WO2001048523A1

WO2001048523A1 - Apparatus, tool and method for removing a coating layer from a portion of optical fibre

Info

Publication number: WO2001048523A1
Application number: PCT/EP2000/012920
Authority: WO
Inventors: Marco Marazzi; Danilo Scarano; Benjamino Mariani
Original assignee: Optical Technologies Italia S.P.A.
Priority date: 1999-12-27
Filing date: 2000-12-18
Publication date: 2001-07-05
Also published as: AU3014201A; WO2001048523A9

Abstract

An apparatus (1) for removing a coating layer from a portion (100) of optical fibre, comprises a support frame (2); a tool (200) for removing a coating layer from a portion (100) of optical fibre; a pair of fibre positioning devices (6a, 6b) mounted on the support frame (2) from opposing sides with respect to the tool (200), and adapted to house opposing end parts of said portion (100) of optical fibre so as to hold the latter in a substantially stretched position along a fibre-alignment axis X-X. The apparatus (1) further comprises a moving device (20) to automatically impart a controlled relative motion (for example, a motion with a constant speed) between said portion (100) of fibre and the tool (200) along the fibre-alignment axis X-X. The tool (200) comprises a pair of cutting blades (203, 204) operating on a plane YZ perpendicular to the fibre-alignment axis X-X and positionable with a controlled motion with respect to said axis to cut into said coating layer of said portion (100) of optical fibre. This apparatus (1) allows the removal of the acrylate layer from portions of fibre having even relevant lengths without imparting undesidered mechanical stresses; this guarantees a high mechanical reliability of the fibre itself during operation.

Description

Apparatus , tool and method or removing a coating layer from a portion of optical fibre

DESCRIPTION

The present invention relates to an apparatus, a tool and a method for removing a coating layer from a portion of optical fibre. In particular, the invention relates to an apparatus, a tool and a method for mechanically removing an acrylate coating layer from a portion of optical fibre so as to allow splicing, manufacturing of fused-fibre couplers, and writing of Bragg gratings.

As known, optical fibres are largely used in the field of telecommunications for transmitting signals. They essentially comprise an inner cylindrical region, called core, in which the signal is transmitted, and an outer annular region, called cladding, having a lower index of refraction with respect to that of the inner region so as to confine the transmitted signal within the latter. Both the above-mentioned regions are made of a glass material.

Due to the very small dimensions (typically, 125 μm) and to the fragile material (glass) of which they are made, optical fibres are intrinsically subject to breaking. For the purpose of ensuring a high mechanical reliability in operation, during the spinning process the fibres are coated with a soft material (typically, acrylate) consisting basically of polymers, which has the function of protecting the fibre during handling and from atmospheric agents .

In special uses with optical fibre, such as for example for splicing, manufacturing of fused-fibre couplers, or writing of Bragg grating, the acrylate coating must be removed from the fibre so as to uncover the glassy region.

In this description and following claims, the term "Bragg grating on optical fibre" refers to the presence of a portion of optical fibre wherein the core and/or the cladding has an index of refraction which is permanently modulated along the axis of propagation of the optical fibre .

Different methods for removing the acrylate coating from an optical fibre are known; they can be essentially classified into two categories: methods by chemical removal and methods by mechanical removal.

The methods by chemical removal (see, for example, the doctorate thesis no. 1828 of 1998 by Dimitrios Varelas, Ecole Polytechnigue Federale de Lausanne) usually provide for the dipping of a portion of fibre into a hot bath of sulphuric acid at about 150° for few minutes; afterwards, the fibre is rinsed into a water bath and then dried through a hot-air jet.

A method of the type described above, besides being particularly disadvantageous as regards to costs and safety (in fact, to the purpose of carrying it out in a production process, it is necessary to provide for suitable acid baths, and hoods for the removal of harmful vapours, besides having operators trained in the use of acids), presents the disadvantage that the sulphuric acid can go up the fibre for capillarity, thus swelling and possibly tearing the acrylate coating; this could imply long-term problems of reliability of the fibre due to the penetration of water in the form of humidity.

Generally, the methods by mechanical removal are simpler, cheaper and more reliable than the methods by chemical removal and they do not require either the use of trained operators, or the use of specific system components (acid baths, hoods, etc.). On the contrary, they provide for the use of mechanical tools or devices that are manually operated by the operator to remove the acrylate layer from the optical fibre.

Tools and/or devices for mechanically removing an acrylate coating layer from an optical fibre have already been proposed in the past.

US 5,298,105 describes a tool for removing the acrylate coating from an optical fibre, comprising a hollow cylindrical body adapted to house a portion of the optical fibre. The cylindrical body presents an inlet passage for a stripping fluid adapted to soften and expand the acrylate coating of the fibre. In addition, at one of its ends, the cylindrical body is provided with an annular shoulder surface having inner diameter only marginally greater than the outer diameter of the coated fibre; said inner diameter is in any case smaller than the outer diameter of the fibre when the coating layer of the latter has been softened and expanded by the injected fluid. The acrylate coating is removed by manually pulling the fibre through the shoulder surface after the coating has been softened under the action of the fluid. Said tool is adapted for removing the acrylate coating from an end portion of the fibre for splicing; it is not adapted for Bragg grating, that is to say, when the acrylate coating must be removed from an intermediate fibre portion.

US 5,896,787 describes a device for removing the acrylate coating from an optical fibre, comprising a hollow cylindrical body, a holding member provided with jaws adapted to grip the fibre, and a cylindrical container for injecting a fluid for softening the plastic coating of the fibre. The hollow cylindrical body has an inner surface having a threaded cylindrical portion and a truncated-cone end portion. The jaws of the holding member have an outer surface adapted to abut against the truncated-cone portion of the inner surface of the cylindrical body. The cylindrical container is provided with a threaded outer portion adapted to co-operate with the inner threading of the cylindrical body, and with an end surface adapted to co-operate surface-to-surface with a corresponding end surface of the holding member. Once the coating has been softened by injection of the fluid, the container is screwed into the cylindrical body; in this way, the holding member is pushed against the truncated-cone portion of the inner surface of the cylindrical body, thus causing the closing of the jaws onto the fibre itself. The plastic coating is removed by manually moving the device along the axial direction of the fibre. Said device is adapted for removing the acrylate coating from an end portion of the fibre having reduced length (few cm) for splicing; it is not suitable either for removing acrylate from an intermediate fibre portion (for Bragg grating) or for removing acrylate from a longer end portion of the fibre, due to the lack of a discharge path for the removed acrylate .

US 5,819,602 describes an apparatus for stripping a thin colour-encoded plastic coating from an optical fibre, comprising a support base onto which clamps are positioned for fixedly holding a fibre portion spaced above and parallel to the support base. A chuck provided with radially convergent jaws is mounted on the support base and is capable of sliding thereon along a longitudinal direction. The apparatus comprises a lifting mechanism for lifting the chuck towards the fibre in order to house the fibre within the chuck and coaxial therewith. The coating layer is removed by closing the jaws of the chuck onto the fibre, and manually and repeatedly sliding the chuck back and forth along the axial direction of the fibre. Said apparatus is adapted for removing the acrylate coating from a fibre portion having reduced length (few cm); it is not adapted for removing acrylate from a longer fibre portion due to the lack of a discharge path for the removed acrylate .

