Surface inspection device, method for installing oblique lighting in surface inspection device, and method for manufacturing steel plate

Abstract

To provide a surface inspection device that can be installed without protruding oblique lighting from the width direction of a steel plate, an installation method for oblique lighting for the same, and a steel plate manufacturing method.SOLUTION: In a surface inspection device 1, an oblique lighting 11 is divided into two parts in a width direction (x-x direction) of a steel plate S, and it becomes a first oblique lighting 11a and a second oblique lighting 11b. In addition, they are separated in a longitudinal direction (y-y direction) of the steel plate S so that the first oblique lighting 11a and the second oblique lighting 11b do not interfere with each other. The first oblique lighting 11a and the second oblique lighting 11b are installed so that respective light L11a, L11b from the first oblique lighting 11a and the second oblique lighting 11b is irradiated from the inside of the width direction of the steel plate S to the outside of the width direction of the steel plate S.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a surface inspection device, a method for installing oblique lighting in a surface inspection device, and a method for manufacturing a steel plate. [Background technology]

[0002] Conventionally, in a surface inspection process for steel sheets, for example, a surface inspection process for pickled hot-rolled steel sheets, the surface of the hot-rolled steel sheet is inspected before shipping, and if a defect is found on the surface of the hot-rolled steel sheet, the defective steel sheet portion is cut off, etc. The surface inspection device used for this surface inspection generally includes an illumination device that irradiates the surface of the traveling steel sheet with light (e.g., LED light), and an imaging device that images the surface of the steel sheet irradiated with light by the illumination device.

[0003] This lighting device generally employs a normal lighting configuration and is equipped with a rod-shaped light source that extends along the width direction of the steel sheet and has a length that covers the entire width direction of the steel sheet so that it can irradiate light across the entire width direction of the steel sheet.The rod-shaped light source is installed relative to the steel sheet so that the direction of light irradiated from the rod-shaped light source is parallel to the longitudinal direction of the steel sheet (the sheet passing direction). However, in surface inspections using an illumination device with this normal illumination configuration, it can be difficult to detect irregular defects on the surface of a steel sheet. The reason for this is that when light is irradiated onto the surface of the steel sheet, images of normal and defective parts on the surface of the steel sheet do not show a significant difference between the images of the normal and defective parts, making it difficult to distinguish between the normal and defective parts.

[0004] In response to this, in order to detect uneven defects on the surface of steel sheets with high accuracy, a surface inspection device equipped with an illumination device that provides oblique illumination has been proposed in the past, for example, as shown in Patent Document 1. The steel surface device shown in Patent Document 1 is equipped with a color line camera arranged on a steel surface inspection line, widthwise oblique illumination from a first rod-shaped light source (green) and a second rod-shaped light source (blue), an image processing device, a processing device having a means for revealing unevenness in the longitudinal and width directions in the sheet passing direction using RGB color images and GB differential images, and a processing device having a means for detecting and identifying defects.

[0005] The width direction oblique illumination of the first rod-shaped light source (green) and second rod-shaped light source (blue) used in the steel surface device shown in Patent Document 1 has the first rod-shaped light source and second rod-shaped light source each extending along the width direction of the steel and having a length covering the entire width direction of the steel so that light can be irradiated over the entire width direction of the steel. The first rod-shaped light source and second rod-shaped light source are installed with respect to the steel so that the width direction oblique light angle formed by the direction of light irradiated from each of the first rod-shaped light source and second rod-shaped light source and the longitudinal direction of the steel (sheet passing direction) is 15 to 45 degrees. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2018-36175 Summary of the Invention [Problem to be solved by the invention]

[0007] However, the conventional surface device for steel materials shown in Patent Document 1 has the following problems. Specifically, the width direction oblique lighting using the first rod-shaped light source and the second rod-shaped light source used in the steel surface treatment device disclosed in Patent Document 1 has a length sufficient to cover the entire width direction of the steel material, and is installed relative to the steel material so that the width direction oblique lighting angle formed by the direction of light emitted from the first rod-shaped light source and the second rod-shaped light source and the longitudinal direction (sheet passing direction) of the steel material is 15 to 45 degrees. Therefore, each of the first rod-shaped light source and the second rod-shaped light source protrudes from the width direction end of the steel material. Therefore, extra installation space for the width direction oblique lighting is required by the amount that each of the first rod-shaped light source and the second rod-shaped light source protrudes from the width direction end of the steel material. Therefore, if there is no extra installation space for the width direction oblique lighting when it is installed, there is a problem that the width direction oblique lighting will interfere with surrounding equipment.

[0008] Therefore, the present invention has been made to solve this conventional problem, and its object is to provide a surface inspection device in which oblique lighting can be installed without protruding from the width direction of the steel plate, a method for installing oblique lighting in a surface inspection device, and a method for manufacturing steel plate. [Means for solving the problem]

[0009] In order to solve the above problems, a surface inspection device according to one aspect of the present invention is a surface inspection device comprising an illumination device having an oblique illumination device, an imaging device that images the surface of a steel plate illuminated with light by the illumination device, and an image processing device that performs image processing on the image captured by the imaging device to detect uneven defects on the surface of the steel plate, wherein the oblique illumination device is divided into two in the width direction of the steel plate to form a first oblique illumination device and a second oblique illumination device, the first oblique illumination device and the second oblique illumination device are separated in the longitudinal direction of the steel plate so that the first oblique illumination device and the second oblique illumination device do not interfere with each other, and the first oblique illumination device and the second oblique illumination device are installed so that light from each of the first oblique illumination device and the second oblique illumination device is irradiated from the inside of the steel plate in the width direction toward the outside of the steel plate in the width direction.

