Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Method and apparatus for control of a headbox in a paper machine
The invention relates to a method of controlling one or more cross-direction
property
profiles of a paper web manufactured by a paper machine, which method employs
a control system for regulating a headbox or headboxes of a paper machine and
in
which method said property profile or profiles is/are measured by a
measurement
system, the measurement signal obtained from said measurement system being
supplied to said control system, and which headbox or headboxes is/are
supplied
with at least two feed streams which contain feedstuffs for the paper to be
manufac-
tured suspended in aqueous solution and which feed streams are divided into
feed
zones in cross-machine sections of the headbox or headboxes, which feed zones
are
each supplied with combinatory streams of said feed streams.
In addition, the invention relates to an apparatus for controlling one or more
cross-
direction property profiles of a paper web manufactured by a paper machine,
which
apparatus comprises a control system for regulating a headbox or headboxes of
a
paper machine, a measurement system for measuring said property profile or
profiles, means for feeding the measurement signal obtained from said
measurement
system to said control system, means for supplying at least two feed streams
to the
headbox or headboxes, which feed streams contain feedstuffs for the paper to
be
manufactured in aqueous solution, and means for dividing the feed streams into
feed
zones in cross-machine sections of the headbox or headboxes, which feed zones
are
each supplied with combinatory streams of said feed streams.
v
As is known in prior art, systems for controlling the cross-direction grammage
of
paper manufactured by paper machines operate in the following way. The flow of
thickstock coming into a wire pit of a paper machine is regulated by a
grammage
valve based on grammage measurement at the dry end of the paper machine. The
grammage of the paper web is measured by means of measuring sensors traversing
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in a cross direction thereof, and the measurement result of the cross-
direction
grammage profile is averaged and passed as a feedback signal of a control
system.
The flow of thickstock is passed from the grammage valve, as known in prior
art,
to the wire pit, into which white water from the wire section of the paper
machine
is also passed. The thickstock flow and whitewater are mixed in the wire pit
and the
thus obtained diluted stock flow is passed, as known in itself, through pulp
cleaning
and deaeration devices to an inlet header of a headbox and therefrom further
through
a distribution tube bank of the headbox, possibly through an equalization
chamber
and a turbulence generator to a slice channel of the headbox. A pulp
suspension jet
is discharged from the slice channel onto a forming wire or into a forming gap
between forming wires.
As is known in prior art, the cross-direction grammage profile of paper
manufac-
tured by paper machines is regulated by profiling the height of a slice
opening in a
headbox based on the aforesaid grammage measurement at the dry end of the
paper
machine. Recently, so-called dilution regulations have also become more
common,
comprising supplying dilution water, usually whitewater or a stock that is
more
dilute than the headbox stock, to individual feed points situated in the cross-
direction
in connection with a headbox. This dilution water feed system serves to
profile the
cross-direction grammage profile of a slice jet together with the regulation
of a
profile bar or without it. A special advanta-e of dilution regulation is that
the
headbox can be operated with a slice opening of a uniform height so that the
cross-
direction flows in the slice jet and after it, caused by the profiling of the
height of
the slice opening, as well as distortions of the fiber orientation profile of
paper
resulting from them may be avoided.
The present invention is directed towards allowing more accurate and faster
control of
properties of the paper web, by means of a novel method and arrangement of
devices,
and exploiting the benefits offered by them.
The present invention is also directed towards taking advantage of several
recent
technologies in combination, including development of dilution headboxes,
concentration measure-
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ment devices suited to the paper industry, and the potential for advanced
control
strategies in modem control systems.
Prior-art dilution headboxes are subdivided into several feed zones across the
headbox. Additionally, there may be more than one layer of such feed zones.
Two
or more streams of feedstuff supply each layer of feed zones, and each stream
of
feedstuff may supply one or more layers of feed zones. Each feed zone in each
layer
is equipped with means of controlling the combinatory proportions of streams
fed to
that feed zone, normally using a suitable valve arrangement. Additionally,
there may
be one or more layers of feed zones which are supplied by only one feed
stream, or
are supplied by plural feed streams without means of controlling combinatory
proportions of feed streams fed to each feed zone.
Commonly, two feed streams are provided, one supplying the main feedstuff, and
the other supplying a feedstuff of different properties. Normally, the second
stream
is more dilute than the main stream, but this need not always be so. The
dilute
feedstuff is normally whitewater taken from the wire pit or short circulation,
often
with some processing, such as deaeration, cleaning, or filtration. The main
feedstuff
also normally contains whitewater, to which a thickstock is added. In some
cases,
clarified water may be used instead of whitewater as the dilute feedstock.
More than two feed streams may be provided, where each feed stream supplies
feedstuffs of different material composition. For instance both whitewater and
clear
water streams may be supplied as well as the main feedstuff stream;
alternatively,
two main feed streams may carry different feedstuffs, with a third feed stream
carrying a dilute feedstuff. However, it is also possible that more than one
stream
contains the same feedstuff; in this case, all streams carrying an identical
feedstuff
are treated as a single consolidated stream for the purposes of this
invention.
= Applicability of this invention requires that not all streams carry exactly
the same
feedstuff.
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The streams fed to each feed zone are mixed together in any of several ways in
the
feed zone, producing an aggregate stream. The aggregate streams from all feed
zones are merged, forming a single jet discharged across the whole headbox.
There
may be some mixing between streams in adjacent feed zones in this merging.
An example of a dilution headbox is the Valmet Sym-Flo D.
With respect to different details of structures of dilution headboxes and
equivalent
we refer to the following patents and patent applications: FI-92229 (corres.
EP-
0633352 Al) and US-5560807.
In some cases, multiple conventional (non-dilution) headboxes may be operated
to
form in combination a dilution headbox. This is possible if the headboxes do
not all
have the same feed streams, and there is a difference in composition between
some
of the feed streams to the individual headboxes. In this case, modulating the
slice lip
profiles has the effect of changing the combinatory proportions of the feed
streams
at each location across the web. However, the streams are not mixed, so the
effect
is similar to operation of a multilayer dilution headbox.
