Visual inspection device

Abstract

To enable high-precision visual inspection. [Solution] The appearance inspection device 1 comprises a first illumination unit 11 that illuminates the surface of the object to be inspected W, an imaging unit 13 that images the surface of the object to be inspected W illuminated by the first illumination unit 11, and an inspection unit (control unit 21) that inspects the surface condition of the object to be inspected W based on the image captured by the imaging unit 13. The first illumination unit 11 includes a light source 112 surrounding the central axis WA of the object to be inspected W, the normal A of the light-emitting surface 112a of the light source 112 is perpendicular to the central axis WA or within 45 degrees, and the length T of the light source 112 in the direction along the central axis WA is greater than or equal to the radius r of the light source 112 surrounding the central axis WA.

Description

Technical Field

[0001] The present disclosure relates to an appearance inspection apparatus.

Background Art

[0002] Conventionally, appearance inspection has been performed for quality control in the manufacturing processes of various products. For example, Patent Document 1 describes a surface defect detection apparatus that detects defects such as cracks and scratches on the surface of an inspection object.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the invention described in Patent Document 1, since the diffused light in the light irradiated from the light source to the inspection object is insufficient, the detection accuracy of defects such as scratches on the surface of the inspection object may be low. [[ID=3)]]

[0005] An object of the present disclosure is to provide an appearance inspection apparatus capable of performing high-precision appearance inspection.

Means for Solving the Problems

[0006] To solve the above problems, the appearance inspection apparatus of the present disclosure includes a first illumination unit that illuminates the surface of an inspection object, an imaging unit that images the surface of the inspection object illuminated by the first illumination unit, an inspection unit that inspects the surface state of the inspection object based on the captured image captured by the imaging unit, and the first illumination unit includes a light source surrounding the central axis of the inspection object, The normal to the light-emitting surface of the light source is perpendicular to or within 45 degrees of the central axis, and the length of the light source in the direction along the central axis is greater than or equal to the radius of the light source surrounding the central axis. [Effects of the Invention]

[0007] According to this disclosure, high-precision visual inspection can be performed. [Brief explanation of the drawing]

[0008] [Figure 1] This is a block diagram of the visual inspection apparatus according to this embodiment. [Figure 2] This is a perspective view showing the configuration of the inspection unit. [Figure 3] This is a perspective view showing another example of the configuration of the inspection unit. [Figure 4] This is a plan view showing the configuration of the first lighting unit. [Figure 5] This is a perspective view showing another example of the configuration of the first lighting unit. [Figure 6] This is a perspective view showing another example of the configuration of the first lighting unit. [Figure 7] This is a perspective view showing another example of the configuration of the first lighting unit. [Figure 8] This is a flowchart showing the visual inspection process. [Figure 9] This is a plan view showing the configuration of the first illumination unit according to Modification Example 1. [Figure 10] This is a flowchart showing the visual inspection process related to Modification Example 1. [Modes for carrying out the invention]

[0009] Embodiments of this disclosure will be described below with reference to the drawings. However, this disclosure is not limited to those shown in the drawings.

[0010] <Configuration of the visual inspection device> The configuration of the visual inspection apparatus according to this embodiment will be described. FIG. 1 is a block diagram of the appearance inspection apparatus 1 according to the present embodiment. As shown in FIG. 1, the appearance inspection apparatus 1 includes an inspection unit 10 and a processing device 20. FIG. 2 is a perspective view showing the configuration of the inspection unit 10. In FIG. 2, the X-axis direction and the Y-axis direction are two horizontal directions orthogonal to each other, and the vertical direction orthogonal to the X-axis and the Y-axis is the Z-axis direction.

[0011] The appearance inspection apparatus 1 is a device for inspecting surface defects of an inspection object W that is an object to be inspected in the appearance inspection process described later. In the present embodiment, the inspection object W is, for example, a vehicle wheel. The inspection object W of the present embodiment has a predetermined thickness and has a complex surface shape including at least one through hole W1 penetrating the inspection object W in the thickness direction. As shown in FIG. 2, the inspection object W is placed on the mounting table D1 so that the thickness direction is along the Z-axis direction in the appearance inspection. The thickness direction of the inspection object W is the direction along the central axis WA (see FIG. 4) of the inspection object W.

