JP2020187020A - Surface inspection method and device therefor - Google Patents

Abstract

To detect a defect on an article, with its surface hairline finished, that is different from the hairline marked on this surface quickly with high accuracy.SOLUTION: The direction a of hairlines formed on an inspection object is detected in a hairline detection step, and a surface defect detection step is carried out utilizing the detection result. In the hairline detection step, a light stripe part 20a and a dark stripe part 20b are formed in an annular shape, respectively, and the surface of an inspection object 4 is irradiated with a first illumination pattern 20 in which these stripe parts are alternately arranged on the concentric circle. Then, the direction a of the hairlines formed on the surface of the inspection object 4 is detected on the basis of an image 21 for hairline detection having been obtained by imaging the surface of the inspection object 4.SELECTED DRAWING: Figure 4

Description

The present invention relates to a surface inspection method for detecting defects different from the hairline attached to the surface of the inspection target for an article having a hairline processed surface, and a surface inspection apparatus for carrying out the method.

The surface of a metal product or the like may be subjected to a surface finish called hairline processing in order to obtain effects such as matting and emphasizing a metallic texture. On the surface of the hairline-processed product, a large number of streaks (that is, hairlines) as thin as hair extending in a single direction are formed.

Now, for products with a smooth surface (glass products, film products, products whose surface is plated or painted, etc.), inspect whether the surface has defects such as irregularities and scratches. As a method, a surface inspection method using pattern illumination in which bright strips and dark strips are alternately arranged is widely known (see, for example, Patent Document 1).

In this type of surface inspection method, the surface of the inspection target is irradiated while shifting the brightness pattern of the pattern illumination, and a plurality of images obtained by imaging the surface of the inspection target are used to determine the difference in the amount of reflected light. The presence or absence of defects on the surface is inspected based on the change in brightness (see, for example, Non-Patent Documents 1 and 2 for the principle of the inspection method).

Utility Model Registration No. 31977666

Osamu Hirose, 3 outsiders, "Detection of film surface unevenness defects using pattern illumination", Journal of Precision Engineering, VOL.66, No.7, 2000, P1098-1102 Nobu Nasuzawa, 1 outside, "Development of defect detection technology using moving pattern light source", Journal of Precision Engineering, VOL.67, No.11, 2001, P1839-1843

However, when the surface to be inspected is subjected to the above-mentioned hairline processing, the presence or absence of scratches can be determined even if the surface is irradiated with light and dark pattern illumination due to the influence of anisotropic reflection by the hairline. The striped pattern may not be projected on the surface to be inspected. As a result, the above-mentioned conventional surface inspection method may not be able to appropriately detect defects such as scratches on the surface of the hairline-processed inspection target, and countermeasures have been desired.

The present invention has been made in view of such circumstances, and is capable of detecting defects different from the hairline attached to the surface of an article having a hairline processed surface with high accuracy and quickly. The purpose is to provide an inspection method and its equipment.

In order to achieve the above object, the surface inspection method of the present invention is a surface inspection method for detecting a defect different from the hairline attached to the surface of the inspection target for an article having a hairline processed surface. ,
The surface of the inspection target was imaged while irradiating the surface of the inspection target with a first illumination pattern in which bright and dark parts having different brightness were arranged in the direction of an arbitrary angle range. A hairline detection step that detects the direction of the hairline formed on the surface of the inspection target based on the hairline detection image, and
Using a second illumination pattern in which bright and dark strips of different brightness are arranged alternately, each of the strips is adjusted so as to extend in a direction orthogonal to the hairline, and each strip is adjusted. While periodically moving in the arrangement direction, the surface of the inspection target is irradiated with the illumination pattern, the surface of the inspection target is imaged, and the surface of the inspection target is attached based on the obtained defect detection image. It is characterized by including a surface defect detection step of detecting a defect different from the hairline.

