JP3384345B2 - Surface flaw inspection equipment - Google Patents

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, such as the surface of a thin steel plate, with light to optically detect surface defects or 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. For the flaw inspection, various methods have been proposed and implemented conventionally.

For example, there is a surface flaw detection method for a metal object in which light is incident on the surface of an object to be inspected and specular reflection light and diffuse reflection light from the surface of the object to be inspected are detected by a camera.
It is proposed in Japanese Patent 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 reflected light from the surface of the object to be inspected is specular reflection direction and 20 ° from the incident direction or the specular reflection direction. Light is received by two cameras installed within the angle direction. Then, the light reception signals of the two cameras are compared, and, for example, the logical sum of the two is calculated. The surface flaw detection method that is not affected by noise is realized by regarding the abnormal value as a flaw only when the two cameras detect the abnormal value at the same time.

Further, there is a flaw inspection method for a surface of an object to be inspected by receiving backscattered light from the object to be inspected.
It is proposed in Japanese Patent No. 228943. In this flaw inspection method, light is incident on a stainless steel plate at a large incident angle, and reflected light returning to the incident side, that is, backscattered light is detected to detect a bald flaw on the surface of the stainless steel plate. .

Further, a flat steel hot flaw detector by detecting a plurality of backscatter reflection destinations is disclosed in Japanese Patent Laid-Open No. 178867/1996.
It is proposed in Japanese Patent Publication No. This flat steel hot flaw detector detects scratches on the hot rolled flat steel. In this flaw detector, the flaw slope angle of the scratch is 10 ° to 40 °.
And a plurality of cameras are arranged in the backscattering / reflecting direction so as to cover all the specularly reflected light from the flaw slope in this range.

Further, a surface measuring device utilizing a bias is disclosed in Japanese Patent Application Laid-Open Nos. 57-166533 and 9-1665.
It is proposed in Japanese Patent Publication No. 52.

In the measuring device proposed in Japanese Unexamined Patent Publication No. 166533/1982, polarized light in the direction of 45 ° is incident on the object to be measured and reflected light is received by the polarizing camera. In a polarization camera, the reflected light is split into three beams using a beam splitter inside the camera, and is received through polarization filters having different azimuth angles. And 3 from the polarized camera
A technique for displaying a book signal on a monitor and visualizing the polarization state by signal processing similar to that of the color T5 system is disclosed. This technique uses the ellipsometry technique, and it is desirable that the light source is parallel light, for example, laser light is used.

Further, in the surface inspection apparatus proposed in Japanese Patent Laid-Open No. 9-166552, Japanese Patent Laid-Open No. 57-166 discloses.
Similar to the technique described in Japanese Patent No. 533, the ellipsometry is used to inspect the surface of the steel sheet for flaws.

[0009]

However, each of the measurement techniques proposed in each of the above-mentioned publications detects a flaw having remarkable unevenness or a flaw in which a foreign substance such as an oxide film exists. However, it was difficult to surely capture all the flaws with respect to the pattern-like hedging defect having no remarkable unevenness.

For example, the flaw detector disclosed in JP-A-58-204353 has two cameras for receiving specular reflection light and scattered reflection light. The purpose is to detect signals detected by the two cameras. The effect of noise is removed by the logical sum. Therefore, a flaw signal having remarkable unevenness, that is, a flaw in which the surface is not cracked and does not turn up is applicable because both cameras can detect the flaw signal.

However, in the case of a defect such as a pattern-shaped hedging defect having no remarkable unevenness such that only one of the cameras can detect the defect signal, all the defects cannot be detected. .

The surface condition inspection method disclosed in Japanese Patent Laid-Open No. Sho 60-228943 is intended for a lifted-up bald flaw that has become apparent on a stainless steel plate having a small surface roughness.
Therefore, it cannot be applied to a steel plate with a rough surface that does not have a raised portion that is not actualized or a portion that does not have a flaw that reflects light returning to the incident side.

The flat steel hot flaw detector disclosed in Japanese Unexamined Patent Publication No. 8-178867 is intended mainly for scratches, and is based on the fact that specularly reflected light on a flaw slope is captured, so that it has remarkable unevenness. In the case of flaws such as pattern-like bald spots that do not have, there were some that could not be caught by backscattering, and there was a problem that detection was missed. In addition, once the camera is installed and it is determined which angle of the reflected component is received, the camera position cannot be easily changed.

Further, the measuring device disclosed in Japanese Patent Laid-Open No. 166533/1982 and the surface inspection device disclosed in Japanese Laid-Open Patent Publication No. 9-166552 use the technique of ellipsometry, and "the thickness and refractive index of a transparent transparent film" are used. "And" unevenness of physical property values "can be detected. However, even if the flaw originally has a physical property value different from that of the base metal part, such as a surface-treated steel sheet, for an object covered with a material having the same physical property value from above. , There was a problem that the effectiveness was reduced.

Further, in the ellipsometry, it is necessary to receive the reflected light from the same point at the corresponding pixel of each CCD and calculate the ellipso parameter for each pixel. Therefore, in Japanese Patent Laid-Open No. 166533/1982, the reflected light is split into three by a beam splitter and detected by three CCDs, which causes a problem that the light amount is reduced and it is difficult to align pixels between CCDs. It was

Further, in Japanese Patent Laid-Open No. 7-28633,
The same area is viewed by arranging the three cameras in the traveling direction of the steel plate, arranging them vertically or horizontally, or changing the inclination of the three cameras. However, there is a problem that the processing when the speed of the steel plate changes is complicated. Also, the optical conditions are not the same because the angles of the cameras are different. Therefore, there is a problem that it is difficult to align the pixels.

Furthermore, in JP-A-58-204353 and JP-A-8-178867, 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 the two images obtained is different. In addition to the difference in size, there is a problem that the field of view may be displaced if there is flapping on the surface to be inspected or if there is a change in distance due to a change in the thickness of the target. Particularly, in JP-A-58-204353, the problem is great because it is required that two cameras take a logical sum for the same field of view.

In general, the flaw signal does not have the same level in the flaw area, and there are variations. Even if such a flaw is found, it is judged as one flaw when the inspector inspects it.
However, in each of the flaw detection techniques described above, it is not possible to detect a region with a low flaw signal level.
Defects that are originally linear in shape may be recognized as multiple dot-like shapes. As a result, the flaw is judged to be a light grade, and there is a concern that defects may be overlooked or underestimated.

When the inspector inspects in this way, 1
A method has been proposed in which, when what is recognized as one flaw is judged as a plurality of flaws by the inspection device, it is judged as one original flaw (Japanese Patent Laid-Open No. H06-011458).

In this method, the surface to be inspected is scanned by a one-dimensional line sensor, the analog signal from the one-dimensional line image sensor is binarized, and the signal is run-length encoded. Then, the run-length encoded data that are close to each other in the sub-scanning direction on the surface to be inspected are compared, and the data that are close to each other within a predetermined distance in the scanning direction are connected. And the number of defects is 1
Whether it is good or bad is judged, and the result is also judged.

