Method for adjusting the print repeat length of a print image in a multicolor rotary printing machine

Abstract

A method of adjusting the print repeat length of a print image in a multicolor rotary printing machine, particularly a flexographic printing press, having a central impression cylinder, a first plate cylinder, and a second plate cylinder, including modifying the peripheral velocity of the first plate cylinder and the peripheral velocity of the second plate cylinder during printing operation, relative to the peripheral velocity of the central impression cylinder, and adjusting the longitudinal register of the first plate cylinder having the modified peripheral velocity and the longitudinal register of the second plate cylinder having the modified peripheral velocity.

Claims

1. A method of adjusting a print repeat length of a print image in a multicolor rotary printing machine having a first plate cylinder and a second plate cylinder, the first plate cylinder and the second plate cylinder being associated with a shared central impression cylinder which conveys a print substrate, and a peripheral velocity of the first plate cylinder and a peripheral velocity of the second plate cylinder being adjusted relative to a peripheral velocity of the central impression cylinder, said method comprising the steps of: modifying the peripheral velocity of the first plate cylinder during a printing operation, relative to the peripheral velocity of the central impression cylinder, and adjusting a longitudinal register of the first plate cylinder having the modified peripheral velocity; and as the print substrate travels from the modified and adjusted first plate cylinder to the second plate cylinder, modifying the peripheral velocity of the second plate cylinder relative to the peripheral velocity of the central impression cylinder, and adjusting the longitudinal register of the second plate cylinder having the modified peripheral velocity, with, for the first plate cylinder, the steps of modifying the peripheral velocity and adjusting the longitudinal register being effected simultaneously, and for the second plate cylinder, the steps of modifying the peripheral velocity and adjusting the longitudinal register being effected simultaneously.

2. The method according to claim 1, further comprising employing a control and/or regulating program having a procedure for controlling the peripheral velocity and having a procedure for controlling the longitudinal register, and calling the procedure for controlling the longitudinal register simultaneous with calling the procedure for controlling the peripheral velocity, with a modified value of the peripheral velocity being a basis for a new control value.

3. The method according to claim 1, wherein the velocity that is modified in the step of modifying of the peripheral velocity associated with the adjusting of the longitudinal register has a same magnitude, but an opposite sign, with respect to a desired modified peripheral velocity of the first plate cylinder and the second plate cylinder.

4. The method according to claim 1, wherein the multicolor rotary printing machine is a flexographic printing press.

5. A method of adjusting a print repeat length of a print image in a multicolor rotary printing machine having a first plate cylinder and a second plate cylinder, the first plate cylinder and the second plate cylinder being associated with a shared central impression cylinder which conveys a print substrate, and a peripheral velocity of the first plate cylinder and a peripheral velocity of the second plate cylinder being adjusted relative to a peripheral velocity of the central impression cylinder, said method comprising the steps of: modifying the peripheral velocity of the first plate cylinder and the peripheral velocity of the second plate cylinder during a printing operation, relative to the peripheral velocity of the central impression cylinder; adjusting a longitudinal register of the first plate cylinder having the modified peripheral velocity and a longitudinal register of the second plate cylinder having the modified peripheral velocity, with the step of modifying of the peripheral velocity and the step of adjusting of the longitudinal register being effected simultaneously; and employing a control and/or regulating program having a procedure for controlling the peripheral velocity and having a procedure for controlling the longitudinal register, and calling the procedure for controlling the longitudinal register simultaneous with calling the procedure for controlling the peripheral velocity, with a modified value of the peripheral velocity being a basis for a new control value.

6. The method according to claim 5, wherein the method includes modifying the peripheral velocity of the second plate cylinder simultaneously with the modifying of the peripheral velocity of the first plate cylinder.

7. The method according to claim 6, wherein the multicolor rotary printing machine includes another plate cylinder, and wherein the method includes modifying a peripheral velocity of the other plate cylinder simultaneously with the modifying of the peripheral velocity of the first plate cylinder and the second plate cylinder.

