Note: Descriptions are shown in the official language in which they were submitted.
CA 02263211 1999-02-12
~l.~.itWPTEiy~.3
WO~=98/06897 PCT/EP97/03859
Process for Elimination of Paper Defects
in Continuous Paper Production
The present invention relates to a process for
elimination of paper defects in continuous paper production.
Paper machinery that operates continuously comprises a material
intake section, a screen section, a press section, a drying
section, dry-smoothing machinery, and winding machinery. The
aqueous suspension of the material is distributed evenly_across
(U the width of the web in the material intake section, primarily to
ensure optimal sheet formation. In the following screen section,
the actual sheet of paper is formed by a filtration process. The
individual paper fibres are fixed in their ultimate position in a
wet random-fibre web. Then, the excess water is expelled from the
random fibre paper web by pressure that is applied in the press
section. To this end, the paper web moves through a plurality of
presses that are arranged one after the other. After drying,
which follows this, the paper web is smoothed, to which end
smoothing machinery that comprise--as a rule-- two rollers is
used and these, in addition to the smoothing, act to compress the
paper and thus exert a simultaneous influence on the thickness of
the paper. Finally, the web of paper is wound up onto a drum.
Defects may be formed in the web of paper during the
above-described production process. These defects can be in the
-1-
25476-211
CA 02263211 1999-02-12
A0 98/06897 PCT/EP97/03859
form of holes or splits along the long edge of the paper web, and
they may also be in the form of dark or light patches on the
paper web. In addition, undesirable lumps may be formed during
production, there may be creases in the running paper web. As a
rule, such defects do not disrupt the further movement of the
paper web through the paper machinery. In contrast to this, in
the processing stations that follow, such as in subsequent
coating machinery, splitting or tearing may occur in the
defective places. For this reason,_it is essential_to eliminate
defects of this kind in the paper, even before the paper web
passes into the subsequent processing stage.
Up to now, defects in the paper web have been
eliminated manually by marking the paper web that has been
monitored for defects by means of sensors at the places where the
defects are located and then, in a subsequent station, slowing
the paper web down as the section of the paper web that has been
so marked approaches, so that as the web creeps past, an operator
can attach a sticker to the defective area. Depending on the type
of defect, the whole of the defective section of the paper web
can be eliminated by the operator and an adhesive patch can be
applied across the whole width of the paper web. This type of
defect elimination is time consuming, since the speed of the
paper roll and thus of the whole paper web has to be reduced to
creep speed or even to a standstill in order that the defective
_2_
25476-211
CA 02263211 1999-02-12
area can be eliminated. However, not even this time-consuming
and thus costly elimination is enough to prevent paper defects
from causing rips and tears in subsequent processing stages.
It is the objective of the present invention to
create a process by which the lost time that is caused by the
elimination of defects in the paper web during paper production
can be reduced.
In order to achieve this objective , the invention
provides a process for automated elimination of paper defects
during paper production in a paper machine, comprising the
following steps: a) identification, localization, and recording
of a paper defect by means of a first sensor that is directed
onto a running paper web; b) recording or calculating the speed
of the paper web between the sensor and a defect-elimination
station located downstream of the sensor; c) calculating the
time when the web section that contains the paper defect will
arrive in the defect-elimination station on the basis of the
speed of the paper web; d) automatically eliminating the paper
defect in the defect-elimination station; characterized in that
the first sensor and the defect-elimination station are
arranged spaced along the continuous paper web; and in that
elimination of the paper defect is effected at full paper web
speed during continuous paper production.
According to the present invention, the identification
and localization of the paper defect is carried out solely by
conventional means, namely, suitable sensors, the recording
elements of which are directed towards the running paper web.
- 3-
25476-211
CA 02263211 1999-02-12
In contrast to the previously used means, the speed of the
paper web is recorded or calculated between the sensor and a
subsequent defect-elimination station that follows the sensor.
This speed is used to calculate the time when the web section
that contains the paper defect will enter the defect-elimination
station, when prior to its arrival, the speed of the web section
is reduced to a value that is less than the value for the
normal speed, or even to zero. Then, at the time that has been
calculated on the basis of the speed of the paper web, the
elimination of the paper defect is effected automatically by
appropriate devices. Subsequently, the speed of the web section
is increased to its normal value.
