Patent Grant
12076993
This application is the U.S. national phase of PCT Application No. PCT/GB2020/051840, filed Jul. 31, 2020, which claims priority to GB 1911217.6, filed Aug. 6, 2019, the disclosures of which are incorporated, in their entirety, by reference herein.
The present disclosure relates to a nozzle plate for a droplet ejection device, a method of droplet ejection using such a nozzle plate, and a droplet ejection apparatus comprising a droplet ejection device using such a nozzle plate. The nozzle plate may be used with particular benefit in applications that require printing a high resolution image onto a textured or flexible surface at high speeds.
Droplet ejection apparatuses are now in widespread usage, whether in more traditional applications, such as inkjet printing, or in 3D printing, or other rapid prototyping techniques. Amongst other things, droplet ejection devices, or inkjet printheads, have been developed that are capable of depositing ink directly onto paper, card, ceramic tiles and other deposition media, with high reliability and throughput. In other applications, droplet ejection heads may be used to form elements such as colour filters in LCD or OLED displays used in flat-screen television manufacturing.
Droplet ejection apparatuses and their components continue to evolve so as to meet the requirements of ever more challenging applications, generally improving resolution and throughput at high print quality.
Aspects of the invention are set out in the appended independent claims, while particular embodiments of the invention are set out in the appended dependent claims.
The following disclosure describes, in one aspect, a nozzle plate for a droplet ejection head, the nozzle plate comprising a first row of nozzles arranged to deposit droplets onto a deposition media; wherein the first row of nozzles extends in a row direction and comprises one or more nozzle clusters, each nozzle cluster being arranged along the row direction for a cluster length c, and extending along a cluster depth direction perpendicular to the row direction by a cluster depth d; wherein each nozzle cluster comprises a plurality of nozzles of which one or more nozzles within each nozzle cluster define the cluster length c and two or more nozzles within each nozzle cluster define the cluster depth d; wherein each nozzle cluster is spaced apart from an adjacent nozzle cluster along the row direction by a cluster spacing a such that an air flow path is created for forced air to pass through the row of nozzles in a controlled manner; and wherein at least a majority of nozzles of the first row, when projected in a transverse direction onto the row direction, are equidistantly spaced from one another by a projected nozzle spacing.
In one exemplary embodiment the first row of nozzles comprises a first set of subrows comprising first and second subrows that extend alongside one another in respective subrow directions, the first and second subrows extending parallel to the row direction; wherein the first and second subrows are spaced apart by a first subrow spacing b in the transverse direction, perpendicular to the row direction; and wherein each of the first and second subrows comprises the one or more nozzle clusters; wherein each nozzle cluster within a subrow is spaced apart from a neighbouring nozzle cluster by the cluster spacing a; and wherein each projected nozzle cluster of the first and second subrows is spaced apart from an adjacent projected nozzle cluster by the projected nozzle spacing.
In another exemplary embodiment each nozzle cluster is spaced apart from an adjacent nozzle cluster along the row direction by a cluster spacing a greater than a nozzle spacing ns between adjacent nozzles of a nozzle cluster.
A method of depositing droplets (e.g. printing) using such a nozzle plate, a drive signal controller operable to carry out such a method, a droplet ejection device (e.g. printhead) comprising such a nozzle plate, and a droplet ejection apparatus (e.g. printer) comprising such a nozzle plate, are also provided.
Embodiments of the invention will now be described, by way of example only, and with reference to the drawings in which:
In the Figures, like elements are indicated by like reference numerals throughout.
To highlight the functionality of the embodiments and their various implementations that will be described with respect to
Details of typical patterns of nozzles 12 are shown in plan view in
In
In
The stagger offset distance is related to a combination of mechanical, electrical and fluidic considerations, and is typically determined empirically. The offset distances in
In some circumstances when using a conventional nozzle arrangement of
An illustration of a typical woodgrain pattern is shown in the test print sample in
In some applications, it is desirable to use a droplet ejection apparatus 1, such as that shown in
An alternative arrangement is that of a scanning droplet ejection apparatus, in which the droplet ejection head 2 is moved back and forth in the y-direction orthogonally to the media transport direction x. In this arrangement, the droplet ejection head 2 travels at high speed relative to the surrounding (stationary) air, causing the air to flow around the droplet ejection head 2. As part of this flow of air around the droplet ejection head 2, some air flow is forced into the gap between the deposition media 3 and the nozzle plate of the droplet ejection head 2, with a velocity profile characteristic to the scanning application. The conditions of air flow in such an arrangement differs from that of the single pass set up, but drop deviation and woodgrain patterns still may occur.
More generally, whether the droplet ejection head 2 is moved with respect to the deposition media 3, or the deposition media 3 is moved with respect to the droplet ejection head 2, a velocity difference exists between the droplet ejection head 2 and the deposition media 3, which gives rise to forced air flow around the droplet ejection head 2, and/or in the gap G between the head droplet ejection 2 and the deposition media 3. Particularly in high gap distance applications, in which the gap G may measure several millimetres, and which may additionally require high resolution nozzle density and/or high throughput (high relative speed between the droplet ejection head and the deposition media) and/or high print frequency, the forced air flow needs to be carefully managed to maintain high print quality.
The inventors have found that the effect of woodgrain can be reduced or removed by providing a modified nozzle arrangement in a nozzle plate 10 that will now be described with respect to
Overview
In general, the present embodiments of a nozzle plate for a droplet ejection head employ an overarching principle in which the nozzle plate comprises a first row of nozzles arranged to deposit droplets onto a deposition media, wherein the first row of nozzles extends in a row direction and comprises two or more nozzle clusters. Each nozzle cluster is arranged along the row direction for a cluster length c, and extends along a cluster depth direction perpendicular to the row direction by a cluster depth d. Each nozzle cluster comprises a plurality of nozzles of which one or more nozzles within each nozzle cluster define the cluster length c and two or more nozzles within each nozzle cluster define the cluster depth d. Each nozzle cluster is spaced apart from an adjacent nozzle cluster along the row direction by a cluster spacing a such that an air flow path is created for forced air to pass through the row of nozzles in a controlled manner; and wherein at least a majority of nozzles of the first row, when projected in a transverse direction onto the row direction, are equidistantly spaced from one another by a projected nozzle spacing. In other words, when the first row is projected in a transverse direction onto the row direction, a transition region between adjacent nozzle clusters comprises two or more nozzles from a first cluster and two or more nozzles from a second cluster, the second cluster being adjacent to the first cluster, and the nozzles in the transition region being equidistantly spaced from one another by a projected nozzle spacing.
In a first embodiment, the first row of nozzles comprises a first set of subrows comprising first and second subrows that extend alongside one another in respective subrow directions, the first and second subrows extending parallel to the row direction. The first and second subrows are spaced apart by a first subrow spacing b in a transverse direction perpendicular to the row direction, and each of the first and second subrows comprises the one or more nozzle clusters. Each nozzle cluster within a subrow is spaced apart from a neighbouring nozzle cluster by the cluster spacing a; wherein the two or more nozzles from the first cluster and two or more nozzles from the adjacent, second cluster comprised within the transition region are comprised within the first and second subrows, respectively, and each projected nozzle cluster of the first and second subrows is spaced apart from an adjacent projected nozzle cluster by the projected nozzle spacing.
In some variants, the cluster depth d may be the same as the stagger offset distance sd. In other words, the cluster depth may be the depth of one subrow.
Optionally, the first set of subrows may further comprise a third subrow, wherein one or more nozzle clusters of each of the first, second and third subrows define a first subrow spacing between the first and second subrows and a second subrow spacing between the first and third subrows. The first and second subrow spacings may be the same as one another, or they may be different from one another.
