CN111791594A

CN111791594A - Ink jet print head cleaning with ultrasonic waves

Info

Publication number: CN111791594A
Application number: CN202010274039.8A
Authority: CN
Inventors: M·波斯特尔斯; S·布奇科; M·沃尔夫
Original assignee: Heidelberger Druckmaschinen AG
Current assignee: Heidelberger Druckmaschinen AG
Priority date: 2019-04-09
Filing date: 2020-04-09
Publication date: 2020-10-20
Anticipated expiration: 2040-04-09
Also published as: CN111791594B; DE102020105736A1

Abstract

The invention relates to a device for cleaning a printing head (5) of an inkjet printer (7), comprising a sound source (14) and an application unit (9, 19), wherein the application unit (9, 19) applies a cleaning liquid to a surface (18) of the printing head (5) such that the sound source cleans the printing head in a contactless manner by means of correspondingly introduced sound waves, characterized in that the device (21) is a mobile device which is designed such that it cleans the printing head (5) in the installed state in the inkjet printer (7).

Description

Ink jet print head cleaning with ultrasonic waves

Technical Field

A cleaning apparatus for maintaining an inkjet print head is disclosed.

The present invention is in the field of ink jet printing technology.

Background

In inkjet printers, printing heads are used, which usually use printing nozzles, which may also be referred to as printing beams (Druckbalken), arranged in rows. Each printing head prints ink of a specific printing color. The more different print heads an inkjet printer has, the more different printing colours can be used. In order to ensure constant, high-value printing results in terms of quality, the printing nozzles of all the printing heads used must always operate with constant performance. For this reason, regular maintenance of the print head is necessary. These maintenance steps mainly include cleaning of the inkjet print head, for example, to prevent dried-out ink residues and other contaminants (e.g., dust particles, etc.) from adhering to the nozzle channels of the printing nozzles. Such contamination often results in reduced performance of the individual print nozzles of the print head (or even failure of these print nozzles). In this case, individual defective printing nozzles or printing nozzles which are switched off in the event of too strong a performance reduction can also be compensated for by a defined compensation method. However, if too many printing nozzles are involved, the print heads have to be replaced, which results in high costs and the short operating duration of the inkjet printer involved. In addition to the prospective maintenance of the printing heads, therefore, the printing heads which are no longer available are reprocessed by a corresponding cleaning process, which is also a more common application.

Different approaches exist in the prior art for cleaning inkjet print heads. For example, one approach is to perform contactless inkjet head cleaning by means of a cleaning device that ejects, sucks and then flushes the print head with a cleaning agent. This is typically triggered periodically by the operator when the operator sees that a certain print head is necessary for cleaning. Another approach is a cleaning device which wipes the inkjet print head by means of a cloth and thus cleans it. However, these solutions have the disadvantage that the cleaning result is not optimal in many cases.

Other solutions consist in disassembling the print head, which can then be cleaned in a defined cleaning device by means of ultrasound. Such a solution is known, for example, from european patent application EP 09997290 a 1. Furthermore, improved cleaning results can be achieved when the printing head is immersed in a bath with a cleaning liquid in addition to the ultrasonic cleaning. Such a cleaning device is in turn known from european patent application EP 2955027 a 1. However, a disadvantage in these solutions is that in all cases this involves stationary equipment, and therefore the inkjet print head has to be removed from the machine, cleaned and reloaded. This is very laborious and therefore results in a time and corresponding cost during which the printing press cannot be operated. Furthermore, there is a risk that the inkjet print head may be damaged during mounting and dismounting.

Disclosure of Invention

It is therefore an object of the present invention to provide a system for cleaning inkjet print heads which operates more quickly and/or more fully than the cleaning systems known from the prior art.