According to the present invention, by first carrying out the hairline detection step using the first illumination pattern, it is possible to grasp the formation direction of the hairline formed on the surface of the inspection target. Then, by adjusting the second illumination pattern so that each band-shaped portion extends orthogonally to the formation direction of the hairline and irradiating the surface of the inspection target with the illumination pattern, the influence of anisotropic reflection by the hairline is obtained. Is minimized, and the light and darkness of each band is clearly visible on the same surface. Therefore, it is possible to detect defects different from the hairline attached to the surface of the inspection target with high accuracy based on the defect detection image obtained by imaging the surface of the inspection target. As a result, it is possible to avoid inconveniences such as inability to inspect due to the fact that the light and darkness of the illumination pattern does not appear on the surface of the inspection target as in the conventional case, and it is possible to quickly carry out the surface inspection.

Here, in the first illumination pattern, the bright portion is formed by a bright band-shaped portion, the dark portion is formed by a dark strip-shaped portion, and the bright strip-shaped portion and the dark strip-shaped portion are formed in an annular shape, respectively. It is preferable that the illumination pattern is such that the strips are alternately arranged on concentric circles.
By using such an illumination pattern, each band-shaped portion is arranged in all directions (360 °) in two dimensions. As a result, since a part of each band-shaped portion forming the first illumination pattern always crosses the hairline orthogonally, the direction of the hairline can be detected from the image by irradiating and imaging the hairline once. , It becomes possible to carry out the surface inspection more quickly.

Further, the hairline detection step includes a luminance scanning step of detecting the luminance along a plurality of parallel scanning lines at regular intervals with respect to the hairline detecting image, and the luminance scanning step of the hairline is based on the luminance on each scanning line. It is characterized by detecting the direction.

Next, the present invention relating to a surface inspection apparatus for carrying out the above-mentioned surface inspection method
A pattern illumination unit that selects the first illumination pattern and the second illumination pattern and irradiates the surface to be inspected, and a pattern illumination unit.
An imaging unit that images an inspection target to obtain an image for hairline detection and an image for defect detection,
A control unit that controls the pattern illumination unit and the imaging unit to execute the hairline detection process and the surface defect detection process.
An inspection processing unit that detects the direction of the hairline formed on the surface of the inspection target based on the hairline detection image and detects defects different from the hairline attached to the surface of the inspection target based on the defect detection image. It is characterized by having.
According to this surface inspection apparatus, the hairline detection step and the surface defect detection step of the surface inspection method according to the present invention can be efficiently carried out by one unit.

As described above, according to the present invention, it is possible to realize highly accurate and rapid detection of defects different from the hairline attached to the surface of an article having a hairline processed on the surface.

It is a schematic diagram which shows the outline of the surface inspection apparatus which concerns on embodiment of this invention. It is a flowchart which shows the procedure for carrying out the surface inspection method by the surface inspection apparatus which concerns on embodiment of this invention. It is a figure for demonstrating the hairline detection process in the surface inspection method which concerns on embodiment of this invention, (a) is the figure which shows the example of the inspection object which hairline was formed on the surface, (b) is the 1st illumination pattern. It is a figure which shows the example of. It is a figure for demonstrating the hairline detection process in the surface inspection method which concerns on embodiment of this invention, (a) is the figure which shows the state which the surface of the inspection object which has a hairline is irradiated with the 1st illumination pattern, ( b) is a diagram showing an example of a hairline detection image. It is a figure for demonstrating the hairline detection process in the surface inspection method which concerns on embodiment of this invention, (a) is the figure which shows the process of scanning the image for hairline detection and detecting the luminance data, (b) (c). Is a diagram showing luminance detection data obtained by scanning an image for hairline detection. It is a figure for demonstrating the surface defect detection process in the surface inspection method which concerns on embodiment of this invention, (a) is the figure which shows the example of the 2nd illumination pattern, (b) is the surface of the inspection object which has a hairline. On the other hand, it is a figure which shows the irradiated state of the 2nd illumination pattern. It is a figure which shows the example of the image for defect detection obtained by the surface defect detection process in the surface inspection method which concerns on embodiment of this invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
First, the surface inspection apparatus according to this embodiment will be described.
FIG. 1 is a schematic view showing an outline of the surface inspection apparatus according to the present embodiment.
The surface inspection device includes a pattern illumination unit 1, an image pickup unit 2, and a computer 3.

