EP0676284B1 - Flexographic printing machine particularly for multicolour printing - Google Patents

Abstract

The printing machine has machine frame (1) deflector rollers (7), a counter pressure cylinder (6), a continuous belt (11), pin wheels (4,5), and a drive. The two pin-wheels are freely rotary mounted. The drive for the two pin wheels is divided into two separately controlled part drive mechanisms (18,24). A meter (21,27,22,28) measures the momentary angular positions of the two pin-wheels and the drive moments of the two part-drives. A regulator controls drive moments of equal amount by the two part-drive mechanisms for the pin wheels. The two part drives are connected by an electric shaft for synchronising the momentary angular positions of the two pin wheels. The two part drives each have an electric motor (19,25) to which is connected to shaft-encoder as constituent part of the meter. <IMAGE>

Description

The invention relates to a flexographic printing machine, in particular for multi-color printing, with at least one printing unit, which has a machine frame, deflection rollers mounted therein, a counter-pressure cylinder for guiding the web to be printed, which is accommodated in bearings which are preferably fixedly arranged in the machine room, a support cylinder, two pin wheels provided coaxially therewith and has at least one tensioning cylinder around which an endless belt carrying at least one cliché and provided with perforations for the pin wheels is guided, an ink transfer device assigned to the cliché of the endless belt, one acting on the endless belt via the pin wheels Drive and an additional drive acting on the endless belt with respect to the support cylinder, which can be freely rotated relative to the pin wheels, are provided to prevent the perforations of the endless belt from jumping over the pin wheels. Such flexographic printing machines are used in particular in packaging technology, and the web to be printed can consist of paper, cardboard, aluminum foil, plastic film or the like. Such a flexographic printing machine for multi-color printing has at least one printing unit per color.

A flexographic printing machine of the type described in the opening paragraph is known from EP-PS 18 147. The web to be printed is guided over deflection rollers on the machine frame and over an impression cylinder for each printing unit. The impression cylinder is slidably mounted in the machine frame for adjustment purposes, which has an unfavorable effect on the web tension conditions, but on the other hand provides the advantage that the unit comprising the support cylinder and pin wheels can be rotatably mounted in the machine frame. Opposite the impression cylinder, this unit consisting of a support cylinder and two coaxially provided pin wheels is stationary, but the support cylinder and both mechanically connected pin wheels can be rotated independently of one another, over which an endless belt is guided, which is connected to at least one, but often with a large number of clichés is provided. A first positive drive is provided for the endless belt, which acts on the endless belt via both pin wheels, in that the pin wheels are connected to one another in a rotationally fixed manner and the pins of the pin wheels engage in perforations in the endless belt for the purpose of registering. When the clichés on the endless belt are passed through the gap between the support cylinder and the impression cylinder or the web to be printed, a bulge arises in the resilient material of the cliché and thus a deformation work or a backward deformation force. This form-changing force, which can also be called the resistance of the cliché, only occurs when printing on, but not when there is a distance between the cliché and the web to be printed, as is the case in the non-printing state. This deformation force changes when the plate passes through the pressure gap in accordance with the design of the plate. In a certain operating state, this deformation force can be greater during printing or can be greater than the maximum driving force that can be transmitted to the endless belt by means of the drive via the pins of the pin wheels. In such a case, this will result in the perforations of the endless belt skipping over the pin wheels, which of course means that the register accuracy is lost and the printing result becomes unusable. In order to solve this problem, an additional drive is proposed in the known flexographic printing machine, that is to say a drive which, in addition to the torque which is positively transmitted to the endless belt via the pin wheels, transmits its torque to the endless belt via frictional engagement. This additional drive acts on the support cylinder as a drive roller on the endless belt, with the support cylinder being freely rotatable relative to the two pin wheels. Since the backward shaping work during printing only occurs when the endless belt rotates, if there is a cliché in the printing nip where the shaping work occurs, but it certainly corresponds to a frequently occurring case that the cliché is not continuous over the circumference of the endless belt is provided, times arise during printing in which the deformation force also disappears. The shape change work also changes as the cliché passes through the printing nip. The size of the deformation work also depends on the printing area of the printing block located in the printing gap. In order to take account of this changing deformation force, a complicated control device is provided in the known flexographic printing press. This control device has sensor elements for the continuous detection of a variable which is at least proportional to the deformation force and which are switched on in the drive in the area of the pin wheels. The Measurement data must be forwarded via slip rings. The sensor elements are based on a force or torque measurement with the help of strain gauges. The control device also includes a clutch and a brake, which are part of a control loop and via which the additional drive on the support cylinder is influenced in a regulating manner. The additional drive is removed from the machine drive. The drive via the pin wheels is also derived from the machine drive. In this known flexographic printing machine, the unit is formed from pinwheels and support cylinders which can be rotated in relation to one another, the drive via the pin wheels together and the additional drive via the support cylinder being introduced into the endless belt alone. It is disadvantageous that the introduction of the drive on the one hand and the additional drive on the other hand is not easy to implement in the coaxial design between pin wheels and support cylinders and due to the cramped conditions there. Furthermore, these sensitive parts and in particular the sensor elements of the control device are located in an area of the flexographic printing machine in which they are exposed to washing water and other cleaning agents and also to the paint. In addition, the mechanical coupling of the pin wheels via the common drive is susceptible to wear, which can have a negative effect on the register accuracy.

