Note: Descriptions are shown in the official language in which they were submitted.
CA 02060769 1999-OS-06
METHOD FOR REGULATION OF THE TRANSVERSE PROFILE
OF THE COATING QUANTITY ON A WEB MATERIAL AND
COATING STATION FOR CARRYING OUT THE METHOD
The present invention is related to the regulation of
the quantity of coating agent remaining in a coating machine
on a paper or any other web, in particular in the transverse
direction of the machine. More specifically, the invention
concerns a method for regulation of the transverse profile
of the coating quantity on a paper of any other web material
in a coating station, in which the web is passed over a
backup roll and the coating agent is smoothed by means of a
coating blade loaded against the web and in which the
quantity of coating agent applied onto the web is regulated
by means of actuators acting upon the coating station, and
in which method the transverse profile of the coating
quantity applied onto the web is measured constantly.
Further, the invention concerns a coating station
intended for carrying out the method, wherein the web is
passed to run over a backup roll and which coating station
is provided with a coating blade loaded against the web, the
blade being mounted in a blade holder supported on the frame
beam of the coating station, and which coating station is,
by the intermediate of a regulation and control circuit,
connected with measurement means for measurement of the
transverse profile of the coating quantity.
In respect of the prior art related to the invention,
reference is made to U.S. Patent Nos. 3,079,889, 3,301,214,
and 4,396,648 as well as to Finnish Patent Applications Nos.
851891,
1
~u~i~~~~
871566, and 894842, which concern so-called short-dwell-time
applicators.
Conventionally, the short-dwell-time applicators used far
the coating of paper, board, and equivalent comprise a
coating-agent chamber, which is defined by a coating blade that
rests against the base to be coated, such as paper, board or
equivalent, by a front seal and by lateral seals. The coating
agent is introduced under pressure into the coating-agent chamber
and therein enters into direct contact with the base to be
coated. The coating blade spreads and smooths a layer of the
coating agent of desired thickness onto the surface of the base
to be coated. Substantially two different types of devices of
this sort are known. On one hand, so-called large-angle-blade
coating is known in which, normally, the coating blade forms an
angle of several dozens of degrees with the moving base to be
coated. On the other hand, so-called mall-angle-blade coating is
known, in which the coating blade farms and angle of just a few
degrees (normally about 0 to about 10 °) with the moving base to
be coated.
An advantage of small-angle-blade coating especially in the
coating of board is relatively good unii:ormity of the thickness
of the coating layer, which is of signii:icance in view of uniform
absorption of printing ink. Further, impurities in the coating
mix and/or in the board can by-pass the blade without adhering to
it, in which case no streaks arise from the blade. A drawback in
small-angle-blade coating is the difficulty in controlling the
quantity of coating, for, e.g., when the small angle between the
blade and the moving base is changed even just a little to
regulate the coating quantity, the quantity of the coating mix
applied to the waving base is changed highly extensively.
In small-angle-blade coating, the mast important parameter
or regulation of the coating quantity is, as a rule, so-called
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pre-stressing of the coating blade, which means that the tip of
the coating blade is bent mechanically adjusting the distance of
the whole applicator device .from the moving base. Further
parameters of regulation are the load on the tip portion of the
coating blade as well as regulation of the blade angle.
With respect to the prior art, reference is additionally
made to bE publication No. 3,446,525, in whose solution the
regulation of the coating quantity is arranged so that the dam
blades are made mobile. One of the drawbacks of the solution in
accordance with said publication is that the dam blade must be .
very rigid in order that the cylinders intended for displacement
of the dam blade must be very rigid in order that the cylinders
intended for displacement of the dam blade should not bend it.
In the solution of said publication, the regulation of the return
flow of the coating agent is arranged as regulation of the size
of the return flow gap, in which case the pressure of the coating
agent may vary even considerably in the transverse direction of
the web. Thus, the device concerned is not suitable for
regulation of the profile of the coating quantity.
Further, FI Pat. Appl. No. 861241 describes a method and a
device for the coating of paper wherein the coating mix is
pre-spread by means of a resilient blade, and the ultimate
doctoring is carried out by means of a dragging doctor blade.
The applicator device is placed at the side of the backup roll,
and the coating mix rests against the web over a long distance.
In said solution, deaeration of the coating mix is difficult, and
integration of the dragging doctor blade in the applicator
equipment makes the maintenance operations more difficult. In
said solution, in the application zone preceding the smoothing
blade, the coating mix is susceptible to disturbances, such as
uneven distribution of the coating material. A typical
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CA 02060769 1999-OS-06
consequence of this is longitudinal streaks that remain in
the coating.
