Note: Descriptions are shown in the official language in which they were submitted.
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Method of centeriny and fixiny a light-conducting fibre in a light
conductor termir~al r~nber, a light cor~uctor termir~1 rnember
produced by that method, and apparatus for carrying out the method
The preser~t invention relates to a method of centering and
fixing a light-conducting fibre in a light conductor ter~nal rne~ber
for optical coupling of two fibre ends, wherein the fibre from which
. the insulation has been removed is pushed into a centering cylinderwhich is provided with an axial bore for receiving the end of the
fibre, in such a way that the fibre projects somewhat beyond the end
of the centering cylinder or is substantially flush therewith.
i Such met'nods are used to achieve a high degree of precision in
$ optical plug connections, in order to avoid light losses due to fibre
ends not being precisely aligned relative to each other, in the coupling
' assembly. DE-OS No 26 54 537 for example already discloses such a
'~ method, wherein light is shon~'on to the free end of the fibre, thecone of light issuing from the fibre is measured by means of a
detector and the light--conducting fibre is secured by adhesive in the
15 centering cylinder, in an optimurn position as determined ky the detector.
Other methods use microscopes which represent the end of the centering
~f,
cylinder on an enlarged scale on an adjusted irMge screen. M~mipulatiny
I the fibre r~akes it possible to detern~ine the optimum position on the
ir~age screen, and the fibre is then glued in the centering cylinder
20 (Suæuki and Koyama in 'Review of the electrical communication' vo-lu
i 26, No 5-6, May/JIme 1978, pages 693 ff). Such methods are much tootime-consuming and complicated for the industrial manufacture of light
` conductor terminal members, as light must be applied to the fibre ends
and the fibre ends have to be manipulated. Another method is disclosed
in CA patent specification No 1 032 796. In accordance with that
publication, the centering cylinder is in the form of a hollow cylinder
with a bottom, which is partially filled with a plastic material. Then,
Ir" in successive working operations, the outside peripheral surface of the
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centeriny cylinder is turn~d down on a precision lathe and the aY.ial bore
is bored. After the fibre end is inserted into the axial bore, pressure
i5 applied to the plastic mat~rial in an axial direction so that the
axial bore form-lockingly or positively closes aro~md the fibre end
and fixes it in position. However, the disadvantage of that rnethod is
that the clearance between the axial bore and the fibre end must be
at a minimum, fran the outset, as otherwise there is no longer any
guarantee in reqard to fixing the fibre end in a central position. In
addition, that method is expensive as it involves a number of l~bour-intensive
working op~ra-tions such as producing a preform, filling the preform with
plastic material, turning off the preform, and so forth.
The problem of the present invention is therefore to provide a
me~hod of the kind set forth above, which avoids the disadvantages of the
known art and which permits light conductor terminal members to be
manufactured in a rational fashion. In particular, the method should also
be suitable for light-conducting fibres, the actual diarneter of which
exhibits substantial differences frorn the naninal diameter. According
to the invention, that problem is solved in that a guide sleeve is first
pushed over the centering cylinder and then a punch member having an
annular upsetting tool is pressed, in the guide sleeve, against the
end of the centering cylinder in such a way that the upsetting tool
concentrically surrounds the bore and the material is plastically
defonned around the fibre, wherein the end of the fibre is fixed
centrally with respect to the outside peripheral surface of the
centering cylin~er.
I-t will be seen that, by virtue of that procedure, at the sarne time
as the fibre end is fixed in position, it is also centered, as the upsetting
tool is guided directly at the outside surface of the~centering cylinder.
In that way, the axial bore rnay readily have considerable clearance
relative to the end of the fibre as the end of the fibre is centered in
~ the upsetting operation, even when the end of the fibre is initially in
- an eccentric position in the axial bore. The relatively large clearance
between the bore and the fibre facilitates insertion thereof and ~akes it
unnecessary accurately to determine the fibre diameter. Fibres with large
tolerance fluctuations can also be readily used.
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If the e~ of the centering cylinder is ground after the upsetting
operation, the annular ridges or beads which are possibly produced by
the upsetting process are removed and the fibre is absolutely flat with
the centering cylinder.
It is particularly advantageous if, before the upsetting operation,
the light-conducting fibre is secured to the centering cylinder by adhesive,
at the insulation around the ibre. By virtue of that arrangement,
on the one hand, the fibre is additionally fixed in place and, on the
other hand, the adhesive location provides protection against the penetration
of moisture and dirt.
