FI75940B - FOERFARANDE OCH ANORDNING FOER FRAMSTAELLNING AV EN SEKUNDAERMANTELKONSTRUKTION FOER ETT FIBERKNIPPE BILDAT AV FLERA OPTISKA FIBER. - Google Patents

Description

ι 75940

Method and apparatus for fabricating a secondary sheath structure of a fiber bundle of multiple optical fibers

The invention relates to a method and an apparatus for manufacturing a secondary sheath structure of a fiber bundle consisting of a plurality of optical fibers. In the method of the invention, a plurality of primary coated optical fibers are fed from separate feed rollers, the fibers are formed into a fiber bundle, a loose secondary sheath is extruded around the fiber bundle to allow mutual axial movement between the fiber bundle and the secondary sheath. The apparatus according to the invention, in turn, is in accordance with the preamble of claim 15.

GB-A-2 079 970 discloses a secondary sheath line in which a plurality of discrete fibers are guided into a single fiber bundle in which the fibers are in precise order with each other. A secondary sheath is then extruded around the fiber bundle, the diameter of which is shrunk so that the sheath loosely surrounds the fiber bundle. In the method disclosed in this application, the exact order between the fibers causes a different fiber excess (BIAS) for the different fibers when the swivel wheels are used, because the fibers travel in different radii around the swivel wheels, resulting in different circumferential lengths. By excess fiber is meant that in the tubular structure, the length of the optical fiber is greater than the length of the plastic secondary sheath tube. Different fiber excesses, i.e. differences in length between the fibers, in turn degrade the temperature behavior of the cable because the coefficients of thermal expansion of the fiber and sheath are very different. The coefficient of thermal expansion of glass (fiber) —6 o is of the order of 10 1 / C and that of plastic (sheath) is of the order of 10 ^ 1 / ° C to 10 ^ 1 / ° C.

U.S. Patent No. 4,458,476, on the other hand, discloses a vertical secondary sheath line of 2,75940 in which the fibers are SZ-wound prior to extrusion of the loose secondary sheath and grease filling of the sheath. The SZ-repetition aims to make the average additional lengths of the fibers the same, so that the 5 swivel castors do not have the same adverse effect as in the case of GB application 2,079,970 described above. However, the SZ repetition brings with it several other disadvantages, which are described below. SZ repetition causes torsion in the fibers and thus static stress. On the other hand, frequent repetitive reversals to reduce stresses slow down the line speed. SZ repetition also tends to unwind because the fibers are rigid and there must be little tension during the process. The center rod around which the fiber rotates brakes the fibers, causing an increase in friction and an increase in tension in pulses according to the rotational frequency.

This "braking factor" increases the relative stress differences between the different fibers, causing variations in the excess fiber and deteriorating the technical properties of the cable. The typical fiber excess requirement (bias requirement) of an optical cable is 0.01 -20 0.05%.

The effect of the braking factor is illustrated by the following example. The tensions of the fibers upon arrival at the SZ multiplier may differ due to the spooling of the fiber after the primary coating and the variations in the output arrangements of the secondary coating. A tension of 860 g causes an elongation of 1.00% in the 125 μM fiber. The elongation of the fiber is linear with respect to the stress in the tension region of the secondary coating process. As a result of the braking factor (K), the tensions of the different fibers increase as follows:! 30 T '^ = K T (K> 1) The braking coefficient for a wire wound around a rod is K = eUÄ>, where u = coefficient of friction and oc = angle of rotation (rad) around the rod. 35 K-values observed in practice with two rounds of rotation: K = 1,4 (Teflon rod) ... K = 2,0 (steel rod) 3 75940

The example assumes K = 1.5 and the tensions of the three fibers: T-j = 70 g, T2 = 70 g and = 90 g, then T '^ = 105 g, T'2 = 105 g and T'3 = 135 g.

