FI86481B - Secondary casing construction for optical cables and procedure for producing same - Google Patents

Description

1 86481

Secondary sheath structure for an optical cable and a method for manufacturing a secondary sheath structure

The invention relates to a secondary sheath structure for an optical cable 5. The secondary sheath structure comprises a secondary sheath bean tube and optical fibers in the fiber channel therein, the tube surrounding the fibers loosely allowing axial movement between the fibers and the tube, and the fiber channel passing through the tube The invention also relates to a method for manufacturing such a secondary sheath structure. In the method, optical fibers are passed to the torpedo end of a plastic press on a torpedo and further out of at least one torpedo end, a loose secondary sheath tube is extruded around the optical fibers at the press end to allow mutual axial movement between the fibers and the tube, and the fibers are provided with the desired length.

It is well known to protect a primary coated or bare optical fiber or a bundle of fibers composed of several such fibers with a loose secondary sheath. The main purpose of the secondary sheath, which is usually a plastic tube, is to protect the fiber or bundle of fibers from external mechanical stresses and strains. The function of the loose secondary sheath tube is also to provide the fibers with an undisturbed space of motion for thermal dimensional changes or dimensional changes caused by mechanical forces acting on the protective sheath. In the secondary sheath, the aim is to give the fibers a certain extra length (bias) so that the fibers do not get stretched, even if the sheath is slightly stretched. Typically, the value of such an excess length is less than 1% *. Due to the loose secondary sheath tube and the excess fiber length of the fibers, the fibers have room for maneuver within the tube 2 86431 as the tube lengthens and shortens, e.g., in cases of thermal motion and stretching. However, due to the relatively small size of the tube, the low modulus of elasticity 2 (<2500 N / mm) and the high coefficients of thermal expansion -4 5 (»10 / ° K) of the plastics used, the tube coating alone does not guarantee a very high" elongation / compression window "for the fibers.

To remedy this shortcoming, it is known to manufacture an optical cable in such a way that the secondary sheath tubes are wound either helically or in the reverse direction (so-called SZ-ker-10 backing) on a common central element. The central element, which is typically a metal or plastic composite, increases the strength of the structure and reduces thermal movement. In addition, the repetition increases the clearance of the fibers even for geometrical reasons: spiraling the secondary sheath tube 15 or oscillatingly around the central element at the same time means bringing it to a certain bending diameter. This, in turn, together with the radial play of the fibers, results in a significant increase in the relative clearance of the fibers with respect to elongation and compression.

Optical cables made as described above are generally reliable even in difficult environmental conditions and effectively protect the fibers from tensile and compressive stresses. However, they lack the high cost of several successive and delicate work-25 steps required by the manufacturing process. Such a cable typically consists of 5-8 secondary sheath tubes, each of which usually contains Ιό fiber. The manufacture thus requires 5-8 secondary coatings and a subsequent joint repetition, the possible failure or discovery of a defect in one of the fiber-30 repetitions nullifies all previous successful work steps. Such a structure is also not optimal in terms of, for example, watertightness or compressive strength, and therefore requires a large number of other work steps and structural components to improve these properties. 35 A structure closely resembling the previous structure 3 8 c 4 31 they are the so-called V-groove cable in which the secondary sheath tubes are replaced by helically or oscillatingly circulating grooves in a common central element in which the optical fibers are placed. There are fewer work steps than in the previous structure, although they are laborious and require a lot of special equipment. In particular, the placement of fibers in their grooves is a sensitive and disruptive procedure.

A cable structure that differs significantly from the structures described above is disclosed in PCT application WO86 / 10 06178. This cable consists of a single, relatively large diameter tube which is grease-filled and within which the fiber bundle or bundles are located. The pipe is reinforced with steel wires and consists of several overlapping layers of plastic and, if necessary, moisture and / or 15 rodent protection. The entire cable structure is manufactured in one work step, and its obvious advantage is the speed and straightforwardness of manufacture as well as the simplicity of the structure. However, such a structure is not able to take advantage of the increase in fiber working capital brought about by the repetition. Admittedly, a certain slight excess length is provided for the fibers, and the steel wire reinforcement must be dimensioned so that that elongation is not exceeded under any circumstances. In the case of compression, when the structure cools to lower temperatures, allows the inner diameter of a large tube of fibers or. . 25 twisting the fiber bundles without subjecting them to compressive stress. However, the fibers or fiber bundles are free to settle at any bending plane that is unfavorably different from the helical space. In this case, the minimum radii of curvature of the individual fibers may be exceeded, resulting in an increase in attenuation or a shortening of the life of the fiber. The large diameter hole also requires the use of a rigid filling grease, which contributes to the phenomenon described above. The function of the steel wires is apparently also to stabilize the structure against pu-35 crossings.

