EP3539777B1 - Method and device for correcting the printing position of a printing unit and printing machine - Google Patents

Description

The invention relates to a method for correcting a printing position of a printing unit according to claim 1. Furthermore, the invention relates to a device according to claim 11 and a printing machine according to claim 12.

A printed product, such as a magazine, newspaper or packaging, is usually produced by means of a printing machine. Printing machines are also used for functional printing and decor printing. The printing press has at least one printing unit, which thus represents an assembly or component of the printing press. As a rule, the printing unit comprises a rubber or printing cylinder and often, for example, an inking and / or dampening unit. If the printed product or the printed copy is to be multicolored, so-called multicolor printing is used as the printing process. A color separation takes place in the individual printing inks, since the print image that is to be printed on a substrate in order to create the print product is broken down into basic colors and special colors. Printing machines for multi-color printing therefore generally have a separate printing unit for each printing color. For example, four-color printing is broken down into the colors cyan, magenta, yellow and black. The colors of the print image or the colourfulness of the print image are determined by the composition of the printing inks. In current printing machines, a series construction is often used, that is, the individual printing units are arranged one behind the other.

In order to obtain the highest possible quality of the printed product, the individual colors must be in a fixed, in particular exact, position can be printed one above the other, so that the print image is perceived particularly sharply. Print marks are used in order to be able to measure the position of the printing inks relative to one another. In this way, a so-called register, which is also referred to as a register or color register and describes how the individual colors match in multi-color printing, can be checked. In the case of the aforementioned multicolor printing, the process colors or printing inks are printed one after the other and one above the other and / or next to one another and thus result in the complete print image. If the printing inks are not printed exactly on top of one another and / or next to one another, the printed image appears blurred or blurred or has color shifts which have a quality-reducing effect.

It is said that the print image is in register when the printing inks are exactly on top of each other. If this is not the case, one can speak of a so-called register or register error. If the printing machine is designed as a sheet-fed printing machine, this can arise, for example, from inaccurate transport of the sheet of printing material through the printing machine. Registration problems can also occur, for example, in a web press. In order to bring the print image into the register, a register control is used, for which additional information, the print mark, is applied to the printing material by each printing unit. With the help of the respective print mark, the position of the individual print images printed in the respective color can be determined. For each print copy, a so-called brand field is printed which contains the individual print marks. In each mark field, the offset of the individual print marks in the longitudinal and / or lateral direction is measured by a sensor unit. As a rule, an error is now calculated from a target position and an actual position of the print mark, which is corrected. By arranging the individual printing units, for example in a row, in the printing machine For example, the distance between the sensor unit and a respective printing unit can be particularly large, in particular if only one sensor unit is arranged after the last printing unit. This is referred to as a so-called end-of-line arrangement, with particularly large distances between the printing unit, i.e. the control point, and the sensor unit, i.e. the measuring point. By the time a copy of the printed product that was printed in the printing unit reaches the sensor unit, a number of further printed copies have usually already been printed by the printing unit, which are then measured by the sensor unit in the order in which they were printed. This means that the correction carried out is not yet visible in the next measurements of the position of the print mark by the sensor unit.

If no additional measures are now taken to carry out the register control, the error that has already been corrected would be corrected again, which leads to an overshoot or instabilities in the control.

The prior art discloses two ways in which the problem is solved. In the first variant or the first type, no further correction is carried out until the printed copy with the correction has arrived at the measuring point or the sensor unit. In the second type, a gain of the controller is reduced, so that a correction value, which regulates the print position of the print image in the printing unit, is calculated, which is smaller than the actual register error. The two mentioned measures used in the prior art, however, have the disadvantage that there is a particularly sluggish control behavior, which in particular becomes more sluggish the greater the distance between the printing unit and the sensor unit, i.e. between the printing point and the measuring point, becomes.

The US patent application US 2006/0236885 A1 shows a method for applying a register-keeping pattern to a continuous material web. A position is adjusted transversely to the web and the pattern is rotated so that it lies essentially along the longitudinal course of the web. As a result, patterns are applied to the web in register and follow an uneven web course.

