EP2769848A2 - Method for producing a printed image - Google Patents

Abstract

The method involves measuring first and second position values (H1,H2) of an object (3) at first and second positions (P1,P2) respectively. A position change of the object perpendicular to a conveying direction (5) is determined by using position values. The position change is compensated, when printing one portion (A2) of a print image (2) to other portion (A1) by essentially seamless printing by using position change of corresponding number of nozzles within an overlap region (L) of one field (F2) and complementary number of nozzles outside of overlap region.

Description

The present invention relates to a method for producing a printed image having the features of the preamble of claim 1.

The invention is in the technical field of printing, in particular the printing of three-dimensional bodies by means of a plurality of ink jet printing units.

From the US 7,955,456 B2 is already the inkjet printing of blister packs known. These have a substantially two-dimensional to be printed sealing film and are conveyed linearly. Despite high production speeds conveying and printing is therefore usually easily possible. Far more difficult is the printing of three-dimensionally shaped bodies with curved outer surfaces in space.

It is already known to use a plurality of inkjet printing units when producing a printed image on an object to be printed, since the width of the printing units is usually less than the width of the printed image. The printing units are arranged side by side in such a way that the respective sections of the printed image to be printed seamlessly adjoin one another. However, since the printing units also have a greater width than their respective array of inkjet nozzles, it is also necessary to arrange the printing units spaced apart in the conveying direction of the object, ie to print the object at two different positions or locations of the object. Furthermore, it is already known to produce the seamless connection of two sections to be printed with overlapping nozzle fields to allow a smooth (and not an abrupt) transition of the sections. The two sections engage in the overlap so to speak "intertwined" and complement each other there to a complete printed image. However, with screen-printed images, this "meshing" can lead to unwanted interference.

These known measures work well as long as the object to be printed does not undergo undesirable positional changes during conveyance, e.g. perpendicular to the conveying direction. Objects, such as Bottles in bottling plants, in contrast to flat substrates, however, can not usually be conveyed with high precision, at least not with precision on the order of the printing resolution of an inkjet printing unit. Therefore, there may be changes in position of the objects resulting in undesired disturbances, e.g. light stripes, of the printed image. So far, attempts have been made to improve the conveyance of the objects, so that undesired changes in position can be avoided. However, this approach is the more difficult the faster it is to be produced.

Against this background, it is an object of the present invention to provide a method for producing a printed image which is improved compared with the prior art and makes it possible to produce a substantially trouble-free printed image on the object with at least two ink-jet printing units spaced apart in the conveying direction of an object to generate, in particular for the case that the object undergoes an undesirable change in position on the way from the first to the second printing unit.

An inventive solution to this problem is the method with the features of main claim 1. Advantageous developments of this invention will become apparent from the accompanying dependent claims and from the description and the accompanying drawings.

An inventive method for producing a printed image on an object to be printed, wherein for printing the object, a first ink jet printing unit having a first array of ink jet nozzles and a second ink jet printing unit with a second array of ink jet nozzles and for conveying the object a conveying unit being used in a conveying direction, wherein the first field and the second field extend substantially perpendicular to the conveying direction and partially overlap in an overlapping area, comprising the steps of: printing a first section of the printed image with the first printing unit on a first printing unit Position, - conveying the object from the first position to a second position spaced from the first position Position, and - printing a second portion of the print image with the second printing unit at the second position, characterized by the further steps of: - measuring a first position value of the object at the first position and a second position value of the object at the second position, - Determining a positional change of the object substantially perpendicular to the conveying direction using the first and second position values, and compensating the positional change in printing the second portion by substantially seamlessly printing the second portion to the first portion using a number of positions corresponding to the change in position Nozzles within the overlap area of the second field and a complementary number of nozzles out of the overlap area of the second field.