[0010] Another aspect of the present invention relates to a method for installing oblique lighting in a surface inspection device, which is a method for installing oblique lighting in a surface inspection device comprising an illumination device having oblique lighting, an imaging device that images the surface of a steel plate illuminated with light by the illumination device, and an image processing device that processes the image captured by the imaging device to detect uneven defects on the surface of the steel plate, wherein the oblique lighting is divided into two in the width direction of the steel plate to form a first oblique lighting and a second oblique lighting, the first oblique lighting and the second oblique lighting are separated in the longitudinal direction of the steel plate so that the first oblique lighting and the second oblique lighting do not interfere with each other, and the first oblique lighting and the second oblique lighting are installed so that light from each of the first oblique lighting and the second oblique lighting is irradiated from the inside of the steel plate in the width direction toward the outside of the steel plate in the width direction. A method for producing a steel sheet according to another aspect of the present invention is summarized as including a step of inspecting the surface of the steel sheet using the above-mentioned surface inspection device. [Effects of the Invention]

[0011] According to the surface inspection device, the method for installing an oblique illuminator in the surface inspection device, and the method for manufacturing a steel plate according to the present invention, the oblique illuminator can be installed without protruding from the width direction of the steel plate, thereby preventing the oblique illuminator from interfering with surrounding equipment. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a front view seen from the axial direction of a bridle roll, showing a schematic configuration of a surface inspection device according to an embodiment of the present invention. FIG. [Figure 2] FIG. 2 is a right side view of the surface inspection device shown in FIG. [Figure 3] 10 is a graph showing the spectral distribution of red LED lighting used for the first oblique lighting, green LED lighting used for the second oblique lighting, and blue LED lighting used for the specular lighting in the surface inspection device shown in FIG. [Figure 4]This explains typical normal lighting, where (a) is a plan view showing how light from normal lighting is irradiated onto the surface of a steel plate to detect vertically elongated irregular defects formed on the steel plate, and (b) is an enlarged cross-sectional view taken along line 4b-4b in (a). [Figure 5] This explains oblique lighting, where (a) is a plan view showing how light from an oblique lighting source is irradiated onto the surface of a steel plate to detect vertically elongated irregular defects formed on the steel plate, and (b) is an enlarged cross-sectional view taken along line 5b-5b in (a). [Figure 6] FIG. 6 is a diagram for explaining an example in which the first oblique lighting and the second oblique lighting interfere with each other when the oblique lighting shown in FIG. 5 is divided into two in the width direction of the steel plate to form a first oblique lighting and a second oblique lighting. [Figure 7] FIG. 6 is a diagram for explaining a surface inspection device according to this embodiment in which the oblique lighting shown in FIG. 5 is divided into two in the width direction of the steel plate to form a first oblique lighting and a second oblique lighting, the first oblique lighting and the second oblique lighting are spaced apart in the longitudinal direction of the steel plate so as not to interfere with each other, and the first oblique lighting and the second oblique lighting are installed so that light from each of the first oblique lighting and the second oblique lighting is irradiated from the inside of the steel plate in the width direction toward the outside of the steel plate in the width direction. [Figure 8] FIG. 10 is a diagram for explaining a modified example of the surface inspection device according to the present embodiment. [Figure 9] FIG. 8 is a diagram for explaining how the first oblique illumination imaging device and first oblique illuminator, and the second oblique illumination imaging device and second oblique illuminator are respectively installed in the surface inspection device according to the present embodiment shown in FIGS. 1 and 7 so that the fields of view of the first oblique illumination imaging device and the second oblique illumination imaging device overlap in the width direction of the steel plate. [Figure 10] 10A and 10B show an example of an uneven defect formed on the surface of a steel sheet, where (a) is a plan view and (b) is a cross-sectional view taken along line 10b-10b in (a). [Figure 11] FIG. 1 is a diagram showing a captured image of an example of a concavo-convex defect formed on the surface of a steel plate. [Figure 12]12 is a graph showing a waveform of brightness for a concave-convex defect detected from the captured image shown in FIG. 11. [Figure 13] This figure shows an image of an example of a uneven defect when the defect exists on the surface of a steel plate corresponding to the overlapping area where the field of view of the first oblique illumination imaging device and the field of view of the second oblique illumination imaging device overlap. [Figure 14] 14 is a graph showing a waveform of brightness for a concave-convex defect detected from the captured image shown in FIG. 13. [Figure 15] 10 is a graph showing a waveform of brightness for a concave-convex defect detected from an image captured in the field of view of the first oblique illumination imaging device. [Figure 16] 10 is a graph showing a waveform of brightness for a concave-convex defect detected from an image captured in the field of view of the second oblique illumination imaging device. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments of the present invention will be described with reference to the drawings. The embodiments shown below are examples of devices and methods for embodying the technical concept of the present invention, and the technical concept of the present invention is not limited to the following embodiments in terms of the materials, shapes, structures, arrangements, etc. of the components. In addition, the drawings are schematic, and therefore it should be noted that the relationship between thickness and planar dimensions, ratios, etc. may differ from the actual relationship, and the dimensional relationships and ratios may differ between the drawings.

[0014] FIG. 1 shows a schematic configuration of a surface inspection device according to one embodiment of the present invention. The surface inspection device 1 shown in Fig. 1 is installed in a pickling line for hot-rolled steel sheets, and detects uneven defects 50 (see Fig. 10) on the surface Sa of a hot-rolled steel sheet (hereinafter simply referred to as steel sheet) S transported in the direction of arrow A by bridle rolls 2. The uneven defects 50 refer to uneven defects such as point defects and longitudinally elongated opening defects that are recessed from the surface Sa of the steel sheet S or protrude from the surface Sa. The surface inspection device 1 includes an illumination device 10, an imaging device 20, and an image processing device 30. The lighting device 10 includes an oblique lighting unit 11 and a specular lighting unit 12 .

[0015] As shown in FIG. 2, the oblique illuminator 11 is divided into two parts in the width direction (xx direction) of the steel sheet S, that is, a first oblique illuminator 11a and a second oblique illuminator 11b. The first oblique light illuminator 11a is a rod-shaped red LED light illuminator and is installed so as to extend along the width direction (xx direction) of the steel sheet S. The second oblique light illuminator 11b is a rod-shaped green LED light illuminator and is installed so as to extend along the width direction of the steel sheet S. The combined length of the first oblique light illuminator 11a in the width direction (xx direction) and the length of the second oblique light illuminator 11b in the width direction (xx direction) is longer than the width W (see FIG. 2) of the steel sheet S in the width direction (xx direction). The first oblique light illuminator 11a and the second oblique light illuminator 11b are installed apart from each other in the longitudinal direction (yy direction) of the steel plate so that the first oblique light illuminator 11a and the second oblique light illuminator 11b do not interfere with each other.

[0016] Specifically, as shown in Fig. 1, the first oblique light illuminator 11a is installed above the horizontal plane HS through which the central axis of the bridle roll 2 passes, in the longitudinal direction (yy direction). The second oblique light illuminator 11b is installed below the horizontal plane HS through which the central axis of the bridle roll 2 passes, in the longitudinal direction (yy direction). As shown in Figs. 1 and 7(b), the first oblique light illuminator 11a irradiates light L 11a The angle of irradiation (light L) is the horizontal line HL on the surface Sa, which is the intersection line between the horizontal plane HS and the surface Sa of the steel sheet S. 11a and the horizontal plane HS)θ 11a = 35°. As shown in FIG. 1 and FIG. 7(c), the second oblique illuminator 11b is installed so that the light L 11b The angle of irradiation (light L) is the horizontal line HL on the surface Sa, which is the intersection line between the horizontal plane HS and the surface Sa of the steel sheet S. 11b and the horizontal plane HS)θ 11b = 35°.

