Patent Grant
7496426
The invention relates to a method for controlling the cut register in a web-fed rotary press and a computer program for cut register control.
DE 199 36 291 A1 describes a method for determining the positions of cuts of part webs of a longitudinally cut printing material web in a web-fed rotary press, in which the part webs are combined into strands, these are each folded on a former and are finally crosscut by a knife cylinder. In a departure from the aforementioned document, here the cut individual web halves are designated part webs and the cut webs combined after the former are designated strands. The positions of the cuts determined are used to control the cut register, a dedicated control loop being provided for each part web and, in addition, an outer control loop for the already folded strand. The intention is to make it possible to keep the positions of the cuts of all the part webs of each folded strand at a desired value in each case.
Such a control system with a cascade structure is complicated and in particular requires a large number of sensors to register the actual values of the positions of the cut on the individual part webs and also on each folded strand. This is not only costly but as the number of sensors used rises, the probability of failure of the cut register control also increases, since failures of automated systems are generally caused to a predominant extent by sensor failures.
Furthermore, the position of the cut after the folding can be registered with conventional optical means only by using a mark on the respective outer part web of each strand. A displacement of the position of the cut of the inner part webs between the folding former and the knife cylinder can no longer be measured, for which reason the aforesaid cascade control system of the position of the cut of a strand is based on the assumption that a displacement of the position of the cut taking place after the folding has the same extent in all part webs of a folded strand.
An object of the present invention is to provide a method for controlling the cut register in a web-fed rotary press that minimizes the cut register error, i.e., the deviation of the position of the cut from a predefined desired value, in the most simple, cost-effective and reliable manner with high accuracy.
The object is achieved by a method and a computer program for controlling a cut register in a web-fed rotary press, wherein a plurality of printing material webs are combined into one strand which is cross cut and folded in the web-fed rotary press, the method comprising the steps of measuring a position of a cut register mark on a printed material web and thereby registering an actual value measurement of the position of the cut register mark on the printed material web, using the registered position in a control loop as an actual value of the positions of the cut register mark for cut register control, and correcting, in the control loop, a first set value of a cut register setting element assigned to the printing material web based on a mathematical model to approximately compensate for an error contribution of a proportion of the path of the printing material web that is not registered by the actual value measurement. The first set value is the value necessary to achieve a control difference of zero and the control difference is the difference between the measured actual value of the position of the cut and a desired value of the position of the cut.
The object is also achieved by a method and a computer program for controlling a cut register in a web-fed rotary press, wherein a plurality of printing material webs are combined into one strand which is cross cut and folded in the web-fed rotary press, the method comprising the steps of measuring a position of a cut register mark on a first printed material web of the plurality of printed material webs and registering the actual value measurement of the position of the printing cut register mark on the first printed material web, using the measured position of the cut register mark in a control loop as an actual value of the position of the cut register mark for cut register control of the first printing material web, and calculating, from the registered position of the cut register mark, the actual value of a second printing material web of the plurality of printing material webs for the cut register control of the second printing material web based on a mathematical model which takes into account the differences in the paths of the plurality of printing material webs through the press.
A first basic embodiment of the invention is based on the finding that, in a web-fed rotary press, the contribution of the turner unit and the folding unit to the cut register error, therefore to the displacement of the position of the cut with respect to its desired position, in relation to the contribution of the other units of the press, can be predicted. In particular in the controlled case it can be assumed that the contribution to the cut register error arising in the aforesaid units has approximately a fixed relationship with the contributions arising in the other units of the press.
At least on the webs located in the interior of a strand, for the last time shortly before the combining to form a strand at the start of the folding unit, the position of a cut register mark can be measured. According to the present invention, therefore, by using a measured value registered at this point of the position of a cut register mark, the position of a cut of a printing material web or part web with which the measured value is associated is predicted, to approximately simulate the behaviour of a fictional control loop in which the actual value for forming the control difference for each web would have been registered directly on the knife cylinder.
To this end, when determining the set value of a cut register setting element assigned to a printing material web, that set value which would be necessary in order to achieve a control difference of zero between a measured actual value associated with the respective printing material web and a predefined desired value of the position of the cut is corrected on the basis of a mathematical model for the error contribution of a proportion of the path of the printing material web in the press that is not registered by the actual value measurement, such that the aforesaid error contribution is at least approximately compensated for. This set value is also called the first set value in the following text. In this case, a linear relationship between the registered and the non-registered error contribution is primarily suitable for the mathematical model.
