Method and apparatus for droplet deposition - Patents.com

Abstract

A method for depositing droplets of a fluid onto a medium using a droplet deposition head, the method comprising, in terms of an operating cycle, the following steps: accepting input data; assigning all of the fluid chambers in the array to either ejection chambers or non-ejection chambers based on the input data to create bands of one or more contiguous ejection chambers separated by bands of one or more contiguous non-ejection chambers; In each non-ejection chamber, when the non-ejection chamber is adjacent to a strip of the ejection chamber, one wall is actuated in the first direction while the other wall remains in the neutral position; if the non-ejection chamber is a single non-ejection chamber between bands of ejection chambers, both walls are actuated in the first direction simultaneously; if the non-ejection chamber is not adjacent to a strip of the ejection chamber, then both walls remain in the neutral position, are simultaneously actuated in the first direction, or are simultaneously actuated in the second direction; In each injection chamber, such that each of the first and second walls are actuated sequentially in the first direction; actuating the walls of the chamber; The method includes: Other methods, droplet deposition heads, droplet deposition devices, and computer programs are also provided.

Description

[Technical field]

[0001] The present invention relates to a method of depositing droplets of a fluid onto a medium using a droplet deposition head, such as a printhead, and to a droplet deposition head configured to carry out such a method, and to a droplet deposition apparatus including such a droplet deposition head. [Background technology]

[0002] Droplet deposition heads are now widely used in both traditional applications such as inkjet printing, as well as in material deposition applications such as 3D printing and other rapid prototyping techniques, and printing raised patterns on surfaces such as Braille or decorative raised patterns. In such material deposition applications, it may be desirable to deposit relatively large volumes of fluid onto a medium using a droplet deposition head. In some cases, the fluid may have novel chemical properties to adhere to the new medium and enhance the functionality of the deposited material.

[0003] In recent years, inkjet printheads have been developed that can deposit inks and varnishes directly onto ceramic tiles with high reliability and throughput, allowing tile patterns to be customized to customers' exact specifications, reducing the need to stock a full range of tiles.

[0004] In yet other applications, droplet deposition heads can be used to form elements such as color filters in LCD or OLED displays, such as those used in the manufacture of flat panel televisions.

[0005] It will thus be appreciated that droplet deposition heads continue to evolve and become specialized to suit new and / or increasingly challenging deposition applications. Nevertheless, while there has been a great deal of development in the field of droplet deposition heads, there remains room for improvement in the field of droplet deposition heads.

[0006] As background to this work, the mechanism by which droplets of fluid are ejected from an array of fluid chambers is shown in FIG. 1, which shows an array 10' of fluid chambers 12 forming part of a droplet deposition head, with a simplified version of the same array shown below. The chambers are surrounded on one side by a substrate 15. Adjacent fluid chambers 12 are separated by actuatable side walls 14 formed of a piezoelectric material such as lead zirconate titanate (also known as PZT). The chambers 12 on each side of each piezoelectric wall 14 are internally coated with a metal layer that acts as an electrode for applying a potential difference to the respective wall. That is, in this initial example, within a given chamber 12, a metal electrode layer extends from the inner wall on one side of the chamber to the inner wall on the other side of the chamber. However, this is not the only electrode configuration that can be used. For example, an electrode that extends from the inner wall on one side of the chamber to the inner wall on the opposite side of the chamber may be cut (e.g., by a laser) along the center of the fluid chamber, effectively splitting the electrode into two independently addressable electrodes (as shown in FIG. 2).

[0007] If the same potential is applied to electrodes on either side of a given wall, such that there is no potential difference across the wall, the wall will remain stationary. On the other hand, if different potentials are applied to electrodes on either side of a given wall, the wall will move due to the inverse piezoelectric effect, in which a potential difference is converted into motion. A wall that moves is sometimes referred to as an "active" wall, while a wall that remains stationary is sometimes referred to as an "inactive" wall.

[0008] FIG. 1 shows a simplified arrangement of chambers, where two chambers undergo a decrease in volume due to the inward movement of their walls. As a result, the pressure in these two chambers increases (indicated by "+") and the pressure in the adjacent chamber decreases (indicated by "-"). When the potential difference between the walls is high enough (e.g. to overcome the effects of surface tension and losses caused by the device), a droplet of fluid is forced out of the chamber with the increased pressure ("+") through the nozzle 16. Such chambers eject ("eject") droplets of fluid and are therefore referred to herein as "ejecting" chambers. FIG. 1 also shows two chambers (at the far right of the figure) whose walls are stationary and therefore do not change in volume. These chambers are referred to as "non-ejecting" chambers because they do not eject droplets of fluid. It should be noted that the chambers marked with "-" are either ejecting chambers (because they can be ejected later in the same actuation cycle) or non-ejecting chambers (if their walls do not react in the same actuation cycle and do not move in a way that causes ejection). However, for simplicity, throughout this description, ejection chambers are designated with a "+" or "-", while non-ejection chambers are blank, since the associated pressure increase / decrease is insufficient to cause ejection.

[0009] The chambers 12 are formed as channels surrounded on one side by a cover member 17 that contacts the actuatable wall. For each chamber, a nozzle 16 for fluid ejection is provided within the cover member 17. The cover member 17 may comprise a metal or ceramic cover plate that provides structural support and an overlying thin nozzle plate in which the nozzles are formed. Alternatively, a relatively thin nozzle plate may be used alone as the cover member.

[0010] In the example of FIG. 1 (and indeed throughout this disclosure), each of the actuatable piezoelectric walls 14 can comprise an upper half and a lower half split in a plane defined by the alignment direction (left to right in FIG. 1) and the channel extension direction (into the page in FIG. 1). The upper and lower halves of the piezoelectric walls can be polarized in opposite directions perpendicular to the channel extension direction and the alignment direction, such that when a potential difference is applied to the wall perpendicular to the alignment direction, the two halves deflect to bend towards one of the fluid chambers. Because the shape the deflected wall adopts resembles a chevron, this is sometimes referred to as a "chevron mode" of actuation. Alternatively, each of the actuatable piezoelectric walls can be polarized in a single way in a single direction (i.e., rather than the upper and lower halves being polarized in opposite directions), such that when a potential difference is applied to the wall, the wall deflects in a "shear mode" of actuation. Other methods of providing electrodes and polarized walls that can deflect the walls in a similar bending action have also been proposed.

[0011] Particularly relevant background art is described in WO 2010 / 055345, which discloses a method for depositing droplets on a substrate (so-called "print mode 1"). The method uses an apparatus such as an inkjet printhead having an array of channels, acting as fluid chambers and separated by interspersed walls, each channel communicating with an opening or nozzle for ejecting droplets of a fluid such as ink contained within the channel. Each wall separates two adjacent channels and is operable in response to a first potential difference to deform to reduce the volume of one channel and increase the volume of the other channel, and in response to a second potential difference to oppositely affect the volume of the adjacent channel. The method includes receiving input data, such as an array of image data pixels, assigning all channels in the array as either an ejection channel or a non-ejection channel based on the input data to generate a group of one or more consecutive ejection channels separated by a group of one or more consecutive non-ejection channels, and actuating walls of certain channels such that for each non-ejection chamber the walls move in the same direction or remain stationary and for each ejection chamber the walls move in opposite directions (see FIG. 3), or one wall remains stationary and the other moves (see FIG. 4). These actuations cause each of the ejection channels to eject at least one fluid droplet, and the resulting droplets form dots arranged in a straight line on the substrate, e.g., to form a representation of a line of image data pixels. The dots are separated in a line by gaps corresponding to the non-ejection channels.

[0012] 2 shows a droplet deposition head comprising an array 10 of fluid chambers 12 separated by spaced apart walls 14 formed of a piezoelectric material (e.g., PZT), each fluid chamber 12 communicating with an opening (nozzle) 16 for emitting droplets of fluid. Each of said walls 14 separates two adjacent fluid chambers 12, each fluid chamber 12 being defined by a first wall in a first direction relative to the fluid chamber and a second wall in a second direction relative to the fluid chamber, the second direction being opposite to the first direction.

[0013] In this example, on one side of each wall 14 (the right side in the illustrated example) there is a "common" electrode 19 to which a common potential is applied, and on the other side of each wall 14 (the left side as illustrated) there is an "active" electrode 18. The electrodes are connected to a drive circuit (not shown). Wall motion is induced by applying a drive potential to the "active" electrode 18 by a drive waveform that includes a series of drive pulses. If the drive potential is greater or less than the common potential, the wall will move. It will move towards the electrode with the highest potential.

[0014] 3 shows the wall movement in more detail in print mode 1. In this figure, and throughout this disclosure, underlining of fluid chambers indicates that they are assigned (based on input data) as the ejection chamber in a given cycle, a "-" in a chamber indicates that the chamber is undergoing a decrease in pressure (because the chamber's volume increases as a result of actuation of one or both walls of the chamber), and a "+" in a chamber indicates that the chamber is undergoing an increase in pressure (because the chamber's volume decreases as a result of actuation of one or both walls of the chamber).

[0015] In print mode 1, shown in Figure 3, the walls of the ejection chambers move in opposite directions. This means that the volume of the chambers alternately increases and decreases to cause ejection, while the walls of the non-ejection chambers move in the same direction. This means that there is no change in volume / pressure in the chambers and therefore no fluid is ejected.

[0016] At this point, it should be noted that the common potential applied to the "common" electrode is between the highest and lowest drive potentials in order for the walls of the droplet deposition head to move in a bidirectional manner in print mode 1. This droplet deposition head electrode configuration, and the application of a common potential to the electrodes of each wall, ensures that at least the walls of the non-firing chambers that are located between different swaths of firing chambers always move in the same direction.

[0017] In other words, if the drive potential applied to the "active" electrode is greater than the common potential, the wall moves toward the "active" electrode, whereas if the drive potential applied to the "active" electrode is less than the common potential, the wall moves toward the "common" electrode. If the drive potential applied to the "active" electrode is substantially equal to the common potential applied to the "common" electrode, the wall remains stationary (i.e., remains in a neutral, unactuated, resting position).

[0018] In print mode 1, wall movement of the non-ejection chambers prevents stagnation of fluid that can cause clogging of the chambers' nozzles over time. However, moving the walls of the non-ejection chambers is energy inefficient and can induce undesirable levels of heat in the droplet deposition head. Furthermore, it is difficult to eject a single droplet, i.e. 1 dpd (dpd = droplets per dot), because there is not enough energy in the wall movement to eject such a droplet.

[0019] It would therefore be desirable to provide a more energy-efficient printing method that overcomes the limitations of print mode 1 and also ejects single droplets when required.

[0020] Further relevant background art is provided in WO 2010 / 055344 A1, WO 2017 / 118843 A1, and WO 2018 / 224821 A9. Summary of the Invention

[0021] Aspects of the invention are set out in the accompanying independent claims and particular embodiments of the invention are set out in the accompanying dependent claims.

