JP7207443B2 - Surface defect detection device, surface defect detection method, steel plate manufacturing method, steel plate quality control method, and steel plate manufacturing equipment - Google Patents

Description

The present invention relates to a surface defect detection apparatus, a surface defect detection method, a steel sheet manufacturing method, a steel sheet quality control method, and steel sheet manufacturing equipment.

2. Description of the Related Art In recent years, in material manufacturing processes, evaluation of the beauty of the appearance of material surfaces has become stricter. For example, a steel plate, which is a plate-like object used for passenger cars, switchboards, etc., is required not only to have functional aspects such as strength and toughness, but also to have no minute irregularities or flaws on the surface. This is an evaluation criterion focused on whether the appearance is good or bad. Therefore, even if there is no functional problem, it is not uncommon for the product to be determined as non-conforming due to its poor appearance.

Among the defects that pose a problem in terms of appearance, there is a striped unevenness defect. A striped unevenness defect means an undulating unevenness defect that occurs on the surface, and that unevenness changes in a specific direction. For example, in the process of pickling a steel sheet after hot rolling in the steel sheet manufacturing process, minute striped irregularities called "waist folds" may occur on the surface of the steel sheet. A wrinkle is an undulating defect having minute unevenness on the order of about 10 [μm] in height and on the order of about 10 [mm] in pitch, and occurs along the conveying direction of the steel plate. Such folds become conspicuous when the specularity is improved by painting or plating, and often poses a problem in terms of appearance.

Conventionally, as a technique for detecting a striped uneven defect, a technique using irradiation or reflection of light is known. For example, in Patent Document 1, the surface of a moving steel plate or the like is irradiated with a linear laser beam, the position to be measured is imaged with an area imaging sensor, and surface unevenness information is obtained from the shape of the linear light that is imaged. A method of obtaining is disclosed. In addition, in Patent Document 2, parallel light is irradiated to the object to be measured, the reflected light is projected on a screen, and a calculation is performed on the light and dark pattern to detect a striped uneven defect of the object to be measured. A method is disclosed. In addition, in Patent Document 3, the surface of the steel plate is irradiated with light with a wavelength of 10.6 [μm] or more, and the bright points and dark points obtained by the convergence and divergence of the light specularly reflected from each point of the minute unevenness defect , methods for detecting concave and convex defects, respectively, are disclosed. Further, Patent Document 4 discloses a method of photographing a plurality of patterns reflected on a specular or semi-specular surface of a measurement object and measuring surface unevenness from the distortion of the reflected patterns.

JP 2010-79841 A JP-A-05-256630 JP 2011-174942 A JP 2008-224341 A

However, in any of the methods disclosed in Patent Literatures 1 to 4, it is difficult to detect the above-described stripe-shaped irregularity defect due to the bending. That is, for example, a steel plate after pickling has a rough surface and diffuse reflection is dominant, and the intensity of the reflected light to be measured is greatly reduced with respect to the incident light. As in the methods disclosed in Patent Documents 1 to 4, when performing measurement based on the positional variation of the reflected light and the light amount distribution pattern, a screen for projecting the reflected light may be installed. However, it is considered difficult to secure a sufficient amount of light to detect the reflected light. Further, when the screen is replaced with an imaging device, the reflected light may not be able to be measured due to reasons such as the inability to sufficiently collect the reflected light to a size comparable to that of the imaging device.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide a surface defect detection apparatus and a surface defect detection method capable of accurately detecting uneven defects on the surface of an object. be. Another object of the present invention is to provide a steel plate manufacturing method and steel plate manufacturing equipment capable of accurately detecting irregularities on the surface of an object to improve the manufacturing yield of steel materials. Further, another object of the present invention is to provide a steel plate quality control method capable of accurately detecting irregularities on the surface of an object to provide a high-quality steel plate.

In order to solve the above-described problems and achieve the object, a surface defect detection apparatus according to the present invention includes a light source for irradiating the surface of an object with light, and a screen on which the reflected light reflected from the surface of the object is projected. a tilt detection means for detecting information about the tilt of the surface of the object from the projection position where the reflected light from the object is projected onto the screen; and from the information about the tilt detected by the tilt detection means, the and defect detection means for detecting unevenness defects on the surface of an object, wherein the screen has transparency for transmitting the projected reflected light and transmits the transmitted light at a predetermined angle. and the inclination detection means receives the transmitted light diffused within the predetermined angle range and measures the projection position. It is characterized by comprising

Further, in the surface defect detection apparatus according to the present invention, in the above invention, the inclination detection means has an imaging device for measuring the position of the reflected light projected on the screen, and the imaging device measures the position of the reflected light projected on the screen. It is arranged at a position calculated from the transmission characteristics, the intensity of the reflected light from the object, the range in which the projection position fluctuates on the screen, and the background brightness on the screen. is.

Further, the surface defect detection method according to the present invention includes an irradiation step of irradiating the surface of an object with light, and from a projection position where the reflected light reflected by the surface of the object is projected onto a screen, the inclination of the surface of the object is determined. A surface defect detection method comprising: a tilt detection step of detecting information; and a defect detection step of detecting uneven defects on the surface of the object from the information about the tilt detected by the tilt detection step, wherein the screen has a transparency for transmitting the projected reflected light and a transmission characteristic for diffusing the transmitted light within a predetermined angle range. The projection position is measured by receiving the transmitted light diffused inside.

Further, in the surface defect detection method according to the present invention, in the above invention, the imaging device for measuring the position of the reflected light projected on the screen is configured to measure the transmission characteristics of the screen and the intensity of the reflected light from the object. and the range in which the projection position fluctuates on the screen and the background brightness on the screen.

A steel sheet manufacturing method according to the present invention includes a steel sheet manufacturing step and an inspection step of inspecting the surface of the steel sheet manufactured in the manufacturing step by the surface defect detection method of the above invention. and

Further, a steel sheet quality control method according to the present invention includes an inspection step of inspecting the surface of a steel sheet by the surface defect detection method of the above invention, and quality control of the steel sheet from the inspection results obtained by the inspection step. and a quality control step.

Further, a steel plate manufacturing facility according to the present invention comprises manufacturing equipment for manufacturing a steel plate, and the surface defect detection device of the above invention for inspecting the surface of the steel plate manufactured by the manufacturing equipment. and

INDUSTRIAL APPLICABILITY The surface defect detection apparatus and the surface defect detection method according to the present invention have the effect of being able to accurately detect uneven defects on the surface of a flat plate-like object. Further, the steel sheet manufacturing method and the steel sheet manufacturing equipment can manufacture the steel sheet with a high yield. Furthermore, the steel sheet quality control method can provide high quality steel sheets.

