Device and method for inspecting fiber, and method for manufacturing fiber

Abstract

A device (1) for inspecting a fiber comprises: a light irradiation unit (3) that emits light from a direction orthogonal to the axial direction of a fiber; a light collection unit (5) that is disposed between the light irradiation unit (3) and the fiber and that is a light collection means that condenses the light emitted from the light irradiation unit (3) to the position of the focal point of the fiber between the light collection unit (5) and the fiber; an imaging unit (2) that, after the light is emitted from the light irradiation unit (3) toward the fiber via the light collection unit (5), is condensed at the focal point, passes through the focal point, and is then transmitted through the fiber, captures this light; and a defect detection unit (4) that detects a defect of the fiber on the basis of an image signal acquired by the imaging unit (2).

Description

Fiber inspection device and method, fiber manufacturing method

[0001] The present invention relates to a fiber inspection device and method capable of accurately detecting defects present in a fiber, and also to a fiber manufacturing method.

[0002] Fibers made of glass or resin, such as optical fibers, can have problems with reduced strength and light transmittance if they have defects such as foreign matter inside or around them. This is why it is important to inspect the fiber. The following description focuses on optical fibers used for optical communications and lighting, but it can also be applied to fishing line and tennis racket string.

[0003] Optical fibers are composed of a core with a high refractive index and a cladding that surrounds it, and light that enters the core is confined in the core and propagates due to reflection and refraction at the cladding interface. The propagation state of light varies depending on the core diameter and refractive index distribution, and the transmission characteristics and connectivity also vary, so each type is used to take advantage of its respective characteristics. These cross-sectional refractive index distributions can be achieved with various glass and plastic materials. Optical fibers that use silica glass for both the core and cladding are used as transmission media for public communications. High-purity SiO ２ is used as the host glass, and GeO is used as the core to increase the refractive index. ２ Ya P ２ O ３ A refractive index profile is formed by adding a material such as F to the cladding to lower the refractive index.

[0004] Optical fibers made of glass are manufactured by forming a preform (base material) using a method such as MCVD (membrane chemical vapor deposition) or PCVD (plasma chemical vapor deposition), and then stretching it.

[0005] Optical fibers made of plastic are easier to manufacture and process and are less expensive than quartz-based optical components with the same structure, and in recent years have been used in a variety of applications, such as optical fibers, optical lenses, optical waveguides, etc. Among these optical components, plastic optical fibers (hereinafter referred to as POF) are particularly flexible, lightweight, and easy to process, since they are made entirely of plastic.

[0006] POF is manufactured by discharging a resin that will become a core portion from a mouthpiece and coating the core portion with another resin that has a different refractive index (generally a lower refractive index).

[0007] However, optical fibers manufactured in this manner may contain defects such as minute foreign particles or bubbles inside during the manufacturing process, which can cause deterioration in the optical transmission characteristics and physical strength of the optical fiber.

[0008] Therefore, Patent Document 1 discloses a method of inspecting defects inside an optical fiber by arranging at least three light irradiating means and imaging means at equal intervals around the optical fiber.

[0009] In addition, in Patent Document 2, air bubbles are detected by a light emitting unit and a light receiving unit, and a laser beam is used as the light emitting unit and an image sensor is used as the light receiving unit to examine the intensity distribution of forward scattered light and detect air bubbles from the intensity distribution pattern. In this method, as shown in Figure 14, a laser 25 is irradiated onto an optical fiber 10, and the light that is transmitted and refracted within the optical fiber 10 is received by an image sensor (not shown).

[0010] Japanese Unexamined Patent Publication No. 2005-283465 Japanese Unexamined Patent Publication No. 4-106448

[0011] However, the method of Patent Document 1 requires at least three light irradiation means and imaging means, which increases the cost of the inspection machine and requires a large space for installing the inspection machine.

