METHOD AND APPARATUS FOR THE CONTINUOUS MANUFACTURE OF FIBER-OPTIC CABLE

Abstract: The present invention relates to a method and apparatus for continuous manufacture of a fiber-optic cable (15). According to the method, single optical fibers (2) of certain length are formed into a fiber-optic cable (15) enclosed by a secondary sheath (16). According to the invention, a certain length of the optical fibers (2) is accumulated into an active buffer (5), and the end of an exhausting fiber (2) is connected by a splice to the end of a new fiber (2), while the fiber (2) is being fed into the process during the splicing operation from the buffer (5).

Description: Method and apparatus for the continuous manufacture of fiber-optic cable The present invention relates to a method according to the preamble of claim 1 for continuously manufacturing fiber-optic cable. The invention also concerns an apparatus for continuously manufacturing fiber-optic cable. A viable method for continuously manufacturing fiber¬ optic cable is not known from the patent literature. FR patent document 2,564,987 describes a system in which optical fibers are reeled off from cylindrical fiber reels in the axial direction of the reels, whereby the goal of the invention is to achieve a continuous fiber¬ optic cable manufacturing process by way of splicing the tail of exhausting reels to the start end of a new reel during the process. This method does not make use of an active fiber buffer, but instead, the fiber reserve is located resting in containers which have no capability of active take-up or reel-off of fiber during the splicing operation. The method has a number of serious disadvantages. For instance, the fiber reels received from the fiber supplier must be unwound and re-coiled into said containers, which is a time-consuming step. A more serious complication is related to the fiber reel- off direction. Namely, the reeling-off of the fiber in the axial direction of the reel can cause sticking of the fiber between the underlaying fiber turns that may cut the fiber. Furthermore, this solution has no reliable means of detecting the end of an exhausting fiber reel, and any possible fiber damage during the fiber reel-off halts the entire cable manufacturing process. The traditional discontinuous cable manufacturing process in turn is hampered by losses through discarded material in the process start-up and shut-down phases, and the long start-up time of the process. Moreover, when a fiber lot is ordered from a supplier trimmed to a specified length, in practice the delivered lot always contains a certain number of shorter fibers trimmed exactly to the specified length, while the other fibers may be somewhat overlength, whereby typically about 7 % of the fiber material is lost due to the trimming of the overlength fibers in this conventional process. The shut-down and start-up losses of this process are in the order of a few percent, which causes the overall material loss of the conventional process to be about 10 %. It is an object of the present invention to overcome the disadvantages of the above-described techniques and offer an entirely novel type of method and apparatus for continuously manufacturing fiber-optic cable. The goal of the invention is achieved by providing the cable manufacturing process with a fiber buffer serving to facilitate run-time splicing of the fiber. More specifically, the method according to the invention is characterized by what is stated in the characterizing part of claim 1. Furthermore, the apparatus according to the invention is characterized by what is stated in the characterizing part of claim 8. The invention offers significant benefits. The present continuous process can offer an at least 20 % increase in the cable manufacturing capacity. By making optically functional splices of the fiber ends, the mate¬ rial savings can be as high as ten percent, and even if only temporary factory splices are used to join the fiber ends, the fiber raw material savings may be several per¬ cent as the start-up and shut-down losses of the process are eliminated. In the following the invention is described in greater detail with the help of exemplifying embodiments illus¬ trated in the appended diagrams in which Figure 1 is a diagrammatic side view of an apparatus according to the invention; Figure 2 is a cross section of a fiber-optic cable manu¬ factured using the method according to the invention/ Figure 3 is a side view of a fiber buffer in an apparatus according to the invention; Figure 4 is a side view of another embodiment of a fiber buffer according to the invention; Figure 5 is a side view of a third embodiment of a fiber buffer according to the invention; Referring to Fig. 1, the fiber-optic cable manufacturing apparatus shown therein includes fiber reels 1, which are conventional factory reels. In the embodiment according to the invention, the optical fibers 2 are reeled off from reels 1 tangentially with respect to the perimeter of the cylindrical reels, whereby no torsional stresses will be imposed on the fiber 2. From the factory reels 1, the fibers 2 are routed at the exhaustion of the fiber via a fiber exhaustion detector 3 to a splicing device 4, and therefrom, to an active buffer 5. The fiber exhaus- tion detector 3 may be implemented by optical means, or alternatively, using mechanical sensors. When