JP2022087382A - Inspection method and inspection system - Google Patents

Abstract

To provide an inspection method and an inspection system that can perform inspection with higher accuracy.SOLUTION: An inspection method includes: a first image acquisition step of acquiring a first image by photographing an inspected position at a first angle with respect to an inspected surface in a state where the inspected position on the inspected surface is irradiated with light; a second image acquisition step of acquiring a second image by photographing the inspected position at a second angle different from the first angle with respect to the inspected surface in the state where the inspected position is irradiated with light; and a difference calculation step of calculating difference between the first image and the second image after normalizing difference in an amount of light reflected at the inspected position due to difference between the first angle and the second angle.SELECTED DRAWING: Figure 7

Description

The present invention relates to an inspection method and an inspection system.

When inspecting whether the surface to be inspected has irregularities, it is not easy to distinguish between irregularities and stains such as black lines. In this regard, according to the surface inspection apparatus of Patent Document 1, it is said that uneven scratches and stains on the surface of a thin steel plate or a thick steel plate can be discriminated.

Japanese Unexamined Patent Publication No. 2006-177852

An object of the present invention is to provide an inspection method and an inspection system capable of performing an inspection with higher accuracy.

According to one aspect of the present invention, in a state where the inspected position on the inspected surface is irradiated with light, the inspected position is photographed at a first angle with respect to the inspected surface to acquire a first image. 1 In the image acquisition step and in a state where the inspected position is irradiated with light, the inspected position is photographed at a second angle different from the first angle with respect to the inspected surface to acquire a second image. After normalizing the difference in the amount of light reflection at the position to be inspected due to the difference between the second image acquisition step and the first angle and the second angle, the first image and the second image An inspection method comprising a difference calculation step for calculating the difference between the two is provided.

The inspection method may include a determination step of determining whether or not the inspected position has irregularities based on the difference between the first image and the second image.

The first angle may be an angle facing the surface to be inspected.

In the first image acquisition step and the second image acquisition step, in a state where the inspected position is irradiated with near-infrared light, the inspected position is passed through a band pass filter having a wavelength of the near-infrared light as a pass band. The first image and the second image may be acquired by photographing the image.

In the first image acquisition step and the second image acquisition step, the light to be inspected may be irradiated with light in a mesh shape.

In the first image acquisition step and the second image acquisition step, the first image and the second image may be acquired, respectively, by taking pictures from a camera mounted on the moving body.

In the first image acquisition step and the second image acquisition step, the light source mounted on the moving body may irradiate the position to be inspected with light.

In the first image acquisition step and the second image acquisition step, the light source may irradiate the position to be inspected with light via an optical member mounted on the moving body.

According to another aspect of the present invention, a light source that irradiates a position to be inspected with light on the surface to be inspected, and a state in which the position to be inspected is irradiated with light, at a first angle with respect to the surface to be inspected. The position to be inspected is photographed to acquire a first image, and the position to be inspected is at a second angle different from the first angle with respect to the surface to be inspected while the position to be inspected is irradiated with light. After normalizing the difference in the amount of light reflected at the position to be inspected due to the difference between the first angle and the second angle, and one or more cameras that capture the second image. An inspection system including a difference calculation unit for calculating the difference between the first image and the second image is provided.

Since the difference in the amount of light reflected at the position to be inspected due to the shooting angle is normalized, the inspection can be performed with high accuracy.

The figure which shows typically the ideal diffuse reflection model in a reflection surface. The figure explaining the outline of the measurement method in this embodiment. The figure explaining the case where there is no unevenness and black line in the position A-B to be inspected. The figure explaining the case where there is no unevenness and black line in the position A-B to be inspected. The figure explaining the case where the inspected position AB is uneven. The figure explaining the case where the inspected position AB is uneven. The figure explaining the case where there is a black line in the inspection position AB. The figure explaining the case where there is a black line in the inspection position AB. The block diagram which shows the schematic structure of the inspection system which concerns on one Embodiment. A flowchart showing an example of the processing operation of the inspection system. The figure which shows typically the arrangement example of the camera Cx, Cy. The figure which shows typically the case where the surface to be inspected moves.

