EP1717030B1 - Device for printing flat workpieces - Google Patents

Description

The invention accordingly relates to a device for transporting the workpieces and at least one printing unit in which an applicator roll rolls on the workpieces transported through the printing unit and in this case a printed image on the workpiece surface applies. The transport device is provided with a lateral guide for the workpieces on which the same are transported through the printing unit. The applicator roll may be formed as a printing cylinder or as a transfer roller for the transfer of ink from a printing cylinder, such as a gravure cylinder, on the workpiece surface, while usually a counter roll is present, which cooperatively forms a pressure nip with the applicator roll. In multicolor printing several printing units are connected in series in a generic device, which are successively traversed by the workpieces.

In particular, to give wood-based panels the appearance of real wood, due to the cost advantages over a real wood veneer or foil coatings increasingly printed images of decors and grains are printed directly on the wood-based panels. For a high quality impression, however, a simple single-color printing is not enough. Rather, it is desirable to apply the grain or the decoration in multi-color printing on the material plate. This is certainly not the case only with wood-based panels. Also applications for other materials that can be qualitatively improved by surface pressure, such as stone or artificial leather surfaces, can be upgraded through a multi-color print.

However, especially for high quality multi-color printing, it is indispensable that the individual print images on the workpiece are each positioned within very narrow tolerances, typically in the range of ± 0.1 mm. Only in this way can an optical quality comparable to the conventional film coating be achieved. However, these requirements are much harder to comply with the existing sheet-like workpieces, as in machines for paper or films. Because the present sheet-like workpieces do not run endlessly as a substrate web through the printing press, and printing on the model of paper-sheet printing machines is usually not possible because of the intransigence of the present flat workpieces.

A device of the type mentioned, which solves the problems just described with excellent results, is from the DE 103 33 626 A1 known. There, among other things, the printed image is automatically evaluated by an image processing device, whether the print image position and the print image length are within the specified tolerances or not. The results obtained act on the drives of the transport device and / or the drives of the cylinders involved in the printing in order to influence the print image position or the print image length if necessary in the direction of smaller tolerances. It is therefore a control loop that performs a correction during production, in particular by accelerating or decelerating individual or all involved in the pressure cylinder and / or the transport device.

When printing on workpieces with grains, however, it is often problematic to recognize the exact superimposition of the printed images or to determine in which direction must be corrected in order to improve a poor print image; because the grains are naturally intentionally kept irregular, which in particular enormously hampers automatic recognition of the printed image position by means of image processing facilities. Remedy here can be separate print image position markers, for example in the form of registration marks or create color lights, which are applied in addition to the actual pressure on the workpiece surface and enable automatic evaluation of the corresponding print image position - and with a corresponding number of print image position markers and the print image length - with high accuracy. However, when printing the work piece surfaces with decors or grain text over the entire surface, it is naturally not possible to use such printed image layer markings in the ongoing production process. Instead, test runs must be carried out repeatedly in order to check the exact positioning of the print images. The production must be interrupted for this.

The present invention is therefore based on the object to enable automatic monitoring and, where appropriate, control of the exact print image positioning even during production, when the workpieces are printed over the entire surface.

This object is achieved by a device having the features of claim 1.

Preferred developments of this device are set forth in claims 2 to 11.

The device for printing flat workpieces according to the present invention, in which the workpieces are transported by means of a transport device with lateral guidance through the printing unit, in which an applicator roll applies a print image on the workpiece surface, according to the invention thus provided with a lateral guide, the sections motor is adjustable between a neutral position and a test position. By this measure, it is possible to use a normal workpiece from the production as a sample for checking the printed image position and length, simply by the motorized lateral guide is at least in that section in which the workpiece is currently located, so that its lateral edge is not transported along the neutral position of the lateral guide, but laterally offset along the test position, ie compared to the normal production. This results Even with a full-surface pressure on the surface of the workpiece not printed with the actual print image edge on which printed image position markings such as registration marks or color lights applied and can be clearly recognized by the detection device at the end of the device. The inventive motorized adjustment of the lateral guide sections ensures that the sections are adjusted in each case exactly by the same amount and that after that the neutral position is again taken exactly as well. Otherwise, the result of the detection of the printed image position markings would hardly meaningful. Under motorized adjustment, all measures should be understood that do not adjust the corresponding sections of the lateral guide by hand, such. As the adjustment with electric motor, hydraulic or pneumatic drives.