FIG. 1 is a schematic diagram showing a schematic configuration of a surface defect detection apparatus according to an embodiment. FIG. 2A is a diagram showing the relationship between the angle formed by the incident light from the light source and the flat plate-like object and the amount of variation in the reflection direction of the reflected light with respect to each surface of the flat plate-like object. FIG. 2(b) is a diagram showing the relationship between the amount of variation in the projected position on the screen of the reflected light reflected at the inspection position on the surface of the plate-like object. FIG. 2(c) is a diagram showing the displacement of the reflected light RL2 with respect to the reflected light RL1 using the shift amount. FIG. 3 is a diagram showing the details of the behavior of transmitted light on the screen. FIG. 4 is a diagram showing an example of transmission characteristics f(Φ, θ) of the screen. FIG. 5 is a diagram explaining the principle of intensity fluctuation of the reflected light RL due to vibration. FIG. 6 is a diagram showing an example of changes in physical quantities accompanying changes in the surface inclination of the object to be measured. FIG. 7 is a diagram showing an example of changes in physical quantities associated with plate thickness variations. FIG. 8 is a schematic diagram showing the configuration of a surface defect detection apparatus that is another embodiment of the present invention. FIG. 9 is a diagram showing the measurable range of each of the two imaging devices. FIG. 10 is a layout diagram of an experimental apparatus used in Examples. FIG. 11 is a detailed layout diagram of the experimental apparatus used in the examples. FIG. 12 is a diagram showing the transmission characteristics f(Φ, θ) of the diffusion plate used in the example. 13A and 13B are diagrams showing experimental results according to Example 1 of the present invention. FIG. FIG. 14 is a diagram showing a first example of experimental results according to Example 2 of the present invention. FIG. 15 is a diagram showing a second example of experimental results according to Example 2 of the present invention.

EMBODIMENT OF THE INVENTION Below, embodiment of the surface defect detection apparatus, the surface defect detection method, the manufacturing method of a steel plate, the quality control method of a steel plate, and the manufacturing equipment of a steel plate which concerns on this invention is described. It should be noted that the present invention is not limited by this embodiment.

FIG. 1 is a schematic diagram showing a schematic configuration of a surface defect detection apparatus 1 according to an embodiment. In the present embodiment, an object to be detected for surface defects by the surface defect detection apparatus 1 will be described as a plate-like object 3 . Examples of the plate-like object 3 include belt-like objects, paper products, resin sheets, metal plates, and the like. Here, the metal plate includes, for example, an iron plate, a steel plate, an aluminum plate, an aluminum alloy plate, a titanium plate, a titanium alloy plate, and the like. Further, in the present embodiment, the object is not limited to the flat plate-like object 3, and may be an object having a shape different from the flat plate shape, such as a tubular object or a coil-like object.

A surface defect detection apparatus 1 according to the embodiment includes a light source 4, a screen 5, an imaging device 6, a computer 7, a display device 8, and the like as main components. A surface defect detection apparatus 1 according to an embodiment detects uneven defects on the surface of a flat plate-like object 3 conveyed in the direction of arrow A in FIG. Specifically, in the surface defect detection apparatus 1, the incident light IL emitted from the light source 4 and incident on the flat plate-shaped object 3 is reflected at the inspection position IP on the flat plate-shaped object 3, and is reflected on the screen 5 as the reflected light RL. projected. The screen 5 has transparency to transmit the projected reflected light RL. Furthermore, the screen 5 not only transmits the reflected light RL as the transmitted light TL, but also has a transmission characteristic of diffusing the transmitted transmitted light TL within a predetermined angle range. That is, the screen 5 is made of a material that transmits part of the projected reflected light RL and diffuses the transmitted light TL within a predetermined angle range. This transmission characteristic will be described later in detail. The transmitted light TL transmitted through the screen 5 and diffused is received at the light receiving position SP of the imaging device 6 . The computer 7 measures the projection position, which is the position of the reflected light RL projected on the screen 5, based on the image transmitted from the imaging device 6 in response to the received transmitted light TL, and measures the projection position of the flat plate-like object from the projection position. 3 detects information about the tilt with respect to the reference plane. Then, an uneven defect on the surface of the plate-like object 3 is detected based on the information about the detected inclination. For example, from the information about the tilt, it is possible to detect that there is an uneven defect at the inspection position IP on the surface of the plate-like object 3 which is tilted with respect to the reference plane. By continuously performing such an inspection along the conveying direction (direction of arrow A in FIG. 1) on the surface of the flat plate-like object 3 conveyed by the conveying rolls 2, the flat plate-like object 3 is inspected. It is possible to detect striped irregularities on the surface. Further, by displaying the detection result of the striped uneven defect on the display device 8, for example, as an image, the operator can easily grasp the striped uneven defect.

The incident angle of the incident light IL from the light source 4 at the inspection position IP on the plate-like object 3 is preferably 80[°] or more. It is more preferable if it is 86[°] or more. The incident angle of the incident light IL from the light source 4 is defined as the angle between the normal line of the plate-like object 3 at the inspection position IP and the incident light IL from the light source 4 . The reason why this angle of incidence is preferable is that by increasing the angle of incidence, the specular reflectance increases even on a surface with a certain degree of surface roughness, and a sufficient amount of reflected light can be ensured. Here, as an example of a surface having a certain degree of roughness, a surface having an arithmetic mean surface roughness Ra of several [μm] to several ten [μm], in particular, the surface of a metal plate can be mentioned. More specifically, the surfaces of iron plates, steel plates, aluminum plates, aluminum alloy plates, titanium plates, and titanium alloy plates can be used.

In the surface defect detection apparatus 1 according to the embodiment, the imaging device 6 receives the transmitted light TL diffused within a predetermined angle range by the screen 5, and projects the reflected light RL onto the screen 5. It functions as projection position detection means for measuring the position PP. Further, in the surface defect detection apparatus 1 according to the embodiment, the tilt detection means for detecting the information regarding the tilt of the surface of the plate-like object 3 with respect to a preset reference plane from the projection position PP is detected by the imaging device 6 and the computer 7. It is configured. Further, in the surface defect detection apparatus 1 according to the embodiment, the computer 7 can also be used as defect detection means for detecting uneven defects on the surface of the plate-like object 3 based on the information about the inclination detected by the inclination detection means. It is functioning.

Here, a method for detecting inclination information of the surface of the plate-like object 3 according to the present invention will be described. FIG. 2(a) shows the angle formed between the incident light IL from the light source 4 and the flat plate-like object 3 with respect to the surfaces 3a and 3b of the flat plate-like object 3, and the amount of variation in the reflection direction γ of the reflected lights RL1 and RL2. It is a figure which showed the relationship. In the following description including FIG. 2(a), only the surfaces 3a and 3b of the flat plate-like object 3 are drawn with lines, and other parts in the thickness direction of the flat plate-like object 3 are drawn to make the drawings easier to see. Illustration is omitted. FIG. 2(b) is a diagram showing the relationship between the amounts of variation of the projection positions PP1 and PP2 of the reflected lights RL1 and RL2 reflected at the inspection positions IP on the surfaces 3a and 3b of the plate-like object 3 on the screen 5. . FIG. 2(c) is a diagram showing the displacement of the reflected light RL2 with respect to the reflected light RL1 using the shift amount Δ.