A preferred procedure consists in correcting the control difference of a respective cut register control loop, resulting on the basis of the aforesaid measured value, in that, in the respective control loop, a control correction value is added to the control difference between the measured actual value and a predefined desired value of the position of the cut, the said value being calculated by multiplying the difference between the uncorrected control difference and a corrective term, derived from the instantaneous set value of the cut register setting element, with a fixed correction factor.
Such a correction can be carried out very simply in signal processing terms and, therefore, as compared with a cut register control system in which the position of a cut register mark before the formation of the strand is controlled without taking any account of the subsequent influence of the folding unit on the position of the cut, is associated with only a very small additional expenditure on operations. In particular, it requires no additional sensors for measuring the position of a cut register mark on the outer web of an already folded strand.
On the assumption that the disruptive effects which cause the cut register error in each case supply an amount per unit length of the path which is approximately constant on average within the individual units of a press, there is a functional relationship between the error contributions of the individual units, which incorporate the lengths of the paths of the printing material within the individual units. Given the same error contribution per unit length in the aforesaid machine, the error contribution of each unit is proportional to the path length of the printing material in the respective unit.
Therefore, a preferred embodiment of the invention provides for the value of the correction factor to depend on the ratio of the path length of the printing material web between the measurement location of the cut register mark and the location of the cross-cut and the path length of the printing material web between the press unit and the measurement location of the cut register mark, and preferably corresponds at least approximately to this ratio. The aforesaid path lengths in each press are known, as technical specification data.
The subtraction of a corrective term is used for the purpose of ensuring a stable response of the control loop in spite of the manipulation of the control difference. To this end, the corrective term used is the difference between the instantaneous set value of the cut register setting element and a reference value, an expedient reference value being the set value of the cut register setting element at which, following the last change in the predefined desired value, the control difference reached the value zero for the first time. This criterion for defining the reference value can be evaluated automatically without difficulty. In addition, the operations for forming the corrective term require only little additional effort.
The cut register setting element used can be the press unit in which the printing material is printed, in that the rotational speed of the impression cylinders is changed for some time in order to adjust the cut register. However, the method according to the invention can be applied equally well to presses in which setting elements of another type are provided on their own or in addition to the press unit for the purpose of cut register setting. In the event of a change in the rotational speed of the impression cylinders of a press unit, it is expedient to change the rotational speed of the driven cylinders of all the following clamping points of the printing material web originating from this press unit simultaneously in such a way that, overall, the result is the same change in the circumferential speed. This achieves the situation where the adjustment of the cut register is propagated substantially more quickly then at the web running speed, specifically at approximately the speed of sound in the printing material, which shortens the reaction time of the respective cut register control loop enormously.
In a press, generally, the invention permits compensation for an unmeasured contribution to the cut register error. This in no way relates just to the folding unit but in particular also to the turner unit. In the case of application to the turner unit, the cut register setting of a turned part web with respect to a straight-ahead part web originating from the same printing material web is corrected on the basis of a mathematical model for the error contribution of the additional path of the turned part web in the turner unit. In this way, separate measurement and control of the turned part web is rendered superfluous, which represents a considerable saving in effort. For the error contribution of the additional path of the turned part web, a linear model is primarily suitable.
The invention can also be used in a folding unit having a plurality of former levels. In this case, the correction of the cut register setting of a printing material web depends on the former level at which the printing material web runs into the folding unit.
A second basic embodiment of the invention is based on the finding that, in a web-fed rotary press, given knowledge of the exact cut register error of a single printing material web, conclusions about the cut register error of the other webs are possible by using the courses of the paths of the various webs, that is to say, by using the measurement of the cut register error of a single web, those of the other webs are predictable with a certain accuracy, which is sufficient in many cases, on the basis of a mathematical model.
Such a mathematical model preferably incorporates the different path lengths of the individual webs as parameters, to be specific, in the simplest case, in the form of a linear relationship between the cut register error of the measured web and that of another, unmeasured web.