The pattern illumination unit 1 is a component that serves as a light source for irradiating the surface of the inspection target 4 with pattern illumination for surface inspection, and in this embodiment, a liquid crystal illumination device including a liquid crystal drawing unit 10 is adopted. .. The liquid crystal lighting device can draw various illumination patterns on the liquid crystal drawing unit 10 according to the drawing data, and irradiates the inspection target 4 with light rays from the backlight 11 through the liquid crystal drawing unit 10.

The imaging unit 2 is a component for capturing an image of the surface of the inspection target 4 and obtaining a surface image thereof. For example, a digital video camera or the like can be adopted for the image pickup unit 2.

The computer 3 has a function as a control unit for synchronously controlling the pattern illumination unit 1 and the imaging unit 2 and executing the hairline detection step and the surface defect detection step of the surface inspection method described later.
Further, the computer 3 detects the direction of the hairline formed on the surface of the inspection target based on the hairline detection image acquired by the imaging unit 2, and inspects based on the defect detection image acquired by the imaging unit 2. It has a function as an inspection processing unit that detects defects different from the hairline attached to the surface of the target.

The pattern illumination unit (liquid crystal illumination device) 1 has a built-in control device for drawing an illumination pattern in the liquid crystal drawing unit 10. Specifically, FPGA (Field Programmable Gate Array) 12 is adopted as a control device.
The FPGA 12 is a semiconductor integrated circuit in which an arithmetic program can be constructed by hardware, and is characterized in that the arithmetic program circuit can be freely set by the user and can be freely changed thereafter. Further, the FPGA 12 has a feature that it can realize extremely high-speed arithmetic processing as compared with a microcomputer that reads an arithmetic program by software and executes arithmetic processing in order to execute arithmetic processing with an arithmetic program built by hardware. Have.
The pattern illumination unit 1 according to the present embodiment realizes high-speed drawing processing of the illumination pattern by executing the drawing processing of the illumination pattern on the liquid crystal drawing unit 10 by the FPGA 12.

FIG. 2 is a flowchart showing a procedure for carrying out the surface inspection method by the surface inspection apparatus according to the present embodiment.
The computer 3 that functions as a control unit synchronously controls the pattern illumination unit 1 and the image pickup unit 2, and first executes a hairline detection step (step S1). By the same process, the direction of the hairline formed on the surface of the inspection target 4 can be grasped. Next, the arrangement direction of the illumination pattern is adjusted with respect to the direction of the hairline grasped by the hairline detection step, and the surface defect detection step is executed (step S2).

Next, the surface inspection method according to the present embodiment will be described. As described above, the surface inspection method according to the present embodiment includes a hairline detection step and a surface defect detection step.
3 to 5 are diagrams for explaining a hairline detection step in the surface inspection method according to the present embodiment.
On the surface of the inspection target 4 of the surface inspection method according to the present embodiment, a large number of fine streaks called hairlines are formed in a single direction. For example, FIG. 3A shows an inspection target 4 in which hairlines are formed in the vertical direction (vertical direction), but it goes without saying that the direction a of the hairlines is divided by the inspection target 4.
In the surface inspection method according to the present embodiment, a hairline detection step is first performed to detect the direction a of the hairline.

In the hairline detection step, the pattern illuminating unit 1 inspects the first illumination pattern 20 in which the bright band-shaped portions 20a and the dark strip-shaped portions 20b having different brightness are alternately arranged in the direction of an arbitrary angle range. Irradiate toward the surface of. Then, the surface of the inspection target 4 is imaged by the imaging unit 2.

