JPH11295240A - Method and equipment for inspecting surface flaw - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect a pattern-like scab detect having no conspicuous irregularities surely regardless of surface unevenness. SOLUTION: The surface flaw inspection equipment comprises a light source 22 for illuminating a plane 21 to be inspected having an unevenness on the surface with illumination light polarized linearly in the direction parallel with or normal to the plane 21, a first light receiving means 27 receiving the component of the regular reflected light of illumination light polarized in same direction as the illumination light and having a light receiving angle from the plane 21 being set at the Brewster's angle of a substance causing unevenness, a second light receiving means 28 receiving the component of the regular reflected light of illumination light polarized orthogonally to the illumination light and having a light receiving angle from the plane 21 being set at the Brewster's angle of a substance causing unevenness, and a section 31 for making a decision whether a flaw is present or not on the plane 21 based on both components received by the first and second light receiving means.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface flaw inspection apparatus and a surface flaw inspection method for irradiating a surface to be inspected such as a thin steel sheet surface with light to optically detect surface flaws on the surface to be inspected.

[0002]

2. Description of the Related Art Surface flaw inspection for optically detecting surface flaws present on a surface to be inspected by irradiating light to a surface to be inspected such as a thin steel sheet surface and analyzing reflected light from the surface to be inspected. Conventionally, various methods have been proposed and implemented.

For example, light is incident on the surface of a subject,
Japanese Patent Application Laid-Open No. 58-204353 proposes a surface flaw detection method for a metal object in which specular reflected light and diffuse reflected light from the surface of an object are detected by a camera. In this surface flaw detection method, light is incident on the surface of the subject at an angle of 35 ° to 75 °, and reflected light from the surface of the subject is reflected at an angle within 20 ° from the specular reflection direction and the incident direction or the specular reflection direction. Light is received by two cameras installed in different directions. Then, the light reception signals of the two cameras are compared, and, for example, the logical sum of the two is obtained. Then, only when two cameras simultaneously detect abnormal values, the abnormal values are regarded as flaws, thereby realizing a surface flaw detection method that is not affected by noise.

A method for inspecting a flaw on the surface of an object by receiving backscattered light from the object is disclosed in Japanese Patent Laid-Open No. 60-228943.
No. 1993. In this flaw inspection method,
Light is incident on the stainless steel plate at a large angle of incidence, and reflected light returning to the incident side, that is, backscattered light is detected, thereby detecting a barbed flaw on the surface of the stainless steel plate.

Further, Japanese Patent Application Laid-Open No. 8-17867 proposes a flat steel hot flaw detector which detects a plurality of backscattered reflected lights. This flat steel hot flaw detector detects a scratch on a hot-rolled flat steel. In this flaw detection device, the angle of the flaw slope of the flaw is 10 to 40 °, and a plurality of cameras are arranged in the backward diffuse reflection direction so as to cover all the specularly reflected light from the flaw slope in this range. Have been.

Further, Japanese Patent Application Laid-Open No. 58-204353 and
In Japanese Patent Application Laid-Open No. 8-178867, since the optical axes of a plurality of cameras are not common and the emission angles are different, the field of view size of the corresponding pixels of the two images obtained is different, and the fluttering of the inspected surface and the thickness variation of the object There is a problem in that if there is a distance change due to, a positional shift occurs in the visual field. Particularly, in Japanese Patent Application Laid-Open No. 58-204353, the problem is great because it is required that two cameras take a logical sum for the same field of view.

A surface measuring apparatus using polarized light has been proposed in Japanese Patent Application Laid-Open Nos. 57-166533 and 9-166552. In the measuring device proposed in Japanese Patent Application Laid-Open No. 57-166533, polarized light in a direction of 45 ° is incident on a measuring object and reflected light is received by a polarizing camera. In a polarizing camera, the reflected light is split into three using a beam splitter inside the camera, and the reflected light is received through polarizing filters having different azimuth angles. A technique is disclosed in which three signals from a polarization camera are displayed on a monitor by signal processing similar to that of a color TV system, and the polarization state is visualized. This technology uses the technology of ellipsometry,
The light source is desirably parallel light, for example, laser light is used.

Further, in the surface inspection apparatus proposed in Japanese Patent Application Laid-Open No. Hei 9-165552, similarly to the technology described in Japanese Patent Application Laid-Open No. 57-166533, the surface of a steel sheet is inspected for defects using ellipsometry. I have.

Japanese Patent Application Laid-Open No. Sho 53-23678 proposes a surface inspection apparatus for measuring the color of a printed surface or a painted surface without being affected by a varnish applied to the surface. In this surface inspection apparatus, the incident light on the object is p-polarized light having an electric field parallel to the incident surface, and the incident angle of the incident light on the object is set as the Brewster angle of the object.

When the incident angle is set to the Brewster angle, the reflected light does not include a polarized light component (p-polarized light) parallel to the incident surface. Therefore, when the incident light is p-polarized light, the reflected light becomes zero. Therefore, by setting the incident angle to the Brewster angle of the varnish, the glossy reflection on the surface of the varnish applied to the object to be measured is eliminated, and the difference in color between the painted surface and the printed surface under the varnish is reduced. Inspection is possible.

[0011]

However, each of the measuring techniques proposed in each of the above-mentioned publications detects a flaw having remarkable unevenness or detects a flaw having a foreign substance such as an oxide film. Therefore, it is difficult to reliably capture all flaws with respect to pattern-shaped scab defects and the like having no noticeable unevenness.

For example, the flaw detection method disclosed in Japanese Patent Application Laid-Open No. 58-204353 has two cameras that receive specularly reflected light and scattered reflected light. The purpose of the method is to detect detection signals from the two cameras. This is to remove the influence of noise due to OR. Therefore, flaws having remarkable unevenness, that is, flaws having cracks, digging, and curling up on the surface are applicable because both cameras can detect the flaw signal. However, in the case of a flaw such as a pattern-shaped scab defect having no noticeable unevenness such that only one of the cameras can capture the flaw signal, it is not possible to detect all the flaws.

Further, the surface condition inspection method disclosed in Japanese Patent Application Laid-Open No. 60-228943 is directed to a raised barbed flaw that has become apparent on a stainless steel plate having a small surface roughness. Therefore, it is not possible to apply a flaw having no raised portion that has not been exposed or a flaw-free part to a steel plate having a rough surface that reflects light returning to the incident side.

The flat steel hot flaw detector disclosed in Japanese Patent Application Laid-Open No. 8-17867 is intended for scratches and does not have remarkable unevenness because it is based on catching specularly reflected light on the flaw slope. In the case of a flaw such as a patterned scab, there are some which cannot be caught by the backscattered reflected light, and there has been a problem that a detection leak occurs.

