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`AUSTRALIA
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`PATENTS ACT 1990
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`PROVISIONAL SPECIFICATION
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`FOR THE INVENTION ENTITLED:-
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`"MODULAR PRINTHEAD"
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`The invention is described in the following statement:-
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`HP 1008
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`AUSTRALIA
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`PATENTS ACT 1990
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`PROVISIONAL SPECIFICATION
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`FOR THE INVENTION ENTITLED:-
`
`"MODULAR PRINTHEAD"
`
`The invention is described in the following statement:-
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`HP 1008
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`The invention relates broadly to printers and in particular to digital inkjet printers.
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`Traditionally, inkjet printers have used a printing head that traverses back and forth
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`across the width of a page as it prints. Recently, it has been possible to form printheads
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`that extend the entire width of the page so that the printhead can remain stationary as the
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`5 page is moved past it. As pagewidth printheads do not move back and forth across the
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`page, much higher printing speeds are possible.
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`Pagewidth printheads are micro-electro-mechanical devices that are manufactured
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`in a manner similar to silicon computer chips. In this process, the ink nozzles and
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`ejector mechanisms are formed in a series of etching and deposition procedures on
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`silicon wafers.
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`As an industry standard, the silicon wafers are produced in 6 or 8 inch diameter
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`disks. Consequently only a small strip across the diameter of each wafer can be used to
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`produce printing chips of sufficient width for pagewidth printing. As a large part of
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`these wafers are essentially wasted, the production costs ofpagewidth printhead chips is
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`relatively high.
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`The costs are further increased because the chip defect rate is also relatively high.
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`Faults will inevitably occur during silicon chip manufacture and some level of attrition is
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`always present. A single fault will render an entire pagewidth chip defective, as is the
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`case with any silicon chip production. However, because the pagewidth chip is larger
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`than regular chips, there is a higher probability that any particular pagewidth chip will be
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`defective thereby raising the defect rate as a whole in comparison to regular silicon chip
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`production.
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`It is an object of the present invention to overcome or ameliorate at least one of
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`the disadvantages of the prior art, or to provide a useful alternative.
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`Accordingly, the present invention provides a modular printhead for a digital
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`inkjet printer, the modular printhead including:
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`an elongate support frame; and,
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`a plurality of printhead modules mounted end to end along the support frame.
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`Preferably, the combined length of the printhead modules is substantially equal
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`to the width of the pages to be printed.
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`In a further preferred form, the printhead modules are adapted to be individually
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`removed and replaced. To achieve this the printhead modules may be conveniently
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`adapted for snap-locking engagement with the support frame.
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`1 o
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`In one particularly preferred form, the printhead modules are mounted to the
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`support frame such that the printing width of each individual module overlaps with the
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`printing width adjacent modules.
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`It will be appreciated that the adjacent positioning of a number of small modular
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`printheads permits full pagewidth printing while allowing a much higher utilisation of
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`the silicon wafer. Furthermore, the defect rate is effectively lower because a single fault
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`will mean that a relatively smaller printhead chip will be rejected rather than a large full
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`pagewidth printhead chip. Accordingly, the production costs per chip are significantly
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`reduced.
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`By providing each modular printhead with snap-lock formations, defective
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`20 modules can be individually removed and replaced if any faults develop during
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`operation. Furthermore, by providing a small degree of overlap between the printing
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`widths of the printhead modules, it is possible to ensure that there are no gaps in the
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`printing produced by the modular printhead as a whole.
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`A preferred embodiment of the present invention will now be described by way of
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`example only with reference to the accompanying drawings in which:
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`Figure 1 is a perspective view showing the underside of a modular printhead
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`according to the present invention;
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`Figure 2 shows a rear view of the modular printhead at figure 1;
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`Figure 3 is a plan view of the modular printhead shown in figure 1;
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`Figure 4 is a front view of the modular printhead shown in figure 1;
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`Figure 5 is an underneath view of the modular printhead shown in figure 1;
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`Figure 6 is a left end view of the modular printhead shown in figure 1;
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`Figure 7 is a perspective view of the underside of a modular printhead with several
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`of the printhead modules removed;
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`Figure 8 shows an exploded perspective view of a printhead module;
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`Figure 9 shows an underside view of a printhead module;
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`Figure 10 shows an end view of a printhead module; and
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`Figure 11 shows a cross-sectional view of the modular printhead shown in figure
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`1.
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`Referring to the figures, the modular printhead has a metal chassis (1) which is
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`fixedly mounted within a digital inkjet printer (not shown). Snap-locked to the metal
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`chassis (1) are a plurality of replaceable printhead modules (2). The modules (2) are
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`sealed units with four separate ink channels that feed a printhead chip (3). As best seen
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`in figure 7, each printhead module (2) is plugged into a reservoir molding ( 4) that
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`supplies ink to the integrally moulded funnels (5).
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`The ink reservoir (4) may itselfbe a modular c-omponent so the entire modular
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`printhead is not necessarily limited to the width of a page but may extend to any
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`arbitrarily chosen width.
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`Referring to figures 8 to 11, the printhead modules (2) each comprise a printhead
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`chip (3) bonded to a TAB (tape automated bond) film (6) accommodated and supported
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`by a micromolding (7). This is, in turn, adapted to mate with a cover molding (8). The
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`printhead chip (3) is a MEMS (micro-electro-mechanical) device. The particular
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`printhead chips designed by the present Applicant are known as memjetTM chips. The
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`memjet printhead module has 1600 nozzles per inch for each different colour. As an
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`industry standard, the chips are provided with cyan, magenta, yellow and black (CMYK)
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`ink. This provides colour printing at an image resolution of 1600 dots per inch (DPI)
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`which is the accepted standard for photographic image quality. A 21 mm CMYK
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`memjet chip has 5280 nozzles, each with its own mechanical ink droplet ejection
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`mechanism.