[0022] According to a first aspect of the present invention there is provided a method for depositing droplets of a fluid onto a medium utilising a droplet deposition head comprising: an array of fluid chambers separated by spaced apart walls formed from a piezoelectric material, each fluid chamber communicating with an opening for ejecting droplets of fluid, each of said walls separating two adjacent fluid chambers, each fluid chamber being defined by a first wall in a first direction relative to the fluid chamber and a second wall in a second direction relative to the fluid chamber opposite the first direction; each of the walls having a first electrode on a first side of the wall and a second electrode on a second side of the wall, the second electrode of each of the walls being connected to a common potential, the first electrode of each of the walls being selectively settable to one of (a) a drive potential different from the common potential and (b) the common potential, each of the walls being operable to move from a neutral position to a deformed position in the first direction in response to application of the drive potential to each of the first electrodes and to return or remain in the neutral position in response to application of the common potential to each of the first electrodes; and accepting input data in an operating cycle. assigning all of the fluid chambers in the array to either ejection chambers or non-ejection chambers based on the input data to create bands of one or more contiguous ejection chambers separated by bands of one or more contiguous non-ejection chambers; applying the common potential to the second electrode and selectively applying either the drive potential or the common potential to the first electrode based on the input data so that, for each non-emission chamber, one wall is actuated in the first direction and the other wall remains in the neutral position if the non-emission chamber is adjacent to a strip of ejection chambers, and both walls are actuated in the first direction simultaneously if the non-emission chamber is a single non-emission chamber between strips of ejection chambers, and both walls remain in the neutral position, are actuated in the first direction simultaneously, or are actuated in the second direction simultaneously if the non-emission chamber is not adjacent to a strip of ejection chambers; In each injection chamber, and actuating the walls of the chamber such that each of the first and second walls is actuated sequentially in the first direction; Upon actuation during the actuation cycle, each of the ejection chambers in the band of one or more contiguous ejection chambers ejects at least one droplet, the resulting droplets forming fluid masses arranged in a line on the medium, the fluid masses being separated in the line by intervals in each of the bands of non-ejection chambers, the size of each interval generally corresponding to the size of each of the bands of non-ejection chambers.

[0023] Because the ejection walls move in the same direction but at different times within the actuation cycle, this provides a more energy efficient method of printing compared to print mode 1 above, which is also capable of ejecting single drops when required.

[0024] According to a second aspect of the present invention there is provided a method for depositing droplets of a fluid onto a medium utilising a droplet deposition head comprising: an array of fluid chambers separated by spaced apart walls formed from a piezoelectric material, each fluid chamber communicating with an opening for ejecting droplets of fluid, each of the walls separating two adjacent fluid chambers, each fluid chamber being defined by a first wall in a first direction relative to the fluid chamber and a second wall in a second direction relative to the fluid chamber opposite the first direction, each of the walls having a first electrode on a first side of the wall and a second electrode on a second side of the wall, the second electrode of each of the walls being connected to a common potential, the first electrode of each of the walls being selectively settable to one of (a) a drive potential different from the common potential and (b) the common potential; Each of the walls is operable, in response to application of the drive potential to each of the first electrodes, for each of the walls to move in the first direction from a neutral position to a deformed position, and, in response to application of the common potential to each of the first electrodes, for each of the walls to return to or remain in the neutral position, in an actuation cycle: accepting input data; assigning all of the fluid chambers in the array to either ejection chambers or non-ejection chambers based on the input data to produce strips of one or more contiguous ejection chambers separated by strips of one or more contiguous non-ejection chambers; applying the common potential to the second electrode and selectively applying either the drive potential or the common potential to the first electrode based on the input data; In at least the first injection chamber, the first wall of the first injection chamber is repeatedly actuated in the first direction and then returned to the neutral position while the second wall of the first injection chamber is held in the neutral position; and selectively actuating the wall of the chamber such that, during the actuation cycle, when the first ejection chamber ejects a droplet of the fluid therein, the second wall of the first ejection chamber is selectively actuated in the first direction substantially simultaneously with the first wall of the first ejection chamber returning to the neutral position, thereby causing the first ejection chamber to eject a droplet of the fluid therein and thereafter causing the second wall of the first ejection chamber to return to the neutral position, wherein the actuation during the actuation cycle causes each of the ejection chambers of the one or more contiguous ejection chambers to eject at least one droplet, the resulting droplets forming a fluid mass arranged in a line on the medium, the fluid masses being separated in the line by respective intervals in each of the non-ejection chamber bands, the size of each interval generally corresponding to the size of each of the non-ejection chamber bands.

[0025] According to a third aspect of the present invention there is provided a method of depositing droplets of a fluid onto a medium utilising a droplet deposition head comprising: the array of fluid chambers separated by spaced apart walls formed from a piezoelectric material, each fluid chamber communicating with an opening for ejecting droplets of fluid, each of the walls separating two adjacent fluid chambers, each fluid chamber being defined by a first wall in a first direction relative to the fluid chamber and a second wall in a second direction relative to the fluid chamber opposite the first direction, each of the walls having a first electrode on a first side of the wall and a second electrode on a second side of the wall, the second electrodes of each of the walls being connected to a common potential, the first electrodes of each of the walls being: (a) connected to a first electrode connected to a second electrode ... first electrode connected to a second electrode connected to a second electrode connected to a first electrode connected to a first electrode connected to a second electrode connected to a second electrode connected to a first electrode connected to a first electrode connected to a second electrode connected to a second electrode connected to a first electrode connected to a first electrode connected to a first electrode connected to a second electrode connected to a second electrode connected to a first electrode connected and (c) a common potential, the common potential being between the first drive potential and the second drive potential, each of the walls being operable to move from a neutral position to a deformed position in the first direction in response to application of the first drive potential to each of the first electrodes, to move from the neutral position to a deformed position in the second direction in response to application of the second drive potential to each of the first electrodes, and to return or remain in the neutral position in response to application of the common potential to each of the first electrodes, in an actuation cycle: accepting input data; assigning all of the fluid chambers in the array as either ejection chambers or non-ejection chambers based on the input data to create strips of one or more contiguous ejection chambers separated by strips of one or more contiguous non-ejection chambers; applying the common potential to the second electrode and selectively applying either the first drive potential, the second drive potential, or the common potential to the first electrode based on the input data to generate at least a first ejection chamber; the first wall of the first ejection chamber is repeatedly actuated in the first direction and then in the second direction while the second wall of the first ejection chamber is held in the neutral position, and during the actuation cycle, when the first ejection chamber ejects droplets of the fluid therein, the second wall of the first ejection chamber is selectively actuated in the first direction substantially simultaneously as the first wall of the ejection chamber is actuated in the second direction, thereby causing the first ejection chamber to eject droplets of the fluid therein, and thereafter the second wall of the first ejection chamber is returned to the neutral position; Optionally, actuating the wall of the first ejection chamber such that the second wall of the first ejection chamber is actuated in the second direction simultaneously with actuation of the first wall of the first ejection chamber in the first direction, immediately prior to the first ejection chamber ejecting a droplet of the fluid therein in the actuation cycle, wherein said actuation during the actuation cycle causes each of the one or more consecutive ejection chambers in a band-like region to eject at least one droplet, the resulting droplets forming fluid masses arranged in a line on the medium, the fluid masses being separated in the line by respective intervals in each of the band-like regions of non-ejection chambers, the size of each interval generally corresponding to the size of each of the band-like regions of non-ejection chambers.

[0026] In the second and third aspects of the invention, the repetitive actuation preferably occurs substantially at the resonant frequency of the ejection chamber, or substantially at a harmonic or sub-harmonic of the resonant frequency of the ejection chamber.

[0027] Thus, advantageously, the print modes of the second and third aspects of the present invention allow the droplet deposition head to be operated at a high frequency while simultaneously reducing the number of accidental droplets during use and the amount of ink seeping out of the fluid chamber, which may otherwise result in the generation and ejection of unexpectedly large droplets.

[0028] Also provided are a droplet deposition head, a droplet deposition apparatus and a computer program for carrying out the methods of the first, second and third aspects of the invention. [Brief description of the drawings]

[0029] Embodiments of the present invention will now be described, by way of example only, with reference to the drawings in which: [Figure 1] FIG. 1 shows an array of fluid chambers forming part of a droplet deposition head with some of the chambers having actuated walls, below which is shown a simplified diagram of the same array with the same actuated walls. [Diagram 2] FIG. 2 is an end view of an array of fluid chambers showing the common and active electrodes connected to a common potential. [Diagram 3] FIG. 3 shows a simplified version of what is called "print mode 1." [Figure 4] FIG. 4 is another simplified diagram of print mode 1. [Diagram 5] FIG. 5 is a simplified diagram illustrating so-called "print mode 2" across an array of fluid chambers and the respective steps of ejecting droplets. [Figure 6] FIG. 6 illustrates first and second mirror image arrangements of fluid chambers, each configured to implement print mode 2 of FIG. [Figure 7] FIG. 7 is another diagram of print mode 2 and the steps of ejecting droplets. [Figure 8] FIG. 8 illustrates a pattern of pixels printed using the print mode of FIG. [Figure 9] FIG. 9 illustrates an arrangement of fluid chambers in which particular chamber walls are repeatedly actuated according to a first "harmonic" mode of actuation. [Figure 10] FIG. 10 illustrates an arrangement of the fluid chambers of FIG. 9 in which additional walls are selectively actuated to cause the ejection of droplets. [Figure 11]FIG. 11 illustrates an arrangement of fluid chambers in which certain chamber walls are repeatedly actuated according to a second "harmonic" actuation mode, while other walls are selectively actuated to cause the ejection of droplets. [Figure 12] FIG. 12 illustrates the printing of multiple consecutive lines (in this case four) using a swath of consecutive firing chambers. [Figure 13] FIG. 13 illustrates a pattern of pixels printed using the print mode of FIG. [Figure 14] FIG. 14 illustrates a variation of the print mode of FIG. 11 in which a selectively actuable portion of the wall is activated by a so-called "priming pulse" immediately prior to drop ejection. [Figure 15] FIG. 15 illustrates a pattern of pixels printed using the print mode of FIG. [Figure 16] FIG. 16 is a diagram showing an example of a driving waveform including a priming pulse immediately before an ejection pulse. [Figure 17] FIG. 17 illustrates another variation of the print mode of FIG. 11, in which a portion of the selectively actuable wall is driven by a so-called "cancel pulse" prior to drop ejection. [Figure 18] FIG. 18 illustrates the pattern of pixels printed using the print mode of FIG. [Figure 19] FIG. 19 shows an example of a drive waveform that includes a cancel pulse before the ejection pulse.

[0030] In the drawings, like elements are designated with like reference numbers. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] The present embodiment represents the best way known to applicant to carry out the invention, although it is not the only way that it may be accomplished.

[0032] This embodiment relates to what is referred to herein as "print mode 2."

