CN115071277A

CN115071277A - Method for cleaning a print head for ink jet printing

Info

Publication number: CN115071277A
Application number: CN202210257935.2A
Authority: CN
Inventors: A·米勒
Original assignee: Heidelberger Druckmaschinen AG
Current assignee: Heidelberger Druckmaschinen AG
Priority date: 2021-03-16
Filing date: 2022-03-16
Publication date: 2022-09-20
Anticipated expiration: 2042-03-16
Also published as: CN115071277B; DE102021106328B4; DE102021106328A1

Abstract

The invention relates to a method for cleaning a printing head for inkjet printing, having at least one printing nozzle (5) and a piezoelectric actuator (6) associated with the printing nozzle, having the steps: providing a cleaning device (10) with an ultrasonic actuator (14) and actuating the ultrasonic actuator during cleaning, characterized by the steps of: controlling (15) the piezoelectric actuator (6) during cleaning, wherein the piezoelectric actuator is controlled in coordination with the controlling (16) of the ultrasonic actuator (14). The invention advantageously makes it possible to improve the cleaning of the print head using ultrasound and to avoid damage to the print head.

Description

Method for cleaning a print head for ink jet printing

Technical Field

The present invention relates to a method for cleaning a print head for inkjet printing.

The invention is in the field of graphic industry technology and in this case in particular in the field of industrial, i.e. high-throughput Inkjet printing (Inkjet), on flat substrates, i.e. fine droplets of liquid ink are applied in an image-wise manner by means of a print head to a sheet-like, web-like, foil-like or label-like printing substrate, preferably made of paper, cardboard, plastic, metal or composite material.

Background

Each print head of a printing press usually has a plurality of individually controllable printing nozzles. The nozzles are usually arranged parallel or inclined to the direction of transport of the printing material in a nozzle row or in a plurality of nozzle rows. Each nozzle produces an ink drop when actuated. If the nozzle is permanently actuated, it prints a visible line in the ink color on the substrate.

The print head and in particular its nozzle plate may become contaminated and therefore the print head must be cleaned from time to time. For this purpose, it is known to use automatic cleaning devices. It is also known to use cleaning liquids here. It is also known to improve the cleaning process by using ultrasound.

However, in practice, the use of ultrasound has been shown to be not without problems and in extreme cases can lead to damage to the print head and in particular to the sensitive piezoelectric actuators thereof.

EP997290a1 discloses a method for cleaning with ultrasound in the field of ink-jet printing. This is also true of EP2955027a 1.

DE102020105736a1 discloses cleaning of inkjet print heads using ultrasound. This document also discloses that the meniscus pressure in the print head can be varied during cleaning (similar to so-called cleaning): from pure pumping to rinsing of the cleaning solution. However, this document does not mention any further details of the measure and does not describe what should be noted here either.

Disclosure of Invention

The object of the present invention is to provide an improvement over the prior art, which improves the cleaning of the print head, in particular using ultrasound, and thereby prevents damage to the print head.

Solution of the stated object according to the invention

According to the invention, this object is achieved by a method having the features of the preferred embodiments.

Advantageous and therefore preferred further developments of the invention emerge from the alternative embodiments and from the description and the drawings.

The invention relates to a method for cleaning a print head for inkjet printing, having at least one print nozzle and a piezoelectric actuator assigned to the print nozzle, having the steps: providing a cleaning device with an ultrasonic actuator and actuating the ultrasonic actuator during cleaning, characterized by the steps of: controlling the piezoelectric actuator during cleaning, wherein the piezoelectric actuator is controlled in coordination with the controlling of the ultrasonic actuator.

Advantageous configurations and effects of the invention

The invention advantageously makes it possible to improve the cleaning of the print head using ultrasound and to avoid damage to the print head.

In solving the problem, it was found within the framework of experiments that in ultrasonic cleaning without damaging the print head, the solution window for the control parameters of the ultrasonic actuator is very small and therefore greatly limits the cleaning efficiency: because each print head has a different resonant or sensitive frequency, different parameters are required for each print head (or for each ink used); passive piezos in the print head are excited into motion together by active ultrasonic actuators, possibly falling into resonance and thereby being damaged; furthermore, by such generated and undesired movements of the piezo-electric device in the print head, undesired voltages are generated, which may damage the drive electronics of the piezo-electric device.