The invention also relates to a light conductor terminal member
which is pr~du~ed in accordance with the above-indicated method. ~uch
a light conductor terminal member has particularly advantageous properties
if the end of the fibre is fixed and centered in the centering cylinder
k~ means of concentric upsetting of material, at the end thereof. The
concentric upsetting effect causes the fibre to be securely fixed in
place, the central ixing effect extending to a position directly at the
end of the centering cylinder. Further advantages are attained if the
centering cylinder comprises a hollow-cylindrical outer portion of
~0 relatively hard material, which is filled at least in the region of the
end thereof with a core portion which is made from plastically deforrnable
material. ~ light conductor termir~l member of that kind has orlly a small
nurnber of parts and rn~y be easily assembled. It will be seen that the outer
portion protects the sensitive and delicate fibre, while the core portion
permits easy processing. ~le parts are uncornp]icated and can be produced
in a finished condition, in a srnall number of working operations.
The light conductor terminal mernber is further samplified if the
core portion extends substantially over the entire length of the outer
portion and, besides the axial bore for accommodating the fibre end
fr~n which the insulation has been rernoved, it has a second ~ore of larger
diarneter, for acco~odating an insulation-bearing portion of fibre. In
that way, there is no need to provide an additional component, for
accom~odating the insulation-bearing -fibre portion. The insulation can be
secared directly to t e core portion by adhesive, there y making it
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impossible for the insulation to be torn out of the light conductor
terminal mernker.
Assembly is in particular facilitated, as already referred to above,
if the ~iarneter of the axial hore for accorr~dating the end of the fibre
is larger than the largest admissible fibre diameter.
It is particularly advantageous for the outer portion to be made
frorn hard metal or alloy or cerr~nted carbide. That rnaterialensures
a precise guiding action iJI respect of the upsetting tool or the guide
sleeve, as there is virtually no possibility of bending or buckling due
to a mechanical force acting thereon.
The upsetting process can be carried out in a particularly simple
manner and witho~lt the application of excessive force, if the core portion
cGmprises a relatively soft metal, preferably a metal alloy. Ideal
material properties can be achieved in a particularly simple rr~nner, by
using a metal alloy. Particular ease in assembly of the core portion is
attained if it is secured in the outer portion by soldering. Soldering
permits relatively high operating ternperatures. Depending on the use
involved, it will be appreciated that the core portion may also be
secured by being glued in position, by being pressed in position or even
by being cast in position.
The apparatus for carrying out the method is c}~racterised by a
guide sleeve which can be fitted on to the centering cylinder and by a punch
me~ber ~hich is displaceable in the guide sleeve and the end of which is
provided with an upsetting tool which has an annular upsetting edge, the
diameter of which is larger than the diameter of the axial bore in the
centering cylinder. In that arrangernent, the upsetting tool is guided k~
the outside surface of the centering cylinder. The outside surface of the
centering cylinder also later carries the coupling meJ~ber of the plug
connection which holds the two light conductor terminal mernbers together.
It will be seen that this ensures that the upsetting of material which is
produced by the upsetting tool, at the end of the centering cylinder, is
precisely concentric with respect to the outside surface of the centering
cylinder so that the fibre end also necessarily occupies that position.
An upsetting tool rnay be produced in a particularly simple manner
if it is a ring which is substantially wedge-shaped in cross-section,
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the tip of the wed~3e portion forrlling the upsettinc~ edge. Such a tool
may bè produced in a relatively simple manner. An upsetting effect
which goes deep into the centering cylinder may be attained if the wedge
angle is less than 90. In order to achieve a particularly high degree
5 of precision and in order to avoid rapid wear, it is advantageous for the
upsetting tool to be made from hard metal or alloy or cemented carbide.
An err~odiment of the invention is described in greater detail
hereinafter and illustrated in the drawings in which:
Figure 1 shows a view in cross-section on a greatly enlarged scale,
10 through a light conductor terminal member with the upsetting tool
applied thereto, after the upsetting operation,
Figure 2 shows a plan view on to the end of a light conductor
terminal member after the upsetting operation, and
Figure 3 shows a view on to the underside of an upsetting tool.
As shown in Figure 1, a light conductor terminal member 1 comprises
a hollow-cylindrical outer portion 10 of relatively hard material,
and a core portion 11 of relatively soft material. The outer portion 10
preferably cornprises hard metal or alloy or cemented carbide, but in
certain uses, may also be made fran another hard or hardened metal or
~ 20 even a hard plastics material. The core portion 11 comprises a plastically
i deforrnable metal or possibly a suitahle plastics material. Particularly
good results were achieved for example with a silver-bearing alloy. In
sorne uses, it is possible for the entire centering cyllnder 4 to be made
; from the same material which is plastically defonnable. It will be
25 appreciated that in -that case the diameter of the outer peripheral surface
14 would have to be such that the upsetting process does not cause any
deformation of the outside surface 14. ~t would also be possible for the
core portion simply to be formed as an insert at the end of the centering
cylinder.
