Automatic control of armour tape tension

A method and system are provided for automatically controlling tension of an armour tape being wrapped around a continuous strand of material, such as an electrical cable, travelling through an armouring machine having a reel of tape and tape feed rolls rotating around the strand and having a motor or suitable variable speed drive (such as a P.I.V. variable speed drive) for controlling the speed of rotation of the tape feed rolls and thus of tape feed rate. To achieve automatic control, the diameter of the strand entering the machine is measured, preferably by a laser, and the diameter of the armour over the strand exiting the machine is also measured, also preferably by a laser. The measurements are communicated to a computer which compares them to preset values. The computer drives the motor or variable speed drive and adjusts them when required depending on the measurements of the two diameters and so as to maintain the preset values during the wrapping operation.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to an automatic control of armour tape tension, 
particularly when wrapping metal tape around electrical cables for 
mechanical protection. More particularly, the invention relates to a 
method and a system for continuously and automatically controlling such 
armour tape tension during the wrapping operation. 
2. Description of the Prior Art 
Wrapping of tapes around continuously moving objects, in particular the 
wrapping of metal tapes around electrical cables is accomplished by 
continuous armouring machines, such as those known as "BX" machines, which 
are designed to wrap the tape around the cable from a reel on a spindle 
which rotates around the cable at high rpm (e.g. in the range of 1000 
rpm). 
The machine is provided with tape feed rolls which must be set up so that 
the tape forms a tube around the cable which neither cuts the cable nor 
allows it to be too loose within the armour. To control this tube, the 
machine uses a P.I.V. variable speed drive (P.I.V. standing for 
"PROPORTIONAL INFINITELY VARIABLE" transmission), which pushes the tape 
out by means of the feed rolls to be wrapped around the cable. Such P.I.V. 
drives are available on the market; for example, there is one sold under 
the trademark LINK BELT.RTM. by FMC Corporation. By adjusting the ratio of 
push to rotational speed, the size of the tube can be controlled. Instead 
of the P.I.V., two motors with two 
drives can also be used. 
Presently, to control the size or tightness of the tube, the operator 
manually adjusts the P.I.V. using a hand wheel or the speed control of 
drives on the motors using a potentiometer. These control methods, 
however, are unsatisfactory since once the run has started, the operator 
cannot check the tightness of the armour on the cable and, as a result, 
cables are often damaged by tight armour or rejected for loose armour. 
It should be mentioned, in this regard, that there are fairly strict UL 
(Underwriters Laboratories) standards for metal-clad cables, which require 
that "Interlocked, corrugated, or smooth armour on a cable containing any 
No. 4 AWG or larger insulated conductor(s) shall grip the cable to keep 
the conductor assembly from being withdrawn from a sample 10 ft or 3 m 
long by the application of a pull of 30 lbf or 133N or 13.6 kgf". At the 
same time, of course, the tape should not be so tightly wrapped as to cut 
into the cable. 
SUMMARY OF THE INVENTION 
An object of the present invention is, therefore, to provide an automatic 
control of the armour tape tension as it is wrapped, so as to satisfy the 
above mentioned requirements and to produce consistent quality performance 
of the product. 
Another object is to provide a system whereby the tape feed rolls would 
adjust automatically to maintain constant tension of the tape around the 
cable. 
Other objects and advantages of the invention will be apparent from the 
following description thereof. 
Thus, the invention comprises a method of automatically controlling tension 
of an armour tape being wrapped around a continuous strand of material, 
such as an electrical cable or cable core, travelling through an armouring 
machine having a reel of tape and tape feed rolls rotating around the 
strand and having means for controlling the speed of rotation of the tape 
feed rolls and thus of tape feed rate, which comprises: continuously 
measuring the diameter of the strand entering the machine and the diameter 
of the armour over the strand exiting the machine; comparing the resulting 
measurements against preset values by means of a computer; and operating 
by the computer the means controlling the speed of rotation of the tape 
feed rolls, thereby automatically adjusting the feed rate of the tape when 
required, so as to maintain said preset values during the wrapping 
operation. 
The invention also includes a system for automatically controlling tension 
of an armour tape being wrapped around a continuous strand of material, 
such as an electrical cable, travelling through a machine having a reel of 
tape and tape feed rolls rotating around said strand and having means for 
controlling the speed of rotation of the tape feed rolls and thus tape 
feed rate, comprising: means for measuring the diameter of the strand at a 
point of entry to the machine; means for measuring the diameter of the 
armour over the strand at a point of exit from the machine; a computer 
responsive to the output of said measurements and to corresponding preset 
values stored in its memory for operating said means controlling the speed 
of rotation of the tape feed rolls, said computer automatically adjusting 
the feed rate of the tape when required so as to maintain said preset 
values during operation of the machine. 
