EP2644392A2 - System for printing of an object - Google Patents

Abstract

The printing system (1) has an inkjet print head (4) that includes nozzles (7). A robot (5) generates a primary movement (17) such that two printing paths (A,B) of inkjet print head are located laterally to each other. A movement generating device (18) generates a secondary movement (16) which is perpendicular to the primary movement such that printing paths are adjoined laterally to each other.

Description

The present invention relates to a system for printing an object according to claim 1, which prints at least one non-planar area of the surface of the object with an image.

In the prior art, it is already known, non-planar areas of the surface of an object, for. B. curved sections of bodies of vehicles to print with an inkjet printhead and thereby produce any multicolored images on the surface. For this purpose, the printhead is attached to a robot, e.g. As an articulated arm robot, guided along the surface of the object at a defined distance from the surface, so that the ejected from the print head ink droplets reach the desired locations on the surface and generate the desired image there. Since the surface of the object is usually much larger than the extent of the print head, it is necessary to repeatedly guide the print head on so-called print paths along the surface and build the desired print image from the juxtaposed print webs. In this case, it is again necessary for the printing webs to adjoin one another in such a way that no visually perceptible disturbances are produced at the edges of the printing webs. If z. For example, if a second printing web is generated at too great a distance from the first printing web, then it may be that a perceptible strip is formed between the two printing webs, which disturbs the desired printed image. Likewise, it may be possible that the two printing webs overlap too far and thus also creates a noticeable strip between the two printing webs, which can disturb the desired printed image. Such disturbances in the printed image can arise, for example, when the mechanics of the print head guide does not have sufficient precision. However, they may also arise, for example, when the printhead is subjected to centrifugal forces during its movement, so that the ejected drops are not placed at the desired locations on the surface.

It is for example from the DE 102 02 553 A1 known to move an applicator with spray nozzles manually, semi-automatically or fully automatically along the surface of an object, such as an object of building construction, civil engineering and civil engineering, and thereby apply any image on this surface. First of all, the object surface is recognized and digitized, and the image to be printed is virtually superimposed on the digitization. When printing the surface with the application device, it is necessary to know the position of the application device exactly. For this purpose, a number of measurement methods are proposed, for. B. method of distance and / or angle measurement, the remote measurement or the imaging measurement. The position error of the position measurement value is used for a limit value check and no color is output if the position error is outside an acceptance threshold.

In the originating from the same patent applicant DE 103 90 349 B4 is also described that the inking is prevented when at the position of the inking member the corresponding color or paint has already been fully applied.

The DE 69005185 T2 and the US 2004/0036725 A1 instead describe two methods of influencing the drop speed and droplet size of the ink drops of ink jet printheads via the particular type of pulse applied to piezo actuators of the printhead. Are varied z. As the pulse length, the pulse height (voltage) and the pulse shape. The US patent describes, for example, how a pre-pulse can be used to specifically influence the size and also the direction of flight of the ink droplet triggered by the actual pulse. It is thus possible to eject individual drops of ink obliquely from the nozzle opening and thus to apply to a different location on the surface of the object to be printed, as it would happen without such pre-pulse.

The DE 31 40 486 A1 describes a device for coating objects, such as glass bottles with plastic. The device comprises for this purpose a nozzle head with a plurality of nozzles arranged distributed, from which plastic in the form of each other following droplets is ejected. Further, drive means are provided which cause a relative movement between the surface to be coated of the article and the nozzle head. Relative to the direction of the relative movement, the nozzles are arranged such that the tracks of the plastic emerging from adjacent nozzles overlap on the object. However, such overlapping can, as already mentioned above, lead to visible disturbances in the printed image due to excessive inking values and therefore adversely affect the desired printed image.

