Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
L
This -invention relates to the manufacture of
telecommunica-tions cable core units.
A telecommunications cable is cons-tructed with a core having
a multiplicity of twisted units of conductors, each unit conventionally
being a twisted pair of conductors. A core may be typically forrned dS
a single core unit of twisted pa1rs, e.g. 50 or 100 pairs, or larger
cores, e.g. up to 4,200 twisted pairs, each comprises d plurality of
core units. The twisted pairs are assembled together, e.g. by
stranding, to form d core unit with the conductors of each pair twisted
together with a predetermined lead to the twist, i.e. the distance
taken along the pair for each conductor to comple-te a single revolution
along its path. This distance will be referred to in this
specification as the "twist lay" of d pair. The angle which each
conductor makes with the longitudinal axis of its conductor unit as it
extends along its twisted path will be referred to as the "angle of
twist lay". There are different twist lays provided for the twisted
pairs in a core unit with each pair having a particular lay and being
adjacent to other pairs of different lays. Care is taken, so far as is
practicable, to ensure that pairs of equal or substantially equal tiwst
lays are separated from each other. The reason for this arrangement is
to attempt to maximize the communications performance of the cable,
i.e. to lessen pair-to-pair capacitance unbalance and to reduce
crosstalk between pairs.
Ilowever, the use of dif-ferent twist lays for the different
pairs presents its own problems as the mutual capacitance between
conductors in a pair is influenced by the twist lay. In a pair with a
short twist lay, the mutual capacitance between conductors tends to be
higher than in a pair with a longer twist lay. It is believed that
~ ~y~
3~l
this variation in mutual capacitance is caused by the degree of
compression oF insulation between the conductors which brings
conductors of a pair closer together for shorter twist lays. l~hile
conductors having a plastic insulation show some mutual capacitance
variation for different twist lays, a larger variation is found wi-th
conductors having pulp insulation which is more compressible under a
given load than plastic.
It is particularly importan-t to strive towards providing a
telecommunications cable with minimized differences between mutual
capacitances between conductors in the differen-t conductor pairs, and
both empirical data and theoretical considerations have shown that such
a movement towards equalizing mutual capacitances would provide smaller
variations in other electrical characteristics of the cable, e.g.
inductance between conductors and pairs, impedance and attentuation.
Deviations of these electrical characteristics from the desired or
nominal values would be less.
Conventionally, the conductors of each pair are twisted
together in a completely separate operation from forming of twisted
pairs into a core unit. The conductors of each pair are twisted
together in a high speed twisting machine in which the two conductors
are held upon reels which are freely rotatable in a reel cradleO The
two conductors are fed from their reels, are brought together into a
common path and are twisted into the pa1r by rotating a flyer. The
twisted pair is then wound onto another reel immediately after
twisting. This reel is removed from the twisting machine and stored
until required for forming into a core unit. At this stage, it is
placed in supply stands for a core unit forming means with other reels
of twisted pairs and the core unit is built. A problem with this
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process is that a large inventory and storage for reels of twisted
pairs of different conductor gauges, insulation colors and of twist lay
are required for making core uni-ts which may be of different gauge,
color or arrangement of twist lays in the pairs from one unit to the
next. As an example of the inventory and storage for twisted pairs for
one cable design~ a cable core of 3,600 twisted pairs of pulp insulated
conductor may re4uire up to twenty-five different lengths of twist
pitch for the manufacture of its core units.
The present invention provides a method and apparatus for the
manufacture of a core unit in which the inventory and storage for reels
of twisted pairs is avoided. In the present invention, a plurality of
twisting machines are placed in tandem with a core unit forming and
take-up means, and the flyers of at least some twisting machines are
driven at different rotational speeds from others and with the
rotational speed of at least one flyer changeable independently of the
speeds of other flyers.
According to one aspect of the present lnvention, an
apparatus is provided for making a core unit for a telecommunications
cable from twisted units of individually insulated conductors
comprising a plurality of twisting machines disposed in an in-parallel
relationship to one another relative to a general passline through the
apparatus, each machine for carrying a plurality of reels of insulated
conductor and each machine comprising a flyer which is rotatable to
introduce twist into conductors to cause them to twist to form a
twisted unit, means for rotating each of the flyers and for changing
the ratio of the rotational speed of at least two of the flyers; and a
cored unit -Forming and take-up means in tandem with and downstream from
the twisting machines to draw the twisted units together and form a
core unit, the -forming and take-up means comprising drawing means to
draw twisted units into the forming and take-up means.
