U.S. patent application number 10/787408 was filed with the patent office on 2004-08-26 for electric furnace extension method and extension apparatus for optical fiber glass preform.
This patent application is currently assigned to THE FURUKAWA ELECTRIC CO., LTD. Invention is credited to Komura, Yukio, Kuwabara, Masahide, Wada, Tetsuro.
Application Number | 20040163421 10/787408 |
Document ID | / |
Family ID | 13465052 |
Filed Date | 2004-08-26 |
United States Patent
Application |
20040163421 |
Kind Code |
A1 |
Wada, Tetsuro ; et
al. |
August 26, 2004 |
Electric furnace extension method and extension apparatus for
optical fiber glass preform
Abstract
An electric furnace extending method and apparatus for an
optical fiber glass body alignment when connecting the extension
use body and pulling member and making it possible to immediately
start the extension after the fusing of the connection portion. A
centering mechanism for centering the free end portion of the body
and member on the furnace center side is provided between the
furnace pipe of the electric furnace and grips of the extension use
glass body and between the furnace pipe and the pulling member. The
free end portion is centered by this centering mechanism, then the
gripped sides of the body and member are fixed, the front ends of
the two free end portions are abutted and fused and bonded at the
highest temperature portion inside the electric furnace, then the
highest temperature portion is moved to the extension portion of
the glass body side and the extending of the glass body is
commenced.
Inventors: |
Wada, Tetsuro; (Tokyo,
JP) ; Kuwabara, Masahide; (Tokyo, JP) ;
Komura, Yukio; (Tokyo, JP) |
Correspondence
Address: |
ARENT FOX KINTNER PLOTKIN & KAHN
1050 CONNECTICUT AVENUE, N.W.
SUITE 400
WASHINGTON
DC
20036
US
|
Assignee: |
THE FURUKAWA ELECTRIC CO.,
LTD
|
Family ID: |
13465052 |
Appl. No.: |
10/787408 |
Filed: |
February 27, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10787408 |
Feb 27, 2004 |
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09778107 |
Feb 7, 2001 |
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6729162 |
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09778107 |
Feb 7, 2001 |
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09047373 |
Mar 25, 1998 |
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6279353 |
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Current U.S.
Class: |
65/486 |
Current CPC
Class: |
C03B 37/0124 20130101;
Y02P 40/57 20151101; C03B 37/01486 20130101 |
Class at
Publication: |
065/486 |
International
Class: |
C03B 037/07 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 25, 1997 |
JP |
9-71590 |
Claims
What is claimed is:
1. An apparatus for extending an optical fiber body, comprising: an
upper holder for holding an upper end of an extension optical fiber
glass body to be extended; a lower holder, provided at a position
coinciding with an axial center of said upper holder and facing
said upper holder, said lower holder holding a lower end of a pull
glass member connected to a lower end of the extension optical
fiber glass body, an axial center of said pull glass member
coinciding with an axial center of said extension optical fiber
glass body, and said lower holder being pulled toward a lower
portion in response to an extension of said extension optical fiber
glass body; an electric furnace provided between said upper holder
and said lower holder and which heats said extension optical glass
preform; a moving means moving at least said lower holder toward a
low position to pull said extending optical fiber glass preform;
and a control means, wherein said control means controls the
following, when extending said optical fiber glass preform in said
electric furnace, and after joining of the lower end of said
optical fiber glass preform and the upper end of said pull glass
member by heat-melting manner, moving the maximum temperature
portion of said electric furnace to a joined portion to heat and
connect the joined portion, and controlling said movement means to
lower said lower holder, and to move the maximum temperature
portion of said electric furnace from said joined portion to the
extending portion of said optical fiber glass body.
2. An apparatus for extending an optical fiber body according to
claim 1, wherein a dummy member is connected to the lower end of
said extension optical fiber glass body, a diameter of a lower tip
of said dummy member being smaller than a diameter of the upper tip
of said pulling glass member, a diameter of an upper tip of said
dummy member being substantially equal to or close to a diameter of
said extension optical fiber glass body, said dummy member has a
semi-conical shape in the upper tip and said dummy member being
formed by a material equal to that of said extension optical fiber
glass body, and wherein said control means controls the movement of
said moving means to move said lower holder downward to extend said
extension optical fiber glass body connected to said dummy member
at the lower tip thereof.
3. An apparatus or extending an optical fiber body according to
claim 2, wherein said diameter of said lower tip of said dummy
member is approximately 1/2 to 1/3 of the diameter of said upper
end of said pulling glass member.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an electric furnace
extension method for extending an optical fiber glass body
(preform) so as to obtain a predetermined outer diameter, and to an
apparatus of the same.
[0003] Note that, in the present specification, an "optical fiber
glass body" includes, other than the usual glass body for
extension, an extension optical fiber glass body obtained by
extending this glass body, i.e., a "preform".
[0004] 2. Description of the Related Art
[0005] Usually, an optical fiber is produced by synthesizing an
optical fiber porous glass body by a VAD process or an external CVD
process, then dehydrating and sintering the optical fiber porous
glass body to obtain a transparent glass body for the optical
fiber, extending this to obtain an outer diameter suited for
wire-drawing to form a drawn optical glass body (referred to here
as a "preform"), and then wire-drawing this preform to form an
optical fiber including a core and a cladding.
[0006] Heretofore, the optical fiber glass body has been drawn by
heat extension of the optical fiber glass body using a burner using
an oxyhydrogen flame as a heat source, that is, the burner
extension method. In this burner extension method, control of the
outer diameter of the extended optical fiber glass body is
relatively easy, but the extension rate is slow--usually 8 to 10
mm/min.
[0007] Due to recent technical advances and along with demands for
improvement of manufacturing efficiency, the outer diameter of the
porous optical fiber glass body synthesized by the VAD process or
external CVD process has become much greater than in the past.
Along with this, it suffers from the disadvantage in terms of the
heat in the burner extension method using a burner using an
oxyhydrogen flame as the heat source in the case of an optical
fiber glass body having an outer diameter before extension of more
than a certain value.
