Printing press, method and apparatus for correcting a printing position of a printing unit

Abstract

An apparatus, a printing press and method for correcting the printing position of a printing unit of a printing press that has at least one sensor unit, where the method includes the steps of detecting an actual position of at least one print mark via the sensor unit, where the print mark is printed onto a printing material via the printing unit, determining of a deviation of the detected actual position from a setpoint position, determining at least one difference value that characterizes the deviation, determining a buffer value from a number of basic values previously stored in a memory, determining a correction value by subtracting the buffer value from the difference value, storing the determined correction value in the memory as one of the basic values, and correcting the printing position based on the determined correction value.

Claims

1. A method for correcting a printing position of a printing unit of a printing press which includes at least one sensor unit, the method comprising: detecting an actual position of at least one print mark via the sensor unit, said print mark being printed onto a printing material via the printing unit; determining at least one difference value which characterizes a deviation of the detected actual position from a setpoint position; determining of a buffer value from a number of basic values which were previously stored in a memory; subtracting the buffer value from the difference value to determine a correction value; storing the determined correction value in the memory as one of the basic values; and correcting the printing position based on the determined correction value.

2. The method as claimed in claim 1, wherein the basic value having a longest period of storage in the memory in relation to the basic values which are stored in the memory is deleted from the memory and replaced by the determined correction value.

3. The method as claimed in claim 1, wherein the memory is configured as a shift register.

4. The method as claimed in claim 2, wherein the memory is configured as a shift register.

5. The memory as claimed in claim 1, wherein the number of basic values which are stored in the memory is determined by at least one of (i) a spacing between a printing location of the at least one print mark in the printing unit and a reading position of the sensor unit and (ii) a format length of the printing material.

6. The method as claimed in claim 1, wherein a plurality of actual positions of respective print marks which are printed onto respective printing materials via the printing unit are detected via the sensor unit, an actual position mean value being formed from the plurality of actual positions, and the difference value being determined via the actual position mean value.

7. The method as claimed in claim 6, wherein the number of basic values which are stored in the memory corresponds to a sum of a first number and a second number, the first number being determined by at least one of (i) the spacing between the printing location and the reading position and (ii) the format length of the printing material, the second number corresponding to a number of actual positions which are used to form the actual position mean value.

8. The method as claimed in claim 1, wherein the buffer value is determined as a sum of the basic values.

9. The method as claimed in claim 8, wherein at least one basic value of the basic values is weighted during said determination of the sum.

10. The method as claimed in claim 1, wherein the at least one sensor unit includes at least one of (i) a camera sensor and (ii) a fiber optic system.

11. The method as claimed in claim 1, wherein the printing material comprises at least one of (i) paper, (ii) cardboard, (iii) plastic, (iv) metal, (v) wood and (vi) glass.

12. An apparatus for correcting a printing position of a printing unit of a printing press, the apparatus comprising: at least one electronic computing device which is configured to: detect an actual position of at least one print mark which is printed onto a printing material via the printing unit, based on of sensor data which are received by a sensor unit; determine at least one difference value which characterizes a deviation of the detected actual position from a setpoint position; determine a buffer value from a number of basic values which were previously stored in a memory; subtract the buffer value from the difference value to determine a correction value; store the correction value in a memory as one of the basic values; and provide a signal for correction of the printing position based on the determined correction value.

13. A printing press having the apparatus as claimed in claim 12.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Exemplary embodiments of the invention will be described in greater detail in the following text using diagrammatic drawings, in which:

(2) FIG. 1 shows a diagrammatic view of a printing press which has a sensor unit and at least one printing unit in accordance with the invention;

(3) FIG. 2 shows a diagrammatic flow chart of one exemplary embodiment of a method for correcting a printing position of at least one of the printing units of the printing press in accordance with the invention; and

(4) FIG. 3 is a flowchart showing the steps of the method in accordance with the invention.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

(5) FIG. 1 shows a diagrammatic view of a printing press 10 that has a sensor unit 12 and at least one printing unit 14. What are known as register errors can occur, in particular, in the case of multiple color printing, in which a printed image is separated into primary colors, where each printing unit 14 prints one of the primary colors onto a printing material 16. In the case of a register error, the individual printing colors do not lie exactly above one another, with the result that the finished printed copy or printed product appears to be, for example, blurred. The register error can be compensated for in a particularly dynamic and therefore efficient manner via the proposed method, as a result of which the printed image and therefore the finished printed copy or its individual colors are in register.

