JP6500364B2 - Optical fiber manufacturing method and manufacturing apparatus - Google Patents

Description

  The present invention relates to an optical fiber manufacturing method and apparatus for manufacturing an optical fiber while detecting an abnormal point of an optical fiber heated and drawn in a drawing furnace.

The optical fiber is manufactured by heating and melting an optical fiber glass base material (hereinafter referred to as glass base material) in an optical fiber drawing furnace (hereinafter referred to as a drawing furnace) and drawing the wire from below the drawing furnace. .
When manufacturing a glass base material, the abnormal point of a bubble, a foreign material, etc. may generate | occur | produce inside the glass base material by the impurity in the atmosphere at the time of the manufacture, or glass. If drawing is performed using a glass base material in which this abnormal point occurs, the abnormal point remains in the optical fiber and there is a possibility that the strength of the optical fiber is insufficient or the transmission loss is reduced. There is a need.

For example, Patent Document 1 discloses a technique in which an example bubble sensor is provided. In this example of the bubble sensor, the emitted light from the drawn optical fiber installed inside the cooling device is measured, and the bubble in the optical fiber is detected from the change of the measured value.
In addition, when the outer diameter of the optical fiber is measured during drawing, steep and large glass diameter fluctuation may appear (spiky glass diameter fluctuation, air bubbles generated in the glass base material, In the following, it is referred to as “glass diameter abnormality caused by the glass base material” because it is considered to be generated due to the foreign matter. Patent Document 2 discloses a technique for detecting a change in an optical fiber take-up speed to detect a glass diameter abnormality caused by a glass base material. In addition, since the glass diameter abnormality caused by the glass base material becomes spike-like glass diameter fluctuation as described above, when this abnormality location is detected by the outer diameter measuring instrument, it depends on the sensing cycle and the averaging frequency, The outer diameter measuring device can not follow and may be measured smaller than the actual glass diameter fluctuation value. For this reason, generally, the threshold value is lowered (when the standard of the glass outer diameter of the optical fiber is 125 ± 1 μm, it is made stricter than this), and the glass diameter abnormal part is detected.

Unexamined-Japanese-Patent No. 7-229813 gazette Japanese Patent Application Laid-Open No. 6-239641

However, there are a wide variety of abnormal points in the optical fiber. For example, in a general air bubble sensor as described in Patent Document 1, air bubbles caught by relatively long period fluctuation can be almost detected. The detection cycle and sensitivity of the air bubble sensor and the like are affected, and there is a problem that it is difficult to detect air bubbles which are caught by fluctuation of a short cycle. In addition, even bubbles captured by relatively long period fluctuations may be missed.
On the other hand, in the method of detecting an abnormal point by measuring the glass outer diameter, it is possible to detect, for example, air bubbles caught by short-period fluctuation that can not be detected by the air bubble sensor, but when the glass diameter fluctuation becomes large, There is a problem that it is difficult to detect an abnormal point because it is buried in this fluctuation. In particular, when drawing using a gas containing argon gas or nitrogen gas having a thermal conductivity lower than that of helium gas as the gas in the drawing furnace, the turbulence in the gas flow in the drawing furnace becomes large, etc. Since a problem arises that the glass diameter fluctuation of the target long period becomes large, it becomes easier to be buried in such glass diameter fluctuation.

The present invention has been made in view of the above-described circumstances, and an object thereof is to provide an optical fiber manufacturing method and apparatus capable of detecting an abnormal point almost without leak.

A method and an apparatus for manufacturing an optical fiber according to an aspect of the present invention is an optical fiber manufacturing method for manufacturing an optical fiber by heating and drawing a glass base material for an optical fiber in a drawing furnace, A signal (sorted data) having a frequency higher than a predetermined frequency (2 Hz) is determined from the step of determining the location detected by the bubble sensor as an abnormal point of the optical fiber and measurement data of the glass outer diameter of the drawn optical fiber. Determining a point exceeding the first threshold as an abnormal point of the optical fiber in comparison with the first threshold, and detecting the point detected and determined by the air bubble sensor, or / and sorting of the glass outer diameter A portion where the data exceeds the first threshold is determined as an abnormal point and processed.

  According to the above, the abnormal point can be detected almost without leak.

