U.S. patent application number 12/330884 was filed with the patent office on 2009-04-23 for apparatus and method for monitoring the transfer of a material web.
This patent application is currently assigned to Voith Paper Patent GmbH. Invention is credited to Uwe Joos, Tobias Wanke.
Application Number | 20090101299 12/330884 |
Document ID | / |
Family ID | 35456012 |
Filed Date | 2009-04-23 |
United States Patent
Application |
20090101299 |
Kind Code |
A1 |
Wanke; Tobias ; et
al. |
April 23, 2009 |
APPARATUS AND METHOD FOR MONITORING THE TRANSFER OF A MATERIAL
WEB
Abstract
A machine, for at least one of producing and treating a web of
fibrous material in which the web is guided along a web guide path
by at least one web guide device from one of a web production
section and a web input section to pass at least one web treatment
device, includes a first apparatus configured for forming a
transfer strip of the web and for transferring the transfer strip
through the machine, the machine being configured for transferring
the web along the web guide path in that the first apparatus is
configured for forming the transfer strip which is a leading
transfer strip of the web, for guiding the transfer strip through
the machine, and for increasing the transfer strip to a full width
of the web and thereby performing tail widening; and a second
apparatus configured for detecting a break in the web, the second
apparatus being configured for responding to a break in one of the
transfer strip and the web during a transfer of the web and during
an increase in a width of the transfer strip.
Inventors: |
Wanke; Tobias; (Neu-Ulm,
DE) ; Joos; Uwe; (Konigsbronn, DE) |
Correspondence
Address: |
TAYLOR & AUST, P.C.
P.O. Box 560, 142. S Main Street
Avilla
IN
46710
US
|
Assignee: |
Voith Paper Patent GmbH
|
Family ID: |
35456012 |
Appl. No.: |
12/330884 |
Filed: |
December 9, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11233966 |
Sep 23, 2005 |
7473335 |
|
|
12330884 |
|
|
|
|
Current U.S.
Class: |
162/255 ;
162/263 |
Current CPC
Class: |
D21F 7/04 20130101; D21G
9/0063 20130101; D21F 5/042 20130101 |
Class at
Publication: |
162/255 ;
162/263 |
International
Class: |
D21F 7/04 20060101
D21F007/04; D21F 7/06 20060101 D21F007/06 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 27, 2004 |
DE |
10 2004 046 795.1 |
Claims
1. A machine for at least one of producing and treating a web of
fibrous material in which the web is guided along a web guide path
by at least one web guide device from one of a web production
section and a web input section to pass at least one web treatment
device, said machine comprising: a first apparatus configured for
forming a transfer strip of the web and for transferring the
transfer strip through the machine, the machine being configured
for transferring the web along the web guide path in that said
first apparatus is configured for forming said transfer strip which
is a leading transfer strip of the web, for guiding said transfer
strip through the machine, and for increasing said transfer strip
to a full width of the web and thereby performing tail widening;
and a second apparatus configured for detecting a break in the web,
said second apparatus being configured for responding to a break in
one of said transfer strip and the web during a transfer of the web
and during an increase in a width of said transfer strip.
2. The machine as claimed in claim 1, wherein said second apparatus
is configured for responding to a break in one of said transfer
strip and the web on a basis of at least one detection variable
representing said width of said transfer strip, one of directly and
indirectly.
3. The machine as claimed in claim 2, wherein said at least one
detection variable representing said width of said transfer strip
is pressure.
4. The machine as claimed in claim 2, wherein said second apparatus
has at least one of an optical detection arrangement and a
temperature detection arrangement in order one of to detect said
break in the web and to provide said at least one detection
variable.
5. The machine as claimed in claim 2, wherein said second apparatus
has at least one of a pressure detection arrangement and a pressure
change detection arrangement in order at least one of to detect
said break in the web and to provide a plurality of pressure values
as said at least one detection variable.
6. The machine as claimed in claim 5, wherein said second apparatus
includes at least one of a vacuum device and a positive pressure
device acting on one of the web and said transfer strip, wherein
said at least one of said pressure detection arrangement and said
pressure change detection arrangement is configured for detecting
at least one instantaneous operating pressure of said at least one
of said vacuum device and said positive pressure device acting on
one of the web and said transfer strip.
7. The machine as claimed in claim 6, wherein said at least one of
said vacuum device and said positive pressure device is configured
for at least participating in guiding one of the web and said
transfer strip as part of the web guide device.
8. The machine as claimed in claim 6, wherein said vacuum device
includes at least one of a suction roll, a suction box, and a
vacuum transport belt.
9. The machine as claimed in claim 8, wherein said at least one of
said pressure detection arrangement and said pressure change
detection arrangement includes at least one pressure sensor which
is arranged in one of said suction box and said blower box.
10. The machine as claimed in claim 9, wherein said suction box
includes a transfer suction zone and an operating suction zone,
said transfer suction zone being assigned to said transfer strip,
said operating suction zone being, together with said transfer
suction zone, assigned to said full width of the web, said
operating suction zone being one of connected and configured for
being connected via said transfer suction zone to a vacuum source,
said pressure sensor being arranged in said operating suction
zone.
11. The machine as claimed in claim 6, wherein said positive
pressure device includes at least one of a blower roll, a blower
box, and an air turn.
12. The machine according to claim 6, further including an
evaluation unit configured for (a) comparing one of a plurality of
detected said pressure values and a plurality of consequential
values dependent on said plurality of detected pressure values at
least one of with one another and with at least one predefined
reference value, and (b) outputting a break signal when at least
one break condition is fulfilled.
13. The machine as claimed in claim 12, wherein said evaluation
unit is configured for comparing a magnitude of one of said
plurality of detected pressure values and said plurality of
consequential values corresponding to said plurality of detected
pressure values recorded successively in order to check said break
condition, said break condition being fulfilled when one of said
plurality of detected pressure values and said plurality of
consequential values deviates from a predefined reference
curve.
14. The machine as claimed in claim 13, wherein said break
condition is fulfilled when one of (a) in a case of said vacuum
device, a pressure value that is assigned to a later time is one of
greater than and equal to a pressure value that is assigned to an
earlier time, and (b) in a case of said positive pressure value
device, a pressure value that is assigned to a later time is one of
less than and equal to a pressure value that is assigned to an
earlier time.
