EP3493992B1

EP3493992B1 - Arrangement of actuator components for a droplet deposition apparatus, droplet deposition apparatus, method of operating the droplet deposition apparatus and control circuitry for the droplet deposition apparatus

Info

Publication number: EP3493992B1
Application number: EP16750237.6A
Authority: EP
Inventors: Juan REYERO; Jesus Garcia Maza
Original assignee: Xaar Technology Ltd
Current assignee: Xaar Technology Ltd
Priority date: 2016-08-05
Filing date: 2016-08-05
Publication date: 2022-06-22
Anticipated expiration: 2036-08-05
Also published as: CN109562626A; JP2019527637A; EP3493992A1; SG11201900313QA; CN109562626B; WO2018025003A1; JP7026099B2

Description

The present techniques generally relate to apparatus and methods for reducing visible artefacts which arise when adjacent actuator components are misaligned.
Generally speaking, a droplet deposition apparatus, such as an inkjet printer, print dots by ejecting small droplets of fluid (e.g. ink) onto receiving media. Such a droplet deposition apparatus typically comprises at least one droplet deposition head having a nozzle array. The nozzle array comprises multiple nozzles, where each nozzle is configured to eject droplets of fluid (e.g. ink) in response to a command signal received from control circuitry, to reproduce an image on a receiving medium.
Typically, a droplet deposition apparatus may divide an image (or a swathe of an image) into several sub-images. Each sub-image may be printed either by a droplet deposition head which passes over the receiving medium multiple times to reproduce each sub-image on the receiving medium. Alternatively, each sub-image may be printed by multiple droplet deposition heads located in different positions with respect to the receiving medium, where each droplet deposition head may be responsible for printing a particular sub-image. In this latter case, each droplet deposition head may remain in a fixed position, or may pass over the receiving medium multiple times.
A droplet deposition apparatus comprising multiple droplet deposition heads (each having one or more nozzle arrays), and/or multiple nozzle arrays, is usually fabricated such that the nozzle arrays are arranged in parallel but offset from each other along a media feed axis (or in the direction of droplet deposition). This enables the nozzle arrays to cover adjacent swathes. Such arrangements often suffer from alignment problems that result in a visible fault or artefact in the printed image at the point where adjacent swathes meet (i.e. along a seam between adjacent swathes). The visible fault typically presents itself as a light or dark band in the printed image, which is noticeable to the human eye. However, it is time-consuming and expensive to arrange the nozzle arrays located in separate actuator components, or within separate droplet deposition heads, within a droplet deposition apparatus in such a way as to limit the misalignment and to reduce or avoid resulting visible faults in the printed image.
The present applicant has recognised the need for an improved technique to reduce or avoid the visible fault which arises when adjacent nozzle arrays are misaligned.
Background art is provided in US 2008/158295 A1 and US 2006/279606 A1 .
US 2008/158295 A1 discloses an inkjet head which includes a nozzle array including plural nozzles. The nozzle array has a first nozzle group arranged in the centre thereof and second nozzle groups arranged further on outer sides than the first nozzle group. Inter-nozzle pitches of the second nozzle groups are larger than inter-nozzle pitches of the first nozzle group. A direction in which nozzles of the second nozzle group eject an ink and a direction in which nozzles of the first nozzle group eject the ink are different.
US 2006/279606 A1 discloses an inkjet print head, inkjet printing apparatus, and method for manufacturing an inkjet print head. The inkjet print head includes a plurality of chips, in each of which adjacent nozzle lines are formed. The relative positions of the chips are set depending on the amounts of misdirection of ink ejected from overlapping nozzles in a joining portion between adjacent nozzle lines.
Aspects of the present techniques are set out in the appended claims.
The techniques are diagrammatically illustrated, by way of example, in the accompanying drawings, in which:

Figure 1a is a schematic of two overlapping actuator components, each actuator component having a nozzle array;
Figure 1b is a schematic of two overlapping droplet deposition heads;
Figure 2a is a schematic of a nozzle array in an actuator component, the nozzle array comprising a first portion having a constant nozzle pitch and a second portion having a variable nozzle pitch;
Figure 2b is a schematic of a nozzle array in an actuator component, the nozzle array comprising a first portion having a constant nozzle pitch, a second portion having a variable nozzle pitch, and a third portion having a further variable nozzle pitch;
Figure 3a illustrates a single row of the nozzle array of Figure 2a;
Figure 3b illustrates how two single rows in adjacent nozzle arrays of the type shown in Figure 2a are arranged to overlap;
Figure 4a illustrates a single row of the nozzle array of Figure 2b;
Figure 4b illustrates how two single rows in adjacent nozzle plates of the type shown in Figure 2b are arranged to overlap;
Figure 5 is a schematic diagram of how fluid may be deposited using overlapping actuator components;
Figure 6a is a schematic diagram of a nozzle array of an actuator component, the array comprising multiple rows of nozzles;
Figure 6b illustrates an arrangement of the rows of nozzles of the nozzle array of Figure 6a;
Figure 7 illustrates how to deposit fluid using overlapping actuator components having multiple rows of nozzles;
Figure 8 illustrates how to deposit a first fluid and a second fluid using overlapping actuator components having multiple rows of nozzles;
Figure 9a illustrates a misalignment in overlapping actuator components;
Figure 9b illustrates how to compensate for the misalignment shown in Figure 9a;
Figure 10a shows a (default) constant nozzle pitch between nozzles in an overlap region of two overlapping actuator components;
Figure 10b shows, for 1200dpi actuator components having the constant nozzle pitch of Figure 10a, how it becomes more difficult to find a suitably aligned pair of nozzles as the misalignment between overlapping actuator components increases, and Figure 10c shows how the absolute percentage jump in pitch at a switch point between the actuator components of Figure 10a varies as a function of misalignment;
Figure 10d shows the same information as Figure 10b but for 600dpi actuator components and Figure 10e shows the same information as Figure 10c but for 600dpi actuator components;
Figure 11a shows two overlapping actuator components which have a variable nozzle pitch defined by a sinusoidal function;
Figure 11b shows, for 1200dpi actuator components having the sinusoidal variable nozzle pitch of Figure 11a, how it becomes more difficult to find a suitably aligned pair of nozzles as the misalignment between overlapping actuator components increases, and Figure 11c shows how the absolute percentage jump in pitch at a switch point between the actuator components of Figure 11a varies as a function of misalignment;
Figure 11d shows the same information as Figure 11b but for 600dpi actuator components, and Figure 11e shows the same information as Figure 11c but for 600dpi actuator components;
Figure 12a shows two overlapping actuator components where one actuator component has a first variable nozzle pitch and the other actuator component has a second variable nozzle pitch;
Figure 12b shows, for 1200dpi actuator components having the variable nozzle pitches of Figure 12a, how it becomes more difficult to find a suitably aligned pair of nozzles as the misalignment between overlapping actuator components increases, and Figure 12c shows how the absolute percentage jump in pitch at a switch point between the actuator components of Figure 12a varies as a function of misalignment;
Figure 12d shows the same information as Figure 12b but for 600dpi actuator components, and Figure 12e shows the same information as Figure 12c but for 600dpi actuator components; and
Figure 13 is a flowchart showing steps to calibrate a droplet deposition apparatus.

