EP2955027A1

EP2955027A1 - Device and method for cleaning inkjet printheads

Info

Publication number: EP2955027A1
Application number: EP13874401.6A
Authority: EP
Inventors: Francisco Javier GAYA FUENTES
Original assignee: Personas y Tecnologia SL
Current assignee: Personas y Tecnologia SL
Priority date: 2013-02-08
Filing date: 2013-10-29
Publication date: 2015-12-16
Anticipated expiration: 2033-10-29
Also published as: EP2955027A4; PL2955027T3; TR201901126T4; CN104321198B; CN104321198A; IN2014KN00873A; ES2492090A1; ES2492090B1; ES2709055T3; BR112015019025B1; BR112015019025A2; WO2014122336A1; EP2955027B1

Abstract

A system for cleaning inkjet printing heads that is intended for cleaning these heads by means of a pressurized fluid, selected between a liquid solvent and a gaseous fluid, such as air. The pressurized fluid passes through various spaces inside the ink printing heads, through which ink normally flows when sprayed, in such a way that this path is taken in two circulation directions for much more effective cleaning.

For cleaning, the ink printing head is placed inside a main tub, in such a way that the lower portion of the ink printing head is soaked in a liquid solvent contained within said first tub, further including, among other elements, a level control device that regulates the optimal height of the liquid solvent inside the main tub.

Description

SUBJECT MATTER OF THE INVENTION

The present invention, as expressed in the heading of this specification, relates to a system and method for cleaning inkjet printing heads used in the industrial decoration of various items.
Industrial decoration is applied to ceramics and other products where the surfaces to be decorated are large, and uses inks which, due to their chemical composition, tend to block up the printing heads with relative frequency.
As the cost of these printing heads is high, it is important to have optimal means for cleaning inside of them to unblock them, which constitutes an undeniable advantage.
As such, the aim of the invention is to achieve optimal cleaning of these printing heads, with a high level of efficiency and a low cost.

BACKGROUND OF THE INVENTION

At present, when an ink printing head gets blocked up, the common solution consists of disconnecting the ink inlet tube and using a syringe to apply a liquid solvent, usually of the organic sort, which, as it passes through the inside and exits through the spraying area, where several piezoelectric devices are found, carries away the ink or other matter responsible for the blockage.
Nevertheless, the method described above has the disadvantage of being a rather ineffective against serious and complicated blockage.

DESCRIPTION OF THE INVENTION

In order to meet the aims and avoid the disadvantages mentioned in the preceding paragraphs, this invention proposes a system and method for cleaning inkjet printing heads, where the temperature of the solvent used in cleaning is controlled, as well as the pressure of the solvent and the pressure of an air fluid that takes part in cleaning in combination with the solvent. The cleaning times are also controlled, depending on the type of head and the type of ink used by the printing head, and also depending on the amount of blockage.
The system of the invention, then, is intended for cleaning, with a solvent, various spaces inside the ink printing heads, through which ink normally flows when sprayed; of note is that the path of at least one pressurized fluid that passes through the internal spaces of the heads is taken in two circulation directions, thus cleaning more effectively.
It comprises:

A main tub, inside of which an ink printing head is housed for cleaning, in such a way that a lower spraying portion of the ink printing head is continuously soaking in a liquid solvent contained within the main tub.
A level control device that regulates the optimum height, acting as an overflow for the liquid solvent contained within the main tub, which liquid solvent covers the lower portion of the printing head.
A passage device into which the ink printing head fits so as to match up with the ink outlet holes.
A direction switch, which selects the circulation direction of a solvent fluid, selected between a gaseous fluid and a liquid solvent; wherein this fluid circulates through various spaces inside the ink printing head through a first fluid inflow/outflow passage in a first circulation direction, and through a second fluid inflow/outflow passage in a second circulation direction.
A first pipe that connects the first passage to the inlet of the ink printing head.
A second pipe that connects the second passage to the passage device which the ink printing head fits into.
A level tank associated with a drain valve, wherein the level tank receives the excess solvent emptied from the main tub through the level control device.

The system of the invention further comprises:

A main drum for new solvent that feeds a first working solvent drum by means of a conduit, in which a second new solvent filter and a valve for filling with new solvent are interpolated.
A second working drum for working solvent.
A return switch that incorporates outlets into which an equal number of conduits converge, connecting to the first and second working tanks; wherein the return switch has a first inlet that connects to the direction switch by means of a conduit, and a second outlet that connects to the first working solvent filter, which connects to the direction switch.
A return valve that incorporates two outlets into which an equal number of conduits converge, which are directed towards the two working drums, both the first and the second, wherein this return valve incorporates an inlet that connects to the level tank through a conduit.