15. The machine as claimed in claim 13, wherein said break
condition is fulfilled when one of (a) in a case of said vacuum
device, a pressure value assigned to a later time exceeds a
pressure value assigned to an earlier time by a predefined
threshold value, and (b) in a case of said positive pressure
device, a pressure value assigned to a later time falls below a
pressure value assigned to an earlier time by a predefined
threshold value.
16. The machine as claimed in claim 13, wherein said evaluation
unit is configured for comparing one of said plurality of detected
pressure values and said plurality of consequential values
dependent on said plurality of detected pressure values with one
said predefined reference value in order to test a tail-widening
finished condition which is fulfilled when said pressure value
reaches a threshold value corresponding to said predefined
reference value.
17. The machine as claimed in claim 16, wherein said second
apparatus is configured for being changed over to a normal
operation monitoring mode when said tail-widening finished
condition is fulfilled.
18. The machine as claimed in claim 1, wherein the machine is
configured for initiating at least one reactive measure
automatically in response to detecting said break in one of said
transfer strip and the web in order at least one of to avoid damage
to the machine as a result of said break and to prepare for a
renewed transfer of the web.
19. The machine as claimed in claim 18, wherein said at least one
reactive measure is at least one of triggering a web knock-off,
setting components of the machine into one of a waiting and a safe
state, activating one of said positive pressure device and said
vacuum device for said renewed transfer of the web, and activating
said first apparatus for said renewed transfer of the web.
20. A machine for at least one of producing and treating a web of
fibrous material in which the web is guided along a web guide path
by at least one web guide device from one of a web production
section and a web input section to pass at least one web treatment
device, said machine comprising: an apparatus including a vacuum
device and at least one pressure sensor, said vacuum device
including a suction box, said at least one pressure sensor arranged
in said suction box and being configured for detecting an operating
pressure of said vacuum device, said apparatus being configured for
detecting a break in the web on a basis of a detected said
operating pressure of said vacuum device.
21. The machine as claimed in claim 20, wherein the machine is
configured for forming a transfer strip of the web, said suction
box including a transfer suction zone and an operating suction
zone, said transfer suction zone being assigned to said transfer
strip, said operating suction zone being, together with said
transfer suction zone, assigned to a full width of the web, said
operating suction zone being one of connected and configured for
being connected via said transfer suction zone to a vacuum source,
said pressure sensor being arranged in said operating suction
zone.
22. An apparatus, comprising: structure configured for monitoring a
transfer of a web of fibrous material along a web guide path of a
machine for at least one of producing and treating said web such
that said transfer of said web is carried out in that a leading
transfer strip of said web is guided through said machine and a
width of said transfer strip is increased to a full width of said
web such that tail widening is thereby performed, said structure
being configured for monitoring, during said transfer of said web,
for a break in one of said transfer strip and said web.
23. The apparatus as claimed in claim 22, wherein said structure is
configured for monitoring, during said transfer of said web, for
said break in said transfer strip on a basis of at least one
detection variable representing said width of said transfer strip.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This is a division of U.S. patent application Ser. No.
11/233,966, entitled "APPARATUS AND METHOD FOR MONITORING THE
TRANSFER OF A MATERIAL WEB", filed Sep. 23, 2005, which is
incorporated herein by reference and which claims priority under 35
U.S.C. .sctn.119 to German Patent Application No. 10 2004 046 795.1
filed on Sep. 27, 2004, the disclosure of which is expressly
incorporated by reference herein in its entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to producing and/or treating a
material web, and, more particularly, to a transfer strip of the
material web.
[0004] 2. Description of the Related Art
[0005] What is known as web threading in a machine for producing
and/or treating a material web, specifically a material web of
paper or board, is normally carried out by way of at least one
transfer strip, which is divided off from the material web and is
then guided through following guide and/or treatment devices. This
type of web threading is standard both in papermaking and
boardmaking machines having in each case at least one head box, a
wet end (in particular wire section and/or press section), and a
drying section, possibly one or more processing sections (for
example a coating section) and also in paper or board processing
machines provided for the off-line treatment of a material web
produced in another way, for example what are known as coating
machines. In order to form or divide off the transfer strip,
diverse devices are known. For example, what are known as strip
knock-off devices, water jet cutting devices, laser cutting devices
and so on are used. In connection with papermaking machines, use is
normally specifically made of what is known as a "couch jet" which,
on a wire of the wire section, cuts a strip into the paper web (or
board or tissue web), which is then guided through the further
sections of the machine, in particular at least one press section
and at least one drying section and, if appropriate, at least one
treatment section. In the case of transfer devices which are
mounted downstream of the drying section, what is known as a tip
cutter is used instead of the couch jet. As soon as the transfer
strip is running stably through the machine, it is then possible,
by using the couch jet on the wire, to move to the "full width",
that is to say approximately from a strip position adjacent to the
operator side to the drive side or, vice versa, from a strip
position adjacent to the drive side to the operator side, as a
result of which the full web width then automatically runs through
the machine. In the specialist field, one speaks of what is known
as "tail widening" in this connection. This type of web threading
or similar type of web threading (for example, the transfer strip
could also be formed in a central region of the material web) has
also proven worthwhile in relation to all the conventional material
web treatment devices, those designed as an online material web
treatment device and designed as an off-line material web treatment
device, such as press sections, predryer sections, afterdryer
sections, coating machines, smoothing units (for example
calenders), reelers and so on.
[0006] However, existing web break detection systems only monitor
the "normal operation" for a web break, specifically when the
material web has already been threaded. Various types of web break
detector are known, for example based on detecting the web speed
(cf., for example, DE 101 57 914 A1), the detection of a
temperature change (cf., for example, DE 101 31 281 A1), the
optical detection of surface characteristics (cf., for example, DE
201 03 070 U1 and DE 42 16 653 C2) and the detection of pressures
or pressure changes in connection with a vacuum web guiding device,
in particular suction roll (cf., for example, EP 0 660 898 B1 and
DE 100 31 163 A1). Conventionally, break monitoring is therefore
not effective or is deactivated during tail widening. If a break
occurs during tail widening, this must be detected by the operating
personnel and it is then necessary for all the measures to be
initiated manually in order to avoid damage to the machine and in
order to be able to re-thread (to transfer) the material web. This
applies in spite of the fact that, in modern papermaking machines,
the aim is generally to increase the production efficiency. What
stands in the way of automatic web break detection is the thought
that the introduction of the transfer strip into the machine and
tail widening are transient, not steady state, processes or states,
which should be monitored better by human beings for greater
reliability.
