EP1500504A2 - Apparatus for printing flat articles produced from wood-fibre material - Google Patents

Abstract

A system for color printing onto flat panels, e.g. wooden effect panels, has the panels (4) moved through the separate color print stages on a horizontal feed (7). Each print stage is preceded by a sensor (8) which monitors the leading edge of the panels or checks print markings. The process control modulates the transport feed and/or the drives for the print rollers, to ensure accurate overlay for the separate print colors. The panels are transported separately and each print stage comprises a print roller (5), a print transfer roller (1) and a pressure roller (2), with the latter supporting the underside of the panels.

Description

The invention relates to a device for printing flat workpieces according to the preamble of claim 1.

Accordingly, such a device comprises an applicator roll on the zu unrolls the printing workpiece surface and this directly or indirectly depending according to whether the application roller itself is designed as a printing cylinder or as Transfer roller cooperates with such, a printed image on the Workpiece surface applies, as well as a counter-roller, in cooperation forms a nip with the applicator roll through which the workpiece moved through during the printing process. In addition, one is Transport device for feeding and removing the workpiece in and out of the present by the applicator roll and the backing roll formed nip.

In particular to give wood-based panels the appearance of real wood, are due to the cost advantages over a real wood veneer or foil coatings increasingly printed images of decors and grains directly applied to the wood-based panels.

For a high quality impression, however, a simple single-color printing is sufficient not from. It is rather desirable, the grain or the decor Apply in multi-color printing on the material plate. This is not at all only for wooden materials; also applications with other materials, which can be qualitatively improved by surface pressure, such as Stone or artificial leather, can be upgraded by a multi-color print become.

Especially for a high-quality multi-color printing, it is indispensable that the print image on the workpiece within very tight tolerances typically positioned in the range of ± 0.1 mm. Only then can one achieved with the conventional film coating comparable optical quality become.

These requirements are, however, in the present sheet-like workpieces harder to comply with than paper or foil machines. Because the flat workpieces present here do not go through endlessly the printing machine, and a printing modeled on paper sheet printing machines is usually because of the intransigence of those concerned flat workpieces not possible.

The present invention is therefore based on the object, a device for printing on flat workpieces of the type mentioned so too Improve that the print image is more accurate than previously possible on the workpiece surface is positioned.

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

Advantageous embodiments and further developments of the invention are in the patent claims 2 to 24 laid down.

The inventive measures for improving a generic Device therefore consist in that, seen in the transport direction of the workpiece, before the printing gap, a detection device for detecting the position of a Workpiece leading edge or a top mark is present and that this so cooperating with the transport device and / or the printing cylinder is designed that the transport of the workpiece even before reaching the printing gap accelerates or decelerates and / or the angular position of the printing cylinder by accelerating or decelerating the rotational movement can be changed to the beginning of the print image with the leading edge of the workpiece or the intended repeat length in accordance bring to.

It is therefore essential that by means of the detection device a clear position determination the leading edge of the workpiece or a corresponding one Image start mark relative to the rotational angle position known in the control of the device the impression cylinder is possible, so taking into account the fixed distance between the detection site and the nip the location the print image start on the workpiece accurately calculated and, where appropriate by brief braking or accelerating the transport movement of the Workpiece, or by brief braking or accelerating the Pressure cylinder can be corrected. Of course, it is also a combination of these two measures possible.

Particular advantages, the invention unfolds when multiple applicator rolls with in each case a counter-roller and a transport device in line one behind the other are arranged, which is the rule in multi-color printing. The workpiece then goes through all formed between the applicator rolls and the counter rolls Pressure column in a single operation in succession and is in each pressure nip printed with a different color. This continuous line process requires synchronous transport through the attachment by means of a parent Control. Nevertheless, each printing gap is preceded by its own Detection device for detecting the position of the workpiece leading edge or the image start mark provided, and each pressure cylinder or this directly assigned transport device can due to the detected sensor values briefly accelerated or delayed to the beginning of the image with to synchronize the workpiece and optionally outside the specified Correct tolerances lying displacements. The messages of the Detection devices then solve a corrective intervention in selected Drives of the superordinated synchronized composite out.

This modular construction of a multicolour printing line ensures that the achievable Positional accuracy of the print image on the workpiece surface is not depends on the number of successive printing units. The modular In addition, construction makes it possible for individual printing units to be used across the board Printing line can be extended to a color or roll change perform. If at the same time a simple distance distance in the pressure line is retracted, the production must not be significantly interrupted.