It should be noted that the feedstuffs used in the paper industry are of
complex
composition, containing many distinct material components suspended in an
aqueous
solution. The principal material components are fibers of different kinds,
with
properties which depend on the fiber source (Norway spruce, silver birch,
Eastern
hemlock, bagasse, kenaf, etc.), and pulping process used. Resins and synthetic
polymers, as well as various clays, minerals (ash), and other inorganic
material may
be added. Substances such as dyes, brighteners, anti-brighteners, bleaches.
and
opacity agents may occur in quantities which have negligible effects on the
weight,
strength, or other material properties of the web, but which have major
effects on
color, brightness, opacity, and other optical properties of the web. There may
also
be solutes dissolved in the aqueous solution, affecting its pH and other
chemical
properties, thus modulating the effect of other feedstuff components on
properties of
the web.
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As is known in prior art, in initially forming a paper web, the aqueous
solution is
drained through porous fabric (the "wire" of a forming section) into the wire
pit, as
whitewater, leaving much of the suspended material to substantially form the
web.
The whitewater at each section of the wire contains substantially the same
suspended
5 components as the suspension layer above it, but in lesser concentrations.
Normally,
whitewater is combined from all sections of the wire into a single stream.
When
several forming units are used, as in manufacture of a multilayer web, the
whitewater streams from each forming unit may be kept separate in the process,
or
may be merged into a composite whitewater stream.
The fraction of each component suspended in the jet which remains in the web
is
referred to as the "retention" of that component. Different components can
have
greatly differing retentions, and the retentions of some components is
affected by
chemical properties of the aqueous suspension (such as pH), and by
concentrations
of other components (such as polymers). Thus, the whitewater varies in its
compo-
nent concentrations differently to the jet. Moreover, the retention of each
component
can vary differently with process conditions.
The retention of each component generally increases if the web is made
heavier, but
to different extents. Since a single property of the web such as weight may
vary
across the web, and since the composition of the jet can vary across the web,
the
retention of each component in the jet can also vary across the web. As the
whitewater from the wire pit is a mixture of whitewater drained from all
locations
across the machine, the average retention can be inferred from concentration
measurements in the feed streams to a headbox.
Some paper machines make only a few grades of paper, and employ substantially
the
same feedstuffs under substantially similar process conditions whenever a
particular
= grade is being manufactured. Under these circumstances, each grade likely
has a
characteristic narrow range of retentions, and there is little variation in
concentra-
tions of the main feedstock or the whitewater.
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More commonly, however, paper machines make a variety of grades from
feedstuffs
of divers properties, and adjust process conditions accordingly. Under these
circum-
stances, retention of each component can vary greatly within a single grade,
and
across grades. Similarly, whitewater concentrations can vary differently for
each
component, both within and across grades. Large variations can occur over
short
times within a single grade.
Recycled fiber tends to be more variable in properties than new fiber, and its
use is
increasing in many paper machines. Use of a paper machine's repulped off-
specifi-
cation production (broke) varies from time to time, even in single grade
machines.
Thus, the plural feed streams to a dilution headbox normally contain different
concentrations of each feedstuff component. In general, the ratio of
concentrations
of a component in the several feed streams is different for each component. In
particular, a whitewater feed stream will be relatively richer in solutes and
fine
suspended solids than in fibers, and relatively richer in short fibers than in
long
fibers, when compared to the main feed stream.
The physical and chemical properties of the major feedstuff components exhibit
considerable variation. This is partly due to their natural origin, and partly
due to
variations in processing. These component variations, together with variation
in
blending of components to form a feedstuff, cause variation in the properties
of
feedstuffs. Variation in the operation of the short circulation of the paper
machine
can be a further cause of feedstuff property variation.
Until recently, it was labourious to perform more than a superficial
laboratory
analysis of concentrations and other properties of typical paper industry feed
streams. Accordingly, paper mill laboratories measure only a total retention,
and the
practice in the paper industry is to treat retention as a single quantity.
More sophisti-
cated laboratory instruments are now available, but due to remoteness from the
process and other practical concerns, analyses of headbox feed streams are
infre-
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quent. Moreover, a laboratory analysis is unlikely to be sufficiently timely
for
control purposes when retention is varying.
Devices which measure viscosity or freeness as an analogue of consistency (an
aggregate concentration of suspended solids) have been available for many
years, but
have been of mediocre reliability and accuracy. The technology underlying such
devices is also unsuited to low consistency regimes, such as those encountered
in
feed streams to the headbox. Accordingly, such devices have seldom been
installed
in headbox feed streams, and have not been employed previously in cross
machine
control of dilution systems.
Newer, more sophisticated measurement devices are suitable for continuously
and
rapidly measuring concentrations of low consistency streams. These are capable
of
measuring distinct component concentrations, or distinct aggregate
concentrations of
groups of components (such as total ash concentration or total fiber
concentration)
as well as, or instead of measuring the total consistency.
An example of such a concentration measurement device is the device marketed
by
the trademark Kajaani RM-200TM.
In addition to concentration, instruments are available for on-line
measurement of
other feed stream properties such as color and brightness of a sample, and for
measuring the distribution of fiber lengths in a sample.
Other factors, such as pH or temperature, may determine the extent to which a
feedstuff property affects web properties. Devices for measuring pH, various
solvated ionic species (as pNa, pK, etc.), or temperature are commonly
available,
including some suitable for use in headbox feed streams.
Many properties of the moving web can be measured during manufacture of paper.
Commonly, a paper machine is equipped with a number of measurement devices
which traverse the moving web at one or more locations on the paper machine.
-- - -- ------ ------
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Alternatively, an array of sensors may be deployed across the web, or
stationary
sensors may remotely measure properties across the web. Typical properties
measured are basis weight, water weight, ash weight, caliper, gloss,
brightness,
opacity, fiber orientation, and strength. Some of these properties may be
measured
in greater detail, such as distinguishing between different species of ash
(A1,)03,
CaCO3, Si02, Ti02, etc.) or different resins. Other properties, such as dry
weight,
fiber weight or percent moisture may be derived from these measurements.