From the DE 37 37 455 A1 For example, a direction and a method of producing color patterns, such as stripes on vehicle bodies, is known. The inking can be done with a printhead, which in turn is guided on a robot along the surface of the object to be printed. The printhead has multiple spray nozzles and the width of the strip to be printed can be changed by changing the number and distribution of currently active spray nozzles. The location of a strip in a direction perpendicular to the movement of the printhead can be changed as the printhead is moved overall by the robot. The location of the strip can also be changed by activating a different amount of spray nozzles. As a result, a fine control of the strip position can be achieved, which is superimposed on the control by the robot and represents an improvement with respect to the application of strips.

Against this background, it is an object of the present invention to provide a system for printing an object which imprints at least one non-planar area of the surface of an object with an image, which prevents or at least reduces striping when printing the surface in multiple printing webs in that the remaining strips are not perceived as disturbing.

This object is achieved with the features of claim 1. Advantageous developments of the invention will become apparent from the accompanying dependent claims and from the description and the drawings.

An inventive system for printing an object which imprints at least one non-planar area of the surface of the object with an image has the following features: an ink-jet printhead with nozzles; a robot which generates a primary movement, the primary movement comprising at least two laterally juxtaposed printing paths of the inkjet printhead; and a device which generates a secondary movement, wherein the secondary movement is substantially perpendicular to the primary movement and whereby the pressure paths laterally adjoin one another.

The provision of the device for generating secondary movements in the system according to the invention advantageously leads to positional deviations of the inkjet printhead, i. H. Deviations of the actual position from the desired position for printing a defect-free image, during the primary movement can be compensated, whereby visible and therefore disturbing stripes between the printing webs can be prevented or reduced sufficiently. The fact that the pressure paths laterally adjoin one another, means that the edges of the individual printing webs are so exactly adjacent to each other that neither too large distances between the edges still too much overlap is generated and thereby annoying, especially too light or too dark stripes in the area the edges of the printing lines are prevented or reduced sufficiently. The primary movement, which is generated by the robot is preferably a movement of the inkjet printhead, which passes through, for example, a plurality of laterally juxtaposed printing webs in the same direction or in the opposite direction. For example, a first printing web can be generated during a forward movement of the print head over the surface of the object, and a second printing web adjacent thereto during a return movement of the print head adjacent to the first printing web. However, it can also be provided to initially return the print head inactive and to move it forward again parallel to the first print web. The robot may be an articulated arm robot or a portal robot.

An advantageous development of the system according to the invention provides that the device comprises a piezoactuator or an electro-mechanical component and the secondary movement is a movement of the inkjet printhead. The piezo actuator acts on the inkjet printhead as a whole and causes it to perform perpendicular to the primary movement, the secondary movement as a compensating movement.

According to a further advantageous embodiment of the system according to the invention, it is provided that the device comprises a piezoelectric actuator and the secondary movement is a movement of at least one nozzle of the inkjet printhead. According to this embodiment, therefore, not the printhead as a whole, but only at least one nozzle is moved perpendicular to the primary movement. It can be provided that the at least one nozzle, a nozzle group or even all nozzles are movably received on the inkjet printhead, so that the secondary movement by means of the piezo actuator takes place as a relative movement with respect to the inkjet printhead.

According to a further advantageous development, it can also be provided that the secondary movement does not detect the printhead as a whole nor individual nozzles of the printhead, but that according to a preferred embodiment of the system according to the invention the device comprises a piezoactuator and the secondary movement comprises a movement of at least the droplets a nozzle of the inkjet printhead is. The piezo actuator is not a piezoactuator that generates the droplet, but a separate and separate piezoactuator.

A further advantageous development of the system according to the invention can be characterized in that the device comprises a detector which detects the actual positions of pressure points of a first pressure path; in that the apparatus comprises a computer which calculates the deviation of the actual positions of the pressure points from their desired positions; and that the device generates as a secondary movement a compensating movement substantially compensating for the deviation on the second printing web. In other words, the (possibly disturbing stripes) compensating secondary movement takes place on the basis of a desired-actual-value comparison of already printed pressure points.