However, in this method, data that are close to each other at a predetermined distance or less are unconditionally linked based on the run length code. At this time, since it is based on the run length code, the connection processing is performed only by the positional relationship regardless of the type of flaw. As a result, there is a problem in that flaws of different types are connected to each other and are judged as one flaw simply because they are close to each other. That is, in this method, there is a problem that it is not possible to accurately evaluate the type and extent of a new connected flaw.

Further, in the surface inspection apparatus incorporated in the product quality inspection line, it is absolutely necessary from the viewpoint of quality assurance of manufactured products that no defects are detected.
However, a surface flaw inspection device for inspecting surface-treated steel sheets and the like has not been put into practical use.

The present invention has been made in view of the above circumstances, and detects the specular reflection component and the specular diffuse reflection component included in the reflected light from the surface to be inspected, and determines the type of flaw. By connecting the flaws in consideration, it is possible to reliably detect a pattern-like hedging defect that does not have remarkable unevenness such as surface cracks, gouging, and curling up on the surface to be inspected.
An object of the present invention is to provide a surface flaw inspection device 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 problems, in the surface flaw inspection apparatus of the present invention, an azimuth component parallel to the surface to be inspected and an azimuth component perpendicular to the surface to be inspected. A linear diffused light source with polarized light incident on it, and a large amount of specular reflection components are extracted from the specular reflection components and specular diffuse reflection components contained in the specularly reflected light from the surface to be inspected. The first light receiving means having an azimuth analyzer, and the specular diffuse reflection component are increased more than the specular reflection component of the specular reflection component and specular diffuse reflection component included in the specular reflection light from the surface to be inspected. Second light receiving means having an azimuth angle analyzer to be extracted, and evaluation processing for evaluating the surface flaw of 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. And a section.

Further, the evaluation processing section has a flaw determination means for determining the presence or absence of a surface flaw on the surface to be inspected, the type of the surface flaw and the position of occurrence, based on the received specular reflection component and specular diffuse reflection component, and this flaw. Based on the type and generation position of each surface flaw judged by the judging means, there is provided a flaw connecting means for joining adjacent surface flaws of the same kind to newly form one surface flaw.

According to another aspect of the invention, a feature quantity of a new surface flaw connected by the same type is obtained from the feature quantity of each surface flaw in the evaluation processing section in the surface inspection apparatus of the above invention. A grade determination means for determining the grade of each defect based on this feature amount is added.

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

First, the form of optical reflection on the surface of the steel sheet to be inspected by the surface flaw inspection apparatus of the present invention will be described in relation to the microscopic uneven shape of the steel sheet surface.

For example, when the object to be inspected is an alloyed zinc-plated steel sheet, as shown in FIG. 8 (a), the cold-rolled steel sheet as the base is hot dip galvanized and then passes through an alloying furnace. During this time, the iron element of the base steel sheet 1 diffuses into the zinc of the plating layer 2, and usually columnar crystals 3 of an alloy are formed as shown in FIG. 8 (c). This plated steel plate 4 is then temper rolled by rolls 5a, 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 remain in the original shape of the columnar crystal 3.

Then, the temper-rolled rolls 5a, 5b
The part that is flattened by is called the temper part 6, and the part that remains the original uneven shape that the other temper rolling rolls 5a and 5b do not contact is called the non-temper part 7.

FIG. 9 is a schematic sectional view modeling what kind of optical reflection occurs on the surface of the steel plate 4 having the 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 5a and 5b is specularly reflected 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 which is not brought into contact with the temper-rolled rolls 5a and 5b
The incident light 8 incident on the non-tempered portion 7 that retains the structure is mirror-reflected by one of the minute surface elements on each surface of the columnar crystal 3 in a microscopic view. The specular diffuse reflection light 10 does not necessarily match the specular reflection direction.

Therefore, the angular distributions of the reflected lights of the tempered portion 6 and the non-tempered portion 7 on the surface of the steel plate 4 are macroscopically as shown in FIGS. 10 (a) and 10 (b), respectively. That is, in the temper part 6, sharp specular reflection occurs in the regular reflection direction of the steel plate, and in the non-temper part 7, the reflected light has a spread corresponding to the angular distribution of minute surface elements on the surface of the columnar crystal 3. As described above, the reflected light from the temper portion 6 is referred to as specular reflected light 9, and the reflected light from the non-temper portion 7 is referred to as specular diffuse reflected light 10.

In reality, since the temper part 6 and the non-temper part 7 are macroscopically mixed, the angular distribution of the reflected light observed by an optical measuring device such as a camera is shown in FIG.
As shown in, the angular distributions of the specular reflected light 9 and the specular diffuse reflected light 10 are added according to the area ratios of the temper portion 6 and the non-temper portion 7.

Although the tempered portion 6 and the non-tempered portion 7 have been described above by taking an alloyed galvanized steel sheet as an example, the present invention is generally applicable to other steel sheets in which a flat portion is formed by temper rolling.

Next, the optical reflection characteristics of a defect called a pattern-shaped hedging defect having no remarkable unevenness which is a detection target of the present invention will be described.

As shown in FIG. 11, a hegging defect (heald portion 11) found in the galvannealed steel sheet is present in the cold-rolled steel sheet base plate before plating. Then, the plating layer 2 rides on it, and further the alloying of the hedging defects due to the diffusion of the iron element in the base steel sheet 1 progresses.

In general, the heald portion 11 has a difference in, for example, the plating thickness or the degree of alloying as compared with the base material 12 showing the normal portion of the steel plate 4. As a result, for example, when the plating thickness of the hedging portion 11 is thick and convex to the base material 12, the temper rolling is applied, so that the area of the temper portion 6 becomes larger than that of the non-temper portion 7. On the contrary, the heald part 1
When the plating thickness of No. 1 is thinner than that of the base material 12, the rolls 5a and 5b of the temper rolling do not come into contact with the hegged portion 11, and the non-tempered portion 7 occupies the majority. Further, in the case where the heald portion 11 is shallowly alloyed, the angular distribution of the micro-plane elements is strong in the direction of the steel sheet direction, and the diffusivity becomes small.

Next, such a beard portion 11 and a base material portion 12 are formed.
The appearance of the pattern-like hegging defect due to the difference in the surface texture of will be described.

When the difference between the beard portion 11 and the base material portion 12 is classified based on the above model, it is generally classified into the following three types.

(A) The area ratio of the tempered portion 6 and the angular distribution of the minute surface elements of the non-tempered portion 7 in the hedging portion 11 are determined by the area ratio of the tempered portion 6 and the minute surface of the non-tempered portion 7 in the base material portion 12. It is different from the angular distribution of the element (Fig. 13 (a), Fig. 12).
(A)).