In a printing line with several printing units of the invention it brings special advantages, if before the first application roller a flow sensor for Position detection of the workpiece leading edge or a top mark and a cooperating with this acceleration or deceleration distance for coarse alignment of the workpiece to the printed image position of the first Pressure cylinder is provided. The modular correction option before each further pressure gap then only needs the fine adjustment and the fine correction take.

In front of the pressure line arranged flow can accelerate a longer distance or delaying the workpiece to be provided, which is for the Grobausrichtung the workpiece naturally suitable. To be defined in each case To ensure conditions in coarse alignment, the acceleration section be formed essentially by a calender, which is the Workpiece defined in the pass clamps and so provided by the controller Position correction without further friction can be transferred to the workpiece.

In the present technique of printing on flat workpieces, in particular Wood-based panels, these usually go through several first other processing stations in line, before they on the flow sensor for Grobausrichtung arrive at the device according to the invention. This makes it difficult to give up the individual workpieces right at the beginning of the Synchronize machining line with the printing line, especially in the necessary accuracy. This for one, because the task for the Workpieces is usually far away in space and otherwise no precision requirements must suffice. On the other hand, those upstream of the printing line Processing stations with regard to the position and orientation of the flat Workpieces permanent sources of error. A very even sequence of Workpieces on the transport device when approaching the printing line This makes it almost impossible.

An existing from several printing units printing line, each with an inventive Forming control loop for the modular correction of the print image beginning due to the recurrent with each incoming workpiece control processes a vibratory system. The preferably provided Coarse alignment of the workpieces stops before reaching the actual pressure line In this case, the vibration amplitudes small and prevents a possible rocking. The individual control loops of the pressure column must then only each make even minor corrections.

The coarse alignment also prevents two workpieces from coming too close together, at the individual pressure gaps separated from each other finely adjusted to be able to. Normally, the coarse alignment ensures that the Distance between the individual workpieces a whole-line multiple of the provided image length is.

The preferably present coarse alignment of the workpieces by the flow sensor and the acceleration section thus decouples the pressure line from the normally preceding workstations. Particularly preferred works the coarse alignment so that it basically accelerates the workpieces and does not slow down; because delaying would be a danger of backwater in the production line.

Both the applicator roll and the counter roll can each with a Drive be provided, as has been customary. To increase the accuracy the image on the workpiece surface and to avoid Of undesirable image distortions, it is advantageous if the drive of the Counter roll gives a lower torque than that of the applicator roll. Thus it can be ensured that the applicator roll without slippage on the Rolls workpiece surface. Alternatively it can be provided that the drive the counter roller depending on any existing image distortions can be controlled to specifically prevent slippage between the applicator roll and to produce or eliminate the workpiece.

The image length during printing depends directly on the slippage of the applicator roll on the workpiece or also with the slip between the applicator roll and the transfer roller together. The goal in printing is therefore avoidance a slip; but more important is the correct position superimposed of different colors when in successive printing gaps is printed one after the other. According to a particularly preferred embodiment The invention is therefore a drive of a roller of a pressure nip, expediently the drive of the applicator roll, chosen as the master drive and its Torque taken as a reference value. All others interacting with this drive Drives of a pressure nip are then controlled so that the values of their torques keep their sign under all circumstances, So no zero passes of the torque values take place. This can be on easiest achieved by a kind of torque cascade, so by a conscious descending choice of the torques of all drives over the Master of torque. By preventing zero crossings is achieved that all drive trains of the drives run without play, since they are permanently "open Oscillations in the drive trains, for example due to backlash, Clutch play, torsion etc. that result in image distortions would be, thereby, in the simplest way, without much effort or absolute value measurements, excluded. Also fluctuations in the action radius the involved rolls, due to the resilience of the roll surfaces and the thickness tolerances of the workpieces are present, through this measure of the torque control does not lead to image length distortions, and in particular not to different image length distortions at different Lead colors.

To comply with the tight tolerances for the pressure in the lateral direction to be able to have a lateral guide for the workpieces, the workpieces being transported adjacent to this guide by the device become. As a result, the workpieces are aligned laterally exactly.