The system of the invention comprises a discharge tank that connects to the drain valve by means of a conduit.
The system of the invention further comprises:

A compressed air pressure/vacuum switch, into which two pipes converge that originate at the first and second working tanks.
A vacuum generator that is connected to the pressure/vacuum switch through a pipe.
A control valve into which three ducts converge, which are linked to: the main drum, the pressure/vacuum switch and a gaseous fluid filter that connects to a compressed air intake.

The system of the invention further comprises an ultrasound device located within the main tub, to break apart and break loose the particles making up the blockage inside the ink printing head, further comprising a return device that recirculates the solvent back to the ink printing head, and which is attached to the level device.
The pressure control valve, pressure/vacuum switch, and vacuum generator, which are part of an air pressure/negative pressure circuit, are elements that generate variations in pressure inside the drums in order to push/suck the liquid solvent held in the drums; this generates a difference in pressure between the inlet/outlet of the ink printing head, in accordance with the circulation direction of the liquid solvent inside the ink head.
The system of the invention further comprises a fluid-tight seal between the ink printing head and the passage device during cleaning, wherein the fluid-tight seal between the two elements takes the form of a gasket that has a top base, a bottom base, and at least one through slot around which at least one perimeter lip is located, which protrudes above the top base of the gasket.
The gasket is supported by the passage device, whereas each perimeter lip of the gasket presses against the bottom face of the ink printing head, wherein the opposing force between the ink printing head and the passage device during cleaning causes each perimeter lip to bend towards the inner space of the through slot.
The gasket sits into a mortise in the passage device, selected between a smaller mortise into which a smaller gasket with just one through slot sits, and a larger mortise into which a larger gasket with several through slots fits. It should be pointed out that each one of the perimeter lips has an angular profile.
Thus, in one embodiment, the bottom of the smaller mortise is interrupted by a central opening surrounded by a perimeter ridge that sits against the inner face of the through slot of the smaller gasket.
In another embodiment, the bottom of the larger mortise is interrupted by several central openings surrounded by perimeter ridges that sit against the respective inner faces of the through slots of the larger gasket.
In one embodiment, each through slot is surrounded by a single perimeter lip, wherein one of its flanks is a prolongation of the inner face of this through slot, whereas its other flank has a converging inclination over the top face of the gasket.
In another embodiment, each through slot is surrounded by several perimeter lips, wherein one of its flanks is perpendicular to the top base of the gasket, whereas its other flank has a converging inclination over the top face of the gasket. In this case, one of the perimeter lips has a flank that is a prolongation of the inner face of the through slot.
The method for cleaning inkjet printing heads carried out by the system described in any one of the previous claims comprises the following stages:

Placing the ink printing head together with the passage device inside the main tub.
Pouring a liquid solvent into the main tub up to a height delimited by the level control overflow device, such that the liquid solvent covers a lower portion of the ink printing head.
Shooting a pressurized solvent fluid into the ink printing head, selected between a gaseous fluid and a liquid solvent, wherein this pressurized fluid passes through the entire internal path taken by the ink inside the ink printing head when sprayed, said internal path being taken in both circulation directions.
Creating a vacuum at the inlet/outlet of the ink printing head opposite the one that the pressurized solvent is being shot into.
During the cleaning cycle, activating the ultrasound device to break apart and descale the dirt inside the ink printing head.
Filtering the solvent that passes through the cleaning circuit and carries away the particles that break loose from the ink printing head to less than 1 micron to prevent these particles from going back inside the ink printing head, and in order to consume less solvent.
The level tank receiving the excess liquid solvent emptied from the main tub through the level control device.

For the purpose of helping to make this specification more readily understandable, a set of drawings constituting an integral part of the same has been included below, wherein by way of illustration and not limitation the subject matter of the invention is represented.

