U.S. patent application number 10/158804 was filed with the patent office on 2002-10-24 for optical fiber manufacture method, preform manufacture method, and preform manufacture apparatus.
Invention is credited to Hatayama, Kazuhisa, Hirasawa, Hideo, Moriya, Jiro, Nagano, Takaaki, Sakashita, Mitsukuni, Shimada, Tadakatsu, Shimizu, Yoshiaki, Suzuki, Shinji, Taya, Minoru, Watanabe, Masataka, Yamamura, Waichi.
Application Number | 20020152772 10/158804 |
Document ID | / |
Family ID | 27585903 |
Filed Date | 2002-10-24 |
United States Patent
Application |
20020152772 |
Kind Code |
A1 |
Shimizu, Yoshiaki ; et
al. |
October 24, 2002 |
Optical fiber manufacture method, preform manufacture method, and
preform manufacture apparatus
Abstract
A method for manufacturing an optical fiber comprises setting a
heating condition for heating a glass rod, which is a parent
material of the optical fiber, and an elongating speed of the glass
rod based on a prescribed numerical value which changes with a
progress of elongation of the glass rod; heating and elongating the
glass rod to generate a preform based on the heating condition and
the elongating speed which are set by the setting; and drawing the
preform to a filament-like form by further heating the preform to
generate the optical fiber.
Inventors: |
Shimizu, Yoshiaki;
(Annaka-shi, JP) ; Nagano, Takaaki; (Annaka-shi,
JP) ; Shimada, Tadakatsu; (Annaka-shi, JP) ;
Hirasawa, Hideo; (Annaka-shi, JP) ; Watanabe,
Masataka; (Annaka-shi, JP) ; Hatayama, Kazuhisa;
(Annaka-shi, JP) ; Sakashita, Mitsukuni;
(Annaka-shi, JP) ; Taya, Minoru; (Annaka-shi,
JP) ; Yamamura, Waichi; (Annaka-shi, JP) ;
Suzuki, Shinji; (Annaka-shi, JP) ; Moriya, Jiro;
(Niigata, JP) |
Correspondence
Address: |
Pillsbury Winthrop LLP
Intellectual Property Group
1600 Tysons Boulevard
McLean
VA
22102
US
|
Family ID: |
27585903 |
Appl. No.: |
10/158804 |
Filed: |
June 3, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10158804 |
Jun 3, 2002 |
|
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09434280 |
Nov 5, 1999 |
|
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6386001 |
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Current U.S.
Class: |
65/486 ; 65/488;
65/491 |
Current CPC
Class: |
C03B 2205/47 20130101;
C03B 37/01205 20130101; C03B 23/047 20130101; C03B 37/0124
20130101; C03B 37/01202 20130101; C03B 37/027 20130101 |
Class at
Publication: |
65/486 ; 65/488;
65/491 |
International
Class: |
C03B 037/07 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 5, 1998 |
JP |
10-314553 |
Nov 5, 1998 |
JP |
10-314564 |
Nov 5, 1998 |
JP |
10-314574 |
Nov 6, 1998 |
JP |
10-315849 |
Nov 6, 1998 |
JP |
10-315856 |
Jan 19, 1999 |
JP |
11-010197 |
Jan 25, 1999 |
JP |
11-015293 |
Jan 26, 1999 |
JP |
11-016840 |
Feb 23, 1999 |
JP |
11-044902 |
Feb 24, 1999 |
JP |
11-046141 |
Mar 11, 1999 |
JP |
11-064994 |
Mar 12, 1999 |
JP |
11-067199 |
Mar 12, 1999 |
JP |
11-067366 |
Mar 12, 1999 |
JP |
11-065819 |
Mar 19, 1999 |
JP |
11-075129 |
Apr 20, 1999 |
JP |
11-112354 |
Apr 26, 1999 |
JP |
11-118094 |
Claims
What is claimed is:
1. A method for manufacturing an optical fiber comprising: setting
a heating condition for heating a glass rod, which is a parent
material of said optical fiber, and an elongating speed of said
glass rod based on a prescribed numerical value which changes with
a progress of elongation of said glass rod; heating and elongating
said glass rod to generate a preform based on said heating
condition and said elongating speed which are set by said setting;
and drawing said preform to a filament-like form by further heating
said preform to generate said optical fiber.
2. A method as claimed in claim 1, wherein said setting sets said
heating condition and said elongating speed based on a progress
time of said elongation as said numerical value.
3. A method as claimed in claim 2, wherein: said heating and
elongating includes end drawing for reducing a diameter of an end
of said glass rod; and said end drawing end-draws said end of said
glass rod with heat and elongation based on said progress time of
said end drawing.
4. A method as claimed in claim 2, wherein said setting sets a
location of a burner, which heats said glass rod, and an amount of
gas supplied to said burner as said heating condition based on said
progress time of said elongation.
5. A method as claimed in claim 2, wherein said setting sets a
moving speed of a chuck, which holds said glass rod, as said
elongating speed based on said progress time of said
elongation.
6. A method as claimed in claim 1, wherein said setting sets said
heating condition and said elongating speed based on an elongation
length of said glass rod in said elongation as said numerical
value.
7. A method as claimed in claim 6, wherein: said heating and
elongating includes end drawing for reducing a diameter of an end
of said glass rod; and said end drawing end-draws said end of said
glass rod with heat and elongation based on said elongation length
of said glass rod.
8. A method as claimed in claim 6, wherein said setting sets a
moving distance of a burner, which heats said glass rod, and an
amount of gas supplied to said burner as said heating condition
based on said elongation length of said glass rod.
9. A method as claimed in claim 6, wherein said setting sets a
moving speed of a chuck, which holds said glass rod, as said
elongating speed based on said elongation length of said glass
rod.
10. A method as claimed in claim 9, wherein said setting uses a
encoder, which is provided on a motor that drives said chuck, to
measure a moving distance of said chuck by measuring a rotation
angle of said motor.
11. A method as claimed in claim 1, wherein said setting sets said
heating condition and said elongating speed based on a tensile
stress generated on said glass rod in said elongation as said
numerical value.
12. A method as claimed in claim 11, wherein a heating source,
which heats said glass rod, moves along a longitudinal direction of
said glass rod with a progress of said elongation, and said heating
and elongating controls said elongating speed so that said tensile
stress before said heating source moves prescribed distance becomes
substantially 110 percent or below an average value of said tensile
stress after said heating source moves said prescribed
distance.
13. A method as claimed in claim 12, wherein said heating and
elongating controls said tensile stress so that said tensile stress
before said heating source moves said prescribed distance become
substantially from 80 to 110 percent of an average value of said
tensile stress after said heating source moves said prescribed
distance.
14. A method as claimed in claim 12, wherein said prescribed
distance is substantially between 50 mm to 150 mm.
15. A method as claimed in claim 12, wherein said heating and
elongating controls said elongating speed to be a constant speed
when said heating source moves said prescribed distance.
16. A method as claimed in claim 11, wherein said setting sets a
moving speed of a chuck, which holds said glass rod, as said
elongating speed based on said tensile stress.
17. A method as claimed in claim 11, wherein said setting sets said
heating condition and said elongating speed based on a location of
a mark provided on a connection between said glass rod and each of
dummy rods, which are welded to each of ends of said glass rod, as
said numerical value.
18. A method as claimed in claim 17, wherein: said heating and
elongating includes end drawing for reducing a diameter of an end
of said glass rod; and said end drawing end-draws said end of said
glass rod with heat and elongation based on said location of a
mark.
19. A method as claimed in claim 17, wherein said setting sets said
heating condition and said elongating speed based on a location of
a cut provided on a connection between said glass rod and each of
said dummy rods as said location of a mark.
20. A method as claimed in claim 17, wherein said setting sets said
heating condition and said elongating speed based on a location of
a fluorescent paint applied on a connection between said glass rod
and each of said dummy rods as said location of a mark.
21. A method as claimed in claim 1, wherein said setting sets said
elongating speed at a plurality of locations along axial direction
of said glass rod based on a diameter at said plurality of
locations along axial direction of said glass rod as said numerical
value and said heating condition based on an average value of a
diameter at said plurality of locations of said glass rod.
22. A method as claimed in claim 1, wherein a end of said glass rod
is end-drawn of which diameter is reduced, and said setting has:
detecting a location of an end-drawn region where said glass rod is
end-drawn based on a diameter at a plurality of locations along
axial direction of said glass rod and a change of a length of said
glass rod along axial direction of said glass rod by said
elongation as said numerical value; and setting a polishing range
where said glass rod is polished by a flame based on said location
of said end-drawn region and also setting a heating power condition
of said flame based on a diameter of said end-drawn region, and
said heating and elongating polishes said polishing range of said
glass rod by said flame of said heating power condition.
23. A method for manufacturing an optical fiber comprising: heating
and elongating a glass rod, which is a parent material of an
optical fiber, to generate a preform, drawing said preform with
further heating to a filament-like form to generate an optical
fiber; and said heating and elongating has: pre-heating said glass
rod until prescribed region of said glass rod softens; and end
drawing said prescribed region for reducing a diameter of said
prescribed region and for making an end of said glass rod by
further heating and elongating said prescribed region.
24. A method as claimed in claim 23, wherein said end drawing
further includes second heating which heats by a flame a region
which is more towards a middle side of said glass rod than a center
of said prescribed region, a thickness of said flame being smaller
than a thickness of said flame of said pre-heating.
25. A method for manufacturing a preform, which is a parent
material of an optical fiber, comprising: setting a heating
condition for heating a glass rod, which is a parent material of
said optical fiber, and an elongating speed of said glass rod based
on a prescribed numerical value which changes with a progress of
elongation of said glass rod; heating and elongating said glass rod
to generate a preform based on said heating condition and said
elongating speed which are set by said setting.
26. A method as claimed in claim 25, wherein said setting sets said
heating condition and said elongating speed based on a progress
time of said elongation as said numerical value.
27. A method as claimed in claim 26, wherein: said heating and
elongating includes end drawing for reducing a diameter of an end
of said glass rod; and said end drawing end-draws said end of said
glass rod with heat and elongation based on said progress time of
said end drawing.
28. A method as claimed in claim 25, wherein said setting sets said
heating condition and said elongating speed based on an elongation
length of said glass rod in said elongation as said numerical
value.
29. A method as claimed in claim 28, wherein: said heating and
elongating includes end drawing for reducing a diameter of an end
of said glass rod; and said end drawing end-draws said end of said
glass rod with heat and elongation based on said elongation length
of said glass rod.
30. A method as claimed in claim 25, wherein said setting sets said
heating condition and said elongating speed based on a tensile
stress generated on said glass rod in said elongation as said
numerical value.
31. A method as claimed in claim 30, wherein a heating source,
which heats said glass rod, moves along a longitudinal direction of
said glass rod with a progress of said elongation, and said heating
and elongating controls said elongating speed so that said tensile
stress before said heating source moves prescribed distance becomes
substantially 110 percent or below an average value of said tensile
stress after said heating source moves said prescribed
distance.
32. A method as claimed in claim 31, wherein said heating and
elongating controls said tensile stress so that said tensile stress
before said heating source moves said prescribed distance become
substantially from 80 to 110 percent of an average value of said
tensile stress after said heating source moves said prescribed
distance.
33. A method as claimed in claim 31, wherein said prescribed
distance is substantially between 50 mm to 150 mm.
34. A method as claimed in claim 31, wherein said heating and
elongating controls said elongating speed to be a constant speed
when said heating source moves said prescribed distance.
35. A method as claimed in claim 25, wherein said setting sets said
heating condition and said elongating speed based on a location of
a mark provided on a connection between said glass rod and each of
dummy rods, which are welded to each of ends of said glass rod, as
said numerical value.
36. A method as claimed in claim 35, wherein: said heating and
elongating includes end drawing for reducing a diameter of an end
of said glass rod; and said end drawing end-draws said end of said
glass rod with heat and elongation based on said location of a
mark.
37. A method as claimed in claim 25, wherein said setting sets said
elongating speed at a plurality of locations along axial direction
of said glass rod based on a diameter at said plurality of
locations along axial direction of said glass rod as said numerical
value and said heating condition based on an average value of a
diameter at said plurality of locations of said glass rod.
38. A method as claimed in claim 25, wherein a end of said glass
rod is end-drawn of which diameter is reduced, and said setting
has: detecting a location of an end-drawn region where said glass
rod is end-drawn based on a diameter at a plurality of locations
along axial direction of said glass rod and a change of a length of
said glass rod along axial direction of said glass rod by said
elongation as said numerical value; and setting a polishing range
where said glass rod is polished by a flame based on said location
of said end-drawn region and also setting a heating power condition
of said flame based on a diameter of said end-drawn region, and
said heating and elongating polishes said polishing range of said
glass rod by said flame of said heating power condition.
39. A method for manufacturing a preform, which is a parent
material of an optical fiber, comprising: pre-heating said glass
rod until a prescribed region of said glass rod softens; and end
drawing said prescribed region for reducing a diameter of said
prescribed region and for making an end of said glass rod by
further heating and elongating said prescribed region.
40. A method as claimed in claim 39, wherein said end drawing
further includes second heating which heats by a flame a region
which is more towards a middle side of said glass rod than a center
of said prescribed region, a thickness of said flame being smaller
than a thickness of said flame of said pre-heating.
41. An apparatus for manufacturing a preform, which is a parent
material of an optical fiber, comprising: a heating source which
heats a glass rod, which is a parent material of said preform; an
elongating unit which elongates said glass rod; a measurement
device for measuring a numerical value which changes with a
progress of elongation of said glass rod; and a control unit which
controls a heating condition of said heating source and a
elongating speed of said elongating unit based on said numerical
value measured by said measurement device.
42. An apparatus as claimed in claim 41, wherein said measurement
device measures a progress time of said elongation as said
numerical value, and said control unit controls said heating
condition and said elongating speed based on said progress time of
said elongation measured by said measurement device.
43. An apparatus as claimed in claim 41, wherein said measurement
device measures a moving distance of said elongating unit which
changes with a progress of said elongation as said numerical value,
and said control unit controls said heating condition and said
elongating speed based on said moving distance of said elongating
unit measured by said measurement device.
44. An apparatus as claimed in claim 41, wherein said measurement
device measures a tensile stress generated on said glass rod by
said elongation as said numerical value, and said control unit
controls said heating condition and said elongating speed based on
said tensile stress generated on said glass rod measured by said
measurement device.
45. An apparatus as claimed in claim 44, wherein said heating
source moves along a longitudinal direction of said glass rod with
a progress of said elongation, and said control unit controls said
elongating speed so that said tensile stress before said heating
source moves prescribed distance becomes substantially 110 percent
or below an average value of said tensile stress after said heating
source moves said prescribed distance.
46. An apparatus as claimed in claim 45, wherein said control unit
controls said tensile stress so that said tensile stress before
said heating source moves said prescribed distance becomes
substantially from 80 to 110 percent of an average value of said
tensile stress after said heating source moves said prescribed
distance.
47. An apparatus as claimed in claim 45, wherein said prescribed
distance is substantially between 50 mm to 150 mm.
48. An apparatus as claimed in claim 45, wherein said control unit
controls said elongating speed to be a constant speed when said
heating source moves said prescribed distance.
49. An apparatus as claimed in claim 41, wherein said measurement
device measures a location of a mark provided on a connection
between said glass rod and each of dummy rods, which are welded to
each of ends of said glass rod, as said numerical value, and said
control unit controls said heating condition and said elongating
speed based on said location of a mark measured by said measurement
device.
50. An apparatus as claimed in claim 41, wherein said measurement
device measures a diameter at a plurality of locations along axial
direction of said glass rod as said numerical value, and said
control unit controls said elongating speed at said plurality of
locations along axial direction of said glass rod based on a
diameter at said plurality of locations along axial direction of
said glass rod, and said heating condition based on an average
value of a diameter at said plurality of locations.
Description
[0001] This patent application claims priority based on Japanese
patent applications, H11-067366 filed on Mar. 12, 1999, H11-075129
filed on Mar. 19, 1999, H10-315856 filed on Nov. 6, 1998,
H10-314564 filed on Nov. 5, 1998, H11-015293 filed on Jan. 25,
1999, H11-16840 filed on Jan. 26, 1999, H10-314574 filed on Nov. 5,
1998, H11-067199 filed on Mar. 12, 1999, H10-315849 filed on Nov.
6, 1998, H11-010197 filed on Jan. 19, 1999, H11-112354 filed on
Apr. 20, 1999, H11-046141 filed on Feb. 24, 1999, H10-314553 filed
on Nov. 5, 1998, H11-065819 filed on Mar. 12, 1999, H11-118094
filed on Apr. 26, 1999, H11-044902 filed on Feb. 23, 1999, and
H11-064994 filed on Mar. 11, 1999, the contents of which are
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of Invention
[0003] The present invention relates to an optical fiber
manufacture method, a preform manufacture method and a preform
manufacture apparatus that can manufacture a preform and an optical
fiber with reduced variation in their diameters.
