JPH06281593A - Method and apparatus for inspecting surface - Google Patents

Abstract

PURPOSE:To make it possible to detect the defect of a surface high accuracy by efficeintly designing the arranging direction of the detecting part of a surface inspecting apparatus. CONSTITUTION:Light is emitted downward from a rod-shaped light source 10 on a cold rolled steel plate S in the vertical direction. The optical axis of each light receiving edge of an optical fiber bundle 11 is set at an angle thetawith respect to the light emitting direction. A line cameral 12 is made to scan in the width direction of the steel plate S, and the light is received with the line camera 12 through the optical fiber bundle 11. The received signal is processed with an image processing device 18. Thus, the defect of the surface of the steel plate S is detected. At this time, the distribution of the slant angle of the surface caused by the surface defect is obtained beforehand based on the minute-shape data of the steel plate S, and the light receiving angle THETAof the optical fiber bundle 11 determined based on the specificity of the distribution of the slant angle.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface inspection method and an apparatus therefor, and more particularly, a surface inspection method and an apparatus capable of detecting uneven surface defects such as surface flaws with high sensitivity by, for example, optical detection means. Regarding the device.

[0002]

2. Description of the Related Art For example, it is extremely important to detect abnormal portions of surface defects such as surface defects that occur on the surface of a steel sheet, in order to maintain product quality and to properly manage the process. Therefore, various detection methods and techniques related to detection devices have been developed and put into practical use.

In developing this surface defect detection technique, it is possible to distinguish the signal generated by the surface defect to be detected from the normal portion from the surface signals detected by the surface detecting means, that is, S / It is extremely important to detect how high the N ratio is. Therefore, for the surface defect inspection apparatus, the quality of the design of the arrangement direction of the detection unit (detection direction of the reflected wave) determines the inspection performance.

In particular, in in-process defect detection in a manufacturing line, in addition to requiring high sensitivity detection,
Since high speed is also required, it is possible to use an optical method, for example, a method of detecting a defect from a change in reflection intensity of laser light, a method of processing a captured image by a camera to detect a defect, or the like. Many. In the method and apparatus for detecting these defects, for example, the irradiation angle of illumination with respect to the target surface,
Designing the light receiving angle of the reflected light from the target surface, the shooting angle of the camera, etc. to be optimum for the surface defect to be detected is positioned as the most basic development factor.

[0005]

However, in designing the direction in which the detector (including the camera) of the surface defect inspection apparatus is arranged with respect to the surface to be inspected, the basic data required for that purpose is required. However, conventionally, the basic data must be determined experimentally by collecting a large number of surface defect samples such as surface flaws, or relying on the empirical rule of deciding based on visual observation. There wasn't. Therefore, a huge amount of sample experiments and their data analysis work are required, or the visual observation know-how of a trained inspector is required, which not only makes the device design inefficient, but also detects it by the conventional method described above. The device in which the arrangement direction of the parts is designed has a problem that sufficient surface inspection capability cannot be obtained.

The present invention has been made in order to solve the above-mentioned conventional problems, and can efficiently design the arrangement direction of the detecting portion of the inspection apparatus, and by using the inspection apparatus obtained as a result, high sensitivity can be obtained. An object of the present invention is to provide a surface inspection method and an apparatus therefor capable of detecting surface defects.

[0007]

SUMMARY OF THE INVENTION The present invention is a surface inspection method for detecting a reflected wave from a surface to be inspected and extracting a surface defect to be detected from the reflected wave, from fine shape data of the surface to be inspected. , The surface inclination angle distribution due to surface defects is obtained in advance, and based on the peculiarity of the inclination angle distribution, by determining the detection direction of the reflected wave from the surface to be inspected, the above problems have been solved. is there.

According to the present invention, in the surface inspection method, the inclination angle distribution of the surface is obtained by dividing the surface to be inspected into minute surface elements and calculating from a unit normal vector in each minute surface element. .

According to the present invention, in a surface inspection apparatus for detecting a reflected wave from a surface to be inspected and extracting a surface defect as an object to be detected from the reflected wave, the same angle with respect to the surface to be inspected over the entire width direction Irradiation means for irradiating inspection waves with
The above problem is similarly solved by providing a receiving unit that receives a reflected wave from the surface to be inspected at the same angle over the entire width direction.

