EP0683729B1 - Process for controlling a cylinder-type silk screen printing machine - Google Patents

Abstract

In said machine, a printing cylinder that collects the object to receive the print and a screen carriage with printing blades applied against the screen pattern, which travels over the cylinder, are moved during the printing process at a synchronized speed. In order to reduce the consumption of printing material and hence the environmental pollution, and at the same time to ensure synchronization of the printing cylinder and screen carriage by simple technical means, the printing cylinder and screen carriage are driven independently of one another; data for adjustment of the printing travel and printing speed are programmed into an electronic control system, stored therein and processed to obtain control signals for the drives, and the relevant movement positions of the printing cylinders and screen carriage are determined during the printing process by travel measurement systems and further processed in the electronic control system in order to adjust the control signals.

Description

The invention relates to a method for controlling a screen printing cylinder machine, wherein during the printing process a printing cylinder receiving the printing material and driven by a drive motor and a screening carriage traveling over it are moved with synchronized speed with a squeegee lowered onto the screen template. The invention further relates to a screen printing cylinder machine with a printing cylinder receiving the printing material and driven by a drive motor, a screen carriage traveling over it, a squeegee which can be lowered onto the screen stencil and a device for synchronizing the movement of the printing cylinder and the screen frame during the printing process, which according to the above described method works.

From the prior art, see e.g. EP-A-0463258, two such methods are known, in which the printing cylinder and the trolley are moved synchronously due to a mechanical coupling by a single drive motor. The mechanical coupling takes place in both cases via a gearwheel arranged on each end face of the pressure cylinder, which meshes with a toothed rack arranged on the corresponding side of the screening carriage. The printing path covered by the screen carriage corresponds exactly to one full revolution of the printing cylinder.

The first method makes use of a so-called oscillating cylinder, which has a single toothed wheel on each end face, which is permanently in engagement with the toothed rack attached to the corresponding side of the screening carriage. After the printing process, the cylinder reverses to the initial position in which it receives the next print item, with the printing process immediately starting again.

A disadvantage of this method is that the oscillating cylinder changes from a rotational movement into the opposite direction without a rest, so that the newly fed printing material must be grasped by the printing cylinder immediately. It happens that the print material is not placed correctly or not optimally on the printing cylinder, which affects the print quality.

The second known method tries to avoid this disadvantage in that the synchronization between the printing cylinder and the trolley takes place during the forward and return through two gears on each end of the printing cylinder. The first gearwheel engages with the toothed rack arranged on the relevant side of the screening carriage during the printing process (advance). At the end of the printing process, this toothed wheel and the toothed rack are decoupled in that the teeth are cut out by milling at a corresponding point on the toothed wheel. The rack can run back freely through the stopped gear. The return of the screening carriage is effected by a second gear, which is brought into engagement with the rack arranged on the relevant side of the screening carriage during the return. During the return, the first gear is held in place by a mechanical device. After returning, the first gear is rotated again and brought into engagement with the rack of the screening carriage, whereby a new printing process begins. The two gears are driven by a drive motor. Since the printing cylinder coupled to the first gearwheel always rotates in the same direction and stops during the return of the screening carriage, the printed matter can be applied to the printing cylinder for a sufficient period of time at a corresponding printing speed.

A disadvantage of the second method, however, is the technically very complex mechanical synchronization of the two gears. This also leads to a correspondingly high one Repair requirement and relatively frequent maintenance of the screen printing cylinder machine. In addition, the print speed is limited by the mechanics. Each increase in the printing speed also leads to a reduction in the downtime of the printing cylinder during the return of the screen carriage, which impairs the exact application of the printing material to the printing cylinder. Overall, the economy of the two methods is very unsatisfactory due to the disadvantages described.

The present invention has for its object to provide a method for controlling a screen printing cylinder machine, which is characterized by high print quality and great economy through simple technical means and high printing speeds. It is a further object of the present invention to provide a corresponding screen printing cylinder machine with the advantages mentioned above.

As a solution to the problem relating to the method, it is proposed according to the invention that the printing cylinder and the screening carriage are driven independently of one another and the drive motor of the screening carriage is decoupled from the movement of the screening carriage synchronized with the printing cylinder during the printing process and then drives the screening carriage during the return, the printing cylinder being brought to a standstill before completion of the return.

