EP2524806B2 - Method for regulating the web tension in a web processing machine - Google Patents

Description

The present invention relates to a method of controlling web tension in a web processing machine.

Although reference will be made below mainly to web-fed printing presses, the invention is not limited thereto, but rather directed to all types of machine tools in which a web is processed (hereinafter "web-processing machine"). However, the invention is particularly applicable to web-fed printing machines, such as e.g. Newspaper printing machines, commercial printing machines, gravure printing machines, packaging printing machines, digital printing machines or securities printing machines, as well as other web-processing machines, e.g. Pouch machines, envelope machines or packaging machines, can be used. The web can be made of paper, cloth, cardboard, plastic, metal, rubber, in foil form, etc.

State of the art

In the case of web-processing machines in question, in particular web-fed printing presses, a web of material is conveyed along driven axes (web transport axes or devices), such as, for example, webs. Pull rollers or feed rollers, and non-driven axles (such as deflection, guide, drying or cooling rollers) moves. The web is simultaneously processed (e.g., printed, punched, cut, folded, etc.) by means of usually also powered processing means (such as printing units, cutters).

In such a machine usually a longitudinal and / or side register (longitudinal register - in the web running direction, side register - transversely to the web running direction) regulated. This serves to regulate the positions of the processing of the individual processing devices (for example the layers of individual, differently colored printed images) relative to one another and takes place, for example, by means of a so-called angular adjustment of the processing device to be corrected. In the case of printing presses, the web tension is often also regulated (for example by speed adjustment of a transport device) in order to achieve an optimum printing result.

Known regulators, such as P controllers, D controllers, I controllers, etc., and any combinations thereof, include controller parameters that must be set. Typical controller parameters are the proportional gain Kp, the integral gain K _I , the differential gain K _D , the reset time T _N , the derivative time T _V , delays T, etc.

• Bspw. ist in der EP 1 790 601 A2 dargestellt, dass Reglerparameter in Abhängigkeit von Warenbahnparametern (z.B. E-Modul), Maschinenparametern (z.B. Warenbahnlänge, Warenbahngeschwindigkeit oder Trägheitsmoment) und Betriebsparametern (z.B. Regelabweichung) bestimmt werden können.

The Applicant has heretofore developed a number of methods to simplify the parameterization of web tension controllers:

• For example. is in the EP 1 790 601 A2 shown that controller parameters depending on web parameters (eg E-module), machine parameters (eg web length, web speed or moment of inertia) and operating parameters (eg control deviation) can be determined.

In the DE 10 2008 035 639 A1 is shown that in addition to these variables and dead times in the controlled system are available and can be used to determine the controller parameters.

In the DE 10 2009 019 624 A1 is a controller parameter as a function of at least one parameter characterizing the product web, such as the modulus of elasticity and / or the cross section, at least one parameter characterizing the processing machine, such as the web speed and / or the section length, and at least one, in particular constant (ie non-web speed dependent ) and / or speed-dependent, dead time, such as a transmission time and / or a measurement time described. It is also disclosed that the parameterization is carried out regularly, so that, for example, the change in the modulus of elasticity can be automatically reacted by adapting the controller parameters. As a result, the best possible controller parameters should be specified at all times. Furthermore, it is proposed to optimize the control with respect to the disturbance behavior, so that the highest possible control loop dynamics with respect to disturbances of the web tension actual value is achieved (ie a disturbance in the web tension actual value should be corrected as dynamically as possible (= fast)). This can be achieved that a Bahnspannungsistwert hardly deviates from the associated web tension setpoint.

However, it was observed (see publication " Online reconstruction of elastic modulus changes of the web in web presses ", lecture by Prof. Brandenburg at SPS / IPC / Drives 2008 ) that in web presses especially when changing roles large register deviations occur. This was attributed inter alia to a sudden change in the modulus of elasticity E. This disturbance is introduced into the machine, which, when passing each nip, stimulates equalization, resulting in web tension, color and cut register errors. In this case, large register deviations occur, which can not be quickly compensated by an existing register control. Because of the long path from the origin of the disturbances, the unwinder, to the cutting cylinder of the folder, the resulting total register deviation can be particularly large. This leads to relatively high waste numbers, especially in offset-illustration printing machines because of the required high cut-sheet accuracy, but will probably play an increasingly important role in newspaper printing presses in the future.

The WO 02/07975 A1 discloses a method of controlling a web tension in which an elongation of the web during operation is monitored and wherein a detected change in strain is counteracted by a change in voltage.

It is therefore desirable to reduce register deviations caused by erratic changes in web tension.

Disclosure of the invention

Based on this prior art, the present invention proposes a method for operating a web-processing machine having the features of claims 1 and 4, respectively. Advantageous embodiments are the subject of the dependent claims and the following description.

