WO1999066126A1

WO1999066126A1 - Method and system for regulation of nip profile

Info

Publication number: WO1999066126A1
Application number: PCT/FI1999/000516
Authority: WO
Inventors: Pekka Kivioja; Juha Ehrola
Original assignee: Valmet Corporation
Priority date: 1998-06-15
Filing date: 1999-06-14
Publication date: 1999-12-23
Also published as: AU4784499A; DE19983355T1; FI981386A; FI981386A0; FI111743B

Abstract

The invention concerns a method and a system for regulation of the nip profile in a nip (N) formed by a roll (10) adjustable in zones and by backup roll (20). The nip (N) is loaded adjustably by means of hydraulic glide shoes (13) in the roll (10) adjustable in zones, and the cross-direction profile of the web (W) is measured constantly after the nip (N), and the differential profile between the measured cross-direction profile and the target cross-direction profile is computed, which differential profile is used in a closed regulation circuit as a regulation parameter so as to regulate the nip profile to the desired form. The regulation parameter that represents the differential profile is fed in the closed regulation circuit into an optimizing part (60), which contains an optimizing routine and which contains the data on the profile responses, cross-effects and physical limitations of the actuators in the roll (10) adjustable in zones. Based on the differential profile and while taking into account said cross-effects and physical limitations, the optimizing routine computes new set values in order to minimize the overall error of the cross-direction profile and the differential profile. The set values are fed as regulation parameters to the regulation apparatuses that regulate the nip profile so as to correct the cross-direction profile.

Description

Method and system for regulation of nip profile

The invention concerns a method for regulation of the nip profile in a nip formed by a roll adjustable in zones and by a backup roll, through which nip a paper or board web has been passed in view of controlling the cross-direction profile of the web and which nip is loaded adjustably by means of hydraulic glide shoes which form the zones in the roll adjustable in zones, and in which method the cross-direction profile of the web is measured constantly after the nip and the differential profile between the measured cross-direction profile and the target cross-direction profile is computed, which differential profile is used in a closed regulation circuit as a regulation parameter so as to regulate the nip profile to the desired form.

The invention also concerns a system for regulation of the nip profile in a nip formed by a roll adjustable in zones and by a backup roll, through which nip a paper or board web has been passed in view of controlling the cross-direction profile of the web, in which connection the nip has been arranged to be loaded adjustably by means of hydraulic glide shoes which form the zones in the roll adjustable in zones, in which connection the system has been formed as a closed regulation circuit, which comprises an equipment for measurement of the cross-direction profile, which equipment has been fitted after the nip, as viewed in the running direction of the web, and which equipment has been fitted to measure the cross-direction profile of the web constantly, and which system comprises a computing unit, into which the target cross-direction profile has been fed in advance, the data corresponding to the measured cross-direction profile being fitted to be fed into said computing unit, and which computing unit has been arranged to compute the differential profile between the measured cross-direction profile and the target cross-direction profile, in which connection said differential profile has been arranged to operate as a regulation parameter in the closed regulation circuit so as to regulate the nip profile to the desired form. In paper machines and in paper finishing devices, a number of rolls are used which form a dewatering press nip, an equalizing nip, a size-press nip, a calendering nip, or equivalent with a backup roll. In such applications of operation, it is important that the distribution of nip pressure, i.e. the nip profile in the axial direction of the rolls, remains invariable or that this profile can be adjusted in the desired way, for example, in view of controlling the cross-direction moisture profile or thickness profile or any other, corresponding property profile of the web. For regulation of the nip profile, various adjustable-crown and variable-crown rolls are used, in particular rolls adjustable in zones, by whose means the nip profile can be controlled in a suitable way. Currently, as such variable-crown rolls or rolls adjustable in zones, most commonly such rolls are used as comprise a stationary roll axle and a roll mantle arranged revolving around said axle as well as hydraulically loaded glide shoe arrangements fitted between the roll mantle and the axle and acting upon the inner face of the mantle, by means of which glide shoes the axial profile of the mantle at the nip can be aligned or regulated in the desired way. In a roll adjustable in zones, two or more adjacent glide shoes always form one zone, which is controlled by means of a zone-specific hydraulic valve. The number of the glide shoes included in different zones can differ from zone to zone in a way required by a purposeful control of the compression force between the zone roll and its backup roll.