[0033] Overview of droplet deposition head and droplet deposition device Referring again in particular to FIG. 2, the droplet deposition head used in print mode 2 comprises an array 10 of fluid chambers 12 separated by spaced apart walls 14 formed from a piezoelectric material, each fluid chamber 12 communicating with an opening 16 for ejecting droplets of fluid, each of said walls 14 separating two adjacent fluid chambers 12, each fluid chamber 12 being defined by a first wall in a first direction relative to said fluid chamber 12 and a second wall in a second direction opposite to said first direction relative to said fluid chamber 12. In the embodiment shown in FIG. 2, the first direction is left and the second direction is right, although this need not be the case. It should also be noted that said array 10 of fluid chambers 12 may not be the total number of fluid chambers present in the droplet deposition head. Additional arrays of fluid chambers may be present (e.g., as shown in FIG. 6), optionally separated or terminated by one or more non-ejecting chambers.

[0034] Each wall 14 has a first ("active") electrode 18 on a first side of the wall and a second ("common") electrode 19 on a second side of the wall, which are connected to drive circuitry (not shown). In the illustrated embodiment, the first side is in a first orientation relative to the wall and the second side is in a second orientation relative to the wall, although this need not be the case and in alternative embodiments the first and second electrodes could be reversed.

[0035] The second electrode 19 on each wall is connected to a common potential (which may be ground, 0V, or another value such as a positive potential higher than ground). The first electrode 18 on each wall is selectively settable by a drive waveform to one of (a) a drive potential different from the common potential, and (b) a common potential. In the illustrated embodiment, the drive potential (e.g. +V) is higher than the common potential (e.g. 0V). However, as discussed above, in alternative embodiments, the drive potential may be lower than the common potential.

[0036] In the illustrated embodiment, to simplify the drive circuitry and control electronics, all second electrodes 19 are exposed to the same common potential at the same time and all the time. However, in alternative embodiments, all second electrodes 19 need not be exposed to the same common potential. Instead, different groups of one or more second electrodes 19 may be exposed to different common potentials. Thus, the common potential need not be the same on each wall 14. Furthermore, different groups of one or more second electrodes 19 may receive the common potential at different times, rather than at the same time and all the time.

[0037] Each of the walls 14 is operable to move from a neutral position to a deformed position in the first direction in response to application of the drive potential to each of the first electrodes 18, and to return or remain in the neutral position in response to application of the common potential to each of the first electrodes 18.

[0038] In other words, by applying a drive potential signal to the first electrode 18 and a common potential signal to the second electrode 19, a potential difference is applied across each wall 14, the potential difference being the difference between the drive potential signal and the common potential signal. Such a potential difference causes deformation (actuation) of the walls. For the walls to not deform, there should be no potential difference across them. This is achieved by applying the same signal (i.e. the common potential signal) to both the first and second electrodes.

[0039] Devices such as that shown in FIG. 2 are commonly referred to as "side shooters" because the nozzles are located approximately to the sides of the fluid chamber. The nozzles are usually provided at equal distances from each end. In such structures, the ends of the channels are often left open so that all channels can communicate with one or more common fluid manifolds. This further allows a flow to be established along the length of the channels during use of the device to prevent stagnation of the fluid and to sweep debris in the fluid away from the nozzles. It is often found to be advantageous to make this flow along the length of the channels greater than the maximum flow through the nozzles due to fluid ejection. In other words, when the device operates at its maximum ejection frequency, the average flow rate of the fluid through each nozzle is less than the flow rate along each channel. Preferably, this flow rate is at least three times, and even more preferably five times, greater than the maximum flow rate through the nozzles due to fluid ejection.

[0040] To maximise the density of deposited droplets, it is preferred that during use all of the channels or chambers in the array are filled with an ejection fluid, such as ink, and are provided with openings or nozzles for ejecting the fluid.

[0041] Print mode 2 To address the increased temperatures and high power consumption that occurs with print mode 1, the current print mode 2 was introduced, in which the walls of the firing chamber generally move in the same direction (same orientation) but at different times within a single actuation cycle.

[0042] Figure 5, described in more detail below, shows a first example of the apparatus of Figure 2 undergoing a sequence of operations according to printing mode 2 and serves to explain the general principles of this mode. The nomenclature and directional conventions used above (i.e. references to first and second directions) are maintained.

[0043] At different times within a single cycle, chambers 1-5 experience an increase in pressure (denoted by a "+") due to one of their walls moving inward, causing a decrease in their volume. As can be seen, this inward movement causes a pressure drop (denoted by a "-") in two adjacent chambers, as the same wall movement acts to increase the volume of those two chambers. In the simplified representation used here, walls are represented by chevrons ("<" or ">") or vertical lines. The direction of wall deflection is represented by the direction the chevrons point, while undeformed walls are represented by vertical lines.

[0044] More specifically, Figure 5 shows a schematic of an actuator including an array of seven fluid chambers separated by actuatable walls, configured as shown in Figure 2. A band of ejection chambers 1 through 5 (shown underlined) is separated by non-ejection chambers 0 and 6.

[0045] Thus, in this example, every fluid chamber in the array of fluid chambers is assigned as either an ejection chamber (1 through 5) or a non-ejection chamber (0 and 6). A characteristic of wall-sharing devices is that each fluid chamber shares its wall with an adjacent chamber, which means that in a swath of ejection chambers, not all fluid chambers eject at exactly the same time.

[0046] Previous applications (e.g. WO2010 / 055345A1) have described (substantially) half of the ejection chambers ejecting in one half of a cycle, while the remaining (substantially) half of the ejection chambers ejecting in the other half of the cycle, but with the ejection of droplets from all ejection chambers (early and late cycle) occurring substantially simultaneously to form a single line of droplets separated by gaps in the deposition medium corresponding to the non-ejecting chambers.

[0047] In contrast, in the present print mode 2, all wall motions involved in droplet ejection are provided in at least two stages (e.g., stages 2.1 and 2.2 in FIG. 5, or stages 2.1, 2.2 and 2.3 in FIG. 7), with droplet ejection in these stages occurring within one cycle.

[0048] In the illustrated printing mode 2, each of the walls 14 is operable to move from its neutral (rest) position to a deformed position in response to application of a drive potential to each of the first electrodes 18, and to return or remain in the neutral position in response to application of a common potential to each of the first electrodes 18.

[0049] The method of operation includes, in a given (single) operating cycle, the following steps: accepting input data; assigning all of the fluid chambers 12 in the array 10 to either ejection chambers or non-ejection chambers based on the input data to create bands of one or more contiguous ejection chambers separated by bands of one or more contiguous non-ejection chambers; Applying a common potential to a second electrode 19 and selectively applying either a drive potential or the common potential to a first electrode 18 based on the input data to actuate the wall 14 of the chamber 12.

[0050] More specifically, in each non-ejection chamber: When the non-ejection chamber is adjacent to a strip of the ejection chamber, one wall is actuated in a first direction while the other wall remains in a neutral position (i.e., stationary); if the non-ejection chamber is a single non-ejection chamber between bands of ejection chambers, both walls are actuated simultaneously in a first direction (so as not to change the volume of the chamber); If the non-ejection chamber is not adjacent to a strip of the ejection chamber, then both walls may remain in a neutral position, may be configured to be actuated in a first direction simultaneously, or may be actuated in a second direction simultaneously (or may be actuated in the second direction simultaneously if the chambers are configured to be actuated in the second direction).

[0051] Meanwhile, in each injection chamber, Each of the first and second walls are actuated sequentially in a first direction (although it is not necessary that a particular wall be in front of the other wall).

[0052] Upon actuation during an actuation cycle, each ejection chamber in a band of one or more contiguous ejection chambers ejects at least one droplet, the resulting droplets forming fluid masses arranged in a line on the medium, the fluid masses being separated in a line by intervals in each of the bands of non-ejection chambers, the size of each interval corresponding generally to the size of each of the bands of non-ejection chambers.

[0053] -Example in Figure 5 In the particular example of FIG. 5, actuation of the wall 14 is carried out in the following steps.

[0054] Step 1: Start of one actuation cycle and assign all fluid chambers as ejection chambers (1-5) or non-ejection chambers (0 and 6).

[0055] For simplicity, at the start of an actuation cycle, all walls 14 in the array of fluid chambers 10 are in a neutral position (i.e., at rest) by applying a common potential to the first electrode 18. In this manner, the volume of each fluid chamber 12 is initially constant, although this may not always be the case.

[0056] Based on the input data, all fluid chambers 12 in the array 10 are assigned to either an ejection chamber or a non-ejection chamber to create bands of one or more contiguous ejection chambers separated by bands of one or more contiguous non-ejection chambers.

[0057] Steps 2.1 and 2.2: Actuate the wall to eject one or more droplets.

[0058] For each fluid chamber assigned as a non-injection chamber: If a non-ejection chamber is adjacent to a strip of an ejection chamber, one wall is actuated in a first direction while the other wall remains in a neutral position, i.e., stationary (e.g., as shown by fluid chambers 0 and 6 in FIG. 5). (Note that while movement of a single wall creates a pressure wave, it is not sufficient by itself to cause ejection.) If the non-ejection chamber is a single non-ejection chamber between bands of ejection chambers, then both walls are actuated in a first direction simultaneously to leave the volume of that chamber unchanged (e.g., as shown by fluid chamber 2 in Figure 7). If the non-ejection chamber is not adjacent to a strip of the ejection chamber, then both walls may remain in a neutral position or may be actuated simultaneously in a first direction (or may be actuated simultaneously in a second direction if the chambers are configured to actuate in a second direction).

[0059] Meanwhile, for each injection chamber, each of the first and second walls 18, 19 are actuated sequentially in a first direction (although not necessarily one prior to the other, as will be explained in more detail below). For example, as shown in FIG. 5, the walls may be actuated in two stages with a shared wall architecture as follows: In the first stage (step 2.1): Walls W1, W3, W5 act simultaneously in a first direction, increasing the volume of ejection chambers 1, 3, 5 and drawing in fluid (e.g. ink) (the first stage, the so-called "draw" step); Walls W2, W4, and W6 remain in a neutral position (i.e., stationary); After a short time has elapsed between steps 2.1 and 2.2, walls W1, W3 and W5 are released and return to their neutral position, the volume of injection chambers 1, 3 and 5 decreases and the pressure in the injection chambers increases (the "release" step in the first phase); Second stage (step 2.2): Walls W2, W4, and W6 act simultaneously in the same first direction, decreasing the volume of ejection chambers 1, 3, and 5, intensifying their actuation and forming droplets at the nozzles for ejection (the so-called "intensification" step of the first stage), while simultaneously drawing in an increasing amount of fluid (e.g., ink) into ejection chambers 2 and 4 (the "draw" step of the second stage); Walls W1, W3 and W5 remain in a neutral position (i.e. stationary).

[0060] Step 3: End of the cycle

[0061] After a short period of time, walls W2, W4, and W6 release and return to their neutral positions, the volume of ejection chambers 2 and 4 decreases, the pressure in the ejection chambers increases (the second stage "release" step), and droplets are ejected from their respective nozzles.

