METHOD AND APPARATUS FOR PASSING OPTICAL FIBERS THROUGH TUBULAR PRODUCTS

Abstract: A tube (1) is wound into a coil, and the resulting coil of tube (5) is vibrated so that a given point of the tube reciprocates along a helical path. An optical fiber (7) is fed into the coil of tube that is being thus vibrated. Because of the vibration, the inner wall of the tube exerts such a force as to move the optical fiber diagonally upward and forward. This force causes the optical fiber to jump in the tube diagonally upward and forward and slide forward along the inner wall of the tube. The intermittent conveying force exerted by the inner wall of the tube in the direction of the circumference of the coil causes the optical fiber in the tube to travel forward, thereby pulling in additional length of the optical fiber from outside the tube.

Description: This invention relates to a method and apparatus for passing optical fibers through tubular products, and more particularly to a method and apparatus for making optical fiber core wires, optical fiber cords and/or optical fiber cables comprising optical fibers passed through protective tubes or sheaths. For the purpose of this invention, optical fibers are defined as element fibers comprising a core and a cladding layer, such element fibers being coated with syntetic resins, metals and ceramics and their variations comprising a single fiber, multiple fibers and stranded fibers. Tubular products are such metal tubes as those of steel and aluminum, and such nonmetal tubes as those of plastic. Recently optical fiber cables have come to be used widely for communications services. And many of them are metal-coated to make up for the limited strength of optical fibers. Optical fibers passed through metal and other tubes have been made by a method that combines tape forming and welding (see JP-B-46 869/85) and a method that passes an optical fiber through a tube (see JP-B-25 606/83). In the former method, an optical fiber is passed through a metal tube while a metal tape is being formed into a tubular shape and both edges of the tape are being welded together. But there is a shortcoming that the optical fiber is liable to degenerate under the influence of welding heat when it passes the welding point. Also, an optical fiber is difficult to pass through tubes whose diameter is as small as 2 mm or under. In the latter method, an aluminum tube is made with a steel wire passed therethrough. After the tube is subjected to a diameter-reducing process, the steel wire inside the tube is replaced with an optical fiber. This method requires intricate processes. Besides, the force with which the steel wire is pulled out for replacement should not exceed the strength of the optical fiber in order to avoid the risk of fiber breaking. Accordingly, optical fiber cable having a length of 200 m or more have been difficult to make. EP-A-0,091,717 describes a method and a device of passing an optical fiber through a tube by means of vibrating a coil of the tube. It is an object of the invention to facilitate and accelerate the manufacturing process. This object is solved with the features of claims 1 and 9. To facilitate passing, the difference between the inside diameter of the tube and the diameter of the optical fiber should be not less than 0.1 mm and the diameter of the coil of tube should be not smaller than 150 mm or preferably 300 mm or more. For the matter of vibration, the angle of vibration (i.e., the lead angle of helix) should be not smaller than 1 degree, or preferably between 5 and 30 degrees, the frequency of vibration not less than 5 Hz, or preferably between 10 and 30 Hz, and the total amplitude of vibration in terms of vertical component not less than 0.1 mm, or preferably between 0.5 and 2.0 mm. The passing apparatus may also incorporate a sensor to detect the difference between the passing speed and unwinding speed of the optical fiber and a device to control the unwinding speed of the optical fiber supply device on the basis of the speed difference detected by the aforementioned sensor. The method and apparatus of this invention permits passing an optical fiber through a tube of small diameter (such as one having an outside diameter of 2 mm or under) and long length (such as one having a length of 1 km or over) without deteriorating or damaging the optical fiber. Their simplicity is conducive to cutting down the production cost of optical fibers covered with protective tubes. With the unwinding speed of an optical fiber controlled by the supply device of this passing apparatus, the optical fiber can be fed into a tube in the most favorable condition, without applying excessive tension on the optical fiber and exerting any backward force to prevent the admission thereof into the tube. Fig. 1 is a side elevation showing a preferred embodiment of an optical fiber passing apparatus according to this invention; Fig. 2 is a plan view of a vibrating table of the same apparatus; Fig. 3 is a front view showing an example of a bobbin mounted on the vibrating table; Fig. 4 shows cross-sectional profiles of grooves cut in the bobbin at (a) and (b); Fig. 5 is a cross-sectional view of an example of an