Note: Descriptions are shown in the official language in which they were submitted.
~73~
This invention relates to the forming of cable core units.
It is known that the twisting of insulated electrical
conductors together to form twisted conductor units with a single
direction of twist offers physical and electrical advantages when used in
telecommunications cable cores. For example, the provision of twisted
conductor units improves electrical characteristics such as a reduction in
crosstalk. Normally a twisted conductor unit consists of two insulated
conductors twisted together as a twisted pair.
Conventionally, to twist conductors together in twisted
pairs, high speed twisting machines are used. In such twisting machines,
two lengths of insulated conductors are held upon reels which are freely
rotatably mounted upon reel shafts in a reel cable. To twist the
conductor lengths together, each length is fed from its reel, around a
rotatable pulley system and the lengths are then brought into side-by-side
positions in which they are caused to rotate by means of a flyer or other
framework, around an axis of the cradle. This rotation provides a double
twist in the conductors and thus forms the twisted pair. The twisted pair
is wound onto another reel immediately after twisting. After winding,
this reel is removed from the twisting machine and subsequently placed
with other reels of twisted pairs as supply to a machine to draw the
twisted pairs together to form a core unit. The twisted pairs are then
drawn through the core unit forming machine to provide a core unit of a
plurality of pairs, e.g. 50 or 100 pairs. ~ence, twisting into pairs is
performed as a separate operation and on a different machine from the core
unit forming machine.
While it may be a manufacturing aim to twist the conductors
into twisted pairs in tandem with the core unit forming operation, this
' ~
12173~5
is extremely difficult to achieve in practice for the following reasons.
During forming into core units, problems are found in drawing twisted
conductor pairs under substantially equal tensions into the core unit
forming machine when a tandem operation is followed at high line speeds,
e.g. in excess of 400 ft.~minute.
This is because the tensions induced into each twisted pair
as it is drawn into the core unit forming machine depend partly upon the
distance between the twisting head and the forming machine and upon the
amount of contact between the conductors and machine surfaces. Thus with
present knowledge, one theoretical way of reducing tension differences
would be to position all of the twisting heads at substantially equal
distances from the core unit forming machine. This is impractical, or
even impossible, when it is considered that cable core units may include
up to 100 twisted pairs of conductors. Design and floor space
considerations do not enable 100 twisting machines to be located at
substantially equal distances from the core unit forming machine. On the
other hand, the largely differing unequal tensions between twisted pairs
achieved with differently spaced twisting machines in a tandem operation
would result in great tension differences between twisted pairs after
forming into core units. In an attempt to relieve these tensions, the
core units would become uncontrollably contorted along their lengths.
Further processing of the units, e.g. to provide cable sheathing and
jacketing, would present insurmountable problems as the core units would
need to be non-contorted for these operations. In addition, the differing
tensions between the twisted pairs in the cable cause tightening together
of the conductors in some regions of the cable more than in others thus
~Z173~5
varying the spacing between the conductors. This effects variations in
mutual capacitance which is extremely undesirable in cable design.
In United Kingdom Patent No. 1,428,130, there is a
description of apparatus for twisting conductor pairs and for stranding
cable core units in a tandem operation. In this particular apparatus,
twisting machines are arranged in banks extending away from a stranding
machine and conductors are fed from these banks into the stranding
machines. There is no discussion in this prior specification concerning
the difficulties associated with different tensions or tension build-up in
the twisted pairs as they approach the stranding machine. Possibly the
reason for this omission is that as tension build-up increases with
operational speed and as this apparatus is built to operate at extremely
low line speeds, e.g. up to 220 ft./min., the problem of tension in the
twisted pairs is not sufficiently important to significantly affect the
finished product or its electrical performance.
This particular apparatus could not nullify any tension
differential effect between twisted pairs nor could it solve the problem
of excessive tension build-up in pairs approaching the stranding machine
in manufacture of a core unit at faster speeds, e.g. at around 600
ft./min.
