EP1409257A1

EP1409257A1 - Inkjet digital printing device and ink reservoir

Info

Publication number: EP1409257A1
Application number: EP02784873A
Authority: EP
Inventors: Ludovic Talon; Norbert Peytour; Eric Auboussier; Yannick Suzanne; Sarah Suzanne
Original assignee: Gilles Leroux SA
Current assignee: Entrust Corp
Priority date: 2001-07-13
Filing date: 2002-07-12
Publication date: 2004-04-21
Anticipated expiration: 2022-07-12
Also published as: JP2004535952A; EP1409257B1; DE60223376T2; DE60223376D1; WO2003006247A1

Abstract

The invention concerns a device for dot or drop on demand ink jet digital printing on open or closed surface medium comprising at least an integrated ink reservoir (13) provided with an anti-wave partition system, at least a printing head and a buffer reservoir. The assembly is located in a printing module (1) mobile relative to the medium (5) to be printed. The invention is characterised in that it comprises means for producing during the operation of the printing module an air depression in the integrated reservoir and means for active control of said air depression by adjusting the ink level detected via a sensor attached to the integrated reservoir and an air pressure in the integrated reservoir required for cleaning phases of the printing head.

Description

Digital inkjet printing device and ink tank

The present invention relates to a digital printing device operating by spraying ink onto a support, whether on an “open” surface, that is to say absorbent surface such as for example paper or cardboard, or whether "closed" surface, that is to say a non-absorbent surface such as certain plastics or glass. The principle of this so-called inkjet technology consists in projecting fine drops of ink onto the support in a matrix-based pattern, so as to print characters or graphics from digital data.

This printing principle has been used since the 1970s for black and white and the 1980s for color printing. Applications exist in particular in the field of very high speed printing, economical color printers for personal computers, or industrial printing on various media. The present description applies to printing on any support, "open" or "closed", for example by a machine for personalizing plastic cards or other portable objects, but it is obvious that such an invention can also apply to many other cases. In the case of printing by industrial machines, the printing is carried out by a printing head comprising one or more printing nozzles controlled by electronics and supplied by an ink tank in liquid form. These nozzles can operate according to a “drop (or point) on demand” principle “Drop or Dot On Demand” in English, these drops being triggered for example by piezoelectric effect. Other systems operate on the principle of the "deflected jet", where an ink jet is constantly propelled in the direction of the support, and where electrically charged electrodes deflect this jet in a gutter outside the moments when the printing of a point is requested. The unused ink is collected and returned to the ink tank.

These elements are brought together in a printing module which moves above the support to be printed so as to cover the entire desired printing surface while being connected to a fixed control bay. This assembly can constitute one of the stations of a machine or a chain of machines for the production or personalization of plastic cards or other portable objects.

On machines designed to work at high speed, for example above 2000 cards per hour, the movements of the printing module are done at a speed high enough for the liquid ink contained in the reservoir to present large waves or restlessness. Such agitations can be the cause of numerous drawbacks: variation in ink height, therefore pressure and therefore size of the ink drops deposited on the support, formation of bubbles in the reservoir, lack of ink at the start of the output even if the tank is not empty, difficulty obtaining a valid measurement of the ink level in the tank.

The present invention aims to overcome one or more disadvantages of the prior art. Thus, the invention provides a digital printing device on a support with an “open” or “closed” surface by drop-on-demand ink jet comprising at least one on-board ink tank provided with a system of anti-bulkheads. -waves, of at least one print head and a buffer tank, the assembly located in a mobile print module with respect to the support to be printed, characterized in that it comprises means for producing during operation of the printing module on the one hand, an air depression in the on-board tank and means for active regulation of this air depression by adjusting the ink level detected via a sensor attached to the on-board tank, and on the other hand share an air pressure in the on-board tank necessary for the printhead cleaning phases.

According to one feature, the device is characterized in that it comprises means for producing an air overpressure in the reservoir during the cleaning of the nozzle or nozzles of the print head.