US 4,969,703 describes an apparatus for positioning an optical fibre into a device for removing the coating from an end portion of said optical fibre. The device for removing the coating is of the collet type with notched cutting blades to cut into the coating layer to be removed, and it comprises, at one end, an annular cylindrical protuberance in axial alignment with the notches of the cutting blades. Said stripping device is intended to be slidably associated to the positioning apparatus of the optical fibre so as to obtain an axial alignment between the optical fibre and the cutting blades of the device itself. The apparatus comprises a block in which is defined a first through bore extending longitudinally and having a width approximately equal to, or slightly lower than, the diameter of the coated fibre, so as to exert a clamping force on a fibre portion housed into said bore, keeping said fibre portion aligned with the longitudinal axis of the bore; at one end of the block a second bore is defined, coaxial to the first one, and dimensioned so as to precisely receive the cylindrical protuberance of the device for removing the fibre coating, thus obtaining the axial alignment between the blades of the stripping device and the fibre axis. The coating is removed by first positioning the fibre into the first bore of the block and inserting an end portion of the fibre into the cylindrical protuberance of the stripping device; the latter is moved so that the protuberance is housed into the second bore of the block. At this point, a pressure is exerted on the handles of the stripping device so that the blades cut into the fibre coating; said coating is then manually removed after having removed the device. The Applicant has noted that said apparatus is adapted to remove the acrylate coating from an end portion of the fibre having reduced length (few cm) for splicing; it is not suitable for removing acrylate from a longer fibre portion, due to the difficulty of maintaining the alignment of said fibre portion during the manual removal of the coating, nor it is suitable for removing acrylate from an intermediate fibre portion (for Bragg gratings), due to the particular procedure of manual removal and to the need of axially inserting an end of the fibre into the protuberance of the removing device before the coating removal occurs .

Additionally, collet-type tools are known (for example, the tools called "stripper Millers") provided with a pair of cutting blades adapted to cut into the acrylate coating layer of the fibre. The procedure for removing the acrylate is of the manual-type, and consists in positioning a portion of the fibre between the blades of the tool, clamping the tool so as to cut into the acrylate layer and sliding the tool clamped onto the fibre so as to remove the acrylate layer. In order to prevent damage or breaking of the fibre, care must be taken to keep the tool perpendicular to the fibre during the entire operation for removing the acrylate.

The inventors of the present invention have carried out several experimental tests for removing acrylate from optical fibres, using a tool above described type (in particular, a stripper Miller) and each time measuring the values of the ultimate tensile strength of the fibres after having removed the acrylate. They have verified that the results obtained presented strong deviations; in addition, said deviations increased as the fibre length portion from which the acrylate was removed increased. This was essentially due to the difficulty, for the operator who handled the tool, of repeating the operation at the same speed, always exerting the same force and keeping the same relative position between tool and fibre for the entire predetermined fibre length.

In addition, the particularly low values of tensile strength obtained showed that, during the operation of acrylate removal, the fibre was subject to high mechanical stresses, thus reducing its mechanical reliability during operation; this was essentially due to the difficulty of keeping always the same relative position and speed between tool and fibre for the entire predetermined fibre length. Said values, among the other things, were ever decreasing as the fibre length portion from which the acrylate was removed increased.

The applicant has thus posed the problem of realising a suitable apparatus to allow the removal of the acrylate coating from fibre portions having even great lengths to allow splicing, manufacturing of fused-fibre couplers and writing of Bragg grating, carrying out a simple, inexpensive and repeatable method of removal. This for the purpose of guaranteeing predictable and repeatable results, besides high mechanical reliability of the fibres during operation.

The Applicant has found that, by arranging with controlled motion a pair of cutting blades into a cutting position with respect to the acrylate layer, after that the fibre portion to be machined has been stretched between two supports, and carrying out a controlled relative motion between the blades and the fibre (for example, through the movement of a slide on which a tool housing the blades is mounted, or through the rotation of a fibre-winding spool) , it is possible to remove the acrylate for a predetermined length with a particularly high precision and repeatability, in particular preventing the glassy material of the fibre from being cut and hence, avoiding the relevant worsening of the fibre ultimate tensile strength deriving therefrom.

In a first aspect thereof, the present invention thus relates to an apparatus for removing a coating layer from a portion of optical fibre, comprising: a support frame; a tool for removing a coating layer from a portion of optical fibre; a pair of fibre positioning devices mounted on the support frame from opposing sides with respect to the tool, and adapted to house opposing end parts of said portion of optical fibre so as to hold said portion of optical fibre in a substantially stretched position along a fibre- alignment axis X-X; characterised in that it comprises a moving device to automatically impart a controlled relative motion between said portion of fibre and the tool along the fibre- alignment axis X-X, and in that the tool comprises a pair of cutting blades operating on a plane YZ perpendicular to the fibre-alignment axis X-X and positionable with a controlled motion with respect to said axis to cut into said coating layer of said portion of optical fibre.

In the present description and in the following claims, the expression "controlled motion" preferably refers to a motion having constant speed.

Advantageously, in the apparatus of the present invention both the relative motion between fibre and tool and the positioning of the blades of the tool with respect to the fibre for cutting into the acrylate layer occur with a controlled motion; more advantageously, the relative motion between fibre and tool occurs automatically. This ensures a high repeatability of the operations for removing the acrylate (and thus, of the values of ultimate tensile strength of the fibre after having removed the acrylate) , a limitation of the mechanical stresses on the fibre and, as a consequence, a high mechanical reliability of the fibre itself during operation. By the use of the apparatus of the invention, in fact, it is ensured that during the entire operation for removing the acrylate and for the entire length of fibre desired, the position of the tool is always perpendicular to the fibre axis, that the relative motion between tool and fibre always occurs at the same speed and that the cutting action of the blades onto the tool always occurs with the same strength. This advantageously allows removing the acrylate layer for a greater length of fibre with respect to what was possible with the devices and tools of the prior art.

Advantageously, the apparatus of the invention comprises a device for emitting an air or nitrogen jet which is integrally mounted on the tool and adapted to impact with the air jet the fibre so as to remove the acrylate just removed.

The apparatus of the invention allows removing the acrylate from an intermediate portion of the fibre; this is especially advantageous in the applications for Bragg grating, or for manufacturing fused-fibre couplers together with an analogous portion without acrylate of another fibre. Nevertheless, the apparatus can be used also in the applications for splicing: in fact, in this case, after having removed the acrylate, it is sufficient to cut the fibre in correspondence of the portion without acrylate.

Preferably, said moving device comprises a slide which is slidably mounted on the frame and movable in parallel with said fibre-alignment axis X-X with controlled motion, said tool being mounted integral with said slide. More preferably, said slide is driven at constant speed by motor means. The automation of the relative movement between tool and fibre is thus obtained by operating a slide carrying the tool; in this case, the fibre is fixedly positioned on the apparatus and the tool slides along a direction parallel to the fibre axis.

In an alternative embodiment, the moving device comprises a motorised fibre-winding spool, pivotally mounted on the frame and adapted to rotate with a controlled motion around an axis of rotation perpendicular to the fibre-alignment axis X-X, so as to make the fibre sliding with respect to the fibre-alignment axis X-X. Preferably, the apparatus also comprises a fibre-unwinding spool pivotally mounted on the frame from a side opposed to the fibre-winding spool with respect to the tool and adapted to be driven in rotation by the fibre-winding spool. In this case, the tool is fixedly positioned onto the apparatus, and the fibre slides along its axis X-X.

Both the above mentioned embodiments allow obtaining an automatic and controlled motion between tool and fibre in a simple and functional way. Advantageously, with the second of the above mentioned embodiments of the apparatus, it is possible to remove the acrylate from a portion of fibre having an ideally unlimited length.

In the preferred embodiment of the apparatus of the present invention, said pair of fibre-positioning devices comprises respective fibre-clamping elements, each of which including a first body provided with a first seat adapted to house an end part of said portion of optical fibre, and a second body adapted to co-operate with the first body to hold said end part of said portion of optical fibre into position inside the first seat. Preferably said first seat comprises a V-shaped groove; the presence of such V-shaped groove advantageously allows easily and firmly positioning the fibre.

Preferably, said pair of fibre-positioning devices comprises respective devices for adjusting the position of said fibre-clamping elements on the support frame. This facilitates the positioning of the fibre into the desired alignment position.

Preferably, said tool comprises: a first blade fixedly mounted with respect to the plane YZ and provided with a first groove (preferably, a V- groove) adapted to house a part of said fibre portion; - a second blade provided with a second groove (preferably, a V-groove) and mobile onto the plane YZ between a first operating position, wherein said second blade is in distal position with respect to said portion of optical fibre, and a second operating position wherein said second blade houses said part of said portion of optical fibre into the second groove, and co-operates with the first blade to cut into the coating layer of said portion of optical fibre.