Further, the measuring device of Japanese Patent Application Laid-Open No. 57-166533 and the surface inspection device of Japanese Patent Application Laid-Open No. 9-166552 use ellipsometry technology. And "uneven physical property values" can be detected. However, even if the flaw originally has a property value different from that of the base material portion, such as a surface-treated steel sheet, for an object covered with a material having the same property value from above, However, there is a problem that the effectiveness is reduced.

In each of the above-mentioned prior arts, a thin film adheres to the surface and the unevenness is regarded as a pattern-like scab defect for an inspection object in which the presence or absence of the thin film is observed as unevenness. There was a problem that it was detected by mistake.

When the presence of surface unevenness is not significant in appearance and the degree of unevenness is small, the presence of unevenness does not affect the performance of the steel sheet at all, and the unevenness itself is harmless. However, the surface flaw inspection apparatus is erroneously recognized as the above-mentioned pattern-shaped scab defect, and is overdetected.

In particular, when the surface coating is incomplete and minute unevenness is generated over the entire surface to be inspected, the number of unevennesses generated is very large. There is a problem that the processing capability cannot follow the unevenness detection speed.

The above-described surface inspection apparatus disclosed in Japanese Patent Application Laid-Open No. 53-23678 is directed to an apparatus having a film adhered to the surface, but receives reflected light only in one direction of the regular reflection direction. Therefore, when this surface inspection apparatus is used to detect a defect having no noticeable unevenness such as a patterned barbed defect on a steel plate and having almost no difference in color, all the defects are captured. It is not possible.

In a surface inspection apparatus to be incorporated in a product quality inspection line, it is an absolute condition that there is no omission of flaw detection from the viewpoint of quality assurance of a manufactured product. However, a surface flaw inspection apparatus for inspecting even a surface-treated steel sheet or the like has not been put to practical use.

The present invention has been made in view of such circumstances, and by setting the incident angle of the p-polarized illumination light and the light reception angle of the specularly reflected light using the Brewster angle, the object of the present invention is improved. A pattern that can accurately detect the specular reflection component and the specular diffuse reflection component contained in the specular reflection light from the inspection surface, and has no noticeable unevenness such as surface cracks, gouges, or curling up on the surface to be inspected. Surface flaw inspection equipment and surface flaw inspection that can reliably detect barge defects and distinguish them from surface irregularities that can not be regarded as defects, can demonstrate high defect detection accuracy, and can be fully incorporated into product quality inspection lines The aim is to provide a method.

[0022]

According to a first aspect of the present invention, there is provided a surface flaw inspection apparatus for linearly polarizing a surface to be inspected having an uneven surface in a direction parallel to an incident surface with respect to the surface to be inspected. The light source irradiating with the illuminated light and the light reception angle from the surface to be inspected are set to the Brewster angle of the unevenness factor substance, and the polarization component of the specular reflection light of the illuminating light in the same direction as the polarization direction of the illuminating light is set. First light receiving means for receiving light,
A light receiving angle from the surface to be inspected is set to a Brewster angle of a substance causing unevenness, and a second light receiving unit that receives a polarization component in a direction orthogonal to a polarization direction of the illumination light in the regular reflection light of the illumination light, A determination processing unit that determines the presence or absence of a surface flaw on the surface to be inspected based on the polarization components in the same direction and the orthogonal direction received by the first and second light receiving units.

According to a second aspect of the present invention, the light source in the surface flaw inspection apparatus of the invention is formed of a linear diffused light source.
Further, in the surface flaw inspection method according to the third aspect, the surface to be inspected having unevenness is illuminated with illumination light linearly polarized in a direction parallel to the incident surface with respect to the surface to be inspected. From the light receiving direction set at the star angle,
The polarization direction of the illumination light in the specular reflection light of the illumination light is received from the light receiving direction set at the Brewster angle of the substance causing unevenness, receiving the polarization component in the same direction as the polarization direction of the illumination light in the reflection light of the illumination light. Then, the presence or absence of a surface flaw on the surface to be inspected is determined based on the received polarization components in the same direction and the orthogonal direction.

Next, the principle of operation of the above-described surface flaw inspection apparatus and surface flaw inspection method of the present invention will be described with reference to the drawings. First, the form of optical reflection on the steel sheet surface to be inspected by the surface flaw inspection apparatus of the present invention will be described in relation to the microscopic unevenness on the steel sheet surface.

For example, when the inspection target is an alloyed galvanized steel sheet, as shown in FIG. 6A, the cold rolled steel sheet as the base passes through the alloying furnace after being hot-dip galvanized. During this time, the iron element of the base steel sheet 1 diffuses into the zinc of the plating layer 2, and usually forms columnar crystals 3 of the alloy as shown in FIG. The plated steel sheet 4 is then temper rolled on rolls 5a and 5b. Then, as shown in FIG. 6D, particularly protruding portions of the columnar crystal 3 are flattened by the rolls 5a and 5b, and the other portions maintain the original shape of the columnar crystal 3.

Then, the rolls 5a, 5b of the temper rolling are
The portion flattened by is referred to as a temper portion 6, and the remaining portion of the temper rolls 5 a and 5 b which does not contact the original uneven shape is referred to as a non-tempered portion 7.

FIG. 7 is a schematic cross-sectional view modeling what kind of optical reflection occurs on the surface of the steel plate 4 having such a tempered portion 6 and the non-tempered portion 7. This steel plate 4
The surface (the surface to be inspected) is composed of countless minute surface elements 13 oriented in various directions when viewed microscopically.

The incident light 8 incident on the temper portion 6 crushed by the temper rolling rolls 5a and 5b is reflected specularly in the regular reflection direction of the steel plate 4 by each of the micro-surface elements 13 of the temper portion 6 so as to have a mirror surface. It becomes reflected light 9. On the other hand, the rolls 5a, 5
The incident light 8 incident on the non-tempered part 7 which leaves the structure of the columnar crystal 3 where the b does not come into contact with the non-tempered part 7 is mirror-reflected by one microplane element 13 on each surface of the columnar crystal 3 when viewed microscopically. However, the direction of reflection is specular diffuse reflection light 10 which does not necessarily match the direction of regular reflection of the steel plate 4.

Therefore, the angular distribution of each reflected light of the tempered portion 6 and the non-tempered portion 7 on the surface of the steel plate 4 is as shown in FIGS. 8 (a) and 8 (b) when viewed macroscopically. That is, sharp specular reflection occurs in the regular reflection direction of the steel plate 4 in the tempered portion 6, and the columnar crystal 3 is generated in the non-tempered portion 7.
The reflected light has a spread corresponding to the angular distribution of the micro-surface element 13 on the surface of the light-emitting device. As described above, the reflected light from the tempered portion 6 is referred to as specular reflected light 9, and the reflected light from the non-tempered portion 7 is referred to as specular diffused reflected light 10.