Optionally, the nozzle plate may have a second row of nozzles extending in a second row direction, the second row direction being parallel to the first row direction. The second row of nozzles comprises a second set of subrows comprising first and second subrows that extend alongside one another in respective subrow directions, the first and second subrows of the second set of subrows extending parallel to the second row direction. The first and second subrows of the second set of subrows are spaced apart by a third subrow spacing b in a transverse direction, perpendicular to the second row direction. Each of the first and second subrows of the second set of subrows comprises one or more nozzle clusters, each nozzle cluster comprising a plurality of nozzles extending along the respective subrow direction for a cluster length c. Each nozzle cluster within a subrow of the second set of subrows is spaced apart from a neighbouring nozzle cluster by a cluster spacing a. At least a majority of nozzles of the first and second subrows of the second set of subrows, when projected in the transverse direction onto the second row direction, are equidistantly spaced from one another by a second projected nozzle spacing, and each projected nozzle cluster of the first and second subrows of the second set of subrows is spaced apart from an adjacent projected nozzle cluster by the second projected nozzle spacing. In other words, a second transition region between adjacent nozzle clusters of the first and second subrow of the second set of subrows comprises two or more nozzles from the first subrow and two or more nozzles from the second subrow of the second set of subrows, and the nozzles in the second transition region are equidistantly spaced from one another by a second projected nozzle spacing. The air flow path is created by the cluster spacings a so as to create a flow path for forced air to pass through the second row of nozzles in a controlled manner.
At least a majority of nozzles of the first and second sets of subrows, when projected in the transverse direction onto the row direction, may be equidistantly spaced from one another by a third projected nozzle spacing, the third projected nozzle spacing being less than the first projected nozzle spacing. In other words, when projected in the transverse direction onto the row direction, in an overlap region of the first and second transition regions, the projected consecutive nozzles are equidistantly spaced from one another by a third projected nozzle spacing, the third projected nozzle spacing being less than the first projected nozzle spacing.
Optionally, the one or more nozzle clusters of the first subrow of the first set of subrows has a cluster length different from the cluster length of one or more nozzle clusters of the second subrow of the first set of subrows.
Optionally, one of the subrows comprises first and second subsets of nozzle clusters, the cluster length of the first subset of nozzle clusters being different to the cluster length of the second subset of nozzle clusters.
The first subrow spacing b may be greater than 150 μm, optionally greater than 300 μm, and more further optionally greater than 500 μm.
It will be appreciated that, in embodiments having subrows, the air flow path is created by the cluster spacing a in combination with the subrow spacing b.
In a second embodiment, each nozzle cluster may be spaced apart from an adjacent nozzle cluster along the row direction by a cluster spacing a greater than a nozzle spacing ns between adjacent nozzles of a nozzle cluster.
Optionally, each projected nozzle cluster of the first row may be spaced apart from an adjacent projected nozzle cluster by the projected nozzle spacing.
Additionally or instead, in some variants one or more of the plurality of nozzle clusters may comprise two or more subclusters of nozzles extending substantially along the row direction, wherein the subclusters are arranged parallel to one another so as to form a matrix of nozzles, and wherein each nozzle cluster is arranged so as to overlap with an adjacent nozzle cluster along the row direction and along a direction perpendicular to the row direction.
Additionally or instead, in some variants the nozzle clusters may be arranged in one or more of a parallelogram, trapezoidal or triangular shape.
In some hybrid variants, the nozzle clusters of variants according to the first embodiment that are located adjacent one another along the row direction may be offset from one another along the cluster depth direction. In other words, two subrows of clusters may be created, each subrow extending parallel to the row direction, the subrows spaced apart from another by a subrow spacing b in a transverse direction, the transverse direction being perpendicular to the row direction.
In some variants of either embodiment, the one or more of the plurality of nozzle clusters may comprise two or more subclusters of nozzles extending substantially along the row direction, wherein the subclusters are arranged parallel to one another so as to form a matrix of nozzles. The subclusters may be offset from one another in a direction perpendicular to the row direction by a stagger offset distance sd.
First Embodiment of the Nozzle Plate
In contrast to
The first and second subrows 22_1 and 22_2 extend parallel to one another in respective subrow directions, and the subrow directions in turn extend parallel to the general row direction 26 of row 20. The first and second subrows are therefore spaced apart by a subrow spacing b, which in
This is further illustrated in
Nozzles 12 of each nozzle cluster 24_1a, 24_1b, 24_2a and 24_2b extend over a cluster length c along the respective subrow direction, which in
Cluster 24_1a is spaced from adjacent cluster 24_1b by a cluster spacing a in the respective subrow direction. In
Cluster 24_2a is also spaced from adjacent cluster 24_2b by a cluster spacing a in the respective subrow direction. Nozzle clusters 24_1a and 24_1b define subrow 22_1 and nozzle clusters 24_2a and 24_2b define subrow 22_2, where subrow 22_1 extends parallel to subrow 22_2 and at a subrow spacing b to subrow 22_2.
In this embodiment therefore, a nozzle plate 10 for a droplet ejection head 2 is provided, the nozzle plate 10 comprising at least a first row 20 of nozzles 12 arranged to deposit droplets onto a deposition media. The first row of nozzles extends in a row direction 26, and comprises a first set of first and second (or more) subrows 22 extending alongside one another in respective subrow directions, where the subrow directions extend parallel to the row direction 26. The first and second subrows 22 are spaced apart by a first subrow spacing b in a transverse direction, perpendicular to the row direction 26, wherein each subrow comprises one or more nozzle clusters 24. Each nozzle cluster 24 comprises a plurality of nozzles 12 which extend along the respective subrow direction for a cluster length c, wherein each nozzle cluster 24 within a subrow 22 is spaced apart from an adjacent nozzle cluster by a cluster spacing a. Preferably the first subrow spacing b is greater than 300 μm. The nozzles 12 of the first set of subrows, when projected in the transverse direction onto the row direction 26, are equidistantly spaced apart from adjacent projected nozzles by a projected nozzle spacing, and each projected nozzle cluster of the first and second subrows 22 is spaced apart from an adjacent projected nozzle cluster by the projected nozzle spacing. In some implementations, the subrow spacing may be smaller than 900 μm. Alternatively, the subrow spacing may be greater than 400 μm, or greater than 500 μm.
In the illustrative embodiment of
In the example embodiment of
The two subrows shown in
The specific fluid arrangement behind the nozzle plate indicated in
Returning to
The droplet displacement caused by the forced air flow, from here on referred to as primary flow, is considered to be uniform across the drop ejection head 2. This part of the droplet displacement can be managed by knowledge of the media speed and coordinating the timing of ejection accordingly.
Meanwhile, secondary air flows and their interaction with the primary flow can lead to an additional unpredictable displacement of the droplet in the direction of media transport, x, or in the row direction. This part of the deviation is not possible to control by conventional measures, e.g. through timing.
One example of secondary air flow is that thought to be caused by the ejection of droplets from the nozzles 12. Each droplet, moving for example at 6 m/s, drags air downwards with it, causing a downward columnar air flow. Such air columns may combine along the row direction to form a “curtain” of air flow around a group of neighbouring nozzles 12. This may particularly be the case for high resolution droplet ejection heads, which have smaller nozzle spacings and the columns are more densely packed.
The “air curtain” and its associated flow may be stronger the faster the droplets are and the higher the frequency at which the droplets are ejected. The forced flow induced by the droplets impinging on the deposition media 3, and the interaction of the air curtain with the forced flow leads to the formation of circulating eddies. This is schematically shown in
It is thought by the inventors that the forced air flow may break through the “air curtain” set up by the droplet curtain, and, upon passing the droplet curtain, will form eddies with a circulating motion crossing the media transport direction. This may occur at particular at weak points or gaps in the droplet curtain. Weaknesses in the droplet curtain, and therefore gaps in the barrier presented by the “air curtain”, may occur due to non-uniformities across a row of nozzles, for example due to some nozzles producing lower droplet volumes and/or slower droplets compared to their neighbours, due to some nozzles not ejecting droplets coaxially with the nozzle axis, or due to nozzles that are non-active due to image information.
Taken alone or in combination, the different sources of eddies or vortices introduce flow components in the gap G that cross the media transport direction x and are antiparallel to the droplet ejection direction, and it is these components that cause the perceived “woodgrain” pattern shown in
Considering first a conventional nozzle row 13 according to
The dark areas in
The inventors propose that by providing nozzle clusters 24, the vortex 60 caused by the forced air flow, instead of uncontrollably breaking through the droplet curtain of a conventional nozzle row 13 of
Illustrating this proposal,
To assess different cluster designs, simulations were performed for droplet landing positions using an adapted MPPICFoam solver (OpenFOAM software). The simulations were performed on a rectangular box with the following dimensions: 7.5 cm in the print direction (x-direction), 9 cm in the width direction (y-direction) and the height of the domain was constrained by the gap distance G. The top wall of the domain was constrained as a fixed wall with zero-velocity condition. The bottom wall simulated the moving deposition media for which adequate velocity conditions were imposed. The nozzles were located 3 cm downstream (in direction of media transport) from the inlet into the gap G. The total length of the row of nozzles 20 was equal to 3 cm, so that with respect to the 9 cm domain width the flow was allowed to flow around the ends of the droplet curtain. A velocity profile for the couette flow was imposed at the inlet and a zero pressure boundary at the outlet. All the simulations were timed to create 12 cm long images in the print direction (along the x-direction).