[0012] Furthermore, in the method of Patent Document 2, the light reception distribution of the image sensor becomes a distribution as shown by reference numeral 70 in Fig. 14, and the ends of the image sensor receive light that has been significantly refracted within the optical fiber 10. For this reason, the amount of light received at the ends of the image sensor is extremely small compared to the central part of the image sensor, and the detection sensitivity at the ends of the image sensor becomes extremely low.

[0013] An object of the present invention is to provide a fiber defect detection device and method that can detect defects with high accuracy.

[0014] In order to achieve the above-mentioned object, a fiber inspection device and a fiber inspection method according to the present invention are characterized by the following features [1] to [5]. [1] A device for inspecting the presence or absence of defects in a fiber, comprising: a light irradiation unit that irradiates light from a direction perpendicular to the axial direction of a fiber to be inspected; a light focusing unit that is arranged between the light irradiation unit and the fiber and focuses the light irradiated from the light irradiation unit at a focal position of the fiber between the focusing unit and the fiber; an imaging unit that images light that is irradiated from the light irradiation unit through the focusing unit toward the fiber, once focused at the focal point, and then transmitted through the fiber; and a defect detection unit that detects defects in the fiber based on an image signal acquired by the imaging unit. [2] The fiber inspection device according to [1], wherein the imaging unit is a line sensor camera, and the line sensor camera is arranged so that the arrangement direction of the image sensors is perpendicular to the axial direction of the fiber and perpendicular to the light irradiation direction of the light irradiation unit. [3] The fiber inspection device according to [1] or [2], wherein the focusing unit is a rod lens, and the rod lens is arranged so that its axial direction is parallel to the axial direction of the fiber. [4] The fiber inspection device according to [1], wherein the light irradiating unit irradiates near-infrared light, and the imaging unit is a near-infrared camera. [5] A method for inspecting the presence or absence of defects in a fiber, comprising: irradiating light from a direction perpendicular to the axial direction of the fiber; focusing the light at a focal position of the fiber; irradiating the fiber with the light that has passed through the focal point; imaging the light that has transmitted through the fiber; and detecting defects in the fiber based on the image obtained by imaging.

[0015] According to the fiber inspection device and inspection method of the present invention, defects such as foreign matter in a fiber can be inspected with high accuracy using a small number of light irradiating means and imaging means.

[0016] 1 is a schematic diagram showing the configuration of an embodiment of the fiber inspection device of the present invention. FIG. 1 is a diagram showing how light incident on a focusing unit passes through the focusing unit. FIG. 2 is a diagram showing how light incident on an optical fiber passes through the optical fiber. FIG. 3 is an example of an image obtained by the fiber inspection device of the present invention. FIG. 4 is a diagram showing how light incident on an optical fiber passes through the optical fiber in a fiber inspection device that does not have a focusing unit. FIG. 5 is an image of the optical fiber acquired by the imaging unit in the embodiment of FIG. 5. FIG. 6 is a diagram showing an image of a defect in an optical fiber and an extracted defect. FIG. 7 is an image obtained in Example 3 and Comparative Example 2. FIG. 8 is a diagram showing how light travels inside the focusing means. FIG. 9 is a diagram showing the distance between the optical fiber and the focusing unit. FIG. 10 is a diagram explaining a fiber inspection device that uses a ball lens as the focusing unit and an image obtained by the inspection device. FIG. 11 is a diagram explaining a fiber inspection device that uses a rod lens as the focusing unit and an image obtained by the inspection device. FIG. 12 is a diagram showing how light incident on an optical fiber passes through the optical fiber in a fiber inspection device that has two sets of a light irradiation unit, a focusing unit, and an imaging unit. FIG. 13 is a diagram showing the received light distribution obtained by the imaging unit in Patent Document 2. FIG. 14 is an image obtained in Example 2.

[0017] The following description focuses on optical fibers for optical communications and lighting, but it can also be applied to fishing line and tennis racket strings.

[0018] Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to these embodiments.

