Note: Descriptions are shown in the official language in which they were submitted.
22
BACKGROUND OF T~E IN~NTION
The present invention relates to a cable elemen-t and an
optical f`iber cable, capable more especially of withstanding high tractive
efforts and/or pressures and a process for manufac-turing same.
In the prior art an optical fiber cable elemen-t is known
in which the optical f`ibers are disposed in grooves or notches, arranged
helically or with al-ternate pitch provided in the surf`ace of a cylindrical
structure. The cylindrical struc-ture is formed generally of a central
carrier surrounded by plastic material. The shape of the notches as well
as their surface condition are important elements in ~his structure. For
example, French patent n 2 419 524 filed by the Applicant discloses ~
grooved cylindrical structure in which the grooves assume a curvilinear
V-shaped pro~ile, the concavity of the sides being directed outwardly of
the groove.
rrhe present inven-tior. thus relates to an optical fiber
cable element presenting all the desired characteristic~ for the grooved
cylindrical structure but which presents an increased resistance to
tractive efforts and/or to pressure.
SUMMAR~ OF T~E lNV~NllON
An optical fiber cable element in accordance with the
lnvention comprises a plurality of threads twisted helically or with
alternate pitch so as -to form a rigid assembly, said threads presenting
therebetween at least one gap, and at least one optical ~iber freely
disposed in at least one gap between the elements.
According to one embodiment of the invention, the threads
are twisted about a central core, preferably made from metal. The central
core may be solid or else be formed for example by a strand.
According to a varia-tion, the threads and the central
3~
core are formed from the same material. The ou-ter cover may also be
~ormed ~rom the same material.
According -to a variation, the gaps present between the
internal part of the thrcads and the core are filled with a thermoplastic
material or a resin.
According to another ~ariation, the internal profile o~
the -threads corresponds to the external pro~ile of the core.
Finally, according to yet another variation, the threads
are disposed in helical or alternate pitch grooves provided in the core.
The invention also relates to a process ~or manufacturing
a cable element such as mentioned above, and which consists in laying
helically or with al-ternate pitch a plurality of -threads so as to form a
rigid assembly and in disposing at least one optical fiber in at least
one gap between the threads.
According to a variation, -the twisting takes place about
a central core and i-t comprises a preliminary step for coating said core
or said threads with a thermoplastic material or a resin. The thickness
of said layer is advantageously determined so as to compensate fDr the
volume of the internal gaps between the threads and the central core.
BRIE~ DESCRIPTION OF THE DR~WINGS
Fig. 1 shows a cable element in accordance with the
invention ;
Figs. 2a and 2b illustrate a variation of Fig. 1 compris-
ing a s-tep ~or coa-ting a central core ;
Figs. 3a and 3b shows a variation o~ Fig. 1 ~ mprising a
step ~or coating twisted threads ;
Figs. 4a to 4 e shows pro~ile variations of the twisted
threads ;
~9~7~2~
Figs. 5, 6a, 6b and 7 show varia-tions of -the invention
comprising a grooved central core ;
Figs. 8a, 8b and g show variations of the invention not
presen-ting a central core ;
Fig. 10 sho~s a variation of the invention in which a
central core extends radially as far as the external diameter of the
element ;
Fig. 11 shows an optical fiber cable comprising a plurality
of cable elements in accordance with the inven-tion.
D~SCBI~TION OE TH~ PREFERRED EMBODIMENT~
Fig. 1 shows a central core 1 about which are twisted
th~eads 2, here eight in number. ~he central core 1 may be solid or may
be formed for example by a strand. Threads 2 have a shape cyli~arical in
revolution and are laid ~ helically or with alternate pitch, each of the
.. .. . . .. . .. .
threads being tangent to the -two adjacent threads as ~ell as to the
central core 1. Curvilinear txiangles 5 thus exist between two threads
and the central core, as well as external open gaps ~. These gaps 6 have
in section the shape of a curved V ~/hose concavity is directed outwaraly.
These gaps, whose shape corresponds to that taught by the abo~e mentioned
20 French pa-tent 2 ~19 524, are used for disposing optical fibers 3 therein.
Thus, in Fig. 1, there is shown an optical fiber disposed in each of the
gaps. Of course, to form a cable in accordance with the invention, it is
no-t necessary to lay an optical fiber in each of the gaps. Furthermore,
seve~al optical fibers may be disposed in the same gap. A cable element
in accordance with the invention is surrounded by taping or wrappin~
and/or a sheath andfor an outer e~ver 4. More specifically, a -taping or
wrapping will perform the function of holding the -fibers in the gaps,
while a sheath or an ou-ter cover will be able to protec-t the fibers -from
mechanical stresses and/or damage.
Figures 2a and 2b show a variation of Fig. l in which the
curvilinear triangles 5 are filled for example with a thermoplastic mat-
erial or a resin. For -this, the central core 1 is coated wi-th a layer 8
of plas-tic material or resin and elements 2 are then -twisted, possibly
after pre-hea-ting of layer 8. During twisting, layer 8 assumes the shape
shown in Fig. 2b at 8' and fills up the inner closed gaps 5. The thickness
of layer 8 will be chosen so tha-t, after twisting, the amount of material
which it represents just fills the curvilinear triangles 5. Such a
variation allows a structure to be obtained which is mechanically more
coherent since the twisted threads 3 are held in place by layer 8' which
fills the curvilinear triangles and thus avoids sliding about central
core 1, more especially during an untwisting movement o~ the cable element.