In the simulations, three types of nozzle clusters 24 were assessed: 4, 6 and 8 nozzles per nozzle cluster. The nozzles 12 were staggered by a stagger distance sd=84.67 μm and spaced at a nozzle spacing ns/2=84.67 μm according to the same spacing definitions as shown in
Each cluster type was tested at four different subrow spacings b which were multiples of the nozzle distance ns: 2, 4, 6, 8 times, i.e. 169.33 μm, 338.67 μm, 508.00 μm and 677.34 μm.
The tables include an image quality indicator DE for the visual perception of the dynamic element (DE) of the woodgrain effect. The analysis is with respect to the same gap, cluster arrangement and frequency, essentially comparing the visual quality of the smallest subrow spacing to the next largest subrow spacing, and so on, up to the largest subrow spacing. ‘DE Removed’ means that for visual absence of the dynamic element of the woodgrain effect, ‘Yes’ is entered in the column. Increasing appearance of the dynamic element DE is indicated by ‘almost’, ‘significantly reduced’ and ‘No’, where ‘No’ indicates a strong presence of the DE.
For a selection of the simulated images indicated by (*) in Tables 1A, 1B and 2A, 2B (6×6 and 8×8 having the largest subrow spacing),
For the 3 mm gap tests and a subrow spacing b=677.34 μm,
Comparing
At 60 kHz, the 6×6 clusters (
For the 4 mm gap,
At 20 kHz, both the 6×6 and 8×8 clusters show a typical undulating woodgrain effect (DE not removed). While it is not entirely removed for any of the subrow spacings b tested, the DE of the woodgrain effect is less visible for the 8×8 cluster with a subrow spacing b of 677.34 μm than for the 6×6 cluster at the same subrow spacing b. However, it should be noted that, while the DE is more visible for the 6×6 arrangement than for the 8×8 arrangement, for the 6×6 arrangement the largest subrow spacing of b=677 μm still has a significantly reduced DE compared to the smallest subrow spacing (b=169 μm) for that arrangement, which is shown in
At 60 kHz droplet frequency and a gap of 4 mm, as listed in Table 2B, the DE of the woodgrain effect appears less dominant compared to 20 kHz droplet frequency. Tables 2A and 2B suggest that the smallest, 4×4 type, cluster, while providing a reduction in DE, is less beneficial than the 6×6 and 8×8 clusters, and the 6×6 and 8×8 clusters may provide a suitable degree of reduction of the DE at any subrow spacing b higher than b=169 μm. At higher droplet frequencies therefore the cluster length c and/or the cluster spacing a may have a more significant effect on reducing the DE of the woodgrain effect than the subrow spacing b.
The reduction of the dynamic element DE of the woodgrain effect with increasing subrow spacing b may be clearly seen in
The simulations shown in
To illustrate the visual impact the provision of a flow path through the clusters might have if suitable cluster dimension and spacings (cluster and subrow) are chosen, further simulation results for the dynamic development of droplet placement for low frequency/small gap (20 kHz, 3 mm) are shown in
Similarly,
The simulation results described above were tested by experiments using a nozzle plate arrangement similar to, but having a subrow spacing intermediate to, the 6×6 nozzle arrangements of Test Nos 23 and 24: For a nozzle spacing ns/2=84.67 μm, the 6×6 experimental nozzle cluster arrangement had a cluster length c=423.3 μm, a cluster spacing a=592.7 μm and a subrow spacing b=592.7 μm, so that in this case a=b. These nozzle plates were built into a droplet ejection head and compared to a conventional droplet ejection head of same ns/2 but without nozzle clusters (i.e. using the arrangement of
The experimental tests therefore show how 6×6 clusters arranged in two subrows spaced apart by a subrow spacing b may be used to achieve a reduction in the dynamic element DE of the visible woodgrain effect, leaving a static effect of ‘banding’ only, and which may be mitigated further by adjusting the droplet volume (trimming) to remove the banding effect also. This will be described further below.
Returning to the example embodiment of
Optionally, the first subrow spacing b between a first subrow and a second subrow may be equal to the cluster spacing a between nozzle clusters of the first subrow. Additionally, or instead, the subrow spacing b may be substantially equal to the cluster length c; for example the first subrow spacing b between a first subrow and a second subrow may be equal to the cluster length c of the first subrow.
Additionally, or instead, the cluster spacing a may be substantially equal to the cluster length c within the same subrow and/or to the cluster length c of a different subrow.
Alternatively,
For example, the nozzle clusters 24 nearer the sides of the droplet ejection head 2 may be arranged to provide a wider flow path for the forced air to pass through the droplet curtain.
Turning now to
The second and third nozzle clusters 24_1b, 24_1c of the first subrow 22_1 and the first and second nozzle clusters 24_2a and 24_2b of the second subrow 22_2 are an example of a “6×6” cluster, each nozzle cluster having 6 nozzles. In this implementation, c12=c12=b12, i.e. the cluster spacing a12 between the second and third nozzle 24_1b and 24_1c clusters of the first subrow 22_1 is defined by the cluster length of the first cluster 24_2a of the second subrow 22_2, which is the same as the cluster length c12 of the second nozzle cluster 24_1b of the first subrow 22_1.
In addition, when viewed along the transverse projection direction of the set of subrows onto the row direction 26, the spacing between nozzles 12 located at adjacent ends of nozzle clusters, e.g. between nozzle clusters 24_1b and 24_2a, is the same as the nozzle spacing ns within the same nozzle cluster 24. This means that, when viewed along the projection direction of the set of subrows onto the row direction, the nozzles 12 of the nozzle clusters of the first subrow, the second subrow and the third subrow form a continuous row of nozzles 12 of projected constant nozzle spacing.
With the arrangement of
In an alternative implementation, more than one pair of nozzle clusters may have longer lengths and subrow spacings near the end of the row. The nozzle clusters near the end of the row may have a gradually widening path for forced air flow to pass through, by nozzle clusters that are gradually longer and comprise more nozzles 12 nearer to the end of the row than they do near the centre of the row.
Alternatively to the implementation of the
To address the demands of many applications in the field of printing, the resolution of a droplet ejection head may need to be higher than can be provided with one row as shown in the above embodiment and its various implementations. This may be achieved by providing further row(s) of nozzles 12, with the nozzles 12 of the further row(s) spaced at intermediate positions with respect to the nozzles 12 of the first row, when viewed along the projection direction of the set of subrows onto the row direction. An example of a nozzle configuration for two rows of nozzles 12 to double the resolution of one row is shown in
In the implementation of
Further, the nozzle clusters of row 20A each extend for a cluster length cA and are spaced apart from an adjacent nozzle cluster of the same subrow 22A_1, 22A_2 by a cluster spacing aA. Similarly, the nozzle clusters of row 20B each extend for a cluster length cB and are spaced apart from an adjacent nozzle cluster of the same subrow 22B_1, 22B_2 by a cluster spacing aB. While in the implementation of
Therefore the nozzle plate 10 may comprise a second row of nozzles 12 comprising a second set of two or more subrows extending alongside one another in the respective subrow directions. At least two subrows (i.e. first and second subrows) of the second set of subrows are spaced apart by a third subrow spacing in a transverse direction, perpendicular to the row direction. Each subrow 22 of the second set of subrows is comprised of one or more nozzle clusters 24 each comprising a plurality of nozzles 12. Furthermore, each nozzle cluster 24 extends along the respective subrow direction for a cluster length c, and is spaced apart from a neighbouring cluster 24 by a cluster spacing a. Preferably the third subrow spacing is greater than 300 um.
For some applications, the subrow spacing between a first and second subrow of a set of subrows may be greater than 400 um, or greater than 500 um. In some implementations, the subrow spacing may be smaller than 900 um.
The second set of subrows may comprise more than two subrows. For example, one or more nozzle clusters of each of a first, second and third subrow of the second set of subrows may define the third subrow spacing b3 between the first and second subrow of the second set of subrows and a fourth subrow spacing b4 between the first and third subrow of the second set of subrows, wherein the third subrow spacing is different to the fourth subrow spacing.
