Method of and an apparatus for manufacturing a SZ twisted strand of elongated elements for telecommunication cables

A plurality of elongated elements is maintained at a distance from one another by a spacing element, joined together at an inlet nipple, and twisted in the same twisting direction at a constant twisting speed by a twisting head located downstream of the inlet nipple, to emerge from the twisting head through an outlet nipple. The distance of the spacing element from the inlet nipple is cyclically varied by displacing the spacing element at a displacement speed which is lower than the advancement speed of the elements. The displacement speed is increased to the advancement speed during the displacement of the spacing element from a terminal position of a trajectory of displacement of the separating element which is more remote from the twisting head than the other terminal position, in a section of the trajectory having a length which is a predetermined fraction of the length of the trajectory. When a plurality of SZ-twisted strands is to be united into a single braid downstream of the outlet nipples from which the individual strands emerge, the spacing elements associated with the individual strands are all displaced in the same displacement cycles, but the cycles of the respective spacing elements are time-shifted relative to one another so that the transmission from the S-twist to the Z-twist will occur at a different location of the braid for each of the strands.

BACKGROUND OF THE INVENTION 
The present invention relates to the manufacture of SZ-twisted strands or 
braids of such strands in general, and particularly to the manufacture of 
such strands or braids for use in telecommunication cables. 
There is already known, for instance, from the German Pat. No. 2,138,239, a 
method of and an apparatus for SZ twisting of individual elongated 
elements each of which may be constituted by a bunch of non-twisted or 
twisted filaments, particularly for use in telecommunication cables. It is 
also already known from this patent to advance the elongated elements 
longitudinally thereof, after withdrawing the elements from stationary 
supplies, and to twist the elongated elements by resorting to the use of a 
twisting head which is arranged between an inlet nipple and an outlet 
nipple, to thereby obtain a twisted strand of the elements which is 
subsequently wound on stationary drums, reels or other storage equipment. 
In this prior-art arrangement, the twisting head is stationary but for its 
continuous rotation at the same twisting speed and in the same twisting 
direction, while a spacing element which keeps the individual elongated 
elements at a distance upstream of the inlet nipple is cyclically 
displaced in and contrary to the advancement direction of the elongated 
elements at a displacement speed which is lower than the advancement speed 
of the elongated elements, thereby cyclically varying the distance of the 
spacing element from the inlet nipple. On the other hand, the distance 
between the twisting head and the outlet nipple remains constant. 
It is also already known from the above-mentioned patent to unite a 
plurality of the strands obtained in the above-mentioned manner into a 
braid. In this connection, it has been proposed in order to electrically 
decouple the twisted elements of the braid, to vary the displacement speed 
of the individual spacing elements with respect to one another. These 
variations in the displacement speeds can be accomplished solely as a 
function of the location, that is, by individually controlling the 
displacement speeds of the individual twisting arrangements, or as a 
function of both the location and the time. In the first instance, the 
displacement speed is constant for each of the strands which are to be 
united into the braid, but the displacement speed of each of the spacing 
elements is different by a certain factor from those of all of the other 
spacing elements. This results in a situation where the lengths of the 
same-twist zones of the same strand are the same, but such lengths are 
different for each of the strands. In the second instance, the 
displacement speeds of the individual separating elements associated with 
the respective strands will somewhat vary in time independently of one 
another. 
Experience with the above-discussed arrangement has shown that twist-free 
regions develop at the transition from a twisted zone of one twisting 
direction to the twisting zone of the other direction, as a result of the 
fact that the direction of displacement of the spacing element is reversed 
at the two terminal positions of the trajectory of displacement of the 
spacing element. Of course, such twist-free regions are undesirable in the 
twisted strand or cable. On the other hand, it has also been established 
by experience that, when it is desired to stagger the transition regions 
at which the twist of the individual strands takes place in accordance 
with the prior-art proposals, it is impossible to displace the respective 
spacing elements from a single driving arrangement, because of the 
different displacement speeds of the individual spacing elements. Rather, 
it is necessary to arrange transmissions of a step-up or step-down type 
between the individual spacing elements, as a result of which undesirably 
high expenditures are incurred. 
SUMMARY OF THE INVENTION 
Accordingly, it is a general object of the present invention to avoid the 
disadvantages of the prior art. 
More particularly it is an object of the present invention to develop a 
method of manufacturing SZ-twisted strands or braids of such strands which 
is not possessed of the disadvantages of the prior-art methods. 