The use of the press unit as a cut register setting element and taking account of the former level in relation to a correction of the respective set value of the cut register is possible in the same way in the second basic embodiment of the invention as in the first embodiment.
The particular advantage of the second basic embodiment of the invention is that it requires very little effort and can therefore be implemented cost-effectively, since it needs only a single cut mark sensor with associated signal processing electronics for the entire press, which, as compared with the cut mark measurement on each individual web or part web, means an enormous reduction in the scope of the sensors and the signal processing electronics connected downstream, and therefore an enormous saving in costs. It goes without saying that, with the omission of an individual measurement on each web, a potential greater residual error has to be accepted. For applications which do not have excessively high accuracy requirements, the accuracy of the control can, however, nevertheless be sufficient.
A further embodiment of the present invention is based on the finding that, given a constant operating speed of a press, the position of a cut remains virtually constant and therefore, for a predefined speed, a sufficient accuracy of the position of the cut can even be achieved with a static setting of the cut register, that is to say in theory even without cut register control. In the case of speed changes, that is to say in particular when running up from the setup speed to the continuous printing speed and when returning to the setup speed in the course of running down the printing operation, a comparatively large dynamic cut register error occurs. However, for a predefined time curve of the operating speed, this dynamic cut register error has a characteristic time curve, which can be reproduced well given otherwise constant operating parameters of the press.
According to the invention, therefore, in addition to the cut register control explained, a predetermined speed function, which describes a time variation of the operating speed of the press starting from a predetermined initial value, is assigned a cut register function which describes a time variation of a further set value of the cut register. In the event of a variation in the operating speed of the press according to the predetermined speed function, this second set value of the cut register is changed continuously and synchronously in accordance with the associated cut register function. In this case, the cut register function is chosen empirically such that it counteracts a change in the actual value of the cut position as a result of the change in the operating speed. The second set value is available to the cut register control system to determine the first set value, so that part of the control error determined can already be compensated for in advance. Consequently, according to this embodiment of the invention, only a residual error has to be corrected by means of the first set value, as a result of which faster cut register control is available.
On the assumption that a press represents an approximately linear system in relation to the cut register, the cut register function used can be the negative value of a function which describes the time variation of the actual value of the cut position with respect to the value present at the predetermined initial value of the operating speed of the press for the case in which a variation in the operating speed is carried out in accordance with the predetermined speed function, keeping the set value of the cut register constant.
Such a function can be determined by measurements, for example by the operating speed being changed in accordance with the speed function of interest for the real operation and, in the process, the actual value of the cut position with a constant cut register setting being measured by measurements, either manually by using sample copies removed or by sensors using suitable marks on the printing material. For the purpose of simplification, a mathematical approximation function for the curve determined by measurement can then be used as a cut register function.
In this case, it is advantageous to store at least some of the parameters of such an approximation function in a memory in such a way that they can be indicated to the operator of the press and can be changed manually by the operator to provide the possibility that, given the occurrence of a drift of the cut position in the course of successive printing processes, suitable adaptation of the cut register function can be carried out. The use of a mathematical approximation function, whose shape can be varied by a few adjustable parameters, is of great advantage from this point of view.
It is typical of the real printing operation that a variation in the operating speed does not run irregularly or randomly but that the time curve of the speed is subdivided into various characteristic sections. These sections are then also assigned characteristic sections of the cut register function.
In particular, a real speed function generally starts from a phase of constant initial speed, which is followed successively by a rise in the speed with a constant rate of rise, constancy of the speed over an interval of variable length but predetermined minimum length, and a fall in the speed at a constant rate of fall. A phase of constant final speed generally terminates the speed function.
In this case, the associated cut register function has a constant first value during the constant starting phase of the speed function. During the constant phase of higher speed, it reaches a constant second value. In the rise phase of the speed, the cut register function has a curved course, which can contain a maximum whose magnitude exceeds the constant second value. This results from a characteristic peak in the cut register error, which is to be observed in the case of a linear rise in the speed in the case of a constant cut register setting.
The cut register function belonging to the speed function previously described, which has a constant first value during the constant starting phase of the speed function, not only reaches a constant second value during the constant phase of higher speed but also a constant third value during the constant end phase of the speed. In the phase of falling speed between the constant second value and the constant third value, it then runs approximately linearly.
