Optical fiber manufacturing method

Abstract

To provide a method for manufacturing an optical fiber that rapidly detects that a glass fiber comes into contact with a cooling device due to vibration of the glass fiber.SOLUTION: A method for manufacturing an optical fiber G3 that manufactures the optical fiber G3 in which a glass fiber G1 is coated with a resin using a cooling device 140 for cooling the glass fiber G1 drawn from a drawing furnace 120 and a resin coating die 160 for applying the resin to the glass fiber G1 that has passed through the cooling device 140 includes: a vibration frequency measurement step S110 of measuring a vibration frequency f of in-plane vibration of the glass fiber G1 at a measurement surface intersecting a travel direction of the glass fiber G1 using a fiber position measuring device 130 that is disposed upstream from the resin coating die 160; and a contact determination step S120 of determining whether the glass fiber G1 comes into contact with the cooling device 140 on the basis of the vibration frequency f of the glass fiber G1 which is measured in the vibration frequency measurement step S110.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for manufacturing an optical fiber.

Background Art

[0002] Conventionally, in a method for manufacturing an optical fiber in which a glass fiber is drawn from a glass base material to manufacture an optical fiber, there is no fixed point for suppressing the vibration of the glass fiber between the neck-down portion on the tip side of the glass base material and the coating device for applying resin to the glass fiber. Therefore, the glass fiber between the lower end of the neck-down portion and the coating device may vibrate like a string (string vibration) with the lower end of the neck-down portion and the coating device as fixed points. Since this string vibration of the glass fiber vibrates in an intersection plane that intersects the traveling direction of the glass fiber, the glass fiber contacts the wall surface of the cooling device that cools the glass fiber drawn from the glass base material, and the strength of the optical fiber may be reduced due to damage to the glass fiber caused by this contact.

[0003] Therefore, in order to prevent the strength reduction of the optical fiber due to this string vibration, the traveling position of the glass fiber in the horizontal direction that intersects the traveling direction of the glass fiber hanging from the glass base material is detected by a fiber position measuring device, and position adjustment control is performed to horizontally move the glass base material so that the traveling position of the glass fiber is arranged at the center of the heating furnace that heats the glass base material. A method for manufacturing an optical fiber is known (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document ①

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, since the glass matrix is ​​long and large in diameter, and considering the inertia of the glass matrix, there are limits to how much the movement speed of the glass matrix can be increased. Therefore, in the optical fiber manufacturing method described in Patent Document 1 above, the position of the glass matrix in the horizontal plane is changed with respect to the average travel position of the glass fiber in the horizontal plane at a predetermined sampling time (for example, 0.1 seconds, i.e., 10 Hz). Therefore, if the glass fiber intermittently comes into contact with the cooling device during the sampling time, the position of the glass base material does not change, and there is a risk that the glass fiber may come into contact with and be damaged.

[0006] Therefore, the present invention solves the problems of the prior art described above, and that is, the object of the present invention is to provide a method for manufacturing optical fibers that can quickly detect contact with a cooling device due to string vibration of the glass fiber. [Means for solving the problem]

[0007] The present disclosure is a method for manufacturing an optical fiber in which a glass fiber is coated with a resin, comprising: a drawing furnace for heating and softening a glass base material; a cooling device disposed downstream of the drawing furnace for cooling the glass fiber drawn from the drawing furnace; and a resin coating die for applying a resin to the glass fiber that has passed through the cooling device, the method comprising: a vibration frequency measurement step for measuring the vibration frequency of in-plane vibration of the glass fiber at a measuring surface intersecting the direction of travel of the glass fiber using a fiber position measuring instrument disposed upstream of the resin coating die; and a contact determination step for determining whether the glass fiber has come into contact with the cooling device based on the vibration frequency of the glass fiber measured in the vibration frequency measurement step. [Effects of the Invention]

[0008] According to the above, contact with the cooling device due to string vibration of the glass fiber can be quickly detected. [Brief explanation of the drawing]

