EP2050868B1 - Regulating device and method for regulating the basis weight in a paper machine - Google Patents

Description

The invention relates to a control device for the basis weight control of a paper web with an operating controller for controlling the headbox to a desired value. Such control devices are used to maintain a setpoint of the basis weight in the longitudinal direction. In addition, other control devices for maintaining a target value of the basis weight in the transverse direction are present, which are not the subject of this invention.

Basic material for producing a paper web is a fiber suspension, the so-called substance. This consists of about 0.1% to 1% of solid fibers in aqueous solution. In some cases, further chemical additives and fillers may be included. The fabric is applied to a sieve via the headbox and subsequently subjected to a multi-stage drying process. The amount or the layer thickness of the fabric applied to the fabric significantly determines the basis weight of the finished paper web. The subsequently arranged presses and calenders only affect their thickness and density at a constant weight per unit area.

In order to allow a constant basis weight of the produced paper web over its length, a control device is used, which adjusts the headbox to a predetermined target value. In this control process, the target value, namely the basis weight of the paper web, only at the end of the paper machine, so measured after the drying process. The controlled system thus has a large dead time, which is given by the passage time of the paper web through the paper machine. This can take up to several minutes.

To solve this problem, it has been proposed in the prior art to control the head box by means of a control by the speed of the paper machine with delayed response of the drives. A disadvantage of this solution, however, is that errors in the consistency measurement of the substance or different effective consistencies with the same consistency measured values but different chemical composition of the substance result in errors in basis weight. Likewise, according to the prior art, no influences of the backwater system on the basis weight are taken into account. The control according to the prior art is thus subject to errors. Since the influence of the dead time on the headbox remains large, there is an increased effort in the adjustment of the control. During this setup time usually no salable paper can be made.

The US 3,619,360 describes a device for controlling a basis weight of a paper web, in which a material flow is adjusted as a function of an adapted predicted weight per unit area. The adjusted predicted basis weight is determined based on an actual basis weight, a desired basis weight, and a basis weight predicted based on consistency and flow of the fabric and a speed of a drive.

From the EP 0 898 014 A2 It is known to use for longitudinal regulation of a basis weight of a paper web two independent control loops. The basis weight is determined both before the reel and in the wet area of the paper machine. Detected deviations are then corrected by tracking the applied amount of substance and the substance concentration.

The invention has for its object to provide a control of the basis weight of a paper web, which over the prior art, a simpler operation has, is faster adjustable and allows a higher accuracy of the control process.

The object is achieved by a control device for longitudinal control of the basis weight of a paper web in a paper machine according to claim 1.

Furthermore, the solution of the object in a method for longitudinal control of the basis weight of a paper web in a paper machine according to claim 13.

The device according to the invention uses a so-called operating controller, which per unit time from the chest on the quantity of material supplied to the sieve is regulated to a predetermined nominal value. As a controller, for example, a PI controller or a PID controller can be used. This operating controller represents the basic control loop. In order to minimize the influence of the dead time, the setpoint of the operating controller is dynamically adapted to the operating conditions. For this purpose, according to the invention, a pilot control device is available, which calculates a run-up quantity.

In a further development of the invention, the pre-control device is made available at least the consistency of the substance and the desired speed of the paper machine as input variables for determining the desired value.

Since a change in the setpoint speed only has a delayed effect on the weight per unit area of the paper web produced, the drives of the paper machine are triggered with a delay. However, a planned change in the desired speed is already taken into account beforehand by the pilot control device for re-measuring the setpoint of the headbox.

Furthermore, the pilot control device takes into account the consistency of the substance. By consistency is meant the fiber content in comparison to the water content of the substance. The fiber content is typically 0.1 to 1%. Thus, the pilot control device at lower consistency set an increased set point for the headbox and vice versa.

Furthermore, the pre-control device takes into account a data record from a sort file, which indicates the type of paper to be produced and in particular its weight per unit area. Thus, different types of paper can be made from the identical fabric.

