JPH11183400A - Surface defect inspection apparatus and method - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To surely detect a pattern-shaped scab defect having no remarkable unevenness. SOLUTION: The surface flaw inspection apparatus according to the present invention comprises a surface to be inspected 2
1, a linear diffused light source 22 for entering illumination light, and among specular reflection components and specular diffuse reflection components included in specular reflection light from the surface to be inspected, more specular reflection components than the specular diffuse reflection components A first light receiving means 27a for extracting and receiving light, and a second light receiving means 27b for extracting and receiving a specular diffuse reflection component of the specular reflection component and the specular diffuse reflection component contained in the specular reflection light from the surface to be inspected. A determination processing unit 40 for determining the presence or absence of a surface flaw on the surface to be inspected based on the specular reflection component, the specular diffuse reflection component, and the diffuse reflection component 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 detector, 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. Has been established.

A surface measuring apparatus utilizing 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. Then, 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 a 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 the steel sheet is inspected for defects using ellipsometry. I have.

[0008]

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 for receiving specularly reflected light and scattered reflected light. 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.

[0010] The surface condition inspection method disclosed in Japanese Patent Application Laid-Open No. 60-228943 is directed to a raised bark defect 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.

[0011] The flat steel hot flaw detector disclosed in Japanese Patent Application Laid-Open No. Hei 8-178867 is intended for scratches and has no noticeable unevenness because it is based on catching specularly reflected light on the slopes of the flaws. 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. Also, once the camera is installed and the angle of the reflected component to be received is determined, the camera position cannot be easily changed.

Further, the measuring device disclosed in Japanese Patent Application Laid-Open No. 57-166533 and the surface inspection device disclosed in Japanese Patent Application Laid-Open No. Hei 9-166552 use an ellipsometry technique. 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 the ellipsometry, it is necessary to receive reflected light from the same point at corresponding pixels of each CCD and calculate ellipsometric parameters for each pixel. For this reason, in JP-A-57-166533, the reflected light is divided into three by a beam splitter and detected by three CCDs, and there is a problem that the amount of light is reduced and it is difficult to align pixels between the CCDs. Was.

[0014] In Japanese Patent Application Laid-Open No. 7-28633, three cameras are arranged in the traveling direction of the steel plate, arranged vertically or horizontally, and the inclination of the three cameras is changed to view the same area. I have to. However, there is a problem that processing when the speed of the steel sheet changes is complicated. Also, since the angles of the cameras are different, the optical conditions are not the same. for that reason,
There is a problem that pixel alignment is difficult.

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.

In a surface inspection apparatus to be incorporated in a product quality inspection line, it is an absolute condition that there is no omission in detection of flaws 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 distinguishes between a specular reflection component and a specular diffuse reflection component included in light reflected from a surface to be inspected, thereby detecting the surface to be inspected. It can reliably detect pattern-like barbed defects that do not have noticeable unevenness such as surface cracks, gouges, and curling up, exhibit high defect detection accuracy, and be fully incorporated into product quality inspection lines. It is an object of the present invention to provide a surface flaw inspection device and a surface flaw inspection method that can perform the inspection.

[0018]

According to a first aspect of the present invention, there is provided a surface flaw inspection apparatus comprising: a linear diffused light source for illuminating light incident on a surface to be inspected; and a specularly reflected light from the surface to be inspected. First light receiving means for extracting and receiving more specular reflection components than the specular diffuse reflection components among the specular reflection components and the specular diffuse reflection components included therein, and a mirror surface included in the specular reflection light from the surface to be inspected; A second light receiving means for extracting and receiving the specular diffuse reflection component from the reflection component and the specular diffuse reflection component, and receiving the light based on the specular reflection component and the specular diffuse reflection component received by the first and second light receiving means. A judgment processing unit for judging the presence or absence of surface flaws on the inspection surface.

According to the second aspect of the present invention, the linear diffused light source in the above-described surface defect inspection apparatus receives polarized light having an azimuth component parallel to and perpendicular to the incident surface with respect to the inspection surface. The first light receiving means has an analyzer with an azimuth angle for extracting more specular reflection components, and the second light receiving means is adjusted in a direction for extracting only specular diffuse reflection light contained in specular reflection light. １ ／ wavelength plate and an analyzer.

Further, in the surface defect inspection method according to the third aspect, the illumination light is incident on the surface to be inspected from the linear diffused light source, and the specular reflection component and the specular diffuse reflection component contained in the specular reflection light from the surface to be inspected. Among them, more specular reflection components are extracted and received compared to the specular diffuse reflection components, and among the specular reflection components and the specular diffuse reflection components included in the specular reflection light from the surface to be inspected,
A specular diffuse reflection component is extracted and received, and the presence or absence of a surface flaw on the surface to be inspected is determined based on the received specular reflection component and the specular diffuse reflection component.

Next, the principle of operation of the above-described 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. 5 (a), the cold rolled steel sheet as a base passes through an alloying furnace after being 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 the columnar crystal 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. 5D, 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. 6 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. The incident light 8 that has entered the temper portion 6 crushed by the temper rolling rolls 5 a and 5 b is specularly reflected in the specular reflection direction of the steel plate 4 to become specular reflected light 9. On the other hand, the rolls 5a, 5
The incident light 8 that has entered the non-tempered portion 7 that leaves the original structure of the columnar crystal 3 where b does not abut, is microscopically reflected by one of the microplane elements on each surface of the columnar crystal 3 when viewed microscopically. However, the direction of reflection is the specular diffuse reflection light 10 which does not always coincide with 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. 7 (a) and 7 (b) when viewed macroscopically. That is, a sharp specular reflection occurs in the regular reflection direction of the steel sheet in the tempered portion 6, and reflected light having a spread corresponding to the angular distribution of the microplane on the surface of the columnar crystal 3 in the non-tempered portion 7. 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.