Still another object of the present invention is to shorten the transitory 
regions between the zones of different twists of the strand, thereby 
reducing the extent to which the individual elements extend parallel to 
one another. 
Still another object of the present invention is to devise a method of the 
type here under consideration which renders it possible to stagger the 
transition regions of the individual strands within the braid with respect 
to one another, without incurring substantial equipment and operating 
expenditures. 
A concomitant object of the present invention is to design an apparatus 
which is capable of performing the above-mentioned objects. 
Yet another object of the present invention is to so construct the 
apparatus as to be simple in construction, inexpensive to manufacture and 
operate, and reliable nevertheless. 
In pursuance of these objects and others which will become apparent 
hereafter, one feature of the present invention resides, briefly stated, 
in a method of manufacturing SZ-twisted strand of elongated elements for 
use in cables particularly telecommunication cables, which comprises the 
steps of advancing the elements at a constant advancement speed along a 
path; maintaining the elements at a distance from one another at a first 
location of the path; joining the elements into a bundle at a second 
location of the path situated downstream of the first location; twisting 
the bundle into the strand at a constant twisting speed and in the same 
direction at a third location situated downstream of said second location; 
and cyclically reciprocating said first location along a portion of the 
path between two terminal positions, including displacing said first 
location at a displacement speed lower than said advancement speed and 
increasing said displacement speed during the displacement of said first 
location along a section of the path portion commencing at, and in 
direction away from, at least one of said terminal positions. As a result 
of the increase in the displacement speed, the difference between the 
advancement speed V.sub.o and the displacement speed V.sub.s becomes very 
small for a predetermined period of time so that the twist 
EQU D = (n/v) = n/(v.sub.o - v.sub.s), 
wherein n is the number of revolutions of the twisting head and v is the 
relative speed of movement of the twisting zone, becomes very large of the 
entire duration of the time period during which the displacement speed 
v.sub.s is increased. As a result of this, a very rapid transition from 
one of the twisting directions into the other is achieved at the time 
reversal of the movement of the spacing element, owing to which the length 
of the transition region having the parallel elements is reduced in the 
twisted strand or the cable. 
In a currently preferred embodiment of the present invention, the 
increasing step includes raising the displacement speed to the advancement 
speed so that the relative speed between the advancement speed v.sub.o and 
the displacement speed v.sub.s is reduced to zero. Advantageously, the 
increasing step is performed at that terminal position which is more 
remote from the second location than the other terminal position. In this 
manner, the time period which is necessary for converting from the 
relatively small twist during the opening of the twist of the strand into 
the relatively large twist during the closing of the twist of the strand, 
is shortened. 
According to a further advantageous aspect of the present invention the 
path section during the displacement in which the speed of the spacing 
element is increased has a length x related to the length 1 of the path 
portion in accordance with the formula 
EQU x = 1 .multidot. a/(a.sup.1-a) 
wherein a = v.sub.s /v.sub.o, v.sub.s being the displacement speed and 
v.sub.o the advancement speed. The above formula is valid for the event 
that the displacement speed v.sub.s is equal to the advancement v.sub.o, 
and for the same displacement speed v.sub.s of the spacing element both in 
the forward and the rearward displacement mode. Based on the 
above-formula, the optimum length of the path section of increased 
displacement speed can be calculated based on the given advancement speed 
v.sub.o, displacement speed v.sub.s, and the length 1 of the path portion 
in which the separating element reciprocates. 
A further concept of the present invention resides in an apparatus for 
manufacturing a SZ-twisted strand of elongated elements for use in cables, 
particularly telecommunication cables, which comrpises means for advancing 
the elements with a constant advancement speed along a path; a spacing 
element for maintaining the elements at a distance from one another; an 
inlet nipple for joining the elements into a bundle downstream of said 
spacing element; a twisting head for twisting the bundle into the strand 
at a constant twisting speed and in the same direction downstream of said 
inlet nipple; an outlet nipple downstream of said twisting head; means for 
mounting said spacing element for displacement along said path in a 
trajectory toward and away from said twisting head between two terminal 
positions; and means for cyclically reciprocating said spacing element in 
said trajectory, including means for displacing said spacing element at a 
displacement speed lower than said advancement speed, and means for 
increasing said displacement speed during the displacement of said spacing 
element in a section of said trajectory commencing at, and in direction 
away from, at least one of said terminal postions. Advantageously, the 
displacing means includes a first drive constantly moving at the 
displacement speed and operatively connected to said spacing element 
during the displacement thereof in said trajectory. Then the increasing 
means includes a second drive constantly moving at an increased speed and 
operatively connected to said spacing element only during the displacement 
of said spacing element in said section of said trajectory away from said 
one terminal position, the reciprocating means further including means for 
deactivating the first drive during the operation of said second drive. 
