DE102019111034B4 - DIGITAL PRINTING MACHINE WITH ARC-SHAPED WORKPIECE WEB AND PRINTING METHOD - Google Patents

Abstract

Digital printing system (100), in particular for printing a non-flat, preferably curved surface of an object (O), which has the following: - an object positioning device (20) which is designed to be moved at least in a feed direction (X), and that to position the object (O) to be printed; - a printing station (10) comprising at least two print heads (11) each having a different color, the print heads (11) being designed so that in the advance direction (X) are arranged and aligned one behind the other along an arc, with the object positioning device (20) being height-adjustable in the height direction (Z) in such a way that the object (O) can traverse an arc shape during the printing process, characterized in thatfor imaging a large number of different arc shapes for different objects (O) the radius of the arc of the arranged print heads (11) can be changed and adapted to the object to be printed (O ) is adaptable, for which purpose the print heads (11) are each adjustable along a distance direction from the object (O) to be printed, the print heads (11) each being adjustable in their angular position about a pivot point, the rotation about an axis of rotation in the depth direction ( Y) oriented perpendicularly to the height direction (Z) and perpendicularly to the feed direction (X).

Description

The invention relates to a digital printing system and a method for printing.

Methods and devices for digital printing are known. Compared to conventional printing processes, they offer an advantage in that the print data is prepared in a digital workflow, so that costs such as for the production of the necessary printing plates can be saved with conventional printing processes.

However, currently known digital printing systems and methods for printing are limited to the fact that the object to be printed is at least essentially flat and/or can only be printed in one color. In particular, it is difficult to print objects with a non-planar surface in multiple colors.

The pamphlet DE 10 2009 040 959 A1 relates to a device for printing a non-planar, in particular cambered, surface of a plastic workpiece by means of an inkjet printing process, the device having a printing device, a workpiece carrier and a traversing device. The printing device has at least one ink nozzle which is designed to emit an ink directed in a target direction. The workpiece carrier has a workpiece holder which is designed to fix the workpiece relative to the workpiece holder. The workpiece holder and the paint nozzle are arranged such that they can be displaced relative to one another along an adjustment direction. The workpiece holder and the traversing device are arranged such that they can be displaced relative to one another, and the printing device and the workpiece carrier are arranged such that they can be displaced relative to one another along a feed direction by means of the traversing device.

The pamphlet DE 10 2016 209 649 A1 relates to a device for printing multidimensional objects, having an object carrier for holding and moving the object to be printed, a tool carrier for receiving stationary processing tools, and a frame to which the tool carrier is attached. In this case, it is provided that the object carrier has three guide tracks which are orthogonal to one another, each aligned along a movement axis, and slides which can be moved thereon for the translatory movement of the object relative to the stationary processing tools.

The pamphlet U.S. 2013/0215206 A1 relates to an ink jet printer.

The pamphlet DE 10 2015 200 986 A1 relates to a device for printing and radiation treatment of a curved surface of an object, with a printing unit, a radiation unit, and a moving unit, either for moving the printing unit and the radiation unit at a working distance along the surface or for moving the object at a working distance along the printing unit and the radiation unit. It is provided that a shielding unit is provided, which can be adjusted and/or deformed relative to the printing unit and/or relative to the radiation unit and during the printing.

The pamphlet DE 10 2014 006 991 A1 relates to a device for printing with an inkjet printhead on a curved surface of an object, the printhead comprising at least one row of nozzles with nozzles for ejecting inkjet droplets and the printhead and/or the object being driven by a movement device for generating a relative speed component is moved between the print head and the surface. It is provided that the print head and/or the row of nozzles is inclined about an axis parallel to the row of nozzles at an angle to the direction of the relative speed component between the print head and the surface in such a way that ejected ink jet drops receive a relative speed component between the drop and the surface , which essentially compensates for the relative velocity component between the print head and the surface.

The invention is therefore based on the object of specifying a digital printing system and a method for printing that eliminate the above-mentioned problems and disadvantages of the prior art. In particular, it is the object of the present invention to specify a digital printing system and a method for printing, in which a satisfactory and in particular reproducible result is possible in multicolored digital printing of non-flat, preferably curved surfaces of an object.

