PRINT HEAD COMPRISING A MAINTENANCE CIRCUIT AND COATING INSTALLATION

A print head for applying a coating material to an object to be coated, the print head including a body wherein a plurality of nozzles are arranged, each including an ejection hole and an outlet channel opening into an ejection zone for ejecting the coating product via the ejection hole, as well as a coating product feeder circuit connected to the nozzle. The print head further includes a maintenance circuit for carrying a maintenance fluid and extending inside the body to the ejection zone of the nozzle. The maintenance circuit includes a plurality of internal channels each opening into the ejection zone of a single nozzle associated with the first internal channel. The number of first channels is equal to the number of nozzles.

REFERENCE TO RELATED APPLICATION

This application is a U.S. non-provisional application claiming the benefit of French Application No. 22 03285, filed on Apr. 11, 2022, the contents of which are incorporated herein by reference in their entirety.

TECHNICAL FIELD OF THE INVENTION

The technical field of the invention is that of the application, by means of printing, of a coating product on an object to be coated.

The present invention relates more particularly to a print head for applying a coating product to an object to be coated and to a coating installation including the print head.

BACKGROUND OF THE INVENTION

The customization of decorations and coatings affixed to objects is becoming more and more frequent. This is the case, e.g., in the automotive industry, for vehicle body coatings. There can be coatings of one-color, two-tone or multi-color paints. Furthermore, the production of patterns with a specific geometry is interesting for other markets, in particular for visually differentiating two products according to the purpose thereof or the manufacture thereof. In such context, the coating industry has recently explored solutions of “printing” paint using print heads, rather than spraying the paint with sprayers.

The paints used to produce coatings by printing have viscosities on the order of 50 to 200 millipascal-second (MPAs) and contain pigment particles with dimensions on the order of one micrometer. To apply such paints, a print head equipped with a plurality of nozzles is usually used. The print head is, e.g., mounted on the arm of a multi-axis robot. Each nozzle includes an outlet channel opening out to the outside via an ejection hole of small diameter, typically on the order of 100 μm to 200 μm, which is much smaller than the dimensions of a sprayer outlet hole (generally greater than 800 μm).

Given the small diameter of the nozzle ejection holes, there is a risk of clogging the nozzles with paint residues. Nozzle cleaning operations are thus performed between the printing phases so as to prevent nozzle clogging and maintain good print quality.

Moreover, for economy and practical reasons, the same print head is generally used for applying paints of different colors. Hence, each nozzle has to be cleaned during a change of paint.

Patent application EP3725421A1 describes an installation for applying a coating product including a print head equipped with a set of nozzles and a nozzle cleaning station. The cleaning station includes a plurality of injectors designed for simultaneously cleaning a plurality of nozzles, by injecting a cleaning fluid into the outlet channels of the nozzles, through the ejection holes thereof.

When it is necessary to clean the nozzles, e.g., in anticipation of a change of paint color, the print head is moved by the multi-axis robot to be positioned above the cleaning station.

In order to maximize the printing time, and thus the production rate, it would be advantageous to fit the cleaning station with the print head on the arm of the multi-axis robot. The EP3725421A1 Document Cleaning Station is, however, too large to be fitted along with the print head and to be compatible with the short print distance; i.e., the distance between the nozzles and the object to be coated.

It is also known from U.S. Pat. No. 5,877,788A how to clean the nozzles of a print head with a fluid conveyed by channels common to all the nozzle ejection holes. The ejection holes situated near the outlet of the channels are cleaned before and with a cleaner fluid than the channels situated far from the outlet. The cleaning of the nozzle ejection zones is thus not homogeneous.

SUMMARY OF THE INVENTION

There is thus a need to be able to homogeneously clean different nozzles of a print head when the print head is in position for printing; i.e., in the vicinity of the object to be coated.

According to a first aspect of the invention, such need tends to be met by providing a print head for applying a coating product to an object to be coated, the print head including a body wherein are fitted:a plurality of nozzles each including an ejection hole and an outlet channel opening into an ejection zone of the coating product through the ejection hole;a feeder circuit for coating product, connected to the nozzle; the print head further includes a maintenance circuit for conveying a maintenance fluid, the maintenance circuit extending inside the body to the nozzle ejection zone and including a first internal channel opening into the ejection zone of at least one nozzle. According to the invention, the maintenance circuit includes a plurality of first internal channels, each first internal channel opening into the ejection zone of only one nozzle associated with the first internal channel, the number of first internal channels being equal to the number of nozzles.

The maintenance circuit conveys the maintenance fluid into the ejection zone of each nozzle or, on the contrary, discharges the maintenance fluid from the ejection zone, and thus cleans the ejection holes of the nozzles, in an individualized and homogeneous manner. The maintenance circuit thus provides a cleaning solution which is integrated into the print head and which is not bulky like the solutions of the prior art, and is more efficient. Cleaning may thus be carried out when the print head is in position for printing.