[0017] As shown in FIG. 2, the first oblique illuminator 11a and the second oblique illuminator 11b respectively emit light L 11a , L 11b is installed so that it irradiates from the inside of the steel plate S in the width direction toward the outside of the steel plate S in the width direction. Specifically, as shown in FIG. 2, the first oblique illuminator 11a emits light L 11a The angle of the light (light L) is from the inside of the steel sheet S in the width direction to the outside of the width direction toward the horizontal line HL on the surface Sa of the steel sheet S. 11a The angle of the oblique light with respect to the line VL in the longitudinal direction (yy direction) of 11a The beam is set so that it is irradiated at 30°.

[0018] As shown in FIG. 2, the second oblique illuminator 11b emits light L 11b The angle of the light (light L) is from the inside of the steel sheet S in the width direction to the outside of the width direction toward the horizontal line HL on the surface Sa of the steel sheet S. 11b The angle of the oblique light with respect to the line VL in the longitudinal direction (yy direction) of 11b The beam is set so that it is irradiated at 30°. As described above, a red LED light is used as the first oblique light 11a, and a green LED light is used as the second oblique light 11b. 11a and the wavelength of the light L from the second oblique illuminator 11b 11b The wavelength of the light is different from that of the light having a wavelength of 1000 MHz.

[0019] As shown in FIG. 2 and FIG. 7(a), the light L from the first oblique illuminator 11a 11a and the light L from the second oblique illuminator 11b. 11b The first oblique light illuminator 11a and the second oblique light illuminator 11b are installed so that the irradiation ranges of the first and second oblique light illuminators 11a and 11b overlap at the boundary in the width direction (xx direction) of the steel sheet S. The first oblique light illuminator 11a and the second oblique light illuminator 11b are installed in an oblique light illuminator installation member such as a housing (not shown).

[0020] The reason for adopting the oblique illumination 11 in this embodiment will now be described with reference to FIGS. As shown in FIG. 4(a), the normal lighting (specular reflection lighting) 101 is configured with a rod-shaped light source extending along the width direction (xx direction) of the steel sheet S, and emits light L 101 4(a) and 4(b), the normal lighting 101 has a length that covers the entire width direction (x-x direction) of the steel sheet S so that the light L irradiated from the normal lighting 101 can be 101 The direction of the y-axis is parallel to the longitudinal direction (yy direction) of the steel plate S.

[0021] In the case of normal lighting 101, light L 101 is irradiated onto the surface Sa of the steel sheet S, and the surface Sa of the steel sheet S is imaged by an imaging device 102. When detecting an uneven defect 103 formed on the surface Sa of the steel sheet S, there is not much difference in the captured image between the uneven defect 103 and the portion of the surface Sa of the steel sheet S other than the uneven defect 103, making it difficult to detect the uneven defect 103. On the other hand, as shown in FIG. 5(a), the oblique light source 11 is composed of a rod-shaped light source extending along the width direction (xx direction) of the steel sheet S, and emits light L 11 5(a) and 5(b), the oblique lighting 11 has a length that covers the entire width direction (x-x direction) of the steel sheet S so that the light L irradiated from the oblique lighting 11 can be 11 The light source is placed on the steel plate S so that the direction of the light source forms an oblique angle with respect to the longitudinal direction (yy direction) of the steel plate S.

[0022] In the case of the oblique lighting 11, the light L 11 is irradiated onto the surface Sa of the steel sheet S, and the surface Sa of the steel sheet S is imaged by the imaging device 102. When detecting an uneven defect 103 formed on the surface Sa of the steel sheet S, a shadow 103a is cast on the uneven defect 103, so that a large difference appears in the captured image between the uneven defect 103 and the portion of the surface Sa of the steel sheet S other than the uneven defect 103, and the uneven defect 103 can be easily detected. For this reason, in this embodiment, oblique lighting 11 is adopted.

[0023] Next, the reason why the oblique illuminator 11 is divided into two in the width direction (x--x direction) of the steel sheet S to form the first oblique illuminator 11a and the second oblique illuminator 11b will be explained. When the oblique lighting 11 is used, as shown in FIG. 5(a), the light L irradiated from the oblique lighting 11 11 The oblique illuminators 11 are installed with respect to the steel plate S so that the direction of the oblique illuminators 11 forms an oblique angle with respect to the longitudinal direction (yy direction) of the steel plate S. Therefore, compared to the case of the normal illuminators 101, the width direction ends of the oblique illuminators 11 protrude by δ in the width direction (xx direction) of the steel plate S. Therefore, extra installation space is required by the amount that the oblique illuminators 11 protrude from the width direction (xx direction) ends of the steel plate S, and when the oblique illuminators 11 extending in the width direction are installed, if there is not enough extra installation space, the oblique illuminators 11 may interfere with surrounding equipment.

[0024] Therefore, in this embodiment, the oblique illuminator 11 is divided into two in the width direction (x--x direction) of the steel sheet S, and is configured as a first oblique illuminator 11a and a second oblique illuminator 11b. However, if the first oblique light illuminator 11a and the second oblique light illuminator 11b are installed side by side in the width direction (xx direction) of the steel sheet S as shown in FIG. 6, the first oblique light illuminator 11a and the second oblique light illuminator 11b will interfere with each other. Therefore, in this embodiment, as shown in Figures 1, 2, and 7(a), (b), and (c), the first oblique light illuminator 11a and the second oblique light illuminator 11b are installed at a distance from each other in the longitudinal direction (yy direction) of the steel plate S so that the first oblique light illuminator 11a and the second oblique light illuminator 11b do not interfere with each other.

[0025] The first oblique illuminator 11a and the second oblique illuminator 11b are respectively light L 11a , L 11b is installed so that it is irradiated from the inside of the steel plate S in the width direction to the outside of the steel plate S in the width direction. This allows the oblique light illuminator 11 to be installed without protruding from the width direction of the steel sheet S while avoiding interference between the first oblique light illuminator 11a and the second oblique light illuminator 11b, as shown in FIGS.

[0026] In this embodiment, a red LED light is used as the first oblique light 11a, a green LED light is used as the second oblique light 11b, and the light L from the first oblique light 11a 11a and the wavelength of the light L from the second oblique illuminator 11b 11b As will be described later, each of the first oblique lighting imaging devices 21a captures light L irradiated from the first oblique lighting device 11a and reflected by the surface Sa of the steel sheet S. 11a The first oblique illumination imaging devices 21a are provided with a first filter 23a that transmits light of a wavelength (red) of the first oblique illumination 11a. 11a Each second oblique light illuminator 11b captures an image of the surface Sa of the steel sheet S illuminated with the light L. 11b The second oblique illumination imaging devices 21b are provided with second filters 23b that transmit light of wavelengths (green) of the second oblique illumination 11b. 11b The surface Sa of the steel sheet S irradiated with the light is imaged.