This side guide can be a simple ruler, but better a roller conveyor or a vertical conveyor belt. At the same time, it offers advantages when means for generating a perpendicular to the transport direction and to the side Guide out oriented transport force component for the workpiece available are. Such means could for example be an inclined roller conveyor, a small entanglement of counter roll and applicator roll in the horizontal Axis position to each other or a slight inclination relative to the direction of passage be.

For fine adjustment of the lateral position of the workpieces, the impression cylinder be formed axially adjustable. This transverse adjustment of the printing cylinder can also automatically via the feedback of an image recognition system done by the image recognition system on the on the workpiece surface transferred print image detects a need for correction and this to the axial adjustment the pressure cylinder returns.

Other special advantages arise when the application roller with a Drive is provided for generating or eliminating a slip between the applicator roll and the workpiece and / or optionally between the printing cylinder and the application roller formed as a transfer roller is controllable. Because the inventive position detection of the workpiece leading edge or a beginning of the image marker relative to the position of the printed image Initially only the exact position of the print image beginning on the workpiece surface. The printed image length and thus the position of the image end is dependent on it from the relative speed between the applicator roll and the Workpiece surface or indirect pressure also from the relative speed between the impression cylinder and the transfer roller. Only if this Relative speeds are exactly equal to zero, so there is no slip is, the print image is transferred on a scale of 1: 1 to the workpiece surface. By different parameters, such as the admission pressure setting the Applicator roll, the workpiece thickness tolerance or the inhomogeneity of the applicator roll surface Slip and thus inaccuracies in the printed image generated. A targeted generation of a "counter slip" between the applicator roll and the workpiece or even between the impression cylinder and an optionally existing transfer roller can eliminate this disturbance and keep the print image length almost at the level of a 1: 1 image.

In contrast to the inventive adjustment of the print image start on the Workpiece surface affects the generation of slippage between the applicator roll and the workpiece or between the impression cylinder and a transfer roller trained applicator roll to compensate for errors in the Print image length only on the following workpieces; it is this So a trend correction.

The recognition of printed image length errors after the successful printing and the appropriate correction by creating or eliminating a slip can visually and by hand. It is advantageous, however, if the Pressure gap means for detecting image length tolerances are connected downstream, which preferably consist essentially of a digital camera. If Then there is an image processing device that is on hand of the obtained from the camera digital image on the regulation of the applicator roll acting to compensate for image length tolerances is an automatic control system given that minimizes the image length tolerances.

As mentioned above, the digital camera and the associated image processing device also recognize the tolerance compliance in the lateral direction and correct by an axial adjustment of the impression cylinder.

In particular wood-based workpieces have thickness tolerances, the one usually do not allow direct pressure with a pressure cylinder. Therefore, it is preferable the applicator roll is not designed as a printing cylinder, but it is a separate printing cylinder is present, which prints the image on the applicator roll transfers, after which this transmits the printed image on the workpiece surface. The applicator roll is then designed as a transfer roller. The printing cylinder is preferably a gravure roll with recesses, which are in Fill the inking unit with paint as you attach it to the transfer roller submit. The transfer roller is expediently as rubberized Steel roller formed, the rubber outer surface was ground smooth.

The thus formed as a transfer roller applicator roller is then in simultaneous contact with the printing cylinder and the workpiece surface, while taking over the print image from the impression cylinder and onto the workpiece surface transfers.

As already mentioned above, can be used for printing image length adjustment alternatively or in addition to generating the slip between the applicator roll and transfer roll and the workpiece surface also slip between the Printing cylinder and the applicator roll or transfer roller are generated. Because an existing, accidental slip between the impression cylinder and the transfer roller results in slight print image distortions, which eventually leads to errors in the print image length.

In this respect, a digital camera for image recognition and an image processing device are present, the latter can on the regulation of the printing cylinder and / or the applicator roll to compensate for image length tolerances. This measure leads to an automatically controlled error correction method in terms of print image length.

In order to increase the quality impression of the printed surface, you can It may be advantageous to coat the same with a melamine resin and so printed and coated workpiece of a downstream embossing device, For example, an embossing roll or press supply. This shapes one Structure on the surface, however, the previously applied print image exactly to achieve the intended effect.

If in a device according to the invention at least two in the transport direction the workpiece spaced apart detection devices are provided, these two can not only for location detection, but also used to measure the current transport speed of the workpiece become. When a device according to the invention not only a Pressure nip, but several consecutively arranged pressure column or Comprises printing units in which anyway each printing unit with its own Detection device according to the invention is provided, can for measuring the Transport speed of the workpiece even two such actually individually arranged detection devices cooperate.