An implementation for which a row 20A has a different arrangement of nozzle clusters 24A to a second row 20B having nozzle clusters 24B is shown in
The specific arrangement of nozzle clusters may vary depending on the requirement of the application, such as the gap G, the print frequency, and/or the droplet velocity and mass. For example, it is believed that the first subrow or first row of nozzles 12 to experience the forced air flow may require an arrangement allowing more frequent or specifically tailored air escape routes than the second row of nozzles 12.
Within a row, this may be achieved by spacing nozzle clusters 24 of short length c1 and at short cluster spacings a1 to an adjacent nozzle cluster in the first subrow of the row of nozzles, and a similar arrangement of nozzle clusters of short length c2 spaced apart by a cluster spacings a2 to an adjacent nozzle cluster in a second subrow of the row of nozzles, so that c1=a2 and a1=c2. For example, the nozzle clusters may each comprise only 4, 6 or 8 nozzles. In addition, a third subrow comprising some of the nozzle clusters may provide a second subrow spacing b2 to the first subrow, for example near the ends of the row, to reduce any side flow effects due to forced air flow passing the sides of the printhead. In this case, the first and second subrows comprise nozzle clusters near the centre of the row, and the first and third subrow comprise nozzle clusters near the ends of the row.
An implementation of such an arrangement is schematically shown in
The aim of the implementation of
As an alternative to the implementation of
As may be seen from
Due to the nozzle cluster arrangement of the implementation of
In some nozzle plates 10, arrangements according to implementations of
The nozzle clusters of the nozzle plates according to the above embodiment and its various implementations may further be arranged as follows.
Additionally, or instead, the first subrow spacing b1 may be substantially equal to the cluster spacing a. Additionally, or instead, the first subrow spacing b1 may be substantially equal to the cluster length c.
Furthermore, a first group comprising one or more nozzle clusters of a first of the subrows of the row of nozzles may have a cluster length c11 that is different to a cluster length c12 of a second group of one or more nozzle clusters of the first subrow.
Furthermore, or instead, the first group comprising one or more nozzle clusters of a first of the subrows of the row of nozzles may have a cluster length c11 different to a cluster length c21 of a first group of one or more nozzle clusters of a second subrow.
Additionally, or instead, the nozzle cluster length c of one or more clusters of the one or more subrows may be defined by comprising four or more nozzles 12.
Additionally, or instead, the nozzle cluster length c of one or more clusters of the one or more subrows may be defined by comprising six nozzles 12.
For nozzle plates 10 having more than one row, and where a second row comprises a second set of subrows, the cluster length of the nozzle clusters of the first set of subrows may be the same as the cluster length of the nozzle clusters of the second set of subrows, and wherein the cluster spacing for the nozzle clusters of the first set of subrows is the same as the cluster spacing for the nozzle clusters of the second set of subrows. In alternative implementations meanwhile, the cluster spacing between the nozzle clusters of the first set of subrows is different to the cluster spacing between the nozzle clusters of the second set of subrows.
In addition, each nozzle 12 of each of the rows, when projected onto the row direction, may be directly adjacent another nozzle 12 of another row. In other words, all nozzles 12 of all rows contribute to the resolution of the droplet ejection head 2 and may be used to print into the same pixel line. Furthermore, more than 50% (i.e. a majority), or at least 75%, of the projected nozzles are equidistant from the adjacent projected nozzles so as to allow for different distances between nozzles near each end of the row, in order to allow alignment between multiple nozzle plates 10, for example. When viewed along the projection direction of the first and second sets of subrows onto the row direction, the nozzles 12 of all nozzle clusters 24 of the first set and the second set of subrows form a continuous row of nozzles 12 of modified projected constant nozzle spacing. For example, the projected nozzle spacing may be half that of the projected nozzle spacing between adjacent projected nozzles of the first set of subrows. The two sets of subrows may thus be used to double the resolution of the nozzle plate. The ends of the first and second sets of subrows may in some cases have a different projected nozzle spacing, for example so as to enable accurate alignment between rows of nozzles of two partially overlapping nozzle plates. The number of nozzles of each row that have a different projected nozzle spacing may be 25% or even approaching 50% of the total number of nozzles of the row, for example.
In any of the above implementations, the nozzles of each nozzle cluster may be arranged in parallel subclusters that extend along the row direction, wherein the subclusters are spaced apart from one another in a direction perpendicular to the row direction by a subcluster spacing sd. In
Nozzle Shift Considerations
Returning to
Therefore, in the above embodiment and its various implementations, the subrow spacing b of each of the subrows may be larger than 300 μm and less than 900 μm. In some implementations, the subrow spacing b of each of the subrows may be more than 500 μm, or more than 600 μm. In some instances, the subrow spacing may be up to 75% of the total pressure chamber length.
While the total range over which subrow spacings may be created is limited by the length of the pressure chamber 14, where the pressure chamber 14 is elongate and extends along the plane of the nozzle plate 10 (i.e. in the x-direction), staggering the nozzles with respect to the centre-line CL to create nozzle clusters 24, but not staggering the pressure chambers 14, allows for simpler fluid supply paths compared to those required for a design comprising clusters of staggered pressure chambers 14 where the nozzles 12 remain in a central or near central position with respect to the elongate side of the pressure chamber 14.
The nozzle clusters of the implementations shown in
Second Embodiment of the Nozzle Plate
Creating controlled paths through the droplet curtain is not limited to nozzle plates having nozzle arrangements as described above. In some nozzle plates, according to a second embodiment, the nozzle clusters may comprise a plurality of nozzles arranged in an array that extends along the row direction and over several nozzles along a cluster depth direction, where the cluster depth direction is perpendicular to the row direction. Each nozzle cluster is arranged at a cluster spacing from its nearest neighbour along the row direction. The nozzle plate may comprise one or more rows of such nozzle clusters, and the nozzle clusters in each row may be further offset from one another in a direction perpendicular to the row direction. The arrangement of nozzle clusters of embodiments of this type, as for the previous embodiment and its various implementations, also define a path between nozzle clusters through which forced air may pass in a controller manner. Nozzle clusters of the second embodiment may for example have shapes with sides that extend along an angle with respect to the cluster depth direction. For example, the nozzle clusters may be trapezoidal, triangular or parallelogram shaped. Each nozzle cluster may be defined by a plurality of subrows each having one or more nozzles 12. When viewed along the projection direction, which in this case is the cluster depth direction, of the subrows onto the row direction, the pluralities of nozzles of all nozzle clusters form a continuous row of nozzles such that each projected nozzles is equidistantly spaced apart from its nearest projected neighbour by a projected nozzle spacing. In other words, the projected nozzles do not overlap so that in use, each nozzle of the row of nozzle clusters deposits one or more droplets into a corresponding pixel in the same pixel line.
Implementations according to an embodiment of a nozzle arrangement suitable for mitigating or preventing woodgrain effects are shown in
It is however not essential that the nozzles within each nozzle cluster are spaced apart by a constant spacing sd; instead, sd may vary between successive nozzles. This would create a non-linear path for the air to pass between the nozzle clusters.
In both
The nozzle arrangements shown in
The nozzle arrangement according to
The nozzle arrangement according to
It can be seen that for either implementation, a significant reduction in the woodgrain effect can be achieved, that for some applications be provide an acceptable image quality, or an image quality that may further be improved by other measures in combination with the present implementations.
It is therefore apparent that the provision of flow paths through a row of nozzles according to implementations of the present embodiment may reduce or prevent the visible occurrence of woodgrain patterns by controlling the passage of air through the row of nozzles, and thereby reducing or preventing at least the dynamic element of the woodgrain effect.
In the variants shown in
Next, an alternative implementation comprising more than one nozzle per nozzle cluster along the cluster length c will be described with reference to
Each nozzle cluster 24 takes the shape of a parallelogram, for which both the short and long edges form an acute angle towards the row direction 26. In some implementations of this nozzle arrangement, the nozzle plate 10 itself may be parallelogram shaped to follow the long edges of the nozzle clusters, for example to aid abutting of nozzle plates side by side; however the nozzle plate may take different shapes.