[0004] 2. Description of Related Art
[0005] FIG. 1 shows a conventional glass base material first
elongating apparatus 400. A glass base material 102, which is a
base material of an optical fiber, is usually elongated by the
glass base material first elongating apparatus 400. This reduces
the diameter of the glass base material 102, to produce a glass rod
106. The glass rod 106 has a diameter from 3 mm to 5 mm larger than
the most convenient diameter to draw an optical fiber. The most
convenient diameter for drawing an optical fiber is 30 mm to 80
mm.
[0006] A glass base material first elongating apparatus 400
comprises a heating furnace 100 that heats the glass base material
102 and a drawing chuck 104 that holds and elongates the heated
glass base material 102. To elongate the glass base material 102,
the glass base material first elongating apparatus 400 supplies the
glass base material 102 to the heating furnace 100. Here the glass
base material 102 is heated to approximately 2000.degree. C. The
first elongating apparatus 400 then holds the glass base material
102 by the drawing chuck 104, and draws the glass base material 102
from the heating furnace 100 downward continuously to form a glass
rod 106.
[0007] FIG. 2 shows a configuration of a conventional glass lathe
110. The glass rod 106 made by the glass base material first
elongating apparatus 400 undergoes secondary elongation by the
glass lathe 110 to produce a preform 107. At this time, the
diameter of the glass rod 106 is reduced to prescribed diameter.
The glass lathe 110 comprises chucks 118 and 119 that hold the
glass rod 106, a tail stock 116 which moves the chuck 119, and a
heating source 122 which heats the glass rod 106. One side of the
chuck 118 is fixed, and the other side of the chuck 119 movable. A
traction force can be applied to the chuck 119. The glass rod 106,
which is held by the chucks 118 and 119, is heated by the heating
source 122. The heated glass rod 106 is elongated by moving the
tail stock 116 which pulls the glass rod 106. The result is, the
diameter of the glass rod 106 reduces to become the prescribed
diameter.
[0008] There was the possibility of manufacturing bent glass rods
106 when using a conventional glass base material first elongating
apparatus 400 to elongate the glass base material 102. Also, when
using a conventional glass lathe 110 to elongate the glass rod 106
to manufacture the preform 107 further problems often arose. These
problems included variation in the diameter of the preform 107
because the amount of gas provided to the heating source 122 and
the speed of moving the tail stock 116 differed for each preform
107 produced.
[0009] When elongating a bent glass rod 106, which is made by a
conventional glass base material first elongating apparatus 400, to
make a preform 107 by the glass lathe 110, the diameter of the
preform 107 varied. When manufacturing optical fibers by drawing a
preform 107 with a varying diameter, the diameter of the optical
fibers produced also varies. This makes it difficult to manufacture
an optical fiber of high quality.
SUMMARY OF THE INVENTION
[0010] As stated, it is an object of the present invention to
provide an optical fiber manufacture method, a preform manufacture
method and a preform manufacture equipment that can solve the
problems outlined above. The object of the present invention can be
achieved by the combinations of features described in the
independent claims of the present invention. The dependent claims
define further advantageous embodiments of the present
invention.
[0011] According to the first aspect of the present invention, a
method for manufacturing an optical fiber can be provided which
comprises setting a heating condition for heating a glass rod,
which is a parent material of the optical fiber, and an elongating
speed of the glass rod based on a prescribed numerical value which
changes with a progress of elongation of the glass rod; heating and
elongating the glass rod to generate a preform based on the heating
condition and the elongating speed which are set by the setting;
and drawing the preform to a filament-like form by further heating
the preform to generate the optical fiber.
[0012] A method for manufacturing an optical fiber can be provided
such that the setting sets the heating condition and the elongating
speed based on a progress time of the elongation as the numerical
value. The heating and elongating may include end drawing for
reducing a diameter of an end of the glass rod, and the end drawing
end-draws the end of the glass rod with heat and elongation based
on the progress time of the end drawing.
[0013] A method for manufacturing an optical fiber can be provided
such that the setting sets a location of a burner, which heats the
glass rod, and an amount of gas supplied to the burner as the
heating condition based on the progress time of the elongation. The
setting may set a moving speed of a chuck, which holds the glass
rod, as the elongating speed based on the progress time of the
elongation.
[0014] A method for manufacturing an optical fiber can be provided
such that the setting sets the heating condition and the elongating
speed based on an elongation length of the glass rod in the
elongation as the numerical value.
[0015] A method for manufacturing an optical fiber can be provided
such that the heating and elongating includes end drawing for
reducing a diameter of an end of the glass rod, and the end drawing
end-draws the end of the glass rod with heat and elongation based
on the elongation length of the glass rod. The setting may set a
moving distance of a burner, which heats the glass rod, and an
amount of gas supplied to the burner as the heating condition based
on the elongation length of the glass rod. The setting can further
set a moving speed of a chuck, which holds the glass rod, as the
elongating speed based on the elongation length of the glass
rod.
[0016] A method for manufacturing an optical fiber can be provided
such that the setting uses a encoder, which is provided on a motor
that drives the chuck, to measure a moving distance of the chuck by
measuring a rotation angle of the motor.
[0017] A method for manufacturing an optical fiber can be provided
such that the setting sets the heating condition and the elongating
speed based on a tensile stress generated on the glass rod in the
elongation as the numerical value.
[0018] A method for manufacturing an optical fiber can be provided
such that a heating source, which heats the glass rod, moves along
a longitudinal direction of the glass rod with a progress of the
elongation, and the heating and elongating controls the elongating
speed so that the tensile stress before the heating source moves
prescribed distance becomes substantially 110 percent or below an
average value of the tensile stress after the heating source moves
the prescribed distance.
[0019] A method for manufacturing an optical fiber can be provided
such that the heating and elongating controls the tensile stress so
that the tensile stress before the heating source moves the
prescribed distance become substantially from 80 to 110 percent of
an average value of the tensile stress after the heating source
moves the prescribed distance.
[0020] The prescribed distance can be substantially between 50 mm
to 150 mm. The heating and elongating may control the elongating
speed to be a constant speed when the heating source moves the
prescribed distance. The setting may set a moving speed of a chuck,
which holds the glass rod, as the elongating speed based on the
tensile stress.
[0021] A method for manufacturing an optical fiber can be provided
such that the setting sets the heating condition and the elongating
speed based on a location of a mark provided on a connection
between the glass rod and each of dummy rods, which are welded to
each of ends of the glass rod, as the numerical value.
[0022] A method for manufacturing an optical fiber can be provided
such that the heating and elongating includes end drawing for
reducing a diameter of an end of the glass rod, and the end drawing
end-draws the end of the glass rod with heat and elongation based
on the location of a mark. The setting can set the heating
condition and the elongating speed based on a location of a cut
provided on a connection between the glass rod and each of the
dummy rods as the location of a mark.
[0023] A method for manufacturing an optical fiber can be provided
such that the setting sets the heating condition and the elongating
speed based on a location of a fluorescent paint applied on a
connection between the glass rod and each of the dummy rods as the
location of a mark.
[0024] A method for manufacturing an optical fiber can be provided
such that the setting sets the elongating speed at a plurality of
locations along axial direction of the glass rod based on a
diameter at the plurality of locations along axial direction of the
glass rod as the numerical value and the heating condition based on
an average value of a diameter at the plurality of locations of the
glass rod.
[0025] A method for manufacturing an optical fiber can be provided
such that a end of the glass rod is end-drawn of which diameter is
reduced, and the setting has detecting a location of an end-drawn
region where the glass rod is end-drawn based on a diameter at a
plurality of locations along axial direction of the glass rod and a
change of a length of the glass rod along axial direction of the
glass rod by the elongation as the numerical value, and setting a
polishing range where the glass rod is polished by a flame based on
the location of the end-drawn region and also setting a heating
power condition of the flame based on a diameter of the end-drawn
region, and the heating and elongating polishes the polishing range
of the glass rod by the flame of the heating power condition.
[0026] According to the other aspect of the present invention, a
method for manufacturing an optical fiber can be provided which
comprises heating and elongating a glass rod, which is a parent
material of an optical fiber, to generate a preform, drawing the
preform with further heating to a filament-like form to generate an
optical fiber, and the heating and elongating has pre-heating the
glass rod until prescribed region of the glass rod softens, and end
drawing the prescribed region for reducing a diameter of the
prescribed region and for making an end of the glass rod by further
heating and elongating the prescribed region.
[0027] A method for manufacturing an optical fiber can be provided
such that the end drawing further includes second heating which
heats by a flame a region which is more towards a middle side of
the glass rod than a center of the prescribed region, a thickness
of the flame being smaller than a thickness of the flame of the
pre-heating.
[0028] According to the first aspect of the present invention, a
method for manufacturing a preform, which is a parent material of
an optical fiber, can be provided which comprises setting a heating
condition for heating a glass rod, which is a parent material of
the optical fiber, and an elongating speed of the glass rod based
on a prescribed numerical value which changes with a progress of
elongation of the glass rod, heating and elongating the glass rod
to generate a preform based on the heating condition and the
elongating speed which are set by the setting.
[0029] A method for manufacturing a preform can be provided such
that the setting sets the heating condition and the elongating
speed based on a progress time of the elongation as the numerical
value.
[0030] A method for manufacturing a preform can be provided such
that the heating and elongating includes end drawing for reducing a
diameter of an end of the glass rod, and the end drawing end-draws
the end of the glass rod with heat and elongation based on the
progress time of the end drawing. The setting may set the heating
condition and the elongating speed based on an elongation length of
the glass rod in the elongation as the numerical value. The heating
and elongating can include end drawing for reducing a diameter of
an end of the glass rod, and the end drawing end-draws the end of
the glass rod with heat and elongation based on the elongation
length of the glass rod.
[0031] A method for manufacturing a preform can be provided such
that the setting sets the heating condition and the elongating
speed based on a tensile stress generated on the glass rod in the
elongation as the numerical value.
[0032] A method for manufacturing a preform can be provided such
that a heating source, which heats the glass rod, moves along a
longitudinal direction of the glass rod with a progress of the
elongation, and the heating and elongating controls the elongating
speed so that the tensile stress before the heating source moves
prescribed distance becomes substantially 110 percent or below an
average value of the tensile stress after the heating source moves
the prescribed distance.
[0033] A method for manufacturing a preform can be provided such
that the heating and elongating controls the tensile stress so that
the tensile stress before the heating source moves the prescribed
distance become substantially from 80 to 110 percent of an average
value of the tensile stress after the heating source moves the
prescribed distance. The prescribed distance can be substantially
between 50 mm to 150 mm. The heating and elongating may control the
elongating speed to be a constant speed when the heating source
moves the prescribed distance.
[0034] A method for manufacturing a preform can be provided such
that the setting sets the heating condition and the elongating
speed based on a location of a mark provided on a connection
between the glass rod and each of dummy rods, which are welded to
each of ends of the glass rod, as the numerical value. The heating
and elongating can include end drawing for reducing a diameter of
an end of the glass rod, and the end drawing end-draws the end of
the glass rod with heat and elongation based on the location of a
mark.
[0035] A method for manufacturing a preform can be provided such
that the setting sets the elongating speed at a plurality of
locations along axial direction of the glass rod based on a
diameter at the plurality of locations along axial direction of the
glass rod as the numerical value and the heating condition based on
an average value of a diameter at the plurality of locations of the
glass rod.
[0036] A method for manufacturing a preform can be provided such
that a end of the glass rod is end-drawn of which diameter is
reduced, and the setting has detecting a location of an end-drawn
region where the glass rod is end-drawn based on a diameter at a
plurality of locations along axial direction of the glass rod and a
change of a length of the glass rod along axial direction of the
glass rod by the elongation as the numerical value, and setting a
polishing range where the glass rod is polished by a flame based on
the location of the end-drawn region and also setting a heating
power condition of the flame based on a diameter of the end-drawn
region, and the heating and elongating polishes the polishing range
of the glass rod by the flame of the heating power condition.
[0037] According to the other aspect of the present invention, a
method for manufacturing a preform, which is a parent material of
an optical fiber, can be provided which comprises preheating the
glass rod until a prescribed region of the glass rod softens, and
end drawing the prescribed region for reducing a diameter of the
prescribed region and for making an end of the glass rod by further
heating and elongating the prescribed region. The end drawing may
further include second heating which heats by a flame a region
which is more towards a middle side of the glass rod than a center
of the prescribed region, a thickness of the flame being smaller
than a thickness of the flame of the pre-heating.
[0038] According to the first aspect of the present invention, an
apparatus for manufacturing a preform, which is a parent material
of an optical fiber, can be provided which comprises a heating
source which heats a glass rod, which is a parent material of the
preform, an elongating unit which elongates the glass rod, a
measurement device for measuring a numerical value which changes
with a progress of elongation of the glass rod, and a control unit
which controls a heating condition of the heating source and a
elongating speed of the elongating unit based on the numerical
value measured by the measurement device.
[0039] An apparatus for manufacturing a preform can be provided
such that the measurement device measures a progress time of the
elongation as the numerical value, and the control unit controls
the heating condition and the elongating speed based on the
progress time of the elongation measured by the measurement
device.
[0040] An apparatus for manufacturing a preform can be provided
such that the measurement device measures a moving distance of the
elongating unit which changes with a progress of the elongation as
the numerical value, and the control unit controls the heating
condition and the elongating speed based on the moving distance of
the elongating unit measured by the measurement device.
[0041] An apparatus for manufacturing a preform can be provided
such that the measurement device measures a tensile stress
generated on the glass rod by the elongation as the numerical
value, and the control unit controls the heating condition and the
elongating speed based on the tensile stress generated on the glass
rod measured by the measurement device.
[0042] An apparatus for manufacturing a preform can be provided
such that the heating source moves along a longitudinal direction
of the glass rod with a progress of the elongation, and the control
unit controls the elongating speed so that the tensile stress
before the heating source moves prescribed distance becomes
substantially 110 percent or below an average value of the tensile
stress after the heating source moves the prescribed distance.
[0043] An apparatus for manufacturing a preform can be provided
such that the control unit controls the tensile stress so that the
tensile stress before the heating source moves the prescribed
distance becomes substantially from 80 to 110 percent of an average
value of the tensile stress after the heating source moves the
prescribed distance. The prescribed distance can be substantially
between 50 mm to 150 mm. The control unit may control the
elongating speed to be a constant speed when the heating source
moves the prescribed distance.
[0044] An apparatus for manufacturing a preform can be provided
such that the measurement device measures a location of a mark
provided on a connection between the glass rod and each of dummy
rods, which are welded to each of ends of the glass rod, as the
numerical value, and the control unit controls the heating
condition and the elongating speed based on the location of a mark
measured by the measurement device.
[0045] An apparatus for manufacturing a preform can be provided
such that the measurement device measures a diameter at a plurality
of locations along axial direction of the glass rod as the
numerical value, and the control unit controls the elongating speed
at the plurality of locations along axial direction of the glass
rod based on a diameter at the plurality of locations along axial
direction of the glass rod, and the heating condition based on an
average value of a diameter at the plurality of locations.
BRIEF DESCRIPTION OF THE ELONGATINGS
[0046] FIG. 1 shows a conventional glass base material first
elongating apparatus 400.
[0047] FIG. 2 shows a configuration of a conventional glass lathe
110.
[0048] FIG. 3 shows a system of an optical fiber manufacturing
apparatus of present invention.
[0049] FIG. 4 shows an optical fiber manufacturing method of the
present invention.
[0050] FIG. 5 shows a configuration of a glass base material first
elongating apparatus 900.
[0051] FIG. 6 shows a first elongating device 402 that holds a
standard rod 138 by a base material fix unit 136 to adjust the axis
for elongating a glass base material 102.
[0052] FIG. 7 shows a detailed flow chart of a glass base material
first elongating (S204) shown in FIG. 4.
[0053] FIG. 8 shows the first elongating device 402 that holds the
standard rod 138 by the elongating chuck 142.
[0054] FIG. 9 shows the first elongating device 402, which holds
the standard rod 138 by both of the hanging mechanism 134 and the
elongating mechanism 140.
[0055] FIG. 10 shows an example using elongating rollers 144a and
144b instead of the elongating chuck 142 on the elongating
mechanism 140.
[0056] FIG. 11 shows an example using elongating rollers 144a and
144b instead of the elongating chuck 142 on the elongating
mechanism 140.
[0057] FIG. 12 shows the glass base material 102, the bending
degree of which is measured.
[0058] FIG. 13 shows a mechanism by which the first elongating
device 402 controls the speed of rotation of the elongating roller
144a and 144b.
[0059] FIG. 14 shows a relationship between the amount of deviation
between the center position of the heat softened region of the
glass base material 102 and elongating axis 154, and the degree of
bend of the glass rod 106.
[0060] FIG. 15 shows a deformation of the surface of the elongating
rollers 144a and 144b.
[0061] FIG. 16 shows displacement of the metal pipe when the metal
pipe is carried by the elongating rollers 144a and 144b of batch
number 300 shown in FIG. 15.
[0062] FIG. 17 shows the displacement of the center position of the
heat softened region by the first elongating device 402 of the
embodiment.
[0063] FIG. 18 shows a fluctuation of the center position of the
heat softened region when the rotation speed of the elongating
rollers 144a and 144b are controlled at the same rotation
speed.
[0064] FIG. 19 shows an another embodiment of the burner 176 used
in the glass rod fusing apparatus 370 shown in FIG. 5.