4 8 6 4 5 '!

The object of the present invention is to overcome the above-mentioned drawbacks and to provide a secondary sheath structure for an optical cable which allows the fibers a large range of motion without the risk of compression or the minimum bending radii, while allowing a safe and easy method of manufacturing the cable. These advantages are achieved by the secondary sheath structure according to the invention, which is characterized in that the inner end of the fiber channel remains substantially rotated along the central axis of the tube as it rotates.

The idea of the invention is to replace the above-described repetition of secondary sheath tubes around a central element with a fiber channel inside the secondary sheath tube, which forces the fibers into a helical space, thereby simplifying and significantly reducing cable fabrication while retaining the above advantages.

With the secondary sheath structure according to the invention, the maximum movement margin of the fiber bundle is achieved with the smallest possible cross-section of the rotating channel. This guarantees the high compressive and tensile strength of the secondary jacket pipe without additional reinforcements. The small cross-sectional fiber channel also allows a greater degree of freedom in the choice of filler grease, i.e. softer greases can be used without the risk of spillage. This avoids the use of expensive and difficult to process, crosslinkable fillers. The shape of the fiber channel also forces the excess length fibers to conform to the channel's own spiral, i.e., the fibers cannot oscillate on either side of the central axis. As stated at the outset, the invention also relates to a method of manufacturing a secondary sheath structure. According to the invention, the secondary sheath structure can be manufactured in three alternative ways. The methods are characterized by the features described in the characterizing parts of claims 10, 13 and 15.

5 86481

The invention will now be described in more detail with reference to the examples according to the accompanying drawings, in which Figures 1 to 5 show a cross-section of secondary jacket structures according to different embodiments of the invention, Fig. 6 shows a perspective view of Fig. 8b shows graphically the relative elongation of the secondary sheath with respect to the fiber bundle by zones in the line of Fig. 8a and at the same time the primary way of generating the excess length of the fiber overhead. the location, dimensions and shape of the fiber duct and / or a remarkably rigid filling grease t is the free movement of the fiber bundles up to the wheel of the traction device, Fig. 8d shows a wheel to be added to the line of Fig. 8a, by means of which it is easier to generate excess fiber in such secondary sheath structures according to the invention,. Fig. 9 shows in more detail a part of the secondary sheath line according to Fig. 8a to illustrate a first embodiment of the method according to the invention, Fig. 9a shows the shape and position of the torpedo head seen along line II in Fig. 9, Fig. 10 shows part of the secondary sheath line according to the invention. to illustrate a second embodiment, Fig. 11 shows in more detail a secondary jacket tube exiting the press head in the apparatus of Fig. 10, Fig. 12 schematically shows a side production line for manufacturing a secondary jacket structure by means of a third embodiment of the method according to the invention, Fig. 13 shows a line 14 is a cross-sectional view of yet another preferred secondary sheath structure made by the method shown in Figures 12 and 13.

Figure 1 shows a cross-section of a secondary sheath tube 1 with fiber channels 2.1 according to a first embodiment of the invention, in which fiber bundles 4 consisting of separate fibers 3 pass. In the structure of Figure 1, each fiber bundle contains six fibers. Each of the three fiber channels 2.1 is circular in cross-section and is located entirely outside the longitudinal central axis A of the tube 1. In addition, the fiber channels 2.1 are evenly spaced in the circumferential direction of the tube 1 and equidistant from the central axis A. Each fiber channel 2.1 rotates helically forward in the longitudinal direction of the tube 1 with an equal helical pitch. The rotation of the fiber channels 2.1 is shown in Figure 1 by broken lines and the direction of rotation by arrow B.

Figure 2 shows a cross-section of a secondary jacket bean-housing 1 with a fiber channel 2.2 according to a second embodiment of the invention, which is also circular in cross-section. The inner edge of the fiber channel 2.2 extends just to the central axis A of the tube and remains there as the fiber channel spirals forward in the longitudinal direction of the tube 1, as indicated by the broken lines.

