Method and apparatus for dispensing droplets of liquid - Patents.com

Abstract

A liquid dispensing element is provided that includes a dispense plate with a plurality of orifices at least partially defining a fluid flow path; and a plurality of piezoelectric transducers, each with a piston configured to move perpendicular to the dispense plate between a first position in which the piston is proximate to the dispense plate and a second position in which the piston is moved away from the dispense plate. Movement between the first and second positions results in the ejection of droplets of fluid via a surface cavitation droplet ejection process, where the diameter of the droplet is smaller than the diameter of the orifice.

Description

[Technical field]

[0001] The present invention relates to a method and apparatus for dispensing droplets of liquid. [Background technology]

[0002] Dispensing droplets through a nozzle is known in the art, and a wide variety of devices for doing so can be found in the field of inkjet printers.

[0003] Dispensing of fluids for coating and digital imaging applications is achieved using a variety of technologies, typically by applying energy to a fluid in a confined volume to cause droplets to be ejected from a nozzle. Drop-on-demand (DOD) inkjet is a well-established technique for high-resolution printing that uses piezoelectric elements to generate pressure waves in a confined chamber to eject droplets of several picoliters in volume. Inkjet printheads are typically designed with a high density of piezoelectric dispensing elements to achieve a native printing resolution of 300-600 dots per inch (DPI). Printhead designs are highly complex, including micromachined fluid paths, laser-drilled nozzles, and complex assemblies. Inkjet printheads are typically non-reworkable due to the design of the fluid flow paths and the integration of the piezoelectric elements. Additionally, the high level of engineering complexity ensures that industrial inkjet is a relatively high-cost printing technology.

[0004] Typically, the drop size is determined by the nozzle diameter, which is typically larger than the orifice. It has been found that to achieve high resolution printing, the nozzle diameter should typically be less than 50 microns, and most preferably 25 microns or less. In addition, to achieve high resolution with high throughput, the nozzle must be operated at a frequency of approximately 50 kHz. This places severe constraints on the fluids that can be used, such that only fluids with a viscosity lower than 10 cPoise (0.01 Pa·s) can be dispensed, and solid particles must not exceed 1 μm in diameter. Furthermore, such small nozzle diameters mean that the orifice is highly vulnerable to fluid evaporation, which can clog the nozzle and eventually cause the printhead to fail.

[0005] Alternatively, piezoelectric injectors are well known as single-unit dispensers for a much wider range of fluid viscosities than drop-on-demand inkjets. However, these techniques can only achieve low-resolution dispenses at low throughput. Dispensing orifices are typically in the range of 500 μm to 1000 μm, and valves can typically only operate up to 100 Hz, making them unsuitable for imaging applications. Piezoelectric injectors typically require a footprint that precludes their use in arrays for imaging applications. [Prior art documents] [Non-patent literature]

[0006] [Non-Patent Document 1] Phys. Rev. Lett. 102, 034502――Published 23 January 2009 Summary of the Invention [Problem to be solved by the invention]

[0007] It is an object of the present invention to provide a method and apparatus for dispensing small droplets. In particular, it is an object of the present invention to produce droplets smaller than the minimum size achievable using prior art nozzle-integrated dispensing devices. The method and apparatus of the present invention have particular applicability in the field of ink-based printing, since smaller droplet sizes enable the production of prints having a higher number of dots per inch (DPI), and thus higher image resolutions can be achieved through printers incorporating the present invention.

[0008] It is a further object of the present invention to provide for reliable use of the method and apparatus of the present invention. In particular, the device configuration must be carefully tuned to achieve a jetting effect that creates droplets smaller than the orifice through which they are dispensed. Particular attention is paid to the fluid flow paths and piston configuration to facilitate droplet dispensing.

[0009] A recognized problem in piezoelectrically actuated printing systems results from ink seeping out of the intended fluid path and concomitant contact with the piezoelectric actuator, which can cause the piezoelectric actuator to malfunction.