A flexographic printing press is known from EP-OS 308 367, in which the impression cylinder is already mounted in a stationary manner in the machine frame, so that the web tension conditions advantageously do not change during a setting process. However, this presupposes that the support cylinder is movable relative to the machine frame for adjustment purposes. The bearings of the support cylinder are arranged to be displaceable in at least two directions and the bearings of the clamping cylinder in at least one direction in the machine frame. There are two drive units for the tensioning cylinder on the one hand and for the support cylinder on the other hand, it remains open whether and how these two drives are coordinated. In addition, there is another Machine drive is provided, via which the impression cylinder is driven.

DE-OS 41 00 871 shows a flexographic printing machine with an impression cylinder which is also fixed in the machine frame. While avoiding a complicated control device, a drive via the pin wheels and an additional drive for the endless belt are coordinated. The additional drive is attached to the endless belt via the tensioning cylinder. The support cylinder, on the other hand, is designed to run freely, ie it has no drive. An actuating device is provided for the control of the additional drive, via which an additional force acting on the endless belt can be controlled in such a way that, on the one hand, when printing, it is greater than the difference between the backward deformation force when the cliché passes through the gap between the web and Support cylinder and the maximum force transmitted from the pin wheels to the endless belt and, on the other hand, when not printing is smaller than the maximum force that can be transmitted from the pin wheels to the endless belt.

In many cases, however, the cliché on the endless belt will not be designed or applied symmetrically to the vertical longitudinal center plane of the flexographic printing machine, which results in different levels of stress on the perforation on one side of the machine compared to the perforation on the other side of the machine. The pin wheel on the one hand transmits a larger proportion of the drive torque than the pin wheel on the other side in order to overcome the respective proportions of the deformation work. Since the endless belt with the applied clichés represents a quasi-elastic body, an uneven load or an uneven drive due to relative rotation of the angular position has a disadvantageous effect on the register accuracy on the right and left. As a result, uneven layers (perforation reveal pressure) in the area of the perforations on the right and left can adhere to the result in both pin wheels. Uneven wear also occurs, which only increases the problems. Ultimately, this can lead to the pin wheel, which is subject to greater stress, jumping over the associated perforations of the endless belt, so that an unusable printing result is produced as a result.

The invention is therefore based on the object of providing a flexographic printing machine of the type described at the outset with at least one printing unit, but preferably with a plurality of printing units for multi-color printing, with which printing can be carried out in conjunction with other similar printing units with improved register accuracy, without the risk there is a limit to the skipping of a pin wheel compared to its perforations on the endless belt.