If a press has a number of setting elements for cut register setting, as is the case in newspaper presses, in which a number of webs printed simultaneously are combined to form a single product, then each of these setting elements can be assigned an individual cut register function, to compensate for different effects of a speed change of the machine as a result of different web guidance and path lengths of the individual webs or the part webs and strands produced therefrom by longitudinal cutting and folding within the context of what is possible.
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:
A brief overview of the path of a printing material in a press is shown in
The web 2, like the webs coming from the other press units, is first of all cut longitudinally into two part webs 3A and 3B. Only one part web 3B of the two part webs 3A and 3B is turned in a turner unit 4, before the two part webs 3A and 3B are combined with other part webs coming from other press units but not illustrated to form a strand 5 and the latter is folded at a former 6. As a result of the folding at the former 6, the strand 5 is rotated through 90° and then runs to a knife cylinder 7, where it is cross-cut into individual sections. In the process, the position of the cut has to be coordinated with the position of the printed image, to maintain a constant, predetermined spacing of the printed image from the cut edges in the longitudinal direction.
To set the cut register, i.e., position the cut in relation to the printed image, the web 2 or the part webs 3A, 3B and, if appropriate, also the strand 5, is/are guided over transversely displaceable rolls, with the aid of which the path length to be run through from the press unit 1 as far as the knife cylinder 7 can be varied specifically. Another possibility is to adjust the rotational angle of the impression cylinders of the press unit 1 by temporarily adjusting the speed, to displace the printed image with respect to the position of the cut with a constant path length from the press unit 1 to the knife cylinder 7. The latter type of adjustment has the advantage that additional cut register setting elements are not needed for all the part webs but only for the part webs turned in the turner unit 4. The applicability of the method according to the invention specifically does not depend on the type of setting elements with which the cut register setting is implemented but, in the following text, the use of the press unit 1 for cut register setting will be assumed.
In order to control the cut register, before running into the folding unit, that is to say before the combining of the part webs to form a strand 5, an optical sensor 8 which registers the position of a cut register mark on the part web 3A, 3B is provided for each part web 3A, 3B. For example, the knife cylinder 7 can be equipped with an incremental encoder which supplies a clock signal having a predetermined number of pulses and one reference pulse per revolution of the knife cylinder. In this case, when the cut register mark occurs at the sensor 8, the number of such pulses generated up to that point since the last reference pulse can be used as a measure of the position of the cut register mark. A position of the cut register mark measured in this way represents a measure of the actual value of the position of the cut, that is to say of the spacing to be expected of the cut from the mark, and can be used to control the cut register of the respective printing material web.
The path of the printing material web 2 or the part webs 3A, 3B cut therefrom from the press unit 1 as well as the location of the cut register measurement by the sensor 8 is marked as L1 in
It goes without saying that, if the measured signal M from the sensor 8 is used as an actual value of the position of the cut in a control loop for cut register control, a systematic error is perpetrated, in that the contribution of the portion L2 of the path to the cut register error is not taken into account. Since the path L2 in practice quite possibly has a similar length to the path L1, the effectiveness of such cut register control is necessarily restricted from the start.
The procedure according to the invention for improving the cut register control on the basis of registering an actual value before the folding unit corresponding to
In
The portion L1 of the path is followed by the portion L2 of the path in the folding unit. In
In a conventional control loop for cut register control, the measured value M registered by the sensor 8 is subtracted from the desired value W of the position of the cut, which can be set by the printer, and the control difference D formed in this way is supplied to a controller having the transfer function R(p). In this case, the aforesaid desired value W is the position of the cut register mark on the measured printing material part web 3 in relation to the rotational angle position of the knife cylinder 7. The control correction value KW which, according to
It is clear that the conventional control loop described above is aimed at maintaining agreement between the measured value M and the desired value W, so that the error of the actual distance Y between the cut register mark and the cut on the knife cylinder 7 is determined substantially by the contribution of the disturbance Z2 of the portion L2 of the path. In practice, however, the portion L2 of the path is of the same order of magnitude as the portion L1 of the path, and this is also true of the respective disturbance contributions Z1 and Z2, so that the effectiveness of the control system overall is definitely in need of improvement.
