Glass manufacturing – Processes of manufacturing fibers – filaments – or preforms – With measuring – controlling – sensing – programming – timing,...
Reexamination Certificate
1997-12-08
2001-01-30
Hoffmann, John (Department: 1731)
Glass manufacturing
Processes of manufacturing fibers, filaments, or preforms
With measuring, controlling, sensing, programming, timing,...
C065S382000, C065S491000, C065S486000
Reexamination Certificate
active
06178778
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to the manufacturing apparatus and method of the preform that is the raw material rod of the optical fiber used in the fields such as telecommunication.
The optical fiber is manufactured in the following procedures. First, the soot of the quartz as synthesized by the VAD (Vapor Axial Deposition) method is dehydrated and sintered into an ingot of synthetic quartz. This ingot is then heated in a furnace, drawn under heating and reduced in diameter into a rod, namely the preform for optical fiber.
An ingot drawing apparatus is disclosed in the Japanese Patent Provisional Publication No. 7-2539. The ingot is fed from the top of a heating furnace. The rod as drawn under heating condition is taken out from the bottom of the furnace. The diameter of glass rod coming out of the furnace after drawing is measured at a position. Based on the temporal variation in the measured values, the rod diameter after drawing is controlled in compliance with a process model that can compensate for the idle time.
Because the preform for optical fiber that the authors of this invention are going to manufacture uses, as raw materials, far greater diameters of synthetic quartz ingot and the rod after drawing, it is necessary for us to have a larger size of the heating furnace. Such large size of furnace tends to disturb the air current in it and/or the temperature distribution due to the displacement of the ingot. These disturbances having a large influence over the rod diameter of the preform for optical fiber thus manufactured, an attempt to control the drawing rate based on the outer diameter of the rod coming out of the furnace will cause some hunting. This varies the rod diameter cyclically, which brings obstacle to the manufacture of a preform for optical fiber with stable diameter. Further, the disturbance in temperature distribution may sometimes curve the rod or deform its outline into elliptical.
SUMMARY OF THE INVENTION
It is the primary object of this invention to provide a manufacturing method of a preform for optical fiber wherein the diameter of a rod may be controlled exactly when it is drawn from the ingot, the raw material, with a specifically large diameter. The manufacturing method of the preform for optical fiber according to this invention as intended to achieve the primary objective, wherein an ingot from synthetic quartz is passed through a heating furnace to be drawn under heating, is characterized in that the drawing rate can be controlled based on the outer diameter of the ingot measured at least at two positions in said heating furnace.
A further object of the present invention is the provision of a manufacturing apparatus for optical fiber preform wherein the outer diameter of the rod may be controlled exactly when it is drawn from the raw material ingot with specifically large diameter. The manufacturing apparatus for optical fiber preform by this invention contrived to perform the second objective has a heating furnace through which an ingot made of synthetic quartz is passed and heated, a drawing means that draws the ingot in the furnace, at least two outer diameter measuring devices installed in the furnace, and a control means that controls the drawing speed by said drawing means based on at least two values of the outer diameter as measured by said outer diameter measuring devices.
Still a further object of this invention is the provision of a manufacturing apparatus for optical fiber preform wherein the rod drawn from the ingot may be formed into true circularity without being curved or bent. The manufacturing apparatus for optical fiber preform by this invention contrived to perform the third objective has a heating furnace through which a circular ingot made of synthetic quartz is passed and heated, a suspending means to suspend said ingot in said heating furnace, a rotary means accompanying said suspending means that rotates said ingot, a rotary holding means to hold the circular rod as heated and drawn from said ingot rotating it in synchronization with the rotation of said ingot, a drawing means coupled with said rotary holding means that draws out said circular rod, outer diameter measuring devices that measure the outer diameter of a cone formed by the drawing of said ingot, a comparison means that compares the outer diameter of said cone as measured by said outer diameter measuring devices to output a signal, a control means that controls the rotational amount of said rotary means and finally another control means to control the rotational amount of said rotary holding means.
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Patent Abstracts of Japan, vol. 96., No. 8, Aug. 30, 1996, JP 08 091861A Furukawa Electric Co., Ltd.
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Patent Abstract of Japan, vol. 5, No. 106 (C-62), Jul. 10, 1981, JP 56 045843A—NT&T Corp.—Apr. 25, 1981.
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Hirasawa Hideo
Kenmochi Soichiro
Shimada Tadakatsu
Shimizu Yoshiaki
Suzuki Akihiko
Hoffmann John
Reed Smith LLP
Shin-Etsu Chemical Co. , Ltd.
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