As mentioned briefly above, a droplet deposition apparatus (e.g. a printer) typically comprises at least one droplet deposition head having at least one actuator component. The or each actuator component comprises a nozzle array having a plurality of nozzles. The actuator component may comprise a nozzle plate which is a layer containing the nozzles. In embodiments, an actuator component may be a die stack which comprises multiple actuators (and therefore, multiple nozzle arrays) and a single nozzle plate which contains the nozzles for all of the actuators of the actuator component. In any case, the or each nozzle array of an actuator component comprises multiple nozzles arranged in one or more rows, where each nozzle is configured to eject droplets of fluid (e.g. ink) in response to a command signal received from control circuitry, to reproduce an image on a receiving medium. To form a droplet deposition apparatus with a long droplet deposition head (e.g. for an industrial printer), typically two or more droplet deposition heads, or two or more actuator components within a droplet deposition head, may be arranged along an axis of the apparatus. Each droplet deposition head, (and/or each actuator component) may comprise at least one nozzle array. The droplet deposition heads or actuator components are arranged along the axis in a staggered arrangement, such that adjacent heads/actuator components partially overlap each other. In this arrangement, some or all of the nozzles of one head/actuator component are used to print part of an image, and another part of the image is printed using the nozzles of another, adjacent head/actuator component, and so on. In the overlap region, a printing process transitions between adjacent heads/actuator components. The point at which the printing process transitions is referred to herein as the "switch point" or "switchover point" or "transition point".
The overlapping arrangement introduces an inaccuracy or visible artefact at the seams (i.e. in the overlap region) between sub-images printed by each one of the printheads/actuator components. For example, the visible artefact may be a darker line (because the overlapping nozzles are too close together, i.e. closer together than a nominal nozzle separation) or a lighter line (because the overlapping nozzles are too far apart, i.e. further apart than a nominal nozzle separation). The visible artefact may be caused by misalignments between the adjacent heads/actuator components in the overlap region.
For droplet deposition heads/actuator components in which the nozzle pitch (i.e. a centre-to-centre separation between adjacent nozzles) is constant, the nozzles of one actuator component/head roughly align with the nozzles of an adjacent actuator component/head in the overlap region. It is possible to perform a fine adjustment of the overlapping actuator component/head to accurately align the nozzles in the overlap region, such that transitioning from one actuator component/head to the adjacent actuator component/head results in no visual artefacts (or minimal artefacts). For example, the heads could be moved relative to each other once installed within a droplet deposition apparatus, and/or the actuator components may be more accurately fixed within the droplet deposition head during manufacture, but these processes may be very expensive given the high accuracy required. The process of head-to-head fine alignment also has to be repeated each time a head is replaced within the apparatus (e.g. when the component becomes faulty).
The human eye is sensitive to step changes in optical density and can detect even small faults or artefacts within a printed image, such as those that might be caused by a small misalignment between nozzle rows in the overlap region. Depending on the print medium, the human eye may be able to detect misalignments or faults that constitute a step change along a printed line around 5µm wide. In graphics printing and/or when using UV curable inks, the fluid/ink does not spread as much once on the medium, such that limited 'blurring' occurs which might otherwise reduce the appearance of a fault to the human eye.
Broadly speaking, embodiments of the present techniques provide apparatus and methods to minimise or reduce the effects of actuator component (and therefore, nozzle array) misalignment. In particular, the present techniques provide an actuator component comprising at least one array of nozzles. In the or each array, the nozzles of the array are arranged in at least two portions: a first portion in which the nozzles in a row of the array are separated by a constant nozzle pitch, and a second portion in the nozzles in a row of the array are separated by a variable nozzle pitch. A variable portion of a nozzle array of a first actuator component is arranged such that it overlaps a variable portion of a nozzle array of a second actuator component when provided within a droplet deposition head containing multiple actuator components, or when provided in adjacent droplet deposition heads. Together, the variable portions of the overlapping nozzle arrays provide a Vernier scale-like mechanism/system, in which the possibility of finding the most suitable pair of nozzles which define the switchover point between overlapping nozzle arrays is increased. As explained in more detail below, the most suitable pair of nozzles may be the pair of nozzles which are best aligned (i.e. which have a minimal misalignment between them), or may be the pair of nozzles which result in the lowest jump in pitch at the switch point (i.e. where the pitch either side of the switch point is as close as possible), or a combination of both.
The term "variable nozzle pitch" is used herein to mean that the nozzle pitch between neighbouring nozzles in a particular section of a nozzle array (i.e. a variable pitch portion) varies with distance across that section. The term is not used to mean that the nozzle pitch is dynamically varied in use of the actuator component: the position of each nozzle in the nozzle array is fixed during manufacture of the actuator component. Rather, the term is used to mean that the nozzle pitch in the variable pitch portion of a nozzle array results in non-constant nozzle pitches between successive nozzles. For example, the pitch between a first pair of nozzles in variable pitch portion may be Δ, the pitch between the next pair of nozzles may be 2Δ, the pitch between the next pair of nozzles may be 3Δ, and so on. The term "variable nozzle pitch" is not limited to an increasing nozzle pitch or a decreasing nozzle pitch, and may be defined by a linear or non-linear function that depends on distance across the variable pitch portion or nozzle position/number.
In use, multiple actuator components of the types described herein may be provided within a droplet deposition head, or between adjacent droplet deposition heads, such that they are arranged in an overlapping manner. In order to minimise or remove a visible artefact in the overlap region between adjacent actuator components, a pair of nozzles is selected, one from each actuator component in the overlap region, which determines where the transition from one actuator component to the adjacent actuator component is to be made during a droplet ejection process (i.e. determines the switch point during the droplet ejection process). The pair of nozzles which are selected may be those nozzles which are best (or most suitably) aligned and/or those nozzles which result in a minimal change in pitch, or suitably non-detectable (to the human eye) change in optical density, on either side of the switch point, and the transition will take place at this aligned pair of nozzles. One of the nozzles in the pair will be disabled, to prevent both nozzles printing the same portion of an image. Droplet ejection is performed using the nozzles of one actuator component up to (or including, if it is enabled) the first nozzle of the nozzle pair, and then using the nozzles of the adjacent actuator component following (or from, if it is enabled), the second nozzle of the nozzle pair.
An advantage of the present techniques is that misalignments between adjacent actuator component may be compensated for without requiring expensive and time-consuming alignment processes. In particular, adjacent actuator components do not need to be carefully fine-aligned in order to compensate for misalignments - instead, a pair of suitable nozzles is selected (one nozzle from the overlapping portions of the nozzle arrays of each actuator component) which determine the point at which droplet ejection switches between the first and second actuator components. (As mentioned above, and explained in more detail below, the pair of suitable nozzles may be those nozzles which are best aligned and/or those nozzles which result in a minimal change in pitch, or to the human eye undetectable change in colour density, on either side of the switch point.) The variable nozzle pitch of each nozzle array of each actuator component improves the chance of finding a suitably aligned pair of nozzles. The transition between nozzle pitches of adjacent nozzles in the variable portion of each nozzle array is a gradual, per-nozzle (or per pair of nozzles) change in pitch. The variable pitch in the variable portion of each nozzle array may enable larger misalignments between overlapping actuator components to be compensated for while reducing the magnitude of the step change resulting in the dot spacing between dots printed from the relevant nozzles in the transition region.
According to claim 1, there is provided an actuator component comprising a plurality of nozzles arranged in at least one nozzle array, the nozzle array comprising: a first portion comprising a first subset of the plurality of nozzles, wherein the first subset of nozzles are arranged along a nozzle array axis and are separated by a constant nozzle pitch which is constant between a first end of the first portion and a second end of the first portion; and a second portion comprising a second subset of the plurality of nozzles, wherein the second subset of nozzles are arranged along the nozzle array axis and are separated by a variable nozzle pitch which varies between a first end of the second portion and a second end of the second portion, wherein the first end of the second portion abuts the second end of the first portion.
According to a related aspect of the present techniques, there is provided a nozzle plate comprising: a plurality of nozzles arranged in an array; a first portion comprising a first subset of the plurality of nozzles, wherein the first subset of nozzles are arranged along a nozzle plate axis and are separated by a constant nozzle pitch which is constant between a first end of the first portion and a second end of the first portion; and a second portion comprising a second subset of the plurality of nozzles, wherein the second subset of nozzles are arranged along the nozzle plate axis and are separated by a variable nozzle pitch which varies between a first end of the second portion and a second end of the second portion, wherein the first end of the second portion abuts the second end of the first portion.
According to a related aspect of the present techniques, there is provided a nozzle array comprising: a plurality of nozzles; a first portion comprising a first subset of the plurality of nozzles, wherein the first subset of nozzles are arranged along a nozzle array axis and are separated by a constant nozzle pitch which is constant between a first end of the first portion and a second end of the first portion; and a second portion comprising a second subset of the plurality of nozzles, wherein the second subset of nozzles are arranged along the nozzle array axis and are separated by a variable nozzle pitch which varies between a first end of the second portion and a second end of the second portion, wherein the first end of the second portion abuts the second end of the first portion.
According to claim 5, there is provided a droplet deposition apparatus comprising at least one arrangement of actuator components as described herein.
According to claim 6, there is provided a method of operating a droplet deposition apparatus as described herein, the method comprising: arranging the first actuator component in the droplet deposition apparatus in a plane of (or along an axis of) the droplet deposition head; and arranging the second actuator component in the droplet deposition apparatus in the plane of the droplet deposition head in a staggered arrangement relative to the first actuator component, such that the second portion of the nozzle array of the first actuator component at least partially overlaps the third portion of the second actuator component.
The following features apply equally to each of the above aspects.
In embodiments, the variable nozzle pitch of a nozzle array of an actuator component is defined by a first function which varies with distance between the first end of the second portion and the second end of the second portion.
In embodiments, the variable nozzle pitch of the second portion varies gradually away from the constant nozzle pitch with distance between the first end and the second end of the second portion. The variable nozzle pitch gradually decreases away from the constant nozzle pitch, such that the variable nozzle pitch changes away from the constant nozzle pitch with distance towards the second end of the second portion. In other words, the further the nozzles of the second portion are away from the first end of the second portion, the more the pitch between the nozzles differs from the constant nozzle pitch.
In particular embodiments, the variable nozzle pitch of the second portion may be substantially similar to (or the same as) the constant nozzle pitch at the first end of the second portion, and gradually decreases away from the constant nozzle pitch with distance towards the second end of the second portion. In other words, a pitch between a pair of nozzles in the second portion that is closest to the first portion is similar to or equal to the constant nozzle pitch of the first portion. Thus, the variable nozzle pitch at the first end of the second portion may be similar to or equal to the constant nozzle pitch, and then decreases gradually away from this pitch with distance towards the second end.
In embodiments, the first function defining the variable nozzle pitch may be a linear function. The linear function may be equal to, for example, a constant value multiplied by distance away from one end of the variable pitch portion (or nozzle position). The linear function may be defined in terms of the nozzle position along the variable nozzle pitch portion of the nozzle array of an actuator component, where the first nozzle may be defined as the nozzle closest to the constant nozzle pitch portion of the nozzle array. For example, a pitch function P_n may be defined as P_n = P1 + (a ± Δn), where n is nozzle position (e.g. distance from one end of the variable pitch portion) or nozzle number (as counted from one end of the variable pitch portion), Δ is a fixed value, P1 is a nominal pitch (e.g. the constant nozzle pitch of the first portion) and a is an optional offset. Thus, the variable nozzle pitch in this example decreases by a fixed amount between neighbouring nozzles, i.e. starting from a 1Δ pitch between the first pair (defined as the first pair closest to the constant nozzle pitch portion of the nozzle array), to a 2Δ pitch between the second pair, a 3Δ pitch between the third pair, and so on up to nΔ.
In embodiments, the first function defining the variable nozzle pitch is a non-linear function. The non-linear function may be dependent on distance along the variable nozzle pitch portion, or on nozzle position along the variable nozzle pitch portion of the nozzle array (where the first nozzle may be defined as the nozzle closest to the constant nozzle pitch portion of the nozzle array). The non-linear function may be any non-linear function, such as a sinusoidal function or exponential function. For example, a pitch function P_n may be defined as P_n =P1 + (a± bsin(x_n)) where 0.5π<x<π, where x is distance along the variable nozzle pitch portion of the nozzle array, a, is an optional offset, and b is a fixed multiplier. In another example, a pitch function may be defined as P_n =P1+ce^-dx where c and d are fixed multipliers and x is distance along the variable nozzle pitch portion of the nozzle array. It will be understood that these are merely illustrative example functions and are non-limiting.
In preferred embodiments of the actuator component, the nozzle array comprises a third portion comprising a third subset of the plurality of nozzles, wherein the third subset of nozzles are arranged along the nozzle array axis and separated by a further variable nozzle pitch which varies from a first end of the third portion to a second end of the third portion.
