FI119113B - An adjustment method and system for adjusting the machine direction thickness of a fibrous web - Google Patents

Description

FIELD OF THE INVENTION The present invention relates to a fiber web machine. The present invention relates to fiber web machines. More particularly, the present invention relates to a method and system for adjusting the thickness of a paper or similar web material when the calendering web passes through a roller of a calendar of a fiber web machine comprising one or more nipples.

The method according to the invention encompasses both the normal controls required in production situations and those in situations of transition to a production space or vice versa. A normal production situation is one in which there is no significant change in machine speed or changes in machine speed do not affect quality. Machine speed change situations and machine up / down represent situations when the 1S enters, out of production, or changes and moves in the production space.

Calendering is basically a simple step of processing a fibrous web. In the calendar, the web is pressed repeatedly against overlapping rolls. ·. *. nip (s) formed between them so that the web becomes thinner and • * · • · 20 smoother. However, it is problematic to predict how much thinner and • ·; . the smoother the web as a result of such processing becomes, because the processing • · «•; *: The result depends on very many variables and the properties of the web itself.

• ·· * ♦ ·· ····: Of the up to 20 variables that affect the calendering result, one can mention, for example.

25 web-squeezing nip load, roll diameters, roll temperatures, machine direction • * ί, ν 'web speed through the nip, web moisture, and roll bulk entering the calender roll: ... · properties that all have their effect on the calendering result achieved. Because different variables and bulk properties give different :: calendering responses, calender design has relied heavily on experience and test data ···. · ': 30. However, reliable experience and / or test data is difficult to obtain, so individual calendars are more and less Estimates and / or extrapolations of experience data. At present, calendars rely heavily on 2,119,113 for measuring the moisture of the web, as well as for pre-, intermediate, and intermediate humidification of the web, since web moisture has been found to correlate empirically with web uniformity and thickness. In the prior art, reference is further made to: - / 1 / RH. Crotogino, Towards a Comprehensive Calendering Equation, Transactions, Technical Section Montreal, Canada. December 1980, Canadian Pulp & Paper Association, 10 - / 2 / R.H. Crotogino, M.F. Gratton, J. Hamel, 1988, A Design Procedure for Machine

Calends, T APPI Proceedings, Finishing and Converting Con- ference, Richmond, USA, October 2-6,

- / 3 / R.H. Crotogino, S.M. Hussain. J.D. McDonald, 1983, Mill Application Home Calendering Equation, Journal of Pulp and Paper Science, November 1983, p. TR

15 128-134, - / 4 / J. Hamel, R.H. Crotogino, M.F. Gratton, 1992. Measurement otNip Load Distribution in Calenders Using Uncalendered Paper, Journal of Pulp and Paper Science, Vol. 18, No. 1, January 1992, p. JI7-23.

• V. Publications / 1 ... 4 / discuss the paper compression or thickness change model • · 20 in nip events.

• ·: "*: 1. / 5 / L. Ljung, T. Söderström. Theory and Practice of Recursive Identification, Mff • · ·: Press, Cambridge 1983.

*: * Publication / 5 / deals with the recursive least squares method, or • · * φ * • * *!, I (! Kalma filter for paper thickness change to formulate a model such that the model is linear with unknown parameters.

The object of the invention is to eliminate or at least substantially reduce the weaknesses and uncertainties associated with the traditional calendering process. It is an object of the invention to provide a new and inventive method for adjusting the machine direction thickness of a fiber web. According to another aspect of the invention, it is an object of the invention to provide a novel and inventive system for adjusting the machine direction thickness of a fiber web. According to a general aspect of the invention, the object is to achieve precise overall control of the machine-directional thickness of the fibrous web, preferably paper, in all production situations and / or when moving from calender to production mode or vice versa in accordance with another general aspect of the invention.