In the surface inspection apparatus of the present invention, the inspection wave is light, and the receiving means has light-receiving end faces arranged in the width direction of the surface to be inspected, and all of the light-receiving end faces can be oriented in the same direction. The optical fiber bundle and a light receiving section for receiving the reflected light transmitted by the optical fiber bundle are provided.

According to the present invention, in the above-mentioned surface inspection apparatus, the irradiation means includes a laser oscillating device, a scanning means for scanning the laser beam in the width direction of the surface to be inspected, and a laser beam scanned in the width direction. And a collimator lens for irradiating the surface to be inspected at the same angle over the entire width direction.

[0012]

The inventors of the present invention analyzed the shape of the surface defects in order to detect surface defects such as surface defects with high sensitivity and examined the reason why the surface defects were identified as normal parts. There is a big difference in the distribution of the inclination angle of the surface from the normal part, and it is possible to measure the inclination angle of the surface and extract the peculiarity of that distribution, and evaluate the peculiarity of the inclination angle distribution. It was found that it is extremely effective in detecting defects with high sensitivity.

Here, the peculiarity of the inclination angle distribution of the surface represents the peculiarity when the inclination angle distribution of the surface is evaluated by a statistical numerical value. For example, the average value of the distribution state, the standard It indicates that the value defined by the deviation, the moment, the kurtosis, the skewness, etc. shows a value different from that of the normal portion in the defective portion.

The present invention has been made based on the above findings. For example, a defect inspection utilizing a reflection echo of ultrasonic waves,
Techniques such as detecting defects from the light reflection intensity and detecting defects by imaging the target surface and analyzing the obtained image, etc., receive signals (information) from the surface to be inspected or image the surface. In this case, by arranging the signal detection unit or the camera light receiving unit in the direction in which the peculiarity of the inclination angle distribution due to the surface defect is observed, the surface defect can be detected with high sensitivity.

Further, most of the surface defects are visually detected,
Since an optical method is generally used for the surface inspection because it can be recognized, it is also preferable in the present invention to detect the surface defect based on the peculiarity of the distribution of the inclination angle of the surface by the optical method. Is. The reason why it is particularly preferable to use the optical method will be described in detail below.

It is clear that the distribution of the reflected light from the surface to be inspected is greatly influenced by the fine shape of the surface, but the distribution and the direction of the reflected light depend on the light diffraction phenomenon and the geometrical specular reflection. Can be explained. That is, since the inclination of the reflecting surface governs the reflection direction, the distribution of the reflected light and the luminance distribution in the image captured by the camera can be obtained by analyzing the inclination angle of the surface irradiated with light. You can

On the other hand, the surface to be inspected can be regarded microscopically as an aggregate of minute inclined surfaces (minute surface elements). Therefore, in the defective portion, the inclination angle in this minute surface element is different from that in the normal portion. Visual detection is possible. Therefore, the peculiarity of the tilt angle distribution of the defect is obtained by analyzing the tilt angles of the minute surface elements that form the surface to be inspected, and the direction in which this peculiarity appears most is determined as the detection direction of the reflected wave. By disposing, for example, a photodetector for detecting reflected light or a light-receiving surface of a photo-taking device in that direction, an optimum surface inspection with a high S / N ratio can be performed.

Further, in the present invention, when the surface inclination angle distribution is obtained by dividing the surface to be inspected into minute surface elements and calculating from the unit normal vector in each minute surface element, the distribution of the inclination angle of the minute surface elements. Can be represented accurately and intelligibly, so that the arrangement direction of the photodetector and the like can be easily determined.

In the present invention, the surface inspection apparatus includes an irradiation means for irradiating the surface to be inspected with an inspection wave at the same angle over the entire width direction, and a reflected wave from the surface to be inspected.
Receiving means for receiving at the same angle over the entire width direction,
With this configuration, it is possible to reliably detect reflected waves in the same direction in the entire width direction, so that surface defects that have peculiarity in the inclination angle distribution of the surface can be reliably extracted over the entire surface to be inspected. Is possible.

Further, in the surface inspection apparatus, the inspection wave is light, and the receiving means has the light receiving end faces arranged in the width direction of the surface to be inspected, and all of the light receiving end faces can be oriented in the same direction. And a light receiving portion for receiving the reflected light transmitted by the optical fiber bundle, the reflected light in the same direction reflected from the surface to be inspected can be reliably detected over the entire width direction. It becomes possible.