The first portion of the nozzle array is provided between the second portion and the third portion, such that the second end of the third portion abuts the first end of the first portion, and the second end of the first portion abuts the first end of the second portion. In other words, the first portion (constant nozzle pitch portion) is sandwiched between the second and third portions (the two variable nozzle pitch portions).
The further variable nozzle pitch of the third portion is defined by a second function which varies with distance between the first end of the third portion and the second end of the third portion.
In embodiments, the further variable nozzle pitch of the third portion varies gradually away from the constant nozzle pitch with distance between the first end and the second end of the third portion. The variable nozzle pitch may gradually increase or gradually decrease away from the constant nozzle pitch. The variable nozzle pitch of the third portion may, at the second end of the third portion, vary gradually (i.e. increase or decrease) away from the constant nozzle pitch, such that the variable nozzle pitch changes away from the constant nozzle pitch with distance towards the first end of the third portion. In other words, the further the nozzles of the third portion are away from the second end of the third portion, the more the pitch between the nozzles differs from the constant nozzle pitch.
In embodiments, the further variable nozzle pitch of the third portion is substantially similar to (or equal to) the constant nozzle pitch at the second end of the third portion, and varies gradually away from the constant nozzle pitch with distance towards the first end of the third portion. Thus, the variable nozzle pitch at the second end of the third portion is similar to or equal to the constant nozzle pitch, and then either increases or decreases gradually away from this pitch with distance towards the first end of the third portion.
The second function defining the further variable nozzle pitch may be, in embodiments, equal to the first function. For example, both the first and second function may be defined by P_n=P1 + (a±Δn). In alternative embodiments, the second function may be the same type of function (e.g. linear, sinusoidal, exponential, etc.) as the first function but may differ in multiplier value and/or offset value. For example, the first function may be P_n=P1+(a±3n), while the second function may be P_n =P1+(a±2.5n). In alternative embodiments, the first and second function may be different, e.g. one may be a linear function and the other may be non-linear, or one may be sinusoidal and the other may be exponential, etc. The function chosen to define the variable nozzle pitch may be determined using computer modelling or simulations to establish how likely it would be to find a pair of best aligned nozzles using the function.
In embodiments, the variable nozzle pitch of the second portion is similar to the constant nozzle pitch at the first end of the second portion, and decreases gradually away from the constant nozzle pitch with distance towards the second end of the second portion; and the further variable nozzle pitch of the third portion is similar to the constant nozzle pitch at the second end of the third portion, and increases gradually away from the constant nozzle pitch with distance towards the first end of the third portion.
In embodiments, the variable nozzle pitch of the second portion decreases gradually away from the constant nozzle pitch with distance between the first end and the second end of the second portion; and the further variable nozzle pitch of the third portion may increase gradually away from the constant nozzle pitch with distance between the first end and the second end of the third portion. Additionally or alternatively, the variable nozzle pitch of the second portion may be similar to the constant nozzle pitch at the first end of the second portion, and decreases gradually away from the constant nozzle pitch with distance towards the second end of the second portion; and the further variable nozzle pitch of the third portion may be similar to the constant nozzle pitch at the second end of the third portion, and increases gradually away from the constant nozzle pitch with distance towards the first end of the third portion. In either case, when looking at the nozzle array as a whole, the nozzle pitch begins at a first value at one end of the nozzle array (i.e. the second end of the second portion) and gradually increases towards a second value, stays at the second value for some distance (i.e. in the first portion), and then gradually increases towards a third value at another end of the nozzle array (i.e. the first end of the third portion), such that the nozzle pitch generally increases across the length of the nozzle array.
In embodiments, the nozzle array comprises at least one row which extends across the nozzle array, and the plurality of nozzles of the nozzle array are arranged in the at least row. The at least one row may extend across each portion of the nozzle array. In embodiments, the nozzle array comprises a plurality of staggered rows which extend across the nozzle array, and the plurality of nozzles are arranged in the plurality of staggered rows. Each row of the plurality of staggered rows may extend across each portion of the nozzle array.
In embodiments, at least two actuator components (i.e. a first actuator component and a second actuator component) of the types described herein are provided in a droplet deposition head. A variety of alternative fluids may be deposited by a droplet deposition head. For instance, a droplet deposition head may eject droplets of ink that may travel to a droplet receiving medium, such as a sheet of paper or card, textile, foil or to other receiving media, such as ceramic tiling or shaped articles (e.g. cans, bottles, etc.) to form an image, as is the case in inkjet printing applications (where the droplet deposition head may be an inkjet printhead or, more particular, a drop-on-demand inkjet printhead). Thus, the term 'droplet deposition head' is used interchangeably herein with the term 'inkjet printhead' or 'printhead', without loss of generality. Similarly, the term 'fluid' is used interchangeably herein with the term 'ink', without loss of generality. The term 'ink-ejecting nozzle' is used interchangeably herein with 'nozzle'.
Alternatively, droplets of fluid may be used to build structures. For example, electrically active fluids may be deposited onto receiving media such as a circuit board so as to enable prototyping of electrical devices. In another example, polymer containing fluids or molten polymer may be deposited in successive layers so as to produce a prototype model of an object (as in 3D printing). In other examples, droplet deposition heads may be adapted to deposit droplets of solution containing biological or chemical material onto a receiving medium such as a microarray. Droplet deposition heads suitable for such alternative fluids may be generally similar in construction to printheads, and/or may be adapted to handle the specific fluid in question. Droplet deposition heads as described in the following disclosure may be drop-on-demand droplet deposition heads. In such heads, the pattern of droplets ejected may vary, dependent upon the input data provided to the head.
In embodiments, the first and second actuator components may be arranged in a plane of the droplet deposition head such that the second portion of the nozzle array of the first actuator components at least partially overlaps the third portion of the nozzle array of the second actuator components. The plane in which the actuator components are arranged may be substantially perpendicular to a direction of droplet ejection from the droplet deposition head.
In embodiments of the droplet deposition head, the variable nozzle pitch of the second portion of each nozzle array of each actuator component decreases gradually away from the constant nozzle pitch with distance between the first end and the second end of the second portion.
In embodiments of the droplet deposition head, the further variable nozzle pitch of the third portion of each nozzle array of each actuator component varies gradually away from the constant nozzle pitch with distance towards the first end of the third portion.
In embodiments, the constant nozzle pitch of the nozzle array of the first actuator components may be different to the constant nozzle pitch of the nozzle array of the second actuator components. This may be useful to enable the droplet deposition head to adjust a colour density when depositing droplets of different colours, for example.
Generally speaking, the constant nozzle pitch of a nozzle array of an actuator component may differ between actuator components, and may depend on the resolution of the droplet deposition head in which the actuator component is to be used. For example, a high resolution droplet deposition head may require an actuator component in which the nozzles are close together, such that a constant nozzle pitch is small, while in a lower resolution droplet deposition head, the nozzles of the actuator component may be further apart with a larger constant nozzle pitch between them. The variable nozzle pitch vary gradually away from the constant nozzle pitch and therefore, may also differ in magnitude between actuator components.
In embodiments of the droplet deposition head, the nozzle array of each actuator component comprises a plurality of staggered rows which extend across each nozzle array, and the plurality of nozzles of each nozzle array are arranged in the plurality of staggered rows.
In embodiments, the droplet deposition head may comprise a plurality of fluid chambers in fluid communication with the plurality of nozzles of each nozzle array. In embodiments, pairs of staggered rows on each nozzle array are in fluid communication with a subset of the plurality of fluid chambers.
In embodiments, operating a droplet deposition head comprising a first actuator component and a second actuator component comprises selecting a first nozzle from the second portion of the nozzle array of the first actuator component, and selecting a second nozzle from the third portion of the nozzle array of the second actuator component, the selected first nozzle and second nozzle forming a suitably aligned pair of nozzles. The suitably aligned pair of nozzles may be substantially exactly aligned, or may be the best aligned pair of nozzles within the overlap portion between actuator components. In embodiments, the pair of nozzles may be the nozzles which are best aligned and/or which result in a minimal change in pitch (or a sufficiently small change in pitch that it is not noticeable by the human eye) on either side of the switch point. The selected pair of nozzles define the point at which droplet ejection switches from the first actuator component to the second actuator component in the overlap portion.
As mentioned earlier, in order to minimise or remove a visible artefact that results from the overlap region between adjacent actuator components in a droplet deposition device, a pair of nozzles are selected, one from each actuator component in the overlap region, which determine where the transition from one actuator component to the adjacent actuator component is to be made during a droplet ejection process. The pair of nozzles which are selected are usually those nozzles which are best aligned and/or which result in a minimal change in pitch (or a sufficiently small change in pitch that it is not noticeable by the human eye) on either side of the switch point, and the transition will take place at this aligned pair of nozzles. One of the nozzles in the pair will be disabled, to prevent both nozzles printing the same portion of an image. Droplet ejection is performed using the nozzles of one actuator component up to (or including, if it is enabled) the first nozzle of the nozzle pair, and then using the nozzles of the adjacent actuator component following (or from, if it is enabled), the second nozzle of the nozzle pair. Thus, the unselected and disabled nozzles in the variable pitch portions of the overlapping actuator component are unused in a droplet ejection process.
An actuator component may comprise a nozzle array having 355 nozzles in each row, and may comprise four such rows of nozzles. The variable pitch portion(s) of each nozzle array may be relatively small compared to the constant nozzle pitch portion of each nozzle array. For example, the or each variable pitch portion may comprise 14 nozzles in each row (i.e. 56 nozzles in the overlap region), which is ~4% of the nozzles in the row. Thus, a nozzle array having one or more variable pitch portion may reduce the occurrence of artefacts in the overlap region between actuator components, without significantly reducing the number of nozzles in the nozzle array. That is, the nozzle arrays described herein may advantageously reduce or remove visually-detectable artefacts that arise in the overlap region between actuator components, without significantly increasing the number of potentially redundant nozzles. Redundant nozzles are those nozzles in the variable pitch portion(s) which are not used once a suitable pair of nozzles has been selected for the switch point.
Selecting the first nozzle and the second nozzle may comprise selecting a first nozzle and a second nozzle which have a minimal misalignment value, i.e. are aligned or more closely aligned than other pairs of nozzles. Additionally or alternatively, selecting the first nozzle and the second nozzle may comprise selecting a first nozzle and a second nozzle which provide a minimal jump in pitch at a switch point between the first and second actuator components. Preferably, the selected nozzles are those which have a minimal misalignment value and provide a minimal jump in pitch at the switch point. A jump in pitch (or change in pitch) may occur at the switch point because the function defining the variable pitch in the overlapping variable pitch portions of the nozzles arrays may be different. For example, in the overlap region, the variable pitch of one nozzle array may result in a successive increase in distance by (n ^∗ 0.036)µm between neighbouring nozzles in one row (where n is the nozzle number/position or distance of the nozzle from a specific end of the variable pitch portion), while in the other nozzle array, the variable pitch may be result in a successive increase in distance by (n ^∗ 0.05)µm between neighbouring nozzles in one row. As a result, at the switch point, while the selected nozzles may be aligned or closely aligned, there could be a significant difference in the pitch on either side of the switch point. If the pitch on one side of the switch point is sufficiently larger than the pitch on the other side of the switch point, a white line or gap may appear during droplet deposition. Similarly, if the pitch on one side of the switch point is sufficiently smaller than the pitch on the other side of the switch point, a dark line may appear during droplet deposition. Thus, it may be advantageous to find a pair of nozzles which satisfy or balance both the requirement to have a minimal misalignment value, and the requirement to minimise the jump in pitch at the switch point.
In embodiments, operating the droplet deposition head comprises disabling one of the first nozzle and the second nozzle of the aligned pair of nozzles; disabling the nozzles of the second portion extending from the selected first nozzle towards the second end of the second portion; and disabling the nozzles of the third portion extending from the selected second nozzle towards the first end of the third portion. For example, the first nozzle may be disabled and the droplet deposition process continues from the second nozzle of the aligned pair. Alternatively, the first nozzle may be enabled and the droplet deposition process continues from the nozzle adjacent to the second nozzle of the aligned pair.
In embodiments, operating the droplet deposition head comprises controlling the droplet deposition apparatus to deposit fluid from the nozzles of the nozzle array of the first actuator component and from the nozzles of the nozzle array of the second actuator component, other than the disabled nozzles. In embodiments, the droplet deposition head may be a printhead configured to print in a single colour (e.g. black). In this case, the fluid deposited from each actuator component is the same colour.
