Note: Descriptions are shown in the official language in which they were submitted.
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l`he presellt invention relates to wlitary elements comprising optical
fibers, S'JCh elemellts being usefully employable in the construction of tele-
communication cables. Tllis application is a division of application Serial
No. 302,612, filed May 4, 1978.
The expression a "unitary element" is intended to mean a cylindrical
elongated body of the type described in Canadian Patent No. 1,01~'~, issued
March 6, 1979, entitled "Sheathed Optical Fiber Element and Cable and Process
for Production Thereof", and assigned to the assignee of this application.
Such an element comprises one or more optical fibers, either bare or clad by
at least one protective layer, which are layed up in a sheath, preferably of a
plastic material (e.g., polyethylene, polypropylene, etc.) or an elastomeric
material (e.g. cross-linked polyethylene) in a tubular form, such a sheath be-
ing referred to herein as a "tube". The tube has an internal surface that
does not adhere to the external surface of said fiber or fibers, and the
internal dialneter of the tube is greater than the external diameter of said
fibers, or of a hypothetical circle circumscribing said fibers, so that the
said fiber (or fibers) lies loose inside the tube.
In a preferred embodiment, the said fiber (or fibers) possesses a
greater length than the tube containing it. This construction allows for
loading of the unitary element with a greater axial force than the one to
which a single fiber (or the fibers) could be subjected.
The unitary element has a long length, that is, it has a body having
longitudinal dimensions that are very much greater than the transverse dimen-
sions. The length of the unitary element is, in fact, preferably of the order
of one kilometer, whereas the diameter measured on the external surface of the
tube is about a few millimeters. The reason for this is that telecommunica-
tion cables have a long length, and it is desirable to make such cables with-
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out joints, except at their encls, because of signal losses at such joints.
In said Canadian Patent No. 1,049,2~1, there is described a methodfor making such a unitary element. This method, in which a tube is extruded
directly onto the optical f-iber (or fibers) and is cooled immediately after,
is characterized by the fact that it comprises the step of lubricating the
said fiber (or fibers) upstream of the extrusion phase of the tube with an
appropriate anti-adhesive. Said tube is extruded so as to have an internal
diameter such as to maintain, at an ambient temperature, a diameter greater
than the external diameter of the enclosed fiber (or fibers).
This method has, to date, given excellent experimental results.
Nevertheless, there is a reasonable doubt as to the method being any longer
advisable because of the high precision technological progress in the field of
telecommunication cables with optical fibers, and in particular, because of
the adoption of miniature tubes, i.e. with tubes having inside diameters of
smaller size. However, even with such miniature tubes the internal diameter
is greater than the fiber (or fibers) enclosed in the tube.
It could, for example, happen that in spite of the narrow path of
the advancing trajectory of the fioer (or fibers) and of the tube being ex-
truded around it along the production line of the unitary element, minute
oscillations may place the internal tube walls into contact, at one or more
points, with the fiber (or fibers) thereby entrapping, or causing local adhe-
sion, of the fiber and the tube. The succeeding cooling of the tube gives
rise ~o a contraction force which is applied to the fiber ~or fibers) and
which causes rupture of the fiber (or fibers) or a variation in the transmis-
sion characteristics of the fiber (or fibers).
At times, moreover, it may be necessary to fill the tube with a
filling material that does not allow migration to take place inside the tube,
ll3sass
such as migration of moisture or any other contaminat-Lng l-iquids. Until the
present invention, a working procedure was quite unknown for permitting
satisfactory filling of the tube.
The above-identified parent application describes and claims a process
for producing unitary elements, which does not have the drawbacks described
above; and also describes and claims an apparatus which allows for the
production of unitary elements with using the method described therein.
The present invention may be generally defined as a unitary optical
cable which comprises a self-sustaining tube of elastic material enclosing one
or more fibers. This tube has an inner wall of a diameter larger than the
diameter of a circle circumscribing the fiber or fibers being free of material
interiorly thereof which prevents movement of the fiber or fibers laterally of
the axis of the tube so that the fiber or fibers are permitted to move laterally
with respect to the inner wall of the tube. This tube has a longitudinally
extending cut therein which extends from the outer surface of the tube to the
inner surface of the tube and which provides a pair of tube wall edge faces at
opposite sides of the cut. The resilient nature of this tube is such that it
inherently presses said edge faces against each other and assumes a tubular
cross-section having said diameter larger than the diameter of a circle circum-
scribing the fiber or fibers.