[0010] It is against this background that the present invention was born. [Means for solving the problem]

[0011] According to the present invention, there is provided a method of dispensing droplets of liquid comprising: providing a dispensing plate having an orifice; providing a piston arranged so as to be movable between a first position in which the piston is close to the dispensing plate and a second position in which the piston is remote from the dispensing plate and covers the orifice; flowing a stream of liquid onto the dispensing plate; and moving the piston from the first position to the second position sufficiently fast to cause a cavitation event that ejects droplets from the orifice, the droplets having a diameter smaller than the orifice and caused by the cavitation event.

[0012] Further in accordance with the present invention, there is provided a liquid dispensing element comprising: a dispensing plate having a plurality of orifices at least partially defining a fluid flow path; and a plurality of piezoelectric transducers, each having a piston configured to move perpendicular to the dispensing plate between a first position where the piston is close to the dispensing plate and a second position where the piston is spaced far away from the dispensing plate; wherein when actuated by the piezoelectric component, each piston is configured to move between the first and second positions to create a pressure wave directed at a corresponding orifice in the dispensing plate, thereby causing a surface cavitation event in the fluid flowing along the fluid path and resulting in the ejection of fluid droplets having a diameter smaller than a diameter of the orifice.

[0013] In the first position, the piston may be at a distance of 5 μm to 500 μm from the plane of the dispensing plate, optimally at a distance of approximately 10 μm. In the second position, the piston may be at a distance of 5 nm to 1000 nm from the first position of the piston, optimally at a distance of approximately 10 nm. In the liquid dispensing element according to any one of the above clauses, the piezoelectric transducer moves the piston at a distance of 10 -3 ms -1 It is configured to move at a speed of 10 -2 ms -1 From 10 -4 ms -1 The range may be:

[0014] The orifice has a diameter of 25 μm to 150 μm, particularly a diameter of 100 μm, and the exiting droplets produced by the cavitation event are 10 μm in diameter. m The droplet diameter is caused by cavitation rather than by the size of the orifice.

[0015] The piston may contact the stream of liquid in the first position.

[0016] The piston may be moved from a first position to a second position to force a droplet of liquid through the orifice using the piezoelectric element. A top plate may be provided above the dispense plate to form a channel therebetween, and directing the stream of liquid over the dispense plate may comprise directing the stream of liquid into the channel. The piston may pass through a hole in the top plate at the first position and at the second position. Sealing means may be provided between the piston and the top plate to insulate the stream of liquid from a volume above the top plate. The sealing means may comprise an O-ring or a rubber grommet.

[0017] The liquid may be ink.An inkjet printer may comprise a dispensing device according to the invention.

[0018] Furthermore, the present invention provides a liquid dispensing element comprising: a dispensing plate having a plurality of orifices, the dispensing plate at least partially defining a fluid flow path; and a plurality of piezoelectric transducers, each having a piston, configured to move perpendicular to the dispensing plate between a first position in which the piston is away from the dispensing plate and a second position in which the piston is closer to the dispensing plate; wherein movement between the first and second positions results in the ejection of droplets of fluid via a surface cavitation droplet ejection process, such that the diameter of the droplet is smaller than the diameter of the orifice.

[0019] Each piston may be configured to contact the fluid flow path when it is in the first position. Each piston may be tapered. The tapered form of the piston, which may otherwise be cylindrical, increases the pressure delivered to the nozzle.

[0020] The orifices may have a diameter in the range of 25 μm and 150 μm. The orifices may have a diameter in the range of 50 μm to 150 μm, for example a diameter of 50 μm or 75 μm. The dispense plate may be metal, for example stainless steel.

[0021] The element may further comprise a top plate disposed substantially parallel to the dispense plate and defining a fluid flow path. The top plate may comprise a plurality of orifices through which the piston is configured. The top plate may be formed from an elastic material having a thickness in the range of 50 μm to 300 μm, for example a thickness of 150 μm.

[0022] The element may further comprise a seal between each orifice and the corresponding piston, which may be an O-ring or a rubber grommet.

[0023] An array of the fluid dispensing elements described above can be combined to form a printhead. This system reliably achieves the required mechanical interface between the piezoelectric transducers and the corresponding pistons, along with proper management of the fluids. It further enables consistent operation of the printhead through management of the fluid flow.

