PATENT DOCUMENT

Abstract:
A method of fabricating a plurality of inkjet nozzles on a substrate. The method comprises the steps of: (a) providing a substrate having a plurality of trenches corresponding to ink inlets; (b) depositing sacrificial material so as fill the trenches and form a scaffold on the substrate; (c) defining openings in the sacrificial material; (d) depositing roof material over the sacrificial material to form nozzle chambers and filter structures simultaneously; (e) etching nozzle apertures through the roof material; and (f) removing the sacrificial material.

Full Description:
FIELD OF THE INVENTION 
     The present invention relates to printers and in particular inkjet printers. Specific aspects of the invention relate to cartridges for printers, printhead design and maintenance, as well as other facets of printer operation. 
     CO-PENDING APPLICATIONS 
     The following applications have been filed by the Applicant simultaneously with the present Application Ser. Nos.: 11/305,273, 11/305,275, 11/305,152, 11/305,158, 11/305,008 
     The disclosures of these co-pending applications are incorporated herein by reference. 
     Some applications have been listed by their docket number. These will be replaced when application numbers are known. The disclosures of these applications and patents are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     Traditionally, most commercially available inkjet printers have a print engine which forms part of the overall structure and design of the printer. In this regard, the body of the printer unit is typically constructed to accommodate the printhead and associated media delivery mechanisms, and these features are integral with the printer unit. 
     This is especially the case with inkjet printers that employ a printhead that traverses back and forth across the media as the media is progressed through the printer unit in small iterations. In such cases the reciprocating printhead is typically mounted to the body of the printer unit such that it can traverse the width of the printer unit between a media input roller and a media output roller, with the media input and output rollers forming part of the structure of the printer unit. With such a printer unit it may be possible to remove the printhead for replacement, however the other parts of the print engine, such as the media transport rollers, control circuitry and maintenance stations, are typically fixed within the printer unit and replacement of these parts is not possible without replacement of the entire printer unit. 
     As well as being rather fixed in their design construction, printer units employing reciprocating type printheads are considerably slow, particularly when performing print jobs of full colour and/or photo quality. This is due to the fact that the printhead must continually traverse the stationary media to deposit the ink on the surface of the media and it may take a number of swathes of the printhead to deposit one line of the image. 
     Recently, it has been possible to provide a printhead that extends the entire width of the print media so that the printhead can remain stationary as the media is transported past the printhead. Such systems greatly increase the speed at which printing can occur as the printhead no longer needs to perform a number of swathes to deposit a line of an image, but rather the printhead can deposit the ink on the media as it moves past at high speeds. Such printheads have made it possible to perform full colour 1600 dpi printing at speeds in the vicinity of 60 pages per minute, speeds previously unattainable with conventional inkjet printers. 
     The ink ejection nozzles in modern inkjet printers are typically MST (micro systems technology) devices in the form of a printhead integrated circuit (IC). They are fabricated on silicon wafer substrates using lithographic etching and deposition techniques. Printhead IC&#39;s have closely packed nozzles which provide good image resolution image but introduces some production difficulties. One issue is providing the printhead IC with power and print data from the print engine controller. A flexible printed circuit board (flex PCB) is usually used for this. Flex PCB&#39;s have tracks of conductive material in a polymer film. The tracks are spaced so that they are in registration with a line of bond pads on the printhead IC. The tracks are then directly connected to the bond pads. This requires the flex PCB to be very accurate and a high degree of precision when aligning the flex PCB and the bond pads. Consequently, this can be a time consuming stage of the overall printhead production process. 
     The situation is exacerbated in the production of the pagewidth printheads discussed above. The printhead IC&#39;s that make up a pagewidth printhead are generally longer than the printhead IC&#39;s used in scanning type printheads. Hence the line of bonds pads on each IC is longer so the track spacing must match the bond pad spacing more closely. It will be appreciated that a slight inaccuracy in the track spacing can be accommodated by the width of the bond pad. However, the spacing inaccuracy compounds with each successive track across the flex PCB so by the end of a long line of bond pads, the slight inaccuracy is no longer accommodated by the pad width. 
     Accordingly, there is a need to provide a more time efficient and commercially practical method for connecting the tracks of a flex PCB with the corresponding bond pads of a printhead IC. 
     SUMMARY OF THE INVENTION 
     Accordingly, one aspect of the present invention provides a method of producing a printhead for an inkjet printer with a print engine controller for controlling the printhead operation, the method comprising the steps of: 
     providing a printhead IC having an array of ink ejection nozzles formed on a substrate;
         providing circuitry for electrical connection to the print engine controller;   providing a support member for supporting the printhead IC and the circuitry within the printer;   providing a polymer film;   securing the polymer film to a surface of the support member by applying beat and pressure for a predetermined time;   mounting the printhead IC and the circuitry to the support member via the polymer film; and,   electrically connecting the circuitry to the printhead IC.       

     Attaching both the printhead IC and the flex PCB to the support member with a polymer film is a relatively quick and simple step as the highly precise alignment of the tracks and the bond pads is not critical. The tracks can be subsequently connected to the bond pads in an automated process. Equipment is available that will optically locate the end of the track and wire it to the corresponding bond pad on the printhead IC. Small inaccuracies in the registration of the tracks and the bond pads will not prevent the flex PCB from connecting to the printhead IC, especially long IC&#39;s used in pagewidth printhead. As a result the overall process is more time efficient and commercially practical. 
     In a first preferred form, the circuitry is a flex PCB with tracks of conductive material in layers of polyimide film, and the printhead IC and the flex PCB are simultaneously attached to the support member via the polymer film. In a second preferred form, the circuitry is a flex PCB with tracks of conductive material in layers of polyimide film, and the flex PCB is attached to the polymer film after the printhead IC is attached. Optionally the flex PCB has an adhesive area for attachment to the polymer film once the polymer film has cooled and hardened after the printhead IC attachment process. According to a third preferred form, the circuitry is tracks of conductive material laid within the polymer film. It will be appreciated that in this form, the polymer film effectively becomes the flex PCB. 
     In preferred forms, the printhead IC has a series of bond pads and the circuitry is a series of conductive tracks, whereby the step of electrically connecting the circuitry to the printhead IC involves lacing fine wiring between the bond pads and the corresponding conductive track before covering the fine wiring in a line of protective encapsulator material. 
     In some preferred embodiments, the support member has a plurality of ink feed conduits for establishing fluid communication with at least one ink storage compartment; and, 
     the polymer film is attached to the support member between the ink feed conduits and the printhead integrated circuits, the polymer film having an array of apertures such that the ejection nozzles are in fluid communication with the ink feed conduits. 
     In a particularly preferred form, the polymer film is more than 25 microns thick. In specific embodiments, the polymer film is about 50 microns thick. 
     To feed ink to the individual nozzles on the printhead integrated circuit (IC), it is often convenient to etch channels in the reverse side of the silicon wafer substrate. These channels need to be sealed and the polymer film can provide an adequate seal as well as a means to secure the IC to a support structure. However, if the surface of the support structure is uneven, the seal provided by the polymer film can be compromised. The surface that the IC is secured to, is typically uneven because of more ink feed channels that deliver ink to the channels in the IC. As the film seals across the open channels in the support, it can also bulge or sag into them. The section of film that sags into a support structure channel runs across several of the etched channels in the printhead IC. The sagging may cause a gap between the walls separating each of the etched channels. Obviously, this breaches the seal and allows ink to leak out of the printhead IC and or between etched channels. To guard against this, the polymer sealing film should be thick enough to account for any sagging into the support structure channels while maintaining the seal over the etched channels in the IC. 
     The minimum thickness of the polymer sealing film will depend on a number of factors to be discussed in detail with reference to the preferred embodiments. However, the Applicant&#39;s analysis and testing has shown that a polymer sealing film thickness of 25 microns is adequate for the printhead IC&#39;s formed using lithographically masked etching and deposition techniques. Increasing the thickness to 50, 100 or even 200 microns will correspondingly increase the reliability of the seal provided. 
     In some embodiments the array of apertures is an array of laser drilled holes in registration with respective ends of the ink feed conduits. Optionally, the polymer sealing film is a laminate with an adhesive layer on both sides of a thermoplastic film. Optionally, the thermoplastic film is a PET or polysulphone. Optionally, the polymer sealing film is more than 150 microns thick. Optionally, the ink feed conduits are formed in a liquid crystal polymer micro molding. 
     Preferably, the circuitry is a flex PCB with tracks of conductive material in layers of polyimide film, and the printhead IC and the flex PCB are simultaneously attached to the support member via the polymer film. 
     Preferably, the circuitry is a flex PCB with tracks of conductive material in layers of polyimide film, and the flex PCB is attached to the polymer film after the printhead IC is attached. 
     Preferably, the flex PCB has an adhesive area for attachment to the polymer film once the polymer film has cooled and hardened after the printhead IC attachment process. 
     Preferably, the circuitry is tracks of conductive material laid within the polymer film. 
     Preferably, the support member has a plurality of ink feed conduits for establishing fluid communication with at least one ink storage compartment; and,
         the polymer film is attached to the support member between the ink feed conduits and the printhead integrated circuits, the polymer film having an array of apertures such that the ejection nozzles are in fluid communication with the ink feed conduits.       

