JP2024027044A - Optical fiber manufacturing method - Google Patents

Abstract

The present invention provides an optical fiber manufacturing method that quickly detects contact of a glass fiber with a cooling device due to string vibration. The glass fiber G1 is coated with resin using a cooling device 140 that cools the glass fiber G1 drawn from a drawing furnace 120 and a resin coating die 160 that applies resin to the glass fiber G1 that has passed through the cooling device 140. A method for manufacturing an optical fiber G3 coated with glass fiber G3 using a fiber position measuring device 130 disposed upstream of a resin coating die 160. A vibration frequency measurement step S110 that measures the vibration frequency f of in-plane vibration of the fiber G1, and whether the glass fiber G1 has contacted the cooling device 140 based on the vibration frequency f of the glass fiber G1 measured in the vibration frequency measurement step S110. A contact determination step S120 is provided to determine whether or not there is a contact. [Selection diagram] Figure 1

Description

The present invention relates to a method of manufacturing an optical fiber.

Conventionally, in an optical fiber manufacturing method in which an optical fiber is manufactured by drawing a glass fiber from a glass base material, a glass fiber is inserted between the neck down part on the tip side of the glass base material and a coating device that applies resin to the glass fiber. Since there is no fixed point to suppress vibration, the glass fiber between the lower end of the neck-down section and the coating device vibrates like a string (string vibration) with the lower end of the neck-down section and the coating device as fixed points. Sometimes I put it away.
This chordal vibration of the glass fiber vibrates in a plane that intersects the running direction of the glass fiber, so the glass fiber comes into contact with the wall of the cooling device that cools the glass fiber drawn from the glass base material, and this contact causes the glass fiber to The strength of the optical fiber may be reduced due to damage to the fiber.

Therefore, in order to prevent the strength of the optical fiber from decreasing due to this string vibration, a fiber position measuring device is used to detect the running position of the glass fiber in the horizontal direction that intersects the running direction of the glass fiber suspended from the glass base material. An optical fiber manufacturing method is known in which position adjustment control is performed to move a glass base material in the horizontal direction so that the running position of the glass fiber is placed in the center of a heating furnace (see, for example, Patent Document 1). .

Japanese Patent Application Publication No. 2013-220972

However, the glass base material is long and has a large diameter, and considering the inertia of the glass base material, there is a limit to increasing the moving speed of the glass base material. In the manufacturing method, the position of the glass base material in the horizontal plane is changed with respect to the average running position of the glass fiber in the horizontal plane at a predetermined sampling time (for example, 0.1 seconds, that is, 10 Hz).
Therefore, if the glass fiber comes into contact with the cooling device intermittently during the sampling period, the position of the glass base material will not change, and there is a risk that the glass fiber will come into contact and be damaged.

SUMMARY OF THE INVENTION Therefore, the present invention is intended to solve the problems of the prior art as described above, and an object of the present invention is to provide a method for manufacturing an optical fiber that quickly detects contact of a glass fiber with a cooling device due to string vibration. It is to provide.

The optical fiber manufacturing method of the present disclosure includes: a drawing furnace that heats and softens a glass base material; a cooling device that is disposed downstream of the drawing furnace and cools the glass fiber drawn from the drawing furnace; A method for manufacturing an optical fiber, comprising: manufacturing an optical fiber in which the glass fiber is coated with the resin using a resin coating die that applies resin to the glass fiber that has passed through the cooling device, the method comprising: manufacturing an optical fiber in which the glass fiber is coated with the resin; a vibration frequency measurement step of measuring the vibration frequency of the in-plane vibration of the glass fiber in a measurement plane intersecting the running direction of the glass fiber using a fiber position measuring device disposed in the vibration frequency measurement step; and a contact determination step of determining whether or not the glass fiber has contacted the cooling device based on the vibration frequency of the glass fiber.

According to the above, it is possible to quickly detect contact of the glass fiber with the cooling device due to string vibration.

1 is a schematic diagram of an optical fiber manufacturing apparatus used in the optical fiber manufacturing method of the present disclosure. FIG. 2 is a schematic diagram illustrating position measurement of a glass fiber by the fiber position measuring device shown in FIG. 1. FIG. 5 is a flowchart of abnormality determination in an optical fiber manufacturing process according to one aspect of the present disclosure.