[0024] The top plate may seal the fluid flow path from the piezoelectric transducer. Providing a continuous seal between the fluid flow path across the dispense plate and the piezoelectric transducer is key to protecting the piezoelectric transducer from fluids. Providing a continuous seal also improves the consistency of fluid flow by minimizing turbulence caused by additional sealing parts. Furthermore, providing a consistent seal ensures that there is a consistent pressure at each dispense orifice.

[0025] The top plate may have a series of protrusions configured to engage the pistons. The protrusions ensure that mechanical energy from the piezoelectric transducer is consistently transferred through the pistons to the fluid in the fluid flow path. This configuration is advantageous in that it is not necessary to provide an additional seal around each piston, as the top plate is continuous and provides a complete seal.

[0026] The top plate may have a two-layer construction. The top plate may comprise a first soft compliant layer that seals the fluid flow path from the piezoelectric transducer, and one or more further layers that provide protrusions configured to mate with the piston. The protrusions may be harder to ensure efficient transfer of energy from the piston into the fluid flow path to cause the creation of liquid droplets.

[0027] The invention will now be described with reference to the accompanying drawings. [Brief description of the drawings]

[0028] [Figure 1a] 1 shows a schematic cross-sectional view of a dispensing element according to the invention, with the piston in a first position; [Figure 1b] 2 shows a schematic cross-sectional view of a dispensing element according to the invention, with the piston in a second position; [Diagram 2] 1 shows a schematic perspective view of a printhead according to the present invention; [Diagram 3] 3 shows diagrammatically a further view of the printhead shown in FIG. 2; [Figure 4] FIG. 1 shows an example of a side view of two dispensing elements incorporating membranes. [Diagram 5] 1 illustrates an alternative configuration for the membrane. [Figure 6] 13 shows a further alternative configuration for the membrane. [Figure 7] 1A-1D show side views of a dispensing element fabricated by one of two different techniques. [Figure 8A] 1 shows a side view of a dispensing element fabricated by the other of two different techniques. [Figure 8B] FIG. 8B shows a top view of the dispensing element of FIG. 8A. [Figure 9] 1 shows an embodiment of a piezoelectric transducer array that is a single component providing multiple piezoelectric transducers. [Figure 10A] FIG. 2 is a side view of a printhead. [Figure 10B] FIG. 2 is an end view of a printhead. [Figure 10C] FIG. 2 is a plan view of a printhead. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] 1a shows a cross-sectional view of a dispensing element 10 according to a first embodiment of the invention. The dispensing element 10 comprises a dispensing plate 12.

[0030] A flow of liquid 14 is maintained on the upper surface of dispense plate 12, which thereby defines, in part, fluid flow path 13. Liquid 14 is constantly moving in the direction indicated by arrow A. Liquid 14 may be kept in motion by pumping the liquid across dispense plate 12, or by using gravity, or by any other suitable process well known in the art.

[0031] A piston 16 is suspended above dispense plate 12 in a first position. Piston 16 is preferably held in close proximity to dispense plate 12. For example, as shown in FIG. 1a, piston 16 may contact liquid 14 above dispense plate 12 in the first position. Piston 16 is arranged to move from this first close position in the direction indicated by arrow B to a second position spaced from dispense plate 12 shown in FIG. 1b. As piston 16 moves away from dispense plate 12, it moves to a position approximately 300 μm away from dispense plate 12. For example, it may move from within 100 μm of dispense plate 12 in the first position to a second position approximately 300 μm away from dispense plate 12. The selection of the distance the piston moves from dispense plate 12 is balanced with the selection of the piezoelectric actuation. The greater the distance from dispense plate 12 in the first position, the greater the force provided by the piezoelectric actuator will be. If the distance between the first position of the piston and dispensing plate 12 is very small, the reduced force on the piezoelectric actuator may still provide enough force to cause the ejection of a droplet of fluid through the orifice.

[0032] Dispensing orifice 18 is present in dispense plate 12. As shown in Figures 1a and 1b, piston 16 is located directly above dispensing orifice 18 when dispensing element 10 is fully assembled. Dispensing orifice 18 may be stamped or drilled into dispense plate 12, or may be formed by any other suitable process well known in the art.

[0033] With the piston 16 in its first position, the liquid 14 does not enter or pass through the dispensing orifice 18 due to its inertia.