Hereinafter, embodiments according to the present invention will be specifically described with reference to the drawings.

The method disclosed in Patent Document 1 described above is an application of the optical cutting method, and the misalignment of the line of irradiating light is identified by a camera. It does not consider that the amount of reflection depends on the angle of reflection. In addition, in the light cutting method, it is extremely difficult to detect unevenness smaller than the line width of the irradiated light. Therefore, the inventors of the present application have noticed that the method of Patent Document 1 cannot always detect unevenness in the inspected object with high accuracy.

Therefore, in the present embodiment, considering that the amount of light reflected depends on the reflection angle, it is possible to detect the unevenness of the surface to be inspected with higher accuracy. First, the principle will be explained.

FIG. 1 is a diagram schematically showing an ideal diffuse reflection model on a reflecting surface. In the present specification, the angle with respect to the normal direction of the reflecting surface is referred to as an "angle with respect to the reflecting surface". As a premise, the amount of reflection does not depend on the incident angle of light.

As shown in the figure, the amount of reflection in the normal direction is high, and the larger the angle θ with respect to the reflecting surface, the lower the amount of reflection. Specifically, when the amount of reflection (light intensity) in the normal direction is I0, the amount of reflection (light intensity) in the direction forming an angle θ with respect to the reflecting surface is I0cosθ (Lambert's principle). ).

FIG. 2 is a diagram illustrating an outline of the measurement method in the present embodiment. The position to be inspected in the figure is assumed to be between the points A and B on the surface T to be inspected (hereinafter referred to as "positions AB to be inspected").

In one example of the present embodiment, the inspected positions A and B are photographed by the cameras Cx and Cy while the inspected positions A and B are irradiated with light, and two images IMGx and IMGy are acquired, respectively. Here, the shooting angles of the cameras Cx and Cy with respect to the surface T to be inspected (the angle formed by the optical axis of the cameras Cx and Cy and the normal direction, the same applies hereinafter) are different from each other. In order to simplify the explanation, the shooting angle of the camera Cx is 0 degrees (that is, facing the surface T to be inspected), and the shooting angle of the camera Cy is θ. Then, by comparing two images having different shooting angles after performing the following normalization, unevenness can be detected without detecting a black line.

In this embodiment, it is assumed that the distance between the cameras Cx and Cy and the surface T to be inspected is about 10 m, and the angle of view of the cameras Cx and Cy is about 30 degrees. In this case, the distance between the arbitrary position between the inspected positions AB and the cameras Cx and Cy can be regarded as substantially constant.

3A and 3B are diagrams illustrating a case where the inspected positions AB have neither unevenness nor black lines.

3A (a) and 3A (b) show the brightness Ix and Iy of the corresponding pixels between the inspected positions AB in the images IMGx and IMGy from the cameras Cx and Cy, respectively. When there is no unevenness or black line between the inspected positions A and B, the brightness Ix and Iy of the pixels corresponding to the inspected positions A and B in both images IMGx and IMGy are constant values. More specifically, for the reason described in FIG. 1, when the brightness Ix in the image IMGx is I0, the brightness Iy in the image IMGy is I0cosθ. The size of the vector indicated by the reference numeral a in FIG. 3A corresponds to the brightness I0, and the size of the vector indicated by the reference numeral b corresponds to the brightness I0 cos θ.

FIG. 3B (a) is a reprint of FIG. 3A (a).

FIG. 3B (b) shows the brightness Iy ′ obtained by normalizing the brightness Iy of the pixels corresponding to the inspection positions AB in the image IMGy shown in FIG. 3A (b). The normalization here is a process for canceling the difference in the shooting angles of the cameras Cx and Cy. Specifically, Iy'is calculated by dividing the brightness Iy by cosθ. That is, Iy'= Iy / cosθ. As shown in FIG. 3A (b), when there are no irregularities or black lines at the inspected positions AB, the brightness is Iy = I0cosθ, so the brightness Iy'= Iy / cosθ = I0.