The constructions of rolls adjustable in zones have been developed so that, in principle, by their means, it would be possible to provide a very precise regulation of the profile if the system of control of the roll were capable of controlling the roll in the desired way. On a level of principle, regulation of the nip profile by controlling a roll adjustable in zones is quite simple, for, firstly, the starting values or initial values in compliance with which the nip profile must be regulated are determined by the paper grade that is aimed at. The zones in the roll are then regulated and controlled in a purposeful way in compliance with these target values. After the nip, it is then measured from the paper web how well the values aimed at have been achieved by means of regulation of the roll. When measured values differ from the target values, the values of regulation of the zones in the roll are changed so that, after this correction, the measured values correspond to the target values with an optimal and adequate accuracy. Thus, the principle is quite simple. However, ever higher and higher requirements are constantly imposed on the quality of paper, and this is why it is also necessary to be able to improve the accuracy of regulation of a roll adjustable in zones and in particular of the system of control of the roll.

In multi-zone regulation, when conventional algorithms of regulation have been used, it has been a considerable factor limiting the accuracy of regulation that the system of regulation has not been sufficiently well, or actually at all, capable of taking into account that there are cross-effects in different zones of a roll adjustable in zones, or that the effects of different zones are not equal, among other things, owing to different numbers of shoes in the zones and owing to locations of the zones. Moreover, in this way, a control of the physical limitations of the actuators to be monitored has become difficult. Earlier, for improving the accuracy of regulation, besides the regulation in zones, regulation by means of temperature has also been employed so that the roll has been heated from outside and locally in the axial direction of the roll. Such use of differences in temperature for regulation of the profile and especially the effect of this regulation was reasonably local, and this regulation by means of temperature did not have significant cross-effects. Thus, with this regulation by means of temperature, it was locally possible to correct and to adjust the effects of regulation in zones. However, even this mode of regulation did not provide an adequate accuracy of regulation, and, on the other hand, in view of simplification of the regulation, it was desirable to get rid of such temperature regulation.

The object of the present invention is to provide a significant improvement over the prior-art methods and systems for regulation of the nip profile by means of a roll adjustable in zones. In view of achieving this objective, the method in accordance with the invention is mainly characterized in that, in the method, the regulation parameter that represents the differential profile is fed in the closed regulation circuit into an optimizing part, which contains an optimizing routine and which contains the data on the profile responses, cross-effects and physical limitations of the actuators in the roll adjustable in zones, in which connection, based on the differential profile and while taking into account said cross-effects and physical limitations, the optimizing routine of the optimizing part computes new set values in order to minimize the overall error of the cross-direction profile and the differential profile, which set values are fed as regulation parameters to the regulation apparatuses that regulate the nip profile so as to correct the cross-direction profile.

On the other hand, the system in accordance with the invention is mainly character- ized in that, in the closed regulation circuit, the system comprises an optimizing part fitted after the computing unit, which optimizing part contains an optimizing routine and into which the regulation parameter that represents the differential profile has been arranged to be fed from the computing unit, and which optimizing part contains the data concerning the profile responses, cross-effects, and physical limitations of the actuators of the roll adjustable in zones, in which connection, based on the differential profile and while taking into account said cross-effects and physical limitations, the optimizing routine of the optimizing part has been arranged to compute new set values in order to minimize the overall error of the cross-direction profile and the differential profile, which set values have been arranged to be fed further in the regulation circuit as regulation parameters to the regulation apparatuses that regulate the nip profile in order to correct the cross-direction profile.

As compared with the prior-art systems and methods of regulation, the present invention provides significant advantages, and of these advantages it might be mentioned, among other things, that regulation of the nip profile carried out in accordance with the present invention is considerably quicker and more accurate than in the prior-art. In the method and system in accordance with the present invention, individual actuators are not regulated individually and alone, but cross-effects of the actuators are taken into account, in which case physical limitations of the actuators do not impose limitations on the accuracy or speed of regulation, or these limitations of actuators are at least not encountered equally early as in the prior-art systems. The further advantages and characteristic features of the invention will come out from the following more detailed description of the invention.

In the following, the invention will be described by way of example with reference to the figures in the accompanying drawing.

Figure 1 is a schematic illustration of a pair of rolls which comprises a roll adjustable in zones and a backup roll and which pair of rolls forms a nip.

Figure 2 is a schematic illustration of a closed circuit of regulation for use in regulation of the nip profile.

In the figures in the drawing, the roll adjustable in zones has been denoted generally with the reference numeral 10. The roll 10 comprises a stationary roll axle 11, on which a tubular roll mantle 12 has been fitted revolving. The roll mantle 12 is supported on the roll axle by means of hydraulic glide shoes 13 acting upon the inner face of the roll mantle, by means of which glide shoes the nip N is loaded adjustably. The shoes 13 have been fitted in a certain way in groups and divided into zones Zι ...Z₆ in the axial direction of the roll 10 so that each zone is regulated separately. In the figure, six zones have been illustrated, but the number of the zones is not confined to this number. The reference numeral 70 denotes a regulation and setting device, which communicates, through pressure ducts 14, with the glide shoes 13 in each zone Z_j. - .Zg. The roll 10 adjustable in zones forms a nip N with the backup roll 20. The nip N can be, for example, a press nip, an equalizing nip, a size-press nip, a calendering nip, or equivalent. As is shown in Fig. 2, the paper or board web W has been passed through said nip N.