The present invention is directed towards achieving a
substantial improvement over the prior art so that the
coating quantity can be regulated in the desired way in the
transverse direction of the machine.
In one aspect of the present invention, there is
provided a method for regulation of the quantity of coating
applied to a web in a coating station, in which the web is
passed over a backup roll and a layer of the coating agent
is applied by means of a coating blade loaded against the
web, the quantity of coating agent applied to the web being
regulated by means of an actuator acting upon the
constructions of the coating station, the coating quantity
applied to the web being constantly monitored, characterized
in that, in order to regulate the transverse profile of the
coating quantity, the thickness of the coating is measured
in a plurality of transverse zones so as to calculate a
measured transverse profile, a differential profile is
calculated by comparing the measured transverse profile with
the desired transverse profile, and the differential profile
is fed as a regulation quantity to a plurality of actuators
arranged to adjust the transverse profile of the coating
quantity so as to correct the said transverse profile.
In the method aspect of the invention, therefore, a
differential profile of the measured transverse profile and
the desired transverse profile is calculated. The
differential profile is fed as a regulating quantity to the
actuators that adjust the transverse profile of the coating
quantity so as to correct the transverse profile.
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CA 02060769 1999-OS-06
According to a preferred embodiment of the invention,
in the method, an equation is approximated by means of
calculation, which equation corresponds to the transverse
differential profile of the web coating quantity and, out of
said equation, the average error and/or the skewness and/or
the curvature of the differential profiled and/or the
frequency of a cyclic error of coating quantity is/are
determined, the parameters corresponding to said values
being fed as regulation quantities to the regulators that
regulate said properties of the coating quantity so as to
correct the transverse profile.
In the method in accordance with the invention, the
measured transverse profile of the coating quantity and the
desired transverse profile are computed, and the magnitude
of the movement of regulation required at the locations of
regulation is calculated, by means of which movement of
regulation the transverse profile is changed in compliance
with the desired transverse profile. In the calculation,
the knowledge is utilized that a change in the doctoring
force perpendicular to the paper face and present at the tip
of the coating blade or a change in the coating quantity to
be doctored produces a change in the ultimate coating
quantity.
In the coating station aspect of the invention,
therefore, the coating station or a separate coating blade
arranged after the coating station is provided with support
and/or regulation constructions connected with separate
actuators and divided in zones in the transverse direction
of the web and/or with actuators connected with the frame
beam of the coating station or with a separate coating
blade, said constructions and/or actuators being
CA 02060769 1999-OS-06
connected to said regulation and control circuit in view of
correcting the transverse profile of the coating quantity on
the basis of the measurement data arriving from the
measurement means.
By means of the invention, a number of advantages are
achieved over the prior art, a most significant one of these
advantages being that the regulation of the coating quantity
is carried out as closed regulation and automatically.
According to the invention, the transverse regulation
of the coating quantity takes place in several locations of
regulation in the transverse direction of the machine. For
regulation, constructions mechanically connected to the
coating blade are employed, by means of which constructions
the doctoring force present at the tip of the blade or the
differences produced in the coating quantity to be doctored
can be altered.
The further advantages and characteristic features of
the invention come out from the following detailed
description of the invention.
The following drawings are schematic illustrations of
different alternative embodiments of the coating station in
accordance with the invention for carrying out the method in
accordance with the invention, and are not meant to limit
the scope of the invention as encompassed by the claims in
which:
Figure 1 is a schematic and partial perspective view of
a first alternative embodiment of the coating station in
accordance with the invention, in which a support
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CA 02060769 1999-OS-06
construction that has been divided into zones and that can
be pressurized is arranged behind the coating blade;
Figure 2 is a schematic side view of a second
alternative embodiment of the coating station in accordance
with the invention, in which a rigid support rib is fitted
behind the coating blade and in which the doctoring force of
the coating blade can be altered by bending the support rib
in the desired way;
Figure 3 is substantially equivalent to Fig. 2 viewed
from above;
Figure 4 shows an alternative embodiment of the coating
station in accordance with the invention in which the
coating blade is profiled inductively or magnetically;
Figure 5 is equivalent to Fig. 4 viewed from above;
Figure 6 shows an exemplifying embodiment of the
coating station in accordance with the invention in which
the regulation of the coating quantity is carried out by
restricting the return flows and/or the inlet flows of the
coating agent and/or by mechanically profiling the spreading
blade;
Figure 7 is an alternative embodiment of the coating
station in accordance with the invention in which the
curvature of the frame beam of the coating station is
corrected and regulated;
Figure 8 is a schematic overall illustration of the
regulation system in view of illustrating the various steps
in the method of the invention.
