Method and apparatus for manufacturing optical fiber

Abstract

To effectively prevent a poor optical fiber from being manufactured in a mass.SOLUTION: A method for manufacturing an optical fiber drawn from an optical fiber preform and cooled by a cooling device comprises steps of: acquiring monitoring results at the line position of the optical fiber on a path line up to a direct lower roller firstly contacting the optical fiber drawn from the optical fiber preform; and detecting discontinuity at the line position of the optical fiber on the basis of the monitoring results.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to methods and apparatus for manufacturing optical fiber. [Background technology]

[0002] Conventionally, techniques have been developed for manufacturing devices that manufacture optical fibers by drawing the optical fibers from optical fiber preforms. For example, Patent Document 1 discloses a device that detects the drawing position of the optical fiber upstream and downstream of a cooling device in order to prevent the manufacturing of defective optical fibers due to contact between the cooling device and the optical fiber. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 11-130458 Summary of the Invention [Problem to be solved by the invention]

[0004] However, during drawing of an optical fiber, the inclination of the entire tower supporting the preform may change from moment to moment as the weight of the preform changes, and in such a case, the drawing position of the optical fiber also changes constantly. Therefore, for example, a manufacturing method in which the drawing position of the optical fiber is measured and drawing is stopped depending on the displacement of the drawing position from the initial position may not be effective as a method for preventing the mass production of defective optical fibers.

[0005] An object of the present disclosure is to more effectively prevent the mass production of defective optical fibers. [Means for solving the problem]

[0006] The method for producing an optical fiber according to the present disclosure includes the steps of: A method for producing an optical fiber in which an optical fiber is drawn from an optical fiber preform and cooled by a cooling device, comprising the steps of: acquiring a monitoring result of a line position of the optical fiber on a pass line from the optical fiber preform to a roller immediately below the pass line with which the optical fiber first comes into contact; and detecting discontinuities in the line position of the optical fiber based on the monitoring results.

[0007] The optical fiber manufacturing apparatus of the present disclosure comprises: an optical fiber preform; a cooling device for cooling the optical fiber drawn from the optical fiber preform; a roller directly below the optical fiber that first comes into contact with the roller; a monitor provided on a path line from the optical fiber preform to the rollers directly below the optical fiber preform for monitoring a line position of the optical fiber; and a detection device that detects discontinuity in the line position of the optical fiber based on the monitoring results of the monitor. Effect of the Invention

[0008] According to the present disclosure, it is possible to more effectively prevent mass production of defective optical fibers. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic diagram showing the configuration of a manufacturing apparatus according to this embodiment. [Diagram 2] FIG. 2 is a block diagram showing a configuration of the control device shown in FIG. [Diagram 3] FIG. 3 is a diagram for explaining the position of the optical fiber on the measurement surface detected by the detection unit shown in FIG. [Figure 4] FIG. 4 is a diagram for explaining discontinuity in the line position of the optical fiber detected by the detection unit shown in FIG. [Diagram 5]FIG. 5 is a flowchart for explaining the flow of operations when detecting discontinuity in the line position of an optical fiber by the optical fiber manufacturing apparatus according to the embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] [Description of the embodiments of the present disclosure] First, the contents of the embodiments of the present disclosure will be listed and described. The method for producing an optical fiber according to the present disclosure includes the steps of: (1) A method for producing an optical fiber in which an optical fiber is drawn from an optical fiber preform and cooled by a cooling device, comprising the steps of: acquiring a monitoring result of a line position of the optical fiber on a pass line from the optical fiber preform to a roller immediately below the pass line with which the optical fiber first comes into contact; and detecting discontinuities in the line position of the optical fiber based on the monitoring results.

[0011] As described above, by detecting discontinuity in the line position of the optical fiber, it is possible to estimate the occurrence of an event that may cause a position shift or distortion of the cooling device, such as opening and closing of the cooling device, the occurrence of an earthquake, etc. Therefore, appropriate measures such as stopping the production of optical fiber can be taken, and the mass production of defective optical fiber can be more effectively prevented.

[0012] (2) The method for producing an optical fiber according to (1) above further comprises: The method may further include a step of stopping drawing of the optical fiber if the discontinuity is detected during a target period that includes a timing when an opening / closing operation of the cooling device is performed.