[0007] What is needed in the art is an apparatus and a method for
automated monitoring for a break in the transfer strip of the
material web.
SUMMARY OF THE INVENTION
[0008] The present invention provides an apparatus and a method for
automated monitoring for a break in the transfer strip of the
material web.
[0009] The invention relates to a machine for producing and/or
treating a material web, in particular of paper or board, in which
the material web can be guided along a material web guide path by
way of at least one material web guide device from a material web
production section or material web input section, in order to pass
at least one material web treatment device, having an apparatus for
forming a transfer strip of the material web and transferring the
transfer strip through the machine, it being possible for the
material web to be transferred along the material web guide path in
that, by way of the apparatus for forming and transferring the
transfer strip, a leading transfer strip of the material web is
formed and guided through the machine, and the width of the
transfer strip is increased to the full material web width (what is
known as "tail widening"), and having an apparatus for detecting a
break in the material web.
[0010] The invention relates further to a method for monitoring the
transfer of a material web of paper or board along a material web
guide path of a machine for producing and/or treating the material
web, the transfer of the material web being carried out in that a
leading transfer strip of the material web is guided through the
machine and the width of the transfer strip is increased to the
full material web width (what is known as "tail widening").
[0011] Surprisingly, it has been shown that, even in connection
with the transfer of the transfer strip and, above all, in
connection with the tail widening, automatic, machine-based
monitoring for the occurrence of a web break can be carried out
with high reliability. For the machine mentioned at the beginning,
according to a first aspect of the invention, it is accordingly
proposed that the apparatus for detecting a break in the material
web be provided and designed for the purpose of responding to a
break in the transfer strip or the material web during the transfer
of the material web, in particular during the increase in the width
of the transfer strip. In relation to the method mentioned at the
beginning, the invention proposes that, during the increase in the
width of the transfer strip, monitoring for a break in the transfer
strip or the material web is carried out.
[0012] On the basis of the invention, failures during web
threading, specifically during tail widening, can be detected
automatically and therefore quickly, and a re-start of the web
threading and tail widening can be introduced quickly and
automatically. The transfer times occurring over the operation of
the machine can be reduced in this way, which means that a higher
level of productivity is reached. The automated monitoring and, if
appropriate, initiation of suitable reactive measures is also
advantageous inasmuch as damage to machine components as a result
of a web break can be avoided, in particular by triggering web
knock-off in the event of a web break. Furthermore, as already
mentioned, thought is above all also given to all the necessary
reactive measures being initiated automatically in response to the
detection of a web break, in order to be able to re-transfer the
material web. For example, by activating the appropriate actuators,
for example vacuum breaker valves can be closed, the couch jet or,
generally, a transfer strip forming device can be moved to the
strip position, fan rotational speeds can be lowered, to name only
a few examples. The web transfer can therefore be carried out more
quickly and more successfully. The initiation of appropriate
measures (knocking off the web and preparing the renewed web
transfer) manually by the operating personnel can be dispensed
with.
[0013] If the tail widening was successful, that is to say no break
occurred during the transfer of the transfer strip and during the
tail widening, then a change can expediently be made automatically
to "normal operation", in which the conventional break monitoring
can then be carried out, for example in accordance with the
solutions from the prior art mentioned above.
[0014] Thought is above all given to the apparatus for detecting a
break in the material web being designed for the purpose of
responding to a break in the transfer strip or the material web on
the basis of at least one detection variable representing the width
of the transfer strip, directly or indirectly. As based on the
method according to the invention, provision can accordingly be
made for monitoring for a break in the transfer strip or the
material web to be carried out on the basis of at least one
detection variable representing the width of the transfer strip,
directly or indirectly.
[0015] The development proposal is based on the thought that the
width of the transfer strip at a given position along the material
web guide path is a measure of the progress of the tail widening.
In the case of successful web threading, the width of the transfer
strip at a reference position must correspond to the width of the
transfer strip at the location of the formation of the transfer
strip at a preceding time depending on the web running speed. If,
by way of appropriate activation of the couch jet or, generally,
the device for forming the transfer strip, provision is made for
the transfer strip to become continuously wider during tail
widening, this must also apply at another point along the material
web guide path, as long as the web threading is carried out
properly and, in particular, no web break occurs.
[0016] In principle, all the web break detection and monitoring
techniques known from the prior art are suitable in connection with
the break detection and monitoring according to the invention. For
example, the apparatus for detecting a break can for example have
an optical detection arrangement in order to detect a web break or
to provide the detection variable. As based on the method according
to the invention, it is proposed that the monitoring be carried out
on the basis of optical detection, in particular optical detection
of the width of the transfer strip. Furthermore, the apparatus for
detecting a break can have a temperature detection arrangement, in
order to detect a web break or to provide the detection variable.
As based on the method according to the invention, it is proposed
that the monitoring be carried out on the basis of detection of
temperature values.
[0017] By contrast, provision is particularly preferably made for
the apparatus for detecting a break to have a pressure detection
arrangement or pressure change detection arrangement, in order to
detect a web break or to provide pressure values as detection
variable. In relation to the method according to the invention, it
is proposed as particularly preferable that the monitoring be
carried out on the basis of detection of pressure values or
pressure change values or a pressure change.
[0018] Advantageously, in each case at least one dedicated pressure
detection arrangement or pressure change detection arrangement can
be provided for a plurality of sections of the machine, for example
a plurality of drying groups or other treatment devices, in order
in each section to detect a web break immediately and therefore
with very quick reaction in each case or to provide pressure values
as detection variable for the web break detection.
[0019] In connection with these development proposals, thought is
above all given to the pressure detection arrangement or pressure
change detection arrangement being designed and arranged for the
purpose of detecting at least one instantaneous operating pressure
of at least one vacuum device acting on the material web or the
transfer strip. For example, thought is given to what is known as a
suction roll, which is used for material web guidance and,
possibly, web deflection. Alternatively or additionally, a or the
pressure detection arrangement or pressure change detection
arrangement can be designed and arranged for the purpose of
detecting at least one instantaneous operating pressure of at least
one positive pressure device acting on the material web or the
transfer strip. In this connection, thought is given, for example,
to what is known as an air turn, which is used for non-contact web
guidance and, possibly, web deflection.