[0027] As a result, the optical system of the first oblique illuminator 11a and the optical system of the second oblique illuminator 11b are separated in the width direction (xx direction) of the steel sheet S, and the light L from the first oblique illuminator 11a is 11a and the light L from the second oblique light source 11b. 11b The separation of the optical system of the first oblique illuminator 11a and the optical system of the second oblique illuminator 11b in the width direction (xx direction) of the steel sheet S will be described in detail later.

[0028] As shown in FIG. 2, the specular reflection light 12 in the lighting device 10 extends along the width direction (xx direction) of the steel sheet S, and emits light L 12The specular reflection illuminator 12 has a length that covers the entire width direction (xx direction) of the steel sheet S so that the irradiated light L 12 The specular reflection illuminator 12 is installed with respect to the steel sheet S so that the direction of the specular reflection illuminator 12 is parallel to the longitudinal direction (yy direction) of the steel sheet S. The length L of the specular reflection illuminator 12 along the width direction (xx direction) of the steel sheet S is longer than the width W of the steel sheet S and is the same as the length of the specular reflection illuminator 12 along the width direction (xx direction) of the bridle roll 2.

[0029] The specular reflection illuminator 12 is a light source. 12 The angle of irradiation (light L) is the horizontal line HL on the surface Sa, which is the intersection line between the horizontal plane HS and the surface Sa of the steel sheet S. 12 and the horizontal plane HS)θ 12 = 10°. The specular reflection light 12 uses a rod-shaped blue LED light. In addition, the imaging device 20 is used to image the surface Sa of the steel plate S, and is equipped with a plurality (two in this embodiment) of first oblique lighting imaging devices 21a, a plurality (two in this embodiment) of second oblique lighting imaging devices 21b, and a plurality (four in this embodiment) of specular reflection lighting imaging devices 22.

[0030] Here, the plurality of first oblique illumination imaging devices 21a capture light L 11a The first oblique light illuminator 11a is disposed at a predetermined interval along the width direction (xx direction) of the surface Sa of the steel sheet S on the side where the first oblique light illuminator 11a is installed. Each of the first oblique light illuminator imaging devices 21a captures light L irradiated from the first oblique light illuminator 11a and reflected by the surface Sa of the steel sheet S. 11a The first filter 23a transmits light of the wavelength (red).

[0031] The plurality of second oblique illumination imaging devices 21b capture light L 11bThe second oblique light illuminator 11b is disposed at a predetermined interval along the width direction (xx direction) of the surface Sa of the steel sheet S on the side where the second oblique light illuminator 11b is installed. Each second oblique light illuminator 21b captures light L irradiated from the second oblique light illuminator 11b and reflected by the surface Sa of the steel sheet S. 11b The second filter 23b transmits the wavelength (green).

[0032] 1 and 7(b), each of the first oblique illumination imaging devices 21a has a central axis CL 21a The camera is installed so that the angle between the camera and the horizontal plane HS is 0°. 1 and 7(c), each of the second oblique illumination imaging devices 21b has a central axis CL 21b The camera is installed so that the angle between the camera and the horizontal plane HS is 0°.

[0033] Furthermore, as shown in Figure 9, the multiple first oblique lighting imaging devices 21a and the multiple second oblique lighting imaging devices 21b are installed so that the fields of view 41 (shown by solid lines) of the multiple first oblique lighting imaging devices 21a (only one first oblique lighting imaging device 21a is shown in Figure 9) and the fields of view 42 (shown by dashed lines) of the multiple second oblique lighting imaging devices 21b (only one second oblique lighting imaging device 21b is shown in Figure 9) overlap at the boundary in the width direction (xx direction) of the steel plate S.

[0034] In addition, the plurality of specular reflection illumination imaging devices 22 capture light L 12 2, the specular reflection illumination imaging devices 22 are arranged at predetermined intervals along the width direction (xx direction) of the steel sheet S over the entire width of the surface Sa of the steel sheet S. Each specular reflection illumination imaging device 22 captures light L irradiated from the specular reflection illumination 12 and reflected by the surface Sa of the steel sheet S. 12 The third filter 24 transmits the wavelength (blue). As shown in FIG. 1, each of the specular reflection illumination imaging devices 22 has a central axis CL 22 The camera angle θ between the horizontal plane HS and 22 is set to 10°.

[0035] The reason why the lighting device 10 is equipped with a specular reflection lighting device 12 and the imaging device 20 is equipped with an imaging device for specular reflection lighting 22 is to detect uneven defects 50 on the surface Sa of the steel sheet S that are difficult to detect using the oblique lighting device 11, the first imaging device for oblique lighting 21a, and the second imaging device for oblique lighting 21b. FIG. 3 shows the spectral distributions of a red LED light used as the first oblique illuminator 11a, a green LED light used as the second oblique illuminator 11b, and a blue LED light used as the specular illuminator 12. As shown in FIG.

[0036] In Figure 3, the red wavelength is indicated by a dashed line, the green wavelength by a broken line, and the blue wavelength by a solid line. The red wavelength is 590 to 660 nm, the green wavelength is 480 to 600 nm, and the blue wavelength is approximately 400 to 500 nm. In this embodiment, the light L from the first oblique illuminator 11a 11a The wavelength of the light L from the second oblique light source 11b (red: 590 to 660 nm) 11b The wavelength of the light L emitted from the first oblique illuminator 11a and reflected by the surface Sa of the steel sheet S is different from that of the light L emitted from the first oblique illuminator 11a and reflected by the surface Sa of the steel sheet S. 11a The imaging device 20 is provided with a first filter 23a that transmits light of wavelengths (red: 590 to 660 nm). The imaging device 21b for second oblique illumination transmits light L irradiated from the second oblique illumination 11b and reflected by the surface Sa of the steel sheet S. 11b The second filter 23b is provided to transmit light of wavelengths (green: 480 to 600 nm).

