Visual inspection system

Abstract

To accurately detect a defect on the inner wall surface of a through-hole provided in an inspection object.SOLUTION: A visual inspection system includes an illumination device which has a first light-emitting area and a black or chromatic color background area surrounded by the first light-emitting area, an imaging device which includes a lens and is arranged to face the illumination device, and an image processing device which includes a boundary detection part and a defect detection part. The imaging device acquires the image of the inspection object which is the inspection object arranged between the illumination device and the imaging device and has the through-hole. The boundary detection part detects a boundary between the background area and the inner wall surface of the through-hole on the basis of the difference of at least one of hue and lightness in the image of the inspection object acquired by the imaging device. The defect detection part detects the defect on the inner wall surface.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a visual inspection system, and more particularly to a system for detecting defects on the inner wall surface of a through hole provided in an object to be inspected. [Background technology]

[0002] In the inspection of members with through holes, such as steel pipes and bearings, it is sometimes necessary to detect defects (such as scratches or foreign matter) on the inner wall surface that defines the through hole. For example, the following Patent Document 1 discloses a foreign matter inspection device that has a light source that irradiates light from one end of a pipe, which is an object to be inspected, toward the inside of the pipe, and a camera that takes an image of the inside of the pipe from the other end of the pipe. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2023-067531 A Summary of the Invention [Problem to be solved by the invention]

[0004] In the inspection of a member having a through hole, it would be beneficial to improve the accuracy of detecting defects on the inner wall surface of the through hole. [Means for solving the problem]

[0005] According to the present invention, the following inventions are provided. [1] An appearance inspection system comprising: an illumination device having a first light-emitting region and a black or chromatic background region surrounded by the first light-emitting region; an imaging device including a lens and arranged opposite the illumination device; and an image processing device including a boundary detection unit and a defect detection unit, wherein the imaging device acquires an image of an inspection object having a through hole, the inspection object being arranged between the illumination device and the imaging device; the boundary detection unit detects a boundary between the background region and an inner wall surface of the through hole based on a difference in at least one of hue and brightness in the image of the inspection object acquired by the imaging device; and the defect detection unit detects defects on the inner wall surface. [2] A visual inspection system as described in [1], wherein the lighting device includes a cylindrical housing having a through hole along a central axis, a plurality of light sources housed in the housing, and a support positioned opposite the first light-emitting region and supporting the housing, and the background region is at least a portion of the area of ​​the surface of the support that appears inside the through hole of the housing. [3] The visual inspection system described in [1], wherein the lighting device includes a light source device having an upper surface including the first light-emitting region as a part thereof, and a filter member having a black or chromatic surface, disposed on the upper surface of the light source device and covering at least a portion of the upper surface, and the background region is at least a portion of the surface of the filter member. [4] An appearance inspection system as described in any one of [1] to [3], wherein the first light-emitting region is ring-shaped surrounding the background region. [5] A visual inspection system as described in any one of [1] to [4], wherein the lighting device irradiates the inner wall surface of the through hole of the object to be inspected, which is disposed between the lighting device and the imaging device, with diffused light. [6] A visual inspection system as described in any one of [1] to [5], wherein the background region is defined as a region of the lighting device that is cut out by a cone whose apex is the position of the principal point of the lens and which is tangent to the opening of the through hole on the lighting device side when the object to be inspected is placed between the lighting device and the imaging device. Effect of the Invention

[0006] According to at least any one of the embodiments of the present invention, it is possible to improve the accuracy of detecting defects on the inner wall surface of a through hole. [Brief description of the drawings]

[0007] [Figure 1] FIG. 1 is a schematic diagram illustrating an exemplary visual inspection system in accordance with an embodiment of the present invention. [Diagram 2] 2 is a schematic ZX cross-sectional view of the illumination device 10 and the imaging device 20 when the workpiece W is placed between them. [Diagram 3] 2 is a diagram showing an example of an image captured by an imaging device 20. FIG. [Figure 4] FIG. 2 is a schematic diagram for explaining an example of preprocessing by the image processing device 30. [Diagram 5] 1 is a schematic top view showing a first example of a lighting device 10. FIG. [Figure 6] 6 is a cross-sectional view taken along line VI-VI of FIG. 5. [Figure 7] 1 is a schematic cross-sectional view for explaining the relationship between the field of view of an imaging device 20 and a background region RB of an illumination device 10A. [Figure 8] 1 is a schematic cross-sectional view showing a second example of the lighting device 10. FIG. [Figure 9] 10 is a schematic cross-sectional view for explaining the relationship between the field of view of an imaging device 20 and a background region RB of an illumination device 10B. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] <1. Problems Found by the Inventor> According to the inventor's research, one of the factors that reduces the accuracy of visual inspection of components with through holes is excessive detection of defects. Such "excessive detection" occurs, for example, when a foreign object attached to a position other than the inner wall surface of a through hole or dust floating in the air is judged to be a defect on the inner wall surface. "Excessive detection" can result in a product that is not actually defective being judged to be defective.