On a practical basis~ means is provided -to change the ratio
of rotational speeds of more than two and preferably all of the flyers.
The Flyers may be arranged with their rotational speeds in
groups. The speed ratlos of groups may be changed. Preferably,
however, each flyer is independently drivable to enable it to have i-ts
rotational speed changed without affecting the speeds of any other
flyers, whereby its speed ratio relative to any other flyer is
changeable. This may be made possible by providing a suitable
individual and changeable speed drive to each flyer such as a
mechanical drive having manually or automatically selectable gear
ratios. In a practical sense, it is advantageous to provide each o-F
the twisting machines wi-th its own individual variable speed drive
motor, and this conveniently is an a.c. electric motor.
The angle and length of twist lay of any twisted pair is, of
course~ influenced by the relationship of the speed of rotation of its
flyer and the feed speed o-f the conductors through the twisting
machine, the latter governed by the line speed of the core unit being
formed.
With the use of the invention, the ratio o-F speeds of
rotation of the flyers may be changed after manufacture of a core unit
thereby changing the relationship between the twist lays of the pairs,
thus resulting in the succeeding core unit being of different design.
It follows that the present invention provides apparatus which produces
a plurality of twisted pairs and then forms a core unit in tandem with
the twisting operation, thereby avoiding the use of two distinct and
separate process steps for these operations and the consequent need for
an inventory and storage of reels o-f twisted conductor pairs of
different twist lay and colors. In addition, in providing for changing
ratios of speeds o-f the Flyers, the apparatus has a universal
application -For core unit manufacture in thdt it is capable of
producing many distinct and different -twist lays from each twisting
machine to provide the capability for a change in design of core unit.
To control closely the twist lay of each twisted pair, means
is provided to measure the line speed of the core unit being made and a
signal sent from the measuring means influences the ro-tating means for
the flyers to vary flyer rotation according to any variation in core
unit line speed.
According to a further aspect of the present invention,
apparatus is provided for making a core unit as defined above and in
which means is provided to change the ratios of speeds of flyers during
operation of the means to drive the core uni-t forming and take-up
means. The flyer speed is preferably changeable in a continuously
changing or cycling basis between upper and lower limits for angles of
twist lays, e.g. angles which correspond to twist lays between 2.7
inches and 5.1 inches. While it is possible to provide a complete
cycle of change in angle of twist lay between upper and lower limits
over different lengths of the core unit for different twisted pairs,
this would provide crossover points of the cycles thus producing equal
angles oF twist lays for different pairs at specific locations along
the core unit. As the occurrence of such a phenomenon should be
~5 minimized as much as possible, it is preferable that all of the cycles
are of the same length and are out of phase with one another.
The invention also includes a method of making a core unit of
twisted insulated conductor units comprising twisting insulated
r~3,~,
conductors together in twisting sta~ions into a plurality of twisted
insulated conductor uni-ts to provide angles of twist lay which differ
between conductor units at any cross-section through the core unit,
with each conductor unit hav-ing a s-ingle d-irection o-f twist along its
length, and controlling the angle of twist lay oF each conductor unit
while changing the angles of twis-t lay of some at least o-f the twisted
conductor units during their formation; and moving the twisted
conductor units downstream -from the twisting sta-tions and in an
in parallel relationship to one another relative to a general passline
of the pairs, and into a core unit forming and ta~e-up means -to draw
the twisted units -together to form the core unit.
The method of the invention preferably includes controlling
the anyle of twist lay of each of the conductor units so that, at any
position along the core unit, the angle of lay either differs from that
of another conductor unit or is changing in a different sense from that
of another conductor unit which has the same angle of twist lay. It is
also preferable to change the angle of twist lay of at leas-t some units
continuously.
In a particular method, the angles of twist lay of all of the
conductor units are changed continuously in cycles which have
substantially equal lengths, amplitudes and cycle shapes. With this
particular method, the average twist lay of each unit is substantially
equal to that of each other unit, thereby reducing to substantially
zero, the variation in mutual capacitance due to each conductor unit
having different twist lays.
While the angles of twist lays of all the conductor units may
be changed continuously, it is possible to leave the lay angle of one
or more o-f the twisted conductor units unchanged in a case where the
twist lays of these certain uni-ts are outside -the limits of the
changing lays.