In one embodiment of the print head, the maintenance circuit further includes a plurality of second internal channels, each second internal channel being associated with a first internal channel and opening into the ejection zone of the only one nozzle associated with the first internal channel. Such embodiment combines practicality (many possible maintenance operations) and cleaning performance.

According to a development of the embodiment, each second internal channel is situated opposite the associated first internal channel with respect to the ejection hole of the nozzle in the ejection zone from which the second channel opens out. Such arrangement of the first and second internal channels improves the cleaning of the ejection hole and facilitates the flow of the maintenance fluid.

According to another development compatible with the preceding development, each first internal channel and associated second internal channel are oriented along the same direction. Such arrangement further facilitates the flow of the maintenance fluid.

In another embodiment, the maintenance circuit includes a first maintenance fluid storage chamber, the first storage chamber communicating with the nozzle ejection zone through a first opening.

According to a development of the third embodiment, the print head includes a plurality of nozzles connected to the feeder circuit, each nozzle including an ejection hole and an outlet channel opening into an ejection zone, and the first storage chamber for the maintenance fluid communicates with the ejection zone of a plurality of nozzles (preferably of all nozzles) through a plurality of first openings.

According to another development compatible with the previous development, the maintenance circuit further includes a second chamber for storing the maintenance fluid, the second storage chamber communicating with the ejection zone of the nozzle or of a plurality of nozzles (preferably of all nozzles) through one or a plurality of second openings.

In addition to the features just mentioned in the preceding paragraphs, the print head according to the first aspect of the invention may have one or a plurality of complementary features among the following, considered individually or in all technically possible combinations:the first internal channel is directed toward the nozzle ejection hole;the print head includes an ejection face wherein the ejection hole of a nozzle of the plurality of nozzles is fitted;each first internal channel is arranged so that the maintenance fluid flows in contact with the ejection face;each first internal channel is oriented parallel to the ejection face;each first internal channel is inclined with respect to the ejection face towards the nozzle ejection hole;each first internal channel is fitted in a plate arranged on the ejection face of the print head;each first internal channel has an end open to the ejection zone and situated at a distance less than or equal to 1 mm from the ejection hole of a nozzle of the plurality of nozzles;the maintenance circuit includes a first chamber for storing the maintenance fluid, the first storage chamber communicating with the ejection zone of each nozzle through one of the first internal channels, the length of which is between 0.5 mm and 10 mm;the maintenance circuit further includes a first maintenance fluid storage chamber, the first internal channel connecting the first storage chamber for the maintenance fluid to the nozzle ejection zone;the first internal channels or openings extend through an internal wall of the body which separates the first storage chamber and the nozzle ejection zones;the first internal channels are provided in an external maintenance plate arranged on an ejection face of the body, wherein are provided the ejection holes of the nozzles;the first internal channel extends through an internal wall separating the first storage chamber for the maintenance fluid and the nozzle ejection zone;the first internal channels have a cross-section with characteristic dimensions less than or equal to 0.5 mm, preferably less than or equal to 0.25 mm;the second internal channel is directed towards the nozzle ejection hole;the second internal channel is arranged so that the maintenance fluid flows in contact with the ejection face;the second internal channel is oriented parallel to the ejection face;the second internal channel is inclined with respect to the ejection face towards the nozzle ejection hole;the second internal channel is fitted in a plate arranged on the ejection face of the print head;the second internal channel has one end open to the ejection zone and situated at a distance less than or equal to 1 mm from the ejection hole of the nozzle;the maintenance circuit further includes a second storage chamber for storing the maintenance fluid, the second internal channel connecting the second storage chamber to the ejection zone of the nozzle;the second internal channel extends through an internal wall separating the second storage chamber for the maintenance fluid and the nozzle ejection zone;

the second internal channel further extends partially into the second storage chamber for the maintenance fluid; and

the coating product feeder circuit includes a storage chamber for the coating product and a plurality of dispensing channels connecting the storage chamber for the coating product to the nozzles.

A second aspect of the invention relates to a coating installation including:a print head according to the first aspect of the invention;an injection circuit for the maintenance fluid, connected to at least one inlet of the print head; anda suction circuit for the maintenance fluid, connected to at least one outlet of the print head.

Advantageously, the suction circuit includes:a vacuum generator;a first suction valve connected to the vacuum generator and to a first outlet of the print head; anda second suction valve connected to the vacuum generator and to a second outlet of the print head.

In one embodiment, the first outlet of the print head is merged with a first inlet-outlet of the maintenance circuit, and the second outlet of the print head is merged with a supply inlet of the feeder circuit.