It is therefore the object of the present invention to provide a method and a device by means of which register regulation can be carried out in a particularly advantageous manner and thus print images of particularly high quality can be realized.

According to the invention, this object is achieved by a method and a device having the features of the independent patent claims. Advantageous refinements with expedient developments of the invention are specified in the remaining claims.

A first aspect of the invention relates to a method for correcting a printing position of a printing unit. The printing unit is a component or part of a printing machine that has at least one sensor unit. The printing machine can, for example, produce a printed product by means of flexographic printing, gravure printing, screen printing, digital printing or offset printing. The printing press can be, for example, both a printing press for roll printing and a printing press for sheet-fed printing. In principle, the printing press can be any printing press.

In order to be able to correct the printing position of a printing unit, that is to say the position of a printed image or print motif, on a printing material in order to generate a printed copy or a printed product, the method comprises several steps:
In a first step or method step, an actual position of at least one print mark printed on the printing material by means of the printing unit is detected by means of the sensor unit. This means that the sensor unit is designed, for example by means of a sensor, to detect the actual position of the printed print mark on the printing material. In a second step of the method, a deviation of the recorded actual position from a target position is determined. In other words, the deviation equals one Offset, in particular in the longitudinal direction and / or transverse direction, of the actual position of the print mark to the position required, in particular for a particularly high quality of the print product. In a third step of the method, at least one difference value characterizing the deviation is determined. This difference value can be, for example, a distance between the target position and the actual position. In addition to the distance, that is to say the length of the distance, the difference value can have a directional value, for example. For example, the difference value can also be represented as a vector, the amount of which is the distance between the setpoint and actual position. In a fourth step or method step, a buffer value is determined from a number of support values previously stored in a memory.

The memory is, for example, a memory area of an electronic computing device in which a plurality of values, in particular support values, can or can be stored. When the method is carried out for the first time, that is to say when it is carried out for the first time, the supporting values stored in the memory are each determined individually to be zero, for example. The first implementation of the method can be carried out, for example, when a pressure is started or the like. The memory is preferably designed as a buffer memory, that is, it is used for intermediate storage of the support values and not for permanent storage of the support values. In a fifth step of the method, a correction value is determined by subtracting the buffer value from the difference value. In a sixth step, the determined correction value is stored as one of the supporting values in the memory, that is to say the correction value is stored in the memory so that it can be used when the method is carried out again for forming or determining the buffer value. Finally, in a seventh step of the method, the printing position is corrected on the basis of the correction value determined. This means that the printing unit is manipulated in such a way that the print position of the print image to be printed is on the Printing substrate is changed, in particular in such a way that the actual position was changed by at least the correction value for a future print. This changes a control difference which reflects the difference between the target position and the currently measured actual position.

In other words, it can be achieved by means of the described method that each individual measured value of the respective actual position detected by the sensor unit can be used for correction and thus a respective register correction can be carried out for each printed copy. For this purpose, the current correction value determined when the method is carried out is entered in the memory. When the method is carried out again, the current system deviation and the correction already in the route can be taken into account when determining or calculating the new, more current correction value. The distance is to be understood as the path between the printing unit and the sensor unit, whereby the "correction in the path" is to be understood as the at least one former correction value stored in the memory as a reference value.

The respective support value is formed from a previous correction value determined in a previous implementation of the method. That is, if the method according to the invention is carried out at least a second time, for example, the correction value of the first execution becomes the support value of the second execution. If the method is repeated so often that the number of repetitions corresponds to the number of support values stored in the memory, the memory is completely filled with support values which are each formed from a correction value from one of the previous implementations of the method. An initialization of the support values with a predetermined value each, for example in the case of a new print job, is used to carry out the method until the support values can each be formed from a correction value.

With the method described, each actual position detected by the sensor unit can be used for register control and thus for correction. As a result, the register correction, that is to say the correction of the printing position, can be carried out for each printed copy, that is to say for each individual printed product that is printed by the printing unit and conveyed or moved by the printing machine to the sensor.