[0019] 1 is a schematic diagram of one embodiment of a fiber inspection device of the present invention. As shown in the figure, the fiber inspection device 1 includes an imaging unit 2, a light irradiation unit 3, a defect detection unit 4, and a light collection unit 5. The fiber inspection device 1 inspects an optical fiber 10 as an inspection target.

[0020] The optical fiber 10 to be inspected may run continuously in the longitudinal direction, or may run intermittently, stopping when an image is taken and running after the image is taken. Alternatively, the optical fiber 10 may be cut to a predetermined length, fixed, and imaged in a stationary state. The diameter of the optical fiber 10 is not particularly limited, but a diameter of 0.05 mm or more is preferable because it is easy to inspect.

[0021] The light irradiation unit 3 can be a device in which LED elements are arranged in a plane, or a device in which a light source such as an LED is guided to an exit surface using an optical fiber light guide to emit light. A device in which an optical fiber light guide is used to guide light to an exit surface to emit light is preferred because it can irradiate a large amount of light in the imaging axis direction. Here, the area in the light irradiation unit 3 that is irradiated with light is referred to as the "exit surface."

[0022] The irradiation axis of the light emitted from the light irradiation unit 3 is perpendicular to the axial direction (longitudinal direction) of the optical fiber 10. Here, in the present invention, the "perpendicular direction" includes directions within 90 degrees ±5 degrees.

[0023] The focusing unit 5 has the function of focusing the parallel components of the light irradiated from the illumination unit 3 into a single point or a single line, and can be a lens that transmits light to focus, such as a convex lens, or a concave mirror that reflects light to focus. Considering ease of placement, a lens is preferable. Examples of lenses that can be used include rod lenses, ball lenses, hemispherical lenses, and cylindrical lenses. It is more preferable to use rod lenses or ball lenses with strong refractive power. When using a rod lens, the axial direction of the rod lens and the axial direction of the optical fiber 10 are arranged parallel to each other. Here, "parallel" includes an angle between the two axes of 0 degrees ±3 degrees.

[0024] The light collecting unit 5 is disposed between the optical fiber 10 and the light irradiating unit 3 so that the axial center of the optical fiber 10, the center of the light collecting unit 5, and the center of the exit surface of the light irradiating unit 3 are aligned on a straight line. Here, "on a straight line" means that the above three centers exist within a cylinder with a radius of 0.5 mm. The distance between the light collecting unit 5 and the light irradiating unit 3 is preferably within 5 mm.

[0025] The imaging unit 2 is disposed opposite the light irradiation unit 3 across the optical fiber 10. As the imaging unit 2, a line sensor camera in which a plurality of light receiving elements are arranged one-dimensionally or an area sensor camera in which a plurality of light receiving elements are arranged two-dimensionally can be used. When a line sensor camera is used, the imaging unit 2 is disposed so that the arrangement direction of the light receiving elements of the line sensor camera is perpendicular to the axial direction of the optical fiber 10 and perpendicular to the light irradiation direction of the light irradiation unit 3. When an area sensor camera is used, the imaging unit 2 is disposed so that the arrangement surface of the light receiving elements of the area sensor camera is perpendicular to the light irradiation direction of the light irradiation unit 3. Here, "perpendicular" includes angles up to 90 degrees ±5 degrees.

[0026] A lens is attached to the front of the imaging unit 2, and the lens magnification can be changed according to the size of the defect to be detected. Then, the distance between the imaging unit 3 and the optical fiber 10 can be set according to the lens magnification so that the optical fiber 10 is in focus.

[0027] The output image from the imaging unit 2 is sent to the defect detection unit 4. The defect detection unit 4 is made up of a computer that operates according to a program, and determines whether the output image contains any defects by subjecting the output image to grayscale image processing, area processing, image processing using AI, etc.

[0028] Next, the distance between the focusing portion 5 and the optical fiber 10 will be described with reference to FIGS. 9 and 10. FIG. 9 is a diagram illustrating how light travels through a ball lens or a rod lens. Parallel light incident on the effective diameter D2 of a lens with a diameter D1 is refracted as it travels from the air to the lens and from the lens to the air, and is focused at a single point (focal point 11). If the refractive index of the lens is n, the distance EFL (focal length) between the lens center 6 and the focal point 11 and the distance BFL (back focus) between the lens edge and the focal point 11 can be calculated using the following equations (1) and (2), respectively.

