Apparatus for visual inspection and method for visual inspection

Abstract

To allow visual inspection of the whole circumference of a surface of an object to be inspected in a short time, thereby reducing inspection cost.SOLUTION: A visual inspection device (11) comprises: a prism (17) that is formed in a ring shape having a hollow part (19) extending in an axial direction at a center part, opening on the front and rear faces, and arranged with an object to be inspected, includes a flat surface (17a) orthogonal to the axial direction on the front side, and includes a tapered reflection surface (25) inclined with respect to the axial direction on the rear face; an illumination device (13) that irradiates, with light, the whole circumference of a surface of the object to be inspected in the hollow part through the flat surface of the prism; and an imaging apparatus (14) that is arranged in front of the prism to capture a photographed image of the surface of the object to be inspected. In a state where the whole circumference of the surface of the object to be inspected is arranged in the hollow part opposite to an inner wall surface of the hollow part, the whole circumference of the surface of the object to be inspected is irradiated with the light emitted from the illumination device, reflected light from the object to be inspected is reflected on the reflection surface through the prism and output forward, and the imaging apparatus captures an image (I) of a state where the whole circumference of the surface of the object to be inspected is developed in a ring shape.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an appearance inspection apparatus and an appearance inspection method for imaging an inspection object and inspecting the surface state of the inspection object based on the imaging data.

Background Art

[0002] For example, in products such as in-vehicle electrical components, appearance inspections such as inspecting for the presence or absence of foreign matter adhesion on the surface are carried out. As an apparatus for this, an inspection apparatus that performs inspection using a camera is known (see, for example, Patent Document 1). In the foreign matter detection apparatus disclosed in Patent Document 1, in order to detect epoxy resin as foreign matter adhering to the surface of the inspection object during the manufacturing process, a violet light that emits fluorescence from a synthetic resin such as epoxy resin is adopted as an illumination light source. And, based on imaging the reflected light from the surface of the inspection object with a camera via a filter unit, it is configured to detect the adhesion of epoxy resin.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Incidentally, when inspecting an object as described above, for example, a cylindrical part, there are cases where a visual inspection is desired for the entire outer surface of the cylindrical object. In this case, conventionally, in order to inspect the entire circumference of the object, the object is rotated relative to the camera, for example, in 45-degree increments, and multiple imaging processes are performed. However, because multiple imaging is required, the inspection process is time-consuming and labor-intensive, resulting in a high overall inspection cost. Furthermore, in order to irradiate the surface of the object with violet light at a sufficiently high intensity, it is desirable to place the lighting device as close to the object as possible, but there have been problems such as physical interference between the lighting device and the object, making it difficult to take good images.

[0005] The present invention has been made in view of the above circumstances, and its purpose is to provide an appearance inspection device and an appearance inspection method that capture images of an object to be inspected and inspect the surface condition of the object based on the image data, enabling a quick appearance inspection of the entire circumference of the surface of the object to be inspected, and thereby reducing inspection costs. [Means for solving the problem]

[0006] To achieve the above objective, the appearance inspection device (11) described in claim 1 images an object to be inspected (3) and inspects the surface condition of the object to be inspected based on the imaging data, and comprises a prism (17) which is ring-shaped with a hollow portion (19) extending axially in the center and opening on the front and rear surfaces in which the object to be inspected is placed, and has a flat surface (17a) on the front side perpendicular to the axial direction and a tapered reflective surface (25) on the rear side inclined with respect to the axial direction, and an illumination device which irradiates light onto the entire circumference of the surface of the object to be inspected in the hollow portion through the flat surface of the prism The system comprises a lighting device (13) and an imaging device (14) positioned in front of the prism for capturing an image of the surface of the object to be inspected. With the entire circumference of the surface of the object to be inspected positioned within the hollow section facing the inner wall surface of the hollow section, light emitted by the lighting device is shone onto the entire circumference of the surface of the object to be inspected, and the reflected light from the object to be inspected is reflected by the reflective surface through the prism and output forward, and the imaging device captures an image (I) of the entire circumference of the surface of the object to be inspected unfolded in a ring shape.