According to the invention, it is now assumed that the contribution of the portion L2 of the path to the cut register error has a fixed ratio F to that of the portion L1 of the path, and that this ratio F is even given approximately by the length ratio L2/L1. The result of this is that, doing a measurement of Y instead of M, an existing control difference W−Y would be greater overall by the factor 1+L2/L1 than the difference D=W−M. While maintaining the measurement of M, this can be taken into account by using only mathematical additional operations in the control loop, which are represented in the signal flowchart of
Were the control correction value designated KW in
To avoid this, from that proportion of the control difference D which, weighted by the correction factor F=L2/L1, is added to the uncorrected control difference D, the previous change ΔRI of the cut register set value RI is subtracted before the weighting. In this case, the previous change ΔRI means the difference between the current value of RI and a reference value RB, which is the value of RI at the first time at which the measured value M agreed with the desired value W after a change to the desired value W.
In the previous example with L2/L1=1, in a steady state with M=W, RB would equal RI, therefore ΔRI=0. In the event of a disturbance Z1=Z2, after an initial overcontrol of RI on account of KD=2D=−2Z1, a value ΔRI=−2Z1 would be present. Although the overcontrol of the controller would initially cause, as previously mentioned, just as large a control difference as the original but with opposite sign, the formation of the difference D−ΔRI before the weighting with the factor L2/L1 would now compensate for the overcontrol of D, so that the build-up of an oscillation in the control loop is prevented. Here, the value ΔRI includes the corrections to the cut register setting RI already carried out by the control loop.
The set value RI of the cut register must also change when the desired value W is changed. However, this does not constitute any reaction of the control loop to disturbances Z1 and Z2, for which reason, after the transient response to a steady state following a change of W, the new value of RI is stored as the reference value RB of the cut register setting for the further control.
As those skilled in the art will know, the preceding stability considerations do not take into account the dynamic characteristics of the transfer elements R(p) and G1(p) involved. To this extent, they are highly simplified and should therefore not be understood as a complete stability analysis of the control loop. Instead, they are in principle intended only to explain the sense in subtracting the corrective term ΔRI.
In order to illustrate a further aspect of the invention,
The printing material web 2 is cut along the length on a longitudinal cutting cylinder 9 into two part webs 3A and 3B, namely a straight-ahead part web 3A and a turned part web 3B. The straight-ahead part web 3A runs directly into the folding unit, while the turned part web 3B is first deflected in the turner unit 4 on turner bars 10, indicated schematically, and is turned as a result before being fed to the folding unit. It is clear that the path of the turned part web 3B in the turner unit 4 is as a result considerably longer than that of the straight-ahead part web 3A, and that the turned part web 3B is subjected to additional frictional forces and, consequently, to greater stretch by the deflection on the turner bars 10.
To measure a cut register mark on the straight-ahead part web 3A, a sensor 8 already shown in
To control the position of the cut of all the part webs, exactly the same number of sensors 8 as part webs and exactly the same number of individual control loops would be needed. However, if the additional contribution to the cut register error experienced by a turned part web 3B in comparison with the associated straight-ahead part web 3A is predictable, then it is sufficient to measure only the position of the cut mark on the straight-ahead part web 3A and to correct the cut register setting of the turned part web 3B in accordance with the aforementioned prediction with respect to that of the straight-ahead part web 3A, in order to achieve adequate accuracy of the position of the cut in both part webs 3A and 3B.
As a rule, it is assumed that the additional stretch of the turned part web 3B in the turner unit 4 has a fixed relationship with the stretch of the straight-ahead part web 3A between the longitudinal cutting cylinder 9 and the sensor 8, so that the aforesaid correction can be carried out simply and, for example, can consist in the addition of a corrective value that is constant or linearly dependent on the cut register setting of the straight-ahead part web 3A.
It goes without saying that different cut register settings for the straight-ahead part web 3A and for the turned part web 3B require separate setting elements for the two part webs. This can be implemented, for example, by the straight-ahead part web 3A being adjusted on its own by means of the impression cylinders of the press unit 1 and, for the correction of the turned part web 3B, a displaceable register roll being provided as an additional adjusting element, by means of which a setting differing from the straight-ahead part web 3A can be made for the turned part web 3B.
