Device for printing on surfaces with multiple, movable printheads

Abstract

Device for printing on surfaces with different surface sections in their respective topology, - with multiple movable printheads (3a-d) and - with at least one printing position (5a) and at least one parking position (5b-d) for the printheads (3a-d), wherein the printheads (3a-d) are movable into the respective positions (5a-d) and wherein in a first mode the first printhead (3a) is arranged in a printing position (5a) and the second printhead (3b-d) is arranged in a parking position (5b-d) and in a second mode the first printhead (3a) is arranged in a parking position (5b-d) and the second printhead (3b-d) is arranged in a printing position (5a), characterized in that - that at least a first printhead (3a) and a second printhead (3b-d), each comprising several individually controllable nozzles (4a-d), have different nozzle arrangements (10a-d), wherein the different nozzle arrangements (10a-d) differ in their respective number of nozzles (4a-d) and wherein the number of nozzles (4a) of the nozzle arrangement (10a) of the first printhead (3a) is less than the number of nozzles (4b) of the nozzle arrangement (10b) of the second printhead (3b) and - that the nozzle arrangement is used locally which is provided for the respective topology, wherein at least the first printhead (3a) and the second printhead (3b-d) are arranged on a common transport device (6) which moves the printheads (3a-d) to the respective positions (5a-d).

Description

[0001] The present invention relates to a device for printing on surfaces with several movable printheads having the features of the preamble of claim 1.

[0002] Inkjet printers with movable printheads are known from the prior art. These are used, for example, in homes and offices to print on paper in multiple colors. A separate printhead is available for each color. The individual printheads and their respective nozzle arrangements are identical. When producing multicolor prints, the printheads move simultaneously relative to the paper and eject ink droplets at the same time; that is, all printheads are active. After printing, all printheads are moved to a common parking position, where they are usually also cleaned; that is, all printheads are inactive. Furthermore, industrial applications with inkjet printheads are also known, in which the printheads are mounted, for example, on large XY frames and used to print on large sheets of paper or fabric.It is also already known to mount inkjet printheads on freely movable robot arms in order to print not only on flat but also on (arbitrarily) curved surfaces, such as vehicle body panels. However, spray nozzles are usually used for printing on body panels, meaning the parts are treated with a spray mist. Unlike inkjet printheads, such spray nozzles cannot eject individual droplets via individual control pulses. It is therefore considerably more difficult to generate (locally multicolored) image information (especially based on raster pixels), and instead, for example, a body panel is usually painted in only one or more colors (i.e., globally multicolored, but locally only one color). Examples from the prior art are described below.

[0003] German patent DE 41 20 293 A1 describes a rotatable inkjet printhead (with individually controllable nozzles, e.g., based on the piezoelectric principle) mounted on an XY frame, which can print curves of any shape with a constant line thickness. For multicolor printing (yellow, cyan, magenta, black), a corresponding number of identical printheads can be used.

[0004] DE 10 2008 053 ​​178 A1 describes a coating device, e.g., for vehicle body parts, in which an inkjet printhead (with individually controllable nozzles, e.g., based on the piezoelectric principle) is mounted on a robot arm and can thus be positioned and moved along any desired path. The printhead can have a section that continuously ejects the coating material and a section that ejects it drop by drop. The printhead can also have nozzle openings of different sizes, e.g., rows of large nozzles and rows of small nozzles. Multiple identical printheads can also be provided, which can be pivoted relative to each other to achieve better adaptation to the surface of a curved component (see [reference]). Fig. 22 of DE 10 2008 053 ​​178 A1).

[0005] EP 970 811 A1 describes an automatic painting system for vehicles, which includes spray guns for four colors. The four identical spray guns are mounted on an XY frame and their distance in the Z direction to the vehicle surface can be individually adjusted.