According to a further advantageous development it can be provided that the device comprises at least one detector, that the robot is an articulated arm robot, and that the detector comprises a rotary encoder which detects the angular position of a joint of the articulated arm robot. If the articulated arm robot has a plurality of joints, a detector is preferably provided at each joint, so that the position of the robot in space and in particular of the print head recorded on the robot can be determined exactly in space as the actual position. If this actual position deviates from a predetermined desired position, tracking of the robot can take place. The tracking serves as (possible disturbing stripes) compensating secondary movement. Alternatively, acceleration sensors, inclination sensors, gyrometers can be used to determine the coordinates of the print head in space and possibly also in chronological order.

It can also be provided according to a further advantageous development of the system according to the invention, that the detector comprises an optical sensor or an ultrasonic sensor, which is directed to the surface of the object. By way of example, the sensor can detect previously printed print dots of the image on the surface and determine therefrom an edge of the previously printed print web. It is advantageous if at least for the ink of near-edge nozzles of the print head such printing inks are used, which can be easily taken with the detector. Particularly advantageous is the use of special additives in the printing ink, which for example have a fluorescence property and whose fluorescent light can be detected by the detector with high precision. It may therefore be provided according to a further advantageous embodiment of the system according to the invention that the optical sensor is directed to already printed pressure points on the surface and detects their fluorescence radiation. In this way, it becomes possible to precisely detect the edge of a previously printed web and to precisely align the edge of a web to be printed with the detected edge and thereby prevent or reduce troublesome banding.

It can also be provided according to a further advantageous embodiment of the system according to the invention to use a so-called tracking system, which the Position of the inkjet printhead detected. Thus, there is always information about the current actual position of the print head in the room and it can constantly correction movements in the form of (possible disturbing stripes) balancing secondary movements are performed in space. The tracking system tracks a specific point of the print head or a mark on it and determines its path in space. Alternatively, there are three laser pointers on the print head whose (preferably perpendicular to each other) rays generate light spots on the surrounding walls or specially provided detection screens. These points of light can be detected camera-technically in their movement. In turn, the current position of the printhead can be calculated.

It can also be provided according to a further advantageous development of the system according to the invention that the device comprises a detector which detects the actual positions of pressure points of a first pressure path; in that the apparatus comprises a computer which calculates the deviation of the actual positions of the pressure points from their desired positions; and in that the device generates, as a secondary movement, a lateral displacement, which substantially corresponds to the deviation, of the image to be printed relative to the nozzles. An advantage of this development is that in the secondary movement no components of the print head are moved, but that only a shift of the image takes place, such that a pressure point not with a first nozzle, but z. B. is printed with an adjacent to this second nozzle. This ensures that the pressure point offset by one or more pressure nozzle or pressure nozzles on the surface of the object passes without the printhead or the nozzle itself must be moved. Since no masses have to be moved, such compensatory movements are possible very quickly and even in real time, depending on the computing capacity of the required computer.

The invention will be described below with reference to the drawings with reference to several embodiments. In the drawings, corresponding elements are provided with the same reference numerals.

Figur 1

eine schematische Ansicht eines bevorzugten Ausführungsbeispiels eines erfindungsgemäßen Systems;

Figuren 2 bis 8

Ausschnitte schematischer Ansichten von verschiedenen, bevorzugten Ausführungsbeispielen eines erfindungsgemäßen Systems.

The drawings show:

FIG. 1

a schematic view of a preferred embodiment of a system according to the invention;

FIGS. 2 to 8

Cut-outs of schematic views of various preferred embodiments of a system according to the invention.

FIG. 1 shows a system 1 for printing a three-dimensional object 2, with a non-planar surface 3. The system has a print head 4 (eg Spectra Galaxy JA 256/80 AAA), which on an articulated arm robot 5 (eg Kuka KR 60-3 ) is recorded. In the example shown, the robot 5 has three joints 5a, 5b and 5c, with which the robot 5 moves the print head 4 along the surface 3 of the object 2. The print head 4 is also connected via a color and data connection 6 with a color supply and a computer. The connection 6 therefore comprises color supply lines and also signal lines for the individual nozzles 7 of the print head 4.

