Machine vision lighting device for detecting surface defects of steel product, and method for detecting surface defects of steel product

Abstract

The present invention relates to a machine vision lighting device for detecting surface defects of a steel product, and a method for detecting surface defects of a steel product. The machine vision lighting device (70) for detecting surface defects of a steel product (20) having a predetermined width and extending in the longitudinal direction comprises: an LED element (71) that emits light at the surface of the steel product (20); and a diffuser filter (75) disposed between the LED element (71) and the steel product (20), wherein the diffuser filter diffuses light (72, 74) incident on the diffuser filter by a first diffusion angle (A1) in a first direction (1st) intersecting, at an intersecting angle (j), an extension direction (E) of a grinding valley (25) provided on the surface of the steel product (20), and diffuses light (72, 74) incident on the diffuser filter by a second diffusion angle (A2) smaller than the first diffusion angle (A1) in a second direction (2nd) intersecting the first direction (1st).

Description

Lighting device for machine vision to detect surface defects in steel products and method for detecting surface defects in steel products

[0001] The present invention relates to a machine vision lighting device for detecting surface defects in steel products and a method for detecting surface defects in steel products, and more specifically, to a machine vision lighting device for detecting surface defects in steel products and a method for detecting surface defects in steel products that can improve the detection performance of machine vision.

[0002] Generally, steel products, such as billets, blooms, and slabs, are produced through a continuous casting process. That is, a continuous casting machine (10) (see FIG. 1) receives molten steel produced in a steelmaking furnace into a tundish and supplies it to a mold to produce a cast billet (11) of a certain size. The cast billet is conveyed through pinch rolls and then cut by a cutter to be manufactured into billets, blooms, slabs, etc., having a predetermined shape.

[0003] The slab produced through this continuous casting process undergoes surface inspection, such as visual inspection by a worker, and is transferred to an appropriate correction flow depending on the type of defect. Defects occurring in the cast slab (11) may include vertical cracks, double injection, inclusions, pinholes, etc. (see FIG. 2).

[0004] However, defect inspections such as visual inspection by workers are at risk of burns to workers because the slab is at a high temperature, and there is also a risk of safety accidents such as the falling of heavy objects in the workplace.

[0005] Meanwhile, machine vision refers to a system composed of components such as high-performance cameras, processors, and image processing software that inspects physical shapes, defects, surface finishes, and colors during the manufacturing process, instead of relying on human visual inspection. Its application is expanding widely in manufacturing sectors, such as the semiconductor, automotive, and steel industries, as a product inspection device to enhance product quality, productivity, and work efficiency, while ensuring regulatory compliance.

[0006] In particular, since information regarding product defects is obtained from images of inspection targets acquired by imaging devices, it is necessary to provide an artificial lighting environment so that various defects can be clearly represented in image form. Furthermore, because machine vision is installed in manufacturing sites and must complete defect detection tasks within a relatively short time, lighting and imaging devices capable of producing clear and distinct images are critical.

[0007] [Prior Art Literature]

[0008] [Patent Literature]

[0009] (Patent Document 1) Republic of Korea Published Patent 10-2024-0171468

[0010] The present invention is devised to solve the aforementioned problems and provides a machine vision lighting device for detecting surface defects in steel products that can improve the detection performance of machine vision.

[0011] In addition, the present invention is devised to solve the aforementioned problems and provides a method for detecting surface defects in steel products that can improve the detection performance of machine vision.

[0012]

[0013] The objects of the present invention are not limited to those mentioned above, and other unmentioned objects and advantages of the present invention may be understood from the following description and will be more clearly understood by the embodiments of the present invention. Furthermore, it will be readily apparent that the objects and advantages of the present invention can be realized by the means and combinations thereof set forth in the claims.

[0014] To solve the above-mentioned problem, the present invention provides a vision machine lighting device (70) for detecting surface defects of a steel product (20) that has a predetermined width and is extended in the longitudinal direction, comprising: an LED element (71) that emits light toward the surface of the steel product (20); and a diffuser filter (75) disposed between the LED element (71) and the steel product (20), wherein the diffuser filter diffuses light (72, 74) incident on the diffuser filter by a first diffusion angle (A1) in a first direction (1st) that intersects the extension direction (E) of the grinding groove (25) provided on the surface of the steel product (20) at an intersection angle (j), and diffuses by a second diffusion angle (A2) that is smaller than the first diffusion angle (A1) in a second direction (2nd) that intersects the first direction (1st).