In a variant embodiment, the first outlet of the print head is merged with a first inlet-outlet of the maintenance circuit, and the second outlet of the print head is merged with a second inlet-outlet of the maintenance circuit.

Advantageously, the injection circuit includes:a first pressurized tank containing a cleaning fluid;a second pressurized tank containing a wetting liquid;a first injection valve connected to the first and second pressurized tanks and to a first inlet of the print head; anda second injection valve connected to the first and second pressurized tanks and to a second inlet of the print head.

In one embodiment, the first inlet of the print head is merged with a first inlet-outlet of the maintenance circuit, and the second inlet of the print head is merged with a supply inlet of the feeder circuit.

In a variant embodiment, the first inlet of the print head is merged with a first inlet-outlet of the maintenance circuit, and the second inlet of the print head is merged with a second inlet-outlet of the maintenance circuit.

For greater clarity, identical or similar elements are identified by identical reference signs in all the figures.

DETAILED DESCRIPTION

FIGS.1A and1Bare partial three-dimensional views of a print head1according to a first embodiment of the present invention. The view shown inFIG.1Aresults from a section of print head1along a transverse plane and along a first longitudinal plane. The partial view shown inFIG.1Bresults from a section of print head1along a second longitudinal plane parallel to the first longitudinal plane. These figures thus show internal elements of print head1.

Print head1includes a body10and a plurality of nozzles11situated inside body10. Preferably, nozzles11are arranged in one or a plurality of rows. For simplicity, only one row of nozzles11is shown inFIG.1A(the first longitudinal section plane passing through the row of nozzles). The number of nozzles11in each row may be between 2 and 500.

Print head1is intended for applying a coating product over an object to be coated; e.g., a body of a motor vehicle. Print head1preferably works according to drop on demand (DOD) technology. Each nozzle11is then configured for depositing the coating product drop by drop. To this end, each nozzle11may be equipped with a valve which is controlled for opening or closing, and for allowing or preventing respectively, the coating product from flowing through nozzle11. The valves of nozzles11are, e.g., pneumatic valves each including a membrane which may be controlled. Such a valve is pneumatically controlled (e.g., using compressed air). The valves of nozzles11may also be solenoid valves.

Alternatively, print head1is a continuous jet print head; i.e., print head1has permanently open circuits. In such a case, nozzles11do not have valves.

The coating product taken hereinafter as an example is paint, but the coating product may also be a primer, a varnish or a more viscous product such as a glue or a putty.

FIG.2is a sectional view on a larger scale of a portion A of print head1, the portion A being situated around a nozzle11(cf.FIG.1A). Portion A will be described jointly withFIGS.1A and1B.

Each nozzle11includes an outlet channel111and an ejection hole112. Outlet channel111opens out to the outside of body10via ejection hole112, in a paint ejection zone2. Each nozzle11is thus associated with an ejection zone2which extends in the continuation of outlet channel111of nozzle11.

Outlet channel111and ejection hole112of nozzles11are fitted into body10of the print head1. More particularly, ejection hole112is fitted into an ejection face100of body10. Ejection hole112has a diameter which may be between 100 μm and 500 μm, e.g., equal to 150 μm. Ejection face100partly delimits ejection zones2. The ejection axis z of each nozzle11, defined as the axis of ejection hole112, is preferably oriented perpendicularly to ejection face100.

Print head1further includes two internal fluid circuits; i.e., fitted inside body10:a feeder circuit12connected to nozzles11and intended for conveying the paint;a maintenance circuit13intended for conveying a maintenance fluid.

The function of feeder circuit12is to feed paint into nozzles11. Feeder circuit12includes a so-called supply inlet121and extends inside body10from supply inlet121to nozzles11. Supply inlet121is an inlet through which paint enters print head1. Feeder circuit12may also include a so-called purge or recirculation outlet122(cf.FIG.1B). Purge outlet122is an outlet through which paint may be discharged from print head1(and conveyed to recovery and processing manifolds or to the feeder tanks). Purge outlet122is used for purging feeder circuit12, e.g., when changing paint color. Feeder circuit12may also be primed; i.e., filled with paint before a printing phase, by circulating paint from supply inlet121to purge outlet122(but not through nozzles11). Supply inlet121and purge outlet122are fitted into an outer wall of body10.

As shown inFIGS.1A and1B, feeder circuit12may further include a storage chamber123(for paint) connected to supply inlet121and a plurality of dispensing channels124(for paint) connecting storage chamber123to nozzles11. Advantageously, storage chamber123is further connected to purge outlet122. Two elements of the same fluidic circuit (or two elements belonging to two different fluidic circuits) are considered to be connected when they are in fluidic communication.