As normalization, a process of normalizing the distortion of the position to be inspected due to the difference in the photographing angle may be further performed by affine transformation or the like.

FIG. 3B (c) shows the difference dI between the brightness Ix and Iy'. As described above, when there are no irregularities or black lines at the inspected positions AB, the brightness Ix = Iy'= I0, so the difference dI = Ix-Iy'= 0.

As described above, when there are no irregularities or black lines at the inspected positions AB, the difference dI is 0.

4A and 4B are views for explaining the case where the inspected positions AB have irregularities. FIG. 4A shows an example in which there are no irregularities or black lines between positions A and C and between positions A and B, but there are recesses (cracks) at positions C and D. For the sake of simplicity, the cross section of this recess is an isosceles triangle with the deepest position M, which is the center between positions CD.

FIG. 4A (a) shows the brightness Ix of the pixels corresponding to the inspection positions AB in the image IMGx from the camera Cx. Since there are no irregularities or black lines between positions A and C and between positions D and B, the brightness Ix is a constant value I0.

Between the positions C and M, the shooting angle of the camera Cx with respect to the surface including the positions C and M deviates from the normal direction (it is no longer 0 degrees), so that the brightness Ix is smaller than I0. Similarly, even between the positions MD, the shooting angle of the camera Cx with respect to the surface including the positions MD deviates from the normal direction, so that the brightness Ix is smaller than I0. The size of the vector represented by the reference numeral c in FIG. 4A corresponds to the brightness Ix between the positions CM and MD.

FIG. 4A (b) shows the brightness Iy of the pixels corresponding to the inspection positions AB in the image IMGy from the camera Cy. Since there are no irregularities or black lines between positions A and C and between positions D and B, the brightness Iy is a constant value I0cosθ.

Between the positions C and M, the shooting angle of the camera Cy with respect to the surface including the positions C and M approaches the normal direction (smaller than θ), so that the brightness Iy is larger than I0cosθ. The size of the vector indicated by the reference numeral d in FIG. 4A corresponds to the brightness Iy between the positions CM.

Between the positions MD, the shooting angle of the camera Cy with respect to the surface including the position MD is largely deviated from the normal direction to be almost 90 degrees (the shooting angle is almost parallel to the surface including the position MD). Therefore, the brightness Iy is almost 0.

FIG. 4B (a) is a reprint of FIG. 4A (a).

4B (b) shows the brightness Iy'normalized to the brightness Iy of the pixel corresponding to the area between the inspected positions AB in the image IMGy shown in FIG. 4A (b). As shown in the figure, the brightness Iy'= Iy / cosθ = I0 because there are no irregularities or black lines between the positions A and C and between the positions A and B among the positions A and B to be inspected. Of the positions A to B to be inspected, between positions C and M, the brightness is Iy> I0cosθ, so Iy'> I0. Of the positions A to B to be inspected, between positions M and D, the brightness is Iy <I0cosθ, so Iy'<I0. In any case, the brightness Iy'≠ I0 between the positions C and D.

FIG. 4B (c) shows the difference dI between the brightness Ix and Iy'. As described above, since the brightness Ix = Iy'= I0 between the positions A and C and between the positions A and B among the positions A and B to be inspected, the difference dI = Ix-Iy'= 0. On the other hand, since the brightness Iy'≠ I0 between the positions C and D having irregularities, the difference dI ≠ 0.

As described above, among the positions AB to be inspected, the difference dI is 0 at the position where there is no unevenness or the black line, and the difference dI is not 0 at the position where there is unevenness. Therefore, it is possible to specify the unevenness and its position based on the difference dI.

5A and 5B are diagrams illustrating a case where there is a black line at the inspected position AB. FIG. 5A shows an example in which there are no irregularities or black lines between positions A and C and between positions A and B, but there are black lines at positions C and D among the positions A and B to be inspected.

FIG. 5A (a) shows the brightness Ix of the pixels corresponding to the inspection positions AB in the image IMGx from the camera Cx. Since there are no irregularities or black lines between positions A and C and between positions D and B, the brightness is Ix = I0.