Particularly advantageously, the invention can be used during ongoing production, namely by a control for the lateral guide is present, which adjusts the lateral guidance, if necessary, such sections that a certain workpiece from a series of located on the conveyor workpieces successively to each in the test position adjusted portions of the lateral guide comes to rest and is thereby transported laterally offset by the printing unit, while the remaining workpieces rest against the located in the neutral position sections of the lateral guide and insofar continue the production seamlessly. The controller can then be programmed, for example, so that every hundredth workpiece as a sample laterally offset by the printing unit or the multiple printing units runs to continuously monitor the production quality and possibly intervene regulating.

As already mentioned, it is advantageous to provide in the device according to the invention that the printing unit prints printed image position markings on the side beyond the neutral position of the lateral guide edge - the test edge - the workpiece surface of the laterally offset in the test position workpiece while behind the printing unit a detection device for detecting the printed image position markings is arranged.

In this case, it is expedient for the detection device to interact with the controller in such a way that the control changes the neutral position of the lateral guide if necessary in order to correct lateral print image shifts.

Alternatively, the detection device may also cooperate with the controller in such a way that, if necessary, it axially displaces the printing cylinder in order to correct lateral print image displacements. Alternatively or in addition to the axial displacement of the printing cylinder and the entire printing unit or other individual components of the same can be moved laterally.

As is known per se, the detection device can be equipped with an optical sensor, which may in particular be a digital camera. With such a digital camera, print images and registration marks can be digitally resolved not only according to their structure but also according to their color.

Due to the height differences, which normally have the materials of the present type, it is advantageous if the optical sensor is arranged vertically adjustable, so that the surface of the printed workpiece is always reliably in the focus of the optical sensor.

Particularly preferred, especially in multi-color printing with multiple printing units, a control station is present in the apparatus according to the invention, which controls the drives of the printing units, the drives of the transport device and the drives of the lateral guide and also controls, in response to the signals of the detection device. In this case, for example, on the test edge of a workpiece transported in the test position through the device, a front and a rear color lights are applied, each of which a registration mark is printed by a respective printing unit. Accordingly, the detection device can visually check the correctness of the individual registration marks and thereby recognize the correctness of the print image position in the transport direction, the print image position in the transverse direction and by comparison of the two color lights the print image length. If the values are outside a specified tolerance, the control center then controls the corresponding drives in such a way that the print image position or the print image length into the tolerance values. This may, as from the DE 103 33 626 A1 basically known, by accelerating or decelerating one or more drives in the printing unit and / or by accelerating or decelerating the transport device in front of the printing unit and / or by changing the neutral position of the lateral guide and / or by axial adjustment of cylinders involved in the pressure of the printing unit , A correction of the print image length can be done by selectively generating a slip between the image-bearing cylinders of the printing unit or the applicator roll and the workpiece surface.

Finally, there are further advantages when means are provided for generating a perpendicular to the transport direction and the lateral guide oriented transport force component for the workpiece. Because this makes it possible with only one side guide and does not have to provide lateral guides on both sides of the transport route. The lateral guide is then a stop against which the workpieces are automatically pressed, resulting in an exact lateral alignment of the workpieces. Such means may be a helical roller track, or in a small entanglement of the applicator roll with a counter roll in the nip in the horizontal axis position to each other or in a slight misalignment relative to the direction of passage.

With the invention, it is possible that from the DE 103 33 626 A1 to use known correction method for particular multi-color printing on flat workpieces, even if they are printed over the entire surface and it is hardly possible due to the irregular print image, such as a wood grain, print image shifts and print image length changes by means of an image-processing sensor reliably. With the invention, individual randomly selected workpieces can be printed laterally offset during production and in this case provided with a test edge with the ability to register marks and Farbampeln provided.

The printed image position with respect to the beginning can then in the from DE 103 33 626 A1 Known manner are made by sensors that detect the front edge of the workpiece before the respective printing unit, which coincides with the full-area printing with the repeat position, and hold by specific acceleration or deceleration of the transport device and / or the printing cylinder start the print image within very narrow tolerances. Inaccuracies in the printed image length resulting from the fact that the pre-pressure adjustment of the applicator roll and the workpiece thicknesses vary and from the usually present inhomogeneity of the applicator roll surface, can be detected by the registration marks on the test edge of the sample workpieces from the downstream detection unit using the registration marks or color samples be eliminated by means of a tendency correction by generating a targeted slip between the workpiece surface and the applicator roll and / or between the applicator roll and an optional additional printing cylinder. Lateral print displacements, which are also recognizable from the registration marks or color marks on the test rim of the sample workpieces, are also eliminated by way of tendency correction by lateral displacement of the impression cylinder or by altering the neutral position of the lateral guide.