[0015] In one embodiment of the present invention, the diffuser filter (75) may include an LDS (laser-direct structuring) film.

[0016] In one embodiment of the present invention, the first diffusion angle (A1) may be 30 to 70 degrees.

[0017] In one embodiment of the present invention, the second diffusion angle (A2) may be 1 to 5 degrees.

[0018] In one embodiment of the present invention, the intersection angle (j) is substantially right angle, and the first direction and the second direction may be substantially orthogonal.

[0019] In one embodiment of the present invention, the LED elements (71) may be arranged in a plurality to form an array in parallel with the extension direction (E) of the grinding groove (25).

[0020] In one embodiment of the present invention, the array may be provided in a plurality of ways in the second direction.

[0021] In one embodiment of the present invention, the lighting device (70) for the vision machine further comprises a plano-convex cylindrical lens (73) disposed between the LED element (71) and the diffuser filter (75), the diffuser filter (75) diffuses light (74) emitted from the LED element (71) and transmitted through the cylindrical lens (73), and the axial direction (L) of the plano-convex cylindrical lens (73) may be parallel to the arrangement direction of the array.

[0022] In one embodiment of the present invention, the plano-convex cylindrical lens (73) may be arranged such that the axial direction (L) of the plano-convex cylindrical lens (73) is orthogonal to the first direction.

[0023] In one embodiment of the present invention, the plano-convex cylindrical lens (73) may be positioned such that the axial direction (L) of the plano-convex cylindrical lens (73) is parallel to the extension direction (E) of the grind groove (25).

[0024] In one embodiment of the present invention, the steel product may be any one of a billet, a bloom, or a slab.

[0025] The present invention provides a method (800) for detecting surface defects in a steel product, comprising the steps of: forming at least one groove (25) having a predetermined length on at least a portion of the surface of the steel product (20) using a steel product surface processing tool (810); and irradiating the at least one groove (25) formed on the at least a portion of the surface of the steel product (20) by passing light emitted from an LED element (71) through a diffuser filter (75) disposed between the steel product (20) and the LED element (71) (820) - wherein the diffuser filter (75) is configured to diffuse the light emitted from the LED element (71) by a first diffusion angle (A1) along a first direction (1st), and to diffuse it by a second diffusion angle (A2) that is smaller than the first diffusion angle (A1) along a second direction (2nd) orthogonal to the first direction (1st). The method may include the step (830) of arranging the diffuser filter (75) such that the first direction forms a predetermined intersection angle (j) with the longitudinal direction of the at least one groove (25) formed on at least a portion of the surface of the steel product (20); the step (840) of receiving light reflected by the at least one groove (25) through a shooting device (60) to acquire an image; and the step (850) of processing the acquired image through a processor (88) in which image processing software is executed to detect surface defects of the steel product (20).

[0026] In one embodiment of the present invention, the tool for processing the surface of the steel product may be a grinder (30).

[0027] In one embodiment of the present invention, the diffuser filter (75) is an LDS (laser-direct structuring) film, and the first diffusion angle (A1) of the diffuser filter (75) may be 30 to 60 degrees.

[0028] In one embodiment of the present invention, the second diffusion angle (A2) of the diffuser filter (75) may be 1 to 5 degrees.

[0029] In one embodiment of the present invention, the intersection angle may be a right angle.

[0030] In one embodiment of the present invention, the LED elements (71) are a plurality of and may be configured to be arranged in a row parallel to the length direction of the grinding groove (25).

[0031] In one embodiment of the present invention, the steel product may be any one of a billet, a bloom, or a slab.

[0032] In one embodiment of the present invention, the rotation axis (31) of the grinder (30) may be parallel to the conveying direction.

[0033] According to various embodiments of the present invention, a machine vision lighting device for detecting surface defects of a steel product and a method for detecting surface defects of a steel product are provided, which can improve the detection performance of machine vision.

[0034] FIG. 1 is a perspective view of a continuous casting machine that produces steel products.

[0035] Figure 2 illustrates defects that may occur in steel products.

