A method and device for stripping optical fibre ribbons

Abstract: For removing coating material from an end (5) of a fibre ribbon (1) over a length L, while using a chemical softening agent, the end is received and clamped between clamping parts (9, 35) of a holder. The clamping parts form a casing wall of a space in which the fibre ribbon with the end extends inwardly over said length L. The softening agent is supplied into said space via the supply opening (47), and brought into contact with coating material of the end, preferably via a layer of material (49) soakable for the softening agent. Adjacent to the point where the end extends inwardly through the wall formed by the clamping parts, scoring knives (33, 43) are mounted for scoring the coating material, and one of the clamping parts is provided with an exhaust opening (51) for exhausting surplus softening agent. After softening the fibre ribbon (1) is withdrawn, with the end clamped, from holder (9).

Description: A. Background of the invention 1. Field of the invention The invention is in the field of optical fibre ribbon technology. More particularly, it refers to a method and device for removing coating material from a fibre ribbon end. 2. Prior art Optical fibre cables are more and more constructed as fibre ribbon cables, in which the often large numbers of fibres are no longer incorporated separately, but for example parallelly arranged with eight or sixteen fibres in ribbon-shaped structures of coating material, the so-called fibre ribbons. The fibre connecting techniques are also attuned to this by no longer carrying out connecting processes such as the fusion-weld process fibrewise, but per fibre ribbon. For this purpose, the coating material has to be removed from the fibre ribbon ends. The removal of the coating material from an end of a fibre ribbon will hereinafter also be referred to as stripping a fibre ribbon end. Reference [1] discloses a method and device for removing coating layers, i.e. the coating of the ribbon and the coating of the fibres in the ribbon, from a fibre ribbon end. In that connection a fibre ribbon end, of which the coating layers have to be removed, is clamped into two holders coupled by means of guiding bars. The holders can be mutually displaced longitudinally of the ribbon via the guiding bars. Between the holders, one of the holders is provided with knife blades. Said knife blades are arranged and adjusted such that, when clamping, the coating layers of a ribbon are scored over the entire width on the upper and under side to (nearly, but not entirely) the (cladding of the) fibres. By then mutually pushing the holders away, from the score, the fibres of the ribbon end are pulled out of the clamped coating layers. Said known stripping technique only works well, when especially the fibre coating is fairly loose or at least only slightly adhered around the fibres. If this is not the case, large forces are necessary to pull the fibres out of the fibre coating, causing an enhanced change of fibre rupture. As a consequence of upsetting the coating material, the fibre ends can moreover spread in a manner such that welding operations in the ribbon weld apparatus are impeded. An improvement of said stripping technique is disclosed in reference [2]. Here the holder, into which the part of the ribbon end to be stripped is clamped, is provided with a heating element. With this the coating layers to be removed are first heated for a certain period of time, as a result of which the coating material softens, before the holders are mutually moved away. Both the softening temperature of especially the fibre coating material and the duration of the heating can be critical under certain circumstances and be fairly divergent for different coating materials. The heating element in such cases requires a very accurate setting of the temperature and of the heating time. Another problem occurs when fibre connections have to be produced between fibres of two conventional fibre cables or of a conventional fibre cable and a ribbon fibre cable. As welding ribbon-wise can be carried out more speedily, it can be preferable to first form the loose fibres of each conventional cable into fibre ribbons, then to remove the coating thereof, and only then to carry out the welding. A known phenomenon of fibre cables several years old is that the coating material can show ageing phenomena. These can reveal themselves in a hardening of the coating material, which hinders a thermal softening, and sometimes in a larger adhering of the coating material to the actual fibre. In either case, the ribbon-wise stripping with the prior-art techniques is consequently impeded. As with mechanically stripping, whether or not preceded by thermal softening, in some places often rests of coating material remain it is