These web property measurements are made in each of several subdivisions of
the
web in the cross machine direction, presented as a "profile" across the web.
With
modern measurement systems, the web subdivisions may be less than 1 cm in
width.
A control system for regulating the plural values of such a profile property
common-
ly provides a means for entering the desired shape of the profile. Moreover,
there
may be several properties, each with a different desired profile shape.
Moreover, properties of the suspension discharged from the headbox may be
measured during formation of the web on the wire. Such measurements should
also
be construed as web property measurements in the context of this invention,
pro-
vided a property is measured at plural locations in the cross machine
direction.
The ability to control the combinatory proportions of feed streams at each
feed zone
allows properties of the web to be controlled during manufacture. A change in
combinatory proportions at all feed zones' across the headbox can affect one
or more
properties of the web at all locations across the web. A change in combinatory
proportions at a single feed zone can affect one or more properties of the web
over
a portion of the web. The width of the affected portion of the web may not
corre-
spond to the width of the feed zone, and the effect may be unevenly
distributed in
magnitude or sign within the affected portion of the web. When more than one
property is affected, the effect on each property may be differently
distributed over
portions of the web which may differ in width and location.
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The effect on a material property of the web, such as ash weight, of changing
the
combinatory proportion of feed streams depends on the different concentrations
within those streams of each component which influences that property.
The effect on other properties of the web, such as color or opacity, depends
both on
material properties of the feed streams, and on non-material properties, such
as
brightness. The retention of each feed stream component over the affected
portion
of the web may also affect the magnitude of the effect, and this retention may
be
influenced by several measurable properties of the feed streams, such as pH or
temperature.
A control system can more effectively modulate the combinatory proportions of
the
feed streams if it can more accurately model the process effect of such
modulation
on each of the properties to be regulated. Such modelling requires that the
appropri-
ate feed stream properties are measured, and that the dependencies between
feed
stream properties and web properties be substantially known. Many such depend-
encies are common knowledge.
Since the plural feed streams to a dilution headbox contain different relative
amounts
of the various feedstuff components, and since each feedstuff component
affects one
or more web properties to various extents, it is evident that changing the
combinatory proportions of the feed streams can have dissimilar effects on
plural
web properties.
For example, if a dilution headbox utilizes two feed streams, one carrying
whitewater and the other carrying the main stock, the fiber in the web is
supplied
predominantly by the main stock stream, but the ash component may be supplied
in
similar degree by both streams. Thus, changing the combinatory proportions of
the
feed streams at one or more feed zones will clearly affect the web fiber and
ash
profiles differently.
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Nowadays, control systems exist which can effectively modulate one or more
cross
machine actuator systems to regulate one or more property profiles. The
regulation
of web properties can be enhanced by providing suitable measurements of
properties
of the plural feedstreams to a control system, and utilizing a process model
which
5 relates changes in web properties to the combinatory proportions of feed
streams and
to the properties of the feed streams.
An example of such a control system is the system marketed by the trademark
Valmet Damatic XDTM.
Regarding prior-art control systems of a paper machine, reference is also made
by
way of example to US Patent 5,381,341 (corres. EP Patent 0 401 188 and FI Laid-
Open Publication 85731.
The salient points of the above discussion can be summarized as
= The plural feed streams to a dilution headbox contain different relative
amounts of the various feedstuff components, and differ in other properties
such as
color, brightness, pH, temperature, etc.
= Each feedstuff component affects one or more web properties to various
extents. Web properties are also affected by other properties of the
feedstuffs, such
as color, brightness, pH, temperature, etc.
= Changing the combinatory proportions of the feed streams can have tangible
effects on plural web properties. The extent to which a web property is
affected by
a change in the combinatory proportions of feed streams depends on the
properties
of those feed streams.
= By deploying suitably accurate and reliable measurements of concentration or
other pertinent properties of the feed streams to a dilution headbox, a
control system
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can better regulate one or more property profiles of the web, by modulating
the
combinatory proportions of the feed streams at each feed zone of a dilution
headbox.
With a view to achieving the objectives stated above and those that will come
out
later, the method of the invention is mainly characterized in that a property,
such as,
concentration and/or consistency and/or brightness and/or color and/or
equivalent,
of one or more feedstuffs of said feed streams is measured and the thus
obtained
measurement signal is fed to said control system, and that, based on said
measure-
ment of the property profile or profiles and based on said measurements of
said
property, such as, concentration and/or consistency and/or brightness and/or
color
and/or equivalent, and based on setpoint values or equivalent, control signals
are
formed for regulating an actuator or an actuator combination situated at each
feed
zone of the headbox or headboxes, by which actuator or actuator combination
combinatory proportions of different feed streams supplied to the feed zone in
question are affected to achieve a desired property profile or profiles of the
web.
The apparatus of the invention is mainly characterized in that the apparatus
addi-
tionally comprises in combination the following means:
means for sampling continuously or at intervals each of two or more feed
streams
supplied to a headbox or headboxes;
means for measuring properties of said * feed streams, such as, concentrations
of
constituents in and/or brightness of and/or color of said samples;
regulation means for regulating combinatory proportions of said feed streams
at each
of a plurality of feed zones of the headbox or headboxes in a cross direction
thereof;
and
means for supplying the measurements of properties of said feed streams or
factors
calculated therefrom to said regulation means responsive to one or more
measured
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properties of the paper web and modulating the aforesaid combinatory
proportions
to regulate the aforesaid properties of the paper web.
In this invention, means are provided for sampling, continuously or at
intervais. the
material in each of two or more of the feed streams to a headbox which is
equipped
with means for controlling combinatory proportions of those feed streams at
each of
plural feed zones across the headbox, and means are provided for measuring
properties such as the concentrations of constituents in these samples, and
means are
provided for supplying those measurements or factors calculated therefrom to
any
regulatory means responsive to one or more measured properties of the web and
modulating the aforesaid combinatory proportions to regulate the aforesaid
prop-
erties.