[0036] FIG. 3 is a conceptual diagram of a machine vision lighting device for detecting surface defects of steel products according to an embodiment of the present invention applied to a steel product production line.

[0037] FIG. 4 is a conceptual diagram of a machine vision lighting device for detecting surface defects of a steel product according to an embodiment of the present invention (Fig. 4(a) is a front view, Fig. 4(b) is a perspective view).

[0038] FIG. 5 illustrates a form in which light emitted from a single LED element is diffused in a first direction and a second direction by various diffuser filters and irradiated onto a plane.

[0039] FIG. 6 is a conceptual diagram illustrating the path of light emitted from a machine vision lighting device according to a comparative example (Fig. 6 (a)) and an embodiment of the present invention (Fig. 6 (b)), the path of light irradiated onto a grinding groove formed on a slab, and the path of light reflected by the same.

[0040] FIG. 7 illustrates images obtained using a lighting device for a vision machine according to a comparative example (Fig. 7 (a)) and an embodiment of the present invention (Fig. 7 (b)).

[0041] FIG. 8 illustrates a method for detecting surface defects in a steel product according to another embodiment of the present invention.

[0042] The advantages and features of the present invention and the methods for achieving them will become clear by referring to the embodiments described below in detail together with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below but may be implemented in various different forms. These embodiments are provided merely to ensure that the disclosure of the present invention is complete and to fully inform those skilled in the art of the scope of the invention, and the present invention is defined only by the scope of the claims. Throughout the specification, the same reference numerals refer to the same components.

[0043] Although terms such as "first," "second," etc., are used to describe various components, it goes without saying that these components are not limited by these terms. These terms are used merely to distinguish one component from another, and unless specifically stated otherwise, the first component may also be the second component.

[0044] Throughout the specification, unless specifically stated otherwise, each component may be singular or plural.

[0045] In the following, the statement that any configuration is placed on the "upper (or lower)" of a component or on the "upper (or lower)" of a component may mean not only that any configuration is placed in contact with the upper (or lower) surface of said component, but also that another configuration may be interposed between said component and any configuration placed on (or below) said component.

[0046] In addition, where it is stated that one component is "connected," "combined," or "contacted" with another component, it should be understood that while the components may be directly connected or joined to each other, another component may be "interposed" between each component, or each component may be "connected," "combined," or "contacted" through another component.

[0047] Singular expressions used in this specification include plural expressions unless the context clearly indicates otherwise. In this application, terms such as "composed of" or "comprising" should not be interpreted as necessarily including all of the various components or steps described in the specification, and should be interpreted as meaning that some of the components or steps may be omitted or additional components or steps may be included.

[0048] Throughout the specification, "A and / or B" means A, B, or A and B unless specifically stated otherwise, and "C to D" means C or more and D or less unless specifically stated otherwise.

[0049]

[0050] Various embodiments are described below with reference to the attached drawings.

[0051]

[0052] Referring to FIG. 3, a conceptual diagram of a machine vision lighting device for detecting surface defects of a steel product according to an embodiment of the present invention applied to a steel product production line is shown. A steel product, such as a slab (20), can be transported in a transport direction (arrow) by a conveyor system (50). For example, the slab (20) has a rectangular surface shape having a predetermined width and length, and the longitudinal direction of the slab (20) and the transport direction by the conveyor system (51) may be parallel.

[0053] While the slab (20) is being transported on the first conveyor (51), the surface of the slab (20) is ground. Accordingly, a grinding mark is formed on the surface of the slab (20). The grinding mark extends in the direction in which the grinder (30) moves relative to the surface of the slab (20) as the grinding proceeds.

[0054] For example, when the slab (20) is transported while the grinder (30) presses against the surface of the slab (20) and rotates, the grinding marks extend in a direction parallel to the transport direction of the slab (20).

[0055] The grinder (30) may be provided in multiple locations at different positions in a direction intersecting the conveying direction, that is, in the width direction of the slab (20). Accordingly, multiple grinding marks extend in the conveying direction of the slab (20) and are arranged adjacently in a direction intersecting the conveying direction.

[0056] The direction of the rotation axis (31) of the grinder (30) and the direction of transport of the slab (20) may intersect, for example, parallel, orthogonal, or at an acute angle such as 45 degrees.