[0029]

[0030]

[0031] Now, let us consider the reverse direction of light travel in Fig. 9. In other words, when light is irradiated from the focal point 11 toward the lens, the light traveling from the focal point 11 toward the lens becomes parallel light after passing through the lens.

[0032] Therefore, as shown in FIG. 10 , by setting the distance L between the light-collecting unit 5 and the optical fiber 10 to the sum of the back-flush length (BFL) of the light-collecting unit 5 and the back-flush length (BFL) of the optical fiber 10, the parallel light incident on the light-collecting unit 5 becomes parallel light after passing through the optical fiber 10. That is, the parallel light incident on the light-collecting unit 5 is first focused at the focal point 11 of the lens by the light-collecting unit 5. Since the focal point 11 is also the focal point of the optical fiber 10, the light passing through the focal point 11 and then the optical fiber 10 becomes parallel light. In practice, the light irradiated from the light-irradiating unit 3 is not completely parallel, so it is preferable to fine-tune the distance L while viewing the image obtained by the imaging unit 2. Here, the emission width at the exit surface in a direction perpendicular to the axial direction of the optical fiber 10 is preferably 30 times or more the diameter of the optical fiber 10. The lens effective diameter D2 in FIG. 9 is preferably 30 to 50 times the diameter of the optical fiber 10.

[0033] Next, a method for detecting defects in the optical fiber 10 using the fiber inspection device 1 will be described with reference to FIGS.

[0034] 2 , light 401 that is incident from incident position P1 and passes through the center 6 of the light collecting unit 5 travels straight without being refracted. Light 402 that is incident from a position away from this incident position P1 becomes refracted light 403 that is refracted inside the light collecting unit 5 in a direction approaching light 401. When radiated from the light collecting unit 5 into the air, refracted light 403 is further refracted in a direction approaching light 401, becoming refracted light 404. The refraction angles of refracted light 403 and 404 increase as the incident position of light 402 moves away from incident position P1. The point where refracted light 404 and light 401 intersect becomes focal point 11. Refracted light 404 that is condensed at focal point 11 then diffuses in a direction away from light 401.

[0035] 3 , light 401 enters optical fiber 10 at incident position P2 and passes through the axial center of optical fiber 10. Light 401 travels straight without being refracted. Diffused refracted light 404 enters optical fiber 10 from a position away from incident position P2, and becomes refracted light 405, which is refracted in a direction approaching light 401 upon entering. Refracted light 405 becomes refracted light 406, which is refracted further in a direction approaching light 401 upon exiting optical fiber 10. The refraction angles of refracted light 405 and 406 increase as the incident position of refracted light 404 moves away from incident position P2, and refracted light 406 becomes approximately parallel to light 401. Light 401 and refracted light 406 enter imaging unit 2, and an image of the interior of optical fiber 10 as shown in FIG. 4 is obtained.

[0036] If a defect 30 exists inside the optical fiber 10, the defect will block the refracted light 405, preventing it from entering the imaging unit 2. In FIG. 3, the refracted light passing through the defect 30 is indicated by 405b. Therefore, in the image obtained by the imaging unit 2, the defect 30 will appear darker than its surroundings, as shown in FIG. 7(a). By subjecting the captured image shown in FIG. 7(a) to image processing such as binarization by the defect detection unit 4, the defect portion 31 can be extracted, as shown in FIG. 7(b).

