EP2536570A1

EP2536570A1 - Device and method for printing surfaces of material panels, especially wood panels, with a multi-colour image

Info

Publication number: EP2536570A1
Application number: EP11713670A
Authority: EP
Inventors: Thomas Peter; Martin Griesdorn; Sven Sattler; Thilo Solawa
Original assignee: Dieffenbacher System Automation GmbH
Current assignee: Dieffenbacher System Automation GmbH
Priority date: 2010-02-17
Filing date: 2011-02-17
Publication date: 2012-12-26
Also published as: BR112012020680A2; ES1079068U; CN102858550A; ES1079070U; ES1079070Y; CL2012002291A1; EP2536566A2; ES1079068Y; CN102858549A; EP2536569A1; WO2011101151A3; CN102844195B; EP2536568A2; CN102844194A; CA2823433A1; EP2536567A1; US20130016151A1; US20130229450A1; WO2011101151A2; BR112012020677A2

Abstract

The invention relates to a printing device (100) for printing surfaces of material panels (30), especially wood panels (10), with a multi-colour image, comprising: means for holding a material panel (30) in an oriented position; a printing unit (110) for printing a surface of the material panel (30), the printing unit (110) comprising a plurality of adjacently arranged printing heads (12, 112), respectively for a plurality of colours, according to the width of the surface to be printed; means for moving the printing unit (110) along an area of displacement over the surface of the material panel (30) held in place; and means for preventing air turbulences in the area of displacement of the printing unit (110). The invention also relates to a method for printing surfaces of material panels, especially wood plates, with a multi-colour image, comprising: the orientation of the material panel (30) such that the surface thereof is in a defined position and at a defined height; holding the material panel (30) in place; moving a printing unit (110) along a path of displacement over the surface of the material panel (30) held in place; and printing the surface of the material panel held in place, by means of the printing unit, the printing unit (110) comprising a plurality of adjacently arranged printing heads (12, 112), respectively for a plurality of colours, according to the width of the surface to be printed. Air turbulences in the path of displacement of the printing unit (110), along the edges of the material panel (30), are prevented by the passage of air guiding devices (130, 132).

Description

Apparatus and method for printing surfaces of material boards, in particular wood panels, with a multi-colored image

The present invention relates to a method and an apparatus for printing surfaces of material plates, in particular wood panels, with a multi-colored image.

It has already been known in the prior art that wood panels can be printed directly with a multicolor image in the manner of inkjet printing. For example, document WO 02/00449 proposes to print front panels for a kitchen by moving a front panel on a conveyor belt to a printing device and moving the printing apparatus to move a single printhead on a moving carriage across the front panel to cover the area below the front panel Print head to print. After a press run, the front panel is moved with the conveyor belt by a corresponding distance, whereupon the next printing operation takes place and so on until the surface of the front panel is completely printed.

This multi-pass printing process is uneconomical for industrial production because a small printhead has to travel tens of times over the workpiece to print on a larger area. This makes the process very slow and therefore time-consuming. In addition, the method does not provide satisfactory print quality since, when repeated printing of only single strips on the front

CONFIRMATION COPY plate often comes to a noticeable offset between the individual strips.

It has already been proposed in document WO 02/00449 to modify this multi-pass method in such a way that the only moving printhead is replaced by nozzle bars arranged one behind the other in the conveying direction, which extend across the conveyor belt, in order to cover the front panels in their entirety Width to print.

The same is also known from the document EP 1 872 959 AI. This document proposes a method of printing flat wood-based element surfaces as shown in FIG. In that method, a wood panel 10 is moved by a conveyor 14 opposite fixed printheads 12 for multiple colors. The printheads 12 cover the entire width of the surface to be printed. While the conveyor belt 14 conveys the wood board, the print heads 12 release small droplets of ink to print on the surface of the wood board.

From the document JP 2000-334684 is also known for printing on wooden objects to drive them with a conveyor belt on a fixed printhead.

These processes, in which the wood panels are printed in a single pass "single pass" with fixed printheads, with the wood panels being continuously conveyed past the unit and past the printheads with a conveyor belt, provide a significant over-the-board capability Improvement in the economy. However, these methods have several disadvantages. In particular, it is not possible to achieve printing results satisfying high and highest requirements in these methods in which the printing heads are fixed and the wood plates are moved on a conveyor belt relative to the printheads. In particular, the transport of the workpieces to be printed on the conveyor belt leads to fluctuations in the speed with which the workpieces are moved past the print heads due to inherent elasticities of the conveyor belt. Other influences from the outside, such as load changes, measuring accuracy, measuring errors of external (running) measuring systems on transport media, straight running of the material plates and the like influence the print result accordingly. This means that the dots or "dots" of individual colors no longer come to rest in the intended places, but instead the workpiece travels under the individual color heads at a time lag, and the printing of the individual color dots then inevitably takes place with an offset to the next one Accordingly, the pressure points, such as for cyan C, gastric ta M, yellow Y or black K, slip on the surface of the workpiece in their position relative to each other as shown in Fig. 3, rather than at regular scheduled intervals as in Figs This will in particular lead to a perceptible impairment of the print quality if dots of different colors are to be printed congruently to one another in order to represent a mixed color Due to the offset due to the fluctuating transport speed, these dots will only overlap in partial areas, to create the mixed color, in R But areas lead to a color fringe, which adversely affects the color.