Ano-ther variation is shown in Figs. 3a and 3b and corresponds
to coating thread~ 16 with a layer 17 of thermoplastic material and/or
adhesive. After twisting, an element is obtained such as shown in Fig.
3b and in which the curvilinear triangles 17" are also filled up and in
which the outer gaps are defined by the geometrical connection o~ layer
17 corresponding to adjacent threads 16. For defining the geometrieal
parameters of the notches, the diameter of threads 16 corrected by layer
17 must be taken into account. The threads may be secured against movem-
ent fairly close to one another by ex-truding a thermoplas-tic material
around -threads 16 after twisting thereof. In this case, they are ~e?eured
against movement from the outside and the dimensions of notches 6 must,
as in the preceding case, be corrected by the thickness of layer 17'.
The curvilinear triangles 17" then rem-ain empty.
Fig. ~a shows threads 7 t~isted about a central core 1.
Each of the threads has a concave part 10 whose profile corresponds to
the outer profile of the central core 1. Thus, a better contact surfac(?
is obtained be-tween -threads 7 and central core 1, which cor esponds -to
a bettt!l r;ech~lnical binding together of the assembly. In Fig. ~b, threads
7' have their concave part 10' extended until the inner gaps are caused
to disappear.
Fig. 4c shows threads 20 whose lateral parts comprise
flat portions 11. Fig. ~d shows a combination of -the two preceding
solutions in the form of -threads 27 having a concave part 10 as well as
~lat pPrtions 11. F~g. 4e shows threads 27' ha~ing flat portions 11 and
whose profile has been modified so that, with two half grooves provided
in each of threads 27', gaps 6' with rounded profile receive the
optical fibers 3. In this case also~ a concave part 10 may be provided.
Fig. 5 shows a central core 21 whose periphery is provided with helical
or alternate pitch grooves 22 and which are joined together. Threads 2
are then laid in these grooves under the same conditions as in the
case of Fig. 1, except that grooves 22 hold threads 2 in place.
Fig. 6a shows a central core 21 having grooves 22' whose
radius is greater than that of threads 2, the corresponding gaps 25
being filled for example with a resin and/or a thermoplastic material.
This filling of gaps 25 is achieved by previously coating the central
core 21.
~ig. 6b shows a variation of Fig. 6a where such ~illing
is achieved by previously coating threads 36 with a layer 37 of a thermo-
plastic ma-terial and/or resin.
Fig. 7 shows a variation of Figs. 5 and 6 in which grooves
32 are no-t interconnected, but present therebetween a narrow portion 33,
which means tha~t -the gaps in which optical fibers 3 are disposed present
-this time a flat bottom.
Fig. 8a illustrates a varia-tion of the inven-tion in which
the -threads 2 are twisted directly together to form a triplet, without
using a central core. Fig. 8b corresponds -to twisting threads 2 so as to
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form a quadruplet.
Fig. 9 shows a plurali-ty of threads 71 twisted together
wi-thout central core and which are secured mechanically solidly together
by means of lateral flat portions 73 which extend practically as far as
the center of the element concerned.
Fig. 10 shows a variation ~ Fig. 9 in which a thread 12
extends radially from one edge to the other of the cable element and thus
fulfils both -the mechanical function of a central element and Or two
threads. The assembly is twisted from threads 72 having lateral flat
portions 74.
Fig. 11 shows a cable formed from a plurality of cable
elements in accordance with the invention, twisted together and each
being possibly provided with an outer cover 4' such as wrapping, taping,
or by means of a thin extruded sheath. The assembly is then surrounded
with a sheath and/or envelope 4".
Since the i~vention relates more especially to a cable
element capable of resisting high tractive efforts and~or prsssures,
while maintaining a correct environment for the fiber, the material
forming -the -threads and -the material forming the central core will in
this case be chosen so that the core ~ thread assembly does not creep
when high -tractive efforts and/or pressures, which the cable is likely
to ~mdergo,is applied thereto. Thus, for example, me-tal t~reads may
be chosen for example obtained by extrusion and assembled helically or
with an al-terna-t,e pitch, if need be about a central core preferably
formed from the same metal (solid or stranded for example).
1~en the cable element is intended to withs-t~nd high
temperatures,-the same ma-terial is preferably used for the threads, the
core and -the ou-ter cover. This material may be for example Invar so as
~97~ 'Z
obtain very good stability.
The dimensions of the notches, which must be imposed for
fixing the freedom of the op-tical fibers, allows the radills r oE the
threads -to be determined. The number of notches desired determines the
radius R of the circle on which the centers oE the threads are located,
from which the diameter o:E the central core may be deduced.
The process for manufacturing a cable element in accord-
ance with the invention consists in laying together helically or with
an alternate pitch a plurality of threads so as to form a rigid assembly.
The laying may take place about a central core. It may in this case
comprise a preliminary step for coating the core or the threads with a
thermoplastic material or resin layer, the thickness of said layer being
preferably chosen so as to compensate for the volume of -the gaps between
the threads and the centralcore.
If a thermoplastic material is used about the core or
about the threads, it will be chosen so that its softening temperature
is greater than the m~;mllm -temperature in use of the cable element. The
assembly of the threads takes place then at a temperature slightly
greater than -the softening temperature of the thermoplas-tic material.
