JP2001141583A - Fiber drawing tension measuring method of optical fiber and its device and fiber drawing tension control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fiber drawing tension measuring method and a device and a tension control device capable of heightening control reliability of an automatic control operation and guaranteeing stable production of a highest- quality optical fiber, by enabling accurate detection of a natural frequency peak value and by enabling accurate drawing out by using a tension having a calculated optimum drawing condition different in each base material. SOLUTION: In this fiber drawing tension measuring method of an optical fiber for measuring a vibration waveform of the optical fiber which is just being drawn by a vibration measuring means and for obtaining the tension of the optical fiber from a natural frequency peak of the vibration waveform, the vibration waveform of the optical fiber 3 which is just being drawn is measured by the noncontact-type vibration measuring means 11, and frequency analysis of the vibration waveform is executed by using a maximum entropy method, and a distinguished peak frequency is taken as the natural frequency peak.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improved tension measuring method for accurately and stably measuring the drawing tension of an optical fiber in the production of an optical fiber, and moreover, it is suitable for implementing the measuring method. The present invention relates to a tension measuring device used and a drawing tension control device contributing to the production of high quality optical fibers.

[0002]

2. Description of the Related Art A typical prior art for measuring the drawing tension of an optical fiber is known as disclosed in Japanese Patent Application Laid-Open No. Hei 10-316446. The vibration waveform of an optical fiber during drawing, which is detected by a non-contact fiber vibration detection sensor represented by a laser system, is generally subjected to frequency analysis by a Fourier transform (FFT) method. In this case, the applied tension is small, and the length of the optical fiber (span; span) between the non-free points at both ends is long, and a flow of cooling air or the like is generated in the surrounding area.
Disturbance is added to the optical fiber. From this, in addition to the fundamental frequency of the peak, a noise having a vibration waveform similar to this is included at a close position, and accordingly, the above-described FF
Even if T analysis is performed, it is difficult to identify the fundamental frequency because it cannot be distinguished from noise, and it has been difficult to accurately determine the tension from the result of the frequency analysis.

For this reason, in the prior art described in Japanese Patent Application Laid-Open No. Hei 10-316446, when performing a FFT analysis on a vibration waveform, a search median a and a search width b are set in advance to set a search range. A method of narrowing down and specifying, and a method of using the peak value detected last time in the measurement work several times as the median value for the next search are adopted.

However, in the above-mentioned prior art, even if an attempt is made to share a laser type outer diameter measuring device usually provided near a drawing furnace with a vibration detecting sensor, the FFT analysis is performed because the portion is a portion containing a large amount of disturbance. Because it is still difficult, it is necessary to separately provide a laser type vibration detection sensor of a similar type in another location, for example, on the upstream side of the coating die, and there is a problem of occupying space. In addition, do a preliminary test before measuring the tension,
Alternatively, it is necessary to predict the set value empirically, and it is inevitable that there is a troublesome point in handling. In addition, if the setting at that time is not appropriate, an incorrect frequency may be detected and converge to an erroneous tension value.

[0005] Apart from such an example, there is a well-known technique disclosed in Japanese Patent Application Laid-Open No. Hei 10-53431 as another example of a typical prior art. This technique optically detects the vibration of an optical fiber, and The tension is calculated by the FFT analysis, and the descending speed of the base material and the output of the furnace are controlled based on the measured value of the tension. The purpose of this prior art is to prevent runaway of the drawing apparatus due to overheating of the base material, that is, to eliminate the manual operation of the operator and automatically continue the drawing operation at a stable speed. is there.