[Description of embodiments of the present disclosure]
First, the contents of the embodiments of the present disclosure will be listed and explained.
The optical fiber manufacturing method of the present disclosure includes (1) a drawing furnace that heats and softens a glass base material; and a cooling device that is disposed downstream of the drawing furnace and cools the glass fiber drawn from the drawing furnace. An optical fiber manufacturing method for manufacturing an optical fiber in which the glass fiber is coated with the resin using an apparatus and a resin coating die that applies resin to the glass fiber that has passed through the cooling device, the method comprising: a vibration frequency measuring step of measuring the vibration frequency of in-plane vibration of the glass fiber in a measurement plane intersecting the running direction of the glass fiber using a fiber position measuring device disposed upstream from the die; and the vibration frequency measuring step. and a contact determination step of determining whether the glass fiber has contacted the cooling device based on the vibration frequency of the glass fiber measured by.
A vibration frequency measurement step in which the vibration frequency of the in-plane vibration of the glass fiber is measured on a measurement plane intersecting the running direction of the glass fiber using a fiber position measuring device placed upstream of the resin coating die; and a contact determination step of determining whether or not the glass fiber has contacted the cooling device based on the vibration frequency of the glass fiber measured in the measurement step. is determined based on the vibration frequency of the glass fiber, so the contact of the glass fiber to the cooling device due to chordal vibration of the glass fiber is much smaller than when determining the contact of the glass fiber to the cooling device based on the position of the glass fiber on the measurement surface. can be detected quickly.

In the above optical fiber manufacturing method, (2) in the contact determination step, it is determined that the glass fiber has contacted the cooling device when the vibration frequency of the glass fiber is outside a predetermined range.
This makes it easy to determine whether the glass fiber is in contact with the cooling device because it can be determined whether the glass fiber is in contact with the cooling device simply by frequency analysis of the positional fluctuation of the glass fiber on the measurement surface. I can do it.

In the above optical fiber manufacturing method, (3) in the contact determination step, the predetermined range is calculated based on the tension of the glass fiber measured by a fiber tension measuring device.
As a result, the vibration frequency range of the glass fiber, which is the basis for determining whether the glass fiber is in contact with the cooling device, is calculated based on the state of the glass fiber being drawn. It is possible to more accurately determine whether there is contact with the cooling device.

The method for manufacturing an optical fiber described above further includes (4) a drawing stop step of stopping drawing of the glass fiber when it is determined in the contact determination step that the glass fiber is in contact with the cooling device. .
Thereby, drawing of the glass fiber is stopped based on contact of the glass fiber with the cooling device due to string vibration, so that quality defects of the optical fiber can be suppressed.

[Details of embodiments of the present disclosure]
Hereinafter, a specific example of the method for manufacturing an optical fiber according to the present disclosure will be described.

<1. Overview of optical fiber manufacturing equipment>
First, regarding the optical fiber manufacturing apparatus used in the optical fiber manufacturing method according to the present disclosure.
FIG. 1 is a schematic diagram of an optical fiber manufacturing apparatus used in the optical fiber manufacturing method of the present disclosure, and FIG. 2 is a schematic diagram illustrating position measurement of a glass fiber by the fiber position measuring device shown in FIG. 1.

As shown in FIG. 1, the optical fiber manufacturing apparatus 100 includes, in order from the most upstream side, 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, A fiber tension measuring device 150 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. (referred to as "UltraViolet cured resin") to produce a resin-coated fiber G2, and a resin coating die 160 that cures the UV cured resin applied to the surface of the resin-coated fiber G2 to produce an optical fiber G3. It is equipped with a UV curing furnace 170 that generates UV curing, a direct roller 180 that changes the running direction 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. ing.
Therefore, this optical fiber manufacturing apparatus 100 manufactures an optical fiber G3 in which a glass fiber G1 is coated with a UV curing resin.

The base material feeding unit 110 rotatably grips a dummy rod Gd provided at the upper end of the glass base material G, and moves it in the horizontal direction (XY direction) orthogonal to the central axis direction (Z direction), which is the longitudinal direction of the glass base material G. A horizontal movement mechanism 111 that moves the glass base material G in the direction), a rotation mechanism 112 that rotates the glass base material G around the central axis, and a rotation mechanism 112 that moves the glass base material G (i.e., the horizontal movement mechanism 111) according to the progress of drawing. The feeder 113 is provided with a feeder 113 that is moved up and down.
In the embodiment, the central axis direction of the glass preform G matches the running direction of the optical fiber G3 up to the roller 180 directly below it.

The drawing furnace 120 includes a cylindrical furnace tube 121 into which the glass preform G is supplied, and a heating element 122 surrounding the furnace tube 121. It is formed.
The drawing furnace 120 is also provided with a gas supply section 123 that supplies purge gas to the heating region.