anti-vibrating guide provided to the apparatus; Fig. 6 is a cross-sectional view of an example of a protective guide provided to the apparatus; Fig. 7 illustrates a principle on which an optical fiber is carried forward in a tube; Fig. 8 diagramatically shows vibrating conditions of a coil of tube at (a) and (b) Fig. 9 shows front views of other exmaples of bobbins at (a) and (b); Fig. 10 is a front view showing an example of means to fasten a coil of tube to a bobbin; Fig. 11 is a perspective view showing an example of an elastic belt used as the fastening means; Fig. 12 is a front view showing another example of the means to fasten a coil of tube; Fig. 13 is a perspective view of a bobbin used with the fastening means shown in Fig. 12; Fig. 14 is a front view of an elastic belt used with the fastening means shown in Fig. 12; Fig. 15 is a partially cross-sectional front view showing still another example of the means to fasten a coil of tube; Fig. 16 is a cross-sectional view showing another example of the anti-vibrating guide; and Fig. 17 is a cross-sectional view showing another example of the protective guide provided at the inlet end of a tube. Now preferred embodiments of this invention will be described by reference to the accompanying drawings. Fig. 1 is an overall view of a passing apparatus according to this invention, and Fig. 2 is a plan view of a vibrating table. A base 11 is firmly fastened to a floor surface 9 so as not to vibrate. Coil springs 18 to support a vibrating table are mounted at the four corners of the top surface of the base 11. A square panel-like vibrating table 14 is placed on the base 11, with the support springs 18 interposed therebetween. A support frame 15 extends downward from the bottom surface of the vibrating table 14. The support frame 15 under the vibrating table 14 carries a pair of vibrating motors 21, 22. The vibrating motor 22 is placed in such position and posture, with respect of the other vibrating motor 21 as those which are obtainable if the vibrating motor 21 would be rotated about the central axis C of the vibrating table 14 through an angle of 180 degrees. The rotating shafts of the vibrating motors 21, 22 are respectively parallel to a vertical plane containing the central axis C and oppositely tilted with respect to the surface of the vibrating table at an angle of 75 degrees. Unbalanced weights 24 are fastened to both ends of the rotating shafts of the vibrating motors 21, 22. The centrifugal force resulting from the rotation of the unbalanced weights 24 applies a vibrating force to the vibrating table 14 that works aslant to the surface thereof. The paired vibrating motors 21, 22 are driven in such a manner that vibrations they cause have equal frequency and amplitude, and vibrating forces they exert are displaced 180 degrees from each other. Accordingly, when the vibrations caused by the paired vibrating motors 21, 22 are combined, the vibrating table 14 vibrates in such a manner as to move along a helical whose central axis coincides with the central axis C of the vibrating table 14. The vibration of the vibrating table 14 is not transmitted to the base 11 because the support springs 18 are interposed therebetween. In place of the vibrating motors 21, 22, such vibrating means as those employing cranks, cams or electromagnets may be used. Also, vibrating motors 21, 22 may be fastened to the vibrating table 14 in other ways than shown in Fig. 1. A bobbin 27 is fastened on the vibrating table 14 in such a manner that the axis of the bobbin 27 coincides with the central axis C of the vibrating table 14. A tube 1 through which an optical fiber 7 is to be passed is coiled around the bobbin 27, forming a coil 5 of tube 1. The optical fiber 7 is inserted into the tube 1 from the lower end of the tube coil 5. To avoid the development of excessive bending stress in the optical fiber, the diameter of the coil of tube should preferably be not smaller than 150 mm. The optical fiber 7 used in this embodiment consists of an element optical fiber precoated with resin. The tube 1 is a steel tube. The outer periphery of the bottom flange 29 of the bobbin 27 is fastened to the vibrating table 14 with fastening jigs 31 so that the vibration of the vibrating motors 21, 22 is surely received. As is shown in Fig. 3, a groove 30 is cut around the circumference of the barrel 28 of the bobbin 27 using a shaper so that ridges and recesses pointing to the axis of the bobbin are successively formed. The groove 30 is shaped so that the tube 1 comes in contact therewith closely. In cross-sectional profile, the groove 30 may be either a triangular groove 30a as shown at (a) of Fig. 4 or an arc-shaped groove 30b as shown at (b) of the same figure. Any other cross-sectional profile is allowable so long as the tube 1, which is shown by a broken line, is firmly retained on the bobbin 27. The optical fiber 7 is passed through the tube 1 gradually while the bobbin 27 is being vibrated. If the directly vibrated bobbin 27 and the tube 1 would therearound are not kept in close contact with each other, precise transmission of the vibration to the tube 1 and, therefore, smooth passing of the optical fiber 