JP2000187009A - Surface flaw inspecting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable the reliable detection of scab flaws having a pattern not noticeable in irregularities such as cracking, scooping, curling up, by distinguishing the specular reflection components and diffuse reflection components contained in reflected light from a surface to be inspected, detecting them, and connecting adjacent surface flaws of the same type together. SOLUTION: Mean value thinning parts 30a-30c average each of optical intensity signals a-c for every scanning cycle of light receiving cameras 29a-29c and outputs one line of signals in the case that a steel plate moves a predetermined distance. The processed signals a-c are inputted to preprocessing parts 31a-31c, and the luminance irregularity of the one line of signals is corrected. A specular flaw determining part 34 and a specular diffuse flaw determining part 35 determine the types and the extent of flaws on the basis of characteristic amounts computed by characteristic amount extracting parts 33a-33c corresponding to the light receiving cameras 29a-29c. A flaw comprehensive determining part 36 performs the processing of connecting surface flaws on the basis of the results of flaw determination at the characteristic amount extracting parts 33a-33c and flaw determining parts 34 and 36 and determines the final types and extent of flaws.

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 A surface for optically detecting a surface flaw existing on a surface to be inspected 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. Conventionally, various methods have been proposed for 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 test object at an angle of 35 ° to 75 °, and the reflected light from the test object surface is reflected by the specular reflection direction and the incident direction or 20 ° from the specular reflection direction. Light is received by two cameras installed at angles within the range. 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
Similar to the technique described in Japanese Patent Application Publication No. 533, the surface of the steel sheet is inspected for defects 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.

In general, flaw signals are not at the same level in a flaw area, and there are variations. When such a flaw is inspected by the inspector, it is determined to be one flaw.
However, in each of the flaw detection techniques described above, since a region with a low flaw signal level cannot be detected, for example,
A flaw that is originally a linear form may be recognized as a plurality of point forms. As a result, flaws of a light grade are determined, and there is a concern that defects may be overlooked or underestimated.

In this way, when the inspector inspects, 1
A method has been proposed in which, when an inspection apparatus determines that a single flaw is a plurality of flaws, the inspection apparatus determines the plurality of flaws as one original flaw (Japanese Patent Laid-Open No. 06-011458).

In this method, a surface to be inspected is scanned by a one-dimensional line sensor, an analog signal from the one-dimensional line image sensor is binarized, and the signal is run-length encoded. Then, run-length encoded data adjacent to each other in the sub-scanning direction on the surface to be inspected are compared, and data adjacent to each other within a predetermined distance or less in the scanning direction are connected. And the number of occurrences of flaws is 1
It is determined whether or not it is successful, and the pass / fail is also determined.

However, in this method, data that are close to each other within a predetermined distance or less are unconditionally linked based on the run-length code. At this time, since the run-length code is used as the basis, the connection process is performed based only on the positional relationship regardless of the type of the flaw. As a result, there is a problem that flaws of different types are connected and determined to be one flaw simply because they are close to each other. That is, in this method, there is a problem that the type of the new connected flaw and the degree of the flaw cannot be accurately evaluated.

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

The present invention has been made in view of such circumstances, and distinguishes and detects specular reflection components and specular diffuse reflection components contained in light reflected from a surface to be inspected, and determines the type of flaw. By taking into account the connection of flaws, it is possible to reliably detect pattern-shaped barge defects that do not have noticeable irregularities such as surface cracks, gouges, and curls on the surface to be inspected,
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 inspection line.

[0024]

In order to solve the above-mentioned problems, a surface flaw inspection apparatus according to the present invention provides a component having an azimuth angle parallel to and perpendicular to the surface to be inspected. A linear diffused light source that emits polarized light having a polarization, and more specularly reflected components among the specularly reflected components and the specularly diffused reflected components included in the specularly reflected light from the surface to be inspected as compared with the specularly diffused reflected components. A first light receiving means having an analyzer with an azimuth angle, and 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 with an azimuth angle to be extracted, and evaluation processing for evaluating surface flaws 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 means Section.