[0013] In this way, discontinuities that are likely to be caused by opening and closing the cooling device can be more reliably detected and the drawing of optical fiber can be stopped, thereby more effectively preventing the mass production of defective optical fiber.

[0014] (3) The method for producing an optical fiber according to (1) above further comprises: The method may include a step of applying screening tension to the optical fiber by a screening roller provided downstream of the direct below roller when the discontinuity is detected during a target period including the timing when the cooling device is opened or closed.

[0015] In this way, discontinuities likely to be caused by opening and closing the cooling device can be detected more reliably, and a screening tension can be applied, allowing appropriate action to be taken, such as stopping drawing if the optical fiber breaks and continuing drawing if the optical fiber does not break.

[0016] (4) In the method for producing an optical fiber according to (3) above, In the step of applying the screening tension, the optical fiber may be drawn to a length of 5 km or more with the screening tension set to 300 gf or more.

[0017] By using such a method, it is possible to more reliably prevent the mass production of defective optical fibers.

[0018] (5) In any one of the methods for producing an optical fiber according to (1) to (4), The method may further include a step of stopping drawing of the optical fiber if the discontinuity is detected during a target period that includes the occurrence of an earthquake with a seismic intensity of 1 or more.

[0019] In this way, discontinuities that are likely to be caused by an earthquake can be detected more reliably and the drawing of optical fiber can be stopped, thereby more effectively preventing the mass production of defective optical fiber.

[0020] (6) In any one of the methods for producing an optical fiber according to (1) to (4), The method may include a step of applying screening tension to the optical fiber by a screening roller provided downstream of the direct below roller when the discontinuity is detected during a target period including the occurrence of an earthquake with a seismic intensity of 1 or higher.

[0021] In this way, discontinuities that are likely to be caused by an earthquake can be detected more reliably and screening tension can be applied, allowing appropriate measures to be taken, such as stopping drawing if the optical fiber breaks and continuing drawing if the optical fiber is not broken.

[0022] (7) In the method for producing an optical fiber according to (6) above, In the step of applying the screening tension, the optical fiber may be drawn to a length of 5 km or more with the screening tension set to 300 gf or more.

[0023] By using such a method, it is possible to more reliably prevent the mass production of defective optical fibers.

[0024] (8) In any one of the above methods for producing an optical fiber (1) to (7), In the step of detecting a discontinuity in the monitoring results, if a change in the moving average value of the line position of the optical fiber over a target period of a predetermined length is 20 μm / sec or more, it may be determined that the line position has a discontinuity.

[0025] This makes it possible to more accurately determine whether or not measures such as stopping the production of optical fibers should be taken.

[0026] (9) In the method for producing an optical fiber according to (8), In the step of detecting a discontinuity in the monitoring results, if a change in the moving average value of the line position of the optical fiber over a target period of a predetermined length is 50 μm / sec or more, it may be determined that the line position has a discontinuity.

[0027] This allows a more accurate determination of whether or not measures should be taken, such as halting the production of optical fibers.

[0028] The optical fiber manufacturing apparatus of the present disclosure comprises: (10) an optical fiber preform; a cooling device for cooling the optical fiber drawn from the optical fiber preform; a roller directly below the optical fiber that first comes into contact with the roller; a monitor provided on a path line from the optical fiber preform to the rollers directly below the optical fiber preform for monitoring a line position of the optical fiber; and a detection device that detects discontinuity in the line position of the optical fiber based on the monitoring results of the monitor.

[0029] As described above, by using a configuration for detecting discontinuity in the line position of the optical fiber, it is possible to estimate the occurrence of an event that may cause a position shift or distortion of the cooling device, such as opening and closing of the cooling device, the occurrence of an earthquake, etc. This allows appropriate measures to be taken, such as stopping the production of optical fiber, and makes it possible to more effectively prevent the mass production of defective optical fiber.

[0030] [Details of the embodiment of the present disclosure] Specific examples of optical fiber manufacturing methods and manufacturing apparatuses according to embodiments of the present disclosure will be described below with reference to the drawings. Note that the present invention is not limited to these examples, but is intended to include all modifications within the meaning and scope of the claims as set forth in the claims. In addition, the scale of each drawing used in the following description has been appropriately changed so that each component can be recognized.