It is well known that in order to produce a high quality optical fiber in the drawing process, it is sufficiently important to accurately control the temperature of the preform in the furnace. Although the temperature cannot be directly measured, the tension is usually used as an alternative control object, whereas the furnace power, that is, the furnace temperature can be used for the drawing speed control in the above-described method, although it is actually possible. As described above, the result of FFT analysis has an unfavorable effect on the fiber quality because it is difficult to obtain an accurate calculated value, and is not necessarily an appropriate method.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to solve the problems of the prior art, and a main object of the present invention is to reduce the vibration waveform of an optical fiber. By being able to accurately analyze based on a new calculation method that was not considered, it was possible to accurately detect the natural frequency peak value in the process of calculating the tension from the frequency peak. An object of the present invention is to improve the control reliability of the automatic control operation and to assure stable production of high-quality optical fiber by making it possible to accurately draw the optimum drawing conditions different for each material using the calculated tension. Further, the present invention can be realized by effectively utilizing existing detection equipment without newly using a fiber vibration detection sensor having a special structure, thereby reducing the installation space for the control auxiliary equipment in the drawing apparatus. It is also a main object to suppress the increase and to simplify the device for detecting the tension to reduce the cost of the drawing device.

[0008]

The present invention has the following configuration to achieve the above object. That is, the invention of claim 1 in the present invention is a tension measuring method for measuring the vibration waveform of an optical fiber being drawn by a vibration measuring means and obtaining the tension of the optical fiber from the natural frequency peak of the vibration waveform. The vibration waveform of the optical fiber being drawn is measured by the contact-type vibration measuring means, and the frequency analysis of the vibration waveform is performed using the maximum entropy method, and the frequency of the preeminent peak is set as the natural frequency peak. This is a characteristic method for measuring the drawing tension of an optical fiber.

Further, the invention of claim 2 of the present invention provides:
Non-contact vibration measuring means provided in proximity to the optical fiber being drawn and optically measuring the vibration of the optical fiber,
Frequency peak calculation means for determining the peak frequency from the spectrum of the measured vibration waveform based on the maximum entropy method and determining this as the natural frequency peak, and the drawing speed in the optical fiber being drawn, between the non-free points at both ends. A tension calculating means for calculating a target tension from the natural frequency peak based on an optical fiber length and a mass per unit length.

[0010] The invention of claim 3 in the present invention provides:
In the optical fiber drawing tension measuring apparatus according to the invention of claim 2, the vibration measuring means measures the vibration of the uncoated optical fiber during drawing from the drawing furnace to the cooling pipe by using a laser beam. The apparatus is characterized in that it is formed in a common type capable of measuring a vibration waveform and a change in outer diameter of an uncoated optical fiber during drawing.

[0011] The invention of claim 4 in the present invention provides:
An optical fiber drawing tension measuring apparatus having the configuration according to claim 2 or 3, a tension setting means for setting a target tension for the optical fiber being drawn, and a measurement tension by the tension measuring apparatus and a setting by the tension setting means. A draw furnace output adjusting means for lowering the output of the drawing furnace when the set tension is larger than the tension, and increasing the output when the set tension is small to match the measured tension to the set tension. This is an optical fiber drawing tension control device.

In the tension measuring method according to the first aspect of the present invention and the tension measuring apparatus according to the second aspect, the frequency analysis of the vibration waveform of the optical fiber during drawing measured by the non-contact vibration measuring means is performed. It is performed using the maximum entropy method, and the frequency of the preeminent peak is used as the natural frequency peak, and the spectrum analysis is performed using the maximum entropy method which is excellent in satisfying the requirement of high frequency resolution. There is a characteristic in the place. In other words, the maximum entropy method, also known as an autoregressive model or a linear prediction model, is a method that can perform high-resolution spectral analysis from short data, and clearly distinguishes noise due to disturbance from the vibration waveform unique to the optical fiber. And the accuracy of detecting the natural frequency can be improved. As a result, the fluctuation range of the target tension calculation result is also reduced, and a highly accurate and stable control signal can be promptly provided to a control target such as a furnace output.

