Surface inspection apparatus, surface inspection methods, steel manufacturing methods, steel quality management methods, and steel manufacturing equipment.

Abstract

The surface inspection apparatus of the present invention comprises: two or more oblique light sources that illuminate the inspection area of ​​a steel material with oblique light; one or more line sensors that receive and capture images of each reflected light from the oblique light from each oblique light source at the inspection area; and a detection unit that uses the images captured by the one or more line sensors to detect linear surface defects at the inspection area, wherein the orthogonal projections of at least two of the oblique light sources onto the surface of the steel material are orthogonal on the inspection area.

Description

Technical Field

[0001] This invention relates to a surface inspection apparatus, a surface inspection method, a steel manufacturing method, a steel quality management method, and steel manufacturing equipment. Background Technology

[0002] In steel product production lines, surface quality assurance is extremely important. Therefore, especially in the field of steel plates, line light sources and line sensors have been used to automate surface defect inspection in order to detect various types of surface defects (see Patent Document 1). However, if only a line light source is used to illuminate along the long side (the conveying direction of the steel plate), it is difficult to detect long, linear surface defects along the long side. Therefore, to solve this problem, an oblique line light source with a width-direction component for the illumination light is proposed (see Patent Document 2). Furthermore, Patent Documents 3 and 4 also propose a method where a line light source illuminates the surface from two directions, and a line sensor receives the reflected light from each illumination light separately and obtains the differences.

[0003] Patent Document 1: Japanese Patent Application Publication No. 2008-275424

[0004] Patent Document 2: Japanese Patent Application Publication No. 2006-242866

[0005] Patent Document 3: Japanese Patent Application Publication No. 2017-9523

[0006] Patent Document 4: Japanese Patent Application Publication No. 2018-36175

[0007] Patent Document 5: Japanese Patent Application Publication No. 2015-125089

[0008] Patent Document 6: Japanese Patent No. 6447637

[0009] Among the harmful defects on the surface of steel plates that are the objects of inspection, there are defects such as rolling marks that have a certain degree of elongated linear shape and whose long axis can be generated in all directions. However, as mentioned above, the technology described in Patent Document 1 cannot detect surface defects with relatively long linear shapes in the long side direction. In addition, in the technology described in Patent Document 2, the detection capability is significantly reduced when the long axis direction of the surface defect is aligned with the irradiation direction. Furthermore, the technologies described in Patent Documents 3 and 4 only assume surface defects with the long axis direction pointing towards the width direction or the long side direction as surface defects that are the objects of inspection, without considering that linear surface defects with the long axis direction can be generated in various directions. Summary of the Invention

[0010] This invention was made in view of the above-mentioned problems, and its object is to provide a surface inspection apparatus and a surface inspection method capable of detecting linear surface defects that may occur in all directions along the long axis with high precision. Furthermore, another object of this invention is to provide a steel manufacturing method, a steel quality management method, and steel manufacturing equipment capable of detecting linear surface defects that may occur in all directions along the long axis with high precision, thereby improving the steel manufacturing yield.

[0011] The surface inspection apparatus of the present invention comprises: two or more oblique light sources that illuminate the inspection area of ​​a steel material with oblique light; one or more line sensors that receive and capture images of each reflected light from the oblique light from each oblique light source at the inspection area; and a detection unit that uses the images captured by the one or more line sensors to detect linear surface defects at the inspection area, wherein at least two of the oblique light sources orient their projections onto the surface of the steel material are orthogonal on the inspection area.

[0012] Preferably, within the field of view of the aforementioned line sensor, relative to the inspected object, at least one of the two or more oblique light sources is positioned upstream or downstream of the steel conveying direction.

[0013] Preferably, within the field of view of the line sensor, relative to the inspection target area, at least one of the two or more oblique light sources is positioned upstream of the steel conveying direction, and within the field of view of the line sensor, relative to the inspection target area, at least one of the two or more oblique light sources is positioned downstream of the steel conveying direction.

[0014] The surface inspection method of the present invention includes: an irradiation step, in which oblique illumination light is used to irradiate the inspection target area of ​​the steel using two or more oblique light sources; an imaging step, in which the reflected light from the oblique illumination light from each oblique light source at the inspection target area is received by one or more line sensors, and an image of the inspection target area is captured; and a detection step, in which the image captured in the imaging step is used to detect linear surface defects at the inspection target area, wherein at least two of the oblique illumination lights from the two or more oblique light sources have orthogonal projections onto the surface of the steel on the inspection target area.

[0015] The steel manufacturing method of the present invention includes the following steps: manufacturing steel while using the surface inspection device of the present invention to detect linear surface defects in the steel.

[0016] The steel quality management method of the present invention includes the following steps: using the surface inspection device of the present invention, classifying steel based on the presence or absence of linear surface defects, thereby managing the quality of steel.

[0017] The steel manufacturing equipment of the present invention includes the surface inspection device and the steel manufacturing equipment of the present invention, wherein the surface inspection device inspects the surface of the steel manufactured by the steel manufacturing equipment.

[0018] According to the surface inspection apparatus and method of the present invention, linear surface defects that may occur in all directions along the long axis can be detected with high precision. Furthermore, according to the steel manufacturing method, steel quality management method, and steel manufacturing equipment of the present invention, linear surface defects that may occur in all directions along the long axis can be detected with high precision, thereby improving the steel manufacturing yield. Attached Figure Description

[0019] Figure 1 It is a diagram showing the cross-sectional shape of a linear surface defect.

[0020] Figure 2 This is a diagram used to illustrate the direction of illumination light relative to surface defects.

[0021] Figure 3 This is a diagram illustrating an example of the change in the SN ratio of reflected light relative to the direction of illumination.

[0022] Figure 4 This is a diagram illustrating an example of the change in the SN ratio of reflected light relative to the direction of illumination.

[0023] Figure 5 This is a diagram illustrating an example of the change in the SN ratio of reflected light relative to the direction of illumination.

[0024] Figure 6 This is a diagram illustrating an example of the change in the SN ratio of reflected light relative to the change in the angle between one illumination light and another.

[0025] Figure 7 This is a diagram illustrating an example of the change in the SN ratio of reflected light relative to the direction of illumination.

[0026] Figure 8 This is a schematic diagram showing the structure of a surface inspection device as an embodiment of the present invention.

[0027] Figure 9 This is a diagram showing the projection angle α of the oblique light source and the light reception angle β of the line sensor.

[0028] Figure 10 This is a diagram illustrating an example of the placement of a slanted light source.

[0029] Figure 11 These are diagrams illustrating other examples of the placement of oblique light sources.

[0030] Figure 12 This is a diagram used to illustrate the uneven brightness of reflected light at the field of view of a line sensor.