A sudden change in the modulus of elasticity E leads (as in the prior art with sufficiently strong or dynamic) controlled (ie substantially constant) web tension σ due to the known relationship σ = ε · E to a corresponding abrupt change in the web elongation ε. This strain change propagates from the location of the modulus of elasticity change throughout the machine. During this compensation phase, there are therefore different expansion ratios at the individual processing devices which lead to different processing positions of the same relative to one another and thus to register deviations.

The invention now comprises the measure of an upcoming change of at least one parameter influencing the web tension (this is a parameter characterizing the web, in particular the modulus of elasticity E), which in the uncontrolled case would lead to a sudden change in the web tension namely, the strain due to unchanged machine speed constant), the effects of the web tension control to reduce the web elongation, in particular to reduce the control loop dynamics of the web tension controller.

As a result, the change in the parameter influencing the web tension leads to a greater change in the web tension in comparison with a conventional web tension control, but thereby to a smaller change in the web elongation.

The invention uses to implement a reduction of the influence or the dynamics of the web tension control, by suitable modification of the controller parameters (eg reduction of K _P ), activation of limits in the controller (especially for the controller output variable) or by adjustment of the setpoint. Here, the web tension setpoint can be changed so that a strain change remains low. The new desired value can be determined, for example, by determining the web tension resulting after the change without regulation (for example, by using the changing material parameter and calculating therefrom the resulting web tension for a constant web elongation). Alternatively, the web tension resulting after the change can also be measured with the web tension control switched off and used as the new web tension setpoint. Subsequently, the web tension control would be switched on again with the new setpoint. Starting from the new web tension setpoint, the current setpoint is reset to the original value with sufficiently low dynamics.

Simply switching off the web tension control can not solve the problem, because then the strain changes and thus the register errors occur when the web tension control is switched on later.

In principle, the reduced dynamics of the web tension controller result in a change in the actual web tension (which can be kept essentially constant if the web tension control has a greater influence, for example in the case of strong or dynamic controller settings). However, the invention is based on the recognition that the longitudinal register is influenced less by a web tension than by a web elongation. By reducing the web tension control dynamics, the strain change due to a change in the controller output will also be less dynamic.

The less dynamic strain changes lead to less dynamic register deviations, which can be easily compensated by a register control, so that waste can be reduced or completely avoided. A less strong engagement of a web tension controller will cause the duration of the compensation process is extended, but in conjunction with a register controller whose closed loop control dynamics is greater than or equal to the dynamics of the web tension controller, the maximum amount of register deviation decreases. Preferably, the effect of the web tension control on the web stretch is reduced so that the amount of register deviation occurring does not exceed an upper threshold, so that preferably just no waste occurs.

The invention provides a possibility, with knowledge of a pending change of at least one parameter influencing the web tension, to take measures beforehand in order to minimize paper waste. The time of a change is known, for example, in the case of a flying roll change, a change in the color or moisture input into the material web or a change in the temperature in the machine in advance. The conversion of the web tension control can therefore preferably take place automatically within the control device.

The change in the color or moisture input into the web comes in printing offset printing, Gravure printing, flexographic printing, etc., for example, by "pressure on" / "pressure from" settings or by changes in the amount of ink or water supplied during printing.

In digital presses, the amount of ink in one format may be due to another printed image. Digital printing machines are characterized e.g. by being able to directly print different products from format to format without stopping the machine. That By color changes, a sudden change in web material properties is also obtained here.

Also, the change in temperature in the machine can be relatively abrupt, e.g. Dryers can be changed very dynamically in their heating power or if the drying process of the paint or the web can be changed relatively quickly (for example, turning on an LED dryer).

The invention leads to a targeted reduction in the dynamics of the web tension control. However, high dynamics are found under normal operating conditions or e.g. during machine start-up as advantageous to achieve a short settling time of the web tension controller and there to produce less waste. For this reason, the dynamics of the web tension controller after the change of at least one parameter affecting the web tension is increased again or reset to the normal state. This can be time-dependent or falls below a register deviation threshold. The switching is expediently not abruptly, but continuously or in small steps. For example, the controller parameters are linearly interpolated between reduced and high dynamics to achieve a smooth transition.

Preferably, at least in the control with reduced influence, a smoothing of the actual web tension value is undertaken. Smoothing can be realized, for example, with a PT1 element by correspondingly increasing the time constant T ₁ . Greater smoothing leads to an additional delay (dead time) in the system and reduces the possible control loop dynamics. Depending on the reduction of the control loop dynamics, the smoothing time constant T ₁ can be automatically adapted, in this case increased. Assuming that the dynamics of the closed loop is inversely proportional to an actual value smoothing, smoothing elements can be introduced or already existing smoothing time constants can be increased with a small predetermined control loop dynamics, without the control loop becoming unstable as a result. As a result, in particular broadband noise interference can be counteracted on a web tension actual value. Unwanted fluctuations in the controller output can be reduced as a result.