[0037] FIG. 5 is a diagram showing the state of light passing through the optical fiber 10 when the light collecting unit 5 is removed from the fiber inspection device 1. As shown in FIG. 5 , without the light collecting unit 5, light 401 and 402 irradiated from the light irradiating unit 3 are directly incident on the optical fiber 10. Light 401 incident from the incident position P2 and passing through the center of the optical fiber 10 travels straight without refracting and is incident on the imaging unit 2. Light 402 incident from a position away from the incident position P2 is incident on the optical fiber 10 and becomes refracted light 405, which is refracted in a direction approaching light 401. When radiated from the optical fiber 10 into the air, refracted light 405 is further refracted in a direction approaching light 401, becoming refracted light 406. The refraction angles of the refracted light 405 and 406 increase as the incident position of light 401 moves away from the incident position P2. The point where this refracted light 406 and light 401 intersect is the focal point 12. Refracted light 406 focused at focal point 12 diffuses in a direction away from light 401. If imaging unit 2 is positioned farther from optical fiber 10 than focal point 12, only light incident near incident position P2 is incident on imaging unit 2. The diffused refracted light 406 is not incident on imaging unit 2, and a non-inspection region 61 where the inside of optical fiber 10 cannot be inspected becomes large. Therefore, the image obtained by imaging unit 2 is bright only near the center of optical fiber 10 and dark at the ends, as shown in FIG. 6 . Therefore, defects 30 present near the imaging axis can be imaged, but defects 30 present in non-inspection region 61 cannot be imaged.

[0038] In this way, the fiber inspection device 1 of the present invention can inspect almost the entire inside of the optical fiber 10, and the inspection accuracy of the optical fiber 10 can be significantly improved.

[0039] Furthermore, although FIG. 3 shows an example of defect 30 existing inside optical fiber 10, if defect 30 exists on the outer periphery of optical fiber 10 or if the outer diameter of optical fiber 10 is partially different, an image different from that of a normal portion will be obtained, and these defects can be extracted by applying appropriate image processing in defect detection unit 4.

[0040] FIG. 13 illustrates the state of light passing through the optical fiber 10 when a fiber inspection device including two sets of a light emitting unit 3, a light collecting unit 5, and an image capturing unit 2 is used. One set is positioned so that the first imaging axis 23 captures an image from a first imaging direction 24, and the other set is positioned so that the second imaging axis 23b captures an image from a second imaging direction 24b tilted at a predetermined angle relative to the first imaging direction 24. As shown in FIG. 3 , even in the fiber inspection device 1 of the present invention, if there is only one set of a light emitting unit 3, a light collecting unit 5, and an image capturing unit 2, a small non-inspection region 61 exists. The non-inspection region 61 is located near the outer periphery of the optical fiber 10 and is a very small region. Therefore, even if a defect exists only in the non-inspection region 61, it has almost no effect on the quality (light transmission characteristics, etc.) of the optical fiber 10.

[0041] When detecting minute defects present in the non-inspection region 61, as shown in FIG. 13, two sets of the light irradiation unit 3, the light collecting unit 5, and the imaging unit 2 can be tilted at a predetermined angle to eliminate the non-inspection region 61, further improving inspection accuracy. The predetermined angle θ is preferably 40 to 60 degrees. More specifically, at least a portion of the non-inspection region 61 of the inspection device in the first imaging direction 24 becomes the inspection region (region other than the non-inspection region 61b) of the inspection device in the second imaging direction 24b. Conversely, at least a portion of the non-inspection region 61b of the inspection device in the second imaging direction 24b becomes the inspection region (region other than the non-inspection region 61) of the inspection device in the first imaging direction 24. This allows the non-inspection regions 61 and 61b to be reduced or eliminated.

[0042] FIG. 11 shows an embodiment in which a ball lens 51 is used as the light collecting unit 5. When the light collecting unit 5 is a ball lens 51 as shown in FIG. 11( a), the light irradiated from the light irradiating unit 3 is collected at one point and then emitted in a cone shape. Therefore, when an area camera is used as the imaging unit 2 to capture an image of an imaging range 80 as shown in FIG. 11( b), the captured image has a bright central portion as shown in FIG. 11( c). By using this portion as the inspection range, defects can be detected with high accuracy. Furthermore, when a line sensor camera is used as the imaging unit 2 to capture an image of the imaging range 80, even when a ball lens 51 is used as the light collecting unit 5, capturing an image near the center of the imaging range 80 is preferable because it allows the entire optical fiber 10 to be brightly imaged.