It is a figure explaining the outline of the manufacture device of the optical fiber concerning one mode of the present invention. It is a figure explaining the structure of the control part of FIG. It is a figure which shows the result of having frequency-analyzed the glass outer diameter measurement data of an optical fiber. It is a figure explaining another structure of the control part of FIG. It is a figure explaining another structure of the control part of FIG.

Description of the embodiment of the present invention
First, the contents of the embodiment of the present invention will be listed and described.
The method for producing an optical fiber according to one aspect of the present invention is (1) a method for producing an optical fiber by producing an optical fiber by heating and drawing a glass base material for an optical fiber in a draw furnace, A signal (sorted data) having a frequency higher than a predetermined frequency (2 Hz) is determined from the step of determining the location detected by the bubble sensor as an abnormal point of the optical fiber and measurement data of the glass outer diameter of the drawn optical fiber. Determining a point exceeding the first threshold as an abnormal point of the optical fiber in comparison with the first threshold, and detecting the point detected and determined by the air bubble sensor, or / and sorting of the glass outer diameter A portion where the data exceeds the first threshold is determined as an abnormal point and processed. Thus, the abnormal point of the optical fiber is detected by using two routes in combination. In the first route, a bubble sensor is used to detect an abnormal point by measuring the intensity of light emitted from the optical fiber. With the bubble sensor, although it is difficult to detect a bubble captured by a short cycle fluctuation, a bubble captured by a relatively long cycle fluctuation can be detected almost without leak. On the other hand, in the second route, in order to complement the detection by the air bubble sensor, by measuring the outer diameter of the glass, an abnormal point captured by a short cycle fluctuation is detected. However, in order to reduce the influence of long-period glass diameter fluctuation, a signal (sorting data) of a frequency component higher than a predetermined frequency is used to determine the abnormal point of the optical fiber by the threshold value of the glass outer diameter. Anomalous points that can be detected by the fluctuation of can also be detected.
A method for manufacturing an optical fiber (2) (1), from the measurement data of the glass outer diameter of the optical fiber, as a method for selecting the predetermined high frequency signal than the frequency (selection data), the high-pass filter Use By using a high pass filter, it is possible to reliably sort out signals of frequencies higher than a predetermined frequency.
(3) The method of manufacturing an optical fiber according to (1 ) , further comprising comparing the measurement data of the glass outer diameter with a second threshold larger than the first threshold, the measurement data being the second threshold. A point that exceeds the point is determined as an abnormal point and processed. The air bubble sensor alone may miss air bubbles that are caught by relatively long-period fluctuation, and because it is necessary to detect abnormal points other than air bubbles, measurement data of the glass outer diameter that does not pass through the high-pass filter Use to determine an abnormal point. However, if the first threshold is used, false detection may occur frequently, so the second threshold larger than the first threshold is used to determine the abnormal point. By doing this, abnormal points can be detected more.

An optical fiber manufacturing apparatus according to an aspect of the present invention is (4) an optical fiber manufacturing apparatus for manufacturing an optical fiber by heating and drawing an optical fiber glass base material in a drawing furnace, A comparison / determination unit of a bubble sensor signal that determines a point detected by a bubble sensor as an abnormal point of the optical fiber and measurement data of the glass outer diameter of the drawn optical fiber indicate that the frequency is higher than a predetermined frequency (2 Hz) And a first comparison and determination unit configured to compare a signal (sorted data) with a first threshold and determine a point exceeding the first threshold as an abnormal point of the optical fiber. By using the present manufacturing apparatus, as described above, an abnormal point captured by long and short various fluctuations can be detected, and an abnormal point can be detected almost without leakage.
(5) The apparatus for manufacturing an optical fiber according to (4), further comprising comparing measurement data of the glass outer diameter with a second threshold diameter larger than the first threshold, the measurement data being the second And a second comparison / determination unit that determines a point exceeding the threshold as an abnormal point of the optical fiber. By using this manufacturing apparatus, an abnormal point can be further detected as described above.