[0037] As a result, the optical system of the first oblique illuminator 11a and the optical system of the second oblique illuminator 11b are separated in the width direction (xx direction) of the steel sheet S, and the light L from the first oblique illuminator 11a is 11aand the light L from the second oblique light source 11b. 11b This can prevent interference with the 3, first filter 23a (dashed line) is configured as a long-pass filter that transmits light with wavelengths of 600 nm or more, and shows how it transmits red wavelengths. Also, in FIG. 3, second filter 23b (dashed line) is configured as a long-pass filter that transmits light with wavelengths of 500 nm or more and a short-pass filter that transmits light with wavelengths of 575 nm or less, and shows how it transmits green wavelengths. Furthermore, in FIG. 3, third filter 24 (solid line) is configured as a short-pass filter that transmits light with wavelengths of 475 nm or less, and shows how it transmits blue wavelengths.

[0038] The image processing device 30 processes the image captured by the imaging device 20 to detect uneven defects 50 on the surface Sa of the steel sheet S, and is connected to the first oblique illumination imaging device 21a, the second oblique illumination imaging device 21b, and the specular reflection illumination imaging device 22, which constitute the imaging device 20, as shown in Figures 1 and 2. The image processing device 30 is a computer system having an arithmetic processing function for realizing the functions of the image processing device 30 by executing programs on computer software. This computer system is configured with a ROM, a RAM, a CPU, etc., and realizes the above-mentioned functions on software by executing various dedicated programs pre-stored in the ROM, etc. Here, as shown in Table 1, the uneven defects 50 on the surface Sa of the steel sheet S are classified into ranks according to the priority of removal as defects based on the amount of unevenness d (see FIG. 10(b) , the difference in brightness B in Table 1) and the size of the unevenness as seen from the surface Sa (dimension b in Table 1 (see FIG. 10(a))).

[0039] [Table 1]

[0040] The rank of the uneven defect 50 will be explained below with reference to Figs. 10, 11, 12 and Table 1. Fig. 10 shows an example of an uneven defect 50 formed on the surface Sa of a steel sheet S. Fig. 11 shows a captured image of an example of an uneven defect 50 formed on the surface Sa of the steel sheet S. Fig. 12 shows a brightness waveform for the uneven defect 50 detected from the captured image shown in Fig. 11. Table 1 shows the rank of the uneven defect 50.

[0041] 10(a) and 10(b) is formed on the surface Sa of the steel sheet S. This uneven defect 50 has a width of dimension b in the width direction (xx direction) of the steel sheet S and a length of dimension a in the length direction (yy direction) of the steel sheet S. In this embodiment, when ranking the uneven defect 50, the dimension b of the uneven defect 50 in the width direction (xx direction) of the steel sheet S is used as the ranking criterion, as the size of the unevenness as viewed from the surface Sa.

[0042] The dimension b of this uneven defect 50 in the width direction (xx direction) of the steel sheet S is calculated from the captured image as follows. 11 and 12, the dimension b of the uneven defect 50 is calculated as the distance between the widthwise position x1 where the brightness in the widthwise direction (xx direction) of the steel sheet S suddenly drops from brightness B1 in the captured image of the uneven defect 50, and the widthwise position x4 where the brightness in the widthwise direction (xx direction) of the steel sheet S suddenly drops from brightness B4. In other words, it is expressed as b=x4-x1.

[0043] 10(a) and 10(b) is recessed from the surface Sa of the steel sheet S by an amount of unevenness d. When ranking the uneven defect 50, in this embodiment, the amount of unevenness d of the uneven defect 50 is used as a criterion for ranking as the size of the unevenness as seen from the surface Sa. When the uneven defect 50 protrudes from the surface Sa of the steel sheet S, the amount of protrusion from the surface Sa is taken as the amount of unevenness d. Since the amount of unevenness d of this uneven defect 50 cannot be calculated directly from the captured image, the difference B between the maximum brightness value and the minimum brightness value of the uneven defect 50 is calculated based on the brightness waveform of the uneven defect 50 detected from the captured image shown in Figure 12, and this brightness difference B is used as the amount of unevenness d.

[0044] 12, the brightness difference B in the uneven defect 50 is calculated from the difference between the maximum brightness value B2 (brightness of the brightest part 51) in the captured image of the uneven defect 50 and the minimum brightness value B3 (darkest part 52) ​​in the captured image. That is, B=B2-B3. The rank of the uneven defect 50 is determined by determining which rank of the uneven defect 50 shown in Table 1 the combination of the calculated large, medium, or small dimension b and the large, medium, or small brightness difference B corresponds to.

[0045] The rank of the irregular defect 50 indicates the priority of removal as a defect, with a higher numerical rank indicating a higher priority of removal as a defect and a lower numerical rank indicating a lower priority of removal as a defect. The ranks of the irregular defect 50 shown in Table 1 are stored in advance in the image processing device 30. The image processing device 30 detects uneven defects 50 on the surface Sa of the steel sheet S in the field of view 41 (see Figure 9) of the first oblique lighting imaging device 21a based on the captured image captured by the first oblique lighting imaging device 21a, and determines the rank of the uneven defects 50 by referring to Table 1.

[0046] In addition, the image processing device 30 detects uneven defects 50 on the surface Sa of the steel sheet S in the field of view 42 (see Figure 9) of the second oblique lighting imaging device 21b based on the captured image captured by the second oblique lighting imaging device 21b, and determines the rank of the uneven defects 50 by referring to Table 1. Then, the image processing device 30 outputs the detection result of the uneven defect 50, "defect present" or "no defect present," as well as the judgment result, in the case of "defect present," the rank of the uneven defect 50, to an output device not shown.

[0047] 9, there may be a case where a concavo-convex defect 50 is present on the surface Sa of the steel sheet S corresponding to an overlapping portion 43 where the field of view 41 of the first oblique illumination imaging device 21a and the field of view 42 of the second oblique illumination imaging device 21b overlap. The processing performed by the image processing device 30 in this case will be described. In this case, the image processing device 30 detects and judges the uneven defect 50 on the surface Sa of the steel plate S corresponding to the overlapping portion 43 in the field of view 41 of the first oblique lighting imaging device 21a and in the field of view 42 of the second oblique lighting imaging device 21b. If the ranks of the irregularity defect 50 determined in the visual fields 41 and 42 are the same, the image processing device 30 adopts the same rank as the rank of the irregularity defect 50.

[0048] On the other hand, when the rank of the uneven defect 50 determined in the field of view 41 of the first oblique-light illumination imaging device 21a differs from the rank of the uneven defect 50 determined in the field of view 42 of the second oblique-light illumination imaging device 21b, the image processing device 30 performs the following processing. That is, in this case, the image processing device 30 adopts the rank of the uneven defect 50 with a higher priority from the rank of the uneven defect 50 determined in the field of view 41 of the first oblique-light illumination imaging device 21a and the rank of the uneven defect 50 determined in the field of view 42 of the second oblique-light illumination imaging device 21b. This is to ensure safety by adopting the rank of the uneven defect 50 with a higher priority when removing the uneven defect 50 on the surface Sa of the steel sheet S corresponding to the overlapping portion 43. The reason why the judgments of the uneven defect 50 on the surface Sa of the steel sheet S corresponding to the overlapping portion 43 may differ between the fields of view 41 and 42 is because the brightness of the uneven defect 50 is perceived differently between the two.