The surface 3a of the plate-like object 3 shown in FIG. 2(a) is in a non-tilted state. On the other hand, the surface 3b of the flat plate-like object 3 has a slight inclination angle α with respect to the surface 3a of the flat plate-like object 3 at the inspection position IP so that the screen 5 side is positioned above the light source 4 side. It is in a state of Then, as shown in FIG. 2A, the angle formed by the incident light IL from the light source 4 at the inspection position IP on the surface 3a of the flat plate-like object 3 and the surface 3a of the flat plate-like object 3 is β. do. On the other hand, the angle formed by the incident light IL incident on the inspection position IP on the surface 3b of the flat plate-like object 3 and the surface 3b of the flat plate-like object 3 is (β+α). That is, the angle formed by the reflected light RL2 reflected on the surface 3b of the flat plate-like object 3 and the surface 3b of the flat plate-like object 3 is also (β+α). Further, when the surface 3a of the flat plate-like object 3 is used as a reference plane, the surface 3b of the flat plate-like object 3 is inclined by an angle α with respect to the surface 3a. and the reflected light RL2 is (β+2α). Let this angle γ be the reflection direction of the reflected light RL.

From the above, the reflection direction γ of the reflected light RL reflected at the inspection position IP on the surface of the flat plate-like object 3 can be expressed by the following formula (1).

Therefore, as can be seen from the above formula (1), since the surface of the plate-like object 3 is tilted at the angle α, the reflection direction γ of the reflected light RL is changes by an angle of 2α. That is, as shown in FIG. 2B, the traveling direction of the reflected light RL2 reflected at the inspection position IP on the surface 3b of the flat plate-like object 3 is It fluctuates by an angle 2α with respect to the traveling direction of the reflected light RL1. Therefore, when the optical path length of the reflected light RL1 from the inspection position IP to the screen 5 is D, the reflected light RL2 is perpendicular to the reflected light RL2 at the position of the optical path length D from the inspection position IP. direction by D sin2α.

On the other hand, the angle formed by the reflected light RL1 and the screen 5 is _Ψ0 , and the projection position PP1 of the reflected light RL1 on the screen 5 is used as a reference, and the deviation amount of the projection position PP2 of the reflected light RL2 from the projection position PP1 is Δ. and Then, the displacement of Dsin2α can be expressed as Δcos(90[°]+2α−ψ ₀ ) using the shift amount Δ, as shown in FIG. can be rewritten.

In the above formula (2), since |α|<<1, it is approximated by sin2α≈2α and cos2α≈1. Therefore, the above formula (2) can be rewritten as the following formula (3).

In the above formula (3), especially when Ψ ₀ ≈90[°], the above formula (3) can be rewritten as the following formula (4).

Then, based on the above formula (4) and the following formula (5), the deviation amount Δ of the projection position P2 with respect to the projection position PP1 on the screen 5 is calculated as the inclination angle α of the surface 3b of the flat plate-like object 3 at the inspection position IP. can be calculated.

In this way, the angle α can be detected as tilt information of the surface of the plate-like object 3 with respect to the reference plane. The above is the principle of tilt detection in the present invention.

Next, an example of a method of arranging the imaging devices 6 in this embodiment will be described. The transmittance of the transmitted light TL in the screen 5 is not necessarily uniform under all conditions, and varies depending on the arrangement of each piece of equipment. For example, it varies depending on the angle formed by the reflected light RL and the screen, and the arrangement of the imaging device 6 with respect to the projection position PP of the reflected light RL. Under the condition that the intensity of the reflected light RL is not necessarily sufficient, it is more preferable to optimize the arrangement of the imaging device 6 in terms of high noise resistance and reliable measurement.

FIG. 3 is a diagram showing the details of the behavior of the transmitted light TL on the screen 5. As shown in FIG. The reflected light RL enters the screen 5 at an incident angle Φ. The incident angle Φ is defined as the angle formed by the normal line N at the projection position PP on the screen 5 and the reflected light RL. The reflected light RL is projected onto the projection position PP on the screen 5 and transmitted to the back side of the screen 5, that is, toward the imaging device 6 side. Transmitted light transmitted through the screen 5 is diffused on the back side of the screen 5 centering on the projection position PP.

Here, as shown in FIG. 3, of the transmitted light diffused by the screen 5, the direction angle of the transmitted light TL directed from the projection position PP to the light receiving position SP of the imaging device 6 is θ. This directional angle θ is defined as the angle between the normal line N at the projection position PP on the screen 5 and the transmitted light TL on the imaging device 6 side of the screen 5 . Also, here, for the sake of simplification of explanation, it is assumed that the reflected light RL and the transmitted light TL are all contained within the plane of the paper, and that there is no inclination in the depth direction of the plane of the paper.

Assuming that the screen 5 is isotropic, the intensity I _t of the transmitted light TL received by the imaging device 6 is a function f(Φ , .theta.) and the intensity _Ir of the reflected light RL, it is determined by the following formula (6).

The function _f (Φ, θ) is the ratio of the intensity _Ir of the reflected light RL to the intensity It of the transmitted light TL with respect to the incident angle Φ and the direction angle θ. determined by A state in which the transmitted light TL, which is part of the reflected light RL, is diffused within a range of a predetermined angle (that is, the directional angle θ of the transmitted light TL) is represented by this function f(Φ, θ). Hereinafter, f(Φ, θ) will be referred to as transmission characteristics of the screen 5 .

Next, examples of the transmission characteristics f(Φ, θ) of the screen 5 and features in each case will be described. 4A and 4B are diagrams showing examples of transmission characteristics f(Φ, θ) of the screen 5. FIG. In the following, the incident angle Φ is assumed to be 0[°] for simplification of explanation. In FIG. 4A, the value of the transmission characteristic f(Φ, θ) of the screen 5 does not change with the directional angle θ. Therefore, the intensity It of the transmitted light _TL is uniform regardless of the direction angle θ. On the other hand, in FIG. 4B, the value of the transmission characteristic f(Φ, θ) of the screen 5 changes depending on the direction angle θ, and the closer to θ=0 [°], the more the transmission characteristic f(Φ, θ) of the screen 5 The value of θ) is high, and the value of the transmission characteristic f(Φ, θ) of the screen 5 decreases as the distance from θ=0 [°] increases. This means that the intensity It of the transmitted light _TL is higher on the extension line of the reflected light RL, and the intensity It of the transmitted light _TL is lower on the extension line of the reflected light RL. When the energy of the transmitted and diffused light is equal at the projection position PP on the screen 5, considering the conservation of energy, as shown in FIG. As shown in FIG. 4B, when the light amount ratio is high only in a specific direction, the light amount ratio increases near the peak.

When a screen having the transmission characteristics f(Φ, θ) shown in FIG. 4A is used, transmitted light is diffused in all directions, so restrictions on the arrangement of the imaging device 6 are relaxed. On the other hand, since the energy of the incident light IL is diffused in directions other than the imaging device 6, the amount of light obtained by the imaging device 6 can be improved by using the transmission characteristics f(Φ, θ) shown in FIG. can also be disadvantageous.

On the other hand, when using the screen 5 having the transmission characteristics f(Φ, θ) of FIG. By arranging it, the intensity It of the transmitted light _TL incident on the imaging device 6 can be increased. When the screen 5 having the transmission characteristics _f (Φ, θ) shown in FIG. 4B is used, the direction in which the intensity It of the transmitted light TL increases is limited. In this case, when the reflection direction of the reflected light RL fluctuates during measurement and the projection position PP on the screen 5 fluctuates, the intensity fluctuation of the transmitted light TL tends to become more pronounced than in the case of FIG. be. A detailed description will be given below of how to deal with intensity fluctuations of the transmitted light TL when the screen 5 having the transmission characteristics f(Φ, θ) shown in FIG. 4B is used.

