Optical fiber manufacturing method and manufacturing device

Abstract

The present invention provides a method for manufacturing an optical fiber, wherein an optical fiber is formed as a result of an optical fiber preform being drawn while being heated in a drawing furnace, said method including: a step for acquiring, before drawing the optical fiber preform, a captured image obtained by simultaneously photographing the optical fiber preform and an opening of the drawing furnace; and a step for adjusting the position of the optical fiber preform, on the basis of the captured image, such that the positions of the center of the optical fiber preform and the center of the opening coincide with each other.

Description

[Technical Field]

[0001] The present disclosure relates to a method and apparatus for manufacturing an optical fiber. This application claims priority to Japanese Application No. 2020-189691, filed on November 13, 2020, and incorporates by reference all of the contents of said Japanese application. [Background technology]

[0002] Patent Document 1 discloses an optical fiber preform centering device for optically positioning an optical fiber preform without contact, in which a light source and a photodetector are arranged on the same optical axis, a light beam emitted from the light source is directed toward the photodetector, and the optical fiber preform is arranged so that it crosses the light beam midway between the light source and the photodetector. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 60-231438 Summary of the Invention

[0004] A method for manufacturing an optical fiber according to one aspect of the present disclosure includes: A method of manufacturing an optical fiber by drawing an optical fiber preform while heating it in a drawing furnace, before inserting the optical fiber preform into the upper opening of the drawing furnace; and Before drawing the optical fiber preform, the optical fiber preform and the drawing furnace The aforementioned acquiring an image simultaneously capturing the aperture; and adjusting the position of the optical fiber preform based on the captured image so that the center of the optical fiber preform and the center of the opening coincide with each other. fruit, the captured images include a first captured image and a second captured image, In the step of acquiring the captured image, a first camera photographs the optical fiber preform and the opening to obtain the first captured image, and a second camera installed at a position different from the first camera photographs the optical fiber preform and the opening to obtain the second captured image; The first camera and the second camera are provided so as to face downward and obliquely inward with respect to the central axis of the optical fiber preform in the horizontal direction.

[0005] Furthermore, an optical fiber manufacturing apparatus according to an aspect of the present disclosure includes: a drawing furnace for drawing an optical fiber preform while heating it to form an optical fiber; a feeder that holds an upper end of the optical fiber preform and can move the position of the optical fiber preform; before inserting the optical fiber preform into the upper opening of the drawing furnace; and Before drawing the optical fiber preform, the optical fiber preform and the drawing furnace The aforementioned Shooting the aperture simultaneously a first camera and a second camera installed at a different position from the first camera; and, The first camera and the second camera and a control unit that controls the feeder based on the captured image acquired by the optical fiber preform so that the center of the optical fiber preform and the center of the opening coincide with each other. And, The first camera and the second camera are provided so as to face downward and obliquely inward with respect to the central axis of the optical fiber preform in the horizontal direction. [Brief explanation of the drawings]

[0006] [Figure 1] FIG. 1 is a schematic diagram illustrating an optical fiber manufacturing apparatus according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a schematic diagram showing the upper configuration of the manufacturing apparatus including the imaging unit and the drawing furnace. [Figure 3] FIG. 3 is a top view of the imaging unit shown in FIG. [Figure 4A] FIG. 4A is an image showing the optical fiber preform and the opening of the drawing furnace, captured by the first camera included in the imaging unit without illumination by the illumination device. [Figure 4B] FIG. 4B is an image showing the optical fiber preform and the opening of the drawing furnace, captured by the second camera included in the imaging unit without illumination by the illumination device. [Figure 5A] FIG. 5A is an image showing an optical fiber preform and an opening of a drawing furnace, captured by a first camera under illumination by a first illumination device provided in the imaging section. [Figure 5B]FIG. 5B is an image showing the optical fiber preform and the opening of the drawing furnace, captured by the second camera under illumination by the second lighting device provided in the imaging section. [Figure 6] FIG. 6 is a diagram showing the center position of the optical fiber preform and the center position of the opening of the drawing furnace detected by image processing. [Figure 7] FIG. 7 is a timing chart showing the timing of light emitted from the first illumination device and the second illumination device according to the modified example, and the opening and closing of the shutters of the first camera and the second camera. DETAILED DESCRIPTION OF THE INVENTION

[0007] (Problem to be solved by this disclosure) When the centering of the optical fiber preform is performed by irradiating it with a light beam in order to optically adjust the position of the optical fiber preform without contact as in Patent Document 1, if the positions of the light source or photodetector are misaligned, the centering of the optical fiber preform cannot be performed accurately. Therefore, periodic maintenance of these devices is required to prevent misalignment of the light source and photodetector.

[0008] Therefore, an object of the present disclosure is to provide an optical fiber manufacturing method and manufacturing apparatus that can accurately and easily align the center of an optical fiber preform with a drawing furnace.