[0034] When it is desired to dispense a drop of liquid from dispensing element 10, piston 16 is moved to its second position where piston 16 is moved away from dispensing plate 12. Using piezoelectric transducer 17, piston 16 is moved to its second position. Movement of the piston in the direction of arrow B creates a negative pressure in the area of ​​dispensing orifice 18, whereby the fluid flow not only moves laterally but is also forced towards dispensing orifice 18. This negative pressure causes the liquid to overcome the surface tension of liquid 14 adjacent to the dispensing orifice.

[0035] Eventually, the meniscus formed adjacent the dispensing orifice 18 breaks, forcing a droplet of liquid through the dispensing orifice, as depicted at item 20 (in FIG. 1b). This occurs via surface cavitation, which results in the ejection of a droplet having a diameter smaller than the diameter of the orifice 18 through which the droplet is dispensed. As a result of the use of a surface cavitation process, the droplet size is independent of the size of the orifice through which it is dispensed. The diameter of the droplet can thus be selected to be smaller than the orifice, which may simplify the manufacture of the device, as an orifice smaller than the droplet to be dispensed, and a corresponding flow path, is no longer required.

[0036] The mechanism of drop ejection relies on piston displacement in close proximity to the dispensing orifice 18 creating a directional pressure wave that results in the creation of the drop. The mechanism underpinning this effect differs from conventional drop-on-demand ink jets in that a non-directional pressure wave is generated in the dispensing volume adjacent to the dispensing orifice. The reported ejection mechanism is based on the phenomenon of induced surface cavitation.

[0037] It is known that when a solid object is dropped onto a liquid surface, jets will form that oppose the momentum of the object: these are the so-called "Worthington Jets".

[0038] This mechanism, which has been characterized and modeled in detail (see Phys. Rev. Lett. 102, 034502 -- Published 23 January 2009), describes the observation of jets as a result of a near-surface cavitation-implosion process, in which cavities collapse and produce jets in a direction opposite to the momentum of the solid object.

[0039] Our jetting principle also involves the creation of a cavitation phenomenon at the fluid surface that creates the fluid jetting process and results in the ejection of a well-defined drop from the fluid meniscus. The creation of piezoelectrically actuated "Jetting Cavities" underpins our approach to drop formation where the cavity dimensions govern the drop volume, rather than the dimensions of the dispensing orifice associated with conventional drop-on-demand ink jets.

[0040] Although the dispensing element depicted in Figures 1a and 1b includes a single piston and a single orifice, it is understood that multiple pistons and multiple orifices may be combined to form an array.

[0041] The choice of separation between adjacent pistons in an array is influenced by several factors, including the requirement to avoid "crosstalk" between one piston and an adjacent piston, provided that the separation of the pistons is sufficient such that any disruption to the fluid flow caused by the first piston is negligible when the liquid has traveled a further predefined threshold distance.

[0042] The piston 16 passes through a hole in the top plate 22 as shown. Fluid flow path 13 and the volume above top plate 22. Sealing means 24 may comprise, for example, a sealing ring, such as an O-ring, or a rubber grommet.

[0043] This arrangement has the beneficial effect that items located in the volume above the top plate 22 are insulated from the liquid 14. This can be useful in protecting sensitive components (e.g., electronics such as the piezoelectric transducer 17) that may be damaged by exposure to the liquid. This arrangement also has the beneficial effect of confining the liquid 14 to the channel 15, which allows the pressure of the fluid flow to be better monitored and controlled compared to an arrangement in which the liquid traverses across an open surface. This arrangement also reduces the rate at which the liquid flow dries out. This may be particularly desirable when the liquid used is a fast drying liquid such as ink.

[0044] FIG. 2 shows a perspective view of a printhead 30 with an array of dispensing elements 10 as described above with reference to FIG. 1. In this exemplary embodiment, the printhead comprises a 3×20 array. However, it will be readily appreciated that this particular choice of array configuration is not required. There may be more or fewer pistons in each dimension. Returning to the exemplary embodiment, three pistons are indicated at 104. Each piston has an associated piezoelectric element. Three piezoelectric elements are indicated at 102. The operation of the printhead 30 is the same as described above with reference to FIG. 1, but instead of a single piston, three are arranged in a row, and twenty of these rows are stacked side by side to form the array.