the custom to clean the stripped end in a cleaning agent. For this purpose, usually volatile liquids of hydrocarbon compounds as acetone and dichloromethane are used. As is disclosed, in for example reference [3], such liquids soften the coating material and reduce the degree of adherence to the cladding material of the fibre. Therefore, they can also be used with chemically stripping single fibres. Thus, references [4] and [5] for example disclose stripping tools with which a single fibre to be stripped has to be inserted, through an opening in a membrane or between two jawlike elements, into a reservoir containing such a coating material softening liquid, and has to be retracted after softening. In this connection, the softened and normally also swollen coating material is retained by the membrane or jawlike elements respectively. These known stripping tools for chemically stripping a single fibre are not, or at least not immediately suitable for stripping fibre ribbons. Furthermore, the coating material removed remains in the reservoir of the softening liquid, and can only be removed therefrom with the liquid. Consequently, contamination of the softening liquid can occur and the reservoir can become blocked with rests of coating material. An advantage of stripping chemically with a softening liquid consists in that without much effort the coating material can often be pushed off the fibre as a loose sleeve. B. Summary of the invention The object of the invention is to provide a method and a device for removing coating material from a fibre ribbon end while using a chemical softening agent, and with which the above-mentioned problems do not occur. The claimed method of removing coating material from a fibre ribbon end over a predetermined length, comprising the steps as defined in claim 1. In order to prevent the softening agent from also attacking the coating material beyond the scoring point, in a preferred embodiment of the invention the method comprises a step of exhausting surplus swelling liquid adjacent to the point where the fibre ribbon is scored. In a further preferred embodiment of the invention the softening agent is a liquid which is at least partly brought into contact with the coating material of the fibre ribbon end via a layer of material soakable for the liquid. In another preferred embodiment the softening agent is a liquid which is at least partly brought into contact with the coating material of the fibre ribbon end by capillary attraction between surfaces of the clamping parts of the second holder and the surface of the fibre ribbon end which is clamped between the clamping parts. A device for removing coating material from a fibre ribbon end and in accordance to the invention comprises: a first holder for receiving and clamping a substantially flat fibre ribbon end over a predetermined length of the fibre ribbon, scoring means mounted on the first holder for scoring the coating material on the flat upper and under side of a clamped fibre ribbon at a point corresponding to said length, wherein the first holder includes a recessed space and supply openings arranged to supply and bring into contact the coating material of the fibre ribbon end with a chemical softening agent, when the fibre is clamped. In a preferred embodiment the device of the invention is provided with exhaust means for exhausting surplus softening agent. Further preferred embodiments of the invention are summarised in further method and device claims. Further, a device for softening coating material of a fibre ribbon end is claimed in claim 12. C. References [1] Patents Abstracts of Japan, vol. 13, no. 263, 19-06-89; & JP-A-1057204 (Mitsubishi Cable Ind Ltd) 03-03-89; [2] Patents Abstracts of Japan, vol. 13, no. 406, 89-09-08; & JP-A-1147503 (Sumitomo Electric Ind. Ltd. & NTT) 09-06-89; [3] O.S. Gebizlioglu and I.M. Plitz: "Self-stripping of optical fiber coatings in hydrocarbon liquids and cable filling compounds", Optical Engineering, June 1991, Vol. 30, No. 6, p. 749-762; [4] EP-A-0190519; [5] FR-A-2551557; [6] Specification of Ribbon fiber fusion splicer FSM-20RS, Fujikura Ltd.. Tokyo, Japan, Accessory Map ('Fiber holder for ribbon fiber or for arranged fiber'). D. Short description of the drawing Hereinafter the invention will be more fully described with the help of the description of an exemplary embodiment with reference to a drawing which consists of the following figures: FIG.1 shows a fibre ribbon received and clamped into a known fibre ribbon holder; FIG.2 shows a device for removing coating material from a fibre ribbon end of the invention; FIG.3 shows in detail part of the device of FIG. 2 in a view direction indicated by arrow III; FIG.4 shows a cross section of the device of FIG. 2 in accordance with the line IV - IV; FIG.5 shows the device of FIG. 