In Fig. 1, the backup roll is denoted with the
reference numeral 1 and the web that is passed over the
backup roll, such as a paper web, with the reference W.
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CA 02060769 1999-OS-06
The coating blade 3 included in the coating station
construction as shown in Fig. 1 is mounted in a blade holder
7, to which it is attached by means of a blade fastening rib
6. Behind the coating blade 3, near the free tip of the
coating blade, a hollow support construction 4 is fitted,
which is made of a resilient material and which has been
divided into zones in the transverse direction of the
coating station.
A pressure regulation pipe 5 is connected to each zone
in said resilient, hollow support construction 4, through
which pipe a pressure medium, such as gas or liquid, is
passed into each zone. The pressure in each zone can be
varied in the desired way so that the doctoring force, which
acts at that tip of the coating blade 3 upon the material
web W and upon the coating agent introduced onto its
surface, can be varied in the desired way. Thus, the
coating blade 3 can be profiled by feeding pressures of
different magnitudes into the different zones in the
resilient, hollow support construction 4.
In Fig. 1, only the coating blade 3 with its fastening
means and the coating blade 3 with its regulating members
are shown of the coating station construction. A
construction as shown in Fig. 1 can, however, be applied,
e.g., in connection with prior-art applicators of the short-
dwell-time type described above or with applicators of the
extruder-spreading type, and equivalent. The coating blade
3 may also be used just in order to smooth and to profile a
coating agent that has been spread onto the face of a
material web before the coating station construction as
shown in Fig. 1. Corresponding applications are
7A
also possible in connection with the embodiments of the invention
described below.
Figs. 2 and 3 show an embodiment alternative to the coating
station construction shown in Fig. 1. In Fig. 2 as well, the
backup roll is denoted with the reference numeral 1 and the paper
web or equivalent with the reference W. In the embodiment shown
in Fig. 2, a rigid support rib 11 is fitted behind the coating
blade 10, which rib extends across the width of the coating blade
in the transverse direction of the machine. In a way
10 corresponding to Fig. 1, the coating blade 10 is mounted in a
blade holder 16, to which it is attached by means of a blade
fastening rib 15.
In the embodiment of Fig. 2, a number of actuators 13 are
installed in the coating station in the transverse direction of
the machine, the spindles 12 of said actuators 13 being attached
to the support rib 11. Thus, the support rib 11 has been divided
into zones in the transverse direction of the machine, so that an
actuator 13 of its own ants upon each zone by the intermediate of
a spindle 22. The actuator 13 is such that the spindle 12 of the
actuator can be shifted back and forth, i.e. pulled ar pushed.
Thus, by means of each actuator 13, by the intermediate of
the spindle 12 and the support rib 11, the coating blade 10 can
be loaded towards, or away from, the web W. The actuators 13 are
mounted on the frame constructions of the coating station by
means of an actuator support 14.
The possibilities of movement of the actuators 13 can be
accomplished in a number of different alternative ways. One
possible embodiment is an actuator 13 in which the movement
produced by it in the spindle 12 is based on the effect of
thermal expansion. In such a case, by altering the temperature
of the actuator 13, the spindle 12 can be made to move towards,
or away from, the web S. Thus, by changing the temperature of
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the actuators 13, it is possible to locally alter the doctoring
force acting, at the tip of 'the coating blade 10, upon the web W
and upon the coating present on the web. The actuator 13 may
also operate mechanically, or it may be accomplished as operating
in some other suitable way.
The actuators can also be accomplished so that their
movement is based on the intensity of an inductively produced or
amplified magnetic field. Such an embodiment of the invention is
shown in Figs. 4 and 5. In the embodiment of Fig. 4, the backup
roll continues to be denoted with the reference numeral 1 and the
web with the reference S. Similarly to the preceding
embodiments, the coating blade 24 is mounted in a blade holder
26, to which it is attached by means of the blade fastening rib
25.
