WO1998022289A1

WO1998022289A1 - Droplet deposition apparatus

Info

Publication number: WO1998022289A1
Application number: PCT/GB1997/003206
Authority: WO
Inventors: Michael George Arnott
Original assignee: Xaar Technology Limited
Priority date: 1996-11-22
Filing date: 1997-11-21
Publication date: 1998-05-28
Also published as: GB9624324D0; AU5062398A

Abstract

Inkjet printhead with array of parallel channels has groups (42a, 42b) of successive channels associated with different ink colours. A cover makes a seal with a channel side wall (62') lying between neighbouring groups. To accommodate small misalignments in manufacturing, the channels (70a, 70b) at either side of this sealing wall, are rendered inactive and do not eject ink.

Description

DROPLET DEPOSITION APPARATUS

The present invention relates to droplet deposition apparatus, in particular an in jet printhead, comprising an array of channels arranged side-by-side and separated one from the next by longitudinal side walls. Such apparatus is known, for example, from EP-A-0 278 590, incorporated herein by reference, and is shown in figures 1 (a) and (b) . The channels 2 making up the array are each connected to a nozzle 6 at one end and are supplied with ink at the other end from a common ink supply manifold. The printhead comprises actuators which allow the channel side walls 1 1 to be deflected in either direction transverse to the longitudinal axis of the channels, thereby to eject an ink droplet from the nozzle of the channel lying either side of the respective wall. EP '590 discusses a further feature of such construction, namely cross-talk between channels, and points out that this increases with the increase in compliance of the side walls relative to that of the ink.

Apparatus of this type can also be used as the separate colour arrays (generally firing cyan, magenta, yellow and black) of a colour printer. This latter arrangement is known, for example, from WO 94/27827 and comprises four separate arrays of channels formed in a common base.

It has been recognised by the present inventors that it is advantageous to be able to make both monochrome and colour printheads from the same channelled component. To this end, it has been proposed in the co-pending application WO 97/04963 to divide a single uniform array of channels into groups, each group being separated from the next by a single active channel wall. Whilst this arrangement has advantages as regards simplicity of operation and compactness, the dividing element formed in the cover to separate one colour ink from the next has proved difficult to manufacture: tight tolerances are necessary if the dividing portion is to mate successfully with the top of the single channel wall and yet not impair operation of the two channels located either side of that wall. The present invention has as an objective a multiple array printhead that can be more easily manufactured from a single array of channels separated one from the next by channel walls of uniform width.

Accordingly, the present invention consists in one aspect in droplet deposition apparatus, in particular an inkjet printhead, comprising an array of channels arranged side-by-side and separated one from the next by longitudinal side walls of uniform width in the array direction; the array comprising first and second groups of active channels supplied from respective first and second droplet liquid supply means; each group of active channels comprising successive channels in the array each communicating with a nozzle for ejection of droplets therefrom and with respective droplet liquid supply means and being associated with means for applying a pressure pulse to the droplet liquid thereby to eject a droplet; wherein at the neighbouring extremities of said first and second groups, there is located directly adjacent each group a respective inactive channel communicating with the droplet liquid supply means of said each group but being disabled for droplet ejection, the respective inactive channels being further separated by at least one longitudinal side wall. Such an arrangement allows that portion of the apparatus that divides one group of channels from the other to be made only to those tolerances necessary to ensure that those channels lying adjacent the portion function as inactive, liquid filled channels. The present inventors have recognised that the intolerances required for such inactive channels are far wider than, for example, the active channels 63, 64 lying adjacent the dividing portion 60 in the arrangement of figure 3(a) . Such an arrangement also facilitates the use of an array of channels separated by side walls of uniform width which can also be common to monochrome designs utilising a single colour ink supply. A reduction in product costs due to reduction of manufacturing tolerances in the one hand and an increase in component commonality on the other is therefore achievable.

From this recognition also flows a second aspect of the present invention, namely droplet deposition apparatus, in particular an inkjet printhead, comprising a base having an array of open-topped channels arranged side-by-side and separated one from the next by longitudinal side walls of uniform width in the array direction; and a cover to close the open top of said channels; the array comprising first and second groups of active channels supplied from first and second droplet liquid supply means via first and second manifolds formed in said cover; each group of active channels comprising successive channels in the array each communicating with a nozzle and being associated with means for applying a pressure pulse to the droplet liquid thereby to eject a droplet from the respect nozzle; wherein at the neighbouring extremities of said first and second groups, there is located directly adjacent each group a respective inactive channel communicating with the droplet liquid supply means of said each group but being disabled for droplet ejection, the respective inactive channels being further separated by at least one longitudinal side wall; and wherein the cover situated between said first and second manifolds mates with said at least one longitudinal side wall.