Preferably, said first groove is in alignment position along axis X-X with the first seats of said clamping elements. Advantageously, the alignment along the axis X-X between the grooves of the tool and the seats of the fibre- positioning devices ensures the alignment between fibre and blades of the tool once the fibre has been fixed into position on the apparatus of the invention, and guarantees that the blades of the tool always stay in perpendicular position with respect to the fibre axis during the entire operation for removing the acrylate and for the entire length of fibre desired.

According to a first embodiment, said tool comprises a first and a second arm, reciprocally pivoted, and a counter spring between said first arm and said second arm, wherein the first and the second blade are respectively associated to the first and the second arm at respective end portions thereof, and wherein said counter spring is adapted to hold, when at rest, said second blade into said first operating position.

Preferably, said tool is a Stripper Miller. In fact, the inventors of the present invention have tested different commercial tools for removing acrylate from optical fibres, and have noted that the best results in terms of values of measurement of ultimate tensile strength were obtained by using Strippers Miller; at the same time, the use of a Stripper Miller in the apparatus of the invention allows overcoming all of the above-mentioned problems associated to a manual use of the Stripper Miller.

Preferably, the apparatus of the present invention comprises a device operating on said tool to automatically move said second blade from the first to the second operating position. Thus, the blades are positioned with respect to the fibre to cut into the acrylate coating layer in an extremely precise, controlled and repeatable way by means of the above device; in this way, the fibre is not subject to undesired stresses, to the advantage of its mechanical reliability during operation. In a first embodiment of the invention, said device comprises a pneumatic cylinder and a piston active in a thrust configuration on the second arm of the tool. In an alternative embodiment of the invention, the piston is active in a pull configuration on the second arm of the tool. In both cases, the precise positioning of the blades of the tool with respect to the fibre is obtained in a constructively simple and functional way.

Nevertheless, it is possible to use other types of conventional devices to automatically move the tool from the first to the second operating position; for example, it is possible to use mechanical (with worm screw) , magnetic (with solenoid), electromechanical devices, etc.

Moreover, the inventors have designed an alternative embodiment of the tool used on the apparatus of the present invention, capable of guaranteeing a high repeatability of the results.

Thus, in a second embodiment thereof, the tool used on the apparatus of the present invention comprises a first and a second block provided with respective second seats housing the first and the second cutting blades, said blocks being respectively associated to a first and a second tool body, wherein said first and second block and said first and second tool body in turn comprise a plurality of alignment elements adapted to allow the precise positioning of said first and second blade when said second blade is in the second operating condition. Advantageously, the presence of the alignment elements guarantees the correct positioning of the blades with respect to the fibre for cutting into the acrylate layer; more advantageously, should the blades be damaged, it is sufficient to remove the latter from their respective seats and replace them with new blades, without having to remove the entire tool, whose correct positioning would require particular attention.

Preferably, said plurality of alignment elements comprises at least one pair of spheres associated to one between the first and the second block and adapted to be housed into respective third seats formed into the other one between the first and the second block. More preferably, the spheres of said at least one pair of spheres are associated to the first block from opposed sides with respect to the fibre-alignment axis X-X. Thus, the precise alignment of said first and second blade in vertical and horizontal direction is obtained in a constructively simple and functional way.

Preferably, said plurality of alignment elements also comprises at least one pair of rounded longitudinal elements associated to one between the first and the second tool body and adapted to be housed into respective fourth seats formed into the other one between the first and the second tool body. More preferably, the longitudinal elements of said at least one pair of longitudinal elements are associated to the first tool body from opposed sides with respect to the fibre-alignment axis X-X. The presence of the longitudinal elements contributes to obtain a precise alignment.

Preferably, each of said first and second blocks also comprises a cylinder pivotable (preferably, through a ball bearing) around an axis perpendicular to the fibre- alignment axis X-X, said cylinder being provided with a groove, preferably a V-groove, adapted to house a part of said portion of optical fibre, the groove of the cylinder associated to said first block being in a condition of alignment along the axis X-X with said first seats of said clamping elements.

Advantageously, said first and second block comprise respective notches formed downstream of said first and second blade with respect to the sliding direction of the tool, said notches being adapted to operate as collection chamber for the residues of the removed acrylate. This allows reducing the risk that said residues, as they do not have a discharge path, could obstruct the tool blades, thus breaking the fibre.

Preferably, said tool comprises a plunger system active on said second tool body and adapted to move said second blade from the first to the second operating position. More preferably, said plunger system comprises a shock absorbing system active on the second tool body when said second blade is moved to the second operating position. Thus, also in the second embodiment of the tool, the positioning of the blades with respect to the fibre for cutting into the acrylate coating layer is carried out in a precise, controlled and repeatable way, through the above plunger system; thus, the fibre is not subject to undesired stresses, to the advantage of its mechanical reliability during operation.

The apparatus of the present invention can be manufactured in such a way that the fibre-alignment axis X-X is substantially horizontal or vertical. The embodiment with vertical axis X-X is preferable in such cases wherein the length of the acrylate layer to be removed from a portion of fibre is of about 1 m or more. In fact, experimental tests have proved that, for lengths of about 1 m, a fibre arranged horizontally is subject to flexure, with a maximum shift of about 100 μm; since the diameter of the fibre is of about 125 μm, the probability of cutting into the region of glassy material while removing the acrylate is in this case extremely high. Advantageously, said disadvantage can be overcome using an apparatus with vertical fibre- alignment axis X-X.

In a second aspect thereof, the invention relates to a tool for removing a coating layer from a portion of optical fibre, comprising a first and a second cutting blade adapted to operate on a plane YZ perpendicular to a fibre- alignment axis X-X, characterised in that it comprises a plunger system for positioning with controlled motion said first and second blade with respect to said fibre-alignment axis X-X to cut into said coating layer of said portion of fibre.

Preferably, said tool comprises a first block housing the first cutting blade into a respective first seat and a second block housing the second cutting blade into a respective second seat, wherein the first blade is adapted to be fixedly mounted with respect to the plane YZ and is provided with a first groove adapted to house a part of said fibre portion, and wherein the second blade is provided with a second groove and is mobile in the plane YZ between a first operating position, wherein said second blade is in distal position with respect to said portion of optical fibre, and a second operating position, wherein said second blade houses said part of said portion of optical fibre and co-operates with the first blade to cut into the coating layer of said portion of optical fibre, said first and second block being in turn respectively associated to a first and a second tool body and wherein said first and second block and said first and second tool body comprise a plurality of alignment elements adapted to allow the precise alignment of said first and second blade in vertical and horizontal position when said second blade is moved to the second operating condition.

Preferably, said plurality of alignment elements comprise at least one pair of spheres associated to one between the first and the second block and adapted to be housed into respective seats formed into the other one between the first and the second block. More preferably, the spheres of said at least one pair of spheres are associated to the first block from opposed sides with respect to the fibre- alignment axis X-X.

Preferably, said plurality of alignment elements also comprise at least one pair of rounded longitudinal elements associated to one between the first and the second tool body and adapted to be housed into respective seats formed into the other one between the first and the second tool body. More preferably, the longitudinal elements of said at least one pair of longitudinal elements are associated to the first tool body from opposed sides with respect to the fibre-alignment axis X-X.

Preferably, each of said first and second block further comprises a cylinder pivotable around an axis perpendicular to the fibre-alignment axis X-X, said cylinder being provided with a groove, preferably a V-groove, adapted to house a part of said portion of optical fibre, the V-groove of the cylinder associated to said first block being in alignment condition along the axis X-X with the seats of said clamping elements.

Preferably, said tool comprises a plunger system active on said second tool body and adapted to move said second blade between the first and the second operating position. More preferably, said plunger system comprises a shock absorbing system active on the second tool body when said second blade is moved to the second operating position.

In a third aspect thereof, the invention relates to a method for removing a coating layer from a portion of optical fibre, comprising the following steps: - a) arranging, on a plane YZ, a pair of cutting blades of a tool for removing a coating layer from said portion of optical fibre; b) positioning a portion of fibre into a stretched position along a fibre-alignment axis X-X perpendicular to plane YZ; c) positioning, with a controlled motion, said pair of cutting blades with respect to said axis X-X so as to cut into said coating layer of said portion of optical fibre; d) automatically imparting a controlled relative motion between said tool and said portion of fibre along said fibre-alignment axis X-X.

