FR2827212A1 - Digital ink-jet printer, uses compressed air to project droplets from ink reservoir with capacitive level detection and with adjustable orientation of ink nozzles to control print quality - Google Patents

Abstract

The ink jet printer has a pneumatic circuit with a source (A) of compressed air housed in a fixed control bay (2) in the printer, a pre-set adjustment mechanism to control resolution by orientation of the print head (14), an ink reservoir (13) including an anti-wave device and a capacitive ink level detector (18) external to the reservoir, and a cleaning station (24) for the print nozzles.

Description

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Digital inkjet printing device and ink circuit
The present invention relates to a digital printing device operating by spraying ink onto a support, whether with an open surface, ie absorbent, for example paper or cardboard, or with a closed surface. is to say nonabsorbent like for example 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 be applied to many other case.

 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 on a drop (or dot) principle on demand (Dot On Demand), these drops being triggered for example by piezoelectric effect. Other systems operate on the deflected jet principle, where an ink jet is continuously propelled in the direction of the support, and where electrically charged electrodes deflect this jet in a gutter outside the

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 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 positions of a machine or a chain of machines for the production or personalization of plastic cards or other portable objects.

l'encre dans les buses ou pour purger le réservoir ou les buses lors d'un nettoyage, et une dépression pour récupérer l'encre inutilisée ou pour retenir l'encre dans le réservoir ou la tête en dehors des instants d'impression. On machines working at a speed of the order of 3000 cards per hour, the supply of liquid ink to the print head is often obtained by one or more pumps located in the print module and circulating the ink , either directly or via a pneumatic circuit which makes it possible to put certain parts of the ink circuit under overpressure or under vacuum. Overpressure can be used to propel

the ink in the nozzles or to purge the reservoir or the nozzles during cleaning, and a vacuum to recover the unused ink or to retain the ink in the reservoir or the head outside of the printing instants.

 However, such an on-board arrangement has the drawback of representing a significant weight in the mobile part of the machine, that is to say the printing module. This weight requires in particular powerful motors and resistant guides, which represents a source of costs in manufacturing and maintenance. In addition, the importance of the different moving masses constitutes an additional constraint which is an obstacle to increasing the speeds of movement of the module, therefore of the printing speed of the machine, while the printing technologies themselves could allow such an increase.

 With this in mind, it would appear natural to use the possibilities offered by current technologies to reduce these moving masses, by miniaturizing these elements of on-board motors or pumps.

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 However, the use of more and more miniaturized mechanisms represents a source of fragility and does not allow the reliability and the precision that allow classic but heavy and bulky industrial materials which would be usable in fixed position.

 The present invention aims to overcome one or more disadvantages of the prior art.

 The invention proposes to offset a large part of the pneumatic mechanisms in the control bay, that is to say the fixed part of the machine. It is then possible to use all standard industrial systems making it possible to obtain a source of compressed air, possibly filtered and pressure regulated, in a precise, reliable and economical manner.

 Compressed air can be transmitted through a flexible line from the fixed control bay to the mobile printing module. To obtain the useful vacuum in certain parts of the printing module, the invention then proposes the use of this same compressed air to generate a vacuum by a known device with venturi effect, simple and light, located in the printing module. .

 Thus, the invention provides a digital printing device on a support with an open or closed surface by ink jet using a pneumatic circuit and a printing module in relative displacement relative to the support to be printed, characterized in that it has a control bay and that at least a large part of the compressed air used in the print module comes from to the control bay and is supplied by a source external to this same print module.

 According to one feature, the device is characterized in that the printing module is movable relative to the control bay and is connected by one or more flexible pipes to said control bay, this pipe

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 flexible being of sufficient length to allow movement of the printing module.

 According to a feature, the device is characterized in that the printing module comprises at least one so-called buffer tank capable of storing a certain amount of air under overpressure or under vacuum, this buffer tank attenuating the pressure variations occurring in the circuit pneumatic.

 According to one feature, the device is characterized in that the printing module comprises a vacuum generator which can use a part of the compressed air supplied to the printing module to generate a vacuum by venturi effect in at least part of the circuit air.

