PATENT DOCUMENT

Abstract:
A printhead module is provided having an ink delivery member supporting at least one printhead integrated circuit via an ink distribution member. The ink distribution member incorporates a laminated stack of layers for distributing ink from the ink delivery member to inkjet nozzles of the printhead integrated circuit via distribution apertures. The distribution apertures of each successive layer of the stack from the ink delivery member to the inkjet nozzles has a successively smaller diameter.

Full Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]     The present application is a continuation of U.S. Ser. No. 11/478,594 filed on Jul. 3, 2006, which is a continuation of U.S. Ser. No. 10/760,187 filed on Jan. 21, 2004, now issued as U.S. Pat. No. 7,083,271, all of which is herein incorporated by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates to a printhead unit for use in a printing system. More particularly, the present invention relates to a printhead module of a printhead assembly which is mountable to and demountable from a printing unit.  
       CROSS-REFERENCE TO CO-PENDING APPLICATIONS  
       [0003]     The following applications have been filed by the Applicant simultaneously with the present application:  
                                                       7156508   7159972   7165834   7080894   7201469   7090336       7156489   10/760233   10/760246   7083257   10/760201   7219980       10/760253   10/760255   10/760209   7118192   10/760194   10/760238       7077505   7198354   7077504   10/760189   7198355   10/760232       10/760231   7152959   7213906   7178901   7222938   7108353       7104629   10/760254   10/760210   10/760202   7201468   10/760198       10/760249   10/760263   10/760196   10/760247   7156511   10/760264       10/760244   7097291   10/760222   10/760248   7083273   10/760192       10/760203   10/760204   10/760205   10/760206   10/760267   10/760270       7198352   10/760271   10/760275   7201470   7121655   10/760184       7232208   10/760186   10/760261   7083272   10/760180   7111935       10/760213   10/760219   10/760237   10/760221   10/760220   7002664       10/760252   10/760265   10/760230   7168654   7201272   6991098       7217051   6944970   10/760215   7108434   10/760257   7210407       7186042   10/760266   6920704   7217049   10/760214   10/760260       7147102   10/760269   10/760199   10/760241                  
 
         [0004]     The disclosures of these co-pending applications are incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0005]     Pagewidth printheads, for use in printing systems, are known. Such printheads typically span the width of the print media on which information is to be printed, and as such the dimensions and configuration of the printheads vary depending upon the application of the printing system and the dimensions of the print media. In this regard, due to the large variation in the required dimensions of such printheads, it is difficult to manufacture such printheads in a manner which caters for this variability.  
         [0006]     Accordingly, the applicant has proposed the use of a pagewidth printhead made up of a plurality of replaceable e printhead tiles arranged in an end-to-end manner. Each of the tiles mount an integrated circuit incorporating printing nozzles which eject printing fluid, e.g., ink, onto the print media in a known fashion. Such an arrangement has made it easier to manufacture printheads of variable dimensions and has also enabled the ability to remove and replace any defective tile in a pagewidth printhead without having to scrap the entire printhead.  
         [0007]     However, apart from the ability to remove and replace any defective tiles, the previously proposed printhead is generally formed as an integral unit, with each component of the printhead fixedly attached to other components. Such an arrangement complicates the assembly process and does not provide for easy disassembly should the need to replace components other than just the defective tiles be necessary. Accordingly, a printhead unit which is easier to assemble and disassemble and which is made up of a number of separable individual parts to form a printhead unit of variable dimensions is required.  
       SUMMARY OF THE INVENTION  
       [0008]     In one embodiment of the present invention, there is provided a printhead module for a printhead assembly, comprising at least two printhead integrated circuits, each of which has nozzles formed therein for delivering printing fluid onto the surface of print media, a support member supporting the printhead integrated circuits and at least two fluid distribution members individually mounting a respective one of the at least two printhead integrated circuits to the support member,  
         [0009]     wherein the support member has at least one longitudinally extending channel for carrying the printing fluid for the printhead integrated circuits and includes a plurality of apertures extending from the at least one channel through a wall of the support member, and each of the fluid distribution members is formed as a laminated stack of layers for directing the printing fluid from the apertures of the support member to the nozzles of the associated printhead integrated circuit.  
         [0010]     The at least two printhead integrated circuits, the support member and the at least two fluid distribution members may be formed as a unitary arrangement with an electrical connector for connecting electrical signals to the at least two printhead integrated circuits.  
         [0011]     Each laminated stack may have at least three layers comprising an upper layer upon which the associated printhead integrated circuit is mounted, a middle layer and a lower layer which is attached to an upper surface of the support member.  
         [0012]     The lower layer includes first distribution apertures arranged to align with respective ones of the apertures in the support member and first distribution channels in an upper surface thereof associated with respective ones of the first distribution apertures, the first distribution apertures having substantially the same diameter as the apertures in the support member.  
         [0013]     The middle layer includes second distribution apertures arranged to align with the first distribution channels of the lower layer, the second distribution apertures having a smaller diameter than the first distribution apertures.  
         [0014]     The upper layer includes second distribution channels in a lower surface thereof arranged to align with the second distribution apertures of the middle layer and third distribution apertures associated with the second distribution channels, the third distribution apertures having a smaller diameter than the second distribution apertures.  
         [0015]     The associated printhead integrated circuit include nozzle supply apertures arranged to align with the third distribution apertures of the upper layer and to direct fluid to respective ones of the nozzles, the nozzle supply apertures having substantially the same diameter as the third distribution apertures, with the apertures of the support member having a diameter of the order of millimetres and the nozzle supply apertures of the at least two printhead integrated circuits having a diameter of the order of micrometres.  
         [0016]     The unitary arrangement of the printhead module allows it to be removably mounted to the printhead assembly.  
         [0017]     The support member may be formed with a plurality of the channels, each of which is arranged to carry a different printing fluid for direction to associated groups of the nozzles in the both, or if more than two, all of the printhead integrated circuits by way of respective ones of the fluid distribution members. A further channel for delivering air to the printhead integrated circuits for maintaining the nozzles of the printhead integrated circuits substantially free from impurities may be provided.  
         [0018]     For attaching the fluid distribution members to the support member, a lower surface of the fluid distribution members may be attached to the upper surface of the support member by an adhesive material. This adhesive material may be used to form a seal between the respective apertures by being deposited to surround each of the apertures of the support member and each of corresponding apertures formed in the lower surface of the fluid distribution members.  
         [0019]     In an arrangement having the apertures of the support member formed in a row extending across the support member with respect to the longitudinally extending direction of the support member, two deposits of the adhesive material may be deposited on either side of the row of apertures to provide stability for the mounting arrangement. The adhesive material may be a curable resin.  
         [0020]     An embodiment of a printhead module that incorporates features of the present invention is now described by way of example with reference to the accompanying drawings, as is an embodiment of a printhead assembly that incorporates the printhead module. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]     In the drawings:  
         [0022]      FIG. 1  shows a perspective view of a printhead assembly in accordance with an embodiment of the present invention;  
         [0023]      FIG. 2  shows the opposite side of the printhead assembly of  FIG. 1 ;  
         [0024]      FIG. 3  shows a sectional view of the printhead assembly of  FIG. 1 ;  
         [0025]      FIG. 4A  illustrates a portion of a printhead module that is incorporated in the printhead assembly of  FIG. 1 ;  
         [0026]      FIG. 4B  illustrates a lid portion of the printhead module of  FIG. 4A ;  
         [0027]      FIG. 5A  shows a top view of a printhead tile that forms a portion of the printhead module of  FIG. 4A ;  
         [0028]      FIG. 5B  shows a bottom view of the printhead tile of  FIG. 5A ;  
         [0029]      FIG. 6  illustrates electrical connectors for printhead integrated circuits that are mounted to the printhead tiles as shown in  FIG. 5A ;  
         [0030]      FIG. 7  illustrates a connection that is made between the printhead module of  FIG. 4A  and the underside of the printhead tile of  FIGS. 5A and 5B ;  
         [0031]      FIG. 8  illustrates a “female” end portion of the printhead module of  FIG. 4A ;  
         [0032]      FIG. 9  illustrates a “male” end portion of the printhead module of  FIG. 4A ;  
         [0033]      FIG. 10  illustrates a fluid delivery connector for the male end portion of  FIG. 9 ;  
         [0034]      FIG. 11  illustrates a fluid delivery connector for the female end portion of  FIG. 8 ;  
         [0035]      FIG. 12  illustrates the fluid delivery connector of  FIG. 10  or  11  connected to fluid delivery tubes;  
         [0036]      FIG. 13  illustrates a tubular portion arrangement of the fluid delivery connectors of  FIGS. 10 and 11 ;  
         [0037]      FIG. 14A  illustrates a capping member for the female and male end portions of  FIGS. 8 and 9 ;  
         [0038]      FIG. 14B  illustrates the capping member of  FIG. 14A  applied to the printhead module of  FIG. 4A ;  
         [0039]      FIG. 15A  shows a sectional (skeletal) view of a support frame of a casing of the printhead assembly of  FIG. 1 ;  
         [0040]      FIGS. 15B and 15C  show perspective views of the support frame of  FIG. 15A  in upward and downward orientations, respectively;  
         [0041]      FIG. 16  illustrates a printed circuit board (PCB) support that forms a portion of the printhead assembly of  FIG. 1 ;  
         [0042]      FIGS. 17A and 17B  show side and rear perspective views of the PCB support of  FIG. 16 ;  
         [0043]      FIG. 18A  illustrates circuit components carried by a PCB supported by the PCB support of  FIG. 16 ;  
         [0044]      FIG. 18B  shows an opposite side perspective view of the PCB and the circuit components of  FIG. 18A ;  
         [0045]      FIG. 19A  shows a side view illustrating further components attached to the PCB support of  FIG. 16 ;  
         [0046]      FIG. 19B  shows a rear side view of a pressure plate that forms a portion of the printhead assembly of  FIG. 1 ;  
         [0047]      FIG. 20  shows a front view illustrating the further components of  FIG. 19 ;  
         [0048]      FIG. 21  shows a perspective view illustrating the further components of  FIG. 19 ;  
         [0049]      FIG. 22  shows a front view of the PCB support of  FIG. 16 ;  
         [0050]      FIG. 22A  shows a side sectional view taken along the line I-I in  FIG. 22 ;  
         [0051]      FIG. 22B  shows an enlarged view of the section A of  FIG. 22A ;  
         [0052]      FIG. 22C  shows a side sectional view taken along the line II-II in  FIG. 22 ;  
         [0053]      FIG. 22D  shows an enlarged view of the section B of  FIG. 22C ;  
         [0054]      FIG. 22E  shows an enlarged view of the section C of  FIG. 22C ;  
         [0055]      FIG. 23  shows a side view of a cover portion of the casing of the printhead assembly of  FIG. 1 ;  
         [0056]      FIG. 24  illustrates a plurality of the PCB supports of  FIG. 16  in a modular assembly;  
         [0057]      FIG. 25  illustrates a connecting member that is carried by two adjacent PCB supports of  FIG. 24  and which is used for interconnecting PCBs that are carried by the PCB supports;  
         [0058]      FIG. 26  illustrates the connecting member of  FIG. 25  interconnecting two PCBs;  
         [0059]      FIG. 27  illustrates the interconnection between two PCBs by the connecting member of  FIG. 25 ;  
         [0060]      FIG. 28  illustrates a connecting region of busbars that are located in the printhead assembly of  FIG. 1 ;  
         [0061]      FIG. 29  shows a perspective view of an end portion of a printhead assembly in accordance with an embodiment of the present invention;  
         [0062]      FIG. 30  illustrates a connector arrangement that is located in the end portion of the printhead assembly as shown in  FIG. 29 ;  
         [0063]      FIG. 31  illustrates the connector arrangement of  FIG. 30  housed in an end housing and plate assembly which forms a portion of the printhead assembly;  
         [0064]      FIGS. 32A and 32B  show opposite side views of the connector arrangement of  FIG. 30 ;  
         [0065]      FIG. 32C  illustrates a fluid delivery connection portion of the connector arrangement of  FIG. 30 ;  
         [0066]      FIG. 33A  illustrates a support member that is located in a printhead assembly in accordance with an embodiment of the present invention;  
         [0067]      FIG. 33B  shows a sectional view of the printhead assembly with the support member of  FIG. 33A  located therein;  
         [0068]      FIG. 33C  illustrates a part of the printhead assembly of  FIG. 33B  in more detail;  
         [0069]      FIG. 34  illustrates the connector arrangement of  FIG. 30  housed in the end housing and plate assembly of  FIG. 31  attached to the casing of the printhead assembly;  
         [0070]      FIG. 35A  shows an exploded perspective view of the end housing and plate assembly of  FIG. 31 ;  
         [0071]      FIG. 35B  shows an exploded perspective view of an end housing and plate assembly which forms a portion of the printhead assembly of  FIG. 1 ;  
         [0072]      FIG. 36  shows a perspective view of the printhead assembly when in a form which uses both of the end housing and plate assemblies of  FIGS. 35A and 35B ;  
         [0073]      FIG. 37  illustrates a connector arrangement housed in the end housing and plate assembly of  FIG. 35B ;  
         [0074]      FIGS. 38A and 38B  shows opposite side views of the connector arrangement of  FIG. 37 ;  
         [0075]      FIG. 39  illustrates an end plate when attached to the printhead assembly of  FIG. 29 ;  
         [0076]      FIG. 40  illustrates data flow and functions performed by a print engine controller integrated circuit that forms one of the circuit components shown in  FIG. 18A ;  
         [0077]      FIG. 41  illustrates the print engine controller integrated circuit of  FIG. 40  in the context of an overall printing system architecture;  
         [0078]      FIG. 42  illustrates the architecture of the print engine controller integrated circuit of  FIG. 41 ;  
         [0079]      FIG. 43  shows an exploded view of a fluid distribution stack of elements that form the printhead tile of  FIG. 5A ;  
         [0080]      FIG. 44  shows a perspective view (partly in section) of a portion of a nozzle system of a printhead integrated circuit that is incorporated in the printhead module of the printhead assembly of  FIG. 1 ;  
         [0081]      FIG. 45  shows a vertical sectional view of a single nozzle (of the nozzle system shown in  FIG. 44 ) in a quiescent state;  
         [0082]      FIG. 46  shows a vertical sectional view of the nozzle of  FIG. 45  at an initial actuation state;  
         [0083]      FIG. 47  shows a vertical sectional view of the nozzle of  FIG. 46  at a later actuation state;  
         [0084]      FIG. 48  shows in perspective a partial vertical sectional view of the nozzle of  FIG. 45 , at the actuation state shown in  FIG. 46 ;  
         [0085]      FIG. 49  shows in perspective a vertical section of the nozzle of  FIG. 45 , with ink omitted;  
         [0086]      FIG. 50  shows a vertical sectional view of the nozzle of  FIG. 49 ;  
         [0087]      FIG. 51  shows in perspective a partial vertical sectional view of the nozzle of  FIG. 45 , at the actuation state shown in  FIG. 46 ;  
         [0088]      FIG. 52  shows a plan view of the nozzle of  FIG. 45 ; and  
         [0089]      FIG. 53  shows a plan view of the nozzle of  FIG. 45  with lever arm and movable nozzle portions omitted. 
