Ink recirculation device for inkjet printing and associated process

Abstract

"Ink recirculation device for inkjet printing and associated method" Ink recirculation device for inkjet printing (1), referred to as device (1); said device comprising a single reservoir (2), at atmospheric pressure, for receiving printing ink, a pump (3), referred to as inlet pump (3), arranged to circulate the ink in a first ink circulation circuit (4), referred to as first circuit (4), from the single reservoir to an inkjet printhead (5) of the device, a pump (6), referred to as outlet pump (6), arranged to circulate the ink in a second ink circulation circuit (7), referred to as 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 print head is arranged to ensure ink circulation from the first to the second circuit and the flow of some of the ink circulating in said print head out of the print head through at least one ejection nozzle. Figure for the abbreviation: Figure 1.

Description

Title of the invention: Ink recirculation device for inkjet printing and associated method. Technical field

[0001] The present invention relates to the field of processes and systems for material deposition by material recirculation in the print head.

[0002] The present invention relates, in particular, to digital printing systems and methods, additive manufacturing on flat or complex 3D substrates.

[0003] By way of example, the invention relates to the fields of industrial printing, graphic printing, printing of transactional and marketing documents, packaging printing or even the printing of functional materials.

[0004] A preferred field of application according to the invention is that of inkjet printing devices and methods. Prior art

[0005] The technique of printing devices by ink recirculation in the print head by means of one or two intermediate gas reservoirs under controlled gas pressure is known in the state.

[0006] 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 flows from an ink storage reservoir through the pressurized intermediate gas reservoirs to the print head.

[0007] In practice, the ink is pumped from the ink storage tank to a first intermediate gas tank. The pressurized gas in the first intermediate gas tank expels the ink towards the printhead inlet. The pressurized gas in the second intermediate gas tank draws the ink from the printhead outlet. The ink level in the second intermediate gas tank is controlled by an ink pump, which returns the ink to the ink storage tank or to the first intermediate gas tank, depending on the implementation.

[0008] Thus, in state-of-the-art printing devices, the gas pressure in each intermediate reservoir must be modulated and controlled to regulate the flow rate and pressure of the ink injected into the print head. It is the air pressure in each intermediate pressurized gas reservoir that enables, in particular, the control of the printing process.

[0009] State-of-the-art printing devices have several drawbacks.

[0010] One drawback of state-of-the-art printing devices is that the pressurized air used to force the ink into circulation causes the gas to dissolve in the ink. This dissolved gas alters the characteristics of the ink.

[0011] The ink thus modified induces a degradation of the result of the printing, that is to say of the quality of the ink printed on the substrate.

[0012] Furthermore, modifying the ink characteristics affects the ink flow in the printhead nozzle actuators because the deposition conditions are closely linked to the characteristics of the ink being printed. In other words, modifying the ink characteristics degrades the quality of the printing step itself.

[0013] 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 to the pneumatic system for pressurizing the gas in the intermediate tank.

[0014] This risk of overflow therefore requires the integration of sensors, a control system, and a safety system for the printing device. This adds complexity and increases the manufacturing and maintenance costs of the printing device.

[0015] Such an arrangement also entails a risk of ink leakage at the various joints and interfaces in the intermediate reservoirs.

[0016] 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 pressurizing the gas in the intermediate tanks.

[0017] In addition, for the reasons detailed above, the intermediate reservoirs 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.

[0018] Another drawback of state-of-the-art printing devices is that pigmented inks tend to settle in the intermediate reservoirs. This significantly increases the frequency of maintenance operations required for these devices.

[0019] Finally, a significant drawback of state-of-the-art devices lies in the presence of a considerable stabilization time when the ink recirculation is stopped or restarted, or when the recirculation conditions change. Indeed, the use of pressurized gas to compress and cause the flow of The ink in the printing device and then out of the print head causes an imbalance in the flow and flow rate of ink during changes in operating conditions.

[0020] Also, drips or irregularities may be observed when stopping or restarting printing or when changing the deposition conditions during printing.

[0021] Also, according to the invention, an inkjet printing device by ink recirculation and an inkjet printing process is proposed which makes it possible to overcome at least some of the disadvantages, preferably making it possible to overcome all or part of the disadvantages, of state-of-the-art devices.

[0022] In particular, one object of the invention is: - to improve print quality, or to obtain high-quality printed substrates, and / or - to avoid, at least partially or even totally, the contamination of the ink by the dissolution of a gas in the ink, and / or - to propose a printing device with a low cost, or at least a cost lower than state-of-the-art printing devices, and / or - to propose a printing device whose design and / or assembly and / or operation is simplified, and / or - to propose a printing device whose maintenance is easier and / or reduced, or at a minimum whose maintenance is easier and / or reduced compared to state-of-the-art devices, and / or - to propose a printing device with a reduced risk of ink leakage into the printing device, and / or - to propose a printing device with a reduced footprint, or at least a footprint smaller than that of state-of-the-art devices. Presentation of the invention

[0023] To this end, an ink recirculation device for inkjet printing, referred to as the device, is proposed. The device comprises: - a reservoir, preferably a single reservoir, at atmospheric or ambient pressure, intended to receive printing ink, - a pump, called the 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, - 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.

