Classifications

• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
  • G02B6/44—Mechanical structures for providing tensile strength and external protection for fibres, e.g. optical transmission cables
  • G02B6/4479—Manufacturing methods of optical cables
  • G02B6/4486—Protective covering
  • G02B6/4488—Protective covering using metallic tubes

Definitions

• This invention relates to a method of producing an optical multi-fibre conductor element provided with a secondary sheathing, comprising extruding a secondary sheathing loosely around a fibre bundle of several optical fibres;
• the fibres are positioned against the inside of the sheathing, so that the sheathing is stretched between the drawing means and the locking wheel while the fibres slide axially with respect to the sheathing.
• the locking wheel causes variation in the length of the fibres as the turning radius of the fibres around the wheel varies.
• fibres in the fibre bundle are SZ twisted before the extrusion of the loose secondary sheathing around the fibres and before the sheathing is filled with grease.
• the fibres remain twisted to some extent, which ensures that the fibres have a greater length than the sheathing.
• the twisting de- vice required for realizing this kind of method makes the secondary sheathing device complicated, long and slow.
• a few major dis ⁇ advantages are caused by the twist remaining in the finished conductor element.
• the SZ twisting creates a torque in the fibres, which results in the formation of static strains.
• the middle rod around which the fibres are twisted brakes the sliding of the fibres, thus increasing friction and strains, whereby the differences between the strains of different fibres are increased with resultant variation in the fibre lengths and impairment of the technical properties of the conductor element.
• Finnish Patent Specification 75 940 (NOKIA) teaches that the fibres in the fibre bundle will not be passed onto the locking wheel of the stretching device always in the same order with respect to each other when the order of the individual fibres in the fibre bundle which is passed into the extruder for providing it with a secondary sheathing is varied re- peatedly in the step of forming the fibre bundle. In this way it is ensured that the fibres in the sheathed fibre bundle are passed onto the wheel in a continuously changing order, which compensates for the variation in the fibre length and improves the properties of the conductor element.
• the device required for realizing the method i.e. for varying the order of the fibres, makes the sheathing equipment relatively complicated and expensive.
• the object of the present invention is to pro- vide a method for the production of an optical multi- fibre conductor element, which avoids the above- mentioned disadvantages and enables the fibres in the fibre bundle to be passed in parallel with each other into the extruder without any risk of the stretching device causing variation in the length of the fibres in the secondary-sheathed fibre bundle.
• This object is achieved by means of the method of the invention which is characterized in that
• the fibres are removed from the equalizer wheel while still positioned side by side and passed to the extrusion step.
• the invention is based on the idea that individual fibres are locked on the equalizer wheel before the extrusion of the secondary sheathing to avoid variation in the length of the fibres in the sheathed conductor element.
• the fibres On leaving the starting reels, the fibres have approximately the same tension and pass over the equalizer wheel with the same- tension over a short period of time, so that it is obvious that the fibres around which the secondary sheathing is extruded are of equal length.
• the equalizer wheel . and the locking wheel of the stretching device there occurs variation in the tension of individual fibres as the fibres are posi- tioned one upon another on the periphery of the lock ⁇ ing wheel, so that the outer fibres stretch more than the inner fibres.
• the method of the invention enables the fibres to be fed in parallel with each other inside the secondary sheathing, which is of great importance when aiming at a parallel spiral fibre configuration in so-called maxi tubes. It has proved that it is very difficult to attain a spiral configuration in a SZ twisted fibre bundle, and the firmness of the obtained fibre bundle is not such as desired.
• the initial tension of the fibres is not critical. With higher production rates and stiffer greases, ever increasing initial tensions are required in accurate control of the extra fibre length and variation in the fibre length.
• the invention is also concerned with an apparatus for realizing the method, which apparatus is characterized by what is disclosed in claim 3.
• the apparatus is very simple in structure, and does not require any external control or operation. It does not restrict the initial tension of the fibres as compared with central tube or secondary tube twisting machines.
• Figure 1 is a schematic side view of the production of a secondary sheathing for a fibre bundle of an optical cable
• FIG. 2 is an enlarged, more detailed view of an equalizing device of one embodiment of the apparatus according to the invention.
• a number of primary-sheathed fibres 1 are passed from fibre reels 2 through a collector 3 into an equalizing device 4 and further into an extruder 5.
• the secondary- sheathed fibre bundle 6 is then passed through a cooling chute 7 into a stretching device 8 to provide the fibres with an extra length with respect to the secondary sheathing.
• the stretching device comprises a braking means 9 and a locking wheel 10.
• a finished cable element 11 is wound on a reel 12.
• the equalizing device 4 comprises an equalizer wheel 13 with a cylindrical peripheral surface, an inlet comb 14, and an outlet comb 15.
• the equalizer wheel is mounted rotatably on a support not shown.
• the fibre collector 3, the slits of the combs, the highest point of the equalizer wheel and the guide means before the extrusion head of the extruder are positioned substantially on the same line.
• the fibres are wound once around the equalizer wheel, and the combs spread the fibres in a plane apart from each other, so that each fibre is positioned against the peripheral surface of the equalizer wheel.
• the fibres are locked on the equalizer wheel so that they are not able to move in their axial direction with respect to each other on the wheel.
• the fibres On leaving the braked reels 2, the fibres have approximately the same tension, so that they are of substantially equal length when they are locked on the equalizer wheel, and are passed in parallel with each other inside the secondary sheathing.
• the fibres are locked axially immovably to each other and to the secondary sheathing when they are passed around the locking wheel 10.
• variation will occur in the tension of the fibres between the equalizer wheel and the locking wheel.
• the fibres are, however, locked to the equalizer wheel, so that the tension differences will not go beyond the equalizer wheel, but the differences are levelled out and the length variation caused by these differences disappears when the fibres are released after the locking wheel.
• the tensions of the fibres advancing from the braked reels are indicated with the reference tl; these tensions are substantially equal before the equalizer wheel.
• Fibre tensions be- tween the equalizer wheel and the locking wheel are indicated t2, t3, t4 and t5; these tensions may differ from each other.
• Fibre tensions after the locking wheel are indicated with the reference t6, and they are substantially equal.
• the apparatus of the invention compensates for variation in the tension of the fibres caused in the secondary sheathing step, so that a permanent variation in length is avoided in the secondary-sheathed fibre bundle.
• fibre bundle does not only refer to two or more fibres positioned separately in the same sheathing but also to a fibre bunch of two or more fibres bound together e.g. by gluing, by a bind- ing thread or a binding hose.
• the secondary-sheathed optical conductor element may form a part of a multi ⁇ element cable (minitube structure), or it may be the basic element of a single-element cable (maxitube). In the multi-fibre cable element, the fibres may form a bundle, a bunch or several bunches.