[0031] (Optical fiber manufacturing equipment) Fig. 1 is a schematic diagram showing the configuration of a manufacturing apparatus 1 according to this embodiment. As shown in Fig. 1, the manufacturing apparatus 1 is provided with a heating furnace 21 for heating a glass preform (optical fiber preform) 200 for an optical fiber on the upstream side. The heating furnace 21 includes a cylindrical furnace tube 3 to which the glass preform 200 is supplied and a heating element 4 surrounding the furnace tube 3, and the heating element 4 forms a heating region for softening the glass preform 200. The heating furnace 21 is also provided with a gas supply unit 5 for supplying a purge gas to the heating region.

[0032] The glass preform 200 is supported by a dummy rod D at the top of the glass preform 200 being held by a holding mechanism 6, and is sent into the heating furnace 21 so that its lower end portion is positioned in the heating region inside the furnace tube 3. The lower end portion of the glass preform 200 is stretched downward to reduce its diameter, and an optical fiber G1 before being resin-coated is drawn.

[0033] The holding mechanism 6 includes a feeder 22 that lowers the held glass base material 200 as drawing progresses. The feeder 22 includes a rotation mechanism that rotates the glass base material 200 around its axis and a horizontal movement mechanism that moves the glass base material 200 in the horizontal direction (XY direction).

[0034] Further, a cooling device 7 is provided downstream of the heating furnace 21. The cooling device 7 has a configuration that allows, for example, a pair of cooling bodies to be brought close to each other (closed state) or separated from each other (open state). When the cooling device 7 is in the closed state, cooling of the optical fiber G1 is performed.

[0035] A die 9 for applying an ultraviolet-curable resin to the optical fiber G1 and an ultraviolet irradiator 10 for curing the applied ultraviolet-curable resin are provided downstream of the cooling device 7. The optical fiber G1 that has passed through the die 9 and the ultraviolet irradiator 10 has a coating layer of an ultraviolet-curable resin formed on its outer periphery, and becomes the optical fiber G2.

[0036] After passing through the ultraviolet ray irradiation device 10, the optical fiber G2 is hung on a roller 11 disposed immediately below the heating furnace 21, and the running direction is changed by the roller 11.

[0037] A guide roller 12 is provided downstream of the direct-below roller 11, and the optical fiber G2 that has passed through the guide roller 12 is sent to a screening section 13. Thereafter, the optical fiber G2 is guided by a guide roller 17 through the screening section 13, and sent to a take-up bobbin 20 via dancer rollers 18 and 19 to be wound up. Hereinafter, each of the optical fiber G1 and the optical fiber G2 will also be referred to as "optical fiber G."

[0038] The screening unit 13 includes a capstan 14, a guide roller 15, and a screening roller 16. In this screening unit 13, the optical fiber G2 is taken up by the capstan 14, guided by the guide roller 15, and a screening tension is applied by the screening roller 16. The screening roller 16 is, for example, a friction roller, and can apply a screening tension to the optical fiber G2 whose value corresponds to the difference in rotation speed between the capstan 14 and the screening roller 16.

[0039] The manufacturing apparatus 1 also includes a control device (detection device) 2. A feeder 22, a screening unit 13, and the like are communicatively connected to the control device 2, and the control device 2 appropriately controls these.

[0040] Specifically, the screening section 13 generates a screening tension according to the difference in rotation speed between the capstan 14 and the screening roller 16 by controlling the rotation speed of the capstan 14 and the screening roller 16 by the control device 2, respectively.

[0041] (Detection of optical fiber line position) The manufacturing apparatus 1 further includes one or more monitors 30 that are provided on a path line from the glass base material 200 to the rollers 11 directly below and monitor the line position of the optical fiber G. In the manufacturing apparatus 1 shown in FIG. 1, as an example, a first monitor 30A, a second monitor 30B, and a third monitor 30C are provided as the monitors 30.

[0042] The first monitor 30A is provided on the pass line between the glass base material 200 and the cooling device 7. The second monitor 30B is provided on the pass line between the cooling device 7 and the die 9. The third monitor 30C is provided on the pass line between the ultraviolet ray irradiation device 10 and the roller 11 just below.