In FIG. 1 is also shown that the print head 4 in the position 4 'a printing web A on the surface 3 of the object 2 prints. The movement of the robot 5 and the print head 4 takes place, for example, either into or out of the figure plane. Furthermore, it is shown that the print head previously printed a printing web B on the surface 3 of the object 2 in a position 4 ", whereby the print head 4, for example, either moved into or out of the picture plane B with their respective edges adjoin one another at the point 8 on the surface 3 such that there is no unprinted strip and no overlapping strip between the two printing lines ") or in several print runs (" multi pass ").

It can now be provided that the robot 5 and the printhead 4 received therefrom deviate from its current setpoint position and therefore the printing web A is applied at a distance from the printing web B overlaps the printing web B. In both Cases can lead to visible and therefore disturbing banding at the point 8. However, such disturbances can be prevented according to the invention. In the following FIGS. 3 to 8 Advantageous developments of the system according to the invention are shown, which just avoid or reduce such errors.

In FIG. 2 However, it is first shown again how such an error can look in a corresponding magnification. Shown is the print head 4 in its two positions 4 'and 4 "and individual pressure points 9 (or halftone dots of the printed image in eg AM or FM grids) of the printing webs A and B. It can be seen that the respective average distance between pressure points D1 in printing web A and D2 in printing web B is approximately the same, while the distance D3 between the two printing dots 9 at the respective edge of the printing webs A and B is greater than the distances D1 and D2 a bright streak disturbs the print image between the two printing webs A and B. Since the printing dots originate from the nozzles 7 of the printhead 4 by droplets and these droplets have a certain distance between the nozzle and the surface 3, eg about 1 centimeter in the Flight, the positions of the pressure points 9 on the surface 3 are not exactly predictable, so the distances D1, D2 and D3 are only as a mean to look at It is also possible to set the pressure points of the printing webs A and B tight and thereby produce solid areas.

Specific and preferred example: The drop size of the drops 9 (average diameter) on the surface 2 is about 100 microns. The center distance of the drops 9 from each other is also about 100 microns. The variation of the impact points and the path accuracy of the robot 5 are also about 100 microns. Thus, the production of a secondary movement of this magnitude, the annoying banding can be reduced or prevented.

In FIG. 3 is a system according to the invention with a printhead to see 4, wherein between the printhead 4 and a holder 19 of the robot 5, a piezo-actuator 10 is arranged such that the printhead 4 by means of the piezo-actuator 10 relative to Robot 5 and the holder 19 is movable. The piezo actuator receives via the connection 6 of the print head 4 control signals, which cause that as secondary movement 16 (see. Fig. 1 ) a compensation movement takes place. As a result of the vibration of the piezoactuator 10, this compensating movement leads to an offset 11 of the print head 4, so that the two marginal printing dots 9 of the respective printing webs A and B lie relative to one another such that their spacing corresponds to the average spacing of the printing dots of the respective printing webs. The control signals for the piezo actuator 4 are supplied by a computer which calculates the necessary offset 11 from the currently determined actual position of the print head 4 and the desired position of the print head 4 and sends a corresponding control signal to the piezo actuator. The necessary actual position can be detected by a detector. For example, rotary encoders 12a, 12b, 12c (cf. FIG. 1 ), which detect the respective angular positions of the joints 5 a, 5 b, 5 c, from which the current actual position of the print head 4 can be determined.

The vibrations of the piezoelectric actuator 10 produce variations of the impact points of the droplets or the pressure points 9. These variations may preferably be in the order of magnitude of 10 to 100 micrometers in the preferred example. The vibrations may correspond to a white noise. The vibrations may also be periodic over time, but then have to be in a non-integer ratio to the clock frequency with which the pressure points 9 are generated.

The amplitude of the disturbance of the print head 4 by the piezo actuator 10 corresponds to the amplitude of the variation of the impact point of the drops, provided that the secondary movement 16 in the plane of the print head 4, e.g. whose bottom is located.