2, in which the device receives the fibre ribbon holder of FIG. 1 with a clamped fibre ribbon, in a first stage of the method in accordance with the invention; FIG.6 shows the device of FIG. 2, in which the device receives the fibre ribbon holder of FIG. 1 with a clamped fibre ribbon, in a second stage of the method in accordance with the invention; E. Description of an exemplary embodiment For preparing welding operations or other operations on a fibre ribbon it is customary, as is shown in FIG. 1, to receive a respective fibre ribbon 1 and to clamp it into a fibre ribbon holder 3. Such a fibre ribbon holder 3 is known per se, for example through reference [6], and will not be discussed here in further detail. To remove the coating material from an end 5 of the fibre ribbon over a length L, the fibre ribbon 1 is received into the fibre ribbon holder 3 in such manner that the end 5 extends out of the fibre ribbon holder 3 over (slightly more than) said length L. FIG. 2 shows a device for removing coating material from a fibre ribbon end in accordance with the invention. Said device substantially consists of two parts, viz. a receptacle block 7 and a stripper block 9, mutually coupled by a sliding bar system 11. Through the sliding bar system, the receptacle block 7 and the stripper block 9 can be mutually displaced in accordance with a fixed translation direction X over a distance being at least equivalent to the length L from a position in which the receptacle block 7 and the stripper block 9 abut each other. The receptacle block 7 has a receptacle space 13 for receiving a fibre ribbon holder 3 (see FIG. 1) up to and against a stop 15, with a fibre ribbon received in the fibre ribbon holder and running parallel to the translation direction X. At an upper side 17, the stripper block 9 is provided with a groove-like recess 19 for receiving the end 5 of the fibre ribbon 1. The groove-like recess 19, for shortness hereinafter called groove 19, runs from an edge 21 where the upper surface 17 of the stripper block 9 abuts to the receptacle space 13 of the receptacle block 7, and in line with the receptacle space. The groove 19 consists of four parts, partly shown in a detail enlargement A. These parts are, successively seen from the edge 21, a first threshold element 23 formed by the upper side of a first knife block 25 mounted into the stripper block, a first recessed part, hereinafter called exhaust trough 27, a second threshold element 29, and a second recessed part, hereinafter called soaking through 31. At the position of the first and second threshold elements, the groove 19 is of identical depth. In the first knife block 25 a first scoring knife 33 is received, extending somewhat above the plane of the first threshold element 23. The groove 19 is longer than the length L of end 5. A pushing plate 35 is mounted with hinged means, such as for example a ball hinge assembly (not shown), in the stripper block 9 to an end 37, furthermost from the edge 21, of the upper surface 17 in line with the groove 19. On the free end 39 of the pushing plate 35 a second knife block 41 is mounted, which receives a second scoring knife 43 (see FIG. 3). The pushing plate 35 is pivotable around an axis perpendicular to the longitudinal direction of the groove 19 between two extreme positions. The pushing plate 35 is dimensioned in such a manner that in one extreme position of the pushing plate 35, hereinafter called the closed position, it can abut on the upper surface 17, with the groove 19 being covered over its entire length up to edge 21 and the second scoring knife being located exactly over the first scoring knife 33. In the other extreme position of the pushing plate 35, hereinafter called the opened position, the groove 19 is uncovered. The pushing plate 35 receives a window 45 of transparent material, such as quartz, which window 45 is provided with a supply opening 47. These features are implemented in such manner that, with the pushing plate 35 abutting on the upper surface 17 of the stripper block 9, a large part of the soaking trough 31 is visible and the supply opening 47 is located over the soaking trough 31. Adjacent to the free end 39 between the second knife block 41 and the window 45 a thumb grip 48 is mounted, with which the pushing plate 35 can be pushed against the surface 17 of the stripper block 9 or can be lifted. The depth of the threshold elements 23 and 29 is such that, on pushing the pushing plate 35 in its closed position, a fibre ribbon end positioned in the groove 19 is clamped between the threshold elements, and a corresponding surface part 50 of the pushing plate 35 between the second scoring knife 43 and the window 45; see FIG. 3 for more details. In this connection the scoring knifes 33 and 43 in their knife blocks 25 and 41 respectively are