[0008] For this reason, a heat extension method using a heating
furnace having a larger heating capacity than a burner, more
specifically an electric heater (hereinafter referred to as the
"electric furnace extension method") is being adopted for optical
fiber glass bodies having an outer diameter before extension of
more than a certain value. Such an electric furnace extension
method can increase the extension rate since the heating capacity
is large. For example, in contrast to the extension rate of the
burner extension method of 8 to 10 mm/min, the extension rate is 30
mm/min or more in the electric furnace extension method. For this
reason, the electric furnace extension method is advantageous from
the viewpoint of productivity not only for the extension of an
optical fiber glass body having a large outer diameter, but also
for an extension glass body having a small outer diameter.
[0009] Note that in this electric furnace extension method, since
the heating range is wide, it is limited to use for vertical bodies
long in the vertical direction. Accordingly, the preform is
extended from top to bottom.
[0010] In this electric furnace extension method, it is necessary
to connect an extension-glass-body support rod (pulling glass
member) to the end portion of the optical fiber glass body or the
extension glass body (preform) before extension. In the past, this
connection was generally achieved in a separate step of flame
extension, but it is preferable to achieve this connection in the
same electric furnace extension process.
[0011] Where this connection is performed in the same electric
furnace extension process, however, it suffers from the
disadvantage that this connection is difficult. That is, it is
necessary to align the axial center of the end portion of the glass
body with the axial center of the end portion of the extension
support rod (pulling use glass member), but the centers tend to be
offset in connection. When the axial centers are offset in
connection, the distribution of stress in the cross-section of the
connection portion becomes nonuniform, so trouble such as a bending
in the drawn body or breakage of the connection portion sometimes
occurs.
[0012] The axial alignment at the time of extension an optical
fiber glass body using an electric furnace is usually performed as
follows.
[0013] The two glass members (extension use glass body and pulling
use glass member), one end of each of which is held elsewhere, are
inserted into the heated furnace from reverse directions to each
other and made to abut against each other. The abutting ends of the
two are heated and fused to each other, then the gripping member
gripping the pulling use glass member is moved downward at a
predetermined speed while moving the gripped portion of the
extension use glass body downward at a constant speed so as to
stretch the extension use glass body and extend it to the
predetermined outer diameter.
[0014] FIG. 1 is a view of an example of the configuration of this
type of extension apparatus for an optical fiber glass body of the
related art.
[0015] In FIG. 1, 91a denotes an extension use glass body (or
optical fiber glass body) to be extended, and 91b denotes a dummy
pulling use glass member (extension-out use glass member).
Reference numeral 93 denotes a furnace body. A furnace pipe 94
containing an electric heater is disposed in the furnace body
93.
[0016] One end portion of each of the extension use glass body 91a
and the pulling use glass member 91b is gripped and affixed by
gripping members 95 and 96 comprising for example three-claw
chucks. The gripping members 95 and 96 can be moved by a moving
stand 97 to which the gripping members 95 and 96 are affixed in the
vertical direction in a state illustrated in FIG. 1. Reference
numeral 98 denotes a guide rail for guiding the moving stand
97.
[0017] The optical fiber glass body is extended (stretched) by the
above optical fiber body extension apparatus as follows:
[0018] (1) The fixed ends of the extension use glass body 91a and
the pulling use glass member 91b are gripped and affixed by the
gripping members 95 and 96, respectively. The front ends of the
free end portions of the affixed extension use glass body 91a and
pulling use glass member 91b are axially aligned, then the two are
moved into the furnace pipe 94 and made to abut against each
other.
[0019] (2) The furnace pipe 94 is heated to the predetermined
temperature to heat and fuse the abutted end surfaces of the two to
join them, then the gripping member 95 gripping the pulling use
glass member 91b is moved downward to extend the extension use
glass body 91a to the predetermined outer diameter.
[0020] (3) The axial alignment of the extension use glass body 91a
and the pulling use glass member 91b is carried out when heating
and fusing the abutted end surfaces of the two in the furnace pipe
94 by the extension-apparatus. For this axial alignment
(centering), the fixed end portions of the extension use glass body
91a and the pulling use glass member 91b are for example moved
delicately by hand within the range of free play of the gripping
members 95 and 96, for example, the three-claw chucks, to center
the axial centers of the front ends of the free end portions, then
are fixed in place. The fixed front ends of the free end portions
are then made to abut in the furnace pipe 94. The state of axial
alignment is confirmed visually from an observation window 94A
provided in the furnace pipe 94.
[0021] This centering method of the related art takes a long time.
Also, also the precision of alignment is not very good. For
example, an axial deviation of .+-.1 to .+-.2 mm (5 to 10% of the
diameter of the glass member) occurs in the horizontal plane. If
the precision of the axial alignment is poor, the distribution of
stress at the cross-section of the connection portion of the
extension use glass body 91a and the pulling use glass member 91b
will become nonuniform at the time of extending, and trouble such
as occurrence of bending in the extended fiber glass body or
breakage of the connection portion may occur.
[0022] Further, where the optical fiber glass body is extended by
the electric furnace extension method explained above, bending or
waviness sometimes occur in the extended fiber glass body (preform)
or variation sometimes occurs in the outer diameter, so the outer
diameter sometimes deviates from the prescribed value.
[0023] Further, improvement of the extension rate of preforms has
also been demanded from the viewpoint of productivity.
SUMMARY OF THE INVENTION
[0024] An object of the present invention is to overcome the
disadvantages encountered when an optical fiber glass body and a
pulling use glass member are connected in the electric furnace
extension process and provide an electric furnace extension method
and extending apparatus for an optical fiber glass body capable of
easily and simply performing axial alignment (centering) of the
front ends of the free end portions of the glass body and pulling
use glass member to be abutted and connected in an electric
furnace. More specifically, the object thereof is to provide an
electric furnace extension method for fixing the optical fiber
glass body to the extending apparatus, connecting the two in the
electric furnace, and then starting the extension.
[0025] Another object of the present invention is to provide an
electric furnace extension method and extending apparatus for an
optical fiber glass body capable of improving the precision of the
extended outer diameter of the optical fiber glass body.
