Patent Description:
Continuous ink jet printers comprise a print head, which comprises a generator of drops of ink associated with a cavity for forming jets which contains means, most often one or several electrodes, in order to separate the trajectories of drops produced by the generator and direct them to a printing support or towards a gutter for recovering.

A <NUM>st problem linked to this type of print head is the deposition of dirt (or projections of ink) inside the cavity, in particular on the electrode or electrodes or on the walls or in the gutter for recovering drops not used for printing.

A solution to this problem of dirt consists in carrying out a manual cleaning of the cavity, which requires disassembling it beforehand. This means removing the head from its location in the product chain in order to bring it to a maintenance station, so as to recover the cleaning solvent without dirtying the conveyor or the products of the user (that the latter was in the process of marking or was going to mark before the interruption). Another solution is to bring a maintenance station around the head, as long as there is room. The head is then simply displaced, it is not disassembled from the production chain. However, the cover of the print head has to be removed or opened.

It is desirable to avoid manual intervention from the operator on the one hand because, in particular, such an intervention is a loss of time and that dirt is possible during this operation, but also, on the other hand, because the impact of this intervention on the effectiveness of the print head is not controlled (there can in particular be a disturbance effect on later operation).

Another problem is that of the forming of a jet, for example a jet of solvent, for the cleaning of the ink circuit; this jet is projected, by the nozzles that are usually used to form the ink jets, outside of the cavity which can be dirty and expensive (the liquid projected is indeed then not recoverable).

The same problems arise for a print head of the CIJ type.

<CIT>, discloses a method for cleaning a print head of a continuous ink jet printer. The print head comprises a cavity (inside head (<NUM>)) for the circulation of jets, and means for producing at least one inkjet in said cavity.

The invention first has for object a method for cleaning print head of a continuous inkjet printer, said print head comprising:.

According to the invention, the cavity comprises means, for example at least one spraying nozzle, in the cavity, for example in the <NUM>nd side wall (or in the bulk material under said <NUM>nd side wall) and/or arranged in such a way as to emit a jet of cleaning fluid, for example a gas, such as air, and/or solvent, from the <NUM>nd side wall of the cavity and/or which opens in this <NUM>nd side wall, in order to inject at least one cleaning fluid into the cavity.

At least one spraying nozzle can have a body at least partially cylindrical and comprise at least one nozzle or nozzle that opens into its cylindrical wall.

Said spraying nozzle can be fixed or movable.

In a method according to the invention, the print head can comprise at least one further spraying nozzle, fixed or movable, which projects a cleaning fluid toward a different portion of the cavity than said first fixed spraying nozzle. The spraying nozzle can comprise at least one body, preferably of tubular or cylindrical shape, provided with a nozzle.

The print head can further comprise means for driving the, or at least one of said, spraying nozzle(s), for example of the type comprising a body at least partially cylindrical and comprising at least one nozzle that opens into its cylindrical wall, in rotation about an axis (x), for example an axis perpendicular to a direction of flow of the jets in the cavity and/or parallel to a plane in which a plurality of jets flow and/or an axis parallel to the plane of the nozzle plate for forming jets (or means for producing an ink jet), preferably in such a way that it can project a cleaning fluid into the cavity at least towards the means for producing at least one ink jet in said cavity and, after or before rotation, to the gutter for recovering.

For example said means make it possible to drive said spraying nozzle in rotation over an angle at least equal to <NUM>° or <NUM>° or <NUM>°.

These means for driving said spraying nozzle in rotation comprise for example at least one motor and means of transmission between the motor and the spraying nozzle.

Preferably means for sealing are provided between, on the one hand, means for supplying at least said spraying nozzle with cleaning fluid and, on the other hand, the means for driving said spraying nozzle in rotation.

Thus, the latter being integrated into the print head, the risk of a flow or of a leak of cleaning fluid in the direction of the means for driving is reduced or prevented.

A print head according to the invention can further comprise means for evacuating, outside of the cavity, at least one portion of a cleaning fluid injected into the cavity, for example through at least one side wall comprising at least one orifice, or a slot, for evacuation.

For example said at least one orifice or slot for evacuating can be formed in the <NUM>nd side wall.

The print head can further comprise at least one orifice or at least one channel or slot for evacuating formed in the <NUM>st side wall, preferably in the vicinity of the means in order to produce a plurality of inkjets in the cavity.

The presence of several orifices or channels or slots for evacuation allows the print head to be used indifferently in several positions or orientations. In particular, when an orifice for evacuating is formed in each one of the side walls, and wherein the gutter for recovering can also be used as a channel for evacuation, there are at least three routes or channels for evacuating the cleaning liquid contained in the cavity.

According to a particular embodiment of a method according to the invention, the print head can comprise an accelerometer, which will make it possible to provide information concerning the orientation of the print head. This accelerometer is for example arranged inside the cavity for the circulation of jets or inside a dedicated cavity with one or several electronic components, which can be located in the vicinity of the cavity for the circulation of jets.

Information relative to the orientation of the print head makes it possible, in particular when the print head comprises several zones or channels for evacuation, to optimise, and/or to control, the cleaning sequences. In particular, it is possible to carry out a method of cleaning, separately or successively, of different zones and/or various zones or channels inside the cavity of the print head, with this method being according to the information relative to said orientation.

If the cavity comprises several orifices or channels for evacuation, the latter can advantageously be connected to the same actuation system, for example using the same pump.

In a method, at least one spraying nozzle advantageously projects a cleaning fluid in the form of a jet that diverges along an axis parallel to a flow direction of the ink jets and/or along an axis (x) according to which the nozzles for forming ink jets are aligned.

Preferably, at least one spraying nozzle projects a cleaning fluid in the form of a jet that diverges with an angle between <NUM>° and <NUM>° along an axis parallel to a flow direction of the ink jets.

The print head of a method can be with a binary continuous jet.

The print head of a method can be of the CIJ type, comprising at least one charging electrode (in addition to the elements already mentioned hereinabove concerning a print head according to the invention) and one or several deviation electrodes (for example: two deviation electrodes parallel to one another). A sensor for detecting charges carried by the drops can also be provided in the CIJ print head. Possibly, the means, comprising for example at least one spraying nozzle, in order to inject at least one cleaning fluid into the cavity, arranged in said cavity, can project at least one cleaning fluid, for example following a possible rotation of these means in order to inject at least one cleaning fluid, for example towards said at least one charging electrode.

According to a particular embodiment, the print head can comprise means for closing off the outlet slot. Thus, during the cleaning operations carried out using means for injecting or projecting a cleaning fluid into the cavity, leaks of this liquid through the outlet slot are prevented, leaks that could lead to splashes or to stains on a support intended for printing. An evacuation of this liquid can be carried out, for example, by the gutter for recovering or, possibly, by a channel or channels or orifice(s) for evacuation such as mentioned hereinabove.

The invention also relates to a continuous ink jet printer comprising at least a print head including,:.

For example, at least one of the following parameters can be a function of, and/or can be controlled based on, the information relative to the orientation of the print head:.

In a method for cleaning a print head according to the invention, the print head further comprising an accelerometer, one or more of the spraying nozzle(s) can have a plurality of possible orientations with respect to the inside of the cavity. The succession of orientations of the spraying nozzle(s) during the method of cleaning can then be a function of, and/or can be controlled based on, a piece of information relative to the orientation of the print head, given by the accelerometer: a <NUM>st succession of orientations is implemented for a <NUM>st orientation of the print head, while a <NUM>nd succession of orientations, different from said <NUM>st succession of orientations, is implemented for a <NUM>nd second orientation of the print head, different from the <NUM>st orientation.

The invention also relates to a method of cleaning according to the invention, or a method of cleaning a print head according to the invention, for example of the type comprising means for driving the spraying nozzle(s) in rotation about an axis (x), for example perpendicular to a direction of flow of the jets in the cavity and/or parallel to a plane in which a plurality of jets flow, comprising:.

