SYSTEM OF REGULATION FOR A PAPER MACHINE

Abstract: A feedback-connected on-line system of regulation of the headbox (10) of a paper or board machine. The headbox (10) comprises a flow duct for stock suspension or separate flow ducts placed one above the other, which flow duct(s) extend(s) from the inlet header (11) of the headbox (10) into its slice channel (14), the stock suspension jet (J) being discharged from the slice opening (16) of said slice channel onto the forming wire or into the forming gap formed between forming wires. The system of regulation comprises a regulator unit (30; 40, 41, 42) and a set value unit (32). To the regulator unit (30; 40, 41, 42), measurement values (MV) are passed from the headbox system. From the regulator unit (30; 40, 41, 42), control values (CV) are obtained, by whose means the actuators of the headbox system are controlled. The system of regulation includes an on-line arrangement of measurement of the dried paper web (W; Wout) or of the paper web to be dried, by means of which arrangement, in the plane of the paper web (W; Wout), the distribution (OE) of its fibres is measured. By means of the measurement signal obtained from this measurement arrangement, the actuators of the headbox (10) are controlled by means of feedback so as to achieve a distribution of fibre orientation and a corresponding MD/CD ratio of strength in accordance with the set value (SV; sva, ha, svs) in the paper web (Wout) to be produced under control of the system of regulation in accordance with the present invention.

Description: System of regulation for a paper machine The invention concerns a feedback-connected on-line system of regulation of the headbox of a paper or board machine, which headbox comprises a flow duct for stock suspension or separate flow ducts placed one above the other, which flow duct(s) extend(s) from the inlet header of the headbox into its slice channel, the stock suspension jet being discharged from the slice opening of said slice channel onto the forming wire or into the forming gap formed between forming wires, which system of regulation comprises a regulator unit and a set value unit, to which regulator unit measurement values are passed from the headbox system, and from which regulator unit control values are obtained, by whose means the actuators of the headbox system are controlled. As is known from the prior art, in paper or board machines, a stock suspension jet is discharged out of the slice opening onto the forming wire or into the gap between forming wires. The cross-direction profile of the slice opening also determines the profile of the stock jet. The profile of the slice opening is regulated, in which way it is also partly possible to compensate for the faults in the stock jet that have arisen in or before the headbox. A headbox, in particular a multi-layer headbox, is a difficult item of regulation, because the process involves a number of different parameters, which have various cross effects, which effects may further depend on the raw-materials that are used, on the grade that is being produced, and/or on the geometry of the headbox and on the mode of running. However, in the manufacture of a paper product of good quality, in particular of printing and writing paper, in particular when the multi-layer technique is applied, the ratios of speed and flow quantities between the different stock flows and the settings of these parameters in relation to the wire speed must be sufficiently precisely controllable. 2 From the prior art, a system for the control of the basis weight profile of the headbox in a paper machine is known, which comprises an angular-gear/stepping- motor actuator, by whose means the top slice bar which regulates the slice profile is controlled by means of adjusting spindles attached to said bar at a spacing of about 10...15 cm, which spindles are displaced by said actuator placed at one of their ends. The profiling of the top slice bar of the headbox usually takes place so that each regulation gear is controlled separately in a sequence of treatment taking place one after the other. In order that the positioning could be carried out with the required precision of about 10 μm, an electronic system for measurement of the locations of the regulation spindles is also needed. Errors in the fibre orientation in a paper web arise mainly from the following causes. A smaller amount of stock flows at the edges of the stock flow channel in the headbox. This edge effect causes a very strong linear distortion in the profile. Errors of profile in the turbulence generator in the headbox usually cause a nonlinear distortion inside the lateral areas of the flow channels. The acceleration produced in the slice cone of the headbox equalizes the profile errors in the main flow, but it is exactly that effect that produces the cross-direction flow. Errors of orientation in the paper web are indirectly also caused by the operation of the dryer section, because, during drying, the paper web can shrink unevenly in the cross direction so that the lateral areas shrink to a considerably greater extent than the middle area. Attempts are made to compensate for the unevenness of the basis weight profile caused by the drying shrinkage by means of crown formation of the slice opening so that the slice opening is thicker in the middle area of the stock jet. This, however, results in