Doctor blade device of a gravure printing press and method for setting the effective stiffness of a doctor blade

Abstract

The invention relates to a doctor blade device of a gravure printing press, comprising a doctor blade holder (10), which has a doctor-blade-holder lower part (11) and a doctor-blade-holder upper part (12) which have clamping surfaces for clamping a doctor blade (14), wherein the doctor blade (14), when clamped, has a free portion (15) having a doctor blade edge (16) oriented parallel to a longitudinal axis of the doctor blade holder (10). The invention also relates to a method for setting the effective stiffness of a doctor blade (14) of a gravure printing press during a printing method in progress. In a method for extending the service life of a doctor blade (14) so that the throughput of a gravure printing press can be increased, it is firstly proposed that the doctor blade holder (10) of the doctor blade device has a claw (20) which is mounted for translation along a translation path (21) and which has a contact surface (22), the contact surface (22) of the claw (20) running parallel to the longitudinal axis of the doctor blade holder (10) and being designed to contact the free portion (15) of the clamped doctor blade (14) at a specifiable position so that the effective stiffness of the doctor blade (14) can be set by positioning of the claw (20). It is also provided that the setting of the effective stiffness of the doctor blade (14) is controlled by means of a control loop, according to which the effective stiffness of the doctor blade (14) is set in response to a control deviation in such a way that the control deviation is minimized.

Description

[0001] Squeegee device of a gravure printing machine and method for adjusting the effective stiffness of a squeegee

[0002] The invention relates to a doctor blade device of a gravure printing machine with a doctor blade holder which has a doctor blade holder lower part and a doctor blade holder upper part which have clamping surfaces for clamping a doctor blade, wherein the doctor blade in the clamped state has a free section with a doctor blade edge which is aligned parallel to a longitudinal axis of the doctor blade holder.

[0003] Furthermore, the invention relates to a method for adjusting the effective stiffness of a doctor blade of a gravure printing machine during an ongoing printing process.

[0004] Fig. 1 shows, by way of example and to explain the functioning of a doctor blade device, a schematic representation of a printing unit 1 of a prior art gravure printing press. In the gravure printing process, elements to be reproduced are introduced as depressions, the so-called cells, into the surface of a printing cylinder 2, which rotates within an ink bath 3 and absorbs ink over its entire surface. Excess ink is doctored or wiped off the surface of the printing cylinder 2 by a doctor blade device 4 arranged downstream in the direction of rotation Pi, comprising a doctor blade holder 5, a doctor blade 6 held therein and an (optional) support doctor blade 7, so that the ink remains only in the cells of the printing cylinder 2. The ink remaining in the cells is then transferred to a substrate 9, which for this purpose is guided between the printing cylinder 2 and a counter-rotating impression cylinder 8.Viewed in the direction of rotation Pi of the printing cylinder 2, the printing cylinder 2 then absorbs ink again in the ink bath 3 and a continuous printing process results.

[0005] The quality of the print result depends in particular on the amount of ink transferred from the printing cylinder to the substrate and thus on whether the tonal value is as specified or deviates significantly from it. The tonal value varies depending on the squeegee setting. A squeegee that is too flexible / soft will result in too much ink remaining on the printing cylinder and being transferred to the substrate, resulting in an undesirable increase in tonal value. In contrast, a squeegee that is set too stiff will result in too much ink being doctored off the printing cylinder, meaning too little ink is transferred to the substrate, which also results in an undesirable decrease in tonal value. Therefore, precise adjustment of the squeegee in terms of its stiffness and / or the pressure the squeegee applies to the printing cylinder is crucial for optimal printing results.

[0006] Due to the rubbing contact of the doctor blade with the printing cylinder, the doctor blade wears out, making it a consumable part that must be replaced after a certain period of use. Replacing a worn doctor blade is labor-intensive and requires the printing unit of the gravure printing press to be temporarily shut down, which adversely reduces the throughput of the gravure printing press.

[0007] Based on this, the object of the invention is to propose a doctor blade device and a method with which the service life of a doctor blade can be increased so that the throughput of a gravure printing machine can be increased.

[0008] This object is achieved by the doctor device according to claim 1 and the method according to claim 10.

[0009] According to the invention, it is first provided that the doctor blade holder of the doctor blade device has a claw which is mounted so as to be movable along a displacement path and has a contact surface, wherein the contact surface of the claw runs parallel to the longitudinal axis of the doctor blade holder and is designed to rest on the free section of the clamped doctor blade in a predeterminable position, so that the effective stiffness of the doctor blade can be adjusted by means of a positioning of the claw.