Further, the evaluation processing section includes a flaw determining means for determining the presence or absence of a surface flaw on the surface to be inspected, the type and the position of the surface flaw on the surface to be inspected based on the received specular reflection component and specular diffuse reflection component, There is provided a flaw connecting means for connecting adjacent surface flaws of the same type to form one new surface flaw based on the type and occurrence position of each surface flaw determined by the determining means.

According to another aspect of the present invention, a characteristic amount of a new surface defect connected by the same type is obtained from the characteristic amount of each surface defect by the evaluation processing unit in the surface inspection apparatus of the invention described above. A grade judging means for judging the grade of each flaw based on the feature amount is added.

Next, the operation principle of the above-described invention will be described with reference to the drawings.

First, the form of optical reflection on the surface of a steel sheet 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. 8A, the cold rolled steel sheet as the base passes through the alloying furnace after being hot-dip galvanized. During this time, the iron element of the base steel sheet 1 diffuses into the zinc of the plating layer 2 and usually forms columnar crystals 3 of the alloy as shown in FIG. The plated steel sheet 4 is then temper rolled on rolls 5a and 5b. Then, as shown in FIG. 8D, 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. 9 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 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 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. 10 (a) and 10 (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.

In fact, since the tempered portion 6 and the non-tempered portion 7 are macroscopically mixed, the angular distribution of the reflected light observed by an optical measuring instrument such as a camera is shown in FIG.
As shown in (1), the angular 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 also 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. 11, the barge defects (barge portions 11) found in the galvannealed steel sheet are the same as those of the cold-rolled steel sheet before plating. Then, the plating layer 2 is placed thereon, and further, alloying of barge defects due to diffusion of the iron element of the base steel sheet 1 progresses.

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 12
A description will be given of how the pattern-like scab defect looks due to the difference in the surface properties.

When the differences between the barbed portion 11 and the base material portion 12 are classified based on the above-described model, they are generally classified into the following three types.

(A) The area ratio of the tempered portion 6 in the barbed portion 11 and the angular distribution of the micro-surface elements 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. 13 (a) and 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-plane elements of the non-tempered part 7 in the base material part 12 (FIGS. 13B and 12B).

(C) The angle distribution of the small surface element of the non-tempered portion 7 in the barbed portion 11
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. 13C and 12C). .

As shown in FIG. 14, 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 sheet 4 of the steel plate 4 is defined as the normal angle ξ of the minute surface element 13, and this normal line FIG. 13A shows the relationship between the angle ξ and the area ratio S (パ) of the temper portion 6 in the above three cases (a), (b), and (c).
(B) and (c).

The difference between the area ratio S (ξ) of the tempering portion 6 and the angular distribution of the microscopic element 13 is shown in FIG.
(B) It is observed as a difference in the angular distribution of the amount of reflected light as shown in (c). The angle distribution indicated by the solid line in the figure is
And the angle distribution indicated by a dotted line in the figure is a base material angle distribution 12a corresponding to the base material 12.
a.

That is, FIG. 12 (a) shows a case where there is a difference between the specular reflection component and the specular diffuse reflection component between the barge angle distribution 11a and the base metal angle distribution 12a. (B) shows a case where there is a difference only in the specular reflection component, and FIG. 12 (c) 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. 12 (a) and 12 (b). , The difference is observed from the specular reflection direction. Specifically, the case where the reflected light of the barbed portion 11 is measured from the specular reflection direction and the case where the base material portion 12 is measured
When the reflected light is measured, the area ratio S (ξ) of the tempered portion 6 of the barbed portion 11 is equal to the area ratio S of the tempered portion 6 of the 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.

