GB2096348A

GB2096348A - Terminations for fibre-optic monofilaments

Info

Publication number: GB2096348A
Application number: GB8204911A
Authority: GB
Original assignee: Elliott Brothers London Ltd
Current assignee: Allard Way Holdings Ltd
Priority date: 1981-03-18
Filing date: 1982-02-19
Publication date: 1982-10-13

Abstract

A termination for a fibre optic monofilament comprising a collet consisting of two parts. A tapered male part 11 has an axial bore 17 through which the monofilament is threaded, and an axial slit which defines a pair of jaws 23 which extend from one end 21 of the male part. A complementary tapered female part 13 surrounds the male part and has a radial force/flexure characteristic so that, as a result of relative axial movement between the two parts, an elastic radial expansion of the female part occurs, the female part then exerting a force on the male part so as to deflect the jaws of the male part into frictional engagement with the monofilament. <IMAGE>

Description

SPECIFICATION Terminations for fibre optic monofilaments This invention relates to terminations for fibre optic monofilaments.

In a known such termination the jaws of the male part of a collet are under radial pressure from a cincture of a shape and size memory effect material and are held apart by a heat softenable spacer material. When heated the spacer material softens and the cincture contracts in girth towards a "remembered" state and in contracting deflects the jaws so that they grip a fibre optic monofilament threading the male part.

The possibility exists with the termination referred to above that excessive compression forces may be applied to the monofilament and a liability to filament fracture may as a consequence arise. Whilst this may be avoided or mitigated by closer control of manufacturing tolerances such control would necessarily entail higher manufacturing costs. It is an object of the invention to provide a termination for a fibre optic monofilament wherein this problem is alleviated.

According to the invention a termination for a fibre optic monofilament incorporates a collet including: a male part having an axial bore and an externally tapered portion formed with a slit defining longitudinally extending jaws which extend from one end of said male part: and a complementary internally tapered female part which surrounds at least the jaws of the male part and which, by virtue of having been radially expanded by being moved axially relative to the male part with the tapered surfaces of the two parts in engagement, exerts an inwardly directed radial force on the jaws of the male part, thereby to cause said jaws to frictionally engage a fibre optic monofilament threaded through said axial bore.

In one particular embodiment the jaws have weakened portions at intervals along their length so that under the radial force of the female part the jaws hinge at the weakened portions.

One termination in accordance with the invention will now be described, by way of example, with reference to the accompanying drawing which is a prespective view of a collet used in the termination.

Referring to the drawing, the collet has a male part 11 and a female part 13. The male part 11 has a conically tapered external surface 1 5 and there is an axial passage 17 through the part capabie of being threaded with the fibre optic monofilament (not shown) to be terminated. A slit 1 9 extending from one end 21 of the male part defines a pair of jaw parts 23. There are annular grooves 23a, 23b formed at intervals around the male part. A portion of the male part remote from the end 21 is stepped so as to provide a shoulder 25.

The female part 13 has a complementary conically tapered internal surface 27. A collar 29 is provided on the female part 1 3 for facilitating engagement of the part by a suitable tool (not shown) for the purpose of driving the female part lengthwise of the male part, until the collar 29 engages the shoulder 25.

The female part 1 3 has a radialy force/flexure characteristic such that it expands elastically as a result of relative axial movement of the two parts and the consequential contact between the two complementary mating surfaces 1 5, 27. The inwardly radially acting force deflects the jaws 23 of the male part 11, the jaws hinging at the annular grooves 23a, 23b, so as, with a monofilament threaded through the passage 17, the monofilament is gripped at least at portions distributed along the length of the jaws if not substantially continuously along the jaws.

The radial force causing the monofilament to be gripped must not be so great as to be liable to damage the monofilament but at the same time should produce a frictional engagement between the jaws and the monofilament capable of withstanding a pull of between approximately eighteen and forty-five Newtons.

The complementary tapers may be such that with the collar 29 in contact with the shoulder 25 the stress in the female part 13 is below the elastic limit but it may be advantageous to choose the material and the radial dimensions of the female part such that though the yield point of the female part is exceeded in driving the collar 29 up to the shoulder 25 the resultant radial force on the monofilament is yet within the desired range.

In one particular collet as described by way of example the male and female parts 11 and 13 consist of brass and have tapers of 20, and the female part 13 has a wall thickness of 0.076 millimetres.

When monofilaments terminated in such collets are subjected to tension, the monofilament breaking force is found to be not less than 26 Newtons and the breakage of the monofilaments appears to follow no recognizable pattern. Failure appears to be likely to occur at any fault locus along the monofilament. The presence of the collet does not appear to give rise to any increase in liability to fracture within the collet.

The pull strength is not measurably affected by repeated temperature cycling of the collet through a temperature C to + 1 250C.

It may be desirable to employ a collet of, say stainless steel; and in such event the female part would be of even smaller radial thickness or it might, if this should prove to be advantageous, be in the form of a C-spring.

Further the male part may be of a moulded plastics material, for example, a fluorinated polyurethane. A male part made from such material has the advantage of being devoid of machine marks. Such marks are known to be liable to create sites in tahe monofilament from which cracks may propagate and failure occur.

