EP2022893B1 - Method for identifying a break in a sheet of fibrous material in a section of a production machine for fibrous sheet material and device for implementing the method - Google Patents

Description

The invention relates to a method for detecting a tear of a fibrous web in a section of a machine for producing the fibrous web, wherein the fibrous web is guided by at least one at least one constituent web carrier through the section, wherein the demolition by at least one optical device for web tear detection, the at least one light source and a detector is detected, and wherein a tee for the fibrous web is activated by the device for web tear detection directly or indirectly.

The invention further relates to a device for detecting a tear of a fibrous web in a section of a machine for producing the fibrous web guided through the section by at least one web component, comprising at least one optical device for web break detection, which comprises at least one light source and one detector. and with a through the device for web tear detection directly or indirectly activatable tee for the fibrous web.

The machine for producing the fibrous web may, for example, be a paper, board or tissue machine. By contrast, the section of the machine for producing the fibrous web may be at least one wire section, one press section and one dryer section. Thus, it may be in the at least several components having web support for Guiding the fibrous web act at least a Formiersieb, a press felt and a drying wire. The web carrier is referred to in professional circles as stringing.

In the manufacture of all paper grades formed essentially of pulp suspensions, the rapid and reliable detection of fiber web breaks during their manufacture is extremely important to prevent damage to parts of the fibrous web making machine.

In places where the fibrous web is in free fall, web breaks can be detected very reliably, for example by light barriers.

However, photoelectric barriers are not suitable in situations in which the fibrous web rests on a clothing also serving as a web carrier, such as a forming screen, a press felt or a drying wire. As a rule, optical systems are used in which a detector and a light or radiation source of the device for web tear detection are mounted on the same side of the fibrous web.

Various methods for web tear detection are known.

Thus, in the known method "color detection" the color difference between the fibrous web and the dryer fabric is used to detect the web break. In the FIG. 1 is an example of the waveform of an optical device for web tear detection in the occurrence of a web break in a color intensity-time diagram (Ft diagram) outlined. When exceeding or falling below a predetermined tripping threshold value S (dashed line) of the color intensity F, a signal is given to a stripping device. For example, the trigger threshold value S for the signal to the tee device may be 50% of the color intensity F. This method works especially good at a distinct color difference, such as between a white fibrous web and a green dryer wire.

A disadvantage of color recognition systems is that they become all the more unreliable the smaller the color difference between the fibrous web and the dryer fabric. This is the case, for example, in machines for producing cardboard or packaging papers where brownish paper or board webs rest on red or amber dry sieves. Here it can no longer be clearly differentiated between fibrous web and dryer fabric. This results in either a web tear detection without demolition or a demolition without web tear detection. The former leads to an unnecessary production shutdown and thus to financial losses for the plant operator, the latter involves the risk of damaging the machine in itself.

Another disadvantage of color detection systems is that their functionality can be disturbed by ambient light.

Moreover, dryer fabrics can become very dirty with increasing service life, whereby the actual color of the dryer fabric is covered by the dirt deposits. In such cases, it has been found that a color detection system also no longer works reliably.

It is also known that the colors of dryer fabrics change during use, for example fade, and thus cause problems in the demolition detection. This can be remedied at best by constantly readjusting the web tear detection device. But there may also be cases where despite the readjustment web breaks can not be reliably detected.

In some cases, it has also been found that fluctuations in the residual moisture in the fibrous web can have a lasting adverse effect on the functionality of web tear detection devices. This can be up to be brought to a certain degree by regular readjustment of the detector under control. For this purpose, the reference signals and the trigger threshold can be reset, it is also the detection wavelength range can be adjusted.

Another known method is the "detection of changes in the light scattering (pseudo-pattern recognition)", wherein light is scattered differently on the structured dryer than on the fibrous web. This difference is used to detect web breaks. The measurement takes place at wavelengths slightly above the visible range.

It has also been found that pseudo-structure recognition systems also do not work reliably. This is probably due to contamination in the dryer fabric or to the transparency of the still partially moist fibrous web.

Furthermore, in the case of the two methods mentioned, narrow-band detection is carried out, that is to say measurement is carried out within a wavelength range of only a few nanometers, from about 20 to 100. Although some sensor models allow the intensities of different wavelength ranges to be combined to form a sum signal, as occurs, for example, when adding the three intensity channels of an RGB sensor. However, here too the spectrum is not recorded continuously.