[0026] Still another object of the present invention is to provide
an electric furnace extension method and extending apparatus
capable of increasing the extension rate of an optical fiber
preform.
[0027] According to a first aspect of the present invention, there
is provided an apparatus for extending an optical fiber glass body,
comprising: an electric furnace for heating an extension optical
fiber glass body to be extended; a first holding member positioned
above said electric furnace, and holding a fix end of a upper
portion of said extension optical fiber glass body to be extended;
a second holding member positioned below said electric furnace and
holding a fix end of a lower portion of a pulling glass member; a
first axial center alignment, mechanism provided between said
electric furnace and said first holding member and for aligning an
axial center of a tip of a free end of a lower portion of said
extension optical fiber glass body; and a second axial center
alignment mechanism provided between said electric furnace and said
second holding member and for aligning an axial center of a tip of
a free end of a upper portion of said pulling glass member, an
axial center of said axial center alignment mechanism being met
with an axial center of said second axial center alignment
mechanism.
[0028] The first axial center alignment mechanism may comprise a
pair of axial center alignment holders provided a pair of V-shaped
grooves facing to a longitudinal direction of said extension
optical fiber glass body at facing centers thereof, and having self
axial center alignment function, a pair of supporting bars provided
at facing portions to support said pair of axial center alignment
holders, and a pair of bases having movement mechanisms for moving
said pair of axial center alignment holders and said pair of
supporting bars as a unit in a horizonal direction.
[0029] The second axial center alignment mechanism may also
comprise a pair of axial center alignment holders provided a pair
of V-shaped grooves facing to a longitudinal direction of said
pulling glass member at facing centers thereof, and having self
axial center alignment function, a pair of supporting bars provided
at facing portions to support said pair of axial center alignment
holders, and a pair of bases having movement mechanisms for moving
said pair of axial center alignment holders and said pair of
supporting bars as a unit in a horizontal direction.
[0030] According to a second aspect of the present invention, there
is provided a process of connecting and fixing an extension optical
fiber glass body to be extended and a pull glass member in an
apparatus for extending the optical fiber glass body, comprising:
an electric furnace for heating the optical fiber glass body; a
first holding member positioned above said electric furnace, and
holding a fix-end of a upper portion of said extension optical
fiber glass body to be extended; a second holding member positioned
below said electric furnace and holding a fix end of a lower
portion of a pulling glass member; a first axial center alignment
mechanism provided between said electric furnace and said first
holding member and for aligning an axial center of a tip of a free
end of a lower portion of said extension optical fiber glass body;
and a second axial center alignment mechanism provided between said
electric furnace and said second holding member and for aligning an
axial center of a tip of a free end of a upper portion of said
pulling glass member, an axial center of said axial center
alignment mechanism being met with an axial center of said second
axial center alignment mechanism, said process including the steps
of:
[0031] provisionally fixing a fix end of a upper portion of said
extension optical fiber glass body to said first holding
member;
[0032] holding a tip of a free end of a lower portion of said
extension optical fiber glass body by said first axial center
alignment mechanism and aligning an axial center of said tip of
said free end;
[0033] holding and fixing said fix end of the lower portion of said
extension optical fiber glass body by said first holding
member;
[0034] releasing said pair of axial center holding members of said
first axial center alignment mechanism and positioning the tip of
the free end of said extension optical fiber glass body at a
predetermined position in said electric furnace;
[0035] holding and fixing the fix end of the lower portion of said
pulling glass member by said second holding member;
[0036] holding a tip of a free end of a upper portion of said
pulling glass member by said pair of second axial center alignment
mechanism having a self axial center alignment function to align
the axial center of the tip of said free ends;
[0037] holding and fixing the fix end of the lower portion of said
pulling glass member by said second holding member; and
[0038] releasing said pair of axial center holding members of said
second axial center alignment mechanism and positioning the tip of
the free end of said pulling glass member, to thereby coincide the
tip of the free end of said extension optical fiber glass body and
the tip of the free end of said pulling glass member to meet each
axial center.
[0039] The process may include the steps of:
[0040] holding and fixing the fix end of the lower portion of said
pulling glass member by said second holding member;
[0041] holding a tip of a free end of a upper portion of said
pulling glass member by said pair of second axial center alignment
mechanism having a self axial center alignment function to align
the axial center of the tip of said free ends;
[0042] holding and fixing the fix end of the lower portion of said
pulling glass member by said second holding member;
[0043] releasing said pair of axial center holding members of said
second axial center alignment mechanism and positioning the tip of
the free end of said pulling glass, member,
[0044] provisionally fixing a fix end of a upper portion of said
extension optical fiber glass body to said first holding
member;
[0045] holding a tip of a free end of a lower portion of said
extension optical fiber glass body by said first axial center
alignment mechanism and aligning an axial center of said tip of
said free end;
[0046] holding and fixing said fix end of the lower portion of said
pulling glass member body by said first holding member;
[0047] releasing said pair of axial center holding members of said
first axial center alignment mechanism and positioning the tip of
the free end of said extension optical fiber glass body at a
predetermined position in said electric furnace; to thereby
coincide the tip of the free end of said extension optical fiber
glass body and the tip of the free end of said pulling glass member
to meet each axial center.
[0048] The process may also include the steps of:
[0049] provisionally fixing a fix end of a upper portion of said
extension optical fiber glass body to said first holding member,
and holding and fixing the fix end of the lower portion of said
pulling glass member by said first holding member;
[0050] holding a tip of a free end of a lower portion of said
extension optical fiber glass body by said first axial center
alignment mechanism and aligning an axial center of said tip of
said free end; and holding a tip of a free end of a upper portion
of said pulling glass member by said pair of second axial center
alignment mechanism having a self axial center alignment function
to align the axial center of the tip of said free ends;
[0051] holding and fixing said fix end of the lower portion of said
extension optical fiber glass body by said first holding member;
and
[0052] holding and fixing the fix end of the lower portion of said
pulling glass member by said second holding member; and
[0053] releasing said pair of axial center holding members of said
first axial center alignment mechanism and positioning the tip of
the free end of said extension optical fiber glass body at a
predetermined position in said electric furnace; and
[0054] releasing said pair of axial center holding members of said
second axial center alignment mechanism and positioning the tip of
the free end of said pulling glass member, to thereby coincide the
tip of the free end of said extension optical fiber glass body and
the tip of the free end of said pulling glass member to meet each
axial center.