7, will not be achieved. The tube 1 wound around the barrel 28 of the bobbin 27 easily clings to the barrel 28 in the direction of the diameter of the bobbin 27, but not in the direction of the axis thereof. Then, it becomes difficult to uniformly vibrate the entirety of the tube 1 vertically. But if the tube 1 is held tightly in the groove 30 around the barrel of the bobbin 27, the vibration of the bobbin 27 will be precisely transmitted to the tube 1, thereby ensuring smooth and efficient vibration and passing of the optical fiber 7. A supply spool 34 that constitutes an optical fiber feeder 33 is placed beside the bobbin 27. The spool 34 is rotatably supported on a bearing stand 35. The spool 34 pays off the optical fiber 7 wound therearound into the coil of tube 1. The point at which the spool 34 pays off the optical fiber 7 is substantially at the same level as the point at which the optical fiber 7 is supplied into the tube 1. A drive motor 38 is positioned next to the spool 34. The spool 34 and drive motor 38 are interlocked by a belt transmission 40. Rotated by the drive motor 38, the spool 34 pays off the optical fiber 7 into the tube 1 wound around the bobbin 27. A support guide 43 is provided near the optical fiber pay-off point of the feed spool 34. Consisting of a short tubular guide proper 44 and a stand 45 that horizontally supports the guide proper 44, the support guide 43 supports the optical fiber 7 paid off from the spool 34. An optical fiber supply condition sensor 47 is installed downstream of the support guide 43. The optical fiber supply condition sensor 47 is made up of a support column 48 and an optical fiber level sensor 49 attached thereto. The optical fiber level sensor 49 consists of an image sensor and an oppositely disposed light source. Installed in the pass line of the optical fiber 7, the optical fiber level sensor 49 senses the sagging condition thereof. A CCD line sensor is used as the image sensor. To the optical fiber supply condition sensor 47 is connected a rotation speed controller 52 that controls the voltage of power supply 39 to said drive motor 38 on the basis of signals sent from the optical fiber supply condition sensor 47. That is, the rotation speed of the drive motor 38 or, in other words, the pay-off speed of the optical fiber 7 is controlled depending on the level at which the optical fiber 7 interferes with the travel of light from the light source in the optical fiber level sensor 49. The speed with which the optical fiber 7 is passed through the tube 1 is not always constant but may vary when a resonance occurs or depending on the condition of the inner surface of the tube 1 and the surface of the optical fiber 7. A change in the running speed of the optical fiber 7 in the tube 1 affects the paying off condition of the optical fiber 7 on the outside. If the paying off speed does not follow the passing speed, the optical fiber 7 on the outside may either sags excessively or break as a result of overtight stretching. Either way, smooth paying off of the optical fiber 7 will be hindered. But the optical fiber 7 can always be paid off at a pay-off speed within the desired range if the spool 34 is rotated so that the rotation thereof is varied or stopped depending on the travelling condition of the optical fiber 7 in the tube 1. Namely, the optical fiber 7 is then kept in the optimum condition (in which the optical fiber 7 sags slightly as shown in Fig. 1), without oversagging or getting overstretched. As a consequence, the optical fiber 7 is passed through the tube without a hitch, with no load placed thereon or no resistance built up against the passing thereof. Incidentally, an optical fiber 0.4 mm in diameter will not enter a steel tube having an inside diameter of 0.5 mm if a force of 20 gf or greater directed to the feeder side works on the optical fiber. The optical fiber supply condition sensor 47 is not limited to the illustrated image sensor, but may consist of a pair of photoelectric tubes that are vertically spaced away to detect the upper and lower limits of the sagging of the optical fiber 7. In this case, the drive motor 38 is on-off controlled. Instead of sensing the position and form of the optical fiber 7, just the supply speed of the optical fiber 7 may be sensed to control the motor speed in accordance with signals based on the sensed results. An anti-vibrating guide 54 is installed between the optical fiber supply condition sensor 47 and the inlet end 2 of the tube. The anti-vibrating guide 54 consists of a cylindrical guide proper 55 and a stand 58 that horizontally supports the guide proper. As shown in Fig. 5, both ends of the guide proper 55 of the anti-vibrating guide 54 expand outward to form tapered (funnel-shaped) portions 57. The boundary between each tapered portion 57 and a cylindrical portion 56 should preferably be shaped into a smooth curved surface. The length of the anti-vibrating guide 54 may be chosen appropriately depending on the distance between the inlet end 2 of the tube and the spool 34. When the distance is long, the anti-vibrating guide 54 should naturally be long. The anti-vibrating guide 54 must be made of such materials as glass