[0009] For example, "excessive detection" may occur in the following manner. As in the technology described in Patent Document 1, when the inside of a through hole is irradiated with light through one opening of the through hole and the inside of the through hole is photographed from the other opening, not only the inner wall surface of the through hole but also the area located inside the opening closer to the light source out of the two openings of the through hole is brightly reflected in the acquired image. That is, in the image, it may be difficult to distinguish between the inner wall surface of the through hole and the part of the light source that appears inside the opening of the through hole. In such a case, dust or scratches on the surface of the light source may be erroneously determined to be a defect on the inner wall surface of the through hole.

[0010] In view of these circumstances, the inventors have made extensive studies and completed the present invention. As will be described in detail below, in an embodiment of the present invention, when an image of the inner wall surface of a through hole is taken, a difference in at least one of hue and brightness is generated between the inner wall surface of the through hole and the "background" located farther from the through hole. That is, a difference in at least one of hue and brightness is intentionally generated, and the boundary between the inner wall surface of the through hole and the area located inside the opening of the through hole can be detected, so that, for example, a part corresponding to the inner wall surface of the through hole can be extracted from the acquired image. This makes it possible to avoid judging dust or the like that appears in a part other than the inner wall surface of the through hole as a defect on the inner wall surface.

[0011] Hereinafter, embodiments of the present invention will be described with reference to the drawings. The features of the embodiments described below can be combined with each other. Also, each feature can be an invention independently.

[0012] <2. Outline of visual inspection system> FIG 1 shows an exemplary appearance inspection system according to an embodiment of the present invention. The appearance inspection system 1 shown in FIG 1 includes an illumination device 10, an imaging device 20, and an image processing device 30. For convenience of explanation, FIG 1 shows an X-axis, a Y-axis, and a Z-axis that are orthogonal to each other. Of these, the Y-axis is, for example, parallel to the vertical direction. Hereinafter, these orthogonal axes may also be shown in other drawings of the present application.

[0013] The lighting device 10 has a first light-emitting region R1. In the configuration illustrated in FIG. 1, the first light-emitting region R1 has a ring shape. The lighting device 10 further has a background region RB. As shown in FIG. 1 by hatching, the background region RB is a region having a low brightness achromatic color (typically black) or a chromatic color. In this example, the background region RB has a disk shape surrounded by the first light-emitting region R1. The background region RB may be on the same plane as the first light-emitting region R1, or may be on a different plane from the first light-emitting region R1.

[0014] The imaging device 20 may be, for example, a digital video camera or a digital still camera, and includes a lens 22. The lens 22 may be a compound lens made up of an assembly of lenses.

[0015] The imaging device 20 is disposed in the appearance inspection system 1 at a distance from the lighting device 10 and facing the lighting device 10. More specifically, the imaging device 20 is disposed in the appearance inspection system 1 such that the imaging surface of the image sensor faces the light-emitting surface of the lighting device 10 (here, the surface including the first light-emitting region R1 as a part thereof). In the example shown in Fig. 1, the imaging device 20 is supported by the arm 40 and disposed at a predetermined distance in the Z direction in the figure from the lighting device 10 fixed to the arm 40.

[0016] The image processing device 30 is connected to at least the imaging device 20 by a wireless or wired method, and detects defects in the inspection object by analyzing the image acquired by the imaging device 20. In this example, the image processing device 30 includes a boundary detection unit 32 and a defect detection unit 34. Hereinafter, the inspection object will be referred to as a "workpiece W" for convenience.

[0017] In an embodiment of the present invention, the workpiece W is assumed to be a member having an upper surface Wa and a lower surface Wb opposite to the upper surface Wa, and having a through hole WT connecting these surfaces. In addition to the upper surface Wa and the lower surface Wb, the workpiece W has one or more inner wall surfaces Wc that define the through hole WT. Here, the terms "upper surface" and "lower surface" are used merely for convenience to distinguish between the two surfaces that constitute the outer shape of the workpiece W, and are not intended to limit the orientation of the workpiece W in the actual product.

