Laying of optical waveguides onto a support filament

Laying optical waveguides into sinuous grooves of a support filament while holding the grooves in the same position as the filament passes through a waveguide laying station by causing the filament to twist in oscillatory fashion during passage through the station. The grooves are held in the same positions by positionally fixed guide projections located in the grooves. By this laying method, the waveguides themselves are not oscillated around the support filament as they are fed into the laying station. Also, guide elements to feed the waveguides into the grooves extend downstream to a wrapping station whereby tape wrapped around the support filament also is wrapped around the guide elements. The waveguides exit from the guide elements after the tape has been wrapped.

This invention relates to the laying of optical waveguides onto a support 
filament. 
Suggestions have been made in the manufacture of optical cable to locate 
optical waveguides in a grooved support filament. In U.S. Pat. No. 
4,205,899, granted June 3, 1980 to F. D. King and T. S. Swiecicki, there 
is described an optical cable with a grooved support or central filament 
in which the grooves are helical, i.e. they change hand along the length 
of the filament. Hence the grooves are sinuous. To manufacture the cable, 
the filament is extruded by an extrusion unit provided at the die orifice 
with radially inwardly extending fingers which form the grooves in the 
filament during extrusion. To introduce the sinuous form to the grooves, a 
twist unit is located downstream from the extrusion unit and this twist 
unit oscillates in one direction and then the other direction alternately 
while holding the filament, thereby causing the filament to twist 
immediately it leaves the extrusion unit. Waveguides are then located in 
the grooves by being passed through a reciprocal plate which surrounds the 
path of the support filament, the waveguides extending along guide fingers 
or tubes radially inner ends of which are disposed within the grooves. As 
the filament passes through the reciprocal plate, the plate is caused to 
rotate by engagement of the fingers within the grooves, the location and 
path of the grooves dictating the reciprocating motiion of the plate. In 
other U.S. patents granted to F. D. King and T. S. Swiecicki, namely U.S. 
Pat. Nos. 4,154,049 and 4,195,468 granted May 15, 1979 and Apr. 1, 1980 
respectively, the waveguides are fed into the grooves of the support 
filament in the same manner as in the U.S. patent just discussed. 
It is known in practice that difficulties are caused by the use of the 
reciprocating plate in that as the waveguides pass through the plate and 
down into the grooves, they are caused, at the plate position, to rotate 
around the filament with the plate thereby drawing lengths of filament 
upstream from the plate radially inwards towards the filament and thus 
towards contact with the filament. Upon contact with the filament in this 
position it is known that there is a tendency for the waveguides to be 
drawn by the filament towards the centre of the plate instead of being fed 
along their predetermined paths through the plate and down the tubes. 
Obviously, if this is allowed to happen, it could result in broken or 
distorted waveguides and stoppage of the machine to disentangle the 
waveguides from each other and from the support filament. Hence, it is 
always necessary for an operator to keep a watchful eye on the position of 
the waveguides as they move towards the reciprocating plate to ensure that 
the laying in procedure is followed correctly. It would be an advancement 
in the art, therefore, if some way could be found to avoid the possibility 
of the above problem arising. 
A further problem which arises is caused by the wrapping of the support 
filament carrying the laid waveguides, with binding tape. After the 
waveguides are laid, the filament passes through a binding station in 
which binding tape is wrapped around the filament from a spool surrounding 
the feed path of the filament. If, as sometimes occurs, the waveguides are 
more loosely laid into the grooves than is desirable, they may project 
above the grooves. As the binding tape is wrapped around, it happens that 
a projecting waveguide is forced by the tape around the adjacent rib 
formation of the filament to be nipped between tape and filament. Such a 
poor wrapping operation obviously does not protect the particular 
waveguide in the desired manner and may deleteriously affect its 
attenuation properties. 
According to the present invention, there is provided a method of laying 
optical waveguides into grooves of a support filament wherein the grooves 
extend sinuously along the support filament comprising passing the 
filament through a waveguide laying station while holding the filament to 
retain each of its grooves substantially in the same angular position, 
with respect to a datum, around the longitudinal axis of the filament by 
providing an oscillatory twist in the filament upstream and downstream of 
the laying station, the degree of twist dependent upon the sinuous path of 
the grooves, and laying the filaments into the grooves at the laying 
station. 