[0055] According to the present invention, there is also provided
an apparatus for extending an optical fiber body, comprising: a
upper holder for holding a upper end of an extension optical fiber
glass body to be extended; a lower holder, provided at a position
coinciding an axial center with that of said upper holder and
facing to said upper holder, holding a lower end of a pull glass
member connected to a lower end of the extension optical fiber
glass body, an axial center of said pull glass member being
coincided an axial center of said extension optical fiber glass
body, and said lower holder being pulled toward a lower portion, in
response to an extension of said extension optical fiber glass
preform; an electric furnace, provided between said upper holder
and said lower holder, heating said extension optical glass
preform; a moving means moving at least said lower holder toward a
low position to pull said extending optical fiber glass preform;
and a control means. The control means controls the following, when
extending said optical fiber glass preform in said electric
furnace, and after junction of the lower end of said optical fiber
glass body and the upper end of said pull glass member by
heat-melting manner,
[0056] moving the maximum temperature portion of said electric
furnace to the junction portion to heat and connect the junction
portion, and
[0057] controlling said movement means to lower said lower holder,
to thereby move the maximum temperature portion of said electric
furnace from said junction portion to the extending portion of said
optical fiber glass preform.
[0058] Preferably, a dummy member is connected to the lower end of
said extension optical fiber glass body, a diameter of a lower tip
of said dummy member being smaller than a diameter of the upper tip
of said pulling glass member, a diameter of a upper tip of said
dummy member being substantially equal to or close to a diameter of
said extension optical fiber glass body, said dummy member has a
semi-conical shape in the upper tip and said dummy member being
formed by a material equal to that of said extension optical fiber
glass body, and said control means controls the movement of said
moving means to move said lower holder downward to thereby extend
said extension optical fiber glass body connected said dummy member
at the lower tip thereof.
[0059] Preferably, the diameter of said lower tip of said dummy
member is approximately 1/2 to 1/3 of the diameter of said upper
end of said pulling glass member.
[0060] According to the present invention, there is further
provided an apparatus for extending an extension optical fiber
glass body, comprising: a upper holder for holding a upper end of
an extension optical fiber glass body to be extended; a lower
holder, provided at a position where an axial center thereof
coincides with and an axial center of said upper holder, holding a
lower end of a pulling glass member a upper end of which is
connected to a lower end of said extension optical fiber glass body
to coincide both axial centers, and movable downward in response to
the extension of said extension optical fiber glass body; an
electric furnace provided between said upper holder and said lower
holder and heating said extension optical fiber glass body; a
temperature measurement unit for measuring the temperature of an
extending portion of said extension optical fiber glass body; a
speed meter for measuring an extension speed of said extension
optical fiber glass body after extension; a moving means for moving
at least said lower holder downward to pull said extension optical
fiber glass body after extension; and a control means; the control
means reads the temperature from the temperature measurement unit
and the extension speed from said speed meter, and controls said
moving means to continuously raise set extension speed to a
predetermined steady extension speed from the beginning of the
extension to the steady extension state.
[0061] Preferably, said control means controls the heat power of
said electric furnace to raise the temperature of said electric
furnace in response to the increase of said extension speed.
[0062] Preferably, the apparatus for extending an extension optical
fiber glass body further comprises an extension shape measurement
means for measuring a shape of said extending portion of said
extension optical fiber glass body, and said control means reads
the shape information from said-extension shape measurement means
and controls the movement speed of said moving means to control
said extension speed and the heat power of said electric furnace to
control said heat temperature, to thereby maintain a meniscus angle
of said extending portion, said meniscus angle being determined by
said read shape information.
[0063] Preferably, said control means controls said moving means
and said electric furnace so that said extending meniscus angle is
kept 2 to 4 degree.
[0064] According to the present invention, there is provided a
method of extending an optical an fiber glass body in an electric
furnace, the method including the step of raising an extension
speed of an extended optical fiber glass body to a predetermined
extension speed, from the beginning of the extension to the steady
extension state.
[0065] The method may include a step of controlling said extension
speed so that a meniscus angle at an extending portion of said
optical fiber glass body is kept 2 to 4 degree.
[0066] The method may further include a step of raising a heating
temperature of the electric furnace in response to the raise of
said extension speed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0067] These and other objects and features of the present
invention will be more apparent from the following description of
the preferred embodiments given with reference to the accompanying
drawings, wherein:
[0068] FIG. 1 is a view of the configuration of an extension
apparatus for a optical fiber glass body of the related art;
[0069] FIG. 2 is a view of an example of the configuration of an
extension apparatus of an optical fiber glass body of the present
invention;
[0070] FIG. 3 is a view of an example of a gripping member provided
in the extension apparatus of the optical fiber glass body
illustrated in FIG. 2 for gripping and affixing the glass
member;
[0071] FIG. 4 is an explanatory view of an example of a centering
mechanism provided in the extension apparatus of the optical fiber
glass body illustrated in FIG. 2 for centering a front end of a
free end portion of the glass member;
[0072] FIG. 5 is an explanatory view of an electric furnace
extension apparatus and a state of a glass body being extended by
the apparatus;
[0073] FIG. 6 is an explanatory view of the main control system
relating to the present invention;
[0074] FIG. 7 is an explanatory view of an internal portion of the
electric furnace extension apparatus illustrated in FIG. 2 and
shows the state in which a dummy member is attached to the end
portion of the glass body and before connection of the end portion
of the glass body and the end portion of a pulling use glass
member;
[0075] FIG. 8 is an explanatory view in which a first maximum
heating portion is defined as a connection portion P1 and the
maximum heating portion is shifted to an extension portion P2 of
the body;
[0076] FIG. 9A and FIG. 9B are explanatory views of a state where a
dummy member of the end portion of the glass body is connected to
the end portion of the pulling use glass member, in which FIG. 9A
shows a good connection state and FIG. 9B shows a poor connection
state;
[0077] FIG. 10 is a view of a state of deformation of the glass
body before the start of drawing; and
[0078] FIG. 11 is a view of the shape of the extended portion of
the glass body when an extended meniscus shape is formed after the
start of the extending.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0079] Below, an explanation will be given of preferred embodiments
of an electric furnace extending method and extension apparatus for
an optical fiber glass body of the present invention by referring
to the attached drawings.