cross- direction flows in the slice jet and further in the wire part, which again causes distortion of the fibre orientation. The same phenomenon also affects the cross-direction strength profiles of the web. In the prior art, a method is known for on-line regulation and measurement of the fibre orientation in a web that is produced by means of a paper machine from the applicant's FI Patent No. 81,848 (equivalent EP Patent No. 408,894). The method of regulation of a paper machine known from said patent is characterized in that, 3 with the machine configuration and the parameters at each particular time applied in the paper machine to be regulated, data are collected concerning the relationship between the cross-direction distribution of fibre orientation and the basis weight distribution of the web that is being produced so that response runs are carried out with the paper machine in different states of operation of the machine. The data on the relationship that were obtained in the stage defined above are stored in the memory of the computer or equivalent included in the system of regulation of the paper machine. While making use of said data on the relationship, by means of the system of regulation, the distribution of the fibre orientation in the web that is being produced is corrected by regulating the cross-direction profile of the slice opening or equivalent of the headbox. The method of measurement of said FI patent comprises said two first-mentioned stages and, further, a stage in which, while making use of said data on the relationship, the distribution of the fibre orientation in the web is expressed based on the measurement of the cross-direction basis weight profile of the paper web. In said FI patent, response runs are carried out in order to determine the relationship between fibre orientation and basis weight at each particular time, in connection with which response runs the distribution of the fibre orientation is measured in the laboratory by taking samples out of the web that is being produced, from which samples the fibre orientations are determined with sufficiently dense spacing in the cross direction of the web by making use of prior- art commercial methods and apparatuses of laboratory measurement or of tests of diagonal tensile strength. Such a high number of response runs and related series of laboratory measurements are carried out that, while average values are computed from the measurement results, a sufficiently good explanatory quality is obtained between the basis weight profile and the fibre orientation profile. In the manufacture of paper, one of the most important factors that affect the functional properties of paper is the so-called machine-direction/cross-direction ratio of strength. This ratio is controlled by regulating the difference in speed between the jet speed at the headbox and the speed of the forming wire or wires or the ratio of said speeds (in the following, the s/v ratio). As a rule, the wire speed is kept invariable, and the regulation takes place by means of regulation of the headbox jet speed. 4 The ratio of the tensile strengths of paper in the machine direction and in the cross direction is regulated in a way known from the prior art, for example, as follows: The tensile strengths are measured in the laboratory at regular intervals, typically from a sample of paper taken from each machine reel. If the tensile strengths are not at the specified level, as a rule said s/v ratio at the headbox is altered. The tensile strengths can also be affected by means of properties of the stock, but the s/v ratio is the primary parameter of regulation. It is considerably more difficult to act upon the properties of the stock, because such changes, for example grinding and ratios of different stock components, affect almost all quality factors of paper. In a way known from the prior art, the headbox jet speed is monitored by measuring the static pressure at the beginning of the slice cone and by converting the pressure value, by means of computing, into the jet speed. In the computing, it is necessary to take into account the geometry of the headbox and the friction and turbulence losses caused by the walls and by possible vanes. In particular, it is very difficult to produce a mathematical model for the losses arising from vanes, which results in problems in the control of the jet speed when changes take place in the running parameters of the headbox, such as the geometry of the slice part, or when the grade that is produced or the raw-material is changed, in which case a considerable proportion of the paper can be lost in connection with a change of grade before the quality can be regulated and stabilized at an appropriate level. From the prior art, devices for direct measurement of the speed of the discharge jet are also known, but fitting of such devices in the area of the forming gap, in which the space is very limited, is quite difficult and, moreover, said detectors disturb the stability of the jet. Some of the critical parameters of a paper web are the fibre orientation ratio (in the following, fibre ratio) and the orientation angle, because the fibre ratio affects the properties of strength of paper and board so that the tensile strength of the web in the plane of the paper is substantially higher in the direction of the fibres as com- pared with the direction perpendicular to said fibre direction. The MD/CD ratio of tensile strength of the web is determined by the orientation ratio, i.e. the fibre ratio Om aχ . Oπ ύ n, and the definition of this ratio will be dealt with in more detail in 5 connection with the description related to Fig. 3. The fibre ratio also affects the runnability of a paper machine and of a printing and copying machine. This is why, as a rule, the aim is that the paper should be stronger in the machine direction than in the cross direction, in which case, for example in a printing machine, a paper web that runs in its machine direction endures tension to a greater extent than in the cross direction. Typically, the MD/CD ratio of tensile strength is in a range of 0.9 ... 