FIG. 4 shows a further embodiment in which the piezoelectric actuator 10 is not arranged on the print head 4 but between a nozzle carrier 7 'for the individual inkjet nozzles 7 and a holder 19. The piezoelectric actuator 10, which in turn is supplied with control signals from a computer, allows the compensating movement as a relative movement of the nozzle carrier 7 ', so that the marginal pressure points 9 of the respective printing webs A and B have the desired for a streak-free printing distance.

In the FIG. 5 The embodiment shown also has a piezoactuator 10, but this is arranged on a nozzle carrier 7 ", which only comprises a nozzle 7. The nozzle 7 prints a pressure point 9 which comes to lie on the edge of the printing web A. By appropriate control signals for By balancing the actual position with respect to the desired position of the print head 4, the piezo actuator 10 is guided as a compensating movement to a secondary movement 16. As a result of this secondary movement of the nozzle 7, the pressure point 9 printed with this nozzle comes at a distance to a corresponding pressure point 9 adjacent printing web B, so that a streak-free printing between the two printing webs A and B is possible.

The embodiment which is in FIG. 6 is shown, also has a piezoelectric actuator 10, but this is so coupled to a peripheral nozzle 7 of the print head 4, that upon actuation of the piezoelectric actuator 10 as a result of a corresponding control signal to be printed with the nozzle pressure point 9 is offset obliquely and in this way, the distance to an adjacent printing dot 9 of the previously printed printing web B is corrected for streak-free printing. As in FIG. 6 represented by the separately provided piezoelectric actuator 10, the direction of flight of the ink droplet, which forms the pressure point 9 of the printing web A, be influenced such that the droplet is not substantially perpendicular to the bottom of the printhead 4, but at an angle ≠ 90 ° , In this procedure, care must be taken to ensure that the corrected printing dot 9 actually reduces possible stripes and that new stripes are not formed within the printing web A. This can be achieved under given conditions that the pressure point 9 of the printing web A is offset so far that neither left nor right (with respect to in FIG. 6 shown drawing) from the pressure point 9 strips are recognizable by changing distances between the pressure points. The piezoactuator can also be used to generate statistical variations in the trajectories (and / or magnitudes) of successive drops, thereby achieving edge blurring of the print web which reduces or prevents spurious streaks.

FIG. 7 shows a further preferred embodiment of the system according to the invention. This time in addition a camera 13 is used. A marginal printing point 9 'of the previously printed printing web B has been printed with a special ink. This printing ink has, for example, special additives which can be excited and have a fluorescent property. With the camera 13 and optionally with one of these upstream bandpass filter 14, the fluorescent light of the marginal pressure point 9 'can be detected. An unillustrated computer, with which the camera 13 is connected via a line 15, can calculate the edge of the positions of the individual marginal pressure points 9 'in the printing web B and from this correction values for a secondary movement 16 of the printing head 4 during printing of the printing web A. to calculate. These correction values can be applied to the device which initiates the secondary movement via the in FIG. 1 shown connection 6 are fed. Such devices may, for example, in the FIGS. 3 to 6 be shown embodiments with respective piezo actuators 10.

Another preferred embodiment is in FIG. 8 shown. The printing head 4 shown is guided during the printing of the printing web A with a certain overlap to the previously printed printing web B. A pressure point 9a which would be printed without correction with the nozzle 7b is now printed using correction values with an adjacent nozzle 7a. As a result, the pressure point 9a moves closer to the marginal pressure point 9 of the previously printed printing web B, thereby enabling streak-free printing. The correction necessary for this purpose can be based, for example, on the detection with a camera 13 (as in FIG FIG. 7 shown). The detected with the camera edge of the printing web B is used by a computer, not shown, for the correction of the assignment of nozzles and pressure points. If, for example, it is determined that without correction there is too great a distance between the marginal pressure points of the two printing webs, the pressure points of the printing web A are brought closer to the pressure points of the printing web B. This can be done, for example, by printing the print dots from adjacent nozzles, as in FIG FIG. 8 for the pressure point 9a and the two nozzles 7a and 7b represented by the offset 11 and described above. If on the other hand, it is determined that the printing dots of the respective printing webs A and B would overlap too much, the printing dots are shifted by the correction in the opposite direction, ie printing dots of the printing web A are printed by adjacent nozzles, so that their distance to the printing web B increases becomes.

