Patent Application
20080148981
1. Field of the Invention
The invention relates to a method and apparatus for controlling the cutting register on a web running through a web-fed rotary press.
2. Description of the Related Art
In web-fed rotary presses, it is known to use an actuating roll which can be moved in linear guides as an actuating element for correcting errors in the position of the cutting register on a web. In this case, the actuating roll changes the paper path length between two draw units to correct the cutting register error. Register rolls of this type are shown, for example, in DE 85 01 065 U1. The adjustment is generally carried out by an electric stepping motor. Apparatuses of this type are afflicted with a relatively high mechanical and electrical complexity.
It is an object of the invention to provide a simple method of controlling the cutting register error in a web-fed rotary press.
In the specification and claims, the term ‘clamping point’ refers to a nip through which the web runs in the rotary printing press such as, for example, in a printing unit, cooling unit, turner unit or knife cylinder unit. The ‘cutting register error’ is the deviation of the cutting register from its intended position, the ‘total cutting register error’ is the deviation of the cutting register, at the time of cutting by the knife cylinder, from its intended position, and the ‘partial cutting register error’ is the deviation of the cutting register from its intended position at a clamping point prior to or upstream of the knife cylinder.
The object is achieved by registering a cutting register on a web running through a rotary press by a sensor arranged upstream of or at a knife cylinder of the rotary press. The registration information is supplied to a control device which determines a cut register error. A relative position or speed of the knife cylinder or other clamping point in the rotary press is influenced in response to the determined cutting register error to correct the cutting register error.
In the method according to the invention, the running time of the web image points along a constant web path is adjusted whereas, in the prior art, a change is made in the web length at constant web speed.
It is important that the measurement of the cutting register error is carried out before the knife cylinder, the knife cylinder having a controlled-angle individual drive and register control being superimposed on its position and/or rotational speed control. Furthermore, the cutting register control may be achieved with the aid of a subordinated control loop, in which the partial cutting register error Y*13 at or before the turner unit, for example as early as at the end of the cooling unit, is measured and compensated for via the lead of the turner unit.
It is important that, to control the cutting register error, a specific or striking item of image information of the printed web is registered by at least one sensor and is supplied to a control device. It is not necessary for this image information to be a placed mark. An item of image information suitable for the deviation of the position of the printed image with respect to its intended position, based on the location and time of the cut, that is to say for the cutting register error Y14, is measured immediately before or on a knife cylinder (clamping point 4) and, by at least one control loop, is controlled to its predefined set point, for example to the value zero, in the case of correction via the knife cylinder, a controller predefining an angle set point α14w for an angle control of the knife cylinder. As an alternative, the correction may be made via at least one non-printing clamping point (clamping point 2 or 3) located before the knife cylinder, using a controller predefining the register set point Y*12w or Y*13w for a subordinated register controller, which corrects the part register error Y*12 or Y*13 via the speed or lead at the clamping point 2 or 3. As a further alternative, if at least two non-printing clamping points i and k and their speeds are used for the correction, associated control groups being coordinated in such a way that the cutting register error Y14 is controlled to the predefined set point Y*14w, for example equal to zero. In the following text, for simplicity, mention will always be made of the value zero in the case of the set point Y*14w, it also being possible for another suitable value to occur in its place.
For the determination of the controlled variables, the use of sensors is the preferred embodiment. However, models may also partly or completely replace the sensors, that is to say the variables are estimated in an equivalent way with the aid of mathematical or empirical models.
It is significant that, when the limits of a control variable, e.g., the control variable ω3w, are exceeded, the control of the part register error Y*13 is transferred from the controller of the clamping point 3 to a controller 1.1 of the clamping point 1, that is to say the angle of the clamping point 1 is tracked and the excessively small or excessively large value of ω3w is moved back into the permissible range. The tracking of the angle of the clamping point 1 is carried out for all operating states in which ω3w lies within the limits by an adaptation element 1.2, a set point for the readjustment of the angle α1w being calculated with the aid of a mathematical model, as a result of which a sufficient reserve of the manipulated variable, e.g., the control variable ω3w or lead of the clamping point 3, is always ensured. In the mathematical model, the relationship between the lead change needed for the correction of the part register error Y*13 and the resultant correction value α1w is calculated. The tracking of the angle of the clamping point 1 is advantageously carried out slowly as compared with the control of Y*13, as a result of which ghosting arising from excessively fast position changes of the printing units (clamping point 1) is avoided and decoupling of the control loops is achieved.