Claims

1. A termination for a fibre optic monofilament incorporating a collet which includes: a male part

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Terminations for fibre optic monofilaments This invention relates to terminations for fibre optic monofilaments. In a known such termination the jaws of the male part of a collet are under radial pressure from a cincture of a shape and size memory effect material and are held apart by a heat softenable spacer material. When heated the spacer material softens and the cincture contracts in girth towards a "remembered" state and in contracting deflects the jaws so that they grip a fibre optic monofilament threading the male part. The possibility exists with the termination referred to above that excessive compression forces may be applied to the monofilament and a liability to filament fracture may as a consequence arise. Whilst this may be avoided or mitigated by closer control of manufacturing tolerances such control would necessarily entail higher manufacturing costs. It is an object of the invention to provide a termination for a fibre optic monofilament wherein this problem is alleviated. According to the invention a termination for a fibre optic monofilament incorporates a collet including: a male part having an axial bore and an externally tapered portion formed with a slit defining longitudinally extending jaws which extend from one end of said male part: and a complementary internally tapered female part which surrounds at least the jaws of the male part and which, by virtue of having been radially expanded by being moved axially relative to the male part with the tapered surfaces of the two parts in engagement, exerts an inwardly directed radial force on the jaws of the male part, thereby to cause said jaws to frictionally engage a fibre optic monofilament threaded through said axial bore. In one particular embodiment the jaws have weakened portions at intervals along their length so that under the radial force of the female part the jaws hinge at the weakened portions. One termination in accordance with the invention will now be described, by way of example, with reference to the accompanying drawing which is a prespective view of a collet used in the termination. Referring to the drawing, the collet has a male part 11 and a female part 13. The male part 11 has a conically tapered external surface 1 5 and there is an axial passage 17 through the part capabie of being threaded with the fibre optic monofilament (not shown) to be terminated. A slit 1 9 extending from one end 21 of the male part defines a pair of jaw parts 23. There are annular grooves 23a, 23b formed at intervals around the male part. A portion of the male part remote from the end 21 is stepped so as to provide a shoulder 25. The female part 13 has a complementary conically tapered internal surface 27. A collar 29 is provided on the female part 1 3 for facilitating engagement of the part by a suitable tool (not shown) for the purpose of driving the female part lengthwise of the male part, until the collar 29 engages the shoulder 25. The female part 1 3 has a radialy force/flexure characteristic such that it expands elastically as a result of relative axial movement of the two parts and the consequential contact between the two complementary mating surfaces 1 5, 27. The inwardly radially acting force deflects the jaws 23 of the male part 11, the jaws hinging at the annular grooves 23a, 23b, so as, with a monofilament threaded through the passage 17, the monofilament is gripped at least at portions distributed along the length of the jaws if not substantially continuously along the jaws. The radial force causing the monofilament to be gripped must not be so great as to be liable to damage the monofilament but at the same time should produce a frictional engagement between the jaws and the monofilament capable of withstanding a pull of between approximately eighteen and forty-five Newtons. The complementary tapers may be such that with the collar 29 in contact with the shoulder 25 the stress in the female part 13 is below the elastic limit but it may be advantageous to choose the material and the radial dimensions of the female part such that though the yield point of the female part is exceeded in driving the collar 29 up to the shoulder 25 the resultant radial force on the monofilament is yet within the desired range. In one particular collet as described by way of example the male and female parts 11 and 13 consist of brass and have tapers of 20, and the female part 13 has a wall thickness of 0.076 millimetres. When monofilaments terminated in such collets are subjected to tension, the monofilament breaking force is found to be not less than 26 Newtons and the breakage of the monofilaments appears to follow no recognizable pattern. Failure appears to be likely to occur at any fault locus along the monofilament. The presence of the collet does not appear to give rise to any increase in liability to fracture within the collet. The pull strength is not measurably affected by repeated temperature cycling of the collet through a temperature C to + 1 250C. It may be desirable to employ a collet of, say stainless steel; and in such event the female part would be of even smaller radial thickness or it might, if this should prove to be advantageous, be in the form of a C-spring. Further the male part may be of a moulded plastics material, for example, a fluorinated polyurethane. A male part made from such material has the advantage of being devoid of machine marks. Such marks are known to be liable to create sites in tahe monofilament from which cracks may propagate and failure occur. Claims

1. A termination for a fibre optic monofilament incorporating a collet which includes: a male part having an axial bore and an externally tapered portion formed with a slit defining longitudinally extending jaws which extend from one end of said male part; and a complementary internally tapered female part which surrounds at least the jaws of the male part and which by virtue of having been radially expanded by being moved axially relative to the male part with the tapered surfaces of the two parts in engagement exerts an inwardly directed radial force on the jaws of the male part, thereby to cause said jaws to frictionally engage a fibre optic monofilament threaded through said axial bore.

2. A termination according to Claim 1 in which said jaws have weakened portions at intervals along their length so that under the radial force of the female part the jaws hinge at the weakened portions.

3. A termination according to Claim 1 or Claim 2 in which said male and female parts are made from brass.

4. A termination according to Claim 1 or Claim 2 in which said male and female parts are made from stainless steel.

5. A termination according to Claim 4 in which said female part is in the form of a C-spring.

6. A termination according to Claim 1 or Claim 2 in which said male part is made from a moulded plastics material.

7. A termination according to any one of the preceding claims in which a portion of said male part remote from said end is stepped to provide a shoulder which engages a collar on said female part.

8. A termination according to Claim 7 in which said collar is adapted for engagement by a tool for the purpose of moving the female part axially relative to the male part.

9. A termination for a fibre optic monofilament substantially as hereinbefore described with reference to the accompanying drawing.

1 0. A collet for use in a termination according to any one of the preceding claims.