[0031] Figure 13 It means Figure 10 A diagram showing an embodiment of the configuration position of the oblique light source.

[0032] Figure 14 It means Figure 11 A diagram showing an embodiment of the configuration position of the oblique light source.

[0033] Figure 15 This is a diagram used to illustrate the following image, which was obtained by illuminating a harmless pattern with uneven linear surface defects and elongated, non-uneven shapes with oblique illumination from two directions.

[0034] Figure 16 This is a diagram used to illustrate the following image, which was obtained under conditions where the long axis direction of a linear surface defect differs to the same extent relative to oblique illumination from two directions.

[0035] Figure 17 It is a diagram showing the images and surface defect detection results captured when illumination light is shone from the upstream and downstream sides of the conveying direction. Detailed Implementation

[0036] 〔principle〕

[0037] First, the principles of the surface inspection apparatus and surface inspection method involved in this invention will be explained.

[0038] According to Lambert's diffuse reflection model, the amount of reflected light I2 from an inclined plane when illumination light of magnitude I is incident on the inclined plane is expressed as shown in the following mathematical formula (1). Here, in mathematical formula (1), r represents the diffuse reflectivity of the inclined plane, L represents the normalized vector from the inclined plane toward the light source, and N represents the normalized normal vector of the inclined plane. As shown in mathematical formula (1), according to Lambert's diffuse reflection model, the amount of reflected light I2 from the inclined plane is proportional to the inner product (L·N) of the normalized vector L from the inclined plane toward the light source and the normalized normal vector N of the inclined plane.

[0039] [Mathematical Expression 1]

[0040] l2=r(L·N)I...(1)

[0041] Therefore, based on the above-mentioned Lambert diffusion reflection model, the amount of reflected light at the cross-sectional positions along the long axis and the short axis is examined when illumination light is irradiated from the long axis and short axis of the linear surface defect.

[0042] When illumination light is emitted from the long axis of a linear surface defect, at the cross-section along the short axis of the linear surface defect, the direction of change of the normal vector of the inclined plane relative to the intact portion is orthogonal to the long axis of the illumination direction. Therefore, compared to the intact portion, the dot product (L·N) of the normalized vector L from the inclined plane toward the light source and the normalized normal vector N of the inclined plane hardly changes. In contrast, at the cross-section along the long axis of the linear surface defect, the direction of change of the normal vector of the inclined plane relative to the intact portion is parallel to the long axis of the illumination direction. Therefore, the dot product (L·N) changes significantly on both the near-front and deep sides of the illumination direction. Thus, when illumination light is emitted from the long axis of a linear surface defect, the greater the change in inclination of the inclined plane at the cross-section along the long axis compared to the intact portion, the greater the intensity of the reflected light and the SN ratio. On the other hand, when illumination is applied from the short axis direction of the linear surface defect, the greater the change in inclination of the slope at the cross-sectional position in the short axis direction compared to the intact portion, the greater the intensity of the reflected light and the SN ratio. Furthermore, it is assumed here that the surface characteristics of the intact portion are uniform, and that the noise level is the same when illumination is applied from the long axis direction and when illumination is applied from the short axis direction.

[0043] Here, Figure 1 This shows the cross-sectional shape of a linear surface defect. For example... Figure 1 As shown, the cross-section along the long axis of a linear surface defect changes smoothly, with a smaller inclination compared to the healthy portion. Conversely, the cross-section along the short axis of a linear surface defect changes abruptly, with a larger inclination compared to the healthy portion. Therefore, the closer the direction of illumination is to the long axis of the linear surface defect, the smaller the SN ratio of the reflected light; conversely, the closer the direction of illumination is to the short axis of the linear surface defect, the larger the SN ratio of the reflected light. Figure 2 As shown, the imaging unit 1 is positioned directly above the linear surface defect D. The illumination direction of the light source 2 is changed by rotating it along the dashed line in the horizontal plane with the position of the linear surface defect D as the center of rotation. The results of evaluating the SN ratio of the reflected light are as follows: Figure 3 As shown. Figure 3In the mountainous regions with an SN ratio of 2.5 or higher, the irradiation light is directed parallel to the short axis of the linear surface defects. Conversely, in the valley regions near an SN ratio of 1, the irradiation light is directed parallel to the long axis of the linear surface defects. For example... Figure 3 As shown, it can be confirmed that the SN ratio of the reflected light varies periodically with respect to the direction of illumination. Furthermore, Figure 2 In the diagram, the L direction indicates the conveying direction of the steel (long side direction), and the X direction indicates the width direction of the steel.

[0044] For linear surface defects, there are surface defects whose long axis direction is always in the same direction and surface defects whose long axis direction is randomly generated relative to the transport direction of the steel. Examples of surface defects whose long axis direction is always in the same direction include scratches, while examples of surface defects whose long axis direction is randomly generated relative to the transport direction of the steel include surface defects caused by pressing in slender foreign objects in random directions. From the viewpoint of preventing the outflow of linear surface defects, it is preferable that linear surface defects can be detected with a high SN ratio regardless of the orientation of their long axis. Here, in order to study an optical system that can stably detect linear surface defects regardless of the orientation of their long axis, we attempt to approximate the periodicity of the SN ratio of the reflected light using a sine wave. The approximate formula for the SN ratio of the reflected light is SN... L1 As shown in the following mathematical formula (2). Here, the SN ratio of the reflected light is set as SN. L1 The angle between the direction of steel transport and the orientation of the linear surface defect is set as... Let the direction of illumination be θ, and let arbitrary constants be a and b. In addition, regarding the illumination direction θ, the transport direction (L direction) of the steel when projected onto the surface of the steel will be set to 0°.

[0045] [Mathematical Expression 2]

[0046]

[0047] Assuming the angle between the direction of steel transport and the direction of the linear surface defect... The changes in the illumination direction θ and the SN ratio of the reflected light when the illumination angle is set to 60°, constant a = 3, and constant b = 2 are as follows: Figure 4 As shown. Figure 4 The thick line in the diagram represents the locus of the SN ratio = 3 - 2cos(2(60° - θ)), where θ is in degrees (°). For example... Figure 4As shown, if illumination light is incident from only one direction, the direction of illumination inevitably results in a lower SN ratio for the reflected light. Therefore, if illumination light is incident from two directions and the reflected light is captured for each of the reflected light sources, it can be expected that the reflected light will have a high SN ratio in at least one of the optical systems. Therefore, the change in the SN ratio of the two reflected lights obtained by incident illumination light from two directions and capturing the reflected light for each of the reflected light sources is studied, as follows... Figure 5 As shown. Here, the SN of the reflected light produced by an illumination light is greater than the SN. L1 As expressed by mathematical formula (2), the SN of the reflected light produced by another illuminating light is greater than the SN of the reflected light. L2 The angle between the direction of steel transport and the direction of surface defects is represented by the following mathematical formula (3). Let it be 60°. Additionally, in mathematical formula (3), Δθ represents the angle between one illuminating light source and the other. Figure 5 The thick line represents the trajectory for the maximum value of the SN ratio between the reflected light of each pair of illumination lights.

