JPH11295238A - Method and equipment for inspecting surface flaw - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect a pattern-like scab defect having no conspicuous irregularities surely. SOLUTION: The surface flaw inspection equipment comprises a linear diffusion light source 22 for irradiating a plane 21 to be inspected with an illumination light polarized linearly in the direction parallel with or normal to the plane 21, a first light receiving means 28 receiving the polarized light component in same direction as the polarizing direction of the illumination light contained in regular reflected light from the plane 21, a second light receiving means 29 receiving the polarized light component orthogonal to the polarizing direction of the illumination light contained in regular reflected light from the plane 21, and a section 31 for making a decision whether a flaw is present or not on the plane 21 based on both polarized light components received by first and second light receiving means. The mirror face reflection component contained in the reflected light from the plane 21 is discriminated from the mirror face diffusion reflection component and a defect unobservable from mirror face reflection component can be detected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

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

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

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

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

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

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

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

[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 with respect to pattern-shaped scab defects and the like having no noticeable unevenness.

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

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

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

Further, the measuring device disclosed in Japanese Patent Application Laid-Open No. 57-166533 and the surface inspection device disclosed in Japanese Patent Application Laid-Open No. Hei 9-166552 use 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 a surface inspection apparatus to be incorporated in a product quality inspection line, it is an absolute condition that no defect is detected from the viewpoint of quality assurance of a manufactured product. However, a surface flaw inspection apparatus for inspecting even a surface-treated steel sheet or the like has not been put to practical use.

The present invention has been made in view of such circumstances, and distinguishes between a specular reflection component and a specular diffuse reflection component contained in light reflected from a surface to be inspected to thereby detect the surface to be inspected. It can reliably detect pattern-like barbed defects that do not have noticeable unevenness such as surface cracks, gouges, and curling up, exhibit high defect detection accuracy, and be fully incorporated into product quality inspection lines. It is an object of the present invention to provide a surface flaw inspection device and a surface flaw inspection method that can perform the inspection.

[0016]

According to a first aspect of the present invention, there is provided a surface flaw inspection apparatus which is linearly polarized with respect to a surface to be inspected in a direction parallel or perpendicular to a plane of incidence with respect to the surface to be inspected. A linear diffused light source that receives illumination light, a first light receiving unit that receives a polarization component in the same direction as the polarization direction of the illumination light included in the specular reflection light from the inspection surface, and a regular reflection from the inspection surface A second light receiving means for receiving a polarized light component in a direction orthogonal to the polarization direction of the illumination light included in the light, and a light receiving means based on the polarized light components in the same direction and the orthogonal direction received by the first and second light receiving means. A judgment processing unit for judging the presence or absence of surface flaws on the inspection surface.

According to the second aspect of the present invention, in addition to the surface flaw inspection apparatus of the present invention, a light branching means for branching regular reflection light from the surface to be inspected into first and second light receiving means is further provided. Have.

According to a third aspect of the present invention, the first and second light receiving means in the surface flaw inspection apparatus of the present invention are arranged in a direction parallel to the linear diffusion light source. Further, in the surface defect inspection method according to the fourth aspect, the linearly diffused light source irradiates linearly polarized illumination light to the surface to be inspected in a direction parallel or perpendicular to an incident surface with respect to the surface to be inspected, and Receiving a polarization component in the same direction as the polarization direction of the illumination light included in the specular reflection light from the surface, and receiving a polarization component in the direction orthogonal to the polarization direction of the illumination light included in the specular reflection light from the surface to be inspected; The presence or absence of a surface flaw on the surface to be inspected is determined based on the received polarization components in the same direction and the orthogonal direction.

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

For example, when the inspection target is an alloyed galvanized steel sheet, as shown in FIG. 7A, 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. 7 (c). The plated steel sheet 4 is then temper rolled on rolls 5a and 5b. Then, as shown in FIG. 7D, particularly protruding portions of the columnar crystal 3 are flattened by the rolls 5a and 5b, and the other portions maintain the original shape of the columnar crystal 3.

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

FIG. 8 is a schematic cross-sectional view modeling what kind of optical reflection occurs on the surface of the steel plate 4 having such a tempered portion 6 and the non-tempered portion 7. This steel plate 4
The surface (the surface to be inspected) is composed of countless minute surface elements 13 oriented in various directions when viewed microscopically.

