WO2005078189A2

WO2005078189A2 - Control method and control system to adjust a machine directional thickness of a fibre web

Info

Publication number: WO2005078189A2
Application number: PCT/FI2005/000079
Authority: WO
Inventors: Tapio MÄENPÄÄ
Original assignee: Metso Paper, Inc.
Priority date: 2004-02-13
Filing date: 2005-02-07
Publication date: 2005-08-25
Also published as: WO2005078189A3; FI20045038L; FI119113B; FI20045038A0

Abstract

Control method and control system to adjust a machine directional thickness of a fibre web, when the film-strip (W) to be calendered goes through a set of rollers (10, 11) of a calender (5) of a fibre web machine, set of rollers comprises one or more roller nips (N). According to the invention for calculating set values of surface temperatures of chill rollers (10) and nip-specific line loads there is utilized a model of compression of the fibre web to control and adjust the compression.

Description

Control method and control system to adjust a machine directional thickness of a fibre web

The present invention concerns a fibre web machines. The present invention in more detail relates to a control method and a control system to be utilized for adjusting thickness of paper or of similar web material when the web to be calendered goes through a set of rollers of a calender of the fibre web machine, which set of rollers comprises one or more roller nips.

The method according to the present invention covers both controls required by normal production situations and controls in the situations, whereby there is taking place transition to a production state or vice versa. The normal production situation refers to a mode, in which case a machine speed does not meet essential changes or the changes in the machine speed do not affect quality. The change situations of the machine speed and machine up-run / machine shut-down represent situations, in which case it is moved to the production mode, out of the production mode or change modes and transition modes of the production state.

The calendering is in principal a simple processing phase of the fibre web. The web is repeatedly pressed in the calender by rollers that pressed against each other and form there between a roller nip/-s so that the web will become thinner and more even. Problematic is however, to anticipate, how much thimier and more even the a web may become as the consequence of the processing like this, because the result of the processing is dependent on very many variables and properties of the web itself.

From those even about 20 variables having effect on the calendering result one can mention among others the nip load, which presses the web, diameters of rollers, temperatures of rollers, track speed in a machine direction through the roller nip, moisture of the web and properties of the web bulk, each of which has its own effect on the calendering result to be achieved. Because the different variables and the properties of the bulk give different calendering responses, a calender planning has been depended largely on an experience and knowledge based on test results. However, it is difficult to get a reliable experience and/or test result data so the individual calenders and more and less estimations and/or the extrapolation results of the experience knowledge. Nowadays and concerning calender controls it is much stuck in the calenders for the measurement of the moisture of the web both pre- and intermediate moisturizmgs for, because it has been empirically considered that the moisture of the web correlates the smoothness and thickness of the web that are acquired by the calendering. It has been known from before

Concerning the prior art it is referred additionally to publications:

III RH. Crotogino, Towards a Comprehensive Calendering Equation, Transactions, Technical Section Montreal, Canada. December 1980, Canadian Pulp & Paper Association - 111 R.H. Crotogino, M.F. Gratton, J. Hamel 1988, A Design Procedure for Machine Calends, T FATHER-IN-LAW Proceedings, Finishing and Converting Conference, Richmond, USA October 2-6,

- 131 R.H. Crotogino, S.M. Hussain. J.D. McDonald, 1983, Mill Application of the Calendering Equation, Journal of Pulp and Paper Science, November 1983, pp. TR 128-134,

- 141 J. Hamel, R.H. Crotogino, M.F. Gratton, 1992. Measurement of Nip Load the in of the Distribution Calenders Using Uncalendered Paper, Journal of Pulp and Paper Science, Vol. 18, Number. 1, January 1992, pp. JI7-23. Publications /l ... 4/ comprise a compressibility or pattern of thickness change of the paper in the event of the nip.

- 151 L. Ljung, T. Sδderstrδm. Theory and Practice of Recursive Identification, Mff Press, Cambridge 1983. The publication 151 describes a method of the smallest square metre sum or the Kalman filter to formulate a model describing a thickness change of paper such that the model will be linear in regard to unknown parameters.