[0007] The visual inspection method according to claim 3 is a method for imaging an object to be inspected (3) and inspecting the surface condition of the object to be inspected based on the imaging data, comprising a ring-shaped prism (17) having a hollow portion (19) extending axially in the center and opening on the front and rear surfaces where the object to be inspected is placed, a flat surface (17a) perpendicular to the axial direction on the front side, and a tapered reflective surface (25) inclined with respect to the axial direction on the rear side, wherein the entire circumference of the surface of the object to be inspected faces the inner wall surface of the hollow portion. The process includes an inspection object setting step (P1) in which the inspection object is positioned, an illumination step (P2) in which a lighting device (13) illuminates the entire circumference of the surface of the inspection object in the hollow part through the flat surface of the prism, and an imaging step (P3) in which the reflected light reflected from the entire circumference of the surface of the inspection object is reflected forward by the prism and output by an imaging device (14) positioned in front of the prism, and an image I of the surface of the inspection object is captured with the entire circumference of the surface unfolded in a ring shape.

[0008] In the above configuration, a prism is used that is ring-shaped with a hollow section extending axially in the center and opening at the front and rear surfaces where the object to be inspected is placed. The front side has a flat surface perpendicular to the axial direction, and the rear side has a tapered reflective surface inclined with respect to the axial direction. The object to be inspected is placed inside the hollow section of the prism so that its entire surface is facing the inner wall surface of the hollow section (object to be inspected setting step). In this state, the illumination device illuminates the entire surface of the object to be inspected inside the hollow section through the flat surface of the prism (illumination step). The reflected light from the entire surface of the object to be inspected passes through the prism, is reflected by the reflective surface and output forward, and an imaging device positioned in front of the prism captures an image of the entire surface of the object to be inspected in a ring shape (imaging step).

[0009] In this configuration, the ring-shaped prism allows the imaging device to obtain an image of the entire surface of the object being inspected, unfolded in a ring shape. Based on this single image data, the entire surface condition of the object can be inspected simultaneously. This not only allows for a relatively simple configuration of the entire device, but also enables inspection of the entire circumference in a single imaging process, simplifying the inspection process and reducing the time required. As a result, it becomes possible to perform a visual inspection of the entire surface of the object being inspected in a short time, achieving the excellent effect of reducing inspection costs. [Brief explanation of the drawing]

[0010] [Figure 1] This is a longitudinal cross-sectional side view showing the main components of an appearance inspection device, illustrating one embodiment. [Figure 2] Perspective view of the prism unit [Figure 3] Longitudinal cross-sectional view of a prism [Figure 4] Block diagram illustrating the overall configuration of the visual inspection device. [Figure 5] A schematic diagram showing the visual inspection process. [Figure 6]Perspective view showing the appearance of the ignition coil. [Figure 7] This figure illustrates another embodiment, specifically an example where the connector portion is the object to be inspected. [Modes for carrying out the invention]

[0011] Hereinafter, an embodiment of the present invention will be described with reference to Figures 1 to 6. In this embodiment, the object to be inspected is an ignition coil, which is an electrical component for an engine used in a vehicle. Specifically, the inspection is performed on the entire circumference of the surface of the high-voltage tower of the ignition coil, in the case of checking for the adhesion of foreign matter.

[0012] First, with reference to Figure 6, the configuration of the ignition coil 1 will be briefly described. This ignition coil 1 has a case 2 made of insulating material that is roughly rectangular in shape, and a cylindrical high-voltage tower 3 protrudes from the front of the case 2. A connector 4 is also provided on the top of the case 2. Although not shown in the figure, an igniter, primary coil, secondary coil, etc. are arranged inside the case 2 of the ignition coil 1, and an insulating resin is filled and hardened to cover them. For example, a thermosetting resin such as epoxy resin is used as the insulating resin. The high-voltage tower 3 is inserted into an engine spark plug hole (not shown) and is configured to output high voltage from its tip.

[0013] The visual inspection device 11 according to this embodiment inspects the surface of the outer periphery of the high-voltage tower 3 for the adhesion of insulating resin as foreign matter. The visual inspection device 11 will be described below with reference to Figures 1 to 4. Figure 4 schematically shows the overall configuration of the visual inspection device 11, which is composed of a prism unit 12, an illumination device 13, an imaging device 14, a control device 15, and the like. In this embodiment, a workpiece transport mechanism 16 is also provided to automatically load and unload the ignition coil 1, which is the workpiece, into the prism unit 12. For example, a robot may be used as the workpiece transport mechanism 16.

[0014] The prism unit 12 comprises a prism 17 and a prism holder 18 that holds it. As shown in Figure 1, the prism 17 is provided with a hollow section 19 into which the object to be inspected, i.e., the high-voltage tower 3 of the ignition coil 1, is inserted from the rear (left side in Figure 1). The prism 17 has a central axis O extending in the left-right direction in Figure 1, and the hollow section 19 is a circular hole that extends axially with the central axis O of the prism 17 as its center and opens on the front and rear surfaces. Details of this prism unit 12 will be described later.