(B) Although the area ratio of the tempered portion 6 in the hedging portion 11 is different from the area ratio of the tempered portion 6 in the base material portion 12, the angular distribution of the minute surface elements of the non-tempered portion 7 in the hedging portion 11 is It is the same as the angular distribution of the minute surface elements of the non-tempered portion 7 in the base material portion 12 (FIGS. 13B and 12B).

(C) The angle distribution of the minute surface elements of the non-tempered portion 7 of the heald portion 11 is determined by
Although it is different from the angular distribution of the micro-plane element of No. 2, the area ratio of the temper part 6 in the heald part 11 is the same as the area ratio of the temper part 6 in the base material part 12 (FIGS. 13C and 12C). .

As shown in FIG. 14, the inclination angle of the normal direction of the micro surface element 13 with which the incident light 8 abuts with respect to the steel plate normal direction of the steel plate 4 is defined as the normal angle ξ of the micro surface element 13. FIG. 13A shows the relationship between the angle ξ and the area ratio S (ξ) of the temper part 6 in the three cases (a), (b) and (c) described above.
Shown in (b) and (c).

The difference in the area ratio S (ξ) of the temper portion 6 and the angular distribution of the minute surface element 13 is shown in FIG. 12 (a).
It is observed as a difference in the angular distribution of the reflected light amount as shown in (b) and (c). The angle distribution shown by the solid line in the figure is the heald portion 11.
The angle distribution 11a corresponds to the base metal part 12 and the angle distribution indicated by the dotted line in the drawing corresponds to the base metal part 12
a.

That is, FIG. 12A shows a case where there is a difference in both the specular reflection component and the specular diffuse reflection component between the hedging portion angle distribution 11a and the base material portion angle distribution 12a. 12B shows the case where there is a difference only in the specular reflection component, and FIG. 12C shows the case where there is a difference only in the specular diffuse reflection component.

When the area ratio S (ξ) of the tempered portion 6 is different between the beveled portion angle distribution 11a and the base material portion angle distribution 12a, as shown in FIGS. 12 (a) and 12 (b). , The difference is observed from the direction of specular reflection. Specifically, the case where the reflected light of the heald portion 11 is measured from the regular reflection direction and the base material portion 12
When the reflected light of is measured, the area ratio S (ξ) of the temper part 6 of the heald part 11 is the area ratio S of the temper part 6 of the base material part 12.
When it is larger than (ξ), the barbed portion 11 looks relatively brighter than the base material portion 12. On the contrary, when the temper ratio 6 of the beard portion 11 is smaller than the base material portion 12, the beard portion 11 is observed relatively darker than the base material portion 12.

Angular distribution 11a of the barbed portion and angular distribution 1 of the base metal portion
When there is no difference in the area ratio S (ξ) of the temper part 6 from 2a, as shown in FIG. We cannot observe our existence. However, when there is a difference in the diffusivity (angle distribution) of the specular diffuse reflection components, defects are observed from the diffusion directions other than the specular reflection direction as shown in FIG.

For example, when the diffusivity (angle distribution) of the specular diffuse reflection component of the heald portion 11 is small, generally, the heald portion 11 is observed bright from the diffusion direction relatively close to the regular reflection direction, and from the regular reflection direction. The brightness decreases with distance,
It becomes unobservable at a certain angle. Further, when the distance from the regular reflection direction is increased, the shadow 11 is observed darker.

In order to surely distinguish and detect such a barbed portion 11 from the base material portion 12, in FIG. 13, what angle (normal angle ξ) the reflected light from the minute surface element 13 is extracted. It is necessary to consider whether or not. For example, as in the example of FIGS. 12A and 12B described above, detecting the difference between the beard portion 11 and the base material portion 12 in the specular reflection direction is similar to FIG.
Of the angular distribution of the micro-plane element 13 indicated by 3, the micro-plane element 1
It means that the normal angle ξ = 0 of 3 is extracted and the difference between the beard portion 11 and the base material portion 12 is detected.

Mathematically expressing the extraction of the reflected light of the normal surface angle ξ = 0 of the micro-plane element 13, the characteristics (area ratio S (ξ)) of FIG.
This is equivalent to multiplying by a function showing the extraction characteristic represented by the delta function δ (ξ) shown in (a) (hereinafter, this function is referred to as a weighting function I (ξ)) and integrating.

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

As shown in FIG. 14, the reflection angle θ '
And the relationship between the normal angle ξ of the minute surface element 13 and the incident angle θ of the incident light 8 can be obtained by the equation (1) by a simple geometrical consideration.

Θ ′ = − θ + 2ξ (1) That is, what angle (normal angle ξ) the minute surface element 13 has
It can be understood that whether to extract the reflected light from is equivalent to what kind of weighting function I (ξ) is designed.

From this point of view, FIG. 13 (a) (b)
Considering a weighting function I (ξ) for discriminating and detecting each of the barbed portions 11 as shown in FIG.
5 (a) and (b), the delta functions δ (ξ), δ (ξ + 1
0) is also one of the effective weight functions I (ξ).

The weighting function I (ξ) is not always the same as in FIG.
The width for extracting only the specific normal angle shown in 5 does not have to be the infinitesimally small delta function δ (ξ), and it is possible to have a certain signal width.

However, in such a discrimination method, the fields of view of the two optical systems cannot be the same. Further, once the camera is installed to measure the diffuse reflection light, changing the weighting function I (ξ) of the camera is not easy because it is necessary to change the installation position of the camera.

For the former problem, measurement on the same optical axis is necessary. That is, instead of capturing diffuse reflection light,
It is desirable that both the specular reflection component and the specular diffuse reflection component be captured only by measuring from the regular reflection direction of the steel plate 4. Then, for the latter problem, the weighting function I (ξ)
It is desirable to be able to set with some degree of freedom.

Therefore, in the present invention, first, as the light source, a linear light source having a diffusion characteristic, that is, a linear diffused light source is used 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 regular 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. 16A and 16B, the linear diffused light source 1
4 is arranged parallel to the surface of the steel plate 4, and is in a plane perpendicular to the light source, and the reflection characteristics when a point on the steel plate 4 is observed from the steel plate specular reflection direction, which is the direction in which the incident angle matches the exit angle, 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 temper portion 6 is reflected specularly, and the steel plate is regularly reflected. All can be caught in the direction. On the other hand, the light incident on the non-tempered portion 7 is specularly diffusely reflected, and only the amount reflected by the minute surface element 13 that happens to be in the same direction as the normal direction of the steel plate is captured. Since the number of the minute surface elements 13 facing such a direction is very small, the specular reflected light from the temper part 6 is dominant in the reflected light captured by the light receiving camera arranged 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 central portion of the linear diffused light source 14, the light incident on the temper portion 6 is mirror-reflected and reflected in a direction different from the steel plate regular reflection direction. Therefore, the light specularly reflected cannot be captured in the regular reflection direction of the steel plate. On the other hand, the light incident on the non-tempered portion 7 is specularly diffused and reflected, and the portion reflected in the regular reflection direction of the steel plate is captured by the light receiving camera. Therefore, all the reflected light captured by the light receiving camera arranged in the regular reflection direction of the steel plate is specular diffuse reflected light reflected by the non-temper portion 7.