[0006] JP 2009-175213A describes an electro-optical display device that suppresses flicker fringes in an AC-driven light source without changing its drive frequency. The device comprises a multi-pixel display panel, an image data storage unit, a control signal output circuit, and a driver circuit. A control circuit varies the scan period by switching between control signal frequencies within a predetermined frequency set at intervals of one or more scans. The image data is read out synchronously with this control signal and fed to the driver. This avoids a fixed phase relationship with the light source, reduces interference, and effectively suppresses flicker fringes. US 2005 / 0238794A1 describes a method for coloring a three-dimensional object in which the object or a pigment spray nozzle is moved according to geometry and color data.First, the movement path is defined based on the configuration data. Then, narrow color regions with high curvature and a small coloring area, as well as wide color regions with low curvature and a large coloring area, are identified. These different areas are selectively colored with spray nozzles of varying sizes while the object or the nozzles are guided along the predefined movement path to achieve precise and efficient color application. DE 10 2008 053 ​​178 A1 describes a coating device and a method for applying coating materials, in particular paint, to body components. At its core is an application device as a printhead that precisely ejects the coating material from at least one coating material nozzle. This enables precise dosing, high reproducibility, and flexible pattern and layer design, especially for automated, high-quality painting processes in vehicle production.JP 2000-103 041 A describes a stamping device in which stamp content can be freely created, corrected, and registered, and multi-color stamping at any position is possible using a moving inkjet head. Stamp shapes are read from a medium, edited using PC word processing, and precisely applied to the paper during stamping by a rotating nozzle head. US 2005 / 0115421 A1 describes an automated parts marking system with a multi-axis gantry driver, calibration stand, vision / localization systems, and fluid-dispensing (inkjet) end effectors. An end effector marks precise lines or dispenses fluids using a pick-shaped stylus, coupled to a fluid supply and a high-frequency pulsed valve, to precisely deposit liquids in geometrically defined areas.

[0007] In the current state of the art, when using multiple printheads, identical printheads, i.e., identical nozzle arrangements, are always used. Furthermore, all printheads are always simultaneously active and printing or inactive and not printing. Adaptation to the surface of a curved component is achieved only by moving the printhead close to the component and maintaining a safe distance along the component, or by positioning multiple printheads relative to each other. Printing on highly curved surfaces (with small radii of curvature) and especially on surfaces with undercuts (with surface sections that protrude freely and, for example, obstruct access to other surface sections) can therefore still lead to problems.

[0008] Another problem can arise from the dimensions of the printhead. With an inkjet printhead of length L, given a working distance A to the surface to be printed and a given tolerance of this working distance TA, only a surface with a minimum radius of curvature Rmin can be printed due to geometric constraints (L and A: see...). Fig. 1). Examples: L [mm] A [mm] TA [mm] Rmin [mm] 10 10 0,5 25,3 50 10 0,5 625,3 100 10 0,5 2500,3 10 10 1 13,0 50 10 1 313,0 100 10 1 1250,5 10 10 2 7,3 50 10 2 157,3 100 10 2 626 10 10 3 5,7 50 10 3 105,7 100 10 3 418,2

[0009] The table shows that Rmin increases with increasing L and decreases with increasing TA. Theoretically, i.e., purely from a geometric perspective, Rmin is independent of A. Therefore, A was set to a reasonable value of 10 mm. In practice, however, Rmin does depend on A, because it cannot be expected that a printhead can achieve the same print resolution at every distance A from the surface, and therefore Rmin decreases with increasing A (given a specific print resolution).

[0010] Against this background, the object of the present invention is to create a device improved compared to the prior art, which overcomes the problems mentioned above and allows or creates favorable conditions for printing on surfaces of any shape and, in particular, of any degree of curvature.

[0011] These problems are solved according to the invention by a device having the features of claim 1. Advantageous embodiments of the invention will become apparent from the dependent claims, the description, and the accompanying drawings.