[0012] The inspection unit 10 includes a first illumination unit 11 and a second illumination unit 12 that illuminate the surface of the inspection object W, an imaging unit 13 that images the surface of the inspection object W, and the like.

[0013] The first illumination unit 11 has a cylindrical shape, and a light source is disposed on the inner peripheral surface of the cylindrical shape. The configuration of the first illumination unit 11 will be described in detail later. The first illumination unit 11 is disposed on the positive Z-axis side of the inspection object W and illuminates the inspection object W from the positive Z-axis side.

[0014] The second illumination unit 12 is disposed on the surface of the mounting table D1 on which the inspection object W is placed, and illuminates the inspection object W from the negative Z-axis side. In other words, the second illumination unit 12 illuminates the surface of the inspection object W from the opposite side of the first illumination unit 11 with the inspection object W interposed therebetween. Therefore, the light emitted from the second illumination unit 12 can illuminate the inner wall of the through-hole W1 of the object to be inspected W. Consequently, the imaging unit 13 can image the inner wall of the through-hole W1 of the object to be inspected W, thereby improving the inspection performance in visual inspection. The light emitted from the second illumination unit 12 is sufficiently diffused so that it does not cause overexposure when captured in the image captured by the imaging unit 13. If the object to be inspected W does not have a through hole W1, the inspection unit 10 does not need to be equipped with a second illumination unit 12.

[0015] The imaging unit 13 includes two cameras positioned to image the object to be inspected W from the positive Z-axis direction. The two cameras are arranged to image the object to be inspected W at different shooting angles. The imaging unit 13 images the surface of the object W to be inspected, which is illuminated by the first illumination unit 11 and the second illumination unit 12, and outputs a monochrome or color image to the processing unit 20.

[0016] Figure 3 shows another example of the configuration of the inspection unit 10. In the example shown in Figure 3, the inspection unit 10 includes a turntable D2 on which the mounting table D1 is placed, and a drive unit 14 that rotates the turntable D2 in the horizontal plane (XY plane). The drive unit 14 is connected to the processing unit 20, which controls the operation of the drive unit 14. In this case, the imaging unit 13 is equipped with one camera and images the surface of the object to be inspected W on the rotating table D2 which is rotated by the drive unit 14. The processing unit 20 acquires the image captured by the imaging unit 13 and also acquires rotation angle information from the drive unit 14, which indicates the rotation angle of the rotating table D2 at the time the image was captured.

[0017] The processing unit 20 is, for example, a personal computer. The processing unit 20 is connected to the imaging unit 13 of the inspection unit 10 via wiring (not shown) and controls the operation of the imaging unit 13. Alternatively, the processing unit 20 may be connected to the first illumination unit 11 and the second illumination unit 12 via wiring and control the operation of the first illumination unit 11 and the second illumination unit 12. The processing unit 20 comprises a control unit 21, a storage unit 22, a communication unit 23, an operation unit 24, and a display unit 25.

[0018] The control unit 21 includes, for example, a processor such as a CPU (Central Processing Unit) and an MPU (Micro Processing Unit), and memory such as RAM (Random Access Memory). The control unit 21 executes programs 22a stored in the memory such as RAM and the storage unit 22, thereby realizing various processes, including visual inspection of the object to be inspected W. The control unit 21 controls the imaging unit 13 of the inspection unit 10 to image the surface of the object W to be inspected.

[0019] The storage unit 22 includes, for example, any storage module such as an HDD (Hard Disk Drive), SSD (Solid State Drive), ROM (Read Only Memory), and RAM. The storage unit 22 stores, for example, system programs, application programs, and various data. Specifically, the storage unit 22 stores a program 22a for performing visual inspection processing of the object to be inspected W.

