DE102010004496B4 - Method for operating a device for coating and / or printing a workpiece - Google Patents

Abstract

Method for operating a device for coating and / or printing a workpiece (10) with an inkjet printhead arrangement (13), wherein either the workpiece (10) or the printhead arrangement (13) is attached to the movable part of the device The device is designed as a multi-axis robot (1), on the rotary head (6) of which either the workpiece (10) or the printhead arrangement (13) is arranged, the workpiece (10) along a movement path (11, 12 ) is moved in a controlled manner relative to the printhead arrangement (13), characterized in that a three-dimensional path deviation (dx, dy, dz) between the path of travel actually traversed, real path (11), and a required path of movement, target path (12), in real time is used as a correction signal for controlling the print head matrix (14-17) of the print head arrangement (13), and the correction method for controlling individual pixels (27-30) each of a print head matrix (14-17) with the following procedural steps: 1.1 reading the current position of the robot (1) with a web-tracking measuring device, 1.2 comparing the real position of the robot (1) with the required position, 1.3 calculating the three-dimensional deviation (dx, dy, dz), 1.4 calculating a resulting correction value (32-35) in an at least two-dimensional matrix for dx and dy, 1.5 transfer of the correction value (32-35) to the print head matrix (14-17) 1.6 change of the individual pixels (27-30) each printhead matrix (14-17) corresponding to the calculated pixel-related path deviation by rotation and / or translation of pixel positions (27, 27a, 28, 28a, 29, 29b, 30, 30a), 1.7 printing the corrected pixel Matrix on the workpiece (10), 1.8 repetition of process steps 1.1 to 1.7 until each row and / or column of the matrix of the print head matrix (14-17) is printed out in a certain period of time.

Description

The invention relates to a method for operating a device for coating and / or printing a workpiece with an inkjet printhead arrangement according to the preamble of claim 1. The invention also relates to a device for carrying out the method.

A method mentioned at the outset is, for example, the subject of DE 600 04 022 T2 known. The method described there provides for printing on three-dimensionally curved objects in such a way that the object to be printed is attached to a table which rotates the object to each successive position. In an alternative embodiment, it is attached to an assembly that moves along a straight path between the printheads. Since the position of the object relative to its axis of rotation is always known, the images can be linked by the different print heads in order to produce a desired image in the desired color.
However, the cited document has the disadvantage that the device on which the object to be printed is moved under the print heads does not work in real time or almost in real time, so that only a reduced print quality with possible distortions of the printed image has to be accepted.

From the DE 10 2009 058 212 A1 the result is a method and a device for printing on containers, in which a robot positions an object to be printed accordingly in front of a print head. The contour of the object to be printed is detected and it is determined which ink outlet nozzles of the print head may be controlled without a predetermined printing distance being exceeded. The nozzles are controlled such that on the one hand they do not spray the paint next to the object and on the other hand they are not too far away from the object.

The DE 10 2008 061 203 A1 relates to a method and an apparatus for painting a three-dimensional surface. A robot is used which carries a print head for painting the three-dimensional surface, the robot being moved over the surface during the painting and thereby, at least temporarily, following a three-dimensional trajectory (path).

In the publications mentioned above, it is not described that the print head and the object to be printed are guided along a movement path (real path), a path deviation between the real path and a required target path being detected in real time and used as a correction signal for controlling the print head matrix becomes.

US 2009/016 7817 discloses the closest prior art and an apparatus and method for printing three-dimensional objects, wherein a print head is arranged on a robot arm and this print head is guided by the robot arm relative to the surface of the object to be printed. The current position of the print head relative to the surface of the object is determined and the print nozzles of the print head are controlled accordingly. It is not explicitly described that a three-dimensional path deviation between a target path and an actual path is detected and the print head matrix is controlled as a function of this deviation.

The object of the invention is to coat or print any two-dimensional or three-dimensional object with ink jet printing of the most varied of colors, the coating or printing taking place with the highest resolution and quality.

To achieve the object, the invention is characterized by the technical teaching of claim 1.

A movement path between the movable end (e.g. the rotary head) of a multi-axis robot and an ink jet arrangement which can be moved relative to it is recorded in almost real time, and the path curve is corrected in almost real time, so as to achieve a practically ideal path curve for the relative movement between the Object and the inkjet printing arrangement to achieve.

For the sake of simpler description, the following description assumes that a three-dimensional object is to be printed. The invention is not restricted to this. Two-dimensional objects (ie surfaces) can also be printed with the highest resolution and accuracy using the method according to the invention.

The printing or coating of a three-dimensional object is only described for the sake of simpler description.

