Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to the control of diameter of fiber
insulation on conductors and is particularly concerned with such
insulation on conductors for use in telecommunications cable.
In one process of insulating conductors, the conductors are
fed through a pulp vat or bath and after drying of the water from the
pulp, a paper fiber insulation results surrounding the conductors. In
practice, a plurality of conductors are fed in spaced lateral positions
around a cylinder mould disposed within the pulp vat to submerge the
conductors as they pass around the mould. The mould is formed upon its
peripheral surface with spaced annular perforate regions in which the
conductors lie, one to each region, as they pass around the mould. In
practice, therefore, the conductors are fed downwardly into the vat,
around the cylinder mould, while lying in engagement with a perforate
region, and then outwardly around a cylinder mould and a press roll before
proceeding further along with the process. ~hile the conductors are
submerged in the pulp, the water from the pulp passes through the
perforate regions of the cylinder mould, thus causing the pulp fibers to
be strained out by the perforate regions so that they become deposited
upon the conductors. The conductors surrounded by the pulp move away from
the cylinder mould, after passage around the press roll, and the pulp at
this stage is ir, the form of two wings extending outwardly from each side
of the pulp. To form the pulp into a substantially cylindrical state of
substantially constant diameter around the conductors, the conductors are
then moved through a polishing machine which effectively changes the shape
of the pulp into that desired. The pulp covered conductors then move
through a drying oven to remove substantially all of the remaining
moisture and the insulated conductors are then would onto take-up reels.
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It has been found in practice that when a plurality of
conductors have been coated with pulp insulation in the above fashion,
that there can be large variations in pulp diameter upon the conductors.
This leads to variations in the electrical characteristics of the
insulated conductors such as variation in capacitance or the dielectric
constant. One reason for this which has been suggested is that in a case
where up to 60 conductors are being insulated with pulp fiber at one time,
then a sufficiently wide bath is required to accommodate the conductors in
laterally spaced fashion. It is believed with such a width of vat9 the
flow of the water through the perforate regions differs from one region to
another and it is suspected that the flow through the perforate regions
varies progressively from the perforate regions around the median plane of
the roll towards its axial endsO The result of this obviously is that the
pulp fiber applied to the conductors towards the ends of the mould differ
substantially from the amount of fiber applied to conductors towards the
median plane.
The present invention is concerned with a pulp vat apparatus
for applying pulp fiber to conductors in which the diameter of the fiber
may be more closely controlled. The invention is also concerned with a
method of controlling the diameter of fiber insulation applied to
electrical conductors.
Accordingly, the present invention provides a pulp vat
apparatus for applying a layer of pulp fiber to conductors comprising a
vat, a cylinder mould rotatable within the vat about an axis to move any
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part of its periphery alternately towards and away from the bottom of the
vat, the mould having axially spaced annular perforate regions each for
accommodating a conductor as the conductors pass in laterally spaced
positions downwardly into the vat beneath the mould and upwardly out of
the vat, an outlet for water from within the mould, partition means within
the vat extending radially outwards from the cylinder mould in positions
between perforate regions to divide the vat into compartments with each
perforate region associated solely with one compartment, flow inlet means
for pulp to each compartment, means to vary the rate of flow of pulp
through each inlet means independently of the other inlet means, means for
guiding a plurality of electrical conductors through the vat in laterally
spaced positions along the annular perforate regions of the mould, means
for measuring the diameter of the fiber insulation surrounding each of the
conductors after drying of the fiber and for producing a signal
corresponding to the measured diameter, and means to operate the flow rate
varying means dependent upon the variation of the produced signal from a
datum signal representative of a desired diameter, to raise or lower ~he
level of the pulp in each compartment independently of other compartments
and corresponding to a required increase or decrease in the diameter of
the fiber towards the desired diameter.
The flow inlet means could be in the form of delivery pipes,
one for each compartment, and the means to vary the rate of flow could be
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in the form of valves located in the delivery pipes. Preferably, however,
the apparatus is provided with a pulp reservoir and independently
adjustable inlets are provided between the reservoir and the compartments.
In an ideal arrangement, the reservoir is disposed alongside the bath and
is separated therefrom by a side member of the vat.
In a preferred arrangement, the pulp flow rate varying means
comprises a slidable gate for each compartment, the slidable gate being
movable across an opening in the side member of the vat to vary the size
of the inlet from the reservoir into the compartment. The slidable gate
is preferably movable vertically, i.e. as a sluice gate for each
operation. In this case, the rate of flow varying means may be a motor,
for instance a servo-motor positioned above the gate, and is connected to
the gate by a means drivable by the motor to raise and lower the gate.