The novelty of this invention is in the use of means of sampling two or more
feed
streams to a headbox which is so equipped, together with means of measuring
properties such as the concentrations of constituents of those samples,
together with
means of supplying those measurements or factors calculated therefrom to a
means
of regulating properties of the web during manufacture.
The benefits of this invention include more effective modulation of the
combinatory
proportions of the feed streams by any regulatory means responsive to one or
more
properties of the web, where such means includes means for modulation of the
combinatory proportions of the feed streams at each of several feed zones
across a
headbox. The importance of this benefit is greatest in situations where one or
more
of the feed streams undergoes, or is likely to undergo a change in
concentration of
one or more of its constituents, or a change in brightness or color, or a
change in
another measured property, such changes occurring either continuously or
intermit-
tently, and in divers amounts.
The feed stream property measurements are used to calculate the effective
proportionality factors between changes in the combinatory proportions of the
feed
streams and changes in properties of the web which are influenced by these
feed
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stream properties and combinatory proportions. Such effective proportionality
factors
may be for changes in the average combinatory proportions of the feed streams
across the headbox, and may also or alternatively be for changes in the local
combinatory proportions in each feed zone of the headbox. Such effective
proportionality factors may be for the change in the average of a property
across the
web, or for the local property at each of several subdivisions of the web
across the
machine, where such subdivisions normally correspond substantially to the feed
zones, but may alternatively correspond to narrower or broader subdivisions of
the
sheet.
Normally, each feed stream to the headbox is sampled, or such streams are
sampled
as are combined to substantially form each feed stream. However, it is not
necessary
to measure each property in all feed streams, since it may be known that a
particular
property is negligibly present or invariant in some feed streams. Similarly,
it is
possible that some feed streams may be unsampled, and have no property measure-
ments. For example, if a feed stream supplies fresh clear water, it is
unnecessary to
measure the amount of fibre present in the stream, since the stream is a
priori known
to contain none. Similarly, if a stream is formed by dosing a colorant of
substantially
known hue and intensity into a stream of substantially known color, and said
dosing
ratio is regulated and known, it is unnecessary to measure the color of the
resulting
stream, as its color can be calculated ab initio from known quantities.
Each means of sampling a stream may be situated at any convenient point in the
stream. In the case that more than one means of measuring a concentration or
other
property is supplied with a sample from a stream, a means of sampling the
stream
may be provided for each means of property measurement, or a means of sampling
the stream may be shared among several means of property measurement.
Normally, the sampled streams are the main stock stream and the dilution
stream, or
such streams as are combined to substantially form the main stock stream and
the
dilution stream, and each means of sampling a stream may be situated at any
convenient point in the stream in the case that more than one means of
measuring a
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concentration or other property is supplied with a sample from a stream, a
means of
sampling the stream may be provided for each means of property measurement, or
a means of sampling the stream may be shared among several means of property
measurement.
Means for measuring concentration or other property may be one or more instru-
ments attached permanently, periodically, or intermittently to a means for
sampling
a stream, or may be one or more instruments remote from the means for sampling
the streams, and to which samples must be brought. Additionally or
alternatively,
means for sampling a stream may be integral to a means for measuring
concentration
or other property, including cases where the sampling of the stream takes
place
within the stream, by exposure within the stream of an element of the means
for
property measurement. Means for sampling the streams may be autonomous or
manually operated, and a means for measuring properties of a sample may be
autonomous or manually operated. Means for measuring sample properties may be
a laboratory procedure, carried out manually or mechanically.
Each means of measuring concentration may be responsive to the individual
concen-
tration of one or more constituents of the sample of the stream, or may be
respon-
sive to one or more aggregate concentrations of combined constituents of the
sample
of the stream, or may be responsive to both individual and aggregate
concentrations.
The measured concentrations are commonly for constituents such as a particular
fiber type or a particular chemical species, or aggregates of constituents
such as total
fiber or total ash content. Each means of measuring other properties may be
responsive to one or more optical properties, such as brightness or color, or
may be
responsive to one or more thermal or mechanical properties, such as viscosity,
or
may be responsive to chemical properties, such as pH, or to other properties,
such
as conductivity or magnetic reluctance. In practice, a single instrument may
provide
measurements of several properties, which may include concentration, optical,
electromagnetic, thermal, mechanical, and chemical properties.
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In the following, the invention is described in detail with reference to some
exemp-
lifying embodiments of the invention illustrated in the figures of the
accompanying
drawing, to the details of which embodiments the invention is in no way
narrowly
limited.
5
Figure 1 schematically illustrates a simple embodiment of the invention.
Figures 2a, 2b, and 2c schematically illustrate some variant arrangements for
parts
of Figure 1.
Figure 3 schematically illustrates another embodiment of the invention, in
which a
third feed stream is supplied to the headbox.
Figure 4 schematically illustrates another embodiment of the invention, in
which
there are two layers of feed zones in the headbox, with independent modulation
of
combinatory proportions in each layer.
Figure 5 schematically illustrates another embodiment of the invention, in
which the
slice lip of a dilution headbox is modulated in conjunction with modulation of
combinatory proportions of a feed stream at each feed zone.
Figure 6 schematically illustrates another embodiment of the invention, in
which two
dilution headboxes are supplied with two feed streams each, with their webs
spliced
together during manufacture.
Figure 7 schematically illustrates a variant on the embodiment depicted in
Figure 1,
in which the controlled web property profiles are measured at several
locations in the
paper machine, including a web measurement apparatus situated in the forming
section.
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Figure 8 schematically illustrates another embodiment of the invention, in
which two
conventional headboxes are supplied with different feed streams, with their
webs
spliced together during manufacture.
Figures 9, 10, 11, and 12 depict block diagrams for embodiments of the
invention
which comprise methods of regulating web properties.
Figures 13a, 13b, 13c, and 13d depict variations on certain parts of the
embodiments
shown in the preceding figures.