[0009] (Description of Embodiments of the Present Disclosure) First, embodiments of the present disclosure will be listed and described. A method for manufacturing an optical fiber according to one aspect of the present disclosure includes: (1) A method for manufacturing an optical fiber by drawing an optical fiber preform while heating it in a drawing furnace, before inserting the optical fiber preform into the upper opening of the drawing furnace; and Before drawing the optical fiber preform, the optical fiber preform and the drawing furnace The aforementioned acquiring an image simultaneously capturing the aperture; and adjusting the position of the optical fiber preform based on the captured image so that the center of the optical fiber preform and the center of the opening coincide with each other. fruit, the captured images include a first captured image and a second captured image, In the step of acquiring the captured image, a first camera photographs the optical fiber preform and the opening to obtain the first captured image, and a second camera installed at a position different from the first camera photographs the optical fiber preform and the opening to obtain the second captured image; The first camera and the second camera are provided so as to face downward and obliquely inward with respect to the central axis of the optical fiber preform in the horizontal direction. According to the present disclosure, it is possible to accurately and easily center the optical fiber preform (glass preform) and the drawing furnace. This prevents the optical fiber preform being drawn with its central axis tilted, which can cause the melting point of the optical fiber preform to become eccentric, resulting in breakage or asymmetry of the drawn optical fiber, and can prevent the optical fiber preform from colliding with the opening of the drawing furnace when being inserted into the furnace. Furthermore, when adjusting the centering using a laser or the like, as described above, periodic maintenance of the position adjustment mechanism is required to accurately align the laser. The method of the present disclosure enables the position adjustment of the optical fiber preform using a captured image that includes both the optical fiber preform and the opening of the drawing furnace. Therefore, the imaging mechanism can be misaligned as long as it can obtain an image that includes both the optical fiber preform and the opening of the drawing furnace, eliminating the need for periodic maintenance of the imaging mechanism. It should be noted that "the positions of the center of the optical fiber preform and the center of the opening coincide" does not necessarily mean that they coincide perfectly, and a deviation of about 1 mm is acceptable. Furthermore, according to the present disclosure, by using the first and second cameras, it is possible to obtain the first captured image and the second captured image captured from different locations, and since the misalignment between the center of the optical fiber preform and the center of the opening of the drawing furnace can be detected from two directions, it is possible to more accurately align the center of the optical fiber preform and the opening of the drawing furnace.

[0011] (3) In the step of acquiring the captured image, irradiating the optical fiber preform with first light emitted from a first lighting device; irradiating the optical fiber preform with second light emitted from a second lighting device and having a wavelength different from that of the first light; a first filter that can transmit only the first light; The aforementioned A first camera photographs the optical fiber preform and the opening. The aforementioned Acquire a first captured image; a second filter that can transmit only the second light; The aforementioned A second camera photographs the optical fiber preform and the opening. The aforementioned A second captured image may be acquired. According to the present disclosure, a first camera acquires an image illuminated only with a first light from a first illumination device suitable for acquiring a first captured image using a first filter, and the influence of light of other wavelengths from other illumination sources is reduced, thereby enabling an image in which the outer edge of the optical fiber preform can be easily recognized. As a result, the optical fiber preform and the drawing furnace can be accurately centered. A similar effect can be obtained with a second camera using a second filter and a second illumination device. Although each filter transmits only the wavelengths of the first light and the second light, the first filter provided in the first camera does not block all wavelengths of the second light, but transmits some wavelengths (overlapping with the wavelength distribution of the first light).Similarly, the second filter provided in the second camera does not block all wavelengths of the first light, but transmits some wavelengths (overlapping with the wavelength distribution of the second light). The first filter transmits light of the first wavelength but does not transmit only light emitted from the first lighting device, and similarly, the second filter transmits light of the second wavelength but does not transmit only light emitted from the second lighting device.

[0012] (4) The wavelength of the first light may be red, and the wavelength of the second light may be blue. By using red light and blue light for the colors of the first light and the second light, respectively, the difference in wavelength between the first light and the second light is large, so that the first light is blocked by the second filter and is less likely to enter the second camera, and similarly, the second light is blocked by the first filter and is less likely to enter the first camera. In this way, by reducing the influence of light of other wavelengths, it is possible to obtain a captured image in which the outer edge of the optical fiber preform is easily recognized. Note that "red" refers to a wavelength of approximately 600 to 800 nm, and "blue" refers to a wavelength of approximately 400 to 500 nm.

[0013] (5) The step of acquiring the captured image includes: irradiating the optical fiber preform with first light emitted from a first lighting device at a first timing; According to the first timing The aforementionedThe shutter of the first camera is opened and the image is illuminated only by the first light. first acquiring a captured image; irradiating the optical fiber preform with second light emitted from a second lighting device at a second timing different from the first timing; According to the second timing The aforementioned The shutter of the second camera is opened and the image is illuminated only by the second light. second The method may include a step of acquiring a captured image. As in the present disclosure, by using multiple lighting devices with different light emission timings and capturing images in accordance with the light emission timings of the lighting devices, it is possible to capture images in which only the light from each lighting device that is appropriate for capturing the captured image from each camera is irradiated, thereby enabling the capture of captured images in which the outer edge of the optical fiber preform is easily recognized. As a result, the optical fiber preform and the drawing furnace can be more accurately centered.