In embodiments, a droplet deposition head may be configured to operate in multiple modes. For example, a droplet deposition head may be configured to operate in a first mode at a first resolution and in a second mode at a second resolution, wherein the second resolution is a multiple of the first resolution. The first resolution may be, for example 600 dpi (dots per inch), and the second resolution may be, for example 1200 dpi. The resolution may depend on the number of nozzles on each actuator component. A droplet deposition head that can operate in multiple modes may be able to switch between the different modes for different droplet deposition tasks. By way of example only, for a 1200 dpi resolution, each row of nozzles in a nozzle array of an actuator component may be used for a droplet deposition task, while for a 600 dpi resolution, some of these rows will be disabled. For instance, in 600 dpi mode, alternate rows or alternate pairs of rows may be disabled. This means that the best aligned pair of nozzles in the overlap region may be different when operating the droplet deposition head in different modes. Accordingly, the droplet deposition head may need to be calibrated for each operation mode, in order to select a suitably aligned pair of nozzles for each operation mode. The pair of nozzles may be the same or could be different between operation modes.
Thus, in embodiments where the droplet deposition head is configured to operate in a first mode at a first resolution and in a second mode at a second resolution, wherein the second resolution is a multiple of the first resolution, and wherein the method further comprises: selecting, for the first mode, a first nozzle from the second portion of the nozzle array of the first actuator component, and selecting a second nozzle from the third portion of the nozzle array of the second actuator component, the selected first nozzle and second nozzle forming a suitably aligned first pair of nozzles for the first mode; and selecting, for the second mode, a third nozzle from the second portion of the nozzle array of the first actuator component, and selecting a fourth nozzle from the third portion of the nozzle array of the second actuator component, the selected third nozzle and fourth nozzle forming a suitably aligned second pair of nozzles for the second mode. The first pair of nozzles may be the same as the second pair of nozzles, or may be different.
Alternatively, a droplet deposition head may be able to deposit multiple different fluids. For example, in embodiments where the droplet deposition head is printhead that may be able to print multiple colours, one row of nozzles in each nozzle array of each actuator component may be configured to deposit fluid droplets of one colour, another row of nozzles may be configured to deposit fluid droplets of another colour, and so on. Accordingly, in embodiments, at least one row in each nozzle array of the first actuator component and the second actuator component is configured to deposit a first fluid, and at least one row in each nozzle array of the first actuator component and the second actuator component is configured to deposit a second fluid, the method comprising: selecting, from the row configured to deposit the first fluid, a first nozzle in the second portion of the nozzle array of the first actuator component, and selecting a second nozzle in the third portion of the nozzle array of the second actuator component, the selected first nozzle and second nozzle forming a suitably aligned first pair of nozzles; and selecting, from the row configured to deposit the second fluid, a third nozzle in the second portion of the nozzle array of the first actuator component, and selecting a fourth nozzle in the third portion of the nozzle array of the second actuator component, the selected third nozzle and fourth nozzle forming a suitably aligned second pair of nozzles.
In this multi-fluid operation mode, operating the droplet deposition head comprises: disabling one of the first nozzle and the second nozzle of the first aligned pair of nozzles; disabling, in the row configured to deposit the first fluid in the nozzle array of the first actuator component, the nozzles of the second portion extending from the selected first nozzle towards the second end of the second portion; disabling, in the row configured to deposit the first fluid in the nozzle array of the second actuator component, the nozzles of the third portion extending from the selected second nozzle towards the first end of the third portion; disabling one of the third nozzle and the fourth nozzle of the second aligned pair of nozzles; disabling, in the row configured to deposit the second fluid in the nozzle array of the first actuator component, the nozzles of the second portion extending from the selected third nozzle towards to the second end of the second portion; and disabling, in the row configured to deposit the second fluid in the nozzle array of the second actuator component, the nozzles of the third portion extending from the selected fourth nozzle towards the first end of the third portion.
In embodiments, operating the droplet deposition head comprises controlling the droplet deposition apparatus to deposit the first fluid and the second fluid from the nozzles of nozzle array of the first actuator component and from the nozzles of nozzle array of the second actuator component, other than from the disabled nozzles.
In embodiments, operating the droplet deposition head further comprises using a masking technique to determine a number of sub-droplets to be deposited by each non-disabled nozzle of the first actuator component and the second actuator component in a region where the actuator components at least partially overlap. This may be required in the region where two actuator components overlap, since the varying pitch between the nozzles could affect the quality of a printed image relative to the part of the image printed by the nozzles in the constant pitch portion of each nozzle array. In other words, a masking technique may be used because pixel colour density (i.e. a value which indicates how many droplets are required to form each pixel of an image on a receiving medium) may depend on the nozzle pitch. Thus, to ensure that the nozzles in the overlap region provide the required pixel colour density, a masking technique may be required which specifies how many droplets each nozzle has to eject to achieve the required pixel colour density and to compensate for the variable nozzle pitch. This may be achieved by configuring the selected/non-disabled nozzles in the overlap region to deposit fewer or more droplets than the nozzles in the constant pitch portion, to provide a required pixel colour density.
Thus, in embodiments, the droplet deposition apparatus comprises a processor and/or control circuitry to perform the methods of operating the droplet deposition apparatus described herein.
According to a related aspect of the present technique, there is provided a non-transitory data carrier carrying code which, when implemented on a processor, causes the processor to carry out any of the methods described herein.
As will be appreciated by one skilled in the art, the present techniques may be embodied as a system, method or computer program product. Accordingly, present techniques may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware aspects.
Furthermore, the present techniques may take the form of a computer program product embodied in a computer readable medium having computer readable program code embodied thereon. The computer readable medium may be a computer readable signal medium or a computer readable storage medium. A computer readable medium may be, for example, but is not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing.
The techniques further provide processor control code (or logic) to implement the above-described methods, for example on a general purpose computer system, or on a digital signal processor (DSP), or on a Field-programmable gate array (FPGA). The techniques also provide a carrier carrying processor control code to, when running, implement any of the above methods, in particular on a non-transitory data carrier - such as a disk, microprocessor, CD- or DVD-ROM, programmed memory such as read-only memory (firmware), or on a data carrier such as an optical or electrical signal carrier. The code may be provided on a carrier such as a disk, a microprocessor, CD- or DVD-ROM, programmed memory such as non-volatile memory (e.g. Flash) or read-only memory (firmware). The program code or logic (and/or data) to implement embodiments of the techniques may comprise source, object or executable code in a conventional programming language (interpreted or compiled) such as C, or assembly code, code for setting up or controlling an ASIC (Application Specific Integrated Circuit) or FPGA (Field Programmable Gate Array), or code for a hardware description language such as Verilog^™ or VHDL (Very high speed integrated circuit Hardware Description Language). As the skilled person will appreciate, such code and/or data may be distributed between a plurality of coupled components in communication with one another. The techniques may comprise a controller which includes a microprocessor, working memory and program memory coupled to one or more of the components of the system.
Computer program code for carrying out operations for the above-described techniques may be written in any combination of one or more programming languages, including object oriented programming languages and conventional procedural programming languages. Code components may be embodied as procedures, methods or the like, and may comprise sub-components which may take the form of instructions or sequences of instructions at any of the levels of abstraction, from the direct machine instructions of a native instruction set to high-level compiled or interpreted language constructs.
It will also be understood by a person skilled in the art that all or part of a logical method according to the preferred embodiments of the present techniques may suitably be embodied in a logic apparatus comprising logic elements to perform the steps of the above-described methods, and that such logic elements may comprise components such as logic gates in, for example a programmable logic array or application-specific integrated circuit. Such a logic arrangement may further be embodied in enabling elements for temporarily or permanently establishing logic structures in such an array or circuit using, for example, a virtual hardware descriptor language, which may be stored and transmitted using fixed or transmittable carrier media.
In an embodiment, the present techniques may be realised in the form of a data carrier having functional data thereon, said functional data comprising functional computer data structures to, when loaded into a computer system, or processor, or network, and operated upon thereby, enable said computer system (or processor or network) to perform all the steps of the methods described herein.
Turning now to the Figures, Figure 1a is a schematic diagram of two overlapping actuator components in an arrangement 10. In arrangement 10, a first actuator component 12a and a second actuator component 12b are arranged in a plane (or along an axis) in a staggered manner. The staggered arrangement means the first actuator component 12a partially overlaps the second actuator component 12b. The region where the two actuator components 12a, 12b overlap is shown in Figure 1a as overlap region 16. Each actuator component 12a, 12b comprises a nozzle array having a plurality of nozzles. In the illustrated example, the nozzle array comprises multiple rows 14, such that the nozzles of each actuator component are arranged in rows 14. It will be understood that the actuator components may have any number of rows, and that the number of rows may differ between actuator components.
In the overlap region 16, droplet ejection from the nozzles switches from being performed by the first actuator component 12a to being performed by the second actuator component 12b. It is important to carefully select the nozzles at which the transition from the first actuator component 12a to the second actuator component 12b takes place, in order to minimise or remove the possibility of a visible artefact occurring in the overlap region. Thus, in use, a pair of nozzles are selected, one from each actuator component 12a, 12b in the overlap region 16, which determine where the transition from the first actuator component 12a to the adjacent actuator component 12b is to be made during a droplet ejection process. The pair of nozzles which are selected are preferably those nozzles which have a minimal misalignment value and provide a minimal jump in pitch at the switch point, and the transition will take place at this pair of nozzles. One of the nozzles in the pair will be disabled, to prevent both nozzles printing the same portion of an image. Droplet ejection is performed using the nozzles of one actuator component up to (or including, if it is enabled) the first nozzle of the nozzle pair, and then using the nozzles of the adjacent actuator component following (or from, if it is enabled), the second nozzle of the nozzle pair.
Figure 1b is a schematic of two overlapping droplet deposition heads 18a and 18b in an arrangement 10'. ( Elements 12a and 12b may represent die stacks). In arrangement 10', each droplet deposition head 18a, 18b comprises two actuator components, though it will be understood that each droplet deposition head 18a, 18b may comprise any number of actuator components. Droplet deposition head 18a comprises a first actuator component 12a and a second actuator component 12b, which are arranged within the droplet deposition head 18a in a staggered manner. The staggered arrangement means the first actuator component 12a partially overlaps the second actuator component 12b. Similarly, droplet deposition head 18b comprises a third actuator component 12c and a fourth actuator component 12d, which are arranged within the droplet deposition head 18b in a staggered manner. The staggered arrangement means the third actuator component 12c partially overlaps the fourth actuator component 12d. The region where the two actuator components 12a, 12b overlap in droplet deposition head 18a is indicated as overlap region 16.
The droplet deposition heads 18a and 18b are themselves arranged in a staggered manner. For example, the droplet deposition heads 18a, 18b may be provided within a droplet deposition apparatus (e.g. a printer) and arranged in a plane of the apparatus in a staggered manner, such that the droplet deposition heads overlap. The region where the two droplet deposition heads 18a, 18b overlap is indicated as overlap region 16a. Each actuator component 12a to 12d comprises a plurality of nozzles arranged in an array. In the illustrated example, the nozzle array comprises multiple rows 14, such that the nozzles in each nozzle array are arranged in rows 14. It will be understood that the nozzle arrays may have any number of rows, and that the number of rows may differ between actuator components.
In the illustrative arrangement of Figure 1b, a suitably aligned pair of nozzles may need to be selected for each overlap portion 16 and 16a. That is, a suitably aligned pair of nozzles may need to be selected for the overlapping actuator components within a droplet deposition head, and for the overlapping actuator components in the region where two droplet deposition heads overlap.
The terms "suitably aligned pair of nozzles" and "best aligned pair of nozzles" are used interchangeably and are used to mean the nozzles which have a minimal misalignment value and/or provide a minimal jump in pitch at the switch point, or a switch resulting in a colour density change that is substantially undetectable to the human eye.
Figure 2a is a schematic diagram of an example (not in the scope of the claimed invention) actuator component 12 that comprises a plurality of nozzles arranged in an array. The array may comprise multiple rows 14, such that the nozzles are arranged in rows on the actuator component 12. The rows 14 shown here appear to be aligned such that nozzles between adjacent rows are aligned in a direction perpendicular to the row direction, but in embodiments, the rows may be provided in a staggered arrangement where nozzles between adjacent rows are offset from each other (as shown in Figure 6b). The offset may be a distance less than a nominal pitch within each row in a direction perpendicular to the row direction. The nozzle array of the actuator component 12 is divided into two portions, as indicated by the dashed line. The nozzle array of the actuator component 12 comprises a first portion 22 in which the nozzles along each row 14 are separated by a constant nozzle pitch. Pitch is defined as a centre-to-centre separation between adjacent nozzles. The nozzle array of the actuator component 12 comprises a second portion 24 in which the nozzles along each row 14 are separated by a variable nozzle pitch. This means that the separation between adjacent nozzles in a row 14 in the second portion 24 varies with distance along the length of the second portion 24. This is shown in Figure 3a and described in more detail below. In use, the actuator component 12 may be arranged adjacent to another actuator component (e.g. in the arrangements shown in Figures 1a and 1b), such that the second portion 24 is in the overlap region 16.