To achieve these objects, there is according to the invention, control method, wherein the fibers of the web to adjust a fiber web thickness, the web to be calendered passes through one or more nips of a fiber web machine 10 calendar through a set of rollers, generally characterized in that the nip shall apply to the fibrous web in the machine direction the thickness of the compression of controlling and adjusting the fiber web machine direction compression of calculating the nips line load and set point surface temperatures for the die rolls, and the thickness predicted value obtained by the compressibility model is verified by a value of at least 15 nip or after caliper thickness measurement.

It is preferred that the thickness prediction value obtained by the model is verified, at least post-nip or calendar, to verify its accuracy. *. *. thickness measurement value. In this case, it is also advantageous to verify the forecast value • ·: *. *. 20 · pre-nip or calendar thickness measurement or laboratory thickness measurement · · · * "·.

• · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · For one example, when calculating nipple-specific line load and • · · ·; set points for surface temperatures of molten rolls, the nipples use a fiber web compressibility model in a chained manner to illustrate the overall calendar process.

According to the invention, the method can be applied both in normal production mode and in the case of changes in machine speed. The adjustment method according to the invention has • ·; * ": It is also characteristic that the parameters of the mathematical model equation are updated by species-specific * · ·; 30 on-line algorithm, and that the updated parameters are stored in tables of species · · · φ · ..,.

4,119,113

An embodiment of the invention is characterized by determining the thickness change at each nip by means of the compressibility pattern of the fibrous web, and that by linking the patterns of thickness changes at different nips, a concatenated pattern of the overall system is obtained. Thus, the 5 thickness change output data calculated in the previous nip is then used as the thickness value input data for the next nip.

In a production mode where machine speed is unchanged and other process changes are dynamically slow, feedback control for paper thickness control is utilized, utilizing the model-estimated nip-10 line load and surface temperature predictions to achieve the desired fiber web thickness.

In transformation mode, when the machine speed either increases or decreases, the adjustment is implemented as a model-based proactive adjustment.

15

To achieve the above objectives, there is provided a control system according to the invention which applies a fiber web compressibility model to control the fiber web thickness when the calendering web passes one or more nipples. . through the roller system of the fiber web machine, it is a common feature that the adjustment system • · · · · · 20 applies a nip in the nip to compression of the machine direction thickness of the fiber web to calculate the set point and load temperature of the die rolls. a model for controlling and adjusting the mechanical compression of the fiber web, • * φ ··· ·.:. and that the control system verifies the thickness prediction value obtained by the model at least nip or • * ♦. * "after calender thickness measurement.

* · · 25: ': *: It is preferable that the adjustment system verifies the thickness prediction value obtained by the model to verify its accuracy, · ·: * * *: at least after the nip or calendar • * *: ·. *. thickness measurement value. In this case, it is also advantageous for the control system to verify • · • ·. · **. Thickness measurement or thickness φ ··. * before the nip or calendar. 30 laboratory assays.

• ·· • · m • ·

In an embodiment of the invention, when calculating setpoint values for nip-specific line loads and die roll surface temperatures, the system applies a fiber web compressibility model in nip control and adjustment to control and adjust the overall calendar process.

S According to a preferred embodiment, the rigid system is a control system of both the normal production mode and the machine speed change mode. The control system according to the invention is also characterized by an on-line algorithm that updates the parameters of the mathematical model equation on a species and action point basis and that the updated parameters are stored in species-specific tables.

10

In general, the novelty and inventiveness of the present invention relates to the approach used to provide a mathematical model for nip compressibility in a nip, which is utilized in calculating nip-specific controls for line loads and surface temperatures of heated molten rolls. The method is suitable for single-, double-15 or multi-calender calendars as well as multi-roll calendars.

In one embodiment of the system of the invention, the compressibility pattern of the fibrous web determines the thickness of the fibrous web at each nip. . change and by combining the pattern thickness changes in different nips • · · 20 to form a concatenated model of the overall calendar system. Thus, the thickness change output information calculated in the previous nip is the input of the thickness value for the next nip.