In fact, since the tempered portion 6 and the non-tempered portion 7 are macroscopically mixed, the angular distribution of the reflected light observed by an optical measuring instrument such as a camera is shown in FIG. As shown in (1), the angular distribution of the specular reflected light 9 and the specular diffuse reflected light 10 is obtained by adding the angular distributions of the tempered portion 6 and the non-tempered portion 7 in accordance with the respective area ratios.

As described above, the tempered portion 6 and the non-tempered portion 7 have been described using an alloyed galvanized steel plate as an example. However, the present invention is generally applicable to other steel plates in which a flat portion is formed by temper rolling. Next, a description will be given of the optical reflection characteristic of a defect called a pattern-shaped scab defect having no noticeable unevenness to be detected in the present invention.

As shown in FIG. 9, the barge defect (barge portion 11) found in the galvannealed steel sheet is the same as that of the cold-rolled steel sheet before plating. And
The plating layer 2 is laid thereon, and alloying of barge defects due to the diffusion of the iron element of the base steel sheet 1 has progressed.

In general, the barbed portion 11 has a difference in plating thickness or a degree of alloying, for example, as compared with the base material 12 indicating a normal portion of the steel plate 4. As a result, for example, when the plating thickness of the barbed portion 11 is large and is convex with respect to the base material 12, the area of the tempered portion 6 becomes larger than that of the non-tempered portion 7 by applying the temper rolling. Conversely, hege part 1
In the case where the plating thickness of 1 is thinner than that of the base material 12 and is concave, the non-tempered portion 7 occupies most of the barb portion 11 because the rolls 5a and 5b of the temper rolling do not abut. When the alloy of the barbed portion 11 is shallow, the angular distribution of the microscopic surface element 13 is strong in the normal direction of the steel sheet, and the diffusivity is small.

Next, the scab 11 and the base material 12
A description will be given of how the pattern-like scab defect looks due to the difference in the surface properties. Hege part 1 based on the model described above
1 and the base material 12 are generally classified into the following three types.

(A) The area ratio of the tempered portion 6 in the barbed portion 11 and the angular distribution of the micro-surface elements 13 in the non-tempered portion 7 are determined by the area ratio of the tempered portion 6 in the base material portion 12 and the non-tempered portion 7.
Is different from the angular distribution of the minute surface element 13 of FIG.

(B) Although the area ratio of the tempered portion 6 in the barbed portion 11 is different from the area ratio of the tempered portion 6 in the base material portion 12, the angular distribution of the minute surface element 13 of the non-tempered portion 7 in the barbed portion 11 is Is not different from the angular distribution of the micro-plane element 13 of the non-tempered part 7 in the base material part 12.

(C) The angular distribution of the micro-surface elements 13 of the non-tempered portion 7 in the barbed portion 11 is different from the angular distribution of the micro-surface elements 13 of the non-tempered portion 7 in the base material portion 12.
Is the same as the area ratio of the tempered portion 6 in the base material portion 12.

That is, FIG. 10 (a) shows the specular reflection component and the specular diffuse reflection between the barge portion angle distribution 11a corresponding to the barge portion 11 and the base material portion angle distribution 12a corresponding to the base material portion 12. FIG. 1 shows a case where there is a difference between both components.
0 (b) shows the case where there is a difference only in the specular reflection component, and FIG. 10 (c) shows the case where there is a difference only in the specular diffuse reflection component.

If there is a difference in the area ratio of the tempered portion 6 between the barge angle distribution 11a and the base metal angle distribution 12a, the difference is as shown in FIGS. 10 (a) and 10 (b). Observed from the specular direction. More specifically, the area ratio of the tempered portion 6 of the barbed portion 11 is reduced when the reflected light of the barbed portion 11 is measured from the specular reflection direction and when the reflected light of the base material portion 12 is measured. When the area ratio of the tempering portion 6 is larger than that of the base portion 12, the barbed portion 11 looks relatively brighter than the base material portion 12. Conversely, when the tempered portion 6 of the barb portion 11 is smaller than the base material portion 12, the barge portion 11 is observed relatively darker than the base material portion 12.

Severe part angle distribution 11a and base material part angle distribution 1
FIG. 1 shows the case where there is no difference in the area ratio of
As shown in FIG. 0 (c), the presence of the stub 11 cannot be observed simply by observing the difference in the received light intensity from the specular reflection direction. However, the diffusivity (angular distribution) of the specular diffuse reflection component
When there is a difference, the defect is observed from a diffusion direction other than the regular reflection direction as shown in FIG.

For example, when the diffusivity (angular distribution) of the specular diffuse reflection component of the barb portion 11 is small, the barb portion 11 is generally observed brightly from a diffusion direction relatively close to the specular reflection direction, and is observed from the specular reflection direction. The brightness decreases as you move away,
It becomes unobservable at a certain angle. As the distance from the specular reflection direction further increases, the barbed portion 11 is observed darker.

In order to detect each barbed portion 11 as shown in FIGS. 10 (a), 10 (b) and 10 (c) from the base material portion 12 and to surely detect it, the reflected light temper portion 6 is used. If only the light intensity of the specular reflection component is detected, the scab 11 shown in FIG. 10C cannot be detected separately from the base material 12.

In order to detect such a pattern-shaped scab defect without detecting it, it is necessary to independently obtain a light amount corresponding to specular reflection and a light amount corresponding to specular diffuse reflection.
Here, a process of generating surface unevenness will be described. For example, the steel plate 4 to be electroplated passes through a strongly acidic plating bath, passes through a strong alkali neutralization bath through wetting, and is washed with hot water, thereby completing the electroplating process. During the plating process, if there is a residual plating solution or neutralizing solution due to poor drawing of a squeezing roll for preventing the plating solution or neutralizing solution from remaining on the steel sheet, uneven cleaning during hot water washing, etc. Are observed as irregularities on the surface of the product. In addition, even if the steel plate 4 that is not electroplated passes through the above-described cleaning bath, the above-described unevenness occurs.

The material of the base material of the steel sheet is not limited to one type, but there are many types. The surface unevenness is caused by various films such as a residual film of the chemical solution, a film formed by the reaction between the base material and the chemical solution, and an oxide film of the base material. Has occurred due to The shape of the surface unevenness is also various such as a band shape, a line shape, and a polka dot shape. It is necessary that the presence of these various types of unevenness is not detected by a photodetector that detects a pattern-shaped scab defect.