According to the invention the goal is to eliminate or to reduce at least essentially weaknesses and uncertainties that are related to the traditional calendering process. According to an aspect of the invention the goal is to accomplish a new and ingenious method for adjusting thickness of the fibre web in the machine direct. According to another aspect of the invention the goal is to accomplish a new and ingenious system to adjust thickness of the fibre web in the machine direct. According to the general aspect of the invention it is striven for an exact total control of the thickness of the fibre web, advantageously paper, in the machine direct in all production situations and/or when it is switched to the production state from the up-run state on the calender or vice versa. According to another general aspect of the invention the goal is to adjust the thickness of the paper wanted using nip-specific controls.

To accomplish these goals, it is characteristic to the control method according to the invention, when a web to be calendered goes through the set of rollers of the calender of the fibre web machine, which calender contains one or more roller nips, that when calculating set values of a line load and surface temperatures of kookily rollers, a compressibility model of the fibre web is used in the roller nip for controlling and adjusting a compression.

It is advantageous according to the invention that a prognosis value of thickness, which is achieved by the model, is verified at least by a value of a thickness measuring after the roller nip or the calender in order to certify correctness thereof. Then it is also further advantageous that the prognosis value is verified by a value of a thickness measuring preceding the calender or by a laboratory definition of thickness.

It is specific to a preferred embodiment, that when calculating nip-specific set values of line loads and surface temperatures of kookily rollers, the compressibility model of the fibre web is used in a chaining manner for describing a total process of a calender.

According to a preferred embodiment of the invention, the method is adapted both in a normal production state and in connection with the changes in the machine speed. It is also specific to the present control and adjusting method according to the invention, that the parameters of the mathematical model equation are updated on a type basis and on an operation point basis by an on-line algorithm and that the updated parameters are recorded in the type-specific tables.

To a realization example of the invention it is characteristic that by means of the compression model of the fibre web, the change in the thickness which takes place in each roller nip is determined and that by connecting the models of changes in the thicknesses to each other in different roller nips a linked model of the total system is obtained. Then the thickness change, which was calculated in the preceding roller nip and which forms an output data, is used to the following roller nip as the input data of the thickness value having calculated.

In the production state, when changes do not take place in the machine speed and other changes in the process are slow concerning from their dynamics, it is used a back fed adjustment for the adjustment of the thickness of the paper, then it is utilized estimated nip-specific prognosis of the line load and of the surface temperature given by the model to reach the desired thickness of the fibre web.

In the state of changes, in which case the machine speed either increases or decreases, the adjustment is carried out as an anticipating adjustment, which is based on the model.

To reach the above mentioned goals, it is specific to the control system according to the invention, when the web to be calendered goes through a set of rollers of a calender of a fibre web machine, which contains one or more roller nips, that in the calculation of the set values of the line load of the roller nip and the surface temperatures of chill roller the system adapts the compression model of the fibre web to control and adjusting the compressibility.

It is advantageous according to the invention that the control system verifies the prognosis value of the thickness, which has been received with the model, to secure its validity, by at least the value of the thickness measuring subsequent to a roller nip or to a calender. In that case it will be furthermore advantageous that the control system verifies the prognosis value with the value of the laboratory definition of a thickness or with the value of the thickness measuring, which precedes the roller nip or the calender.

It is specific to an embodiment example of the invention that, in the calculation of the set values of the nip-specific line loads and the surface temperatures of the chill rollers, the system adapts the compression model of the fibre web in a chaining manner for the control and for the adjustment of the roller nips in order to control and adjust the total process of the calender.

According to a preferred form of the realization of the invention, the system is a control system both for the normal production state and for the state of change of the machine speed. It is specific to the present control system according to the invention also an online algorithm, which updates the parameters of the mathematical model equation on a type basis and on an operation point basis, and that the updated parameters are recorded in the type-specific tables.

In general the novelty and the inventiveness relate to the used way of approach to form in the roller nip the mathematical model, which is utilised, when there are calculated nip-specifically controls to the line loads and to the surface temperatures of chill roller to be warmed. The method is applicable both to calenders having one, two or more roller nips and to multi-roller calenders.

In a realisation example of the system, which is in accordance with the invention, the compression model of the fibre web determines thickness changes, which take place in each roller nip, and by connecting the thickness changes, which are in accordance with the model, in different roller nips to each other, a chained model of the total system of the calender is formed. So the output data from the preceding roller nip is the calculated thickness change and then the same will be the input data of the thickness value to the following roller nip.