4.5, in the case of printing and writing papers, as a rule, in a range of 1.5 ... 3.5. In a paper machine, in the web formation, the fibre ratio is affected above all by said s/v ratio. If the wire speed differs from the jet speed, the fibres have a tendency of orienting in the machine direction to a greater extent than in the cross direction, in which case the tensile strength of the web in the machine direction is increased, which is desirable, as a rule. If the slice jet has a cross-direction speed component when it is discharged from the slice opening of the headbox, the principal direction of orientation can differ from the machine direction, in which case the orientation angle (angle , Fig. 3) becomes larger than zero. Recently, detectors and systems of measurement of tensile strength / tensile rigidity and of fibre orientation have been introduced in the market. With respect to these, reference is made, by way of example, to the paper in the journal Svensk Popper s- tidning/Nordisk Cellulosa No. 6:1997, pages 64...66, Gunnar Lindblad: "Infra- Ijudsmatning - ett nytt sάtt att styra pappersmaskinen " (Tnfrasonic measurement - a new mode of controlling the paper machine'). Further, with respect to the prior art related to the present invention, reference is made to the following published patent applications and patents: WO 97/01088, US 4,133, 713, US 4, 151,415, and US 5, 145,560. The object of the present invention is to provide a novel method of regulation of a paper machine, by means of which method it is possible to produce a paper that meets ever stricter requirements of quality, in particular writing and printing paper. The method in accordance with the present invention is supposed to be suitable both for single-layer and for multi-layer web formation. 6 An object of the present invention is to take advantage of the recent development that has taken place in detector technology, in particular in respect of on-line detectors for fibre orientation and tensile strength of paper web. In view of achieving the objectives stated above and those that will come out later, the invention is mainly characterized in that the system of regulation includes an online arrangement of measurement of the dried paper web or of the paper web to be dried, by means of which arrangement, in the plane of the paper web, the distribution of its fibres is measured, and that, by means of the measurement signal obtained from said measurement arrangement, the actuators of the headbox are controlled by means of feedback so as to achieve a distribution of fibre orientation and a corresponding MD/CD ratio of strength in accordance with the set value in the paper web to be produced under control of the system of regulation. In the method of the present invention, the tensile strength, the ratio of tensile strength, the fibre ratio and/or the fibre orientation angle is/are measured directly from a dry paper web, i.e. from a finished paper product. This measurement can be carried out by means of a measurement head traversing in the cross direction across the entire width of the web in the paper machine or, as an alternative, by means of a stationary measurement head/heads, which is/are placed in a certain chosen location(s) in the cross direction of the paper web. When a traversing measurement head is used, it is possible to compute the average value of the fibre orientation profile or equivalent, or the profile can also be used as a control signal in the regulation of profile, for example in regulation of the profile of the slice opening of the headbox. As an alternative, out of a number of successive scannings of fibre orientation profiles, for example, an average value can be formed, which value is used as a control signal for the system of regulation. In the system of regulation of the present invention, as expressly the fibre orientation is measured directly on-line from a finished web and as it is not necessary to resort to indirect or slow laboratory measurements, a reliable regulation parameter is 7 obtained quickly to control the regulation system so that a paper with the preset MD/CD ratio of tensile strength can be produced. It is a further advantage of the present invention that, with the system of regulation of the invention, for example, in connection with change of paper grade, it is possible to make the paper machine to produce a paper that meets the criteria of quality quickly, so that the proportion of paper that becomes broke is reduced substantially from what is was in the prior art. This is a considerable advantage in paper machines in which changes of grade are carried out repeatedly at relatively short intervals. Since the cross-direction