[0024] Preferably, the inkjet printhead is connected to the first and second circuits. Preferably, the printhead includes at least one ink ejection nozzle. Preferably, the printhead is arranged to ensure: - ink circulation from the first to the second circuit, - a leakage of some of the ink, preferably only a part of the ink, circulating in said print head, out of the print head through at least one ejection nozzle.

[0025] Ink recirculation can be understood as: a recirculation of ink in the printing device, preferably a recirculation, in addition, in the print head of the printing device.

[0026] Preferably, the printing device does not include any tank, or intermediate or additional tank, containing pressurized gas.

[0027] Preferably, the printing device does not include any reservoir, or intermediate or additional reservoir, containing pressurized gas to ensure or permit or cause the circulation and / or recirculation of ink in the printing device and, in particular, the circulation and / or recirculation of ink in the print head.

[0028] Inkjet printing can be understood to mean: printing by material jet, fluid jet, graphic or functional inkjet.

[0029] 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, a pressure between 100 and 5 x 10⁵ Pascals.

[0030] Preferably, the single tank includes means for gas communication between the exterior of the single tank, preferably between the atmosphere surrounding the device, and the interior of the single tank. Preferably, the gas communication means between the exterior and interior of the single tank allow the single tank, or the interior of the single tank, to be maintained at atmospheric pressure.

[0031] Preferably, the device includes an ink circulation loop.

[0032] Preferably, the recirculation loop comprises the first and second circuits. Preferably, the recirculation loop includes the print head. Preferably, the recirculation loop includes the single reservoir.

[0033] Preferably, the recirculation loop consists or is made up of the first and second circuits, the single reservoir and / or the print head.

[0034] 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 at least one ejection nozzle. Preferably, the device is arranged so that only a part of the ink circulating in said print head flows out of the print head through at least one ejection nozzle so that at least a part of the ink circulating in the first circuit flows into or through the print head towards the second circuit.

[0035] The device may include several print heads. Preferably, the device is arranged to ensure parallel ink flow in the print heads.

[0036] Preferably, the device comprises one or more pulsation dampeners disposed between the inlet pump and the printhead and / or one or more pulsation dampeners disposed between the printhead and the outlet pump. Preferably, the pulsation dampener(s) 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 printhead.

[0037] Preferably, a pulsation of the inlet and outlet pumps is greater than or equal to 30 Hz.

[0038] Preferably, an inlet pump pulse and / or an outlet pump pulse is greater than or equal to 30 Hz, preferably 32 Hz, preferably even more 34 Hz, particularly preferably 35 Hz, even more preferably 36 Hz, advantageously 37 Hz, particularly advantageously 38 Hz, even more particularly advantageously 39 Hz and most preferably of all 40 Hz.

[0039] Particularly advantageously, an inlet pump pulse and / or an outlet pump pulse is greater than or equal to 40 Hz, preferably 42 Hz, preferably even more 44 Hz, particularly preferably 45 Hz, even more preferably 46 Hz, advantageously 47 Hz, particularly advantageously 48 Hz, even more particularly advantageously 49 Hz and most preferably of all 50 Hz.

[0040] Preferably, the device includes a control unit.

[0041] Preferably, the control unit is arranged and / or configured and / or programmed to command and / or regulate and / or operate and / or control, among other things, the inlet and outlet pumps.

[0042] Preferably, the control unit is arranged and / or configured and / or programmed to synchronize the inlet and outlet pumps.

[0043] In the present application, "synchronize" may be understood as: coordinating in time one, several or each of the operating parameters of the inlet and outlet pumps.

[0044] Preferably, the device includes a flow sensor disposed in one and / or the other of the first and second circuits.

[0045] Preferably, the control unit is arranged and / or configured and / or programmed to regulate and / or command and / or operate and / or control at least one operating parameter of the inlet and / or outlet pump based on data measured by the flow sensor(s).

[0046] Preferably, the control unit is arranged and / or configured and / or programmed to regulate and / or to command and / or operate and / or control at least one operating parameter of the inlet and / or outlet pump, based on data measured by the flow sensor(s), so as to maintain and / or modulate and / or modify a flow of ink circulating in the print head.

[0047] Preferably, the control unit is arranged to regulate at least one operating parameter of the inlet and / or outlet pump so that an ink flow in the first circuit is equal to or differs from an ink flow in the second circuit.

[0048] Preferably, the device includes a pressure sensor disposed in one and / or the other of the first and second circuits.

[0049] 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 inlet and / or outlet pump based on data measured by the pressure sensor(s).

[0050] Preferably, the device includes a pressure sensor, preferably located 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.

[0051] Preferably, the device includes a pressure sensor, preferably located 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.

[0052] Preferably, in the present description, the terms "upstream" and "downstream" are expressed with respect to a direction of ink flow from the single reservoir to the print head and then from the print head back to the single reservoir.

[0053] 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 inlet and / or outlet pump, based on data measured by the pressure sensor(s), so as to maintain and / or modulate and / or to modify the ink pressure at the print head inlet and the pressure at the print head outlet.

[0054] The pressure at the output of the print head can be defined as an ink extraction pressure from the print head.

