AUTOMATIC CABLE TENSION CONTROL SYSTEM FOR A PULLER/TENSIONER MACHINE

SYSTEME DE REGULATION AUTOMATIQUE DE LA TENSION DES CABLES POUR UN TENDEUR-DEROULEUR

English Abstract

A cable tension control system for maintaining a
substantially constant tension on a cable being wound or
unwound from a support spool is described. The tension
control system comprises a hydraulic motor for driving a
spool support shaft. A hydraulic pressure circuit is
connected to the motor and has a controllable pressure
relief valve for controlling the operating hydraulic
pressure fed to the motor. A diameter sensing mechanism is
provided for monitoring the change in the diameter of the
cable wound about the spool. The diameter sensing mechanism
is connected to a valve control linkage for controlling the
pressure relief valve in relationship to the diameter of the
cable present about the spool and thereby varying the
operating hydraulic pressure of the motor to control a
resistance drive force applied to the spool support shaft to
control the tension on the cable being wound or unwound.

Claims

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CLAIMS,
1. A cable tension control system for maintaining a
substantially constant tension on a cable being wound or
unwound from a support spool, said tension control system
comprising a hydraulic motor for driving a spool support
shaft, a hydraulic pressure circuit connected to said motor
and having a controllable pressure relief valve for
controlling the operating hydraulic pressure fed to said
motor, diameter sensing means for monitoring the change in
diameter of said cable wound about said spool, said diameter
sensing means being connected to valve control means for
controlling said pressure relief valve in relationship to
the diameter of said cable present about said spool and
thereby varying the operating hydraulic pressure of said
motor to control a resistance drive force applied to said
spool support shaft to control the tension on said cable
being wound or unwound.
2. A cable tension control system as claimed in claim
1 wherein there is further provided selective adjustment
means connected to said valve control means for presetting
said valve control means to a desired selected tension value
for said cable being wound or unwound.
3. A cable tension control system as claimed in claim
2 wherein said diameter sensing means is a spool diameter
sensing arm having a contact end biased against said cable
wound about said spool, said sensing arm being connected at
an opposed end to said valve control means, said valve
control means being a valve control linkage.
4. A cable tension control system as claimed in claim
3 wherein said valve control linkage comprises a cam secured
to a cam displacement rod, said displacement rod being
secured to said opposed end of said sensing arm and axially
rotated by the displacement of said sensing arm, a cam

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follower secured to a pivotal valve control arm, said cam
follower being biased in frictional contact with said cam
and axially displaceable to thereby displace said pivotal
valve control arm on a pivot, said pivotal control arm
having an abutment portion in contact with a contact end of
a control rod of said pressure relief valve to control the
hydraulic pressure fed to said hydraulic motor, said control
rod being biased against said pivotal lever abutment portion
by its internal spring and hydraulic charge pressure.
5. A cable tension control system as claimed in claim
4 wherein said pivotal control arm is a spring biased arm
biasing said cam follower against said cam.
6. A cable tension control system as claimed in claim
4 wherein said pivotal control arm has a displaceable pivot
pin secured to a displaceable carriage which is connected to
a control cable, said control cable being a push-pull cable
secured to a displaceable lever which constitutes said
selective adjustment means, said lever being pivotally
displaced and extending through a gauge slot in a control
console and having cable tension markings to select said
desired tension value, said pivot pin being displaced along
a slot of said pivotal control arm to and away from said
contact end of said control rod of said pressure relief
valve to vary the displacement of said abutment portion of
said pivotal control arm and accordingly the amount of
displacement of said control rod of said pressure relief
valve dependent on the diameter of cable present on said
spool and detected by said sensing arm.
7. A cable tension control system as claimed in claim
6 wherein said sensing arm is provided with a contact roller
bearing element at said contact end, said bearing element
being biased by a spring force exerted on said sensing arm
by a pulling action of one or more springs secured between
said sensing arm and a stationary member.

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8. A cable tension control system as claimed in claim
6 wherein said valve control means automatically adjusts the
maximum pressure differential (.DELTA.P) that can be reached
according to the winding radius of said cable wound on said
spool (R) to maintain said desired selected tension (T) in
said cable during said winding or unwinding, and wherein
<IMG>
where Ct is a constant dependent on the displacement of the
hydraulic motor and an associated gearbox, if present.
9. A cable tension control system as claimed in claim
8 wherein said displaceable pivot pin when positioned
axially aligned with said contact end of said control rod of
said pressure relief valve results in .theta. psi pressure applied
to said hydraulic motor, said pressure applied to said motor
increasing to a maximum pressure of said circuit as said
pivot pin is displaced way from said contact end.
10. A cable tension control system as claimed in claim
1 wherein said system is associated with a puller/tensioner
apparatus for stringing cables on arial supports.