The invention also relates to a method of cleaning according to the invention, or a method of cleaning a print head according to the invention, with this method comprising the projecting of several pulses of a cleaning jet alternating with pulses for ejecting solvent, in the cavity, by the means for producing at least one ink jet.

The invention also relates to a method of cleaning according to the invention, or a method of cleaning a print head according to the invention, with this method comprising the projecting of several pulses of a cleaning jet, with <NUM> successive pulses being separated by a duration chosen in such a way that, during this duration, a mixture of solvent and of ink, which results from the preceding pulse, can flow at least partially from the walls on which the cleaning liquid was projected but cannot dry. Thus, the later pulse will project cleaning liquid on a surface that is at least partially cleared, on the one hand of the cleaning liquid that was projected during the preceding pulse and, on the other hand, of the ink that was conveyed by this same cleaning liquid projected during the preceding pulse.

For example, each pulse is of a duration between <NUM> and <NUM>, with <NUM> successive pulses of jet being separated by a duration between <NUM> and <NUM>.

The invention also relates to a device for controlling an ink jet printer, for example of the binary or continuous jet (CIJ) type, able to, or specially programmed to, implement a method for cleaning or for controlling a print head such as described hereinabove or in this application.

Embodiments of the invention shall now be described in reference to the accompanying drawings wherein:.

In the figures similar or identical technical elements are designated by the same reference numbers.

An example of a structure of a print head to which the invention can be applied is explained hereinbelow, in liaison with <FIG>.

The head comprises a drop generator <NUM>. This generator comprises a nozzle plate <NUM> on which are aligned, along an axis X (contained in the plane of the figure), a whole number n of nozzles <NUM>, of which a first <NUM><NUM> and a last nozzle <NUM>n.

The first and last nozzles (<NUM><NUM>, 4n) are the nozzles that are the farthest apart from each other.

Each nozzle has an axis of emission of a jet parallel to a direction or an axis Z (located in the plane of <FIG>), perpendicular to the nozzle plate and to the axis X mentioned hereinabove. A third axis, Y, is perpendicular to each one of the two axes X and Z, the two axes X and Z extending in the plane of <FIG>.

In the figure, the nozzle <NUM>x is shown. Each nozzle is in hydraulic communication with a pressurised stimulation chamber. The drop generator comprises as many stimulation chambers as there are nozzles. Each chamber is provided with an actuator, for example a piezoelectric crystal. An example of the design of a stimulation chamber is described in document <CIT>.

Downstream of the nozzle plate are means, or sorting block, <NUM> that make it possible to separate the drops intended for printing from the drops or segments of jets that are not used for printing.

The drops emitted or segments of jets, emitted by a nozzle and intended for printing, follow a trajectory along the axis Z of the nozzle and will strike a printing support <NUM>, after having passed through an outlet slot <NUM>. This slot is open onto the exterior of the cavity and allows for the exiting of the drops of ink intended for printing; it is parallel to the direction X of alignment of the nozzles, the axes of direction Z of the nozzles passing through this slot, which is located on the face opposite the nozzle plate <NUM>. It has a length at least equal to the distance between the first and the last nozzle.

In the rest of this application as well as in the claims, the term "cavity" designates the zone of the space in which the ink circulates between the nozzle plate <NUM> and the outlet slot <NUM> of the drops intended for printing or between the nozzle plate and the gutter for recovering. The nozzle plate <NUM> forms in fact an upper wall of the cavity.

The drops emitted or segments of jets, emitted by a nozzle and not intended for printing, are deviated by the means <NUM> and are recovered by a gutter for recovering <NUM> then recycled. The gutter has, in the direction X, a length at least equal to the distance between the first and the last nozzle.

A cross-section view of this structure of a print head is shown in <FIG>. This cross-section is made along a plane parallel to the plane YZ, and containing the axis Z of a nozzle <NUM>x. The cross-section retains the same form over the distance going, in the direction X (perpendicular to the plane of <FIG>), from the first nozzle <NUM><NUM> to the last nozzle <NUM>n. This figure shows the cavity <NUM> in which the jets circulate.

P<NUM> is used to designate the plane which passes through the nozzle 4x and which is parallel to the plane XZ. This plane is perpendicular to <FIG> and passes through all of the nozzles, which are aligned along X. It also passes through the slot <NUM>. A lug of this plane is shown in <FIG> as broken lines.

The upper portion of the cavity is delimited by the wall <NUM>, which also forms, or comprises, the nozzle plate or comprises the nozzles. The lower portion of the cavity is delimited by a lower wall <NUM>, passed through by the slot <NUM>, and by a portion of the gutter <NUM>. Walls <NUM> and <NUM> limit the lateral extension, according to the Y axis. It can be noted that the notion of a portion or of "upper" or "lower" wall is to be understood in relation to the flow direction of the jet or jets in the cavity: indeed, the print head can be used to print a substrate arranged under the print head, as shown in <FIG>; but the print head can be turned, with the jet being directed upwards, in order to print a substrate arranged above the print head (this configuration is not shown in the figures, but it is sufficient to turn <FIG> in order to obtain it). It can also be used in the horizontal position.

The cavity comprises in addition, on one side of the plane P<NUM>, a side wall <NUM>, preferably parallel to the plane P<NUM> and joining with the nozzle plate <NUM>. A wall <NUM>, located on the other side of the plane P<NUM>, faces the wall <NUM>. The cavity is therefore delimited, on either side of the plane P<NUM>, by these <NUM> walls <NUM> and <NUM>. By convention the side of the plane P<NUM> where the wall <NUM> and the gutter <NUM> are is called the first side of this plane, the other side (where the wall <NUM> is), is called the second side.

The wall <NUM> has ends, in the direction X, which are joined with the nozzle plate <NUM>. In the portion close to the nozzle plate <NUM> and over a length that is, preferably, slightly greater than the distance between the first <NUM><NUM> and the last nozzle <NUM>n, this wall can comprise a slot <NUM>, that will make it possible to suck the ink that has just been deposited on the nozzle plate or in the vicinity thereof.

At the bottom of this wall <NUM> is the input slot of the gutter for recovering <NUM> in order to make it possible to recover the drops which are deviated so that they do not pass through the slot <NUM>.

The gutter can be placed in hydraulic communication with the slot <NUM>, using a duct <NUM> that opens into the gutter and which is located at the rear of the wall <NUM> in relation to the plane P<NUM>.

On the wall <NUM>, are means <NUM>, which are preferably flush with wall <NUM>, for selecting and for deviating the drops that are not intended for printing. These means mainly comprise an electrode or electrodes. They are intended to be connected to means for supplying voltage, not shown in figure.

Preferably, the distance between the wall <NUM> and the plane P<NUM>, measured in the direction Y, perpendicular to the plane P<NUM>, is, starting from the plate <NUM>, first of all constant; this corresponds to a <NUM>st portion <NUM><NUM> of the wall <NUM>, which is substantially parallel to P<NUM>.

Then, in a second portion <NUM><NUM>, farther from the plate <NUM> than the <NUM>st portion <NUM><NUM>, starting from a point <NUM> of inclination of the wall <NUM>, the distance between the wall <NUM> and the plane P<NUM> increases with the separation of the nozzle plate.

This structure allows the wall <NUM> to be close to the plane P<NUM>, and parallel to the latter, in a <NUM>st portion of the cavity located in the vicinity of the nozzles <NUM>x, where the path of the drops is hardly modified, even when the drops located farther downstream on this path are deviated in order to enter into the gutter for recovering <NUM>.

This is what is seen in <FIG>, where a path of drops is deviated towards the gutter <NUM>: the upper portion of the jet is not, or is hardly, deviated, while, starting from a point <NUM> of inclination of the wall <NUM>, the jet is increasingly moved apart, almost linearly, from the plane P<NUM>. This can be considered a ballistic trajectory of the jet downstream of the electrostatic field zone.