In the production state, when changes do not take place in the machine speed and other changes, which take place in the process, are slow concerning dynamics thereof, the adjustment of the thickness of the fibre web is a back fed adjustment, which utilises the estimated nip-specific prognosis of the line load and of the surface temperature given by the model, to reach the desired thickness

In the state of change, in which case the machine speed either increases or decreases, the adjustment of the thickness of the fibre web is an anticipating adjustment, which is based on the model.

Concerning the scope of the invention, it is referred to the accompanying set of claims and the inventions as well as the specific embodiment thereof are explained in more detail in the following specific part of description of the invention by referring to the enclosed patent drawings, in which

FIG.l presents a finishing part, which is provided with covering unit, of the paper machine generally starting from the covering unit and ending to the reel-up unit, to which there is implemented the control and adjustment according to the invention are implemented,

FIG.2 presents the adjustment of the thickness of the paper web in a calender having two roller nips,

FIG.3 presents the adjustment of the thickness of the paper in an OptiLoad calender, when a) an even distribution of a line load dominates and b) a change concerning the line loads takes place c) a parallel transfer of the distribution of the line load takes place and d) a discontinuous distribution of the line load dominates,

FIG.4 describes a modified OptiLoad calender, in which an upper set of rollers and a lower set of rollers are separately from each other so that a turn roller nip is open and in which the upper set of rollers and the lower set of rollers have the different distributions of the line loads, in which case it has been increased the opportunity to the control and to an one-sided gloss adjustment of the web,

FIG.5 presents a process state in the calender when the machine speed changes for the anticipating control and adjustment of the calender, and

FIG.6 presents the process state of the calender that is an up run, in which the machine speed is increased step by step. The present invention can be adapted for both to so-called off-line calender constructions and to so called on-line calender constructions.

Reference is made to the figure 1, in which has been presented schematically the finishing unit between the covering unit 1 and the reel-up unit 6 of the on-line paper machine, in which case the finishing part includes furthermore i. dryers, advantageously infrared dryer 2 and float-up dryer 3, ii. cylinder dryer unit 4, iii. calender 5, which is in the example of figure 1 a multi-roller calender, which comprises soft surface polymer rollers 11 and/or paper rollers or other soft surface rollers as well as chill roller 10, one of which or more can be, typically, a hard thermo roller to be warmed.

In order to implement the invention to a paper machine, it is advantageous, according to the invention, that there is arranged a measuring station 7 of the thickness of the web W after the calender 5 and that there is arranged a measuring station 8 of the machine speed of the web in the connections of the reel-up unit 6, and that selectively either a measuring unit 9a of the thickness of the web W is arranged before the calender 5, or a definition unit 9b of the thickness of the web W is arranged before the calender 5, the output of which will be the input value for the method and system according to the invention for controlling and adjusting the thickness of the web in the machine direction and utilizing thickness values base on laboratory measurements.

So the present invention utilizes in this way, thickness and square weight measurements, which can be obtained from the quality measurement system. Then the measuring stations of the quality measurement system, for controlling the thickness of the fibre web in the calender 5, can locate before and after the calender 5, whereby there is one measuring station 9a of the thickness of the web before the calender and another measuring station 7 of the thickness of the web is after the calender. According to the invention the arrangement of the measuring station 7 can be arranged also so that only one measuring station 7, which in that case is located after the calender 5, will be used to adjust and to control the thickness of the fibre web W. In the arrangement of the measuring station like this according to the invention, there is a reason to use the thickness values of the fibre web, which are accomplished by the laboratory definitions instead of the values that are accomplished by the measuring station 9b, which precedes the calender 5.

A change in the thickness of the paper-taking place in each roller nip N can be determined by means of the model of the compressibility of the fibre web, such as. By connecting the model equations of different roller nips to each other paper, the chained/linked model of the total system is obtained, hi that case, the change of the thickness of the paper, which was calculated in the previous roller nip, will be the output data that will be used as the input data of the thickness of the paper in the following roller nip .