Since the tempered portion 6 and the non-tempered portion 7 are actually mixed macroscopically, 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 distributions of the specular reflected light 9 and the specular diffuse reflected light 10 are added in accordance with the respective area ratios of the tempered portion 6 and the non-tempered portion 7.

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 can be generally applied 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. 8, the barge defects (barge portion 11) found in the galvannealed steel sheet are the same as those in 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. Further, when the alloying of the barbed portion 11 is shallow, the angular distribution of the minute surface element is strong in the direction of the steel plate, 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 as follows:
Divided into types.

(A) The area ratio of the tempered portion 6 in the barb portion 11 and the angular distribution of the micro-surface element 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 minute surface of the non-tempered portion 7. 10 (a), FIG.
(A)).

(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 angle distribution of the small surface element of the non-tempered portion 7 in the barbed portion 11 is It is not different from the angular distribution of the micro-surface elements of the non-tempered part 7 in the base material part 12 (FIGS. 10B and 9B).

(C) The angle distribution of the minute surface element of the non-tempered portion 7 in the barbed portion 11 is determined by the non-tempered portion 7 in the base material portion 12.
However, the area ratio of the tempered portion 6 in the barbed portion 11 is not different from the area ratio of the tempered portion 6 in the base material portion 12 (FIGS. 10C and 9C). .

As shown in FIG. 11, the angle of inclination of the normal direction of the minute surface element 13 with which the incident light 8 comes into contact with respect to the normal direction of the steel plate 4 of the steel plate 4 is defined as the normal angle ξ of the minute surface element 13. FIG. 10A shows the relationship between the angle ξ and the area ratio S (ξ) of the temper portion 6 for the three cases (a), (b), and (c) described above.
(B) and (c).

The difference between the area ratio S (ξ) of the tempering portion 6 and the angular distribution of the micro-surface element 13 is shown in FIGS. 9A and 9B.
This is observed as a difference in the angular distribution of the reflected light amount as shown in FIG. An angle distribution indicated by a solid line in the drawing is a barbed portion angle distribution 11a corresponding to the barbed portion 11, and an angle distribution indicated by a dotted line in the drawing is a base material portion angle distribution 12a corresponding to the base material portion 12.

That is, FIG. 9A shows the angular distribution 1 of the scab.
FIG. 9B shows a case where there is a difference between the specular reflection component and the specular diffuse reflection component between 1a and the base material part angle distribution 12a, and FIG. 9B shows a case where only the specular reflection component exists. FIG. 9C shows a case where there is a difference only in the specular diffuse reflection component.

If there is a difference in the area ratio S (パ) of the tempered portion 6 between the barge angle distribution 11a and the base metal angle distribution 12a, as shown in FIGS. 9 (a) and 9 (b). , The difference is observed from the specular reflection direction. Specifically, the area ratio S (ξ) of the tempered portion 6 of the barbed portion 11 is determined when the reflected light of the barbed portion 11 is measured from the regular reflection direction and when the reflected light of the base material portion 12 is measured. Area ratio S of tempered portion 6 of base material portion 12
(Ξ) When the size is larger, the barbed portion 11 looks relatively brighter than the base material portion 12. Conversely, when the tempering ratio 6 of the barb portion 11 is smaller than the base material portion 12, the barge portion 11 is observed to be relatively darker than the base material portion 12.

Heavy part angle distribution 11a and base metal part angle distribution 1
If there is no difference in the area ratio S (ξ) of the temper portion 6 with that of the second portion 2a, as shown in FIG. I cannot observe its existence. However, when there is a difference in the diffusivity (angle distribution) of the specular diffuse reflection component, a defect is observed from a diffusion direction other than the regular reflection direction as shown in FIG.

For example, when the diffuseness (angular distribution) of the specular diffuse reflection component of the barb portion 11 is small, the barge portion 11 is generally observed brightly from a diffusion direction relatively close to the specular reflection direction, and 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 reliably detect such a scab 11 in distinction from the base material 12, the reflected light from the microscopic element 13 at an angle (normal angle ξ) is extracted in FIG. It is necessary to consider whether or not. For example, as in the example shown in FIGS.
1 and the base material portion 12 are detected, as shown in FIG.
Of the angular distribution of the micro-surface element 13
Is extracted for the normal angle ξ = 0, and the difference between the barbed portion 11 and the base material portion 12 is detected.

Here, the extraction of the reflected light at the normal angle ξ = 0 of the microscopic element 13 is mathematically expressed as follows. The characteristics (area ratio S (ξ)) of FIG.
This corresponds to integration by multiplying by a function indicating an extraction characteristic represented by a delta function δ (ξ) shown in (a) (hereinafter, this function is referred to as a weight function I (ξ)).

For example, measuring the reflected light at an angle of 40 ° shifted from the specular reflection direction by 20 ° at an incident angle of 60 ° requires a delta function δ as shown in FIG.
This corresponds to calculation using a weighting function I (ξ) of (ξ + 10).

As shown in FIG. 11, the reflection angle θ '
And the normal angle ξ of the microscopic element 13 and the incident angle θ of the incident light 8 can be obtained from the equation (1) by simple geometrical considerations. θ ′ = − θ + 2ξ (1) That is, what angle (normal angle ξ) is the small plane element 13
It can be understood that extracting the reflected light from is equivalent to what kind of weighting function I (ξ) is designed.

From this viewpoint, FIGS. 10A and 10B
Considering a weighting function I (ξ) for discriminating and detecting each barbed portion 11 from the base material portion 12 as shown in FIG.
Delta functions δ (ξ) and δ (ξ + 1) shown in FIGS.
0) is also one of the effective weight functions I (ξ).