For this reason, in the present invention, a p-polarized light including only a polarized light component parallel to the incident surface is employed as a light source, and the light source irradiates the surface to be inspected, and the reflected light reflected from the surface to be inspected. The specularly reflected light is received at a Brewster angle of a film, for example, which is a substance causing the surface unevenness of the surface to be inspected.

Next, the optical reflection characteristics when a thin film is present on the steel sheet surface will be described. FIG. 11A shows what optical reflection occurs on the surface of the steel plate 4 when the tempered portion 6 and the non-tempered portion 7 are formed when the transparent film 14 exists on the surface of the steel plate 4. FIG. 3 is a schematic cross-sectional view in which is modeled.

For example, consider a case where a thin film 14 is formed on the surface of an alloyed galvanized steel sheet. The thickness of the film 14 is 10
11 nm, which is sufficiently thin compared to the uneven shape.
As shown in (a), both the tempered portion 6 flattened by the temper rolling rolls 5a and 5b and the non-tempered portion 7 where the temper rolling rolls 5a and 5b do not abut and the crystal structure remains. It is considered that the film 14 was formed uniformly.

Therefore, when the steel plate 4 is observed from the regular reflection direction, the tempered portion 6 is observed, and when the steel plate 4 is observed from other directions, the non-tempered portion 7 happens to be the minute surface element 13 whose regular reflection direction coincides with the observation direction. As shown in the enlarged view of FIG. 11B, multiple reflection occurs at the air / film 14 interface and the film 14 / steel plate 4 interface.

Next, the polarization characteristic of multiple reflection by the film 14 will be described. FIGS. 12A and 12B show the dependence of the reflectance r in the regular reflection direction of the reflected light on the incident angle φ when the incident light 8 is incident on the steel plate 4. However, the steel sheet 4 was measured using an alloyed galvanized steel sheet. As shown in FIG. 12B, when the incident light 8 is s-polarized light, the reflectance r
Has a monotonically increasing relationship with respect to the incident angle φ.
Comparing the case without the film 14 and the case where the film 14 with a thickness of 10 nm is formed, the reflectance r as a whole increases without the film 14.

On the other hand, as shown in FIG. 12A, when the incident light 8 is p-polarized light, when the film 14 is not provided, the incident angle φ = 0 to the incident angle φ = near 75 °. In the angle range described above, it decreases with an increase. When the incident angle φ exceeds 75 °, the reflectance r sharply increases.

In the case where the film 14 is provided, in the angle range from the incident angle φ = 0 to the vicinity of the incident angle φ = 75 °, the reflectance r does not depend much on the incident angle φ and maintains a substantially constant value. I do. When the incident angle φ exceeds 75 °, the reflectance r increases. Then, the reflectance characteristic without the film 14 and the reflectance characteristic with the film 14 intersect at an incident angle φ of about 50 ° to 60 °.

That is, as shown in FIG. 11A, when the film 14 is formed on the steel plate 4 and multiple reflection occurs as shown in FIG. 11B, the incident angle φ is small (in the normal direction). When the incident angle φ is large, the reflectivity r becomes higher when the film is present.
Then, when the incident angle φ is 50 ° to 60 °, the reflectance r between the case with the film 14 and the case without the film 14 is the same. Therefore, if the incident angle φ is set to this angle, the surface unevenness due to the presence of the film 14 cannot be observed, and the light intensity of the specularly reflected light can be measured without being affected by the film 14.

The fact that this angle matches the Brewster angle of the film 14 is shown as follows. The reflectance at the incidence of p-polarized light is represented by the following Fresnel reflection formula. r _01P = (n ₁ cos φ _{0 −cos} φ ₁ ) / (n ₁ cos φ ₀ + cos φ ₁ ) r _12P = (n ₂ cos φ ₁ −n ₁ cos φ ₂ ) / (n ₂ cos φ ₁ + n ₁ cos φ ₂ ) (1) Here, r _01P and r _12P are Fresnel reflection coefficients at an air / film interface and a film / steel interface, respectively, n ₁ and n ₂ are fluorine refractive indexes of the film 14 and the steel plate 4, and φ ₀ is an incident angle. It is.
Φ ₁ and φ ₂ are angles satisfying the following Snell's refraction equation.

Sinφ ₀ = n ₁ sinφ ₁ = n ₂ sinφ ₂ (2) Here, assuming that the film 14 is a transparent film, the incident angle φ ₀ is the Brewster angle with respect to this film 14 as described above. , The following relationship is known.

Sin φ ₁ = cos φ ₀ (3) Accordingly, the following equation is derived. sinφ ₀ = cosφ ₁ (4) Expression (5) is obtained from Expressions (2), (3), and (4).

Cosφ ₁ = n ₁ cosφ ₀ (5) When the expression (5) is substituted into the expression (1), the following relationship is established. r _01P = 0 (6) r _12P = (n ₂ cos φ _{0 −cos} φ ₂ ) / (n ₂ cos φ ₀ + cos φ ₂ ) (7) That is, the equation (6) employs p-polarized light as the incident light 8. However, when the incident angle is set to the Brewster angle, there is a known property that there is no reflection at the air / film 14 interface.

Equation (7) represents the Fresnel reflection coefficient of the reflection at the air / steel plate 4 interface when the film 14 does not exist. That is, when the p-polarized light is adopted as the incident light 8 and the incident angle is set to the Brewster angle, the film 14 /
This indicates that the reflection at the interface of the steel plate 4 coincides with the reflection at the air / steel plate 4 interface when the film 14 is not provided. From these two relations, it can be said that the total reflection also matches when there is no film 14.

Therefore, regardless of the complex refractive index of the steel plate 4 located below the film 14, p-polarized light is adopted for the incident light 8,
It can be understood that if the incident angle is set to the Brewster angle, the presence or absence of the film 4 cannot be determined at all.

The prior art disclosed in Japanese Patent Application Laid-Open No. 53-23678 focuses only on eliminating strong reflected light on the surface of the film 14 represented by the formula (6). We do not use or need the relationships represented by the formulas.

Next, a description will be given of a method of the present invention in which the specular reflection component and the specular diffuse reflection component of the specularly reflected light from the surface to be inspected are captured based on the above findings and the surface unevenness is not detected. In the present invention, a linear light source having a diffusion characteristic, that is, a linear diffusion light source, is used as a light source instead of a parallel light source such as a laser. Since it is necessary to separate and extract the specular reflection component and the specular diffuse reflection component from the specular reflection direction of the steel plate 4, polarized light is used.

In order to explain the effect of the linear diffusion light source, as shown in FIGS.
4 is arranged in parallel with the surface of the steel plate 4, and the reflection characteristic when observing one point on the steel plate 4 from the steel plate regular reflection direction, which is in a plane perpendicular to the light source and in which the incident angle coincides with the emission angle, is shown. Think.