Figure 1 schematically depicts an embodiment of the invention where a dilution
headbox 3 is provided with two feed streams 11 and 12. One stream 11 supplies
a
stock suspension, while the other 12 supplies a dilution medium. The two feed
streams 11,12 feed each feed zone of the headbox 3 by means of a suitable
valve
arrangement 10. The valve means 10 of the feed zones to the headbox feed zones
are
regulated by a computer or other instrument 110 which can conununicate with
other
computers or instruments. Each feed stream 11,12 is equipped with a stream
sampling arrangement 21,22, and these stream sampling arrangements 21,22 are
connected to concentration measurement devices 31,32 which measure one or more
concentrations or other properties of the streams.
The feed stream property measurement devices 31,32 are connected to a computer
or other instrument 130 which can communicate the measured properties or
factors
calculated therefrom to other computers or instruments. The headbox discharge
forms the paper web 5, which moves along the machine. A measurement device 40,
commonly a frame with a traversing sensor platform, situated on the machine
measures one or more properties of each subdivision of the web 5 as it passes
the
device 40. This device 40 is connected to a computer or other instrument 140
which
can communicate with other computers or instruments. A control system 150
communicates with the feed zone regulating computers or instruments, with the
stream property measurement computers or instruments 130, and with the web 5
property measurement computers or instruments 140. The control system 150
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17
regulates one or more web 5 property profiles supplied by the web 5
measurement
system 140 by modulating the combinatory proportions of the two feed streams
11,12 at each feed zone, by means of the actuation system 110, and employs in
its
control calculations the feed stream property measurements or factors
calculated
therefrom, supplied by the stream measurement system 130 for both of the
streams
11,12. Means 151 are normally provided to furnish information from the control
system to human operators, and for the operators to enter commands and
setpoint
values to the control system.
The number of feed zones may be greater than three, and the feed zones may be
of
equal or unequal capacity and characteristics. It is not necessary for all
means of
combining flows to be identical, and not all need be modulated by the web
property
profile regulator, provided at least three are so modulated. The various
measurement
and control systems may be embodied in a greater or lesser number of elements
than
shown. There may be plural means 151 for interaction with human operators, or
none, and when such plural means are employed, they may be similar or
dissimilar.
Note that the number of feed zones shown in Figure 1 is three, but the
embodiment
includes greater numbers of feed zones, of equal or unequal flow capacity and
evenly or unevenly distributed across the headbox. Note that the salient
functions of
the various systems may in practice be combined in a lesser number of distinct
units,
or divided among a greater number of units. Note that the concentrations or
other
properties of the feed streams are used in the control calculations for
regulating web
properties by modulating combinatory proportions of feed streams in each feed
zone
of the headbox 3.
Figure 2a schematically depicts a simple variation of the embodiment presented
in
Figure 1, and described above. In this variant, a feed stream has two sampling
arrangements 21,26, each with a single device for measuring stream properties
31,
36. These devices 31,36 are connected to a computer or other instrument 130
capable of communicating with other computers or instruments. The control
system
150 employs in its control calculations the feed stream property measurements
or
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18
factors calculated therefrom, supplied by the stream measurement system 130
for all
three of the stream measurement devices 31,32,36.
Figure 2b schematically depicts a simple variation of the embodiment presented
in
Figure 1, and described above. In this variant, both feed streams 11,12 have
two
sampling arrangements 21,22,26,27, each with a single device for measuring
stream
properties 31,32,36,37. These devices are connected to a computer or other
instru-
ment 130 capable of communicating with other computers or instruments. The
control system 150 employs in its control calculations the feed stream
property
measurements or factors calculated therefrom, supplied by the stream
measurement
system 130 for all four of the stream measurement devices 31,32,36,37.
Figure 2c schematically depicts a simple variation of the embodiment presented
in
Figure 1, and described above. In this variant, two property measurement
devices
35, 36 are connected to one of the sampling arrangements 26. These devices are
connected to a computer or other instrument 131 capable of communicating with
other computers or instruments. The control system 150 employs in its control
calculations the feed stream property measurements or factors calculated
therefrom,
supplied by both stream measurement systems 130,131 or the four stream measure-
ment devices 31,32,35,36.
Figure 3 schematically depicts a variation of the embodiment presented in
Figure 1,
and described above. In this embodimeni, three feed streams 11,12,13 are fed
to
each feed zone of the headbox, and each feed zone of the headbox 3 has means
10
suitable for modulating the flow proportions from the three feed streams 11,12
,13 .
A sampling arrangement 23 for the third stream 13 is connected to a feed
stream
property measurement device 33, which is connected to a computer or other
instru-
ment 130 capable of communicating the measurements to other computers or
instruments. The control system 150 regulates one or more profiles supplied by
the
web measurement system 140 by modulating the combinatory proportions of the
three feed streams at each feed zone of the headbox 3, by means of the
actuation
system 110, and employs in its control calculations the feed stream property
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19
measurements or factors calculated therefrom, supplied by the stream
measurement
system 130 for each of the three streams 11,12,13.
The control system 150 regulates one or more profiles of the web 5 supplied by
the
web 5 measurement system 140 by modulating the combinatory proportions of the
three feed streams (11,12,13) at each feed zone by means of the actuation
system
110, by employing in control calculations the concentration measurements or
factors
calculated therefrom, supplied by the stream measurement system 130 for each
of
the three streams (11,12,13).
Figure 4 schematically depicts a variation of the embodiment presented in
Figure 1,
and described above. In this variant, three feed streams 11,12,13 are fed to a
dilution headbox 3 equipped with two layers of independently modulated feed
zones.
One feed stream 13 supplies the upper layer only, another 11 supplies both
layers,
and the third 12 supplies the lower layer only. The combinatory proportions in
each
feed zone in each of the two layers of feed zones of the headbox are modulated
by
means of suitable valve arrangements 10a, lOb provided for each layer. The
valve
arrangements 10a,10b to the headbox feed zones in both layers are regulated by
a
computer or other instrument 110,111 capable of communicating with other com-
puters or instruments. The control system 150 regulates one or more profiles
supplied by the measurement system 140 by modulating the combinatory
proportions
of the feed streams at each feed zone of each layer, by means of their
actuation
systems 110,111, and employs in its control calculations the feed stream
property
measurements or factors calculated therefrom, supplied by the stream
measurement
system 130 for the three stream measurement devices 31,32,33. Additionally,
the
control system 150 may similarly modulate the combinatory proportions of
layers,
either of entire layers or of subdivisions of layers.