[0055] Preferably, the control unit is arranged to regulate at least one operating parameter of the inlet and / or outlet pump so that an ink pressure in the first circuit is equal to or differs from an ink pressure in the second circuit.

[0056] Preferably, the inlet pump and / or outlet pump is a diaphragm pump.

[0057] Preferably, the control unit is arranged and / or configured and / or programmed to time-coordinate the oscillations of the inlet pump diaphragm with the oscillations of the outlet pump diaphragm.

[0058] It can be understood by temporally coordinating the oscillations of the inlet pump diaphragm with the oscillations of the outlet pump diaphragm: commanding and / or modulating and / or controlling a phase shift between the oscillations of the inlet pump diaphragm and the oscillations of the outlet pump.

[0059] The phase shift between the oscillations of the inlet pump diaphragm and the oscillations of the outlet pump may be zero or may be non-zero.

[0060] 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 inlet pump diaphragm and / or an oscillation amplitude of the outlet pump diaphragm.

[0061] Preferably, the control unit is arranged so that an oscillation amplitude of the inlet pump diaphragm is equal to or differs from an oscillation amplitude of the outlet pump diaphragm.

[0062] Preferably, the control unit is arranged and / or configured and / or programmed to modulate and / or control and / or regulate and / or control an opening time and a closing time of an inlet valve and a discharge valve of the inlet pump and / or outlet pump.

[0063] Preferably, the control unit is arranged so that: - 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 - 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.

[0064] The minimum operating parameter of the inlet and / or outlet pump may be: - the pulsation of the inlet pump and / or the pulsation of the outlet pump, and / or - the pulsation of the inlet pump diaphragm and / or the pulsation of the outlet pump, and / or - the phase shift between the oscillations of the inlet pump diaphragm and the oscillations of the outlet pump diaphragm, and / or - the oscillation amplitude of the inlet pump diaphragm and / or the oscillation amplitude of the outlet pump diaphragm, and / or - 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 - the opening time of the inlet pump discharge valve and / or the opening time of the outlet pump discharge valve, 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 - the closing time of the discharge valve of the inlet pump and / or the closing time of the discharge valve of the outlet pump.

[0065] According to the invention, a method for inkjet printing by ink recirculation, referred to as the method, is also proposed. The method comprises: - ink circulation, by means of the inlet pump, in the first ink circulation circuit, from the single reservoir to the inkjet print head, - an ink circulation, by means of the outlet pump, in the second ink circulation circuit from the print head to the single reservoir.

[0066] Preferably, the method further comprises an ink circulation, in or through the print head from the first to the second circuit.

[0067] Preferably, the method further comprises a flow of a portion of the ink, which is circulating in the print head, out of the print head through at least one ejection nozzle of the print head.

[0068] 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.

[0069] 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.

[0070] Preferably, a continuous flow of ink through 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 flows, preferably continuously, through the print head to the second circuit during printing.

[0071] Preferably, in the present application, printing or printing step means the flow of ink, or part of the ink, circulating in the print head, out of the print head through at least one ejection nozzle.

[0072] Preferably, during printing, a portion of the ink circulating in the print head is evacuated or picked up or flows through at least one ejection nozzle.

[0073] Preferably, the method includes a step of damping oscillations of flow and / or flow rate and / or ink pressure downstream of the inlet and / or outlet pumps, and therefore, preferably, in the print head, respectively by means of a pulsation damper disposed between the inlet pump and the print head and / or a pulsation damper disposed between the print head and the outlet pump.

[0074] 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.

[0075] 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 to control and / or operate and / or control at least one operating parameter of the inlet and / or outlet pump as a function of data measured by the flow sensor(s).

[0076] 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 to control and / or operate and / or control at least one operating parameter of the inlet and / or outlet pump as a function of data measured by the pressure sensor(s).

[0077] 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 diaphragm of the inlet diaphragm pump with the oscillations of the diaphragm of the outlet diaphragm pump.

[0078] 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 regulate an oscillation amplitude of the inlet diaphragm pump membrane and an oscillation amplitude of the outlet diaphragm pump membrane.

[0079] 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 diaphragm pump and / or the outlet diaphragm pump.

[0080] Preferably, the method includes control and / or regulation and / or modulation, by the control unit, of at least one operating parameter of the inlet and outlet pumps so as to: - to synchronize, that is, to activate or control at the same instant, one, several, or each operating parameter of the inlet and outlet pumps, including, for example, the pump pulsation or the pump diaphragm pulsation, the phase shift between the oscillations of the pump diaphragm, or the opening and / or closing time of the inlet and / or outlet valve of the pumps, or - introduce a time lag or phase shift between one, several, or each operating parameter of the inlet and outlet pumps, including, for example, pump pulsation or pump diaphragm pulsation, the phase shift between pump diaphragm oscillations, or the opening and / or closing time of the pump inlet and / or outlet valve, and / or - introduce a difference in oscillation amplitude or apply the same oscillation amplitude between the pump diaphragms.