In the embodiment of Figs. 4 and 5, the actuators, a number
of which are placed in the transverse direction of the machine,
consist of an electromagnetic device, in which the core 19 of
each magnet corresponds to the spindle of an actuator in
accordance with the embodiment shown in Figs. 2 and 3. The core
19 of the magnet is provided with a coil 22, which is connected
to the voltage source 21 by means of the current circuit 20 of
the electromagnet. By changing the intensity and/or the sense of
the electric current in the current circuit 20 of the
electromagnet, the core 19 of the magnet can be made to move in a
way corresponding to the spindle 12 of the actuators shown in
Figs. 2 and 3. The core 19 of the magnet may act either directly
upon the coating blade 24 or upon a support rib 23 placed behind
the coating blade 24, in a way corresponding to Figs. 2 and 3.
Thus, by means of the embodiment shown in Figs. 4 and 5, the
same effect is produced on the regulation of the coating quantity
as is produced by means of the embodiment shown in Figs. 2 and 3.
9
Fig. 6 is a schematic illustration of a further embodiment
for carrying out the method in accordance with the invention. In
Fig. 6, the backup roll is denoted with the reference numeral 1
and the web that runs over the roll with the reference W. In the
construction of a coating station as shown in Fig. 6, the
spreading blade 30 is mounted in a conventional way in a blade
holder, which, together with its fastening members, is denoted
with the reference numeral 31 in Fig. 6. In Fig. 6, the coating
station construction further includes a guide wall 32, which
forms a lip between the inlet flow 41 and the outlet flow of 'the
coating agent in the coating station. The return flow duct 40 is
defined between the guide wall 32 and the support construction of
the spreading blade.
In the coating station in accordance with Fig. 6, the
quantity of the coating agent can be changed and regulated in the
transverse direction of the machine so that the spreading blade
30 is pushed or pulled in relation to the backup roll 1 by means
of the first actuators 34 connected mechanically with the
spreading blade 30. There are several actuators 34 connected
mechanically with the spreading blade 30. There are several
actuators 34 in the transverse direction of the machine so that
each of the spindles 35 of the actuators corresponds to a zone of
its own in the transverse direction of the machine.
On the other hand, in the embodiment of Fig. 6, the quantity
of the coating agent can be changed and regulated in the
transverse direction of the machine so that, in the coating
station, the return flow of the coating agent is restricted or
facilitated by changing the geometry of the return flow duct 40.
This is illustrated in Fig. 6 so that the coating station is
provided with second actuators 36, a number of such second
actuators fitted in the transverse direction of the machine. The
spindle 37 of these actuators are connected to a rib or
equivalent placed in the return flow duct 40 so that, by
displacing said spindles 37, said rib in the return flaw duct 40
can be shifted to choke or to ease the return flow locally.
Thirdly, in the embodiment of Fig. 6, the quantity of the
coating agent can be changed and regulated in the transverse
direction of the machine so that the length of the profile bar 33
at the lip between the inlet flow and the return flow is changed
or the lip or the profile bar is shifted closer to, or further
away from, the backup roll 1. This is illustrated in Fig. 6 so
that a number of actuators 38 have been connected to the profile
bar 33 by the intermediate of spindles 39, by means of which
actuators 38 the profile base 33 can be shifted in the way
described above.
In the method in accordance with the invention, the coating
quantity on 'the web material is additionally regulated by
correcting the curvature of the frame beam of the coating
station. This is fully illustrated schematically in Fig. 7.
The operation of the coating station is disturbed by a
distortion of the frame beam as a result of the effect of thermal
expansion and of mechanical strains. This particular phenomenon
is called the curvature of the frame b~aam of the coating station.
In Fig. 7, the coating blade is denoted with the reference
numeral 27 and the frame beam of the coating station
schematically with the reference numeral 28. The curvature of
the frame beam 28 can be corrected, e.g., so that, in the way
shown in Fig. 7, the frame beam is provided with ducts for
circulation of liquid or gas. Said ducts are fitted in the frame
beam 28 so that their distance from the coating blade 27 is
different. As said ducts in 'the frame beam 28 axe placid at
unequal distances from the coating blade 27, the frame beam can
be bent in the desired direction by feeding licyuid ar gas at
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different temperatures into the duct placed next to the blade and
into the duct placed further apart from the blade.
In Fig. 7, 'the temperature of the medium in the duct placed
next to the blade is denoted with the reference T~, and the
temperature of the medium in the duct placed further apart from
the blade is denoted with the reference T2. In Fig. 7, the
temperature of the frame beam itself is denoted with the
reference TP. The frame beam 28 can also be bent, e.g., by means
of hydraulic pressure. As a third alternative, it is possible to
use a heating member 29 shown in Fig. 7 and attached to the
construction of the frame beam 28, the frame beam 28 being bent
in the desired way by changing the temperature TL of said heating
member 29.