The row 20 is indicated to follow the general direction of the row of nozzle clusters, along the y-direction. The nozzle clusters are spaced apart by a cluster spacing a as measured along the row direction so as to define parallel flow paths of width w for air to pass between the nozzle clusters. As in
Each nozzle cluster 24 may be defined as comprising subclusters of nozzles arranged along the cluster depth direction and defining a cluster depth d, whereby each subcluster is spaced from a subsequent subrow by a sub cluster spacing sd. The nozzles within each sub cluster are spaced from is nearest neighbour along the row direction by a nozzle spacing ns. Each subcluster extends at an acute angle to the row direction 26. The cluster depth direction, as before, extends in a direction perpendicular to the row direction 26.
The nozzles 12 within the nozzle clusters 24 of the row 20 are arranged such that, when all nozzles of all nozzle clusters are projected onto the row direction 26, the nozzles of the row 20 form a continuous row of equidistant nozzles 12 spaced apart by a constant spacing smaller than ns. This is indicated by the pixel line 8, in which each pixel correspondents to one nozzle of the row, so that the nozzles 12 of row 20 are in a 1:1 correspondence to the pixels in the pixel line 8.
In this way, nozzles arranged in an n×m matrix within each nozzle cluster of a row 20 can be used to deposit one or more droplets each into the same pixel line on the deposition media, such that each nozzle deposits one or more droplets into one pixel each. The nozzle cluster arrangement of Figure may be used to create parallel flow paths through nozzles arranged in an n×m matrix within each nozzle cluster of a row 20 for forced air to pass so that the woodgrain effect can be reduced to a non-dynamic element that can be further reduced by trimming droplet volumes.
In some implementations, the short edge of the nozzle clusters may not form an acute angle with the row direction; for example the subrows of three nozzle each may be aligned in parallel to the row direction. The specific location of the nozzle along the nozzle cluster depth direction determines the timing at which each nozzle needs to eject a droplet so that all droplets land in the pixel line 8 on the deposition media. Furthermore, each nozzle cluster is not limited to having nine nozzles each; nozzle clusters of different nozzle numbers arranged in n×m matrices may be envisaged that fulfil the same purpose of creating flow paths for forced air to pass through the row of nozzles.
The flow paths of any of the implementations of
Next, variants will be described that share the concepts of the first and second embodiment and may be thought of as hybrids having the same aim of creating flow paths for forced air to pass through the row of nozzles so as to prevent or reduce the dynamic element of the woodgrain effect.
To achieve the arrangement of nozzles of row 20, the row 13 is divided into equal submatrices having a 5×3 nozzle array each, and alternate 5×3 matrices are translated along a direction perpendicular to the row direction to form nozzle clusters 24 that create a flow path through the row 20 that allows forced air to pass. In this implementation, each nozzle cluster 24 takes the shape of a parallelogram, and has a length c as defined by five nozzles spaced apart by a nozzle spacing ns along the row direction 26, and by three nozzles along the cluster depth direction spaced apart by an offset spacing sd. In addition to the linear paths between nozzle clusters of the same subrow, the subrow spacing b between the subrows defines a flow path for air to pass around the nozzle clusters 24_2 of the second subrow 22_2. This nozzle arrangement may be comprised in nozzle plates that are parallelogram shaped, although the shape of the nozzle plate is not essential to generating the nozzle arrangement of row 20.
Using a similar approach as the one in
In a further implementation shown in
Each nozzle cluster comprises subclusters of nozzles arranged along a cluster depth direction, whereby each subcluster is spaced from a subsequent subcluster by a subcluster spacing sd. Each nozzle within each subcluster is spaced from its nearest neighbour along the row direction 26 by a nozzle spacing ns. The nozzles of each subcluster are offset with respect to their neighbours in an adjacent, parallel subcluster, such that, when all nozzles of all nozzle clusters are projected onto the row direction 26, the nozzles of the entire row 20 form a continuous row of equidistant nozzles 12.
In this way, all nozzles of the row 20 can be used to deposit one or more droplets each into the same pixel line on the deposition media. When viewed along the direction of printing (along the x-direction), which is the same direction over which the cluster depth extends, the first subcluster of nozzles for nozzle clusters 24_1a,b has a cluster length of c1, while the first subclusters of nozzle cluster 24_2a,b have a cluster length of c2. For nozzle clusters 24_1a,b the cluster length gradually increases along the cluster depth direction up to a cluster length c2, and for nozzle clusters 24_2a,b the cluster length gradually decreases along the cluster depth direction down to a cluster length c1.
Nozzle cluster arrangements of a trapezoidal shape may be used in nozzle plates of parallelogram shape, or in trapezoidally shaped nozzle plates such as shown in
The narrow flow path regions NR between the nozzle clusters may be reduced or prevented by increasing the subrow spacing b, and/or by inverting the nozzle clusters of one of the subrows, such that the trapezoidal shapes face each other with the short length from one subrow and the long length from the other subrow. An inversion of nozzle clusters is shown in
In all implementations of
Optionally, the number of subrows is not limited to two subrows. Instead, the nozzle clusters may be arranged in more than two subrows, for example in three or four subrows, to further increase the width of, and/or reduce the length of narrow flow passages so as to reduce the flow resistance of the flow path through the nozzle clusters.
According to the second embodiment and its implementations, therefore, a nozzle plate 10 for a droplet ejection head is provided, comprising at least a first row 20 of nozzles 12 arranged to deposit droplets onto a deposition media, the first row 20 of nozzles extending in a row direction 26, and comprising one or more nozzle clusters 24. Each nozzle cluster 24 is arranged along the row direction 26 for a cluster length c and extends along a cluster depth direction perpendicular to the row direction by a cluster depth d. Each nozzle cluster 24 comprises a plurality of nozzles 12 of which one or more nozzles within each nozzle cluster define the cluster length c and two or more nozzles within each nozzle cluster define the cluster depth d, and each nozzle cluster 24 is spaced apart from an adjacent nozzle cluster along the row direction 26 by a cluster spacing a greater than a nozzle spacing ns between adjacent nozzles of the same nozzle cluster. Furthermore, the nozzles of the first row, when projected onto the row direction 26, are equidistantly spaced apart from adjacent projected nozzles by a projected nozzle spacing.
Optionally, each projected nozzle cluster of the first row may be spaced apart from an adjacent projected nozzle cluster by the projected nozzle spacing. For example, this is the case for the nozzle clusters 24 of
In some implementations, the cluster spacing a may be greater than the spacing between four adjacent nozzles.
Additionally, or instead, the plurality of nozzle clusters of the row 20 may comprise two or more subclusters of nozzles. The subclusters extend substantially along the row direction, and are arranged parallel to one another so as to form a matrix of nozzles. An example of such subclusters is shown in
In some implementations, the nozzle clusters may be arranged in one or more of a parallelogram, trapezoidal or triangular shape. Parallelogram or trapezoidal cluster shapes are illustrated in
Additionally, the nozzle clusters adjacent one another along the row direction may be offset from one another along the cluster depth direction, such as shown in
In the clusters shown in
In all of the above embodiments and their various implementations, an air flow path is created by the cluster spacing a so as to create a flow path for forced air to pass through the row of nozzles in a controlled manner. ‘In a controlled manner’ may be understood to mean a reduction or prevention of the dynamic element of the woodgrain effect, reducing the effect to banding only, for example, which is not a dynamic effect.
Generally therefore, a nozzle plate 10 is provided for a droplet ejection head 2 comprising at least a first row 20 of nozzles 12 arranged to deposit droplets onto a deposition media, wherein the first row of nozzles extends in a row direction 26, and comprises one or more nozzle clusters 24. Each nozzle cluster 24 is arranged along the row direction 26 for a cluster length c, and each nozzle cluster is spaced apart from an adjacent nozzle cluster along the row direction 26 by a cluster spacing a so as to create a flow path for forced air to pass through the row of nozzles in a controlled manner. When viewed along a projection direction of the nozzle clusters 24 onto the row direction 26, the plurality of nozzles 12 of row 20 forms a continuous row of nozzles in which the projected nozzles are equidistantly spaced apart from one another by a projected nozzle spacing. In other words, none of the projected nozzles overlap fully with any other nozzles of the same row, so that in use, each nozzle of the row of nozzle clusters may be used to deposit one or more droplets into a corresponding pixel in the same pixel line on the deposition media.
