Method and device for manufacturing optical transmission elements

A method and device for manufacturing optical transmission elements which contains a SZ-stranded bundle of several optical waveguides received in a tubular jacket characterized by stranding the waveguides into the bundle while they are moving in a vertical direction, applying a filling material to the waveguides adjacent a stranding point to prevent the unstranding of the bundle until at least the tubular jacket has been applied. Preferably, the application of the jacket is by extruding the jacket onto the bundle and the method can include the application of an additional filling material to complete the filling of the jacket.

BACKGROUND OF THE INVENTION 
The present invention is directed to a method for manufacturing an optical 
transmission element which contains a SZ-stranded bundle of several 
optical waveguides which bundle is disposed in a tubular covering or 
jacket and to a device for manufacturing the element. 
In the case of SZ-stranding of waveguides or elements, a danger exists that 
the stranded product will become unstranded or unwound at the reversal 
location of the stranding or twisting direction. It is known to prevent 
this untwisting or unwinding by virtue of the fact that a retaining 
binding or coil is applied which prevents the stranded elements from again 
changing the configuration forced upon them by the stranding operation. In 
the case of stranding very sensitive optical waveguides, a difficulty 
exists because the waveguides can be deformed in a undesirable manner by 
this retaining binding or coil. However, on the other hand, it must be 
insured that the fiber shaped optical waveguides are prevented from 
unstranding at least until the application of a tubular cover or jacket 
which surrounds the stranded bundle. 
SUMMARY OF THE INVENTION 
The present invention is directed to providing a method and device for 
SZ-stranding a plurality of optical waveguides such as fibers into a 
bundle of SZ-stranded elements and subsequently enclosing the bundle in a 
tubular jacket or covering which method and device prevents the optical 
waveguides from becoming unstranded after the SZ-stranding operation. 
To accomplish these goals and objects, the present invention is directed to 
an improvement in a method and device for manufacturing optical 
transmission elements which contains a SZ-stranded bundle of several 
optical waveguides which are received in a tubular jacket or covering 
which method includes the steps of SZ-stranding a plurality of waveguides 
into a bundle of SZ-stranded waveguides at a stranding point and then 
applying a tubular jacket to the bundle. The improvements comprise that 
the SZ-stranding and applying of the jacket is accomplished while the 
waveguides and bundle are traveling in a vertical direction and includes 
applying a filling material to the waveguides near the point of stranding 
and prior to the applying of the jacket. The applying of the filling 
compound which adheres to the waveguide will prevent the optical 
waveguides of the bundle from becoming unstranded at least for a short 
period of time. Since the filling compound is frequently always required 
for the purpose of sealing a loosely fitting bundle within a outer 
covering or jacket, neither additional materials or additional work will 
be needed to perform the present method and thus the present method and 
the present device will not increase the cost of the optical element. The 
otherwise necessarily and relatively complicated spinning devices for 
applying the retaining coil or binding can be eliminated. 
Preferably, the filling compound is contained in a receptacle, which has an 
opening in the bottom and the bundle is passed through the receptacle in a 
vertical direction to move through the opening which will act as a 
stranding nipple. Preferably, the means for covering is an extrusion head 
which extrudes a heated plastic jacket onto the bundle and the device may 
include means for adding additional filling compounds into the extruded 
jacket which additional filling compound acts to accelerate the cooling of 
the jacket. It should also be noted that a second or additional jacket may 
be placed on the first mentioned jacket by a second extrusion means and 
that the multilayer jacket formed in this manner while traveling in a 
vertical direction is then introduced into cooling means such as a water 
bath.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The principles of the present invention are particularly useful in a device 
generally indicated at 10 in FIG. 1 for forming an optical transmission 
element 11. The optical transmission element 11 contains an SZ-stranded 
bundle of several optical waveguides which are received in a tubular 
jacket. 
The device 10 is illustrated as operating with only two fiber shaped 
optical waveguides, LW1 and LW2, which after being drawn from storage 
reels (not illustrated) are passed over deflection rollers UR1 and UR2 and 
brought into a vertically extending path. Each of the optical waveguides 
LW1 and LW2 are provided with corresponding protective layers or coating 
which may be rendered distinguishable by means of different identification 
such as by colors. In practice, more than the two waveguides are 
customarily stranded together into a bundle and expediently the number can 
be in a range of 2 to 12 optical waveguides. Preferably these waveguides 
are optical fibers. 