[0015] The lighting device 13 consists of a ring light positioned in front of the prism unit 12 and is configured to perform so-called low-angle lighting, irradiating light around the entire surface of the high-pressure tower 3, which is the object to be inspected, inside the hollow section 19 through the prism 17. As shown in Figure 1, in this embodiment, the lighting device 13 is configured by arranging a plurality of purple LEDs 13b as light sources in a ring shape on a ring-shaped holder 13a, and is configured to irradiate violet light, that is, light containing purple and ultraviolet light, in an oblique direction towards the rear.

[0016] The imaging device 14 is for capturing an image I of the surface of the high-pressure tower 3, which is the object to be inspected, and includes a camera 20, such as a CCD camera, and an optical system 21 consisting of lenses, filters, etc. This imaging device 14 is positioned in front of the prism unit 12, and as will be described in more detail later, it is configured to receive reflected light from the prism 17 directed forward.

[0017] The control device 15 is primarily composed of a computer and includes a control unit 22 that controls the entire system and an image processing unit 23 that processes the image data captured by the camera 20. An input / output unit 24 is also connected to the control device 15. The control unit 22 controls the lighting device 13 and the imaging device 14 to capture images of the object to be inspected. The control unit 22 also provides command signals to the workpiece transport mechanism 16 to carry in and out the ignition coil 1.

[0018] The image processing unit 23 binarizes the data of the captured image I by the camera 20 to generate a binarized image B (see FIG. 1). From the data of the binarized image B, the number of pixels of the contaminated portion due to the adhesion of foreign matter, that is, the white portion, is obtained and compared with a threshold value. If it is below the threshold value, it is judged as a good product, and if it exceeds the threshold value, it is judged as a defective product. Further, various instruction signals are input to the control device 15 and the output of the appearance inspection result is performed by the input / output unit 24.

[0019] Now, the prism unit 12 will be described with reference to FIGS. 1 to 3 as well. The prism 17 is made of a highly transparent resin material such as transparent acrylic resin, and as described above, it has a conical shape with a hollow portion 19 penetrating along the central axis O. In this case, the front surface portion of the prism 17 is a flat surface 17a orthogonal to the central axis O, and a tapered reflecting surface 25 inclined with respect to the central axis O is provided on the rear surface side.

[0020] At this time, the reflecting surface 25 is subjected to precision polishing, so-called lapping finish, and the surface is in a mirror state without scratches. As shown in FIG. 3, in this embodiment, the inclination angle θ of the reflecting surface 25 is 45° with respect to the direction in which the central axis O extends. Further, the front surface portion of the prism 17 integrally has a flange portion 17b that continuously extends in the circumferential direction from the flat surface 17a portion.

[0021] On the other hand, as shown in FIGS. 1 and 2, the prism holder 18 has a rectangular block shape, has a circular hole 18a having a size corresponding to the prism 17, and has a recess 18b having an outer diameter and depth corresponding to the flange portion 17b of the prism 17 around the circular hole 18a on the front surface side. A thin plate-like lid portion 26 is arranged on the front surface portion of the prism holder 18. The lid portion 26 is provided with a circular opening 26a, and the circular opening 26a has a diameter slightly larger than the diameter dimension of the circular hole 18a and slightly smaller than the outer diameter dimension of the flange portion 17b.

[0022] The prism 17 is fitted into the circular hole 18a of the prism holder 18 from the front. At this time, the flange portion 17b of the prism 17 is positioned within the recess 18b. In this state, the cover portion 26 is positioned on the front of the prism holder 18, and as shown in Figure 2, it is secured by four screws 27 at the four corners, sandwiching the flange portion 17b. Thus, as also shown in Figure 1, the prism 17 is held in the prism holder 18, and the prism unit 12 is formed. The flat front surface 17a of the prism 17 faces into the circular opening 26a. The rear part of the reflective surface 25 of the prism 17 is an open space.

[0023] As shown in Figure 1, the illumination device 13 is positioned near the front side of the prism unit 12 having the above configuration. When the purple LED 13b of this illumination device 13 is lit, illumination light, i.e., violet light, is emitted and is incident at an oblique angle into the prism 17 from the flat surface 17a. Within the hollow portion 19 of the prism 17, the entire circumference of the surface of the high-voltage tower 3 of the ignition coil 1 is positioned facing the inner wall surface of the hollow portion 19.