One embodiment oF the invention will now be described by Wdy
of example w-ith reference to the accompanying drawings~ in which:-
Figure l is a plan view of maln parts of apparatus -for
forming a stranded core unit of one hundred twisted insulated conductor
pairs;
Fiyure 2 is d side eleva-tional view of -the appdra-tus of
Figure 1 in the direc-tion of arrow II in Figure l;
Figure 3 is d pldn 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 d cross-sectional view taken along line IV-IV in
Figure 2 of a tension equali~ing means and on a larger scale than in
Figure 2;
Figure 5 is a view taken in the direction of arrow V in
Figure 2 of a twisting machine and on a larger scale;
Figure 6 is a control circuit for rotating flyers of twisting
machines at different speed ratios;
Figure 7 is a chart showing the values of changing twist lays
in a core unit; and
Figure ~3 is a chart similar to Figure 7 of another core
unit.
As shown in Figures 1 and 2 apparatus for making a stranded
core unit of one hundred twisted pairs of conductors comprises
apparatus for twisting the conductor pairs including a hundred
twisting machines 10 arranged in four straight banks 12 of machines
with twenty-five machines in each bank. The appardtus is capable of
making cable core unit at speeds of up to and possibly in excess of 600
ft/min~ Spaced from one end oF the four banks 12 there is located a
core unit forming and take-up means comprising a stranding machine 14,
which is of conventional construction. The forming and take-up means
also comprises~ in normal fashion, a closing head 16 for drawing
twisted conductor units together and a binder 18. The stranding
machine comprises a stranding flyer 17 having a "helper" capstan 19 to
assist in drawing the conductor pairs through the head 16 and binder 18
in forming the core unit 23~ The main drawing means comprises d
take-up reel 21 with its drive motor 20. The construc-tion of the
forming and take-up medns is conventional and will be described no
further.
Each of the twisting machines 10 comprises a cabinet 22,
(Figure 3), the cabinets together forming the rectangular shape of the
banks 12 in Figures 1 and 2. Within each cabinet there is located a
reel cradle 24 for holding in rotatable fashion, two reels 26 of
individually insulated conductors, as shown by Figure 5, 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 enabling 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 Patent Application
Serial No. 444,294 entitled "Twisting Machine", filed December 23, 1983
and in the names of J. Bouffard, A. Dumoulin and 0. Axiuk. As
described in that specification, each twisting machine comprises two
flyers 28 and associated pulleys to provide a balanced rotational
structure while avoiding conventional balance weights. The two
conductors 30 being removed from the reels 26 pass downwardly together
dS described in the aforementioned specification and then through a
selected one only of the flyers 28. As the conductors move through the
flyer, the flyers are rotated to provide the conductors with twist, by
a drive motor 31 which is an individual a.c. motor mounted on top of a
frame structure 32 and drivably connected to the flyers by means of a
pulley 34 and pulley wheels 36. Each of the a.c. electric motors is a
variable speed drive motor and provides a means for changing the
rotational speed of the flyer, according to a feature oF this invention
as will be described,
As may be seen from Figures 1, 2, 3, 4 and 5, each of the
twisted pairs 38, as it emerges from the top of its twisting machine,
moves along the line of its associated bank 12 of twisting machines and
proceeds towards the stranding machine 14.
The apparatus also includes a tension equalizing means and a
tension reducing means as described in a copending Canadian Patent
Application Serial No. 444,295, filed December 23, 1983, and entitled
"Forming Cable Core Units" in the names of J. Bouffard, A. Dumoulin and
M. Seguin. The tension equalizing means comprises a plurality of such
means 40, one above the downstream end of each twisting machine 10.
This is clearly seen from Figures 2 and 3, wh-ile the equalizing means
is omitted from Figures 1 and 5 for clarity.
As described in the application entitled "Forming Cable Core
Units~', each tension equalizing means comprises a shaft 42 extending
from side-to-side of the feedpaths for the twisted pairs, the shaft
being rotatable at its ends. One end of the shaft enters an upstanding
housing 44 and has a pulley 46 engaged by a drive belt 48. This drive
belt drives a group of five of the shafts 42, each of which has a
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pulley 46. One o~ the drive shafts for each group o-F -five is driven by
a drive motor 50 through a drive member 52. A tubular member 54 is
carried in bearings around each shaft 42~ so that it is in slipping,
drivable engayemen-t with the sha-f-t in -that it rotates at substantially
the same angular speed as its shaf-t unless it is res-trained. I~hile -the
bearings carryiny -the tubular member may suffice -for this purpose, the
inside of the rnernber rnay also be packed wi-th grease to hold it in more
positive driving engagement with the shaft. Each member 54 extends
beneath the feedpaths for the tw-isted pairs of conductors.