The fiber position measuring device 130 is an optical measuring device that measures the position of the glass fiber G1 on a measurement plane that intersects the running direction of the glass fiber G1 (in this embodiment, the position of the glass fiber G1 on a horizontal plane that intersects orthogonally with the running direction of the glass fiber G1). (position of glass fiber G1) is detected.
As shown in FIG. 2, this fiber position measuring device 130 includes a first direction measuring means 131 for detecting the position of the glass fiber G1 in the first direction X on the horizontal plane, and a first direction measuring means 131 for detecting the position of the glass fiber G1 in the first direction and a second direction measuring means 132 for detecting the position of the glass fiber G1 in a second direction Y perpendicular to the second direction Y.

As shown in FIG. 2, the first direction measuring means 131 emits and receives the laser beam L in the second direction Y, and includes a light projecting section 131a that emits the laser light L, and this light projecting section 131a. The light receiving section 131b receives the laser beam L emitted from the laser beam L.
As shown in FIG. 2, the second direction measuring means 132 is for projecting and receiving the laser beam L in the first direction The light receiving section 132b receives the laser beam L emitted from the laser beam L.
Therefore, the fiber position measuring device 130 transmits and receives the laser beam L in two directions perpendicular to each other, thereby allowing the fiber position measuring device 130 to transmit and receive the laser beam L in two directions (in this embodiment, the first direction X and the second direction Y). It is possible to recognize the position of the glass fiber G1 on the measurement surface (in this embodiment, the horizontal surface) formed by.
Note that, as shown in FIG. 2, the detection range by the fiber position measuring device 130 (that is, the range through which the laser beam L passes) is larger than the diameter of the glass fiber G1.

Furthermore, this fiber position measuring device 130 can calculate the vibration frequency of the glass fiber G1 in the horizontal plane by frequency-analyzing the fluctuation in the position of the glass fiber G1 in the horizontal plane, which is the measurement surface.

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

The controller 190 can communicate with the horizontal movement mechanism 111 of the base material feeding unit 110, the rotation mechanism 112, the feeder 113, the fiber position measuring device 130, the fiber tension measuring device 150, a bobbin rotation mechanism (not shown) that rotates the bobbin B, etc. It is connected.
The controller 190 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 device 130. It has a material position control means 191.

<2. Manufacturing optical fiber using optical fiber manufacturing equipment>
Next, a method for manufacturing an optical fiber using the optical fiber manufacturing apparatus 100 will be described in detail based on FIGS. 1 and 3.
FIG. 3 is a flowchart of abnormality determination in the optical fiber manufacturing process according to one aspect of the present disclosure.

<2.1. Overview of optical fiber manufacturing method>
First, a method for manufacturing an optical fiber will be outlined with reference to FIG.
In order to manufacture the optical fiber G3, the glass preform G is sent into the furnace tube 121 of the drawing furnace 120 by the preform feeding unit 110.
Then, when the lower end portion of the glass preform G is softened by the heating of the furnace tube 121 by the heating element 122 and drawn downward, the glass fiber G1 constituting the optical fiber G3 is formed.
This glass fiber G1 has a core portion and a cladding portion, and is an optical waveguide having an outer diameter of, for example, 125 μm.

After the running position of the glass fiber G1 drawn from the glass base material G in the horizontal plane is measured by the fiber position measuring device 130, the glass fiber G1 passes through the cooling device 140, thereby increasing the surface temperature of the glass fiber G1. is lowered to about room temperature.

After the tension of the glass fiber G1 cooled to about room temperature is measured by the fiber tension measuring device 150, the glass fiber G1 passes through a resin coating die 160, whereby a UV curable resin is applied around the glass fiber G1. This results in a resin-coated fiber G2.
Then, as the resin-coated fiber G2 passes through the UV curing furnace 170, the UV curing resin applied to the surface of the glass fiber G1 is cured by being irradiated with ultraviolet rays in the UV curing furnace 170, producing an optical fiber G3. Ru.

The optical fiber G3 whose traveling direction has been changed by the direct roller 180 is then wound onto the bobbin B.

<2.2. Abnormality determination>
When an optical fiber is manufactured using the method for manufacturing optical fiber G3 described above, as the glass fiber G1 runs, the glass fiber G1 forms a section whose both ends are the tip P1 of the glass base material G and the entrance P2 of the resin coating die 160. vibrates horizontally.
If the amplitude of the vibration of the glass fiber G1 is large, there is a risk that the glass fiber G1 will come into contact with the inner surface of the cooling device 140, and if the glass fiber G1 comes into contact with the inner surface of the cooling device 140, it will lead to poor quality of the glass fiber G1. Therefore, early detection of contact between the glass fiber G1 and the inner surface of the cooling device 140 is important.
Therefore, abnormality determination in manufacturing the optical fiber G3, that is, contact detection between the glass fiber G1 and the inner surface of the cooling device 140 and subsequent processing will be described below.

