JP2000162151A - Surface flaw inspecting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely detect a pattern-like scab defect having remarkable irregular property. SOLUTION: This device is provided with a linear diffused light source 22 for making a polarized light incident on a surface to be inspected 21; first light receiving means 28a, 29a having analyzers of the azimuth for extracting the mirror reflected component included in the regular reflected light from the surface to be inspected 21 more; second light receiving means 28b, 29b having analyzers of the azimuth for extracting the mirror diffused reflected component included in the regular reflected light from the surface to be inspected 21 more; and a judgment processing part 40 for judging the presence of a surface flaw on the surface to be inspected 21 on the basis of the mirror reflected component and mirror diffused reflected component received by the first and second light receiving means. Light quantity reducing filters 20a-20f for controlling the each light quantity incident on the first and second light receiving means to a prescribed value are inserted to the optical path of the regular reflected light from the surface to be inspected 21 to be incident on 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 inspection apparatus for irradiating a surface to be inspected, for example, a thin steel sheet surface, with light to optically detect surface flaws and the like on the surface to be inspected.

[0002]

2. Description of the Related Art By irradiating a surface to be inspected such as a thin steel plate surface with light and analyzing reflected light from the surface to be inspected, surface defects existing on the surface to be inspected are optically detected. Conventionally, various methods have been proposed and implemented for surface flaw inspection.

For example, Japanese Patent Laid-Open No. Sho 58-2 discloses a method for detecting flaws on a metal object by irradiating light to the surface of the object to be inspected and detecting specularly reflected light and diffusely reflected light from the surface of the object to be inspected by a camera.
No. 04353. In this surface flaw detection method, light is incident on the surface of the object to be inspected at an angle of 35 ° to 75 °, and the light reflected from the surface of the object to be inspected is reflected within the specular direction and the incident direction or within 20 ° from the specular direction. Light is received by two cameras installed in the angle directions of. 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 the two cameras simultaneously detect an abnormal value, the abnormal value is regarded as a flaw, thereby realizing a surface flaw detection method which is not affected by noise.

A method for inspecting the surface of an object to be inspected for flaws by receiving backscattered light from the object to be inspected is disclosed in
228943. In this flaw inspection method, light is incident on the stainless steel sheet at a large incident angle, 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 sheet. .

Further, a flat steel hot flaw detection apparatus which detects a plurality of backscattering reflection points is disclosed in Japanese Patent Application Laid-Open No. Hei 8-178687.
No. 1993. This flat steel hot flaw detector detects a scratch on a hot-rolled flat steel. And in this flaw detection device, the flaw slope angle of the scratch is 10 ° to 40 °.
゜, a plurality of cameras are arranged in the backscattering reflection direction so as to cover all the specularly reflected light from the flaw slopes in this range.

A surface measuring device utilizing bias is disclosed in Japanese Patent Application Laid-Open Nos. Sho 57-166533 and Hei 9-1665.
No. 52 has proposed this.

In a measuring device proposed in Japanese Patent Application Laid-Open No. 57-166533, a polarized light 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. And 3 from the polarization camera
A technique of displaying a book signal on a monitor by signal processing similar to that of the color T5 system and visualizing the polarization state is disclosed. This technique utilizes an ellipsometry technique, and it is desirable that the light source be parallel light, for example, a laser beam.

In the surface inspection apparatus proposed in Japanese Patent Application Laid-Open No. 9-166552, Japanese Patent Application Laid-Open
In the same manner as the technique described in JP-A-533, the flaw on the surface of the steel sheet is inspected by using ellipsometry.

[0009]

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 in a pattern-shaped scab defect having no noticeable unevenness.

For example, the flaw detector disclosed in Japanese Patent Application Laid-Open No. 58-204353 has two cameras for receiving specularly reflected light and scattered reflected light. The purpose 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 that do not crack or turn up on the surface, are applicable since both cameras capture 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 catch the flaw signal, all the flaws cannot be detected. .