[0010] The effective stiffness of the doctor blade refers to the stiffness of the doctor blade in relation to a force acting on the doctor blade edge in the direction of rotation of the printing roller. This allows the effective stiffness of the doctor blade to be adjusted during the printing process. In particular, the effective stiffness of the doctor blade can be increased with increasing wear by moving the claw in the direction of the doctor blade edge, which compensates for the wear-related decrease in the ability to doctor ink from the printing cylinder. An overly stiff setting of the doctor blade can also be compensated for by moving the claw in the opposite direction. This allows both unwanted dot gains and dot decreases to be corrected immediately, significantly increasing the service life of a clamped doctor blade and thus the throughput of the gravure printing press. Furthermore, the installation of a support doctor blade is no longer necessary.

[0011] Furthermore, the method according to the invention provides for the adjustment of the effective stiffness of the doctor blade to be controlled by means of a control loop, according to which the effective stiffness of the doctor blade is adjusted in response to a control deviation such that the control deviation is minimized. The method according to the invention allows for automated adjustment of the effective stiffness of the doctor blade and thus a direct optimization of the printing result, which also significantly increases the service life of a clamped doctor blade and thus the throughput of the gravure printing press.

[0012] Advantageous embodiments of the invention are specified below and in the subclaims.

[0013] According to a preferred embodiment of the invention, it is provided that the claw is mounted on the doctor blade holder upper part in a sliding manner, wherein the displacement path is preferably aligned perpendicular to the longitudinal axis of the doctor blade holder and parallel to the clamping surfaces.

[0014] The doctor blade device preferably has an actuator that is connected to the claw in a force-transmitting manner, wherein the actuator is preferably designed as a drive motor. The drive motor is preferably an eccentric that converts a rotational movement of the eccentric into a longitudinal movement of the claw.

[0015] To prevent an unintentional change in the position of the clamp in the event of an acute power failure, the drive motor is preferably equipped with a self-locking mechanism. This is achieved by a advantageous refinement using a planetary gear system upstream of the electric motor. Another alternative to using a drive motor with an eccentric shaft is a spindle drive, which translates the rotation of the electric motor into a linear movement of the clamp.

[0016] Preferably, the contact surface is formed, at least in sections, on a sealing element that is connected to the claw. The sealing element is preferably made of polyurethane and prevents squeegeed ink running down the top side of the squeegee from penetrating the cavity that forms between the claw and the upper part of the squeegee holder and the lower part of the squeegee holder. The sealing element is preferably embedded in a groove in the claw that runs parallel to the longitudinal axis of the squeegee holder. Irrespective of this, the contact surface can also be formed, at least in sections, directly on a section of the claw that is free of the sealing element, so that the adjustment of the effective stiffness of the squeegee is independent of the elasticity of the sealing element.

[0017] According to a further advantageous embodiment of the invention, the clamping surface of the lower squeegee part transitions into a contact surface designed to support the clamped squeegee, wherein a drainage channel for removing the squeegeed substance is preferably incorporated into the contact surface. Such a drainage channel is preferably oriented downwards on at least one side of the squeegee holder, thus also preventing squeegeed substance from entering the cavity between the lower squeegee holder part, the upper squeegee holder part, and the claw.

[0018] Preferably, when the doctor blade device is in its intended installation position on the gravure printing press, the claw is arranged on the upper part of the doctor blade holder such that the contact surface of the claw is in contact with the doctor blade on the side facing away from the doctor blade with respect to the direction of rotation of the printing cylinder. As a result, when the doctor blade device is used as intended, the rotation of the printing cylinder presses the doctor blade onto the contact surface of the claw. This allows the effective stiffness of the doctor blade to be precisely specified by the positioning of the claw, and improves the sealing effect of the sealing element against the penetration of ink. According to a particularly preferred embodiment of the invention, the doctor blade device comprises a doctor blade and a control device.The squeegee is clamped between the lower and upper sections of the squeegee holder such that the squeegee forms the free section and the squeegee edge is aligned parallel to the longitudinal axis of the squeegee holder. The control device comprises a control unit with a comparison element and a controller, the actuator, and a measuring element. The measuring element is designed, in particular, as a web monitor, which is configured to determine an actual tonal value of the substrate printed with the gravure printing press.

[0019] According to an advantageous embodiment of the method according to the invention, the effective stiffness of the doctor blade is adjusted using a doctor blade device comprising a doctor blade and a control device. The doctor blade is clamped between the lower and upper doctor blade holders in such a way that the doctor blade forms the free section and the doctor blade edge is aligned parallel to the longitudinal axis of the doctor blade holder. The control device comprises the control unit with the comparison element and the controller, the actuator, and the measuring element. The effective stiffness of the doctor blade is adjusted by positioning the clamp along the displacement path.