In some implementations, the cluster spacing may vary along the row direction. For example, the nozzle cluster spacing between a first pair of adjacent nozzle clusters may be different to the cluster spacing between a second pair of adjacent nozzle clusters of the row.
Additionally, or instead, the nozzle cluster spacing may vary along a cluster depth direction, where the cluster depth direction is perpendicular to the nozzle row direction.
The nozzle clusters may be arranged in two or more subrows, where the subrows extend along the row direction and are parallel to one another, so as to create flow paths of a width according to a subrow spacing b between adjacent subrows for forced air to pass from one subrow to the next. The subrow spacing between a first and second subrow may be the same or may be different to the subrow spacing between a second and third subrow.
The nozzle clusters may additionally, or instead of being arranged in subrows, comprise two or more subclusters, where each subcluster within a nozzle cluster substantially extends along the row direction, and the subclusters within each nozzle cluster are arranged in parallel to one another and spaced apart by a subcluster spacing sd.
The subclusters may be arranged to extend at an acute angle to the row direction, such that ‘substantially extends along the row direction’ may mean at an acute angle of up to 45° to the row direction.
The clusters of the second embodiment are shown to comprise a matrix of up to 15 nozzles each. The modelled results of variants of the first embodiment suggest that it is the combination of the cluster length c and the air gap formed by the cluster spacing a/subrow spacing b for forced air to pass through the row of nozzles in a controlled manner, that determines the reduction in the woodgrain effect. Similar results may be expected for the second embodiment with respect to the first subrow of nozzles met by the forced air, or by the first sub cluster of the first subrow, for example for a cluster length of up to 10 nozzles wide and a cluster length c less than or equal to 800 μm.
Method
Alongside the nozzle clusters 24 and the drive pulses 32, the effect on the pixel line 8 on the deposition media is illustrated at the different timings t for the drive pulse 32.
A method for controlling actuators corresponding to the nozzles 12 to cause each nozzle 12 to eject one or more droplets per line pixel is based on stagger groups 28 of nozzles 12 within the same subrow arranged at the same stagger offset distance in a direction orthogonal to the row direction (along the y-direction). The stagger groups 28_1(i) and 28_1(ii) are comprised within the nozzle clusters 24_1 of the first subrow, and stagger groups 28_2(i) and 28_2(ii) are comprised within the nozzle clusters 24_2 of the second subrow. Cluster group 28_1(i) of nozzle clusters 24_1 are the first to have to eject droplets as the deposition media passes underneath in the printing direction (along the x-direction), followed by cluster group 28_1(ii), cluster group 28_2(i), and finally cluster group 28_2(ii).
The actuator signals 30 applied to the actuators of the corresponding nozzles 12 comprise drive pulses 32 and are offset along the amplitude (V) axis for visual simplicity. Each stagger group 28 is arranged to eject a droplet in response to the application of a corresponding drive pulse 32 within an actuating signal 30 The respective drive pulses are linked to each stagger group by a dotted line.
For simplicity, only one drive pulse for ejecting one droplet is shown; in practice, several droplets may be ejected from the same nozzle to be deposited into the same pixel.
For visual simplicity,
As the position of the pixel line 8 to be printed passes underneath the droplet ejection head 2, the actuation of droplets from the four stagger groups 28 is timed such that as the pixel line 8 passes underneath the first stagger offset group (subcluster group) 28_1(i) of row 20, the first stagger offset group 28_1(i) receives a drive pulse 32_1(i) first, at time to, to eject a droplet from each of the nozzles 12 of stagger offset group 28_1(i) into corresponding pixels on the pixel line 8.
As the pixel line 8 moves further to pass underneath the second stagger group 28_1(ii), stagger group 28_1(ii) receives its drive pulse 32_1(ii) at a time t1 to eject a droplet from each of the nozzles 12 of the stagger offset group 28_1(ii) into corresponding pixels on the pixel line 8.
Next, as the position of the pixel line on the deposition media moves underneath the third stagger group 28_2(i) of the row 20, which is the first stagger offset group of the second subrow, a drive pulse 32_2(i) is applied at time t2 to eject a droplet from each of the nozzles 12 of stagger offset group 28_2(i) into corresponding pixels on the pixel line, and finally as the pixel line passes underneath the fourth stagger offset group 28_2(ii) of the row 20, which is the second stagger offset group of the second subrow, a drive pulse 32_2(ii) is applied at a time t3 to eject a droplet from each of the nozzles 12 of stagger offset group 28_2(ii) into corresponding pixels on the pixel line. The pixel line 8 is now complete.
A similar principle applies for printing into the same pixel line from more than two subrows of a row 20, or from more than one row 20 having one or more subrows each.
While
The hybrid arrangements of
A method of using the nozzle plates 10 according to the above embodiments and their implementations is provided, comprising the step of: depositing one or more droplets from one or more nozzles of the nozzle clusters of the row into a pixel line, wherein each nozzle of the row corresponds to one pixel of the pixel line.
In some implementations in which the row 20 comprises a first subrow and a second subrow, each subrow extending in the row direction and parallel to one another, the first subrow comprises a first group of nozzle clusters and the second subrow comprises a second group of nozzle clusters, the method may comprise the further step of: depositing droplets from the nozzles of the first group of nozzle clusters into the pixel line at a time t1, and depositing droplets from the nozzles of the second group of nozzle clusters into the pixel line at a time t2.
In nozzle plates with two rows, the method may further comprise the steps of: depositing droplets from the nozzles of the nozzle clusters of the first subrow of the second row into the pixel line at a time t3; and depositing droplets from the nozzles of the nozzle clusters of the second subrow of the second row into the pixel line at a time t4.
Alternatively, where one or more of the nozzle clusters comprise a plurality of subclusters, the subclusters generally extending along the row direction and parallel to one another, the method may instead comprise the further step of: depositing droplets from the nozzles of a first subcluster into the pixel line at a time t1, and depositing droplets from the nozzles of a second subcluster into the pixel line at a time t2.
The method as carried out for example by a control system may comprise the steps of receiving image data for the pixel line; receiving media encoder signals; and determining, based on the image data and the media encoder signals, drive data 33, wherein the drive data defines the timing t for actuating one or more nozzle within one or more of the nozzle clusters to deposit a droplet into a corresponding pixel in the pixel line.
Furthermore, the step of determining the drive data 33 further may comprise determining the drive data for a second set of subrows of a second row, wherein the drive data for second set of subrows defines the timing t for nozzles of each subrow of the second set of subrows for depositing droplets into the pixel line.
The method may further comprise the step of: generating actuating signals 30 based on the drive data 33 for causing one or more nozzles of one or more of the subrows to deposit a droplet into the pixel line, and providing the actuating signals 30 to actuators 11 corresponding to the nozzles, so as to cause the one or more nozzles to deposit a droplet into the pixel line. This step may in some implementations be carried out of a droplet ejection head 2 by a droplet ejection head controller provided on the droplet ejection head 2.
Optionally, the method may comprise the step of adjusting the droplet volume of each nozzle in response to printed image data so as to reduce or prevent banding due to forced air flows. This step may be used to mitigate the non-dynamic element of banding of the woodgrain effect. This is achieved by generating test print data for darker and lighter bands and adjusting the droplet volume deposited into the bands so as to reduce or prevent the visual variations in pigment density along the pixel line. For example, test print data 40 may be generated from test prints by measuring the pixel densities across a pixel line achieved with specific process settings (e.g. gap distance, pixel frequency, media speed), for a range of measured print pixel densities, and by determining adjustment values 42 to achieve target densities required to prevent banding. This may for example be done by using a look-up table that converts perceived pigment densities into target pigment densities per pixel and per nozzle by applying an adjustment value to each nozzle. This adjustment value may for example be an adjustment value for the nominal drive voltage of the actuation pulse that causes the ejection of a droplet from a nozzle. The peak to peak actuation pulse voltage may for example be reduced to reduce the droplet volume for nozzles contributing to the darker bands of the printed image. Additionally, or instead, it may be increased to increase the droplet volume for nozzles contributing to the lighter bands of the printed image. The adjustment values 42 may be identified empirically, by a series of experimental print tests, for modified droplet volumes per nozzle across the row 20 and stored in a look-up table and used during printing to increase or decrease droplet volumes per nozzle so as to reduce or prevent visual banding effects. For example, nozzles contributing to dark bands may be caused to eject smaller droplet volumes leading to a lower pixel density, while nozzles contributing to lighter bands may be caused to eject larger droplet volumes leading to higher pixel densities, as a result of the adjustment values 42 identified and used to modify the drive pulses 32. The adjustment values may be provided as adjustment signals to the droplet ejection head controller as part of the drive data 33.