SUMMARY OF THE DRAWINGS

Figure 1 .- Shows a schematic view of a system for cleaning inkjet printing heads, object of the invention.
Figure 2 .- Represents an exploded perspective view showing an ink printing head and a passage device, as well as a smaller liquid-tight gasket with a single through slot.
Figure 3 .- Represents a cross-section view essentially showing the smaller gasket sitting into a smaller mortise in the passage device.
Figure 4 .- Shows an exploded perspective view showing a multiple ink printing head associated with a passage device, together with a larger liquid-tight gasket.
Figure 5 .- Represents a view similar to what is represented in figure 2, showing a multiple ink printing head and a passage device, together with a larger gasket with several through slots.
Figure 6 .- Shows a cross-section view during cleaning of the heads, highlighting the inward bending of a pair of perimeter lips of the gasket when they are touching a bottom face of the ink printing head.

DESCRIPTION OF AN EXEMPLARY EMBODIMENT OF THE INVENTIONS

Following the numbering used in the figures, the system for cleaning inkjet printing heads comprises a supporting structure 21 that holds a main tub 25, which is filled with a liquid solvent up to a height that is sufficient to cover a lower spraying portion of an ink printing head 16 to be cleaned, which is housed within the main tub 25; in said lower spraying portion there are several piezoelectric devices that are in charge of regulating and applying ink spraying, and which are not represented in the figures.
To regulate the optimum level of solvent in the main tub 25, a level control device 17 has been provided, located inside the main tub 25, such that the excess liquid solvent in the main tub is emptied by the level control device 17 into a level tank 13 to keep the ink printing head 16 from getting wet, and to keep this solvent from mixing with a pressurized recirculated solvent that passes through the inside of the ink printing head 16 in two circulation directions for better and more effective cleaning. Said control device 17 basically comprises a level-controlling tube.
The level device 13 is associated with a drain valve 14 that deviates part of the solvent of the level tank 13 into a discharge tank 24.
Two solvent taps reach the ink printing head 16, a first tap through a first inlet/outlet passage 19a, and a second tap through a second inlet/outlet passage 19b.
The first passage 19a connects to the ink inlet of the ink printing head 16, while the second passage connects to a passage device 18, into the which the ink printing head 16 fits such that it matches up with the outlet holes of the lower inking area, such that the solvent circulates through the inside of the ink printing head 16, in a first circulation direction from its outlet holes to the inlet of the ink printing head 16, first passing through the passage device 18 before flowing into the first passage 19a, and in a second circulation direction from the inlet to the outlet holes of the ink printing head 16, passing through the passage device 18 before flowing into the second passage 19b.
In this way we make the solvent circulate through the inside of the ink printing head 16 in two directions, for a much greater cleaning and descaling effect.
The two inlet/outlet passages, first 19a and second 19b, are associated with a direction switch 19, for selecting the circulation direction of the solvent.
The system of the invention also includes a main drum 4 that contains clean solvent, and which supplies two working drums, a first one 7 and a second one 8, as needed. The connection between the main tank 4 and the two drums 7 and 8, provides an enormous reduction in the consumption of the solvent that is commonly used for cleaning the ink printing head 16, as the solvent is recirculated through a circuit with various ducts and elements that are described further on.
Additional volume of solvent is released into the circuit from the main drum only when a decrease in solvent is detected.
The level tank 13 is also associated with the first 7 and second 8 working drums by means of ducts that connect to said drums 7-8, with an interposed return valve 9.
Other ducts originate at the first 7 and second 8 drums, which converge at a pressure/vacuum switch 5, in turn associated with a vacuum generator 6, as well as with a control valve 3 controlling the air pressure in both the two drums 7-8 as well as in the main drum 4.
The air pressure control valve 3 is associated with a compressed air regulating filter 2, which in turn connects to a compressed air intake 1.
Other ducts originate at the two working drums, the first one 7 and the second one 8, which converge at an entry/return switch 20, at which a first duct originates, which flows into the direction switch 19, with an interposed first working solvent filter 11, and a second duct that flows directly into the direction switch 19.
The circuit of the system of the invention also has a conduit that goes from the main drum 4 to the first working drum 7; in this conduit are interpolated a second new solvent filter 10 and new solvent filling valve 12, through which this new solvent passes into the first work drum 7.
The system of the invention also has a return device 17a that recirculates the solvent back to the ink printing head 16, and which is attached to the level control device 17.
Both the main tub 25 and the rest of the elements and devices are held by a supporting structure 21, which also holds a pneumatic and hydraulic control board 22 as well as an electrical control board 23.
Inside the main tub 25 there is an ultrasound device 15, for breaking apart and breaking loose the particles making up the blockage inside the ink printing head.
The solvent in the first 7 and second 8 working drums passes through the first working filter 11 by way of the entry/return switch 20 so as to constantly ensure the intended quality.
The excess solvent from the main tub 25 can be returned to the first 7 and second 8 working drums, through the level control tank 13 and the return valve 9, and may also optionally be returned to the discharge tank 24 through the level tank 13 and the drain valve 14.
In the invention at hand, the liquid solvent may be sprayed into the ink printing head 16, with a selection of the fluid circulation direction for cleaning the ink printing head 16. The first 11 and second 10 filters are meant to retain the particles that break loose from the stoppage, and thus recycle the liquid cleaning solvent in order to avoid consuming in excess. Filtering is done down to less than 1 micron.
