reflected light received by the first image sensor 314 is higher and brighter than light reflected from a flat portion.

[0125] In this way, when the first to third imaging elements 314 to 316 are arranged to be able to capture diffusely reflected light, the amount of diffusely reflected light received changes depending on the inclination of the slope of the uneven defect. Therefore, the defect determination unit 324c can determine the inclination of the slope of the uneven defect based on the change in the amount of reflected light.

[0126] As shown in FIG. 28, by providing the first to third imaging elements 314 to 316 so that they can capture diffusely reflected light, the defect determining unit 324c can acquire information about the inclination of the inclined portion of the uneven defect.

[0127] Next, a description will be given of a case where light beams of different color tones are emitted from the first light-emitting element 311 to the third light-emitting element 313. Specifically, a description will be given of a case where the first light-emitting element 311 emits light of a blue color tone, the second light-emitting element 312 emits light of a red color tone, and the third light-emitting element 313 emits light of a green color tone.

[0128] 7, when the first light-emitting element 311 to the third light-emitting element 313 and the first image capturing element 314 to the third image capturing element 316 are arranged, the image capturing ranges AR1 to AR3 form different angles with respect to one direction D. Furthermore, the image capturing ranges AR1 to AR3 intersect at the center in the width direction of the metal strip 10 when viewed from the one direction D. Note that the following describes an example in which the first image capturing element 314 to the third image capturing element 316 are arranged so as to be able to receive specularly reflected light from the first light-emitting element 311 to the third light-emitting element 313.

[0129] Fig. 29 is a cross-sectional view of a metal strip 10 showing an example of a concave-convex defect. As shown in Fig. 29, the metal strip 10 has a concave-convex defect 11 formed by being recessed from the surface. Fig. 30 shows an example of imaging data of the concave-convex defect 11 in Fig. 29. As shown in Fig. 30, the area having the concave-convex defect has a deeper (darker) color than the surrounding area.

[0130] Figure 31 shows composite data obtained by combining the image data captured by the first to third image sensors 314 to 316 after angle and position correction. Figure 31 also shows a schematic representation of the shading of each color. The uneven defect is circular when viewed from above. In an uneven defect, emitted light of a specific wavelength band is attenuated in a specific direction. In the example shown in Figure 31, the image data is generated based on specular reflection. Therefore, the reflected light intensity is approximately the same for both positive and negative slopes of the uneven defect. The flat portions of the metal strip 10 appear white due to a mixture of blue, red, and green hues. However, in the field of metal strip surface inspection technology, displaying the flat portions in white can sometimes make it difficult to detect irregularities such as metallic luster. For this reason, the image data is often corrected to adjust the brightness so that the flat portions appear gray. Therefore, Figure 31 shows an image in which the flat portions of the metal strip 10 are also adjusted to appear gray rather than white.

[0131] 31, in image area IM1 located in the left-right direction, the influence of blue light is small among the light emitted from the first light emitting element 311 to the third light emitting element 313. For this reason, the area of ​​image area IM1 is colored yellow.

[0132] In image region IM2 located from the upper left to the lower right, the influence of green light is small among the light emitted from first light emitting element 311 to third light emitting element 313. For this reason, the image region IM2 is colored pink.

[0133] In image region IM3 located from the lower left to the upper right, the influence of red color is small among the light emitted from the first light emitting element 311 to the third light emitting element 313. For this reason, the image region IM3 is colored a light (bright) blue.

[0134] In this way, in an area where a concave-convex defect is formed, there is a change in the intensity of the specularly reflected light received by the first to third imaging elements 314 to 316. This allows the defect determining unit 324c to determine the concave-convex defect by color.

[0135] Next, a description will be given of an example in which the first to third imaging elements 314 to 316 are arranged so as to be able to receive diffusely reflected light from the first to third light emitting elements 311 to 313. The cross-sectional shape of the metal band 10 is the same as that in FIG. 29, and therefore description thereof will be omitted.

[0136] Fig. 32 is an example of imaging data of the uneven defect 11 in Fig. 29. As shown in Fig. 32, in the area having the uneven defect, the area to the left of the center has a lighter (brighter) color than the surrounding area.