[0081] Preferably, the recirculating inkjet printing process according to the invention is suitable, more preferably is particularly suitable, even more preferably is designed, and most advantageously is specially designed, for implementation by the recirculating inkjet printing device according to the invention. Furthermore, any feature of the printing device according to the invention is directly transferable to the printing process according to the invention and vice versa. Description of the figures

[0082] Other advantages and features of the invention will become apparent from the detailed description of implementations and embodiments, which are by no means limiting, and from the following accompanying drawings:

[0083] [Fig-1] [Fig.1] is a schematic representation of one embodiment of the printing device according to the invention,

[0084] [Fig.2] [Fig.2] is a schematic representation of a set of heads printing according to the invention,

[0085] [Fig.3] [Fig.3] is a schematic side view representation of a mode of fabrication of a diaphragm pump according to the invention. Description of the implementation methods

[0086] The embodiments described below are in no way limiting; variants of the invention may include, in particular, a selection of the described features, isolated from the other described features (even if this selection is isolated within a sentence containing these other features), if this selection of features is sufficient to confer a technical advantage or to differentiate the invention from the prior art. This selection includes at least one feature, preferably a functional one without structural details, or with only a portion of the structural details if this portion alone is sufficient to confer a technical advantage or to differentiate the invention from the prior art.

[0087] With reference to [Fig. 1], an embodiment of the recirculating inkjet printing device 1, referred to as device 1, according to the invention, is shown. Device 1 comprises a reservoir 2 for receiving the printing ink. Reservoir 2 is an ink reservoir or a reservoir for storing the printing ink.

[0088] The device 1 includes a pump 3, called the inlet pump 3. The inlet pump is arranged to circulate ink in a first ink circulation circuit 4, called the first circuit 4, from the single reservoir 2 to an inkjet printhead 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 printhead.

[0089] The device includes a pump 6, referred to as the output pump 6. The output pump 6 is arranged to circulate the ink in a second ink circulation circuit 7, referred to as the second circuit 7, from the print head 5 to the single reservoir 2. The output pump 6 draws the ink from the print head 5 and then forces the ink through the second circuit 7 to the ink reservoir 2.

[0090] By way of non-limiting examples, the inlet pump 3 and / or the outlet pump 6 may be a peristaltic pump, a gear pump or a diaphragm pump.

[0091] It is also envisaged that the device 1 may include 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.

[0092] Such a configuration is usable when high ink circulation / recirculation rates are required.

[0093] The print head 5 is advantageously an inkjet print head 5.

[0094] The print head 5 is connected to the first circuit 4 and the second circuit 7.

[0095] The print head 5 is arranged to ensure ink circulation from the first circuit 4 to second circuit 7.

[0096] In practice, with reference to [Fig.2], and by way of non-limiting example, the print head 5 includes a circulation channel 8 or a fluidic channel 8 ensuring the circulation of ink through the print head 5.

[0097] The print head 5 includes at least one ink ejection nozzle 9. Preferably, the print head 5 includes several ink ejection nozzles 9.

[0098] The print head 5 is arranged to ensure that some of the ink flowing in the print head 5 flows out of the print head 5 through at least one ejection nozzle 9.

[0099] According to the invention, the device 1 advantageously comprises a single reservoir 2. The invention allows the use of 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.

[0100] The possibility of using a single reservoir 2 allows the printing device 1 to have a simplified design, assembly and operation.

[0101] Maintenance of the printing device 1 according to the invention is also facilitated and its cost reduced.

[0102] In addition, the size of the printing device 1 according to the invention is reduced compared to state-of-the-art devices.

[0103] According to the invention, the reservoir 2 is advantageously at atmospheric pressure. The invention allows the use of 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.

[0104] The printing device 1 according to the invention thus makes it possible to avoid, at least partially or even completely, ink contamination by the dissolution of a gas in the ink. Indeed, in prior art printing devices, dissolution of the gas used to compress and circulate the ink within the printing device and to allow the gas to flow out of the device via the print head is unavoidable.

[0105] 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 pressurized tanks, the absence of gas circuits and pneumatic circuits to compress the ink as well as the absence of series gas circulation circuits upstream of the print head.

[0106] With reference to [Fig. 2], according to an advantageous but not limiting embodiment, the device 1 comprises a print head assembly 5 mounted in parallel. The ink is pumped by the inlet pump 3 into the first circuit 4. The ink from the first circuit 4 flows in parallel, through a circulation channel 8 or a fluidic channel 8, into each print head 5 (the circulation channel 8 of only one of the print heads 5 is shown in [Fig.2]).

[0107] The injection nozzles 9 are connected to the circulation channel 8. Part of the ink circulating in the circulation channel 8 flows out or is ejected out of the print head 5 via the injection nozzles 9.

[0108] After circulating through the print head 5, the ink is drawn by the output pump 6 into the second circuit 7.

[0109] Preferably, when the device 1 includes several printheads 5, the device 1 includes two collectors / distributors 10, 11 (also called "manifolds"), or one collector 10 and one distributor 11. The distributor 10 allows the simultaneous supply of ink to all the printheads 5 by distributing ink with negligible pressure losses. The distributor 10 is mounted on the first circuit 4 upstream of the printheads 5. It ensures ink distribution among all the printheads 5.

