JP3188403B2 - Drawing method and drawing apparatus for optical fiber preform - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a drawing method and a drawing apparatus for suppressing bending of an optical fiber preform ingot in a step of drawing the preform rod into a preform rod having a smaller diameter.

[0002]

2. Description of the Related Art Conventionally, in a method of manufacturing an optical fiber preform by stretching a preform ingot into a preform rod having a smaller diameter, the optical fiber preform is heated and softened in an oxyhydrogen flame or an electric furnace. While measuring the outer diameter of the heat-softened portion using an outer diameter measuring device or the like, a method of controlling the take-off speed based on the measured value has been adopted. In this case, for holding the base material ingot, a holding dummy bar is fused to both ends of the base material ingot using a glass lathe or the like, and the base material ingot is set in the stretching device by holding the holding dummy bar. ing. The fusion of the gripping dummy rods is performed while the operator visually adjusts the axis centers of the base metal ingot and the dummy rods using a glass lathe or the like, so that the dummy rods are centered at the time of fusion. The accuracy depends on the skill of the worker, and the alignment accuracy tends to vary.
Further, since the base material ingot shrinks when the porous body is turned into transparent glass, if the degree of the shrinkage varies in the circumferential direction, the base material ingot may be bent during the formation of the transparent glass. The bent base material ingot is
The bending is corrected by the operator when the dummy rod is fused, but the correction of the bending is entirely manual work, and the finishing accuracy is greatly affected by the skill of the worker. Therefore, the bent base material ingot cannot completely remove the bent. Therefore, there is a case where a so-called misalignment occurs in which the base material ingot that is bent at the time of the vitrification is shifted from the center of the fused dummy bar. In such a case, since the drawn base material rod bends, it has been necessary to straighten the base material rod using a glass lathe or the like after the drawing step. In addition, it was necessary to measure the bending of the base material rod after the correction and check whether the bending was within the standard.

[0003]

The base material rod may be bent due to the base material ingot or the drawing operation as described above. Such bending of the preform rod is a factor that greatly impairs workability during drawing and stability of fiber characteristics. Therefore, it is necessary to correct the bent base material rod. For this reason, development of a stretching method and a stretching apparatus that does not cause bending in the stretching step of the base material rod has been desired. On the other hand, Japanese Patent Application Laid-Open No. 8-40741 discloses an apparatus for extending a rod having no bending from an ingot when the dummy rod is not directly mounted on the base material ingot. However, in a drawing apparatus using an electric furnace as a heating means like this apparatus, it is necessary to raise the temperature of the furnace to 1600 to 2000 ° C., which is higher than the softening temperature of glass, in order to heat and soften the ingot. The material must not generate impurity gas that adversely affects the optical fiber preform with the temperature. Therefore, in most cases, a heating element, a heat insulating material, a furnace tube, or the like made of a carbon material is used in the furnace. However, in an electric furnace using carbon material,
It is necessary to replace the inside of the furnace with an inert gas to protect the carbon material. In a stretching furnace used in a stretching apparatus, an upper opening is attached to an ingot and then sealed with a sealing material using a heat-resistant and non-combustible material. Therefore, there is a problem that even if an attempt is made to move the upper hanging chuck by the XY stage as in this apparatus, the movement of the hanging chuck is limited by the sealing material, so that only the position control of about 1 mm can be performed. .

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a method for drawing an optical fiber preform for drawing an optical fiber preform ingot into a preform rod having a smaller diameter. The rod center position detecting means is provided at three or more points below the lower end of the heater, and the bending or direction of the rod is calculated based on the detected value. It is characterized by controlling the position of the rod take-up device without being restricted, and further comprises a heater for heating the base material ingot in the furnace, and an opening and a lower part for inserting the ingot from the upper part. A drawing furnace having an opening from which a base material rod is drawn out, and a suspension for hanging a dummy rod fused to the ingot above the drawing furnace and sending the dummy rod into the drawing furnace at a predetermined speed. And a rod take-off device for grasping a dummy bar fused to the ingot below the drawing furnace and drawing the base material at a predetermined speed, and drawing the ingot heated and softened in the drawing furnace. In an optical fiber preform stretching apparatus for manufacturing a rod having a predetermined diameter, two sets of laser measuring devices that are orthogonal to and below a heater of the above-mentioned drawing furnace are provided at predetermined intervals at three stages, and a rod take-off apparatus is provided with an X-axis.
Amount of movement calculation control for calculating the bending or direction of the rod from the rod center position measured by the orthogonal laser measuring instrument, and moving the XY table so that the rod center axis is vertical. It is characterized by comprising a unit. That is, in the present invention, since the movement control of the position of the base material is performed by the movement of the rod take-up device, the movement is not restricted by the sealing material, and the effect that the rod without bending can be extended. is there.