The method according to the invention advantageously makes it possible to produce a substantially trouble-free printed image on the object with the ink-jet printing units spaced apart from one another in the conveying direction of the object. An undesired change in position of the object is thereby determined from measured values and compensated in an advantageous manner: An intended overlap of the nozzle fields according to the invention is used to produce e.g. to avoid bright stripes in the printed image in an advantageous manner. If an undesired change in position of the object necessitates a countermeasure, nozzles in the overlap area are, so to speak, switched on and the print image or the second section is "pushed towards the first section". For this purpose, the second printing unit is preferably supplied with the compensation corresponding, that is, to some extent also "shifted", printing data.

A preferred further development of the method according to the invention can be distinguished by the fact that, when measuring the two position values, a marking is detected on the object or on the conveyor unit. By providing such markings and on the markers directed and tuned to these measurement units, the respective measurement can be sufficiently improved. In addition, the marking can also be applied to the object by the first printing unit, or a partial area of the first section of the printed image can serve as a marking. Such a printed mark may be coated with a non-visible ink containing fluorescent substances. be generated and illuminated for example for visualization or measurement with so-called black light (UV-A radiation).

A preferred development of the method according to the invention can be distinguished by the fact that the object is a three-dimensional body and the printed image is generated on its outer surface. The invention is currently in the printing of three-dimensional objects, e.g. Bottles, because such bodies can often be conveyed less precisely than e.g. flat, essentially two-dimensional substrates and compensation measures may be required.

A preferred development of the method according to the invention can be distinguished by the fact that the second ink-jet printing unit additionally experiences a change in position to compensate for a change in position of the object whose value is smaller than the printing resolution of the second printing unit. If, despite compensation by the use of the overlap nozzles still unwanted disturbances in the printed image are to be expected, the second printing unit can advantageously undergo an additional change in position, i. be moved in a balancing position. Such a compensation movement can preferably take place using a piezo actuator.

The above-mentioned inventive method can also be described by the following synonymous main claim or its combination of features: A method for generating a printed image with two sections on a three-dimensional object using ink jet nozzles, wherein a change in position of the object between the printing of the sections by the use of additional Ink jet nozzles is compensated.

The invention as such as well as structurally and / or functionally advantageous developments of the invention will be described below with reference to the accompanying drawings with reference to a preferred embodiment and a concrete example.

Figur 1

Eine schematische Darstellung eines bevorzugten Ausführungsbeispiels des erfindungsgemäßen Verfahrens anhand der Abläufe beim Betrieb einer Vorrichtung zum Bedrucken von Objekten, und

Figur 2

Eine schematische Darstellung eines konkreten Ausführungsbeispiels des erfindungsgemäßen Verfahrens anhand der Abläufe beim Betrieb einer Vorrichtung zum Bedrucken von Objekten.

The drawings show:

FIG. 1

A schematic representation of a preferred embodiment of the method according to the invention with reference to the procedures in the operation of a device for printing objects, and

FIG. 2

A schematic representation of a concrete embodiment of the method according to the invention with reference to the procedures in the operation of a device for printing objects.

FIG. 1 shows a device 1 for generating a printed image 2 on an object 3, for example a bottle or any rotationally symmetrical body, or a device for carrying out the method according to the invention. The object is shown twice in the figure: once "left" in a first position P1 and once "right" in a second position P2. During the execution of the method, the object is conveyed from the first position in the conveying direction 5 to the second position by means of a conveying unit 4. The conveyor may have a so-called plate 6, on which the object is arranged during conveying.

FIG. 1 also shows a first ink jet printing unit D1 and a second ink jet printing unit D2: printing unit D1 prints at position P1 and printing unit D2 at position P2. Printing unit D1 prints an "upper" first section A1. Printing unit D2 prints a "lower" second section A1. Printing unit D1 has a first field F1 of ink jet nozzles and printing unit D2 has a second field F2 of ink jet nozzles. Both printing units can preferably be constructed identically. The nozzles of the two fields are each arranged on a straight line G1 or G2, which runs essentially perpendicular to the conveying direction 5.

Bottles 3 in bottling plants are partly conveyed on circular tracks 5. The representation in the figure can be understood as a side view of such a circular path. The printing units D1 and D2 would then be arranged substantially tangentially to the circular path 5 and directed radially to the bottles.