According to one feature, the device is characterized in that the means for regulating consist of a non-contact sensor measuring the level without contact with the ink through the walls of the on-board tank, said sensor being associated with means for switching off the ink flow interrupting the arrival of ink in the on-board tank, these cutting means being controlled by a circuit receiving the level information from the contactless sensor to regulate the level of ink in the tank.

According to a particular feature, the device is characterized in that the active regulation means of the air vacuum consist of a pneumatic circuit comprising means for measuring the vacuum value and means generating vacuum, and of which the vacuum is controlled by an electronic circuit based on information from the level sensor, control information from an ink circuit supply solenoid valve and control information from an air circuit solenoid valve.

According to one feature, the device is characterized in that the means for generating depression are of venturi effect.

According to one feature, the device is characterized in that the vacuum generation means comprise a regulated vacuum pump. According to one feature, the device is characterized in that the printing module includes a so-called buffer tank which can store a certain amount of air under overpressure or under vacuum, this buffer tank attenuating the pressure variations occurring in the pneumatic circuit.

According to one feature, the device is characterized in that the on-board tank forms a storage space which contains several separating elements dividing this storage space into several regions over all or part of the height of the tank, these regions having a horizontal section of the order of cm ² to limit the agitation of the ink.

According to one feature, the device is characterized in that the separating elements include a plurality of intersecting vertical walls.

According to one feature, the device is characterized in that during the nozzle cleaning phase, a flexible blade is brought into position in contact with the face of the head provided with nozzles and displacement means ensure the relative displacement of the head relative to the flexible blade so as to wipe the nozzle plate.

According to one feature, the device is characterized in that a printing module is movable relative to a fixed control bay and at least a large part of the compressed air used in the printing module comes from the bay. control by at least one flexible pipe and of sufficient length to allow movement of the printing module.

According to a feature, the device is characterized in that the wall of the ink tank has a thinning at the level of the sensor allowing a better functioning of the ink level sensor through this thinning, the thinning being such that the thickness of the wall at this level is less than 1 mm.

According to a feature, the device is characterized in that at least one print head carries a plurality of print nozzles arranged in a row forming an angle of inclination with a plane orthogonal to the direction of relative movement of this head with respect to the medium to be printed, and in that it comprises means for adjusting this angle of inclination, these adjustment means determining several preset positions allowing passage from one to the other without requiring additional adjustment of the angle of inclination and without changing the setting of these preset positions. According to one feature, the device is characterized in that the different preset positions correspond to angular positions allowing, for the same spacing of the print nozzles on the print head, printing according to predetermined resolutions by varying the spacing of the dots printed on the support, this spacing decreasing with increasing the angle of inclination.

According to one feature, the device is characterized in that the displacement means move at least one so-called cleaning blade, which can be dipped in a solvent or rubbed on an absorbent felt before scraping the print head, and the means for displacement move at least one other so-called drying blade scraping the outer surface of the print head after the passage of the cleaning blade.

According to one feature, the device is characterized in that it comprises a so-called control data processing system receiving information from at least one ink level sensor or pressure sensor or both, and controlling the means of pressure regulation of the compressed air supply or the cut-off means or the distribution means or the non-return means or a combination of these, via at least one electronic interface. According to one feature, the device is characterized in that the printing module comprises an electronic interface communicating with the control system by a serial link.

According to a particular feature, the device is characterized in that it comprises a purge tank, brought opposite the head to receive the ink ejected from the head during the purge operations.