With regard to the digital printing system, the object on which the invention is based is achieved by the subject matter of independent patent claim 1, advantageous developments of the digital printing system according to the invention being specified in dan dependent patent claims 2 to 11. With regard to the method, the object on which the invention is based is achieved by the subject matter of the independent claim 12 . An advantageous development of the method according to the invention is specified in dependent claim 13 .

The solution according to the invention consists in particular in specifying a digital printing system, in particular for printing a non-flat, preferably curved surface of an object, which has the following: an object positioning device which is designed to be moved at least in one feed direction and to position the object to be printed position; a printing station which has at least two (preferably four) print heads, each of which has a different color, the print heads being designed in such a way that they can be arranged and aligned in the feed direction one behind the other along an arc, the object positioning device being height-adjustable in this way in the height direction that the object can follow an arc shape during the printing process.

With the digital printing system according to the invention, the task is solved in a satisfactory manner.

In particular, since the object positioning device can be adjusted in the height direction in such a way that the object can traverse an arc shape during the printing process, it is possible to obtain a satisfactory and reproducible print result on the object to be printed.

The object is preferably a piece of white goods, in particular a panel for washing machines, dishwashers, dryers or the like.

The object to be printed (for example the panel) can be positioned in an object positioning device, that is to say arranged or inserted. The object positioning device is designed in such a way that it positions the object in a targeted and reproducible manner during the entire printing process.

For this purpose, the object positioning device can be assigned a monitoring device, for example an optical monitoring device, which monitors and, if necessary, corrects the position of the object to be printed in the printing station and in any preceding and following stations.

The feed direction is the direction in which the object positioning device moves from the location at which the object to be printed is arranged in the object positioning device to the location at which the object to be printed is printed (the printing station).

The two or more (preferably four) different print heads, ie print heads of different colors, are preferably based on the CMYK color model, ie they correspond to the color components cyan, magenta, yellow and black (key). However, it would of course also be conceivable in this connection for more than four print heads to be arranged, in which case white or an extension of the color space with spot colors (additional inks in specific shades) would be conceivable. It is also possible to use pre-treated inks such as primers.

The print heads are designed to be adjustable, in particular in such a way that they can be arranged and aligned one behind the other along an arc, as seen in the feed direction, which matches the radius of the bent or curved surface of the object to be printed.

The object positioning device is designed in such a way that it can traverse the arc specified by the curved surface of the object and correspondingly simulated by the arrangement of the print heads. For this purpose, the object positioning device can be adjusted in the height direction in such a way that the object positioning device or the object can traverse an arc shape during the printing process.

According to the invention, the print heads can each be adjusted along a distance direction from the object to be printed. In detail, the print heads can each be adjusted in their angular position about a pivot point, with the rotation taking place about an axis of rotation in the depth direction, which is aligned perpendicularly to the height direction and perpendicularly to the feed direction.

When printing the object, the print head must be arranged at least essentially perpendicular to the surface area of the object to be printed. In addition, an optimal printing distance (e.g. 1 mm) must be at least essentially maintained in order to be able to produce a good printing result. Therefore, the distance direction from the object to be printed must be adjustable.

In order to be able to depict a large number of different arc shapes for different objects, the radius of the arc of the arranged print heads must be changed and adapted to the object to be printed. For this purpose, the individual print heads must be pivotable, ie their angular position must be adjustable around a pivot point.

According to an advantageous development of the invention, at least two, preferably a large number of print heads are arranged one behind the other arranged in the depth direction extending perpendicular to the height direction and perpendicular to the feed direction.

Due to the optimal distance to be maintained from the object, only an area of a certain width can be printed at any one time. Since this area is usually smaller than the width of the object to be printed, the object to be printed passes through the printing station several times, with a different area of the object to be printed (at least substantially perpendicular) being arranged below the print heads. Because several print heads are arranged one behind the other in the depth direction, it is accordingly possible to print a wider area of the object to be printed in one "printing pass".

