JP2006193397A - Method and apparatus for drawing glass preform - Google Patents

Method and apparatus for drawing glass preform Download PDF

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JP2006193397A
JP2006193397A JP2005009277A JP2005009277A JP2006193397A JP 2006193397 A JP2006193397 A JP 2006193397A JP 2005009277 A JP2005009277 A JP 2005009277A JP 2005009277 A JP2005009277 A JP 2005009277A JP 2006193397 A JP2006193397 A JP 2006193397A
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base material
stretching
preform
outer diameter
speed
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JP4318646B2 (en
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Kazuichi Yamamura
和市 山村
Mitsukuni Sakashita
光邦 坂下
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Shin Etsu Chemical Co Ltd
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    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
    • C03B37/00—Manufacture or treatment of flakes, fibres, or filaments from softened glass, minerals, or slags
    • C03B37/01—Manufacture of glass fibres or filaments
    • C03B37/012—Manufacture of preforms for drawing fibres or filaments
    • C03B37/01205—Manufacture of preforms for drawing fibres or filaments starting from tubes, rods, fibres or filaments
    • C03B37/01225—Means for changing or stabilising the shape, e.g. diameter, of tubes or rods in general, e.g. collapsing
    • C03B37/0124—Means for reducing the diameter of rods or tubes by drawing, e.g. for preform draw-down
    • C03B37/01242—Controlling or regulating the down-draw process
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P40/00—Technologies relating to the processing of minerals
    • Y02P40/50—Glass production, e.g. reusing waste heat during processing or shaping
    • Y02P40/57—Improving the yield, e-g- reduction of reject rates

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  • Chemical & Material Sciences (AREA)
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  • General Life Sciences & Earth Sciences (AREA)
  • Geochemistry & Mineralogy (AREA)
  • Manufacturing & Machinery (AREA)
  • Materials Engineering (AREA)
  • Organic Chemistry (AREA)
  • Re-Forming, After-Treatment, Cutting And Transporting Of Glass Products (AREA)
  • Manufacture, Treatment Of Glass Fibers (AREA)

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and an apparatus for drawing a glass preform by which the outside diameter is controlled with high precision in drawing the glass preform for an optical fiber, particularly a large diameter preform ingot into a preform. <P>SOLUTION: In the method of drawing the glass preform of the optical fiber to reduce the diameter to a prescribed size, 1st outside diameter measuring equipment 7 and 2nd outside diameter measuring equipment 8 are mounted respectively at a 1st measuring position in the way to draw the glass preform 1 in a heating furnace 5 and at a 2nd measuring position in the almost finnishing the drawing to measure the outside diameter and a setting value at the 1st position is sequentially changed based on a value measured at the 2nd measuring position. At the same time, the pull-down speed of the glass preform 1 and the taking-up speed of the drawn preform 2 are also controlled so as to eliminate the difference between the changed setting value and the value measured at the 1st measuring position. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

本発明は、合成石英からなる光ファイバ用ガラス母材の延伸に係り、特には、延伸して得られるプリフォームの外径を精密に制御するガラス母材の延伸方法及び延伸装置に関するものである。   The present invention relates to the stretching of a glass preform made of synthetic quartz for an optical fiber, and more particularly to a glass preform stretching method and stretching apparatus for precisely controlling the outer diameter of a preform obtained by stretching. .

合成石英を素材とする光ファイバ用プリフォームの従来の製造方法では、VAD法やOVD法等で合成したスート体を脱水、焼結し、透明ガラス化することで、母材インゴットが得られる。
通常、母材インゴットの直径は、150〜200mmφであるが、実際に、光ファイバの線引きに使用されるプリフォームの直径は50〜120mmφであるため、母材インゴットを電気炉で延伸・縮径して、所望の外径を有するプリフォームを製造している。 In the conventional manufacturing method for optical fiber preforms made of synthetic quartz, a soot body synthesized by the VAD method, OVD method, or the like is dehydrated, sintered, and made into a transparent glass to obtain a base material ingot.
Normally, the base material ingot has a diameter of 150 to 200mmφ, but the preform used for optical fiber drawing is actually 50 to 120mmφ, so the base material ingot is stretched and reduced in an electric furnace. Thus, a preform having a desired outer diameter is manufactured.

近年、光ファイバ及び光ファイバ用母材の生産性を向上するために、光ファイバ用母材は大型化されてきている。これにともない、光ファイバの線引きに好適な径に母材インゴットを縮径する延伸加工の困難さが増し、その延伸精度、すなわち、延伸して得られるプリフォームの外径精度を高めることが求められている。   In recent years, in order to improve the productivity of optical fibers and optical fiber preforms, the optical fiber preforms have been increased in size. As a result, it becomes difficult to stretch the base material ingot to a diameter suitable for drawing an optical fiber, and it is required to increase the stretching accuracy, that is, the outer diameter accuracy of the preform obtained by stretching. It has been.