The invention, with its characteristics and advantages, will emerge more clearly on reading the description made with reference to the appended drawings in which: - Figure 1 shows a schematic view of the device according to the invention in one embodiment;

- Figure 2 shows a side view in vertical section of an on-board ink tank of the device according to the invention in one embodiment;

- Figures 3a and 3b show a top view in horizontal section of an on-board ink tank of the device according to the invention in an embodiment comprising an anti-rag device in the form of interwoven partitions and honeycomb respectively;

- Figure 4 shows a side sectional view of a cleaning station of the device according to the invention in one embodiment;

- Figure 5 shows a top view of the positions of the print nozzles with respect to the medium to be printed when passing a print head for a device according to the invention in one embodiment;

- Figures 6 and 7 respectively show a partial side sectional view and bottom sectional view of the part of the printing module carrying the print head.

The following description applies to a chip card printing device by a process operating in a “drop-on-demand” mode, but may also apply in whole or in part to a device operating in “jet of 'deviated ink' or other operating modes, as well as on any other type of support, whether with an 'open' or 'closed' surface.

In one embodiment, the printing device according to the invention consists of a fixed part called the control bay (2) and a mobile part called the inkjet printing module (1) of the type drop on demand, ordered in a known manner and which carries one or more heads printing (14). Each printhead comprises one or more printing nozzles (141) of a known type, distributed in a matrix figure which can comprise for example 128 or 500 nozzles over a few centimeters wide. In another embodiment (not shown), the medium to be printed moves during printing while the printing module is stationary.

The assembly can be integrated into a production or personalization chain, and be programmed to print texts or images on a support (5) with an "open" or "closed" surface, for example consisting of a plastic card or any other portable object, conveyed along a conveyor in front of the control bay (2) or under the printing module (1). Each time a new support is in place, the print module makes one or more passes, depending on the surface to be printed and the width of the print head. The nozzles are electronically and individually controlled to project drops of ink onto the support, and therefore print marks, for example in the form of dots, as the module moves over the support or the support under the module. , and according to this displacement. Depending on the applications, it is possible to equip the device with one or more printing modules capable of producing juxtaposed or nested prints, in one or more colors.

Depending on the applications, it is also possible to equip a printing module with one or more heads positioned in relation to each other, for example to produce juxtaposed or nested prints, in one or more colors.

Depending on the applications, it is also possible to connect each print head to one or more on-board tanks, for example to be able to replace or clean a tank without prolonged printing stoppage. Depending on the applications, it is also possible to connect each tank to one or more printheads, for example to increase the printable width achievable with each color.

The present description applies to a device comprising a single printing module (1) which carries a single on-board ink tank (13) and a single printing head, but its characteristics are applicable to other combinations of these elements without departing from the spirit of the invention. Similarly, the various functions of the device are described as being controlled by the same computer control system (3) using an electronic interface (31) located in the printing module (1), but may as well be managed by several systems or different interfaces, or a combination of these, without departing from the spirit of the invention.

The print head (14) uses print nozzles (141) projecting a drop of ink on demand using a piezoelectric actuator. In such an operating mode, the liquid ink tank which supplies the print head is kept in slight depression compared to the ambient pressure, so that the nozzles do not let ink escape without control. of the actuator. On the other hand, to purge the nozzles before a prolonged stop or to unblock them in the event of an incident, the tank may be subjected to an overpressure, for example of the order of 0.5 bar.

In an embodiment shown in FIG. 1, the print head (14) is supplied with ink by an on-board reservoir (13). This on-board tank is supplied through a flexible pipe (c20) by a main tank (23) pressurized by a source (A) of compressed air of a known type via a pressure regulator (21c ), this same main tank (23) being located in the control bay (2) and provided with a level sensor (28) connected to the control system (3) to deliver level information. The ink level in the on-board reservoir (13) is regulated by the control system (3), via the electronic interface (31), by acting on cut-off means (17) comprising a solenoid valve closing the ink passage upstream of said on-board reservoir (13). This regulation is carried out on the basis of information supplied by at least one contactless ink level sensor (18) with a capacitive effect located on the on-board reservoir (13). In one embodiment, a source of compressed air (A) supplies part of the pneumatic circuit located in the control bay (2) through adjustment means (21a, 21b), for example pressure regulators, piloted in association with pressure measuring means (22a, 22b) by the piloting system (3). These pressure measurement means (22a, 22b) may include pressure switches controlling directly or indirectly the pressure adjustment means (21a, 21 b), which may consist of pressure regulators. These pressure measurement means can also be simple pressure sensors transmitting a value to the control system (3), which controls the adjustment means (21a, 21 b).