[0014] (6) In the step of acquiring the captured image, the optical fiber preform may be irradiated with light reflected by a screen disposed on the rear surface of the optical fiber preform. By using transmitted illumination of light reflected by a screen, the optical fiber preform can be evenly illuminated from the direction facing the camera, making it possible to obtain an image in which the outer edges of the optical fiber preform are more easily recognized.

[0015] Furthermore, an optical fiber manufacturing apparatus according to an aspect of the present disclosure includes: (7) a drawing furnace for drawing an optical fiber preform while heating it to form an optical fiber; a feeder that holds an upper end of the optical fiber preform and can move the position of the optical fiber preform; before inserting the optical fiber preform into the upper opening of the drawing furnace; and Before drawing the optical fiber preform, the optical fiber preform and the drawing furnace The aforementioned Shooting the aperture simultaneously a first camera and a second camera installed at a different position from the first camera; and, The first camera and the second cameraand a control unit that controls the feeder based on the captured image acquired by the optical fiber preform so that the center of the optical fiber preform and the center of the opening coincide with each other. And, The first camera and the second camera are provided so as to face downward and obliquely inward with respect to the central axis of the optical fiber preform in the horizontal direction. According to the present disclosure, an optical fiber manufacturing apparatus can be provided that can accurately and easily perform core alignment of an optical fiber preform, thereby preventing breakage or asymmetry of the optical fiber after drawing, and preventing the optical fiber preform from colliding with the opening of the drawing furnace.

[0016] (Effects of the present disclosure) According to the present disclosure, it is possible to provide an optical fiber manufacturing method and manufacturing apparatus that can accurately and easily align the center of an optical fiber preform with a drawing furnace.

[0017] (Details of the embodiments of the present disclosure) Specific examples of optical fiber manufacturing methods and optical fiber manufacturing apparatuses according to embodiments of the present disclosure will be described with reference to the drawings. Note that the present disclosure is not limited to these examples, but is defined by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0018] FIG. 1 is a configuration diagram showing an optical fiber manufacturing apparatus 1 according to this embodiment. As shown in FIG. 1, the optical fiber manufacturing apparatus 1 includes a drawing tower 2, a feeder 3, an imaging unit 4, a control unit 5, a support rod 6, a drawing furnace 7, a forced cooling device 8, a coating device 9, a capstan device 10, a winding device 11, and a glass outer diameter measuring device 12.

[0019] The feeder 3 is provided at the top of the drawing tower 2 and is configured to be able to move the position of the optical fiber preform (glass preform) G1. The feeder 3 has a chuck 31, a chuck support part 32, a vertical movement part 33, and a horizontal movement part 34.

[0020] The chuck 31 grips the support rod 6 provided on the upper part of the optical fiber preform G1. The chuck support unit 32 supports the chuck 31 in a cantilever manner on the drawing tower 2. The vertical movement unit 33 is provided along the vertical direction (Z direction) of the manufacturing apparatus 1 and is configured to be able to move the chuck support unit 32 in the vertical direction. The vertical movement unit 33 moves the chuck support unit 32 in the vertical direction, thereby moving the optical fiber preform G1 gripped by the chuck 31 together with the chuck support unit 32. The horizontal movement unit 34 is configured to be able to move the optical fiber preform G1 gripped by the chuck 31 in horizontal directions (X direction and Y direction) perpendicular to the vertical direction.

[0021] The imaging unit 4 is provided at least above the drawing furnace 7 in the vertical direction. For example, the imaging unit 4 is provided so as to be able to simultaneously capture images of an opening formed in the upper part of the drawing furnace 7 and the optical fiber preform G1 accommodated in the opening. In the example shown in FIG. 1, the imaging unit 4 is provided above the drawing furnace 7 and below the chuck 31. The detailed configuration of the imaging unit 4 will be described later with reference to FIGS. 2 and 3.

[0022] The drawing furnace 7 is supported above the drawing tower 2 and is equipped with a heater 71 to heat the optical fiber preform G1 contained therein. The optical fiber preform G1 heated and melted in the drawing furnace 7 is then drawn from its tip to form a glass fiber G3. The forced cooling device 8 forcibly cools the high-temperature glass fiber G3 drawn in the drawing furnace 7. The coating device 9 coats the glass fiber G3 cooled by the forced cooling device 8 with resin. The glass fiber G3 is coated with resin to form the optical fiber G2. If the resin is an ultraviolet-curable resin, an ultraviolet irradiation device may be provided below the coating device 9 to irradiate the optical fiber G2 with ultraviolet light to cure the resin. After the resin has cured, the optical fiber G2 passes through a capstan device 10 and is wound around a winding device 11 at a constant tension. The capstan device 10 is controlled based on a signal from a glass outer diameter measuring device 12, and an optical fiber G2 having a predetermined glass outer diameter is obtained.