Combining the above two cases, what is captured by the observation from the regular reflection direction of the steel plate is that of all the incident light 8 emitted from the entire lengthwise direction of the linear diffused light source 14 is observed from the temper part 6. It is the sum of the specular reflection light and the specular diffuse reflection light from the non-temper 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.

In general, in reflection on a mirror-like metal surface, in the light whose electric field direction is parallel to the incident surface (p-polarized light) or the light perpendicular to the incident surface (s-polarized light), the polarization characteristic is also reflected. Saved. That is, the light is emitted as it is as p-polarized light or as s-polarized light. Further, 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, it becomes elliptically polarized light according to the reflectance ratio tan Ψ and the phase difference Δ of p and s-polarized light and emerges. To do.

Linear diffused light source 14 on alloyed galvanized steel sheet
A case where light is emitted from the above 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 temper portion 6 of the steel plate 4 and observed in the regular reflection direction of the steel plate. In this regard, the reflection on the general mirror-like metal surface is established as it is.

On the other hand, as shown in FIG. 17B, the light emitted from a position other than the central portion of the linear diffused light source 14 is generated by the inclined fine surface element 13 of the crystal surface of the non-tempered portion 7 of the steel plate 4. It is specularly reflected and observed in the direction of regular reflection of the steel plate. In this case, when considering a tilted microscopic surface element 13 that actually reflects p-polarized light parallel to the incident surface of the steel plate 4, the incident surface is not parallel to the microscopic surface element 13. Without p, s
Since it is linearly polarized light having both polarization components, it is emitted as elliptically polarized light. The same applies when s-polarized light is incident from the linear diffused light source 14.

Further, when linearly polarized light having an arbitrary polarization angle α having both p and s polarization components is incident on the steel plate 4 from the linear diffused light source 14, a minute tilted position other than the central portion of the linear diffused light source 14 is obtained. 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 regular reflection direction of the steel plate is
It is different from the light that is incident from the central portion of the linear diffused light source 14 and is specularly reflected by the temper portion 6.

The case where linearly polarized light having both p and s components is incident on the steel sheet 4 from the linear diffused light source 14 will be detailed below.

First, as shown in FIG. 18, the incident light 8 from the linear diffused light source 14 is linearly polarized by the polarizing plate 15 having the azimuth angle (polarization angle) α, and then the horizontally arranged steel plate 4 is formed. 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 temper part 6 of the steel plate 4 and the normal line in the non-temper part 7 happen to be the steel plate 4. Normal angle ξ =
Steel plate 4 is the component that is specularly diffused and reflected from the minute surface element 13 of 0.
It 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, with respect to the incident light 8 from the point A deviated by the angle φ from the point O of the steel plate 4 on the linear diffused light source 14, the specular reflection component is the light receiving camera 1.
Since the light is reflected in directions different from the six directions, only the specular diffuse reflection component by the minute surface element 13 having the normal angle ξ described above contributes.

Here, the angle φ indicating the incident direction of the incident light 8
The relationship between the normal angle ξ of the micro surface element 13 and the incident angle θ of the incident light 8 with respect to the steel plate 4 is given by the equation (2) by a simple geometrical consideration.

COS ξ = [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, consider the polarization state of the light reflected in this way.

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, and the polarization state E _C is Using the Jones matrix generally used in, E _C = T · Ein (3) However, Ein represents the linear polarization vector of the azimuth angle (polarization angle) α of the polarizing plate 15, and T represents the reflection characteristic matrix of the steel plate 4. The linear polarization vector Ein and the reflection characteristic matrix T are given by the equations (4) and (5), respectively.

[0076]

[Equation 1]

However, tan Ψ: p, s polarized light amplitude reflectance ratio Δ: p, s polarized light reflectance phase difference r _S : s polarized light amplitude reflectance The polarization state E _A of the emitted incident light 8 reflected by the minute surface element 13 having the normal angle ξ in the direction of the light receiver 16 is such that the incident surface is orthogonal to the polarizing plate 15 and the analyzer of the light receiving camera 16. If so (6)
Given by the formula.

E _A = R (ξ) TR (−ξ) Ein (6) where R is a rotation matrix and is given by the equation (7).

[0079]

[Equation 2]

The equation (3) is a special case where the normal angle ξ = 0 of the minute surface element 13 in the equation (6) is used, and the equation (6) is used for both the specular reflection component and the specular diffuse reflection component. You can think in a unified way. The equation (6) is calculated, and the elliptically polarized state of the reflected light from the minute surface element 13 with the normal angle ξ is shown in FIG.

However, here, the azimuth angle (polarization angle) of the incident polarized light
α is 45 °, the incident angle θ is 60 °, and the reflection characteristic of the steel plate 4 is the arctangent Ψ = 28 ° of the amplitude reflectance ratio of p and s polarized light, p,
The phase difference Δ of reflectance of 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 ξ = O, that is, the value of the normal angle ξ with respect to the ellipse in the case of specular reflection.

Therefore, for example, by inserting the analyzer 17 in front of the light-receiving camera 16 and setting the analysis angle β thereof, which normal angle ξ is more reflected light from the micro-plane element 13 is extracted. Can be selected.

In order to quantify this, as shown in FIG. 19, after inserting the analyzer 17 of the detection angle β into the reflected light of the polarization state E _A represented by the equation (3), When the polarization state E ₀ is obtained, the equation (8) is obtained.

E ₀ = R (β) · A · R (−β) · E _A = R (β) · A · R (−β) · R (ξ) · T · R (−ξ) · Ein ... (8) However, A is a matrix showing the analyzer 17, and is shown by Formula (9).

[0085]

[Equation 3]

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

As described above, when the area ratio of the corresponding micro-plane 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 ・ tan Ψ ・ cos ∆ ・ cos (ξ−α) ・ sin (ξ−α) × cos (ξ−β) ・ sin (ξ−β) + sin ² (ξ−α) ・sin ² (β−ξ) (10) As described above, I (ξ, β) is a weighting function that indicates how much reflected light from the minute surface element 13 with the normal angle ξ can be extracted. And depends on the polarization characteristics of the optical system and the subject. Then, the product of the reflectance r _S ² of the steel plate 4, the incident light quantity E _P ² , and the area ratio S (ξ) is the detected light intensity.

The value of the reflectance r _S ² is considered to be constant when considering an object such as a surface-treated steel sheet whose surface material is uniform. Further, the incident light amount E _P ² may be a constant value as long as the incident light amount is uniform regardless of the position of the light source.