A lower portion of the wall <NUM> and a wall <NUM>, located at the rear of the wall <NUM> in relation to the plane P<NUM>, define, by facing a wall <NUM>, a duct, or gutter <NUM> for evacuating drops that will not be used for printing.

The walls <NUM> and <NUM> are, preferably, joined together, with the reference <NUM> designating the junction line of these two walls <NUM> and <NUM>; this line is parallel, or substantially parallel, to the direction X. They form an upper wall of the gutter.

The wall <NUM> forms a lower wall of the gutter. It comprises a <NUM>st portion <NUM><NUM>, the most upstream in the direction of circulation of the drops in the duct <NUM>, <NUM> and a second portion <NUM><NUM>, the most downstream.

The possible duct <NUM> can open into the upper wall <NUM> and hydraulically connect the gutter for recovery <NUM> to a duct <NUM> hydraulically connected to the slot <NUM>.

The reference <NUM> designates a junction line of the portions <NUM><NUM> and <NUM><NUM> of the wall <NUM>; this line is parallel, or substantially parallel, to the direction X and to the line <NUM>.

The portion <NUM><NUM> the most upstream, at the inlet of the duct <NUM> of the lower wall <NUM>, ends with an end portion <NUM>, which, advantageously, forms its apex (or top). This is the point of the surface <NUM> which is the closes to the plane P<NUM>.

Preferably, this apex <NUM> is also part of a wall <NUM> which is parallel to the plane P<NUM> and which forms one of the walls surrounding or delimiting the outlet slot <NUM>. In other words, the point the farthest upstream of the gutter is in line with the outlet slot <NUM> of the cavity. This makes it possible to optimise the recovery of the drops: thanks to this configuration, any deviated drop, even slightly, will be recovered by the gutter.

The slot <NUM> forms an opening of the cavity <NUM> through which pass the drops intended for printing. <FIG> shows as a dotted line a line that materialises the axis of the nozzle <NUM>x. This axis passes through the centre of the slot <NUM>.

Another wall of the cavity is formed by the wall <NUM>: it is substantially parallel to the plate <NUM>, but the farthest away from the latter in the cavity <NUM>. In other terms, it is located on the side of the outlet slot <NUM>. An end of this wall can form an entry edge of the slot <NUM>, facing the wall <NUM> already mentioned hereinabove.

A wall <NUM>, substantially perpendicular to the wall <NUM>, delimits, with the wall <NUM>, the outlet slot <NUM>: the drops will circulate between these <NUM> walls, before exiting from the slot <NUM> and becoming crushed on the printing support <NUM>.

The reference <NUM> designates the outer surface of the cavity, into which the outlet of the slot <NUM> opens.

An example of the operation of this cavity is as follows.

A continuous jet of ink is emitted by the drop generator. The deflection of this jet is carried out or controlled by the electrode or electrodes <NUM> in order to create, according to a pattern to be printed and the position of the support <NUM>, drops intended or not for printing.

According to an embodiment, segments of ink are generated, which are intended to not be printed, adjacent segments are able to be separated by a drop, which is intended to be printed. This technique is explained in document <CIT> or <CIT>. In such a case, the cavity:.

In other embodiments, and in particular in the case of continuous ink jet printers (of which an example is given further on in liaison with <FIG>) drops are formed, then possibly charged (with at least one charging electrode) and then possibly deviated (with at least one deviation electrode), according to the printing, or not, of the generated drops. The drops not used for printing are recovered in the gutter.

The drops intended for printing are displaced along the axis Z (in the plane P<NUM>) and pass through the slot <NUM>.

The drops, or the segments of ink, not intended for printing are deviated from the axis Z (or from the plane P<NUM>), and follow a trajectory that leads them to strike the lower wall <NUM> of the gutter <NUM>.

As the gutter is connected to a source of a vacuum, the ink that struck the wall <NUM>, leaves, with air, the cavity <NUM> by the gutter.

Moreover, the duct <NUM> and the slot <NUM> can maintain a slight vacuum on the nozzle plate <NUM>. This vacuum makes it possible to absorb ink that, via capillarity, is deposited on the nozzle plate <NUM>.

A problem linked with this type of print head is the deposition of dirt (or projections of ink) inside the cavity, in particular on the electrode or electrodes <NUM> or on the walls <NUM>, <NUM>, or in the gutter <NUM> for recovering drops not used for printing.

An example of a structure of print head according to the invention is shown in <FIG>.

This example includes most of the elements presented hereinabove in liaison with <FIG>. Consequently, numerical references identical to those of these figures designate therein the same elements, or corresponding elements.

In the example shown in <FIG>, at least one spraying nozzle comprising a nozzle <NUM>, allowing for the projection of a fluid or cleaning fluid, for example a gas and/or a liquid, is at least partly mounted in the wall <NUM>, and/or in the material delimited by said wall <NUM> and or in a cavity made in said wall, as shown in <FIG>; preferably it is able, from said wall <NUM>, to project or to send a cleaning fluid towards at least the wall <NUM> and/or towards the nozzle(s) and/or towards the input or inlet slot of the gutter for recovering <NUM>; if the cavity comprises N nozzles <NUM>x for forming jets (which nozzle(s) are different from the spraying nozzle(s) <NUM>), arranged along an axis parallel to the X axis, the cleaning jet <NUM> is preferably projected over the entire length of the cavity, measured according to the X axis. As shown in the example of <FIG>, which is a top view, the spraying nozzle can comprise an element, or spraying nozzle body, <NUM>, for example of tubular or substantially cylindrical shape, whereon or wherein the nozzle <NUM> is mounted; the spraying nozzle is preferably rotating about an axis parallel to the X axis (as explained in more detail hereinbelow). <FIG> show view of an embodiment of the spraying nozzle.

In the body of the spraying nozzle <NUM>, a channel 24c for supplying with gas and/or with solvent makes it possible to bring cleaning fluid to the nozzle <NUM>. This channel is interior to the body of the spraying nozzle <NUM>, and it is itself supplied by a side feed channel 28a (<FIG>) which is made in an end part <NUM> (<FIG>) that makes it possible to direct the fluid supplied by means for supplying <NUM>, <NUM>, <NUM> to the channel 24c interior to the body of the spraying nozzle <NUM>. This part <NUM> is fixed in relation to the print head if the body <NUM> of the spraying nozzle is rotating. This part <NUM> forms a connection between the means for supplying <NUM>, <NUM>, <NUM> and the channel 24c. According to an embodiment, the channel 28a is bent, as can be seen in <FIG>. This configuration favours the conveying of the fluid from the means for supplying <NUM>, <NUM>, <NUM> to the inner channel 24c of the body of the spraying nozzle.

Preferably, the means for supplying <NUM>, <NUM>, <NUM>, made in the print head, comprise one or several channels, for example several channels for introducing air and/or solvent <NUM>, <NUM>; one and/or the other of these channels can for example be closed off by a valve, for example of the plunger type. For example, the channel <NUM> and the channel <NUM> can bring different fluids (one able to bring a gas, for example air, and the other solvent): means for closing off, for example a valve, for example also of the plunger type, make it possible to close off the channel <NUM> when using the fluid that passes through the channel <NUM>, and/or means for closing off make it possible to close off the channel <NUM> while when using the fluid that passes through the channel <NUM>. According to an embodiment, a common channel <NUM> is supplied by channels <NUM>, <NUM>. The channel <NUM> joins, at one of its ends, the channel 28a of the part <NUM>. The outlet orifice of the nozzle <NUM> is preferably such that the cleaning jet <NUM> that exits therefrom is divergent: it is projected, in a plane perpendicular to the X axis, by widening from the nozzle <NUM>, the jet is symbolised by broken lines in the cross-section view of <FIG>. The angle α, formed by the upper and lower limits of the jet, is for example between <NUM>° and <NUM>°.

