FI108475B - Method for measuring the paper path - Google Patents

Description

108475

Method for measuring the paper path Förfarande för mätning av en pappersbana 5

The invention relates to a method for predicting the tensile strength ratio of a paper web.

The invention also relates to a method for predicting the degree of drying of a paper web.

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In paper machines and the like, in which a continuous web of material is produced, it is necessary to identify the position of the edges of the web at different stages of the process. Defining the track edges provides information about track width and track center. It is previously known to perform edge recognition by photoelectric sensing devices which are either mounted fixed to the edge of the track or which traverse across the track.

Applicant's FI Patent 94176 discloses a method and apparatus for detecting an edge of a web, wherein a transmitter / receiver assembly is positioned at the web and detects its position and presence. A demanding environment with high temperature, high humidity and 20 interference from backlight and electromagnetic radiation sets high standards. requirements for identification devices.

«·« «« · ·. ···. The position of the edge of the paper path and the width of the web can also be measured using a traverse probe • · ·. One period of transversion typically lasts 20-40 seconds. 25 During this time, the track may move in the transverse direction up to 1-2 cm. As a result, · · when measuring one edge, the exact position of the other edge is not known. This leads to inaccuracies in the measurement results.

• · · »· · · · · · ·. It is an object of the present invention to further develop the above technology): '; 30 levels and provide a new device for determining the position of the edges of the paper path, which is reliable, resilient and more versatile in use. and more accurate and faster in terms of expression.

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A further object of the invention is to provide a method in which web position and shrinkage changes can be utilized in a web cross-alignment alignment algorithm.

A further object of the invention is to provide a method in which the tensile strength ratio of the paper 5 can be determined on the basis of the web width.

In order to achieve the foregoing and subsequently elucidated goals, the method of predicting the tensile strength of a paper web according to the invention is essentially characterized in that it comprises the steps of: a) providing a mathematical model between tensile strength, web width and jet / wire ratio b) determining the position of the rear edge of the paper web at the edge cutter, c) determining the position of the leading edge of the paper web at the edge cutter, d) determining the web width · *. measuring cameras, • ·

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* i · f) determine the shrinkage of the paper path between the edge-cutting member and the * * 25 cameras; and * g) calculate the tensile strength value based on the track width, shower / wire ratio and mathematical model mentioned in a).

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The method for predicting the paper web drying rate according to the invention is essentially characterized in that it comprises the steps of: a) forming a mathematical model between the paper web drying degree and the web width 5, based on laboratory determination and / or on-line measurement, b) determining the paper web width d) determining the transverse drying shrinkage of the paper web formed between the above steps b) and c);

By detecting the paper web edges and determining the web width and the center of the web 20 therefrom, information can be obtained to adjust the papermaking process.

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: Nowadays, track gauge is mainly used for profile adjustment. Track width .1 ··. however, the change can also be used eg to predict tensile strength • · · •; · · · Changes. The tensile strength ratio has so far only been investigated on the basis of laboratory measurements: Y: By comparing laboratory measurements and on-line measurement, the · ·: T: 25 measurable track width can be used to form a model between track gauge change and tensile strength change. To take advantage of such a model, accurate • 1 · Y: real-time measurement of the width of the paper web is required, so a traverse measuring device cannot be · ·. v · use for this purpose.

*>> * · «• · ·:“ ': 30 The change in the width of the paper web is mainly due to the change in the degree of drying of the web. This information can be utilized in the drying section of the papermaking machine for monitoring drying 4,108,475. Measuring the width of the paper web before the drying section, between the drying cylinders and after the drying section gives information on the change in the drying degree. Based on this information, the operation of the drying cylinders can be adjusted.

In the method according to the invention, edge measurement cameras are placed at both edges of the paper web, which can be used to measure the position of each edge simultaneously and continuously. An edge measurement camera performs pattern-based edge detection based on pattern recognition. The result of the determination is sent to the data processing equipment for analysis and processing. Edge-measuring camera pairs can be placed in a plurality of locations in different directions of the papermaking process.

The method according to the invention provides more accurate information on the position of the edges of the paper web at the time of measurement compared to conventional measuring methods. Information about changes in the position and shrinkage of the paper path is utilized, for example, in the transverse alignment algorithm 15. In addition, this data can be used to predict the value of the tensile strength ratio of the paper web, which previously could only be determined by laboratory measurements. This takes advantage of the tensile strength value in real-time control of the paper machine.

The invention will now be described in detail with reference to the accompanying drawing:. ·. Examples of the invention shown in the figures for which the invention is not intended

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. ***. exclusively restricts.

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Figure 1 shows schematically the headbox of the paper machine, the paper path and the location of the measuring instruments.

Fig. 2 shows the line width to tensile strength ratio of the jet wire ratio (w / w); function.

Fig. 3 is a block diagram showing a system according to the invention for a paper web. ·: ·. dan edge.

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Figure 4 illustrates the principle of headbox pressure control.

Figure 1 shows an apparatus for measuring the edges of a paper web W. A jet of pulp suspension comes out of the 10 lip openings in the headbox. At this point, the exact initial width L0 of the web 5 is known. Each edge of the paper web W is cut to a certain exact width by the trailing edge cutting member 15 and the leading edge cutting member 16. The width of the paper web W at this point is denoted by P. The paper web W then shrinks further as a result of dewatering.

ίο The posterior measurement camera 17 measures the exact position of the trailing edge WB of the paper web W and the measurement camera 18 of the leading edge measures the exact position of the leading edge WF of the web. The width of the paper web W at the edge measurement cameras 17,18 is denoted by Q. Also shown in the figure is a prior art traverse measuring device 20.