[0009] [Figure 1] This is a schematic diagram of an optical fiber manufacturing apparatus used in the optical fiber manufacturing method disclosed herein. [Figure 2] A schematic diagram illustrating the position measurement of a glass fiber using the fiber position measuring device shown in Figure 1. [Figure 3] A flowchart for determining abnormalities in the manufacturing process of optical fibers according to one aspect of this disclosure. [Modes for carrying out the invention]

[0010] [Description of Embodiments in this Disclosure] First, the embodiments of this disclosure will be listed and described. The present disclosure is a method for manufacturing an optical fiber, comprising: (1) a drawing furnace for heating and softening a glass base material; a cooling device disposed downstream of the drawing furnace for cooling the glass fibers drawn from the drawing furnace; and a resin coating die for applying a resin to the glass fibers that have passed through the cooling device, wherein the optical fiber is coated with a resin, the method comprising: a vibration frequency measurement step for measuring the vibration frequency of in-plane vibration of the glass fiber at a measuring surface intersecting the direction of travel of the glass fiber using a fiber position measuring instrument disposed upstream of the resin coating die; and a contact determination step for determining whether the glass fiber has come into contact with the cooling device based on the vibration frequency of the glass fiber measured in the vibration frequency measurement step. As described above, the system includes a vibration frequency measurement step that measures the vibration frequency of the in-plane vibration of the glass fiber on a measurement surface intersecting the direction of travel of the glass fiber using a fiber position measuring instrument positioned upstream of the resin coating die, and a contact determination step that determines whether or not the glass fiber has come into contact with the cooling device based on the vibration frequency of the glass fiber measured in the vibration frequency measurement step. Therefore, contact with the cooling device due to the string vibration of the glass fiber is determined based on the vibration frequency of the glass fiber, which allows for faster detection of contact with the cooling device due to the string vibration of the glass fiber compared to determining contact based on the position of the glass fiber on the measurement surface.

[0011] In the above method for manufacturing optical fibers, (2) in the contact determination step, if the vibration frequency of the glass fiber is outside a predetermined range, it is determined that the glass fiber has come into contact with the cooling device. This allows for easy determination of whether or not the glass fiber is in contact with the cooling device, simply by performing frequency analysis on the positional variation of the glass fiber on the measurement surface.

[0012] In the above method for manufacturing optical fibers, (3) in the contact determination step, the predetermined range is calculated based on the tension of the glass fiber measured by the fiber tension measuring instrument. This allows for a more accurate determination of whether or not the glass fiber is in contact with the cooling device, as the range of vibration frequencies of the glass fiber, which serves as the basis for determining whether or not the glass fiber is in contact with the cooling device, is calculated based on the state of the glass fiber where the boundary lines are drawn.

[0013] In the above-described method for manufacturing optical fibers, (4) the method further includes a wire drawing stop step in which the wire drawing of the glass fiber is stopped when it is determined by the contact determination step that the glass fiber is in contact with the cooling device. This allows the drawing of the glass fiber to stop based on contact with the cooling device caused by the string vibration of the glass fiber, thereby suppressing defects in the quality of the optical fiber.

[0014] [Details of the embodiments of this disclosure] The following describes specific examples of the optical fiber manufacturing method related to this disclosure.

[0015] <1. Overview of Optical Fiber Manufacturing Equipment> First, regarding the optical fiber manufacturing apparatus used in the optical fiber manufacturing method related to this disclosure. Figure 1 is a schematic diagram of an optical fiber manufacturing apparatus used in the optical fiber manufacturing method of this disclosure, and Figure 2 is a schematic diagram illustrating the measurement of the position of a glass fiber using the fiber position measuring instrument shown in Figure 1.