In yet a further aspect, the present invention consists in droplet deposition apparatus comprising an array of channels arranged side by side in a unitary base structure and separated one from the next by longitudinal side walls of uniform width in the array direction; the array comprising first and second groups of successive active channels supplied from respective first and second droplet liquid supply means, each active channel communicating with a nozzle for the ejection of droplets therefrom and being associated with means for applying a pressure pulse to the droplet liquid thereby to eject a droplet, there being a droplet liquid seal in contact with at least one longitudinal side wall lying between said groups of active channels, there being provided an inactive channel on at least one side of said one longitudinal side wall to accommodate small misalignment of the seal in the array direction without interference with operation of said active channels. Preferably, there is an inactive channel on both sides of said one longitudinal side wall. Suitably, the extent of said seal in the array direction is substantially equal to the width of the side walls in the array direction.

Further advantageous embodiments of the present invention are given in the dependent claims and description.

The invention will now be described by way of reference to the following diagrams, of which:

Figure 1 (a) shows an exploded perspective view of a conventional printhead comprising an array of channels arranged side-by-side and separated one from the next by longitudinal side walls;

Figure 1 (b) shows a sectional view taken transversely to the direction of elongation of the channels;

Figure 2 shows a perspective view of a printhead of the kind disclosed in co-pending PCT application pct/gb96/01789 and comprising more than one group of channels;

Figures 3(a) and (b) respectively show views at the section lines B-B and C-C of figure 2;

Figure 4 illustrates a problem that may occur at section line B-B of the printhead shown in figure 2;

Figure 5 is a view corresponding to the view at section line B-B of figure 2 for a printhead according to a first embodiment of the invention; Figure 6 is a view corresponding to the view at section line B-B of figure 2 for a printhead according to a second embodiment of the invention;

Figure 7 is a view corresponding to the view at section line B-B of figure 2 for a printhead according to a third embodiment of the invention;

Figure 1 (a) shows a conventional printhead of the kind disclosed in the aforementioned EP-A-0 278 590 and also EP-A-0 364 136, both of which are incorporated herein by reference. Parallel grooves 20, formed in an array in a base 10, are each closed by a cover 12 to form channels 22. Each channel communicates at one end with a window 32 in the cover through which ink is supplied. The other end of each channel communicates with a nozzle 38, formed in a nozzle plate 14, through which ink droplets are expelled. The method of ink expulsion is illustrated in figure 1 (b): one or both of the side walls of a channel are deflected transversely, thereby reducing the volume of the channel and expelling an ink droplet from the nozzle. In the example shown, the channel walls themselves form the actuators, being formed of piezoelectric material that is so poled (in direction of arrow P in figure 1b) that the application of an electric field by means of electrodes 30 (fed with voltages from a circuit board 16) located on the channel-facing surfaces of the walls causes the walls to deflect transversely in shear mode as indicated by dashed lines.

Figure 2 shows a similar printhead where the array of channels has been divided into a number of groups 42a, 42b, each group being supplied (generally with different coloured ink) from a separate ink supply window 32a, 32b. Such an arrangement is disclosed in co-pending PCT application no. pct/gb96/01789, incorporated herein by reference. As is clear from the sectional view of figure 3a, the two ink supply windows 32a, 32b are separated by a dividing portion 60 that mates with the top of the channel wall 62 so as to prevent ink from window 32a from entering the channels belonging to group 42b and vice versa. In the closed sections of the channel (see figure 3b), a glue bond between the cover 40 and the tops of all the channel walls prevents flow of ink between all channels, not only between those belonging to the different channel groups 42a, 42b. Particular care is necessary in the manufacture of the cover 40 including dividing portion 60 and in its assembly with the channelled component 10: inaccurate positioning of the portion 60 relative to the top of dividing wall 62 will endanger not only the seal between the two ink supply windows 32a, 32b but may also affect the functioning of the channels 63, 64 lying either side of the dividing wall 62. For example, it has been found that a dividing portion inaccurately positioned as shown in figure 4 will result in the channel 63 having a higher droplet ejection velocity for a given actuation voltage than the other channels in the array. As will be appreciated, non-uniformity in droplet ejection velocity between channels will give rise to faults in the resulting printed image. Figure 5 shows a section corresponding to figure 3(a) but according to a first embodiment of the present invention. Corresponding features have been designated by corresponding reference figures. It has been recognised that the necessary manufacturing tolerances can be reduced if the channels lying adjacent the dividing portion 60 are not used for firing droplets i.e. these channels are made inactive. However, it has also been recognised that such inactive channels must also be connected to the ink supply if they are not to adversely affect the operation of adjacent active channels: if such inactive channels were not filled with ink but with air instead, for example, the channel wall separating the inactive channel from the adjacent active channel would response differently to a given actuation pulse than would a wall separating two active, ink-filled channels. As a result, the droplet ejection velocity from the active channel lying adjacent the inactive channel would differ from the velocities of the droplets ejected from the other active channels in the group - an undesirable situation as explained above.