Therefore, in order to obtain the light intensity detected by the light-receiving camera 16, it is sufficient to consider the area ratio S (ξ) of the minute surface element 13 with the normal angle ξ and the weighting function I (ξ, β).

Now, consider the weighting function I (ξ, β). When an analysis angle β ₀ of the analyzer 17 that maximizes the contribution of the normal surface angle ξ from the micro-plane element 13 is selected, the candidate is given by solving the following equation (11) for β. To be

[0092]

[Equation 4]

From the equation (11), when the normal angle ξ = 0, that is, the detection angle β that maximizes the contribution of the specular reflection component is obtained, the detection angle β is about −45 °. However, also here, the arctangent Ψ = 28 ° of the reflectance ratio and the phase difference Δ = 120 ° are adopted as the reflection characteristics of the steel plate 4, and the orientation of the polarizing plate 15 with respect to the incident light 8 from the linear diffused light source 14 is adopted. The angle (polarization angle) α = 45 ° was adopted.

In FIG. 21, the analysis angle β of the analyzer 17 is -45.
The relationship between the normal angle ξ of the minute surface element 13 and the weighting function I (ξ, −45) in the case of ° is shown. However, for ease of viewing, the maximum value of the weighting function I (ξ, −45) is standardized to [1].

From the characteristics of FIG. 21, 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 in the vicinity of ± 35 ° is most extracted.

On the contrary, the analysis angle β of the analyzer 17 that best extracts the reflected light with the normal angle ξ = ± 35 ° is (10)
From the equation and the equation (11), β = 45 °.
FIG. 22 shows the relationship between the normal angle ξ of the minute surface element 13 and the weighting function I (ξ, 45) with respect to the analysis angle β = 45 ° of the analyzer 17.

Note that the characteristic of the weighting function I (ξ, β) in FIG. 22 is not bilaterally symmetric, considering that it is based on the incident surface (the plane stretched by the incident light 8 on the minute surface element 13 and the reflected light). When the normal angle ξ of the micro-plane element 13 is positive, the azimuth angle (polarization angle) α of the polarization of the incident light 8 apparently becomes small (p
It is closer to 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 analysis angles β = −45 ° and 45 ° of the analyzer 17.

As shown in the equation (10), the intensity of the reflected light from the minute surface element 13 with the normal angle ξ is given by the product of the weighting function I (ξ, β) and the area ratio S (ξ). Finally, the light intensity received by the light receiving camera 16 is [S (ξ) · I (ξ,
β)] is integrated 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 light intensity actually received is obtained by weighting and integrating with the weighting function I (ξ, β) shown in.

Then, on the surface of the steel plate 4, as shown in FIG.
Consider a case where there is a heddle portion 11 having characteristics as shown in (b) and (c). Each area ratio S (ξ) in that case is as shown in FIGS. 13 (a), 13 (b), and 13 (c).

First, consider the 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 detection angle β = −45 ° is the area ratio S shown in FIG.
Since it corresponds to a product obtained by multiplying (ξ) by the weighting function I (ξ, β) shown in FIG.
It is possible to detect the difference in the amount of reflected light with respect to 1.

FIG. 13 shows the light intensity when the same flaw is received through the analyzer 17 having the detection angle β = 45 °.
As shown in (b), since there is no difference in the specular diffuse reflection component, the weighting function I (ξ, β) of the detection angle β = 45 ° in FIG.
As is apparent from the consideration of integrating by multiplying by, it is impossible to detect the difference between the base material portion 12 and the heald portion 11.

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

However, the normal angle ξ at which there is no difference in the specular diffuse reflection components of the base material portion 12 and the hedging portion 11 is shown in FIG.
In (c), the normal angle ξ was around ± 20 °, but if there was a flaw that happened to be around ± 30 degrees, the angle was also detected through the analyzer 17 with the analysis angle β = 45 °. become unable.

In that case, another weighting function (eg I
(Ξ, 90)) such that the detection angle β (eg 90 °)
The other analyzer 17 may be prepared separately so that the third light receiving camera 16 receives the light.

In general, the reflection characteristics of the base material portion 12 and the hedging portion 11 on the surface of the steel plate 4 are as shown in FIGS. 12 (a), 12 (b) and 12 (c). In order to eliminate it, it is necessary to use the analyzers 17 with three different analysis angles β and extract and receive the reflected light from the corresponding microplane elements 13 with the three normal angles ξ. is there.

When there are differences in the specular reflection component and the specular diffuse reflection component as shown in FIGS. 12A and 13A, basically, for example, either -45 ° or + 45 ° is used. The difference between the base material portion 12 and the beard portion 11 can be detected even by the reflected light passing through the analyzer 17.

Therefore, in the present invention, the linear diffused light source 14 is used.
Of the specular reflection component and specular diffuse reflection component included in the specular reflection light from the surface to be inspected by the first light receiving means, more specular reflection component is extracted and received as compared with the specular diffuse reflection component, The second light receiving unit extracts a larger amount of the specular diffuse reflection component from the specular reflection component and the specular diffuse reflection component included in the specularly reflected light from the surface to be inspected.

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

With such an optical system, since the measurement is performed on the common optical axis from the regular reflection direction, it is possible to correspond to each of specular reflection and specular diffuse reflection without being affected by the steel plate distance variation and the velocity change. It is possible to get one signal,
(EN) A surface flaw inspection apparatus capable of detecting a pattern-like bald flaw having no remarkable unevenness without causing omission.

However, in general, the flaw signal does not have the same level in all the flaw areas, and there are variations. Even if such a flaw is found, it is judged as one flaw when the inspector inspects it. However, in the case of such a flaw, the surface flaw inspecting apparatus cannot detect a region having a low flaw signal level, and determines that the flaw is a plurality of mild flaws.

Therefore, in the present invention, in the evaluation processing unit for evaluating surface flaws, the presence / absence of surface flaws, the type,
The generation position is determined, and when the adjacent surface defects are of the same type, these surface defects are connected and recognized as one new surface defect. Further, the feature amount of each surface flaw before connection and the connection processing for obtaining the maximum absolute value are performed, and the grade of the defect after connection is determined based on the addition processing.

As a result, the judgment result can be made more accurate, and the pattern-like bald spots can be detected without omission or underestimation.

[0114]

BEST MODE FOR CARRYING OUT THE INVENTION 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 surface flaw inspection apparatus.

The surface flaw inspection apparatus of this embodiment is installed in a quality inspection line of an alloyed galvanized steel sheet in an iron factory. A linear diffused light source 22 is arranged in the width direction of the strip-shaped steel plate 21 above the conveyance path of the steel plate 21 in the conveying state in the direction of the arrow in the figure. This linear diffused light source 22
Emits the light of the metal halide light source from both ends of the transparent light guide rod partly coated with the diffuse reflection paint, thereby obtaining a uniform outgoing light in the width direction.