The surface condition inspection method disclosed in Japanese Patent Application Laid-Open No. Sho 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 mainly intended for scratches, and is based on catching specularly reflected light on a flaw slope. In the case of a flaw, such as a pattern-shaped barbed flaw, which is not provided, some of the flaws cannot be caught by the backscattering, and there has been a problem that detection is omitted. 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 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 the ellipsometry, it is necessary to receive reflected light from the same point at a corresponding pixel of each CCD and calculate an ellipsometric parameter 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.

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 so that the same area is viewed. 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. Therefore, there is a problem that it is difficult to perform pixel alignment.

Furthermore, in Japanese Patent Application Laid-Open Nos. 58-204353 and 8-17867, since the optical axes of a plurality of cameras are not common and the emission angles are different, the field of view of the corresponding pixels of two obtained images is different. In addition to the difference in size, there is a problem that a positional shift occurs in the visual field due to flapping of the surface to be inspected or a change in distance due to a change in thickness of the object. Particularly, in Japanese Patent Application Laid-Open No. 58-204353, it is necessary to take a logical sum for the same field of view with two cameras, so that the problem is serious.

Japanese Patent Laid-Open No. 57-166 using polarized light
According to Japanese Patent Application Laid-Open No. 533 and JP-A-9-166552, when the manufacturing conditions of the steel sheet are changed or the type of the steel sheet is changed, the amount of light received by the camera set at each azimuth greatly changes. However, there was a problem that a signal having a good S / N ratio could not be obtained.

That is, if the manufacturing conditions of the steel sheet are changed or the type of the steel sheet is different, the physical property values of the base material on the surface to be inspected are different, so that the reflection characteristic of the surface to be inspected with respect to the polarized light changes, and the ratio of the intensity of the polarized light component to be received. Changes. For this reason, in a camera set to receive the polarization intensity of different azimuth angle components, even when the steel sheet surface under certain conditions is set to the optimal light amount, when the steel sheet surface under different conditions is used, In some cases, the light intensity was low or saturated, and normal inspection could not be performed.

For 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 the 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 and detects specular reflection components and specular diffuse reflection components contained in light reflected from a surface to be inspected, and detects the amount of light of each component. By controlling to a predetermined value, it is possible to reliably detect a pattern-shaped scab defect having no remarkable unevenness such as surface cracks on the surface to be inspected, support, and turning up,
An object of the present invention is to provide a surface flaw inspection apparatus which can exhibit high defect detection accuracy and can be sufficiently incorporated in a product quality assurance line.

[0022]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a method for injecting polarized light having an azimuth component parallel to and perpendicular to the surface to be inspected. Linear diffuse light source, and an azimuth analyzer that extracts more specular reflection components than specular reflection components among specular reflection components and specular reflection components contained in specular reflection light from the surface to be inspected. And a first light receiving unit having an azimuth angle for extracting more specular diffuse reflection components than specular reflection components among specular reflection components and specular diffuse reflection components included in specular reflection light from the surface to be inspected. Second light receiving means having an analyzer;
A surface flaw inspection apparatus comprising: a determination processing unit that determines the presence or absence of a surface flaw on a surface to be inspected based on specular reflection components and specular diffuse reflection components received by first and second light receiving units.

Further, in order to control each light amount incident on the first and second light receiving means to a predetermined value in an optical path of the regular reflection light from the surface to be inspected incident on the first and second light receiving means. Light intensity reduction filter is inserted.

According to another aspect of the present invention, in the above-described surface flaw inspection apparatus, a plurality of light quantity reduction filters having different light transmittances are incorporated, and the light quantity reduction filters having an optimum transmittance are provided in accordance with a change in the surface to be inspected. Is provided for switching the amount of light into each optical path.