It is important in this case that tracking, in particular of the controlled-angle clamping point 2, is carried out with angular synchronism with respect to the clamping point 1 and, as a result, the web time constant between clamping point 1 and clamping point 2 becomes ineffective.
Tracking the lead of clamping point 2 can also replace tracking the angle at clamping point 1, provided that a change in the lead of the clamping point 2 does not entail self-compensation of the force F23. This is the case if moisture and/or heat is input into the web in the preceding web sections. The cooling unit of a web-fed press, in particular of a web-fed rotary offset press, can therefore be used in particular as clamping point 2.
The solution according to the invention does not require any additional mechanical web guiding element. For the purpose of cutting register error correction, existing, non-printing draw units or clamping points may be used, such as in the cooling unit, pull rolls in the folder superstructure, the former roll or further draw units located in the web course between the last printing unit and knife cylinder, which are preferably driven by variable-speed individual drives.
Because of the special characteristics of the control system, the cutting register control with the aid of the lead of a clamping point is dynamically faster than in the case of the conventional solution by a register roll, since a change in the lead at the relevant clamping point replaces a path change. A significant advantage of this register control with the aid of the lead of a clamping point is that barely any wear of the mechanical transmission elements occurs, as would be the case in dynamically fast control with the aid of changing the path of an actuating roll. A further advantage is that the control engineering expenditure in the case of this cutting register error control with the aid of the lead of a clamping point is lower than in the case of a dynamically fast control with the aid of the path change of an actuating roll.
The parameters that enter into the cutting register error control system are largely independent of the properties of the rotary press. Furthermore, the cutting register accuracy can be increased substantially by the new method.
The tracking of the web tension may also be achieved with the aid of the dancer roll force, this being determined from the pressure of an associated pneumatic cylinder, the force being measured, supplied to a web tension controller and compared with the force set point, the output variable from the controller either being directly the manipulated variable for the pneumatic cylinder or the set point F01w, if there is a subordinate control loop for the input web tension F01. A web tension control loop for the web tension F01 can also replace the dancer roll. This force adaptation always ensures that the force change which occurs quickly because of a disturbance being controlled out is dissipated relatively slowly as compared with this control.
The invention also relates to an apparatus for implementing the method for controlling the cutting register error, whose clamping points 1 to 4 can be driven independently of one another by drive motors with associated current, rotational speed and possibly angle control, and in which the cutting register and/or associated further register deviations Y*13, Y*1i, Y*ik on or before a knife cylinder and/or at or before one or more clamping points i, k, 1 to 4 arranged before this knife cylinder (clamping point 4) can be registered by at least one sensor using a specific item of image information or measuring marks of the printed web and, in order to influence the cutting register error νY14, can be supplied to a closed-loop and/or open-loop control device in order to change angular positions or circumferential speeds ν1 to ν4, νi, νk of the respective clamping point Ki, Kk, K1 to K4.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.
In the drawings, wherein like reference characters denote similar elements throughout the several views:
The function of the present invention will be explained using the exemplary embodiments on a four-roll system. It is pointed out that, in a real press, as many printing units as desired, that is to say, for example, four printing units, of a web-fed offset illustration press or newspaper press or another type of rotary press may replace a clamping point 1 of the illustrated four-roll system. The principle of register correction described in the following text by two control loops superimposed on each other, one being given as actual value the register error measured immediately before the knife cylinder, the other the error from a clamping point located further in front, can be transferred with the same effect to all rotary presses.
