WO2002046716A1

WO2002046716A1 - Tensile testing machine for optical fibers

Info

Publication number: WO2002046716A1
Application number: PCT/SE2001/002650
Authority: WO
Inventors: Sasan Esmaeili
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2000-11-29
Filing date: 2001-11-29
Publication date: 2002-06-13
Also published as: SE0004398L; AU2002224307A1; SE0004398D0; SE519520C2

Abstract

A tensile testing machine for testing of tensile strength in to each other spliced optical fibres has got tension rollers (15) to hold and stretch the optical fibres around the splice. A furnace (17) is placed in between the dies and may in connection with tensile test of a fibre splice be used to heat a shrinking terminal for protection of the splice. The furnace has got a deep space in the shape of a groove, through which sections of the spliced fibres are passed, such that they are fairly completely surrounded by the walls of the space in shape of a groove. The furnace is constructed as a metal block and flat shaped heating elements are in direct contact with the lateral surfaces of the metal block.

Description

TENSILE TESTING MACHINE FOR OPTICAL FIBERS TECHNICAL FIELD

The present invention relates to a tensile testing machine for optical fibers. BACKGROUND OF THE INVENTION

5 In splicing two optical fibers to each other often welding is used. Then, protective layers on end portions of the fibers are removed, the naked fiber ends are cut off so as to obtain clean, fresh section surfaces located perpendicularly, the obtained new end surfaces are placed opposite each other and are heated by an electric arc so that the ends are melted to each other. The naked end portions are then protected by a protective sleeve, o often called a "shrinking sleeve". The shrh king sleeve 1 usually comprises, see the cross-sectional view of Fig. 1, outermost a shrinking hose 3 that encloses a short pin or rod 5 for receiving the mechanical load of the splice and a melting sleeve of thermoplastic material located at the side of the pin 7 in which the naked portions 9 connected to each other of the spliced fibers are placed. The total length of the naked portions is typic- 5 ally 10 - 20 mm. Before the very splicing step such a shrinking sleeve is slid over one of the optical fibers which are to be spliced to each other, and after the fusion to each other it is moved or displaced to cover the naked portions of the spliced fibers, in particular so that the melting sleeve 7 encloses them. Thereafter the shr-i-king hose is heated using commonly an oven to which the fibers are moved after the fusion to each other. In the o oven the shrinking sleeve is heated so as to make the outermost part, the shrinking hose 3, retract transversely to a smaller diameter and thereby will be fixedly applied to and retain the inner part, the reinforcement pin 5 and the material of the melting sleeve 7. The latter one melts and is thereby permanently applied tightly to the naked portions of the fibers. It extends a short distance up over the portions of the fibers that have their pro- 5 tective coating left and that are directly connected to the naked portions.

In some applications it is also desired that the tensile strength of the produced splices is tested. It is most often made before the splice portion of the fibers is protected by applying a shrinking sleeve. Then suitably the fibers are moved to a tensile testing machine, whereafter the fibers are transported to the heating device, i.e. the oven, for the 0 final applying of the protective sleeve. These different operational steps are usually executed in separate units, between which the splice together with the unprotected fiber portions must be moved by an operator. These transports of the unprotected fiber portions increase the risk of damage to the splice and of reducing the strength of the splice.

A tensile testing machine for testing the strength of splices between optical fibers is 5 disclosed in U.S. patent 4,736,632. The tensile testing machine comprises a support table in the top surface of which a support groove for a fiber splice is provided. The support table constitutes a station for applying a shrinking sleeve and in the station a shrinking sleeve placed over a fiber splice can be heated. Information on the way in which the heating is made and how the groove is designed is not given. SUMMARY OF THE INVENTION

It is an object of the invention to provide a tensile testing machine for testing splices between optical fibers, that reduces the manual handling in the tensile testing step and in applying shrinking sleeves over the splices. 5 It is another object of the invention to provide a tensile testing machine for testing splices between optical fibers comprising an oven constructed in an advantageous way for heating shrinking sleeves applied over the splices.

Thus, a tensile testing machine having pulling blocks for retaining the optical fibers at the sides of the splice and stretching the portion of the fiber between the pulling 0 blocks, is provided with an oven for heating a shrinking sleeve for protecting the splice.

The oven is placed mainly between the pulling blocks and has a space designed as a groove that is rather deep and is located in such a way that at least most of the portion of the fibers between the pulling blocks is located quite inside the groove-shaped space and preferably at the bottom thereof, so that the fiber portion between the pulling blocks and 5 a shrinking sleeve applied around the splice have a distance from their upper surfaces to the opening of the groove that at least is larger than the diameter of the shrinking sleeve.

The shrinking sleeve can then be surrounded by the walls of the groove-like space over an angle of at least 120° taken around the longitudinal axis of the shrinking sleeve.