Incident light 23 emitted from each position of the linear diffused light source 22 to the steel plate 21 is incident angle θ of, for example, 60 ° with respect to the entire width of the steel plate 21 in the traveling state via the cylindrical lens 24 and the polarizing plate 25. Is illuminated by. Polarizing plate 2
The azimuth angle (polarization angle) α of 5 is set to 45 °.

The reflected light 26 reflected by the steel plate 21 is incident on the light receiving portion 27 which is arranged in the regular reflection direction of the steel plate. In the light receiving section 27, the detection angle β is -45 ° in front of the lens,
Analyzers 28a, 28b, 2 set at 45 ° and 90 °
It is composed of light receiving cameras 29a, 29b and 29c which are three linear array cameras having 8c.

Then, each of the light receiving cameras 29a, 29b, 2
The optical axes of 9c are maintained parallel to each other. Also, 3
The shift of the visual fields of the light receiving cameras 29a, 29b, 29c of the stand is corrected by the signal processing unit 40. In this way, if the optical axes of the respective light receiving cameras 29a, 29b, 29c are maintained in parallel, the three light receiving cameras 29a, 29b, 2
Each pixel of 9c has a one-to-one correspondence with the same visual field size. As described above, by adopting the linear array camera as the light receiving camera, loss of light amount is eliminated and efficient measurement can be performed as compared with the case of using the 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 type photodetector in which a single photodetection element is combined with a galvano mirror or a polygon mirror.

A fluorescent lamp may be used as the linear diffused light source 22. It is also possible to use a fiber light source in which the emitting ends of the bundle fibers are aligned in a straight line. The light emitted from each fiber is the N / A of the fiber.
This is because the fiber light source in which the fiber light sources are aligned has a sufficient divergence angle, and is substantially a linear diffused light source.

The light intensities of the reflected light 26 received by the light receiving cameras 29a, 29b, 29c for each pixel in the width direction of the steel plate 21 are converted into the light intensity signals a, b, c, respectively, and evaluated. It is transmitted to the signal processing unit 40 as a processing unit.

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

First with built-in -45 ° analyzer 28a
Light receiving camera 29a as a second camera, and light receiving camera 2 as a second camera incorporating an analyzer 28b of + 45 °
Light receiving camera 29 having 9b and 90 ° analyzer 28c incorporated therein
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 decimation unit 30a, 30b, 30c
Is an average of the light intensity signals a, b, c input from the light receiving cameras 29a, 29b, 29c, 29c for each scan cycle of the light receiving cameras 29a, 29b, 29c, and the steel plate 2
When 1 has moved a distance corresponding to the longitudinal resolution in signal processing, a signal for one line is output.

By performing such thinning-out processing,
Even if the transport speed of the steel plate 21 changes, the resolution in the steel plate moving direction of one line in the signal processing can be made constant. Also, the light intensity signals a, b, and
Since c is averaged, the resolution in the moving direction of the steel plate for one line in the signal processing is equal to that of the light receiving cameras 29a, 29b, 29.
Even when the field size of c in the moving direction of the steel sheet is sufficiently larger, the average value obtained by finely measuring the interval can be used, so that oversight can be eliminated.

Each average value decimation unit 30a, 30b, 30c
The respective light intensity signals a, b, c which have been subjected to the signal processing in (4) are input to the following respective preprocessing sections 31a, 31b, 31c.

Each preprocessing section 31a, 31b, 31c has 1
Corrects the luminance unevenness of the line signal. The brightness unevenness referred to here includes unevenness caused by the optical system and unevenness caused by the reflectance of the steel plate 21. In addition, each of the preprocessing units 31a, 31
b and 31c also detect the edge positions on both sides of the steel plate 21,
A process for preventing erroneous recognition of a rapid change in the light intensity signals a, b, and c at the edge as a flaw is also performed. Each preprocessing unit 3
The respective light intensity signals a, b, c processed by the signals 1a, 31b, 31c are converted into the following binarization processing units 32a, 32b, 32.
Input to c.

Each binarization processing section 32a, 32b, 32c
Compares the data of each pixel included in each light intensity signal a, b, c with a predetermined threshold value, extracts a defect candidate point, and extracts the next feature amount calculation unit 33a, 33b, 33c. Send to.

The feature quantity extraction units 33a, 33b, 33c are
A continuous defect candidate point is determined as one defect candidate area, and for example, a position feature amount indicating the occurrence position of a start address (defect start coordinate), an end address (defect end coordinate), a peak value, etc. The density feature amount and the like are calculated.

In the specular flaw determination unit 34 and the specular diffuse flaw determination unit 35, based on the feature amounts calculated by the feature amount extraction units 33a, 33b, 33c corresponding to the respective light receiving cameras 29a, 29b, 29c, Determine the type and degree of defects.

Therefore, the feature quantity extraction units 33a, 33
b, 33c, the specular flaw determination unit 34, and the specular diffusive flaw determination unit 35 constitute a determination unit that determines presence / absence, type, and generation position of the surface flaw.

The flaw comprehensive determination unit 36 is a feature quantity extraction unit 33.
a, 33b, 33c, the specular flaw determination unit 34, and the specular diffusive flaw determination unit 35, based on the flaw determination results, the adjacent surface flaws of the same type are joined to form a new surface flaw. Carry out. Furthermore, when the above-described connection processing is completed, the flaw comprehensive determination unit 36 determines the steel plate 21 to be inspected.
The final flaw type and its degree for each flaw after the connection processing that occurs in 1) are determined.

Next, the defect linking process in the defect comprehensive determination unit 36 will be described using a specific example.

Now, the feature quantity extraction units 33a, 33b, 33
c, the specular flaw determination unit 34 and the specular diffusive flaw determination unit 35 two-dimensionally scan a certain area of the steel plate 21. As a result, as shown in Table 1 and FIG. , Area 37 having types of “health” and “dirt”
It is assumed that five defects (defects) having a, 37b, 37c, 37d, and 37e are detected.

[0136]

[Table 1]

Then, the defect comprehensive judging section 36 detects the different areas 37a, 37b, 37c, 37d,
Whether or not the 5 flaws having 37e can be connected is verified for every two combinations, and if possible, both are connected.

As a concrete condition for connection, it is judged whether or not each area should be connected based on the relative positional relationship between each kind of flaws and each area 37a, 37b, 37c, 37d, 37e. If the inspector visually recognizes a long flaw as a plurality of short flaws, the condition for connecting them is that the flaw type is the same and that the flaw area is the same as the other flaw areas in the width direction. It is assumed that the coordinates are overlapped and are also close to each other in the longitudinal direction.

FIG. 3 shows, for example, two regions 37b, 37.
It is a flow chart which shows the processing which judges whether each flaw of c is connectable.

Each flaw type determination result, each flaw start coordinate P3x, P5x, and each flaw end coordinate P4x, P4 in the width direction.
6x, the flaw start coordinate P3y. P5y, flaw end coordinates P4y, P6y, and the type of flaw are read.