shrinkage of paper depends on the orientation profile, a variation in the cross-direction shrinkage has no detrimental effect in the system of regulation, because the measurement of the orientation takes place from a dry paper web after the web has shrunk into its ultimate state in the cross direction. In the following, the prior art related to the present invention and some exemplifying embodiments of the invention will be described in more detail with reference to the schematic illustrations in the accompanying drawing, which illustrations show the following: Figure A is a schematic illustration, representing the background and an environment of application of the present invention, of a prior-art stock feed system of a headbox provided with dilution regulation of the CD basis weight profile and of a system of control of said stock feed system. Figure 1A shows a simplified system diagram of an embodiment of the method of regulation in accordance with the present invention. Figure IB illustrates a second exemplifying embodiment of the system of regulation in accordance with the present invention more widely than Fig. 1A does. 8 Figure 2 is a schematic vertical sectional view in the machine direction of a headbox for use in the method in accordance with the present invention. Figure 3 illustrates a typical distribution of fibre orientation in a machine-direction (MD) / cross-direction (CD) system of coordinates. Fig. A also shows the system 100 of regulation of the headbox, by whose means the CD profiles in the paper machine, the dilution ratio, and the speed of the discharge jet J of the headbox 10 are controlled. The discharge jet J of the headbox 10 is discharged into the forming gap defined by the forming wires (not shown). In the manufacture of paper, one important control parameter is the ratio of the speed of the discharge jet J to the speed of the forming wires (not shown) (in the following, s/v ratio). The stock feed system shown in Fig. A includes a wire pit 61, which communicates through a pump 62 with the short circulation 70 of the paper machine, from which circulation the main stock flow FM is obtained, which is passed through the main stock pipe 67 into the inlet header 11 of the headbox 10. The wire pit 61 communicates with a first feed pump 63 of dilution liquid, which pump passes the dilution liquid into the de-aerator 65. The dilution liquid is fed from the de-aerator 65 by means of a pump 64 through a pressure screen 66 into a dilution header 72, which can be separate from the inlet header 11 of the headbox or integrated with the inlet header, for example, in the way described in the applicant's said FI Patent Application 970140, in which case it also comprises arrangements for regulation of the edge feed, which have been fitted in both of the lateral areas of the headbox mainly in view of control of the fibre orientation profile. From the inlet header 72 the dilution flows FD^ . -FDN are fed through a series of regulation valves 71^ __ N into the set of distributor tubes 13 in the turbulence generator 12 of the headbox 10 and further through the slice channel 14 to constitute the stock jet J. To begin with, with reference to the simplified system diagram in Fig. 1A, the principle of the system of regulation of the invention will be described. By means of the system as shown in Fig. 1A, the value of the tensile strength / tensile strength ratio (MD/CD ratio) of the paper web produced by means of the paper machine is 9 measured and regulated by means of feedback. In Fig. 1A, the paper machine and the papermaking process are represented generally by the block 50. In the paper machine, in its dry end, an on-line system of measurement of tensile strength has been fitted, which system is, for example, similar to that described in the above paper in the journal Svensk Papperstidning/Nordisk Cellulosa. From the on-line system of measurement of tensile strength, a measurement signal hm is obtained, which is fed into the system 40 of regulation of tensile strength / tensile-strength ratio. Into this system 40 of regulation, the set value ha of tensile strength and the permitted range sva of the s/v ratio are passed. The system 40 includes a model of interdependence of tensile strength and s/v ratio, on the basis of which model the system 40 determines the set value svs of the s/v ratio. This set value svs is transferred to the system 41 of regulation of s/v ratio, which system is, for example, the system of regulation marketed by the applicant with the trade mark Optijet. From the system 41 of regulation, the set value pa is obtained for the pressure in the slice part of the headbox, the pressure in the headbox being regulated on the basis of said set value pa by means of the system 42. By means of the system 42, the set value of the static pressure of the headbox is measured, on the basis of which value the control signal sp for the feed pump of the headbox of the paper machine is obtained, by means of which control signal sp a s/v ratio in compliance with the set value ha of tensile strength is obtained. Fig. 3 illustrates a typical distribution of fibre orientation OE for paper in a machine-direction (MD) / cross-direction (CD) system of coordinates. The distribution of fibre orientation OE is shaped as an ellipse, and the radius from the origin of the MD-CD system of coordinates to the ellipse of distribution OE represents the relative proportion of the fibres of the paper in the direction of said radius in the plane of the paper. The ellipse of distribution OE has an main axis MOX, in which the distribution O max is at the maximum. The main axis MOX is placed at an angle in relation to the machine direction MD. The angle is a so-called orientation angle. In the direction perpendicular to the axis MOX, the distribution of orientation has a minimal value O min . The ratio O max /O min is called said fibre ratio. The fibre ratio O maχ /O min mainly determines the MD/CD tensile-strength ratio of the paper. 