     Preferably, the polymer film is more than 25 microns thick. 
     Preferably, the polymer film is about 50 microns thick. 
     Preferably, the array of apertures is an array of laser drilled holes in registration with respective ends of the ink feed conduits. 
     Preferably, the polymer sealing film is a laminate with an adhesive layer on both sides of a thermoplastic film. 
     Preferably, the thermoplastic film is a PET or polysulphone. 
     Preferably, the ink feed conduits are formed in a liquid crystal polymer micro molding. 
     In a second aspect the present invention provides a method of attaching a MST device to a support member with an adhesive film, the MST device having an attachment face and a first fluid conduit connected to a first aperture in the attachment face; 
     the support member having a mounting face and a second fluid conduit connected to a second aperture in the mounting face; and, 
     the polymer film has an opening for fluid communication between the first aperture and the second aperture, the method comprising the steps of: 
     forming the opening in the polymer film; 
     aligning the opening with at least part of the second aperture; 
     applying heat and pressure to attach the polymer film to the mounting face; and, 
     positioning the MST device such that the opening is aligned with at east part of the first aperture. 
     By forming any holes or openings in the polymer film before it is attached to the support member is far less time consuming than forming any openings after the film is attached to the mounting surface. Furthermore, as the openings are usually formed by laser drilling, there is a significant risk that some of the underlying support member is also ablated. This ablated material can lodge in the opening or fluid conduit to constrict or clog the fluid flow. 
     Preferably, the polymer film is a laminated film having a central web between two outer layers of thermosetting adhesive. 
     Preferably, the MST device has an array of inlet apertures in the attachment face connected to a plurality of first fluid conduits, the attachment face has an array of outlet apertures connected to a plurality of second fluid conduits and the laminated film has an array of openings for establishing fluid communication between corresponding apertures in the inlet and outlet arrays. 
     Preferably, the opening in the laminated film is laser drilled. 
     Preferably, the laminated film is drilled with a UV laser so as to not cure the thermosetting adhesive layers immediately adjacent the opening. 
     Preferably, the central web is a polyimide film. 
     Preferably, the polyimide film is more than 25 microns thick. 
     Preferably, the polyimide film about 50 microns thick. 
     Preferably, each of the thermosetting adhesive layers is more than 12 microns thick. 
     Preferably, each of the thermosetting adhesive layers are about 25 microns thick. 
     Preferably, the array of inlet apertures is a series of open channels in the attachment face. 
     Preferably, the channels are more than 50 microns wide and spaced from adjacent channels by more than 50 microns. 
     Preferably, the attachment face has recesses adjacent the channels to hold thermosetting adhesive displaced from between the attachment face and polyimide layer. 
     Preferably, the laminated film is sandwiched between two protective liners, the liner on the support member side of the laminated film being removed after laser drilling the opening but before the attachment of the support structure and the protective liner on the MST device side is removed prior to attaching the MST device. 
     Preferably, the protective liners are PET. 
     Preferably, the thermosetting adhesive layers are initially made tacky when the laminated film is first attached to the support member and the MST device and subsequently heated to their curing temperature. 
     Preferably, the thermosetting adhesive layers have different curing temperatures so that the laminated film is cured to the support member before the MST device is attached without the MST device side thermosetting adhesive curing until after the MST device is attached. 
     Preferably, the opening is formed before the laminated film is attached to the mounting surface of the support member. 
     Preferably, the MST devices are printhead ICs and the support structure is a liquid crystal polymer (LCP) molding. 
     Preferably, the laminated film is aligned with the fiducial markers on the support structure with a vision system that calculates a point on or within one of the opening in the array of openings for each MST device. 
     In a third aspect the present invention provides laminated film for mounting a MST device to a support structure for sealed fluid communication therebetween, the laminated film comprising: 
     a polymer carrier web between two thermosetting adhesive layers; and, 
     an opening formed in the film for establishing fluid communication between a first fluid conduit in the MST device and a second fluid conduit in the support member. 
     Using a laminated film with thermosetting adhesive one each side provides a far more reliable seal than heated thermoplastic film. The bond between the thermoplastic film and the MST device surface is prone to thermal fatigue and leakage or outright failure. A laminate with a central carrier web and thermosetting adhesive can be drilled by a UV laser and later heated to a known curing temperature so that the adhesive sets and forms a strong bond to the MST device surface. 
     Preferably, the MST device has an array of inlet apertures in the attachment face connected to a plurality of first fluid conduits, the attachment face has an array of outlet apertures connected to a plurality of second fluid conduits and the laminated film has an array of openings for establishing fluid communication between corresponding apertures in the inlet and outlet arrays. 
     Preferably, the opening is laser drilled. 
     Preferably, the thermosetting adhesive has a maximum curing temperature of 150 degrees Celsius. 
     Preferably, the laser is a UV laser so as to not cure the thermosetting adhesive layers immediately adjacent the opening. 
     Preferably, the central web is a polyimide film. 
     Preferably, the polyimide film is more than 25 microns thick. 
     Preferably, the polyimide film about 50 microns thick. 
     Preferably, each of the thermosetting adhesive layers is more than 12 microns thick. 
     Preferably, each of the thermosetting adhesive layers is about 25 microns thick. 
     Preferably, the array of inlet apertures is a series of open channels in the attachment face. 
     Preferably, the channels are more than 50 microns wide and spaced from adjacent channels by more than 50 microns. 
     Preferably, the attachment face has recesses adjacent the channels to hold thermosetting adhesive displaced from between the attachment face and polyimide layer. 
     In a further aspect there is provided laminated film further comprising two protective liners on each outer surface, the liner on the support member side of the polymer film being removed after laser drilling the opening but before the attachment of the support structure and the protective liner on the MST device side is removed prior to attaching the MST device. 
     Preferably, the protective liners are PET. 
     Preferably, the thermosetting adhesive layers can be heated to a temperature less than the curing temperature to make them for initially attaching the support member and the MST device prior to subsequent heating to the curing temperature. 
     Preferably, the thermosetting adhesive layers have different curing temperatures so that the polymer film is cured to the support member before the MST device is attached without the MST device side thermosetting adhesive curing until after the MST device is attached. 
     Preferably, the thermosetting adhesive layers have a viscosity between 100 centPoise and 10,000,000 centiPoise. 
     Preferably, the MST device is a printhead IC and the support structure is a liquid crystal polymer (LCP) molding. 
     Preferably, the support structure has at least one fiducial marker on the mounting face and the array of openings is aligned with the array of outlet apertures using a vision system tracking a predetermined opening within the array of openings, relative to the at least one fiducial marker. 
     In a fourth aspect the present invention provides a method of sealing an attachment face of a MST device to a mounting surface on a support member, the attachment face having an aperture connected to a first fluid conduit, the attachment face having a second aperture connected to a second conduit, the method comprising the steps of: 
     applying a thermosetting adhesive to the mounting surface; 
     aligning the first aperture with at least part of the second aperture; 
     pressing the MST device and the mounting surface together; and, 
     curing the thermosetting adhesive; wherein, 
     the thermosetting adhesive has a viscosity of between 100 centiPoise and 10,000,000 centipoise. 
     Using a thermosetting adhesive instead of a thermoplastic adhesive provides a far more reliable seal. The bond between the thermoplastic adhesive and the MST device surface is prone to thermal fatigue and leakage or outright failure. A thermosetting adhesive can be heated until it is tacky for preliminary positioning of the MST device, and later heated to a known curing temperature so that the adhesive sets and forms a strong chemical bond to the MST device surface. However, the viscosity of the adhesive must be low enough to allow the MST device to properly embed into it, yet high enough that it does not extrude into the conduits to the extent that the flow is blocked or overly restricted. 
     Preferably, the thermosetting adhesive is applied to the mounting surface as a laminated film having a central web with a layer of the thermosetting adhesive on either side and an opening for fluid communication between the first aperture and the second aperture. 
     Preferably, the MST device has an array of inlet apertures in the attachment face connected to a plurality of first fluid conduits, the attachment face has an array of outlet apertures connected to a plurality of second fluid conduits and the laminated film has an array of openings for establishing fluid communication between corresponding apertures in the inlet and outlet arrays. 
     Preferably, the opening in the laminated film is laser drilled. 
     Preferably, the laminated film is drilled with a UV laser so as to not cure the thermosetting adhesive layers immediately adjacent the opening. 
     Preferably, the central web is a polyimide film. 
     Preferably, the polyimide film is more than 25 microns thick. 
     Preferably, the polyimide film about 50 microns thick. 
     Preferably, each of the thermosetting adhesive layers is more than 12 microns thick. 
     Preferably, each of the thermosetting adhesive layers are about 25 microns thick. 
     Preferably, the array of inlet apertures is a series of open channels in the attachment face. 
     Preferably, the channels are more than 50 microns wide and spaced from adjacent channels by more than 50 microns. 
     Preferably, the attachment face has recesses adjacent the channels to hold thermosetting adhesive displaced from between the attachment face and polyimide layer. 
     Preferably, the laminated film is sandwiched between two protective liners, the liner on the support member side of the laminated film being removed after laser drilling the opening but before the attachment of the support structure and the protective liner on the MST device side is removed prior to attaching the MST device. 
     Preferably, the protective liners are PET. 
     Preferably, the thermosetting adhesive layers are initially made tacky when the laminated film is first attached to the support member and the MST device and subsequently heated to their curing temperature. 
     Preferably, the thermosetting adhesive layers have different curing temperatures so that the laminated film is cured to the support member before the MST device is attached without the MST device side thermosetting adhesive curing until after the MST device is attached. 
     Preferably, the opening is formed before the laminated film is attached to the mounting surface of the support member. 
     Preferably, the MST device is a printhead IC and the support structure is a liquid crystal polymer (LCP) molding. 
     Preferably, the support structure has at least one fiducial marker on the mounting face and the array of openings is aligned with the array of outlet apertures using a vision system tracking a predetermined opening within the array of openings, relative to the at least one fiducial marker. 
     In a fifth aspect the present invention provides a method of attaching MST devices to a support member via an adhesive film, the MST devices each having an attachment face with a first aperture and the support member having a mounting surface with second apertures corresponding to each of the first apertures respectively and a fiducial marker for each of the MST devices respectively, and the adhesive film having a plurality of openings, the method comprising the steps of: 
     positioning the adhesive film using the fiducial marker and the corresponding opening such that the openings register with at least part of the second apertures in the mounting surface; 
     applying the adhesive film to the mounting surface; 
     positioning each of the MST devices relative to the respective openings; and, 
     attaching the MST devices with heat and pressure such that the openings establish the respective first and second apertures. 
     Instead of putting fiducial markers on both the film and the support member for alignment, the vision system use the fluid openings themselves. This is far more direct and precise as the fiducial markers on the film—usually very small holes—are prone to gross distortion and closing over when the film is heated prior to attachment. The openings are much larger features that suffer less distortion relative to their overall shape. Because the openings are large features, the vision system may need to determine a point on or within the opening, such a the centre, using any convenient technique for calculating this point for shapes that will have a degree of variance due to deformation. 
     Preferably, the adhesive film is a laminated film having a central web with a layer of the thermosetting adhesive on either side and an opening for fluid communication between the first aperture and the second aperture. 
     Preferably, the MST device has an array of inlet apertures in the attachment face connected to a plurality of first fluid conduits, the attachment face has an array of outlet apertures connected to a plurality of second fluid conduits and the laminated film has an array of openings for establishing fluid communication between corresponding apertures in the inlet and outlet arrays. 
     Preferably, the opening in the laminated film is laser drilled. 
     Preferably, the laminated film is drilled with a UV laser so as to not cure the thermosetting adhesive layers immediately adjacent the opening. 
     Preferably, the central web is a polyimide film. 
     Preferably, the polyimide film is more than 25 microns thick. 
     Preferably, the polyimide film about 50 microns thick. 
     Preferably, each of the thermosetting adhesive layers is more than 12 microns thick. 
     Preferably, each of the thermosetting adhesive layers are about 25 microns thick. 
     Preferably, the array of inlet apertures is a series of open channels in the attachment face. 
     Preferably, the channels are more than 50 microns wide and spaced from adjacent channels by more than 50 microns. 
     Preferably, the attachment face has recesses adjacent the channels to hold thermosetting adhesive displaced from between the attachment face and polyimide layer. 
     Preferably, the laminated film is sandwiched between two protective liners, the liner on the support member side of the laminated film being removed after laser drilling the opening but before the attachment of the support structure and the protective liner on the MST device side is removed prior to attaching the MST device. 
     Preferably, the protective liners are PET. 
     Preferably, the thermosetting adhesive layers are initially made tacky when the laminated film is first attached to the support member and the MST device and subsequently heated to their curing temperature. 
     Preferably, the thermosetting adhesive layers have different curing temperatures so that the laminated film is cured to the support member before the MST device is attached without the MST device side thermosetting adhesive curing until after the MST device is attached. 
     Preferably, the opening is formed before the laminated film is attached to the mounting surface of the support member. 
     Preferably, the MST devices are printhead ICs and the support structure is a liquid crystal polymer (LCP) molding. 
     Preferably, the laminated film is aligned with the fiducial markers on the support structure with a vision system that calculates a point on or within one of the opening in the array of openings for each MST device. 
     In a sixth aspect the present invention provides a MST device for attachment to an adhesive surface, the MST device comprising: 
     an attachment surface for abutting the adhesive surface; 
     a first fluid conduit connected to a first aperture in the attachment surface; and, 
     a recess in the attachment surface adjacent the first aperture to hold adhesive displaced from between the attachment surface and the adhesive surface when the MST device is attached such that displaced adhesive does not block fluid flow in the first conduit. 
     By profiling the attachment surface so there is a recess next to the first aperture, there is less risk that adhesive will be squeezed into the conduit and impair fluid flow. 
     Preferably, the MST device has an array of inlet apertures in the attachment face for connection to a plurality of first fluid conduits, the mounting face has an array of outlet apertures connected to a plurality of second fluid conduits and the attachment face further comprising an array of recesses interspersed with the array of inlet apertures. 
     Preferably, the array of inlet apertures is series of open channels in the attachment surface. 
     Preferably, the array of recesses is an arrangement of pits in the attachment surface. 
     Preferably, the channels are more than 50 microns wide and each separated by more than 50 microns of the attachment face. 
     Preferably, the channels are about 80 microns wide and separated by about 80 microns of attachment face. 
     Preferably, the pits are more than 5 microns wide and more than 5 microns deep. 
     Preferably, the adhesive is a thermosetting adhesive that cures at a predetermined temperature. 
     Preferably, the thermosetting adhesive has a maximum curing temperature of 150 degrees Celsius. 
     Preferably, the thermosetting adhesive are is more than 12 microns thick. 
     Preferably, the MST device is a printhead IC and the support structure is a liquid crystal polymer (LCP) molding. 
     Preferably, the thermosetting adhesive has a viscosity between 100 centiPoise and 10,000,000 centiPoise. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be described by way of example only, with reference to the preferred embodiments shown in the accompanying figures, in which: 
         FIG. 1  shows a front perspective view of a printer with paper in the input tray and the collection tray extended; 
         FIG. 2  shows the printer unit of  FIG. 1  (without paper in the input tray and with the collection tray retracted) with the casing open to expose the interior; 
         FIG. 3  shows a schematic of document data flow in a printing system according to one embodiment of the present invention; 
         FIG. 4  shows a more detailed schematic showing an architecture used in the printing system of  FIG. 3 ; 
         FIG. 5  shows a block diagram of an embodiment of the control electronics as used in the printing system of  FIG. 3 ; 
         FIG. 6  shows a perspective view of a cradle unit with open cover assembly and cartridge unit removed therefrom; 
         FIG. 7  shows the cradle unit of  FIG. 6  with the cover assembly in its closed position; 
         FIG. 8  shows a front perspective view of the cartridge unit of  FIG. 6 ; 
         FIG. 9  shows an exploded perspective view of the cartridge unit of  FIG. 8 ; 
         FIG. 10  shows an exploded front perspective view of the main body of the cartridge unit shown in  FIG. 9 ; 
         FIG. 11  shows a bottom perspective view of the ink storage module assembly that locates in the main body shown in  FIG. 9 ; 
         FIG. 12  shows an exploded perspective view of one of the ink storage modules shown in  FIG. 11 ; 
         FIG. 13  shows a bottom perspective view of an ink storage module shown in  FIG. 12 ; 
         FIG. 14  shows a top perspective view of an ink storage module shown in  FIG. 12 ; 
         FIG. 15  shows a top perspective view of the printhead assembly shown in  FIG. 9 ; 
         FIG. 16  shows an exploded view of the printhead assembly shown in  FIG. 15 ; 
         FIG. 17  shows an inverted exploded view of the printhead assembly shown in  FIG. 15 ; 
         FIG. 18A  shows a cross-sectional end view of the printhead assembly of  FIG. 15 ; 
         FIG. 18B  is a schematic sectional view of a known technique for attaching the printhead IC&#39;s to a support molding; 
         FIGS. 18C-18E  are schematic sectional views showing three embodiments of the printhead IC attached to the LCP molding in accordance with one aspect of the present invention; 
         FIG. 19  shows a magnified partial perspective view of the drop triangle end of a printhead integrated circuit module as shown in  FIGS. 16 to 18 ; 
         FIG. 20  shows a magnified perspective view of the join between two printhead integrated circuit modules shown in  FIGS. 16 to 19 ; 
         FIG. 21A  shows an underside view of the printhead integrated circuit shown in  FIG. 19 ; 
         FIG. 21B  shows an underside view of the printhead integrated circuit shown in  FIG. 19  with a series of recesses in its attachment face; 
         FIG. 22A  shows a transparent top view of a printhead assembly of  FIG. 15  showing in particular, the ink conduits for supplying ink to the printhead integrated circuits; 
         FIG. 22B  is a partial enlargement of  FIG. 28A ; 
         FIG. 23  is a partial schematic section view of the attachment of the printhead integrated circuit to the LCP moulding via the film; 
         FIG. 24  is a schematic partial section view of the laminate structure of the adhesive film prior to laser drilling; 
         FIG. 25  shows the laser drilling of the film pre-attachment; 
         FIG. 26  is a schematic partial section view of the laminate structure of the adhesive film during laser drilling; 
         FIG. 27  shows the attachment of the film to the LCP moulding; 
         FIG. 28  shows the attachment of the film to the printhead integrated circuits; 
         FIG. 29  shows a vertical sectional view of a single nozzle for ejecting ink, for use with the invention, in a quiescent state; 
         FIG. 30  shows a vertical sectional view of the nozzle of  FIG. 35  during an initial actuation phase; 