Heddle portion angle distribution 11a and base metal portion angle distribution 1
In the case where 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 microscopic element 13 at what angle (normal angle ξ) is extracted in FIG. It is necessary to consider whether or not. For example, detecting the difference between the barb portion 11 and the base material portion 12 in the regular reflection direction as in the example of FIGS.
Of the angular distribution of the micro-surface element 13 indicated by 3
This means that the difference between the barbed portion 11 and the base material portion 12 has been detected by extracting the normal angle ξ = 0 of 3.

Here, the extraction of the reflected light with 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 regular 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. 14, 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 minute surface 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 such a viewpoint, FIGS. 13 (a) and 13 (b)
Considering a weighting function I (ξ) for discriminating and detecting each barbed portion 11 from the base material portion 12 as shown in FIG.
The delta functions δ (）) and δ (ξ + 1) shown in FIGS.
0) is also one of the effective weight functions I (ξ).

The weighting function I (ξ) is not necessarily the one shown in FIG.
The width for extracting only the specific normal angle shown in FIG. 5 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. In other words, instead of capturing diffuse reflected light,
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. For the latter problem, the weight function I (ξ)
Is desirably 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 the linear diffusion light source, as shown in FIGS.
4 is arranged in parallel with the surface of the steel plate 4, and the reflection characteristic when observing one point on the steel plate 4 from the steel plate regular reflection direction, which is in a plane perpendicular to the light source and in which the incident angle coincides with the emission angle, is shown. Think.

As shown in FIG. 16 (a), 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 specularly 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, of the incident light 8 radiated from the entire longitudinal direction of the linear diffused light source 14, what is captured by observation from the steel plate regular reflection direction is 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 characteristic changes when observed using the linear diffused light source 14 from the regular reflection direction of the steel plate 4 will be described.

In general, when light is reflected on a mirror-like metal surface, the polarization characteristics of light whose direction of the electric field is parallel to the incident surface (p-polarized light) or light perpendicular to the incident surface (s-polarized light) are also affected by the reflection. Will be saved. 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 is reflected, the light is emitted as elliptical polarized light according to the reflectance ratio tanｐ of p and s-polarized light and the phase difference Δ. I do.

A linear diffusion light source 14 is applied to an alloyed galvanized steel sheet.
17 (a) and 17 (b) will be described with reference to FIGS.

As shown in FIG. 17A, the light emitted from the central portion of the linear diffused light source 14 is specularly reflected by the tempering portion 6 of the steel plate 4 and is observed in the steel plate 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. 17B, 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 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-polarized light 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.

Hereinafter, the case where linearly polarized light having both p and s components is incident on the steel plate 4 from the linear diffused light source 14 will be described in detail.

First, as shown in FIG. 18, the incident light 8 from the linear diffused light source 14 is linearly polarized by a polarizing plate 15 having an azimuth angle (polarization angle) α, and then the light is applied to a horizontally disposed steel plate 4. The light is made incident, and the specularly reflected light is received by the 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 =
The component that is specularly diffusely reflected from the minute surface element 13 of the steel sheet 4
This contributes to the light reflected from the upper point O toward the light receiving camera 16.

On the other hand, as shown in FIG. 19, 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 diffusion 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 · 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 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.

[0076]

(Equation 1)

[0077] 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).

[0079]

(Equation 2)

Equation (3) is a special case where the normal angle 微小 = 0 of the micro-plane element 13 in equation (6). 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 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
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 °. From FIG. 20, it can be understood 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 microscopic element 13. Can be selected.

[0083] To quantify this, as shown in FIG. 19, 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.

[0084] _{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).

[0085]

(Equation 3)

Next, from this equation (8), the light intensity of the reflected light from the micro surface element 13 at the normal angle ξ detected by the light receiving camera 16 is obtained.

As described above, if the area ratio of the microscopic element 13 is S (ξ), the following equation (10) is established.