• * · ··· * • · ”··. In the production mode, where there is no change in machine speed and other changes in the process, the adjustment of the fiber web thickness is. *. *. feedback control that utilizes the model's estimated nipple-specific • ♦ line load and surface temperature predictions to achieve the desired thickness ··· ··· · · · ·

In conversion mode, where the machine speed either increases or decreases, adjusting the fiber web thickness • »30 is a model-based proactive adjustment.

• · «• ·· · ·

With respect to the scope of the invention, reference is made to the appended claims, and specific embodiments of the invention and 6,119,113 are described in more detail in the following specific part of the specification, with reference to the accompanying drawings, in which FIG. 1 generally describes a finishing section of an on-line 2, illustrates adjusting the paper web thickness in a two-nip calendar.

FIG.3 illustrates the control of paper thickness in the OptiLoad calender when a) there is a uniform line load distribution and b) a change in line loads occurs, 10 c) a parallel line load distribution occurs and d) a discontinuous line load distribution FIG.4 illustrates a modified OptiLoad where and are spaced apart with the pivot nip open and the top and bottom spindles having different line load distributions, increasing the possibility of both one-sided 15 and gloss control of the web, F1G.S describes the process space on the calendar as machine speed changes for proactive control and adjustment FIG.6 illustrates a calendar process state, i.e.. ramp-up in which the machine speed is increased incrementally.

«» · ·· * 20 • · »» v • · • ·. * * *. The present invention can be applied to both so-called. off-line and on-line • · ···: for calender constructions.

* * »» ·· * ··· * · ·: “*: Reference is made to Figure 1, which schematically shows the finishing section of the on-line paper machine ··« 25 between the coating station 1 and the retractor 6, wherein: • · »!.,.: I. Dryers, preferably infrared dryers 2 and fluidized dryers 3, ί V. ii. cylinder dryer unit 4, • i iii. calender 5, which in the example of FIG. 1 is a multi-roll calender comprising: soft-roll polymer rolls 11 and / or paper rolls or other soft-surfaced rolls and mold rolls 10, one or more of which may be heated, typically hard surface thermo rolls.

7119113

In order to implement the invention in a paper machine, it is preferred according to the invention that after calender 5, a web thickness measuring station 7 is provided and that web machine speed measuring station 8 is arranged in connection with roller 6, and that S optionally either: a thickness measuring station W of the web tracked prior to the calender 5, which is output as input to the web thickness control and adjustment method of the invention, and a thickness value based on laboratory measurements.

10

Thus, the present invention utilizes the fiber web thickness and basis weight measurements obtained from the quality measurement system. Hereby, the measuring stations of the quality measuring system for adjusting the thickness of the fibrous web in the calendar 5 may be located before and after the calender 5, whereby there is one web thickness measuring station 9a before the calender and another web thickness measuring station 7.

According to the invention, for measuring and controlling the thickness of the fibrous web W, the measuring station deflection may also be imitated by using only one #. tφ the measuring station 7, which is then located after the calender 5. In such a • · ·; ·. According to the invention, instead of the measuring station preceding the calender 5, the thickness values obtained by the laboratory determination 9b should be used instead of the measuring station.

e · • · i »· • · · t *«.:. A fiber web, such as a paper compression model, can be used to determine the change in paper thickness at each n · n · n. By connecting the different nip model equations ·· »25 to each other, the chain pattern of the total node is obtained. the output information is used as the paper thickness input information in the following nip.

·· · • · · • φ • ·. ' * *. In the method, the thickness of the fibrous web, such as paper, after calender 5 or • tt /. The 30 rollers 6 are adjusted using a «tt (| tt | model) of paper compressibility. The model seeks to account for the effects of all significant variables on the paper compression. The unknown parameters included in the mathematical model 8 119113 are determined by a recursive algorithm. exemplified by the recursive algorithm, the Kalma filter and the least squares method can be used to calculate control and adjustment setpoints for each node N to achieve the desired paper thickness.