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 object is an alloyed galvanized steel sheet, as shown in FIG. 5A, 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 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 the above is referred to as a tempered portion 6, and the other portion having the original concavo-convex shape not contacting the temper rolling rolls 5 a and 5 b 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 incident on the temper 6 crushed by the temper rolling rolls 5 a and 5 b is reflected specularly in the regular reflection direction of the steel plate 4 to become specular reflected light 9. On the other hand, the original columnar crystal 3 to which the rolls 5a and 5b of the temper rolling do not abut.
The incident light 8 incident on the non-tempered part 7 which leaves the structure of FIG. 2 is mirror-reflected by one micro-plane element on each surface of the columnar crystal 3 in a microscopic view. The specular diffuse reflection light 10 does not always coincide with the regular reflection direction.

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.

Actually, since the tempered portion 6 and the non-tempered portion 7 are 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 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. 8, 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. 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 stub 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 barbed portion 11 and the angular distribution of the minute surface element of 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 inclination angle 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 sheet 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).

FIGS. 9A and 9B show the difference between the area ratio S (及 び) of the temper portion 6 and the angular distribution of the minute surface element 13.
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.

Severe part angle distribution 11a and base material 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 diffusivity (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 micro-surface element 13 at what 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 can be mathematically expressed by 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, the small plane element 13 at what angle (normal angle ξ)
It can be understood that extracting the reflected light from is equivalent to what kind of weighting function I (ξ) is designed.

From such a 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).

Note that the weighting function I (ξ) is not always
The width for extracting only the specific normal angle shown in FIG. 2 does not need to be an infinitesimal delta function δ (ξ), and 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 radiated 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 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 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 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. When linearly polarized light having an arbitrary polarization angle having both p-polarized light component and s-polarized light component at the same time is reflected, the reflectance ratio of p and s-polarized light tanΨ
And elliptically polarized light corresponding to the phase difference Δ is emitted.

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 center 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. 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, minute linear light inclined from a position other than the center of the linear diffused light source 14. Since the light incident on the surface element 13 acts with the polarization angle α inclined, the shape of the elliptically polarized light emitted in the steel plate regular reflection direction is
This is different from light that is incident from the center of the linear diffused light source 14 and is specularly reflected by the tempering unit 6.

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 below. 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 shifted by an angle φ when viewed from the point O of the steel plate 4 on the linear diffused light source 14, 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 · cosθ · 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 as described above 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 the 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.

[0067]

(Equation 1)

[0068] However, tan: p, s-polarized light amplitude reflectance ratio of the delta: p, the phase difference r _S of the reflectance of s-polarized light: s-polarized light amplitude reflectance similarly, from the point A on the linear diffusion light source 14 emitting the incident light 8 which is found in 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 plane of incidence orthogonal to the analyzer of the polarizing plate 15 and the light receiving camera 16 If you have (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).

[0070]

(Equation 2)

The equation (3) is a special case where the normal angle ξ = 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 angle (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 detection angle β, it is possible to determine which normal angle ξ to extract more reflected light from the micro-plane element 13. Can be selected.

[0074] 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.

[0075] _{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).

[0076]

(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 established.

[0078] _{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, the weight function I (ξ, β) will be considered. 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

[0082]

(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.

Conversely, the angle of analysis β of the analyzer 17 that best extracts the reflected light with the normal angle ξ = ± 35 ° is defined as (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 a characteristic intermediate 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 element 13 at the normal angle ξ is given by the product of the weighting function I (ξ, β) and the area ratio S (ξ). The light intensity finally received by the light receiving camera 16 is [S (ξ) · I (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. 18
The weighted function I (ξ, β) shown in (1) and the weighted integral are the integrated light intensity.

Then, 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 °. Cannot be detected, and can be detected when the light passes through an analyzer 17 having an analysis angle β = 45 °.

However, 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 as 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 is detected through the analyzer 17 with the analysis angle β = 45 °. become unable.

In that case, another weighting function (for example, I
(Ξ, 90)) is the analysis angle β (eg, 90 °)
Another analyzer 17 may be prepared separately, and the third light receiving camera 16 may receive the light.