母材インゴットの延伸装置は、母材インゴットを炉の上部から送り込み、約2000℃に加熱した炉内で一端から順次加熱軟化させ、炉の下方から延伸したプリフォームを引き取るようになっている。このような延伸装置については、例えば、特許文献１に開示されているが、これには、最大で直径52mmφのガラスロッドを直径４mmφに延伸して縮径する例が記載され、さらに、延伸後のガラスロッド径を制御する方法についても記載している。それによるとこの方法では、加熱炉から出てきたガラスロッドの径を一箇所で測定し、測定値の時間変化を基に、延伸前後のガラスロッドの外径を、むだ時間を補償するプロセスモデルに基づいて制御している。   The base material ingot drawing apparatus feeds a base material ingot from the upper part of the furnace, heat-softens it sequentially from one end in a furnace heated to about 2000 ° C., and draws the preform drawn from the lower part of the furnace. Such a stretching apparatus is disclosed in, for example, Patent Document 1, which describes an example in which a glass rod having a maximum diameter of 52 mmφ is stretched to a diameter of 4 mmφ to reduce the diameter. A method for controlling the glass rod diameter is also described. According to this method, in this method, the diameter of the glass rod coming out of the heating furnace is measured at one location, and the outer diameter of the glass rod before and after stretching is compensated for dead time based on the time change of the measured value. Control based on.

特許文献２〜４は、２箇所に設けた外径測定器を用いて外径制御する方法を開示している。これらの方法は、第一の目標径の設定を間欠的に行うもの、第一の外径測定器の目標径を一定にするもの、あるいは既に延伸を終了したところに第二の外径測定器を設置するものである。   Patent Documents 2 to 4 disclose methods for controlling the outer diameter using outer diameter measuring instruments provided at two locations. These methods are the one that intermittently sets the first target diameter, the one that makes the target diameter of the first outer diameter measuring instrument constant, or the second outer diameter measuring instrument that has already been extended. Is to be installed.

特開平7‐2539号公報JP-A-7-2539 特開平10‐167745号公報JP-A-10-167745 特開2001‐10839号公報Japanese Patent Laid-Open No. 2001-10839 特開2002‐293564号公報JP 2002-293564 A 特許第2,697,927号Patent No. 2,697,927

しかし、本発明が対象としている母材インゴット及び延伸後のプリフォームの径は、従来のものに比べて非常に大きいため、加熱炉も大型化する必要があった。その結果、炉内の断熱材が占める熱容量が増大し、このことにより、炉内では母材インゴットの温度分布がその軸方向において変化していた。   However, since the diameter of the base material ingot and the stretched preform targeted by the present invention is much larger than that of the conventional one, it is necessary to enlarge the heating furnace. As a result, the heat capacity occupied by the heat insulating material in the furnace is increased, and this causes the temperature distribution of the base material ingot to change in the axial direction in the furnace.

光ファイバ用ガラス母材の合成石英ガラスの軟化温度は1600℃以上であるが、実際に延伸する場合には十分加熱し、粘度を低くする必要があるため、通常、加熱炉の最高温度は2000℃前後に設定される。しかし、延伸され炉から出てきたプリフォームの外径に基づいて、延伸速度を制御しようとすると、加熱部から炉外部までの時間遅れが大きく、延伸速度が異常に変動し、ハンチングを起こすため、この方法ではプリフォーム径を制御することができない。また、これらの径変動は製品の歩留まりを低下させ、ガラス旋盤による再加工が必要となるなど、コスト低減の妨げになるという問題があった。   The softening temperature of synthetic quartz glass, which is a glass base material for optical fibers, is 1600 ° C or higher. However, when it is actually stretched, it must be heated sufficiently to reduce its viscosity. Set around ℃. However, when trying to control the drawing speed based on the outer diameter of the preform that has been drawn out of the furnace, the time delay from the heating section to the outside of the furnace is large, the drawing speed fluctuates abnormally, and hunting occurs. In this method, the preform diameter cannot be controlled. In addition, these diameter fluctuations reduce the product yield and require reworking with a glass lathe, which hinders cost reduction.

例えば、特許文献２によれば、延伸中、第一の目標径の設定が間欠的で不連続に行われるため、結果として得られるプリフォームの外径は、ある許容範囲には入るものの、目標径を変更した箇所で径が変動していた。
特許文献３の方法では、第二の外径測定器の測定位置が延伸の終了後の位置にあるため、前述のごとく、加熱部から炉外部までの移動距離が長く、そのため母材が縮径する時間も長くなり、制御上、大きな時間遅れを生じ、延伸速度が大きく変動してハンチングを起こし、なかなか良好なものが得られなかった。 For example, according to Patent Document 2, since the setting of the first target diameter is performed intermittently and discontinuously during stretching, the outer diameter of the resulting preform falls within a certain tolerance, but the target The diameter changed at the place where the diameter was changed.
In the method of Patent Document 3, since the measurement position of the second outer diameter measuring instrument is in the position after the end of the stretching, as described above, the moving distance from the heating unit to the outside of the furnace is long, so that the base material is reduced in diameter. As a result, the time required for the control was increased, a large time delay was caused in the control, the stretching speed fluctuated greatly and hunting occurred, and a good product could not be obtained.

特許文献４は、引き下げ速度を、第一の外径測定器の目標径と測定値の偏差から制御し、引き取り速度を、第二の外径測定器の目標径と測定値の偏差から制御する構成を記載しているが、外径変動を有した大型の母材の場合、第一の外径測定器の目標径が一定のままでは、結果として、長手方向で安定した良好な精度のプリフォームが得られない。   In Patent Document 4, the pulling-down speed is controlled from the deviation between the target diameter of the first outer diameter measuring instrument and the measured value, and the take-up speed is controlled from the deviation between the target diameter of the second outer diameter measuring instrument and the measured value. Although the configuration is described, in the case of a large base material with a variation in outer diameter, if the target diameter of the first outer diameter measuring instrument remains constant, the result is a stable and accurate accuracy profile in the longitudinal direction. Renovation is not obtained.