In the illustrated example of Fig. 2a, the first portion 22 comprises a first end 221 and a second end 222, and the second portion 24 comprises a first end 241 and a second end 242. The second portion 24 abuts the first portion 22, such that the second end 242 of the second portion 24 abuts the first end 221 of the first portion 22. However, it will be understood that the second portion 24 could equally be provided such that the first end 241 of the second portion 24 abuts the second end 222 of the first portion 22.
Figure 2b is a schematic diagram of an example actuator component 12' that comprises a plurality of nozzles arranged in an array. The array may comprise multiple rows 14', such that the nozzles are arranged in rows on the actuator component 12'. The rows 14' shown here appear to be aligned, but in embodiments, the rows may be provided in a staggered arrangement. The nozzle array of the actuator component 12' is divided into three portions, as indicated by the dashed lines. The nozzle array of the actuator component 12' comprises a first portion 22 in which the nozzles along each row 14' are separated by a constant nozzle pitch. The nozzle array of the actuator component 12' comprises a second portion 24 in which the nozzles along each row 14' are separated by a variable nozzle pitch. This means that the separation between adjacent nozzles in a row 14' in the second portion 24 decreases with distance along the length of the second portion 24. The nozzle array of the actuator component 12' comprises a third portion 26 in which the nozzles along each row 14' are separated by a further variable nozzle pitch. This means that the separation between adjacent nozzles in a row 14' in the third portion 26 varies with distance along the length of the third portion 26. In use, a first actuator component 12' may be arranged adjacent to a second actuator component 12' (e.g. in the arrangements shown in Figures 1a and 1b), such that the third portion 26 of the first actuator component (i.e. the third portion of the nozzle array of the first actuator component) overlaps the second portion 24 of the second actuator component (i.e. the second portion of the nozzle array of the second actuator component) in the overlap region 16.
In the illustrated embodiment, the first portion 22 comprises a first end 221 and a second end 222, the second portion 24 comprises a first end 241 and a second end 242, and the third portion 26 comprises a first end 261 and a second end 262. The second portion 24 abuts the first portion 22, such that the second end 242 of the second portion 24 abuts the first end 221 of the first portion 22. The third portion 26 abuts the first portion 22, such that the first end 261 of the third portion abuts the second end 222 of the first portion 22. However, it will be understood that the positions of the second portion 24 and third portion 26 could be swapped, and that the labelling of each end of each portion is arbitrary
Figure 3a (a reference example not covered by the scope of the claimed invention) illustrates a single row 14 of the nozzle array of actuator component 12 shown in Figure 2a. The row 14 comprises a plurality of nozzles, some of which are in the first portion 22 and some of which are in the second portion 24 of the nozzle array. (Here, the second portion 24 is shown as being to the left of the first portion 22, whereas in Figure 2a, the second portion 24 is shown as being on the right of the first portion 22. It will be understood that the nozzle array may be provided in either arrangement). In Figure 3a, each nozzle 28 (represented by a black circle) in the first portion 22 is separated from an adjacent nozzle by a constant nozzle pitch P1. That is, the nozzle pitch between each pair of neighbouring nozzles in the first portion 22 is substantially constant or identical. In contrast, each nozzle 28 (represented by a white circle) in the second portion 24 is separated by a variable nozzle pitch P2. That is, the nozzle pitch between pairs of neighbouring nozzles in the second portion 24 varies, and P2 may be a function that depends on distance or on nozzle position. For example, the function defining the variable nozzle pitch P2 may result in a nozzle pitch that varies with distance D away from the boundary with the first portion 22. As mentioned earlier, the nozzle pitch P2 may vary gradually with distance D away from the constant nozzle pitch P1.
Figure 3b (a reference example not covered by the scope of the claimed invention) illustrates how two actuator components 12 of the type shown in Figure 2a may be arranged to overlap in an arrangement similar to that shown in Figure 1a. For the sake of simplicity, a single row from each overlapping actuator component is shown only. In the overlapping arrangement 20, at least one row 14a from a first actuator component 12 partially overlaps at least one row 14b from a second actuator component 12. In particular, the actuator components 12 are arranged such that the second portion 24 (i.e. the variable nozzle pitch portion) of the nozzle array of each actuator component overlaps in an overlap region 16. It will be understood that the second actuator component is rotated 180° relative to the first actuator component to enable the second portion 24 of each actuator component to overlap. As shown, the actuator components are not perfectly aligned, as the nozzles of row 14a in the overlap region 16 are not in alignment with the nozzles of row 14b in the overlap region 16. A suitably aligned pair of nozzles 28 are selected in the overlap region 16, which defines the transition point between using the first actuator component to eject droplets and using the second actuator component to eject droplets. This process is described in more detail below.
Figure 4a illustrates a single row 14' of the actuator component 12' shown in Figure 2b. The row 14' comprises a plurality of nozzles 28, some of which are in the first portion 22, some of which are in the second portion 24, and some of which are in the third portion 26 of the nozzle array of the actuator component. In Figure 4a, each nozzle 28 in the first portion 22 is separated from an adjacent nozzle in portion 22 by a constant nozzle pitch P1. That is, the nozzle pitch between each pair of neighbouring nozzles in the first portion 22 is substantially constant or identical. In contrast, each nozzle 28 in the second portion 24 is separated by a variable nozzle pitch P2. That is, the nozzle pitch between pairs of neighbouring nozzles in the second portion 24 decreases, and P2 may be a function that depends on distance away from one end of the second portion 24 (e.g. from the edge closest to/abutting the first portion 22), or on nozzle position/number. (That is, the function may be dependent on a continuous variable, i.e. distance from a specific end of the second portion 24, or on a discrete variable, i.e. nozzle number or position as counted from a specific end of the second portion 24). For example, the function defining the variable nozzle pitch P2 may result in a nozzle pitch that varies with distance D away from the boundary with the first portion 22. As mentioned earlier, the nozzle pitch P2 decreases gradually with distance D away from the constant nozzle pitch P1.
Similarly, each nozzle 28 in the third portion 26 is separated by a variable nozzle pitch P3. That is, the nozzle pitch between pairs of neighbouring nozzles in the third portion 26 varies, and P3 may be a function that depends on distance away from one end of the third portion 26 (e.g. from the edge closest to/abutting the first portion 22) or on nozzle position/number. (That is, the function may be dependent on a continuous variable, i.e. distance from a specific end of the third portion 26, or on a discrete variable, i.e. nozzle number or position as counted from a specific end of the third portion 26). For example, the function defining the variable nozzle pitch P3 may result in a nozzle pitch that varies with distance D' away from the boundary with the first portion 22. As mentioned earlier, the nozzle pitch P3 may vary gradually with distance D' away from the constant nozzle pitch P1.
The variable nozzle pitch P2 is preferably different to the variable nozzle pitch P3. In embodiments, one or both of the variable pitches P2 and P3 may be defined by a linear function. The linear function may be equal to, for example, a constant value multiplied by distance D or D' away from one end of the variable pitch portion (or nozzle position). The linear function may be defined in terms of the nozzle position along the variable nozzle pitch portion of the nozzle array, where the first nozzle may be defined as the nozzle closest to the first portion 22 of the nozzle array. For example, a pitch function P_n may be defined as P_n = P₁ + a±Δn, where n is nozzle position /number (as explained above) in portions 24, 26; Δ is a fixed value; and a is an optional positive or negative offset. (In an example where both pitches P2 and P3 are defined by similar functions, the pitch P2 may be defined as P2=P1+a-Δn and the pitch P3 may be defined as P3=P1+a+ Δn). Thus, the variable nozzle pitch in this example as defined by P_n = P₁ - Δn decreases by a fixed amount Δ between neighbouring nozzles, i.e. starting from a 1Δ decrease between the first pair (defined as the first pair closest to the constant nozzle pitch portion of the nozzle array), to a 2Δ decrease between the second pair, a 3Δ decrease between the third pair, and so on up to a decrease of nΔ. Such a linearly decreasing nozzle pitch is illustrated schematically in Figure 4a by the nozzle positions shown in portion 24. Likewise, a nozzle pitch as may be defined by P_n = P₁ + Δn increases by a fixed amount Δ between neighbouring nozzles, i.e. starting from a 1Δ increase between the first pair (defined as the first pair closest to the constant nozzle pitch portion of the nozzle array), to a 2Δ increase between the second pair, a 3Δ increase between the third pair, and so on up to an increase of nΔ. Such a linearly increasing nozzle pitch is illustrated schematically in Figure 4a by the nozzle positions shown in portion 26. It will be appreciated that the number of nozzles, n, in portions 24 and 26 may not be equal.
In embodiments, one or both of the variable pitches P2 and P3 may be defined by a non-linear function. The non-linear function may be dependent on distance along the variable nozzle pitch portion, or on nozzle position along the variable nozzle pitch portion of the nozzle array (where the first nozzle may be defined as the nozzle closest to the constant nozzle pitch portion of the nozzle array). The non-linear function may be any non-linear function, such as a sinusoidal function or exponential function. For example, a pitch function P_n may be defined as P_n = P₁ + a ± bsin(D_n) where 0.5π<D<π, where D is distance along the variable nozzle pitch portion of the nozzle array, a, is an optional offset, and b is a fixed multiplier. In another example, a pitch function may be defined as P_n= P₁ ± ce^-dD where c and d are fixed multipliers and D is distance along the variable nozzle pitch portion of the nozzle array. It will be understood that these are merely illustrative example functions and are non-limiting.
In embodiments, the variable nozzle pitch P3 of the third portion 26 may vary gradually away from the constant nozzle pitch P1 with distance D' between the second end 262 and the first end 261 of the third portion 26. The variable nozzle pitch P3 may gradually increase or gradually decrease away from the constant nozzle pitch P1. The variable nozzle pitch P3 of the third portion 26 may, at the second end 262 of the third portion 26, vary gradually (i.e. increase or decrease) away from the constant nozzle pitch P1, such that the variable nozzle pitch P3 changes away from the constant nozzle pitch P1 with distance D' towards the first end 261 of the third portion 26. In other words, the further the nozzles 28 of the third portion 26 are away from the second end 262 of the third portion 26, the more the variable nozzle pitch P3 between the nozzles differs from the constant nozzle pitch P1.
The variable nozzle pitch P2 may be defined by a first function, and the variable nozzle pitch P3 may be defined by a second function. The second function defining the variable nozzle pitch P3 may be, in embodiments, equal to the first function defining the variable nozzle pitch P2. For example, both the first and second functions may be defined by P_n=P1+aΔn. In alternative embodiments, the second function may be the same type of function (e.g. linear, sinusoidal, exponential, etc.) as the first function but may differ in multiplier value and/or offset value. For example, the first function may be P_n= P1+a-3n, while the second function may be P_n= P1+ a-2.5n. In alternative embodiments, the first and second function may be different, e.g. one may be a linear function and the other may be non-linear, or one may be sinusoidal and the other may be exponential, etc. The function chosen to define each variable nozzle pitch P2, P3 may be determined using computer modelling or simulations to establish how likely it would be to find a pair of best aligned nozzles using the selected functions when the actuator components are arranged to overlap.
Figure 4b illustrates how two actuator components 12' of the type shown in Figure 2b may be arranged to overlap in an arrangement similar to that shown in Figure 1a. For the sake of simplicity, a single row from each overlapping actuator component is shown only. In the overlapping arrangement 20', at least one row 14'a from a first actuator component 12' partially overlaps at least one row 14'b from a second actuator component 12'. In particular, the actuator components 12' are arranged such that the second portion 24 of the nozzle array of the first actuator component 12' overlaps the third portion 26 of the nozzle array of the second actuator component 12' in an overlap region 16. A suitably aligned pair of nozzles 28 is selected in the overlap region 16, which defines the transition point between using the first actuator component to eject droplets and using the second actuator component to eject droplets. This process is described in more detail below.
Figure 5 is a zoomed-in view of the overlap region 16 in Figure 4b. (Here, it will be understood that the depicted arrangement is a reflection of the arrangement shown in Figure 4b, about the axis along which the actuator components are arranged. Thus, the actuator components may be arranged in any suitable configuration relative to each other, as long as the actuator components are arranged along the same axis, or in the same plane, or along an array direction, and such that neighbouring actuator components partially overlap). The second portion 24 of the nozzle array of the first actuator component overlaps the third portion 26 of the nozzle array of the second actuator component. Here, the variable nozzle pitch P2 of the second portion 24 of the nozzle array of the first actuator component is defined by a first function, and the variable nozzle pitch P3 of the third portion 26 of the nozzle array of the second actuator component is defined by a second function. In this example, the first function results in a variable nozzle pitch P2 which decreases in an array direction, between the first end and the second end of the second portion 24. The second function in this example results in a variable nozzle pitch P3 which also decreases in the array direction, between the first end and the second end of the third portion 26, but at a different rate/by a different magnitude compared to P2.
To reduce any visual artefacts arising when printing using overlapping actuator components, it is necessary to determine a suitable point at which to switch between printing with the first actuator component to printing with the second actuator component. This may be determined by selecting the best aligned pair (BAP) or a suitably aligned pair of nozzles in the overlap region 16, where one nozzle of the pair is selected from the nozzle array of the first actuator component and the other nozzle of the pair is selected from the nozzle array of the second actuator component. The nozzles in the best aligned pair are usually those which align more closely than any other pair of nozzles, and/or which result in a minimal jump (change) in pitch (or a sufficiently small change in pitch that it is not noticeable by the human eye) at the switch point. The transition will take place at this substantially aligned or suitably aligned pair of nozzles. One of the nozzles in the pair will be disabled, to prevent both nozzles printing the same portion of an image. Droplet ejection is performed using the nozzles of one actuator component up to (or including, if it is enabled) the first nozzle of the nozzle pair, and then using the nozzles of the adjacent actuator component following on from (or from, if it is enabled) the second nozzle of the nozzle pair. For example, in Figure 5, all of the nozzles in the depicted row of the first actuator component up and including the nozzle of the aligned pair may be used to eject droplets. The remaining nozzle(s) of this row are disabled, for example by not addressing them with drive signals during a droplet deposition process. The nozzles of the depicted row of the second actuator component in the overlap portion are disabled up to and including the nozzle of aligned pair. The remaining nozzles in this row are used to continue the droplet ejection. In this way, a 'super row' is formed which spans two or more actuator components.