Therefore, where the drive data 33 is further determined based on adjustment values and comprises adjustment signals based on adjustment values, the adjustment signals may cause the droplet volumes of one or more nozzles of the row to be modified to reduce the effect of banding.
Controller
The timing of actuating the actuators of the stagger offset groups 24 may be controlled by a drive signal controller 4 as shown as part of the droplet ejection apparatus 1 of
The control system 50 of
The drive signal controller 4 is configured to receive the media encoder signals 34 and is further configured to receive image data 36, for example from a PC comprised within or associated with the droplet ejection apparatus 1. The drive signal controller 4 is configured to determine drive signals from the media encoder signals 34 and the image data 36 and to provide the drive signals to the droplet ejection head controller 9 of the droplet ejection head 2.
The droplet ejection head 2 comprises actuators 11, and each actuator 11 is configured to cause at least one nozzle 12 each to eject a droplet based on an actuation signal 30. The actuation signals 30 are provided by the droplet ejection head controller 9 to the actuators 11 based on the drive data 33 received from the controller 4, such that droplets for each stagger group are deposited into the pixel line at correct timings t. Therefore the timings of t0 to t3 of
A drive signal controller 4 is therefore provided to carry out the methods described using the nozzle arrangements of the above embodiments and their various implementations. The drive signal controller is configured to receive image data and media encoder signals, and to determine drive data 33 based on the image data and based on the media encoder signals. The drive signal controller is further configured to provide the drive data 33 to a droplet ejection head controller for causing one or more of the nozzles 12 of the one or more nozzle clusters 24 comprised within a nozzle row 20 to eject one or more droplets each into a pixel of a pixel line 8, each pixel of the pixel line corresponding to a different nozzle of the row 20.
In some implementations, the drive signal controller is further configured to provide timing signals as part of the drive data 33 to the droplet ejection head controller for causing the nozzles 12 of a first group of nozzle clusters 24_1 of the nozzle clusters 24 to eject droplets into the pixel line at a time t1, and for causing the nozzles 12 of a second group of nozzle clusters 24_2 of the nozzle clusters 24 to eject droplets into the pixel line at a time t2. The first group of nozzle clusters may be comprised within a first subrow 22_1 and the second group of nozzle clusters may be comprised within a second subrow 22_2 of the row 20.
Additionally, or instead, the drive signal controller may be further configured to provide the drive data 33 to the droplet ejection head controller for causing the nozzles 12 of one or more subclusters comprised within at least one of the nozzle clusters 24 to eject droplets into the pixel line at a time t1, and for causing the nozzles 12 of one or more nozzle clusters 24_2 of the second subrow 22_2 to eject droplets into the pixel line at a time t2.
Optionally, the drive signal controller may be configured to receive data based on printed test images.
This data may comprise adjustment values 42 to mitigate the effect of banding due to the non-dynamic element of the woodgrain effect as caused by forced air passing around the nozzle clusters 24. Alternatively, the data may be in the form of test print pixel densities achieved with the process settings (e.g. gap distance, pixel frequency, media speed) for a particular application, and the test print pixel densities may be used by the drive signal controller to determine adjustment values 42 for each nozzle from a look-up table accessible by the drive signal controller. The look-up table may for example comprise pixel density data for a range of measured print pixel densities, as determined prior to printing, and adjustment values to achieve the required target densities.
Optionally therefore, the drive signal controller circuitry may be further configured to: receive printed image data, and determine, based on the printed image data, adjustment values for droplet volumes to reduce or prevent banding due to forced air flows, and to provide adjustment signals based on the adjustment values to the printhead controller so as to adjust the droplet volume ejected from the nozzles.
The drive signal controller 4 in both cases may be configured to provide adjustment signals 44 based on the adjustment values 42 and provide the adjustment signals 44 as part of the drive data 33, wherein the adjustment signals 44 cause the actuation signals 30 to eject droplets of increased or decreased the droplet volume so as to achieve an adjusted density across the pixel line that mitigates the banding effect due to the non-dynamic element of the woodgrain effect. For example, nozzles contributing to dark bands may be caused to eject smaller droplet volumes, while nozzles contributing to lighter bands may be caused to eject larger droplet volumes as a result of the adjustment signals 44 provided by the drive signal controller 4.
In some implementations, the drive signal controller 4 may be located externally to the droplet ejection head as indicated in
In other implementations, the drive signal controller 4 may be located within the droplet ejection head 2, and may comprise the droplet ejection head controller 9.
Additionally to any of the implementations above, the drive signal controller 4 may be configured to generate drive data 33 that comprises image signals based on image data 36 and common to more than one of the actuators 11, and timing signals based on media encoder signals 34 individual to each actuator, and provide the drive data 33 in the form of a synchronised stream of common image signals and individual timing signals to the droplet ejection head controller.
The individual timing signals may additionally comprise adjustment signals 44 for each actuator so as to adjust (trim) the droplet volume ejected from the corresponding nozzle so as to mitigate the effect of banding.
In implementations where the drive controller is located onboard the droplet ejection head 2, the drive signal controller and the droplet ejection head controller may be comprised within a control system.
The droplet ejection head controller may be configured to: generate the actuating signals 30 based on the timing signals and image data, and provide the actuating signals 30 to actuators 11 corresponding to the nozzles, so as to cause one or more nozzles of at least one of the nozzle clusters 24 to deposit one or more droplets into the pixel line 8.
In some control systems, the drive signal controller 4 may comprise the droplet ejection head controller 9, and be located onboard the droplet ejection head 2.
General Considerations
In some implementations, it may be beneficial to arrange the nozzle clusters 24 so as to create a balanced flow of forced air through the nozzle clusters. To achieve this, the nozzle clusters 24 may be of the same length and the same spacing, and further arranged between the subrows such that the length of clusters 24 of one subrow equals the cluster spacing of the other subrow. This means that the forced air flow meeting the first row of nozzles 12 is split in equal and evenly spaced parts and recombines in equal and evenly spaced parts. This is thought to avoid or reduce significant differences in pressure between different regions along the row length.
In the above implementations, the nozzles 12 within the nozzle clusters of each row may be arranged such that, when viewed along the projection direction of the row onto the row direction, the nozzles 12 of all nozzle clusters 24 of the row form a continuous row of equidistant nozzles 12 spaced apart from another by a projected constant nozzle spacing. In other words, all nozzles of row 20, when projected onto the row direction, form a continuous row of projected nozzles equidistantly spaced from one another by a projected nozzle spacing in which none of the nozzles overlap with any other nozzles of the same row, so that in use, each nozzle of the row of nozzle clusters deposits one or more droplets into a corresponding pixel in the same pixel line.
In addition, the spacing between nozzles 12 located at adjacent ends of nozzle clusters 24, when viewed along the projection direction of the row onto the row direction, may be the same as the projected nozzle spacing. On other implementations, when projected onto the row direction, some nozzles of adjacent nozzle clusters may mesh, such that more than one projected nozzle of one nozzle cluster is adjacent a projected nozzle of a neighbouring nozzle cluster.
In some implementations, the start and end of the row of nozzles 12 may have a different nozzle spacing compared to nozzle clusters nearer the centre of the row. For example, the nozzle spacing in one or more nozzle clusters near the ends of the row of nozzles may be larger compared to the nominal nozzle spacing ns at one end, and smaller compared to the nominal nozzle spacing ns at the opposite end of the row.
Alternatively, the nozzle spacing in one or more nozzle clusters near the ends of the row of nozzles 12 may vary gradually from the nominal nozzle spacing ns nearer the centre or the row to a smaller or larger nozzle spacing towards the ends of the row. This may provide for accurate alignment between rows of nozzles 12 of different nozzle plates 10 within the same printhead 2.
Therefore, some or all of the rows of nozzles 12 of the nozzle plates 10 described according to the various embodiments and implementations may be arranged so that each nozzle 12 of each of the subrows, when projected onto the row direction, is directly adjacent another nozzle 12, and more than 50% (i.e. a majority) or even 75% of the nozzles 12 are spaced apart from the adjacent nozzle 12 by a constant distance. Preferably none of the projected nozzles overlap fully, such that, in use, each printed pixel is addressed by a corresponding nozzle.