     
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS  
       [0090]     The exemplary embodiments of the present invention are described as a printhead assembly and a printhead module that is incorporated in the printhead assembly.  
         [0000]     General Overview  
         [0091]     The printhead assembly  10  as shown in  FIGS. 1 and 2  is intended for use as a pagewidth printhead in a printing system. That is, a printhead which extends across the width or along the length of a page of print media, e.g., paper, for printing. During printing, the printhead assembly ejects ink onto the print media as it progresses past, thereby forming printed information thereon, with the printhead assembly being maintained in a stationary position as the print media is progressed past. That is, the printhead assembly is not scanned across the page in the manner of a conventional printhead.  
         [0092]     As can be seen from  FIGS. 1 and 2 , the printhead assembly  10  includes a casing  20  and a printhead module  30 . The casing  20  houses the dedicated (or drive) electronics for the printhead assembly together with power and data inputs, and provides a structure for mounting the printhead assembly to a printer unit. The printhead module  30 , which is received within a channel  21  of the casing  20  so as to be removable therefrom, includes a fluid channel member  40  which carries printhead tiles  50  having printhead integrated circuits  51  incorporating printing nozzles thereon. The printhead assembly  10  further includes an end housing  120  and plate  110  assembly and an end plate  111  which are attached to longitudinal ends of the assembled casing  20  and printhead module  30 .  
         [0093]     The printhead module  30  and its associated components will now be described with reference to FIGS.  1  to  14 B.  
         [0094]     As shown in  FIG. 3 , the printhead module  30  includes the fluid channel member  40  and the printhead tiles  50  mounted on the upper surface of the member  40 .  
         [0095]     As illustrated in  FIGS. 1 and 2 , sixteen printhead tiles  50  are provided in the printhead module  30 . However, as will be understood from the following description, the number of printhead tiles and printhead integrated circuits mounted thereon may be varied to meet specific applications of the present invention.  
         [0096]     As illustrated in  FIGS. 1 and 2 , each of the printhead tiles  50  has a stepped end region so that, when adjacent printhead tiles  50  are butted together end-to-end, the printhead integrated circuits  51  mounted thereon overlap in this region. Further, the printhead integrated circuits  51  extend at an angle relative to the longitudinal direction of the printhead tiles  50  to facilitate overlapping between the printhead integrated circuits  51 . This overlapping of adjacent printhead integrated circuits  51  provides for a constant pitch between the printing nozzles (described later) incorporated in the printhead integrated circuits  51  and this arrangement obviated discontinuities in information printed across or along the print media (not shown) passing the printhead assembly  10 . This overlapping arrangement of the printhead integrated circuits is described in the Applicant&#39;s issued U.S. Pat. No. 6,623,106, which is incorporated herein by reference.  
         [0097]      FIG. 4  shows the fluid channel member  40  of the printhead module  30  which serves as a support member for the printhead tiles  50 . The fluid channel member  40  is configured so as to fit within the channel  21  of the casing  20  and is used to deliver printing ink and other fluids to the printhead tiles  50 . To achieve this, the fluid channel member  40  includes channel-shaped ducts  41  which extend throughout its length from each end of the fluid channel member  40 . The channel-shaped ducts  41  are used to transport printing ink and other fluids from a fluid supply unit (of a printing system to which the printhead assembly  10  is mounted) to the printhead tiles  50  via a plurality of outlet ports  42 .  
         [0098]     The fluid channel member  40  is formed by injection moulding a suitable material. Suitable materials are those which have a low coefficient of linear thermal expansion (CTE), so that the nozzles of the printhead integrated circuits are accurately maintained under operational condition (described in more detail later), and have chemical inertness to the inks and other fluids channelled through the fluid channel member  40 . One example of a suitable material is a liquid crystal polymer (LCP). The injection moulding process is employed to form a body portion  44   a  having open channels or grooves therein and a lid portion  44   b  which is shaped with elongate ridge portions  44   c  to be received in the open channels. The body and lid portions  44   a  and  44   b  are then adhered together with an epoxy to form the channel-shaped ducts  41  as shown in  FIGS. 3 and 4 A. However, alternative moulding techniques may be employed to form the fluid channel member  40  in one piece with the channel-shaped ducts  41  therein.  
         [0099]     The plurality of ducts  41 , provided in communication with the corresponding outlet ports  42  for each printhead tile  50 , are used to transport different coloured or types of inks and the other fluids. The different inks can have different colour pigments, for example, black, cyan, magenta and yellow, etc., and/or be selected for different printing applications, for example, as visually opaque inks, infrared opaque inks, etc. Further, the other fluids which can be used are, for example, air for maintaining the printhead integrated circuits  51  free from dust and other impurities and/or for preventing the print media from coming into direct contact with the printing nozzles provided on the printhead integrated circuits  51 , and fixative for fixing the ink substantially immediately after being printed onto the print media, particularly in the case of high-speed printing applications.  
         [0100]     In the assembly shown in  FIG. 4 , seven ducts  41  are shown for transporting black, cyan, magenta and yellow coloured ink, each in one duct, infrared ink in one duct, air in one duct and fixative in one duct. Even though seven ducts are shown, a greater or lesser number may be provided to meet specific applications. For example, additional ducts might be provided for transporting black ink due to the generally higher percentage of black and white or greyscale printing applications.  
         [0101]     The fluid channel member  40  further includes a pair of longitudinally extending tabs  43  along the sides thereof for securing the printhead module  30  to the channel  21  of the casing  20  (described in more detail later). It is to be understood however that a series of individual tabs could alternatively be used for this purpose.  
         [0102]     As shown in  FIG. 5A , each of the printhead tiles  50  of the printhead module  30  carries one of the printhead integrated circuits  51 , the latter being electrically connected to a printed circuit board (PCB)  52  using appropriate contact methods such as wire bonding, with the connections being protectively encapsulated in an epoxy encapsulant  53 . The PCB  52  extends to an edge of the printhead tile  50 , in the direction away from where the printhead integrated circuits  51  are placed, where the PCB  52  is directly connected to a flexible printed circuit board (flex PCB)  80  for providing power and data to the printhead integrated circuit  51  (described in more detail later). This is shown in  FIG. 6  with individual flex PCBs  80  extending or “hanging” from the edge of each of the printhead tiles  50 . The flex PCBs  80  provide electrical connection between the printhead integrated circuits  51 , a power supply  70  and a PCB  90  (see  FIG. 3 ) with drive electronics  100  (see  FIG. 18A ) housed within the casing  20  (described in more detail later).  
         [0103]      FIG. 5B  shows the underside of one of the printhead tiles  50 . A plurality of inlet ports  54  is provided and the inlet ports  54  are arranged to communicate with corresponding ones of the plurality of outlet ports  42  of the ducts  41  of the fluid channel member  40  when the printhead tiles  50  are mounted thereon. That is, as illustrated, seven inlet ports  54  are provided for the outlet ports  42  of the seven ducts  41 . Specifically, both the inlet and outlet ports are orientated in an inclined disposition with respect to the longitudinal direction of the printhead module so that the correct fluid, i.e., the fluid being channelled by a specific duct, is delivered to the correct nozzles (typically a group of nozzles is used for each type of ink or fluid) of the printhead integrated circuits.  
         [0104]     On a typical printhead integrated circuit  51  as employed in realisation of the present invention, more than 7000 (e.g., 7680) individual printing nozzles may be provided, which are spaced so as to effect printing with a resolution of 1600 dots per inch (dpi). This is achieved by having a nozzle density of 391 nozzles/mm 2  across a print surface width of 20 mm (0.8 in), with each nozzle capable of delivering a drop volume of 1 pl.  
         [0105]     Accordingly, the nozzles are micro-sized (i.e., of the order of 10 −6  metres) and as such are not capable of receiving a macro-sized (i.e., millimetric) flows of ink and other fluid as presented by the inlet ports  54  on the underside of the printhead tile  50 . Each printhead tile  50 , therefore, is formed as a fluid distribution stack  500  (see  FIG. 43 ), which includes a plurality of laminated layers, with the printhead integrated circuit  51 , the PCB  52 , and the epoxy  53  provided thereon.  
         [0106]     The stack  500  carries the ink and other fluids from the ducts  41  of the fluid channel member  40  to the individual nozzles of the printhead integrated circuit  51  by reducing the macro-sized flow diameter at the inlet ports  54  to a micro-sized flow diameter at the nozzles of the printhead integrated circuits  51 . An exemplary structure of the stack which provides this reduction is described in more detail later.  
         [0107]     Nozzle systems which are applicable to the printhead assembly of the present invention may comprise any type of ink jet nozzle arrangement which can be integrated on a printhead integrated circuit. That is, systems such as a continuous ink system, an electrostatic system and a drop-on-demand system, including thermal and piezoelectric types, may be used.  
         [0108]     There are various types of known thermal drop-on-demand system which may be employed which typically include ink reservoirs adjacent the nozzles and heater elements in thermal contact therewith. The heater elements heat the ink and create gas bubbles which generate pressures in the ink to cause droplets to be ejected through the nozzles onto the print media. The amount of ink ejected onto the print media and the timing of ejection by each nozzle are controlled by drive electronics. Such thermal systems impose limitations on the type of ink that can be used however, since the ink must be resistant to heat.  
         [0109]     There are various types of known piezoelectric drop-on-demand system which may be employed which typically use piezo-crystals (located adjacent the ink reservoirs) which are caused to flex when an electric current flows therethrough. This flexing causes droplets of ink to be ejected from the nozzles in a similar manner to the thermal systems described above. In such piezoelectric systems the ink does not have to be heated and cooled between cycles, thus providing for a greater range of available ink types. Piezoelectric systems are difficult to integrate into drive integrated circuits and typically require a large number of connections between the drivers and the nozzle actuators.  
         [0110]     As an alternative, a micro-electromechanical system (MEMS) of nozzles may be used, such a system including thermo-actuators which cause the nozzles to eject ink droplets. An exemplary MEMS nozzle system applicable to the printhead assembly of the present invention is described in more detail later.  
         [0111]     Returning to the assembly of the fluid channel member  40  and printhead tiles  50 , each printhead tile  50  is attached to the fluid channel member  40  such that the individual outlet ports  42  and their corresponding inlet ports  54  are aligned to allow effective transfer of fluid therebetween. An adhesive, such as a curable resin (e.g., an epoxy resin), is used for attaching the printhead tiles  50  to the fluid channel member  40  with the upper surface of the fluid channel member  40  being prepared in the manner shown in  FIG. 7 .  
         [0112]     That is, a curable resin is provided around each of the outlet ports  42  to form a gasket member  60  upon curing. This gasket member  60  provides an adhesive seal between the fluid channel member  40  and printhead tile  50  whilst also providing a seal around each of the communicating outlet ports  42  and inlet ports  54 . This sealing arrangement facilitates the flow and containment of fluid between the ports. Further, two curable resin deposits  61  are provided on either side of the gasket member  60  in a symmetrical manner.  
         [0113]     The symmetrically placed deposits  61  act as locators for positioning the printhead tiles  50  on the fluid channel member  40  and for preventing twisting of the printhead tiles  50  in relation to the fluid channel member  40 . In order to provide additional bonding strength, particularly prior to and during curing of the gasket members  60  and locators  61 , adhesive drops  62  are provided in free areas of the upper surface of the fluid channel member  40 . A fast acting adhesive, such as cyanoacrylate or the like, is deposited to form the locators  61  and prevents any movement of the printhead tiles  50  with respect to the fluid channel member  40  during curing of the curable resin.  
         [0114]     With this arrangement, if a printhead tile is to be replaced, should one or a number of nozzles of the associated printhead integrated circuit fail, the individual printhead tiles may easily be removed. Thus, the surfaces of the fluid channel member and the printhead tiles are treated in a manner to ensure that the epoxy remains attached to the printhead tile, and not the fluid channel member surface, if a printhead tile is removed from the surface of the fluid channel member by levering. Consequently, a clean surface is left behind by the removed printhead tile, so that new epoxy can readily be provided on the fluid channel member surface for secure placement of a new printhead tile.  
         [0115]     The above-described printhead module of the present invention is capable of being constructed in various lengths, accommodating varying numbers of printhead tiles attached to the fluid channel member, depending upon the specific application for which the printhead assembly is to be employed. For example, in order to provide a printhead assembly for A3-sized pagewidth printing in landscape orientation, the printhead assembly may require 16 individual printhead tiles. This may be achieved by providing, for example, four printhead modules each having four printhead tiles, or two printhead modules each having eight printhead tiles, or one printhead module having 16 printhead tiles (as in  FIGS. 1 and 2 ) or any other suitable combination. Basically, a selected number of standard printhead modules may be combined in order to achieve the necessary width required for a specific printing application.  
         [0116]     In order to provide this modularity in an easy and efficient manner, plural fluid channel members of each of the printhead modules are formed so as to be modular and are configured to permit the connection of a number of fluid channel members in an end-to-end manner. Advantageously, an easy and convenient means of connection can be provided by configuring each of the fluid channel members to have complementary end portions. In one embodiment of the present invention each fluid channel member  40  has a “female” end portion  45 , as shown in  FIG. 8 , and a complementary “male” end portion  46 , as shown in  FIG. 9 .  
         [0117]     The end portions  45  and  46  are configured so that on bringing the male end portion  46  of one printhead module  30  into contact with the female end portion  45  of a second printhead module  30 , the two printhead modules  30  are connected with the corresponding ducts  41  thereof in fluid communication. This allows fluid to flow between the connected printhead modules  30  without interruption, so that fluid such as ink, is correctly and effectively delivered to the printhead integrated circuits  51  of each of the printhead modules  30 .  
         [0118]     In order to ensure that the mating of the female and male end portions  45  and  46  provides an effective seal between the individual printhead modules  30  a sealing adhesive, such as epoxy, is applied between the mated end portions.  
         [0119]     It is clear that, by providing such a configuration, any number of printhead modules can suitably be connected in such an end-to-end fashion to provide the desired scale-up of the total printhead length. Those skilled in the art can appreciate that other configurations and methods for connecting the printhead assembly modules together so as to be in fluid communication are within the scope of the present invention.  
         [0120]     Further, this exemplary configuration of the end portions  45  and  46  of the fluid channel member  40  of the printhead modules  30  also enables easy connection to the fluid supply of the printing system to which the printhead assembly is mounted. That is, in one embodiment of the present invention, fluid delivery connectors  47  and  48  are provided, as shown in  FIGS. 10 and 11 , which act as an interface for fluid flow between the ducts  41  of the printhead modules  30  and (internal) fluid delivery tubes  6 , as shown in  FIG. 12 . The fluid delivery tubes  6  are referred to as being internal since, as described in more detail later, these tubes  6  are housed in the printhead assembly  10  for connection to external fluid delivery tubes of the fluid supply of the printing system. However, such an arrangement is clearly only one of the possible ways in which the inks and other fluids can be supplied to the printhead assembly of the present invention.  
         [0121]     As shown in  FIG. 10 , the fluid delivery connector  47  has a female connecting portion  47   a  which can mate with the male end portion  46  of the printhead module  30 . Alternatively, or additionally, as shown in  FIG. 11 , the fluid delivery connector  48  has a male connecting portion  48   a  which can mate with the female end portion  45  of the printhead module  30 . Further, the fluid delivery connectors  47  and  48  include tubular portions  47   b  and  48   b , respectively, which can mate with the internal fluid delivery tubes  6 . The particular manner in which the tubular portions  47   b  and  48   b  are configured so as to be in fluid communication with a corresponding duct  41  is shown in  FIG. 12 .  