As shown in FIG. 13A, in the case of the incident light 8 emitted from the center of the linear diffused light source 14, the incident light 8 incident on the tempering portion 6 is reflected specularly, and All are captured in the reflection direction. On the other hand, the light incident on the non-tempered portion 7 is specularly reflected, and only the light reflected by the minute surface element 13 that happens to be oriented in the same direction as the normal direction of the steel sheet is captured. Since the number of micro-plane elements 13 oriented in such a direction is extremely small, the mirror-reflected light from the tempering unit 6 is dominant among the reflected light captured by the light-receiving camera arranged in the regular reflection direction of the steel sheet. is there.

On the other hand, as shown in FIG.
In the case of the incident light 8 emitted from a position other than the center of the linear diffusion light source 14, the light incident on the tempering portion 6 is specularly reflected and reflected in a direction different from the regular reflection direction of the steel plate. Therefore, the specularly reflected light cannot be captured in the regular reflection direction of the steel plate. On the other hand, the light incident on the non-tempered portion 7 is specularly reflected, and the light reflected by the steel plate in the regular reflection direction is captured by the light receiving camera. Therefore, all the reflected light captured by the light receiving camera arranged in the regular reflection direction of the steel plate is the specular diffuse reflection light reflected by the non-tempered portion 7.

When the above two cases are combined, the observation from the regular reflection direction of the steel plate out of all the incident light 8 emitted from the entire lengthwise direction of the linear diffused light source 14 shows that Is the sum of the specular reflected light from the non-tempered part 7 and the specular reflected light from the non-tempered portion 7.

Next, how the polarization characteristics change when observed using the linear diffused light source 14 from the regular reflection direction of the steel plate 4 will be described. Generally, in reflection from a mirror-like metal surface, the direction of the electric field is parallel to the incident surface (p
In the case of (polarized light) or light perpendicular to the plane of incidence (s-polarized light), the polarization characteristics are preserved even by reflection. That is,
The light is emitted as p-polarized light or s-polarized light. Further, when linearly polarized light having an arbitrary polarization angle having both p-polarized component and s-polarized component is reflected, it is emitted as elliptically polarized light according to the reflectance ratio of p and s polarized light and the phase difference.

A linear diffusion light source 14 is applied to an alloyed galvanized steel sheet.
14 (a) and 14 (b) will be described. As shown in FIG. 14A, the linear diffused light source 1
The light emitted from the central part of the steel sheet 4 is specularly reflected by the tempering part 6 of the steel sheet 4 and is observed in the steel sheet regular reflection direction. In this regard, reflection on the above-mentioned general mirror-like metal surface is established as it is.

On the other hand, as shown in FIG. 14B, light emitted from a position other than the central portion of the linear diffused light source 14 is generated by the inclined minute surface element 13 of the crystal surface of the non-tempered portion 7 of the steel plate 4. Specular reflection is observed in the specular direction of the steel plate. in this case,
Even if p-polarized light parallel to the incident surface of the steel plate 4 is incident, the incident surface is not parallel to the minute surface element 13 when it is considered with respect to the tilted minute surface element 13 that actually reflects the light. ,
Since the light is linearly polarized light having s-polarized light components, it is emitted as elliptically polarized light. The same applies to the case where s-polarized light is incident from the linear diffusion light source 14.

In the present invention, the incident light 8 from the linear diffusion light source 14 is, for example, parallel (p-polarized) to the incident surface. further,
The reflected light of the p-polarized incident light 8 from the regular reflection direction of the steel plate is received by two light receiving cameras. Each of the two light receiving cameras captures a parallel (p-polarized) component on the incident surface and a perpendicular (s-polarized) component on the incident surface.

Now, most of the reflected light reflected by the tempering portion 6 of the steel plate 4 and captured in the regular reflection direction of the steel plate is emitted from the central portion of the linear diffused light source 14, and the polarization is preserved by the reflection. Therefore, the light incident with p-polarized light is reflected as p-polarized light, and is captured by one of the light-receiving cameras that takes in the p-polarized component. On the other hand, the other light receiving camera that captures the s-polarized light component cannot capture the p-polarized light emitted from the central portion of the linear diffused light source 14.

On the other hand, the reflected light reflected by the non-tempered part 7 of the steel plate 4 and captured in the regular reflection direction of the steel plate is the sum of the light emitted from all the points of the linear diffused light source 14, A large amount of light emitted from other than the central portion of the light source 14 is included,
Since polarization is not preserved, light is captured by the receiving camera that captures s-polarization. Although a part of the light is captured by a light-receiving camera that captures p-polarized light, it is much smaller than the light emitted from the center of the linear diffused light source 14.

The farther the emission position from the linear diffuse light source 14 is from the center, the higher the amount of light received by one of the light-receiving cameras that takes in s-polarized light. The amount of light increases.

From the above, considering both the reflection at the tempered portion 6 and the reflection at the non-tempered portion 7, one of the light-receiving cameras that captures the p-polarized component extracts the specular reflected light and captures the s-polarized component. The other receiving camera extracts the specular diffuse reflection.

Then, it is assumed that there is a pattern-like barbed defect on the surface of the steel plate 4. At this time, if there is a difference in the area ratio of the tempered portion 6 between the barge portion 11 and the base material portion 12, and if the area ratio of the tempered portion of the barge portion 11 is larger than that of the base material portion 12, it is p-polarized light. Is captured by one of the light-receiving cameras that receives the component,
The scab 11 is observed brightly.

If there is no difference in the area ratio of the tempered surface 6 between the barge portion 11 and the base material portion 12, it is difficult for one of the light receiving cameras that receives the p-polarized light component to detect the hair defect. Can not. However, there is a difference in the diffusivity of the specular diffuse reflection component. For example, if the diffusivity is small in the barb portion 11, in the other light-receiving camera that receives the s-polarized component,
The barb portion 11 is observed darker than the base material portion 12. As a result, it becomes possible to detect this scab defect.

Further, by using the linear diffused light source 14 and the polarized light, even if a linear array camera or other scanning type photodetector is used as each light receiving means, the light is reflected to the specularly reflected light from the surface to be inspected. The specular reflection component and the specular diffuse reflection component contained can be reliably detected.

With such an optical system, since the measurement is performed on the common optical axis from the specular reflection direction, it is not affected by the change in the steel sheet distance or the change in speed, and the pattern-shaped hair has no remarkable unevenness. A surface flaw inspection device capable of detecting a defect without causing undetection is realized.