the fiber is exhausted, the detector 3 issues an alarm and a signal for the fiber buffer 5 to start reeling off the fiber 2 accumulated therein. The splicing device 4 can be an apparatus capable of making a flawless optical splice, e.g., of the type commercially available and typically used for making a field splice in conjunction with the repair of cable damages. Alternatively, the splicing device 4 may be a simpler factory-splicing apparatus that only joins the fibers 2 with a temporary knot or glued splice. Furthermore, the splicing device 4 may within the scope of the invention be a splicer unit joining a bundle of fibers to another fiber bundle. The fiber buffer 5 is followed by a conventional cable manufacturing process with a sheathing line 6 in which a polymer sheath is formed about the fiber bundle, and when required, a filler material is introduced enclosing the fibers under the sheath. Typically, the sheathing line 6 includes an extruder adapted to form a sheath about the fibers from a melted polymer raw material. Subsequent to the extruder is typically adapted a cooling line formed by a series of water baths at different temperatures, permitting controlled processing of the polymer sheath. While the line run speed is typically in the order of 100 m/min, production lines with higher speeds are being designed. From the sheathing line 6, the finished cable 15 is taken to a continuously running upwinder having two uptake rolls 7 and 8 in order to allow for an uninterrupted process. As shown in Fig. 2, the cable 15 made in the process of Fig. 1 comprises optical fibers 2 whose number in the cable cross section illustrated in the diagram is 16. The length of the fibers 2 typically varies in the range 4000 - 25,000 m. Prior to the cable manufacturing pro¬ cess, the fiber 2 is coated with a so-called primary coating 18 which may be coloured with a suitable coding colour if so desired. Typically, the diameter of the fiber 2 is 125 μm. A suitable protective gel 17 is extruded about the fibers 2 to seal the fibers 2 against moisture. The secondary sheath 16 is formed essentially simultaneously with the gel extrusion about the fibers 2 by extrusion using melted polymer. The outer diameter of the cable 15 is typically about 5-10 mm. Typically, the cables 15 are combined into larger-diameter cables called stranded cables in which the total number of cables can be 48, for instance. With reference to Fig. 3, the active fiber buffer 5 shown therein may in its simplest embodiment be a system formed by a single dancer sheave 11, whereby the fiber 2 in the running process is passed over fixed sheaves 10 and 9 to the dancer sheave 11 such that in the normal operating state the sheave 11 is kept in its lowermost position, and when a splice is being made, the sheave 11 is elevat¬ ed thus permitting the fiber on the ingoing side of the buffer system to be halted for splicing. Due to the limited buffer capacity of the system shown in Fig. 3, this embodiment permits only a temporary splice to be formed between the fiber ends. If the travel of the sheave 11 is made to be 5 m, for instance, the system gives a fiber buffer reserve of 10 m, whereby a splicing time of 6 seconds remains at full line speed. Such a short time is sufficient for making a so-called temporary factory splice that has no optical continuity properties. When the cable is made using temporary factory splices, the location of the splice must be marked on the cable or recorded in the memory of the equipment to permit later elimination of the temporary factory splice from the cable. As shown in Fig. 4, the active fiber buffer may be made designed into a multipass system, m which case the active travel of 5 m allowed for the dancer sheave provides a six-fold buffer capacity as compared with the system illustrated in Fig. 3. Then, the splicing time is extended to 36 s, which may already be considered sufficient for making an optically functional splice. Here, the sheave set 13 may be fixed and the sheave set 12 movable. However, within the scope of the invention it is obviously irrelevant which one of the sheave sets is made movable, and even both sheave sets can be designed movable. The only constraint to the number of multipass travels within the buffer systems 5 is dictated by the footprint available in the vicinity of the cable manufacturing equipment. The lateral space need of the sheaves is minimal. With reference to Fig. 5, the active buffer may also be designed into a container 20 in which the end length of the fiber 2 is forced to fold with the help of a com- pressed air j et and from which the fiber is reeled off during the splicing of the fiber. Instead of a compressed air jet, the fiber 2 could be forced into the container 20 by means of, e.g., a sheave pair 21. It must be noted that the buffering of the fiber into the container 20 is done actively only when the fiber 2 is close to its end. Alternatively, the buffer 5 may also be implemented with the help of a variator-type variable-diameter cone system in which the capacity of the fiber buffer is controlled by adjusting the longitudinal position of the cones. The buffer 5 can be designed for single fibers as well as entire fiber bundles. When the temporary factory splice is made by glueing the ends of the entire fiber bundle together, also the buffer 5 must be implemented as a bundle buffer.