Figure 6a is a schematic diagram of an actuator component 12a comprising a nozzle array having multiple rows R1 to R4 of nozzles. The number of nozzles in each row R1 to R4 may be the same or may be different. In embodiments, the rows R1 to R4 may be aligned. In alternative embodiments, the rows R1 to R4 may be staggered relative to each other, such that the nozzles in each row are not aligned to each other but are offset from one another along the array direction. This is shown more clearly in Figure 6b which illustrates how the rows R1 to R4 of nozzles may be provided in a staggered arrangement on an actuator component 12a, for example by an offset of half a pitch between R1 and R2 and between R3 and R4, and where the pairs of rows R1, R2 and R3, R4 are further offset by a quarter pitch from one another.
The nozzles shown in each row R1 to R4 in Figure 6b are separated by a constant nozzle pitch P. For example, nozzle 28a is separated by a constant nozzle pitch P from neighbouring nozzle 29a in row R1. It can be seen from Figure 6b that in the space between nozzles 28a and 29a, there are three other nozzles: nozzle 28b in row R3, nozzle 28c in row R2 and nozzle 28d in row R4. In use, the number of nozzles used to deposit droplets of fluid may depend on the resolution required. For example, if a low resolution is acceptable, only the nozzles in row R1 may be used to deposit droplets of a specific fluid: in this case, a large gap may appear between droplets on a droplet deposition medium, given the distance P between the nozzles in row R1. If a high resolution is required, all of the nozzles in rows R1 to R4 may be used: in this case, there may be a small gap or no gap between droplets. In a high resolution mode, nozzle 28a may first deposit a droplet, followed by nozzle 28c, then 28b and then 28d, such that the gap P between the droplets depositable by nozzles 28a and 29b is filled with droplets deposited by the intermediate nozzles 28b-28d. Droplets deposited from successive rows are ejected with specific time delays between them such that they land at the same pixel row on the print medium as the medium passes underneath the nozzles. If the delays are correctly chosen, the droplets appear on the medium as one row of dots. In this case, the constant nozzle pitch between neighbouring nozzles may effectively be the distance between nozzle 28a and the next nozzle used to deposit droplets, i.e. nozzle 28b. Thus, the constant nozzle pitch may be P', as shown, where P' = P/4.
In embodiments, an intermediate resolution may be required. For example, if a high resolution (e.g. 1200 dpi) corresponds to using all of the nozzles in rows R1 to R4 to deposit a fluid, an intermediate resolution (e.g. 600 dpi) may correspond to using half of all of the nozzles. This may, in the example shown in Figure 6b, be achieved by the nozzles located in adjacent pairs of rows. For example, rows R1 and R2 may be used, while rows R3 and R4 are disabled. In this case, the nozzles in R1 (28a, 29a,... ) may first deposit droplets, followed by the nozzles in R2 (28c, 29c, ...), such that the gap P between the droplets depositable by the nozzles in R1 is filled with droplets deposited by intermediate nozzles in R2. In this example, the constant nozzle pitch between neighbouring nozzles may effectively be the distance between nozzle 28a in R1 and the next nozzle used to deposit droplets, i.e. nozzle 28c in R2. Thus, the constant nozzle pitch may be P", as shown, where P" = P/2.
Thus, the term "constant nozzle pitch" used herein may mean the centre-to-centre separation between neighbouring nozzles in a single row, or the separation between the neighbouring nozzles used during droplet deposition. The principle of having a fixed, constant separation does not depend on how "neighbouring nozzles" is defined.
Similarly, it will be understood that in the or each variable nozzle pitch portion of an array of an actuator component, the term "variable nozzle pitch" may mean the varying centre-to-centre separation between neighbouring nozzles in a single row, or the varying separation between the neighbouring nozzles used during droplet deposition. The principle of having a varying separation does not depend on how "neighbouring nozzles" is defined.
Figure 7 illustrates a zoomed-in view of an overlap portion between overlapping actuator components, and a schematic of how fluid may be deposited using overlapping actuator components. Here, the second portion 24 of the nozzle array of the first actuator component overlaps the third portion 26 of the nozzle array of the second actuator component. Each nozzle array in this example comprises four rows of nozzles, R1 to R4, where the rows are staggered relative to each other as per the arrangement in Figure 6b. The white circles represent nozzles on each actuator component. The black circles indicate which nozzles have been/will be used to deposit fluid droplets, and the hatched circles indicate which nozzles have been disabled. In this example, all of the nozzles in each row are used to deposit droplets, i.e. this schematic shows a high resolution operation mode.
To reduce any visual artefacts arising when depositing droplets using overlapping actuator components, it is necessary to determine a suitable point at which to switch between depositing droplets from nozzles of the first actuator component to depositing nozzles from the nozzles of the second actuator component. This may be determined by selecting the best aligned pair (BAP) or a suitably aligned pair of nozzles, where one nozzle of the pair is selected from the first actuator component and the other nozzle of the pair is selected from the second actuator component. The nozzles in the suitably aligned pair are those which align more closely than any other pair of nozzles and/or which provide a minimal jump in pitch (or a sufficiently small change in pitch that it is not noticeable by the human eye) either side of the switch point. In this case, nozzle 30b of the first actuator component and nozzle 32a of the second actuator component appear to be the best aligned pair. This pair of nozzles 30b, 32a defines where the transition between actuator components will occur (i.e. the switch point).
As mentioned earlier, one of the nozzles in the pair of nozzles will be disabled, to prevent both nozzles from depositing fluid for the same pixels of an image. In Figure 7, nozzle 30b is disabled and nozzle 32a is enabled. Accordingly, droplet deposition takes place as follows: the nozzles of the first actuator component are used to deposit fluid up to nozzle 30a (the nozzle immediately before disabled nozzle 30b), and then the nozzles of the second actuator component starting from nozzle 32a are used to deposit fluid. Thus, the nozzles of the first actuator component located to the right of nozzle 30a are all disabled, or not used for droplet ejection, and the nozzles of the second actuator component located to the left of nozzle 32a are all disabled, or not used for droplet ejection. In this way, a 'super row' of nozzles (or an 'effective row') is formed which spans the two actuator components.
Figure 7 also illustrates how the selection of the suitably aligned pair of nozzles may depend on (i) how closely aligned the pair of nozzles are, and (ii) the change in pitch on either side of the switch point. In the illustrated example, nozzles 30b and 32a are closely aligned (i.e. have a minimal misalignment value), but they also result in a relatively minimal change in pitch at the switch point. That is, the pitch between nozzles 30a and 32a is about the same (or within some acceptable tolerance range) as the pitch between nozzles 32a and 32b, such that there is a minimal jump in pitch at the (or a sufficiently small change in pitch that it is not noticeable by the human eye) switch point between the first actuator component and the second actuator component.
Nozzle x on the first actuator component and nozzle 32b on the second actuator component may be considered to be closely aligned. However, this pair of nozzles does not satisfy the second criterion, i.e. the provision of a small change in pitch on either side of the selected pair of nozzles. If nozzle x is disabled in the pair of nozzles, the nozzles up to nozzle y of the first actuator component are used to deposit droplets, and then the nozzles from nozzle 32b of the second actuator component are used to deposit droplets. As shown in Figure 7, the pitch between nozzle y and nozzle 32b is P', but P' is clearly much shorter than the pitch P" between nozzle 32b and nozzle z. Thus, nozzle pair x, 32b result in a relatively large jump in pitch on either side of the switch point. Consequently, nozzle pair x, 32b may not be as suitable as nozzle pair 30b, 32a which better satisfies both criteria. In embodiments, this may mean that (depending on the functions defining the variable pitches in the overlap region between the actuator components), it is more likely to find a suitable nozzle pair that satisfy both criteria near the centre of the overlap region.
As mentioned earlier, rows of nozzles may be operated in pairs or groups depending on a resolution required for a droplet deposition task. Similarly, rows of nozzles may be operated in pairs or groups to deposit different fluids, e.g. different colour inks. Figure 8 illustrates how rows of nozzles may be operated in groups to deposit a first fluid and a second fluid. Here, the second portion 24 of the nozzle array of the first actuator component overlaps the third portion 26 of the nozzle array of the second actuator component. Each nozzle array in this example comprises four rows of nozzles, R1 to R4, where the rows are staggered relative to each other as per the arrangement in Figure 6b. On each actuator component, nozzle rows R1 and R2 are operated together to deposit a first fluid, and nozzle rows R3 and R4 are operated together to deposit a second fluid. The nozzles in rows R1 and R2 may be considered a first group G1 (or G1') of nozzles, and the nozzles in rows R3 and R4 may be considered a second group G2 (or G2') of nozzles. The boxes around the groups are provided merely for illustrative purposes. It will be understood that rows may be grouped together in alternative ways. For example, alternate rows may be grouped together, e.g. rows R1 and R3, and rows R2 and R4, depending on the design of the fluid supply to the rows within a droplet deposition head or droplet deposition apparatus.
In Figure 8, groups G1 and G1' deposit a first fluid, as represented by the black circles, and groups G2 and G2' deposit a second fluid, as represented by the white circles. The black circles indicate which nozzles have been/will be used to deposit droplets of the first fluid, and the white circles indicate which nozzles have been/will be used to deposit droplets of the second fluid.
To reduce any visual artefacts arising when depositing droplets using overlapping actuator components, it is necessary to determine a suitable point at which to switch between depositing droplets from nozzles of the first actuator component to depositing nozzles from the nozzles of the second actuator component, as explained above. In this case, two pairs of nozzles are required, one pair for each fluid. That is, a transition point between the nozzles depositing the first fluid is required, as well as a transition point between the nozzles depositing the second fluid. As shown, a first best aligned pair, BAP1, is determined for the nozzles depositing the first fluid: one nozzle in pair BAP1 is selected from group G1 of the first actuator component, and one nozzle is selected from group G1' of the second actuator component. This pair of nozzles BAP1 defines where the transition between actuator components will occur for the first fluid. A second best aligned pair, BAP2, is determined for the nozzles depositing the second fluid: one nozzle in pair BAP2 is selected from group G2 of the first actuator component, and one nozzle is selected from group G2' of the second actuator component. This pair of nozzles BAP2 defines where the transition between actuator components will occur for the second fluid.
In embodiments, the group G1 of the first actuator component may represent those nozzles used when depositing droplets in a low resolution mode. For example, groups G1 and G2 of the first actuator component may both be used in a high resolution mode (e.g. 1200 dpi), in which all of the nozzles are used to deposit the same fluid (e.g. one of black, magenta, yellow or cyan ink). In a low resolution mode (e.g. 600 dpi), half of the nozzles, or one group of nozzles, may be disabled. Figure 8 therefore also represents how a best aligned pair may be selected for different operation modes or different resolutions. For example, BAP1 may represent the best aligned pair of nozzles when operating in a first mode (e.g. high resolution), and BAP2 may represent the best aligned pair of nozzles when operating in a second mode (e.g. low resolution). In embodiments, BAP1 may be the same as BAP2.
Figure 9a illustrates how overlapping actuator components may be misaligned. The second portion 24 of the nozzle array of the first actuator component 12a overlaps the third portion 26 of the nozzle array of the second actuator component 12b. An offset between two features which should be aligned defines the misalignment between the actuator components 12a and 12b. For example, the misalignment may be the difference between an ideal (aligned) placement of specific nozzles on the two actuator components, or between alignment marks on the actuator components, etc. In Figure 9a, the misalignment of two nozzles, one from actuator component 12a and one from actuator component 12b, is used to determine the misalignment between the two actuator components. There is a range of possible misalignment values, which ranges from 0 (i.e. perfectly aligned) to a value representing a severe misalignment (e.g. if a nozzle on one actuator component aligns with the gap between nozzles on another actuator component, or is aligned/partially aligned with a nozzle other than the nozzle it should align with). Generally speaking, and as mentioned above, the function defining the variable nozzle pitch of the or each variable pitch portion of the nozzle array of an actuator component is selected using computer modelling to determine which functions provide the best chance of find a best aligned pair of nozzles for the widest range of displacement values. A maximum delta value (max delta) may be defined as the difference between a constant nozzle pitch P1 (i.e. an ideal pitch between nozzles that form the 'super row') and the displacement E between the nozzles at the transition point. For example, Figure 9a shows a possible best aligned pair (BAP) of nozzles - one of these nozzles will be used to deposit fluid droplets and the other will be disabled. Figure 9b shows the transition between the actuator components 12a and 12b. Here, black circles represent nozzles used to deposit fluid and white circles represent disabled nozzles. The nozzle of the second actuator component in the BAP is disabled, and thus, at the transition point, the neighbouring nozzle N is used to continue the droplet deposition process. However, unless the best aligned pair of nozzles are perfectly aligned, the separation E between the nozzles at the transition point may not be equal to the ideal pitch P1. Thus, generally speaking, a function which defines the or each variable nozzle pitch is required which minimises the max delta over the largest range of possible displacements/misalignments.
Figure 9b also shows how an absolute jump in pitch at a transition point may be defined. The jump in pitch may be calculated as the difference between the pitch on each side of the transition point, divided by the one of those pitches. In this example, pitch P' is the pitch between the last two nozzles used to deposit fluid of the first actuator component, and pitch P" is the pitch between the first two nozzles used to deposit fluid of the second actuator component. The absolute jump in pitch is the modulus of the difference between P' and P" divided by P". (It will be understood that an alternative definition may be used to calculate the absolute jump in pitch. For example, the jump in pitch may be the modulus of the difference between P' and P" divided by P'). The absolute jump in pitch may be provided as a percentage.