In the method, the thickness of the fibre web, such as paper, is adjusted at the reel-up unit 6 is or adjusted a calender by utilising the paper, describing the compressibility model. The model tries to pay attention to the effects of all the significant variables on the compressibility of the paper. The unknown parameters, which are included in a mathematical model, are determined with a recursive algorithm. Applying the recursive one has been known as such, which is why it has been brought out here only as a mention. Kalman filter method and the smallest square meter method sum can be mentioned as examples of the recursive algorithm. With the help of the model is calculated to each roller nip N, such set values of the control and adjustment variables in order that the desired thickness of the paper will be reached.

In a normal production state, whereby changes do not take place in the machine speed and other changes which take place in the process have slow dynamics, a back fed adjustment is used for the adjustment of the thickness of the paper. In that case the adjustment will utilise nip-specific prognoses of the line load and of the surface temperature given by the model that have been estimated so that the desired thickness of the paper will be reached, h connections with the states of changes the machine speed either increases or decreases, an adjustment is carried out as an anticipating adjustment, which is based on the model. Essential is that with the help of the model the validity of the prognosis values is verified at least on the thickness measuring 7 following the roller nip N or the calender 5. It is advantageous in that case to utilise thickness measuring 9a or the laboratory definition 9b of the thickness 5, which precedes the calender 5.

The compressibility model of the fibre web, such as paper and the recursive updating of the parameters of the model are calculated either in an automation system or in a separate charge unit here in an immediate connection. To the paper the compression, in other words the compressibility model pays attention by binding the nip event to each other:

- bulk of the used paper that and not calendered has been calendered (cmVg),

- thickness of the fibre web W (μm), - nip line load of the roller nip N (kN/m),

- machine speed of the fibre web (m/s),

- radiuses of rollers 10, 11 of the calender 5 (m),

- temperature of the fibre web (°C) and

- moisture of the fibre web (%). The model contains a group of parameters which depend only and only on the properties of the paper to be calendered. Coefficients of the model one can determine for example experimentally to each separate paper quality, where after the model can be applied to any calender 5 comprising a soft nip or a hard nip. Because a term, which would pay attention to the 10 flexibilities of the soft roller, is not included in the model equation, the model parameters are depending also from a calender to be used. However, the model can be applied when its coefficients are determined to each calender 5, separately. The most significant controlled variables by which have their effects traditionally to the thickness change, are the line load and the temperature of the chill roller 10. Track speed and the radiuses of the rollers 10, 11 have an influence on the delay time in the roller nip N or the nip time, but in general the machine speed is tried to keep constant, except during the controlled speed changes. By marking off for example the change in the radiuses of rollers 10, 11, the number of the unknown parameters of the model equation can be reduced in a controlled way. Method according to the present invention, however, covers all the alternatives.

The model describing the thickness change of the fibre web has been formulated according to the invention so that it is linear in regard to unknown parameters. So it is possible to apply directly different kind of off-line or on-line identification methods for the determination of the unknown parameters of the model. For example recursive method of the smallest square metre sum or of the Kalman filter is suitable for a task. In the method calculating the estimations to the line load in a roller nip N and for example to the 10 surface temperatures of the chill roller with the help of the estimated parameters and the model equation checks the validity of the identified parameters by comparing for example the actual value of the line load and the estimation of the line load that has been calculated with the help of the system model, one can conclude if the estimations reached of parameters are acceptable.

According to the invention the acceptable functions point values of the parameters of the model equation of a paper species and process are saved in a separate database or to species recipes of the automation system, from which they can be brought into use when the paper species in question will come to the production.

According to the general basic idea of the invention, to adjust the thickness of the paper in the machine direction, the model based thickness regulator of the paper forms of the difference of a measured thickness value and of the desired thickness value a control message, which is based on the joined nip-specific compression model of the paper. With the help of the models it is calculated to each roller nip N such set values of the control and adjusting variables that the desired final thickness value will be reached. In this case unknown parameters of the model have been determined or loaded from the database in the process conditions in question to paper species in the production, hi connection with the states of change of the machine speed the adjustment algorithm will calculate the need for change of the nip-specific line load and of the surface temperature of chill roller when the track speed changes. In normal production situation, when the track speed does not change, the adjustment is carried out by a back fed adjustment, in which case the information about the thickness difference is formed on the basis of the set value and measuring of the thickness of the paper, on the basis of which thickness difference the adjustment algorithm makes the necessary changes in the line loads of roller nips and/or in the surface temperatures of the chill rollers or only in the line loads. In the method all the roller nips can be chosen to a computer adjustment.