Description

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AUTOMATIC CABLE TENSION CONTROL SYSTEM
FOR A PULLER/TENSIONER MACHINE
TECHNICAL FIELD
s The present invention relates to a cable tension
control system for maintaining a substantially constant
tension on a cable being wound or unwound from a spool on
which the cable is wound when stringing said cables on arial
supports.
~o
BACKGROUND ART
Systems currently on the market for stringing
wires on arial supports, and particularly systems utilizing
puller/tensioner devices, utilize operators to operate the
~s winding or unwinding of cables wound on a drum and these
operators have no knowledge of the mechanical tension at
which they are installing the cable. The operators know
that they are installing cables in a known range of tension,
for example 0 to 2000 lbs . of tension on the cable and the
2o rating of these puller/tensioner devices are established as
a maximum mechanical tension that the machine is able to
reach at maximum hydraulic pressure (and bare drum). The
actual tension in the cable depends upon the hydraulic
pressure at which the pump is operating and the reel
2s diameter of the cable on the drum. However, the operator of
the machine does not have any knowledge of what the
mechanical tension is in the cable being installed at any
moment.
In order to have an idea of this tension, with
so prior art technology, the operator had to evaluate the
diameter of the reel, that is to say the cable wound about
the spool, and refer to a chart using the hydraulic
pressure. In most of the cases, these charts are not
available. It is then a matter of judgment or "feeling"
35 based on the operator's experience to gauge the actual
mechanical tension at which the machine is operating.

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All these uncertainties create hazardous
conditions for the operator and the equipment. For example,
when the cable installation process stops, the operator has
no idea of what is going on. For example, did the puller
reach its maximum mechanical capacities? _ If.not, what are
the chances of an accident occurring if the operator decides
to raise the mechanical tension in the cable? Will it brake
down an isolator or a Gross arm of the arial support? Is
the tensioner putting too much brake on the system? If not,
~o what will happen if the operator gives more loose to the
cable? Will it eventually touch the ground?
The above are all possibilities of what can happen
with existing puller/tensioner equipment. Thus, there is a
need on the market for a system capable of managing the
~5 actual mechanical tension of the cable in the process of
being installed. Furthermore, with the advent of fiber
optic cables, it can be appreciated that because of the
fragile aspects of such cables, it is becoming essential to
control mechanical tension during installation of these.
zo With reference now to some prior art patents,
examples of existing systems will be described. It is
pointed out that all known tensioning mechanisms are not
incorporated with the spool support shaft to control
mechanical breaking through the control of a hydraulic
25 motor. For example, as shown in U.S. Patent 3,326,528, a
tension or resisting force in a cable being wound or unwound
is controlled by an independent system or tensioning
equipment which consists of wheels about which the cable
passes and is wound several times to provide tension in the
3o cable .
In U.S. Patent 4,372,535, a special tension pulley
is provided on a shaft which extends coaxially with the drum
shaft but not connected thereto. The tension pulley is
connected to a brake control mechanism which is operated by
35 an operator. In U.S. Patent 4,596,380, there is shown a
hydraulic system for pulling light cables such as optical

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fiber cables. The system only controls~maximum tension and
it is not a practical design as the shaft of the take-up
reel assembly would have to be very large to handle large
diameter cables. Accordingly, this makes the system
s unpractical for stringing heavy steel cables. U.S. Patent
2,999,655 also uses braking systems which are mechanically
adjusted by the operator and relies on friction between the
cable and drums to provide resistance.
1o SUMMARY OF INVENTION
It is therefore a feature of the present invention
to provide a cable tension control system for use with a
cable spool on a puller/tensioner machine and which
substantially overcomes the above-mentioned disadvantages of
i5 the prior art.
Another feature of the present invention is to
provide a cable tension control system whereby the operator
may select on a console, and by the use of a control arm, a
desired tension at which he wants to wind or unwind the
zo cable about the spool.
Another feature of the present invention is to
provide a cable tension control system which utilizes only
mechanical and hydraulic devices to control the tension in
the cable, making the system highly reliable.
2s Another feature of the present invention is to
provide a cable tension control system for use with a cable
spool on a puller/tensioner apparatus providing control of
cable tension and safety to the operator and to the
apparatus and the cable.
3o According to the above features, from a broad
aspect, the present invention provides a cable tension
control system for maintaining a substantially constant
tension on a cable being wound or unwound from a support
spool. The tension control system comprises a hydraulic
35 motor for driving a spool support shaft. A hydraulic
pressure circuit is connected to the motor and has a