Figur 1

eine schematische seitliche Darstellung einer erfindungsgemäßen Vorrichtung mit drei Druckwerken;

Figur 2

eine ebensolche Darstellung des Vorlaufs der Vorrichtung aus Figur 1.

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

FIG. 1

a schematic side view of a device according to the invention with three printing units;

FIG. 2

a similar representation of the flow of the device of Figure 1.

Figure 1 shows a total of three as a transfer roller 1 for the indirect pressure trained application rollers, which each interact with a counter-roller 2 and form a pressure nip 3, which is traversed by a workpiece 4. The print image is in each case by a printing cylinder 5 on the transfer roller 1 and transferred from this to the workpiece surface 6.

The workpiece 4 runs on a roller conveyor 7, wherein the transfer roller 1, the counter roll 2 and the pressure cylinder 5 are driven synchronously and thereby also produce the transport movement of the workpiece 4.

Each printing nip 3 is at least one detection device designed as an optical sensor 8 for detecting the position of the front edge 9 of the workpiece. 4 preceded, here is an approximately necessary corrective action to the situation perform the leading edge 9 relative to the angular position of the impression cylinder 5, by briefly accelerating or decelerating the impression cylinder 5 and the transfer roller 1 is made. To include the current transport speed monitor the printing line shown in Figure 1 in real time can, here are two detection devices 8 for the position detection of Leading edge 9 of the workpiece 4 is present.

The printing cylinders 5 are each provided with a registration mark 10, on hand which a arranged next to the print image marker in per se known Way can be applied to the workpiece surface 6. This registration mark, usually a color cross or a color lamp, allows one very fast detection of aberrations, which in particular to the invention Print image length correction is important. Registration marks and, if necessary Adjacent prints can also easily from a digital Camera captured and evaluated automatically. Preferably set at both the beginning of the image and the forming registration marks, with the former the tolerances of the print image beginning and by the latter the Tolerances of the print image length can be checked for compliance.

Figure 2 finally shows the flow of the device shown in Figure 1, wherein Here is a device for coarse alignment of the workpiece 4 is present. About that In addition, it becomes clear that a calender 11 precedes the first printing unit is to the acceleration or deceleration of the invention Workpiece 4 targeted and reproducible perform.

The device for coarse alignment has a calender 12, which the braking or acceleration of the workpiece 4 defined and without friction causes.

The calender 11 acts as acceleration for the first printing unit assigned to it. or delay line, so that the drives of the applicator roll or here the transfer roller 1, the impression cylinder 5 and the counter roll 2 not necessarily need to be addressed for corrective purposes.

Finally, it should be noted that it is especially in wood-based materials but also other non - flexible workpieces, will be appropriate, the principle of apply indirect pressure, as shown by the figures in the figures Embodiments is described; Here is the printed image of the printing cylinder 6 transferred to the transfer roller 1 and then from this to the Workpiece surface 6. Nevertheless, the invention can also be used in a direct Pressure to be used; the transfer roller 1 would be omitted in the case and the pressure cylinder 5 would be used directly as an applicator roll and on the Unroll workpiece surface 6.

LIST OF REFERENCE NUMBERS

1

transfer roller

2

backing roll

3

nip

4

workpiece

5

pressure cylinder

6

Workpiece surface

7

roller conveyor

8th

detection device

9

Workpiece front edge

10

registration mark

11

calender

12

calender

Claims (24)