(6) The method for correcting the printing position of the (in particular, respective) printing unit 14 of the printing press 10 which has at least the sensor unit 12 comprises a plurality of steps, where in a first step of the method, an actual position of at least one print mark 18 that is printed onto the printing material 16 via the printing unit 14 is detected via the sensor unit 12. In a second step, a deviation of the detected actual position from a setpoint position is determined. In a third step, at least one difference value that characterizes the deviation is determined. In a fourth step, a buffer value is determined from a number or plurality of basic values 22 that were 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 that is determined in the fifth step is stored in the memory as one of the basic values 22. In a seventh step, the printing position of the printing unit 14 is corrected based on the determined correction value.

(7) The printing press 10 can print, for example, packaging via what is known as flexographic printing, for example. Moreover, the printing press 10 can also be a printing press that is configured for offset printing. Furthermore, the printing material 16 or the printing materials 16 can be printed via, for example, web-fed printing or sheet-fed printing. In order for it to be possible for the printing material 16 to be printed particularly advantageously, the respective printing unit 14 advantageously has in each case at least one impression cylinder 24. Depending on the type of printing method or the printing press 10, the respective printing unit 14 can have, for example, a print head instead of the impression cylinder 24, as can be the case in digital printing, for example.

(8) The respective printing color can be applied to the printing material 16 in a particularly advantageous way via the respective impression cylinder 24 of the respective printing unit 14. Here, the printing material 16 is advantageously paper, cardboard, plastic and/or metal, as a result of which a particularly great variety of different printed products can be produced via the printing press 10. In the exemplary illustrated embodiment, the printing press 10 has two printing units 14 that are arranged behind one another. One form of multiple color printing is what is known as four color printing, in the case of which, in particular, the colors cyan, magenta, yellow and black are used to produce colored printed products. In the case of four color printing, four printing units 14 would therefore be provided, but only two printing units 14 are shown in FIG. 1 for the sake of simplicity. In the case of the method, the number of printing units 14 of the printing press 10 can be selected freely. The sensor unit 12 advantageously has a camera sensor and/or a fiber optic system, as a result of which the respective print mark 18 is detectable or can be detected particularly simply by the sensor unit 12.

(9) FIG. 1 additionally shows that a spacing between the printing units 14 and the sensor unit 12 has a defined length. This length can be, for example, the length of two printing materials 16, as shown in FIG. 1. This leads to a dead time, i.e., the print mark 18 that is detected by the sensor unit 12 at a first time has already been printed at an earlier second time. Conversely, the print mark 18 that is printed at the first time is only detected by the sensor unit 12 at a later third time. The spacing between the first time and the second or third time is called the dead time. This can also be interpreted or understood to mean a dead travel. Thus, in the printing press 10 of FIG. 1, the printing materials 16 to be printed run from the left one after another first of all via the first printing unit 14 and then via the second printing unit 14, and finally arrive behind one another and therefore after one another at the sensor unit 12. In the exemplary illustrated embodiment, a printed copy 26 is arranged between the printing unit 14 that prints last (the right hand printing unit 14 of FIG. 1) and the sensor unit 12 in the printing press 10. That is, by the time the sensor unit 12 sees a printed print copy 26 or the printing material 16 that has been printed via the printing unit 14 that prints last, two further printed copies 26 have already been printed via the printing unit 14.

(10) The respective print mark 18 can be formed from individual rectangles or triangles, as shown in the example, where at least one rectangle or at least one triangle, in particular, is provided for each color to be printed. The method is fundamentally independent of the shape of the print marks 18. For the method, measured values have to be available merely at a defined time. In the exemplary embodiment, the printing unit 14 that prints last is configured to print the triangle of the print mark 18, where the triangle lies on the left in FIG. 1. As an alternative or in addition, in particular according to the type of sensor unit 12, the print marks can be, for example, dots in the respective printing color. Thus, the rectangular and triangular configuration of the print marks 18 or the mark fields has established itself for a fiber optic detection of the print mark, with the result that they are configured as wedge or block marks, whereas what are known as dot marks are frequently used for camera-based sensor units 12.