According to a third aspect of the present invention, in the tension measuring apparatus according to the second aspect of the present invention, the non-contact type vibration measuring means includes a non-contact type vibration measuring means which is not used during drawing from the drawing furnace to the cooling pipe. It is composed of a shared laser-type vibration measuring device that measures the vibration waveform and outer diameter change of the coated optical fiber using laser light. That is, since it is a measuring instrument having both the outer diameter measuring function and the vibration measuring function, it is possible to measure the optical fiber vibration waveform using the outer diameter measuring instrument which is always provided in the conventional drawing apparatus, and a special Existing detection equipment can be effectively used without newly using a fiber vibration detection sensor having a structure.

According to a fourth aspect of the present invention, there is provided a tension control device for an optical fiber having the configuration according to the second or third aspect as an element member based on a measured natural frequency peak. Since the output (temperature) of the drawing furnace is automatically controlled so that the tension value becomes a preset optimum set value, the base material temperature (tension) can be controlled to the optimum base material temperature for each base material, and high quality Optical fibers can be stably produced.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be specifically described below with reference to the accompanying drawings. First,
Before describing this embodiment, the maximum entropy method (Maxim
um EntropyMethod (hereinafter abbreviated as MEM)).

The MEM passes the given time-series data {x _i } of N points through an assumed m-point prediction error filter γ _m, and from = 1 so that the output P _{m at} that time is minimized. This is a method of recursively calculating a filter coefficient γ _m , a filter output P _m , and an autocorrelation function C _m . The frequency spectrum P (f) is represented by the following formulas Motoma' autocorrelation function C _m (A), is calculated using a relational expression of Wiener-Khintchine shown in (B).

(Equation 1)

The filter output P _m is supplied to the prediction error filter γ _m by the time series data {x _i } as shown in the following equation.
Is defined as the sum of squares (see the following equation (C)) of the output {y _i } when passing through from the front and the output {y _i ^′ } when passing backward, and the condition that the value (≒ entropy) is minimized To determine the coefficient.

(Equation 2)

[0018] Specifically filter output P _m is try to calculate the recurrence-batch for imposing smallest condition is as follows.

(Equation 3)

The above equation is for the case of m <3, where m ≧ 3.
In No. 3, calculation is generally performed by the following equation.

(Equation 4)

Determination of ◇ γ _{m, k} γ _{m, k} is calculated from γ _{m-1, k} already obtained and γ _{m, m} obtained by the above formula (D) according to the Levinson algorithm. _{γ m, k = γ m-} 1, k + γ m, m * γ m-1, mk ...... (E) ◇ calculation of _{P m P m = P m-} 1 (1-γ m, m 2) ...... (F) 計算 Calculation of autocorrelation function C _m C _m = − [γ _m1 C _m−1 + γ _m2 C _m−2 +... + Γ _mm C ₀ ] (G)

[0021] Then, the frequency spectrum P occupying become maximum entropy (f) is the following equation using the filter coefficients γ _m (H).

(Equation 5)

The MEM described above has an advantage that the number of data can be freely selected without having to select the number of data to a power of 2 unlike the Fourier transform. So, MEM
When calculating the tension from the natural frequency peak using, it is necessary to select the sampling frequency of the vibration signal and the number of data so as to achieve the desired tension calculation accuracy and minimize the calculation time. The points will be described later based on an embodiment described later.

In FIG. 1, an example of an optical fiber vibration signal measured by an optical fiber drawing apparatus (hereinafter, abbreviated as a drawing apparatus) is shown in FIG. 1A, and a frequency analysis result when the signal is analyzed by MEM is shown in FIG. (B) shows the result of frequency analysis when the same signal is analyzed by Fourier transform. In FIG. 1A, the horizontal axis is time, which is a vibration signal for a total of 4 seconds. In the Fourier transform of FIG. 1C, peaks are established and peaks having amplitudes close to the resonance frequency are close to each other. Therefore, it is difficult to determine the resonance frequency. On the other hand, in the case of (b), the frequency spectrum has a smooth curve, and therefore, there is no possibility that the peak frequency is mistaken for noise.