First Embodiment
[0080] An extension apparatus for an optical fiber glass body
according to a first embodiment of the present invention and a
method of affixing the optical fiber glass body in the extension
apparatus will be explained first by referring to FIG. 2 to FIG.
4.
[0081] In FIG. 2, 1 denotes an extension (stretch) optical fiber
glass body (optical fiber glass body or preform) to be extended
(stretched), and 2 denotes a dummy pulling use glass member
(extension (stretch)-out use glass member). Reference numeral 3
denotes an electric furnace body. A furnace pipe 4 containing an
electric heater is disposed in the electric furnace body 3.
Reference numeral 4A denotes an observation window for observing
the interior of the furnace pipe 4.
[0082] A gripping member 5 for gripping and affixing the fixed end
portion 1A of the upper portion of the extension use glass body 1
is provided in the upper portion of the furnace pipe 4. A gripping
member 6 for gripping and affixing the fixed end portion 2A of the
lower portion of the pulling use glass member 2 is provided in the
lower portion of the furnace pipe 4.
[0083] The gripping (holding) members 5 and 6 can move in the
vertical direction by the moving stand 7 to which the gripping
members 5 and 6 are affixed. Reference numeral 8 denotes a guide
rail for guiding the moving stand 7.
[0084] The gripping member 5 for gripping and affixing the
extension use glass body 1 has for example two key-like glass
member support claws 5A and 5A arranged in parallel as shown in
FIG. 3. A glass member fixing member 5B having a spherical front
end for affixing the upper portion of the fixed end portion 1A of
the extension use glass body 1 gripped in the space between these
support claws 5A and 5A is provided above the space between the two
glass member support claws 5A and 5A. The glass member fixing
member 5B can be moved in the vertical direction by for example a
hydraulic drive. Note that the glass member fixing member 5B is not
limited to a hydraulic drive. Another appropriate drive source, for
example, an electric motor, hand screw, and air pressure drive may
also be used.
[0085] Note that, the shape of the gripping member 5 comprising the
two glass member support claws 5A and 5A and glass member fixing
member 5B is not limited to that of FIG. 3 and may be another
shape.
[0086] The gripping member 6 for gripping and affixing the fixed
end portion 2A of the pulling use glass member 2 is for example a
well known three-claw chuck.
[0087] The extension (stretching) apparatus for an optical fiber
glass body of the present invention is further provided with a
first (upper portion) centering mechanism 90 for the axial
alignment and centering of the front end of the free end portion 1B
of the lower portion of the extension use glass member 1 between
the furnace pipe 4 and the gripping member 5.
[0088] The centering mechanism 90 is provided with for example, as
shown in FIG. 4, a pair of centering grips 90A and 90A having a
self-centering action (a self alignment function), a pair of
support rods 90B and 90B provided at opposing positions for
supporting the centering grips 90A and 90A, and a pair of bases (or
pedestals) 90C and 90C having movement mechanisms using a hydraulic
drive for integrally moving the centering grips 90A and 90A and the
support rods 90B and 90B in the horizontal direction. Note that the
movement mechanisms provided in the pedestals 90C and 90C are not
limited to hydraulic drives. Other appropriate drive sources, for
example, electric motors, hand screws, and air pressure drives may
also be used. In the figure, 90D and 90D on the two sides denote
guide rails.
[0089] The pair of centering grips 90A and 90A are provided with a
pair of opposing V-grooves 90E and 90E in the axial direction of
the extension use optical fiber glass body 1 at the center of the
opposing surfaces thereof.
[0090] The extension apparatus for an optical fiber glass body of
the first embodiment of the present invention is further provided
with a second (lower portion) centering mechanism 92 for performing
the axial alignment for the front end of the free end portion 2B of
the lower portion of the pulling use glass member 2 between the
furnace body 3 and the gripping member 6 for gripping and affixing
the pulling use glass member 2.
[0091] The structure of the lower portion centering mechanism 92
for performing the axial alignment and centering for the front end
of the free end portion 2B of the pulling use glass member 2 is
similar to the structure of the upper portion centering mechanism
90 illustrated in FIG. 4 for performing the axial alignment and
centering for the front end of the free end portion 1B of the
drawing use glass body 1, therefore a detailed explanation will be
omitted.
[0092] Note that the shape of the upper portion centering mechanism
90 and the lower portion centering mechanism 92 is not limited to
the shape shown in FIG. 4. Other shapes can be adopted too.
[0093] The method of fixing the glass body to the extension
apparatus for an optical fiber glass body constituted as described
above is as follows.
[0094] 1. Temporary Fixing of Extension use Glass Body 1
[0095] First, the disk-shaped fixed end portion 1A of the upper
portion of the extension use optical fiber glass body 1 is attached
between the two key-shaped glass member support claws 5A and 5A
arranged in the gripping member 5 and temporarily affixed.
[0096] 2. Gripping of Lower Portion of Drawing use Glass Body 1 by
Upper Portion Centering Mechanism 90
[0097] Next, the front end of the free end portion 1B of the lower
portion of the extension use optical fiber glass body 1 is gripped
by the pair of centering grips 90A and 90A having a self-centering
action of the upper portion centering mechanism 90 and the axial
center of the front end of the free end portion 1B is centered.
Namely, since the front end of the free end portion 1B is in a free
state, when it is pressed by the pair of centering grips 90A and
90A having the V-grooves 90E and 90E in the axial direction of the
extension use optical fiber glass body 1, the axial center of the
free end portion 1B will be set at the center of the circle
inscribed by the two V-grooves 90E and 90E. At this time, by
aligning the center of the circle inscribed by the two V-grooves
90E and 90E with the axial center of for example the furnace pipe 4
in advance, the axial center of the free end portion 1B can be
aligned with the axial center of the furnace pipe 4.