[0057] While the above slab (20) is being transported in the transport direction on the first conveyor (51), the grinding direction formed by the grinder (30), which rotates around an axis (31) parallel to the transport direction, can be 90 degrees to the transport direction. If the grinder (30) is configured in this way, the grinding trace may be in the shape of a grinding groove (25) extending in a direction parallel to the transport direction of the slab (20). Accordingly, the width direction of the grinding groove (25) is orthogonal to the transport direction of the first conveyor (51), and the grinding groove (25) may have a roughly arc-shaped profile in which the center of the width direction is more sunken than the ends. Accordingly, a crest (28) exists between adjacent grinding grooves (25).

[0058] On the surface of the slab (20) on the first conveyor (51), a grinding groove (25) of a roughly concave shape is formed by a grinder (30). In this embodiment, the grinding groove (25) is formed by a grinder (30), but the groove may also be formed on the surface of the steel product using other tools known in the art. FIG. 3 illustrates that the grinding groove (25) is formed in a shape that extends in the width direction of the slab (20). However, the direction in which the grinding groove is formed is not limited thereto. For example, the grinding groove may be formed in a direction parallel to the length direction of the slab (20) as previously described, or it may be formed to form a predetermined intersection angle with the length direction of the slab (20). The extension direction of the grinding groove may be determined by considering the installation location of the machine vision optical device (70) to be described later, and conversely, the installation location of the machine vision optical device (70) may be set in correspondence with the extension direction of the grinding groove.

[0059] Additionally, as previously exemplified, the rotation axis (31) of the grinder (30) may be positioned to form an angle of 90 degrees or 45 degrees with respect to the direction of the grinding groove (25). However, the positioning direction of the rotation axis (31) is not limited to this and may be determined at a different angle by reviewing the image obtained by the imaging device (60).

[0060] The grinding grooves (25) may be formed in multiple numbers so as to be adjacent to each other in parallel, as in the slab (27). The grinding grooves may be formed on the entire surface of the slab (20) or only on a specific part requiring inspection.

[0061] The slab (27), after the work by the grinder (30) is completed, is transported onto the second conveyor (52) located downstream. On the upper side of the slab (27) placed on the second conveyor (52), a lighting device (70) for machine vision (90), described later, for irradiating light onto the surface of the slab (27), and a shooting device (60) for capturing light reflected from the surface of the slab (27) may be installed. The location of the lighting device (70) is not limited to the location shown, but is possible wherever light can be irradiated onto the grinding groove (25) formed on the surface of the slab (27) by the grinder (30). For example, it may be placed on the upper side of the first conveyor (51) or in a measurement room (not shown), etc., located downstream of the second conveyor (52). In addition, the location of the shooting device (60) is not limited to the illustrated location, and may be any location where light reflected from the surface of the slab (20, 27) formed by the grinding groove (25) and floor (28) is irradiated from the lighting device (70).

[0062] The image acquired by the shooting device (60) can be transmitted to the processor (88). The processor (88) can process the received image by executing image processing software stored in the memory (85). Through this processing, the processor (88) can detect surface defects of the slab (27).

[0063] The aforementioned shooting device (60), lighting device (70), processor (88), and memory (85) for storing image processing software can constitute machine vision (90). Machine vision is widely known in the technical field, so a detailed description thereof is omitted.

[0064] Referring to FIG. 4, a conceptual diagram of a machine vision lighting device (70) for detecting surface defects of a steel product according to one embodiment of the present invention is shown (Fig. 4(a) is a perspective view, Fig. 4(b) is a front view, Fig. 4(c) is a side view). As described above, the lighting device (70) may include an LED element (71) configured to emit light (72) on the surface of a steel product, such as a slab (27), a plano-convex cylindrical lens (73) positioned below the LED element (71) to concentrate the light (72) emitted from the LED element (71) into convergent light (74), and a diffuser filter (75) positioned below the cylindrical lens (73) and configured to diffuse the convergent light (74) by a first diffusion angle (A1) along a first direction and by a second diffusion angle (A2) that is smaller than the first diffusion angle (A1) along a second direction orthogonal to the first direction. Light (76) transmitted through the diffuser filter (75) can be irradiated onto the surface of the slab (27) (grinding groove (25) and / or floor (28)). In this embodiment, the first direction (1st) and the second direction (2nd) of the diffuser filter are described as being orthogonal, but are not limited thereto, and the second direction may be determined at an angle other than a right angle considering the characteristics of the light diffused in the first direction.