[0048] [Mathematical Expression 3]

[0049]

[0050] like Figure 5 As shown, it can be seen that within the range of illumination direction θ = 0 to 180°, the dashed line SN representing mathematical formula (2) L1 The single-dot dash SN representing mathematical expression (3) L2 The point with the smaller illumination direction θ at the intersection of the two points achieves the minimum SN ratio. Here, if we solve mathematical formulas (2) and (3) simultaneously to find the SN of the dashed line... L1 With single-dot dashed line SN L2 The coordinates (θ, SN) of the intersection point are represented as shown in the following mathematical expression (4). In mathematical expression (4), n represents an integer value, and SN represents the SN ratio component of the coordinates of the intersection point.

[0051] [Mathematical Expression 4]

[0052]

[0053] According to mathematical formula (4), for the dashed line SN L1 With single-dot dashed line SN L2The SN ratio component of the intersection point (θ, SN), i.e., SN, is a+bcosΔθ when n is odd and a-bcosΔθ when n is even. In other words, the smaller of the two is the lowest SN ratio in both directions of illumination. Therefore, if we calculate Δθ that makes the function f(Δθ) shown in the following mathematical formula (5) the maximum value, then linear surface defects can be detected with a high SN ratio regardless of the direction of the major axis of the linear surface defect. Furthermore, the function f(Δθ) represents the minimum value of the function a+bcosΔθ or the function a-bcosΔθ with respect to Δθ.

[0054] [Mathematical Expression 5]

[0055] f(Δθ)=min(a-bcosΔθ, a+bcosΔθ)...(5)

[0056] If the function f(Δθ) is represented as a coordinate graph, then it becomes Figure 6 The thick line makes the function f(Δθ) maximized when Δθ is 90°. Furthermore, Figure 6 In the diagram, the dashed line represents the locus of SN = a - bcosΔθ, and the dotted-dashed line represents the locus of SN = a + bcosΔθ. Furthermore, the change in the SN ratio of reflected light with a Δθ of 90° relative to the change in the illumination direction θ is shown below. Figure 7 As shown. Figure 7 In the diagram, the dashed line represents the locus of SN = a - bcosθ, and the dotted-dashed line represents the locus of SN = a - bcos(θ - 90°). Furthermore, Figure 7 The thick lines in the diagram represent the change in the maximum SN ratio of the two reflected rays for every two illuminating lights. For example... Figure 7 As shown, by setting the light source so that the illumination direction of one light source is orthogonal to the illumination direction of another light source, the SN ratio of the reflected light can be any constant a, regardless of the direction of the major axis of the linear surface defect. Figure 7 In the example shown, a = 3 or more.

[0057] Furthermore, while the above principle was explained using two illumination lights, the same considerations can be applied when using three or more illumination lights. That is, although detailed explanations are omitted, when using three or more illumination lights, the lights are arranged in such a way that their illumination directions are equal, thereby suppressing the decrease in the SN ratio regardless of the direction of the linear surface defect. For example, it is preferable that, when using three illumination lights, the angle formed by the illumination directions of adjacent illumination lights, in the orthographic projection onto the surface of the steel S, is 120 degrees at the inspection site on the surface of the steel S. The more illumination directions there are, the higher the SN ratio can be ensured.

[0058] Hereinafter, a surface inspection apparatus according to an embodiment of the present invention, which is based on the principles of the surface inspection apparatus and surface inspection method of the present invention described above, will be described.

[0059] [Overall Structure]

[0060] Figure 8 (a) and (b) are schematic diagrams illustrating the structure of a surface inspection apparatus according to an embodiment of the present invention. Figure 8 As shown in (a) and (b), a surface inspection apparatus 10 according to an embodiment of the present invention is an apparatus for detecting linear surface defects formed on the surface of steel S that have a long axis in all directions, and includes an oblique light source 11, a line sensor 12, and a detection unit 13. Here, a line light source refers to a light source with a long light-emitting surface in one direction. On the other hand, a line sensor refers to an imaging unit having a linear field of view. The line sensor of the present invention is not limited to just one line. For example, it is also included in the "line sensor" of the present invention when using a region sensor with a two-dimensional field of view.

[0061] in addition, Figure 8 (a) indicates the view of the surface inspection device's structure from an obliquely upward perspective. Figure 8 (b) shows the case where the same device is viewed from directly above the steel S, i.e., the orthographic projection onto the surface of the steel S. Furthermore, in Figure 8 In (a) and (b), the plane containing the surface of the steel S and the inspection target area on the surface of the steel S is defined as the XY plane. Here, the transport direction (L direction) of the steel S is defined as the Y-axis. On the other hand, the direction perpendicular to the transport direction (L direction) on the surface of the steel S is defined as the X-axis. When the steel S is a steel plate or strip, the X-axis becomes the width direction of the steel S. Furthermore, the normal direction relative to the surface of the steel S is defined as the Z-axis. The X-axis, Y-axis, and Z-axis are defined with the point where the shooting direction of the line sensor 12 intersects with the inspection target area on the surface of the steel S as the origin O. In addition, the direction of travel to the right relative to the paper is defined as the positive side of the X-axis, the L direction of the steel S is defined as the positive side of the Y-axis, and the side where the oblique light source 11 is arranged is defined as the positive side of the Z-axis. Furthermore, in Figure 8 In (a), any point A (called the emitting point A, coordinates (x, y, z)) at the emitting position of the oblique illumination light L1 is projected onto the XY plane as point B (coordinates (x, y, 0)), and point B is projected onto the X-axis as point B' (coordinates (x, 0, 0)). Furthermore, the area to be inspected is a localized section of the surface of the steel S, defined as a long straight line segment in the width direction (X direction) of the steel S, with the same length as the width of the steel S. Figure 8 In (a) and (b), the lines are represented by light gray lines.