         FIG. 31  shows a vertical sectional view of the nozzle of  FIG. 36  later in the actuation phase; 
         FIG. 32  shows a perspective partial vertical sectional view of the nozzle of  FIG. 35 , at the actuation state shown in  FIG. 31 ; 
         FIG. 33  shows a perspective vertical section of the nozzle of  FIG. 29 , with ink omitted; 
         FIG. 34  shows a vertical sectional view of the of the nozzle of  FIG. 39 ; 
         FIG. 35  shows a perspective partial vertical sectional view of the nozzle of  FIG. 35 , at the actuation state shown in  FIG. 36 ; 
         FIG. 36  shows a plan view of the nozzle of  FIG. 35 ; 
         FIG. 37  shows a plan view of the nozzle of  FIG. 35  with the lever arm and movable nozzle removed for clarity; 
         FIG. 38  shows a perspective vertical sectional view of a part of a printhead chip incorporating a plurality of the nozzle arrangements of the type shown in  FIG. 35 ; 
         FIG. 39  shows a schematic cross-sectional view through an ink chamber of a single nozzle for injecting ink of a bubble forming heater element actuator type. 
         FIGS. 40A to 40C  show the basic operational principles of a thermal bend actuator; 
         FIG. 41  shows a three dimensional view of a single ink jet nozzle arrangement constructed in accordance with  FIG. 40 ; 
         FIG. 42  shows an array of the nozzle arrangements shown in  FIG. 41 ; 
         FIG. 43  shows a schematic showing CMOS drive and control blocks for use with the printer of the present invention; 
         FIG. 44  shows a schematic showing the relationship between nozzle columns and dot shift registers in the CMOS blocks of  FIG. 43 ; 
         FIG. 45  shows a more detailed schematic showing a unit cell and its relationship to the nozzle columns and dot shift registers of  FIG. 44 ; 
         FIG. 46  shows a circuit diagram showing logic for a single printer nozzle in the printer of the present invention; 
         FIG. 47  shows a front perspective view of the maintenance assembly of the cartridge unit shown in  FIG. 9 ; 
         FIG. 48  shows an exploded front perspective view of the maintenance assembly of  FIG. 47 ; 
         FIG. 49  shows an exploded front perspective view of the underside of the maintenance assembly of  FIG. 47 ; 
         FIG. 50  shows a sectional view of the maintenance assembly operationally mounted to the cartridge unit of the present invention in a capped state; 
         FIG. 51A and 51B  show front and rear perspective views of the frame structure of the cradle unit according to one embodiment of the present invention; 
         FIGS. 52A-52B  show left and right perspective views of the maintenance drive assembly of the present invention remote from the frame structure of  FIGS. 51A and 51B ; 
         FIG. 53  shows a perspective view of the support bar assembly of  FIGS. 51A and 51B  assembled to the PCB assembly; 
         FIG. 54  shows a perspective side view of the arms of the support bar assembly of  FIG. 53  connected to a spring element associated with the cover assembly; 
         FIGS. 55A-55C  show various views of the cradle unit according to one embodiment of the present invention; 
         FIGS. 56A and 56B  show sectional side views of the cradle unit with the cover assembly in a closed and open position respectively; 
         FIGS. 57A and 57B  show top and bottom perspective views of the ink refill unit according to one embodiment of the present invention; 
         FIG. 57C  shows an exploded view of the ink refill unit of  FIGS. 57A and 57B ; 
         FIG. 58  shows a perspective view of the ink refill unit of  FIGS. 57A and 57B  docked with the docking ports of the cover assembly; 
         FIG. 59  shows a plan view of the cradle with the cartridge inside and the cover closed; 
         FIG. 60A  shows a cross-sectional view of the ink refill unit and the print engine along line A-A of  FIG. 59 ; 
         FIG. 60B  shows a cross-sectional view of the ink refill unit and the print engine along line B-B of  FIG. 59 ; 
         FIG. 60C  shows a cross-sectional view of the ink refill unit in docking position with the print engine along line C-C of  FIG. 59 ; and 
         FIG. 60D  a cross-sectional view of the ink refill unit in docking position with the print engine along line D-D of  FIG. 59 . 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       FIG. 1  shows a printer unit  2  embodying the present invention. Media supply tray  3  supports and supplies media  8  to be printed by the print engine (concealed within the printer casing). Printed sheets of media  8  are fed from the print engine to a media output tray  4  for collection. User interface  5  is an LCD touch screen and enables a user to control the operation of the printer unit  2 . 
       FIG. 2  shows the lid  7  of the printer unit  2  open to expose the print engine  1  positioned in the internal cavity  6 . Picker mechanism  9  engages the media in the input tray  3  (not shown for clarity) and feeds individual streets to the print engine  1 . The print engine  1  includes media transport means that takes the individual sheets and feeds them past a printhead assembly (described below) for printing and subsequent delivery to the media output tray  4  (shown retracted). 
       FIG. 3  schematically shows how the printer unit  2  is arranged to print documents received from an. external source, such as a computer system  702 , onto a print media, such as a sheet of paper. In this regard, the printer unit  2  includes an electrical connection with the computer system  702  to receive pre-processed data. In the particular situation shown, the external computer system  702  is programmed to perform various steps involved in printing a document, including receiving the document (step  703 ), buffering it (step  704 ) and rasterizing it (step  706 ), and then compressing it (step  708 ) for transmission to the printer unit  2 . 
     The printer unit  2  according to one embodiment of the present invention, receives the document from the external computer system  702  in the form of a compressed, multi-layer page image, wherein control electronics  766  buffers the image (step  710 ), and then expands the image (step  712 ) for further processing. The expanded contone layer is dithered (step  714 ) and then the black layer from the expansion step is composited over the dithered contone layer (step  716 ). Coded data may also be rendered (step  718 ) to form an additional layer, to be printed (if desired) using an infrared ink that is substantially invisible to the human eye. The black, dithered contone and infrared layers are combined (step  720 ) to form a page that is supplied to a printhead for printing (step  722 ). 
     In this particular arrangement, the data associated with the document to be printed is divided into a high-resolution bi-level mask layer for text and line art and a medium-resolution contone color image layer for images or background colors. Optionally, colored text can be supported by the addition of a medium-to-high-resolution contone texture layer for texturing text and line art with color data taken from an image or from flat colors. The printing architecture generalises these contone layers by representing them in abstract “image” and “texture” layers which can refer to either image data or flat color data. This division of data into layers based on content follows the base mode Mixed Raster Content (MRC) mode as would be understood by a person skilled in the art. Like the MRC base mode, the printing architecture makes compromises in some cases when data to be printed overlap. In particular, in one form all overlaps are reduced to a 3-layer representation in a process (collision resolution) embodying the compromises explicitly. 
       FIG. 4  sets out the print data processing by the print engine controller  766 . As mentioned previously, data is delivered to the printer unit  2  in the form of a compressed, multi-layer page image with the pre-processing of the image performed by a mainly software-based computer system  702 . In turn, the print engine controller  766  processes this data using a mainly hardware-based system. 
     Upon receiving the data, a distributor  730  converts the data from a proprietary representation into a hardware-specific representation and ensures that the data is sent to the correct hardware device whilst observing any constraints or requirements on data transmission to these devices. The distributor  730  distributes the converted data to an appropriate one of a plurality of pipelines  732 . The pipelines are identical to each other, and in essence provide decompression, scaling and dot compositing functions to generate a set of printable dot outputs. 
     Each pipeline  732  includes a buffer  734  for receiving the data. A contone decompressor  736  decompresses the color contone planes, and a mask decompressor decompresses the monotone (text) layer. Contone and mask scalers  740  and  742  scale the decompressed contone and mask planes respectively, to take into account the size of the medium onto which the page is to be printed. 
     The scaled contone planes are then dithered by ditherer  744 . In one form, a stochastic dispersed-dot dither is used. Unlike a clustered-dot (or amplitude-modulated) dither, a dispersed-dot (or frequency-modulated) dither reproduces high spatial frequencies (i.e. image detail) almost to the limits of the dot resolution, while simultaneously reproducing lower spatial frequencies to their full color depth, when spatially integrated by the eye. A stochastic dither matrix is carefully designed to be relatively free of objectionable low-frequency patterns when tiled across the image. As such, its size typically exceeds the minimum size required to support a particular number of intensity levels (e.g. 16×16×8 bits for 257 intensity levels). 
     The dithered planes are then composited in a dot compositor  746  on a dot-by-dot basis to provide dot data suitable for printing. This data is forwarded to data distribution and drive electronics  748 , which in turn distributes the data to the correct nozzle actuators  750 , which in turn cause ink to be ejected from the correct nozzles  752  at the correct time in a manner which will be described in more detail later in the description. 
     As will be appreciated, the components employed within the print engine controller  766  to process the image for printing depend greatly upon the manner in which data is presented. In this regard it may be possible for the print engine controller  766  to employ additional software and/or hardware components to perform more processing within the printer unit  2  thus reducing the reliance upon the computer system  702 . Alternatively, the print engine controller  766  may employ fewer software and/or hardware components to perform less processing thus relying upon the computer system  702  to process the image to a higher degree before transmitting the data to the printer unit  2 . 
       FIG. 5  provides a block representation of the components necessary to perform the above mentioned tasks. In this arrangement, the hardware pipelines  732  are embodied in a Small Office Home Office Printer Engine Chip (SOPEC)  766 . As shown, a SoPEC device consists of  3  distinct subsystems: a Central Processing Unit (CPU) subsystem  771 , a Dynamic Random Access Memory (DRAM) subsystem  772  and a Print Engine Pipeline (PEP) subsystem  773 . 
     The CPU subsystem  771  includes a CPU  775  that controls and configures all aspects of the other subsystems. It provides general support for interfacing and synchronizing all elements of the print engine  1 . It also controls the low-speed communication to QA chips (described below). The CPU subsystem  771  also contains various peripherals to aid the CPU  775 , such as General Purpose Input Output (GPIO, which includes motor control), an Interrupt Controller Unit (ICU), LSS Master and general timers. The Serial Communications Block (SCB) on the CPU subsystem provides a full speed USB1.1 interface to the host as well as an Inter SoPEC Interface (ISI) to other SoPEC devices (not shown). 
     The DRAM subsystem  772  accepts requests from the CPU, Serial Communications Block (SCB) and blocks within the PEP subsystem. The DRAM subsystem  772 , and in particular the DRAM Interface Unit (DIU), arbitrates the various requests and determines which request should win access to the DRAM. The DIU arbitrates based on configured parameters, to allow sufficient access to DRAM for all requestors. The DIU also hides the implementation specifics of the DRAM such as page size, number of banks and refresh rates. 
     The Print Engine Pipeline (PEP) subsystem  773  accepts compressed pages from DRAM and renders them to bi-level dots for a given print line destined for a printhead interface (PHI) that communicates directly with the printhead. The first stage of the page expansion pipeline is the Contone Decoder Unit (CDU), Lossless Bi-level Decoder (LBD) and, where required, Tag Encoder (TE). The CDU expands the JPEG-compressed contone (typically CMYK) layers, the LBD expands the compressed bi-level layer (typically K), and the TE encodes any Netpage tags for later rendering (typically in IR or K ink), in the event that the printer unit  2  has Netpage capabilities (see the cross referenced documents for a detailed explanation of the Netpage system). The output from the first stage is a set of buffers: the Contone FIFO unit (CFU), the Spot FIFO Unit (SFU), and the Tag FIFO Unit (TFU). The CFU and SFU buffers are implemented in DRAM. 
     The second stage is the Halftone Compositor Unit (HCU), which dithers the contone layer and composites position tags and the bi-level spot layer over the resulting bi-level dithered layer. 
     A number of compositing options can be implemented, depending upon the printhead with which the SoPEC device is used. Up to 6 channels of bi-level data are produced from this stage, although not all channels may be present on the printhead. For example, the printhead may be CMY only, with K pushed into the CMY channels and IR ignored. Alternatively, any encoded tags may be printed in K if IR ink is not available (or for testing purposes). 
     In the third stage, a Dead Nozzle Compensator (DNC) compensates for dead nozzles in the printhead by color redundancy and error diffusing of dead nozzle data into surrounding dots. 
     The resultant bi-level 5 channel dot-data (typically CMYK, Infrared) is buffered and written to a set of line buffers stored in DRAM via a Dotline Writer Unit (DWU). 
     Finally, the dot-data is loaded back from DRAM, and passed to the printhead interface via a dot FIFO. The dot FIFO accepts data from a Line Loader Unit (LLU) at the system clock rate (pclk), while the PrintHead Interface (PHI) removes data from the FIFO and sends it to the printhead at a rate of ⅔ times the system clock rate. 
     In the preferred form, the DRAM is 2.5 Mbytes in size, of which about 2 Mbytes are available for compressed page store data. A compressed page is received in two or more bands, with a number of bands stored in memory. As a band of the page is consumed by the PEP subsystem  773  for printing, a new band can be downloaded. The new band may be for the current page or the next page. 
     Using banding it is possible to begin printing a page before the complete compressed page is downloaded, but care must be taken to ensure that data is always available for printing or a buffer under-run may occur. 
     The embedded USB 1.1 device accepts compressed page data and control commands from the host PC, and facilitates the data transfer to either the DRAM (or to another SoPEC device in multi-SoPEC systems, as described below). 
     Multiple SoPEC devices can be used in alternative embodiments, and can perform different functions depending upon the particular implementation. For example, in some cases a SoPEC device can be used simply for its onboard DRAM, while another SoPEC device attends to the various decompression and formatting functions described above. This can reduce the chance of buffer under-run, which can happen in the event that the printer commences printing a page prior to all the data for that page being received and the rest of the data is not received in time. Adding an extra SoPEC device for its memory buffering capabilities doubles the amount of data that can be buffered, even if none of the other capabilities of the additional chip are utilized. 
     Each SoPEC system can have several quality assurance (QA) devices designed to cooperate with each other to ensure the quality of the printer mechanics, the quality of the ink supply so the printhead nozzles will not be damaged during prints, and the quality of the software to ensure printheads and mechanics are not damaged. 
     Normally, each printing SoPEC will have an associated printer unit QA, which stores information relating to the printer unit attributes such as maximum print speed. The cartridge unit may also contain a QA chip, which stores cartridge information such as the amount of ink remaining, and may also be configured to act as a ROM (effectively as an EEPROM) that stores printhead-specific information such as dead nozzle mapping and printhead characteristics. The refill unit may also contain a QA chip, which stores refill ink information such as the type/colour of the ink and the amount of ink present for refilling. The CPU in the SoPEC device can optionally load and run program code from a QA Chip that effectively acts as a serial EEPROM. Finally, the CPU in the SoPEC device runs a logical QA chip (i.e., a software QA chip). 
     Usually, all QA chips in the system are physically identical, with only the contents of flash memory differentiating one from the other. 
     Each SoPEC device has two LSS system buses that can communicate with QA devices for system authentication and ink usage accounting. A large number of QA devices can be used per bus and their position in the system is unrestricted with the exception that printer QA and ink QA devices should be on separate LSS busses. 
     In use, the logical QA communicates with the ink QA to determine remaining ink. The reply from the ink QA is authenticated with reference to the printer QA. The verification from the printer QA is itself authenticated by the logical QA, thereby indirectly adding an additional authentication level to the reply from the ink QA. 
     Data passed between the QA chips is authenticated by way of digital signatures. In the preferred embodiment, HMAC-SHA1 authentication is used for data, and RSA is used for program code, although other schemes could be used instead. 
     As will be appreciated, the SoPEC device therefore controls the overall operation of the print engine  1  and performs essential data processing tasks as well as synchronising and controlling the operation of the individual components of the print engine  1  to facilitate print media handling, as will be discussed below. 
     Print Engine 
     The print engine  1  is shown in detail in  FIGS. 6 and 7  and consists of two main parts: a cartridge unit  10  and a cradle unit  12 . 
     The cartridge unit  10  is shaped and sized to be received within the cradle unit  12  and secured in position by a cover assembly  11  mounted to the cradle unit. The cradle unit  12  is in turn configured to be fixed within the printer unit  2  to facilitate printing as discussed above. 
       FIG. 7  shows the print engine  1  in its assembled form with cartridge unit  10  secured in the cradle unit  12  and cover assembly  11  closed. The print engine  1  controls various aspects associated with printing in response to user inputs from the user interface  5  of the printer unit  2 . These aspects include transporting the media past the printhead in a controlled manner and the controlled ejection of ink onto the surface of the passing media. 
     Cartridge Unit 
     The cartridge unit  10  is shown in detail in  FIGS. 8 and 9 . With reference to the exploded view of  FIG. 9 , the cartridge unit  10  generally consists of a main body  20 , an ink storage module assembly  21 , a printhead assembly  22  and a maintenance assembly  23 . 
     Each of these parts are assembled together to form an integral unit which combines ink storage means together with the ink ejection means. Such an arrangement ensures that the ink is directly supplied to the printhead assembly  22  for printing, as required, and should there be a need to replace either or both of the ink storage or the printhead assembly, this can be readily done by replacing the entire cartridge unit  10 . 
     However, the operating life of the printhead is not limited by the supply of ink. The top surface  42  of the cartridge unit  10  has interfaces  61  for docking with a refill supply of ink to replenish the ink storage modules  45  when necessary. The ink refill unit and the process of docking with the cartridge are discussed in greater detail below. To further extend the life of the printhead, the cartridge unit carries an integral printhead maintenance assembly  23  that caps, wipes and moistens the printhead. This assembly is also described in more detail later. 
     Main Body 
     The main body  20  of the cartridge unit  10  is shown in more detail in  FIG. 10  and comprises a substantially rectangular frame  25  having an open top and an open longitudinally extending side wall. A pair of posts  26  project from the underside of the frame at either end. These posts  26  are provided to mount the maintenance assembly  23  to the main body  10 , in a manner described below. 
     An ink outlet molding  27  has ink outlets (not shown) in its underside corresponding to each of the ink storage modules  45  to be housed in the main body  20 . Each of the ink outlets has a pair of inwardly extending silicone rings seals. The rings seals are co-molded with the ink outlet molding  27  and seal against the ink inlets to the printhead assembly described below. The ink outlet molding  27  is ultra sonically welded to the underside of the rectangular frame  25 . 
     Along one longitudinal wall of the frame  25  are a series of ink downpipes  30 . Each downpipe  30  has an O-ring seal  29  at its upper end to form a sealed connection with the ink outlet of respective ink storage modules (described below). When the ink outlet molding  27  is welded to the body  20 , each ink downpipe  30  is in fluid communication with respective ink outlets in the underside of the molding  27 . 
     The air sleeve  31  is connected to a pressurized air source (not shown) and provides an air flow into the printhead assembly where it is directed across the printhead nozzles to avoid paper dust clogging (discussed further below). 
     Ink filing ports  35  are formed in the lower parts of each ink downpipe  30 . These filling ports are for the initial charging of the ink storage assemblies  21  only. Any subsequent refilling of the ink storages assemblies, uses the ink refill units described below. To assist the initial filling process, a vacuum is applied to the air vents  41  in the top surface  42  of the cartridge unit  10  (see  FIG. 9 ). The air vents  41  are connected to the interior of the ink bag in each ink storage module  45  (described below). Ink is fed through the filling port  35  and drawn up the ink downpipe  30  into the ink storage volume. During the filling process, the cartridge unit is tilted so that the air vents  41  are the highest point in each of the respective ink bag, and filled until the vacuum draws ink through the air vent  41 . This ensures that each ink bag is completely filled and purged of air. Skilled workers in this field will appreciate that air bubbles entrained with the ink flow to the printhead can harm the operation of the nozzles. 