[0018] In the example shown in FIG. 1, the through hole WT is a space having a cylindrical shape perpendicular to the upper surface Wa and the lower surface Wb. The through hole WT includes a first opening W1 located on the lower surface Wb and a second opening W2 located on the upper surface Wa. Here, the first opening W1 and the second opening W2 are both circular. Of course, the shape of the through hole WT is not limited to this example. The outer shape of the workpiece W is also not limited to a specific shape.

[0019] 3. Operational Example of Illumination Device 10 and Imaging Device 20 In the inspection of the inside of the through hole WT of the workpiece W, the workpiece W is moved between the lighting device 10 and the imaging device 20 by a conveying device such as a taught robot arm. FIG. 1 shows a state in which the workpiece W is placed between the lighting device 10 and the imaging device 20 by a robot arm (not shown). The imaging device 20 performs imaging of the workpiece W placed between the lighting device 10 and the imaging device 20. Here, the lower surface Wb of the workpiece W faces the upper surface 10a of the lighting device 10. As shown in FIG. 1, in a typical embodiment, a space is formed between the lower surface Wb of the workpiece W and the lighting device 10. In other words, it is not essential that the workpiece W be brought into contact with the upper surface 10a of the lighting device 10. Similarly, here, a space is also formed between the upper surface Wa of the workpiece W and the imaging device 20.

[0020] The transport device (here, a robot arm) supports the workpiece W between the lighting device 10 and the imaging device 20 so that the central axis of the through hole WT is roughly parallel to the Z axis in the figure. With the workpiece W placed between the lighting device 10 and the imaging device 20, the visual inspection system 1 causes the lighting device 10 to emit light (typically white light) toward the workpiece W. With the workpiece W placed between the lighting device 10 and the imaging device 20 so that at least the entire inner wall surface Wc of the through hole WT falls within the field of view of the camera of the imaging device 20, the visual inspection system 1 photographs the inner wall surface Wc with the imaging device 20.

[0021] Here, an example of the relationship between the background region RB of the illumination device 10 and the through hole WT of the workpiece W will be described. Fig. 2 shows a schematic ZX cross section of the illumination device 10 and the imaging device 20 when the workpiece W is placed between them. For simplicity, it is assumed here that the upper surface Wa and the lower surface Wb of the workpiece W are parallel to the XY plane, and that in a cross section including the central axis of the through hole WT, the inner wall surface Wc is perpendicular to the lower surface Wb.

[0022] A dotted line FV in Fig. 2 typically indicates the field of view of the imaging device 20. As can be seen from Fig. 2, the field of view of the imaging device 20 includes not only the through hole WT of the workpiece W, but also a part of the illumination device 10 that is visible through the through hole WT, and a part of the upper surface Wa of the workpiece W that is located outside the second opening W2 of the through hole WT.

[0023] 2 is a schematic diagram showing an example in which the upper surface 10a of the lighting device 10 includes both the first light-emitting region R1 and the background region RB. As shown by the dashed line BL in FIG. 2, the background region RB can be defined as a region of a part of the lighting device 10, for example, a region cut out by a cone (Cone) having a vertex at the position of the principal point 22p of the lens 22 of the imaging device 20 and contacting the first opening W1 of the through hole WT (i.e., one of the two openings of the through hole WT that is closer to the lighting device 10). For example, when the through hole WT is a cylindrical space, the background region RB is a disk region on the upper surface 10a of the lighting device 10 cut out by a cone having a vertex at the position of the principal point 22p of the lens 22 and a side surface contacting the first opening W1 of the through hole WT. When the lens 22 is a compound lens, "the position of the principal point 22p of the lens 22" in this specification means the position of the principal point of a single thin lens when the compound lens is replaced with an equivalent thin lens.

[0024] 2, in the embodiment of the present invention, the first light-emitting region R1 is located outside the background region RB. As described later, the background region RB may be a part of the light-emitting surface of the lighting device 10, or may be a part of the lighting device 10 that does not emit light. Note that, in the radial direction, the innermost part of the first light-emitting region R1 does not need to coincide with the outer edge of the background region RB.

[0025] <4. Example of defect detection by image processing device 30> 3 shows an example of an image captured by the imaging device 20. In the example shown in FIG. 3, the disk region Db inside the first opening W1 corresponds to the above-mentioned background region RB. The inner wall surface Wc of the through hole WT of the workpiece W is shown as the outer annular region Dc. The region Da further outside the region Dc corresponds to the top surface Wa of the workpiece W.

[0026] In the image captured by the imaging device 20, the region Dc between the outermost region Da and the disk region Db is expressed as a relatively bright region because the inner wall surface Wc of the through hole WT is illuminated by the light from the first light-emitting region R1. In contrast, for example, when the background region RB of the illumination device 10 is black, the disk region Db corresponding to the background region RB is expressed as dark in the image as shown diagrammatically by shading in Fig. 3. The region Da outside the region Dc corresponding to the inner wall surface Wc is also expressed as relatively dark, similar to the disk region Db.

