Appearance inspection apparatus

Abstract

To provide a technique capable of shortening inspection time in inspection of an object including portions having different surface inclinations.SOLUTION: An appearance inspection apparatus for inspecting the appearance of an object includes: a plurality of light sources arranged concentrically to irradiate the object with light; a plurality of wall parts surrounding the light sources concentrically; a control unit for controlling irradiation of light from each of the light sources; an imaging unit for acquiring an image taken of an object in a state where light sources positioned closer to the center of the concentric circles emit light with higher illumination intensity; and a determination unit for determining the presence or absence of an abnormality in the appearance of the object using luminance values of the different pixels in the image.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a visual inspection apparatus. [Background technology]

[0002] Conventionally, there has been known a technique for inspecting the appearance of an object by capturing an image of light reflected from the object upon irradiating the object with light. For example, Patent Document 1 discloses an inspection system including an inspection illumination device and an imaging device, in which a first light-shielding mask, a second light-shielding mask, a lens, and a half mirror are arranged along the direction in which light irradiated from a surface light source travels. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-180621 Summary of the Invention [Problem to be solved by the invention]

[0004] When inspecting the appearance of an object, it is necessary to align the object with high precision so that the imaging device can receive light reflected from the object's surface. However, if the object's surface includes areas with different slopes, aligning each of these areas separately may result in a long inspection time. Furthermore, there is room for improvement in shortening the inspection time by simultaneously inspecting such areas with different slopes. Note that Patent Document 1 does not take into consideration the inspection of objects with surfaces that include areas with different slopes.

[0005] The present invention has been made to solve at least part of the above-mentioned problems, and aims to provide a technology that can shorten the inspection time when inspecting an object whose surface includes areas with different slopes. [Means for solving the problem]

[0006] The present invention has been made to solve at least part of the above-mentioned problems, and can be realized in the following aspects.

[0007] (1) According to one aspect of the present invention, there is provided an appearance inspection device for inspecting the appearance of an object, the appearance inspection device including: a plurality of light sources arranged concentrically and irradiating light onto the object; a plurality of walls concentrically surrounding each of the light sources; a control unit controlling the irradiation of light from each of the light sources; an imaging unit capturing an image of the object in a state in which the light sources located closer to the center of the concentric circles irradiate light with higher illumination intensity; and a determination unit using the luminance value of each pixel in the image to determine whether or not there is an abnormality in the appearance of the object.

[0008] According to this configuration, light emitted from each of the light sources concentrically surrounded by the wall sections is multiple-reflected by the walls surrounding the light source before being emitted outside the wall sections. Therefore, these light sources can be considered to form a circular surface light source. In other words, according to this configuration, a circular surface light source can emit uniform circular light. The inventors have also previously proposed an invention for an appearance inspection device that enables simultaneous inspection of areas with different surface slopes by acquiring a brightness-integrated image (Patent Application No. 2023-040568). However, the present invention can acquire an image equivalent to a brightness-integrated image in a shorter time. While the proposed invention creates a brightness-integrated image using images prepared by multiple captures, the present invention can acquire an image equivalent to a brightness-integrated image with a single capture, thereby shortening the inspection time when inspecting an object with areas with different surface slopes.

[0009] (2) According to another aspect of the present invention, there is provided an appearance inspection device for inspecting the appearance of an object, the appearance inspection device comprising: a display capable of illuminating all or part of the screen; a control unit capable of adjusting the illumination intensity of each part of the screen; an imaging unit that captures an image of the object while the display is irradiating the screen with light at a higher illumination intensity at a position closer to the center of the screen; and a determination unit that determines whether or not there is an abnormality in the appearance of the object using the luminance value of each pixel in the image.

[0010] According to this configuration, when inspecting an object whose surface includes portions with different slopes, it is possible to obtain an image equivalent to a brightness integrated image, which enables simultaneous inspection of those portions. Therefore, it is possible to perform simultaneous inspection of portions with different slopes. Furthermore, according to this configuration, while a brightness integrated image is created using images prepared by capturing images multiple times, an image equivalent to a brightness integrated image can be created with a single capture, thereby reducing the inspection time when inspecting an object whose surface includes portions with different slopes.