In the secondary sheath structure shown in Fig. 3, the fiber channel 2.3 is elongated in the radial direction of the tube 1 so that the semicircular ends 2.3a and 2.3b are connected by substantially straight side walls 2.3c and 2.3d.

35 The outer end 2.3a is close to the circumferential edge of the tube, and the inner end 2.3b extends somewhat to the opposite side of the central axis A of the tube, forming a longitudinally straight central channel K in the longitudinal direction of the tube into a helical fiber channel 2.3. The central channel K is shown more clearly below in connection with Fig. 6.

The fiber channel 2.4 shown in Figure 4 is substantially similar in shape to the fiber channel 2.3 of Figure 3, but is centrally located with respect to the central axis A of the tube, i.e. the channel 2.4 rotates in the longitudinal direction of the tube about the central axis A10. The direction of rotation is again marked with an arrow B.

Fig. 5 shows a further secondary jacket structure, in which the tube 1 has a fiber channel 2.2 according to Fig. 2, the inner edge of which is constantly located on the central axis A of the tube 1. The outer circumference of the tube further has a guide and locking groove 5 rotating in the longitudinal direction of the tube. The significance of the guide and locking groove 5 will be explained in more detail below in connection with Figures 12-14. For the sake of clarity, the optical fibers 3 in the fiber channels 2.2-2.4 are not shown in Figures 20 2-5.

Fig. 6 shows a perspective view of a secondary jacket structure corresponding to Fig. 3, in which, however, the spiral has the opposite direction of rotation compared to Fig. 3. As can be seen from the figure, a direct central channel K is formed in the middle of the secondary jacket beans 25 as part of the fiber channel 2.3. The forward rotating fiber channel 2.3 and the envelope of the spiral thus formed, as well as the boundaries of the central axis A and the central channel K formed around it, are shown in Fig. 6 by broken lines. The rise of the spiral is marked with the reference mark 30 P.

The secondary sheath structure shown in Fig. 7 otherwise corresponds to the structure shown in Fig. 6, but the direction of rotation of the fiber channel spiral in the structure according to Fig. 7 changes from time to time to the opposite, i.e. opposite. The reversal point of the rotation-35 is indicated in Fig. 7 by reference numeral 8 86481 VP. Although the change of direction of rotation is shown only for the embodiment according to Fig. 3, it is clear that in any of the above-mentioned structures, the direction of rotation of the fibrous helix-spiral can be reversed at certain intervals.

Next, the manufacture of the above-mentioned secondary sheath structures according to the invention will be explained in more detail. Reference is first made to Figure 8a, which shows an example of a complete secondary sheath line suitable for the manufacture of a secondary sheath structure with a helical fiber channel according to the invention. The separate fibers 3 leave their own output coils 10, each of which can be individually adjusted to achieve the correct output voltage. In order to maintain the fibers in their regular, helical state as well as possible during the manufacturing stage and later in the conditions of use, and to avoid the formation of unfavorable, small bending radii, it is advantageous to increase their rigidity by bundling them together. To do this, the fibers first pass through a binder 11, where they are bundled together, e.g. with an identification wire.

Bundling can also be performed with a vulcanizable polymer or adhesive, for example the so-called with hot melt glue. For example, the bundle 4 may contain six fibers, preferably of different colors, and the bundles 4 may also have more than one, each with a separately identifiable bond. The bundle 4 further advances through the fat mouthpiece 12 to the press head 13, the torpedo of which is rotated at line speed by a synchronized mechanism 14 in the manner described below in connection with Fig. 9. From the press head, the bundle 4 30 and the filling grease proceed to the melt zone 15 surrounded by the coating material and further to the cooling basin 16.1, where the coating material crystallizes into a spiral fiber channel secondary jacket tube 18. ; 9 The temperature and post-crystallization of the pipe 1 are controlled by the cooling tank 16.2 of 86481. After the cooling basin 16.2, there is a traction device 19 on the line, which at the same time acts as a generator of the excess length of the fibers and as the main speed point according to which the other devices in the line are synchronized. The traction device includes a belt traction device 19.1 and a wheel 19.2. The traction device 19 is followed by a third cooling basin 16.3, in which the secondary jacket structure is brought to ambient temperature, as well as a tension accumulator 20 and a receiving coil 21.