This object is achieved by a device for cleaning a printing head of an inkjet printer, comprising a sound source and an application unit, wherein the application unit applies a cleaning liquid to a surface of the printing head, so that the sound source cleans the printing head contactlessly by means of correspondingly introduced sound waves, characterized in that the device is a mobile device which is designed such that it cleans the printing head in the installed state in the inkjet printer. The cleaning device is compact in such a way that it can be placed directly on the printing head in the installed state in the inkjet printer. The application unit then surrounds the surface of the printing head with a cleaning liquid, so that the sound source can clean the printing head contactlessly by means of the correspondingly introduced sound waves. Most easily, the device according to the invention can be implemented as a movable cleaning device, which is then locked and applied at a corresponding location in the inkjet printer for cleaning each inkjet print head. Naturally, it is alternatively also possible for the respective cleaning device to be mounted directly fixed in the inkjet printer, in which the inkjet print head is then cleaned. This is much more comfortable for the user of the ink jet printer, but increases the constructional expenditure of the printer.

Advantageous and therefore preferred embodiments of the device according to the invention result from the dependent claims and from the description with the associated drawings.

In this case, a preferred embodiment of the device according to the invention provides that the application unit has an infeed line via which the application unit is permanently supplied with the cleaning liquid, and that the infeed line feeds a volume flow of the cleaning liquid which is so large that the space between the application unit and the surface of the printing head is completely filled with the cleaning liquid. This is necessary in order to guide out the dirt particles (for example dust or dried-out ink residues) which are removed by means of cleaning in each case, and thus to improve the cleaning result. Furthermore, for an optimal cleaning result, it is necessary that only cleaning liquid and no air be present between the application unit and the surface of the printing head, since otherwise the sound waves of the sound source cannot exert an optimal cleaning action.

In this case, a further preferred development of the device according to the invention provides that the application unit is a cleaning basin (Wanne) of corresponding depth, wherein the cleaning basin is filled with a cleaning liquid and has an opening, the size of which is adapted to the surface of the printing head to be cleaned, and a gap of a defined height exists between the surface of the printing head and the opening, through which gap the cleaning liquid flows out. In this case, the cleaning basin should be completely filled with the cleaning liquid, so that the gap (through which the cleaning liquid flows out) is correspondingly filled with the cleaning liquid and no air remains between the sound source and the surface to be cleaned of the inkjet printing head. The size of the opening here determines the surface that can be cleaned at once by means of the device according to the description. If this surface is smaller than the entire surface of the print heads to be cleaned in each case, the cleaning device must be placed several times per print head.

In this case, a further preferred development of the device according to the invention provides that a collecting basin is arranged next to the cleaning basin, which collecting basin has an outflow opening and which collects the outflowing cleaning liquid and is connected to the feed line of the cleaning basin. Preferably, a filter (or filter system) is then connected downstream of the collection basin, which filter (or filter system) removes the cleaning liquid from the removed contaminating particles, so that the respective purified cleaning liquid can be reused via a feed line connected to the cleaning basin. This increases the efficiency of the device according to the invention, since the cleaning liquid can be reused accordingly. Naturally, the filter should be replaced (or cleaned itself) at regular intervals, i.e. before or after each cleaning process.

In this case, a further preferred development of the device according to the invention provides that a pressure sensor is attached to the cleaning basin, which pressure sensor measures the level of the cleaning liquid in the cleaning basin. As soon as the cleaning basin is completely filled with cleaning liquid and no more air is present between the sound source and the surface to be cleaned of the inkjet print head and thus the cleaning process can be started (or started automatically), the operator can be very easily shown by means of this level indication.

A further preferred development of the device according to the invention consists in that the application unit is a plate and that a gap of defined height is present between the surface of the printing head and the opening, through which gap the cleaning liquid flows out, wherein the gap is filled with the cleaning liquid via the supply line through the slot nozzle. This is an alternative embodiment variant in which the application unit does not clean the basin but merely a plate element with slit nozzles, via which cleaning liquid is filled into the space between the plate element and the surface of the printing head. The advantage of this variant embodiment is a much more compact design.

