WO2013024186A1

WO2013024186A1 - Method for the adjustment of pressures in a flexographic printing press and flexographic printing press for the implementation thereof

Info

Publication number: WO2013024186A1
Application number: PCT/ES2012/000219
Authority: WO
Inventors: Jordi PUIG VILÀ; Alfonzo CORBACHO TEJADA; Sebastià BOTA OLIVERAS
Original assignee: Comexi Group Industries, Sau
Priority date: 2011-08-12
Filing date: 2012-08-09
Publication date: 2013-02-21
Also published as: ES2395183B1; DE202012000246U1; ES2395183A1

Abstract

The method comprises: in a first step, linearly moving a printing roll and an inking roll towards a central, counterpressure roll, causing said rolls to rotate, and monitoring the torque thereof, and, upon detection of a variation in torque, performing a first adjustment of pressure between said printing roll and one of said central, counterpressure or inking rolls; and, in a second step, a) carrying out printing; b) capturing an image from said printing; c) examining the quality of said captured image; and d) varying the pressure exerted between the printing roll and one of said central, counterpressure or inking rolls; and repeating said sequence of actions a) to d) to achieve an optimum level of pressure between the rolls. The press is designed in order to implement the method.

Description

METHOD FOR PRESSURE ADJUSTMENT IN A FLEXOGRAPHIC PRINTER MACHINE AND FLEXOGRAPHIC PRINTER MACHINE FOR YOUR

IMPLEMENTATION Technical sector

The present invention concerns in a first aspect a method for adjusting the printing pressure, using information captured from the printed image, applicable to a flexographic machine, equipped as is conventional with several printing groups arranged around a central backpressure cylinder on which the material to be printed is supported, and each of said printing groups integrating at least one printing cylinder and an inking cylinder (also called an ink applicator) that receives ink feed, said adjustment being necessary to achieve a correct impression.

It is well known in this sector that in order to execute printing tasks using an flexographic machine and achieve an optimal ink transfer, it is necessary to provide a correct pressure adjustment both between the inking cylinder and the printing cylinder, and between said printing cylinder and the material to be printed, that is to say the correct pressure between said cylinders, inking cylinder and printing cylinder and between the latter and the central backpressure cylinder, which supports the material to be printed.

The correct pressure between the cylinders of the inking group (printing cylinder and applicator cylinder and between the printing cylinder and the central counterpressure cylinder (material) is a critical factor for correct printing, and depends among other factors of the type of cliché a print, of the adhesive with which the cliché has been fixed to the cylinder, of the material on which it is to be printed, of the motif to be printed, etc. and therefore must be adjusted in each new print job.

In a second aspect, the invention also provides a printing machine for implementing said method. Background of the invention

Numerous methods are known for adjusting the printing pressure in a flexographic machine.

In patent ES 2308716 an automatic adjustment is described by reading the printed surface and based on the comparison of the position of each of the monochrome prints of the different groups registered at different times by at least one sensor station. The method requires a sensor system by each printing group, where during one registration process one print cylinder is located after another in the printing position, and which comprises the following steps:

- a single sensor station registers each monochrome print obtained - the correction signals for the actuator (s) of a printing cylinder are obtained from the monochrome image of each printing cylinder and the information regarding the rotational movements of At least one printing cylinder.

Said patent ES 2308716 solves the problem of making the correct adjustment of the working pressures, but the described method implies that no more than one color can be made at the same time (being monochrome images) and this entails a great waste of material and of time when adjusting.

To solve the problem of the material and time spent in making the adjustment, we can find in the state of the art various patents that try to make more or less precise adjustments with minimum waste.

Thus, in EP 1 916 102 an adjustment system is proposed based on a series of theoretical calculations on the outside of the machine, where the value of the diameter of the sleeves of the printing and inking cylinders is estimated. From these theoretical calculations, the final positions of the positioning drives are recalculated. This procedure minimizes wastage in time and material, but since it is a purely theoretical procedure the reliability of the adjustment is very low, since in the printing process not only the diameter of the rollers is involved, but also and fundamentally the type of cliché to print, the ink, the substrate on which it is printed, ... all factors determining the correct printing pressure. This procedure is valid to find the point of contact of the printing and inking cylinders with each other and of the printing cylinder with the material, but not to determine the correct pressure between them.