As described above, the light source receives the p-polarized component of the specularly reflected light of the surface to be inspected of the p-polarized irradiation light,
In addition, by receiving the s-polarized component of the specularly reflected light of the surface to be inspected with the p-polarized irradiation light from the light source, it is possible to detect a pattern-shaped barge defect having no noticeable unevenness without causing undetection. It is. Furthermore, the angle of incidence of the light source and the p
Since the light receiving angles of the polarized light component and the s-polarized light component are set to the Brewster angle of the substance causing the surface unevenness, the measured p-polarized light component and the s-polarized light component do not include an error factor due to the surface unevenness. Therefore, the measurement accuracy of the pattern-shaped scab defect is further improved.

[0078]

Embodiments of the present invention will be described below with reference to the drawings. (First Embodiment) FIG. 1A is a side view of a surface flaw inspection apparatus employing a surface flaw inspection method according to a first embodiment of the present invention, and FIG. It is a top view.

The surface flaw inspection apparatus according to the first embodiment is installed in a quality inspection line of an alloyed galvanized steel sheet in an iron making factory. A linear diffused light source 22 is arranged in the width direction of the strip-shaped steel plate 21 at a position above the transfer path of the steel plate 21 in the transfer state in the arrow direction in the drawing. This linear diffusion light source 2
2 is to emit uniform light in the width direction by projecting light from a metal halide light source into the inside from both ends of the transparent light guide bar, which is partially coated with a diffuse reflection paint.

The incident light 23 emitted from each position of the linear diffusion light source 22 to the steel plate 21 as the irradiation light is transmitted through the cylindrical lens 24 and the polarizing plate 25 to the entire width of the running steel plate 21 at an incident angle θ. Irradiation. Polarizing plate 25
Is set in a direction parallel to the plane of incidence of the incident light 23 on the steel plate 21.
That is, the incident light 23 emitted from the linear diffusion light source 22 to the steel plate 21 is in a p-polarized state.

The surface of the steel plate 21 has irregularities in the afterimage film of the chemical solution, the reaction product film, the oxide film and the like in the electroplating process. The Brewster angle of the film that is the cause of the unevenness is measured in advance. The measured value of the Brewster angle of the film in this embodiment is 60 °.

A part of the specularly reflected light 26 reflected by the steel plate 21 forms a beam splitter 27 disposed in a specular reflection direction of the steel plate, that is, in a light receiving angle γ direction equal to the incident angle θ with respect to the normal direction of the steel plate 21. The light passes through and enters the first light receiving camera 28 constituted by, for example, a linear array camera. A part of the specularly reflected light 26 is reflected by the beam splitter 27 and is incident on a second light receiving camera 29 also formed of a linear array camera.

Here, the incident angle θ of the incident light 23 and the light receiving angle γ which is equal to the incident angle θ are set to 60 °, which is the Brewster angle of the film which is a factor of the surface unevenness of the steel sheet 21 ( θ = γ = 60 °).

Analyzers 30a and 30b are mounted on the front surfaces of the lenses of the first and second light receiving cameras 28 and 29, respectively. The analyzer 30a on the front surface of the lens of the first light receiving camera 28 has the polarizing direction of the polarizing plate 25 of the linear diffused light source 22.
Is set in the same direction as. That is, the first light receiving camera 28 receives only the p-polarized light component of the regular reflection light 26. As described above, the analyzer 3 of the first light receiving camera 28
Since the polarization direction of Oa coincides with the polarization direction (p-polarized light) of the polarizing plate 25 of the linear diffused light source 22, the first light receiving camera 28 receives the specular reflection component of the specularly reflected light 26 on the steel plate 21. .

The polarization direction of the analyzer 30 b on the front surface of the lens of the second light receiving camera 29 is set to be orthogonal to the polarizing plate 25 of the linear diffusion light source 22. That is, the second
Receive only the s-polarized component of the specularly reflected light 26. As described above, the polarization direction of the analyzer 30 b of the second light receiving camera 29 is the same as the polarization plate 25 of the linear diffused light source 22.
The second light receiving camera 28 receives the specular diffuse reflection component of the specularly reflected light 26 on the steel plate 21 because the direction (s-polarized light) is orthogonal to the polarization direction (p-polarized light).

Further, since the incident angle θ and the light receiving angle γ are set to the Brewster angle of the surface unevenness, the incident light of each of the light receiving cameras 28 and 29 does not include the fluctuation due to the presence of the surface unevenness.

Here, as each of the light receiving cameras 28 and 29,
A two-dimensional CCD camera can be used instead of a linear array camera. Furthermore, it is also possible to use a scanning photodetector in which a single photodetector is combined with a galvanometer mirror or a polygon mirror.

Further, a fluorescent lamp can be used as the linear diffusion light source 22. Further, a fiber light source in which the output ends of the bundle fiber are aligned in a straight line can be used. The light emitted from each fiber is the N / A of the fiber.
This is because the fiber light source having a sufficient divergence angle corresponds to a linear diffusion light source.

Each pixel of one line in the width direction of the steel plate 21 of the p-polarized component (specular reflection component) and the s-polarized component (specular diffuse reflection component) in the specularly reflected light 26 received by each of the light receiving cameras 28 and 29. Are the light intensity signals a and b, respectively.
And transmitted to the signal processing unit 31 as a determination processing unit.

FIG. 2 is a block diagram showing a schematic configuration of the signal processing section 31. A first light receiving camera 28 that receives a p-polarized component (specular reflection component) of the specularly reflected light 26 reflected by the steel plate 21, and a second light reception that receives an s polarized component (specular diffuse reflection component) of the specularly reflected light 26 The light intensity signals a and b output from the camera 29 are input to the average value thinning units 32a and 32b, respectively.

Each of the average value thinning sections 32a and 32b is provided for each of the light receiving cameras 28 and 29 for each scanning cycle.
The respective light intensity signals a and b input from 8, 29 are averaged,
When the steel plate 21 moves a distance corresponding to the longitudinal resolution in the signal processing, a signal for one line is output.

By performing such thinning processing,
Even if the conveying speed of the steel plate 21 changes, the resolution of one line in the moving direction of the steel plate in the signal processing can be kept constant. Also, since the light intensity signals a and b for each scan cycle are averaged, if the resolution of one line in the moving direction of the steel plate in the signal processing is sufficiently larger than the visual field size of the light receiving cameras 28 and 29 in the moving direction of the steel plate. Also, since an average value obtained by measuring the interval can be used, oversight can be eliminated.

Each of the light intensity signals a and b subjected to signal processing in each of the average value thinning sections 32a and 32b is converted into the following preprocessing sections 33a and 32b.
33b. Each pre-processing unit 33a, 33b
Corrects the luminance unevenness of the line signal. The luminance unevenness here includes unevenness caused by the optical system and unevenness caused by the reflectance of the steel plate 21. Further, each of the pre-processing units 33a, 33
b also detects the edge positions on both sides of the steel plate 21 and also executes processing for preventing a sudden change in the light intensity signals a and b at the edge from being erroneously recognized as a flaw. Each pre-processing unit 33a, 33b
The light intensity signals a and b that have been subjected to the signal processing are input to the following respective binarization processing units 34a and 34b.