[0098] 3. Gripping and Affixing of Fixed End Portion 1a of Upper
Portion of Extension Use Glass Body 1 by Gripping Member 5
[0099] After the front end of the free end portion 1B of the lower
portion of the extension use optical fiber glass body 1 is gripped
by the upper portion centering mechanism 90 and the axial center of
the front end of the free end portion 1B is centered as explained
above, the disk-shaped fixed end portion 1A of the upper portion of
the extension use optical fiber glass body 1 is gripped and affixed
again by the gripping member 5. The gripping and affixing of the
fixed end portion 1A are carried out by pressing the upper portion
of the fixed end portion 1A of the extension use optical fiber
glass body 1 gripped in the space between the two support claws 5A
and 5A by the glass member fixing member 5B having spherical front
end. Namely, the extension use optical fiber glass body 1 is
gripped and affixed in a state where the axial center of the front
end of the free end portion 1B is centered by the upper portion
centering mechanism 90 by two support claws 5A and 5A and one glass
member fixing member 5B as illustrated in FIG. 3.
[0100] 4. Retraction of Centering Grips 90a and 90a of the Upper
Portion Centering Mechanism 90 from Axial Center Next, the pair of
centering grips 90A and 90A of the upper portion centering
mechanism 90 are retracted from the axial center to thereby set the
front end of the free end portion 1B at a predetermined position in
the furnace pipe 4.
[0101] 5. Gripping and Affixing of Pulling use Glass Member 2 by
Gripping Member 6
[0102] Next, the pulling use glass member 2 is gripped and affixed
by the gripping member 6. The fixed end portion 2A of the lower
portion of the pulling use glass member 2 is temporarily affixed to
the gripping member 5 in a state with a predetermined amount of
free play.
[0103] 6. Centering of Axial Center of Front End of Free End
Portion 2b by Lower Portion Centering Mechanism 92
[0104] The front end of the free end portion 2B of the upper
portion of the pulling use glass member 2 is gripped by the pair of
centering grips 92A and 92A having a self-centering action of the
lower portion centering mechanism 92 in this state to center the
axial center of the front end of the free end portion 2B.
[0105] The method of centering the axial center of the front end of
the free end portion 2B by the lower portion centering mechanism 92
is similar to the centering of the axial center of the front end of
the free end portion 1B of the extension use optical fiber glass
body 1 using the upper portion centering mechanism 90, therefore a
detailed explanation will be omitted.
[0106] 7. Main Gripping and Affixing of Pulling use Glass Member
2
[0107] After the axial center of the front end of the free end
portion 2B of the upper portion of the pulling use glass member 2
is centered, the fixed end portion 2A of the lower portion of the
pulling use glass member 2 is gripped and affixed again by the
gripping member 6. At this time, the pulling use glass member 2 is
gripped and affixed in a state where the axial center of the front
end of the free end portion 2B is centered by the lower portion
centering mechanism 92.
[0108] 8. Retraction of Centering Grips 92a and 92a of Lower
Portion Centering Mechanism 92 from Axial Center and Alignment of
Axial Centers of Two Free End Portions 1b and 2b
[0109] Next, the pair of centering grips 92A and 92A of the lower
portion centering mechanism 92 are retracted from the axial center
to thereby set the front end of the free end portion 2B at the
predetermined position in the furnace pipe 4, then the front end of
the free end portion 1B of the extension use optical fiber glass
body 1 and the front end of the free end portion 2B of the pulling
use glass member 2 are abutted. The two free end portions 1B and 2B
are centered in the axial center of the furnace pipe 4, therefore
they will be abutted in a state where the two axial centers
align.
[0110] 9. Extending (Stretching) Work
[0111] Next, in the same way as in the related art, the furnace
pipe 4 is heated to the predetermined temperature to heat and fuse
the two abutted end surfaces to join the members, then the gripping
member 6 gripping the pulling use glass member 2 is moved downward
at a predetermined speed while moving the gripping member gripping
the extension use optical fiber glass body 1 downward at a constant
speed so as to stretch the extension use optical fiber glass body 1
and extend it to a predetermined outer diameter.
[0112] 10. Drawing Extended Optical Fiber Glass Body to Final
Optical Fiber Cable.
[0113] The above extended optical fiber glass body (preform) 1 is
drew as a final optical fiber, such as a single optical fiber
including a core having a diameter of 10 mm, a cladding formed an
outer circumference of the core and having a diameter of 125 .mu.m,
and a resin coating provided an outer circumference of the
cladding.
[0114] Note, the above steps 1 to 8 can be changed in its
sequence.
Experiment of First Embodiment
[0115] The following experiment was carried out by the extension
apparatus for an optical fiber glass body shown in FIG. 2 to FIG.
4.
[0116] The used glass body 1 had an outer diameter of 70 mm and a
length of 1000 mm. The outer diameter of the dummy material of the
end portion of the body on the pulling use glass member side was 15
mm. Also, the outer diameter of the end portion of the pulling use
glass member was 20 mm.
[0117] As a result of the experiment, the deviation of the axial
centers of the two free end portions 1B and 2B in the furnace pipe
4 was within the range of .+-.0.1 to 0.2 mm (0.5 to 1% of the
diameter of the glass member) in the horizontal plane, so the
precision of the centering of the axial centers was improved to
about 10 times that of the related art.
[0118] As a result of extending the glass body 1 as described
above, no bending occurred in the drawn glass body for the optical
fiber. Further, the vicinity of the connection portion did not
break at the time of drawing.
Effect of First Embodiment
[0119] According to the extension apparatus for an optical fiber
glass body of the first embodiment, since a centering mechanism
provided with a pair of centering grips is provided between each
end portion of the furnace pipe and the two glass member grips, the
axial alignment of the free ends of the two glass members can be
easily and simply carried out.
[0120] Further, according to the method of fixing the optical fiber
body to the extension apparatus explained above, since the axial
centers of the front ends of the free end portions of the two glass
members temporarily fixed by the glass member grips are adjusted by
the centering mechanisms provided with the pairs of centering
grips, the axial alignment thereof can be easily and simply carried
out in a short time.