As for the vacuum generator 6, it should be pointed out that, by means of the pressure/vacuum switch 5, air pressure is applied to either of the two working drums, first 7 or second 8 (the one that is full of solvent at that moment), such that the solvent is pushed towards the ink printing head 16, passing, in all cases, through the first filter 11.
At the same time, there are two options that the system of the invention decides automatically depending on the chosen recipe.
A first option in which is let the solvent to circulate through the ink printing head 16 and to return, by force of the pressure itself, to the working drum that does not have air pressure.
A second option in which is generated a vacuum inside the working drum that does not have pressure so that it sucks in the solvent and helps even more to descale the particles inside the ink printing head. All of this is done while the ultrasound device 15 is activated, which helps to break apart the blockage and dissolve the particles inside the ink printing head 16.
Thus, the ultrasound device 15 has the function of breaking apart and detaching the particles that make up the blockage inside the ink printing head 15. In order to clean more effectively, the ultrasound device 15 is activated for short cycles to keep the temperature from rising past 45 degrees. These cycles are carried out intermittently throughout the cleaning time. This keeps the solvent from becoming too hot. The return device 17a is a connection to the level control tube 17 that is used to connect the recirculation outlet of some ink printing heads 16.
For example, some types of ink printing heads 16 use recirculation, in which case the recirculation outlet is connected to the level control device 17 which in turn sends all of this excess solvent to the tank 13.
On the other hand, there are other ink printing heads 16 that do not have this recirculation outlet, and so in such cases the return device 17a is not used.
The pressurized air fluid is used to generate pressure inside the drums and push the solvent. In this way we avoid using impeller pumps, which require a great deal of maintenance. Thus, in the invention at hand we move the liquid solvent via air pressure.
To do so, pressure is generated in the upper portion of the respective drum 4-7-8, causing the solvent to come out the lower portion. The pressure in the upper portion of the respective drum makes the liquid solvent come out the lower portion. This is much better if we also create a vacuum in the other drum that does not have pressure, such that we are sending pressurized liquid solvent into one inlet/outlet of the ink printing head 16, and sucking it out of the other inlet/outlet.
The liquid solvent is carried from the main drum 4 to the first 7 and second 8 working drums by applying air pressure through the pressure control valve 3 and sending this volume of liquid solvent into the first 7 and second 8 working drums, through the second new solvent filter 10.
Furthermore, if we add air pressure inside the first working drum 7, the liquid solvent comes out, and in the second drum 8 we can either create a vacuum in order to suck, or can leave it alone and the solvent from the first working drum 7 will enter, and vice versa. All of these operations are carried out by means of the pressure control valve 3, the pressure/vacuum switch 5 and the vacuum generator 6.
A first pipe 26 connects the first passage 19a to an inlet of the ink printing head 16; while a second pipe 27 connects the second passage 19b to the passage device 18, which the ink printing head 16 fits into.
Furthermore, it has been concluded that the seal between the passage device 18 and the ink printing head 16 is crucial in order for the system of the invention to function properly.
In practice, it is not enough to use an O-ring with a shape fitted to the set of ink outlet holes of the head. The seal is only efficient if strong front-wise pressure is made by the contact faces between the passage device 18 and the ink printing head 16, which in practice is impossible since some of these ink printing heads 16, which come at a high cost, are not resistant enough and could break.
In order to avoid the problems set out in the preceding paragraph, a special, totally fluid-tight seal between the ink printing head 16 and the passage device 18 during the cleaning process has been provided, which comprises a parallelepiped-shaped gasket 28-28' that has a top base 29, a bottom base 30, and at least one through slot 31 running between both bases 29-30.
Thus, in a first embodiment shown in figures 2 and 3, there is a smaller gasket 28 that has at least one perimeter lip 32 on its top base 29 around the through slot 31, which makes contact against a bottom face 16a of the ink printing head 16, such that the ink outlet holes open onto this bottom face 16a in an area delimited by the perimeter lip 32.
When the gasket 28-28' sits against the bottom face 16a of the ink printing head 16, the perimeter lip 32 bends inward as shown in figure 6, such that the pressure of the cleaning fluid itself pushes said perimeter lip 32 outwards against the bottom face 16a of the ink printing head 16, generating a hermetic seal that increases proportionally as the level of the pressure of the circulating fluid rises.
Given that the bottom base 30 of the gasket 28-28' sits upon a horizontal plane, the perimeter lip 32, which has an angular profile, has one vertical flank, as a continuation of an inner lateral face of the through slot 31 of the gasket 28-28', while the other flank of this angular profile has a converging upward inclination.
As can be seen more clearly in figures 3 and 6, in one embodiment the gasket 28-28' incorporates two perimeter lips 32: an inner one corresponding to the one that has already been described, and a second perimeter lip that is identical and adjacent to the first.
As is shown in figure 3, the smaller gasket 28 sits into a smaller mortise 33 in the passage device 18. The bottom of this smaller mortise 33 is interrupted by a central opening 34 surrounded by a perimeter ridge 35 that sits against the inner face of the through slot 31.
On the other hand, figures 5 and 6 show a larger gasket 28' that has several through slots 31 enabling it to be applied to a multiple ink printing head 16. In this case, the larger gasket 28' has a perimeter lip 32 around each through slot 31, as shown more clearly in figure 5, although it may clearly incorporate various perimeter lips 32 around each through slot 31. In this case, the larger gasket 28' also sits into a larger mortise 33' in the passage device 18, such that the bottom of this larger mortise 33' is affected by several central openings 34 surrounded by respective perimeter ridges 35 that sit against the inner faces of the through slots 31.