FIG. 2 is a schematic overall structural view of a drawing apparatus according to an embodiment of the present invention. The drawing apparatus in FIG. 2 includes a base material feeder 10, a drawing furnace 2, a cooling pipe 4, a first coating die 5, and a base material feeding apparatus 10, which are arranged in the order from the top to the bottom.
The first resin curing device 6, the second coating die 7, the second resin curing device 8, and the take-up capstan 9 are configured with respective component devices (however, a winding machine for collecting an optical fiber is omitted). Between the drawing furnace 2 and the cooling pipe 4, an outer diameter vibration measuring device 11 is located at a position close to the optical fiber 3 being drawn.
The outer diameter vibration measuring device 12 is provided between the first resin curing device 6 and the second coating die 7 at a position close to the optical fiber 3 being drawn. And provided so as to surround the optical fiber 3,
Immediately below the second resin curing device 8, an outer diameter vibration measuring device 13 is provided.
Is provided so as to be surrounded at a position close to the optical fiber 3 being drawn.

A tension measuring device is formed by combining the outer diameter vibration measuring device 11 and a tension measuring device 14 into which a vibration signal from the measuring device 11 is introduced. This tension measuring device constitutes a drawing tension measuring device according to the embodiment of the present invention, and the outer diameter vibration measuring device 11 optically measures the vibration of the optical fiber 3 by a non-contact type, for example, a laser type. On the other hand, the tension measuring device 14 calculates a peak frequency from the spectrum of the measured vibration waveform based on the maximum entropy method and determines the peak frequency as a natural frequency peak, It corresponds to a calculating means including a tension calculating means for obtaining a target tension from the natural frequency peak.

The outer diameter vibration measuring device 12 and the measuring device 12
A tension measuring device is formed by combining with a tension measuring device 15 to which a vibration signal from is introduced, and the outer diameter vibration measuring device 13 and a tension measuring device 16 to which a vibration signal from the measuring device 13 are introduced. Are combined to form a tension measuring device, and the tension measuring device has a configuration similar to the tension measuring device including the outer diameter vibration measuring device 11 and the tension measuring device 14.

Such a drawing apparatus is composed of a base material feeder 1
The optical fiber preform 1 attached to the optical fiber 3 is sent to a drawing furnace 2 where it is superheated and melted at a predetermined temperature, and is drawn by a take-up capstan 9 to produce the optical fiber 3. In this case, the optical fiber 3 is the outer diameter vibration measuring device 1
The outer diameter and vibration are measured by 1 and the rotational speed of the take-off capstan 9 is controlled so that the measured outer diameter becomes a predetermined diameter.

Optical fiber 3 unreeled from drawing furnace 2
Is sent to the cooling pipe 4 after the outer diameter is measured by the outer diameter vibration measuring device 11, where it is cooled by the cool air, and then the first coating resin 5 is used as the primary resin in the first coating die 5. Is coated, and then the coating resin is cured by the first resin curing device 6. Then, the outer diameter vibration measuring device 12 measures the coating diameter of the first layer. Similarly, the second layer of resin coating called secondary is performed, and the diameter of the second layer coating is measured.

The outer diameter vibration measuring devices 11, 12, and 13 have the function of the "fiber vibration measuring sensor" in addition to the conventional function of the "outer diameter measuring sensor" as described above. Referring to FIG. 4 showing an explanatory diagram of the measurement of the diameter and the vibration of the optical fiber, the laser beam is irradiated to the optical fiber 3 so that the distance x ₁ of the nearest surface of the optical fiber 3 to the reference point and the farthest surface calculating the distance x _2, from the calculation result, determine the outer diameter D of the optical fiber 3 by D = x ₂ -x _{1, also, O = (x 2 + x} 1) / 2 by the optical fiber 3
It is possible to obtain a change in the distance between the center and the reference point, that is, the vibration of the optical fiber 3.