Each drive motor SO is coupled electrically to a means (not
shown) which registers the speed of the core unit through -the core un-it
forming and take-up means. This registering means which is
conveniently a rotor pulser is of conventional construction and will be
described no further. By the electrical coupling, the speed of the
drive rnotor 50 is such as 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
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 may exceed the speed of the twisted units into the stranding
machine by up to five percent and preferably between two and three
percent.
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 38, i.e. that pair from the furthest
twisting machine. The number of twisted pairs supported by equalizing
means lncreases along each bank 12, from equalizing means to equalizing
means "Intil twen-ty-five pairs are carried by the equalizing means
closest to the stranding machine.
Guide means in the form of guide rods 56 is provided for
holding the twisted pairs 38 spaced from one another as they extend
across -the banks 12 of machines and thus prevents the tension in one
pdir from inFluencing that in another. Conveniently these guide rods
56 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.
As the twenty-five twisted pairs of conductors ernerge from
the downstream end of each of the banks 12, they pass through a tension
reducing means for the purpose of reducing the tension in the twisted
pairs. As is shown in Figures 1 and 2 and more fully described in the
copending Application Serial No. 444,295, entitled "Forming Cable Core
Units", the tension reducing means comprises for each bank 12 of
twisting machines, two driven rotatable cylinders 5g and 60, around
each of which the conductors must pass on the way to the stranding
machine. The two cylinders 58 and 60, are of substantially equal
diarrleter and have a common drive (not shown). As described in the
aforementioned application entitled "Forming Cable Core Units", a drive
motor for the cylinders is electrically influenced by the line speed of
the core unit within the forming and take-up means to provide a
peripheral speed of each of the cylinders 58 and 60, 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 is up
to five percent and is preferably in the region of three percent.
3~
It is importan-t to reali~e that the two cylinders 5~ and 60
are not operated to draw the twisted pairs along their feedpaths at the
peripheral speed of the cylinders. The cylinders 58 and 60 do not
engage each of the twisted pairs along d sufficiently long arc of
contact to provide enough Frictional 9fi p to draw the pairs from the
twisting machines without -the assistance of tension upon the pairs
downstream of the cylinders and provided by the rotation of the reel
18. This downstream tension provided by motor 16 actually draws the
pairs from the twis-ting machines. In doing 503 it pulls the twisted
pairs onto the cylinder surfaces to increase frictional contact to
enable the cylinders to drive the pairs under friction at a speed
substantially that of the draw speed of reel 18. Hence if the
stranding machine were omitted, the cylinders 58 and 60 would be
incapable of drawing twisted pairs from the twisting machines. While
this downstream tension is maintained the cylinders will provide a
drive to the twisted pairs with some slippage because of the excess
peripheral speed of the cylinders.
During use of the apparatus, there is tension in each of the
conductors created by the pull of the motor 20. This tension which
differs from one pair to another, is at least partly governed by
resistance to rotation of each reel 26 and flyer and the resistance
offered by each guiding pulley or other surface wi-th which a pair comes
into contact. If these tension differences were still present when the
twisted pairs reached the forming and take-up means, they would create
differing tension conditions in the core unit which would lead to
variations in the electrical characteristics. Also, the finished core
unit would be contorted along i-ts length, which would render it
difficult or impossible to further process the cable. The tension
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equalizing means overcomes this problem and the tension reducing means
reduces the tensions in the pairs to enable -the stranding machine to
operate with no overdue strain to draw the total of a hundred twisted
pairs for the stranding operation.
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 unit 23 being formed
by the forming and take-up means. 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 42, the
upstream tensions in the twisted pairs and the effect of their relative
speeds combined to slow down the speed of rotation of the tubular
member to a speed which is in-Fluenced 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
member with a greater reduction in tension in the more highly tensioned
pairs than in the 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 62 shown in Figure
3. The tension in this twisted pair, which at -this stage may be
relatively high, is immediately reduced by the influence of -tensions in
the other pairs through the intermediary of the tubular member.
