Ink recirculation device for inkjet printing and associated method

Abstract

An ink recirculation device (1) for inkjet printing, or device (1), comprising a single reservoir (2), at atmospheric pressure, intended to receive printing ink, a pump (3), or inlet pump (3), arranged to circulate the ink, in a first ink circulation circuit (4), or first circuit (4), from the single reservoir to an inkjet printhead (5) of the device, a pump (6), or outlet pump (6), arranged to circulate the ink, in a second ink circulation circuit (7), or second circuit (7), from the printhead to the single reservoir. The inkjet printhead is connected to the first and second circuits and comprises at least one ink ejection nozzle (9). The printhead is arranged to ensure ink circulation from the first to the second circuit and a flow of some of the ink, circulating in the printhead, out of the printhead and through the at least one ejection nozzle.

Description

[0001] DESCRIPTION

[0002] TITLE: Ink recirculation device for inkjet printing and associated method

[0003] Technical field

[0004] The present invention relates to the field of methods and systems for depositing material by recirculating material in the print head.

[0005] The present invention relates, in particular, to systems and methods for digital printing and additive manufacturing on flat or complex 3D substrates.

[0006] By way of examples, the invention relates to the fields of industrial printing, graphic printing, printing of transactional and marketing documents, packaging printing or even printing of functional materials.

[0007] A preferred field of application according to the invention is that of inkjet printing devices and methods.

[0008] State of the prior art

[0009] The technique of printing devices by recirculating ink in the print head by means of one or two intermediate gas reservoirs under controlled gas pressure is known in the state of the art.

[0010] In state-of-the-art printing devices, the intermediate reservoirs each contain a gas whose pressure differs from one reservoir to another. The ink to be deposited circulates, from a storage reservoir for the ink to be deposited, through the intermediate gas reservoirs under pressure towards the print head.

[0011] In practice, the ink is pumped from the ink storage tank to be deposited to a first intermediate gas tank. The pressurized gas in the first intermediate gas tank expels the ink toward the inlet of the print head. The pressurized gas in the second intermediate gas tank draws the ink from the outlet of the print head. The ink level in the second intermediate gas tank is controlled by an ink pump that returns it to the ink storage tank or to the first intermediate gas tank depending on the implementation. Thus, in state-of-the-art printing devices, the gas pressure in each intermediate tank must be modulated and controlled to control the flow rate and pressure of the ink injected into the print head. It is the air pressure in each intermediate pressurized gas tank that allows printing to be controlled in particular.

[0012] State-of-the-art printing devices have several drawbacks.

[0013] A disadvantage of state-of-the-art printing devices is that the pressurized air that presses the ink into circulation causes the gas to dissolve in the ink. The dissolved gas changes the characteristics of the ink.

[0014] The ink thus modified induces a degradation of the printing result, that is to say of the quality of the ink printed on the substrate.

[0015] Furthermore, changing the ink characteristics impacts the ink flow in the printhead nozzle actuators because the deposition conditions are closely linked to the characteristics of the ink to be printed. In other words, changing the ink characteristics degrades the quality of the printing step itself.

[0016] Another disadvantage of state-of-the-art printing devices is that the ink level in each intermediate tank must be controlled and regulated so that the volume of ink in each intermediate tank does not exceed a limit level beyond which the ink overflows from the intermediate tank into the pneumatic system for pressurizing the gas in the intermediate tank.

[0017] This risk of overflow therefore requires the integration of sensors, a control system and a safety system for the printing device. This complicates the system, increases the manufacturing cost and the maintenance cost of the printing device.

[0018] Such an arrangement also carries a risk of ink leakage at the various seals and interfaces in the intermediate reservoirs.

[0019] An additional disadvantage is that state-of-the-art printing devices also have a significant footprint due to the volume occupied by the intermediate tanks, sensors and pneumatic systems for pressurising the gas in the intermediate tanks.

[0020] Furthermore, for the reasons detailed above, the intermediate tanks must necessarily be positioned vertically in the printing device so that the ink they contain does not spill into the various circuits to which they are connected.

[0021] Another disadvantage of state-of-the-art printing devices is that pigment inks settle in the intermediate tanks. This significantly increases the frequency of maintenance operations on state-of-the-art devices.

[0022] Finally, a notable drawback of state-of-the-art devices lies in the presence of a significant stabilization time when stopping or restarting ink recirculation or when changing recirculation conditions. Indeed, the use of pressurized gas to compress and cause the flow of ink into the printing device and then out of the print head causes an imbalance in the flow and ink flow rate during changes in regime.

[0023] Also, drips or irregularities may be observed when stopping or restarting printing or when changing deposition conditions during printing.

[0024] Also, according to the invention, there is proposed an inkjet printing device by ink recirculation and an inkjet printing method making it possible to overcome at least some of the drawbacks, preferably making it possible to overcome all or part of the drawbacks, of the devices of the state of the art.

[0025] In particular, an aim of the invention is:

[0026] - to improve the quality of printing, or to obtain quality printed substrates, and / or

[0027] - to avoid, at least in part or even completely, the pollution of the ink by dissolving a gas in the ink, and / or - to propose a printing device having a low cost, or at least a lower cost than state-of-the-art printing devices, and / or

[0028] - to propose a printing device whose design and / or assembly and / or operation is simplified, and / or

[0029] - to propose a printing device whose maintenance is facilitated and / or reduced, or at least whose maintenance is facilitated and / or reduced compared to state-of-the-art devices, and / or

[0030] - to offer a printing device with a reduced risk of ink leakage into the printing device, and / or

[0031] - to propose a printing device with reduced size, or at least a size smaller than the size of state-of-the-art devices.

[0032] Presentation of the invention

[0033] For this purpose, an ink recirculation device for inkjet printing, called a device, is proposed. The device comprises:

[0034] - a reservoir, preferably a single reservoir, at atmospheric or ambient pressure, intended to receive printing ink,

[0035] - a pump, called an inlet pump, arranged to circulate the ink, in a first ink circulation circuit, called the first circuit, from the single reservoir to an inkjet print head of the device,

[0036] - a pump, called the output pump, arranged to circulate the ink, in a second ink circulation circuit, called the second circuit, from the print head to the single reservoir.

[0037] Preferably, the inkjet printhead is connected to the first and second circuits. Preferably, the printhead comprises at least one ink ejection nozzle. Preferably, the printhead is arranged to provide:

[0038] - ink circulation from the first to the second circuit,

[0039] - a flow of a portion of the ink, preferably only a portion of the ink, circulating in said print head, out of the print head through the at least one ejection nozzle.

[0040] Ink recirculation may be understood to mean: ink recirculation in the printing device, preferably recirculation, in addition, in the print head of the printing device. Preferably, the printing device does not comprise any reservoir, or intermediate or additional reservoir, comprising pressurized gas.

[0041] More preferably, the printing device does not comprise any reservoir, or intermediate or additional reservoir, comprising pressurized gas to ensure or allow or cause circulation and / or recirculation of the ink in the printing device and, in particular, circulation and / or recirculation of the ink in the print head.

[0042] It can be understood by inkjet printing: printing by material jet, fluid jet, graphic or functional inkjet.