According to an advantageous development of the invention, the object positioning device has a lifting table which has at least one lifting device at a front end viewed in the feed direction and a rear end viewed in the feed direction, by means of which the object positioning device can be adjusted in the height direction.

This makes it possible for the object positioning device to be adjustable in height in such a way that the object can traverse an arc shape during the printing process. Of course, it would also be conceivable in this context for two lifting devices to be arranged at the front end viewed in the feed direction and at the rear end viewed in the feed direction, so that not only a front area is higher or lower than a rear area of the object to be printed , but also a right area can be arranged higher or lower than a left area of the object to be printed.

According to an advantageous development of the invention, the angular position of the object on the object positioning device can be changed at a pivot point, with the rotation taking place along an axis of rotation that extends in the feed direction of the object positioning device.

Because the angular position of the object can be changed, the positioning of the object can be changed during the entire printing process in such a way that the entire object can be optimally printed. The object to be printed may have a curved or curved surface in the longitudinal direction (advance direction) and transverse direction (depth direction). As already mentioned, when printing, it is necessary to arrange the print heads at least essentially perpendicular to the surface to be printed (or vice versa).

Accordingly, it may be necessary to change or compensate for the position of the object to be printed relative to the print heads. The arc or the curvature in the longitudinal direction of the object to be printed is compensated for by the print heads being arranged in a corresponding arc shape and by the object being able to follow an arc shape during the printing process (e.g. by means of the lifting device). On the other hand, the arc is compensated for in the transverse direction in that the angular position of the object on the object positioning device can be changed.

According to an advantageous development of the invention, the digital printing system has a traversing device that is designed to move the object positioning device in the feed direction.

According to an advantageous development of the invention, the traversing device has a linear motor axis.

By combining the movement of the traversing device (in the feed direction) and the movement of the lifting device (in the height direction), the object can follow an arc shape.

According to an advantageous development of the invention, the movement of the linear motor axis and the object positioning device can be coupled and controlled in such a way that the object moves at an at least essentially uniform or constant speed during the printing process.

In order to achieve a good print result, it is necessary for the object to be printed to always move at an at least essentially constant speed (relative to the print heads). It is possible, for example, to correspondingly throttle or accelerate the speed of the linear motor axis when the lifting device is moving. The movement of the linear motor axis and the object positioning device are therefore coupled in such a way that a uniform movement of the object that can be reproduced for the printing process is possible.

According to an advantageous development, the digital printing system has a pre-treatment station, with the pre-treatment station preferably being a plasma treatment station.

The task of the pre-treatment station is to clean the surface of dust or other dirt and to increase the surface tension. So a stable adhesion and high quality of the print image on the object to be printed can be ensured.

According to an advantageous development of the invention, the digital printing system has a post-treatment station, with the post-treatment station preferably being a UV drying station.

The post-treatment station is particularly preferably an LED UV drying station. The after-treatment station is used in particular to dry the previously applied ink, but can also be used to activate it. For example, if the printed ink is UV ink, it is cured with the help of ultraviolet light in the UV curing station.

According to an advantageous development of the invention, at least one pinning unit is arranged between the print heads arranged in the feed direction along an arc, with a pinning unit preferably being arranged behind each print head in the feed direction.

The pinning unit can preferably be a small UV drying station that works, for example, in the range of up to 2 watts and serves to harden the applied ink directly after the print head. This prevents the colors from smudging during the printing process. A corresponding pinning unit is preferably assigned to each print head.

According to an advantageous development, the printing station is an inkjet printing station, with the print heads preferably using UV ink.

The advantage of UV ink is that it does not penetrate completely into the material and dries there, but lies on the material to be printed. Accordingly, it is possible to print on a wide range of materials.

• - Anordnen des zu bedruckenden Objekts in einer Objektpositionierungseinrichtung; und
• - Bewegen der Objektpositionierungseinrichtung in einem Druckschritt in einer Bogenform entlang einer in Bogenform angeordneten Reihe von mindestens zwei Druckköpfen unterschiedlicher Farbe einer Druckstation.