[0110] The same description given above for the distributor 10 applies to the collector 11. In practice, it is the same element performing the reverse function. The collector 11 is mounted on the second circuit 7 downstream of the print heads 5.

[0111] Advantageously, as illustrated in [Fig. 1], the device 1 comprises a pulsation damper 12 disposed between the inlet pump 3 and the print head 5 and / or a pulsation damper 13 disposed between the print head 5 and the outlet pump 6. According to the non-limiting embodiment, the device 1 comprises a pulsation damper 12 disposed between the inlet pump 3 and the print head 5 and a pulsation damper 13 disposed between the print head 5 and the outlet pump 6.

[0112] The pulse dampers 13, 12 have the function of limiting the oscillations of ink flow downstream of the inlet pumps 3 and / or outlet pumps 6.

[0113] According to an advantageous embodiment, the 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 to 50 Hz.

[0114] In practice, it has been observed that a pulse of the inlet pump 3 and the outlet pump 6 greater than or equal to 30 Hz, particularly a pulse greater than or equal to 40 Hz and even more markedly a pulse greater than or equal to 50 Hz, makes it easier and improves the damping of flux oscillations and / or makes the control faster of device 1 to compensate, in particular, for the sudden change in volume in the ink circuit due to the volume of the ink droplets ejected by the print head 5.

[0115] According to this embodiment, the inlet pump 3 and the outlet pump 6 are gear pumps or diaphragm pumps.

[0116] The use of high-frequency inlet 3 and outlet 6 pumps in a synchronous manner 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 deposition by limiting defects and / or inaccuracies in 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.

[0117] Device 1 includes a control unit 14.

[0118] The control unit 14 is arranged to control the inlet pump 3 and the outlet pump 6.

[0119] Preferably, the control unit 14 is arranged to synchronize the operation of the inlet pump 3 and outlet pump 6. In particular, the control unit 14 is arranged to coordinate the pulsations of the inlet pump 3 and outlet pump 6.

[0120] The device 1 includes a flow sensor 21 disposed in one and / or the other of the first 4 and second circuits 7. According to the non-limiting embodiment, the device 1 includes a flow sensor 21 disposed in the second circuit 7 downstream of the print head 5 and upstream of the output pump 6.

[0121] The control unit 14 can be arranged to command and / or modulate and / or control the inlet pump 3 and / or the outlet pump 6 according to the data measured by the flow sensor(s) 21.

[0122] The device 1 includes a pressure sensor 22, 23 disposed in one and / or the other of the first 4 and second circuits 7. According to the non-limiting embodiment, the device 1 includes a pressure sensor 22 disposed downstream of the inlet pump 3 and upstream of the print head 5 and a pressure sensor 23 disposed in the second circuit 7 downstream of the print head 5 and upstream of the outlet pump 6.

[0123] The control unit 14 can be arranged to command and / or modulate and / or control the inlet pump 3 and / or the outlet pump 6 according to the data measured by the pressure sensor(s) 22, 23.

[0124] 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 a pressure differential ink 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 outlet of the print head 5.

[0125] According to an advantageous, but not limiting, embodiment of the invention, the inlet pumps 3 and outlet pumps 6 are diaphragm pumps.

[0126] According to a particularly advantageous but non-limiting aspect of the embodiment, the inlet pump 3 and outlet pump 6 are solenoid diaphragm pumps or a piezoelectric pump. In other words, the inlet pump 3 and outlet pump 6 can be pumps whose diaphragm oscillations 15 are controlled or actuated by a solenoid or a piezoelectric actuator.

[0127] The remainder of the description of the embodiment will relate to a device 1 comprising solenoid or piezoelectric diaphragm inlet 3 and outlet 6 pumps.

[0128] However, this advantageous embodiment does not limit the invention, in particular the aspects of the invention described above, to the use of solenoid or piezoelectric diaphragm pumps.

[0129] With reference to [Fig.3], a schematic representation of a 3,6 solenoid diaphragm pump is shown.

[0130] All diaphragm pumps include a diaphragm 15 set in oscillation by an actuator. The oscillations of the diaphragm 15 change the volume of a chamber 16, one wall of which is formed by the diaphragm 15. An inlet valve 17 and a discharge (or check) valve 18 allow the admission and discharge of a fluid into the chamber, respectively. In operation, diaphragm pumps comprise a discharge cycle and an admission cycle. During the discharge cycle, the movement of the diaphragm 15 reduces the volume of the chamber 16, which results in overpressure in the chamber 15 and forces the fluid contained in the chamber 15 out by pushing the discharge valve 18 and closing the inlet valve 17.The admission cycle includes 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 vacuum in the chamber 15 and closing the discharge valve 18 and opening the inlet valve 17 by suction and thus admitting the fluid into the chamber.

[0131] The operation described above is identical to that of 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 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). Therefore, fine regulation and / or modulation of the ink pressure in the first 4 and second circuits 7, and thus 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.

[0132] Also, according to the advantageous embodiment of the invention, the use of solenoid or piezoelectric diaphragm inlet pumps 3 and outlet pumps 6 allows the amplitude of the oscillations, the pulsation of the diaphragm 15, and the phase shift between the oscillations / pulsation of the diaphragm 15 of the inlet pump 3 and the outlet pump 6 to be controlled. The control unit 14 controls and / or modulates the activation voltage and the duration of the activation voltage applied to 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 diaphragm 15. The oscillation amplitude of the diaphragm 15 is thus modulated.

