Textiles: spinning – twisting – and twining – Apparatus and processes – Unitary multiple twist devices
Reexamination Certificate
1999-12-03
2001-08-14
Calvert, John J. (Department: 3741)
Textiles: spinning, twisting, and twining
Apparatus and processes
Unitary multiple twist devices
C057S058520, C057S058540, C057S058830
Reexamination Certificate
active
06272828
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to cable twisting machines, and more particularly, to a machine which longitudinally distributes the eccentricities of the individual cables, where the helical propagation of the eccentricity is not conformal to the helix formed by the geometric shape of the cables.
RELATED ART
High performance data cable using twisted pair transmission media have become extremely popular. Such cable constructions are comparatively easy to handle, install, terminate and use. They also are capable of meeting high performance standards.
One common type of conventional cable for high-speed data communications includes multiple twisted pairs. In each pair, the wires are twisted together in a helical fashion forming a balanced transmission line. When twisted pairs are placed in close proximity, such as in a cable, electrical energy may be transferred from one pair of the cable to another. Such energy transfer between pairs is undesirable and is referred to as crosstalk. Crosstalk causes interference to the information being transmitted through the twisted pair and can reduce the data transmission rate and can cause an increase in the bit error rate.
Crosstalk is primarily capacitively coupled or inductively coupled energy passing between adjacent twisted pairs within a cable. Among the factors that determine the amount of energy coupled between the wires in adjacent twisted pairs, the center-to-center distance between the wires in the adjacent twisted pairs is very important. The center-to-center distance is defined herein to be the distance between the center of one wire of a twisted pair to the center of another wire in an adjacent twisted pair. Crosstalk is also affected by the eccentricity of the conductors as explained below. Eccentricity refers to the departure of the shape of the insulator surrounding the conductor from a circle centered on the center of the conductor. Because it is very difficult to form the insulator around the conductor in a perfect circle, an irregular thickness of insulator may be formed about the conductor. The irregular thickness has a varying egg like shape around the conductor. This irregularity is called eccentricity.
The magnitude of both capacitively coupled and inductively coupled crosstalk varies inversely with the center-to-center distance between wires, approximately following an inverse square law. Increasing the distance between twisted pairs will thus reduce the level of crosstalk interference. Another important factor relating to the level of crosstalk is the distance over which the wires run parallel to each other. Twisted pairs that have longer parallel runs will have higher levels of crosstalk occurring between them.
Machines known in the art for forming twisted pairs of conductors are of two basic types: single-twisting and double-twisting cable machines. Single twisting machines are machines that create a single twist on the conductor for each turn of the flybar. Double-twisting machines are machines which create two twists of the conductor for each turn of the flybar. In either machine, the cable take up can be located either within the flybar or outside the flybar. If the take up is located outside the flybar, either one or both of the cable give ups can be located within the flybar. However, uniform impedance is difficult to achieve using current state of the art single-twisting or double-twisting cable machines.
Modern high performance twisting machines are mostly double twisters, which provide some predetermined amount of back torsion on each conductor. That means, that for each turn of the conductors forming the pair, the conductors themselves are torsioned by a predetermined angular rotation in the opposite direction of the twist of the cable. It has been found that a small amount of back torsioning of the conductors is sufficient to give the resulting cable a very good impedance consistency as function of frequency. However, it can be shown that upon full back torsioning no performance advantage is achieved at all in the cable.
An example of one conventional system is now described. If one of the cable give ups is located within the flybar, then the cable give up that is located outside the flybar is stationary and the conductor is fed through the flybar towards the twist forming area. In these twisters (with the exception of the single twist machine with one stationary give up outside the flybar) any eccentricity formed by the insulation over each conductor is rotated one turn per 90° of cable twist. This is shown in FIG.
1
.
In these cables the cable twist direction is the same direction as the torsion twist of the individual conductors. In this configuration each conductor twists a full 360° relative to the other conductor for every 90° of cable twist. Thus, at a 45° twist of the cable, the conductors are each oriented with a 180° of twists relative to each other; this orientation of the conductors also repeats every 90°. As a result of these repeating orientations, there is a very pronounced cyclic variation in the center to center distance between the adjacent conductors which is offset by the phase angle between the different cyclic variations. This cyclic repetition of the center to center distance between the conductors influences the impedance of the cable as a function of frequency, and therefore, causes a structural return loss.
Furthermore, the overall eccentric wire is turning in the same direction as the helical center line of each conductor. Thus, the eccentricity of the cable is distributed longitudinally with the same helical pitch as the twist lay. That, combined with the variation of center-to-center distance of the conductors inside the insulation, causes structural impedance changes and increases the impedance irregularity of the cable. Both single twisting and double-twisting machines will yield these same results.
Single twisting machines, having one give up outside the flybar, and one give up inside the flybar, and having the cable take up of the twisted pairs outside the flybar, yield an improved, but not completely satisfactory, impedance consistency. This improved impedance consistency results because one conductor follows the above described twisting and the second conductor passes through the flybar without being subject to any torsion. The non-torsional wire is subject only to what is generally termed a “false twist,” meaning the conductor is torsioned upon entering the flybar in one direction and is torsioned in the opposite direction as the twist formation point upon leaving the flybar.
A cable formed by this method is shown in FIG.
2
. The conductor
20
is subject to the “false twist”. This orientation of the cable generally yields lower center to center distance variations of the conductors inside the insulation and therefore yields smaller impedance variations. However, in the twisting machines that create these cables, the tension controls of the conductors just prior to the twist formation point are very difficult to control. This can increase the difficulty in obtaining data grade wires that have sufficient balance and sufficiently small impedance irregularities.
Other twisters have individual give ups, each of which is located inside a flybar. Each of these flybars imparts a predetermined back torsion upon each of the conductors before they enter either a single or double twisting machine. The desired level of back torsion imparted by these machines is approximately one third of the torsion which the conductors are subjected to in the subsequent twisting operation.
Because this torsion is applied to the conductor in the opposite direction that the cable is twisted, these machines are frequently and misleadingly referred to as cable twisters with “back twisting”. A more properly descriptive term would be “twister with back torsion” of the conductors.
FIG. 3
shows a pair of eccentric conductors where one of the conductors is back torsioned at a rate of 33.3% of the cable twist lay. This back torsion rate results in a repetitive pattern where a half
Richard Jean-Francois
Saad Omar
Walling Jorg-Hein
Calvert John J.
Hurley Shaun R
Nordx/CDT, Inc.
Wolf Greenfield & Sacks P.C.
LandOfFree
Double-twisting cable machine and cable formed therewith does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Double-twisting cable machine and cable formed therewith, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Double-twisting cable machine and cable formed therewith will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2493373