[0016] As shown in Figure 1, the optical fiber manufacturing apparatus 100 comprises, in order from the upstream end, a base material feeding unit 110 that grips the upper part of the glass base material G, a drawing furnace 120 that heats and softens the glass base material G, a fiber position measuring device 130 that detects the position of the glass fiber G1 drawn from the glass base material G, a cooling device 140 that cools the glass fiber G1 that has passed through the fiber position measuring device 130 with a cooling gas such as helium gas, and a fiber tension measuring device 150 that measures the tension of the glass fiber G1 from the refractive index of the glass fiber G1 that has passed through the cooling device 140, and The optical fiber manufacturing apparatus 100 includes a resin coating die 160 that applies an ultraviolet-curing resin (hereinafter referred to as "UV (UltraViolet) curing resin") to a glass fiber G1 that has passed through a fiber tension measuring device 150 to produce a resin-coated fiber G2, a UV curing furnace 170 that cures the UV curing resin applied to the surface of the resin-coated fiber G2 to produce an optical fiber G3, a lower roller 180 that changes the direction of travel of the optical fiber G3 toward the bobbin B on which the optical fiber G3 is wound, and a controller 190 that controls each element of the optical fiber manufacturing apparatus 100. Therefore, this optical fiber manufacturing apparatus 100 manufactures optical fibers G3 in which glass fibers G1 are coated with UV-curing resin.

[0017] The base material feeding unit 110 includes a horizontal movement mechanism 111 that rotatably grips a dummy bar Gd provided at the upper end of the glass base material G and moves the glass base material G in a horizontal direction (XY direction) orthogonal to the central axis direction (Z direction) in the longitudinal direction of the glass base material G, a rotation mechanism 112 that rotates the glass base material G around the central axis, and a feeder 113 that moves the glass base material G (that is, the horizontal movement mechanism 111) up and down according to the progress of the wire drawing. In the embodiment, the central axis direction of the glass base material G coincides with the traveling direction to the lower roller 180 directly below the optical fiber G3.

[0018] The wire drawing furnace 120 includes a cylindrical furnace core tube 121 into which the glass base material G is supplied inside, and a heating element 122 that surrounds the furnace core tube 121, and a heating region for softening the glass base material G is formed by the heating element 122. In addition, the wire drawing furnace 120 is provided with a gas supply unit 123 that supplies purge gas to the heating region.

[0019] The fiber position measuring device 130 is an optical measuring device, and detects the position of the glass fiber G1 on a measurement plane that intersects the traveling direction of the glass fiber G1 (in this embodiment, the position of the glass fiber G1 on a horizontal plane that is orthogonal to the traveling direction of the glass fiber G1). As shown in FIG. 2, the fiber position measuring device 130 has a first direction measuring means 131 that detects the position of the glass fiber G1 in a first direction X on the horizontal plane, and a second direction measuring means 132 that detects the position of the glass fiber G1 in a second direction Y orthogonal to the first direction X on the horizontal plane.

[0020] As shown in FIG. 2, the first direction measuring means 131 emits and receives laser light L in the second direction Y, and has a light emitting unit 131a that emits the laser light L and a light receiving unit 131b that receives the laser light L emitted from the light emitting unit 131a. As shown in Figure 2, the second direction measuring means 132 emits and receives laser light L in the first direction X, and has a light emitting unit 132a that emits laser light L and a light receiving unit 132b that receives the laser light L emitted from the light emitting unit 132a. Therefore, the fiber position measuring device 130 can recognize the position of the glass fiber G1 on a measuring surface (in this embodiment, a horizontal plane) formed by the two directions (in this embodiment, a first direction X and a second direction Y) by emitting and receiving laser light L in two mutually orthogonal directions. As shown in Figure 2, the detection range by the fiber position measuring device 130 (i.e., the range through which the laser beam L passes) is larger than the diameter of the glass fiber G1.

[0021] Furthermore, this fiber position measuring device 130 can calculate the vibration frequency of the glass fiber G1 in the horizontal plane by performing frequency analysis on the variation in the position of the glass fiber G1 in the horizontal plane, which is the measurement surface.

[0022] The cooling device 140 includes a cooling cylinder cooled with a liquid refrigerant. This cooling cylinder is filled with a cooling gas such as helium. Therefore, as the glass fiber G1 passes through the inside of the cooling cylinder, the glass fiber G1 is cooled by the cooling gas.