[0011] (3) In the visual inspection device of the above aspect, the determining unit may determine whether or not there is an abnormality in the visual appearance of the object using a normalized luminance value obtained by normalizing the luminance value of each pixel in the image. When an object is covered with machining oil, the intensity of light reflected from the object decreases, which tends to decrease the luminance values ​​of the pixels that make up the object in an image captured of the object. According to this configuration, the normalized luminance values ​​obtained by normalizing the luminance values ​​of each pixel are used to determine whether the object has an abnormal appearance. Therefore, the luminance values ​​of the pixels that make up the object that is covered with machining oil or has machining oil partially attached in the captured image are corrected by normalization, making it possible to inspect the object's appearance while reducing the effects of the machining oil.

[0012] The present invention can be realized in various forms, for example, in the form of an appearance inspection device, an appearance inspection system, an appearance inspection method, a method for controlling appearance inspection operations, a computer program for executing these devices and methods, a server device for distributing this computer program, a non-transitory storage medium on which a computer program is stored, etc. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is an explanatory diagram illustrating the configuration of a visual inspection apparatus according to a first embodiment. [Figure 2] 3A to 3C are explanatory views showing cross sections of the light source unit. [Figure 3] FIG. 1 is an explanatory diagram illustrating an example of an object to be inspected by a visual inspection device. [Figure 4] 10A and 10B are explanatory diagrams for explaining advantages of the light source unit having a wall portion. [Figure 5] FIG. 10 is an explanatory diagram of a visual inspection device of a comparative example. [Figure 6] FIG. 10 is an explanatory diagram illustrating a case where an image of a concave mirror, which is an example of an object, is captured. [Figure 7] 10A and 10B are explanatory diagrams of a luminance integrated image and an image. [Figure 8] FIG. 10 is an explanatory diagram of a method for determining whether or not an object has an abnormality in its appearance. DETAILED DESCRIPTION OF THE INVENTION

[0014] First Embodiment FIG. 1 is an explanatory diagram illustrating the configuration of a visual inspection apparatus 1 according to a first embodiment of the present invention. FIG. 1 illustrates mutually orthogonal X, Y, and Z axes. The X axis corresponds to the direction of light emitted from a light source unit 5 (described later), and the Y and Z axes correspond to directions orthogonal to the X axis. These X, Y, and Z axes are common to all figures subsequent to FIG. 1. The visual inspection apparatus 1 is an apparatus for inspecting the appearance of an object OB. In other words, the visual inspection apparatus 1 is an apparatus for determining whether or not there are any abnormalities, such as chips, dents, or dents, in the appearance of the object OB. The visual inspection apparatus 1 includes a light source unit 5, a plano-convex lens 40, a half mirror 50, a camera 60, and a control unit 70. In FIG. 1, an optical axis AX indicates the optical axis of the light source unit 5.

[0015] FIG. 2(A) shows a cross section of the light source unit 5 taken along line F2A-F2A in FIG. 1. FIG. 2(B) shows a cross section of the light source unit 5 taken along line F2B-F2B in FIG. 2(A). As shown in FIG. 1, the light source unit 5 is a unit in which a plate-shaped member 10, a wall member 20, and a diffusion member 30 are stacked in the X-axis direction. As shown in FIG. 2(B), light sources 11-15 that irradiate light onto the object OB are arranged on the surface of the plate-shaped member 10 facing the +X-axis direction. In detail, as shown in FIG. 2(A), when viewed from the +X-axis direction, one light source 11 is arranged in the center, and multiple light sources 12 are arranged in a circle surrounding the light source 11. Furthermore, multiple light sources 13 are arranged in a circle surrounding the multiple light sources 12. Similarly, multiple light sources 14 are arranged in a circle surrounding the multiple light sources 13, and multiple light sources 15 are arranged in a circle surrounding the multiple light sources 14. That is, the light sources 12 to 15 are arranged concentrically on the surface of the plate-shaped member 10 facing the +X-axis direction. In this embodiment, each of the light sources 11 to 15 is an LED that emits light at a constant illumination intensity, and the light source closer to the center of the concentric circle emits light at a higher illumination intensity. Illumination intensity refers to the intensity of light emitted from a light source, and is expressed in units of luminous flux (lumens: lm). In this embodiment, the light source 11 is arranged at the center of the concentric circle. In this embodiment, if the illumination intensity of light emitted from light source 15 is 1x intensity, the illumination intensity of light emitted from light source 14 is 2x intensity, the illumination intensity of light emitted from light source 13 is 3x intensity, the illumination intensity of light emitted from light source 12 is 4x intensity, and the illumination intensity of light emitted from light source 11 is 5x intensity.