[0043] Each monitor 30 is, for example, an optical measuring device, and measures the line position of the optical fiber G on a measurement plane intersecting the running direction of the optical fiber G. More specifically, each monitor 30 constantly measures the line position of the optical fiber G in a first direction (hereinafter referred to as the "X direction") on the measurement plane, and the line position of the optical fiber G in a second direction (hereinafter referred to as the "Y direction") on the measurement plane. Then, each monitor 30 transmits the measurement results (monitoring results) to the control device 2 via wire or wirelessly.

[0044] The control device 2 controls the feeder 22 so that the line position of the optical fiber G is constant, for example, based on the measurement result transmitted from the first monitor 30A.

[0045] Furthermore, the control device 2 detects discontinuity in the line position of the optical fiber G based on the measurement results transmitted from each monitor 30. When the control device 2 detects discontinuity in the line position of the optical fiber G, the control device 2 stops drawing the optical fiber G, for example, by controlling the feeder 22 to pull the glass preform 200 upward.

[0046] (Control device configuration) Fig. 2 is a block diagram showing a configuration of the control device 2 shown in Fig. 1. Referring to Fig. 2, the control device 2 includes an acquisition unit 31, a detection unit 32, a storage unit 33, and a control unit 34. The storage unit 33 is a ROM (Read Only Memory), a RAM (Random Access Memory), or the like.

[0047] The acquisition unit 31 acquires data transmitted from an external device. For example, when the acquisition unit 31 receives a measurement result transmitted from each monitor 30, the acquisition unit 31 stores the received measurement result in the storage unit 33 together with time information.

[0048] In addition, the acquisition unit 31 can receive earthquake alerts transmitted from external devices. When the acquisition unit 31 receives an earthquake alert, the acquisition unit 31 stores in the storage unit 33, for example, the seismic intensity and the occurrence timing of the earthquake indicated in the earthquake alert.

[0049] The control unit 34 periodically checks, for example, the measurement results from the first monitor 30A stored in the memory unit 33, and controls the feeder 22 so that the line position of the optical fiber G is constant, as described above. The control unit 34 also controls the opening and closing of the cooling device 7 by sending a control signal to the cooling device 7. The control timing of the cooling device 7 by the control unit 34 is stored in the memory unit 33.

[0050] The detection unit 32 judges whether or not there is a discontinuity in the line position of the optical fiber G based on the measurement results stored in the storage unit 33.

[0051] 1, the optical fiber G may come into contact with the cooling device 7, which may reduce the strength of the optical fiber G. Furthermore, if the die 9 is displaced or distorted, the application of the ultraviolet-curable resin to the optical fiber G may vary, resulting in the manufacture of an optical fiber G with a thickness deviation. For this reason, the control device 2 detects discontinuity in the line position of the optical fiber G based on the measurement results from the monitor 30.

[0052] Fig. 3 is a diagram for explaining the line position of the optical fiber G measured by the monitor 30 shown in Fig. 1. Fig. 4 is a diagram for explaining discontinuity in the line position of the optical fiber G detected by the detection unit 32 shown in Fig. 2.

[0053] 3 and 4, specifically, assume that the line position of the optical fiber G measured by one of the monitors 30 shown in Fig. 1 during the period from timing t1 to timing t2 is at the position indicated by reference character A (XY coordinates: 10, 40) in Fig. 3. Also assume that at timing t2, the line position of the optical fiber G changes due to the occurrence of an event such as control of the cooling device 7 or an earthquake. Then, assume that at timing t3 after timing t2, the line position of the optical fiber G measured by that monitor 30 is at the position indicated by reference character B (XY coordinates: 20, 40) in Fig. 3.

[0054] The detection unit 32 constantly monitors the line position of the optical fiber G, for example, by referring to the measurement results stored in the storage unit 33. Specifically, the detection unit 32 periodically calculates a moving average value in the X direction and a moving average value in the Y direction.

[0055] Then, when at least one of the moving average value in the X direction and the moving average value in the Y direction is equal to or greater than a threshold value, the detection unit 32 determines that the line position of the optical fiber G has discontinuity. The threshold value is, for example, 20 μm / sec, and may be 50 μm / sec. This makes it possible to more accurately determine whether or not to take action such as stopping the manufacture of the optical fiber. Furthermore, when the detection unit 32 detects discontinuity in the line position of the optical fiber G, it outputs a detection signal to the control unit 34.