First, it is determined whether or not the types of flaws in the areas 37b and 37c are the same (S1). If the types of defects are different, such as "heavy" and "dirt", it is determined that the 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 it is not between P3x ≦ P5x ≦ P4x, the width start coordinates P3x of the area 37b of another flaw
Is between the width start coordinate P5x and the width end coordinate P6x of the one flaw region 37b (S4).

Unless P5x ≦ P3x ≦ P6x, the regions 37b and 37c are the steel plate 21.
Since there is no overlap in the x-coordinate on the two-dimensional coordinate of, it is determined that they cannot be connected (S2).

In S3 or S4, when the width start coordinates of one of the flaws overlap in the width direction of the other flaw, the process proceeds to S5, in which the longitudinal end coordinate P5y of the other flaw region 37b,
The distance between the longitudinal start coordinates P4y of one flaw (P5y-
P4y) determines whether it is smaller than a predetermined threshold value 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 joined, and the joining processing is executed (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 judging section 36 detects the different areas 37a, 37b, 37c and 37, respectively.
Whether or not the five flaws having d and 37e are connectable is verified for every two combinations, and if possible, both are joined to form a new flaw. For example, after the flaw connection processing was performed on the five flaws shown in Table 1 and previously shown in FIG. 4, the flaws were aggregated into the three flaws shown in Table 2 and FIG.

[0147]

[Table 2]

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

Next, the feature amount that determines the degree of the flaw for each flaw alone or connected is recalculated. For example, for the flaw in the new connected area 37f, the length and width are obtained from the coordinates of P11 and P12, and the area and the concentration integrated value in the flaw area are the original flaw areas 37c, 37d, and 37e. Obtained by adding the integrated values of area and concentration. Furthermore, the density peak value is the area 37c, 37d, 37e of each defect.
The maximum of the peak value of is adopted. Based on these feature quantities, the degree of each flaw is re-determined and used as the final result.

Although the above embodiment has described the case where the flaws are connected in the longitudinal direction, in the case of connecting them in the width direction, the width may be changed according to the connection determination processing procedure in which the longitudinal direction and the width direction are interchanged. Directional connection processing is possible.

Further, the comprehensive judgment unit 36 also corrects the visual field deviation in each of the light receiving cameras 29a, 33b, 29c based on the position characteristic amount from each characteristic amount extraction unit 33a, 33b, 33c. In this way, since the visual field shift between the light receiving cameras 29a, 29b, 29c is corrected in the feature amount unit, it is not necessary to adjust the visual field between the light receiving cameras 29a, 29a, 29c in pixel units.

[0152]

EXAMPLE FIG. 6 and FIG. 7 show measurement results of surface flaws of an alloyed zinc-plated 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. 12 (b) is larger than that of the base material portion 12 in the heald portion 11, but the diffusivity of the non-tempered portion 7 does not change. There is no significant difference between the defect and the area ratio S (ξ) of the temper part 6 shown in FIG. 12 (c) between the beard part 11 and the base material part 12, but there is a difference in diffusivity.

Then, in the central portion of the steel plate 21 in the width direction, as shown in FIG.
In the case where a flaw of the type shown in 2 (b) occurs, −
At 45 °, 45 ° and 90 °, each analyzer 28a, 28b,
Each light-receiving camera 29a, 2 for which the detection angle β of 28c is 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 for one line in the width direction with 9b and 29c.

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

Further, in the center portion of the steel plate 21 in the width direction, as shown in FIG.
When a flaw of the type shown in (c) occurs, -4
Each analyzer 28a, 28b, 2 at 5 °, 45 ° and 90 °
Each of the light receiving cameras 29a, 29 for which the detection angle β of 8c is set
7 (a), (b) and (c) 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 for one line with the widths b and 29c. .

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

[Table 3]

As for the flaws of the type shown in FIG. 12C, as shown in the figure, there are generally angles that cannot be detected in the diffuse reflection direction, but two types of flaws having different angles were measured.

For comparison, an incident angle of 6 was used in the prior art.
At the same time, the results obtained by injecting light at 0 ° and measuring with no polarization from the specular reflection direction (60 °) and the light receiving angle (-40 °) direction deviated by 20 ° from the incident direction are also shown.

In the prior art, light is received at two light-receiving angles and a logical sum is taken for noise removal, but it is impossible to detect two light-receiving angles at the same time for these flaws. Furthermore, there are flaws that cannot be detected at either light receiving angle.

On the other hand, in the embodiment of the present invention, the reflected light components corresponding to three different light receiving angles are analyzed by the analyzer 28.
Since the light is extracted from the specular reflection direction by using a, 28b, and 28c, any one of the light receiving cameras 29a and 29a
It is possible to detect with b and 29c. It is also easy to set the detection angle β to an optimum value in accordance with the reflection characteristics of the flaw that needs to be detected.

The present invention is not limited to the above embodiment.

In the apparatus of the embodiment shown in FIG. 1, three light receiving cameras 29a, 29b and 29c are used, but -4
A light receiving camera 29a having a 5 ° analyzer 28a, +4
Even with only two light-receiving cameras including the light-receiving camera 29b having the 5 ° analyzer 28b, the presence of the heald portion 11 is distinguished from the base material portion 12 from the optical axis direction of the specularly reflected light from the steel plate surface. It can be detected sufficiently.

Further, the test piece having linear defects (defects) such as “line baldness” and “belt baldness” and point defects (defects) such as “camis” and “foreign matter” was also tested. The inspection results before and after performing the connection process for the defect in the defect comprehensive determination unit 36 of the signal processing unit 40 in the configuration apparatus and after performing the connection process, and the visual evaluation result of the inspector under each condition Table 4 and Table 5 show the comparison with the above.

Table 4 shows the number of detections for each type of defect detected in the state where the connection process is not performed for each defect (defect). Then, under this condition, it is shown that, as compared with the visual evaluation by the inspector, 24 missing points occurred due to the linear defects (defects).

[0166]

[Table 4]

Further, Table 5 shows the number of detections for each defect (defect) after each type of detected defects after the connection processing is performed. Under these conditions, linear defects (defects) were found in comparison with the visual evaluation by the inspector.
Indicates that three misses occurred. This Table 4 and Table 5
By performing a concatenation process on each detected number, as is clear by comparing each missed number in
It is possible to more accurately match the result of visual inspection by the inspector.

[0168]

[Table 5]

Further, in Table 6, for each defect (scratch) in which the blemish type is a line baldness and a banded baldness, the grade determination result of the inspecting device for the visual grade determination of the inspector without the connection processing being performed. Shows the evaluation of. In Table 6, the larger the number of shaded portions, the better the inspection device is in visual agreement. Then, under this condition, it is shown that, as compared with the evaluation result of the inspector, 23 missing points were generated due to the linear defects (defects).