In color recognition systems, it often happens that only a small signal difference between the reflected intensities of the dryer fabric and the fibrous web is achieved. This is the case, for example, as already stated, in machines for producing cardboard or packaging papers where brownish paper or board webs rest on red or amber dry sieves. Here it can either come to a web tear detection without demolition or to a demolition without Bahnabrisserfassung. The former leads to an unnecessary production shutdown and thus to financial losses for the plant operator, the latter carries the risk of damage to the machine in itself.

From the German patent application DE 42 16 653 A1 For example, a method for detecting web breaks is known in which the change in color tone of the dryer fabric is corrected by automatic post-referencing.

From the not pre-published EP 1936030A1 is known to guide the demolition detection by measuring the reflected intensity in the range of 200-1100 nm through 20.

The invention is therefore based on the object, a method and an apparatus of the types mentioned in such a way that compared to the prior art, a more reliable detection of web breaks in a section of a machine for producing a fibrous web is made possible. This section should in particular be a single-row dryer section of a machine for producing a fibrous web.

This object is achieved in a method of the aforementioned type in that the reflected from the fibrous web and / or at least one component of the web carrier intensity of the light source is measured in a wavelength range between 1380 to 2,600 nm by means of the detector to a breakdown of the Reliable detection of fibrous web.

In addition to the detection of components of the fibrous web, such as cellulose, filler or lignin, and / or components of the web support, such as PET, the method according to the invention has the great advantage that in the said wavelength range the difference between the reflected intensity of the fibrous web and the reflected intensity of at least one component of the web carrier is very pronounced. As a result, the effects of web carrier aging, web carrier contamination and residual moisture in the fibrous web are significantly lower than in conventional processes. Moreover, this method is not affected by the color of the fibrous web and the moisture of the web carrier, in particular the dryer affected.

In addition, the inventive method has a low susceptibility to extraneous light. In addition, the components of the web carrier can be detected.

The intensity of the light source reflected by the fibrous web and / or by at least one constituent of the web support is preferably in a wavelength range in a range between 1380 and 1650 nm, between 1,600 and 1,700 nm, between 2,200 and 2,500 nm or between 2,400 and 2,600 nm by means of Detector measured. These wavelength ranges allow a reliable detection of said components of the fibrous web.

With regard to a practical and solid embodiment, it is provided that the light source preferably emits specific light. Such a light source has already proven itself in adjacent areas and similar applications.

In order that the method according to the invention can be used in as many, and possibly also in different applications, at least one filter is preferably interposed between the light source and the detector of the optical device for web tear detection. The use of at least one filter allows the implementation of larger measurement modifications with only minor conversion measures, including associated costs.

Through the filter, the wavelength range is preferably set or limited from 1380 to 2,600 nm. With multiple filters, the measured wavelength range can be easily limited up and down within the desired wavelengths.

The detector measures in a preferred embodiment in a wavelength range of 1380 to 2,600 nm, since in turn the wavelengths of the essential components of the fibrous web, such as lignin and / or cellulose, are metrologically included.

Furthermore, the wavelength range for the measurement by the detector and / or by the filter can also be limited. This allows a greater application flexibility of the method with a low technical complexity and manageable costs.

For the direct or indirect activation of the tee for the fibrous web by the device for web tear detection is preferably set at least one trigger threshold, which is preferably adjustable. Thus, depending on the properties of the fibrous web, the "activation behavior" of the tapping device can be adjusted in a targeted manner.

The object of the invention is achieved in a device of the type mentioned in that the reflected from the fibrous web and / or at least one component of the web carrier intensity of the light source in a wavelength range between 1380 to 2,600 nm by means of the detector is measurable to a breakdown of Reliable detection of fibrous web.

The object of the invention is again completely solved in this way and it results in the aforementioned advantages of the invention.

Further features of the device according to the invention and further advantages of the invention will become apparent from the following description of preferred embodiments with reference to the drawings.

Figur 1

einen beispielhaften Signalverlauf einer optischen Einrichtung zur Bahnabrisserfassung beim Auftreten eines Bahnabrisses;

Figur 2

eine schematische Darstellung eines Teilabschnitts einer Maschine zur Herstellung einer Faserstoffbahn gemäß einem Ausführungsbeispiel der Erfindung; und

Figur 3

eine schematische Darstellung einer Anordnung einer erfindungsgemäßen Vorrichtung mit einer optischen Einrichtung zur Bahnabrisserfassung.

Show it

FIG. 1

an exemplary waveform of an optical device for web break detection when a web break occurs;

FIG. 2

a schematic representation of a portion of a machine for producing a fibrous web according to an embodiment of the invention; and

FIG. 3

a schematic representation of an arrangement of a device according to the invention with an optical device for web tear detection.