These means are controlled to deliver to the printing module (1) a flow of compressed air at a determined pressure through a first pipe (c10a) and a second pipe (c10b), the pressures and flows in these two pipes can be different. The first pipe (c10b) coming from the control bay (2) supplies compressed and regulated air to a vacuum generator (12) with a venturi effect of a known type, located in the printing module (1), which generator of depression (12) puts in slight depression a part (c12) of the pneumatic circuit (d) in this same printing module. The printing module (1) comprises distribution means (15), such as a solenoid valve, controlled by the control system (3) via the electronic interface (31). As required, these distribution means put the on-board tank (13) into communication with either the vacuum part (d 2) of the pneumatic circuit, or the overpressure part (c13) located in the printing module which is supplied with air compressed and regulated by the second flexible pipe (c10b) coming from the control bay (2).

A computer system (3) uses the information coming from the various pressure sensors or pressure switches and controls the pressure regulators so as to maintain, apart from the head cleaning phases, in the on-board tank (13) a vacuum whose value is calculated to be sufficient to retain ink in the nozzles in normal times without preventing its ejection by the piezoelectric actuator. In order to overcome atmospheric pressure variations and avoid the adjustments which could result therefrom, the control system (3) can be programmed to maintain a vacuum in the on-board tank (13) such that the pressure difference between the inside and outside of said tank is stabilized at a known and independent value in ink level.

The stabilization of this pressure difference makes it possible to obtain that the size of the drops and therefore of the printed dots is regular and predictable, which is important for obtaining quality and regularity in printing, both over time and during changes of support, or type of support for example between "open" and "closed".

The pneumatic circuit in the printing module (1) comprises non-return means (16), such as one or more piloted valves, or one or more valves, or a combination of these elements. These elements of a known type are configured or controlled to hermetically block the air inlet of the on-board ink tank (13) in the event of a pressure drop due to an incident. In one embodiment, the pneumatic circuit in the printing module (1) comprises a buffer tank (11) located between the distribution means (15) and the on-board tank (13). This reservoir can contain a certain amount of air in overpressure or in depression, and thus allows the regulation of the pressure levels in the onboard ink reservoir (13) for example during an ink arrival or in the case of '' irregularities in supplying the printing module (1) with compressed air, or during pressure variations caused either by the drop in the ink level due to consumption, or by the rise in the ink level during filling.

By way of example and in one embodiment, the capacity of the buffer tank (11) is of the order of 25% of the interior volume of the on-board ink tank (13).

In the embodiment shown in FIG. 2, a vertical wall of the on-board reservoir (13) of the printing module (1) has, in its lower part, a thinning (131) of a material that does not conduct electricity. In this thinning and outside the tank is housed a contactless electronic sensor (18) for example with capacitive effect of a known type, electronically connected to the control system (3) or to the electronic interface (31) or a combination of the two. By a variation of the signal representing the electrical capacity of the sensor, due to the presence or not of liquid on the other side of the wall, the control system detects the fact that the ink level in the on-board reservoir (13) is located below a determined height corresponding to the position of this ink level sensor (18).

The thinning (131) is such that the wall of the reservoir has a thickness of approximately 1 mm, for a wall of Nylon ™ or Delrin ™. This information on the ink level is used by the control system (3), for example to control the opening of the cutting means (17) and allow the ink to arrive in the on-board reservoir (13) coming from the main tank (23) as soon as the sensor no longer detects sufficient ink. When ink arrives in the tank, the control system can interrupt this ink arrival as soon as the sensor again detects the presence of a desired ink level.