[0045] Figure 3 illustrates generally a further view of printhead 30 shown in Figure 2. In this view, a number of dispense orifices are visible in dispense plate 106. The position of each dispense orifice corresponds to the position of a piston suspended above dispense plate 106. Three dispense orifices are indicated at 108.

[0046] In each of the above embodiments, the pistons are configured to align with the orifices through which the fluid is to be ejected. The alignment of the pistons and orifices ensures consistency in the ejection of droplets, both in terms of the size of the dispensed droplets and the direction of the dispense relative to the dispense plate. It also ensures symmetry of the ejection from each orifice.

[0047] Actuation of the piezoelectric actuator is achieved by applying a voltage step from 0 to +50V over a period of a few microseconds. The print head may operate at a frequency of approximately 10 kHz. The voltage profile may be trapezoidal in shape. The use of a voltage pulse profile minimizes the time it takes to reset the miniscule shape to allow another drop to be ejected. In some embodiments, a trapezoidal pulse is deployed that includes a voltage rise with a higher slew rate than the voltage drop. For example, our voltage rise rate is 50V msec -1The relatively high voltage rise rates, ranging from 150 V / ms to 10 V / ms, allow the jetting principle to operate in the system.

[0048] The piezoelectric transducers used are typically around 200×10 -12 The transducers are stacked with a D31 value of m / V and a Q factor of 100. Based on an actuation drive pulse of ~50V, we can expect a linear displacement of about 10nm.

[0049] Piezoelectric actuation is typically applied at frequencies between 1 kHz and 100 kHz, and most preferably at frequencies in the range of 10 kHz to 50 kHz. Repeated ejection of droplets is essential for inkjet printing applications, and we have observed stable, repeated dispensing of droplets at up to 50 kHz using the design disclosed in this application. A large portion of the time between droplet dispenses is spent refilling the relevant portion of the fluid flow path. Factors that affect this refilling process are the surface tension of the fluid, the viscosity of the fluid, and whether the fluid is Newtonian or non-Newtonian.

[0050] [Piston-diaphragm component design] The design of the membrane 22 depicted in FIG. 4 is shaped to provide a substantially piston-like geometry, allowing the transfer of mechanical energy from the piezoelectric transducer 17 to the fluid without the need for a separate seal. In FIG. 4, the membrane 22 has a cylindrical protrusion 23 that extends perpendicular to the plane of the membrane 22. The dispensing plate 12 is shaped to provide a series of substantially cylindrical wells 21. The wells 21 have a diameter of approximately 1 mm, and the cylindrical protrusions 23 have a diameter of about 0.3 mm. This means that the protrusions can easily move up and down within the wells 21. The membrane 22 depicted in FIG. 4 is a single homogenous layer. The material selection is based on the requirement for compliance such that a liquid seal can be effectively made. It may be formed from silicon, for example.

[0051] Figure 5 shows a bi-layer membrane 22. The two layers may be made of different materials. The top layer 22a may be made of a material selected for its excellent sealing properties, such as silicone. The bottom layer 22b may be made of a low compressibility material to ensure that the energy from the piezoelectric transducer 17 is transferred into the fluid 14 rather than absorbed by the membrane 22. In the depicted configuration, there is a 5mm pitch between adjacent dispensing elements. The top layer 22a of the membrane is 1mm thick and the protrusions 23 are 4mm high.

[0052] Figure 6 shows a side view of two dispensing elements 10. In this view, the fluid flow path is into / out of the page. In this embodiment, the protrusions 23 are tapered. The tapered protrusions 23 in the illustrated embodiment are part of a homogenous membrane 22, but one skilled in the art will appreciate that tapered protrusions could also be arranged in a bi-layer configuration as shown in Figure 5. Tapered protrusions 23 are easier to manufacture than constant radius cylinders. Furthermore, the tapered shape may focus drop formation.

[0053] High reliability of the electrical connection is achieved by separating the fluid-containing areas from the non-fluid-containing areas with an integral membrane that serves to seal the components.