[0012] An inventive device for printing surfaces with surface sections differing in their respective topology, using several movable printheads, each comprising several individually controllable nozzles, and with at least one printing position and at least one parking position for the printheads, wherein the printheads are movable into the respective positions, is characterized in that at least a first and a second printhead have different nozzle arrangements, that in a first mode the first printhead is arranged in a printing position and the second printhead in a parking position, and that in a second mode the first printhead is arranged in a parking position and the second printhead in a printing position.

[0013] The surfaces to be printed are preferably of any shape and, in particular, of any degree of curvature. They may also have undercuts. According to the invention, the selection of different nozzle arrangements makes it possible to print both, for example, flat surface sections and (strongly) curved surface sections. Advantageously, surfaces with surface sections differing in their respective topologies can also be printed. The nozzle arrangement intended for flat, curved, or strongly curved sections, or for sections with undercuts, is used locally in each case. The device therefore allows switching between heads; that is, it can be determined which head with which nozzle arrangement should be active and which should be inactive.

[0014] The heads are preferably freely movable in space and therefore advantageously able to be brought into contact with surfaces (or sections thereof) of any shape and guided along paths of any shape along these surfaces (or sections thereof). A predetermined working distance to surfaces of any shape can also be maintained.

[0015] The nozzles are preferably droplet-generating inkjet nozzles in a one- or two-dimensional arrangement. The nozzles are preferably not spray mist-generating nozzles or are different from such nozzles.

[0016] The parking positions can be identical for the different printheads. Alternatively, a separate parking position can be provided for each printhead. The same applies to the print position(s).

[0017] A further development of the device according to the invention, advantageous for the rapid printing of large, flat surfaces and the slow printing of small, curved surfaces, is characterized in that the different nozzle arrangements differ in their respective number of nozzles, wherein the number of nozzles in the nozzle arrangement of the first printhead is less than the number of nozzles in the nozzle arrangement of the second printhead. For example, one printhead can have more than ten nozzles and another printhead can have fewer than ten nozzles. In this context, the terms "rapid" and "slow" do not refer to the relative speed between the substrate and the nozzles, but rather to the printed area per unit of time – i.e., in the unit [square meters per minute].

[0018] A further advantageous and therefore preferred embodiment of the device according to the invention, suitable for the rapid printing of large, flat surfaces and the slow printing of small, curved surfaces, is characterized by the fact that the different nozzle arrangements differ in their respective spatial arrangement of the nozzles. For example, one printhead can have a straight, linear nozzle arrangement, and another printhead can have a curved, linear nozzle arrangement. Furthermore, the nozzle arrangement can be hook-shaped and thus be used for printing edges or folds.

[0019] A further development of the device according to the invention, which is advantageous for changing the printheads and is therefore in accordance with the invention, is characterized in that at least a first and a second printhead are arranged on a common transport device that moves the printheads to their respective positions. By means of the transport device, an active printhead can be moved to a park position and an inactive printhead to a print position, thereby changing the activity states. Preferably, the transport device is a rotary device that allows the individual printheads mounted on it to be changed in their respective positions (and activity states) by rotating them. Alternatively, a circulating belt or a (e.g., electric) linear drive can be provided.

[0020] A further development of the device according to the invention, which is advantageous and therefore preferred for free spatial positioning and movement, can be characterized in that the common transport device is arranged on a controllable and multi-segmented robot arm or an XYZ frame, wherein X, Y and Z denote the three spatial directions in which the transport device can be moved independently of each other by means of the frame.

[0021] The invention as such, as well as structurally and / or functionally advantageous embodiments of the invention, are described in more detail below with reference to the accompanying drawings and at least one preferred embodiment. Corresponding elements in the drawings are provided with the same reference numerals.

[0022] A system consisting of a robot arm and a device according to the invention is provided.

[0023] The drawings show: Fig. 1 Schematic side view of a preferred embodiment of a device according to the invention for printing on surfaces; Fig. 2 the situation when printing on undercuts; Fig. 3 Schematic side view of another preferred embodiment of a device according to the invention for printing on surfaces; and Fig. 4a -e Schematic perspective views of preferred embodiments of devices according to the invention.