Turning now to Figures 10 to 12, these show example simulations of various functions defining a variable nozzle pitch. Figure 10a illustrates a row of nozzles of a nozzle array of a first actuator component, and a row of nozzles of a nozzle array of a second actuator component, in the region where the two actuator components overlap. As mentioned above, in an actuator component comprising rows of 1420 nozzles, 56 nozzles may be assigned to the or each variable pitch portion of the nozzle array of the actuator component. Thus, Figure 10a shows how the pitch varies between the 56 nozzles of the variable pitch portion of two overlapping actuator components. A nominal nozzle pitch (which may be the same as the constant nozzle pitch of the nozzle array) between nozzles of an actuator component may be 21.2 µm. In Figure 10a, the nozzle pitch between the nozzles in the overlap portion of the first actuator component is 21.2 +0.5 µm, while the nozzle pitch between the nozzles in the overlap region of the second actuator component is 21.2 -0.5 µm. That is, in this example, the nozzle arrays do not have a variable nozzle pitch portion at all; instead, the nozzle pitch of each array in the overlap region is fixed/constant, though it does differ from the nominal pitch (i.e. the pitch of the constant nozzle pitch portion of the nozzle array). This is a default arrangement that is also referred to as a 'Vernier' arrangement.
Figure 10b shows, for 1200dpi actuator components having the non-variable nozzle pitch of Figure 10a, how it becomes more difficult to find a suitably aligned pair of nozzles as the misalignment between overlapping actuator components increases. In other words, as the misalignment increases above 800 µm, it becomes increasingly difficult to find a pair of nozzles which are suitably aligned to avoid any visual artefacts. Figure 10c shows how the absolute percentage jump in pitch at a switch point between the actuator components of Figure 10a varies as a function of misalignment. In this case, since the nozzle pitch of each array in the overlap region is fixed/constant, the change in pitch at the switch point does not vary as a function of misalignment: the jump in pitch remains at 4.7% regardless of the misalignment between the actuator components, simply because the nozzle pitch itself does not vary. However, a 4.7% change in pitch at the switch point is significant and may result in a sharp, visible change in optical density (i.e. a visual artefact in a printed image).
Figure 10d shows the same information as Figure 10b but for 600dpi actuator components, (or a 1200dpi nozzle arrays in which half the nozzles are disabled), and Figure 10e shows the same information as Figure 10c but for 600dpi actuator components. In Figure 10d, as the misalignment increases above 400 µm, it becomes increasingly difficult to find a pair of nozzles which are suitably aligned to avoid any visual artefacts. Figure 10e shows that the absolute percentage jump in pitch remains at 4.7% regardless of the misalignment between the actuator components, because the nozzle pitch in the 600dpi actuator component does not vary in the overlap region.
A typical misalignment between actuator components arranged within a droplet deposition head (e.g. the arrangement of Figure 1a) may be quite small, e.g. below 10 µm. However, the misalignment between two overlapping droplet deposition heads having actuator components (e.g. the arrangement of Figure 1b) may be over 100 µm. In this case, the misalignment may depend on the design of the droplet deposition head. The simulations shown in Figures 10b to 10e cover typical misalignments as well as more severe misalignments.
Thus, for a default Vernier (i.e. the scheme shown in Figure 10a), there may be a good chance of finding a suitably aligned pair for a 1200dpi actuator component or a 600dpi actuator component that is misaligned by the typical values mentioned above (e.g. between 0 µm and 200 µm), and larger misalignments could be tolerated. However, the jump in pitch of 4.7% at the transition point between the actuator components is sharp, and can be detected by the human eye. Thus, the default, non-varying nozzle pitch may not be suitable for reducing visual artefacts in the overlap region between actuator components.
Figure 11a illustrates a row of nozzles of a nozzle array of a first actuator component, and a row of nozzles of a nozzle array of a second actuator component, in the region where the two actuator components overlap. As mentioned above, in an actuator component comprising rows of 1420 nozzles, 56 nozzles may be assigned to the or each variable pitch portion of the nozzle array of the actuator component. Figure 11a shows how the pitch varies between the 56 nozzles of the variable pitch portion of two overlapping actuator components.
In the example of Figure 11a, both actuator components comprise a constant portion in which the nozzle pitch between nozzles is constant/fixed. This constant nozzle pitch is 21.2 µm. A variable nozzle pitch portion of the first actuator component overlaps a variable nozzle pitch portion of the second actuator component. The variable nozzle pitch of the first actuator component is defined by a sinusoidal function, e.g. P1_n = 21.2 + bsin(x_n) µm, where xn is distance of nozzle n measured from one end of the variable pitch portion (e.g. from the first end, or from the end closest to the constant pitch portion) and b is a fixed multiplier. Similarly, the variable nozzle pitch of the second actuator component is defined by a sinusoidal function, e.g. P2_n = 21.2 - bsin(x_n) µm. As shown in Figure 11a, the pitch between neighbouring nozzles in the variable nozzle pitch portion of each actuator component varies with distance (or nozzle position) in accordance with the sine function.
Figure 11b shows, for two overlapping 1200dpi actuator components having the variable nozzle pitches shown in Figure 11a, how it becomes more difficult to find a suitably aligned pair of nozzles as the misalignment between overlapping actuator components increases. In other words, as the misalignment increases above 500 µm, it becomes increasingly difficult to find a pair of nozzles which are suitably aligned to avoid any visual artefacts. Figure 11c shows how the absolute percentage jump in pitch at a switch point between the actuator components of Figure 11a varies as a function of misalignment. In this example, the change in pitch at the switch varies as a function of misalignment: the jump in pitch varies from less than 1% to 5%. The change in pitch at the switch point may therefore be lower than for the default Vernier example in Figure 10a for particular misalignments.
Figure 11d shows the same information as Figure 11b but for 600dpi actuator components, (or a 1200dpi nozzle arrays in which half the nozzles are disabled), and Figure 11e shows the same information as Figure 11c but for 600dpi actuator components. For this particular sinusoidal function, the max delta value increases significantly faster with increasing misalignment for the 600dpi actuator component (or operation mode) than for the 1200dpi actuator component (or operation mode). Figures 11c and 11d illustrate how, in comparison to the effect of the default Vernier shown in Figures 10c and 10d, the overall percentage jump in pitch may be reduced by employing this nozzle arrangement scheme, and reduced significantly for certain misalignment values where the absolute percentage jump may be lower than 1%.
Figure 12a illustrates a row of nozzles of a nozzle array of a first actuator component, and a row of nozzles of a nozzle array of a second actuator component, in the region where the two actuator components overlap. As mentioned above, in an actuator component comprising rows of 1420 nozzles, 56 nozzles may be assigned to the or each variable pitch portion of the nozzle array of the actuator component. Figure 12a shows how the pitch varies between the 56 nozzles of the variable pitch portion of two overlapping actuator components. Specifically, in the example of Figure 12a, the variable pitch of the first actuator component (in the overlap region) is defined by P1_n = 21.2 + (n ^∗ 0.7/N) µm, and the variable pitch of the second actuator component is defined by P2_n = 21.2 -(n' ^∗ 0.5/N') µm), where N, N' are the total number of nozzles in the variable pitch portions of the first actuator component and second actuator component respectively, and n is the nozzle number within the variable pitch portion of the actuator component (defined relative to an end of the variable pitch portion, e.g. the first end, or the end closest to the constant pitch portion).. In other words, the variable pitch of the first actuator component increases from the constant/nominal pitch of 21.2 µm at one end of the variable pitch portion to 21.2 µm + 0.7 µm at the other end of the variable pitch portion, such that the pitch between each pair of neighbouring nozzles gradually increases between one end and the other end of this variable portion. Similarly, the variable pitch of the second actuator component in the overlap portion increases from the constant/nominal pitch of 21.2 µm at one end of the variable pitch portion to 21.2 µm + 0.5µm at the other end of the variable pitch portion, such that the pitch between each pair of neighbouring nozzles gradually increases between one end and the other end of this variable portion.
Figure 12b shows, for two overlapping 1200dpi actuator components having the variable nozzle pitches shown in Figure 12a, how it becomes more difficult to find a suitably aligned pair of nozzles as the misalignment between overlapping actuator components increases. In other words, as the misalignment increases above 800 µm, it becomes increasingly difficult to find a pair of nozzles which are suitably aligned to avoid any visual artefacts. Figure 12c shows how the absolute jump in pitch at a switch point between the actuator components of Figure 12a varies as a function of misalignment. In this example, the change in pitch at the switch varies as a function of misalignment: the jump in pitch varies between 2 and 4% over misalignments ranging between 0 µm to 500 µm. The change in pitch at the switch point is therefore lower than for the default Vernier example in Figure 10a for particular misalignment values.
Figure 12d shows the same information as Figure 12b but for 600dpi actuator components, (or a 1200dpi nozzle arrays in which half the nozzles are disabled), and Figure 12e shows the same information as Figure 12c but for 600dpi actuator components. For these particular linearly variable pitch functions, the max delta value increases faster with increasing misalignment for the 600dpi actuator component (or operation mode) than for the 1200dpi actuator component (or operation mode). However, compared to the sinusoidal example shown in Figures 11a-11e, the overall jump in pitch in Figure 12c is reduced to less than 4% over a displacement range of up to 500 µm, and to around 3% for smaller displacements. In the 600dpi arrangement, Figure 12e shows that for certain displacement values a percentage jump in pitch as low as about 2% may be achieved.
Figure 12a demonstrates an advantage of having a nozzle array with a first constant portion, a second variable portion and a third variable portion, as per the arrangement shown in Figure 2b. In this example, the second variable portion of the nozzle array of each actuator component may have a pitch defined by P1 = 21.2 +0.7 µm, and the third variable portion of the nozzle array of each actuator component may have a pitch defined by P2 = 21.2 -0.5 µm. The arrangement of Figure 12a may be achieved by arranging a first actuator component next to a second actuator component such that the second variable portion of the first actuator component overlaps the third variable portion of the second actuator component, as described earlier (and shown in Figure 4b). Thus, this simulation shows how actuator components having nozzle arrays with a third variable portion and a second variable portion may be used to reduce visual artefacts during droplet deposition, compared to nozzle arrays having a second and third portion that have a fixed pitch (which may be different from the constant pitch).
Figure 13 is a flowchart showing steps to calibrate a droplet deposition apparatus. The calibration process comprises selecting a suitably aligned nozzle pair for use in the or each operation mode of the droplet deposition apparatus, for each pair of overlapping actuator components. That is, since a droplet deposition apparatus may comprise multiple actuator components arranged in a staggered, overlapping arrangement, a suitably aligned nozzle pair is required for each overlap portion, and for each operation mode (e.g. different resolutions, single fluid, multi-fluid, etc.) The calibration process may be performed manually by a user of the apparatus, may be automated, or may be a combination of both.
The process starts at start step S100, and at step S102, for each overlap portion, a nozzle pair is selected which defines the transition point between the overlapping actuator components. The selected nozzle pair may be a default nozzle pair, i.e. a pair that is always selected at the start of a calibration process. For example, the pair of nozzles which is in, or close to, the centre of the overlap region, may be selected by default. A test pattern is then printed using the selected nozzle pair to define the transition point (step S104). The test pattern is optically inspected (step S106), either by a user of the apparatus or by an image scanning device coupled to a computer. The next step in the calibration process comprises determining if there are any visual artefacts in the test pattern (step S108), which arise in the region(s) of the pattern corresponding to the overlap region between overlapping actuator components. This may be performed by visual inspection by a user, or may be performed using software to analyse an image captured of the test pattern by the image scanning device. If no, or an acceptably low number of, visual artefacts are detected, the selected nozzle pair is stored for future use (step S114), preferably with information about the operation mode for which they were selected. The process then ends at step S118.
As mentioned earlier, a masking technique may be required to ensure that a pixel colour density required to reproduce a pixel of an image on a receiving medium is produced by the overlapping actuator components, because pixel colour density (i.e. a value which indicates how many droplets are required to form each pixel of an image on a receiving medium) may depend on the nozzle pitch. Thus, to ensure that the nozzles in the overlap region between actuator components provide the required pixel colour density for each pixel of an image, a masking technique may be required which specifies how many droplets each nozzle has to eject to achieve the required pixel colour density and to compensate for the variable nozzle pitch. This may be achieved by configuring the selected/non-disabled nozzles in the overlap region to deposit fewer or more droplets than the nozzles in the constant pitch portion, to provide a required pixel colour density.
In embodiments, the process optionally comprises selecting and storing a masking technique which determines a number of sub-droplets to be deposited by each non-disabled nozzle of the overlapping actuator components in the overlap region (step S116). An example suitable masking technique is described in United Kingdom patent application number GB 1522809.1 .
At step S108, if unacceptable visual artefacts are detected, a different nozzle pair is selected (step S110) and a new test pattern is printed. Thus, steps S104 to S112 are repeated until a suitable nozzle pair is identified which reduces or removes visual artefacts in a printed image.
In embodiments, the selecting the best aligned pair of nozzles may comprise selecting a pair of nozzles which satisfies one, or preferably both, of the selection criteria: (i) how closely aligned the pair of nozzles are, and (ii) the change in pitch on either side of the switch point. In embodiments, a lookup table or similar data may be provided for an actuator component, or for a droplet deposition head comprising multiple actuator components. The lookup table may indicate which pairs of nozzles may satisfy these criteria for differing misalignment values. The lookup tables are variable pitch function-specific.
No doubt many other effective alternatives will occur to the skilled person. For example, it will be understood that whilst various concepts are described above with reference to an inkjet printhead, such concepts are not limited to inkjet printheads, but may be applied more broadly in printheads, or more broadly still in droplet deposition heads, for any suitable application. As noted above, droplet deposition heads suitable for such alternative applications may be generally similar in construction to printheads, with some adaptations made to handle the specific fluid in question. The preceding description should therefore be understood as providing non-limiting examples of applications in which such a droplet deposition head may be used. Furthermore, it will be understood that the invention is limited by the scope of the appended claims.

