Optical fiber drawing apparatus

An optical fiber drawing apparatus which includes a heating furnace which fuses a forward end of an optical fiber preform for drawing an optical fiber, and a screening portion which applies tension to the optical fiber through in-line, for guarantee of its strength. The screening portion further includes a suction device disposed along a passage of the optical fiber running through it for sucking in the optical fiber.

BACKGROUND OF THE INVENTION 
The present invention generally relates to a drawing arrangement, and more 
particularly, to a drawing apparatus for drawing an optical fiber in the 
manufacture thereof. 
The optical fiber normally has a tensile strength of several hundred 
kg/mm.sup.2 (breaking elongation at several%), and in the longitudinal 
direction of the optical fiber, it is necessary to remove portions having 
low strength below 70 Kg/mm.sup.2 (breaking elongation at 1%). For this 
purpose, it has been a conventional practice to effect screening for 
strength guarantee by applying a constant tension over an entire length of 
the optical fiber so as to break the low strength portions thereof for 
removal. In many cases, such screening process is generally incorporated, 
through in-line, in the optical fiber drawing apparatus arranged to fuse 
an optical fiber preform by heating for drawing the optical fiber. 
In a conventional optical fiber drawing apparatus as shown in FIG. 3, it is 
so arranged that an optical fiber preform 1 lowered at a constant speed by 
a feeding device 2 has its lower end fused through heating by a heating 
furnace 3 so as to be drawing into an optical fiber 10, and thereafter, 
the optical fiber thus formed is coated with resin by a coating device 4, 
with subsequent curing of the resin by a curing furnace 5, and then, taken 
up onto a capstan 6. The optical fiber is further passed through a 
screening portion 7, and subsequently, wound onto a winding machine 8 as a 
finished optical fiber 10. 
In the known optical fiber drawing apparatus as described above, however, 
there has been such a disadvantage that when the optical fiber is broken 
at its low strength portion in the screening portion 7, the portion of the 
optical fiber 10 continuously drawing out by the capstan 6 gets entangled 
with the capstan 6, thus requiring a great deal of time for restoring its 
normal running passage, with a consequent loss in the productivity of the 
optical fiber. 
SUMMARY OF THE INVENTION 
Accordingly, an essential object of the present invention is to provide an 
optical fiber drawing apparatus, having an improved screening portion free 
from entanglement of a broken optical fiber with respect to other 
surrounding devices. 
Another object of the present invention is to provide an optical fiber 
drawing apparatus of the above described type, which is simple in 
construction and stable in functioning with high reliability. 
In accomplishing these and other objects, according to one preferred 
embodiment of the present invention, there is provided an optical fiber 
drawing apparatus which includes a heating furnace which fuses a forward 
end of an optical fiber preform for drawing an optical fiber therefrom, 
and a screening portion which applies tension to the optical fiber through 
in-line to for guarantee strength thereof. The screening portion further 
includes a suction device disposed along a passage of the optical fiber 
running therethrough for sucking in the optical fiber thereinto. 
By the above arrangement according to the present invention, when the low 
strength portion of the optical fiber is broken at the screening portion, 
the optical fiber to be continuously paid out subsequently is 
advantageously sucked into the suction device without being entangled with 
other devices.

DETAILED DESCRIPTION OF THE INVENTION 
Before the description of the present invention proceeds, it is to be noted 
that like parts are designated by like reference numerals throughout the 
accompanying drawings. 
Referring now to the drawings, there is shown in FIGS. 1 and 2, an optical 
fiber drawing apparatus according to one preferred embodiment of the 
present invention, which generally includes a heating furnace 3A for 
fusing the forward end of the optical fiber preform 1 lowered by a feeding 
device 2 at a constant speed so as to be drawn into an optical fiber 10, a 
coating device 4A for coating the optical fiber thus drawn with resin, a 
curing furnace 5A for curing the resin applied onto the optical fiber 10, 
a capstan 6A for taking-up the optical fiber thus processed, a screening 
portion 7A particularly provided with a suction device S, and a winding 
machine 8A for winding the finished optical fiber 10 thereonto. 
As shown on an enlarged scale in FIG. 2, the above suction device S 
directly related to the present invention includes suction port 11 
provided along a passage of the optical fiber 10, a suction blower 12 
connected to said suction port 11 through a pipe d, and a mesh element 13 
provided in the pipe d between the suction port 11 and the suction blower 
12, with a recess or pocket 14 being formed within said pipe d in a 
position before said mesh element 13 as illustrated. 
Accordingly, when the optical fiber 10 is broken off, at its low strength 
portion in the screening portion 7A, it is sucked in through the suction 
port 11. The fiber is prevented from entering further by the mesh element 
13 located before the blower 12 so that the fiber accumulates in the 
pocket 14 provided prior to said mesh element 13. 
It is to be noted here that, although the suction blower 12 may be operated 
at all times during drawing of the optical fiber, it may be so arranged as 
to be operated at any time through detection of rupture of the optical 
fiber 10 at the screening portion 7A, for example, by variation of a 
position of a dancer roller (not shown) for the winding machine 8A. 
According to an experiment carried out by the present inventors, when an 
optical fiber was drawn by the drawing apparatus having the construction 
as described so above, the optical fiber 10 was broken 10 times at the 
screening portion 7A. The length of the optical fiber required for 
restoring the running line of the optical fiber 10 was about 100m on the 
average. 
Meanwhile, as a comparative example, in the case where an optical fiber was 
drawn through employment of the conventional drawing apparatus as 
described earlier with reference to FIG. 3, the optical fiber broke at the 
screening portion 7 undesirably twisted around the capstan 6, and for 
restoring the running line of the optical fiber, the length in the optical 
fiber in about 1000m was required on average, with breakage occurring 12 
times. 
As is clear from the foregoing description, according to the optical fiber 
drawing apparatus of the present invention, since the suction device 
provided at the screening portion sucks in the broken optical fiber, there 
is no possibility that such broken optical fiber can become twisted around 
other devices of the apparatus, and thus, the restoration of the running 
line of the optical fiber is simplified, thereby making it possible to 
improve the productivity of the optical fiber. 
Although the present invention has been fully described by way of example 
with reference to the accompanying drawings, it is to be noted here that 
various changes and modifications will be apparent to those skilled in the 
art. Thererfore, unless otherwise such changes and modifications depart 
from the scope of the present invention, they should be construed as 
included therein.