[0043] 12 shows an embodiment in which a rod lens is used as the light collecting unit 5. When the light collecting unit 5 is a rod lens 52 as shown in FIG. 12( a), the light irradiated from the light irradiating unit 3 is collected into a single line and then emitted in a rectangular shape. Therefore, when an image capturing range 80 is captured using an area camera as the imaging unit 2 as shown in FIG. 12( b), the captured image is bright all the way to the edges as shown in FIG. 12( c), and therefore the range that can be inspected with high precision in a single image capturing can be expanded.

[0044] An optical fiber 10 that is coated around the clad with a coating may be inspected as an inspection target. If the light irradiated from the light irradiating unit 3 is visible light, the coating around the clad blocks the visible light in the optical fiber 10, preventing the visible light from passing through the inside of the optical fiber 10, making inspection impossible.

[0045] In such a case, if the wavelength of the light irradiated from the light irradiating unit 3 is near-infrared light, for example, light with a wavelength of 1000 to 1500 nm, it can be transmitted through the coating and illuminate the inside of the optical fiber 10. The near-infrared light transmitted through the optical fiber 10 can be imaged using the imaging unit 2 that is sensitive to this wavelength, for example, a camera made up of an InGaAs (indium gallium arsenide) light-receiving element. The imaging unit 2 is fitted with a lens that transmits near-infrared light.

[0046] Since the refractive index of the optical fiber 10 and the light collecting unit 5 changes depending on the wavelength of the light irradiated by the light irradiating unit 3, the distance between the optical fiber 10 and the light collecting unit 5 can be determined in accordance with the above-mentioned formulas (1) and (2) using the refractive index of the wavelength to be used.

[0047] By providing an inspection process before or after the optical fiber is manufactured and wound onto a reel, and inspecting the optical fiber using the optical fiber inspection method of the present invention, it is possible to prevent optical fiber containing defects from being shipped. In addition, by feeding back the inspection results to the manufacturing process, it is possible to eliminate the causes of defects.

[0048] Furthermore, the grade of the optical fiber can be determined based on the inspection results of the optical fiber inspection method, that is, the presence or absence of defects and the size and amount of defects, and the use of the optical fiber can be determined based on the grade.

[0049] Example 1 An optical fiber 10 having a core material made of PMMA, a cladding material made of a fluorine-containing polymer, a core diameter of 240 μm, and a cladding diameter of 250 μm was inspected. The optical fiber 10 was run in the axial direction at 10 m / min.

[0050] The light irradiating unit 3 uses a white LED as a light source and an optical fiber light guide with an emission diameter of 10 mm.

[0051] The light collecting part 5 was a rod lens having a diameter of 10 mm and made of BK7 material.

[0052] The imaging unit 2 used an area sensor camera with 640 x 480 20 μm light receiving elements arranged vertically and horizontally. The lens was a telecentric lens for visible light with a magnification of 4x. In this case, the resolution was 20 / 4 = 5 μm / pixel. The exposure time of the area sensor camera was 40 μsec, and the frame rate was 60 Hz.

[0053] The distance between the light exit surface of the light irradiating unit 3 and the rod lens was set to 1 mm.

[0054] The distance between the rod lens and the optical fiber 10 was set to 2.36 mm, which is the sum of the BFL (back focus) of the rod lens, which is 2.3 mm, and the BFL of the optical fiber, which is 0.06 mm.

[0055] The image obtained by the imaging unit 2 is shown in Fig. 7(a), and it was possible to image the defect 30. By performing shading processing and area processing on this image, it was possible to detect only the defect 31, as shown in Fig. 7(b).

[0056] Comparative Example 1 An inspection was carried out under the same conditions as in Example 1, except that the light collecting unit 5 was not used.