[0137] In the area having the irregular defect, the area to the right of the center is darker in color than the surrounding area.

[0138] FIG. 33 shows composite data obtained by combining the image data captured by the first to third image capture elements 314 to 316 after angle and position correction processes. FIG. 33 shows a schematic representation of the shading of each color. The uneven defect is circular when viewed from above. In the uneven defect, emitted light of a specific wavelength band is attenuated in a specific direction. In the example shown in FIG. 33, the image data is generated based on diffusely reflected light. Note that the flat portion of the metal strip 10 appears white due to a mixture of blue, red, and green hues.

[0139] 33, for example, in image region IM4 located on the left side, the influence of blue light is large among the light emitted from the first light emitting element 311 to the third light emitting element 313. For this reason, the image region IM4 is colored blue.

[0140] Image region IM5 located in the upper left corner has a large influence of green light among the light emitted from the first light emitting element 311 to the third light emitting element 313. For this reason, the image region IM5 is colored green.

[0141] Image region IM6 located at the bottom left has a large influence of red light among the light emitted from the first light emitting element 311 to the third light emitting element 313. For this reason, the image region IM6 is colored red.

[0142] In image region IM7 located to the right, the influence of blue light is reduced among the light emitted from the first light emitting element 311 to the third light emitting element 313. For this reason, the image region IM7 is colored a light (bright) yellow.

[0143] In image region IM8 located in the upper right direction, the influence of red color is small among the light emitted from the first light emitting element 311 to the third light emitting element 313. For this reason, the image region IM8 is colored a light (bright) blue.

[0144] In image region IM9 located in the lower right direction, the influence of green color is small among the light emitted from first light emitting element 311 to third light emitting element 313. For this reason, the region of image region IM9 is colored pink.

[0145] 33, the intensity of the diffused light received by the first to third imaging elements 314 to 316 varies depending on whether the inclination is positive or negative with respect to one direction D. Therefore, the defect discriminator 324c can discriminate the presence or absence of an uneven defect based on the color. Furthermore, the defect discriminator 324c can discriminate information regarding the inclination direction of the inclined surface of the uneven defect, i.e., whether the inclination is positive or negative, based on the color.

[0146] Specifically, the color of a specific emitted light is emphasized in the image depending on the degree of inclination of the uneven defect with respect to one direction D. Therefore, the defect determining unit 324c can determine the degree of inclination of the uneven defect with respect to one direction D from the color of the imaging data.

[0147] In this way, by arranging the first to third imaging elements 314 to 316 so as to capture diffusely reflected light, the direction of inclination of the inclined portion of the uneven defect can be determined. That is, in this embodiment, it is possible to obtain not only the outline shape of the uneven defect in a top view, but also information about the shape of its inclined surface.

[0148] As described above, the surface inspection method for metal strip 10 of the present invention makes it possible to detect uneven defects on the metal strip 10 with high precision. Therefore, even uneven defects with minute shapes or uneven defects with gentle shapes can be detected with high accuracy.

[0149] Furthermore, by using the data obtained by performing angle correction and position correction on each of the imaging data generated in the imaging ranges AR1 to AR3 to determine the irregular defect, more detailed information can be obtained. This improves the accuracy of detecting irregular defects. In other words, by using the combined data obtained by combining these data to determine the irregular defect, it is possible to detect not only the contour shape of the irregular defect but also the shape and degree of inclination of its inclined surface.

[0150] It is preferable to store a composite image of a representative example of the uneven defect to be identified using the surface inspection device of this embodiment as a sample in the storage unit 322. The defect discrimination unit 324c may compare the representative example with the imaging data (including the composite data) to identify the uneven defect. By making such a discrimination, the defect discrimination unit 324c can further improve the accuracy of identifying the uneven defect.