Claims: Claims : 1. A method for continuously manufacturing fiber-optic cable (15), in which method - single, cut-to-length optical fibers (2) are formed into a fiber-optic cable (15) enclosed by a secondary sheath (15), c h a r a c t e r i z e d in that - during the manufacturing process, fibers (2) are accumulated in an active buffer (5, 20), and - the end of an exhausting fiber (2) is joined with the end of a new fiber (2), and during the splicing operation, the fiber (2) is reeled off to the manufacturing process from said buffer (5, 20). 2. A method as defined in claim 1, c h a r a c t e r ¬ i z e d in that a separate buffer (5) is provided for each fiber (2) . 3. A method as defined in claim 1, c h a r a c t e r ¬ i z e d in that a single buffer (5) is provided for the entire bunch of fibers. 4. A method as defined in claim 1, c h a r a c t e r - i z e d in that the fibers (2) are connected to each other by an optically functional splice. 5. A method as defined in claim 1, c h a r a c t e r ¬ i z e d in that the fibers (2) are connected to each other by a temporary factory splice lacking optical continuity properties. 6. A method as defined in claim 5, c h a r a c t e r - i z e d in that the temporary splices are removed from the finished cable (15) . 7. A method as defined in claim 1, c h a r a c t e r ¬ i z e d in that the exhausting fiber (2) is accumulated in a container (20) prior to its exhaustion. 8. An apparatus for continuously manufacturing fiber¬ optic cable (15), said apparatus including - feed means (1) for passing optical fiber (2) into the manufacturing process, - means (6) for forming a sheath (16) about said fibers (2), c h a r a c t e r i z e d in that said apparatus comprises - a splicing device (4) suitable for forming a splice between the optical fibers, and - located after said splicing device (4) in the process, an active buffer (5) suitable for con¬ tinuously feeding the optical fibers (2) into the process also during the splicing operation. 9. An apparatus as defined in claim 8, c h a r a c ¬ t e r i z e d in that a separate buffer (5) is provided for each fiber (2) in the apparatus. 10. An apparatus as defined in claim 8, c h a r a c ¬ t e r i z e d in that a single buffer (5) is provided for the entire bunch of fibers. 11. An apparatus as defined in claim 8, c h a r a c ¬ t e r i z e d in that said splicing device is capable of connecting the fibers (2) to each other by an optically functional splice. 12. An apparatus as defined in claim 8, c h a r a c ¬ t e r i z e d in that said buffer (5) is formed by a single movable sheave (11) . 13. An apparatus as defined in claim 8, c h a r a c - t e r i z e d in that said buffer (5) is formed by a multipass movable sheave assembly (12). 14. An apparatus as defined in claim 5, c h a r a c ¬ t e r i z e d in that said apparatus includes means for accumulating the end length of the exhausting fiber (2) into a container (20) acting as the fiber buffer.

Inventors: KARVONEN LEEVI, PUHAKKA TIMO, SUVANTO MARKKU T, KARVONEN, LEEVI, PUHAKKA, TIMO, SUVANTO, MARKKU, T.
Applicants: KARVONEN LEEVI, NOKIA KAAPELI OY, PUHAKKA TIMO, SUVANTO MARKKU T, KARVONEN, LEEVI, PUHAKKA, TIMO, SUVANTO, MARKKU, T.
Application year: 1997
Main classification: G02B6
IPC codes: G02B6