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

Therefore, the angular distributions of the reflected light of the tempered portion 6 and the non-tempered portion 7 on the surface of the steel plate 4 are macroscopically shown in FIGS. 9A and 9B, respectively. 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 minute surface element 13 on the surface of the columnar crystal 3 in the non-tempered portion 7. As described above, the reflected light from the tempered portion 6 is referred to as specular reflected light 9, and the reflected light from the non-tempered portion 7 is referred to as specular diffused reflected light 10.

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

As described above, the tempered portion 6 and the non-tempered portion 7 have been described as an example of a galvanized steel sheet. However, the invention can be generally applied to other steel sheets 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. 10, the barge defects (barge portions 11) found in the galvannealed steel sheet are the same as those in 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. When the alloy of the barbed portion 11 is shallow, the angular distribution of the microscopic surface element 13 is strong in the normal direction of the steel sheet, and the diffusivity is small.

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

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

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

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

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

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

Severe part angle distribution 11a and base material part angle distribution 1
FIG. 1 shows the case where there is no difference in the area ratio of
As shown in FIG. 1C, it is not possible to observe the presence of the scab 11 only by observing the difference in the received light intensity from the regular reflection direction. However, the diffusivity (angular distribution) of the specular diffuse reflection component
When there is a difference, the defect is observed from a diffusion direction other than the regular reflection direction as shown in FIG.

For example, when the diffusivity (angular distribution) of the specular diffuse reflection component of the barb portion 11 is small, the 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 detect each barbed portion 11 as shown in FIGS. 11 (a), 11 (b) and 11 (c) from the base material portion 12 and to surely detect the same, the reflected light temper portion 6 is used. If only the light intensity of the specular reflection component is detected, the scab 11 shown in FIG. 11C cannot be detected separately from the base material 12.

In order to detect such a pattern-shaped scab defect without any detection, it is necessary to independently obtain a light amount corresponding to specular reflection and a light amount corresponding to specular diffuse reflection.
Here, in order to make the fields of view of the two optical systems for detecting each light quantity the same, it is necessary to measure the light quantity on the same optical axis. Therefore, it is desirable that both components can be captured by measurement from the specular reflection direction instead of capturing the diffuse reflection light from a direction other than the specular reflection direction.

In the present invention, a linear light source having a diffusion characteristic, that is, a linear diffusion light source, is used as a light source instead of a parallel light source such as a laser. Since it is necessary to separate and extract the specular reflection component and the specular diffuse reflection component from the specular reflection direction of the steel plate 4, polarized light is used.

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

As shown in FIG. 12A, in the case of the incident light 8 emitted from the center of the linear diffused light source 14, the incident light 8 incident on the tempering portion 6 is reflected specularly, and All are captured in the reflection direction. On the other hand, the light incident on the non-tempered portion 7 is specularly reflected, and only the light reflected by the minute surface element 13 that happens to be oriented in the same direction as the normal direction of the steel sheet is captured. Since the number of micro-plane elements 13 oriented in such a direction is extremely small, the mirror-reflected light from the tempering unit 6 is dominant among the reflected light captured by the light-receiving camera arranged in the regular reflection direction of the steel sheet. is there.

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

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

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

A linear diffusion light source 14 is applied to an alloyed galvanized steel sheet.
13 (a) and 13 (b) will be described with reference to FIGS. As shown in FIG. 13A, the linear diffused light source 1
The light emitted from the central part of the steel sheet 4 is specularly reflected by the tempering part 6 of the steel sheet 4 and is observed in the steel sheet regular reflection direction. In this regard, reflection on the above-mentioned general mirror-like metal surface is established as it is.

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

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

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

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

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

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

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

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

The operating principle described above is based on the linear diffused light source 1
In the case where the incident light 8 from 4 to the steel plate 4 is perpendicular to the incident surface (s-polarized light), the other light-receiving camera that receives the s-polarized component captures the specular reflection component and receives the p-polarized component. Since one of the light receiving cameras captures the specular diffuse reflection component, the same holds true.

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

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

[0057]

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

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

The incident light 23 irradiating the steel plate 21 from each position of the linear diffused light source 22 as the irradiation light through the cylindrical lens 24 and the polarizing plate 25 is, for example, 60 ° with respect to the entire width of the running steel plate 21. At an incident angle θ. The azimuth angle (polarization angle) α of the polarizing plate 25 is
3 is set in a direction parallel to the incident surface with respect to the steel plate 21. That is, the linear diffused light source 22 outputs
The incident light 23 irradiated to 1 is in a p-polarized state.