[0020] Based on the method according to the invention, it is
proposed that at least one instantaneous operating pressure of at
least one vacuum device or positive pressure device acting on the
material web or transfer strip be detected.
[0021] The background to these development proposals is that,
during tail widening, the vacuum device or positive pressure device
is increasingly covered by the transfer strip becoming wider or the
material web becoming wider, which, in a vacuum device increases
the vacuum as a result of an air stream becoming smaller, that is
to say reduces the prevailing operating pressure, and, in a
positive pressure device, because of increasing throttling of the
air discharge, increases the positive pressure, that is to say can
increase the operating pressure. The operating pressure prevailing
in the vacuum or positive pressure device to this extent reflects
the width of the material web or of the transfer strip on the
device.
[0022] As a rule, it will be expedient if the relevant vacuum
device or positive pressure device is provided in any case, in
order at least to participate in the guidance of the material web
or of the transfer strip as part of the material web guide
device.
[0023] The vacuum device can include at least one suction roll
and/or at least one suction box and/or at least one vacuum
transport belt. The positive pressure device can include at least
one blower roll and/or at least one blower box and/or at least one
air turn.
[0024] As particularly preferred, it is proposed that at least one
pressure sensor of the pressure detection arrangement be arranged
in the/a suction box or blower box. In the case of a suction roll,
the pressure sensor is preferably arranged in a suction box
assigned to the suction roll. As compared with a solution known per
se, in which the pressure sensor is provided in a line connecting
the suction box to a vacuum source, this offers the great advantage
that high pressure fluctuations occurring acyclically, the cause of
which has not yet been fully explained, can be avoided. The problem
of measuring the pressure in a suction line could be that the
pressure measurement is influenced by the flow velocity of the air.
Influences of this type are avoided if the pressure is measured in
the suction box. More reliable monitoring of the transfer of the
material web and, generally, more reliable break monitoring are
achieved.
[0025] If the suction box includes a transfer suction zone which is
assigned to the transfer strip and an operating suction zone which,
together with the transfer suction zone, is assigned to the full
material web width and which is connected or is able to be
connected via the transfer suction zone to a vacuum source, then
the pressure sensor is preferably arranged in the operating suction
zone. Between the transfer suction zone and the operating suction
zone, at least one connecting opening or connecting line that can
be closed by a valve flap or the like can be provided and, for the
pure introduction of the narrow threading section of the transfer
strip, is closed, in order to be able to attract the latter with
sufficient vacuum. For the tail widening, this connecting opening
or connecting line is then opened, in order to be able to monitor
the proper widening of the transfer strip or the material web via
the operating pressure.
[0026] The machine can advantageously have an evaluation unit which
is designed for the purpose of comparing detected pressure values
or consequential values depending on the latter with one another
and/or with at least one predefined reference value and of
outputting a break signal when at least one break condition is
fulfilled. On the basis of the break signal, the reactive measures
mentioned can then be initiated and the break can be signaled to
the operating personnel. Based on the method according to the
invention, it is proposed that detected pressure values or
consequential values dependent on the latter be compared with one
another and/or with at least one predefined reference value in
order to determine the fulfillment or non-fulfillment of at least
one break condition.
[0027] Thought is above all given to the evaluation unit being
designed for the purpose of comparing the magnitude of pressure
values or consequential values corresponding to the latter recorded
successively in order to check a break condition, the break
condition being fulfilled when the values deviate from a predefined
reference curve. In relation to the method according to the
invention, it is accordingly proposed that, according to one break
condition, pressure values or consequential values corresponding to
the latter recorded successively be compared with one another, and
that the break condition be determined to be fulfilled when the
values deviate from a predefined reference curve.
[0028] According to an expedient embodiment, the break condition is
fulfilled when, in the case of a vacuum device, a pressure value
that is assigned to a later time is greater than or equal to a
pressure value that is assigned to an earlier time or, in the case
of a positive pressure device, a pressure value that is assigned to
a later time is less than or equal to a pressure value that is
assigned to an earlier time. Based on the method according to the
invention, it is proposed that the break condition be determined to
be fulfilled when, in the case of a vacuum device, a pressure value
that is assigned to a later time is greater than or equal to a
pressure value that is assigned to an earlier time or, in the case
of a positive pressure device, a pressure value that is assigned to
a later time is less than or equal to a pressure value that is
assigned to an earlier time.
[0029] This embodiment of the evaluation unit and the method is
expedient and reliable when the pressure values or consequential
values compared with one another are assigned to times which, as
based on the web speed and the rate at which the transfer strip or
the material web is widened, have a certain minimum spacing in
time, so that in the event of a successful, proper curve, it is
always ensured that for increasing times the operating pressure
falls (in the case of a vacuum device) or rises (in the case of a
positive pressure device), which, in the case of processing
consequential values derived from the pressure values, applies
appropriately to these. If, on the other hand, an evaluation of
pressure values or consequential values lying closer to one another
in time is provided, then, on account of relatively small pressure
fluctuations which may possibly occur, this could lead to the
detection of a break although such a one has actually not occurred.
In order to avoid such erroneous detection, it is possible for a
tolerance band, for example expressed by a threshold value, also to
be included in the comparison. In this regard, it is proposed in
practical terms that the break condition be fulfilled when, in the
case of a vacuum device, a pressure value assigned to a later time
exceeds a pressure value assigned to an earlier time by a
predefined threshold value or, in the case of a positive pressure
device, a pressure value assigned to a later time falls below a
pressure value assigned to an earlier time by a predefined
threshold value. Based on the method according to the invention, it
is accordingly proposed that the break condition be determined to
be fulfilled when, in the case of a vacuum device, a pressure value
assigned to a later time exceeds a pressure value assigned to an
earlier time by a predefined threshold value or, in the case of a
positive pressure device, a pressure value assigned to a later time
falls below a pressure value assigned to an earlier time by a
predefined threshold value.