Each dispensing channel124may connect storage chamber123to one or a plurality of nozzles11, e.g., two consecutive nozzles in the row. Preferably, the number of dispensing channels124is equal to the number of nozzles11, and each dispensing channel124serves only one nozzle11.

Storage chamber123and dispensing channels124are fitted in body10. Supply inlet121and purge outlet122may open directly into storage chamber123, or may be connected to storage chamber123by so-called inlet and outlet conduits, respectively.

Maintenance circuit13extends inside body10as far as ejection zone2of at least some of nozzles11, preferably all of nozzles11. Maintenance circuit13is configured for conveying maintenance fluid to ejection zone2of at least some of nozzles11and/or to discharge the maintenance fluid from ejection zone2from at least some of nozzles11(preferably all of nozzles11).

In such first embodiment, maintenance circuit13includes a plurality of first internal channels131, called maintenance channels. One or a plurality of nozzles11are associated with each first internal channel131. Each first internal channel131opens into ejection zone2of the nozzle(s) associated with first internal channel131.

Maintenance circuit13is advantageously configured so that maintenance fluid may be brought into each ejection zone2or discharged from each ejection zone2via at least one first internal channel131. All nozzles11of print head1may thus be serviced.

Advantageously, the number of first internal channels131is equal to the number of nozzles11and each first internal channel131opens into ejection zone2of only one nozzle11(in other words, each first internal channel131is associated with only one nozzle11). Maintenance is thus carried out in the same way and with the best performance level for all nozzles.

In addition to first internal channels131, maintenance circuit13includes a first storage chamber132for maintenance fluid, and a first inlet-outlet133. An inlet-outlet herein refers to an inlet and/or outlet hole for maintenance fluid in print head1. First inlet-outlet133may open directly into first storage chamber132, or may be connected by a conduit to first storage chamber132. First inlet-outlet133is fitted into an external wall of body10. First storage chamber132(also called the first distribution chamber for maintenance fluid) is connected to ejection zones2by first internal channels131.

Each first internal channel131extends through an internal wall separating first storage chamber132and ejection zones2from nozzles11. Each first internal channel131may further extend partially into first storage chamber132, as shown inFIG.1A.

Maintenance circuit13makes it possible to carry out maintenance operations on print head1. In the first embodiment, the possible maintenance operations are the following:a cleaning operation (or rinsing) of at least a part of nozzles11and at least a portion of supply circuit12, using a cleaning fluid; anda wetting operation of at least a part of nozzles11, using a non-volatile liquid.
Thus, the nature of the maintenance fluid varies according to the desired maintenance operation.

Such operations are described in more detail in the preferable case of simultaneous maintenance of all nozzles11of print head1.

The operation of cleaning nozzles11and at least a part of feeder circuit12consists in removing paint residues situated in nozzles11(typically in outlet channel111and ejection hole112) and in feeder circuit12.

Cleaning fluid may be brought into ejection zone2of nozzles11by means of first internal channels131of maintenance circuit13, then be discharged by passing through nozzles11and feeder circuit12(cf.FIG.2). Cleaning fluid then flows through nozzles11in the opposite direction to the direction of flow of paint, which is also called the normal direction of flow. Conversely, cleaning fluid may be brought into ejection zone2by passing through nozzles11by means of feeder circuit12, then be evacuated from ejection zone2by first internal channels131of maintenance circuit13. Cleaning fluid then flows through nozzles11in the normal direction of flow. Cleaning fluid may be a liquid (whether volatile or not), a gas (e.g., air) or a mixture of liquid and gas. Cleaning liquid advantageously includes a solvent (in order to “dissolve” the dry paint residues), preferably the same solvent as the solvent used in composition of the paint.

Such an operation may be carried out for unblocking the obstructed nozzles11and for re-establishing optimum operation (in particular, for guaranteeing repeatable drop trajectories). This operation may also be carried out between two phases of printing the object, during a change of color of paint, or after a prolonged stop of print head1. Feeder circuit12is advantageously drained prior to such operation.

A wetting operation of nozzles11consists in forming a film of non-volatile liquid at the level of ejection hole112of nozzles11, in order to prevent paint from drying during a prolonged stop of printing and from obstructing nozzles11. Non-volatile liquid, also called wetting liquid or stopping liquid, may be brought to ejection hole112of nozzles11via first internal channels131at the end of a printing phase, and then discharged before the next printing phase begins, either through feeder circuit12or through first internal channels131. Alternatively, wetting liquid may be brought to ejection hole112of nozzles11through feeder circuit12, then discharged through feeder circuit12or through first internal channels131.

Thus, maintenance circuit13carries only one or a plurality of maintenance fluids (cleaning fluid and/or wetting liquid), unlike feeder circuit12which may receive paint and maintenance fluids.