[0005]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings. FIG. 1 shows an optical fiber preform stretching apparatus of the present invention when a rod pulling roller is used as a rod pulling apparatus, and FIG. 2 shows a drawing apparatus of the present invention when a rod pulling chuck is used as a rod pulling apparatus. 1 shows a detailed view of a drawing furnace. In the figure, reference numeral 1 denotes a base material ingot, 2 denotes a base material rod, 3 denotes a base material fixing portion, 41 denotes a laser measuring device (light emitting portion), 42 denotes a laser measuring device (light receiving portion), 5 denotes a heater, 6 Is a drawing furnace, 71 is a rod take-up roller (FIG. 1), 72 is a rod take-up chuck (FIG. 2), 8 is an XY table, 9 is a suspending unit, and 10 is a moving amount calculation by an arithmetic and control unit (PID controller). Reference numeral 11 denotes a sealing material, 12 denotes a heat insulating material, 13 denotes an inert gas inlet, and 14 denotes a molten portion of the ingot, which contains a control unit. In the present invention, first, the base material ingot 1 is set in the drawing furnace 6 in which the heater 5, the sealing material 11, the heat insulating material 12, and the inert gas inlet 13 are arranged as shown in FIG. Then, when the base material rod 2 passes through a laser measuring device composed of two orthogonal sets of light projecting parts 41 and light receiving parts 42 at three points A, B and C, the light receiving parts A, B and C The coordinate position information of the center position of each point is sent to the PID controller 10 as needed, and the sent data and the displacement amount from the preset center axis coordinate are calculated, and the bending amount (radius r) is calculated by the following equation. (1), the direction of the bend is measured by calculating the direction in which the coordinate position of point B has moved from the preset position, and the rod center axis is determined based on the amount of the bend and the direction of the bend. The movement amount calculation control unit (PID controller) The X-Y table 8 which rod withdrawal device is attached by internal) to over La 10 performs stretching while moving controlled, preform rod without bending is being manufactured.

As shown in FIG. 4, assuming that the base material rod is bent in an arc shape, point A is a central position provided on the upper part of the rod, and point B is a lower part of the rod. When the center position provided at the point C is represented by the center position provided at the center of the rod, it can be represented by a radius r shown in equation (1). r = (L ² + 4h ² ) / 8h ‥‥‥ (1) In the formula, h represents the distance of the point C from the straight line AB, and L represents the distance between AB. Further, the direction of the bending can be measured by calculating in which direction the point B is shifted from the axis of the stretching apparatus from the coordinate axis of the point B.

[0007] The drawing of the base material ingot is usually performed by a vertical drawing device. In these devices, the drawn base material rod bends due to various factors. This bending cannot be avoided in the current production equipment. Therefore, as described above, the laser-type measuring devices are provided at three points as the rod center position measuring means at substantially equal intervals below the heat-welded portion, so that the three central axes of the base material rod immediately after stretching can be measured. It becomes possible. Further, the coordinate position data of the three points is taken into a computer, and the computer is supposed to be bent in an arc shape, and is subjected to arithmetic processing to calculate the bending of the base material rod as a radius r by the above equation (1). It becomes possible. Among the three coordinate positions, point A is the coordinate position obtained from the data obtained from the laser measuring device provided at the upper part, and point B is the coordinate position obtained from the data obtained from the laser measuring device provided at the lower part. The position and the point C are coordinate positions obtained from data obtained from a laser measuring instrument provided at the center, and are obtained from a distance h from a straight line passing through the points A and B and a distance L between the points A and B. The bend r is obtained by the equation (1), and it is possible to calculate in which direction the point B deviates from the axis of the stretching apparatus from the coordinate axis of the point B. As described above, by measuring three positions in-line during the stretching operation, it is possible to measure the amount and direction of the bending as continuous values. Then, the XY table on which the take-off roller and the take-off chuck are attached is controlled on the basis of the amount of the bend or the inclination obtained from this, thereby making it possible to manufacture a base material rod having a small bend.