<FIG> is a top view of a preferred embodiment of geometry of the jet <NUM> projected: in this example, the cleaning nozzle <NUM> is designed so that the cleaning jet <NUM> diverges, in the plane xy, from the outlet of the nozzle <NUM>. Due to this widening of the jet from the nozzle <NUM>, practically the entire cavity (according to the X axis) can be cleaned. <FIG> shows the means <NUM> for deviating jets (arranged in or against the wall that faces the wall <NUM> from which the cleaning jet comes), the front <NUM> and rear <NUM> walls of the cavity and the spraying nozzle <NUM>. The other elements of the cavity are not shown. But it is understood well, in this figure, that the cleaning jet can reach a large portion of the cavity, measured according to the X axis. If, in addition, the spraying nozzle <NUM> is rotating (about an axis parallel to the X axis), then it can successively reach the nozzles <NUM>x for forming jets, then the means <NUM>, then the suction slot of the deviated jets.

The nozzle makes it possible to project the solvent along a substantially rectangular surface, extended according to the length of the nozzle plate (therefore along the axis x); in other terms, each cross-section, according to a plane perpendicular to the X axis, is identical or substantially identical to the cross-section shown in <FIG>. Such a geometry for the projection of solvent makes it possible to obtain a good compromise between the effectiveness of the cleaning and the quantity of solvent used.

The walls of the nozzle <NUM> are therefore preferably oriented in order to obtain a shape of the jet <NUM> that is diverging, widening from the outlet of the nozzle <NUM>, in the plane yz (<FIG>) as well as in the plane yx (<FIG>).

<FIG> diagrammatically show examples of walls <NUM><NUM>, <NUM><NUM>, <NUM><NUM>, <NUM><NUM> of the nozzle <NUM> that make it possible to favour this widening of the jet, in a plane xy as well as in the plane yz.

<FIG> show a device with a single nozzle <NUM>. Alternatively, several cleaning nozzles <NUM>, <NUM>', <NUM>" can be mounted in the cavity, as shown in <FIG>.

In <FIG> the nozzles are aligned along an axis (parallel to X). <FIG> shows an alternative wherein several nozzles 20a, 20b, <NUM>'a, <NUM>'b, <NUM>"a, <NUM>"b are arranged along different axes, parallel to x.

According to an embodiment, at least two of the nozzles <NUM>, <NUM>', <NUM>" of <FIG> or at least two of the nozzles 20a, 20b, <NUM>'a, <NUM>'b, <NUM>"a, <NUM>"b of <FIG> make it possible to direct a cleaning fluid towards the various portions inside the cavity. According to an advantageous configuration, a nozzle makes it possible to direct a cleaning fluid towards the gutter for recovering drops.

Preferably, all of the nozzles make it possible to reach all the walls of the inside of the cavity; this can depend on the shape of the interior walls of the cavity. The embodiment shown in <FIG> and described further on in this application makes it possible to reach all of the interior walls of the cavity.

Preferably, each one of the nozzles of <FIG> can emit a cleaning jet that has for example, seen from above, a diverging shape as shown in <FIG> and <FIG>.

<FIG> shows an embodiment of the supplying with fluid(s) of the cleaning device according to the invention. A channel <NUM> for supplying comprises a valve <NUM>, of the plunger type, provided with a head <NUM> that makes it possible to close off the end of the channel <NUM> when it is in the high position (the low position, open, being shown in <FIG>). Thus, when a fluid (air and/or solvent) arrives via the channel <NUM> (because it was pressurised), it pushes the valve <NUM> upwards, which closes the channel <NUM>. Inversely, a fluid (air and/or solvent) arrives under pressure via the channel <NUM>, this fluid pushes the valve <NUM> downwards, which thus opens the channel <NUM>. The head <NUM> of the valve <NUM> can be provided with means <NUM> (for example one or several seals) that ensure the seal of the closing of the canal <NUM> and when the valve is in its top position.

The fluid introduced into this system is then sent inside the spraying nozzle <NUM> (as symbolised by the arrows 24f of <FIG>) by the intermediary of the channel 28a of the part <NUM>.

As indicated hereinabove, preferably, the spraying nozzle <NUM> is rotating about an axis which is, preferably, parallel to the X axis, i.e. substantially perpendicular to a direction of flow of the jets in the cavity (but other orientations of this axis of rotation are possible, for example parallel to said flow direction of the jets and/or parallel to a plane in which a plurality of jets flow); means, in particular an electric motor, are provided to drive the nozzle in such a movement of rotation; it is therefore possible to carry out a rotation of the spraying nozzle <NUM> over a certain angle, for example at least <NUM>° or at least <NUM>° or <NUM>°. According to an embodiment, the movement of rotation makes it possible to project a cleaning liquid, successively towards the N nozzles <NUM><NUM> - <NUM>, for forming jets, then towards the means <NUM> of deflection, then towards the gutter for recovering <NUM> (or in a different order). The entire cavity, or a substantial portion of the latter, can then be cleaned. It is also possible to carry out a rotation of the spraying nozzle <NUM> over an angle greater than <NUM>°, for example up to <NUM>°, so as to also be able to clean the portions of the system arranged behind the spraying nozzle <NUM> (when the nozzle is turned towards the cavity <NUM>).

<FIG> is a cross-section view, along a plane parallel to the plane xz, of a portion of the print head, in particular of the spraying nozzle <NUM> (of which, because of the cross-section view, only one portion, the front portion, can be seen, and in particular the nozzle <NUM> does not appear); it shows how this spraying nozzle <NUM> can be driven in rotation.

The spraying nozzle <NUM> is inserted into a cavity <NUM> made in the print head, with a substantially cylindrical shape. If the spraying nozzle can be driven in rotation according to a sufficient angle, the inside of this cavity <NUM> can be cleaned by the jet coming from the nozzle <NUM>. Means of sealing <NUM> can be provided between the spraying nozzle <NUM> and the surface of the cavity <NUM> in which it is arranged.

A motor <NUM> is arranged in a cavity 40c made also in the print head. Means of transmission <NUM> makes it possible to drive in rotation an axis <NUM>, of which one end is inserted into an opening 24o with a substantially cylindrical shape made in the body of the spraying nozzle <NUM> itself. The axis <NUM> is also press-fitted into a part <NUM> present in the cavity 50i (between the cavity <NUM> and the cavity 40c), preferably with a general cylindrical exterior shape. This part <NUM> makes it possible to provide the seal with respect to the motor: for this purpose, the outer surface of this part <NUM> can advantageously be provided with means <NUM> that make it possible to provide the seal at the interface between its outer surface and the inner surface of the cavity 50i.

The part <NUM> can be driven in rotation by the axis <NUM> in the cavity 50i. Preferably, this part <NUM> is glued or brazed on the axis <NUM>, the gluing or the brazing contributes to the seal of the system.

The axis <NUM> is enlarged, at its base, by a plate <NUM> p, which is driven in rotation by a reduction box <NUM> which retransmits the movement imposed by the motor <NUM>.

The movement of the latter is therefore transmitted to the axis <NUM> by the intermediary of the set <NUM>, 46p, with the part <NUM> being driven in rotation while still ensuring a seal with the means <NUM>.

The cleaning fluid is injected into the spraying nozzle <NUM> (more exactly into the cavity <NUM> c) by the end of the latter opposite that located on the side of the means <NUM>, <NUM>, <NUM> for driving it in rotation. The cavity 24c extends along a portion of the spraying nozzle <NUM>, while the opening 24o extends along another portion of the spraying nozzle <NUM>.

If the device comprises the means of sealing <NUM>, <NUM>, liquid that would escape from the circuit for supplying with cleaning fluid would first be blocked by the means <NUM> for sealing, then by the means <NUM> and by the gluing or the brazing of the part <NUM> on the axis <NUM>.

<FIG> also shows the channel 28a through which the cavity 24c is supplied.