[0088] _{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

[0092]

(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. 21 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. 21, the normal angle ξ = 0 °, that is, the specular reflection component is the most dominant, while the normal angle 法 =
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 given by (10)
According to the equations (11) and (11), β is approximately 45 °.
FIG. 22 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. When the normal angle ξ of the microscopic element 13 is positive, the azimuth angle (polarization angle) α of the polarization of the incident light 8 is apparently 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. 22 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 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. 23 is received through the analyzer 17 having the analysis angle β of −45 °, the area ratio S (ξ) shown in FIG. 21
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 respective area ratios S (ξ) are as shown in FIGS. 13A, 13B, and 13C, respectively.

First, consider a case where there is a difference only in the specular reflection component as shown in FIGS. 12 (b) and 13 (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 shown in FIG.
(Ξ) multiplied by the weight function I (ξ, β) shown in FIG.
It is possible to detect the difference in the amount of reflected light from 1.

FIG. 13 shows the light intensity when the same flaw is received through an analyzer 17 having an analysis angle β = 45 °.
As shown in (b), since there is no difference in the specular diffuse reflection component, the weight function I (ξ, β) at the analysis angle β = 45 ° in FIG.
As is apparent from the fact that the integration is performed by multiplying, the difference between the base material portion 12 and the scab 11 cannot be detected.

If there is a difference only in the specular diffuse reflection component as shown in FIGS. 12 (c) and 13 (c),
It cannot be detected by passing through the analyzer 17 with the analysis angle β = −45 °, but can be detected by passing through the degree analyzer 17 with the 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.

In general, 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. 12 (a), 12 (b) and 12 (c). 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 surface 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. 12 (a) and 13 (a), 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 cope with both specular reflection and specular diffuse reflection without being affected by fluctuations in the steel plate distance or changes in speed. Two signals,
A surface flaw inspection apparatus capable of detecting a pattern-shaped bald flaw having no remarkable unevenness without causing any omission is realized.

However, in general, flaw signals are not at the same level in all flaw areas, and there are variations. When such a flaw is inspected by the inspector, it is determined to be one flaw. However, in the case of such a flaw, the surface flaw inspection apparatus cannot detect an area having a low flaw signal level, and determines that the area is a plurality of mild flaws.

Accordingly, in the present invention, the presence / absence, type, and
The occurrence position is determined, and when the adjacent surface flaws are of the same type, these surface flaws are connected and recognized as one new surface flaw. Further, a connection process for adding the feature amounts of the respective surface flaws before connection and obtaining the maximum value of the absolute value is performed, and based on the result, the grade of the flaw after connection is determined.

As a result, the determination result can be made more accurate, and the pattern-like barbed flaw can be detected without any omission or underestimation.

[0114]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 (a) is a side view of a surface flaw inspection apparatus according to an embodiment of the present invention, and FIG. 1 (b) 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 at 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 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 passes through the cylindrical lens 24 and the polarizing plate 25 and is incident at an 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 unit 27 arranged in the regular reflection direction of the steel plate. The light receiving section 27 has an analysis angle β of -45 ° before the lens,
Analyzers 28a, 28b, 2 set at 45 ° and 90 °
The light receiving cameras 29a, 29b, and 29c are composed of three linear array cameras having 8c.

Each of the light receiving cameras 29a, 29b, 2
The optical axes 9c are maintained parallel to each other. Also, 3
The shift in the field of view of the two light receiving cameras 29a, 29b, 29c is corrected by the signal processing unit 40. When the optical axes of the light receiving cameras 29a, 29b, and 29c are maintained in parallel as described above, the three light receiving cameras 29a, 29b, and 2
Each pixel 9c has one-to-one correspondence with the same visual field size. As described above, by employing a linear array camera as the light receiving camera, the loss of light amount is reduced and efficient measurement becomes 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.

Further, as the linear diffusion light source 22, a fluorescent lamp can be used. 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 received by each of the light receiving cameras 29a, 29b, and 29c is converted into light intensity signals a, b, and c, respectively, and evaluated. It is transmitted to a signal processing unit 40 as a processing unit.