 According to one feature, the device is characterized in that the printing module comprises at least one on-board reservoir supplying ink with at least one ink jet print head, this on-board reservoir being connected for its supply to at least one fixed main tank located in or near the control bay.

 According to a feature, the device is characterized in that a compressed air source puts the main ink tank under pressure, this main tank having in its lower part an opening which then supplies ink to the on-board tank through a pipe. .

 According to a feature, the device is characterized in that the printing module comprises pneumatic distribution means which can put the on-board tank in connection with a part in vacuum of the air circuit or with a part in overpressure of the air circuit .

 According to one feature, the device is characterized in that it comprises means for adjusting the pressure of the compressed air supply and means for measuring pressure at at least one location in the pneumatic circuit, these means cooperating to regulate either the pressure of the compressed air supplying the printing module, either the vacuum generated by the vacuum generator, or both.

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 According to a feature, the device is characterized in that the pneumatic circuit comprises adjustment and servo control means stabilizing the vacuum inside the on-board tank at a value determined as a function of atmospheric pressure.

 According to a feature, the device is characterized in that the printing module comprises non-return means comprising one or more valves or valves capable of isolating one or more parts of the pneumatic circuit.

 According to a particular feature, the device is characterized in that it comprises cut-off means capable of interrupting the arrival of ink in the on-board tank and at least one ink level sensor for this same on-board tank, these cut-off means being controlled according to this level sensor to regulate the ink level in this same on-board tank.

 According to a particular feature, the device is characterized in that one or more ink level sensors are attached to the outer surface of the vertical wall of one or more of the ink tanks and detect the presence of liquid by capacitive effect through a wall of the reservoir, at a location situated at a determined height from the bottom of the reservoir and corresponding to an ink level threshold which should trigger information or commands.

 According to a particular feature, the device is characterized in that the wall of the ink tank comprises a thinning allowing a better functioning of the ink level sensor through this thinning.

 According to one feature, the device is characterized in that the storage space of the on-board tank contains one or more 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 determined dimensions small enough to limit the agitation of the ink; these separating elements themselves having a shape allowing between these same regions little or no horizontal flow.

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

 According to a feature, the device is characterized in that these separating elements comprise a honeycomb structure having contiguous ducts of hexagonal section arranged vertically, over a large part of the height of the tank.

 According to a feature, the device is characterized in that the ink inlet opening in the on-board tank opens out opposite a part having a so-called debubbling surface located below said ink inlet or so close enough for the ink flow to enter the on-board tank flows, over a determined distance, in contact with this same surface before joining the contents of this same on-board tank.

 According to a feature, the device is characterized in that at least one print head carries a plurality of print nozzles arranged in one or more rows forming an angle of inclination with a plane orthogonal to the direction of relative movement of this head relative to the support 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 adjustment angle of tilt and without changing the setting of these preset positions.

 According to a particular feature, the device is characterized in that the different preset positions correspond to angular positions printing according to predetermined resolutions by the variation of the spacing of the dots printed on the support, this spacing decreasing with increasing angle tilt for the same spacing of the print nozzles on the print head and thus increasing the print resolution.

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 According to one feature, the device is characterized in that it comprises means for adjusting the angle of inclination, these adjustment means allowing an adjustment of the value of this angle relative to its value determined by at least one of the preset positions and thus making it possible to adjust the spacing of the printed points without modifying the setting value of these preset positions.

 According to a feature, the device is characterized in that it comprises a so-called cleaning station comprising at least one blade and means for relative displacement of the print head relative to the blade allowing said blade to scrape the outer surface of the print head after a prolonged stop or after purging of these same print nozzles.

 According to one feature, the device is characterized in that the cleaning station comprises displacement means mobilizing at least one so-called cleaning blade, which is dipped in a solvent or rubbed on an absorbent felt before scraping the print head, and displacement means mobilizing 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 lifting means capable of lifting all or part of the cleaning station to bring it up to the surface of the scraping surface of the print nozzles.

 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

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 control system via a serial link operating according to the USB (Universal Serial Bus) communication standard.

 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-wave device in the form of interwoven partitions and respectively of nest of bees; - 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 during a passage of 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 can also be applied in whole or in part to a device operating in deflected inkjet or other modes of operation,

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 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 printing module (1), controlled in a known manner and which carries one or more printheads (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. , routed 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 the

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 others for example to make 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.