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`If there is a defect in the chip it usually appears as a line or void in the printing. If
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`the printhead were to be formed from a single chip then the entire printhead would need
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`replacement. By modularising the printheads there is less probability that any particular
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`printhead module will be defective. It will be appreciated that the replacement of single
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`printhead modules and the greater utilisation of silicon wafers provide a significant
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`saving in production and operating costs.
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`The TAB film (6) has a slot to accommodate the memjet chip (3) and gold plated
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`contact pads (9) that connect with the flex PCB (flexible printed circuit board) (10) and
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`busbar (11) to get data and power respectively to the printhead. The busbars (11) are
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`thin fingers of metal strip separated by an insulating strip. The busbar sub-assembly (11)
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`is mounted on the underside of the side wall ink reservoir ( 4).
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`The flex PCB (10) is mounted to the angled side wall of the reservoir (4). It wraps
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`beneath the side wall of the reservoir (4) and up the external surface carrying data to the
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`5 memjet modules (2) via a 62 pin header (12). Side wall of the ink reservoir (4) is angled
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`to correspond with the side of the cover molding (8) so that when the printhead module
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`(2) is snap-locked in place, the contacts (9) wipe against the corresponding contacts on
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`the flex PCB to promote a reliable electrical connection. The angle also assists the easy
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`removal ofthe modules (2). The flex PCB (11) is "sprung" by the action of a foam
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`backing (13) mounted between the wall and the underside ofthe contact area.
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`Rib details on the underside of the micromolding (7) provide support for the TAB
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`film (6) when they are bonded together. The TAB film (6) forms the underside wall of
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`the printhead module (2) as there is enough structural integrity between the pitch of the
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`ribs to support a flexible film. The edges of the TAB film (6) are sealed on the
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`underside ofthe walls ofthe cover molding (8). The chip (3) is bonded onto 100 micron
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`wide ribs that run the length of the micromolding (7) providing the final ink feed into the
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`memjet print nozzles .
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`. The design of the micromolding (7) allows for a physical overlap of the memjet
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`chips (3) when the modules (2) are mounted adjacent one another. Because the.
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`printhead modules (2) form a continuous strip with a generous tolerance, they can be
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`electronically adjusted to produce a continuous print pattern, rather than relying on very
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`close tolerance mouldings and exotic materials to perform the same function. According
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`to this embodiment, the printing chips (3) are 21 mm long but are angled such that they
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`provide a printing width of20.33 mm.
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`The micromolding (7) fits inside the cover molding (8) where it bonds onto a set of
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`vertically extending ribs. The cover molding (8) is a two shot precision injection
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`molding that combines an injected hard plastic body with soft elastomeric sealing collars
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`at the inlet to each ink chamber defined within the module.
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`Four snap-lock barbs (15) mate with the outer surface of the ink reservoir (4)
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`which acts as an extension of metal chassis (1). The ink funnels (5) sealingly engage
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`with the elastomeric collars (14).
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`The modular design conveniently allows the memjet printhead modules (2) to be
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`removably snap-locked onto the ink reservoir (4). Accurate alignment of the memjet
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`chip (3) with respect to the metal chassis is not necessary as a complete modular
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`printhead will undergo digital adjustment of each chip (3) during final quality assurance
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`testing.
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`The TAB film ( 6) for each module (2) interfaces with the flex PCB (11) and the
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`busbars (11) as it is clipped onto the ink reservoir (4). To disengage a memjet printhead
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`15 module (2) the snap-lock barbs (15) may be configured for release upon the application
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`of sufficient force by the user. Alternatively, the snap-lock barbs (15) can be configured
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`for a more positive engagement with the ink reservoir (4) such that a customised tool
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`(not shown) is required for disengagement of the module.
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`The invention has been described herein by way of example only and skilled
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`20 workers in this field will readily recognise many variations and modifications which do
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`not depart from the spirit and scope of the broad inventive concept.
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`THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:-
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`1.
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`A modular printhead for a digital ink:jet printer, a modular printhead including:
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`a support frame; and,
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`a plurality ofprinthead modules mounted adjacent each other on the support frame.
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`5
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`2.
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`A modular printhead according to claim 1 wherein the combined length of the
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`printhead modules is substantially equal to the width of the pages to be printed.
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`3.
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`A modular printhead according to claim 2 wherein the printhead modules are
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`adapted to be individually removed and replaced.
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`4.
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`A modular printhead according to claim 3 wherein the printhead modules are
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`adapted for snap-locking engagement with the support frame.
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`5.
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`A modular printhead according to claim 4 wherein the printhead modules are
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`mounted to the support frame such that the printing width of each individual module
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`overlaps with the printing width of adjacent modules.
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`6.
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`A modular printhead for a digital inkjet printer substantially as herein before
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`described with reference to the accompanying drawings.
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`DATED this 2nd day of March, 2000
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`SIL VERBROOK RESEARCH PTY LTD
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`Attorney: JOHN D. FORSTER
`Fellow Institute of Patent and Trade Mark Attorneys of Australia
`of BALDWIN SHELSTON WATERS
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`MJ22
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