The number of feed layers may be greater than two, and not all layers need
have a
means of combining flows to their feed zones. Also, not all layers which have
means
of combining flows to their feed zones need be modulated by the web property
profile regulator. The means of combining flows to feed zones in different
layers
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may be of equal or unequal capacity and characteristics. The number and
character
of feed zones and associated means may differ between layers, but at least one
layer
should have at least three means of combining flows, where such means are modu-
lated by the profile regulator.
5
The embodiment of Figure 4 may be generalized to more than two layers, of
equal
or unequal characteristics. The number of feed streams to feed zones may
differ
between layers. Each feed stream may feed one layer or more than one layer.
More
than one feed stream may convey the same feedstuff, provided at least one
layer of
10 feed zones is supplied with two or more different feed streams.
Figure 5 schematically depicts a variation of the embodiment presented in
Figure 1,
and described above. In this embodiment, arrangements 15 are also provided for
modulating the slice lip of the headbox 3 at plural locations across the web
5. The
15 arrangement 15 for modulating the slice lip of the headbox is regulated by
a com-
puter or other instrument 115 capable of communicating with other computers or
instruments. The control system 150 regulates one or more profiles supplied by
the
measurement system 140 by modulating the combinatory proportions of the feed
streams at each feed zone of the headbox 3 by means of their actuation system
110,
20 and by modulating the shape of the headbox slice lip by means of its
actuation
system 115, and employs in its control calculations the feed stream property
measurements or factors calculated therefrom, supplied by the stream
measurement
system 130 for both of the streams 11,12.
In the embodiment of Figure 5 one or more property profiles can be regulated
by the
combined modulation of feed stream combinatory proportions and slice lip
shape.
Usually two or more property profiles are of interest, such as fiber
orientation and
dry weight or caliper.
Figure 6 schematically depicts a variation of the embodiment presented in
Figure 1,
and described above. In this embodiment, four feed streams 11,12,13,14 are fed
to
two dilution headboxes 3a,3b equipped with independently modulated feed zones,
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21
where the webs 5a,5b produced by the headboxes 3a,3b are spliced into a single
web
before the measurement device 40. Two feed streams 11,12 supply the lower
headbox 3a only, and the other two feed streams 13,14 supply the upper headbox
3b
only. The combinatory proportions in each feed zone in each of the two
headboxes
5 3a,3b are modulated by means of a suitable valve arrangement 10a, lOb for
each
headbox 3a,3b. The valve arrangements 10a, lOb for the feed zones in each
headbox
3a,3b are regulated by a computer or other instrument 110,111 capable of
communi-
cating with other computers or instruments. The control system 150 regulates
one or
more profiles of the web 5 supplied by the measurement system 140 by
modulating
the combinatory proportions of the feed streams at each feed zone of each
layer, by
means of their actuation systems 110,111, and employs in its control
calculations the
feed stream property measurements or factors calculated therefrom, supplied by
the
stream measurement system 130 for the four stream measurement devices 31,32,
33,34. Additionally, the control system 150 may similarly modulate the
combinatory
proportions of layers of headboxes 3a,3b, either of entire headboxes or of
subdivi-
sions of headboxes.
The number of headboxes may be greater than two, and not all headboxes need
have
a means of combining flows to their feed zones. Also, not all headboxes which
have
means of combining flows to their feed zones need be modulated by the web
property profile regulator. The means of combining flows to feed zones in a
headbox
may be of equal or unequal capacity and characteristics. The number and
character
of feed zones and associated means may differ between headboxes, but at least
one
headbox should have at least one layer which has at least three means of
combining
flows, where such means are modulated by the profile regulator.
This embodiment may be generalized to more than two headboxes, of equal or
unequal characteristics, where their webs are spliced together during
manufacture.
Each headbox may have its own forming section, or more than one headbox may be
on the same forming section. For regulation of web property profiles, multiple
headboxes are analogous to a single headbox with number and type of layers
equal
to the sum of the actual headbox layers.
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22
Figure 7 schematically depicts a simple variation of the embodiment presented
in
Figure 1, and described above. In this variant, three web measurement devices
40,
41,42 are deployed at different locations on the paper machine, and each is
con-
nected to a computer or other instrument 140,141,142 which can communicate
with
other computers or instruments. The control system 150 regulates one or more
profiles supplied by one or more of the web measurement instruments
140,141,142
by modulating the combinatory proportions of the two feed streams at each feed
zone, by means of the actuation system 110, and employs in its control
calculations
the feed stream property measurements or factors calculated therefrom,
supplied by
the stream measurement system 130 for both of the streams 11,12.
The various measurement devices and systems may be embodied in a greater or
lesser number of elements than shown. A web measurement device may be con-
nected to more than one web measurement computer or instrument, and a web
measurement computer or instrument may be connected to more than one web
measurement device. A web measurement computer or instrument may be incorpor-
ated within a web measurement device.
Where means of measuring web property profiles are deployed at plural
locations in
the machine, each means may measure single or plural or all measured property
profiles. Each measured property profile may be measured at single or plural
or all
means. Where plural means each measure plural web property profiles, each of
the
plural means may measure the same or a different plurality of web property
profiles.
Figure 8 schematically depicts another embodiment of the invention, in which
two
conventional headboxes 3a,3b are supplied with different feed streams 11,12.
The
arrangements for modulating the slice lip of each headbox are regulated by a
computer or other instrument 115,116 capable of communicating with other com-
puters or instruments. The control system 150 regulates one or more profiles
supplied by the web measurement system 140 by modulating the combinatory
proportions of the feed streams at each feed zone of each layer of the
headbox, by
means of the slice lip actuation systems 15a,15b,115. and employs in its
control
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23
calculations the feed stream property measurements or factors calculated
therefrom,
supplied by the feed stream measurement system 130 for the feed stream
property
measurement devices 31,32. Additionally, the control system 150 may similarly
modulate the combinatory proportions of headboxes, either of entire headboxes
or of
subdivisions of headboxes.