In a further construction suggested in Canadian Patent
Application Serial No. 409,994, filed August 24, 1982, in the name of
J.N. Garner et al and entitled "Forming Cable Core Units", there is
described an apparatus for tandemizing the twisting and stranding
operation. With this arrangement, the twisting operation is performed by
oscillating a guide means, which may be in the form of tubes, to provide
twisted pairs of conductors. This apparatus, however, will only provide
l~i73~5
twisted pairs with alternating twist, i.e. with the twist extending first
in one direction around the pair and then in the other. This structure is
sometimes referred to as an 'S-Z' twist. This type of twist is relatively
unknown in cable design and its use in large multi-pair cables has yet to
be evaluated together with any attendant difficulties which may at present
be unknown. It is known, however, that there would be difficulty in
controlling the pitch of the twist in 'S-Z' twist cables and the tensions
in the twisted pairs. Varying tensions may have undesirable effects upon
the electrical characteristics of the cable and excessive tensions could
damage fragile conductor insulation. There are also potential mechanical
problems involved. With the use of a continuous direction of twist in
each pair, however, the pairs are potentially easier to handle.
The present invention is concerned with an apparatus for
tandemizing the operation of twisting units, e.g., pairs of conductors
with a continuous twist in one direction and then for forming a core unit
while avoiding or minimizing the problems discussed above regarding the
build-up of tension in the twisted pairs and the tension differences for
high speed operation.
Accordingly, the present invention provides an apparatus for
making a core unit of twisted units of individually insulated conductors
comprising:-
a plurality of twisting machines each for carrying a
plurality of reels of insulated conductors and for twisting
the conductors together to form a twisted unit;
a core unit forming and take-up means to draw the twisted
conductor units together to form a core unit;
. .
~2173~a~
drawing means to draw twisted units into the forming and
take-up means;
and along feedpaths between the twisting machines and the
core unit forming and take-up means, there is provided a
tension reducing means comprising rotatable members, and
drive means controlled to drive the rotatable members, said
drive means dependent upon the drive speed of the drawing
means to ensure that the unrestrained peripheral speed of
the rotatable members is in excess of the draw speed of the
twisted units into the forming and take-up means, lengths of
peripheral surfaces of the rotatable members presented to
the feedpaths being insufficient to impart a driven speed to
the conductors above that of the draw speed into the forming
and take-up means.
The core unit forming and take-up means may comprise a
stranding machine or a machine which merely groups the twisted units
together without stranding.
According to a further aspect, the invention provides
apparatus for making a core unit from twisted units of individually
0 insulated conductors comprising:-
a plurality of twisting machines each for carrying a
plurality of reels of insulated conductor and for twisting
the conductors together to form a twisted unit;
a core unit forming and take-up means in tandem with the
twisting machines to draw the twisted conductor units
together to form a core unit;
~Z173~5
the forming and take-up means comprising drawing means to
draw twisted units into the forming and take-up means; and
between each twisting machine and the forming and take-up
means, there is provided a tension equalizing means
comprising a rotatable member disposed along the feedpaths
of the twisted units, and drive means controlled to drive
the rotatable member, said drive means having a drive speed
dependent upon the drive speed of the drawing means to
ensure that the unrestrained peripheral speed of the
rotatable member is in excess of the draw speed of the
twisted units into the forming and take-up means, lengths of
the peripheral surface of the rotatable member presented to
the feedpaths being insufficient to impart a driven speed to
the twisted units above that of the draw speed into the
forming and take-up means.
In a preferred arrangement, the tension equalizing means
comprises rotatable members comprising drivable shafts surrounded by
tubular members which are in slipping drivable engagement therewith. To
provide the slipping drivable engagement, the tubular members may be held
in bearings upon the drivable shaft. In this construction it is intended
that the unrestrained peripheral speed of the tubular members should
exceed the draw speed of the unit into the forming and take-up means. For
this purpose, it may be necessary to provide packed grease between the
shafts and tubular members to increase the drive between them. The
tension equalizing means operates so that as twisted pairs of conductors
travel side-by-side across and in contact with the tubular members, the
rotational speeds of the tubular members are lessened compared to their
~173~S
unrestrained speeds and these lessened speeds are governed by a
combination of tensions and speeds in all of the conductor pairs passing
over the members.
To enable the equalizing means to operate, it is essential
to place the twisting machines in series so that the feedpaths for the
twisted pairs lie side-by-side and the tension equalizing means lies in
the paths of the twisted pairs as they approach the forming and take-up
means.