According to the invention this is achieved in the flexographic printing machine of the type described in the introduction in that the two pin wheels are freely rotatable relative to one another, in that the drive for the two pin wheels is divided into two separately controllable partial drives, that a measuring device for the current angular positions of the two pin wheels relative to one another and the instantaneous drive torques of the two sub-drives are provided to each other, and that a control device is provided, which on the one hand is designed to compensate for drive torques of the same size via the two sub-drives for the pin wheels and, on the other hand - if a limit value of these aforementioned drive torques is exceeded - to initiate a requirement adjusted additional torque via the additional drive of the support cylinder on the endless belt.

The invention is based on the knowledge of working to ensure that essentially the same drive parts are transmitted to the two perforations of the endless belt via both pin wheels. As soon as that via the pin wheel on the one perforation of the endless belt due to asymmetrical The vertical longitudinal center plane of the flexographic printing machine to be overcome and the deformation work to be overcome increases at the expense of the drive torque to be transmitted via the other pinwheel, the adjustment is carried out in such a way that the larger drive torque is reduced and the smaller drive torque is increased by the two drive torques transmitted on the right and left again as quickly as possible to bring an equal value. This equally large value can and will fluctuate in the course of the passage of a cliché through the pressure gap, that is, it can become larger and smaller in time. The total drive torque to be transmitted via the pin wheels is divided into two partial drive moments so that each partial drive torque increases by only half the amount when the total drive torque of the pin wheels increases. This has the advantage that the limit value at which the pin wheels skip at the perforations is only reached much later with increasing work on the shape change. The risk of the pin wheels skipping is thus considerably reduced. A prerequisite for this mode of operation is, of course, that the two pin wheels are no longer mechanically coupled as before by a common drive, but that two separately controllable partial drives are each provided for only one of the two pin wheels. The instantaneous angular positions of the two pin wheels relative to one another are continuously monitored via the measuring device. A work of deformation occurring asymmetrically to the vertical longitudinal center plane manifests itself in a deviation of the instantaneous angular positions of the two pin wheels from one another. As a result, different drive torques of the two partial drives would occur. However, the control device ensures that this is counteracted until the two drive torques on the two partial drives for the pin wheels are again the same size. Since the endless belt with the applied cliché is to be regarded as a quasi-elastic body, this regulation is possible, and there are even loads in the area of the perforations on the pin wheels on the right and left. The perforation reveal pressure on the right and left is the same, and so is that Wear will occur evenly, so that overall there is a significantly increased lifespan of the endless belt with the cliché. Above all, however, the improvement in register accuracy is astonishing and significant. Changes in the angular positions to the right and left to one another are always compensated for and eliminated, so that these cannot have a negative effect on the subsequent printing units as a deterioration in the register. The result is better print quality. As a result of the measure not to overwrite the perforation reveal pressure with regard to a limit value for the drive torques on the right and left and to introduce an adapted additional torque, that is to say in accordance with the requirements, on the endless belt via the auxiliary drive of the support cylinder, a considerable safety threshold is maintained.

The two partial drives for synchronizing the current angular positions of the two pin wheels can be connected to one another by an electrical shaft, as is also known in printing technology. This means that the two pin wheels are connected to each other at a rotational angle. A mechanical coupling between the two pin wheels is advantageously eliminated.

The two partial drives can each have an electric motor, to each of which a rotary encoder is connected as part of the measuring device for determining the instantaneous angular positions of the two pin wheels. These electric motors are, in particular, digitally controlled individual motors, which can also be connected to one another per printing unit via electrical shafts in synchronism with the angle of rotation. The new drive concept eliminates the entire complex and fault-prone state-of-the-art system. With the new measuring device, the instantaneous drive torques of the two pinwheels are measured directly via a device for measuring the instantaneous current consumption of each of the two electric motors. The current consumption is proportional to the drive torque and can be immediately measured and processed for control purposes. The respective drive torque corresponds to the partial torque which is transmitted to the respective perforation of the endless belt via the pin wheel. The control device is also digital. It regulates the electric motor for the right pinwheel and the electric motor for the left pinwheel in their relative angular position to each other until an equal moment distribution is achieved.