[0023] The control unit 5 is connected to the vertical movement unit 33 and horizontal movement unit 34 of the feeder 3, the imaging unit 4, etc. The control unit 5 controls the horizontal movement unit 34 to adjust the horizontal position (XY direction) of the optical fiber preform G1 held by the chuck 31. The control unit 5 also controls the vertical movement unit 33 to adjust the vertical position (Z direction) of the optical fiber preform G1 held by the chuck 31. Then, based on the imaging information acquired by the imaging unit 4, the control unit 5 controls the feeder 3 so that the center of the optical fiber preform G1 and the center of the opening 72 are aligned.

[0024] Fig. 2 is a schematic diagram showing the upper configuration of the manufacturing apparatus 1 including the imaging unit 4 and the drawing furnace 7 in Fig. 1. Fig. 3 is a top view of the imaging unit 4 shown in Fig. 2. As shown in Figures 2 and 3, the imaging unit 4 includes a first camera 41, a second camera 42, a red filter 43 (an example of a first filter), a blue filter 44 (an example of a second filter), a red LED 45 (an example of a first lighting device), a blue LED 46 (an example of a second lighting device), and a screen 47.

[0025] The first camera 41 and the second camera 42 are provided so as to simultaneously capture images of the opening 72 formed in the upper part of the drawing furnace 7 and the optical fiber preform G1 before being accommodated in the opening 72 (inside the drawing furnace 7) from different positions. The optical fiber preform G1 before being accommodated in the opening 72 is the optical fiber preform G1 before being drawn, and is held by the chuck 31 via the support rod 6. The first camera 41 and the second camera 42 are provided at positions approximately symmetrical with respect to the optical fiber preform G1 in the X direction. The first camera 41 and the second camera 42 are provided at positions above the opening 72 of the drawing furnace 7 in the Z direction. The first camera 41 and the second camera 42 are provided so as to face diagonally inward and downward in order to simultaneously capture images of the optical fiber preform G1 and the opening 72.

[0026] A red filter 43 that can transmit red light is attached to the first camera 41. A blue filter 44 that can transmit blue light is attached to the second camera .

[0027] The red LED 45 and the blue LED 46 are provided at positions approximately symmetrical with respect to the X direction with the optical fiber preform G1 in between. The red LED 45 is disposed on the second camera 42 side, to which the blue filter 44 is attached, with respect to the optical fiber preform G1 in the X direction. The blue LED 46 is disposed on the first camera 41 side, to which the red filter 43 is attached, with respect to the optical fiber preform G1 in the X direction. In addition, the red LED 45 is disposed on the outer side of the second camera 42 with respect to the optical fiber preform G1 in the X direction. The blue LED 46 is disposed on the outer side of the first camera 41 with respect to the optical fiber preform G1 in the X direction.

[0028] The red LED 45 and the blue LED 46 are rod-shaped linear light sources provided along the longitudinal direction (Z direction) of the optical fiber preform G1. As shown in Fig. 3, the red LED 45 and the blue LED 46 are provided with approximately U-shaped frames 45A and 46A that cover the periphery of each LED 45, 46. The frames 45A and 46A are made of, for example, aluminum and block the light emitted from each LED 45, 46 from directly entering the first camera 41 and the second camera 42. The inner surfaces of the frames 45A and 46A may be reflective surfaces that reflect the light emitted from each LED 45, 46 so that the light is efficiently irradiated toward the screen 47.

[0029] The screen 47 is provided on the opposite side of the optical fiber preform G1 from the first camera 41 and the second camera 42 in the Y direction. The screen 47 is provided at a position where it diffuses and reflects the light emitted from the red LED 45 and the blue LED 46 toward the optical fiber preform G1. The screen 47 is provided on the drawing tower 2 side (the rear side of the optical fiber preform G1) of the optical fiber preform G1 in the Y direction. The screen 47 is made of, for example, polyvinyl chloride resin with a white paint applied to its surface (reflective surface). The screen 47 reflects the light emitted from the red LED 45 and the blue LED 46 toward the optical fiber preform G1 so as to scatter the light over a wide angle.

[0030] As shown in FIG. 3, the light emitted from the red LED 45 is reflected by a screen 47 and irradiated onto the optical fiber preform G1. The light reflected by the screen 47 is irradiated onto the optical fiber preform G1 as transmitted illumination, and is photographed through a red filter 43 by a first camera 41 provided on the opposite side of the optical fiber preform G1 from the screen 47 in the Y direction. Similarly, the light emitted from the blue LED 46 is reflected by the screen 47 and irradiated onto the optical fiber preform G1. The light reflected by the screen 47 is irradiated onto the optical fiber preform G1 as transmitted illumination, and is photographed through a blue filter 44 by a second camera 42 provided on the opposite side of the optical fiber preform G1 from the screen 47 in the Y direction. The first camera 41 and the second camera 42 are disposed at positions with respect to the optical fiber preform G1 that form predetermined angles θ1 and θ2 (e.g., 30 to 60 degrees) with respect to a perpendicular line 47a drawn from the screen 47 and passing through the center position of the optical fiber preform G1. The red LED 45 and the blue LED 46 are provided at positions where they can efficiently irradiate the light reflected by the screen 47 towards the first camera 41 and the second camera 42 .