FIG. 2 is a block diagram showing a schematic configuration of the signal processing section 40.

The first in which the -45 ° analyzer 28a is incorporated
Light-receiving camera 29a as a second camera and a light-receiving camera 2 as a second camera incorporating a + 45 ° analyzer 28b
9b, light receiving camera 29 incorporating 90 ° analyzer 28c
The light intensity signals a, b, and c input from c are input to the average value thinning units 30a, 30b, and 30c, respectively.

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 29a, 29b, 29c, and 29c for each scan cycle of each of the light receiving cameras 29a, 29b, and 29c,
When 1 moves a distance corresponding to the longitudinal resolution in signal processing, a signal for one line is output.

By performing such thinning processing,
Even if the transport 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 made constant. Further, each light intensity signal a, b,
Since c is averaged, the resolution of one line in the moving direction of the steel plate in the signal processing can be determined by the light receiving cameras 29a, 29b, 29
Even when the field of view is sufficiently larger than the field of view in the moving direction of the steel sheet c, the 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, 31c
Corrects the luminance unevenness of the line signal. The luminance unevenness here includes unevenness caused by the optical system and unevenness caused by the reflectance of the steel plate 21. Also, each of the pre-processing units 31a, 31
b, 31c also detect the edge positions on both sides of the steel plate 21,
Processing is also performed to prevent a sudden change in the light intensity signals a, b, and c at the edge from being erroneously recognized as a flaw. Each pre-processing unit 3
Each of the light intensity signals a, b, and c that have been subjected to signal processing in 1a, 31b, and 31c are converted into the following binarization processing units 32a, 32b, and 32, respectively.
c.

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 calculates the next feature amount calculation units 33a, 33b, and 33c. Send to

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 quantity indicating a generation position such as a start address (flaw start coordinate), an end address (flaw end coordinate), a peak value, or the like. Calculate the density feature amount and the like.

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

Therefore, the feature amount extraction units 33a, 33
b, 33c, the specular flaw determining unit 34, and the specular diffusible flaw determining unit 35 constitute determining means for determining the presence / absence, type, and occurrence position of surface flaws.

The flaw comprehensive judgment section 36 includes a feature quantity extraction section 33
a, 33b, 33c, based on the result of the flaw judgment by the specular flaw judgment unit 34 and the specular diffusible flaw judgment unit 35, connecting adjacent surface flaws of the same type to form a new single surface flaw Is carried out. Further, when the above-described connection processing is completed, the flaw comprehensive determination unit 36 determines that the steel plate 21 as an inspection target
The final flaw type and the degree of each flaw after the consolidation processing occurring in the above are determined.

Next, the flaw connection process in the flaw comprehensive judgment section 36 will be described using a specific example.

Now, the feature amount extraction units 33a, 33b, 33
c, As a result of two-dimensional scanning of a certain area of the steel sheet 21 in the specular flaw judgment unit 34 and the specular diffusion flaw judgment unit 35, as shown in Table 1 and FIG. , An area 37 having the type of “scab” and “dirt”
Assume that five defects (flaws) having a, 37b, 37c, 37d, and 37e are detected.

[0136]

[Table 1]

Then, the flaw comprehensive judgment section 36 detects the different areas 37a, 37b, 37c, 37d,
It is verified whether or not five flaws having 37e can be connected for every combination of two flaws, and if possible, both are connected.

As a specific condition of the connection, it is determined from the type of each flaw and the relative positional relationship between the regions 37a, 37b, 37c, 37d, and 37e whether or not each region should be connected. If the inspector visually recognizes a long flaw as a plurality of short flaws on the inspection device, the conditions for connecting them are the same type of flaw, and the flaw area is in the width direction with other flaw areas. It is assumed that the coordinates are overlapping and also close to the longitudinal direction.

FIG. 3 shows two regions 37b and 37, for example.
It is a flowchart which shows the process which determines whether each flaw of c is connectable.