[0016] As shown in FIG. 2(A), the wall member 20 includes wall portions 21-25 that concentrically surround the light sources 11-15 when viewed from the +X-axis direction. Each of the wall portions 21-25 is formed to surround the light sources 11-15 when viewed from the +X-axis direction, and extends along the X-axis direction (see FIG. 2(B)). In detail, each of the wall portions 21-24 is formed in a circular shape when viewed from the +X-axis direction, and is arranged to surround the light sources 11-14. The wall portion 25 is formed in a rectangular parallelepiped shape having a cylindrical through-hole (a space in which the light sources 11-15 and the wall portions 21-24 are arranged) in the center when viewed from the +X-axis direction, and is arranged to surround the light source 15. In other words, the light sources 11-15 are arranged in five concentric circles by each of the wall portions 21-25. The diffusion member 30 diffuses the light emitted from the light sources 11-15. In addition, in FIGS. 2(A) and 2(B), the wall portions 21 to 24 are cross-sectional views and should be shown by hatching, but for convenience of illustration, hatching has been omitted.

[0017] 1, the plano-convex lens 40 is disposed in the X-axis direction between the light source unit 5 and a half mirror 50 (described later). The plano-convex lens 40 collects light emitted from the light sources 11 to 15 via the diffusing member 30. The half mirror 50 is disposed in the X-axis direction between the plano-convex lens 40 and a position where the object OB is disposed. The half mirror 50 transmits a portion of the light emitted from the light sources 11 to 15 via the diffusing member 30 toward the object OB, and reflects a portion of the light reflected from the object OB toward a camera 60 (described later).

[0018] The camera 60 is an imaging unit that captures light reflected from the object OB to obtain an image of the object OB. A telecentric lens 62 attached to the camera 60 transmits only light parallel to the optical axis of the telecentric lens 62 to the camera 60. The control unit 70 is a computer including a ROM, a RAM, and a CPU, and performs various controls of the appearance inspection apparatus 1. For example, the control unit 70 controls the irradiation of light from each of the light sources 11 to 15. The control unit 70 is also capable of receiving the image captured by the camera 60.

[0019] FIG. 3 is an explanatory diagram showing an example of an object OB inspected by the visual inspection apparatus 1. The object OB shown in FIG. 3 includes portions with different inclinations on its surface. Specifically, the surface of the object OB facing the −X-axis direction includes surfaces S0 to S3. Surface S1 is an inclined surface inclined at an angle of 1° with respect to surface S0. Surfaces S2 and S3 are inclined surfaces inclined at angles of 2° and 3° with respect to surface S0, respectively. In other words, these surfaces S1 to S3 correspond to portions with different inclinations included on the surface of the object OB. Furthermore, surfaces S2 and S3 correspond to portions with a relatively greater inclination than surface S1. In other words, surface S1 corresponds to a portion with a relatively smaller inclination than surfaces S2 and S3.

[0020] 4(A) to 4(C) are explanatory diagrams illustrating the advantages of the light source unit 5 including the wall portions 21 to 25. The configurations of the plate-shaped member 10, light sources 11 to 13, wall portions 21 to 23, and diffusing member 30 used in the explanation of FIGS. 4(A) to 4(C) are the same as those described above with the same reference numerals. The left side of FIGS. 4(A) to 4(C) shows the plate-shaped member 10 and the diffusing member 30 as viewed from the -Y-axis direction (the same perspective as in FIG. 1). The right side of FIGS. 4(A) to 4(C) shows the diffusing member 30 as viewed from the +X-axis direction. In FIGS. 4(A) and 4(B), the light sources 11 to 13 are arranged on the plate-shaped member 10, but the wall portions 21 to 23 are not. When light is emitted from the light sources 11 and 12 arranged in this manner, the outline of the light emitted from the diffusing member 30 has a shape of overlapping circles, as shown on the right side of FIG. 4(A). In such a shape, there is a difference in brightness between the overlapping portions of the circles and the non-overlapping portions of the circles, resulting in uneven brightness. Furthermore, when light is further irradiated from light source 13 in the state shown in Fig. 4(A), the outline of the light irradiated from diffusing member 30 approaches a circle, as shown on the right side of Fig. 4(B). However, even with the addition of light from light source 13, the outer edge of the light irradiated from diffusing member 30 does not become smooth, and the outline of the light irradiated from diffusing member 30 still has the shape of multiple overlapping circles, resulting in uneven brightness.