The aforementioned variations in the transport speed of the workpiece also lead to problems to start the printing in time on the edge of the workpiece. The document WO 02/00449 proposes to provide sensors for detecting the position of the workpiece on the conveyor belt, as well as the contour and thickness of the workpiece. For example, using a sensor The edge of the workpiece is detected before the workpiece enters the area under the print head. Thus, the starting signal for the start of printing can be given based on the conveying speed and the distance between the sensor and the print head. Due to the mentioned speed fluctuations of the conveyor belt, however, there will be corresponding position fluctuations, so that the pressure begins too early or too late and ends accordingly too early or too late. Again, this will have a negative impact on the appearance as a visible, unprinted area.

In addition, it is difficult with a conveyor belt to keep a workpiece always in a defined, fixed distance to the printheads. In principle, such printheads require that for a consistently good image quality, a predetermined distance between the print head and the surface to be printed must be maintained, the distance is often only 1 mm or less. Even small deviations can negatively influence the print image. Since the conveyor belts may wear off over time and / or increase in thickness due to unwanted ink deposits, which effects do not occur uniformly over the entire belt, the prior art processes cause the conveyor belts to move the workpieces with varying distances Pass the printheads, where the distances from workpiece to workpiece and with the passage of time can change. A consistently good print quality can therefore not be guaranteed with these methods. In addition, there is a risk that the workpieces are required to be too high, so there is a risk of contact and damage to the printheads.

Moreover, as shown in FIG. 4, due to the movement of the wood panel 10, or the material panel 30, air swirls 20 at the edges often occur as it moves through the conveyor belt 14 and at high speed to the printheads 12 approaches. This Luftverwirbelungen 20 cause when printing in the vicinity of the edge of the material plate 30, respectively the wooden plate 10, the ejected from the individual printheads 12 ink droplets are swirled uncontrollably and no longer come to rest in the intended places. This results in deterioration of the printed image, and such deterioration is noticeable in a range of 0.5 to 2 cm from the edge. In addition, the air swirls 20 occur in each of the separately provided by color printheads 12, these air swirls 20 will differ for each printhead 12 due to the different spatial and aerodynamic conditions. As a result, the color droplets of the different colors are swirled differently, which further adversely affects the print quality. Corresponding effects also occur at the rear edge of the workpiece, which forms a trailing edge for the air flow.

These influences, which adversely affect the print quality in the known single-pass method, increase with increasing production speed, and thus greater transport speed of the workpieces, as well as with increasing size, thickness and / or weight of the workpieces, so that the known methods especially forever faster production lines for ever larger workpieces are increasingly deteriorating with regard to the print quality that can be achieved with them.

It is therefore an object of the invention to provide a method and an apparatus for printing surfaces of material plates, in particular wood panels, with a multi-color image, which offers a consistently high print quality with high productivity.

A first aspect relates to a printing apparatus for printing surfaces of material plates, in particular wood panels, with a multi-colored image. compression, comprising means for holding a material plate in an aligned position; a printing unit for printing a surface of the material plate, the printing unit for a plurality of colors each having a plurality of juxtaposed print heads corresponding to the width of the surface to be printed; and means for moving the printing unit along a travel range over the surface of the rigidly held material plate.

Preferably, the printing unit is moved in a direction which is perpendicular to a direction in which a material plate of the printing unit is supplied.

In a preferred embodiment, the means for holding a material plate in an aligned position are formed as one or more support plates on which the material plate rests flat and is held by a vacuum.

In a further preferred embodiment, the means for holding a material plate in an aligned position are adapted to receive a material plate at a first height and to raise to a second height, wherein the second height corresponds to a position on which the surface of the work fabric plate is printed by the printing unit.

In a further preferred embodiment, the device further comprises louvers, which are arranged in the printing direction on both sides of the material plate. The louvers can also be called Luftfuhrungsein- directions.

In a further preferred embodiment, the device also has a cleaning device which extends along the travel range of the printing device is arranged and arranged to perform a cleaning cycle for the printing unit.

In a further preferred embodiment, the device further comprises a partial cleaning device which is arranged along the travel range of the printing device and is adapted to collect and collect color droplets emitted by nozzles of the print heads for partial cleaning. ,

In a further preferred embodiment, the apparatus further comprises printing quality monitoring means disposed along the printing unit traversing means, the printing quality monitoring means comprising means for feeding a control printing tape to a position in which the control printing tape is in contact with the printing unit can be printed with a test pattern, and the means for monitoring the print quality further comprises an optical system for detecting the printed test pattern, and means for comparing the detected printed test pattern with a desired pattern for monitoring the print quality.

In a further preferred embodiment, the device further comprises a system for collision avoidance, wherein a sensor arranged on the printing unit may recognize objects located on the surface of the material plate, and when an object is detected, the means for moving the printing unit causes an immediate braking reaction is and / or the printing unit is caused by lifting means to an evasive upward movement.

In a further preferred embodiment, the means for moving the printing unit are arranged to move the printing unit at least over the surface. to move the material plate in speed control at a predetermined, constant speed V pressure.

In a further preferred embodiment, the means for moving the printing unit to a linear motor drive.

Preferably, the printing device is a part of a manufacturing plant for printing surfaces of material plates, in particular wood panels, with a multi-colored image.

More preferably, the manufacturing facility further comprises an alignment device, wherein the alignment device is adapted to align a material plate in a first direction and in a second direction perpendicular to the first direction.

In a further embodiment, the production plant has a storage system for temporarily storing a multiplicity of already printed material plates, wherein the material plates can be introduced into the storage system on strips, supported therein and executed on several levels, without touching the printed surface of the material plates.