     As shown in  FIGS. 15 to 17 , the lower member  65  is provided with a plurality of priming inlets  85  at one end thereof. Each of the priming inlets  85  communicate directly with one of the channels  67  and provide an alternative, or additional means for priming the ink storage modules  45  with ink prior to shipment and use. 
     When the ink storage modules are full, a polymer sealing ball  33  is inserted into the filling port  35  and the air vent  41 . 
     A metal plate  34  mounts to the underside of the frame  25  and the outlet molding  30  to provide the cartridge unit  10  with structural rigidity. It is snap locked into place by hooking the detents  38  into slots (not shown) in the back wall of the frame  25  and rotating the plate  34  until the line of barbed snap lock formations  32  clip into the outer line of apertures  37 . 
     The plate  34  has holes  39  to receive the ink outlets (not shown) that project from the lower surface of the outlet molding  27 . The pressed metal plate  34  also has a flange portion  40  projecting downwardly with respect to the frame  25 , which acts as a load bearing surface discussed in more detail below. 
     The ink storage assembly lid  21  of the cartridge unit  10  is shown in detail in  FIGS. 11 to 14 . The lid  21  is configured to mate with the frame  25  of the main body  20  to form an enclosed unit. As best shown in  FIG. 11 , the ink storage modules  45  are mounted to the underside of the lid  21  and extend into the individual cavities  36  provided by the main body  20  (see  FIG. 10 ). 
     One of the ink storage modules  45  is shown in isolation in  FIG. 12 ,  13  and  14 . Ink bag  46  is made from a flexible, air impermeable thermoplastic film such as Mylar® which allows ink to be retained therein in a pressurised state. The flexible bag  46  can expand as it is filled with ink and collapse as ink is consumed. This is discussed in more detail later with reference to the refilling process shown in  FIGS. 60A to 60D . 
     The ink bag  46  extends between an upper plate member  47  and a lower plate member  48 . It is heat welded (or similar) to the plates  47  and  48  for an air tight seal. The upper plate member  47  is arranged to receive a valve insert  49 . The valve insert has an inlet valve  18  and an outlet valve  17 . The valve insert  49  is positioned such that it can communicate directly with a port  51  formed in the top surface  42  to receive ink from an ink refill unit, as well as an outlet  52  to deliver ink to the printhead assembly  22 . As best shown in  FIG. 14 , the inlet valve  15  receives the ink delivery needle of an ink refill unit (discussed later) through a slit positioned in the port  51  in the upper surface  42 . The inlet valve  18  is biased closed and opens when the refill unit (described below) docks with the cartridge unit  10 . 
     Conversely, the outlet valve  18  is biased open and closes when the refill unit docks. A filter  215  covers the entrance to the outlet valve in the upper plate member  47 . The filter is sized to remove solid contaminants and air bubbles. As discussed above, compressible air bubbles can prevent a nozzle from operating. 
     The outlet valve connects to a conduit  52  in the underside of the lid  21  which leads to the downpipe collar  216 . When the ink storage assembly  21  is placed into the main body  20 , the collar  216  seals over the O-ring seal  29  on the end of the downpipe  30 . 
     The upper plate  47  is fixed to the underside of the lid  21  to hold the valve insert  49  in position. The lower plate  48  slides within the collar  57  and the inside edges of the four struts  19  extending from the underside of the lid  21 . The plate  48  slides down the struts  19  as the bag  46  fills and expands. Conversely, it slides back towards the lid  21  as the bag  21  empties. The length of the bag  46  limits the travel of the lower plate  48  before it reaches the retaining bar  55 . A constant force spring  54  extends between the retaining bar  55  and the recessed peg  59  to bias the plate  48  towards the retaining bar  55 . In turn, this biases the bag  46  to expand and thereby maintains the ink within the bag at a negative pressure. This avoids ink leakage from the printhead nozzles. 
     Bag Constrictor. 
     Each ink storage module  45  has a bag constrictor  43  to re-establish the negative pressure in the ink after each refilling operation. The constrictor  43  has a lower collar  57  that abuts the ends of the struts  19  and is held in place by the retaining bar  55 . The lower plate  48  slides upwardly within lower collar  57  as the ink bag  46  empties. Four bowed panels  58  extend upwardly from the lower collar  57  to an upper collar  59 . The panels  58  bow slightly inwards. The ink refill unit (described below) has four constrictor actuators. When the refill docks with the cartridge unit, the constrictor actuators extend through the apertures  60  in the lid  21  to push the upper collar  59  towards the lower collar  57 . This causes the panels  58  to bow further inwards to press on each side of the bag  46 . 
     During refilling, the negative pressure in the ink bag  46  draws ink out of the refill unit. The negative pressure is created by the constant force spring  54  biasing the lower plate  48  to wards the retainer bar  55 . When the ink bag is full, the negative pressure disappears. Without negative pressure in the ink bag  46 , there is a risk of ink leakage from the nozzles. The negative pressure is re-established in the bag  46  when the refill unit is removed from the cartridge. As the four constrictor actuators retract through the apertures  60  in the lid  21 , the bowed panels  58  can push the upper collar  59  back towards the upper plate member  47 . The panels  58  straighten so that they are not pressing on the sides of the bag  46  as much. This allows the bag  46  to bulge slightly, and as the inlet valve  18  is closed, the slight increase in bag volume restores the negative pressure. 
     Printhead Assembly 
     The printhead assembly  22  is shown in more detail in  FIGS. 15 to 18E , and is adapted to be attached to the underside of the main body  20  to receive ink from the outlets molding  27  (see  FIG. 10 ). 
     The printhead assembly  22  generally comprises an elongate upper member  62  which is configured to extends beneath the main body  20 , between the posts  26 . A plurality of U-shaped clips  63  project from the upper member  62 . These pass through the recesses  37  provided in the rigid plate  34  and become captured by lugs (not shown) formed in the main body  20  to secure the printhead assembly  22 . 
     The upper element  62  has a plurality of feed tubes  64  that are received within the outlets in the outlet molding  27  when the printhead assembly  22  secures to the main body  20 . The feed tubes  64  may be provided with an outer coating to guard against ink leakage. 
     The upper member  62  is made from a liquid crystal polymer (LCP) which offers a number of advantages. It can be molded so that its coefficient of thermal expansion (CTE) is similar to that of silicon. It will be appreciated that any significant difference in the CTE&#39;s of the printhead integrated circuit  74  (discussed below) and the underlying moldings can cause the entire structure to bow. However, as the CTE of LCP in the mold direction is much less than that in the non- mold direction (−5 ppm/° C. compared to −20 ppm/° C.), care must be take to ensure that the mold direction of the LCP moldings is unidirectional with the longitudinal extent of the printhead integrated circuit (IC)  74 . LCP also has a relatively high stiffness with a modulus that is typically 5 times that of ‘normal plastics’ such as polycarbonates, styrene, nylon, PET and polypropylene. 
     As best shown in  FIG. 16 , upper member  62  has an open channel configuration for receiving a lower member  65 , which is bonded thereto, via an adhesive film  66 . The lower member  65  is also made from an LCP and has a plurality of ink channels  67  formed along its length. Each of the ink channels  67  receive ink from one of the feed tubes  64 , and distribute the ink along the length of the printhead assembly  22 . The channels are 1 mm wide and separated by 0.75 mm thick walls. 
     In the embodiment shown, the lower member  65  has five channels  67  extending along its length. Each channel  67  receives ink from only one of the five feed tubes  64 , which in turn receives ink from one of the ink storage modules  45  (see  FIG. 10 ) to reduce the risk of mixing different coloured inks. In this regard, adhesive film  66  also acts to seal the individual ink channels  67  to prevent cross channel mixing of the ink when the lower member  65  is assembled to the upper member  62 . 
     In the bottom of each channel  67  are a series of equi-spaced holes  69  (best seen in  FIG. 17 ) to give five rows of holes  69  in the bottom surface of the lower member  65 . The middle row of holes  69  extends along the centre-line of the lower member  65 , directly above the printhead IC  74 . As best seen in  FIG. 22A , other rows of holes  69  on either side of the middle row need conduits  70  from each hole  69  to the centre so that ink can be fed to the printhead IC  74 . 
     Referring to  FIG. 18A , the printhead IC  74  is mounted to the underside of the lower member  65  by a polymer sealing film  71 . This film may be a thermoplastic film such as a PET or Polysulphone film, or it may be in the form of a thermoset film, such as those manufactured by AL Technologies, Rogers Corporation or Ablestik (a subsidiary of Nation Starch &amp; Chemical Company). The polymer sealing film  71  is a laminate with adhesive layers on both sides of a central film, and laminated onto the underside of the lower member  65 . A particularly effective film is the Ablestik 5205 SI and its structure is schematically shown in  FIG. 24 . The central polyimide web  222  is sandwiched between thermosetting adhesive layers  220  and  224 . The outer surfaces of the thermosetting adhesive layers are protected by PET liners  234  and  236 . Mylar liners would also be suitable. 
       FIGS. 17 ,  22 A and  22 B, show the pattern of holes  72  laser drilled through the adhesive film  71  to coincide with the centrally disposed ink delivery points (the middle row of holes  69  and the ends of the conduits  70 ) for fluid communication between the printhead IC  74  and the channels  67 .  FIGS. 25 and 26  schematically show the laser ablation process in more detail. The laminated film  71  is fed from reel  240 , past the laser  238 , and spooled onto reel  242 . The laser is an excimer laser which uses UV light so that the thermosetting adhesive does not cure and harden. If the adhesive hardens before the printhead IC  74  or the LCP moulding  65  is attached, the seal may be compromised. Lasers that use longer wavelength light are more likely heat the adhesive above its curing temperature.  FIG. 26  shows a hole  72  drilled by the laser. The hole  72  is a blind hole that terminates somewhere in the lower PET liner  236 . Keeping the lower PET liner unbroken helps to keep contaminants out of the hole  72 . The upper PET liner  234  collects some of the ablated material  244  removed from the hole  72  by the laser  238 . Removing the liner immediately prior to attaching the film to the LCP moulding  65  removes the ablated material  244  and any other detritus that may affect the fluid seal. 
       FIG. 27  shows the attachment of the film  71  to the LCP moulding  65 . The laser drilled film  71  is fed from the reel  242  to the LCP moulding  65 . As the LCP moulding is a relatively long polymer moulding, it is not very straight because of the inherent material weakness and the moulding process. The moulding is gripped and held straight while the film is attached. A heated die  246  softens, but does not cure, the thermosetting adhesive so that it tacky. A vision system (not shown) aligns the film  71  so that the appropriate holes  72  are at least partially in registration with the ends of the ink conduits  70  etched into the moulding  65  (see  FIG. 22B ). This can be done using fiducial markings on both the LCP moulding  65  and the film  71  or by using a vision system that references to predetermined features of both the moulding and/or the film. This can be particularly useful for the film as the heating process can often cause gross deformation or removal of the fiducial marks (typically very small holes). If the vision system looks for one or more predetermined holes  72  in the pattern of drilled holes, the alignment with the ink conduits  70  is more direct and accurate. The relative deformation of the ink holes  72  is less because they are physically much larger but the vision system can use a simple geometric technique to calculate a centre point, and then reference to that. The PET liner  236  is peeled away before attachment, and reciprocating knives  248  trim the film to size after attachment. 
     Drilling the holes in the film  71  before it is attached to the LCP moulding is faster and more reliable than attaching the film to the moulding and then drilling. Drilling the film when it is attached to the moulding needs to be carefully controlled so that the hole extend completely through the film, but there is no overdrilling where a part of the underlying LCP is ablated by the laser. Ablated LCP easily lodges in the holes  72  and causes flow blockages. 
     Turning to  FIG. 28 , the individual printhead ICs  74  are sequentially attached to the film  71 . Heated die  260  holds each printhead IC  74  and attaches it to the film  71  once the vision system  262  has aligned it with the previously attached printhead IC  74  and the holes  72 . The LCP moulding.  65  is no longer held straight because the deviation from exactly straight in the LCP moulding between one end of a printhead IC and the other is within acceptable tolerances. As discussed above, the vision system can reference to fiducials or it may reference to predetermined points on one or more of the holes  72  in the film  71 . The PET liner  234  is peeled away immediately prior to attachment to avoid contamination. Again the die  260  heats the thermosetting adhesive  220  (through the printhead IC  74 ) until it is tacky but not cured. Only when the series of printhead ICs  74  are stuck to the LCP moulding  65  via the film  71 , is it finally cured by raising the temperature above the known curing temperature. 
     Alternatively, the film can use thermosetting adhesive layers with different curing temperatures. By giving the layer  224  a lower curing temperature than the layer  220 , the film can be attached and cured to the LCP moulding  65  before the printhead ICs  74  are attached and cured. Thermosetting adhesives provide a more reliable fluid seal than a thermoplastic film. A thermoplastic film is heated and softened so the printhead IC and LCP moulding can embed into the surface of the film. After the film cools, it attaches to the LCP with an essentially mechanical bond. This is prone to fail and leak with prolonged thermal fatigue during operation. The thermosetting resin adhesive cures to form a strong bond with the surface of the printhead IC that withstands the differential thermal expansions within the printhead assembly. 
       FIG. 23  is a schematic partial section of the LCP moulding attached to the printhead IC via the polymer film as shown in  FIG. 22A . Ink flows through the conduits  70  in the underside of the LCP moulding  65 . The open channels  70  are sealed by the thermosetting adhesive layer  224  and the inner ends of the channels  70  align with the holes  72  through the film. It is important to get the viscosity of the thermosetting adhesive low enough to allow the printhead IC and the LCP moulding to adequately embed into the film surface, but no so low as to allow the adhesive to bulge into the fluid conduits to the extent that it causes a blockage or harmful constriction. However, a small amount of adhesive sagging or ‘tenting’ (see  228 ,  230  and  232  of  FIG. 23 ) into the fluid channels is necessary for proper bonding and is not detrimental to ink flow. Therefore the adhesive viscosity range that provides a reliable seal without flow constriction will also depend on the dimensions and configuration of the apertures in the MST device and the support. Thermosetting adhesives with a viscosity between 100 centiPoise and 10,000,000 centiPoise will seal micron-scale apertures of MST devices. Deeper and wider apertures can use adhesives with viscosities at the lower end of the range and smaller, shallower apertures need adhesives with a higher viscosity. 
     The printhead IC  74  has inlet apertures in the form of distribution channels  77 . These channels distribute ink to the inlets  226  leading to each individual nozzle (not shown). While  FIG. 24  is not to scale, it will be appreciated from  FIG. 22A  that the distribution channels  77  are much smaller than the supply conduits  70  in the LCP moulding  65 . Hence the channels  77  are more prone to clogging or constriction by adhesive displaced from between the carrier web  22  and upper face of the IC  74 . To avoid this, recesses can be formed in the attachment surface of the printhead IC to hold ink that would otherwise be squeezed into the channels  77 . As shown in  FIG. 21B , these recesses may be a series of pits  264  about 10 microns in diameter and 5 microns deep extending along both sides of the 80 micron wide channels, spaced apart by 80 microns. The added texture and relief they give the attachment surface also aids the adhesion to the film  71 . 
     The thickness of the polymer sealing film  71  is critical to the effectiveness of the ink seal it provides. As best seen in  FIGS. 21A to 22B , the polymer sealing film seals the etched channels  77  on the reverse side of the printhead IC  74 , as well as the conduits  70  on the other side of the film. However, as the film  71  seals across the open end of the conduits  70 , it can also bulge or sag into the conduit. The section of film that sags into a conduit  70  runs across several of the etched channels  77  in the printhead IC  74 . The sagging may cause a gap between the walls separating each of the etched channels  77 . Obviously, this breaches the seal and allows ink to leak out of the printhead IC  74  and or between etched channels  77 . 
     To guard against this, the polymer sealing film  71  should be thick enough to account for any sagging into the conduits  70  while maintaining the seal over the etched channels  77 . The minimum thickness of the polymer sealing film  71  will depend on: 
     the width of the conduit into which it sags; 
     the thickness of the adhesive layers in the film&#39;s laminate structure; 
     the ‘stiffness’ of the adhesive layer as the printhead IC  74  is being pushed into it; and, 
     the modulus of the central film material of the laminate. 
     A polymer sealing film  71  thickness of 25 microns is adequate for the printhead assembly  22  shown. However, increasing the thickness to 50, 100 or even 200 microns will correspondingly increase the reliability of the seal provided. In the Ablestik laminate described above, the thermosetting layers are 25 microns thick and the polyimide carrier web is 50 microns thick. The PET or mylar liners are typically one 12 microns thick. 
     Ink delivery inlets  73  are formed in the ‘front’ surface of a printhead IC  74 . The inlets  73  supply ink to respective nozzles  801  (described below with reference to  FIGS. 35 to 36 ) positioned on the inlets. The ink must be delivered to the IC&#39;s so as to supply ink to each and every individual inlet  73 . Accordingly, the inlets  73  within an individual printhead IC  74  are physically grouped to reduce ink supply complexity and wiring complexity. They are also grouped logically to minimize power consumption and allow a variety of printing speeds. 
     Each printhead IC  74  is configured to receive and print five different colours of ink (C, M, Y, K and IR) and contains 1280 ink inlets per colour, with these nozzles being divided into even and odd nozzles (640 each). Even and odd nozzles for each colour are provided on different rows on the printhead IC  74  and are aligned vertically to perform true 1600 dpi printing, meaning that nozzles  801  are arranged in 10 rows, as clearly shown in  FIG. 19 . The horizontal distance between two adjacent nozzles  801  on a single row is 31.75 microns, whilst the vertical distance between rows of nozzles is based on the firing order of the nozzles, but rows are typically separated by an exact number of dot lines, plus a fraction of a dot line corresponding to the distance the paper will move between row firing times. Also, the spacing of even and odd rows of nozzles for a given colour must be such that they can share an ink- channel, as will be described below. 
     Production Method 
     Various aspects of the production process discussed below with reference to the schematic sectional views shown in  FIGS. 18B-18E . One known technique is shown in  FIG. 18B . The polyimide film is removed from one end of the flex PCB  79  to expose the conductive tracks  200 . The tracks  200  are spaced so that they are in registration with a line of bond pads on the printhead IC  74 . The tracks  74  are then directly connected to the bond pads. This technique is commonly known as ‘TAB bonding’ and requires the flex PCB to be very accurate as well as a high degree of precision when aligning the flex PCB and the bond pads. Consequently, this can be a time consuming stage of the overall printhead production process. It also requires the support molding  65  to have a stepped section  204  to support the flex PCB  79  at the height of the printhead IC  74 . The stepped section  204  is an added design complexity. 
     This aspect of the present invention attaches both the printhead IC  74  and the flex PCB  79  (or at least the conductive tracks  200 ) to the support molding  65  with the polymer film  71  before wiring  206  the conductive tracks  200  to the printhead IC  74 . Attaching both the printhead IC and the flex PCB to the support member with a polymer film is a relatively quick and simple step as the highly precise alignment of the tracks and the bond pads is not critical. The subsequent wiring of the flex PCB to the bond pads can be done by automated equipment that optically locates the tracks and their corresponding bond pad on the printhead IC. Small inaccuracies in the registration of the tracks and the bond pads will not prevent the flex PCB from connecting to the printhead IC, especially long IC&#39;s used in pagewidth printhead. As a result the overall process is more time efficient and commercially practical. 
       FIG. 18C-18E  show different options for the flex PCB and IC attachment that all use the same basic technique of the present invention. In  FIG. 18C , the flex PCB  79  is attached to the polymer film  71  after the printhead IC  74  is attached. To do this, the flex PCB  79  has an adhesive area  208  to attach to the polymer film  71  because the polymer film  71  cools, hardens and loses its own adhesive qualities after the printhead IC  74  attachment process. With the flex PCB and the IC attached, the wire connections  206  are made and the protective encapsulator  202  added. 