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controllable pressure relief valve for controlling the
operating hydraulic pressure fed to the motor. Diameter
sensing means monitors the change in diameter of the cable
wound about the spool. The diameter sensing means is
s connected to valve control means for. controlling the
pressure relief valve in relationship to the diameter of the
cable present about the spool and thereby varying the
operating hydraulic pressure of the motor to control the
resistance drive force applied to the spool support shaft to
~o control the tension on the cable being wound or unwound.
BRIEF DESCRIPTION OF DRAWINGS
A preferred embodiment of the present invention
will now be described with reference to the accompanying
drawings in which:
FIG. 1 is a simplified, partly fragmented,
schematic side view showing a portion of a puller/tensioner
apparatus incorporating the cable tension control system of
the present invention in association with a spool on which a
zo cable is wound;
FIG. 2 is a simplified top view illustrating the
construction of the spool diameter sensing arm;
FIG. 3A is a schematic view of the hydraulic
motor and associated hydraulic pressure circuit and its
z5 connection to the spool support shaft;
FIG. 3B is a schematic side view of the spool
showing a cable being dispensed from the spool;
FIG. 4 is a plan view of the valve control
linkage secured to an end of the spool diameter sensing arm;
3o FIG. 5 is a side section view along section
lines A-A of Figure 4;
FIG. 6 is a side section view along section
lines B-B of Figure 4; and
FIG. 7 is a front view of a control panel
3s associated with the puller/tensioner apparatus of the
present invention and incorporating the control lever which

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selects the desired tension value of a cable being wound or
unwound on a spool.
DESCRIPTION OF PREFERRED EMBODIMENTS
s The cable tension control system of the present
invention provides a system which permits the operator to
select a desired cable tension by simple means of the
displacement of a lever arm on a console. It is also
pointed out that the selected tension has no effect on the
~o speed of the drum. The operator selects the desired tension
in the cable, for example from 0 to 2000 lbs. Then the
operator decides whether he wants to reel or unreel the
cable and at what speed he wants this to happen. As he
engages the system, the drum slowly begins to rotate at the
is specific characteristics chosen by the operator.
As companies are striving to adopt the ISO-9000
quality assurance specifications, the growing issue of
control is a necessity. In order to fully control the
installation of a cable, one has to know the mechanical
2o strain that will be placed on the network. Safety is also
an obvious issue when it comes to handling steel cables with
mechanical tensions of up to 2000 lbs. Not only safety to
the operator but also safety for the equipment and for the
material under the cable distribution network. Today, very
z5 few systems provide safety features. Some existing systems
use constant tensions and operate via a microprocessor and
an optic detector, such systems being considered to be very
fragile. In field applications where heat, rain and
vibration are often present, this electronic technology is
so considered unreliable. The cable tension control system of
the present invention uses only mechanical and hydraulic
devices to control the tension in the cable thereby
increasing the reliability of the system.
Referring now to the drawings, and more
35 particularly to Figures 1 and 2, there is shown at 10 a
portion of a puller/tensioner apparatus which is provided

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with a spool support frame 11 for supporting a spool 12
about which a cable 13 is wound. A hydraulic motor 14 is
secured to the spool support shaft 15. A spool diameter
sensing arm 16 is urged against the outer diameter 13' of
s the cable 13 wound about the spool by two biasing springs
17. As hereinshown, the arm 16 is displaceable from a
position illustrated at 16' when a cable completely fills
the spool 12 to its position as shown at 16 where the cable
is fully dispensed from the spool.
~o The spool diameter sensing arm 16 is provided with
a contact roller bearing 18 at a free end thereof which
consists of a smooth wheel rotatable against the outer
diameter 13' of the cable 13 as it is being wound or unwound
from the spool depending on the direction of drive imparted
by the hydraulic motor 14. The springs 17 bias the roller
bearing 18 against the outer diameter 13' of the cable. The
lower end 19 of the spool diameter sensing arm 16 is secured
to a valve control means or linkage which is housed in the
housing 20 and which varies the hydraulic pressure fed to
zo the motor to control the resistance force applied to the
spool support shaft as it is rotated by the motor to control
the tension on the cable being wound or unwound about the
spool. A gear box 9 may interface the motor and the support
shaft 15, as shown in Figure 2.
z5 Referring now to Figures 3A and 3B, there will be
briefly described the function of the cable tension control
system. The valve control linkage, as will be described
later with reference to Figures 4 to 6, controls a pressure
relief valve 21 which is connected in parallel with the
3o hydraulic motor 14 and a hydraulic pressure circuit 22
whereby to control and adjust the pressure differential ~P
across the hydraulic motor 14. The hydraulic motor 14 may
be connected to the spool support shaft 15 through the gear
box 9. The maximum pressure differential 0P that can be
35 reached, depends on the winding radius R identified by
reference numeral 23, as shown in Figure 3B, which is the