[0054] Additionally, the components used in the dispensing element 10 affect the ease and cost of manufacture. A printhead 30 formed from an array of dispensing elements 10 can replace hundreds of individual pistons with a single component. This has a significant simplification effect on the manufacture of the entire printhead assembly.

[0055] Furthermore, this jetting element design, which employs a membrane 22 to define one side of a microfluidic flow channel, allows for a more consistent fluid flow to be achieved as compared to multi-component assemblies.

[0056] [Design of Piezoelectric Transducer Components] The piezoelectric transducer 17 may be of stacked design, connected to the protrusion 23 of the membrane 22 in direct mechanical contact with the membrane 22 at right angles to the electrode-electrode axis. Direct mechanical contact is essential to ensure that the mechanical motion of the piezoelectric transducer is transmitted to the piston membrane at frequencies up to 100 kHz. Two examples are depicted in Fig. 7 and Fig. 8A. Fig. 7 shows the membrane 22 deformed to fit the piezoelectric transducer 17. Fig. 8A shows an adhesive bond 26 applied between the piezoelectric transducer 17 and the membrane 22. It should be understood that Fig. 7 and Fig. 8 show different bonding techniques, but depending on the configuration of the dispensing element, these techniques can be combined with each other and / or with other mechanical interference fits not shown in the illustrated embodiment.

[0057] 8B shows a top view of the membrane 22 showing adhesive 26 provided at six locations for attaching six piezoelectric transducers 17. In this embodiment, the piezoelectric transducers are 3 mm by 0.3 mm. The shallow transducers 17 allow the printheads 30 to be densely stacked, since the distance between adjacent wells 21 is governed by the diameter of the protrusions and not by the depth of the piezoelectric transducers 17.

[0058] 9 shows an embodiment of a piezoelectric transducer array 90, which is a single component providing multiple piezoelectric transducers 17. This "comb" configuration consists of several electrically isolated and mechanically integrated piezoelectric transducers 17.

[0059] [Print head assembly] The printhead 30 depicted in Figures 10A, 10B, and 10C is based on an array of ejection or dispensing elements 10. The construction of the array is essential to provide sufficient native resolution (ejection element pitch) to achieve high resolution printing based on on-demand delivery of ink drops.

[0060] The printhead 30 is most preferably constructed from a stack of interlocking layers, as best seen in the plan view of Figure 10C. A manifold 92 is provided for directing fluid into and collecting fluid from a single row of dispensing elements 10. Each dispensing element 10 includes a dispensing orifice 18, a well 21, a piezoelectric transducer 17, and a membrane 22 configured to provide a seal between a wetted portion of the printhead and a fluid-free portion housing the piezoelectric transducer 17.

[0061] 10B, the piezoelectric transducer 17 is aligned with a protrusion 23 that extends from and forms part of the membrane 22. The piezoelectric transducer 17 is also aligned with a dispensing orifice 18.

[0062] In the illustrated embodiment, the printhead 30 utilizes a membrane 22 that includes an array of protrusions 23 that are aligned with the dispenser orifices 18. This serves to align the dispenser orifices 18 with the array of protrusions 23, overcoming alignment problems associated with hundreds of separate piston elements.

[0063] [Fluid flow path] The piston ejection systems are most preferably configured in an array to create an imaging capable printhead 30. Each dispensing orifice 18 serves two main functions: 1.Delivers a continuous flow of ink to maintain particle suspension and eliminate air bubbles; 2. Maintaining a consistent meniscus pressure at the dispensing orifice; The ink is filled from a fluid delivery manifold 92 which performs the steps of:

[0064] Most preferably, the printhead 30 is configured as shown in Figures 10A, 10B, and 10C in which the dispense elements 10 are filled from a manifold 92 that is substantially parallel to the discharge manifold 94. This flow path design ensures consistent pressure in the dispense elements 10 based on substantially uniform pressure in the inlet manifold 92 and the outlet manifold 94 because the flow resistance in the manifolds is substantially lower than through the dispense elements 10. Of course, to ensure consistent flow through, the pressure is higher in the inlet manifold 92 than in the outlet manifold 94. The flow rate through is most preferably less than 0.1 mL min per nozzle. -1 ~0.5mLmin -1 It is.