A further solution to the proposed object is a method for cleaning a print head of an inkjet printer by means of the device according to the invention, characterized in that during the cleaning process the meniscus pressure (meniskusdrive) in the print head is changed in such a way that the cleaning liquid is sucked into the print head and is discharged again together with the ink residues. By means of this change in the meniscus pressure in the printing head, a so-called Purging process (purge-Vorgang) is simulated, by means of which the ink residues remaining in the printing head can be reliably eliminated. This increases the efficiency of the method according to the invention, since the print head is thereby cleaned not only passively by the cleaning device, but rather by an active intake and discharge of cleaning fluid, which improves the cleaning action compared to purely passive methods.

In this case, a preferred embodiment of the method according to the invention is to operate the sound source with ultrasound or megasonic waves (Megaschall), the frequency of which is variable. Whether ultrasonic or megasonic waves are used depends on the characteristics and degree of contamination of the respective print head to be cleaned. Furthermore, different cleaning actions can be achieved by means of frequency changes, which cleaning actions are also adapted to the respective degree of contamination of the inkjet print head.

In this case, a preferred embodiment of the method according to the invention is that different cleaning liquids can be used depending on the print head to be cleaned. Here, which cleaning liquid is used in which cleaning process also depends on the configuration of the print head to be cleaned and the degree of contamination. Since only one liquid should be used for each cleaning process (i.e., different cleaning liquids should not be mixed with one another) and the corresponding effort is associated with the replacement of the cleaning liquids, the selection of the cleaning liquids to be used in each case should be taken into account by the user.

Drawings

The invention itself and the structurally and/or functionally advantageous embodiments of the invention are explained in more detail below with reference to the attached drawings, according to at least one preferred exemplary embodiment. In the drawings, elements corresponding to each other are provided with the same reference numerals, respectively.

The figures show:

fig. 1 shows an example of a configuration of a sheet inkjet printer used;

figure 2 shows a preferred embodiment of the cleaning device in cross-section;

FIG. 3 shows a print head surface to be cleaned in a top view;

figure 4 shows an alternative embodiment of the cleaning device in cross-section;

fig. 5 shows a schematic flow of the method according to the invention.

Detailed Description

A preferred application area of the embodiment variant is an inkjet printer 7. Fig. 1 shows an example of a basic configuration for a machine 7 of this type, which machine 7 comprises a feeder 1 for feeding a print substrate 2 into a printing unit 4 as far as a delivery unit 3, in which printing unit 4 the print substrate 2 is printed by a print head 5. Here, a sheet-fed ink-jet printer 7 is involved, which sheet-fed ink-jet printer 7 is controlled by a control computer 6. During operation of such a printing machine 7, individual printing nozzles in the printing head 5 of the printing unit 4 may fail, as already explained.

Fig. 2 shows a cleaning device 21 according to the invention, which cleaning device 21 has a cleaning basin 9 filled with a cleaning liquid, to which cleaning basin 9 an ultrasonic drive 14 is fastened. The cleaning basin 9 has a precisely defined edge with a defined gap 11 to the surface 18 of the print head 5 to be cleaned. The basin 9 is continuously supplied with cleaning liquid via the feed line 12. Depending on the gap 11 and depending on the inclination Δ h of the printing head, the volume flow of the cleaning liquid must be so great that the space between the surface 18 to be cleaned and the ultrasonic drive 14 (or the gap 11) is completely filled with liquid.

The cleaning liquid flowing through the gap 11 is led via the outflow opening 13 into the collecting basin 10. From there, the cleaning liquid can be conducted out and filtered via a further outflow opening 13. After the filtration, the cleaning liquid is then conveyed into the cleaning basin 9 again. By means of the pressure sensor 15 it can be checked that: whether the liquid level is sufficient.