If, instead of a sensor 8 and a dedicated control loop for each part web, only a single sensor 8 and a single control loop with correction for each printing material web 2, 12, 22 is needed, then this means overall a considerable reduction in the expenditure on sensors and signal processing technology. This prediction of the additional error contribution of the turner unit 4 in the case of the turned part web 3B can be combined with the previously mentioned prediction of the error contribution of the folding unit in all the part webs, but can also be applied independently of the latter.
Not illustrated by an individual figure is an aspect of the invention which relates to complex folding units having a plurality of former levels following one another. In this case, the extent of the necessary correction of the cut register set value obviously also depends on the former level at which a printing material web or part web runs into the folding unit, so that the former level has to be incorporated in the determination of the correction. In this case, the previously described path-length-dependent correction already takes the former level into account implicitly, in that the path length in the folding unit of course depends on the former level at which a printing material web or part web runs into the folding unit.
A correction depending specifically on the former level can be added both as an additional measure as required to a path-length-dependent correction and also replace such a correction for the purpose of simplification. In the simplest case, a manually adjustable correction value is provided for each former level, which is added to the set value of the cut register of all the printing material webs running over the respective former level. The former-level-specific correction value could, however, also be chosen in functional dependence on the cut register settings of the printing material webs running over the respective former level. In particular, it could be a linear function of the respective cut register setting.
The action of the method according to the invention is illustrated by
The curve designated ΔY0 shows the time curve of the cut register error which results with the speed profile v when no kind of countermeasures are applied. It can be seen that the error rises nonlinearly during the linear speed rise, flattens out after reaching the phase of constant continuous printing speed and likewise remains at least approximately constant, falls nonlinearly during the linear speed fall and changes into the negative area approximately when the setup speed is reached again.
The curve identified by ΔY1 shows the time curve of the cut register error which results with the speed profile v when a conventional control system with actual value measurement before the folding unit is applied without taking any account of the error contribution of the folding unit. This conventional control system would correspond to a weighting factor F=0 in the illustration of
The curve designated ΔY2 shows the time curve of the cut register error which results with the speed profile v when a control system according to the invention with actual value measurement before the folding unit and account taken of the error contribution of the folding unit by means of a correction according to
The curve identified by ΔY3 shows the time curve of the cut register error which results with the speed profile v when a control system according to the invention with actual value measurement before the folding unit and account taken of the error contribution of the folding unit by means of a correction with a false weighting factor F is applied. In the case of the curve ΔY3, the weighting factor F does not correspond to the ratio L2/L1 of the portions L2 and L1 of the paths of the printing material in the press, but is considerably greater than this ratio, namely twice as large. This means that the curve ΔY3 illustrates the effect of a false configuration of the control loop from
The courses of the curves shown above in
The application of the method according to the invention to the folding unit, as compared with a conventional cut register control system which does not take any account of the folding unit, requires only a little additional effort, which, in the case of a digital implementation of the control loop, is predominantly in the area of programming. The application of the invention to the turner unit even produces a considerable reduction in effort as compared with a conventional cut register control system in which cut register marks are measured on all the part webs.
As opposed to the embodiment of
On the assumption that the turned part web 3B emerging from the printing material web 2 forms the outermost layer of the strand 5, on which the cut register mark registered by the sensor 8′ is printed, the measured mark position can be used directly as actual value of the position of the cut only for the control of the cut register of this part web 3B. However, the total length of the path of the part web 3B from the press unit 1 as far as the knife cylinder 7 is known. The difference in the length of the paths covered by the other part webs in the press from the path length of the part web 3B is also known.
If, to a first approximation, it is assumed that the entire stretch of a part web is proportional to its path length, then, from the cut register error measured on the outer part web 3B with the aid of the sensor 8′, it is possible to predict the cut register error of each other part web in a simple manner, that is to say on the basis of a linear relationship. Thus, the cut register error of the other part web 3A cut from the same web 2 is smaller, since its path is shorter, while the errors of all the other part webs are greater, since the webs 12 and 22 from which these part webs are cut come from press units which are further removed, not illustrated in
Of course, the accuracy of the mathematical model can be increased if required as compared with the linear approach mentioned previously by means of nonlinear terms, for example in the form of a polynomial expression.