FIG. 5(a) shows the principle of the intensity variation of the transmitted light TL due to the variation of the reflection direction of the reflected light RL when the screen 5 having the transmission characteristics f(Φ, θ) of FIG. 4(b) is used. It is a diagram. In FIG. 5(a), the reflected light RL1 represents the reflected light when the surface of the flat plate-like object 3 is not tilted, like the surface 3a of the flat plate-like object 3 shown in FIG. 2(a). . Also, the reflected light RL2 is the reflected light when the surface of the flat plate-like object 3 is tilted, similar to the surface 3b of the flat plate-like object 3 shown in FIG. 2B. represent. That is, in FIG. 5A, the surface of the plate-like object 3 changes from the state of the surface 3a to the state of the surface 3b during measurement, and the reflection direction γ changes from the reflected light RL1 to the reflected light RL2. The intensity fluctuation of the transmitted light TL will be described.

In FIG. 5A, the reflected light RL1 is projected onto the projection position PP1 on the screen 5 and enters the imaging device 6 as the transmitted reflected light TL1. Since the projection position PP1 is a position where the reflected light RL1 is projected when the surface of the flat plate-like object 3 is not tilted, the projection position PP1 is hereinafter also referred to as a reference point. Further, in FIG. 5A, the reflected light RL2 is projected onto the projection position PP2 on the screen 5 and enters the imaging device 6 as the transmitted light TL2.

Here, as shown in FIG. 5A, when the Y axis is taken as a coordinate axis along the screen 5 and the projection position PP1 on the screen 5 is set as the origin, the position of the projection position PP2 on the screen 5 is Y = Δ.

FIG. 5(b) is a graph showing transmission characteristics f(Φ, θ) of the screen 5 for each of the reflected lights RL1 and RL2. For each of the reflected lights RL1 and RL2, the transmission characteristics f(Φ, θ) of the screen 5 are given as shown in the graph of FIG. 5(b). Further, as can be seen from FIG. 5A, the directional angle θ of the transmitted light TL1 is 0 [°], and the directional angle θ of the transmitted light TL2 is θ ₀ [°] (0<θ ₀ <90). . Therefore, as shown in FIG. 5B, the transmission characteristic f(Φ, Since the value of θ ₎ is halved, it can be seen that the intensity It of the transmitted light _TL2 is reduced to half the intensity It of the transmitted light TL1.

If the intensity It of the transmitted light _TL is too small, the transmitted light TL cannot be detected by the imaging device 6, and the projection position PP cannot be measured. From the above, in order to detect the surface defect of the plate-like object 3 using the screen 5 having the transmission characteristics f(Φ, θ) of FIG. Preferably, device 6 is placed at a specific location.

In principle, it is also possible to perform similar measurements by removing the screen 5, allowing the reflected light RL to enter directly into the light receiving element of the imaging device 6, and directly detecting variations in the reflected light RL. be. However, in this case, the relationship between the thickness of the reflected light RL and the size of the imaging device becomes a problem. In general, the surface of the plate-like object 3 has surface roughness, and the thickness of the line of the reflected light RL is greater than the thickness of the line at the inspection position IP. Due to the arrangement of the imaging device 6, the lower limit of the thickness of the line at the inspection position IP is about 0.1 [mm]. However, the thickness of the line of the reflected light RL is increased to a maximum of several millimeters depending on the surface roughness of the plate-like object 3 . Therefore, the size is about the same as the size of the image sensor, making measurement difficult. In such a case, it is conceivable to place a lens (not shown) in front of the imaging device 6 to reduce the thickness of the line of the reflected light RL. In this case, it is necessary to directly irradiate the lens with the reflected light RL. However, in the tilt measurement according to the present invention, the projection position PP of the reflected light RL may fluctuate by 50 [mm] or more depending on the design of the optical system. However, it is difficult to obtain and make such lenses. Also, if the imaging device 6 is placed close to the flat plate-like object 3, the line of the reflected light RL can be made thinner, but there is a possibility that the imaging device 6 and the flat plate-like object 3 come into contact with each other, which is not preferable. .

On the other hand, when the screen 5 having the transmission characteristics f(Φ, θ) is arranged, the optical system of the imaging device 6 is changed, that is, the lens is changed. Detection becomes possible. In this case, there is no need to directly irradiate the lens with the reflected light RL, so there is no need to pay particular attention to the diameter of the lens itself.

Based on the above description, the transmission characteristics f(Φ, θ) of the screen 5, the intensity of the reflected light RL from the plate-like object 3, the background brightness _Ib that is the brightness of the background on the screen 5, and the fluctuation of the projection position PP A method for calculating the condition of the arrangement of the imaging device 6, that is, the distance L between the screen 5 and the imaging device 6, which enables the detection of the transmitted light TL by the imaging device 6, will be described.

The background luminance _Ib is the luminance of a portion of the image of the screen 5 photographed by the imaging device 6, excluding the reflected light RL projected onto the projection position PP. The background luminance _Ib is caused by the dark current of the imaging device 6, that is, noise generated in an amplifier circuit for light-receiving element signals, ambient light entering from the periphery of the imaging device 6, and the like. When the imaging device 6 captures an image of the screen 5, if the brightness at the position of the image of the reflected light RL projected on the screen 5 is about the same as or smaller than the background brightness _Ib , the imaging device 6 determines the projection position. Identifying a PP can be difficult. As a result, it may become difficult to inspect defects by the surface defect detection apparatus 1 . Therefore, it is highly preferable to employ a surface defect detection apparatus or a surface defect detection method such that the brightness of the image of the reflected light RL projected on the screen 5 is sufficiently higher than the background brightness _Ib .

First, (A) the transmission characteristic f(Φ, θ) of the screen 5 is derived. Specific derivation methods include methods such as conducting experiments, estimating theoretically, and using product data.

Next, (B) the background luminance _Ib is derived so that the imaging device 6 can measure the projection position PP on the screen 5 . The background luminance _Ib is determined experimentally or theoretically. As one example of the method for measuring the background luminance _Ib , the surface of the screen 5 is photographed by the imaging device 6 in a state in which no light is emitted from the light source 4, and the luminance value of the obtained image is the background luminance _Ib . And it is sufficient. As another example of the method for measuring the background luminance _Ib , the light-receiving part of the image pickup device 6 is shielded to completely block light from entering the image, and the luminance value of the obtained image is calculated as the background luminance _Ib may be

Subsequently, (C) changes in the intensity of the reflected light RL, the incident angle Φ, the direction angle θ, the position Δ of the projection position PP on the screen 5, and the screen 5 and the distance L from the imaging device 6 will be organized. Since these relationships depend on the design of the optical system, the methodology cannot be generalized. In many cases, when the position of the projection position PP on the screen 5 is Y=Δ, Relational expressions between the intensity change of the reflected light RL, the incident angle Φ, the direction angle θ, the projection position coordinate Δ, and the distance L between the screen 5 and the imaging device 6 may be derived.

Finally, (D) from the relational expression derived in (C) above, the distance between the screen 5 and the imaging device 6 such that the intensity I _t of the transmitted light TL is greater than or equal to the background luminance I _b determined in (B) above Find the condition of L. That is, using the relational expression of the intensity change rate k (Δ) of the reflected light RL, the incident angle Φ (Δ), and the direction angle θ (Δ, L), the screen 5 that satisfies the following inequality (7) and the imaging A range of distance L from the device 6 is obtained. However, _I0 is the light amount of the incident light IL.