10 Fig. IB is a schematic and simplified illustration of a papermaking process and of the on-line system in accordance with the invention for regulation of the ratio of fibre orientation to tensile strength, which system regulates said papermaking process. Fig. IB shows the headbox 10 of the paper machine, into whose inlet header 11 the feed pump 20 feeds the stock flow FM. The inlet header 11 is followed, for example, by a distributor tube bank, a stilling chamber, a turbulence generator, and the slice channel 14, through whose slice opening 16 the stock suspension jet is discharged onto the forming wire or into the forming gap formed by the forming wires (not shown). In the paper machine, the paper web W is formed and dried, which web is passed at the dry end of the paper machine through a measurement frame 24 placed before the reel-up. The measurement frame 24 includes measurement heads 25, which preferably traverse in the cross direction of the paper web across its whole width. By means of the measurement frame 24, cross-direction profiles, i.e. CD profiles, of the ready-dried paper web W out are measured on-line, such as basis weight profile, thickness profile, moisture profile, and, in the system of regulation in accordance with the present invention, expressly also the fibre orientation profile or the fibre orientation at a certain specified point or points of the paper web in its cross direction. The measurement detector of fibre orientation or fibre orientation profile can be, for example, a detector based on microwave technology, and the construction and operation of such a detector is described in more detail in said International Patent Application WO 97/01088 of Valtion Teknillinen Tutkimuskeskus (Technical Research Centre of Finland) . Said measurement device measures the fibre orientation angle illustrated in Fig. 3 as well as the what is called fibre ratio O max /O min of the orientation, both of which depend on the s/v ratio, as was described above. The measurement signals of orientation and of the other cross-direction profiles from the measurement head 25 are fed to the unit 26, which is connected to the computer 27 connected with the system of regulation of the paper machine, which computer comprises the necessary display and data transfer devices. As is shown in Fig. IB, a series of measurement signals M j is obtained from the unit 26 through the bus 28, which measurement signals also include a measurement value 11 of the orientation ratio maχ /O ιa ^ a and a measurement value of the orientation angle at a certain point in the cross direction of the paper web W, or the CD profiles of said measurement values. The measurement values M j are fed to the regulation system 30, to which the measurement signal p t of static pressure is also fed from the measurement detector 29 of the slice channel 14 of the headbox 10. The signals M j and p t constitute the measurement values MV of the regulation system 30. Set values SV are fed from the set value unit 32 to the regulation system 30. Further, the regulation system 30 is controlled and/or modified by means of the unit 31 , which communicates with the computer 27 through the bus 32. The unit 31 can include, for example, a multi-variable model of the papermaking process, whose construction and application are described in more detail in the applicant's FI Pat. Appl. No. 980319. As is shown in Fig. IB, the regulation signals CV are obtained from the regulation system 30, which signals include the control signal sp for the feed pump 20 of the headbox and the signal sh, which regulates the CD profile of the slice opening 16 of the headbox 10. By means of the signal sh, the series of actuators 23 of the headbox is regulated, by means of which series of actuators the spindles 22 are regulated, which again regulate the top slice bar 21, by whose means the CD profile of the slice opening 16 and, thereby, the basis- weight and fibre-orientation profiles of the paper web W that is being formed are controlled in a way in itself known. The system of regulation as shown in Fig. IB can operate, for example, so that, by means of the fibre orientation profile measured by means of the measurement head 25, expressly fine adjustment of the headbox pressure p t is carried out so that the orientation ratio O max /O min of the paper W out that is being produced is maintained in compliance with the preset set value sv. As was stated above, the measurement head 25 can be either traversing and scanning in the CD direction and connected with other traversing measurement detectors in the measurement frame 24, such as basis- weight and moisture detectors, or alternatively a separate orientation measure- ment head(s) 25 can monitor a certain point/points of the web alone with fixed installation. 