The invention further includes a method of forming a core
unit of twisted insulated conductor units comprising twistiny insulated
conductors together into a plurality of twisted insulated conductor units
with each unit having a single direction of twist along its length;
drawing the twisted units as they are being formed, through a core unit
forming and take-up means to form the core unit; and, as the twisted units
approach the forming and take-up means, reducing the tension in all of the
units by contacting them with a peripheral surface of at least one
rotating member disposed in a tension reducing station and driven at a
peripheral speed in excess of the draw speed into the forming and take-up
means while the draw speed applies tension to the units as they leave the
tension reducing station, peripheral surface contact with each unit in the
tension reducing station sufficient only to increase the speed of the
units towards, but not beyond, that of the draw speed.
The invention also includes a method of forming a core unit
of twisted insulated conductor units comprising:-
twisting insulated conductors together into a plurality of
twisted insulated conductor units with each unit having a
single direction of twist along its length;
~Z~73~
drawing the twisted units as they are being formed through a
core unit forming and take-up means to form the core unit;
and, as the twisted units approach the forming and take-up
means, reducing differences in tension between the units by
contacting them with the peripheral surface of a rotating
member to reduce its peripheral speed to a speed influenced
by a combination of tensions in all of the units upstream of
the rotatable member.
One embodiment of the invention will now be described by way
of example, with reference to the accompanying drawings in which:
Figure 1 is a plan view of main parts of apparatus for
forming a stranded core unit of 100 twisted insulated conductor pairs;
Figure 2 is a side elevational view of the apparatus of
Figure 1 in the direction of Arrow 'II ' in Figure 1;
Figure 3 is a plan view of twisting machines and tension
equalizing means forming part of the apparatus and shown on a larger scale
than in Figure 1;
Figure 4 is a cross-sectional view along line 'IV-IV' in
Figure 2, of a tension equalizing means and on the same scale as Figure 3;
Figure 5 is a side elevational view of a twisting machine
and tension equalizing means taken in the direction of arrow 'V' in
Figure 3;
Figure 6 is a side elevational view of a tension reducing
means of the apparatus in the direction of arrow 'VI' in Figure 1 but on a
larger scale; and
Figure 7 is a view of the tension reducing means taken in
the direction of arrow 'VII' in Figure 6.
i2173~i
As shown in Figures 1 and 2, apparatus for making a stranded
core unit of 100 twisted pairs of conductors comprises apparatus for
twisting the conductor pairs including a hundred twisting machines 10
arranged in four straight banks 12 with twenty-five machines in each
bank. The apparatus is capable of making cable core unit at a speed of
up to and possibly in excess of 600 ft/min. Spaced from one end of the
four banks 12 is located a core unit forming and take-up means. This
comprises a stranding machine 13 comprising a stranding flyer 14 and
including a "helper" capstan 15. The "helper" capstan is to assist in
the drawing of the core unit into the machine 13, the main force for
which is taken by a motor 16 which drives a core unit take-up reel 17.
Upstream of the machine 13 is a drawing means in the form of a closing
die 18 for drawing twisted conductor pairs together, and a binding head
20. This structure of closing die, binding head and stranding machine
is conventional.
As shown by Figure 5, each of the twisting machines 10
comprises a cabinet 22 within which is located a reel cradle 24 for
holding two reels 26 of individual insulated conductors in a
rotatable fashion to enable the conductors to be drawn from the reels
under the drawing influence of the stranding machine 14. Each twisting
machine may be of conventional construction for enabl,ng the conductors
to be drawn from the reels and to be twisted together as they pass
through and outwardly from the machine. However, in this embodiment,
each twisting machine is of the construction described in a copending
Canadian Application No. 444,294, entitled "Twisting Machine", filed
December 23, 1983 and in the names of J. Bouffard, A. Dumoulin and E.D.
Lederhose. As shown in that construction each twisting machine
A:
12173~S
comprises two flyers 28 and associated pulleys to provide a balanced
rotational structure while avoiding conventional balancing weights.
The two conductors 30 being removed from the reels 26 pass downwardly
together as described in the aforementioned specification and then
through a selected one of the flyers 28 only. As the conductors move
through their flyer, the flyers are rotated by a drive motor (not
shown) which is either an individual motor for each twisting machine or
the twisting machines are driven from a common motor or motors. Flyer
rotation causes the two conductors 30 to twist together with a double
twist as is known. Each twisting machine forms a sub-assembly on a
main frame which extends lengthwise of its bank 12. As described in
greater detail in a copending Canadian Application No. 444,292, filed
December 23, 1983, entitled "Apparatus For Twisting Insulated
Conductors", and in the names of J. Bouffard, A. Dumoulin and 0. Axiuk,
each sub-assembly of twisting machine is detachable from the apparatus
in a complete form.