[0062] In this embodiment, there are two oblique light source 11s. Therefore, the following description will focus on oblique light source 11a and 11b. Regarding the oblique light source 11a and 11b, when the direction orthogonal to the axis of the light source is set to 0° and the axis of the light source is set to 90°, illumination light at any angle exceeding 0° but less than 90° will be used as oblique illumination light to illuminate the inspection target area of ​​the steel S. Furthermore, in this embodiment, the width direction (X direction) of the steel S is aligned with the axis of the oblique light source 11a and 11b... Figure 8 In (a) and (b), the oblique light sources 11a and 11b are arranged in a parallel manner (with single-dot dashes). That is, the axis of each of the oblique light sources 11a and 11b is the X direction, and the long side direction of the steel S (Y direction, L direction, or the conveying direction of the steel S) intersects the axis of the oblique light sources 11a and 11b at a right angle. Moreover, in this embodiment, the illumination direction of the oblique illumination light from the oblique light source 11a ( Figure 8 (b) The dashed line from the oblique illumination light component L1' in the diagram is related to the direction of illumination of the oblique illumination light from the oblique light source 11b. Figure 8 The dashed line from the oblique illumination light component L2' in (b) is orthogonal to the inspection target area in the orthogonal projection onto the surface of the steel S. Specifically, the oblique illumination light components L1' and L2' projected orthogonally onto the surface of the steel S by the oblique illumination light L1 from the oblique light source 11a and the oblique illumination light L2 (not shown) from the oblique light source 11b intersect at a right angle on the inspection target area of ​​the steel S. More specifically, the oblique light sources 11a and 11b are configured such that both the oblique illumination light components L1' and L2' projected orthogonally onto the surface of the steel S by the oblique illumination light L1 from the oblique light source 11a and the oblique illumination light L2 (not shown) from the oblique light source 11b have an inclination of 45° relative to the axis (X direction) of the light source. In addition, in Figure 8 In cases (a) and (b), the configuration is also tilted at 45° relative to the conveying direction (L direction) of the steel S. In this case, the oblique light source 11a and oblique light source 11b are symmetrical with respect to the XZ plane.

[0063] right Figure 8The parameters of angles (a) and (b) will be explained. In the oblique illumination light L from the oblique light source 11, the angle between the oblique illumination light component projected onto the YZ plane and the normal (i.e., the Z-axis) relative to the surface of the steel S is taken as the projection angle α. Specifically, in the oblique illumination light L1 from the oblique light source 11a, the angle between the oblique illumination light component projected onto the YZ plane and the normal (i.e., the Z-axis) relative to the surface of the steel S is taken as the projection angle αa. Similarly, in the oblique illumination light L2 (not shown) from the oblique light source 11b, the angle between the oblique illumination light component projected onto the YZ plane and the normal (i.e., the Z-axis) relative to the surface of the steel S is taken as the projection angle αb (not shown). The projection angles αa and αb take the Z-axis as 0°. Here, the YZ plane is the plane with the axis of the oblique light source 11 as the normal. In addition, the YZ plane is the plane with the width direction of the steel S as the normal.

[0064] The angle between the shooting direction of the line sensor 12 and the normal (i.e., the Z-axis) relative to the surface of the steel S is defined as the light-receiving angle β. In this case, the angle from which the line sensor 12 is observed when viewed from the oblique light source 11a side is defined as the light-receiving angle βa. On the other hand, the angle from which the line sensor 12 is observed when viewed from the oblique light source 11b side is defined as the light-receiving angle βb (not shown). Figure 8 Therefore, there is only one line sensor 12, and thus βa = -βb. The light-receiving angles β, βa, and βb are also treated as 0° on the Z-axis. Furthermore, to facilitate understanding of the light-receiving angles β, βa, and βb, in... Figure 8 In (a), the line sensor 12 is depicted at an angle relative to the Z-axis, but in reality... Figure 8 As in (b), it lies on the Z-axis.

[0065] In the oblique illumination light L (not shown) from the oblique light source 11, the angle formed by the oblique illumination light component L' (not shown) projected orthogonally onto the XY plane and the transport direction of the steel S (i.e., the L direction or the Y direction) is taken as the illumination angle θ (not shown). More specifically, in the oblique illumination light L1 from the oblique light source 11a, the angle formed by the oblique illumination light component L1' projected orthogonally onto the XY plane and the transport direction of the steel S (i.e., the L direction or the Y direction) is taken as the illumination angle θa. Figure 8In (a), the angle between the oblique illumination light component L1' and the dashed line orthogonal to the axis of the oblique ray light source 11a (i.e., parallel to the Y direction) is used to represent the angle. Similarly, in the oblique illumination light L2 (not shown) from the oblique ray light source 11b, the angle between the oblique illumination light component L2' projected onto the XY plane and the transport direction of the steel S (i.e., the L direction or the Y direction) is used as the illumination angle θb (not shown). This angle can also be represented by the angle between the oblique illumination light component L2' and the dashed line orthogonal to the axis of the oblique ray light source 11b (i.e., parallel to the Y direction). Furthermore, Figure 8 In (b), the illumination angle θa is represented by the angle between the dashed line orthogonal to the axis of the oblique ray light source 11a (i.e., parallel to the Y direction) and the oblique ray illumination component L1', and the illumination angle θb is represented by the angle between the dashed line orthogonal to the axis of the oblique ray light source 11b (i.e., parallel to the Y direction) and the oblique ray illumination component L2'. Based on the above explanation, it can be concluded that: Figure 8 The illumination angles θ, θa, θb in (a) and (b) are... Figures 2-7 The illumination angle θ becomes the same parameter. Additionally, in Figure 8 In cases (a) and (b), the illumination angles θa and θb of the oblique light sources 11a and 11b are tilted at 45°.

[0066] In the oblique illumination light L from the oblique light source 11, the angle between the oblique illumination light L and the line connecting any luminous point and the x-coordinate of that luminous point is taken as the oblique light angle ξs. Specifically, in the oblique illumination light L1 from the oblique light source 11a, the angle between the oblique illumination light L1 and the line connecting any luminous point A and point B' is taken as the oblique light angle ξa. The oblique light angle ξa is a parameter different from the previously described illumination angles θ and θa, as it lies on the plane connecting the origin O, point B', point A, and coordinates (0, y, z). The oblique light angle ξa makes the line connecting point A and point B' 0°. Similarly, for the oblique light source 11b and the oblique illumination light L2 (not shown), the same angle is taken as the oblique light angle ξb (not shown). The oblique light sources 11a and 11b are symmetrical with respect to the XZ plane. Therefore, they are the same as the oblique light angle ξa, but different from the previously described illumination angles θ and θb. In addition, the oblique light angle ξb is defined as 0° by the straight line connecting the coordinates (x, -y, z) and point B'.

[0067] Furthermore, in this embodiment, for convenience, two oblique light sources are used to illuminate the oblique illumination light from two directions, but it is also possible to illuminate the oblique illumination light from three or more directions. In other words, the surface inspection apparatus according to the present invention comprises: two or more oblique light sources that illuminate the steel inspection target area from two or more directions; one or more line sensors that receive the reflected light from each oblique light source at the inspection target area for each reflected light and capture an image; and a detection unit that uses the image captured by the one or more line sensors to detect linear surface defects at the inspection target area, wherein the orthographic projections of at least two of the two or more oblique illumination lights onto the surface of the steel are orthogonal on the inspection target area.