[0065] FIG. 20 shows a configuration of a glass rod transportation
device 380.
[0066] FIG. 21 shows a storage container 224 of the first
elongating device 402.
[0067] FIG. 22 shows a movement of the glass rod transportation
device 380 when transporting the glass rod 106.
[0068] FIG. 23 shows an another embodiment of the glass rod
transportation device 380.
[0069] FIG. 24 shows a movement of the glass rod transportation
device 380 shown in FIG. 23 when the glass rod transportation
device 380 transports the glass rod 106.
[0070] FIG. 25 shows a configuration of a glass rod second
elongating apparatus 111 of the present invention.
[0071] FIG. 26 shows a detailed flow chart of the glass rod second
elongating (S206) shown in FIG. 4.
[0072] FIG. 27 shows an example where a cooling device 330 is
provided on the fixed chuck 118 and the movable chuck 119 of the
glass rod second elongating apparatus 111.
[0073] FIG. 28 shows the temperature of the fixed chuck 118 and the
movable chuck 119 of the example and the comparative example.
[0074] FIG. 29 shows a relationship between the distance between
the heating source 122 and the diameter measurement device 124, and
the percentage of the fluctuation of the diameter of the glass rod
106.
[0075] FIG. 30 shows a glass rod second elongating apparatus 111
that has a tensile stress measurement device 282.
[0076] FIG. 31 shows a detailed flow chart of the elongating (S154)
shown in the FIG. 26.
[0077] FIG. 32 shows the process of diameter fluctuation during the
elongation of the glass rod 106.
[0078] FIG. 33 shows a glass rod 106 that is elongated according to
the elongating (S154) shown in FIG. 31.
[0079] FIG. 34 shows the tensile stress of the glass rod 106 at the
early stage of the elongation of the example.
[0080] FIG. 35 shows the fluctuation of the tensile stress of the
glass rod 106 at an early stage of the elongation of the
comparative example.
[0081] FIG. 36 shows fluctuation of the diameter of the glass rod
106 after the elongation of the glass rod 106.
[0082] FIG. 37 shows a detailed flow chart of the end drawing
(S158) shown in FIG. 26.
[0083] FIG. 38 shows a cut 284 which is provided on the connection
between the glass rod 106 and the dummy rod 108 at the end drawing
position detecting (S169) shown in FIG. 37.
[0084] FIG. 39 shows a marking 287 that is applied on the
connection between the glass rod 106 and the dummy rod 108 as
another example of a mark.
[0085] FIG. 40 shows the glass rod second elongating apparatus 111
that detects the cut 284 at end drawing position detecting (S169)
FIG. 41 shows the movements of the heating source 122 and the tail
stock 116 during the end drawing process of the glass rod 106 shown
in flow chart of FIG. 37.
[0086] FIG. 42 shows an example of the settings of an another
method of the end drawing process at the end drawing (S158) shown
in FIG. 37.
[0087] FIG. 43 shows another example of the settings of another
method of the end drawing process at the end drawing (S158) shown
in FIG. 37.
[0088] FIG. 44 shows a configuration of the heating source 122 of
the glass rod second elongating apparatus 111.
[0089] FIG. 45 shows a plan view of the top of the heating source
122.
[0090] FIG. 46 shows a relationship between the linear speed of the
oxygen gas and the temperature of the top of the heating source
122.
[0091] FIG. 47 shows a shape of a tip of the preform 107, the
diameter of which is reduced and fused at the end drawing
(S158).
[0092] FIG. 48 shows another shape of the tip of the preform 107
that was end elongated.
[0093] FIG. 49 shows damage of the preform 107 before the preform
107 is surface treated in the surface treatment (S168) shown in the
FIG. 26.
[0094] FIG. 50 shows the preform 107a, which was treated by the
hydrofluoric acid etching on the example shown in FIGS. 51 and FIG.
52.
[0095] FIG. 51 shows the number of hydrofluoric concaves generated
on the preform 107 counted by visual inspection of the example and
the comparative example.
[0096] FIG. 52 shows the unevenness of the surface of the preform
107 after treatment of the hydrofluoric acid etching of the example
and the comparative example.
[0097] FIG. 53 shows another shape of the preform 107 which is
surface treated.
[0098] FIG. 54 shows an ultrasonic cleaning apparatus 404, which
cleans the heating source 122.
[0099] FIG. 55 shows a configuration of the preform drawing
apparatus 500 that elongates the preform 107 to produce an optical
fiber.
DETAILED DESCRIPTION OF THE INVENTION
[0100] The present invention will be explained using embodiments of
the present invention. The following embodiments however, do not
limit the scope of the present invention described in the claims.
Moreover, not all the features or their combinations described in
the embodiments are necessarily essential for the present
invention.
[0101] Although the present invention has been described with
reference to specific embodiments, the scope of the present
invention is not limited to these embodiments. Those skilled in the
art can make various modifications and improvements to the
embodiments of the present invention. It is clear from the appended
claims that such modifications or improvements are also covered by
the scope of the present invention.
[0102] FIG. 3 shows a system of an optical fiber manufacturing
apparatus of the present invention. The system of the optical fiber
manufacturing apparatus of present invention comprises a glass base
material generating apparatus 600 which generates a glass base
material 102 being a base material of an optical fiber; a glass
base material dehydrating and sintering apparatus 700 which
dehydrates and sinters the glass base material 102; a glass base
material first elongating apparatus 900 which elongates the glass
base material 102 to generate a glass rod 106; a glass rod
transportation device 380 which transports the glass rod 106; a
glass rod second elongating apparatus 111 which elongates the glass
rod 106 a second time to generate a preform 107; and a preform
drawing apparatus 500 which draws the preform 107 to generate an
optical fiber.
[0103] FIG. 4 shows an optical fiber manufacturing method of the
present invention. The glass base material 102 is generated by the
glass base material generating apparatus 600 using the VAD method,
vapor-phase axial deposition method, or the like (S200). The glass
base material 102 is then dehydrated within a chlorine gas
atmosphere and sintered within an inert-gas atmosphere by the glass
base material dehydrating and sintering apparatus 700 (S202).
[0104] The diameter of the glass base material 102 is normally 110
mm to 200 mm, compared to a diameter of 30 mm to 80 mm which is
most practical for drawing to an optical fiber. Therefore, the
dehydrated and sintered glass base material 102 is elongated
firstly by the glass base material first elongating apparatus 900
to produce a glass rod 106 (S204). The glass rod 106 has a diameter
3 mm to 5 mm larger than the diameter convenient for drawing to an
optical fiber, which is from 30 mm to 80 mm.
[0105] The glass rod 106 is transported by the glass rod
transportation device 380 (S205). The glass rod 106 is then heated
and elongated by the glass rod second elongating apparatus 111 to a
prescribed diameter, thus producing a preform 107 (S206). The
preform 107 is heated and drawn to a filament-like form by the
preform drawing apparatus 500 to produce an optical fiber
(S210).
[0106] FIG. 5 shows a configuration of a glass base material first
elongating apparatus 900. The glass base material first elongating
apparatus 900 comprises a first elongating device 402 which heats
and elongates the glass base material 102 and a glass rod fusing
apparatus 370 which fusing the glass rod 106. The first elongating
device 402 has a elongating furnace 130, which has a heating
furnace 100, and a hanging mechanism 134 which is provided above
the elongating furnace 130. The hanging mechanism 134 supplies the
glass base material 102 to the inside of the elongating furnace 130
at a prescribed speed.
[0107] The first elongating device 402 further has an elongating
mechanism 140 which is provided under the elongating furnace 130 to
hold the glass rod 106 of reduced diameter and to pull the glass
rod 106 at a prescribed speed. The hanging mechanism 134 has a base
material fix unit 136 that holds the glass base material 102. The
elongating mechanism 140 has an elongating chuck 142 that holds the
glass rod 106. The glass rod fusing apparatus 370 has a burner 176,
a rotating table 210, a timing belt 214, a motor 212, a supporting
leg 208, a burner stand 216, an elongating device 206, and an
elongating fusion chuck 218.
[0108] The glass base material 102 is installed on the base
material fix unit 136, and sent into the heating furnace 100 at a
prescribed speed. The glass base material 102 heated by the heating
furnace 100 is held and pulled by the elongating chuck 142 to
reduce the diameter thus producing a glass rod 106. The glass rod
106 is pulled by the elongating device 206 at a speed which is
suitable for the diameter to be obtained, so that the glass base
material 102 is elongated to the desired diameter. At this time,
the diameter of the glass rod 106 is measured by a diameter
measuring device 152. The feeder 204, heating furnace 100, and
elongating device 206 are controlled based on this measurement in
order to elongate the glass rod 106 to the desired diameter.
[0109] The glass rod 106, which has been elongated to a prescribed
diameter and length, is fused by the burner 176 at the part that
does not include the bubble or does not include the bubble of which
diameter is substantially 0.3 mm or above. A flame of oxygen and
hydrogen is a desirable heating means of the burner 176. A gas
flame of based on hydrocarbon fuels such as propane and oxygen can
also be used for the burner 176.
[0110] The burner 176 is installed on the rotating table 210 via
the supporting leg 208. The rotating table is rotated by a driving
device such as motor 212 via the timing belt 214. The rotating
table 210 is installed on the burner stand 216. The glass rod
fusing apparatus 370 fuses the glass rod 106 by heating the glass
rod 106 with the rotating the burner 176 and elongates the glass
rod 106 using the elongating fusion chuck 218 with a prescribed
speed and pull strength.
[0111] FIG. 6 shows a first elongating device 402 which holds a
standard rod 138 by a material fix unit 136 to adjust the axis for
elongating a glass base material 102. The hanging mechanism 134 has
a mechanism not shown in the figure, that adjusts the vertical
inclination of the base material fix unit 136. The elongating
mechanism 140 has a mechanism, also not shown in the figure, that
adjusts the vertical inclination of the elongating chuck 142. The
elongating mechanism 140 further has a mechanism, again not shown
in the figure, that adjusts the position of the elongating
mechanism 140 within the horizontal phase in the directions back
and forth and left and right.
[0112] FIG. 7 shows a detailed flow chart of a glass base material
first elongating (S204) shown in FIG. 4. The glass base material
first elongating (S204) has a process to adjust the elongating axis
of the first elongating device 402. First, a metal or ceramic rod
is prepared as a standard rod 138. The straightness of the standard
rod 138 should be guaranteed. The standard rod 138 usually has a
length of a glass base material 102 and dummy rod that is welded
onto the glass base material 102. The straightness of the axis of
the standard rod 138 is guaranteed along the full length.
[0113] As shown in FIG. 6, the standard rod 138 is held by the base
material fix unit 136 of the hanging mechanism 134 (S110). Then,
the inclination A of the hanging mechanism 134 is adjusted so that
the direction of the standard rod 138 matches with the vertical
direction (S112). Following this, the standard rod 138 is removed
from the base material fix unit 136 after finishing the adjustment
(S114).
[0114] FIG. 8 shows the first elongating device 402 that holds the
standard rod 138 by the elongating chuck 142. The standard rod 138
is held by the elongating chuck 142 of the elongating mechanism 140
(FIG. 7, S116), Then the inclination B of the elongating mechanism
140 is adjusted so that the direction of the standard rod 138
matches with the vertical direction (FIG. 7, S118). At this time,
it is desirable that the elongating chuck 142 maintains the
approximate center of longitudinal direction of the standard rod
138. The procedure for adjusting the hanging mechanism 134 and the
elongating mechanism 140 can be reversible. The elongating
mechanism 140 can be adjusted first, and then the hanging mechanism
134 can be adjusted.
[0115] FIG. 9 shows the first elongating device 402, which holds
the standard rod 138 by both the hanging mechanism 134 and the
elongating mechanism 140. After finishing the adjustment of the
hanging mechanism 134 and the elongating mechanism 140, by holding
the standard rod 138 by the base material fix unit 136, the lower
end of the standard rod 138 is held by the elongating chuck 142
(FIG. 7, S120). Then, the horizontal direction position C of the
elongating mechanism 140 or the horizontal direction position C of
the hanging mechanism 134 is adjusted so that the difference in
horizontal direction between the vertical axis and the standard rod
138 is less than 0.5 mm per 1 m length (FIG. 7, S122).
[0116] Following this, a glass rod 106 is generated by elongating
the glass base material 102 using the first elongating device 402,
the elongating axis of which is adjusted (FIG. 7, S124). Finally,
the glass rod 106 is fused by the glass rod fusing apparatus 370
(FIG. 7, S126).
[0117] FIG. 10 and FIG. 11 show examples that use elongating
rollers 144a and 144b on the elongating mechanism 140 instead of
the elongating chuck 142. To adjust the vertical inclination of the
axis connecting the hanging mechanism 134 and the elongating
mechanism 140 in the case of using the elongating rollers 144a and
144b, the following method is adopted. The standard rod 138 is held
by the elongating rollers 144a and 144b as opposed to the holding
of the standard rod 138 by the elongating chuck 142 (FIG. 7,
S116).
[0118] Following this, the inclination of the elongating mechanism
140 is adjusted by adjusting the horizontal inclination of the line
F. The line F connects the two rotation axis between the elongating
rollers 144a and 144b. After the adjustment of the inclination of
the elongating mechanism 140 (FIG. 7, S118), the elongating rollers
144a and 144b can hold the standard rod 138 vertically.
[0119] Next, as shown in FIG. 11, the standard rod 138 is held by
the base material fix unit 136 of the hanging mechanism 134 and the
elongating rollers 144a and 144b of the elongating mechanism 140 at
the step corresponding to holding the standard rod 138 by the base
material fix unit 136 and the elongating chuck 142 (FIG. 7, S120).
Then, the vertical inclination E of the axis which connects the
hanging mechanism 134 and elongating mechanism 140 is adjusted.
This adjustment is made either by adjusting the position of the
elongating mechanism 140 in the horizontal direction or adjusting
the position of the hanging mechanism 134 in the horizontal
direction at the step corresponding to adjustment of the horizontal
direction position of the hanging mechanism 134 and the elongating
mechanism 140 (FIG. 7, S122).
[0120] The vertical inclination of the axis connecting the hanging
mechanism 134 and elongating mechanism 140 can be readily adjusted
using the adjusting method shown above. This method is suitable not
only for elongating the straight glass base material 102 without
any gap between the dummy rod and the glass base material 102, but
also for elongating a glass base material 102 with some bending, to
obtain a glass rod 106 with reduced diameter within a desired range
of straightness. This is possible, provided the glass base material
102 is welded onto the dummy rod without a gap between the axis of
the glass base material 102 and the dummy rod.
[0121] The first elongating device 402 can adjust the vertical
inclination of the elongating axis accurately for the methods of
holding the glass base material 102 by either the hanging mechanism
134, the elongating mechanism 140 or by both the hanging mechanism
134 and the elongating mechanism 140. Therefore, the bending
moment, which causes bending on the heat softened region of the
glass base material 102 can be decreased. Bending is generated by
the weight of the elongated glass base material 102 as it bears on
the elongating mechanism 140. The glass base material 102 can
therefore be elongated within a desired range of straightness
without causing a gap between the axis of the glass base material
102 and the dummy rod.
[0122] FIG. 12 shows the glass base material 102, the bending
degree of which is measured. The glass base material 102 is
elongated by the first elongating device 402, the vertical
inclination of which is adjusted by the adjusting method shown
above. Then, the degree of bending of the glass rod 106 is
measured. First, the glass rod 106 is placed on two bearings 148
and 149, which are installed horizontally so that the line
connecting the top of bearings 148 and 149 can be a standard line.
Next, the maximum or minimum value of the height from the standard
line is measured by scanning the measuring device 150 along the
glass rod 106 using a device such as a dial gauge.
[0123] Then, the glass rod 106 is rotated 180 degrees, and the
maximum and minimum value of the height from the standard line is
measured in the same way. The maximum value of the difference
between the first measured maximum value and the next measured
minimum value or the difference of the first measured minimum value
and the next measured maximum value is set as "2h". The value that
divides the "h" by the length L1, which is a distance between two
bearings 148 and 149, represents the straightness of the glass rod
106 per unit of length.
[0124] 5 pieces of the straight glass base material 102 without the
gap of axis with dummy rod were elongated by the first elongating
device 402 with an adjusted elongating axis to produce 5 of glass
rod 106. The straightness of each of the glass rods 106 was
measured by the method shown in FIG. 12. The "h" of the glass rods
106 were all within 0.5 mm. Next, the glass rods 106 were elongated
by the first elongating device 402 without adjustment of the
elongating axis. An average of 90 percent of the glass rods 106
were bent which indicates that the glass rod 106 should be
corrected through adjustment of the elongating axis.
[0125] FIG. 13 shows a mechanism by which the first elongating
device 402 controls the speed of rotation of the elongating rollers
144a and 144b. The first elongating device 402 controls the
rotation speed of each of the elongating rollers 144a and 144b
respectively. The glass base material 102 is hung by the base
material fix unit 136 of the first elongating device 402 and sent
to the heating furnace (not shown in the figure) at a prescribed
speed. The glass rod 106, which is heated and softened by the
heating furnace, is taken by the pair of elongating rollers 144a
and 144b.
