Droplet deposition method and apparatus

Abstract

The present invention relates to a method and apparatus for depositing droplets of a fluid onto a medium, particularly in the field of printing. The apparatus 10 comprises an array of chambers including a first plurality of chambers 12 configured to selectively deposit droplets of a fluid and a second plurality of chambers 13 not configured to selectively deposit droplets of a fluid. The first plurality of chambers 12 are arranged in pairs separated from adjacent chambers by at least one chamber 13 of the second plurality of chambers. Each chamber is separated from an adjacent chamber by a wall 14, which is operable to eject droplets of a fluid from the chambers 12.

Description

[Technical field]

[0001] The present invention relates to a method and apparatus for depositing droplets of a fluid onto a medium. For example, the apparatus may include a printhead. [Background technology]

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

[0003] In recent years, reliable, high throughput inkjet printheads have been developed that can apply inks and varnishes directly to ceramic tiles, allowing tile patterns to be customized to customers' exact specifications, reducing the need to stock every type of tile.

[0004] In other applications, droplet deposition heads may be used to form elements such as color filters in LCD or OLED displays used, for example, in the manufacture of flat screen televisions.

[0005] It will thus be appreciated that droplet deposition heads will continue to evolve and become specialized to suit new and / or increasingly difficult deposition applications. However, while much development has occurred in the field of droplet deposition heads, there remains room for improvement in the field.

[0006] As background to this work, the mechanism by which droplets of fluid are ejected from an array of fluid chambers is shown in Figure 1. It shows an array 10' of fluid chambers 12 that form part of a droplet deposition head, with a simplified diagram of the same array shown below. The chambers are bounded 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 either side of each piezoelectric wall 14 are coated on the inside 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 particular chamber 12, the metal electrode layer extends from an inner wall on one side of the chamber to the opposing inner wall of the chamber (as better shown in other examples described herein, see, for example, Figure 2). However, this is by no means the only electrode configuration that can be used. For example, the electrodes that extend from the inner wall on one side of each electrode chamber to the opposing inner wall of the chamber can be cut (e.g., by a laser) along the center of the fluid chamber, effectively splitting it into two independently positionable electrodes.

[0007] If the same potential is applied to electrodes on either side of a wall, and 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 wall, and there is a potential difference across the wall, the wall will move due to the inverse piezoelectric effect, which converts the potential difference into movement. The moving wall is called the "active" wall, and the non-moving wall is called the "inactive" wall.

[0008] FIG. 1 shows a simplified arrangement of chambers in which the walls of two chambers move inward, decreasing their volume. This results in an increase in pressure in these two chambers (denoted by "+") and a decrease in pressure in the adjacent chamber (denoted by "-"). If the potential difference across the walls is high enough (e.g., to overcome the effects of surface tension), a droplet of fluid is forced out of the chamber under increased pressure ("+") through nozzle 16. Such chambers eject ("eject") droplets of fluid and are referred to herein as "ejecting" chambers. Also shown in FIG. 1 are two chambers (at the far right of the figure) whose volumes do not change because their walls are stationary. 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 a "-" may be ejecting chambers since they can be ejected later in the same actuation cycle, or non-ejecting chambers if their walls do not move in a manner that would cause ejection in the same actuation cycle. As a particular example, if only one wall of a chamber moves during an actuation cycle, this may not cause the ejection of a droplet, but if both walls move in an actuation cycle, a droplet may be ejected. In another example, a droplet may be ejected when only a single wall of a chamber moves during a given actuation cycle. For example, if a potential difference is applied to one wall, and that potential difference is large enough, it may cause a large volume change in response to that chamber ejecting a droplet.

[0009] The chambers 12 are formed as channels surrounded on one side by a cover member 17 in contact with the actuatable wall and, in this arrangement, each chamber is provided with a nozzle 16 in the cover member 17 for discharging fluid. The cover member 17 consists of a metal or ceramic cover plate which provides structural support and a thinner upper nozzle plate in which the nozzles are formed. Alternatively, a relatively thin nozzle plate can be used alone as the cover member.

[0010] In the example of FIG. 1 (and throughout this disclosure), each of the actuatable piezoelectric walls 14 is composed of an upper half and a lower half, separated by a plane defined by the alignment direction (left to right in FIG. 1) and the channel extension direction (into the plane of the page in FIG. 1). The upper and lower halves of the piezoelectric wall are polarized in opposite directions perpendicular to the channel extension and alignment directions, such that when a potential difference is applied across the wall perpendicular to the alignment direction, the two halves deflect to bend toward one of the fluid chambers. Because the shape of the deflected wall resembles a chevron, this is referred to as a "chevron mode" of actuation (also shown in more detail in another example in FIG. 2). Alternatively, each of the actuatable piezoelectric walls may be polarized 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 across the wall, the wall deflects in a "shear mode" of actuation.

[0011] A further development of this basic idea is shown in FIG. 2, which shows an array of fluid chambers 10 arranged to operate in a multi-cycle print mode (specifically, a "shared wall" three-cycle print mode). In this mode, the chambers 10 are first divided into three groups A, B, and C (labeled in FIG. 2), each of which operates in a different print cycle (cycles A to C, respectively). In a three-cycle print mode, chambers in different groups cannot fire simultaneously in the same cycle. For example, chambers in group A can only fire in cycle A, chambers in group B can only fire in cycle B, and chambers in group C can only fire in cycle C. Thus, there is a time delay between the firing of chambers in groups A, B, and C, as indicated by the droplets fired from chamber A being higher (fired earlier) than the droplets fired from chamber B, which itself is higher (fired earlier) than the droplets fired from chamber C. The complete firing sequence of A->B->C defines one actuation sequence for a particular print line to be printed on the medium. On the next line, a new series of chambers are commanded to fire based on the required print pattern, with the corresponding chambers in the A group being fired, followed by the corresponding B chambers, then the C chambers.

[0012] Despite this asynchronous firing scheme between the three groups, horizontal lines can be produced on the medium by staggering the nozzles / chambers or inputting a waveform that varies the velocity of the droplets fired in different cycles. However, by dividing the chambers 10 into three groups and firing in three staggered cycles, the maximum printing frequency of all nozzles is limited to one-third of the printing frequency of any individual nozzle, since adjacent chambers cannot fire in the same cycle. As a result, the print mode has relatively low productivity, a relatively low maximum printing frequency and a relatively low laydown capacity.

[0013] A solution to the drawbacks of the multi-cycle mode described above is to seal off every other chamber and allow all remaining nozzles to fire simultaneously in the same cycle in order to improve productivity, printing frequency and laydown. This printing mode is shown in Figures 3 and 4 and is described in WO2007 / 007079. Figure 3 in particular shows an alternating blocking arrangement in which the chambers between walls 0 and 1, 2 and 3, 4 and 5, and 6 and 7 are not equipped with nozzles and therefore cannot eject droplets. In contrast, the chambers located between walls 1 and 2, 3 and 4, and 5 and 6 are equipped with nozzles and therefore can eject droplets in the actuation cycle. A representation of the print pattern of the current actuation cycle is shown at the bottom of Figure 3. Here, an X is shown in the chambers without nozzles, indicating that droplets cannot be ejected at that location. The remaining chambers are assigned the color black (droplets are ejected by actuating the walls using the corresponding electrodes 4a, 6a) or white (no droplets are ejected, a signal is applied to electrode 2a so that walls 1 and 2 are not actuated). Walls 3, 4, 5, and 6 are shown with dashed outlines to indicate the general shape they assume when a chevron actuation mode is used to eject droplets as part of the actuation cycle described herein In contrast, walls 1 and 2 are shown without such dashed outlines to indicate that these walls do not need to move in this actuation cycle.

[0014] An operating cycle according to the above description is shown in Figure 4. The cycle begins by first moving all of the walls of the ejection chambers outward (walls 3 and 4 move apart, as do walls 5 and 6), increasing the volume of the ejection chambers between those pairs. This allows fluid (such as ink) to flow into each ejection chamber. In the second part of the cycle, the walls of each ejection chamber move inward, decreasing the chamber volume and increasing the pressure within the chamber, forcing fluid out of the nozzles, similar to the multi-cycle configuration above. In this print mode, the active chambers no longer have a shared wall, because alternating chambers are sealed (thereby reducing crosstalk caused by the proximity of active chambers) and do not contain nozzles. All nozzles can be fired, but the overall resolution is halved as there are no nozzles in the sealed chambers.

[0015] It is therefore desirable to overcome the above limitations of various printing systems and provide a more energy-efficient printing method that can eject single droplets and simultaneously eject droplets with fine resolution when required.

[0016] Further relevant background art is described in WO2010 / 055344 A1 and WO2018 / 224821 A9. Summary of the Invention

[0017] 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.