The four-roll system of
In the following text, the terms “speed” and “lead” will be used synonymously. The web tension in a section i-1, i will be designated Fi-1,i. The changes in the modulus of elasticity and in the cross section of the incoming web are combined in zT. The cutting register error Y14 at the knife cylinder is to be designated the total cutting register error or, in brief, the cutting register error. A register error Y*1i which has occurred previously, measured at a non-printing clamping point i, will be called the partial cutting register error or, in brief, partial register error.
The system 1 of
The unsteady or steady mass flow of the web supplied to the system via the input of the clamping point 1 (K1), measured in kgs−1, is determined by the circumferential speed ν1 of the clamping point 1 (K1) and the extension ε01. In the case of Hookean material, the force F01 is proportional to the extension ε01. The force F01 is set by the pressing force of a dancer roll or self-aligning roll on the web passing through or by a tension control loop which—in accordance with the position set point or force set point—directly or indirectly via a further device for adjustment of the web tension—controls the circumferential speed of a clamping point 0 (e.g., an unwind device). Only the circumferential speed of the unwind device is capable of changing the steady mass flow introduced into the system in a steady manner. In the following text, it will be assumed that changes in F01 or in ν1 effected as a result of the change in the circumferential speed of the unwind device change the unsteady or steady mass flow into the sections following them. The circumferential speeds of the other clamping points—assuming Hookean material—can not change the mass flow in a steady manner. The circumferential speeds will be called speeds in brief in the following text.
The partial register error Y*13 measured before the clamping point 3 (K3)—for example a turner unit—by a sensor 6 is, as
Subordinated to this register control loop is a rotational speed control loop 3.3 of the drive motor assigned to the clamping point 3 (K3). The very fast dynamic behavior of the current control loop subordinated to the rotational speed control loop is negligible. The set point for the angular velocity (or for the rotational speed) of the clamping point 3 (K3) is ω3w.
If the set point for the part register error measured at the turner unit (K3) is zero, that is to say Y*13w=0, and, thus on average, so is the actual value, then in spite of this measure, the total cutting register error Y14 would generally not be zero, since, on the path between turner unit (K3) and knife cylinder (K4), the web is subjected on the further guide elements through which it must pass (for example former roll, former, slipping transport rolls in the folder, etc.) to forces which produce permanent cutting register errors in the event of a change in the web tensions, for example in the event of a reel change. Therefore, the total register error Y14 is also measured and influenced, a plurality of variants occurring. These variants are preferably explained for single-web operation using the exemplary embodiments. For multi-web operation, reference is made to the parallel German Application No. DE 103 35 886.
Instead of the above-described register control I for the partial register error Y*13, a register control loop for the total cutting register error Y14 may be provided directly. The manipulated variable is the lead or position of the knife cylinder 4. For this purpose, The cutting register error is measured shortly before the knife cylinder 4 using a sensor 5. the cutting register error supplied to the comparison point of a cutting register controller 4.1 and compared with a set point Y14w=0 (dashed line in
However, the control loop for the total cutting register error Y14 may also be superimposed on the control loop for the part register error Y*13 in accordance with the principle of cascade control. For this purpose, the total register error, as described in a) and in the section “Register control loop I”, is measured shortly before the knife cylinder with a further sensor 6, supplied to the comparison point of the cutting register control of 3.1 and compared with the set point Y14w=0. The subordinate loop (register control 3.2) detects, as early as at the location of the turner unit (K3), that a subsequent cutting register error will occur. The cutting register controller 3.1 guides the set point Y*13w such that, within the scope of the dynamic possibilities, Y14w=0 is always maintained. With the aid of the speed ν3 of the turner unit (K3), the total cutting register error at the knife cylinder (K4) is therefore influenced suitably in this way. The cutting register controller 3.1 may, for example comprise a PI controller, which is optimized in accordance with the magnitude optimum or the symmetrical optimum (see Föllinger, O.: Regelungstechnik [Control engineering], Heidelberg: Hüthig-Verlag 1988). The output variable from the register controller 3.1 is limited by a limit 3.6. The adaptation of the control loop to the machine speed and also the compensation of dynamic elements of these register control systems are carried out in an adaptation element 3.4. This may also be implemented directly in the register controller 3.1. In this case, an adaptation element is understood to mean an adaptation of the parameters (for example gain factors) of the closed control loop to the machine speed. For this purpose, characteristics (characteristic curves and/or dynamic transfer elements) are stored in the adaptation element.