Each of the binarization processing sections 34a and 34b compares the data of each pixel contained in each of the light intensity signals a and b with a predetermined threshold value, extracts flaw candidate points, and It is sent to the feature amount calculation units 35a and 35b.

The characteristic amount extraction units 35a and 35b determine continuous flaw candidate points as one flaw candidate area, and for example, position characteristic amounts such as a start address and an end address and density characteristics such as a peak value. Calculate the amount etc.

The specular flaw judging section 36 and the specular diffusible flaw judging section 37 determine the type of the flaw based on the characteristic amounts calculated by the characteristic amount extracting sections 35a and 35b corresponding to the respective light receiving cameras 28 and 29. Determine the degree.

The flaw comprehensive judgment section 38 determines the final flaw type and degree of the steel sheet 21 to be inspected based on the judgment results and the characteristic amounts of the specular flaw judgment section 36 and the specular diffuse flaw judgment section 37. Is determined.

[0098]

FIG. 3 shows the results of measuring the surface flaws of an alloyed galvanized steel sheet using the surface flaw inspection apparatus of the first embodiment shown in FIG. Each of the measured flaws is the temper portion 6 shown in FIG.
The area ratio of the non-tempered portion 7 is larger than that of the base material portion 12 at the barb portion 11 and the diffusivity of the non-tempered portion 7 is larger than that of the base material portion 12 at the barge portion 11 and the tempered portion 6 shown in FIG. Although the area ratio of the barbed portion 11 is larger than that of the base material 12 but the diffusibility of the non-tempered portion 7 does not change, the area ratio of the tempered portion 6 shown in FIG. There are no significant differences between the portions 12, but there are a total of three types of flaws including flaws having a difference in diffusivity.

The surface of the alloyed galvanized steel sheet as the surface to be inspected has surface irregularities such as a reaction product film and an oxide film in the electroplating process. Then, when a flaw of the type shown in FIG. 10A is generated at the center in the width direction of the steel plate 21 and the above-described surface unevenness is generated near the end in the width direction, a first surface for receiving a specular reflection component is received. The change of the light intensity signals a and b for one width of the steel material 21 obtained by scanning the light receiving camera 27 of the above and the second light receiving camera 28 for receiving the specular diffuse reflection component by one line in the width direction of the steel plate 21 is shown. FIG.
(A) and (b).

As shown in the drawing, a peak waveform 40 in the positive direction (bright direction) corresponding to the flaw (the stub 11) is generated in the light intensity signal a of the first light receiving camera 28. Further, a peak waveform 40 corresponding to the flaw (the scab 11) is generated in the light intensity signal b of the second light receiving camera 29.

FIG. 10 shows a central portion of the steel plate 21 in the width direction.
(B) When a flaw of the type shown in the figure occurs and the aforementioned surface unevenness occurs near the end in the width direction, a first light receiving camera 28 for receiving a specular reflection component and a second light receiving camera for receiving a specular diffuse reflection component. FIGS. 3C and 3D show changes in light intensity signals a and b for one width of the steel material 21 obtained by scanning the light receiving camera 29 for one line in the width direction of the steel plate 21.

As shown in the figure, a peak waveform 40 in the positive direction (bright direction) corresponding to the flaw (heavy portion 11) is generated in the light intensity signal a of the first light receiving camera 28. However, a peak waveform corresponding to the flaw (the scab 11) does not occur in the light intensity signal b of the second light receiving camera 28.

Further, FIG. 1 is attached to the center of the steel plate 21 in the width direction.
When a flaw of the type shown in FIG. 0 (c) occurs and surface unevenness occurs near the end, a first light receiving camera 28 for receiving the specular reflection component and a second light receiving camera 29 for receiving the specular diffuse reflection component are provided. FIGS. 3E and 3F show changes in the light intensity signals a and b for one width of the steel material 21 obtained by scanning one line in the width direction of the steel plate 21.

As shown in the figure, the light intensity signal a of the first light receiving camera 28 does not have a peak waveform in the positive direction (bright direction) corresponding to the flaw (the scab 11). However, a peak waveform 40 corresponding to the flaw (severed portion 11) is generated in the light intensity signal b of the second light receiving camera 29.

As described above, even if any of the typical three types of pattern-shaped barge defects shown in FIGS. 10 (a), (b) and (c) occurs, It is possible to reliably detect a scab defect. Furthermore, FIG.
As shown in (f), the types of the three types of pattern-like barbed defects can also be determined.

Then, as shown in FIGS. 3A to 3F, only the pattern-shaped scab defect is detected, and the waveform due to the surface unevenness is not detected. In order to confirm the excellent detection function of the device of the first embodiment, the inventors et al.
(B) The flaws and surface unevenness shown in (c) were measured by a conventional surface flaw inspection device.

In the conventional apparatus, the steel plate 21
From the linear light source arranged in the width direction of the
Specularly reflected light is received by a first light receiving camera disposed in the regular reflection direction of non-polarized incident light incident at 0 °. Therefore, the light receiving angle of the first light receiving camera is the same as the light receiving angle of the first camera 28 of the first embodiment. On the other hand, the second light-receiving camera disposed at a direction different from the specular reflection direction of the incident light, for example, at 40 ° with respect to the normal direction of the steel plate 21, receives the specular diffuse reflection light.

FIGS. 4A, 4B, 4C, and 4D show the measurement results.
(E) and (f). As shown in FIG.
It is possible to detect a pattern-like scab defect of the type shown in FIG. However, as shown in FIG.
In addition to the positive peak waveform 40 corresponding to 1), a waveform 41 due to surface unevenness is generated. In general, only by observing the waveform, it is not possible to distinguish the peak waveform 40 corresponding to the flaw (severed portion 11) from the waveform 41 due to the surface unevenness. There is a concern that the peak waveform 40 corresponding to 11) is erroneously recognized.

Further, as shown in FIGS. 4E and 4F, it is not possible to detect a pattern-shaped scab defect of the type shown in FIG. 10C. In this case, not only the pattern-shaped barge defect cannot be detected, but also a waveform 41 due to surface unevenness is generated.

In this case, although the pattern-shaped scab defect actually exists as shown in FIG. 10C, the pattern-shaped scab defect cannot be detected, and the surface unevenness which does not need to be detected is detected. Inconvenience occurs.

As described above, in the surface flaw inspection apparatus according to the first embodiment, a pattern-shaped scab defect, which could not be detected by the conventional apparatus, is removed while eliminating the presence of surface unevenness.
As a result, it is possible to reliably detect the pattern-shaped barbed flaw having no remarkable unevenness without fail and with high accuracy.