The object is also achieved by a method for printing a non-flat, preferably curved surface of an object using a digital printing system, the method having the following steps in particular:

• - arranging the object to be printed in an object positioning device; and
• - moving the object positioning device in a printing step in an arc along a row of at least two print heads of different colors of a printing station arranged in an arc.

All the aspects and advantages already mentioned with regard to the digital printing system apply to the process.

Accordingly, the method for printing satisfactorily solves the problem in that the object positioning device or the object to be printed arranged on the object positioning device is moved in a printing step in an arc shape along a row of at least two print heads of different colors arranged in arc shape. It is thus possible to use digital printing to print in multiple colors even on non-flat, preferably curved, surfaces of an object.

As an alternative to the object positioning device with a lifting table, it would also be possible at this point to use a robot that takes over the task of the object positioning device and, if necessary, the task of the traversing device (or linear motor axis). Correspondingly, the robot as the object positioning device moves the object in an arc shape along the arc-shaped row of at least two print heads of different colors.

According to an advantageous development of the invention, a pretreatment step takes place before the printing step, in which the surface of the object is cleaned of contamination and its surface tension is increased, with a post-treatment step preferably taking place after the printing step, in which the applied ink is dried.

The pre-treatment step can be carried out by the pre-treatment station described above, preferably as a plasma treatment station. The after-treatment can accordingly be carried out by the above-mentioned after-treatment station, preferably the UV drying station. The term "drying" related to the paint is also to be understood as hardening or hardening of the paint.

The invention is explained in more detail below on the basis of the description of exemplary embodiments with reference to the accompanying drawings.

• 1 eine schematische Darstellung einer Digitaldruckanlage gemäß einer Ausführungsform der vorliegenden Erfindung; und
• 2 eine vergrößerte schematische Darstellung einer Objektpositionierungseinrichtung gemäß der vorliegenden Erfindung.

The drawings show in:

• 1 a schematic representation of a digital printing system according to an embodiment of the present invention; and
• 2 an enlarged schematic representation of an object positioning device according to the present invention.

The following is first on 1 Reference is made, which shows the schematic representation of a digital printing system 100 .

In 1 A coordinate system (XYZ) is shown to describe the directions more clearly. The X-direction is the feed direction of a traversing device 30 (linear motor axis). The Y direction is the depth direction and the Z direction is the height direction of the plant in the figure.

The digital printing system 100 has an object positioning device 20 . Although in 1 three object positioning devices 20 are shown, it is always the same object positioning device 20 that is shown in the course of the printing process.

The object positioning device 20 has a lifting table 21 with two lifting devices 22 . In addition, the object positioning device 20 has a workpiece holder, not shown here, for holding an object O.

The object positioning device 20 or the part of the object positioning device 20 (for example workpiece holder) that holds the object O can, as indicated by the curved double arrow, be pivoted about the X-axis (advance direction). Particularly preferably, the workpiece holder can be pivoted relative to the rest of the object positioning device 20 accordingly. The angular position of the object O on the object positioning device 20 can thus be changed.

In addition, the object positioning device 20 can be moved in the feed direction X. For this purpose, the object positioning device 20 is connected to the traversing device 30, preferably a linear motor axis.

at the in 1 Left position of the object positioning device 20 loading or unloading of the object positioning device 20 takes place. That is, at this point, the object O is placed on the object positioning device 20 before printing or removed therefrom after printing.

The next station in the feed direction X is the pre-treatment station 40, at which the object O or the surface of the object O is subjected to a pre-treatment. This is used, for example, to clean the surface of dirt and increase its surface tension for better adhesion of the paint drops. The pre-treatment station 40 is designed to be adjustable in height, as shown by the double arrow arranged in the Z-direction.

The actual printing station 10 is arranged further in the feed direction X. The printing station 10 has a multiplicity of print heads 11, six print heads 11 being shown here, for example. As indicated by a double arrow shown inside the print heads 11, the distance between the print heads 11 and the object O to be printed can be adjusted along a distance direction. The spacing direction runs parallel to the main extension direction of the respective print heads 11. Since the print heads 11 are designed so that they can be arranged in an arc shape along the feed direction X, the spacing direction has a Z component and an X component accordingly.