The printing of a three-dimensional object is also described for the sake of simplicity, although the invention is not limited to a printing process alone. All coating processes which are customary and known with ink jet printers can be carried out. Therefore the invention is not limited to printing on three-dimensional objects, but encompasses all coating processes.

Finally, as a further simplification of the following description, it is assumed that the object to be printed is guided past a fixed ink jet printing arrangement by a multi-axis robot along a movement path. Again, this simplification is only due to the simplified description. Embodiments are also described in which the kinematic reversal is given, namely that the object to be printed is fixed in space and the printing inkjet arrangement is guided on a three-dimensional movement path around and along the object to be printed.

Only for the sake of simplicity of description, it is assumed in the following description that the object to be printed is attached to the multi-axis robot and that a three-dimensional path curve can be carried out by controlling the multi-axis robot on the essentially fixed ink jet printing arrangement.

An essential feature of the invention is that the trajectory of the multi-axis robot is corrected in real time in such a way that there is practically an ideal trajectory and the correction signals with regard to the deviation from an actual trajectory (hereinafter also referred to as real trajectory) compared to one ideal target path (hereinafter also referred to as target path) is used for the correction of the individual inkjet nozzles in the matrix of an inkjet printer.

The correction of trajectories of multi-axis robots is known. In the DE 196 48 430 A1 the path curve of a multi-axis robot is corrected, at the free end of which a machining tool is arranged in connection with a workpiece to be machined.

In the DE 10 2007 024 143 A1 A motion control for elastic robot structures is described, in which the path correction values for the individual path points on the robot path will soon be calculated using a dynamic robot model and corrected axis coordinates for the individual path points will be generated therefrom.

Until now, however, it was not known to use a multi-axis robot as a printing tool for printing a two- or three-dimensional object, in which the path deviation is corrected in almost real time.

The decisive factor is not that the trajectory is corrected, as taught by the two aforementioned documents, but that it is crucial in the sense of the present invention that the correction signal is used for direct control of the ink jet nozzles arranged in a print head matrix.

The term “printhead matrix” of an inkjet printer means that a multiplicity of inkjet nozzles are arranged in a row and column arrangement, the flow through each inkjet nozzle being able to be regulated separately. It is therefore preferably a two-dimensional printhead matrix in which the individual controllable printheads are arranged in rows and columns.

However, the invention is not restricted to this. The invention can also only provide line-by-line print heads in which the individually controllable print heads are only aligned in succession in a single line.

For the sake of simpler description, however, the following description assumes a matrix arrangement of a printhead matrix extending in the X-Y direction.

It goes without saying that curved printhead arrays can also be provided for certain applications, such as, for example, the DE 10 2004 046 096 B3 teaches.
Due to the direct transmission of the web correction signal to the control arrangement for the control of the individual ink jet nozzles in the print head matrix, an almost real-time correction takes place, namely at a speed and with such a small time delay, as was not previously known. It is just being avoided to provide the correction signal for correcting the path curve, but the correction signal is used directly as a correction signal for the color control of the print head matrix.

In a preferred embodiment, the multi-axis robot is designed as a six-axis robot. However, the invention is not restricted to this. All other robot arrangements can also be used, such as e.g. B. Three-axis, four-axis, five-axis, etc. robots can be used.

• 1.1 Lesen der aktuellen Position des Roboters (1) mit einem bahnerfassenden Messgerät
• 1.2 Vergleichen der realen Position des Roboters (1) mit der geforderten Position
• 1.3 Berechnen der Abweichung (dx, dy, dz)
• 1.4 Berechnen eines daraus resultierenden Korrekturwertes (32-35) in einer mindestens zwei-dimensionalen Matrix
• 1.5 Übertragung des Korrekturwertes (32-35) auf die Druckkopf-Matrix (14-17)
• 1.6 Veränderung der einzelnen Pixel (27-30) jeder Druckkopf-Matrix (14-17) entsprechend der berechneten pixel-bezogenen Bahnabweichung durch Rotation und/oder Translation von Pixel-Positionen (27, 27a, 28, 28a, 29, 29b, 30, 30a)
• 1.7 Drucken der korrigierten Pixel-Matrix auf das Werkstück (10)
• 1.8 Wiederholung der Verfahrensschritte 1.1 bis 1.6 bis jede Reihe und/oder Spalte der Matrix der Druckkopf-Matrix (14-17) in einem bestimmten Zeitraum ausgedruckt ist.