[0121] Further, since the fixed end-portions of the two glass
members are affixed after the axial centers of the front ends of
the free end portions of two glass members are aligned as described
above, they can be abutted and connected in a state where the axial
centers of the front ends of the free end portions of two glass
members moved into the furnace pipe are aligned. As a result, the
distribution of stress at the cross-section of the connection
portion of the two becomes uniform, the vicinity of the connection
portion of the two no longer becomes slanted, and breakage can be
avoided.
Second Embodiment
[0122] As a second embodiment of the present invention, an
explanation will be given of an electric furnace extending
(stretching) method comprising the steps of: abutting the end
portion of the optical fiber glass body and the end portion of the
pulling use glass member, heating and fusing them in the electric
furnace extending process by the first embodiment for connection,
moving the highest temperature portion of the electric furnace to
this connection portion for heating and fusing, moving this highest
temperature portion from the heat fused portion to the extending
portion of the extension optical fiber glass body side, then
drawing of the glass body.
[0123] FIG. 5 is a view of the configuration of the electric
furnace drawing apparatus according to the second embodiment and
the state of extending the glass body by this apparatus.
[0124] In FIG. 5, 30 denotes the furnace body, 31 a furnace pipe,
32 a heater, 33 a heat insulation material, 34 and 35 denote
windows, 36 an outer diameter measurement unit, 37 a temperature
meter, 38 an outer diameter measurement unit of the extending rod,
and 39a and 39b denote gripping portions.
[0125] Reference numeral 20 denotes the optical fiber glass body
for extending, 21 a drawn portion (portion of changed outer
diameter), 22 an extension rod, 23 a pulling use (extend-out use)
glass member, and 24 a connection portion. In the second embodiment
of the present invention, the extending is carried out by using the
apparatus illustrated in FIG. 5.
[0126] The second embodiment of the present invention can be
carried out by a control apparatus shown in FIG. 6.
[0127] FIG. 6 is a view of the configuration of the control system
in the electric furnace extension apparatus for an optical fiber
glass body according to a fourth embodiment of the present
invention.
[0128] The control system includes a control means 40 such as
computer, the first outer diameter measurement unit 36 for
measuring an outer diameter of the extension start position
(meniscus portion) 21a of the extension optical fiber glass body to
measure a meniscus shape of the extension start position, i.e., an
angle of the meniscus shape of the meniscus portion 21a, the
temperature measurement unit 37 for measuring the temperature of
the meniscus portion 21a, the second outer diameter measurement
unit 38 for measuring an outer diameter of the extended (stretched)
optical fiber glass body (preform) 22 at the out side of the
electric furnace 30, the moter 41 for moving downward the gripping
member 39b to extend (stretch) the extended optical fiber glass
preform 22 downward, and the speed meter 42 such as a taco-meter
for measuring the rotation speed of the motor 41 to measure the
extension speed of the extended optical fiber glass body 22.
[0129] Basically, the control means 40 reads the second diameter of
the extended optical fiber glass body 22 from the second outer
diameter measurement unit 38, the extension speed from the speed
meter 42 and the temperature from the temperature measurement unit
37, and controls the heater power of the electric furnace 30 and
the rotation speed of the moter 41 to maintain the second outer
diameter of the extend optical fiber glass body 22 at a
predetermined value.
[0130] In this embodiment, the control means 40 controls the
heating and fusing the junction (abutting) portion of the extension
optical fiber glass body 20 and the pulling glass member 23 by
controlling the heater power of the electric furnace 30, after
abutting the end portion of the extension optical fiber glass body
20 and the end portion of the pulling glass member.
[0131] Next, the control unit 40 controls the movement of the
highest temperature portion of the electric furnace 30 to the
junction (abutting) porion. Further, the control unit 40 controls
the movement of the highest temperature portion from the heat fused
portion to the extension portion 22B of the extension optical fiber
glass body 20. Therefore, the control unit 40 controls the normal
extension of the extension optical fiber glass body 20 to produce
the extended optical fiber glass body having the predetermined
diameter (second outer diameter).
[0132] At the initial state of the extension of the optical fiber
glass body 20, the control means 40 changes the heating temperature
in the electric furnace 30 and the extension speed, as shown in
FIG. 10. This will be discussed later.
[0133] In the normal extension process, the control unit 40
controls the shape, especially, the angle of the meniscus portion
22a in a predetermined value, for example 4 degree, or in a
predetermined range, preferably, 2 to 4 degree. This will be
discussed later.
[0134] FIG. 7 is a view of an internal portion of the electric
furnace drawing apparatus. FIG. 7 shows the state before connection
of the end portion of the optical fiber glass body 20 and the end
portion of the pulling use glass member 23. A dummy material 25 is
attached to the end portion of the glass body in advance.
[0135] FIG. 8 is an explanatory view of the movement of the highest
temperature portion in the electric furnace in FIG. 6 from the
connection portion P.sub.1 of the two members to the extending
portion P.sub.2 of the glass body side and the extending of the
same. A distance L between the connection portion P.sub.1 and the
extending portion P.sub.2 is for example about 10 to 40 mm.
[0136] According to the second embodiment, after the connection of
the glass body 20 and the pulling use glass member (dummy
extend-out use glass member) 23, the extension work immediately
becomes possible in the same step, therefore the efficiency of the
extension work is improved.
[0137] FIGS. 9A and 9B show the shape of the two end portions when
the end portion 24 of the glass body 20 and the end portion of the
pulling use glass member 23 are connected.
[0138] As shown in FIG. 9A, the outer diameter d.sub.1 of the dummy
material 25 of the end portion of the optical fiber glass body 20
is made smaller than the outer diameter d.sub.2 of the end portion
of the pulling use glass member 23. By doing this, a preferable
reliable connection is obtained. The outer diameter of the end
portion of the pulling use glass member 23 is preferably made two
to three times the outer diameter of the dummy material of the end
portion of the optical fiber glass body.