In the illustrated embodiment of the device 10, an SZ-stranding is 
accomplished in a stranding region VSZ by means of a so-called tube store, 
which is composed of a tube RO which coacts with a first stranding disc VE 
and a second stranding disc VA. Thus, during stranding, the tube RO is 
already covered with a stranding material which is twisting in one 
direction and then in another direction. On the surface of the tube RO, 
the optical waveguides such as LW1 and LW2 are disposed and roll off of 
the tube and as a consequence, a torsion in the fibers during the 
stranding is avoided. The tube RO exhibits in the upper portion an 
extension AN, which is mounted for rotation in a frame 13 by a bearing LA. 
To rotate the tube RO, a toothed belt ZR engages a tooth wheel mounted on 
the extension AN and is connected to means which will move the belt in two 
directions indicated by the double arrow 12 so that the tube RO will be 
rotated both in a clockwise or in a counterclockwise direction as 
indicated by arrow 14. One of the two stranding discs such as VE is 
rigidly mounted on a frame 13 such as by a support 15 and has a bearing 
for rotatably receiving the vertically extending tube store RO. The other 
stranding disc VA is rigidly mounted on the tube RO and is mounted in the 
member 16 by a bearing which allows it to rotate in either a clockwise or 
counterclockwise direction. Each of the stranding discs VE and VA are 
provided with openings which correspond in number to the number of 
waveguides such as LW1 and LW2 which pass through the openings and are 
then twisted or wrapped around the tube RO as the tube is rotated in 
either direction. A more detailed discussion of the structure of the 
stranding unit composed of the tube store RO is provided in allowed U.S. 
patent application, U.S. Ser. No. 229,170, filed Jan. 28, 1981, which 
issued as U.S. Pat. No. 4,386,496 and is based on the same German 
application which resulted in German Auslegeschrift No. 30 06 054, and 
U.S. patent application, U.S. Ser. No. 229,169, filed Jan. 28, 1981, which 
issued as U.S. Pat. No. 4,359,857 and was based on the German application 
resulting in Offenlegungsschrift No. 30 06 055 and the specification of 
both of these applications are incorporated herein by reference. 
As the waveguides LW1 and LW2 pass through the lower stranding discs VA, 
they will run together in a stranding point VP. This stranding point VP is 
disposed in the interior of the funnel shaped receptacle BT, which is 
filled with a corresponding filling compound or material FM1 which will 
adhere to the waveguides. The level of the filling compound is always 
maintained above the stranding point VP by an amount, which is 
approximately 10 to 50 mm. The filling compound is a thixotropic so that 
it does not run off and it prevents a dissociation of the stranding 
connection or union at the location of each reversal direction and will 
stand the minimum shear stress of approximately 200 to 500 dyn/cm.sup.2. 
In addition to containing the filling material FM1, the bottom of the 
container BT has an opening DS through which the bundle BD formed at the 
stranding point VP will pass. The opening DS will have an inside diameter 
approximately corresponding to the diameter of the bundle BD and thus 
simultaneously acts as a stranding nipple. It should be noted that the 
filling compound FM1 by adhering to the various waveguides will prevent 
any unstranding or untwisting of the stranded waveguides. 
The filling compound which is mentioned hereinabove is thixotropic. 
Particular suitable materials for use as the filling compound are liquid 
paraffin, polybutene and "aerosil". * 
FNT * This is a trade name for ultrafine vapor depositor silica powder. 
Immediately below the receptable BT, the device 10 is provided with means 
for providing or applying a coating or jacket to the bundle. As 
illustrated, this means preferably comprises a first extruder EX1, which 
will serve the purpose of applying the jacket or first coating UH1 to the 
bundle BD as the bundle passes through a bore 17 in the extruder EX1. The 
interior diameter of the covering or jacket UH1 is expediently 0.2 mm to 1 
mm greater than the diameter of the bundle BD. Thus, the bundle BD will be 
loosely supported inside the interior covering or jacket UH1. In order to 
produce a filled cable or element, an additional filling compound or 
material FM2 of the above mentioned types will be required and is supplied 
by a feed line ZL to an injection needle NA. The quantity of the fillling 
compound is so selected that the entire interior space of the jacket UH1 
is entirely build up with the filling compound FM1. For this purpose, it 
is expedient to provide a speed proportion control for controlling the 
quantity of the filling compound FM2 being supplied through the needle NA 
which control operates independently of the feed of the stranding device. 
The filling compound FM2 is expediently inserted in a cold state such as 
at room temperature and therefore the needle NA extends through the bore 
17 in the extruder EX1 into that area where the newly extruded coating UH1 
is being stretched in a converging conical shape as best illustrated in 
FIG. 2. Thus, the application of this additional filling material FM2 
helps to cool the heated material that is being extruded from the extruder 
EX1. 