Figure 2 in which the adjustment of the thickness of the paper is presented in the calender comprising two roller nips, h that case the actual value of the thickness of the paper, which the adjustment programme compares with a set value, is obtained from the quality-measuring sensor of the measuring station 7 before the reeling-up or after the calender 5. A corresponding total thickness (Δμm) change is calculated on the basis of the thickness difference of the set value and of the measuring, which change the roller nips N were intended to bring about, which roller nips were selected to the computer adjustment. The total thickness difference (Δμm) it is divided emphasised to the roller nips (i = 1 ... N) chosen to the computer adjustment with a relative weighting coefficient (0-100%) so that, however, the sum of weighting coefficients will be 100. One must emphasise that the present invention also covers the different ways to divide the thickness difference on the roller nips. In a relative distribution the share of the thickness difference shown by each weighting coefficient is directed to a chosen roller nip Ni. The compressibility model of the paper is used when calculating the required changes in the set values of the controls of each roller nip (ΔSetPoints). The new set values are transmitted after this to the unit control circuit, which will carry out the changes in the set values.

Figure 3 is referred to and a multi-roller OptiLoad calender and the different load situations will be next examined in the OptiLoad calender.

When the OptiLoad calender is run with even load, in other words there is the even line load in all the roller nips, so a correction of the total thickness difference (Δμm) is made by a load change of the set of rollers by controlling the load of an upper cylinder and/or an lower cylinder. So in that case one will not want to do a change to the form of the line load distribution (FIG.3 a).

If the OptiLoad calender is not run as evenly loaded and if the changes in the line loads distribution are allowed, either nip-specific load levels of upper roller nips are changed (figure 3b), in which case the load level of the lower roller nip remains unchanged, or the nip-specific load levels of the lower roller nips are changed (not presented), in which case the load level of the upper roller nip remains unchanged.

It also is possible to make in the OptiLoad calender "a parallel transmission of the load distribution" in which case the form of the load distribution can be retained (figure). In that case the place of the load point of the upper roller nip and the lower roller nip will be changed with the kN/m axis, in other words it is added or lightened the load of roller nips by the same kN/m number.

It also is possible to change, within certain limits, load distribution, so that it will not be linear but discretely discontinuous (figure 3d). In that case masses of the intermediate rollers of the OptiLoad calender are over or under lightened within allowed limits.

Figure 4 is referred to. The invention can be adapted also to a modified OptiLoad calender, in which the rollers of the turn nip are fixed and/or can be positioned so that the turn nip can be open to form a separate upper set of rollers and a separate lower set of rollers, whereby the line load distribution can be adjusted in the upper set of rollers and in the lower set of rollers separately. Then the load of the upper set of rollers can be accomplished by the upper roller/rollers the load of the lower set of rollers can be accomplished by the lower roller/rollers. In this kind of the modified calender both of the set of rollers can indeed be controlled by a different load distribution depending on the quality criteria. In that case the advantage is that the a one-sidedness of the paper can be better managed by connecting with each other for example the control of the temperature of chill roller and the control of vapour boxes set of roller specifically (the upper set of rollers / the lower set of rollers). In the adjustment of the one-sidedness also a glossy measuring also can be connected to a system. It is also possible to carry out control principles of the line load distribution of the normal OptiLoad calender, which were explained above in the connection of figure 3, in the upper set of rollers and in the lower set of rollers of the modified OptiLoad calender.

Figures 5 and 6 are referred to. Figure 6 illustrates transmission of set values incrementally as distinct from figure 5.

In the state, which is in accordance with figure 5 and in which the machine speed changes, an adjustment is anticipatorily carried out so. A normal calender (not the

OptiLoad) will be first examined. When making a change in the machine speed from the point A to the point C in the machine speed, it is acted as follows. The set values of line load and/or of surface temperatures, which correspond to the point C, are calculated in the point A by means of the model so that corrections to the controls, which are caused of the change in the machine speed (ΔSpeed), are considered.