[0021] On the other hand, in FIG. 4(C), as in the visual inspection apparatus 1 described above, light sources 11-13 are arranged on a plate-like member 10, and each of the light sources 11-13 is covered by a wall portion 21-23. When light is emitted from such light sources 11-13, the outline of the light emitted from the diffusing member 30 becomes circular, as shown on the right side of FIG. 4(C). This is because the light emitted from each of the light sources 11-13, which are concentrically surrounded by the walls 21-23, is multiple-reflected by the walls 21-23 and then emitted outward from the walls 21-23. In other words, the light sources 11-13 can be considered to form a circular surface light source due to the arrangement of the walls 21-23. Similar to the configuration described in FIG. 4(C), in the visual inspection apparatus 1 described above, each of the light sources 11-15 is concentrically surrounded by the walls 21-25, and therefore the light sources 11-15 can be considered to form a circular surface light source. Such a surface light source emits uniform circular light.

[0022] 5 is an explanatory diagram of a comparative appearance inspection device 1p. The characteristic of the appearance inspection device 1 of this embodiment is that, while the comparative appearance inspection device 1p creates a brightness integrated image IN using images prepared by capturing images multiple times, the appearance inspection device 1 of this embodiment can create an image EQ equivalent to the brightness integrated image IN by capturing images only once. Details of the brightness integrated image IN and the image EQ will be described later with reference to FIG. 7.

[0023] In the appearance inspection device 1 of this embodiment, the light sources 11 to 15 emit light with a higher illumination intensity as they are positioned closer to the center of the concentric circles, whereas in the appearance inspection device 1p of the comparative example, the light sources 11 to 15 emit light with approximately the same illumination intensity regardless of their distance from the center of the concentric circles. That is, the configuration of the appearance inspection device 1p of the comparative example is apparently the same as the configuration of the appearance inspection device 1 of this embodiment, and only the illumination intensity of the light emitted from each of the light sources 11 to 15 is different. Note that, for convenience of illustration, the camera 60, telecentric lens 62, and control unit 70 are not shown in Figures 5(A) to 5(C).

[0024] Fig. 5(A) shows a state in which all light sources arranged inside wall 21 are illuminated. Fig. 5(B) shows a state in which all light sources arranged inside wall 23 are illuminated. Fig. 5(C) shows a state in which all light sources arranged inside wall 25 are illuminated.

[0025] In the comparative example, the control unit 70 (not shown in FIG. 5 ) controls the illumination outer diameters (see illumination outer diameters D1, D3, and D5 in FIG. 5 ) defined by the light emitted from each light source 11-15 to change the illumination angle θ of the light irradiated onto the object OB. As shown in FIG. 5 , the illumination angle θ increases as the illumination outer diameter increases. The imaging unit, a camera 60 (not shown in FIG. 5 ), captures images of the object OB when light is irradiated at each illumination outer diameter by capturing images of the light reflected from the object OB when light is irradiated at each illumination outer diameter. Note that when multiple images of the object OB are acquired by changing the illumination outer diameter, the positional relationship between the camera 60 and the object OB is fixed. Even if the surface of the object OB includes portions with different inclinations, as shown in FIG. 3 , the larger the illumination angle θ of the light irradiated onto the object OB, the more easily the reflected light reflected from those portions is captured by the camera 60. In other words, the larger the illumination outer diameter of the image of the object OB that is irradiated with light, the lower the contrast of each pixel that constitutes the object OB in the image.

[0026] FIG. 6 is an explanatory diagram illustrating an image of a concave mirror CM, which is an example of an object OB. FIG. 6(A) shows a cross section of the concave mirror CM. The concave mirror CM includes a mirror portion MR and an enclosing member EC. The mirror portion MR has a concave surface CC formed by cutting out a portion of a spherical surface. The enclosing member EC is a member that encloses the mirror portion MR. The illumination outer diameter DS and illumination outer diameter DL shown in FIG. 6(A) exemplify the illumination outer diameter of the light irradiated onto the concave surface CC.

[0027] FIG. 6B is an explanatory diagram of five images 1D to 5D of reflected light 1R to 5R reflected from the concave surface CC when light is irradiated at different illumination outer diameters. Images 1D to 5D are images captured by a comparative visual inspection device 1p. Image 1D is an image of light reflected from the concave surface CC when light source 11 arranged inside wall 21 is irradiated. Image 2D is an image of light reflected from the concave surface CC when all light sources (light sources 11 and 12) arranged inside wall 22 are irradiated. Similarly, images 3D and 4D are images of light reflected from the concave surface CC when all light sources (light sources 11 to 13 and light sources 11 to 14) arranged inside wall 23 and wall 24 are irradiated, respectively. Image 5D is an image of light reflected from the concave surface CC when all light sources (light sources 11 to 15) arranged inside wall 25 are irradiated.