[0030] According to a particularly expedient development, the
evaluation unit is designed for the purpose of comparing detected
pressure values or consequential values dependent on the latter
with a predefined reference value, in order to check a
tail-widening finished condition which is fulfilled when the
pressure value reaches a threshold value corresponding to the
reference value. In relation to the method according to the
invention, it is proposed that detected pressure values or
consequential values dependent on the latter be compared with a
predefined reference value, in order to determine the fulfillment
or non-fulfillment of a tail-widening finished condition, which is
determined to be fulfilled when the pressure value reaches a
threshold value corresponding to the reference value.
[0031] On the basis of the fulfillment of the tail-widening
finished condition, the apparatus for detecting a break in the
material web can be changed over to a normal operation monitoring
mode, in which monitoring for the occurrence of a web break can
then be carried out in a conventional way.
[0032] Thought is specifically given, in the case of a machine with
a plurality of sections (in particular a plurality of drying groups
and material web treatment devices) in each case monitored
separately for a break during the increase in the width of the
transfer strip, to changing to the normal operation monitoring mode
in each case separately for the respective section when the
fulfillment of the tail-widening finished condition is determined
for this section. Conventional break detection systems are
activated only when the material web has been widened completely
over the entire machine.
[0033] It has already been mentioned that the machine can
expediently be designed for the purpose of initiating at least one
reactive measure automatically in response to the detection of a
break in the material web, in order to avoid damage to the machine
as a result of the break and/or to prepare for a renewed transfer
of the material web. The reactive measure provided can be one or
more of the following measures: triggering a web knock-off, setting
machine components into a waiting or safe state, activating the
positive pressure or vacuum device for the renewed transfer of the
material web, activating the apparatus for forming and transferring
the transfer strip for the renewed transfer of the material
web.
[0034] According to the first aspect, the invention also provides
an apparatus for implementing the method according to the
invention, for example for providing a machine according to the
invention, for example by equipping or retrofitting a machine as
mentioned at the beginning.
[0035] According to another (second) aspect, the invention further
provides a machine for the production and/or treatment of a
material web, in particular of paper or board, in which the
material web can be guided along a material web guide path by way
of at least one material web guide device from a material web
production section or material web input section, in order to pass
at least one material web treatment device, having an apparatus for
detecting a break in the material web on the basis of a detected
operating pressure of a vacuum device having a suction box.
[0036] According to the invention, provision is made for at least
one pressure sensor for detecting the operating pressure to be
arranged in the suction box. It has been shown that a pressure
sensor arranged at this point can respond particularly reliably to
pressure changes resulting from a web break. The same applies to
web break detection in conjunction with the threading or tail
widening of the material web according to the first aspect of the
invention. Furthermore, on the basis of the pressure detected here,
a diagnosis of components of the vacuum device or of an associated
vacuum source (for example a fan arrangement) can be carried out
particularly reliably. Erroneous detections of a break and
erroneous diagnoses relating to such components are avoided in this
way. If the suction box has a transfer suction zone which is
assigned to the transfer strip and an operating suction zone which,
together with the transfer suction zone, is assigned to the full
material web width and is connected or is able can be connected via
the transfer suction zone to a vacuum source, it is preferred for
the pressure sensor to be arranged in the operating suction
zone.
[0037] With regard to the machine and the apparatus according to
the first aspect of the invention, reference should further be made
to the following. The evaluation unit can be constructed on the
basis of an electronic computer unit, in particular a
microprocessor arrangement, on which there runs an evaluation
program which has software functionalities providing the comparison
of the values and the testing of the various conditions. With
regard to the values to be compared, it should be pointed out that
it is not absolutely necessary for original pressure measured
values to be processed but that values or data derived from these,
the "consequential values" mentioned above, can be processed in
order to test for the break condition or break conditions and the
tail-widening finished condition. It is also possible for
electrical signals to be compared with one another as the pressure
or consequential values mentioned, for example measuring sensor
output signals or converter output signals, for example output
signals from a P-I converter without conversion into pressure
values, possibly even in an analog manner not providing any digital
to analog conversion.
[0038] Within the context of the invention, in addition to the
criteria and characteristic values mentioned directly here for the
instantaneous state during the tail widening or the occurrence of a
break, other criteria and characteristic values can also be used,
in particular including the criteria and characteristic values
quoted in the publications mentioned above. Reference is made in
particular to the documents DE 101 31 281 A1, DE 201 03 070 U1, DE
42 16 653 C2 and EP 0 660 898 B1.
[0039] According to the invention, monitoring both of the normal
operation of the machine and at least of the tail widening during
the web transfer (web threading) is possible and provided.
Developing this, thought is also given to monitoring the transfer
of the transfer strip or its threading section with regard to a
break automatically as well, for example on the basis of the known
detection techniques mentioned.
BRIEF DESCRIPTION OF THE DRAWINGS
[0040] The above-mentioned and other features and advantages of
this invention, and the manner of attaining them, will become more
apparent and the invention will be better understood by reference
to the following description of embodiments of the invention taken
in conjunction with the accompanying drawings, wherein:
[0041] FIG. 1 shows a schematic illustration of a portion of a
papermaking machine according to an exemplary embodiment of the
invention;
[0042] FIG. 2 shows a plan view of a vacuum device having a
pressure detection arrangement according to the invention;
[0043] FIG. 3 shows a front side view of the vacuum device from
FIG. 2; and
[0044] FIG. 4 shows the curve over time of the pressure within the
vacuum device during the tail widening of a transfer strip of a
material web.
[0045] Corresponding reference characters indicate corresponding
parts throughout the several views. The exemplifications set out
herein illustrate embodiments of the invention, and such
exemplifications are not to be construed as limiting the scope of
the invention in any manner.
DETAILED DESCRIPTION OF THE INVENTION
[0046] Referring now to the drawings, and more particularly to FIG.
1, there is shown in schematic form a side view of a detail of a
drying section of a papermaking machine or paper processing machine
designated generally by 10. In a manner known per se, a drying
section within a paper machine fulfills the function of extracting
moisture from a material web that has been produced or processed,
that is to say of drying said web. In the example shown in FIG. 1,
this is carried out by way of contact drying, a material web 12 to
be fed in from the left in the drawing being dried by direct
contact with a plurality of drying cylinders 14 on one side and an
endless dryer felt 16 running around the drying cylinders 14 on the
other side. In FIG. 1, two dryer felts 16 are illustrated over
their complete circulation path, each of the dryer felts 16 in each
case running around a group of drying cylinders 14. More precisely,
each dryer felt 16 runs up and down in the form of a wave in the
region of the drying cylinders 14, the dryer felt 16 being
deflected by a drying cylinder 14 at the peak of the wave and being
deflected by a suction roll of a respective vacuum device 18 in the
trough of the wave. After leaving the last drying cylinder 14 of
the corresponding group, the dryer felt 16 is guided back to the
first drying cylinder 14 of the group again over a plurality of
guide rolls 20.