[0024] As a result, the incident violet light is irradiated through the prism 17 onto the entire surface of the high-pressure tower 3 within the hollow section 19. The reflected light from the surface of the high-pressure tower 3 is then reflected by the reflective surface 25 through the prism 27 and output forward. This configuration allows the imaging device 14 to capture an image I of the entire surface of the high-pressure tower 3 unfolded in a ring shape.

[0025] In the visual inspection apparatus 11 configured as described above, the control device 15 controls the imaging device 14, the lighting device 13, the workpiece transport mechanism 16, etc., to execute the visual inspection method according to this embodiment for the high-voltage tower 3 of the ignition coil 1, which is the object to be inspected. Specifically, as will be described in more detail later, the control device 15 executes each step of the visual inspection, which consists of the object to be inspected setting step P1, the lighting step P2, the imaging step P3, etc.

[0026] In the inspection object setting process P1, the workpiece transport mechanism 16 moves the ignition coil 1, which is the object to be inspected, into the prism 17 from the rear so that the entire circumference of the surface of the high-pressure tower 3 faces the inner wall surface of the hollow section 19. In the illumination process P2, the illumination device 13 irradiates the entire circumference of the surface of the high-pressure tower 3 inside the hollow section 19 through the flat surface 17a of the prism 17. In the imaging process P3, the imaging device 14, positioned in front of the prism 17, captures an image I of the surface of the high-pressure tower 3 with the entire circumference of the surface unfolded in a ring shape. After the imaging process P3, the image processing process P4 and the judgment process P5 are performed.

[0027] Next, the operation of the above configuration will be described with reference to Figure 5. Figure 5 shows the process of visual inspection according to this embodiment, and the following steps are performed in order. That is, first, in the workpiece setting step P1, the ignition coil 1 is transported by the workpiece transport mechanism 16, and its high-voltage tower 3 is set by inserting it into the hollow section 19 from behind the prism 17 in the direction of arrow A (see Figure 4). As a result, as shown in Figure 1, the entire circumference of the surface of the high-voltage tower 3 is set in a predetermined position facing the inner wall surface of the hollow section 19.

[0028] In the next lighting process P2, each purple LED 13b of the lighting device 13 is turned on. As a result, as described above, the illumination light, i.e., violet light, is incident at an oblique angle from the flat surface 17a into the prism 17 and further irradiates the outer surface of the high-pressure tower 3 inside the hollow section 19. The light reflected from the surface of the high-pressure tower 3 outward is incident through the inner wall surface of the hollow section 19 towards the reflective surface 25 inside the prism 17, and is reflected at a 90° change in angle at the reflective surface 25 which is inclined at a 45° angle with respect to the central axis O, and is emitted forward from the flat surface 17a.

[0029] Under these lighting conditions, the imaging process P3 is executed, and the image I of the surface of the high-pressure tower 3, emitted forward from the prism 17, is captured by the imaging device 14. In this case, as shown in Figure 1, the entire circumference of the surface of the high-pressure tower 3 is projected onto a single screen by the tapered reflective surface 25, and the imaging device 14 can capture an image I of the entire surface.

[0030] Furthermore, since violet light is used for the illumination of the lighting device 13 at this time, the insulating resin adhering to the surface of the high-voltage tower 3 is excited by the violet light and begins to fluoresce. Therefore, even if the adhesion of insulating resin does not provide sufficient contrast with the original color of the surface of the high-voltage tower 3 in visible light, the resin-adhered portion will appear white in the captured image I input to the imaging device 14, making it easy to distinguish it from the surface of the high-voltage tower 3.

[0031] Subsequently, in the image processing step P4, the image processing unit 23 binarizes the data of the captured image I to generate a binarized image B (see Figure 1), and the number of pixels in the foreign matter portion, i.e., the white portion, due to the adhesion of insulating resin is determined. In the next judgment step P5, the number of pixels in the white portion is compared with a threshold to determine whether it is a good product or a defective product. Although not shown in detail, if it is determined to be a good product, the ignition coil 1 is transported to the next process by the workpiece transport mechanism 16, and if it is determined to be a defective product, the ignition coil 1 is sent to, for example, a defective product discharge section by the workpiece transport mechanism 16. At the same time, the input / output unit 24 notifies the results of the visual inspection.