As also indicated by several curved double arrows, the individual print heads 11 can be pivoted about an axis of rotation in the Y direction. This is necessary in particular because the print heads 11 must be arranged at least substantially perpendicular to the surface to be printed during the printing process.

The print heads 11 can thus be adjusted relative to one another, relative to the printing station 10 and relative to the object O to be printed in terms of their angular position and a spacing direction. Accordingly, the print heads 11 arranged in the form of an arc can be adapted in their arrangement and orientation to the curved or curved surface of the object O to be printed.

A pinning unit 12 is arranged behind each print head 11 and is used to dry or harden the ink on the corresponding print head 11 after printing. This prevents the color from smudging as the printing progresses.

In addition, the object positioning device 20 is again shown below the printing station 10, which can be moved due to the lifting devices 22 in such a way that it can trace the arc shape specified by the print heads 11. Here, a lifting device 22 arranged at the front end 20a of the object positioning device 20 is extended further than a lifting device 22 arranged at the rear end 20b.

During the printing process, the elevators 22 are moved so that the object O moves along the desired arch shape. The movement of the object positioning device 20 or the movement of the lifting devices 22 is coupled to the traversing device 30 (the linear motor axis) in such a way that the object O moves relative to the print heads 11 in an at least essentially uniform, reproducible movement, preferably at an at least essentially constant speed.

A plurality of print heads 11 of the same color can be arranged one behind the other in the depth direction Y, so that the printing width of the printing station 10 can be increased.

The print heads 11 can each only produce a high-quality print over a certain print width, so that the object O has to pass through the printing station 10 several times if there are not enough print heads 11 arranged in the depth direction Y. In this case, the object O does not always have to pass through the printing station 10 from left to right (ie in the feed direction X), but can also pass through it in the opposite direction (from right to left). This can save time.

It is thus possible for the printing station 10 to be run through in a number of passes in a printing process. A different area of the object O is printed from run to run. The angular arrangement of the object O relative to the printing station 10 can be adjusted on the object positioning device 20, as already described, so that an object with a surface that is bent or curved in the depth direction Y can also be printed correctly (at least essentially at a right angle). can.

Furthermore, the position in the depth direction Y of the object O or the object positioning device 20 or the lifting table 21 relative to the printing station 10 can be adjusted. As an alternative to this, the position in the depth direction Y of the printing station 10 relative to the object positioning device 20 can also be adjustable.

The after-treatment station 50, in which the ink is dried or hardened, is arranged after the printing station 10 in the feed direction X. When using UV ink, this is UV curing of the ink. Here, the ink precured by the smaller pinning units 12 is finally cured.

2 shows an enlarged representation of the object positioning device 20. The object O is held on the object positioning device 20 by a workpiece holder.

The workpiece holder can in particular be a rotating workpiece holder, so that the object can be rotated.

The object positioning device 20 also has the lifting table 21 with two lifting devices 22 . More precisely, a lifting device 22 is arranged at a front end 20a and a lifting device 22 at a rear end 20b of the object positioning device 20 and the lifting table 21, respectively. With the lifting devices 22, a front end 20a of the object positioning device 20 or of the lifting table 21 can thus be arranged higher in the Z direction than a rear end 20b or vice versa.

If the entire object positioning device 20 now also moves in the feed direction (X-direction), the object O can traverse an arc shape. It is thus possible by means of the lifting device 22 with a corresponding coupling of the traversing device 30 (linear motor axis) to move the object O past the print heads 11 arranged in an arc in a uniform, reproducible movement.

This makes it possible to print on objects O that are bent or arched in the longitudinal direction. It is thus possible with the contour-dependent object positioning of the present invention to print objects with complex shapes in color by means of digital printing.