Claims

System for cleaning inkjet printing heads, which, being intended for cleaning, with a solvent, various spaces, inside ink printing heads, through which ink normally flows when sprayed,
is characterized in that it comprises:
- a main tub (25), inside of which an ink printing head (16) is housed for cleaning, in such a way that a lower spraying portion of the ink printing head (16) is continuously soaking in a liquid solvent contained within the main tub (25);

- a level control device (17) that regulates the optimum height, acting as an overflow for the liquid solvent contained within the main tub (25), which liquid solvent covers the lower portion of the printing head (3);

- an ultrasound device (15) located within the main tub (25), which breaks apart and breaks loose the dirt particles blocking up the inner spaces of the ink printing head (16);

- a passage device (18) into which the ink printing head (16) fits so as to match up with the ink outlet holes;

- a direction switch (19), which selects the circulation direction of a solvent fluid, selected between a gaseous fluid and a liquid solvent; wherein this fluid circulates through various spaces inside the ink printing head (16) through a first fluid inflow/outflow passage (19a) in a first circulation direction, and through a second fluid inflow/outflow passage (19b) in a second circulation direction;

- a first pipe (26) that connects the first passage (19a) to an inlet of the ink printing head (16);

- a second pipe (27) that connects the second passage (19b) to the passage device (18) which the ink printing head (16) fits into;

- a level tank (13) associated with a drain valve (14), wherein the level tank (13) receives the excess solvent emptied from the main tub (25) through the level control device (17).
System for cleaning inkjet printing heads, according to claim 1, characterized in that it further comprises:
- a main new solvent drum (4) that feeds a first working solvent drum (7) by means of a conduit, in which a second new solvent filter (10) and a valve (12) for filling with new solvent are interpolated;

- a second working drum (8) for working solvent;

- a return switch (20) that incorporates inlets and outlets into which a number of conduits converge, connecting to the first (7) and second (8) working tanks; wherein the return switch (20) has a first inlet that connects to the direction switch (19) by means of a conduit, and a second outlet that connects to the first working solvent filter (11), which connects to the direction switch (19);

- a return valve (9) that incorporates two outlets into which a number of conduits converge, which are directed towards the two working drums, both the first (7) and the second (8), wherein this return valve (9) incorporates an inlet that connects to the level tank (13) through a conduit.
System for cleaning inkjet printing heads, according to claim 2, characterized in that it comprises a discharge tank (24) that connects to the drain valve (14) by means of a conduit.
System for cleaning inkjet printing heads, according to any one of the previous claims 2 or 3, characterized in that it comprises:
- a compressed air pressure/vacuum switch (5), into which two pipes converge that originate at the first (7) and second (8) working tanks;