[0043] Preferably, the single tank or the interior of the single tank is at atmospheric pressure or is maintained at atmospheric pressure. Alternatively, the single tank or the interior of the single tank may be at working pressure, or may be maintained at any working pressure, such as, for example, at a pressure between 100 and 5.10 5 Pascals.

[0044] Preferably, the single reservoir comprises means for gas communication between the exterior of the single reservoir, preferably between the atmosphere surrounding the device, and the interior of the single reservoir. Preferably, the means for gas communication between the exterior and the interior of the single reservoir make it possible to maintain the single reservoir, or the interior of the single reservoir, at atmospheric pressure.

[0045] Preferably, the single reservoir is at atmospheric pressure.

[0046] Preferably, the single reservoir is intended to receive the ink.

[0047] Preferably, the device comprises an ink circulation loop.

[0048] Preferably, the recirculation loop comprises the first and second circuits. Preferably, the recirculation loop comprises the print head. Preferably, the recirculation loop comprises the single reservoir.

[0049] Preferably, the recirculation loop consists of or is comprised of the first and second circuits, the single reservoir, and / or the printhead.

[0050] Preferably, the device is arranged so that only a portion of the ink circulating in said print head flows out of the print head through the at least one ejection nozzle. Preferably, the device is arranged so that only a portion of the ink circulating in said print head flows out of the print head through the at least one ejection nozzle so that at least a portion of the ink circulating in the first circuit circulates in or through the print head to the second circuit. The device may comprise several print heads. Preferably, the device is arranged to ensure parallel circulation of ink in the print heads.

[0051] Those skilled in the art will understand that the term "arranged to ensure" means "arranged to implement", "arranged to carry out" or "arranged for".

[0052] Preferably, the device comprises one or more pulsation dampers arranged between the inlet pump and the print head and / or one or more pulsation dampers arranged between the print head and the outlet pump. Preferably, the pulsation dampers are arranged to dampen oscillations in ink flow and / or flow rate and / or pressure downstream of the inlet pump and / or upstream of the outlet pump and therefore, preferably, in the print head.

[0053] Preferably, a pulsation of the inlet and outlet pumps is greater than or equal to 30 Hz.

[0054] Preferably, an inlet pump pulsation and / or an outlet pump pulsation is greater than or equal to 30 Hz, preferably 32 Hz, more preferably 34 Hz, particularly preferably 35 Hz, even more preferably 36 Hz, advantageously 37 Hz, most particularly advantageously 38 Hz, even more particularly advantageously 39 Hz and most preferably 40 Hz.

[0055] Particularly advantageously, a pulsation of the inlet pump and / or a pulsation of the outlet pump is greater than or equal to 40 Hz, preferably 42 Hz, more preferably 44 Hz, particularly preferably 45 Hz, even more preferably 46 Hz, advantageously 47 Hz, very particularly advantageously 48 Hz, even more particularly advantageously 49 Hz and most preferably 50 Hz.

[0056] Preferably, the device comprises a control unit.

[0057] Preferably, the control unit is arranged and / or configured and / or programmed to control and / or regulate and / or operate and / or control, among other things, the inlet and outlet pumps. Preferably, the control unit is arranged and / or configured and / or programmed to synchronize the inlet and outlet pumps.

[0058] In the present application, "synchronize" may be understood to mean: temporally coordinate one, some or each of the operating parameters of the input and output pumps.

[0059] Preferably, the device comprises a flow sensor disposed in one and / or the other of the first and second circuits.

[0060] Preferably, the control unit is arranged and / or configured and / or programmed to regulate and / or control and / or operate and / or monitor at least one operating parameter of the inlet and / or outlet pump based on data measured by the flow sensor(s).

[0061] Preferably, the control unit is arranged and / or configured and / or programmed to regulate and / or to control and / or operate and / or monitor at least one operating parameter of the input and / or output pump, based on data measured by the flow sensor(s), so as to maintain and / or modulate and / or modify an ink flow rate circulating in the print head.

[0062] Preferably, the control unit is arranged to regulate at least one operating parameter of the input and / or output pump such that an ink flow rate in the first circuit is equal to or different from an ink flow rate in the second circuit.

[0063] Preferably, the device comprises a pressure sensor disposed in one and / or the other of the first and second circuits.

[0064] Preferably, the control unit is arranged and / or programmed and / or configured to regulate and / or to control and / or operate and / or monitor at least one operating parameter of the inlet and / or outlet pump based on data measured by the pressure sensor(s).

[0065] Preferably, the device comprises a pressure sensor, preferably arranged downstream of the inlet pump, arranged to measure the ink pressure in the first circuit, preferably the ink pressure downstream of the inlet pump and upstream of the print head.

[0066] Preferably, the device comprises a pressure sensor, preferably arranged upstream of the output pump, arranged to measure the ink pressure in the second circuit, preferably the ink pressure upstream of the output pump and downstream of the print head.

[0067] Preferably, in the present description, the terms "upstream" and "downstream" are expressed relative to a direction of ink circulation from the single reservoir to the print head and then from the print head to the single reservoir.

[0068] Preferably, the control unit is arranged and / or programmed and / or configured to regulate and / or to command and / or operate and / or control at least one operating parameter of the input and / or output pump, as a function of data measured by the pressure sensor(s), so as to maintain and / or modulate and / or modify an ink pressure at the input of the print head and a pressure at the output of the print head.

[0069] The printhead outlet pressure can be defined as the pressure to extract ink from the printhead.

[0070] Preferably, the control unit is arranged to regulate at least one operating parameter of the input and / or output pump such that an ink pressure in the first circuit is equal to or different from an ink pressure in the second circuit.

[0071] Preferably, the inlet pump and / or the outlet pump is a diaphragm pump.

[0072] Preferably, the control unit is arranged and / or configured and / or programmed to temporally coordinate the oscillations of the membrane of the inlet pump with the oscillations of the membrane of the outlet pump.

[0073] It can be understood as temporally coordinating the oscillations of the inlet pump membrane with the oscillations of the outlet pump membrane: commanding and / or modulating and / or controlling a phase shift between the oscillations of the inlet pump membrane and the oscillations of the outlet pump.

[0074] The phase shift between the oscillations of the membrane of the inlet pump and the oscillations of the outlet pump may be zero or may be non-zero. Preferably, the control unit is arranged and / or programmed and / or configured to modulate and / or control and / or regulate and / or command an oscillation amplitude of the membrane of the inlet pump and / or an oscillation amplitude of the membrane of the outlet pump.

[0075] Preferably, the control unit is arranged so that an oscillation amplitude of the membrane of the inlet pump is equal to or different from an oscillation amplitude of the membrane of the outlet pump.

[0076] Preferably, the control unit is arranged and / or configured and / or programmed to modulate and / or control and / or regulate and / or monitor an opening time and a closing time of an inlet valve and a discharge valve of the inlet pump and / or the outlet pump.

[0077] Preferably, the control unit is arranged so that:

[0078] - the opening time and / or closing time of the inlet valve of the inlet pump is equal to or different from the opening time and / or closing time of the inlet valve of the outlet pump, and / or

[0079] - the opening time and / or closing time of the discharge valve of the inlet pump is equal to or different from the opening time and / or closing time of the discharge valve of the outlet pump.