A part of the specularly reflected light 26 reflected by the steel plate 21 is a light arranged in a specular reflection direction of the steel plate, ie, a light receiving angle γ = 60 ° direction equal to the incident angle θ with respect to the normal direction of the steel plate 21. The light passes through a beam splitter 27 as a branching means and enters a first light receiving camera 28 constituted by, for example, a linear array camera. A part of the specularly reflected light 26 is reflected by the beam splitter 27 and is incident on a second light receiving camera 29 also formed of a linear array camera.

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

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

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

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.

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

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

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

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

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

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

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

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

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

[0074]

FIG. 3 shows 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. In each of the measured flaws, the area ratio of the tempered portion 6 shown in FIG. 11A is larger at the barb portion 11 than at the base material portion 12, and the diffusivity of the non-tempered portion 7 is at the barge portion 11 at the base material portion 12. FIG. 11C shows a larger flaw and a flaw in which the area ratio of the tempered portion 6 shown in FIG. 11B is larger than that of the base material portion 12 in the barb portion 11, but the diffusivity of the non-tempered portion 7 does not change. Although the area ratio of the tempering portion 6 shown in FIG.
These are a total of three types of flaws, including flaws having a difference in diffusivity.

FIG. 1 shows a central portion of the steel plate 21 in the width direction.
When a flaw of the type shown in FIG.
It is obtained by scanning one line of light in the width direction of the steel plate 21 with the first light receiving camera 28 for receiving the polarized light component (specular reflection component) and the second light receiving camera 29 for receiving the s-polarized light component (specular diffuse reflection component). 3 (a) and 3 (b) show changes in the light intensity signals a and b for one width of the steel material 21.

As shown in the figure, a peak waveform in the positive direction (bright direction) corresponding to the flaw (severed portion 11) is generated in the light intensity signal a of the first light receiving camera 28. In addition, a peak waveform corresponding to the flaw (the scab 11) is generated in the light intensity signal b of the second light receiving camera 29.

FIG. 11 shows a central portion of the steel plate 21 in the width direction.
(B) The first light-receiving camera 28 that receives a p-polarized component (specular reflection component) when a flaw of the type shown occurs.
And the change of the light intensity signals a and b for one width of the steel material 21 obtained by scanning the second light receiving camera 29 for receiving one line in the width direction of the steel plate 21 for receiving the s-polarized component (specular diffuse reflection component). Are shown in FIGS. 3 (c) and 3 (d).

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

Further, FIG. 1 is attached to the center of the steel plate 21 in the width direction.
First light receiving camera 2 for receiving a p-polarized component (specular reflection component) when a flaw of the type shown in FIG.
Second to receive 8 and s polarized light components (specular diffuse reflection components)
3 (e) and 3 (f) show changes in the light intensity signals a and b for one width of the steel material 21 obtained by scanning the light receiving camera 29 for one line in the width direction of the steel plate 21.

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

As described above, even if any of the typical three types of pattern-shaped barge defects shown in FIGS. 11 (a), (b) and (c) occurs, It is possible to reliably detect a scab defect. Furthermore, FIG.
As shown in (f), the types of the three types of pattern-like barbed defects can also be determined.

The inventors measured the flaws shown in FIGS. 11A, 11B and 11C with a conventional surface flaw inspection apparatus in order to show the excellent detection function of the embodiment apparatus. In this conventional device, the first light receiving portion arranged in the regular reflection direction of the unpolarized incident light incident on the steel plate 21 at an incident angle of 60 ° from the linear light source disposed in the width direction of the steel plate 21 is used. The camera receives the specularly reflected light. On the other hand, the second light-receiving camera disposed at a direction different from the specular reflection direction of the incident light, for example, at 40 ° with respect to the normal direction of the steel plate 21, receives the specular diffuse reflection light.

FIGS. 4A, 4B, 4C, and 4D show the measurement results.
(E) and (f). As shown in FIG.
It is possible to detect a pattern-like scab defect of the type shown in FIG. However, it is not possible to detect a pattern-like barbed defect of the type shown in FIG. FIG.
(A) It is not possible to distinguish the types of pattern-shaped barbed defects of the types shown in (b).

As described above, the surface flaw inspection apparatus according to the embodiment can reliably detect a pattern-shaped scab defect of a type that could not be detected by the conventional apparatus. It has become possible to reliably detect spot flaws without leakage.

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

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

Even with such a configuration, the first and second light receiving cameras 28a and 29a independently receive the p-polarized component and the s-polarized component of the specularly reflected light 26, and change the respective light intensities. Output the respective light intensity signals a and b corresponding to
Almost the same functions and effects as those of the surface flaw inspection apparatus of the first embodiment shown in FIG. 1 can be obtained.