In normal production conditions, where there is no change in the machine speed and other changes in the process are dynamically slow, feedback control is used to adjust the thickness of the paper. In this case, the adjustment utilizes the estimated nip-specific line load and surface temperature prediction provided by the model 10 so that the desired paper thickness is achieved. In case of change modes, where the machine speed either increases or decreases, the adjustment is implemented as a model-based proactive adjustment. It is essential that the accuracy of the prediction values obtained by the model is verified by at least thickness measurement 7 following nip N or calendar S. It is also advantageous for 1S to utilize thickness measurement 9a prior to nip N or calendar 5 or laboratory thickness determination 9b.

The recursive update of a fiber web, such as a paper compression model, as well as a Va of the model parameters is calculated either in the automation system or immediately * 4 f. 'P 1 20 in a separate unit of account. The paper compressibility, i.e., ·, · · ·, thickness change model takes into account the nip event by tying together: • ·: - the caliper of the calendered paper used (cm3 / g), · · · ·· * · - the thickness W of the fibrous web; - line load of nip N (kN / m), - • 4 25 - machine speed (m / s) of fiber web, - radius (m) of rolls of calender 5, - ·: ***: - temperature of fiber web (eC) and; v, - moisture content of the fibrous web (%).

• ♦ • *, ·· *. The model contains a set of parameters that depend exclusively on the · · ». *. 30 paper properties. For example, model coefficients can be determined experimentally • * ·· [! individually for each paper grade, then the model equation can be applied to any • hard or soft nip calendar 5. Since the model equation does not include a term that takes into account the flexibility of the soft roll 10, the model parameters also depend on the calendar used. However, the model can be applied when its coefficients are determined separately for each calender 5. The most important control variables traditionally used to influence thickness change are the line load and the temperature of the die roll. The web speed and the radii of the rolls 10.11 affect the dwell time at nip, i.e. nip time, but generally the machine speed is sought to be kept constant, except during controlled speed changes. By limiting, for example, the radius change of the rolls 10.11, the number of unknown parameters of the model equation can be reduced in a controlled manner. However, the method of the present invention encompasses all alternatives.

10

According to the invention, the pattern illustrating the change in thickness of the fibrous web W is formulated to be linear with respect to unknown parameters. In this case, various offline or on-line identification methods can be applied directly to determine unknown parameters of the model. For example, the recursive least squares method 15 or the Kalma filter are suitable for the problem. In the method, the correctness of the identified parameters is verified by calculating estimates for the line load at nip N and e.g. the surface temperature of the chuck roll 10 using the estimated parameters and the model equation. By comparing, for example, the actual value of the line load and the one calculated by the system model ('line load estimate), it can be concluded whether the achieved parameter estimates * «· 20 are acceptable.

In accordance with the invention, the acceptable values for the paper type and process point-specific ·· »* model equation parameters are stored in a separate database or automation. ·· *. system species recipes from which they can be introduced when the paper type will be ♦ ·· 25 for production.

• · • · • · · ·

In accordance with the general idea of the invention, for adjusting the paper thickness IV, in the machine direction, the model-based paper thickness adjuster provides a measured • · • *. ** ·. thickness difference to target thickness value control message based on combined M »

. *. 30 nipple-specific paper compression models. The models are used to calculate N for each

• ·· '] "! Nip set the control and adjustment variables so that the desired final thickness value is achieved. · The unknown parameters of the model are then defined for the current value.

ίο 119113 in process conditions for a paper type in production or downloaded from a database. In machine speed change modes, the control algorithm calculates the nip per line load and the need for changing the surface temperature of the chuck roll as the line speed changes.

5 Under normal production conditions with no change in web speed, the control is implemented as a feedback control, whereby a paper thickness setpoint and measurement generates a thickness difference, which adjusts the control algorithm to make necessary adjustments to the nip line loads and / or surface temperatures In the method, all 10 nips are selectable for computer control.