(Second Embodiment) FIG. 5 is a top view of a surface flaw inspection apparatus according to a second embodiment of the present invention. The first shown in FIG.
The same parts as those of the surface flaw inspection apparatus of the embodiment are denoted by the same reference numerals. Therefore, the detailed description of the overlapping part will be omitted.

In the surface flaw inspection apparatus of the second embodiment, the first light receiving camera 28a for receiving the p-polarized light component of the specularly reflected light 26 which is parallel to the incident surface of the incident light 23 with respect to the steel plate 21; The second light-receiving camera 29a that receives an s-polarized light component of the reflected light 26 that is orthogonal to the plane of incidence of the incident light 23 with respect to the steel plate 21 and the second light-receiving camera 29a in the width direction of the steel plate 21, that is, at a minute interval Open and arranged in parallel.

The incident angle θ of the incident light 23 and the specular reflection light 2
6 is set to 60 °, which is the Brewster angle of the substance causing the surface unevenness. Even with such a configuration, the first and second light receiving cameras 28a and 29a independently receive the p-polarized component and the s-polarized component of the specularly reflected light 26, and correspond to each light intensity. Since the light intensity signals a and b are output, substantially the same operation and effect as those of the surface flaw inspection apparatus of the first embodiment shown in FIG. 1 can be obtained.

Incidentally, the first and second light receiving cameras 28a, 28
Since the optical axes of 9a do not coincide, it is necessary to correct the field of view in the first and second light receiving cameras 28a and 29a. The correction of the visual field shift is performed by the signal processor 3
1 can be easily implemented by the overall determination unit 38.

[0116]

As described above, in the surface flaw inspection apparatus and the surface flaw inspection method of the present invention, the incident angle of the illumination light, which is p-polarized light, and the reception angle of the specular reflection light are set to the Brewster angle. By receiving the p-polarized light component and the s-polarized light component of the specularly reflected light, it is possible to prevent a factor due to unevenness on the surface to be inspected from being included in each of the received reflected lights.

Therefore, the specular reflection component and the specular diffuse reflection component contained in the reflected light from the surface to be inspected can be detected with high accuracy, and the surface of the surface to be inspected has remarkable irregularities such as cracks, gouges, and curling up. Pattern-like balding defects without
It can be reliably detected in distinction from surface irregularities that cannot be regarded as defects, can exhibit high defect detection accuracy, and can be sufficiently incorporated into a product quality inspection line.

[Brief description of the drawings]

FIG. 1 is a side view and a top view showing a schematic configuration of a surface flaw inspection apparatus according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing a schematic configuration of a signal processing unit of the surface flaw inspection apparatus.

FIG. 3 is a waveform diagram of a light intensity signal measured by the surface flaw inspection apparatus.

FIG. 4 is a waveform diagram of a light intensity signal measured by a conventional surface flaw inspection device.

FIG. 5 is a top view showing a schematic configuration of a surface flaw inspection apparatus according to a second embodiment of the present invention.

FIG. 6 is a view showing a manufacturing method and a detailed cross-sectional structure of an alloy galvanized steel sheet to be inspected by a surface flaw inspection apparatus.

FIG. 7 is a schematic cross-sectional view showing a relationship between incident light and reflected light in a tempered portion and a non-tempered portion of a steel plate to be inspected.

FIG. 8 is an angle distribution diagram of reflected light between the tempered portion and the non-tempered portion.

FIG. 9 is a view for explaining a generation process of a barbed portion existing in a steel sheet.

FIG. 10 is a diagram showing a relationship between a specular reflection component and a specular diffuse reflection component in a stub, and a specular reflection component and a specular diffuse reflection component in a base material portion.

FIG. 11 is a schematic cross-sectional view showing a relationship between incident light and reflected light in a tempered portion and a non-tempered portion of a steel plate to be inspected when a film is present on the surface.

FIG. 12 is a diagram illustrating a relationship between an incident angle of incident light on a surface to be inspected and a reflectance;

FIG. 13 is a diagram showing a relationship between each incident light from each position of the linear diffused light source and the incident position on the steel plate.

FIG. 14 is a diagram illustrating a polarization state of reflected light when each incident light of the linear diffusion light source is polarized.

[Description of Signs] 4,21 ... Steel plate 6 ... Tempered part 7 ... Non-tempered part 8,23 ... Incident light 9 ... Specular reflection light 10 ... Specular diffuse reflection light 11 ... Heavy part 12 ... Base part 13 ... Micro plane element Reference numeral 22: linear diffusion light source 25: polarizing plate 26: specularly reflected light 27: beam splitter 28: first light receiving camera 29: second light receiving camera 30a, 30b: analyzer 31: signal processing unit 40: peak waveform 41 Waveform

Continued on the front page (72) Inventor Yuji Matoba 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (72) Masakazu Inomata 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Sun Inside the Kokan Co., Ltd. (72) Shoji Yoshikawa, 1-2-1, Marunouchi, Chiyoda-ku, Tokyo, Japan Inside Nihon Kokan Co., Ltd. (72) Tsutomu Kawamura 1-2-1, Marunouchi, Chiyoda-ku, Tokyo, Japan Inside Steel Tube Co., Ltd. (72) Inventor Hiroyuki Sugiura 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Japan Steel Tube Co., Ltd.

Claims (3)

[Claims] A light source for irradiating a surface to be inspected having unevenness with illumination light linearly polarized in a direction parallel to an incident surface with respect to the surface to be inspected; A first light receiving unit that receives a polarization component of the specular reflection light of the illumination light in the same direction as the polarization direction of the illumination light, and a light reception angle from the surface to be inspected is A second light receiving unit that is set to a Brewster angle of the unevenness factor substance and receives a polarization component of specular reflection light of the illumination light in a direction orthogonal to a polarization direction of the illumination light; 2. A surface flaw inspection apparatus comprising: a determination processing unit that determines presence / absence of a surface flaw on the surface to be inspected based on each polarization component in the same direction and the orthogonal direction received by the light receiving unit. 2. The surface flaw inspection apparatus according to claim 1, wherein the light source is a linear diffusion light source. 3. A surface to be inspected having an uneven surface is illuminated with illumination light linearly polarized in a direction parallel to an incident surface with respect to the surface to be inspected. Direction, the polarization component of the illumination light in the specular reflection light of the illumination light is received in the same direction as the polarization direction of the illumination light. Receiving a polarization component of the light in a direction orthogonal to the polarization direction of the illumination light, and determining the presence or absence of a surface flaw on the surface to be inspected based on the received polarization components in the same direction and the orthogonal direction. Surface flaw inspection method.