Method of operating a rotary printing press

Abstract

In a method for operating a rotary printing press, preferably a flexographic printing press that processes webs, disturbances of a rotating printing cylinder are detected and reduced by changing the printing speed. Here, the disturbances are detected at an actuating drive of the printing cylinder. This leads to a cost-efficient way of printing without disturbances.

Claims

1. A method of operating a rotary printing press, the method comprising: providing a rotating printing cylinder with an actuating drive, the actuating drive comprising a spindle and a servomotor with a transducer; providing an impression cylinder associated with the rotating printing cylinder; adjusting, via the spindle, the position of the rotating printing cylinder relative to the impression cylinder and thereby controlling a contact pressure between the rotating printing cylinder and the impression cylinder; during an operation of the printing press, detecting disturbances of the rotating printing cylinder by monitoring the transducer of the actuating drive of the printing cylinder; when disturbances at the rotating printing cylinder are detected via the transducer of the actuating drive of the printing cylinder, changing a printing speed of the rotary printing press in order to reduce or eliminate the disturbances.

2. The method according to claim 1, which comprises, when disturbances at the printing cylinder are detected via the actuating drive, reducing the printing speed of the rotary printing press.

3. The method according to claim 1, wherein the transducer is an encoder providing output signals.

4. The method according to claim 3, which comprises examining the output signals of the encoder for vibration.

5. The method according to claim 1, wherein the actuating drive controls a position of the printing cylinder.

6. The method according to claim 1, which comprises detecting further disturbances that are dependent on the printing speed of the rotary printing machine at an actuating drive of at least one further rotating cylinder and reducing the disturbances and the further disturbances by changing the printing speed of the rotary printing machine.

7. The method according to claim 6, which comprises decreasing or increasing the printing speed of the rotary printing machine until the disturbance and the further disturbance are reduced to below a predefined maximum disturbance threshold.

8. The method according to claim 1, wherein the disturbances are dependent on a print image on a printing forme at the printing cylinder.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

(1) FIG. 1 is a diagrammatic illustration of a machine for implementing the method according to the invention.

(2) FIG. 2 is a diagrammatic side view of a machine for implementing a method of the invention.

(3) FIG. 3 is a chart illustrating the method according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

(4) Referring now to the figures of the drawing in detail and first, in particular, to FIG. 1 thereof, there is shown an exemplary web-fed flexographic printing machine 1 implementing a preferred embodiment of the method according to the invention.

(5) The machine 1 has an in-line configuration with two longitudinal sides: a drive side 1a and an opposite operator side 1b. The machine processes, or rather prints on, a web of printing substrate 2. In preferred embodiments, the web 2 is made of paper, cardboard, paperboard, foil, or a composite material. The web may be supplied by means of a device for unwinding a web. The machine comprises a number of printing units 3 preferably arranged to succeed one another in a processing direction. Every printing unit has at least one motor 4 for driving the printing unit or at least one cylinder of the printing unit during the printing operation. Having been printed on, the web may be subjected to further processing such as die-cutting or punching.

(6) The machine 1 comprises a number of printing cylinders 5 and 21, in particular flexographic printing cylinders, and associated impression cylinders 6 and screen rollers 7 (cf. FIG. 3). A printing forme 8 (also known as a stereotype), in particular a flexographic printing plate with raised printing areas, bearing an image 9 to be printed that consists of printing and non-printing areas is received on each printing cylinder.

(7) At least one or two printing units, and preferably all of the printing units 3, preferably comprise a control device 15 including a respective actuating drive 16 or 22.

(8) The machine 1 further includes a digital computer 23. Connections for exchanging signals or data with the machine and the components thereof such as the motors 4 or actuating drives 16 are provided even though they are not shown for reasons of clarity.

(9) FIG. 2 illustrates a control device 15, or closed-loop controller 15, as it implements a preferred embodiment of the method of the invention.