Details of the Embodiment of the Present Invention
An outline of an optical fiber manufacturing method and manufacturing apparatus to which the present invention is applied will be described with reference to the drawings. Although the resistance furnace which heats a core tube with a heater is explained to an example below, the present invention is applicable also to the induction furnace which applies high frequency power supply to a coil and carries out induction heating of a core tube.
FIG. 1 is a view for explaining an outline of an optical fiber manufacturing apparatus according to an embodiment of the present invention. The optical fiber manufacturing apparatus 1 includes a wire drawing furnace 10, a heating device (heater) 13, an outer diameter measuring unit 14, a cooling device 15, a coating device (resin coating die) 16, a curing device 17, a guide roller 18, a capstan 18a, The air bubble sensor 19, the winding drum 20, and the control unit 21 are provided.

  The glass base material 11 is set in the wire drawing furnace 10 from above. The glass base material 11 has a core part in the center part, and has a clad part around the core part. When the lower end portion of the set glass base material 11 is heated by the heating device 13 in the wire drawing furnace 10, the lower end portion of the glass base material 11 melts and hangs down and is drawn downward from the lower chamber 10a, It becomes an optical fiber 12.

In order to prevent the oxidation deterioration in the wire drawing furnace 10, the wire drawing furnace 10 is provided with a mechanism (not shown) for supplying gas in the furnace with an inert gas or the like. As the furnace gas, for example, argon gas is supplied into the wire drawing furnace 10, and this gas is released from the lower chamber 10a together with the drawn optical fiber 12.
The drawn optical fiber 12 is forcibly cooled by the cooling device 15 and then protected by applying, for example, an ultraviolet curing resin by the coating device 16. This resin is cured by the curing device 17. Then, the optical fiber 12 is pulled by the capstan 18 a through the guide roller 18 and taken up by the take-up drum 20.

  Also, for example, an outer diameter measurement unit 14 is installed between the lower chamber 10 a and the cooling device 15. The outer diameter measurement unit 14 measures the glass outer diameter of the optical fiber 12 by, for example, monitoring a light projection image of the side surface of the drawn optical fiber 12 and performing image processing. The measurement result is sent to the control unit 21. The outer diameter measurement unit may be installed between the cooling device 15 and the coating device 16. Also, there may be a plurality of outer diameter measuring units.

  Furthermore, for example, a bubble sensor 19 is installed on the inner surface of the cooling device 15. The light generated by the heating of the glass base material 11 is irradiated to the drawn optical fiber 12, and the air bubble sensor 19 measures the intensity of the light emitted to the outside from the side surface of the optical fiber 12, for example. Is detected. The detection result is also sent to the control unit 21. The method of detecting the air bubble by the air bubble sensor may not be the method of measuring the light intensity, and the interference light pattern may be analyzed. Also, the measurement position may not be in the cooling device 15, but may be between the cooling device 15 and the coating device 16. Moreover, you may measure in multiple places.

  When the air bubble sensor 19 detects air bubbles, or as described later, when detecting the glass outer diameter exceeding the threshold value, the control unit 21 determines that the point is an abnormal point of the optical fiber. Then, for example, the control unit 21 stores the position of the abnormal point in the storage unit 25 or marks the surface of the covering portion of the optical fiber to wind the optical fiber 12 around the winding drum 20.

FIG. 2 is a diagram for explaining the configuration of the control unit of FIG. 1, and the control unit 21 includes an outer diameter signal input unit 22, a processing unit 23, a set value input unit 24, a storage unit 25, and an output unit 26. .
The set value input unit 24 can be used, for example, for the operator of the optical fiber manufacturing apparatus 1 to input various set values and operation values. The storage unit 25 can store these various set values, operation values, and output values (the positions of abnormal points). The output unit 26 can output the processing result of the processing unit 23 to the storage unit 25 or the like.

  Here, the processing unit 23 includes the bubble sensor signal comparison and determination unit 23a and the first comparison and determination unit 23c, and the first to the output unit 26 via the bubble sensor signal comparison and determination unit 23a. It is divided into a route and a second route from the outer diameter signal input unit 22 to the output unit 26 via the first comparison and determination unit 23c.

  Specifically, in the first route, the detection signal 32 is sent from the air bubble sensor 19 to the air bubble sensor signal comparison / determination unit 23a. The comparison determination unit 23a of the bubble sensor signal may use the detection result of the bubble sensor 19 as it is to determine it as an abnormal point of the optical fiber as it is, or add some kind of determination to determine it as an abnormal point.