[0080] The at least one operating parameter of the inlet and / or outlet pump can be:

[0081] - the inlet pump pulsation and / or the outlet pump pulsation, and / or

[0082] - the pulsation of the inlet pump membrane and / or the pulsation of the outlet pump, and / or

[0083] - the phase shift between the oscillations of the inlet pump membrane and the oscillations of the outlet pump membrane, and / or

[0084] - the oscillation amplitude of the inlet pump membrane and / or the oscillation amplitude of the outlet pump membrane, and / or

[0085] - the opening time of the inlet valve of the inlet pump and / or the opening time of the inlet valve of the outlet pump, and / or

[0086] - the opening time of the discharge valve of the inlet pump and / or the opening time of the discharge valve of the outlet pump, and / or - the closing time of the inlet valve of the inlet pump and / or the closing time of the inlet valve of the outlet pump, and / or

[0087] - the closing time of the inlet pump discharge valve and / or the closing time of the outlet pump discharge valve.

[0088] According to the invention, there is also provided an inkjet printing method by ink recirculation, called method. The method comprises:

[0089] - ink circulation, by means of the inlet pump, in the first ink circulation circuit, from the single reservoir to the inkjet print head,

[0090] - ink circulation, by means of the output pump, in the second ink circulation circuit from the print head to the single reservoir.

[0091] Preferably, the method further comprises circulating ink, in or through the printhead from the first to the second circuit.

[0092] Preferably, the method further comprises flowing a portion of the ink, currently circulating in the printhead, out of the printhead through the at least one ejection nozzle of the printhead.

[0093] Preferably, the ink is pumped, by the inlet pump, into the single reservoir and then circulates in the first circuit, to be injected into the print head. Preferably, the ink is pumped, by the inlet pump, into the single reservoir and then circulates in the first circuit, to be injected into the print head without the ink circulating in an additional reservoir and / or coming into contact with a gas between the single reservoir and the print head.

[0094] Preferably, the ink is pumped, by the output pump, into the print head, then circulates in the second circuit, to be injected into the single reservoir.

[0095] Preferably, a circulation, preferably a continuous circulation of ink in the print head, from the first circuit to the second circuit, is maintained during printing. In other words, a portion of the ink from the first circuit circulates, preferably continuously, through the print head, to the second circuit, during printing.

[0096] Preferably, in the present application, printing or printing step is understood to mean: the flow of ink, or of a portion of the ink, circulating in the print head, out of the print head through the at least one ejection nozzle.

[0097] Preferably, during printing, a portion of the ink circulating in the print head is evacuated or drawn off or flows through the at least one ejection nozzle.

[0098] Preferably, the method comprises a step of damping oscillations in ink flow and / or flow rate and / or pressure downstream of the inlet and / or outlet pumps, and thus preferably in the print head, respectively by means of a pulsation damper arranged between the inlet pump and the print head and / or a pulsation damper arranged between the print head and the outlet pump.

[0099] Preferably, the method further comprises a step of controlling the inlet and outlet pumps, by means of the control unit, consisting of synchronizing the inlet and outlet pumps.

[0100] Preferably, the method further comprises a step of controlling the inlet and outlet pumps, by means of the control unit, consisting of regulating and / or controlling and / or operating and / or monitoring the at least one operating parameter of the inlet and / or outlet pump as a function of data measured by the flow sensor(s).

[0101] Preferably, the method further comprises a step of controlling the inlet and outlet pumps, by means of the control unit, consisting of regulating and / or controlling and / or operating and / or monitoring the at least one operating parameter of the inlet and / or outlet pump as a function of data measured by the pressure sensor(s).

[0102] Preferably, the method further comprises a step of controlling the inlet and outlet pumps, by means of the control unit, consisting of temporally coordinating the oscillations of the membrane of the inlet membrane pump with the oscillations of the membrane of the outlet membrane pump. Preferably, the method further comprises a step of controlling the inlet and outlet pumps, by means of the control unit, consisting of modulating and / or regulating an oscillation amplitude of the membrane of the inlet membrane pump and an oscillation amplitude of the membrane of the outlet membrane pump.

[0103] Preferably, the method further comprises a step of controlling the inlet and outlet pumps, by means of the control unit, consisting of modulating and / or regulating an opening time and a closing time of an inlet valve and a discharge valve of the inlet membrane pump and / or the outlet membrane pump.

[0104] Preferably, the method comprises a control and / or a regulation and / or a modulation, by the control unit, of at least one operating parameter of the inlet and outlet pumps so as to:

[0105] - make synchronous, that is to say to actuate or control at the same time, one, several or each operating parameter of the inlet and outlet pumps among, for example, the pulsation of the pumps or the pulsation of the pump membrane, the phase shift between the oscillations of the pump membrane or the opening and / or closing time of the inlet valve and / or the discharge valve of the pumps, or

[0106] - introduce a time lag or phase shift between one, several or each operating parameter of the inlet and outlet pumps among, for example, the pulsation of the pumps or the pulsation of the diaphragm of the pumps, the phase shift between the oscillations of the diaphragm of the pumps or the opening and / or closing time of the inlet valve and / or the discharge valve of the pumps, and / or

[0107] - introduce a difference in oscillation amplitude or apply the same oscillation amplitude between the membrane of the pumps.

[0108] Preferably, the ink recirculation inkjet printing method according to the invention is suitable, more preferably is particularly suitable, more preferably is designed and particularly advantageously is specially designed, to be implemented by the ink recirculation inkjet printing device according to the invention. Also, any characteristic of the printing device according to the invention is directly transposable to the printing method according to the invention and vice versa.

[0109] Description of figures

[0110] Other advantages and particularities of the invention will appear on reading the detailed description of implementations and embodiments which are in no way limiting, and the following appended drawings: [Fig. 1] FIGURE 1 is a schematic representation of an embodiment of the printing device according to the invention,

[0111] [Fig. 2] FIGURE 2 is a schematic representation of a set of print heads according to the invention,

[0112] [Fig. 3] FIGURE 3 is a schematic side view representation of one embodiment of a diaphragm pump according to the invention.

[0113] Description of the embodiments

[0114] The embodiments described below being in no way limiting, it will be possible in particular to consider variants of the invention comprising only a selection of the described characteristics, isolated from the other described characteristics (even if this selection is isolated within a sentence comprising these other characteristics), if this selection of characteristics is sufficient to confer a technical advantage or to differentiate the invention compared to the state of the prior art. This selection comprises at least one characteristic, preferably functional without structural details, or with only a part of the structural details if this part only is sufficient to confer a technical advantage or to differentiate the invention compared to the state of the prior art.

[0115] The state of the art includes controlled inkjet or on-demand inkjet (or "drop on demand" or ink recirculation) printing devices and continuous inkjet printing devices. The invention relates to a controlled inkjet device.

[0116] Continuous inkjet printing devices have a fluid junction connected to the inlet of the continuous jet print head. During printing, all of the ink supplied to the print head is ejected from the print head. Typically, a gutter or trough is provided to collect some of the ink ejected from the print head that was not used for printing.