[0065] In FIG. 4, the LED elements (71) are arranged in a row and configured as a set, but are not limited thereto. Depending on the size of the surface to be inspected, for example, they may be configured as a set of multiple LED elements or as only one LED element. Additionally, the plano-convex cylindrical lens (73) is shown as a single component for light collection, but depending on the brightness and type of the LED elements (71), it may be configured as a different lens, combined with another lens to form an optical system, or omitted.

[0066] As shown in FIG. 4(c), the longitudinal direction (L) or axis of the cylindrical lens (73) may be parallel to a set of multiple LED elements arranged in a row. The longitudinal direction (L) or axis of the cylindrical lens (73) may be parallel to the extension direction (E) of the grinding groove (25).

[0067] The diffuser filter (75) may be composed of an LDS (laser direct structuring) film. The diffuser filter (75) may be arranged or configured so that the first direction (1st) in which light (76) is diffused intersects the extension direction (E) of a grinding groove (25) formed on the surface of the slab (27) and forms a predetermined intersection angle (j).

[0068] Referring to FIG. 5, light (72, 74) emitted from a single LED element (71) is shown diffused in a first direction and a second direction by various diffuser filters and irradiated onto a plane. FIG. 5(a) is the case without diffuser filters, FIG. 5(b) is the case where the first diffusion angle (A1) along the first direction and the second diffusion angle (A2) along the second direction are 30 degrees, FIG. 5(c) is the case where the first diffusion angle (A1) along the first direction is 30 degrees and the second diffusion angle (A2) along the second direction is 5 degrees, and FIG. 5(d) is the case where the first diffusion angle (A1) along the first direction is 60 degrees and the second diffusion angle (A2) along the second direction is 1 degree. The first diffusion angle (A1) of the diffuser filter (75) according to one embodiment of the present invention may be approximately 30 to 60 degrees. If the first diffusion angle is smaller than the above range, the frequency of concentrated light occurring in the reflected light reflected from the slab surface in the first direction increases, and if it is larger than this range, the intensity of the diffused light may decrease to a level unsuitable for defect detection. The second diffusion angle (A2) of the diffuser filter (75) according to one embodiment of the present invention may be approximately 1 to 5 degrees. If the second diffusion angle is larger than this range, the effect of diffusion in the first direction is no longer effective, and if it is smaller than this range, the frequency of concentrated light occurring in the reflected light increases. Preferably, the first diffusion angle is approximately 60 degrees, and the second diffusion angle is approximately 1 degree. However, the first diffusion angle and the second diffusion angle may be determined by the characteristics of the grinding groove, such as depth, width, or radius of curvature, without being limited thereto, or by the characteristics of the LED element.

[0069] Referring to FIG. 6, the path of light emitted from a machine vision lighting device according to a comparative example (Fig. 6 (a)) and an embodiment of the present invention (Fig. 6 (b)) is shown, and the path of light reflected by the same is shown.

[0070] In the case of FIG. 6(a), a machine vision lighting device is used in which the diffuser filter (75) is removed from the lighting device (70) of FIG. 5. The path (74) of light irradiated onto the grinding groove (25) may have a diffusion angle inclined approximately 5 degrees in the first direction or nearly vertically. The path (78) of reflected light has paths of different angles. When such reflected light is captured by a shooting device (60) to acquire an image, there is a high risk that the reflected light incident on the shooting device (60) is not in a state of even scattering or diffuse reflection but is in a state of concentrated light. Consequently, the contrast ratio is uneven, such as the brightness of certain parts being excessively high and the brightness of certain parts being excessively low, which lowers the clarity of the image and, consequently, the accuracy of detecting surface defects by image processing may be lowered (see FIG. 7(a)).