[0020] Preferably, the control deviation is the difference between a reference variable and a controlled variable, wherein the reference variable is preferably a target tonal value of the printed substrate and the controlled variable is preferably the actual tonal value of the printed substrate. Preferably, the controlled variable is measured by the measuring element and the control deviation is determined by the comparison element, wherein the control deviation results from the difference between the reference variable and the controlled variable.

[0021] In all of this, the individual components of the doctor blade holder, in particular the doctor blade holder lower part, the doctor blade holder upper part and the claw, are preferably made of aluminum or stainless steel.

[0022] Specific embodiments of the present invention are explained below with reference to the figures. In the figures: Fig. 1 shows a schematic representation of a printing unit of a gravure printing machine according to the prior art,

[0023] Fig. 2a, b each show a schematic representation of a printing unit of a gravure printing machine,

[0024] Fig. 3a a top view of a doctor blade holder with a clamped doctor blade,

[0025] Fig. 3b a side view of a doctor blade holder with a clamped doctor blade,

[0026] Fig. 3c, d each show a cross-sectional view of a doctor blade holder with a doctor blade in the assembled state (Fig. 4a) and in an exploded view (Fig. 4b) and

[0027] Fig. 4 is a block diagram of a control loop.

[0028] Fig. 2a shows, analogous to Fig. 1, a printing unit 1 of a gravure printing press with a printing cylinder 2 which rotates in the direction of rotation Pi through an ink bath 3 and absorbs ink, an impression cylinder 8 and a web-shaped substrate 9 which is guided between the printing cylinder 2 and the impression cylinder 8 so that the ink is transferred from the printing cylinder 2 to the substrate 9. For doctoring off excess ink on the printing cylinder 2, a doctor blade device 100 with a doctor blade holder 10 is provided, which is shown in detail in Figs. 3a-d. According to this, the doctor blade holder 10 has a doctor blade holder lower part 11 and a doctor blade holder upper part 12, which have clamping surfaces 131, 132 for clamping a doctor blade 14. The doctor blade 14 is designed as a ground steel belt and, when clamped, has a free section 15 with a doctor blade edge 16 which, when used as intended, rests against the printing cylinder 2 of the gravure printing machine.To achieve a uniform squeegee result, the squeegee edge 16 is aligned parallel to a longitudinal axis A of the squeegee holder 10. The squeegee holder upper part 12 and the squeegee holder lower part 11 are connected to one another by a screw connection with several bolts 17, for which purpose the squeegee holder upper part 12 has several stepped receiving bores 18 and the squeegee holder lower part 11 has several corresponding threaded bores 19. The squeegee holder lower part 11 has several spaced-apart rows of threaded bores 19 so that the squeegee holder 10 can be adapted to different squeegee widths. The squeegee 14 is free of any recesses and, when clamped, is held in a force-fitting manner and is not penetrated by threaded bolts, which simplifies replacement of the squeegee 14 due to wear.

[0029] The doctor blade holder 10 has a claw 20 which is mounted on the doctor blade holder upper part 12 for sliding movement along a displacement path 21 and has a contact surface 22 which runs parallel to the longitudinal axis A of the doctor blade holder 10 and is designed to bear against the free section 15 of the clamped doctor blade 14, whereby the effective stiffness of the doctor blade 14 can be adjusted by positioning the claw 20. The displacement path 21 is limited by a rear stop and a front stop, with the front stop facing the doctor blade edge 16 and the rear stop facing away from the doctor blade edge 16. The effective stiffness of the doctor blade 14 refers to the stiffness of the doctor blade 14 with respect to a force applied in the direction of arrow P2. The further the claw 20 is moved from the rear stop towards the front stop, the greater the effective stiffness of the doctor blade 14 is set.The claw 20 and the doctor blade holder upper part 12 are connected to each other via a guide rail 23, which blocks any displacement of the claw 20 in a direction not along the displacement path 21. To loosen and tighten the bolts 17 that connect the doctor blade holder upper part 12 and the doctor blade holder lower part 11, the claw 20 has elongated holes that are aligned with the bolts 18 and thus allow access.