Maintenance fluid is sucked in so as to be discharged from ejection zone2of nozzles11. First internal channels131—or nozzles11and feeder circuit12—are thus subjected to a negative pressure. The negative pressure is preferably between 0.1 bar and 0.8 bar, e.g., equal to 0.5 bar. Maintenance fluid is injected into print head1at a pressure which may be between 0.1 bar and 1 bar.

Values of pressure and of negative pressure depend on the type of operation desired and on the properties of the maintenance fluid. For a cleaning operation, e.g., it is advantageous to circulate fluid rapidly in ejection zone2and thus to have high pressure/negative pressure values. For a nozzle wetting operation, wetting liquid is slowly brought into ejection zone2so as to form the wet film which will close the nozzle.

First storage chamber132is preferably arranged for providing identical pressure/negative pressure along print head1, and thus to ensure identical operation for all nozzles11.

By virtue of first internal channels131opening into ejection zone2of nozzles11, maintenance operations may be carried out without external flow, when print head1is in position for printing; i.e., in the immediate vicinity of the object to be coated. It then becomes possible to dispense with a recovery tray.

With reference toFIG.2, first internal channel131may be arranged so that maintenance fluid flows in contact with ejection face100. Ejection face100may thus be cleaned and cleared of paint residues between the end of first internal channel131and ejection hole112of the associated nozzle(s)11. First internal channel131preferably includes a wall forming a plane surface with ejection face100, as illustrated. First internal channel131is oriented, e.g., parallel to ejection face100.

In another configuration, not shown in the figures, first internal channel131is inclined with respect to ejection face100towards ejection hole112of the nozzle(s) associated with first internal channel131.

First internal channel131opens into ejection zone2at a distance d from the axis z of ejection hole112, which is advantageously less than or equal to 1 mm, e.g., equal to 0.25 mm. A small distance d between the end of first internal channel131and ejection hole112improves cleaning or wetting of the ejection hole (by limiting dispersion of the jet of fluid) and facilitates suction of maintenance fluid.

First internal channel131preferably has a cross-section with characteristic dimensions less than or equal to 0.5 mm, preferably less than or equal to 0.25 mm. Such section is, e.g., round (diameter less than or equal to 0.5 mm) or rectangular (height and width less than or equal to 0.5 mm).

The length of first internal channel131may be between 0.5 mm and 10 mm. Such a length makes it possible to properly “guide” maintenance fluid to ejection zone2.

Preferably, all first internal channels131of maintenance circuit13have the same configuration and the same dimensions. In other words, same are identical.

First internal channels131are advantageously arranged in a plate (or layer)101called an external maintenance plate, and arranged on ejection face100. External maintenance plate101has a very small thickness, e.g., between 0.1 mm and 1 mm, and thus does not significantly increase the bulk of print head1.

FIG.3is a partial three-dimensional view of print head1according to a second embodiment.FIG.3results from a section of print head1along a transverse plane.

Print head1according to the second embodiment (FIG.3) differs from print head1according to the first embodiment (FIGS.1A and1B) essentially in the arrangement of maintenance circuit13.

In the second embodiment, maintenance circuit13includes, in addition to first internal channels131, second internal channels135. Each second internal channel135is associated with a first internal channel131and opens into ejection zone2of the nozzle(s)11associated with first internal channel131.

Like first internal channels131, second internal channels135serve for conveying maintenance fluid to ejection zones2, or for discharging maintenance fluid from ejection zones2.

Advantageously, the number of second internal channels135is equal to the number of nozzles11, and each second internal channel135opens into ejection zone2of only one nozzle11; i.e., each second internal channel135is associated with only one nozzle11.

Maintenance circuit13further includes a second storage (or distribution) chamber136for maintenance fluid and a second inlet-outlet137connected to second storage chamber136. Second inlet-outlet137may be fitted into an external wall of body10and open directly into second storage chamber136, or may be connected by a conduit to second storage chamber136. Second storage chamber136is preferably arranged for providing identical pressure/negative pressure along print head1, thus to ensure identical operation for all nozzles11.

Maintenance circuit13herein extends from first inlet-outlet133to ejection zones2of nozzles11, and from ejection zones2to second inlet-outlet137.

Second internal channels135connect second storage chamber136to ejection zones2of nozzles11. Each second internal channel135extends through an internal wall separating second storage chamber136and ejection zones2from nozzles11. Each second internal channel135may further extend partially into second storage chamber136, as shown inFIG.3.

FIG.4is a sectional view on a larger scale of a portion B of print head1, portion B being situated around a nozzle11(cf.FIG.3).FIG.4shows a preferably arrangement of first internal channel131and of associated second internal channel135.