adjusted in such manner that, on the upper and under side, only the coating material of the fibre ribbon end is scored and the cladding material is not contacted. The soaking trough 31 and the exhaust trough 27 are provided with a layer of feltlike material 49 with a thickness such that the upper surface of the layer approximately is on the same level as the upper surfaces of both threshold elements 23 and 29, but preferably extends somewhat above it so that the feltlike material is somewhat squeezed by a clamped end. In FIG. 4 a cross-section is shown of the stripper block 9 in accordance with a plane (see line IV - IV in FIG. 2) through the exhaust trough 27 perpendicular to the longitudinal direction of the groove 19. The exhaust trough 27 is provided with an exhaust opening 51 to an exhaust channel 53 which debouches into a feed-through channel 55 running transversely through the stripper block 9. At one end, the feed-through channel 55 is provided with a connect nipple 57 for connecting a vacuum pump (not shown), whereas the other end is airtightly sealed with a sealing screw 59. As coating materials for individual optical fibres or for fibre ribbons thermally hardening silicones, and acrylates and silicones hardening under UV light are known (see for example reference [3]). Suitable softening agents are liquid, preferably somewhat volatile hydrocarbon compounds. Especially for the said acrylates dichloromethane alone, or a half-and-half mixture of dichloromethane and methanol, appear to be very suitable, with a softening period of approx. 30 to 60 seconds. Hereinafter the application of the device will be described with such a volatile hydrocarbon compound being used as a softening agent. A fibre ribbon holder 3 which receives a fibre ribbon 1, such as shown in FIG.1, is placed into the receptacle block 7 of the device in a position, in which the receptacle block 7 abuts against the stripper block 9, and in opened position of the pushing plate 35, the end 5 of the fibre ribbon to be stripped is positioned into the groove 19 [sic]. Subsequently the pushing plate 35 is brought into the closed position with the help of the thumb grip 48. This stage is shown in FIG. 5. Then, with the help of a pipette or dispenser a measured quantity of the softening liquid is supplied via the supply opening 47 to the feltlike material layer 49 in the soaking trough 31. The measured quantity is such that the liquid spreads out over the entire length of the soaking trough 31 via the layer of feltlike material and moistens the under side of the clamped end, which starts the softening process of the coating material of the clamped fibre ribbon end. Since the liquid is furthermore volatile it easily evaporates out of the feltlike material, so that the remaining space between the window 45 received in the pushing plate 35 and the end 5 of the fibre ribbon 1 which is situated in the groove 19 is filled with a more or less saturated vapour of softening agent, as a result of which the softening process can also take place from the upper side of the end. As during the softening process the coating material also swells, the progress of the process is visible through the window 45 in the pushing plate 35. Meanwhile an exhaust pump (not shown) connected to the connect nipple 57 is put into action, as a result of which the softening agent, permeating from the soaked felt material 49 in the soaking trough 31 in liquid and/or vapour form into the exhaust trough 27 is exhausted out of the device through the exhaust opening 51 in the exhaust through 27 and via the exhaust channel 53 and the feed-through channel 55, preferably to a place where it does not constitute danger to operating personnel. Hereby it is prevented that, for example through capillary attraction, the softening agent creeps further between the surface of the threshold elements and the possibly longitudinal ridged surface of the fibre ribbon end, and reaches and attacks the coating material of the fibre ribbon also beyond the point where the scoring knifes score the coating material. When the softening process is completed, the clamping plate 35 is pushed in by the thumb grip 48, and subsequently the receptacle block 7 together with the stripper block 9 and the fibre ribbon holder 3 incorporated therein are mutually pulled away over at least a distance L. With this, the fibres in the fibre ribbon end 5 are released from the scoring point out of the coating material which remains clamped in the stripper block 9 as a loose sleeve. This stage is shown in FIG. 6. Subsequently, the fibre ribbon holder is taken out of the receptacle block 9 and the fibre ribbon 1 with the stripped end is available for further processing. During the mutually pulling away of the receptacle block and stripper block, the exhaust pump preferably