CN111791594B

CN111791594B - Inkjet printhead cleaning by means of ultrasound

Info

Publication number: CN111791594B
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: 2023-07-21
Anticipated expiration: 2040-04-09
Also published as: CN111791594A; 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 onto a surface (18) of the printing head (5) so that the sound source cleans the printing head contactlessly by means of correspondingly induced sound waves, characterized in that the device (21) is a mobile device which is embodied in such a way that it cleans the printing head (5) in the state of being inserted into the inkjet printer (7).

Description

Inkjet printhead cleaning by means of ultrasound

Technical Field

A cleaning apparatus for maintaining an inkjet printhead is disclosed.

The present invention is in the field of inkjet printing technology.

Background

In inkjet printers, printheads are used, which generally employ printing nozzles arranged in a row, which may also be referred to as printing beams (Druckbalken). Here, each print head prints out ink of a defined print color. The more different printheads an inkjet printer has, the more different printing colors can be employed. In order to ensure a constant, high-value printing result 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 mainly include cleaning the inkjet printheads to, for example, prevent dried-out ink residues and other contaminants (e.g., dust particles, etc.) from adhering in the nozzle channels of the printing nozzles. Such contaminants often cause reduced performance of individual printing nozzles of the printhead (or even failure of these printing nozzles). In this case, individual malfunctioning printing nozzles or printing nozzles which are shut off in the event of too great a performance reduction can also be compensated for by a defined compensation mode. However, if too many printing nozzles are involved, the print head must be replaced, which results in high costs and a short operating duration of the inkjet printer involved. Therefore, in addition to the prospective maintenance of the printing heads, the printing heads which are no longer available are reprocessed by means of a corresponding cleaning process, which is also a more common application case.

In order to clean the inkjet print head, different treatments exist in the prior art. For example, one approach is to perform contactless inkjet head cleaning by means of a cleaning device that ejects, draws in a cleaning agent and then flushes the print head. This is typically triggered periodically by the operator when he sees that a certain print head is necessary to be cleaned. Another solution consists in a cleaning device which wipes the inkjet print head by means of a cloth and thus cleans it. However, these solutions are disadvantageous in that the cleaning results are not optimal in many cases.

Other solutions include dismantling 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 099 290A1. Furthermore, improved cleaning results can be achieved when the print head is immersed in a bath with cleaning liquid in addition to ultrasonic cleaning. Such a cleaning device is also known from european patent application EP 29 55 027a 1. However, it is disadvantageous in these solutions that in all cases this involves stationary equipment, and therefore the inkjet print head has to be detached from the machine, cleaned and reloaded. This is very time consuming and thus results in inoperability time and corresponding costs for the printing press. Furthermore, there is a risk of damage to the inkjet print head during loading and unloading.

Disclosure of Invention

The object of the present invention is therefore to create a system for cleaning an inkjet print head that works more quickly and/or more comprehensively 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 embodied in such a way that it cleans the printing head in the state of having been inserted into the inkjet printer. That is, the decisive point of the present device is that the cleaning device is so compact that it can be placed directly onto the print head in the state of being loaded into the inkjet printer. The application unit then encloses the surface of the print head with a cleaning liquid, so that the sound source can clean the print head without contact by means of the correspondingly introduced sound waves. Most easily, the device according to the invention can be implemented as a removable 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 also possible, instead, for the respective cleaning device to be mounted directly stationary in the inkjet printer, in which the inkjet print head is then cleaned. This, while much more comfortable for the user of the inkjet printer, increases the structural costs of the printer.

From the associated preferred embodiments and from the description with the associated drawings, advantageous and therefore preferred developments of the device according to the invention result.

In this case, a preferred development of the device according to the invention provides that the application unit has a supply line via which the application unit is permanently supplied with the cleaning liquid and that the supply line is fed with a volume flow of the cleaning liquid which is so great 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 correspondingly remove dirt particles (e.g. dust or dried-out ink residues) removed by means of cleaning again and thus to improve the cleaning result. Furthermore, for optimal cleaning results, it is necessary that only the cleaning liquid, and not the air, is between the application unit and the surface of the print head, since otherwise the sound waves of the sound source cannot exert an optimal cleaning action.

A further preferred development of the device according to the invention is that the application unit is a cleaning basin (Wanne) having a corresponding depth, wherein the cleaning basin is filled with a cleaning liquid and has openings, the size of which is adapted to the surface of the print head to be cleaned, and a gap of defined height is present between the surface of the print head and the openings, through which the cleaning liquid flows out. The cleaning basin should be completely filled with cleaning liquid, so that the gap (through which the cleaning liquid flows out) is correspondingly filled with cleaning liquid, and no air remains between the sound source and the surface of the inkjet print head to be cleaned. The size of the opening determines the surface that can be cleaned at one time by means of the device according to the illustration. If the face is smaller than the entire surface of the print heads to be cleaned respectively, the cleaning device has to be placed multiple times for each print head.