[0018] The present disclosure relates to an apparatus for depositing droplets of a fluid onto a medium, the apparatus comprising: an array of chambers, the array comprising a first subset of chambers comprising a plurality of chambers arranged to selectively deposit droplets of a fluid; and a second subset of chambers comprising a plurality of chambers not configured for selective deposition of droplets of a fluid, at least one of the chambers in the first subset of chambers is an active chamber, the active chamber having a first wall adjacent to a chamber from the first subset of chambers and a second wall opposite the first wall, the second wall being formed from a piezoelectric material and adjacent to a chamber from the second subset of chambers, at least one of the chambers in the second subset of chambers is an inactive chamber, each inactive chamber having two opposing walls, at least one of the walls of the inactive chamber adjacent to a chamber from the first subset of chambers, each active chamber having two opposing walls, the active chambers have a first electrode on a surface of the second wall inside the active chamber and a second electrode on an opposing surface of the second wall outside the active chamber, and a surface of the first wall located inside the active chamber either having no electrode thereon or having a third electrode thereon, the third electrode being controllable independently of the first and second electrodes or the third electrode being an electrically isolated electrode, configured to supply an actuation potential independently from the first and second electrodes of each active chamber, each of the second walls being operable such that in response to the supply of the actuation potential to the second electrode, the second wall is arranged to deform, and each chamber in a first subset of the chambers is in communication with an opening for ejecting droplets of fluid and in communication with a fluid source to selectively deposit the fluid in response to the supply of an actuation potential to the second electrode on the second wall of each active chamber.

[0019] This arrangement allows active chambers (i.e., chambers that can be controlled to selectively eject droplets in response to an input print pattern) to be arranged in pairs separated by other chambers. An example arrangement includes a pair of active chambers separated by a single inactive chamber. In this arrangement, the chambers of the first and second subsets are arranged such that a pair of first subsets are separated by individual members of the second subset, and the ratio of first subset chambers to second subset chambers approaches 2:1 (within the limit of an infinitely long array). In another example, a pair of first subset chambers may be separated by multiple second subset chambers.

[0020] The above defined arrangements may themselves be a subset of the total number of chambers in the printhead, in other words, a portion of the printhead may have such an arrangement, and this portion may be embedded within a larger arrangement of a different configuration, for example the types of arrangements described above.

[0021] The chambers of the first subset that do not qualify as active chambers still have many of the same characteristics, e.g., they can be operated independently of and simultaneously with other chambers of the first subset. The main difference is that a chamber of the first subset is not necessarily adjacent to both another chamber of the first subset and a chamber of the second subset. This is because the regular pattern of the current arrangement (ideally two active, one inactive, repeated) is not always maintained towards the end of the arrangement. At the end of the arrangement, a different pattern of active and inactive chambers may be required locally. However, with this in mind, in this document the terms "active chambers" and "chambers of the first subset" are used somewhat interchangeably.

[0022] Note also that the orientation of the position of the first wall relative to a particular chamber is independent of the absolute orientation. This is because, for a pair of adjacent first subset chambers (arbitrarily labeled "left" and "right" for simplicity), the first wall of the left chamber is the wall adjacent to the right chamber; that is, the right wall of the left chamber is the first wall. Similarly, for the right chamber, the first wall is adjacent to the left chamber, and therefore is the left wall of the right chamber.

[0023] The first and second electrodes are separately controllable, which as used herein means that the electrodes of each pair are separately controllable from each other. Each chamber is also independently actuable, which in some cases means that each first and second electrode in the array is separately controllable from every other first or second electrode in the array. In other cases, as shown below, one electrode of each pair is coupled to a common potential and the other electrode of each pair is independently controllable from each other electrode. In this way, each active chamber can be independently actuated to eject droplets by moving the second wall of that chamber to adjust the volume of that chamber. That is, when the second wall of a particular chamber is deformed, the volume of that chamber changes. Depending on the potential difference applied between the electrodes on either side of the second wall, the movement of the wall causes the volume of the chamber to become larger or smaller depending on whether the second wall moves away from or toward the corresponding first wall. Based on principles similar to those described above, the change in volume causes the ejection of droplets. In some cases, the ejection process may simply involve reducing the volume of the chamber and then returning it to a neutral volume. Alternatively, the chamber may increase in volume to draw in liquid and then decrease in volume to expel droplets, which may involve returning to a neutral position or decreasing the volume below the neutral configuration.

[0024] As for the first wall of each chamber, if it is not intended to have controllable mobility, several options may each be preferred depending on the specific construction method adopted. For example, some construction methods may require the provision of electrodes on each wall, while other construction methods may make it more convenient to omit electrodes in certain locations. Examples of options in this regard: 1. The first wall may not have electrodes on either side, and therefore may not be controlled at all. 2. The first wall is formed from a non-polarized piezoelectric crystal in which the dipoles of the individual unit cells are randomly oriented, resulting in no deformation or net response to an electric field (because the random orientations cancel out in the bulk material). Such a non-polarized crystal therefore does not deform when a potential difference is applied to electrodes on the opposite face. 3. The first wall has an electrode on each side (i.e. a pair of third electrodes) but the potential of each electrode is held such that V1 ≡ V2 (e.g. by electrically coupling the electrodes to each other) so that there is no potential difference across the wall. 4. The first wall is formed from a polarized piezoelectric material and has a pair of electrically isolated electrodes on each side (i.e., a pair of third electrodes). These are electrically isolated from all parts of the circuit. This provides additional stiffness to the first wall and reduces crosstalk between adjacent chambers of the first subset, as described below.

[0025] In still other cases, the third electrode is independently controllable. It is usually not desirable to use this electrode to control the first wall in the same way as the second wall (as this would impair the ability to eject droplets simultaneously). The third electrode can be used to correct induced wall motion when only one of a pair of active chambers is the ejection chamber.

[0026] Optionally, the arrangement includes at least a pair of adjacent active chambers, the pair of adjacent active chambers being operable substantially simultaneously. In this example, "substantially simultaneously" means that droplets are ejected from the two chambers with a time difference that is much shorter than the time it takes for an actuation cycle to occur (e.g., less than 10%, preferably less than 5%, and more preferably less than 1% of the actuation cycle time). In another example, "substantially simultaneously" means that adjacent chambers eject droplets and that the movement of a first wall of the chamber overlaps with the movement of a second wall of the chamber. In other words, the period during which one of the second walls is moving substantially overlaps with the period during which the other of the second walls is moving (50%, preferably 80%, and more preferably 95% or more overlap). In any case, the difference in timing of droplet ejection from two adjacent chambers is typically 5 μs or less, preferably less than 2 μs, or 1 μs or less.

[0027] Optionally, one or more of the inactive chambers are not in communication with the supply / s of printing fluid, have no openings for selective release of fluid, and / or are filled with a gas or gas mixture such as air. These arrangements ensure that the inactive chambers are unable to eject droplets, either by not supplying them with droplets, or by not providing them with nozzles, outlets or openings that can accommodate droplets but eject droplets to the medium, respectively. Providing no openings is typically the preferred way to achieve this effect.

[0028] Optionally, the arrangement includes a pair of adjacent active chambers separated from another pair of adjacent active chambers by an inactive chamber. Optionally, the array includes a repeating pattern of three chambers arranged such that two adjacent active chambers are followed by a single inactive chamber. When this pattern is repeated for a portion of the array, the highest resolution of the active chambers is achieved, consistent with the features of the present model (as disclosed herein).

[0029] Optionally, the terminal chamber of the arrangement is a chamber of the second subset of chambers, or an active chamber, the penultimate chamber of the arrangement is a chamber of the second subset of chambers, or the endmost wall of the device is movable independently of the other walls of the arrangement. In some cases, both end chambers are either a chamber of the second subset of chambers, or an active chamber, the penultimate chamber of the arrangement is a chamber of the second subset of chambers, or the endmost wall of the device is movable independently of the other walls of the arrangement (although each end chamber need not be one of these options). This arrangement ensures that the benefits of the system are available all the way to the end of the array.

[0030] In some examples, it is common to have the end of the arrangement as a movable wall (adjacent to the inactive gap). This has some similarities with the inactive chambers (and the chambers of the second subset) described here, meaning that the first and third options above for the chambers at the end of the arrangement are in some cases roughly equivalent. In other cases, the first and third options may be different, since the chambers at the end of the arrangement in Example 3 may be specifically designed for that role.

[0031] Optionally, the or each non-active chamber may have a different shape and / or size than the or each active chamber, for example, a non-active chamber may be narrower, wider, longer, shorter, deeper, and / or shallower than an active chamber.

[0032] Optionally, the first wall has a width different from that of the second wall, and / or the first wall is formed from a material different from that forming the second wall. A thicker wall is more rigid, which may help improve insulation and reduce crosstalk. On the other hand, a thinner wall allows less space to be allocated to the wall. For example, the first wall may be thicker than the second wall, since it separates two chambers that may eject simultaneously. With regard to the material, as mentioned above, the first wall may be made from a non-piezoelectric or non-polarized piezoelectric material, thereby preventing the wall from deforming in response to a potential difference across the wall. In a particularly advantageous embodiment, the first wall may be thinner than the second wall, but an electrically insulated electrode is provided on the piezoelectric wall material. In this way, the loss of rigidity due to the thinness of the wall is compensated for by the reinforcing effect of the insulated electrode. This allows the wall that is not intended to move to take up less space, improving the resolution of the array.