[0117] On-demand inkjet printing devices have a fluid junction connected to an inlet of the on-demand inkjet printhead and another fluid junction connected to an outlet of the on-demand inkjet printhead. Typically, the on-demand inkjet printhead includes a conduit or distribution chamber, communicating with the ejection nozzle(s), and connecting the inlet and the outlet. At least a portion of the ink supplied to the printhead is not ejected through the nozzle(s) but returns, through the outlet of the printhead, to the recirculation circuit of the controlled inkjet printing device such that the ink continuously circulates through the printhead. Prior art controlled inkjet printing devices include an ink reservoir and at least one additional reservoir.The additional reservoir(s) are intended to control, regulate or compensate for variations in the pressure of the ink supplying the print head (or any other parameter of the ink influencing the pressure of the ink supplying the print head, for example the flow rate, the viscosity of the ink supplying the print head).

[0118] In a majority of state-of-the-art controlled inkjet printing devices, the reservoirs comprise pressurized gas. The pressurized gas is used to move the ink towards the reservoir. A differential gas pressure is maintained across the reservoirs. The gas volume in each reservoir has the effect of limiting and damping ink pulsations (i.e., variations in ink flow rates / flows feeding the print head). Pulsation dampers are also used in state-of-the-art devices.

[0119] With reference to FIGURE 1, an embodiment of the inkjet printing device by ink recirculation 1, called device 1, according to the invention is presented. The device 1 comprises a reservoir 2 intended to receive the ink to be printed. The reservoir 2 is an ink reservoir or a reservoir intended to store the ink to be printed.

[0120] The device 1 comprises a pump 3, called the inlet pump 3. The inlet pump is arranged to circulate the ink in a first ink circulation circuit 4, called the first circuit 4, from the single reservoir 2 to an inkjet print head 5 of the device 1. The inlet pump 3 draws ink from the reservoir 2 and then forces the ink through the first circuit 4 into the print head.

[0121] The device comprises a pump 6, called the output pump 6. The output pump 6 is arranged to circulate the ink in a second ink circulation circuit 7, called the second circuit 7, from the print head 5 to the single reservoir 2. The output pump 6 sucks the ink from the print head 5 and then delivers the ink through the second circuit 7 to the ink reservoir 2. By way of non-limiting examples, the inlet pump 3 and / or the output pump 6 may be a peristaltic pump, a gear pump or a membrane pump.

[0122] It is also provided that the device 1 may comprise several inlet pumps 3 mounted in parallel on the first circuit 4 and / or several outlet pumps 6 mounted in parallel on the second circuit 7.

[0123] Such a configuration is usable when high ink circulation / recirculation rates are required.

[0124] The print head 5 is advantageously an inkjet print head 5.

[0125] The print head 5 is connected to the first circuit 4 and the second circuit 7.

[0126] The print head 5 is arranged to ensure circulation of ink from the first circuit 4 to the second circuit 7.

[0127] In practice, with reference to FIGURE 2, and by way of non-limiting example, the print head 5 comprises a circulation channel 8 or a fluidic channel 8 ensuring the circulation of the ink through the print head 5.

[0128] The print head 5 comprises at least one ink ejection nozzle 9. Preferably, the print head 5 comprises several ink ejection nozzles 9.

[0129] The print head 5 is arranged to ensure a flow of a portion of the ink circulating in the print head 5 out of the print head 5 via the at least one ejection nozzle 9.

[0130] According to the invention, the device 1 advantageously comprises a single reservoir 2. The invention makes it possible to use a single reservoir 2. No other reservoir, in particular a gas reservoir, is required to be able to print with the device 1 according to the invention.

[0131] The ability to use a single tank 2 allows the printing device 1 to have simplified design, assembly and operation.

[0132] The maintenance of the printing device 1 according to the invention is also facilitated and its cost reduced. In addition, the size of the printing device 1 according to the invention is reduced compared to the devices of the state of the art.

[0133] According to the invention, the reservoir 2 is advantageously at atmospheric pressure. The invention makes it possible to use a reservoir 2 at atmospheric pressure. The ink does not need to be compressed by a gas to carry out the printing according to the invention.

[0134] The printing device 1 according to the invention thus makes it possible to avoid, at least in part or even completely, the pollution of the ink by dissolution of a gas in the ink. Indeed, in the printing devices of the state of the art, a dissolution of the gas used to compress, circulate the ink in the printing device and allow the flow of the gas out of the device via the print head is inevitable.

[0135] For these reasons, the printing device 1 according to the invention also makes it possible to reduce or even eliminate the risk of ink leakage in the printing device due to the absence of pressure tanks, the absence of gas circuits and pneumatic circuits for compressing the ink as well as the absence of gas circulation circuits in series upstream of the print head.

[0136] With reference to FIGURE 2, according to an advantageous non-limiting embodiment, the device 1 comprises a set of print heads 5 mounted in parallel. The ink is discharged by the inlet pump 3 into the first circuit 4. The ink coming from the first circuit 4 circulates in parallel, through a circulation channel 8 or a fluidic channel 8, in each print head 5 (the circulation channel 8 of only one of the print heads 5 is shown in FIGURE 2).

[0137] The injection nozzles 9 are connected to the circulation channel 8. A portion of the ink circulating in the circulation channel 8 flows or is ejected out of the print head 5 via the injection nozzles 9.

[0138] After circulating in the print head 5, the ink is sucked by the outlet pump 6 into the second circuit 7.

[0139] Preferably, when the device 1 comprises several print heads 5, the device 1 comprises two collectors / distributors 10, 11 (also called "manifold" in English), or a collector 10 and a distributor 11. The distributors 10 allow the simultaneous supply of all the print heads 5 by distributing ink with negligible pressure losses. The distributor 10 is mounted on the first circuit 4 upstream of the print heads 5. It ensures distribution of the ink between all the print heads 5.

[0140] The same description above made for the distributor 10 applies to the collector 11. In practice, it is the same element performing the opposite function. The collector 11 is mounted on the second circuit 7 downstream of the print heads 5.

[0141] Advantageously, as illustrated in FIGURE 1, the device 1 comprises a pulsation damper 12 arranged between the inlet pump 3 and the print head 5 and / or a pulsation damper 13 arranged between the print head 5 and the outlet pump 6. According to the non-limiting embodiment, the device 1 comprises a pulsation damper 12 arranged between the inlet pump 3 and the print head 5 and a pulsation damper 13 arranged between the print head 5 and the outlet pump 6.

[0142] The function of the pulsation dampers 13, 12 is to limit the ink flow oscillations downstream of the inlet 3 and / or outlet 6 pumps.

[0143] According to an advantageous embodiment, a pulsation of the inlet pump 3 and the outlet pump 6 is greater than or equal to 30 Hz. Particularly advantageously, the pulsation of the inlet pump 3 and the outlet pump 6 is greater than or equal to 40 Hz and even more particularly advantageously 50 Hz.

[0144] In practice, it has been observed that a pulsation of the inlet pump 3 and the outlet pump 6 greater than or equal to 30 Hz, particularly notably a pulsation greater than or equal to 40 Hz and even more markedly a pulsation greater than or equal to 50 Hz, makes it possible to facilitate and improve the damping of the flow oscillations and / or to make the control of the device 1 faster to compensate, in particular, for the sudden variation in volume in the ink circuit due to the volume of the ink droplets ejected by the print head 5.