This duct is arranged in fact in the part <NUM>, which forms both a closure cap of the end of the body of the spraying nozzle <NUM> as well as a connector between the latter and the means for supplying <NUM>, <NUM>, <NUM>. Means of sealing <NUM> can be provided between this cap <NUM> and the cavity 48c in which it is arranged. Here again, these means of sealing <NUM> makes it possible to obstruct any flow of the cleaning liquid outside of the channels wherein it circulates.

<FIG> show <NUM> views of the spraying nozzle <NUM> wherein numerical references identical to those of the preceding figures are marked in order to designate therein the elements that have already been described hereinabove. The nozzle <NUM> for projecting is in particular present. When the spraying nozzle is driven in rotation about its longitudinal axis, the nozzle <NUM> is directed towards various portions of the cavity that it can thus clean. Alternatively, as already explained hereinabove in liaison with <FIG>, the spraying nozzle <NUM> can comprise several slots for projecting cleaning liquid: the supplying with fluids is then the same as that described hereinabove, for example in liaison with <FIG>, <FIG> and <FIG> and/or the spraying nozzle <NUM> can be driven in rotation in the same way as described hereinabove.

Means can be provided for carrying out a suction of the solvent projected into the cavity.

First of all, according to an embodiment, this suction is carried out by the gutter <NUM>. Possibly, as shall be seen hereinbelow, a <NUM>nd gutter can be provided, which can also contribute to the suction of the cleaning solvent that streams in the cavity.

Moreover, solvent can be sucked by a suction slot <NUM> made at the top of cavity (<FIG>), by the intermediary of a duct <NUM>.

Finally, solvent can be sucked by a suction slot <NUM> made in the wall wherein the spraying nozzle <NUM> is positioned; this slot is shown in <FIG>, but also in <FIG>. The corresponding cleaning liquid can be driven towards the outside of the cavity by an evacuation slot 15e, shown in <FIG>, which can, for example, be extended by a suction duct, which can possibly be connected to the main suction circuit by means of a valve, which makes it possible or not to suck the liquid that is in the cavity. Advantageously, the wall has a locally pyramidal shape, with locally inclined side walls so that, regardless of the position of the print head, gravity favours the flow of the cleaning liquid.

Means for suction, for example a pump (not shown in the figures) can be specific to each suction channel, but are preferably common to the various evacuation channels.

The presence of the <NUM> evacuation routes mentioned hereinabove makes it possible to use the head in any position whatsoever, with the cleaning liquid able to be evacuated by the intermediary of any one of them whatsoever. Indeed, as already indicated hereinabove, the print head can be used as shown in <FIG>, with a printing support <NUM> being arranged under the head and the jet flowing from the nozzle to the slot <NUM>, then towards the support <NUM>; but it is also possible to use the print head in any other position, in particular in the position that is the reverse of that of <FIG>, with the printing support being arranged above the head, with the latter being turned over and the jet rising from <NUM> the nozzle to the outlet slot <NUM>, in the direction of the support <NUM>. As described elsewhere in this application, an accelerometer can make it possible to detect the position of the print head.

In order to reinforce the effectiveness of the means of suction, it is possible, during the operations of cleaning the inside of the cavity, to close the slot <NUM>, for example with a plate 17p, shown in <FIG>, which can be actuated, for example switched, between an open position (as in <FIG>), and a closed position wherein it obstructs the slot <NUM>. The actuating of this plate 17p can be manual or controlled by means for controlling such as the controller of the printer with which the print head is used. Another example of means for closing the slot is the use of a <NUM>nd gutter, that is movable, as explained hereinbelow. Regardless of the embodiment implemented, the closing of the slot makes it possible to force the liquid used for the cleaning of the inside of the cavity to flow through one of the suction routes mentioned hereinabove.

An example of the method of cleaning is as follows:.

During each orientation of the nozzle <NUM>, the cleaning liquid can be sent by pulses, for example pulses between <NUM> and <NUM>, with each pulse being separated from the following one by a duration that can be about a few seconds, for example between <NUM> and <NUM> seconds. Possibly, these pulses can be synchronised with solvent ejection pulses by the printing nozzles <NUM>x. Indeed, the latter emit jets which are much more powerful than the jet emitted by the cleaning nozzle <NUM>. It is then possible to carry out, successively: the emitting of a cleaning jet by the nozzle <NUM>, then of jets by the nozzles <NUM>x, then again the emitting of a cleaning jet by the nozzle <NUM>. etc. Furthermore, it is possible, after a projecting of cleaning liquid by the nozzle <NUM> towards the nozzles <NUM>x, to suck solvent by these same nozzles <NUM>x, which makes it possible to remove the impurities (that can result from the deposition of ink or of particles contained in the ink) which may have entered into the stimulation changers and in the ducts which are upstream of these same nozzles <NUM>x.

The duration of separation of <NUM> successive pulses of cleaning liquid emitted by the nozzle <NUM> is preferably chosen in such a way that the mixing of solvent and of ink that is flowing due to the pulse of the preceding cleaning liquid has not yet dried. In other terms, this duration of separation is chosen so that said mixture has already been able to flow from the walls on which the cleaning liquid was projected (thus, the following pulse will not be ineffective) but also so that this mixture is not yet dry. Indeed, the drying can intervene rather quickly after a single pulse, in particular in the case of a solvent of the MEK (methyl-ethyl-ketone) type.

The invention was described hereinabove with the presence, for example in a wall of the cavity, of a spraying nozzle, movable or fixe, and provided with one or several nozzles for projecting cleaning fluid.

But the cavity can comprise several spraying nozzles, with each one being one of the types described hereinabove.

For example, the cavity can comprise at least one movable spraying nozzle and at least one fixed spraying nozzle. In particular, at least one fixed spraying nozzle can be positioned in order to direct a cleaning jet towards a specific zone, for example the gutter for recovering.

In the case, disclosed further on, wherein the print head further comprises a movable gutter:.

<FIG> diagrammatically shows a cavity, such as it was described hereinabove but comprising a plurality of spraying nozzles (here <NUM> spraying nozzles are shown) <NUM>, 24a, 24b, which are for example fixed and which are directed in such a way that the jets that they project make it possible to reach various portions inside the cavity. <FIG> does not show the wall <NUM> wherein the spraying nozzles are integrated. It can be seen, in this figure that one of the jets makes it possible to reach an upper portion of the cavity, preferably the nozzles <NUM>x for projecting ink jets into the cavity, while another jet is directed towards the electrode <NUM> and the third is directed towards the input slot of the gutter for recovering.

During a stopping phase of the machine, as no nozzle <NUM>x is producing any jet of ink, it is possible to carry out a cleaning, for example by at least one spraying nozzle (fixed or movable) and/or by ejecting solvent by the printing nozzles <NUM>x.

An embodiment of the <NUM>st gutter <NUM> was given hereinabove, in liaison with <FIG>.

Another embodiment (<FIG>) can be taken in combination, or not, with the preceding one. The device then comprises <NUM> gutters, of which one is mobile in translation in relation to the print head.

A <NUM>nd gutter <NUM> is shown in <FIG>, wherein the numerical references identical to those of the preceding figures designate therein identical elements. Thus, there is the electrode or the electrodes <NUM>, the spraying nozzle <NUM>, the nozzle <NUM>, the <NUM>st gutter <NUM>. It can also be seen, in this embodiment, that the slot <NUM> is located in the part wherein the <NUM>st gutter is made.

As can be seen in <FIG>, the <NUM>nd gutter <NUM> can comprise:.

Means can be provided to actuate this <NUM>nd gutter in translation, between a position, referred to as "closed" in which its input slot comes into the extension of the outlet slot <NUM> of the cavity, and a position, referred to as "open", of which the outlet slot <NUM> of the cavity is cleared.