Fig. 8b graphically illustrates the relative elongation e of the secondary sheath with respect to the fiber bundle 4 by zones in the line according to Fig. 8a, as well as the generation and adjustment of the excess length. The relative elongation of the secondary sheath is illustrated by a solid line A1 and the fiber bundle 15 4 by a dashed line A2 which is straight because the fibers run at a constant speed and substantially unstressed from the output coil 10 to the take-up coil 21. In the melt zone 15/1 the secondary sheath is drawn so that . At the same time, its 20 velocity and relative elongation ε increase. In zone II, the secondary jacket 1 begins to crystallize under the effect of cooling, its density increases, i.e. it shrinks and at the same time its speed decreases in the direction of travel of the line. In Zone III, the mantle structure is maintained at a higher temperature than the environment. 25 sa, in which case it has a certain thermal elongation and its Kimmo coefficient is lower than at normal temperature (+ 20 ° C). In zone IV, the secondary jacket is stretched by a precisely controlled speed difference between the belt drive device 19.1 and the wheel 19.2, the corresponding elongation of which is indicated in the figure by reference numeral ε ^. When the secondary jacket rotates several turns around the wheel 19.2, and when the fiber bundle 4 can slide relatively freely inside the secondary jacket, the bundle 4 settles on the inner circumference of the secondary jacket and locks in it under the effect of the initial tension. In zone V, the secondary jacket comes off the wheel 19.2, its elongation is removed and when it is brought to ambient temperature (approx. + 20 ° C) in the cooling pool ίο 3 6 4 81 16.3, it is further shortened, increasing the relative length difference of the fibers inside. In zone VI, the constant tension winding on the take-up reel 21 no longer substantially changes the excess length ε of the fibers. Thus, in the situation described, the final excess length eQ is the result of a combination of two factors; the recovery of elongation f.g and the shortening caused by cooling eT. The above-mentioned biasing method is known per se 10 and will not be explained in this connection as part of the actual inventive idea. The method is described in more detail in Finnish patent application FI-831 928.

Figure 8c graphically illustrates the case where the location, dimensions and shape of the fiber channel 15 and / or the substantially rigid filling fat prevent the fiber bundle from moving freely up to the wheel 19.2. In this case, the locking of the fiber bundle 4, i.e. the adhesion to the inner surface of the secondary sheath, takes place by means of the filling grease and the shape of the channel in zone II. The exact point of adhesion can be adjusted by the initial tension of the fiber bundle and, if necessary, enhanced by a freely rotating wheel 32 positioned on the line behind the cooling basin 16.1 as shown in Figure 8d. In zones III and IV, the secondary sheath is further cooled and allowed to shrink to create excess fiber. The secondary casing is pulled by the traction device 19.1, but it passes the wheel 19.2 or rotates around it without pre-stretching ε. By adjusting the temperatures of the cooling tanks 16.1, 16.2 and 16.3 and the initial tension of the fibers, the generation of the correct length of the 30-mouthed iron is controlled. In practice, the generation of excess fiber is simpler according to Fig. 8b, and in that sense the structures according to Figs. 3 and 4 are advantageous, because in them the straight central channel K ensures the free movement of the fiber bundle on the wheel 19.2 as-35 ti.

li 11 86431

Fig. 9 shows in more detail a part of the secondary sheath line according to Fig. 8a, in which the manufacturing method according to the first embodiment of the invention is applied. The fiber bundles 4 are directed under a uniform output voltage to the tool end of the plastic press, i.e. the press head 13, which contains a fixed matrix 23 and a rotating torpedo holder 24 with a fixed torpedo 25 as it rotates in a helical fiber channel. The shapes and dimensions of the matrix 23 and the torpedo 25, as well as their relative position, determine the dimensions and shape of the formed and crystallized secondary shell element 1. A central channel 26 is formed in the torpedo holder and the torpedo, in which a fixed, non-rotating supply and protective tube 27 is arranged, along which the fiber bundles 4 and the filling grease 28, indicated by the arrow, are introduced into the secondary jacket element 1.