[0023] The controller 190 is connected to the horizontal movement mechanism 111, rotation mechanism 112, and feeder 113 of the base material feeding unit 110, the fiber position measuring instrument 130, the fiber tension measuring instrument 150, and a bobbin rotation mechanism (not shown) for rotating the bobbin B, etc., in a manner that enables communication. Furthermore, the controller 190 includes a glass base material position control means 191 that controls the horizontal movement mechanism 111, rotation mechanism 112, feeder 113, etc. of the base material feeding unit 110 based on the horizontal vibration frequency of the glass fiber G1 calculated by the fiber position measuring instrument 130.

[0024] <2. Manufacturing of optical fibers using optical fiber manufacturing equipment> Next, the method for manufacturing optical fibers using the optical fiber manufacturing apparatus 100 will be explained in detail with reference to Figures 1 and 3. Figure 3 is a flowchart of abnormality detection in the manufacturing process of optical fibers according to one aspect of this disclosure.

[0025] <2.1. Overview of Optical Fiber Manufacturing Methods> First, we will outline the manufacturing method of optical fibers, referring to Figure 1. To manufacture optical fiber G3, the glass base material G is fed into the furnace core tube 121 of the drawing furnace 120 by the base material feeding unit 110. Then, when the lower end portion of the glass base material G is heated by the heating element 122 and drawn downwards, the glass fiber G1 that constitutes the optical fiber G3 is formed. This glass fiber G1 has a core and a cladding, and is an optical waveguide with an outer diameter of, for example, 125 μm.

[0026] Then, after the horizontal position of the glass fiber G1 drawn from the glass base material G is measured by the fiber position measuring instrument 130, the glass fiber G1 passes through the cooling device 140, thereby lowering the surface temperature of the glass fiber G1 to approximately room temperature.

[0027] After the tension of the glass fiber G1, which has been cooled to approximately room temperature, is measured by a fiber tension meter 150, the glass fiber G1 passes through a resin coating die 160, where UV-curing resin is applied around the glass fiber G1, resulting in a resin-coated fiber G2. Then, as the resin-coated fiber G2 passes through the UV curing furnace 170, the UV-curable resin applied to the surface of the glass fiber G1 is cured by ultraviolet light in the UV curing furnace 170, and the optical fiber G3 is produced.

[0028] Then, the optical fiber G3, whose direction of travel has been changed by the roller 180 directly below it, is wound onto bobbin B.

[0029] <2.2. Abnormality determination> When an optical fiber is manufactured using the optical fiber G3 manufacturing method described above, as the glass fiber G1 moves, the glass fiber G1 vibrates horizontally in the section between the tip P1 of the glass base material G and the inlet P2 of the resin-coated die 160. If the amplitude of vibration of the glass fiber G1 is large, there is a risk that the glass fiber G1 may come into contact with the inner surface of the cooling device 140. Since contact between the glass fiber G1 and the inner surface of the cooling device 140 can lead to a defect in the quality of the glass fiber G1, early detection of contact between the glass fiber G1 and the inner surface of the cooling device 140 is important. Therefore, the abnormality detection process in the manufacturing of optical fiber G3, specifically the detection of contact between the glass fiber G1 and the inner surface of the cooling device 140, and the subsequent processing will be described below.

[0030] As shown in Figure 3, the abnormality detection in the manufacturing of optical fibers according to this disclosure consists of a vibration frequency measurement step S110, a contact detection step S120, and a wire drawing stop step S130.

[0031] The vibration frequency measurement step S110 is a step that is always performed during the manufacturing of optical fibers. It measures the vibration frequency f of the in-plane vibration of the glass fiber G1 on a measurement surface (in this embodiment, a horizontal plane) that intersects with the direction of travel of the glass fiber G1, using a fiber position measuring instrument 130 located upstream of the resin coating die 160.

[0032] The contact determination step S120 determines whether the glass fiber G1 has come into contact with the cooling device 140 based on the vibration frequency f of the glass fiber G1 measured by the fiber position measuring instrument 130. Specifically, in the contact determination step S120, it is determined whether the vibration frequency f of the glass fiber G1 measured by the fiber position measuring instrument 130 falls within a predetermined range.