また、特許文献５は、外径測定器を設置する位置を指定しているが、実施例に記載された火炎による延伸方法は、被延伸母材の外径が13〜23mmφと非常に小さいために加熱溶融部の長さは短くて済み、このため、指定された部分を測定し制御することで良好な精度のものが得られていたと思われる。しかし、電気炉で大径の母材を延伸する場合には、溶融に大きな熱量が必要とされるため、加熱溶融部を長い範囲に取る必要がある。さらに外径変動を伴う母材を延伸する場合には、一箇所の測定では十分とは云えない。   Further, Patent Document 5 designates the position where the outer diameter measuring device is installed. However, in the flame stretching method described in the examples, the outer diameter of the base material to be stretched is as small as 13 to 23 mmφ. In addition, the length of the heated and melted portion may be short, and therefore, it is considered that the one with good accuracy was obtained by measuring and controlling the designated portion. However, when a large-diameter base material is stretched in an electric furnace, a large amount of heat is required for melting, and thus it is necessary to take a heating and melting portion in a long range. Furthermore, when a base material with a variation in outer diameter is stretched, it is not sufficient to measure at one location.

本発明は、上記問題に鑑みなされたもので、光ファイバ用ガラス母材、特に大径の母材インゴットをプリフォームに延伸する際に、高い精度で外径制御を行うことのできるガラス母材の延伸方法及び延伸装置を提供することを目的としている。   The present invention has been made in view of the above problems, and a glass base material capable of controlling the outer diameter with high accuracy when a glass base material for optical fibers, particularly a large-diameter base material ingot, is drawn into a preform. An object of the present invention is to provide a stretching method and a stretching apparatus.

本発明のガラス母材の延伸方法は、光ファイバ用ガラス母材を延伸して所定の径に縮径する方法であって、該ガラス母材が加熱炉で延伸される途中の第一の測定位置に第一の外径測定器を、延伸が概ね終了した第二の測定位置に第二の外径測定器をそれぞれ設置して外径を測定し、第二の測定位置で得られた測定値に基づき、第一の測定位置での設定値を逐次変更して延伸することを特徴としており、変更された設定値と第一の測定位置で測定された測定値との差がなくなるように、ガラス母材１の引き下げ速度と延伸されたプリフォーム２の引き取り速度が同時に制御される。
なお、第一の測定位置での設定値は、第二の測定位置での設定値と測定値に基づき、PID制御により設定変更される。さらに、第一の測定位置での設定値と測定値をもとに、PID制御によりガラス母材の引き下げ速度とプリフォームの引き取り速度が制御される。 The glass base material stretching method of the present invention is a method of stretching a glass base material for an optical fiber to reduce the diameter to a predetermined diameter, and is a first measurement while the glass base material is stretched in a heating furnace. The first outer diameter measuring device is installed at the position, the second outer diameter measuring device is installed at the second measuring position where the stretching is almost finished, the outer diameter is measured, and the measurement obtained at the second measuring position. Based on the value, the setting value at the first measurement position is sequentially changed and stretched, so that there is no difference between the changed setting value and the measurement value measured at the first measurement position. The pulling speed of the glass base material 1 and the drawing speed of the stretched preform 2 are simultaneously controlled.
The setting value at the first measurement position is changed by PID control based on the setting value and the measurement value at the second measurement position. Further, based on the set value and the measured value at the first measurement position, the glass base material pulling speed and the preform pulling speed are controlled by PID control.

上記ガラス母材の引き下げ速度と延伸されたプリフォームの引き取り速度を同時に制御するに際して、ガラス母材の延伸該当部（直胴部）の長手方向の平均外径をＤav、プリフォームの仕上がり径をd、予め設定した加熱炉内へのガラス母材の引き下げ速度をＶ１svとし、式（Ｄav／ｄ）2×Ｖ１svから求められる加熱炉からのプリフォームの引き取り速度をＶ２sv、制御機器より演算された引き下げ速度及び引き取り速度を順にＶ１sp、Ｖ２spとするとき、
Ｖ１sp ＝Ｖ１sv ＋k(Ｖ２sv −Ｖ２sp ) …ただし、kは正の実数
の関係式を満たしながら制御される。
なお、本発明においては、ガラス母材の延伸該当部（直胴部）の外径がその長手方向に0〜20%の範囲で連続的に変化しているものであっても、高い外径精度を有するプリフォームに延伸することができる。 When simultaneously controlling the pulling speed of the glass base material and the drawing speed of the stretched preform, the average outer diameter in the longitudinal direction of the stretched portion (straight body portion) of the glass base material is D av , and the finished diameter of the preform D, the preset pulling speed of the glass base material into the heating furnace is V1 sv, and the preform pulling speed from the heating furnace obtained from the formula (D av / d) 2 × V1 sv is V2 sv When the lowering speed and the taking-off speed calculated from the equipment are V1 sp and V2 sp in order,
V1 sp = V1 sv + k (V2 sv −V2 sp )... However, k is controlled while satisfying a positive real number relational expression.
In the present invention, even if the outer diameter of the stretched portion (straight body portion) of the glass base material is continuously changing in the longitudinal direction in the range of 0 to 20%, the outer diameter is high. It can be drawn into a preform having accuracy.