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At -the downstream end o-f each bank 12, the pairs of
conductors with their rela-tive tensions substantially closer than at
upstream positions, approach and go through their tens-ion reducing
means. As the twisted pairs pass around the cylinders 58 and 60 and
proceed through gu-ides (no-t shown) -towards the closing die 16, the pull
by the s-tranding rnachine increases -the frictional contact of the
twisted pairs against the surfaces of the cylinders. 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 o-F grip upon the pairs is insufficient to draw the pairs from
the twisting machines at the peripheral speeds of the cylinders because
oF the small arc of contact between the cylinders and the twisted pairs
as discussed 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, the drive by the
cylinders upon each pair is purely frictional and serves to reduce
tension in the twisted pairs. Any slight increase in the tension
downstream from the cylinders will improve their frictional engagement
wi-th the pair, thereby reducing the tension again. I-t 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 1~0 lbs) for drawing into the strandiny machine. It is stressed
that the driving force applied to each twisted pair is dependent upon
the downstream tension in that pair. Hence, the cylinders 58 and 60
drive each twisted pair at any moment at its own individual speed
irrespective of the speed of any of the other pairs. The speeds on the
pairs must, of course, differ from one another because of the different
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path lengths they will occupy in the core unitO The operation of
cylinders 58 and 60 thus conveniently allows for this.
It is a particularly important aspect of the present
invention that each of the drive motors 31 is independently drivable a-t
a speed such as to provide a particular twist lay to the pair of
conductors being formed by the associated machine 10. This -twist lay
may be completely independent of twist lays of other pairs and may be
changed either during the -twisting of the pairs and forming of a core
unit or after formation of one core unit and before start-up of a
subsequent pair twisting and core unit forming operation.
Figure 6 shows a control means for controlling the rotational
speeds of the flyers. This control means comprises a hundred
microprocessors 66, i.e. one microprocessor for each motor 31. A
computer 68 is connected by an address bus 70 to each of the
microprocessors. The conventional means provided for measuring the
actual line speed of a core unit as it is being drawn into the
stranding machine is connected to each of the microprocessors by lines
71 to send frequency signals on a continuous basis, these signals
corresponding to the actual core unit line speed.
The computer contains instructions for issuing to each of the
microprocessors for controlling its associated a.c. motor 31 to drive
the flyers of its twisting machine at the appropriate speed and provide
the required twist lay to the pair of conductors being twisted upon
that machine. These instructions correspond to a particular or actual
line speed of the core unit being made. The computer addresses the
microprocessors on the address bus 70 and sends the instructions to
each microprocessGr in the form of a digital signal which corresponds
to the required twist lay produced by that particular twisting
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machine. This signdl is stored in a memory medns of the rnicroprocessor
until it is replaced by a new digital signal sent on the address bus.
A signal is then sent by each microprocessor along line 72 to an a.c.
inverter drive 74. This signal is an a.c. signal having a frequency
5 corresponding to the digi-tal signal sent on the address bus, but
influenced by the frequency signal for the line speed received on line
71 so that it is modified to control the d ppropridte mo-tor 31 to
produce the twist lay required for the actual line speed oF the core
unit. Upon receiving the signal, the d.C. inverter drive 74 converts
the incoming signdl to d.c. current and scrambles it to reconvert it
into an a.c. output signal of the required frequency to drive the a.c.
motor 31 at the desired speed. The inverter drive has the effect of
reducing the frequency from that received by i-t From the microprocessor
and this -frequency is one which is suitable for sending to the motor
15 31.
Hence, with this control means d signal may be sent from the
computer to each microprocessor for start-up of a core unit Forming
operation, and then the angles of twist lays produced by edch of the
twisting machines is as desired and controlled by the rotational speeds
20 of each a.c. drive motor 31. Thus, at the end of manufacture for each
core unit, fresh instructions may be fed into the computer to send
signdls to the microprocessors upon a subsequent operation to form a
core unit with twisted pairs having different twist lay angles from the
core unit which was formed previously. Hence the control means enables
25 the apparatus together with the individual a.c. drive motors, to avoid
the conventional necessity of having a storage and inventory of reeled
twisted pairs of conductors of different gauges, colors and lay angles.
As will be apprecidted with the apparatus of the present invention,
L r~
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core units of different design, different lay angles, di-FFerent
conductor gauges, different color and different -types of insulation may
be produced merely by changing the reels 25 -For fresh reels in the
twisting machines and by providing d-ifFerent instructions to the
computer 68 for controlling the microprocessors.