The objects and advantages of the invention will be apparent to thoseskilled in the art from the following description of the presently preferred
embodiments thereof, which description would be considered in conjunction with
the accompanying drawings, in which:
Figure 1 illustrates schematically the production line of a plant
capable of carrying out the method of parent application;
Figure 2 is a schematic perspective view which illustrates means for
carrying out certain phases of the said method;
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Figure 3 is simi.lar to F:Lgure 2t and illustrates a further means for
carrying out certain phases of said method;
Figure 4 is a fragmentary cross-sectional end view of a modified
. - 3a -
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rorm of the means ShOWIl ill FIGURE 2; and
l:IGURE 5 is a plan view of an element made in accordance with t;l~
invention whicll is cut alollg a helical line.
The plant, represented schematically in FIGURE 1, comprises at least
one feeder for the optical fiber or fibers 11. In a special case, this feeder
10 is a bobbin 12. Parallel to the bobbin 12, there is a feeder 13 for a tube
14, preferably of a thermoplastic material or of an elastomeric material hav-
ing sufficient elasticity as described hereinafter, and having an internal
diameter greater than the external diameters of the fiber or group of fibers
11. The illustrated feeder 13 is a bobbin.
The tube 14 is previously stabilized. This means that it has under-
gone a thermal and even a mechanical treatment that has brought the material
constituting the tube to an optimal condition of stability and resistance.
The preferred mechanical treatment is a stretching process that gives to the
tube molecules a preferential orientation that improves the mechanical
quality.
In series with the feeders 10 and 13 (FIGURE 1), there is shown a
block 16 that represents an assembly for cutting the tube 14 and inserting the
optical fiber or fibers with the tube 14. Such assembly 16 includes a cutting
means 20 in the form of a cutting blade (FIGURE 2), capable of cutting the
tube 14 to provide a longitudinally extending cut or slit therein which ex-
tends from the outer periphery to the inside of the tube. Preferably, the
means 20 is adjustable by the means 28 for calibrating, in the desired manner,
the desired cut in such a way that the cut corresponds to a depth equal to the
thickness of the tube wall. By tube wall thickness is meant the thickness
which is found along the cutting plane. Preferably, the adjusting means 26
also includes means for varying the angle of the cutting means 20 with respect
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to a ~lane ~assing through the axis of the tube 14 and hence, the cut inclina-
tion and the assembly includes a separating mcans 24 for simultaneously
separating the edges 22 and 23 of the cut and a suitably shaped guiding means
for the fiber or fibers 11. In the plant illustrated, the separating means 24
is also the fiber guiding means, but the separating means can be distinct from
the guiding means. The guiding means 24 preferably is a metallic capillary
tube.
The assembly represented by the block 16 can also comprise a means
25 capable of inserting a filling material into the tube 14 through the gap 21
~see FIGURE 3). The means 25 illustrated is a capillary tube parallel to the
metallic capillary tube 24 and is made of a suitable material having proper-
ties that are compatible with the nature of the filling material.
Instead of inserting the filling material in the gap 21 which
receives the fiber or fibers 11, the edges 22 and 23 can be separated down-
stream of the gap 21 to provide a second gap, and the filling material can be
inserted through such second gap created for this purpose.
Downstream of the assembly 16, there is a rectilinear traction means
17, followed, in turnJ by at least a collecting means 18. The collecting
means 18, in the plant illustrated, is a bobbin which rotates around its own
axis 19. In the preferred embodiment illustrated, between the rectilinear
traction means 17 and the bobbin 18, there is provided a traction controlling
device 26, such as a pulling wheel, for exerting a pulling and stretching
force on the tube 14. Alternatively~ the traction controlling device 26 can
be omitted, and the collecting bobbin 18 can be provided with means for regu-
lating the pull on the element in the collecting phase.
The bobbin 13 feeds the tube 14 uniformly, and the rectilinear trac-
tion 17 applies, on the tube that is passing through it, a first traction
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force that puts the part of the tube upstream of the means 17 under tension,
nd defilles a rectilinear path for the tube clownstream of the means 17.
Uystream of the rectilinear traction means 17, the tube, under ten-
sion) passes through the field of action of the cutting means 20 (see FIGURE
2) that cuts it in the longitudinal sense and continuously along the length of
the tube 14 andJ for example, (but not necessarily) along a generatrix. In
practiceJ "longitudinal" signifies a line that extends along almost the entire
tube length, but it can also be other than a rectilinear line. The cut which
is made has a depth equal to the thickness of the tube 14 on the cutting plane.