In an embodiment, the at least one control loop comprises a plurality of control loops superimposed on each other in a cascade structure, where upon starting up the control loops, an identification process is performed to determine all the data of the mechanical controlled rotary press system while it is at a standstill or in operation, with and without a paper web passing through, and the controllers are optimized in accordance with analytical optimization equations. Here, the optimization is carried out with computer assistance or in a fully automated manner.
In the case of single-web operation, it is also possible for the control loop for the total cutting register error Y14 to be superimposed on a control loop for the partial cutting register error before the former roll instead of before the turner unit (K3), in accordance with the principle of cascade control (not shown in
Another clamping point i (Ki), for example located before the clamping point 3 (K3), may also replace the former roll or the turner unit. Accordingly, the partial cutting register error Y*1i is measured and controlled at or before this clamping point i (Ki). The register correction is made either by the speed (lead) νi of this clamping point or Y*1i is supplied to another control loop (for example including for the purpose of feedforward control). It is also possible to measure the partial cutting register error or errors at a plurality of non-printing clamping points i and k (Ki; Kk) located before the knife cylinder (K4) and correct it or them with the aid of associated control loops via the speeds of νi and νk. The two control loops may also be combined in a suitable manner. In particular, the two control loops may comprise at least one periodic controller which, in terms of its action, is matched to a periodic disturbance (see U.S. Pat. No. 5,988,063).
Since the register control via the lead of the clamping point 3 (K3) (or other suitable clamping points, as shown above) is associated with a change in the web tension F23, it is not possible to rule out the situation in which large disturbances cause excessively small or excessively large web tensions F23, which can cause a web break. The web tension F23 must therefore be restricted. For this purpose, the speed ν3 is limited by predefining an upper and lower limit 3.5 on the output variable ω3w of a register controller 3.2. When one of the upper and lower lead limits 3.5 is reached, the angular position of the printing units, that is to say the clamping point 1 (K1) in
To allow a manipulated variable to always be sufficiently available for the register correction via the speed (lead) of clamping point 3 (K3) with regard to the permissible range of the web tension F23, a set point for the readjustment of the angle α1w is always calculated in an adaptation element 1.2 with the aid of a mathematical model from the lead of clamping point 3 (K3). This mathematical model describes the relationship between the lead changes occurring for the correction of the part register error Y*13 and the resultant correction value α1w. While the register correction via the lead of clamping point 3 (K3) is carried out as fast as possible, the readjustment of the angle α1w is a correction which is slow by contrast. As a result, fast movements of the printing units, which cost energy and may possibly cause ghosting, are avoided. For this purpose, the adaptation element 1.2 additionally contains a delay element of first or higher order. This additionally ensures that, in normal operation, that is to say during operation within the limits of the register controller 3.2, the register control loop and the angular readjustment of clamping point 1 (K1) are decoupled. The changeover between the control loops is carried out in an electronic switch 1.3, which is controlled by the evaluation of the limit 3.5. In normal operation, therefore, the angular readjustment by the adaptation element 1.2 always ensures that the change in the lead of the clamping point 3 (K3) that has occurred as a result of a disturbance being controlled out quickly is dissipated again slowly.
In addition, the superimposed controller 3.1 is provided with a limitation on the output variable. Since this superimposed control for Y14 must in principle be adjusted more slowly than the subordinate one for Y*13, even in the case of large disturbances, it is hardly to be expected that an excessively large set point Y*13 will be predefined. Nevertheless, for example in the case of erroneous failure of the adaptation element 3.4 or of the sensor for Y14, there could be too large a swing of the controller 3.1, for which reason a limitation is necessary.