[0033] Here, we will explain the predetermined range of vibration frequencies of the glass fiber G1, which serves as the basis for determining that the glass fiber G1 is not in contact with the cooling device 140. If the glass fiber G1 is not in contact with the cooling device 140, the natural frequency Fn [Hz] of the glass fiber G1 is as follows:

number

[0034] The predetermined range of vibration frequencies of the glass fiber G1, which serves as the basis for determining that the glass fiber G1 is not in contact with the cooling device 140, is the range obtained by adding a predetermined error range to the natural frequency Fn of the glass fiber G1 calculated by the above equation 1.

[0035] In the contact determination step S120, if the vibration frequency f of the glass fiber G1 is within a predetermined range, it is determined that the glass fiber G1 is not in contact with the cooling device 140, and the manufacturing of the optical fiber continues. In the contact determination step S120, if the vibration frequency f of the glass fiber G1 is outside a predetermined range, the controller 190 determines that the glass fiber G1 is in contact with the cooling device 140, and executes the wire drawing stop step S130 to stop drawing the glass fiber G1.

[0036] In the fiber drawing stop process S130, the drawing of the glass fiber G1 is stopped either by controlling the base material feeding unit 110 with the glass base material position control means 191, or by controlling a bobbin rotation mechanism (not shown) with the controller 190.

[0037] The optical fiber manufacturing method configured in this way includes a vibration frequency measurement step S110 in which a fiber position measuring instrument 130 positioned upstream of the resin coating die 160 is used to measure the vibration frequency f of the in-plane vibration of the glass fiber G1 on a horizontal plane which is a measuring surface intersecting the direction of travel of the glass fiber G1, and a contact determination step S120 in which the glass fiber G1 is determined to have come into contact with the cooling device 140 based on the vibration frequency f of the glass fiber G1 measured in the vibration frequency measurement step S110. As a result, contact with the cooling device 140 due to string vibration of the glass fiber G1 is determined based on the vibration frequency f of the glass fiber G1, so contact with the cooling device 140 due to string vibration of the glass fiber G1 can be detected more quickly than when contact with the cooling device 140 of the glass fiber G1 is determined based on the position of the glass fiber G1 on the horizontal plane.

[0038] Furthermore, in the contact determination step S120, if the vibration frequency f of the glass fiber G1 is outside a predetermined range, it is determined that the glass fiber G1 has come into contact with the cooling device 140. Therefore, the presence or absence of contact between the glass fiber G1 and the cooling device 140 can be determined simply by frequency analysis of the positional fluctuation of the glass fiber G1 in the horizontal plane, making it easy to determine whether or not the glass fiber G1 has come into contact with the cooling device 140.

[0039] Furthermore, in the contact determination step S120, since a predetermined range is calculated based on the tension of the glass fiber G1 measured by the fiber tension measuring instrument 150, the range of vibration frequency f of the glass fiber G1, which serves as the basis for determining whether or not the glass fiber G1 is in contact with the cooling device 140, is calculated based on the state of the glass fiber G1 on which the line has been drawn. This makes it possible to determine more accurately whether or not the glass fiber G1 is in contact with the cooling device 140.

[0040] Furthermore, by including a line drawing stop step S130 that stops drawing the glass fiber G1 when the contact determination step S120 determines that the glass fiber G1 is in contact with the cooling device 140, the line drawing of the glass fiber G1 is stopped based on contact with the cooling device 140 due to string vibration of the glass fiber G1, thereby suppressing defects in the quality of the optical fiber G3.

[0041] [Differentiation] Although embodiments of the present invention have been described above, the present invention is not limited to those described above. Furthermore, the elements of the embodiments described above can be combined to the extent that it is technically possible, and such combinations are also included within the scope of the present invention insofar as they include the features of the present invention.

[0042] For example, although the measurement surface in the fiber position measuring instrument 130 of the optical fiber manufacturing apparatus 100 described above was a horizontal plane, the measurement surface in the fiber position measuring instrument of the optical fiber manufacturing apparatus is not limited to a horizontal plane; it may be an inclined plane as long as it intersects with the direction of travel of the glass fiber.