The weighting function I (重 み) is not necessarily the one shown in FIG.
The extraction width of the specific normal angle shown in FIG. 2 does not need to be an infinitesimal delta function δ (、), but may have a certain signal width.

However, in such a discrimination method, the two optical systems cannot have the same field of view. Further, once a camera is installed for measuring diffuse reflection light, it is not easy to change the weight function I (ξ) because it is necessary to change the installation position of the camera.

For the former problem, measurement on the same optical axis is required. That is, it is desirable that both the specular reflection component and the specular diffuse reflection component can be captured only by measurement from the specular reflection direction of the steel plate 4 instead of capturing the diffuse reflection light.
For the latter problem, it is desirable that the weighting function I (ξ) can be set with a certain degree of freedom.

Therefore, 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. Also,
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 this linear diffused 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 central portion of the linear diffused light source 14, the incident light 8 incident on the tempering portion 6 is specularly reflected, and the steel plate is regularly reflected. All are captured in the 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 the micro-plane elements 13 oriented in such a direction is extremely small, the mirror-reflected light from the temper portion 6 is dominant among the reflected light captured by the light-receiving camera disposed in the steel plate regular reflection direction. .

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 steel plate regular reflection direction. Therefore, the specularly reflected light cannot be captured in the steel plate regular reflection direction. On the other hand, the light incident on the non-tempered portion 7 is specularly diffusely reflected, of which the light reflected in the steel plate regular reflection direction is captured by the light receiving camera. Therefore, all the reflected light captured by the light receiving camera disposed in the steel plate regular reflection direction is the specular diffuse reflection light reflected by the non-tempered portion 7.

When the above two cases are combined, the observation of the incident light 8 from the entire longitudinal direction of the linear diffused light source 14 in the regular reflection direction of the steel sheet is only This is the sum of the specular reflected light and the specular diffuse reflected light from the non-tempered part 7.

Next, how the polarization characteristics change when observed using the linear diffusion 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 a p-polarized component and an s-polarized component at the same time is reflected, the reflectance ratio ta of the p and s polarized light is ta.
The light is emitted as elliptically polarized light according to nΨ and the phase difference Δ.

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 diffusion light source 14 is generated by the inclined minute surface element 13 on the crystal surface of the non-tempered portion 7 of the steel plate 4. Specularly reflected and observed in the direction of regular reflection of the steel sheet. In this case, even if the 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 in consideration of the tilted minute surface element 13 that actually reflects. No, p, s
Since it is linearly polarized light having both polarization 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.

When linearly polarized light having an arbitrary polarization angle α having both p and s polarization components is incident on the steel plate 4 from the linear diffused light source 14, a minute plane element is positioned from a position other than the center of the linear diffused light source 14. Since the light incident on the light source 13 acts with the polarization angle α inclined, the shape of the elliptically polarized light emitted in the specular reflection direction of the steel sheet is the same as the light incident from the central part of the linear diffused light source 14 and specularly reflected by the temper part 6. Is different.

Hereinafter, the case where linearly polarized light having both p and s components is incident on the steel plate 4 from the linear diffusion light source 14 will be described in detail. First, as shown in FIG.
After the incident light 8 from 4 is linearly polarized by a polarizing plate 15 having an azimuth (polarization angle) α, the light is made incident on a horizontally arranged steel plate 4, and the specularly reflected light is received by a light receiving camera 16. As described above, with respect to the incident light 8 emitted from the point C on the linear diffused light source 14, the component specularly reflected by the tempered portion 6 of the steel plate 4 and the normal of the non-tempered portion 7 happens to be the normal line. Normal angle ξ = 0 facing the vertical direction
Are reflected from the point O on the steel plate 4 and contribute to the light reflected toward the light receiving camera 16.

On the other hand, as shown in FIG. 16, for the incident light 8 from the point A which is shifted from the point O of the steel plate 4 on the linear diffused light source 14 by an angle φ, the specular reflection component is
Since the light is reflected in directions different from the six directions, only the specular diffuse reflection component by the micro-plane element 13 having the normal angle ξ contributes.

Here, the angle φ indicating the incident direction of the incident light 8
And the normal angle ξ of the microscopic element 13 is given by Expression (2) by simple geometric consideration using the incident angle θ of the incident light 8 with respect to the steel plate 4.

COSξ = [2 · cos θ · cos ² (φ / 2)] / [sin ² φ + 4 · ｛cos ² θ · cos ⁴ (φ / 4) + sin ² θ · sin ⁴ (φ / 2)}] ^{1 / 2} (2) Next, the polarization state of the light reflected in this manner will be considered.

The polarization state E _C after the incident light 8 emitted from the point C passes through the polarizing plate 15 having an azimuth angle (polarization angle) α and is specularly reflected at the point O on the steel plate 4 is represented by polarization optics. Using a Jones matrix generally used in Eq., E _C = T · Ein (3) Here, Ein indicates a linear polarization vector of the azimuth angle (polarization angle) α of the polarizing plate 15, and T indicates a reflection characteristic matrix of the steel plate 4. Then, the linear polarization vector Ein and the reflection characteristic matrix T are given by equations (4) and (5), respectively.

[0062]

(Equation 1) However, tan: p, an amplitude reflectance ratio of s-polarized light delta: p, the phase difference between the reflectance of s-polarized light r _S: s similar amplitude reflectance of the polarized light, the incident emitted from point A on the linear diffusion light source 14 by the light 8, the polarization state E _a of light reflected by the light receiver 16 direction in the minute area element 13 of the normal angle xi], the incident plane is perpendicular to the analyzer of the polarizing plate 15 and the light receiving camera 16 BA (6)
Given by the formula. E _A = R (ξ) · T · R (−ξ) · Ein (6) where R is a rotation matrix and is given by equation (7).