8. The method according to claim 6, wherein the modified peripheral velocity of the first plate cylinder and the modified peripheral velocity of the second plate cylinder are identical.

9. The method according to claim 5, wherein the velocity that is modified in the step of modifying of the peripheral velocity associated with the adjusting of the longitudinal register has a same magnitude, but an opposite sign, with respect to a desired modified peripheral velocity of the first plate cylinder and the second plate cylinder.

10. The method according to claim 5, wherein the multicolor rotary printing machine is a flexographic printing press.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further embodiments are found in the additional claims and the drawings, wherein:

(2) FIG. 1 shows a schematic view of a flexographic printing press with a control device,

(3) FIG. 2 shows the process of a method according to the invention for adjusting the print repeat length, and

(4) FIG. 3 shows various velocity curves of a plate cylinder when the velocity thereof is modified.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(5) Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

(6) FIG. 1 shows a schematic illustration of a flexographic printing press 1, which has a central impression cylinder 2. A web of print substrate 3 is fed in the direction of the arrow T, and is laid onto the central impression cylinder 2 by means of a pressure roller 4. Multiple—and particularly 4 in the shown embodiment—plate cylinders 5, 6, 7, 8 are distributed about the periphery of the central impression cylinder 2, each printing one color. However, only the first has not been shown [sic], but devices for the purpose of conveying ink are part of each printing machine, wherein the letterpress printing regions of the plate cylinders are supplied with color ink via the same. In flexographic printing presses, such a device generally comprises an anilox roll for the purpose of inking the print regions, and a doctor blade which works together with the anilox roll.

(7) In addition, FIG. 1 shows components of the flexographic printing press 1 which serve the purpose of driving cylinders. As such, the central impression cylinder 2 is driven by its own drive 12. The letter M in the illustration stands for ‘motor’. Even if the motor is operated at a prespecified power, which should lead to a constant rotation speed, fluttering can occur. In order to make it possible to determine the actual rotation speed, a rotation speed detection device is included, indicated overall with the reference number 22. The rotation speed detection device has a sensor 23 by means of which it is possible to detect the markings 24 which are arranged on the central impression cylinder 2. The detected markings are relayed to the analysis and control device 26 via a data line 25, which analyzes the markings therefrom per unit of time, and from this determines the actual angular and peripheral velocity. If a deviation from the desired angular velocity is found, the motor can be accordingly controlled such that target and current velocities equalize. A control path is therefore available for this case. A control line leads from the analysis and control device 26 to the motor 12.

(8) In flexographic printing presses in the prior art, the individual plate cylinders should have the same peripheral velocities at every point in time as the central impression cylinder 2. For this purpose, the same control path is used as for the central impression cylinder 2. Such a control path is only illustrated for the plate cylinder 5, but is likewise present for the other plate cylinders. It is initially important that the rotation of each plate cylinder is started by its own drive. The drive in the case of plate cylinder 5 has the reference number 15. The control device in this case also includes the markings 31, the sensor 32, and the control line 33, which relays the number of the markings measured by the sensor to the analysis and control device 26. The latter evaluates the measured value with respect to a unit of time, and in turn determines the current peripheral velocity of the plate cylinder 5. The current peripheral velocity is also compared to a target velocity, wherein in this case the target velocity is not a prespecified velocity, but rather the current velocity of the central impression cylinder. As a result of this approach, the method ensures that the peripheral velocities of the central impression cylinder and the plate cylinders are always the same.

(9) At this point, if the peripheral velocities of the plate cylinders 5, 6, 7, 8 are intended to be modified relative to the central impression cylinder, the corresponding differences are added to the target velocities of the plate cylinders. These differences can result in a higher peripheral velocity, and result in a slightly shortened print repeat length. In contrast, a reduced peripheral velocity leads to an elongated print image.