Here, the intensity change rate k is the ratio of the intensity of the reflected light RL to the intensity of the incident light IL, and the relationship of the following formula (8) is established.

Since the intensity change rate k depends on the incident angle of the incident light IL, it is a function of the angle α of the inclination of the surface of the plate-like object 3, but the angle α can be represented by the position Δ according to the above equation (5). , the intensity change rate k can also be described as a function of the position Δ.

At this time, the photographing position coordinate Δ may change depending on the surface inclination of the object to be measured. In that case, the screen 5 and the imaging device 6 and the distance L is set.

Using the example shown in FIG. 6 and the screen 5 having the transmission characteristics f(Φ, θ) shown in FIG. FIG. 6 is a diagram showing an example of changes in physical quantities accompanying changes in the surface inclination of the object to be measured.

In FIG. 6, the optical path of the reflected light RL1 reflected at the inspection position IP on the surface 3a of the flat plate-shaped object 3 with no inclination and the inspection position IP on the surface 3b of the flat plate-shaped object 3 inclined by an angle α are shown. and the optical path of the reflected light RL2. The projection position PP2 of the reflected light RL2 on the screen 5 varies with respect to the projection position PP1 of the reflected light RL1 on the screen 5 due to the change in the reflection direction of the reflected light RL2 with respect to the reflected light RL1.

The surface 3a and the surface 3b of the plate-like object 3 cause reflection at different angles of incidence and reflection. When the surface 3b of the plate-like object 3 is inclined at an angle α with respect to the surface 3a of the plate-like object 3, the incident angle of the incident light IL and the reflection angle of the reflected light RL2 at the inspection position IP on the surface 3b of the plate-like object 3 are both , with respect to the incident angle of the incident light IL and the reflection angle of the reflected light RL1 at the inspection position IP on the surface 3a of the plate-like object 3 by an angle α. Therefore, the change in the intensity of the reflected light RL based on the physical model is obtained experimentally or theoretically. In the case of FIG. 6, since the inclination angle α of the surface 3b of the plate-like object 3 is about several millimeters [rad], k(Δ) is considered to take a constant value. Therefore, regardless of Δ, the intensity _Ir of the reflected light RL takes a constant value.

Next, the incident angle Φ of the reflected light RL2 with respect to the screen 5 shown in FIG. 6 changes as the reflection direction of the reflected light RL2 changes. Here, as described with reference to FIG. 2(a), when the surface 3b is inclined at an angle α with respect to the surface 3a of the plate-like object 3, the reflection direction of the reflected light RL2 is the reflected light RL1. changes by an angle 2α with respect to the reflection direction of . Therefore, the incident angle Φ of the reflected light RL2 is Φ=2α. Since the angle α is extremely small, regardless of the position Δ on the screen 5, it is approximated that Φ=0 [°] and the transmission characteristic f(Φ, θ) does not change.

Next, the directional angle θ of the transmitted light TL changes depending on the position Δ on the screen 5, and using the distance L between the screen 5 and the imaging device 6, there is a relationship of θ=arctan (Δ/L).

In summary, in the case of FIG. 6, k(Δ) is constant, Φ(Δ)≈0, and θ(Δ, L)=arctan(Δ/L). The transmission characteristics f(Φ, θ) of the screen 5 can be represented by a uniform distribution that does not depend on the direction angle θ, like the transmission characteristics f(Φ, θ) in FIG. 4A when Φ=0 [°]. Then, the above formula (7) can be rewritten as the following formula (9). However, in the following formula (9), C represents a value (constant value) taken by a uniform distribution.

Since the above formula (9) does not depend on Δ, if the intensity I _r of the reflected light RL and the constant value C of the uniform distribution satisfy the above formula (9), the distance L The amount of reflected light can be captured regardless of the However, as a precondition, it should be noted that the inclination angle α of the surface 3b is about several millimeters [rad].

From the above, the transmission characteristics f (Φ, _θ ) of the screen 5 shown in FIG. From _Ib , the range of the distance L between the screen 5 and the imaging device 6 can be determined.

Next, using the example shown in FIG. 6 and the screen 5 having the transmission characteristics f(Φ, θ) shown in FIG.

First, consider the intensity of the reflected light RL. As described in paragraph [0060] above, k(Δ)=1, and it is considered that there is almost no variation in the intensity _Ir of the reflected light RL.

Next, the transmission characteristic f(Φ, θ) will be considered. As described in paragraph [0061] above, regardless of the position Δ on the screen 5, the transmission characteristic f(Φ, θ) is the transmission characteristic f(0 [° ], θ).

Next, the directional angle θ of the transmitted light TL will be considered. As described in paragraph [0062] above, there is a relationship θ=arctan(Δ/L).

In summary, in the case of FIG. 6, k(Δ) is constant, Φ(Δ)≈0, and θ(Δ, L)=arctan(Δ/L). Assuming that the transmission characteristic f(Φ, θ) of the screen 5 can be represented by a Gaussian distribution of the direction angle θ at Φ=0[°], the above formula (7) can be rewritten as the following formula (10). . However, in the following formula (10), A and σ are parameters of Gaussian distribution expressing transmission characteristics.

Solving the above equation (10) for L yields the following equation (11).

From the above, the transmission characteristics f (Φ, _θ ) of the screen 5 shown in FIG. From _Ib , the range of the distance L between the screen 5 and the imaging device 6 can be determined.

It is also possible to apply a similar study to the plate thickness variation of the plate-like object 3 .

FIG. 7 shows a case where the plate thickness of the plate-like object 3 varies. It shows the optical path of the reflected light RL2 reflected at the inspection position IP2 on the surface 3b of the plate-like object 3 thickened by Δh.

When the screen 5 having the transmission characteristics f(Φ, θ) shown in FIG. 4(a) is used, an example of changes in physical quantities due to plate thickness variations shown in FIG. 7 will be described.

By increasing the plate thickness of the flat plate-like object 3 by Δh, the incident light IL on the same optical path is positioned at the inspection position IP2 on the surface 3b of the flat plate-like object 3 more than the inspection position IP1 on the surface 3a of the flat plate-like object 3. is displaced by a distance x toward the light source 4 side. Therefore, the projection position PP2 of the reflected light RL2 on the screen 5 fluctuates with respect to the projection position PP1 of the reflected light RL1 on the screen 5 . Here, as shown in FIG. 7, when the Y axis is taken as a coordinate axis along the screen 5 and the projection position PP1 of the reflected light RL1 on the screen 5 is set as the origin, the projection position of the reflected light RL2 on the screen 5 is Let the position of PP2 be Y=Δ.

At this time, the intensity change rate k(Δ), the incident angle Φ(Δ), and the direction angle θ(Δ, L) of the reflected light RL2 are considered as follows.

First, the intensity _Ir of the reflected light RL is constant because the incident angle and the reflection angle do not change. That is, k(Δ) is constant.

Next, the incident angle Φ of the reflected light RL with respect to the screen 5 is constant regardless of changes in plate thickness. Therefore, regardless of the position Δ on the screen 5, approximating Φ=0[°], it is approximated that the transmission characteristic f(Φ, θ) of the screen 5 does not change.