The frequency of the ink supply cycles of the on-board ink tank (13) is reduced due to the existence of a hysteresis cycle specific to the level sensor (18), and the use of a delay in taking taking into account information from the sensor, for example 0.5 s, in order to avoid taking account of level oscillations due to waves in the tank.

Due to its position outside the tank, the presence of this ink level sensor (18) poses no problem of sealing or pollution of the ink and is easy to clean; and because of its operation without heating it does not cause any degradation of the quality of the ink contained in this same tank, in particular when the ink used is chosen precisely to be sensitive to heat in the case of certain applications. In one embodiment, the main ink reservoir (23) of the control bay (2) carries an ink level sensor (28) of the same type. This sensor (28) is electronically connected to the control system (3). By this ink level sensor (28), the control system (3) detects that the ink level in the main tank (23) is below a determined height corresponding to the position of this ink level sensor (28). This information is used by the control system (3), for example to warn a human operator of the need for a next replenishment of ink.

The on-board ink tank (13) shown in FIGS. 2 and 3a has the shape of a container of parallelepiped shape, the upper opening of which is closed by a cover provided with sealing means such as a seal (137) in rubber.

In its lower part, the on-board ink tank (13) has an ink outlet opening (139) connected to the print head (14) and supplying the latter with ink.

The upper cover has an air passage opening (138) connected to the pneumatic circuit in the printing module (1). This connection makes it possible to place the interior space of the reservoir under vacuum or respectively under over pressure according to the setting of the distribution means (15), in order on the one hand to compensate for the ink pressure due to the gravity and retain the ink in each print nozzle (141) of the print head (14) between two actuations of the actuators of said print nozzles and respectively on the other hand to purge or unclog this reservoir (13) or said printing nozzles (141) or the pipes connecting the reservoir (13) to the nozzles during the cleaning phases.

In order to reduce the agitation of the ink inside the on-board reservoir (13), the interior space of said reservoir is separated into several regions (130) by separating elements (132) made up of intersecting vertical partitions, these partitions being for example molded with the tank or subsequently added. These partitions occupy the interior space of the tank over a large part of its height while leaving free a space (133a) located at the bottom of this same tank and a space (133b) located at the top of the tank. Thus, these partitions prevent or limit any horizontal circulation inside the tank during its movements, except in its lower part (133a) where the ink can circulate so as to be distributed in all the regions (130) of the interior space of this on-board tank (13). In the upper part of the tank, the free space (133b) above the separating elements (132) allows the air to circulate so as to be distributed throughout the regions (130) of the interior space of this on-board tank (13).

The part of the height of the interior space of the on-board ink tank (13) occupied by the separating elements (132) can vary according to the applications. By way of example and in one embodiment, the separating elements (132) occupy more than 75% of this height. Depending on the applications, the separating elements (132) can have transverse holes at various places along their height, increasing the possibilities of ink circulation.

The regions (130) delimited by these separating elements (132) have in their section dimensions sufficiently small so that the differences in ink height due to the waves caused by the movements of the tank are less than a given value, for example 10 mm. In one embodiment, the partitions constituting these separating elements (132) have a distance of approximately 6 mm between them.

The upper cover also includes an ink inlet opening (135) receiving the ink under pressure from the main reservoir (23) of the control bay (2) through a flexible pipe (c20) and the cutting means (17) ink arrival.

Such an anti-wave device makes it possible to use rapid speeds of displacement of the head (14), therefore of printing, without there being any agitation or significant variations in level in the tank, which would risk causing variations in static and dynamic pressure between the different nozzles (141) of the head or over time, and therefore irregular sizes for the drops and dots printed on the support.

