PRINTING MACHINE AND METHOD OF OPERATING A PRINTING MACHINE

Abstract

A printing machine (10) comprises a doctor blade (14), a drive system (20) for urging the doctor blade (14) against a printing cylinder (16) of the printing machine (10), a sensor (32) adapted for sensing a force with which the doctor blade (14) is urged against the printing cylinder (16), and a mechanical locking element (34) adapted for locking the drive system (20) in its operating position.

Further, a method of operating a printing machine (10) is presented.

Claims

1. A printing machine comprising: a doctor blade, a drive system for urging the doctor blade against a printing cylinder of the printing machine, a sensor adapted for sensing a force with which the doctor blade is urged against the printing cylinder when the printing cylinder is substantially static, and a mechanical locking element adapted for locking the drive system in an operating position.

2. The printing machine according to claim 1, wherein the drive system comprises a piston for applying the force on the doctor blade.

3. The printing machine according to claim 1, wherein the sensor is arranged between the mechanical locking element and the doctor blade.

4. The printing machine according to claim 1, wherein the printing machine further comprises a control unit, which is connected to the drive system, the mechanical locking element and the sensor, by a programmable logic controller.

5. The printing machine according to claim 4, wherein the control unit has a storage module for storing sensor values received from the sensor.

6. The printing machine according to claim 5, wherein the control unit comprises an analysis module configured to analyze changes in the sensor values in dependence of time and/or frequency.

7. A method of operating a printing machine including a doctor blade, a drive system for urging the doctor blade against a printing cylinder of the printing machine, a sensor adapted for sensing a force with which the doctor blade is urged against the printing cylinder when the printing cylinder is substantially static, a mechanical locking element adapted for locking the drive system in an operating position, and a control unit, the method comprising: setting a target force for urging the doctor blade against the printing cylinder, moving the drive system in the operating position, wherein in the operating position, the force as measured by the sensor is the target force, locking the position of the drive system by the mechanical locking element, measuring an actual force by the sensor and comparing the actual force with the target force, and unlocking the position of the drive system and repeating the moving and the locking when the actual force is not equal to the target force, wherein the measuring is repeated at least once after a set time interval.

8. The method according to claim 7, further comprising providing a warning by the control unit of the printing machine when the measured actual force is not equal to the target force.

9. The method according to claim 7, further comprising: storing values of the measured actual force in a storage module of the control unit, and analyzing changes of the values of the measured actual force in dependence of time and/or frequency in an analyzing module of the control unit.

10. The method according to claim 7, further comprising providing a warning by the control unit when the target force cannot be reached by moving the drive system.

11. The method according to claim 7, further comprising calibrating the drive system in a calibration position, wherein in the calibration position a maximum force is measured by the sensor.

12. The method according to claim 7, further comprising measuring the force by the sensor for a second pre-set time, and locking the position of the drive system only when the force is constant during the second pre-set time, and providing a warning when the force is not constant during the second pre-set time.

13. The method according to claim 7, wherein the moving the drive system is performed by operating a piston of the drive system.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Further advantages and features will become apparent from the following description of the invention and from the appended figures which show a non-limiting exemplary embodiment of the invention and in which:

[0059] FIG. 1 shows a schematic representation of a printing machine according to a preferred embodiment of the invention;

[0060] FIG. 2 shows a detail view of a printing machine according to another embodiment of the invention; and

[0061] FIG. 3 shows a block scheme of a method according to the invention for operating the printing machine of FIG. 1.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0062] In FIG. 1, a schematic representation of a printing machine 10 according to the invention is shown.

[0063] The printing machine 10 has an ink reservoir 12 formed between a chamber doctor blade 14 and a printing cylinder 16, which is an anilox roll. Accordingly, the printing machine 10 is a flexographic printing unit.

[0064] The anilox roll rotates in the direction illustrated in FIG. 1 by the arrow A and takes up ink from the ink reservoir 12 into cells engraved in the surface of the anilox roll during its rotation.

[0065] The chamber doctor blade 14 scrapes of excess ink from the surface of the anilox roll.