         [0122]     As shown in FIGS.  10  to  13 , seven tubular portions  47   b  and  48   b  are provided to correspond to the seven ducts  41  provided in accordance with the above-described exemplary embodiment of the present invention. Accordingly, seven internal fluid delivery tubes  6  are used each for delivering one of the seven aforementioned fluids of black, cyan, magenta and yellow ink, IR ink, fixative and air. However, as previously stated, those skilled in the art clearly understand that more or less fluids may be used in different applications, and consequently more or less fluid delivery tubes, tubular portions of the fluid delivery connectors and ducts may be provided.  
         [0123]     Further, this exemplary configuration of the end portions of the fluid channel member  40  of the printhead modules  30  also enables easy sealing of the ducts  41 . To this end, in one embodiment of the present invention, a sealing member  49  is provided as shown in  FIG. 14A , which can seal or cap both of the end portions of the printhead module  30 . That is, the sealing member  49  includes a female connecting section  49   a  and a male connecting section  49   b  which can respectively mate with the male end portion  46  and the female end portion  45  of the printhead modules  30 . Thus, a single sealing member is advantageously provided despite the differently configured end portions of a printhead module.  FIG. 14B  illustrates an exemplary arrangement of the sealing member  49  sealing the ducts  41  of the fluid channel member  40 . Sealing of the sealing member  49  and the fluid channel member  40  interface is further facilitated by applying a sealing adhesive, such as an epoxy, as described above.  
         [0124]     In operation of a single printhead module  30  for an A4-sized pagewidth printing application, for example, a combination of one of the fluid delivery connectors  47  and  48  connected to one corresponding end portion  45  and  46  and a sealing member  49  connected to the other of the corresponding end portions  45  and  46  is used so as to deliver fluid to the printhead integrated circuits  51 . On the other hand, in applications where the printhead assembly is particularly long, being comprised of a plurality of printhead modules  30  connected together (e.g., in wide format printing), it may be necessary to provide fluid from both ends of the printhead assembly. Accordingly, one each of the fluid delivery connectors  47  and  48  may be connected to the corresponding end portions  45  and  46  of the end printhead modules  30 .  
         [0125]     The above-described exemplary configuration of the end portions of the printhead module of the present invention provides, in part, for the modularity of the printhead modules. This modularity makes it possible to manufacture the fluid channel members of the printhead modules in a standard length relating to the minimum length application of the printhead assembly. The printhead assembly length can then be scaled-up by combining a number of printhead modules to form a printhead assembly of a desired length. For example, a standard length printhead module could be manufactured to contain eight printhead tiles, which may be the minimum requirement for A4-sized printing applications. Thus, for a printing application requiring a wider printhead having a length equivalent to 32 printhead tiles, four of these standard length printhead modules could be used. On the other hand, a number of different standard length printhead modules might be manufactured, which can be used in combination for applications requiring variable length printheads.  
         [0126]     However, these are merely examples of how the modularity of the printhead assembly of the present invention functions, and other combinations and standard lengths could be employed and fall within the scope of the present invention.  
         [0127]     The casing  20  and its associated components will now be described with reference to FIGS.  1  to  3  and  15 A to  28 .  
         [0128]     In one embodiment of the present invention, the casing  20  is formed as a two-piece outer housing which houses the various components of the printhead assembly and provides structure for the printhead assembly which enables the entire unit to be readily mounted in a printing system. As shown in  FIG. 3 , the outer housing is composed of a support frame  22  and a cover portion  23 . Each of these portions  22  and  23  are made from a suitable material which is lightweight and durable, and which can easily be extruded to form various lengths. Accordingly, in one embodiment of the present invention, the portions  22  and  23  are formed from a metal such as aluminium.  
         [0129]     As shown in  FIGS. 15A  to  15 C, the support frame  22  of the casing  20  has an outer frame wall  24  and an inner frame wall  25  (with respect to the outward and inward directions of the printhead assembly  10 ), with these two walls being separated by an internal cavity  26 . The channel  21  (also see  FIG. 3 ) is formed as an extension of an upper wall  27  of the support frame  22  and an arm portion  28  is formed on a lower region of the support frame  22 , extending from the inner frame wall  25  in a direction away from the outer frame wall  24 . The channel  21  extends along the length of the support frame  22  and is configured to receive the printhead module  30 . The printhead module  30  is received in the channel  21  with the printhead integrated circuits  51  facing in an upward direction, as shown in FIGS.  1  to  3 , and this upper printhead integrated circuit surface defines the printing surface of the printhead assembly  10 .  
         [0130]     As depicted in  FIG. 15A , the channel  21  is formed by the upper wall  27  and two, generally parallel side walls  24   a  and  29  of the support frame  22 , which are arranged as outer and inner side walls (with respect to the outward and inward directions of the printhead assembly  10 ) extending along the length of the support frame  22 . The two side walls  24   a  and  29  have different heights with the taller, outer side wall  24   a  being defined as the upper portion of the outer frame wall  24  which extends above the upper wall  27  of the support frame  22 , and the shorter, inner side wall  29  being provided as an upward extension of the upper wall  27  substantially parallel to the inner frame wall  25 . The outer side wall  24   a  includes a recess (groove)  24   b  formed along the length thereof. A bottom surface  24   c  of the recess  24   b  is positioned so as to be at the same height as a top surface  29   a  of the inner side wall  29  with respect to the upper wall  27  of the channel  21 . The recess  24   b  further has an upper surface  24   d  which is formed as a ridge which runs along the length of the outer side wall  24   a  (see  FIG. 15B ).  
         [0131]     In this arrangement, one of the longitudinally extending tabs  43  of the fluid channel member  40  of the printhead module  30  is received within the recess  24   b  of the outer side wall  24   a  so as to be held between the lower and upper surfaces  24   c  and  24   d  thereof. Further, the other longitudinally extending tab  43  provided on the opposite side of the fluid channel member  40 , is positioned on the top surface  29   a  of the inner side wall  29 . In this manner, the assembled printhead module  30  may be secured in place on the casing  20 , as will be described in more detail later.  
         [0132]     Further, the outer side wall  24   a  also includes a slanted portion  24   e  along the top margin thereof, the slanted portion  24   e  being provided for fixing a print media guide  5  to the printhead assembly  10 , as shown in  FIG. 3 . This print media guide is fixed following assembly of the printhead assembly and is configured to assist in guiding print media, such as paper, across the printhead integrated circuits for printing without making direct contact with the nozzles of the printhead integrated circuits.  
         [0133]     As shown in  FIG. 15A , the upper wall  27  of the support frame  22  and the arm portion  28  include lugs  27   a  and  28   a , respectively, which extend along the length of the support frame  22  (see  FIGS. 15B and 15C ). The lugs  27   a  and  28   a  are positioned substantially to oppose each other with respect to the inner frame wall  25  of the support frame  22  and are used to secure a PCB support  91  (described below) to the support frame  22 .  
         [0134]      FIGS. 15B and 15C  illustrate the manner in which the outer and inner frame walls  24  and  25  extend for the length of the casing  20 , as do the channel  21 , the upper wall  27 , and its lug  27   a , the outer and inner side walls  24   a  and  29 , the recess  24   b  and its bottom and upper surfaces  24   c  and  24   d , the slanted portion  24   e , the top surface  29   a  of the inner side wall  29 , and the arm portion  28 , and its lugs  28   a  and  28   b  and recessed and curved end portions  28   c  and  28   d  (described in more detail later).  
         [0135]     The PCB support  91  will now be described with reference to  FIGS. 3 and 16  to  22 E. In  FIG. 3 , the support  91  is shown in its secured position extending along the inner frame wall  25  of the support frame  22  from the upper wall  27  to the arm portion  28 . The support  91  is used to carry the PCB  90  which mounts the drive electronics  100  (as described in more detail later).  
         [0136]     As can be seen particularly in  FIGS. 17A and 17B , the support  91  includes lugs  92  on upper and lower surfaces thereof which communicate with the lugs  27   a  and  28   a  for securing the support  91  against the inner frame wall  25  of the support frame  22 . A base portion  93  of the support  91 , is arranged to extend along the arm portion  28  of the support frame  22 , and is seated on the top surfaces of the lugs  28   a  and  28   b  of the arm portion  28  (see  FIG. 15B ) when mounted on the support frame  22 .  
         [0137]     The support  91  is formed so as to locate within the casing  20  and against the inner frame wall  25  of the support frame  22 . This can be achieved by moulding the support  91  from a plastics material having inherent resilient properties to engage with the inner frame wall  25 . This also provides the support  91  with the necessary insulating properties for carrying the PCB  90 . For example, polybutylene terephthalate (PBT) or polycarbonate may be used for the support  91 .  
         [0138]     The base portion  93  further includes recessed portions  93   a  and corresponding locating lugs  93   b , which are used to secure the PCB  90  to the support  91  (as described in more detail later). Further, the upper portion of the support  91  includes upwardly extending arm portions  94 , which are arranged and shaped so as to fit over the inner side wall  29  of the channel  21  and the longitudinally extending tab  43  of the printhead module  30  (which is positioned on the top surface  29   a  of the inner side wall  29 ) once the fluid channel member  40  of the printhead module  30  has been inserted into the channel  21 . This arrangement provides for securement of the printhead module  30  within the channel  21  of the casing  20 , as is shown more clearly in  FIG. 3 .  
         [0139]     In one embodiment of the present invention, the extending arm portions  94  of the support  91  are configured so as to perform a “clipping” or “clamping” action over and along one edge of the printhead module  30 , which aids in preventing the printhead module  30  from being dislodged or displaced from the fully assembled printhead assembly  10 . This is because the clipping action acts upon the fluid channel member  40  of the printhead module  30  in a manner which substantially constrains the printhead module  30  from moving upwards from the printhead assembly  10  (i.e., in the z-axis direction as depicted in  FIG. 3 ) due to both longitudinally extending tabs  43  of the fluid channel member  40  being held firmly in place (in a manner which will be described in more detail below), and from moving across the longitudinal direction of the printhead module  30  (i.e., in the y-axis direction as depicted in  FIG. 3 ), which will be also described in more detail below.  
         [0140]     In this regard, the fluid channel member  40  of the printhead module  30  is exposed to a force exerted by the support  91  directed along the y-axis in a direction from the inner side wall  29  to the outer side wall  24   a . This force causes the longitudinally extending tab  43  of the fluid channel member  40  on the outer side wall  24   a  side of the support frame  22  to be held between the lower and upper surfaces  24   c  and  24   d  of the recess  24   b . This force, in combination with the other longitudinally extending tab  43  of the fluid channel member  40  being held between the top surface  29   a  of the inner side wall  29  and the extending arm portions  94  of the support  91 , acts to inhibit movement of the printhead module  30  in the z-axis direction (as described in more detail later).  
         [0141]     However, the printhead module  30  is still able to accommodate movement in the x-axis direction (i.e., along the longitudinal direction of the printhead module  30 ), which is desirable in the event that the casing  20  undergoes thermal expansion and contraction, during operation of the printing system. As the casing is typically made from an extruded metal, such as aluminium, it may undergo dimensional changes due to such materials being susceptible to thermal expansion and contraction in a thermally variable environment, such as is present in a printing unit.  
         [0142]     That is, in order to ensure the integrity and reliability of the printhead assembly, the fluid channel member  40  of the printhead module  30  is firstly formed of material (such as LCP or the like) which will not experience substantial dimensional changes due to environmental changes thereby retaining the positional relationship between the individual printhead tiles, and the printhead module  30  is arranged to be substantially independent positionally with respect to the casing  20  (i.e., the printhead module “floats” in the longitudinal direction of the channel  21  of the casing  20 ) in which the printhead module  30  is removably mounted.  
         [0143]     Therefore, as the printhead module is not constrained in the x-axis direction, any thermal expansion forces from the casing in this direction will not be transferred to the printhead module. Further, as the constraint in the z-axis and y-axis directions is resilient, there is some tolerance for movement in these directions. Consequently, the delicate printhead integrated circuits of the printhead modules are protected from these forces and the reliability of the printhead assembly is maintained.  
         [0144]     Furthermore, the clipping arrangement also allows for easy assembly and disassembly of the printhead assembly by the mere “unclipping” of the PCB support(s) from the casing. In the exemplary embodiment shown in  FIG. 16 , a pair of extending arm portions  94  is provided; however those skilled in the art will understand that a greater or lesser number is within the scope of the present invention.  
         [0145]     Referring again to FIGS.  16  to  17 B, the support  91  further includes a channel portion  95  in the upper portion thereof. In the exemplary embodiment illustrated, the channel portion  95  includes three channelled recesses  95   a ,  95   b  and  95   c . The channelled recesses  95   a ,  95   b  and  95   c  are provided so as to accommodate three longitudinally extending electrical conductors or busbars  71 ,  72  and  73  (see  FIG. 2 ) which form the power supply  70  (see  FIG. 3 ) and which extend along the length of the printhead assembly  10 . The busbars  71 ,  72  and  73  are conductors which carry the power required to operate the printhead integrated circuits  51  and the drive electronics  100  located on the PCB  90  (shown in  FIG. 18A  and described in more detail later), and may be formed of copper with gold plating, for example.  
         [0146]     In one embodiment of the present invention, three busbars are used in order to provide for voltages of Vcc (e.g., via the busbar  71 ), ground (Gnd) (e.g., via the busbar  72 ) and V+ (e.g., via the busbar  73 ). Specifically, the voltages of Vcc and Gnd are applied to the drive electronics  100  and associated circuitry of the PCB  90 , and the voltages of Vcc, Gnd and V+ are applied to the printhead integrated circuits  51  of the printhead tiles  50 . It will be understood by those skilled in the art that a greater or lesser number of busbars, and therefore channelled recesses in the PCB support can be used depending on the power requirements of the specific printing applications.  
         [0147]     The support  91  of the present invention further includes (lower) retaining clips  96  positioned below the channel portion  95 . In the exemplary embodiment illustrated in  FIG. 16 , a pair of the retaining clips  96  is provided. The retaining clips  96  include a notch portion  96   a  on a bottom surface thereof which serves to assist in securely mounting the PCB  90  on the support  91 . To this end, as shown in the exemplary embodiment of  FIG. 18A , the PCB  90  includes a pair of slots  97  in a topmost side thereof (with respect to the mounting direction of the PCB  90 ), which align with the notch portions  96   a  when mounted so as to facilitate engagement with the retaining clips  96 .  
         [0148]     As shown in  FIG. 3 , the PCB  90  is snugly mounted between the notch portions  96   a  of the retaining clips  96  and the afore-mentioned recessed portions  93   a  and locating lugs  93   b  of the base portion  93  of the support  91 . This arrangement securely holds the PCB  90  in position so as to enable reliable connection between the drive electronics  100  of the PCB  90  and the printhead integrated circuits  51  of the printhead module  30 .  
         [0149]     Referring again to  FIG. 18A , an exemplary circuit arrangement of the PCB  90  will now be described. The circuitry includes the drive electronics  100  in the form of a print engine controller (PEC) integrated circuit. The PEC integrated circuit  100  is used to drive the printhead integrated circuits  51  of the printhead module  30  in order to print information on the print media passing the printhead assembly  10  when mounted to a printing unit. The functions and structure of the PEC integrated circuit  100  are discussed in more detail later.  