[0063]

(Equation 2)

The equation (3) is a special case where the normal angle 微小 = 0 of the microscopic element 13 in the equation (6), and the equation (6) is used for both the specular reflection component and the specular diffuse reflection component. Can be considered in a unified way. (6) is calculated, and the elliptically polarized light state of the reflected light from the microscopic surface element 13 at the normal angle ξ is illustrated in FIG.

Here, the azimuth (polarization angle) of the incident polarized light is
α is 45 °, the incident angle θ is 60 °, and as the reflection characteristics of the steel plate 4, the arctangent of the amplitude reflectance ratio of p, s polarized light Ψ = 28 °, p,
The phase difference Δ of the reflectance of the s-polarized light was set to 120 °. It can be understood from FIG. 17 that the ellipse is inclined as the value of the normal angle に 対 し て changes with respect to the ellipse in the case of the normal angle ξ = O, that is, the specular reflection.

Therefore, for example, by inserting the analyzer 17 in front of the light-receiving camera 16 and setting the analysis angle β, it is possible to determine which normal angle 反射 to extract more reflected light from the microscopic element 13. Can be selected.

[0067] To quantify this, as shown in FIG. 16, definitive after inserting the analyzer 17 of the detection optical angle β with respect to the reflected light of the polarization state E _A represented by the formula (3) When the polarization state E ₀ is obtained, the equation (8) is obtained.

[0068] _{E 0 = R (β) ·} A · R (-β) · E A = R (β) · A · R (-β) · R (ξ) · T · R (-ξ) · Ein ... (8) where A is a matrix representing the analyzer 17 and is represented by the equation (9).

[0069]

(Equation 3)

Next, from this equation (8), the light intensity of the reflected light from the microscopic surface element 13 at the normal angle ξ detected by the light receiving camera 16 is obtained. As described above, when the area ratio of the microscopic element 13 is S (ξ), the following equation (10) is satisfied.

[0071] _{S (ξ) · | E 0} | 2 = r S 2 E P 2 · S (ξ) · I (ξ, β) I (ξ, β) = tan 2 Ψ · cos 2 (ξ-α) · Cos ² (ξ-β) + 2 · tanΨ · cos Δ · cos (ξ-α) · sin (ξ-α) × cos (ξ-β) · sin (ξ-β) + sin ² (ξ-α) · sin ² (β−ξ) (10) In the above equation, I (ξ, β) is a weighting function indicating how much the reflected light from the microscopic surface element 13 having the normal angle ξ can be extracted as described above. And depends on the optical system and the polarization characteristics of the subject. Then, it reflectance r _S ² of the steel plate 4, the incident light amount E _P ^2, multiplied by the area ratio S (xi]) is the light intensity detected.

When considering an object having a uniform surface material such as a surface-treated steel sheet, the value of the reflectance r _S ² is considered to be constant. Further, the incident light amount E _P ² good as well constant value if uniform regardless of the position of the incident light amount is a light source.

Therefore, the light intensity detected by the light receiving camera 16 can be obtained by considering the area ratio S (ξ) of the small plane element 13 at the normal angle ξ and the weight function I (ξ, β). Here, consider the weight function I (ξ, β). If an attempt is made to select an analysis angle β ₀ of the analyzer 17 such that the contribution of the normal angle ξ from the micro-plane element 13 is greatest, the candidate is given by solving the following equation (11) for β. Can be

[0074]

(Equation 4)

When the normal angle ξ = 0, that is, the analysis angle β that maximizes the contribution of the specular reflection component, is obtained from the equation (11), the analysis angle β is about −45 °. However, also in this case, as the reflection characteristics of the steel plate 4, the inverse tangent 反射 = 28 ° and the phase difference Δ = 120 ° of the reflectance ratio described above are adopted, and the azimuth of the polarizing plate 15 with respect to the incident light 8 from the linear diffusion light source 14 is adopted. Angle (polarization angle) α = 45 ° was employed.

FIG. 18 shows that the detection angle β of the analyzer 17 is -45.
The relationship between the normal angle ξ of the microscopic element 13 and the weighting function I (ξ, −45) in the case of ° is shown. However, the maximum value of the weight function I (ξ, -45) is normalized to [1] for easy viewing.

From the characteristics of FIG. 18, the normal angle ξ = 0 °, that is, the specular reflection component is the most dominant, and conversely, the normal angle ξ =
It can be understood that the specular diffuse reflection light from the minute surface element 13 near ± 35 ° is least extracted.

On the other hand, the angle of analysis β of the analyzer 17 for extracting the reflected light with the normal angle ξ = ± 35 ° best is given by (10)
According to the equations (11) and (11), β is approximately 45 °.
FIG. 19 shows the relationship between the normal angle ξ of the microscopic element 13 and the weighting function I (ξ, 45) with respect to the analysis angle β = 45 ° of the analyzer 17.

The reason why the characteristics of the weighting function I (ξ, β) in FIG. 19 are not bilaterally symmetric is based on the incident surface (the plane formed by the incident light 8 and the reflected light with respect to the minute surface element 13). When the normal angle ξ of the microscopic element 13 is positive, the apparent azimuth angle (polarization angle) α of the polarization of the incident light 8 becomes small (p
(Nearly polarized light) and the p-polarized light reflectance of the steel plate 4 is smaller than the s-polarized light reflectance.