[0145] Advantageously, the higher the frequency of the inlet pumps 3 and / or outlet pumps, the greater the amplitude of movement of the diaphragm of the pump makes it possible to effectively maintain a high flow rate setpoint range without significantly impacting the amplitude of the pulsation of the fluid pressure. In particular, it has been observed that this phenomenon is particularly effective for frequencies equal to or greater than 30 Hz. According to this embodiment, the inlet pump 3 and the outlet pump 6 are gear pumps or diaphragm pumps.

[0146] The use of high-frequency and synchronous inlet 3 and outlet 6 pumps has the effect of controlling the inlet 3 and outlet 6 pumps without phase delay. This makes it possible to improve the quality of the deposit by limiting defects and / or inaccuracies in the size and / or positioning of the printed droplets during changes in regimes such as, for example, stopping printing and starting printing, moving from one line to another or from one area to be printed to another area to be printed or during a change in speed or printing conditions during printing.

[0147] The device 1 comprises a control unit 14.

[0148] The control unit 14 is arranged to control the inlet pump 3 and the outlet pump 6.

[0149] Preferably, the control unit 14 is arranged to synchronize the operation of the inlet 3 and outlet 6 pumps. In particular, the control unit 14 is arranged to coordinate the pulsations of the inlet 3 and outlet 6 pumps.

[0150] The device 1 comprises a flow sensor 21 arranged in one and / or the other of the first 4 and second circuits 7. According to the non-limiting embodiment, the device 1 comprises a flow sensor 21 arranged in the second circuit 7 downstream of the print head 5 and upstream of the output pump 6.

[0151] The control unit 14 can be arranged to control and / or modulate and / or monitor the inlet pump 3 and / or the outlet pump 6 as a function of the data measured by the flow sensor(s) 21.

[0152] The device 1 comprises a pressure sensor 22, 23 arranged in one and / or the other of the first 4 and second circuits 7. According to the non-limiting embodiment, the device 1 comprises a pressure sensor 22 arranged downstream of the inlet pump 3 and upstream of the print head 5 and a pressure sensor 23 arranged in the second circuit 7 downstream of the print head 5 and upstream of the outlet pump 6. The control unit 14 can be arranged to control and / or modulate and / or monitor the inlet pump 3 and / or the outlet pump 6 as a function of the data measured by the pressure sensor(s) 22, 23.

[0153] Preferably, the control unit 14 is arranged to control and / or modulate and / or control the inlet pump 3 and / or the outlet pump 6 so as to maintain and / or impose and / or modulate and / or regulate and / or control an ink pressure differential between the part of the first circuit 4 located downstream of the inlet pump 3 and the part of the second circuit 7 located downstream of the outlet pump 6. In other words, the control unit 14 is arranged to control and / or modulate and / or control the inlet pump 3 and / or the outlet pump 6 so as to maintain and / or impose and / or modulate and / or regulate and / or control an ink pressure differential between the inlet and the outlet of the print head 5.

[0154] According to an advantageous, but non-limiting, embodiment of the invention, the inlet 3 and outlet 6 pumps are membrane pumps.

[0155] According to a particularly advantageous but non-limiting aspect of the embodiment, the inlet 3 and outlet 6 pumps are solenoid diaphragm pumps or a piezoelectric pump. In other words, the inlet 3 and outlet 6 pumps may be pumps whose oscillations of the membrane 15 are controlled or actuated by a solenoid or a piezoelectric actuator.

[0156] Advantageously, for each pulsation of the membrane of the pumps 3 and / or 6, the displacement of the membrane is controlled in speed and amplitude to reduce and control the amplitude of the pulsation of the liquid. Advantageously, the displacement of the membrane of the pumps 3 and / or 6 is implemented by means of an electromechanical device, by way of non-limiting example by means of:

[0157] - an axis mounted on a magnetic solenoid (bistable or monostable with spring) whose magnetic field intensity is controlled, or

[0158] - a motor whose rotation axis is controlled in speed and position.

[0159] The remainder of the description of the embodiment will relate to a device 1 comprising inlet 3 and outlet 6 pumps with solenoid or piezoelectric membrane. However, this advantageous embodiment does not limit the invention, in particular the aspects of the invention described above, to the use of a solenoid or piezoelectric membrane pump.

[0160] Referring to FIGURE 3, there is illustrated a schematic representation of a solenoid diaphragm pump 3, 6.

[0161] All diaphragm pumps comprise a diaphragm 15 set into oscillation by an actuator. The oscillations of the diaphragm 15 modify the volume of a chamber 16 of which the diaphragm 15 constitutes one of the walls. An inlet valve 17 and a discharge (or non-return) valve 18 respectively allow the admission and discharge of a fluid into the chamber. In operation, diaphragm pumps comprise a discharge cycle and an inlet cycle. During the discharge cycle, the movement of the diaphragm 15 reduces the volume of the chamber 16, which has the effect of causing an overpressure in the chamber 15 and discharging the fluid contained in the chamber 15 by pushing the discharge valve 18 and closing the inlet valve 17.The intake cycle comprises the reverse steps, i.e. the movement of the membrane 15 increases the volume of the chamber 16, which has the effect of causing a depression in the chamber 15 and closing the discharge valve 18 and opening the intake valve 17 by suction and thus admitting the fluid into the chamber.

[0162] The operation described above is identical to all diaphragm pumps. However, the majority of diaphragm pumps use a conventional motor as an actuator. The oscillations of the diaphragm 15 are therefore fixed. The oscillations of the diaphragm 15 of traditional motor-driven diaphragm pumps cannot be modulated in amplitude or pulsation (synchronization in phase or phase shift of the oscillations). Also, the regulation and / or fine modulation of the ink pressure in the first 4 and second circuits 7, and therefore the ink pressure in the print head 5, is not possible with traditional motor-driven diaphragm pumps. A fortiori, the same observation applies to peristaltic pumps.

[0163] Also, according to the advantageous embodiment of the invention, the use of inlet 3 and outlet 6 pumps with solenoid or piezoelectric membrane makes it possible to control the amplitude of the oscillations, the pulsation of the membrane 15 and the phase shift between the oscillations / pulsation of the membrane 15 of the inlet pump 3 and the outlet pump 6. The control unit 14 controls and / or modulates the activation voltage and the duration of application of the activation voltage of the solenoid 19. Thus, the stroke of the electromagnet 20 inside the solenoid 19 (or the coil 19) is modulated. The electromagnet 20 is connected to the membrane 15. The oscillation amplitude of the membrane 15 is thus modulated.

[0164] The same description given above for the solenoid pump can be transposed to the piezoelectric pump by substituting the solenoid actuator 19 with a piezoelectric actuator.

[0165] According to an advantageous embodiment, the control unit 14 is arranged to regulate at least one operating parameter of the inlet pump 3 and / or the outlet pump 6.

[0166] Among the operating parameters of the inlet 3 and outlet 6 pumps, we can list, as non-limiting examples:

[0167] - the pulsation of the inlet pump 3 and / or the pulsation of the outlet pump 6, and / or

[0168] - the pulsation of the inlet pump membrane and / or the pulsation of the outlet pump, and / or

[0169] - the phase shift between the oscillations of the inlet pump membrane and the oscillations of the outlet pump membrane, and / or

[0170] - the oscillation amplitude of the inlet pump membrane and / or the oscillation amplitude of the outlet pump membrane, and / or

[0171] - the opening time of the inlet valve of the inlet pump and / or the opening time of the inlet valve of the outlet pump, and / or

[0172] - the opening time of the discharge valve of the inlet pump and / or the opening time of the discharge valve of the outlet pump, and / or

[0173] - the closing time of the inlet valve of the inlet pump and / or the closing time of the inlet valve of the outlet pump, and / or

[0174] - the closing time of the inlet pump discharge valve and / or the closing time of the outlet pump discharge valve.