In position P1, the object 3 is at a height H1, which is measured as a first position value. Note: The term "height" in this application does not say anything about the orientation of the object in space. If the object shown were lying instead of standing transported and the two printing units D1 and D2 would also be lying instead of standing arranged, so the "height" would not be measured in the vertical, but in the horizontal direction (parallel to the then lying straight lines G1 and G2) , Further note: The height H1 is shown in the figure for reasons of clarity at the top of the plate 4. However, the measurement of the height H1 is effected by means of a first measuring unit M1 at a measuring mark 7, which can be attached to the object or to the plate or at another point of the conveying unit 4.

In position P2, the object 3 is at a height H2, which is measured as a second position value (corresponding to the first position value). In FIG. 1 It can be seen that the plate 4 and thus also the object 3 undergoes a change in position "upward" during conveyance in the conveying direction 5. Both position values are therefore supplied to a control device 8 via data connections (indicated only by short dashes). The control device can now determine a position change Delta_H from the two position values H1 and H2, for example by subtraction. This change in position can now be used according to the invention for compensation during printing.

In order to be able to carry out the compensation according to the invention, it is necessary for the two printing units D1 and D2 to have an overlapping area L in which the nozzle fields F1 and F2 overlap, ie by arranging both nozzles of the field F1 and nozzles of the field F2 are. Since, in the example shown, the object 3 has undergone a positional change Delta_H "upward", according to the invention the second section A2 is printed essentially seamlessly on the first section A1 by activating one or more nozzles 9 of the second field F2 in the overlap area. The number of nozzles 9 activated for the compensation is determined by the control unit 8: The number corresponds to the position change Delta_H, ie so many nozzles 9 are used for the compensation that the width of their pressure range essentially corresponds to the position change Delta_H. In addition, at the Printing unit D2 activates a complementary number of nozzles outside the overlap area, so that the entire second section A2 can be printed. For clarification, the respectively active nozzles, ie those involved in the respective printing of the sections A1 and A2, of the fields F1 and F2 are shown dark.

At the printing unit D2, the information Delta_H is thus used to define the active pressure nozzles. The difference H2-H1 (e.g., in microns) is e.g. is converted into a digital value K (e.g., the concrete value 2) which is a K-fold (corresponding to, for example, 2 times) the printing resolution of the two printing units. This digital value is routed to a multiplexer. The multiplexer has an input with n channels, which is supplied with the n print data for the print image with n pixels (perpendicular to the conveying direction 5). Each channel controls a nozzle. The output is connected to the n inputs of the printhead. The compensation can now take place in increments of the print resolution (corresponding to, for example, 2 nozzles for the compensation with K = 2). The multiplexer may be part of the control unit 8.

In this way, the compensation can be used to compensate for the position change Delta_H in increments of the nozzle distances, that is, in accordance with the print resolution. In the event that the position change Delta_H can not be compensated precisely by such a compensation, for example because the position change Delta_H is not an integer multiple of the nozzle pitch, and the uncompensated remainder of the position change Delta_H would lead to undesired disturbances in the printed image, the following is provided: Control unit 8 can cause an adjustment of the printing unit D2 via a fast and highly accurate piezo actuator 10, which is finer than the printing resolution. As a result, a compensation of the hitherto not compensated remainder of the position change Delta_H is possible.

Hereinafter, with reference to FIG. 2 a given example with concrete numerical values.