A precise dosing pump synchronized to the line speed feeds the filling fat 28 into the grease nozzle 12, where it 20 covers the fiber bundles 4, from where they together advance into the protective tube 27. At the same time, the grease nozzle 12 prevents grease. : van 28 excessive backflow. The molten plastic mass 29 from the plastic press, which is described by the arrow, fills. the empty spaces of the press head 13 and proceeds towards the matrix. 25 an annular gap formed by a torpedo 25. As stated above, this gap determines the dimensions and shape of the final secondary jacket element 1. However, since the plastic mass 29 is still in the molten state for a while in the melt zone 15 as it exits the press head 13, it can be stretched 30, thereby reducing its diameter. Thus, the dimensions of the secondary jacket tube can be influenced by the adjustment ratio of the press mass flow and the line drawing speed. ·. ; From the melt zone 15, the secondary jacket tube advances to the cooling element 16.1, where it crystallizes to its final dimensions.

:: 35 Attached to the rear end of the torpedo holder 24 is a gear wheel 30 86 4 oi which is driven by a toothed belt 31. When the torpedo holder 24 is rotated therethrough, the Torpedo 25 at the end of the holder 24 rotates relative to the matrix 23, causing the inner hole 5 of the deformable secondary jacket tube to rotate about the central axis of the jacket. By synchronizing the rotational speed of the Tor beast holder 24 and the line pulling speed in the right relationship, a spiral pitch of the desired length is obtained for the fiber channel (P, Fig. 6).

Rotating the holder 24 continuously in the same direction results in a continuous helical rotating channel as shown in Fig. 6. If the direction of rotation is changed from time to time, a reversing helical channel as shown in Fig. 7 results.

Fig. 9a is a front view of the torpedo head 25a taken along line I-I of Fig. 9. The central axis of the supply and protective tube along which the fiber bundles 4 are fed also forms the axis C of rotation of the torpedo 25. The torpedo head 25a, which determines the shape of the inner hole 20 in the secondary jacket tube 1, is arranged eccentric to this axis, creating a helical fiber channel as described above. If, for example, a central, oval or elongate head is used in the torpedo, a non-fibrous chicken-25 va according to Fig. 4 is formed in the secondary jacket tube. By thus changing the shape and position of the torpedo head 25a with respect to the axis of rotation of the torpedo, the desired shape is obtained for the fiber channel.

An alternative manufacturing method according to the invention will now be described with reference to Figures 10 and 11. The press head 13 includes the same tools and equipment as in the case of Fig. 9, except that the torpedo holder 24 cannot be rotated. The fiber bundles 4 are guided through the fat mouthpiece 12, the feed pipe 27 and the torpedo 25 to the melt zone 15 of the secondary jacket pipe together with the filling fat 35. The torpedo head 25a is arranged eccentrically in the opening of the matrix 864 81 (Fig. 11), i.e. eccentrically with respect to the central axis F of the secondary jacket tube 1. According to Figure 11, the fiber bundles 4 run along the central axis F. The secondary jacket tube 1 extends through the cooling basin 16.1 to a freely rotating wheel 32 supported by a support arm 33. The support arm is mounted concentric with the central axis F of the secondary jacket tube 1 and a gear or pulley 34 is attached to rotate it about the central axis F. As the secondary jacket tube 1 advances pulled by the line traction device 10 and rotates around the wheel 32 gripping its circumference, the support 33 and with it the wheel 32 are rotated by means of a belt 35 and a gear or pulley 34, whereby the secondary jacket tube 1 rotates about its central axis F. Since the secondary jacket tube 1 is crystallized in the cooling 15 basin 16.1, but not yet crystallized in the melt zone 15, it rotates in the melt zone so that the eccentric hole generated by the fixed non-central torpedo head 25a rotates around the central axis F of the secondary jacket tube. By synchronizing the rotational speed of the wheel 32 20 about the central axis F with the line travel speed in the right proportion, the desired helical pitch is obtained. If the rotation takes place continuously in the same direction, the line pulling and receiving devices following the wheel 32 must also rotate in the same direction with approximately the same synchronization. However, a more preferred procedure is one in which the secondary jacket tube is rotated alternately at certain intervals and the distance between the wheel 32 and subsequent fixed traction and receiving devices is arranged long enough for the secondary jacket tube rotation 30 to remain in the elastic range and return to zero cumulatively. The result is a helical fiber channel, the direction of rotation of which spiral changes from time to time. Since the free-rotating wheel 32 is used in the manufacturing method shown in Figs.