[0033] Optionally, the arrangement includes adjacent chambers arranged in a row, and optionally the row is substantially linear, In other examples, depending on the intended application, it may be preferred for the row to have one or more curves, arcs, or other non-linear shapes.

[0034] Optionally, the device includes multiple linear rows extending parallel to each other. These repeating rows work particularly well in the long repeating 2-1-2-1 pattern described above, but can also be used in shorter lengths than described herein. Each row may be further offset from the other rows in the direction of the row extension, and optionally each row is arranged to be actuated at a different time to deposit the droplets ejected from each row in a substantially straight line on the medium. The offset in the row direction can be selected to align the active chambers of one row to a position corresponding to a wall or inactive chamber of another row. Since there is usually a relative motion between the device and the medium, the time delay between the ejection of droplets of different rows corresponds to a distance offset in the direction across the rows. Thus, the timing offset can be selected to align the output of different rows in space on the medium, taking into account the relative motion of the device with respect to the medium.

[0035] It should be noted that the timing difference between columns is optional, since it may be desired to deposit at different locations on the medium. For example, if there are enough columns that there is full redundancy (e.g., each location is covered multiple times at the desired resolution), the device may be able to print two complete lines at a time, spatially offset, or print at twice the frequency. Each of these will affect the timing offset between columns, and it may be that a time delay between some columns is not necessary or desirable.

[0036] Optionally, the magnitude of the offset of the columns in the direction the columns extend is selected to achieve a particular printing resolution, in particular for a linear drop density where each drop is within a distance x of the nearest drop, the offset can be selected to be no greater than x.

[0037] In some examples, there are N rows, each row including a repeating section having a repeating unit of chambers of total length D, and the offset d between the rows is an integer multiple of the ratio D / N, meaning that the droplets produced by each row are in evenly spaced increments over the entire length of the repeating unit.

[0038] Advantageously, providing active chambers at equivalent positions along the rows of different rows (i.e. directing multiple active chambers at the same position on the medium) can be avoided whenever possible, thereby improving the resolution of the system: the positions of the inactive chambers (and walls) of one row can be covered by one of the active chambers of another row.

[0039] In general, if a column is formed of a repeating unit of x active chambers and y inactive chambers (x>0, y>0), it is possible for each inactive position in the first column to be covered by an active position in another column formed from the same repeating unit, in this case using N columns.

number

[0040] As an example of this, three multiple row arrangements and their offsets are shown. In each case, the repeating unit of the chambers is the current arrangement of two active repeating units and one inactive repeating unit. Also, note that in each case, the first row, second row, third row, etc. are labels for convenience, and the columns do not have to be arranged in this order. In other words, the second row is not necessarily directly adjacent to (i.e., between) the first and third rows. Thus, the four row arrangement could be in the order 1-2-3-4, but it could also be 3-1-4-2, 4-3-2-1, or any of 21 other arrangements of four rows. Also, because the active and inactive chambers are arranged in a repeating pattern of total width D (i.e., the system can be effectively described using modular arithmetic), the following description describes an offset of a distance L in a first direction, but this could equally be implemented by an offset of a different distance DL in a second direction opposite the first direction.

[0041] Note that there may be groups of multiple columns, with each column in a group offset the same amount (and direction) to the adjacent column along the row. This simplifies manufacturing by allowing the etching tool to move in a single diagonal direction, etching multiple rows in one sweep without the need for repositioning or realignment.

[0042] In Example 1, there are at least four parallel linear rows, and in each row, the widths of the active chamber, the inactive chamber, and the first and second walls in the direction in which the row extends are all equal to a distance d, a second row is offset from a first row by a distance 2d in a first direction along the direction in which the rows extend, a third row is offset from the second row by a distance d in the first direction, and a fourth row is offset from the third row by a distance 2d in the first direction.

[0043] Due to the repeating nature of the rows, the fourth row is offset from the first row by a distance of 5d in the first direction, which corresponds to (-1)d in the first direction, or d in a second direction opposite the first direction along the direction of the rows. This arrangement covers the entire extent of the row once every d, and possibly twice at each position, i.e., each position in the first row corresponding to an active chamber, inactive chamber, or wall is covered once or twice.

[0044] In a six row variation, there are at least six parallel linear rows, in each row, the widths of the active chamber, the inactive chamber, and the first and second walls in the row extension direction are all equal to a distance d, the second row is offset from the first row by a distance 2d in a first direction along the row extension direction, the third row is offset from the second row by a distance 2d in the first direction, the fourth row is offset from the third row by a distance d in the first direction, the fifth row is offset from the fourth row by a distance 2d in the first direction, and the sixth row is offset from the fifth row by a distance 2d in the first direction.

[0045] Thus, the sixth column is offset in the first direction from the first column by a distance 9d, which corresponds to 3d or (-3)d in the first direction, or 3d in a second direction opposite the first direction along the direction of extension of the columns, such that the full extent of the column is covered once every d, twice at each location, i.e. twice at each location of the first column corresponding to the active chamber, the inactive chamber, or the wall.

[0046] Finally, in a three-row variant, there are at least three parallel linear rows, in each row, the width of each active chamber in the direction of extension of the row is a distance d, the combined width of each inactive chamber and two second walls adjacent each active chamber is a distance 2d, the width of each first wall adjacent an adjacent pair of active chambers is a distance 2d, the second row is offset from the first row by a distance d in a first direction along the direction of extension of the rows, and the third row is offset from the second row by a distance d in the first direction.

[0047] Thus, the third row is offset in the first direction from the first row by a distance 2d, which corresponds to (-1)d in the first direction, or d in a second direction opposite the first direction along the extension of the rows.

[0048] This covers the full extent of the columns once every d at each position: that is, because each active chamber is evenly spaced from its two neighbors by a distance of 2d, an offset of d between the first and second columns covers the first half of the intervening space, and an offset of a further d between the second and third columns covers the remaining half of the intervening space.

[0049] In yet another example, the location of the opening in an active chamber may be offset from the center of that chamber, or may be arranged to direct the ejected droplets onto the medium in a manner that is not aligned with the center of the active chamber. This allows the arrangement to space the ejected droplets evenly. For example, if the opening (or droplet location on the medium) is arranged toward the left end of the left chamber of each chamber pair and toward the right end of the right chamber of each chamber pair, the output of two adjacent active chambers may be shifted to overlap the area corresponding to the inactive chamber that separates the chamber pair. This overlap may be selected such that the spacing between the left and right droplets of an adjacent pair is equal to the spacing between the droplets of the left chamber of a pair and the right chamber of an adjacent pair (i.e., separated by one or more inactive chambers). This means that the linear droplet density will be lower compared to the linear density of the chambers (considering both active and inactive chambers), but even increments may still be used to cover the entire length of the arrangement, even though only up to two of the three chambers are active chambers.

[0050] Optionally, the second wall is arranged to deform in a first direction in response to a first potential difference applied across the second wall, and the second wall is arranged to deform in a second direction opposite the first direction in response to a second potential difference applied across the second wall. The potentials supplied to the first and second electrodes are independent of each other such that a desired potential difference can be applied across a given wall.

[0051] In some examples, the first direction corresponds to an increase in the volume of the active chamber (and a corresponding decrease in the volume of the adjacent inactive chamber) and the second direction corresponds to a decrease in the volume of the active chamber (and a corresponding decrease in the volume of the adjacent inactive chamber). In other examples, the first direction corresponds to a decrease in the volume of the active chamber and the second direction corresponds to an increase in the volume of the active chamber. In any event, the most common ejection mode in the methods disclosed herein is to first move the second wall of a given chamber in a direction that expands the chamber volume to suck in fluid, and then move the second wall of the chamber in the opposite direction to expel the fluid as droplets.

[0052] Optionally, one or more second walls can be actuated either by the or each first electrode being held at a fixed potential and the device being arranged to supply to the or each corresponding second electrode one of a first potential higher than the fixed potential or a second potential lower than the fixed potential, or by the or each second electrode being held at a fixed potential and the device being arranged to supply to the or each corresponding first electrode one of the first potential higher than the fixed potential or the second potential lower than the fixed potential. The use of a common potential can reduce the complexity of the control circuit. Alternatively, the device is arranged to actuate one or more second walls by independently supplying different potentials to one or more first electrodes and corresponding second electrodes.

[0053] Optionally, the one or more third electrodes are fully electrically isolated from all other electrodes and potential supplies, which, as mentioned above, has the advantage of strengthening the first wall and reducing crosstalk between the chambers.