Due to the distance between the printing unit and the sensor unit, a so-called dead time, which is also called the running or transport time, occurs between the printing of the print mark and the detection of the same. Since the dead time depends on the known distance between the printing unit and the sensor unit, it can also be referred to as dead travel. Due to the dead travel, a correction that has already been carried out is not yet visible in the currently recorded actual position. However, this correction or the associated correction value is entered in the memory. If the method is now carried out again, the at least one current correction value of the correction carried out is taken into account when a new correction value is determined. For example, the correction can be carried out in a certain area so that the correction does not falsify the print marks.

By means of the method according to the invention, a particularly advantageous register control for correcting the printing position of the printing unit can be implemented, in particular in the case of large distances between the printing unit and the sensor unit. The register control can work particularly dynamically and stably, which means that, for example, overshoots can be avoided.

In an advantageous embodiment of the invention, the reference value stored in the memory for the longest time in relation to the support values stored in the memory is deleted from the memory and replaced by the correction value determined. As already mentioned, the first time the Method each have support values initialized to zero. The storage locations in the memory, that is to say the areas in which a reference value is or can be stored, also have a fixed reference with regard to a time sequence. Thus, the support values, which are each formed from an old correction value or correspond to it, can be read out from the memory in such a way that the chronological sequence of their entry into the memory can be recognized. If a first correction value is now entered in the memory as a new reference value, the correction value which was last entered, before the first correction value, moves from a first memory location to a second memory location. A correction value, which is in the last memory location, is deleted from the memory or removed and occupied by the reference value of the penultimate memory location, which becomes the last reference value of the memory when the new reference value is entered. By deleting or shifting the support value stored in the memory for the longest time and adding the currently determined correction value as a new support value, a current number of support values can be stored in the memory, which in particular consists of respective correction values, which in each case when the inventive Method generated, are held so that the correction of the printing position can be carried out particularly efficiently and / or particularly precisely. If the process has been repeated so often that the number of repetitions corresponds to the number of memory locations in the memory, the memory is completely filled with the most recent reference values.

In an advantageous embodiment of the invention, the memory, which can also be referred to as a buffer, is designed as a shift register. In a shift register, the number of available memory locations in which a reference value can be stored is constant. Each time the shift register is written to, a reference value is shifted one memory location further, so that the first or stored single value leaves the memory first. Pushing in and out, or reading in and reading out, usually take place synchronously. By using the shift register as a memory when performing the method, the method can be carried out in a particularly advantageous manner, since the respective correction values entered as support values in the memory or shift register can be used particularly easily to determine the respective current correction value.

In an advantageous embodiment of the invention, the number of support values stored in the memory is determined by a distance between a print location of the print mark in the printing unit and a read-out position of the sensor unit. This number is also determined by the format length of the printing material. The number is advantageously the rounded quotient of the distance and the format length. The format length is the length which the printing material has along the direction in which the printing material can be or is transported through the printing machine and in particular through the printing unit. In other words, the number of supporting values stored in the memory corresponds to the number of the following print copies: the print copy whose print mark is detected at a point in time by means of the sensor unit, the print copy which is printed at that point in time by means of the printing unit and the print copy or copies which is or are located in the printing machine at the time and was or were already being printed by means of the printing unit at the time, but not yet detected by means of the sensor unit. The current correction value can be calculated particularly dynamically through the number of said printed copies, which corresponds to the number of support values stored in the memory. Furthermore, an overshoot can be avoided, for example, since the control difference, the difference between the target position and the actual position, is due to the dead time or the dead path can be compensated for by the number of supporting values held, or the supporting values are taken into account when correcting the printing unit. In particular, the number of print copies that have already been printed, but whose respective print mark has not yet been recorded, is to be understood as such that, with continuous operation of the printing machine, corresponds to the number of print copies that are currently moving from the printing unit, for example by means of a conveyor, on the way to the sensor unit.