and plastic that have such a low coefficient of friction that the transfer of the optical fiber by vibration is not impeded. A lubricant supply 59 filled with a lubricant is attached to the cylindrical portion 56 of the anti-vibrating guide 54. The lubricant is a solid lubricant comprising a powder of carbon, talc, molybdenum disulfide and so on. The lubricant S that falls from the lubricant supply 59 into the cylindrical portion 56 adheres to the surface of the optical fiber when passing therethrough. When the coil of tube 5 into which the optical fiber 7 has been inserted is vibrated, the optical fiber 7 immediately ahead of the tube 1 may swing wildly. The swinging optical fiber 7 may impede smooth vibration and passing thereof and, at the same time, may damage the surface thereof on coming in contact with the edge of the inlet end 2 of the tube 1. When the swing is very wild, even cracks may occur inside the optical fiber. But the anti-vibrating guide 54 keeps down the swing outside the end of the tube 1, thereby allowing the optical fiber 7 to be conveyed in good condition, without damaging the optical fiber 7 and offering no resistance to the vibration and passing thereof. A separately prepared protective guide 61 is fastened to the inlet end of the tube 1, as shown in Fig. 6. The protective guide 61 is made of such material as plastic that has a low coefficient of friction and provided with a tapered guide 62 having an outwardly diverged surface. The optical fiber 7 passed through the coiled tube 1 by the vibration of the tube 1 may move forward while bumping against the inlet end 2 of the tube 1 because the optical fiber 7 is also vibrating. Then, the edge of the inlet end 2 of the tube may produce such longitudinal scratches on the optical fiber 7 as may cause the cracking of the optical fiber 7 and the deterioration of a final product. But the protective guide 61 of the above-described structure enables the optical fiber 7 to be readily inserted into the tube 1 and smoothly carried forward therein, without causing any surface defect or damage after insertion. Next, a method of passing an optical fiber 7 through a tube 1 using the above-described apparatus will be described. In advance, a coil 5 is formed by winding a tube 1 around the bobbin 27, while an optical fiber 7, which consists of a precoated element fiber, is wound around the spool 34. The tube 1 need not always be wound around the bobbin 27 in a single ring, but are often wound in multiple rings. In a coil of multiple rings, the first ring fits closely in the groove 30 cut around the barrel 28 of the bobbin 27, but the second and subsequent rings will fit in the recessed portion formed by the tube 1 of the preceding ring. Then, the bobbin 27 carrying the wound tube 1 is fastened on the vibrating table 14 in such a manner that the axis of the coil coincides with the central axis C of the vibrating table 14. The leading end of the optical fiber 7 pulled out of the spool 34 is inserted through the protective guide 61 into the inlet end 2 of the tube 1, after passing through the support guide 43, optical fiber supply condition sensor 47 and anti-vibrating guide 54. With the inlet end 2 of the tube being positioned at the lowermost end of the coil 5, the optical fiber 7 is passed through the tube 1 substantially along the tangent of the coil 5. In the beginning, the optical fiber 7 is manually pushed into the coil 5 by the length of 5 to 150 m. After this, the inner surface of the vibrating tube 1 exerts adequate conveying force to cause the optical fiber 7 to steadily move forward through the tube. The length of the pushed-in optical fiber (i.e., the length of initial insertion) depends on the inside diameter of the tube, outside diameter of the optical fiber, and coefficient of friction between the optical fiber and the inner wall surface of the tube. The insertion is readily achieved if the optical fiber is inserted while vibrating the tube. To ensure the smooth entry of the optical fiber into the tube, a certain amount of clearance must be left between the optical fiber and tube. The clearance should preferably be not less than 0.1 mm. When the vibrating motors 21, 22 are started, the vibrating table 14 is subjected to a torque working around the central axis C thereof and a force working therealong because of the position and posture in which the vibrating motors 21, 22 are placed as described previously. Consequently, a given point on the table 14 vibrates in such a manner as to move along a helical H shown in Fig. 1. The vibration is transmitted from the vibrating table 14 through the fastening jigs 31, bobbin 27 and coil of tube 5 to the optical fiber 7. The motion of the optical fiber 7 varies with the type of the vibration, properties of the optical fiber, inside diameter of the tube 1 and other parameters. The optical fiber 7 is considered to move forward through the tube 1 in the following manner. As is shown in Fig. 7, the bottom surface of the inner wall of the tube is moving with a vibration V centered on O. While the angle of the vibration is ϑ, the maximum acceleration is n times (n sin ϑ > 1) the acceleration g of gravity. The optical fiber