Fig. 1

eine schematische Draufsicht auf ein Beispiel einer erfindungsgemäßen Vorrichtung;

Fig. 2

eine Draufsicht wie Fig. 1, mit einem verstellten seitlichen Führungsabschnitt;

Fig. 3

eine schematische Frontansicht des Druckwerks des Ausführungsbeispiels aus den Figuren 1 und 2;

Fig. 4

eine Ansicht wie Fig. 3, jedoch mit seitlich versetztem Werkstück;

Fig. 5

eine Draufsicht auf ein als Stichprobe bedrucktes Werkstück mit Passmarken auf einem Prüfrand;

Fig. 6

die Passmarke X aus Fig. 5;

Fig. 7

die Passmarke X aus Fig. 5, mit anderem Druckergebnis.

An embodiment of the device according to the invention is described below with reference to the accompanying drawings and explained in more detail. Show it:

Fig. 1

a schematic plan view of an example of a device according to the invention;

Fig. 2

a top view like Fig. 1 with an offset lateral guide section;

Fig. 3

a schematic front view of the printing unit of the embodiment of the Figures 1 and 2 ;

Fig. 4

a view like Fig. 3 , but with laterally offset workpiece;

Fig. 5

a plan view of a sample-printed workpiece with registration marks on a test edge;

Fig. 6

the registration mark X out Fig. 5 ;

Fig. 7

the registration mark X out Fig. 5 , with different print result.

This in Fig. 1 illustrated embodiment of an inventive device comprises a diagonal roller conveyor 1, a belt conveyor 2, a printing unit 3 with an applicator roll 4 and a gravure roller 5 and a roller conveyor 6, which are arranged in line one behind the other and each have sections of a lateral guide 7. The lateral guide 7 consists in the present case each of a vertically arranged conveyor belt. As a rule, three to five printing units between the printing unit 3 and the roller conveyor 6 shown here will be present at the outlet of the production line in order to apply multicolour printing to continuous workpieces 8. For the sake of a simplified representation, however, only one printing unit 3 is shown here.

The printing unit 3 consists not only of the application roller 4 and the gravure roller 5; below the applicator roll 4 (not visible here) counter-roller is provided to form a pressure nip, while a conveyor belt 16 ensures as possible slip-free transport of the workpiece 8 along the applicator roller 4 rolling thereon. In particular, workpieces 8 of wood-based material have thickness tolerances that normally do not allow direct pressure with a printing cylinder. For this reason, the applicator roller 4 of the present invention is formed as a transfer roller made of a rubberized steel roller whose rubber peripheral surface has been ground smooth. The printed image is accordingly removed from the gravure cylinder 5, which has depressions which fill in the inking unit (not shown) with ink and subsequently deliver it to the applicator roll 4. The application roller 4 is thus during the pressure in simultaneous contact with the gravure cylinder 5 and the surface of the workpiece 8, while it takes over the printed image from the gravure cylinder 5 and transmits to the workpiece 8.

An exact 1: 1 transfer of the print image on the surface of the workpiece 8 is only when there is no slip on the surface of the workpiece 8 on both the rolling movement of the engraving cylinder 5 on the applicator roll 4 and during the rolling movement of the applicator roll 4. By different disturbing influences, such as the pre-pressure setting of the applicator roll 4, the thickness tolerance of the workpieces 8 or an inhomogeneity the surface of the application roller 4, such a slip results, resulting in print image distortions and at the same time always in fluctuations of the print image length. Especially in multi-color printing with multiple printing units 3, this is disturbing in the print image, as usually the distortions in the print image do not occur identically in each printing unit 3 and accordingly the individual colors in the print image are then no longer exactly one above the other.

So that the workpieces 8 are printed laterally aligned exactly, they are subjected to a lateral force during transport through the device, which presses them against the lateral guide 7 and ensures that the workpieces 8 are printed adjacent to the lateral guide 7. In the entrance area of the production line, this is done via the inclined roller conveyor 1, which also allows larger lateral movements of the workpieces 8 to the side guide 7, while the belt conveyor 2, a conveyor belt 9 is combined with overlying rollers 10, which exert the lateral force on the workpiece 8 , In the printing unit 3, a slight entanglement of the applicator roll 4 to the (not visible) counter roll for a force component to the side guide 7 provides.