Each flaw type determination result, flaw start coordinates P3x and P5x in the width direction, and flaw end coordinates P4x and P
6x, longitudinal flaw start coordinates P3y. P5y, flaw end coordinates P4y, P6y, and flaw type are read.

First, it is determined whether or not the types of the flaws in the areas 37b and 37c are the same (S1). For example, when the types of flaws are different, such as "scab" and "dirt", it is determined that connection is impossible (S2). In the case of the same type, it is checked whether the width start coordinate P5x of the one flaw area 37c is between the width start coordinate P3x and the width end coordinate P4x of the other flaw area 37b (S3).

If not between P3x ≦ P5x ≦ P4x, the width start coordinate P3x of the other flaw area 37b
Is checked between the width start coordinate P5x and the width end coordinate P6x of the one flaw area 37b (S4).

If not between P5x ≦ P3x ≦ P6x, the region 37b and the region 37c are
Since there is no overlap at the x coordinate on the two-dimensional coordinates, it is determined that the two cannot be connected (S2).

In S3 or S4, if the width start coordinate of one of the flaws overlaps in the width direction of the other flaw, the process proceeds to S5, where the longitudinal end coordinate P5y of the other flaw area 37b is obtained.
The distance between the longitudinal start coordinate P4y of one flaw (P5y-
P4y) determines whether it is smaller than a predetermined threshold Yth (S5).

If Yth> P5y-P4y is smaller than the threshold value Yth, it is determined that the flaw in the area 37b and the flaw in the area 37c can be connected, and a connection process is performed (S6). If it is larger than the threshold value Yth, it is determined that the flaw in the area 37b and the flaw in the area 37c cannot be connected, and the connection is not performed (S2).

As described above, the flaw comprehensive judgment unit 36 detects the different areas 37a, 37b, 37c, 37
Whether or not five flaws having d and 37e can be connected is verified for every combination of two flaws, and if possible, both are connected to form a new flaw. For example, after the flaw coupling process was performed on the five flaws shown in Table 1 and FIG. 4 detected earlier, the flaws were collected into three flaws shown in Table 2 and FIG.

[0147]

[Table 2]

That is, the areas 37c, 37d, 3
As shown in FIG. 5, 7e is a new flaw area 37f surrounded by Pll and P12.

Next, the characteristic amount for determining the degree of the flaw for each of the flaws alone or connected is recalculated. For example, the length and width of the connected new flaws in the area 37f are obtained from the coordinates of P11 and P12, and the area and the integrated density in the flaw area are the same as those of the original flaw areas 37c, 37d, and 37e. It is determined by adding the integrated values of the area and the density. Further, the density peak values are calculated for the areas 37c, 37d, and 37e of each flaw.
The maximum value of the peak value is adopted. Based on these feature amounts, the degree of each flaw is re-determined and the final result is obtained.

In the above embodiment, the case where each flaw is connected in the longitudinal direction has been described. However, in the case where the flaws are connected in the width direction, if the connection determination processing procedure in which the longitudinal direction and the width direction are exchanged is handled, the width is determined. Direction connection processing is possible.

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

[0152]

EXAMPLE FIGS. 6 and 7 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 3 shows the determination results based on the measurement results.

In each of the measured flaws, the area ratio S (ξ) of the tempered portion 6 shown in FIG. 12B is larger than that of the base material portion 12 at the barb portion 11, but the diffusivity of the non-tempered portion 7 does not change. The flaw and the area ratio S (ξ) of the tempered part 6 shown in FIG. 12C do not have a large difference between the barge part 11 and the base material part 12, but have a difference in diffusivity.

FIG. 1 shows a central portion of the steel plate 21 in the width direction.
When flaws of the type shown in FIG.
At 45 °, 45 ° and 90 °, each analyzer 28a, 28b,
Each of the light receiving cameras 29a, 29 having the detection angle β of 28c set.
FIGS. 6A, 6B, and 6C 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 9b and 29c.