In the illustrated embodiment of the device 10, a two layer jacket or 
covering is being provided by the means for applying and thus a second 
extruder EX2 is positioned to apply a second jacket or covering layer UH2 
onto the layer UH1 in a tightly fitting fashion. It should be pointed out 
that not only is bundle BD and the first inner layer UH1 moving in a 
vertical direction, but the second layer which is being provided from the 
second extruder EX2 is also moving in a vertical layer. From the second 
extruder EX2, the element passes into a housing GH, which is maintained at 
a temperature .theta.2 which is greater than the exterior or the ambient 
temperature .theta.1 in which the stranding operation and the covering 
operation occurs. The transmission element after entering the housing GH1 
enters into a trough WA in which a cooling fluid KF, such as water, is 
present. The trough WA has a deflection roller UR3 which will deflect the 
element after it has been cooled from a downward vertically extending 
direction back up to a substantially upward extending direction to an 
additional or second deflection roller UR4 which is arranged above the 
deflection roller UR3. This deflection roller UR4 is provided with a 
drawing off arrangement or element BA which is illustrated as a moving 
pressure belt which moves over a plurality of pulleys or sheaves. A 
rotating plate TE is provided within the housing GH and receives the 
element 11 and supports it as it is coiled in a horizontal layer of a 
large diameter. The coaction of the drawing off element BA, the deflection 
roller UR4 and the rotating plate TE forms a depositing device which is 
described in greater detail and is the subject of the invention described 
in copending U.S. patent application, Ser. No. 357,699, filed Mar. 12, 
1982 which issued as U.S. Pat. No. 4,414,165 and was based on German 
application No. P 31 11 963.8 and assigned to the assignees of the present 
application. The disclosure of this copending application is incorporated 
by reference thereto. 
In order for the stranding operation and method to be expediently 
accomplished, the following dimensions have been observed. The 
SZ-stranding is carried out with a long lay in a range between 100 and 500 
mm and preferably the lay is approximately 300 mm. The stranding 
preferably proceeds with reversal locations at a distance of 8 to 10 lays. 
The filling compound FM1 should expediently surround the stranding bundle 
BD on all sides. This is accomplished by all of the optical waveguides 
being completely covered by the filling material by the means for applying 
the filling material. This has the additional advantage of the optical 
waveguide such as LW1 and LW2 do not come into contact with the interior 
surface of the first covering UH1 and therefore a possible sticking or 
adherence of these waveguides to the interior layer is prevented. 
While the oscillating or rotating tube store RO was disclosed and suggested 
for the SZ-stranding, it is also possible to use other types of 
oscillating drive stores for the stranding region VSZ. When introducing 
the optical waveguides LW1 and LW2 into the stranding device, there is a 
preferred advantage that these be introduced with a retarding or braking 
force. For example, the amount of this force should be in a range of 
approximately 0.1 N to 1 N which may be accomplished by braking means 
applied to the rollers such as UR1 and UR2 or to the spools or reels on 
which the waveguides have been wound. 
When additional filling material, such as FM2 is introduced into the 
interior jacket UH1, it is expediently for it to be the same substance as 
the filling material FM1 provided in the receptacle BT. 
The interior temperature .theta.2 in the housing GH is expediently 
stablized and kept at a specific value which corresponds to the intended 
contraction of the jacket layers following cooling of the jacket. 
Fluctuations of temperatures are not to exeed beyond the range of 
.+-.1.5.degree. C. The complete transmission element 11 is placed on the 
plate TE with a winding diameter or apporoximately 1300.+-.200 mm. Since 
the optical waveguides, which are introduced into the stranding device, 
are under a specific braking force provided by retarding the flow of the 
fibers into the device. The fiber bundle BD always becomes placed on the 
inner radius of the bent or coiled jacket. This leads to a lenght of error 
amount of the fiber of approximately 2.times.10.sup.-4, which is 
compensated through the contraction of the jacket by cooling to the 
ambient temperature after termination of the fabrication. 
The transmission element 11, which was provided on the plate TE, can be the 
core of the optical waveguide cable for which purposes the wall 
thicknesses of the jackets UH1 and UH2 are to be dimensioned 
correspondingly. However, it is also possible to employ the transmission 
element 11 as a basic bundle for an additional stranding operation in 
which several basic bundles of this type are stranded to form a larger 
optical waveguide cable and are surround by a common exterior cladding or 
sheath. 
Although various minor modifications may be suggested by those versed in 
the art, it should be understood that we wish to embody within the scope 
of the patent granted hereon, all such modifications as reasonably and 
properly come within the scope of our contribution to the art.