Apparatus for printing on flat workpieces, with an applicator roll, which rolls on the workpiece surface to be printed (6) and thereby applying a printed image on the workpiece surface (6), wherein the applicator roll a pressure cylinder (5) or one with a pressure cylinder (5) cooperating Transfer roller (1), with a counter-roller (2) which forms in cooperation with the applicator roll a pressure nip (3) through which the workpiece (4) moves through during the printing operation, and with a transport means (7) for closing and Discharging the workpiece (4) into and out of the printing nip (3) formed by the application roller and the counter-roller (2),
characterized in that , as seen in the transport direction of the workpiece (4), there is a detection device (8) for detecting the position of a workpiece leading edge (9) or a start of image mark in front of the printing nip (3), which is thus in contact with the transport device (7, 11) and / or the printing cylinder (5) is designed to cooperate such that the transport of the workpiece (4) can be accelerated or decelerated before reaching the printing gap (3) and / or the angular position of the printing cylinder (5) can be changed by accelerating or decelerating the rotational movement, to bring the beginning of the printed image with the workpiece front edge (9) or the intended repeat position in accordance. Device according to claim 1,
characterized in that a plurality of applicator rollers, each with a counter-roller (2) and a transport device (7, 11) are arranged in line one behind the other, wherein each printing nip (3) assigned its own detection device (8) for detecting the position of the workpiece front edge (9) or a top image is, while the transport means (7, 11) are coordinated so that the workpiece (4) passes through all the pressure gaps (3) formed between the applicator rollers and the counter rollers (2) in a single operation. Device according to claim 2,
characterized in that in front of the first printing nip (3) a flow sensor (8) for detecting the position of the workpiece leading edge (9) or a beginning image mark and a cooperating with this acceleration or deceleration distance (12) for coarse alignment of the workpiece (4) to the printed image position of the first Pressure cylinder (5) is provided. Device according to claim 3,
characterized in that the acceleration section is formed essentially by a calender (12). Device according to one of claims 3 or 4,
characterized in that the flow sensor (8) a task device, which gives the workpieces (4) on the transport device (7), controls. Device according to one of claims 1 to 5,
characterized in that the applicator roll and the counter roll (2) are each provided with a drive, wherein the drive of the counter roll (2) generates a lower torque than that of the applicator roll. Device according to one of claims 1 to 5,
characterized in that the application roller and the counter-roller (2) and optionally further rollers of a pressure nip (3) are each provided with a drive, wherein the drives are controlled so that a drive sets a torque value and all other drives so regulated in their torques will be that there is no sign change in the torque value during the printing process. Device according to claim 7,
characterized in that the controlled according to the default value of the torque of the master drive drives are each acted upon by a torque which is at least slightly below the master torque. Device according to one of claims 1 to 5,
characterized in that the applicator roll and the counter roll (2) are each provided with a drive, wherein the drive of the counter roll (2) for generating or eliminating a slip between the applicator roll and the workpiece (4) is controllable. Device according to one of claims 1 to 9,
characterized in that a lateral guide for the workpiece (4) is present. Device according to claim 10,
characterized in that the guide is formed of a ruler, a roller conveyor or a vertical conveyor belt. Device according to one of claims 10 or 11,
characterized in that means for generating a perpendicular to the transport direction and the lateral guide out oriented transport force component for the workpiece (4) are present. Device according to one of claims 1 to 12,
characterized in that the pressure cylinder (5) is designed to be axially adjustable for the transverse adjustment of the printed image. Device according to one of claims 1 to 13,
characterized in that the applicator roll is provided with a drive which is controllable for producing or eliminating slippage between the applicator roll and the workpiece (4). Device according to one of claims 1 to 14,
characterized in that the printing gap (3) means for detecting image length tolerances are connected downstream. Device according to claim 15,
characterized in that the means comprise a digital camera. Device according to claims 14 and 16 or 9 and 16,
characterized in that an image processing device is provided which acts on the hand of the digital image obtained from the camera on the control of the drive of the applicator roll and / or the counter roll (2) to compensate for image length tolerances. Device according to claims 13 and 17,
characterized in that the image processing device also acts on the axial displacement of the printing cylinder (5). Device according to one of claims 1 to 18,
characterized in that the impression cylinder (5) is a gravure roll. Device according to one of claims 1 to 19,
characterized in that the application roller is formed as a transfer roller (1) and provided with a drive, that the impression cylinder (5) is provided with its own drive and that the drive of the transfer roller (1) and / or the drive of the impression cylinder (5) is controllable to create or eliminate slippage between the impression cylinder (5) and the transfer roller (1). Device according to claims 16 and 20,
characterized in that the image processing device on the basis of the digital image obtained from the camera on the control of the printing cylinder (5) and / or the transfer roller (1) acts to compensate for image length tolerances. Device according to one of claims 1 to 21,
characterized in that the printing gap (3) is followed by a stamping device. Device according to one of claims 1 to 22,
characterized in that the workpiece (4) consists of wood or a wood material. Device according to one of claims 1 to 23,
characterized in that at least two in the transport direction of the workpiece (4) spaced apart detection means (8) are provided, which are arranged cooperatively so that they measure the transport speed of the workpiece (4).

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