[0024] Fig. Figure 1 shows a schematic side view of a preferred embodiment of a device according to the invention for printing on arbitrarily shaped surfaces (in short: 3D surfaces). As in Fig. As shown in Figure 1, the surface 1 has at least one curvature. The surface could, for example, be a body part of a vehicle to be painted. With the device 2 according to the invention, it is possible to paint curved or arbitrarily shaped surfaces in one or more colors or to provide them with multicolored information (image, pattern, or text).

[0025] The device 2 has several movable printheads 3a to 3c of different geometries, each comprising several individually controllable nozzles 4a to 4c. In the illustrated embodiment, three printheads are shown as examples. Each of the three printheads can be moved to an (active) print position 5a or an (inactive) park position 5b or 5c. The print position 5a is a position in which the printhead 3a is arranged within a tolerance TA at a working distance A from the surface 1. When using so-called inkjet printheads, the working distance can be limited, for example, by their range, i.e., the essentially undisturbed flight path of the ink droplets. The working distance can also be limited by a minimum distance, e.g., to avoid collisions. Fig. 1 is a printhead 3a in print position 5a, while two printheads 3b and 3c are in their respective park positions 5b and 5c. The park position is a position in which the printhead is not printing and can instead be cleaned, for example. The inactive printhead can be cleaned while the active printhead is printing.

[0026] As in Fig. As shown in Figure 1, the three printheads 3a-c are arranged on a common transport device 6 designed as a rotary device 7 (see arrow 7'), which moves or rotates the printheads 3a-c into their respective positions 5a-c. Alternatively, more than three or only two printheads can be provided. Each individual printhead 3a-c can in turn be rotatably mounted on the rotary device 7 (see arrows 7'').

[0027] A 120° counterclockwise rotation 7' ​​moves the first (active) printhead 3a from print position 5a to park position 5c and the second (inactive) printhead 3b from park position 5b to print position 5a (the second printhead then becomes active, the first printhead inactive). The third printhead 3c alternates between the two park positions 5c and 5b. The rotation device 7 can have a rotatable, central support 8 for the printheads, as shown. The rotation can be performed by an electric motor or pneumatically. Instead of a 360° or more rotation, a simple back-and-forth rotation is also possible.

[0028] The use of the rotary device allows for quick and precise changes between the printheads, especially in conjunction with a fast control system designed for changing the printheads and adapting the image data accordingly. The nozzle positions 4a-c of the printheads 3a-c are chosen such that no disruptive effects occur in the printed image during the image transition when changing the active printhead; that is, the printed image from the first printhead seamlessly transitions to the printed image from the second printhead, and vice versa.

[0029] Each individual printhead 3a-c can have nozzles 4a-c for different colors, varnishes, or inks, particularly for so-called CMYK printing (cyan, magenta, yellow, black). Alternatively, each individual printhead 3a-c can also be composed of several, preferably four, sub-heads, each printing only one color. The color gamut achievable through imaging can be expanded, for example, by 6-color printing (CMYK, light cyan, and light magenta) as well as by other color systems. In particular, the achievable color gamut can be expanded by the additional use of white colors, varnishes, or inks.

[0030] It is also possible that a hydrostatic compensation mechanism for maintaining constant ink pressure in the inkjet head's piping system (or the respective ink meniscus at the nozzle outlets) forms a single unit together with the printhead. This unit is then moved as a whole when switching from the printing position to the parking position.

[0031] In the first mode, the first printhead 3a is in print position 5a and the second printhead 3b is in a park position 5b. In the second mode, the first printhead 3a is in a park position 5b or 5c and the second printhead 3b is in print position 5a. Alternatively, it is also possible to move two printheads into print position simultaneously and switch from one to the other to create image transitions without any disruptive effects. A third printhead remains in a park position.