One of the two partial drives for the two pin wheels is provided as a guide drive for the control device, while the other partial drive is designed as a follow-up drive. In the event of deviations from one another, the two drives are always directed in opposite directions. It is in itself irrelevant which of the two partial drives is used as a guide drive and which as a follow-up drive. However, it makes sense that the partial drive serving as the guide drive is arranged coaxially with the common axis of the pin wheels and the support cylinder, so that the shortest possible drive path can be used for the guide drive.

The additional drive for the support cylinder can be provided coaxially to the common axis of the pin wheels and the support cylinder and have an electric motor to which a rotary encoder is connected as a component of the measuring device, the partial drive serving as the follower drive being offset from the common axis of the pin wheels and the support cylinder is. As such, the position and the starting point of the additional drive and the subsequent drive, which are arranged on the same side of the machine, could also be exchanged for one another in order to have a particularly rapid intervention possibility for the additional drive, which is intended to prevent the pin wheels from jumping over it makes sense to arrange the additional drive coaxially and to provide an additional transmission stage for bridging the parallel axes with regard to the subsequent drive.

The support cylinder and / or the clamping cylinder can essentially consist of a carbon fiber composite material in order to reduce the diameter and the moment of inertia. This reduces the moment of inertia by about 80%, which is the basis for faster control. The reduction in diameter also leads to a reduction in the minimum length of the endless belt and thus in many cases to a reduction in printing plate costs in the case of multiple printing in the direction of the printing unit.

For several printing units, as is usually the case with a flexographic printing press for multi-color printing, a higher-level control device is provided, via which the rotary encoders of the partial drives of the printing units serving as guide drives, the rotary encoders of the partial drives of the printing units serving as follow-up drives, and the rotary encoders of the additional drives Printing units are interconnected.

Figur 1

die Darstellung der wesentlichen Teile eines Druckwerkes, teilweise geschnitten,

Figur 2

die beispielsweise rechte Seite eines Druckwerks in vergrößernder Darstellung,

Figur 3

die beispielsweise linke Seite eines Druckwerkes in vergrößernder Darstellung,

Figur 4

einen Vertikalschnitt durch ein Druckwerk mit seinen wesentlichen Teilen und

Figur 5

die wesentlichen Elemente einer Regeleinrichtung eines Druckwerkes sowie der Flexodruckmaschine.

The invention is further explained and described on the basis of a preferred exemplary embodiment. Show it:

Figure 1

the representation of the essential parts of a printing unit, partially cut,

Figure 2

the right side of a printing unit, for example, in an enlarged view,

Figure 3

the left side of a printing unit, for example, in an enlarged view,

Figure 4

a vertical section through a printing unit with its essential parts and

Figure 5

the essential elements of a control device of a printing unit and the flexographic printing machine.

Figure 1 shows schematically a machine frame 1 of a printing unit 2. In the machine frame 1, a support cylinder 3 is rotatably mounted in bearings which can be displaced for adjustment purposes. The support cylinder 3 has a width corresponding to the working width of the printing unit 2 or the flexographic printing press. A pin wheel 4 is provided to the left of the support cylinder 3 and a pin wheel 5 is provided to the right of the cylinder 3. The pin wheels 4 and 5 are rotatable with respect to each other as well as with respect to the support cylinder 3.

As can be seen in FIG. 4, the back-up cylinder 3 is assigned a counter-pressure cylinder 6, which is accommodated in bearings which are preferably arranged fixed in the machine frame 1. The web 8 to be printed is guided around deflection rollers 7 and the impression cylinder 6 and runs through the printing unit according to arrow 9. A clamping cylinder 10 is assigned to the support cylinder 3 and the pin wheels 4 and 5. An endless belt 11 is wound around the support cylinder 3 and the pin wheels 4 and 5 on the one hand and around the tensioning cylinder 10 on the other hand, which is filled with clichés in single or multiple uses. Depending on the length of the endless belt 11, the tensioning cylinder 10 can be moved or adjusted to a corresponding distance from the support cylinder 3. In dash-dotted lines, the tensioning cylinder 10 'is shown as it is set with an endless belt 11 of minimal length. Since the impression cylinder 6 is preferably mounted fixed in the machine frame 1, the unit comprising the support cylinder 3, pin wheels 4, 5 and clamping cylinder 10 is held by a carrying device 12 and can be displaced by the dimension e for adjustment purposes. Each printing unit has an ink transfer device 13 with an anilox roller 14 and a doctor blade 15. A second anilox roller 16 can be mounted on a swivel arm 17.