As is shown in Fig. 2, the method and the system in accordance with the present invention for regulation of the nip profile comprise a closed circuit of regulation, by whose means the linear load in the nip N is regulated by means of regulation of the set pressures passing to the hydraulic glide shoes 13 in the roll 10 adjustable in zones. As is shown in Fig. 2, a paper or board web W or equivalent has been passed to run through the nip N, and by means of said nip, which is, for example, a calendering nip, attempts are made to produce a certain effect in the web W that runs through the nip N. In the case of a calender, attempts are made to keep the distribution of the linear load in the nip, i.e. the profile in the axial direction of the rolls, as uniform and invariable as possible. Thus, into the system, the data have been fed concerning the nip profile aimed at, i.e. the effect that is supposed to be produced by means of the nip N in the web W that runs through the nip.

On the run of the web W after the nip N, a measurement equipment 30 has been fitted, by whose means the cross-direction profile of the web W is measured constantly in order to find out how well the cross-direction profile aimed at is achieved by means of the set values that have been fed into the zones Zι ...Z₆ in the roll 10 adjustable in zones. The equipment 30 for measurement of the cross-direction profile can comprise, for example, a measurement beam passing across the web W, on which beam measurement detectors have been installed with a specified spacing in the cross-direction of the web so as to measure the cross-direction profile. The measurement equipment can also comprise a measurement head or equivalent traversing back and forth across the web W. Thus, as a result of the measurement of the cross-direction profile, information is obtained concerning the measured profile, i.e. the factual profile 40. This measured factual profile 40 is then passed as input data 41 into the computing unit 50 included in the system, into which unit the data concerning the target cross-direction profile have been fed in advance. The computing unit 50 compares the measured profile with the target profile and, on this basis, performs a calculation in order to form an error profile or a differential profile, i.e. in order to find out to what extent the measured profile differs from the target profile. Further, based on the differential profile thus determined, this computing unit 50 carries out a computation in order to regulate the linear load so that, in the nip N, the cross-direction profile aimed at could be achieved based on the computed regulation parameter.

The target 51 of linear load or the regulation parameter is, however, not transmitted directly to the regulation and setting device 70 that regulates the set pressures in the zones Z_j ...Z₆, but this target of linear load, i.e. regulation parameter computed in compliance with the differential profile, or a corresponding control signal is fed into an optimizing part 60, which is included in the closed regulation circuit and which contains an optimizing routine. The optimizing part contains advance information on the profile responses of the actuators and on the physical limitations of the actuators and of the whole roll 10, and so also on factors of non-linearity related to the roll. Further, the optimizing part contains information on the cross-effects of different actuators, i.e. on the way in which a change in the settings of one actuator acts upon the settings of some other actuator. Based on these data and based on the linear-load target data 51 computed on the basis of the differential profile, the optimizing part 60 computes new set values at the same time for all actuators in order to minimize the overall error of cross-direction profile and the differential profile as well as, thus, determines the control necessary for the differential profile at each particular time. In this computing, the optimizing part takes into account the cross-effects of all actuators, among other things of the zones Zι ...Z₆ in the roll 10, and the physical limitations of the actuators. Thus, the optimizing part attempts to take maximal advantage of the profiling potential of the roll 10 adjustable in zones.

The new set values of the actuators are transmitted as input data 61, i.e. as regula- tion parameters, to the regulation and setting device 70 for regulation of the set pressures for the zones. Depending on the optimizing routine, i.e. on the quality of the model employed by the optimizing, the speed of regulation can be increased considerably in this way because the response of a regulation to a regulation parameter is very precisely known. The system has been fitted to determine the required movement of the actuators placed at the regulation locations so that the known profile response of each regulation location, i.e. the change in the cross- direction profile caused by a movement of the actuator, is compared with the differential profile prevailing at said regulation location, and that corresponding regulation impulses are given to the actuators, while taking into account the cross- effects and physical limitations of the actuators, so as to correct the differential profile. Besides regulation taking place during running, by means of this method it is possible, for example, to predict a need of profiling after a break and, thus, to shorten the time of recovery after the break. Reference being made further to Fig. 2, the system comprises a closed regulation circuit in which measurement of the profile and regulation carried out on the basis of the measurement are carried out during running constantly and without interruption.

Above, the invention has been described by way of example with reference to the figures in the accompanying drawing. The invention is, however, not confined to the exemplifying embodiments illustrated in the figures alone, but different embodiments of the invention can show variation within the scope of the inventive idea defined in the accompanying patent claims.