Next, the directional angle .theta. changes with the position .DELTA.

In summary, in the case of FIG. 7, k(Δ) is constant, Φ(Δ)=0, and θ(Δ, L)=arctan(Δ/L). Since this is the same condition as in the case of FIG. 6, the range of the distance L between the screen 5 and the imaging device 6 can be obtained by the above formula (9).

When using the screen 5 having the transmission characteristics f (Φ, θ) of FIG. 4B, the same conditions as in FIG. That is, since k(Δ) is constant, Φ(Δ)=0, and θ(Δ, L)=arctan(Δ/L) are obtained, the range of the distance L between the screen 5 and the imaging device 6 is It can be obtained by Equation (11).

If theoretical analysis is difficult, the range of the distance L between the screen 5 and the imaging device 6 may be obtained by performing a simulation using the above formula (7) using a computer or the like.

Also, in order to simplify the explanation, the above discussion was made on the premise that all optical paths are included in a two-dimensional plane. is also possible.

The above consideration is not only for determining the distance L between the screen 5 and the imaging device 6, but also when the distance L between the screen 5 and the imaging device 6 and the range of the coordinate Δ of the projection position PP are obtained, It can also be used to estimate the number of imaging devices 6 required to capture the transmitted light TL.

FIG. 8 is a schematic diagram showing a schematic configuration of another example of the surface defect detection device 1A according to the embodiment. A surface defect detection apparatus 1A shown in FIG. 8 is provided with two imaging devices 6a and 6b and an arithmetic unit 9 in contrast to the surface defect detection apparatus 1 shown in FIG. As will be described later, the calculation unit 9 is a calculation unit that integrates the projection positions PP measured by the two imaging devices 6a and 6b and calculates information regarding the inclination. Information about the inclination calculated by the calculation unit 9 is transmitted to the computer 7 . The imaging device 6a receives transmitted light TLa that has passed through the screen 5 and has been diffused, and the imaging device 6b has received transmitted light TLb that has passed through the screen 5 and has been diffused.

According to the configuration of the present invention, the range in which the coordinates Δ of the projection position PP fluctuate during measurement fluctuates according to the inclination angle α of the surface of the object to be measured. This can be explained based on the following formula (12) obtained by modifying the above formula (3).

According to the above formula (12), the coordinate Δ of the projection position PP during measurement is the slight inclination angle α on the surface of the plate-like object 3, the optical path length D of the reflected light RL1 from the inspection position IP to the screen 5, It is determined by the angle _Ψ0 between the reflected light RL1 and the screen 5. The only amount that changes during measurement is the slight tilt angle α, and the optical path length D and the angle _ψ0 are determined at the time of design. Therefore, it is assumed that the coordinate Δ of the projection position PP fluctuates in accordance with the fluctuation of the slight inclination angle α on the surface of the plate-like object 3 within the range of α1≦α≦α2, and the range is Δ1′≦Δ≦Δ2′. .

On the other hand, the measurable range of each imaging device 6 can be obtained by solving the above formula (7) for Δ instead of L, the transmission characteristic f(Φ, θ) of the screen 5, the intensity I _r of the reflected light RL, the screen 5 and the imaging device 6, and the background luminance _Ib , the range Δ1≦Δ≦Δ2 of the coordinates Δ of the measurable projection position PP can be calculated.

For example, solving Equation (10) for Δ yields Equation (13) below.

The above formula (13) is the transmission characteristic f (Φ, _θ ) of the screen 5 shown in FIG. _b shows that the range of the position Δ of the projection position PP on the screen 5 that can be measured by the imaging device 6 can be determined.

On the other hand, FIG. 9 is a diagram showing the measurable range of the projection position PP on the screen 5 by each of the two imaging devices 6a and 6b. The region F1 of the projection position PP on the screen 5 measurable by the lower imaging device 6a of the two imaging devices 6a and 6b included in the surface defect detection apparatus 1A is the Y-axis direction along the screen 5. , where Δ11 is the lower end position and Δ12 is the upper end position, the range is Δ11≦Y≦Δ12. Further, the region F2 of the projection position PP on the screen 5 measurable by the image pickup device 6b located above the image pickup device 6a has a lower end position of Δ21 and an upper end position of Δ22 in the Y axis direction. It is within the range of Y≦Δ22.

At this time, as shown in FIG. 9, if Δ21<Δ12, the area F1 of the imaging device 6a and the area F2 of the imaging device 6b have an overlapping area F3 that overlaps with each other. At this time, if the range of variation Δ1′≦Δ≦Δ2′ of the coordinate Δ of the projection position PP on the screen 5 during measurement is included in the range of Δ11≦Y≦Δ22, the two imaging devices At least one of 6a and 6b enables measurement of the projection position PP.

Specifically, information on whether or not measurement is possible by the imaging devices 6a and 6b and position information on the measured projection position PP are transmitted from the imaging devices 6a and 6b to the calculation unit 9 . Then, when the projection position PP can be measured by only one of the imaging device 6a and the imaging device 6b, the calculation unit 9 performs processing for calculating the inclination of the surface of the plate-like object 3 based on the measured value. . Further, when the projection position PP can be measured by both imaging devices 6a and 6b, the positions of the measurement values of both the imaging devices 6a and 6b are aligned to determine the position of the projection position PP. The calculation unit 9 performs processing for calculating the inclination of the surface of the plate-like object 3 based on the determined measured value. Further, when the projection position PP cannot be measured by either of the imaging devices 6a and 6b, the calculation unit 9 performs a process of disabling the measurement of the projection position PP.

Note that when the range of variation Δ1′≦Δ≦Δ2′ of the coordinate Δ of the projection position PP on the screen 5 being measured is not included in the range of Δ11≦Y≦Δ22, three or more imaging devices 6 is installed to expand the measurement range of the projection position PP. That is, in FIG. 8, the case where the surface defect detection apparatus 1A includes two imaging devices 6a and 6b has been described. By arranging the imaging devices 6 so as to overlap the measurable regions of , the measurement range of the projection position PP can be expanded.

[Example 1]
This embodiment shows an example of determining the allowable range of the light receiving position SP of the imaging device 6 with respect to the fluctuation of the projection position PP on the screen 5 by using the present invention. In the following experiment, the intensity variation of the transmitted light TL with respect to the plate thickness variation of the plate-like object 3 was calculated.

FIG. 10 is a schematic diagram showing a schematic configuration of an experimental apparatus used in this example. FIG. 11 is a diagram showing the details of the arrangement from the screen 5 to the imaging device 6 in the experimental device. In this embodiment, a steel plate piece cut into a size of 5 [mm] or less in thickness and about 300 [mm] on a side is used as the flat plate-like object 3 . Then, the plate-like object 3 was placed on the linear stage 10, and the plate-like object 3 was moved in the direction of arrow B in FIG. Then, while moving the flat plate-like object 3 in the direction of arrow B, the incident light IL from the light source 4 is reflected at the inspection position IP on the surface of the flat plate-like object 3, and the reflected light RL is transmitted through the screen 5 and diffused. The transmitted light TL is received by the imaging device 6 . As the screen 5, a diffusion plate having transmission characteristics f(Φ, θ) shown in FIG. 4B was used. A monochrome area camera was used as the imaging device 6 . In addition, the reflected light RL is vertically incident on the screen 5, the distance L between the screen 5 and the imaging device 6 is set to L=300 [mm], and the screen 5 and the imaging device 6 are arranged so as to face each other. bottom. The intensity I _t of the transmitted light TL was evaluated using the luminance value I _c of the image obtained by photographing the screen 5 with the imaging device 6 .