The method of the present invention can be carried out, for example, by the apparatus and the tool of the invention described above (in their various embodiments) ; said method allows to obtain all the advantages mentioned above with reference to said apparatus.

Preferably, the step b) of positioning the portion of fibre into a stretched position along the axis X-X comprises the step of housing a part of said fibre portion into a groove formed on a blade of the tool and opposing end parts of said fibre portion on respective seats formed on positioning devices positioned at opposed sides with respect to the tool and adapted to hold said end parts of said portion of optical fibre into position.

Preferably, the step d) of imparting a controlled relative motion between tool and fibre portion comprises the step of activating motor means active on a slide on which the tool is integrally mounted.

In an alternative embodiment of the method of the present invention, the step d) of imparting a controlled relative motion between tool and fibre portion comprises the step of activating motor means active on a fibre-winding spool.

Preferably, the step c) of positioning with controlled motion the blades of the tool with respect to the axis X-X comprises the step of activating a device adapted to automatically move at least one of said blades from a first operating position, wherein the blades are in a distal position from one another, to a second operating position, wherein the blades cut into said coating layer of said portion of optical fibre.

Further features and advantages of the present invention will appear more clearly from the following detailed description of some preferred embodiments, made with reference to the attached drawings. In such drawings:

Figure 1 is a perspective schematic view of a first preferred embodiment of the apparatus of the present invention;

Figure 2 is a perspective schematic view of an alternative embodiment of a control device of the tool for removing the acrylate used on the apparatus of figure 1;

Figure 3 is a perspective schematic view of a second preferred embodiment of the apparatus of the present invention; - Figure 4 is a perspective schematic view of a tool used on the apparatus of figure 3, in a first operating configuration;

Figure 5 is a perspective schematic view of the tool of figure 4, in a second operating configuration; - Figure 6 is an enlarged view of a first detail of a tool used on the apparatus of figure 3;

Figure 7 is an enlarged view of a second detail of a tool used on the apparatus of figure 3.

In figure 1, numeral reference 1 indicates a first preferred embodiment of an apparatus for removing an acrylate coating layer from a portion of optical fibre.

Apparatus 1 comprises a support frame 2 provided with a support base 3, a plurality of uprights, all referred to with numeral 4, and a crosspiece 5 for supporting most of the structural components of the apparatus itself. Crosspiece 5 is connected to the support base 3 by the uprights 4.

A pair of fibre-positioning devices 6a, 6b are mounted on the crosspiece 5 of the frame 2 at opposing ends 5a, 5b thereof. Devices 6a, 6b are adapted to house opposing end parts of a portion 100 of optical fibre (preferably having a length greater than 1 metre) so as to hold the latter in a substantially stretched position along a substantially horizontal fibre-alignment axis X-X.

The fibre-positioning devices 6a, 6b are arranged on the crosspiece 5 of the frame 2 at opposed sides with respect to a tool 200 adapted for removing the acrylate coating layer from a portion, having a predetermined length (preferably, from few cm to about 1 metre) of the portion 100 of optical fibre.

Each fibre-positioning device 6a, 6b comprises a clamping element 7a, 7b of one of the end parts of the portion 100 of optical fibre, and a device 8a, 8b for adjusting, on three axes X, Y, Z, perpendicular to one another, the position of the clamping element 7a, 7b on the frame 2 of apparatus 1.

Clamping elements 7a, 7b and adjusting devices 8a, 8b are both of the conventional type; thus, they will not be described in detail.

Each clamping element 7a, 7b is mounted on a support plate 9a, 9b connected, on the upper part, to the adjusting device 8a, 8b. The position of the clamping element 7a, 7b on frame 2 (in horizontal and vertical direction) is adjusted by the operator who operates on driving members 10, in the specific case knobs, associated to each device 8a, 8b. In particular, the rotation of each knob 10 causes the vertical movement of the respective plate 9a, 9b and thus, of the clamping element 7a, 7b associated therewith.

In turn, each clamping element 7a, 7b comprises a base body 71a, 71b and an upper body 72a, 72b adapted to reciprocally co-operate so as to hold into position one of the end parts of portion 100 of optical fibre. The base body 71a, 71b and the upper body 72a, 72b are reciprocally connected by a support arm 73a, 73b. The base body 71a, 71b is integrally mounted on the plate 9a, 9b and in its upper part it is provided with a seat, for example a V-groove (or a groove having similar shape) adapted to house the end part of the portion 100 of optical fibre. The upper body 72a, 72b is connected to the support arm 73a, 73b by a threaded screw (not visible) which, at an upper end, is provided with a hand grip 74a, 74b for controlling the rotation; by rotating said hand grip the upper body 72a, 72b moves in vertical direction, moving close to, and away from, the base body 71a, 71b.

A Teflon element (non shown) is connected to the upper body 72a, 72b, and is intended to be at least partly housed into the seat of the base body 71a, 71b to hold into position the end part of the portion 100 of optical fibre.

A pair of fibre-collecting spools 75a, 75b and a pair of further fibre-clamping elements 76a, 76b, positioned on the support plate 9a, 9b, contribute to obtaining the desired tensioning degree of the portion 100 of optical fibre before the acrylate is removed.

Additionally, apparatus 1 comprises a moving device 20 adapted to impart a relative motion between the portion 100 of fibre and the tool 200 along the fibre-alignment axis X- X.

In particular, the moving device comprises a slide 21 (of the conventional type) , which slides along a rack 22 (also conventional) connected to the crosspiece 5. Motor means 23 are active on the slide 21 to automatically impart to the latter a controlled motion (preferably with a constant speed, for example of 100 mm/min) along a direction which is parallel to the fibre-alignment axis X-X.

Tool 200 is integrally mounted on a support arm 30 which overhangs from a plate 31 integral with the slide 21. Thus, the portion 100 of fibre is fixedly positioned onto the apparatus 1, while tool 200 automatically moves along a direction which is parallel to the fibre axis X-X and with controlled motion.

In an alternative embodiment (not shown) of the apparatus of the present invention, the tool 200 is fixedly mounted onto the frame 2 of apparatus 1, while the fibre slides along the axis X-X. In this type of embodiment, the spool 75a for collecting and/or winding the fibre is pivotally mounted on the frame 2 and is driven by suitable motor means around a vertical rotation axis perpendicular to the axis X-X. On the contrary, the spool 75b, positioned on the support plate 5 at an opposed side of the collecting spool 75a with respect to the tool 200 serves as fibre-unwinding spool; it is also pivotally mounted on the support plate 5, and it is pulled in rotation by the fibre-collecting spool 75a, which pulls the fibre. Of course, the function of the two spools 75a and 75b can be reversed, that is to say, spool 75a can operate as winding spool and spool 75b as unwinding spool; in addition, both spools 75a, 75b can be motorised so as to rotate in the same direction and at the same speed.

As an alternative, the two spools 75a, 75b can be independent from the frame 2 and the latter can be provided, at its ends, with idle pulleys to receive the fibre from the first spool and feed it to the second one.

In a particularly advantageous embodiment, the apparatus 1 of the present invention may comprise, below one of the two fibre-positioning devices 6a, 6b (in particular, below the device 6a, 6b arranged at the opposed side with respect to the direction of movement of tool 200) a load cell for the purpose of acquiring by a computer the values of the strip force needed to remove a portion of acrylate having a predetermined length, so as to have an on-line monitoring of the acrylate removal process, and a quality control on the single fibre sample from which the acrylate has been removed. Moreover, it is possible to provide for an automatic control system for the slide 21 on which the tool 200 is mounted, so as to make the process completely automated and thus, perfectly repeatable. Advantageously, the apparatus 1 can also comprise, below the fibre- positioning device 6a, 6b opposed to that on which the load cell is mounted, a second slide controlled via computer so as to allow a pre-tensioning of the fibre before the acrylate is removed; even more advantageously, an apparatus of the type described above can be used for carrying out screen tests immediately after having removed the acrylate (in particular, these are tests for checking the ultimate tensile strength of the fibre, for example after splicing or writing of Bragg grating, consisting in applying a predetermined load to the fibre itself for a predetermined time, generally less than 1 second) .