Claims

1. A method for regulation of the nip profile in a nip (N) formed by a roll (10) adjustable in zones and by a backup roll (20), through which nip a paper or board web (W) has been passed in view of controlling the cross-direction profile of the web (W) and which nip (N) is loaded adjustably by means of hydraulic glide shoes (13) which form the zones (Z╬╣ ...Z₆) in the roll (10) adjustable in zones, and in which method the cross-direction profile of the web (W) is measured constantly after the nip (N) and the differential profile between the measured cross-direction profile and the target cross-direction profile is computed, which differential profile is used in a closed regulation circuit as a regulation parameter so as to regulate the nip profile to the desired form, characterized in that, in the method, the regulation parameter that represents the differential profile is fed in the closed regulation circuit into an optimizing part (60), which contains an optimizing routine and which contains the data on the profile responses, cross-effects and physical limitations of the actuators in the roll (10) adjustable in zones, in which connection, based on the differential profile and while taking into account said cross-effects and physical limitations, the optimizing routine of the optimizing part (60) computes new set values in order to minimize the overall error of the cross-direction profile and the differential profile, which set values are fed as regulation parameters to the regulation apparatuses that regulate the nip profile so as to correct the cross-direction profile.

2. A method as claimed in claim 1, characterized in that, in the optimizing part (60), new set values are computed at the same time for all actuators of the roll (10) adjustable in zones.

3. A method as claimed in claim 1 or 2, characterized in that the computed set values are fed to the regulation and setting device (70) for the glide shoes (13) in the roll (10) adjustable in zones in view of regulation of the set pressures in the zones (Z! ...Z₆).

4. A method as claimed in any of the preceding claims, characterized in that the required movement of the actuators placed at the regulation locations is determined so that the known profile response of each regulation location, i.e. the change in the cross-direction profile caused by a movement of the actuator, is compared with the differential profile prevailing at the regulation location concerned and that corresponding regulation impulses are given to the actuators while taking into account the cross-effects and physical limitations of the actuators so as to correct the differential profile.

5. A system for regulation of the nip profile in a nip (N) formed by a roll (10) adjustable in zones and by a backup roll (20), through which nip a paper or board web (W) has been passed in view of controlling the cross-direction profile of the web (W), in which connection the nip (N) has been arranged to be loaded adjustably by means of hydraulic glide shoes (13) which form the zones (Zi ...Z₆) in the roll (10) adjustable in zones, in which connection the system has been formed as a closed regulation circuit, which comprises an equipment (30) for measurement of the cross- direction profile, which equipment has been fitted after the nip (N), as viewed in the running direction of the web (W), and which equipment has been fitted to measure the cross-direction profile of the web (W) constantly, and which system comprises a computing unit (50), into which the target cross-direction profile has been fed in advance, the data corresponding to the measured cross-direction profile being fitted to be fed into said computing unit (50), and which computing unit (50) has been arranged to compute the differential profile between the measured cross-direction profile and the target cross-direction profile, in which connection said differential profile has been arranged to operate as a regulation parameter in the closed regulation circuit so as to regulate the nip profile to the desired form, characterized in that, in the closed regulation circuit, the system comprises an optimizing part (60) fitted after the computing unit (50), which optimizing part (60) contains an optimizing routine and into which the regulation parameter that represents the differential profile has been arranged to be fed from the computing unit (50), and which optimizing part (60) contains the data concerning the profile responses, cross- effects, and physical limitations of the actuators of the roll (10) adjustable in zones, in which connection, based on the differential profile and while taking into account said cross-effects and physical limitations, the optimizing routine of the optimizing part (60) has been arranged to compute new set values in order to minimize the overall error of the cross-direction profile and the differential profile, which set values have been arranged to be fed further in the regulation circuit as regulation parameters to the regulation apparatuses (70) that regulate the nip profile in order to correct the cross-direction profile.

6. A system as claimed in claim 5, characterized in that the optimizing routine of the optimizing part (60) has been fitted to compute new set values at the same time for all actuators of the roll (10) adjustable in zones.

7. A system as claimed in claim 5 or 6, characterized in that the optimizing part (60) feeds the computed set values to the regulation and setting device (70) for the glide shoes (13) of the roll (10) adjustable in zones in view of regulation of the set pressures for the zones (Z╬╣ ...Z₆).

8. A system as claimed in any of the claims 5 to 7, characterized in that the system has been fitted to determine the required movement of the actuators placed at the regulation locations so that the known profile response of each regulation location, i.e. the change in the cross-direction profile caused by a movement of the actuator, is compared with the differential profile prevailing at the regulation location concerned and that corresponding regulation impulses are given to the actuators while taking into account the cross-effects and physical limitations of the actuators so as to correct the differential profile.