The core portion 11 has a first axial bore 5 ~or accomrr~dating the
fibre end 2. A second bore 13 of larger diameter accornmodates a portion
of the light-cor~ucting fibre, which is provided with insulation 3.
m e light-conducting fibre is secured by adhesive to the core portion 11,
at the insulation 3, at an adhesive location 16. m e axial bore 15
35 already extends concentrically with respect to the outside surface 14 of
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the centering cylinder 4. 'I'he clearance between the axial kore 5
and the end 2 v~ the fibre hc~ever may be c~rrparatively large That
ensures ease of assernhly, even in the event of the end 2 of the
fibre exhibiting considerable deviations frorn the n~ninal diameter. In
5 order to illustrate the dirnensional conditions, a few irnportant dirnensions, in rnillirnetres, are set out below by way oE exarnple:
Fibre diameter at the fibre end 2 = 125 + 4 jU
Diameter of the axial bore 5 = about 135 y
Diarneter of the outside surface 14 = 3.5 rrrn + 0 - 1 JU
Concentricity of outside surface/axial bore -- less than 1~.
A concentric upsetting of rnaterial, as indicated at 12, is formed
at the end 9 of the centering cylinder 4, to fix and centre the fibre
end 2. A particularly substantial advantage with that arrangement is that
the fibre end 2 is also fixed and centered directly at the end. It
15 will be seen that, par-ticulæly in the plane of the end 2, a very high
degree of dimensional accuracy and a secure holding action must be
ensured in order to avoid light losses in the coupling assembly. The
upsetting of material at 12 does not in any way impair the coupling
mechanisrn, as the end 9 of the cylinder is ground and polished after
20 the upsetting operation. In that way, in the finished light conductor
terminal member, the light-conducting fibre is fixed at one end by the
`upsetting 12 of material and at the other end by the adhesive location
16.
I'he rnaterial upsettirlg operation is performed by mearls of a
25 rarn or punch men~er 7 which is guided in a highly accurate fashion in a
guide sleeve 6. I'he punch rnem~er 7 has an upsetting tool 8 which,
as can be seen in particular frc~n Figure 3, is in the`form of a ring.
It will be seen that the diarneter of the upsetting edge 15 must be larger
than the largest possible diameter of the axial b~re 5 The upsetting
30 tool 8 can either be directly integrated into the punch merr~er 7 or it
may be releasably secured to the punch m~T~er 7. Ihe punch merr~er 7
c~n ~e clamped in a conventional press.
Both the guide sleeve 6 and the upsetting tool preferably comprise
hard metal or cernented carbide.
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A light conductor terminal m~nbe~r assembly operation proceeds as
follows: firstly, a portion of the fibre is stripped of insulation 3,
thereby exposing an end 2 of the fibre. The end 2 of the fibre is then
pushed into a fully prepared centering sleeve, the end of the fibre
projecting beyond the end 9. The insulation is then fixedly joined to the
centering cylinder 4 by neans of the adhesive at 16. The end 2 of the
fibre is cut or broken off, about 30 to 50 ~u beyond the end 9.
When the light conductor tenninAl member has been prepared in that
way, it is then upset at its end. For that purpose, the guide sleeve 6
is fitted over the outside surface 14 of the centering cylinder. The
punch men~er 7 is pressed in the direction indicated by the arrcw A,
in the guide sleeve, against the end 9 of the centering cylinder. When
that is done, the upsetting edge 15 of the upsetting tool 8 penetrates
into the soft rnaterial of the core portion and produces plastic deformation
in the direction indicated by the arrow B. By virtue of the plastic
deformation, the core portion 11 form-lockingly or positively encloses the
end 2 of the fibre and fixes it in place. Any eccentricity of the end 2
of the fibre within the axial bore 5 is compensated by the annular upset
portion 12 so that, after the upsetting process, the er~ 2 of the fibre
is absolutely concentric with respect to the outs;de surface 14. The end
surface 9 is ~hen ground and polished so that the light conductor terminal
rnember may be provided with the remaining coupling m~bers (not sho~n in
the drawings).
It will be seen that the foregoing is an e~tremely rational assembly
process so that large quantities of light conductor terminal members can
be produced at low cost. The end 2 of the fibre is centered by means of
the upsetting tool 8 in a very simple manner, without ~he necessity for
complicated manipulation operations and measuring processes. The fact
that the fibre is simultaneously fixed without adhesive directly in the
- 30 region of the end face 9 ensures a very high degree of precision and a firm
hold. It will be seen that the absence of adhesive or synthetic resin
in the region of the end 9 also facilitates the subsequent operations
of grinding and polishing the end face.
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