         [0150]     The exemplary circuitry of the PCB  90  also includes four connectors  98  in the upper portion thereof (see  FIG. 18B ) which receive lower connecting portions  81  of the flex PCBs  80  that extend from each of the printhead tiles  50  (see  FIG. 6 ). Specifically, the corresponding ends of four of the flex PCBs  80  are connected between the PCBs  52  of four printhead tiles  50  and the four connectors  98  of the PCB  90 . In turn, the connectors  98  are connected to the PEC integrated circuit  100  so that data communication can take place between the PEC integrated circuit  100  and the printhead integrated circuits  51  of the four printhead tiles  50 .  
         [0151]     In the above-described embodiment, one PEC integrated circuit is chosen to control four printhead tiles in order to satisfy the necessary printing speed requirements of the printhead assembly. In this manner, for a printhead assembly having 16 printhead tiles, as described above with respect to  FIGS. 1 and 2 , four PEC integrated circuits are required and therefore four PCB supports  91  are used. However, it will be understood by those skilled in the art that the number of PEC integrated circuits used to control a number of printhead tiles may be varied, and as such many different combinations of the number of printhead tiles, PEC integrated circuits, PCBs and PCB supports that may be employed depending on the specific application of the printhead assembly of the present invention. Further, a single PEC integrated circuit  100  could be provided to drive a single printhead integrated circuit  51 . Furthermore, more than one PEC integrated circuit  100  may be placed on a PCB  90 , such that differently configured PCBs  90  and supports  91  may be used.  
         [0152]     It is to be noted that the modular approach of employing a number of PCBs holding separate PEC integrated circuits for controlling separate areas of the printhead advantageously assists in the easy determination, removal and replacement of defective circuitry in the printhead assembly.  
         [0153]     The above-mentioned power supply to the circuitry of the PCB  90  and the printhead integrated circuits  51  mounted to the printhead tiles  50  is provided by the flex PCBs  80 . Specifically, the flex PCBs  80  are used for the two functions of providing data connection between the PEC integrated circuit(s)  100  and the printhead integrated circuits  51  and providing power connection between the busbars  71 ,  72  and  73  and the PCB  90  and the printhead integrated circuits  51 . In order to provide the necessary electrical connections, the flex PCBs  80  are arranged to extend from the printhead tiles  50  to the PCB  90 . This may be achieved by employing the arrangement shown in  FIG. 3 , in which a resilient pressure plate  74  is provided to urge the flex PCBs  80  against the busbars  71 ,  72  and  73 . In this arrangement, suitably arranged electrical connections are provided on the flex PCBs  80  which route power from the busbars  71  and  72  (i.e., Vcc and Gnd) to the connectors  98  of the PCB  90  and power from all of the busbars  71 ,  72  and  73  (i.e., Vcc, Gnd and V+) to the PCB  52  of the printhead tiles  50 .  
         [0154]     The pressure plate  74  is shown in more detail in  FIGS. 19A  to  21 . The pressure plate  74  includes a raised portion (pressure elastomer)  75  which is positioned on a rear surface of the pressure plate  74  (with respect to the mounting direction on the support  91 ), as shown in  FIG. 19B , so as to be aligned with the busbars  71 ,  72  and  73 , with the flex PCBs  80  lying therebetween when the pressure plate  74  is mounted on the support  91 . The pressure plate  74  is mounted to the support  91  by engaging holes  74   a  with corresponding ones of (upper) retaining clips  99  of the support  91  which project from the extending arm portions  94  (see  FIG. 15A ) and holes  74   b  with the corresponding ones of the (lower) retaining clips  96 , via tab portions  74   c  thereof (see  FIG. 20 ). The pressure plate  74  is formed so as to have a spring-like resilience which urges the flex PCBs  80  into electrical contact with the busbars  71 ,  72  and  73  with the raised portion  75  providing insulation between the pressure plate  74  and the flex PCBs  80 .  
         [0155]     As shown most clearly in  FIG. 21 , the pressure plate  74  further includes a curved lower portion  74   d  which serves as a means of assisting the demounting of the pressure plate  74  from the support  91 .  
         [0156]     The specific manner in which the pressure plate  74  is retained on the support  91  so as to urge the flex PCBs  80  against the busbars  71 ,  72  and  73 , and the manner in which the extending arm portions  94  of the support  91  enable the above-mentioned clipping action will now be fully described with reference to  FIGS. 22 and 22 A to  22 E.  
         [0157]      FIG. 22  illustrates a front schematic view of the support  91  in accordance with a exemplary embodiment of the present invention.  FIG. 22A  is a side sectional view taken along the line I-I in  FIG. 22  with the hatched sections illustrating the components of the support  91  situated on the line I-I.  
         [0158]      FIG. 22A  particularly shows one of the upper retaining clips  99 . An enlarged view of this retaining clip  99  is shown in  FIG. 22B . The retaining clip  99  is configured so that an upper surface of one of the holes  74   a  of the pressure plate  74  can be retained against an upper surface  99   a  and a retaining portion  99   b  of the retaining clip  99  (see  FIG. 21 ). Due to the spring-like resilience of the pressure plate  74 , the upper surface  99   a  exerts a slight upwardly and outwardly directed force on the pressure plate  74  when the pressure plate  74  is mounted thereon so as to cause the upper part of the pressure plate  74  to abut against the retaining portion  99   b.    
         [0159]     Referring now to  FIG. 22C , which is a side sectional view taken along the line II-II in  FIG. 22 , one of the lower retaining clips  96  is illustrated. An enlarged view of this retaining clip  96  is shown in  FIG. 22D . The retaining clip  96  is configured so that a tab portion  74   c  of one of the holes  74   b  of the pressure plate  74  can be retained against an inner surface  96   c  of the retaining clip  96  (see  FIG. 20 ). Accordingly, due to the above-described slight force exerted by the retaining clip  99  on the upper part of the pressure plate  74  in a direction away from the support  91 , the lower part of the pressure plate  74  is loaded towards the opposite direction, e.g., in an inward direction with respect to the support frame  22 . Consequently, the pressure plate  74  is urged towards the busbars  71 ,  72  and  73 , which in turn serves to urge the flex PCBs  80  in the same direction via the raised portion  75 , so as to effect reliable contact with the busbars  71 ,  72  and  73 .  
         [0160]     Returning to  FIG. 22C , in which one of the extending arm portions  94  is illustrated. An enlarged view of this extending arm portion  94  is shown in  FIG. 22E . The extending arm portion  94  is configured so as to be substantially L-shaped, with the foot section of the L-shape located so as to fit over the inner side wall  29  of the channel  21  and the longitudinally extending tab  43  of the fluid channel member  40  of the printhead module  30  arranged thereon. As shown in  FIG. 22E , the end of the foot section of the L-shape has an arced surface. This surface corresponds to the edge of a recessed portion  94   a  provided in each the extending arm portions  94 , the centre of which is positioned substantially at the line II-II in  FIG. 22  (see  FIGS. 16 and 17 B). The recessed portions  94   a  are arranged so as to engage with angular lugs  43   a  regularly spaced along the length of the longitudinally extending tabs  43  of the fluid channel member  40  ( FIG. 4A ), so as to correspond with the placement of the printhead tiles  50 , when the extending arm portions  94  are clipped over the fluid channel member  40 .  
         [0161]     In this position, the arced edge of the recessed portion  94   a  is contacted with the angled surface of the angular lugs  43   a  (see  FIG. 4A ), with this being the only point of contact of the extending arm portion  94  with the longitudinally extending tab  43 . Although not shown in  FIG. 4A , the longitudinally extending tab  43  on the other side of the fluid channel member  40  has similarly angled lugs  43   a , where the angled surface comes into contact with the upper surface  24   d  of the recess  24   b  on the support frame  22 .  
         [0162]     As alluded to previously, due to this specific arrangement, at these contact points a downwardly and inwardly directed force is exerted on the fluid channel member  40  by the extending arm portion  94 . The downwardly directed force assists to constrain the printhead module  30  in the channel  21  in the z-axis direction as described earlier. The inwardly directed force also assists in constraining the printhead module  30  in the channel  21  by urging the angular lugs  43   a  on the opposing longitudinally extending tab  43  of the fluid channel member  40  into the recess  24   b  of the support frame  20 , where the upper surface  24   d  of the recess  24   b  also applies an opposing downwardly and inwardly directed force on the fluid channel member. In this regard the opposing forces act to constrain the range of movement of the fluid channel member  40  in the y-axis direction. It is to be understood that the two angular lugs  43   a  shown in  FIG. 4A  for each of the recessed portions  94   a  are merely an exemplary arrangement of the angular lugs  43   a.    
         [0163]     Further, the angular lugs  43   a  are positioned so as to correspond to the placement of the printhead tiles  50  on the upper surface of the fluid channel member  40  so that, when mounted, the lower connecting portions  81  of each of the flex PCBs  80  are aligned with the corresponding connectors  98  of the PCBs  90  (see  FIGS. 6 and 18 B). This is facilitated by the flex PCBs  80  having a hole  82  therein ( FIG. 6 ) which is received by the lower retaining clip  96  of the support  91 . Consequently, the flex PCBs  80  are correctly positioned under the pressure plate  74  retained by the retaining clip  96  as described above.  
         [0164]     Further still, as also shown in  FIGS. 22C and 22E , the (upper) lug  92  of the support  91  has an inner surface  92   a  which is also slightly angled from the normal of the plane of the support  91  in a direction away from the support  91 . As shown in  FIG. 17B , the upper lugs  92  are formed as resilient members which are able to hinge with respect to the support  91  with a spring-like action. Consequently, when mounted to the casing  20 , a slight force is exerted against the lug  27   a  of the uppermost face  27  of the support frame  22  which assists in securing the support  91  to the support frame  22  of the casing  20  by biasing the (lower) lug  92  into the recess formed between the lower part of the inner surface  25  and the lug  28   a  of the arm portion  28  of the support frame  22 .  
         [0165]     The manner in which the structure of the casing  20  is completed in accordance with an exemplary embodiment of the present invention will now be described with reference to  FIGS. 1, 2 ,  15 A and  23 .  
         [0166]     As shown in  FIGS. 1 and 2 , the casing  20  includes the aforementioned cover portion  23  which is positioned adjacent the support frame  22 . Thus, together the support frame  22  and the cover portion  23  define the two-piece outer housing of the printhead assembly  10 . The profile of the cover portion  23  is as shown in  FIG. 23 .  
         [0167]     The cover portion  23  is configured so as to be placed over the exposed PCB  90  mounted to the PCB support  91  which in turn is mounted to the support frame  22  of the casing  20 , with the channel  21  thereof holding the printhead module  30 . As a result, the cover portion  23  encloses the printhead module  30  within the casing  20 .  
         [0168]     The cover portion  23  includes a longitudinally extending tab  23   a  on a bottom surface thereof (with respect to the orientation of the printhead assembly  10 ) which is received in the recessed portion  28   c  formed between the lug  28   b  and the curved end portion  28   d  of the arm portion  28  of the support frame  22  (see  FIG. 15A ). This arrangement locates and holds the cover portion  23  in the casing  20  with respect to the support frame  22 . The cover portion  23  is further held in place by affixing the end plate  111  or the end housing  120  via the end plate  110  on the longitudinal side thereof using screws through threaded portions  23   b  (see  FIGS. 23, 29  and  39 ). The end plates  110  and/or  111  are also affixed to the support frame  22  on either longitudinal side thereof using screws through threaded portions  22   a  and  22   b  provided in the internal cavity  26  (see  FIGS. 15A, 29  and  39 ). Further, the cover portion  23  has the profile as shown in  FIG. 23 , in which a cavity portion  23   c  is arranged at the inner surface of the cover portion  23  (with respect to the inward direction on the printhead assembly  10 ) for accommodating the pressure plate(s)  74  mounted to the PCB support(s)  91 .  
         [0169]     Further, the cover portion may also include fin portions  23   d  (see also  FIG. 3 ) which are provided for dissipating heat generated by the PEC integrated circuits  100  during operation thereof. To facilitate this the inner surface of the cover portion  23  may also be provided with a heat coupling material portion (not shown) which physically contacts the PEC integrated circuits  100  when the cover portion  23  is attached to the support frame  22 . Further still, the cover portion  23  may also function to inhibit electromagnetic interference (EMI) which can interfere with the operation of the dedicated electronics of the printhead assembly  10 .  
         [0170]     The manner in which a plurality of the PCB supports  91  are assembled in the support frame  22  to provide a sufficient number of PEC integrated circuits  100  per printhead module  30  in accordance with one embodiment of the present invention will now be described with reference to  FIGS. 16 and 24  to  27 .  
         [0171]     As described earlier, in one embodiment of the present invention, each of the supports  91  is arranged to hold one of the PEC integrated circuits  100  which in turn drives four printhead integrated circuits  51 . Accordingly, in a printhead module  30  having 16 printhead tiles, for example, four PEC integrated circuits  100 , and therefore four supports  91  are required. For this purpose, the supports  91  are assembled in an end-to-end manner, as shown in  FIG. 24 , so as to extend the length of the casing  20 , with each of the supports  91  being mounted and clipped to the support frame  22  and printhead module  30  as previously described. In such a way, the single printhead module  30  of sixteen printhead tiles  50  is securely held to the casing  20  along the length thereof.  
         [0172]     As shown more clearly in  FIG. 16 , the supports  91  further include raised portions  91   a  and recessed portions  91   b  at each end thereof. That is, each edge region of the end walls of the supports  91  include a raised portion  91   a  with a recessed portion  91   b  formed along the outer edge thereof. This configuration produces the abutting arrangement between the adjacent supports  91  shown in  FIG. 24 .  
         [0173]     This arrangement of two abutting recessed portions  91   b  with one raised portion  91   a  at either side thereof forms a cavity which is able to receive a suitable electrical connecting member  102  therein, as shown in cross-section in  FIG. 25 . Such an arrangement enables adjacent PCBs  90 , carried on the supports  91  to be electrically connected together so that data signals which are input from either or both ends of the plurality of assembled supports  91 , i.e., via data connectors (described later) provided at the ends of the casing  20 , are routed to the desired PEC integrated circuits  100 , and therefore to the desired printhead integrated circuits  51 .  
         [0174]     To this end, the connecting members  102  provide electrical connection between a plurality of pads provided at edge contacting regions on the underside of each of the PCBs  90  (with respect to the mounting direction on the supports  91 ). Each of these pads is connected to different regions of the circuitry of the PCB  90 .  FIG. 26  illustrates the pads of the PCBs as positioned over the connecting member  102 . Specifically, as shown in  FIG. 26 , the plurality of pads are provided as a series of connection strips  90   a  and  90   b  in a substantially central region of each edge of the underside of the PCBs  90 .  
         [0175]     As mentioned above, the connecting members  102  are placed in the cavity formed by the abutting recessed portions  91   b  of adjacent supports  91  (see  FIG. 25 ), such that when the PCBs  90  are mounted on the supports  91 , the connection strips  90   a  of one PCB  90  and the connection strips  90   b  of the adjacent PCB  90  come into contact with the same connecting member  102  so as to provide electrical connection therebetween.  