[0066] The ink from the anilox roll is then transferred to other printing cylinders of the printing machine 10, of which only a plate cylinder 18 is shown in part in FIG. 1. Accordingly, the further parts of the printing machine 10 for the actual printing on a substrate are not shown in FIG. 1 and are known in the art.

[0067] The plate cylinder 18 is counter-rotating compared to the anilox roll, as illustrated by the arrow B in FIG. 1.

[0068] The ink is supplied by a (not shown) ink supply into the chamber doctor blade 14 and therefore into the ink reservoir 12.

[0069] The chamber doctor blade 14 is urged against the anilox roll by a drive system 20. The drive system 20 can be moved along the directions illustrated by the double-arrow C shown in FIG. 1.

[0070] The drive system 20 comprises a double-acting pneumatic cylinder 22 which can move a piston 24 by supplying air through a first inlet 26 or a second inlet 28. The double-acting pneumatic cylinder 22 is controlled by a pneumatic/electric/pneumoelectric converter 30.

[0071] The drive system 20 could also use a single-acting pneumatic cylinder. Alternatively, the drive system 20 can use hydraulically or electrically driven pistons and/or cylinders.

[0072] The actual force F with which the drive system 20 urges the chamber doctor blade 14 against the anilox roll can be measured by a sensor 32.

[0073] The sensor 32 can measure actual forces and has a digitization/resolution in the range of from 10 to 20 N, preferably of 10 N.

[0074] The sensor 32 can be of any form which allows measuring the desired force. As an example, the sensor 32 can be a compression force transducer, a tension/compression force transducer, a column force sensor, a ring force sensor, a strain gauge, a bending beam, a shear beam, a load cell, a load pin and/or a tension link.

[0075] The measured actual force F can also be converted into a pressure with which the chamber doctor blade 14 is pressed against the anilox roll.

[0076] In the shown embodiment, the sensor 32 is arranged between the pneumatic cylinder 22 and the chamber doctor blade 14.

[0077] However, the type of sensor 32 used and the arrangement of the sensor 32 relative to the chamber doctor blade 14 and to the drive system 20 can be different from the shown embodiment, as long as a reliable measurement of the actual force F is ensured.

[0078] Further, the printing machine 10 comprises a mechanical locking element 34 which is adapted for locking the piston 24 and therefore the drive system 20 in place.

[0079] The mechanical locking element 34 is controlled by a locking control unit 36, which can also be a second pneumoelectric converter.

[0080] The mechanical locking element 34 is able to ensure a secure lock of the drive system 20 even when much higher forces than F.sub.max are acting on the drive system 20. In the shown embodiment, the locking element 34 ensures a reliable lock of the drive system 20 even when a force of up to 2000 N act on the drive system 20 in the directions as shown by the double-arrow C in FIG. 1.

[0081] The printing machine 10 further comprises a control unit 38 which is connected by means of a programmable logic controller (PLC) 40 to the drive system 20 via the pneumoelectric converter 30, to the mechanical locking element 34 via the locking control unit 36 and to the sensor 32.

[0082] The control unit 38 comprises control elements 42 which an operator can use to interact with the control unit 38.

[0083] The control unit 38 further comprises a display 44.

[0084] The display 44 can also be a touch-sensitive display. In this case, the control elements 42 can also be omitted as the operator can use the display 44 for interaction with the control unit 38.

[0085] The control unit 38 further comprises a storage module 46 and an analysis module 48.

[0086] In the following, a method of operating the printing machine 10 will be described which can be used to ensure that ink cannot leak out from the ink reservoir 12 during printing.

[0087] First, a target force F.sub.target for urging the chamber doctor blade 14 against the anilox roll can be set via the control unit 38 by an operator (step S1 in FIG. 3). Alternatively, the target force F.sub.target can be read from the storage module 46.

[0088] Afterwards, the pneumoelectric converter 30 is activated and drives the piston 24 within the pneumatic cylinder 22, resulting in a movement of the drive system 20. Due to this movement, the chamber doctor blade 14 is pressed against the anilox roll.