[0032] In the respective parking positions 5b or 5c, the printheads 3a-c can remain attached to the transport device or be detached and, for example, placed down. Preferably, the ink supply for the printheads remains connected to the transport device when printheads are placed down.

[0033] Fig. Figure 1 also shows that the common transport device 6 is arranged on a controllable, multi-segmented robot arm 9. Using the robot arm, the transport device, including the printheads 3a-c, can be positioned relative to the surface 1 and guided along it for printing, i.e., moved relative to the surface. The robot arm allows for arbitrary movements and thus the tracing of any contours within the working distance A (within the tolerance TA). A conventional robot arm or a flexible arm (e.g., the so-called bionic handling assistant from Festo in Esslingen) can be used. Alternatively, the transport device can be arranged on an XYZ frame.

[0034] The printheads 3a-c shown in the figure by way of example each comprise several individually controllable nozzles 4a-c. Preferably, the printheads are so-called inkjet printheads, preferably based on piezoelectrically activated nozzles. It can also be provided that, in addition to the inkjet printheads 3a-c, at least one spray mist generating head (i.e., a head without several individually controllable nozzles) is provided on the transport device 6, which is used for large-area, single-color painting. Furthermore, it is also possible to use so-called "continuous wave" systems, so-called "valve-jet" printing systems, or so-called "bubble-jet" systems according to the invention.

[0035] The in Fig. The printheads 3a-c shown as examples have different nozzle arrangements 10a-c. The different nozzle arrangements differ in their respective number of nozzles, with, for example, the number of nozzles 4a in nozzle arrangement 10a of the first printhead 3a being less than the number of nozzles 4b in nozzle arrangement 10b of the second printhead 3b. The first printhead has only a few individually controllable nozzles. The second printhead, on the other hand, has many individually controllable nozzles. The first printhead is therefore particularly suitable for (slow) printing of surfaces 1 with small radii of curvature R1, and the second printhead for (fast) printing of surfaces with large radii of curvature R2 or flat surfaces. As shown, the surface can have both convex and concave sections. The small printhead 3a is particularly suitable for printing concave sections with a small radius of curvature.According to the invention, depending on the topology of the surface segment to be printed, a suitable printhead 3a-c can be brought into the printing position 5a near the segment.

[0036] Fig. Figure 1 also shows a section of the surface 1 to be printed with a so-called undercut 11, which may be formed, for example, by a groove. In a car body part, such an undercut might be found, for example, at a door handle or on the folded outer edges. Printing this section is only possible with a very small printhead 3c. The third printhead 3c is specifically designed for printing such undercuts. For this purpose, the third printhead has a very small nozzle assembly 10c. This nozzle assembly is also attached to a curved section 12 of the printhead, which allows the nozzle assembly to be guided into the interior of the undercut. An example of such a situation is shown below. Fig. 2 shown.

[0037] The various printheads 3a-c can be mounted on the rotary device 7 at equal intervals from each other. Alternatively, the various printheads can also be mounted on the rotary device at unequal intervals from each other, so that the entire system of rotary device and printheads is balanced. Alternatively, a separate balancing weight 13 can also be mounted on the rotary device.

[0038] Fig. Figure 3 shows a schematic side view of another preferred embodiment of a device according to the invention for printing on surfaces. Instead of the one shown in Fig. In the rotating device shown in Figure 1, a circulating belt 14 is provided on which the various printheads 3a-d with different nozzle arrangements 10a-d are arranged. The belt serves to move the printheads into their respective positions 5a-d. Printhead 3a is in a printing position 5a, all other printheads 3b-d are in parking positions 5b-d, with printhead 3d simultaneously occupying a cleaning position 5d. In the printing position, the active printhead, for example, protrudes from the row of inactive printheads and can thus be easily brought to the working distance A from the surface 1.

[0039] The belt 14, or a device comprising the belt and its guide rollers, can in turn be arranged on a robot arm 6 or an XYZ frame. Alternatively, instead of the rotary device or the belt device, a linear drive can also be provided for moving the printheads 3a-d.