According to the invention, the piezoelectric actuator in the print head does not remain passive or inactive during cleaning, but is likewise actuated, that is to say it is active (within the framework of its actuation) -at least partially superimposed on the movement of the ultrasonic actuator. By the inventive coordination between the actuation of the ultrasonic actuator (of the cleaning device) and the piezoelectric actuator (of the printing head), damage and the associated costs can be prevented. Accordingly, the coordination is carried out in such a way that damage to the print head and in particular to the piezoelectric actuators of the print head is avoided. This coordination is carried out in particular in such a way that the piezoelectric actuator does not execute movements and/or vibrations that damage itself and/or other piezoelectric actuators during the ultrasonic cleaning. The coordination can take place synchronously (or synchronously with one another; or synchronously).

In the prior art, for example, "cleaned" (gepured) "during ultrasonic cleaning. However, this is not a coordinated control, since the "cleaning" process is carried out here only with ultrasound at a certain time during cleaning and the process can of course lead to damage.

Development of the invention

The following describes an embodiment of the invention (shortly: embodiment).

One development may be characterized in that the actuation of the piezoelectric actuator is coordinated in antiphase with the actuation of the ultrasonic actuator.

The inverted phase actuation effectively prevents undesired damage to the print head or its piezoelectric actuators. A harmful overpressure in the print head can be effectively prevented. This anti-phase coordination effectively prevents the piezoelectric actuator from passively vibrating together, since the piezoelectric actuator actively executes an anti-motion. In this context, "antiphase" means that the piezoelectric actuator is simultaneously actuated such that it actively executes a movement or oscillation which is in the opposite direction to the passive movement or oscillation (transmitted by the active ultrasonic actuator). In the optimal case of optimal coordination, the piezoelectric actuator then does not execute a movement or oscillation, but in addition at least one strongly reduced movement or oscillation.

In other words, one development may be characterized in that the piezoelectric actuator is controlled in phase opposition to the control of the ultrasonic actuator in such a way that passive oscillation of the piezoelectric actuator is avoided.

One development may be characterized in that the actuation of the piezoelectric actuator is coordinated in phase opposition and with a phase shift with respect to the actuation of the ultrasonic actuator.

This phase shift advantageously allows a brief setting of an intensified fluid flow (ink, cleaning agent) directly in the inlet of the printing nozzle, which specifically removes dirt and corresponding particles in this extremely sensitive region and thus improves the cleaning effect. In order to achieve a particularly good cleaning effect in the region of the printing nozzles, the piezoelectric actuators in the print head can even be actuated in phase for a short time in order to achieve a particularly large fluid flow in this region. However, so short that it does not cause damage to the piezoelectric actuators or their drive electronics in the printhead.

That is, one development may be characterized in that the actuation of the piezoelectric actuator and the actuation of the ultrasonic actuator are first coordinated in phase and then in phase opposition.

The pulse length of the actuation of the piezoelectric actuator can be varied, if necessary, in order to achieve the desired result of cleaning effect and protection against damage or destruction.

The features and feature combinations (in any combination with one another) disclosed in the above technical field, summary and development paragraphs and in the following example paragraphs constitute further advantageous developments of the invention.

Drawings

The figures show preferred embodiments and developments of the invention. In the figures, features that correspond to each other are provided with the same reference numerals. Reference numerals repeated in the drawings have been partially omitted for clarity.

FIG. 1 shows an apparatus in carrying out a preferred embodiment of the method of the present invention;

fig. 2 and 3 show diagrams of preferred embodiments of the method of the invention.

Detailed Description

Fig. 1 shows a printing machine 1, in particular an inkjet printing machine, for printing a printing material 2, in particular paper, cardboard or foil, comprising at least one printing head 3, preferably a plurality of printing heads. Each print head of the printer has a so-called nozzle plate 4, in which a plurality of printing nozzles 5 are formed (as corresponding openings of the nozzle plate). Each nozzle is assigned an actuator 6 which has a piezo element that can be driven into motion and/or oscillation and is therefore referred to as a piezo actuator. During printing, the actuators are controlled by the digital computer 7 in such a way that the printing nozzles eject the ink 8 as ink drops and thereby produce a printed image on the transported printing material. Fig. 1 also shows that dirt 9 can adhere to the nozzle plate or dirt can enter the printing nozzle.