[0065] Membrane 22 forms part of the fluid flow path and serves to seal one side of the microfluidic flow channel. The other side of the channel is formed by dispense plate 12. The nature of membrane 22 being a continuous, single component minimizes any turbulence effects associated with the interface between piezoelectric transducer 17 and membrane 22. This allows a highly consistent fluid flow to be achieved within print head 30.

[0066] The above described embodiments are exemplary only and other possibilities and alternatives within the scope of the invention will be apparent to those skilled in the art. [Aspect 1] a dispense plate including a plurality of orifices at least partially defining a fluid flow path; a plurality of piezoelectric transducers, each with a piston, configured to move perpendicular to the dispense plate between a first position in which the piston is proximate to the dispense plate and a second position in which the piston is spaced farther away from the dispense plate; A liquid dispensing element comprising: A liquid dispensing element, wherein each piston is configured, when actuated by a piezoelectric component, to move between the first position and the second position to create a directed pressure wave at a corresponding orifice in the dispensing plate, thereby causing a surface cavitation event in fluid flowing along the fluid path and resulting in the ejection of a droplet of fluid having a diameter smaller than a diameter of the orifice. [Aspect 2] 2. The liquid dispensing element according to claim 1, Each piston is configured to contact the fluid flow path when the piston is in the first position. [Aspect 3] The liquid dispensing element according to any one of the first and second aspects, A liquid dispensing element, wherein in a first position, the piston is at a distance of 5 μm to 500 μm from a plane of the dispensing plate. Aspect 4 The liquid dispensing element according to any one of the first to third aspects, A liquid dispensing element, wherein the second position of the piston is between 5 nm and 1 μm from the first position of the piston. Aspect 5 The liquid dispensing element according to any one of the first to fourth aspects, The piezoelectric transducer moves the piston by 10 -2 ms -1 From 10 -4 ms -1 The liquid dispensing element is configured to move at a speed of Aspect 6 6. The liquid dispensing element according to any one of the preceding aspects, Each piston is a tapered, liquid dispensing element. Aspect 7 7. The liquid dispensing element according to any one of the preceding aspects, The liquid dispensing element, wherein the orifice has a diameter in the range of 25 μm and 150 μm. Aspect 8 8. The liquid dispensing element of any one of the preceding aspects, comprising: The fluid dispensing element further comprising a top plate disposed substantially parallel to the dispense plate and defining the fluid flow path. Aspect 9 9. The liquid dispensing element according to embodiment 8, A liquid dispensing element, wherein the top plate defines a plurality of orifices through which the piston is configured to pass. Aspect 10 9. The liquid dispensing element according to embodiment 8, The liquid dispensing element, wherein the top plate is formed from a resilient material. Aspect 11 11. The liquid dispensing element according to claim 10, The liquid dispensing element, wherein the elastic material has a thickness in the range of 50 μm to 300 μm. Aspect 12 12. The liquid dispensing element of any one of the preceding aspects, comprising: The liquid dispensing element further comprises a seal between each orifice and the corresponding piston. Aspect 13 A printhead comprising an array of fluid dispensing elements according to any one of aspects 1 to 12. Aspect 14 14. The printhead according to claim 13, when dependent on claim 8, further comprising: The top plate seals the fluid flow path from the piezoelectric transducer. Aspect 15 14. The printhead according to claim 13, when dependent on claim 8, further comprising: The top plate has a series of protrusions configured to engage the pistons. Aspect 16 14. The printhead according to claim 13, when dependent on claim 8, further comprising: The top plate of the printhead has a two-layer construction. Aspect 17 1. A method for dispensing droplets of liquid, comprising: providing a dispensing plate having an orifice; providing a piston arranged such that the piston is movable between a first position in close proximity to the dispensing plate and a second position in which the piston is remote from the dispensing plate and covers the orifice; flowing a stream of liquid onto the dispensing plate; and moving the piston from the first position to the second position sufficiently fast to create a cavitation event that ejects droplets from the orifice, the droplets having a diameter smaller than the orifice and created by the cavitation event. [Explanation of symbols]