Further, in the above-mentioned surface inspection apparatus, the irradiation means has a laser oscillating device, a scanning means for scanning the laser beam in the width direction of the surface to be inspected, and a laser beam scanned in the width direction onto the surface to be inspected. In the case of having a collimator lens that emits light at the same angle over the entire width direction,
It is possible to irradiate the laser beam scanned in the width direction of the surface to be inspected in the same direction, for example, in the direction perpendicular to the surface to be inspected, and as a result, it is possible to perform highly accurate surface inspection.

[0022]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 1 is an explanatory view showing a schematic structure of a surface inspection apparatus of a first embodiment according to the present invention. This surface inspection device is for inspecting the surface of a cold-rolled steel sheet S conveyed in the direction of the arrow on the manufacturing line. The rod-shaped light source 10 arranged above the steel sheet S and an optical fiber for transmitting a captured image Bunch 1
1 and a line camera 12 for photographing the surface of the steel plate S,
Speedometer 14 for detecting the transport speed (line speed) of the steel plate S
A camera controller 16 that controls the line camera 12 based on the measurement result of the speedometer 14, an image processing device 18 that processes image information input via the camera controller 16, and an image processing device 18. And an output device 20 for outputting the processed result.

In the above surface inspection apparatus, the rod-shaped light source 10 can uniformly irradiate the surface of the cold-rolled steel sheet S in the width direction, and the optical fiber bundle 11 has the light receiving end face in the width direction of the steel sheet S. Since the optical axes of all the light receiving end faces are arranged in the same direction,
With the optical fiber bundle 11, a photographic image can be transmitted to each photographic element of the line camera 12 while maintaining a constant photographic angle.

Further, the surface of the steel sheet S can be continuously photographed by the line camera 12 without scanning in the width direction, and the scanning speed of the line camera 12 is set along the manufacturing line. The camera controller 16 controls the measured value of the transport speed of the steel sheet S measured by the speedometer 14.

Further, in the image processing device 18, the inspection of the surface defect of the cold-rolled steel sheet S taken by the line camera 12 to extract the surface defect and determine the kind and grade of the defect. The inspection result is transmitted to the host computer (not shown) by the output device 20, and the quality control of the product is automatically performed.

In the present embodiment, the arrangement angle of the light receiving end face of each optical fiber forming the optical fiber bundle 11, that is, the angle (center in the figure) for setting the center (optical axis) of each light receiving end face with respect to the surface of the steel plate S (one point in the figure). Θ) indicated by a chain line is obtained by analyzing the inclination angle distribution of the surface of a sample having a surface defect (defect sample) in advance by the method described in detail below,
Based on the result, the reflection direction of the light when the irradiation light from the rod-shaped light source 10 is irradiated vertically downward is set, and the direction is set so that the clearest defect image is obtained as an image.

FIG. 2 is a schematic block diagram showing an example of an apparatus for measuring the fine shape data of the surface to be inspected and obtaining the inclination angle of the fine shape (minute surface element) from the measurement result. It can be used to determine the arrangement angle of the optical axis of each light-receiving end face of the optical fiber bundle 11.

The above-mentioned measuring device is provided with a stylus-type three-dimensional roughness meter 22 for analyzing a surface defect portion, and the three-dimensional roughness meter 22 is used for finely measuring the surface of the cold-rolled steel sheet sample S '. A computer 24 is provided for collecting the shape data and obtaining the distribution of the inclination angles of the micro surface elements from the fine shape data, and a data recording device 26 for recording the collected data.

In this apparatus, the computer 24 calculates the uneven shape of the surface of the sample S'measured by the three-dimensional roughness meter 22.
The inclination angle distribution can be calculated by temporarily recording the data in the data recording device 26 via the, and then reading it again in the computer 24 and analyzing the waveform of the uneven shape.

FIG. 3 shows an example of the unevenness shape data measured on the cold-rolled steel sheet sample S'having a defect by using the measuring apparatus shown in FIG.
This corresponds to the data obtained by measuring the surface 3 mm wide. Further, FIG. 4 shows a tilt angle distribution obtained by waveform analysis from the concave-convex shape data shown in FIG. 3 for a normal portion, and FIG. 5 shows a tilt angle distribution obtained in the same manner. To
It is shown about the abnormal part (the part where the line spacing is rough in FIG. 3).