On the other hand, between positions C and D, the amount of reflection is reduced by the black line (here, it is assumed to be 1 / k). Therefore, the brightness Ix = I0 / k. The size of the vector represented by the reference numeral e in FIG. 5A corresponds to the brightness Ix (= I0 / k) between the positions C and D.

FIG. 5A (b) shows the brightness Iy of the pixels corresponding to the inspection positions AB in the image IMGy from the camera Cy. Since there are no irregularities or black lines between positions A and C and between positions D and B, the brightness Iy is a constant value I0cosθ.

On the other hand, between positions C and D, the amount of reflection is 1 / k due to the black line. Therefore, the brightness Iy = I0cosθ / k. The magnitude of the vector indicated by the reference numeral f in FIG. 5A corresponds to the brightness Iy (= I0cosθ / k) between the positions C and D.
FIG. 5B (a) is a reprint of FIG. 5A (a).

5B (b) shows the brightness Iy'normalized to the brightness Iy of the pixels corresponding to the inspection positions AB in the image IMGy shown in FIG. 5A (b). As shown in the figure, the brightness Iy'= Iy / cosθ = I0 because there are no irregularities or black lines between the positions A and C and between the positions A and B among the positions A and B to be inspected. Of the positions A to B to be inspected, between positions C and D, the brightness is Iy = I0cosθ / k, so Iy'= I0 / k.

FIG. 5B (c) shows the difference dI between the brightness Ix and Iy'. As described above, since the brightness Ix = Iy'= I0 between the positions A and C and between the positions A and B among the positions A and B to be inspected, the difference dI = Ix-Iy'= 0. On the other hand, since the brightness Ix = Iy'= I0 / k between the positions C and D where the black line is located, the difference dI = 0.

As described above, the difference dI is 0 in any of the positions A to B to be inspected, regardless of whether the position has no unevenness or black line or has a black line. Therefore, the black line is not detected.

As described above with reference to FIGS. 3A to 5B, in the present embodiment, two images of the inspected positions AB on the inspected surface T taken from two angles are captured by light due to the difference in angle. The difference in the amount of reflection is normalized and then compared. As a result, unevenness can be detected accurately without detecting black lines.

FIG. 6 is a block diagram showing a schematic configuration of an inspection system according to an embodiment.

The inspection system may include a light source LS in addition to the cameras Cx and Cy described above. The light source LS is, for example, a laser, and irradiates light at a position to be inspected on the surface to be inspected. The type of light is not particularly limited, and visible light may be used, but near-infrared light is preferable. This is because it is not easily affected by external light such as sunlight, especially when inspecting outdoors. In this case, it is desirable that the cameras Cx and Cy take pictures through the band-passing filters Fx and Fy whose passband is the wavelength of near-infrared light.

As an example of light irradiation, the inspection system may include an optical member OM, and light from the light source LS may be irradiated to the inspection position via the optical member OM. The optical member OM is, for example, a mirror such as a polygon mirror. The laser beam from the light source LS is collimated. Therefore, when an optical member OM such as a polygon mirror is used, the spread of light is very small at the distance from the light source LS to the inspected position, and the attenuation of the light until it reaches the inspected position is negligible. be.

As another example of light irradiation, the optical member OM is a lens such as a rod lens, a cylindrical lens, or a Powell lens, and the light from the light source LS spreads the light through the optical member OM to generate a line beam. The position to be inspected may be irradiated. Even if the light from the light source LS is attenuated, the inspection can be performed by intentionally spreading the light. By designing the lens system so that the intensity distribution of the line beam is constant, light of constant intensity is irradiated at any point in the inspected position.

Further, the shape of the irradiated light is not limited to the line shape, and may be, for example, a mesh shape (lattice shape) composed of a plurality of lines (vertical lines and horizontal lines) orthogonal to each other. By making it mesh-like, more positions can be inspected in one shooting.

If the intensity of the light emitted at the inspected position is uneven, the influence of the intensity unevenness can be suppressed by acquiring and calibrating the intensity distribution in advance.