[0133] 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.

[0134] 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.

[0135] Among the operating parameters of the inlet pump 3 and outlet pump 6, the following may be listed by way of non-limiting examples: - the pulsation of the inlet pump 3 and / or the pulsation of the outlet pump 6, and / or - the pulsation of the inlet pump diaphragm and / or the pulsation of the outlet pump, and / or - the phase shift between the oscillations of the inlet pump diaphragm and the oscillations of the outlet pump diaphragm, and / or - the oscillation amplitude of the inlet pump diaphragm and / or the oscillation amplitude of the outlet pump diaphragm, and / or - 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 - the opening time of the inlet pump discharge valve and / or the opening time of the outlet pump discharge valve, 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 - the closing time of the discharge valve of the inlet pump and / or the closing time of the discharge valve of the outlet pump.

[0136] Advantageously, the control unit 14 is arranged to command and / or modulate and / or control 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.

[0137] According to the embodiment, a person skilled in the art has general knowledge of control systems and / or control loops (or PID controller / controller (for "proportional, integral, derivative") enabling them 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 control at least operating parameters of the inlet pump 3 and / or the outlet pump 6" according to their needs and the specific case.

[0138] The control unit 14 is arranged to coordinate temporally the oscillations of the diaphragm 15 of the inlet pump 3 with the oscillations of the diaphragm 15 of the outlet pump 6.

[0139] The control unit 14 is arranged to ensure synchronous operation of the inlet pump 3 and outlet pump 6. In this case, the pulsations of the pumps 3, 6 will be synchronous.

[0140] The control unit 14 can also be arranged to ensure phase-shift operation of the pumps 3, 6. In this case, preferably, the pulsation of the inlet pump 3 can be in opposite phase with the pulsation of the outlet pump 6.

[0141] Thus, the synchronous starting and stopping of the inlet pump 3 and outlet pump 6, and / or the synchronous control of the inlet valve 17 and discharge valve 18, eliminates the overpressures and underpressures observed in prior art devices. This prevents the formation and uncontrolled flow of ink from the ejection nozzles 9, as well as the filling of the ejection nozzles 9 with air.

[0142] Furthermore, the regulation of the pulsation of pumps 3, 6 by the treatment unit 14 also contributes to the formation and ejection of droplets from the ejection nozzles 9 with improved quality and droplet size regularity. It also helps to prevent air from filling the ejection nozzles 9. In addition, the treatment unit 14 can be arranged so that, particularly during the start-up and shutdown of circulation / recirculation, the pulsation of the inlet pump 3 is different from the pulsation of the output pump 6. This also helps to avoid ink loss.

[0143] Although known to those skilled in the art, it should be noted that in an inkjet printing device, the ink is held in the ejection nozzles by the equilibrium between atmospheric pressure and the pressure applied by the fluid in each ejection nozzle. A meniscus of fluid (ink) is thus formed at the orifice of the ejection nozzle. One printing method consists of generating an acoustic wave in the ejection nozzles, or in certain ejection nozzles, for example, by means of a piezoelectric actuator. The acoustic wave generated in the ejection nozzles has the effect of breaking the meniscus and causing the fluid (ink) to be ejected in the form of a droplet. Typically, a droplet can have a volume ranging from 1 picoliter (pL) to 100 pL on average.

[0144] Also, in ink recirculation printing devices, dynamically adjust the ink pressure in the ejection nozzles to compensate for the volume of ink lost from the ejected drops and allow the ejection nozzles to be recharged.

[0145] Also, any parasitic or uncontrolled variation in ink pressure causes it to be ejected through the orifice of the ejection nozzle.

[0146] During the commissioning or start-up of printing in a recirculating ink printing device, there is a temporary state in which the ink changes from zero to its nominal speed. Similarly, when printing stops in a recirculating ink printing device, the recirculation speed must temporarily fluctuate from the nominal speed to zero. Therefore, to prevent any air from entering or ink from circulating in the printing device, prior art recirculating ink printing devices include valves or solenoid valves mounted on the various fluid circulation circuits. Actuating these solenoid valves causes a temporary pressure variation that destabilizes the menisci formed at the nozzle outlets and causes air to enter or ink to leak from the nozzles, which is subsequently detrimental to the proper functioning of the print head.