In this case, a further preferred development of the device according to the invention provides that a collecting basin is mounted next to the cleaning basin, said collecting basin having an outflow opening, said collecting basin collecting the outgoing cleaning liquid and being connected to the supply line of the cleaning basin. It is then preferred that a filter (or filter system) is connected downstream of the collecting basin, which filter (or filter system) removes the removed contaminating particles from the cleaning liquid, so that the corresponding, purified cleaning liquid can be reused via a supply 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 filters should be replaced (or cleaned themselves) 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 is that a pressure sensor is mounted on the cleaning basin, which pressure sensor measures the level of the cleaning liquid in the cleaning basin. Once the cleaning basin is completely filled with cleaning liquid and no more air is present between the sound source and the surface of the inkjet print head to be cleaned, and thus the cleaning process can be started (or automatically started), this level indication can be displayed very easily to the operator.

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 print head and the opening, through which gap the cleaning liquid flows out, wherein the gap is filled with cleaning liquid via the supply line through the gap nozzle. This is an alternative embodiment variant in which the application unit is not a cleaning basin but merely a plate with slit nozzles via which the space between the plate and the surface of the print head is filled with cleaning liquid. The advantage of this embodiment variant is the much more compact design.

A further solution to the proposed task is a method for cleaning the print head of an inkjet printer by means of the device according to the invention, characterized in that the meniscus pressure (Meniskusdruck) in the print head during the cleaning process is changed such 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 meniscus pressure in the print head, a so-called Purging process (purg-Vorgang) is simulated, by means of which residual ink residues in the print head can be reliably eliminated. This increases the efficiency of the method according to the invention, since the print head is thereby not cleaned only passively by the cleaning device, but the cleaning action is improved by the active suction and re-discharge of the cleaning liquid compared to purely passive methods.

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

In this case, a preferred development of the method according to the invention makes it possible to use different cleaning liquids depending on the print head to be cleaned. Here, which cleaning liquid is used in which cleaning process, too, depends on the configuration and the degree of contamination of the print head to be cleaned. 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 outlay is associated with the replacement of the cleaning liquids, the choice of the cleaning liquids to be used respectively should be properly taken into consideration by the user.

Drawings

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

The drawings show:

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

fig. 2 shows a preferred embodiment of the cleaning device in section;

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

FIG. 4 shows an alternative embodiment of the cleaning apparatus in section;

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

Detailed Description

A preferred field of application for the embodiment variant is the 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 to a receiver 3 for feeding a print substrate 2 into a printing unit 4, in which printing unit 4 the print substrate 2 is printed by a printing head 5. In this case, a sheet-fed inkjet printer 7 is involved, the sheet-fed inkjet printer 7 being controlled by a control computer 6. During operation of such a printing machine 7, as already explained, individual printing nozzles in the printing head 5 in the printing unit 4 may malfunction.

Fig. 2 shows a cleaning device 21 according to the invention, which cleaning device 21 has a cleaning basin 9 filled with cleaning liquid, and an ultrasonic drive 14 is fastened to the cleaning basin 9. The cleaning basin 9 has an accurately 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 a supply line 12. Depending on the gap 11 and on the inclination of the print head Δh, the volumetric flow of 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.

Cleaning liquid flowing through the gap 11 is led into the collecting basin 10 via the outflow opening 13. From there, the cleaning liquid can be led out and filtered via a further outflow opening 13. After filtration, the cleaning liquid is then fed back into the cleaning basin 9. 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 Indicating the cleaning direction. The printing heads 5 are preferably arranged together in the form of a printing beam 16, wherein a small gap 17 is left between the individual printing heads 5, so that the printing heads 5 can be easily replaced. The printheads 5 comprise a plurality of nozzle plates 8 (also referred to as printhead mounts), in which nozzle plates 8 the individual printing nozzles of the printheads 5 are arranged in an array. The cleaning basin 9 of the cleaning device 21 should cover a large part of the surface 18 of the printing head 5 to be cleaned, whereby the cleaning device 21 does not have to be arranged too frequently to clean the entire printing beam 16. Ideally, at least one nozzle plate 8 should be covered by a cleaning basin 9.