本発明のガラス母材の延伸装置は、光ファイバ用ガラス母材を延伸して所定の径に縮径する装置であって、第一の外径測定器が、ガラス母材が加熱炉で延伸される途中の第一の測定位置に、第二の外径測定器が、延伸が概ね終了した第二の測定位置にそれぞれ設置され、第一の測定位置に設定された設定値が第二の外径測定器で測定された測定値に基づいて逐次設定変更される設定手段を備えていることを特徴とし、これには、該設定手段で設定された設定値と第一の外径測定位置で測定された測定値との差がなくなるように、ガラス母材の引き下げ速度と延伸されたプリフォームの引き取り速度とを同時に制御する速度制御手段を設けるのが好ましい。   The glass base material stretching device of the present invention is a device that stretches a glass base material for an optical fiber to reduce the diameter to a predetermined diameter, and the first outer diameter measuring device stretches the glass base material in a heating furnace. The second outer diameter measuring device is installed at the second measurement position where the stretching is almost finished, and the set value set at the first measurement position is the second measurement position. It is characterized by comprising setting means for sequentially changing the setting based on the measured value measured by the outer diameter measuring instrument, and this includes the setting value set by the setting means and the first outer diameter measuring position. It is preferable to provide speed control means for simultaneously controlling the pulling speed of the glass base material and the drawing speed of the stretched preform so that there is no difference from the measured value measured in step (1).

さらに、本発明の延伸装置は、第一の測定位置での設定値が第二の測定位置での設定値と測定値との偏差量を基にしたPID演算により設定変更される演算手段を有し、第一の測定位置での設定値と測定値との偏差量を基に、PID演算により延伸速度が制御される速度制御手段を有している。なお、第二の測定位置は、外径が延伸目標径より0.5〜2.5mm太いところ、好ましくは１〜1.5mm太いところを測定位置とするのがよい。   Further, the stretching apparatus of the present invention has a calculation means for setting and changing the setting value at the first measurement position by PID calculation based on the deviation amount between the setting value and the measurement value at the second measurement position. Then, based on the deviation amount between the set value and the measured value at the first measurement position, there is a speed control means for controlling the stretching speed by PID calculation. The second measurement position may be a measurement position where the outer diameter is 0.5 to 2.5 mm thicker than the target drawing diameter, preferably 1 to 1.5 mm thick.

本発明によれば、大径の母材インゴットを延伸する際にも、延伸して得られるプリフォームの外径を精密に制御することができる。その結果、製品の歩留まりが向上し、製品のコスト低減に寄与する。   According to the present invention, even when a large-diameter base material ingot is stretched, the outer diameter of the preform obtained by stretching can be precisely controlled. As a result, the product yield is improved and the product cost is reduced.

本発明のガラス母材の延伸方法及び延伸装置は、合成石英からなるガラス母材が延伸される途中の第一の測定位置と、延伸が概ね終了した第二の測定位置でそれぞれ母材の外径を測定し、第二の測定位置での測定値に基づき、第一の測定位置での設定値を逐次変更し、変更された設定値と第一の測定位置で測定された測定値との差がなくなるように、ガラス母材の引き下げ速度と延伸されたプリフォームの引き取り速度を同時に制御するものである。   The glass base material stretching method and the stretching apparatus of the present invention include a first measurement position in the middle of stretching a glass base material made of synthetic quartz and a second measurement position at which stretching is almost completed. The diameter is measured, and the set value at the first measurement position is sequentially changed based on the measurement value at the second measurement position, and the changed set value and the measurement value measured at the first measurement position are In order to eliminate the difference, the pulling speed of the glass base material and the drawing speed of the stretched preform are simultaneously controlled.

以下、本発明を図に基づいて詳細に説明する。
図１に、本発明によるガラス母材の延伸装置の一例を概略縦断面図で示した。この延伸装置は、母材インゴット１の吊り下げ装置３、引き下げ駆動装置４、加熱炉５、延伸されたプリフォーム２を引き取る延伸駆動装置６、３箇所に設けられた外径測定器７,８，11、これらの外径測定値に基づき引き下げ駆動装置４及び延伸駆動装置６の駆動速度を制御するモータドライバ（速度制御装置）９、さらに制御コンピュータ（制御演算部）10から構成されている。 Hereinafter, the present invention will be described in detail with reference to the drawings.
FIG. 1 is a schematic longitudinal sectional view showing an example of a glass base material stretching apparatus according to the present invention. This stretching device includes a suspension device 3 for a base material ingot 1, a pulling drive device 4, a heating furnace 5, a stretching drive device 6 for pulling a stretched preform 2, and outer diameter measuring devices 7 and 8 provided at three locations. 11, 11, based on these measured outer diameters, a motor driver (speed control device) 9 for controlling the driving speed of the pulling-down drive device 4 and the stretching drive device 6, and a control computer (control operation unit) 10.

OVD法等で合成され、脱水焼結工程を経ることで製造された、直径100〜200mmφ、直胴部の長さ1000〜2000mmの母材インゴット１は、延伸装置上部の吊り下げ装置３に取り付けられ、引き下げ駆動装置４により、引き下げ速度Ｖ１で加熱炉５に挿入される。約2000℃の加熱炉５の中で加熱された母材インゴット１は、長手方向の一部分が軟化する。加熱された母材インゴット１は、加熱炉５の下部に設置された延伸駆動装置６により、予め設定されたプリフォーム径(ｄ＝50〜120mmφ)に引き取り速度Ｖ２で引き取られ、延伸・縮径される。   A base material ingot 1 having a diameter of 100 to 200 mmφ and a length of the straight body of 1000 to 2000 mm, which is synthesized by the OVD method and manufactured through a dehydration and sintering process, is attached to a suspension device 3 at the top of the stretching device. Then, it is inserted into the heating furnace 5 by the pulling drive device 4 at the pulling speed V1. The base material ingot 1 heated in the heating furnace 5 at about 2000 ° C. is softened in part in the longitudinal direction. The heated base material ingot 1 is drawn to a preset preform diameter (d = 50 to 120 mmφ) at a take-off speed V2 by a drawing drive device 6 installed at the lower part of the heating furnace 5, and drawn / reduced. Is done.