         [0176]     To achieve this, the connecting members  102  may each be formed as shown in  FIG. 27  to be a rectangular block having a series of conducting strips  104  provided on each surface thereof. Alternatively, the conducting strips  104  may be formed on only one surface of the connecting members  102  as depicted in  FIGS. 25 and 26 . Such a connecting member may typically be formed of a strip of silicone rubber printed to provide sequentially spaced conductive and non-conductive material strips. A shown in  FIG. 27 , these conducting strips  104  are provided in a 2:1 relationship with the connecting strips  90   a  and  90   b  of the PCBs  90 . That is, twice as many of the conducting strips  104  are provided than the connecting strips  90   a  and  90   b , with the width of the conducting strips  104  being less than half the width of the connecting strips  90   a  and  90   b . Accordingly, any one connecting strip  90   a  or  90   b  may come into contact with one or both of two corresponding conducting strips  104 , thus minimising alignment requirements between the connecting members  104  and the contacting regions of the PCBs  90 .  
         [0177]     In one embodiment of the present invention, the connecting strips  90   a  and  90   b  are about 0.4 mm wide with a 0.4 mm spacing therebetween, so that two thinner conducting strips  104  can reliably make contact with only one each of the connecting strips  90   a  and  90   b  whilst having a sufficient space therebetween to prevent short circuiting. The connecting strips  90   a  and  90   b  and the conducting strips  104  may be gold plated so as to provide reliable contact. However, those skilled in the art will understand that use of the connecting members and suitably configured PCB supports is only one exemplary way of connecting the PCBs  90 , and other types of connections are within the scope of the present invention.  
         [0178]     Additionally, the circuitry of the PCBs  90  is arranged so that a PEC integrated circuit  100  of one of the PCB  90  of an assembled support  91  can be used to drive not only the printhead integrated circuits  51  connected directly to that PCB  90 , but also those of the adjacent PCB(s)  90 , and further of any non-adjacent PCB(s)  90 . Such an arrangement advantageously provides the printhead assembly  10  with the capability of continuous operation despite one of the PEC integrated circuits  100  and/or PCBs  90  becoming defective, albeit at a reduced printing speed.  
         [0179]     In accordance with the above-described scalability of the printhead assembly  10  of the present invention, the end-to-end assembly of the PCB supports  91  can be extended up to the required length of the printhead assembly  10  due to the modularity of the supports  91 . For this purpose, the busbars  71 ,  72  and  73  need to be extended for the combined length of the plurality of PCB supports  91 , which may result in insufficient power being delivered to each of the PCBs  90  when a relatively long printhead assembly  10  is desired, such as in wide format printing applications.  
         [0180]     In order to minimise power loss, two power supplies can be used, one at each end of the printhead assembly  10 , and a group of busbars  70  from each end may be employed. The connection of these two busbar groups, e.g., substantially in the centre of the printhead assembly  10 , is facilitated by providing the exemplary connecting regions  71   a ,  72   a  and  73   a  shown in  FIG. 28 .  
         [0181]     Specifically, the busbars  71 ,  72  and  73  are provided in a staggered arrangement relative to each other and the end regions thereof are configured with the rebated portions shown in  FIG. 28  as connecting regions  71   a ,  72   a  and  73   a . Accordingly, the connecting regions  71   a ,  72   a  and  73   a  of the first group of busbars  70  overlap and are engaged with the connecting regions  71   a ,  72   a  and  73   a  of the corresponding ones of the busbars  71 ,  72  and  73  of the second group of busbars  70 .  
         [0182]     The manner in which the busbars are connected to the power supply and the arrangements of the end plates  110  and  111  and the end housing(s)  120  which house these connections will now be described with reference to  FIGS. 1, 2  and  29  to  39 .  
         [0183]      FIG. 29  illustrates an end portion of an exemplary printhead assembly according to one embodiment of the present invention similar to that shown in  FIG. 1 . At this end portion, the end housing  120  is attached to the casing  20  of the printhead assembly  10  via the end plate  110 .  
         [0184]     The end housing and plate assembly houses connection electronics for the supply of power to the busbars  71 ,  72  and  73  and the supply of data to the PCBs  90 . The end housing and plate assembly also houses connections for the internal fluid delivery tubes  6  to external fluid delivery tubes (not shown) of the fluid supply of the printing system to which the printhead assembly  10  is being applied.  
         [0185]     These connections are provided on a connector arrangement  115  as shown in  FIG. 30 .  FIG. 30  illustrates the connector arrangement  115  fitted to the end plate  110  which is attached, via screws as described earlier, to an end of the casing  20  of the printhead assembly  10  according to one embodiment of the present invention. As shown, the connector arrangement  115  includes a power supply connection portion  116 , a data connection portion  117  and a fluid delivery connection portion  118 . Terminals of the power supply connection portion  116  are connected to corresponding ones of three contact screws  116   a ,  116   b ,  116   c  provided so as to each connect with a corresponding one of the busbars  71 ,  72  and  73 . To this end, each of the busbars  71 ,  72  and  73  is provided with threaded holes in suitable locations for engagement with the contact screws  116   a ,  116   b ,  116   c . Further, the connection regions  71   a ,  72   a  and  73   a  (see  FIG. 28 ) may also be provided at the ends of the busbars  71 ,  72  and  73  which are to be in contact with the contact screws  116   a ,  116   b ,  116   c  so as to facilitate the engagement of the busbars  71 ,  72  and  73  with the connector arrangement  115 , as shown in  FIG. 31 .  
         [0186]     In  FIGS. 30, 32A  and  32 B, only three contact screws or places for three contact screws are shown, one for each of the busbars. However, the use of a different number of contact screws is within the scope of the present invention. That is, depending on the amount of power being routed to the busbars, in order to provide sufficient power contact it may be necessary to provide two or more contact screws for each busbar (see, for example,  FIGS. 33B and 33C ). Further, as mentioned earlier a greater or lesser number of busbars may be used, and therefore a corresponding greater of lesser number of contact screws. Further still, those skilled in the art will understand that other means of contacting the busbars to the power supply via the connector arrangements as are typical in the art, such as soldering, are within the scope of the present invention.  
         [0187]     The manner in which the power supply connection portion  116  and the data connection portion  117  are attached to the connector arrangement  115  is shown in  FIGS. 32A and 32B . Further, connection tabs  118   a  of the fluid delivery connection portion  118  are attached at holes  115   a  of the connector arrangement  115  so as that the fluid delivery connection portion  118  overlies the data connection portion  117  with respect to the connector arrangement  115  (see  FIGS. 30 and 32 C).  
         [0188]     As seen in  FIGS. 30 and 32 C, seven internal and external tube connectors  118   b  and  118   c  are provided in the fluid delivery connection portion  118  in accordance with the seven internal fluid delivery tubes  6 . That is, as shown in  FIG. 34 , the fluid delivery tubes  6  connect between the internal tube connectors  118   b  of the fluid delivery connection portion  118  and the seven tubular portions  47   b  or  48   b  of the fluid delivery connector  47  or  48 . As stated earlier, those skilled in the art clearly understand that the present invention is not limited to this number of fluid delivery tubes, etc.  
         [0189]     Returning to  FIGS. 32A and 32B , the connector arrangement  115  is shaped with regions  115   b  and  115   c  so as to be received by the casing  20  in a manner which facilitates connection of the busbars  71 ,  72  and  73  to the contact screws  116   a ,  116   b  and  116   c  of the power supply connection portion  116  via region  115   b  and connection of the end PCB  90  of the plurality of PCBs  90  arranged on the casing  20  to the data connection portion  117  via region  115   c.    
         [0190]     The region  115   c  of the connector arrangement  115  is advantageously provided with connection regions (not shown) of the data connection portion  117  which correspond to the connection strips  90   a  or  90   b  provided at the edge contacting region on the underside of the end PCB  90 , so that one of the connecting members  102  can be used to connect the data connections of the data connection portion  117  to the end PCB  90 , and thus all of the plurality of PCBs  90  via the connecting members  102  provided therebetween.  
         [0191]     This is facilitated by using a support member  112  as shown in  FIG. 33A , which has a raised portion  112   a  and a recessed portion  112   b  at one edge thereof which is arranged to align with the raised and recessed portions  91   a  and  91   b , respectively, of the end PCB support  91  (see  FIG. 24 ). The support member  112  is attached to the rear surface of the end PCB support  91  by engaging a tab  112   c  with a slot region  91   c  on the rear surface of the end PCB support  91  (see  FIG. 17B ), and the region  115   c  of the connector arrangement  115  is retained at upper and lower side surfaces thereof by clip portions  112   d  of the support member  112  so as that the connection regions of the region  115   c  are in substantially the same plane as the edge contacting regions on the underside of the end PCB  90 .  
         [0192]     Thus, when the end plate  110  is attached to the end of the casing  20 , an abutting arrangement is formed between the recessed portions  112   b  and  91   b , similar to the abutting arrangement formed between the recessed portions  91   b  of the adjacent supports  91  of  FIG. 24 . Accordingly, the connecting member  102  can be accommodated compactly between the end PCB  90  and the region  115   c  of the connector arrangement  115 . This arrangement is shown in  FIGS. 33B and 33C  for another type of connector arrangement  125  with a corresponding region  125   c , which is described in more detail below with respect to  FIGS. 37, 38A  and  38 B.  
         [0193]     This exemplary manner of connecting the data connection portion  117  to the end PCB  90  contributes to the modular aspect of the present invention, in that it is not necessary to provide differently configured PCBs  90  to be arranged at the longitudinal ends of the casing  20  and the same method of data connection can be retained throughout the printhead assembly  10 . It will be understood by those skilled in the art however that the provision of additional or other components to connect the data connection portion  117  to the end PCB  90  is also included in the scope of the present invention.  
         [0194]     Returning to  FIG. 30 , it can be seen that the end plate  110  is shaped so as to conform with the regions  115   b  and  115   c  of the connector arrangement  115 , such that these regions can project into the casing  20  for connection to the busbars  71 ,  72  and  73  and the end PCB  90 , and so that the busbars  71 ,  72  and  73  can extend to contact screws  116   a ,  116   b  and  116   c  provided on the connector arrangement  115 . This particular shape of the end plate  110  is shown in  FIG. 35A , where regions  110   a  and  110   b  of the end plate  110  correspond with the regions  115   b  and  115   c  of the connector arrangement  115 , respectively. Further, a region  110   c  of the end plate  110  is provided so as to enable connection between the internal fluid delivery tubes  6  and the fluid delivery connectors  47  and  48  of the printhead module  30 .  
         [0195]     The end housing  120  is also shaped as shown in  FIG. 35A , so as to retain the power supply, data and fluid delivery connection portions  116 ,  117  and  118  so that external connection regions thereof, such as the external tube connector  118   c  of the fluid delivery connection portion  118  shown in  FIG. 32C , are exposed from the printhead assembly  10 , as shown in  FIG. 29 .  
         [0196]      FIG. 35B  illustrates the end plate  110  and the end housing  120  which may be provided at the other end of the casing  20  of the printhead assembly  10  according to an exemplary embodiment of the present invention. The exemplary embodiment shown in  FIG. 35B , for example, corresponds to a situation where an end housing is provided at both ends of the casing so as to provide power supply and/or fluid delivery connections at both ends of the printhead assembly. Such an exemplary printhead assembly is shown in  FIG. 36 , and corresponds, for example, to the above-mentioned exemplary application of wide format printing, in which the printhead assembly is relatively long.  
         [0197]     To this end,  FIG. 37  illustrates the end housing and plate assembly for the other end of the casing with the connector arrangement  125  housed therein. The busbars  71 ,  72  and  73  are shown attached to the connector arrangement  125  for illustration purposes. As can be seen, the busbars  71 ,  72  and  73  are provided with connection regions  71   a ,  72   a  and  73   a  for engagement with connector arrangement  125 , similar to that shown in  FIG. 31  for the connector arrangement  115 . The connector arrangement  125  is illustrated in more detail in  FIGS. 38A and 38B .  
         [0198]     As can be seen from  FIGS. 38A and 38B , like the connector arrangement  115 , the connector arrangement  125  holds the power supply connection portion  116  and includes places for contact screws for contact with the busbars  71 ,  72  and  73 , holes  125   a  for retaining the clips  118   a  of the fluid delivery portion  118  (not shown), and regions  125   b  and  125   c  for extension into the casing  20  through regions  110   a  and  110   b  of the end plate  110 , respectively. However, unlike the connector arrangement  115 , the connector arrangement  125  does not hold the data connection portion  117  and includes in place thereof a spring portion  125   d.    
         [0199]     This is because, unlike the power and fluid supply in a relatively long printhead assembly application, it is only necessary to input the driving data from one end of the printhead assembly. However, in order to input the data signals correctly to the plurality of PEC integrated circuits  100 , it is necessary to terminate the data signals at the end opposite to the data input end. Therefore, the region  125   c  of the connector arrangement  125  is provided with termination regions (not shown) which correspond with the edge contacting regions on the underside of the end PCB  90  at the terminating end. These termination regions are suitably connected with the contacting regions via a connecting member  102 , in the manner described above.  
         [0200]     The purpose of the spring portion  125   d  is to maintain these terminal connections even in the event of the casing  20  expanding and contracting due to temperature variations as described previously, any effect of which may exacerbated in the longer printhead applications. The configuration of the spring portion  125   d  shown in  FIGS. 38A and 38B , for example, enables the region  125   c  to be displaced through a range of distances from a body portion  125   e  of the connector arrangement  125 , whilst being biased in a normal direction away from the body portion  125   e . The spring portion is formed in the connector arrangement  125  by removing a section of the material making up the body portion  125   e.    
         [0201]     Thus, when the connector arrangement  125  is attached to the end plate  110 , which in turn has been attached to the casing  20 , the region  125   c  is brought into abutting contact with the adjacent edge of the end PCB  90  in such a manner that the spring portion  125   d  experiences a pressing force on the body of the connector arrangement  125 , thereby displacing the region  125   c  from its rest position toward the body portion  125   e  by a predetermined amount. This arrangement ensures that in the event of any dimensional changes of the casing  20  via thermal expansion and contraction thereof, the data signals remain terminated at the end of the plurality of PCBs  90  opposite to the end of data signal input as follows.  
         [0202]     The PCB supports  91  are retained on the support frame  22  of the casing  20  so as to “float” thereon, similar to the manner in which the printhead module(s)  30  “float” on the channel  21  as described earlier. Consequently, since the supports  91  and the fluid channel members  40  of the printhead modules  30  are formed of similar materials, such as LCP or the like, which have the same or similar coefficients of expansion, then in the event of any expansion and contraction of the casing  20 , the supports  91  retain their relative position with the printhead module(s)  30  via the clipping of the extending arm portions  94 .  
         [0203]     Therefore, each of the supports  91  retain their adjacent connections via the connecting members  102 , which is facilitated by the relatively large overlap of the connecting members  102  and the connection strips  90   a  and  90   b  of the PCBs  90  as shown in  FIG. 27 . Accordingly, since the PCBs  90 , and therefore the supports  91  to which they are mounted, are biased towards the connector arrangement  115  by the spring portion  125   d  of the connector arrangement  125 , then should the casing  20  expand and contract, any gaps which might otherwise form between the connector arrangements  115  and  125  and the end PCBs  90  are prevented, due to the action of the spring portion  125   d.    