[0062] Droplets are ejected by the nozzles corresponding to the ejection chambers because each ejection chamber receives energy from both of its walls in both steps 2.1 and 2.2 of the cycle, unlike the non-ejection chambers 6, which do not receive energy from their walls 7 and do not eject in the first stage.

[0063] That is, in step 2.2, walls W2, W4, and W6 are actuated in a first direction to decrease the volume of ejection chambers 1, 3, and 5, pushing droplets out of those chambers, which results in ejection of droplets from those chambers. This is because walls W1, W3, and W5 are actuated in a first direction in step 2.1 to increase the volume of ejection chambers 1, 3, and 5, pulling in fluid. Thus, for ejection chambers 1, 3, and 5, the first and second walls of each ejection chamber are actuated asynchronously, with the first wall actuating before the second wall. Thus, each of ejection chambers 1, 3, and 5 receives energy from both its walls during a cycle.

[0064] On the other hand, as regards the ejection of droplets from ejection chambers 2 and 4, this occurs in stage 3 because walls W2, W4, and W6 return to their neutral positions, reducing the volumes of ejection chambers 2 and 4 to their original size, and because walls W3 and W5 moved earlier in the cycle, i.e., in step 2.1. Thus, in these ejection chambers 2 and 4, each of the first and second walls is non-galvanically actuated, with the second wall being actuated before the first wall. Thus, each of ejection chambers 2 and 4 receives energy from both of its walls during the cycle. Moreover, the initial draw pulses (step 2.1) of walls W3 and W5 can also be considered as pre-push pulses to eject ejection chambers 2 and 4, in order to introduce energy into the chamber in question when the other wall returns to its neutral position. The desired ejection is then possible.

[0065] Chambers 1, 3, and 5 represent a first group of ejection chambers, all of which are actuated to eject droplets simultaneously. Similarly, chambers 2 and 4 represent a second group of ejection chambers, all of which are actuated to eject droplets simultaneously. The second group of ejection chambers is actuated to eject droplets after the first group, with both the first and second groups being actuated within a single actuation cycle. In this manner, the ejection chambers within each group are actuated to eject droplets simultaneously, with the groups themselves being actuated sequentially within the actuation cycle. However, droplets from subsequent groups arrive on the medium at approximately the same time as the first group.

[0066] Thus, in summary, with respect to the steps of FIG. 5, in a first injection chamber (e.g., chamber 1), in an operating cycle, the method of operation includes: actuating a first wall (wall W1) of a first injection chamber (chamber 1) in a first direction while a second wall (wall W2) of said first injection chamber remains in a neutral position, thereby increasing the volume of said first injection chamber and drawing a large amount of fluid into said first injection chamber, and then returning said first wall (wall W1) of said first injection chamber to a neutral position; and then actuating the second wall (wall W2) of the first ejection chamber (chamber 1) in the first direction while the first wall (wall W1) of the first ejection chamber remains in the neutral position, thereby decreasing the volume of the first ejection chamber and causing the first ejection chamber to eject droplets of the fluid therein, and then returning the second wall (wall W2) of the first ejection chamber to the neutral position.

[0067] 5, a second ejection chamber (Chamber 2) is adjacent to a first ejection chamber (Chamber 1) and the second ejection chamber is in a second orientation relative to the first ejection chamber such that a second wall (Wall W2) of the first ejection chamber becomes a first wall of the second ejection chamber. During an actuation cycle, the actuation of the second wall (Wall W2) of the first ejection chamber in the first direction occurs while the second wall (Wall W3) of the second ejection chamber remains in a neutral position, thereby increasing the volume of the second ejection chamber and causing the second ejection chamber to draw in a large volume of fluid simultaneously with the ejection of the droplets from the first ejection chamber.

[0068] As described above, by returning the second wall (wall W2) of the first ejection chamber to a neutral position in the actuation cycle, the already present energy causes droplets of fluid to be ejected from within the second ejection chamber (as a result of the second wall (wall W3) of the second ejection chamber having already moved earlier in the actuation cycle).

[0069] However, if desired, the method may further include a supplemental step in the actuation cycle in which a second wall (wall W3) of a second ejection chamber is actuated in a first direction while a first wall (wall W2) of the second ejection chamber remains in a neutral position, thereby decreasing the volume of the second ejection chamber and causing the second ejection chamber to eject droplets of the fluid therein, and thereafter returning the second wall (wall W3) of the second ejection chamber to a neutral position. Also, by varying the potential difference applied to the second wall in the supplemental step, the characteristics of the ejected droplets (e.g., droplet volume and / or velocity) emitted by the second ejection chamber can be "fine-tuned".

[0070] As noted above, the arrangement of fluid chambers shown in Figure 5 need not be the total number of fluid chambers present in the droplet deposition head. Rather, there may be additional arrangements of fluid chambers, for example as shown in Figure 6, where a first arrangement includes fluid chambers 0-6 and a second arrangement includes fluid chambers 7-13. Chambers 1-5 form a first band of ejection chambers, and chambers 8-12 form a second band of ejection chambers. As shown, the ejection chambers of the first and second fluid chamber arrangements are separated by one or more non-firing chambers (in the illustrated example, chambers 6 and 7), which may advantageously isolate operation of the first arrangement from operation of the second arrangement.

[0071] As shown, the second array of fluid chambers (chambers 7-13) may be positioned as a near mirror image of the first array of fluid chambers (chambers 1-12) to cause the first and second arrays to operate in a balanced manner. Additionally, as also shown, movement of the walls of the second array of fluid chambers may substantially mirror movement of the walls of the first array of fluid chambers, again causing the first and second arrays to operate in a balanced manner. Vibrations in one array essentially cancel out corresponding vibrations in the other array, resulting in more accurate printing.

[0072] 6, both walls of each ejection chamber in the first strip region of ejection chambers (chambers 1-5) move continuously in a first direction, and both walls of each ejection chamber in the second strip region of ejection chambers (chambers 8-12) move continuously in a second direction. The movement of the walls of the second strip region of ejection chambers (chambers 8-12) mirrors the movement of the walls of the first strip region of ejection chambers (chambers 1-5), e.g., two strip regions of ejection chambers are separated by a strip region of non-ejection chambers that includes two fluid chambers (chambers 6 and 7).

[0073] However, it should be noted that not all of these features are necessary. For example, the strip of first and second ejection chambers can be separated by any number of non-ejection chambers, and the movement of the walls of the ejection chambers in the second strip of ejection chambers need not mirror the movement of the walls. The actuation cycle of the first strip of ejection chambers can start at the first wall of each ejection chamber in the strip of first and second ejection chambers, or at the second wall of each ejection chamber in the strip of first and second ejection chambers, or at any combination thereof. (In other words, in the second strip of ejection chambers, instead of walls W9, W11, W13, walls W8, W10, W12 may be actuated in the first stage.)

[0074] Example in Figure 7 Figure 7 shows a second example of the apparatus of Figure 2 undergoing a series of actuations in accordance with print mode 2. Figure 8 shows the pattern of pixels to be printed. In this example, we focus in particular on the highlighted line of pixels, where the first, third and fifth pixels are white pixels, and the second and fourth pixels are black pixels. This means that to print this particular row, fluid chambers 0, 2 and 4 are assigned as non-ejection chambers, and fluid chambers 1 and 3 are assigned as ejection chambers.

[0075] As mentioned above, the walls of each non-ejection chamber operate as follows. When a non-ejection chamber is adjacent to a strip of an ejection chamber, one wall is actuated in a first direction while the other wall remains in a neutral position, i.e., stationary (e.g., as shown by fluid chambers 0 and 6 in FIG. 7). If the non-ejection chamber is a non-ejection chamber between bands of ejection chambers, both walls are actuated simultaneously in a first direction to leave the volume of the chamber unchanged (e.g., as shown by fluid chamber 2 in FIG. 7). If the non-ejection chamber is not adjacent to a strip of the ejection chamber, then both walls remain in a neutral position or actuate simultaneously in a first direction (or may actuate simultaneously in a second direction if the chambers are configured to actuate in a second direction).

[0076] Meanwhile, for each ejection chamber, each of the first and second walls act in sequence in the first direction (although it is not necessary that any particular wall be in front of the other). For example, as shown in FIG. 7, the walls act as follows: In the first stage (2.1), we have: While wall W1 is actuated in a first direction to draw an increasing volume of fluid (e.g., ink) into ejection chamber 1 (first stage "draw" step), Walls W2, W3, and W4 remain in a neutral position (ie, stationary). After a short period between 2.1 and 2.2, wall W1 is released and returns to its neutral position, the volume of injection chamber 1 decreases and the pressure in injection chamber 1 increases (first stage "release" step). Second stage (2.2): Walls W2 and W3 are simultaneously actuated in the same first direction to reduce the volume of ejection chamber 1 and intensify the actuation to form a droplet for ejection at the nozzle (first phase, "intensify" step). Both walls W2 and W3 are moved in the first direction while ejection chamber 2 remains constant by simultaneously increasing and drawing in an increasing volume of fluid (e.g., ink) into ejection chamber 3 (second phase, "draw" step). Walls W1 and W4 remain in a neutral position (i.e., stationary). After a short period between 2.2 and 2.3, walls W2 and W3 are released and return to their neutral position, keeping the volume of non-injection chamber 2 constant and the volume of injection chamber 3 decreasing, increasing the pressure in injection chamber 3 (the second "release" step), and Phase 3 (2.3): Wall W4 acts in the same first direction, decreasing the volume of injection chamber 3, intensifying the actuation and forming droplets at the nozzle for ejection (the "intensification" step of the second phase); and After a short period of time, wall W3 is released and returns to its neutral position.

[0077] More generally, with respect to the steps of FIG. 7, the method of operation of the present invention allows a strip of a first ejection chamber (Chamber 1; the first strip may include one or more chambers) and a strip of a second ejection chamber (Chamber 3; again, the second strip may also include one or more chambers) to be separated by a single non-ejection chamber (Chamber 2). This non-ejection chamber is in a second direction relative to the strip of the first ejection chamber (Chamber 1), and the strip of the second ejection chamber (Chamber 3) is in a second direction relative to the non-ejection chamber (Chamber 2). Thus, In the band-shaped region consisting of the first injection chamber, the second wall (wall W2) of the first injection chamber (chamber 1) adjacent to the non-injection chamber (chamber 2) is the first wall of the non-injection chamber (chamber 2). In the band-shaped region consisting of the second ejection chamber, the first wall (wall W3) of the second ejection chamber (chamber 3) adjacent to the non-ejection chamber (chamber 2) is the second wall of the non-ejection chamber (chamber 2).