According to the invention also, there is provided a method
of controlling the diameter of fiber insulation applied upon each of a
plurality of electrical conductors comprising passing the conductors in
laterally spaced relationship into a pulp vat, beneath a rotating cylinder
mould in the bath and upwardly out of the vat, while locating each
conductor within an annular perforate region of the mould and in a vat
compartment, separated by a partition from other compartments, to deposit
fiber in non-cylindrical fashion upon the conductor as water passes
through the perforate region and into the mould, forming the fiber into a
substantially cylindrical shape, drying the fiber and measuring the
diameter of the fiber upon each conductor to generate a signal
representative of the diameter, and varying the amount of fiber applied to
each conductor in the vat to control the diameter within specified limits
by adjusting the pulp level in its associated compartment, independently
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of levels in other compartments, by activating a means to vary the flow
rate into the compartmen~ in response to the signal generated, and thus
correspondingly altering the length of path of said conductor in contact
with the perforate region of the mould while submerged within the pulp,
the pulp level in the compartment being appropriately adjusted by any
signal which is representative of the fiber diameter of said conductor and
which differs from a datum signal representative of a desired diameter,
said differing signal causing the operation of the means to vary the rate
of flow of pulp into the compartment.
Embodiments of the invention will now be described, by way
of example, with reference to the accompanying drawings, in which:- Figure
1 is a side elevational diagramatic representation of
apparatus for applying pulp insulation to electrical conductors;
Figure 2 is a cross-sectional view taken along 'II-II' in
Figure 1 showing pulp covered core being passed through a diameter
measuring device;
Figure 3 is a side-elevational cross-sectional view of a
pulp vat apparatus forming part of the apparatus of Figure l;
Figure 4 is a view of part of the pulp vat apparatus of
Figure 3 taken in the direction of arrow 'IV-IV' in Figure 3;
Figure 5 is an elevational view of part of the pulp vat
apparatus taken in the direction of arrow 'V-V' in Figure 3; and
Figure 6 is a control block di-agram for controlling amount
of pulp in the pulp vat;
As shown in Figure 1, a plurality of electrical conductors
10, e.g. 60, are drawn by take-up reels 12, side-by-side through a pulp ~ -
vat apparatus 14, which is the subject of the present invention, and then -;
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pass around rolls 16, 18 to submerge the conductors and draw up a
continuous coating of pulp onto the conductors as they leave the vat. In
Figures 1 and 3, only one conductor and take-up reel is shown.
The pulp covered conductors are then drawn upon endless
conveyor 20, passing around roll 18 and forming roll 22 which cooperates
with a forming roll 24 to press the pulp ribbon into a thin strip with the
conductor embedded in it and to remove water from the pulp. From the
rolls, the shaped pulp surrounded conductors are passed through weight
testing apparatus 26.
The apparatus shown in Figure 1 is further as described in
another Canadian patent application No. 403,262 and entitled "Control In
Application of Pulp Insulation to Electrical Conductors" in the names of
W.E. Cowley and M.A. Shannon.
As described in the last mentioned application, the pulp
covered conductors then proceed through rotating polishers 28 to form the
pulp ribbon into a cylinder concentric with the conductor, water sprayers
30, drying oven 32 having three drying zones 34, 36, and 38, a pulp
moisture measuring device 40 and a diameter measuring device 42, before
reaching the take-up reels 12~
By the use of the moisture measuring device 40 and diameter
measuring device 42 and associated control apparatus as described in the
aforementioned application entitled "Control in Application of Pulp
Insulation to Electrical Conductors", the pulp on each conductor is
maintained at an outside diameter which is within preset limits and which,
together with the weight measuring apparatus 26, ensures that a controlled
finished density of pulp is obtained whereby the mutual capacitance
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properties between two pulp insulated conductors are maintained at a
desired value within preset limits.
The moisture measuring device 40 is constructed similarly to
moisture testing apparatus described in United States patent No. 4,309,654
entitled "Method and Apparatus for Testing Moisture Content of Pulp
Insulation During Application Onto An Electrical Conductor", granted
January 5, 1982 in the names of M.A. Shannon and W.E. Cowley and will not
be described in further detail in this specification. For purposes of
this application, it will suffice to say that it comprises upper and lower
pulleys 44 and 46 which contact all of the conductors as they pass
through. The two pulleys are electrically insulated from their mounting
frame (not shown) and the upper pulley 44 is disposed downstream of lower
pulley 46. A first voltage source is connected to the upper pulley to
provide a first voltage divider as described in the patent entitled
"Method and Apparatus For Testing Moisture Content of Pulp Insulation
During Application Onto An Electrical Conductor". A second voltage
divider is provided by connecting a second voltage to the lower pulley 46.