[0068] Furthermore, the surface inspection method of the present invention includes: an irradiation step, in which oblique illumination light is irradiated onto the inspection target area of ​​the steel from two or more directions using two or more oblique light sources; an imaging step, in which the reflected light from each oblique light source at the inspection target area is received by one or more line sensors for each reflected light and an image of the inspection target area is captured; and a detection step, in which the image captured in the imaging step is used to detect linear surface defects at the inspection target area, wherein the orthogonal projections of at least two of the two or more oblique illumination lights onto the surface of the steel are orthogonal on the inspection target area.

[0069] When illuminating oblique light from three or more directions, careful consideration must be given to the configuration and direction of the oblique light sources. Ideally, each oblique light source should not interfere with the others, and the illumination direction should be equal. Furthermore, to ensure the field of view of the line sensor, oblique light sources need to be installed on the production line, thus increasing the complexity and size of the equipment. For example, if it is difficult to illuminate the same position with oblique light from multiple light sources, the inspection position and field of view position need to be set at different locations in the steel conveying direction for each illumination direction, and alignment should be implemented through subsequent processing. Therefore, in the case of practically and compactly installing oblique light sources on the production line at low cost, illuminating oblique light from two directions is preferred. Additionally, from the viewpoint of device maintenance and ease of maintenance, the fewer the number of light sources and cameras, the better, and a simpler mechanism is desired during cleaning, etc. Therefore, using two oblique light sources is preferred. Moreover, it is most preferable to illuminate oblique light from two directions using two oblique light sources capable of achieving both.

[0070] The line sensor 12 captures an image of the inspected portion of the steel S illuminated by oblique illumination from oblique light sources 11a and 11b, and outputs an electrical signal representing the captured image to the detection unit 13. Furthermore, to reduce inconsistencies in detection capability caused by the orientation of the long axis of the linear surface defect, it is optimal that the relationship between the projection angle α of the oblique light source 11 and the light-receiving angle β of the line sensor 12 is as similar as possible in each illumination direction. The definitions of the projection angle α of the oblique light source 11 and the light-receiving angle β of the line sensor 12 are as follows: Figure 9 As shown. Figure 9 This is a diagram observed from the axial direction of the oblique light source 11. (See diagram below.) Figure 9 As shown, the projection angle α of the oblique light source 11 is the angle between the direction of the oblique illumination light and the normal direction of the steel S in the orthogonal projection onto the plane with the axis of the oblique light source 11 as the normal. Similarly, the light-receiving angle β of the line sensor 12 represents the angle between the shooting direction and the normal direction of the steel S in the orthogonal projection onto the plane with the axis of the oblique light source 11 as the normal. Furthermore, for the light-receiving angle β, the angle away from the oblique light source 11 when observing the line sensor 12 from the oblique light source 11 side is considered positive. Incidentally, the angle closer to the oblique light source 11 is considered negative. To explain further in detail... Figure 8 In (a), the projection angles αa and αb and the reception angles βa and βb are the same parameters.

[0071] Furthermore, as a method for capturing images of reflected light on the inspected object area by receiving oblique illumination light from two or more oblique illumination sources for each reflected light, a method using oblique illumination light in different wavelength ranges can be exemplified. Specifically, a combination of two or more oblique illumination sources with different wavelength characteristics and a color line sensor can be used. In this case, the oblique illumination sources with different wavelength characteristics are configured to illuminate from two or more directions. For example, using an oblique illumination source with a red wavelength characteristic and an oblique illumination source with a green wavelength characteristic, an image is captured using a color line sensor.

[0072] Alternatively, another method can be illustrated by utilizing the illumination times of each oblique illumination light from each oblique light source and the exposure time of the line sensor. Specifically, two or more oblique light sources are rapidly illuminated and extinguished at different times, and the exposure time of the line sensor is matched with the illumination of each oblique light source to capture an image. Alternatively, oblique illumination light from two or more directions from oblique light sources is rapidly illuminated and extinguished at different times, and the exposure time of the line sensor is matched with the illumination of each oblique illumination light to capture an image. Furthermore, when there are two oblique light sources or when oblique illumination light is illuminating from two directions, the illuminating oblique illumination light alternates and rapidly illuminates and extinguishes. In this case, the wavelength characteristics of the oblique illumination light from each oblique light source need to be any one of the following: identical, partially overlapping, or different. Moreover, in this case, the wavelength characteristics of the oblique illumination light in each direction need to be any one of the following: identical, partially overlapping, or different. In either case, considering the separation of oblique illumination light from each of two or more oblique light sources or from each of two or more directions, the optimal wavelength characteristics differ. Any method of receiving light according to each reflected light can be implemented by combining known and unknown techniques (oblique light sources, color line sensors, line sensors, and line sensor synchronization control units, etc.). It is also possible to obtain an image of oblique illumination light based on each oblique light source using the methods described above.

[0073] Furthermore, it is also possible to obtain images of oblique illumination light based on each oblique ray source by using oblique ray sources with mutually orthogonal linear polarization characteristics, one for each reflected light. Specifically, a linear polarizer is placed before each of the two oblique ray sources at angles γ° and (γ+90)° (γ is an arbitrary angle), allowing only the mutually orthogonal polarized components of light to pass through. Here, a linear polarizer refers to a filter that allows only the linearly polarized components in a predetermined direction to pass through relative to the incident light. Alternatively, a linear polarizer with the same linear polarization characteristics as the linear polarizer can be placed on a line sensor at angles γ° and (γ+90)°. In this case, a three-channel polarizing camera can also be used, which has three line sensors that can obtain images with different polarization characteristics in one camera. Alternatively, the same number of line sensors as the oblique ray sources can be used, and the optical systems for each illumination direction can be placed at different positions.

[0074] The detection unit 13 detects linear surface defects based on images captured by the line sensor 12. Specifically, after performing conventional brightness correction and frequency filtering on the image signal, the detection unit 13 detects surface defect signals through thresholding. Then, the detection unit 13 determines the linear surface defects based on characteristic quantities of the surface defect signals. The determined surface defect information is collected and used for quality assurance.