In the embodiment shown in Figure 2, the ink inlet (135) opens above an inclined plane formed in the inner wall of the onboard ink tank (13). The upper face of this inclined plane forms a deburring surface (136) on which the ink flow will flow slowly before joining the ink storage space (E) already present in this same on-board tank. The shape, the inclination, or the dimensions of this deburring surface (136) can vary according to the applications, and are determined so that bubbles possibly present in the ink when it arrives can disintegrate during the flow of the ink flow along this same debubbling surface or during its flow from this same surface to the storage space of the reservoir. In another embodiment (not shown), the ink inlet opening (135) in the onboard ink tank (13) can be located on a vertical wall, and the ink flow comes into contact of a bubble removal surface located in the same wall or opposite this ink inlet.

In another embodiment (not shown), the deburring surface (136) is formed from the peripheral surface of a wire substantially cylindrical, connecting the ink inlet (135) to an inner wall of the on-board tank (13) or to a separating element (132). The ink flow meets the wire when it arrives in the tank, and flows along its surface until it joins the ink (E) already present in this same on-board tank. The on-board ink tank (3) of FIG. 2 has on one of its external faces a recess, closed by a cover (111) provided with sealing means (112). The interior space of this recess is connected to the air circuit of the printing module (1) by an air passage opening (113) and constitutes a buffer tank (11) which makes it possible to regulate the pressure at the interior of at least part of said air circuit.

In an embodiment shown in FIG. 3b, the separating elements (132) separating the interior space of the on-board ink tank (13) mainly consist of a structure in the form of a “honeycomb”, the conduits of which are oriented vertically and provide a free space at the bottom of the reservoir allowing a distribution of the ink between the various conduits of this structure. Depending on the applications, the “honeycomb” structure may have transverse holes in various places along its height, increasing the possibilities of horizontal circulation of the ink.

In an embodiment represented in FIG. 4, the device according to the invention can comprise a cleaning station (24) where the print head can be brought on command of the control system (3), either by displacement of the module d printing (1), either by moving said cleaning station (24), or by a combination of the two.

The cleaning station (24) comprises a purge tank (240), provided with a discharge, receiving the ink ejected by the print nozzles (141) when ordering a purge, for example for cleaning or unblock said print nozzles.

The cleaning station (24) comprises a tank containing a solvent (S) and is provided with a first rotating elastic blade called cleaning (241). On a command from the piloting system (3), this cleaning blade comes soak in solvent (S) and then rotate to scrape the outside surface of the print head (14), for example to unclog the print nozzles (141) after a prolonged shutdown or clean these same nozzles after a purge . The cleaning station (24) is provided with a second elastic blade called drying (242). On a command from the control system (3), this drying blade scrapes the external surface of the print head (14), for example to wipe or dry the print nozzles (141) after passing the blade cleaning (241). This device also removes fouling residue that may have come from the previous scraping.

In one embodiment, the cleaning station (24) is provided with lifting means (not shown), for example in the form of a pinion and rack mechanism, bringing this same cleaning station to the level of the line of displacement of the supports to be printed, and allowing cleaning of the print head (14) without disassembly thereof.

In the embodiment shown in FIGS. 5, 6, and 7, the device according to the invention comprises a print head (14), the print nozzles (141) of which are arranged in one or more rows parallel to each other, and the nozzles of the same row have a spacing (e1) between them determined according to their alignment in the row.

So as to be able to modify the print resolution, the print head (14) is integral with a movable part (192) in rotation relative to a fixed part (191) integral with the printing module (1), this rotation taking place around an inclination axis (d19) perpendicular to the plane of the support (5) to be printed.

The print head (14) can then be positioned so that the rows of print nozzles (141) form a determined angle of inclination (as) called the "slantage" angle with a plane perpendicular to the direction (d14) of relative displacement of this printhead (141) above the support (5) during a printing phase. So the dots (541) printed on the support (5) to be printed have a distance between them (e5) less than the distance (e1) existing between the print nozzles (141). Such an arrangement thus makes it possible to increase the print resolution achievable with a given print head, that is to say the number of dots printed over a given length or surface.