As the first illumination pattern 20, in the present embodiment, the bright band-shaped portion 20a and the dark band-shaped portion 20b as shown in FIG. 3B are formed in an annular shape, and the band-shaped portions 20a and 20b are concentrically formed on the concentric circles. Lighting patterns arranged alternately are adopted.

As shown in FIG. 4A, when the surface of the inspection target 4 is imaged by the imaging unit 2 while irradiating the illumination light of the first illumination pattern 20 from the pattern illumination unit 1 toward the surface of the inspection target 4. The hairline detection image 21 as shown in FIG. 4B is obtained.
In the hairline detection image 21, a part of each band-shaped portion 20a, 20b orthogonal to the direction a in which the hairline extends with respect to the first illumination pattern 20 irradiated on the surface of the inspection target 4 is anisotropically reflected by the hairline. It is clearly projected as a striped pattern without being affected by. The directions in which the strips 20a and 20b projected on the hairline detection image 21 extend are orthogonal to the hairline direction a. Therefore, the direction a of the hairline can be detected from the band-shaped portions 20a and 20b projected on the hairline detection image 21.

Specifically, it is sufficient to pay attention to an arbitrary band-shaped portion 20a or 20b projected on the hairline detection image 21 and derive the extending direction of the band-shaped portion 20a or 20b, and various methods can be applied for that purpose. it can.
In the present embodiment, for example, as shown in FIG. 5A, an image is taken along two parallel scanning trajectories S1 and S2 with respect to arbitrary strips 20a and 20b projected on the hairline detection image 21. Detects the brightness of (brightness scanning step).
FIG. 5B is the luminance detection data of the image for the scanning trajectory S1 on the left side, and FIG. 5C is the luminance detection data of the image for the scanning trajectory S2 on the right side.
Next, based on the luminance detection data obtained for each scanning trajectory, a portion having substantially the same luminance value is detected inside the same strip-shaped portion 20a or 20b. For example, in each luminance detection data shown in FIGS. 5 (b) and 5 (c), the positions of the peak values P1 and P2 that first appear are detected. The positions of these peak values P1 and P2 exist in the dark band-shaped portion 20b projected at the beginning (first from the top) of the hairline detection image 21 in FIG. 5 (a), and are lines connecting these P1 and P2. The minute L can be estimated to be approximately the center line of the dark strip 20b. Then, it can be determined that the direction a of the hairline of the inspection target 4 is a direction orthogonal to this line segment L.

In addition, in order to detect the direction in which the arbitrary strips 20a and 20b projected on the hairline detection image 21 extend (that is, the direction orthogonal to the hairline) with higher accuracy, the brightness is within the same strips 20a or 20b. A plurality of different locations having substantially the same value of may be selected, and line segments indicating the extending direction of the strip portion 20a or 20b may be obtained and compared with each other by the same procedure as described above. As the data to be compared, for example, the variation (dispersion) of the brightness on each line segment is preferable, and it can be estimated that the line segment having the smallest variation in brightness is close to the direction in which the strip portion 20a or 20b extends.

In addition, the obtained line segment is rotated around its center point by an arbitrary angle, and a plurality of pixel gradation data of the line segment at each rotation position are acquired, and the rotation position of the line segment with little variation (dispersion) is determined. It may be estimated that the strip 20a or 20b is close to the extending direction.

Next, the surface defect detection step is carried out using the hairline direction a grasped in the hairline detection step.
6 and 7 are diagrams for explaining a surface defect detection step in the surface inspection method according to the present embodiment.
In the surface defect detecting step, for example, a second illumination pattern 30 in which bright strips 30a and dark strips 30b having different brightness are alternately arranged as shown in FIG. 6A is used. The band-shaped portions 30a and 30b are formed in a strip shape and extend in the same direction (horizontal directions on the left and right in the figure) b.