The difference in tension T3 to T2 is 20 g, which in the 125 μm fiber mer-5 reduces the elongation difference for fibers 3 to 0.023% compared to fibers 1 and 2 before the SZ multiplier. After the SZ multiplier, the tension difference of 35 g, corresponding to an absolute elongation difference of 0.035%, has increased significantly due to the effect of the braking factor, causing a significant difference in the excess lengths of the different fibers.

It is therefore an object of the present invention to get rid of the various fiber excesses caused by the swivel wheels, however, so that the disadvantages associated with SZ repetition described above are eliminated. This is achieved by the method according to the invention in such a way that in the step of forming the fiber bundle, the mutual order of the individual fibers in the fiber bundle is repeatedly alternated.

Such alternation or cross stranding is known per se in telephone cable technology, where it is used to reduce crosstalk between pairs of conductors. The basic idea according to the invention is therefore to use this alternation procedure in connection with the secondary sheathing of optical fibers in order to even out the length differences between the fibers and thereby to improve the technical properties of the cable.

In the method according to the invention, the swivel castors do not create length differences between the different fibers. Because the fibers are not twisted, no stresses are generated that would degrade the quality of the cable. The method according to the invention also does not limit the line speed and is suitable for use on both horizontal and vertical lines.

The simplest implementation is achieved when the alternation is controlled by a random pulse generator »in which case there is no need to develop a separate algorithm for controlling the alternation.

The apparatus according to the invention, in turn, is characterized by the fact that there is a mixing device between the feed rollers and the extruder for repeatedly alternating the relative order of the individual fibers in the fiber bundle. In order to reduce the tensions generated at the beginning of the line, it is advantageous to provide at least one of the guide rollers behind the agitator with a separate drive. This guide roller to be used is preferably controlled by means of a tension adjustment.

To further reduce friction and tension variations, the control nozzles of the agitator are provided with rotating rollers.

In the following, the invention will be described in more detail with reference to the example of the attached drawing, wherein Figure 1 shows schematically the optical fibers brought to 15 siovaippauslinjaa, in which the method according to the invention is applied, and Figure 2 shows a toisiovaippauslinjan parallel perspective view of the invention vuorotteluvaihet-O as seen from the direction of the arrow A of Figure 1 split, and 20 of Figure 3 shows the nozzle of the mixing device in more detail.

In Fig. 1, the primary coated optical fibers 1a to 1e are fed from the feed rollers S of the output discharge device to a mixer device 2, which is controlled by means of a generator 3a-25a. The purpose of the mixing device is to repeatedly mix the fibers with each other in such a way that their mutual order varies, whereby the length differences between the different fibers disappear on average. The operation of the mixing device will be described in more detail in connection with Figure 2. From the mixing device 2, a fiber bundle 1 is passed between the successive guide rollers 2a and 2b via a grease filling device 4 to an extruder 5, where a loose secondary jacket is pressed around the fiber bundle. By providing at least one of the guide rollers 2a or 2b with a separate drive device 2c, the tensions generated in the cup of the line a-35, in the outlet discharge devices and in the mixing device can be reduced. The drive is preferably controlled by means of a tension control. During the extrusion, the secondary sheath is greased, which binds the fibers to each other inside the sheath and then prevents the order of the fibers 5 from changing. From the extruder, the sheathed fiber bundle 6 is passed through a two-stage cooling device to a drawing and stretching device 9. The cooling device is two-stage, whereby it comprises separate cooling parts 7a and 7b. The first cooling section 7a has a hot water circulation.

Between the parts 7a and 7b of the cooling device there is a diameter measuring device 8. The fiber bundle 6 sheathed from the drawing and stretching device continues to the take-up reel 10. The drawing and stretching device 9 comprises a drawing device 9a and a stretching device 9b forcibly connected to each other. ). The drive device causes a small speed difference between the traction device 9a and the stretching device 9b so that the traction device tends to brake the jacket with respect to the traction effect of the stretching device. In the stretching device 9b, the fiber bundle is axially locked Liu-20 in the sheath. Such stretching causes the sheath to pre-stretch. When the jacket leaves the stretching device 9b, the pre-stretching of the jacket can be triggered before being wound on the take-up reel. Since the take-up reel prevents the sheath and the fiber bundle from moving axially with respect to each other, the tripping of the pre-25, i.e. shrinkage of the sheath, causes the sheath to be somewhat shorter than the fiber bundle. This way of providing the fibers with an additional length relative to the sheath is known per se and will not be described further in this context as not belonging to the actual inventive idea.