A second aspect relates to a method for printing surfaces of material plates, in particular wood panels, with a multi-colored image, comprising aligning the material plate in a defined position and height of the surface; Holding the material plate; and method of printing unit along a travel path over the surface of the held material plate and printing the surface of the held material plate with printing unit, wherein the printing unit for a plurality of colors each having a plurality of side by side having printheads arranged according to the width of the surface to be printed;

A preferred embodiment of the method further comprises feeding the material plate in a feed direction, wherein the feed direction is perpendicular to the direction in which the printing unit is moved.

A further preferred embodiment of the method further comprises a method of the printing unit to a cleaning position above a cleaning device or to a partial cleaning position above a partial cleaning device, wherein the cleaning position or the partial cleaning position along the travel path are arranged, and carrying out a cleaning cycle for the Print unit or perform a partial cleaning, in which unused nozzles of the printheads are made to deliver small drops of paint.

A further preferred embodiment of the method further comprises methods of the printing unit in a position for a control pressure; Performing a print with a test pattern on a control print strip; Capturing the printed test pattern with a camera; and comparing the detected printed test pattern with a target image to monitor the print quality.

Further, the means for holding a material plate along the louvers can be arranged substantially over the entire surface. It is also conceivable for adaptation to different formats of the material plate and / or for alignment of the material plate in the printing device a Luftleiteinrichtun- gene as a stop and a louver for positioning to arrange movable. The invention will be described below in detail with reference to various embodiments ^¬ forms, reference being made to the accompanying drawings, which show:

Fig. 1 illustrates a method of printing wood panels according to the prior art;

Fig. 2 illustrates an ideal distribution of printing dots of different colors on a printed surface;

Fig. 3 illustrates a distribution of printing dots of different color on a printed surface, in which the printing dots due to

Position offset are shifted from each other;

Fig. 4 detects the occurrence of air turbulence in the method

Fig. 1 is;

5 shows an apparatus for printing surfaces of material plates with a multicolor image according to a first embodiment;

Fig. 6 shows a diagram for a method of printing surfaces of material plates with a multicolor image according to a preferred embodiment; Fig. 7 illustrates an apparatus for printing surfaces of material plates with a multi-color image according to a preferred embodiment;

FIG. 8 is a schematic cross-sectional view through that shown in FIG. 7. FIG

Apparatus for printing surfaces of material plates with a multi-colored image in a rest position;

FIG. 9 is a schematic cross-sectional view through that shown in FIG. 7. FIG

Apparatus for printing surfaces of material plates with a multicolor image during printing; Fig. 10 shows schematically a collision avoidance system according to a preferred embodiment;

Fig. 1 1 shows schematically a first embodiment of a device for

Monitoring print quality; Fig. 12 shows schematically a second embodiment of a device for

Monitoring print quality;

Fig. 13 to 15

schematically show an embodiment of a bearing device according to an embodiment; Fig. 16 schematically illustrates a preferred embodiment of a louvers and

Fig. 17 shows a drying unit attached to the printing unit.

Various embodiments of methods and apparatuses for printing surfaces of material plates, in particular wood panels, with a multi-colored image are described.

The apparatus and methods are suitable for wood panels, or wood-based panels, such as chipboard, medium density fiberboard MDF, high density fiberboard HDF, having a thickness between 0.5 mm and 50 mm, a width of up to 1300 mm, preferably up to 3050 mm, and a length of up to 3000 mm, preferably up to 6000 mm to print. The devices and methods are not limited to wood panels, but can also be applied to other flat and large-scale material plates, such as glass or plastic. Of course, mixing plates made of plastics and wood particles are also conceivable, as are corresponding laminates of material plates which should preferably have a surface prepared or suitable for the printing technique used. Also are metal or non-metal plates, respectively shingles or laminates of the same, conceivable as material plates for printing.

5 shows a first embodiment of a printing device 100. As can be seen in FIG. 5, the material plates 30 are introduced with a conveyor belt 14 into the printing device 100 designed as a printing station of a production line. In the printing device 100, the material plates are aligned in a defined position and position. After the alignment is done, the material plate 30 is held in this aligned position and position. Thereafter, a printing unit 1 10 passes in a single pass, so-called single-pass, the surface of the material plate 30 to produce the desired printed image. For this purpose, the print head 110 is provided with a plurality of print heads 12 (see Fig. 9) for each color covering the entire width of the surface to be printed. The printheads each have a plurality of nozzles, each of which can deliver a small droplet of a color liquid. Preferably, the printheads are designed as piezo inkjet heads. The printheads 12 are driven by a computer system to produce a multicolor image based on digital image data. After the printing is done, the material plate 30 is discharged with the conveyor belt 14 from the printing device. Since the material plate 30 is held firmly in predefined and aligned position, a reproducible print start is possible. Also eliminated are negative influences due to position inaccuracies, height fluctuations or constant velocity fluctuations, as they occur in the known from the prior art method with durchlaufen- the workpiece. This allows a noticeable improvement and reproducibility of the print quality to be achieved. In this case, it is preferred that the movement of the printing unit 110 is carried out in a direction which runs transversely to the direction of transport of the material plates 30 through the printing device. This allows, in an advantageous manner in the printing unit 100 more Provide facilities and functionalities, as will be described below.

Referring now to Fig. 6, a preferred method of printing surfaces of wood panels having a multi-color image will be described. In a step 501, material plates are supplied. The material plates may be provided with uncoated or precoated surfaces, or may be embodied as raw chipboard, MDF medium density fiberboard or HDF high density fiberboard. Preferably, in a short-cycle press or a short-cycle coating plant, material plates are coated with a solid decor or desired design as a barrier layer, for example, white. Preferably, laminated material plates are produced with a melamine surface. The production of the "primer" in this way saves investment and is also cheaper in terms of production costs than a conventional structure of a primer in several layers.