The following process steps are carried out in order to carry out an almost real-time correction of the print head control:

• 1.1 Reading the current position of the robot ( 1 ) with a web-measuring device
• 1.2 Compare the real position of the robot ( 1 ) with the required position
• 1.3 Calculate the deviation ( dx , dy , dz )
• 1.4 Calculate a resulting correction value ( 32-35 ) in an at least two-dimensional matrix
• 1.5 Transfer of the correction value ( 32-35 ) on the printhead matrix ( 14-17 )
• 1.6 Change of the individual pixels ( 27-30 ) each printhead matrix ( 14-17 ) according to the calculated pixel-related path deviation by rotation and / or translation of pixel positions ( 27th , 27a , 28 , 28a , 29 , 29b , 30th , 30a )
• 1.7 Printing the corrected pixel matrix on the workpiece ( 10th )
• 1.8 Repetition of the procedural steps 1.1 to 1.6 to each row and / or column of the matrix of the printhead matrix ( 14-17 ) is printed out within a certain period of time.

With the given technical teaching, there is the significant advantage that no complicated control mechanisms are carried out on the movement path of the robot itself, which require high computing power and complex control, but that the correction signals between the real path and the target path directly for controlling the individual inkjet nozzles of the inkjet printer can be used.

The term ink jet print head arrangement is understood to mean a number of embodiments, all of which are intended to be encompassed by the present invention.

In the simplest case, this is understood to mean a simple two-dimensional or one-dimensional ink jet arrangement which is only suitable for dispensing a single medium.

In other embodiments, however, the print head arrangement will consist of a plurality of different ink jet matrices, each ink jet matrix forming its own print head and the respective matrix of this print head being controllable by the aforementioned correction signals.

In this way, a number of different printheads can be combined in a printhead arrangement, and a plurality of printhead arrangements can also be arranged one behind the other on a movement path of a robot, past which the object to be printed is guided.

It was explained above that the X-Y matrix of the ink jet nozzles is corrected in accordance with the trajectory running in the X-Y direction. Only those inkjet nozzles are activated whose print image (ink delivery) corresponds to the target path of the path curve calculated in almost real time. In a further development it is provided that a correction is also made in the Z axis. This is done by regulating the jet strength and / or jet length (= width) of the individual ink jet nozzles.

An adaptation of the inkjet printing arrangement to a trajectory also extending in the Z-axis is thus achieved.

In the following, the invention is explained in more detail with the aid of drawings that illustrate only one embodiment. Further features and advantages of the invention which are essential to the invention emerge from the drawings and their description.

• 1: schematisierte Darstellung der Bedruckung eines Gegenstandes mit einem Sechs-Achs-Roboter
• 2: schematisiert die Druckkopf-Anordnung nach 1 mit Darstellung weiterer Einzelheiten
• 3: perspektivische Darstellung einer Druckkopfanordnung, die am freien Ende eines Sechs-Achs-Roboters entlang einer Bewegungsbahn geführt wird
• 4: das Druckbild der Druckkopfanordnung bei nicht korrigierter Bewegungsbahn
• 5: das Druckbild der Druckkopfanordnung bei korrigierter Bewegungsbahn
• 6: schematisiert die Darstellung der Erfassung der Korrektursignale
• 7: der Vergleich einer theoretischen Bahn zu einer Echtbahn und die Berechnung der Korrekturwerte
• 8: ein in Fast-Echtzeit ablaufendes Berechnungsprogramm zur Berechnung der Bahnpunkte auf der theoretischen Bahn
• 9: die Korrektur jeder Tintenstrahldüse in Fast-Echtzeit
• 10: die Draufsicht auf die in Form von Pixeln angeordneten Tintenstrahldüsen einer Druckkopfmatrix ohne Korrektur
• 11: die gleiche Darstellung wie 10, wenn die Druckkopfmatrix korrigiert wird
• 12: ein gegenüber 1 abgewandeltes Ausführungsbeispiel, bei dem die Druckkopfanordnung am Mehrachs-Roboter entlang einer Bewegungsbahn an dem im Wesentlichen feststehenden zu bedruckenden Gegenstand entlang geführt wird

Show it:

• 1 : Schematic representation of the printing of an object with a six-axis robot
• 2nd : schematizes the print head arrangement according to 1 with further details
• 3rd : Perspective view of a printhead arrangement which is guided along a movement path at the free end of a six-axis robot
• 4th : the print image of the print head arrangement with an uncorrected movement path
• 5 : the print image of the print head arrangement with corrected movement path
• 6 : schematically shows the acquisition of the correction signals
• 7 : the comparison of a theoretical path to a real path and the calculation of the correction values
• 8th : a calculation program running in real-time to calculate the path points on the theoretical path
• 9 : the correction of each ink jet nozzle in near real time
• 10th : the top view of the ink jet nozzles of a print head matrix arranged in the form of pixels without correction
• 11 : the same representation as 10th when the printhead matrix is corrected
• 12 : one opposite 1 modified embodiment in which the Printhead arrangement on the multi-axis robot is guided along a movement path along the essentially fixed object to be printed

In 1 is a multi-axis robot 1 shown in its design as a six-axis robot, with a bogie on the bottom 2nd a stand 3rd in the direction of the arrows 7 is rotatably arranged.