In the following, a more detailed description will be given
of the method of the invention with reference to Fig. 8 in the
drawing, in which attempts are made to illustrate the various
steps of the method. .
In Fig. 8, the web is denoted with the reference W, the
backup roll with the reference numeral 1, and the actuators with
the reference numeral 55. Each actuator 55 corresponds to one
location of regulation. It is a basic prerequisite of the method
that, in the transverse direction of the web, the form of the
change in the coating quantity produced by a movement of an
actuator in one location or regulation is known. This is called
the form of the profile response of the actuator, and it depends
an the construction of the coating station intended for the
application of the method. The form of the profile response is
practically independent from the location in the transverse
direction of the machine and from the other conditions of the
coating process, such as the composition of the coating agent and
the quantity of the coating layer that remains on the web W. The
12
~~~~~'l
absolute magnitude of the profile response is determined
separately for each casting process.
As the first stage in the method, the amplification
coefficient k is determined, which is obtained by comparing the
absolute magnitude of the profile response with the necessary
velocity of regulation of the coating quantity. The
determination of the amplification coefficient k can be carried
out, for example, so that the operator of the machine determines
the amplification coefficient and feeds it to the programmable
unit 50. The amplification coefficient k may also be
self~determined, so that, during the regulation method, the
control unit 50 constantly calculates and, if necessary, alters
the value of the amplification coefficient.
Secondly, in the method, the transverse profile of the
coating quantity present on the web W is measured and compared
with the desired transverse profile. In Fig. 8, this is
illustrated by means of 'the detectors 54 of measurement of
coating quantity, which detectors measure the thickness of the
coating quantity and feed the signals corresponding to the
measurement data to the control unit 50. Instead of the fixed
measurement detectors 54 as shown in Fig. 8, it is also possible
to use a traversing measurement detector or detectors running
across the web W.
The control unit 50 calculates the difference between the
measured transverse profile and the desired transverse profile
and presents it as a differential profile of coating quantity.
The desired transverse profile has been programmed in advance
into the control unit 50.
After the differential profile has been calculated, further,
by calculation, the following parameters are determined from the
differential profilee
13
~~~v~
a a parameter that represents the average value of the
difference between the measured profile and the desired
profile, i.e. the average error
b_ a parameter that represents the skewness of the
difference between the measured profile and the desired
profile, i.e. of the differential profile
c a parameter that represents the convexity or concavity
of the difference between the measured profile and the
desired profile, i.e. of the differential profile.
I~toreover, the sa-called residual differential profile is
determined from the differential profile by calculation.
The parameters a, b_ and c as well as the residual
differential profile are determined by means of approximation of
a parabolic equation which corresponds to the differential
profile as well as possible. Said parabolic equation is
y = d ~ f (mt) ~ (a -H bx + cx2) ,
wherein y = coating quantity
x = transverse coordinai~e (the origin is in the
middle of the web)
a,b,c = parameters to be determined, mentioned
above
t = time
d = magnitude of cyclic error in coating quantity
a = frequency of cyclic error in coating quantity
The parameters d and W are used in actuators whose frequency
response permits a speed of displacement of about 20 Hz. They
are employed for correction of a cyclic error in the coating
quantity in the machine direction by means of a cyclic movement
fed to all location of regulation. Said cyclic error in the
coating quantity arises, for example, from unevenness in the
14
~~~'~~~
backup roll, and, when these parameters d and w are taken into
account, it is easier to eliminate said cyclic error.
If it is desirable to regulate some of the factors mentioned
above only, i.e. to allow them to be regulated through the
residual differential profile, the parameters that represent the
factoxs to be omitted are given the value 0. The residual
differential profile is determined so that the parabola given
above is subtracted from the calculated differential profile,
which is presented as a function between the transverse position
on the web and the coating quantity.