(10) One embodiment of a circuit or a program procedure is shown in FIG. 2. The individual boxes in this figure are accordingly intended as circuit components or parts of a program—for example as procedures. The drive of a plate cylinder is controlled in this was. As described above, the basis for the control operation of the drive is the current peripheral velocity of the central impression cylinder. This is illustrated in box 100, wherein the path of the central impression cylinder (CIC path) traveled per unit of time is taken as the basis. For a printing wherein not all plate cylinders are yet in the register, the missing path difference is added in order to achieve a satisfactory register. The path difference in the register is generally detected by register sensors which scan the printing marks of the individual colors. The missing path difference continues to be added until the register matches (S.sub.long, register). This is indicated by the reference number 200. The actual addition is performed in the component and/or procedure 400.

(11) At this point, if a velocity difference between the central impression cylinder and the affected plate cylinder is added, the path sum is multiplied by a factor which is greater or smaller than 1. This occurs in the multiplier, which is shown as box 500. The result is a path specification which the periphery of the plate cylinder has traveled during one unit of time. The motor M is controlled according to this specification.

(12) An approach is illustrated in FIG. 3, by means of which it is possible to add the velocity difference for all plate cylinders at the same time, and to prevent a longitudinal register deviation. For this purpose, the velocity difference Δv from the new velocity v.sub.2 is determined proceeding from the original peripheral velocity v.sub.1. A resulting velocity curve is illustrated in FIG. 3 a), wherein the peripheral velocity of the affected plate cylinder was simply modified from v.sub.1 to v.sub.2 at a time point t.sub.Start.

(13) Along with the time point at which the new velocity v2 is added, this difference path is incorporated as a longitudinal register path to be corrected. This longitudinal register path continues to be incorporated from time point t1 until the difference path traveled per unit of time is determined from Δv. This difference path is taken into account as the longitudinal register path to be corrected, along with the time point of the adding of the new velocity. This longitudinal register path is incorporated at this point, starting at v.sub.1, for the time in which the print substrate needs to travel at the given peripheral velocity from the first plate cylinder (see reference number 5 in FIG. 1) to the plate cylinder being adjusted. The duration needed for this is found for the given peripheral velocity of the central impression cylinder, which is equal to v.sub.1, from the radius of the central impression cylinder, which is a constant. The longitudinal register path up to time point t.sub.End is incorporated accordingly. While the time point t.sub.Start is the same for all plate cylinders, the time point t.sub.End depends on the spatial position of the affected plate cylinder relative to the central impression cylinder. Because in this approach the adjustment of the longitudinal register—not measured values—is used which are detected by sensors, this can be considered a correction of a virtual longitudinal register error. Such a correction of the longitudinal register error is shown in FIG. 3 b).

(14) FIG. 3 c) shows the velocity curve resulting from the above for the plate cylinder in question. The velocity difference Δv and the velocity modification resulting from the longitudinal register correction exactly cancel each other out, such that the peripheral velocity v.sub.1 is maintained between the time points t.sub.Start and t.sub.End.

(15) In this manner, a print image which was already in the process of being printed at the original speed, is also completely finished at this speed. This print therefore does not result in any waste paper.

(16) The described approach is advantageous because in this case only little needs to be modified in printing machines of the prior art, in terms of control devices, in order to make it possible to carry out the method according to the invention. The so-called print repeat length correction—that is, the velocity v2—can be easily added. To prevent paper waste, the function for the longitudinal register correction, which is present in the prior art as well, can be modified by the addition of the calculated (rather than measured) values at this point.

(17) In addition to the method according to the invention, a printing machine is also the subject matter of the invention, wherein an analysis and control device 26 is equipped with the described functions.

(18) In the description above, as well as the drawings and the claims, various embodiments and features of a method according to the invention and of a device according to the invention have been described. All of these features can be freely combined with each other to the extent this is technically feasible, without departing from the scope of the present invention.

(19) The invention being thus described, it will be apparent that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be recognized by one skilled in the art are intended to be included within the scope of the following claims.