Inkjet printhead for fluid

Abstract

To provide a printhead for dispensing a fluid.SOLUTION: A printhead (10) for dispensing a fluid comprises: at least one chamber; an array of piezoactuated flow channel dispensers enclosed in the at least one chamber, where each flow channel dispenser comprises a duty cycle configured to control a flow rate through the given piezoactuated flow channel dispenser; a multi-orifice dispensing plate (16); and an air dispensing element (18) comprising a source of compressed air (20) and an air flow controller (22) configured to direct a flow of air.SELECTED DRAWING: Figure 1C

Description

Technical Field

[0001] The present invention relates to a print head and system for dispensing fluids, particularly a print head in a fluid dispensing system. The print head is composed of an array of digitally controlled piezoelectrically actuated flow path distributors and air distribution elements, and the resulting system enables high-precision dispensing or administration of industrial fluids required for material penetration or coating. The materials to be coated include fibers, paper, fabrics, metal surfaces, and plastic surfaces.

Background Art

[0002] Precision coating is achieved by digital control of the dispenser orifices and can control the 2D and 3D distribution of industrial fluids within a few percent of the target value. This principle of precise application of fluids for coating or administration is common and applicable to many industrial applications. Further exemplary applications include fiber coating, application of pretreatment to cardboard for printing, manufacture of multilayer battery materials, manufacture of elements of display devices, and 3D printing molds for metal casting.

[0003] Currently, fiber coating is a process that has an adverse environmental impact mainly because a large amount of wastewater (usually several times the weight of the fibers) is generated. Conventional coating processes are dip coating, spraying, and padding with roller coating mechanisms. All of these methods generally overtake the fiber material and ensure that the coated substance remains in excess throughout the coating process, avoiding the formation of a concentration gradient that would cause the coated substance to slope and leave the fiber material.

[0004] Traditionally, bath immersion coating is performed to enable absorption of the coating material onto the fiber surface. The weight of water used in this process is often many times the weight of the fiber as it is necessary to wash away the excess. The coating can be substantially insoluble in water and takes time to adsorb onto the fiber surface and diffuse and be trapped within the fiber. Alternatively, the coating can be applied via a roller "padding" process.

[0005] In contrast to this background, a new industrial apparatus has arisen based on the present invention for accurately dispensing only the necessary coating onto a fiber substrate without the need to apply excess coating. The disclosed approach enables a step change in the industry's sustainability profile by eliminating or reducing the washing process while only dispensing the required amount of coating. Digital dispensing processes known in this field, namely digital inkjet printing, do not operate at industrial throughput and cannot dispense fluids at a high enough flow rate and high enough droplet velocity to supply the coating to the internal structure of a 3D substrate respectively.

[0006] The apparatus of the present invention is an industrial printing head suitable for applying fluids such as coatings to 2D or 3D substrates, such as fibers and fabrics, via a digitally controlled dosing system, with the advantage that the print head can deliver the coating in the area of the fiber substrate's capacity to absorb the coating. Thus, the apparatus of the present disclosure can be used to reduce the need for an immersion bath and the need to wash excess coating from the fibers.

[0007] Corrugated board is often patterned with coatings to provide barrier properties, printability, and decoration. These coatings are currently applied using analog printing techniques or spray coating.

[0008] The print head that is the subject of the present invention can digitally pattern a series of low to medium viscosity coatings that are not available with conventional digital inkjet print heads. This enables the coating function to be accurately applied only when required. For example, in the case of waterproof carton board, the coating can be applied only to the outer surface of the box. In the case of pre-treatment for digital printing, the coating can be applied only to the area to be printed.

Summary of the Invention

[0009] According to a first aspect of the present invention, there is provided a print head for dispensing a fluid, comprising at least one chamber, an array of piezoelectrically actuated flow path distributors enclosed in the at least one chamber, a multi-orifice distribution plate, and an air distribution element including a source of compressed air and an air flow controller configured to direct an air flow.

[0010] By providing a print head with an array of piezoelectrically actuated flow path distributors, the need for conventional coating methods having a bath of coating fluid is eliminated. Instead, tiny droplets of atomized fluid can be directly dispensed onto the material at a controlled rate.

[0011] The air distribution element can be used, for example, to improve the uniformity of the dispensed tiny droplets by deflecting the droplets into an undercoat area or by drying droplets that are too large in the air. The air flow also functions as an integrated cooling system for the print head.

[0012] The piezoelectrically actuated flow path dispenser can be controlled by a processor, which can be configured to control each piezoelectrically actuated flow path dispenser independently. Since the flow path dispenser can be controlled by the processor and can be controlled independently of each other as needed, the fluid deposition amount can be accurately controlled according to the absorbance capacity of the material. This enables instantaneous fluid switching while switching the types of fluids to be dispensed, allows for the production of multi-component materials in a single staining, and also potentially enables the automatic in-line correction of non-uniform defects detected in the material. For example, if an undercoated fluid region is detected, the amount of fluid dispensed from the dispenser can be increased.

[0013] The air distribution element can be configured to direct an air flow towards the dispenser tip of the flow path dispenser. By directing the air flow towards the tip of the flow path dispenser, the risk of known problems related to the accumulation of fluid droplets in the print head, which can block or reduce the uniformity of the dispensed fluid, can be reduced.

[0014] In some embodiments, the air distribution element can be configured to direct a single air flow towards at least one dispenser tip of at least two flow path dispensers. Directing a single air flow towards the tips of two flow path dispensers can reduce the number of air distribution elements required by up to half, reduce the maintenance of the print head, reduce the compressed air required, make the overall solution less expensive, and result in a more homogeneous print head.