Referring to Figure 2, a paper thickness control in a two-nip calendar is shown. Hereby the actual paper thickness is obtained from the quality measuring sensor 7 of the measuring station 7 before the winding, i.e. after the calender S, which the control program 15 compares with the set value. Based on the difference between the setpoint and the measurement thickness, the corresponding change in total thickness (Ajxm) that the nips N selected for the computer control must achieve is calculated. The total thickness difference (Apm) is divided by the relative weight coefficient (0-100%) of the selected nipples (i = 1 ... N) for the computer adjustment so that the sum of the weight coefficients is 100. It is to be emphasized that the present invention other ways to divide the thickness difference into nipples. In proportional division * · *, · · *. the portion of thickness difference indicated by each weight factor is applied to the selected nip Nj.

** · * j The paper compression model is used to calculate the required changes for each ♦ ·· ♦ • | · Nip control setpoints (ASetPoints). The new setpoints are then transmitted »···: * * *: to the unit control circuits which implement the setpoint changes.

··· 25: V: Referring to Figure 3, we will now consider the multi-roll OptiLoad calender and * ··: § (4! Different load situations in the OptiLoad calender.

·· · • · «• ♦ • ·

When running the OptiLoad calender with equal load, ie all nipples are equal ···. 30 line load, the total thickness difference (Apm) is offset by varying the loading of the roller • ·· by controlling the lower and / or upper cylinder. Thus, you do not want to change the shape of the line load distribution (FIG.3a).

11 119113

If the OptiLoad calender is not run at even load and changes in line load distribution are allowed, either the nip load levels at the top nipples (Figure 3b) will be changed, or the load levels at the nip 5 nip load (not shown) will remain unchanged.

In the OptiLoad, it is also possible to perform a "parallel shift" of the load distribution, thus preserving the shape of the load distribution (Figure 3c).

10 The position of the top and bottom nip load points on the kN / m axis is changed, ie the nipple load is increased or decreased by the same amount of kN / m.

It is also possible, within certain limits, to change the dovetail distribution so that it is not linear but discretely discontinuous (Figure 3d). In this case, the masses of the intermediate rolls of the OptiLoad Calender 15 are over or under-reduced within permitted limits.

Referring to Fig. 4, the invention can also be applied to a modified OptiLoad calender in which the pivoting nip rolls are fixed and / or positioned so that the pivoting nip can be open to form separate top and bottom pivots, whereby *** *: ·, ·. The 20 line load distributions can be adjusted separately for the top and bottom pallets. In this case, • · «*, ···. the load can be applied by the upper roller Z rolls and the lower roller load may be • · · *: applied by the lower roller (s). In such a modified calender, • · · • f · ♦ • |. to control each track with a different load distribution depending on the quality criteria.

»···: * * *: The advantage here is that better control of the paper side can be achieved by connecting ·· * 25 eg chill roll temperature control and steam box control: V: specific to the rack (upper rack / lower rack). In bias control, gloss measurement ··· can also be connected to the waste system.

M · * * · • · • «. '* *. In addition, the modified OptiLoad calender in the top and bottom calendars can be implemented, above

»M

/. 30 The control principles for the normal OptiLoad calender linear load distribution · * explained in connection with Figure 3.

• · 12 119113

Referring to Figures 5 and 6, Fig. 6 illustrates the transmission of setpoints incrementally, unlike Fig. 5.

Thus, in the state of Fig. 5, in which the machine speed changes, the adjustment 5 is proactively implemented. First let's look at a normal calendar (not OptiLoad). When changing the machine speed from A to C, proceed as follows. At point A, the line load and / or surface temperature setpoints corresponding to point C are calculated using the model, taking into account the offsets due to machine speed change (ASpeed) in the controls.