Second internal channel135is situated opposite associated first internal channel131with respect to ejection hole112of nozzle11. Second internal channel135may be arranged so that maintenance fluid flows in contact with ejection face100, as described hereinabove in relation to first internal channel131(FIG.2). In such configuration, first internal channel131and second internal channel135are advantageously oriented along the same direction.

Alternatively, second internal channel135may be inclined with respect to ejection face100towards ejection hole112.

Second internal channel135opens into ejection zone2at a distance d′ from the axis z of ejection hole112, which is advantageously less than or equal to 1 mm, e.g., equal to 0.25 mm. The distance d′ between the end of second internal channel135and the axis z of ejection hole112is preferably equal to the distance d between the end of first internal channel131and the axis z of ejection hole112.

Second internal channel135preferably has a cross-section with characteristic dimensions less than or equal to 0.5 mm, preferably less than or equal to 0.25 mm. Such section is, e.g., round (diameter less than or equal to 0.5 mm) or rectangular (height and width less than or equal to 0.5 mm). The length of second internal channel135may be between 0.5 mm and 10 mm.

First internal channel131and second internal channel135may be arranged symmetrically with respect to ejection hole112of nozzle11.

Preferably, all second internal channels135of maintenance circuit13have the same configuration and the same dimensions. Second internal channels135are thus identical.

Second internal channels135are advantageously fitted into the same external maintenance plate101as first internal channels131.

The following maintenance operations are possible with print head1according to the second embodiment:an operation of cleaning at least a part of nozzles11, and of at least a part of supply circuit12, using a cleaning fluid;a wetting operation of at least a part of nozzles11, using a non-volatile liquid; andan operation of cleaning ejection face100and the ejection hole of at least a part of nozzles11, using a cleaning fluid.

The operation of cleaning at least a part of nozzles11and of at least a part of feeder circuit12, and the wetting operation, have been described hereinabove. Second internal channels135may perform the same function as first internal channels131; i.e., suction or injection of maintenance fluid. Second internal channels135may, e.g., be used for discharging maintenance fluid from ejection zones2after maintenance fluid has circulated through feeder circuit12and nozzles11. Alternatively, second internal channels135may perform a different function from the function of first internal channels131. As an example, second internal channels131may serve for sucking up wetting liquid, whereas first internal channels131serve for bringing wetting fluid to ejection zones2.

The operation of cleaning ejection face100and the ejection hole of nozzles11includes conveying cleaning fluid to ejection zones2via first internal channels131, and discharging cleaning fluid via second internal channels135, or vice versa. Thus, during such operation, cleaning fluid circulates only through maintenance circuit13(between first and second inlet-outlets133,137) and in ejection zones2, in contact with ejection face100.

Since first internal channel131and second internal channel135are situated on either side of ejection zone2(and preferably situated opposite each other), a more thorough cleaning of ejection face100may be obtained.

Print head1according to the second embodiment thus makes it possible to carry out an additional maintenance operation. Values of pressure and negative pressure are similar to the values previously indicated. The implementation is easier because maintenance is completely decorrelated from the feed (valves removed from the circuit).

In another embodiment of print head1, not shown in the figures, maintenance circuit13includes a single first internal channel121opening into ejection zone2of a plurality of nozzles11, preferably all nozzles11.

However, a maintenance circuit13including a plurality of first internal channels131has better performance (in terms of cleaning the nozzles, e.g.) than a maintenance circuit13with only one first internal channel common to a plurality of nozzles. In fact, maintenance fluid may thus be conveyed to nozzle ejection zone2or removed from nozzle ejection zone2in a more precise manner. Multiplying the number of first internal channels131further reduces the size thereof, and thus increases the speed of maintenance fluid circulating inside.

Similarly, maintenance circuit13may include (in addition to first internal channel or channels131) only one second internal channel135opening out in ejection zone2of a plurality of nozzles11, preferably all the nozzles11.

FIG.5shows a third embodiment, wherein maintenance circuit13of print head1has no first internal channels131and no second channels135. First storage chamber132communicates with ejection zone2of at least a portion of nozzles11via one or a plurality of first openings138.

Preferably, first storage chamber132communicates with ejection zone2of each of nozzles11via a single first opening138. The number of first openings138is then equal to the number of nozzles11.

First openings138are fitted in the wall of body10which separates first storage chamber132and ejection zones2. Same result from the overlap between first storage chamber132and ejection zones2(herein in the form of straight cylinders, in the continuation of outlet channels111of nozzles11).

Furthermore, second storage chamber136communicates with ejection zone2of at least a portion of nozzles11via one or a plurality of second openings139. Preferably, second storage chamber136communicates with ejection zone2of each of nozzles11via a single second opening139. The number of second openings139is then equal to the number of nozzles11.

Second openings139are fitted in the wall of body10which separates second storage chamber136and ejection zones2. Same result from the overlap between second storage chamber136and ejection zones2.

