JP4452344B2 - Tower for drawing optical fiber preform - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical fiber preform drawing tower used for drawing which is a part of an optical fiber manufacturing process.
[0002]
[Prior art]
For example, in the VAD method, as is well known, after soot synthesis, dehydration / sintering, and drawing, drawing is performed to form an optical fiber. Further, in this drawing process, for example, an optical fiber preform is hung in a vertical direction using a drawing tower, and the preform is pulled while being heated from below.
[0003]
By the way, when performing a drawing operation with such a configuration, for example, as shown in FIG. 2, in a type in which the optical fiber preform 100 is supported at one point using a support member 101, the tower and the optical fiber preform are Each vibrates at a unique frequency. In other words, this is because the tower building where the tower is installed vibrates due to the influence of cars and wind passing nearby, the floor surface vibrates, and this vibration propagates to the main body of the tower provided on the floor. The vibration propagates to the optical fiber preform supported on the upper side of the tower, and both cause a vibration phenomenon.
[0004]
[Problems to be solved by the invention]
On the other hand, as the drawing process of the optical fiber preform becomes faster, the height of the drawing tower tends to increase. However, as the height increases, the mass m of the tower itself increases and the spring constant K decreases. Therefore, a well-known vibration formula, that is, F = (1 / 2π) √ (k / m)
It can be seen that the frequency F of the tower itself decreases. Therefore, when the tower becomes taller, in the single-point suspension type drawing device, the natural frequencies of both the optical fiber preform and the tower gradually approach, and finally the amplitude of the optical fiber preform is amplified. May cause a so-called pendulum-like movement phenomenon.
[0005]
When the optical fiber preform vibrates like this pendulum, troubles such as the inability to draw the wire are incurred.
[0006]
Therefore, in view of the above-described circumstances, the present invention prevents a resonance phenomenon from occurring with the tower during drawing of the optical fiber preform, thereby ensuring that the drawing work is always stable and good. It is an object of the present invention to provide an optical fiber preform drawing tower that can be used.
[0007]
[Means for Solving the Problems]
That is, the invention described in claim 1 has a gripping part for gripping the upper end of the optical fiber preform suspended in the vertical direction, and draws the wire while pulling the suspended optical fiber preform vertically downward. In a drawing tower for an optical fiber preform provided with a drawing apparatus, the natural frequency f of the optical fiber preform and the natural frequency F of the tower body are expressed by the following relational expression F ≧ 2 · f
It is comprised so that it may satisfy | fill.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a preferred embodiment of the present invention will be described with reference to the accompanying drawings.
FIG. 1 shows a drawing tower for an optical fiber preform according to an embodiment of the present invention. This drawing tower is provided with a support portion 2 on a work table 11 at the top of a main body 1. Two chucks (not shown) for fixing the optical fiber preform 100 to the left and right are provided (may be four front and rear, left and right), and a heating furnace 3 is provided on the upper part of the main body 1 immediately below the chuck. The pass line PL can be secured long in the vertical vertical direction.
[0009]
The tower body 1 is constructed by sequentially stacking and assembling a plurality of construction structures (for example, truss structures) having the same outer diameter in the vertical direction (four in this embodiment, but not limited to this number). Although the steel frame of the outer frame pillar (frame part) 12 to be used is the one with the lower thickness d (cross-sectional area) (d1>d2>d3> d4), for example, Yes. By adopting such a structure, the structural strength as a building is sufficiently secured, and at the same time, the mass of the entire tower is reduced by reducing the thickness. Thereby, even if the height of the tower is increased, as is well known, the natural frequency F of the tower derived from the following equation is
F = (1 / 2π) · √ (k / m)
(Here, k is the spring constant of the tower itself, and m is the mass of the tower.)
It is. As the mass m becomes smaller, the natural frequency F can be increased compared to a conventional tower of the same height. That is, in the present invention, the natural frequency of the tower itself is at least twice the frequency f of the optical fiber preform described later,
F ≧ 2 · f
The tower is lighter.
In addition, the tower main body of this embodiment is configured so that various wirings and pipes for the drawing apparatus are installed using the internal space.
[0010]