The tool 200 is preferably of the collet type, and comprises a first and a second arm, respectively referred to with numerals 201, 202, reciprocally pivoted. At the respective end portions, both arms 201 and 202 are provided with cutting blades, respectively referred to with numerals 203 and 204, active on a plane YZ perpendicular to the fibre-alignment axis X-X, and adapted to cut into the acrylate layer of the portion 100 of optical fibre.

Blades 203, 204 are provided with respective grooves, preferably V-shaped (or U-shaped, or semicircular) adapted to co-operate for removing the acrylate.

The first arm 201 of tool 200 is connected to the support arm 30 and is positioned perpendicularly to the fibre- alignment axis X-X. The groove of the respective blade 203 is perfectly aligned with the grooves of the clamping elements 7a, 7b of the fibre-positioning devices 6a, 6b. In the initial configuration, the groove of the blade 203 of the first arm 201 houses an intermediate part of the portion 100 of optical fibre.

The second arm 202 (and thus, the blade 204) is mobile in the plane YZ between a first operating position, wherein the respective blade 204 is in a distal position with respect to the portion 100 of optical fibre (shown in figure 1), and a second operating position, wherein also the blade 204 houses a portion of the portion 100 of optical fibre into its groove and co-operates with the blade 203 of the first arm 201 to cut into the acrylate layer (said second position is shown with dashed lines in figure 2) .

A counter spring 205 is active between the arms 201 and 202 and is adapted to hold the two blades 203 and 204 in a position at rest wherein they are spaced from one another.

In the preferred embodiment of the apparatus 1 of the present invention (shown in figure 1) , the tool 1 is a conventional Stripper Miller, available on the market, for example, at Advanced Custom Applications, Inc. - Belle Mead, NJ, USA.

Apparatus 1 comprises a device 50, preferably a pneumatic device, active on the mobile arm 202 of the tool 200 to automatically move with a controlled motion (preferably at a constant speed) the blade 204 from the first to the second operating position. Said pneumatic device is driven by the operator by means of a lever distributor 60 (of the conventional type) mounted on the frame 2 of apparatus 1.

In particular, the pneumatic device 50 comprises a pneumatic cylinder 51 inside which a piston 52 slides that, when device 50 is activated, drives the movement of the mobile arm 202 of tool 200 (and thus, of the blade 204).

The pneumatic connection between the lever distributor 60 and the pneumatic cylinder 51 is obtained through a tube 62.

In a first embodiment of the pneumatic device 50 (shown in figure 1), the piston 52 is adapted to push the second arm 202 of the tool 200 from the bottom upwards, overcoming the resistance exerted by the counter spring 205, when the pneumatic device 50 is activated. In particular, the piston 52 presents, at one end thereof, a roller 53 which is in contact with the second arm 202 in the proximity of its free end opposed to the end wherein the blade 204 is provided. In this embodiment, the operation of the pneumatic device 50 causes the pressure inside cylinder 51 to increase, thus pushing the piston 52 outwards.

In an alternative embodiment of the invention (shown in figure 2), the piston 52 is adapted to pull the second arm 202 of the tool 200 from the bottom upwards, overcoming the resistance exerted by the counter spring 205, when the pneumatic device 50 is activated. In this embodiment, the piston 52 presents, at one end thereof, a fork 54 which encloses the second arm 202; in this case, the roller 53 is provided on the free end of the fork 54. Between the slide 21 and the plate 31 a Z-shaped spacer element 80 is interposed. The operation of the pneumatic device 50 causes a depression inside the cylinder 51, which withdraws the piston 52 inside cylinder 51.

In a further alternative embodiment, the device 50 for automatically moving the blade 204 from the first operating position (tool 200 open) to the second operating position (tool 200 closed) is electrically driven.

Nevertheless, it is possible to use other types of conventional devices (not shown) to automatically move the blade 204 of the tool 200 from the first to the second operating position; for example, it is possible to use mechanical (with worm screw) , magnetic (with solenoid) , electromechanical devices, etc.

In a further embodiment not shown, the apparatus of the present invention comprises a device for emitting an air or nitrogen jet (not shown) integrally mounted on the tool 200 and adapted to impact over the fibre with the air jet, so as to remove the acrylate just removed. In the following description, the operation of the apparatus of figure 1 is described.

Apparatus 1 has an initial configuration in which the tool 200 is positioned perpendicularly to the fibre-alignment axis X-X, with the second blade 204 in the first operating position (tool open) .

The portion 100 of optical fibre is positioned into apparatus 1 by housing the end parts of the fibre portion 100 into the seats of the base bodies 71a, 71b of clamping elements 7a, 7b of fibre-positioning devices 6a, 6b, and aligning the portion 100 of optical fibre with the groove of the fixed blade 203 of the tool 200. The alignment can be obtained by vertically and/or horizontally moving the clamping elements 7a, 7b along the three axes X, Y, Z by the devices 8a, 8b.

By means of the hand grips 74a, 74b, the upper bodies 72a, 72b are moved downwards so as to clamp the end parts of the fibre portion 100 into the clamping elements 7a, 7b.

Then, the lever distributor 60 of the pneumatic device 50 is operated; in this way, the closing of the mobile arm 202 of the tool 200 is activated, so that the blade 204 is moved from the first to the second operating position.

Afterwards, the motor means 23 controlling the movement of the slide 21 are activated. The movement of the tool 200 causes the acrylate to be evenly removed from the entire length of fibre desired. At this stage, it is possible to activate at the same time the device for emitting the air jet so as to facilitate the removal of the acrylate removed from the fibre.

Once the desired length has been obtained, the slide 21 is stopped by disactivating the motor means 23. Operating on the lever distributor 60, the mobile arm 202 of the tool 200 is moved back to its first opening position. At this point, it is possible to remove the fibre from the positioning devices 6a, 6b.

The fibre is now ready for all the following steps of the production cycle, for example for Bragg grating, or for the manufacturing of fused-fibre couplers. Should the removal of the fibre be targeted to splicing, proceed by cutting the fibre at the portion without acrylate.

Apparatus 1 of the present invention has been so far described in the embodiment with horizontal fibre-alignment axis X-X (see fig. 1) . However, the above also applies in case the apparatus is manufactured so that the axis X-X is orientated differently, for example vertically. The embodiment with vertical axis X-X is preferable for a portion of fibre having a length greater than 50 cm, more advantageously, in the range of 1 m, or greater than 1 m.

Figure 3 shows a preferred embodiment of the apparatus of the present invention with vertical fibre-alignment axis X- X. Said apparatus (referred to with numeral 500) differs from that with horizontal axis described above essentially for the vertical arrangement, and for the use of a new embodiment of the tool for removing the acrylate (said new embodiment of the tool can be also used in the embodiment of the apparatus with horizontal axis X-X) .

Herein below, the structural elements equal to those mentioned above with reference to figure 1 shall be referred to with the same reference numeral, and they shall not be described in detail, being applicable what said above with reference to the apparatus with horizontal fibre-alignment axis X-X.

The apparatus comprises a support frame 2 provided with a support element 501 for supporting most of the structural components of the apparatus itself, and with a plurality of support feet (all referred to with 502) . The support element 501 is associated to the support feet 502 through the interposition of plates 503. A pair of fibre-positioning devices 6a, 6b are mounted on the element 501 of frame 2 at opposing ends 5a, 5b thereof. The devices 6a, 6b are adapted to house opposing end parts of a portion 100 of optical fibre (preferably having a length greater than 1 metre) so as to hold the latter in a substantially stretched position along a substantially vertical fibre-alignment axis X-X.

The fibre-positioning devices 6a, 6b are slidably mounted on a rail 22 associated to the element 501 of the frame 2, and they are arranged at opposing sides with respect to a tool 600 adapted for removing the acrylate coating layer from a portion of predetermined length of the portion 100 of optical fibre. Each fibre-positioning device 6a, 6b comprises a clamping element 7a, 7b of one of the end parts of the portion 100 of optical fibre.

The fibre-positioning device 6a, 6b are totally similar to those described above with reference to apparatus 1 with horizontal axis X-X; thus, they shall not be described in detail. In a preferred embodiment, one of the two devices 6a, 6b (for example, the lower one, 6b) is mounted on the element 501 by the interposition of a motorised plate 504, so as to automatically regulate its position in parallel to the axis X-X.