     In  FIG. 18D , the printhead IC  74  and the flex PCB  79  are simultaneously attached to the support molding  65  via the polymer film  71 . This is quicker than attaching the flex and IC separately, but more complex.  FIG. 18E  shows a much simpler version where the conductive tracks are incorporated into the polymer film  71 . As discussed above, the polymer film  71  is a laminate so the tracks can be positioned between the layers. In this form, the polymer film effectively becomes the flex PCB. This option is quick and simple but the polymer film with incorporated tracks is not an ‘off the shelf’ product. 
     For context,  FIGS. 18C-18E  show the upper member  62  and lower member  65  of the LCP molding, the individual ink channels  67 , the ink holes  69 , the conduits  70  and the laser drilled holes  72  discussed in detail above. 
     As alluded to previously, the present invention is related to page-width printing and as such the printhead ICs  74  are arranged to extend horizontally across the width of the printhead assembly  22 . To achieve this, individual printhead ICs  74  are linked together in abutting arrangement across the surface of the polymer film  71 , as shown in  FIGS. 16 and 17 . The printhead IC&#39;s  74  may be attached to the polymer sealing film  71  by heating the IC&#39;s above the melting point of the adhesive layer and then pressing them into the sealing film  71 , or melting the adhesive layer of the film  71  under the IC with a laser before pressing it into the film. Another option is to both heat the IC (not above the adhesive melting point) and the adhesive layer, before pressing it into the film  71 . 
     As discussed above, the flex PCB can have an adhesive area for attachment to the polymer film  71 , or a heated bar can press the flex onto the polymer film for a predetermine time. 
     Printhead Linking 
     The length of an individual printhead IC  74  is around 20-22 mm. To print an A4/US letter sized page, 11-12 individual printhead ICs  74  are contiguously linked together. The number of individual printhead ICs  74  may be varied to accommodate sheets of other widths. 
     The printhead ICs  74  may be linked together in a variety of ways. One particular manner for linking the ICs  74  is shown in  FIG. 20 . In this arrangement, the ICs  74  are shaped at their ends to link together to form a horizontal line of ICs, with no vertical offset between neighboring ICs. A sloping join is provided between the ICs having substantially a 45° angle. The joining edge is not straight and has a sawtooth profile to facilitate positioning, and the ICs  74  are intended to be spaced about 11 microns apart, measured perpendicular to the joining edge. In this arrangement, the left most ink delivery nozzles  73  on each row are dropped by 10 line pitches and arranged in a triangle configuration. This arrangement provides a degree of overlap of nozzles at the join and maintains the pitch of the nozzles to ensure that the drops of ink are delivered consistently along the printing zone. This arrangement also ensures that more silicon is provided at the edge of the IC  74  to ensure sufficient linkage. Whilst control of the operation of the nozzles is performed by the SoPEC device (discussed later in the description), compensation for the nozzles may be performed in the printhead, or may also be performed by the SoPEC device, depending on the storage requirements. In this regard it will be appreciated that the dropped triangle arrangement of nozzles disposed at one end of the IC  74  provides the minimum on-printhead storage requirements. However where storage requirements are less critical, shapes other than a triangle can be used, for example, the dropped rows may take the form of a trapezoid. 
     The upper surface of the printhead ICs have a number of bond pads  75  provided along an edge thereof which provide a means for receiving data and or power to control the operation of the nozzles  73  from the SoPEC device. To aid in positioning the ICs  74  correctly on the surface of the adhesive layer  71  and aligning the ICs  74  such that they correctly align with the holes  72  formed in the adhesive layer  71 , fiducials  76  are also provided on the surface of the ICs  74 . The fiducials  76  are in the form of markers that are readily identifiable by appropriate positioning equipment to indicate the true position of the IC  74  with respect to a neighbouring IC and the surface of the adhesive layer  71 , and are strategically positioned at the edges of the ICs  74 , and along the length of the adhesive layer  71 . 
     In order to receive the ink from the holes  72  formed in the polymer sealing film  71  and to distribute the ink to the ink inlets  73 , the underside of each printhead IC  74  is configured as shown in  FIG. 21 . A number of etched channels  77  are provided, with each channel  77  in fluid communication with a pair of rows of inlets  73  dedicated to delivering one particular colour or type of ink. The channels  77  are about 80 microns wide, which is equivalent to the width of the holes  72  in the polymer sealing film  71 , and extend the length of the IC  74 . The channels  77  are divided into sections by silicon walls  78 . Each sections is directly supplied with ink, to reduce the flow path to the inlets  73  and the likelihood of ink starvation to the individual nozzles  801 . In this regard, each section feeds approximately 128 nozzles  801  via their respective inlets  73 . 
       FIG. 22B  shows more clearly how the ink is fed to the etched channels  77  formed in the underside of the ICs  74  for supply to the nozzles  73 . As shown, holes  72  formed through the polymer sealing film  71  are aligned with one of the channels  77  at the point where the silicon wall  78  separates the channel  77  into sections. The holes  72  are about 80 microns in width which is substantially the same width of the channels  77  such that one hole  72  supplies ink to two sections of the channel  77 . It will be appreciated that this halves the density of holes  72  required in the polymer sealing film  71 . 
     Following attachment and alignment of each of the printhead ICs  74  to the surface of the polymer sealing film  71 , a flex PCB  79  (see  FIG. 18 ) is attached along an edge of the ICs  74  so that control signals and power can be supplied to the bond pads  75  to control and operate the nozzles  801 . As shown more clearly in  FIG. 15 , the flex PCB  79  extends from the printhead assembly  22  and folds around the printhead assembly  22 . 
     The flex PCB  79  may also have a plurality of decoupling capacitors  81  arranged along its length for controlling the power and data signals received. As best shown in  FIG. 16 , the flex PCB  79  has a plurality of electrical contacts  180  formed along its length for receiving power and or data signals from the control circuitry of the cradle unit  12 . A plurality of holes  80  are also formed along the distal edge of the flex PCB  79  which provide a means for attaching the flex PCB to the flange portion  40  of the rigid plate  34  of the main body  20 . The manner in which the electrical contacts of the flex PCB  79  contact the power and data contacts of the cradle unit  12  will be described later. 
     As shown in  FIG. 18A , a media shield  82  protects the printhead ICs  74  from damage which may occur due to contact with the passing media. The media shield  82  is attached to the upper member  62  upstream of the printhead ICs  74  via an appropriate clip-lock arrangement or via an adhesive. When attached in this manner, the printhead ICs  74  sit below the surface of the media shield  82 , out of the path of the passing media. 
     A space  83  is provided between the media shield  82  and the upper  62  and lower  65  members which can receive pressurized air from an air compressor or the like. As this space  83  extends along the length of the printhead assembly  22 , compressed air can be supplied to the space  56  from either end of the printhead assembly  22  and be evenly distributed along the assembly. The inner surface of the media shield  82  is provided with a series of fins  84  which define a plurality of air outlets evenly distributed along the length of the media shield  82  through which the compressed air travels and is directed across the printhead ICs  74  in the direction of the media delivery. This arrangement acts to prevent dust and other particulate matter carried with the media from settling on the surface of the printhead ICs, which could cause blockage and damage to the nozzles. 
     Ink Delivery Nozzles 
     One example of a type of ink delivery nozzle arrangement suitable for the present invention, comprising a nozzle and corresponding actuator, will now be described with reference to  FIGS. 35 to 38 .  FIG. 38  shows an array of ink delivery nozzle arrangements  801  formed on a silicon substrate  8015 . Each of the nozzle arrangements  801  are identical, however groups of nozzle arrangements  801  are arranged to be fed with different colored inks or fixative. In this regard, the nozzle arrangements are arranged in rows and are staggered with respect to each other, allowing closer spacing of ink dots during printing than would be possible with a single row of nozzles. Such an arrangement makes it possible to provide a high density of nozzles, for example, more than 5000 nozzles arrayed in a plurality of staggered rows each having an interspacing of about 32 microns between the nozzles in each row and about 80 microns between the adjacent rows. The multiple rows also allow for redundancy (if desired), thereby allowing for a predetermined failure rate per nozzle. 
     Each nozzle arrangement  801  is the product of an integrated circuit fabrication technique. In particular, the nozzle arrangement  801  defines a micro systems technology (MST). 
     For clarity and ease of description, the construction and operation of a single nozzle arrangement  801  will be described with reference to  FIGS. 35 to 37 . 
     The ink jet printhead integrated circuit  74  includes a silicon wafer substrate  8015  having 0.35 micron 1 P4M 12 volt CMOS microprocessing electronics is positioned thereon. 
     A silicon dioxide (or alternatively glass) layer  8017  is positioned on the substrate  8015 . The silicon dioxide layer  8017  defines CMOS dielectric layers. CMOS top-level metal defines a pair of aligned aluminium electrode contact layers  8030  positioned on the silicon dioxide layer  8017 . Both the silicon wafer substrate  8015  and the silicon dioxide layer  8017  are etched to define an ink inlet channel  8014  having a generally circular cross section (in plan). An aluminium diffusion barrier  8028  of CMOS metal  1 , CMOS metal  2 / 3  and CMOS top level metal is positioned in the silicon dioxide layer  8017  about the ink inlet channel  8014 . The diffusion barrier  8028  serves to inhibit the diffusion of hydroxyl ions through CMOS oxide layers of the drive electronics layer  8017 . 
     A passivation layer in the form of a layer of silicon nitride  8031  is positioned over the aluminium contact layers  8030  and the silicon dioxide layer  8017 . Each portion of the passivation layer  8031  positioned over the contact layers  8030  has an opening  8032  defined therein to provide access to the contacts  8030 . 
     The nozzle arrangement  801  includes a nozzle chamber  8029  defined by an annular nozzle wall  8033 , which terminates at an upper end in a nozzle roof  8034  and a radially inner nozzle rim  804  that is circular in plan. The ink inlet channel  8014  is in fluid communication with the nozzle chamber  8029 . At a lower end of the nozzle wall, there is disposed a moving rim  8010 , that includes a moving seal lip  8040 . An encircling wall  8038  surrounds the movable nozzle, and includes a stationary seal lip  8039  that, when the nozzle is at rest as shown in  FIG. 38 , is adjacent the moving rim  8010 . A fluidic seal  8011  is formed due to the surface tension of ink trapped between the stationary seal lip  8039  and the moving seal lip  8040 . This prevents leakage of ink from the chamber whilst providing a low resistance coupling between the encircling wall  8038  and the nozzle wall  8033 . 
     As best shown in  FIG. 36 , a plurality of radially extending recesses  8035  is defined in the roof  8034  about the nozzle rim  804 . The recesses  8035  serve to contain radial ink flow as a result of ink escaping past the nozzle rim  804 . 
     The nozzle wall  8033  forms part of a lever arrangement that is mounted to a carrier  8036  having a generally U-shaped profile with a base  8037  attached to the layer  8031  of silicon nitride. 
     The lever arrangement also includes a lever arm  8018  that extends from the nozzle walls and incorporates a lateral stiffening beam  8022 . The lever arm  8018  is attached to a pair of passive beams  806 , formed from titanium nitride (TiN) and positioned on either side of the nozzle arrangement, as best shown in  FIG. 38 and 37 . The other ends of the passive beams  806  are attached to the carrier  8036 . 
     The lever arm  8018  is also attached to an actuator beam  807 , which is formed from TiN. It will be noted that this attachment to the actuator beam is made at a point a small but critical distance higher than the attachments to the passive beam  806 . 
     As best shown in  FIGS. 35 and 35 , the actuator beam  807  is substantially U-shaped in plan, defining a current path between the electrode  809  and an opposite electrode  8041 . Each of the electrodes  809  and  8041  are electrically connected to respective points in the contact layer  8030 . As well as being electrically coupled via the contacts  809 , the actuator beam is also mechanically anchored to anchor  808 . The anchor  808  is configured to constrain motion of the actuator beam  807  to the left of  FIGS. 38 to 28  when the nozzle arrangement is in operation. 
     The TiN in the actuator beam  807  is conductive, but has a high enough electrical resistance that it undergoes self-heating when a current is passed between the electrodes  809  and  8041 . No current flows through the passive beams  806 , so they do not expand. 
     In use, the device at rest is filled with ink  8013  that defines a meniscus  803  under the influence of surface tension. The ink is retained in the chamber  8029  by the meniscus, and will not generally leak out in the absence of some other physical influence. 
     As shown in  FIG. 36 , to fire ink from the nozzle, a current is passed between the contacts  809  and  8041 , passing through the actuator beam  807 . The self-heating of the beam  807  due to its resistance causes the beam to expand. The dimensions and design of the actuator beam  807  mean that the majority of the expansion in a horizontal direction with respect to  FIGS. 35 to 37 . The expansion is constrained to the left by the anchor  808 , so the end of the actuator beam  807  adjacent the lever arm  8018  is impelled to the right. 
     The relative horizontal inflexibility of the passive beams  806  prevents them from allowing much horizontal movement the lever arm  8018 . However, the relative displacement of the attachment points of the passive beams and actuator beam respectively to the lever arm causes a twisting movement that causes the lever arm  8018  to move generally downwards. The movement is effectively a pivoting or hinging motion. However, the absence of a true pivot-point means that the rotation is about a pivot region defined by bending of the passive beams  806 . 
     The downward movement (and slight rotation) of the lever arm  8018  is amplified by the distance of the nozzle wall  8033  from the passive beams  806 . The downward movement of the nozzle walls and roof causes a pressure increase within the chamber  8029 , causing the meniscus to bulge as shown in  FIG. 36 . It will be noted that the surface tension of the ink means the fluid seal  8011  is stretched by this motion without allowing ink to leak out. 
     As shown in  FIG. 37 , at the appropriate time, the drive current is stopped and the actuator beam  807  quickly cools and contracts. The contraction causes the lever arm to commence its return to the quiescent position, which in turn causes a reduction in pressure in the chamber  8029 . The interplay of the momentum of the bulging ink and its inherent surface tension, and the negative pressure caused by the upward movement of the nozzle chamber  8029  causes thinning, and ultimately snapping, of the bulging meniscus to define an ink drop  802  that continues upwards until it contacts adjacent print media. 
     Immediately after the drop  802  detaches, meniscus  803  forms the concave shape shown in  FIG. 37 . Surface tension causes the pressure in the chamber  8029  to remain relatively low until ink has been sucked upwards through the inlet  8014 , which returns the nozzle arrangement and the ink to the quiescent situation shown in  FIG. 35 . 
     Another type of printhead nozzle arrangement suitable for the present invention will now be described with reference to  FIG. 33 . Once again, for clarity and ease of description, the construction and operation of a single nozzle arrangement  1001  will be described. 
     The nozzle arrangement  1001  is of a bubble forming heater element actuator type which comprises a nozzle plate  1002  with a nozzle  1003  therein, the nozzle having a nozzle rim  1004 , and aperture  1005  extending through the nozzle plate. The nozzle plate  1002  is plasma etched from a silicon nitride structure which is deposited, by way of chemical vapour deposition (CVD), over a sacrificial material which is subsequently etched. 
     The nozzle arrangement includes, with respect to each nozzle  1003 , side walls  1006  on which the nozzle plate is supported, a chamber  1007  defined by the walls and the nozzle plate  1002 , a multi-layer substrate  1008  and an inlet passage  1009  extending through the multi-layer substrate to the far side (not shown) of the substrate. A looped, elongate heater element  1010  is suspended within the chamber  1007 , so that the element is in the form of a suspended beam. The nozzle arrangement as shown is a micro systems technology (MST) structure, which is formed by a lithographic process. 
     When the nozzle arrangement is in use, ink  1011  from a reservoir (not shown) enters the chamber  1007  via the inlet passage  1009 , so that the chamber fills. Thereafter, the heater element  1010  is heated for somewhat less than 1 micro second, so that the heating is in the form of a thermal pulse. It will be appreciated that the heater element  1010  is in thermal contact with the ink  1011  in the chamber  1007  so that when the element is heated, this causes the generation of vapor bubbles in the ink. Accordingly, the ink  1011  constitutes a bubble forming liquid. 
     The bubble  1012 , once generated, causes an increase in pressure within the chamber  1007 , which in turn causes the ejection of a drop  1016  of the ink  1011  through the nozzle  1003 . The rim  1004  assists in directing the drop  1016  as it is ejected, so as to minimize the chance of a drop misdirection. 
     The reason that there is only one nozzle  1003  and chamber  1007  per inlet passage  1009  is so that the pressure wave generated within the chamber, on heating of the element  1010  and forming of a bubble  1012 , does not effect adjacent chambers and their corresponding nozzles. 
     The increase in pressure within the chamber  1007  not only pushes ink  1011  out through the nozzle  1003 , but also pushes some ink back through the inlet passage  1009 . However, the inlet passage  1009  is approximately 200 to 300 microns in length, and is only approximately  16  microns in diameter. Hence there is a substantial viscous drag. As a result, the predominant effect of the pressure rise in the chamber  1007  is to force ink out through the nozzle  1003  as an ejected drop  1016 , rather than back through the inlet passage  1009 . 
     As shown in  FIG. 39 , the ink drop  1016  is being ejected is shown during its “necking phase” before the drop breaks off. At this stage, the bubble  1012  has already reached its maximum size and has then begun to collapse towards the point of collapse  1017 . 
     The collapsing of the bubble  1012  towards the point of collapse  1017  causes some ink  1011  to be drawn from within the nozzle  1003  (from the sides  1018  of the drop), and some to be drawn from the inlet passage  1009 , towards the point of collapse. Most of the ink  1011  drawn in this manner is drawn from the nozzle  1003 , forming an annular neck  1019  at the base of the drop  1016  prior to its breaking off. 
     The drop  1016  requires a certain amount of momentum to overcome surface tension forces, in order to break off. As ink  1011  is drawn from the nozzle  1003  by the collapse of the bubble  1012 , the diameter of the neck  1019  reduces thereby reducing the amount of total surface tension holding the drop, so that the momentum of the drop as it is ejected out of the nozzle is sufficient to allow the drop to break off. 
     When the drop  1016  breaks off, cavitation forces are caused as reflected by the arrows  1020 , as the bubble  1012  collapses to the point of collapse  1017 . It will be noted that there are no solid surfaces in the vicinity of the point of collapse  1017  on which the cavitation can have an effect. 
     Yet another type of printhead nozzle arrangement suitable for the present invention will now be described with reference to  FIGS. 34-36 . This type typically provides an ink delivery nozzle arrangement having a nozzle chamber containing ink and a thermal bend actuator connected to a paddle positioned within the chamber. The thermal actuator device is actuated so as to eject ink from the nozzle chamber. The preferred embodiment includes a particular thermal bend actuator which includes a series of tapered portions for providing conductive heating of a conductive trace. The actuator is connected to the paddle via an arm received through a slotted wall of the nozzle chamber. The actuator arm has a mating shape so as to mate substantially with the surfaces of the slot in the nozzle chamber wall. 
     Turning initially to  FIGS. 34(   a )-( c ), there is provided schematic illustrations of the basic operation of a nozzle arrangement of this embodiment. A nozzle chamber  501  is provided filled with ink  502  by means of an ink inlet channel  503  which can be etched through a wafer substrate on which the nozzle chamber  501  rests. The nozzle chamber  501  further includes an ink ejection port  504  around which an ink meniscus forms. 
     Inside the nozzle chamber  501  is a paddle type device  507  which is interconnected to an actuator  508  through a slot in the wall of the nozzle chamber  501 . The actuator  508  includes a heater means e.g.  509  located adjacent to an end portion of a post  510 . The post  510  is fixed to a substrate. 
     When it is desired to eject a drop from the nozzle chamber  501 , as illustrated in  FIG. 34(   b ), the heater means  509  is heated so as to undergo thermal expansion. Preferably, the heater means  509  itself or the other portions of the actuator  508  are built from materials having a high bend efficiency where the bend efficiency is defined as: 
     