In step 502 of the pre-treatment, the material plates are then provided with a primer. The primer serves to create a suitable surface for printing. Depending on the desired surface, for example high gloss, the primer can be replaced or supplemented by one or more grinding and / or filling operations.

The pretreated material plates are then fed on a conveyor belt to an alignment device 200 (see FIG. 7) in which the material plates are aligned in a step 503. In step 504, the visible print layout, for example a veneer image, is then printed onto the surfaces of the material plates 30 using a printing device 100 in digital printing. The still fresh print image is dried in a step of drying 505. The drying can take place by means of controlled air supply, in particular hot or hot air, by means of UV light or by other known methods. It is also possible that the entire alignment of the material plates takes place in the printing device 100. In this case, step 503 may be omitted.

The dried material plates are preferably temporarily stored in a storage store in step 506 before they are aftertreated in a step of the aftertreatment 507. The storage tank allows a targeted, order-related supply in this treatment of the surface. At the same time, the bearing storage serves as a buffer to accommodate printed material plates, while the devices for performing the post-processing can be temporarily used non-productive in step 507 due to regularly be carried out cleaning work. The storage memory decoupled in this way the printing process of the post-processing and allows to operate regardless of the cleaning work in the post-processing the printing process throughout.

In the after-treatment in step 507, for example, a transparent protective layer of melamine, so-called overlay, a paint application or a reactive PU application is applied to the printed image. The use is optional, depending on customer requirements, possible. When using the overlay as a final layer can be generated by the structuring of the press plates, a surface structure. With reference to FIGS. 7 to 9, a preferred embodiment of a printing device 100 will now be described.

As shown in Fig. 7, the material plate 30 is first fed to an alignment device 200, which is preferably formed as a station of a production line. The material plate 30 can be introduced into the alignment device 200 with a conveyor belt such as the conveyor belt 14 of FIG. 5, or in any other suitable manner. In the alignment device 200 conveyor belts 120 are provided, on which the material plate 30 is deposited. The alignment device 200 performs an alignment of the material plate 30 by the material plate 30 is pushed with a movable stopper 220 against a fixed stopper 210. The movable stop 220 is thereby moved by a traversing device 222, which is controlled by a control unit, not shown. In this way, alignment of the material plate 30 in a direction transverse to the running direction of the conveyor belts 120 is brought about, so that the material plate occupies with its lateral edge defined by the fixed stop 210 lateral alignment. At the same time, with a movable centering unit 240, which is designed in the form of a rake, for example in the form of a liftable or pivotable stop, the material plate 30 moves in a direction parallel to the running direction of the conveyor belts against a stop 230, which preferably also acts as a liftable or pivotable stop can be executed. In this way, the material plate 30 is aligned both in the longitudinal direction and in the transverse direction with respect to the transport direction defined by the conveyor belts 120. After alignment, the moving device 222 moves the movable stop 220 away from the material plate 30, and the liftable or pivotable stop 230 is moved by pivoting or lifting out of the path of movement of the material plate 30 to release it. The conveyor belts 120 then move the laterally oriented material plate 30 toward and into the printing device 100. In order to prevent that during the transport from the alignment device 200 into the printing device Device 100, the material plate 30 loses its orientation, for example by slipping, is preferably provided to hold the material plate 30 by means of a vacuum on the conveyor belts 120 firmly. For this purpose, the conveyor belts 120 are provided with holes through which air can penetrate. Below the conveyor belts 120 chambers are provided, which are connected to an air extraction system, wherein by the suction of the air through the conveyor belts 120 and from the chambers, a vacuum is formed, which holds the material plate 30 on the conveyor belts 120 fixed. The vacuum is preferably a switched vacuum. The vacuum is switched on when the material plate 30 is pressed by the movable stop 220 against the fixed stop 210 to hold the material plate 30 in this laterally defined orientation. With activated vacuum, the material plate 30 is then moved into the printing device 100.

FIG. 8 shows a schematic cross-sectional view through the printing apparatus 100 of FIG. 7. The printing apparatus 100 is preferably designed in portal construction, with a machine bed 102, portal columns 106, 108 and a cross member 104. The printing unit 110 is mounted on a slide 170 attached via a suspension 172. Alternatively, the printing unit 1 10 may also be connected directly to the carriage 170, or be designed in one piece with the carriage 170. The carriage 170 is mounted with longitudinal guides (not shown) on the cross member 104 and held with a drive device (not shown) relative to the cross member 104 movable. The drive device may comprise a spindle drive, which is driven by a servomotor. Preferably, the drive device is designed as a linear motor, in particular as a synchronous linear motor. The rotor of the linear motor is fixedly connected to the carriage 170 and the stator of the linear motor is fixedly connected to the cross member 104. In addition, a linear scale length measuring system is provided, which determines the position of the carriage, and thus of the runner. The use of a linear motor is particularly advantageous since such a drive construction makes it possible to realize a high stiffness traversing axis, whereby a high accuracy of the movement can be achieved. At the same time, linear motors can generate high acceleration forces, which allows the traversing axis to be moved with high dynamics and high traversing speed. As a result, short cycle times can be realized with correspondingly high productivity and economic efficiency.

In the printing device 100, an air guiding device 130 and an adjustable air guiding device 132 are furthermore preferably arranged. Furthermore, a partial cleaning device 150 and / or a cleaning device 160 are preferably provided. Between the movable air guiding device 132 and the cleaning device 160, a unit 140 for monitoring the print quality can be provided.