Fig. 3 shows a corresponding surface view of the print head 5 to be cleaned. Here, V_{Head with a rotatable shaft}Indicating the direction of cleaning. The printing heads 5 are preferably arranged together in the form of a printing bar 16, wherein a small gap 17 remains between the individual printing heads 5, in order to be able to easily replace the printing heads 5. These print heads 5 comprise a plurality of nozzle plates 8 (also referred to as print head mounts), in which nozzle plates 8 the individual printing nozzles of the print heads 5 are arranged in an array. The cleaning basin 9 of the cleaning device 21 should cover a large part of the surface 18 to be cleaned of the print head 5, whereby it is not necessary to place the cleaning device 21 too frequently to clean the entire print beam 16. Ideally, at least one nozzle plate 8 should be covered by a cleaning basin 9.

The cleaning method of the invention itself is schematically illustrated in fig. 5 in short. During cleaning, the meniscus pressure in the print head 5 can be varied: the cleaning liquid is pumped from pure to the point where the cleaning liquid containing the remaining printing ink remains is flushed out again. This process is the standard mode of operation of the print head 5 for cleaning. This is referred to as "purging" and is originally carried out with printing ink, but can also be used for cleaning purposes with the aid of the cleaning device 21. Furthermore, the printing beams 16 should advantageously be moved during cleaning, so that one to all print heads 5 can be cleaned in sequence. In this case, less movement of the cleaning device 21 is necessary. It goes without saying, however, that any choice of print heads 5 to be cleaned is also possible. For this purpose, after the cleaning of the print head 5 has ended, the supply of cleaning liquid to the cleaning device is interrupted and moved towards the next print head 5. The cleaning bowl 9 of the cleaning device 21 is moved along the print head 5 to be cleaned in each case, or is correspondingly locked and then displaced to the next print head 5, which plays a secondary role for the function as a basis. Both of the above are contemplated.

The diameter of the cleaning basin 9 is adapted to the surface 18 to be cleaned. In the case of an arrangement of the print heads 5 adjacent to one another, the gap between the nozzle plates 8 in the case of a volumetric flow must be taken into account. This can be achieved, for example, by a potential energy tank (potential) or a pressure-regulated pump. In order to ensure that the cavitation (Kavitation) is always able to reach these nozzle plates 8, the change in flow conditions should then be kept as small as possible.

Furthermore, the ultrasonic frequency of the ultrasonic driver 14 can be varied during cleaning in order to achieve different cleaning actions.

With the cleaning device 21 according to the invention, it is also possible to clean the printing head 5, which is inserted obliquely into the inkjet printer 7, with the aid of ultrasonic waves, since the small ultrasonic cleaning unit 21 does not need to have a complete bath of cleaning liquid, as in the case of stationary cleaning devices. Furthermore, the cleaning device 21 achieves better cleaning results than other known cleaning methods.

In addition to the preferred embodiment variants described, various alternative embodiments exist. Instead of ultrasound, it is possible to work with the aid of megasonic waves. Different cleaning liquids can also be used depending on which characteristics the print heads 5 to be cleaned have and how high their degree of contamination is.

In a further alternative embodiment with a cleaning basin 9, the ultrasonic drive 14 can also be mounted in direct liquid contact with the basin 9 in a vibration-decoupled manner, which leads to a higher efficiency and better protection of the abutting components. The entire arrangement 21 is then supported either vibration-decoupled on the printing head 5 or by its own guide (for example with respect to the machine frame or the path guide).

Here, the cleaning device 21 may be implemented not only as a small-sized movable type cleaning device but also fixedly installed in the inkjet printer 7. More precisely, a fixedly mounted cleaning device is suitable for use in larger inkjet printers 7, since such a cleaning device represents an increased constructional expenditure, which is reflected in costs. For this reason, these fixedly mounted cleaning devices can naturally be used much more comfortably in terms of application, since here the displacement and the renewed locking of the movable cleaning device is dispensed with.