[0015] The air distribution element can be configured to direct the air flow substantially parallel to the flow of the fluid dispensed from the flow path dispenser in order to deflect the dispensed fluid in a controlled manner. By directing the air flow substantially parallel to the flow of the fluid, the fluid droplets can be guided to form a more homogeneous and accurately directed droplet distribution. Further, by deflecting the dispensed fluid with the air flow, the diffusion region of the fluid onto the material can be advantageously controlled, enabling a wide range of real-time control over the application of the fluid to the fibers.

[0016] The air distribution element can be configured to periodically apply an air flow at a frequency in the range of 1 to 1,000 Hz. The periodic deflection of the spray can be used to enhance the averaging between adjacent nozzles and improve the uniformity of the fluid distributed across the entire array of flow distributors.

[0017] The gas to be distributed can include, and / or can be, compressed air. Alternatively, or in addition, the gas to be distributed can include an inert gas such as helium or nitrogen, or a reactive gas such as ammonia. The gas to be distributed can include a plurality of gas components.

[0018] The chamber or each chamber can be filled with a fluid of known composition and flow profile such that a controlled pressure, which can be negative or positive within the chamber, exists. By filling the chamber containing the internal components of the printhead with a well-characterized fluid, unwanted evaporation and dripping of the fluid from the nozzles of the flow distributor can be reduced, and it helps to seal the chamber from external contamination. Further, the controlled pressure can help to maintain a constant flow rate from the flow distributor.

[0019] The printhead can further include a seal layer configured to resist the flow of fluid through the orifices of the multi-orifice distribution plate. The tip of the flow distributor can be configured to contact and protrude from the opening of the seal layer, and can further be configured to move relative to the seal layer with minimal friction or mechanical resistance during piezoelectric actuation.

[0020] The seal layer can provide additional protection to the printhead components encapsulated within the chamber and reduce unwanted leakage of the distributed fluid. By having the nozzle tip of the flow distributor protrude while in contact with the seal layer, the seal layer can function without interfering with the actual process of distributing the fluid.

[0021] The seal layer can be a viscoelastic film including a plurality of openings, and the film covers each orifice of the multi-orifice distribution plate. Further, the diameter of each opening of the film configured such that the flow path distributor protrudes therefrom may be smaller than the diameter of the tip of the flow path distributor. Thereby, the printing head can be sealed by bringing the nozzle tip into close contact with the film while minimizing mechanical interference with the piezoelectric motion.

[0022] In some embodiments, the diameter of each opening of the seal layer configured such that the flow path distributor protrudes therefrom may be larger than the diameter of the tip of the flow path distributor. The slightly loose seal between the seal layer and the distributor can prevent the resonance frequency of the distributor from being changed or adjusted.

[0023] Alternatively, or in addition, the seal layer can provide damping to the distributor. In some embodiments, this damping may be undesirable. For example, during use, the dispensing element can vibrate to generate a standing wave, which can include at least one node and at least one antinode. Thus, the seal layer can be disposed at or substantially near the position of the node, which is the point where the amplitude of the vibration in the standing wave system is zero. By doing so, the damping effect of the seal on the vibration of the node can be reduced or eliminated. Thereby, the dispensing characteristics of the dispensing element can be optimally maintained.

[0024] In some embodiments, the damping provided by the seal layer is desirable, and the diameter of the opening configured such that the flow path distributor protrudes therefrom can be configured to provide a desired amount of damping to the distributor to achieve a pre-specified resonance frequency.

[0025] The seal layer can be composed of a non-wettable elastomer or an elastomer with a non-wettable coating. The seal layer may be composed of a hydrophobic material and / or may include a hydrophobic coating.

[0026] In some embodiments, the seal layer can be composed of a metal or an alloy. The metal or alloy can include steel and / or aluminum. In some embodiments, the seal layer can include a coating layer. The coating layer can include polytetrafluoroethylene.

[0027] The seal layer of metal or alloy can include a small gap between the seal layer and the dispensing element. In such embodiments, the print head can be pressurized, thus causing a fluid flow from the inside of the print head to the outside of the print head. The fluid flow can be continuous and can be substantially parallel to the dispensing element, and since contaminants need to move against the direction of the fluid flow, it can be configured to prevent contaminants from entering the print head.

[0028] Alternatively or additionally, the tip of the multi-orifice dispensing plate and / or the flow path dispenser may be provided with a non-wetting coating and / or may be manufactured using a hydrophobic material and / or a hydrophobic coating.

[0029] The hydrophobic material and / or coating can include silicone and / or polytetrafluoroethylene. The non-wetting and / or hydrophobic materials and / or coatings can prevent an aqueous fluid from accumulating by the seal, inside or around the seal.

[0030] The flow rate through a given flow path dispenser can be controlled by the duty cycle of the given flow path dispenser. The velocity of the fluid dispensed by the print head can be controllable by a voltage determined by a processor.

[0031] The processor can be configured to control the spread of the dispensed fluid based on a digital image. The piezoelectrically actuated flow path dispenser can be controlled based on real-time feedback received by a processor. The real-time feedback can include at least one of coat weight detection, color detection, flow rate detection, nozzle resonance frequency, and electrical drive requirements for each nozzle.

[0032] In some embodiments, the piezoelectrically actuated flow path dispenser can be horizontal with respect to the substrate on which the fluid is dispensed. In some embodiments, the piezoelectrically actuated flow path dispenser can be tilted with respect to the substrate on which the fluid is dispensed to prevent the fluid from being sucked up into the nozzle seal area.