         [0204]     Accommodation for any expansion and contraction is also facilitated with respect to the power supply by the connecting regions  71   a ,  72   a  and  73   a  of the two groups of busbars  70  which are used in the relatively long printhead assembly application. This is because, these connecting regions  71   a ,  72   a  and  73   a  are configured so that the overlap region between the two groups of busbars  70  allows for the relative movement of the connector arrangements  115  and  125  to which the busbars  71 ,  72  and  73  are attached whilst maintaining a connecting overlap in this region.  
         [0205]     In the examples illustrated in  FIGS. 30, 33B ,  33 C and  37 , the end sections of the busbars  71 ,  72  and  73  are shown connected to the connector arrangements  115  and  125  (via the contact screws  116   a ,  116   b  and  116   c ) on the front surface of the connector arrangements  115  and  125  (with respect to the direction of mounting to the casing  20 ). Alternatively, the busbars  71 ,  72  and  73  can be connected at the rear surfaces of the connector arrangements  115  and  125 . In such an alternative arrangement, even though the busbars  71 ,  72  and  73  thus connected may cause the connector arrangements  115  and  125  be slightly displaced toward the cover portion  23 , the regions  115   c  and  125   c  of the connector arrangements  115  and  125  are maintained in substantially the same plane as the edge contacting regions of the end PCBs  90  due to the clip portions  112   d  of the support members  112  which retain the upper and lower side surfaces of the regions  115   c  and  125   c.    
         [0206]     Printed circuit boards having connecting regions printed in discrete areas may be employed as the connector arrangements  115  and  125  in order to provide the various above-described electrical connections provided thereby.  
         [0207]      FIG. 39  illustrates the end plate  111  which may be attached to the other end of the casing  20  of the printhead assembly  10  according to an exemplary embodiment of the present invention, instead of the end housing and plate assemblies shown in  FIGS. 35A and 35B . This provides for a situation where the printhead assembly is not of a length which requires power and fluid to be supplied from both ends. For example, in an A4-sized printing application where a printhead assembly housing one printhead module of 16 printhead tiles may be employed.  
         [0208]     In such a situation therefore, since it is unnecessary specifically to provide a connector arrangement at the end of the printhead module  30  which is capped by the capping member  49 , then the end plate  111  can be employed which serves to securely hold the support frame  22  and cover portion  23  of the casing  20  together via screws secured to the threaded portions  22   a ,  22   b  and  23   b  thereof, in the manner already described (see also  FIG. 2 ).  
         [0209]     Further, if it is necessary to provide data signal termination at this end of the plurality of PCBs  90 , then the end plate  111  can be provided with a slot section (not shown) on the inner surface thereof (with respect to the mounting direction on the casing  20 ), which can support a PCB (not shown) having termination regions which correspond with the edge contacting regions of the end PCB  90 , similar to the region  125   c  of the connector arrangement  125 . Also similarly, these termination regions may be suitably connected with the contacting regions via a support member  112  and a connecting member  102 . This PCB may also include a spring portion between the termination regions and the end plate  111 , similar to the spring portion  125   d  of the connector arrangement  125 , in case expansion and contraction of the casing  20  may also cause connection problems in this application.  
         [0210]     With either the attachment of the end housing  120  and plate  110  assemblies to both ends of the casing  20  or the attachment of the end housing  120  and plate  110  assembly to one end of the casing  20  and the end plate  111  to the other end, the structure of the printhead assembly according to the present invention is completed.  
         [0211]     The thus-assembled printhead assembly can then be mounted to a printing unit to which the assembled length of the printhead assembly is applicable. Exemplary printing units to which the printhead module and printhead assembly of the present invention is applicable are as follows.  
         [0212]     For a home office printing unit printing on A4 and letter-sized paper, a printhead assembly having a single printhead module comprising 11 printhead integrated circuits can be used to present a printhead width of 224 mm. This printing unit is capable of printing at approximately 60 pages per minute (ppm) when the nozzle speed is about 20 kHz. At this speed a maximum of about 1690×10 6  drops or about 1.6896 ml of ink is delivered per second for the entire printhead. This results in a linear printing speed of about 0.32 ms −1  or an area printing speed of about 0.07 sqms −1 . A single PEC integrated circuit can be used to drive all 11 printhead integrated circuits, with the PEC integrated circuit calculating about 1.8 billion dots per second.  
         [0213]     For a printing unit printing on A3 and tabloid-sized paper, a printhead assembly having a single printhead module comprising 16 printhead integrated circuits can be used to present a printhead width of 325 mm. This printing unit is capable of printing at approximately 120 ppm when the nozzle speed is about 55 kHz. At this speed a maximum of about 6758×10 6  drops or about 6.7584 ml of ink is delivered per second for the entire printhead. This results in a linear printing speed of about 0.87 ms −1  or an area printing speed of about 0.28 sqms −1 . Four PEC integrated circuits can be used to each drive four of the printhead integrated circuits, with the PEC integrated circuits collectively calculating about 7.2 billion dots per second.  
         [0214]     For a printing unit printing on a roll of wallpaper, a printhead assembly having one or more printhead modules providing 36 printhead integrated circuits can be used to present a printhead width of 732 mm. When the nozzle speed is about 55 kHz, a maximum of about 15206×10 6  drops or about 15.2064 ml of ink is delivered per second for the entire printhead. This results in a linear printing speed of about 0.87 ms −1  or an area printing speed of about 0.64 sqms −1 . Nine PEC integrated circuits can be used to each drive four of the printhead integrated circuits, with the PEC integrated circuits collectively calculating about 16.2 billion dots per second.  
         [0215]     For a wide format printing unit printing on a roll of print media, a printhead assembly having one or more printhead modules providing 92 printhead integrated circuits can be used to present a printhead width of 1869 mm. When the nozzle speed is in a range of about 15 to 55 kHz, a maximum of about 10598×10 6  to 38861×10 6  drops or about 10.5984 to 38.8608 ml of ink is delivered per second for the entire printhead. This results in a linear printing speed of about 0.24 to 0.87 ms −1  or an area printing speed of about 0.45 to 1.63 sqms −1 . At the lower speeds, six PEC integrated circuits can be used to each drive  16  of the printhead integrated circuits (with one of the PEC integrated circuits driving  12  printhead integrated circuits), with the PEC integrated circuits collectively calculating about 10.8 billion dots per second. At the higher speeds, 23 PEC integrated circuits can be used each to drive four of the printhead integrated circuits, with the PEC integrated circuits collectively calculating about 41.4 billions dots per second.  
         [0216]     For a “super wide” printing unit printing on a roll of print media, a printhead assembly having one or more printhead modules providing 200 printhead integrated circuits can be used to present a printhead width of 4064 mm. When the nozzle speed is about 15 kHz, a maximum of about 23040×10 6  drops or about 23.04 ml of ink is delivered per second for the entire printhead. This results in a linear printing speed of about 0.24 ms −1  or an area printing speed of about 0.97 sqms −1 . Thirteen PEC integrated circuits can be used to each drive  16  of the printhead integrated circuits (with one of the PEC integrated circuits driving eight printhead integrated circuits), with the PEC integrated circuits collectively calculating about 23.4 billion dots per second.  
         [0217]     For the above exemplary printing unit applications, the required printhead assembly may be provided by the corresponding standard length printhead module or built-up of several standard length printhead modules. Of course, any of the above exemplary printing unit applications may involve duplex printing with simultaneous double-sided printing, such that two printhead assemblies are used each having the number of printhead tiles given above. Further, those skilled in the art understand that these applications are merely examples and the number of printhead integrated circuits, nozzle speeds and associated printing capabilities of the printhead assembly depends upon the specific printing unit application.  
         [0000]     Print Engine Controller  
         [0218]     The functions and structure of the PEC integrated circuit applicable to the printhead assembly of the present invention will now be discussed with reference to FIGS.  40  to  42 .  
         [0219]     In the above-described exemplary embodiments of the present invention, the printhead integrated circuits  51  of the printhead assembly  10  are controlled by the PEC integrated circuits  100  of the drive electronics  100 . One or more PEC integrated circuits  100  is or are provided in order to enable pagewidth printing over a variety of different sized pages. As described earlier, each of the PCBs  90  supported by the PCB supports  91  has one PEC integrated circuit  100  which interfaces with four of the printhead integrated circuits  51 , where the PEC integrated circuit  100  essentially drives the printhead integrated circuits  51  and transfers received print data thereto in a form suitable for printing.  
         [0220]     An exemplary PEC integrated circuit which is suited to driving the printhead integrated circuits of the present invention is described in the Applicant&#39;s co-pending U.S. patent application Ser. Nos. 09/575,108; 09/575,109; 09/575,110; 09/606,999; 09/607,985; and 09/607,990, the dislcosures of which are all incorporated herein by reference.  
         [0221]     Referring to  FIG. 40 , the data flow and functions performed by the PEC integrated circuit  100  will be described for a situation where the PEC integrated circuit  100  is suited to driving a printhead assembly having a plurality of printhead modules  30 . As described above, the printhead module  30  of one embodiment of the present invention utilises six channels of fluid for printing. These are: 
        Cyan, Magenta and Yellow (CMY) for regular colour printing;     Black (K) for black text and other black or greyscale printing;     Infrared (IR) for tag-enabled applications; and     Fixative (F) to enable printing at high speed.        
 
         [0226]     As shown in  FIG. 40 , documents are typically supplied to the PEC integrated circuit  100  by a computer system or the like, having Raster Image Processor(s) (RIP(s)), which is programmed to perform various processing steps  131  to  134  involved in printing a document prior to transmission to the PEC integrated circuit  100 . These steps typically involve receiving the document data (step  131 ) and storing this data in a memory buffer of the computer system (step  132 ), in which page layouts may be produced and any required objects may be added. Pages from the memory buffer are rasterized by the RIP (step  133 ) and are then compressed (step  134 ) prior to transmission to the PEC integrated circuit  100 . Upon receiving the page data, the PEC integrated circuit  100  processes the data so as to drive the printhead integrated circuits  51 .  
         [0227]     Due to the page-width nature of the printhead assembly of the present invention, each page must be printed at a constant speed to avoid creating visible artifacts. This means that the printing speed cannot be varied to match the input data rate. Document rasterization and document printing are therefore decoupled to ensure the printhead assembly has a constant supply of data. In this arrangement, a page is not printed until it is fully rasterized, and in order to achieve a high constant printing speed a compressed version of each rasterized page image is stored in memory. This decoupling also allows the RIP(s) to run ahead of the printer when rasterizing simple pages, buying time to rasterize more complex pages.  
         [0228]     Because contone colour images are reproduced by stochastic dithering, but black text and line graphics are reproduced directly using dots, the compressed page image format contains a separate foreground bi-level black layer and background contone colour layer. The black layer is composited over the contone layer after the contone layer is dithered (although the contone layer has an optional black component). If required, a final layer of tags (in IR or black ink) is optionally added to the page for printout.  
         [0229]     Dither matrix selection regions in the page description are rasterized to a contone-resolution bi-level bitmap which is losslessly compressed to negligible size and which forms part of the compressed page image. The IR layer of the printed page optionally contains encoded tags at a programmable density.  
         [0230]     As described above, the RIP software/hardware rasterizes each page description and compresses the rasterized page image. Each compressed page image is transferred to the PEC integrated circuit  100  where it is then stored in a memory buffer  135 . The compressed page image is then retrieved and fed to a page image expander  136  in which page images are retrieved. If required, any dither may be applied to any contone layer by a dithering means  137  and any black bi-level layer may be composited over the contone layer by a compositor  138  together with any infrared tags which may be rendered by the rendering means  139 . Returning to a description of process steps, the PEC integrated circuit  100  then drives the printhead integrated circuits  51  to print the composited page data at step  140  to produce a printed page  141 .  
         [0231]     In this regard, the process performed by the PEC integrated circuit  100  can be considered to consist of a number of distinct stages. The first stage has the ability to expand a JPEG-compressed contone CMYK layer, a Group 4 Fax-compressed bi-level dither matrix selection map, and a Group 4 Fax-compressed bi-level black layer, all in parallel. In parallel with this, bi-level IR tag data can be encoded from the compressed page image. The second stage dithers the contone CMYK layer using a dither matrix selected by a dither matrix select map, composites the bi-level black layer over the resulting bi-level K layer and adds the IR layer to the page. A fixative layer is also generated at each dot position wherever there is a need in any of the C, M, Y, K, or IR channels. The last stage prints the bi-level CMYK+IR data through the printhead assembly.  
         [0232]      FIG. 41  shows an exemplary embodiment of the printhead assembly of the present invention including the PEC integrated circuit(s)  100  in the context of the overall printing system architecture. As shown, the various components of the printhead assembly includes: 
        a PEC integrated circuit  100  which is responsible for receiving the compressed page images for storage in a memory buffer  142 , performing the page expansion, black layer compositing and sending the dot data to the printhead integrated circuits  51 . The PEC integrated circuit  100  may also communicate with a master Quality Assurance (QA) integrated circuit  143  and a (replaceable) ink cartridge QA integrated circuit  144 , and provides a means of retrieving the printhead assembly characteristics to ensure optimum printing;     the memory buffer  142  for storing the compressed page image and for scratch use during the printing of a given page. The construction and working of memory buffers is known to those skilled in the art and a range of standard integrated circuits and techniques for their use might be utilized in use of the PEC integrated circuit(s)  100 ; and     the master integrated circuit  143  which is matched to the replaceable ink cartridge QA integrated circuit  144 . The construction and working of QA integrated circuits is known to those skilled in the art and a range of known QA processes might be utilized in use of the PEC integrated circuit(s)  100 ;          
         [0236]     As mentioned in part above, the PEC integrated circuit  100  of the present invention essentially performs four basic levels of functionality: 
        receiving compressed pages via a serial interface such as an IEEE 1394;     acting as a print engine for producing a page from a compressed form. The print engine functionality includes expanding the page image, dithering the contone layer, compositing the black layer over the contone layer, optionally adding infrared tags, and sending the resultant image to the printhead integrated circuits;     acting as a print controller for controlling the printhead integrated circuits and stepper motors of the printing system; and     serving as two standard low-speed serial ports for communication with the two QA integrated circuits. In this regard, two ports are used, and not a single port, so as to ensure strong security during authentication procedures.        
 
         [0241]     These functions are now described in more detail with reference to  FIG. 42  which provides a more specific illustration of the PEC integrated circuit architecture according to an exemplary embodiment of the present invention.  
         [0242]     The PEC integrated circuit  100  incorporates a simple micro-controller CPU core  145  to perform the following functions: 
        perform QA integrated circuit authentication protocols via a serial interface  146  between print pages;     run the stepper motor of the printing system via a parallel interface  147  during printing to control delivery of the paper to the printhead integrated circuits  51  for printing (the stepper motor requires a 5 KHz process);     synchronize the various components of the PEC integrated circuit  100  during printing;     provide a means of interfacing with external data requests (programming registers etc.);     provide a means of interfacing with the corresponding printhead module&#39;s low-speed data requests (such as reading the characterization vectors and writing pulse profiles); and     provide a means of writing the portrait and landscape tag structures to an external DRAM  148 .        