[0030] For the demand-dependent positioning of the claw 20 along the displacement path 21, an actuator 24 in the form of a drive motor 241 is provided, which is designed as an eccentric 2411 and is indirectly connected to the claw 20 via a drive rod 25, whereby a rotary movement of the eccentric 2411 is converted into a longitudinal movement of the claw 20. The claw 20 is L-shaped in cross-section and has a groove 26 in the region of the contact surface 22 for receiving a sealing element 27, which in the illustrated embodiment is made of polyurethane. In the illustrated embodiment, the contact surface 22 is designed over the entire surface of the sealing element TI of the claw 20. The clamping surface 131 of the squeegee holder lower part 11 merges into a contact surface 34, which is designed for the contact of the clamped squeegee 14. The contact surface 34 has a drainage channel 33 which is designed to remove a scraped-off substance.To carry out the method 200 and thus adjust the effective stiffness of the doctor blade 14 as needed, a control device 28 is provided, which comprises a control unit 29 with a comparison element 30 and a controller 31, the actuator 24, and a measuring element 32. Two different embodiments of the measuring element 32 are provided within the scope of the present invention. According to the embodiment shown in Fig. 2a, the measuring element 32 is designed as a web monitor 321, which is configured to determine the actual tonal value of a substrate 9 printed with the gravure printing press. The actual tonal value represents a controlled variable x(t) of a control loop. In the embodiment shown in Fig.2b, the measuring element 32 is designed as a light step sensor 322, which is configured to detect the instantaneous geometry of the doctor blade 14 during its intended use, so that an angle 0 between the doctor blade 14 and the printing cylinder 2 can be calculated, which angle is taken into account as the controlled variable x(t) of the control loop.

[0031] In both cases, a control deviation e(t) is determined using the comparator 30. This deviation is the difference between a preset reference variable w(t) and the measurable controlled variable x(t). Therefore, the following applies to the control deviation e(t): e(t)=w(t)-x(t)

[0032] In the embodiment according to Fig. 2a, the predeterminable reference variable w(t) is a target tone value, whereas in the embodiment according to Fig. 2b, the predeterminable reference variable w(t) is the target angle between doctor blade 14 and printing cylinder 2.

[0033] From the control deviation e(t), the control unit 29 calculates a control variable u(t), which is passed on to the actuator 24. In the illustrated embodiment, the control variable u(t) is a specific angle of rotation of the eccentric 2411, by which the eccentric 2411 is to move to displace the claw 20 along its displacement path 21 such that the control deviation e(t) is minimized. The displacement of the claw 20 results in a changed manipulated variable y(t), which in the illustrated embodiment is the effective stiffness of the squeegee 14. The squeegee 14 with its effective stiffness, together with the squeegee holder 10, forms a controlled system 35, which is affected by disturbance variables z(t), such as increasing wear of the squeegee 14 and / or temperature-related changes in the squeegee stiffness. These disturbance variables z(t) result in the controlled variable x(t), which in the embodiments shown refers to the actual tone value (Fig. 2a) or the actual angle (Fig. 2b).The controlled variable x(t) is measured by the respective measuring element 32 of the control device 28 and transferred to the comparison element 30 of the control unit 29, thus closing the control loop. This allows for continuous monitoring of the controlled variable x(t) and immediate readjustment of the doctor blade holder 10 so that the control deviation e(t) is as minimal as possible. Only when further displacement of the clamp 20 fails to minimize the control deviation e(t) does the doctor blade 14 need to be replaced due to wear.

[0034] Reference symbol

[0035] 100 doctor blade device

[0036] 200 procedures

[0037] 1 printing unit

[0038] 2 pressure cylinders

[0039] 3 dye bath

[0040] 4 Squeegee device

[0041] 5 squeegee holders

[0042] 6 squeegees

[0043] 7 support squeegees

[0044] 8 impression cylinders

[0045] 9 Substrat

[0046] 10 squeegee holders

[0047] 11 Squeegee holder lower part

[0048] 12 Squeegee holder upper part

[0049] 131 clamping surface

[0050] 132 clamping surface

[0051] 14 squeegees

[0052] 15 free section

[0053] 16 Squeegee edge

[0054] 17 bolts

[0055] 18 mounting hole

[0056] 19 threaded hole

[0057] 20 claws

[0058] 21 Displacement path

[0059] 22 Contact surface

[0060] 23 Scenery

[0061] 24 actuator

[0062] 241 drive motor

[0063] 242 eccentric

[0064] 25 Drive rod

[0065] 26 Nut io TI sealing element

[0066] 28 Control device

[0067] 29 Control unit

[0068] 30 Comparison term

[0069] 31 controllers

[0070] 32 measuring elements

[0071] 321 Railway monitoring

[0072] 322 Light step sensor

[0073] 33 Drainage channel

[0074] 34 contact surface

[0075] 35 Control system

[0076] A Longitudinal axis

[0077] 0 angles

[0078] Pi rotation direction

[0079] P2Arrow direction w(t) Reference variable x(t) Controlled variable e(t) Control deviation u(t) Control variable y(t) Manipulated variable z(t) Disturbance variable