is assumed to contact the bottom surface of the inner wall with pitches L since it is hardly conceivable that the optical fiber is in contact therewith throughout. A point of contact is defined as "a". The optical fiber is released from its point of contact "a" when the vertical downward acceleration of the bottom surface of the inner wall becomes equal to g, namely at a point of release P₁ on a line of release ℓ₁. The released optical fiber begins to jump at a speed v₁ and an angle of projection ϑ. Meanwhile, a non-contact point b moves differently from the point of contact a since the optical fiber is not a rigid substance. The vibration V does not produce as much lifting force as at the point of contact a. After being released on the line of release ℓ₁, therefore, the optical fiber is subjected to a depressing force resulting from the motion of the point of contact a. Consequently, the optical fiber falls onto a line of contact ℓ₂ at another point of contact b₁ that is different from the first point of contact a. If the vibration V of the bottom surface of the inner wall is in the rising direction, the optical fiber continues to move upward until it is released on the line of release ℓ₁. If the vibration V is in the descending direction, the optical fiber first drops to the lowermost point and then moves upward until it is similarly released on the line of release ℓ₁. Such a surging motion is repeated in each cycle or several cycles of the vibration, whereby the optical fiber 7 is caused to move forward through the tube 1. The most efficient way is such that the optical fiber begins to jump upward the moment it touches the bottom surface of the inner wall when the line of contact ℓ₂ agrees with the line of release ℓ₁. Strictly speaking, friction, repulsion and other phenomena occuring between the optical fiber and the bottom surface of the inner wall of the tube must be considered. If the jumping optical fiber comes in contact with the top surface of the inner wall of the tube, the advancing motion thereof will naturally be different. When n sin ϑ ≦ 1, the optical fiber will not jump, but may slide forward depending on the condition of friction between the optical fiber and the bottom surface of the inner wall of the tube. As is obvious from the above, the optical fiber 7 is driven forward through the tube 1 by a component of a force exerted onto said fibre by the inner wall of the tube 1 in the circumferential direction of the coil of tube. Because the axis of the coil 5 is in coincidence with the central axis C of the vibrating table 14, the optical fiber 7 in the tube makes a circular motion about the central axis C (a circular motion in the counterclockwise direction P in the embodiment shown in Fig. 2). Reference is now made to Fig. 1 again. When the helical vibration is transmitted through the vibrating table 14 to the coil of tube 5, the optical fiber 7 fed from the inlet end 2 of the tube below the coil of tube 5 continuously moves forward through the tube 1 under the influence of the conveying force resulting from the vibration. That is, the vibration of the coil of tube 5 moves forward the optical fiber 7 paid off from the spool 34 through the support guide 43, optical fiber supply condition sensor 47, anti-vibrating guide 54, protective guide 61, inlet end 2 of the tube, coil-formed tube 1 and outlet end 3 of the tube. Thus, the optical fiber 7 is passed through the entire length of the coil of tube 5 in a given time. Any variation in the passing speed of the optical fiber 7 affects the supply condition thereof at the optical fiber level sensor 49, with the resulting change in the supply condition being instantly detected by the optical fiber level sensor 49. If the optical fiber level sensor 49 senses that the optical fiber 7 is overstretched, a corresponding signal will be sent to the drive motor 38 to increase the rotation speed of the spool 34, thereby increasing the supply speed of the optical fiber 7. If an excessive sagging of the optical fiber 7 is sensed, the drive motor 38 will be accordingly controlled to slow down the supply speed of the optical fiber 7. In this way, any abnormal condition in the forward travel of the optical fiber is instantly sensed, corrected and returned to the normal condition. Example To confirm the effect of this invention, optical fibers were passed through steel tubes under the following conditions (Table 1) using the apparatus shown in Fig. 1. The result of passing are shown in Table 1. (1) Specimens Coils of steel tubes: Seven types of steel tube coils prepared by winding seven different steel tubes ranging between 0.8 mm and 2.0 mm in outside diameter and between 0.5 mm and 1.6 mm in inside diameter and having a length of 10 km regularly (in 10 to 20 rings) round steel bobbins having a barrel diameter of 1200 mm. Optical fibers: Optical fibers, 0.4 mm in diameter, of silica glass (125 µm in diameter) coated with silicone resin. (2) Vibrating conditions: Because the numbers of rings were 10 (Coils Nos. 1 to 6 in Table 1) and 20 (Coil No. 7) on the steel tube coils tested, vibrating conditions were substantially the same at any point of the tube. Angle of vibration with