A pair of fibre-collecting spools (not shown) and a pair of further fibre-clamping elements (also not shown, but totally similar to those described above and illustrated in figure 1) positioned on the support element 501 at opposing sides with respect to the tool 600, contribute to maintain the desired degree of tensioning of the portion 100 of optical fibre before the acrylate is removed.

The tensioning degree of the fibre is reached by operating on the above motorised plate 504, and it is controlled by means of a load cell (not shown) mounted on the upper positioning device 6a. The value of the load is read on a display of a control unit 23 conventionally connected to the load cell. Of course, the position of the load cell and of the positioning device 6a ad 6b can be reversed, that is, the load cell can be mounted on the lower positioning device 6b and the motorised plate on the upper positioning device 6a.

Apparatus 500 further comprises a moving device adapted to impart a relative motion between the portion 100 of fibre and the tool 600 along the fibre-alignment axis X-X.

In particular, the moving device comprises a slide 21 (of the conventional type) slidably mounted on a worm screw 220 driven in rotation by motor means 230 (of the conventional type as well) mounted on the support element 501 at one of its ends 5a, 5b (in the specific case, at the upper end 5a) . The motor means 230 are active, through the worm screw 220, on the slide 21 so as to automatically impart to the latter a controlled motion (preferably with constant speed, for example of 100 mm/min) in a direction which is parallel to the fibre-alignment axis X-X.

As shown in figure 4, the tool 600 is integrally mounted on the slide 21 through the interposition of a plate 300. Thus, the portion of fibre 100 is fixedly positioned onto the apparatus 500, whereas the tool 600 automatically moves in parallel to the fibre axis X-X with controlled motion.

In an alternative embodiment (not shown) of the apparatus of the present invention, the tool 600 is fixedly mounted onto the element 501 of frame 2 of apparatus 500, while the fibre slides along the axis X-X. In this embodiment, a first fibre-collecting spool (not shown) can be pivotably mounted on the frame 2, and be activated, by suitable motor means, around an horizontal axis of rotation perpendicular to the axis X-X. A second spool (not shown as well) can be arranged on the support element 501 at an opposed side to the fibre-collecting spool with respect to the tool 600, so as to function as fibre-unwinding spool; it can be pivotably mounted on the support element 501 as well and, in operation, be pulled in rotation by the fibre-collecting spool, which pulls the fibre.

Alternatively, the two spools can be independent from the frame 2 and the latter can be provided, at its ends, with idle pulleys to receive the fibre from the first spool and feed it to the second one.

As shown in the figures from 4 to 7, the tool 600 comprises a first fixed tool body 400a and a second mobile tool body 400b. The first tool body 400a is associated with a fixed block 500 housing the first cutting blade 203 into a respective first seat 505a (in particular, reference shall be made to figure 6) ; the second tool body 400b is associated with a second block 506 housing the second cutting blade 204 into a respective second seat 506a (in particular, reference shall be made to figure 7) . The cutting blades 203 and 204 are active on a plane YZ perpendicular to the fibre-alignment axis X-X and adapted to cut into the acrylate layer of the portion 100 of optical fibre.

Blades 203 and 204 are provided with respective grooves

(referred to with 203a, 204a in figures 6 and 7) preferably semicircular (for example, with a diameter of the groove comprised between 140 μm and 170 μm, if the fibre from which the acrylate has to be removed has an outer diameter equal to 250 μm and a diameter of the glassy region equal to 125 μm) , or V-shaped, adapted to co-operate in removing the acrylate.

The first body 400a of the tool 600 is associated to a block 507, which is in turn associated to the plate 300 mounted onto the slide 21; the first blade 203 is associated to the first block 505 by screws 800, and it is positioned perpendicular to the fibre-alignment axis X-X. The groove 203a of the blade 203 is perfectly aligned with the seats of the clamping elements 7a, 7b of the fibre- positioning devices 6a, 6b. In the initial configuration, the groove 203a of the blade 203 of the first block 505 houses an intermediate part of the portion 100 of optical fibre .

The second body 400b of the tool 600 is associated to the block 507 so that the second blade 204 (associated to the second block 506 by screws 800 as well) is mobile in the plane YZ between a .first operating position, wherein the blade 204 is in a distal position with respect to the portion 100 of optical fibre (shown in figure 4), and a second operating position wherein also the blade 204 houses a portion of the portion 100 of optical fibre into its groove 204a, and co-operates with the blade 203 of the first block 505 to cut into the acrylate layer (said second position is shown in figure 5) .

The tool 600 comprises a device active on the second body 400b of the tool to arrange the latter faced with the first tool body 400a and thus, to position with controlled motion said second blade 204 with respect to said first blade 203 so that said fibre portion 100 is cut by blades 203 and 204. Said device can be activated by the operator by means of a plunger system 601 mounted on the slide 21 of apparatus 500.

In particular, the plunger system 601 comprises a handle

602 active on a small shaft 603 sliding inside a tubular element 604 integral with the block 507. The small shaft

603 co-operates with two first arms 605 so that a substantially angular movement of the first two arms 605 corresponds to a longitudinal sliding of shaft 603. The second tool body 400b is pivoted on the first two arms 605 through two second arms 611, which are associated to the first arms 605 through a connection pivot 612 which engages into corresponding holes formed onto arms 605 and 611.

As shown in figure 5, in the preferred embodiment of the apparatus of the present invention, a shock absorbing system 610 is provided between the second tool body 400b and the second arms 611; in particular, said system comprises a pair of springs 613 interposed between the second arms 611 and the second tool body 400b.

The closing of the bodies 400a and 400b (and thus, of blocks 505 and 506 and of blades 203 and 204 to cut into the acrylate layer of the portion 100 of optical fibre) is obtained by first manually rotating the second arms 611 with respect to the first arms 605 around the connection pivot 612. Then, operating on the handle 602 of the plunger system 601, the actual closing between the tool bodies 400a and 400b is obtained: in particular, exerting a thrust onto said handle 602, the shaft 603 is made slide longitudinally, thus causing a last substantially angular movement of the first arms 605 and thus, a last movement of approach of the second tool body 400b with respect to the first body 400a. The closing position is maintained by inserting a pin 700 into respective holes 750 formed onto the first arms 605, so as to counteract the force exerted by the springs 613 onto the second arms 611, which would tend to pull away the two bodies 400a and 400b. On the other hand, the opening of bodies 400a and 400b (and thus, of blocks 505 and 506) is obtained by first pulling out the pin 700 from holes 705; then, by moving the handle 602 in direction of opening, a first relative motion of separation of the second tool body 400b from the first body 400a is obtained due to the effect of the force exerted by the springs 613 on the second arms 611. Finally, by manually rotating the second arms 611 with respect to the first arms 605, the second tool body 400b is taken away from the first body 400a.

Bodies 400a and 400b and blocks 505 and 506 comprise a plurality of alignment elements adapted to allow the precise alignment of said first and second blade 203, 204 in vertical and horizontal direction when said second blade 204 is moved to the second operating position.

In particular, on the first block 505, at opposed sides with respect to the fibre-alignment axis X-X, a pair of spheres 620 projecting with respect to an abutment surface 621 with the second block 506 are mounted; the latter presents, in a position corresponding to that of the spheres 620, respective spherical-cap or V-shaped seats 620a adapted to house the projecting portion of the spheres 620 when blocks 505 and 506 are in closing position.

In addition, a plurality of pairs of rounded longitudinal elements 630, raised with respect to said abutment surface 621 with the second block 506, are associated to the first tool body 400a and are adapted to be housed inside respective second seats 630a formed into the second tool body 400b. The elements 630 of each pair of elements are mounted onto the first tool body 400a at opposing sides with respect to the fibre-alignment axis X-X and in parallel to the latter.

The concurrent presence of the alignment elements and of the above described shock absorbing system allows to obtain the precise alignment of the blades 203 and 204 without imparting undesired stresses to the optical fibre.