[0056] In this manner, the manufacturing apparatus 1 according to the embodiment of the present disclosure detects discontinuity in the drawing position of the optical fiber G. This makes it possible to estimate the occurrence of an event that may cause a positional shift or distortion of the cooling device 7 or the die 9, and therefore, as described below, it is possible to take appropriate measures, such as stopping the drawing of the optical fiber G, and more effectively prevent the mass production of defective optical fibers G.

[0057] The detection unit 32 is not limited to a configuration that constantly monitors the wire position of the optical fiber G. For example, when an event occurs that may cause a positional deviation or distortion of the cooling device 7 or the die 9, the detection unit 32 may monitor the wire position of the optical fiber G during a period including the occurrence of the event. In other words, the detection unit 32 may be configured to monitor the wire position of the optical fiber G during a period including the occurrence of the event in a state in which the occurrence of an event is confirmed.

[0058] Specifically, when the control timing of the cooling device 7 or the occurrence timing of an earthquake is newly stored in the storage unit 33, the detection unit 32 sets a target period including the control timing or the occurrence timing. The length of the target period is, for example, within a range from 1 second to 10 seconds. Then, the detection unit 32 determines whether or not each of the moving average value in the X direction and the moving average value in the Y direction of the optical fiber G during the target period is equal to or greater than a threshold value, thereby determining whether or not there is discontinuity in the line position of the optical fiber G during the target period.

[0059] In this configuration, since the discontinuity of the line position of the optical fiber G caused by an event can be detected more reliably, more appropriate measures can be taken according to the content of the event. Also, since the monitoring is limited to the target period including the timing of the occurrence of the event, the processing load for monitoring by the detection unit 32 can be reduced.

[0060] Furthermore, the detection unit 32 can detect discontinuity in the line position of the optical fiber G based on the measurement results from each of the multiple monitors 30 (see FIG. 1). When outputting a detection signal indicating that a discontinuity in the line position has been detected to the control unit 34, the detection unit 32 may also notify the control unit 34 of identification information of the monitor 30 that is the transmission source of the measurement result used for the detection.

[0061] (Details of control by the control unit) When the control unit 34 receives a detection signal from the detection unit 32 indicating that discontinuity in the drawing position of the optical fiber G has been detected, the control unit 34 transmits a control signal to the feeder 22 shown in Fig. 1, for example, to stop drawing the optical fiber G. This makes it possible to prevent the mass production of defective optical fibers.

[0062] Furthermore, when the control unit 34 receives the above detection signal from the detection unit 32, the control unit 34 may control the rotation speed of the capstan 14 and the screening roller 16 shown in Fig. 1 for a certain period of time so that a screening tension is applied to the optical fiber G. For example, the control unit 34 controls so that the optical fiber G is drawn over a length of 5 km or more with a screening tension of 300 gf or more.

[0063] In this way, by applying a screening tension when a discontinuity in the drawing position of the optical fiber G is detected, for example, if the optical fiber G breaks, drawing can be stopped to prevent the mass production of defective optical fibers. Also, if the optical fiber G does not break, appropriate measures can be taken, such as continuing drawing.

[0064] (Operation flow) 5 is a flowchart for explaining the flow of operations performed when the optical fiber manufacturing apparatus 1 according to the embodiment of the present disclosure detects discontinuity in the line position of the optical fiber G. Here, a case will be described in which control is performed to close the cooling device 7, and the line position of the optical fiber G is monitored during a target period including the timing of the control.

[0065] 1, 2 and 5, first, when the control unit 34 in the control device 2 performs control to close the cooling device 7, the control unit 34 stores the control timing in the storage unit 33 (step S11).

[0066] Next, when the above control timing is newly stored in the storage unit 33, the detection unit 32 sets a target period including the control timing (step S12).

[0067] Next, the detection unit 32 checks whether or not there is discontinuity in the line position of the optical fiber G during the target period, based on the measurement results from each monitor 30 stored in the storage unit 33 (step S13).

[0068] Next, if the detection unit 32 detects discontinuity in the line position of the optical fiber G during the target period ("YES" in step S13), the control unit 34 controls the screening unit 13 for a certain period of time, for example, so that screening tension is applied to the optical fiber G (step S14).

[0069] Next, the detection unit 32 confirms whether or not the optical fiber G is broken by, for example, acquiring an inspection result indicating whether or not the optical fiber G is broken from an inspection device or the like (not shown) (step S15).