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 light receiving camera 29a in which the detection angle β is set to -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. 12 shows a 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 having the detection angle β of 8c set.
FIGS. 7A, 7B, and 7C show changes in the light intensity signals a, b, and 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 in which the detection angle β is set to 45 ° has a flaw (the hedging 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 °.

[Table 3]

As shown in FIG. 12 (c), there is generally an undetectable angle 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, the reflected light components corresponding to the three different light receiving angles are analyzed by the analyzer 28.
a, 28b, and 28c, the light is extracted from the regular reflection direction.
b, 29c. 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.
A light receiving camera 29a having a 5 ° analyzer 28a;
Even in the case of only two light receiving cameras including the light receiving camera 29b having the 5 ° analyzer 28b, the presence of the barbed portion 11 is distinguished from the base material portion 12 in the optical axis direction of the regular reflection light from the steel plate surface. Sufficiently detectable.

Further, the test was carried out on a test piece having linear defects (scratches) such as "line shave" and "band shave" and point defects (scratches) such as "camis" and "foreign matter". Inspection results before and after performing the connection process on the flaws in the flaw comprehensive determination unit 36 of the signal processing unit 40 in the form device, and the results of the visual evaluation of the inspector under the respective conditions after performing the connection process Tables 4 and 5 show the comparison with Table 1.

Table 4 shows the number of detected defects (flaws) for each type of defect detected without performing the linking process. Under this condition, 24 line defects (flaws) were overlooked as compared with the visual evaluation of the inspector.

[0166]

[Table 4]

Table 5 shows, for each defect (flaw), the number of detections for each type after the connection processing is performed for each detected defect. Under these conditions, the linear defect (flaw) is compared with the visual evaluation of the inspector.
Indicates that three misses occurred. Table 4 and Table 5
As is clear from comparing each overlooked number in, by performing a concatenation process on each detected number,
It is possible to more accurately match the observation result with the visual inspection of the inspector.

[0168]

[Table 5]

Further, in Table 6, for each defect (flaw) whose flaw type is line barge or band barge, the grade determination result of the inspection apparatus with respect to the visual grade determination of the inspector without performing the connection processing. The evaluation is shown. Table 6 shows that the greater the number of shaded portions, the better the visual inspection of the inspection device. Under this condition, it is shown that 23 line defects (flaws) were missed as compared with the evaluation results of the inspector.

Here, the inspection device grade is such that A is light and D is heavy. In addition, the visual judgment grade of the inspector indicates that the upper part of C is mild, the lower part of C, and D is severe.

[0171]

[Table 6]

Table 7 shows the results of the grade determination by the inspection apparatus with respect to the visual grade determination by the inspector after the connection processing is performed for each defect (flaw) of the line type and the band type. The evaluation is shown. Table 7 shows that the larger the number of shaded portions, the better the visual inspection of the inspection apparatus. Then, under this condition, the number of misses was 0 and the number of matches with the visual judgment grade also increased compared to the visual evaluation of the inspector. As is clear from the comparison of each overlooked number in Tables 6 and 7, by performing the linking process on each detected number, it is possible to more accurately match the evaluation result of the degree visually inspected by the inspector. be able to.

[0173]

[Table 7]

[0174]

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, and by appropriately setting the analysis angle from the regular reflection direction of the steel sheet, the component containing more specular reflection component and the specular diffuse reflection component are contained more. A configuration for extracting the components was 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 remarkable unevenness that could not be detected conventionally without missing. It is now possible.

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

In the signal processing device, when there are adjacent flaws of the same flaw type, the flaws are connected to each other to calculate a feature amount as one flaw, and the grade of the surface flaw is reevaluated. With this configuration, the result becomes close to the result determined by the inspector as one flaw in the visual determination, and the flaw inspection accuracy can be improved.