[0067] 10 Dispensing elements 12 Dispensing Plate 14 Fluid 15 Channels 16 Piston 17 Piezoelectric Transducer 18 Dispensing orifice 20 Liquid Drops 21 wells 22 Upper plate, membrane 22a Upper layer 22b Lower layer 23 Protrusion 24 Sealing Means 26 Adhesive Bond 30 Print Head 90 Piezoelectric Transducer Array 92 Fluid delivery manifold, suction manifold 94 Discharge manifold 102 Piezoelectric element 104 Piston 106 Dispensing Plate 108 Dispensing Orifice A The direction in which the liquid moves B Piston movement direction

Claims

1. a dispense plate including a plurality of orifices at least partially defining a fluid flow path configured to provide a steady flow of liquid across an upper surface of the dispense plate; a plurality of piezoelectric transducers, each with a piston, configured to move perpendicular to the dispense plate between a first position in which the piston is proximate to the dispense plate and a second position in which the piston is spaced farther away from the dispense plate; A liquid dispensing element comprising: A liquid dispensing element, wherein each piston is configured, when actuated by a piezoelectric component, to move between the first position and the second position to create a directed pressure wave at a corresponding orifice in the dispensing plate, thereby causing a surface cavitation event in the fluid constantly flowing along the fluid flow path and resulting in the ejection from the orifice of a droplet of liquid having a diameter smaller than a diameter of the orifice.

2. 2. The liquid dispensing element of claim 1, The liquid dispensing element, wherein each piston is configured to contact the fluid flow path when the piston is in the first position.

3. The liquid dispensing element according to claim 1 or 2, A liquid dispensing element, wherein in a first position, the piston is at a distance of 5 μm to 500 μm from a plane of the dispense plate.

4. The liquid dispensing element according to any one of claims 1 to 3, The liquid dispensing element, wherein the second position of the piston is between 5 nm and 1 μm from the first position of the piston.

5. The liquid dispensing element according to any one of claims 1 to 4, The piezoelectric transducer moves the piston by 10 -2 ms -1 From 10 -4 ms -1 The liquid dispensing element is configured to move at a speed of

6. The liquid dispensing element according to any one of claims 1 to 5, Each piston is a tapered, liquid dispensing element.

7. The liquid dispensing element according to any one of claims 1 to 6, The liquid dispensing element, wherein the orifice has a diameter in the range of 25 μm to 150 μm.

8. A liquid dispensing element according to any one of claims 1 to 7, comprising: The fluid dispensing element further comprising a top plate disposed substantially parallel to the dispense plate and defining the fluid flow path.

9. 9. The liquid dispensing element of claim 8, A liquid dispensing element, wherein the top plate includes a plurality of holes through which the piston is configured to pass.

10. 9. The liquid dispensing element of claim 8, The liquid dispensing element, wherein the top plate is formed from a resilient material.

11. 11. The fluid dispensing element of claim 10, The fluid dispensing element, wherein the elastic material has a thickness in the range of 50 μm to 300 μm.

12. The liquid dispensing element of claim 9, The liquid dispensing element further comprises a seal between each bore and the corresponding piston.

13. A printhead comprising an array of fluid dispensing elements according to any one of the preceding claims.

14. 14. The printhead of claim 13, the liquid dispensing element further comprises a top plate disposed substantially parallel to the dispense plate and defining the fluid flow path; The top plate seals the fluid flow path from the piezoelectric transducer.

15. 14. The printhead of claim 13, the liquid dispensing element further comprises a top plate disposed substantially parallel to the dispense plate and defining the fluid flow path; The top plate has a series of protrusions configured to engage the pistons.

16. 14. The printhead of claim 13, the liquid dispensing element further comprises a top plate disposed substantially parallel to the dispense plate and defining the fluid flow path; The top plate of the printhead has a two-layer construction.

17. 1. A method of dispensing droplets of liquid, comprising the steps of: providing a dispense plate with an orifice; providing a piston arranged to be movable between a first position in close proximity to the dispense plate and a second position in which the piston is spaced away from the dispense plate and covers the orifice; directing a stream of liquid onto an upper surface of the dispense plate; moving the piston from the first position to the second position sufficiently fast to create a cavitation event that ejects a droplet of liquid from the orifice, the droplet having a diameter smaller than a diameter of the orifice; A method for providing the above.

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