respect to the horizontal plane of the coil: 15 degrees Frequency of vibration: 20 Hz Vertical component of total amplitude: 1.25 to 1.55 mm The obtained results are shown in Table 1. Fig. 8 (a) and (b) show the vibrations of the bobbin in Example No. 4 of Table 1. While the diagram at (a) shows a condition in which the optical fiber is still not inserted in the tube, the other diagram at (b) shows a condition in which 1000 m of the optical fiber has been inserted in the tube. In these diagrams, A V and A H respectively designate the vertical and horizontal components of vibration amplitude. As is obvious from Fig. 8 (b), a high-frequency component appears in the vibration of the coil when the optical fiber has been inserted in the tube. The amplitudes were measured by an accelerometer attached to the bobbin flange. The exemples prove that optical fibers can be quite smoothly passed through the entire length of steel tubes in the desired periods of time. As is obvious from Table 1, optical fibers can be satisfactorily inserted into tubes having such a small diameter as 2 mm or under and such a large length as about 10 km. Even in such cases, the optical fibers passed through do not deteriorate or get otherwise damaged. Now other variations of the component parts of the embodiment just described will be described in the following. Similar parts are designated by similar reference characters, with the description thereof omitted. In this invention, a number of circular grooves 67 parallel to the flange 66 of the bobbin 64 may be provided as shown at (a) of Fig. 9. Such grooves 67 need not be provided throughout the whole circumference of the barrel 65. Instead, grooves 67 and a smooth portion 68 may be provided in different portions thereof as shown at (b) of Fig. 9. Smooth passing of an optical fiber through a tube is impracticable if the tube is not kept in close contact with the bobbin because precise transmission of vibration is not achieved then. The tube readily clings to the barrel in the direction of the barrel radius, but not so in the direction of the barrel axis. This is likely to entail a disturbance in vertical vibration. In Fig. 10, the tube 1 coiled around the barrel of the bobbin 27 is wrapped by a wide elastic belt 71 shown in Fig. 11. The elastic belt 71 consists of a flat rubber belt 72 and flanges 73 integrally fastened to both ends thereof. The tube 1 is tightly pressed in the direction of the radius of the bobbin 27 by fastening the bolts 75 passed through the bolt holes 74 provided in the opposite flanges 73 with nuts 76 after the coil of tube 5 has been wrapped by the rubber belt 72. The tightening force of the belt 72 can be adjusted by turning the nuts 76. Fig. 12 shows another means for fastening the coil of tube 5 of the bobbin. A bobbin 79 has a slot 81 and a plurality of stopper grooves 82 provided in each flange 80 thereof as shown in Fig. 13. The elastic belt 84 consists of a rubber belt 84 having stopper rods 85, 86 fastened to both ends thereof. After the tube 1 has been wound around the bobbin 79, the top and bottom ends of one stopper rod 85 on the belt 84 are inserted in the slots 81 in the top and bottom flanges. After the belt 84 has been wound around the tube 1, for example, clockwise in such a manner that both ends thereof overlap each other to some extent, the belt 84 is fastened by inserting the top and bottom ends of the other stopper rod 86 in an appropriate stopper groove 82. The elastic belt 84 thus keeps the tube 1 in close contact with the barrel 83 of the bobbin 27, with the tightening force thereof being adjusted by choosing a stopper groove 82 in an appropriate position. Fig. 15 shows still another means for fastening the coil of tube to the bobbin 27. After the tube 1 has been wound around the barrel of the bobbin 27 (in a single or more rings), the tube 1 is fastened in position by a adhesive tape 88 that is wrapped therearound as illustrated. To ensure secure fastening, the adhesive tape 88 is wrapped in a partially or fully overlapped manner. Any kind of adhesive tape serves the purpose so long as it has enough adhesive force to tightly press the tube 1 wound around the barrel of the bobbin 27 thereagainst and keep the tube 1 in such tightly pressed condition for a certain period of time. But the adhesive tape 88 should preferable be of such type as can be easily peeled off by hand when the tube 1 is detached from the bobbin 27 after the optical fiber 7 has been passed therethrough. For example, gummed tape is one of the most suitable adhesive tapes of such kind. Any of the above-described fastening means keeps the tube 1 in close contact with the barrel of the bobbins 27, 79, thereby ensuring precise transmission of the vibration of the bobbin 27, 79 to the tube 1 while keeping to a minimum the freedom and wild vibration of the tube 1. With the undesirable motion of the tube in the direction of the bobbin axis and radius thus effectively held down, the optical fiber can be smoothly and efficiently passed through the coil of tube. There is yet another embodiment in which the tube is wound around a bobbin that is circularly divided into two or more segments. Then, the