[0033] In some embodiments, the flow path dispenser can be titled from horizontal by up to 90 degrees, 60 degrees, 45 degrees, 30 degrees, 25 degrees, 20 degrees, 15 degrees, 10 degrees, or 5 degrees. In some embodiments, the flow path dispenser should not be tilted. For example, the flow path dispenser can be titled between 0 and 60 degrees, more preferably between 5 and 45 degrees, and most preferably between 10 and 30 degrees.

[0034] In some embodiments, the flow path dispensing element is disposed substantially below the bottom of the tank. This can help prevent the fluid within the dispensing element from flowing out of the dispenser and clogging or blocking the fluid path.

[0035] The print head can be moved relative to the substrate in a reciprocating motion to dispense the dispensed fluid over a wide area. The motion can be controlled at least in part based on real-time feedback received by a processor.

[0036] The real-time feedback can be based on color detection across the substrate. There can be increased air pressure within the print head, thereby causing an air flow in a direction from the inside of at least one chamber towards the tip of the flow path dispenser.

[0037] The print head can further include an additional chamber surrounding the tip of the flow path dispenser. The printing head may further include a cooling mechanism, which may include a casing operably connected to the printing head. The casing can be configured to contain a fluid such as water or air, and the fluid is configured to absorb heat from the printing head, thus cooling the printing head. In some embodiments where there are multiple printing heads, water cooling may be a preferred cooling mechanism.

[0038] Alternatively, or in addition, each printing head may include a fan configured to circulate / move warm air near the printing head, exchange it with cooler air, and thus cool the printing head. In some embodiments where there is a single printing head, air cooling may be a preferred cooling mechanism.

[0039] Furthermore, according to the present invention, a system for supplying fluid to a plurality of printing heads is provided. The system includes a plurality of tanks for holding the fluid distributed from the plurality of printing heads, a fluid supply chamber, a sensor for detecting the fluid level in the fluid supply chamber, and a recirculation feed for controlling the supply rate and discharge rate between the fluid supply chamber and each of the plurality of tanks, wherein the fluid supply rate and the fluid discharge rate are determined by a processor based at least in part on the fluid level detected by the sensor.

[0040] With a dynamic and digitally controllable recirculation feed to the plurality of printing heads, the system always maintains a sufficient level of fluid in each tank, returns unnecessary fluid to the main tank, reduces waste fluid, maintains a constant fluid flow, and thus improves efficiency.

[0041] In some embodiments, the system may include a single tank for holding the fluid distributed from the plurality of printing heads. The supply rate and discharge between the fluid supply chamber and each of the plurality of tanks can be the same for each tank. By maintaining a uniform supply rate and discharge rate to each of the plurality of header tanks, the levels of the fluid in each tank can be approximately the same, and thus can be determined by a single sensor that controls the supply rate and discharge rate from a single fluid supply chamber. This allows a single sensor to effectively monitor the fluid levels of a plurality of header tanks, reducing the cost and complexity of the assembly.

[0042] The sensor is a capacitance sensor, and the system can be configured to increase the supply rate to each of the plurality of tanks and decrease the discharge rate from each of the plurality of tanks in response to the sensor being switched on, and to decrease the supply rate to each of the plurality of tanks and increase the discharge rate from each of the plurality of tanks in response to the sensor being switched off.

[0043] In some embodiments, the sensor can be configured to measure the hydrostatic head of the fluid in the tank. In embodiments where a plurality of tanks are provided, the sensor is provided to measure the hydrostatic head of each tank.

[0044] Alternatively, or in addition, the sensor is a pressure sensor, and the system is configured to increase the supply rate to each of the plurality of tanks and decrease the discharge rate from each of the plurality of tanks in response to the sensor detecting a low pressure, and to decrease the supply rate to each of the plurality of tanks and increase the discharge rate from each of the plurality of tanks in response to the sensor detecting a high pressure. speed can be increased.

[0045] At least one fluid flow path can connect the inlets and outlets of each of the plurality of tanks to the fluid supply chamber, and the fluid flow paths of each tank can have equal resistance. The outlet of each tank can be arranged at a higher level than the inlet of each tank, creating a maximum fluid level for each tank based on the principle of a weir.

[0046] Each of the plurality of tanks may further include a vacuum bleed valve disposed adjacent to the tank inlet, and the vacuum bleed valve may be configured to provide a low resistance flow path when the pressure in the tank exceeds a predetermined limit. The pressure in the header tank can be stabilized by using a vacuum bleed valve near the fluid supply, thereby minimizing the overpressure caused by a sudden increase in the height of the tank fluid and allowing air to escape from the headspace through the low resistance route.

[0047] The system may further include at least one vacuum pump, and the vacuum pump may be configured to control the pressure in each of the plurality of tanks. The pressure in the header tank can be set using the vacuum applied to the headspace. Since the dispensing of fluid from the print head is very sensitive to the fluid pressure in the tank, the accurate dispensing of fluid depends greatly on a stable header tank pressure.

[0048] Each of the plurality of tanks may further include an adjustable partition configured to control the fluid level in each tank based on the principle of a weir. The fluid outlet of each of the plurality of tanks can be adjusted and configured to control the fluid level in each tank by adjusting the level at which the fluid is discharged.

[0049] The pressure control of the system can be a closed loop with a latency of less than 1 second per adjustment. The system may be further configured to heat and / or stir the fluid.

[0050] The system may be further configured to degas and / or filter the fluid. The system may include a pump used to recirculate the fluid in each tank. This system may further include an infrared heater configured to minimize fluid movement and maximize the uniformity of the fluid dispensed onto the fibers.

[0051] The system may further include a vacuum pump configured to control the penetration of the airflow into the fibers. The vacuum pump can be operably connected to a channel, and the channel is substantially disposed under the print head. More specifically, the channel can be substantially disposed under the fibers configured to receive the fluid dispensed from the print head.