(10) On at least one side (the drive side 1a or the operator side 1b), the impression cylinder 6 is received in a frame 10 of the machine 1. The journal 11 of the printing cylinder 5 is received in a bearing 12 of a bearing block 13. The bearing block is movable relative to the frame, preferably in a horizontal direction. A guide 14 is provided for this purpose.

(11) A control device 15 is provided on the drive side and/or on the operator side, preferably for controlling the position of the printing cylinder 5 and/or for controlling the contact pressure between the printing cylinder 5 and the impression cylinder 6. The device includes an actuating drive 16, preferably an electric motor 17, especially a servomotor 17 including a transducer 18. The transducer 18 may be an encoder 19 or may include an encoder 19. A spindle 20, preferably a ball screw spindle, is coupled or fixed to the actuating drive 16. In interaction with the guide 14, the spindle 20 converts the rotary movement of the actuating drive into a linear movement of the bearing block 13.

(12) The digital computer 23 is connected to the actuating drive 16, in particular with its transducer 18 and/or encoder 19. The digital computer may control the rotary movement of the actuating drive, thus controlling the position and/or contact pressure between the printing cylinder 5 and the impression cylinder 6.

(13) As the printing cylinder 5 rotates, raised portions of the stereotype 8 may lead to printing cylinder disturbances, in particular vibration (also known as bouncing), which may in turn cause defects in the printed image. Such disturbances may be detected at the actuating drive 16, the electric motor 17, or the transducer 18, because the disturbances/vibrations are transmitted to or fed back to the actuating drive and the components thereof via the bearing block 13 and the spindle 20. Corresponding (current or voltage) signals or data may be picked up at the transducer and forwarded to the digital computer 23. They may then be analyzed by the digital computer. In this process, the disturbances may be computationally detected and measures to reduce them may be taken. The digital computer may actuate the motor 4 of the associated printing unit 3 or all motors 4 of all printing units in such a way that the disturbances/vibrations are reduced or compensated for. In particular, the printing speed may be modified, e.g. increased or decreased.

(14) FIG. 3 illustrates selected steps of a preferred embodiment of the method of the invention.

(15) The Figure schematically shows the digital computer 23 that monitors the four printing unit shown by way of example and computationally evaluates or analyzes the disturbance to compensate for them, reduce them, or prevent them in the process. A diagram plotting the amplitude of a disturbance over the printing speed is shown for every printing unit (first to fourth printing unit, from top to bottom).

(16) In the illustrated example, a printing-speed-related disturbance 24 occurs in a first printing unit and a further disturbance 25 occurs in a further printing unit, for instance a third printing unit. The digital computer 23 detects these disturbances at the respective printing speeds. The disturbances may be detected by means of a comparison between the amplitude and a predefined threshold. For instance, when a disturbance is detected at a first printing speed 27, the printing speed may be modified until, at a second printing speed, no more disturbances occur—neither in the first printing unit nor in any other one. This second printing speed is the one that is subsequently used to operate the machine 1. In other words, the printing speed is increased (or decreased), for instance, until no disturbances occur in any one of the printing units.

(17) The following is a summary list of reference numerals and the corresponding structure used in the above description of the invention:

(18) 1 rotary printing machine

(19) 1a drive side

(20) 1b operator side

(21) 2 web of printing material

(22) 3 printing units

(23) 4 motors

(24) 5 printing cylinder

(25) 6 impression cylinder

(26) 7 screen roller

(27) 8 printing forme/stereotype

(28) 9 print image

(29) 10 frame

(30) 11 cylinder journal

(31) 12 bearing

(32) 13 bearing block

(33) 14 guide

(34) 15 control device

(35) 16 actuating drive

(36) 17 electric motor or servomotor

(37) 18 transducer

(38) 19 encoder

(39) 20 spindle

(40) 21 further printing cylinders

(41) 22 actuating drive

(42) 23 digital computer

(43) 24 disturbances

(44) 25 further disturbances

(45) 26 output signals

(46) 27 first printing speed

(47) 28 second printing speed