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

(Third Embodiment) FIG. 6 is a side view of a surface flaw inspection apparatus according to a third embodiment of the present invention. The first shown in FIG.
The same parts as those of the surface flaw inspection apparatus of the embodiment are denoted by the same reference numerals. Therefore, the detailed description of the overlapping part will be omitted.

In the surface flaw inspection apparatus of the third embodiment, a halogen lamp 41 and a diffusion plate 42, which are close to a point light source, are incorporated as linear diffusion light sources. In this case, the light emitted from the halogen lamp 41 is
1 is uniformly diffused in the width direction and is incident on the next polarizing plate 25. Therefore, the incident light 23 similar to the case of the linear diffusion light source 22 and the cylindrical lens 24 shown in FIG.
Is incident on the steel plate 21, so that substantially the same operation and effect as those of the surface flaw inspection apparatus of the first embodiment can be obtained.

[0091]

As described above, in the surface flaw inspection apparatus and the surface flaw inspection method of the present invention, a linearly diffused light source is used, and p-polarized light or s-polarized light is incident on a surface to be inspected.
From the specular reflection direction, by receiving the polarization component of the same direction as the polarization of the incident light among the specular reflection light, and receiving the polarization component of the incident light and the polarization component of the orthogonal direction among the specular reflection light, The specular reflection component and the specular diffuse reflection component contained in the reflected light are detected separately.

Therefore, it is possible to detect a defect in which no defect can be observed from the specular reflection component, and a pattern having no remarkable unevenness such as a crack, a gouge or a curl up on the surface to be inspected which could not be detected conventionally. It can reliably detect barbed defects, exhibit high defect detection accuracy, and can be fully incorporated into product quality inspection lines.

[Brief description of the drawings]

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

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

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

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

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

FIG. 6 is a side view showing a schematic configuration of a surface flaw inspection apparatus according to a third embodiment of the present invention.

FIG. 7 is a view showing a manufacturing method and a detailed cross-sectional structure of an alloy galvanized steel sheet to be inspected by the surface defect inspection apparatus.

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

FIG. 9 is an angle distribution diagram of reflected light between the tempered portion and the non-tempered portion.

FIG. 10 is a diagram for explaining a generation process of a barbed portion existing in a steel plate.

FIG. 11 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. 12 is a diagram showing a relationship between each incident light from each position of a linear diffused light source and an incident position on a steel plate.

FIG. 13 is a diagram showing a polarization state of reflected light when each incident light of the linear diffusion light source is polarized.

[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 member 13 ... microscopic element 22 ... linear diffusion Light source 25 ... Polarizer 27 ... Beam splitter 28, 28a ... First light receiving camera 29, 29a ... Second light receiving camera 30a, 30b ... Analyzer 31 ... Signal processing unit

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

Claims (4)

[Claims] 1. A linear diffused light source for entering illumination light linearly polarized in a direction parallel or perpendicular to an inspection surface with respect to an inspection surface, and a specular reflection light from the inspection surface. First light receiving means for receiving a polarization component in the same direction as the polarization direction of the illumination light included, and receiving a polarization component in a direction orthogonal to the polarization direction of the illumination light included in the specularly reflected light from the surface to be inspected A second light receiving unit, and a determination processing unit that determines presence / absence of a surface flaw on the surface to be inspected based on polarization components in the same direction and orthogonal directions received by the first and second light receiving units. Surface flaw inspection equipment provided. 2. The method according to claim 1, wherein the light reflected from the surface to be inspected is transmitted to the first surface.
2. The surface flaw inspection apparatus according to claim 1, further comprising a light branching unit that branches to the second light receiving unit. 3. The surface flaw inspection apparatus according to claim 1, wherein the first and second light receiving means are arranged in a direction parallel to the linear diffusion light source. 4. An illumination light linearly polarized in a direction parallel or perpendicular to a surface to be inspected from the linear diffused light source in a direction parallel or perpendicular to the surface to be inspected. Receiving a polarization component in the same direction as the polarization direction of the included illumination light; receiving a polarization component in a direction perpendicular to the polarization direction of the illumination light included in the specularly reflected light from the surface to be inspected; A method for inspecting a surface flaw, wherein the presence or absence of a surface flaw on the surface to be inspected is determined based on each polarization component in the same direction and the orthogonal direction.