[0175] Advantageously, the control unit 14 is arranged to control and / or modulate and / or monitor at least one operating parameter of the inlet pump 3 and / or the outlet pump 6 as a function of data measured by the flow sensor(s) 21 and / or from data measured by the pressure sensor(s) 22, 23. Depending on the embodiment, a person skilled in the art has general knowledge of servocontrol and / or control loop (or PID (for “proportional, integral, derivative”) regulator / corrector) enabling him to choose the appropriate model to implement the characteristic according to which “the control unit 14 is arranged and / or configured and / or programmed to control and / or modulate and / or regulate and / or monitor at least operating parameters of the inlet pump 3 and / or the outlet pump 6” as a function of his needs and the specific case.

[0176] The control unit 14 is arranged to temporally coordinate the oscillations of the membrane 15 of the inlet pump 3 with the oscillations of the membrane 15 of the outlet pump 6.

[0177] The control unit 14 is arranged to ensure synchronous operation of the inlet 3 and outlet 6 pumps. In this case, the pulsations of the pumps 3, 6 will be synchronous.

[0178] The control unit 14 can also be arranged to ensure phase-shifted operation of the pumps 3, 6. In this case, preferably, the pulsation of the inlet pump 3 can be in phase opposition with the pulsation of the outlet pump 6.

[0179] Thus, the synchronous starting and stopping of the inlet 3 and outlet 6 pumps, and / or the synchronous control of the inlet 17 and discharge 18 valves, makes it possible to eliminate the overpressures and depressions observed in the devices of the state of the art. This makes it possible to prevent the formation and untimely flow of ink out of the ejection nozzles 9 as well as the filling of air in the ejection nozzles 9.

[0180] Furthermore, the regulation of the pulsation of the pumps 3, 6 by the processing unit 14 also contributes to the formation and ejection of droplets from the ejection nozzles 9 with better quality and better regularity of drop size. They also contribute to avoiding the filling of the ejection nozzles 9 with air. Furthermore, the processing unit 14 can be arranged so that, in particular when starting and stopping the circulation / recirculation, the pulsation of the inlet pump 3 is different from the pulsation of the outlet pump 6. This also makes it possible to avoid ink losses. Although known to those skilled in the art, it is recalled that in an inkjet printing device, the ink is maintained in the ejection nozzles by the balance between the atmospheric pressure and the pressure applied by the fluid in each ejection nozzle. A meniscus of fluid (ink) is therefore formed at the orifice of the ejection nozzle.One printing method involves generating an acoustic wave in the ejection nozzles, or in some ejection nozzles, for example, using a piezoelectric actuator. The acoustic wave generated in the ejection nozzles has the effect of breaking the meniscus and causing the ejection of the fluid (ink) in the form of a drop. Typically, a drop can have a volume between 1 picoliter (pL) and 100 pL on average.

[0181] Also, in ink recirculation printing devices, to dynamically adjust the ink pressure in the ejection nozzles to compensate for the volume of ink lost from the ejected drops and allow the refilling of the ejection nozzles.

[0182] Also, any parasitic or uncontrolled variation in ink pressure causes it to be ejected through the ejection nozzle orifice.

[0183] When commissioning or starting printing in an ink recirculating printing device, there is a temporary condition in which the ink goes from zero speed to the nominal speed. Similarly, when stopping printing in an ink recirculating printing device, the recirculation speed must temporarily fluctuate from the nominal speed to zero speed. Therefore, to prevent any air ingress or ink circulation in the printing device, the ink recirculating printing devices of the prior art include valves or solenoid valves mounted on the various fluid circulation circuits. By actuating these solenoid valves, this causes a temporary pressure variation which destabilizes the menisci formed at the nozzle outlet and causes air ingress or ink leakage from the nozzles, which is then detrimental to the proper functioning of the print head.

[0184] Compared to printing devices with additional gas-pressurized reservoirs of the prior art, the printing device 1 according to the invention therefore has a significantly better seal and makes it possible to avoid these air intakes and / or ink leaks, in particular during the phases of stopping or starting printing, by, in particular: the control and / or regulation and / or monitoring, by the control unit 14, of the amplitude and / or phase shift of movement of the membrane 15 of the pumps 3, 6 simultaneously. The pressure regulation makes it possible to close the ink circuit without jolts or uncontrolled variations in the ink pressure in the print head 5 and therefore without ink leaks or air intake. The device 1 according to the invention therefore does not comprise valves or a solenoid valve provided for this purpose. In fact, it is the position of the membrane 15 of the pumps 3, 6 which then ensures the sealing of the ink circuit.The same description applies for the commissioning of ink recirculation after a shutdown or power-down of the device 1.

[0185] - the absence of an ink reservoir, and / or an additional reservoir, under pressure to ensure the circulation of the ink is also important. The recirculation of ink in the printing device 1 is carried out by the inlet 3 and outlet 6 pumps arranged directly on the ink circuit. The pumps 3, 6 therefore directly actuate, push, suck and / or move the ink, which is an incompressible fluid in the operating range of the pumps, unlike the pumps of the state-of-the-art devices which actuate a gas to create a differential pressure between the two additional reservoirs of the state-of-the-art devices. Since air is compressible, when the state-of-the-art devices are stopped, the volume of air increases due to the effect of the mass of the fluid and gravity. Thus, the depression is released on the meniscus which tears and causes ink to leak through the nozzles of the print head.

[0186] The control unit 14 is arranged to modulate an oscillation amplitude of the membrane 15 of the inlet pump 3 and / or an oscillation amplitude of the membrane 15 of the outlet pump 6.

[0187] Advantageously, the oscillation amplitude of the membrane 15 is achieved at a fixed pulsation of the membrane 15 of the inlet 3 and outlet 6 pumps. Preferably, only the duty cycle of the high state, i.e. the activation of the electromagnet 20, is modulated.

[0188] Preferably, the control unit is arranged so that the oscillation amplitude of the membrane 15 of the inlet pump 3 is equal to the oscillation amplitude of the membrane 15 of the outlet pump 6. Furthermore, the use of the inlet 3 and outlet 6 pumps with solenoid or piezoelectric membrane also makes it possible to achieve high synchronous pulsation values, typically greater than 50 Hz, which are not accessible with other pumps.

[0189] In addition, the use of the inlet 3 and outlet 6 pumps with solenoid or piezoelectric membrane also makes it possible to ensure synchronization, with phase matching or phase shifting, of the operating parameters of the pumps 3, 6, moreover with great responsiveness; which is not possible with the other pumps.

[0190] Thus, the device 1 comprising inlet 3 and outlet 6 pumps with solenoid or piezoelectric membrane makes it possible to further reduce, or even eliminate, the phase delay between the pumps 3, 6 and therefore to ensure optimal modulation and / or regulation of the flow rate and / or ink pressure in the print head 5.