As shown in FIG. 6B, the FPGA 12 in FIG. 1 has a second illumination pattern so that the extending direction b of each of the strips 30a and 30b is orthogonal to the direction a of the hairline formed on the inspection target 4. Form 30. Further, the FPGA 12 periodically moves the band-shaped portions 30a and 30b in the arrangement direction c, and irradiates the illumination light of the second illumination pattern 30 from the pattern illumination portion 1 toward the surface of the inspection target 4. Then, the surface of the inspection target 4 is periodically imaged by the imaging unit 2 in synchronization with the periodic movement of the band-shaped portions 30a and 30b. As a result, the defect detection image 31 as shown in FIG. 7 is obtained.

Based on this defect detection image 31, defects 32 such as scratches on the surface of the inspection target 4 different from the hairline can be detected.
Since the principle that the defect 32 attached to the surface of the inspection target 4 can be detected based on the defect detection image 31 is already well known, a detailed description thereof will be omitted (for example, Patent Document 1, See Non-Patent Documents 1 and 2).

It goes without saying that the present invention is not limited to the above-described embodiment, and various modifications and applications can be developed.
For example, the first illumination pattern used in the hairline detection step is not limited to the annular pattern as shown in FIG. 3 (b), and may be formed into another shape (for example, radial) as needed. Good.
The method of detecting the direction of the hairline formed on the surface of the inspection target based on the hairline detection image obtained in the hairline detection step is not limited to the method of the above-described embodiment, and is not limited to other methods. It is possible to detect the extending direction of the strip-shaped portion projected on the hairline detection image.

1: Pattern lighting unit 2: Imaging unit 3: Computer 4: Inspection target,
10: Liquid crystal drawing unit, 11: Backlight, 12: FPGA,
20: First illumination pattern, 20a: bright band-shaped part, 20b: dark band-shaped part, 21: image for hairline detection,
30: Second illumination pattern, 30a: Bright band, 30b: Dark band, 31: Defect detection image, 32: Defect

Claims (4)

It is a surface inspection method that detects defects different from the hairline on the surface of the inspection target, targeting the article whose surface has been hairline processed.
Obtained by imaging the surface of the inspection target while irradiating the surface of the inspection target with a first illumination pattern in which bright and dark parts having different brightness are arranged in a direction of an arbitrary angle range. A hairline detection step of detecting the direction of the hairline formed on the surface of the inspection target based on the hairline detection image,
Using a second illumination pattern in which bright bands and dark bands having different brightness are alternately arranged, each of the bands is adjusted so as to extend in a direction orthogonal to the hairline, and each band is adjusted. Is periodically moved in the arrangement direction, the surface of the inspection target is irradiated with the illumination pattern, the surface of the inspection target is imaged, and the surface of the inspection target is subjected to the obtained defect detection image. A surface defect detection process that detects defects different from the attached hairline,
A surface inspection method comprising. In the first illumination pattern, the bright part is formed by a bright band-shaped part, the dark part is formed by a dark band-shaped part, and the bright band-shaped part and the dark band-shaped part are formed in an annular shape, respectively. The surface inspection method according to claim 1, wherein the illumination pattern has parts arranged alternately on concentric circles. The hairline detection step includes a luminance scanning step of detecting the luminance along a plurality of parallel scanning lines at regular intervals with respect to the hairline detecting image, and the luminance scanning step is based on the luminance on each scanning line. The surface inspection method according to claim 1 or 2, wherein the direction of the hairline is detected. A surface inspection apparatus for carrying out the surface inspection method according to any one of claims 1 to 3.
A pattern illuminating unit that selects the first illuminating pattern and the second illuminating pattern to irradiate the surface of the inspection target, and
An imaging unit that images the inspection target to obtain the hairline detection image and the defect detection image.
A control unit that controls the pattern illumination unit and the imaging unit to execute the hairline detection step and also executes the surface defect detection step.
The direction of the hairline formed on the surface of the inspection target is detected based on the hairline detection image, and a defect different from the hairline attached to the surface of the inspection target is detected based on the defect detection image. Inspection processing department and
A surface inspection device characterized by being equipped with.

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