In the support unit 2, the optical fiber preform is supported by a single point contact with a chuck (not shown) as in the conventional case. In this embodiment, the optical fiber preform 5 is drawn by two systems on the left and right. A chuck and a heating furnace may be provided on the front, back, left, and right of the support portion to perform drawing in four systems, or drawing may be performed in three systems, either left, right, or front and back.
[0011]
The optical fiber preform 100 propagates the vibration of the tower body 1 and vibrates at the natural frequency f as shown in FIG. As is well known, regarding the natural frequency f of the optical fiber preform 100, if the spring constant of the optical fiber preform 100 is k ′ and the mass m ′ of the optical fiber preform 100, the following formula f = (1 / 2π) · √ (k ′ / m ′)
Is derived from Here, the spring constant (gravity spring constant) k ′ is obtained by k ′ = m ′ · g · h where h is the length from the rotation center of the optical fiber preform to the center of gravity and g is the acceleration of gravity. It is done.
[0012]
Therefore, according to this embodiment, the lower part of the tower main body such as a television tower or a steel tower that is usually present in the world is different from the one having a larger outer diameter and expanded, and only one side is a vertical surface. Unlike a building with a structure that is set back so that the opposite side goes upward, the tower body 1 itself is configured to have the same outer diameter from the bottom to the top. Can be drawn vertically downwards (in other words, the pass line can be set vertically from top to bottom). In addition, since two drawing devices can be installed at the same time, the optical fiber preform can be drawn in two systems, the work efficiency can be improved, and the economic effect is increased. In this embodiment, the number is not limited to two. For example, four (four systems) may be used, or three (three systems) may be used for a hexagonal tower.
[0013]
Further, according to this embodiment, the tower body 1 is divided into a plurality of parts, and the thickness of the pillar portion (frame member) that becomes a skeleton is reduced from the bottom to the top to reduce the weight. Therefore, the natural frequency F of the tower body 1 can be increased, and by setting the natural frequency f of the optical fiber preform 4 to be twice or more compared to the natural frequency f of the optical fiber preform 4, the occurrence of a resonance phenomenon can be prevented. Thus, it is possible to prevent the pendulum movement from occurring in the optical fiber preform 4 and to prevent the drawing work from being stopped or interrupted.
[0014]
【The invention's effect】
As described above, according to the present invention, the upper part of the optical fiber preform arranged in the vertical direction is held at the upper part, and the optical fiber preform suspended from the upper part is vertically In an optical fiber preform drawing tower having a drawing device that draws while pulling downward, the natural frequency f of the optical fiber preform and the natural frequency F of the tower itself when the optical fiber preform is drawn However, since it is configured so as to satisfy the following relational expression F ≧ 2 · f, the natural frequency of the optical fiber preform and the natural frequency of the tower itself can be reliably prevented from causing a resonance phenomenon, As a result, a stable and good drawing operation can be realized, so that a high-quality optical fiber can be manufactured.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing a drawing tower for an optical fiber preform according to the present invention.
FIG. 2 is a cross-sectional view showing a suspended state of an optical fiber preform when drawing with a drawing apparatus.
[Explanation of symbols]
1 Tower body 2 Support section 3 Heating furnace 4 Optical fiber preform

Claims (2)

The optical fiber preform (100) suspended in the vertical direction has a gripping portion (2) that grips the upper end of the optical fiber preform (100), and is drawn while pulling the suspended optical fiber preform (100) vertically downward. In an optical fiber preform drawing tower equipped with a device,
The natural frequency f of the optical fiber preform (100) and the natural frequency F of the tower body (1) are configured to satisfy the following relational expression F ≧ 2 · f ,
An optical fiber characterized in that the tower body (1) is formed to have substantially the same outer dimensions from top to bottom and the thickness of the tower housing (12) is made thinner toward the top. Tower for drawing the base material. The optical fiber preform (100) suspended in the vertical direction has a gripping portion (2) that grips the upper end of the optical fiber preform (100), and is drawn while pulling the suspended optical fiber preform (100) vertically downward. In an optical fiber preform drawing tower equipped with a device,
The natural frequency f of the optical fiber preform (100) and the natural frequency F of the tower body (1) are configured to satisfy the following relational expression F ≧ 2 · f,
An optical fiber preform drawing tower characterized in that a plurality of optical fiber preforms (100) are suspended symmetrically at opposite positions at the same time so that a plurality of systems can be drawn.

Images