Claims

Claims 1. Doctor blade device (100) of a gravure printing machine with a doctor blade holder (10) which has a doctor blade holder lower part (11) and a doctor blade holder upper part (12) which have clamping surfaces (131, 132) for clamping a doctor blade (14), wherein the doctor blade (14) in the clamped state has a free section (15) with a doctor blade edge (16) which is aligned parallel to a longitudinal axis (A) of the doctor blade holder (10), characterized in that the doctor blade holder (10) has a claw (20) which is mounted so as to be movable along a displacement path (21) and has a contact surface (22), wherein the contact surface (22) of the claw (20) runs parallel to the longitudinal axis (A) of the doctor blade holder (10) and is designed to rest on the free section (15) of the clamped doctor blade (14) in a predeterminable position, so that the effective The stiffness of the squeegee (14) can be adjusted by positioning the claw (20).

2. Squeegee device (100) according to claim 1, characterized in that the claw (20) is mounted on the squeegee holder upper part (12) in a sliding manner, wherein the displacement path (21) is preferably aligned perpendicular to the longitudinal axis (A) of the squeegee holder (10) and parallel to the clamping surfaces (131, 132).

3. Squeegee device (100) according to one of the preceding claims, characterized by an actuator (24) which is connected to the claw (20) in a force-transmitting manner, wherein the actuator (24) is preferably designed as a drive motor (241).

4. Squeegee device (100) according to claim 3, characterized in that the drive motor (241) is designed as an eccentric (2411) which converts a rotary movement of the eccentric (2411) into a longitudinal movement of the claw (20).

5. Squeegee device (100) according to one of the preceding claims, characterized in that the contact surface (22) is formed at least in sections on a sealing element (27) which is connected to the claw (20).

6. Squeegee device (100) according to one of the preceding claims, characterized in that the clamping surface (131) of the squeegee holder lower part (11) merges into a contact surface (34) which is designed for the contact of the clamped squeegee, wherein a drainage channel (33) for the removal of a squeegeed substance is preferably incorporated in the contact surface (34).

7. Doctor blade device (100) according to one of the preceding claims, characterized in that the claw (20) is arranged on the doctor blade holder upper part (12) in the intended installation position of the doctor blade device (100) on the gravure printing machine in such a way that the contact surface (22) of the claw (20) on the side of the doctor blade (14) is in contact with the doctor blade (14) which is facing away from the doctor blade (14) with respect to the direction of rotation (Pi) of the printing cylinder (2).

8. Doctor device (100) according to one of the preceding claims, characterized by - a doctor blade (14) which is clamped between the doctor blade holder lower part (11) and the doctor blade holder upper part (12) in such a way that the doctor blade (14) forms the free section (15) and the doctor blade edge (16) is aligned parallel to the longitudinal axis (A) of the doctor blade holder (10), and - a control device (28) comprising a control unit (29) with a comparison element (30) and a controller (31), the actuator (24) and a measuring element (32).

9. Doctor blade device (100) according to claim 8, characterized in that the measuring element (32) is designed as a web monitoring device (321) which is set up to determine an actual tonal value of a substrate (9) printed with the gravure printing machine.

10. Method (200) for adjusting the effective stiffness of a doctor blade (14) of a gravure printing machine during an ongoing printing process, characterized in that the adjustment of the effective stiffness of the doctor blade (14) is controlled by means of a control loop, according to which the effective stiffness of the Doctor blade (14) is adjusted in response to a control deviation (e(t)) such that the control deviation (e(t)) is minimized.

11. Method (200) according to claim 10, characterized in that the adjustment of the effective stiffness of the doctor blade (14) is carried out with a doctor blade device (100) according to one of claims 8 or 9, so that the adjustment of the effective stiffness of the doctor blade (14) is carried out by positioning the claw (20) along the displacement path (21).

12. Method (200) according to one of claims 10 to 11, characterized in that the control deviation (e(t)) is the difference between a reference variable (w(t)) and a controlled variable (x(t)), wherein the reference variable (w(t)) is preferably a target tonal value of the printed substrate (9) and the controlled variable (x(t)) is preferably the actual tonal value of the printed substrate (9).

13. Method (200) according to one of claims 10 to 12, characterized in that the controlled variable (x(t)) is measured by means of the measuring element (32).

14. Method (200) according to one of claims 10 to 13, characterized in that the control deviation (e(t)) is determined by means of the comparison element (30), the control deviation (e(t)) resulting from the difference between the reference variable (w(t)) and the controlled variable (x(t)).

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