The new set values will be transmitted either immediately the change in the machine speed begins, that is, point A or incrementally during the change in the machine speed (FIG.6). The size of the change in the machine speed and change time (ΔT) affects this choice (ΔL)

During the up run of the machine, it is acted for example according to the manner at of the break-line representation in the figure 5. The new set values, which correspond either to the point B' or to the point C, are calculated in the point A' with the help of the model. In case acceleration of the machine is done via the intermediate phase B', the set values corresponding to a target value C" can be transmitted either in the point A', B' or as incrementally graded (FIG.6) C

According to the invention it is possible to account on the basis of the starting points and end points of set values a freely definable number of increment points, which are activated when the machine speed has reached the speed corresponding to the set value in question. If one wants to include for example the slowness of the heating system of the surface temperature of the chill roller (a time constant t), the set values of the surface temperature, which correspond to the point C, can be transmitted already in the point (A '- 1) or to consider the slowness in the incremental distribution. If the up run of the machine will be made by using the phase B ', it is calculated, depending on time (ΔT'), also the set values of the line loads and/or of surface temperatures, which correspond to the point B' and which are used as starting values when moving to the state C\

One must emphasise, that method according to the invention covers also situations when during the changes in the machine speed or during the up run there are utilised either full profile measurings or measurings of partial profile measurings that are obtainable from quality measuring system.

The measure sensor of the quality measuring system can be in the partial profile measuring a so-called point measuring (non-traversing) or the measure sensor traverses only partly for example from a width of 0,5 - 1.0 m. In that case a correction will be always made to the set values on the basis of the model equation or on the basis of another correction calculation after the new reliable measurement data has completed.

hi order to clarify a applicably of the invention, it is still stated that in the OptiLoad, different distribution possibilities of the line load in which are presented in the figure 3, the set value chances caused by the changes in the machine speed are carried out such that the corrections to the line loads, which have been caused of the change in the machine speed, are calculated to the line load distribution, which was chosen to be a strategic plan, according to the figures 3a-3d. In that case there are changed and controlled the set values of the surface temperatures of chill roller 10 and the line loads of roller nips N during the changes in the machine speed basing to either load of the set of rollers (the figure 3a), nip-specific load levels (the figure 3b), location of the load distribution (the figure 3c) or to the form of the load distribution (the figure 3d) and in the manner described above in the connection of the figures 5 and 6.

The invention has been described above only as an example. However, this does not intend in any way to limit the invention in question and as it is clear to a skilled in the art, many alternative or equivalent solutions, realisation and modifications are possible within a scope of the protection defined in the accompanying claims.

Claims

1. Control method to adjust a machine directional thickness of a fibre web, when the fibre web (W) to be calendered goes through a set of rollers (10, 11) of a calender (5) of a fibre web machine that contains one or more roller nips (N), characterized in that when calculating set values of nip-specific line loads and surface temperatures of chill rollers (10), there is used a model of compression of the fibre web (W) for controlling and adjusting the compression.

2. Method according to the claim 1, characterized in that a prognosis value of the thickness, which has been obtained with by means of the model, is verified at least by a thickness value, measured (7) after the roller nip (N) or the calender (5).

3. Method according to the claim 2, characterized in that the prognosis value is verified with the calender (5) or the nip (N) preceding value of a thickness measuring (9a) or with the calender or the nip preceding value of a laboratory definition of the thickness (9b).

4. Method according to the claim 1, characterized in that when calculating nip-specific set values of line loads and surface temperatures of the chill rollers (10), it is used the model of compression of the fibre web (W) in the nips (N) in a linked manner to describe a total process of the calender (5).

5. Method according to the claim 2, characterized in that a thickness change of the fibre web, which takes place in each nip (N), is defined by means of the model of the compression of the fibre web, in which case the thickness changes, which take place in different nips and which are in accordance with model of the compression, as connected to each other form in the calender (5) the model of the linked total process, in which the output information of the thickness change, which is calculated in a preceding nip, is an input information of the thickness value to the following roller nip.

6. Method according to any of the claims 1 - 3, characterized in that the control method is adapted both in a normal production state, when the machine speed stays unchanged, and in the connection of changes in the machine speed.