[0032] The following effects can be obtained with the visual inspection device 1 and visual inspection method of this embodiment. Specifically, in this embodiment, a prism 17 is used which has a ring shape with a hollow portion 19 in the center that extends in the direction of the central axis O and opens on the front and rear surfaces, and in which the high-voltage tower 3 of the ignition coil 1 is arranged. The prism 17 has a flat surface 17a on the front side that is perpendicular to the direction of the central axis O, and a tapered reflective surface 25 on the rear side that is inclined with respect to the direction of the central axis O.

[0033] Then, in the inspection object setting process P1, the high-pressure tower 3 is positioned inside the hollow portion 19 of the prism 17 so that its entire surface faces the inner wall surface. In this state, in the illumination process P2, the illumination device 13 irradiates the entire surface of the high-pressure tower 3 inside the hollow portion 19 through the flat surface 17a of the prism 17. Then, in the imaging process P3, the reflected light from the entire surface of the high-pressure tower 3 passes through the prism 17, is reflected by the reflective surface 25 and output forward, and the imaging device 14 is configured to capture an image I of the high-pressure tower 3 with its entire surface unfolded in a ring shape.

[0034] At this time, the ring-shaped prism 17 allows the imaging device 14 to capture an image I in which the entire circumference of the surface of the high-pressure tower 3 is unfolded in a ring shape on a single screen. Based on this single image data, the entire surface condition around the high-pressure tower 3 can be inspected all at once. In this case, the entire device 11 can be made with a relatively simple configuration, and since the entire circumference of the high-pressure tower 3 can be inspected in a single imaging process, the inspection process is simple and quick. As a result, this embodiment makes it possible to perform a visual inspection of the entire surface of the high-pressure tower 3, which is the object to be inspected, in a short time, and has the excellent effect of reducing inspection costs.

[0035] In particular, in this embodiment, the lighting device 13 emits violet light, and is configured so that the entire circumference of the surface of the high-voltage tower 3 is irradiated with violet light during the lighting process P2. This makes it possible to detect insulating resin materials and other materials attached to the surface of the high-voltage tower 3 that are excited and emit fluorescence when irradiated with violet light, and even in cases where sufficient contrast cannot be obtained between the surface of the object to be inspected and foreign matter with visible light illumination, foreign matter on the surface can be sufficiently detected.

[0036] Furthermore, in this embodiment, the reflective surface 15 of the prism 17 is configured to be tilted at an angle of 45 degrees with respect to the central axis O. This allows the reflected light from the surface of the high-pressure tower 3, which is the object to be inspected, to enter the reflective surface 25 from the surface of the hollow section 19, bend at 90 degrees, and exit forward. Therefore, the reflected light can be effectively guided to the imaging device 14 to acquire an image.

[0037] Figure 7 shows another embodiment. In this embodiment, the connector 4 of the ignition coil 1 described above is the object to be inspected, and a visual inspection is performed on the surface of the connector 4, that is, the entire circumference of all four outer surfaces, in this case an inspection for the adhesion of insulating resin, which is also a foreign substance. In this case as well, the connector 4 of the ignition coil 1 is inserted into the hollow portion 19 of the prism 17, and the illumination and imaging processes are performed in the same manner. As a result, the entire circumference of the connector 4, that is, all four outer surfaces, can be captured as a single image, and a visual inspection can be performed in the same manner as in the above embodiment.

[0038] Although not described in detail in the above embodiment, when performing image processing in the image processing unit 23 (image processing step), a process to correct distortion occurring in the captured image I may also be performed. This allows for more accurate visual inspection. In addition, in the above embodiment, the object to be inspected is transported by a work transport mechanism 16 such as a robot and set in the hollow section 19, but the setting and transport of the object to be inspected may be performed manually by an operator. Alternatively, it is possible to configure the device to be moved and relatively inserted into the object to be inspected, which is fixedly placed at a predetermined inspection position.

[0039] Furthermore, the lighting device 13 is not limited to one that uses violet light; any device that can perform inspection using visible light may also be used. The inclination angle θ of the reflective surface of the prism 17 is not limited to 45°; any device that can emit reflected light forward is acceptable. In the above embodiment, the inspection of foreign matter adhering to the high-voltage tower 3 and connector 4 of the ignition coil 1 was given as an example, but it can be applied to various visual inspections of various items as objects to be inspected.

[0040] Furthermore, the materials and structure of the prism, the configuration of the prism holder, the configuration of the imaging device, etc., are not limited to the embodiments described above, and can be implemented with various modifications. This disclosure is described in accordance with the embodiments, but is not limited to those embodiments or structures. This disclosure also includes various modifications and variations within the equivalence range. In addition, various combinations and forms, as well as other combinations and forms that include only one, more, or fewer of those elements, fall within the scope and concept of this disclosure.