The above method is conveniently put into practice by engaging the grooves 
of the filament, as it passes through the laying station, by groove guide 
projections which are held in position around the support filament and 
engage with the grooves. Hence the grooves are forced to pass through the 
laying station at the position of the projections whereby the filament is 
caused to twist alternatively in one direction and then the other as 
defined in the last preceding paragraph. 
According to the invention also, apparatus is provided for laying optical 
waveguides into sinuous grooves of a support filament comprising a laying 
device disposed around a feed path for the support filament, the device 
comprising a plurality of elongate guide elements extending inwardly of 
the feed path to guide waveguides into the grooves, and groove guide 
projections upstream of the inner end of the guide elements, the guide 
projections secured in fixed positions, with respect to a datum, around 
the feed path and extending inwardly to engage within grooves of the 
filament and hold the grooves in said fixed positions of the guide fingers 
as the filament passes the guide fingers. 
In practice as the support filament moves through the laying device it is 
twisted to retain the grooves in the fixed positions as dictated by the 
guide projections. As soon as the support filament has passed the laying 
device, it commences to untwist so that the grooves immediately move back 
towards their normal sinuous positions upon the untwisted support 
filament. Hence, as the support filament moves downstream of the laying 
device, the grooves immediately commence to wander away from their fixed 
positions relative to the longitudinal axis of the filament. It follows 
that the inner ends of the guide elements may need to move over an 
extremely small angle around the feed path alternately in one direction 
and then the other to lay the waveguides into the grooves as they start to 
move back to their normal sinuous positions. This movement may be provided 
by securing the guide elements to an oscillatory support element disposed 
around the feed path so that the guide elements follow the slight angular 
movement of the grooves. This slight angular movement will of course not 
create any problem with the waveguides upstream of the laying device as 
there is insufficient oscillatory movement of the waveguides to cause them 
to move substantially towards the support filament whereby contact between 
the support filaments and the waveguides upstream of the laying device is 
completely avoided. 
It is preferred, however, to mount the elongate guide elements in fixed 
positions in the laying device for simplicity of design and operation. 
Hence, the waveguides will more continuously from the upstream position 
towards the laying device along fixed paths in which there is no 
oscillating movement around the support filament imparted to the 
waveguides. In this particular construction, it is essential that the 
inner end portions of the guide elements are flexible. This enables them 
to move one way and then the other in the grooves in which they lie to 
maintain their positions within the grooves as they commence to move back 
to their normal sinuous positions upon the filament as this untwists upon 
leaving the laying device. 
In the above method and apparatus, it is desirable for the inner end 
portions of the guide elements to extend along the grooves beyond a 
binding tape wrapping station. In this case, the binding tape is caused to 
be wrapped also around the inner end portions of the guide elements. As 
the support filament moves along its path from the wrapping station, the 
wrapped tape moves from the end portions of the guide elements at which 
point, the waveguides emerge and are placed into the grooves. Hence, upon 
the waveguides issuing from the guide elements, they are immediately 
covered by the wrapped tape which has been previously applied. Ideally of 
course, the inner ends of the guide elements, should be completely within 
the grooves so as not to be contacted by the wrapped tape. Thus movement 
of the tape off the guide elements is not resisted by any frictional 
contact and the wrapped tape does not become loose upon the support 
filament. 
According to a further aspect of the present invention, there is provided a 
method of laying optical waveguides into grooves of a support filament 
comprising guiding the waveguides into the grooves by passing them along 
tubular guide elements which extend radially inwardly and axially of a 
feed path for the support filament, wrapping the support filament with 
binding tape in a tape wrapping station, the binding tape being wrapped 
around the filament and radially inner ends of the guide elements which 
extend along the feed path as far as the wrapping station and lie 
completely within the grooves, and continued movement of the support 
filament along the feed path causing the waveguides to issue from the 
guide elements after the tape has been wrapped around the filament. 