FIG. 19 also shows the weighting function I (ξ, 90) calculated for β = 90 °, which is an intermediate characteristic between the detection angle β = −45 ° and 45 ° of the analyzer 17. As shown by the equation (10), the intensity of the reflected light from the microscopic surface element 13 at the normal angle ξ is given by the product of the weight function I (ξ, β) and the area ratio S (ξ). The light intensity received by the light receiving camera 16 is obtained by integrating [S (ξ) ξI (ξ, β)] with respect to the normal angle ξ. For example, when the reflected light from the steel plate 4 having the reflection characteristics as shown in FIG. 20 is received through the analyzer 17 having the analysis angle β of −45 °, the area ratio S (ξ) shown in FIG. Weight function I shown in FIG.
The value obtained by integrating with the weight shown by (積分, β) is the actually received light intensity.

Therefore, the surface of the steel plate 4 is placed on the surface of FIG.
(B) Consider a case where the barbed portion 11 having characteristics as shown in (c) exists. In this case, the area ratios S (ξ) are as shown in FIGS.

First, consider the case where there is a difference only in the specular reflection component as shown in FIGS. 9 (b) and 10 (b). The light intensity when such a flaw is received through the analyzer 17 with the analysis angle β = −45 ° is the area ratio S (ξ) shown in FIG.
18 is multiplied by a weighting function I (ξ, β) shown in FIG. 18, the difference in the amount of reflected light between the base material portion 12 and the stub 11 can be detected.

The light intensity when the same flaw is received through the degree analyzer 17 with the analysis angle β = 45 ° is shown in FIG.
0 (b), since there is no difference in the specular diffuse reflection component, the weight function I (ξ,
β) and integrating
It is not possible to detect a difference between the base material portion 12 and the barb portion 11.

When there is a difference only in the specular diffuse reflection component as shown in FIGS. 9C and 10C, on the contrary, the light passes through the analyzer 17 having the analysis angle β = −45 °. In this case, the light cannot be detected, and can be detected when the light passes through a degree analyzer 17 having an analysis angle β = 45 °.

However, each weight function I shown in FIG.
Looking at the characteristics of the weight function I (ξ, 45) of the analyzer 17 with the analysis angle β = 45 ° of (ξ, β), the weight function I (0, 45) is [ 0.2]. That is, even if the analysis angle β of the analyzer 17 is 45 °
The weight function I (0, 45) also extracts a specular reflection component of about １ ／ of the specular diffusion component at the normal angle ξ that is most frequently extracted.

On the other hand, as described above, the angle distribution of the micro-plane elements 13 of the steel sheet 4 temper-rolled by the rolls 5a and 5b generally has a normal angle 法 of the micro-plane elements 13 as shown in FIG.
It protrudes at = 0. Therefore, if there is no difference in the specular reflection component between the scab 11 and the base material 12,
If the difference between the specular diffuse reflection components is small, the area ratio S (ξ) is high and the amount of reflected light is large. The differences may not be apparent.

In order to solve this problem, it is necessary to receive no specular reflection component at all or to reduce the weight of the specular reflection component as much as possible. Therefore, the λ / 4 plate (1 /
4 wavelength plate). Specifically, as shown in FIG. 16, the λ / 4 plate 18
Insert

That is, when the λ / 4 plate 18 is inserted in accordance with the major axis and the minor axis of the elliptically polarized light of the specular reflection light corresponding to the normal angle ξ = 0 of the microscopic element 13 in FIG. The transmitted light has a phase difference Δ of the reflectance of p, s polarized light.
Depending on the sign of (−180 ≦ Δ ≦ 180), as shown in FIG. 21, the light is converted into any linearly polarized light showing a rectangular diagonal line surrounding the incident elliptically polarized light.

If the azimuth angle (polarization angle) β of the analyzer 17 is set so as to be orthogonal to the linearly polarized light, the specular reflection component is completely cut off. On the other hand, the normal angle ξ ≠
Since the major and minor axes of the elliptically polarized light component of the specular diffuse reflection component of 0 are shifted, the shape is converted even when the elliptically polarized light component passes through the λ / 4 plate 18, but remains elliptically polarized light.

As described above, by using the λ / 4 plate 18 and the analyzer 17, the specular reflection component contained in the regular reflection light can be completely cut off, and only the specular diffuse reflection component can be extracted. become.

The normal angle ξ at which the difference between the specular diffuse reflection component of the base material portion 12 and the specular diffuse reflection component of the barge portion 11 is eliminated is shown in FIG.
In (c), the normal angle ξ is around ± 20 °, but if there is a flaw whose angle happens to be around ± 30 degrees, it cannot be detected through the λ / 4 plate 18 and the analyzer 17. .

In that case, another weighting function (for example, I
(Ξ, 90)) is the analysis angle β (eg, 90 °)
It is sufficient to prepare another analyzer 17 and receive light with the third light receiving camera.

However, the weighting function I (ξ, 90) when the analysis angle β of the analyzer 17 is 90 ° is based on the λ / 4 plate 18 and the analyzer 1
7 and the weighting function I (ξ, -45) of the detection angle β = −45 ° are not so small that completely independent information may not be obtained.

In this case, the third light receiving camera is connected to the steel plate 4
May be installed in a general diffuse reflection direction different from the mirror reflection direction. A weight function I in the form of a delta function having a peak at the same position as the analysis angle β = 90 ° of the analyzer 17
In order to realize (ξ), as can be understood from FIG. 11, when the incident angle θ of the incident light 8 is 60 °, the position is shifted by about 35 ° from the specularly reflected light, that is, the diffused position in the 25 ° direction. What is necessary is just to install the 3rd light receiving camera.

Generally, since the reflection characteristics of the base material portion 12 and the barge portion 11 on the surface of the steel plate 4 are any of FIGS. 9A, 9B, and 9C, the oversight of the barge portion 11 can be avoided. To eliminate it, three different weighting functions are used and three normal angles ξ
It is necessary to extract and receive the reflected light from the micro-plane element 13.