In this embodiment, the thickness variation of the steel plate is simulated, and the height of the upper surface of the plate-like object 3, which is the surface on which the incident light IL is incident, is changed at two levels, and the two projection positions PP1, PP1, and PP1 on the screen 5 are changed. PP2 was varied up and down in the Y-axis direction along the screen 5 . As shown in FIG. 11, when the Y axis is taken as a coordinate axis along the screen 5 and the projection position PP1 of the reflected light RL1 on the screen 5 is set as the origin, the projection position of the reflected light RL2 on the screen 5 is Let the position of PP2 be Y=Δ. After that, the screen 5 was photographed using the imaging device 6, and the image projected on the screen 5 was photographed. Finally, it was investigated how the _luminance value _Ic of the image captured by the imaging device 6 (corresponding to the intensity It of the transmitted light TL) changes with respect to the height of the upper surface of the plate-like object 3. .

Subsequently, the intensity change of the transmitted light TL is calculated based on the above formula (7). FIG. 12 is a diagram showing transmission characteristics f(Φ, θ) of the screen 5 used in the experiment of this embodiment. However, Φ=0 [°].

FIG. 12 shows the transmission characteristics f (Φ=0[°], θ) of the screen 5 used. The transmission characteristic f (Φ=0 [°], θ) of the screen 5 is represented by the following formula (14), and is a normal distribution with the direction angle θ centered at 0 [°] and the full width at half maximum of 30 [°] form. However, A=1 and σ=18.05.

Next, the relationship between the height of the surface of the plate-like object 3 and the position Δ of the projection position PP is derived according to the method described in the above embodiment.

Even if the thickness of the plate-like object 3 varies, the incident angles Φ of the reflected light RL1 and the reflected light RL2 on the screen 5 do not vary. It is considered that the intensities of RL1 and RL2 do not change. Note that the influence of light intensity fluctuations of the reflected lights RL1 and RL2 due to displacement of the inspection position IP to the downstream side and the upstream side in the movement direction of the flat plate-like object 3 in FIG. 10 was ignored. Also, the incident angle Φ of the reflected light beams RL1 and RL2 to the screen 5 never changes, and is Φ=0[°]. Also, the directional angle θ is calculated from the position Δ of the projection position PP on the screen 5 and the positional relationship with the imaging device 6 . From FIG. 11, θ(Δ, L)=arctan(Δ/L).

From the above, it can be seen that the experimental conditions in this example match the conditions described in the above-described embodiment. Therefore, the intensity I _t of the transmitted light TL is It matches the left side of the above formula (10).

Next, while changing the height of the plate-like object 3, the projection position Δ of the reflected light RL and the luminance value _Ic measured by the imaging device 6 were measured to investigate the relationship between the two. When the height of the plate-like object 3 was changed, the luminance value _Ic became the largest when Δ=0 [mm], and the value was _Ic0 =16. Hereinafter, the luminance value is evaluated as a relative value obtained by dividing the measured luminance value _Ic by the _Ic0 . In this experiment, the lower limit _IcL of the luminance value required to detect the reflected light RL was 12. The intensity It of the transmitted light TL at this time is equal to the background _{luminance Ib} .

Since the luminance value _Ic and the intensity It of the transmitted light _TL are considered to be proportional, the following formula (15) holds.

By transforming the above formula (15), the following formulas (16) and (17) are obtained.

From Equation (16) above, it can be seen that the luminance relative value I _c /I _c0 matches the transmission characteristic f(Φ, θ) of the screen 5 .

Also, by substituting the above expression (17) into the above expression (13), the conditional expression of the following expression (18) that is satisfied by the measurable Δ can be calculated based on the luminance value.

13A and 13B are diagrams showing experimental results according to Example 1 of the present invention. FIG. FIG. 13 shows experimental results representing the relationship between the position of the projection position PP and the relative luminance value _Ic / _Ic0 . In FIG. 13, the solid line shows the change in the relative luminance value I _c /I _c0 with respect to the projection position Δ calculated using the above equation (11), and the relative luminance value I c with respect to the projection position Δ obtained by experiment. A plot of _c /I _c0 is indicated by a closed circle (●). From FIG. 13, both have the same tendency, and the validity of the above formula (14) has been confirmed.

Further, when the measurable range of the coordinate Δ of the projection position PP2 was obtained based on the above formula (18), |Δ|<51.2 [mm]. From this, it is calculated that the projection position PP2 cannot be measured if it deviates from the front of the camera by 51.2 [mm] or more. The range is indicated by a dotted line in FIG. Actually, the measurement point A shown in FIG.

As described above, in the surface defect detection apparatus 1 according to the embodiment, it is possible to calculate the range of Δ for measuring the surface inclination by the analysis based on the above formula (10).

[Example 2]
Next, the images obtained when the measurement was performed within the allowable angle range obtained in Example 1 and when the measurement was not performed were compared.

FIG. 10 is a schematic diagram showing a schematic configuration of an experimental apparatus used in this example. FIG. 11 is a diagram showing the details of the arrangement from the screen 5 to the imaging device 6 in the experimental device. In this embodiment, a steel plate piece cut into a size of 5 [mm] or less in thickness and about 300 [mm] on a side is used as the flat plate-like object 3 . As the steel plate piece, a steel plate piece having a bent surface was used. Then, the flat plate-like object 3 was placed on the linear stage 10, and the flat plate-like object 3 was moved in the direction of arrow B in FIG. Then, while moving the plate-like object 3 in the direction of arrow B, the incident light IL from the light source 4 is reflected at the inspection position IP on the surface of the plate-like object 3, and the reflected light RL is transmitted through the screen 5 and diffused. The transmitted light TL is received by the imaging device 6 . As the screen 5, a diffusion plate having transmission characteristics f(Φ, θ) shown in FIG. 4B was used. A monochrome area camera was used as the imaging device 6 . In addition, the reflected light RL is vertically incident on the screen 5, the distance L between the screen 5 and the imaging device 6 is set to L=300 [mm], and the screen 5 and the imaging device 6 are arranged so as to face each other. bottom.

In this embodiment, the thickness variation of the steel plate is simulated, and the height of the upper surface of the plate-like object 3, which is the surface on which the incident light IL is incident, is changed in multiple ways, and the projection position PP2 on the screen 5 is shifted to the screen 5. It was changed up and down in the Y-axis direction along. As shown in FIG. 11, when the Y axis is taken as a coordinate axis along the screen 5 and the projection position PP1 of the reflected light RL1 on the screen 5 is set as the origin, the projection position of the reflected light RL2 on the screen 5 is Let the position of PP2 be Y=Δ. After that, the screen 5 was photographed using the imaging device 6, and the image projected on the screen 5 was photographed. Finally, the angle α of the plate-like object 3 was calculated based on the above formula (5), and it was investigated how the calculated result of the angle α would change with the change in the position Y=Δ of the projection position PP2.