The belt conveyor 2 is used in the present production line for coarse adjustment of the printed image position, ie it ensures a synchronization of the angular position of the gravure roller 5 with the front edge of the workpiece 8. For this purpose, a flow sensor 11 is provided which detects the leading edge of the workpiece 8, while the conveyor belt is moved back and forth independently of the remaining transport devices 1, 16, 6. By demand braking, acceleration or even backward movement of the conveyor belt 9 is thus ensured that the workpiece 8 is delivered synchronized to the angular position of the gravure roller 5 to the printing unit 3, so that the beginning of the located on the gravure roller 5 and transferred to the application roller 4 print image coincides approximately with the leading edge of the workpiece 8. A print image position sensor 12 in the printing unit 3, disposed immediately in front of the application roller 4, is used for fine adjustment of the print image beginning in the from DE 103 33 626 A1 known procedure. If the angular position of the gravure roller 5 is not so exact with the timing at which the leading edge of the Workpiece 8 the printed image position sensor 12 happens to be synchronized to superimpose the print image start exactly with the leading edge of the workpiece 8, the conveyor belt 16 is decelerated or accelerated, and additionally or alternatively, the applicator roll and the gravure roller 5 are decelerated or accelerated to a to ensure exact match and thus an exact repeat at the beginning edge of the workpiece 8.

The above-mentioned print image distortion or print image length tolerance, which can arise due to slippage in the printing unit 3, as well as a lateral print image position tolerance can not be detected on the front edge of the workpiece 8, so that in this context the flow sensor 11 and the print image position sensor 12th are ineffective. For this purpose, rather pass marks or, in the case of multiple printing units 3, combined color marks registration marks must be applied to the surface of the workpiece 8 in order to detect fluctuations in the print image length and in the lateral position of the printed image. This is done automatically by a arranged at the outlet of the device camera 13, which can evaluate the pass marks with a digital image processing.

As already mentioned, however, it is not possible for full-surface printing of the surfaces of workpieces 8 to apply registration marks, without disturbing the printed image sensitive; normally, pass marks that lie within the printed image are not accepted by the customer. Accordingly, the lateral guide 7 according to the present invention is adjustable in sections, which in Fig. 2 is shown. Here, a randomly selected workpiece 8 is guided straight laterally offset by the printing unit 3 by the located on the printing unit 3 section of the lateral guide 7 has been adjusted laterally from a neutral position 14 in a test position 15. The other portions of the lateral guide 7 are still in the neutral position 14, so that the other in-line workpieces 8 continue to be printed and processed normally. Only when the staggered workpiece 8 arrives at a corresponding portion of the lateral guide 7, this section is moved to the test position 15 and after passing the corresponding laterally offset workpiece 8 again returned to the neutral position 14, so that in the result only a single workpiece 8 is guided laterally offset by the device.

On the engraved roller 5 next to the printed image registration marks are engraved, which are accordingly transferred to the applicator roll 4, from where they only get to the workpiece 8, when this is transported laterally offset in the test position 15 by the printing unit 3. This leads to a test edge 19 next to the printed image 18, as in Fig. 5 is shown.

The FIGS. 3 and 4 show a schematic view of the printing unit 3 in the direction of passage, so that here in addition to the applicator roll 4 and the gravure roll 5 and a counter roll 17 is visible, which forms a pressure nip together with the applicator roll 4 through which the workpiece 8 is guided resting on the conveyor belt 16 ,

FIG. 3 shows the workpiece 8 in the lateral neutral position 14, while Fig. 4 the workpiece 8 in the laterally offset test position 15 shows. The applicator roll 4, the gravure cylinder 5 and the counter roll 17 are each provided with its own drive. To increase the accuracy of the image on the workpiece surface and to avoid unwanted image distortion of the drive of the backing roll 17, however, a lower torque than that of the applicator roll 4. This ensures the greatest possible slip of the unwinding of the applicator roll 4 on the workpiece 8. In addition, the drives can be regulated in order to produce a specific "counter slip", depending on the image distortions or image length tolerances detected by the camera 13, in order to eliminate the disturbance and keep the print image length as close as possible to a 1: 1 image. To compensate for lateral position tolerances of the printed image 18, the printing unit 3 as a whole, or individual components such as in particular the gravure roll 5 may be arranged axially adjustable. Of course, a correction of a lateral print image position deviation can also be effected by changing the neutral position 14 of the lateral guide 7.

FIG. 5 schematically shows a printed workpiece 8, the side offset in the test position 15 by the present embodiment of the invention has been conducted. Accordingly, the printed image 18 is offset laterally, and a test edge 19 remains free, wherein the test edge 19, a first color ramp 20 with four registration marks and a second color ramp 21 is also applied with four registration marks. In the present case, therefore, there was a four-color printing with a total of four printing units 3. By comparing the two color lights 20 and 21, the correct print image length can be recognized separately for each color.