- a vacuum generator (6) that is connected to the pressure/vacuum switch (5) through a pipe;

- a control valve (3) into which three ducts converge, which are linked to: the main drum (4), the pressure/vacuum switch (5) and a gaseous fluid filter (2) that connects to an intake (1);
wherein the pressure control valve (3), pressure/vacuum switch (5), and vacuum generator (6), which are part of an air pressure/negative pressure circuit, are elements that generate variations in pressure inside the drums (4, 7 and 8) in order to push/suck the liquid solvent held in the drums (4, 7 and 8); this generates a difference in pressure between the inlet/outlet of the ink printing head (16), in accordance with the circulation direction of the liquid solvent inside the ink head (16).
System for cleaning inkjet printing heads, according to any one of the previous claims, characterized in that it comprises a return device (17a) that recirculates the solvent back to the ink printing head (16), and which is attached to the level device (17).
System for cleaning inkjet printing heads, according to any one of the previous claims, characterized in that:
- it comprises a fluid-tight seal between the ink printing head (16) and the passage device (18) during cleaning, wherein the fluid-tight seal between the two elements (16-18) takes the form of a gasket that has a top base (29), a bottom base (30), and at least one through slot (31) around which at least one perimeter lip is located (32), which protrudes above the top base (29) of the gasket;

- the gasket is supported by the passage device (18), whereas each perimeter lip (32) of the gasket presses against a bottom face (16a) of the ink printing head (16), wherein the opposing force between the ink printing head (16) and the passage device (18) during cleaning causes the perimeter lip (32) to bend towards the inner space of the through slot (31).
System for cleaning inkjet printing heads, according to claim 6, characterized in that the gasket sits into a mortise in the passage device (18), selected between a smaller mortise (33) into which a smaller gasket (28) with just one through slot (31) sits, and a larger mortise (33') into which a larger gasket (28') with several through slots (31) fits.
System for cleaning inkjet printing heads, according to claim 7, characterized in that the bottom of the smaller mortise (33) is interrupted by a central opening (34) surrounded by a perimeter ridge (35) that sits against the inner face of the through slot (31) of the smaller gasket (28).
System for cleaning inkjet printing heads, according to claim 7, characterized in that the bottom of the larger mortise (33') is interrupted by several central openings (34) surrounded by perimeter ridges (35) that sit against the respective inner faces of the through slots (31) of the larger gasket (28').
System for cleaning inkjet printing heads, according to any one of the previous claims 6 to 9, characterized in that each one of the perimeter lips (32) has an angular profile.
System for cleaning inkjet printing heads, according to claim 10, characterized in that each through slot (31) is surrounded by a single perimeter lip (32), wherein one of its flanks is a prolongation of the inner face of this through slot (31), whereas its other flank has a converging inclination over the top face (29) of the gasket.
System for cleaning inkjet printing heads, according to claim 10, characterized in that:
- each through slot (31) is surrounded by several perimeter lips (32), wherein one of its flanks is perpendicular to the top base (29) of the gasket, whereas its other flank has a converging inclination over the top face (29) of the gasket;

- one of the perimeter lips (32) has a flank that is a prolongation of the inner face of the through slot (31).
Method for cleaning inkjet printing heads, carried out by the system described in any one of the previous claims,
characterized in that it comprises the following stages:
- placing the ink printing head (16) together with the passage device (18) inside the main tub (25);

- pouring a liquid solvent into the main tub (25) up to a height delimited by the level control overflow device (17), such that the liquid solvent covers a lower portion of the ink printing head (16);

- shooting a pressurized fluid into the ink printing head (16), selected between a gaseous fluid and a liquid solvent, wherein this pressurized fluid passes through the entire internal path taken by the ink inside the ink printing head (16) when sprayed, said internal path being taken in both circulation directions;

- creating a vacuum at the inlet/outlet of the ink printing head (16) opposite the one that the pressurized solvent is being shot into;

- during the cleaning cycle, activating the ultrasound device (15) to break apart and descale the dirt inside the ink printing head (16);

- filtering the solvent that passes through the cleaning circuit and carries away the particles that break loose from the ink printing head (16) to less than 1 micron to prevent these particles from going back inside the ink printing head (16), and in order to consume less solvent;

- the level tank (13) receiving the excess liquid solvent emptied from the main tub (25) through the level control device (17).