 In one embodiment, the print head (14) uses print nozzles (141) projecting a drop of ink 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 shutdown 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

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 type known by means of 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). The ink level in the on-board tank (13) is regulated by the control system (3), via the electronic interface (31), by acting on cut-off means (17) comprising a closing solenoid valve. the passage of ink upstream of said on-board reservoir (13). This regulation is carried out on the basis of information supplied by at least one capacitive effect ink level sensor (18) 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 (21 a, 21 b), for example pressure regulators , controlled in association with pressure measuring means (22a, 22b) by the control system (3).

 These pressure measuring means (22a, 22b) may include pressure switches directly or indirectly controlling the pressure adjusting means (21 a, 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, 21b).

 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.

 In one embodiment, the first pipe (cl Ob) coming from the control bay (2) supplies compressed and regulated air to a vacuum generator (12) with venturi effect of a known type, located in the module printing (1), which vacuum generator (12) slightly depresses part (c12) of the pneumatic circuit (c1) in this same printing module.

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 In one embodiment, 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) in communication with either the vacuum part (c12) 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).

 In one embodiment, the computer system (3) uses the information coming from the various pressure sensors or pressure switches and controls the pressure regulators so as to maintain a vacuum in the on-board tank (13) whose value is calculated so as to be sufficient to retain ink in the nozzles in normal times without preventing its ejection by the piezoelectric actuator. In order to overcome variations in atmospheric pressure and avoid the adjustments that 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 value.

 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 in time and during changes of support, or type of support for example between open and closed.

 In one embodiment, 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 seal the air inlet of the ink tank in the event of a pressure drop due to an incident.

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 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 the supply of the printing module (1) with compressed air, or pressure variations caused by the drop in ink level due to consumption or by the rise in 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 an 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 which does not conduct electricity. In this thinning and outside the tank is housed a capacitive effect electronic sensor (18) 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 in the electrical capacity of components 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).

 In one embodiment, the thinning (131) of the wall of the reservoir has a thickness of approximately 1 mm, for a wall of Nylon or Delrin TM.

 This information is used by the control system (3), for example to control the opening of the cutting means (17) and allow the arrival of ink in the on-board reservoir (13) coming from the reservoir.

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 main (23) as soon as the sensor no longer detects 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 ink.

 In one embodiment, 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 of the use of a time delay in taking the information from the sensor into account, 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 reservoir, 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 the fact 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 an imminent lack of ink and to request a replenishment.

 In an embodiment shown in FIGS. 2 and 3a, the on-board ink tank (13) 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 rubber seal (137).

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 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 in depression or respectively in overpressure according to the adjustment of the distribution means (15), in order on the one hand to compensate for the ink pressure due to gravity and to 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 print nozzles ( 141) or the pipes between them.

 In one embodiment, so as 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) formed 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 in all 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

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 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 reservoir are less than a given value, for example 10 mm . In one embodiment, the partitions constituting these separating elements (132) have a distance between them of approximately 6 mm.

 The upper cover also has an ink inlet opening (135) receiving the ink from the main reservoir (23) under pressure from the control bay (2) through a flexible pipe (c20) and the cut-off means (17) ink supply.

 Such an anti-wave device makes it possible to use rapid speeds of movement 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 therefore the dots printed on the support.

 In an 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 an unpacking surface (136) on which the ink flow will flow slowly before joining the ink (E) already present in this same on-board tank. The shape, the inclination, or the dimensions of this debubbling 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 ink flow along

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 from this same unpacking surface or during its flow from this same surface to the contents of the tank. In another embodiment (not shown), the ink inlet opening (135) in the on-board ink tank (13) is located on a vertical wall, and the ink flow comes into contact with 'a bubble removal surface located in the same wall or opposite this ink inlet.

 In another embodiment (not shown), the deburring surface (136) comprises the peripheral surface of a substantially cylindrical wire, connecting the ink supply (135) to an interior 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 on its surface until it joins the ink (E) already present in this same on-board tank.

 In one embodiment, shown in FIG. 2, the on-board ink tank (3) 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 honeycomb-shaped structure whose conduits 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 at various places along its height, increasing the possibilities of horizontal circulation of the ink.