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 overlook of the barge portion 11 can be avoided. In order to eliminate the reflected light, it is necessary to use the analyzers 17 having three different analysis angles β to extract and receive the reflected light from the micro-plane element 13 having the corresponding three normal angles ξ. is there.

When there is a difference between the specular reflection component and the specular diffuse reflection component as shown in FIGS. 9A and 10A, basically, for example, either -45 ° or + 45 ° The difference between the base material portion 12 and the barb portion 11 can be detected by the reflected light passing through the analyzer 17.

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 specular reflection light from the surface to be inspected by the first light receiving unit, and extracts and receives more specular reflection components as compared with the specular reflection components, The second light receiving means extracts more of the specular reflection component from the specular reflection component and the specular diffusion reflection component included in the specular reflection light from the surface to be inspected as compared with the specular reflection component.

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 in FIG.
(A) The presence of the barbed portion 11 in each reflection characteristic of the surface of the steel plate 4 shown in (b) and (c) can be reliably detected by comparison with the base material portion 12.

With such an optical system, measurement is performed on a common optical axis from the specular reflection direction, so that it is possible to deal with both specular reflection and specular diffuse reflection without being affected by fluctuations in the steel plate distance or speed. Two signals,
A surface flaw inspection apparatus and a surface flaw inspection method capable of detecting a pattern-shaped barbed flaw having no remarkable unevenness without causing any omission are realized.

Further, when the manufacturing conditions of the steel sheet are changed or the type of the steel sheet is changed, since the physical property value of the base material on the surface to be inspected is different, the reflection characteristic with respect to the polarized light of the surface to be inspected is changed, and the intensity of the polarized light component to be received is changed. The ratio changes.

For example, the polarization reflection characteristics of different types A and B of the alloyed galvanized steel sheet are p, p,
The arc tangent of the amplitude reflectance ratio of the s-polarized light ゜ = 28 °, and the phase difference Δ = 120 ° of the reflectance of the p and s-polarized light. On the other hand, in the steel sheet type B, the arc tangent of the amplitude reflectance ratio of p, s polarized light Ψ = 28
The phase difference Δ of the reflectance of ゜, p, and s-polarized light is 80 °. Then, by substituting the polarization reflection characteristic values of the two types into the equation (10), the analysis angles 90 ° and 45
The weight function at {, -45} is calculated and is shown in Table 1.

[0103]

[Table 1]

Since the base material portion is the temper portion 7 crushed flat by temper rolling, the value of the calculated weighting function is set to と し て = 0 in the equation (10), and the amount of received light at each analysis angle is calculated. Can be regarded as a relative value of Here, the azimuth angle (polarization angle) α of the incident polarized light was 45 °, and the incident angle θ was 60 °.

Since the amount of received light differs at each of the three detection angles for each of the steel plate types A and B, S
It is difficult to obtain an optimal amount of light for improving the / N ratio.
Further, comparing the varieties A and B, when the analysis angle is 90 °,
Although there is no change in the amount of received light, the amount of received light changes about twice at 45 ° and −45 °. Therefore, when the type A and the type B are measured under the same optical conditions, an analysis angle of 45 °, −
With respect to 45 °, a signal with an improved S / N ratio cannot be obtained in both types, and the light amount is too low in either type.
Alternatively, a problem of reaching the saturated light amount occurs.

Therefore, in the present invention, before each light receiving means,
A light quantity reduction filter is inserted in the optical path of the specularly reflected light from the surface to be inspected, which is incident on each light receiving means, and the light quantity incident on the light receiving means at each of the three detection angles is adjusted to a predetermined value. I do.

Further, according to the present invention, a light quantity reduction filter switching means for inserting a light quantity reduction filter having an optimum transmittance into each optical path in accordance with a change of the surface to be inspected is provided. Thus, a surface flaw inspection apparatus capable of detecting a pattern-shaped barbed flaw without being affected by a change in the surface polarized light reflection characteristic without causing any omission is realized.