When there is a difference between the specular reflection component and the specular diffuse reflection component as shown in FIGS. 9A and 10A, basically, the reflected light passing through any of the analyzers 17 is used. However, it is possible to detect a difference between the base material portion 12 and the barb portion 11.

Therefore, in the present invention, the linear diffusion light source 14
Of the specular reflection component and the specular diffuse reflection component included in the specularly reflected light from the surface to be inspected by the first light receiving means, for example, using an analyzer to compare the specular reflection component with the specular diffuse reflection component. A large amount of light is extracted and received, and the specular diffuse reflection component included in the specularly reflected light from the inspection surface is,
Extraction is performed using a 波長 wavelength plate and an analyzer.

Therefore, even if the first and second light receiving means for receiving only the specularly reflected light from the surface to be inspected are used as shown in FIG.
(A), (b), and (c), the presence of the barbed portion 11 in each reflection characteristic of the surface of the steel plate 4 can be detected more reliably and more accurately in comparison with the base material portion 12.

With such an optical system, the measurement is performed on the common optical axis from the specular reflection direction, so that the specular reflection component and the specular diffuse reflection component are not affected by variations in the steel plate distance and speed. Two corresponding signals can be obtained, and a surface flaw inspection apparatus and a surface flaw inspection method capable of detecting a pattern-shaped barbed flaw having no noticeable unevenness without causing any omission are realized.

[0100]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1A is a side view of a surface flaw inspection apparatus employing a surface flaw inspection method according to one embodiment of the present invention, and FIG. 1B is a top view of the same surface flaw inspection apparatus.

The surface flaw inspection apparatus of this embodiment is installed in a quality inspection line of an alloyed galvanized steel sheet in a steel plant. 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 22
In this method, light from a metal halide light source is projected into the inside from both ends of a transparent light guide rod partially coated with a diffuse reflection paint, thereby obtaining uniform light emission in the width direction.

The incident light 23 to the steel plate 21 emitted from each position of the linear diffused light source 22 is transmitted through the cylindrical lens 24 and the polarizing plate 25 to the incident angle θ of, for example, 60 ° with respect to the entire width of the running steel plate 21. Irradiation. Polarizing plate 25
Is set to 45 °.

The reflected light 26 reflected by the steel plate 21 is 60 ° with respect to the regular reflection direction of the steel plate, ie, the normal direction of the steel plate 21.
The light enters the first light receiving camera 27a and the second light receiving camera 27b arranged in the directions. Further, the third light receiving camera 28 is arranged in a light receiving angle direction of 25 ° with respect to the normal direction of the steel plate 21.
Are arranged. The third light-receiving camera 28 is one of the diffusely reflected lights that are diffusely reflected by the steel plate 21 in various directions.
Diffuse reflected light in the direction of 25 ° is incident.

The first, second and third light receiving cameras 27
Reference numerals a, 27b, and 28 denote linear array cameras in which each optical axis is set in the width direction of the steel plate 21. And 3
The shift of the field of view of the two light receiving cameras 27a, 27b, 28
The correction is made in the signal processing unit 40. When the optical axes of the respective light receiving cameras 27a, 27b, 28 are maintained in parallel in this manner, the three light receiving cameras 27a, 27b, 28
Pixels in the width direction of the steel plate 21 correspond one-to-one with the same visual field size. As described above, by adopting the linear array camera, the loss of the light amount is eliminated, and efficient measurement can be performed.

An analyzer 29a having an analysis angle β of -45 ° is mounted on the front surface of the lens of the first light receiving camera 27a. A λ / 4 plate (／ wavelength plate) 37 and an analyzer 29b are mounted on the front surface of the lens of the second light receiving camera 27b. The direction of the linearly polarized light converted by the λ / 4 plate 37 and the detection angle β of the analyzer 29b are:
The relationship has already been set with reference to FIG.

Note that no analyzer is attached to the front of the third light receiving camera 28, and the third light receiving camera 28 directly receives diffusely reflected light from the steel plate 21. Here, as each of the light receiving cameras 27a, 27b, 28, a two-dimensional CCD camera can be used instead of the 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.

A fluorescent lamp may 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.

The light intensity of each pixel of one line in the width direction of the steel plate 21 in the reflected light 26 and the diffused reflected light received by each of the light receiving cameras 27a, 27b, 28 is converted into light intensity signals a, b, c, respectively. The signal is converted and transmitted to the signal processing unit 40 as a determination processing unit.

FIG. 2 is a block diagram showing a schematic configuration of the signal processing section 40. First light receiving camera 27a in which -45 degree analyzer 29a is incorporated, λ / 4 plate 37 and analyzer 29
The light intensity signals a, b, and c input from the second light receiving camera 27b in which the light receiving angle b is incorporated and the third light receiving camera 28 in which the light receiving angle is set to 25 ° in which the analyzer is not installed are respectively shown. It is input to the average value thinning units 30a, 30b, 30c.

Each average value thinning section 30a, 30b, 30c
Averages the light intensity signals a, b, and c input from each of the light receiving cameras 27a, 27b, and 28 for each scan cycle of each of the light receiving cameras 27a, 27b, and 28, and makes the steel plate 21 have a longitudinal resolution in the signal processing. When a corresponding distance is moved, a signal for one line is output.

By performing such a thinning process,
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. Further, since the light intensity signals a, b, and c for each scanning cycle are averaged, the resolution of one line in the moving direction of the steel plate in the signal processing is larger than the visual field size of the light receiving cameras 27a, 27b, and 28 in the moving direction of the steel plate. Even in the case of a sufficiently large value, an average value obtained by finely measuring the interval can be used, so that oversight can be eliminated.