In the FIG. 2 is a side view of a section of a section 2 of a generally designated 1 machine for producing a fibrous web 3 shown. The illustrated section 2 is merely a drying section, it can of course also be a wire section or a dryer section.

In a manner known per se, the dryer section 2 within the machine 1 fulfills the function of extracting moisture from a manufactured and / or processed fibrous web 3, ie drying it.

I'm in the FIG. 2 As shown, this is done by contact drying, wherein in the drawing from the left to be supplied fibrous web 3 by direct contact with a plurality of drying cylinders 4 on the one hand and a drying cylinder 4 circulating endless drying wire 5 on the other hand dried. The dryer 5 is here the web carrier.

In the FIG. 2 two dryer fabrics 5 are shown in their complete circulation path, each of the dryer fabrics 5 each circulating a group of drying cylinders 4. More specifically, each drying wire 5 in the region of the drying cylinder 4 is wavy up and down, wherein the drying wire 5 is deflected at the wave crest of a drying cylinder 4 and is deflected in the trough by a suction roll of a respective vacuum device 6. After leaving the last drying cylinder 4 of the corresponding group, the drying wire 5 is again the first through a plurality of guide rollers 7 Drying cylinder 4 of the group returned.

To carry out the inventive method for detecting a tear of a fibrous web 3 in the dryer section 2 of the machine 1 for producing the fibrous web 3 at least one symbolically indicated optical device 8 is provided for web tear detection for each group of drying cylinders 4, which in FIG. 3 is described in principle. Moreover, for each group of drying cylinders 4 there is provided at least one tee-off device 9 for the fibrous web 3 which is indicated only schematically and which is activated directly or indirectly by the optical device 8 for web tear detection.

The FIG. 3 shows a schematic representation of an arrangement of a device 10 with an optical device 8 for web tear detection.

The device 10 with the optical device 8 for web tear detection can be used in a section, in particular in a dryer section of a machine for producing a fibrous web 3. The fibrous web 3 lies on the guided through the dryer section drying wire 5. The dryer 5 is here the web carrier.

The optical device 8 for web tear detection comprises a specific light source 11 in the form of a light source 12, such as a lamp 13 or the like, and a detector 14. The optical device 8 is designed so that from the fibrous web 3 and / or at least one Component of the dryer 5 (dashed line) reflected intensity I _{R of} the light source 11 in a wavelength range L between 1380 to 2,600 nm by means of the detector 14 is measured to reliably detect an outline of the fibrous web 3. The intensity I _{R of} the light source 11 reflected by the fibrous web 3 and / or by at least one constituent of the web carrier 2 is in a range between 1,380 and 1,650 nm, in particular in a wavelength range L, between 1,600 and 1,700 nm, between 1,900 and 2,000 nm, between 2,000 and 2,150 nm, between 2,200 and 2,500 nm or between 2,400 and 2,600 nm by means of the detector 14 measurable.

The light source 11 emits light in said wavelength range L, which is reflected by the fibrous web 3 and / or by at least one component of the dryer fabric 5. The reflected light is then measured by the detector 14 and the signal obtained evaluated in a known manner. The jobs, in particular the angles and distances, both the light source 11 and the detector 14 can be selected in a known to those skilled in the frame.

In the illustrated embodiment, a filter 15 is interposed between the light source 11 and the detector 14 of the optical device 8 for web tear detection, preferably in the manner shown between the fibrous web 3 and the dryer fabric 5 and the detector 14. It is provided that the detector 14 in a wavelength range L of 1380 to 2,600 nm and / or the filter 15 sets the wavelength range L from 1380 to 2,600 nm. Thus, the wavelength range L is limited for the measurement by the detector 14 and / or by the filter 15.

For the direct or indirect activation of the merely indicated tee 9 for the fibrous web 3, at least one triggering threshold S is set by the device 8 for web tear detection.

The in the FIG. 3 illustrated device 10 with the optical device 8 for web tear detection is particularly well suited for carrying out the method according to the invention.

In summary, it should be noted that a method and an apparatus of the aforementioned types are developed such that, compared to the prior art, a more reliable detection of Web breaks in particular single-row drying sections of a machine for producing a fibrous web is made possible.