[0028] FIG. 6C is an explanatory diagram showing the brightness values ​​in the portion indicated by the dashed line d in images 1D to 5D. The horizontal axis in FIG. 6C represents the distance from the left edge of the image along the dashed line d. The vertical axis in FIG. 6C represents the brightness values ​​at each position on the dashed line d. Line segments L1 to L5 represent the brightness values ​​in the portion indicated by the dashed line d in images 1D to 5D. As described above, the larger the illumination angle θ (illumination outer diameter) of the light irradiated onto the object OB (here, the concave mirror CM), the more easily the reflected light reflected from portions with different inclinations can be captured by the camera 60. Referring to FIG. 6A, when the illumination angle θ of the light is small (for the illumination outer diameter DS), the camera 60 can only capture the reflected light reflected from the portion of the concave surface CC that is relatively inclined relative to the YZ plane (the central portion and portions near the center). On the other hand, when the illumination angle θ is large (when the illumination outer diameter is DL), camera 60 can capture not only the light reflected from the portion of concave surface CC that is relatively inclined relative to the YZ plane (the central portion and portions near the center), but also the light reflected from the portion that is relatively inclined relative to the YZ plane (the edge portion close to enclosure member EC). The range along the horizontal axis of line segments L1-L5 in Figure 6(C) can be considered to be the range on object OB that can capture such reflected light, with line segment L1 being the narrowest and line segment L5 being the widest of these ranges. That is, image 5D contains not only the brightness value information contained in image 1D, but also brightness value information due to reflected light reflected from portions with larger inclinations and different angles.

[0029] FIG. 7 is an explanatory diagram of the brightness-integrated image IN and image EQ described above. The brightness-integrated image IN is created using a group of images (e.g., images 1D to 5D) of an object OB captured when light is irradiated with different illumination outer diameters. Specifically, the brightness-integrated image IN is created by calculating a brightness integrated value by integrating the brightness values ​​of pixels constituting each position of the object OB for each of the images in the group of images, and then arranging each of the calculated brightness integrated values ​​corresponding to each position of the object OB. FIG. 7(A) illustrates an example of a brightness-integrated image IN created using images 1D to 5D shown in FIG. 6(B). The line segment LN shown in FIG. 7(B) represents the brightness integrated value at the portion indicated by the dashed line d in the brightness-integrated image IN of FIG. 7(A). The position of the dashed line d in the brightness-integrated image IN is the same as the position of the dashed line d in images 1D to 5D. The horizontal axis of FIG. 7(B) represents the distance from the left edge of the image along the dashed line d. The vertical axis in Figure 7(B) represents the brightness integrated value at each position on the dashed line d. As shown by the line segment LN, the brightness integrated value is higher at positions closer to the center along the horizontal axis, and lower at positions closer to the edges along the horizontal axis. The brightness integrated image IN is created by aggregating not only image 1D, which contains information on the brightness values ​​of light reflected from areas with relatively small slopes, but also image 5D, which contains information on the brightness values ​​of light reflected from areas with relatively large slopes. Therefore, by using the brightness integrated image IN, it is possible to simultaneously inspect areas of an object OB whose surface has different slopes.

[0030] FIG. 7C illustrates an example of image EQ. Image EQ is captured by the visual inspection device 1 of this embodiment. Image EQ is an image acquired by a single image capture by the camera 60 in a state where all light sources arranged inside the wall portion 25 are illuminated. In the visual inspection device 1 of this embodiment, the light sources 11 to 15 are LEDs that emit light at a constant illumination intensity, and light sources located closer to the center of the concentric circles emit light with a higher illumination intensity. Therefore, image EQ is an image of the object OB captured in a state where light sources located closer to the center of the concentric circles emit light with a higher illumination intensity. The line segment LQ shown in FIG. 7D represents the brightness value at the portion indicated by the dashed line d in image EQ of FIG. 7C. The position of dashed line d in image EQ is the same as the position of dashed line d in the brightness-integrated image IN. The horizontal axis of FIG. 7D represents the distance from the left edge of the image along dashed line d. The vertical axis of FIG. 7D represents the brightness value at each position on dashed line d. Similar to line segment LN (see FIG. 7B), line segment LQ has higher luminance values ​​at positions closer to the center along the horizontal axis, and lower luminance values ​​at positions closer to the edges along the horizontal axis. Comparing line segment LN in FIG. 7B with line segment LQ in FIG. 7D, it can be seen that the luminance-integrated image IN and image EQ have the same tendency for luminance distribution.