[0191] Thus, advantageously, the device 1 according to the invention makes it possible to switch instantly from operation in recirculation mode of the device 1 to operation in gravity mode without disturbances or disadvantages such as the appearance of drops and / or leakage of ink from the ejection nozzles 9 and without the injection of air (or the suction of air) into the ejection nozzles 9.

[0192] The recirculation mode of operation is the only mode of operation of the device 1 that has been described so far. In the gravity mode of operation (described in contrast to the recirculation mode of operation), printing, i.e. the flow of ink out of the ejection nozzles of the print head, is carried out, without recirculation of the ink in the print head, by exerting pressure on the ink which flows under the action of gravity out of the ejection nozzle.

[0193] Also, although printing in recirculation mode remains particularly advantageous, another advantage of the invention is to be able to switch from the recirculation operating mode to the gravity operating mode. In operation in gravity mode, the device 1 according to the invention allows precise control of the meniscus formed at the outlet of the nozzles 9 of the print head 5 by regulating the pressure by the pressure sensors 22, 23 by very precisely activating one of the pumps 3, 6, by controlling the at least one operating parameter of the pump 3, 6. A precise volume of ink is supplied in order to ensure a constant meniscus pressure in the nozzles 9 of the print head 5.

[0194] For example, the membrane 15 of the inlet pump 3 is actuated cycle by cycle. Unlike the recirculation operating mode in which the pumps 3, 6 are actuated at a constant pulse, the inlet pump 3 is therefore no longer actuated at a fixed pulse frequency but according to two control laws nested in two control loops. The first law, which can be described as fine control, comprises a control and / or regulation of the cyclic ratio of movement of the membrane 15, by means of the solenoid 19 or the piezoelectric actuator, proportionally to the pressure difference measured between the inlet, at the pressure sensor 22 of the print head 5, and a pressure setpoint dependent on the topological definition of the device 1.The second control law, which can be described as coarse control, is implemented in a second control loop and comprises a control and / or regulation of the frequency of pulsation of displacement of the membrane 15, by means of the solenoid 19 or the piezoelectric actuator, proportionally to the speed of variation of pressure measured at the inlet, at the pressure sensor 22 of the print head 5. This results in a large control dynamic for finely regulating the meniscus at the end of the nozzles 19, but also for supplying the nozzles 19 with sufficient ink depending on the volumes of ink ejected by the nozzles 9.

[0195] Another advantage relating to the gravity mode of operation is that it is possible to place the device 1 in a rest or standby state between two prints. In this case, the pumps 3, 6 are kept in the closed position, that is to say the membrane 15 of the pumps 3, 6 is kept in the high position (position in which an overpressure is created in the chamber 16) or in the low position (position in which a depression is created in the chamber 16). The pumps 3, 6 then act as a closed valve preventing any circulation or movement of the ink in the circuits 4, 7 and in the print head 5.

[0196] In this state, maintenance of the device 1 is possible without having to purge all of the ink from the device. Finally, filling and / or emptying the ink from the reservoir 2 as well as the maintenance of the device 1 is facilitated by the use of a single reservoir 2 at atmospheric pressure. For cleaning the complete system, for example, it is sufficient to replace the reservoir 2 with a reservoir of ink cleaning product and to recirculate the cleaning solution through the entire device. This makes it possible to avoid having to disassemble the different parts of the device 1 during a long shutdown of the device 1 or a possible change of ink.

[0197] Another advantage of the device 1 according to the invention is that the support of the printing station 25 can be arranged in any orientation as long as the ink pressure differential between the inlet and the outlet of the print head 5 is respected. The fine control of the volume of ink in recirculation, by means of at least one parameter of the inlet 3 and outlet 6 pumps, at each pulse makes it possible to avoid the flow of ink out of the nozzles 9.

[0198] An advantage of the device 1 is that the ink station 24 can also be placed either at a long distance from the printing station 25 or directly in the printing station 25.

[0199] The control and / or regulation and / or modulation of at least one parameter of the pumps 3, 6 coupled with the high frequency (pulse greater than 30 Hz, 40 Hz, or even 50 Hz) of oscillation of the membrane 15 makes it possible to perfectly control the volume of ink supplied to the print head 5.

[0200] As a result, the device 1 allows optimal stability of the volume of each drop individually ejected by the nozzles 9 of the print head 5, regardless of the overall ink volumes ejected at any time by the nozzles 9 of the print head 5.

[0201] Furthermore, the placement of the drops on the printing medium will always be the same, that is to say that the ejected drops will always have the same speed, the same volume and the same drop conformation, without the presence of satellite droplets during ejection, this for the same acoustic waveform of the actuators of each nozzle 9. The inventors have observed that this stability is also maintained during transient printing phases, for example between a printed solid color and the unprinted areas around the solid color. Furthermore, the additional stability of the ejected ink volume thanks to the flow rate and pressure regulation device in the nozzle actuator 9, whether during stationary phases (continuous printing of a solid color) or during transient phases (printing of a pattern), allows the mixing of colors, for example CMYK (Cyan Magenta Yellow Black), to have a constant colorimetry and color intensity between different prints.

[0202] Of course, the invention is not limited to the examples which have just been described and numerous adjustments can be made to these examples without departing from the scope of the invention.

[0203] Thus, in variants of the embodiments described above that can be combined with each other: the device 1 comprises at least one filter 26, 27, and / or

[0204] - the device 1 comprises a filter 26 arranged downstream of the reservoir 2, preferably directly at the outlet of the reservoir 2, and upstream of the inlet pump 3, preferably directly at the inlet of the inlet pump 3, and a filter 27 arranged upstream of the print head 5, preferably directly at the inlet of the print head 5, and / or the device 1 comprises a heating means 28, preferably controlled by the control unit 14, arranged to heat the ink, preferably the ink contained or circulating in the first 4 or the second circuit 7, so as to modulate the viscosity of the ink, preferably the viscosity of the ink entering the print head 5, and / or

[0205] - the device 1 comprises an additional pump mounted in parallel with the inlet pump 3, and / or the device 1 comprises an additional pump mounted in parallel with the outlet pump 6, and / or

[0206] - advantageously, the additional pump mounted in parallel with the inlet pump 3 is in phase opposition with respect to the phase of the inlet pump 3, and / or the additional pump mounted in parallel with the outlet pump 6 is in phase opposition with respect to the phase of the outlet pump 6, and / or

[0207] - the additional pump(s) have the effect of further reducing the residual amplitude of the pulsation and thus adapting to the largest range of inkjet heads, and / or the control and / or modulation of the oscillation amplitude of the membrane 15 can allow or correspond to or be associated with or be assimilated, in particular indirectly, to the control and / or modulation of the opening time and a closing time of the inlet valve 17 and the discharge valve 18, and / or

[0208] - the device 1 can be described as comprising an ink station 24 and a printing station 25, and / or

[0209] - the ink station 24 may comprise the reservoir 2 and, preferably, the inlet 3 and outlet 6 pumps and / or a part of the first and second circuits 4, 7 and / or the pulsation dampers 11, 12 and / or a filter 26 and / or a filter 27 and / or the control unit 14 and / or a flow sensor 21 and / or the heating means 28, and / or