The mobile part (192) of the head has a convex surface (196) of conical shape cooperating with a complementary concave surface (197) carried by the fixed part (191) to guide this same mobile part (192) in rotation according to the tilt axis (d19). The movable part (192) also has a part forming a shoulder (198), directed towards the support (5) to be printed. On this shoulder comes to bear an inner shoulder of a ring (193) surrounding the movable part (192). A rotation of this ring (193) then blocks the movable part (192) by clamping its conical surface (196) against the conical surface (197) of the fixed part (191) due to a thread carried by this same ring (193) and cooperating with a thread carried by this same fixed part (191).

In order to be able to be easily adjusted according to one or more preset angular positions, the mobile part (192) comprises a cam (194) having one or more sides (194a, 194c), with radial surfaces, which cooperate with one or more elements of stop (194b, 194d) integral with the fixed part (191) to form one or more stops. Depending on the relative position of the sides (194a, 194c) and stop elements (194, b 194d), one or more preset angular positions are thus selectable, simply by loosening the ring (193) before rotating the movable part ( 192) to one of the stops and then tighten the ring.

In another embodiment, the movable part (192) has an annular surface (195), having substantially the shape of a disc portion perpendicular to the axis of inclination (d19) and having on its surface directed towards the fixed part (191) one or more depressions (195c). On this annular surface (195), a ball (195a) held in an integral blind bore of the fixed part (191) is pressed by the action of a spring (195b) compressed in the same bore. When the movable part (192) rotates relative to the fixed part (191), a ball (195a) facing a depression (195c) comes to center there under the action of the spring ( 195b) and thus determines a precise angular position. The presence of one or more balls and one or more depression thus makes it possible to define a determined number of preset angular positions of the movable part (192) relative to the fixed part (191). Such a device thus makes it possible to quickly vary the angle of inclination of the print head (14), without requiring any new adjustment during these modifications, and thus to adapt the print resolution to the needs of production. in progress in a flexible, fast and precise way, in particular when the change of support, for example between "open" and "closed", requires to change resolution to maintain the best possible print quality while avoiding some of the problems due coalescence or drop size before drying.

The device according to the invention is controlled by a control system (3) comprising a computer, for example of the PC compatible personal computer type (Personal Computer). This system receives information from the ink level sensors (18, 28) or from the pressure sensors (22a, 22b) or from both, and controls the means (21a, 21 b, 21 c) for adjusting the pressure of the compressed air supply or the cut-off means (17) or the distribution means (15) or the non-return means (16) or a combination of these, via at least one electronic interface. In one embodiment, all of the functions and information of the printing module (1) are managed by an electronic interface (31) of a known type, this electronic interface communicating with the control system (3) by a serial link (c30) operating for example according to the USB computer standard (Universal Serial Bus). The use of such a link then allows easy replacement of the control system (3) or of the printing module (1), for example for reasons of maintenance, updating a system, or to replace a printing module with another having different settings or having different performance.

It should be obvious to those skilled in the art that the present invention allows embodiments in many other specific forms without departing from the scope of the invention as claimed. Therefore, the present embodiments should be considered by way of illustration, but may be modified in the field defined by the scope of the appended claims, and the invention should not be limited to the details given above.

Claims

1. Digital printing device on a support with an “open” or “closed” surface by drop-on-demand ink jet comprising at least one on-board ink tank (13) provided with a system of anti-wave partitions , at least one print head and a buffer tank, the assembly located in a print module (1) movable relative to the support (5) to be printed, characterized in that it comprises means for producing during the operation of the printing module on the one hand, an air depression in the on-board tank and means for active regulation of this air depression by adjusting the ink level detected via a sensor attached to the on-board tank, and on the other hand, an air pressure in the on-board tank necessary for the cleaning phases of the print head.

2. Device according to claim 1, characterized in that it comprises means for producing an overpressure of air in the reservoir during the cleaning of the nozzle or nozzles of the print head.