[0054] Also disclosed is a method of depositing droplets of a fluid onto a medium using an apparatus, the apparatus comprising an array of chambers, the array including a first subset of chambers comprising a plurality of chambers arranged to selectively deposit droplets of a fluid, and a second subset of chambers comprising a plurality of chambers not configured for selective deposition of droplets of a fluid, at least one of the chambers in the first subset of chambers is an active chamber, the active chamber having a first wall adjacent a chamber from the first subset of chambers and a second wall opposite the first wall, the second wall being formed from a piezoelectric material and adjacent a chamber from the second subset of chambers, at least one of the chambers in the second subset of chambers is an inactive chamber, each inactive chamber having two opposing walls, at least one of the walls of the inactive chamber adjacent a chamber from the first subset of chambers, each active chamber having a surface of the second wall inside the active chamber, the surface of the second wall being formed from a piezoelectric material, the surface of the first wall being adjacent a chamber from the first subset of chambers, the surface of the second wall being adjacent a chamber from the first subset of chambers, the surface of the second wall being formed from a piezoelectric material, the surface of the first wall being adjacent a chamber from the second subset of chambers, the surface of the second wall being adjacent a chamber from the first subset of chambers, the surface of the second wall being adjacent a chamber from the first subset of chambers, the surface of the first wall being adjacent a chamber from the first ... first wall being adjacent a chamber from the first subset of chambers, the surface of the second wall being adjacent a chamber from the first subset of chambers, the surface of a first electrode and a second electrode on an opposing surface of the second wall exterior to the active chambers, and a surface of the first wall interior to the active chambers, the surface of the first wall having no electrode thereon or having a third electrode thereon, the third electrode being controllable independently of the first and second electrodes or the third electrode being an electrically isolated electrode, the system comprising the steps of: accepting input data in an operating cycle; assigning all of the active chambers in the first subset to either ejection chambers or non-ejection chambers based on the input data to create a band of one or more contiguous ejection chambers separated by a spacing corresponding to a band of chambers that are either non-ejection chambers or non-active chambers; and selectively supplying an operating potential to the first and / or second electrodes based on the input data so as to create a band of one or more contiguous ejection chambers separated by a spacing corresponding to a band of chambers that are either non-ejection chambers or non-active chambers.and actuating the second wall of the active chambers to reduce the volume of the active ejection chambers and deposit droplets of fluid, such that each of the ejection chambers ejects at least one droplet by actuating the second wall, the resulting droplets forming dots arranged in a straight line on the medium, the dots being separated in the straight line by a spacing corresponding to the non-ejection chambers.

[0055] It will be appreciated that this method provides many of the advantages discussed above with respect to the apparatus. Note that in any given operating cycle, only active chambers can be firing chambers. However, not all active chambers are firing chambers in any given operating cycle, since whether a given chamber is fired in an operating cycle ultimately depends on the pattern that one wishes to print (as encoded in the input data). On the other hand, while inactive chambers are never fired, not all non-firing chambers are inactive. Some non-firing chambers are not fired because they are active chambers corresponding to gaps in the cycle, or because they are redundant in view of the presence of multiple rows of chambers.

[0056] If a chamber is assigned as an ejection chamber, the second wall of that chamber is actuated to move to eject droplets in the manner generally described herein. Because the walls are adjacent, this means that an inactive chamber has a wall that moves as needed to eject droplets from an adjacent chamber as needed.

[0057] As mentioned above, there may be multiple rows of chambers forming an array. In these cases, the apparatus may operate the rows asynchronously to form a straight line on the media by carefully selecting the time delay between the rows, or to form multiple lines spaced apart in a direction transverse to the direction of the line on the media. When there is a time offset between the rows, an operating cycle should be considered to be the time it takes for all the rows to operate, including the chambers scheduled to operate in that cycle. In some cases, a particular row may not need to operate, but it should be allocated time in the overall operating cycle so that the system remains synchronized.

[0058] Optionally, during an actuation cycle, at least a pair of adjacent active chambers are both designated as ejection chambers, and the second walls of each of said pair of adjacent active ejection chambers are actuated substantially simultaneously. As mentioned above, this simultaneous ejection at high resolution is a feature of the current system and simplifies the waveforms supplied to the printing device. In some cases, during an actuation cycle, all active chambers designated as ejection chambers are actuated substantially simultaneously. As mentioned above, "substantially simultaneously" as used herein may mean that droplets are ejected from two chambers in a time that is much shorter than the time it takes for an actuation cycle to occur (e.g., less than 10%, preferably less than 5%, and more preferably less than 1% of the actuation cycle time). In other examples, "substantially simultaneously" may mean that adjacent chambers are ejecting droplets such that the movement of one of the second walls of the chambers overlaps with the movement of the second of the second walls of the chambers. In other words, the period during which one of the second walls is moving substantially overlaps with the period during which the other of the second walls is moving (50% overlap, preferably 80%, more preferably 95% overlap or more). In any event, the difference in timing between droplet ejection from two adjacent chambers is typically 5 μs or less, preferably less than 2 μs, or even 1 μs or less.

[0059] The method can be carried out with any of the variations of the apparatus described above, thereby bringing the corresponding advantages of the apparatus to the method. [Brief description of the drawings]

[0060] 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 walls of the chambers actuated, and below that a simplified representation of the same actuated walls of the same array. [Diagram 2] FIG. 2 shows an end view of the array configured to operate in a three-cycle mode. [Diagram 3] FIG. 3 shows an end view of an array of fluid chambers in which every other chamber is sealed. [Figure 4] FIG. 4 shows the wall motion of the array of FIG. 3 which produces the droplet deposition pattern shown in FIG. [Diagram 5] FIG. 5 shows an end view of a variation of the arrangement in which pairs of adjacent active chambers are separated from each other by an inactive chamber, for use in this printing mode. [Figure 6] FIG. 6 shows a plan view of the array of fluid chambers of FIG. 5, illustrating the locations of cuts to be made to separate the electrodes on the walls of each chamber. [Figure 7] FIG. 7 shows an end view of an alternative version of the arrangement of FIG. 5, showing electrically isolated electrodes on the walls separating pairs of adjacent active chambers. [Figure 8] FIG. 8 shows a plan view of the array of fluid chambers of FIG. 7, illustrating the locations of cuts to be made to separate the electrodes on the walls of each chamber. [Figure 9] FIG. 9 shows the movement of the array walls to produce the droplet deposition pattern shown in FIG. [Figure 10] FIG. 10 shows a three row arrangement which is a variation of the arrangement shown in FIG. [Figure 11] FIG. 11 shows a four-row arrangement of the array shown in FIG. [Figure 12] Figure 12 shows a six row arrangement of the array shown in Figure 5, in which like elements are designated with like reference numbers throughout. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0061] The present embodiments represent the best ways known to applicant for carrying out the invention, but are not intended to be the only ways in which the invention may be practiced.

[0062] The embodiments described herein relate to a print mode in which adjacent active chambers are arranged in pairs separated by one or more inactive chambers.

[0063] FIG. 5 shows an example of such a printhead, where pairs of adjacent active chambers 12 are separated from each other by individual inactive chambers 13. A series of first walls 14-1 are disposed between the two active chambers 12 of a particular pair of active chambers 12, and a series of second walls 14-2 separate the active chambers 12 from the inactive chambers 13. Each chamber is provided with two separate electrodes on the opposing walls. This is achieved by implementing a laser cut X to separate the electrode of one chamber 12, 13 from the electrode of the adjacent chamber, as shown in FIG. 6, plus a laser cut Y to cut the electrode of each chamber 12, 13 into two electrodes. Thus, each of the two electrodes of a particular chamber is disposed on each of the two walls 14-1, 14-2 that define the chamber and separate the chamber from the adjacent chambers 12, 13.

[0064] This results in the arrangement shown in FIG. 5. In this arrangement, there are two electrodes on each wall (labeled 0 through 7): a first electrode 1a, 2a, etc., shown as a solid line on the "first direction" side of the wall (left side of FIG. 5), and a second electrode 1b, 2b, etc., shown as a dashed line on the "second direction" side of the wall (right side of FIG. 5). All of these electrodes are electrically isolated from each other by a set of cuts X and Y in FIG. 6. The arrangement of cuts shown in FIG. 6 would result in a pair of separate electrodes being placed on either side of each first wall 14-1, but are not shown in FIG. 5. This is to emphasize that the control protocol described here requires that electrodes be placed only on the second wall 14-2. If electrodes are formed on the first walls 14-1, they can be connected to a fixed (and equal) potential, for example to prevent the first walls from moving. In other examples described elsewhere in this specification, these electrodes can be independently controlled to allow movement of one or more of the first walls 14-1 to compensate for induced wall movement when the active chamber is the only active chamber of a pair of adjacent active chambers that ejects in that actuation cycle.