The groove-like space or groove is arranged in a metal block and extends down- o wards from an upper surface thereof. At the side surfaces of the metal block that can be substantially perpendicular to the upper surface and parallel to the longitudinal direction of the groove-like space, plate-shaped heating elements can be mounted in direct contact with the material of the block for the heating of the metal block that is required for heating a shrinking sleeve introduced in the grooved. An electric control unit for the oven 5 can be arranged at a distance thereof. It results in that the oven can be designed as a compact unit having small exterior dimensions so that it in a simple way can be mounted to a tensile testing machine.

Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be 0 learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the methods, processes, instrumentalities and combinations particularly pointed out in the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS

While the novel features of the invention are set forth with particularly in the 5 appended claims, a complete understanding of the invention, both as to organization and content, and of the above and other features thereof may be gained from and the invention will be better appreciated from a consideration of the following detailed description of non-limiting embodiments presented hereinbelow with reference to the accompanying drawings, in which: - Fig. 1 is a cross-sectional view of a shrinking sleeve applied around spliced optical fibers,

- Fig. 2 is a lateral view of important details of an oven for heating shrinking sleeves,

- Fig. 3 is a perspective view of a tensile testing machine for testing optical fibers com- 5 prising an oven for heating shri---king sleeves that is mounted to the machine,

- Fig. 4 is a perspective view of an oven having a lid obliquely folded up for heating shrinking sleeves,

- Fig. 5a is a view from above of a metal block being part of an oven for heating shrinking sleeves, and o - Fig. 5b is a section through the metal block of Fig. 5a. DETAILED DESCRIPTION

In Fig. 3 a tensile testing machine 11 for testing the tensile strength of splices between optical fibers 13 is shown. The tensile testing machine comprises tension rollers 15 around which portions of two fibers spliced to each other can be rolled up to be fixedly s applied without sliding thereon. At least one of the rollers 15 can be operated by a motor/motors, not shown, to be rotated and thereby stretch the free splice portion of the fibers 13 located between the rollers. Thereby it can be tested and established that the splice can be submitted to some preset tensile load without breaking. Alternatively, linear clamps, not shown, similar to ordinary fiber clamps, can be used instead of the rollers o 15. Such linear clamps are then in the testing operation instead displaced with a linear movement away from each other.

In the space between the fiber clamps or the tension rollers 15 an oven 17 is placed that ϊs intended for heating a shrinking sleeve 1, see Fig. 1, for protecting a naked splice portion of optical fibers spliced to each other. The structure of the ovens also appears 5 rom Figs. 2, 4, 5a and 5b. It comprises as its main part a profiled metal block 19 generally made to have the shape of rectangular block which has a rather deep groove 21 or slot in its upper, substantially flat surface. The groove 21 is located so that the splice portion of two spliced fibers is placed approximately at or a little above the bottom of the groove when the fibers are held by the fiber clamps 15 or have been somewhat detached 0 therefrom. The groove has such a depth that the fibers and a shrinking sleeve placed thereon are completely enclosed by the groove, below the upper surface of the metal block. An electric control unit 23 for the oven 17 is arranged in a separate casing that is located at a distance of the oven as in the embodiment shown, having the oven arranged on the top side of the casing of the tensile testing machine 11, on a side surface of the 5 casing of the machine. The control unit and the oven are interconnected by electrical cables, not shown.

The metal block 19 of the oven has at its two opposite, vertical side surfaces that are parallel to the longitudinal direction of the groove 21, resistive or ohmic heater elements 23, having the shape of rectangular plates and being in a tight, heat transferring contact with the side walls of the block. A transparent lid 25 is by a hinge mounted to an edge of the block that is located between such a side surface and the top surface of the block. The lid 25 can be swung up to an unfolded position to make the interior of the groove 21 accessible and be swung down to a folded down position for protecting a splice portion and the shrinking sleeve 1 placed around it, in the final mounting thereof. The fact that the lid 25 is made from transparent material allows an operator to observe the process of heating a shrinking sleeve 1 and to then check that the sleeve is mounted in the intended manner. The lid 25 can be held in the folded-down position by magnets 27 mounted in the lid and cooperating with soft magnetic material in the oven block 19. Furthermore, the substantially flat lid 25 has at its one end a downwards protruding projection 29 that is provided with a rubber cushion 31 at is lower surface. The rubber cushion can cooperate with lower support element 33 machined in the block 19 at one end of the groove 21. When the lid 25 is swung down and is held in a swung-down position by the magnets 27, the rubber cushion 31 can press against the spliced fibers at a po- sition at a distance from the splice to retain the fibers during the heating of the shrinking sleeve.

In the block 19 a recess 35 is provided extending parallel to the groove 21 and containing a temperature sensor, not shown. It is by cables, not shown, connected to the control unit 23 to allow it to supply the heater elements 23 with a suitably adapted cur- rent during the heating step.