As can be seen from Figures 1 and 2 particularly, each of the
twisted pairs 32 as it emerges from the top of its twisting machine
moves along the line of its associated bank 12 of twisting machines as
it proceeds towards the stranding machine.
Disposed above each of the units 12 are a plurality
of tension equalizing means 34, one above the downstream end
of each twisting machine 10. The equalizing means are omitted
from Figure 1 for clarity. Figure 4 shows one of the tension
equalizing means in detail. Each tension equalizing means comprises
d shaft 36 which extends from side-to-side of the feedpaths for
the twisted pairs, the shaft being held rotatably in bearings 3~.
One end of each shaft 36 extends through a
A
~Z~73~S
bearing 38 into the interior of a housing 40, upstanding from the general
level of the twisting machines. This end of each shaft 36 has a V-grooved
pulley 42 which is engaged by a drive belt 44. The tension equalizing
means are driven conveniently in groups of five whereby each of the belts
44 extends along the twisting machines so as to encompass five of the
pulleys 42. One of the drive shafts for each of the groups of five is
driven directly by a drive motor 46, mounted upon the housing 40 and
connected to its drive shaft 36 by an endless drive member 48 and pulleys
50 and 52 located on the drive shaft 36 and on the driven shaft for the
motor 46. In each tension equalizing means there is provided a tubular
member 54 carried in bearings 56 around shaft 36 so that it is in slipping
drivable engagement with the shaft. The tubular member 54 surrounds the
shaft 36 so as to extend beneath the feedpaths for twisted pairs of
conductors. It is intended that as the shaft 36 is driven then the
tubular member 54 will rotate at substantially the same angular speed as
the shaft unless the member is restrained. While the bearings 56 may
suffice for this purpose, the inside of the tubular member may also be
packed with grease to hold it in more positive driving engagement with the
shaft.
It is an important aspect of the invention and as brought
out in this embodiment that the drive motor 46 is coupled electrically to
the line speed of the assembled twisted conductor units into the stranding
machine, whereby the speed of the drive motor 46 is controlled in relation
to the motor 64 so that the tension equalizing means is driven to provide
a peripheral speed for the unrestrained tubular members 54, which is
slightly in excess of the draw speed of the twisted pairs into the
stranding machine. The line speed of the assembled conductors is measured
lZ173~5
by a conventional means such as a rotor pulser device (not shown). The
reason for this excess speed will be explained below. The peripheral
speed of the unrestrained tubular members is a question of choice
dependent upon the tension reducing effects that are required. It has
been found in practice that the peripheral speed of the tubular members 54
should exceed the speed of the twisted units into the stranding machine by
up to 5% and preferably between 2% and 3%.
As may be seen from the above description, there are
twenty-five tension equalizing means along each bank 12 of twisting
machines. The furthest equalizing means from the stranding machine
supports only one twisted pair 32, i.eL that from the furthest twisting
machine. The number of twisted pairs supported by equalizing means
increases along each bank 12, from equalizing means to equalizing means,
until twenty-five pairs are carried by the equalizing means closest to the
stranding machine.
Guide means is provided along the twisting machines 10 for
holding the twisted pairs 32 spaced from one another to prevent the
tension in one pair from influencing that in another. This guide means
takes the form of a plurality of vertical guide rods 58. These guide rods
are located adjacent to but slightly downstream from each of the tubular
members 54 and are held stationary in support brackets (not shown) in
spaced apart positions axially of the tubular members. The number of
guide rods 58 used in respect of each equalizing means depends on the
number of twisted pairs of conductors which will pass over that particular
equalizing means. At the equalizing means, at Figure 4, there are five
guide rods 58 provided which thus form guide means for four twisted pairs
of conductors.
` lZ173~5
As the twenty-five twisted pairs of conductors emerge from
the downstream end of each of the units 12, they pass through a tension
reducing means for the purpose of reducing the tension which has
accumulated in the twisted pairs during twisting and drawing of the pairs
up to this position. As shown in Figures 1, 2, 6 and 7, the tension
reducing means for each group of twenty-five twisted pairs of conductors,
is in a tension reducing station and comprises two driven rotatable
cylinders 60 and 62 around each of which the conductors must pass on the
way to the stranding machine. The two cylinders are of substantially
equal diameter and have a common drive in the form of a drive motor 64,
which is connected to the cylinder 62 by a drive belt 66. A drive belt
(not shown) also drivably connects the two cylinders together. The drive
motor 64 is electrically influenced by the linespeed also to provide a
peripheral speed to each of the cylinders 60 and 62, which is slightly in
excess of the drawing speed of the twisted pairs of conductors into the
stranding machine. The degree of this excess in speed is again subject to
choice dependent upon design, but in this particular machine lies between
l and 5% and preferably is in the region of 3%.