At the top of the stand 3rd is a swivel arm via a first swivel joint 4th arranged in the direction of the arrow 8th is pivotable, with another swivel arm at its front free end via a further swivel joint 5 is added, which is also in the direction of the arrow 8th is pivotable.

At the front free end of the swivel arm 5 is a turret 6 arranged in the direction of the arrow 9 is rotatable and the workpiece at its front free end to be coated and / or printed 10th wearing.

This workpiece 10th is along a real path specified by the robot controller 11 on a substantially stationary printhead arrangement 13 passed by, using a series of printhead matrices 14-17 an ink jet on the surface of the workpiece 10th deliver and thus print and / or coat it.

It is now important that the real web 11 of the multi-axis robot 1 leads to an undesirable distortion of the printed image, because the real web is flawed and therefore it is not possible to print a distortion-free printed image on the workpiece 10th to apply.

For this purpose, the invention provides that in a control system, not shown in more detail, an idealized target path depending on the real path 12 is calculated and that the printhead arrangement 13 with the printhead matrices arranged there 14-17 is controlled in such a way that the printing takes place in this way, i.e. whether the workpiece 10th on the target track 12 on the printhead assembly 13 would be led past.

In 2nd is the printhead arrangement 13 shown even larger, where it can be seen that, for example, the printhead matrix 14-17 The colors red, yellow, blue and green are given off and that each has a variety of ink jets 24th , 24a , 24b , 24c , 24d from the pixel-shaped the printhead matrix 14-17 forming printheads are given.

Any printhead matrix 14-17 is a measuring axis 19-22 assigned to have a clear geometric reference to the printhead matrix 14-17 to enable. In the area of the measuring axis 19-22 can then be a reference point, for example 23 be defined and the target path 12 with the object to be printed 10th should, for example, all reference points 23 on all measuring axes 19-22 to cut.

The 3rd shows according to the equivalent version of the 1 and as shown in 12 that it is possible the printhead arrangement 13 in the direction of the arrow 31 on an essentially held workpiece 10th to run along, it is of course provided within the scope of the present invention that the workpiece itself can still be moved, z. B. in which it is rotated or moved along a plane with an XY slide.

It is also possible to use an XYZ displacement system instead of an XY displacement system for the displaceable mounting of the workpiece 10th to provide, past the printhead arrangement 13 under the path control of the multi-axis robot 1 is led along.

It can be seen that the real orbit 11 that the robot uses to arrange the printhead 13 along the substantially captured workpiece 10th leads from the ideal target path 12 may differ.

Such a deviation is in the 4th and 5 shown. A single printhead matrix 14-17 then generates a print image with the line and column-shaped print heads 25th where the individual pixels 27-30 the respective ink jet nozzle distorted and inaccurate the printed image 25th to form.

In contrast, the correction signal between the real path 11 and the target path 12 for controlled control of the individual inkjet nozzles in the print head matrix 14-17 used results for each printhead matrix 14 , 17th a corrected print image 25a according to 5 . As a result, the uncorrected pixel 27th converted into the corrected pixel a, and this also applies to the other pixels 28-30 .

The 6 now shows the calculation of the path deviation between the real path 11 and the target path 12 , being for each printhead matrix 14-17 a correction value 32-35 is calculated, and according to this correction value 32-35 other inkjet nozzles are now in the printhead matrix 4th controlled so as to correct a printed image 25a to 5 to reach.

The 7 shows that to calculate the path deviation on the real path 11 the points in a row P1-P4 are calculated and then the next intersection in near real time 36 on the real track 11 must be calculated to get the correction signal very quickly 32-35 to calculate, so the intersection 37 on the target track 12 to calculate. This way, all points on the target path 12 calculated, and the respective correction value 32-35 is used to control the inkjet nozzles in the printhead matrix.

The 8th shows an example of the calculation of the intersection 37 (Point pn ) on the target track 12 , with a linearization between the points P1 , P2 , P3 and P4 the position of the intersection 37 determined by the linearization calculation.