[0031] Next, a method for manufacturing an optical fiber according to this embodiment will be described. The method for manufacturing an optical fiber according to this embodiment is a method for manufacturing an optical fiber G2 using an optical fiber manufacturing apparatus 1 shown in Figures 1 to 3. The method for manufacturing an optical fiber according to this embodiment includes an "image acquisition step" and a "position adjustment step" described below.

[0032] (Image acquisition process) The chuck support part 32 is slid upward by the vertical moving part 33, and the support rod 6 of the optical fiber preform G1 to be used for drawing is held by the chuck 31. With the optical fiber preform G1 held by the chuck 31, before the chuck support part 32 is slid downward, i.e., before the optical fiber preform G1 is inserted into the opening 72 of the drawing furnace 7, images of the optical fiber preform G1 and the opening 72 of the drawing furnace 7 are taken by the first camera 41 and the second camera 42.

[0033] Specifically, the control unit 5 irradiates the optical fiber preform G1 with red light (an example of first light) emitted from the red LED 45, and irradiates the optical fiber preform G1 with blue light (an example of second light) emitted from the blue LED 46. With the optical fiber preform G1 irradiated with the light from each LED, the first camera 41 simultaneously captures an image of the optical fiber preform G1 and the opening 72 of the drawing furnace 7 through a red filter 43 to obtain a first captured image. Similarly, with the optical fiber preform G1 irradiated with the light from each LED, the second camera 42 simultaneously captures an image of the optical fiber preform G1 and the opening 72 of the drawing furnace 7 through a blue filter 44 to obtain a second captured image.

[0034] FIG. 4A is an image of the optical fiber preform G1 and the opening 72 of the drawing furnace 7 captured by the first camera 41 without illumination by the red LED 45. FIG. 4B is an image of the optical fiber preform G1 and the opening 72 of the drawing furnace 7 captured by the second camera 42 without illumination by the blue LED 46. FIG. 5A is an image of the optical fiber preform G1 and the opening 72 of the drawing furnace 7 captured by the first camera 41 with illumination by the red LED 45 (an example of a first captured image). FIG. 5B is an image of the optical fiber preform G1 and the opening 72 of the drawing furnace 7 captured by the second camera 42 with illumination by the blue LED 46 (an example of a second captured image). That is, the images in FIGS. 4A and 4B are images captured without illumination by the red LED 45 and the blue LED 46, and the images in FIGS. 5A and 5B are images captured with illumination by the red LED 45 and the blue LED 46.

[0035] As shown in the images of Figures 5A and 5B, when the optical fiber preform G1 is illuminated by the red LED 45 and the blue LED 46 and imaged through the filters 43 and 44, the background and the center of the optical fiber preform G1, which is a transparent cylinder, appear white due to the transmitted illumination of light reflected by the screen 47, and the edges on both sides of the optical fiber preform G1 appear black. By using transmitted illumination in this way, it is possible to obtain images in which the outer edges of the optical fiber preform G1 are emphasized. Therefore, the outer edges of the optical fiber preform G1 are more easily recognized in the images illuminated by the red LED 45 and the blue LED 46 (images of Figures 5A and 5B) than in the images without illumination (images of Figures 4A and 4B). On the other hand, if an image is taken without passing through a filter while illuminated by the red LED 45 and the blue LED 46, in addition to the transmitted illumination, light illuminating the optical fiber preform G1 from the side is also captured, which weakens the emphasis on the outer edges of the optical fiber preform G1 and makes it difficult to recognize the outer edges.

[0036] (Position adjustment process) The control unit 5 detects the edge coordinates of the optical fiber preform G1 and the edge coordinates of the opening 72 of the drawing furnace 7 by image processing the first captured image taken by the first camera 41 and the second captured image taken by the second camera 42.

[0037] Next, the control unit 5 calculates the center axis of the optical fiber preform G1 based on the detected edge coordinates of the optical fiber preform G1. The center axis can be calculated, for example, as the bisector of two approximate lines obtained from the outer edge coordinates of both sides of the optical fiber preform G1. The control unit 5 also calculates the center point of the ellipse of the opening 72 of the drawing furnace 7 based on the detected edge coordinates of the opening 72. As described above, the first camera 41 and the second camera 42 are each installed facing diagonally downward inward to simultaneously capture images of the optical fiber preform G1 and the opening 72 from different positions. Therefore, the outer edge of the optical fiber preform G1 detected in the images of Figures 5A and 5B moves closer to the center as it goes downward. The shape of the opening 72 detected in the images of Figures 5A and 5B is approximately elliptical.