[0108]

DESCRIPTION OF THE PREFERRED EMBODIMENTS 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 according to an 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 on a quality inspection line of an alloyed galvanized steel sheet in an ironworks. 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 source 22
By projecting the light of the metal halide light source from both ends of the transparent light guide rod having the diffuse reflection paint applied to the part thereof, uniform emission light is obtained in the width direction of the steel plate 21.

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 2
The azimuth (polarization angle) α of No. 5 is set to 45 °.

The reflected light 26 reflected by the steel plate 21 is incident on a light receiving section 27 arranged in the regular reflection direction of the steel plate. The light receiving section 27 has an analysis angle β of -45 in front of the lens.
Analyzers 28a, 28 set to ゜, 45 °, 90 °
The light receiving cameras 29a, 29b, and 29c are composed of three linear array cameras having b and 28c.

Further, a filter switching mechanism 50 as a light amount reduction filter switching means is provided at a position above the transport path.

The filter switching mechanism 50 in this embodiment includes six light quantity reduction filters 20a, 20a.
b, 20c, 20d, 20e, and 20f are incorporated. More specifically, each of the light quantity reduction filters 20a, 20a
Each of b, 20c, 20d, 20e, and 20f is constituted by a neutral density filter capable of weakening the light intensity at a fixed rate regardless of the transmitted polarization component.
The transmittance of each light in each of the light quantity reduction filters 20a to 20f is not the same, but is set to a different value.

The six light amount reduction filters 20a to 20a
20f denotes three light amount reduction filters 20a, 20b,
It is divided into a first group consisting of 20c and a second group consisting of another three light quantity reduction filters 20d, 20e and 20f.

The filter switching mechanism 50 includes three light quantity reduction filters 20 belonging to the first or second group.
a to 20c (or 20d to 20f)
a, 29b, 29c.

Whether the three light quantity reduction filters belonging to the first group or the second group are inserted into the optical path of the reflected light 26 is determined according to the type of the steel plate 21 to be inspected. Is controlled by the filter control unit 51 based on the instruction. In addition, FIG.
Each light reduction filter 20a, 20 of the first group
It is a figure showing the state where b and 20c were inserted in the front of each light receiving camera 29a, 29b and 29c.

Therefore, each light amount reduction filter -20
The amount of light passing through a, 20b, and 20c is set to an optimum level at which the amount of light received by each linear array camera incorporated in each of the light-receiving cameras 29a, 29b, and 29c is sufficiently secured and the amount of light is not saturated. It is possible.

When the type of the steel plate 21 to be inspected is changed, the physical property values such as the complex refractive index and roughness of the surface change for each type, so that the three light receiving cameras 29a, 29b, and 29c
, The amount of each reflected light received changes.

In this case, at the timing when the type of the steel plate 21 changes based on the instruction of the host computer 52, the filter switching mechanism 50 switches the three light amount reduction filters 20a to 20c (or 20d) belonging to the group suitable for each type. ~ 20
f) is switched to the front of the lens.

Each of the light receiving cameras 29a, 29b, 29
The optical axes of c are maintained parallel to each other. Further, the deviation of the field of view among the three light receiving cameras 29a, 29b, 29c is corrected by the sepal processing unit 40.

As described above, each of the light receiving cameras 29a, 29b,
When the optical axis of 29c is maintained parallel, the pixels of the three light receiving cameras 29a, 29b, and 29c correspond one-to-one with the same visual field size. By adopting a linear array camera in this way, the loss of light amount is reduced and efficient measurement is possible as compared with using a beam splitter.