本発明では、少なくとも２箇所に外径測定器７，８が設置される。第一の外径測定器７は、加熱炉５の中で母材インゴット１が延伸途中の第一の測定位置（Ａ点）に設置され、第二の外径測定器８は、第一の外径測定器７の下方でプリフォーム２の外径が最終延伸目標径より0.5〜２mm程度の太さまで延伸される第二の測定位置（Ｂ点）に設置され、これらの外径測定器７，８で測定された値に基づいて、プリフォームの外径が制御される。なお、第三の外径測定器11をプリフォーム２の外径がほぼ安定し、最終延伸径の確認が行えるＣ点に設けても良い。   In the present invention, the outer diameter measuring devices 7 and 8 are installed in at least two places. The first outer diameter measuring device 7 is installed in the heating furnace 5 at the first measurement position (point A) where the base material ingot 1 is being stretched, and the second outer diameter measuring device 8 is the first outer diameter measuring device 8. Below the outer diameter measuring device 7, the preform 2 is installed at a second measuring position (point B) where the outer diameter of the preform 2 is stretched to a thickness of about 0.5 to 2 mm from the final stretch target diameter. , 8 to control the outer diameter of the preform. A third outer diameter measuring device 11 may be provided at point C where the outer diameter of the preform 2 is substantially stable and the final stretched diameter can be confirmed.

なお、第１の外径測定器７が設置される位置は、加熱炉５で母材インゴット１が延伸途中にあるＡ点であり、この位置は、最も急激に延伸、縮径が行われている位置であり、延伸途中にある部分の長さのほぼ中間の位置に相当する。第２の外径測定器８が設置される位置は、母材インゴットの延伸がほぼ終了し、最終目標外径より0.5〜2.5mm程度太い外径となったＢ点の位置であり、かつＡ点に極力近い位置に設定するのが好ましい。そのため、Ａ点とＢ点との間の距離は、母材インゴット１の径が150〜200mmφの場合には、100〜250mmの範囲に設定するのが好ましい。このような大きさの径の母材インゴット１では、加熱炉中で延伸途中にある部分の長さが300〜600mmにも達する。第三の外径測定器11を設置する場合は、プリフォーム２の最終延伸径が確認できる位置であればよい。   In addition, the position where the first outer diameter measuring instrument 7 is installed is the point A where the base material ingot 1 is in the middle of stretching in the heating furnace 5, and this position is most rapidly stretched and contracted. It corresponds to a position approximately in the middle of the length of the part in the middle of stretching. The position where the second outer diameter measuring device 8 is installed is the position of the point B where the stretching of the base material ingot is almost finished and the outer diameter becomes 0.5 to 2.5 mm thicker than the final target outer diameter, and A It is preferable to set the position as close as possible to the point. Therefore, the distance between the points A and B is preferably set in the range of 100 to 250 mm when the diameter of the base material ingot 1 is 150 to 200 mmφ. In the base material ingot 1 having such a diameter, the length of the part in the middle of stretching in the heating furnace reaches 300 to 600 mm. When the third outer diameter measuring instrument 11 is installed, it may be a position where the final stretched diameter of the preform 2 can be confirmed.

母材インゴット１の引き下げ速度と延伸されたプリフォーム２の引き取り速度は、次のようにして制御される。
先ず、加熱炉内への母材インゴット１の引き下げ速度Ｖ１svを設定し、加熱炉５からのプリフォーム２の引き取り速度Ｖ２svを下記の式から求める。
Ｖ２sv＝（Ｄav／ｄ）2×Ｖ１sv
上式において、Ｄavは予め測定しておいた母材インゴット１の直胴部の長手方向の平均外径であり、dはプリフォーム２の仕上がり径（最終延伸径）である。 The pulling speed of the base material ingot 1 and the pulling speed of the stretched preform 2 are controlled as follows.
First, the pulling speed V1 sv of the base material ingot 1 into the heating furnace is set, and the pulling speed V2 sv of the preform 2 from the heating furnace 5 is obtained from the following equation.
V2 sv = (D av / d) 2 × V1 sv
In the above equation, D av is an average outer diameter in the longitudinal direction of the straight body portion of the base material ingot 1 measured in advance, and d is a finished diameter (final stretched diameter) of the preform 2.

第一と第二の測定位置において、一定時間間隔、例えば0.2〜0.3秒毎に母材の外径が測定され、第二の測定位置に予め設定された設定値ｄBと第二の測定位置で測定された測定値に基づいて、PID制御により、第一の測定位置に予め設定された設定値ｄAが逐次変更される。さらに、この設定変更された設定値ｄAと第一の測定位置の測定値に基づいて、PID演算がなされ、その結果、引き下げ駆動装置４を制御するＶ１制御信号及び延伸駆動装置６を制御するＶ２制御信号がモータ制御器を介して発信され、母材インゴット１の引き下げ速度Ｖ１spとプリフォーム２の引き取り速度Ｖ２spとが同時に制御される。 In the first and second measurement position, a predetermined time interval, for example, be measured outside diameter of the preform is every 0.2 to 0.3 seconds, a preset value d B and the second measurement position in the second measuring position Based on the measurement value measured in step 1, the set value d A preset in the first measurement position is sequentially changed by PID control. Further, PID calculation is performed based on the setting value d A changed in setting and the measurement value at the first measurement position, and as a result, the V1 control signal for controlling the pull-down driving device 4 and the stretching driving device 6 are controlled. A V2 control signal is transmitted via the motor controller, and the pulling speed V1 sp of the base material ingot 1 and the pulling speed V2 sp of the preform 2 are simultaneously controlled.