10

The new setpoints are transmitted either immediately when the machine speed change begins, ie. point A, or incrementally during the machine speed change (FIG.6). This choice is affected by the magnitude of change in machine speed (AL) and the change time (AT).

15 During machine ramp-up, for example, the procedure shown in the right-hand representation of the broken line in Fig. S is followed. At point A 'the new setpoints corresponding to either point B' or point C are calculated using the model. If the machine is accelerated via intermediate step B ', the setpoint values corresponding to the target speed C can be transmitted at either point A', B 'or ^. incrementally incrementally (FIG.6).

According to the invention, based on the values of the start and end points of the setpoints, it is possible to calculate a freely definable number of incremental points which are activated when the machine speed has reached the given speed. the speed corresponding to the setpoint. On the other hand, if e.g.

. ***. the slope (time constant t) of the surface temperature heating system of the chill rolls is to be taken with ··· 25, the surface temperature setpoints corresponding to point C can already be transmitted at: * * ': (A' ~ t) or the slowness in incremental distribution. If the machine is to be run using step: ***: B ', depending on the time (AT *), the setpoints for line loads and / or surface temperatures used as starting values for · · when entering state C are also calculated.

»·· 30 <· t • ··! It should be emphasized that the method according to the invention also covers situations where either full profile measurements or partial profile measurements from the Quality Measurement System 13 119113 are utilized during machine speed changes or ramp-up.

In partial profile measurement, the measurement sensor of the quality measurement system may be so-called. with spot measurement (no traversing) or the measuring transducer can only partially traverse, eg 0.5 -5 1.0 m wide. In this case, whenever new reliable measurement data is available, the setpoint is corrected based on the model equation or other kite calculation.

To clarify the applicability of the invention, it is further stated that with the OptiLoad calender such as the various line load distribution options shown in FIG. 10 3, the setpoint changes due to machine speed changes are implemented by calculating machine speed changes to line loads for the selected 3D line load. Here, during machine speed changes, the surface temperatures of the chuck rolls 10 and the set values of line loads on the nipples N 10 are changed and controlled based on the load (Fig. 3a), nip per load (Fig. 3b), load distribution location (Fig. 3c) or load distribution. 5 and 6.

. . The invention has been described above by way of example only. However, in no way is this intended to limit the present invention and as will be apparent to one skilled in the art. · · 1. many alternative or equivalent solutions, implementations and variations are • ·:. within the scope of the following definition of claims.

• · a aa · a • • aa

• »M

· 1 • · · · ··· • 4 • · · · · 4 • · 44 • · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · aa • · a

Claims (18)