On the basis of this solution according to the invention, it is possible to apply the printed matter exactly to the printing cylinder even at high printing speed during a sufficient downtime of the printing cylinder, which can correspond to the total, or at least a remaining time, of the return time of the screening carriage. The technical effort to carry out the method is relatively low. Two drive motors are used to drive the printing cylinder and the screening carriage. However, the process can be done with much simpler technical Means are realized as the second method described in the introduction. It is also characterized by less susceptibility to repairs and greater ease of maintenance.

In a preferred development of the method it is provided that the drive motor of the screening carriage is brought to a standstill during the printing process and the drive motor of the printing cylinder before the return of the screening carriage has ended. The drive motor of the printing cylinder, which is at a standstill before the return has ended, holds the printing cylinder in this position during this time in which the printing material is applied.

As a second solution to the above object, it is proposed according to the invention that the printing cylinder and the screen carriage are driven independently of one another, data for setting the printing path and the printing speed are programmed into an electronic control device, stored therein and processed into control signals for the drives and the respective movement positions of the printing cylinder and of the screen carriage during the printing process are determined by position measuring systems and further processed in the electronic control device for regulating the control signals.

The above-mentioned advantages are also achieved with this method according to the invention. In addition, it is possible to adapt the printing path and the printing speed of the surface to be printed and the other requirements of the respective print material. In the conventional methods, the printing path covered by the screen carriage during the printing process corresponds to a full revolution of the printing cylinder and is adapted to a maximum format size of the printed matter. Therefore, the printing agent is spread by the flood doctor over the entire screen area corresponding to the maximum printing format. The one in the spread of the printing medium on the screen surface evaporation of the solvents contained in the printing medium leads to environmental pollution. Because of the evaporation and other influences during the spreading of the printing medium on the screen surface, the consistency of the printing medium also changes, so that it has to be mixed more frequently in order to ensure a constant print quality. Since the squeegee travels the maximum print format with every printing process, it is also exposed to a corresponding load and wear. These disadvantages are avoided by the second proposed solution, in which the printing path can be adjusted to the respective surface of the printed material to be printed.

In a further development of this solution, the pressure doctor blade and the flood doctor blade are also controlled as a function of the moving position of the screening carriage. This enables a more precise and easier control of the doctor blade application point, regardless of the printing speed.

Overall, the method according to the invention offers the greatest possible flexibility with regard to the printing process.

In a screen printing cylinder machine of the type mentioned at the outset, it is provided according to the first solution that two mutually independent drive motors for driving the printing cylinder during the printing process and for driving the screening carriage during the return, a device with which the drive motor of the screening carriage during the printing process (advance of Screening carriage) can be decoupled from the movement of the screening carriage synchronized with the printing cylinder, and a device with which the printing cylinder can be brought to a standstill before the return of the screening carriage has ended can be used.

In a preferred development, the drive motor of the screening carriage is coupled to the latter via a freewheel, which decouples the drive motor from the screening carriage in the direction of rotation of the motor shaft, which corresponds to the advance of the screening carriage during the printing process, and the drive motor of the printing cylinder is coupled to it via a freewheel, which decouples the drive motor from the pressure cylinder in the direction of rotation of the motor shaft, which corresponds to the return of the screening carriage.

The first freewheel can e.g. are on the hub of the drive motor of the screening carriage and be designed as an industrial freewheel. In particular, if a gear arranged on each end face of the printing cylinder is used as a device for synchronizing the movement of the printing cylinder and the screen carriage, which meshes with a rack arranged on the corresponding side of the screen carriage, the second freewheel can in each case on the two gear wheels of the impression cylinder.

According to the second proposed solution, it is provided in a screen printing machine of the type mentioned at the outset that two mutually independent drive motors for the printing cylinder and the screen carriage and an electronic control device are provided which have an input unit for data for setting the printing path and the printing speed, and an associated programmable memory Computing unit for processing the data in control signals for the drive motors and two control units assigned to the drive motors, which are connected to position measuring systems for the printing cylinder and the screening carriage.