While it is therefore envisaged that the apparatus will
produce core units with different twist lay angles for the conductor
pairs, it is also within the scope of this apparatus to produce core
units in which the lay angles vary in one or more pairs as they extend
along the core unit. Variation in -twist lay angles will tend to reduce
or eliminate any inFluence that the twist lay angles of various pairs
can have upon one another in an electrical or magnetic sense, which
could have deleterious effects upon the communications performance of
the cable core. In use of the apparatus described and according to a
preFerred aspect of this invention, one or all of the twisted pairs may
have twist lay angles which vary and these angles preferably vary on a
continuous cyclical basis between upper and lower twist angle limits.
While it is possible to have twisted pairs in a core unit which are
spaced widely and have substantially the same twist lay angle, this
apparatus makes it possible to provide varying twist lay angles which
at any particular position along the core unit either differ one from
each of the others or two of the angles may be the same as one another
over an insignificantly short distance at cyclic crossover points with
the angles changing in opposite sense from one another. This can be
e-ffectively provided by issuing suitable instructions through the
computer 68 to cause the Flyers 28 to rotate at varying speeds to
produce twist lay angles, which while lying between the same upper and
lower limits, do in fact, cycle between these limits in out-of-phase
D
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relationship wi-th each other~
As an example -for the mdnufacture o-f the one hundred pair
core unit 23 described above, twelve out-of-phase cycling twist lay
angles are provided. Eight of the phases may edch be applied to eight
pairs of conductors and the remaining four phases may each be applied
to nine pairs of conductorsO
In the graph of Figure 7, the twelve cycling twist lay angles
are represented on the vertical scale by the corresponding -twist lays
which would be produced by the angles at polnts on the cycle if each oF
those angles was used without change. For instance, each cycle has the
twist lay angles cycling between an angle which is represented by upper
limit of twist lay of 4.~ inches and one which is represented by a
lower limit of 2.7 inches. A complete cycle for each twisted pair
occurs over a distance of approximately 100 meters of the -finished core
unit. Thus, the cycles of twist lay angle of the pairs have
substantially equal lengths, amplitudes and other cyclic
characteristics to produce avera~e twist lays in the units which are
substantially equal thereby minimizing differences in the mutual
capacitance from one pair to another and which is influenced by the
twist lay. In the stranded core unit, care should be taken to place
all conductor pairs having the same cycle of twist lay angle spaced
from one ano-ther to ensure good crosstalk performance between pairs and
pair-to-pair capacitance unbalance. Undoubtedly, as shown by the chart
of Figure 7, at certain insigniFicantly short distances along the core
unit length, each cycling phase of twist lay angles produces an angle
equal to that of another phase where one twist lay angle is increasing
on i-ts cycle~ while the other is decreasing. For instance, wi-th regard
to the cycle 76, this cycle has the same twist lay and lay angle value
~P~ 5~
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at points 78 and 80 25 cycles 82 and 84 respectively for different
conductor pairs. If the -twis-t lay angles of -the pairs are equal at
these crossover points on the chart, then these points represent
extremely short distances along the core unit which can have only an
extremely minor effect upon the electrical characteristics of the
finished cable. To ensure that these points of crossover are as shor-t
as possible, then the method of producing the varying lay angles
ensures that the motors 31 drive in such a way as to produce movement
along the cycle between the cycle limits in one direc-tion along a
shorter length o-f core unit than in the other direction.
For instance, as shown by Figure 7, the movement -from 4.g to
2.7 inches of each corresponding twist lay (and thus the lay angle
change) occurs over an extremely short length of core unit compared to
movement along the cycle in the opposite direction. This rapid
increase ensures that each crossover point, e.g. 78 or 80, is as short
as possible~
Figure 8 is a graph representing a possible twenty-five
out-of-phase cycles of lay angles. As shown in Figure 8, the varying
twist lay angles are represented by upper and lower limits of twist lay
of 2.7 and 5.1 inches and each cycle occurs over approximately 100
meters.
As described, Figures 7 and 8 show cycles of twist lay angles
with substantially equal lengths and amplitudes. However,
substantially equal average twist lays in the conduc-tor pairs may be
produced by having varying cycle lengths and amplitudes in the cycles
of twist lay angle in each pair, but, of course, this would be more
difficult to accomplish.
Hence, in a cable incorporating the core unit made according
- 2~ -
to the method described above and also according -to the invention, the
average twist lay of each condustor unit is substantially equal to that
of every other unit thereby substantially entirely avoiding differences
in mutual capacitance and mutual inductance between the conductor units
which is influenced by the twist lay.