[0075] [Example of a configuration for a slanted light source]

[0076] use Figure 10 and Figure 11 Examples of configurations for two oblique light sources 11a and 11b will be described. Figure 10 and Figure 11 All images are views observed from above the steel material S. The thick arrows indicate the orthographic projection of the illumination light relative to the surface of the steel material S. The illumination directions of the oblique illumination light from oblique light source 11a and oblique illumination light from oblique light source 11b are orthogonal at the inspection site in the orthographic projection onto the surface of the steel material S. Furthermore, the width direction of the steel material S is taken as the X-axis, and the transport direction of the steel material S is taken as the Y-axis. The L direction represents the transport direction of the steel material S. The Y direction is the same as the L direction. The arrangement of the oblique light sources 11a and 11b allows for... Figure 10 The configuration shown is configured only on the upstream or downstream side of the L direction (configuration A, Figure 10 In the example shown, the upstream side in the L direction) and as Figure 11 The configuration shown is arranged on the upstream and downstream sides in the L direction (Configuration B). Furthermore, in both cases, the axes of the oblique light source 11a and the oblique light source 11b intersect the transport direction (L direction) of the steel S at right angles and are arranged parallel to the width direction (X direction) of the steel S. Additionally, the line sensor 12, which receives reflected light from the inspected object, is preferably positioned on the X-axis. Configurations A and B will be described in more detail below.

[0077] First, in order to reduce the sensitivity difference caused by the directionality of linear surface defects, the following mathematical formulas (6) and (7) are most preferably satisfied for the following projection angle αa of the oblique light source 11a in the orthographic projection of the surface with the axis of the oblique light source 11a as the normal, the light-receiving angle βa of the line sensor 12 in the orthographic projection of the surface with the axis of the oblique light source 11a as the normal, and the projection angle αb of the oblique light source 11b in the orthographic projection of the surface with the axis of the oblique light source 11b as the normal.

[0078] [Mathematical Expression 6]

[0079] αa=αb...(6)

[0080] [Mathematical Expression 7]

[0081] βa=βb...(7)

[0082] Next, given that the conditions shown in mathematical formulas (6) and (7) above are satisfied in configurations A and B respectively, the further states of each configuration will be explained.

[0083] Considering the surface inspection based on configurations A and B, the following situation exists: due to the oblique illumination, uneven brightness of reflected light is generated regardless of the position of the field of view of the line sensor 12, i.e., the width direction of the field of view. Figure 12 The diagram schematically illustrates the uneven brightness received by the line sensor 12 relative to the respective positions of the oblique light sources 11a, 11b1, and 11b2. Figure 12 The horizontal axis represents the position of the surface of steel S in the width direction (X direction), and the vertical axis represents the brightness of the line sensor 12. Figure 12 In this context, the width of the steel material S extends from x0 to x1 along the X-axis. It is preferable to reduce these brightness unevennesses. To reduce such brightness unevenness of reflected light, measures such as increasing the number of line sensors 12 in the width direction as much as possible or correcting the image signal can be taken. Considering cost and maintainability, it is most preferable to perform brightness correction by standardizing the detection brightness through the brightness of the intact parts before threshold processing for the detection brightness required for surface defect detection. Furthermore, the brightness correction methods for unevenness differ in configurations A and B. Specific methods will be explained separately later.

[0084] Furthermore, in addition to the surface inspection apparatus described in this invention, by adding signal information obtained under orthographic reflection conditions and performing surface inspection, it is expected that the detection performance for the same linear surface defects can be improved. However, the limitations of the optical systems that set the orthographic reflection conditions in configurations A and B are different. These limitations will be explained separately later.

[0085] Furthermore, configuration A will be explained. In configuration A, oblique illumination light from two directions is distinguished by a line sensor 12. Therefore, in order to achieve a configuration that satisfies the conditions shown in mathematical formulas (6) and (7), there are no restrictions on the projection angles αa and αb of the oblique light sources 11a and 11b and the light reception angles βa and βb of the line sensor 12. In addition, regarding the brightness correction method, in configuration A (i.e., using oblique light sources 11a and 11b1), the positions where the brightness increases and decreases in the oblique light sources 11a and 11b1 are reversed at both ends of the field of view of the line sensor 12. Therefore, it is preferable to perform brightness correction processing separately for each reflected light.

[0086] Specific examples of configuration A Figure 13 As shown in (a) and (b). Furthermore, in this example, the combination of two oblique light sources 11a and 11b, each with a different wavelength characteristic, and a color line sensor 12 is explained. Figure 13 In the configurations shown in (a) and (b), two-color oblique light sources 11a and 11b are arranged upstream of the steel S in the transport direction. The oblique light sources 11a and 11b are capable of illuminating monochromatic light of different colors respectively. The axial directions of the oblique light sources 11a and 11b are approximately on the same line. Using these oblique light sources 11a and 11b, the oblique illumination light is illuminating the surface of the steel S orthogonally onto the inspection object in two directions. Then, the reflected light from the inspection object is received by the color line sensor 12. In order to make the projection angle conditions of the two optical systems the same (i.e., due to the conditions shown in mathematical formulas (6) and (7)), the oblique light sources 11a and 11b use oblique illumination sources that make the projection angle αa the same as the projection angle αb and can illuminate in two directions in the width direction of the steel S. Furthermore, if the differences between the two optical systems are recognized, the effect of this principle can be achieved to a certain extent even if the projection angles αa and αb are slightly different. In this case, regarding the color of the oblique illumination light, relative to the width direction, the illumination from one side is red, and the illumination from the other side is green, using a color line sensor. Regarding wavelength, if the wavelength domains of the oblique light sources 11a and 11b and the spectroscopic sensitivity characteristics of the color line sensor are not identical, then this optical system is valid.

[0087] Furthermore, in this example, a combination of a slanted light source illuminating different wavelengths of slanted illumination light and a color line sensor is used. For each reflected light, the reflected light from each slanted light source at the inspected object location is received and an image is captured. However, a combination of a slanted light source illuminating light with the same, partially overlapping, or different wavelengths and a line sensor can also be used. In this case, the emission time of the slanted light source and the exposure time of the line sensor are switched at high speed, and the illumination and exposure times are adjusted accordingly.

[0088] Furthermore, multiple sets of oblique light sources and line sensors can be placed at different locations. Additionally, the light-receiving angles βa and βb of the color line sensor can be selected optimally. Furthermore, if the angles are different from the projection angles αa and αb, orthographic reflection conditions can be added. This is used to address linear surface defects with the highest sensitivity under orthographic reflection conditions, and orthographic reflection images can be obtained in the blue channel by adding a standard blue line light source (which has no illumination component in the width direction).

[0089] Furthermore, the optical system of configuration B will be described. In configuration B, oblique illumination light is irradiated from both the upstream and downstream sides of the L direction. When the oblique illumination light from both directions is detected by a single line sensor 12, if the light-receiving angles βa and βb of the line sensor 12 are the same and it is tilted in either the upstream or downstream direction, one sensor will be located closer to the oblique light source, and the other will be located on the opposite side. Therefore, it is most preferable to position the line sensor 12 directly above the steel S with light-receiving angles βa and βb of 0°. Additionally, in configuration B (i.e., using oblique light sources 11a and 11b2), the positions where brightness increases and decreases in oblique light sources 11a and 11b2 are the same. Therefore, brightness correction processing can also be performed by integrating the signals from multiple line sensors 12 through linear combination or the like.