[0049] Specific processing by the image processing device 30 when a surface Sa of the steel sheet S has a roughness defect 50 corresponding to an overlapping portion 43 where the field of view 41 of the first oblique-light illumination imaging device 21a and the field of view 42 of the second oblique-light illumination imaging device 21b overlap, and the rank of the roughness defect 50 determined in the field of view 41 differs from the rank of the roughness defect 50 determined in the field of view 42, will be described with reference to FIGS. 13 to 16 . FIG. 13 is a diagram showing an image of an example of the roughness defect 50 when the surface Sa of the steel sheet S has the roughness defect 50 corresponding to the overlapping portion 43 where the field of view 41 of the first oblique-light illumination imaging device 21a and the field of view 42 of the second oblique-light illumination imaging device 21b overlap. FIG. 14 is a graph showing a brightness waveform for the roughness defect 50 detected from the image shown in FIG. 13 . FIG. 15 is a graph showing a brightness waveform for the roughness defect 50 detected from an image captured in the field of view 41 of the first oblique-light illumination imaging device 21a. FIG. 16 is a graph showing a waveform of brightness for a concave-convex defect 50 detected from an image captured in the field of view 42 of the second oblique illumination imaging device 21b.

[0050] In the captured image shown in FIG. 13, there is a concavo-convex defect 50 on the surface Sa of the steel sheet S corresponding to an overlapping portion 43 where the field of view 41 of the first oblique illumination imaging device 21a and the field of view 42 of the second oblique illumination imaging device 21b overlap. As shown in FIG. 14, the brightness distribution of the uneven defect 50 with respect to the position in the width direction (xx direction) of the steel sheet S is B1 on the surface Sa of the steel sheet S from the left end position in the width direction (xx direction) of the steel sheet S (the left end position in FIG. 14, the left end position on the field of view 41 side) to the position x1 of the left edge of the uneven defect 50. As one moves to the right of the position x1 of the left edge of the uneven defect 50, the brightness decreases (darkens) from B1 to the brightness of the bottom portion of the uneven defect 50. Further to the right, the brightness increases and reaches the position x2 of a bright portion 51 in the uneven defect 50, where it reaches the brightest maximum brightness value B2. Further to the right from the position x2 of the bright portion 51 in the uneven defect 50, the brightness decreases to the brightness of the bottom portion of the uneven defect 50. Further to the right, one reaches the position x3 of a dark portion 52 in the uneven defect 50, where it reaches the darkest minimum brightness value B3. Then, moving to the right from position x3 of the darkest part 52 of the uneven defect 50, the brightness increases and becomes the brightness of the bottom part of the uneven defect 50. Moving further to the right, the brightness increases and reaches position x4 of the right edge of the uneven defect 50, becoming brightness B4 of the surface Sa of the steel sheet S. This brightness B4 is almost the same as brightness B1.

[0051] Here, as shown in Fig. 13, the uneven defect 50 is imaged over the entire width direction (x-x direction) of the steel sheet S in the field of view 41 of the first oblique illumination imaging device 21a. In this case, the brightness distribution of the uneven defect 50 detected from the image captured in the field of view 41 of the first oblique illumination imaging device 21a is as shown in Fig. 15, which is similar to the brightness distribution shown in Fig. 14. When determining the rank of the uneven defect 50 in the field of view 41 of the first oblique lighting imaging device 21a, the image processing device 30 calculates the dimension b of the uneven defect 50 in the width direction (xx direction) of the steel plate S from b = x4 (position of the right edge of the uneven defect 50) - x1 (position of the left edge of the uneven defect 50), and sets the size of the dimension b to "medium."

[0052] In addition, when determining the rank of the uneven defect 50 in the field of view 41 of the first oblique lighting imaging device 21a, the image processing device 30 calculates the brightness difference B in the uneven defect 50 from B = B2 (brightness of the brightest part 51) - B3 (brightness of the darkest part 52), and sets the magnitude of the brightness difference B to "large." Then, the image processing device 30 refers to Table 1 and determines the rank of the uneven defect 50 in the field of view 41 of the first oblique illumination imaging device 21a to be rank 3.

[0053] On the other hand, as shown in FIG. 13 , the uneven defect 50 is imaged in the field of view 42 of the second oblique-light illumination imaging device 21b from position x5 in the width direction (x-x direction) of the steel sheet S to position x4 of the right edge of the uneven defect 50. In this case, the brightness distribution of the uneven defect 50 detected from the image captured in the field of view 42 of the second oblique-light illumination imaging device 21b is as shown in FIG. 16 . That is, position x5 in the width direction (x-x direction) of the steel sheet S corresponds to the brightness of the bottom portion of the uneven defect 50, and as one moves to the right and reaches position x3 of a dark portion 52 in the uneven defect 50, the brightness decreases to a minimum value B3, the darkest value. Then, as one moves from position x3 of the darkest portion 52 in the uneven defect 50 to the right, the brightness increases to the brightness of the bottom portion of the uneven defect 50. Further to the right, the brightness increases and reaches position x4 of the right edge of the uneven defect 50, where it corresponds to brightness B4 of the surface Sa of the steel sheet S.

[0054] When determining the rank of the uneven defect 50 in the field of view 42 of the second oblique lighting imaging device 21b, the image processing device 30 calculates the dimension b of the uneven defect 50 in the width direction (xx direction) of the steel plate S from b = x4 (position of the right edge of the uneven defect 50) - x5 (the leftmost position in Figure 16), and sets the magnitude of the dimension b to "medium." In addition, when determining the rank of the uneven defect 50 in the field of view 42 of the second oblique lighting imaging device 21b, the image processing device 30 calculates the brightness difference B in the uneven defect 50 from B = B4 (brightness of the surface Sa of the steel plate S) - B3 (brightness of the darkest part 52), and sets the magnitude of the brightness difference B to "medium."