The number of headboxes may be greater than two, and not all headboxes need
have
a means of modulating their slice lips. Also, not all headboxes which have
means of
modulating their slice lips need be modulated by the web property profile
regulator.
The number of means of modulating the slice lip may be greater than three, and
may
be evenly or unevenly distributed across the slice lip, and may have equal or
unequal
capacity across the slice lip. The number and character of means of modulating
slice
lips may differ between headboxes, but at least one headbox should have at
least
three means of modulating its slice lip, where such means are modulated by the
profile regulator.
The two conventional headboxes are, within the context of this invention,
operated
as if they formed a single dilution headbox, where modulating the shape of the
slice
lip on each headbox alters the profile of combinatory proportions of the two
jets.
This embodiment may be generalized to more than two headboxes, of equal or
unequal characteristics, where their webs are spliced together during
manufacture.
For regulation of web property profiles, multiple conventional headboxes are
analogous to a single dilution headbox with number and type of feed streams
equal
to the sum of the feed streams to the individual headboxes.
Figure 9 depicts another embodiment of the invention as a block diagram of a
method for regulating a web property profile by modulating combinatory
proportions
of two streams to plural feed zones in a dilution headbox, which uses
measurements
of feed stream properties in its calculations. A property measurement is
provided for
each of the two feed streams m31, m32. These measurements are used in a
calcula-
tion unit 230, to produce the effective proportionality factor p41 between
changes in
combinatory proportions of the two feedstreams and changes in the regulated
web
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24
property. The web property measured profile m41 and its setpoint profile s41
are
supplied to a calculation unit 241 which produces the web property error
profile e41.
The proportionality factor p41 and the web property error profile e41 are used
by
the profile regulation means 210 to modulate its output slO, which is normally
the
combinatory proportion setpoint profile, or a profile of setpoints for such
means as
substantially determine the combinatory proportion profile.
Only the essential elements are shown in this block diagram. The
proportionality
factor calculation unit 230 may employ other measurements and factors in
addition
to those shown, as may be required for the process relation between the
regulated
web property and the feed stream properties. The proportionality factor p41
may be
a single value effective across the whole headbox, or it may be a profile of
values,
each effective in one or more feed zones of the headbox, or it may be a matrix
of
values, each effective in one or more feed zones of the headbox and in some
subdivisions of the web in the cross machine direction, where the number of
rows
in such matrix of values need not be the same as the number of columns. The
proportionality factor p41 may be supplied directly by the feed stream
property
measurement means. The web property profile regulator 210 may employ other
measurements and factors in addition to those shown. The web property profile
error
e41 calculation unit 241 may be contained within the regulator 210, and may
utilize
weighting factors or nonlinear operations in addition to a simple error
calculation.
The operations performed within the regulator 210 may be any commonly known
algorithms for profile regulation, including, but not limited to
i) an array of PID-type regulators, each governing a single feed zone or group
of adjacent feed zones, with or without compensation for cross coupling
between individual regulators,
ii) optimization of a penalty function formed by using nonlinear operations on
the error profile, such as squaring and summation, where said penalty
function may also include other nonlinear operations on other profiles such
as the combinatory proportion profile, such inclusion being by means of
weighted addition, and where said optimization involves minimization by
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adjustment of the combinatory proportions of feed zones, and which optional-
ly includes simulation of the resulting error profile,
iii) an array of controllers employing fuzzy logic techniques, each governing
a
single feed zone or group of adjacent feed zones, with or without compensa-
5 tion for cross coupling between individual regulators,
iv) an artificial neural network, with inputs from inter alia the error
profile and
outputs to combinatory proportions, where said network has been trained, or
has the capability to train itself, to adjust its outputs so that its inputs
are
driven towards zero.
Such operations may additionally include any commonly known time domain
compensation method for profiles, including but not limited to
i) an array of Smith predictors and variants thereon, including variants with
provision for identification of model parameters for use in prediction,
ii) an array of Kalman filters.
Figure 10 depicts a variation of the embodiment presented in Figure 9, and
described
above. In this embodiment, a second web property profile measurement m42 and
its
setpoint profile s42 are supplied to a calculation unit 242 which produces a
second
web property error profile e42. The proportionality factor calculation unit
230
produces a second effective proportionality factor p42, which relates changes
in the
combinatory proportions of the two feed streams to changes in the second
profile.
Both proportionality factors p41, p42 and both web property error profiles
e41, e42
are used by the profile regulation means 210 to modulate its output.
The calculation methods for the second web property error profile, and for the
second effective proportionality factor may differ from those for the first.
The
operation of the profile regulating means may be modulated by use of weight
factors
or similar techniques, such that the regulation of one profile takes
precedence over
the other, or such that the regulation effects a compromise between regulation
of one
or the other.
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26
Figure 11 depicts a variation of the embodiment presented in Figure 9, and
described
above. In this embodiment, a property measurement is provided for a third feed
stream m33, and supplied to a calculation unit 230 which produces effective
proportionality factors p4la, p4lb, which relate changes in the combinatory
propor-
tions of the three feed streams to changes in the regulated profile. Both
proportionality factors p4la, p4lb and the web property error profile e41 are
used
by the web property profile regulation means 210 to modulate its outputs slOa,
slOb,
which are normally the combinatory proportion setpoint profiles, or profiles
of
setpoints for such means as substantially determine the combinatory proportion
profiles.
Figure 12 depicts a variation of the embodiment presented in Figure 9, and
described
above. In this embodiment, a second property measurement is provided for each
of
the two feed streams m36, m37 and supplied to a calculation unit 230, which
produces the effective proportionality factor p41, which relates changes in
the
combinatory proportions of the two feed streams to changes in the regulated
profile.
The calculation unit 230 uses the measurements of both properties in both feed
streams to produce the effective proportionality factor p41.