Each average value thinning section 30a, 30b, 30c
The light intensity signals a, b, and c that have been subjected to the signal processing are input to the following preprocessing units 31a, 31b, and 31c. Each of the pre-processing units 31a, 31b, 31b corrects luminance unevenness of a signal of one line. 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 31a, 31b, 31c
Are also detected, and a process for preventing a sudden change in the light intensity signals a, b, and c at the edge from being erroneously recognized as a flaw is also performed. The light intensity signals a, b, c processed by the pre-processing units 31a, 31b, 31c are input to the following binarization processing units 32a, 32b, 32c.

Each of the binarization processing sections 32a, 32b, 32c
Compares the data of each pixel included in each of the light intensity signals a, b, and c with a predetermined threshold value, extracts flaw candidate points, and sends the flaw candidate points to the next feature amount calculation units 33a, 33b, and 33c. Send out.

The feature amount extraction units 33a, 33b, 33c
The continuous flaw candidate points are determined as one flaw candidate area, and for example, a position feature amount such as a start address and an end address and a density feature amount such as a peak value are calculated.

In the specular flaw determining section 34 and the specular diffuse flaw determining section 35, based on the characteristic amounts calculated by the characteristic amount extracting sections 33a, 33b, 33c corresponding to the light receiving cameras 27a, 27b, 28, respectively. Judge the type and degree of flaw.

The flaw determining section 36 determines the final flaw type and the degree of the final flaw on the steel plate 21 to be inspected, based on the determination results and the characteristic amounts of the specular flaw determining section 34 and the specular diffuse flaw determining section 35. Is determined.

In addition, the comprehensive judgment section 36 also corrects the field of view shift in each of the light receiving cameras 27a, 27b, 28 based on the position feature quantity from each feature quantity extraction section 33a, 33b, 33c. As described above, the correction of the field of view between the light receiving cameras 29a to 29c is performed for each feature amount, so that it is not necessary to adjust the field of view between the light receiving cameras 27a, 27b, and 28 in pixel units.

[0118]

1 and 2 show the results of measuring the surface flaws of an alloyed galvanized steel sheet using the surface flaw inspection apparatus of the embodiment shown in FIG.
Table 1 shows the determination results based on the measurement results.
Each of the measured flaws is a flaw in which the area ratio S (の) of the tempered portion 6 shown in FIG. 9B is larger than the base material portion 12 in the barb portion 11, but the diffusivity of the non-tempered portion 7 does not change. The area ratio S (ξ) of the tempered portion 6 shown in FIG.
There is no significant difference between the two, but a flaw having a difference in diffusivity.

FIG. 9 shows the central portion of the steel plate 21 in the width direction.
When a flaw of the type shown in FIG.
The first light receiving camera 27a having the analysis angle β of the analyzer 29a set to 5 °, the second light receiving camera 27b having the λ / 4 plate 37 and the analyzer 29b, and the light receiving angle set to 25 ° FIGS. 3A, 3B, and 3C show changes in the light intensity signals a, b, and c for one width of the steel material 21 obtained by scanning the third light receiving camera 28 for one line in the width direction. .

As shown in the figure, a peak waveform corresponding to a flaw (severed portion 11) is generated in the light intensity signal a of the first light receiving camera 27a with the detection angle β set at -45 °. In this case, the light intensity signal b of the second light receiving camera 27b in which the detection angle β is set to 45 ° does not have a peak waveform corresponding to the flaw (the stub 11).

Further, the center of the steel plate 21 in the width direction is shown in FIG.
When a flaw of the type shown in FIG.
The first light receiving camera 27a having the analysis angle β of the analyzer 29a set to 5 °, the second light receiving camera 27b having the λ / 4 plate 37 and the analyzer 29b, and the light receiving angle set to 25 ° FIGS. 4A, 4B, and 4C show changes in the light intensity signals a, b, and c for one width of the steel material 21 obtained by scanning the third light receiving camera 28 for one line in the width direction. .

As shown, the light intensity signal b of the second light receiving camera 27b having the λ / 4 plate 37 and the analyzer 29b is shown.
A peak waveform corresponding to the flaw (severed portion 11) is generated.
In this case, the light intensity signal a of the first light receiving camera 27a in which the detection angle β is set to −45 ° does not have a peak waveform corresponding to the flaw (the stub 11).

[0123]

[Table 1]

For comparison, in the prior art, the incident angle was 6
Light was incident at 0 °, and the result of measurement with no polarization from the specular reflection direction (60 °) and the light receiving angle (−40 °) direction shifted by 20 ° from the incident direction was also described.

In the prior art, light is received at two light receiving angles and a logical sum is taken to remove noise. However, it is impossible to detect the two light receiving angles simultaneously for these flaws. Furthermore, there are flaws that cannot be detected at either of the light receiving angles.

On the other hand, in the embodiment of the present invention, the reflected light components corresponding to the three different light receiving angles are converted into the two analyzers 29a, 29b and λ having the different detection angles β.
Since the ４ plate 37 is used and the light receiving angle is set to a value different from the specular reflection direction, any one of the first, second, and third light receiving cameras 27a, 27b, and 11
Can be detected separately from the base material portion 12.

The present invention is not limited to the above embodiment. In the embodiment shown in FIG. 1, three light receiving cameras 27a, 27b, and 28 are used, but a first light receiving camera 27a having a -45 degree analyzer 29a, a λ / 4 plate 37, and an analyzer are used. 29b and the second
Even if only two light receiving cameras with the light receiving camera 27b are used, the scab 11
Can be sufficiently detected separately from the base material 12.