The inspection system may include the moving body 1, and the camera Cx, Cy, the light source LS, and a part or all of the optical member OM may be mounted on the moving body 1. By fixing the cameras Cx and Cy to the moving body 1, the shooting angle can be kept constant. In this case, the cameras Cx and Cy are preferably arranged so that their optical axes are not parallel to each other. The moving body 1 is not particularly limited, but for example, when the inspection target is a road, a vehicle is suitable, and when the inspection target is a blade of a wind power generation device, a drone is suitable.

Further, the inspection system includes an inspection device 2. The inspection device 2 includes an image acquisition unit 21, a normalization unit 22, a difference calculation unit 23, a determination unit 24, and a control unit 25. Some or all of these parts may be implemented in hardware or may be realized by the processor executing a predetermined program. Further, each part of the inspection device 2 may be provided in one device or may be distributed in a plurality of devices.

The image acquisition unit 21 acquires an image IMGx obtained by shooting with the camera Cx and an image IMGy obtained by shooting with the camera Cy. The images IMGx and IMGy may be displayed on a display (not shown).

The normalization unit 22 normalizes the difference in shooting angle between the cameras Cx and Cy, and generates a normalized image obtained by normalizing the image IMGy.

Specifically, the normalization unit 22 normalizes the difference in the amount of light reflected on the surface to be inspected due to the difference in the photographing angle. More specifically, when the shooting angle by the camera Cx is θ1 and the shooting angle by the camera Cy is θ2, the normalization unit 22 multiplies the brightness of each pixel of the image IMGy by (cos θ1 / cos θ2). , Generate a normalized image. The normalized image may be displayed on a display (not shown).

Further, the normalization unit 22 may normalize the distortion of the position to be inspected due to the difference in the photographing angle. Specifically, the normalization unit 22 may perform affine transformation on the image IMGy to align the shooting directions.

The difference calculation unit 23 calculates the difference between the image IMGx and the normalized image, and generates a difference image. That is, the difference calculation unit 23 normalizes the difference in the amount of light reflected at the position to be inspected due to the difference in the shooting angles of the cameras Cx and Cy, and then calculates the difference between the image IMGx and the image IMGy. The difference image may be displayed on a display (not shown).

The determination unit 24 determines whether or not there is unevenness in the position to be inspected based on the difference image (that is, the difference between the image IMGx and the normalized image). Specifically, the determination unit 24 makes a determination by comparing the brightness of the difference image with a predetermined threshold value. For example, the determination unit 24 determines that there is no unevenness in the position corresponding to the pixel whose brightness is less than the threshold value among the positions to be inspected, and the determination unit 24 has unevenness in the position corresponding to the pixel whose brightness is equal to or higher than the threshold value. Judge that there is. By such a determination, the presence or absence of unevenness and the position when there is unevenness can be detected.

The control unit 25 controls the cameras Cx, Cy and the light source LS. Specifically, the control unit 25 controls the shooting timing by the cameras Cx and Cy and the light irradiation timing by the light source LS.

FIG. 7 is a flowchart showing an example of the processing operation of the inspection system. The image acquisition unit 21 acquires an image IMGx obtained by photographing the inspected position at a predetermined shooting angle (for example, an angle facing the camera) while the light source LS irradiates the inspected position with light (step S21). ). Further, the image acquisition unit 21 obtains an image IMGy obtained by photographing the inspected position at a predetermined shooting angle (for example, an angle deviating from the front) while the light source LS irradiates the inspected position with light. Acquire (step S22). The images IMGx and IMGy may be acquired sequentially or simultaneously.

Subsequently, the normalization unit 22 normalizes the shooting angle by the camera Cx and the shooting angle by the camera Cy (step S23). In particular, the normalization unit 22 normalizes the amount of light reflected at the position to be inspected due to the difference in the shooting angle, and normalizes the image IMGy from the camera Cy to generate a normalized image. Then, the difference calculation unit 23 calculates the difference between the image IMGx from the camera Cx and the normalized image, and generates a difference image (step S24). Based on the difference image, the determination unit 24 determines whether or not there is unevenness in the position to be inspected, and if so, the position.