12 In accordance with the invention, the feed pump 20 of the headbox 10 is regulated by means of the regulation signal sp obtained from the system 30 so that the fibre ratio O JJJ ^/O JJJ J JJ remains at the set value. In such a case, changes in the mode of running of the paper machine and of the headbox, such as regulation of the width or CD profiling of the slice opening 16, regulation of dilution flow valves or lateral flow valves, and/or changes in the speed of the machine do not have uncontrollable effects on the fibre ratio O max /O min (Fig. 3). If the measurement head 25 measures the cross-direction profile of the fibre orientation ratio, in such a case the fibre ratio can also be used by means of the regulation signal sh for regulation of the slice opening 16 of the headbox 10, besides for regulation of the pressure p t . It is a further advantage of the system in accordance with the invention that the measurement signal is obtained directly from the fibre ratio O max /O min , in which case the drying shrinkage profile has no disturbing effect on this measurement signal. A rough value of the s/v ratio can be computed, in a way in a way known from the prior art, from the pressure p t of the headbox 10, so that the regulation does not become unstable when the speed of the discharge jet J is determined when running with an upper headbox and with a lower headbox. In the headbox 10 as shown in Fig. 2, the headbox flow FM (corresponds to the flow FM in Fig. A) has been divided into three separate layers of flows F 1 ,F 2 ,F 3 , which flows are separate from each other up to the end of the vanes 15^152 in the slice channel 14. In a way similar to the flow FM shown in Fig. A, in principle, the flow layers F 1 ; F 2 and F 3 can be composed of flows consisting of different raw- materials or of component flows made of the same basic raw-material with different admixtures and fillers, as is described in more detail, for example, in the applicant's said FI Patent 92, 729. Each of the layers placed one above the other in the headbox 10 has an inlet header ll 1 ,ll 2 ,ll 3 of its own, from which the flow is passed into the turbulence generator 13 and further into the distribution tube bank 13. The flows are passed from the distribution tube bank 13 into the slice channel 14. In the slice channel 14, the flows are separated from each other by means of vanes 15 2 ,15 2 , whose initial ends 15a have been linked as pivotal in connection with the final end of the distribution tube bank 13. The vanes 15 γ , 15 2 can pivot into different posi- 13 tions and be positioned so that they substantially equalize the pressures of the component stock flows. The vanes 15^ 15 2 are made of a somewhat elastic material, so that they can also bend. As is shown in Fig. 2, in the middle duct between the vanes 15 j^ and 15 2 , a detector 29 for measurement of the static pressure p t in the slice part 14 of the headbox has been fitted. Owing to the free positioning and/or flexibility of the vanes 15 1 ; 15 2 , the pressure p t measured by means of the measurement detector 29 illustrates the pressure in the whole slice channel 14 well. It should be emphasized in this connection that the system of regulation in accordance with the present invention can be applied to headboxes in which there is/are one or several layers placed one above the other, i.e. both to single-layer headboxes and to multilayer headboxes, the latter sort of headbox being illustrated by Fig. 2 by way of example. In the following, the patent claims will be given, and various details of the invention can show variation within the scope of the inventive idea defined in said claims and differ even to a considerable extent from what has been stated above by way of example only.

Claims: 14 Claims 1. A feedback-connected on-line system of regulation of the headbox (10) of a paper or board machine, which headbox (10) comprises a flow duct for stock suspension or separate flow ducts placed one above the other, which flow duct(s) extend(s) from the inlet header (11) of the headbox (10) into its slice channel (14), the stock suspension jet (J) being discharged from the slice opening (16) of said slice channel onto the forming wire or into the forming gap formed between forming wires, which system of regulation comprises a regulator unit (30;40,41,42) and a set value unit (32), to which regulator unit (30;40,41,42) measurement values (MV) are passed from the headbox system, and from which regulator unit (30;40,41,42) control values (CV) are obtained, by whose means the actuators of the headbox system are controlled, characterized in that the system of regulation includes an on-line arrangement of measurement of the dried paper web (W;W out ) or of the paper web to be dried, by means of which arrangement, in the plane of the paper web (W; W out ), the distribution (OE) of its fibres is measured, and that, by means of the measurement signal obtained from said measurement arrangement, the actuators of the headbox (10) are controlled by means of feedback so as to achieve a distribution of fibre orientation and a corresponding MD/CD ratio of strength in accordance with the set value (SV; sva, ha, svs) in the paper web (W out ) to be produced under control of the system of regulation. 