The printing device 100 further preferably comprises support plates 124, which are supported by pneumatic cylinders 128 by means of piston rods 126 and are movable in height. In Fig. 8, the conveyor belts 120 can also be seen schematically. FIG. 8 shows the printing device 100 in a state in which the printing unit 110 is in a rest position above the partial cleaning device 150. There is no material plate 30 in the printing apparatus 100.

The operation of the printing apparatus 100 will now be described. With the conveyor belts 120, a material plate 30 is transported into the printing device 100. The material plate 30 is already aligned longitudinally and transversely to the transport direction of the conveyor belts 120. In the printing apparatus 100, a stop (not shown) is preferably provided in the direction transverse to the conveyor belts 120. The conveyor belts 120 convey the material plate 30 until it comes into abutment against this stop (not shown). In this way se, the position of the material plate 30 in the longitudinal direction of the conveyor belts 120 is finely aligned. The material plate 30 is now in contact with the carrier plates 124. These are preferably also formed on the type of vacuum technology. The vacuum for the carrier plates 124 is now switched on and the vacuum for the conveyor belts 120 is switched off. The material plate 30 is now held in a defined orientation in both the longitudinal and in the transverse direction of the support plates 124, without causing the surface of the material plate is somehow touched. As a result, on the one hand, the surface is freely accessible for printing and, on the other hand, it is not exposed to any risks of damage or impairment which could adversely affect the printing result. The pneumatic cylinder 128 now lift by means of the piston rods 126, the support plates 124, and thus the material plate 30 held thereon to a predefined height, as shown in FIG. 9.

In the raised position of the material plate 30 shown in FIG. 9, this assumes a predefined position, referred to as zero position. The zero position corresponds to the position of the surface of a material plate of defined thickness, which serves as a reference. It is now possible for material plates 30 with deviating thickness to bring about a positioning in the zero position of the surface in that the support plates 124 are adjustably adjusted in height by means of the pneumatic cylinders 128, which means corresponding adjustable stops with corresponding actuators, or position measuring systems and controls for the plurality of pneumatic cylinders 128 requires. However, it is preferred that an adjustment of the printing device 100 to different thicknesses of the material plates 30 takes place in that the cross member 104 is adjustable by means not shown lifting devices in height to adjust the altitude of the print head to different material plate thicknesses.

The printing unit 1 10 is now moved by means of the driven carriage 170 from its rest position. In this case, the carriage is according to a predefined Acceleration profile is initially greatly accelerated to achieve a predetermined operating speed for the printing process, voruck. The acceleration is designed such that the printing unit has reached the speed v _DruC k before the printing process begins. Since the material plate 30 is held in an aligned and defined position, wherein the position of the edge of the material plate 30 is defined and known, the printing process can be started with high accuracy at the edge. In order to consider even small, possibly remaining deviations in the position of the edge, a sensor system can be used to detect the position of the edge. Since the material plate 30 is kept stationary, the problems of a positional offset known from the prior art due to changing speeds can not occur, so that the pressure can be started exactly at the position of the edge detected by the sensor. The printing unit 110 is then moved forward over the surface of the material plate 30 at a constant speed, with the nozzles of the printing heads 12 of the printing unit 1 emitting 10 small droplets of ink in order to print the desired printed image. When the printing unit 1 10 has run over the surface of the material plate 30 and printed, the carriage is decelerated according to a predetermined deceleration profile until the printing unit 1 10 comes to a standstill. Subsequently, the printing unit 1 10 is moved back to the rest position. Simultaneously with the return to the rest position, the material plate 30 can be lowered by means of the support plates 124 until it comes to rest on the conveyor belts 120. The vacuum of the carrier plates 124 is now switched off and the vacuum for the conveyor belts 120 is switched on in order to convey the printed material plate 30 out of the printing device 100. It can now, preferably simultaneously with the request of the printed material plate 30, a new material plate 30 are promoted for printing in the printing device 100. To achieve an improved print quality, it is preferably provided that the printing unit _{110 is moved} at a constant speed v _DruCk over the firmly held material _plate 30, wherein the drive unit of the carriage 170 operates in a closed speed control loop. The individual ^" colors cyan, magenta, yellow, black, and possibly other colors are as color dots or dots in a fixed fixed by the structure of the printing unit 100 mechanically fixed distance and in by a computer control (not shown) of the printing unit predetermined exactly Since the printing unit 10 travels at a constant speed, the application and the positioning of the individual color dots can be precisely determined since the actual speed of the carriage 170 and thus of the printing unit 110 is measured continuously The drive control of the drive system of the carriage 170 can be compared with the setpoint speed in an internal control loop and any deviations can be corrected immediately. The carriage 170 and the printing unit 110 can be moved very precisely at a constant speed v _DruC he dots are mounted with high precision and reproducibility on the surface of the workpiece 30 and a high print quality can be achieved.