3. Device according to claim 1 or 2, characterized in that the regulating means consist of a contactless sensor measuring the level without contact with the ink through the walls of the on-board tank, said sensor being associated with means cutting the flow of ink interrupting the arrival of ink in the on-board tank, these cutting means being controlled by a circuit receiving the level information from the contactless sensor to regulate the level of ink in the tank.

4. Device according to claim 1, characterized in that the active regulation means of the air vacuum consist of a pneumatic circuit (C1) comprising means for measuring the vacuum value and means generating vacuum, and whose vacuum is controlled by an electronic circuit based on information from the level sensor, control information from a solenoid valve ink circuit supply and control information for an air circuit solenoid valve.

5. Device according to claim 1, characterized in that the means for generating vacuum are venturi effect.

6. Device according to claim 1, characterized in that the vacuum generation means comprise a regulated vacuum pump.

7. Device according to claim 4, characterized in that the printing module comprises a reservoir (11) said buffer capable of storing a certain amount of air in overpressure or in depression, this buffer reservoir attenuating the pressure variations occurring in the pneumatic circuit (C1).

8. Device according to claim 1, characterized in that the on-board tank forms a storage space which contains several separating elements dividing this storage space into several regions over all or part of the height of the tank, these regions having a horizontal section of the order of cm ² to limit the agitation of the ink.

9. Device according to claim 8, characterized in that the separating elements comprise a plurality of intersecting vertical walls.

10. Device according to claim 2, characterized in that during the nozzle cleaning phase, a flexible blade is brought into position in contact with the face of the head provided with nozzles and displacement means ensure the relative displacement of the head relative to the flexible blade so as to wipe the nozzle plate.

11. Device according to one of the preceding claims, characterized in that a printing module is movable relative to a fixed control bay (2) and at least a large part of the compressed air used in the module printing comes from the control bay by at least one flexible pipe (C10a, C10b) of sufficient length to allow movement of the printing module.

12. Device according to one of the preceding claims, characterized in that the wall of the ink tank (13, 23) comprises a thinning (131) at the level of the sensor allowing better operation of the level sensor (18, 28) ink through this thinning, the thinning being such that the wall thickness at this level is less than 1 mm.

13. Device according to one of the preceding claims, characterized in that at least one print head (14) carries a plurality of print nozzles (141) arranged in a row forming an angle of inclination (as) with a plane orthogonal to the direction (d14) of relative movement of this head relative to the support (5) to be printed, and in that it comprises means for adjusting this angle of inclination (as), these means for adjustment determining several preset positions allowing passage from one to the other without requiring additional adjustment of the angle of inclination (as) and without modifying the adjustment of these preset positions.

14. Device according to claim 13, characterized in that the different preset positions correspond to angular positions allowing for the same spacing (e1) of the print nozzles (141) on the print head (14) printing according to resolutions predetermined by the variation in the spacing (e5) of the dots printed on the support (5), this spacing decreasing with the increase in the angle of inclination (as).

15. Device according to claim 10, characterized in that the displacement means move at least one blade (241) called cleaning, which can be dipped in a solvent (S) or rubbed on a felt absorbent before scraping the print head (14), and the displacement means move at least one other blade (242) said to be drying, scraping the external surface of the print head (14) after the passage of the blade of cleaning.

16. Device according to one of the preceding claims, characterized in that it comprises a data processing system (3) called control receiving information from at least one ink level sensor (18, 28) or pressure sensor (22a, 22b) or both, and controlling the means (21a, 21b, 21c) for adjusting the pressure of the compressed air supply or the cut-off means (17) or the distribution means (15) or the non-return means (16) or a combination of these, via at least one electronic interface.

17. Device according to one of the preceding claims, characterized in that the printing module (1) comprises an electronic interface (31) communicating with the control system by a serial link (c30).

18. Device according to claim 15 or 10, characterized in that it comprises a purge tank (240), brought opposite the head to receive the ink ejected from the head during the purge operations.