[0038] Next, the control unit 5 detects the center position of the optical fiber preform G1 based on the calculated central axis of the optical fiber preform G1, and detects the center position of the aperture 72 based on the calculated center point of the ellipse of the aperture 72. FIG. 6 is a diagram showing the center positions of the optical fiber preform G1 and the aperture 72 detected by image processing. In FIG. 6, a target 80 having a radius of, for example, 3 mm to 5 mm, whose center position c is the core of the aperture 72, is displayed. The center position e of the optical fiber preform G1 is plotted in the target 80, which is detected based on edge coordinates of the optical fiber preform G1 detected by image processing of the first image captured by the first camera 41 and the second image captured by the second camera 42. The number displayed in the upper region 81 of the target 80 indicates the deviation (unit: mm) of the center position e of the optical fiber preform G1 from the center position c.

[0039] Next, the control unit 5 controls the horizontal moving unit 34 to adjust (center) the position of the optical fiber preform G1 based on the central position e of the optical fiber preform G1 and the central position c of the opening 72 plotted in Fig. 6 so that the positions of the centers of the optical fiber preform G1 and the opening 72 coincide with each other. Note that the operator may manually move the horizontal moving unit 34 to adjust (center) the position of the optical fiber preform G1. The horizontal moving unit 34 may be provided with a tilt moving unit (not shown) that adjusts the tilt of the optical fiber preform G1 relative to the vertical moving unit 33, and the control unit 5 may control the tilt moving unit so that the tilt of the central axis of the optical fiber preform G1 becomes parallel to the moving direction of the vertical moving unit 33. This allows the optical fiber preform G1 to always be aligned with the center of the opening 72 from the bottom end to the top end.

[0040] It is preferable to continuously calculate the center position e of the optical fiber preform G1 and the center position c of the aperture 72. The control unit 5 may calculate the amount of deviation between the center position of the optical fiber preform G1 and the center position of the aperture 72 based on the data of the calculated center positions, and may display the amount of deviation in real time as a numerical value, for example, as shown in the upper region 81 of Fig. 6 .

[0041] When the position adjustment process is completed, the control unit 5 slides the chuck support part 32 downward, and places the optical fiber preform G1 into the drawing furnace 7 through the opening 72. The subsequent drawing process is the same as the conventional process, and therefore a description thereof will be omitted.

[0042] As described above, the optical fiber manufacturing method according to this embodiment includes the steps of simultaneously photographing the optical fiber preform G1 and the opening 72 of the drawing furnace 7 to acquire a captured image before drawing the optical fiber preform G1, and adjusting the position of the optical fiber preform G1 based on the acquired captured image so that the center of the optical fiber preform G1 coincides with the center of the opening 72 of the drawing furnace 7. This manufacturing method enables the position adjustment of the optical fiber preform G1 by processing the captured image including both the optical fiber preform G1 and the opening 72 of the drawing furnace 7, thereby accurately and easily aligning the center of the optical fiber preform G1 with the opening 72 of the drawing furnace 7. This prevents the optical fiber preform G1 from being drawn with its central axis tilted, resulting in an eccentric melting point of the optical fiber preform G1, which can cause breakage or asymmetry of the optical fiber G2 after drawing, and the optical fiber preform G1 from colliding with the opening 72 of the drawing furnace 7 when the optical fiber preform G1 is inserted into the drawing furnace 7. Furthermore, when the adjustment of the core alignment is conventionally performed using, for example, a laser, periodic maintenance of the position adjustment mechanism is required to accurately align the laser position. In the present manufacturing method, since the position of the optical fiber preform G1 can be adjusted based on a captured image that includes both the optical fiber preform G1 and the opening 72 of the drawing furnace 7, the positions of the imaging cameras 41 and 42 may be shifted as long as a captured image that includes both the optical fiber preform G1 and the opening 72 of the drawing furnace 7 can be obtained, and periodic maintenance of the alignment of the cameras 41 and 42 is not required.

[0043] The captured image includes a first captured image and a second captured image. In the step of capturing the captured image, the first camera 41 captures an image of the optical fiber preform G1 and the opening 72 to capture the first captured image, and the second camera 42, which is installed at a different position from the first camera 41, captures an image of the optical fiber preform G1 and the opening 72 to capture the second captured image. According to this method, by using the first and second cameras 41 and 42, it is possible to capture the first captured image and the second captured image captured from different locations. The misalignment between the center of the optical fiber preform G1 and the center of the opening 72 of the drawing furnace 7 can be detected from two directions. This allows for more accurate centering of the optical fiber preform G1 and the drawing furnace 7.