Here, in the light receiving section 27, a two-dimensional CCD camera can be used instead of the linear array camera. Further, 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 can also 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. This is because the light emitted from each fiber has a sufficient divergence angle corresponding to the N / A of the fiber, so that the fiber light source in which the fibers are aligned becomes a substantially 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 received by each of the light receiving cameras 29a, 29b, 29c is a light intensity signal a, b,
c is 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 unit 40. A light receiving camera 29a as a first camera in which a 45 ° analyzer 28a is incorporated, a light receiving camera 29b as a second camera in which a + 45 ° probe 28b is incorporated, and a + 28 ° analyzer 28c are incorporated. The light intensity signals a, b, and c input from the received light receiving camera 29c are input to average value thinning units 30a, 30b, and 30c, respectively.

Each of the average value thinning sections 30a to 30c is adapted to output each of the light intensity signals a, b, inputted from each of the light receiving cameras 29a to 29c in each scanning cycle of each of the light receiving cameras 29a to 29c.
c is added and averaged, and a signal for one line is output when the steel plate 21 moves a distance corresponding to the longitudinal resolution in the signal processing.

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. In addition, since the light intensity signals a, b, and c for each scan cycle are averaged, 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 29a to 29c in the moving direction of the steel plate. In this case as well, since the average value obtained by measuring the interval can be used, oversight can be eliminated.

Each of the light intensity signals a, b, c processed by each of the average thinning sections 30a to 30c is converted into the following preprocessing section 31a.
To 31c. Each of the pre-processing units 31a to 31c includes:
The uneven luminance of the signal of one line is corrected. The uneven brightness 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 to 31a
In step 1c, the edge positions on both sides of the steel plate 21 are also detected, and a process for preventing the steep changes in the light intensity signals a, b, and c at the edges from being erroneously recognized as flaws is performed. Each pre-processing unit 31a-
The light intensity signals a, b, and c that have been subjected to the signal processing in 31c are input to the following binarization processing units 32a to 32c.

Each of the binarization processing sections 32a to 32c compares the data of each pixel included in each of the light intensity signals a, b, and c with a predetermined threshold value, and extracts flaw candidate points. Then, it is sent to the next feature amount calculation units 33a to 33c. Special trace extraction unit 3
3a to 33c determine a continuous flaw detection point as one flaw detection area, and calculate a position characteristic amount such as a start address and an end address and a density characteristic amount such as a peak value.

The specular flaw judging section 34 and the specular diffusible flaw judging section 35 determine the type of the flaw based on the characteristic amounts calculated by the characteristic amount extracting sections 33a to 33c corresponding to the respective light receiving cameras 29a to 29c. , To determine the degree.

The flaw determining section 36 determines the final flaw type and the degree of the 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 visual field shift in each of the light receiving cameras 29a to 29c based on the position feature amount from each of the feature amount extraction sections 33a to 33c.
As described above, the displacement of the visual field between the light-receiving cameras 29a to 29c is compensated for in the feature amount unit.
It is not necessary to adjust the field of view between the pixels 29c in units of pixels.

[0133]

EXAMPLE FIGS. 3 and 4 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. 1, and Table 2 shows the judgment results based on the results of the measurements. .

In each of the measured flaws, the area ratio S (ξ) of the tempered portion 6 shown in FIG. 9B is larger at the barb portion 11 than at the base material portion 12, but the diffusivity of the non-tempered portion 7 does not change. Scratches and FIG.
The area ratio S (ξ) of the tempering portion 6 shown in FIG.
Although there is no large difference between No. 1 and the base material portion 12, the flaw has a difference in diffusibility.

Then, at the center of the steel plate 21 in the width direction, FIG.
When a flaw of the type shown in FIG.
At 5 °, 45 ° and 90 °, the analyzers 28a, 28b, 2
Each of the light receiving cameras 29a and 29 for which the detection angle β of 8c is set
3 (a), 3 (b) and 3 (c) show changes in the light intensity signals a to c for one width of the steel material 21 obtained by scanning the steel plate 21 by one line in the width direction at b and 29c.