Preferably, the deactivating means includes a free-wheeling mechanism in 
the first drive, between the two drives, or between a common driving 
arrangement and the first drive. 
In a currently preferred embodiment of the apparatus of the present 
invention the first drive includes a portion of the spacing element which 
has an elongated slot, a closed-loop driving element driven for travel at 
the displacement speed, and a pin mounted on the driving element for joint 
travel therewith and received in the elongated slot of the spacing element 
to entrain the latter for joint travel. The, the second drive may include 
an abutment portion of the spacing element, another closed-loop driving 
element driven for travel at the increased speed, and another pin mounted 
on the other driving element for joint travel therewith and abutting 
against the abutment portion of the spacing element when the latter is in 
the above-mentioned one terminal position thereof to entrain the spacing 
element for joint travel. 
Another concept of the present invention resides in a method of 
manufacturing a braid of SZ-twisted strands of elongated elements for use 
in cables, particularly telecommunication cables, which comprises the 
steps of advancing a plurality of sets of elements at a constant 
advancement speed along separate and spaced paths; maintaining the 
elements of each set at a distance from one another at a first location of 
the respective path; joining the elements of each set into a bundle at a 
second location of the respective path situated downstream of the 
respective first location; twisting the respective bundle into a 
respective strand at a constant twisting speed and in the same twisting 
direction at a third location of the respective path downstream of the 
respective second location; uniting the strands into the braid downstream 
of the third locations; varying the distance of the first locations from 
the third locations in the same cycle for all of the sets of elements; and 
performing the cycle of each of the sets in a time-shifted manner relative 
to the cycles of all other sets. This means that the individual spacing 
elements are always at different locations from one another with respect 
to the respective individual paths of the respective sets of elongated 
elements; however, because of the performance of the same cycle of 
displacement by each of the spacing elements, a single driving arrangement 
can simultaneously displace all of the spacing elements, without any need 
for resorting to the use of transmissions of the like. As a result of the 
above-discussed sequence of steps, it is achieved that, in the final 
braid, the regions of each of the strands which have the same twist 
direction, have the same lengths but are staggered with respect to one 
another longitudinally of the braid so that, for instance, in a basic 
braid which is manufactured in a conventional manner from SZ-twisted 
strands, such as four-wire units or pairs, there is avoided the 
possibility that two or more parallel regions of the strands which come 
into existence during the transition between the S-twist could coincide. 
Rather, such parallel regions are staggered along the braid, whereby the 
transmission properties of the braid or the cable including such a braid 
are improved. 
According to a currently preferred aspect of the present invention the 
twisting step includes twisting at least one of the bundles at the 
twisting speed which is different from the twisting speed of another 
bundle. Furthermore, it is advantageous when the twisting step includes 
twisting at least one of the bundles in the twisting direction which is 
opposite to the twisting direction of another bundle. As a result of this, 
there can be achieved different lengths of the twisted regions and 
different directions of twist of such twisted regions so that no 
periodically repeating asymmetries can develop in the braid consisting of 
the strands. In the final analysis, this further contributes to an 
improvement of the transmission properties of the braid and of the cable 
incorporating such a braid. To further improve such transmission 
properties, it is further proposed according to an additional advantageous 
concept of the present invention, to mix the strands prior to the uniting 
step. 
A further advantageous concept of the present invention resides in an 
apparatus for manufacturing a braid of SZ-twisted strands of elongated 
elements for use in cables, particularly telecommunication cables, which 
comprises means for advancing a plurality of sets of the elements at a 
constant advancement speed along separate and spaced paths; a plurality of 
spacing elements each for maintaining the elements of one of the sets at a 
distance from one another; a plurality of inlet nipples each for joining 
the elements of one of the sets into a bundle downstream of the respective 
spacing elememt; a plurality of twisting heads each for twisting one of 
the bundles into a strand at a constant twisting speed and in the same 
twisting direction downstream of the respective inlet nipple, a plurality 
of outlet nipples each arranged downstream of the respctive twisting head; 
means for uniting the strands into the braid downstream of said outlet 
nipples; means for mounting said spacing elements for displacement along 
the respctive paths toward and away from the respective twisting head; 
means for varying the distance of each of said spacing elements from each 
of the twisting heads in the same cycle; and means for performing the 
cycles of the spacing elements in a time-shifted manner with respect to 
each other. Advantageously, the twisting heads are operative for twisting 
at least two of the bundles at different twisting speeds and/or in 
opposite twisting directions. 