[0052] The channel can be negatively pressurized by the vacuum pump and configured to draw air through the fibers from near the dispensing element into the channel. By doing so, the spread of the fluid dispensed from the print head can be further reduced and / or the control of the penetration of the fluid into the fibers can be enhanced.

[0053] The system may further include a filter disposed between the channel and the fibers, and the filter is configured to prevent the fluid and / or contaminants from entering the channel. The filter can be disposable and / or removable. Once the filter is removed, it can be cleaned and reused. Adding a filter to prevent the fluid and / or contaminants from entering the channel also prevents the filter from entering the vacuum pump, thus reducing the maintenance requirements of the system.

[0054] According to the present invention, there is further provided a method for filling, refilling, and / or discharging the fluid in at least one tank. The method of filling and / or refilling the tank may include at least one of the steps of supplying the print head from a supply tank, negatively pressurizing the tank to prevent the fluid from dripping from the dispensing element to fill the tank to a target level with a desired fluid such as ink, establishing recirculation within the tank, and reducing the negative pressure within the tank to completely fill the dispensing element and prevent a pendant drop from forming at the nozzle.

[0055] A method of draining the tank may include at least one of the steps of negatively pressurizing the tank to prevent fluid from dripping from the dispensing element, stopping the fluid supply to the tank, and using a return pump to drain the tank into a supply tank.

[0056] A method of draining the tank may further include the step of adding a detergent composition to the tank and repeating the aforementioned steps. The detergent composition may be water and sodium dodecyl sulfate. Adding the detergent composition dilutes the fluid remaining in the tank, which is then drained from the tank. This step may be repeated multiple times until it is determined that the tank is clean by checking the fluid output from the nozzle.

[0057] In some embodiments, the tank may be negatively pressurized so that the fluid in the dispensing element is completely drawn back into the tank. In some embodiments, the inner surface of the tank may be coated with a hydrophobic material such as polytetrafluoroethylene. The hydrophobic coating allows the fluid to be drained from the tank more easily. Further, such a coating can reduce the maintenance costs resulting from the need to clean the tank between draining and replenishing.

[0058] The present invention will then be further described by way of example only with reference to the accompanying drawings.

Brief Description of the Drawings

[0059]

Figure 1A

Figure 1B

Figure 1C

Figure 1D

Figure 2A

Figure 2B

Figure 3A

Figure 3B

Figure 4

Figure 5A

Figure 5B

Figure 6

Figure 7

Figure 8A

Figure 8B

Figure 9A

Figure 9B

Figure 10

DETAILED DESCRIPTION OF THE INVENTION

[0060] To further illustrate various aspects of the present disclosure, specific embodiments of the present disclosure will be described in detail in conjunction with the accompanying drawings. Referring to FIGS. 1A, 1B, 1C, and 1D, two examples of the print head 10 are shown. The example shown in FIG. 1A is a compact print head 10 with a suitable array of 48 piezoelectrically actuated flow path distributors 14 that provides a printing width of 121 mm. FIGS. 1B, 1C, and 1D are side and isometric views of a 1.8 m wide print head that includes an elongated chamber 12 and a large array of 720 piezoelectrically actuated flow path distributors 14 enclosed within the chamber 12. The piezoelectrically actuated flow path distributor 14 is, for example, in the form of a hollow needle suitable for directing the flow of fluid. The two examples shown in FIGS. 1A through 1D have the same main functions, and the following description applies equally to each example.

[0061] The print head 10 further includes a multi-orifice distribution plate 16 configured such that the tips of the piezoelectrically actuated flow path distributors 14 protrude. As shown in FIG. 2A, the tips of the flow path distributors 14 are in the form of nozzles suitable for distributing fluid.

[0062] Advantageously, providing an array of piezoelectrically actuated flow path distributors 14 eliminates the need for conventional coating methods that require a bath of fluid containing an excess amount of coating. Instead, the apparatus of the present disclosure is configured to directly distribute the micro-droplets of atomized fluid onto a substrate material, such as a fiber or fabric, at a controlled rate.

[0063] Each of the print heads 10 shown in FIGS. 1A and 1B, 1C, and 1D further includes an air distribution element 18 that includes a source 20 of compressed air and an air flow controller 22 configured to direct an air flow 21.

[0064] The air distribution element 18 can be used to control the spread of the droplets and deflect the droplets into the primer area, or alternatively, the air flow 21 can be applied to the dried droplets that are too large in the air to improve the uniformity of the micro-droplets distributed on the substrate.

[0065] The air flow 21 distributed from the air distribution element 18 can function simultaneously as an integrated cooling system to prevent the print head 10 from overheating. Also shown in FIGS. 1A to 1D is a tank 34 hereinafter referred to as a "header tank". The header tank 34 is configured to hold the fluid distributed from the print head 10. In the example shown in FIG. 1A, the tank holds 100 ml to 2.5 l of the distributed fluid.

[0066] Referring now to FIG. 2A, a configuration example of the array of the flow path distributors 14 is shown in more detail. In the illustrated configuration, the length of the flow path distributor 14 in the form of a hollow needle is substantially perpendicular to the direction of the distributed fluid with a nozzle tip of the needle protruding through the orifice 28 of the multi-orifice distribution plate 16.

[0067] The flow path distributor 14 is configured to distribute the fluid in response to the actuation by a vertical piezoelectric actuator (not shown). In particular, during operation, each of the flow path distributors 14 distributes very small or atomized fluid droplets in a direction substantially perpendicular to the length of the flow path.

[0068] Although the piezoelectric actuator is not shown, in one embodiment, the flow path can be actuated by a plurality of piezoelectric actuators in contact with the needle of the flow path distributor. For example, there can be two piezoelectric actuators mounted perpendicular to the flow path, enabling control of the flow path perpendicular to the direction of the substrate on which the fluid is deposited.