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, 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 the surface flaw inspection that has 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 flowchart showing a flaw connection determination process in a flaw comprehensive determination unit of a signal processing unit of the surface flaw inspection apparatus;

FIG. 4 is a view showing an area (occurrence position) of a defect (flaw) before connection detected by the surface flaw inspection apparatus.

FIG. 5 is a diagram showing an area (occurrence position) of a defect (flaw) after connection detected by the surface flaw inspection apparatus.

FIG. 6 is a waveform diagram of a light intensity signal measured by the surface flaw inspection apparatus.

FIG. 7 is a waveform diagram of a light intensity signal measured by the same surface flaw inspection apparatus.

FIG. 8 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. 9 is a schematic cross-sectional view showing a relationship between incident light and reflected light at a tempered portion and a non-tempered portion of a steel plate to be inspected.

FIG. 10 is an angle distribution diagram of reflected light between the tempered portion and the non-tempered portion.

FIG. 11 is a diagram for explaining a generation process of a stub part existing in a steel plate.

FIG. 12 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. 13 is a diagram showing a relationship between a normal angle of a micro planar element and an area ratio in an irradiated part of a steel sheet.

FIG. 14 is a diagram showing a relationship between an incident angle of incident light on a steel plate and a normal angle of a micro-surface element.

FIG. 15 is a diagram illustrating a relationship between a normal angle of a small surface element and a weight function;

FIG. 16 is a diagram showing a relationship between each incident light from each position of the linear diffused light source and an incident position on a steel plate.

FIG. 17 is a diagram illustrating a polarization state of reflected light when each incident light of the linear diffusion light source is polarized.

FIG. 18 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. 19 is a diagram 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. 20 is a diagram showing a relationship between a normal angle of a small plane element and an elliptically polarized state of reflected light.

FIG. 21 is a diagram illustrating a relationship between a normal angle of a small surface element and a weighting function when an analyzer is inserted in an optical path of reflected light.

FIG. 22 is a diagram showing a relationship between a normal angle of a small surface element and a weighting function when an analysis angle of an analyzer is changed.

FIG. 23 is a diagram showing a relationship between a normal angle of a micro planar 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 light receiving camera 17, 28a, 28b, 28c analyzer 24 light cylindrical lens 26 reflected light 27 light receiving unit 33a, 33b, 33c feature amount calculating unit 34 mirror surface Scratch flaw determination unit 35: Specular diffused flaw determination unit 36: Flaw comprehensive determination unit 40: Signal processing unit

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Masakazu Inomata 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Inside Nihon Kokan Co., Ltd. (72) Inventor Shoji Yoshikawa 1-2-1, Marunouchi, Chiyoda-ku, Tokyo No. Nippon Kokan Co., Ltd. (72) Inventor Takahiko Oshige 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (72) Inventor Hiroyuki Sugiura 1-2-1, Marunouchi, Chiyoda-ku, Tokyo F-term (reference) in Nippon Kokan Co., Ltd. 2G051 AA37 AB07 BA11 BA20 BB01 BB20 CA03 CA07 CB01 CB05 CC20 DA06 EA11 EB01 EC01 ED04 ED13 ED22

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 processing unit for evaluating a surface flaw of the surface to be inspected based on the specular reflection component and the specular diffuse reflection component received by the second light receiving unit. Is the received specular reflection component and the specular surface Flaw determining means for determining the presence or absence of surface flaws on the surface to be inspected based on the diffuse reflection component, and the type and occurrence position of the surface flaws; based on the type and location of each surface flaw determined by the flaw determination means And a flaw connecting means for connecting adjacent surface flaws of the same type to form a new single surface flaw. 2. The evaluation processing unit obtains a feature quantity of a new surface flaw connected by the same type from the feature quantity of each surface flaw, and determines a grade of each flaw based on the feature quantity. 2. The surface flaw inspection apparatus according to claim 1, further comprising a determination unit.