As shown in FIGS. 8 to 10, the printing device preferably has two air guiding devices 130 and 132. The louvers 130 and 132 are connected to the superstructure of the portal, so that it moves with an increase or decrease in the cross member and thus the level of the printheads 1 12 of the pressure unit 1 10 to adapt to different material plate thicknesses and such a relative to the level of the printheads 1 12 maintain a constant distance. The louver 130 is formed stationary, while the louver 132 is preferably arranged in the workpiece plane and parallel to the plane of the print heads 1 12 displaceable or movable. In this way, it is possible to position the louver 132 in its position at different Liehe dimensions of the material plates to be printed 30 set. The louvers 130, 132 serve to conceal abrupt transitions at workpiece edges, which can lead to air turbulence, and to ensure an orderly conduction of the resulting during the process of the printing unit 1 10 air streams. For this purpose, the air guiding devices 130, 132, as shown by way of example in FIG. 16, are designed and arranged so that a first section 134 is substantially straight and arranged at the level of the surface of the workpiece 30 to be printed and in close proximity thereto is. This is adjoined by a second section 136 with an aerodynamically shaped profile, in FIG. 16 by way of example as a section sloping downward in the form of a curve. When the printing unit 110 is moved to print the material plate 30, the printing unit 110 first approaches the air guide 130. Due to the aerodynamically shaped profile of the section 136, hard edges do not oppose the air flow and become gradually increased by the portion 136 the air flow is directed so that there is no or only relatively little air turbulence. The portion 134 which is formed straight and parallel to the material plate surface. furthermore ensures that possible air turbulences can be reduced again over the extension of the section. In this way, chaotic air turbulence is avoided and a constant, guided air flow is provided, comparable to the effects that a spoiler causes on a vehicle or occur at the leading edge of an aircraft wing. Therefore, no or only insignificant chaotic air turbulences occur on the actual edge of the material plate 30, which could adversely affect the printed result uncontrollably. On the opposite side of the material plate 30, the second louver 32 ensures in a corresponding manner that there is no air turbulence at a trailing edge and thus also contributes to avoid deterioration of the print quality in the edge regions by air turbulence. Any remaining influences due to the constant, guided air flow occurring at the air guiding devices 130, 132 can also be used in the positioning of the color dots. be taken into account. The louvers 130, 132 can be carried out in various ways. As in the embodiments of the louvers 130, 132 shown in FIGS. 8 to 10 and 16, these can be designed as voluminous elements. It is also possible to provide an undercut below the section 134, or to carry out the louvers 130, 132 only as correspondingly curved plates.

As described above, the printing unit 110 after it has driven over and printed on the material plate 30 is slowed down in its movement and brought to a standstill. This can be done immediately after the printing unit 1 10 has completely overrun the material plate 30. Alternatively, the printing unit 110 can continue to travel and be brought to a standstill via the preferably provided cleaning device 160.

Cleaning of the printing heads 1 12, which is also referred to as "purges", can take place with the aid of the cleaning device 160. The execution of such cleaning cycles is absolutely necessary at regular intervals because of the operating principle of the printing heads used The cleaning device 160 also collects and discharges the quantities of ink discharged from the nozzles, and the periodic cleaning of such parts increases the service life of the expensive wearing parts Because the cleaning device 160 is arranged in the travel range of the carriage 170 and thus of the printing unit 110, the execution of cleaning cycles of this type essentially requires only the time required to carry out the cleaning cycle itself It is not necessary, the printing unit 1 10 and / or the printheads 1 12 to drive out of the printing device 100 out. This represents a significant improvement over the single-pass method known in the art cleaning the printheads from the printing position to the cleaning position are driven out of the system. This is a high level of maintenance. At the same time, during the time required for cleaning, including the time required to move the printheads from the print position to the cleaning position, and vice versa, the printing device is not available for production. which leads to a higher loss of production.

As a matter of principle, it is necessary that all nozzles of the printheads 12 are used at regular intervals, which means that at least small amounts of ink must regularly be dispensed with all the nozzles. Otherwise, an amount of ink threatens to dry up in a nozzle and clog it, resulting in failure of this nozzle and a missing dot in the printed image. This danger threatens in particular if the same pattern is printed repeatedly for large batches and this pattern is such that certain nozzles are not used. Therefore, in the printing apparatus 100, a partial cleaning device 150 is provided. The partial cleaning device 150 serves to collect and collect color droplets emitted by the print heads 12. It may simply be formed as a sheet or board on which a sponge or fleece is placed to retain the trapped paint droplets. The printing unit 1 10 can then be moved at regular intervals, or after a computer-aided evaluation of the use of the nozzles during printing on the partial cleaning device 150 and at least for insufficiently used nozzles deliver small amounts of ink and prevent it in this way preventively cleaning and drying of the nozzles. This is also referred to as partial cleaning or "partial purge." This also represents a significant improvement over the prior art single-pass method in which, because of the fixed printhead, such preventive cleaning and paint application of paint is limited to either one Workpiece or on the continuous trans- Portband can be done. If ink is sprayed onto a workpiece during such cleaning, this usually leads to perceptible impairment of the printed image, so that the workpiece is to be treated as broke and, correspondingly, the productivity decreases. If, however, sprayed onto the conveyor belt, the conveyor belt is dirty and it will form over time and more and more ink deposits on the conveyor belt, so that the workpieces are increasingly higher on the conveyor belt, which in turn negatively affect the print quality and / or the Danger of collisions may increase.

The cleaning device 160, the device 140 for monitoring the print quality and the partial cleaning device 150 are preferably connected to the superstructure of the portal, so that they are at an increase or decrease in the cross member and thus the level of the printheads 1 12 of the printing unit 1 10 for adaptation different material plate thicknesses with moves and maintain a relative to the plane of the printheads 1 12 constant distance.

According to a preferred embodiment, the printing device 100 is equipped with a system for collision avoidance. As shown in FIG. 10, a sensor 174 is arranged for this purpose on the printing unit 1 10, which detects objects 40 or other irregularities, projections, etc., which are located in the path of the printing unit 1 10 and with which a contact or a collision threatens. The sensor may be an ultrasonic sensor, an infrared sensor, a vibration sensor or an image sensor. The sensor may also be formed as a wire, thread or contact plate, which is arranged at a distance in front of the printing unit and triggers a contact when it comes into contact with an object 40. The sensor detects objects 40 in a range of preferably 200 mm in front of the printing unit. When such an object 40 is detected, the drive mechanism of the carriage 170 is caused to initiate an immediate braking reaction. and stop the printing unit to prevent a collision. This prevents possible damage to the expensive wearing parts printheads and avoids longer stoppages to repair damage and thus increases the reliability of the printing device.