In any case, the reduction in the cut register sensors to only a single sensor 8′ on the knife cylinder 7 provides an enormous saving in expenditure on hardware, while the mathematical modeling of the dependence of the cut register error of the unmeasured part webs on the error measured on the part web 3B by the single sensor 8′ lies purely in the area of software and is therefore easily be adapted to different types of presses. To this extent, the embodiment according to
Once the continuous printing speed has been reached, it is maintained in a phase C until a predefined number of printed products has been produced. This phase C is illustrated as highly shortened in
If the cut register control is carried out at the setup speed and then maintained during the variation described above of the speed during the phases B to E, then the result is a cut register error, that is to say a deviation of the position of the cut from its desired value, as shown by the curve 24 in
As long as the setup speed has not yet been left, the cut register error is virtually zero, that is to say, in phase A it is possible to detect only slight fluctuations of the curve 24 close to the zero position. During the rise in the speed in phase B, the cut register error rises sharply, its time curve being distinctly nonlinear and distinctly flattening off as the rise period increases, in spite of the rate of rise of the speed remaining constant.
At the transition from the speed rise to the phase C of constant continuous printing speed, the cut register error falls virtually abruptly by a certain amount to below the value reached at the end of phase B and then remains virtually constant during phase C, apart from slight fluctuations which are comparable with those in phase A. As mentioned previously, the phase C is illustrated as highly shortened in
If the speed is reduced in phase D at a constant rate of fall, starting from the constant value of phase C, then the cut register error likewise falls but by no means inversely with respect to its course during the rise in speed but substantially faster. Here, even the zero line is undershot and the cut register error reaches a negative value at the end of phase D, of which the magnitude is of the same order of magnitude as the approximately constant positive value in phase C. To a first approximation, the course of the cut register error in phase D can be considered to be linear.
When the speed has reached its end value and is kept constant again in phase E, then initially an abrupt reverse in the magnitude of the cut register error is to be observed, which then again remains virtually constantly at a value which is now negative. This applies even if the end speed corresponds to the initial speed. The press is therefore a time-variant system in relation to the cut register error.
The basic idea of this embodiment of the present invention is based on the fact that the cut register error, which has been set to the value zero in phase A by the operator of the machine, is compensated for, that is to say is kept approximately at the value zero, by varying the cut register setting is varied in accordance with the negative value of the curve 24 previously determined empirically, during the passage through a predefined time curve of the machine speed. This mirroring of the curve 24 on the time axis is illustrated in
Since the curve 24 is doubtless subject to certain stochastic fluctuations, it would not be practical to use the negative measured curve 25 actually to compensate for the cut register error. Instead, the curve 25 is described relatively accurately by a mathematical approximation function, which is defined in clearly distinguishable sections in accordance with the subdivision of curves 23 and 24.
In
In
For the purpose of illustration, the compensation curve 26 for the phases of running up B, of continuous printing C and running down D are illustrated once more on their own in
It should be noted that, for the purpose of the mathematical description of the compensation curve 26, a total of more than the aforementioned parameters are needed if phase B and the initial region of phase C are represented, for example, by two cubic polynomials. The adaptation of all the curve parameters, that is to say all the polynomial coefficients in the case of polynomials, to the aforementioned selectable parameters can, however, be carried out automatically by the open-loop or closed-loop control device of the press in accordance with predefined mathematical rules.
If, by means of control measurements during printing operation, the printer establishes that the compensation action is inadequate in one or more phases, that is to say that, in the case of the compensation curve 26 predefined at the start of printing operation, an impermissibly large cut register error occurs, then he can change one or more of the parameters b1, c1, S, b2 and d2 by manual intervention. This change acts directly on the current printing operation and is stored for the next run of the press as a new shape of the compensation curve 26. In this way, the shape of the compensation curve 26 can be made to track slow time changes in the behaviour of the press if required, that is to say the long-term drift of the dynamic cut register error.
It goes without saying that the duration of the setup phase A and the duration of the end phase E are arbitrary, since the compensation only begins with the entry to phase B and, after the end of phase D, the cut register setting d2×S reached there is no longer changed.
The preceding courses of the curves shown in
The method according to the invention can also be applied when a press is to be operated as desired with various rates of rise and fall of the speed and/or with various continuous printing speeds. In this case, an associated compensation function 26 must be stored for every possible speed curve 23, or that present must be expanded differently.
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.
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