FIG. 14 is a diagram showing a first example of experimental results according to Example 2 of the present invention. FIG. 14 shows the result of surface inclination measurement, which is the experimental result of this example. FIG. 14 shows the results for three types of Δ values. The gradation represents the measured surface inclination, and the vertical direction in the drawing corresponds to the moving direction B of the linear stage. Black means missing data due to inability to measure reflected light. As can be seen from FIG. 14, in the case of FIGS. 14(a) and 14(b), the condition |Δ|<51.2 [mm] obtained by the above formula (14) is satisfied. is not seen, and it can be seen that the surface inclination is measured. On the other hand, in the case of FIG. 14(c), a value close to the boundary of the condition according to the above formula (14), that is, |Δ|≈51.2 [mm], causes data omission in many areas. It can be seen that

From the above, it was found that favorable measurement results were obtained within the conditions of Δ obtained by the analysis based on the above formula (10), but measurement results with missing data were obtained outside the conditions of Δ. rice field.

Next, a similar experiment was conducted using a diffusion plate having the transmission characteristics f(Φ, θ) shown in FIG. 4A as the screen 5 . According to the above formula (9), in this case, the propriety of measurement is determined by the constant value C of the transmission characteristics of the screen, regardless of the projection position Δ. A light amount ratio investigation using a power meter revealed that the constant value of transmission characteristics of the screen used in the experiment was C=0.35.

FIG. 15 is a diagram showing a second example of experimental results according to Example 2 of the present invention. FIG. 15 shows the result of the surface tilt measurement, which is the experimental result of this example. FIGS. 15(a), 15(b), and 15(c) show measurement results for two types of Δ. In FIGS. 15(a) and 15(b), the experiment was conducted by setting the amount of incident light IL to a standard value, and in FIGS. 15(c) and 15(d), the amount of incident light IL was set to Experiments were performed with settings twice the standard value. The gradation represents the measured surface inclination, and the vertical direction in the figure corresponds to the moving direction B of the linear stage. Black means missing data due to inability to measure reflected light. As can be seen from FIGS. 15(a) and 15(b), the degree of data omission did not change even when the value of Δ was changed. In addition, in FIGS. 15(c) and 15(d), the area of missing data is reduced, and the amount of received light is below the background luminance _Ib regardless of the change in Δ. not done. In other words, when the amount of incident light IL is sufficient to prevent data omission, stable measurement is possible regardless of the value of Δ.

As described above, in the surface defect detection apparatus 1 according to the embodiment, it is possible to calculate the range of Δ for measuring the surface inclination by the analysis based on the above formula (7).

As described above, in the surface defect detection apparatuses 1 and 1A and the surface defect detection method according to the embodiments, the projection position PP of the reflected light RL on the screen 5 is used to determine the inspection position IP of the incident light IL on the plate-like object 3. , and acquires the tilt information for each position of the plate-like object 3 . Reflected light RL from the plate-like object 3 enters the imaging device 6 through a translucent screen 5 . The transmitted light TL that has passed through the screen 5 is incident on the imaging device 6 while being dispersed within a limited angular range centering on the projection position PP. Therefore, the energy of the transmitted light TL can be concentrated on the imaging device 6 by using the translucent screen 5 having the above-described features, as compared with an opaque screen that dissipates the energy of the reflected light RL in all directions. , highly efficient detection of the reflected light RL is possible.

Further, the present invention may be applied as an inspection device constituting steel plate manufacturing equipment. That is, the surface defect detection apparatus 1, 1A according to the present invention may be used to inspect the surface of a steel plate manufactured by known or existing manufacturing equipment.

Also, the present invention may be applied as an inspection step included in the steel plate manufacturing method. That is, the surface of a steel plate manufactured in a known or existing manufacturing step may be inspected. According to such a steel plate manufacturing facility and a steel plate manufacturing method, a steel plate can be manufactured with a high yield.

Further, the present invention may be applied to a steel plate quality control method, and the quality control of the steel plate may be performed by inspecting the surface of the steel plate. Specifically, in the present invention, the presence or absence of surface defects in the steel sheet can be determined in the detection step, and the quality control of the steel sheet can be performed from the determination result obtained in the inspection step. In the inspection step, the present invention is used to inspect the surface of the steel sheet to obtain results on the presence or absence of surface defects on the steel sheet. In the subsequent quality control step, based on the results of the inspection step regarding the presence or absence of surface defects in the steel sheet, it is determined whether the manufactured steel sheet meets the pre-specified criteria, and the quality of the steel sheet is controlled. do. According to such a steel plate quality control method, a high-quality steel plate can be provided.

1, 1A Surface defect detection device 2 Transport roll 3 Flat object 4 Light source 5 Screens 6, 6a, 6b Imaging device 7 Computer 8 Display device 9 Operation unit 10 Linear stage IL Incident light IP Inspection position N Normal lines RL, RL1, RL2 Reflected light SP Light receiving position TL, TL1, TL2 Transmitted light PP, PP1, PP2 Projection position

Claims (5)

a light source that irradiates the surface of an object with light;
a screen on which reflected light reflected by the surface of the object is projected;
tilt detection means for detecting information about the tilt of the surface of the object from the projection position where the reflected light from the object is projected onto the screen;
defect detection means for detecting uneven defects on the surface of the object from the information about the inclination detected by the inclination detection means;
A surface defect detection device comprising
The screen has a transparency for transmitting the projected reflected light and a transmission characteristic for diffusing the transmitted light within a predetermined angle range,
The tilt detection means includes projection position detection means for receiving the transmitted light diffused within the predetermined angle range and measuring the projection position ,
The tilt detection means has an imaging device that measures the position of the reflected light projected on the screen,
The imaging device is
It is arranged at a position calculated from the transmission characteristics of the screen, the intensity of the reflected light from the object, the range in which the projection position fluctuates on the screen, and the background brightness on the screen. and a surface defect detection device. an irradiation step of irradiating the surface of the object with light;
a tilt detection step of detecting information about the tilt of the surface of the object from a projection position where the reflected light reflected by the surface of the object is projected onto a screen;
a defect detection step of detecting an uneven defect on the surface of the object from the information about the tilt detected by the tilt detection step;
A surface defect detection method comprising:
The screen has a transparency for transmitting the projected reflected light and a transmission characteristic for diffusing the transmitted light within a predetermined angle range,
In the tilt detection step, the transmitted light diffused within the predetermined angle range is received to measure the projection position;
an imaging device for measuring the position of the reflected light projected onto the screen, the transmission characteristics of the screen, the intensity of the reflected light from the object, the range in which the projection position fluctuates on the screen, and the screen A surface defect detection method characterized by arranging at a position calculated from background luminance in and . a steel plate manufacturing step;
an inspection step of inspecting the surface of the steel plate manufactured in the manufacturing step by the surface defect detection method according to claim 2 ;
A method for manufacturing a steel plate, comprising: an inspection step of inspecting the surface of the steel sheet by the surface defect detection method according to claim 2 ;
A quality control step of performing quality control of the steel plate from the inspection results obtained by the inspection step;
A steel plate quality control method comprising: a manufacturing facility for manufacturing a steel plate;
The surface defect detection device according to claim 1, which inspects the surface of the steel plate manufactured by the manufacturing equipment;
A steel plate manufacturing facility comprising:

Images