[0041] The control unit and its method described herein may be implemented by a dedicated computer provided by configuring a processor and memory programmed to perform one or more functions embodied by a computer program. Alternatively, the control unit and its method described herein may be implemented by a dedicated computer provided by configuring a processor by one or more dedicated hardware logic circuits. Alternatively, the control unit and its method described herein may be implemented by one or more dedicated computers configured by a combination of a processor and memory programmed to perform one or more functions and a processor configured by one or more hardware logic circuits. Furthermore, the computer program may be stored as instructions executed by the computer on a computer-readable non-transitional tangible recording medium. [Explanation of Symbols]

[0042] In the drawing, 1 is the ignition coil, 3 is the high-voltage tower (object to be inspected), and 4 is the connector. 11 is the visual inspection device, 12 is the prism unit, 13 is the illumination device, 14 is the imaging device, 15 is the control unit, 16 is the workpiece transport mechanism, 17 is the prism, 17a is the flat surface, 17b is the flange portion, 18 is the prism holder, 19 is the hollow portion, 20 is the camera, 23 is the image processing unit, 24 is the input / output unit, 25 is the reflective surface, I is the captured image, and O indicates the central axis.

Claims

1. An appearance inspection device (11) that images an object to be inspected (3) and inspects the surface condition of the object to be inspected based on the image data, A prism (17) having a ring shape with a hollow portion (19) extending axially in the center and opening on the front and rear surfaces where the object to be inspected is placed, a flat surface (17a) perpendicular to the axial direction on the front side, and a tapered reflective surface (25) inclined with respect to the axial direction on the rear side, An illumination device (13) having a light source (13b) positioned near the flat surface and arranged in a ring shape surrounding the hollow portion, which causes light emitted from the light source to enter the prism from the flat surface of the prism at an oblique angle, thereby illuminating the entire circumference of the surface of the object to be inspected inside the hollow portion through the flat surface of the prism, The system includes an imaging device (14) positioned in front of the prism for capturing an image of the surface of the object to be inspected, An appearance inspection apparatus configured such that, within the hollow portion, the entire surface circumference of the object to be inspected is positioned facing the inner wall surface of the hollow portion, light irradiated by the illumination device is irradiated onto the entire surface circumference of the object to be inspected, reflected light from the object to be inspected passes through the prism and is reflected by the reflective surface and output forward, and an image (I) of the entire surface circumference of the object to be inspected unfolded in a ring shape is captured by the imaging device.

2. The appearance inspection apparatus according to claim 1, wherein the lighting device is configured to emit violet light.

3. The visual inspection apparatus according to claim 1 or 2, wherein the reflective surface of the prism is configured to be inclined at an angle of 45 degrees with respect to the axial direction.

4. An appearance inspection method which involves imaging an object to be inspected (3) and inspecting the surface condition of the object based on the imaging data, A ring-shaped prism (17) has a hollow portion (19) extending axially in the center and opening at the front and rear surfaces where the object to be inspected is placed. The prism (17) has a flat surface (17a) perpendicular to the axial direction on the front side and a tapered reflective surface (25) inclined with respect to the axial direction on the rear side. The object to be inspected is positioned within the hollow portion such that the entire circumference of the surface of the object to be inspected faces the inner wall surface of the hollow portion. A lighting device (13) having a light source (13b) arranged in the vicinity of the flat surface and in a ring shape surrounding the hollow portion is used, and the light emitted from the light source is incident obliquely into the prism from the flat surface of the prism, thereby illuminating the entire circumference of the surface of the object to be inspected inside the hollow portion through the flat surface of the prism, An appearance inspection method comprising: an imaging step (P3) in which reflected light reflected from the entire circumference of the surface of the object to be inspected is reflected forward by the reflective surface after passing through the prism, and an imaging device (14) positioned in front of the prism captures an image of the surface of the object to be inspected with the entire circumference of the surface unfolded in a ring shape.

5. The method for visual inspection according to claim 4, wherein the lighting device is configured to emit violet light, and in the lighting step, violet light is emitted over the entire circumference of the surface of the object to be inspected.

6. The visual inspection method according to claim 4 or 5, wherein the reflective surface of the prism is configured to be inclined at an angle of 45 degrees with respect to the axial direction.

Images