[0044] In the step of acquiring the captured image, the optical fiber preform G1 is irradiated with red light emitted from the red LED 45, and blue light, which is emitted from the blue LED 46 and has a wavelength different from the red light, is irradiated with the optical fiber preform G1, and the optical fiber preform G1 and the opening 72 of the drawing furnace 7 are photographed by a first camera 41 equipped with a red filter 43 that can transmit only the red light to acquire the image shown in Fig. 5A (an example of a first captured image), and the optical fiber preform G1 and the opening 72 of the drawing furnace 7 are photographed by a second camera 42 equipped with a blue filter 44 that can transmit only the blue light to acquire the image shown in Fig. 5B (an example of a second captured image). According to this method, the first camera 41 acquires the first captured image in which only the red light from the red LED 45 is irradiated by the red filter 43, and the influence of the blue light from the blue LED 46 is reduced, thereby making it possible to acquire an image in which the outer edge of the optical fiber preform G1 can be easily recognized. Similarly, the second camera 42 acquires a second captured image in which only the blue light from the blue LED 46 is irradiated by the blue filter 44, and an image in which the outer edge of the optical fiber preform G1 is easily recognized can be acquired by reducing the influence of the red light from the red LED 45. Therefore, based on the first captured image acquired by the first camera 41 and the second captured image acquired by the second camera 42, the center positions of the optical fiber preform G1 and the opening 72 of the drawing furnace 7 can be accurately detected, and the optical fiber preform G1 and the opening 72 of the drawing furnace 7 can be more precisely centered. In addition, by using red light and blue light, the difference in wavelength between the two becomes large, so that the red light is blocked by the blue filter 44 and becomes less likely to enter the second camera 42, and similarly, the blue light is blocked by the red filter 43 and becomes less likely to enter the first camera 41. In this way, by reducing the influence of light of other wavelengths, it is possible to obtain a captured image in which the outer edge of the optical fiber preform G1 is easily recognized.

[0045] In the step of acquiring the captured image, the optical fiber preform G1 is irradiated with light reflected from a screen 47 disposed on the back surface of the optical fiber preform G1. According to this method, by using transmitted illumination of the light reflected from the screen 47, the optical fiber preform G1 can be uniformly illuminated, and an image can be acquired in which the outer edge of the optical fiber preform G1 can be more easily recognized.

[0046] The optical fiber manufacturing apparatus 1 according to the present embodiment includes a drawing furnace 7 for drawing an optical fiber preform G1 while heating it to form an optical fiber G2, a feeder 3 for holding an upper end of the optical fiber preform G1 and moving the position of the optical fiber preform G1, a first camera 41 and a second camera 42 for simultaneously photographing the optical fiber preform G1 and an opening 72 of the drawing furnace 7 before drawing the optical fiber preform G1, and a control unit 5 for controlling the feeder 3 based on the images acquired by the first camera 41 and the second camera 42 so that the center of the optical fiber preform G1 coincides with the center of the opening 72. This configuration allows accurate and easy alignment of the optical fiber preform G1.

[0047] In the above embodiment, the LEDs used in the lighting device are red and blue, but the colors are not limited to these. Any other color may be used as long as the LEDs have different colors (wavelengths). However, the greater the wavelengths of the two, the easier it is to filter out the light of the other wavelength, and the less susceptible one is to the influence of the other light. Therefore, it is preferable to use red and blue.

[0048] (Variation) In the above embodiment, an example has been described in which lighting devices of different colors (wavelengths) (red LED 45 and blue LED 46) are used, but this is not limiting. For example, LEDs of the same color (wavelength) may be used as lighting devices. When LEDs of the same color (lighting devices) are used, the "image acquisition step" in the optical fiber manufacturing method is as follows.

[0049] (Image acquisition process) FIG. 7 is a timing chart showing the timing of the light emitted from the first lighting device and the second lighting device and the opening and closing of the shutters of the first camera and the second camera when LEDs of the same color are used for the first lighting device and the second lighting device.

[0050] 7, the control unit 5 causes the first lighting device to emit a first light at a first timing to irradiate the optical fiber preform G1. The control unit 5 also opens the shutter of the first camera 41 in synchronization with the first timing at which the first light is emitted from the first lighting device, captures an image of the optical fiber preform G1 and the opening 72 of the drawing furnace 7, and obtains a first captured image.

[0051] Subsequently, the control unit 5 emits the second light from the second lighting device at a second timing different from the first timing to irradiate the optical fiber preform G1 with the second light. Furthermore, the control unit 5 opens the shutter of the second camera 42, which is installed at a position different from the first camera 41, in synchronization with the second timing at which the second light is emitted from the second lighting device, to capture an image of the optical fiber preform G1 and the opening 72 of the drawing furnace 7 and obtain a second captured image. During the time when the shutter of the second camera 42 is open, the first light is not emitted from the first lighting device, and during the time when the shutter of the first camera 41 is open, the second light is not emitted from the second lighting device.

[0052] The position adjustment process in this modified example is similar to the position adjustment process in the above embodiment, and involves image processing of the first captured image taken by the first camera 41 and the second captured image taken by the second camera 42, and adjusting (centering) the position of the optical fiber preform G1 so that the center of the optical fiber preform G1 and the center of the opening 72 coincide with each other.