An alternative approach is to move the printhead in multi-pass printing at various speeds at various speeds, thereby producing secondary motion due to variation in the trajectory of the drops.

According to another alternative solution, when printing in "multi-pass" mode in the area of the edge, not all printing dots are printed on a first pass. The gaps between the pressure points of the first pass are filled in a second or further passes. Printing web A and printing web B thus effectively engage each other and there are no straight edges between them.

LIST OF REFERENCE NUMBERS

1 system 2 object 3 surface 4 printhead 4 ' position 4 ' position 5 robot 5a to 5c joints 6 connection 7 jet 7 ' nozzle carrier 7 '' nozzle carrier 7a jet 7b jet 8th Job 9 pressure points 9a pressure points 9b pressure points 10 Piezo actuator 11 offset 12a to 12c encoders 13 camera 14 Bandpass filter 15 connection 16 secondary movement 17 primary movement 18 contraption 19 bracket A print web B print web D1 distances D2 distances D3 distances

Claims (10)

System for printing on an object which imprints at least one non-planar area of the surface (3) of the object (2) with an image, having the following features: - An ink-jet printhead (4) with nozzles (7); - a robot (5) which generates a primary movement (17), the primary movement comprising at least two laterally juxtaposed printing webs (A, B) of the ink jet printing head (4); and - A device (18) which generates a secondary movement (16), wherein the secondary movement (16) substantially perpendicular to the primary movement (17) and whereby the pressure paths (A, B) laterally adjoin one another. System according to claim 1,
characterized,
in that the device (18) comprises a piezoactuator (10) and the secondary movement (16) is a movement of the inkjet printhead (4). System according to claim 1,
characterized,
in that the device (18) comprises a piezoactuator (10) and the secondary movement (16) is a movement of at least one nozzle (7) of the inkjet printhead (4). System according to claim 1,
characterized,
in that the device (18) comprises a piezoactuator (10) and the secondary movement (16) is a movement of at least the droplets (9) of a nozzle (7) of the inkjet printhead (4). System according to one of the preceding claims,
characterized, - That the device (18) comprises a detector (13) which detects the actual positions of pressure points (9) of a first printing web (B); - That the device (18) comprises a computer (19) which calculates the deviation of the actual positions of the pressure points of their desired positions; and - That the device (18) as a secondary movement (16) generates a deviation compensating movement substantially compensating on the second printing web (A). System according to one of claims 1 to 4,
characterized, - That the device (18) comprises at least one detector (12a, 12b, 12c); - That the robot (5) is an articulated arm robot; - And that the detector comprises a rotary encoder (12a, 12b, 12c) which detects the angular position of a joint (5a, 5b, 5c) of the articulated arm robot. System according to claim 5,
characterized,
in that the detector comprises an optical sensor (13) or an ultrasonic sensor which is directed onto the surface (3) of the object (2). System according to claim 7,
characterized,
that the optical sensor (13) is directed to already printed pressure points on the surface (3) and detects their fluorescence radiation. System according to claim 5,
characterized,
in that the detector (13) comprises a tracking system which detects the position of the ink-jet printhead (4). System according to claim 1,
characterized, - That the device comprises a detector (13) which detects the actual positions of pressure points (9) of a first printing web (B); - That the device comprises a computer (19) which calculates the deviation of the actual positions of the pressure point of their desired positions; - That the device as secondary movement generates a deviation substantially compensating, lateral displacement of the image to be printed relative to the nozzles (7).

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