       
         
           
             
               bend 
               ⁢ 
               
                   
               
               ⁢ 
               efficiency 
             
             = 
             
               
                 
                   Young 
                   &#39; 
                 
                 ⁢ 
                 s 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 Modulus 
                 × 
                 
                   ( 
                   
                     Coefficient 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     of 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     thermal 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     Expansion 
                   
                   ) 
                 
               
               
                 Density 
                 × 
                 Specific 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 Heat 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 Capacity 
               
             
           
         
       
     
     A suitable material for the heater elements is a copper nickel alloy which can be formed so as to bend a glass material. 
     The heater means  509  is ideally located adjacent the end portion of the post  510  such that the effects of activation are magnified at the paddle end  507  such that small thermal expansions near the post  510  result in large movements of the paddle end. 
     The heater means  509  and consequential paddle movement causes a general increase in pressure around the ink meniscus  505  which expands, as illustrated in  FIG. 34(   b ), in a rapid manner. The heater current is pulsed and ink is ejected out of the port  504  in addition to flowing in from the ink channel  503 . 
     Subsequently, the paddle  507  is deactivated to again return to its quiescent position. The deactivation causes a general reflow of the ink into the nozzle chamber. The forward momentum of the ink outside the nozzle rim and the corresponding backflow results in a general necking and breaking off of the drop  512  which proceeds to the print media. The collapsed meniscus  505  results in a general sucking of ink into the nozzle chamber  502  via the ink flow channel  503 . In time, the nozzle chamber  501  is refilled such that the position in  FIG. 34(   a ) is again reached and the nozzle chamber is subsequently ready for the ejection of another drop of ink. 
       FIG. 35  illustrates a side perspective view of the nozzle arrangement.  FIG. 36  illustrates sectional view through an array of nozzle arrangement of  FIG. 35 . In these figures, the numbering of elements previously introduced has been retained. 
     Firstly, the actuator  508  includes a series of tapered actuator units e.g.  515  which comprise an upper glass portion (amorphous silicon dioxide)  516  formed on top of a titanium nitride layer  517 . Alternatively a copper nickel alloy layer (hereinafter called cupronickel) can be utilized which will have a higher bend efficiency. 
     The titanium nitride layer  517  is in a tapered form and, as such, resistive heating takes place near an end portion of the post  510 . Adjacent titanium nitride/glass portions  515  are interconnected at a block portion  519  which also provides a mechanical structural support for the actuator  508 . 
     The heater means  509  ideally includes a plurality of the tapered actuator unit  515  which are elongate and spaced apart such that, upon heating, the bending force exhibited along the axis of the actuator  508  is maximized. Slots are defined between adjacent tapered units  515  and allow for slight differential operation of each actuator  508  with respect to adjacent actuators  508 . 
     The block portion  519  is interconnected to an arm  520 . The arm  520  is in turn connected to the paddle  507  inside the nozzle chamber  501  by means of a slot e.g.  522  formed in the side of the nozzle chamber  501 . The slot  522  is designed generally to mate with the surfaces of the arm  520  so as to minimize opportunities for the outflow of ink around the arm  520 . The ink is held generally within the nozzle chamber  501  via surface tension effects around the slot  522 . 
     When it is desired to actuate the arm  520 , a conductive current is passed through the titanium nitride layer  517  within the block portion  519  connecting to a lower CMOS layer  506  which provides the necessary power and control circuitry for the nozzle arrangement. The conductive current results in heating of the nitride layer  517  adjacent to the post  510  which results in a general upward bending of the arm  20  and consequential ejection of ink out of the nozzle  504 . The ejected drop is printed on a page in the usual manner for an inkjet printer as previously described. 
     An array of nozzle arrangements can be formed so as to create a single printhead. For example, in v  FIG. 36  there is illustrated a partly sectioned various array view which comprises multiple ink ejection nozzle arrangements laid out in interleaved lines so as to form a printhead array. Of course, different types of arrays can be formulated including full color arrays etc. 
     The construction of the printhead system described can proceed utilizing standard MST techniques through suitable modification of the steps as set out in U.S. Pat. No. 6,243,113 entitled “Image Creation Method and Apparatus (IJ 41)” to the present applicant, the contents of which are fully incorporated by cross reference. 
     The integrated circuits  74  may be arranged to have between 5000 to 100,000 of the above described ink delivery nozzles arranged along its surface, depending upon the length of the integrated circuits and the desired printing properties required. For example, for narrow media it may be possible to only require 5000 nozzles arranged along the surface of the printhead assembly to achieve a desired printing result, whereas for wider media a minimum of 10,000, 20,000 or 50,000 nozzles may need to be provided along the length of the printhead assembly to achieve the desired printing result. For full colour photo quality images on A4 or US letter sized media at or around 1600 dpi, the integrated circuits  74  may have 13824 nozzles per color. Therefore, in the case where the printhead assembly  22  is capable of printing in 4 colours (C, M, Y, K), the integrated circuits  74  may have around 53396 nozzles disposed along the surface thereof. Further, in a case where the printhead assembly  22  is capable of printing 6 printing fluids (C, M, Y, K, IR and a fixative) this may result in 82944 nozzles being provided on the surface of the integrated circuits  74 . In all such arrangements, the electronics supporting each nozzle is the same. 
     The manner in which the individual ink delivery nozzle arrangements may be controlled within the printhead assembly  22  will now be described with reference to  FIGS. 37-46 . 
       FIG. 37  shows an overview of the integrated circuit  74  and its connections to the SoPEC device (discussed above) provided within the control electronics of the print engine  1 . As discussed above, integrated circuit  74  includes a nozzle core array  901  containing the repeated logic to fire each nozzle, and nozzle control logic  902  to generate the timing signals to fire the nozzles. The nozzle control logic  902  receives data from the SoPEC device via a high-speed link. 
     The nozzle control logic  902  is configured to send serial data to the nozzle array core for printing, via a link  907 , which may be in the form of an electrical connector. Status and other operational information about the nozzle array core  901  is communicated back to the nozzle control logic  902  via another link  908 , which may be also provided on the electrical connector. 
     The nozzle array core  901  is shown in more detail in  FIGS. 38 and 39 . In  FIG. 38 , it will be seen that the nozzle array core  901  comprises an array of nozzle columns  911 . The array includes a fire/select shift register  912  and up to 6 color channels, each of which is represented by a corresponding dot shift register  913 . 
     As shown in  FIG. 39 , the fire/select shift register  912  includes forward path fire shift register  930 , a reverse path fire shift register  931  and a select shift register  932 . Each dot shift register  913  includes an odd dot shift register  933  and an even dot shift register  934 . The odd and even dot shift registers  933  and  934  are connected at one end such that data is clocked through the odd shift register  933  in one direction, then through the even shift register  934  in the reverse direction. The output of all but the final even dot shift register is fed to one input of a multiplexer  935 . This input of the multiplexer is selected by a signal (corescan) during post-production testing. In normal operation, the corescan signal selects dot data input Dot[x] supplied to the other input of the multiplexer  935 . This causes Dot[x] for each color to be supplied to the respective dot shift registers  913 . 
     A single column N will now be described with reference to  FIG. 46 . In the embodiment shown, the column N includes 12 data values, comprising an odd data value  936  and an even data value  937  for each of the six dot shift registers. Column N also includes an odd fire value  938  from the forward fire shift register  930  and an even fire value  939  from the reverse fire shift register  931 , which are supplied as inputs to a multiplexer  940 . The output of the multiplexer  940  is controlled by the select value  941  in the select shift register  932 . When the select value is zero, the odd fire value is output, and when the select value is one, the even fire value is output. 
     Each of the odd and even data values  936  and  937  is provided as an input to corresponding odd and even dot latches  942  and  943  respectively. 
     Each dot latch and its associated data value form a unit cell, such as unit cell  944 . A unit cell is shown in more detail in  FIG. 46 . The dot latch  942  is a D-type flip-flop that accepts the output of the data value  936 , which is held by a D-type flip-flop  944  forming an element of the odd dot shift register  933 . The data input to the flip-flop  944  is provided from the output of a previous element in the odd dot shift register (unless the element under consideration is the first element in the shift register, in which case its input is the Dot[x] value). Data is clocked from the output of flip-flop  944  into latch  942  upon receipt of a negative pulse provided on LsyncL. 
     The output of latch  942  is provided as one of the inputs to a three-input AND gate  945 . Other inputs to the AND gate  945  are the Fr signal (from the output of multiplexer  940 ) and a pulse profile signal Pr. The firing time of a nozzle is controlled by the pulse profile signal Pr, and can be, for example, lengthened to take into account a low voltage condition that arises due to low power supply (in a removable power supply embodiment). This is to ensure that a relatively consistent amount of ink is efficiently ejected from each nozzle as it is fired. In the embodiment described, the profile signal Pr is the same for each dot shift register, which provides a balance between complexity, cost and performance. However, in other embodiments, the Pr signal can be applied globally (ie, is the same for all nozzles), or can be individually tailored to each unit cell or even to each nozzle. 
     Once the data is loaded into the latch  942 , the fire enable Fr and pulse profile Pr signals are applied to the AND gate  945 , combining to the trigger the nozzle to eject a dot of ink for each latch  942  that contains a logic 1. 
     The signals for each nozzle channel are summarized in the following table: 
     
       
         
               
               
               
             
           
               
                   
               
               
                 Name 
                 Direction 
                 Description 
               
               
                   
               
             
             
               
                 D 
                 Input 
                 Input dot pattern to shift register bit 
               
               
                 Q 
                 Output 
                 Output dot pattern from shift register bit 
               
               
                 SrClk 
                 Input 
                 Shift register clock in - d is captured on rising 
               
               
                   
                   
                 edge of this clock 
               
               
                 LsyncL 
                 Input 
                 Fire enable - needs to be asserted for nozzle to fire 
               