Landscapes

• Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• Manufacturing & Machinery (AREA)
• General Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• Communication Cables (AREA)
• Insulated Conductors (AREA)
• Ropes Or Cables (AREA)
• Optical Fibers, Optical Fiber Cores, And Optical Fiber Bundles (AREA)
• Lubricants (AREA)
• Medicines Containing Material From Animals Or Micro-Organisms (AREA)
• Valve Device For Special Equipments (AREA)
• Manufacture, Treatment Of Glass Fibers (AREA)

Priority Applications (2)

Applications Claiming Priority (2)

Publications (1)

Family

ID=8529376

Family Applications (1)

Country Status (7)

Citations (1)

• 1989
  • 1989-11-17 FI FI895497A patent/FI85310C/fi not_active IP Right Cessation
• 1990
  • 1990-11-15 DE DE69018477T patent/DE69018477T2/de not_active Expired - Fee Related
  • 1990-11-15 AT AT90916303T patent/ATE120862T1/de not_active IP Right Cessation
  • 1990-11-15 WO PCT/FI1990/000276 patent/WO1991007679A1/en active IP Right Grant
  • 1990-11-15 JP JP2515167A patent/JP3031704B2/ja not_active Expired - Fee Related
  • 1990-11-15 EP EP90916303A patent/EP0500628B1/en not_active Expired - Lifetime
  • 1990-11-15 AU AU66440/90A patent/AU635085B2/en not_active Ceased

Patent Citations (1)

Also Published As

Similar Documents

Legal Events