The inclination angle distributions shown in FIGS. 4 and 5 are as follows.
The surface of the cold-rolled steel sheet sample S ′ to be measured was 0.1 mm × 0.
It is divided into 1 mm micro-plane elements, the unit normal vector representing the inclination angle direction in each micro-plane element is obtained, and the distribution state thereof is shown. That is, as shown in FIG. 6, the starting point of the unit normal vector in one micro surface element is placed at the origin,
The inclination angle distribution is represented by executing the operation of representing the position of the end point of the orthographic projection when the vector is projected on the plane with a point for each minute surface element. 4 and 5, the horizontal axis and the vertical axis respectively show the x coordinate value and the y coordinate value of the end point of the orthogonal projection of the unit normal vector.

As is clear from FIGS. 4 and 5, the inclination angle of the normal portion shows a distribution form having uniform randomness, whereas that of the defect portion has directionality in the distribution. . Therefore, the light receiving end surfaces of the optical fiber bundle 11 are aligned with the detection direction of the reflected light, that is, the optical axis thereof is aligned with the direction in which the inclination angle of the defect portion is concentrated (the lower left direction in the example of FIG. 5). By installing it, it becomes possible to obtain a defect signal with the highest S / N ratio.

As described above in detail, according to this embodiment, the distribution of the inclination angle of the surface caused by the surface defect is obtained in advance from the fine shape data of the surface to be inspected, and based on the peculiarity of the inclination angle distribution. Since the direction in which the optical axis of each light-receiving end face of the optical fiber bundle 11 is arranged with respect to the surface to be inspected is determined, it becomes possible to detect the surface defects with a high S / N ratio, and the surface defects can be increased. It is possible to detect with sensitivity.

Here, "based on the peculiarity of the inclination angle distribution" means that the result obtained by statistically processing the sectional curve of the inclination angle distribution is used as a reference. In the example of FIG.
Originally, for the steel plate surface where the inclination angle distribution should be isotropic, the standard deviation or second moment of the cross-section curve in the lower left direction clearly shows a larger value than in other directions. It's obvious. Therefore, since the unit normal vector of the minute surface element, that is, the surface inclination is concentrated in the direction in which the statistical parameter shows a peculiar value, the direction in which the surface defect caused by the reflection of the irradiation light can be most noticeably obtained is obtained. Be done.

FIG. 7 shows a second embodiment according to the present invention.
It is explanatory drawing seen from the side surface which shows schematic structure of the surface inspection apparatus provided with the function which detects a defect from the reflection distribution of a laser beam.

The surface inspection apparatus is provided with a laser oscillator 30.
A rotating mirror 32 for irradiating the surface of the cold-rolled steel sheet S conveyed in the direction of the arrow with a beam from the laser oscillator 30 in a width direction, and the surface of the cold-rolled steel sheet S with the laser beam. A collimator lens 33 for irradiating the cold rolled steel sheet S at a constant angle, a first reflected light detection unit 34 and a second reflected light detection unit 36 that receive reflected light from the surface of the cold-rolled steel sheet S, and A processing device 38 for processing the signals received by the first and second reflected light detectors 34 and 36, and an output device 40 for outputting the result processed by the processing device 38 to a host computer, as in the first embodiment. Is equipped with.

The first and second reflected light detectors 34 and 36 receive the reflected light from the surface of the steel plate S at a constant angle over the entire width direction, and transmit it.
4A and 36A, and first and second condenser lenses 34B and 36B for condensing the reflected light on the sensor portion thereof.
It has each. These optical fiber bundles 34A and 36A are substantially the same as the optical fiber bundle 11 of the first embodiment, and are arranged in the direction in which the optical axes of the respective light receiving end faces coincide with the optical paths of the reflected light shown by the arrows. It is arranged.

In the figure, the laser beam is shown as being scanned by the rotating mirror 32 in the moving direction of the steel plate S for the sake of convenience, but in reality, the laser beam is scanned in the direction orthogonal to the moving direction of the steel plate S. It has become so.

In this embodiment, the laser beam is incident on the surface of the steel plate S at the incident angle θ, and
The reflected light detecting section 34 receives the reflected angle of the laser beam θ, that is, the regular reflected light is received, and the second reflected light detecting section 36 receives the reflected light of the angle φ. It is configured.

The second reflected light detector 36 detects the reflected light caused by the surface defect, and the light receiving direction, that is, the light receiving angle φ, is the same as in the case of the first embodiment. It is determined based on the inclination angle distribution obtained from the above. Specifically, the optical fiber is arranged so that the reflection direction of the laser light determined by the inclination angle of the defect portion on the surface of the steel plate S and the optical axis of each light-receiving end face coincide with each other. The bundle 36A is arranged.