[0047] To provide the break monitoring according to the invention,
for each group of drying cylinders 14, at least one vacuum device
18 is equipped with an apparatus for detecting a material web
break, which will be described in more detail later.
[0048] To dry the material web 12, this is introduced into the
system including drying cylinders 14 and vacuum devices 18 such
that it is guided on the drying cylinders 14 pressed between the
dryer felt 16 and the surface of the drying cylinder 14, while it
runs around the vacuum devices on the outside on the dryer felt
16.
[0049] When the machine 10 is started up, following the feeding of
a new material web or after a break in the material web, it is
necessary to re-introduce a leading transfer strip of the material
web into the roll system of the drying section and, in the process,
to transfer it alternately between a drying cylinder 14 and a
vacuum device 18. In order in this case to deflect the transfer
strip deflected on the outside on a vacuum device 18 counter to the
force of gravity and feed it to the following drying cylinder 14,
the vacuum devices 18 are connected to a vacuum source, at least
during the transfer operating state of the machine, so that the
vacuum device 18 forces the transfer strip onto the predefined
material web path by means of suction.
[0050] The transfer strip is generally cut directly out of the
material web automatically before the threading of the material
web, by using a suitable device, for example what is known as a
couch jet. A device of this type can, for example, include a
cutting device that can be displaced transversely with respect to
the running direction of the material web, for example a water jet
or laser cutting device, a circular knife or the like or what is
known as a strip knock-off device. During the cutting or the
formation of the transfer strip, the material web moves in the
running direction. In the following text, the use of a couch jet in
a papermaking machine will be assumed. The couch jet is initially
in a strip position and cuts a narrow frontmost section of constant
width as a threading section or else a ribbon, which is guided
through the machine by way of suitable guide device(s). Following a
specific advance distance of the material web, the couch jet is
moved uniformly in the direction of the opposite edge of the
material web and thus cuts the transfer strip with preferably
uniformly increasing width, until it reaches the full width of the
material web and the cutting of the transfer strip has been
completed. In the process, the material web moves continuously
onward and is threaded into the paper machine.
[0051] A vacuum device 18 provided for use in a paper machine
according to the present exemplary embodiment and serving as a
vacuum deflection device, having an apparatus for detecting a
material web break, will be explained in more detail in the
following text with reference to FIGS. 2 and 3. It includes a
suction roll 22, on which the material web 12 is deflected, and
also a suction box 24. The suction box 24 is connected via a
connecting line 26 to a vacuum source, not shown, in order to be
able to generate a vacuum in the suction box 24. The suction box 24
adjoins the suction roll 22 and has openings 28 facing the latter.
A vacuum built up in the suction box 24 can progress into the
interior of the suction roll 22 through these openings 28 and
through drilled holes 30 in the shell of the suction roll 22, so
that a vacuum can also be built up in the suction roll 22.
[0052] If a vacuum is generated and maintained in the suction box
24 and in the suction roll 22, this vacuum is propagated through
the drilled holes 30 of the suction roll 22 that are currently not
opposite the suction box 24 and through further openings 32 in the
suction box 24 to the outside and through the porous dryer felt 16
running around the vacuum device 18, and attracts by suction a
material web section to be deflected at the vacuum device 18, in
particular a transfer strip to be transferred, in order to hold the
latter on the material web guide path and feed it to the following
drying cylinder 14.
[0053] A valve 34 and a dividing wall 36 are also indicated in FIG.
2. The dividing wall 36 divides the interior of the suction box 24
into a transfer suction zone 38 and an operating suction zone 40,
it being possible for the transfer suction zone 38 and the
operating suction zone 40 to be connected to each other or isolated
from each other by the valve 34. The width of the transfer suction
zone 38, measured in the material web transverse direction,
corresponds approximately to the width of the advancing threading
section of the transfer strip of the material web. During the
transfer of the transfer strip of a material web to be newly
threaded in, the valve 34 is closed, so that air is sucked out only
from the transfer suction zone 38 of the suction box 23 and from
the suction roll 22 via the connecting line 26. In this way, the
regions of the suction box 24 which are not covered by material web
during the transfer of the transfer strip are not evacuated, in
order to be able to use the suction power of the vacuum source to
build up a vacuum in the transfer suction zone 38.
[0054] The front threading section of the transfer strip is
followed by a further section, in which the width of the transfer
strip increases continuously, until the transfer strip ultimately
reaches the full width of the actual material web and, at this
point, merges in one piece into the actual material web or is
connected to the latter. The operating state of the paper machine
in which the continuously widening transfer strip is transported is
designated "tail widening" of the material web. During the tail
widening of the material web, the valve 34 is opened and an
approximately uniform vacuum is built up both in the transfer
suction zone 38 and in the operating suction zone 40 and in the
suction roll 22. This vacuum which builds up is counteracted by the
air taken in, which is taken in through those drilled holes 30 and
those openings 32 which are not yet covered by the transfer strip.
The pressure established in the suction box 24 accordingly depends
on the number of openings 30 and 32 not covered by the transfer
strip, given a constant suction power of the vacuum source. This
number decreases continuously with increasing width of the transfer
strip, so that the air stream entering the suction box 24 from
outside and counteracting the evacuation of the suction box 24 also
decreases. With increasing width of the transfer strip, the
pressure within the suction box 24 thus decreases, until it reaches
a minimum value after the complete tail widening of the material
web. The operating pressure p in the suction box 24, decreasing
with the width of the transfer strip, is illustrated schematically
in the graph of FIG. 2.