Accordingly, each pixel (ink jet nozzle in the matrix 14-17 ) of an uncorrected value 27th into a corrected value 27a transferred, z. B. the uncorrected pixel the matrix coordinate 10th / 25th may have, while the corrected ink jet nozzle, the corrected pixel 27a returns the matrix coordinate 12 / 23 can have.

Accordingly, different ink jet nozzles are controlled, as shown in 10th with comparison of 11 is shown.

If the printhead was not corrected, the ink jet nozzles would correspond to the pixels 27th , 28 , 29 their color on the workpiece to be coated 10th and when the printhead is corrected, a completely different inkjet nozzle is now activated, which is now within the scope of the corrected print image 25a sits at the point where the corrected pixel 27a , 28a , 29a is delivered.

The 12 shows the kinematic inversion to 1 and corresponds to the representation in 3rd . It can be seen there that the relative movement between the workpiece to be printed 10th and the printhead assembly 13 can also be achieved in that the printhead arrangement 13 is arranged at the free front end of the multi-axis robot. It can be designed to be rotatable, or it can be held in a controlled manner in an XY slide system or in an XYZ slide system.

It is important in all embodiments that a print image of previously unattainable quality can now be achieved on the object to be printed in almost real time, because the deviations between the real path traversed and the target path given for the achievement of an ideal print image directly for controlling the individual ink jet nozzles Printhead arrangement can be used.

Reference symbol list

1

Multi-axis robot

2nd

bogie

3rd

Stand

4th

Swivel arm

5

Swivel arm

6

Turret

7

Arrow direction

8th

Arrow direction

9

Arrow direction

10th

workpiece

11

Real track

12

Target path

13

Printhead arrangement a, b

14

Printhead matrix

15

Printhead matrix

16

Printhead matrix

17th

Printhead matrix

18th

Arrow direction

19th

Measuring axis

20th

Measuring axis

21st

Measuring axis

22

Measuring axis

23

Reference point

24th

Inkjet a, b, c, d

25th

Printed image (without correction)

25a

Printed image (with correction)

27th

Pixel a

28

Pixel a

29

Pixel a

30th

Pixel a

31

Arrow direction

32

Correction value

33

Correction value

34

Correction value

35

Correction value

36

Intersection (real path 11 )

37

Intersection (target path 12 )

Claims (5)

Method for operating a device for coating and / or printing a workpiece (10) with an inkjet printhead arrangement (13), wherein either the workpiece (10) or the printhead arrangement (13) is attached to the movable part of the device The device is designed as a multi-axis robot (1), on the rotary head (6) of which either the workpiece (10) or the printhead arrangement (13) is arranged, the workpiece (10) along a movement path (11, 12 ) is moved in a controlled manner relative to the printhead arrangement (13), characterized in that a three-dimensional path deviation (dx, dy, dz) between the path of travel actually traversed, real path (11), and a required path of movement, target path (12), in real time is used as a correction signal for controlling the printhead matrix (14-17) of the printhead arrangement (13), and the correction method for controlling individual pixels (27-30) in each case one printhead matrix (14-17) with the following procedural steps: 1.1 reading the current position of the robot (1) with a web-tracking measuring device, 1.2 comparing the real position of the robot (1) with the required position, 1.3 calculating the three-dimensional deviation (dx, dy, dz), 1.4 calculating a resulting correction value (32-35) in an at least two-dimensional matrix for dx and dy, 1.5 transfer of the correction value (32-35) to the printhead matrix (14-17) 1.6 change of the individual pixels (27-30) each printhead matrix (14-17) corresponding to the calculated pixel-related path deviation by rotation and / or translation of pixel positions (27, 27a, 28, 28a, 29, 29b, 30, 30a), 1.7 printing the corrected pixel Matrix on the workpiece (10), 1.8 repetition of process steps 1.1 to 1.7 until each row and / or column of the matrix of the print head matrix (14-17) is printed out in a certain period of time. Procedure according to Claim 1 , characterized in that the multi-axis robot (1) is a 6-axis robot. Procedure according to one of the Claims 1 or 2nd , characterized in that the deviation of the trajectory in the Z direction is carried out by correcting the spray width of the ink jet nozzles. Procedure according to one of the Claims 1 to 3rd , characterized in that the deviation of the trajectory in the Z direction is carried out by correcting the trajectory (11, 12) of the multi-axis robot (1). Device for carrying out the method according to one of the preceding Claims 1 to 4th , characterized in that the ink jet print head arrangement (13) consists of a plurality of print head matrices (14-17) which are arranged together in a housing block.

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