[0065] As mentioned above, Figure 5 shows an array 10 extending in two opposite directions along an axis, a first direction and a second direction (left and right in Figure 5, respectively). In this array 10, the chambers are arranged in pairs of active chambers 12, with each pair of active chambers 12 separated from an adjacent pair of active chambers 12 by an inactive chamber 13. In the example shown, there is only one inactive chamber 13 separating the pairs of active chambers, but in other examples there may be multiple inactive chambers 13 separating the active chambers 12.

[0066] As shown, each of the active chambers 12 has an opening 16 (sometimes called a nozzle or outlet) for ejecting droplets, whereas the inactive chamber 13 has no such opening. That is, the active chamber 12 can eject droplets when its walls 14-1, 14-2 are actuated according to the protocols disclosed herein, whereas the inactive chamber 13 cannot eject droplets even when its wall 14-2 is actuated. In some instances, other methods of preventing droplet ejection can be employed, such as by completely prohibiting fluid from entering the inactive chamber 13, i.e., preventing fluid from being ejected.

[0067] There are two different types of walls 14. A first wall 14-1 of the array 10 is between two active chambers 12. In other words, both sides of the first wall 14-1 are in different active chambers 12. A second wall 14-2 of the array 10 is between an active chamber 12 and an inactive chamber 13. In other words, a first side of each second wall 14-2 is located in an active chamber 12 and a second side of each second wall 14-2 is in an adjacent inactive chamber 13. If there are multiple inactive chambers 13 between pairs of active chambers, a third type of wall (linking two inactive chambers 13) will exist, but this will not be described in detail here as it does not change the overall picture presented here.

[0068] As is evident, the second wall 14-2 is provided with two electrodes, i.e. wall 1 is provided with a first electrode 1a on the wall side in a first direction and a second electrode 1b on the wall side in a second direction. Similarly, wall 2 is provided with a pair of electrodes 2a, 2b on the opposite side of the wall, and correspondingly, walls 4, 5, 7 are provided with electrode pairs 4a, 4b, 5a, 5b, 7a, 7b, respectively. These second walls 14-2 can thus be arranged to deform, thereby changing the volume of the adjacent chambers 12, 13. Typically, the walls move in the direction in which a higher potential is applied, so that, for example, in the example shown in FIG. 5, if the potential of electrode 1a is higher than the potential of electrode 1b, wall 1 moves in a first direction. However, this is only an example and the opposite effect may occur depending on the polarization direction of the piezoelectric material forming the wall. In the absence of a potential difference, the wall is in a neutral position (usually shown as an undeformed, i.e. straight wall).

[0069] The pair of electrodes on each second wall 14-2 may be separately controllable. As used herein, "separately controllable" means not only separately controllable from each other, but also separately controllable from the pair of electrodes of each other second wall 14-2. In this way, each active chamber can be independently actuated to eject droplets by moving that chamber's second wall 14-2 to adjust the volume of that chamber 12. That is, deformation of the second wall of a given active chamber 12 changes the volume of that chamber 12. Depending on the potential applied to each electrode on the second wall 14-2, the movement of the wall 14-2 makes the volume of the chamber 12 larger or smaller depending on whether the second wall 14-2 moves away from or closer to the corresponding first wall 14-1. The change in volume causes droplets to be ejected based on principles similar to those described above. In some cases, the ejection process may simply involve reducing the volume of the active chamber 12 and then returning it to a neutral volume (the volume when both the first wall 14-1 and the second wall 14-2 of the active chamber 12 are in a neutral position). In other cases, the volume of the chamber may be first increased to draw in fluid and then decreased to expel the droplets, this latter decrease in volume sometimes involving a decrease back to the neutral volume, but in other cases may involve a decrease in volume below the neutral configuration.

[0070] This arrangement also allows different potentials to be applied to each side of each wall. A brute force approach would be to connect each electrode to an independent control signal, thus controlling each wall completely separately. In fact, the number of connections (and control complexity) can be reduced by connecting the electrodes on one side of each second wall (such as the right electrode shown in dashed lines in FIG. 5) to a common fixed potential. This arrangement allows each second wall 14-2 to be controlled individually. This is done by supplying an active potential higher or lower than the common potential to the electrode on the opposite side of that wall (in the present example, the left side of the second wall 14-2 shown in solid lines in FIG. 5). Viewed another way, the volume of each chamber 12 can be adjusted by supplying a corresponding potential to the active electrode of that chamber, or to the active electrode on the opposite side of the wall where the common electrode of that chamber is located. Within this framework, droplet ejection works similarly to the above, with the chambers expanding and contracting to eject droplets.

[0071] It will thus be apparent that in some instances one electrode of an electrode pair on each second wall 14-2 may be connected to a common potential and the other electrode of each pair may be controlled independently of the other electrode to actuate the respective second wall 14-2, or alternatively each electrode on each second wall 14-2 may be controllable independently of all other second wall electrodes.

[0072] It is noted that an increase in the volume of a corresponding active chamber 12 due to movement of the second wall 14-2 necessarily results in a decrease in the volume of the corresponding inactive chamber 13 on the other side of the second wall 14-2. The converse is also implicitly true: a decrease in the volume of a corresponding active chamber 12 results in an increase in the volume of the corresponding inactive chamber 13 on the other side of the second wall 14-2.

[0073] In contrast, the first wall 14-1 (walls 0, 3, and 6) can have electrodes isolated from all electrical connections. This alternative arrangement is shown in Figures 7 and 8. Figure 7 shows the first wall 14-1 with a pair of electrically isolated electrodes on either side of the wall, and Figure 8 shows the arrangement of cuts that results in this electrode arrangement. Again, the electrodes are formed by making additional cuts with laser cutting beyond the standard cut set X along the wall. Specifically, an additional cut Y separates the electrodes on the adjacent second wall 14-2 from each other. An additional cut Z is made to completely separate the electrodes on the first wall 14-1 from all other electrodes. This prevents these isolated electrodes from being connected to an external power source. The result is shown in detail in Figure 7. In the figures, isolated electrodes 0a,b, 3a,b, 6a,b are shown as thin dashed lines with no external connections (i.e., no arrows leading to external voltage control), while active electrodes 1a,b, 2a,b, 4a,b, 5a,b, 7a,b are shown as thick solid or thick dashed lines with external connections represented by arrows.

[0074] In this scheme, the pair of active chambers 12 are ejection chambers, and the walls are divided into two groups. A first wall 14-1 separates adjacent active chambers, and a second wall 14-2 separates the active and non-active chambers. In FIG. 7, the first wall 14-1 is a non-actuated wall, but it carries electrodes. However, these electrodes are physically separated from the tracks carrying the control signals and from each other. Therefore, when a force is applied to these walls, a charge is induced on each of the separated electrodes due to the electrical separation of the electrodes. These charges are not released from the separated electrodes, but create an electric field that is applied to the non-actuated walls, which results in the piezoelectric material of the non-actuated walls exerting a force that opposes the first force. The direct piezoelectric effect effectively strengthens the non-actuated walls in response to pressure in the chamber, opening up the opportunity to use deeper chambers and larger sub-droplet designs.

[0075] Returning now to the present arrangement, in other examples, some or all of the first walls 14-1 may include electrodes (as shown in FIG. 7) on one or both of the surfaces located within the two active chambers 12 adjacent to the first wall 14-1. In other examples, no electrodes may be located on the first walls 14-1, in which case these walls 14-1 are not controllable and therefore not actuated to move. In other examples, these additional electrodes are independently controllable, providing a small corrective action to the droplet ejection process to compensate for induced wall motion, for example when only one active chamber of a pair of adjacent active chambers is the ejection chamber.

[0076] It is clear that the array 10 is based on a basic unit of two adjacent active chambers 12 followed by an inactive chamber 13. This basic unit may be repeated for all or part of the array 10. When this pattern is repeated for a portion of the array 10, the highest resolution of active chambers consistent with the characteristics of the current model (disclosed herein) is achieved for that portion of the array 10. In this optimal case, the ratio of active to inactive chambers approaches 2:1 (the limit for an infinitely long array).

[0077] Turning now to FIG. 9, a suitable ejection pattern is shown to generate the droplet ejection of FIG. 5. It can be seen that FIG. 9 shows a schematic of the wall actuation performed to eject droplets. The droplet ejection pattern is encoded into input data. This input data effectively designates the active chambers 12 as ejection chambers (i.e., intended to eject droplets through the active chamber openings 16) or non-ejection chambers (i.e., not intended to eject droplets). The inactive chambers 13 cannot be designated as ejection chambers since they cannot eject droplets because they have no exit opening or are filled with air. It can be seen that the ejected droplets are located in a line on the medium, the shape of the line corresponding to the shape of the array (e.g., a straight line in the case of a linear array). By introducing a relative motion between the array 10 and the medium in a direction transverse to the extension of the line formed on the medium, a two-dimensional pattern can be printed. It can be seen that the array 10 can be configured to generate different droplet ejection patterns at different times to cover a two-dimensional area with any pattern by triggering the appropriate ejection patterns at the appropriate times. Each period during which all chambers designated as firing chambers in the array 10 eject droplets is called an actuation cycle. Input data can be provided once per actuation cycle, and each actuation cycle can assign active chambers 12 as firing or non-firing chambers, independent of other actuation cycles.