As shown in FIG. 3, the abnormality determination in the production of the optical fiber of the present disclosure includes a vibration frequency measurement step S110, a contact determination step S120, and a drawing stop step S130.

The vibration frequency measurement step S110 is a step that is always performed during the production of optical fibers, and uses the fiber position measuring device 130 placed upstream of the resin coating die 160 to measure the measurement surface that intersects the running direction of the glass fiber G1. The vibration frequency f of the in-plane vibration of the glass fiber G1 in the horizontal plane (in this embodiment, the horizontal plane) is measured.

In the contact determination step S120, it is determined whether the glass fiber G1 has contacted the cooling device 140 based on the vibration frequency f of the glass fiber G1 measured by the fiber position measuring device 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 device 130 is within a predetermined range.

Here, the predetermined range of the vibration frequency of the glass fiber G1, which is the basis for determining that the glass fiber G1 is not in contact with the cooling device 140, will be explained.
When 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.
Note that H[m] is the distance between the tip P1 of the glass base material G and the entrance P2 of the resin coating die 160, and S[N] is the tension of the glass fiber G1 measured by the fiber tension measuring device 150, ρ [kg/m] is the linear density of the glass fiber G1, and A is a coefficient depending on the linear velocity of the glass fiber G1.
Furthermore, since the time when n=1 is called the "fundamental vibration" and the time when n=2... is called the "n-fold vibration," the natural frequency F1 of the glass fiber G1 at n=1 is "the glass in the fundamental vibration." The natural frequency Fn of the glass fiber G1 at n=2... is referred to as the "natural frequency of the glass fiber G1 at n-fold vibration."

The predetermined range of the vibration frequency of the glass fiber G1, which is the basis for determining that the glass fiber G1 is not in contact with the cooling device 140, is a predetermined error in the natural frequency Fn of the glass fiber G1 calculated by the above equation 1. The range is the sum of the ranges.

In the contact determination step S120, if the vibration frequency f of the glass fiber G1 is within the 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 is continued.
In the contact determination step S120, if the vibration frequency f of the glass fiber G1 is outside the predetermined range, it is determined that the glass fiber G1 is in contact with the cooling device 140, and the controller 190 selects a line at which to stop drawing the glass fiber G1. A pull stop step S130 is executed.

In the drawing stop step S130, the glass base material position control means 191 controls the base material feeding unit 110, or the controller 190 controls a bobbin rotation mechanism (not shown) to stop drawing the glass fiber G1.

According to the optical fiber manufacturing method configured as described above, the fiber position measuring device 130 disposed upstream of the resin coating die 160 is used to measure the glass fiber in the horizontal plane, which is the measurement plane intersecting the running direction of the glass fiber G1. Vibration frequency measurement step S110 of measuring the vibration frequency f of in-plane vibration of G1, and whether the glass fiber G1 has contacted the cooling device 140 based on the vibration frequency f of the glass fiber G1 measured by this vibration frequency measurement step S110. By including the contact determination step S120 for determining whether the glass fiber G1 is in contact with the cooling device 140 due to string vibration, it is determined based on the vibration frequency f of the glass fiber G1. The contact of the glass fiber G1 with the cooling device 140 due to string vibration can be detected more quickly than when determining the contact of the glass fiber G1 with the cooling device 140 based on the position of G1.

Further, in the contact determination step S120, it is determined that the glass fiber G1 has contacted the cooling device 140 when the vibration frequency f of the glass fiber G1 is out of a predetermined range, so that the positional fluctuation of the glass fiber G1 in the horizontal plane is reduced to a frequency Since it is determined whether or not the glass fiber G1 is in contact with the cooling device 140 simply by analysis, it is possible to easily determine whether or not the glass fiber G1 is in contact with the cooling device 140.

Further, in the contact determination step S120, the predetermined range is calculated based on the tension of the glass fiber G1 measured by the fiber tension measuring device 150, thereby determining whether or not the glass fiber G1 is in contact with the cooling device 140. Since the range of the vibration frequency f of the glass fiber G1, which is the basis for this, is calculated based on the state of the glass fiber G1 that is drawn, it is possible to more accurately determine whether the glass fiber G1 is in contact with the cooling device 140. It can be carried out.