[0031] The reason why image EQ is equivalent to luminance-accumulated image IN will be explained. In luminance-accumulated image IN, the closer the reflected light originating from a light source located at the center of the concentric circle, the more times the luminance values ​​of that reflected light are integrated. Specifically, for example, in luminance-accumulated image IN of FIG. 7(A), the luminance values ​​of reflected light originating from light source 11 are integrated five times, the luminance values ​​of reflected light originating from light source 12 are integrated four times, the luminance values ​​of reflected light originating from light source 13 are integrated three times, and the luminance values ​​of reflected light originating from light source 14 are integrated twice. Note that only one luminance value of reflected light originating from light source 15 is reflected in luminance-accumulated image IN. On the other hand, image EQ is an image of object OB captured in a state in which light sources located closer to the center of the concentric circle emit light with higher illumination intensity. Therefore, in image EQ, the closer the reflected light originating from a light source located closer to the center of the concentric circle, the higher the luminance value of that reflected light. Furthermore, in the appearance inspection device 1 of this embodiment, if the illumination intensity of light irradiated from light source 15 is taken as 1x, then the illumination intensity of light irradiated from light source 14 is 2x, the illumination intensity of light irradiated from light source 13 is 3x, the illumination intensity of light irradiated from light source 12 is 4x, and the illumination intensity of light irradiated from light source 11 is 5x, and therefore it can be said that image EQ is equivalent to luminance integrated image IN. As described above, a characteristic of the appearance inspection device 1 of this embodiment is that it can create image EQ equivalent to luminance integrated image IN by capturing an image once, whereas the appearance inspection device 1p of the comparative example creates luminance integrated image IN using images prepared by capturing an image multiple times.

[0032] FIG. 8 is an explanatory diagram of a method for determining whether or not an external appearance of an object OB is abnormal. In the appearance inspection device 1 of this embodiment, the control unit 70 functions as a determination unit, determining whether or not an external appearance of the object OB is abnormal using the brightness value of each pixel in the image EQ captured by the camera 60. The details of this method are described below. First, the control unit 70 causes the camera 60 to capture an image of the object OB while each of the light sources 11 to 15 is emitting light, thereby receiving the image EQ from the camera 60. Next, the control unit 70 creates a difference image DF between the reference image ST (described later) and the image EQ. The reference image ST is an image of an object OB with no external abnormality, captured using the appearance inspection device 1 of this embodiment under conditions in which light sources located closer to the center of the concentric circles emit light with higher illumination intensity. The difference image DF is created by calculating the difference in brightness between pixels at the same position on the object OB in each of the reference image ST and the image EQ.

[0033] Next, the control unit 70 calculates the average brightness value of each pixel constituting the differential image DF, and then, as shown in the graph GR in FIG. 8, classifies pixels having brightness values ​​within the average value ±kσ (k is an arbitrary constant) as normal portions NM, and pixels having brightness values ​​not within the average value ±kσ as provisional abnormal portions AB. The graph GR is a histogram of the brightness values ​​of each pixel constituting the differential image DF. Next, the control unit 70 creates an extracted image EX by extracting only the pixels constituting the differential image DF that have been determined to be provisional abnormal portions AB. Next, the control unit 70 draws a rectangle circumscribing a portion of the extracted image EX consisting of the pixels determined to be provisional abnormal portions AB (two portions are shown in FIG. 8). If the shorter side SS of this rectangle is equal to or greater than a predetermined length, the control unit 70 determines that there is an abnormality in the appearance of the object OB. On the other hand, if the shorter side SS of this rectangle is shorter than the predetermined length, the control unit 70 determines that there is no abnormality in the appearance of the object OB. When using the brightness-accumulated image IN to determine whether or not there is an abnormality in the appearance of the object OB, a difference image is created using a brightness-accumulated image created from a group of images of an object OB with a normal appearance, captured under the same conditions as when images 1D to 5D were captured, as a reference image, and the subsequent method is the same as the method described in Figure 8.

[0034] As described above, in the visual inspection apparatus 1 of the first embodiment, light emitted from each of the light sources 11-15, which are concentrically surrounded by the walls 21-25, is multiple-reflected by the walls 21-25 that sandwich the light sources 11-15, and then emitted outside the walls 21-25. Therefore, these light sources 11-15 can be considered to form a circular surface light source. That is, the visual inspection apparatus 1 of the first embodiment can irradiate the object OB with uniform circular light from the circular surface light source. Furthermore, the visual inspection apparatus 1 of the first embodiment can acquire an image EQ equivalent to the brightness integrated image IN, which enables simultaneous inspection of portions of the object OB having different surface slopes. Therefore, simultaneous inspection of portions with different slopes can be performed. Furthermore, in the visual inspection apparatus 1 of the first embodiment, the brightness integrated image IN is created using images prepared by capturing images multiple times, whereas the image EQ equivalent to the brightness integrated image IN can be acquired with a single capture, thereby shortening the inspection time when inspecting an object having portions of different surface slopes.