[0020] The communication unit 23 includes, for example, a communication module including a NIC (Network Interface Card), a receiver, and a transmitter. The communication unit 23 communicates various information, data, etc., with external devices connected via a communication network such as the Internet.

[0021] The operation unit 24 includes, for example, a mouse, keyboard, switches, buttons, etc. The operation unit 24 may be, for example, a touch panel integrated with the display unit 25, or it may be an interface that accepts voice input. The operation unit 24 receives instructions in response to various input operations from the user, converts the received instructions into operation signals, and outputs them to the control unit 21.

[0022] The display unit 25 is, for example, a liquid crystal display, an organic EL (Electro-Luminescence) display, etc. The display unit 25 displays information based on the display data output from the control unit 21.

[0023] <Configuration of the first lighting unit> Figure 4 shows a cross-sectional view in the XZ plane passing through the center of the first illumination unit 11. The first lighting unit 11 includes a cylindrical outer casing 111, a light source 112, a diffuser plate 113, and the like.

[0024] The light source 112 is, for example, a plurality of LEDs (Light Emitting Diodes), OLEDs (Organic Light Emitting Diodes), etc., and is arranged on the inner circumferential surface of the outer casing 111. The light source 112 directs light toward the central axis of the first illumination unit 11. In other words, the light source 112 does not directly illuminate the object W being inspected. This suppresses the occurrence of overexposure caused by reflected light from the light source 112 in the captured image of the object W being inspected, thereby improving the inspection performance in visual inspection.

[0025] The diffuser plate 113 is positioned in the first illumination unit 11 inside the light-emitting surface 112a of the light source 112, and diffuses the light emitted from the light source 112.

[0026] In the first illumination unit 11, as shown in Figure 4, the light source 112 is arranged to surround the central axis WA of the object to be inspected W. For example, the first illumination unit 11 is arranged so that its central axis coincides with the central axis WA of the object to be inspected W. The normal A of the light-emitting surface 112a of the light source 112 is perpendicular to the central axis WA of the object W to be inspected.

[0027] The length T of the light source 112 in the direction along the central axis WA (Z-axis direction) is greater than or equal to the radius r of the light-emitting surface 112a of the light source 112 surrounding the central axis WA. This allows the incident angle θ of the light irradiated from the light source 112 and diffused by the diffuser plate 113 to be 45 degrees or more on the object to be inspected W, so that the light can reach the inner wall of the through hole W1 of the object to be inspected W. Therefore, the imaging unit 13 can image the inner wall of the through hole W1 of the object to be inspected W. Furthermore, as the length T of the light source 112 increases, the amount of light emitted from the light source 112 increases. Therefore, by making the length T of the light source 112 greater than or equal to the radius r, the contrast in the image of the object W being inspected can be enhanced. As a result, the inspection performance in visual inspection can be improved.

[0028] The length T of the light source 112 in the direction along the central axis WA is less than or equal to twice the radius r of the light-emitting surface 112a of the light source 112 surrounding the central axis WA. As the length T of the light source 112 increases, the distance between the imaging unit 13, which is positioned on the positive Z-axis side of the first illumination unit 11, and the object to be inspected W increases. As a result, the field of view of the object to be inspected W of the imaging unit 13 narrows. This can cause shadows to appear in the captured image, potentially leading to a problem where a portion of the surface of the object to be inspected W is not captured (occlusion). In contrast, by setting the length T of the light source 112 to twice the radius r or less, occlusion in the captured image can be suppressed, thereby improving the inspection performance in visual inspection. Furthermore, as the length T of the light source 112 increases, the manufacturing and operating costs of the first illumination unit 11 increase. In contrast, by keeping the length T of the light source 112 to twice the radius r or less, the cost of the first illumination unit 11 can be suppressed.