The signals from the two voltage dividers are fed to two high impedance
amplifiers (not shown) and from there to a differential amplifier.
The apparatus so far described operates satisfactory and in
a general sense to control the diameter of the dried pulp fiber and its
density on the conductors. However, this apparatus does not
satisfactorily provide uniformity in diameter and density across the sixty
conductors from one conductor to another. It has been found that
variation may exist in diameter and density progressively increasing or
decreasing across the sixty conductors. The reason for this is determined
to be caused by the flow characteristics of the pulp in the wide vat 14 in
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that there is differential flow through the cylinder mould of the mould
from one position of the vat to another thereby resulting in differential
amounts of pulp fiber being laid onto the conduckors in the vat.
According to one important aspect of the invention, and as now to be
described, the pulp vat apparatus 14 is constructed to assist in
overcoming this problem.
The pulp vat apparatus 14 is shown in greater detail in
Figures 3, 4 and 5. As shown by Figure 3, the pulp vat apparatus
comprises a cylinder mould 48 rotatably mounted about a horizontal axis
within a bath 50. The cylinder mould 48 is of conventional construction
in that it has axially spaced annular perforate regions 52 (Figures 4 and
5) each region 52 for accommodating an individual conductor 10 as the
conductor passes around ~he cylinder mould, i.e. downwardly into the vat
beneath the mould and upwardly out of the vat as shown in Figures 1 and 3.
These perforate regions operate in conventional fashion to act as filters
for pulp fiber in the vat in use by allowing the water to pass through the
perforate regions into the interior of the mould while retaining the fiber
upon the perforate regions so as to cover the conductors.
The vat 50 is formed by vertical members 54 and a base 56,
the members 54 and base also defining a pulp reservoir 58 which lies
alongside the bath 14 and is separated from it by a divider 60 between
vat and reservoir and which extends across the whole structure of sides 54
and common base 56. Pulp is fed into the reservoir through an inlet 62
which is disposed towards the bottom of the reservoir.
The apparatus 14 is provided with partition means in the
form of walls or partitions 64 which extend between the divider 60 and a
side member 54 so as to pass beneath the cylinder mould 48. As shown by
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Figure 3, each partition 64 extends around the cylinder mould so as to
substantially conform to its shape and may provide a gap 66 between the
cylinder mould and the partition, the gap possibly being of the order of
1/8". Each partition extends upwardly of the side members and terminates
close to the top of the side members as shown. The partition means are
disposed within the vat so as to divide the vat into compartments 68 as
shown in Figure 4 and 5. These compartments are disposed so as to be
associated one with each perforate region 52, i.e. each perforate region
faces into a single compartment as the cylinder mould rotates.
The vat is provided with a flow inlet means for pulp from
the reservoir 58 into each compartment. In the case of each compartment,
the flow inlet means comprises a slidable gate in the form of a sluice
gate 70 which is held by guides (not shown) to the side member 60 whereby
it is movable vertically to open and close an opening 74 between the
reservoir and the pulp vat.
Means is also provided to vary the rate of flow of pulp
through the reservoir to each of the compartments 68.
The means to vary the rate of flow of pulp to each
compartment comprises a servo-motor 76 which is disposed vertically above
its associated gate 70 at the side member 60. Each motor 76 is connected
to its gate 70 by a driving means which comprises a rotatable driving
spindle 78 which extends vertically down the side of the side member 60
inside its respective compartment 68 and the lower end of the spindle 78
is screw-fitted and received within a corresponding nut (not shown) which
is attached to the gate 70. Upon rotation of the spindle 78, therefore,
in the appropriate direction, the gate 70 is caused to move vertically
either upwards or downwards.
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By the use of the partition means, the height of pulp in
each compartment may be different from the height in other compartments.
The small gap formed by a low friction bladder seal (not shown) between
the cylinder mould and each partition 64 allows a negligible amount of
pulp to flow through so that there is no substantial levelling effect of
the pulp between the compartments. The amount of pulp fiber which is
applied to each conductor is dependent not only upon the time that the
conductor is immersed in the pulp in contact with the cylinder mould but
also depends upon the difference in heights between the pulp in the vat
and the outgoing water in the cylinder mould. In other words, fiber is
only applied to the conductor on the ingoing side between position 80, as
shown in Figure 3, at which the conductor first contacts the mould beneath
the surface of the pulp, and position 82 which is at the level of the
water inside the mould. On the outgoing side of the bath, the fiber
accummulates on the conductor between position 84 on the mould at which
the mould moves away from the level of the water inside it, and position
86 at which the conductor either moves out of engagement with the
perforate region or leaves the pulp. It is clear, therefore, that if the
level of the pulp within each compartment is raised or lowered, then the
distance around the cylinder mould at which the fiber can accummulate on
each conductor is also varied and this leads to a variation in the amount
of fiber added to the conductor. In other words, if the pulp is high in a
compartment, then the amount of fiber added to the conductor will be more
than if the pulp is at a lower position. Hence, if the level of the pulp
in any compartment is caused to change to alter the amount of fiber on its
associated conductor to bring that amount towards a desired level, then
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this will have no effect upon the amount of fiber being added to other
conductors.