The cleaning method of the present invention itself is schematically shown in brief in fig. 5. During cleaning, the meniscus pressure in the print head 5 can be varied: from pure suction of the cleaning liquid until the cleaning liquid containing the remaining printing ink residues is flushed out again. This process is the standard mode of operation of the print head 5 for cleaning. This is called "purge" and is originally performed with the aid of printing ink, but can also be used for cleaning purposes with the aid of the cleaning device 21. Furthermore, advantageously, the printing beams 16 should be moved during cleaning so that one to all of the printing heads 5 can be cleaned in sequence. In this case, less movement of the cleaning device 21 is necessary. However, it goes without saying that any choice of print head 5 to be cleaned is also possible. For this purpose, after the cleaning of the print head 5 is completed, the supply of cleaning liquid to the cleaning device is interrupted and moved toward the next print head 5. The cleaning basin 9 of the cleaning device 21 is moved for this purpose along the respective print head 5 to be cleaned or is correspondingly locked and then displaced to the next print head 5, which plays a secondary role for the underlying function. Both of which 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 tank) or a pressure regulating pump. In order to ensure that cavitation is always sufficient for the 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 may be varied during cleaning in order to achieve different cleaning actions.

The cleaning device 21 according to the invention also allows the print head 5, which is inserted obliquely into the inkjet printer 7, to be cleaned by means of ultrasound, since the small ultrasound cleaning unit 21 does not have to have a complete bath of cleaning liquid as in the stationary cleaning device. 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 megasonic waves. Different cleaning liquids may also be used depending on which characteristics the printheads 5 to be cleaned have and how high they are contaminated.

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

The cleaning device 21 can here be implemented not only as a small, mobile cleaning device, but also can be fixedly installed in the inkjet printer 7. Rather, a fixedly mounted cleaning device is suitable for use in larger inkjet printers 7, since such a cleaning device represents an increased structural outlay, which is reflected in costs. For this purpose, these fixedly mounted cleaning devices can naturally be used with great comfort in terms of application, since displacement and re-locking of the movable cleaning device is omitted here.

Fig. 4 also shows an alternative, more compact design of the cleaning device 21. Here, instead of the basin 9, a plate 19 is provided with an ultrasonic drive 14, 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 cleaning liquid via a slit nozzle 20. This is advantageous in particular in an inkjet printer 7 in which there is only a small amount of space for the placement of the cleaning device 21.

List of reference numerals

1 feeder

2 Current printing substrate/current printing sheet

3 receiver

4 inkjet 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 port

13 outflow port

14 ultrasonic driver

15 pressure sensor/level sensor

16 printing beam

17 gap between individual printheads in a print beam

18 print head area comprised by the cleaning basin

19 application plate for cleaning liquid

20 in the applicator plate

21 cleaning apparatus

Measurement of the tilt bit of a Δh print head

V _Head Cleaning direction

Claims

1. An apparatus for cleaning a print head (5) of an inkjet printer (7), the apparatus comprising a sound source (14) and an application unit, wherein the application unit 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 method comprises the steps of,

the device (21) is a mobile device, which is embodied as: so that the movable device cleans the print head (5) in the state of having been loaded into the inkjet printer (7) and so that the meniscus pressure in the print head (5) changes during the cleaning process so that cleaning liquid is sucked into the print head (5) and discharged again together with ink residues, and

the application unit has a supply line (12) via which the application unit is permanently supplied with cleaning liquid and

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

wherein the feed line (12) feeds a volumetric flow of cleaning liquid which is so large that the space between the application Tu Shanyuan and the surface (18) of the printing head (5) is completely filled with cleaning liquid, depending on the gap (11) and on the tilt position (Δh) of the printing head (5).

2. The apparatus according to claim 1,

it is characterized in that the method comprises the steps of,

the application unit is a cleaning basin (9) with a corresponding depth,

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

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

3. The apparatus according to claim 2,

it is characterized in that the method comprises the steps of,

a collecting basin (10) is arranged beside the cleaning basin (9), and is provided with an outflow opening (13) for collecting the outflow cleaning liquid and is connected with a supply pipeline (12) of the cleaning basin (9).

4. An apparatus according to claim 3,

it is characterized in that the method comprises the steps of,

a pressure sensor (15) is mounted on the cleaning basin (9), and the pressure sensor measures the liquid level of the cleaning liquid in the cleaning basin (9).

5. The apparatus according to claim 1,

it is characterized in that the method comprises the steps of,

the application unit is a plate (19), wherein the gap (11) is filled with cleaning liquid via the supply line (12) via a slit nozzle (20).

6. Method for cleaning a print head (5) of an inkjet printer (7) by means of an apparatus (21) according to any one of claims 1 to 5,

it is characterized in that the method comprises the steps of,

meniscus pressure in the print head (5) changes during the cleaning process so that cleaning liquid is drawn into the print head (5) and is expelled again with the ink residues.

7. The method according to claim 6, wherein the method comprises,

it is characterized in that the method comprises the steps of,

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

8. The method according to claim 6 or 7,

it is characterized in that the method comprises the steps of,

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