According to a further preferred embodiment, the control loop dynamics of the web tension controller is adapted to the control loop dynamics of the register controller prior to the pending change in the at least one parameter influencing the web tension. For example, the bandwidth of the closed web tension control loop can be set to a fixed factor (e.g., 1/10) of the bandwidth of the closed loop register by appropriately adjusting (lowering) the controller parameters of the web tension controller. This results in an independent of the control loop dynamics of the register control loop comparable transient behavior in the longitudinal register. By reducing the controller parameters of the web tension controller dominates the control loop dynamics of the register controller. That The web tension controller regulates the sudden change in the modulus of elasticity and thus the web tension slowly back to the desired value, which due to the higher dynamics of the register controller this corrects the strain changes generated by it without waste is generated.

An arithmetic unit according to the invention, e.g. a control unit of a printing press, is, in particular programmatically, adapted to perform a method according to the invention.

Also, the implementation of the invention in the form of software is advantageous because this allows very low cost, especially if an executing processing unit is still used for other tasks and therefore already exists. Suitable data carriers for providing the computer program are, in particular, floppy disks, hard disks, flash memories, EEPROMs, CD-ROMs, DVDs and the like. It is also possible to download a program via computer networks (Internet, intranet, etc.).

Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

It is understood that the features mentioned above and those yet to be explained below can be used not only in the particular combination indicated, but also in other combinations or in isolation, without departing from the scope of the present invention.

The invention is illustrated schematically by means of exemplary embodiments in the drawing and will be described in detail below with reference to the drawing.

figure description

FIG. 1

shows a schematic representation of a machine designed as a printing machine, for which the inventive method is suitable,

FIG. 2

shows a schematic block diagram of an exemplary web tension control loop and

FIG. 3

shows a flowchart of a particularly preferred embodiment of the method according to the invention.

In FIG. 1 a schematic section of a printing machine 10 is shown, in which a material web 101 is transported and processed by five here as printing units 1 to 5 formed clamping points. Between each two adjacent clamping points, a web tension section is formed. For example, a web tension section 12 is limited by the printing units 1 and 2, a web tension section 23 through the printing units 2 and 3, a web tension section 34 through the printing units 3 and 4 and a web tension section 45 through the printing units 4 and 5. Instead printing units can also transport works, such as Feeding or extracting plant, be affected.

The printing machine further has here as load cells 121 to 124 formed web tension sensors for determining the tensile force F in the respective web tension sections. The physical parameters, namely the length 1, the strain ε and the tensile force F of the individual web tension sections are also indicated in the figure. Assuming a usually constant web cross section, the tensile force F is proportional to the web tension σ.

In the illustration shown, the tensile force and thus the web tension over the peripheral speeds v1 to v5 of the printing units 1 to 5 is set, which can be changed by a designed as a computer unit or computer 150 web tension control device. For influencing the web tension, for example in the web tension section 34, two strategies are known. In the upstream strategy, the printing unit 3 (and optionally upstream printing units) is adjusted, and in the downstream strategy, the printing unit 4 (and optionally subsequent printing units) is adjusted. Increasing the speed of the forward nip causes a stationary reduction in web tension and increasing the speed of the rear nip causes a steady increase in web tension in that web tension section.

To carry out the web tension control, the traction force values detected by the sensors 121 to 124 are fed to a device for web tension control (so-called web tension or tension controller) within the arithmetic unit 150. The tension controller then controls the speeds v1 to v5 as a function of the control deviation (deviation between setpoint and actual value), for example by influencing a gearbox factor (so-called fine adjustment) between machine speed (which is usually specified by a virtual master axis) and transport roller.

In FIG. 2 the web tension control on which the invention is based is schematically illustrated by means of a control loop 200. The control loop may, for example, a printing machine according to FIG. 1 underlie. The command variable w (eg., The target pulling force F _soll) is supplied to a comparator or subtracter 201, which includes the controlled variable y (eg., The tensile force _F, which is proportional as mentioned for the web tension) is applied. The resulting control difference or control deviation e is fed to a web tension control element 202, which in the present case is designed as a PI element with a proportional gain K _P and a readjustment time T _N. Without limitation, the control element can also be embodied as a P, PD or PID element or as another regulator, such as a state controller.

According to the illustrated embodiment of the invention, the control member 202 may be supplied by a switching element 203 different controller parameters. The switching element 203 can for this purpose supply to the control element 202 a first set 210 or a second set 211 of controller parameters which determine the influence of the web tension control. For example, the first set of controller parameters may result in dynamic web tension control for normal operation, whereas the second set results in less dynamic web tension control for impending jump changes in web tension (eg, due to a change in modulus of elasticity).