Figure 13a schematically depicts a simple variation of the embodiment
presented in
Figure 9, and described above. In this variant, a means 215 is provided for
convert-
ing a combinatory proportion setpoint profile s10 into setpoint profiles s15a,
s15b
for slice lips of two headboxes such that said combinatory proportion profile
is
achieved between two headboxes. Optionally, a means 225 may also be provided
for
calculating the prevailing combinatory proportion profile mlO from the
measured
slice lip profiles m15a, m15b. The means 215 and 225 may optionally employ
additional measurements and factors in their calculations.
Figure 13b schematically depicts a simple variation of the embodiment
presented in
Figure 9, and described above. In this variant, the prevailing combinatory
proportion
profile mlO is also supplied to the web property profile regulation means 210,
for
use therein.
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27
Figure 13c schematically depicts a simple variation of the embodiment
presented in
Figure 9, and described above. In this variant, the web property profile
regulation
means 210 modulates both the profile of combinatory proportions of the two
feed
streams s10, and the slice lip profile of the headbox s15. Optionally the
prevailing
slice lip profile m15 can be supplied to the web property profile regulation
means
210, for use therein.
Figure 13d schematically depicts a simple variation of the embodiment
presented in
Figure 9, and described above. In this variant, the prevailing combinatory
proportion
profile mlO and the measured web property profile m41 are also supplied to the
calculation unit 230 which may use them in calculating a profile or matrix of
effective proportionality factors p41.
Other embodiments of the invention are the obvious permutations of the salient
features described in these embodiments and their generalizations. For
example, an
immediately obvious generalization is the application of this invention to
multi-layer
machines with one or more dilution headboxes and one or more conventional
headboxes.
In all of these embodiments, the measurement of concentrations or other
properties
of the feed streams allows calculation of effective proportionality factors
between
changes to combinatory proportions of feed streams and changes to property
profiles
at each subdivision of the web in the cross machine direction.
The accurate and timely calculation of such proportionality factors greatly
enhances
the potential effectiveness of a control system, since most control algorithms
can use
them advantageously. When feed stream concentrations change, the controller
can
adjust combinatory proportions of feed streams to the headbox feed zones to
compensate for those changes before any adverse effects occur in the regulated
properties of the web.
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28
Furthermore, accurate knowledge of such proportionality factors allows more
precise
modulation of combinatory proportions of feed streams to the headbox feed
zones.
Since the effect of a modulation is accurately known, a controller can make
exact
rather than approximate control corrections, both in response to a process
disturb-
ance and in response to a change in target.
Example of Proportionality Factor
As one example, the effective proportionality factor between a web 5 property
W
(such as dry weight or ash weight), whose value is Wl at a subdivision i of
the web
in the cross machine direction, and the combinatory proportion Kj of two feed-
streams to feed zone j of the headbox, where the constituent (such as total
consist-
ency or ash consistency) influencing the property has measured concentration
CD in
the stream whose proportion is Kj, and measured concentration CS in the stream
whose proportion is 1-Kj may be calculated as
aWi Rji (CD-CS) Wi
------------
c3Ki CDKj + CS(1-KP
where R.I is a coefficient indicating the degree of influence of feed zone j
of the
headbox over a property in subdivision i of the web. The formulation expressed
above defines a matrix of proportionality values, each effective for a single
headbox
feed zone and a single subdivision of the web. Other formulations may be used
to
relate properties such as opacity, brightness, or color of the web to TiO2 )
concentra-
tion in or brightness or color of the feed streams. Similarly, other
formulations may
be used to relate other properties of the web to pertinent properties of the
feed
streams.
Whereas in the embodiments and drawings described above, particular variants
of
the invention are depicted, it should be understood that the invention is not
restricted
to the variants presented. Its applicability extends to other combinations of
the
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29
features presented in the embodiments and drawings. Its applicability extends
to
obvious generalizations of the various particulars presented.
Whereas in the drawings and embodiments, references are made to a particular
number of feed streams, and to particular combinations of feedstuffs in those
feed
streams, it should be understood that this invention is not restricted to the
particulars
presented. Its applicability extends to any number or arrangement of feed
streams,
provided they are fed to plural feed zones across the headbox with means of
modulating their combinatory proportions at each feed zone, and to any set of
feedstuffs supplied to a headbox in these feed streams. Its applicability
extends
beyond any particular arrangements of computers, communication lines, and
other
equipment which can vary freely between realizations of the invention.
Whereas in the embodiments and drawings, references are made to particular
property profiles and to particular cross machine actuation systems (other
than the
feed stream proportion profile), it should be understood that this invention
is not
restricted to the particulars presented. Its applicability extends to
regulation of any
property profile or combination of property profiles. Its applicability
extends to
regulation of one or more profiles by means of modulating other cross machine
actuation systems in addition to modulating the feed stream proportion
profile.
Whereas in the embodiments and drawings, reference is generally made to a
single
headbox, it should be noted that the invention is not restricted to single
headbox
control configurations. The invention extends to multiple headbox
arrangements, one
or more of which is a dilution headbox with means of modulating combinatory
proportions of two or more feed streams at each of plural feed zones, with
concen-
tration measurements of samples in plural feed streams to one or more such
dilution
headboxes. The invention extends to control of multiple dilution headboxes in
concert, and to combinations of dilution headboxes and conventional headboxes.
The essence of this invention is not in the use of any particular formula in
calculat-
ing effective proportionality factors for a means of regulating one or more
properties
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of the web, nor is it in the use of any particular means of regulating one or
more
properties of the web used in controlling the operation of the headbox. The
essence
of this invention is in the use of means of sampling two or more feed streams
to a
headbox as described above, with means of measuring properties of constituents
of
5 said samples, and in the use of the measured properties or factors
calculated
therefrom in any formulation used in any means of regulating properties of the
web
during manufacture, where such regulatory means modulate the combinatory
proportions of the feed streams at several feed zones across the headbox.
10 The claims are presented in the following and the various details of the
invention
may vary within the inventive idea defined by said claims and differ from the
disclosure given above by way of example only.