[0057] The image captured by the imaging unit 2 is shown in Figure 6. The central part of the optical fiber 10 was brightly imaged because the light from the light irradiating unit 3 was transmitted through it, but the light from the light irradiating unit 3 was not transmitted through parts other than the central part, and it was not possible to image the internal state of the optical fiber 10.

[0058] Example 2 Inspection was carried out under the same conditions as in Example 1, except that the light-collecting portion 5 was a ball lens having a diameter of 10 mm and made of BK7 material.

[0059] The distance between the light emission surface of the light irradiation unit 3 and the ball lens was set to 1 mm.

[0060] The distance between the ball lens and the optical fiber 1 was 2.36 mm, which was the sum of the BFL (back focus) of the rod lens being 2.3 mm and the BFL of the optical fiber being 0.06 mm.

[0061] The image captured by the imaging unit 2 is shown in FIG. 15, and the optical fiber 10 was able to be inspected with high precision within an inspection range 90 in the captured image.

[0062] Example 3 An optical fiber 10 having a total fiber diameter of 300 μm, in which the core material is PMMA, the clad is a fluorine-containing polymer, the core diameter is 244 μm, the clad diameter is 250 μm, and a black carbon coating having a thickness of 25 μm is applied to the core material, was inspected.

[0063] The light irradiating unit 3 used a near-infrared LED with a wavelength of 1450 nm as a light source, and an optical fiber light guide with an emission diameter of 10 mm.

[0064] The light collecting part 5 was a rod lens having a diameter of 10 mm and made of BK7 material.

[0065] The imaging unit 2 used an area sensor camera with 640 x 480 20 μm near-infrared light receiving elements arranged vertically and horizontally. The lens used was a telecentric lens for near-infrared light, with a magnification of 4x. In this case, the resolution was 20 / 4 = 5 μm / pixel. The exposure time of the area camera was 40 μsec, and the frame rate was 60 Hz.

[0066] The distance between the light exit surface of the light irradiating unit 3 and the rod lens was set to 1 mm.

[0067] When near-infrared light of 1450 nm is used, the BFL (back focus) of the rod lens is 2.5 mm and the BFL of the optical fiber is 0.07 mm, so the distance between the rod lens and the optical fiber 10 was set to 2.57 mm, which is the sum of the two.

[0068] The image obtained by the imaging unit 2 is as shown in FIG. 8( a ), and by using near-infrared light, it was possible to image the inside of the optical fiber 10 through the black carbon coating.

[0069] Comparative Example 2 An inspection was carried out under the same conditions as in Example 3, except that the light collecting unit 5 was not used.

[0070] The image obtained by the imaging unit 2 is shown in Fig. 8(b). The central part of the optical fiber 10 was brightly imaged because the light from the light irradiating unit 3 was transmitted through it, but the light from the light irradiating unit 3 was not transmitted through parts other than the central part, and it was not possible to image the internal state of the optical fiber 10.

[0071] Here, the features of the embodiments of the fiber inspection device and fiber inspection method according to the present invention described above will be briefly summarized and listed below in [1] to [5].

[0072] [1] A device for inspecting a fiber (10) for defects, comprising: a light irradiation unit (3) that irradiates light from a direction perpendicular to the axial direction of the fiber being inspected; a light focusing unit (5) arranged between the light irradiation unit and the fiber, the light focusing unit focusing the light irradiated from the light irradiation unit at a focal position of the fiber between the focusing unit and the fiber; an imaging unit (2) that images light that is irradiated from the light irradiation unit through the focusing unit toward the fiber, once focused at the focal point, and then transmitted through the fiber; and a defect detection unit that detects defects in the fiber based on an image signal acquired by the imaging unit. [2] The fiber inspection device according to [1], wherein the imaging unit is a line sensor camera, and the arrangement direction of the image sensors of the line sensor camera is arranged so that the arrangement direction is perpendicular to the axial direction of the fiber and perpendicular to the light irradiation direction of the light irradiation unit. [3] The fiber inspection device according to [1] or [2], wherein the focusing unit is a rod lens (52) and is arranged so that the axial direction of the rod lens is parallel to the axial direction of the fiber. [4] The fiber inspection device according to [1], wherein the light irradiating unit irradiates near-infrared light and the imaging unit is a near-infrared camera. [5] A method for inspecting the presence or absence of defects in a fiber (10), comprising: irradiating light from a direction perpendicular to the axial direction of the fiber; focusing the light at a focal position of the fiber; irradiating the fiber with light that has passed through the focal point; imaging the light that has transmitted through the fiber; and detecting defects in the fiber based on the image obtained by imaging.