For example, in the closed position, the inlet orifice <NUM> of the <NUM>nd gutter, mobile, is bearing against the outer surface <NUM> of the cavity, in such a way that its inlet slot <NUM> comes in the extension of, or in front of, the outlet slot <NUM> of the cavity, both slots facing each other (so that a drop of a jet flowing or circulating through the outlet slot <NUM> then flows through the inlet slot <NUM> and into the <NUM>nd gutter); preferably, the outer surface and/or the <NUM>nd gutter comprise(s) means for sealing <NUM> in such a way that the liquid cannot exit via the support zone of the <NUM>nd gutter against the outer surface <NUM> of the cavity; for example the <NUM>nd gutter comprises one or several seals that bear against the outer surface <NUM>, in the vicinity of the outlet slot <NUM>.

For example, this second gutter makes it possible to recover, at the start-up of the print head, both the initial solvent then the curtain of ink. It has, preferably, the same characteristics, in particular geometrical, as the main gutter.

The <NUM>nd gutter (or, in the embodiment that has just been described, its second portion <NUM>) can also be connected to means for sucking a fluid which is present in this <NUM>nd gutter, for example by the intermediary of a suction channel connected to the <NUM>nd portion <NUM>; preferably, the means for sucking of the <NUM>nd gutter and those of the <NUM>st gutter are connected to the same means of pumping. Possibly, one or several solenoid valves make it possible, or not, to individually activate the operation of each one of these gutters. This second gutter, when it is in the closed position, also forms a means for sucking cleaning solvent that streams or flows in the cavity; it can therefore come as a supplement of the various channels for recovering already mentioned hereinabove.

According to an embodiment (<FIG>): an outlet face of the cavity is inclined in relation to the flow direction of the jets in the cavity (or axis z), for example by an angle β (see <FIG>) between <NUM>° and <NUM>°; the input face of the <NUM>nd gutter is also inclined, substantially by the same angle, in such a way that the <NUM> faces come into contact with one another, or are facing, when the <NUM>nd gutter is in the closed position (as shown in <FIG>). This embodiment with inclined faces is favourable to a good sealing of the cavity when the <NUM>nd gutter is in this closed position.

The <NUM>nd gutter can be placed into a movement of translation according to a direction substantially perpendicular to the flow direction z of the jets in the cavity, in one direction, to its closed position, then in the other direction, from its closed position to its open position; for example an actuator, such as a motor <NUM> or an electric motor, (shown in <FIG> behind the motor <NUM>) makes it possible, by the intermediary of means of transmission, or a transmission device, to displace the <NUM>nd gutter to the position in which its inlet orifice <NUM> comes into the extension of the outlet slot <NUM> of the cavity (as explained above, so that a drop of a jet flowing or circulating through the outlet slot <NUM> then flows through the inlet slot <NUM> and into the <NUM>nd gutter); when it is no longer necessary to maintain the <NUM>nd gutter in the closed position, it is placed into movement in the opposite direction by the same means in order to return to its open position.

Means of return, for example a spring <NUM> (<FIG>) make it possible to maintain the <NUM>nd gutter bearing in one of the open or closed positions; for example, the spring <NUM> is pre-tensioned, and maintains the second gutter in the open position. This spring is wound on an axis <NUM>, which transmits the movement of the motor <NUM>. The latter makes it possible to bring the <NUM>nd gutter <NUM> from the open position to the closed position; one end <NUM> of this spring is connected to the <NUM>nd gutter and drives the latter in translation; the gutter can be guided in its movement of translation by guide lugs, for example the lugs <NUM> of <FIG>. These lugs <NUM> allow the gutter to slide against the outer surface <NUM> of the cavity. Lugs <NUM> (not able to be seen in <FIG>, but visible in <FIG>; note, with respect to these <NUM> figures, the simplified nature of <FIG>), located under the <NUM>nd gutter, allow the latter to slide against the inner surface of a cover <NUM>. Laterally, the gutter can be guided in translation also by lugs <NUM> (of which one can be seen in <FIG>) which slide against side walls, for example of the cover <NUM>, between which it can come and go between its closed position and its open position.

Preferably, for reasons of space, the <NUM>nd gutter is arranged, in relation to a plane such as the plane P0 of <FIG>, on the side opposite the fixed gutter. Furthermore, this arrangement makes it possible to carry out a single movement of translation of the movable gutter.

<FIG> shows a situation wherein the <NUM>nd gutter is in the open position, the ink jet able to exit and be projected onto a printing support; the <NUM>st gutter operates in the usual way, in order to recover the drops of deviated jets.

<FIG> is a perspective view of an embodiment of a movable gutter, that can be incorporated into a print head of the type described hereinabove.

Its inlet slot <NUM> is surrounded by a seal <NUM> which makes it possible to provide the seal when it comes facing the outlet <NUM> of the cavity, in the closed position (as in the <FIG>). An orifice <NUM> can also be seen through which the atmosphere and the liquids sucked by the input slot <NUM> will be removed towards a suction circuit not shown in the figures.

As already indicated hereinabove, it is possible to carry out a print head with <NUM> gutters, one fixed and the other movable, without means for projecting a cleaning jet into the cavity (i.e. without the elements described hereinabove in liaison with <FIG>).

The <NUM>nd gutter can be brought into a closed position:.

An example of a method of cleaning that implements a cleaning nozzle <NUM>, according to one of the embodiments described hereinabove in liaison with <FIG> is the following:.

This type of cleaning can be carried out regularly and/or in the presence of dirt, and/or during stopping and restarting phases of the printer.

During these operations, one and/or the other gutter can be cleaned using a spraying nozzle (for example the spraying nozzle <NUM> of <FIG>) that is dedicated to it and therefore the jet is directed towards it.

The <NUM>nd gutter can be provided with conductive means in order to detect electrical charges carried by drops or segments of inkjets that it will recover.

Thus, it can be seen in <FIG> that at least one portion of the base of the movable gutter comprises at least one conductive portion <NUM> against which the charged drops will come into contact as soon as they penetrate into this <NUM>nd gutter. This conductive portion can be connected to means for detecting, for example means for counting detected charges or for measuring current (for example an ammeter), which will make it possible to measure the charge thus recovered.

These means for detecting are therefore active when the gutter is in the closed position and, for example, charges are detected although all of the jets should be deviated towards the <NUM>st gutter, fixed.

However, it is also possible to provide means that will make it possible to detect the presence of a jet or of charged drops, even when the <NUM>nd gutter is in the open position.

In this embodiment the drops can be charged using means (for example: a voltage generator) in order to apply a voltage to the drop generator.

Thus, in <FIG>, the conductive means <NUM> comprise a spout (or protruding portion) 101a which will make it possible, when the movable gutter is in the open position, to detect (without contact) the presence of a jet, of which the drops are charged, when the latter exits through the slot <NUM> of the device.

Alternatively, and as shown in <FIG> and in <FIG>, conductive means <NUM> form a slot or a ring (with a central opening 103o) which can be of a shape identical or similar to that of the outlet slot <NUM> of the device, and through which the jets that exit from the latter will pass (after having passed through the slot <NUM>). Here again, these means make it possible, when the movable gutter is in the open position, to detect (without contact) the presence of a jet, of which the drops are charged, when the latter exits through the slot <NUM> of the device.

It is thus possible, for example, to detect the presence of a jet that is exiting through the slot <NUM> although it should be deflected towards the <NUM>st gutter.

Preferably, the conductive means <NUM> in the form of a slot or ring have a conductive portion 103d, <NUM> (<FIG>) on either side of the through jets. Thus, if a jet is far from one of the <NUM> conductive portions, the charge induced in the conductive portion farther away is lower than if the jet were correctly centred in the ring, but this is offset by the charge induced in the other conductive portion, thus closer to the jet and which is then stronger. In other words, a symmetrical structure on either path of the jets makes it possible to offset the variations in charge induced by the spatial instabilities of the jet.