An object of the invention is to provide a method of
individually controlling the diameter of pulp fiber insulation upon each
of the conductors being fed through the apparatus and as may be seen, this
is made possible by controlling the amount of fiber applied to each
conductor individually with the bath described above. Of course, some
control is required upon the degree of opening of the gate for each
compartment to control the level of the pulp in that compartment whereby
the diameter of the final insulation is as desired. This control is
provided by the diameter measuring device 42 (Figure 2) which is provided
downstream of the moisture measuring device 40.
The diameter measuring device 42 comprises a radiation
scanning device 90 having two arms 92 and 94 for movement above and below
the passline of the conductors 10, the arms being jointed at one end by a
vertical base 96. A reversible drive motor 98 is connected to the device
90 by a drive screw 100 and sliding guides 102 hold the device 90
correctly in position as it travels laterally of the conductors.
The device 90 comprises a laser radiation emitter 104
mounted at the free end of the lower arm 94, the emitter being directed
across the passline. A radiation detector 106 is mounted in line with the
emitter at the free end of the upper arm 92.
In use, the device 90 moves from left to right
intermittently across the passline and stops each time the emitter 104 and
detector 106 are disposed correctly in position on each side of a
conductor. After the device has been in position sufficiently long, e.g.
about 8 seconds, for the detector to have obtained a light signal from the
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emitter which corresponds to the diameter of the conductor, the motor 98
is energized by a microprocessor 108 (Figure 6) to move the device 90 to
bring the emitter and detector into positions above the next succeeding
conductor.
As shown by the control block diagram in Figure 6, signals
from the measuring device 42 are digital control signals which are sent to
a measuring unit 110. These signals which correspond to the diameter of
each insulated conductor, are sent as digital signals to a digital analog
comparator 112 which compare the digital value with a datum value which
corresponds to the actual desired diameter of the insulated conductor. An
analog voltage is then produced which corresponds to the magnitude of the
difference between the measured value and that of the datum value
representing the desired diameter of insulated conductor. The analog
voltage is then transmitted to the microprocessor. Dependent upon whether
the digital signal received from the measuring unit 110 is above or below
the datum signal for the desired diameter, then the microprocessor
controls the operation of the corresponding servo-motor for a particular
conductor through the servo-motor control 116 to open or close its sluice
gate 70 appropriately to increase or decrease the rate of flow of pulp and
hence to raise or lower the pulp with the object of increasing or
decreasing the fiber on the conductor to move the actual diameter towards
that desired.
In use of the apparatus, as the plurality of conductors pass
through the pulp vat, i.e. each through its own compartment and around its
own perforated region 52, the diameter measuring device 42 measures the
diameter of the insulation individually one each conductor after the
insulation has been dried in the oven 32. When the microprocessor
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receives an analog voltage from the comparator 112, thus indicating that
there is a difference between the actual diameter of the dried pulp and
the desired diameter, the it sends a control message to the servo-motor
control 116 for operating the motor 76 associated with the compartment of
the conductor which has been measured. The sluice gate 70 is then moved
appropriately to increase or decrease the flow of pulp frorn the reservoir
58 into the associated compartment 68, whereby the level of the pulp in
the compartment is raised or lowered appropriately to increase or decrease
the path along which fiber is laid into the conductor. Hence the amount
of fiber applied to each conductor may be controlled and varied with the
object of providing a finished diameter of dried pulp which approximates
the desired diameter of the insulation. It is important to note with this
apparatus that the insulation diameter may be adjusted upon each conductor
individually without affecting the diameter of insulation upon other
conductors. This apparatus compared favourably with conventional
apparatus in which all of the conductors pass through a single
compartmented pulp vat whereby any variation in the height of the pulp in
the vat affects the amount of fiber and therefore the diameter of all of
the conductors at the same time. With such a conventional apparatus,
there can be no control over the amount of fiber applied to each
conductor. As the amount of fiber, and thus the final diameter of the
insulation upon conductors is dependent upon the flow of the pulp through
the vat and through the perforate regions in a conventional construction,
then the height of pulp in a conventional vat can not possibly be used to
control the diameter of insulation on each conductor individually.
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