  On the other hand, in the second route, measurement data 30 of the glass outer diameter from the outer diameter measurement unit 14 is sent from the outer diameter signal input unit 22 to the first comparison and determination unit 23c. The first comparison determination unit 23c compares a signal of a frequency higher than a predetermined frequency (for example, 3 Hz, more preferably 2 Hz) with a threshold to make a determination.

  FIG. 3 is a diagram showing the result of frequency analysis of glass outer diameter measurement data of an optical fiber. When drawing using argon gas or a gas containing 1% or more of nitrogen gas whose thermal conductivity is lower than that of helium gas, disturbance of gas flow in the drawing furnace becomes large as described above, and glass of the optical fiber The diameter variation may be large. For example, when the inert gas in the drawing furnace is Ar 50% and He 50% and the measurement result of the glass diameter fluctuation is frequency analyzed, it is shown in FIG. 3 due to the influence of the disturbance of the gas flow in the drawing furnace. There may be many frequency components below 3 Hz. It is to be noted that even if nitrogen gas is used instead of argon gas, almost similar results are obtained. Since this low frequency component is not due to the glass diameter variation due to the glass base material due to air bubbles or foreign substances, the gas flow in the wire drawing furnace is higher than a predetermined frequency, for example, using a signal with a frequency of 3 Hz or more. An abnormal point of an optical fiber that can be detected by a short-period glass diameter fluctuation component is detected while suppressing the influence of disturbance and the like.

  Returning to FIG. 2, the first comparison / determination unit 23c compares the sorted data 31 with the first threshold value regarding the glass outer diameter, and places the spot where the sorted data 31 exceeds the first threshold as an abnormal point of the optical fiber. judge. The glass outer diameter threshold is a threshold for determining spike-like sharp glass diameter fluctuations such as air bubbles and foreign substances captured by short-period fluctuation, and is set to, for example, ± 0.5 μm. . The first threshold diameter may be set to, for example, ± 0.7 μm or ± 0.6 μm.

Thus, the abnormal point of the optical fiber is detected by using the first route and the second route in combination.
In the first route, a bubble sensor is used to detect an abnormal point by measuring the intensity of light emitted from the optical fiber. The bubble sensor is difficult to detect an abnormal point captured by a short cycle fluctuation, but can detect an abnormal point such as a bubble captured by a relatively long cycle fluctuation. On the other hand, in the second route, in order to complement the detection by the air bubble sensor, by measuring the outer diameter of the glass, an abnormal point captured by a short cycle fluctuation is detected. However, in order to reduce the influence of long-period glass diameter fluctuation, a signal having a frequency higher than a predetermined frequency is selected. With this selection data 31, to determine the abnormal point of the fiber-optic by a first threshold value, even anomalies to be taken by the variation in the short period, it is possible to detect without fail substantially. In the present embodiment, a signal having a frequency higher than a predetermined frequency is compared with the first threshold, but if there is no problem, measurement data of the glass outer diameter is used as the first threshold regardless of the frequency. You may compare.

  In the second route described above, the measurement data 30 of the glass outer diameter is sent as it is to the first comparison and determination unit 23c, but as shown in FIG. A high pass filter (HPF) 23b may be provided between the comparison and determination unit 23c. By providing a high pass filter, it is possible to more reliably sort out signals higher than a predetermined frequency.

  Further, in the second route of FIG. 4, the measurement data 30 of the glass outer diameter is sent from the outer diameter signal input unit 22 to the high pass filter 23b and the first comparison and determination unit 23c, as shown in FIG. The third route may be sent from the outer diameter signal input unit 22 to the second comparison determination unit 23d. The second comparison / determination unit 23d compares the measured data 30 of the glass outer diameter with the second threshold larger than the first threshold described above, and detects light where the measured data 30 exceeds the second threshold. Determined as an abnormal point of fiber. Since the second threshold larger than the first threshold is used, an abnormal point can be determined without frequent occurrence of false detection due to the low frequency outer diameter signal. With such a configuration, it is possible to more easily detect an abnormal point. The second threshold may be larger than the first threshold, and is set to, for example, ± 1.0 μm.