Furthermore, by further comprising a drawing stop step S130 for stopping drawing of the glass fiber G1 when it is determined that the glass fiber G1 is in contact with the cooling device 140 in the contact determination step S120, string vibration of the glass fiber G1 can be achieved. Since the drawing of the glass fiber G1 is stopped based on the contact with the cooling device 140, it is possible to suppress quality defects of the optical fiber G3.

[Modified example]
Although the embodiments of the present invention have been described above, the present invention is not limited to the above.
Furthermore, the elements of the embodiments described above can be combined as technically possible, and combinations of these are also included within the scope of the present invention as long as they include the features of the present invention.

For example, the measuring surface of the fiber position measuring device 130 of the optical fiber manufacturing apparatus 100 described above was a horizontal surface, but the measuring surface of the fiber position measuring device of the optical fiber manufacturing device is not limited to the horizontal surface, and It may be an inclined surface as long as it intersects with the direction.

For example, the fiber position measuring device 130 of the optical fiber manufacturing apparatus 100 described above emits and receives laser light in two directions, but it emits and receives laser light in only one direction and The position on the horizontal plane may also be measured.
In this case, the position of the laser beam projection/reception direction can be determined, for example, from the light reception profile including the area blocked by the fiber obtained by projecting the laser beam with the focal point shifted from the center of the measurement area. Calculate the slope of the received light intensity at the edge portion, and from the correlation between the predetermined slope of the received light intensity at the edge portion and the fiber position in the laser emission/reception direction, calculate the slope of the received light intensity at the edge portion from the fiber position in the laser emission/reception direction. One method is to convert it into a position.

For example, in the optical fiber manufacturing apparatus 100 described above, the fiber position measuring device 130 measures the vibration frequency of the in-plane vibration of the glass fiber, but the controller 190 measures the vibration frequency of the in-plane vibration of the glass fiber detected by the fiber position measuring device 130. Frequency analysis may be performed on variations in the position of G1.

For example, in the optical fiber manufacturing method described above, when it is determined in the contact determination step S120 that the glass fiber G1 is in contact with the cooling device 140, the drawing stop step S130 is executed. If it is determined in step S120 that the glass fiber G1 is in contact with the cooling device 140, the drawing of the optical fiber G3 is not stopped and the length of the glass fiber G1 from the start of drawing at the time of determination is recorded. Then, in a step after drawing, the portions determined to be in contact may be removed.

100 ... Optical fiber manufacturing apparatus 110 ... Base material feeding unit 111 ... Horizontal movement mechanism 112 ... Rotation mechanism 113 ... Feeder 120 ... Drawing furnace 121 ... Furnace tube 122 ... Heating element 123... Gas supply section 130... Fiber position measuring device 131... First direction measuring means 131a... First direction light emitting section 131b... First direction light receiving section 132... Two-direction measuring means 132a... Second direction light emitter 132b... Second direction light receiver 140... Cooling device 150... Fiber tension measuring device 160... Resin coating die 170... UV curing Furnace 180 ... Directly below roller 190 ... Controller 191 ... Vibration frequency calculation means 192 ... Glass base material position control means

B...Bobbin G...Glass base material Gd...Dummy rod G1...Glass fiber G2...Resin coated fiber G3...Optical fiber P1...Tip of glass base material (spinning start point)
P2... Inlet of resin coating die

X: First direction Y: Second direction L: Laser light

Claims (4)

A drawing furnace that heats and softens the glass base material, a cooling device that is disposed downstream of the drawing furnace and cools the glass fiber drawn from the drawing furnace, and a resin applied to the glass fiber that has passed through the cooling device. An optical fiber manufacturing method for manufacturing an optical fiber in which the glass fiber is coated with the resin using a resin coating die, the method comprising:
a vibration frequency measuring step of measuring the vibration frequency of in-plane vibration of the glass fiber in a measurement plane intersecting the running direction of the glass fiber using a fiber position measuring device disposed upstream of the resin coating die;
A method of manufacturing an optical fiber, comprising: a contact determination step of determining whether the glass fiber has contacted the cooling device based on the vibration frequency of the glass fiber measured in the vibration frequency measurement step. 2. The optical fiber manufacturing method according to claim 1, wherein in the contact determination step, it is determined that the glass fiber has contacted the cooling device when the vibration frequency of the glass fiber is outside a predetermined range. 3. The optical fiber manufacturing method 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 device. Any one of claims 1 to 3, further comprising a drawing stop step of stopping 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. The method for manufacturing the optical fiber described in Section 1.