bobbin is expanded outward from inside, using a hydraulic jack, link mechanism or the like, thereby bringing the coil of tube into close contact with the bobbin. Fig. 16 shows another embodiment of the anti-vibrating guide. The guide cylinder proper 91 of an anti-vibrating guide 90 has a heavier wall thickness. The guide ends 92 are rounded off to leave no angular corners thereat. The anti-vibrating guide is of course not limited to the illustrated embodiments, but may be of any shape and structure so long as no damage is caused to the optical fiber at the inlet end 2 of the tube. Fig. 17 shows another embodiment of the protective guide. Instead of attaching a separate protective guide, the inlet end 2 of the tube 1 itself may be expanded to form a larger-diameter portion 94 as shown in Fig. 17. This embodiment will also produce similar results. A pair of rollers covered with sponge or other cushioning material or a piece of cushioning material that may hold the optical fiber in such manner as not to impede the smooth travel thereof may be provided near the inlet end of the tube as the protective guide. The number of optical fibers to be passed through a tube is not limited to one. A plurality of optical fibers may be passed there-through if the relationship between the inside diameter of the tube and the diameter of the optical fiber 7 allows. This invention is of course not limited to a combination of the optical fiber consisting of a precoated element fiber and the steel tube used in the embodiments described hereinbefore. Many other variations are possible, such as those in which an optical fiber or cable is passed through tubes of aluminum, synthetic resin or other materials. The optical fiber passed through the tube may be subjected to a processing that reduces the cross-sectional area thereof. Other appropriate modifications may be introduced as required. The optical fiber may be supplied from the top of the coil of tube. The central axis of the coil of tube should preferably coincide with the central axis of the helical vibration, though such coincidence is not an absolute requisite. The central axis of the coil of tube should preferably be vertical, but need not always be so. For initial insertion of the optical fiber, pinch rollers or other mechanical means may be used instead of hand.

Claims: A method of passing an optical fiber (7) through a tube (1), which comprises the steps of: forming a coil (5) of a tube (1) in which an optical fiber (7) is to be housed; initially inserting a given length of optical fiber provided from an optical fiber supply (34) into one end (2) of the coiled tube (5); and, causing the coiled tube (5) to vibrate, whereby the optical fiber initially inserted into the tube moves forward, under the influence of the intermittent conveying force exerted by the inner wall of the vibrating tube, in the direction of the circumference of the coil (5) of tube, characterized in that the coiled tube (5) is caused to vibrate in such a manner that a given point thereon reciprocates along a helical path (H), and, the optical fiber (7) is actively provided from said optical fiber supply (34) as it advances inside the tube, said active providing being performed at substantially the same speed as the advancing speed of the optical fiber through the tube. The method according to claim 1, in which the initial insertion of the optical fiber (7) into the tube (1) from one end (2) thereof is made over such a length that a conveying force great enough to pull in the optical fiber (7) is developed. The method according to claim 1 or 2, in which the optical fiber (7) is initially inserted into the tube (1) in such a manner that the upstream-oriented force working on the optical fiber (7) at the inlet (2) of the tube (1) is kept smaller than said conveying force. The method according to claim 1, 2 or 3, in which a lubricant is coated on the surface of the optical fiber (7) that is to be passed into the tube (1). The method according to any one of claims 1 to 4, in which the optical fiber (7) upstream the inlet end (2) of the coil (5) of tube (1) is slackened so that a counterforce exerted at said end (2) on the optical fiber (7) is not larger than said conveying force. A method according to any one of claims 1 to 5 which comprises the additional steps of: detecting a difference between the passing speed and the supplying speed of the optical fiber (7); and controlling the supplying speed of the optical fiber (7) on the basis of the speed difference thus detected. The method according to claim 6, in which said speed difference is detected from a slack of the optical fiber (7). The method according to any one of claims 1 to 7, wherein the optical fiber (7) is kept from vibrating upstream of the entry-side of the tube end (2). An apparatus for passing an optical fiber (7) through a tube (1), which comprises: a cylindrical body (27, 64, 79) around which the tube (1) is coiled; an optical fiber supply (34) from which an optical fiber (7) is to be provided as it is passed into the tube; and, means (14, 21, 22) for vibrating the cylindrical body (27, 64, 79) in such a manner that the optical fiber initially inserted over a