In an advantageous embodiment of the invention, several actual positions of the respective print marks printed on respective printing materials by means of the printing unit are detected by means of the sensor unit, an actual position mean value being formed from the several actual positions and the difference value using the actual position Mean value is determined. In other words, the actual position is smoothed or averaged. Alternatively, several actual positions of respective print marks printed on respective printing materials by means of the printing unit are detected by means of the sensor unit. The respective deviations of the recorded actual positions from those of the target positions are determined, with respective deviation values characterizing the respective deviations being determined. The difference value that is used to form the correction value can be determined from the actual position mean value or from the mean value of the deviation values. A number of printed copies, from which the actual position mean value or the mean value of the deviation values is formed, can be referred to as a so-called filter depth. The filter depth thus corresponds to the number of actual positions used to form the actual position mean value. By averaging or averaging the actual positions or the deviation values, it is possible, for example, to compensate for a fluctuation, in particular metrological, when the actual position is recorded.

In an advantageous embodiment of the invention, the number of support values stored in the memory corresponds to the sum of a first number and a second number. The first number is determined by the distance between the printing location and the readout position and / or the format length of the printing material. The first number is advantageously the rounded quotient of the distance and the format length. The second number corresponds to the number of actual positions used to form the actual position mean value and thus the filter depth. In other words, the number of support values stored in the memory corresponds to the sum of a first number and a second number. The first number is the number of the following print copies: the print copy whose print mark is detected at a point in time by means of the sensor unit, the print copy which is printed at the point in time by means of the printing unit and the print copy or copies which are at the point in time is or are located in the printing machine and at that point in time was already being printed by means of the printing unit, but not yet being detected by means of the sensor unit. The second number of the sum, where the sum describes the number of storage locations, corresponds to the number of actual positions used to form the actual position mean value, that is to say the specified filter depth. This is based on the fact that the dead time or the dead path is lengthened in the case of averaging. If the correction of the printing position of the printing unit is regulated with the averaged or smoothed actual position or a specified filter depth and the extended dead path is not taken into account, this can lead to an incorrect calculation of the correction and thus to an unstable behavior of the regulation. By expanding the number of memory locations by the second number, the number of actual positions used to form the actual position mean value, in the memory or shift register, the correction is specified more precisely or the filter depth is taken into account in the correction, so that an unstable behavior of the control can be excluded.

In an advantageous embodiment of the invention, the buffer value is determined as the sum of the support values. This means that the support values stored or stored in the memory, which represent or are in particular the correction values determined at an earlier point in time, that is, when the method was carried out earlier, are added up, whereby the buffer value is formed or determined. By forming the sum and subtracting this sum as a buffer value from the difference value, a current correction value can be determined particularly quickly and, for example, overriding the correction of the printing position of the printing unit can be kept particularly low.

In an advantageous embodiment of the invention, at least one of the supporting values is weighted when determining the sum. That is to say, at least one of the support values is multiplied in particular by a scalar, so that this support value has a particularly large or a particularly small influence on the determination of the correction value compared to the other support values. For example, when using the above-mentioned filter depth and thus expanding the storage locations of the memory by the second number, the last reference values can be weighted. The last support values are to be understood as the support values that have already been passed through the memory so that they are in the last memory locations before leaving the memory, so that the last support values mentioned fall from the memory when a second number of new correction values are entered. That is, if the method is repeated so often that the number of repetitions corresponds to the second number, the mentioned last reference values are removed from the memory, with only the reference value in the last memory location from the memory per execution of the method falls. For example, is the filter depth three, the last reference value can be weighted with 0, the penultimate reference value with 1/3 and the penultimate reference value with 2/3. As a result, the mean value linkage determined by the filter depth can be taken into account in the correction in a particularly advantageous manner.

In an advantageous embodiment of the invention, the sensor unit has a camera sensor and / or fiber optics. By means of the camera sensor, for example, the print mark can be detected in a particularly advantageous manner and, in particular, read out for subsequent processing. Furthermore or alternatively, light which is reflected from the print mark can be guided in a particularly advantageous manner to a suitable sensor of the sensor unit through fiber optics, so that this light can be detected. Furthermore, through the use of fiber optics, the sensor unit can be arranged relatively freely on or in the printing press. As an alternative or in addition, the respective print mark can be detected using other techniques, such as a contrast scanner. The sensor unit should be designed in such a way that it can provide sensor data from which the actual position can be determined or recorded by means of the method according to the invention.