[0126] The center position of the heat softened region of the glass
base material 102 is obtained by measuring the diameter of the heat
softened region of the glass base material 102 using the diameter
measuring device 152. At the same time the center position of the
measured diameter is calculated. A laser beam transmission type
diameter measuring device is used as the diameter measuring device
152. The laser beam is irradiated onto the heat softened region of
the glass base material 102 through the window provided on the
lower part of the heater in the heating furnace.
[0127] The measured diameter is input to the diameter control unit
156, and the difference between the target diameter value and the
measured diameter is calculated. The rotation speed of the
elongating roller 144a is controlled based on the calculated
difference of the diameter. Then, the information on the center
position of the heat softened region is input to the position
control unit 158.
[0128] The position control unit 158 calculates the amount of
deviation between the center position of the heat softened region
and the elongating axis 154 of the first elongating device 402. The
position control unit 158 further calculates the correction value
of the rotation speed, which can reduce the deviation between the
center position of heat softened region and the elongating axis 154
to virtually zero. Then, the position control unit 158 controls the
rotation speed of the elongating roller 144b based on the addition
of the correction value and the rotation speed of the elongating
roller 144a.
[0129] FIG. 14 shows a relationship between the amount of deviation
between the center position of the heat softened region of the
glass base material 102 and the elongating axis 154, and the degree
of bend caused in the glass rod 106. The larger the amount of
deviation between the center position of the heat softened region
of the glass base material 102 and elongated axis 154, the larger
the resultant bend in the glass rod 106.
[0130] When the amount of deviation is large, the heat-resistant
members on the surface of the elongating rollers 144a and 144b are
deformed. The shapes of the elongating rollers 144a and 144b become
slightly different to each other. The result is the rotation speeds
of the surfaces of the elongating rollers 144a and 144b are
different to each other. Since the deformation of the surface of
the elongating rollers 144a and 144b is one of the causes of the
bending of the glass rod 106, the bend of the glass rod 106 can be
reduced by controlling the rotation speed of each of the elongating
rollers 144a and 144b respectively.
[0131] The surfaces of the elongating rollers 144a and 144b are
formed from a heat-resistant material such as non-asbestos or
asbestos. These materials are heat resistant and flexible, so that
the elongating rollers 144a and 144b can easily elongate the glass
rod 106 at high temperatures. The surface of the elongating rollers
144a and 144b that come into contact with the glass rod 106 are
gradually deformed by the high temperature and pinching force or
friction force of the glass rod 106. Because the deformation of the
elongating rollers 144a and 144b is slightly different to each
other, the rotation speed of the surfaces of the elongating rollers
144a and 144b also differs.
[0132] FIG. 15 shows deformation of the surfaces of the elongating
rollers 144a and 144b. The outside shape of the elongating roller
144a and the elongating roller 144b is different. The number of
batches is the number of glass base materials 102 which were
elongated. As the number of batches is increased, the deformation
and abrasion is progressed. The result is, the amount of elongation
becomes different between the elongating rollers 144a and 144b,
which causes fluctuation in the position of the heat softened
region of the glass base material 102 which in turn causes bending
of the glass rod 106.
[0133] FIG. 16 shows displacement of the center position of the
heated region of the metal pipe when the metal pipe is taken by the
elongating rollers 144a and 144b at batch number 300 shown in FIG.
15. The vertical axis shows the displacement of the center position
of the heated region of the metal pipe, and the horizontal axis
shows time. The curve A shows the fluctuation of the amount of
deviation in the direction of rotation of the elongating rollers
144a and 144b. The curve A shows that the displacement fluctuates
largely during a single rotation of the elongating rollers 144a and
144b. The curve B shows that the fluctuation of displacement is
quite small for the axis direction of the elongating rollers 144a
and 144b.
[0134] FIG. 17 shows displacement of the center position of the
heat softened region by the first elongating device 402 of the
embodiment. The vertical axis shows the displacement of the center
position of the heat softened region of the glass base material
102, and the horizontal axis shows the time from the start of the
elongation. The displacement of the heat softened region is
controlled and maintained at a small level after 1500 seconds from
the start of the elongation. Therefore, a glass rod 106 without a
substantial bend can be manufactured by controlling the rotation
speed of the each of the elongating rollers 144a and 144b
respectively. This allows the center position of the heat softened
region to be maintained at a relatively constant point.
COMPARATIVE EXAMPLE
[0135] FIG. 18 shows fluctuation of the center position of the heat
softened region when the rotation speed of the elongating rollers
144a and 144b are controlled at the same rotation speed as each
other. The vertical axis shows the displacement of the center
position of the heat softened region of the glass base material
102, and the horizontal axis shows the time from the start of the
elongation.
[0136] A glass rod 106 having a prescribed diameter was
manufactured by measuring the diameter of the heat softened region
of the glass base material 102 using the same diameter measuring
device 152 in FIG. 17. The rotating speeds of the elongating
rollers 144a and 144b were controlled at the same rotation speed as
each other. The fluctuation of the center position of the heat
softened region was large so that a bend requiring correction was
caused on the elongated glass rod 106.
[0137] FIG. 19 shows another embodiment of the burner 176 used in
the glass rod fusing apparatus 370 shown in FIG. 5. A ring burner
176 has a hydrogen gas supply pipe 190 and a ring-type gas inlet
194, which are connected to an oxygen gas supply pipe 192. The
cooling pipe 196, which is connected to the cooling water supply
pipe 198 and cooling water drainage pipe 200, is provided on the
outer area of the ring burner 176. The ring-type gas inlet 194 can
be a single layer that ejects a mix of hydrogen gas and oxygen gas.
The ring-type gas inlet 194 can also be multiple or triple layered
which eject the hydrogen gas from the upper and lower layers and
oxygen gas from the middle layer.
[0138] The glass rod 106 is set inside the ring of the ring burner
176, after which the hydrogen and oxygen gases are supplied to the
ring burner 176 and ignited. The surface of the glass rod 106 is
fused by the flame 178. The ring burner 178 can heat the glass rod
106 efficiently so that it is unnecessary to over heat the glass
rod 106. Therefore, the opaque region on the surface of the glass,
generated when glass is heated to temperatures higher than
2000.degree. C., cannot be seen on the fused surface of the glass
rod 106.
[0139] According to the embodiments shown above, the glass rod 106
was fused. The glass base material 102 with a diameter of 120 mm
was heated by the ring burner 176 for ten minutes. Hydrogen gas was
supplied to the ring burner 176 at a rate of 300 L/minute and
oxygen gas at 120 L/minute. The glass rod 106 was fused by
elongation when the glass rod 106 was melted. The fused surface of
the glass rod 106 was shaped into a circular cone. The color of the
surface of the glass rod 106 was transparent.
[0140] FIG. 20 shows a configuration of a glass rod transportation
device 380. The glass rod transportation device 380 is used for
transporting the glass rod 106 generated by the first elongating
device 402. The glass rod 106 is held by the movable holding
element 245 and the fixed holding element 246 installed on the air
cylinder storage box 244. When the air cylinder (not shown in the
figure) provided inside the air cylinder storage box 244 is driven,
the movable holding element 245 moves toward the fixed holding
element 246 thereby holding the glass rod 106.
[0141] The force with which the movable holding element 245 pushes
the fixed holding element 246 can be modified by modifying the air
pressure which flows into the air cylinder. The air pressure of the
air cylinder can be modified by operating a switch during the
transportation of the glass rod 106. The switch is provided on the
operating switch box 248.
[0142] The present embodiment has a second level of pushing force
for pushing the movable holding element 245 to the fixed holding
element 246. This is achieved by adjusting the air pressure which
flows into the air cylinder to one of two possible levels. For
example, the weak side of the pushing force, which pushes the
movable holding element 245 to the fixed holding element 246, is
the first holding force, and the strong side of the pushing force
is second holding force. The first holding force is set to 0.5 kg,
and the second holding force is set to 80 kg.
[0143] The air pressure adjustment of the air cylinder does not
have to have only two levels of adjustment. The air pressure
adjustment can be a multiple level adjusting type which adjusts to
more than three levels of air pressure or the continuous adjustment
type that provides a gradual rather than stepped level change. A
rotary actuator 250 rotates the glass rod 106 from the vertical
condition to the horizontal condition by rotating the movable
holding element 245 and the fixed holding element 246 through the
air cylinder storage box 244. A holding flame 252 holds the glass
rod transportation device 380 by connecting the glass rod
transportation device 380 to the first elongating device 402. A
handle 254 is used for operating the glass rod transportation
device 380. A rotation axis 256 rotates the air cylinder storage
box 244.
[0144] FIG. 21 shows a storage container 224 of the first
elongating device 402. The storage container 224 has a saucer 260,
a strut 262, a pair of holding members 234a and 234b which hold the
glass rod 106, and a pair of holding members 236a and 236b which
are provided under the holding members 234a and 234b. The shapes of
the holding members 234a, 234b, 236a, and 236b are substantially
semicircle, which is desirable to securely hold the glass rod 106
inside the storage container 224. Together, each of the pair of
holding members 234a and 234b and holding members 236a and 236b
form circle shaped holding members.
[0145] One end of each of the holding members 234a and 234b and the
holding member 236a and 236b is pin connected to strut 262. The
other end of each is connected to the corresponding pair of holding
members by a pin 257 or a pin 258. The holding members 234a and
234b are connected by the pin 257, and the holding members 236a and
236b are connected by the pin 258. The height of the strut 262 is
1,550 mm. The inside diameter of the saucer 260 is 300 mm. Each of
the inside diameters of the holding members are 180 mm, formed by
the pair of holding members 234a and 234b and the pair of holding
members 236a and 236b.
[0146] In the case of receiving inside the storage container 224, a
glass rod 106 with an outside diameter of 80 mm, 4, the angle of
inclination .alpha. between the strut 262 and the glass rod 106 in
the front and rear direction can range from -3.1.degree. to
+8.1.degree.. The angle of inclination .beta. between the glass rod
106 and the strut 262 in the left and right directions can range
from -5.9.degree. to +5.9.degree. Here, The angle of inclination is
a limited value, and the glass rod 106 can be received inside the
storage container 224 in various angles within this limited value.
The glass rod 106 is in a various angles inside the storage
container 224.
[0147] FIG. 22 shows a movement of the glass rod transportation
device 380 when transporting the glass rod 106. The glass rod 106
inside of the storage container 224 is held by the movable holding
element 245 and fixed holding element 246 with the first holding
force (b). Then, the glass rod 106 is moved so that the glass rod
106 stands vertical to the ground within the holding member 234a
and 234b (C). Because the first holding force is very weak, the
movable holding element 245 will be opened when a force larger than
the first holding force is applied to the movable holding element
245 during movement of the glass rod 106. Moreover, the friction
force acted between the movable holding element 245 and glass rod
106 and between the fixed holding element 246 and glass rod 106 is
very small compared to the weight of the glass rod 106. Therefore,
glass rod cannot be lifted by raising the glass rod transportation
device 380, which holds the glass rod 106 by the first holding
force.
[0148] After confirming that the glass rod 106 stands vertical, the
holding force of the glass rod transportation device 380 is changed
to the second holding force (d). Following this, the pins 257 and
258 are removed, and each of the holding members 234a and 234b and
the holding member 236a and 236b are opened. Next, the glass rod
transportation device 380 takes the glass rod 106 out of the
storage container 224 for transportation. The glass rod 106 taken
from the storage container 224 is rotated to a horizontal position
and placed on the keeping place. During horizontal placement of the
glass rod 106 on the keeping place, air pressure larger than a
constant value is applied to the air cylinder to raise and lower
the glass rod transportation device 380. Therefore, the weight of
the glass rod transportation device 380 is not applied to the glass
rod 106 which prevents damage to the glass rod.
[0149] FIG. 23 shows an another embodiment of the glass rod
transportation device 380. The glass rod transportation device 380
of this embodiment has two rotation mechanisms A and B. Each of the
rotation mechanisms A and B has a rotary actuator. The rotation
mechanism A rotates the glass rod 106 by rotating a rotation axis
256 through the rotary actuator 250. The rotation mechanism B moves
the glass rod 106 up and down or left and right through the
coupling axis 266 by rotating a rotation axis 268 through the
rotary actuator 264. The rotation axis 268 lies at right angles to
the rotation axis 256 horizontally or vertically.
[0150] FIG. 24 shows the movement of the glass rod transportation
device 380 shown in FIG. 23 when the glass rod transportation
device 380 transports the glass rod 106. FIG. 24(a) shows a plan
view of the glass rod transportation device 380, which holds the
glass rod 106. FIG. 24(b) shows the cross sectional view of the
glass rod transportation device 380, which transports the glass rod
106 to the V block 240. As shown in FIG. 24(a), the movable holding
elements 245 and 246, which hold the glass rod 106 vertically, are
rotated from the vertical to horizontal position by operating the
rotary actuator 250. Next, as shown in FIG. 24(b), the movable
holding element 245 and the fixed holding element 246 are rotated
downward by activating the rotary actuator 264.
[0151] The direction of opening and closing of the movable holding
element 245 changes from a vertical direction to horizontal
direction by activating the rotary actuator 264. Therefore, the
movable holding element 245 and the fixed holding element 246 can
release upward after placing the glass rod 106 on the V block 240
by opening the movable holding element 245. By including not only
the rotation mechanism A, which rotates the glass rod 106 from a
vertical to horizontal position, but also the rotation mechanism B,
which has another rotation axis 268 that lies at right angles to
the rotation axis 256, the transportation efficiency of the glass
rod 106 is increased.
[0152] FIG. 25 shows a configuration of a glass rod second
elongating apparatus 111 of the present invention. The glass rod
second elongating apparatus 111 comprises a mounting 112, a fixed
chuck 118, a movable chuck 119, a heating source 122, a mass flow
controller 278, tail stocks 114 and 116, a tail stock driving motor
275, a tail stock driving encoder 273, a diameter measurement
device 124, a moving stand 120, a sliding screw 270, a moving stand
motor 274, a moving stand encoder 272, a chain 276, and a control
unit 280.
[0153] The fixed chuck 118 and the movable chuck 119 hold the glass
rod 106 which has been weld at both ends to a dummy rod 108. The
heating source 122 heats the glass rod 106, which is held by the
fixed chuck 118 and movable chuck 119. The mass flow controller 278
adjusts the amount of gas supplied to the heating source 122. The
tail stock 116 elongates the glass rod 106 by moving the movable
chuck 119. The tail stock driving motor 275 drives the tail stock
116. The tail stock driving encoder 273 detects the amount of the
rotation and controls the speed of the tail stock driving motor
275. The moving distance of the tail stock 116 can be assessed from
the amount of the rotation of the tail stock driving motor 275
detected by the tail stock driving encoder 273.
[0154] The diameter measurement device 124 measures the diameter of
the glass rod 106 corresponding to the position along the axial
direction of the glass rod 106. The heating source 122 and the
diameter measurement device 124 are provided on the moving stand
120. The moving stand 120 moves the heating source 122 and diameter
measurement device 124. The moving stand 120 is provided on the
mounting 112. The moving stand 120 can move along the sliding screw
270, which is installed parallel to the axis that connects the
fixed chuck 118 and movable chuck 119. The moving stand 120 is
driven by the moving stand motor 274 through the sliding screw 270
and the chain 276. The moving stand encoder 272 controls the speed
of the moving stand motor 274.
[0155] The control unit 280 controls the moving distance of the
heating source 122 by controlling the moving stand encoder 272, the
moving stand motor 274, the chain 276, the sliding screw 270 and
the moving stand 120. The control unit 280 controls the amount of
gas provided to the heating source 122 by controlling the mass flow
controller 278. The control unit 280 controls the moving speed of
the tail stock 116 by controlling the tail stock driving encoder
273 which controls the rotation speed of the tail stock driving
motor 275. The control unit 280 controls the elongating speed of
the glass rod 106 by controlling the moving speed of the tail stock
116.
[0156] The tail stock 114 and 116, fixed chuck 118, movable chuck
119, tail stock driving motor 275, and tail stock driving encoder
273 constitute an elongating unit which elongates the glass rod
106.
[0157] The data on the measured diameter and position of
measurement as measured by the diameter measurement device 124, and
the data on the changes in length of the glass rod 106 obtained
from the moving distance of the tail stock 116 are input to control
unit 280. The control unit 280 controls the heating condition based
on input data by controlling factors such as moving distance of the
heating source 122, the amount of gas provided to the heating
source 122, and also controls the elongation speed of the tail
stock 116 based on input data.
[0158] FIG. 26 shows a detailed flow chart of the glass rod second
elongating (S206) shown in FIG. 4. First, the dummy rods 108 are
held by the fixed chuck 118 and the movable chuck 119. Following
this, both ends of the glass rod 106 are welded to the dummy rods
108 (S146) so that the glass rod 106 is set on the glass rod second
elongating apparatus 111. Next, a cut 284 of 3 mm depth is made
around the connection of the glass rod 106 and the dummy rods 108
as a marker.