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 In an embodiment shown in Figure 4, the device according to the invention comprises a cleaning station (24) where the print head can be brought on command of the control system (3), either by moving the module 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 soaks in the solvent (S) then rotates to scrape the outer surface of the print head (14), for example to unclog the nozzles printing (141) after a prolonged stop or cleaning these same nozzles after a purge.

 The cleaning station (24) is provided with a second elastic blade called the drying blade (242). On a command from the piloting 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 dismantling the latter.

 In an embodiment shown in Figures 5,6, and 7, the device according to the invention comprises a print head (14) whose nozzles

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 printing (141) are arranged in one or more rows parallel to each other, and the nozzles of the same row have between them a spacing (e1) determined according to their alignment in the row.

 In order 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 slanting angle with a plane perpendicular to the direction (d14 ) of relative displacement of this print head (141) above the support (5) during a printing phase. Thus, the dots (541) printed on the support (5) to be printed have a spacing between them (e5) less than the spacing (e1) existing between the printing 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) 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 along the axis of tilt (d19). The movable part (192) also has a part forming a shoulder (198), directed towards the support (5) to be printed, a shoulder on which an internal shoulder rests on a ring (193) surrounding the mobile 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).

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 In order to be able to be easily adjusted according to one or more preset angular positions, the movable 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 one embodiment, the movable part (192) has an annular surface (195), having substantially the shape of a portion of disc perpendicular to the axis of inclination (d19) and having on its surface directed towards the part fixed (191) one or more depressions (195c). On this annular surface (195), a ball (195a) held in a blind bore integral with the fixed part (191) is pressed by the action of a spring (195b) compressed in this same bore. When the movable part (192) rotates relative to the fixed part (191), a ball (195a) opposite 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 to coalescence or drop size before drying.

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 In one embodiment, the device according to the invention is controlled by a control system (3) comprising a computer, for example of the PC compatible personal computer (Personal Computer) type. 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 (21 a, 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 computer standard USB (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 of a system, or to replace another printing module with different settings or 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 (25)