(11) FIG. 2 shows a diagrammatic flow chart of one exemplary embodiment of the method for correcting the printing position of the (in particular, respective) printing unit 14 of the printing press 10. The memory 20 is advantageously configured as a shift register, with the result that a basic value that is written into the memory 20 is passed through the memory or shift register when a further basic value 22 is again added, and leaves it after a last memory position of the memory 20 is reached. A fixed temporal relationship of the basic value 22 with the respective detection time, such as the first time, can be established in a particularly simple way via the use of a shift register, as a result of which a temporal sequence of the basic values 22 can be realized in the memory 20. Therefore, the basic value 22 that has been stored the longest in the memory 20 in relation to the basic values 22 that are stored in the memory 20 can be deleted from the memory in a particularly advantageous way and can be replaced by the correction value that is determined via the current repetition of the method as a new or current basic value 22. In particular, as a result of the configuration of the memory 20 as a shift register, there is an attribution between one of the memory positions and a temporal sequence of the repetitions of the method.

(12) In the diagrammatic illustration of the method which is shown in FIG. 2, the respective individual printed copies 26 or printing materials 16 are printed via the printing unit 14, coming from the right and following one another, and the print marks 18 are subsequently detected via the sensor unit 12. Here, the sawtooth-like line 27 indicates the respective position of a master axis of the printing unit 14 or the impression cylinder 24. That is, the master axis has arrived back in its original position after one complete revolution of the impression cylinder 24.

(13) The method is performed for the first time when the first printed copy 26 or its print mark 18 is detected via the sensor unit 12. Here, the memory 20, the memory size 28 of which comprises a number of three memory locations in the example which is shown, which is shown via the left hand curly bracket, corresponds to the number that is predefined, inter alia, via the spacing or the dead travel between the printing unit 14 and the sensor unit 12. Here, the number is defined via the number of following printed copies 26, 30, 32: the printed copy 26, the print mark 18 of which is detected via the sensor unit 12 at a time, the further printed copy 30 that is printed via the printing unit 14 at the time, and the printed copy 32 or the printed copies 32 that is/are situated in the printing press 10 at the time and has/have already been printed via the printing unit 14 at the time, but has/have not yet been detected via the sensor unit 12. In other words, the number of basic values 22 that are stored in the memory is defined via a spacing 42 between a printing location of the print mark 18 in the printing unit 14 and a reading position of the sensor unit 12. Furthermore, the number is defined via a format length 40 of the printing material. Here, the number is the rounded-up quotient of the spacing 42 and the format length 40.

(14) A time axis 34 is defined with respect to the line 27 that determines the position of the master axis. The position of the master axis is shown in a second axis 36 that is perpendicular with respect thereto. Thus, the first print mark of the first printed copy 26 is detected at the first time ZP1, where the basic values 22 of the memory are all fixed as 0 at the time. This represents the first step of the method, where the first step is performed at the time ZP1 in the illustrated example. This is followed in the second step by the determination of the deviation of the detected measured position of the print mark 18 from the setpoint position. In the third step, a difference value that characterizes the deviation is determined from the deviation. In the next fourth step, a buffer value is determined from a number of basic values 22 that were previously stored in the memory 20. During the first performance of the method, in which the memory 20 is situated in the state V1, the buffer value is 0, because no correction has yet been performed before the first performance of the method. 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. Thereupon, in the sixth step of the method, the determined correction value is stored as one of the basic values 22 in the memory 20.