[0159] The starting and finishing position of the diameter
measurement of the glass rod 106 and the target diameter are then
set (S150). The diameter of the glass rod 106 is measured
corresponding to the location along the axial direction of the
glass rod 106 (S152). The elongating speed at a plurality of
locations along the axial direction of the glass rod 106 is set
based on the measured diameter and the location corresponding to
the measured diameter. The heating conditions including the amount
of gas supplied to the heating source 122 and the moving distance
of the heating source 122 are set based on the average value of the
diameter of the glass rod (S153). The glass rod 106 is heated by
the heating source 122 with a preset heating condition and
elongated gradually by the tail stock 116, which moves with a
preset elongating speed (S154).
[0160] The location of the cut 284, which is provided around the
connection of the glass rod 106 and the dummy rods 108, are then
detected by the diameter measurement device 124 in order to detect
the location of both ends of the glass rod 106. The moving distance
of the tail stock 116 is measured by the tail stock driving encoder
273 in order to measure changes in the length of the glass rod 106
along the axial direction.
[0161] The diameter of the glass rod 106 is then measured at a
position approximately 50 mm away from the cut 284 towards the
center of the glass rod 106 (S156). The heating position of the
heating source 122 is set based on the position of the cut 284 and
the changes in length of the glass rod 106 along the axial
direction. The amount of gas supplied to the heating source 122 is
set based on the measured diameter. The moving speed of the tail
stock 116 is also set based on the measured diameter (S157). The
glass rod 106 is end-drawn which heats and elongates the glass rod
106 with a preset heating condition and elongating speed. The shape
of the end of the glass rod 106 therefore becomes similar to a
circular cone shape so that the diameter of end of the glass rod
106 reduced (S158).
[0162] The position of the end-drawn part is theft detected by
measuring the diameter of the end-drawn part and the part elongated
by the end drawing at the corresponding position. These
measurements are undertaken by the diameter measurement device 124.
The change in length of the glass rod 106 along the axial direction
resulting from end drawing is measured by the tail stock driving
encoder 273 (S160). The starting and finishing position of the fire
polishing, which polishes the glass rod 106 with fire, and the
heating power of the fire are then set. This setting is based on
the detected position of the end-drawn part and the change in
length of the glass rod 106 along the axial direction (S161).
[0163] The position of starting and finishing the fire polishing is
set based on the position of the cloud on the glass rod 106. A
cloud is generated in a region that is heated strongly during the
end drawing process. The glass rod 106 is fire polished by the
heating source 122 as per the preset fire condition from the set
fire polishing starting position to the set fire polish finishing
position (S162). After fire polishing, the shape of the glass rod
106 is checked by measuring the finished diameter and length of the
glass rod 106 (S164). The dummy rod 108 is then removed from the
glass rod 106 (S166). Finally, the glass rod 106 is surface treated
to produce a preform 107 (S168).
[0164] As shown above, before each elongating (S154), end drawing
(S158) and fire polishing (S162) process, the diameter is measured
in the corresponding location along the axial direction of the
glass rod 106. From this data, the heating condition and elongating
speed for the next process can be accurately set. Therefore, a
glass rod 106 of consistently high quality can be manufactured.
[0165] FIG. 27 shows an example which provides a cooling device 330
on the fixed chuck 118 and the movable chuck 119 of the glass rod
second elongating apparatus 111. The cooling device 330 protects
the fixed chuck 118 and movable chuck 119 from the radiant heat
generated from the heating source 122. This is achieved by
circulating cooling water around the fixed chuck 118 and the
movable chuck 119. The cooling device 330 uses a gas or liquid as a
cooling medium.
[0166] The deformation of the fixed chuck 118 and the movable chuck
119 can be controlled by providing the cooling device 330 on the
fixed chuck 118 and the movable chuck 119. This allows control of
the degree of temperature rise of the fixed chuck 118 and the
movable chuck 119. Therefore, the accuracy of transfer of the
driving force that rotates the glass rod 106 is maintained, and the
heating of the glass rod 106 becomes more even. Therefore,
fluctuation of the diameter of the glass rod 106 decreases.
(EXAMPLE)
[0167] A glass rod 106 of 50 mm diameter and 1000 mm length was
fire polished by a fixed chuck 118 and movable chuck 119 that has a
cooling device 330 and a heating source 122 shown in FIG. 27.
Oxygen (O.sub.2) of 150 SLM and hydrogen (H.sub.2) of 300 SLM are
supplied to the heating source 122 as combustion gas. The glass rod
106 is rotated at a speed of 15 rpm. The glass rod 106 is fire
polished by moving the heating source 122 relative to the glass rod
106 at a speed of approximately 20 mm/min.
[0168] FIG. 28 shows the temperature of the fixed chuck 118 and
movable chuck 119 of the above example and the comparative example
shown below. The vertical axis shows the temperature of the fixed
chuck 118 and movable chuck 119, and the horizontal axis shows the
processing time of the fire polishing. The temperature of the fixed
chuck 118 and movable chuck 119 of the example was maintained at a
low temperature of about 45.degree. C. The resultant fluctuation of
the driving force that rotates the glass rod 106 caused by the
deformation of the fixed chuck 118 and movable chuck 119 was small.
Therefore the fluctuation of the diameter of the fire polished
glass rod 106 was only 0.02%.
COMPARATIVE EXAMPLE
[0169] The glass rod 106 was fire polished under the same
conditions as the above example except for the removal of the
cooling device 330 from the fixed chuck 118 and movable chuck 119
shown in FIG. 27. As shown in FIG. 28, the temperature of the fixed
chuck 118 and movable chuck 119 reached approximately 100.degree.
C. The fixed chuck 118 and movable chuck 119 were deformed as a
result, so the driving force that rotates the glass rod 106
fluctuates. The fluctuation of the diameter of the glass rod 106
after fire polishing increased to 1.0%, which is larger than the
degree of fluctuation of the above example.
[0170] FIG. 29 shows a relationship between the distance between
the heating source 122 and the diameter measurement device 124 and
the percentage of the fluctuation of the diameter of the glass rod
106. The fluctuation rate (%) of the diameter of the glass rod 106
represents the (maximum value of the diameter of the glass rod
106-minimum value of the diameter of the glass rod 106)/(average
diameter).times.100.
[0171] The diameter measurement device 124 of the glass rod second
elongating apparatus 111 shown in FIG. 25 is provided on a location
which is a constant distance, from 10 mm to 50 mm, away from the
heating source 122. Therefore, the diameter of the glass rod 106
can be accurately measured allowing accurate control of the
diameter of the glass rod 106.
[0172] When elongating the glass rod 106, the position of highest
temperature in the glass rod 106 is slightly different to the
position that the heating source 122 is heating because the heating
source 122 is moving. The elongating speed per unit length becomes
largest at the location where the temperature of the glass rod 106
is highest.
[0173] It is desirable to control the heating power of the heating
source 122 and the moving speed of the movable chuck 119 based on
the diameter at the position of the largest elongating speed and
the target value of the diameter. The moving speed of the movable
chuck 119 is controlled based on the difference between the target
value of the diameter and the diameter that is measured at the
position that the elongating speed of the glass rod 106 is largest.
This can be done by providing the diameter measurement device 124
on a position that is a constant distance away from the heating
source 122.
[0174] The position, which is a constant distance away from the
heating source 122, ranges from 10 mm to 50 mm away from the
position where the heating source 122 is provided in the opposite
direction to the moving direction of the heating source 122.
Therefore, the diameter measurement device 124 is provided on a
position 10 mm to 50 mm away from the heating source 122 in the
opposite direction of the moving direction of the heating source
122.
[0175] If the heating source 122 used to heat the glass rod 106 is
an oxygen hydrogen burner, the flow rate of the hydrogen gas
supplied to the heating source 122 is set from 30 liters/minute to
500 liters/minute. The ratio of the flow rate of the hydrogen gas
to the oxygen gas is set from 1.5 to 3.0. The moving speed of the
heating source 122 is controlled within the limits of 2 mm/minute
and 65 mm/minute. The heat quantity will be insufficient if the
flow rate of the hydrogen gas is less than 30 liters/minute, and
the fuel will be wasted if the flow rate of the hydrogen gas is
more than 500 liters/minute. It is difficult to elongate the glass
rod 106 if the ratio of the flow rate of the hydrogen gas to the
oxygen gas is out of the range shown above because the heat
quantity becomes insufficient.
[0176] If the heating source 122 to heat the glass rod 106 is a
propane gas burner, the flow rate of the propane gas supplied to
the heating source 122 is set from 1 liter/minute to 15
liters/minute. The ratio of the flow rate of the propane gas to the
oxygen gas is set from 0.1 to 0.3. The moving speed of the heating
source 122 is controlled within the limits of 2 mm/minute and 65
mm/minute. The heat quantity will be insufficient if the flow rate
of the propane gas is less than 1 liter/minute, and the fuel will
be wasted if the flow rate of the propane gas is more than 15
liters/minute. Furthermore, it is difficult to elongate the glass
rod 106 if the ratio of the flow rates of the propane gas to oxygen
gas is out of the range shown above because the heat quantity
becomes insufficient. The moving speed of the heating source 122
would preferably be controlled within the limit of 2 mm/minute and
65 mm/minute. It takes too much time elongating the glass rod 106
if the moving speed of the heating source 122 is below 2 mm/minute.
Alternatively, it is difficult to elongate the glass rod 106 if the
moving speed of the heating source 122 is more than 65 mm/minute
because the speed is too fast to heat the glass rod 106 to its
core.
Example 1
[0177] The elongation of the glass rod 106 was begun by setting the
distance between the heating source 122 and the diameter
measurement device 124 as 15 mm. During the elongation of the glass
rod 106, the moving speed of the heating source 122 and the tail
stock 116 were controlled based on the difference between the
measured diameter of the glass rod 106 and the target diameter. The
burning conditions of the heating source 122 were set including the
flow rate of the hydrogen gas at 224 liters/minute, the ratio of
the flow rate of the hydrogen to oxygen as 2.5, and the moving
speed of the heating source 122 as 11 mm/minute. The fluctuation
rate of the diameter of the glass rod 106 after the elongating
process was 0.9%.
Example 2
[0178] The distance between the heating source 122 and the diameter
measurement device 124 was set to 40 mm. The flow rate of the
hydrogen gas was set to 199 liters/minute. The ratio of the flow
rate of the hydrogen to oxygen was set to 2.5. The moving speed of
the heating source 122 was set to 13 mm/minute. The fluctuation
rate of the diameter of the glass rod 106 after the elongating
process was 0.6%.
Comparative Example 1
[0179] The distance between the heating source 122 and the diameter
measurement device 124 was set to 5 mm. The flow rate of the
hydrogen gas was set to 209 liters/minute. The ratio of the flow
rate of the hydrogen to oxygen was set to 2.5. The moving speed of
the heating source 122 was set to 12 mm/minute. Because the
distance between the heating source 122 and the diameter
measurement device 124 was too close, the fluctuation rate of the
diameter of the glass rod 106 after the elongating process was
3.7%. This is larger than the fluctuation rate of example 1 and
example 2 above.
Comparative Example 2
[0180] The distance between the heating source 122 and the diameter
measurement device 124 was set to 60 mm. The flow rate of the
hydrogen gas was set to 237 liters/minute. The ratio of the flow
rate of the hydrogen to oxygen was set to 2.5. The moving speed of
the heating source 122 was set to 10 mm/minute. Because the
distance between the heating source 122 and the diameter
measurement device 124 was too far, the fluctuation rate of the
diameter of the glass rod 106 after the elongating process was
2.5%. This fluctuation rate is larger than the fluctuation rate of
example 1 and example 2 above.
Comparative Example 3
[0181] The distance between the heating source 122 and the diameter
measurement device 124 was set to 15 mm. The flow rate of the
hydrogen gas was set to 215 liters/minute. The ratio of the flow
rate of the hydrogen to oxygen was set to 1.0. The moving speed of
the heating source 122 was set to 12 mm/minute. Because the ratio
of the flow rate of the hydrogen to oxygen was 1.0, which was
smaller than the recommended 1.5 minimum, the glass rod 106 could
not be elongated.
Comparative Example 4
[0182] The distance between the heating source 122 and the diameter
measurement device 124 was set to 15 mm. The flow rate of the
hydrogen gas was set to 195 liters/minute. The ratio of the flow
rate of the hydrogen to oxygen was set to 4.0. The moving speed of
the heating source 122 was set to 13 mm/minute. Because the ratio
of the flow rate of the hydrogen to oxygen was 4.0, which was
larger than the recommended 3.0 maximum, the glass rod 106 could
not be elongated.
Comparative Example 5
[0183] The distance between the heating source 122 and the diameter
measurement device 124 was set to 15 mm. The flow rate of the
hydrogen gas was set to 204 liters/minute. The ratio of the flow
rate of the hydrogen to oxygen was set to 2.5. The moving speed of
the heating source 122 was set to 70 mm/minute. Because the moving
speed of the heating source 122 was 70 mm/minute, which was larger
than the 65 mm/minute recommended maximum speed, the glass rod 106
could not be elongated.
[0184] FIG. 30 shows a glass rod second elongating apparatus 111
which has a configuration providing a tensile stress measurement
device 282 on the glass rod second elongating apparatus 111 shown
in FIG. 25. The glass rod second elongating apparatus 111 has a
tensile stress measurement device 282, which measures the tensile
stress applied to the glass rod 106, on the movable chuck 119.
[0185] The glass rod second elongating apparatus 111 can detect the
position of the heating source 122 on the moving stand 120 using
the moving stand encoder 272. The tensile stress measurement device
282 is connected to a control unit 280. The control unit 280
controls the moving speed of the tail stock 116 based on the
tensile stress of the glass rod 106, provided from the tensile
stress measurement device 282. This is undertaken until the moving
distance of the heating source 122 reaches a prescribed
distance.
[0186] FIG. 31 shows a detailed flow chart of the elongating (S154)
shown in the FIG. 26. First, the glass rod 106 is pre-heated until
the prescribed region of the glass rod 106 is melted and softened
by the heating source 122. This will allow elongation of the glass
rod 106 (s132). Next, the heating source 122, which is provided on
the moving stand 120, is moved via the moving stand 120. The moving
speed of the heating source 122 would ideally be as slow as
possible at the early stage of the elongation so that the
fluctuation of the diameter of the glass rod 106 can be reduced.
The movement of the heating source 122 would also be a constant
speed. The amount of gas supplied to the heating source 122 can be
constant.
[0187] Next, the moving speed of the tail stock 116 is controlled
so that the tensile stress of the glass rod 106 measured by the
tensile stress measurement device 282 lies within substantially 80%
to 110% of the average value of the tensile stress at the steady
state (S136). The steady state will be explained below. The moving
speed of the tail stock 116, which was originally set based on the
diameter at a plurality of locations of the glass rod 106 along the
axial direction, is re-set based on the tensile stress of the glass
rod 106. The glass rod 106 is elongated by the tensile stress load
shown above until the heating source moves substantially 50 mm to
150 mm (S138).
[0188] If the control unit 280 detects that the heating source 122
has moved substantially from 50 mm to 150 mm (S138), the moving
speed of the tail stock 116 changes to the speed at the steady
state, which will be explained below. This is done by controlling
the tail stock driving encoder 273 (S140). The diameter measurement
device 124 measures the diameter of the glass rod 106 during the
elongation of the glass rod 106 (S142). The elongation of the glass
rod 106 is finished when the glass rod 106 is elongated to the
desired diameter and length (S144).
[0189] The speed at the steady state is the speed where the
material balance before the elongation and after the elongation is
balanced. Here, the original diameter of the glass rod 106 before
the elongation is represented as D.sub.1, the target diameter to be
obtained as D.sub.2, the moving speed of the heating source 122 as
V.sub.1, and the speed of the elongation of the glass rod 106 as
V.sub.2.
[0190] For example, assume that the elongation takes place only at
the region heated at that time, so the region heated and elongated
is quite small. The V.sub.2 is equal to the speed at the steady
state when the following equation is valid.
D.sub.1.sup.2V.sub.1=D.sub.2.sup.2(V.sub.1+V.sub.2)
[0191] Therefore, the V.sub.2 can be set by adjusting the V.sub.1
and the moving speed of the tail stock 116 based on the D.sub.1 and
the D.sub.2. The tensile stress of the glass rod 106 at the steady
state is the tensile stress when the glass rod 106 is elongated
with the tail stock 116 moving speed at the steady state.
[0192] FIG. 32 shows a process where the diameter fluctuates during
the elongation of the glass rod 106. The glass rod 106 softens when
heated. As shown in FIG. 32(1), it may happen that the glass rod
106 cannot be softened enough by the pre-heating only to be
elongated. The tensile stress generated on the glass rod 106
increases from twice to triple the normal tensile stress when the
heating source 122 and the tail stock 116 start to move at the
prescribed speed. Then, the region which is pre-heated is elongated
rapidly, and the diameter of the pre-heated region is reduced as
shown in shaded portion of FIG. 32(2). The elongation of the glass
rod 106 occurs almost entirely in the pre-heated region, and the
region which is heated newly by the heating source 122, is less
elongated. Therefore, necking of the diameter has occurred on the
glass rod 106 as shown in FIG. 32(3).
[0193] The fluctuation of the diameter of the glass rod 106 tends
to occur at the region from the starting place of the elongation of
the glass rod 106 to the place 50 mm away from the starting place.