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distance to the outer diameter 13' of the cable 13, in order
to maintain a constant tension T in the cable 13 during
unwinding or winding of the cable on the spool 12. The
desired tension is selected by the operator by positioning a
s lever 24, see Figure 7, on a console 25. supported on the
puller/tensioner apparatus 10 at an operator station (not
shown). It is pointed out that the operator does not have
to adjust the pressure differential according to the winding
radius of the cable on the spool, since the constant tension
to mechanism, that is to say the valve control means, does it
automatically.
Referring now to Figures 4 to 6, there will be
described the operation of the valve control linkage. As
shown in Figure 4, the lower end 19 of the diameter sensing
i5 arm 16 has a sleeve coupling 23 whereby to immovably secure
same to a cam displacement rod 24 whereby to rotate the cam
displacement rod 24 about its longitudinal axis 25 when the
diameter sensing arm 16 is moved in and out from the center
of the spool 12 as the cable is being wound or unwound
2o therefrom. As better seen in Figure 6, a cam 26 is secured
to the cam displacement rod 24 and aligned with a cam
follower member 27. A spring 28 urges the contact head 29
of a cam follower member 27 against the cam profile 30 of
the cam 26. As the cam is rotated by the displacement of
2s the rod 24 secured to the sensing arm 16, the cam follower
member 27 will be displaced axially in the direction of
arrow 31.
As better seen in Figure 4, the cam follower
member 27 is secured at a rear end 32 to a pivotal valve
3o control arm 33 by means of a shoulder screw 34. The pivotal
valve control arm 33 pivots on a pivot pin 35. The pivot
pin 35 is a displaceable pivot pin which is secured to a
displaceable carriage 36. By displacing the carriage, the
pin is displaceable axially within a slot 37 provided on top
35 of the pivotal valve control arm 33, as better seen in
Figure 5. The carriage displacement is controlled by a

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control cable assembly 38 which houses a control wire 39
secured to the carriage 36. The lever arm 24 provided on
the console 25, shown in Figure 7, actuates the control
cable wire 39 to displace the carriage 36 along an axis
s transverse to the longitudinal axis 40 of a control rod or
piston 41 of the stationary pressure relief valve 21. As
previously described, the piston rod 41 of the pressure
relief valve 21 is biased against an abutment portion 33' of
the pivotal valve control arm 33 by its internal spring
~o pressure and the hydraulic pressure in the valve.
When the pivot pin 35 is displaced in line with
the longitudinal axis 40 of the valve piston rod 41, the
valve piston rod 41 is at full extension and 0P - 8 psi.
The valve stays at this position at any position of the
15 pivotal valve control arm 33 which is connected to the
diameter sensing arm 16 of the spool. The further the pivot
pin 35 is positioned in the slot 37 away from the piston rod
41 of the pressure relief valve 21, the greater is the
stroke of the piston and the greater is the OP.
2o With reference again to Figure 7, the tension
selection lever 24 is moved into the gauge slot 45 to a
desired cable tension marking 46 to select a desired cable
tension to be automatically maintained. This selection
displaces the pivot pin 35 with respect to the piston rod
z5 end 41 of the pressure relief valve 21. As the cable is
wound on the spool or dispensed from the spool, the diameter
sensing arm 16 pivots the cam displacement rod 24 which in
turn displaces the cam 26 and pivots the pivotal valve
control arm 33 via the cam follower 26 to vary the hydraulic
3o pressure OP fed to the hydraulic motor 14 by the use of the
pressure relief valve 21. Accordingly, the braking force or
resistance drive force exerted on the spool support shaft 15
is automatically controlled by the diameter of the wire on
the spool and in proportion to the desired tension value
35 that was selected by the operator by the set position of the
lever 24 on the console. The console 26 also has other

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levers, gauges and switches to operate a gas engine, cable
guide pulleys, a small spool which does not require cable
tension control and monitoring equipment for the hydraulic
system. The lever 47 sets the direction of rotation of the
s hydraulic motor 14 for winding or unwinding the spool.
It is within the ambit of the present invention to
cover any obvious modifications of the preferred embodiment
described herein, provided such modifications fall within
the scope of the appended claims.

Representative Drawing