In contrast to known, manual defect elimination, it
is not necessary to slow down the speed of the paper web care-
fully and by hand to the reduced speed that is necessary for
defect
-4-
25476-211
CA 02263211 1999-02-12
WO-98/06897 PCT/EP97/03859
elimination. Rather, on the basis of the information obtained by
analysis of the detection signals, the system decides on the
speed with which the web section must move into the following
defect-elimination station in order that the paper defect can be
eliminated reliably. To this end, the sensor can be so designed
to identify and localize not only the paper defect but also its
character, e.g., the type and shape of the paper defect, and to
localize it relative to the width of the paper web. All of this
information can be used internally by the system, and analysed in
order to set the speed of the web section within the defect
elimination station to the required value. In this way, the time
that is lost by eliminating defects in the paper web during paper
production is reduced to the absolute minimum.
Zn one configuration of the process it is proposed that the
IS paper web pass through an additional sensor before it reaches the
sensor, and that the additional sensor completes a pre-
determination or an approximate determination of the paper
defect, whereas the sensor is designed to identify the character
of the paper defect, e.g., its type and shape. In this way it ~is
possible to run the paper web and thus the paper machine at very
high speed during normal operation, since the additional sensor
need only be designed so as to identify and localize defects
exclusively, in advance. Thus, the measurement characteristics
of this sensor are designed for rapid recording rather than for
25476-2I1
CA 02263211 1999-02-12
WO-98/06897 PCT/EP97/03859
detailed recording. Details are recorded by the sensor that
precedes the defect-elimination station. Such details are the
type of paper defect, its shape, and the position of the paper
defect relative to the width of the paper web.
It is preferred that the time that the pre-detected web
section that contains the paper defect will arrive at the sensor
be calculated on the basis of the speed of the paper °,aeb on the
path to the sensor.
In a further configuration of the process, it is proposed
I~ that the speed of the web section that contains the paper error
be reduced to a value that is lower than the value for the normal
speed even prior to the arrival of the web section at the sensor.
In addition, the speed that has already been reduced can be
further reduced to an even lower value, or even to zero, prior to
the arrival of the web section in the defect-elimination station.
The present invention also proposes that the paper defect be
eliminated by covering the defective area with a quick-hardening
fluid so as to form a flat covering. According to a first
variant, the fluid can be applied by being sprayed onto the,
defective area on one or both sides. According to a second
variant, the fluid can be applied to the defective area by
rollers.
A quick-hardening ultraviolet lacquer is suitable as fluid.
-6-
25476-211
c
CA 02263211 1999-02-12
WO'98/06897 PCT/EP97/03859
The process is suitable for use within the framework of on-
line paper production and also within the framework of off-line
paper production. In the first case, station, sensor, and
additional sensor are arranged along the continuous paper web, so
that the automated elimination of paper defects takes place in
the paper machine at full paper web speed, whereas in the second
case, the additional sensor is arranged on a paper machine, and
station and sensor are arranged along a take-up roll or pre-
roller that precedes the station and the sensor. The take-up
roll or the pre-roller forms the connecting element between the
paper machine and the coating machine.
Add-itional details and advantages of the present invention
are explained in greater detail below on the basis of an
embodiment. In this connection, reference is made to the appended
drawing, which shows a side view of a pre-roller that is arranged
in the production process between the paper machine and the
coating machine.
On the right-hand side, the drawing shows the drum 1 on
which the end of the paper web that is wound on at the end of tie
paper machine is located. This paper web can have paper defects
at various places. The detection of these paper defects is
effected in the previous paper machine, and the localization of
the paper defect relative to the length of the paper web that has
been wound on to the drum is stored internally in a control unit.
_7_
25476-211
CA 02263211 1999-02-12
W0~98/06897 PCT/EP97/03859
Once the drum 1 has been installed on the pre-roller, the system
"knows" where the errors are located within the length of the
paper web that has been wound on. As an alternative, it is also
possible to provide the drum 1 with a built-in memory e.g., an
electronic chip that is arranged on the drum, that contains the
appropriate position data with respect to the paper defects.