The novel features which are considered as characteristic for the invention 
are set forth in particular in the appended claims. The invention itself, 
however, both as to its construction and its method of operation, together 
with additional objects and advantages thereof, will be best understood 
from the following description of specific embodiments when read in 
connection with the accompanying drawings.

DETAILED DISCUSSION OF THE PREFERRED EMBODIMENTS 
Referring now to the drawing in detail, and first to FIG. 1 thereof, it may 
be seen that the apparatus of the present invention includes an inlet port 
1 for each of the individual elongated elements which are advanced at an 
advancement speed v.sub.o in the rightward direction as illustrated in the 
drawing. During their advancement, the individual elongated elements are 
joined into a bundle which enters a twisting head 2 through an inlet 
nipple and emerges from the twisting head through an outlet nipple 3. A 
spacing element 4 is arranged between the inlet ports 1 and the twisting 
head 2 and is displaceable along the guides 12 toward and away from the 
twisting head 2. As illustrated, the spacing element 4 includes a 
plurality of orifices for the individual elongated elements, and an outlet 
orifice for the bundle of the elements. The details of such a spacing 
element 4 are already well known so that they need no detailed discussion 
herein. The spacing element 4 is being reciprocated at a predetermined 
constant displacement speed v.sub.s which is lower than the advancement 
speed v.sub.o of the elongated elements which are to be SZ-twisted in the 
apparatus. A gear 5 is mounted on the twisting head 2 and is operative for 
rotating the twisting head 2 at a constant speed and in the same 
direction, being driven in rotation by a non-illustrated conventional 
drive arrangement. 
A drive 6 is used for displacing the spacing element 4 at the 
above-mentioned displacement speed v.sub.s. The drive 6 includes a driving 
chain 7 or a similar closed-loop driving element, the chain 7 being 
trained about two chain sprockets 8 respectively located at the beginning 
and the end terminal positions of a trajectory of displacement of the 
spacing element 4 between the inlet ports 1 and the twisting head 2. A pin 
9 or another connecting element is connected to the chain 7 for joint 
travel therewith. The pin 9 is received in an elongated slot 10 of a 
displacing portion 11 of the spacing element 4, the portion 11 being 
located underneath the spacing portion of the spacing element 4. As 
mentioned above, the spacing element 4 is mounted on the guide rods 12 for 
displacement longitudinally thereof. 
In order to achieve an increase in the displacement speed of the spacing 
element 4 over a predetermined section x of the trajectory 1 of 
displacement of the spacing element 4, a further drive 13 is arranged 
underneath the drive 6, the length of the drive 13 corresponding to the 
length x of the section of the trajectory. This other drive 13 also 
includes a chain 14 or a similar closed-loop element, which chain 14 is 
trained about sprocket wheels 15, one of which is driven by a 
non-illustrated conventional motor, such as an electromotor. An entraining 
pin 16 is connected to the chain 14 for joint travel therewith, the 
entraining 16 cooperating with an abutment portion 17 of the spacing 
element 4 which is moved in the vertical direction by the pin 9. The two 
drives 6 and 13 are synchronized with one another, that is, when the 
spacing element 4 is located at the forward reversing terminal position, 
that is the terminal position which is more remote from the twisting head 
2 than the other reversing terminal position, the entraining pin 16 of the 
lower drive 13 is located immediately underneath the spacing element 4 so 
that the entraining pin 16 abuts against the abutment portion 17 of the 
spacing element 4, and entrains the spacing element 4 for joint travel at 
a speed which is higher than the original displacement speed v.sub.s. 