[0029] The distance d from the light source 112 to the object W to be inspected in the direction along the central axis WA is less than or equal to the radius r of the light-emitting surface 112a of the light source 112 surrounding the central axis WA. This allows the incident angle θ of the light irradiated from the light source 112 and diffused by the diffuser plate 113 onto the object W to be inspected to be 45 degrees or more, so that the light can reach the inner wall of the through hole W1 of the object W to be inspected. Therefore, the imaging unit 13 can image the inner wall of the through hole W1 of the object W to be inspected, thereby improving the inspection performance in visual inspection.

[0030] The first illumination unit 11 is not limited to the cylindrical shape shown in Figure 4, as long as the light source surrounds the central axis WA of the object to be inspected W. Figures 5 to 7 show alternative examples of the first illumination unit 11, namely the first illumination units 11A to 11C. The exterior part 111A of the first lighting unit 11A shown in Figure 5 has a cylindrical truncated cone shape. In the example shown in Figure 5, the angle B between the normal A of the light-emitting surface 112a of the light source and the central axis WA of the object W being inspected is within 45 degrees.

[0031] The exterior part 111B of the first lighting unit 11B shown in Figure 6 has a cylindrical polygonal shape. The first illumination unit 11C shown in Figure 7 comprises a plurality of long bar light sources 112C arranged to surround the central axis WA of the object to be inspected W.

[0032] <Operation of the visual inspection device> Next, the operation of the visual inspection device 1 according to this embodiment will be described. The control unit 21 of the processing apparatus 20 performs a visual inspection process (see Figure 8) to inspect the surface condition of the object W to be inspected. The control unit 21 functions as an inspection unit.

[0033] (Visual inspection process) The control unit 21 controls the imaging unit 13 to image the surface of the object W to be inspected, which is illuminated by the first illumination unit 11 and the second illumination unit 12, and acquire the image (step S1). Next, the control unit 21 detects defects on the surface of the object to be inspected W based on the image acquired in step S1 (step S2). Defects on the surface of the object to be inspected W include, for example, fine irregularities, scratches, and dirt.

[0034] In step S2, the control unit 21 applies a rule-based method. Specifically, the control unit 21 performs edge detection on the captured image of the object W to be inspected using a differential filter. Edge detection refers to detecting areas in the image where the brightness changes abruptly. Next, the control unit 21 detects discontinuities on the surface of the object W as defects by binarizing the captured image with edge detection using a predetermined threshold.

[0035] In step S2, the control unit 21 may apply a non-rule-based method. Specifically, the control unit 21 inputs the captured image of the object to be inspected W into an object detection model using deep learning, and outputs defects on the surface of the object to be inspected W. Examples of object detection models include an R-CNN model, a Single Shot Multibox Detector (SSD) model, and a You Only Look Once (YOLO) detection model.

[0036] Next, the control unit 21 notifies the user of the information regarding surface defects of the object W detected in step S2 by displaying it on the display unit 25 (step S3), and terminates the visual inspection process. The information regarding surface defects of the object W includes the location of the defect in the captured image, the rotation angle of the turntable D2 at the time the image was captured, and so on.

[0037] <Variation> Although this embodiment has been described above, the specific configuration is not limited to this embodiment and can be modified without departing from the spirit of the invention. Modifications of this embodiment will be described below. In the modifications, the same reference numerals are used for components similar to those in the above embodiment, and their descriptions are omitted.

[0038] Figure 9 shows a cross-sectional view in the XZ plane passing through the center of the first illumination unit 11 in a modified example. In the modified example, the first illumination unit 11 further includes a polarizing plate 114 on the light-emitting surface 112a side of the light source 112. The polarizing plate 114 is positioned inside the diffuser plate 113 in the first illumination unit 11. The polarizing plate 114 transmits linearly polarized light from the light diffused by the diffuser plate 113, which has a vibration plane along the central axis WA of the object W to be inspected (Z-axis direction) or in the circumferential direction of the first illumination unit 11.