[0147] Compared to prior art printing devices with additional pressurized gas tanks, the printing device 1 according to the invention therefore offers significantly superior sealing and makes it possible to avoid these air intakes and / or ink leaks, particularly during the start-up or shutdown phases of printing, by, in particular: - the command and / or regulation and / or control, by the control unit 14, of the amplitude and / or phase shift of the displacement of the diaphragm 15 of the pumps 3, 6 simultaneously. The pressure regulation allows the closing of the The ink circuit operates smoothly, without any jerking or uncontrolled variations in ink pressure in the print head 5, and therefore without ink leakage or air intake. The device 1 according to the invention therefore does not include any valves or solenoid valves for this purpose. Indeed, it is the position of the diaphragm 15 of the pumps 3 and 6 that ensures the ink circuit is sealed. The same description applies to the activation of ink recirculation after a shutdown or power-down of the device 1; the absence of an ink reservoir, and / or an additional pressurized reservoir to ensure ink circulation, is also important. Ink recirculation in the printing device 1 is carried out by the inlet pump 3 and outlet pump 6, which are located directly on the ink circuit.Pumps 3 and 6 directly actuate, push, draw, and / or move the ink, which is an incompressible fluid within their operating range. This contrasts with the pumps in state-of-the-art devices, which actuate a gas to create a differential pressure between two additional reservoirs. Since air is compressible, when state-of-the-art devices are switched off, the air volume increases due to the mass of the fluid and gravity. This pressure drop releases onto the meniscus, causing it to tear and resulting in ink leaking from the printhead nozzles.

[0148] The control unit 14 is arranged to modulate an oscillation amplitude of the diaphragm 15 of the inlet pump 3 and / or an oscillation amplitude of the diaphragm 15 of the outlet pump 6.

[0149] Advantageously, the oscillation amplitude of the membrane 15 is achieved at a fixed pulsation of the membrane 15 of the inlet pumps 3 and outlet pumps 6. Preferably, only the duty cycle of the high state, i.e. the activation of the electromagnet 20, is modulated.

[0150] Preferably, the control unit is arranged so that the oscillation amplitude of the diaphragm 15 of the inlet pump 3 is equal to the oscillation amplitude of the diaphragm 15 of the outlet pump 6.

[0151] In addition, the use of solenoid or piezoelectric diaphragm inlet 3 and outlet 6 pumps also makes it possible to achieve high synchronous pulse values, typically above 50 Hz, which are not accessible with other pumps.

[0152] In addition, the use of solenoid or piezoelectric diaphragm inlet pumps 3 and outlet pumps 6 also makes it possible to ensure synchronization, with phase matching or phase shift, of the operating parameters of the pumps 3, 6, in addition with high responsiveness; which is not possible with other pumps.

[0153] Thus, the device 1 comprising inlet pumps 3 and outlet pumps 6 with solenoid or piezoelectric diaphragm 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 and / or pressure of ink in the print head 5.

[0154] Thus, advantageously, the device 1 according to the invention allows instantaneous switching from operation in recirculation mode of the device 1 to operation in gravity mode without disturbances or inconveniences such as the appearance of drops and / or leakage of ink outside the ejection nozzles 9 and without the injection of air (or the suction of air) into the ejection nozzles 9.

[0155] The recirculating mode of operation is the only operating mode of the device 1 that has been described so far. In the gravity-fed mode of operation (described in contrast to the recirculating 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.

[0156] Also, although recirculating printing remains particularly advantageous, another advantage of the invention is the ability to switch from recirculating to gravity-fed operation. In gravity-fed operation, 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 via the pressure sensors 22, 23, by precisely activating one of the pumps 3, 6, and by controlling at least one operating parameter of pump 3, 6. A precise volume of ink is supplied to ensure a constant meniscus pressure in the nozzles 9 of the print head 5.

[0157] By way of example, the diaphragm 15 of the inlet pump 3 is actuated cycle by cycle. Unlike the recirculation mode in which the pumps 3, 6 are actuated at a constant pulsation, the inlet pump 3 is therefore no longer actuated at a fixed pulsation frequency but according to two control laws nested in two control loops. The first law, which can be described as fine control, includes control and / or regulation of the duty cycle of the diaphragm 15's movement, 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 includes control and / or regulation of the pulse frequency of displacement of the membrane 15, by means of the solenoid 19 or the piezoelectric actuator, proportionally to the rate of pressure variation. measured at the inlet, at the level of the pressure sensor 22 of the print head 5. This results in a large control dynamic to finely regulate the meniscus at the end of the nozzles 19, but also to supply sufficient ink to the nozzles 19 according to the volumes of ink ejected by the nozzles 9.

[0158] Another advantage of the gravity-fed operating mode is that it is possible to place the device 1 in a rest or standby state between two printing operations. In this case, the pumps 3, 6 are held in the closed position, i.e., the diaphragm 15 of the pumps 3, 6 is held in the upper position (a position in which overpressure is created in chamber 16) or in the lower position (a position in which a vacuum is created in chamber 16). The pumps 3, 6 then act as a closed valve, preventing any circulation or movement of ink in the circuits 4, 7 and in the print head 5.

[0159] In this state, maintenance of device 1 is possible without having to purge all the ink from the device.

[0160] Finally, filling and / or emptying the ink from reservoir 2, as well as maintaining the device 1, is facilitated by the use of a single atmospheric pressure reservoir 2. For cleaning the entire system, for example, it is sufficient to replace reservoir 2 with an ink cleaning solution reservoir and recirculate the cleaning solution throughout the device. This eliminates the need to disassemble the various parts of the device 1 during a prolonged shutdown of the device 1 or a possible ink change.