In a preferred embodiment, rotary pulse encoders are provided as displacement measuring systems, which are arranged on the pressure cylinder or a drive wheel for the screening carriage.

In another preferred embodiment, glass measuring rods can also be used instead of the rotary pulse encoder. In addition, any other suitable measuring system can be considered.

Fig. 1

eine schematische Darstellung einer Siebdruckzylindermaschine und

Fig. 2

eine schematische Darstellung einer elektronischen Steuereinrichtung für die in Fig. 1 gezeigte Siebdruckzylindermaschine.

A preferred embodiment of the invention is described below with reference to the drawing. Show it:

Fig. 1

a schematic representation of a screen printing cylinder machine and

Fig. 2

is a schematic representation of an electronic control device for the screen printing cylinder machine shown in Fig. 1.

As can be seen from FIG. 1, the screen printing cylinder machine shown schematically there essentially consists of a printing cylinder 1 receiving the material to be printed, a screen carriage 2 traveling over it, a printing squeegee 3 which can be lowered onto the screen stencil and which is raised in the return shown in FIG. 1, and a flood knife 4 lowered during the return.

In the exemplary embodiment shown, the pressure cylinder 1 is connected to a drive 7 via a coaxial pulley 5 connected to it and a toothed belt 6. The pulley 5 has a coaxial rotary pulse generator, which serves as a path measuring system 8 for the arc angle of the printing cylinder which has been traveled from the initial position.

The sieve carriage 2 runs, reversibly moved by a toothed belt 9, over the pressure cylinder 1. The toothed belt 9 is driven in its reversing movement by a drive wheel 10 and runs via a pulley 11. The drive wheel 10 has a coaxial rotary pulse generator, which acts as a measuring system 12 serves for the distance traveled by the screening carriage 2 from the initial position.

As shown schematically in FIG. 2, the electronic control device for the screen printing cylinder machine shown in FIG. 1 essentially consists of a programmable logic unit 13 with an input unit 14 and in each case a control unit 15 or 16 for the drive motor 17 of the printing cylinder 1 or drive motor 18 of the screening carriage 2.

The two drive motors 17 and 18 are controlled as follows:

Via the input unit 14, e.g. The data for the print path and the print speed are read into the computing unit 13 via a keyboard and stored therein. The computing unit 13 processes the data into control signals for the drive motors 17 and 18. The control signals are fed to the corresponding control units 15 and 16, where they are converted into the corresponding currents and voltages for the drive motors 17 and 18.

In the initial position of a printing process, the printing cylinder 1 and the screen carriage 2 are at rest. The squeegees 3 and 4 are raised. In this position, the printing material, not shown in the drawing, is placed on the printing cylinder 1. At the beginning of the printing process, the squeegee 3 is lowered onto the screen template of the screen carriage 2, not shown in the drawing. The printing cylinder 1 and the screening carriage 2 start up at a synchronized speed on the basis of corresponding control signals.

The two displacement measuring systems 8 and 12 transmit the respective movement positions of the printing cylinder 1 and the screening carriage 2 to the control units 15 and 16, respectively. The movement positions are compared in the control units 15 and 16 with the control signals which determine the pressure path. If the movement positions correspond to the relevant control signals, a signal is sent from the respective control unit 15 or 16 to the Computing unit 13 transmits, which then outputs a control signal for stopping printing cylinder 1 or screen carriage 2 to control unit 15 or 16.

The printing process is ended in that the screen carriage 2 stops after reaching the printing path programmed into the computing unit 13 and the printing squeegee 3 is moved upwards. The printing cylinder 1 runs in the same direction of rotation up to the starting position.

When the screen carriage 2 stops after the printing process has been completed, the flood doctor 4 is lowered onto the screen template of the screen carriage 2. When the screen carriage 2 returns immediately after the printing process, it is moved back to the starting position and stopped by a corresponding control signal. The flood knife 4 is moved up after stopping. As soon as the printing cylinder 1 has reached its starting position again, the printing process is completed and the next printing material is placed on the printing cylinder 1. The printing process then starts again.