If the elongation is progressed further than this place, the speed
of providing the heat to the glass rod 106, the speed that the
glass rod 106 softens, and the elongation speed of the glass rod
106 are balanced to be a steady state. Therefore, the fluctuation
of the diameter of the glass rod 106 will not occur as shown in
FIG. 32(4).
[0194] The glass rod 106 is elongated by controlling the moving
speed of the tail stock 116. The aim is to keep the tensile stress
of the glass rod 106 at the early stage of the elongation at
substantially 110% or less of the average value of the tensile
tension at the steady state. The fluctuation of the diameter at the
early stage of the elongation of the glass rod 106 can thus be
decreased. This is because the heat supply to the glass rod 106,
the soften speed of the glass rod 106, and the elongation speed of
the glass rod 106 can be balanced.
[0195] If the tensile stress of the glass rod 106 at the early
stage is lower than 80% of the steady state, the distance required
for the diameter of the glass rod 106 to reach the target value
becomes long. Therefore, the region of the elongated glass rod 106
that can be used as product becomes short. This decreases the yield
factor of the process and increases the time taken for the glass
rod 106 to reach the target diameter. Therefore, it is desirable to
control the tensile stress of the glass rod 106 at the early stage
of the elongation in the range of substantially from 80% to 110% of
the average value of the tensile stress at the steady state.
[0196] FIG. 33 shows a glass rod 106 that is elongated according to
the elongating (S154) shown in FIG. 31. First, as shown in FIG.
33(1) and (2), the heating source 122 and the tail stock 116 start
to move after the pre-heating of the glass rod 106 to start the
elongation of the glass rod 106. Because the tensile stress of the
glass rod 106 is controlled to be 110 or less of the tensile stress
at the steady state, excessive tensile stress is not applied to the
glass rod 106. No necking therefore occurs on the glass rod 106 due
to rapid elongation. If the heating source 122 moves the prescribed
distance under this balanced condition, the heat supplied to the
glass rod 106, the soften speed of the glass rod 106, and the
elongation speed of the glass rod 106 are balanced. Thus the
fluctuation of the diameter of the glass rod 106 can be
prevented.
[0197] Fluctuation of the diameter may occur if the moving speed of
the tail stock 116 continues to be controlled based on the tensile
stress. The tensile stress of the glass rod 106 will change with
small changes in the heat quantity provided by the heating source
122. The moving speed of the tail stock 116 then fluctuates to
maintain the tensile stress of the glass rod 106 at a constant,
resulting in fluctuation of the diameter of the elongated glass rod
106. Therefore, fluctuations in the diameter of the glass rod 106
caused by subtle fluctuations of the tensile stress can be
prevented by changing the moving speed of the tail stock 116 to the
speed at the steady state after the heating source 122 moves a
prescribed distance on commencement of elongation.
[0198] The change in moving speed of the tail stock 116 to the
speed of the steady state is made when the heating source 122 has
moved substantially from 50 mm to 150 mm from the point of the
start of the elongation. Until the heating source 122 moves 50 mm
from the point of commencement of elongation, the heat supplied to
the glass rod 106, the soften speed of the glass rod 106, and the
elongation speed of the glass rod 106 are not balanced. The result
is, necking of the glass rod 106 will occur due to the fluctuation
of the diameter if the elongation speed is changed to the speed of
the steady state before the heating source 122 has moved 50 mm. The
tensile stress of the glass rod 106 should thus be controlled to be
substantially 110% or less of the steady state until the heating
source 122 moves substantially 50 mm. It is desirable to change the
moving speed of the tail stock 116 to the speed of the steady state
before the heating source 122 moves more than substantially 150
mm.
EXAMPLE
[0199] The glass rod 106 was elongated by the glass rod second
elongating apparatus 111. The glass rod 106 had an outside diameter
of 65 mm and length of 980 mm. The dummy rods 108, which had
outside diameters of 60 mm and lengths of 250 mm, were welded on
both ends of the glass rod 106. The rotation speed around the axis
during the welding of the glass rod 106 and the dummy rod 108 was
30 rpm. An oxygen hydrogen burner was used for the heating source
122. The oxygen gas and hydrogen gas provided to the heating source
122 was 96 liters/minute and 240 liters/minute respectively.
[0200] After pre-heating of the glass rod 106, the elongation of
the glass rod was started by moving the heating source 122 at a
moving speed of 12.4 mm/min. When elongating the glass rod 106 to
reduce the diameter of the glass rod 106 from 65 mm to 50 mm, the
tensile stress at the steady state was about 100 kgf/cm.sup.2, and
the moving speed of the tail stock 116 at the steady state was 8.6
mm/min. The moving speed of the tail stock 116 was controlled so
that the tensile stress did not exceed 110 kgf/cm.sup.2 until the
heating source 122 had moved 100 mm from the starting point of the
elongation. After the heating source 122 moved 100 mm, the glass
rod 106 was elongated by controlling the moving speed of the tail
stock 116 to 8.6 mm/min, which is the speed at the steady
state.
[0201] FIG. 34 shows the tensile stress of the glass rod 106 at the
early stage of the elongation of the example. The vertical axis
shows the tensile stress generated in the glass rod 106 and the
horizontal axis shows the moving distance of the heating source 122
after the start of elongation. The tensile stress of the glass rod
106 was 110 kgf/cm.sup.2 or less at the early stage of the
elongation while the heating source 122 moved forward 100 mm.
[0202] FIG. 36 shows the fluctuation of the diameter of the glass
rod 106 after the elongation of the glass rod 106. The vertical
axis shows the distance along the radiant direction of the glass
rod 106, and the horizontal axis shows the distance along the
longitudinal direction of the glass rod 106. The glass rod 106
elongated by the method according to the example had few diameter
fluctuations such as necking, and the diameter of the glass rod 106
could be reduced to the target diameter at about 100 mm of the
longitudinal distance after the elongation started. The accuracy of
the diameter of the glass rod 106 at the region which was elongated
at the speed of the steady state by the method according to the
example was about the same accuracy as the diameter of the glass
rod 106 which was elongated by the conventional elongating
method.
COMPARATIVE EXAMPLE
[0203] A glass rod 106 with a diameter of 65 mm was elongated to a
diameter of 50 mm. The conditions of the moving speed and the
amount of gas to the heating source 122 were the same as the above
example. The glass rod 106 was elongated by controlling the moving
speed of the tail stock 116 to 8.6 mm/min from the start of the
elongation. This is the speed at the steady state.
[0204] FIG. 35 shows a fluctuation of the tensile stress of the
glass rod 106 at the early stage of the elongation of the
comparative example. The vertical axis shows the tensile stress
generated in the glass rod 106, and the horizontal axis shows the
moving distance of the heating source 122 after commencement of
elongation. The tensile stress of the glass rod 106 increased to
300 kgf/cm.sup.2 at the early stage of the elongating, which is 3
times greater than the tensile stress of the steady state. This
occurred whilst the heating source 122 was moving the initial 100
mm.
[0205] As shown in FIG. 36, the glass rod 106 after the elongation
of the comparative example had large necking at about 100 mm from
the start of the elongation. Because the undulation continues until
about 300 mm from the start of the elongation, this region cannot
be used as product, and the yield rates decreased.
[0206] FIG. 37 shows a detailed flowchart of the end drawing (S158)
shown in FIG. 26. First, the position, of the glass rod 106 which
has been end-drawn is detected (S169). Next, the prescribed region
of the glass rod 106 is pre-heated by the flame of the heating
source 122 (S170) until the prescribed region nearly softens. Then,
the glass rod 106 is elongated by heating the prescribed region of
the glass rod 106 with the heating source 122 and moving the tail
stock 116 so that the diameter of the prescribed region is reduced
(S172).
[0207] The heating source 122 is moved from the center of the
prescribed region to a region towards the middle side of the glass
rod 106. Then, the heating source 122 heats the glass rod 106
secondly (S174) with a flame. The thickness of this flame is
smaller than the thickness of the flame of the pre-heating (S170).
The prescribed region of the glass rod 106 is further elongated by
moving the tail stock 116 so that the diameter of the prescribed
region is reduced (S176). Then, the prescribed region of the glass
rod 106 is fused by the flame. Again the thickness of this flame is
smaller than the thickness of the flame of the pre-heating
(S170).
[0208] FIG. 38 shows a cut 284 that is provided as a mark on the
connection between the glass rod 106 and the dummy rod 108. This
allows the detection of the position of the end drawing at the end
drawing position detecting (S169) shown in FIG. 37. A mark is
provided on the connection between the glass rod 106 and the dummy
rod 108. The device that recognizes the mark is installed on the
glass rod second elongating apparatus 111 to detect the location of
the mark.
[0209] The position of the start of the end drawing process is set
based on the detected mark location. The elongation process of the
glass rod 106 finishes at the set end drawing starting position,
and the end drawing process of the glass rod 106 starts at the same
time. The method shown in FIG. 38 is used when the device that
recognizes the mark is a device that measures the diameter. An
example of such a device would be a diameter measurement device
124.
[0210] FIG. 39 shows a fluorescent paint 287 that is applied on the
connection between the glass rod 106 and the dummy rod 108 as
another example of a mark. The method shown in FIG. 39 is used when
the device that recognizes the mark is an image processing
apparatus.
[0211] FIG. 40 shows the glass rod second elongating apparatus 111
that detects the cut 284 at end drawing position detecting (S169).
First, the dummy rod 108 is welded on both ends of the glass rod
106. The glass rod 106, which has the dummy rod 108 on both sides,
is fixed on the fixed chuck 118 and movable chuck 119, not shown in
the figure. The cut 284 having depth of 3 mm is provided all around
the welded position. The welded position results from the
connection between the glass rod 106 and the dummy rod 108.
[0212] During the elongation of the glass rod 106, the diameter
measurement device 124 measures the diameter of the glass rod 106.
When the diameter measurement device 124 detects the position of
the cut 284 by detecting a change in diameter of the glass rod 106,
the glass rod second elongating apparatus 111 starts the end
drawing. The position of commencement of the end drawing is
slightly towards the middle direction of the glass rod 106 from the
connection between the glass rod 106 and the dummy rod 108. Also,
the position of commencement of the end drawing does not have a
bubble or bubbles with a diameter of 0.3 mm or above. Then, the
process is shifted from elongation to end drawing.
[0213] When a mark is the marking 287, fluorescent paint is applied
on the connection between the glass rod 106 and the dummy rod 108.
The camera of the image processing apparatus, which can detect the
fluorescent paint, is installed on the position of the diameter
measurement device 124, which is provided on the moving stand 120.
The camera processes the picture of the glass rod 106 during the
elongation of the glass rod 106. If the camera detects the
fluorescent paint, the glass rod second elongating apparatus 111
starts the end drawing. The position of commencement of the end
drawing is slightly towards the middle direction of the glass rod
106 from the connection between the glass rod 106 and the dummy rod
108. Also, the position of starting the end drawing does not have a
bubble or bubbles with a diameter of 0.3 mm or above. Then, the
process is shifted from elongation to end drawing.
[0214] FIG. 41 shows the movements of the heating source 122 and
the tail stock 116 after detecting the position of the end drawing
(S169) during the end drawing process of the glass rod 106 shown in
flow chart of FIG. 37. At the pre-heating for end drawing (S170),
the flame of the heating source 122 heats the glass rod 106 at the
prescribed region until the glass rod 106 nearly softens. At
elongating for end drawing (S172), the heating source 122 heats the
prescribed region of the glass rod 106, and the tail stock 116
elongates the prescribed region of the glass rod 106. This
therefore reduces the diameter of the prescribed region.
[0215] At second heating (S174), the tail stock 116 stops, and the
heating source 122 moves in the direction towards the middle side
of the region of the glass rod 106 (to the left in the figure),
from the center of the prescribed region. Then, the heating source
122 heats the glass rod 106 by flame, the thickness of which is
smaller than the thickness of the flame of the pre-heating (S170).
At the second elongating for end drawing (S176), the heating source
122 moves further to the left side in the figure and heats the
glass rod 106. The tail stock 116 also moves to elongate the
prescribed region of the glass rod 106. At fusing for end drawing
(S178), the heating source 122 heats the glass rod 106 by flame,
the thickness of which is smaller than the thickness of the flame
of the pre-heating (S170). The position of the heating source 122
is at the same position as the second elongating for end drawing
(S176). The tail stock 116 moves to fuse the glass rod 106.
[0216] FIG. 42 shows an example of the settings of another method
of the end drawing process at the end drawing (S158) shown in FIG.
37. This method controls the gas amount, the moving distance of the
heating source 122, and the moving speed of the tail stock 116
based on the progress time of the end drawing process of the glass
rod 106.
[0217] The gas amount, the moving distance of the heating source
122, and the moving speed of the tail stock 116 are set once. This
setting is based on the location of the cut 284, the changes of the
length and the diameter of the glass rod 106 along the axial
direction at the second heating condition and elongating speed
setting (S157). The glass rod second elongating apparatus 111 then
resets the gas amount, the moving distance of the heating source
122, and the moving speed of the tail stock 116 based on the
progress time of the end drawing process of the glass rod 106 at
the end drawing (S158).
[0218] For example, at the pre-heating for the end drawing (S170),
which is undertaken for 300 seconds, the moving distance of the
heating source 122 is set to 0 mm. The moving speed of the tail
stock 116 is set to 0 mm/minute. The amount of hydrogen (H.sub.2)
gas for the heating source 122 is set to 250 cc/minute. The amount
oxygen (O.sub.2) gas (inside) that is output from the inside nozzle
of the heating source 122 is set to 30 cc/minute. The amount of
oxygen (O.sub.2) gas (outside) that is output from the outside
nozzle of the heating source 122 is set to 100 cc/minute. The glass
rod 106 is heated by the heating source 122, which is set according
to the above conditions.
[0219] At the elongating for end drawing (S172), which is
undertaken for 60 seconds, the amount of hydrogen (H.sub.2) gas for
the heating source 122 is set to 250 cc/minute. The amount of the
oxygen (O.sub.2) gas (inside) that is output from the inside nozzle
of the heating source 122 is set to 30 cc/minute. The amount of
oxygen (O.sub.2) gas (outside) that is output from the outside
nozzle of the heating source 122 is set to 100 cc/minute. The glass
rod 106 is heated by the heating source 122, which is set according
to the above conditions. With the moving distance of the heating
source 122 at 0 mm, the tail stock 116 is moved at the speed of 10
mm/minute to elongate the glass rod 106.
[0220] At the second heating (S174), which is undertaken for 20
seconds, the moving speed of the tail stock 116 is set to 0
mm/minute. The moving distance of the heating source 122 is set to
15 mm. The amount of hydrogen (H.sub.2) gas for the heating source
122 is set to 130 cc/minute. The amount of oxygen (O.sub.2) gas
(inside) that is output from the inside nozzle of the heating
source 122 is set to 15 cc/minute. The amount oxygen (O.sub.2) gas
(outside) that is output from the outside nozzle of the heating
source 122 is set to 50 cc/minute. The glass rod 106 is heated by
the heating source 122, which is set according to the above
conditions.
[0221] At the second elongating for end drawing (S176), which is
undertaken for 180 seconds, the moving distance of the heating
source 122 is increased from 15 mm to 25 mm. The amount of hydrogen
(H.sub.2) gas for the heating source 122 is set to 130 cc/minute.
The amount oxygen (O.sub.2) gas (inside) that is output from the
inside nozzle of the heating source 122 is set to 15 cc/minute. The
amount of oxygen (O.sub.2) gas (outside) that is output from the
outside nozzle of the heating source 122 is set to 50 cc/minute.
The glass rod 106 is heated by the heating source 122, which is set
according to the above conditions. The tail stock 116 is moved at a
speed of 10 mm/minute to elongate the glass rod 106.
[0222] Finally, at the fusing for end drawing (S178), which is
undertaken for 30 seconds, the heating source 122 does not move
from the position at the second elongating for end drawing (S176),
so the moving distance remains at 25 mm. The amount of hydrogen
(H.sub.2) gas for the heating source 122 is set to 130 cc/minute.
The amount of oxygen (O.sub.2) gas (inside) that is output from the
inside nozzle of the heating source 122 is set to 30 cc/minute. The
amount oxygen (O.sub.2) gas (outside) that is output from the
outside nozzle of the heating source 122 is set to 20 cc/minute.
The glass rod 106 is heated by the heating source 122, which is set
according to the above conditions. The tail stock 116 is moved at a
speed of 120 mm/minute to fuse the glass rod 106.
[0223] The glass rod 106 with a diameter of 60 mm was end-drawn by
the glass rod second elongating apparatus 111 according to the
setting condition shown in FIG. 42. The shape of the preform at the
region that was end-drawn, was a well formed circular cone shape.
The length and the diameter of the region were 61 mm and 60 mm
respectively. The time that was required for the end drawing
process was 12 minutes.
[0224] FIG. 43 shows another example of the settings of other
method of the end drawing process at the end drawing (S158) shown
in FIG. 37. This method controls the gas amount, the moving speed
of the heating source 122, and the moving speed of the tail stock
116 based on the moving distance of the tail stock 116.