The z. B. right-hand pin wheel 5 (Figure 1) is assigned a first partial drive 18 which is separately controllable or adjustable. The partial drive 18 is used only for Drive of the pin wheel 5. The partial drive 18 has an electric motor 19 and a rotary encoder 20 which monitors the angular position of the pin wheel 5. The rotary encoder 20 is part of a measuring device 21 for determining the current angular position of the pin wheel 5. Furthermore, a measuring device 22 is provided for the current drive torque of the pin wheel 5. The partial drive 18 is provided here as a guide drive because it is provided coaxially with the common axis 23 of the support cylinder 3 and the pin wheels 4, 5.

Just as the partial drive 18 is assigned to the pin wheel 5, a partial drive 24 is provided for the pin wheel 4. The partial drive 24 in turn has an electric motor 25 and a rotary encoder 26. A measuring device 27 for determining the current angular position of the pin wheel 4 and a measuring device 28 for the current drive torque of the pin wheel 5 are assigned to the partial drive 24. The axis 29 of the partial drive 24 is provided offset to the axis 23. In order to bring the partial drive 24 onto the pin wheel 4, a gear stage 30, which can have a belt 31, is provided in the manner shown in FIGS. 1 and 3.

An additional drive 32 is provided coaxially to the axis 23 and is assigned exclusively to the support cylinder 3. The auxiliary drive 32 has an electric motor 33 and a rotary encoder 34. The additional drive 32 also has a measuring device 35 for determining the instantaneous additional torque of the support cylinder 3. A further measuring device 36 on the additional drive 32 serves to record the instantaneous drive torque which is transmitted to the endless belt 11 via the support cylinder 3.

FIG. 5 shows how the electric motors 25, 33 of the partial drive 24 and the additional drive 32 are connected to a control device 37 which is assigned to the individual printing unit. An electrical line 38 leads from the measuring devices 21 and 22 of the partial drive 18 designed as a guide drive to the control device 37, from which the partial drive 24 and the auxiliary drive 32 are readjusted. An electrical line 39 leads from a higher-level control device 40 for the entire flexographic printing machine to the electric motor 19 of the partial drive 18. It goes without saying that the partial drives 18 and 24 can also exchange their function. However, it makes sense to choose the more precise partial drive as the guide drive, namely the partial drive, which is not required via a gear stage to bridge an arrangement with offset axes. A line 41 leads from the measuring devices 21 and 22 of the partial drive 18 to the higher-level control device 40. The measuring devices 21, 22, 27, 28, 35, 36 are used to detect the respective angular positions or the respective torques. The control device 37 of each printing unit controls these angular positions and torques relative to one another. The higher-level control device 40 not only controls the relative angular positions and the torques with one another, but also the printing speed through the entire flexographic printing machine. Only lines 39 'and 41' are indicated to illustrate a second printing unit. It goes without saying that the remaining components are also provided, as has been described with reference to the control device and arrangement for the first printing unit. Other printing units, e.g. B. 2 ', are connected to the higher-level control device 40 according to the number of printing units, as indicated in Figure 5.

REFERENCE SIGN LIST

1

- machine frame

2nd

- printing unit

3rd

- support cylinder

4th

- pin wheel

5

- pin wheel

6

- Impression cylinder

7

- pulley

8th

- Train

9

- arrow

10th

- clamping cylinder

11

- endless belt

12th

- carrying device

13

- ink transfer device

14

- Anilox roller

15

- Squeegee

16

- Anilox roller

17th

- swivel arm

18th

- Partial drive

19th

- electric motor

20th

- encoder

21

- measuring device

22

- measuring device

23

- axis

24th

- Partial drive

25th

- electric motor

26

- encoder

27

- measuring device

28

- measuring device

29

- axis

30th

- gear stage

31

- straps

32

- Additional drive

33

- electric motor

34

- encoder

35

- measuring device

36

- measuring device

37

- control device

38

- Management

39

- Management

40

- control device

41

- Management

Claims (9)