Patent application EP 1 018 426 discloses a flexographic printer in which an automatic procedure for adjusting a printing cylinder, an applicator cylinder and a back pressure cylinder can be carried out. Said procedure comprises the following steps:

• first, and with the help of the rotating drive motor of the printing cylinder, said printing cylinder is brought to a slow rotation;

• then the applicator cylinder, which still does not rotate, moves slowly in its radial direction against the printing cylinder; • as soon as the printing cylinder and the applicator cylinder come into contact, a rotation of the rotation torque of the rotating drive motor of the printing cylinder takes place, which is registered by a rotary encoder (of said motor);

«The position that the applicator cylinder has reached at this time is stored by a printer control unit as zero position of said applicator cylinder;

• the printing cylinder - which continues to rotate - is then moved against the counterpressure cylinder until there is another change in the rotation torque of its rotating drive motor;

• the position of the printing cylinder is stored in the control unit as zero position of the printing cylinder; Y

• the path that the print cylinder has traveled until it comes into contact with the backpressure cylinder is added to the zero position of the applicator cylinder The adjustment process according to the approach sequence according to the EP

1 018 426 has, however, disadvantages since the forces acting on the surface of the cylinder when the cylinders come into contact can be very high. The tests have shown that the clichés mounted on the printing cylinders already show damage after some automatic adjustment cycles performed in accordance with this approach process.

On the other hand, patent application WO2010 / 142405 discloses a flexographic printer in which it is tried to solve the inconveniences of the automatic cycle described in the application EP 1 018 426, especially those related to the damages that may be caused on the surface of the cliché. Said patent application WO 2010/142405 proposes a device and a method for adjusting the cylinders of a printer that do not damage the printing cylinder, in which the rotation drive of the cylinders of the inking group is controlled by a control unit of the printer that is arranged in such a way that it operates in a weakened flow mode (limited torque) at least one of the rotational drive motors of the cylinders during their mutual adjustment.

According to patent application WO 2010/142405, in order not to damage the raised areas of the printing cylinder during the adjustment procedure, the control unit reduces the current produced by the torque that is applied to the cylinder drive, so that the drive undergoes a weakening of the field and in this way the magnetic flux in the working area of the motor is reduced below the nominal value, whereby a reduction in the torque at the drive is achieved in the drive same speed When under such conditions a rotating cylinder contacts the turning torque with another cylinder and with it the force that acts during the contact of the cylinders on the surface of the cylinder, they are very small and thus the clichés surfaces are not damaged.

Both in EP 1916102 and in both EP patent applications

1018426 and WO 2010/142405, however, the real problem of adjusting the correct working pressure is not solved. In this background, a zero point of contact of the printing cylinder with the material and contact of the cylinders of the inking group (applicator cylinder and printing cylinder) with each other is detected, but then an approach movement of between 10 and 100 must be applied microns (see page 5 lines 20 to 23 of the application WO 2010/142405) to achieve the optimum working pressure. This approach of between 10 and 100 microns is for the machine operator's consideration, so that an optimal work adjustment is not automatically achieved.

In ES 2300209, a method of positional adjustment of printing bodies in flexographic printing machines is proposed, comprising the following steps: a) move linearly in approximation by guide arrangements of a first printing cylinder towards the support drum by means of a linear motor ; b) detecting that a point of contact has been reached between said first printing cylinder, or a cliché fixed thereon, and the sheet material resting on the support drum;

c) rotate the support drum, and allow rotation of the first printing roller dragged by the friction support drum, through the sheet material, or rotate them both synchronously: the support drum and the first printing cylinder ; Y

d) detecting the linear approach-distance positions on said guide arrangements of the first printing roller.

This method comprises in step c) an action that involves friction that can in some cases result in damage to the material, or errors, and the adjustment depends on the reliability of the detection in the final stage d).

The objective of the present invention is to present a method of adjusting the working pressure applied to inking and printing cylinders, in which the optimum working pressure is actually determined automatically, with the help of an acquisition device for the print image, such as a linear camera and allowing a part of the method to be carried out simultaneously with several printing groups avoiding the dead time between the printing zone and the printing zone. viewed, saving a significant volume of the print material, automating the adjustment and avoiding the intervention of the operator and the possible errors that he may commit. Brief exposition of the invention

For this purpose, the present pressure adjustment method is executed in a conventional flexographic printing machine equipped with several printing groups arranged around a central backpressure cylinder on which the material to be printed is located, each of said printing groups being integrated at least one printing cylinder and an inking cylinder, capable of rotation by means of a rotating drive motor, said printing machine having associated image acquisition means, such as a linear camera or other system, capable of capturing an image of the printing of each printing group and of the set or of a selected group thereof. In addition, the flexographic printing machine has a control unit for detecting one or more parameters of the rotary movement of the cylinders, such as the torque, electrical intensity consumed by said rotating drive motor or the rotation speed.

The pressure adjustment of each of the printing groups in relation to the backpressure cylinder is carried out by means of positioning motors that apply a linear displacement in said radial direction to the bearing axes of said printing and inking cylinders.

The method, for a printing group, comprises two distinct stages. In a first stage the following actions are carried out:

- linearly moving said printing cylinder and said inking cylinder towards said central backpressure cylinder, rotating them, actively or passively, and monitoring their turning torque, and

- making, from a detection of a variation in torque, a first pressure adjustment between at least said printing cylinder with said counterpressure cylinder or between said printing and inking cylinders.