remains operative to exhaust the last remains of softening agent. After opening the clamping plate 35, the remaining coating material is removed from the stripper block 9 and the device is available for stripping a further fibre ribbon. In the figures FIG. 2, 5 and 6, the window 45 is shown as being mounted into the clamping part 35 in such manner that the window with a surface forms a continuation of the surface part 50. With such a mounting, for promoting a capillary contact attraction of the softening liquid with the surface of a clamped fibre ribbon end, said window surface can be provided with a surface structure, such as a wafer structure or a ridge structure transversely of the longitudinal direction of the soaking trough 31. At the under side, the capillary contact attraction can also be used by providing the bottom of the soaking trough with such a surface structure in replacement of the layer of feltlike material. However, only using capillary contact attraction makes the softening process somewhat slower. Another possibility is to mount the window 45 recessedly into the clamping part 35, so that over the part of a clamped fibre ribbon end 1 situated under the window a free space is formed, which can be filled during the softening process with saturated vapour of softening liquid evaporating out of the feltlike material. In a surroundings where an exhaust pump is not available, but compressed air is, said device can also be used. To this end the sealing screw 59 is replaced by a second supply nipple (not shown), to which the compressed air is connected. In the exhaust channel 53, underpressure arises by guiding compressed air through the feed-through channel 55. A softening device consisting of a device described with reference to the figures FIG. 2 to FIG. 4 inclusive and from which the scoring means, viz. the knife blocks 41 and 25, are omitted can be used in combination with the stripping device of reference [1]. In this connection, the softening process occurs in the one device and, after transferring the fibre ribbon, the actual stripping occurs in the other device.

Claims: A method for removing coating material from a fibre ribbon end (5) over a predetermined length, comprising the steps of: receiving and clamping said fibre ribbon end into a holder (3), scoring the coating material on the upper and under side of the fibre ribbon at a point corresponding to said length, softening coating material of said fibre ribbon end over said length by means of a chemical softening agent, withdrawing the fibre ribbon out of the holder, with the fibre ribbon end clamped, while softened coating material of the end remains in the holder, characterised in that the end is received and clamped into a recessed space between two clamping parts (9, 35) forming part of the holder (3) which together form a casing wall around the received end, and that the softening agent is supplied into the recessed space (31), with the end received and clamped, through a supply opening (47) in the casing wall and is brought into contact with the coating material of the fibre ribbon end. A method in accordance with claim 1, characterised in that surplus softening agent is exhausted adjacent to the point where the fibre ribbon is scored. A method in accordance with claim 2, characterised in that the softening agent is a liquid, and that the liquid is at least partly brought into contact with the coating material of the fibre ribbon end by capillary attraction between surfaces of the clamping parts of the second holder and the surface of the fibre ribbon end which is clamped between the clamping parts. A method in accordance with claim 2, characterised in that the softening agent is a liquid which is at least partly brought into contact with the coating material of the fibre ribbon end via a layer of material soakable for the liquid. A method in accordance with any of the claims 3 or 4, characterised in that the coating material of the fibre ribbon is a UV hardening acrylate, and that the liquid is dichloromethane. A method in accordance with any of the claims 3 or 4, characterised in that the coating material of the fibre ribbon is a UV hardening acrylate, and that the liquid is a mixture of dichloromethane and methanol. A device for removing coating material from a fibre ribbon end comprising a first holder (9, 35) for receiving and clamping a substantially flat fibre ribbon end over a predetermined length of the fibre ribbon, scoring means (33, 41) mounted on the first holder for scoring the coating material on the flat upper and under side of a clamped fibre ribbon at a point corresponding to said length, characterised in that the first holder (9, 35) includes a recessed space (31) and an supply opening (47) arranged to supply to the recessed space (31) and bring into contact the