Reference list

1

Impression cylinder

2nd

Screen trolley

3rd

Squeegee

4th

Flood knife

5

Pulley

6

Timing belt

7

drive

8th

Position measuring system

9

Timing belt

10th

drive wheel

11

Pulley

12th

Position measuring system

13

programmable computer unit

14

Input unit

15

Control unit

16

Control unit

17th

Printing cylinder drive motor

18th

Drive motor of the screen carriage

Claims (9)

1. Method for controlling a cylinder screen printing machine, where a printing cylinder, which takes up the material to be printed and is driven by a drive motor, and a screen carriage (2), which runs above it with a squeegee (3) lowered onto the screen stencil, are moved at a synchronised speed during the printing cycle, characterised in that the printing cylinder (1) and the screen carriage (2) are driven independently of one another and that, during the printing cycle, the drive motor of the screen carriage is disengaged from the movement of the screen carriage (18) which is synchronised with the printing cylinder and that the drive motor subsequently drives the screen carriage (2) during the return pass, the printing cylinder (1) being brought to a standstill before the return pass is completed.
2. Method as per Claim 1, characterised in that the drive motor of the screen carriage is brought to a standstill during the printing cycle and the drive motor of the printing cylinder before the return pass of the screen carriage has been completed.
3. Method for controlling a cylinder screen printing machine, where a printing cylinder (1), which takes up the material to be printed and is driven by a drive motor (17), and a screen carriage (2), which runs above it with a squeegee (3) lowered onto the screen stencil, are moved at a synchronised speed during the printing cycle, characterised in that the printing cylinder (1) and the screen carriage (2) are driven independently of one another, data for setting the printing path and the printing speed are programmed and stored in an electronic controller (13, 14, 15, 16) and converted into control signals for the drives, and that the respective movement positions of the printing cylinder and the screen carriage are determined by position sensor systems (8, 12) during the printing cycle and further processed by the electronic controller in order to regulate the control signals.
4. Method as per Claim 3, characterised in that the squeegee and flood coater are activated by the electronic controller based on the movement of the screen carriage.
5. Cylinder screen printing machine with a printing cylinder (1), which takes up the material to be printed and is driven by a drive motor, a screen carriage (2) which runs above it, a squeegee (3) which can be lowered onto the screen stencil and a device for synchronising the movement of the printing cylinder and the screen carriage during the printing cylinder, characterised in that it is designed to use two independent drive motors (17, 18) to drive the printing cylinder (1) during the printing cycle and to drive the screen carriage (2) during the return pass, a device with which the drive motor of the screen carriage can be disengaged during the printing cycle from the movement of the screen carriage which is synchronised to that of the printing cylinder, and a device with which the printing cylinder can be brought to a standstill before the return pass of the screen carriage is completed.
6. Cylinder screen printing machine as per Claim 5, characterised in that the drive motor of the screen carriage is linked to the screen carriage via a freewheel, which disengages the drive motor from the screen carriage in the sense of rotation of the motor shaft corresponding to the forward pass of the screen carriage during the printing cycle, and the drive motor of the printing cylinder is linked to the printing cylinder via a freewheel which disengages the drive motor from the printing cylinder in the sense of rotation of the motor shaft corresponding to the return pass of the screen carriage.
7. Cylinder screen printing machine with a printing cylinder (1), which takes up the material to be printed and is driven by a drive motor (17), a screen carriage (2) which runs above it, a squeegee (3) which can be lowered onto the screen stencil, and a device for synchronising the movement of the printing cylinder (1) and the screen carriage (2) during the printing cycle, characterised in that it is designed to have two independent drive motors (17, 18) for the printing cylinder (1) and the screen carriage (2), and an electronic controller, consisting of a data input unit (14) for setting the printing path and the printing speed, a connected PLC processor (13) to convert the data into control signals for the drive motors (17, 18), and two regulators (15, 16) respectively dedicated to the drive motors (17, 18), which are connected to position sensor systems (8, 12) for the printing cylinder (1) and the screen carriage (12).
8. Cylinder screen printing machine as per Claim 7, characterised in that the position sensor systems (8, 12) are designed as rotary position transducers, which are mounted on the printing cylinder (1) and on a drive wheel (10) for the screen carriage (2).
9. Cylinder screen printing machine as per Claim 7, characterised in that glass scales are envisaged as the position sensor systems (8, 12).

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