As illustrated in figure 5, adoption of the present invention allows a much wider positional and dimensional tolerance to be placed on the dividing portion 60' : 72a and 72b indicate the limiting positions of the left and right hand edges of the dividing portion 60' respectively, in each case guaranteeing communication of the inactive channels 70a and 70b with the ink-supply windows 32' and 32b' . It has been found in practice that one edge can be allowed to extend over at least half of the width of an inactive channel. In a modification - not shown - only one of the channels 70a and 70b is rendered inactive. This arrangement can provide a tolerance in the array direction of plus or minus a quarter of the channel width rather than plus or minus a half of the channel width. To distribute the tolerance equally in both directions, the nominal position of the cover seal may be displaced a quarter channel width toward the inactive channel.

At the right hand side of figure 5 is illustrated the positional variation at the edge of the printhead array. Reference figure 75 indicates an end-of-array "dummy" or "guard" channel as is known in the art. It has been recognised that, since this "dummy" channel is also inactive, similarly wide tolerances are permissable.

Figure 6 illustrates a second embodiment of the present invention, again employing inactive channels 70a and 70b at the neighbouring extremities of the active channel groups 42a and 42b. It has been recognised that yet wider tolerances on the position and dimension of the dividing portion 60" are possible by separating the inactive ink-filled channels 70a and 70b by further inactive channels 80.

Reference figures 72a and 72b indicate the possible left and right- hand extreme positions of the dividing portion respectively - in each case, inactive channels 70a and 70b remain in communication with the respective ink supply windows 32a", 32b". Following manufacture, the actual width of the dividing portion may be narrower than the portion 60" indicated in full lines in figure 6 in which case channels 80 will be open to an ink supply window 32a", 32b". Alternatively, as shown in figure 7, the dividing portion 60'" may extend from limit 72a to limit 72b , thereby closing off the channels 80 in the manifold region and sealing them from inflow of ink. In this case they will generally contain air, although the use of some other gas or material could be forseen. The content of channels 80 has no significant effect on the active channels 42x, 42y at the extremity of each channel group, being as they are buffered by the inactive channels 70a, 70b. It will be appreciated that an effective seal between the dividing portion 60" and at least one of the walls of the inactive channels is the necessary condition for correct operation.

Channels can be rendered inactive by various means including omission of actuating electrodes, omission of connection between the printhead controller and the electrodes. However, particularly in printheads of the kind shown in figure 1 employing piezoelectric wall actuators , the programming of the controller not to eject droplets from certain channels is preferred since this permits bipolar electric fields to be applied to channel actuating walls by means of unipolar voltages applied to channels - such is known in the art e.g. from WO95/25011.

It will be understood that the present invention is applicable to printheads having multiple groups of channels, not merely two groups as shown by way of example in the figures. Although of particular advantage in printheads using side-wall actuators - whether employing piezoelectric, electrostatic or some other means: the present invention is not restricted to those arrangements and is applicable whenever the dimension in the array direction at the interface between two groups of channels in the array is particularly critical.

Claims

1. Droplet depostion apparatus, in particular an inkjet printhead, comprising an array of channels arranged side-by-side and separated one from the next by longitudinal side walls of uniform width in the array direction; the array comprising first and second groups of active channels supplied from respective first and second droplet liquid supply means; each group of active channels comprising successive channels in the array each communicating with a nozzle for ejection of droplets therefrom and with respective droplet liquid supply means and being associated with means for applying a pressure pulse to the droplet liquid thereby to eject a droplet; wherein at the neighbouring extremities of said first and second groups, there is located directly adjacent each group a respective inactive channel communicating with the droplet liquid supply means of said each group but being disabled for droplet ejection, the respective inactive channels being further separated by at least one longitudinal side wall.