R = Q / P

Corresponds to shrinkage loss: 1 = 100 · (1-R) [%]:,, The shrinkage of the paper web W as a result of dewatering is mainly due to paper fibers ♦ ··. changes. Here the shrinkage of the paper web W is considered only in the width direction. The paper web W also shrinks in the machine direction and this is manifested in the paper web · /; 1; dan tension changes. Predicting tensile strength from paper web width changes • · 25 requires a relatively uniform fiber orientation distribution.

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Figure 1 also shows the dotted line position yQ of the center of the paper web W. y · Ideally, the center will remain transversely at the same position y0 • without moving sideways. In practice, however, the paper web W often moves slightly in the direction of the offset · ·: 1: '': 30, and then also the center moves to y0 ', as shown by the dashed line in Figure · 1 · 1 6 108475. The transition of the paper web W is denoted by s = y0 - y0 '·

To predict the correlation between the tensile strength KS / PS of the paper being produced and the web width L, a machine-specific model is made for each paper machine. For this purpose, the tensile strength KS / PS as a function of the jet / wire ratio s / v is determined in the laboratory for each roll of paper. While the change in track width L is also known, a model can be formed between the track width L and the tensile strength ratio KS / PS. This model can be used in real-time to predict tensile strength KS / PS based on track gauge data. Information about the changed tensile strength KS / PS is utilized e.g. to adjust the headstock feed pressure.

A similar pattern may also be formed between the web width L and the moisture level of the paper web W. The resulting model provides one on-line measurement of the moisture content of the paper web W at the measurement point. The information can be used to adjust the drying section parameters of the paper machine.

Figure 2 shows an example of typical curves of measured track width L as a function of jet / wire ratio s / v and tensile strength KS / PS as a function of jet / wire ratio s / v, ·,, 20. Based on these curves, a model is utilized to real-time determine the tensile strength KS / PS in the data processing device 25.

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Figure 3 is a block diagram showing the operation of the track width L measuring apparatus. From the trailing edge measurement camera 17 and the leading edge measurement camera 18, the data measured therein is supplied to the data processing unit 25. The data processing unit 25 further receives the shower / wire ratio from the s / v unit 19 and the edge cutting members 15,16. location. Based on this information, shrinkage loss 1 can be calculated and the value of tensile strength KS / PS can be determined according to the former model. The information obtained • can be displayed by a display device 26, which may be, for example, a display monitor or a printer. 30 In addition, the determined tensile strength KS / PS information is applied to the papermaking machine control unit 27. The tensile strength KS / PS value adjusts the headbox • · · 7 108475 10 pressure setpoint. The tensile strength KS / PS value can also be used to adjust other paper machine quantities.

The determined tensile strength KS / PS value can be used, for example, to determine the set value of the s / v ratio 5 in the following manner.

Figure 4 illustrates the principles of headbox pressure control. The jet / wire ratio control unit 31 calculates the required jet speed from the s / v setpoint and wire speed, and hence the headbox pressure required, which is set to be sent to the headbox pressure control unit 32. The headbox pressure is continuously monitored by the .

The following claims are made within the scope of the inventive idea defined by the various details of the invention, which may differ considerably from those set forth above by way of example only.

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Claims (9)

108475 A method for predicting the tensile strength of a paper web, characterized in that it comprises the steps of: (a) constructing a mathematical model between tensile strength, web width and jet / wire ratio (s / v) based on laboratory determination and / or on line measurement; determining the position of the trailing edge (WB) of the paper web (W) at the edge cutting member (15), c) determining the position of the leading edge (WF) of the paper web (W) at the edge cutting member (16), 15 d) determining the width ) and c), e) determining the position of both edges of the paper web simultaneously. . 2 0 with the help of measuring cameras (17,18), I · | · · ·. f) determining the shrinkage of the paper path between the edge-cutting members (15.16) and the edge-measuring cameras (17.18); and • ♦ 9 108475 Method according to claim 2, characterized in that the tensile strength ratio (KS / PS) is used to change the headbox pressure setpoint. Method according to Claim 2 or 3, characterized in that from the setpoint of the jet / wire ratio (s / v) and the speed of the wire, the speed of the jet required is calculated. Method according to claim 4, characterized in that from said jet speed a setpoint pressure is calculated. Method for predicting the degree of drying of a paper web, characterized in that it comprises the steps of: a) forming a mathematical model between the degree of drying of the paper web (W) and the web width based on laboratory determination and / or on-line measurement; (L) before the drying section of the papermaking machine; c) determining the width (L) of the paper web (W) of the drying cylinders of the drying section,. 20 by measuring the positions of the edges of the paper web (W) simultaneously with the edge-measuring cameras (17,18), d), determined by the steps b) above ) and c) the transverse drying shrinkage of the paper web • · (W) (1) and • · · · · ♦ ♦ · 25 • · ♦ e) determine the drying degree of the paper web from the mathematical model formed in step a) above. • il · <I t «« «*« Method according to Claim 6, characterized in that the drying ratio of the paper web is used to adjust the drying section of the paper machine. • · * ♦ »·« r '»t · 10 108475 Method according to Claim 6 or 7, characterized in that the degree of drying of the paper web (W) is used to adjust the dewatering of the press. Method according to one of Claims 6 to 8, characterized in that the drying degree value of 5 paper webs (W) is used to control the vapor pressures of the drying cylinders and / or drying groups. I I I I I ••••••••••••••••••••• 08 085 11