Thus, a nozzle11and a first opening138may be associated with each second opening139. Each second opening139is advantageously situated opposite the associated first opening138with respect to ejection hole112of the associated nozzle11. In other words, first opening138, second opening139, and the end of ejection hole112are aligned. Such arrangement improves cleaning and wetting of ejection hole111of nozzle11. Furthermore, first and second openings138and139are advantageously arranged so that maintenance fluid flows in contact with ejection face100.

Compared with the first and second embodiments (FIGS.1A,1B and2;FIGS.3and4), first and second openings138and139may be considered to be (first and second) internal channels of zero length.

Print head1shown inFIG.5works in the same way as print head1shown inFIG.3, the other elements, not mentioned, being otherwise identical.

According to a variant of such third embodiment, the maintenance circuit does not have a second storage chamber136. Print head1then works in the same way as print head1shown inFIGS.1A and1B.

Finally, in another embodiment, print head1includes only one nozzle11, a first internal channel131opening into ejection zone2of nozzle11(as described in relation toFIG.2) or a first opening138and, advantageously, a second internal channel132opening into ejection zone2of nozzle11(as described in relation toFIG.4) or a second opening139. Feeder circuit12then includes only one dispensing channel124connecting storage chamber123to nozzle11.

An installation for the application (or printing) of a coating product over an object to be coated will now be described with reference toFIGS.6and7.FIG.6shows a fluidic diagram of a coating installation3according to a first embodiment, including print head1shown inFIG.1A and1B(or of the variant of the third embodiment).FIG.7shows a fluidic diagram of a coating installation3according to a second embodiment, including print head1shown inFIG.3(or inFIG.5).

In both embodiments, coating installation3includes (in addition to print head1):an injection circuit31connected to (at least) one inlet of print head1and configured for injecting maintenance fluid into print head1;a suction circuit32connected to (at least) an outlet of print head1and configured for sucking in maintenance fluid from print head1; anda supply circuit33for coating product (e.g., paint) connected to supply inlet121of feeder circuit12of print head1.

Supply circuit33for coating product may include at least one tank331for coating product, and at least one so-called filling valve332connected to tank331for coating product and connected to supply inlet121of feeder circuit12.

Injection circuit31(also called supply circuit for maintenance fluid) includes at least one pressurized tank311containing maintenance fluid, and at least one so-called injection valve312connected to pressurized tank311and connected to the inlet of print head1. “Pressurized” means that pressure inside the tank is higher than atmospheric pressure. Injection circuit31may also include means for adjusting pressure of the maintenance fluid. Such means of adjustment may be arranged between pressurized tank311and injection valve312. The means of adjustment include, e.g., a variable flow valve313. Alternatively, pressure may be adjusted at pressurized tank311or even further upstream (compressed air source, pump, etc.). Injection circuit31then advantageously includes a two-way valve313arranged between pressurized tank311and injection valve312.

Advantageously, injection circuit31includes:a first pressurized tank311acontaining cleaning fluid;a second pressurized tank311bcontaining wetting liquid;a first injection valve312aconnected to first and second pressurized tanks311aand311band connected to a first inlet of print head1; anda second injection valve312bconnected to first and second pressurized tanks311aand311band connected to a second inlet of print head1(distinct from the first inlet).

The means for adjusting maintenance fluid pressure may then include a variable flow control valve313coupled to each of first and second pressurized tanks311aand311b. First and second injection valves312aand312bare preferably two-way valves (such as a pneumatic valve, a solenoid valve, etc.).

Suction circuit32includes a vacuum generator321(venturi effect system or vacuum pump) and at least one so-called suction valve322connected to vacuum generator321and connected to the outlet of print head1. Furthermore, suction circuit32advantageously includes a collection volume323connected to vacuum generator321and intended for collecting maintenance fluid sucked in.

Advantageously, suction circuit32includes:a first suction valve322aconnected to vacuum generator321and connected to a first outlet of print head1; anda second suction valve322bconnected to vacuum generator321and connected to the second outlet of print head1(distinct from the first outlet).

First and second suction valves322aand322bare preferably two-way valves (such as a pneumatic valve, a solenoid valve, etc.). Conventionally, vacuum generator321may be a venturi effect system including an ejector, a compressed air buffer volume, a pressure gauge and means for adjusting negative pressure generated by vacuum generator321. Alternatively, vacuum generator321may include a vacuum pump arranged above collection volume323.

In the first embodiment (FIG.6), first injection valve312ais connected to first inlet-outlet133of maintenance circuit13, and second injection valve312bis connected to supply inlet121of feeder circuit12(or at purge outlet122of feeder circuit12, not shown inFIG.6).