Reference List

100

digital printing system

10

printing station

11

printhead

12

pinning unit

20

object positioning device

20a

front end

20b

rear end

21

lifting table

22

lifting device

30

traversing device

40

pre-treatment station

50

post-processing station

O

object

X

feed direction

Y

depth direction

Z

height direction

Claims (13)

Digital printing system (100), in particular for printing a non-flat, preferably curved surface of an object (O), the following comprises: - an object positioning device (20) which is designed to be moved at least in a feed direction (X) and to position the object (O) to be printed; - a printing station (10) having at least two print heads (11), each of which has a different color, the print heads (11) being designed in such a way that they are arranged and aligned one behind the other along an arc in the feed direction (X), wherein the object positioning device (20) can be adjusted in height in the height direction (Z) in such a way that the object (O) can traverse an arc shape during the printing process, characterized in that in order to depict a large number of different arc shapes for different objects (O), the radius of the arc of the arranged print heads (11) can be changed and adapted to the respective object (O) to be printed, for which purpose the print heads (11) can each be adjusted along a distance direction from the object (O) to be printed, with the print heads (11) each about a pivot point are adjustable in their angular position, the rotation takes place about an axis of rotation in the depth direction (Y), which is perpendicular to the height Rich direction (Z) and perpendicular to the feed direction (X). Digital printing system (100) according to claim 1 , wherein in each case at least two, preferably a multiplicity of print heads (11) are arranged one behind the other in a respective depth direction (Y), which extends perpendicularly to the height direction (Z) and perpendicularly to the feed direction (X). Digital printing system (100) according to claim 1 or 2 , wherein the object positioning device (20) has a lifting table (21) which has at least one lifting device (22) on a front end (20a) viewed in the feed direction (X) and on a rear end (20b) viewed in the feed direction (X), by means of which the object positioning device (20) can be adjusted in the vertical direction (Z). Digital printing system (100) according to one of the preceding claims, in which the angular position of the object (O) on the object positioning device (20) can be changed at a pivot point, with the rotation taking place along an axis of rotation which moves in the feed direction (X) of the object positioning device (20 ) extends. Digital printing system (100) according to one of the preceding claims, wherein the digital printing system (100) has a traversing device (30) which is designed to move the object positioning device (20) in the feed direction (X). Digital printing system (100) according to claim 5 , wherein the traversing device (30) has a linear motor axis. Digital printing system (100) according to claim 6 , wherein the movement of the linear motor axis and the object positioning device (20) are coupled and controlled in such a way that the object (O) moves at an at least substantially uniform or constant speed during the printing process. Digital printing system (100) according to one of the preceding claims, wherein the digital printing system (100) has a pretreatment station (40), and the pretreatment station (40) is preferably a plasma treatment station. Digital printing system (100) according to one of the preceding claims, wherein the digital printing system (100) has a post-treatment station (50), and wherein the post-treatment station (50) is preferably a UV drying station. Digital printing system (100) according to one of the preceding claims, wherein at least one pinning unit (12) is arranged between the print heads (11) arranged in the feed direction (X) along an arc, wherein preferably in the feed direction (X) behind each print head (11) a pinning unit (12) is arranged. Digital printing system (100) according to one of the preceding claims, wherein the printing station (10) is an inkjet printing station, and wherein the print heads (11) preferably use UV ink. Method for printing a non-planar, preferably curved surface of an object (O), by means of a digital printing system (100) with the following steps: - providing a digital printing system (100) according to one of the preceding claims; - arranging the object to be printed (O) in the object positioning device (20); and - moving the object positioning device (20) in a printing step in an arc along a row of at least two print heads (11) of different colors arranged in an arc of the printing station (10), the object positioning device (20) being height-adjusted in the height direction (Z) in such a way that that the object (O) can traverse an arc shape during the printing process, and the radius of the arc of the print heads (11) arranged being changed and adapted to the object (O) to be printed in each case, in order to depict a large number of different arc shapes for different objects (O), with the print heads (11) each being spaced along a direction from the object (O) to be printed can be adjusted, with the print heads (11) each being adjusted in their angular position around a pivot point, with the rotation taking place around an axis of rotation in the depth direction (Y), which is perpendicular to the height direction (Z) and perpendicular to the Feed direction (X) is aligned. Method for printing a non-planar, preferably curved surface of an object (O) according to claim 12 , wherein before the printing step there is a pre-treatment step, in which the surface of the object (O) is cleaned of impurities and its surface tension is increased, and wherein after the printing step there is preferably a post-treatment step, in which the applied ink is dried.

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