Advantageously this increased speed of the lower drive 13 corresponds to 
the advancement speed v.sub.o at which the elongated elements are being 
advanced. The length of abutment of the lower drive 13 with the spacing 
element 4 corresponds to the length x of the section of the trajectory in 
which the spacing element 4 is to be displaced at the above-mentioned 
increased speed. The above-discussed entrainment of the spacing element 4 
by the lower drive 13 is rendered possible by the fact that a 
free-wheeling mechanism is interposed between the spacing element 4 and 
the upper drive 6, such as, for instance, by being incorporated in an 
upper gear 18 of a transmission between the two drives 6 and 13. At the 
end of the section x of the lower drive 13, the upper drive 6 takes over 
the further displacement of the spacing element 4 at the displacement 
speed v.sub.s. 
The SZ-twisting apparatus of the present invention is designed for 
advancement speeds up to 120 m/min. The twisting head 2 can be rotated at 
up to 5000 revolutions per minute without encountering any difficulties. 
When the twist of a braid of the strands manufactured in the arrangement 
of the present invention is to be, for instance, 7000 mm and the length of 
the SZ-twisted regions of the strands in the braid is to be, for instance, 
100 mm, the following operating conditions result: 
Advancement speed v.sub.o = 120 m/min, displacement speed of the spacing 
element v.sub.s = 40 m/min, twisting speeds of the twisting head n = 3430 
r.p.m. 
Under these circumstances, the trajectory of the spacing element 4 has a 
length 1 = 1.8 m. This results in S-twist or Z-twist regions of the strand 
having lengths of 5.4 m. 
Referring now to FIG. 2 it will be seen therein that the arrangement for 
manufacturing the braid of strands includes five mutually parallel 
SZ-twisting arrangements designated in toto with the reference numeral 21, 
each of them operative for SZ-twisting, for instance, four elongated 
elements 22. The individual elongated elements are withdrawn from 
non-illustrated conventional drums or similar storage arrangements and 
passed through inlet ports 23 on their way toward the respective spacing 
element 24. The spacing elements 24 are conventional and, generally 
speaking, correspond to the above-mentioned spacing elements 4, each of 
the spacing elements 24 having, in the illustrated embodiment, a joining 
orifice 26, at which the individual elongated elements 22 come together. 
The spacing elements 24 are displaced at a constant speed in the 
longitudinal direction of the elements 22, either concurrently with or 
opposite to the advancement direction of the elements 22. 
As will appear from FIG. 2, the individual spacing elements 24 are 
staggered with respect to one another, as a result of which the spacing 
elements 24, while all going through the same cycle of displacement, are 
time-shifted in the cycle with respect to one another. The elements 22, 
after joining one another in a bundle 27 for each of the arrangements 21 
are twisted into individual strands by diagrammatically illustrated 
twisting heads 28 which, in the illustrated embodiment, all rotate in the 
same direction and at the same speed. Thereafter, the strands pass through 
the respective outlet nipples 9 arranged at a distance from and downstream 
of the respective twisting heads 8. Downstream of the outlet nipples 9, 
the individual twisted strands 27 are trained and diverted about diverting 
rollers 30, and are united into a braid in a uniting nipple 31. The 
rotating twisting heads 28 twist the bundles 27 of the elements 22 at the 
twisting regions located between the spacing elements 24 and the twisting 
heads 28, on the one hand, and between the twisting heads 28 and the 
outlet nipples 29, on the other hand, into the SZ-twisted strand 27. 
While, in the illustrated embodiment, all of the twisting heads 28 rotate 
in the same twisting direction, it is also conceivable and proposed by the 
present invention to rotate the respective twisting heads 28 in different 
twisting directions. Also, it is contemplated to rotate the individual 
twisting heads 28 at different twisting speeds. 
It will be understood that each of the elements described above, or two or 
more together, may also find a useful application in other types of 
constructions, differing from the types described above. 
While the invention has been illustrated and described as embodied in a 
method of and an apparatus for manufacturing SZ-twisted strands or braids 
of such strands for use in telecommunication cables, it is not intended to 
be limited to the details shown, since various modifications and 
structural changes may be made without departing in any way from the 
spirit of the present invention. 
So, for instance, the speeds of displacement of the spacing elements 24 of 
FIG. 2 could be varied in the same manner as the speed of the spacing 
element 4 is varied in FIG. 1. 
Without further analysis, the foregoing will so fully reveal the gist of 
the present invention that others can, by applying current knowledge, 
readily adapt it for various applications without omitting features that, 
from the standpoint of prior art, fairly constitute essential 
characteristics of the generic or specific aspects of this invention.