[0027] In the image of the workpiece W, a defect on the inner wall surface Wc is represented as a dark or bright spot in an area Dc corresponding to the inner wall surface Wc. In the example shown in Fig. 3, a dark spot De1 indicating a foreign object on the inner wall surface Wc is captured in the area Dc which is represented relatively brightly. Therefore, it can be said that it is possible to determine whether or not a defect exists on the inner wall surface Wc which defines the through hole WT of the workpiece W by detecting a dark spot (or a bright spot) in the image acquired by the imaging device 20.

[0028] However, if dust or other foreign matter is floating within the range of the angle θ formed by the broken line BL shown in FIG. 2, such foreign matter that is not on the inner wall surface Wc of the through hole WT is also expressed as a dark spot or a bright spot on the disk region Db in the image acquired by the imaging device 20. Similarly, if a foreign matter is attached to the background region RB of the lighting device 10 or a scratch occurs in the background region RB, a similar dark spot or bright spot will appear in the image. In the example shown in FIG. 3, a bright spot De2 indicating such a foreign matter or scratch is captured on the disk region Db. Therefore, simply detecting a dark spot or bright spot in the acquired image may result in picking up a foreign matter such as dust that is not on the inner wall surface Wc as a defect. In other words, "excessive detection" occurs, in which a non-defective product is determined to be defective. Therefore, in this embodiment, the image processing device 30, which receives image data from the imaging device 20, detects the boundary between the area Db corresponding to the background area RB and the area Dc corresponding to the inner wall surface Wc using a boundary detection unit 32, and selectively extracts features located in the area Dc from among the image features (e.g., dark spots) representing foreign objects or defects using a defect detection unit 34.

[0029] The boundary detection unit 32 of the image processing device 30 detects the boundary between the background region RB and the inner wall surface Wc based on at least one difference in hue and brightness in an image related to the workpiece W as shown in FIG. 3. When an image as shown in FIG. 3 is acquired, for example, when a binarization process is performed on the acquired image data, the region Db corresponding to the background region RB is displayed in black, and the region Dc corresponding to the inner wall surface Wc is displayed in white. That is, the position of the first opening W1 of the through hole WT can be detected as a zero cross point regarding brightness. The position of the second opening W2 of the through hole WT can also be detected based on the change in brightness in the image.

[0030] If the background region RB is a chromatic color, a color image may be acquired by the imaging device 20. As in the example shown in FIG. 3, the region Dc corresponding to the inner wall surface Wc of the through hole WT appears bright, while the region Da corresponding to the top surface Wa of the workpiece W appears dark. In the case of a color image, the disk region Db corresponding to the background region RB is represented in a chromatic color in the image. In this case, the boundary between the region Db corresponding to the background region RB and the region Dc (represented in white, for example) corresponding to the inner wall surface Wc can be detected from a change in hue.

[0031] The defect detection unit 34 of the image processing device 30 detects defects on the inner wall surface Wc by utilizing the boundary detection result by the boundary detection unit 32. Prior to detecting defects on the inner wall surface Wc, the boundary detection unit 32 or the defect detection unit 34 may perform preprocessing as described below on the image acquired by the imaging device 20.

[0032] Fig. 4 shows a schematic example of pre-processing by the image processing device 30. For example, the boundary detection unit 32 extracts a ring-shaped region Dc on the image by detecting the boundary between the background region RB and the inner wall surface Wc, and then maps the region Dc to a rectangular region Dd as shown in Fig. 4 by appropriate coordinate transformation.

[0033] As shown in FIG. 4, in mapping from the region Dc to the rectangular region Dd, the dark point De1 on the region Dc is also mapped onto the rectangular region Dd by coordinate conversion. Thereafter, the defect detection unit 34 detects whether or not a defect exists on the inner wall surface Wc by detecting a dark point (or a bright point) on the rectangular region Dd. The defect detection unit 34 detects the dark point De1 mapped onto the rectangular region Dd by an appropriate method, and determines that a defect exists on the inner wall surface Wc by detecting the dark point De1. When a defect on the inner wall surface Wc is found by the defect detection unit 34, the appearance inspection system 1 may inform a user of the appearance inspection system 1 of the presence of the defect by, for example, displaying the position of the defect on a display device not shown in FIG. 1.

[0034] On the other hand, the bright point De2 on the disk region Db is not transferred onto the rectangular region Dd by the above-mentioned coordinate conversion, and is not subject to detection by the defect detection unit 34. In other words, it is possible to avoid detecting a foreign object that is not on the inner wall surface Wc as a defect on the inner wall surface Wc.