2. Droplet deposition apparatus according to claim 1 , wherein said respective inactive channels are separated by at least one further inactive channel.

3. Droplet deposition apparatus according to claim 2, wherein said further inactive channel communicates with one of said first and second droplet liquid supply means.

4. Droplet deposition apparatus according to claim 3 wherein said apparatus comprises two of said further inactive channels communicating with said first and second droplet liquid supply means respectively.

5. Droplet deposition apparatus according to claim 2 wherein said further inactive channel is sealed from said first and second droplet liquid supply means.

6. Droplet deposition apparatus according to any previous claim and comprising a base having open-topped channels and a cover to close the open tops of said channels.

7. Droplet deposition apparatus according to claim 6, wherein communication between first and second droplet liquid supply means and first and second groups of active channels is via first and second manifolds formed in said cover.

8. Droplet deposition apparatus according to claim 7, wherein said cover mates with said at least one longitudinal side wall, thereby to separate said first manifold from said second manifold.

9. Droplet deposition apparatus according to claim 8 when dependent on claim 5, wherein said cover mates with another longitudinal side wall, thereby to seal at least one further inactive channel from said first and second droplet liquid supply means.

10. Droplet depostion apparatus, in particular an inkjet printhead, comprising a base having an array of open-topped channels arranged side- by-side and separated one from the next by longitudinal side walls of uniform width in the array direction; and a cover to close the open tops of said channels; the array comprising first and second groups of active channels supplied from first and second droplet liquid supply means via first and second manifolds formed in said cover; each group of active channels comprising successive channels in the array each communicating with a nozzle and being associated with means for applying a pressure pulse to the droplet liquid thereby to eject a droplet from the respective nozzle; wherein at the neighbouring extremities of said first and second groups, there is located directly adjacent each group a respective inactive channel communicating with the droplet liquid supply means of said each group but being disabled for droplet ejection, the respective inactive channels being further separated by at least one longitudinal side wall; and wherein the cover situated between said first and second manifolds mates with said at least one longitudinal side wall.

11. Droplet deposition apparatus according to claim 10, wherein the cover situated between said first and second manifolds mates with said at least one longitudinal side wall in a mating plane and overhangs at least one of said inactive channels in the mating plane.

12. Droplet deposition apparatus according to claim 11 wherein the cover overhangs at least one of said inactive channels in the mating plane by a distance equal to at least half the width of an inactive channel.

13. Droplet deposition apparatus according to any previous claim wherein said longitudinal side walls are transversely displaceble in said array direction thereby to apply a pressure pulse to the droplet liquid and eject a droplet.

14. Droplet deposition apparatus according to claim 1 3 wherein said longitudinal side walls comprise piezoelectric material actuable by means of an electric field to displace transversely in said array direction.

1 5. Droplet deposition apparatus according to claim 14 wherein said piezoelectric material displaces in shear mode.

1 6. Droplet deposition apparatus according to claim 1 5 wherein said piezoelectric material is polarised in a direction perpendicular to both said array direction and the longitudinal axis of said channels, electrodes for application of an electric field being arranged on the channel-facing surfaces of said side walls.

1 7. Droplet deposition apparatus comprising an array of channels arranged side by side in a unitary base structure and separated one from the next by longitudinal side walls of uniform width in the array direction; the array comprising first and second groups of successive active channels supplied from respective first and second droplet liquid supply means, each active channel communicating with a nozzle for the ejection of droplets therefrom and being associated with means for applying a pressure pulse to the droplet liquid thereby to eject a droplet, there being a droplet liquid seal in contact with at least one longitudinal side wall lying between said groups of active channels, there being provided an inactive channel on at least one side of said one longitudinal side wall to accommodate small misalignment of the seal in the array direction without interference with operation of said active channels.

1 8. Apparatus according to claim 1 7, wherein there is provided an inactive channel on both sides of said one longitudinal side wall.

19. Apparatus according to claim 17 or claim 18, wherein the extent of said seal in the array direction is substantially equal to the width of the side walls in the array direction.