[0161] Another advantage of the device 1 according to the invention is that the support for the printing station 25 can be arranged in any orientation as long as the ink pressure differential between the inlet and outlet of the print head 5 is maintained. Fine control of the recirculating ink volume, by means of at least one parameter of the inlet 3 and outlet 6 pumps, at each pulse, prevents ink from flowing out of the nozzles 9.

[0162] One advantage of device 1 is that the ink station 24 can be placed either at a long distance from the printing station 25 or directly in the printing station 25.

[0163] 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.

[0164] 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.

[0165] In addition, 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 the transient phases of printing, for example between a printed flat area and the areas without printing around the flat area.

[0166] In addition, the additional stability of the ejected ink volume thanks to the flow and pressure regulation device in the nozzle actuator 9, whether during stationary phases (continuous printing of a flat area) 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.

[0167] Of course, the invention is not limited to the examples just described and many modifications can be made to these examples without departing from the scope of the invention.

[0168] Thus, in combinable variants of the embodiments described above: - device 1 includes at least one filter 26, 27, and / or - Device 1 includes a filter 26 disposed downstream of reservoir 2, preferably directly at the outlet of reservoir 2, and upstream of the inlet pump 3, preferably directly at the inlet of the inlet pump 3, and a filter 27 disposed upstream of the print head 5, preferably directly at the inlet of the print head 5, and / or - the device 1 includes 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 - the control and / or modulation of the oscillation amplitude of the diaphragm 15 may 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 - Device 1 can be described as comprising an ink station 24 and a printing station 25, and / or - The ink station 24 may include the reservoir 2 and, preferably, the inlet pump 3 and outlet pump 6 and / or part of the first and second circuits 4, 7 and / or the pulsation dampeners 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 - the printing station 25 may include the print head 5 and, preferably, 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 - the printing station 25 may include the ink station 24, and / or - Device 1 reduces oscillations in ink flow and / or flow rate and / or pressure in the first 4 and second circuit 7 and in the print head 5 to values ​​below ± 0.1 kPa, and / or - the flow sensor 21 is arranged to detect the presence of air bubbles, and / or - the ink circuit in device 1, or the ink circuit of 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 - the control unit 14 is arranged to detect leaks and / or a failure of sensors 21, 22, 23 by detecting a variation in the oscillation amplitude, however small, of the diaphragm 15 of one of the pumps 3, 6, and / or a decrease in the flow measured by the flow sensor 21, and / or - the control unit 14 is arranged to allow pumps 3, 6 to be stopped following the detection of a leak in order to prevent an ink leak, and / or - A recirculating inkjet printing process is proposed, comprising: • 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, • an ink circulation, by means of the outlet pump 6, in the second circuit 7, from the print head 5 to the reservoir 2, • a circulation of ink, in the print head 5 from the first circuit 4 to the second circuit 7, • a flow of 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.

[0169] Furthermore, the different features, forms, variants and embodiments of the invention can be associated with each other in various combinations insofar as they are not incompatible or mutually exclusive.

Claims

Demands

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

2. Device (1) according to the preceding claim, comprising a pulsation damper (12) disposed between the inlet pump (3) and the print head (5) and / or a pulsation damper (13) disposed 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) disposed 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 flow sensor(s).

7. Device (1) according to any one of claims 4 to 6, comprising a pressure sensor disposed (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 diaphragm 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 time-coordinate the oscillations of the diaphragm (15) of the inlet pump (3) with the oscillations of the diaphragm (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 diaphragm (15) of the inlet pump (3) and / or an oscillation amplitude of the diaphragm (15) of the outlet pump (6).

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

12. Inkjet printing process by ink recirculation, said process, said process comprising: - a circulation of ink, by means of a pump (3), said inlet pump (3), in a first ink circulation circuit (4), said first circuit (4), from a single reservoir (2) to an inkjet print head (5);said single reservoir being at atmospheric pressure and intended to receive ink, - an ink circulation, by means of a pump (6), said outlet pump (6), in a second ink circulation circuit (7), said second circuit (7), from the print head to the single reservoir, - an ink circulation, in said print head connected to the first and second circuits, from the first to the second circuit, - a flow of a part 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. A method according to claim 12, comprising a step of damping ink flow oscillations downstream of the inlet pumps (3) and / or outlet pumps (6), respectively, by means of a pulsation damper (12) disposed between the inlet pump and the print head (5) and / or a pulsation damper (13) disposed between the print head and the outlet pump.

14. A method according to 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 according to measured data

15. by one or more flow sensors (21); the flow sensor(s) being disposed in one or both of the first (4) and second circuits (7), and / or - a control step of 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 according to data measured by one or more pressure sensors (22, 23); the pressure sensor(s) being disposed in one or both of the first and second circuits. A method according to claim 12 or 13, further comprising: - a control step for the inlet (3) and outlet (6) pumps, by means of a control unit (14), consisting of temporally coordinating the oscillations of a diaphragm (15) of the inlet diaphragm pump (3) with the oscillations of a diaphragm (15) of the outlet diaphragm 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 diaphragm of the inlet diaphragm pump and an oscillation amplitude of the diaphragm of the outlet diaphragm pump, and / or - modulate an opening time and a closing time of an inlet valve (17) and a discharge valve (18) of the inlet diaphragm pump and / or the outlet diaphragm pump.