[0078] Then, during any given actuation cycle, input data is received and converted into an appropriate trigger signal to actuate the associated wall to eject a droplet from the desired chamber 12. In contrast, any active chamber 12 (and all inactive chambers 13) designated as a non-ejection chamber for that actuation cycle will not eject droplets during that actuation cycle. Specifically, if an active chamber 12 is assigned as an ejection chamber, then the second wall 14-2 of that chamber 12 is actuated to move and eject droplets.

[0079] In more detail, an example of the ejection procedure is shown in Figure 9. Here, the array 10 is shown at five different times t = {0, t1, t2, t3, t4} (not necessarily evenly spaced in time) with the wall movement exaggerated to highlight the process. The chambers 12 are labeled (0) through (5) and the walls are labeled W0 through W6. Chambers (1) and (4) are inactive chambers 13, while the remaining four chambers (0), (2), (3), and (5) are active chambers. Of these, (2) and (3), bounded by a second wall 14-2 labeled W2 and W4 and separated from each other by a first wall 14-1 labeled W3, are designated as ejection chambers, as shown underlined below the array 10 at each time step. (0) and (5) are designated as non-ejection chambers and are therefore not underlined.

[0080] At time t=0, array 10 has received input data and assigned the chambers that correspond to the locations where droplets are to be deposited (chambers (2) and (3)) as ejection chambers. Chambers (0) and (5) are designated as non-ejection chambers. Chambers (1) and (4) are inactive chambers and will never become ejection chambers, so there is no need to assign them.

[0081] At time t=t1, a potential is applied to the array 10 and the deposition process is initiated. In this example, droplet deposition begins with an expansion phase in the relevant chamber, drawing additional fluid into chambers (2) and (3). Note that at this time, the volume of the adjacent inactive chambers (1) and (4) (marked generally with an X to indicate the inactive state) decreases correspondingly due to the deformation of the walls. This can be achieved by applying appropriate potentials to the electrodes of walls W2 and W4. For materials such that the walls move towards a more positive potential, the electrode on the surface of wall W2 inside chamber (1) is applied with a higher potential than the electrode on the surface of wall W2 inside chamber (2). Similarly, the electrode on the surface of wall W4 inside chamber (4) is applied with a higher potential than the electrode on the surface of wall W4 inside chamber (3). This movement causes a decrease in pressure in chambers (2) and (3) (indicated by a "-") and fluid to flow into these chambers. In this example, the other walls do not move.

[0082] At time t=t2, the potential supplied to the array 10 is changed and the relevant walls move again to continue the deposition process. Now, walls W2 and W4 move past their neutral (i.e. vertical) position and occupy positions such that the volumes of chambers (2) and (3) are smaller than when the walls are in their neutral position. As before, this causes the volumes of the adjacent inactive chambers (1) and (4) to increase accordingly. Consistent with the situation described in the previous time step, the electrode on the surface of wall W2 inside chamber (1) is supplied with a lower potential than the electrode on the surface of wall W2 inside chamber (2). Similarly, the electrode on the surface of wall W4 inside chamber (4) is supplied with a lower potential than the electrode on the surface of wall W4 inside chamber (3). The effect of this movement is to cause an increase in pressure (denoted by a "+") in chambers (2) and (3), which causes fluid to flow out of the openings of these chambers and form droplets for deposition on the medium.

[0083] At time t=t3, the potentials applied in the previous step are maintained, holding the array 10 in the configuration of the previous step. This times the return of the walls to counteract as much of the pressure wave remaining in the chamber as possible. Note that this step is optional and in any case may be somewhat shorter than the other steps of the deposition process.

[0084] Finally, at time t=t4, the potentials are changed again and the array 10 is returned to a neutral state, ready for the next input data line to be applied and the process to begin again, as indicated by the underline representing the active ejection chamber being removed and the active chamber 12 being ready to be next assigned as either an ejection chamber or a non-ejection chamber.

[0085] For simplicity, at the start of the above actuation cycle, all walls 14 in the array 10 of fluid chambers 12, 13 are at rest in a neutral position; that is, the same potential is applied to both electrodes on each wall 14 side where an electrode resides. In this way, the volume of each fluid chamber remains constant. The array is also shown to return to this configuration at the end, although in some cases the array 10 need not do this. In particular, corrections can be applied to the movement in subsequent actuation cycles to account for differences in initial conditions.

[0086] From the above it can be seen that the non-active chamber 13 acts as a buffer to prevent cross talk between the chambers. Since the active ejection chamber is by definition actuated by moving only the second wall 14-2 adjacent to the non-active chamber 13, pairs of active chambers can operate simultaneously without affecting each other. Note that the walls 14 of the non-ejecting active chambers do not move at all during the actuation cycle, whereas the only walls that move in the non-active chambers 13 are those adjacent to the ejecting adjacent active chambers.

[0087] In this example, it is clear that at least one pair of adjacent active chambers are both designated as ejection chambers and that the second walls of each of said pair of adjacent active ejection chambers are actuated substantially simultaneously. As previously mentioned, this simultaneous ejection at high resolution is a feature of the current system disclosed herein and simplifies the waveforms supplied to the printing device. In some cases, during an actuation cycle, all active chambers designated as ejection chambers are actuated substantially simultaneously. As used herein, "substantially simultaneously" may mean that droplets are ejected from two chambers with a time difference that is much less than the time it takes for an actuation cycle to occur (e.g., less than 10%, preferably less than 5%, and more preferably less than 1% of the actuation cycle time). In other examples, "substantially simultaneously" may mean that adjacent chambers eject droplets and that the movement of a first wall of the chamber overlaps with the movement of a second wall of the chamber. In other words, the period during which one of the second walls is moving substantially overlaps with the period during which the other of the second walls is moving (75% overlap, preferably 80%, and more preferably 95% overlap or more). In any event, the difference in timing of droplet ejection from two adjacent chambers is typically 0.5 μs or less, preferably less than 0.2 μs or less than 0.1 μs. Another way to think of this is that the difference in vertical position of the droplets deposited on the medium is much smaller than the size of the droplets (e.g., less than 5%, less than 2%, or in some instances less than 1%).

[0088] In the example shown in FIG. 9, the volume of the ejection chamber is increased until it is greater than the neutral volume (the "suction step"), and then decreased to less than the neutral volume (the "discharge step"). However, the suction and discharge steps need not be implemented in this manner. For example, deposition could be implemented by simply decreasing the volume of the ejection chamber without the suction step being required at all (e.g., the actuation cycle would consist only of steps shown at times t=0 and t=t2). Similarly, the suction step could be used to aspirate excess fluid, and then the excess fluid could be expelled by returning to a neutral state. Here, the actuation cycle would consist only of steps shown at t=0, t=t1, and t=t4 (although at t=t4 a drop is formed by the ejection chamber that is not currently shown).

[0089] Although the array 10 has been shown thus far as a generally linear row for ease of explanation, it will be understood that different shapes and arrangements of chambers can be formed depending on the intended application while still maintaining the advantages described herein. Although the array 10 has been described primarily with respect to a single row of chambers, the array can also be formed from multiple linear rows extending parallel to one another. These repeating rows work particularly well with the long repeating 2-1-2-1 pattern described above, but can also be used with shorter lengths than those described herein. Each row can be further offset from the other rows in the direction in which the rows extend, and optionally each row is arranged to be actuated at different times to deposit droplets ejected from each row on the medium in a substantially straight line. The offset in the direction of the rows can be selected to align the active chambers of one row with the wall or inactive chambers of another row. Typically, there is relative motion between the device and the medium, so that the time delay between the ejection of droplets of different rows corresponds to a distance offset in the direction across the rows. Thus, timing offsets can be selected to align the outputs of different columns in space on the media, taking into account the motion of the device relative to the media and the fact that the columns themselves are spaced apart from each other in the transverse direction.

[0090] It should be noted that the timing difference between rows is optional, since it may be desired to deposit at different locations on the media. For example, if there are enough rows such that there is full redundancy (e.g., each location is covered multiple times at the desired resolution), the machine may print two or more complete rows simultaneously, spatially offset, or at twice the frequency, each of which will affect the timing offset between the rows, and a time delay between some rows may not be necessary or desirable. If there is a time offset between the rows (asynchronous firing), the actuation cycle should be considered as the time it takes to fire all columns, if the columns contain chambers that are scheduled to fire in that cycle. In some cases, it may not be necessary to fire a particular column, but time must be allocated to that column in the overall actuation cycle to keep the system synchronized.