Since the register control via the lead of the clamping point 3 (or other suitable clamping points, as shown above) is associated with a change in the web tension F23, as described above, it is not possible to rule out the situation in which large disturbances cause excessively small or excessively large web tensions F23, which can lead to a web break.
The force 2 F01 of the dancer roll or of the dancer roll system 7 (see
The dancer or self-aligning roll system can also be replaced by a web tension control loop, which predefines the force F01 (see
The angle tracking of the printing units (K1) described can also be replaced by tracking of the lead of the cooling unit (K2), as will be described below.
Since the register control via the lead of the clamping point 3 (K3) (or other suitable clamping points, as shown above) is associated with a change in the web tension F23, it is not possible to rule out the situation in which large disturbances cause excessively small or excessively large web tensions F23, which can lead to a web break. The web tension F23 must therefore be restricted. For this purpose, the speed ν3 is limited by predefining an upper and lower limit 3.5 on the output variable ω3w of a register controller 3.2. When one of these lead limits is reached, the lead of the cooling unit, that is to say the clamping point 2 (K2) in
The use of the lead of the cooling unit (K2) for limiting the force F23 is made possible by the fact that when the speed ν2 is adjusted, the force F23 is not self-compensating. This can be attributed to the change in the paper properties as a result of the input of moisture and heat by the printing units and the drying section.
In order that a manipulated variable is always sufficiently available for the cutting register error correction via the speed (lead) of clamping point 3 (K3) with regard to the permissible range of the web tension F23, a set point for the readjustment of the angular velocity ω2w is always calculated in an adaptation element 2.2 with the aid of a mathematical model from the lead of clamping point 3 (K3). This mathematical model describes the relationship between the lead changes occurring for the correction of the part register error Y*13 and the resultant correction value ω2w. While the cutting register error correction via the lead of clamping point 3 (K3) is carried out as fast as possible, the readjustment of the angular velocity ω2w is a correction which is slow by contrast. For this purpose, the adaptation element 2.2 additionally contains a delay element of first or higher order. This additionally ensures that, in normal operation, that is to say during operation within the limits of the register controller 3.2, the register control loop and the angular readjustment of clamping point 2 (K2) are decoupled. The changeover between the control loops is carried out in an electronic switch 2.3, which is controlled by the evaluation of the limit 3.5. In normal operation, therefore, the angular readjustment by means of the adaptation element 2.2 always ensures that the change in the lead of the clamping point 3 (K3) that has occurred as a result of a disturbance being controlled out quickly is dissipated again slowly.
The above-described measures for cutting register control are not intended to relate just to the application in web-fed offset rotary presses but can be applied in all other printing processes, printing materials and presses in an equivalent way, in particular in gravure printing, screen printing, flexographic printing, textile printing, film printing, metal printing, label printing machines, textile printing machines, film printing machines, illustration and newspaper presses.
Thus, while there have shown and described and pointed out fundamental novel features of the invention as applied to a preferred embodiment thereof, it will be understood that various omissions and substitutions and changes in the form and details of the devices illustrated, and in their operation, may be made by those skilled in the art without departing from the spirit of the invention. For example, it is expressly intended that all combinations of those elements and/or method steps which perform substantially the same function in substantially the same way to achieve the same results are within the scope of the invention. Moreover, it should be recognized that structures and/or elements and/or method steps shown and/or described in connection with any disclosed form or embodiment of the invention may be incorporated in any other disclosed or described or suggested form or embodiment as a general matter of design choice. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.
| Number | Date | Country | Kind |
|---|---|---|---|
| 103 35 888.9 | Aug 2003 | DE | national |
This application is a continuation of U.S. patent application Ser. No. 10/913,247 which was filed with the U.S. Patent and Trademark Office on Aug. 6, 2004. Priority is claim on patent application No. 103 35 888.9 filed in Germany on Aug. 6, 2003.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 10913247 | Aug 2004 | US |
| Child | 12001128 | US |