In a further development of the invention, the pilot control device also takes into account that with identical measured consistency, a different effective consistency can be present. For this purpose, a data set of stock preparation is used to further optimize the applied amount of substance. This data set can take into account changes in effective consistency due to other chemical composition, especially fillers. Furthermore, a record of the return water system in the pilot control device can be taken into account.

The pilot control device, which provides a theoretical value for the applied quantity of substance and correction values, can be realized for example by a linear model. By means of this model it is possible to analytically calculate a required amount of substance from the input variables, for example the substance used, the type to be produced, the sieves used or the data of the recycling water system.

In another embodiment, the precontrol can be realized by a numeric map matrix. This matrix consists of discrete values stored in a memory. From such a multi-dimensional value field, the pilot control device can read out a required value for the substance quantity as a function of the input variable.

Another alternative to the realization of the pilot control device is a neural network. Such a network consists of a plurality of input neurons, each receiving an input value, and a plurality of hidden hidden neurons, which are connected to the input neurons and each perform a mathematical operation on the input values. The thus calculated output values of the hidden neurons are fed to an output. The mathematical operations, the number of neurons and the links are chosen so that the neural network to be applied to each n-tuple of input values Provision of substance quantity as initial value. If the map matrix is implemented as a neural network, it is particularly preferably an adaptive neural network. This is able to automatically generate new setpoints from long-term control deviations that change the required amount of material, which then require no or minor corrections during further operation.

Finally, the pilot control device can be realized in fuzzy logic. Such a realization allows reliable statements about the required amount of substance, even if the assigned input variables are blurred and error-prone.

An increased accuracy of the control device according to the invention is achieved in that in addition a so-called measuring controller is provided which outputs a deviation between the measured at the outlet of the paper machine actual value of the basis weight and the target value. These measured deviations are used to detect deviations of the weight per unit area and to correct the setpoint values output by the pilot control device accordingly. The measuring controller is an additional controller to the basic control circuit designated as an operating controller.

According to the invention, not only is a desired value of the headbox determined in the pilot control device, which is then corrected by measured basis weights, but the pilot control device itself calculates correction values for the amount of substance to be applied. On the one hand, these may be multiplicative corrections which stretch or compress the function of the quantity of substance to be applied over time, as well as additive corrections which increase or decrease the amount of substance to be applied by a fixed value. The additive correction serves to compensate for constant fiber losses, for example in the case of changes in the backwash water. The multiplicative correction takes into account deviations in the effective consistency of the measured consistency, for example, changes in the chemical composition or in the treatment of waste paper. Particularly preferably, the output correction values of the precontrol are also available again as an input value. As a result, the precontrol can determine a new desired value, which requires a smaller correction as a result. If the precontrol device is implemented by a self-learning neural network, the output correction values can also be used to optimize the network.

In order to avoid that the paper machine enters an inadmissible operating state, the value of the substance quantity determined by the pilot control device and optimized with measured values and corrections is fed to a limiter. This can limit the amount of substance to be applied to a maximum possible value. Furthermore, the limiter can also be used to limit the rate of change of the amount of substance. As a result, the rate of change of the substance quantity can be limited to the maximum possible rate of change of subsequent plant parts. It is avoided, for example, that a paper web with increased thickness and increased water content is delivered to the dryer section, which can be dried there only with increased heat demand. This would leave the machine in the first few minutes to readjust the heat output too wet and thus unusable paper web. If the machine parts stored downstream of the headbox are brought into a different operating state, the limit value (s) in the limiter can also be adapted during operation of the machine.

In order to provide a more detailed understanding of the above-described features of the present invention, a more detailed description will be given below with reference to an embodiment. It should be understood, however, that the appended drawings illustrate only a typical embodiment of the invention and, therefore, the scope thereof does not restrict. The invention may admit to other equally effective embodiments. The description is made with regard to various functional components, which can optionally be implemented by hardware and / or software elements.