1. Digital printing device on support with open or closed surface by ink jet using a pneumatic circuit (c1) and a printing module (1) in relative displacement relative to the support (5) to be printed, characterized in that it has a control bay (2) and that at least a large part of the compressed air used in the printing module (1) comes from the control bay and is supplied by a source (A) outside this same printing module (1).  2. Device according to the preceding claim, characterized in that the printing module is movable relative to the control bay and is connected by one or more flexible pipes (c10a, c10b) to said control bay (2), this flexible pipe being of sufficient length to allow movement of the printing module.  3. Device according to one of the preceding claims, characterized in that the printing module (1) comprises at least one reservoir (11) said buffer capable of storing a certain amount of air in overpressure or in depression, this buffer reservoir reducing pressure variations occurring in the pneumatic circuit (c1).  4. Device according to one of the preceding claims, characterized in that the printing module (1) comprises a vacuum generator (12) which can use a part of the compressed air supplied to the printing module to generate a vacuum by venturi effect in at least part (c13) of the air circuit.  5. Device according to one of the preceding claims, characterized in that the printing module (1) comprises at least one on-board reservoir (13) supplying ink to at least one ink jet printing head (14) , this on-board tank being connected for its supply to at least one fixed orincipal tank (23) located in or near the control bay (2). <Desc / Clms Page number 23>  6. Device according to one of the preceding claims, characterized in that a compressed air source (A) puts the main ink tank (23) under pressure, this main tank comprising in its lower part an opening which supplies then ink the on-board tank (13) through a pipe (c20).  7. Device according to one of the preceding claims, characterized in that the printing module (1) comprises means (15) for pneumatic distribution which can put the on-board tank (13) in connection with a part (c13) in vacuum of the air circuit (c1) or with a part (c12) in overpressure of the air circuit (c1).  8. Device according to one of the preceding claims, characterized in that it comprises means (21) for adjusting the pressure of the compressed air supply and means (22) for measuring pressure in at least one location of the pneumatic circuit (c1), these means cooperating to regulate either the pressure of the compressed air supplying the printing module (1) or the vacuum generated by the vacuum generator (12), or both.  9. Device according to one of the preceding claims, characterized in that the pneumatic circuit comprises adjustment and control means stabilizing the vacuum inside the on-board tank (13) at a value determined as a function of atmospheric pressure .  10. Device according to one of the preceding claims, characterized in that the printing module comprises non-return means (16) comprising one or more valves or valves capable of isolating one or more parts of the pneumatic circuit (c1).  11. Device according to one of the preceding claims, characterized in that it comprises cutting means (17) which can interrupt the arrival of ink in the on-board tank (13) and at least one sensor (18) <Desc / Clms Page number 24>  of ink level for this same on-board tank, these cut-off means being controlled as a function of this level sensor to regulate the level of ink in this same on-board tank.  12. Device according to one of the preceding claims, characterized in that one or more ink level sensors (18, 28) are attached to the external surface of the vertical wall of one or more of the reservoirs (13, 23) of ink and detect the presence of liquid by capacitive effect through a wall of the tank, at a location situated at a determined height from the bottom of the tank and corresponding to an ink level threshold which should trigger information or commands.  13. Device according to one of the preceding claims, characterized in that the wall of the ink tank (13,23) comprises a thinning (131) allowing better operation of the ink level sensor (18,28) at through this thinning.  14. Device according to one of the preceding claims, characterized in that the storage space of the on-board tank (13) contains one or more separating elements (132) dividing this storage space into several regions (130), on all or part of the height of the reservoir, these regions having a horizontal section of determined dimensions sufficiently small to limit the agitation of the ink; these separating elements (132) themselves having a shape allowing between these same regions (130) a low or zero horizontal flow.  15. Device according to one of the preceding claims, characterized in that the separating elements contained in the on-board tank (13) comprise a plurality of intersecting vertical walls.  16. Device according to one of the preceding claims, characterized in that these separating elements comprise a nest structure <Desc / Clms Page number 25>  bees with contiguous hexagonal cross-sections arranged vertically over a large part of the height of the tank.  17. Device according to one of the preceding claims, characterized in that the inlet opening (135) of ink in the on-board reservoir (13) opens out opposite a part having a surface (136) called de-boiling located below the said ink inlet or close enough for the ink flow to enter the on-board tank flows, over a determined distance, in contact with this same surface (136) before reaching the content (E) of this same on-board tank (13).  18. 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 one or more rows 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 adjustment means 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.  19. Device according to one of the preceding claims, characterized in that the different preset positions correspond to angular positions printing according to predetermined resolutions by varying the spacing (e5) of the dots printed on the support (5), this spacing decreases with increasing tilt angle (as) for the same spacing (e1) of the print nozzles (141) on the print head (14) and thus increasing the print resolution.  20. Device according to one of the preceding claims, characterized in that it comprises means for adjusting the angle of inclination (as), these adjustment means allowing an adjustment of the value of this angle (as ) <Desc / Clms Page number 26>  with respect to its value determined by at least one of the preset positions and thus making it possible to adjust the spacing (e5) of the printed dots without modifying the setting value of these preset positions.  21. Device according to one of the preceding claims, characterized in that it comprises a so-called cleaning station (24) comprising at least one blade and means for relative displacement of the print head (14) relative to the blade allowing said blade to scrape the outer surface of the print head (14) after a prolonged stop or after purging of these same print nozzles.  22. Device according to one of the preceding claims, characterized in that the cleaning station comprises displacement means mobilizing at least one blade (241) called cleaning, which is dipped in a solvent (S) or rubbed on a felt absorbent before scraping the print head (14), and displacement means mobilizing at least one other blade (242) said to dry, scraping the external surface of the print head (14) after the passage of the blade of cleaning.  23. Device according to one of the preceding claims, characterized in that it comprises lifting means capable of lifting all or part of the cleaning station to bring it up to the scraping surface of the print nozzles .  24. 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, 21 c) for adjusting the pressure of the compressed air supply or the means (17) of cut-off or the means (15) of distribution or the non-return means (16) or a combination of these, via at least one electronic interface. <Desc / Clms Page number 27>  25. 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) operating according to the USB communication standard (Universal Serial Bus).