Moreover, both the first and the second block 505 and 506 comprise, at a respective lower end thereof, a cylinder 640 pivotable (through a ball bearing) around an axis perpendicular to the fibre-alignment axis X-X; said cylinder is provided with a groove 641, preferably a V- shaped groove, adapted to house a part of said portion.100 of optical fibre. In particular, the groove 641 of the first block 505 is aligned along the axis X-X with the seats of the clamping elements 7a, 7b.

The first and second block 505 and 506 also comprise respective notches 650 formed downstream of the blades 203 and 204 with respect to the sliding direction of the slide 21 for removing the acrylate, said notches being adapted to operate as collection chamber for the residues of the removed acrylate. As shown in figure 4, said notches 650 are formed below blades 203 and 204; in fact, the tool 600 is preferably intended for moving from top downwards.

Also this embodiment of the apparatus of the present invention is provided with a device for emitting an air or nitrogen jet which is integrally mounted on the tool 600 and adapted to operate, through suitable air inlets and outlets, onto the notches 650 for collecting the acrylate, so as to remove the residues of acrylate just removed; the use of such a device is to be provided above all where it is necessary to remove the acrylate from long portions of fibre (for example, in the range of 1 m or more than 1 m) , for the purpose of preventing the collected acrylate residues from damaging the tool blades.

In the following, the operation of the apparatus of figure 2 is described.

Apparatus 500 has an initial configuration, shown in figure 4, wherein the second blade 204 of the tool 600 is in the first operating position (tool open) .

The portion 100 of optical fibre is positioned into the apparatus 500 by housing the end parts of the fibre portion 100 into the seats of the clamping elements 7a, 7b of the fibre-positioning devices 6a, 6b, and aligning the portion 100 of optical fibre with the groove 203a of the fixed blade 203 of tool 600. The alignment can be obtained by moving the clamping elements 7a, 7b along the three axes X, Y, Z, as described above with reference to the apparatus with horizontal axis X-X.

Then, the plunger system 601 is operated; in this way, the closing of the second mobile body 400b of tool 600 is activated, so that the blade 204 is moved from the first to the second operating position.

Afterwards, the motor means 230 controlling the movement of the slide 21 are activated. The movement of the tool 600 causes the acrylate to be evenly removed from the entire desired length of fibre. At this stage, it is possible to activate at the same time the device for emitting the air jet so as to facilitate the removal of the acrylate removed from the fibre.

Once the desired length has been obtained, the slide 21 is stopped by disactivating the motor means 230. Operating on the plunger system 601, the second mobile body 400b of the tool 600 is moved back to the open position. At this point, it is possible to remove the fibre from the positioning devices 6a, 6b.

EXAMPLES

The inventors of the present invention have carried out several experimental tests on optical fibres in different operating situations, by measuring every time the values of ultimate tensile strength of the fibres; the tool used for a first series of tests was a Stripper Miller, and the apparatus was the one with horizontal axis X-X (see figure 1); in a second series of tests, the tool used was the tool of the present invention (shown in figure 4 and 5) and the apparatus was the one with a vertical axis (see figure 3) .

In both the above series of tests, measures were respectively taken on:

1) fibre as produced (Pristine fibre) ;

2) fibre after the removal of the acrylate coating for 2.5 cm with a conventional manual process (manual stripping) ;

3) fibre after the removal of the acrylate coating for 2.5 cm with the apparatus of the invention (automatic stripping) . The fibres used in the first series of tests were standard single-modal fibres produced by Pirelli S.p.A. The measurements of ultimate tensile strength were carried out with a conventional tensioning machine at a speed of 500 mm/min. 20 measurements of the ultimate tensile strength were carried out for each test. The results of the first series of tests are shown in table 1.

Table 1

The results of table 1 show that, in general, with respect to the fibre as produced, the removal of acrylate from a fibre for a few cm-long portion causes a degradation of the ultimate tensile strengths and an increase of the standard deviation of the results. However, while with the apparatus of the invention the ultimate tensile strengths are in any case above 6 kg (that is to say, they are close to the ultimate tensile strengths of the fibre as produced) with a very low dispersion of data, the values of ultimate tensile strength obtained with the conventional method of removal

(i.e. by manual stripping) are much lower (lower than 4 kg) , with an extremely high dispersion.

Thus, the apparatus of the invention advantageously allows obtaining a high repeatability of the results, a limitation of the mechanical stresses on the fibres and, as a consequence, a high mechanical reliability of the fibres themselves during operation. In the second series of tests, 50 measurements of the ultimate tensile strength were carried out after having removed the acrylate from a length of fibre of 2.5 cm, using the apparatus shown in figure 3.

Also in this case, the fibres used were standard single- modal fibres produced by Pirelli S.p.A. The measurements of ultimate tensile strength were carried out with a conventional tensioning machine at a speed of 500 mm/min . The results are shown in table 2.

Table 2

The results of table 2 show that, in general, with respect to the fibre as produced, the removal of acrylate from a fibre for a few cm-long portion causes a degradation of the ultimate tensile strengths, and an increase of the standard deviation of the results. However, while with the manual removal the ultimate tensile strength decreases by almost half the initial value, by using the apparatus of the invention the ultimate tensile strengths are close to 6 kg (that is to say, they are close to the ultimate tensile strengths of the fibre as produced) .

Advantageously, also in the second preferred embodiment shown in figure 3, the apparatus of the invention allows limiting the mechanical stresses on the fibres and, as a consequence, obtaining a high mechanical reliability of the fibres themselves during operation.

Claims

1. Apparatus (1, 500) for removing a coating layer from a portion (100) of optical fibre, comprising: a support frame (2) ; - a tool (200, 600) for removing a coating layer from a portion (100) of optical fibre; a pair of fibre positioning devices (6a, 6b) mounted on the support frame (2) from opposing sides with respect to the tool (200, 600) and adapted to house opposing end parts of said portion (100) of optical fibre so as to hold said portion (100) of optical fibre in a substantially stretched position along a fibre-alignment axis X-X; characterised in that it comprises a moving device (20) to automatically impart a controlled relative motion between said portion (100) of fibre and the tool (200, 600) along the fibre-alignment axis X-X, and in that the tool (200, 600) comprises a pair of cutting blades (203, 204) operating on a plane YZ perpendicular to the fibre- alignment axis X-X and positionable with a controlled motion with respect to said axis to cut into said coating layer of said portion (100) of optical fibre.

2. Apparatus according to claim 1, wherein said moving device (20) comprises a slide (21) which is slidably mounted on the frame (2) and movable in parallel with said fibre-alignment axis X-X with controlled motion, said tool (200, 600) being integrally mounted with said slide (21).

3. Apparatus according to any one of the preceding claims, wherein said moving device (20) comprises a motorised fibre-winding spool, pivotally mounted on the frame (2) and adapted to rotate with a controlled motion around an axis of rotation perpendicular to the fibre-alignment axis X-X, so as to make the fibre sliding with respect to the tool (200, 600) along the fibre-alignment axis X-X.

4. Apparatus according to claim 3, also comprising a fibre-unwinding spool pivotally mounted on the frame (2) from a side opposed to the fibre-winding spool with respect to the tool (200, 600) and adapted to be driven in rotation by the fibre-winding spool.

5. Apparatus according to any one of the preceding claims, wherein said pair of fibre-positioning devices (6a, 6b) comprises respective fibre-clamping elements (7a, 7b) , each of which includes a first body (71a, 71b) provided with a first seat adapted to house an end part of said portion (100) of optical fibre, and a second body (72a, 72b) adapted to co-operate with the first body (7a, 7b) to hold said end part of said portion (100) of optical fibre into position inside the first seat.

6. Apparatus according to any one of the preceding claims, wherein said tool (200, 600) comprises: - a first blade (203) fixedly mounted with respect to the plane YZ and provided with a first groove adapted to house a part of said portion (100) of fibre; a second blade (204) provided with a second groove and mobile onto the plane YZ between a first operating position, wherein said second blade (204) is in distal position with respect to said portion (100) of optical fibre, and a second operating position wherein said second blade (204) houses said part of said portion (100) of optical fibre into the second groove and co-operates with the first blade (203) to cut into the coating layer of said portion (100) of optical fibre.