[0091] As examples of this, three specific arrangements of multiple rows (Figures 10 through 12) and corresponding offset arrangements are presented to favor spreading deposition across the entire array. In each case, the repeating unit of the chambers is the current system arrangement of two active repeating units and one inactive repeating unit. And because the active and inactive chambers are arranged in this repeating pattern of total width D (i.e., the system can be effectively described using modular arithmetic), the following description describes an offset of a distance L in a first direction, but this could equally be implemented by an offset of a different distance DL in a second direction opposite the first direction.

[0092] It should be noted that there may be multiple distinct groupings of rows, with each row in a group offset the same amount (and direction) along with the adjacent rows. This simplifies manufacturing as the etching tool can move in a single diagonal direction and etch multiple rows in one sweep without the need for repositioning or realignment.

[0093] To achieve a uniform distribution of apertures (corresponding to uniform droplet distribution), multiple rows can be employed. Considering only the case where all chambers and walls have the same width, the simplest arrangement is a four-row layout (Figure 11). This arrangement repeats some (but not all) of the nozzle positions. Alternatively, a six-row layout can be considered (Figure 12). This arrangement doubles the printing resolution in the printing direction, since each nozzle position is repeated.

[0094] With certain adjustments to the arrangement of the chambers, a three-column layout can also be used to neatly spread out the array 10 in equal increments. For example, see FIG. 10, which illustrates such an array 10. In this three-column variation, there are (at least) three parallel linear columns 21, 22, 23. In each column, the width of each active chamber 12 in the direction of its column extension (shown as blank in FIG. 10) is a distance d, the combined width of the inactive chamber 13 (shown as dotted hatching) and the two second walls 14-2 adjacent to the active chamber 12 is a distance 2d, and the width of each first wall 14-1 adjacent to an adjacent pair of active chambers 12 is a distance 2d. The second column 22 is offset from the first column 21 by a distance d in a first direction (left side in FIG. 10) along the direction of the columns extension. The third column 23 is offset from the second column 22 by a distance d in the first direction. Thus, the third column 23 is offset from the first column 21 by a distance 2d in the first direction, which corresponds to (-4)d in the first direction, or 4d in a second direction opposite the first direction along the extension of the columns (i.e., to the right in Figure 10).

[0095] This covers the entire extent of the array 10, allowing one drop to be deposited per distance d across the repeat unit. At each position, each active chamber 12 is evenly spaced a distance 2d from two adjacent chambers, so that the offset d between the first column 21 and the second column 22 covers a first half of the intervening space, and a further offset d between the second column 22 and the third column 23 covers a second half of the intervening space, i.e., there are three deposition positions in a width of 3d. Because there are two active chambers 12 per repeat unit (total width 6d), a complete repeat unit allows a series of drops to be deposited, spaced a distance d apart from each other. This is shown to scale in the bottom left of Figure 10, showing six evenly spaced distances d and how each area of ​​width d relates to the active chambers 12 in the set of three columns.

[0096] Note that the inactive chambers 13 in the three-column arrangement are narrower than the active chambers 12. Also, the first wall 14-1 is thicker than the second wall 14-2. This is to ensure that the pattern repeats each distance of 6d. The line between the two halves of the first wall 14-1 is to guide the eye and indicate that the columns are offset to align with their neighbors, and does not necessarily mean that these walls 14-1 are physically separated into two halves. In general, the inactive chambers 13 can be shaped and sized differently than the active chambers 12 to achieve the required printing density. For example, the inactive chambers 13 can be narrower (as in FIG. 10), wider, longer, shorter, deeper, and / or shallower than the active chambers 12. Similarly, the first wall 14-1 can be different in width from the second wall 14-2 to accommodate the desired printing resolution or arrangement. For example, the first wall 14-1 (width 2d) does not need to be twice the width of the active chambers 12, but only width d. This means that the arrangement is repeated every 5d instead of 6d as in Figure 10. This means that instead of each successive row being offset from the other by a distance d, a shorter offset of 5d / 6 is used. This increases the linear dot deposition density by about 20%, but the distribution is not perfectly even as the dots from any given row are not evenly distributed.

[0097] 11, which shows a four-row arrangement, it can be seen that a complete repeating unit width of 6d can be spanned by four parallel linear rows, each with a row width of the active chamber, inactive chamber, and first and second walls all equal to a distance d. Here, the second row 22 is offset in the first direction along the row extension direction from the first row 21 by a distance 2d. The third row 23 is offset in the first direction from the second row 22 by a distance d. Finally, the fourth row 24 is offset in the first direction from the third row 23 by a distance 2d.

[0098] Due to the repeating nature of the rows, the fourth row 24 is offset from the first row 21 by a distance 5d in the first direction, which is equal to (-1)d in the first direction, or d in a second direction opposite the first direction along the row extension. This arrangement covers the entire range of the row for every distance d, and since there are eight deposition positions spread over a distance of 6d, some positions are covered by two active chambers 12, as shown in the scale at the bottom left of FIG. 11. It is clear that due to the offset arrangement, each different position (separated from each other by a distance d) is aligned with two walls 14 and two chambers 12, 13. In some cases, it is aligned with two active chambers 12, and in other cases, it is aligned with one active chamber 12 and one inactive chamber 13.

[0099] 12 shows a six-column arrangement in which all chambers 12, 13 and walls 14 have a width d and the same number of active chambers 12 are arranged at each location, separated by a distance d. In this six-column arrangement, there are at least six parallel linear rows in which the active chambers, inactive chambers, and first and second walls all have a width equal to the distance d in the direction of the row. Here, the second row 21 is offset from the first row 21 by a distance 2d in the first direction along the row direction. The third row 23 is offset from the second row 22 by a distance 2d in the first direction. The fourth row 24 is offset from the third row 23 by a distance d in the first direction. The fifth row 25 is offset from the fourth row 24 by a distance 2d in the first direction. Finally, the sixth row 26 is offset from the fifth row 25 by a distance 2d in the first direction.

[0100] Thus, the sixth column 26 is offset from the first column 21 by a distance 9d in the first direction, which corresponds to 3d or (-3)d in the first direction, or 3d in a second direction opposite the first direction along the direction of the columns. This covers the full extent of the columns twice at each location, once every d, as shown on scale in the bottom left of Figure 12. The offset arrangement allows each of the different locations (separated by a distance d from each other) to be in line with the three walls 14, the two active chambers 12, and the one inactive chamber 13.

[0101] It is noted that in each of the above multiple column examples, the first column, second column, third column, etc. are labels for convenience, and the columns do not necessarily have to be actually arranged in this order. In other words, the second column is not necessarily directly adjacent to (i.e., between) the first and third columns. Thus, the arrangement of the four columns may not only be 1-2-3-4 in order, but may also be 3-1-4-2, 4-3-2-1, or any of 21 other arrangements of four columns. In terms of Figures 10 to 12, this means that any two columns can be swapped with each other (their horizontal arrangement relative to each other, and their horizontal arrangement with the other columns is preserved). The system then essentially functions in the same way as above. In some cases, a timing offset is applied to the columns such that the droplets generated by the columns are placed on the media as a single line. In this case, the vertical position of the columns determines this timing offset, and so a correction must be made when swapping columns. That is, the timing offset (if any) is related to the vertical position of the columns.

[0102] 10-12, the scale has been exaggerated to emphasize the arrangement of the walls 14 and the chambers 12, 13.

[0103] Finally, note that in some arrangements the size of the row offset can be chosen in the direction of the row spread to achieve a particular printing resolution. In particular, if a linear drop density is desired where each drop is within a distance x of the nearest drop, then the smallest unit of offset between columns can be chosen to be no larger than x.

[0104] In a more generalized example, there are N rows, each row containing a repeating section with a repeating unit of chambers of total length D, and the offset d between the rows can be selected as an integer multiple of the ratio D / N. This means that the droplets generated in each row are equally spaced and incremented over the entire length of the repeating unit. Further advantageously, the provision of active chambers at equivalent locations along the rows of different rows (i.e., multiple active chambers directed to the same location on the medium) can be avoided as much as possible, thus improving the resolution of the system. This means that the location of the inactive chambers (and walls) of one row can be covered by one of the active chambers of a different row with as little repetition as possible.

[0105] In general, for example, if a column is formed of a repeating unit of x active chambers and y inactive chambers (x>0, y>0), it is possible for each inactive position in the first column to be covered by an active position in another column formed from the same repeating unit, in which case N columns are used.

number

[0106] In yet another example, the location of the opening in an active chamber may be positioned off-center within that chamber, or may be positioned to direct droplets ejected onto the medium in a manner that is not aligned with the center of the active chamber. This allows the array to evenly space droplets ejected by the array even when there is only one row. For example, if the opening (or droplet location on the medium) is positioned toward the left end of the left chamber of each chamber pair and toward the right end of the right chamber of each chamber pair, the output of two adjacent active chambers may be shifted to partially overlap the area corresponding to the inactive chamber that separates the chamber pair. This partial overlap may be selected such that the spacing between the left and right droplets of an adjacent pair is equal to the spacing of droplets between the left chamber of a pair and the right chamber of an adjacent pair (i.e., separated by one or more inactive chambers). This means that although the linear droplet density is reduced compared to the linear density of the chambers (considering both active and inactive chambers), the total length of the array can be extended in even increments, even though at most only two of the three chambers are active chambers.