As described above, in the present embodiment, the inspection positions are photographed at different shooting angles to generate two images, the difference in the shooting angles is normalized, and then the two images are compared. Therefore, unevenness at the inspected position can be detected with high accuracy.

The configuration of the inspection system shown in FIG. 6 and the processing operation of the inspection system shown in FIG. 7 are merely examples, and various modifications are possible.

For example, as shown in FIG. 8, the two cameras Cx and Cy may be arranged so that the optical axes are parallel to each other so that the inspected positions AB are located at different positions in the angle of view.

Further, one camera may be used. That is, in a state where the position to be inspected is irradiated with light, a camera may be used to shoot at a certain shooting angle, and then the shooting angle may be changed and the same camera may be used for shooting. Alternatively, the camera may be fixed and the surface to be inspected may move. That is, as shown in FIG. 9, when the surface to be inspected is in the place P1, the camera takes a picture in a state where the positions A and B to be inspected are irradiated with light, and then the surface to be inspected moves to another. The camera may take a picture while irradiating the inspected positions AB with light when the place P2 is located.

Further, a person may perform a part of the processing operation shown in FIG. 7. For example, a person may determine the presence or absence of unevenness and the position of unevenness while looking at the difference image generated by the inspection device 2.

The above-described embodiments have been described for the purpose of allowing a person having ordinary knowledge in the technical field to which the present invention belongs to carry out the present invention. Various modifications of the above embodiment can be naturally made by those skilled in the art, and the technical idea of the present invention can be applied to other embodiments. Accordingly, the invention is not limited to the described embodiments and should be the broadest scope in accordance with the technical ideas defined by the claims.

Cx, Cy Camera LS Light source OM Optical member Fx, Fy Bandpass filter 1 Moving object 2 Inspection device 21 Image acquisition unit 22 Normalization unit 23 Difference calculation unit 24 Judgment unit 25 Control unit

Claims (9)

A first image acquisition step of photographing the inspected position at a first angle with respect to the inspected surface and acquiring a first image while the inspected position on the inspected surface is irradiated with light.
A second image acquisition step of photographing the inspected position at a second angle different from the first angle with respect to the inspected surface while irradiating the inspected position with light to acquire a second image. ,
Difference calculation for calculating the difference between the first image and the second image after normalizing the difference in the amount of light reflected at the position to be inspected due to the difference between the first angle and the second angle. Inspection method with steps. The inspection method according to claim 1, further comprising a determination step of determining whether or not unevenness is present at the position to be inspected based on the difference between the first image and the second image. The inspection method according to claim 1 or 2, wherein the first angle is an angle facing the surface to be inspected. In the first image acquisition step and the second image acquisition step, in a state where the inspected position is irradiated with near-infrared light, the inspected position is passed through a band pass filter having a wavelength of the near-infrared light as a pass band. The inspection method according to any one of claims 1 to 3, wherein the first image and the second image are acquired by photographing the image. The inspection method according to any one of claims 1 to 4, wherein in the first image acquisition step and the second image acquisition step, the inspection position is irradiated with light in a mesh shape. The first image acquisition step and the second image acquisition step, according to any one of claims 1 to 5, wherein the first image and the second image are acquired by taking a picture from a camera mounted on a moving body. Inspection method. The inspection method according to any one of claims 1 to 6, wherein in the first image acquisition step and the second image acquisition step, light is emitted from a light source mounted on a moving body to the position to be inspected. The inspection method according to claim 7, wherein in the first image acquisition step and the second image acquisition step, light is emitted from the light source to the position to be inspected from the light source via an optical member mounted on the moving body. A light source that irradiates the inspected position on the inspected surface with light,
In a state where the inspected position was irradiated with light, the inspected position was photographed at a first angle with respect to the inspected surface to acquire a first image, and the inspected position was irradiated with light. In the state, one or more cameras that capture the position to be inspected at a second angle different from the first angle with respect to the surface to be inspected and acquire a second image.
Difference calculation for calculating the difference between the first image and the second image after normalizing the difference in the amount of light reflected at the position to be inspected due to the difference between the first angle and the second angle. Inspection system equipped with a department.

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