[0078] The method includes, in an operating cycle: actuating a first wall (wall W1) of a first ejection chamber (chamber 1) in a first direction while a second wall (wall W2) of the first firing chamber remains in a neutral position, and returning the first wall (wall W1) of the first ejection chamber to a neutral position; and thereafter actuating the second wall (wall W2) of the first ejection chamber (chamber 1) and the first wall (wall W3) of the second ejection chamber (chamber 3) simultaneously in a first direction while the second wall (wall W4) of the second ejection chamber (chamber 3) remains in a neutral position, thereby ejecting a droplet of fluid from the first ejection chamber (chamber 1) while keeping the volume of the non-ejection chamber (chamber 2) constant, and then returning the second wall (wall W2) of the first ejection chamber (chamber 1) and the first wall (wall W3) of the second ejection chamber (chamber 3) to their neutral positions; actuating a second wall (wall W4) of the second ejection chamber (chamber 3) in a first direction while a first wall (wall W3) of the second ejection chamber (chamber 3) remains in a neutral position, thereby causing the second ejection chamber (chamber 3) to eject droplets of fluid therein, and then returning the second wall (wall W4) of the second ejection chamber (chamber 3) to the neutral position.

[0079] Harmonized Operation Mode At higher printing frequencies, print modes 1 and 2 are observed to be most stable at subharmonics (or narrow bands around) the acoustic resonance frequency. In conventional multi-cycle printing modes, a "cancellation pulse" is used to effectively cancel the pressure wave remaining in the channel after actuation, returning the pressure in the channel to substantially the initial state before actuation. In single cycle ejection schemes, it is not usually possible to use an (effective) cancellation pulse. However, in the "harmonic actuation modes" to be described, the inventors have discovered that it is advantageous to purposefully actuate near the fundamental acoustic resonance frequency (also referred to herein as the "resonance frequency") or its subharmonics (i.e., 1 / N of the acoustic resonance frequency, where N is an integer).

[0080] To this end, a variation of the above-mentioned print mode 2 is described with reference to Figures 9 to 19. Here, certain walls (typically, but not necessarily, alternating walls) within a strip of one or more ejection chambers are repeatedly and oscillatorily actuated simultaneously between a neutral position and a first direction (as in Figures 9 and 10) or between a first direction and a second direction (as in Figure 11). At a particular time in the actuation cycle, when the ejection chamber ejects a droplet, the other wall of the ejection chamber is selectively actuated inwardly within the ejection chamber, substantially simultaneously with the inward movement of the repeatedly actuated wall. The expression "substantially simultaneously" means "simultaneously with, or slightly before or after, the inward movement of the repeatedly actuated wall" and refers to a condition for applying sufficient pressure to the fluid in the ejection chamber to eject a droplet. For example, while the cyclically actuating wall is moving inwardly from a first direction to a neutral direction (as in FIG. 10) or from a first direction to a second direction (as in FIG. 11), the other wall of the chamber may be selectively actuated from its neutral position in the first direction. In such a situation, the movements occur substantially simultaneously. To optimize the efficiency of the actuation process, the cyclically actuating wall preferably operates substantially at the fundamental acoustic resonant frequency of the ejection chamber (also referred to herein as the "resonant frequency") or is actuated at a harmonic or sub-harmonic of the resonant frequency of the ejection chamber.

[0081] Example of Figures 9 and 10 (first example of harmonic operation mode) Figures 9 and 10 show a first example of a harmonic actuation mode. Figure 10 is substantially a continuation of Figure 9, where Figure 9 shows that certain walls (walls W1, W3, and W5) are actuated repeatedly between a first direction and a neutral position, preferably at the resonant frequency of the chamber. In Figure 10, certain fluid chambers designated as ejection chambers (chambers 1-5) are shown drawing in fluid, followed by a timed actuation of the opposing wall in a first direction (inward) to eject a droplet. This coincides with the inward movement of the repeatedly actuated walls.

[0082] Thus, in step 0 of FIG. 9, the alternating walls W1, W3, and W5 are actuated in a first direction and return to a neutral position. This is done at (or near) the resonant frequency of the chambers. This motion is repeated oscillatorily, providing energy to the system without ejecting droplets, since the energy imparted to the meniscus of the fluid in the chamber adjacent to the wall is insufficient to overcome the effects of surface tension and the losses caused by the nozzle. Walls W2, W4, and W6 remain in a neutral position (i.e., stationary). Following the nomenclature and directional conventions used above, the repeatedly actuated walls W1, W3, and W5 can be considered as first walls in a first direction relative to chambers 1, 3, and 5, and walls W2, W4, and W6 are second walls in a second direction relative to chambers 1, 3, and 5.

[0083] As indicated by the underlining in Figure 9 (and maintained in Figure 10), in step 1 of the actuation method, based on input data, all fluid chambers are assigned as ejection chambers (chambers 1-5) or non-ejection chambers (chambers 0 and 6). The iterative actuation of the first wall described above may be performed before the chambers are assigned, but in any case continues after the chambers are assigned.

[0084] Referring now to FIG. 10, the walls of each non-ejection chamber (chambers 0 and 6) operate as follows. If the non-ejection chamber is a single non-ejection chamber between bands of ejection chambers, both walls act simultaneously in the first direction to avoid changing the volume of the ejection chamber. One wall is actuated in a first direction while the other wall remains in a neutral position, or both walls remain in a neutral position.

[0085] The walls of each injection chamber (Chambers 1-5) operate as follows. First stage (step 2.1): Walls W1, W3, and W5 continue to move (substantially) in the first direction at the harmonic frequency of the chamber, while walls W2, W4, and W6 remain in a neutral position (i.e., stationary). After a short period between steps 2.1 and 2.2, walls W1, W3, and W5 are released and return to a (substantially) neutral position at the harmonic frequency of the chambers, the volume of ejection chambers 1, 3, and 5 decreases, and the pressure in ejection chambers 1, 3, and 5 increases. Second stage (step 2.2): At substantially the same time that walls W1, W3, and W5 return to their neutral positions, walls W2, W4, and W6 are actuated in the same first direction under the influence of the ejection pulse of the drive waveform, adding the energy required to eject all drops from all firing chambers, decreasing the volume of ejection chambers 1, 3, and 5, and forming the ejected drops at each corresponding nozzle, and simultaneously increasing the volume of ink and drawing ink into ejection chambers 2 and 4 while walls W1, W3, and W5 remain in their neutral positions (i.e., stationary). After a short period between steps 2.2 and 2.3, walls W2, W4, and W6 are released and return to the neutral position. Third stage (step 2.3): walls W1, W3, and W5 continue to move in a first direction (substantially) at the harmonic frequency of the chambers, reducing the volume of ejection chambers 2 and 4 and forming droplets for ejection at each of the corresponding nozzles; Walls W2, W4, and W6 remain in a neutral position (i.e., stationary); After the short period between steps 2.3 and 3, walls W1, W3, and W5 are released and return to a (substantially) neutral position at the harmonic frequency of the chamber, After injection, walls W1, W3, W5 are again actuated in the initial direction, returning to a (substantially) neutral position at the harmonic frequency of the chamber, as shown in step 0.

[0086] More generally, with respect to the steps of FIGS. 9 and 10, the method comprises, in a given (single) operating cycle: accepting input data; assigning all of the fluid chambers in the array as either ejection chambers or non-ejection chambers based on the input data to create strips of one or more contiguous ejection chambers separated by strips of one or more contiguous non-ejection chambers; applying the common potential to the second electrode and selectively applying either the drive potential or the common potential to the first electrode based on the input data to generate at least a first ejection chamber: the first wall of the first injection chamber is repeatedly actuated in the first direction and then returned to the neutral position while the second wall of the first injection chamber is held in the neutral position; and (c) actuating the walls of the chamber such that, in the actuation cycle, when the first ejection chamber ejects droplets of the fluid therein, the second wall of the first ejection chamber is selectively actuated in the first direction substantially simultaneously with the first wall of the first ejection chamber returning to the neutral position, thereby causing the first ejection chamber to eject droplets of the fluid therein and thereafter causing the second wall of the first ejection chamber to return to the neutral position. The aforementioned "time in the actuation cycle" at which the selective actuation of the second wall occurs may be immediately after the allocation of an ejection chamber, prior to the completion of a first repeated actuation of the first wall, but preferably the first wall is repeatedly actuated at least once before the selective actuation of the second wall occurs.

[0087] said actuation during said actuation cycle causes each of said ejection chambers in said strip of one or more contiguous ejection chambers to eject at least one droplet; the resulting droplets form a fluid mass disposed in a line on the medium; the fluid bodies being separated along the line by intervals in each of the bands of the non-ejection chamber; The size of each of the gaps generally corresponds to the size of each of the bands of non-emission chambers.

[0088] As shown in Figure 10, the first ejection chamber may be part of a first group of one or more ejection chambers (chambers 1, 3 and 5) interleaved with each ejection chamber of a second group of one or more ejection chambers (chambers 2 and 4), where the first walls (walls W1, W3 and 5) of each of the parts of the first group of ejection chambers are repeatedly actuated simultaneously in the first direction and then returned to the neutral position.

[0089] A second ejection chamber (e.g., chamber 2) that is part of the second group of ejection chambers may be adjacent to each first ejection chamber (e.g., chamber 1), and the second ejection chamber is in the second direction relative to the first ejection chamber such that the second wall (e.g., wall W2) of the first ejection chamber becomes the first wall of the second ejection chamber.

[0090] The method further comprises the steps of: maintaining the second wall (Wall W3) of the second ejection chamber (Chamber 2) in the neutral position while the second wall (Wall W2) of the first ejection chamber (Chamber 1) is actuated to eject the droplets of the fluid therein; and thereafter substantially simultaneously while the first wall (wall W2) of the second ejection chamber (chamber 2) is in the neutral position, actuating the second wall (wall W3) of the second ejection chamber (chamber 2) in the first direction, thereby causing the second ejection chamber (chamber 2) to eject droplets of the fluid therein, and thereafter returning the second wall (wall W3) of the second ejection chamber (chamber 2) to the neutral position; It may further include.

[0091] It will be understood that the second wall (wall W3) of the second ejection chamber (chamber 2) is itself repeatedly actuated in the first direction and returned to the neutral position in synchronism with the repeatedly actuating the first wall (wall W1) of the first ejection chamber (chamber 2), since the first ejection chamber (chamber 1) and in particular the second ejection chamber (wall W3) may become the first wall of the subsequent ejection chamber of the first group. All first walls of the firing chambers of the first group are repeatedly actuated in synchronism with each other.

[0092] Chambers 1, 3, and 5 represent a first group of ejection chambers, all of which are actuated to eject droplets simultaneously. Similarly, chambers 2 and 4 represent a second group of ejection chambers, all of which are actuated to eject droplets simultaneously. The second group of ejection chambers is actuated to eject droplets after the first group, with both the first and second groups being actuated within a single actuation cycle. Thus, the ejection chambers within each group are actuated to eject droplets simultaneously within an actuation cycle, with the groups themselves being actuated sequentially.