[0043] For example, the fiber position measuring instrument 130 of the optical fiber manufacturing apparatus 100 described above emitted and received laser light in two directions, but the position of the optical fiber on the horizontal plane may be measured by emitting and receiving laser light in only one direction. In this case, determining the position in the laser emission direction can be done, for example, by emitting laser light with the focal point shifted from the center of the measurement area, obtaining a received profile that includes the region obscured by the fiber, determining the slope of the received light intensity at the edge of the glass fiber, and then converting the slope of the received light intensity at the edge to the fiber position in the laser emission direction based on the correlation between the previously determined slope of the received light intensity at the edge and the fiber position in the laser emission direction.

[0044] For example, in the optical fiber manufacturing apparatus 100 described above, the fiber position measuring instrument 130 measured the vibration frequency of the in-plane vibration of the glass fiber, but the controller 190 may perform frequency analysis on the variation in the position of the glass fiber G1 on the measurement surface detected by the fiber position measuring instrument 130.

[0045] For example, in the optical fiber manufacturing method described above, the line drawing stop step S130 was executed when the contact determination step S120 determined that the glass fiber G1 was in contact with the cooling device 140. However, when the contact determination step S120 determined that the glass fiber G1 was in contact with the cooling device 140, the line drawing of the optical fiber G3 was not stopped. Instead, the length of the glass fiber G1 from the start of line drawing at the time of determination was recorded, and the portion that was determined to be in contact was removed in a subsequent step. [Explanation of Symbols]

[0046] 100 ··· Optical fiber manufacturing equipment 110 ··· Base material feeding unit 111... Horizontal movement mechanism 112 ··· Rotating mechanism 113 ··· Feeder 120 ··· Line drawing furnace 121 ··· Core tube 122 ··· Heating element 123 ··· Gas Supply Department 130 ··· Fiber optic position measuring instrument 131 ... first direction measuring means 131a... First direction projection unit 131b... 1st direction light receiving section 132 ... second direction measuring means 132a... Second direction projection unit 132b...Second direction light receiving section 140... Cooling device 150 ··· Fiber tension measuring instrument 160 ··· Resin-coated dies 170 ... UV curing furnace 180 ··· Direct Roller 190 ··· Controller 191... Vibration frequency calculation method 192 ··· Glass base material position control means B ··· Bobbin G ··· Glass base material Gd ··· Dummy rod G1 ··· Glass Fiber G2 ·· Resin-coated fiber G3... Fiber Optic P1 ··· Tip of the glass matrix (spinning start point) P2 ··· Entrance to resin-coated die X ··· First direction Y ··· Second direction L ··· Laser light

Claims

1. A method for manufacturing an optical fiber, comprising: a drawing furnace for heating and softening a glass base material; a cooling device positioned downstream of the drawing furnace for cooling the glass fibers drawn from the drawing furnace; and a resin coating die for applying resin to the glass fibers that have passed through the cooling device, wherein the glass fibers are coated with the resin, the optical fiber being manufactured by manufacturing an optical fiber. A vibration frequency measurement step involves measuring the vibration frequency of the in-plane vibration of the glass fiber at a measurement surface intersecting the direction of travel of the glass fiber, using a fiber position measuring instrument positioned upstream of the resin coating die. A method for manufacturing an optical fiber, comprising: a contact determination step of determining whether or not the glass fiber has come into contact with the cooling device based on the vibration frequency of the glass fiber measured in the vibration frequency measurement step.

2. The method for manufacturing an optical fiber according to claim 1, wherein in the contact determination step, it is determined that the glass fiber has come into contact with the cooling device if the vibration frequency of the glass fiber is outside a predetermined range.

3. The method for manufacturing an optical fiber according to claim 2, wherein in the contact determination step, the predetermined range is calculated based on the tension of the glass fiber measured by a fiber tension measuring instrument.

4. A method for manufacturing an optical fiber according to any one of claims 1 to 3, further comprising a line drawing stop step for stopping the line drawing of the glass fiber when it is determined by the contact determination step that the glass fiber is in contact with the cooling device.

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