これらの制御・演算は、モータドライバ９及び制御コンピュータ10で行われ、第一、第二の外径測定器７，８から測定値が入力される都度、次式の演算が行われる。
Ｖ１sp ＝Ｖ１sv ＋k(Ｖ２sv −Ｖ２sp )
なお、Ｖ１spは制御機器により演算された母材インゴット１の引き下げ速度であり、Ｖ２spは制御機器により演算されたプリフォーム２の引き取り速度である。kは正の実数である。 These controls / calculations are performed by the motor driver 9 and the control computer 10, and each time a measurement value is input from the first and second outer diameter measuring devices 7, 8, the following equation is performed.
V1 sp = V1 sv + k (V2 sv -V2 sp )
V1 sp is the pulling speed of the base material ingot 1 calculated by the control device, and V2 sp is the pulling speed of the preform 2 calculated by the control device. k is a positive real number.

本発明においては、少なくとも２箇所に設置された外径測定器のうち、第一の外径測定器で測定された母材の外径測定値を第一の測定位置の設定値に合わせるように、引き下げ速度及び引き取り速度を制御するものであり、第一の測定位置での設定値は、第二の測定位置での測定値に基づき逐次設定変更される。   In the present invention, the outer diameter measurement value of the base material measured by the first outer diameter measuring instrument among the outer diameter measuring instruments installed in at least two locations is matched with the set value of the first measurement position. The pull-down speed and the take-off speed are controlled, and the setting value at the first measurement position is sequentially changed based on the measurement value at the second measurement position.

これはカスケード制御と呼ばれる方法で、Ａ点で延伸速度を制御すると、延伸速度の変化に対応して、即座にプリフォーム径の変化となって現れ、遅れ時間が小さいため、プリフォーム径を所定の径に保つことは比較的容易に行うことができる。さらに、第二の外径測定器８によりＢ点で測定された母材径は、予め設定されたＢ点での設定値ｄBと比較される。この設定値ｄBは、Ｂ点から完全に延伸が終了したＣ点との間で、さらにプリフォームが微妙に延伸されることを加味して、最終延伸目標径ｄより0.5〜2.5mm程度大きめの値に設定されている。 This is a method called cascade control. When the stretching speed is controlled at point A, the preform diameter immediately changes in response to the stretching speed change, and the delay time is small. It can be relatively easily performed to keep the diameter. Furthermore, the measured preform diameter at the point B by a second outer diameter measuring device 8 is compared with a set value d B of a preset point B. This set value d B is larger by 0.5 to 2.5 mm than the final target diameter d in consideration of the fact that the preform is further subtly stretched from point B to point C where stretching has been completed. Is set to the value of

例えば、Ｂ点での測定値が設定値ｄBより大きいときには、それに応じてＡ点での径が小さくなるように、Ａ点での第一の外径測定器７の設定値ｄAの値が変更され、延伸速度が速くなるように修正される。これにより、Ｂ点での測定値が設定値ｄBに近づくとともに、より径の安定したプリフォームが得られる。 For example, when the measured value at the point B is larger than the set value d B is such that the diameter at the point A becomes smaller accordingly, the set value d A of the first outer diameter gauge 7 at the point A Is modified so that the stretching speed is increased. Thereby, the measured value at point B approaches the set value dB, and a preform with a more stable diameter is obtained.

しかし従来法による、Ａ点で外径を一定に制御する方法は、即座にまたは遅れ時間を加味しても、径変動を引き起こす外乱に対して十分な対応がとれず、良好な径制御ができない。また、Ｂ点のみで外径制御する方法では、時間遅れの影響が大きく、外径が緩やかにでも連続的に変化する母材に対しては、精度の高い外径制御を行うことができない。さらに、Ｂ点で測定した測定値の時間平均をもとに、Ａ点での目標径を一定時間間隔で修正する方法でも、修正時の外乱の影響を取り除くことができず、外径精度の良い延伸はできない。
これに対して、本発明の上記構成からなる延伸方法及び延伸装置によれば、母材インゴットから極めて高い外径精度を有するプリフォームが得られる。 However, the method of controlling the outer diameter at the point A by the conventional method is not able to sufficiently cope with the disturbance that causes the diameter fluctuation even immediately or with the addition of the delay time, and the good diameter control cannot be performed. . Further, in the method of controlling the outer diameter only at the point B, the influence of the time delay is large, and it is not possible to perform the outer diameter control with high accuracy for a base material that continuously changes even if the outer diameter is moderate. Furthermore, even when the target diameter at point A is corrected at regular time intervals based on the time average of the measurement values measured at point B, the influence of disturbance at the time of correction cannot be removed, and the outer diameter accuracy is improved. Good stretching is not possible.
On the other hand, according to the extending | stretching method and extending | stretching apparatus which consist of the said structure of this invention, the preform which has very high outer diameter precision is obtained from a base material ingot.

以下、本発明を実施例と比較例を挙げてさらに詳細に説明するが、本発明はこれらに限定されず様々な態様が可能である。   EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated further in detail, this invention is not limited to these but various aspects are possible.