Fig. 1 shows: the print head 3 is not in the printing state, but during cleaning. Here, the cleaning device 10 is positioned adjacent to the nozzle plate 4, for example below the nozzle plate. This positioning can be performed in such a way that the cleaning device performs a movement 11 towards the print head, or vice versa.

The illustrated cleaning device 10 comprises a chamber 12, which is preferably configured in a housing, in which a cleaning liquid 13 is received or stored. Furthermore, the cleaning device comprises an actuator 14 which generates ultrasound and is referred to as an ultrasonic actuator. The ultrasonic actuator may also be a piezoelectric actuator. The ultrasonic actuator can be arranged, for example, on or in the floor of the room and is preferably likewise controlled by the digital computer 7 for cleaning. Ultrasound is generated during cleaning and is transmitted to the cleaning fluid. The chamber is partially open, i.e. has an opening 12a, preferably on the upper side of the chamber.

During cleaning, the cleaning liquid 13 contacts the nozzle plate 4 in the region of the openings 12a and cleans it with ultrasonic support. Furthermore, the printing nozzle 5 and preferably also the interior thereof is cleaned, for which purpose a cleaning liquid is introduced into the printing nozzle, for example actively pressed or sucked into the nozzle. In this way the dirt 9 is removed.

According to the invention, the actuation of the piezoelectric actuator 6 or of the piezoelectric actuators during cleaning takes place in coordination with the actuation of the ultrasonic actuator 14.

Fig. 2 shows an example of actuation for this coordination. The controlled amplitude a is recorded in the diagram shown as a function of time t. The upper curve 15 shows the actuation of the piezoelectric actuator 6 and the lower curve 16 shows the actuation of the ultrasonic actuator 14. These two curves are shown simplified and preferably form respective sequences of rectangular signals (each having a high level and a low level). The zero line can preferably be assumed individually for each curve at the level of the low level. It can be seen that the actuation of the two actuators 6 and 14 is preferably coordinated in phase opposition: when the ultrasonic actuator 14 is actuated (or strongly actuated), the piezoelectric actuator is always not actuated (or weakly actuated). What is achieved in this way is that the piezoelectric actuator 6 supports the cleaning process and at the same time prevents the ultrasonic actuator 14 from damaging the piezoelectric actuator 6. The latter means that: the actuation of the piezoelectric actuator and the ultrasonic actuator is preferably controlled in phase opposition such that passive oscillation of the piezoelectric actuator is avoided.

Fig. 3 shows a further example of coordinated actuation in a diagram similar to fig. 2. It can be seen that the piezoelectric actuator 6 is preferably driven in phase opposition to the driving of the ultrasonic actuator 14 and in coordination with the phase shift 17.

List of reference numerals

1 printing machine

2 printing material

3 printing head

4 nozzle plate

5 printing nozzle

6 (of printing nozzles) piezoelectric actuator

7 computer

8 ink

9 dirt, e.g. particles

10 cleaning device

11 movement

12 chambers

12a opening

13 cleaning liquid

14 ultrasonic actuator (of cleaning device)

15 curves: driving and controlling of piezoelectric actuator

Curve 16: driving and controlling of ultrasonic driver

17 phase shift.

Claims

1. A method for cleaning a print head for inkjet printing, the print head having at least one print nozzle (5) and a piezoelectric actuator (6) assigned to the print nozzle, the method having the steps of:

a cleaning device (10) with an ultrasonic actuator (14) is provided, and

the ultrasonic actuator is actuated during cleaning,

the method is characterized by comprising the following steps:

controlling (15) the piezoelectric actuator (6) during cleaning, wherein the piezoelectric actuator is controlled in coordination with the controlling (16) of the ultrasonic actuator (14).

2. Method according to claim 1, characterized in that the piezoelectric actuator (6) is driven in phase opposition coordination with the driving (16) of the ultrasonic actuator (14).

3. Method according to claim 2, characterized in that the piezoelectric actuator (6) is controlled in phase opposition with the control (16) of the ultrasonic actuator (14) in such a way that passive oscillation of the piezoelectric actuator is avoided.

4. Method according to claim 2 or 3, characterized in that the piezoelectric actuator (6) is driven in phase opposition to the driving (16) of the ultrasonic actuator (14) and in phase shift (17) coordination.

5. Method according to any of claims 2 to 4, characterized in that the actuation (16) of the piezoelectric actuator (6) and the ultrasonic actuator (14) is actuated first in phase and then in phase opposition.