FIG. 1 shows a block diagram with an operating controller 1, which regulates the flow of material to the headbox from an inlet 3 via a valve 4. To determine the actual value of the material flow, a measuring device 5 is provided. The operation controller 1 is, for example, a PID controller with a sampling time of about 2 s.

The setpoint for the flow to the headbox is fed to the PID controller 1, the so-called operating controller, via a limiter 13. The operating controller 1 represents the basic control loop. The setpoint of the material flow to the headbox is also supplied via line 23 to the downstream machine parts, for example the control of the dryer section. The limiter 13 limits the output setpoint or its first derivative after the time to a maximum value, which depends on the performance of the downstream system components. These changing maximum values are supplied to the limiter 13 via line 14.

The precontrol device 2 serves to feedforward the setpoint value. This is preferably implemented in the form of a numerical map matrix or a neural network. In some cases mixed forms can also be used. The map 2 are fed via lines 18, 19 and 20 records of stock preparation, the return water system and the sort file. This data can be entered manually by the user or read out from an electronic process control of the production. Based on the knowledge of the variety to be produced, the maps can be made sort-dependent with regard to the other values. The data of the stock preparation 18 and the return water system 19 can also static data from a sequential control or measured values of the corresponding system parts. This allows a dynamic adaptation of the headbox to the operating conditions of the return water system and the substance used.

Furthermore, the map 2, the predetermined target speed of the engine via line 7 is supplied approximately every 2 s. Furthermore, the consistency of the substance is provided via line 6 approximately every 4 s. The reciprocal of the consistency 1 / C is also fed to the map 2 via a filter.

Depending on the substance used, the target speed, the grade to be produced and the operating state of the return water system, the map calculates an amount of substance to be applied and provides this on line 26 ready. This value is fed to a PID controller 9, the so-called measuring controller. The PID controller 9 continues to receive as input value a desired value of the basis weight from the sort file via line 10. A measuring device 8 determines an actual value of the weight per unit area before the reel-up, ie. H. at the exit of the paper machine, or between the pre-dryer section and the after-dryer section. From these values, the PID controller 9, which is clocked in synchronism with the measurement with an interval of about 32 seconds, determines a value corrected for output 26 of the feedforward corrected amount of substance. This value is also provided to the sieve model 16.

The sieve model 16 calculates from the sort file 20 and, if appropriate, correction values 18 to 22, a correction value between the actual consistency present in the plant and the measured consistency. The input values provided to the screen model are averaged over approximately 4 seconds each. Since the sieve model is only intended to correct long-term deviations, the correction value at the output of the sieve model in the integrator 17 will be about 60 seconds integrated. As an alternative to the screen model 16 and the integrator 17, the correction can also be taken into account directly in the pilot control device 2.

The pilot control device 2 outputs a multiplicative correction value for taking into account deviations of the effective consistency from the measured consistency on line 25. Likewise, the measured consistency on line 6 is the multiplicative correction of the flow to the headbox. Before execution of the multiplication, all correction values, that is to say the output of the integrator 17, line 25 and line 6, are added. In the multiplier 11, the multiplicative correction of the control signal is made.

Furthermore, the pilot control device 2 can output an additive correction value on line 24. This additive correction value takes into account constant fiber losses. With changes in the backwash water, such fiber losses can also vary over time. This too can be taken into account by the pilot control device 2. The correction value on line 24 is added to the output value of multiplier 11. This result is still multiplied in multiplier 12 with the speed setpoint 7. The result of this multiplication is then supplied to the above-described limiter 13 and represents at its output the lead variable of the operating regulator 1. The addition of the correction value 24 can, however, also take place between the regulator 9 and the multiplier 11. The speed setpoint value 7 is made available to the drive means 15 of the paper machine via a delay element and controls its speed.

The correction values 24 and 25 of the pilot control device are available to the latter via input 21 and 22 again. As a result, the pilot control device can output a corrected desired value to terminal 26, which subsequently requires only little or no corrections. Furthermore, the correction values on lines 21 and 22 can be used to train an adaptive pilot control device 2.