[0039] The modified imaging unit 13 captures multiple polarized images with different polarization directions. The different polarization directions are, for example, 0 degrees, 45 degrees, 90 degrees, and 135 degrees. Specifically, the imaging unit 13 includes a camera with a linear polarizing filter positioned in front of the lens, and performs imaging while rotating the linear polarizing filter. Alternatively, the imaging unit 13 may include a camera equipped with polarizers in four directions (0 degrees, 45 degrees, 90 degrees, and 135 degrees) on the imager.

[0040] Figure 10 shows a flowchart of the visual inspection process in a modified example.

[0041] (Visual inspection process of modified specimens) The control unit 21 of the processing device 20 controls the imaging unit 13 to image the surface of the object to be inspected W illuminated by the first illumination unit 11 and the second illumination unit 12, and acquires a plurality of polarized images with different polarization directions (step S11). Next, the control unit 21 calculates the degree of linear polarization (DoLP) for each pixel position in the multiple polarization images acquired in step S11 (step S12). The control unit 21 executes step S12 at all pixel positions in the polarized image.

[0042] Next, the control unit 21 generates a single composite image from the multiple polarization images acquired in step S11 based on the linear polarization degree calculated in step S12 (step S13). At pixel positions where the degree of linear polarization calculated in step S12 is greater than a predetermined threshold, it is considered that the specular reflection component of the light from the light source 112 is large. Therefore, in step S13, the control unit 21 applies a polarization image from among multiple polarization images, with a polarization direction orthogonal to the polarization direction of the polarization image with the maximum linear polarization, to pixel positions where the degree of linear polarization is greater than a predetermined threshold. For example, if the polarization direction of a polarized image with the maximum linear polarization is 0 degrees, the control unit 21 applies a polarized image with a polarization direction of 90 degrees, which is perpendicular to 0 degrees. Therefore, in the composite image generated in step S13, the reflected light from the light source 112 reflected off the surface of the object W being inspected is captured, which can suppress the occurrence of overexposure. This improves the inspection performance in visual inspection.

[0043] Next, the control unit 21 detects defects on the surface of the object to be inspected W based on the image generated in step S13 (step S14). Next, the control unit 21 executes step S15, which is the same as step S3 of the visual inspection process in the above embodiment, to complete the visual inspection process of the modified example.

[0044] <Effects> As described above, the visual inspection apparatus 1 according to this embodiment includes a first illumination unit 11 that illuminates the surface of the object W to be inspected. The visual inspection device 1 includes an imaging unit 13 that images the surface of the object to be inspected W, which is illuminated by the first illumination unit 11. The visual inspection device 1 includes an inspection unit (control unit 21) that inspects the surface condition of the object W to be inspected based on the image captured by the imaging unit 13. The first illumination unit 11 includes a light source 112 that surrounds the central axis WA of the object W to be inspected. The normal A of the light-emitting surface 112a of the light source 112 is perpendicular to or within 45 degrees of the central axis WA. Furthermore, the length T of the light source 112 in the direction along the central axis WA is greater than or equal to the radius r of the light source 112 surrounding the central axis WA. Therefore, it is possible to suppress the occurrence of overexposure in the image of the object W being inspected due to the reflection of light from the light source 112 being captured in the image. Furthermore, since the incident angle θ of the light irradiated from the light source 112 and diffused by the diffuser plate 113 to the object W to be inspected can be set to 45 degrees or more, the light can reach the inner wall of the through hole W1 of the object W to be inspected. Therefore, the imaging unit 13 can image the inner wall of the through hole W1 of the object W to be inspected. Furthermore, the contrast can be enhanced in the captured image of the object W being inspected. This allows for the detection of surface defects on the object W being inspected with high precision. Therefore, high-precision visual inspection can be performed.

[0045] In the visual inspection apparatus 1 according to this embodiment, the length T of the light source 112 in the direction along the central axis WA is less than or equal to twice the radius r of the light source 112 surrounding the central axis WA. Therefore, occlusion in the image of the object W being inspected can be suppressed, thereby improving inspection performance in visual inspection. Furthermore, the cost of the first lighting unit 11 can be reduced.