For purposes of clarity and to assist in an understanding of
the operation of each tension reducing means, it is of importance to
realize that the two cylinders 60 and 62 are not a capstan drive and do
not operate as such in the accepted sense for drawing twisted pairs of
conductors through apparatus in cable manufacture. In this embodiment and
according to the invention, the cylinders 60 and 62 do not engage each of
the twisted pairs along a sufficiently long arc of contact to provide
enough frictional grip to draw the pairs from the twisting machines
without the assistance of tension upon the pairs downstream of the
~i73~S
cylinders and provided by the rotation of the reel 18. Hence, if the
stranding machine were omitted, the cylinders 60 and Ç2 would be incapable
of drawing twisted pairs from the twisting machines. Additional
frictional grip by the cylinders upon the twisted pairs is created by
tension downstream of the cylinders pulling the pairs down onto the
cylinder surfaces. While this tension is maintained, the cylinders will
draw the twisted pairs from the twisting machines with some slippage
because of the excess peripheral speed of the cylinders.
If the grip of the cylinders tends to increase the speed of
any pair, in the reducing station, towards its draw speed into the
stranding machine, then the downstream tension from the cylinders
decreases and the frictional grip of the pair around the cylinders is
lessened. Thus the cylinders slip to a greater extent upon the twisted
pair and there is a decrease in the tendency for further increase in speed
of the pair, as caused by the drive of the cylinders. In any event,
because the downstream tension from the cylinders would drop to ~ero, it
is extremely unlikely that the cylinders could drive any twisted pair
through the reducing station at a speed equal to the draw speed of the
stranding machine. Certainly, the twisted pairs could not be drawn
through the reducing station at speeds exceeding the draw speed of the
stranding machine.
As shown by the Figures, the tension reducing means are
arranged in pairs, i.e. two for adjacent units 12. These two pairs are
mounted together one on each side of a vertical framework 70, which is
located at the downstream end of the units 12. Also mounted on the
framework are two guide cylinders 72, one to each tension reducing means.
These guide cylinders are freely rotatably mounted so as not to affect
14
s
unduly the tensions in the twisted pairs and lie in positions below the
cylinders 62. Each of the guide cylinders 72 is provided with twenty-five
guide grooves 74 for accepting and maintaining apart the twenty-five
twisted pairs of conductors. From its cylinder 72, each group of
twenty-five twisted pairs of conductors moves forwardly into the
stranding machine by passing round suitable guide rollers (not shown) for
forming individual paths for the twisted pairs and for ensuring that their
paths converge at the stranding head 16 for forming a core unit 75.
In use of the apparatus, each of the twisting machines is
loaded with two reels 26 of individually insulated conductors as shown in
Figure 5. Upon start-up of the apparatus, the reel 17 is operated by the
motor 16. Each of the motors 46 and 64 is driven at a speed controlled by
the line speed such that the peripheral speeds of each of the driven
cylinders 60 and 62 and each of the unrestrained tubular members 54 is in
excess of the draw speed of the twisted pairs into the stranding machine
as discussed above. Each of the twisted pairs 32 of conductors extends
outwardly from its individual machine and along its own feedpath which
takes it across and in contact with each of the tubular members 54 which
lie in its path as it moves towards the stranding machine. Each of the
conductors also passes around the cylinder 62, the cylinder 60 and then
around its guide cylinder 72 as shown in Figure 6.
During the twisting of the individual twisted pairs, there
is tension in each of the conductors created by the pull of the stranding
machine. This tension varies from one pair to another and is at least
partly governed, in each case, by resistance to rotation of each reel 26
and flyer and the resistance offered by each guiding pulley or other
surface with which a pair comes into contact. Tension in each twisted
`` 12173~5
pair also depends upon its distance from the stranding machine. If these
tension differences were still present when the twisted pairs reached the
stranding machine, they would create differing tension conditions in the
cable core which, undesirably, would lead to variations in the electrical
characteristics and the finished core unit would be contorted along its
length, which would render it difficult or impossible to further process
the cable. The tension equalizing means overcomes this problem as will be
described. In addition, the amounts of tension present in each twisted
pair produced during twisting by this high speed apparatus operating at
around 600 ft. per minute of core production may be around 3 lbs. Without
the tension reducing effect of the tension reducing means, the accumulated
tensions of up to one hundred pairs would be excessive and a conventional
stranding machine would be incapable of drawing in this number of pairs
with such a tensile resistive load. The tension equalizing and reducing
means operate as follows.