(15) At the time ZP2, the first correction value KORR1 is stored in the memory, and the third print mark 18, i.e., the print mark 18 of the printed copy 30, is printed but has not yet been measured. In the case of a renewed performance of the method at the time ZP3 or directly following the time ZP3, the steps of the method are re-performed, with the result that a new correction value KORR2 was written or is written into the memory 20 as a new basic value 22 at the time ZP4, at which the fourth print mark 18 was printed on a further printed copy. At the time ZP5, the third print mark 18, i.e., the print mark of the printed copy 30, is measured, and the method is re-performed for a third time, with the result that the correction value KORR3 has already been input into the memory 20 at the time ZP6, at which a fifth print mark 18 is printed. At the time ZP7, the print mark 18 that is printed fourth is detected, and the method is re-performed, with the result that the fourth correction value KORR4 has already been input into the memory 20 at the time ZP8, at which the sixth print mark 18 is printed. Here, the memory 20 is filled for the first time with basic values 22 that are formed via earlier performances of the method and are formed from the correction values KORR1 to KORR3, with the result that the correction value KORR1 that was written into the memory at the time ZP1 or time ZP2 is expelled from the memory area 28. At the times ZP9 and ZP11, the method is started in each case again, since the first method step is performed at the respective time. In each case at the time ZP10 or time ZP12, the method has been performed completely, and a further print mark 18 is printed in each case.

(16) The buffer value is formed from the sum of the basic values 22 that are stored in the memory 20 with the memory size 28 and are formed from respective correction values (KORRn to KORRn+2) for a respective performance of the method. The buffer value that is updated before each performance of the method is subtracted from the respective current difference value that characterizes the deviation. The memory size 28 is also called the memory depth.

(17) As an alternative, the method can be performed such that a plurality of actual positions of respective print marks 18 that are printed onto respective printing materials 16 via the printing unit 14 are detected via the sensor unit 12, where an actual position mean value is formed from the plurality of actual positions, and the difference value is determined via the actual position mean value. Thus, for example, in the case of three different printed copies, such as the printed copies 26, 30 and 32, the actual positions can initially be detected and averaged, and the deviation of the setpoint position from the averaged actual position or the actual position mean value can be determined. Here, this is called a filter depth that corresponds in the example to three, i.e., the number of print marks 18 that are checked and used to form the mean value. Therefore, the filter depth is identical to the number of actual positions that are used for the formation of the actual position mean value. If a difference value or actual position mean value of this type that is smoothed via the mean value formation is used in the method, or if it is used for the method, the memory size 28 is advantageously increased, i.e., the number of memory locations that can be stored in the memory 20 is increased by the number of actual positions that are used for the formation of the actual position mean value. The additional basic values 22 are advantageously taken into consideration in a weighted manner during the determination of the buffer value via the sum of the basic values 22.

(18) If smoothed deviation values are used, basic values 22 that are taken into consideration via the weighting during the formation of the buffer value can be additionally stored via the extended memory size 28 of the memory 20 that is configured as a shift register. Thus, a faulty deviation can be capable of being avoided during the correction of the printing position, because the dead time or the dead travel is extended via the mean value formation of the actual position mean value. Therefore, with the method, a regulation of print marks 18 via a memory 20 that is configured, in particular, as a shift register can be performed in a particularly efficient and/or dynamic way and therefore lead to printed copies 26, 30, 32 that are printed particularly exactly in quality terms, where it is possible for smoothing of the actual position to be performed.

(19) FIG. 3 is a flowchart of the method for correcting a printing position of a printing unit 14 of a printing press 10 that includes at least one sensor unit 12. The method comprises detecting an actual position of at least one print mark via the sensor unit 12, as indicated in step 310. Here, the print mark 18 is printed onto a printing material 16 via the printing unit 14.

(20) Next, a deviation of the detected actual position from a setpoint position is determined, as indicated in step 320. At least one difference value that characterizes the deviation is now determined, as indicated in step 330.

(21) Next, a buffer value from a number of basic values 22 that were previously stored in a memory 20 is determined, as indicated in step 340.

(22) Next, the buffer value is subtracted from the difference value to determine a correction value, as indicated in step 350.

(23) The determined correction value is now stored in the memory 20 as one of the basic values 22, as indicated in step 360.

(24) The printing position is now corrected based on the determined correction value, as indicated in step 370.

(25) Thus, while there have been shown, 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 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.