According to this embodiment, the surface defects can be detected as in the first embodiment, and at the same time, the first reflected light detecting section 3
4 allows the reflected light from the normal portion and the second reflected light detecting portion 36 to receive the reflected light from the defective portion independently. Therefore, the normal portion and the defective portion on the surface of the cold-rolled steel sheet S can be received. Since it is possible to detect the change in the distribution of reflected light with respect to and very remarkably, it is possible to more reliably detect the defect.

Although the present invention has been specifically described above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the invention.

For example, in the above-mentioned embodiment, the case where the invention is applied to the detection of the surface defect of the cold-rolled steel sheet has been described. However, the application object of the present invention is not limited to this, and a general sheet material such as a hot-rolled steel sheet or aluminum is used. It goes without saying that the same can be applied to the detection of surface defects and the like.

Further, the detection unit included in the surface inspection apparatus is not limited to the optical means, and may be, for example, an ultrasonic wave oscillation / reception means or the like as the detection means.
Even in this case, by analyzing the fine shape data,
The optimum placement direction of the defect detection unit can be determined in the same manner.

The method for measuring the distribution of the tilt angle is not limited to the method using the apparatus shown in FIG.

[0047]

As described above, according to the present invention,
Since the detection direction of the reflected wave is determined based on the inclination angle distribution obtained by analyzing the inclination angle of surface defects such as surface flaws from the fine shape data of the surface to be inspected, surface defects can be detected with high sensitivity. Becomes Further, by using this principle of determining the detection direction, it becomes possible to rationally and quickly design and develop a surface inspection device for detecting a surface defect, which leads to reduction of development cost. It becomes possible.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a schematic configuration of a surface inspection apparatus according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a schematic configuration of a surface fine shape data measuring / analyzing device.

FIG. 3 is a diagram showing an example of unevenness shape data including defects obtained by measuring the surface of a steel sheet.

FIG. 4 is an explanatory diagram showing a tilt angle distribution in a normal portion obtained from uneven shape data.

FIG. 5 is an explanatory diagram showing a tilt angle distribution in a defect portion obtained from uneven shape data.

FIG. 6 is an explanatory diagram for explaining a display method of a tilt angle distribution.

FIG. 7 is an explanatory diagram showing a schematic configuration of a surface inspection apparatus according to a second embodiment of the present invention.

[Explanation of symbols]

 10 ... Rod-shaped light source 11 ... Optical fiber bundle 12 ... Line camera 14 ... Velocity meter 16 ... Camera controller 18 ... Image processing device 20, 40 ... Output device 22 ... Three-dimensional roughness meter 24 ... Calculator 26 ... Recording device 30 ... Laser oscillator 32 ... Rotating mirror 33 ... Collimator lens 34 ... 1st reflected light detection part 34A, 36A ... Optical fiber bundle 34B ... 1st condensing lens 36 ... 2nd reflected light detection part 36B ... 2nd condensing lens 38 ... Processing device S ... Cold rolled steel sheet S '... Cold rolled steel sheet sample

Claims (5)

[Claims] 1. A surface inspection method for detecting a reflected wave from a surface to be inspected and extracting a surface defect to be detected from the reflected wave, comprising: A surface inspection method, wherein a distribution of tilt angles is obtained in advance, and a detection direction of a reflected wave from a surface to be inspected is determined based on the uniqueness of the tilt angle distribution. 2. The surface inspection method according to claim 1, wherein the inclination angle distribution of the surface is obtained by dividing the surface to be inspected into minute surface elements and calculating from a unit normal vector in each minute surface element. 3. A surface inspection apparatus for detecting a reflected wave from a surface to be inspected and extracting a surface defect to be detected from the reflected wave, at the same angle over the entire width direction with respect to the surface to be inspected. A surface inspection apparatus comprising: an irradiation unit that emits an inspection wave; and a reception unit that receives a reflected wave from the surface to be inspected at the same angle over the entire width direction. 4. The optical fiber bundle according to claim 3, wherein the inspection wave is light, and the receiving means has light receiving end faces arranged in the width direction of the surface to be inspected and all of the light receiving end faces can be oriented in the same direction. And a light receiving portion for receiving the reflected light transmitted by the optical fiber bundle. 5. The surface to be inspected according to claim 3, wherein the irradiation means includes a laser oscillating device, a scanning means for scanning the laser light in the width direction of the surface to be inspected, and a laser beam scanned in the width direction. And a collimator lens for irradiating the same at the same angle over the entire width direction.