[0035] Alternatively, the boundary detection unit 32 may specify the position and range of the disk region Db in the image by detecting the boundary between the background region RB and the inner wall surface Wc. In this case, the defect detection unit 34 can actively ignore image features (e.g., bright point De2 in FIG. 4) representing foreign matter or defects even if they are found within the range of the disk region Db, based on the analysis results by the boundary detection unit 32. In other words, even if features that seem to be foreign matter or defects are found, if they are determined to be located within the background region RB, the detection results can be ignored (or discarded), thereby avoiding the occurrence of "excessive detection."

[0036] In this way, according to the embodiment of the present invention, the boundary between the region Db corresponding to the background region RB and the region Dc corresponding to the inner wall surface Wc of the through hole WT can be detected based on the difference in at least one of the hue and brightness in the image acquired by the imaging device 20, for example, by image processing. Therefore, it is relatively easy to selectively extract the region Dc corresponding to the inner wall surface Wc from the image of the workpiece W, or to specify the range of the region Db corresponding to the background region RB. By extracting the region Dc corresponding to the inner wall surface Wc or the region Db corresponding to the background region RB, features on the image that are likely to be foreign objects or defects and that are outside the region Dc can be eliminated, and "overdetection" can be avoided, thereby improving the detection accuracy of defects.

[0037] <5. Configuration Example of Illumination Device 10> 5 and 6 show a first example of the lighting device 10. Fig. 6 corresponds to a cross-sectional view taken along line VI-VI in Fig. 5.

[0038] The lighting device 10A shown in Fig. 5 and Fig. 6 has a columnar housing 12A, a plurality of light sources 14, and a support 18 that supports the housing 12A. In the example shown in Fig. 5 and Fig. 6, the housing 12A has a hollow cylindrical shape having a through hole 12T along a central axis parallel to the Z direction in the figure. As shown in Fig. 6, the plurality of light sources 14 are accommodated inside a recess 12s provided in the housing 12A. For example, an LED can be used as each of the plurality of light sources 14.

[0039] In the configuration illustrated in Fig. 6, the multiple light sources 14 are covered by a diffusion plate 16A. In the example illustrated in Fig. 5 and Fig. 6, the upper surface 16a of the diffusion plate 16A forms a ring-shaped light-emitting surface when viewed from above. That is, here, the first light-emitting region R1 has a ring shape. In this manner, the illumination device 10 of the visual inspection system 1 may be a so-called ring light.

[0040] As can be seen from Fig. 5 and Fig. 6, in this example, a part of the upper surface 18a of the support 18, which is located on the opposite side to the first light-emitting region R1 and supports the housing 12A, appears inside the through-hole 12T of the housing 12A. As shown typically by hatching in Fig. 5, all or a part of the part of the upper surface 18a of the support 18 that appears inside the through-hole 12T of the housing 12A is colored black or a chromatic color, thereby constituting the above-mentioned background region RB. For example, a sticker of any color may be affixed to the area of ​​the upper surface 18a of the support 18 that appears inside the through-hole 12T, or the area may be painted in any color.

[0041] By making the inside of the through hole 12T a non-luminous region, particularly a black or chromatic region, when viewed from the imaging device 20 toward the lighting device 10A, it is possible to make the hue and / or brightness of the region Db (see FIG. 3) corresponding to the background region RB in the image acquired by the imaging device 20 different from that of the region Dc corresponding to the inner wall surface Wc. Note that it is not essential that the entire portion of the upper surface 18a of the support 18 that appears inside the through hole 12T of the housing 12A is black or chromatic. As shown in FIG. 7, a part of the portion of the upper surface 18a of the support 18 that appears inside the through hole 12T may be the background region RB. The inner diameter of the through hole 12T may be larger than the outer diameter of the background region RB.

[0042] As shown in FIG. 5, here, the first light-emitting region R1 has a ring shape surrounding the background region RB. By having the first light-emitting region R1 have a shape surrounding the background region RB, it is possible to more reliably introduce light from the first opening W1 into the through-hole WT while making the background region RB a non-light-emitting region. Here, the "ring shape" in this specification is not limited to a continuous shape without a break, and may be a shape including a plurality of parts arranged intermittently. In addition, the "ring shape" in this specification is not limited to a circular ring shape, and may have an outline such as a distorted circle, a polygon, or an indefinite shape.