2. A system of regulation as claimed in claim 1, characterized in that said distribution of fibre orientation (OE) is measured by means of a detector or series of de- tectors (25), by whose means the so-called fibre ratio (O msx /O nύl of the paper web (W; W out ) and/or the angle (a) of the main direction (MOX) of orientation in relation to the machine direction (MD) is/are detected as on-line measurement (Fig. 3). 3. A system of regulation as claimed in claim 1 or 2, characterized in that the distribution of fibre orientation (OE) is measured by means of a measurement head 15 (25) scanning in the CD direction of the paper web (W; W out ), in which connection the CD profile of the distribution of fibre orientation is obtained. 4. A system of regulation as claimed in claim 3, characterized in that an average value computed from said CD profile of the distribution fibre orientation (OE) or from two or more profiles measured one after the other is used in the system of regulation as a feedback measurement signal (MV), possibly also as a signal that affects the cross-direction profiling of the web. 5. A system of regulation as claimed in claim 1 or 2, characterized in that, in the method, the distribution of fibre orientation (OE) is measured from one or several fixed points by means of a single measurement head or by means of a series of several measurement heads and, when several measurement heads are used, for example, an average value is formed out of different signals, which average value is used in the system of regulation as a feedback measurement signal. 6. A system of regulation as claimed in any of the claims 1 to 5, characterized in that, in the method, based on the signal or signals of measurement of the fibre orientation, the static pressure (p t ) in the slice channel (14) of the headbox (10) is regulated. 7. A system of regulation as claimed in claim 6, characterized in that, in the system of regulation, there is a model (40) of the interdependence of the tensile strength and/or ratio of MD/CD tensile strength of the paper web (W; W out ) and of the ratio of jet speed to wire speed in the headbox (s/v ratio), on the basis of which model, in the system of regulation, a set value (svs) of the s/v ratio has been determined, and that, in the system, a set value (pa) of the static pressure (p t ) in the headbox has been determined, with which set value (pa) the preset s/v ratio (svs) is achieved (Fig. 1A). 8. A system of regulation as claimed in any of the claims 1 to 6, characterized in that, in the system of regulation, there is a regulator unit (30), to which the value of 16 measurement (p t ) of the static pressure in the slice channel (14) of the headbox (10) is passed and to which, from the measurement frame (24) placed in the dry end of the paper machine before the reel-up, the signal of measurement of the distribution of fibre orientation (OE) and possible other measurement signals (M j ) concerning a cross-direction profile of the paper web, such as the basis weight profile and/ or the moisture profile, are passed, and that, from the regulation unit (30), as regulation signals (CV), a signal (sp) is passed to the feed pump (20) of the headbox, and a signal (sh) is passed to the actuator system (22,23) that profiles the top slice bar (21) at the slice opening (16) of the headbox and/or to the dilution profiling system (71t ...N.FDJ ... FD N ,72) (Fig. A). 9. A system of regulation as claimed in any of the claims 1 to 8, characterized in that the on-line measurement head (25) of the distribution of fibre orientation (OE) in the paper web (W; W out ) comprises a detector or a series of detectors, from which a field of oscillation is directed at the paper web (W; W out ), such as sound oscillation or electromagnetic oscillation, such as laser or microwave oscillation, by means of which oscillation a measurement signal is formed which represents the distribution of fibre orientation (OE). 10. A system of regulation as claimed in any of the claims 1 to 9, characterized in that the system of regulation is applied to a single-layer or multi-layer headbox, and that, in an application of a multi-layer headbox, the static pressure (p t ) in the slice channel (14) of the headbox (10) is measured by means of a pressure detector (29) from the middle duct (15 1 , 15 2 ) in the slice channel (14), which middle duct is defined by vanes (15 j , 15 2 ) which can position themselves and/ or which are to some extent flexible (Fig. 2). 17 AMENDED CLAIMS [received by the International Bureau on 1 July 1999 (01.07.99); original claim 1 amended; remaining claims unchanged (3 pages)] 1. A feedback-connected on-line system of regulation of the headbox (10) of a paper or board machine, which headbox (10) comprises a flow duct for stock suspension or separate flow ducts placed one above the other, which flow duct(s) extend(s) from the inlet header (11) of the headbox (10) into its slice channel (14), the stock suspension jet (J) being discharged from the slice opening (16) of said slice channel onto the forming wire or into the forming gap formed between forming wires, which system of regulation comprises a regulator unit (30;40,41,42) and a set value unit (32), to which regulator unit (30;40,41,42) measurement values (MV) are passed from the headbox system, and from which regulator unit (30;40,41,42) control values (CV) are obtained, by whose means the actuators of the headbox system are controlled, characterized in that the system of regulation includes an on-line arrangement of measurement of the dried paper web (W;W 0Ut ) or of the paper web to be dried, by means of which arrangement, in the plane of the paper web (W; W out ), the distribution (OE) of its fibres is measured, and that, by means of the measurement signal obtained from said measurement arrangement, the difference in speed between the jet speed at the headbox (10) and the speed of the forming wire or wires or the ratio of said speeds are controlled by means of feedback so as to achieve a distribution of fibre orientation and a corresponding MD/CD ratio of strength in accordance with the set value (SV;sva,ha,svs) in the paper web (W out ) to be produced under control of the system of regulation. 