Claims (20)

1. Control device for longitudinal control of the grammage of a paper web in a paper machine with an operating controller (1) for controlling a mass flow from a head box (3), wherein the target value for the operating controller (1) can be determined by means of a pre-control device (2), wherein a measuring controller (9) is additionally provided for the determination of the target value, to which measuring controller the mass flow target value (26) specified by the pre-control device (2), a grammage target value and an input value from a measuring device (8) can be supplied for the determination of the actual value of the grammage, wherein the measuring controller is provided to evaluate a deviation between the measured grammage and the grammage target value and to output a mass flow target value (26) corrected accordingly compared with the mass flow target value (26) output by the pre-control device (2), and wherein the mass flow target value output by the measuring controller (9) can be corrected with correction values (25, 24) from the pre-control device (2).
2. Control device according to claim 1,
   characterised in that the pre-control device (2) is designed as a numerical map matrix and/or as a neural network and/or fuzzy logic.
3. Control device according to one of claims 1 or 2, characterised in that at least the consistency of the material and/or the target speed (7) are available to the pre-control device (2) as input variables.
4. Control device according to one of claims 1 to 3, characterised in that the pre-control device (2) is provided to apply a multiplicative correction value (25) and/or an additive correction value (24) to the output value of the measuring controller (9).
5. Control device according to claim 4,
   characterised in that the pre-control device (2) is provided to apply firstly the multiplicative correction value (25) before the additive correction value (24).
6. Control device according to one of claims 1 to 4, characterised in that at least one correction value can additionally be used as an input variable of the pre-control device.
7. Control device according to one of claims 1 to 6, characterised in that a limiter (13) is provided, which limits the target value supplied to the operating controller (1) and/or its derivation over time to a predeterminable limit value.
8. Control device according to claim 7,
   characterised in that the limit value can be adjusted during the operation of the controller.
9. Control device according to one of claims 1 to 8, characterised in that this has a grades file (20), the data of which can be used as an input value of the pre-control device (2) .
10. Control device according to one of claims 1 to 9, characterised in that a screening model (16) is provided, which can provide a multiplicative and/or additive correction value between an effective consistency present in the system and a measured consistency of the material.
11. Paper machine having a control device according to one of claims 1 to 10.
12. Paper machine according to claim 11,
    characterised in that the measuring device for determining the grammage is provided before reeling and/or between the predryer and afterdryer section.
13. Method for longitudinal control of the grammage of a paper web in a paper machine with an operating controller (1) for controlling a mass flow from a head box, wherein the target value for the operating controller (1) is determined by means of a pre-control device (2), wherein a measuring controller (9) is additionally used for the determination of the target value, to which measuring controller the mass flow target value (26) output by the pre-control device (2) is supplied, wherein the measuring controller evaluates a deviation between a measured grammage and a grammage target value and outputs a mass flow target value (26) which is corrected accordingly compared with the mass flow target value output by the pre-control device (2), said mass flow target value subsequently being corrected with correction values from the pre-control device.
14. Method according to claim 13,
    characterised in that the pre-control device outputs a first correction value, which is multiplied by the output signal of the measuring controller and a second correction is then output, which is added to the product of the first correction value and output signal.
15. Method according to claim 14,
    characterised in that a screening model is used to determine a third correction value between an effective consistency present in the system and a measured consistency of the material, and this value is added to the first correction value.
16. Method according to claim 14,
    characterised in that a screening model is used to determine a third correction value between an effective consistency present in the system and a measured consistency of the material, and this value is added to the second correction value.
17. Method according to one of claims 14 to 16, characterised in that the sum of the second correction value and the product of the first correction value and output signal is multiplied by the value of the target speed.
18. Method according to one of claims 13 to 17, characterised in that at least one correction value is used as an input variable of the pre-control device.
19. Method according to one of claims 13 to 18, characterised in that the target value supplied to the operating controller and/or its derivation over time are limited to a predeterminable limit value.
20. Method according to claim 19,
    characterised in that the limit value is changed during the execution of the method.

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