Claims

An arrangement of actuator components (10, 20, 20') for a droplet deposition apparatus, the arrangement comprising:
a first actuator component (12a) and a second actuator component (12b) provided in a staggered arrangement relative to a common axis, wherein said first actuator component (12a) and said second actuator component (12b) each comprises a plurality of nozzles (28) arranged in at least one nozzle array, such that the nozzle array of said first actuator component (12a) partially overlaps with the nozzle array of said second actuator component (12b);

wherein each nozzle array comprises:
a first portion (22) comprising a first subset of the plurality of nozzles (28), wherein the first subset of nozzles are arranged along a nozzle array axis and are separated by a constant nozzle pitch which is constant between a first end (221) of the first portion (22) and a second end (222) of the first portion (22);

a second portion (24) comprising a second subset of the plurality of nozzles (28), wherein the second subset of nozzles are arranged along the nozzle array axis and are separated by a variable nozzle pitch which decreases gradually away from the constant nozzle pitch with distance from a first end (241) of the second portion (24) towards a second end (242) of the second portion (24), wherein the first end (241) of the second portion (24) abuts the second end (222) of the first portion (22); and

a third portion (26) comprising a third subset of the plurality of nozzles (28), wherein the third subset of nozzles are arranged along the nozzle array axis and are separated by a further variable nozzle pitch which varies from a first end (261) of the third portion (26) to a second end (262) of the third portion (26);

wherein the first portion (22) of the nozzle array is provided between the second portion (24) and the third portion (26), such that the second end (262) of the third portion (26) abuts the first end (221) of the first portion (22), and the second end (222) of the first portion (22) abuts the first end (241) of the second portion (24).
The arrangement of actuator components as claimed in claim 1, wherein the further variable nozzle pitch of the third portion (26) increases gradually away from the constant nozzle pitch with distance between the first end (261) and the second end (262) of the third portion (26).
The arrangement of actuator components as claimed in claim 1, wherein the variable nozzle pitch is defined by a first function which varies with distance between the first end (241) of the second portion (24) and the second end (242) of the second portion (24), and wherein the first function defining the variable nozzle pitch is a non-linear function.
The arrangement of actuator components as claimed in claim 1 or claim 2, wherein the actuator components (12a, 12b) are arranged relative to the common axis such that the second portion (24) of the nozzle array of the first actuator component (12a) at least partially overlaps the third portion (26) of the nozzle array of the second actuator component (12b).
A droplet deposition apparatus comprising a droplet deposition head having at least one arrangement of actuator components (10, 20, 20') according to any one of claims 1 to 4.
A method of operating a droplet deposition apparatus according to claim 5,
wherein the first actuator component (12a) is arranged in a plane of the droplet deposition apparatus, and

the second actuator component (12b) is arranged in the plane of the droplet deposition apparatus in a staggered arrangement relative to the first actuator component (12a), such that the second portion (24) of the nozzle array of the first actuator component (12a) at least partially overlaps the third portion (26) of the second actuator component (12b),

the method comprising:
selecting a first nozzle from the second portion (24) of the nozzle array of the first actuator component (12a), and selecting a second nozzle from the third portion (26) of the nozzle array of the second actuator component (12b), the selected first nozzle and second nozzle forming a suitably aligned pair of nozzles.
The method as claimed in claim 6, wherein selecting the first nozzle and the second nozzle comprises: selecting a first nozzle and a second nozzle which have a minimal misalignment value.
The method as claimed in claim 6 or claim 7, wherein selecting the first nozzle and the second nozzle comprises: selecting a first nozzle and a second nozzle which provide a minimal jump in pitch at a switch point between the first and second actuator components.
The method as claimed in any one of claims 6 to 8, further comprising:
disabling one of the first nozzle and the second nozzle of the aligned pair of nozzles;

disabling the nozzles of the second portion (24) extending from the selected first nozzle towards the second end (242) of the second portion (24); and

disabling the nozzles of the third portion (26) extending from the selected second nozzle towards the first end (261) of the third portion (26).
The method as claimed in claim 6, wherein at least one row in each nozzle array of the first actuator component (12a) and the second actuator component (12b) is configured to deposit a first fluid, and at least one row in each nozzle array of the first actuator component (12a) and the second actuator component (12b) is configured to deposit a second fluid, the method comprising:
selecting, from the row configured to deposit the first fluid, a first nozzle in the second portion (24) of the nozzle array of the first actuator component (12a), and selecting a second nozzle in the third portion (26) of the nozzle array of the second actuator component (12b), the selected first nozzle and second nozzle forming a suitably aligned first pair of nozzles; and

selecting, from the row configured to deposit the second fluid, a third nozzle in the second portion (24) of the nozzle array of the first actuator component (12a), and selecting a fourth nozzle in the third portion (26) of the nozzle array of the second actuator component (12b), the selected third nozzle and fourth nozzle forming a suitably aligned second pair of nozzles.
The method as claimed in claim 10, further comprising:
disabling one of the first nozzle and the second nozzle of the first aligned pair of nozzles;

disabling, in the row configured to deposit the first fluid in the nozzle array of the first actuator component (12a), the nozzles of the second portion (24) extending from the selected first nozzle towards the second end (242) of the second portion (24);

disabling, in the row configured to deposit the first fluid in the nozzle array of the second actuator component (12b), the nozzles of the third portion (26) extending from the selected second nozzle towards the first end (261) of the third portion (26);

disabling one of the third nozzle and the fourth nozzle of the second aligned pair of nozzles;

disabling, in the row configured to deposit the second fluid in the nozzle array of the first actuator component (12a), the nozzles of the second portion (24) extending from the selected third nozzle towards the second end (242) of the second portion (24); and

disabling, in the row configured to deposit the second fluid in the nozzle array of the second actuator component (12b), the nozzles of the third portion (26) extending from the selected fourth nozzle towards the first end (261) of the third portion (26).
Control circuitry of a droplet deposition apparatus according to claim 5, configured to perform the method according to any one of claims 6 to 11.
A non-transitory data carrier carrying code which, when implemented on a control circuitry according to claim 12, causes the control circuitry to carry out the method according to any one of claims 6 to 11.