given length into one end (2) of the coiled tube (5) moves forward, under the influence of the intermittent conveying force exerted by the inner wall of the vibrating tube, in the direction of the circumference of the coil of tube, characterized in that the vibrating means (14, 21, 22) are arranged so as to vibrate the cylindrical body (27, 64, 79) in such a manner that a given point of the coiled tube (5) reciprocates along a helical path (H), and, the apparatus further comprises means (38) for actively providing the optical fiber (7) from said optical fiber supply (34) as it advances into the tube, said active providing means being arranged so as to actively provide the optical fiber at substantially the same speed as the advancing speed of the optical fiber through the tube. The apparatus according to claim 9, in which a helical groove (30a, 30b) to admit the tube (1) is cut in the circumference of the cylindrical body (27, 64). The apparatus according to claim 9 or 10, in which a plurality of circular and parallel grooves (30a, 30b) to admit the tube (1) are cut in the circumference of the cylindrical body (27, 64). The apparatus according to claim 9, 10 or 11, in which a belt (71, 84) comprising an elastic member is provided to tighten the tube (1) coiled around the cylindrical body (27, 64, 79) aginst the circumference thereof. The apparatus according to any one of claims 9 to 11, in which an adhesive tape (88) is provided to tighten the tube (1) coiled around the cylindrical body (27, 64, 79) against the circumference thereof. The apparatus according to any one of claims 9 to 13, in which a tubular anti-vibrating guide (54) is provided next to the inlet end of the tube (1) into which the optical fiber (7) is inserted and along the inserting direction of the optical fiber (7), both ends of the tubular anti-vibrating guide (54) being expanded outward to form tapered portions (57). The apparatus according to any one of claims 9 to 13, in which a tubular anti-vibrating guide (90) is provided next to the inlet end of the tube (1) into which the optical fiber (7) is inserted and along the inserting direction of the optical fiber, both ends (92) of the tubular anti-vibrating guide (90) being outwardly expanded and rounded off. The apparatus according to any one of claims 9 to 15, in which means (47) to sense the difference between the passing speed and supplying speed of the optical fiber (7) and means (52) to control the supplying speed of the optical fiber (7) supplying means on the basis of the speed difference sensed by said sensing means (47). The apparatus according to any one of claims 9 to 16, in which the inlet end (61, 94) of the tube (1) to admit the optical fiber (7) is flared toward the upstream side like a funnel. An apparatus for passing an optical fiber (7) through a tube according to any one of claims 9 to 17, in which: said means (14, 21, 22) to vibrate the cylindrical body comprises a base (11), a vibrating table (14) mounted on the basis (11) through springs (18) interposed therebetween, and vibrating means (21, 22) attached to the vibrating table (14) and adapted to vibrate the vibrating table (14) in such a manner that a given point of the vibrating table (14) reciprocates along a helix (H) having a vertical central axis (C); said cylindrical body comprises a bobbin (27, 64, 79) fastened on the vibrating table (14) in such a manner that the axis of the bobbin coincides with the central axis (C) of said helix (H); said optical fiber supply is a spool (34) carrying an optical fiber coil; and said means (38) for actively supplying the optical fiber (7) from said optical fiber spool (34) comprises driving means (38) to rotate the spool (34) in such a manner that the optical fiber (7) wound therearound is directed into one end of the tube (1) coiled around the bobbin (27, 64, 79), a sensor (49) to detect the difference between the passing speed and the unwinding speed of the optical fiber (7), and means (52) to control the spool driving means (38) on the basis of the speed difference detected by the sensor (49). The apparatus according to claim 18, in which the vibrating means (21, 22) comprises a motor having eccentric weights (24) on the rotating shaft thereof. The apparatus according to any one of claims 16 to 19, in which the sensor (49) is an image sensor disposed between the inlet end (2) of the tube (1) and the optical fiber supply (34) to sense the top and bottom positions of the optical fiber (7), thereby determining the amount of sagging of the optical fiber (7). The apparatus according to any one of claims 9 to 20, characterized by means (54) for keeping the optical fiber (7) from vibrating upstream of the entry-side tube end (2).

Inventors: FUKUSHIMA, SHINICHI NIPPON STEEL WELDING PRODUCTS, HAGA, HIROYO, KASHIWAYA, KUNIO NIPPON STEEL CORPORATION, OZOE, KUNIYUKI NIPPON STEEL WELDING PRODUCTS AND, SAEKI, NOBUO NIPPON STEEL WELDING PRODUCTS AND, TABATA, KAZUFUMI NIPPON STEEL WELDING PRODUCTS, YABUKI, YOUICHI NIPPON STEEL WELDING PRODUCTS AND
Applicants: NIPPON STEEL CORPORATION, NIPPON STEEL WELDING PRODUCTS & ENGINEERING CO., LTD.
Application year: 1987
Main classification: G02B6
IPC codes: G02B6