The cutting plane can be radial or tangential to the internal circumference of
the tube, as shown in FIGURE 4, or at any angle which will produce a cut ex-
tending from the outer periphery to the inner wall of the tube 14.
As the cutting means 20 cuts the tube 14, the separating means 24,
immediately downstream of the cutting means 20, separates, preferably
simultaneously$ the edges 22 and 23. The separating means 24, which, in the
example illustrated, is a metallic capillary tube acts also as a guiding means
for the fiber or fibers 11, and said guiding means penetrates, leading end
first, into the tube 14, through the gap 21.
The optical fiber or fibers 11, unwinding with a uniform movement,
advance into the inside of the tube 14 by passing through the capillary tube
24.
Whenever it is required to fill the unitary element that is being
produced, a filling material of a type known in the art is inserted into the
tube 14 by the means 25 (see FIGURE 3) through the gap 21, or as explained
previously through a second gap used for the same purpose.
The gap 21 is spontaneously closed by exploiting the elasticity of
the material downstream of the assembly 16, that is, the material of the tube
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~ el~stic, and \~I-en the edges '2 and 2~ are not held apart, tlley will
naturally assumc all al)uttillg relation as shown in l:lCURES 2 and 3 downstream
of the tube 24 or t]le tube 25.
The fiber (or fibers~ 11 continues in its straight path co-linear
with the tu~e 14, the fiber 11 and the tube 14 constituting the unitary ele-
ment 27 that is now wound around the bobbin 18.
The tube 14, passing through the rectilinear traction means 17 and
owing to the first traction applied to it in that zone, comes under tension.
Said tension can be defined as a "cutting" tension in the path that comprises
at least the length 'a' between assembly 16 and the rectilinear traction means
17. This latter means moreover, acts exclusively on the tube 14, and the
fiber 11 inserted in the tube 14 is not stressed at all.
The traction controlling device 26 puts under tension the tract 'b'
of the tube 14, i.e. the portion between the device 26 and the rectilinear
traction means 17, applying to it a second traction. Also, in this case, the
fiber 11 is not loaded by any force since it is surrounded by the tube 14.
Therefore, it is the tube 14 only, that undergoes the pull, and hence, the
tract 'b' of the tube 14 can stretch in length with respect to the fiber (or
fibers) 11. Thus, downstream of the traction controlling device 26, where
tension on the tube 14 is removed and the tube 14 returns elastically to its
own original dimension, the fiber 11 contained in it, has a greater length
with respect to the tube 14 which, as has been pointed out before, permits
the stressing of the unitary element, by traction, without stressing the fiber
or fibers 11.
However, whenever the lengthening of the tube 14 which is produced
in the tract 'a' by the rectilinear traction means 17, provides a sufficient
excess length of fiber, the traction controlling device 26 can be omitted, and
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hellce, the tube 14 can be utilized as already tension unloaded, downstream of
the said rectilinear traction means 17. Alternatively, the said lengthening
of the tube 14 can be obtained (in order to provide a greater relative
lengthening of the fiber) directly during the collecting phase, by providing a
traction controller (not illustrated) for the pull exercised by the collection
bobbin 18 which acts in such a way as to put the tube 14 of the unitary ele-
ment 27 under tension by operation of said traction controller.
As has been stated, the unitary element 27 can comprise a tube pre-
senting a longitudinal cut equal to the thickness of the tube itself in the
cutting plane, for example, along a generatrix, and also along any non-
rectilinear line. The preferred line is a helicoidal line, such as the line
31 shown in FIGURE 5, that could have, with respect to a rectilinear line, the
advantage of better withstanding the curvature of coiling without any danger
of the fiber (or fibers) escaping out of the tube 14.
The plant, for producing the latter ~ype of unitary element, will
have a feeder 13 for the tube 14~ the rectilinear traction means 17 and the
collecting means 18 which rotates, with a uniform movement, around an axis 29
(FIGURE 1) lying Oll the rectilinear path of the said fiber (or fibers) 11 as
indicated by the arrow 30. The means 18 will, of course, also rotate around
the axis 19, and the assembly 16 will be stationary.
Although preferred embodiments of the present invention have been
described and illustrated, it will be apparent to those skilled in the art
that various modi~ications may be made without departing from the principles
of the invention.