1. 1. Ein Multiplexer 11 schaltet die zu druckenden Bilddaten der Tintenstrahl-Druckeinheit D2 der zweiten Druckreihe R2 auf deren Düsen (bzw. auf die Eingänge von D2) entsprechend der mechanischen Position von D2 an einer Nahtstelle zu einer weiteren Tintenstrahl-Druckeinheit D1 oder D3 der ersten Druckreihe R1 (bei Vorliegen von nur einer Nahtstelle). Der Multiplexer 11 schaltet die zu druckenden Bilddaten von D2 auf deren Düsen entsprechend der mechanischen Position von D2 an zwei Nahtstellen zu zwei weiteren Tintenstrahl-Druckeinheit D1 und D3 der ersten Druckreihe R1 (bei Vorliegen von zwei Nahtstellen). Gezeigt ist in Figur 2 die Situation bei Vorliegen von zwei Nahtstellen. Gezeigt sind in Figur 2 zudem drei verschiedene, mögliche mechanische Positionen von D2 in x-Richtung. Aus darstellungstechnischen Gründen sind diese drei Positionen senkrecht zur x-Richtung nebeneinander und nicht überlagert gezeigt.
2. 2. Der Multiplexer 11 hat für die Anzahl der mit D2 zu druckenden Spuren des Druckbildes eine Anzahl N von Dateneingängen. Die Anzahl N ist stets kleiner (oder gleich) der Anzahl n der verfügbaren Düsen von D2.
3. 3. Der Korrekturbereich, d.h. die Verschiebung der Istposition von D2 gegenüber der Sollposition von D2, bestimmt die Anzahl der notwendigen Ausgänge des Multiplexers 11 und die Anzahl der Schaltverbindungen S des Multiplexers 11.
4. 4. Es gibt den Zustand, dass eine positive Korrektur (z.B. in positive x-Richtung, D2 rechts in Figur 2) durchgeführt werden muss, wobei K_pos = Anzahl der Düsen des positiven Korrekturbereichs.
5. 5. Es gibt den Zustand, dass eine negative Korrektur (z.B. in negative x-Richtung, D2 mittig in Figur 2) durchgeführt werden muss, wobei K_neg = Anzahl der Düsen des negativen Korrekturbereichs.
6. 6. Es auch gibt den Zustand, dass nicht korrigiert werden muss (D2 links in Figur 2).
7. 7. Der Korrekturbereich kann in Millimetern angegeben werden und wird hier zur Vereinfachung symmetrisch betrachtet, z.B. +/- 0,35 mm. Der gesamte Korrekturbereich ist demnach = 0,7 mm. K_pos und K_neg werden nach den folgenden Formeln berechnet:
   • K_pos = aufgerundeter Wert von (K_pos /Auflösung der Druckeinheit),
   • K_neg = aufgerundeter Wert von (K_neg /Auflösung der Druckeinheit).
8. 8. Für die Anzahl aller Korrekturdüsen von D2 gilt: K = K_neg + K_pos.
9. 9. Für die Anzahl der benötigten Düsen von D2 gilt: n > N + K, wobei N Anzahl der druckenden Spuren.
10. 10. Für die Anzahl M der benötigten Ausgänge des Multiplexers gilt: M = N + K_pos + K_neg.
11. 11. Für die Anzahl der Schaltstellungen S eines Multiplexerdatenpfads (Schaltverbindungen) gilt: S = K_pos + K_neg + 1.

Preliminary remarks:

1. 1. A multiplexer 11 switches the image data to be printed of the ink jet printing unit D2 of the second printing series R2 to its nozzles (or to the inputs of D2) corresponding to the mechanical position of D2 at an interface to another ink jet printing unit D1 or D3 first print row R1 (if there is only one seam). The multiplexer 11 switches the image data to be printed from D2 onto its nozzles in accordance with the mechanical position of D2 at two seams to two further inkjet printing units D1 and D3 of the first printing series R1 (in the presence of two seams). Shown is in FIG. 2 the situation in the presence of two seams. Shown are in FIG. 2 also three different possible mechanical positions of D2 in the x-direction. For illustrative reasons, these three positions are shown perpendicular to the x-direction next to each other and not superimposed.
2. 2. The multiplexer 11 has a number N of data inputs for the number of tracks of the print image to be printed with D2. The number N is always smaller (or equal) to the number n of available nozzles of D2.
3. 3. The correction range, ie the shift of the actual position of D2 from the target position of D2, determines the number of necessary outputs of the multiplexer 11 and the number of switching connections S of the multiplexer 11.
4. 4. There is the condition that a positive correction (eg in positive x-direction, D2 right in FIG. 2 ), where K_pos = number of nozzles of the positive correction area.
5. 5. There is the condition that a negative correction (eg in negative x-direction, D2 center in FIG. 2 ), where K_neg = number of nozzles of the negative correction range.
6. 6. It also gives the condition that does not need to be corrected (D2 left in FIG. 2 ).
7. 7. The correction range can be specified in millimeters and is considered symmetrical here for simplicity, eg +/- 0.35 mm. The total correction range is therefore = 0.7 mm. K_pos and K_neg are calculated according to the following formulas:
   • K_pos = rounded value of (K_pos / resolution of the printing unit),
   • K_neg = rounded value of (K_neg / resolution of the printing unit).
8. 8. The following applies to the number of all correction nozzles of D2: K = K_neg + K_pos.
9. 9. For the number of required nozzles of D2: n> N + K, where N is the number of printing tracks.
10. 10. The following applies for the number M of required outputs of the multiplexer: M = N + K_pos + K_neg.
11. 11. The following applies to the number of switching positions S of a multiplexer data path (switching connections): S = K_pos + K_neg + 1.

• Der Bereich zwischen den Druckeinheiten D1 und D3 beträgt 990 Spuren.
• Es sollen nach oben und nach unten (bzw. in positive und negative x-Richtung) jeweils etwa 350 µm korrigiert werden können.
• Bei 70 µm Auflösung der Druckeinheit D2 (Spurabstand der gedruckten Tintenstrahltropfen) entspricht dies nach oben und nach unten jeweils 5 Spuren:
  • ○ 5 Spuren zur Korrektur einer nach oben verschobenen Druckeinheit D2.
  • ○ 5 Spuren zur Korrektur einer nach unten verschobenen Druckeinheit D2.
  • o Plus eine Mittelstellung, für bereits vorhandene, korrekte Einstellung.
• Aus Symmetriegründen ergeben sich dann 11 Schaltstellungen für jeden Multiplexer-Ausgang und somit gilt: K = 10 und S = 11.
• Der Multiplexer muss somit in diesem Beispiel 1000 Eingänge der Druckeinheit D2 adressieren können.
• Die Mittelstellung (bei der keine Korrektur erforderlich ist) wird dann definiert mit Spur 6 für die unterste Spur und mit Spur 995 für oberste Spur.
• Zu beachten ist, dass der Multiplexer intern jeden Eingang auf S verschieden Ausgänge schalten können muss.

Specific numerical example:

• The area between the printing units D1 and D3 is 990 tracks.
• It should be able to be corrected upwards and downwards (or in positive and negative x-direction) each about 350 microns.
• At 70 μm resolution of the printing unit D2 (track pitch of the printed ink jet drops), this corresponds to 5 tracks at the top and at the bottom:
  • ○ 5 tracks for correction of an upwardly shifted printing unit D2.
  • ○ 5 tracks for correction of a down-shifted printing unit D2.
  • o Plus a middle position, for already existing, correct setting.
• For symmetry reasons, there are then 11 switch positions for each multiplexer output, and thus K = 10 and S = 11.
• The multiplexer must thus be able to address 1000 inputs of the printing unit D2 in this example.
• The mid-position (where no correction is required) is then defined with track 6 for the lowest track and track 995 for uppermost track.
• It should be noted that the multiplexer must internally switch each input to S different outputs.

• Die Druckeinheit würde in diesem Fall direkt von einem Piezoelement in seiner Höhe verstellt werden. Die Verstellzeit muss dabei in den Gesamtablauf passen und darf diesen nicht stören.
• Dies geschieht nach der Messung der Größe H2 und vor dem Drucken. Um den Messfehler möglichst klein zu halten, sollte der Messzeitpunkt von H2 unmittelbar vor dem Druckzeitpunkt stattfinden.
• Lässt man z.B. eine Millisekunde Zeit für Messen und Stellen, so muss das mechanische System für eine Grenzfrequenz im kHz-Bereich ausgelegt sein, was mit einem Piezoelement gerade noch möglich ist.