In an advantageous embodiment of the invention, paper and / or cardboard and / or plastic and / or metal and / or wood and / or glass is used as the printing material. The printing material can be designed as a film, for example, which means that the material at least partially forming the printing material, in particular for example plastic and / or metal, is particularly thin. In addition, the method can be used with other materials which are suitable for printing, so that the method can be carried out for a particularly large variety of printing machines and can thus be implemented for a particularly large number of different printed products. Thus, with a large number of printed products, the inventive Method applied and thus the correction of the printing position can be carried out particularly efficiently.

A second aspect of the invention relates to a device for correcting a printing position of a printing unit of a printing machine, with at least one electronic computing device, which is designed to determine an actual position of at least one print mark printed on a printing material by means of the printing unit using sensor data which is received by a sensor unit are received to capture. Furthermore, the electronic computing device is designed to calculate a deviation of the recorded actual position from a target position, at least one difference value characterizing the deviation, a buffer value from a number of support values previously stored in a memory and a correction value by subtracting the buffer value from the To determine the difference value. Furthermore, the electronic computing device is designed to store the correction value as one of the support values in a memory and to provide a signal for correcting the printing position based on the determined correction value, the printing position of the printing unit being able to be corrected by means of the signal.

A third aspect of the invention relates to a printing press which comprises a device according to the invention for correcting a printing position of a printing unit.

Advantages and advantageous configurations of the first aspect of the invention are to be regarded as advantages and advantageous configurations of the second and / or third aspect of the invention and vice versa.

• FIG 1 eine schematische Ansicht einer Druckmaschine, welche eine Sensoreinheit und wenigstens ein Druckwerk aufweist; und
• FIG 2 ein schematisches Ablaufdiagramm eines Ausführungsbeispiels eines Verfahrens zum Korrigieren einer Druckposition wenigstens eines der Druckwerke der Druckmaschine.

Exemplary embodiments of the invention are explained in more detail below with the aid of schematic drawings. It shows:

• FIG 1 a schematic view of a printing machine which has a sensor unit and at least one printing unit; and
• FIG 2 a schematic flow diagram of an embodiment of a method for correcting a printing position of at least one of the printing units of the printing press.

FIG 1 shows a schematic view of a printing press 10, which has a sensor unit 12 and at least one printing unit 14. In particular in multicolor printing, in which a print image is broken down into basic colors, with each printing unit 14 printing one of the basic colors on a printing material 16, so-called register errors can occur. In the event of a register error, the individual printing inks are not exactly on top of one another, so that the finished printed copy or printed product appears, for example, blurred. By means of the method presented, the register error can be compensated for particularly dynamically and thus efficiently, whereby the print image and thus the finished print copy or its individual colors are in register.

The method for correcting the printing position of the, in particular the respective, printing unit 14 of the printing press 10 having at least the sensor unit 12 comprises several steps:
In a first step of the method, an actual position of at least one print mark 18 printed on the printing material 16 by means of the printing unit 14 is detected by means of the sensor unit 12. In a second step, a deviation of the recorded actual position from a target position is determined. In a third step, at least one difference value characterizing the deviation is determined. In a fourth step, a buffer value is determined from a number or a plurality of support values 22 previously stored in a memory 20. In a fifth step, a correction value is determined by subtracting the buffer value from the difference value. In a sixth step, the correction value determined in the fifth step is stored as one of the support values 22 in the memory. In a seventh In step 14, the printing position of the printing unit 14 is corrected on the basis of the correction value determined.

The printing machine 10 can, for example, print on packaging using what is known as flexographic printing. In addition, the printing machine 10 can also be a printing machine which is designed for offset printing. Furthermore, the printing material 16 or the printing materials 16 can be printed by means of, for example, roller printing or sheet printing. In order to be able to print the printing material 16 in a particularly advantageous manner, the respective printing unit 14 advantageously has at least one printing cylinder 24 in each case. Depending on the type of printing process or the printing press 10, the respective printing unit 14 can have, for example, a print head instead of the printing cylinder 24, as can be the case, for example, in digital printing.