[0069] ​Due to the configuration of the flow path and the actuator, several elements of resolution control can be realized, namely, a fixed offset perpendicular to the substrate movement direction of individual nozzles in the array, as well as vibrations perpendicular to the advancing direction of the substrate, and the deposition width of the dispensed fluid.

[0070] In some embodiments, including what is schematically shown in FIG. 8, the array of piezoelectric actuating elements 14 is operated by a processor 50, such as a microprocessor. The processor 50 is configured to independently control each piezoelectrically actuated flow path dispenser such that individual dispensers are operated to dispense less or more fluid, or to dispense at different frequencies.

[0071] By having flow path dispensers 14 that are controlled by the processor 50 and can be independently controlled of each other as needed, precise control of the fluid deposition amount can be achieved to match the determined absorbance capacity of the material. This also enables instantaneous fluid switching, switching the type of fluid dispensed onto the substrate material, and thus enables the manufacture of multi-component materials in a single coating run.

[0072] Furthermore, when a defect is detected in the uniformity of the fluid dispensed onto the substrate material, the above configuration enables automatic in-line correction of such non-uniformity. For example, when an undercoated fluid region is detected, the amount of fluid dispensed from the dispenser can be increased.

[0073] The array of piezoelectrically actuated flow path dispensers 14 is shown as a single row of straight needle-shaped dispensers of uniform length, but other configurations of the array are contemplated herein. For example, the array can include multiple rows of dispensers, or dispensers of various lengths. The flow path dispensers 14 may be curved or curved at different angles relative to each other.

[0074] Figure 2B shows a side view of a single flow path dispenser 14 in the configuration described above in relation to Figure 2A. Further, it is shown that an air flow 21 from the air distribution element 18 is applied to the nozzles of the flow path dispenser 14. In some embodiments, the air flow 21 is substantially parallel to the direction of travel of the dispensed fluid.

[0075] Referring now to Figure 3A, it is shown that the air distribution element 18 of the print head 10 is configured to direct the air flow 21 towards the dispenser tips of the array of flow path dispensers 14. The air flow 21 is in a direction substantially perpendicular to the length of the flow path dispenser 14 and is substantially parallel to the direction of travel of the dispensed fluid.

[0076] By doing so, the air distribution element 18 deflects the droplets of the fluid dispensed from the flow path dispenser 14 in order to control the spreading profile of the droplets of the dispensed fluid on the substrate on which the fluid is being dispensed.

[0077] An example of a droplet spread profile is shown in Figure 3B, which shows the shape of the droplet profile 50 in the absence of the applied flow of air 21 from the air distribution element 18, and the shape of the droplet profile 52 with the applied flow of air 21 from the air distribution element 18.

[0078] Advantageously, by controlling the droplet profile and spread, the fluid can be dispensed at a higher resolution. The velocity of the air flow 21 is controlled by the air flow controller 22 to achieve the desired resolution, and the air flow can be used to deflect and thus direct the dispensed fluid.

[0079] Further, by directing the air flow 21 towards the tip of the flow path dispenser, the risk of known problems in print heads for dispensing other types of fluids such as ink is reduced, and the dispensed fluid accumulates at the nozzle tip of the dispensing element, blocking the nozzle or degrading the uniformity of the dispensed fluid.

[0080] The ability to deflect the fluid distributed by the air stream 21 and thus control the area of fluid diffusion into the material also enables broad real-time control of the application of fluid to the fibers. In some embodiments, the air flow controller 22 of the air distribution element 18 is configured to be periodically applied to the droplets in which the air flow 21 is distributed. For example, the air flow controller can distribute the air flow at a frequency in the range of 1 to 1,000 Hz.

[0081] The use of periodic deflection of the spray can enhance the averaging between adjacent nozzles and improve the uniformity of the fluid distributed across the entire array of flow path distributors. In some embodiments, the air flow is driven at a pressure in the range of 2 to 10 PSI or 14 to 69 kPa and a flow rate of 0.0283 to 2.83 m 3 (1 to 100 cubic feet) or 0.00047 to 0.047 m 3 s -1 per minute.

[0082] Referring now to FIG. 4, an example configuration of the air distribution element 18 for directing the air flow 21 is shown in more detail. As shown, the air distribution element is enclosed within a casing designed to funnel and direct the air flow from a source of compressed air 20. The casing is configured to widen as it approaches the supply from the source of compressed air 20 and narrow at the point within the casing where the air is distributed. Such a configuration enables the air flow 21 to be distributed at high speed and high resolution.

[0083] The air flow controller 22 can take the form of a valve within the casing for controlling whether air is distributed. The air flow controller 22 is digitally controlled by a processor. For example, the air flow controller can be controlled by the processor 50.

[0084] Referring now to FIG. 5, a further aspect of the present disclosure is described, where the printhead 10 further includes a seal layer 26 configured to resist the flow of fluid through the orifices 28 of the multi-orifice distribution plate 16.

[0085] The seal layer 26 is composed of several openings 30, and each opening 30 is configured to align with the orifice 28 of the multi-orifice distribution plate 16 where the tip of the array of flow path distributors 14 protrudes. The diameter of each opening 30 of the seal layer 26, from which the flow path distributor is configured to protrude, is smaller than the diameter of the tip of the flow path distributor 14, and the protruding tip is arranged in close contact with the edge of the opening 30 of the seal layer 26, effectively sealing the chamber 12 of the printhead 10.