<FIG> shows the <NUM>nd gutter in open position, with a jet successively passing through the outlet slot <NUM>, the opening 103o of the means <NUM> and the slot <NUM> made in the cover <NUM>. If the jet is charged, it induces charges in the means <NUM>, charges that can then be detected.

Regardless of the embodiment chosen for these conductive means 101a, <NUM>, the latter can be connected, for example via the conductive means <NUM>, to means for detecting, for example means for counting induced charges detected (for example an ammeter). It is thus possible to measure the charge induced by the charges contained in the jet of drops that pass in the vicinity.

Consequently, even in the open position, the <NUM>nd gutter can play the role for a measurement of the jets.

<FIG> shows the <NUM>nd gutter in the closed position. The portions such as the spout or protruding portion 101a or the means <NUM> will then make it possible to detect short-circuits that are produced when a deposition of ink occurs between these means and another conduction portion, brought to a different potential, for example the cover <NUM>. Such a short-circuit will introduce a variation in the signal in the means for detecting. The spout 101a or the means <NUM> can then ensure a function of detecting, even in the closed position of the <NUM>nd gutter.

The methods for cleaning described hereinabove can be implemented with a device provided with a second movable gutter, with the advantages that have just been explained in liaison with the presentation of the latter.

Whether the print head is of the type described hereinabove in liaison with the presence of at least one cleaning spraying nozzle in the cavity, for example according to one of the <FIG> and/or comprises a second movable gutter, for example according to one of the <FIG>, a print head according to the invention can be provided with an accelerometer, for example located in the cavity for the circulation of jets or in a cavity, for example dedicated to electronic means, and in the vicinity or contiguous with the cavity for the circulation of jets.

An accelerometer makes it possible in particular to provide a piece of information on the orientation of the print head (such as already indicated, the latter can be in the position shown in <FIG>, but also in the inverted position in relation to that of <FIG> or even in horizontal position, or in any other intermediate position between those mentioned hereinabove).

This information makes it possible to adapt the cleaning strategy according to the orientation of the head by acting:.

An accelerometer also makes it possible to detect movements of the print head, and to then implement cleanings that are more frequent than when no movement is detected.

Finally, such an accelerometer allows for the detection of high vibrations and/or accelerations, that can explain printing quality problems.

An accelerometer can in particular make it possible to detect the orientation of the print head, the latter being able to be oriented in order to print upwards (i.e. the jet is projected from bottom to top), or downwards (i.e. the jet is projected from the top to the bottom), or according to any other direction.

When a print head is oriented to print upwards (i.e. the jet is projected from bottom to top), a cleaning sequence of the inside of the cavity is preferably carried out in such a way that the cleaning begins with the portions located in the upper position, in such a way that the liquid flows via gravity inside the cavity, but not on portions that are already cleaned.

An example of a cleaning sequence shall be given for a print head comprising means such as described hereinabove in liaison with <FIG> in order to clean the inside of the cavity and a movable gutter as described hereinabove in liaison with <FIG>, the print head being provided with an accelerometer as described hereinabove. When this print head is oriented to print upwards, the cleaning sequence can be as follows:.

This sequence makes it possible to directly clean the various surfaces inside the cavity and to select the suction channel that is most suited for draining the latter (taking account of gravity).

In the case of a conventional orientation (such as shown in <FIG>, the jets being directed from top to bottom) of this print head, this sequence can be implemented in the reverse order, by starting with cleaning the means <NUM>x, then the means <NUM> and finally the gutters. The latter make it possible to recover the solvent regardless of the portion which is cleaned, which is not the case when the orientation is reversed.

In the same way a specific sequence can be executed for any other orientation of the head, for example horizontal.

In a method for cleaning a print head according to the invention, the print head further comprising an accelerometer, one or more of the spraying nozzle(s) can therefore have a plurality of possible orientations with respect to the inside of the cavity. It is as shown in the examples hereinabove, the succession of orientations of the spraying nozzle(s) during the method of cleaning can then be according to a piece of information relative to the orientation of the print head, given by the accelerometer: a <NUM>st succession of orientations is implemented for a <NUM>st orientation of the print head, while a <NUM>nd orientation succession, different from said <NUM>st succession of orientations, is implemented for a <NUM>nd second orientation of the print head, different from the <NUM>st orientation.

In the case of means such as the means for closing 17p (<FIG>) or of a movable gutter that can be positioned in such a way as to close the cavity as explained hereinabove (the position of <FIG>), it is possible, during the stopping or standby of the machine, to close the cavity, preferably in a sealed way, while still leaving in the latter solvent that has not been sucked in the cavity. In the case of a volatile solvent, it will evaporate until the air in the cavity is saturated with its vapours. The amount of solvent left in the cavity is chosen in order to saturate the air in the cavity with solvent vapour and keep some solvent in liquid phase, to avoid desaturation of the air in the cavity even in case the cavity isn't perfectly sealed.

Thanks to the presence of solvent vapours in the cavity, the residual ink present in the cavity and particularly on the nozzles does not dry. During the next starting the quantity of solvent used is therefore reduced and the cleanliness of the head is improved.

The means for cleaning the inside of a cavity, using at least one nozzle <NUM> arranged inside the latter were described hereinabove in the case of a binary continuous inkjet printer.

However, identical or similar means can be implemented in the framework of a continuous ink jet printer (CIJ).

<FIG> shows a CIJ print head, which comprises from upstream to downstream in the flow direction of the ink jet J:.

Such a print head can possibly comprise at least one device for detecting the directivity of the trajectories of the drops and/or at least one electrostatic sensor, such as described in document <CIT>.

The generator <NUM> comprises in addition means for stimulation of the ink, for example a piezoelectric actuator.

It can be seen, according to <FIG>, that the cavity that comprises these various elements is delimited laterally by <NUM> side walls <NUM> and <NUM>.

The charging electrode or electrodes <NUM> and the deviation electrode or electrodes <NUM> are fixed to, or arranged against, the wall <NUM>.

The left portion of figure 14A, including the wall <NUM>, shows a cleaning device such as already described hereinabove in liaison with <FIG>. Here in particular are the jet <NUM>, the spraying nozzle <NUM>, the nozzle <NUM>, the supply ducts <NUM>, <NUM>, <NUM> and the evacuation channel <NUM>.

It can be seen that the device already described hereinabove, in particular with the use of one or several cleaning nozzles, is entirely compatible with a print head architecture of the CIJ type. The jet projected using the spraying nozzle makes it possible in effect to clean the portions of the head which are arranged against the wall <NUM>. <FIG> shows a jet which is projected in the direction of the charging electrodes <NUM>. Via rotation, and/or via incorporation of several nozzles (as mentioned hereinabove in liaison with <FIG>) and/or of several fixed or movable spraying nozzles (also as mentioned hereinabove), it is entirely possible to clean the other portions of the head, in particular the nozzle <NUM>, and/or the sensor <NUM>, and/or the electrodes <NUM> and/or the gutter for recovering <NUM>.

The various aspects already described hereinabove and relating to the method or methods of cleaning can be applied to the print head structure of the CIJ type, such as the one of <FIG>.

A print head of the CIJ type, such as the one of <FIG>, can be provided with means for closing the cavity, such as the means 17p of <FIG> or a second gutter, movable, as explained hereinabove in liaison with <FIG>: it is then possible to carry out a closing of the cavity, preferably in a sealed manner, in order to carry out a cleaning, for example according to one of the embodiments explained hereinabove; it is also possible, using the possible second movable gutter, brought to closed position, to recover the solvent used during a cleaning operation.

A device according to the invention is supplied with ink by a reservoir of ink not shown in the figures. Various means of fluidic connection can be implemented to connect this reservoir to a print head according to the invention, and in order to recover the ink that comes from the gutter for recovering. An example of a complete circuit is described in <CIT> and can be used in combination with this invention.