As shown in the figure, a peak waveform corresponding to the flaw (the scab 11) is generated in the light intensity signal a of the light receiving camera 29a having the detection angle β set at -45 °. In this case, 4
The light intensity signal b of the light receiving camera 29b for which the detection angle β is set to 5 ° does not have a peak waveform corresponding to the flaw (heavy portion 11).

FIG. 9 shows the central portion of the steel plate 21 in the width direction.
When a flaw of the type shown in FIG.
At 5 °, 45 ° and 90 °, the analyzers 28a, 28b, 2
Each of the light receiving cameras 29a and 29 for which the detection angle β of 8c is set
4 (a), (b) and (c) show changes in the light intensity signals a to c for one width of the steel material 21 obtained by scanning the steel plate 21 by one line in the width direction at b and 29c.

As shown in the figure, the light intensity signal b of the light receiving camera 29b having the detection angle β set to 45 ° has a flaw (the hair portion 1).
A peak waveform corresponding to 1) is generated. In this case, -4
A peak waveform corresponding to the flaw (the stub 11) does not occur in the light intensity signal a of the light receiving camera 29a in which the detection angle β is set to 5 °.

[0139]

[Table 2]

As shown in FIG. 9 (c), there are generally undetectable angles in the diffuse reflection direction as shown in the figure, but two types of flaws having different angles were measured.

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, reflected light components corresponding to three different light receiving angles are analyzed by the analyzer 28.
a, 28b, and 28c, the light is extracted from the regular reflection direction.
It is possible to detect with c. Further, it is easy to set the detection angle β to an optimum value in accordance with the reflection characteristics of the flaw to be detected.

Note that the present invention is not limited to the above embodiment. In the embodiment shown in FIG. 1, three light receiving cameras 29a, 29b, and 29c are used, but the light receiving camera 29a having a -45 degree analyzer 28a is used.
And a light receiving camera 29b having a + 45 ° analyzer 28b
Even if only two light receiving cameras are used, the presence of the barbed portion 11 in the optical axis direction of the specularly reflected light from the surface of the steel plate
And can be detected sufficiently.

Table 3 shows each light quantity reduction filter 20a-2 belonging to the group corresponding to the type A in the steel plate 21.
Receiving camera 2 with detection angle of 90 °, 45 °, -45 °
9a, 29b, and 29c, and the transmittance of the steel plate 21
, The analysis angles 90 ° and 45 ° of the tip amount reduction filters 20d to 20f belonging to the group corresponding to the type B in
The relationship with each transmittance corresponding to the light receiving cameras 29a, 29b, and 29c of -45 ° is shown.

[0146]

[Table 3]

As described above, at the timing when the types A and B of the steel plate 21 are changed, each of the light receiving cameras 29a, 29b,
Each light amount reduction filter 20 inserted in front of 9c
The transmittances a to 20f are switched and set to the values shown in Table 3.

As described above, even if the type of the steel plate 21 is changed, the received light amounts at the three detection angles can be kept equal, so that the detection accuracy of the surface flaws on the inspection surface can be improved. Can be improved.

In the embodiment shown in FIG. 1, each light receiving camera 2 is provided by using a filter switching mechanism 50.
The transmittance of each light amount reduction filter inserted in front of 9a, 29b, 29c is changed for each type A, B of the steel plate 21.

However, if there is a camera set at an analysis angle at which the amount of reflected light does not change even if the types A and B of the steel plate 21 change, for example, the azimuth angle (analysis angle) of the analyzer is 90 °. Even if the light receiving camera has a fixed structure without a transmittance switching mechanism, the light receiving amount of the light receiving camera at each detection angle can be made equal.

When the type of the steel plate 21 is not plural but only one type, the switching mechanism of the transmittance of each light quantity reduction filter is not required, and the filter may be fixed.