7. Method according to any of the claims 1 - 4, characterized in that the parameters of the mathematical model equation of the compression is updated type and functions point specifically by an on-line algorithm, and that the updated parameters are recorded in type-specific tables.

8. Method according to any of the claims 1 - 5, characterized in that in the production state a back fed adjustment is used for the adjustment of the thickness of the paper, whereby the roller nip-specific prognoses of the line load and of the surface temperature given by the model that have been estimated are utilised to reach the desired thickness of the fibre web, and that in the state of change, in which the machine speed either increases or decreases the adjustment is carried out as an anticipating adjustment which is based on the model.

9. Method according to any of the claims 1 - 6, characterized in that, when the machine speed changes from an initial value (A, A ') to a target value (C, C ', C ") it will be first calculated set values of the line loads and surface temperatures observing corrections, which are caused from the change in the machine speed (Δ Speed), corresponding to the target values, that the new set values will be transmitted either immediately when the change in the machine speed begins or incrementally during the change of the machine speed.

10. Method according to any of the claims 1 - 6, characterized in that for observing the slowness of heating system of the surface temperature of the chill rollers (10), the set values of the surface temperatures corresponding to the target value (C, C ',C) are transmitted already in the point (A '-t) or the slowness of the heating system is observed in the increment distribution.

11. Method according to any of the claims 1 - 8, characterized in that when the up run of the machine is made utilizing an intermediate values (B') of the initial value (A, A') and the target value (C, C, C ") it is calculated, depending on change time (ΔT '), also set values of the line loads and/or surface temperatures of the roller nip (N), which corresponded to the intermediate stage, which are used as starting values when moving to the state of the target value.

12. Control system to adjust a machine directional thickness of a fibre web, when the fibre web (W) to be calendered goes through a set of rollers (10, 11) of a calender (5) of a fibre web machine that contains one or more roller nips (N), characterized in that in a calculation of the set value of a line load of a roller nip (N) and surface temperatures of chill rollers (10) the system adapts a model of a compression of the fibre web (W) for controlling and adjusting the compression..

13. Control system according to the claim 12, characterized in that the control system verifies a prognosis value of the thickness, which has been received by means of the model, by means of a value of a thickness measuring (7) following at least a roller nip (N) or calender (5).

14. Control system according to the claim 12, characterized in that the control system verifies a prognosis value of the thickness by means of a value of a thickness measurings (9a), which precedes the roller nip (N) or the calender (5), or by means of a value of a laboratory definition (9b) of the thickness.

15. Control system according to any of the claims 12-14, characterized in that in the calculation of the set values of the roller nip-specific line loads and the surface temperatures of the chill rollers (10) the system adapts in the control of the roller nips (N) the model of the compression of the fibre web (W) in a linked manner for controlling and adjusting a total process of the calender (5).

16. Control system according to the claim 15, characterized in that in the control system the model of the compressibility of the web (W) determines the thickness change of the fibre web taking place in each roller nip (N), whereby the changes of the thickness, which are linked with each other and which are in accordance with the model, in separate roller nips roller, form in the calender (5) the linked model of 5 total systems, in which the output data of the thickness change, which has been calculated in the preceding roller nip, is the input data information to the following roller nip.

17. Control system according to any of the claims 12-16, characterized in that the control system is the control system and adjustment system of both the normal production state and the state of change of the machine speed.

18. Control system according to any of the claims 12-17, characterized in the on-line algorithm, which updates the parameters of the mathematical model equation type- specifically and functions point specifically, and that the system records the updated parameters in the type-specific tables.

19. Control system according to any of the claims 12-18, characterized in that in the production state, when in the machine speed changes do not take place, and other changes taking place in the process have slow dynamics, the adjustment of the thickness of the fibre web is a back fed adjustment, which utilises the roller nip-specific estimated prognoses of the line load and of the surface temperature given by the model, to reach the desired thickness, and that in the state of change, when the machine speed either increases or decreases the adjustment of the thickness of the fibre web (W) is the model based anticipating adjustment.

20. Control system according to any of the claims 12-19, characterized in that the model, which describes the thickness change of the fibre web (W), is linear in regard to unknown parameters.