[0053] In the manufacturing method of this modification, the step of acquiring an image includes irradiating the optical fiber preform G1 with a first light emitted from a first lighting device at a first timing, opening the shutter of the first camera 41 at the first timing to acquire a first image, irradiating the optical fiber preform G1 with a second light emitted from a second lighting device at a second timing different from the first timing, and opening the shutter of the second camera 42 at the second timing to acquire a second image. According to the method of this modification, the first camera 41 can acquire an image of the optical fiber preform G1 at the first timing using only the first light from the first lighting device irradiated from a direction opposite to the optical fiber preform G1 without using a filter. Furthermore, the second camera 42 can acquire an image of the optical fiber preform G1 at the second timing using only the second light from the second lighting device irradiated from a direction opposite to the optical fiber preform G1 without using a filter. Therefore, the first camera 41 and the second camera 42 acquire images illuminated only with light from an illumination device suitable for acquiring each image, and by reducing the influence of light from other illuminations, it is possible to acquire the first captured image and the second captured image, respectively, in which the outer edge of the optical fiber preform G1 is easily recognized. Therefore, based on the first captured image and the second captured image, it is possible to accurately align the center of the optical fiber preform G1 with the opening 72 of the drawing furnace 7.

[0054] Although the present disclosure 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 present disclosure. Furthermore, the number, position, shape, etc. of the components described above are not limited to the above embodiments, and can be changed to the number, position, shape, etc. that are suitable for implementing the present disclosure. [Explanation of symbols]

[0055] 1: Manufacturing equipment 2: Line-drawing Tower 3: Feeder 4: Imaging unit 5: Control unit 6: Support rod 7: Wire drawing furnace 8: Forced cooling device 9: Coating device 10: Capstan device 11: Winding device 12: Glass outer diameter measuring instrument 31: Zipper 32: Chuck support part 33:Vertical moving part 34: Horizontal moving part 41: First Camera 42: Second Camera 43: Red filter 44: Blue filter 45: Red LED (an example of the first lighting device) 46: Blue LED (an example of a second lighting device) 45A, 46A: Frame 47: Screen 47a: Perpendicular 71: Heater 72: Opening 80: Target 81: Upper region (of the target) c: center (of target) e: Center position (of the optical fiber preform) G1: Optical fiber base material G2: Optical fiber G3: Glass fiber θ1, θ2: Angle

Claims

1. A method of manufacturing an optical fiber by drawing an optical fiber preform while heating it in a drawing furnace, acquiring a captured image of the optical fiber preform and the opening of the drawing furnace simultaneously before inserting the optical fiber preform into the opening at the top of the drawing furnace and before drawing the optical fiber preform; and adjusting the position of the optical fiber preform based on the captured image so that the center of the optical fiber preform coincides with the center of the opening, the captured images include a first captured image and a second captured image, In the step of acquiring the captured image, a first camera photographs the optical fiber preform and the opening to obtain the first captured image, and a second camera installed at a position different from the first camera photographs the optical fiber preform and the opening to obtain the second captured image; A method for manufacturing an optical fiber, wherein the first camera and the second camera are arranged in a horizontal direction so that each faces diagonally inward and downward with respect to the central axis of the optical fiber preform.

2. In the step of acquiring the captured image, irradiating the optical fiber preform with first light emitted from a first lighting device; irradiating the optical fiber preform with second light emitted from a second lighting device and having a wavelength different from that of the first light; acquiring the first captured image by capturing an image of the optical fiber preform and the opening using the first camera equipped with a first filter that can transmit only the first light; 2. The method for manufacturing an optical fiber according to claim 1, wherein the second image is obtained by photographing the optical fiber preform and the opening using the second camera equipped with a second filter that can transmit only the second light.

3. 3. The method for producing an optical fiber according to claim 2, wherein the wavelength of the first light is red and the wavelength of the second light is blue.

4. The step of acquiring the captured image includes: irradiating the optical fiber preform with first light emitted from a first lighting device at a first timing; opening the shutter of the first camera at the first timing to acquire the first captured image illuminated only with the first light; irradiating the optical fiber preform with second light emitted from a second lighting device at a second timing different from the first timing; and opening the shutter of the second camera at the second timing to acquire the second captured image illuminated only with the second light.

5. 5. The optical fiber manufacturing method according to claim 1, wherein in the step of acquiring the captured image, the optical fiber preform is irradiated with light reflected by a screen arranged on a back surface of the optical fiber preform.

6. a drawing furnace for drawing an optical fiber preform while heating it to form an optical fiber; a feeder that holds an upper end of the optical fiber preform and can move the position of the optical fiber preform; a first camera and a second camera installed at a position different from the first camera, which simultaneously photograph the optical fiber preform and the opening of the drawing furnace before the optical fiber preform is inserted into the opening at the top of the drawing furnace and before the optical fiber preform is drawn; a control unit that controls the feeder based on the captured images acquired by the first camera and the second camera so that the center of the optical fiber preform and the center of the opening coincide with each other, An optical fiber manufacturing apparatus, wherein the first camera and the second camera are arranged in a horizontal direction so as to face diagonally inward and downward with respect to the central axis of the optical fiber preform.

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