[0152]

As described above, in the surface defect inspection apparatus of the present invention, based on the knowledge that the specularly reflected light on the surface to be inspected comprises a specular reflection component and a specular diffuse reflection component, each component is reflected. Are extracted and detected.
Specifically, by using a linear diffused light source, a polarized light having both p-polarized light and s-polarized light is incident on the surface to be inspected, and by appropriately setting the analysis angle from the specular reflection direction of the steel sheet, specular reflection is performed. A component that contains more components and a component that contains more specular diffuse reflection components are extracted, and a light amount reduction filter is arranged in the middle of the optical path when receiving the intensity of each component of the regular reflection light.

With this configuration, 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 remarkable unevenness, which could not be detected conventionally, without omission. became.

In addition, since both components are caught in the measurement on the same optical axis from the direction of the regular reflection of the steel sheet, the measurement is not affected by the fluctuation of the steel sheet distance or the change of the speed. Further, by adjusting the analysis angle of the analyzer, it is possible to select at which angle the specular diffuse reflection component is extracted.

Further, in accordance with a change in the polarization reflection characteristic of the surface to be inspected, a light amount reducing filter having a different transmittance is provided in front of the light receiving means, or the light receiving means is switched to a light amount reducing filter having a different transmittance. Since the amount of light can be kept constant, even when the type of the object to be inspected or the manufacturing conditions are changed and the intensity ratio between the specular reflection component and the specular diffuse reflection component of the specular reflection light changes, the light receiving means for each component also changes. Was adjusted to a level having a good S / N ratio, and stable surface defect inspection results were obtained.

Further, from the viewpoint of quality assurance, it is an absolute condition that there is no undetected surface flaw inspection device. Therefore,
According to the present invention, a surface inspection device without undetection that can be widely applied to a surface-treated steel sheet or the like can be realized, so that a surface flaw inspection that has conventionally relied on visual inspection by an inspector can be automated. 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 alloyed 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.

[Explanation of symbols]

4, 21 ... steel plate 6 ... tempered part 7 ... non-tempered part 8, 23 ... incident light 9 ... specular reflected light 10 ... specular diffuse reflected light 11 ... hedged part 12 ... base material part 14, 22 ... linear diffused light source 15 , 25 ... Polarizing plate 16, 29a, 29b, 29c ... Receiving camera 17, 28a, 28b, 28c ... Analyzer 20a, 20b, 20c, 20d, 20e, 20f ... Light quantity reducing filter 24 ... Cylindrical lens 26 ... Reflected light 27 ... Light receiving unit 40: signal processing unit 50: filter switching mechanism 51: filter control unit 52: host computer

Continued on the front page (72) Inventor Masakazu Inomata 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (72) Inventor Shoji Yoshikawa 1-1-2, Marunouchi, Chiyoda-ku, Tokyo Japan Inside Kokan Co., Ltd. (72) Inventor Takahiko Oshige 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. F term in the company (reference) 2G051 AA37 AA90 AB07 AC04 BB01 BB09 CA04 CA06 CB01 EA11 EA12 EA16 EA24 EC01 EC03 ED07

Claims (2)

[Claims] 1. A linear diffuse light source for entering polarized light having an azimuth component parallel to and perpendicular to the surface to be inspected with respect to the surface to be inspected, and specularly reflected light from the surface to be inspected. First light receiving means having an azimuth analyzer for extracting more specular reflection components than specular diffuse reflection components among specular reflection components and specular diffuse reflection components included in the inspection target surface; A second light receiving unit having an azimuth analyzer for extracting more specular diffuse reflection components than specular reflection components among specular reflection components and specular diffuse reflection components included in specular reflection light; And a determination processing unit for determining the 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 second light receiving means. The test object incident on the first and second light receiving means The optical path of the specular reflection light from the surface, surface flaw inspection apparatus characterized by inserting the light amount reduction filter for controlling each amount of light entering the predetermined value to said first and second light receiving means. 2. A light quantity reduction filter for incorporating a plurality of light quantity reduction filters having different light transmittances into each of the optical paths according to a change in the surface to be inspected. 2. The surface flaw inspection apparatus according to claim 1, further comprising switching means.