               
                 Pr 
                 Input 
                 Profile - needs to be asserted for nozzle to fire 
               
               
                   
               
             
          
         
       
     
     As shown in  FIG. 46 , the fire signals Fr are routed on a diagonal, to enable firing of one color in the current column, the next color in the following column, and so on. This averages the current demand by spreading it over 6 columns in time-delayed fashion. 
     The dot latches and the latches forming the various shift registers are fully static in this embodiment, and are CMOS-based. The design and construction of latches is well known to those skilled in the art of integrated circuit engineering and design, and so will not be described in detail in this document. 
     The nozzle speed may be as much as 20 kHz for the printer unit  2  capable of printing at about 60 ppm, and even more for higher speeds. At this range of nozzle speeds the amount of ink than can be ejected by the entire printhead assembly  22  is at least 50 million drops per second. However, as the number of nozzles is increased to provide for higher-speed and higher-quality printing at least 100 million drops per second, preferably at least 500 million drops per second and more preferably at least 1 billion drops per second may be delivered. At such speeds, the drops of ink are ejected by the nozzles with a maximum drop ejection energy of about 250 nanojoules per drop. 
     Consequently, in order to accommodate printing at these speeds, the control electronics must be able to determine whether a nozzle is to eject a drop of ink at an equivalent rate. In this regard, in some instances the control electronics must be able to determine whether a nozzle ejects a drop of ink at a rate of at least 50 million determinations per second. This may increase to at least 100 million determinations per second or at least 500 million determinations per second, and in many cases at least 1 billion determinations per second for the higher-speed, higher-quality printing applications. 
     For the printer unit  2  of the present invention, the above-described ranges of the number of nozzles provided on the printhead assembly  22  together with the nozzle firing speeds and print speeds results in an area print speed of at least 50 cm 2  per second, and depending on the printing speed, at least 10 cm 2  per second, preferably at least 200 cm 2  per second, and more preferably at least 500 cm 2  per second at the higher-speeds. Such an arrangement provides a printer unit  2  that is capable of printing an area of media at speeds not previously attainable with conventional printer units. 
     Maintenance Assembly 
     The maintenance assembly  23  is shown in detail in  FIGS. 47-50 , and as previously shown in  FIG. 8 , it is mounted between the posts  26  of the main body  20 , so as to be positioned adjacent the printhead assembly  22 . 
     The maintenance assembly  23  generally consists of a maintenance chassis  88  which receives the various components of the assembly therein. The maintenance chassis  88  is in the form of an open ended channel having a pair of upwardly extending tongue portions  89  at its ends which are shaped to fit over the posts  26  of the main body  20  and engage with the retaining projections provided thereon to secure the maintenance assembly  23  in position. The maintenance chassis  88  is made from a suitable metal material, having rigidity and resilience, such as a pressed steel plate. 
     The base of the maintenance chassis  88  is shown more clearly in  FIG. 49  and includes a centrally located removed portion  90 , window portions  92  and spring arms  91  extending from either side of the window portions  92 . The integral spring arms  91  are angled internally of the chassis  88  and formed by pressing the sheet metal of the chassis. Of course the spring arms  91  could equally be a separate insert placed into the open channel of the chassis  88 . 
     A rigid insert  93  is provided to fit within the chassis  88  to provide added rigidity to the maintenance assembly  23 . A catch element  94  projects from the base of the rigid insert and extends into the centrally located removed portion  90  of the chassis  88  when the rigid insert  93  is located within the chassis  88 . The catch element  94  is provided to move the maintenance assembly between a capped and an uncapped state, as will be described below. A lower maintenance molding  95  is located within the insert  93  and retained within the insert via engagement of a number of lugs  96  formed along the sides of the lower maintenance molding  95  with corresponding slots  97  provided along the sides of the insert  93 . The lower maintenance molding  95  is made from a suitable plastic material and forms a body having closed ends and an open top. The ends of the lower maintenance molding  93  are provided with air vents  98 . Air from the vents  98  flows through filters  181  to ventilate the maintenance assembly. 
     Two pin elements  99  extend from the base of the lower maintenance molding  95 . The pin elements  99  are connected to the base via a flexible web, such as rubber, to allow multi-directional relative movement of the pin elements  99  with respect to the base of the lower maintenance molding. The pin elements  99  pass through two circular openings  100  in the base of the rigid insert  93  and into the window portions  92  of the maintenance chassis  88 . 
     A retainer insert  101  is supported on the pin elements  99  within the lower maintenance molding  95 . The retainer insert  101  is coated steel and provides rigid support for the strips of absorbent media  102  retained therein. The absorbent media  102  is a generally an inverted T-shaped assembly of separate portions—a thin vertical portion which extends upwardly from between two substantially horizontal portions. The absorbent media  102  may be made from any type of material capable of absorbing and retaining ink such as urethane foam or the like. 
     A microfibre fabric  103  fits over the thin vertical portion, around the two horizontal portions, and then attaches to the retainer insert  101  to retain the absorbent media  102 . The microfibre fabric  103  draws into the absorbent media  102 . 
     An upper maintenance molding  104  fits over the lower maintenance molding  95  to enclose the microfibre fabric  103 , absorbent media  102  and retainer insert  101  therebetween. The upper maintenance molding  104  is attached along its bottom surface to the surface of the lower maintenance molding  95  via an appropriate adhesive. An upwardly projecting rim portion  105  extends beyond the thin vertical portion of the absorbent media  102  covered with microfibre fabric  103 . The rim portion  105  defines an open perimeter seal for sealing the nozzles of the printhead assembly  22  when the upper maintenance molding  104  is brought into capping contact with the printhead assembly. 
     In this arrangement, the upper maintenance molding  104 , microfibre fabric  103 , absorbent media  102 , retainer insert  101 , lower maintenance molding  95  and the rigid insert  93  form a capping unit which is adapted to fit within the maintenance chassis  88  and is supported on the spring arms thereof. Within this unit, the microfibre fabric  103 , absorbent media  102  and the retainer insert  101  form a sub-unit supported on the pin elements  99  and movable within the space defined by the lower maintenance molding  95  and the upper maintenance molding  104 . 
     As shown in  FIG. 47 , the capping unit is held in place with a retainer element  106  that fits over the upper maintenance molding  104  and secures to the chassis  88 . The retainer element  106  is essentially in the form of an open ended channel having a slot  107  formed along the upper surface thereof, through which the rim portion  105  of the upper maintenance molding  104  can protrude and cappingly engage with the printhead assembly  22 . The upper surface of the retainer element  106  is curved and acts as a media guide during printing. 
     When assembled in this manner, the components of the maintenance assembly  23  are contained within the retainer element  106  and the chassis  88 , such that both the upper maintenance molding  104  can move with respect to the retainer element  106  to cap the printhead assembly  22 , and the microfibre fabric  103  and absorbent media  102  can move with respect to the upper maintenance molding to contact and wipe the surface of the nozzles of the printhead assembly  22 . 
     Upon assembly and attachment of the maintenance assembly  23  to the posts  26  of the main body  20 , the catch element  94  of the rigid insert extends from the central removed portion  90  of the chassis  88 . Due to the action of the spring arms  91 , the maintenance unit  23  (as previously defined) is raised from the base of the chassis  88  such that the rim portion  105  of the upper maintenance molding  104  extends through the slot  107  of the retainer element  106  and is in capping contact with the printhead assembly  22 . This state is shown in  FIG. 50  and is referred to as the capping state, whereby the nozzles of the printhead are sealed in an almost closed environment within the rim portion  105  and are less likely to dry out and clog with ink. The environment is almost closed and not fully closed, so that the maintenance assembly is not prevented from moving to the uncapped state because of a mild vacuum created within the rim  105 . 
     To remove any paper dust or other particulate matter present in the vicinity of the nozzles of the printhead assembly  22 , the surface of the printhead may be wiped by the microfibre fabric  103 . To perform this, a wiper actuator present in the cradle unit extends into the window portions  92  of the chassis  88  and contacts the pin elements  99  provided in the base of the lower maintenance molding  95 . Any upward force provided by the wiper actuator on the pins  99  causes them to project further against the retainer insert  101 , thereby causing the vertical portion of the absorbent media  102 , which is coated with the microfibre fabric  103 , to extend into and beyond the rim portion  105  of the upper maintenance molding  104 , until it contacts the surface of the printhead assembly  22  proximal the nozzles. The presence of the microfibre fabric  103  ensures that contact is minimised and attracts any ink or moisture present on the surface of the printhead assembly  22  to be retained within the absorbent media  102 . As the pins  99  are free to move in any direction, any lateral motion of the wiper actuator will cause the microfibre fabric  103  to move laterally across the surface of the nozzles hence performing a wiping or cleaning function. Removal of the wiper actuator will then cause the arrangement to return to a position whereby the microfibre fabric  103  and the absorbent media  102  are below the surface of the rim portion  105 . 
     In order to perform printing, the maintenance assembly  23  must be moved from the capping state to a printing state. This is achieved by a maintenance actuator gripping the catch element  94  projecting through the central removed portion  90  of the chassis  88  and applying a downward force thereto. This downward force causes the rigid insert  93  to move against the spring arms  91  of the chassis  88 , towards the base of the chassis. This movement causes the upper rim portion  105  of the upper capping molding  104  to retract into the slot  107  formed in the retainer element  106  such that it is flush with the outer surface of the retainer element  106  and does not protrude therefrom. It will be appreciated that the retainer element  106  does not move and is fixed in position. This creates a gap between the retainer element  106  and the printhead assembly  22  through which the media can pass for printing. In the printing or uncapped state, the retainer element  106  acts as a media guide and the media contacts the retainer element and is supported on the surface of the retainer element  106  as it passes the printhead assembly for printing. 
     Cradle Unit 
     The cradle unit  12  is shown in relation to  FIGS. 6 and 7  and generally consists of a main body  13  which defines an opening  14  for receiving the cartridge unit  10 , and a cover assembly  11  adapted to close the opening to secure the cartridge unit  10  in place within the cradle unit  12 . 
     The main body  13  of the cradle unit  12  includes a frame structure  110  as shown in  FIG. 51A and 51B . The frame structure  110  generally comprises two end plates  111  and a base plate  112  connecting each of the end plates  111 . A drive roller  113  and an exit roller  114  are mounted between the end plates  111  at opposing ends thereof, such that when the cartridge unit  10  is retained within the main body  13 , it sets between the drive roller  113  and exit roller  114 . The drive roller  113  and the exit roller  114  are each driven by a brushless DC motor  115  which is mounted to one of the end plates  111  and drives each of the drive and exit rollers via a drive mechanism  116 , such as a drive belt. Such a system ensures that both the drive roller  113  and the exit roller  114  are driven at the same speed to ensure a smooth and consistent passage of the media through the print engine  1  and past the printhead assembly  22  of the cartridge unit  10 . 
     A maintenance drive assembly  117  is mounted to the other end plate  111 , opposite the DC motor  107 . The maintenance drive assembly  117  comprises a motor  118  which is operatively connected to a maintenance gear  119  and a wiper gear  120 . The maintenance gear  119  is in turn connected to a maintenance actuator  121  which is in the form of a rod having a hooked end that extends a distance within the base plate  112 . The hooked end of the maintenance actuator  121  is shaped to be received within the catch element  94  of the maintenance assembly  23  so as to raise/lower the upper rim portion  105  between the capping state and the printing state. The wiper gear  120  is similarly connected to a wiper actuator  122  in the form of a rod having a pair of projections extending therefrom. The wiper actuator  122  similarly extends within the base plate  112 , and the projections are positioned along the wiper actuator  122  so that they are aligned with the window portions  92  formed in the base of the maintenance chassis  88  so as to contact the pin elements  99  of the maintenance assembly  23 . 
     The maintenance drive assembly  117  is shown in isolation in  FIGS. 52A and 52B . As the motor  118  is bidirectional, operation of the motor in one direction will cause the wiper gear  120  to move in a counter-clockwise direction as shown in  FIG. 52A . The wiper gear  120 , has a raised portion  123  formed on the surface thereof which comes into contact with an arm  124  of the wiper actuator as the wiper gear  120  rotates. As the raised portion  123  contacts the arm  124 , the wiper actuator  122  pivots such that the projections formed thereon move in an upward direction through the window portions  92  in the maintenance chassis  88  and against the pin elements  99 , thereby bring the micro fibre fabric  103  against the surface of the printhead assembly. Further rotation of the wiper gear  120  will result in the arm  124  returning to its neutral position. Lateral movement can be applied to the wiper actuator  122  due to the presence of an additional angled raised portion  125  formed on the wiper gear  120  upon which the arm  124  rides causes the entire wiper actuator to move laterally against the returning spring  126 . A sensor element  127  is provided to sense the position of the wiper actuator such that the state of the printhead can be readily determined. 
     In order to control the capping state of the printhead assembly  22 , the motor  118  is reversed resulting in the wiper gear  120  moving in a clockwise direction as shown in  FIG. 52A  and a counter-clockwise direction as shown in  FIG. 52B . Rotation of the wiper gear  120  in this direction ensures that the wiper actuator pivots in a downward direction away from the maintenance assembly  23 . However as shown more clearly in  FIG. 52B , this rotation causes a flipper gear  128  provided on the inner surface of the wiper gear  120  to engage with the maintenance gear  119  and in turn cause the maintenance gear  119  to rotate in a counter clockwise direction (as shown in  FIG. 52B ). Similarly, a projection  129  formed on the inner surface of the maintenance gear  119  contacts a pivot arm  130  of the maintenance actuator  121 , thereby causing the hooked end of the maintenance actuator to move in a downward direction, which in turn grips the catch element  94  of the maintenance assembly  23  causing the upper rim portion  105  to retract and assume a printing state. Similarly, the sensor element  127  can sense the position of the maintenance actuator to control operation of the motor  118 , and hence the desired state of the printhead. 
     Referring again to  FIGS. 51A and 51B , a pair of cartridge unit guides  131  are attached to the end plates  111  to aid in receiving and guiding the cartridge unit  10  into the cradle unit  12 . The guides  131  are angled to receive a surface of the cartridge unit  10  such that the cartridge unit  10  is orientated correctly with respect to the cradle unit  12 . 
     The control electronics for controlling the operation of the print engine and the ICs  50  of the printhead assembly  22  is provided on a printed circuit board (PCB)  132 . As shown in  FIG. 51A , one face of the PCB  132  contains the SoPEC devices  133  and related componentry  134  for receiving and distributing the data and power received from external sources, whilst the other face of the PCB includes rows of electrical contacts  135  along a lower edge thereof which provides a means for transmitting the power and data signals to the corresponding electrical contacts on the flex PCB  79  for controlling the nozzles of the printhead assembly  22 . 
     As shown in isolation in  FIG. 53 , the PCB  132  forms part of a PCB assembly  140 , and is mounted between two arms  136 , with each of the arms having a claw portion  137  to receive and retain the PCB  132  in position. As shown in  FIG. 54 , each of the arms  136  has a groove  141  formed in the upper portion thereof for receiving a hook portion of a tension spring  142 , the purpose of which will be described below. 
     In order to provide stability to the PCB  132  as it is mounted between the two arms  136 , a support bar  138  is secured to the arms  136  and the PCB along the bottom edge of the PCB  132 , on the face that contains the SoPEC devices  133  and the related componentry  134 . The support bar  138  has a plurality of star wheels  139  mounted along its lower surface. The star wheels are spring loaded such that they can move relative to the lower surface of the support bar to grip with a surface of the exit roller  114  when the PCB assembly  140  is mounted to the end plates  111 , as shown in  FIG. 51A . 
     A heatshield  143  is attached to the PCB  132 , as shown in  FIG. 55A  such that it substantially covers the SoPEC devices  133  and protects the SoPEC devices from any EMI that may be within the vicinity of the printer unit  2 . The heatshield  143  also has a latch mechanism  144  provided therein which mates with a clip provided on the cover assembly  11  to secure the cover assembly in a closed position as shown in  FIG. 55A . 