[0055] Then, the image processing device 30 refers to Table 1 and determines the rank of the uneven defect 50 in the field of view 42 of the second oblique illumination imaging device 21b as rank 2. In this way, the rank (rank 3) of the irregularity defect 50 determined in the field of view 41 is different from the rank (rank 2) of the irregularity defect 50 determined in the field of view 42. In this case, the image processing device 30 adopts the rank (rank 3) of the irregularity defect 50 having the higher priority out of the rank (rank 3) of the irregularity defect 50 determined in the field of view 41 of the first oblique illumination imaging device 21a and the rank (rank 2) of the irregularity defect 50 determined in the field of view 42 of the second oblique illumination imaging device 21b. In this way, when removing the irregularity defect 50 on the surface Sa of the steel sheet S corresponding to the overlapping portion 43, the rank (rank 3) of the irregularity defect 50 having the higher priority is adopted to ensure safety.

[0056] During the production of the steel sheet S, a surface inspection process is performed using a surface inspection device 1 to detect uneven defects 50 on the surface Sa of the steel sheet S. The image processing device 30 of the surface inspection device 1 then outputs the detection result of the uneven defect 50, "defective" or "not defective," as well as the judgment result, in the case of "defective," the rank of the uneven defect 50, to an output device (not shown). Thereafter, if the detection result is "not defective," the steel sheet S is shipped. On the other hand, if the detection result is "defective," the uneven defect 50 is removed in accordance with the rank of the uneven defect 50 in a skin pass process that follows the surface inspection process.

[0057] If the surface inspection device 1 is not installed in the pickling line for hot-rolled steel sheets, the surface of the steel sheet S cannot be inspected in the pickling line for hot-rolled steel sheets using conventional methods. For this reason, in the skin pass process, which is a subsequent process, an operator visually inspects the surface of the steel sheet S. If the result of the surface inspection is "no defects," the steel sheet S is shipped. On the other hand, if the result of the surface inspection is "defective," the uneven defect 50 is removed in the skin pass process. As described above, the steel sheet manufacturing method according to this embodiment includes a surface inspection process in which the surface of the steel sheet S is inspected using the surface inspection device 1, thereby eliminating the need for visual inspection, reducing inspection costs compared to conventional methods, and improving the yield of the steel sheet S.

[0058] According to the surface inspection device 1 and the installation method of the oblique illuminator 11 in the surface inspection device 1 according to this embodiment, the oblique illuminator 11 is divided into two in the width direction (xx direction) of the steel sheet S, that is, the first oblique illuminator 11a and the second oblique illuminator 11b. The first oblique illuminator 11a and the second oblique illuminator 11b are separated in the longitudinal direction (yy direction) of the steel sheet S so that the first oblique illuminator 11a and the second oblique illuminator 11b do not interfere with each other, and the light L from the first oblique illuminator 11a and the second oblique illuminator 11b is 11a ,L 11b The first oblique light 11a and the second oblique light 11b are installed so that the light is irradiated from the inside of the steel sheet S in the width direction toward the outside of the steel sheet S in the width direction. This allows the oblique light illuminator 11 to be installed without protruding from the width direction (xx direction) of the steel plate S, while avoiding interference between the first oblique light illuminator 11a and the second oblique light illuminator 11b. This makes it possible to prevent the oblique light illuminator 11 from interfering with surrounding equipment.

[0059] Furthermore, according to the surface inspection device 1 of this embodiment, the light L from the first oblique illuminator 11a 11a and the wavelength of the light L from the second oblique illuminator 11b 11b The wavelength of the light L emitted from the first oblique illuminator 11a and reflected by the surface Sa of the steel sheet S is different from that of the light L. 11a The first oblique light 11a is provided with a first filter 23a that transmits the wavelength of light L 11a The imaging device 20 is provided with a first oblique lighting imaging device 21a for imaging the surface Sa of the steel sheet S illuminated with light L from the second oblique lighting device 11b. 11b The second oblique illuminator 11b is provided with a second filter 23b that transmits the wavelength of light L 11b The second oblique illumination imaging device 21b is provided to image the surface Sa of the steel sheet S illuminated with the light. As a result, the optical system of the first oblique illuminator 11a and the optical system of the second oblique illuminator 11b are separated in the width direction (xx direction) of the steel sheet S, and the light L from the first oblique illuminator 11a is 11a and the light L from the second oblique light source 11b. 11b This can prevent interference with the

[0060] Furthermore, according to the surface inspection device 1 of this embodiment, uneven defects 50 on the surface Sa of the steel sheet S are ranked according to a priority for removal as a defect, based on the amount of unevenness d and the size of the unevenness as viewed from the surface Sa (the dimension b of the uneven defect 50 in the width direction (xx direction) of the steel sheet S). The image processing device 30 detects uneven defects 50 on the surface Sa of the steel sheet S in the field of view 41 of the first oblique-light illumination imaging device 21a based on the captured image taken by the first oblique-light illumination imaging device 21a, and determines the rank of the uneven defects 50. The image processing device 30 also detects uneven defects 50 on the surface Sa of the steel sheet S in the field of view 42 of the second oblique-light illumination imaging device 21b based on the captured image taken by the second oblique-light illumination imaging device 21b, and determines the rank of the uneven defects 50. This allows the image processing device 30 to detect uneven defects 50 on the entire surface Sa of the traveling steel sheet S, and to determine a rank of the uneven defects 50 according to their priority.

[0061] Furthermore, according to the surface inspection device 1 of this embodiment, the light L from the first oblique illuminator 11a 11a and the light L from the second oblique illuminator 11b. 11b The first oblique lighting imaging device 21a and the second oblique lighting imaging device 21b are installed so that the illumination ranges of the first oblique lighting imaging device 11a and the second oblique lighting imaging device 21b overlap at the boundary in the width direction (xx direction) of the steel plate S. Furthermore, the first oblique lighting imaging device 21a and the second oblique lighting imaging device 21b are installed so that the field of view 41 of the first oblique lighting imaging device 21a and the field of view 42 of the second oblique lighting imaging device 21b overlap at the boundary in the width direction (xx direction) of the steel plate S. This allows the image processing device 30 to reliably detect uneven defects 50 on the entire surface Sa of the traveling steel sheet S, and to determine a rank for the uneven defects 50 according to their priority.

[0062] Furthermore, according to the surface inspection apparatus 1 of this embodiment, when there is a concavo-convex defect 50 on the surface Sa of the steel sheet S corresponding to the overlapping portion 43 where the field of view 41 of the first oblique-light illumination imaging device 21a and the field of view 42 of the second oblique-light illumination imaging device 21b overlap, and the rank of the concavo-convex defect 50 determined in the field of view 41 of the first oblique-light illumination imaging device 21a differs from the rank of the concavo-convex defect 50 determined in the field of view 42 of the second oblique-light illumination imaging device 21b, the image processing device 30 performs processing as follows: In this case, the image processing device 30 adopts the rank of the concavo-convex defect 50 with the higher priority from the rank of the concavo-convex defect 50 determined in the field of view 41 of the first oblique-light illumination imaging device 21a and the rank of the concavo-convex defect 50 determined in the field of view 42 of the second oblique-light illumination imaging device 21b. This allows safety to be ensured by adopting the rank of the irregular defect 50 with a high priority when removing the irregular defect 50 on the surface Sa of the steel plate S corresponding to the overlapping portion 43.