[0139] FIG. 9B illustrates an example of a poor connection in which
the outer diameter of the end portion of the glass body 20 is
larger than the outer diameter of the end portion of the pulling
use glass member 23.
Experiment of Second Embodiment
[0140] A drawing use glass body having an outer diameter of 65 mm
was used. A dummy material 25 (upper portion outer diameter: 35 mm,
lower portion outer diameter: 10 mm, and height: 30 mm) shown in
FIG. 9A was connected to the front end of this. Further, use was
made of a pulling use (draw-out use) glass member having an outer
diameter of 38 mm. After fusing and connecting the end portions of
the two, the highest temperature portion in the electric furnace
was moved from the connection portion to the drawing portion of the
glass body which was then drawn at a drawing rate of 38 mm/min. As
a result, there was no bending in the drawn body, and the precision
of the outer diameter could be controlled to 34 mm.+-.0.5 mm in the
overall length of 1300 mm.
Third Embodiment
[0141] The third embodiment of the present invention is a method
and apparatus of electric furnace extension of an optical fiber
glass body comprising, when extending the optical fiber glass body
at the highest temperature portion inside the electric furnace,
measuring the temperature of the glass body extension portion, the
outer diameter, and the extension rate and, while controlling them,
gradually raising the extension rate, extension speed and heating
temperature from the start of extension to be steady state, as
shown in FIG. 10.
[0142] In this case, preferably the extension operation is
controlled by feeding back to the extension rate extension speed
the value of the first outer diameter measured when the angle of
the extended meniscus of the extension portion 22a of the glass
body 20 is 4.degree. or less.
[0143] By controlling the extension operation of the control means
40 in this way, the bending of the extended body is prevented,
fluctuation of the second outer diameter is eliminated, and the
precision is improved.
[0144] Further, the extension rate (extension speed) is increased
and the productivity is improved. The extension rate referred to in
the present invention means the rate at which the drawn rod is
formed. The extension rate is set at the start of extension for
example 20 to 40 mm/min and gradually made higher to 40 to 70
mm/min at the steady state, as shown in FIG. 10. This is for
improvement of the productivity.
[0145] In the present invention, since the extension rate is
gradually made faster, preferably, it is necessary to also control
the temperature of the furnace. The reason for the slow extension
rate at the start of the extension operation is that there is no
data on the outer diameter measured since the meniscus is not
formed at the start of the extending and also that a fast extension
rate is a cause of trouble, therefore it is necessary to keep the
initial extension rate low.
[0146] On the other hand, in the present invention, when the
meniscus is formed and it becomes possible to measure the outer
diameter of this part, it becomes possible to control the extension
operation by feeding back to the extension rate the measured value
of the outer diameter of the extended meniscus, therefore the
extension rate can be made faster.
[0147] The above control is performed by the control system shown
in FIG. 6.
[0148] FIG. 10 shows the shape of the glass body in the initial
stage of drawing in which the meniscus has not yet been formed.
[0149] FIG. 11 shows the state where the drawn meniscus is formed
after an elapse of a predetermined time and the shape of the glass
body changes.
[0150] In FIG. 11, the first portion 21A for measurement of the
outer diameter of the extended portion 21 of the optical fiber
glass body 20 is located at the position where the meniscus angle
.theta. at the extended meniscus 21a is 40 or less.
[0151] The second portion 21B for measurement of the outer diameter
is located at the position where the meniscus angle exceeds
4.degree. (upper portion of 21A). In the control of the outer
diameter, the measurement value of the outer diameter at the
position where the meniscus angle of the first outer diameter
measurement portion 21A is 2 to 4.degree. is preferred.
[0152] Therefore, preferably the outer diameter value when the
meniscus angle is 2 to 4.degree. is used for control.
[0153] The second measurement portion 21B is too close to the
optical fiber glass body 20, therefore the outer diameter has not
yet become smaller, the meniscus angle is large, and the
measurement position is located in the upper portion, so control is
hard.
Experiment of Third Embodiment
[0154] An extension use glass body having an outer diameter of 70
mm was used. A dummy material 25 (upper portion outer diameter: 45
mm, lower portion outer diameter: 10 mm, and height: 30 mm) shown
in FIG. 9A was connected to the front end of this extension use
glass body. Further, use was made of a pulling use (draw-out use)
glass member having an outer diameter of 38 mm. After fusing and
connecting the end portions of the two, the highest temperature
portion in the electric furnace was moved from the connection
portion to the extending portion of the glass body. The initial
extension rate was set to 30 mm/min, then was gradually raised to
obtain a steady state extension rate of 50 mm/min. In this case,
the temperature, outer diameter, and extension rate of the
extending portion of the glass body were measured and controlled
for the extension operation. Note that the control was carried out
by using the measurement value of the outer diameter when the angle
of the extending meniscus was 3.degree.. As a result, there was no
bending in the extended body, and the precision of the outer
diameter could be controlled to 36.+-.0.5 mm over the entire
length.
[0155] The above embodiments explained above were only examples.
The present invention includes various modifications.
[0156] For example, the first outer diameter measurement unit 36
can be replaced by an imaging apparatus such as a CCD camera for
measuring the shape and angle of the meniscus portion 21a.
[0157] As mentioned above, in the present invention, when
connecting the extension use glass body and the pulling use
(draw-out use) glass member in the electric furnace extending
process of the optical fiber glass body, the axial alignment of the
two can be precisely, easily, and simply carried out. As a result,
the distribution of stress at the cross-section of the connection
portion of the two becomes uniform at the time of drawing, and the
bending of the drawn body can be prevented. Further, the vicinity
of the connection portion of the two no longer becomes slanted, and
breakage is avoided.
[0158] Further, since the extending of the glass body can be
immediately commenced after the fusing and bonding of the two
members, the present invention is effective in the point of work
efficiency.
[0159] Further, the present invention can gradually control and
raise the extension rate, and preferably raise the heating
temperature, from that at the start of extension and, uses the
value of the first outer diameter of a predetermined position of
the meniscus of the extended portion for this control, therefore
can improve the precision of the outer diameter of the extended
optical fiber glass body and the extension rate.
* * * * *