More specifically, when the air bubble in the optical fiber is determined only by the comparison determination section 23a of the air bubble sensor signal based on the detection signal 32 of the air bubble sensor, the air bubble is present. Of the 137 samples in total, 90 were detected as air bubbles in the sample, and the detection rate was about 66%.
On the other hand, in addition to the bubble sensor signal comparison / determination unit 23a, an outer diameter signal of 2 Hz or more is selected to make the first threshold value ± 0.5 μm, and the optical fiber is also used together with the first comparison / determination unit 23c. The air bubbles were determined, and 126 out of 137 samples in total were detected as samples with air bubbles present, and the detection rate was about 92%. As described above, when the air bubbles in the optical fiber are detected using the first route and the second route in combination, it is understood that the detection rate is dramatically improved.
Furthermore, when the second comparison determination unit 23d is used in combination and the second threshold value is ± 1.0 μm and bubbles in the optical fiber are determined, bubbles are present in 128 out of 137 samples in total. Detection rate was about 93%. As described above, it can be seen that the detection rate is further improved by further using the third route.

  The determination results of the comparison determination unit 23a of the bubble sensor signal, the first comparison determination unit 23c, and the second comparison determination unit 23d are sent to the storage unit 25 or the output unit 26, and the storage unit 25 determines the position of the abnormal point. It stores or marks an area determined as an abnormal point by a signal from the output unit 26. The optical fiber 12 taken up on the take-up drum 20 is, for example, the position stored in the storage unit 25 when the take-up drum 20 is set to the line of the next process and taken up on another drum, or It is removed at the marked part.

  It should be understood that the embodiments disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is indicated not by the meaning described above but by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

DESCRIPTION OF SYMBOLS 1 ... Optical fiber manufacturing apparatus, 10 ... Wire drawing furnace, 10a ... Lower chamber, 11 ... Glass base material for optical fibers, 12 ... Wire drawn optical fiber, 13 ... Heating apparatus, 14 ... Outer diameter measurement part, 15 ... Cooling Device 16 16 coating device 17 curing device 18 guide roller 18a capstan 19 air bubble sensor 20 winding drum 21 control section 22 outer diameter signal input section 23 processing section , 23a: bubble sensor signal comparison and determination unit 23b: high-pass filter, 23c: first comparison and determination unit, 23d: second comparison and determination unit, 24: setting value input unit, 25: storage unit, 26: output unit , 30: measurement data of outer diameter, 31: sorting data, 32: measurement data of strength.

Claims (5)

An optical fiber manufacturing method for manufacturing an optical fiber by heating and drawing an optical fiber glass base material in a drawing furnace,
Determining the location detected by the bubble sensor as an abnormal point of the optical fiber;
From the measurement data of the glass outer diameter of the drawn optical fiber, a signal (sorted data) having a frequency higher than a predetermined frequency (2 Hz) is compared with a first threshold, and a location exceeding the first threshold is Determining an abnormal point of the optical fiber,
A method of manufacturing an optical fiber, which determines and processes an area detected and determined by the air bubble sensor and / or an area where the sorting data of the glass outer diameter exceeds a first threshold as an abnormal point. From the measurement data of the glass outer diameter of the optical fiber, as a method for selecting the predetermined high frequency signal than the frequency (selection data), using a high-pass filter, method of manufacturing an optical fiber according to claim 1. The measurement data of the glass outer diameter compared with the first threshold value larger than the second threshold value, processing to determine the location where the measurement data exceeds the second threshold value as abnormal points, to claim 1 The manufacturing method of the described optical fiber. An optical fiber manufacturing apparatus for manufacturing an optical fiber by heating and drawing an optical fiber glass base material in a drawing furnace,
A comparison determination unit of a bubble sensor signal that determines a point detected by the bubble sensor as an abnormal point of the optical fiber;
From the measurement data of the glass outer diameter of the drawn optical fiber, a signal (sorted data) having a frequency higher than a predetermined frequency (2 Hz) is compared with a first threshold, and a location exceeding the first threshold An optical fiber manufacturing apparatus, comprising: a first comparison and determination unit that determines an abnormal point of an optical fiber.   A second comparison in which measurement data of the glass outer diameter is compared with a second threshold diameter larger than the first threshold, and a portion where the measurement data exceeds the second threshold is determined as an abnormal point of the optical fiber The manufacturing apparatus of the optical fiber of Claim 4 provided with the determination part.

Images