[0008]

【Example】

Bending measurement method: As shown in FIG.
Alternatively, the both ends of the base material rod 2 are placed on the gantry 16, the dial gauge 15 is set at the center, and the increase value (2) of the dial gauge 15 when the base material ingot 1 or the base material rod 2 makes one rotation around the central axis. × h) to obtain the maximum h
Was defined as a bend (mm). Example 1 An optical fiber preform stretching device shown in FIG.
A base material rod having an outer diameter of 40 mm was manufactured using a base material ingot having a length m, a length of 1000 mm, and a length of an effective portion of 800 mm, which was bent during transparent vitrification. The bending of the ingot itself was measured by the method of FIG.
It was 2.4 mm in the part. First, holding dummy bars (not shown) were welded to both ends of the bent base material ingot 1 using a glass lathe. In this state, the center axes of the base material ingot and the holding dummy bar do not coincide with each other, and a part of the base material ingot is shifted from a straight line connecting both ends of the holding dummy bar. Therefore, even when this base material ingot is set in the drawing furnace 6, the base material ingot 1 is arranged so as to be shifted from the axial center thereof. In this state, the base material ingot 1 is set in the drawing furnace 6, the drawing is started after the temperature is raised, and the movement of the XY table is controlled by the movement amount calculation control unit based on the measured bending amount and direction of the rod. To produce a base rod having an outer diameter of 40 mm. The obtained base material rod was cut into 1000 mm lengths and divided into 7 parts, and the bending was measured. As a result, as shown in Table 1,
The bending in each division of the base material rod was 0.44 to 0.59 mm, and the average value was 0.51 mm, which was sufficiently small, and there was no problem even if this was used for drawing.

Example 2 An optical fiber preform stretching device shown in FIG.
A base material rod having an outer diameter of 40 mm was manufactured using a base material ingot having a length of 1000 mm, a length of 1000 mm, and an effective portion length of 800 mm, which was bent during transparent vitrification. The bending of the ingot itself was measured by the method shown in FIG.
It was 2.5 mm at the part. First, holding dummy bars (not shown) were welded to both ends of the bent base material ingot 1 using a glass lathe. In this state, the center axes of the base material ingot and the holding dummy bar do not coincide with each other, and a part of the base material ingot is shifted from a straight line connecting both ends of the holding dummy bar. Therefore, even when this base material ingot is set in the drawing furnace 6, the base material ingot 1 is arranged so as to be shifted from the axial center thereof. In this state, the base material ingot 1 is set in the drawing furnace 6, the drawing is started after the temperature is raised, and the movement of the XY table is controlled by the movement amount calculation control unit based on the measured bending amount and direction of the rod. Thus, a base material rod having an outer diameter of 40 mm was produced. The obtained base material rod was cut into 1000 mm lengths and divided into 7 parts, and the bending was measured. As a result, as shown in Table 1, the bending in each division of the base material rod is 0.39 to 0.58 mm.
The average value was 0.47 mm, which was sufficiently small, and there was no problem even if this was used for drawing.