1. A flexographic printing machine, especially a belt-type printing machine for a plurality of colours, comprising at least one printing station (2) containing a frame (1), idler rolls (7) arranged in bearings therein, an impression cylinder (6) for guiding a continuous web (8) to be printed arranged in preferably fixed bearings on the frame (1), a plate cylinder (3), two sprocket wheels (4, 5) coaxially mounted and at least one tensioning cylinder (10), around which an endless belt (11) extends having at least one flexible printing plate and being provided with perforations for the sprocket wheels (4, 5), wherein an inking assembly (13) allocated to the flexible printing plate of the belt (11), a drive acting upon the sprocket wheels (4, 5) to the belt (11) and an additional single drive (32) acting upon the plate cylinder (3) to the belt (11) for the purpose of avoiding the jump movement between the perforations of the belt and the pins of the sprocket wheels are provided, whereby the two sprocket wheels (4, 5) are idler rollers against each other, the drive of the sprocket wheels (4, 5) is divided into two separately controllable partial drives (18, 24), measuring devices (21, 27, 22, 28) for determining the instantaneous angular positions of the two sprocket wheels (5, 4) against each other and the instantaneous driving torques of the two partial drives (18, 24) are provided, and controlling means (37) for the controlling of driving torques equal to each other via the two partial drives (18, 24) to the sprocket wheels (5, 4) each and, in case of overriding a limit of these equal driving torques, of an additional torque adapted to the amount of overriding and to be transmitted by the additional single drive (32) of the plate cylinder (3) to the endless belt (11).
2. The flexographic printing machine of claim 1, whereby the two partial drives (18, 24) are connected to each other by an electric shaft for the purpose of synchronising the instantaneous angular positions of the sprocket wheels (5, 4).
3. The flexographic printing machine of claim 1 or 2, whereby the two partial drives (18, 24) each comprises a single motor (19, 25), with an encoder (20, 26) each being part of the measuring devices (21, 27) connected for detecting the instantaneous angular positions of the two sprocket wheels (5, 4).
4. The flexographic printing machine of claims 1 to 3, whereby a measuring device for detecting the instantaneous current consumption of each of the two single motors (19, 25) is provided as the measuring device (22, 28) for detecting the instantaneous driving torques of the two sprocket wheels (5, 4).
5. The flexographic printing machine of claims 1 to 4, whereby one (18) of the two partial drives (18, 24) for the two sprocket wheels (5, 4) is provided as a leading drive for the controlling means (37) and the other partial drive (24) is a follower drive.
6. The flexographic printing machine of claim 5, whereby the partial drive (18) serving as the leading drive is coaxially mounted to the common axis (23) of the sprocket wheels (4, 5) and the plate cylinder (3).
7. The flexographic printing machine of claims 1 to 6, whereby the additional single drive (32) for the plate cylinder (3) is coaxially mounted to the common axis (23) of the sprocket wheels (4, 5) and the plate cylinder (3) and comprises a single drive (33), to which an encoder (34) as a part of the measuring device (35) is connected, the partial drive (24) serving as a follower single drive being mounted in parallel and spaced apart from the common axis (23) of the sprocket wheels (4, 5) and the plate cylinder (3).
8. The flexographic printing machine of claims 1 to 7, whereby the plate cylinder (3) and/or the tensioning cylinder (10) considerably are made out of carbon fibre material to decrease the diameter and the mass moment of inertia.
9. The flexographic printing machine of claims 1 to 8, whereby a controlling means (40) of a higher order is provided for a plurality of printing stations (2), upon which first the encoders (20) of the partial drives (18) serving as leading drives of the printing stations (2), second the encoders (26) of the partial drives (24) serving as follower drives of the printing stations (2) and third the encoders (34) of the additional single drive (32) of the printing stations (2) are connected to each other each.

Images