The respective printing ink can be applied to the printing material 16 in a particularly advantageous manner by means of the respective printing cylinder 24 of the respective printing unit 14. The printing material 16 is advantageously paper and / or cardboard and / or plastic and / or metal, as a result of which a particularly large variety of different printed products can be produced by means of the printing machine 10. In the exemplary embodiment shown, the printing press 10 has two printing units 14 arranged one after the other. One form of multicolor printing is so-called four-color printing, in which the colors cyan, magenta, yellow and black are used in particular to produce colored printed products. In the case of four-color printing, four printing units 14 would thus be provided; for the sake of simplicity, FIG FIG 1 however, only two printing units 14 are shown. In the method, the number of printing units 14 of the printing press 10 can be freely selected. The sensor unit 12 advantageously has a camera sensor and / or fiber optics, as a result of which the respective print mark 18 can be or can be detected particularly easily by the sensor unit 12.

Furthermore shows FIG 1 that a distance between the printing units 14 and the sensor unit 12 is a certain length. This length can, for example, as in FIG 1 shown, the length of two printing materials 16 are. This leads to a dead time, that is to say the print mark 18, which is detected by the sensor unit 12 at a first point in time, was already printed at an earlier second point in time. The other way around, the print mark 18 printed at the first point in time is only detected by the sensor unit 12 at a later third point in time. The interval between the point in time and the second or third point in time is called the dead time. This can also be interpreted or understood as a dead path. So run in the printing press 10 of the FIG 1 the printing materials 16 to be printed are lined up from the left, first via the first printing unit 14 and then via the second printing unit 14 and finally arrive at the sensor unit 12 one after the other and thus one after the other. In the embodiment shown, a print copy 26 is between the last printing printing unit 14 (the right printing unit 14 of the FIG 1 ) and the sensor unit 12 in the printing press 10. This means that by the time the sensor unit 12 gets to see a printed copy 26 or the printing material 16, which was printed by the last printing unit 14, two further printed copies 26 have already been printed by this printing unit 14.

The respective print mark 18 can, as shown in the example, be formed from individual rectangles or triangles, with at least one rectangle or at least one triangle being provided for each color to be printed. The method is fundamentally independent of the expression of the print marks 18. For the process, measured values only need to be available at a defined point in time. In the exemplary embodiment, the last printing unit 14 is designed to be used in the FIG 1 left triangle of print mark 18 to print. Alternatively or additionally, in particular depending on the type of sensor unit 12, the print marks for example, dots in the respective printing color. For fiber-optic detection of the print mark, the rectangular and triangular design of the print marks 18 or the mark fields has become established, so that these are designed as wedge or block marks, whereas so-called point marks are often used for camera-based sensor units 12.

FIG 2 shows a schematic flowchart of an embodiment of the method for correcting the printing position of the, in particular the respective, printing unit 14 of the printing press 10. The memory 20 is advantageously designed as a shift register so that a support value written into the memory 20 when a further support value 22 is added again by the memory or shift register is passed and leaves it after reaching a last memory position of the memory 20. By using a shift register, a fixed time reference of the support value 22 to the respective acquisition time, for example the first time, can be established in a particularly simple manner, whereby a time sequence of the support values 22 in the memory 20 can be realized. Thus, in a particularly advantageous manner, the support value 22 stored in the memory 20 for the longest time in relation to the support values 22 stored in the memory 20 can be deleted from the memory and replaced by the correction value determined by the current repetition of the method as the new or current support value 22 . In particular, by designing the memory 20 as a shift register, there is an association between one of the memory positions and a time sequence of the repetitions of the method.

In the schematic representation of the process, which in FIG 2 is shown, the respective individual print copies 26 or printing materials 16 coming from the right are successively printed by the printing unit 14 and then the print marks 18 are printed by the sensor unit 12 recorded. The sawtooth-like line 27 indicates the respective position of a guide axis of the printing unit 14 or of the printing cylinder 24. This means that after one complete revolution of the pressure cylinder 24, the guide axis has returned to its original position.