[0093] Example of FIG. 11 (second example of harmonic operation mode) Figure 11 shows a second example of a harmonic actuation mode similar to Figure 10, except that whereas in Figure 10 the walls are actuable between a neutral position and a first orientation, in Figure 11 the walls are actuable between a first orientation and a second orientation. This is accomplished by the second electrode of each wall being connected to a common potential (e.g., +V) and the first electrode of each wall being selectively settable to one of (a) a first drive potential (e.g., 0V), (b) a second drive potential (e.g., ++V), and (c) a common potential (e.g., +V), the common potential being between the first drive potential and the second drive potential. Each of the walls is operable such that in response to application of a first drive potential to a respective first electrode, each wall moves in a first direction from a neutral position to a deformed position, and when a second drive potential is applied to the respective first electrode, each wall moves in a second direction from the neutral position to the deformed position, and in response to application of a common potential to the respective first electrode, each wall returns to or remains in the neutral position.

[0094] Thus, in step 0 of FIG. 11, the pinching walls W1, W3, and W5 are actuated in a first direction and then in a second direction at (or substantially at) the harmonic frequency of the chambers, without stopping in a neutral position. This motion is repeated oscillatorily, providing energy to the system without ejecting droplets, since the energy imparted to the meniscus of the fluid in the chamber adjacent to the wall is insufficient to overcome the effects of surface tension and the losses caused by the nozzle. Walls W2, W4, and W6 remain in a neutral position (i.e., stationary). Following the nomenclature and directional rules used above, the repeatedly actuated walls W1, W3, and W5 can be considered as first walls in a first direction relative to chambers 1, 3, and 5, and walls W2, W4, and W6 can be considered as second walls in a second direction relative to chambers 1, 3, and 5.

[0095] As shown by the underlining in Figure 11, the fluid chambers are assigned as ejection chambers (in this case chambers 1, 3, 5) or non-ejection chambers (chambers 0, 2, 4, 6) based on the input data. The iterative actuation of the first wall described above may be performed before the chambers are assigned, but in any case continues after the chambers are assigned.

[0096] The walls of each injection chamber (Chambers 1-5) operate as follows. First stage (2.1): Walls W1, W3, and W5 are actuated in a first direction (substantially) at the harmonic frequency of the chamber, while walls W2, W4, and W6 remain in a neutral position (i.e., stationary). Second stage (2.2): Walls W1, W3, and W5 are actuated in the second direction (substantially) at the harmonic frequency of the chamber. Meanwhile, walls W2, W4, and W6 are actuated in the first direction by the influence of the ejection pulse in the drive waveform, substantially simultaneously with the actuation of walls W1, W3, and W5 in the second direction, so that the energy required to eject all is available. Droplets from all ejection chambers are added to the actuation cycle, reducing the volume of ejection chambers 1, 3, and 5, forming the droplets that are ejected at each corresponding nozzle. Then, after ejection, walls W1, W3, and W5 are actuated again in the first direction and then in the second direction (substantially) at the harmonic frequency of the chamber, as shown in step 0.

[0097] For each non-ejection chamber, if it is not a single non-ejection chamber between bands of ejection chambers, the walls operate in the following operating cycle: One wall is actuated either in the first direction only (e.g. wall W6), or in both the first and second directions (e.g. wall W1), while the other wall remains in the neutral position (e.g. walls W0 and W7), or both walls remain in the neutral position. On the other hand, if a single non-ejection chamber is located between bands of ejection chambers, the walls operate in an actuation cycle as follows. In a first stage (2.1) one wall (e.g. wall W3) is actuated in a first direction while a second wall (e.g. wall W2) remains in a neutral position. Then in a second stage (2.2) one wall (e.g. walls W2 and W4) is actuated in said first direction and the other wall (e.g. walls W3 and W5) is actuated in said second direction.

[0098] More generally, with respect to the steps of FIG. 11, the method comprises, in a given (single) operating cycle: accepting input data; assigning all fluid chambers in the array to either ejection chambers or non-ejection chambers based on the input data to create bands of one or more contiguous ejection chambers separated by bands of one or more contiguous non-ejection chambers; applying the common potential to the second electrode, and selectively applying either the first driving potential, the second driving potential, or the common potential to the first electrode based on the input data; In at least a first injection chamber (e.g., chambers 1, 3, and 5), a first wall (walls W1, W3, and W5) of the or each first firing chamber is repeatedly actuated in a first direction and then in a second direction without stopping in a neutral position, while a second wall (walls W2, W4, and W6) of the or each first firing chamber remains in a neutral position; In the actuation cycle, when one or more first ejection chambers eject droplets of the fluid therein, the second walls (walls W2, W4, and W6) of each first ejection chamber are selectively actuated in the first direction substantially simultaneously with the actuation of the first walls of the ejection chambers in the second direction, thereby causing each first ejection chamber to eject droplets of the fluid therein, and thereafter, the second walls (walls W2, W4, and W6) of each first ejection chamber are returned to the neutral position. As mentioned above, the aforementioned "time in the actuation cycle" at which the selective actuation of the second walls occurs may be before the first repeated actuation of the first walls is completed and may be immediately after the allocation of the ejection chambers. However, it is preferred that the first walls are repeatedly actuated at least once before the selective actuation of the second walls occurs.

[0099] The or each first ejection chamber may be part of a first group of one or more ejection chambers (chambers 1, 3 and 5) interleaved with each ejection chamber of a second group of one or more ejection chambers (chambers 2 and 4), and the first walls (walls W1, W3, W5) of each of the components of the first group of group ejection chambers are repeatedly actuated simultaneously in the first direction and then in the second direction.

[0100] Example of Figure 12 Printing multiple lines 12, if it is desired to print a series of five drops in chambers 1 through 5, then all chambers from chamber 1 through chamber 5 are assigned as ejection chambers. However, in practice, the release of walls W2 and W4 and the movement of walls W3 and W5 in a first direction may or may not be sufficient to cause drops to be ejected from chambers 2 and 4.

[0101] If the drive pulses applied to walls W2 and W4 have a high enough potential difference to overcome the effects of surface tension when these walls are released, droplets will be ejected from chambers 2 and 4. However, there is expected to be some variability in these droplets; as the speed and volume increase, the print becomes less uniform.

[0102] One way to solve this problem is to print the droplets as multiple consecutive lines, as shown in Figure 12. This results in the pattern shown in Figure 13. In this way, the energy of the previous pulse will overcome the surface tension effect and eject all chambers 1-5 as shown in Figure 12. However, this can cause consecutive droplets to merge in flight, again affecting the uniformity of the print.

[0103] Note that the wall motion described with reference to Figures 11 and 12 is identical. Droplets may be fired from every other nozzle or from every nozzle. This may vary depending on the number of rows being printed. This basic implementation is likely to result in non-uniform drop formation within the printhead, but is improved upon in more advanced techniques described next with reference to Figures 14 to 19.

[0104] A variation of FIG. 14 using a priming pulse Figure 14 shows a variation of the harmonic actuation mode of Figure 11. In this example, a so-called "priming pulse" is included in the drive waveform to ensure well-defined drop ejection.

[0105] Similar to the example of Figure 11, in Figure 14 alternating walls W1, W3, and W5 are actuated in a first direction and a second direction (substantially) at the harmonic frequency of the chamber. This motion is repeated to energize the system without ejecting droplets (step 0 in Figures 11 and 14).

[0106] For ejection, all fluid chambers are assigned as ejection chambers (1, 2, 3, 4, and 5) or non-ejection chambers (0 and 6). Figure 14 shows the wall movement to eject a line, resulting in the pattern shown in Figure 15.

[0107] To illustrate the effect of the priming pulse, note that the wall W2 (second wall of the first ejection chamber, chamber 1), which remained in a neutral position in stage 2.1 of FIG. 11, is actuated in a second direction (by a priming pulse) simultaneously with the actuation in the first direction of the first wall (W1) of the first ejection chamber in stage 2.1 of the variant of FIG. 14. This actuation of the second wall (W2) of the first ejection chamber occurs immediately before stage 2.2, when the first ejection chamber ejects droplets of fluid therein. In effect, the actuation of wall W2 in stage 2.1 serves to prime wall W2 so that it gives more energy when it is actuated to cause droplet ejection in stage 2.2. As a result, even after stage 2.2, wall W2 still possesses enough energy to effectively contribute to the success of droplet ejection in stage 2.3.

[0108] More specifically, the walls of each injection chamber (chambers 1-5) operate as follows. First stage (2.1): Walls W1, W3, and W5 operate in a first direction (substantially) at a harmonic frequency of the chamber to provide some energy within the chamber; Walls W2 and W4 act in a second direction under the influence of the priming pulse, providing some priming energy to the chamber. Second stage (2.2): Walls W1, W3, and W5 operate in a second direction (substantially) at the harmonic frequency of the chamber; Walls W2, W4, and W6 are actuated in a first direction under the influence of firing pulses in the drive waveform substantially simultaneously with actuation of walls W1, W3, and W5 in a second direction such that the energy required to eject all of them is available. Drops from all firing chambers are added to the actuation cycle, decreasing the volume of firing chambers 1, 3, and 5 to form droplets that are ejected at each corresponding nozzle. Third stage (2.3): Walls W1, W3, and W5 are again actuated in a first direction (substantially) at the chamber harmonic frequency to provide some energy to the chamber; Walls W2, W4, and W6 are released, chambers 2 and 4 eject droplets due to the priming energy previously provided by the priming pulse, and after ejection, walls W1, W3, and 5W are again actuated in the first direction and are actuated (substantially) in the second direction at the harmonic frequency of the chambers, as shown in step 0.

[0109] For each non-ejection chamber, the walls operate as follows. One wall is actuated either in a first direction only (e.g., wall W6), or in both the first and second directions (e.g., wall W1), while the other wall remains stationary (e.g., walls W0 and W7), or both walls remain in a neutral position.

[0110] FIG. 16 shows, for example, an exemplary drive waveform that may be applied to wall W2 of FIG. 14, which includes a priming pulse (a pulse at a “second drive potential” of nominal level ++V, causing actuation in the second direction in stage 2.1) immediately preceding an ejection pulse (a pulse at a “first drive potential” of nominal level 0V, causing actuation in the first direction in stage 2.2) before returning to common potential (nominal level +V).

[0111] From FIG. 16, it can be seen that when sending a priming pulse, the relative magnitudes of the second drive potential (++V), the first drive potential (0V), and the common potential (+V) may optionally be such that the difference between the second drive potential (++V) and the common potential (+V) is less than the difference between the common potential (+V) and the first drive potential (0V).

[0112] - A variant of FIG. 17 using a cancellation pulse Figure 17 shows a variation of the harmonic operating mode of Figure 11. In this example, a so-called "cancel pulse" is included in the drive waveform to ensure that only every other nozzle ejects a drop.

[0113] Similar to the examples of Figures 11 and 14, in Figure 17, alternating walls W1, W3, and W5 are moved (substantially) in a first direction and a second direction at the harmonic frequency of the chamber. This motion is repeated to energize the system without ejecting droplets (step 0).