[0055] The apparatus according to the invention for detecting a
break in the material web uses the curve previously described of
the pressure within the suction box 24 during the tail widening of
the transfer strip of the material web in order to monitor correct
tail widening and, in particular, to detect the occurrence of a
break in the transfer strip. For this purpose, in the suction box
24, more precisely in the operating suction zone 40 of the suction
box 24, a pressure sensor 42 which detects the pressure in the
suction box 24 is arranged. The pressure sensor 42, as shown in
FIG. 2, is preferably arranged close the behind the dividing wall
36 in the suction box 24. The arrangement of the pressure sensor 42
in the suction box 24 is advantageous, since the flow cross section
is relatively large in the suction box 24 and, as a result,
pressure fluctuations are relatively small.
[0056] The pressure sensor 42 is connected to a P-I converter
(pressure-current converter, not shown), which outputs a current
signal representing the magnitude of the measured pressure to an
electronic control unit (not shown). The electronic control unit
can also be supplied a position signal, which indicates the travel
position of the couch jet transversely with respect to the running
direction of the material web. From the speed of the material web
and the distance from the couch jet as far as the monitoring vacuum
device, an instantaneous reference web width of the transfer strip
at the monitoring vacuum device can then be determined in the
electronic control unit or in a computing unit connected upstream,
in order to provide said reference web width to the control
unit.
[0057] The control unit is configured in such a way that, in a
manner to be described in more detail later, on the basis of the
instantaneous current value transmitted to it by the P-I converter
and, possibly, also the instantaneous reference web width, it makes
a decision as to whether there is a break in the material web, in
particular its transfer strip, or not. The electronic control unit
is also set up and implemented in the paper machine such that, in
the event that a web break is established, it can initiate or carry
out specific measures in reaction to the web break. In particular,
thought is given to the electronic control unit being connected to
a knock-off device, which knocks the material web off upstream of
the break point in the event of a break, in order to avoid damage
to the machine by winding operations and to prepare the web for new
threading. As further measures, provision can be made to move the
couch jet for cutting the transfer strip to a strip position, to
transfer various device units of the production or processing
sections into a waiting position, to move vacuum transport devices
back or to initialize them (close vacuum breaker valves) or to
indicate the occurrence of the web break to the operating
personnel. Further measures which have to be taken upon the
occurrence of a web break are obvious to those skilled in the
art.
[0058] The electronic control unit according to the exemplary
embodiment of the invention is further set up for the purpose of
detecting the successful completion of the tail widening and
outputting a corresponding tail-widening finished signal. As a
reaction to this tail-widening finished signal, the paper machine
can be changed automatically to a normal operating mode, in which
for example a normal operating monitoring mode for the detection of
a break in the material web is switched on, in which, for example,
the break in the material web can be detected in a manner known per
se. Further measures which have to be carried out when the paper
machine is changed from the transfer and tail-widening mode to the
normal operating mode are familiar to those skilled in the art.
[0059] With reference to FIG. 4, in the following text the
functioning of the electronic control unit of the exemplary
embodiment for detecting a web break and for detecting completely
successful tail widening of the material web will be explained. The
graphical illustration shows the curve of the pressure p measured
by the pressure sensor 42 in the period beginning shortly before
the start of the tail widening t.sub.1 (shortly before the opening
of the valve 34) as far as a time shortly after the complete tail
widening of the material web. During the transfer of the threading
section of the transfer strip, that is to say for times
t<t.sub.1, the valve 34 is closed and the pressure p within the
operating suction zone assumes relatively high values in the
vicinity of normal atmospheric pressure. As soon as the width of
the transfer strip begins to become greater, the valve 34 is
opened, which means that the operating suction zone 40 is then also
connected to the connecting line 26 and air is extracted from the
operating suction zone 40. The measured pressure p therefore falls
rapidly shortly after the time t.sub.1 of the opening of the valve
34 and, shortly thereafter, at a time t.sub.2, reaches a pressure
p.sub.2 which corresponds to the presence of a transfer strip of
minimum width. During the further transport of the transfer strip,
its width increases gradually, so that more and more of the
openings 30 and 32 are covered by material web and the pressure p
consequentially decreases continuously. The pressure p reaches its
minimum value p.sub.3 at the time t.sub.3, when the width of the
transfer strip becomes a maximum and reaches the width of the
actual material web. After the complete tail widening of the
material web, that is to say for times t>t.sub.3, the pressure p
remains substantially constant, since the number of holes 30 and 32
covered by the material web then no longer changes.
[0060] The pressure curve shown in FIG. 4 corresponds to a
reference pressure curve during proper tail widening of the
material web. The electronic control unit detects the occurrence of
a web break during the tail widening in that at least one pressure
value measured at a specific time deviates significantly from the
pressure curve illustrated in FIG. 4. In this case, the accuracy
and reliability of the break detection depend on the knowledge of
operating parameters and on fluctuations of the operating
parameters over time. These operating parameters include in
particular the position of the valve 34 (throttle angle) and the
power of the vacuum source connected to the suction box.
[0061] In order to detect a web break, in particular the following
three design variants of a method for break detection can
expediently be used.
[0062] In a first design variant, the reference pressure curve
shown in FIG. 4 is stored in a memory of the electronic control
unit and/or can be calculated by the control device on the basis of
the instantaneous reference web width and on the basis of operating
parameters of the paper machine, in particular the suction power of
the vacuum source. In principle, the knowledge of a single point on
the pressure curve would be sufficient to be able to carry out the
detection of a web break at this time, but advantageously the
reference pressure curve will be available to the electronic
control unit for a large number of times, in order to be able to
provide the most continuous possible web break monitoring. The
reference pressure values of the reference pressure curve available
to the electronic control unit are now compared with the actual
pressure values measured by the pressure sensor 42, and the break
in the material web is detected exactly at the point when the
actual pressure at a specific time exceeds the corresponding
reference pressure significantly, that is to say by a predetermined
threshold value (tolerance band). In the event of a web break, this
is because the openings 30 and 32 of the suction roll 22 and the
suction box 24 are exposed in a short time, so that air can
penetrate through these into the suction roll 22 and the suction
box 24 and effects a sudden pressure rise. In any case, however,
there is a lack of increasing coverage of further openings 30, 32,
so that the pressure at least does not fall further.
[0063] The magnitude of the threshold value can be set as a
function of the magnitude of possible pressure fluctuations in the
suction box 24, such that a random pressure rise, for example on
account of short-term fluctuations in the suction power of the
vacuum source or on account of short-term lifting of the material
web at some points, does not lead to detection of a web break.