[0086] In an exemplary embodiment, the seal layer 26 is a multi-orifice plate composed of a viscoelastic material such as silicone or fluoropolymer. The seal layer 26 can be, for example, a viscoelastic film. The orifice of the seal layer is usually about 10% smaller in diameter than the orifice at the tip of the flow path distributor 14. For example, a flow path distribution needle with an outer diameter of 900 microns needs to be sealed with an opening with a diameter of 800 microns.

[0087] The above configuration enables the movement of the flow path distributor 14 relative to the seal layer with minimal friction or mechanical resistance when the flow path distributor 14 is actuated, while effectively sealing the fluid within the chamber 12. Therefore, the seal layer of the present disclosure does not impede fluid distribution.

[0088] In some embodiments, the seal layer 26 is composed of a non-wetting elastomer or an elastomer with a non-wetting coating 31. Optionally, non-wetting coatings are also provided at the tips of the multi-orifice distribution plate 16 and the flow path distributor 14. The seal layer and the non-wetting coating provide additional protection to the components enclosed within the chamber and reduce unwanted leakage of the dispensed fluid.

[0089] ​The non-wetting coating is selected from any of the following materials, namely, hydrophobic polymers such as parylene, fluoropolymers, polyolefins, polyimides, etc. In some embodiments, the anti-wetting, low-adhesion surface coating described herein is the reaction product of a reactant mixture. The reaction mixture can be composed of at least one triisocyanate and a perfluoropolyether diol compound containing an ethoxylated spacer. In some embodiments, suitable triisocyanates are Desmodur® Mondur® or Impranil®, for example, Desmodur® N available from Materials Science under the names 3300, Desmodur® N 3790.

[0090] Referring now to FIG. 6, an exemplary configuration of a chamber 12 enclosing a piezoelectrically actuated flow path dispenser 14 is shown, the chamber 12 including an additional chamber 24 surrounding the tip of the flow path dispenser 14, the additional chamber 24 being used to provide a further degree of control of the air flow and gas composition around the dispenser tip.

[0091] For example, the additional chamber can be filled with a fluid of known composition and flow profile such that the pressure within the chamber is controlled in the range of -100 to 1000 mmHg2O or -980 to 9800 Pascals. In some embodiments, the same or different controlled pressures are applied to the chamber 12.

[0092] Filling the chamber 12 containing the internal components of the print head 10 with a known fluid helps to reduce unwanted evaporation or dripping of the fluid from the nozzles of the flow path dispenser 14, as well as to seal the chamber 12 from external contamination. Further, the controlled pressure helps to maintain a constant flow rate from the flow path dispenser 14.

[0093] Next, with reference to FIG. 7, a system 32 for supplying fluid to a plurality of print heads will be described. The print heads to which fluid is supplied are, for example, the same as the above-described print head 10.

[0094] System 32 includes a plurality of header tanks 34 corresponding to each of the plurality of print heads 10. As a result, each header tank 34 contains the fluid dispensed by each respective print head 10. System 32 further includes a fluid supply chamber 38 for supplying fluid to each of the plurality of tanks 34 and a sensor 36 for detecting the level of fluid within the fluid supply chamber.

[0095] System 32 further includes a digitally controlled recirculation feed 40 for controlling the supply rate and discharge rate between the fluid supply chamber 38 and each of the plurality of tanks 34, and the fluid supply rate and fluid discharge rate are determined by a processor based at least in part on the fluid level detected by sensor 36. at least in part on the fluid level detected by sensor 36.

[0096] Each header tank 34 includes an inlet 42 for receiving fluid from the recirculation feed and an outlet 44 through which fluid is discharged by the recirculation feed 40 and returned to the fluid supply chamber 38.

[0097] The above-described aspects of system 32 provide a dynamically digitally controllable system that can maintain a sufficient level of fluid in each header tank 34 at all times and return unwanted or unused fluid to the fluid supply chamber 38. This reduces waste fluid, maintains a constant fluid flow, reduces the risk of clogging, and improves efficiency.

[0098] Further, in some embodiments, the supply rate and discharge between the fluid supply chamber 38 and each of the plurality of header tanks 34 are the same for each tank, the fluid flow paths between the fluid supply chamber 38 and each header tank 34 have equal resistance, and a substantially uniform flow of fluid into and out of each header tank 34 is maintained.

[0099] By maintaining substantially uniform supply and discharge rates to each of the plurality of header tanks 34, the level of fluid in each tank becomes substantially the same and can thus be determined by a single sensor that controls the supply and discharge rates from a single fluid supply chamber 38. This configuration reduces the cost and complexity of the assembly by enabling a single sensor 36 to effectively monitor and maintain the fluid levels of the plurality of header tanks.

[0100] Thus, in the above configuration, in response to the sensor 36 detecting that the fluid level has reached above a specific point in the fluid supply chamber 38, the system is configured to increase the supply rate to each of the plurality of tanks 34 and decrease the discharge rate from each of the plurality of tanks 34. Similarly, in response to the sensor detecting that the fluid level in the fluid supply chamber 38 has reached below a specific point, the system 32 is configured to decrease the supply rate to each of the plurality of tanks 34 and increase the discharge rate from each of the plurality of tanks.

[0101] In some embodiments, the above configuration allows for a periodically varying level of fluid in the fluid supply chamber 38 with variations of less than 1 mm and maintains the tank pressure within the range of + / - 0.5 mm.

[0102] The level of the fluid supply tank is maintained by infeed and outfeed pumps. In some embodiments, the sensor is a capacitance sensor with an on / off level change of + / - 0.25 mm. The infeed pump is programmed to increase the flow rate more than the outfeed pump when the level sensor is off to raise the tank level, and vice versa when the level sensor is on, causing the tank level to decrease.