[0114] For ejection, all fluid chambers are assigned as ejection chambers (1, 3, 5) or non-ejection chambers (0, 2, 4, 6).

[0115] To explain the effect of the cancel pulse, it should be noted that stages 2.3 and 2.4 in FIG. 17 correspond to stages 2.1 and 2.2 in FIG. 11. However, FIG. 17 further includes stages 2.1 and 2.2 (the latter in which a cancel pulse is delivered), which occur before stages 2.3 and 2.4. Referring again to wall W2 (first ejection chamber, second wall of chamber 1), in stage 2.2 in FIG. 17, wall W2 is actuated (by a cancel pulse) in the second direction simultaneously with the actuation of the first wall (W1) in the second direction of the first ejection chamber. This occurs before stage 2.4 in FIG. 17 in which the first ejection chamber ejects a droplet of fluid therein. The same actuation occurs in stage 2.2 at walls W3 and W4 of the next ejection chamber, chamber 3, which is separated from chamber 1 by a non-ejection chamber, chamber 2, and at walls W5 and W6 of the next ejection chamber, chamber 5, which is separated from chamber 3 by another non-ejection chamber, chamber 4. The effect of the cancel pulse in stage 2.2 of FIG. 17 is that non-ejection chambers 2 and 4 move in the same direction (i.e., the second direction) at the same time (i.e., stage 2.2). This ensures that the effects of surface tension are not overcome in non-ejection chambers 2 and 4 during the remainder of the actuation cycle. As a result, no droplets are ejected from non-ejection chambers 2 and 4 when droplets are ejected from ejection chambers 1, 3, and 5, respectively, in stage 2.4.

[0116] More specifically, the walls of each chamber operate as follows. First stage (2.1): Walls W1, W3, and W5 operate in a first direction (substantially) at a harmonic frequency of the chamber; Walls W2, W4 and W6 remain stationary. Second stage (step 2.2): Walls W1 to W6 are all actuated in the second direction under the influence of a cancel pulse (more specifically applied to walls W2, W4 and W6 so that no droplets are ejected from chambers 2, 4 and 6); Third stage (2.3): Walls W1, W3 and W5 are again actuated in the first direction (substantially) at the harmonic frequency of the chamber, Walls W2, W4 and W6 remain stationary. Fourth stage (2.4): Walls W1, W3, and W5 are again (substantially) actuated in a second direction at the channel harmonic frequency; Walls W2, W4, and W6 are actuated in the first direction under the influence of an ejection pulse in the drive waveform substantially simultaneously with actuation of walls W1, W3, and W5 in the second direction, such that the energy required to eject all of the droplets from all of the ejection chambers is added to the actuation cycle, the volume of ejection chambers 1, 3, and 5 is reduced, and the droplets ejected at each corresponding nozzle are formed; After injection, as shown in step 0, walls W1, W3 and 5W are again actuated in a first direction and then (substantially) in a second direction at the harmonic frequency of the chamber.

[0117] Figure 19, for example, shows an exemplary drive waveform that may be applied to wall W2 of Figure 17, including a cancel pulse (a pulse at a "second drive potential" of nominal level +V, causing actuation in a second direction) before an eject pulse (a pulse at a "first drive potential" of nominal level 0V, causing actuation of stage 2.4 in a first direction) before returning to common potential (nominal level +V). It can be seen that the drive waveform also returns to common potential for a short period between the cancel and eject pulses, corresponding to the period of stage 2.3 when wall W2 is temporarily in a neutral position.

[0118] From FIG. 19, it can be seen that when sending a cancellation pulse, the relative magnitudes of the second drive potential (++V), the first drive potential (0V), and the common potential (+V) may optionally be such that the difference between the second drive potential (++V) and the common potential (+V) is less than the difference between the common potential (+V) and the first drive potential (0V). General Considerations

[0119] With all of the printing modes described above, the droplet deposition apparatus (comprising one or more droplet deposition heads) may further comprise a computer in data communication with the droplet deposition heads, the computer being programmed to perform the allocating step based on input data. The computer may further be programmed to instruct the droplet deposition heads to perform the actuating step.

[0120] Alternatively, or in addition, the or each droplet deposition head may include an on-board processor programmed to perform the allocating step based on the input data.

[0121] A computer program may be provided that includes instructions for causing a droplet deposition head or droplet deposition device to carry out the printing method.

[0122] Further details regarding how the droplet deposition head is controlled in response to supplied image data, and the generation of the drive waveforms used to provide the potential signals to actuate the walls of the ejection chamber, are provided, for example, in WO2018 / 224821 A9.

[0123] It will be appreciated that depending on the application, a variety of fluids can be deposited using the methods and droplet deposition heads described herein.

[0124] For example, the droplet deposition head can eject droplets of ink that travel to a sheet of paper or card, or other receiving medium such as a ceramic tile or molded article (e.g., a can, a bottle, etc.), to form an image, as in inkjet printing applications (the droplet deposition head can be an inkjet printhead, more specifically a drop-on-demand inkjet printhead).

[0125] Alternatively, droplets of fluid can be used to build structures: for example, electrically active fluids can be deposited onto a receiving medium such as a circuit board to enable the prototyping of electrical devices.

[0126] In another example, polymers, including fluids or molten polymers, can be deposited in successive layers to generate a prototype model of an object (e.g., 3D printing).

[0127] In yet other applications, the droplet deposition head may be adapted to deposit droplets of a solution containing biological material or chemicals onto a receiving medium such as a microarray.

[0128] Droplet deposition heads suitable for such alternative fluids may generally be similar in construction to printheads, with some modifications to handle the particular fluids in question.

[0129] The droplet deposition heads described herein may be drop-on-demand droplet deposition heads, in which the pattern of ejected droplets varies depending on input data provided to the head.

[0130] In all of the print modes described above, the potential difference applied across the walls of the chamber can be varied to "fine tune" the characteristics (such as volume and / or velocity) of the ejected droplets. Additionally, additional wall motions of different amplitudes can also or instead be used to "fine tune" such characteristics of the ejected droplets.

[0131] Additionally, in the example drive waveforms above, the potential levels applied to the electrodes on the walls of the chamber are described as positive (e.g., +V or ++V) or 0 / ground potential, although if the drive electronics permit, one or more of the drive potentials and the common potential could be negative, provided, of course, that the relative relationship of the drive potentials and the common potential results in the required actuation movement of the walls (if two drive potentials are used to enable bidirectional actuation of the walls, the common potential is between the first and second drive potentials).

[0132] Finally, it should be noted that a wide range of examples and modifications are contemplated within the scope of the appended claims. Therefore, the above description should be understood as providing a number of non-limiting examples to aid those skilled in the art in understanding the invention and to demonstrate how the invention may be practiced.

Claims

1. 1. A method for depositing droplets of a fluid onto a medium using a droplet deposition head, comprising: the droplet deposition head comprises an array of fluid chambers separated by spaced-apart walls formed from a piezoelectric material; each fluid chamber communicates with an opening for ejecting droplets of fluid; each of said walls separating two adjacent fluid chambers; each fluid chamber is defined by a first wall in a first direction relative to the fluid chamber and a second wall in a second direction relative to the fluid chamber opposite the first direction; each of the walls having a first electrode on a first side of the wall and a second electrode on a second side of the wall; the second electrode on each of the walls is connected to a common potential; the first electrode on each of the walls is selectively settable to one of (a) a drive potential different from the common potential and (b) the common potential; each of the walls is operable to move from a neutral position to a deformed position in the first direction in response to application of the drive potential to each of the first electrodes, and to return or remain in the neutral position in response to application of the common potential to each of the first electrodes; In the operating cycle, accepting input data; assigning all of the fluid chambers in the array to either ejection chambers or non-ejection chambers based on the input data to create bands of one or more contiguous ejection chambers separated by bands of one or more contiguous non-ejection chambers; applying the common potential to the second electrode, and selectively applying either the drive potential or the common potential to the first electrode based on the input data; In each non-ejection chamber: When the non-ejection chamber is adjacent to a strip of ejection chamber, one wall is actuated in the first direction while the other wall remains in the neutral position; if the non-ejection chamber is a single non-ejection chamber between bands of ejection chambers, both walls are actuated simultaneously in the first direction; if the non-ejection chamber is not adjacent to a strip of ejection chamber, both walls remain in the neutral position, are simultaneously actuated in the first direction, or are simultaneously actuated in the second direction; In each injection chamber: such that each of the first and second walls is actuated sequentially in the first direction; actuating the wall of the fluid chamber; Including, said actuation during said actuation cycle causes each of said ejection chambers in said band of one or more contiguous ejection chambers to eject at least one droplet; the resulting droplets form a fluid mass arranged in a line on the medium; the fluid masses are separated along the line by intervals in each of the one or more continuous bands of non-ejection chambers; The size of each of the intervals generally corresponds to the size of each of the bands of non-ejection chambers.

2. In the first injection chamber, in the operating cycle: actuating the first wall of the first injection chamber in the first direction while the second wall of the first injection chamber remains in the neutral position, thereby increasing the volume of the first injection chamber and drawing a quantity of fluid into the first injection chamber, and then returning the first wall of the first injection chamber to the neutral position; and actuating the second wall of the first ejection chamber in the first direction while the first wall of the first ejection chamber remains in the neutral position, thereby decreasing the volume of the first ejection chamber and causing the first ejection chamber to eject droplets of the fluid therein, and then returning the second wall of the first ejection chamber to the neutral position; The method of claim 1 , comprising:

3. a second injection chamber adjacent to the first injection chamber, the second injection chamber in the second direction relative to the first injection chamber such that the second wall of the first injection chamber becomes the first wall of the second injection chamber; 3. The method of claim 2, wherein during the actuation cycle, the actuation of the second wall of the first ejection chamber in the first direction occurs while the second wall of the second ejection chamber remains in the neutral position, thereby increasing the volume of the second ejection chamber and causing the second ejection chamber to draw in a certain amount of fluid simultaneously with the ejection of the droplet from the first ejection chamber.

4. 4. The method of claim 3, wherein the second wall of the first ejection chamber is returned to the neutral position during the actuation cycle, thereby ejecting droplets of the fluid from within the second ejection chamber.

5. 4. The method of claim 3, further comprising, in the actuation cycle, actuating the second wall of the second ejection chamber in the first direction while the first wall of the second ejection chamber remains in the neutral position, thereby decreasing the volume of the second ejection chamber and causing the second ejection chamber to eject droplets of the fluid therein, and then returning the second wall of the second ejection chamber to the neutral position.