[0035] Second Embodiment The appearance inspection device of the second embodiment differs from the appearance inspection device 1 of the first embodiment in the method of determining whether or not there is an abnormality in the appearance of the object OB. In the second embodiment, the presence or absence of an abnormality in the appearance of the object OB is determined using a normalized luminance value obtained by normalizing the luminance value of each pixel in the image EQ. In addition, in the second embodiment, the luminance value of each pixel in the reference image ST is normalized in the same way as in the image EQ, and the difference image DF is created by taking the difference in luminance values ​​between pixels that constitute the same position on the object OB in the normalized reference image ST and the normalized image EQ. Details of normalization will be described later.

[0036] In the visual inspection apparatus of the second embodiment, each of the light sources 11 to 15 is an LED whose illumination intensity is adjustable. That is, each of the light sources 11 to 15 can emit light at an illumination intensity adjusted by the control unit 70. Of course, each of the light sources 11 to 15 can also emit light at a higher illumination intensity as the light source located closer to the center of the concentric circle, as in the first embodiment.

[0037] Normalization will now be described. For normalization, a normalization image is used, which is captured using the appearance inspection device of the second embodiment while irradiating light from all light sources (light sources 11 to 15) while matching the illumination intensities of the light from all light sources when capturing the image EQ and the reference image ST. The normalization image used for normalizing the image EQ is a normalization image captured of the object OB (object OB being inspected) captured in the image EQ, and the normalization image used for normalizing the reference image ST is a normalization image captured of the object OB (object OB with no abnormalities in appearance) captured in the reference image ST. The brightness value of each pixel in the image EQ is normalized by dividing the brightness value of each pixel in the image EQ by the brightness value of the pixel at the same position in the normalization image. Similarly, the brightness value of each pixel in the reference image ST is normalized by dividing the brightness value of each pixel in the reference image ST by the brightness value of the pixel at the same position in the normalization image.

[0038] When the object OB is covered with machining oil, the intensity of light reflected from the object OB decreases, which tends to reduce the luminance values ​​of the pixels constituting the object OB in the image EQ captured of the object OB. In this regard, in the appearance inspection device of the second embodiment, the presence or absence of an abnormality in the appearance of the object OB is determined using normalized luminance values ​​obtained by normalizing the luminance values ​​of each pixel in the image EQ. Therefore, the luminance values ​​of the pixels constituting the object OB that are covered with machining oil or have machining oil partially attached thereto in the image EQ are corrected by normalization, making it possible to inspect the appearance of the object OB after reducing the effects of the machining oil.

[0039] An example of an object OB covered with processing oil or partially adhered with processing oil is a part immediately after press processing. A part immediately after press processing refers to a part immediately after press processing while covered with processing oil for lubrication within the press die. Because pressed parts are continuously produced using a press die, if a problem such as foreign matter adheres to the press die, there is a risk of abnormalities such as chips, dents, and dents appearing on the exterior of many of the same parts. However, in the past, it was difficult to inspect parts covered with processing oil. To detect such abnormalities, it was necessary to remove the processing oil from the parts before inspection. This tends to increase the time required for inspection, and if parts with visual abnormalities are continuously produced during that time, this can lead to a decrease in yield. In this regard, the appearance inspection device of the second embodiment can inspect parts immediately after press processing without removing the processing oil, thereby enabling early detection of abnormalities in the appearance of parts immediately after press processing. Therefore, since the worker can recognize problems such as adhesion of foreign matter to the press die at an early stage, the yield can be improved.

[0040] <Modification of this embodiment> The present invention is not limited to the above-described embodiment, and can be embodied in various forms without departing from the spirit of the invention. For example, the following modifications are also possible.

[0041] In the above-described embodiment, the light sources 11 to 15 are LEDs, but this is not limiting. The light sources 11 to 15 may be point light sources other than LEDs (for example, halogen lamps) or surface light sources.