Alternatively or additionally, it is also possible to provide a lifting device (not shown) in the printing unit 110. When an object 40 is detected by the sensor 174, the lifting device lifts the printing unit 110 in the direction of the carriage 170, for example using one or more pneumatic cylinders. In this way, the printing unit 110 is caused to move out of the way of the object 40 as it were. This improves the protection against collisions. In order to prevent the printing unit 1 10 during this lifting movement against the carriage 170 and / or parts of the suspension 172 strikes hard and is thus exposed to strong shocks that could damage the pressure unit 1 10 or affect their function, preferably damping means (not shown) on the printing unit 1 10 and / or provided on the carriage 170. The damping means may for example be rubber buffers which can dampen any impact.

Referring now to Figs. 11 and 12, embodiments of print quality monitoring means 140 will now be described.

FIG. 11 shows a first embodiment of a device 140 for monitoring the print quality. As shown in Fig. 1 1, a paper web 142 is unwound from a roll of paper 143 and guided over deflection rollers to a printing position and serves as a control print strip 145. The printing unit 1 10 moves to a freely defined number of prints on the workpieces 30 in addition via the arranged in the area behind the material plate 30 control pressure strip 145 and printed this with a test pattern. After the printing with a test pattern, the control print strip 145 is wound up as part of the paper web from the roll 144. In this case, the control pressure strip 145 is guided past a camera 141, which records an image of the printout of the test pattern on the control print strip 145. The camera 141 may be, for example, a line-based black and white camera or a color camera. Additionally or alternatively, a color measurement system, in particular a color spectrometer can be used. A computer system connected to the camera then compares the test image taken by the camera with a target image and creates a print quality error log. As a result, possibly missing pressure points or dots can be found, which are an indication of clogged pressure nozzles, whereby a malposition of the print heads and a color deviation of the print can be checked promptly for a printing process and thus quasi "online" For example, you can initiate cleaning cycles or perform a necessary color correction.The allowable tolerances can be defined and adjusted.This allows you to quickly identify and correct any problems that could negatively affect or affect your print quality The use of a separate control print strip 145 separate from the work piece also allows a test image to be used that differs significantly from the image applied to the work piece plate 30 st is printed. In addition, since the printing of the control printing strip 145 in the immediate vicinity of the material plate 30, it is possible that the printing unit 1 10 performs a test pressure in one operation with the printing of the material plate 30. The print quality control is thus fully integrated into the printing process.

If monitoring of the print quality were carried out with a system that reproduces an image of the print image on the material plate 30 with a reference image of this Depending on the printed image, certain errors could not or only insufficiently be detected. For example, if certain nozzles are not used in a print image, clogging of the nozzles not used in the print image may not be detected. Also, with a print image consisting only of a uniform color, or a gradually changing color gradient, it is not possible to detect an offset of the printing unit and / or the individual print heads. At best, it would only be possible with such a system to sacrifice a material plate as a whole or at least partially as a "test pattern" for monitoring the print quality, resulting in corresponding rejects, and thus at a corresponding loss of time and money.

FIG. 12 shows an alternative embodiment of a device 140 for monitoring the print quality. In FIG. 12, the control strip used is not a continuous paper strip, but a control pattern strip 146. The control pattern strip 146 has a predefined size and may be a pattern of paper, cardboard or the like. Preferably, the control pattern strip 146 is made of the same material as the material plate 30. The control pattern strip 146 is supplied and removed laterally. A camera 147, preferably a color camera, creates an image of the test print applied to the control pattern strip 146. Also in this case, comparison with a target image takes place to monitor the print quality as described above with reference to FIG. 11.

Reference is now made to FIG. 17. As shown in FIG. 17, a drying device 180 is preferably attached to the printing unit 110. The drying device 180 is disposed on the rear side of the printing device 1 10 seen in the printing direction and serves to dry the printed on the surface of the printheads 1 12 color dots so that they do not run. The drying device 180 can be used with UV radiation, with infrared Radiation or work with hot air. Since the drying device 180 is moved with the printing unit, a uniform drying of the color dots on the surface can be achieved.

13 to 15 illustrate an embodiment of a storage system 300 for temporarily storing material plates 30 already printed. Since freshly printed or painted material plates 30 can not be stacked on one another due to the risk of damage to the surface, in some cases, be stored for further processing must, however, not be used in wood processing otherwise conventional storage systems in which wood-based material plates are stacked on one another or stored in a reversible forklift and thereby turned. It is therefore provided that the bearing system 300 receives the material plates 30 without contacting the surface in several levels. The printed material plates 30 are fed to the storage system 300 lying one behind the other on bands 310, for example, carrying strip bands. The last band 320 in front of the bearing can control the different levels by a height adjustment of the band 320. The individual consecutively arriving material plates 30 are likewise taken over by strip tapes 310 in the storage stages. The bearing 300 can be emptied in the outlet over a height-adjustable band 330 again. An emptying can also be done by reversing the conveying direction via the feed belts (belts 320). Alternatively, it is also possible, instead of adjusting the bands 320 and 330 in height, to configure the levels of the bands 310 in a height-adjustable manner in the storage system 300.