In the FIGS. 6 and 7 is the color light 21 shown in and FIG. 6 with registration marks 22, 23, 24 and 25, each exactly within the given tolerances, while FIG. 7 Correction requirement indicates: The registration mark 22 for the first printing unit 3 shows a too short print image 18. The registration mark 23 is within the predetermined tolerance, so that it follows that the second printing unit works exactly. The registration mark 24 for the third printing unit shows a need for correction both in the print image length (this is too long) and in the lateral print image position. The same applies to the registration mark 25 for the fourth printing unit.

The color lights or registration marks are detected and evaluated by the camera 13 at the outlet of the printing line, so that an automatic correction of the corresponding printing units by means of rules of the drives and the other adjustment in the context of a tendency correction on the subsequent workpieces 8 effects. This results in a control loop or a system of control loops, which ensures the maintenance of very tight tolerances for the print image position and the print image length automatically during full-scale printing of workpieces 8 during production.

LIST OF REFERENCE NUMBERS

1

Diagonal roller conveyor

2

Belt conveyors

3

printing unit

4

applicator roll

5

engraved roll

6

roller conveyor

7

lateral guidance

8th

workpiece

9

conveyor belt

10

roll

11

Flow sensor

12

Image position sensor

13

camera

14

Neutral position (from 7)

15

Test position (from 7)

16

conveyor belt

17

backing roll

18

print image

19

test edge

20

Color traffic light (first)

21

Color traffic light (second)

22

Pass mark (first)

23

Pass mark (second)

24

Pass mark (third)

25

Pass mark (fourth)

Claims (11)

1. Apparatus for printing flat workpieces, with a transport means (1, 6, 9, 16) for the workpieces (8) and with at least one printing unit (3), in which an applicator roller (4) rolls on the workpieces (8) transported through the printing unit (3) and in this case applies a printed image (18) to the workpiece surface, wherein the transport means (1, 6, 9, 16) is provided with a lateral guide (7) for the workpieces (8), characterised in that the lateral guide (7) is movable section by section by motor power between a neutral position (14) and a test position (15).
2. Apparatus as claimed in Claim 1, characterised in that a control for the lateral guide (7) is provided which if need be moves the lateral guide section by section in such a way that a specific workpiece (8) from a series of workpieces (8) located on the transport means (1, 6, 9, 16) comes to rest successively on particular sections of the lateral guide (7) which are moved respectively into the test position (15) and as a result is transported, laterally offset, through the printing unit (3), whilst the other workpieces (8) of this series rest on the sections of the lateral guide (7) which are located in the neutral position (14).
3. Apparatus as claimed in Claim 2, characterised in that the printing unit (3) is designed in such a way that it prints printed image position markers (20, 21) onto the edge (19) of the surface of the workpiece (8) offset into the test position (15) which extends laterally beyond the neutral position (14) of the lateral guide (7).
4. Apparatus as claimed in Claim 3, characterised in that a detector (13) for recognition of the printed image position markers (20, 21) is disposed after the printing unit (3).
5. Apparatus as claimed in Claims 3 and 4, characterised in that the detector (13) is designed to co-operate with the control means in such a way that if need be the control means alters the neutral position (14) of the lateral guide (7) in order to correct lateral displacements of the printed image.
6. Apparatus as claimed in Claims 3 and 4, characterised in that the detector (13) is designed to co-operate with the control means in such a way that if need be the control means moves the printing unit (3) and/or the printing cylinder (5) transversely with respect to the direction of movement of the workpieces (8) in order to correct lateral displacements of the printed image.
7. Apparatus as claimed in any one of Claims 4 to 6, characterised in that the detector (13) comprises an optical sensor, in particular a digital camera.
8. Apparatus as claimed in Claim 7, characterised in that the detector (13) is disposed so as to be adjustable in height.
9. Apparatus as claimed in any one of Claims 4 to 8, characterised in that a control station for adjusting the drives of the printing unit (3) and/or the transport means (1, 9, 16) and/or the lateral guide (7) is provided which is designed to co-operate with the detector (13) in such a way that it accelerates or decelerates the drives of the printing unit (3) and/or the transport means (1, 9, 16) depending upon the position of the printed image markers (20, 21) and/or changes the neutral position (14) of the lateral guide (7) in order to correct displacements of the printed image and/or longitudinal distortions of the printed image.
10. Apparatus as claimed in Claim 9, characterised in that at least one cylinder (4, 5) of the printing unit (3) which participates in the printing is axially displaceable for transverse adjustment of the printed image (18), wherein the control station brings about the axial displacement according to the position of the printed image markings (20, 21).
11. Apparatus as claimed in any one of Claims 1 to 10, characterised in that means are provided for producing a transport force component for the workpiece which is oriented perpendicular to the transport direction and to the lateral guide (7).

Images