 
         [0249]     In order to perform the page expansion and printing process, the PEC integrated circuit  100  includes a high-speed serial interface  149  (such as a standard IEEE 1394 interface), a standard JPEG decoder  150 , a standard Group 4 Fax decoder  151 , a custom halftoner/compositor (HC)  152 , a custom tag encoder  153 , a line loader/formatter (LLF)  154 , and a printhead interface  155  (PHI) which communicates with the printhead integrated circuits  51 . The decoders  150  and  151  and the tag encoder  153  are buffered to the HC  152 . The tag encoder  153  establishes an infrared tag(s) to a page according to protocols dependent on what uses might be made of the page.  
         [0250]     The print engine function works in a double-buffered manner. That is, one page is loaded into the external DRAM  148  via a DRAM interface  156  and a data bus  157  from the high-speed serial interface  149 , while the previously loaded page is read from the DRAM  148  and passed through the print engine process. Once the page has finished printing, then the page just loaded becomes the page being printed, and a new page is loaded via the high-speed serial interface  149 .  
         [0251]     At the aforementioned first stage, the process expands any JPEG-compressed contone (CMYK) layers, and expands any of two Group 4 Fax-compressed bi-level data streams. The two streams are the black layer (although the PEC integrated circuit  100  is actually colour agnostic and this bi-level layer can be directed to any of the output inks) and a matte for selecting between dither matrices for contone dithering. At the second stage, in parallel with the first, any tags are encoded for later rendering in either IR or black ink.  
         [0252]     Finally, in the third stage the contone layer is dithered, and position tags and the bi-level spot layer are composited over the resulting bi-level dithered layer. The data stream is ideally adjusted to create smooth transitions across overlapping segments in the printhead assembly and ideally it is adjusted to compensate for dead nozzles in the printhead assembly. Up to six channels of bi-level data are produced from this stage.  
         [0253]     However, it will be understood by those skilled in the art that not all of the six channels need be present on the printhead module  30 . For example, the printhead module  30  may provide for CMY only, with K pushed into the CMY channels and IR ignored. Alternatively, the position tags may be printed in K if IR ink is not available (or for testing purposes). The resultant bi-level CMYK-IR dot-data is buffered and formatted for printing with the printhead integrated circuits  51  via a set of line buffers (not shown). The majority of these line buffers might be ideally stored on the external DRAM  148 . In the final stage, the six channels of bi-level dot data are printed via the PHI  155 .  
         [0254]     The HC  152  combines the functions of halftoning the contone (typically CMYK) layer to a bi-level version of the same, and compositing the spot1 bi-level layer over the appropriate halftoned contone layer(s). If there is no K ink, the HC  152  is able to map K to CMY dots as appropriate. It also selects between two dither matrices on a pixel-by-pixel basis, based on the corresponding value in the dither matrix select map. The input to the HC  152  is an expanded contone layer (from the JPEG decoder  146 ) through a buffer  158 , an expanded bi-level spot1 layer through a buffer  159 , an expanded dither-matrix-select bitmap at typically the same resolution as the contone layer through a buffer  160 , and tag data at full dot resolution through a buffer (FIFO)  161 .  
         [0255]     The HC  152  uses up to two dither matrices, read from the external DRAM  148 . The output from the HC  152  to the LLF  154  is a set of printer resolution bi-level image lines in up to six colour planes. Typically, the contone layer is CMYK or CMY, and the bi-level spot1 layer is K. Once started, the HC  152  proceeds until it detects an “end-of-page” condition, or until it is explicitly stopped via its control register (not shown).  
         [0256]     The LLF  154  receives dot information from the HC  152 , loads the dots for a given print line into appropriate buffer storage (some on integrated circuit (not shown) and some in the external DRAM  148 ) and formats them into the order required for the printhead integrated circuits  51 . Specifically, the input to the LLF  154  is a set of six 32-bit words and a DataValid bit, all generated by the HC  152 . The output of the LLF  154  is a set of 190 bits representing a maximum of 15 printhead integrated circuits of six colours. Not all the output bits may be valid, depending on how many colours are actually used in the printhead assembly.  
         [0257]     The physical placement of the nozzles on the printhead assembly of an exemplary embodiment of the present invention is in two offset rows, which means that odd and even dots of the same colour are for two different lines. The even dots are for line L, and the odd dots are for line L−2. In addition, there is a number of lines between the dots of one colour and the dots of another. Since the six colour planes for the same dot position are calculated at one time by the HC  152 , there is a need to delay the dot data for each of the colour planes until the same dot is positioned under the appropriate colour nozzle. The size of each buffer line depends on the width of the printhead assembly. Since a single PEC integrated circuit  100  can generate dots for up to 15 printhead integrated circuits  51 , a single odd or even buffer line is therefore  15  sets of 640 dots, for a total of 9600 bits (1200 bytes). For example, the buffers required for six colour odd dots totals almost 45 KBytes.  
         [0258]     The PHI  155  is the means by which the PEC integrated circuit  100  loads the printhead integrated circuits  51  with the dots to be printed, and controls the actual dot printing process. It takes input from the LLF  154  and outputs data to the printhead integrated circuits  51 . The PHI  155  is capable of dealing with a variety of printhead assembly lengths and formats. The internal structure of the PHI  155  allows for a maximum of six colours, eight printhead integrated circuits  51  per transfer, and a maximum of two printhead integrated circuit  51  groups which is sufficient for a printhead assembly having 15 printhead integrated circuits  51  (8.5 inch) printing system capable of printing on A4/Letter paper at full speed.  
         [0259]     A combined characterization vector of the printhead assembly  10  can be read back via the serial interface  146 . The characterization vector may include dead nozzle information as well as relative printhead module alignment data. Each printhead module can be queried via its low-speed serial bus  162  to return a characterization vector of the printhead module. The characterization vectors from multiple printhead modules can be combined to construct a nozzle defect list for the entire printhead assembly and allows the PEC integrated circuit  100  to compensate for defective nozzles during printing. As long as the number of defective nozzles is low, the compensation can produce results indistinguishable from those of a printhead assembly with no defective nozzles.  
         [0000]     Fluid Distribution Stack  
         [0260]     An exemplary structure of the fluid distribution stack of the printhead tile will now be described with reference to  FIG. 43 .  
         [0261]      FIG. 43  shows an exploded view of the fluid distribution stack  500  with the printhead integrated circuit  51  also shown in relation to the stack  500 . In the exemplary embodiment shown in  FIG. 43 , the stack  500  includes three layers, an upper layer  510 , a middle layer  520  and a lower layer  530 , and further includes a channel layer  540  and a plate  550  which are provided in that order on top of the upper layer  510 . Each of the layers  510 ,  520  and  530  are formed as stainless-steel or micro-moulded plastic material sheets.  
         [0262]     The printhead integrated circuit  51  is bonded onto the upper layer  510  of the stack  500 , so as to overlie an array of holes  511  etched therein, and therefore to sit adjacent the stack of the channel layer  540  and the plate  550 . The printhead integrated circuit  51  itself is formed as a multi-layer stack of silicon which has fluid channels (not shown) in a bottom layer  51   a . These channels are aligned with the holes  511  when the printhead integrated circuit  51  is mounted on the stack  500 . In one embodiment of the present invention, the printhead integrated circuits  51  are approximately 1 mm in width and 21 mm in length. This length is determined by the width of the field of a stepper which is used to fabricate the printhead integrated circuit  51 . Accordingly, the holes  511  are arranged to conform to these dimensions of the printhead integrated circuit  51 .  
         [0263]     The upper layer  510  has channels  512  etched on the underside thereof ( FIG. 43  shows only some of the channels  512  as hidden detail). The channels  512  extend as shown so that their ends align with holes  521  of the middle layer  520 . Different ones of the channels  512  align with different ones of the holes  521 . The holes  521 , in turn, align with channels  531  in the lower layer  530 .  
         [0264]     Each of the channels  531  carries a different respective colour or type of ink, or fluid, except for the last channel, designated with the reference numeral  532 . The last channel  532  is an air channel and is aligned with further holes  522  of the middle layer  520 , which in turn are aligned with further holes  513  of the upper layer  510 . The further holes  513  are aligned with inner sides  541  of slots  542  formed in the channel layer  540 , so that these inner sides  541  are aligned with, and therefore in fluid-flow communication with, the air channel  532 , as indicated by the dashed line  543 .  
         [0265]     The lower layer  530  includes the inlet ports  54  of the printhead tile  50 , with each opening into the corresponding ones of the channels  531  and  532 .  
         [0266]     In order to feed air to the printhead integrated circuit surface, compressed filtered air from an air source (not shown) enters the air channel  532  through the corresponding inlet port  54  and passes through the holes  522  and  513  and then the slots  542  in the middle layer  520 , the upper layer  510  and the channel layer  540 , respectively. The air enters into a side surface  51   b  of the printhead integrated circuit  51  in the direction of arrows A and is then expelled from the printhead integrated circuit  51  substantially in the direction of arrows B. A nozzle guard  51   c  may be further arranged on a top surface of the printhead integrated circuit  51  partially covering the nozzles to assist in keeping the nozzles clear of print media dust.  
         [0267]     In order to feed different colour and types of inks and other fluids (not shown) to the nozzles, the different inks and fluids enter through the inlet ports  54  into the corresponding ones of the channels  531 , pass through the corresponding holes  521  of the middle layer  520 , flow along the corresponding channels  512  in the underside of the upper layer  510 , pass through the corresponding holes  511  of the upper layer  510 , and then finally pass through the slots  542  of the channel layer  540  to the printhead integrated circuit  51 , as described earlier.  
         [0268]     In traversing this path, the flow diameters of the inks and fluids are gradually reduced from the macro-sized flow diameter at the inlet ports  54  to the required micro-sized flow diameter at the nozzles of the printhead integrated circuit  51 .  
         [0269]     The exemplary embodiment of the fluid distribution stack shown in  FIG. 43  is arranged to distribute seven different fluids to the printhead integrated circuit, including air, which is in conformity with the earlier described exemplary embodiment of the ducts of the fluid channel member. However, it will be understood by those skilled in the art that a greater or lesser number of fluids may be used depending on the specific printing application, and therefore the fluid distribution stack can be configured as necessary.  
         [0000]     Nozzels and Actuators  
         [0270]     Exemplary nozzle arrangements which are suitable for the printhead assembly of the present invention are described in the Applicant&#39;s following co-pending and granted applications:  
                                                       6227652   6213588   6213589   6231163   6247795   6394581       6244691   6257704   6416168   6220694   6257705   6247794       6234610   6247793   6264306   6241342   6247792   6264307       6254220   6234611   6302528   6283582   6239821   6338547       6247796   6557977   6390603   6362843   6293653   6312107       6227653   6234609   6238040   6188415   6227654   6209989       6247791   6336710   6217153   6416167   6243113   6283581       6247790   6260953   6267469   6273544   6309048   6420196       6443558   6439689   6378989   6848181   6634735   6299289       6299290   6425654   6623101   6406129   6505916   6457809       6550895   6457812   6428133   10/407212   10/407207   10/683064       10/683041   6390605   6322195   6612110   6480089   6460778       6305788   6426014   6364453   6457795   6315399   6338548       6540319   6328431   6328425   6991320   6595624   6417757       7095309   6854825   6623106   6672707   6588885   7075677       6428139   6575549   6425971   6383833   6652071   6793323       6659590   6676245   6464332   6478406   6439693   6502306       6428142   6390591   7018016   6328417   6322194   6382779       6629745   6565193   6609786   6609787   6439908   6684503       6755509   6692108   6672709   7086718   6672710   6669334       7152958   6824246   6669333   6820967   6736489   6719406       10/728804   7128400   7108355   6991322   10/728790   7118197       10/728970   10/728784   10/728783   7077493   6962402   10/728803       7147308   10/728779                  
 
         [0271]     the disclosures of which are all incorporated herein by reference.  
         [0272]     Of these, an exemplary nozzle arrangement will now be described with reference to FIGS.  44  to  53 . One nozzle arrangement which is incorporated in each of the printhead integrated circuits  51  mounted on the printhead tiles  50  (see  FIG. 5A ) includes a nozzle and corresponding actuator.  FIG. 44  shows an array of the nozzle arrangements  801  formed on a silicon substrate  815 . The nozzle arrangements are identical, but in one embodiment, different nozzle arrangements are fed with different coloured inks and fixative. It will be noted that rows of the nozzle arrangements  801  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. The multiple rows also allow for redundancy (if desired), thereby allowing for a predetermined failure rate per nozzle.  
         [0273]     Each nozzle arrangement  801  is the product of an integrated circuit fabrication technique. As illustrated, the nozzle arrangement  801  is constituted by a micro-electromechanical system (MEMS).  
         [0274]     For clarity and ease of description, the construction and operation of a single nozzle arrangement  801  will be described with reference to FIGS.  45  to  53 .  
         [0275]     Each printhead integrated circuit  51  includes a silicon wafer substrate  815 . 0.42 Micron 1 P4M 12 volt CMOS microprocessing circuitry is positioned on the silicon wafer substrate  815 .  
         [0276]     A silicon dioxide (or alternatively glass) layer  817  is positioned on the wafer substrate  815 . The silicon dioxide layer  817  defines CMOS dielectric layers. CMOS top-level metal defines a pair of aligned aluminium electrode contact layers  830  positioned on the silicon dioxide layer  817 . Both the silicon wafer substrate  815  and the silicon dioxide layer  817  are etched to define an ink inlet channel  814  having a generally circular cross section (in plan). An aluminium diffusion barrier  828  of CMOS metal 1, CMOS metal 2/3 and CMOS top level metal is positioned in the silicon dioxide layer  817  about the ink inlet channel  814 . The diffusion barrier  828  serves to inhibit the diffusion of hydroxyl ions through CMOS oxide layers of the drive circuitry layer  817 .  
         [0277]     A passivation layer in the form of a layer of silicon nitride  831  is positioned over the aluminium contact layers  830  and the silicon dioxide layer  817 . Each portion of the passivation layer  831  positioned over the contact layers  830  has an opening  832  defined therein to provide access to the contacts  830 .  
         [0278]     The nozzle arrangement  801  includes a nozzle chamber  829  defined by an annular nozzle wall  833 , which terminates at an upper end in a nozzle roof  834  and a radially inner nozzle rim  804  that is circular in plan. The ink inlet channel  814  is in fluid communication with the nozzle chamber  829 . At a lower end of the nozzle wall, there is disposed a movable rim  810 , that includes a movable seal lip  840 . An encircling wall  838  surrounds the movable nozzle, and includes a stationary seal lip  839  that, when the nozzle is at rest as shown in  FIG. 45 , is adjacent the moving rim  810 . A fluidic seal  811  is formed due to the surface tension of ink trapped between the stationary seal lip  839  and the moving seal lip  840 . This prevents leakage of ink from the chamber whilst providing a low resistance coupling between the encircling wall  838  and the nozzle wall  833 .  
         [0279]     As best shown in  FIG. 52 , a plurality of radially extending recesses  835  is defined in the roof  834  about the nozzle rim  804 . The recesses  835  serve to contain radial ink flow as a result of ink escaping past the nozzle rim  804 .  
         [0280]     The nozzle wall  833  forms part of a lever arrangement that is mounted to a carrier  836  having a generally U-shaped profile with a base  837  attached to the layer  831  of silicon nitride.  
         [0281]     The lever arrangement also includes a lever arm  818  that extends from the nozzle walls and incorporates a lateral stiffening beam  822 . The lever arm  818  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  FIGS. 48 and 51 . The other ends of the passive beams  806  are attached to the carrier  836 .  
