Glass manufacturing – Processes of manufacturing fibers – filaments – or preforms – With measuring – controlling – sensing – programming – timing,...
Reexamination Certificate
2000-03-27
2002-08-27
Colaianni, Michael (Department: 1731)
Glass manufacturing
Processes of manufacturing fibers, filaments, or preforms
With measuring, controlling, sensing, programming, timing,...
C065S381000, C065S411000, C065S435000, C065S491000, C065S029140
Reexamination Certificate
active
06438997
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Filed of the Invention
The present invention relates to a method of elongating a glass preform for optical fiber.
2. Related Background Art
When making an optical fiber, in a step of disposing a cladding layer outside a core or a step of drawing the optical fiber as a final product, it is necessary to elongate a glass preform, which is an intermediate product of the optical fiber, to a predetermined outside diameter. As a method of precisely elongating the :glass preform for such a purpose, there have conventionally been known methods by use of a burner elongating machine disclosed in Japanese Patent Application Laid-Open No. 61-295,251 or No. 61-295,252. In these method, both end s of the glass preform are held with chucks, and these chucks are moved with a different speed while a part of the glass preform is heated and softened by the burner, so as to elongate the glass preform by a tensile force applied thereto. In these methods, the outside diameter in the tapered region of the glass preform in the process of elongating is measured, and the moving speeds of chucks are changed according to the difference between thus actually measured outside diameter and a preset outside diameter, i.e. outside diameter deviation, so as to carry out precision elongating to yield an elongated body with a predetermined outside diameter.
In the elongating methods disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 61-295,251 or No. 61-295,252, however, since the moving speeds of the chucks (chuck speeds) are changed according to the outside diameter deviation, the chuck speeds would be changed by a certain specific ratio, regardless of the magnitude of the preset outside diameter, when a certain particular outside diameter deviation occurs. For example, even in the cases with different preset outside diameters of 50 mm and 100 mm, their amounts of change in chuck speeds would be identical to each other when the same outside diameter deviation of 1 mm occurs. The deviation of 1 mm at the preset outside diameter of 50 mm is 2% in terms of ratio, whereas the deviation of 1 mm at the preset outside diameter of 100 mm is 1% in terms of ratio, whereby their influences upon the elongated body would differ from each other by a factor of 2, whereas the amount of control of chuck speed for correcting the deviation would be kept constant. Consequently, there has been a problem that, when preset outside diameters are different from each other, a difference may occur between effects obtained after the chuck speed control. Though this problem can be coped with by reviewing the control system every time when the preset outside diameter is changed, it requires an operation of modifying the control system on each occasion, thus being troublesome.
Also, in the elongating methods disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 61-295,251 or No. 61-295,252, the glass preform is heated and softened by a burner. Since the heating with a burner can be effected locally, it can narrow the melted area, thus being suitable for precision elongating. However, it cannot yield a sufficient amount of heat for softening a glass preform having a large outside diameter. Therefore, the glass preform having a large outside diameter has been elongated by an electric furnace elongating machine using such as a resistance furnace or induction furnace which can yield a sufficient amount of heat, to such an outside diameter that it can be precision-elongated by a burner elongating machine, and then has further been precision-elongated by the burner elongating machine.
Such a method, however, has been problematic in that a glass preform having such a large outside diameter that it cannot be elongated by a burner elongating machine cannot directly be precision-elongated, and in that two steps are employed, thereby necessitating time and cost upon making. In the extension by use of an electric furnace elongating machine, the heated and softened part becomes wider as compared with that obtained by a burner elongating machine, thus making it difficult to carry out the extension so as to yield a predetermined outside diameter. Therefore, the precision elongating has not yet been carried out by use of an electric furnace elongating machine alone.
SUMMARY OF THE INVENTION
As a result of diligent studies, the inventors have found that, by controlling extension process according to a specific value obtained from a reference outside diameter in a tapered region elongated by heating and softening and an actually measured one, precision elongating can be carried out by an electric furnace elongating machine alone even when the outside diameter of the glass preform before extension and the target elongated outside diameter vary, whereby the above-mentioned problems can be overcome. Based on this finding, it is an object of the present invention to provide a method of elongating a glass preform which can precision-expand the glass preform with a favorable accuracy and a favorable manufacturing efficiency regardless of the glass preform outside diameter and the target elongated outside diameter.
The method of elongating a glass preform in accordance with the present invention comprises the steps of holding both ends of the glass preform with first and second holding sections, respectively; with the moving speed of the first holding section faster than that of the second holding section; heating and softening the glass preform by a heating section successively from the end portion on the first holding section side as the first and second holding sections move in the longitudinal direction of the glass preform; and elongating the glass preform by means of a tensile force applied to the glass preform. In this method, an electric furnace is employed in the heating section. And the method further comprises the steps of setting a reference value R
1
with respect to an outside diameter at a specific position in a tapered region of the glass preform in the process of elongating, acquiring an actually measured value R
2
which is an outside diameter at the specific position and controlling the moving speeds of the first holding section and/or second holding section according to a value (R
2
/R
1
) obtained from the reference value R
1
and actually measured value R
2
.
In the present invention, the moving speed of the first holding section and/or second holding section is not controlled by the difference between the reference value R
1
and actually measured value R
2
in the tapered region, i.e., the so-called outside diameter deviation, but by a value (R
2
/R
1
) obtained from the reference value R
1
and actually measured value R
2
. Consequently, with respect to any preset outside diameter, the control is carried out by using the ratio of amount of fluctuation in the preset outside diameter, whereby more precise extension can be effected. Though it has conventionally been difficult to carry out precise extension by use of an electric furnace elongating machine alone, it can be effected by the above-mentioned method, whereby precision elongating can be performed by the electric furnace elongating machine alone, thus making it possible to precision-expand a glass preform having a greater outside diameter in a single step. Based on the above-mentioned value, proportional control, differential control, and integral control can be effected in combination.
Preferably, the moving speed-of the first holding section and/or second holding section is controlled according to the following expression (I), (II):
Vd/Ud
=(
R
2
/
R
1
)
K
(I)
Vu/Uu
=(
R
2
/
R
1
)
−K
(II)
Here, Vd is a target moving speed [mm/min] of the first holding section under control, Ud is a preset moving speed [mm/min] of the first holding section, Vu is a target moving speed [mm/min] of the second holding section under control, Uu is a preset moving speed [mm/min] of the second holding section, and K is a control coefficient (any posit
Moriya Tomomi
Saito Tatsuhiko
Colaianni Michael
McDermott & Will & Emery
Sumitomo Electric Industries Ltd.
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