Regardless of the embodiment considered, the instructions, in order to activate the means <NUM><NUM>-<NUM>n for producing ink jets and the means for pumping the gutter, and/or for controlling a cleaning in the cavity and/or for controlling the displacement of the movable gutter <NUM>, are sent by the means for controlling (also called "controller"). It is also these instructions that will make it possible to circulate the ink under pressure in the direction of the means <NUM><NUM>-<NUM>n, then to generate the jets according to patterns to be printed on a support <NUM>. These means for controlling are for example carried out in the form of an electric or electronic circuit or a processor or a microprocessor, programmed to implement a method according to the invention.

It is this controller that controls the means <NUM><NUM>-<NUM>n for producing one or several jets of ink and/or of solvent, and/or the means for pumping of the printer, and in particular of the gutter, and/or the cleaning spraying nozzle or nozzles <NUM> of the cavity (in particular their orientation) and/or the opening and the closing of valves on the path of the various fluids (ink, solvent, gas).

This controller, or these means for controlling, can also memorise data, and possible process it, for example:.

This controller, or these means for controlling, comprises the instructions for implementing a method of cleaning according to this invention and/or for controlling the displacement of the movable gutter <NUM>.

This controller can also receive the data from an accelerometer and control the cleaning and/or the suction of cleaning solvent according to the orientation of the print head.

<FIG> shows the main blocks of an ink jet printer that implements one or several embodiments described hereinabove. The printer comprises a console <NUM>, a compartment <NUM> containing in particular the circuits for putting into condition the ink and solvents, as well as reservoirs for the ink and the solvents (in particular, the reservoir to which the ink recovered by the gutter is conveyed). Generally the compartment <NUM> is in the lower portion of the console. The upper portion of the console comprises the control electronics as well as means for viewing. The console is hydraulically and electrically connected to a print head <NUM> by an umbilical cord <NUM>.

A door not shown makes it possible to install the print head facing a printing support <NUM>, which is displaced according to a direction materialised by an arrow. This direction can be perpendicular to an axis of alignment of the nozzles. For certain applications, the angle between the direction of the displacement of the printing support and the direction of alignment of the nozzles can differ from <NUM>°, it can be for example between <NUM>° and <NUM>°, in order to increase the resolution obtained.

The drop generator comprises nozzles and a cavity of the type according to one of the embodiments described hereinabove.

The invention is particularly interesting in applications where the flow rate of air or of gas, in the cavity, is substantial, because a substantial flow rate of air generates a risk that is all the more so high of allowing solvent to escape.

For example, the flow rate can be about several hundred l/h, for example between <NUM>/h or <NUM>/h and <NUM>/h, for example about <NUM>/h. These values are applied in particular in the case of a nozzle plate of <NUM> nozzles, but the invention also applies in the case of a nozzle plate with a lower number of nozzles, for example <NUM>, or in the case of a nozzle plate with a higher number of nozzles, for example <NUM>. The speed of the jets can be between <NUM>/s and <NUM>/s, for example it is about <NUM>/s.

An example of fluidic circuit <NUM> of a printer to which the invention can be applied is shown in <FIG>. This fluidic circuit <NUM> comprises a plurality of means <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, with each one associated with a specific functionality. There is also the head <NUM> and the umbilical cord <NUM>.

To this circuit <NUM> are associated a removable ink cartridge <NUM> and a cartridge <NUM> of solvent, also removable.

The reference <NUM> designates the main reservoir, which makes it possible to receive a mixture of solvent and of ink.

The reference <NUM> designates the set of means that make it possible to sample, and possibly store, solvent using a cartridge <NUM> of solvent and to provide solvent thus sampled to other portions of the printer, whether it entails supplying the main reservoir <NUM> with solvent, or cleaning or maintaining one or several of the other portions of the machine.

The reference <NUM> designates the set of means that make it possible to sample ink from an ink cartridge <NUM> and to provide the ink thus sampled to supply the main reservoir <NUM>. As can be seen in this figure, according to the embodiment shown here, the sending, to the main reservoir <NUM> and using the means <NUM>, of solvent, passes through these same means <NUM>.

At the outlet of the reservoir <NUM>, a set of means, globally designated by the reference <NUM>, makes it possible to pressurise the ink sampled from the main reservoir, and to send it towards the print head <NUM>. According to an embodiment, shown here by the arrow <NUM>, it is also possible, by the means <NUM>, to send the ink towards the means <NUM>, then again towards the reservoir <NUM>, which allows for a recirculation of the ink inside the circuit. This circuit <NUM> also makes it possible to drain the reservoir in the cartridge <NUM> as well as to clean the connections of the cartridge <NUM>.

The system shown in this figure also comprises means <NUM> for recovering fluids (ink and/or solvent) that comes back from the print head, more exactly from the gutter <NUM> of the print head or from the rinsing circuit of the head. These means <NUM> are therefore arranged downstream of the umbilical cord <NUM> (in relation to the flow direction of the fluids that come back from the print head).

As can be seen in <FIG>, the means <NUM> can also make it possible to send solvent directly towards these means <NUM>, without passing through the umbilical cord <NUM> or through the print head <NUM> or through the gutter for recovering.

The means <NUM> can comprise at least <NUM> parallel supplies with solvent, one towards the head <NUM>, the <NUM>nd towards the means <NUM> and the <NUM>rd towards the means <NUM>.

Each one of the means described hereinabove is provided with means, such as valves, preferably solenoid valves, that make it possible to orient the fluid concerned towards the chosen destination. Thus, using the means <NUM>, it is possible to send solvent exclusively towards the head <NUM>, or towards the means <NUM> or towards the means <NUM>.

Each one of the means <NUM>, <NUM>, <NUM>, <NUM> described hereinabove can be provided with a pump that makes it possible to treat the fluid concerned (respectively: <NUM>st pump, <NUM>nd pump, <NUM>rd pump, <NUM>th pump). These various pumps provide different functions (those of their respective means) and are therefore different from one another, although these different pumps can be of the same type or of similar types (in other words: none of these pumps provides <NUM> of these functions).

In particular, the means <NUM> comprise a pump (<NUM>st pump) that makes it possible to pump the fluid, recovered, as explained hereinabove, from the print head, and to send it to the main reservoir <NUM>. This pump is dedicated to the recovery of fluid coming from the print head and is physically different from the <NUM>th pump of the means <NUM> dedicated to the transfer of ink or of the <NUM>rd pump of the means <NUM> dedicated to the pressurising of the ink at the outlet of the reservoir <NUM>.

The means <NUM> comprise a pump (the <NUM>nd pump) that makes it possible to pump solvent and to send it towards the means <NUM> and/or the means <NUM> and/or towards the print head <NUM>.

Claim 1:
Method for cleaning a print head of a continuous ink jet printer, said print head comprising:
* a cavity (<NUM>) for the circulation of jets,
* means (<NUM>, <NUM><NUM>, <NUM>x, <NUM>n) for producing at least one ink jet in said cavity (<NUM>),
* means (<NUM>), for sorting drops or segments of one or several of said jets intended for printing from drops or segments that are not used for printing;
* at least one spraying nozzle (<NUM>, <NUM>), arranged in said cavity, said at least one spraying nozzle (<NUM>, <NUM>) being different from said means (<NUM>, <NUM><NUM>, <NUM>x, <NUM>n) for producing at least one inkjet,
* an outlet slot (<NUM>), open onto the exterior of the cavity (<NUM>) and allowing the exiting of the drops or segment of ink intended for printing,
* at least one gutter for recovering (<NUM>, <NUM>) drops or segments not intended for printing,
said method comprising :
- supplying said spraying nozzle (<NUM>, <NUM>) with cleaning fluid, and
- projecting several pulses of a cleaning fluid by said spraying nozzle into the cavity and towards at least :
* the means (<NUM>, <NUM><NUM>, <NUM>x, <NUM>n) for producing at least one ink jet in said cavity (<NUM>);
*and/or the gutter for recovering;
*and/or said means (<NUM>) for sorting drops or segments.