Furthermore, first suction valve322ais connected to first inlet-outlet133of maintenance circuit13, and second suction valve322bis connected to supply inlet121of feeder circuit12(or to purge outlet122of feeder circuit12, not shown inFIG.6).

In other words, the first outlet of print head1and the second inlet of print head1are merged with first inlet-outlet133of maintenance circuit13. The second outlet of print head1and the first inlet of print head1are merged with supply inlet121of feeder circuit12.

In the second embodiment (FIG.7), first injection valve312ais connected to first inlet-outlet133of maintenance circuit13, and second injection valve312bis connected to second inlet-outlet137of maintenance circuit13.

Furthermore, first suction valve322ais connected to first inlet-outlet133of maintenance circuit13, and second suction valve322bis connected to second inlet-outlet137of maintenance circuit13.

In other words, the first outlet of print head1and the second inlet of print head1are merged with first inlet-outlet133of maintenance circuit13. The second outlet of print head1and the first inlet of print head1are merged with second inlet-outlet137of maintenance circuit13.

The two injection valves312aand312b, and the two suction valves322aand322bmay be used for carrying out the many maintenance operations described hereinabove.

First injection valve312aand first suction valve322aare advantageously controlled in anti-phase. In other words, when one is open, the other is closed, and vice versa. Second injection valve312band second suction valve322bare also advantageously controlled in anti-phase.

Advantageously, first injection valve312ais open only when second suction valve322bis open, and second injection valve312bis open only when first suction valve322ais open. Thus, injection of maintenance fluid always takes place at the same time as the suction.

According to a particular cleaning mode, first suction valve322a(second suction valve322b, respectively) is permanently open (continuous suction), and second injection valve312b(first injection valve312a, respectively) is intermittently opened, so as to produce pulses of cleaning fluid.

The two injection valves312aand312band the two suction valves322aand322ballow cleaning fluid to flow in both directions inside print head1, thus improving the cleaning operations. In the embodiment, e.g., shown inFIG.6, cleaning fluid may first be injected via first inlet-outlet133and sucked in via supply inlet121, then injected via supply inlet121and sucked in via first inlet-outlet133(or in the reverse order).

According to a variant of embodiment, coating installation3shown inFIG.7further includes a third suction valve connected to vacuum generator321and to supply inlet121, as well as a third injection valve connected to first and second pressurized tanks311aand311band connected to supply inlet121. Such variant of embodiment makes it possible to clean (in both directions) nozzles11and at least a portion of feeder circuit12. Cleaning fluid, e.g., may be injected via supply inlet121and sucked in via first inlet-outlet133and second inlet-outlet137(or vice versa).

Body10of print head1(containing nozzles11, feeder circuit12, and maintenance circuit13) may be manufactured in different ways. Examples include diffusion welding or brazing of metal foils, selective laser sintering of metal powder, micro-molding and silicon microelectromechanical systems (MEMS) manufacturing techniques.

Body10may also be composed of machined elements which are assembled by bonding or threading, where a seal may be installed between the different components to provide sealing.

A process for manufacturing body10of print head1may include:supply of a plurality of plates, wherein are fitted all or part of the components (channels, chambers, conduits, inlet and/or outlet holes, etc.) of nozzles11, of feeder circuit12, and of maintenance circuit13; andassembly of the plates together, e.g., by means of a welding, brazing or bonding technique.

The plates are preferably made of metal, e.g., of stainless steel. The plates are machined to form the different parts of nozzles11, of feeder circuit12, and of maintenance circuit13, e.g., by chemical cutting, laser cutting or electrical discharge machining (EDM). The plates (also called “strata”) preferably have a thickness between 10 μm and 1000 μm.

In a preferred embodiment of the manufacturing process, the metal plates are assembled by diffusion welding. The assembly then includes:putting the plates in contact so as to form a stack;pressure constraining of the stack, e.g., between 300 bar and 500 bar; andannealing (or heat treatment) of the pressure-constrained stack, in order to diffuse (or migrate) the atoms of the metal at the interfaces between the plates.

The annealing is preferably performed at a temperature between 0.6Tfand 0.8Tf, where Tfis the melting temperature of the metal. The annealing time may be between 1 h and 3 h.

The surfaces of the plates which are brought into contact preferably have a low surface roughness, typically less than 0.5 μm. The roughness value is expressed as a root-mean-square value.

Such a manufacturing process is precise, simple and rapid to implement (and thus inexpensive). Furthermore, when the diffusion welding technique is used, body10produced is robust, because body10is finally formed of only one piece (body10has a monolithic appearance). The diffusion welding technique is also advantageous in that this technique does not require any additional material (glue, filler metal, etc.) at the interfaces between the metal plates.

The membranes of the pneumatic valves belonging to nozzles11(in the case of a DOD head) are advantageously formed after manufacturing of body10.