     The PCB assembly  140  is pivotally mounted to the end plates  111  at pivot points  141  provided at the bottom of the arms  136 . In this arrangement, the PCB assembly  140  is able to swing about its pivot points  141  between an open position, wherein the electrical contacts  135  are remote from the electrical contacts of the flex PCB  79  and the cartridge unit  10  can be readily removed from the cradle unit  12 , and a closed position, where the electrical contacts  135  are in operational contact with the fr electrical contacts provided on the flex PCB  79  to transmit control data and power to facilitate printing from the nozzles of the printhead assembly  22 . 
     As shown in  FIG. 55B , an idle roller assembly  145  is secured to the end plates  111  at the rear of the cradle unit  12  and includes a plurality of roller wheels  152  which are positioned to contact the surface of the drive roller  113  and rotate therewith. The idle roller assembly  145  ensures that any media that is presented to the print engine  1  from the picker mechanism  9  of the printer unit  2 , is gripped between the drive roller  113  and the roller wheels  146  of the idle roller assembly  1145  for transport past the printhead assembly  22  of the cartridge unit  10  for printing. 
     The cover assembly  11 , is shown in its closed position in  FIGS. 55A and 55B , and is pivotally attached to the end plates  111  at an upper rear portion thereof. A pair of attachment plates  147  extend from the cover assembly  11  for attaching the cover assembly to the end plates  111  via a pin  148 . The attachment plates  147  extend beyond the pin  148  and have a hole formed therein into which is received the free end of the tension spring  142  as discussed previously in relation to  FIG. 54 . 
     When the cover assembly  11  is in the closed position, as shown in  FIG. 55B , the spring is in full tension which in turn causes the PCB assembly  40  to pivot towards the closed position, as shown in cross-section in  FIG. 56A . In this position, the electrical contacts  135  of the PCB  132  are in operational contact with the corresponding electrical contacts of the flex PCB  79  of the printhead assembly  22  such that power and data signals can be transferred therebetween. 
     When the cover assembly is moved to its open position, as shown in  FIG. 55C , the attachment plates  147  pivot towards the front of the cradle assembly thereby relieving tension in the spring  142  and causing the spring to become slack. This in turn, allows the PCB assembly to pivot away into an open position as shown in  FIG. 56B . In this position, the electrical contacts  135  of the PCB  132  move away from contacting the corresponding contacts of the flex PCB  79  of the printhead assembly  22 , to thereby enable the cartridge unit  10  to be removed from the cradle unit  12 . 
     In this regard, the act of opening/closing the cover assembly  11  also performs the function of disengaging/engaging electrical communication between the cartridge unit  10  and the cradle unit  12 . 
     Referring again to  FIGS. 55A-55C , the cover assembly  11  includes a number of docking ports  149  formed in the upper surface thereof. In the embodiment shown there are five docking ports  149  provided, with each docking port corresponding to one of the ink storage modules  45 . Each docking port  149  has an upwardly projecting lip portion which is shaped to receive an ink refill unit for supplying refill ink to the ink storage modules  45 . As more clearly shown in  FIG. 55C , each docking port  149  has a large, substantially circular opening  151  and two small circular openings  152  provided therein, which enable the delivery of ink between the ink refill unit and the cartridge unit  10  to occur in the manner as described below. 
     Four T-shaped openings  182  are positioned at the corners of each docking portion  149  to receive the bag constrictor actuators on the refill. These were briefly discussed above in relation to the ink storage modules  45  and are described in more detail below. 
     Refill Unit 
       FIGS. 57A-57C  show the ink refill unit  155  for supplying refill ink to the cartridge unit  10 . The ink refill unit  155  is provided as a unit comprising a base assembly  156  which houses internal ink refilling components and a cover  157  which fits over the base assembly  156 . The base assembly and cover may be moulded from a plastics material and the base assembly  156  may be moulded as a single piece or in sections. 
     The underside of the base assembly  156  is shown in more detail in  FIG. 57B  and includes a ridge portion  160  that projects therefrom and which mates with docking port  149  formed in the cover assembly  11 , to retain the ink refill unit in docking position. A substantially cylindrical ink outlet  158  also projects from the underside of the base assembly for delivering ink into the cartridge unit  10 . A two valve actuating pins  159  also project from the underside of the base assembly  156  for actuating the inlet and outlet valves of the ink storage modules  45  respectively. In the embodiment shown, the two valve actuating pins  159  have a tri star cross section for good unidirectional bending resistance and buckling strength. A QA chip  161  is also provided to project from the underside of the base assembly  156  and has a plurality of QA chip contacts  162  exposed thereon which are read by a QA chip reader provided in the cover assembly  111  when the ink refill unit  155  is docked therewith. 
     A constrictor actuator  190  projects from adjacent each corner of the base assembly  156 . The constrictor actuators  190  are slightly arcuate and rounded at their ends. The constrictor apertures  60  (see  FIG. 14 ) in the top  42  of the cartridge unit  10 , are correspondingly arcuate. The rounded ends and arcuate cross section allow the user to easily align one constrictor actuator  190  with its corresponding aperture  60 , and the curved surfaces intuitively guide the other constrictor actuators  190  into alignment with their respective apertures  60 . This helps to dock the refill unit with the interface  61  quickly and with minimal fine positioning by the user. As best shown in  FIG. 57B , each constrictor actuator  190  has a buttress reinforcement  191 . This gives the constrictor actuators  190  a high bending strength in order to withstand large lateral forces in the event that users apply excessive force when aligning the refill unit with the docking port. 
     As described above with reference to  FIG. 12 , the constrictor actuators  190  actuate the bag constrictor  43  of the ink storage module  45 . 
     The base assembly  156  also has a filling port  192 . The bag  163  receives its initial charge of ink through this port which is then sealed with a plastic sealing ball  193 . 
     Referring to the exploded view of  FIG. 57C , an ink bag  163  is sealed to the inner surface of the base assembly  156  for storing the refill ink therein, and is made from a deformable material which allows the ink bag  163  to expand/collapse as ink is supplied to/removed from the ink refill unit  155 . An ink delivery needle  164  extends into the space provided between the bag  163  and the base assembly  156  and provides a passage for ink to flow to the outlet  158 . The end of the ink delivery needle  164  extends into the cylindrical outlet  158 , and is surrounded by a seal ring  165  which is spring loaded via a compression spring  166  within the open end of the cylindrical outlet  158 . When the ink refill unit  155  is not docked with the cartridge unit  10 , the delivery needle is protected by the seal ring  165 . As a further precaution, a plastic cap  187  is slid over the outlet and held in place by a slight interference fit. 
     An ink level indicator  167  is also provided within the cover  157  of the ink refill unit  155 . The ink level indicator  167  comprises a flexible strip having an indication portion  168 , such as a coloured section. The strip is attached to the upper surface of the deformable ink bag  163  at its ends and to the underside of the cover  157  at its centre, so that when the ink supply within the bag  163  is exhausted, i.e., the bag is substantially empty, the indication portion  168  aligns itself with a transparent window  169  provided in the top surface of the cover  157 . In this regard, at any other time, i.e., when the bag is other than substantially empty, the indication portion is hidden from view. 
     As the ink dispenses, the nature of the ink bag material causes it to deform and collapse in a non-uniform manner. Each of the edges of the upper surface of the bag are unlikely to collapse at the same rate. As such, the length of the ink level indicator  167  is ensures that the indication portion  168  only aligns with the window  169  in the cover  157  once all of the edges of the deformable bag&#39;s upper surface have fully collapsed. In this regard, the ink level indicator strip  182  is initially in a folded state with the indication portion  168  being located on the strip  182  so as to be hidden from the window  169  when the bag  163  is full. The strip  167  is attached at either end to opposite edges of the bag&#39;s upper surface. A point (not shown) intermediate the ends is secured beneath the transparent window  169 . When the bag  46  fully collapses the strip  167  lengthens and unfolds. This brings the previously hidden indication portion  168  into view through the window  169 . The use of the ink level indicator  167  means that the one refill unit  155  can be used for multiple refill operations if the refill unit is not fully exhausted. This may occur when the amount of ink necessary for refilling the corresponding ink storage module  45  of the cartridge unit  10  in one operation is less than the capacity of the refill unit. 
     The cover  157  fits over a portion of the base assembly  156  to enclose the ink bag  163  and ink level indicator  167 . Likewise, U-shaped docking clasp  183  fits over the cover  157  such that its legs extend beyond the base assembly  156  to engage the cartridge unit  10  when docked. Clips  170  on opposing legs of the clasp  183  snap lock onto the sides of the cartridge unit  10 . This holds the refill unit  155  substantially fixed relative the cover assembly  11  for reliable and efficient transfer of ink. 
     An opposing pair of leaf springs  184  extend from inside each leg of the U-shaped clasp to press against the sides of the cover  157 . Adjacent each leaf spring is a pivot  185  designed to engage a fulcrum ledge  186  on the side of the cover  157 . This pushes the legs outwardly, however as the pivot  185  engages the fulcrum  186 , the clips are levered inwardly to maintain engagement with the cartridge unit  10 . 
     A label panel  188  is fixed to the outer surface of the clasp  183 . The label panel  188  can display trademark and other information. It may also be coloured to match the ink within the refill. The label panel  188  also has finger grip pads  189  on each leg. The finger grip pads  189  are positioned so that finger pressure at these points will overcome the force of the leaf springs  184  to lever the clips  170  out of engagement with cartridge unit  10 . The refill unit  155  may then be pulled off the docking port  149  of the cover assembly  11 . 
       FIG. 58  shows the refill unit  155  docked directly with one of the interfaces  61  of the ink storage module assembly  11  of the cartridge unit  10 . The cover assembly  11  and remainder of the cradle unit have been removed for clarity. The refill unit  155  is shaped, or ‘keyed’, such that it can only be received within the docking port  149  in one particular orientation. The ends of each leg of the U-shapes clasp  183  are significantly different widths so that the user is less likely attempt to dock the unit  155  back-to-front. The cylindrical ink outlet  158  is offset from the lateral centre line to also guard against back-to-front docking of the refill unit  155 . As previously discussed, the base of the docking port  149  has a large circular opening  151 , into which is received the cylindrical ink outlet  158 , and two smaller openings  152 , into which the valve actuators  159  are received. The cross sections of each of these interacting elements are shaped so that only the correctly coloured ink refill unit, in the correct orientation, can be used to refill each particular ink storage module  45 . For example, the two tri star cross sections of the valve actuators  159  can each be rotated to give a large number of combinations that will only mate with corresponding tri star apertures, each with a matching rotational orientation. 
     A QA chip reader  172  is also provided in the base of the docking port  149  for mating with the QA chip contacts  162  of the QA chip  161  of the refill unit  155  and reading and receiving information stored thereon. Such information may include the storage capacity of the refill unit  155  (e.g., about 30 to about 50 ml), the colour of the ink contained within the refill unit  155 , and the source of the ink contained within the-ink refill unit  155 . The information can be readily transferred to the control circuitry of the cradle unit  12  when the refill unit  155  is docked into position within the docking port  149 . For example, the control circuitry of the cradle unit  12  is able to determine which of the ink storage modules  45  require refilling and whether the refill unit  155  contains the correct type/colour and amount of ink to facilitate refilling. 
     As shown more clearly in  FIG. 59 , the valve insert  49  of each of the ink storage modules  45  (see  FIG. 10 ) is arranged such that the ink inlet  15  is aligned with the large circular opening  151  formed in the docking port  149 , and the ink inlet and oulet valves  16  and  18  respectively, are aligned with the tri star openings  152 . As the ink refill unit  155  is brought into position within the docking port  149 , the ink outlet  158  of the refill unit  155  contacts the ink inlet  15  of the ink storage assembly  45 , and the valve actuator pins  159  contact each of the ink inlet valve  16  and ink outlet valve  18 . 
     In this position, the ink delivery needle  164  penetrates the ink inlet  15  of the valve insert  49  as the spring loaded seal ring  165  retracts within the cylindrical ink outlet  158  to form a tight seal around the surface of the ink inlet  15 . The seal ring  165  is able to ‘ride’ up the ink delivery needle  164  and is loaded such that upon removal of the refill unit  155  from the docking port  149 , the seal ring is returned to its protection position via action of a seal spring  166 . 
     As discussed previously, the ink retained within ink bag  46  of the ink storage module  45  is in a constant state of negative pressure due to the spring element  54  applying a constant expansion force to the ink bag  46 . This produces a negative or back pressure in the ink, thereby preventing ink from leaking from the nozzles of the printhead assembly  22 . This back pressure also provides a simple means for extracting the refill ink from the refill unit  155  when the refill unit is docked into position. Due to a pressure gradient between the ink bag of the refill unit  155  (which is at atmospheric pressure) and the ink bag of the ink storage module  45 , when the ink delivery needle  164  penetrates the ink inlet  15 , the refill ink simply flows from the refill init  155  into the ink bag  46  of the ink storage module  45 . 
     In order to alternate between a refilling operation and a printing operation and to maintain the ink in the printhead assembly  22  in a constant state of back pressure such that ink does not leak from the nozzles during refilling, valves  16  and  18  are provided in the valve insert as discussed above. Both valves are controlled by the valve actuator pins  159  when the refill unit is docked into position with the docking port  149 . The manner in which the valves are controlled is shown with reference to  FIGS. 60A-60D . 
       FIGS. 60A and 60B  show different cross-sectional views respectively along lines A-A and B-B in  FIG. 59  illustrating a state of the valve arrangement before refilling, and  FIGS. 60C and 60D  respectively show the views of  FIGS. 60A and 60B  illustrating a state of the valve arrangement during refilling. 
     Prior to refilling, as shown in  FIGS. 60A and 60B , the ink inlet valve  16  is in a closed position, thereby preventing the passage of ink or air from entering the ink inlet  15  and making its way into the ink bag  46 . This is shown in  FIG. 60B , whereby any ink present in the passage between the ink inlet  15  and the ink inlet valve  16  remains in this space. An o-ring seal is provided at the ink inlet  15  to maintain an air tight seal around the ink delivery needle  164  of the refill unit  155 . In this state, the ink outlet valve  18  is in an open position thereby providing a passage for ink to flow out the ink outlet  52 , down the ink downpipe  30  and to the printhead assembly  22 . As discussed, the spring element  54  establishes a state of back pressure within the ink bag  46 , and the printhead  22  draws the ink from the ink bag  46  against this back pressure during printing. 
     During refilling, as shown in  FIGS. 60C and 60D , the ink refill unit  155  is docked into the docking port  149  such that the ink outlet  158  engages with the ink inlet  15  of the valve insert  49  and the valve actuator pins  159  come into engagement with the valves  16  and  18 . As shown in  FIG. 60C , contact of the valve actuator pin with the ink outlet valve  18  causes the valve  18  to be depressed and close, thereby preventing further ink flow from the ink outlet  52  to the printhead assembly  22 . In this regard, ink present in the passage from the closed ink outlet valve  18  to the printhead assembly  22  remains stationary until the ink outlet valve  18  opens. 
     As shown more clearly in  FIG. 60D , when the valve actuator pin  159  contacts the ink inlet valve  16  and depresses the valve, the valve opens allowing a passage for the ink to flow from the refill unit  155  to the ink bag  46 . Due to the back pressure present in the ink bag  46 , the ink is drawn into the ink bag due to the pressure differential and as the ink bag  46  fills and expands with ink, the spring element  54  maintains a constant force between the ink bag  46  and the retainer element  55 , thereby also maintaining a constant back pressure within the ink in the ink bag  46 . This continues until the ink bag  46  reaches its maximum capacity whereby the pressure of the ink present in the ink bag  46  equalises with the pressure of the ink of the refill unit  155  and no more ink is drawn from the refill unit  155 . 
     Bag constrictor actuators  190  extend through the apertures  60  to press the upper constrictor collar  59  towards the lower constrictor collar  57  to bow the side panels  58  inwards and constrict the bag  46 . As discussed above with reference to  FIG. 12 , the bag constrictor  43 , re-establishes the negative pressure in the ink bag  46  as the refill unit is removed, by releasing the constriction. 
     While the present invention has been illustrated and described with reference to exemplary embodiments thereof, various modifications will be apparent to and might readily be made by those skilled in the art without departing from the scope and spirit of the present invention. Accordingly, it is not intended that the scope of the claims appended hereto be limited to the description as set forth herein, but, rather, that the claims be broadly construed.