[0040] The Fig. Figures 4a to 4e show schematic perspective views of preferred embodiments of the devices according to the invention. Fig. 4a shows that the spatial arrangement of the nozzles 4a of the nozzle arrangement 10a of the printhead 3a is linear and has a larger number of nozzles. Fig. Figure 4b shows a similar printhead 3a with a smaller number of nozzles 4a. Both printheads 3a, due to their hook-shaped design, can be used for printing undercuts 11. In Fig. Figure 4c shows that the spatial arrangement of the nozzles 4a of the nozzle arrangement 10a can itself be hook-shaped, so that appropriately shaped surfaces 1 can be printed. Fig. Figure 4d shows a spatial arrangement of the nozzles 4a of the nozzle arrangement 10a, which is curved, in particular segment-shaped. This nozzle arrangement can be used for printing on convex surfaces 1. Fig. Figure 4e shows a spatial arrangement of the nozzles 4a of the nozzle arrangement, which is also curved, in particular segment-shaped. This nozzle arrangement can, however, be used for printing on concave surfaces 1. Fig. It can therefore be deduced from 4a to 4e that the different nozzle arrangements 10a may differ in their respective spatial arrangement of the nozzles 4a. Reference symbol list 1 surface to be printed 2. Printing device 3a (active) printhead 3b-d (inactive) printheads 4a-c nozzles 5a Print position 5b-c Parking position 5d Parking / Cleaning Position 6 Transport device 7 Rotating device 7' rotational movement 7'' rotary movements 8 central carriers 9 robot arm 10a-d nozzle arrangements 11 Undercut 12 curved section 13 Balancing weight 14 circumferential band A working distance TA tolerance of the working distance R1, R2 radii of curvature

Claims

Device for printing on surfaces with surface sections differing in their respective topology, - with several movable printheads (3a-d) and - with at least one printing position (5a) and at least one parking position (5b-d) for the printheads (3a-d), wherein the printheads (3a-d) are movable into the respective positions (5a-d) and wherein in a first mode the first printhead (3a) is arranged in a printing position (5a) and the second printhead (3b-d) is arranged in a parking position (5b-d) and in a second mode the first printhead (3a) is arranged in a parking position (5b-d) and the second printhead (3b-d) is arranged in a printing position (5a), characterized in that at least a first printhead (3a) and a second printhead (3b-d), each comprising several individually controllable nozzles (4a-d), have nozzle arrangements (10a-d) that differ from one another.wherein the different nozzle arrangements (10a-d) differ in their respective number of nozzles (4a-d) and wherein the number of nozzles (4a) of the nozzle arrangement (10a) of the first printhead (3a) is less than the number of nozzles (4b) of the nozzle arrangement (10b) of the second printhead (3b) and wherein the nozzle arrangement provided for the respective topology is used locally, wherein at least the first printhead (3a) and the second printhead (3b-d) are arranged on a common transport device (6) which moves the printheads (3a-d) into the respective positions (5a-d). Device according to claim 1, characterized in that the different nozzle arrangements (10a-d) differ in their respective spatial arrangement of the nozzles (4a-d). Device according to claim 2, characterized in that the spatial arrangement of the nozzles (4a-d) of the nozzle arrangement (10a-d) of at least one printhead (3a-d) is linear. Device according to claim 2, characterized in that the spatial arrangement of the nozzles (4a-d) of the nozzle arrangement (10a-d) of at least one printhead (3a-d) is hook-shaped. Device according to claim 2, characterized in that the spatial arrangement of the nozzles (4a-d) of the nozzle arrangement (10a-d) of at least one printhead (3a-d) is curved. Device according to claim 1, characterized in that the common transport device (6) is a rotary device (7) or a transport device with a circulating belt (14). Device according to claim 6, characterized in that the common transport device (6) is arranged on a robot arm (9). System consisting of a robot arm and a device according to one of claims 1 to 7.

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