The method is carried out for the first time when the first print copy 26 or its print mark 18 is detected by the sensor unit 12. The memory 20, the memory size 28 of which in the example shown comprises a number of three memory locations, which is represented by the left curly brackets, corresponds to the number which is specified, among other things, by the distance or the dead travel between the printing unit 14 and the sensor unit 12. The number is determined by the number of the following print copies 26, 30, 32: the print copy 26, the print mark 18 of which is detected at a point in time by the sensor unit 12, the further print copy 30 which is printed at the point in time by the printing unit 14 and the printed copy 32 or the printed copies 32, which is or are located in the printing machine 10 at the time and was or were already being printed by the printing unit 14 at the time, but not yet detected by the sensor unit 12. In other words, the number of support values 22 stored in the memory is determined by a distance 42 between a printing location of the printing mark 18 in the printing unit 14 and a read-out position of the sensor unit 12. This number is also determined by a format length 40 of the printing material. The number is the rounded up quotient from the distance 42 and the format length 40.

A time axis 34 is defined with respect to the line 27, which determines the position of the master axis. The position of the master axis is shown in a second axis 36 perpendicular thereto. Thus, at the first point in time ZP1, the first print mark of the first print copy 26 is recorded, with the support values 22 of the memory all being 0 at this point in time are set. This represents the first step of the method, which in the example shown is carried out at time ZP1. This is followed in the second step by determining the deviation of the detected measurement position of the print mark 18 from the target position. In the third step, a difference value characterizing the deviation is determined from this deviation. In the next fourth step, a buffer value is determined from a number of support values 22 previously stored in memory 20. When the method is carried out for the first time, in which the memory 20 is in the state V1, the buffer value is 0, since no correction has yet been carried out before the method was carried out for the first time. In a next fifth step of the method, the correction value is formed from the buffer value by subtracting the buffer value from the difference value. Then, in the sixth step of the method, the determined correction value is stored as one of the support values 22 in the memory 20.

At the point in time ZP2, the first correction value KORR1 is stored in the memory and the third print mark 18, that is to say the print mark 18 of the print copy 30, is printed but not yet measured. When the method is carried out again at time ZP3 or immediately after time ZP3, the steps of the method are carried out again, so that at time ZP4, at which the fourth print mark 18 was printed on a further print copy, a new correction value KORR2 is the new one Support value 22 was written or is being written into memory 20. At the point in time ZP5, the third print mark 18, i.e. the print mark of the print copy 30, is measured and the method is carried out again a third time, so that the correction value KORR3 is already entered in the memory 20 at the point in time ZP6, at which a fifth print mark 18 is printed is. At the point in time ZP7, the fourth print mark 18 printed is detected and the method is carried out again, so that at the point in time ZP8, at which the sixth print mark 18 is printed, the fourth correction value KORR4 is entered in memory 20. Here, the memory 20 is filled for the first time with support values 22 formed by earlier implementation of the method and formed from the correction values KORR1 to KORR3, so that the correction value KORR1 written in the memory at time ZP1 or time ZP2 is pushed out of memory area 28. The method is started repeatedly at times ZP9 and ZP11, since the first method step is carried out at the respective time. In each case at time ZP10 or time ZP12, the method is run through completely and a further print mark 18 is printed in each case.

The buffer value is formed from the sum of the support values 22 stored in memory 20 with memory size 28, which are formed from respective correction values (KORRn to KORRn + 2) for a respective implementation of the method. This buffer value, updated each time the method is carried out, is subtracted from the current difference value characterizing the deviation. The memory size 28 is also referred to as the memory depth.

The method can alternatively be carried out in such a way that several actual positions of respective print marks 18 printed on respective printing materials 16 by means of the printing unit 14 are detected by means of the sensor unit 12, an actual position mean value being formed from the several actual positions and the difference value is determined by means of the actual position mean value. For example, with three different printed copies, for example printed copies 26, 30 and 32, the actual positions can first be recorded and averaged and the deviation of the target position from the averaged actual position or the actual position mean value can be determined. In this context, one speaks of a filter depth which, in the example, corresponds to three, that is to say the number of checked print marks 18 used for averaging. Thus the filter depth is equal to the number of the Actual position mean actual positions used. If such a difference value or actual position average value smoothed by the averaging is used in the method or if this is used for the method, the memory size 28, i.e. the number of memory locations that can be kept in the memory 20, is advantageously increased by the number of those for formation actual positions used for the average actual position. Advantageously, the additional support values 22 are weighted and taken into account when determining the buffer value by the sum of the support values 22.