[0225] The glass rod second elongating apparatus 111 detects the
moving distance of the tail stock 116. The moving distance of the
heating source 122, and the moving speed of the tail stock 116 are
set once based on the location of the cut 284, the change of the
length of the glass rod 106 along the axial direction, and the
diameter of the glass rod 106 at the second heating condition and
elongating speed setting (S157). The glass rod second elongating
apparatus 111 resets the gas amount, the moving distance of the
heating source 122, and the moving speed of the tail stock 116
based on the detected moving distance of the tail stock 116 at the
end drawing (S158).
[0226] There is a case where the moving distance of the tail stock
cannot be measured because the tail stock does not move. This might
occur from lack of power of the tail stock driving motor 275 when
the glass rod 106 is not heated sufficiently during the end drawing
process. When the output of the tail stock driving motor 275 is not
large enough, the AC servomotor, which can detect the torque of the
output shaft, can be used for driving the tail stock 116. A
threshold value can be set for the torque generated in the tail
stock driving motor 275. When the torque exceeds the threshold
value, the glass rod second elongating apparatus 111 can judge that
the heating is insufficient. Then, the glass rod second elongating
apparatus 111 can stop the driving of the tail stock 116 for a
period of time and increase the gas amount supplied to the heating
source 122.
[0227] The settings shown in FIG. 43 are the same as the settings
shown in FIG. 42 except that the "Progress Time" setting changes to
the "Tail Stock 116 Moving Distance" setting. The end drawing
method shown in FIG. 43 also has the processes of pre-heating for
end drawing (S170), elongating for end drawing (S172), the second
heating (S174), second elongating for end drawing (S176), and
fusing for end drawing (S178). The gas amount and moving distance
of the heating source 122, and the moving speed of the tail stock
116 are set based on the moving distance of the tail stock 116 at
each stage of the process.
[0228] For example, at the pre-heating for the end drawing (S170),
because the moving speed of the tail stock 116 is set to 0
mm/minute, the time after the commencement of the pre-heating for
end drawing is measured for 300 seconds. That is, for 300 seconds
the moving distance of the heating source 122 is set to 0 mm. The
amount hydrogen (H.sub.2) gas for the heating source 122 is set to
250 cc/minute. The amount of oxygen (O.sub.2) gas (inside) that is
output from the inside nozzle of the heating source 122 is set to
30 cc/minute. The amount of oxygen (O.sub.2) gas (outside) that is
output from the outside nozzle of the heating source 122 is set to
100 cc/minute. The glass rod 106 is heated by the heating source
122, which is set according to the above conditions. When the time
after the commencement of the pre-heating for end drawing passes
300 seconds, the process is shifted to next step.
[0229] At the elongating for end drawing (S172), whilst the moving
distance is changed from 0 mm to 30 mm, the amount hydrogen
(H.sub.2) gas for the heating source 122 is set to 250 cc/minute.
The amount of oxygen (O.sub.2) gas (inside) that is output from the
inside nozzle of the heating source 122 is set to 30 cc/minute. The
amount oxygen (O.sub.2) gas (outside) that is output from the
outside nozzle of the heating source 122 is set to 100 cc/minute.
The glass rod 106 is heated by the heating source 122, which is set
according to the above conditions. With the moving distance of the
heating source 122 as 0 mm, the tail stock 116 is moved at a speed
of 10 mm/minute to elongate the glass rod 106.
[0230] At the second heating (S174), the moving speed of the tail
stock 116 is set to 0 mm/minute so that the moving distance of the
tail stock 116 remains at 30 mm. The moving distance of the heating
source 122 is set to 15 mm. The amount of hydrogen (H.sub.2) gas
for the heating source 122 is set to 130 cc/minute. The amount of
oxygen (O.sub.2) gas (inside) that is output from the inside nozzle
of the heating source 122 is set to 15 cc/minute. The amount of
oxygen (O.sub.2) gas (outside) that is output from the outside
nozzle of the heating source 122 is set to 50 cc/minute. The glass
rod 106 is heated by the heating source 122, which is set according
to the above conditions. After the heating source 122 has moved 15
mm, the process is shifted to next step.
[0231] Then, at the second elongating for end drawing (S176),
whilst the moving distance of the tail stock 116 is increased from
30 mm to 55 mm, the moving distance of the heating source 122 is
increased from 15 mm to 25 mm. The amount hydrogen (H.sub.2) gas
for the heating source 122 is set to 130 cc/minute. The amount of
oxygen (O.sub.2) gas (inside) that is output from the inside nozzle
of the heating source 122 is set to 15 cc/minute. The amount of
oxygen (O.sub.2) gas (outside) that is output from the outside
nozzle of the heating source 122 is set to 50 cc/minute. The glass
rod 106 is heated by the heating source 122, which is set according
to the above conditions. The tail stock 116 is moved at a speed of
10 mm/minute to elongate the glass rod 106.
[0232] Finally, at the fusing for end drawing (S178), whilst the
moving distance of the tail stock 116 increased from 55 mm to 100
mm, the heating source 122 did not move from the position at the
second elongating for end drawing (S176). The moving distance
therefore remains at 25 mm. The amount hydrogen (H.sub.2) gas for
the heating source 122 is set to 130 cc/minute. The amount of
oxygen (O.sub.2) gas (inside) that is output from the inside nozzle
of the heating source 122 is set to 30 cc/minute. The amount of
oxygen (O.sub.2) gas (outside) that is output from the outside
nozzle of the heating source 122 is set to 20 cc/minute. The glass
rod 106 is heated by the heating source 122, which is set according
to the above conditions. The tail stock 116 is moved at a speed of
120 mm/minute to fuse the glass rod 106.
Example 1
[0233] A glass rod 106 having a diameter of 60 mm was end-drawn
according to the setting values shown in FIG. 43. An AC servomotor
of 200 W was used for the tail stock driving motor 275. A rotary
encoder that can detect the amount of rotation of the tail stock
driving motor 275 was used as the tail stock driving encoder 273.
The rotation speed of the tail stock driving motor 275 was
controlled by the output of the tail stock driving encoder 273. The
moving distance of the tail stock 116 was obtained by measuring the
output of the tail stock driving encoder 273. The time required for
the end drawing was 15 minutes. The shape of the processed glass
rod 106 at the region which was end-drawn was a well formed
circular cone shape. The length and the diameter of the region were
61 mm and 60 mm respectively.
Example 2
[0234] A glass rod 106 having a diameter of 60 mm was end-drawn
according to the setting values shown in FIG. 43. A linear encoder
that can detect the moving distance of the tail stock 116 was
provided on the tail stock 116. The gas amount and the moving
distance of the heating source 122, and the moving speed of the
tail stock 116 were controlled based on the moving distance of the
tail stock 116 detected by the linear encoder. The shape of the
processed glass rod 106 at the region that was end-drawn was a well
formed circular cone. The length and the diameter of the region
were 65 mm and 60 mm respectively.
[0235] FIG. 44 shows a configuration of the heating source 122 of
the glass rod second elongating apparatus 111. The bottom end of
the outside pipe 285 of the heating source 122 is closed. The
outside pipe 285 is connected to a combustible gas channel 312.
This is a channel for hydrogen gas which is an example of a
suitable combustible gas. The heating source 122 has a combustible
gas flow rate control unit 314 placed in the combustible gas
channel 312. All of the inside pipes 286 are connected to an oxygen
gas channel 308 through the branching tool 316. The oxygen channel
308 is a channel for oxygen gas. An inert-gas channel 296 is
connected to the oxygen gas channel 308 by the connecting element
302. An oxygen gas flow rate control unit 310 is installed between
the connecting element 302 and the entrance of the oxygen gas
channel 308.
[0236] The inert-gas channel 296 has a valve 300 and an inert-gas
flow rate control unit 298. The heating source 122 has a control
element 304 which controls a driving source 306 based on the data
of the flow rate that is output from the oxygen gas flow rate
control unit 310. The driving source 306 is connected to the valve
300. The combustible gas flow rate control unit 314 and the oxygen
gas flow rate control unit 310 control the flow rate of the
hydrogen gas H.sub.2 and oxygen gas 02 shown in the FIG. 42 and
FIG. 43. A valve such as an electric valve or electromagnetic valve
can be used as the valve 300. A three directional pipe or a three
directional valve can be used for the connecting element 302.
[0237] FIG. 45 shows a plan view of the top of the heating source
122. A plurality of the inside pipes 286, each of which has an
inside diameter of 1 mm and an outside diameter of 3 mm, is
inserted into the outside pipe 285, which has an inside diameter of
30 mm. The inside pipes 286 are placed around the center of the
outside pipe 285 in a plurality of rows of concentric circles.
[0238] The inside pipes 286 are placed with regular spacing
intervals for each row. The closer the rows are towards the outside
of the outside pipe 285, the higher the density of the intervals of
the inside pipe 286 for the each row becomes. The inside pipes 286
can be installed inside the outside pipe 285 with a homogeneous
density. Oxygen gas flows inside the oxygen gas outlet 288, which
is inside of the inside pipe 286. A combustible gas flows inside
the combustible gas outlet 290, which is inside of the outside pipe
285.
[0239] The movement of the heating source 122 will be explained
below. Hydrogen gas flows into the outside pipe 285 through the
combustible gas channel 312 from a hydrogen gas supply source, not
shown in the figure. Oxygen gas is distributed to the inside pipe
286 by the branching tool 316. Oxygen gas is supplied from an
oxygen gas supply source (not shown in the figure) through the
oxygen gas channel 308. The hydrogen and oxygen gas are mixed at
the top of the outside pipe 285. A flame 294 can be obtained by
igniting the mixed gas.
[0240] According to the purpose of the processing of the glass rod
106, the quantity of the hydrogen and oxygen gas were adjusted by
using the oxygen gas flow rate control unit 310 and the combustible
gas flow rate control unit 314 to obtain the optimum flame
condition. At this time, the signal that shows the flow rate of the
oxygen gas is output from the oxygen gas flow rate control unit 310
to the control element 304. The linear speed of the oxygen gas is a
value derived by dividing the flow rate of the oxygen gas by the
area of the inside of the inside pipe 286.
[0241] If the linear speed of the oxygen gas is 1.0 m/sec or under,
the control element 304 drives the driving source 306 and opens the
valve 300. Then, nitrogen gas, which is an inert gas, flows into
the oxygen gas channel 308 with a linear speed of 0.5 m/sec and is
mixed with the oxygen gas. When changing the flow rate of the
oxygen, the control element 304 drives the driving source 306 and
closes the valve 300 if the linear speed of the oxygen reaches 1.1
m/sec.
[0242] When reducing the flow rate of the combustible gas and
oxygen gas to make the flame smaller, the region of high
temperature near the top of the inside flame moves from the top of
the heating source 122. This is because the flame 294 diffuses as a
result of mixing the inert-gas with oxygen gas. Therefore, the
surface temperature of the top of the heating source 122 is
maintained below 400.degree. C., so that e oxidation of the heating
source 122 can be prevented.
[0243] When strong heating power is needed, the valve 300 for the
inflow of the inert gas is closed because the combustion
temperature drops if inert gas is mixed. At this time, because the
flame 294 is large owing to the increase of the flow rate of the
combustible gas and oxygen gas, the region of high temperature of
the flame 294 is no longer at the top of the heating source 122.
Therefore, the surface temperature of the top of the heating source
122 is maintained below 400.degree. C. The generation of a pulse
caused by the opening and closing of the valve 300 can be prevented
by setting a different linear speed value for the oxygen gas at the
time of opening and closing of the valve 300. This should be set to
1.0 m/sec or below for opening and 1.1 m/sec or above for
closing.
[0244] It is desirable that the inert gas has a linear speed of
between 0.5 m/sec to 2 m/sec as it flows by the opening of the
valve 300. The linear speed of the inert gas is calculated by
dividing the flow rate of the inert gas by the area inside the
oxygen gas outlet 288 of the inside pipe 286. If the linear speed
of the inert gas is 0.5 m/sec or below, it is difficult to control
the temperature of the top of the heating source 122. On the other
hand, if the linear speed of the inert gas is 2.0 m/sec or above,
the hydrogen gas burns incompletely, and the temperature of the
flame 294 decrease.
[0245] If using a heating source 122 to heat the glass rod 106 with
the flame 294, a metal oxide will not usually be generated at the
top of the heating source 122. This is because the temperature of
the top of the heating source 122 is maintained at 400.degree. C.
or below. Therefore, a metal oxide does not attach to the glass rod
106, and a glass rod 106 of high quality can be manufactured.
[0246] A glass rod 106 having an average diameter of 65 mm was
elongated by a glass rod second elongating apparatus 111 that has
heating source 122 controlling the flow rate of the inert gas. The
ratio of the number of glass rods 106 having foreign matter such as
metal oxide to the total numbers of processed glass rod 106 was
0.2%. This is a low value compared to the ratio of glass rods made
by the conventional heating source 122. For comparison, the ratio
of the number of glass rods 106 having foreign matter such as metal
oxide to the total numbers of the processed glass rods 106 became a
high value of 15% when the glass rod 106 was elongated by always
closing the valve 300.
[0247] FIG. 46 shows a relationship between the linear speed of the
oxygen gas and the temperature of the top of the heating source
122. This is illustrated for the case of always mixing oxygen gas
with nitrogen gas having linear speed of 0.5 m/sec and of not
mixing the oxygen gas with the nitrogen gas. The temperature of the
top of the heating source 122 does not exceed 400.degree. C. when
mixing the nitrogen gas. The temperature reached 400.degree. C. to
700.degree. C. at the region where the linear speed of the oxygen
gas was 1 m/sec or under when the nitrogen gas was not mixed.
Therefore, the surface temperature of the heating source 122 can be
controlled by mixing the oxygen gas with nitrogen gas when the
linear speed of the oxygen gas is 1 m/sec or below.
[0248] FIG. 47 shows the shape of a tip of the preform 107, the
diameter of which is reduced and which is fused at the end drawing
(S158). The D represents the diameter of the preform 107. The O
represents the location where the diameter of the preform 107
starts to be reduced. The P represents the location where the
diameter D of the preform 107 is reduced to 1% or below the
original diameter. The preform 107 has a taper shape, both ends of
which can be shown by the equation 1/3D.ltoreq.L3D. Here, L
represents the length between the location O and the location
P.
[0249] The time that the drawing reaches the steady state is the
time from the setting of the preform 107 on the preform drawing
apparatus 500 until the diameter and the drawn speed of the optical
fiber reaches the prescribed value. When the preform 107 is drawn
to an optical fiber, the original shape of the preform 107
influences the time it takes for the drawing to reach the steady
state. This influence becomes larger as the diameter of the preform
107 becomes larger. Then, the time taken for the drawing to reach
the steady state becomes longer.
[0250] The preform 107 having the shape of the equation
1/3D.ltoreq.L.ltoreq.3D can reduce the time taken for the drawing
to reach the steady state. If L<1/3D, the time taken for the
diameter and the drawn speed of the optical fiber to reach the
prescribed value increases because the time that the tip of the
preform 107 drops down becomes longer. If L>3D, the time taken
for the tip of the preform 107 to drop down can be decreased, but
the time taken for the taper shape of the preform 107 to become the
shape of the steady state of the drawing takes longer. Then, the
time taken for the diameter and the drawn speed of the optical
fiber to reach the prescribed value becomes longer. Therefore, it
is best to make the shape of the taper of the preform 107 as
L=D.
[0251] In the case of fusing the preform 107 by heating part of the
preform 107 by a flame, a residual strain remains on both ends of
the taper part of the preform 107. If the residual strain in the
taper part is large, cracks can be generated on both ends of the
preform 107 when a strong impact is applied on the preform 107. The
cracks can also be generated on both ends of the preform 107 by a
thermal impact generated by the welding of the preform 107 and the
dummy rod. The quantity of the strain on both ends of the preform
107 would ideally be 40 kgf/cm.sup.2 or below. The cracks generated
on the preform 107 can be prevented by controlling the quantity of
the residual strain remaining in the preform 107 at 40 kgf/cm.sup.2
or below.
EXAMPLE
[0252] A preform 107 with a diameter of 30 mm was drawn. The length
L was set to 30 mm. The quantity of the strain remaining in the
taper part of the preform 107 was 40 kgf/cm.sup.2, and cracks were
not generated during the welding of the preform 107 and the dummy
rod. When the set diameter of the optical fiber was 125 .mu.m and
the speed of the drawing was 100 mm/min, the time that the drawing
took to reach the steady state was a total of 20 minutes. The time
from the setting of the preform 107 on the preform drawing
apparatus 500 to the dropping of the tip of the preform 107 was 10
minutes. The time taken for the diameter and the drawn speed of the
optical fiber to reach the prescribed value was 10 minutes.
Comparative Example 1
[0253] A preform 107 with a diameter of 30 mm was drawn. The length
L was set to 5 mm. The quantity of the strain remaining in the
taper part of the preform 107 was 40 kgf/cm.sup.2, and cracks were
not generated during the welding of the preform 107 and the dummy
rod. When the set diameter of the optical fiber was 125 .mu.m and
the speed of the drawing was 100 mm/min, the time that the drawing
reached d the steady state was a total of 50 minutes. The time from
the setting of the preform 107 on the preform drawing apparatus 500
to the dropping of the tip of the preform 107 was 20 minutes. The
time taken for the diameter and the drawn speed of the optical
fiber to reach the prescribed value was 30 minutes.