As the twisted pairs pass across and are supported by the
tubular members 54, they travel at different speeds dependent upon their
positions and path lengths in the cable core being formed by the stranding
machine. There is a tendency for the tubular members to urge the twisted
pairs in the forward direction because of the faster driven peripheral
speed of the members. However, with regard to each tubular member 54,
because of the slipping driving engagement between the tubular members and
their shafts 36, the upstream tensions in the twisted pairs and the effect
of their relative speeds combine to slow down the speed of rotation of the
tubular member to a speed which is influenced by these tensions and
relative speeds of the pairs. At this speed of the members, the tensions
in the pairs are changed from the upstream to the downstream side of each
16
12173~5
member with a greater reduc~ion in tension in the more highly tensioned
pairs than in less tensioned ones. There is an influence, therefore,
towards equalizing the tensions in the pairs moving across each tubular
member and this equalizing effect increases as the pairs move towards the
final member 54. At each tubular member after the furthest upstream in
any bank 12 of twisting machines, a twisted pair of conductors is brought
directly from the adjacent twisting machine and over the member by guide
pulleys such as pulleys 35 (Figure 5). The tension in this twisted pair,
which at this stage may be relatively high, is immediately affected and
reduced by the tensions in the other pairs crossing the tubular member by
the rotational speed of the member.
For each bank 12, the pairs of conductors with their
relative tensions substantially closer than their upstream tensions, then
approach and go through their tension reducing means. As the twisted
pairs pass round the cylinders 60, 62 and 72 in the manner shown and
proceed through the guides (not shown) to the stranding machine, the pull
by the stranding machine increases the frictional contact of the twisted
pairs against the surfaces of the cylinders 60 and 62. Although these
cylinders are rotating at a peripheral speed which is greater than the
throughput speed of the twisted pairs into the stranding machine, their
degree of grip upon the pairs is insufficient to draw the pairs from the
twisting machines at the peripheral speeds of the cylinders. The reason
for this is explained above. Rather, the degree of drive by the cylinders
is dependent upon the frictional grip upon them by the pairs which
increases and decreases in proportion to the downstream tension created by
the draw of the stranding machine. Hence, as already explained, the pull
by the cylinders upon each pair increases its speed until it approaches
12i73~S
that of the draw speed of that pair into the stranding machine
sufficiently to reduce the frictional grip of the pair upon the cylinders
to remove the driving force. Any slight increase in the downstream
tension from the cylinders will improve their driving engagement with the
pair thereby reducing the tension again. It follows that the tension in
any twisted pair upstream of the cylinders (e.g. up to 3 lbs.) is reduced
on the downstream side to an acceptable level (e.g. about 0.5 lbs.) for
drawing into the stranding machine. It is stressed at this point that the
driving force applied to each twisted pair is dependent upon the
downstream tension in that pair. Hence, the cylinders 60 and 62 drive
each twisted pair at any moment at its own individual speed irrespective
of the speed of any of the other pairs. The speeds of the pairs must, of
course, differ from one another because of the different path lengths they
will occupy in the core unit. The operation of cylinders 60 and 62 thus
conveniently allows for this. On the other hand, a conventional machine
capstan which itself draws twisted pairs through a machine would be
useless for the purpose. Capstan control would ensure that exactly equal
lengths of twisted pairs would be fed into the stranding machine per unit
of time. As the core unit needs different lengths of twisted pairs per
unit length of core unit, some pairs would be at greater tensions than
others, thus resulting in all the disadvantages which the present
invention avoids. Thus, a conventional capstan would be incapable of
solving the problem.
In the above apparatus, the tension equalizing means and the
tension reducing means operate conveniently together. The finished core
unit is free of any contorted shape thus showing that internal tension
differences are minor and negligible. Also, electrical properties do not
18
~2~73~5
differ significantly along the finished cable and, in particular, mutual
capacitance variations are extremely slight and are well within
commercially acceptable limits.