         [0282]     The lever arm  818  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 .  
         [0283]     As best shown in  FIGS. 48 and 51 , the actuator beam  807  is substantially U-shaped in plan, defining a current path between the electrode  809  and an opposite electrode  841 . Each of the electrodes  809  and  841  is electrically connected to a respective point in the contact layer  830 . 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.  45  to  47  when the nozzle arrangement is in operation.  
         [0284]     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  841 . No current flows through the passive beams  806 , so they do not expand.  
         [0285]     In use, the device at rest is filled with ink  813  that defines a meniscus  803  under the influence of surface tension. The ink is retained in the chamber  829  by the meniscus, and will not generally leak out in the absence of some other physical influence.  
         [0286]     As shown in  FIG. 46 , to fire ink from the nozzle, a current is passed between the contacts  809  and  841 , 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.  45  to  47 . The expansion is constrained to the left by the anchor  808 , so the end of the actuator beam  807  adjacent the lever arm  818  is impelled to the right.  
         [0287]     The relative horizontal inflexibility of the passive beams  806  prevents them from allowing much horizontal movement the lever arm  818 . 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  818  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 .  
         [0288]     The downward movement (and slight rotation) of the lever arm  818  is amplified by the distance of the nozzle wall  833  from the passive beams  806 . The downward movement of the nozzle walls and roof causes a pressure increase within the chamber  29 , causing the meniscus to bulge as shown in  FIG. 46 . It will be noted that the surface tension of the ink means the fluid seal  11  is stretched by this motion without allowing ink to leak out.  
         [0289]     As shown in  FIG. 47 , 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  829 . 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  829  causes thinning, and ultimately snapping, of the bulging meniscus to define an ink drop  802  that continues upwards until it contacts the adjacent print media.  
         [0290]     Immediately after the drop  802  detaches, the meniscus forms the concave shape shown in  FIG. 45 . Surface tension causes the pressure in the chamber  829  to remain relatively low until ink has been sucked upwards through the inlet  814 , which returns the nozzle arrangement and the ink to the quiescent situation shown in  FIG. 45 .  
         [0291]     As best shown in  FIG. 48 , the nozzle arrangement also incorporates a test mechanism that can be used both post-manufacture and periodically after the printhead assembly is installed. The test mechanism includes a pair of contacts  820  that are connected to test circuitry (not shown). A bridging contact  819  is provided on a finger  843  that extends from the lever arm  818 . Because the bridging contact  819  is on the opposite side of the passive beams  806 , actuation of the nozzle causes the priding contact to move upwardly, into contact with the contacts  820 . Test circuitry can be used to confirm that actuation causes this closing of the circuit formed by the contacts  819  and  820 . If the circuit is closed appropriately, it can generally be assumed that the nozzle is operative.  
         [0000]     Exemplary Method of Assembling Components  
         [0292]     An exemplary method of assembling the various above-described modular components of the printhead assembly in accordance with one embodiment of the present invention will now be described. It is to be understood that the below described method represents only one example of assembling a particular printhead assembly of the present invention, and different methods may be employed to assemble this exemplary printhead assembly or other exemplary printhead assemblies of the present invention.  
         [0293]     The printhead integrated circuits  51  and the printhead tiles  50  are assembled as follows: 
        A. The printhead integrated circuit  51  is first prepared by forming 7680 nozzles in an upper surface thereof, which are spaced so as to be capable of printing with a resolution of 1600 dpi;     B. The fluid distribution stacks  500  (from which the printhead tiles  50  are formed) are constructed so as to have the three layers  510 ,  520  and  530 , the channel layer  540  and the plate  550  made of stainless steel bonded together in a vacuum furnace into a single body via metal inter-diffusion, where the inner surface of the lower layer  530  and the surfaces of the middle and upper layers  520  and  510  are etched so as to be provided with the channels and holes  531  and  532 ,  521  and  522 , and  511  to  513 , respectively, so as to be capable of transporting the CYMK and IR inks and fixative to the individual nozzles of the printhead integrated circuit  51  and air to the surface of the printhead integrated circuit  51 , as described earlier. Further, the outer surface of the lower layer  530  is etched so as to be provided with the inlet ports  54 ;     C. An adhesive, such as a silicone adhesive, is then applied to an upper surface of the fluid distribution stack  500  for attaching the printhead integrated circuit  51  and the (fine pitch) PCB  52  in close proximity thereto;     D. The printhead integrated circuit  51  and the PCB  52  are picked up, pre-centred and then bonded on the upper surface of the fluid distribution stack  500  via a pick-and-place robot;     E. This assembly is then placed in an oven whereby the adhesive is allowed to cure so as to fix the printhead integrated circuit  51  and the PCB  52  in place;     F. Connection between the printhead integrated circuit  51  and the PCB  52  is then made via a wire bonding machine, whereby a 25 micron diameter alloy, gold or aluminium wire is bonded between the bond pads on the printhead integrated circuit  51  and conductive pads on the PCB  52 ;     G. The wire bond area is then encapsulated in an epoxy adhesive dispensed by an automatic two-head dispenser. A high viscosity non-sump adhesive is firstly applied to draw a dam around the wire bond area, and the dam is then filled with a low viscosity adhesive to fully encapsulate the wire bond area beneath the adhesive;     H. This assembly is then placed on levelling plates in an oven and heat cured to form the epoxy encapsulant  53 . The levelling plates ensure that no encapsulant flows from the assembly during curing; and     I. The thus-formed printhead tiles  50  and printhead integrated circuits  51  are ‘wet’ tested with a suitable fluid, such as pure water, to ensure reliable performance and are then dried out, where they are then ready for assembly on the fluid channel member  40 .        
 
         [0303]     The units composed of the printhead tiles  50  and the printhead integrated circuits  51  are prepared for assembly to the fluid channel members  40  as follows: 
        J. The (extended) flex PCB  80  is prepared to provide data and power connection to the printhead integrated circuit  51  from the PCB  90  and busbars  71 ,  72  and  73 ; and     K. The flex PCB  80  is aligned with the PCB  52  and attached using a hot bar soldering machine. The fluid channel members  40  and the casing  20  are formed and assembled as follows:     L. Individual fluid channel members  40  are formed by injection moulding an elongate body portion  44   a  so as to have seven individual grooves (channels) extending therethrough and the two longitudinally extending tabs  43  extending therealong on either side thereof. The (elongate) lid portion  44   b  is also moulded so as to be capable of enclosing the body portion  44   a  to separate each of the channels. The body and lid portions are both moulded so as to have end portions which form the female and male end portions  45  and  46  when assembled together. The lid portion  44   b  and the body portion  44   a  are then adhered together with epoxy and cured so as to form the seven ducts  41 ;     M. The casing  20  is then formed by extruding aluminium to a desired configuration and length by separately forming the (elongate) support frame  22 , with the channel  21  formed on the upper wall  27  thereof, and the (elongate) cover portion  23 ;     N. The end plate  110  is attached with screws via the threaded portions  22   a  and  22   b  formed in the support frame  22  to one (first) end of the casing  20 , and the end plate  111  is attached with screws via the threaded portions  22   a  and  22   b  to the other (second) end of the casing  20 ;     O. An epoxy is applied to the appropriate regions (i.e., so as not to cover the channels) of either a female or male connector  47  or  48 , and either the female or male connecting section  49   a  or  49   b  of a capping member  49  via a controlled dispenser;     P. An epoxy is applied to the appropriate regions (i.e., so as not to cover the channels) of the female and male end portions  45  and  46  of the plurality of fluid channel members  40  to be assembled together, end-to-end, so as to correspond to the desired length via the controlled dispenser;     Q. The female or male connector  47  or  48  is then attached to the male or female end portion  46  or  45  of the fluid channel member  40  which is to be at the first end of the plurality of fluid channel members  40  and the female or male connecting section  49   a  or  49   b  of the capping member  49  is attached to the male or female end portion  46  or  45  of the fluid channel member  40  which is to be at the second end of the plurality of fluid channel members  40 ;     R. Each of the fluid channel members  40  is then placed within the channel  21  one-by-one. Firstly, the (first) fluid channel member  40  to be at the first end is placed within the channel  21  at the first end, and is secured in place by way of the PCB supports  91  which are clipped into the support frame  22 , in the manner described earlier, so that the unconnected end portion  45  or  46  of the fluid channel member  40  is left exposed with the epoxy thereon. Then, a second member  40  is placed in the channel  21  so as to mate with the first fluid channel member  40  via its corresponding end portion  45  or  46  and the epoxy therebetween and is then clipped into place with its PCB supports  91 . This can then be repeated until the final fluid channel member  40  is in place at the second end of the channel  21 . Of course, only one fluid channel member  40  may be used, in which case it may have a connector  47  or  48  attached to one end portion  46  or  45  and a capping member  49  attached at the other end portion  45  or  46 ;     S. This arrangement is then placed in a compression jig, whereby a compression force is applied against the ends of the assembly to assist in sealing the connections between the individual fluid channel members  40  and their end connector  47  or  48  and capping member  49 . The complete assembly and jig is then placed in an oven at a temperature of about 100° C. for a predefined period, for example, about 45 minutes, to enhance the curing of the adhesive connections. However, other methods of curing, such as room temperature curing, could also be employed;     T. Following curing, the arrangement is pressure tested to ensure the integrity of the seal between the individual fluid channel members  40 , the connector  47  or  48 , and the capping member  49 ; and     U. The exposed upper surface of the assembly is then oxygen plasma cleaned to facilitate attachment of the individual printhead tiles  50  thereto.        
 
         [0316]     The printhead tiles  50  are attached to the fluid channel members  40  as follows: 
        V. Prior to placement of the individual printhead tiles  50  upon the upper surface of the fluid channel members  40 , the bottom surface of the printhead tiles  50  are argon plasma cleaned to enhance bonding. An adhesive is then applied via a robotic dispenser to the upper surface of the fluid channel members  40  in the form of an epoxy in strategic positions on the upper surface around and symmetrically about the outlet ports  42 . To assist in fixing the printhead tiles  50  in place a fast acting adhesive, such as cyanoacrylate, is applied in the remaining free areas of the upper surface as the adhesive drops  62  immediately prior to placing the printhead tiles  50  thereon;     W. Each of the individual printhead tiles  50  is then carefully aligned and placed on the upper surface of the fluid channel members  40  via a pick-and-place robot, such that a continuous print surface is defined along the length of the printhead module  30  and also to ensure that that the outlet ports  42  of the fluid channel members  40  align with the inlet ports  54  of the individual printhead tiles  50 . Following placement, the pick-and-place robot applies a pressure on the printhead tile  50  for about 5 to 10 seconds to assist in the setting of the cyanoacrylate and to fix the printhead tile  50  in place. This process is repeated for each printhead tile  50 ;     X. This assembly is then placed in an oven at about 100° C. for about 45 minutes to cure the epoxy so as to form the gasket member  60  and the locators  61  for each printhead tile  50  which seal the fluid connection between each of the outlet and inlet ports  42  and  54 . This fixes the printhead tiles  50  in place on the fluid channel members  40  so as to define the print surface; and     Y. Following curing, the assembly is inspected and tested to ensure correct alignment and positioning of the printhead tiles  50 .        
 
         [0321]     The printhead assembly  10  is assembled as follows: 
        Z. The support member  112  is attached to the end PCB supports  91  so as to align with the recessed portion  91   b  of the end supports  91 ;     AA. The connecting members  102  are placed in the abutting recessed portions  91   b  between the adjacent PCB supports  91  and in the abutting recessed portions  112   b  and  91   b  of the support members  112  and end PCB supports  91 , respectively;     BB. The PCBs  90 , each having assembled thereon a PEC integrated circuit  100  and its associated circuitry, are then mounted on the PCB supports  91  along the length of the casing  20  and are retained in place between the notch portions  96   a  of the retaining clips  96  and the recessed portions  93   a  and locating lugs  93   b  of the base portions  93  of the PCB supports  91 . As described earlier, the PCBs  90  can be arranged such that the PEC integrated circuit  100  of one PCB  90  drives the printhead integrated circuits  51  of four printhead tiles  50 , or of eight printhead tiles  50 , or of 16 printhead tiles  50 . Each of the PCBs  90  include the connection strips  90   a  and  90   b  on the inner face thereof which communicate with the connecting members  102  allowing data transfer between the PEC integrated circuits  100  of each of the PCBs  90 , between the printhead integrated circuits  51  and PEC integrated circuits  100  of each of the PCBs  90 , and between the data connection portion  117  of the connector arrangement  115 ;     CC. The connector arrangement  115 , with the power supply, data and fluid delivery connection portions  116 ,  117  and  118  attached thereto, is attached to the end plate  110  with screws so that the region  115   c  of the connector arrangement  115  is clipped into the clip portions  112   d  of the support member  112 ;     DD. The busbars  71 ,  72  and  73  are inserted into the corresponding channelled recesses  95   a ,  95   b  and  95   c  of the plurality of PCB supports  91  and are connected at their ends to the corresponding contact screws  116   a ,  116   b  and  116   c  of the power supply connection portion  116  of the connector arrangement  115 . The busbars  71 ,  72  and  73  provide a path for power to be distributed throughout the printhead assembly;     EE. Each of the flex PCBs  80  extending from each of the printhead tiles  50  is then connected to the connectors  98  of the corresponding PCBs  90  by slotting the slot regions  81  into the connectors  98 ;     FF. The pressure plates  74  are then clipped onto the PCB supports  91  by engaging the holes  74   a  and the tab portions  74   c  of the holes  74   b  with the corresponding retaining clips  99  and  96  of the PCB supports  91 , such that the raised portions  75  of the pressure plates  74  urge the power contacts of the flex PCBs  80  into contact with each of the busbars  71 ,  72  and  73 , thereby providing a path for the transfer of power between the busbars  71 ,  72  and  73 , the PCBs  90  and the printhead integrated circuits  51 ;     GG. The internal fluid delivery tubes  6  are then attached to the corresponding tubular portions  47   b  or  48   b  of the female or male connector  47  or  48 ; and     HH. The elongate, aluminium cover portion  23  of the casing  20  is then placed over the assembly and screwed into place via screws through the remaining holes in the end plates  110  and  111  into the threaded portions  23   b  of the cover portion  23 , and the end housing  120  is placed over the connector arrangement  115  and screwed into place with screws into the end plate  110  thereby completing the outer housing of the printhead assembly and so as to provide electrical and fluid communication between the printhead assembly and a printer unit. The external fluid tubes or hoses can then be assembled to supply ink and the other fluids to the channels ducts. The cover portion  23  can also act as a heat sink for the PEC integrated circuits  100  if the fin portions  23   d  are provided thereon, thereby protecting the circuitry of the printhead assembly  10 .        
 
         [0331]     Testing of the printhead assembly occurs as follows: 
        II. The thus-assembled printhead assembly  10  is moved to a testing area and inserted into a final print test machine which is essentially a working printing unit, whereby connections from the printhead assembly  10  to the fluid and power supplies are manually performed;     JJ. A test page is printed and analysed and appropriate adjustments are made to finalise the printhead electronics; and     KK. When passed, the print surface of the printhead assembly  10  is capped and a plastic sealing film is applied to protect the printhead assembly  10  until product installation.        
 
         [0335]     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.