coating material of the fibre ribbon end with a chemical softening agent when the fibre ribbon is clamped. Device in accordance with claim 7, characterised in that on the first holder one of the clamping parts adjacent to the point where the scoring means are mounted is provided with an exhaust opening (27) for exhausting softening agent. A device in accordance with claim 8, characterised in that the first holder comprises first and second clamping parts (9, 35), which in tightly-clamped position each form a wall part of a casing wall of the recessed space (31) for the fibre ribbon end, that one of the wall parts is provided with the supply opening (47) for supplying a liquid softening agent to said recessed space (31), and that at least part of one of the wall parts is provided with a layer of material (49) soakable for the liquid softening agent, said layer abutting, with the fibre ribbon end clamped, said clamped end. Device in accordance with claim 8, characterised in that the first holder comprises first and second clamping parts (9, 35), which in tightly-clamped position each form a wall part of a wall casing of the recessed space for the fibre ribbon end, that one of the wall parts is provided with the supply opening (47) for supplying a liquid softening agent, and that at least part of one of the wall parts is provided with a surface structure for promoting a capillary contact attraction with the liquid softening agent, said part with said surface structure abutting, with the fibre ribbon end clamped, against said clamped end. Device in accordance with any of the claims 7, 8, 9 or 10 characterised in that the device furthermore comprises a second holder (7) arranged to receive and clamping part of a fibre ribbon, which second holder is connected to the first holder by means of guiding means (11), via said guiding means, the two holders being mutually displaceable longitudinally of a fibre ribbon to be clamped over at least a distance corresponding to said length. A device for softening coating material of a fibre ribbon end, comprising a first holder for receiving and clamping a substantially flat fibre ribbon end over a predetermined length of the fibre ribbon, characterised in that the first holder (9, 35) includes a recessed space (31) and an supply opening (47) arranged to supply to the recessed space (31) and bring into contact the coating material of the fibre ribbon end with a chemical softening agent when the fibre ribbon is clamped. A device in accordance with claim 12, characterised in that one of the clamping parts adjacent to said wall opening is provided with an exhaust opening (27) for exhausting softening agent. Device in accordance with claim 13, characterised in that the first holder comprises first and second clamping means (9, 35), which in tightly-clamped position each form a wall part of a casing wall of the recessed space (31) for the fibre ribbon end, said casing wall comprising a wall opening through which a fibre ribbon part following an received fibre ribbon end extends outwardly through a casing wall, that one of the wall parts is provided with the supply opening (47) arranged to supply a liquid softening agent to said recessed space, and that at least part of one of the wall parts is provided with a layer of material soakable for the liquid softening agent, said layer abutting, with the fibre ribbon end clamped, against said clamped end. A device in accordance with claim 13, characterised in that the first holder comprises first and second clamping parts (9, 35) which in tightly-clamped position each form a wall part of a casing wall of the recessed space for the fibre ribbon end, said casing wall comprising a wall opening through which a fibre ribbon part following an received fibre ribbon end extends outwardly through the casing wall, that one of the wall parts is provided with the supply opening (47) arranged to supply a liquid softening agent, and that at least part of one of the wall parts is provided with a surface structure for promoting a capillary contact attraction with the liquid softening agent, said part with said surface structure abutting, with the fibre ribbon end clamped, against said end. A device in accordance with any of the claims 12, 13, 14 or 15, characterised in that the device furthermore comprises a second holder (7) arranged to receive and clamping part of a fibre ribbon, said second holder being connected to the first holder by means of guiding means (11), via said guiding means, the two holders being mutually displaceable longitudinally of a fibre ribbon to be clamped over at least a distance corresponding to said length.

Inventors: JACOBS JOHAN FREDERIK, JACOBS, JOHAN FREDERIK
Applicants: KONINKL KPN NV, KONINKLIJKE KPN N.V.
Application year: 1995
Main classification: G02B6
IPC codes: G02B6