In the pre-roller, the paper web is drawn off the drum 1 and
then passes over a first guide roller 2 and a second guide roller
3. In the drawing, the paper web itself is numbered 4. -
lU Between the drum 1 and the guide roller 2 there is a sensor
5, the recording characteristics of which are different to those
of the additional sensor that is integrated in the preceding
paper machine. Whereas the additional sensor is designed simply
. to record paper defects at a high web speed and localize these,
at least approximately, the sensor 5 that is secured to the pre-
rollerer is designed to identify the paper defect that has
already been detected with respect to its precise character, and
to localize the size and extent of the paper defect. In addition,
it is possible to provide a degree of sensitivity with respect to
additional characteristics of the paper defect, e.g., the
identification of light/dark shading or of blisters and creases.
Then, based of the measured values obtain from the sensor 5, the
system reaches a decision with respect to the scope of defect
elimination and the manner in which this is to be done.
_g_
25476-211
CA 02263211 1999-02-12
WO'98/06897 PCT/EP97/03859
Since the approximate locality of the paper defect is
already known on the basis of the measurement results obtained
from the additional sensor, the speed of the paper web section
that contains the paper error can be reduced to a value that is
less than the normal speed even before this web section arrives
at the sensor 5. This entails the advantage that the sensor 5 has
been prepared for the arrival and the approximate localization by
error signals, and can use the detailed identification of the
defect without any delay. _ -
The paper defect is eliminated in a station 6 that in the
embodiment that is shown is located between the guide roller 2
and the guide roller 3. At this location, there is a spray head 7
that is directed onto the paper web 4, through which a quick-
hardening ultraviolet lacquer is sprayed onto the defective area.
Alternatively, the fluid can be applied by rollers. As is shown
in the drawing, application can be made on one side or on both
sides. As an alternative to a quick-hardening ultraviolet
lacquer, it is also possible to use a suitable plastic adhesive.
What is important is that the fluid itself can cover the
defective area in a manner that is flat and forms a film, and in
this way protect the paper in the area of the paper defects
during further processing, as in a coating machine or a printing
machine. It is important that the agent that is used be easy to
25476-211
CA 02263211 1999-02-12
WO'98/06897 PCT/EP97/03859
separate from the paper during the processes that are used to
process waste paper or recycle it.
The fluid is applied automatically in the station 6, i.e.,
without any human intervention. To this end, the precise time at
which the web section with the paper defect reaches the working
area of these spray head 7 must be known. Critical in this
respect is the speed with which the paper web and thus the
defective web section moves from the sensor to the spray head 7.
For this.reason, the speed of the paper web between the sensor 5
and the station 6 that follows the sensor 5 must be recorded or
calculated, and the exact time of arrival of the web section that
contains the paper defect in the station 6 must be calculated on
the basis of the speed that has been determined. The results of
the measurements completed by the sensor 5 are also taken into
IS account in the control system of the spray head 7, which is to
say that the spray head 7 does not work across the whole width of
the paper web in every case, but rather only in the area that has
been identified as being defective within the longitudinal
direction and the width of the web. More advantageously, the -
spray head 7 comprises a plurality of spray nozzles that are
arranged across the width of the paper web and can be controlled
individually.
Before the web section that has the paper defects arrives in
the station 6, the speed of the paper web is reduced to a value
-IO-
25476-211
CA 02263211 1999-02-12
~0~98/06897 PCT/EP97/03859
that is less than the value for the normal speed, or to zero.
Once the station 6 has been passed and the drying process has
been completed, the speed of the paper web is restored to its
normal value.
The drawing shows the process as it is used off line, i.e.,
the additional sensor is located in the paper machine and the
station 6 together with the sensor 5 are arranged in the pre-
roller. However, the process can also used on line, when the
station, sensor, and additional sensor are arranged along a
continuous paper web, as in a combined paper and coating machine.
The sensors operate optically across the whole width of the
paper web. Infra-red photosensors or CCD line cameras can be used
as such sensors.
-11-
25476-211
CA 02263211 1999-02-12
WO 98/06897 PCT/EP97/03859
~Pference numbers used in the drawing
1 Drum
2 Guide roller
3 Guide roller
4 Paper web
Sensor
6 Station
7 Spray head
-12-
25476-211