Each of the vibration signals detected in this way is introduced into the corresponding tension measuring devices 14, 15, and 16. Here, after the natural frequency peak value is obtained based on the MEM,
The tension is calculated by the following equation (I). T = μ [fL + (f ² L ² + v ² ) ^1/2 ] ² (I) where T: tension, f: natural frequency, v: drawing speed, L: first from drawing furnace 2 Length (span) up to the coating die 5 (between non-free points at both ends), μ: mass of the optical fiber 3 per unit length,

At the time of calculating the tension, vibration data (= 12000 points) at a sampling frequency of 100 Hz for 2 minutes obtained for each linear velocity obtained by variously changing the drawing speed v was measured, for example, every 4 seconds (400 points). ME
M analysis and FFT analysis were attempted. FIG. 5 shows a comparison diagram of the tension fluctuation width in FIG. According to FIG. 5, the variation width obtained by the MEM method at any linear velocity is smaller than that obtained by the FFT method. Therefore, the result obtained by the MEM method is superior in the detection accuracy of the natural frequency. I understand.

Further, the drawing apparatus shown in FIG. 2 is provided with a drawing tension control apparatus according to the embodiment of the present invention. The drawing tension control device includes a drawing tension measuring device including an outer diameter vibration measuring device 11 and a tension measuring device 14, and a drawing furnace 2.
Drawer power panel 1 for adjusting the output (heating source output) of the furnace
7, a drawing furnace output adjusting means comprising a control unit 18 having an operation / control element member such as a microcomputer, and a tension setting means realized by a tension setting device 20 for setting a target tension for the optical fiber 3 being drawn. And a comparator 19 for comparing and calculating the measured tension and the set tension.

The above-described drawing tension control device is an automatic control device for automatically performing tension adjustment during the drawing operation and stably producing a high-quality optical fiber. The control mode is shown in FIG. This will be described below with reference to a flowchart.

[0034] In STEPS _1, after a preset target tension value at a tension setting device 20, starting the drawing operation (STEPS
₂ ) Do it. In this case, the tension value increases in proportion to the drawing speed. In order to stabilize the running of the optical fiber 3 at a low speed, the temperature of the glass as the base material is low (the glass is hard) in the low speed range, and the glass temperature is increased as the speed increases, and a specific linear speed, for example, 300 to 600 It is common to operate manually or automatically so as to reach a predetermined temperature at m / min.
Hayashi increase in speed increase command is given to the preform feeder 10 or the like in STEPS _3, when it is determined that reached a steady speed of the target linear velocity at STEPS _4, linear velocity and tension proceeds to STEPS ₅ Check if is stable. In this check, if the state of the glass in the drawing furnace 2 becomes stable, both the linear velocity and the tension should be substantially constant.

[0035] Turning to STEPS ₇ in a state became stable measured tension (DerutaT≡ target tension - measured tension), the following STEPS ₈
In The higher towards the actual tension as compared with the target tension (glass hard state), increasing the power output by increasing the set temperature of the drawing furnace 2 (STEPS _10). Conversely, if the temperature is low (the glass is soft), lower the set temperature and reduce the power output (st
epS ₉ ). Usually, if the temperature of the drawing furnace 2 is changed, the melting state of the glass changes, and the glass becomes unstable, and both the linear velocity and the tension change. Accordingly, after waiting until the re-stable state, by repeated similar control between the STEPS ₅ to STEPS _10, is controlled so as to match the measured tension to the target tension.

As described above, since the automatic control of the drawing tension is continuously performed, a high-quality optical fiber can be stably manufactured.

[0037]

The present invention is embodied in the form described above and has the following effects.

According to the first and second aspects of the present invention, the frequency analysis of the vibration waveform of the optical fiber being drawn is performed by using the maximum entropy method, and the frequency of the predominant peak is changed to the natural frequency peak. Therefore, high-resolution spectral analysis can be performed from short data, and noise due to disturbance can be clearly distinguished from vibration waveform peculiar to the optical fiber, and the detection accuracy of the natural frequency is improved. I can do it. As a result, the fluctuation range of the target tension calculation result is also reduced, and a highly accurate and stable control signal can be promptly provided to a control target such as a furnace output.