[0103] In some embodiments, the fluid outlet of each header tank 34 is positioned at a higher level than the inlet 42 of each tank 34, creating a maximum fluid level for each tank in the case of an accidental over-supply of fluid.

[0104] In some embodiments, each of the plurality of tanks 34 further includes a vacuum bleed valve 46 disposed adjacent to the tank inlet 42. The vacuum bleed valve is configured to provide a low resistance flow path when the pressure in the tank 34 exceeds a predetermined limit. This aspect of the system 32 allows air to escape from the headspace through the low resistance path which minimizes the overpressure caused by a sudden increase in the height of the tank fluid and ensures that the header tank pressure can be stabilized.

[0105] The dispensing of fluid from the print head is very sensitive to the fluid pressure in the tank, and variations exceeding 2 mm H20 or 20 Pa are observed in the dispensing of the fluid. Therefore, accurate dispensing of the fluid depends greatly on a stable header tank pressure.

[0106] Therefore, in some embodiments, the system further includes at least one vacuum pump 48, which is configured to control the pressure in the headspace of each of the plurality of header tanks 34. The vacuum pump can be a high frequency piezoelectric air pump to minimize periodic variations in pressure.

[0107] Here, with reference to FIGS. 8A, 8B, 9A and 9B, a configuration example of the header tank 34 and the recirculation feed 40 will be described in more detail. FIGS. 8A and 8B show an embodiment in which the fluid level and meniscus pressure in each of the plurality of header tanks 34 are controlled by an adjustable weir 45. In particular, each header tank 34 is configured such that the fluid inlet 42 supplies fluid to the first part of the tank from above, and a rotatable, retractable, or otherwise adjustable weir divides the first part from the second part of the tank, and the fluid outlet 44 is disposed at a low position on the wall of the second part of the tank 34.

[0108] In such a configuration, by adjusting the height of the adjustable weir 45 by rotation, contraction, or other means, the fluid in the first part of the tank spills over the weir into the second part of the tank, and by changing the level at which it is discharged through the fluid outlet 44, the fluid level in the tank can be controlled. Such a configuration eliminates the need for a vacuum pump.

[0109] In FIG. 8A, the header tank 34 is shown in a closed configuration. In FIG. 8B, the header tank 34 is shown in an open configuration. The open configuration of FIG. 8B simplifies the cleaning and maintenance of the tank.

[0110] The illustrated embodiment shows a fluid inlet 42 disposed vertically above the tank and a fluid outlet 44 disposed at a low position on the rear wall, but other configurations are possible, and both the fluid inlet and outlet can be disposed on or on any side wall of the header tank.

[0111] Alternative header tank configurations for controlling the fluid level and meniscus pressure are shown in FIGS. 9A and 9B. In the embodiments of FIGS. 9A and 9B, instead of an adjustable weir, the fluid outlet 44 itself is adjustable. For example, in the illustrated embodiment, both the fluid inlet 42 and the fluid outlet 44 are disposed vertically above the header tank 34, and the fluid outlet 44 is adjustable in a retractable or other manner such that the level reaching the header tank 34 is controllable. Thus, the fluid level in the tank 34 can be controlled using the level at which the fluid outlet 44 reaches into the tank.

[0112] In FIG. 9A, the header tank 34 is shown in a closed configuration. In FIG. 9B, the header tank 34 is shown in an open configuration. The open configuration of FIG. 9B simplifies the cleaning and maintenance of the tank.

[0113] Referring now to FIG. 10, the digital control of the elements of the present invention will be described in more detail. As described above, the array of piezoelectrically actuated flow distributors 14 is individually and independently controlled by the processor 50. Similarly, the air flow 21 from the air distribution element 18 is adjusted by an air flow controller 22 that is digitally controlled by a processor that may be the processor 50 or another processor. Further, both the sensor 36 and the recirculation feed 40 communicate with a processor that determines the supply and discharge rates described above based on readings from the sensor 36. The control processor may be the processor 50 or another processor. In the illustrated embodiment, the same processor 50 communicates with and controls the array of piezoelectrically actuated flow distributors 14, the air flow controller 22, and the sensor 36 and the recirculation feed 40.

[0114]

[0115] In an exemplary embodiment, the processor 50 corresponds to a microcontroller, a system-on-chip, or a single-board computer. The processor 50 includes volatile memory, non-volatile memory, and an interface. In certain other embodiments, the processor 50 may include multiple volatile memories, non-volatile memories, and / or interfaces. The volatile memory, non-volatile memory, and interface communicate with each other via a bus or other form of interconnect. The processor 50 executes computer-readable instructions, such as one or more computer programs for controlling certain aspects of the system described herein. The computer-readable instructions are stored in the non-volatile memory. The processor 50 is powered from a power source that may include a battery.​

Claims

1. A print head (10) for distributing a fluid, comprising at least one chamber (12), an array (14) of piezoelectrically actuated flow path distributors enclosed in said at least one chamber, a multi-orifice distribution plate (16), and an air distribution element (18) comprising a source of compressed air (20) and an air flow controller (22) configured to direct an air flow, comprising a print head.

2. The piezoelectrically actuated flow path distributor is controlled by a processor (50), the processor being configured to control each piezoelectrically actuated flow path distributor independently, The print head according to claim 1.

3. The air distribution element is configured to direct an air flow towards the distributor tip of the flow path distributor, The print head according to claim 1 or 2.

4. The air distribution element is configured to direct the air flow substantially parallel to the flow of the fluid distributed from the flow path distributor and deflect the distributed fluid in a controlled manner, The print head according to claim 3.

5. The air distribution element is configured to periodically apply the air flow at a frequency in the range of 1 to 1,000 Hz, The print head according to any one of claims 1 to 4.