Comparative Example 2
[0254] A preform 107 with a diameter of 30 mm was drawn. The length
L was set to 100 mm. The quantity of the strain remaining in the
taper part of the preform 107 was 40 kgf/cm.sup.2, and cracks were
not generated during the welding of the preform 107 and the dummy
rod. When the set diameter of the optical fiber was 125 .mu.m and
the speed of the drawing was 100 mm/min, the time taken for the
drawing to reach the steady state was a total of 40 minutes. The
time from the setting of the preform 107 on the preform drawing
apparatus 500 to the dropping of the tip of the preform 107 was 10
minutes. The time taken for the diameter and the drawn speed of the
optical fiber to reach the prescribed value was 30 minutes.
Comparative Example 3
[0255] A preform 107 with a diameter of 30 mm was drawn. The length
L was set to be 30 mm. The quantity of the strain remaining in the
taper part of the preform 107 was 60 kgf/cm.sup.2. The preform 107
could not be drawn because cracks were generated during the welding
of the preform 107 and the dummy rod.
[0256] As shown above, the time required for drawing the preform
107 to an optical fiber can be reduced by making the shape of the
tip of the preform 107 as 1/3D.ltoreq.L.ltoreq.3D.
[0257] FIG. 48 shows another shape of the tip of the preform 107
that was end-drawn. The preform 107 shown in FIG. 48 has a fused
part 332 on one end formed by a flame, and a cutting face 334 on
the other end, which is cut mechanically. The fused part 332, which
is shown in FIG. 48(a), is fused rapidly by a flame. The fused part
332, which is shown in FIG. 48(b), is fused gradually by reducing
the diameter to form a taper part 336. A thin part 338 is provided
on the tip of the fused part 332 shown in FIG. 48(c).
[0258] When drawing a preform 107 which has the taper part 336 as
shown in FIG. 48(b), the time taken for the tip of the preform 107
to dropdown is short, and the quantity of preform 107 to be dropped
is also small because the diameter of the fused part 332 is small.
When drawing a preform 107 which has the taper part 336 and thin
part 338 as shown in FIG. 48(c), the time taken for the tip of the
preform 107 to drop down can be reduced to one third or less of the
time required for the conventional shape of the preform 107. The
loss in material caused by the dropping of the preform 107 can be
limited to the small quantity of the thin part 338.
[0259] It is desirable that the shape of the thin part 338 occupies
between 0.1 percent to 15 percent of the weight of the fused part
332. If the weight of the thin part 338 is smaller than 0.1 percent
of the weight of the fused part 332, the effect produced by
providing the thin part 338 cannot be obtained. On the other hand,
if the weight of the thin part 338 is larger than 15 percent of the
weight of the fused part 332, the time taken for the tip of the
preform 107 to drop becomes long, and the loss of preform 107
increases during the drawing.
[0260] It is desirable that the diameter of the thin part 338 be
between 1/2 to {fraction (1/10)} of the diameter of the main body
of the preform 107. If the diameter of the thin part 338 is within
this range, the time required for the dropping of the tip of the
preform 107 at the early stage of the drawing can be short. If the
length of the thin part 338 is approximately one to five times this
diameter, the loss of the preform 107 can be limited to a small
quantity.
[0261] FIG. 49 shows a preform 107 that is damaged, before the
preform 107 is surface treated at the surface treatment (S168)
shown in the FIG. 26. The preform 107, which is elongated by the
glass rod second elongating apparatus 111, is etched by
hydrofluoric acid as a surface treatment. This cuts the cladding of
the preform 107 chemically so that the preform 107 has the
prescribed ratio of thickness of core to cladding.
[0262] The hydrofluoric acid etching treatment is a treatment that
decomposes the bonds between the Silicon and oxygen of the glass.
The hydrofluoric acid etching treatment cuts the surface of the
preform 107 chemically at a speed of about 8 mm per one hour.
However, if there is a crack or a concave on the surface of the
preform 107, the place having the crack or concave is cut further
to form a larger concave than the concave made on the other parts
of the preform 107. This concave caused by the treatment of
hydrofluoric acid etching is called a hydrofluoric concave. This
hydrofluoric concave is the cause of the breaking of an optical
fiber during the drawing of the preform 107 to an optical
fiber.
[0263] A preform 107 without hydrofluoric concaves on its surface
can be obtained by removing cracks and concaves on the preform 107
by polishing before the treatment of hydrofluoric acid etching.
There is a method of fire polishing the preform 107 with the
temperature above the strain point of the preform 107. During the
fire polishing, the preform 107 is fire polished so that the
unevenness of the surface will be within a 0.3 mm range. The
generation of the hydrofluoric concave can be prevented by fire
polishing the preform 107 before etching the preform 107 with
hydrofluoric acid. This is possible because the quantity of the
strain in the preform 107 can be decreased and a smooth surface
without cracks can be obtained. Not only is fire polishing
suitable, but also mechanical polishing can be used for polishing
the preform 107.
[0264] FIG. 51 shows a number of hydrofluoric concaves generated in
the preform 107 counted by visual inspection of the example and the
comparative example. FIG. 52 shows the unevenness of the surface of
the preform 107 after the treatment with the hydrofluoric acid
etching of the example and the comparative example. In the
pre-treating 1 shown in FIG. 51 and FIG. 52, the preform 107a
having a diameter of 60 mm and a length of 1000 mm was damaged.
First, the preform 107a and the other preform 107b, which had the
same shape as the preform 107a, were placed on the floor.
[0265] Next, one end of the preform 107a was lifted to height of 10
cm while the other end remained on the floor. Then, the end of the
preform 107 that was lifted was dropped onto the preform 107b so
that the preform 107a had a crack. Each of a plurality of the
preform 107a was damaged in 3 places at 20 cm intervals by the same
method shown above. On the pre-treating 2 shown in FIG. 51 and FIG.
52, the preform 107a was lifted to a height of the 20 cm. The other
procedure of damaging the preform 107 was same as pre-treating
1.
[0266] On the example shown in FIG. 51 and FIG. 52, each of the
preform 107a was treated by the pre-treating 1 and pre-treating 2.
Then, each of the preform 107a was fire polished with a burner that
was provided with hydrogen gas at 250 ml/min and oxygen gas at 145
ml/min. Each of the fire polished preform 107a was treated by
hydrofluoric acid etching at room temperature. The thickness of
material etched from the exterior diameter of the preform 107 was
one of 4 steps of 0.2 mm, 1.2 mm, 2.2 mm, and 3.2 mm. 10 pieces of
the preform 107a were etched by hydrofluoric acid for each of the 4
steps of the etching thickness. The number of the hydrofluoric
concaves was checked by visual inspection after the treatment by
hydrofluoric acid etching.
[0267] FIG. 50 shows the preform 107a, which was treated by the
hydrofluoric acid etching in the example shown in the FIG. 51 and
FIG. 52. The unevenness of the surface of the preform 107a was
obtained by measuring the difference of the diameter between the
point which was shown by the mark X and the diameter of the point
which was shown by the mark O. The point which was shown by the
mark X was the place damaged by contacting with preform 107b. The
point which was shown by the mark O was a place 10 cm away from the
point of the mark X, which was not damaged by contacting with
preform 107b. The average value of the diameter of the 3 points
shown by the mark X were used as the diameter of the each of the
preform 107a.
[0268] In the comparative example shown in FIG. 51 and FIG. 52,
each of the preform 107 treated by pre-treatment 1 and pretreatment
2 were treated by hydrofluoric acid etching without fire polishing.
The number of hydrofluoric concaves was assessed by visual
inspection, and the unevenness of the surface was measured in the
same way as the example. As shown in FIG. 52 and FIG. 53, the
unevenness of the surface of the pre-treatment 2 was larger than
the unevenness of the surface of the pre-treatment 1. This is
because pretreatment 2 was lifted higher pre-treatment 1 in the
damage process. Also, the number of hydrofluoric concaves generated
by the hydrofluoric acid etching of the pre-treatment 2 was larger
than the number of the hydrofluoric concaves of the pre-treatment
1.
[0269] The larger the quantity of the etching, the larger the
unevenness of the surface of the preform 107. Also, the larger the
quantity of the etching, the larger the number of hydrofluoric
concaves generated by the hydrofluoric acid etching. The unevenness
of the surface of the preform 107a of the example which was fire
polished, was lower than the unevenness of the surface of the
preform 107a of the comparative example, which was not fire
polished.
[0270] The number of the hydrofluoric concave generated on the
example is smaller than the number of the hydrofluoric concave
generated on the comparative example as shown in FIG. 51.
Therefore, the number of the hydrofluoric concave in the preform
107a and the unevenness of the surface of the preform 107a can be
decreased by fire polishing the preform 107a before etching the
preform 107a with hydrofluoric acid.
[0271] FIG. 53 shows another shape of the preform 107 which is
surface treated. The preform 107 has a handle 340. The handle 340
is made of a silica glass and is installed on the cutting face 334
of the surface treated preform 107 shown in FIG. 48(c) by welding
or mechanical processing. The preform 107 with a handle 340 can be
installed onto the preform drawing apparatus 500 promptly when
drawing the preform 107 to an optical fiber. The diameter of the
handle 340, installed on the cutting face 334, can be smaller than
the diameter of the preform 107 as shown in FIG. 53(b).
[0272] FIG. 54 shows an ultrasonic cleaning apparatus 404, which
cleans the heating source 122. The ultrasonic cleaning apparatus
404 comprises an ultrasonic oscillator 396. A cleaning liquid 398
is contained inside of the ultrasonic cleaning apparatus 404. The
cleaning liquid 398 contains 10 percent hydrofluoric acid and 3
percent nitric acid. The hydrofluoric acid dissolves the metal
oxide generated on the surface of the outside pipe 285 and inside
pipe 286 of the heating source 122. Oxidation of the surface of the
outside pipe 285 and the inside pipe 286 does not readily occur if
the outside pipe 285 and the inside pipe 286 are made of stainless
steel. This is because iron, chromium, and nickel, which are
contained in stainless steel, form a passive thin film on the
surface of the stainless steel from the effect of the nitric acid,
thus protecting the surfaces.
[0273] The cleaning liquid 398 can contain a soluble organic
solvent. Examples of soluble organic solvents are alcohol, acetone,
acetonitrile, and tetrahydrofuran. The heating source 122 can be
soaked in the cleaning liquid 398 containing hydrofluoric acid and
then soaked in the other cleaning liquid 398 which contains nitric
acid. The ultrasonic oscillator 396 oscillates an ultrasonic wave
of strength of 1 W/cm.sup.2 to 2 w/cm.sup.2.
[0274] The heating source 122 to be cleaned is made of stainless
steel. The heating source 122 has a plurality of inside pipes 286,
which have an internal diameter of 1 mm and an outside diameter of
3 mm. The inside pipes 286 are inside the outside pipe 285, which
has an internal diameter of 30 mm. Hydrogen gas flows inside the
outside pipe 285, and oxygen gas flows inside the inside pipe 286.
The outside pipe 285 is connected to a hydrogen inlet pipe 392, and
all the inside pipes 286 are connected to an oxygen inlet pipe
394.
[0275] When the glass rod 106 is heated by the flame of the heating
source 122, the temperature of the top of the heating source 122
increases to a high temperature of between 400.degree. C. to
700.degree. C. Therefore, a metal oxide will be generated on the
surface of the top of the heating source 122. The metal oxides
gradually dislodges to become free floating particles if the
heating source is used for a long time.
[0276] Particles of metal oxide or foreign matter impurities such
as glass particles attached to the heating source 122 may be
dislodged during the heat treatment of the glass rod 106. These
particles can attach to the surface of the glass rod 106 in which
case the surface layer of the glass rod 106 has to be polished. If
the glass rod 106 is polished, the ratio of the diameter of the
cladding and the core of the glass rod 106 will change. The
characteristic of light transmission of an optical fiber made from
the glass rod 106 will deteriorate as a result. Therefore, foreign
matter impurities and metal oxides attached to the heating source
122 are removed from the heating source 122 by cleaning the heating
source 122.
[0277] To clean the heating source 122 using the ultrasonic
cleaning apparatus 404, first, the hydrogen inlet pipe 392 and
oxygen inlet pipe 394 are opened to the outside. Then, the heating
source 122 is soaked in the cleaning liquid 398 with the flame
nozzle 390 directed downward. Any air remaining inside the outside
pipe 285 and the inside pipe 286 is released through the hydrogen
inlet pipe 392 and oxygen inlet pipe 394. Following this, the
outside pipe 285 and the inside pipe 286 are immersed and soaked in
the cleaning liquid 398 to the top of the water level. The
ultrasonic cleaning apparatus 404 then cleans the heating source
122 by oscillating the ultrasonic wave using the ultrasonic
oscillator 396. The vibration frequency of the ultrasonic waves is
10 kHz to 100 kHz.
[0278] The heating source 122 was cleaned using the ultrasonic
cleaning apparatus 404. Metal oxide was present around the
stainless steel flame nozzle 390 of the heating source 122, which
is used for heating the glass rod. The area around the flame nozzle
390 of the heating source 122 was soaked in the cleaning liquid
398. To clean the heating source 122, an ultrasonic wave with a
vibration frequency of 10 kHz to 100 kHz was oscillated for 30
minutes by the ultrasonic oscillator 396 having output of 500 W.
Then, the heating source 122 was removed from the ultrasonic
cleaning apparatus 404 and any cleaning liquid 398 remaining on the
surface of the heating source 122 was cleaned with pure water. The
heating source 122 was then dried.
[0279] The top of the outside pipe 285 and the inside pipe 286 were
inspected, and metal oxides and foreign matter impurities were not
found in the outside pipe 285 and the inside pipe 286. The surface
of the glass rod 106 was heat treated by the cleaned heating source
122. The ratio of the number of glass rods 106, which had foreign
matter impurities attached, compared to the total number of treated
glass rods 106 was 6 percent.
[0280] The surface of the glass rod 106 was heat treated by the
heating source 122, which was not cleaned, for a comparison. In
this case, the ratio of the number of glass rods 106, which had
foreign matter impurities attached, to the total number of heat
treated glass rods 106 was 15 percent. This is larger value than
the ratio obtained by the cleaned heating source 122.
[0281] As shown above, the metal oxide and attached foreign matter
generated on the top of the heating source 122 can be removed by
cleaning the heating source 122 with the ultrasonic cleaning
apparatus 404. A preform 107 of high quality can be obtained by
heating the glass rod 106 with a heating source 122, which is
cleaned by the ultrasonic cleaning apparatus 404, because less
foreign matter is attached to glass rod 106.
[0282] FIG. 55 shows a configuration of the preform drawing
apparatus 500 that draws the preform 107 to an optical fiber. The
preform drawing apparatus 500 comprises a chuck 346, which holds a
dummy rod 342 that is welded to the preform 107; a heating means
348 which heats the preform 107; movable support 344 which supplies
the preform 107 to the heating means 348; a diameter measurement
device 352 which measures the diameter of an optical fiber 350
drawn from the preform 107; a first coating device 354 which
undertakes the first coating of the optical fiber 350; a first
curing device 356 which cures the first coated optical fiber 350 by
a ultraviolet rays; a second coating device 358 which coats the
optical fiber 350 a second time; a second curing device 360 which
cures the second coated optical fiber 350 by a ultraviolet rays;
and a tractor 362 which winds the optical fiber 350.
[0283] To draw the preform 107 into an optical fiber 350 using the
preform drawing apparatus 500, first, the dummy rod 342, which is
welded to the preform 107, is held by the movable support 344 with
the chuck 346. The starting end of the preform 107 is then set to
the prescribed position of the heating means 348, and the preform
107 is heated. When the tip of the preform 107 softens and drops,
the dropped tip of the preform 107 is caught and drawn out to be
passed through the diameter measurement device 352.
[0284] When the diameter of the optical fiber 350 reaches the
desired diameter, the optical fiber 350 is first coated with resin
by passing through the first coating device 354. The first coated
optical fiber 350 is then passed through the first curing device
356 to be cured. The optical fiber 350 is then second coated by the
second coating device 358 and cured by the second curing device
360. When the diameter and the speed of the drawing of the optical
fiber 350 reaches a prescribed value, t he optical fiber 350 is
wound onto a bobbin, not shown in the figure, through the tractor
362.
[0285] A preform 107 of high quality and little variation in
diameter can be manufactured by the glass base material first
drawing apparatus 900 and the glass rod second elongating apparatus
111 shown above. Therefore, optical fibers of high quality and
reduced diameter variation can be manufactured by drawing the
preform 107, manufactured by the glass base material first drawing
apparatus 900 and the glass rod second elongating apparatus 111,
using the preform drawing apparatus 500.
[0286] Although the present invention has been described by
reference to specific embodiments, the scope of the present
invention is not limited to these embodiments. Those skilled in the
art can make various modifications and improvements to these
embodiments of the present invention. It is clear from the appended
claims that such modifications or improvements are also covered by
the scope of the present invention.
* * * * *