Also, according to yet another aspect of the invention, apparatus is 
provided for laying optical waveguides into grooves of a support filament 
comprising a laying device disposed around the feed path for the support 
filament and a tape wrapping station disposed downstream of the laying 
device for wrapping binding tape around the filament, the laying device 
comprising a plurality of tubular guide elements to guide waveguides into 
the grooves, the tubular guide elements extending along the feed path and 
having radially inner ends for waveguide exit disposed downstream of the 
elements, said inner ends extending at least as far as the tape wrapping 
station.

As shown by FIG. 1, apparatus for laying optical waveguides onto an 
extruded plastic support filament during optical cable manufacture 
comprises a laying device 12 disposed in a waveguide laying station along 
a feed path for the filament. 
A set of optical waveguides 16 are fed from an upstream position and 
through a replacement spool 18 holding binding tape and carried by a 
replacement spool support means 20. The replacement spool 18 is to replace 
a spool 22 disposed in the binding station slightly downstream from the 
laying device 12, when the spool 22 has been used. 
The laying device 12 comprises a holding means comprising two yolks 24 as 
shown in FIG. 2. These yolks are carried by a supporting structure 26 to a 
support plateform 28 and are pivotally mounted so as to be moved from a 
closed position as shown in FIG. 2 to an open position (not shown) in 
which the replacement spool 18 is movable along the filament 10 into the 
position occupied by the spool 22 as shown in FIG. 1. This construction, 
which will not be described further in this specification, is according to 
the invention described and claimed in U.S. application Ser. No. 208,565 
filed Nov. 20, 1980, now U.S. Pat. No. 4,309,866, entitled "Laying and 
Binding Optical Waveguides Onto A Support Filament" in the name of Miguel 
Fombollida. 
As shown by FIGS. 2 and 3, the yolks 24 of the laying device securely hold 
a laying unit 30 in the laying station. This unit 30 comprises an annular 
housing 32 within which is a bearing 34 rotatably mounting a short tube 36 
having a large diameter passageway 38 at its upstream end terminating in a 
radial shoulder 40. This larger diameter passageway houses a die 42 which 
abuts against the shoulder 40. As shown by FIG. 2, the die 42 is provided 
with three equally spaced apart flat depressions 44 in its peripheral 
surface and these depressions are occupied by location pegs 46 
screw-fitted radially inwardly through the tube 36. Thus the die is held 
in position relative to the tube. As shown by FIG. 2, the die has a 
substantially circular orifice 48, the periphery of which is interrupted 
by three equally spaced apart groove guide projections 50 which extend 
inwardly slightly into the orifice. These projections are provided for 
engagement with alternative grooves 52 formed in sinuous fashion along the 
support filament 10, as will be described. The die also holds six elongate 
guide elements for laying waveguides into each of the six grooves of the 
support filament and, for this purpose, is formed with six equally spaced 
apart holes 54 which are inclined towards the feed path of the support 
filament as it passes downstream through the die, as shown in FIG. 3. Each 
guide element comprises a flexible plastic tube 56 which extends through 
its associated hole 54 radially inwardly towards the feed path of the 
support filament as it passes downstream through the die, as shown in FIG. 
3. Each guide element comprises a flexible plastic tube 56 which extends 
through its associated hole 54 radially inwardly towards the feed path of 
the support filament, the tube being held securely in position within its 
hole by a rubber sheath 58 closely surrounding the tube and fitting 
tightly within the hole. 
Hence, the tube 36 and die 42 are rotatable together within the housing 32 
by means of a bearing 34 unless restrained from doing so. However, it is 
an important aspect of the invention that the grooves of the support 
filament as they pass through the laying device are retained in fixed 
positions around the axis of the filament with respect to any chosen 
datum. To enable this to be achieved, means is provided to secure the 
guide projections 50 also in fixed positions with respect to the datum 
during use of the apparatus. This is achieved by holding the tube 36 and 
die 42 non-rotatably in the housing. The means for securing the tube and 
die non-rotatably in position also provides a means to adjust the location 
of tube and die between one fixed position and another around the axis of 
the support filament to enable the projections 50 to be located in the 
median position of movement of the grooves along the filament so as to 
effect substantially equally twisting of the filament, first in one 
direction and then the other. This securing and adjusting means comprises 
a ring 60 which abuts against the upstream end 62 of the housing 30, and 
comprises two abutment projections 64 which are closely spaced apart so as 
to accept between them a location peg 66 which extends outwardly from the 
tube 36 whereby any rotational movement of the tube and die is prevented 
as shown clearly by FIG. 2. The ring is detachably held in position by 
three securing clamps 68 which extend inwardly from the surface 62 of the 
housing and are normally secured thereto by three screws 70. Loosening of 
the screws and thus of the clamps enables freedom of movement of the ring 
so that it may be rotated into any position of adjustment in which 
position the peg 66 is held securely when the screws are retightened. 