[0090] Specific examples of configuration B Figure 14 As shown in (a) and (b). Furthermore, in this example, the combination of two oblique light sources 11a and 11b, each with a different wavelength characteristic, and a color line sensor 12 is explained. Figure 14 In the configurations shown in (a) and (b), oblique light sources 11a and 11b are provided such that the color of the illumination light on the upstream side of the conveying direction is red and the color of the illumination light on the downstream side of the conveying direction is green. Furthermore, using these oblique light sources 11a and 11b, the oblique illumination light is projected orthogonally onto the inspection target area from two directions. Moreover, a color line sensor 12 is used to receive reflected light from the inspection target area. The color line sensor 12 is set to receive angles βa and βb of 0° so that the projection and reception angles of the two optical systems are the same (i.e., to satisfy the conditions shown in mathematical formulas (6) and (7)). Furthermore, by recognizing the difference between the two optical systems, even if the light is slightly deviated from directly above, the effect of this principle is achieved to a certain extent. At this point, it is preferable to adjust the oblique light sources 11a and 11b on the upstream and downstream sides of the transport direction in a manner that minimizes the misalignment of the two sets of optical systems (i.e., the deviation of the projection angles αa and αb and the deviation of the receiving angles βa and βb). Furthermore, by changing the angle from directly above, it is also possible to set positive reflection conditions.

[0091] Furthermore, in this embodiment, when the oblique illumination light L1 and L2 of the oblique light sources 11a and 11b are projected onto the surface of the steel S, the oblique illumination light components L1' and L2' are tilted at 45° relative to the axis of the oblique light source. However, when one oblique illumination light has a tilt of ω° relative to the axis of the oblique light source and the other oblique illumination light has a tilt of ψ° relative to the axis of the oblique light source, the same effect is obtained if ω° + ψ° = 90° (this formula is derived from (90° - ω°) + (90° - ψ°) = 90°). However, the difference between the projection angle α and the reception angle β in the two or more optical systems should be small. Poor detection performance caused by changes in background noise can be reduced, and uneven brightness of reflected light caused by the increase in the oblique angle can be minimized. Therefore, it is most preferable that the oblique illumination light components are tilted at 45° relative to the axis of the oblique light source.

[0092] Furthermore, in this embodiment, an example has been described in which the oblique light sources 11a and 11b are arranged such that the transport direction (L direction) of the steel S is perpendicular to the axis of the oblique light sources 11a and 11b, respectively; however, the present invention is not limited to this arrangement. As long as the irradiation direction of the oblique illumination light from the oblique light source 11a and the irradiation direction of the oblique illumination light from the oblique light source 11b are orthogonal to the inspection target area in their orthogonal projection onto the surface of the steel S, the effects of the present invention can be obtained even if the smaller angle between the axis of each oblique light source 11a and 11b and the transport direction of the steel S is a right angle (in other words, 90° or less). In particular, when a right angle cannot be formed due to layout issues of the manufacturing equipment, the smaller angle can be made to be a right angle or less within the range where the effect of oblique illumination can be expected. Considering the effect of oblique illumination, empirically it is preferable that the smaller angle between the axis of the oblique light sources 11a and 11b and the transport direction of the steel S is 60° or more, and more preferably 80° or more. As a configuration for oblique light sources, the closer it is to 90°, the more ideal it becomes.

[0093] Furthermore, while a line sensor 12 was described in this embodiment, a region sensor can also be used instead. When using a region sensor, it is most preferable to extract only a linear field of view from the region sensor's field of view. Also, while this embodiment describes a single line sensor 12, multiple line sensors 12 can be used to receive reflected light from various light sources. However, considering alignment accuracy, a single line sensor is most preferable. Furthermore, while this embodiment describes an inspection target area as a line, it is not limited to this. It is self-evident that the inspection target area can be a point, line, or surface, depending on the field of view of the line sensor 12 or the region sensor. Furthermore, while this embodiment describes only the optical system that irradiates oblique illumination light from the two directions described in this invention, this invention is not limited to this. For example, completely different optical systems, such as a positive reflection optical system, can be combined with the optical system irradiating oblique illumination light from the two directions to perform the inspection of the same linear surface defects that are the inspection target of this invention.

[0094] Furthermore, by processing two images obtained using oblique illumination from two directions, linear surface defects can be detected with high precision. Figure 15 Images (a) and (b) are used to illustrate images obtained by illuminating harmless patterns with linear surface defects and elongated shapes without surface defects from two directions with oblique illumination. Figure 15 As shown in (a), in the linear surface defect D, the sensitivity varies significantly with respect to the direction of oblique illumination, thus causing a large variation in image density depending on the direction of the oblique illumination. In contrast, as... Figure 15 As shown in (b), in a harmless pattern P with a slender shape lacking any unevenness, the sensitivity hardly changes relative to the direction of oblique illumination. Therefore, the image density does not change according to the direction of oblique illumination. Thus, by comparing two images with different directions of oblique illumination and using difference, ratio, etc., to grasp the changes in image density, it is possible to distinguish between linear surface defects and harmless patterns.

[0095] Furthermore, due to the different relationship between the direction of the linear surface defect and the direction of the oblique illumination light, even for linear surface defects with uneven surfaces, the amount of variation in image density varies. When one oblique illumination light is nearly parallel to the long axis of the linear surface defect and the other is nearly perpendicular, a significant difference in image density is observed. However, for example... Figure 16As shown, when the long axis of a linear surface defect D differs by the same degree relative to oblique illumination from two directions, almost no difference in image density is produced. In this case, as long as the surface defect is a linear defect with unevenness, different density is produced within the defect area depending on the direction of the oblique illumination, but in the case of harmless patterns, the defect area appears the same, so it can be distinguished by comparing images.

[0096] Furthermore, when it is desired to efficiently distinguish harmless patterns, acquiring the difference between images obtained from two directions is also quite effective (see Patent Document 5). For example, in steel products, there are cases where harmless patterns are generated across the entire surface due to composition and processing. In this case, if defect detection based on existing threshold processing and defect determination based on image processing are to be implemented, the entire surface of the steel plate is identified as a defect candidate through threshold processing. Therefore, the following problem arises: due to the large number of defect candidates, the processing speed is insufficient, the inspection is invalid, and it is impossible to distinguish harmless signals through subsequent image processing. Under such conditions, by acquiring the difference between two images illuminated from two directions, only the signal of flat harmless patterns is removed, while the signal of elongated surface defects with only one sensitivity due to unevenness, and surface defects that appear different within a region, remains due to the difference processing.