[0043] Furthermore, in this example, the multiple light sources 14 are covered with a diffusion plate 16A. That is, when the imaging device 20 acquires an image of the inner wall surface Wc, the illumination device 10A irradiates the inner wall surface Wc of the through hole WT of the workpiece W with diffused light. When the light from the first light-emitting region R1 is diffused light, the inner wall surface Wc of the through hole WT can be illuminated more effectively. In this manner, the illumination device 10 of the visual inspection system 1 may include a diffused light source.

[0044] Fig. 8 shows a second example of the lighting device 10. The lighting device 10B shown in Fig. 8 includes a light source device 15 having a housing 12B, a plurality of light sources 14, and a diffusion plate 16B that covers these light sources 14. The housing 12B of the light source device 15 has a recess 12s for accommodating the light source 14 therein, similar to the housing 12A of the lighting device 10A described with reference to Figs. 5 to 7, and supports the diffusion plate 16B above the light source 14. However, unlike the housing 12A of the lighting device 10A described above, the housing 12B does not have a through hole penetrating through the center thereof.

[0045] The housing 12B has, for example, a rectangular parallelepiped or cylindrical shape. The upper surface 16a of the diffusion plate 16B has a rectangular or circular shape according to the shape of the housing 12B when viewed from above. The upper surface 16a of the diffusion plate 16B constitutes the upper surface of the light source device 15, and the light source device 15 functions as a surface-emitting diffuse light source. In this example, the illumination device 10B does not have a support 18 that supports the housing 12B. The illumination device 10B may have a support 18.

[0046] In the configuration illustrated in FIG. 8, the lighting device 10B further includes a filter member 17 disposed on the upper surface 16a of the diffusion plate 16B. The surface of the filter member 17 is black or chromatic. The shape of the filter member 17 when viewed in the Z direction in the figure is, for example, a disk shape. The filter member 17 covers a part of the upper surface 16a of the diffusion plate 16B, and when the upper surface 16a has, for example, a circular shape when viewed from above, the part of the upper surface 16a exposed from the filter member 17 forms a ring-shaped first light-emitting region R1 surrounding the filter member 17. In other words, the upper surface of the light source device 15 includes the first light-emitting region R1 in a part thereof.

[0047] FIG. 9 is a schematic diagram showing the relationship between the field of view of the imaging device 20 and the background region RB of the illumination device 10B as viewed through the through hole WT of the workpiece W. As can be seen from FIG. 9, the area of ​​the upper surface 17a of the filter member 17 between two imaginary lines (broken lines BL in FIG. 9) connecting the principal point 22p of the lens 22 and the first opening W1 of the through hole WT in a cross-sectional view corresponds to the background region RB of the illumination device 10B. It can also be said that the entire area of ​​the upper surface 17a of the filter member 17 that can be seen inside the first opening W1 of the workpiece W when the filter member 17 is viewed through the through hole WT of the workpiece W from the upper surface Wa side of the workpiece W is the background region RB of the illumination device 10B. In this sense, it is not necessary for the entire upper surface 17a of the filter member 17 to be the background region RB, and it is sufficient that at least a part of the upper surface 17a functions as the background region RB.

[0048] In the lighting device 10B, the first light-emitting region R1 is located outside the background region RB, similarly to the lighting device 10A described as the first example. That is, by emitting light from the first light-emitting region R1 toward the workpiece W, the inner wall surface Wc of the through hole WT can be illuminated from an oblique direction with diffused light, for example, in the same manner as in the case where the above-mentioned lighting device 10A is applied.

[0049] In the image acquired by the imaging device 20, the inner wall surface Wc of the through hole WT is illuminated with light from the first light-emitting region R1 and is thus represented as a bright region, whereas the background region RB is represented as a relatively dark region by, for example, coloring the surface (particularly the upper surface 17a) of the filter member 17 black. That is, even when the illumination device 10B shown in FIG. 8 is applied, the boundary between the background region RB and the inner wall surface Wc of the through hole WT can be detected by utilizing, for example, a difference in brightness in the image, as in the case of applying the illumination device 10A. If the surface of the filter member 17 is a chromatic color, the boundary between the background region RB and the inner wall surface Wc of the through hole WT can be similarly detected by utilizing a difference in hue in the image.

[0050] The filter member 17 may be a light-shielding member, because it is possible to make the region Db (see FIG. 3) corresponding to the background region RB a relatively dark region in the image acquired by the imaging device 20. In this sense, the filter member 17 does not need to be a member that completely blocks light, and some light transmission is permitted.

[0051] For example, a colored tape having a sufficient thickness can be used as the filter member 17. Alternatively, a coating film obtained by applying a black or chromatic paint to a part of the light-emitting surface of the light source device 15 may be used as the filter member 17. Note that the filter member 17 may be a member that covers the entire upper surface 16a of the diffusion plate 16B and includes a light-shielding portion and a light-transmitting portion.