Further, according to the invention of claim 3 of the present invention, the non-contact type vibration measuring means detects the vibration waveform and outer diameter change of the uncoated optical fiber during drawing from the drawing furnace to the cooling pipe. Since it is composed of a common type laser vibration measuring device that measures with laser light, it is possible to measure the optical fiber vibration waveform using the outer diameter measuring device that is always provided in the conventional drawing device, and special An existing detection device can be effectively used without additionally using a fiber vibration detection sensor having a structure, and a low-cost and high-precision vibration measurement device can be provided.

According to the invention of claim 4 of the present invention, the drawing furnace is used as an element member so that the tension value based on the measured natural frequency peak becomes the preset optimum set value. Since the output (temperature) is automatically controlled, it is possible to control the base material temperature (tension) optimally for each base material, and it is possible to stably produce a high-quality optical fiber.

[Brief description of the drawings]

FIG. 1 is a diagram of an oscillation signal of an optical fiber in an optical fiber drawing apparatus, (a) is a measurement example, (b) is a frequency analysis result of the same signal by a maximum entropy method, and (c) is a signal of the same signal. It is a frequency analysis result by Fourier transform.

FIG. 2 is a schematic overall structural view of an optical fiber drawing apparatus according to an embodiment of the present invention.

FIG. 3 is a flowchart illustrating a control mode of a drawing tension control device in the drawing device shown in FIG. 2;

FIG. 4 is an explanatory diagram of measurement of diameter and vibration of an optical fiber.

FIG. 5 is a comparison diagram of a tension fluctuation width in an optical fiber being drawn based on analysis results of a maximum entropy method and a Fourier transform method.

[Explanation of symbols]

1. Optical fiber preform 2. Drawing furnace 3
... Optical fiber 4 ... Cooling pipe 5 ... First coating die 6
... First resin curing device 7 ... Second coating die 8 ... Second resin curing device 9
… Removal capstan 10… Base material feeder 11… Outer diameter vibration measuring instrument 1
2: Outer diameter vibration measuring device 13: Outer diameter vibration measuring device 14: Tension measuring device 1
5 ... Tension measuring device 16 ... Tension measuring device 17 ... Drawing furnace power panel 1
8 ... Control unit 19 ... Comparator 20 ... Tension setting device

Claims (4)

[Claims] 1. A tension measuring method for measuring a vibration waveform of an optical fiber during drawing by a vibration measuring means and obtaining a tension of the optical fiber from a natural frequency peak of the vibration waveform. The optical fiber is characterized by measuring the vibration waveform of the optical fiber being drawn, analyzing the frequency of the vibration waveform using the maximum entropy method, and setting the predominant peak frequency as the natural frequency peak. Tension measurement method. 2. A non-contact type vibration measuring means which is provided close to an optical fiber being drawn and optically measures the vibration of the optical fiber, and a method of measuring a peak from a spectrum of the measured vibration waveform based on a maximum entropy method. Frequency peak calculating means for obtaining a frequency and determining this as a natural frequency peak,
Tension calculating means for obtaining a target tension from the natural frequency peak based on the drawing speed of the optical fiber being drawn, the length of the optical fiber between the non-free points at both ends, and the mass per unit length. Optical fiber drawing tension measuring device. 3. A laser vibration measuring device for measuring the vibration of an uncoated optical fiber during drawing from a drawing furnace to a cooling pipe by using a laser beam, wherein the vibration measuring means is an uncoated optical fiber during drawing. 3. The optical fiber drawing tension measuring apparatus according to claim 2, wherein the apparatus is formed as a common type capable of measuring a vibration waveform and a change in outer diameter of the optical fiber. 4. An apparatus for measuring the drawing tension of an optical fiber according to claim 2 or 3, tension setting means for setting a target tension for an optical fiber being drawn, and a tension and a tension measured by the tension measuring apparatus. When the set tension is compared with the set tension by the setting means, the output of the drawing furnace is reduced when the set tension is large, and when the set tension is small, the output is increased to match the measured tension with the set tension. An optical fiber drawing tension control device.