[0063] Furthermore, according to the surface inspection device 1 of the present invention, the illumination device 10 has a specular reflection illumination 12, and the imaging device 20 captures light L by the specular reflection illumination 12. 12 The apparatus is provided with a specular reflection illumination imaging device 22 that images the surface Sa of the steel sheet S illuminated with the light. This makes it possible to detect uneven defects 50 on the surface Sa of the steel sheet S that are difficult to detect using the oblique lighting 11, the first oblique lighting imaging device 21a, and the second oblique lighting imaging device 21b.

[0064] Although the embodiment of the present invention has been described above, the present invention is not limited to this and various modifications and improvements can be made. For example, the surface inspection device 1 is installed in a pickling line for hot-rolled steel sheets, but is not limited to this and may be installed in a production line for cold-rolled steel sheets or the like. 1 and 7(a), (b), and (c), each of the first oblique illumination imaging devices 21a and each of the second oblique illumination imaging devices 21b may be installed in the manner shown in Fig. 8(a), (b), and (c). Specifically, each of the first oblique illumination imaging devices 21a may be installed such that the central axis CL of the first oblique illumination imaging device 21a is aligned with the center axis CL of the first oblique illumination imaging device 21a as shown in Fig. 8(a) and (b). 21a The camera angle θ between the horizontal plane HS and 21a 8(a) and 8(c), the second oblique illumination imaging device 21b is installed so that the central axis CL 21b The camera angle θ between the horizontal plane HS and 21b is installed at a specified angle.

[0065] Further, although a plurality of first oblique illumination imaging devices 21q, second oblique illumination imaging devices 21b, and specular illumination imaging devices 22 are provided, there may be only one of each. Furthermore, the size of the unevenness that serves as the criterion for ranking the uneven defect 50 may not only be the dimension b of the uneven defect 50 in the width direction (xx direction) of the steel plate S, but may also be the dimension a of the uneven defect 50 in the longitudinal direction (yy direction) of the steel plate S, or the area as viewed from the surface Sa of the uneven defect 50. [Explanation of symbols]

[0066] 1. Surface inspection equipment 2 Bridle Roll 10. Lighting equipment 11 Oblique lighting 11a 1st oblique illumination 11b 2nd oblique illumination 12 Specular Reflection 20 Imaging device 21a First oblique illumination imaging device 21b Second oblique illumination imaging device 22 Imaging device for specular reflection illumination 23a First filter 23b Second filter 24 Third Filter 30 Image processing device 41 Field of view of first oblique illumination imaging device 42 Field of view of second oblique illumination imaging device 43 Overlapping part 50 Unevenness defects L 11a Light from the first oblique lighting L 11b Light from the second oblique lighting L 12 Light from specular reflection S steel plate (hot rolled steel plate) Sa surface

Claims

1. A surface inspection device comprising: an illumination device having oblique illumination, which is composed of a rod-shaped light source extending along the width direction of a steel plate and is installed relative to the steel plate so that the direction of light emitted from the rod-shaped light source is at an oblique angle relative to the longitudinal direction of the steel plate; an imaging device that images the surface of the steel plate illuminated with light by the illumination device; and an image processing device that processes the image captured by the imaging device to detect uneven defects on the surface of the steel plate, the oblique illuminator is divided into two in the width direction of the steel plate, into a first oblique illuminator and a second oblique illuminator, the first oblique illuminator and the second oblique illuminator are spaced apart in the longitudinal direction of the steel plate so that the first oblique illuminator and the second oblique illuminator do not interfere with each other, and the first oblique illuminator and the second oblique illuminator are installed so that light from each of the first oblique illuminator and the second oblique illuminator is irradiated from an inner side in the width direction of the steel plate toward an outer side in the width direction of the steel plate, the wavelength of the light from the first oblique illumination and the wavelength of the light from the second oblique illumination are made different, and the imaging device comprises: a first oblique illumination imaging device that images the surface of the steel plate irradiated with light by the first oblique illumination, and is equipped with a first filter that transmits the wavelength of light irradiated from the first oblique illumination and reflected by the surface of the steel plate; and a second oblique illumination imaging device that images the surface of the steel plate irradiated with light by the second oblique illumination, and is equipped with a second filter that transmits the wavelength of light irradiated from the second oblique illumination and reflected by the surface of the steel plate, uneven defects on the surface of the steel plate are classified into ranks with a priority for removal as defects based on the amount of unevenness and the size of the unevenness as seen from the surface, and the image processing device detects uneven defects on the surface of the steel plate in the field of view of the first oblique lighting imaging device based on the image captured by the first oblique lighting imaging device and determines the rank of the uneven defects, and detects uneven defects on the surface of the steel plate in the field of view of the second oblique lighting imaging device based on the image captured by the second oblique lighting imaging device and determines the rank of the uneven defects, a surface inspection device characterized in that the first oblique light illuminator and the second oblique light illuminator are installed so that the illumination range of light from the first oblique light illuminator and the illumination range of light from the second oblique light illuminator overlap at a boundary in the width direction of the steel plate, and the first oblique light illumination imaging device and the second oblique light illumination imaging device are installed so that the field of view of the first oblique light illumination imaging device and the field of view of the second oblique light illumination imaging device overlap at a boundary in the width direction of the steel plate.

2. 2. The surface inspection device of claim 1, wherein, when there is a concavo-convex defect on the surface of the steel plate corresponding to the overlapping portion where the field of view of the first oblique illumination imaging device and the field of view of the second oblique illumination imaging device overlap, if the rank of the concavo-convex defect determined in the field of view of the first oblique illumination imaging device differs from the rank of the concavo-convex defect determined in the field of view of the second oblique illumination imaging device, the image processing device adopts the rank of the concavo-convex defect with a higher priority from the rank of the concavo-convex defect determined in the field of view of the first oblique illumination imaging device and the rank of the concavo-convex defect determined in the field of view of the second oblique illumination imaging device.

3. 2. The surface inspection device according to claim 1, wherein the illumination device has a specular reflection illumination, and the imaging device includes a specular reflection illumination imaging device that images the surface of the steel plate illuminated with light by the specular reflection illumination.

4. A method for manufacturing a steel plate, comprising a surface inspection step of inspecting the surface of the steel plate using the surface inspection device according to any one of claims 1 to 3.

Images