［実施例１］
図１に示した延伸装置を用いて、直胴部の長さ1600mmで直径165mmφの母材インゴット１を延伸して、直径65mmφのプリフォーム２に加工した。加熱炉５は2000℃に設定し、母材インゴット１を炉内に挿入する引き下げ速度Ｖ１は23mm/分とした。Ａ、Ｂ点での測定値に基づいて、引き取り速度（延伸速度）Ｖ２を制御し延伸した（平均延伸速度=148.2mm/分）。Ｂ点での設定値ｄBは66.7mmに設定し、Ａ点での設定値ｄAは、Ｂ点での設定値ｄBと測定値との差により逐次連続的にPID制御により設定変更した。その結果、図２に示すように、Ａ点とＢ点で測定された外径と延伸速度は経時変化し、最終的なプリフォーム径を65±0.3mmに制御することができた。 [Example 1]
Using the stretching apparatus shown in FIG. 1, a base material ingot 1 having a straight body length of 1600 mm and a diameter of 165 mmφ was stretched and processed into a preform 2 having a diameter of 65 mmφ. The heating furnace 5 was set to 2000 ° C., and the lowering speed V1 for inserting the base material ingot 1 into the furnace was 23 mm / min. Based on the measured values at points A and B, the drawing speed (stretching speed) V2 was controlled to stretch (average stretching speed = 148.2 mm / min). The set value dB at point B was set to 66.7 mm, and the set value dA at point A was changed continuously by PID control due to the difference between the set value dB at point B and the measured value. . As a result, as shown in FIG. 2, the outer diameter and stretching speed measured at points A and B changed with time, and the final preform diameter could be controlled to 65 ± 0.3 mm.

［比較例１］
図１に示した延伸装置を用いて、Ｂ点に設置した外径測定器８の測定値をもとに、一定時間毎に平均値を算出し、この結果をもとに、Ａ点での設定値を修正した。母材インゴット１は実施例１と同様に、直胴部の長さ1200mmで直径120mmφのものを使用し、延伸して得られるプリフォーム２の最終延伸径が54mmφとなるように加工した。その結果を図３に示した。
図３からは、Ａ点での設定変更の影響を受け、Ｂ，Ｃ点にも外径変動が生じ、正確な径制御ができず、プリフォーム径は53.5±1mmの範囲で変動していた。なお、Ａ点での設定値を一定にしても、Ｂ点での外径が一定にならないことが図３から読みとれる。 [Comparative Example 1]
Using the stretching apparatus shown in FIG. 1, based on the measured value of the outer diameter measuring device 8 installed at the point B, the average value is calculated at regular intervals, and based on this result, the value at the point A is calculated. Fixed the setting value. In the same manner as in Example 1, the base material ingot 1 was a straight body having a length of 1200 mm and a diameter of 120 mmφ, and was processed so that the final stretched diameter of the preform 2 obtained by stretching was 54 mmφ. The results are shown in FIG.
From Fig. 3, affected by the setting change at point A, the outer diameter fluctuated at points B and C, accurate diameter control could not be performed, and the preform diameter fluctuated in the range of 53.5 ± 1mm. . It can be seen from FIG. 3 that the outer diameter at point B does not become constant even if the set value at point A is constant.

本発明によれば、外径精度の高いプリフォームが低コストで得られる。   According to the present invention, a preform with high outer diameter accuracy can be obtained at low cost.

本発明によるガラス母材の延伸装置の一例を示す概略縦断面図である。It is a schematic longitudinal cross-sectional view which shows an example of the drawing apparatus of the glass base material by this invention. 実施例１における、Ａ点〜Ｃ点での外径経時変化を示したグラフである。2 is a graph showing changes in outer diameter with time at points A to C in Example 1. FIG. 比較例１における、Ａ点〜Ｃ点での外径経時変化を示したグラフである。5 is a graph showing changes in the outer diameter with time at points A to C in Comparative Example 1.

符号の説明Explanation of symbols

1…母材インゴット、
2…プリフォーム、
3…吊り下げ装置、
4…引き下げ駆動装置、
5…加熱炉、
6…延伸駆動装置、
7、8、11…外径測定器、
9…モータドライバ（速度制御装置）、
10…制御コンピュータ（制御演算部）、
V1…引き下げ速度、
V2…引き取り速度。
1 ... base material ingot,
2 ... Preform,
3 ... Hanging device,
4 ... Pull-down drive device,
5 ... heating furnace,
6 ... Stretching drive,
7, 8, 11 ... Outer diameter measuring instrument,
9… Motor driver (speed control device),
10: Control computer (control operation unit),
V1 ... Pulling speed,
V2 ... Pick-up speed.

Claims (10)