Here, in the inspection apparatus grade, A is mild and D is severe. In addition, the visual judgment grade of the inspector indicates that C is light, C is under, and D is severe.

[0171]

[Table 6]

Further, in Table 7, the grade judgment result of the inspection apparatus for the visual grade judgment of the inspector after the connection processing is performed for each defect (scratch) of which the defect type is line baldness and band baldness The evaluation is shown. In Table 7, the larger the number of shaded portions, the better the inspection device is in visual agreement. Under these conditions, the number of missing points was 0 and the number matching the visual judgment grade was also increased, as compared with the visual evaluation by the inspector. As is clear from the comparison between the numbers of missed points in Table 6 and Table 7, by performing the concatenation process on each of the detected numbers, 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, in the surface flaw inspection apparatus and the surface flaw inspection method of the present invention, based on the finding that the specularly reflected light on the surface to be inspected is composed of the specular reflection component and the specular diffuse reflection component. , Each component is separately extracted and detected. Specifically, using a linear diffused light source, p
Polarized light having both s-polarized light and s-polarized light is incident on the surface to be inspected, and by appropriately setting the inspection angle from the steel plate regular reflection direction, a component containing more specular reflection component and more specular diffuse reflection component are included. The structure that extracts the components and is adopted.

With this configuration and method, it is possible to detect a flaw that cannot be observed only from the specular reflection component, and it is possible to detect a pattern-like bald flaw that does not have remarkable unevenness which could not be detected in the past without missing. It became possible.

Further, since both components are captured by the measurement on the same optical axis from the regular reflection direction of the steel plate, the measurement which is not affected by the steel plate distance variation and the velocity change is realized. Further, by adjusting the analysis angle of the analyzer, it becomes possible to select which angle the specular diffuse reflection component is extracted.

Then, in the signal processing device, when there are adjacent flaws having the same flaw type, the flaws are connected and the feature amount is calculated as one flaw to re-evaluate the grade of the surface flaw. By doing so, the result is close to the result determined by the inspector as one defect by visual inspection, and the defect inspection accuracy can be improved.

Further, from the viewpoint of quality assurance, it is an absolute condition that the surface flaw inspection apparatus does not detect any defects. Therefore,
The present invention enables the realization of an undetected surface flaw inspection device that can be widely applied to surface-treated steel sheets and the like for the first time, so that it has become possible to automate the surface flaw inspection that has hitherto relied on visual inspection by an inspector. In this respect, the industrial use effect is great.

[Brief description of 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 defect connection determination process in the defect comprehensive determination unit of the signal processing unit of the surface defect inspection apparatus,

FIG. 4 is a view showing a region (occurrence position) of a defect (defect) before being connected, which is detected by the surface defect inspection apparatus.

FIG. 5 is a diagram showing a region (occurrence position) of a defect (defect) after connection, which is detected by the surface defect 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 diagram showing a manufacturing method and a detailed cross-sectional structure of an alloyed zinc-plated steel sheet to be inspected by the surface flaw inspection apparatus.

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

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

FIG. 11 is a diagram for explaining a generation process of a heald portion existing on a steel plate.

FIG. 12 is a diagram showing a relationship between a specular reflection component and a specular diffuse reflection component in the heald portion and a specular reflection component and a specular diffuse reflection component in the base material portion.

FIG. 13 is a diagram showing a relationship between a normal angle of a micro surface element and an area ratio in an irradiated portion 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 line angle of a minute surface element.

FIG. 15 is a diagram showing a relationship between a normal angle of a minute surface element and a weighting function.

FIG. 16 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. 17 is a diagram showing a polarization state of reflected light when each incident light of the linear diffused light source is polarized.

FIG. 18 is a diagram showing reflected light from a minute surface element when each incident light from the central portion of the linear diffused light source is polarized.

FIG. 19 is a diagram showing reflected light from a minute surface element in the case where each incident light from a position other than the central portion of the linear diffused light source is polarized.

FIG. 20 is a diagram showing a relationship between a normal angle of a micro surface element and an elliptically polarized state of reflected light.

FIG. 21 is a diagram showing a relationship between a normal angle of a micro-plane element and a weighting function when an analyzer is inserted in an optical path of reflected light.

FIG. 22 is a diagram showing the relationship between the normal angle of the micro-plane element and the weighting function when the analysis angle of the analyzer is changed.

FIG. 23 is a diagram showing a relationship between a normal angle of a minute surface element and an area ratio.

[Explanation of symbols]

4, 21 ... Steel plate 6 ... Temper 7 ... Non-tempered part 8, 23 ... Incident light 9 ... Specular reflection light 10 ... Specular diffuse reflection light 11 ... Head 12 ... Base metal part 14, 22 ... Linear diffused light source 15, 25 ... Polarizing plate 16, 29a, 29b, 29c ... Light receiving camera 17, 28a, 28b, 28c ... Analyzer 24 ... Cylindrical lens 26 ... Reflected light 27 ... Light receiving part 33a, 33b, 33c ... Feature amount calculation unit 34 ... Specular flaw determination unit 35 ... Specular diffusive flaw determination unit 36 ... Defect comprehensive judgment section 40 ... Signal processing unit

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Shoji Yoshikawa, 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Within Nippon Kokan Co., Ltd. (72) Takahiko Oshige, 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Japan Steel Pipe Co., Ltd. (72) Inventor Hiroyuki Sugiura 1-2-2 Marunouchi, Chiyoda-ku, Tokyo Japan Steel Pipe Co., Ltd. (56) Reference JP-A-9-217012 (JP, A) JP-A-2000-65755 ( (58) Fields investigated (Int.Cl. ⁷ , DB name) G01N 21/84-21/958

Claims (2)

(57) [Claims] 1. A linear diffused light source for injecting polarized light having an azimuth angle component parallel to the inspection surface and a vertical azimuth angle component to the inspection surface, and specular reflection light from the inspection surface. Of the specular reflection component and the specular diffuse reflection component included in the first spectroscopic reflection component, and a first light receiving unit having an analyzer with an azimuth angle for extracting more specular reflection component than the specular reflection component; A second light-receiving means having an azimuth analyzer for extracting a larger amount of the specular diffuse reflection component than the specular reflection component of the specular reflection component and the specular diffuse reflection component included in the specular reflection light; And a surface flaw inspection apparatus for evaluating the 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 means. Is the received specular reflection component and specular surface Presence or absence of surface flaws on the surface to be inspected based on the diffuse reflection component, flaw determining means for determining the type and generation position of surface flaws, and based on the type and occurrence position of each surface flaw determined by this flaw determining means And a surface flaw inspection device having a flaw connecting means for newly connecting one surface flaw of the same type to a new surface flaw. 2. The evaluation processing unit obtains a feature amount of a new surface flaw connected by the same type from the feature amount of each surface flaw, and determines the grade of each flaw based on the feature amount. The surface flaw inspection apparatus according to claim 1, further comprising a determination unit.