[0210] - the printing station 25 may comprise the printing head 5 and, preferably, a part of the first and second circuits 4, 7 and / or the control unit 14 and / or the pressure sensor(s) 22, 23, and / or a filter 27 and / or a flow sensor 21 and / or the heating means 28, and / or

[0211] - the printing station 25 may comprise the ink station 24, and / or

[0212] - the device 1 makes it possible to reduce the oscillations of flow and / or flow rate and / or ink pressure in the first 4 and second circuits 7 and in the print head 5 to values ​​lower than ± 0.1 kPa, and / or

[0213] - the flow sensor 21 is arranged to detect the presence of air bubbles, and / or

[0214] - the ink circuit in the device 1, or the ink circuit of the device 1, comprises the first circuit 4, the second circuit 7 and the circulation channel 8 or a fluidic channel 8 of the print head 5, and / or

[0215] - the control unit 14 is arranged to detect leaks and / or a failure of sensors 21, 22, 23 by detecting a variation in the amplitude of oscillation, even tiny, of the membrane 15 of one of the pumps 3, 6, and / or a reduction in the flow rate measured by the flow sensor 21, and / or

[0216] - the control unit 14 is arranged to allow the pumps 3, 6 to be stopped following the detection of a leak so as to prevent an ink leak, and / or

[0217] - an inkjet printing process by ink recirculation is proposed comprising:

[0218] • a circulation of ink, by means of the inlet pump 3, in the first circuit 4, from the reservoir 2 to the print head 5, • a circulation of ink, by means of the outlet pump 6, in the second circuit 7, from the print head 5 to the reservoir 2,

[0219] • a circulation of ink, in the print head 5 from the first 4 to the second circuit 7, “a flow of a part of the ink, circulating in the print head 5, out of the print head 5 through at least one ejection nozzle 9 of the print head 5. In addition, the different characteristics, forms, variants and embodiments of the invention can be associated with each other in various combinations to the extent that they are not incompatible or exclusive of each other.

Claims

CLAIMS 1. Ink recirculation device for inkjet printing (1), said device (1); said device comprising: - a single reservoir (2); said single reservoir being at atmospheric pressure and being intended to receive printing ink, - a pump (3), called the inlet pump (3), arranged to circulate the ink, in a first ink circulation circuit (4), called the first circuit (4), from the single reservoir to an inkjet print head (5) of the device, - a pump (6), called the output pump (6), arranged to circulate the ink, in a second ink circulation circuit (7), called the second circuit (7), from the print head to the single reservoir, - said inkjet print head is connected to the first and second circuits and comprises at least one ink ejection nozzle (9), said print head being arranged to ensure: • ink circulation from the first to the second circuit, • a flow of a portion of the ink, circulating in said print head, out of the print head through the at least one ejection nozzle.

2. Device (1) according to the preceding claim, comprising a pulsation damper (12) arranged between the inlet pump (3) and the print head (5) and / or a pulsation damper (13) arranged between the print head and the outlet pump (6); the pulsation damper(s) are arranged to dampen ink flow oscillations downstream of the inlet pump and upstream of the outlet pump.

3. Device (1) according to claim 1 or 2, wherein a pulsation of the inlet (3) and outlet (4) pumps is greater than or equal to 30 Hz.

4. Device (1) according to any one of the preceding claims, comprising a control unit (14) arranged to control the inlet (3) and outlet (6) pumps.

5. Device (1) according to the preceding claim, wherein the control unit (14) is arranged to synchronize the inlet (3) and outlet (6) pumps.

6. Device (1) according to claim 4 or 5, comprising a flow sensor (21) arranged in one and / or the other of the first (4) and second circuits (7); the control unit (14) is arranged to regulate at least one operating parameter of the inlet pump (3) and / or outlet pump (6) based on data measured by the flow sensor(s).

7. Device (1) according to one of claims 4 to 6, comprising a pressure sensor arranged (22, 23) in one and / or the other of the first (4) and second circuits (7); the control unit (14) is arranged to regulate at least one operating parameter of the inlet (3) and / or outlet (6) pump as a function of data measured by the pressure sensor(s).

8. Device (1) according to any one of the preceding claims, wherein the inlet pump (3) and / or the outlet pump (6) is a membrane pump.

9. Device (1) according to claim 8 taken in combination with any one of claims 4 to 7, wherein the control unit (14) is arranged to temporally coordinate the oscillations of the membrane (15) of the inlet pump (3) with the oscillations of the membrane (15) of the outlet pump (6).

10. Device (1) according to claim 9, or according to claim 8 taken in combination with any one of claims 4 to 7, wherein the control unit (14) is arranged to modulate an oscillation amplitude of the membrane (15) of the inlet pump (3) and / or an oscillation amplitude of the membrane (15) of the outlet pump (6).

11. Device (1) according to claim 9 or 10, or according to claim 8 taken in combination with any one of claims 4 to 7, in which the control unit (14) is arranged to modulate an opening time and / or a closing time of an inlet valve (17) and / or a discharge valve (18) of the inlet pump (3) and / or the outlet pump (6).

12. Inkjet printing method using ink recirculation, said method, said method comprising: - a circulation of ink, by means of a pump (3), called the inlet pump (3), in a first ink circulation circuit (4), called the first circuit (4), from a single reservoir (2) to an inkjet print head (5); said single reservoir being at atmospheric pressure and being intended to receive ink, - an ink circulation, by means of a pump (6), called the output pump (6), in a second ink circulation circuit (7), called the second circuit (7), from the print head to the single reservoir, - a circulation of ink, in said print head connected to the first and second circuits, from the first to the second circuit, - a flow of a portion of the ink, circulating in said print head, out of the print head through at least one ejection nozzle (9) of said print head.

13. Method according to claim 12, comprising a step of damping ink flow oscillations downstream of the inlet (3) and / or outlet (6) pumps, respectively by means of a pulsation damper (12) arranged between the inlet pump and the print head (5) and / or a pulsation damper (13) arranged between the print head and the outlet pump.

14. The method of claim 12 or 13, further comprising: - a step of controlling the inlet (3) and outlet (6) pumps, by means of a control unit (14), consisting of synchronizing the inlet and outlet pumps, and / or - a step of controlling the inlet and outlet pumps, by means of a control unit, consisting of regulating at least one operating parameter of the inlet and / or outlet pump as a function of data measured by one or more flow sensors (21); the flow sensor(s) being arranged in one and / or the other of the first (4) and second circuits (7), and / or - a step of controlling the inlet and outlet pumps, by means of a control unit, consisting of regulating at least one operating parameter of the inlet and / or outlet pump as a function of data measured by one or more pressure sensors (22, 23); the pressure sensor(s) being arranged in one and / or the other of the first and second circuits.

15. The method of claim 12 or 13, further comprising: - a step of controlling the inlet (3) and outlet (6) pumps, by means of a control unit (14), consisting of temporally coordinating the oscillations of a membrane (15) of the inlet membrane pump (3) with the oscillations of a membrane (15) of the outlet membrane pump (6), and / or - a step of controlling the inlet and outlet pumps, by means of a control unit, consisting of modulating an oscillation amplitude of the membrane of the inlet membrane pump and an oscillation amplitude of the membrane of the outlet membrane pump, and / or - modulate an opening time and a closing time of an inlet valve (17) and a discharge valve (18) of the inlet membrane pump and / or the outlet membrane pump.

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