30 This method and the related equipment are described in more detail in Finnish patent application FI-831 928.

Figure 2 shows the generator 3 controlled by the mixer device 2, seen in the direction of arrow A direction in Figure 1. The mixing device comprises a nozzle wall 2d transverse to the direction of travel of the fibers and body parts 2e on both sides, containing control and operating devices. The die wall has five overlapping, through-wall, slits 16 transverse to the direction of travel of the fibers, one for each individual fiber. Each transverse-5 slit 16 has a nozzle 17 through which an individual fiber passes through the opening 17a. The nozzles 17 are located in grooves 18 in the walls of the slits 16, where they move in the direction of the slits, i.e. in a direction transverse to the direction of travel of the fibers. This movement is effected by a double-headed arrow B. The lateral position of each nozzle 17 in the slot 16 is controlled by a motor which moves the nozzle to the desired position. The motor stops and starts according to the pulses it receives from the generator 3. By thus moving each nozzle 17 separately 15 repeatedly in the lateral direction, the mutual order of the fibers is varied, whereby the length differences between the fibers which would otherwise be caused by the Swivel Wheels in the process are eliminated. The control is preferably performed by means of a random pulse generator. Such a generator generates pulses controlling the mixer device 20 on the basis of, for example, the noise spectrum of the transistor. Of course, control could also be performed according to a well-defined logic, but this, as stated earlier, would be a more complex option than using a random pulse signer.

Figure 3 shows a single nozzle 17 seen from the outlet side. The nozzle is provided with two pairs of crossed, bearing-mounted rollers 19 and 20, between which a single fiber passes through the opening 17a. Roller pairs reduce the friction caused by the nozzles by 30. When a high friction primary coating material is used in the fibers, this arrangement substantially reduces tension variations.

Although the invention has been described above with reference to the example according to the accompanying drawing, it is clear that the invention is not limited thereto, but can be modified in many ways without departing from the scope of the inventive idea defined by the appended claims. Thus, for example, the extra length of the fibers relative to the sheath can be achieved in other ways than by means of drawing, drive and stretching devices as described above. This could be done, for example, in a manner similar to the aforementioned U.S. Patent 4,458,476, i.e., by keeping the sheathed fiber bundle with its receiving coils at a well-defined temperature to provide controlled shrinkage.

Claims (6)

A method of producing a secondary manifold structure for a fiber bundle formed by a plurality of optical fibers, according to which method: - multiple primary coated optical fibers (la - le) feed from separate feed coils (S), - a fiber bundle (1) is formed of the fibers (la - le); and - the secondary sheath structure formed is wound up on a receiving coil (10), characterized in that - in the formation of the fiber bundle (1), the mutual order of the separate fibers (la - le) is continuously varied in the fiber bundle (1). 20 2. A method according to claim 1, characterized in that the mutual arrangement of the separate fibers (la - le) is determined in each case by means of a random pulse generator (3). Apparatus for producing a secondary mandrel structure for a fiber bundle formed by a plurality of optical fibers (la - le), comprising: - several feed rollers (S), each measuring a separate primary coated optical fiber (la - - an extruder (5) for extruding a fiber bundle (1) formed at a secondary sheath about one of the optical fibers (la - le), which secondary shaft permits a mutual axial movement between the fiber bundle (1) and the secondary sheath, and - means (9a, 9b) by which a desired overlap length A is obtained for the fibers in relation to the men prior to the secondary jacket construction is rolled onto a receiving