In other words, for at least two adjacent clusters, the nozzles 12 for each subrow are arranged such that, when the nozzles 12 are projected onto the row direction, at least in a transition region comprising a plurality of nozzles 12 from a first cluster to a plurality of nozzles 12 from an adjacent cluster, each nozzle 12 is directly adjacent another nozzle 12, and each nozzle 12 is spaced apart from an adjacent nozzle 12 by a constant distance. The transition region represents a region comprising nozzles from adjacent sub row ends (adjacent when projected onto the row direction).
The above embodiments and their various implementations provide nozzle clusters of nozzles that are arranged to provide flow paths for forced air to pass through the row of nozzles so as to provide a reduction or even prevention of at least the dynamic element of the woodgrain effect. The degree of reduction depends on the specific combination of media speed, droplet frequency, droplet volume (mass) and gap G of a specific application, and may be further reduced by varying the cluster length c and the cluster spacing a and, where applicable, the subrow spacing b. The non-dynamic element of the woodgrain effect, called banding, may be further mitigated by adjusting the droplet volume of the relevant nozzles.
The pressure chambers 14 that supply the nozzles 12 may be elongate along the cluster depth direction, along the x-direction, and extend parallel to one another, as shown in
The above examples of droplet ejection devices comprising nozzle clusters show a recirculation path behind the nozzle 12 in some of the implementations of the nozzle plate 10 within an inkjet droplet ejection head 2. The nozzle plate 10 may equally be utilised in a droplet ejection head not having recirculation or supply from both ends of the pressure chamber 14. In some droplet ejection heads, the pressure chamber 14 may be elongate in a direction other than perpendicular to the row direction or extending along the plane of the nozzle plate 10. In some droplet ejection heads, the pressure chamber 14 may extend in the direction orthogonal to the plane of the nozzle plate 10 according to the implementations described herein. In other droplet ejection heads, the pressure chambers extend along the plane of the nozzle plate 10 but not perpendicular to the row direction; for example they may be angled at less than 90° to the perpendicular to the row direction.
In other nozzle plates 10, a pixel line may be printed so that more than one nozzle 12 of the one or more rows of the nozzle plate 10 eject one or more droplets into the same pixel of the pixel line. In some droplet ejection heads the pressure chamber may be round or square with maximum dimensions less than a pixel width. Such droplet ejection heads may still employ the nozzle plates 10 or variants thereof described in the implementations herein, providing suitably sized clusters to mitigate the forced air effect.
In some variants, the nozzle clusters 24 of nozzles 12 defining the subrows may not be aligned along the row direction. Instead, they may be angled with respect to the row direction while being parallel to adjacent nozzle clusters 24 of the same subrow. In this case, the subrow direction is the average direction described by the subrow of nozzle clusters, and the row direction is the average direction of the subrow(s).
Finally, the nozzle plates 10 according to the above embodiments and their various implementations may be provided within a droplet ejection apparatus 1. The droplet ejection apparatus 1 may comprise a droplet ejection device such as a droplet ejection head 2.
The droplet ejection device may be configured such that the first row of nozzles 12 is arranged to be in fluidic communication with a corresponding first row of pressure chambers 14.
Furthermore, the pressure chambers 14 of the first row of pressure chambers 14 may be elongate in a direction non-parallel to the row direction, and may extend side by side; the nozzles 12 being arranged in an elongate side wall of respective pressure chambers 14, the side wall being formed by the nozzle plate, wherein at least a group of the nozzles 12 are arranged off-centre with respect to pressure chambers 14 in the direction of elongation such that the nozzle positions in the first row of pressure chambers 14 define nozzle clusters 24 and air flow paths for forced gas to pass through the first row of nozzles.
The nozzles in this case are offset from the centre of the pressure chamber such that the Helmholtz frequency of the chamber is substantially maintained at the same value for all chambers, and such that the drive voltage to achieve a target droplet velocity is substantially maintained at the same value for all nozzles.
The nozzles of one cluster of the first row may be arranged at a first distance from the centre of the pressure chambers in the direction of elongation, and the nozzles of the adjacent cluster along the row direction may be arranged at a second distance from the centre of the pressure chambers in the direction of elongation, so that the first cluster is spaced apart from the adjacent cluster along the row direction by the cluster spacing a to create the air flow path.
Furthermore, the first distance and the second distance may thus define the spacing of the first and second subrows, wherein the first row of nozzles may comprise the first set of subrows comprising first and second subrows that extend alongside one another in respective subrow directions, wherein the first and second subrows extend parallel to the row direction. The first and second subrows are thus spaced apart by the first subrow spacing b in the transverse direction, perpendicular to the row direction; and the first and second distance define the subrow spacing b.
Such an arrangement may be beneficial in droplet ejection heads that may not be easily manufactured in such a way that allows clustering of the pressure chambers themselves, so that the nozzles may be maintained at or close to the centre of the elongate pressure chamber. An example of such a droplet ejection head is a shared wall head, in which opposing walls are formed from a sheet of piezoelectric material into which parallel grooves have been sawn that form the pressure chambers. In such a device, the pressure chambers are arranged in parallel side by side, with a 100% overlap in the row direction, and clustering may only be achieved by providing nozzles according to the required cluster length and subrow spacing. As described, it has been found that the nozzles may be offset from a central position midway along the length direction of the pressure chamber without significant change in performance. Thus the required clusters may be formed simply at the nozzle ablation stage. This type of device is not made by MEMS fabrication and therefore the proposed embodiments may be readily applied to an existing design of ejection head within a short timeframe and without major modification of the process.
In other droplet ejection heads, the fluid path within the head may be defined by a small number of layers only, for example by the nozzle plate, the pressure chamber layer and an actuator layer, capped by a cap wafer that may provide a common fluid path to the pressure chambers. Such a head may be made by a MEMS fabrication method which allows greater flexibility in arrangement of the fluid path. In a compact device however the nozzle is still directly provided within the pressure chamber, rather than at the end of a supply path leading from the pressure chamber. Such a pressure chamber may cause the ejection of droplets by making use of reflection of pressure waves from each end of the elongate chamber and their subsequent interference to an enhanced pressure profile near the centre of the chamber. While it may be possible to create a clustering of pressure chambers by a MEMS method, some pressure chambers provide recirculation past the nozzle by having an ink supply at one end and an ink return at the other. Clustering of the chambers may make the ink supply from a common manifold more complex or time intensive to manufacture. Thus in such a device it may therefore be beneficial to create clustering only via the nozzle plate, at the nozzle formation stage, leading to an offset of the nozzles within at least some of the clusters from the centre of each longitudinal chamber to define the clusters.
Alternatively, in some ejection heads the pressure chambers 14 of the first row of pressure chambers 14 may be elongate in a direction non-parallel to the row direction, and may extend side by side, the nozzles 12 being arranged centrally, with respect to the direction of elongation, in an elongate side wall of respective pressure chambers 14, and wherein the pressure chambers 14 are arranged so as to define nozzle clusters 24 and air flow paths for forced gas to pass through the first row 20 of nozzles.
Additionally or instead, the first row of nozzles 12 may be supplied via the corresponding first row of pressure chambers 14 from a common manifold.
The droplet ejection apparatus 1 and/or the droplet ejection device may be configured to provide a pixel line frequency of 50 kHz or more.
Each nozzle 12 may be configured to eject droplets independently from all other nozzles 12.
References above and herein to “air” around the printhead 2, or in the gap G between the printhead and the substrate (deposition media), should be understood to equally apply to any gas that forms the environment around the printhead and/or between the printhead and the substrate (deposition media). The environment may be the ambient air atmosphere, or may be an imposed/controlled gas environment, provided, for example, by encasing the droplet ejection apparatus 1 in a chamber that, in use, contains a desired gas (e.g. an inert gas such as helium or argon) or mixtures of gases.
The nozzle arrangements of
It is thus not essential in order to achieve this effect that the nozzle arrangements of the embodiments according to
Nor is it essential that the fluid path provides recirculation at the back of the nozzles 12 in order to achieve a reduction or to prevent the occurrence of the woodgrain effect. For example, in some implementations of the nozzle arrangements shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| 1911217 | Aug 2019 | GB | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/GB2020/051840 | 7/31/2020 | WO |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2021/023975 | 2/11/2021 | WO | A |
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