Comparative Example Using a conventional optical fiber preform stretching apparatus without a take-off position control system, using a preform ingot having an outer diameter of 120 mm, a length of 1000 mm, an effective portion length of 800 mm, and having a bend during transparent vitrification. Thus, a base material rod having an outer diameter of 40 mm was manufactured. The bending of the ingot itself was measured by the method shown in FIG. 5 and found to be 2.2 mm at a portion of 1000 mm below the ingot. First, holding dummy bars (not shown) were welded to both ends of the bent base material ingot 1 using a glass lathe. In this state, the center axes of the base material ingot and the holding dummy bar do not coincide with each other, and a part of the base material ingot is shifted from a straight line connecting both ends of the holding dummy bar. Therefore, even when this base material ingot is set in the drawing furnace 6, the base material ingot 1 is arranged so as to be shifted from the axial center thereof. In this state, the base material ingot 1 was set in the drawing furnace 6, and after elevating the temperature, drawing was performed to prepare a base material rod having an outer diameter of 40 mm. The resulting base rod is 1000 long
It was cut into mm units and divided into seven parts, and the bending was measured.
As a result, as shown in Table 1, the bending in each division of the base material rod was 1.29 to 1.71 mm, and the average value was as large as 1.42 mm, which was a problematic value when used for drawing.

[0011]

[Table 1]

[0012]

According to the present invention, when the base material ingot is bent or the bending caused by the holding dummy bar due to the base material ingot can be regarded as the bending of the base material rod immediately thereafter, the bending can be realized. By adjusting the direction and the size of the device, the bending of the base material rod can be suppressed to a small value.

[Brief description of the drawings]

FIG. 1 is a view showing an example of an optical fiber preform stretching apparatus of the present invention.

FIG. 2 is a view showing another example of the optical fiber preform stretching apparatus of the present invention.

FIG. 3 is a view showing details of a drawing furnace of the present invention.

FIG. 4 is a model diagram for calculating a bending amount in the present invention.

FIG. 5 is a diagram showing a bending value measuring device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Base material ingot 2 ... Base material rod 3 ... Base material fixing part 41 ... Laser measuring device (light emitting part) 42 ... Laser measuring device (light receiving part) 5 ... Heater 6 ... Stretching furnace 71 ... Rod taking-off roller 72 ... Rod Pick-up chuck 8 ... XY table 9 ... Hanging part 10 ... Operation control device (PID controller) 11 ... Seal material 12 ... Insulation material 13 ... Inert gas inlet 14 ... Mold part of ingot 15 ... Dial gauge 16 ... Stand

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Soichiro Kenmochi 2-6-1 Otemachi, Chiyoda-ku, Tokyo Shin-Etsu Chemical Co., Ltd. (72) Inventor Akihiko Suzuki 2-6-Otemachi, Chiyoda-ku, Tokyo No. 1 Shin-Etsu Chemical Co., Ltd. Head Office (72) Inventor Hideo Hirasawa 2-13-1 Isobe, Annaka-shi, Gunma Prefecture Shin-Etsu Chemical Co., Ltd.Precision Functional Materials Research Laboratories (56) References JP-A-8-40741 (JP, a) JP flat 9-30827 (JP, a) JP flat 5-78139 (JP, a) JitsuHiraku flat 3-99731 (JP, U) (58 ) investigated the field (Int.Cl. ⁷ , DB name) C03B 37/012

Claims (2)

(57) [Claims] 1. An optical fiber preform stretching method for stretching an optical fiber preform ingot into a preform rod having a smaller diameter, comprising three or more rod center position detecting means below a lower end of a preform heating heater. A method for calculating the bending or direction of the rod based on the detected value, and controlling the position of the rod take-up device so that the center axis of the rod is vertical. 2. A drawing furnace provided with a heater for heating a vitrified base material ingot in a furnace, having an opening for inserting the ingot from an upper part and an opening for drawing a base material rod from a lower part; A hanging part for hanging a dummy rod fused to the ingot above the drawing furnace and feeding the dummy rod into the drawing furnace at a predetermined speed; and a dummy fused to a base material ingot below the drawing furnace. In a stretching apparatus for an optical fiber preform, which comprises a rod taking-up device for grasping a rod and taking up a preform at a predetermined speed and stretching the ingot heated and softened in a drawing furnace to produce a rod having a predetermined diameter, Two sets of laser measuring devices perpendicular to the heater of the drawing furnace are provided in three stages at a predetermined interval, a rod take-off device is attached to an XY table, and the rods measured by the perpendicular laser measuring devices are measured. A moving amount calculation control unit for calculating the bending or direction of the rod from the center position of the rod and moving the XY table so that the rod central axis is vertical. apparatus.