光ファイバ用ガラス母材を延伸して所定の径に縮径する方法であって、該ガラス母材が加熱炉で延伸される途中の第一の測定位置に第一の外径測定器を、延伸が概ね終了した第二の測定位置に第二の外径測定器をそれぞれ設置して外径を測定し、第二の測定位置で得られた測定値に基づき、第一の測定位置での設定値を逐次変更して延伸することを特徴とするガラス母材の延伸方法。 A method of stretching a glass preform for an optical fiber to reduce the diameter to a predetermined diameter, the first outer diameter measuring instrument at a first measurement position while the glass preform is stretched in a heating furnace, Measure the outer diameter by installing a second outer diameter measuring device at the second measuring position where stretching is almost completed, and based on the measured value obtained at the second measuring position, A method for stretching a glass base material, wherein the set value is sequentially changed and stretched. 前記変更された設定値と第一の測定位置で測定された測定値との差がなくなるように、ガラス母材の引き下げ速度と延伸されたプリフォームの引き取り速度を同時に制御する請求項１に記載のガラス母材の延伸方法。 The glass base material pulling-down speed and the stretched preform pulling speed are simultaneously controlled so that the difference between the changed set value and the measured value measured at the first measurement position is eliminated. Glass base material stretching method. 第一の測定位置での設定値が、第二の測定位置での設定値と測定値に基づき、PID制御により設定変更される請求項１又は２に記載のガラス母材の延伸方法。 The glass base material stretching method according to claim 1 or 2, wherein the setting value at the first measurement position is changed by PID control based on the setting value and the measurement value at the second measurement position. 第一の測定位置での設定値と測定値をもとに、PID制御によりガラス母材の引き下げ速度とプリフォームの引き取り速度が制御される請求項３に記載のガラス母材の延伸方法。 The glass base material stretching method according to claim 3, wherein the glass base material pulling speed and preform pulling speed are controlled by PID control based on the set value and the measured value at the first measurement position. ガラス母材の引き下げ速度と延伸されたプリフォームの引き取り速度を同時に制御するに際し、ガラス母材の延伸該当部の長手方向の平均外径をＤav、プリフォームの仕上がり径をd、予め設定した加熱炉内へのガラス母材の引き下げ速度をＶ１svとし、式（Ｄav／ｄ）2×Ｖ１svから求められる加熱炉からのプリフォームの引き取り速度をＶ２sv、制御機器より演算された引き下げ速度及び引き取り速度を順にＶ１sp、Ｖ２spとするとき、
Ｖ１sp ＝Ｖ１sv ＋k(Ｖ２sv −Ｖ２sp ) …ただし、kは正の実数
の関係式を満たしながら制御する請求項１乃至４のいずれかに記載のガラス母材の延伸方法。 When simultaneously controlling the pulling speed of the glass base material and the drawing speed of the stretched preform, the average outer diameter in the longitudinal direction of the stretched portion of the glass base material was set to D av , and the finished diameter of the preform was set in advance. The pulling rate of the glass base material into the heating furnace is V1 sv , the pulling rate of the preform from the heating furnace obtained from the formula (D av / d) 2 × V1 sv is V2 sv , and the pulling rate calculated by the control device When the speed and the pick-up speed are V1 sp and V2 sp in order,
V1 sp = V1 sv + k (V2 sv -V2 sp ) ... where k is controlled while satisfying a positive real number relational expression, and the glass base material stretching method according to any one of claims 1 to 4. ガラス母材の延伸該当部の外径が、長手方向に0〜20%の範囲で連続的に変化している請求項１乃至５のいずれかに記載のガラス母材の延伸方法。 The method for stretching a glass base material according to any one of claims 1 to 5, wherein the outer diameter of the portion corresponding to the stretching of the glass base material is continuously changed in the range of 0 to 20% in the longitudinal direction. 光ファイバ用ガラス母材を延伸して所定の径に縮径する装置であって、第一の外径測定器が、ガラス母材が加熱炉で延伸される途中の第一の測定位置に、第二の外径測定器が、延伸が概ね終了した第二の測定位置にそれぞれ設置され、第一の測定位置に設定された設定値が第二の外径測定器で測定された測定値に基づいて逐次設定変更される設定手段を備えていることを特徴とするガラス母材の延伸装置。 An apparatus for stretching a glass preform for an optical fiber to reduce the diameter to a predetermined diameter, wherein the first outer diameter measuring instrument is at a first measurement position while the glass preform is being stretched in a heating furnace, A second outer diameter measuring device is installed at each of the second measurement positions where stretching is almost completed, and the set value set at the first measurement position becomes the measured value measured by the second outer diameter measuring instrument. An apparatus for drawing a glass base material, comprising setting means for sequentially changing the setting based on the setting means. 前記設定手段で設定された設定値と第一の外径測定位置で測定された測定値との差がなくなるように、ガラス母材の引き下げ速度と延伸されたプリフォームの引き取り速度とを同時に制御する速度制御手段を有する請求項７に記載のガラス母材の延伸装置。 Simultaneously control the pulling-down speed of the glass preform and the drawing speed of the stretched preform so that there is no difference between the setting value set by the setting means and the measurement value measured at the first outer diameter measurement position. The glass base material stretching apparatus according to claim 7, further comprising a speed control unit that performs the control. 第一の測定位置での設定値が、第二の測定位置での設定値と測定値との偏差量を基にしたPID演算により設定変更される演算手段を有し、第一の測定位置での設定値と測定値との偏差量を基に、PID演算により延伸速度が制御される速度制御手段を有する請求項７又は８に記載のガラス母材の延伸装置。 The setting value at the first measurement position has a calculation means for changing the setting by PID calculation based on the deviation amount between the setting value at the second measurement position and the measurement value. The glass base material stretching apparatus according to claim 7 or 8, further comprising a speed control means for controlling a stretching speed by a PID calculation based on a deviation amount between the set value and the measured value. 第二の測定位置が、外径が延伸目標径より0.5〜2.5mm太いところであり、好ましくは１〜1.5mm太いところを測定位置とする請求項７乃至９のいずれかに記載のガラス母材の延伸装置。 The glass base material according to any one of claims 7 to 9, wherein the second measurement position is a place where the outer diameter is 0.5 to 2.5 mm thicker than the drawing target diameter, preferably a place where the outer diameter is 1 to 1.5 mm thick. Stretching device.
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