Fig. 4 also shows an alternative, more compact design of the cleaning device 21. Here, instead of the basin 9, a plate 19 with an ultrasonic drive 14 is provided, which ultrasonic drive 14 has a small gap 11 of 0.1mm to 1mm below the print head 5. The gap 11 is filled with a cleaning liquid via the slot nozzle 20. This is advantageous in particular in inkjet printers 7, in which there is only a small amount of space for accommodating the cleaning device 21.

List of reference numerals

1 feeder

2 Current substrate/Current sheet

3 material collector

4 ink-jet printing mechanism

5 ink jet print head

6 computer

7 ink jet printer

8 nozzle plate

9 cleaning basin with cleaning liquid

10 collecting basin

11 gap

12 inflow opening

13 outflow port

14 ultrasonic driver

15 pressure sensor/liquid level sensor

16 printing beam

17 gap between individual print heads in a print beam

18 print head region encompassed by the cleaning basin

19 application panel for cleaning liquids

20 slit nozzle in an application plate

21 cleaning device

Measurement of delta h print head tilt state

V_{Head with a rotatable shaft}Direction of cleaning

Claims

1. An apparatus for cleaning a print head (5) of an inkjet printer (7), comprising a sound source (14) and an application unit (9, 19), wherein the application unit (9, 19) applies a cleaning liquid onto a surface (18) of the print head (5) such that the sound source cleans the print head in a contactless manner by means of correspondingly introduced sound waves,

it is characterized in that the preparation method is characterized in that,

the device (21) is a mobile device, which is implemented to: so that the mobile device cleans the print head (5) in the state of being loaded in the inkjet printer (7).

2. The apparatus as set forth in claim 1, wherein,

it is characterized in that the preparation method is characterized in that,

the application unit (9, 19) has an infeed line (12) via which the application unit is permanently supplied with cleaning liquid, and the infeed line (12) feeds a volume flow of cleaning liquid, which is so large that the space between the application unit (9, 19) and the surface (18) of the printing head (5) is completely filled with cleaning liquid.

3. The apparatus according to any one of the preceding claims,

it is characterized in that the preparation method is characterized in that,

the application units (9, 19) are cleaning basins (9) with corresponding depths,

wherein the cleaning basin (9) is filled with a cleaning liquid and has an opening, the size of which is adapted to the surface (18) to be cleaned of the printing head (5), and

between the surface (18) of the printing head (5) and the opening there is a gap (11) of a defined height, through which cleaning liquid flows out.

4. The apparatus as set forth in claim 3, wherein,

it is characterized in that the preparation method is characterized in that,

clean basin (9) side is other to be installed and is collected basin (10), it has outlet (13) to collect the basin, collect the basin and collect the cleaning solution that flows and with the feeding pipeline (12) of clean basin (9) are connected.

5. The apparatus as set forth in claim 4, wherein,

it is characterized in that the preparation method is characterized in that,

install pressure sensor (15) on clean basin groove (9), pressure sensor measures clean basin groove (9) has the liquid level of cleaning fluid.

6. The apparatus of any one of claims 1 to 2,

it is characterized in that the preparation method is characterized in that,

the application unit (9, 19) is a plate (19) and a gap (11) of a defined height is present between the surface (18) to be cleaned of the printing head (5) and the opening, through which gap cleaning liquid flows out,

wherein the gap (11) is filled with a cleaning liquid via the supply line (12) through the slot nozzle (20).

7. Method for cleaning a print head (5) of an inkjet printer (7) by means of an apparatus (21) according to any one of the preceding claims,

it is characterized in that the preparation method is characterized in that,

the meniscus pressure in the print head (5) is changed during the cleaning process, so that cleaning fluid is sucked into the print head (5) and is discharged again together with ink residues.

8. The method of claim 7, wherein the first and second light sources are selected from the group consisting of,

it is characterized in that the preparation method is characterized in that,

the sound source (14) operates with ultrasonic waves or megasonic waves, the frequency of which can be varied.

9. The method according to claim 7 or 8,

it is characterized in that the preparation method is characterized in that,

different cleaning liquids can be used depending on the print head (5) to be cleaned.