[0089] The actual force F is measured by the sensor 32 and sent to the control unit 38 which stops the drive system 20 when the target force F.sub.target is reached, i.e. when the drive system 20 is in an operating position (step S2 in FIG. 3).

[0090] Subsequently, the drive system 20 is locked in the operating position by the mechanical locking element 34 (step S3 in FIG. 3).

[0091] If the target force F.sub.target cannot be reached at all, a warning is shown on the display 44 so that the operator can check whether the chamber doctor blade 14 is correctly installed and the drive system 20 is not blocked.

[0092] At this point, the printing machine 10 can start to print without the danger of ink leakage, as the chamber doctor blade 14 is in tight contact with the anilox roll and the drive system 20 is securely locked.

[0093] The actual force F is measured by the sensor 32 and the sensor value is transmitted to the control unit 38, compared with the target force F.sub.target and saved in the storage module 46 (step S4 in FIG. 3). If the actual force F is still equal to F.sub.target, operation of the printing machine 10 will continue in the current state.

[0094] After a set time interval t.sub.1, e.g. after 5 to 60 seconds, the actual force F is measured again by the sensor 32, transmitted to the control unit 38 and compared with the target force F.sub.target.

[0095] This procedure of measuring the actual force F and comparing the measured actual force F with the target force F.sub.target is repeated every t.sub.1 as long as the actual force F is equal to F.sub.target. This mode of the printing machine 10 is called monitoring mode, i.e. the position of the drive system 20 is not actively adjusted but the actual force F is monitored by the sensor 32.

[0096] If at some point the actual force F is not any more equal to F.sub.target, the control unit 38 shows a warning on the display 44 to inform the operator.

[0097] The control unit 38 will send a signal to the locking control unit 36 to unlock the drive system 20.

[0098] Then, the drive system 20 will again be moved in the operating position, i.e. the piston 24 will be moved such that the actual force F as measured by the sensor 32 is again equal to F.sub.target. As soon as F.sub.target is reached again, the position of the drive system 20 is locked by the mechanical locking element 34, and the monitoring mode is resumed (Step S5 in FIG. 3).

[0099] During longer operation of the printing machine 10, a number of sensor values will be stored in the storage module 46. These sensor values can be used by the analysis module 48 to identify and/or classify changes in the sensor values in dependence of time and/or frequency.

[0100] Optionally, prior to the above-described method, a calibration step can be done. During calibration, the drive system 20 moves into a calibration position in which the chamber doctor blade 14 is pressed with the maximum force F.sub.max against the anilox roll.

[0101] If the maximum force F.sub.max cannot be reached at all or is not reached within an expected time interval after activation of the drive system 20, a warning is shown on the display 44.

[0102] For further ensuring correct functionality of the printing machine 10, the actual force F can be measured over a second pre-set time t.sub.2 after the drive system 20 has been moved in the operating position and before locking the drive system 20. This allows to check whether the actual force F can also be sufficiently controlled just by the drive system 20 itself, even without the mechanical locking element 34.

[0103] The method according to the invention allows to reliably operate the printing machine 10 without the danger of ink leakage. By constantly monitoring the force with which the doctor blade is pushed against the anilox roll, immediate adjustment of the force is possible.

[0104] As shown a bit more in detail in FIG. 2 a sensor 32 adapted for sensing a force, is arranged between a cylinder 22 of the drive system 20 and a mounting bracket 50 of the chamber doctor blade 14, constantly monitoring the force towards the anilox roll. The cylinder 22 is mechanically looked with constant force towards the anilox roll being independent from any short term process changes like ink viscosity, air in the system or ink flow fluctuations.

[0105] As soon as the sensor 32 detects a permanent change on the force toward the anilox roll, time, frequency of change and force, are considered before a new force is set and locked.

[0106] Following an exemplary sequence is described. [0107] cylinder pressure is set considering set up pressure and repulsive force; [0108] unlock the cylinder 22 [0109] change pressure on the cylinder 22 e.g. via electric/pneumatic transformer, until new set up pressure is reached [0110] lock cylinder.