If smoothed deviation values are used, the expanded memory size 28 of the memory 20 designed as a shift register can additionally hold support values 22 which are taken into account by the weighting in the formation of the buffer value. Thus, when correcting the printing position, an incorrect deviation can be avoided, since the dead time or the dead travel is lengthened by the averaging of the actual position average. Thus, the method can regulate print marks 18 in a particularly efficient and / or dynamic manner by means of a memory 20, in particular designed as a shift register, and thus lead to print copies 26, 30, 32 that are qualitatively particularly precisely printed, with a smoothing of the actual position can be carried out.

Claims (12)

1. Method for the correction of a printing position of a printing unit (14) of a printing press (10) which has at least one sensor unit (12), with the steps of:

   - detecting by means of the sensor unit (12) of an actual position of at least one printing mark (18) which is printed onto a printing material (16) by means of a printing unit (14);

   - determining of a deviation of the detected actual position from a setpoint position;

   - determining of at least one differential value which characterizes the deviation;

   - determining of a correction value,

   - correction of the printing position on the basis of the determined correction value,

   characterized by the following steps:

   - determining of a buffer value from a number of basic values (22) which have previously been stored in a memory (20) ;

   - determining of the correction value, by the buffer value being subtracted from the differential value;

   - storing of the determined correction value as one of the basic values (22) in the memory (20).
2. Method according to Claim 1, characterized in that the basic value which has been stored in the memory (20) for the longest time in relation to the basic values (22) which are stored in the memory (20) is deleted from the memory (20) and is replaced by the determined correction value.
3. Method according to Claim 1 or 2, characterized in that the memory (20) is configured as a shift register.
4. Method according to one of the preceding claims, characterized in that the number of basic values (22) which are stored in the memory (20) is determined by way of:

   - a spacing (42) between a printing location of the printing mark in the printing unit and a read-out position of the sensor unit, and/or

   - a format length (40) of the printing material (16).
5. Method according to one of the preceding claims, characterized in that a plurality of actual positions of respective printing marks (18) which are printed onto respective printing materials (16) by means of the printing unit (14) are detected by means of the sensor unit (12), an actual position mean value being formed from the plurality of actual positions, and the differential value being determined by means of the actual position mean value.
6. Method according to Claim 5, characterized in that the number of basic values (22) which are stored in the memory (20) corresponds to the sum of a first number and a second number, the first number being determined by way of:

   - the spacing (42) between the printing location and the read-out position, and/or

   - the format length (40) of the printing material (16),
   and the second number corresponding to the number of actual positions which are used for the formation of the actual position mean value.
7. Method according to one of the preceding claims, characterized in that the buffer value is determined as a sum of the buffer values (22).
8. Method according to Claim 7, characterized in that, in the case of the determination of the sum, at least one of the basic values (22) is weighted.
9. Method according to one of the preceding claims, characterized in that the sensor unit (12) has a camera sensor and/or a fibre optic system.
10. Method according to one of the preceding claims, characterized in that paper and/or cardboard and/or plastic and/or metal and/or wood and/or glass are/is used as the printing material (16).
11. Apparatus for the correction of a printing position of a printing unit (14) of a printing press (10), with at least one electronic computing device which is configured:

    - to detect an actual position of at least one printing mark (18) which is printed onto a printing material (16) by means of the printing mark (14) on the basis of sensor data which are received by a sensor unit (12);

    - to determine a deviation of the detected actual position from a setpoint position;

    - to determine at least one differential value which characterizes the deviation;

    - to determine a correction value;

    - to provide a signal for the correction of the printing position on the basis of the determined correction values;

    characterized in that, furthermore, the at least one electronic computing device is configured:

    - to determine a buffer value from a number of basic values (22) which have previously been stored in a memory (20);

    - to determine the correction value by way of subtraction of the buffer value from the differential value;

    - to store the correction value as one of the basic values (22) in a memory (20).
12. Printing press (10) with an apparatus according to Claim 11.

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