Figures 12 and 13 schematically show a production line 5 using a third embodiment of the method according to the invention, according to which the secondary sheath structure is manufactured in a subsequent cabling step from a secondary sheath tube 1.1 with a straight, eccentric fiber channel. Such a secondary jacket tube is made with the press heads 13 according to Figures 10 or 11 with their associated tools, but without rotating the torpedo 25 or rotating the secondary jacket tube 1 in the melt zone 15. The method according to Figure 8b is primarily used for bia-sounding. The secondary jacket tube 1.1 with a straight eccentric fiber channel leaving the output spool 36 advances through the rotating drive belt device 38, pulled by the traction device 37. The rotary drive belt device 38 has transversely angled belts 38.1 (Fig. 13) which force the secondary jacket tube 1.1 to rotate about a longitudinal axis. Twisted belt devices are known per se from conventional cable manufacturing and will not be explained in more detail in this connection. From the rotary drive belt device 38, the secondary jacket tube advances to a heating resistor 39, which raises the temperature of the secondary jacket tube 1.1 high enough to allow the rotation to take place plastically and with less force. At the press head 40, the twisted secondary jacket tube 1 is surrounded by a plastic jacket 41 (Fig. 14) which locks its rotation.

In certain cable structures, a support wire 42 may be used to enhance the locking 30, which is pulled from its own output spool 43 through the press head 40 into the same plastic sheath 41.

After crystallization and cooling in the cooling tank 44, the plastic sheath 41, the support wire 42 and the twisted secondary sheath tube form a cable structure 1.2 with a helical 15 B cm S1 fiber channel 2.5, the cross-section of which is previously shown in Figure 14. To facilitate twisting in connection with Figure 5. In order to create a guide and locking groove 5 in the manufacturing step of the secondary jacket tube 1.1, the matrix 23 according to Figs. 9 and 11 must have a corresponding protruding shape.

If a continuous spiral-like fiber channel is desired for the secondary jacket pipe 1, only one rotary drive device 38 is used in the line according to Figures 12 and 13. In this case, the output coil 36 must rotate synchronously with the secondary jacket pipe 1.1. If a reversible fiber channel is desired, two rotary drive devices 15 are used, one of which (38a) is drawn in phantom in Figures 12 and 13. In this case, the rotary drive belt devices are open and closed alternately, whereby they rotate the secondary jacket bundles 1.1 in an alternating direction. In this case, it is not necessary to rotate the starting spool 36 if the distance between the rotary drive belt devices 38 of the spool 36 and 20 is arranged to be large enough compared to the distance between the locking point of the rotary drive belt devices and the press head 40. Thus, the rotation of the secondary jacket tube 1.1 between the output coil and the torsion belt devices remains in the elastic range and returns to zero. The rotary drive devices can be driven synchronously with the main drive 37 or freely rotating. The transverse angle of the belts 38.1 of the traction devices 38 and the diameter of the secondary jacket tube 1.1 determine the magnitude of the helical pitch of the fiber channel.

Instead of the rotary drive belt devices, a guide and locking groove 5 in the tube can be used to rotate the secondary jacket tube 1, so that the rotating device, mouthpiece or wheel has a protruding shape corresponding to the groove 5 which presses into the groove and obtains a sufficiently strong grip.

80431 BC

The rotation of the secondary jacket tube 1.1 and the locking of the rotation can take place in other ways and in a different work step than the jacket. For example, in the reinforcement line, where the tensile, compressive and impact strength of the secondary sheath tube is increased by a steel wire layer, locking occurs in the reinforcing mouthpiece, where the steel wires twist and compress around the twisted secondary sheath tube 1.

Although the invention has been described above with reference to the examples according to the accompanying drawings, it is clear that it is not limited thereto, but can be modified in many ways within the scope of the inventive idea set forth in the appended claims. Thus, although the manufacturing methods of the invention have been described in Figures 15a-14 with reference only to the single fiber channel structures of Figures 2-5, it is clear that the multi-fiber secondary sheath structure of Figure 1 can be manufactured in the same manner. In this case, the torpedo must, of course, have 20 more ends for the outgoing fibers. The cross-sectional shape of the fiber channel can also be modified in many ways.