LIST OF REFERENCE NUMBERS

1

Machine for producing a fibrous web

2

Drying section (section)

3

Fibrous web

4

drying cylinders

5

Dryer fabric (web carrier)

6

Vacuum device

7

leadership

8th

Device for web break detection

9

cutting device

10

contraption

11

light source

12

light source

13

lamp

14

detector

15

filter

F

color intensity

I _R

Reflected intensity

L

Wavelength range

S

triggering

t

Time

Claims (16)

1. Method for detecting a break in a fibrous web (3) in a section (2) of a machine (1) for producing the fibrous web (3), the fibrous web (3) being guided through the section (2) by means of at least one web carrier (5) having at least several constituent parts, the break being detected by at least one optical device (8) for web break detection, which comprises at least one light source (11) and a detector (14), and a knock-off device (9) for the fibrous web (3) being activated directly or indirectly by the device (8) for web break detection,
   characterized in that
   the intensity (I_R) of the light source (11) that is reflected from the fibrous web (3) and/or from at least one constituent part of the web carrier (5) is measured by means of the detector (14) in a wavelength range (L) between 1380 and 2600 nm, in order to detect a break in the fibrous web (3) reliably.
2. Method according to Claim 1,
   characterized in that
   the intensity (I_R) of the light source (11) that is reflected from the fibrous web (3) and/or from at least one constituent part of the web carrier (5) is measured by means of the detector (14) in a wavelength range (L) in a range between 1380 and 1650 nm, between 1600 and 1700 nm, between 1900 and 2000 nm, between 2000 and 2150 nm, between 2200 and 2500 nm or between 2400 and 2600 nm.
3. Method according to Claim 1 or 2,
   characterized in that
   the light source (11), such as in particular a lamp (13), emits specific light.
4. Method according to one of the preceding claims,
   characterized in that
   at least one filter (15) is interposed between the light source (11) and the detector (14) of the optical device (8) for web break detection.
5. Method according to Claim 4,
   characterized in that
   the wavelength range (L) from 1380 to 2600 nm is set or limited by the filter (15).
6. Method according to one of the preceding claims,
   characterized in that
   the detector (14) measures in a wavelength range (L) from 1380 to 2600 nm.
7. Method according to one of the preceding claims,
   characterized in that
   the wavelength range (L) for the measurement is limited by the detector (14) and/or by the filter (15).
8. Method according to one of the preceding claims,
   characterized in that
   at least one triggering threshold (S) is set for the direct or indirect activation of the knock-off device (9) for the fibrous web (3) by the device (8) for web break detection.
9. Device (10) for detecting a break in a fibrous web (3) in a section (2) of a machine (1) for producing the fibrous web (3), guided through the section (2) by means of at least one web carrier (5) having at least several constituent parts, having at least one optical device (8) for web break detection, which comprises at least one light source (11) and a detector (14), and having a knock-off device (9) for the fibrous web (3) that can be activated directly or indirectly by the device (8) for web break detection, in particular for implementing a method according to one of the preceding claims,
   characterized in that
   the intensity (I_R) of the light source (11) that is reflected from the fibrous web (3) and/or from at least one constituent part of the web carrier (5) can be measured by means of the detector (14) in a wavelength range (L) between 1380 and 2600 nm, in order to detect a break in the fibrous web (3) reliably.
10. Device (10) according to Claim 9,
    characterized in that
    the intensity (I_R) of the light source (11) that is reflected from the fibrous web (3) and/or from at least one constituent part of the web carrier (5) can be measured by means of the detector (14) in a wavelength range (L) in a range between 1380 and 1650 nm, between 1600 and 1700 nm, between 1900 and 2000 nm, between 2000 and 2150 nm, between 2200 and 2500 nm or between 2400 and 2600 nm.
11. Device (10) according to Claim 9 or 10,
    characterized in that
    the light source (11) is a specific light source (12), such as in particular a lamp (13).
12. Device (10) according to one of Claims 9 to 11,
    characterized in that
    at least one filter (15) is interposed between the light source (11) and the detector (14) of the optical device (8) for web break detection.
13. Device (10) according to Claim 12,
    characterized in that
    the wavelength range (L) from 1380 to 2600 nm can be set or limited by the filter (15).
14. Device (10) according to one of Claims 9 to 13,
    characterized in that
    the detector (14) measures in a wavelength range (L) from 1380 to 2600 nm.
15. Device (10) according to one of Claims 9 to 14,
    characterized in that
    the wavelength range (L) for the measurement is limited by the detector (14) and/or by the filter (15).
16. Device (10) according to one of Claims 9 to 15,
    characterized in that
    at least one triggering threshold value (S) is set for the direct or indirect activation of the knock-off device (9) for the fibrous web (3) by the device (8) for web break detection.

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