[0071] On the other hand, in the case of FIG. 6(b), a machine vision lighting device (70) according to an embodiment of the present invention is used. As shown, the path (76) of light irradiated onto the grinding groove (25) is formed by the first diffusion angle of the diffuser filter (75) (76-1 and 76-2 are light emitted from each of the adjacent LED elements). Accordingly, the reflected light reflected by the grinding groove (25) is incident on the imaging device (60) in a state of even scattering or diffuse reflection (77), so the contrast ratio is evenly distributed, which can improve the quality of the image (Fig. 7(b)) obtained by the imaging device (60), and furthermore, the accuracy of surface defect detection obtained after image processing by the processor (88) can also be improved.

[0072] Referring to FIG. 7, images obtained using a comparative example (Fig. 7(a)) (a lighting device without a diffuser filter (75)) and a lighting device for a vision machine according to an embodiment of the present invention (Fig. 7(b)) are illustrated. In the case of FIG. 7(a), the brightness of the image is uneven in the longitudinal direction of the slab, and thus the accuracy of surface defect detection by image processing may be lowered. On the other hand, in the case of FIG. 7(b), the brightness of the image is uniform in the longitudinal direction, and the image quality is relatively excellent. Therefore, the accuracy of surface defect detection obtained after image processing by the processor (88) may also be improved.

[0073]

[0074] Hereinafter, with reference to FIG. 8, a method (800) for detecting surface defects of a steel product according to another embodiment of the present invention is described.

[0075] According to a method (800) for detecting surface defects of a steel product according to an embodiment of the present invention, at least one grinding groove (25) or other groove (hereinafter referred to as 'grinding groove') having a predetermined length is formed on at least a part of the surface of a steel product, such as a slab (20), by a grinder (30) or other tool capable of processing the surface of the steel product (810). Light emitted from an LED element (71) is irradiated onto this at least one grinding groove (25) formed on a part of the surface of the steel product by passing it through a diffuser filter (75) placed between the steel product (20) and the LED element (71) (820). Here, the diffuser filter (75) may be configured or formed to diffuse the light emitted from the LED element (71) by a first diffusion angle (A1) along a first direction, and to diffuse it by a second diffusion angle (A2) that is smaller than the first diffusion angle (A1) along a second direction orthogonal to the first direction (820). The diffuser filter (75) is positioned so that its first direction intersects the longitudinal direction of at least one grinding groove (25) formed on at least a portion of the surface of the steel product (20) at a predetermined intersection angle or is orthogonal to it (830). Next, the light (77) reflected by the grinding groove (25) is received by the imaging device (60) and an image is acquired (840). The acquired image is processed by a processor (88) that executes image processing software stored in memory (85), and surface defects of the steel product can be detected (850).

[0076]

[0077] In the above-described embodiment, the lighting device (70) is described as irradiating light onto a slab, but the lighting device (70) according to one embodiment of the present invention can be applied to various steel products other than slabs, such as billets, blooms, etc.

[0078]

[0079] The machine vision lighting device for detecting surface defects of a steel product and the method for detecting surface defects of a steel product according to the embodiment of the present invention described above can improve the quality of the image obtained by the imaging device and further improve the accuracy of surface defect detection obtained after image processing by the machine vision processor by using a diffuser filter capable of diffusing light in a first direction that intersects or is orthogonal to the longitudinal direction of the groove formed on the surface of the steel product to be inspected.

[0080]

[0081] Although the present invention has been described above with reference to the illustrated drawings, the present invention is not limited by the embodiments and drawings disclosed in this specification, and it is obvious that various modifications can be made by a person skilled in the art within the scope of the technical concept of the present invention. Furthermore, even if the effects of the configuration of the present invention were not explicitly described while describing the embodiments of the present invention above, it is natural to acknowledge that the effects predictable by said configuration should also be recognized.

[0082]

[0083] [Explanation of the symbol]

[0084] 10: Continuous casting machine 20, 27: Slab (steel product)

[0085] 25: Goal (Grinding Goal) 28: Floor

[0086] 50: Conveyor system 60: Shooting device

[0087] 70: Lighting device 71: LED element

[0088] 73: Plano-convex cylindrical lens

[0089] 75: Diffuser Filter 85: Memory

[0090] 88: Processor 90: Machine Vision

[0091] A1: First diffusion angle

Claims

1. A lighting device (70) for a vision machine for detecting surface defects of a steel product (20) that has a predetermined width and is extended in the longitudinal direction, LED element (71) that emits light toward the surface of the above steel product (20); and It includes a diffuser filter (75) disposed between the LED element (71) and the steel product (20), and The above diffuser filter is a lighting device for a vision machine that diffuses light (72, 74) incident on the above diffuser filter by a first diffusion angle (A1) in a first direction (1st) that intersects the extension direction (E) of the grinding groove (25) provided on the surface of the steel product (20) at an intersection angle (j), and diffuses it by a second diffusion angle (A2) that is smaller than the first diffusion angle (A1) in a second direction (2nd) that intersects the first direction (1st).