[0064] In the method according to the first design variant, the
successful complete tail widening can additionally be detected by
the fact that, for times t>t.sub.3, the measured pressure, apart
from a threshold value, is equal to a pressure p.sub.3, that is to
say a tail-widening finished signal can be output when the
difference between the measured actual pressure and the reference
pressure p.sub.3 falls below the threshold value.
[0065] The pressure p.sub.3 corresponds to an extremely small
pressure when the material web tail is widened completely and which
is also established during the normal operating mode. The pressure
p.sub.3 should advantageously lie close to a minimum pressure
p.sub.min, which corresponds to the best possible evacuation of the
suction box 24 and the suction roll 22 by the vacuum source. In
most cases, however, the pressure p.sub.3 will be higher than the
minimum achievable pressure p.sub.min, since the material web will
barely cover the openings 30 and 32 completely in a sealing manner
(in particular also when a narrower material web is used) and
certain leaks normally occur in the vacuum device.
[0066] In a second design variant, the electronic control device
does not compare measured pressure values directly with reference
pressure values from the reference pressure curve but compares two
pressure values p.sub.4 and p.sub.5 recorded at different time
t.sub.4 and t.sub.5 with each other. In the case of proper tail
widening of the transfer strip, in accordance with the curve shown
in FIG. 4, the pressure value p.sub.5 recorded at the later time
t.sub.5 must be smaller than the pressure value p.sub.4 recorded at
the time t.sub.4. If this is not the case, the control device
concludes that there is a break in the transfer strip. This design
variant has the advantage that it manages without any predefinition
or calculation of reference pressure values and detects a web break
by using the simple break condition that a pressure value recorded
at a later time is not smaller than a pressure value recorded at an
earlier time.
[0067] Furthermore, a third design variant for detecting a break of
the transfer strip during tail widening is conceivable, in which
the break is detected on the basis of the comparison of two
pressure values p.sub.6, p.sub.7 recorded at a short time interval
(at t.sub.6, t.sub.7). Although in this case, too, the use of a
break condition according to the second design variant is in
principle possible, it would be possible for erroneous triggering
of a break signal to occur in the case of pressure measurements
following one another closely in time, because of random pressure
fluctuations within the suction box 24. As can be seen in FIG. 4,
this is because the reference pressure values p.sub.6 and p.sub.7
are also relatively close to each other and their difference can
lie in the range of the order of magnitude of random pressure
fluctuations. According to the third design variant, a web break
signal is therefore generated only when the pressure p.sub.7
measured at the time t.sub.7 exceeds the pressure p.sub.6 measured
at the earlier time t.sub.6 by at least a predetermined threshold
value s, therefore when p.sub.7(t.sub.7)>p.sub.6(t.sub.6)+s. By
using such a break condition, reliable break detection is possible
even during the evaluation of pressure measurements following one
another closely over time.
[0068] The aforementioned three design variants for detecting a
material web break in the region of the profile strip can be
combined with one another as desired, in order to provide the most
optimal break detection possible. It is viewed as particularly
preferred if the electronic control unit is continuously supplied
with pressure values from the pressure sensor 42 (or the current
values from the P-I converter representing the pressure values) and
the electronic control unit monitors the instantaneously received
pressure values continuously for a deviation from the reference
pressure curve shown in FIG. 4. Furthermore, a combination of the
first and third design variants can be configured in such a way
that the threshold value s used for the break condition according
to the third design variant is adapted as a function of the
measured pressure, in order to provide a variable threshold value s
(p) which takes account of the changing rise in the pressure curve
or a variable amplitude of the fluctuation of the pressure as a
function of the pressure.
[0069] A combination of the above-described three design variants
can also expediently be used in assessing tail widening which has
been completed successfully, in order to generate the tail-widening
finished signal. For example, a tail-widening finished condition
can be used which indicates successful tail widening when the break
conditions according to the design variants 1 and 2 have not been
triggered and the pressure p reaches a reference pressure value
p.sub.3 (third design variant).
[0070] The paper machine described in more detail above is to be
understood as a preferred exemplary embodiment of the invention.
Within the scope of the invention, it is not only possible for a
continuous pressure drop (vacuum rise) in the suction box to be
used as a monitoring variable for current tail widening of the
transfer strip; instead it is also possible to monitor the
continuous widening of the transfer strip with a large number of
optical sensors or temperature sensors or the like arranged
transversely with respect to the material web. In principle, the
same electronic control device as has been described above in
detail can then be used for various measuring methods, as long as a
signal representing the instantaneous actual width of the transfer
strip is supplied to it. In this connection, it should be
underlined once more that the pressure variables (p.sub.1 to
p.sub.7, see FIG. 4) used in the description of the embodiment were
merely designated pressure variables for improved illustration.
However, in most cases, instead of the direct pressure values, the
electronic control unit will process equivalent signal values
(current signal values, voltage signal values, etc.) which are
related to the pressure p measured by the pressure sensor 42. In
the case in which a directly proportional relationship is provided
for the relationship between these signal values and the actual
pressure p, all the statements relating to pressure values (break
conditions etc.) made in this description and in the claims can be
applied in an equivalent way to the corresponding signal values. In
the case in which other relationships between the signal values
processed in the electronic control unit and the pressure values
are used, those skilled in the art will readily be in a position to
formulate break conditions or processing rules for the electronic
control unit by using the above-described relationships.
[0071] Furthermore, it should be pointed out once again that the
method according to the invention can also be applied to other
sections of the paper machine, for example to the press section,
the predryer and/or afterdryer section, to a coating machine, a
calender, a reeler, etc.
[0072] It is noted that the foregoing examples have been provided
merely for the purpose of explanation and are in no way to be
construed as limiting of the present invention. While the present
invention has been described with reference to an exemplary
embodiment, it is understood that the words which have been used
herein are words of description and illustration, rather than words
of limitation. Changes may be made, within the purview of the
appended claims, as presently stated and as amended, without
departing from the scope and spirit of the present invention in its
aspects. Although the present invention has been described herein
with reference to particular means, materials and embodiments, the
present invention is not intended to be limited to the particulars
disclosed herein; rather, the present invention extends to all
functionally equivalent structures, methods and uses, such as are
within the scope of the appended claims.
* * * * *