This ensures a contact position between the different cylinders.

In a second stage a fine pressure adjustment is carried out by at least one sequence that includes the following actions:

a) make an impression on a sheet material arranged on said central backpressure cylinder, b) capture at least one image of at least part of said print, for example by a linear camera,

c) analyze the quality of said captured image; Y

d) vary the pressure exerted by the printing cylinder on the central counterpressure cylinder, or the pressure between said two cylinders, by means of said positioning motors.

And the aforementioned sequence of actions a) to d) will be repeated until an optimum pressure point between the cylinders is reached determined by the optimum quality of the captured image.

According to the proposed method, the first pressure adjustment stage is carried out simultaneously in several printing groups and said second stage can be performed group by group or simultaneously depending on the type of reason to be printed.

In addition, the second fine adjustment stage is carried out with monitoring of the driving torque of at least one of said printing and inking cylinders.

During the said first pressure adjustment stage, it is also planned to monitor the torque of the positioning motors, and that said motors operate in at least said first stage in a torque limitation mode (reduced torque).

Other features of the invention will appear more clearly from the reading of an exemplary embodiment which is described below with the help of sheets of drawings.

Brief description of the drawings

Fig. 1 is a schematic view of a photographic printing machine for implementing the method of this invention.

Fig. 2 schematically illustrates the elements involved in the adjustment method of the present invention, in accordance with an exemplary embodiment.

Fig. 3 is a block diagram explaining the proposed method. Detailed description of an execution example

A typical printing group of a photographic printing machine is shown in Fig. 2, associated with a central backpressure cylinder 1, integrating a printing cylinder 2 and an inking cylinder 3, which in a printing situation are facing and capable of rotation with the aid of a respective rotating drive motor 5, 4. The printing machine to implement the method of this invention has means associated with a control unit (not illustrated) for detecting one or more parameters of the rotary movement of the cylinders 2, 3, in particular the torque, the electrical intensity consumed by said drive motors in rotation 4, 5, or the rotation speed (obtained by means of detectors 6, 7, such as rotary transducers).

Figure 2 shows pressure adjustment means 8, 9, 10, 11, implemented in this exemplary embodiment by means of an electric motor-spindle assembly, hereinafter referred to as positioning motors, which apply to the ends of the bearing axes of said printing cylinders 2 and inking 3, in their radial direction, a linear displacement in approximation or distance from the central counterpressure cylinder 1.

The printing machine also has image capture means C (see Fig. 1) for acquiring visual information of the prints made by each group G1 to G8, by several groups or by the set of groups G1 to G8 of the machine .

The method proposed by this invention comprises, for each printing group:

A first stage in which said printing cylinder 2 and said inking cylinder 3 move linearly towards said central counterpressure cylinder 1, rotating them (by means of engines 4, 5), actively or passively, and monitoring their torque of turn (by conventional means such as by monitoring the evolution of the intensity of the current consumed by each motor 4, 5), and performing, from a detection during said monitoring, a torque variation (increase above of a certain threshold) a first pressure setting between at least said printing cylinder 2 with said counterpressure cylinder 1 or between said printing cylinders 2 and inking 3, thereby ensuring that a contact position between the different cylinders has been reached .

In a second stage a fine adjustment of pressures is performed by one or more sequences, said sequence including the following actions:

a) making an impression on a sheet material L arranged on said central backpressure cylinder 1,

b) capture at least one image of at least part of said print, for example by a linear camera C,

c) analyze the quality of said captured image; Y d) vary the pressure exerted by the printing cylinder 2 on the central counterpressure cylinder 1, or the pressure between said two cylinders 2, 3, by means of said positioning motors 8, 9, 10, 11.

One or more sequences with the aforementioned actions will be used until an optimum pressure point is reached between the printing cylinder 2 and the inking cylinder 3, and between the printing cylinder 2 and the backpressure cylinder 1.

Fig. 3 clearly shows the proposed method and in it it is appreciated that said first pressure adjustment stage can be performed simultaneously in several printing groups (GROUP01 to GROUP n) which represents a significant saving by avoiding printing successive of the different groups, also avoiding the dead time that exists between the printing groups and the viewing area, saving a significant number of meters of test sheet material.

On the other hand, said second stage is carried out group by group and advantageously with a monitoring of the driving torque of at least one of said printing cylinders 2 and inking 3.

According to other characteristics of the proposed method:

• in said first adjustment stage it is also planned to also monitor the torque of the positioning motors 8, 9, 10, 11;

· In said first stage the positioning motors 8, 9, 10, 11, will operate in torque limitation mode (reduced torque);

• the linear displacements of the cylinders 2, 3, are performed alternatively by actuating the positioning motors 8, 11 on one end of a bearing shaft of the cylinders 2, 3, or the motors 9, 10 on the other end or all the motors of positioning 8, 9, 10 and 11, on both ends of both cylinders 2, 3 at the same time.