2. In Claim 1, The above diffuser filter (75) is a lighting device for a vision machine comprising an LDS (laser-direct structuring) film.

3. In Claim 1, A lighting device for a vision machine, wherein the first diffusion angle (A1) is 30 to 70 degrees.

4. In Claim 1, A lighting device for a vision machine, wherein the second diffusion angle (A2) is 1 to 5 degrees.

5. In Claim 1, A lighting device for a vision machine, wherein the above-mentioned intersection angle (j) is substantially right angle and the above-mentioned first direction and second direction are substantially orthogonal.

6. In Claim 1, A lighting device for a vision machine, wherein the above LED elements (71) are arranged in a plurality to form an array in parallel with the extension direction (E) of the grinding groove (25).

7. In Claim 6, The above array is a lighting device for a vision machine, having a plurality of arrays arranged in the above second direction.

8. In Claim 6, The lighting device (70) for the vision machine above is, It further includes a plano-convex cylindrical lens (73) disposed between the LED element (71) and the diffuser filter (75), and The diffuser filter (75) diffuses the light (74) emitted from the LED element (71) and transmitted through the cylindrical lens (73), and A lighting device for a vision machine, wherein the axial direction (L) of the plano-convex cylindrical lens (73) is parallel to the arrangement direction of the array.

9. In Claim 8, The above plano-convex cylindrical lens (73) is a lighting device for a vision machine, wherein the axial direction (L) of the plano-convex cylindrical lens (73) is arranged to be orthogonal to the first direction.

10. In Claim 8, The above plano-convex cylindrical lens (73) is a lighting device for a vision machine, wherein the axial direction (L) of the plano-convex cylindrical lens (73) is arranged parallel to the extension direction (E) of the grind groove (25).

11. In Claim 1, A lighting device for a vision machine, wherein the above steel product is one of a billet, a bloom, or a slab.

12. A method (800) for detecting surface defects of steel products, Step (810) of forming at least one groove (25) having a predetermined length on at least a portion of the surface of the steel product (20) using a steel product surface processing tool; Step (820) of irradiating light emitted from an LED element (71) onto at least one groove (25) formed on at least a portion of the surface of the steel product (20) by passing it through a diffuser filter (75) disposed between the steel product (20) and the LED element (71) - the diffuser filter (75) is configured to diffuse the light emitted from the LED element (71) by a first diffusion angle (A1) along a first direction (1st), and to diffuse it by a second diffusion angle (A2) that is smaller than the first diffusion angle (A1) along a second direction (2nd) orthogonal to the first direction (1st) -; Step (830) of arranging the diffuser filter (75) such that the first direction forms a predetermined intersection angle (j) with the longitudinal direction of the at least one groove (25) formed on the at least part surface of the steel product (20); A step (840) of receiving light reflected by at least one groove (25) through a shooting device (60) to obtain an image; and A method comprising the step (850) of detecting surface defects of the steel product (20) by processing the acquired image through a processor (88) in which image processing software is executed.

13. In Claim 12, The above method is a tool for processing the surface of the steel product, which is a grinder (30).

14. In Claim 12, The above diffuser filter (75) is an LDS (laser-direct structuring) film, and A method in which the first diffusion angle (A1) of the diffuser filter (75) is 30 to 60 degrees.

15. In Claim 12, A method in which the second diffusion angle (A2) of the diffuser filter (75) is 1 to 5 degrees.

16. In Claim 12, The above intersection angle is a right angle, method.

17. In Claim 12, A method in which the above LED elements (71) are a plurality of and are configured to be arranged in a line parallel to the length direction of the grinding groove (25).

18. In Claim 12, The above steel product is one of a billet, a bloom, or a slab, a method.

19. In Claim 13, The rotation axis (31) of the grinder (30) is parallel to the direction of transport.

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