6. A first band of ejection chambers and a second band of ejection chambers separated by a single non-ejection chamber, the non-ejection chamber being in the second direction relative to the first band of ejection chambers, and the second band of ejection chambers being: the second wall of a first injection chamber adjacent to the non-injection chamber in the first band-shaped region made up of the injection chambers becomes the first wall of the non-injection chamber, the first wall of a second injection chamber adjacent to the non-injection chamber in the second band-shaped region made up of the injection chambers becomes the second wall of the non-injection chamber; in the second orientation relative to the non-ejection chamber; In the operating cycle, actuating the first wall of the first injection chamber in the first direction while the second wall of the first injection chamber remains in the neutral position, and then returning the first wall of the first injection chamber to the neutral position; and then simultaneously actuating the second wall of the first ejection chamber and the first wall of the second ejection chamber in the first direction while the second wall of the second ejection chamber remains in the neutral position, thereby causing the first ejection chamber to eject a droplet of the fluid therein, and then returning the second wall of the first ejection chamber and the first wall of the second ejection chamber to the neutral position; 2. The method of claim 1, comprising: actuating the second wall of the second ejection chamber in the first direction while the first wall of the second ejection chamber remains in the neutral position, thereby causing the second ejection chamber to eject droplets of the fluid therein; and then returning the second wall of the second ejection chamber to the neutral position.

7. 1. A method for depositing droplets of a fluid onto a medium using a droplet deposition head, comprising: the droplet deposition head comprises an array of fluid chambers separated by spaced-apart walls formed from a piezoelectric material; each fluid chamber communicates with an opening for ejecting droplets of fluid; each of said walls separating two adjacent fluid chambers; each fluid chamber is defined by a first wall in a first direction relative to the fluid chamber and a second wall in a second direction relative to the fluid chamber opposite the first direction; each of the walls having a first electrode on a first side of the wall and a second electrode on a second side of the wall; the second electrode on each of the walls is connected to a common potential; the first electrode on each of the walls is selectively settable to one of (a) a drive potential different from the common potential and (b) the common potential; each of the walls is operable to move from a neutral position to a deformed position in the first direction in response to application of the drive potential to each of the first electrodes, and to return or remain in the neutral position in response to application of the common potential to each of the first electrodes; In the operating cycle, accepting input data; assigning all of the fluid chambers in the array to either ejection chambers or non-ejection chambers based on the input data to create bands of one or more contiguous ejection chambers separated by bands of one or more contiguous non-ejection chambers; applying the common potential to the second electrode, and selectively applying either the drive potential or the common potential to the first electrode based on the input data; In at least the first injection chamber, the first wall of the first injection chamber is repeatedly actuated in the first direction and then returned to the neutral position while the second wall of the first injection chamber is maintained in the neutral position; during the actuation cycle, when the first ejection chamber ejects droplets of the fluid therein, the second wall of the first ejection chamber is selectively actuated in the first direction substantially simultaneously with the first wall of the first ejection chamber returning to the neutral position, thereby causing the first ejection chamber to eject droplets of the fluid therein, and thereafter the second wall of the first ejection chamber is returned to the neutral position; actuating the wall of the fluid chamber; Including, said actuation during said actuation cycle causes each of said ejection chambers in said band of one or more contiguous ejection chambers to eject at least one droplet; the resulting droplets form a fluid mass arranged in a line on the medium; the fluid masses are separated along the line by intervals in each of the one or more continuous bands of non-ejection chambers; The size of each of the intervals generally corresponds to the size of each of the bands of non-ejection chambers.

8. the first ejection chamber is part of a first group of ejection chambers interleaved with each ejection chamber of a second group of one or more ejection chambers; 8. The method of claim 7, wherein the first walls of each of the components of the first group of injection chambers are simultaneously repeatedly actuated in the first direction and then returned to the neutral position.

9. a second injection chamber that is part of the second group of injection chambers is adjacent to the first injection chamber, and the second injection chamber is in the second direction relative to the first injection chamber such that the second wall of the first injection chamber becomes the first wall of the second injection chamber; In the operating cycle, maintaining the second wall of the second ejection chamber in the neutral position while the second wall of the first ejection chamber is actuated to eject the droplets of the fluid therein; and thereafter substantially simultaneously with the first wall of the second ejection chamber in the neutral position, actuating the second wall of the second ejection chamber in the first direction, thereby causing the second ejection chamber to eject droplets of the fluid therein, and thereafter returning the second wall of the second ejection chamber to the neutral position; The method of claim 7 further comprising:

10. 10. The method of claim 9, wherein the second wall of the second injection chamber is repeatedly actuated in the first direction and returned to the neutral position in synchronization with the repeatedly actuating the first wall of the first injection chamber.

11. In the operating cycle, in each non-ejection chamber: If the non-ejection chamber is a single non-ejection chamber between bands of ejection chambers, both walls are actuated simultaneously in the first direction; otherwise, The method of claim 7 , wherein one wall is actuated in the first direction and the other wall remains in the neutral position, or both walls remain in the neutral position.

12. 12. The method according to claim 1, wherein the common potential is ground potential or 0V, or a positive potential higher than ground potential, and / or the drive potential is higher than the common potential.

13. 1. A method for depositing droplets of a fluid onto a medium using a droplet deposition head, comprising: the droplet deposition head comprises an array of fluid chambers separated by spaced-apart walls formed from a piezoelectric material; each fluid chamber communicates with an opening for ejecting droplets of fluid; each of said walls separating two adjacent fluid chambers; each fluid chamber is defined by a first wall in a first direction relative to the fluid chamber and a second wall in a second direction relative to the fluid chamber opposite the first direction; each of the walls having a first electrode on a first side of the wall and a second electrode on a second side of the wall; the second electrode on each of the walls is connected to a common potential; the first electrode on each of the walls is selectively settable to one of (a) a first drive potential, (b) a second drive potential, and (c) the common potential; the common potential is between the first drive potential and the second drive potential; each of the walls is operable such that in response to application of the first drive potential to the respective first electrode, each wall moves from a neutral position to a deformed position in the first direction, in response to application of the second drive potential to the respective first electrode, each wall moves from the neutral position to a deformed position in the second direction, and in response to application of the common potential to the respective first electrode, each wall returns to or remains in the neutral position; In the operating cycle, accepting input data; assigning all of the fluid chambers in the array to either ejection chambers or non-ejection chambers based on the input data to create bands of one or more contiguous ejection chambers separated by bands of one or more contiguous non-ejection chambers; applying the common potential to the second electrode, and selectively applying the first drive potential, the second drive potential, or the common potential to the first electrode based on the input data; In at least the first injection chamber, the first wall of the first injection chamber is repeatedly actuated in the first direction and then in the second direction while the second wall of the first injection chamber is held in the neutral position; during the actuation cycle, when the first ejection chamber ejects droplets of the fluid therein, the second wall of the first ejection chamber is selectively actuated in the first direction substantially simultaneously with the first wall of the first ejection chamber being actuated in the second direction, thereby causing the first ejection chamber to eject droplets of the fluid therein, and thereafter the second wall of the first ejection chamber is returned to the neutral position; actuating the wall of the fluid chamber; Including, said actuation during said actuation cycle causes each of said ejection chambers in said band of one or more contiguous ejection chambers to eject at least one droplet; the resulting droplets form a fluid mass arranged in a line on the medium; the fluid masses are separated along the line by intervals in each of the one or more continuous bands of non-ejection chambers; The size of each of the intervals generally corresponds to the size of each of the bands of non-ejection chambers.

14. the first ejection chamber is part of a first group of ejection chambers interleaved with each ejection chamber of a second group of one or more ejection chambers; 14. The method of claim 13, wherein the first wall of each of the components of the first group of injection chambers is simultaneously and repeatedly actuated in the first direction and then in the second direction.

15. During the operating cycle, in each non-ejection chamber, the wall If the band of non-ejection chambers is not a single non-ejection chamber between bands of ejection chambers, one wall is actuated in the first direction only, or in both the first and second directions, while the other wall remains in the neutral position; or The method of claim 13 wherein both walls are actuated to remain in the neutral position.

16. During the operating cycle, in each non-ejection chamber, the wall If a single non-ejection chamber is located between bands of ejection chambers, One wall is actuated in the first direction and the second wall remains in the neutral position, and then 14. The method of claim 13, wherein actuation is performed such that one wall is actuated in the first direction and the other wall is actuated in the second direction.

17. 14. The method of claim 13, wherein in a band of a plurality of contiguous ejection chambers, the ejection chambers are activated to deposit droplets as a plurality of contiguous lines.

18. 14. The method of claim 13, wherein the second wall of the first ejection chamber is actuated in the second direction simultaneously with actuation of the first wall of the first ejection chamber in the first direction, just prior to the time in the actuation cycle when the first ejection chamber ejects a droplet of the fluid therein.

19. 14. The method of claim 13, wherein the second wall of the first ejection chamber is actuated in the second direction simultaneously with actuation of the first wall of the first ejection chamber in the second direction and prior to the time in the actuation cycle when the first ejection chamber ejects droplets of the fluid therein.

20. 19. The method of claim 18, wherein the actuation of the second wall of the first ejection chamber in the second direction is effected by applying the second drive potential to the first electrode on the second wall of the first ejection chamber, the second drive potential being such that a difference between the second drive potential and the common potential is less than a difference between the common potential and the first drive potential.

21. 21. A method according to claim 13, wherein the common potential is a positive potential higher than ground potential, and optionally the first drive potential is higher than the common potential and the second drive potential is lower than the common potential, and further optionally the second drive potential is ground potential or 0V.

22. 14. The method of claim 7 or claim 13, wherein the repeatedly actuated wall is actuated one or more times before the step of assigning all of the fluid chambers in the array to either ejection chambers or non-ejection chambers based on the input data.

23. 14. A method according to claim 7 or claim 13, wherein the first wall of the or each ejection chamber is operated substantially at the resonant frequency of the ejection chamber, or substantially at a harmonic or sub-harmonic of the resonant frequency of the ejection chamber.

24. 14. The method of claim 1, claim 7 or claim 13, wherein the array of fluid chambers is a first array of fluid chambers, and the droplet deposition head further comprises a second array of fluid chambers, optionally the ejection chambers of the first and second arrays of fluid chambers are separated by one or more non-ejection chambers, and further optionally the second array of fluid chambers is arranged substantially as a mirror image of the first array of fluid chambers, and further optionally the movement of the walls of the second array of fluid chambers is substantially the same as the movement of the walls of the first array of fluid chambers.

25. 14. The method of claim 1, claim 7 or claim 13, wherein different walls or different groups of walls can be set to different common potentials.

26. 14. A droplet deposition head configured to perform the method of claim 1, claim 7 or claim 13, comprising a processor programmed to perform the allocating step, optionally based on the input data.

27. 14. A droplet deposition apparatus comprising one or more droplet deposition heads and configured to perform the method of claim 1, claim 7 or claim 13, optionally further comprising a computer in data communication with the one or more droplet deposition heads, the computer being programmed to perform the allocating step based on the input data, and optionally further programmed to send instructions to the one or more droplet deposition heads to cause them to perform the actuating step.

28. 27. A computer program comprising instructions to cause a droplet deposition head according to claim 26 to carry out the method of claim 1, claim 7 or claim 13.

29. 28. A computer program comprising instructions to cause a droplet deposition apparatus according to claim 27 to carry out the method of claim 1, claim 7 or claim 13.

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