6. Said or each chamber is filled with a fluid having a known composition and flow profile such that a controlled pressure, which can be negative or positive, exists within the chamber, The print head according to any one of claims 1 to 5.

7. Further comprising a seal layer (26) configured to resist the flow of fluid through the orifices (28) of the multi-orifice distribution plate, The print head according to any one of claims 1 to 6.

8. The tip of the flow path distributor contacts the opening (30) of the seal layer and is configured to project from the opening (30), the tip of the flow path distributor being further configured to move relative to the seal layer with minimal friction or mechanical resistance during piezoelectric actuation, The print head according to claim 7.

9. The seal layer is a viscoelastic membrane comprising a plurality of openings, the membrane covering each orifice of the multi-orifice distribution plate, the diameter of each opening of the membrane through which the flow path distributor projects being smaller than the diameter of the tip of the flow path distributor, The print head according to claim 7 or 8.

10. The seal layer is composed of a non-wetting elastomer or an elastomer with a non-wetting coating. The print head according to any one of claims 7 to 9.

11. A non-wetting coating is provided at the tip of the multi-orifice distribution plate and / or the flow path distributor. The print head according to any one of claims 1 to 10.

12. The flow rate through a given flow path distributor is controlled by the duty cycle of the given flow path distributor. The print head according to any one of claims 1 to 11.

13. The velocity of the fluid dispensed by the print head is controllable by a voltage determined by the processor. The print head according to any one of claims 1 to 12.

14. The processor controls the spread of the dispensed fluid based on a digital image. The print head according to any one of claims 1 to 13.

15. The piezoelectrically actuated flow path distributor is controlled based on real-time feedback received by the processor. The real-time feedback includes a) detection of coat weight, b) color detection, c) flow rate detection, d) nozzle resonance frequency, e) electrical drive requirements for each nozzle, and includes at least one of them. The print head according to any one of claims 1 to 14.

16. The piezoelectrically actuated flow path is inclined with respect to the substrate on which the fluid is dispensed to prevent the fluid from being sucked up in the nozzle seal area. The print head according to any one of claims 1 to 15.

17. The print head is moved relative to the substrate in a reciprocating motion to dispense the dispensed fluid over a wide area. The print head according to claim 16.

18. The motion is controlled at least in part based on real-time feedback received by the processor. The print head according to claim 17.

19. The real-time feedback is based on color detection of the entire substrate. The print head according to claim 18.

20. There is an increased air pressure within the print head. The air pressure causes an air flow in a direction from the inside of the at least one chamber towards the tip of the flow path distributor. The print head according to any one of claims 1 to 19.

21. The print head further includes an additional chamber surrounding the tip of the flow path distributor. ​ The print head according to any one of claims 1 to 20.

22. A system (32) for supplying fluid to a plurality of print heads according to any one of claims 1 to 21, A plurality of tanks (34) for holding the fluid dispensed from the plurality of print heads, A fluid supply chamber (38), A sensor (36) for detecting the fluid level in the fluid supply chamber, A recirculation feed (40) for controlling the supply rate and the discharge rate between the fluid supply chamber and each of the plurality of tanks, wherein the fluid supply rate and the fluid discharge rate are determined by the processor based at least in part on the fluid level detected by the sensor, the recirculation feed (40), Comprising System.

23. The supply rate and the discharge between the fluid supply chamber and each of the plurality of tanks are the same for each tank, The system according to claim 22.

24. The sensor is a capacitance sensor, The system is In response to switching on of the sensor, increasing the supply rate to each of the plurality of tanks and decreasing the discharge rate from each of the plurality of tanks, In response to switching off of the sensor, decreasing the supply rate to each of the plurality of tanks and increasing the discharge rate from each of the plurality of tanks Is configured to The system according to claim 22 or 23.

25. The sensor is a pressure sensor, The system is In response to the sensor detecting a low pressure, increasing the supply rate to each of the plurality of tanks and decreasing the discharge rate from each of the plurality of tanks, In response to the sensor detecting a high pressure, decreasing the supply rate to each of the plurality of tanks and increasing the discharge rate from each of the plurality of tanks Is configured to The system according to claim 22 or 23.

26. A fluid flow path connects the inlets (42) and outlets (44) of each of the plurality of tanks to the fluid supply chamber, The fluid flow paths of each tank have equal resistance, The system according to any one of claims 22 to 25.

27. The outlet of each tank is arranged at a higher level than the inlet of each tank, creating a maximum fluid level for each tank based on the principle of a weir. The system according to claim 26.

28. Each of the plurality of tanks further comprises a vacuum bleed valve (46) disposed adjacent to the tank inlet, The vacuum bleed valve is configured to provide a low resistance flow path when the pressure in the tank exceeds a predetermined limit. The system according to claim 26 or 27.

29. The system further comprises at least one vacuum pump (48), The vacuum pump is configured to control the pressure of each of the plurality of tanks. The system according to any one of claims 22 to 28.

30. Each of the plurality of tanks further comprises an adjustable partition configured to control the fluid level in each tank based on the principle of a weir. The system according to any one of claims 22 to 28.

31. The fluid outlet of each of the plurality of tanks is adjustable, The fluid outlet of each tank is configured to control the fluid level in each tank by adjusting the level at which the fluid is discharged. The system according to any one of claims 26 to 28.

32. The pressure control is a closed loop with a latency of less than 1 second per adjustment. The system according to claim 29.

33. The system is further configured to heat and / or stir the fluid. The system according to any one of claims 22 to 32.

34. The system is further configured to degas and / or filter the fluid. The system according to any one of claims 22 to 33.

35. A pump is used to recirculate the fluid in each tank. The system according to any one of claims 22 to 34.

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