[0107] The print resolution in the arrangement described herein can be further improved by reducing the width of the inactive chambers, the active chambers, the width of the walls separating the individual active chambers (e.g., FIG. 5, walls 3, 6) or the width of the actuating walls (e.g., FIG. 5, walls 1, 2, 4, 5, 7). As is evident from FIG. 10, reducing the width of the active walls allows for a three-column layout, with each column configured to provide a native print resolution of, for example, 120 dpi. A two-column layout can also be achieved by reducing the width of the first wall 14-1 separating the individual active chambers.

Claims

1. A device for depositing liquid droplets onto a medium, Equipped with an array of chambers, The aforementioned array is, A first subset of chambers comprising multiple chambers arranged to selectively deposit droplets of fluid, A second subset of chambers comprising multiple chambers not configured for the selective deposition of fluid droplets, At least one of the chambers in the first subset of the chambers is an active chamber. The active chamber has a first wall adjacent to the chamber from a first subset of the chamber, and a second wall opposite the first wall. The second wall is formed of a piezoelectric material and is adjacent to one of the chambers in the second subset of the chamber, In the second subset of the chambers, at least one of the chambers is an inactive chamber. Each inactive chamber has two opposing walls. At least one of the walls of the inactive chamber is adjacent to a chamber in the first subset of the chamber, Each active chamber is A first electrode on the surface of the second wall inside the active chamber, and a second electrode on the opposing surface of the second wall outside the active chamber, The surface of the first wall located inside the active chamber, The surface of the first wall either has no electrodes on it or has a third electrode on it. The third electrode is either independently controllable from the first electrode and the second electrode, or electrically insulated from them. The device is configured to supply an operating potential independently of the first and second electrodes of each active chamber. Each of the second walls is operable to deform in response to the supply of the operating potential to the second electrode, An apparatus wherein each chamber in a first subset of the chambers communicates with an opening for releasing droplets of fluid and with a fluid supply unit, and selectively deposits the fluid in response to the supply of an operating potential to the second electrode on the second wall of each active chamber.

2. The apparatus according to claim 1, wherein the array includes at least one pair of adjacent active chambers, the pair of adjacent active chambers being substantially simultaneously operable.

3. One or more inactive chambers, A supply unit containing printing fluid, or not in communication with said supply unit, Without openings for selective fluid discharge, and / or The apparatus according to claim 1, which is filled with a gas or a mixture of gases such as air.

4. The apparatus according to claim 1, wherein the array includes a pair of adjacent active chambers separated from another pair of adjacent active chambers by an inactive chamber.

5. The apparatus according to claim 4, wherein the arrangement includes a repeating pattern of three chambers arranged such that two adjacent active chambers are followed by a single inactive chamber.

6. The terminal chamber of the aforementioned array is A second subset of the chamber, or an active chamber, The second chamber from the end in the aforementioned array is either a chamber of a second subset of the aforementioned chamber, or The apparatus according to claim 5, wherein the outermost wall of the apparatus is movable independently of the other walls of the array.

7. The apparatus according to claim 1, wherein the aforementioned or each inactive chamber differs in shape and / or size from the aforementioned or each active chamber.

8. The apparatus according to claim 1, wherein the first wall has a width different from the width of the second wall, and / or the first wall is formed from a material different from the material forming the second wall.

9. The apparatus according to claim 1, wherein the arrangement includes adjacent chambers arranged in a row, and optionally the row is substantially linear.

10. The apparatus according to claim 9, comprising a plurality of linear rows extending parallel to each other.

11. The apparatus according to claim 10, wherein each row is offset from the other rows in the direction in which the row extends, and optionally each row is arranged to be operated at different times to deposit the droplets ejected from each row onto the medium in a substantially straight line.

12. The apparatus according to claim 11, wherein the size of the offset is selected to achieve a specific print resolution.

13. The apparatus according to claim 11, wherein there are N columns, each column comprising a repeating portion having repeating units of chambers with a total length D, and the offset d between the columns is an integer multiple of the ratio D / N.

14. There are at least four parallel linear rows, and in each row, the width in the direction in which the active chamber, the inactive chamber, and the first and second walls extend is all equal to the distance d. The second column is offset from the first column by a distance 2d in the first direction along the direction in which the column extends. The third column is offset from the second column by a distance d in the first direction. The apparatus according to claim 11, wherein the fourth column is offset from the third column by a distance 2d in the first direction.

15. There are at least six parallel, linear rows, and in each row, the width in the direction in which the active chamber, the inactive chamber, and the first and second walls extend is all equal to the distance d. The second column is offset from the first column by a distance 2d in the first direction along the direction in which the column extends. The third column is offset from the second column by a distance of 2d in the first direction. The fourth column is offset from the third column by a distance d in the first direction, The fifth column is offset from the fourth column by a distance of 2d in the first direction. The apparatus according to claim 11, wherein the sixth column is offset from the fifth column by a distance 2d in the first direction.

16. There are at least three parallel, linear rows, and in each row, the width in the direction in which each row of active chambers extends is distance d, the combined width of each inactive chamber and the two second walls adjacent to each active chamber is distance 2d, and the width of each first wall adjacent to an adjacent pair of active chambers is distance 2d. The second column is offset from the first column by a distance d in the first direction along the direction in which the column extends. The apparatus according to claim 11, wherein the third column is offset from the second column by a distance d in the first direction.

17. The apparatus according to claim 1, wherein the second wall is arranged to deform in a first direction in response to a first potential difference applied to the entire second wall, and the second wall is arranged to deform in a second direction opposite to the first direction in response to a second potential difference applied to the entire second wall.

18. One or more second walls, The above or each first electrode is held at a fixed potential, and the device is arranged to supply to the above or each corresponding second electrode either a first potential higher than the fixed potential or a second potential lower than the fixed potential, or The apparatus according to claim 17, wherein the above or each second electrode is held at a fixed potential, and the apparatus is operable by either supplying the above or each corresponding first electrode with either a first potential higher than the fixed potential or a second potential lower than the fixed potential.

19. The apparatus according to claim 1, wherein one or more second walls are activated by independently supplying different potentials to one or more first electrodes and corresponding second electrodes.

20. The apparatus according to claim 1, wherein one or more third electrodes are electrically completely insulated from all other electrodes and potential supply units.

21. A method for depositing liquid droplets onto a medium using an apparatus, The apparatus comprises an array of chambers, The aforementioned array is, A first subset of chambers comprising multiple chambers arranged to selectively deposit droplets of fluid, A second subset of chambers comprising multiple chambers not configured for the selective deposition of fluid droplets, At least one of the chambers in the first subset of the chambers is an active chamber. The active chamber has a first wall adjacent to the chamber from a first subset of the chamber, and a second wall opposite the first wall. The second wall is formed of a piezoelectric material and is adjacent to one of the chambers in the second subset of the chamber, In the second subset of the chambers, at least one of the chambers is an inactive chamber. Each inactive chamber has two opposing walls. At least one of the walls of the inactive chamber is adjacent to a chamber in the first subset of the chamber, Each active chamber is A first electrode on the surface of the second wall inside the active chamber, and a second electrode on the opposing surface of the second wall outside the active chamber, The surface of the first wall located inside the active chamber, The surface of the first wall either has no electrodes on it or has a third electrode on it. The third electrode is either independently controllable from the first electrode and the second electrode, or electrically insulated from them. In the operating cycle, The process of receiving input data, A step of assigning all the active chambers in the first subset to either injection chambers or non-injection chambers, based on the input data, so as to create a strip-shaped region consisting of one or more consecutive injection chambers separated by intervals corresponding to a continuous strip-shaped region consisting of chambers that are either non-injection chambers or inactive chambers, Based on the input data, the operating potential is selectively supplied to the first electrode and / or the second electrode. In each active chamber assigned to a non-injection chamber, the second wall remains in the neutral position. In each active chamber assigned to the injection chamber, the second wall is operated to reduce the volume of the active injection chamber and deposit fluid droplets. By activating the second wall, each injection chamber releases at least one droplet. The resulting droplets form dots arranged in a straight line on the medium. A method comprising the step of acting the second wall of the active chamber such that the dots are separated on the line by intervals corresponding to the non-injection chambers.

22. The method according to claim 21, wherein during the operating cycle, at least one pair of adjacent active chambers are both designated as injection chambers, and the second walls of each of the pair of adjacent active injection chambers are operated substantially simultaneously.

23. The method according to claim 21, wherein all active chambers designated as injection chambers are operated substantially simultaneously during the operating cycle.

24. The method according to claim 21, wherein the apparatus is the apparatus described in any one of claims 1 to 20.

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