[0052] <6. Modification Examples> In a typical embodiment of the present invention, the lighting device 10 has an upper surface including at least a first region that emits light and a second region of black or chromatic color surrounded by the first region. For example, by arranging a member colored in a color different from the light-emitting surface of the lighting device 10 in the lighting device 10 to form a second region in the lighting device 10, a difference in brightness or color can be intentionally generated between the region Db appearing inside the first opening W1 of the through hole WT of the workpiece W and the region Dc corresponding to the inner wall surface Wc of the through hole WT in the image acquired by the imaging device 20. The specific size and shape of the background region RB of the lighting device 10 may be appropriately determined according to the expected geometric properties of the workpiece W, the angle of view of the imaging device 20, the arrangement of the workpiece W in the appearance inspection system 1, and the like.

[0053] 1, the workpiece W is disposed between the lighting device 10 and the imaging device 20 at a distance from the lighting device 10. The distance from the lighting device 10 to the bottom surface Wb of the workpiece W is, for example, about 30 mm. When the distance from the top surface 10a of the lighting device 10 to the bottom surface Wb of the workpiece W is particularly small, the size of the background region RB becomes approximately equal to the region obtained by vertically projecting the first opening W1 of the through hole WT onto the lighting device 10 in the Z direction in the figure.

[0054] The light-emitting surface of the lighting device 10 is not limited to being parallel to the bottom surface Wb of the workpiece W, and may be inclined with respect to the bottom surface Wb of the workpiece W. The angle of inclination is, for example, in the range of 0 degrees or more and less than 90 degrees. By inclining the light-emitting surface of the lighting device 10 with respect to the through hole WT, the inner wall surface Wc of the through hole WT can be more effectively illuminated, and the boundary between the background region RB and the inner wall surface Wc of the through hole WT can be made clearer. In other words, it is possible to more effectively avoid "excessive detection."

[0055] In the example shown in Fig. 1, the workpiece W is disposed between the illumination device 10 and the imaging device 20 with a gap therebetween from the imaging device 20. The distance from the imaging device 20 to the top surface Wa of the workpiece W depends on the angle of view of the imaging device 20 and the thickness of the workpiece W (which may be said to be the depth of the through-hole WT). The thickness TH of the workpiece W (see Fig. 2) is, for example, in the range of about 15 mm. The diameter DM of the through-hole WT (see Fig. 2) is, for example, about 9 mm.

[0056] As described above, in the image acquired by the imaging device 20, the area Da corresponding to the upper surface Wa of the workpiece W is expressed darker than the area Dc corresponding to the inner wall surface Wc of the through hole WT of the workpiece W (see FIG. 3). Therefore, similar to the detection of the boundary between the area Dc and the disk area Db corresponding to the background area RB, the boundary between the area Dc and the area Da corresponding to the upper surface Wa of the workpiece W can also be detected. That is, according to the embodiment of the present invention, even if a bright spot (or a dark spot) caused by a foreign object or a scratch on the upper surface Wa of the workpiece W exists in the area Da, it is possible to determine whether the bright spot is on the area Dc or the area Da, so that the bright spot can be actively ignored as not being a defect on the inner wall surface Wc. For example, after detecting the boundary between the area Dc and the area Da corresponding to the upper surface Wa of the workpiece W, the pixel value of the area Da may be "painted" to a constant value. By masking the areas other than the area Dc corresponding to the inner wall surface Wc in this manner, it is possible to avoid mistakenly detecting defects that are not on the inner wall surface Wc as defects on the inner wall surface Wc.

[0057] In addition, since the distance between the lighting device 10 and the workpiece W is relatively small, even in the presence of external light such as general lighting, the area Da corresponding to the top surface Wa of the workpiece W usually appears darker than the area Dc corresponding to the inner wall surface Wc. It goes without saying that the appearance inspection system 1 may further be provided with a member such as a plate or cover that blocks external light.

[0058] In detecting the boundary between regions, for example, instead of directly adopting the contour obtained by calculating the change in adjacent pixel values, the boundary between regions may be determined by fitting to a reference figure. When the first opening W1 and / or the second opening W2 of the through hole WT have a shape with good symmetry, such as a circle, the shape of the opening may be fitted by an approximation circle, a minimum circumscribing circle, or a maximum inscribing circle. By appropriately using the approximation circle, the minimum circumscribing circle, and the maximum inscribing circle, for example, it becomes possible to detect chips and / or burrs that occur on the edge of the opening.