[0128]

As described above, the surface flaw inspection apparatus and the surface flaw inspection method of the present invention are based on the knowledge that the specular reflection light on the surface to be inspected comprises a specular reflection component and a specular diffuse reflection component. , Each component is separately extracted and detected. Specifically, using a linear diffused light source, p
Polarized light having both polarized light and s-polarized light is incident on the surface to be inspected, a component containing more specular reflection components is extracted from the specular reflection direction of the steel sheet using an analyzer, and the quarter-wave plate and the analyzer are separated. A configuration for extracting the specular diffuse reflection component in combination is adopted.

With this configuration and method, it is possible to detect a flaw that cannot be observed only from the specular reflection component, and it is possible to detect a pattern-shaped scorch flaw having no noticeable unevenness, which could not be detected conventionally, without any omission. It is now possible.

Further, from the viewpoint of quality assurance, it is an absolute condition that the surface flaw inspection apparatus has no undetection. Therefore,
According to the present invention, for the first time, an undetected surface flaw inspection apparatus that can be widely applied to surface-treated steel sheets and the like can be realized, so that surface flaw inspection that conventionally relied on visual inspection by inspectors can be automated. In this respect, the industrial utilization effect is great.

[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 an 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 the same surface defect inspection apparatus.

FIG. 5 is a view showing a manufacturing method and a detailed cross-sectional structure of an alloy galvanized steel sheet to be inspected by the surface defect inspection apparatus.

FIG. 6 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. 7 is an angle distribution diagram of reflected light between the tempered portion and the non-tempered portion.

FIG. 8 is a diagram for explaining a generation process of a scab on a steel plate;

FIG. 9 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. 10 is a diagram showing a relationship between a normal angle of a micro planar element and an area ratio in an irradiated portion of a steel sheet.

FIG. 11 is a diagram showing a relationship between an incident angle of incident light on a steel plate and a normal angle of a small surface element.

FIG. 12 is a diagram showing a relationship between a normal angle of a small surface element and a weight function;

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.

FIG. 15 is a view showing reflected light from a minute surface element when each incident light from the center of the linear diffused light source is polarized.

FIG. 16 is a view showing reflected light from a minute surface element when each incident light from a position other than the center of the linear diffused light source is polarized.

FIG. 17 is a diagram showing a relationship between a normal angle of a small plane element and an elliptically polarized state of reflected light.

FIG. 18 is a diagram showing a relationship between a normal angle of a small plane element and a weighting function when an analyzer is inserted in an optical path of reflected light.

FIG. 19 is a diagram illustrating a relationship between a normal angle of a microscopic element and a weighting function when the analysis angle of the analyzer is changed.

FIG. 20 is a diagram showing a relationship between a normal angle of a small surface element and an area ratio.

FIG. 21 is a diagram showing the relationship between the polarization state of reflected light and the linear polarization state obtained by inserting a quarter-wave plate.

[Explanation of symbols]

 4, 21 ... steel plate 6 ... tempered part 7 ... non-tempered part 8, 23 ... incident light 9 ... specular reflected light 10 ... specular diffused reflected light 11 ... hedged part 12 ... base part 14, 22 ... linear diffused light source 15, 25: Polarizing plate 16: Receiving camera 17, 29a, 29b: Analyzer 18, 37: λ / 4 wavelength plate 24: Cylindrical lens 26: Reflected light 27a: First receiving camera 27b: Second receiving camera 28: Second 3 light receiving camera 40 ... signal processing unit

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yuji Matoba 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (72) Masakazu Inomata 1-1-1, Marunouchi, Chiyoda-ku, Tokyo No. 2 Inside Nippon Kokan Co., Ltd. (72) Inventor Shoji Yoshikawa 1-1-2 Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Co., Ltd. (72) Inventor Tsutomu Kawamura 1-1-2 Marunouchi, Chiyoda-ku, Tokyo No. Nippon Kokan Co., Ltd. (72) Inventor Hiroyuki Sugiura 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Co., Ltd.

Claims (3)

[Claims] 1. A linear diffuse light source for irradiating illumination light on a surface to be inspected, and a specular reflection component and a specular diffuse reflection component among specular reflection components and specular diffuse reflection components included in specular reflection light from the surface to be inspected. A first light-receiving means for extracting and receiving more specular reflection components, and extracting and receiving a specular diffuse reflection component of a specular reflection component and a specular diffuse reflection component included in the specular reflection light from the surface to be inspected. A second light receiving unit; and a determination processing unit that determines presence or absence of a surface flaw on the surface to be inspected based on the specular reflection component and the specular diffuse reflection component received by the first and second light receiving units. Surface flaw inspection device. 2. The linear diffuse light source receives polarized light having an azimuth component parallel and a azimuth component perpendicular to a plane of incidence with respect to the surface to be inspected, and the first light receiving unit includes specular reflection. An azimuth analyzer for extracting more components, wherein the second light receiving unit is adjusted to 1/1 adjusted in a direction to extract only specular diffuse reflection light included in the regular reflection light.
2. The apparatus according to claim 1, further comprising a four-wave plate and an analyzer.
The described surface flaw inspection device. 3. An illumination light is incident on a surface to be inspected from a linear diffuse light source, and is compared with a specular diffuse reflection component among a specular reflection component and a specular diffuse reflection component included in the specular reflection light from the surface to be inspected. Extracting and receiving more specular reflection components, and extracting and receiving the specular diffuse reflection component of the specular reflection component and the specular diffuse reflection component included in the specular reflection light from the surface to be inspected; A method for inspecting a surface flaw, comprising determining the presence or absence of a surface flaw on the surface to be inspected based on a reflection component and a specular diffuse reflection component.