As the invention has indicated in a second aspect, it proposes a flexographic printing machine having a conventional general structure, which is illustrated in Fig. 1, formed by a central counterpressure cylinder 1, on which a sheet material runs L displaced from a reel by a rewinder D and rolled into a reel of printed material by means of a rewinder R.

The flexographic printing machine proposed by the second aspect of the invention has associated a linear camera C or another system for acquiring print images, and as a feature incorporates a control unit (not illustrated), in connection with said torque detection means and with said system of acquisition of images C, intended to execute said first and second stages of the explained method.

A person skilled in the art could introduce changes and modifications in the described embodiments without departing from the scope of the invention as defined in the appended claims.

Claims

1.- Method for adjusting pressures in a flexographic printing machine, equipped with several printing groups (G1 to G8) arranged around a central backpressure cylinder (1) on which the material to be printed (L) is located, integrating each of said printing groups (G1 to G8) at least one printing cylinder (2) and an inking cylinder (3), capable of rotation by means of a rotating drive motor (4, 5), the printer having means (6, 7) associated with a control unit for detecting one or more parameters of the rotary movement of the cylinders (2, 3), such as the torque, electrical intensity consumed by said rotating drive motor (4, 5) or the speed of rotation, and the printer having pressure adjustment means that apply to the ends of said printing cylinders (2) and inking (3), in their radial direction, a linear displacement, and integrate positioning motors (8, 9, 10, 11), comprising the method, for each printing group (G1 to G8):

- in a first stage:

- linearly moving said printing cylinder (2) and said inking cylinder (3) towards said central backpressure cylinder (1), rotating them, actively or passively, and monitoring their turning torque, and - performing, from a detection of a variation of torque, a first pressure adjustment between at least said printing cylinder (2) with said central backpressure cylinder (1) or between said printing cylinders (2) and inking (3); Y

- in a second stage, perform a fine pressure adjustment using at least one sequence that includes the following actions:

a) make an impression on a sheet material (L) disposed on said central backpressure cylinder (1),

b) capture at least one image of at least part of said print, c) analyze the quality of said captured image; Y

d) varying the pressure exerted by the printing cylinder (2) on the central counterpressure cylinder (1), or the pressure between said two printing cylinders (2) and inking (3), by means of said positioning motors (8, 9, 10, 11);

and repeat said sequence of actions a) to d) until an optimum pressure point is reached between the cylinders.

2- Method according to claim 1, characterized in that said first pressure adjustment stage is performed simultaneously in several printing groups (G1 to G8) and said second stage is performed group by group.

3- Method according to claim 1, characterized in that said first pressure adjustment stage is performed simultaneously in several printing groups (G1 a

G8) and said second stage is also performed simultaneously in several printing groups (G1 to G8).

4. - Method according to claim 1, characterized in that said second fine adjustment stage is carried out with monitoring of the driving torque of at least one of said printing cylinders (2) and inking (3).

5. - Method according to any one of the preceding claims, characterized in that said first stage also comprises monitoring the torque of the positioning motors (8, 9, 10, 11).

6. - Method according to claim 5, characterized in that said positioning motors (8, 9, 10, 11) operate in at least said first stage in a torque limitation or reduced torque mode.

7. - Method according to claim 1, characterized in that said linear displacements are performed alternatively by actuating the positioning motors (8, 9, 10, 11) on one end of a cylinder bearing axle (2, 3), on the other extreme or over both at the same time.

8- Method according to claim 1, characterized in that said first stage is performed by applying a variable tangential speed to the material supported in the central counterpressure cylinder (1) and to the printing cylinders (2) and inking (3).

9. - Method according to claim 8, characterized in that said first stage is performed by applying a tangential speed difference between the material supported in the central counterpressure cylinder (1) and the printing cylinders (2) and inking (3).

10. - Method according to claim 9, characterized in that said first stage is performed by applying a tangential speed difference between the printing cylinders (2) and inking (3).

11.- Flexographic printing machine, comprising:

- a central counterpressure cylinder (1), rotatable, and at least one printing cylinder (2) and an inking cylinder (3), rotatable and linearly operable;

- drive means (4, 5) for carrying out said rotational drives; - drive means (8, 9, 10, 11) for carrying out said linear drives;

- at least one image acquisition unit (C) of the printed material;

- means for measuring torque arranged to detect the torque of at least said printing cylinder (2); Y

- a control unit, in connection with said turning torque detection means and with said image acquisition unit (C), and intended to implement the method according to any one of the preceding claims.

12. Flexographic printing machine according to the preceding claim, comprising means for measuring the torque arranged to detect the torque of both printing cylinders (2) and inking (3).