2. A system of regulation as claimed in claim 1 , characterized in that said distribution of fibre orientation (OE) is measured by means of a detector or series of detectors (25), by whose means the so-called fibre ratio (O max /O min ) of the paper web (W; W out ) and/or the angle ( ) of the main direction (MOX) of orientation in relation to the machine direction (MD) is/are detected as on-line measurement (Fig. 3). 3. A system of regulation as claimed in claim 1 or 2, characterized in that the distribution of fibre orientation (OE) is measured by means of a measurement head (25) 18 scanning in the CD direction of the paper web (W; W out ), in which connection the CD profile of the distribution of fibre orientation is obtained. 4. A system of regulation as claimed in claim 3, characterized in that an average value computed from said CD profile of the distribution fibre orientation (OE) or from two or more profiles measured one after the other is used in the system of regulation as a feedback measurement signal (MV), possibly also as a signal that affects the cross- direction profiling of the web. 5. A system of regulation as claimed in claim 1 or 2, characterized in that, in the method, the distribution of fibre orientation (OE) is measured from one or several fixed points by means of a single measurement head or by means of a series of several measurement heads and, when several measurement heads are used, for example, an average value is formed out of different signals, which average value is used in the system of regulation as a feedback measurement signal. 6. A system of regulation as claimed in any of the claims 1 to 5, characterized in that, in the method, based on the signal or signals of measurement of the fibre orientation, the static pressure (p t ) in the slice channel (14) of the headbox (10) is regulated. 7. A system of regulation as claimed in claim 6, characterized in that, in the system of regulation, there is a model (40) of the interdependence of the tensile strength and/or ratio of MD/CD tensile strength of the paper web (W; W out ) and of the ratio of jet speed to wire speed in the headbox (s/v ratio), on the basis of which model, in the system of regulation, a set value (svs) of the s/v ratio has been determined, and that, in the system, a set value (pa) of the static pressure (p t ) in the headbox has been determined, with which set value (pa) the preset s/v ratio (svs) is achieved (Fig. 1A). 8. A system of regulation as claimed in any of the claims 1 to 6, characterized in that, in the system of regulation, there is a regulator unit (30), to which the value of measurement (p t ) of the static pressure in the slice channel (14) of the headbox (10) is 19 passed and to which, from the measurement frame (24) placed in the dry end of the paper machine before the reel-up, the signal of measurement of the distribution of fibre orientation (OE) and possible other measurement signals (M;) concerning a cross- direction profile of the paper web, such as the basis weight profile and/or the moisture profile, are passed, and that, from the regulation unit (30), as regulation signals (CV), a signal (sp) is passed to the feed pump (20) of the headbox, and a signal (sh) is passed to the actuator system (22,23) that profiles the top slice bar (21) at the slice opening (16) of the headbox and/or to the dilution profiling system (71 1---N ,FD, ... FD N ,72) (Fig. A). 9. A system of regulation as claimed in any of the claims 1 to 8, characterized in that the on-line measurement head (25) of the distribution of fibre orientation (OE) in the paper web (W; W out ) comprises a detector or a series of detectors, from which a field of oscillation is directed at the paper web (W; W out ), such as sound oscillation or electromagnetic oscillation, such as laser or microwave oscillation, by means of which oscillation a measurement signal is formed which represents the distribution of fibre orientation (OE). 10. A system of regulation as claimed in any of the claims 1 to 9, characterized in that the system of regulation is applied to a single-layer or multi-layer headbox, and that, in an application of a multi-layer headbox, the static pressure (p t ) in the slice channel (14) of the headbox (10) is measured by means of a pressure detector (29) from the middle duct (15 1 ,15 2 in the slice channel (14), which middle duct is defined by vanes (15ι,15 2 ) which can position themselves and/or which are to some extent flexible (Fig. 2).

Inventors: LUONTAMA MATTI, MUSTONEN HARRI, PAKARINEN PEKKA, LUONTAMA, MATTI, MUSTONEN, HARRI, PAKARINEN, PEKKA
Applicants: VALMET CORP, VALMET CORPORATION
Application year: 1999
Main classification: D21F7
IPC codes: D21F1, D21F7, D21G9