[0151] As described above, by manufacturing a metal strip 10 using the surface inspection device 100 for a metal strip 10 of the present invention, it is possible to provide the metal strip 10 with fewer irregular defects to customers, thereby improving customer satisfaction. [Explanation of symbols]

[0152] 100 Metal strip surface inspection device 10 Metal Strips 20 Conveying section 30 Defect detection section 31 Imaging unit 311~313 Light-emitting elements 314~316 Image sensor 32 Judgment section 324a Angle correction section 324b Position correction section 324c Defect detection section AR1~AR3 Imaging range (irradiation range)

Claims

1. an imaging unit having a plurality of light-emitting elements whose optical axes are directed toward a metal strip conveyed in one direction, and a plurality of imaging elements whose optical axes are directed toward the metal strip and which are provided so as to be paired with the plurality of light-emitting elements; a determination unit that determines defects in the metal strip based on the imaging data generated by the imaging unit, each of the plurality of light-emitting elements emits light having a wavelength that can be distinguished from one another, and is provided such that an irradiation range of the emitted light includes the width direction of the metal strip; an imaging range of each of the plurality of imaging elements is set so as to include the illumination range of the pair of light-emitting elements; each of the imaging ranges is linear along the width direction of the metal strip and is provided so as to form different angles with respect to the one direction; the determination unit includes an angle correction unit that corrects image data captured by the image sensor so that an angle formed by the image capture range with respect to the one direction becomes a reference angle; The determination unit determines defects in the metal strip based on the imaging data corrected by the angle correction unit.

2. 2. The metal strip surface inspection device according to claim 1, wherein the angle formed by the optical axes of the pair of imaging elements in the one direction is equal to the angle formed by the optical axes of the pair of light-emitting elements in the one direction.

3. 2. The metal strip surface inspection device according to claim 1, wherein the angle formed by the optical axes of the pair of imaging elements in the one direction is different from the angle formed by the optical axes of the pair of light-emitting elements in the one direction.

4. the determination unit includes a position correction unit that selects, from the plurality of imaging data, imaging data in which a portion of the metal band included in one of the imaging data matches the portion of the metal band included in another of the imaging data, 2. The metal strip surface inspection device according to claim 1, wherein the determination unit determines defects in the metal strip based on the imaging data selected by the position correction unit.

5. the determination unit includes a position correction unit that selects, from the plurality of imaging data, imaging data in which a portion of the metal band included in one of the imaging data matches the portion of the metal band included in another of the imaging data, 3. The metal strip surface inspection device according to claim 2, wherein the determination unit determines defects in the metal strip based on the imaging data selected by the position correction unit.

6. the determination unit includes a position correction unit that selects, from the plurality of imaging data, imaging data in which a portion of the metal band included in one of the imaging data matches the portion of the metal band included in another of the imaging data, 4. The metal strip surface inspection device according to claim 3, wherein the determination unit determines defects in the metal strip based on the imaging data selected by the position correction unit.

7. 7. The metal strip surface inspection device according to claim 1, wherein each of said imaging elements is arranged so that at least two of said imaging ranges intersect at one point.

8. 7. The metal strip surface inspection device according to claim 1, wherein the imaging range of at least one of the imaging elements extends in the width direction of the metal strip.

9. a conveying step of conveying the metal strip in one direction; an irradiation step of irradiating a plurality of emission lights having mutually distinguishable wavelengths toward a plurality of irradiation ranges set along the width direction of the metal strip; a setting step of setting a plurality of linear imaging ranges that are set to be paired with the illumination range and extend along the width direction of the metal strip so as to form different angles with respect to the one direction; an imaging data generating step of generating imaging data of the metal strip, the imaging data being captured so as to include the irradiation range paired with the imaging range, in accordance with the imaging range set in the setting step; a determining step of determining defects in the metal strip based on the plurality of pieces of imaging data, The determining step an angle information acquisition step of acquiring angles formed by each of the imaging ranges in the one direction; and an angle correction step of correcting the imaging data so that the angle acquired in the angle information acquisition step becomes a reference angle.

10. 10. The surface inspection method according to claim 9, wherein the determination step includes a position correction step of selecting, from the plurality of imaging data, imaging data in which the portion of the metal band included in one of the imaging data matches the portion of the metal band included in another of the imaging data.

11. A method for manufacturing a metal strip using the metal strip surface inspection device according to any one of claims 1 to 6.

Images