[0059] The specific method of detecting the boundary between the inner wall surface Wc and the background region RB, and the boundary between the inner wall surface Wc and the upper surface Wa of the workpiece W is not limited to the detection of the zero crossing point of the brightness, and various methods can be applied. Boundary detection may be performed by the difference in pixel values ​​between adjacent pixels, the absolute value of the gradient of the pixel value, the position of the zero crossing point of the second derivative of the pixel value, etc. When a color image is acquired, boundary detection may be performed for each RGB component, for example. Alternatively, the boundary may be detected by applying an edge filter. Edge enhancement or the like may be applied to the image as a preprocessing for boundary detection. The detection of defects by the defect detection unit 34 is also not limited to a specific method. The function of the defect detection unit 34 may be realized by detection using image segmentation, machine learning (for example, supervised learning or unsupervised learning), etc.

[0060] The image processing device 30 of the visual inspection system 1 typically has a calculation device such as a CPU and one or more memories. Other examples of the calculation device are a Graphics Processing Unit (GPU), an Application Specific Integrated Circuit (ASIC), a Simple Programmable Logic Device (SPLD), a Complex Programmable Logic Device (CPLD), and a Field Programmable Gate Array (FPGA). Examples of the memory are a Random Access Memory (RAM) and a Solid State Drive (SSD). The functions of the image processing device 30 may be realized by hardware resources, or may be realized by a combination of software held in the memory and hardware resources.

[0061] This specification also discloses a method for producing image data for inspection, which includes a step (a) of photographing an object to be inspected having a through hole by irradiating an inner wall surface defining the through hole with light from a first opening on one side of the through hole while photographing the object to be inspected so that an area visible inside the first opening when viewed from a second opening on the other side of the through hole appears black or chromatic, and an inspection method which includes the step (a) and a step (b) of selectively detecting defects on the inner wall surface by detecting a boundary between a first area corresponding to the inner wall surface of the through hole and a second area surrounded by the first area based on a difference in at least one of hue and brightness in the image of the object to be inspected.

[0062] Various embodiments of the present invention have been described above, but these are presented as examples and are not intended to limit the scope of the invention. The novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. The embodiments and modifications thereof are included in the scope and spirit of the invention, and are included in the scope of the invention and its equivalents described in the claims. [Explanation of symbols]

[0063] 1: visual inspection system, 10, 10A, 10B: lighting device, 10a: top surface, 12A, 12B: housing, 12T: through hole, 14: light source, 15: light source device, 17: filter member, 17a: top surface, 18: support, 18a: top surface, 20: imaging device, 22: lens, 22p: principal point, 30: image processing device, 32: boundary detection unit, 34: defect detection unit, R1: first light-emitting region, RB: background region, W: workpiece, W1: first opening, WT: through hole, Wc: inner wall surface

Claims

1. A visual inspection system, comprising: A lighting device having a first light-emitting region and a black or chromatic background region surrounded by the first light-emitting region; an imaging device including a lens and disposed opposite the illumination device; an image processing device including a boundary detection unit and a defect detection unit; Equipped with The imaging device acquires an image of an inspection object that is disposed between the illumination device and the imaging device and has a through hole; the boundary detection unit detects a boundary between the background region and an inner wall surface of the through hole based on a difference in at least one of a hue and a brightness in an image of the object to be inspected acquired by the imaging device; The defect detection unit detects defects on the inner wall surface.

2. The visual inspection system according to claim 1, The lighting device includes: A columnar housing having a through hole along a central axis; A plurality of light sources housed in the housing; a support member positioned on an opposite side to the first light-emitting region and supporting the housing; Contains A system, wherein the background area is at least a portion of the surface of the support that appears inside the through hole of the housing.

3. The visual inspection system according to claim 1, The lighting device includes: a light source device having an upper surface including the first light-emitting region as a part thereof; a filter member having a black or chromatic surface, the filter member being disposed on the upper surface of the light source device to cover at least a portion of the upper surface; Contains The background region is at least a portion of the surface of the filter member.

4. The visual inspection system according to any one of claims 1 to 3, The system wherein the first light-emitting region is a ring surrounding the background region.

5. The visual inspection system according to any one of claims 1 to 3, The illumination device illuminates the inner wall surface of the through hole of the object to be inspected, which is disposed between the illumination device and the imaging device, with diffused light.

6. The visual inspection system according to any one of claims 1 to 3, A system in which the background area is defined as an area of ​​the lighting device that is cut out by a cone whose vertex is the position of the principal point of the lens and which is tangent to the opening of the through hole on the lighting device side when the object to be inspected is placed between the lighting device and the imaging device.

Images