[0073] Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention.

[0074] This application is based on a Japanese patent application (Patent Application No. 2023-209866) filed on December 13, 2023, the contents of which are incorporated herein by reference.

[0075] The present invention can provide a fiber inspection device and a fiber inspection method that can accurately inspect for defects such as foreign matter in a fiber using a small number of light irradiation units and imaging units. The present invention that achieves this effect is useful for a fiber inspection device and a fiber inspection method.

[0076] REFERENCE SIGNS LIST 1 Fiber inspection device 2 Imaging unit 3 Light irradiation unit 4 Defect detection unit 5 Light collecting unit 6 Center of light collecting unit 10 Optical fiber 11 Fiber focus (focus of light collecting unit) 20, 404 Light incident on optical fiber 20b Light incident on optical fiber in second imaging axis 21, 405, 405b Light refracted after entering optical fiber 21b Light refracted after entering optical fiber in second imaging axis 22, 406 Light refracted after passing through optical fiber 22b Light refracted after passing through optical fiber in second imaging axis 23 First imaging axis 23b Second imaging axis 24 First imaging direction 24b Second imaging direction 30 Internal defect 30b Internal defect present in optical fiber near the imaging axis 31 Detected internal defect 40, 402 Light emitted from light irradiation unit 3 41, 403 Light refracted at the light collecting section 51 Ball lens 52 Rod lens 61 Non-inspection area in optical fiber 70 Light reception distribution of image sensor in Patent Document 2 80 Imaging area 81 Captured image 90 Inspection range in captured image when using a ball lens D1 Diameter of lens D2 Effective diameter of lens EFL Distance between lens center and focal point (focal length) BFL Distance between lens end and focal point (back focus) L Distance between light collecting section and optical fiber

Claims

1. A device for inspecting the presence or absence of defects in a fiber, comprising: a light irradiation unit which irradiates light from a direction perpendicular to the axial direction of the fiber being inspected; a light focusing unit which is disposed between the light irradiation unit and the fiber and which focuses the light irradiated from the light irradiation unit at a focal position of the fiber between the light focusing unit and the fiber; an imaging unit which images the light which is irradiated from the light irradiation unit through the light focusing unit towards the fiber, once focused at the focal position, and then transmitted through the fiber after passing through the focal position; and a defect detection unit which detects defects in the fiber based on an image signal acquired by the imaging unit.

2. The fiber inspection device according to claim 1, wherein the imaging unit is a line sensor camera, and the arrangement direction of the imaging elements of the line sensor camera is arranged perpendicular to the axial direction of the fiber and perpendicular to the light irradiation direction of the light irradiation unit.

3. The fiber inspection device according to claim 1 or 2, wherein the light collecting section is a rod lens, and the axial direction of the rod lens is arranged parallel to the axial direction of the fiber.

4. The fiber inspection device according to claim 1, wherein the light irradiating unit irradiates near-infrared light, and the imaging unit is a near-infrared camera.

5. A method for inspecting the presence or absence of defects in a fiber, comprising: irradiating the fiber with light from a direction perpendicular to the axial direction of the fiber; focusing the light at a focal position of the fiber; irradiating the fiber with the light that has passed through the focal position; capturing an image of the light that has passed through the fiber; and detecting defects in the fiber based on the captured image.

Images