As described above, it is preferable to align the material plates 30 with the aid of the alignment device 200. Alternatively, it is also possible to carry out the alignment in the printing apparatus 100. For this purpose, it is possible, for example, to use the air guiding devices 130, 132 simultaneously as a stop for the material plate 30. It is also possible to replace the conveyor belts 120 and carrier plates 124 by a cassette system. In this case, at least one cassette is provided with the printing unit 100, which serves as a conveyor and support for the material plates 30. The cassette may also be formed in the manner of the vacuum technique to hold the material plates firmly. The cassette can preferably also be designed to be movable in height.

The foregoing description of preferred embodiments is not limitative. In particular, the described devices and methods can be modified in various ways.

As described above, it is preferably provided with height-adjustable support plates 124 to raise the material plate 30 in height, wherein the material plate 30 is raised above the level of the conveyor belts 120. If the stroke is dimensioned such that the level of the material plate 30 is at such a height that also the units preferably provided, such as louvers 130, 132, device for monitoring the print quality 140, partial cleaning device 150 and / or cleaning device 160 on a are arranged sufficiently level above the conveyor belt 120, it is also possible not to let the conveyor belt 120, as preferably provided, transverse to the printing device 100 but longitudinally therethrough.

Likewise, the pneumatic cylinders mentioned in the above description can be replaced by hydraulic cylinders, servomotor drives or other suitable drive means. Moreover, various aspects of the embodiments described above are not limited to these. So it is conceivable, for example, to use the collision avoidance system described above, even in the known from the prior art method in which material plates are printed in a single pass "single pass" with fixed printheads, the material plates continuously with a conveyor belt 120th It is also conceivable to use air guiding devices such as the air guiding device 130 or 132 described above on a conveyor belt 120 in such a method as with reference to FIG Fig. 1 to be described, wherein the material plates 30 are conveyed lying between the louvers.

List of reference numbers:

10 wooden plate 143, 144 paper rolls

5 12 print heads 30 145 control print strips

14 conveyor belt 146 control pattern strip

16 pulleys 147 camera

20 air turbulences 150 partial cleaning device

30 material plate

35 160 cleaning device

10 40 object

170 sleds

100 printing device

172 suspension

102 machine bed

174 sensor for Kollisions¬

104 cross member

avoidance

106, 108 supporting the portal

40 180 drying device

15 110 printing unit

200 alignment device

112 printheads

210 Fixed stop

120 conveyor belts

220 movable stop

124 carrier plates

222 Track unit

126 piston rod

45 230 Liftable or swiveling

20 128 pneumatic cylinder stop

130, 132 louvers 240 centering device

134 first section 300 storage system

136 second section 310 bands

140 device for 50 320 belts (supply unit)

25 Monitoring of

330 tapes (discharge unit) print quality

501 - 507 steps of the procedure

141 camera

142 paper web

Claims

claims

Printing device for printing surfaces of material boards, in particular wood boards, with a multi-colored image, comprising:

Means for holding a material plate (30) in an aligned position; a printing unit (1 10) for printing a surface of the material plate (30), wherein the printing unit (1 10) for a plurality of colors each have a plurality of juxtaposed print heads (12, 1 12) corresponding to the width of the surface to be printed having;

Means for moving the printing unit (110) along a travel area over the surface of the rigidly held material plate (30); and means for preventing air turbulence in the travel range of the printing unit (110).

Printing device according to claim 1, which is arranged as a means for avoiding Luftverwirbelungen an air guiding device (130, 132).

Printing device according to one of the preceding claims, wherein two air guiding devices (130, 132) are arranged in the printing direction on both sides of the material plate (30).

Printing device according to one of the preceding claims, wherein the louver (130, 132) has a first portion (134) substantially straight and at the level of the surface of the material to be printed plate (30), which is arranged in close proximity to the material plate.

5. A printing apparatus according to any one of the preceding claims, wherein the air guiding means (130, 132) comprises a second portion (136) having an aerodynamically shaped profile adjacent the first portion (134), the second portion (136) being in particular curved down sloping section is executed.

Printing device according to one of the preceding claims, wherein the means for holding a material plate (30) in an aligned position as one or more support plates (124) are formed, on which the material plate (30) rests flat and is held by a vacuum.

Printing device according to one of the preceding claims, wherein the air guiding device (130, 132) have an undercut below the section (134).

Printing device according to one of the preceding claims, wherein the air guiding device (130, 132) are designed as curved plates.

9. A printing device according to any one of the preceding claims, wherein the means for holding a material plate (30) in an aligned position are adapted to receive a material plate (30) at a first height and to raise to a second height, wherein the second height of a layer corresponds, on which the surface of the material plate (30) by the printing unit (1 10) is printed.

10. Printing device according to one of the preceding claims, wherein the means for holding a material plate (30) along the louvers (130, 132) are arranged substantially over the entire surface. Printing device according to one of the preceding claims, wherein for adaptation to different formats of the material plate (30) and / or for alignment of the material plate (30) in the printing device (100) an air guide devices (130) as a stop and an air guide (132) for positioning movable is arranged.

Method for printing surfaces of material boards, in particular wood boards, with a multi-colored image, comprising:

Aligning the material plate (30) in a defined position and height of the surface;

Holding the material plate (30); and

Method of a printing unit (1 10) along a travel path over the surface of the held material plate (30) and

Printing the surface of the held material plate with printing unit (110),

wherein the printing unit (1 10) for a plurality of colors each having a plurality of juxtaposed print heads (12, 1 12) corresponding to the width of the surface to be printed; and wherein air turbulence in the travel of the printing unit (1 10) along the edges of the material plate (30) by passing over louvers (130, 132) are avoided.

A method for printing surfaces of material plates according to claim 13, wherein remaining influences by air turbulence or a constant, guided air flow in the positioning of the color dots during printing on the surface of the material plate (30) are taken into account.