A control method wherein the fiber web compressibility model (W) is applied to control the thickness of the fiber web, since the web (W) to be calendered runs through a roll stack (10, 5 11) in a calender (5) of the fiber web machine comprising one or more nips ( N), characterized in that in the nip (N), compressible model for the machine-directional thickness of the fiber web (W) is used for controlling and controlling the machine-directional compressibility of the fiber web when calculating setting values for a nip pressure of the nip and a surface temperature of the mold rollers (10), and the forecast the thickness obtained by means of the compressibility model is at least verified by values from the thickness measurement (7) after the nip (N) or calender (5). Control method according to claim 1, characterized in that the forecast value is verified with a value from the thickness measurement (9a) before the nip (N) or calender (5) or the laboratory determination (9b) of the thickness. Control method according to claims 1 and / or 2, characterized in that, in calculating the setting values for the nip pressure of the nip and the surface temperatures of the mold rolls (10), a compressibility model coupled to the description of the overall process in the calender (5) is used in the nip (N). Regulatory method according to claim 3, characterized in that, by means of the fiber web compressibility model, the thickness change is determined by the fiber web occurring in each nip (N), whereby coupled, modelable thickness changes in different nip form in the calender (5) the model of an interconnected overall process. , where specified thickness change information calculated in the preceding nip is input information about the thickness change for the following nip. Control method according to any of claims 1-4, characterized in that the control method is applied both in a normal production mode, since the machine speed is unchanged and in connection with changes in the machine speed. Control method according to any of claims 1-5, characterized in that parameters in the mathematical equation of the compressibility model are updated according to varieties and 19 operating points using an online algorithm, and that the updated parameters are stored in tables according to varieties. Control method according to any one of claims 1-6, characterized in that in the production mode a paper thickness is used for controlling the paper thickness, wherein estimated nip pressure and surface temperature forecasts obtained from the model are used to achieve a desired thickness of the fiber web. that in the change mode, as the machine speed either increases or decreases, the regulation is implemented as a model predicting government. 10 Control method according to any one of claims 1-7, characterized in that when the machine speed changes from the initial value (A, A ') to the setpoint (C, C \ C "), the first correction is taken into account for corrections in the changes caused by the change in the machine speed ( Speed), the nip pressure setting values and / or surface temperatures corresponding to set values, and that the new set values are communicated either immediately as the change in machine speed begins or incrementally during the change in machine speed. Control method according to any of claims 1-8, characterized in that in order to take into account the slowness of the heating system for the surface temperature of the mold rolls (10), the setting values for the surface temperature corresponding to setpoints (C, C ', C ") are already communicated in point (A'- 1) or the slowness of the heating system is taken into account in the incremental division. Control method according to any of claims 1-9, characterized in that the running of the machine is done by using the intermediate stage B 'of the initial value (A, A') and the set value (C, C ', C'), calculated according to the change time (Τ ') also the setting values for nip pressure and / or surface temperatures of the nip (N) corresponding to the intermediate stage and used as initial values when switching to the setpoint position. 11. Control system applying the fiber web (W) compressibility model for controlling the thickness of the fiber web, wherein the web (W) to be calendered runs through a roll stack (10, 11) of a calender (5) in the fiber web machine comprising one or more nips (N characterized in that in the nip (N), the control system applies when calculating setting values for a nip pressure of the nip and a surface temperature of the mold roll (10) compressibility model for the machine-directed thickness of the fiber web 119113 (W) for controlling and controlling the machine direction of the fiber web, the control system verifies the forecast value for the thickness obtained by using the compressibility model at least with values from the thickness measurement (7) after the nip (N) or calender (5). 5 Control system according to claim 11, characterized in that the control system verifies the forecast value with a value from the thickness measurement (9a) before the nip (N) or the calendar (5) or from the laboratory determination (9b) of the thickness. Control system according to claims 11 and / or 12, characterized in that when calculating setting values for the nip pressure of the nip and the surface temperature of the mold rolls (10), the control system applies the fiber web (W) compressibility model coupled to control and control the whole process in the calender (5). Control method according to claim 13, characterized in that in the control system, the compressibility model of the fiber web (W) determines the thickness change of the fiber web that occurs at each nip (N), whereby coupled, modelable thickness changes in different nips form in a calender (5) an overall system, where indicated information about the thickness change calculated in the preceding nip is input information about the thickness change for the following nip. Control system according to any of claims 11-14, characterized in that the control system is a control and control system both in a normal production mode and in the mode where the machine speed changes. 25 Control system according to any of claims 11-15, characterized by an online algorithm that updates parameters in the mathematical equation of the compressibility model according to varieties and operating points and that the system stores the updated parameters in tables according to varieties. 30 17. Regulatory process according to any of claims 11-16, characterized in that in the production state where no change in the machine speed occurs and since other changes in the process are slow to its dynamics, the regulation of the fiber web (W) thickness is an interconnected government, which uses estimated forecasts. for nip pressure and surface temperature of the 2i 119113 nip obtained in the modellenη model to achieve a desired thickness, and that in the change mode, as the machine speed either increases or decreases, the regulation of the fiber web (W) thickness is model prediction. Control system according to any of claims 11 - 17, characterized in that the model describing the thickness change of the fiber web (W) is linear in relation to unknown parameters.