[0070] If the optical fiber G is broken ("YES" in step S15), the detector 32 controls, for example, the feeder 22 shown in FIG. 1 to stop drawing the optical fiber G1 (step S16).

[0071] On the other hand, if the detection unit 32 does not detect any discontinuity in the line position of the optical fiber G during the target period ("NO" in step S13), or if the optical fiber G is not broken even when the screening unit 13 is controlled ("NO" in step S15), the detection unit 32 continues drawing the optical fiber G.

[0072] As described above, the detection unit 32 in the control device 2 may be configured to constantly monitor the line position of the optical fiber G regardless of the occurrence of an event. In this case, the processes of steps S11 and S12 shown in FIG. 5 may not be performed.

[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 present invention. 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 invention. [Explanation of symbols]

[0074] 1 Manufacturing equipment 2. Control device 3. Core tube 4 Heating element 5 Gas supply section 6 Gripping mechanism 7 Cooling device 9 Dice 10 Ultraviolet irradiation device 11 Directly below roller 12,15,17 Guide rollers 13 Screening Department 14 Capstan 16 Screening roller 18,19 Dancerola 20 Bobbin 21 Furnace 22 Feeder 30 Monitor 30A 1st Monitor 30B 2nd monitor 30C 3rd monitor 31 Acquisition Department 32 Detection unit 33 Storage section 34 Control section 200 Glass preform (optical fiber preform) G, G1, G2 optical fiber t1, t2, t3 Timing

Claims

1. A method for producing an optical fiber in which an optical fiber is drawn from an optical fiber preform and cooled by a cooling device, comprising the steps of: acquiring a monitoring result of a line position of the optical fiber on a pass line from the optical fiber preform to a roller immediately below the pass line with which the optical fiber first comes into contact; and detecting discontinuities in line position of the optical fiber based on the monitoring results.

2. The manufacturing method further comprises:

2. The method for producing an optical fiber according to claim 1, further comprising the step of stopping drawing of the optical fiber if the discontinuity is detected during a target period that includes a timing when the cooling device is opened or closed.

3. The manufacturing method further comprises:

2. The method for manufacturing an optical fiber according to claim 1, further comprising the step of applying a screening tension to the optical fiber by a screening roller provided downstream of the immediate below roller when the discontinuity is detected during a target period including the timing when the cooling device is opened or closed.

4. 4. The method for producing an optical fiber according to claim 3, wherein in the step of applying a screening tension, the optical fiber is drawn over a length of 5 km or more while the screening tension is set to 300 gf or more.

5. The manufacturing method further comprises: The method for producing an optical fiber according to claim 1 , further comprising the step of stopping drawing of the optical fiber if the discontinuity is detected during a target period that includes the occurrence of an earthquake having a seismic intensity of 1 or more.

6. The manufacturing method further comprises:

2. The method for manufacturing an optical fiber according to claim 1, further comprising the step of applying a screening tension to the optical fiber by a screening roller provided downstream of the immediately below roller when the discontinuity is detected during a target period including the occurrence of an earthquake with a seismic intensity of 1 or more.

7. 7. The method for producing an optical fiber according to claim 6, wherein in the step of applying a screening tension, the optical fiber is drawn over a length of 5 km or more while the screening tension is set to 300 gf or more.

8. 8. The method for manufacturing an optical fiber according to claim 1, wherein, in the step of detecting discontinuity in the monitoring results, if a change in a moving average value of the line position of the optical fiber over a target period of a predetermined length is 20 μm / sec or more, the line position is determined to have a discontinuity.

9. 9. The method for manufacturing an optical fiber according to claim 8, wherein in the step of detecting discontinuity in the monitoring results, if a change in a moving average value of the line position of the optical fiber over a target period of a predetermined length is 50 μm / sec or more, the line position is determined to have a discontinuity.

10. an optical fiber preform; a cooling device for cooling the optical fiber drawn from the optical fiber preform; a roller directly below the optical fiber that first comes into contact with the roller; a monitor provided on a path line from the optical fiber preform to the rollers directly below the optical fiber preform for monitoring a line position of the optical fiber; a detection device that detects discontinuity in a line position of the optical fiber based on a monitoring result of the monitor.

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