As the next step in the method, the value of the parameter a
is transmitted from the control unit 50 to the first regulation
device 51, by whose means the value of the coating quantity in
the machine direction can be changed. The value in the machine
direction can be changed by means of the regulation device 51
either directly through the spindle of the actuators 55 or by
displacing the coating unit as a whole, which is illustrated by
the regulation line L in Fig. 8. In a corresponding way, the
value of the determined parameter b is transmitted to the second
regulation device 52, b whose means the: skewness of the coating
station can be corrected. Further, thE: value of the parameter c
is transmitted to the third regulation device 53, by whose means
the curvature of the frame beam of the coating station can be
corrected. Thus, the regulation devices 51,52 and 53 operate as
"pre--regulators", and the fine adjustment of the profile is
carried out by means of the actuators 55.
Next, the movement of the actuator required at the locations
of regulation is determined by, each in its turn, comparing the
known profile responses of the locations of regulation with the
residual differential profiles prevailing to them, by multiplying
the local value of the residual differential profile with the
amplification coefficient k, by dividing the result by the
profile response of the location of regulation, and by adding
together the results for the different locations of regulation.
The corresponding required movement profile of the actuator
is determined by combining the required movements of actuator
calculated in respect of each location of regulation. In such a
case, the control unit 50 and the regulation devices 51,52,53
attempt to regulate the profile of coating quantity so that, in
the parabalic equation given above, the values of the parameters
a,b,c and the residual differential profile become equal to
zero.
The movements of regulation calculated by the method produce
a time-dependent error in the coating quantity arriving on the
web W especially when the embodiments illustrated in Figs. Z to 3
are used in a coating station in accordance with the invention.
Z5 Since the regulation method in accordance with the invention,
however, follows the principle of a closed regulation circuit in
accordance with the above, the closing of the regulation has the
effect that the error produced is corrected immediately during
the next cycle of regulation. In this way, the error is
eliminated with a delay determined by t:he velocities of the
measurement and calculation methods and by the speeds of movement
of the actuators.
As was already stated above, the coating stations intended
for carrying out the method in accordance with the invention
convert the movement profiles of the actuators produced by mans
of measurement and calculation into doctoring forces of the
coating blade or into coating quantities to be doctored at the
locations of regulation placed in the transverse direction of the
web. Regarding the constructions of coating stations, it should
be stated further that, for example, when such solutions of the
embodiments as shown in Figs. 2 to 5 are employed in which the
area of contact with the coating blade, 10,24, which is produced
16
by the actuators, is very near the free tip of the coating blade,
the advantage is obtained that the angle between the coating
blade 10,24 and the web W remains almost invariable during the '
movements of regulation. This is why, after a movement of
regulation, the coating quantity is changed directly to its
correct value and a grinding of the coating blade 10,24 does not
cause time-dependent errors in the coating quantity, which errors
are noticed in most coating processes. Earlier, this possibility
was limited by sensitivity to variations in the doctoring force
produced by dynamic disturbance arising either from the
construction of the equipment or from the process, with resulting
errors in the coating quantity.
In the embodiments of the coating station as shown in Figs.
2 to 5 with the exception of fully mechanical operation, the
physical processes that produce the movements of the actuators
are very rapid, so that they can be regulated rapidly immediately
after the disturbance noticed by means of measurement. They can
also be synchronized with a possible dynamic disturbance that may
occur cyclically. By means of a solution as shown in Fig. 1, it
is also possible to achieve corresponding rapid operation,
because the volumes in the hollow support construction 4 are
small.
Besides those described above, the embodiment as shown in
Figs. 4 and 5 is also self~adjusting so that a dynamic
disturbance produces a movement in the actuators, which movement
produces a change opposed to the movement in 'the current circuit.
The tip of the coating blade 24 remains at the same angle in
relation to the web W, but the doctoring force is changed.
Hereby it is possible to avoid a time-dependent error in the
coating quantity arising from a change in the blade angle.
It is an advantage of the embodiments shown in Fig. 6 that
the coating blade 30 does not have to be affected to produce
17
regulation in the transverse direction. This completely
eliminates the formation of a time-dependent error in coating
quantity which might result from a change in the blade angle.
Here the starting point has been practical observations according
to which, when a solution of equipment is used in which a layer
of coating agent is first spread onto the face of the web W,
which layer is then smoothed by means of a smoothing blade placed
after the coating device proper, the quantity of coating agent
that was spread onto the face of the web W affects the quantity
of coating agent that remains on the web W after the ultimate
doctoring coating blade.
Above, the invention has been described by way of example
with reference to the exemplifying embodiments shown in the
figures in the accompanying drawing. The examples provided above
are not meant to be exclusive. Many other variations of the
present invention would be obvious to those skilled in the art,
and are contemplated to be within the scope of the appended
claims.
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