The continuous strand of material is normally an electrical cable, or cable 
core, usually consisting at least of a conductor and an insulating jacket, 
which is then wrapped with metal tape for mechanical protection by passing 
it through an armouring machine such as a "BX" machine. The prior 
jacketing and cabling operations are usually remote from the tape wrapping 
operation and the cable resulting from such prior operations may have 
variations in its diameter which are detected by the first measurement of 
the input cable diameter entering the armouring machine. Then, at the exit 
from the machine, the diameter of the armour on the cable is again 
measured. Although there are various ways that could be used to measure a 
diameter of a moving object, such as by the use of a source of radiation, 
by optronic sensors and the like, it has been found that for the purposes 
of the present invention, the preferred manner is by means of lasers. Such 
lasers are, for example, supplied by BETA Corporation under the name 
"Envelope Measurement System". 
The information from the above measurements is transmitted to a computer 
which compares it with preset values in its memory. The computer operates 
the means which control the speed of rotation of the tape feed rolls on 
the machine and will automatically adjust the tension of the tape and thus 
its feed rate so as to take into account any variations in the two 
diameters measured by the lasers and continuously and automatically adjust 
them to the preset values contained in its memory. In this manner a 
product of consistent quality is produced which will pass the UL pull out 
test and the load test consistently, with reduced material give away and 
reduced scrap. 
The armouring machines, such as the BX machine, are available on the market 
from suppliers such as Ceeco Limited or Cancab Corporation. Such machines 
contain means that control the speed of rotation of the tape feed rolls 
and which consist of P.I.V. variable speed drives or of motors using, for 
example, two DC drives that can be adjusted to control the tension of the 
armour tape being wound on the cable.

BEST MODE FOR CARRYING OUT THE INVENTION 
In the figure the armouring machine 10 is illustrated in section view. It's 
main spindle 12 is rotatable by motor 14 at a high rpm. A reel 16 with 
armour tape 18 is mounted on the spindle 12 for rotation therewith. Head 
20 of the machine supports tape feed rolls 22 and is also rotatable around 
cable 24 in the same direction as the spindle 12. P.I.V. or motor 26 is 
used to control the feed rate of tape 18 as it is wrapped around cable 24. 
A wheel or handle 28 is used to adjust the ratio of the P.I.V. or motor 
input and output drives to control the tension of tape 18. By controlling 
the P.I.V. ratio, the tension and thus the rate of advance of tape 18 by 
feed rolls 22 is either increased or decreased. The known practice is for 
the operator to adjust this ratio manually using the hand wheel 28. 
According to the present invention, the diameter of cable 24 is 
continuously measured by laser 30 just as the cable enters the machine 10. 
As armour tape 18 is wrapped around cable 24 by the machine, it produces 
armoured cable 32. At the exit from the machine, the diameter of the 
armoured cable 32 is measured by laser 34. The measurements made by lasers 
30 and 34 are transmitted to computer 36 which compares them with preset 
values in its memory that were pre-programmed for this particular cable 
armouring operation and which depend on the size of the cable, speed of 
feeding the cable into the machine, etc. 
Computer 36 operates a gear motor 38 and automatically adjusts the P.I.V. 
or motor 26 ratio depending on the measurements fed by laser 30 and 34 and 
their comparison with the preset values. The computer will make the 
required adjustments automatically so as to maintain the preset values 
during the entire wrapping operation by adjusting the rate of input and 
output gear of the P.I.V. or motor 26 trough gear motor 38 and handle 28 
and thus automatically controlling the tension of the armour tape 18. 
This, in turn, will adjust the feed rate of tape 18 which is being wrapped 
around cable 24. For example, increasing the rate of feed of tape 18 
increases the amount of interlock and thus the diameter of armoured cable 
32 and vice versa, if the tape rate is reduced the diameter of armoured 
cable 32 will be reduced due to lesser interlock of the tape. In the event 
of changes in diameter measurements by lasers 30 and/or 34, the computer 
36 will automatically make stepped adjustments until the preset values are 
again achieved. This is done on a continuous basis, without stopping the 
machine and results in more consistent product diameter of armoured cable 
32 as well as consistent quality of the product. 
The invention has been described above with reference to a preferred 
embodiment thereof and many modifications obvious to a person skilled in 
the art can be made without departing from the spirit of the invention and 
the scope of the following claims.