The shape of the groove 21 appears from Figs. 3, 5a and 5b. It has a symmetric shape around a center plane extending perpendicularly to the upper surface of the block 19. At the top the groove has parallel side surface 37 located perpendicular to the top surface of the block 19. They connect to intermediate surfaces 39 that at their bottoms connect to a bottom surface 41. The bottom surface is substantially parallel to the top surface of the block and is in its central portion, taken in the longitudinal direction of the groove, recessed. The recessed portion gives room to the shrinking sleeve when it is moved to its correct place over the splice portion of the fibers. The intermediate surfaces 39 are in their central portion designed as flat, sloping surfaces which can be located in an angle of for example about 30° in relation to the upper side walls 37 of the groove. The central portions of the intermediate surfaces then form a wedge-shaped space supporting the shrinking sleeve and being in contact with it when it is placed on its correct position to be heated. The lateral portions of the intermediate surfaces 39 can have a concave, hollow and round shape. At the top edges of the groove, on the top surface of the block visual indications 43 are provided, see Fig. 5a, in order to facilitate the introduction of the fibers with their splice portion centrally in the oven and also for placing the shrinking sleeve in a central position in the oven.

While specific embodiments of the invention have been illustrated and described herein, it is realized that numerous additional advantages, modifications and changes will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details, representative devices and illustrated examples shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents. It is therefore to be understood that the appended claims are intended to cover all such modifications and changes as fall within a true spirit and scope of the invention.

Claims

1. A tensile testing machine for testing tensile strength of optical fibers spliced to each other comprising

- pulling blocks for holding the optical fibers at the sides of a splice so that the portion of the fibers between the pulling blocks is substantially straight and extends substantially freely and the splice is part of this portion and is located between the pulling blocks, and

- an oven for heating a shrinking sleeve for protecting a splice between two optical fibers, the oven including a metal block having an upper surface, in which a groove- shaped space is made and is so located that for spliced fibers held by the pulling blocks the portion of the fibers between the pulling blocks and a sl-ri-nking sleeve placed over the splice are located in the groove-shaped space, characterized in that the groove-shaped space is made to have a relatively large depth so that said portion of the fibers with the shrinking sleeve is located completed inside the groove-shaped space and below the top surface and has a distance from its upper surfaces to the upper surface that at least is larger than the diameter of the sl-ri king sleeve.

2. A tensile testing machine according to claim 1, characterized in that the groove- shaped space has such a large depth and such a width that said portion of the fibers with the shrinking sleeve is surrounded by the walls of the groove-shaped space over an angle of at least 120° taken around the longitudinal axes of the fibers and the shrinking sleeve.

3. A tensile testing machine according to claim 1, characterized in that the groove- shape space at its central portion, taken in the longitudinal direction of the groove-shaped space has a bottom surface that is recessed in relation to the bottom surfaces at the ends of the groove-shaped space so as to in the central region give room to said shrinking sleeve placed over a splice and introduced in the groove-shaped space.

4. A tensile testing machine according to claim 1, characterized in that the groove- shaped space at its central portion has sloping side surface forming a wedge-shaped space, so that the sloping side surfaces come in contact with a shrinking sleeve introduced in the groove-shaped space.

5. A tensile testing machine according to claim 1, characterized in that the metal block has side surfaces substantially perpendicular to the top surface and parallel to the longitudinal direction of the groove-shaped space, plate-shaped heater elements arranged in a direct contact with the side walls for heating the metal block and thereby heating a shrinking sleeve introduced in the groove-shaped space.

6. A tensile testing machine according to claim 1, characterized by a lid mounted by a hinge to the top surface for closing the groove-shaped space in a heating operation and movable between a swung-up position and a swung-down position, the lid having at least one projection that in the swung-down position of the lid acts against fibers introduced in the groove-shaped space for retaining them.

7. A tensile testing machine according to claim 6, characterized in that the lid is transparent.

8. A tensile testing machine according to claim 1, characterized in that the pulling blocks include tension rollers, around which portions of fibers can be wound to be held at the tension rollers, at least one of the tension rollers being arranged to be rotated so as to tension the fibers between the tension rollers.

9. A tensile testing machine for testing tensile strength of optical fibers spliced to each other comprising

- an oven for heating a slm-----άng sleeve for protecting a splice between two optical fibers, the oven including a groove-shaped space so located that for spliced fibers hold by the pulling blocks the portion of the fibers between the pulling blocks and a shrinking sleeve placed over the splice are located in the groove-shaped space, characterized in that the pulling blocks comprise tension rollers around which portions of fibers can be wound to be held at the tension rollers, at least one of the tension rollers being arranged to be rotated so as to tension the fibers between the tension rollers.