The control element 202 calculates, based on the controller parameters supplied to it, a controller output variable u _R which is supplied to the controlled system (G) 204. Behind the controlled system affects a disturbance d (in the example shown also additively via an adder 205), which changes the controlled variable or the actual value y . This is measured, for example, with the aforementioned sensors and returned to the comparator 201 again. The controller output u _R can be a fine adjustment fa , which influences the rotational speed of the device to be controlled.

In FIG. 3 a flow chart of an embodiment of the method according to the invention is shown and designated as a whole by 300. In step 301, the processing machine is in a defined state ("normal operation"), in which the web tension control device with a first parameter set, for example. The set 210, is applied.

In step 302, the method waits for a pending change 311 of at least one parameter influencing the web tension, usually the modulus of elasticity E. Such a change occurs predictably, for example, in a roll change or in other events already explained above. Accordingly, the time of change within the controller is known, so that the conversion can be done automatically. It is understood, however, that the method according to the invention can, in principle, be informed in any manner of a corresponding change. For example, separate data lines may be used for this or user input may be provided in a corresponding device is made to be included.

In step 303, the system takes a change in controller dynamics, in the example of FIG FIG. 1 For example, by changing the controller parameters 210 to 211 before. The parameters can, for example, be taken from a lookup table or database. However, a corresponding automatic calculation of the parameter sets can also be carried out.

The newly selected parameters are maintained until a suitable condition is met and the previous parameters 210 are reentered in step 304. In particular, the condition may be the elapse of a time period or the decrease in register deviation or web tension deviation below a predetermined threshold. Thereafter, the system returns to wait state 302 and waits for another change.

It is understood that in the illustrated figure, only exemplary embodiments of the invention are shown. In addition, any other embodiment is conceivable without departing from the scope of this invention.

Claims (12)

1. Method for controlling the web tension of a product web (101) in a web processing machine (1), wherein an actual value (y) of the web tension is controlled by means of a control element (202) of a web tension control loop (200) to a target value (w) of the web tension, a control deviation (e) being fed to the control element (202), a controller output variable (u_R ) being output by the control element (202), wherein, before an impending change in at least one parameter influencing the web tension, the effects of the web tension control on a web stretch (ε) are reduced, wherein the at least one parameter influencing the web tension is a parameter characterizing the product web (101), wherein the effects of the web tension control on the web stretch (ε) are reduced by changing controller parameters (210, 211) of the control element (202), limiting the controller output variable (u_R ) and/or changing the bandwidth of the closed web tension control loop (200).
2. Method according to Claim 1, wherein the effects of the web tension control on the web stretch (ε) are increased again when a predetermined condition is fulfilled.
3. Method according to Claim 2, wherein the predetermined condition is an expiry of a predetermined time interval.
4. Method for controlling the web tension of a product web (101) in a web processing machine (1), wherein an actual value (y) of the web tension is controlled by means of a control element (202) of a web tension control loop (200) to a target value (w) of the web tension, a control deviation (e) being fed to the control element (202), a controller output variable (u_R ) being output by the control element (202), wherein, before an impending change in at least one parameter influencing the web tension, the effects of the web tension control on a web stretch (ε) are reduced, wherein the at least one parameter influencing the web tension is a parameter characterizing the product web (101), wherein the effects of the web tension control on the web stretch (ε) are reduced by changing the set point (w) of the web tension, wherein the effects of the web tension control on the web stretch (ε) are increased again when a predetermined condition is fulfilled, wherein the predetermined condition is an expiry of a predetermined time interval.
5. Method according to Claim 4, wherein the new set point (w) of the web tension used is an actual value of the web tension resulting after the change without control.
6. Method according to one of the preceding claims, wherein the effects of the web tension control on the web stretch (ε) are reduced only when the impending change in the at least one parameter influencing the web tension exceeds a predetermined threshold value.
7. Method according to one of the preceding claims, wherein the parameter characterizing the product web (101) is the modulus of elasticity.
8. Method according to one of the preceding claims, wherein, at least during the control with reduced effects of the web tension control on the web stretch, changed or additionally added smoothing of the actual value (y) is carried out.
9. Method according to one of the preceding claims, wherein, before the impending change in the at least one parameter influencing the web tension, the control loop dynamics of the web tension control loop (200) are set to a value less than the control loop dynamics of an existing register control loop.
10. Method according to one of the preceding claims, wherein the effects of the web tension control on the web stretch (ε) are reduced such that a register deviation resulting from the change in the at least one parameter influencing the web tension remains below a predefined threshold value.
11. Computing unit which is set up to carry out a method according to one of the preceding claims.
12. Web processing machine, in particular a printing press, having a computing unit according to Claim 11.

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