[0046] In the visual inspection apparatus 1 according to this embodiment, the distance d from the light source 112 to the object to be inspected W along the central axis WA is less than or equal to the radius r of the light source 112 surrounding the central axis WA. This allows the incident angle θ of the light irradiated from the light source 112 and diffused by the diffuser plate 113 onto the object W to be inspected to be 45 degrees or more, so that the light can reach the inner wall of the through hole W1 of the object W to be inspected. Therefore, the imaging unit 13 can image the inner wall of the through hole W1 of the object W to be inspected, thereby improving the inspection performance in visual inspection.

[0047] In the visual inspection apparatus 1 according to this embodiment, the object to be inspected W is provided with a through hole W1 that penetrates the object to be inspected W in a direction along the central axis WA. The visual inspection device 1 includes a second illumination unit 12 that illuminates the surface of the object to be inspected W from the opposite side of the first illumination unit 11, with the object to be inspected W in between. Therefore, the light emitted from the second illumination unit 12 can illuminate the inner wall of the through-hole W1 of the object to be inspected W. Consequently, the imaging unit 13 can image the inner wall of the through-hole W1 of the object to be inspected W, thereby improving the inspection performance in visual inspection.

[0048] In the visual inspection apparatus 1 according to this embodiment, the first illumination unit 11 is equipped with a polarizing plate 114 on the light-emitting surface 112a side of the light source 112. The imaging unit 13 captures multiple polarization images with different polarization directions. Therefore, in a composite image generated from multiple polarization images with different polarization directions, it is possible to suppress the occurrence of overexposure caused by reflected light from the light source 112 reflected from the surface of the object W being inspected. This improves the inspection performance in visual inspection.

[0049] Although the embodiments described above have been specifically explained based on the embodiments of this disclosure, this disclosure is not limited to the embodiments described above and may be modified without departing from its essence. For example, in the above embodiment, the case in which the object to be inspected W is a wheel for a vehicle was illustrated and explained, but this disclosure is not limited to this. High-precision visual inspection can also be performed on objects to be inspected other than wheel for a vehicle by applying this disclosure. [Explanation of Symbols]

[0050] 1. Visual inspection device 10 Inspection Units 11,11A,11B,11C 1st lighting section 111,111A,111B Exterior part 112 Light source 112C Bar Light Source 112a Light-emitting surface 113 Diffuser 114 Polarizing plate 12. Second Lighting Section 13 Imaging Unit 14 Drive Unit 20 Processing Units 21 Control Unit (Inspection Unit) 22 Memory section 23 Communications Department 24 Control section 25 Display section A normal vector D1 Mounting platform D2 Rotating Stand W: Items to be inspected W1 through hole WA center axis

Claims

1. A first illumination unit that illuminates the surface of the object to be inspected, An imaging unit that images the surface of the object to be inspected, which is illuminated by the first illumination unit, An inspection unit that inspects the surface condition of the object to be inspected based on the image captured by the imaging unit, Equipped with, The first illumination unit comprises a light source surrounding the central axis of the object to be inspected, An appearance inspection device wherein the normal of the light-emitting surface of the light source is perpendicular to or within 45 degrees with respect to the central axis, and the length of the light source in the direction along the central axis is greater than or equal to the radius of the light source surrounding the central axis.

2. The appearance inspection apparatus according to claim 1, wherein the length of the light source in the direction along the central axis is no more than twice the radius of the light source surrounding the central axis.

3. The appearance inspection apparatus according to claim 1, wherein the distance from the light source to the object to be inspected in the direction along the central axis is less than or equal to the radius of the light source surrounding the central axis.

4. The object to be inspected has a through hole that penetrates the object in a direction along the central axis, The appearance inspection apparatus according to claim 1, further comprising a second illumination unit that illuminates the surface of the object to be inspected from the opposite side of the first illumination unit, with the object to be inspected in between.

5. The first illumination unit is equipped with a polarizing plate on the light-emitting surface side of the light source, The appearance inspection apparatus according to claim 1, wherein the imaging unit captures a plurality of polarized imaging images with different polarization directions.

Images