[0042] In the above-described embodiment, if the illumination intensity of light emitted from light source 15 is set to 1, the illumination intensity of light emitted from light sources 14 to 11 is set to 2 to 5 times that of light source 15, but this is not limited to this. The illumination intensity of light from each light source can be set arbitrarily, as long as the light source located closer to the center of the concentric circle emits light with a higher illumination intensity. In the above-described embodiment, the illumination intensity of light from each light source was set so that an image EQ equivalent to the luminance integrated image IN could be obtained. However, if a reference luminance integrated image IN does not exist, the illumination intensity of light from each light source may be set arbitrarily, as long as the light source located closer to the center of the concentric circle emits light with a higher illumination intensity.

[0043] In the above-described embodiment, one light source 11 is surrounded by the wall portion 21, but this is not limited to this. A plurality of light sources 11 may be arranged in a circle inside the wall portion 21. Furthermore, in the above-described embodiment, the light sources 12 to 15 surrounded by each of the wall portions 22 to 25 are respectively arranged in a single circle, but they may each be arranged in two or more circles. In other words, the light sources 11 to 15 may be arranged in any manner as long as they are surrounded by the wall portions 21 to 25 in a concentric circle.

[0044] In the above-described embodiment, the diffusing member 30 is used as a member for diffusing the light emitted from the light sources 11 to 15. However, this is not limiting. For example, instead of the diffusing member 30, a resin material in which a diffusing material or a phosphor is dispersed may be filled between each of the wall portions 21 to 25.

[0045] In the above-described embodiment, the object OB to be inspected is an object including portions with different slopes on its surface, but this is not limited to this. The object OB to be inspected in the above-described embodiment may also be an object that does not include portions with different slopes on its surface. In other words, the object OB to be inspected in the above-described embodiment may also be an object with a flat surface.

[0046] In the second embodiment described above, the normalization image was captured by the same appearance inspection device that captured the image EQ and the reference image ST, but this is not limited to this. In other words, the normalization image, the image EQ, and the reference image ST were captured by the same appearance inspection device, but this is not limited to this. If the light source in the appearance inspection device that captured the image EQ and the reference image ST can only emit light at a certain illumination intensity, the normalization image may be captured by a device other than the appearance inspection device that captured the image EQ and the reference image ST. In this case, the appearance inspection device used to capture the normalization image has light sources arranged in the same manner as the appearance inspection device that captured the image EQ and the reference image ST, and these light sources are capable of emitting light simultaneously with the illumination intensity of all light sources being consistent when capturing the image EQ and the reference image ST.

[0047] In the above-described embodiment, the light sources 11 to 15, which are LEDs arranged in an array, are used as the light sources that irradiate the object with light, but this is not limited thereto. For example, the light source that irradiates the object with light may be a display that can illuminate all or part of the screen. In this case, if the control unit 70 is capable of adjusting the illumination intensity of each part of the screen, the control unit 70 can acquire the above-described image EQ and reference image ST by having the camera 60 capture the light reflected from the object OB while the display irradiates light with a higher illumination intensity toward the center of the screen.

[0048] This aspect has been described above based on embodiments and modifications. However, the above-described embodiments are intended to facilitate understanding of this aspect and are not intended to limit this aspect. This aspect may be modified or improved without departing from the spirit and scope of the claims, and equivalents thereof are included in this aspect. Furthermore, if a technical feature is not described as essential in this specification, it may be deleted as appropriate. [Explanation of symbols]

[0049] 1...Appearance inspection device 5...Light source unit 10...Plate-shaped member 11~15…Light source 20...Wall components 21~25…Wall part 30...Diffusion element 40...Plano-convex lens 50...Half mirror 60...Camera 62...Telecentric lens 70...Control unit

Claims

1. An appearance inspection device that inspects the appearance of an object, A plurality of light sources arranged concentrically to irradiate the object with light; a plurality of wall portions concentrically surrounding each of the light sources; a control unit that controls the emission of light from each of the light sources; an imaging unit that captures an image of the object in a state in which the light sources that are located closer to the center of the concentric circle irradiate light with higher illumination intensity; a determination unit that determines whether or not there is an abnormality in the appearance of the object using the brightness value of each pixel in the image.

2. An appearance inspection device that inspects the appearance of an object, a display that can emit light from all or part of the screen; a control unit capable of adjusting the illumination intensity in each part of the screen; an imaging unit that acquires an image of the object in a state in which the display irradiates light with the illumination intensity that is higher at a position closer to the center of the screen; a determination unit that determines whether or not there is an abnormality in the appearance of the object using the brightness value of each pixel in the image.

3. 3. The visual inspection apparatus according to claim 1, The judgment unit judges whether or not there is an abnormality in the appearance of the object using a normalized brightness value obtained by normalizing the brightness value of each pixel in the image.

Images