Claims (21)

17. A r Ο t H u I A secondary sheath structure for an optical cable, the structure comprising a secondary sheath tube (1) and optical fibers (3) in a fiber channel (2.2) therein, wherein the tube loosely surrounds the fibers allowing axial movement between the fibers and the tube, and wherein the tube (1) the fiber channel (2.2) rotates helically forward in the longitudinal direction of the tube and is located eccentrically in the respective cross section of the tube (1) 10 with respect to the central axis (A) of the tube, characterized in that the inner end of the fiber channel remains substantially on the central axis (A). Secondary sheath structure according to Claim 1, characterized in that the fiber channel (2.2) has a circular cross-section. Secondary sheath structure according to Claim 1, characterized in that the fiber channel (2.2) is elongated in cross section in the radial direction of the tube (1). Secondary sheath structure according to one of the preceding claims, characterized in that the direction of rotation of the fiber channel (2.2) changes from time to time. Secondary sheath structure according to Claim 1, characterized in that the optical fibers (3) form at least one solid fiber bundle (4). Secondary sheath structure according to Claim 5, characterized in that the fibers (3) are glued to one another. Secondary sheath structure according to Claim 5, characterized in that the fibers (3) are bundled together with a vulcanizable polymer. Secondary sheath structure according to Claim 5, characterized in that the fibers (3) are connected to one another by a detection wire. ie 5 c 4 81 Secondary jacket structure according to one of the preceding claims, characterized in that the outer circumference of the secondary jacket tube has at least one guide and locking groove (5). A method of manufacturing a secondary sheath structure of an optical cable, the structure comprising a secondary sheath tube (1) and optical fibers (3) in a helical fiber channel (2.2) therein, the method comprising: - guiding the optical fibers (3) to the cross-head of a plastic press (10); 13) to the torpedo (25) and further out of the at least one torpedo head (25a), - a loose secondary jacket tube (1) is extruded around the optical fibers (3) at the press head (13), allowing mutual axial movement between the fibers and the tube 15, and - providing the fibers ( 3) the desired additional length relative to the jacket tube (1), characterized in that - the torpedo (25) is rotated about an axis (C) determined by the direction of travel of the fibers 20, and - the torpedo (25) uses at least one end asymmetrical with respect to the axis of rotation (C); 25a). Method according to Claim 10, characterized in that the direction of rotation of the torpedo (25) is changed periodically. Method according to Claim 10 or 11, characterized in that the torpedo (25) is rotated by means of a holder (24) which supports it. A method of manufacturing a secondary sheath structure of an optical cable, the structure comprising a secondary sheath tube (1) and optical fibers (3) in a helical fiber channel (2.2) therein, the method comprising: - passing optical fibers to a torpedo end (13) of a plastic press (25) and further out of at least one of the torpedo heads (25a) - extruding a loose secondary sheath tube (1) around the optical fibers (3) at the press end, allowing mutual axial movement between the fibers and the tube 5, and - providing the fibers (3) with the desired additional length with respect to the jacket tube (1), characterized in that - the secondary jacket tube (1) is rotated about a central axis-10 sa (F) in the melt zone (15), and - at least one secondary jacket tube is used asymmetrically with respect to the central axis (F) located at the end (25a). Method according to Claim 13, characterized in that the direction of rotation of the secondary jacket tube (1) is changed periodically. A method of manufacturing a secondary sheath structure of an optical cable, the structure comprising a secondary sheath tube (1) and optical fibers (3) in a helical fiber channel 20 (2.2) therein, the method comprising: - guiding the optical fibers (3) to a press head (13) to the torpedo (25) and further out of the at least one torpedo head (25a), - at the press head (13), a loose secondary sheath tube (1) is extruded around the optical fibers (3), allowing mutual axial movement between the fibers and the tube, and - providing the fibers (3) desired additional length with respect to the jacket tube (1), characterized in that - the torpedo (25) uses at least one end (25a) asymmetrical with respect to the central axis of the secondary jacket tube (1), and - - a finished secondary jacket (35) containing fibers (3) (1.1) ) is rotated about its longitudinal axis in a subsequent 20 8 6 4 £ 1 cabling step, followed by n the rotation of the secondary jacket tube (1.1) is locked by coating it with the desired protective structure (41). Method according to Claim 15, characterized in that the direction of rotation of the secondary jacket tube (1.1) is changed periodically. Method according to Claim 15 or 16, characterized in that a second plastic sheath (41) is used as the protective structure. Method according to Claim 15 or 16, characterized in that a layer of steel wire is used as the protective structure. Method according to one of Claims 15 to 18, characterized in that the secondary jacket tube 15 (1.1) is preheated (39) before rotation. li 21 Q. </ C 'I z-x υ C * -! υ I