[0097] When implementing the aforementioned differential processing, it is preferable that the projection angle and receiving angle of the two optical systems illuminating from two directions are equal at each position in the field of view (see Patent Document 6). If the projection angle and receiving angle differ between the two optical systems, even if the object is flat, areas with different specularity or diffusion cannot be removed by differential processing, and will remain as signals. Therefore, when implementing differential processing, it is preferable not to only configure... Figure 10 The pattern shown is not the upstream or downstream side pattern in the L direction (configuration A), but rather configured in... Figure 11 The pattern shown is an upstream and downstream side pattern in the L direction (configuration B). That is, preferably, the orthogonal projections of the illumination light from the upstream side and the illumination light from the downstream side onto the surface of the steel S are orthogonal on the inspection object part that becomes the field of view of the line sensor. In addition, the projection angle α and illumination angle θ of the two light sources are equal.

[0098] Furthermore, the steel used in this embodiment includes steel strip, thin steel plate, thick steel plate, slab, strip steel, section steel, hot-rolled steel plate, or cold-rolled steel plate.

[0099] [Example]

[0100] The actual results show the photographic and inspection findings of linear surface defects that may have a long axis in all directions. The optical system used... Figure 14The optical system in configuration B shown has its projection angles αa and αb set to 25° and its reception angles βa and βb set to 0°. Images captured when illumination light is applied from the upstream and downstream sides of the steel's conveying direction (L direction) and the detection results of linear surface defects are shown below. Figure 17 As shown in (a) and (b). When illumination light is shone from the downstream side in the conveying direction, as... Figure 17 As shown in (b), the surface defect portion enclosed by the dashed circle is more difficult to detect. In contrast, when illumination light is shone from the upstream side in the transport direction, as... Figure 17 As shown in (a), the detectable level of surface defect signal can be identified in the area surrounded by the solid line circle. Thus, according to the present invention, it has been confirmed that even linear surface defects that are at risk of being missed due to insufficient sensitivity under illumination from only one side of oblique light can be detected.

[0101] The embodiments of the invention made by the inventors have been described above, but the invention is not limited by the description and drawings that form part of the disclosure of this invention. For example, by using a surface inspection apparatus or method according to an embodiment of the present invention, steel can be manufactured while detecting linear surface defects, thereby improving the steel production yield by detecting linear surface defects with high precision. Furthermore, by using a surface inspection apparatus or method according to an embodiment of the present invention to classify steel based on the presence or absence of linear surface defects, the quality of the steel can be managed. In other words, linear surface defects can be detected with high precision, thereby improving the steel production yield. Additionally, by using a surface inspection apparatus or method according to an embodiment of the present invention to inspect the surface of steel manufactured by known or existing manufacturing equipment, linear surface defects can be detected with high precision, thereby improving the steel production yield. Thus, all other embodiments, examples, and application techniques made by those skilled in the art based on this embodiment are included within the scope of the present invention.

[0102] Industrial availability

[0103] According to the present invention, a surface inspection apparatus and a surface inspection method are provided that can accurately detect linear surface defects that may occur in all directions along the long axis. Furthermore, according to the present invention, a steel manufacturing method, a steel quality management method, and steel manufacturing equipment are provided that can accurately detect linear surface defects that may occur in all directions along the long axis, thereby improving the steel manufacturing yield.

[0104] Explanation of reference numerals in the attached figures

[0105] 1... Imaging unit; 2... Light source; 10... Surface inspection device; 11a, 11b... Oblique light source; 12... Line sensor, color line sensor; 13... Detection unit; D... Linear surface defect; S... Steel; L1... Oblique illumination light from oblique light source 11a; L2... Oblique illumination light from oblique light source 11b (not shown); L1'... Component of oblique illumination light projected orthographically onto the surface of steel S by oblique illumination light from oblique light source 11a; L2'... Component of oblique illumination light projected orthographically onto the surface of steel S by oblique illumination light from oblique light source 11b (not shown). The composition of the oblique illumination light on the surface of material S; θ...irradiation direction (when projected orthogonally onto the surface of the steel), illumination angle (when projected orthogonally onto the surface of the steel); θa, θb...illumination angle (when projected orthogonally onto the surface of the steel); α, αa, αb...projection angle; β, βa, βb...received angle; ξa, ξb...oblique angle; γ...the setting angle of a linear polarizer (unit °); ω...the tilt of one oblique illumination light relative to the axis of the oblique light source (unit °); ψ...the tilt of another oblique illumination light relative to the axis of the oblique light source (unit °).

Claims

1. A surface inspection device, characterized in that, have: Two oblique light sources illuminate the steel material being inspected. One or more line sensors, which receive and capture images of each reflected light from oblique illumination light from each oblique light source at the inspected object location; as well as The detection unit uses images captured by one or more line sensors to detect linear surface defects at the inspected area. The oblique illumination light from the two oblique light sources projects orthogonally onto the surface of the steel material at the inspection site. The detection unit performs a calibration on each reflected beam to standardize the detection brightness by passing through the healthy part before processing the threshold brightness required for surface defect detection.

2. The surface inspection device according to claim 1, characterized in that, Within the field of view of the line sensor, relative to the inspected object, at least one of the two oblique light sources is positioned upstream or downstream of the steel in the conveying direction.

3. The surface inspection device according to claim 1, characterized in that, Within the field of view of the line sensor, relative to the inspected object, one of the two oblique light sources is positioned upstream of the steel conveying direction. Within the field of view of the line sensor, relative to the inspected object, the other of the two oblique light sources is positioned downstream of the steel in the conveying direction.

4. A surface inspection method, characterized in that, include: The irradiation step involves using two oblique light sources to irradiate the inspected area of ​​the steel with oblique illumination light. The shooting step involves using one or more line sensors to capture images of the object being inspected by receiving each reflected light from the oblique illumination light from each oblique light source at the object being inspected. as well as The detection step involves using the images captured in the imaging step to detect linear surface defects at the inspected area. The oblique illumination light from the two oblique light sources projects orthogonally onto the surface of the steel material at the inspection site. The detection step includes a step of standardizing the detection brightness by passing through the brightness of the healthy portion for each reflected beam before threshold processing of the detection brightness required for surface defect detection.

5. A method for manufacturing steel, characterized in that, Includes the following steps: Steel is manufactured while using the surface inspection apparatus according to any one of claims 1 to 3 to detect linear surface defects in the steel.

6. A method for quality management of steel, characterized in that, Includes the following steps: Using the surface inspection apparatus according to any one of claims 1 to 3, steel is classified based on the presence or absence of linear surface defects, thereby managing the quality of the steel.

7. A steel manufacturing equipment, characterized in that, A surface inspection apparatus and a steel manufacturing equipment according to any one of claims 1 to 3, wherein the surface inspection apparatus inspects the surface of steel manufactured by the steel manufacturing equipment.

Images