The correction can be calculated or determined electronically and used for additional compensation by means of an actuating element (piezoelectric element) at D2.

• The printing unit would be adjusted in this case directly by a piezoelectric element in its height. The adjustment time must fit into the overall process and must not disturb it.
• This happens after measuring the size H2 and before printing. In order to keep the measurement error as small as possible, the measurement time of H2 should take place immediately before the printing time.
• If, for example, one millisecond of time is left for measuring and setting, the mechanical system must be designed for a cut-off frequency in the kHz range, which is just possible with a piezo element.

Instead of just two pressure units (as in FIG. 1 shown) can also be provided three, four or more printing units, arranged overlapping to a printing line and used and controlled according to the invention. The overlap area of a middle printing unit of the printing line would thus be divided into two parts: arranged once to one side and once to the other neighboring printing unit (as in FIG FIG. 1 shown). In addition, it can also be provided that a plurality of printing lines (from at least two laterally arranged printing units) are arranged consecutively in the conveying direction and that the individual printing lines print different colors, eg CMYK printing lines for four-color printing.

LIST OF REFERENCE NUMBERS

1

contraption

2

print image

3

object

4

delivery unit

5

conveying direction

6

Plate

7

measuring mark

8th

control device

9

jet

10

Piezo actuator

11

Muliplexer

A1

first section

A2

second part

D1

first inkjet printing unit

D2

second ink jet printing unit

D3

third inkjet printing unit

G1

Just

G2

Just

H1

first position value

H2

second position value

L

Overlap area

M1

first measuring unit

M2

second measuring unit

P1

first position

P2

second position

R1

first printing series

R2

second print row

x

direction

Claims (7)

A method for producing a printed image on an object to be printed, wherein for printing the object (3) has a first ink jet printing unit (D1) with a first field of ink jet nozzles (F1) and a second ink jet printing unit (D2) with a second Field of ink jet nozzles (F2) and for conveying the object (3) in a conveying direction (5) a conveyor unit (4) are used, wherein the first field (F1) and the second field (F2) substantially perpendicular to the conveying direction ( 5) and partially overlap in an overlap area (L), with the steps: Printing a first section (A1) of the printed image (2) with the first printing unit (D1) at a first position (P1), - conveying the object (3) from the first position (P1) to a second position (P2) spaced from the first position (P1), and Printing a second section (A2) of the printed image (2) with the second printing unit (D2) at the second position (P2), characterized by the further steps: Measuring a first position value (H1) of the object (3) at the first position (P1) and a second position value (H2) of the object (3) at the second position (P2), - Determining a change in position (Delta_H) of the object (3) substantially perpendicular to the conveying direction (5) using the first and the second position value (H1, H2), and Compensation of the change in position (Delta_H) during printing of the second section (A2) by essentially seamless printing of the second section (A2) on the first section (A1) using a number of nozzles (9) within the overlapping zone corresponding to the position change Area (L) of the second field (F2) and a complementary number of nozzles outside the overlap area (L) of the second field (F2). Method according to claim 1,
characterized,
in that a mark (7) is detected on the object (3) or on the conveyor unit (4) when measuring the two position values (H1, H2). Method according to claim 1,
characterized,
that the mark (7) with the first printing unit (D1) is printed. Method according to claim 1,
characterized,
that the object (3) is a three-dimensional body and the printed image (2) is produced on its outer surface. Method according to claim 1,
characterized,
that the second ink jet printing unit (D2) for compensating for a change in position of the object, whose value is smaller than the printing resolution of the second printing unit (D2), in addition undergoes a position change. Method according to claim 5,
characterized,
that the additional change in position is effected by a piezo-actuator (10). Method according to claim 1,
characterized,
in that a control unit (8) is used which determines and controls the nozzles (9) within the overlap area (L) of the second panel (F2).

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