7. Apparatus according to claim 6, wherein said tool (200) comprises a first and a second arm (201, 202) , reciprocally pivoted, and a counter spring (205) between said first and second arm (201, 202), wherein the first and the second blade (203, 204) are respectively associated to the first and second arm (201, 202) in proximity of end portions of said arms (201, 202), and wherein said counter spring (205) is adapted to hold, when at rest, said second blade (204) into said first operating position.

8. Apparatus according to any of the preceding claims, wherein said tool is a Stripper Miller.

9. Apparatus according to claim 6, comprising a device (50) operating on said tool (200) to automatically move said second blade (204) from the first to the second operating position.

10. Apparatus according to claims 7 and 9, wherein said devise (50) comprises a pneumatic cylinder (51) and a piston (52) active in thrust or pull configuration on the second arm (202) of the tool (200) .

11. Apparatus according to claim 6, wherein said first and second blades (203, 204) are housed into respective second seats (505a, 506a) formed on a first and a second block (505, 506) which are respectively associated to a first and a second body (400a, 400b) of the tool (600), said first and second block (505, 506) and said first and second body

(400a, 400b) of the tool (600) in turn comprising a plurality of alignment elements (620, 620a, 630, 630a) adapted to allow the precise positioning of said first and second blade (203, 204) when said second blade (204) is in the second operating condition.

12. Apparatus according to claim 11, wherein said plurality of alignment elements (620, 620a, 630, 630a) comprises at least one pair of spheres (620) associated to one between the first and the second block (505, 506) and adapted to be housed into respective third seats (620a) formed into the other one between the first and the second block (505, 506) .

13. Apparatus according to claim 11 or 12, wherein said plurality of alignment elements (620, 620a, 630, 630a) comprises at least one pair of rounded longitudinal elements (630) associated to one between the first and the second body (400a, 400b) of the tool (600), adapted to be housed into respective fourth seats (630a) formed into the other one between the first and the second body (400a, 400b) of the tool (600) .

14. Apparatus according to any one of the claims from 11 to

13, wherein each of said first and second blocks (505, 506) also comprises a cylinder (640) pivotable around an axis perpendicular to the fibre-alignment axis X-X, said cylinder (640) being provided with a groove (641) adapted to house a part of said portion (100) of optical fibre, the groove (641) of the cylinder (640) associated to said first block (505) being in a condition of alignment along the axis X-X with said first seats of said clamping elements (7a, 7b) .

15. Apparatus according to any one of the claims from 11 to

14, comprising a plunger system (601) active on said second body (400b) of said tool (600) and adapted to move said second blade (204) from the first to the second operating position.

16. Apparatus according to claim 15, wherein said plunger system (601) comprises a shock absorbing system (610) active on the second body (400b) of said tool (600) when said second blade (204) is moved to the second operating position .

17. Apparatus according to any one of the preceding claims, wherein the fibre-alignment axis X-X is substantially horizontal.

18. Apparatus according to any one of the claims from 1 to 16, wherein the fibre-alignment axis X-X is substantially vertical .

19. Tool (600) for removing a coating layer from a portion (100) of optical fibre, comprising a first and a second cutting blade (203, 204) adapted to operate on a plane YZ perpendicular to a fibre-alignment axis X-X, characterised in that it comprises a plunger system (601) for positioning with controlled motion said first and second blade (203, 204) with respect to said fibre-alignment axis X-X to cut into said coating layer of said portion (100) of fibre.

20. Tool according to claim 19, further comprising a first block (505) housing the first cutting blade (203) into a respective first seat (505a) and a second block (506) housing the second cutting blade (204) into a respective second seat (506a), wherein the first blade (203) is adapted to be fixedly mounted with respect to the plane YZ and is provided with a first groove adapted to house a part of said fibre portion (100) , and wherein the second blade (204) is provided with a second groove and is mobile in the plane YZ between a first operating position, wherein said second blade (204) is in distal position with respect to said portion of optical fibre (100), and a second operating position, wherein said second blade (204) houses said part of said portion (100) of optical fibre and co-operates with the first blade (203) to cut into the coating layer of said portion (100) of optical fibre.

21. Tool according to claim 20, wherein said first and second block (505, 506) are in turn respectively associated to a first and a second tool body (400a, 400b) and wherein said first and second block (505, 506) and said first and second tool body (400a, 400b) comprise a plurality of alignment elements (620, 620a, 630, 630a) adapted to allow the precise alignment of said first and second blade (203, 204) in vertical and horizontal position when said second blade (204) is moved to the second operating condition.

22. Tool according to claim 21, wherein said plurality of alignment elements (620, 620a, 630, 630a) comprise at least one pair of spheres (620) associated to one between the first and the second block (505, 506) and adapted to be housed into respective seats (620a) formed into the other one between the first and the second block (505, 506) .

23. Tool according to claim 22, wherein the spheres of said at least one pair of spheres (620) are associated to the first block (505) from opposed sides with respect to the fibre-alignment axis X-X.

24. Tool according to claim 22 or 23, wherein said plurality of alignment elements (620, 620a, 630, 630a) also comprise at least one pair of rounded longitudinal elements (630) associated to one between the first and the second tool body (400a, 400b) and adapted to be housed into respective seats (630a) formed into the other one between the first and the second tool body (400a, 400b) .

25. Tool according to claim 24, wherein the longitudinal elements of said at least one pair of longitudinal elements (630) are associated to the first tool body (400a) from opposed sides with respect to the fibre-alignment axis X-X.

26. Tool according to any one of the claims from 20 to 25, wherein each of said first and second block (505, 506) further comprises a cylinder (640) pivotable around an axis perpendicular to the fibre-alignment axis X-X, said cylinder (640) being provided with a groove (641) adapted to house a part of said portion (100) of optical fibre.

27. Tool according to any one of the claims from 20 to 26, wherein said first and second block (505, 506) comprise respective notches (650) formed downstream of said first and second blade (203, 204) with respect to the sliding direction of the tool (600) .

28. Tool according to any one of the claims from 20 to 27, further comprising a plunger system (601) active on said second tool body (400b) and adapted to move said second blade (204) between the first and the second operating position .

29. Tool according to claim 28, wherein said plunger system (601) comprises a shock absorbing system active on the second tool body (400b) when said second blade (204) is moved to the second operating position.

30. Method for removing a coating layer from a portion (100) of optical fibre, comprising the following steps: a) arranging, on a plane YZ, a pair of cutting blades (203, 204) of a tool (200, 600) for removing a coating layer from said portion (100) of optical fibre; b) positioning a portion (100) of fibre into a stretched position along a fibre-alignment axis X-X perpendicular to plane YZ; c) positioning, with a controlled motion, said pair of cutting blades (203, 204) with respect to said axis X-X so as to cut into said coating layer of said portion (100) of optical fibre; d) automatically imparting a controlled relative motion between said tool (200, 600) and said portion (100) of fibre along said fibre-alignment axis X-X.

31. Method according to claim 30, wherein the step b) of positioning the portion (100) of fibre into a stretched position along the axis X-X comprises the step of housing a part of said fibre portion (100) into a groove formed on a blade of the tool and opposing end parts of said fibre portion on respective seats formed on positioning devices

(6a, 6b) positioned at opposed sides with respect to the tool (200, 600) and adapted to hold said end parts of said portion (100) of optical fibre into position.

32. Method according to claim 30 or 31 , wherein the step d) of imparting a controlled relative motion between tool (200, 600) and fibre portion (100) comprises the step of activating motor means active on a slide (21) on which the tool (200, 600) is integrally mounted.

33. Method according to claim 30 or 31, wherein the step d) of imparting a controlled relative motion between tool (200, 600) and fibre portion (100) comprises the step of activating motor means active on a fibre-winding spool.

34. Method according to any one of the claims from 30 to 33, wherein the step c) of positioning with controlled motion the blades (203, 204) of the tool (200, 600) with respect to the axis X-X comprises the step of activating a device (50, 601) adapted to automatically move at least one of said blades (203, 204) from a first operating position, wherein the blades (203, 204) are in a distal position from one another, to a second operating position, wherein the blades (203, 204) cut into said coating layer of said portion (100) of optical fibre.