Finally, on constructional details, as shown by FIG. 3, each tube 56 has a 
downstream waveguide exit end portion 72 which extends sufficiently far to 
reach at least to the wrapping station 74 in which binding tape 76 
actually contacts the filament 10 from spool 22 as it is wrapped onto the 
filament. The exit end portions 72 pass beyond the station 74 as shown. 
In use of the apparatus, the support filament is fed along the feed path as 
shown in FIG. 1 and through the die as shown in FIGS. 2 and 3. After 
passing through the laying device 12, the binding tape 74 from the spool 
22 is wrapped around the filament which is already laid with the 
waveguides in position, and thus the binding tape holds the waveguides in 
the grooves. As shown by FIG. 3, as the support filament passes through 
the die 42, the tubes 56 enter into the grooves and guide the waveguides 
from the tubes into the grooves whereby the waveguides are laid in 
position. As the support filament passes through the die 42, the three 
projections 50 engage with three of the grooves 52. As the projections 50 
are not rotatable, then the support filament is twisted first in one 
direction and then the other alternately and this twisting action takes 
place from the upstream end from its release position from a reel and then 
to a downstream position beyond the spool 22 at which it is reeled with 
the waveguides and binding tape in position. Hence, the distance upstream 
and downstream from the laying device along which the twisting action must 
take place is relatively long and torque placed upon the support filament 
is substantially small and may be ignored. 
The effect of maintaining the sinuous grooves in fixed positions as they 
pass through the laying device is that there is no need to rotate the 
guide elements 56 to feed the waveguides into the grooves and hence the 
waveguides themselves do not rotate around the support filament as they 
move from their upstream positions into the die 42. It follows that no 
problem arises with regard to twisting of the waveguides around the 
support filament leading to the possibility of the waveguides contacting 
the filament surface and thereby being drawn into the die with the support 
filament. Thus once the waveguides are disposed in position for laying 
into the grooves they are held fixedly in these positions until they 
actually lie in the sinuous grooves of the support filament. With the 
above invention, a further problem may be overcome with certain 
constructions. It is required to accommodate electrical conductors within 
the grooves of a support filament in addition to the waveguides. In such 
arrangements it is difficult to locate the electrical conductors in the 
grooves at the same time as the waveguides. This is because the conductors 
and waveguides are drawn into the grooves under different conditions of 
tension and as they oscillate normally during laying around the support 
filament, it is found that there is a greater risk of the conductors and 
waveguides contacting each other and being drawn into the die orifice with 
a support filament than is the case if waveguides are used completely on 
their own. It is clear that with the present invention and with the above 
described embodiment, because the oscillating movement of the die 42 is 
prevented, then where electrical conductors are also being laid into the 
grooves, then the lack of oscillatory movement does not permit either 
waveguides or electrical conductors to depart from their preset paths and 
this problem also cannot arise. 
Further, as shown by FIG. 3, the ends 72 of the guide tubes 56 lie 
completely within the grooves and because of the extended tube position, 
the binding tape 76 is actually wrapped around the tube exit end portions 
as well as the filament. Thus as the filament moves downstream, the 
wrapped tape does not contact the tube end portions but moves axially off 
them at which point the waveguides emerge from the tubes. Hence, when the 
waveguides actually move into the grooves away from the tubes 56, the 
binding tape is already wrapped around the filament and even if any 
waveguide is tending to move outwards from the groove, it cannot do so at 
this stage but is held in by the wrapping. 
Hence, the invention as shown by the above-described embodiment, clearly 
improves the procedure for laying in waveguides onto support filament 
during optical cable manufacture.