CROSS REFERENCE TO RELATED APPLICATION 
   The present application is a Continuation of U.S. application Ser. No. 10/636,196 filed on Aug. 8, 2003 now U.S. Pat. No. 6,918,649 which is a Divisional application of U.S. application Ser. No. 10/102,699 filed on Mar. 22, 2002, now issued U.S. Pat. No. 6,767,076, the entire contents of which are herein incorporated by reference. 
   CO-PENDING APPLICATIONS 
   Various methods, systems and apparatus relating to the present invention are disclosed in the following co-pending patent/applications filed by the applicant or assignee of the present invention: 
   
     
       
             
             
             
             
             
           
         
             
                 
                 
             
           
           
             
                 
               6,428,133 
               6,526,658, 
               6,795,215, 
               09/575,109. 
             
             
                 
                 
             
           
        
       
     
   
   The disclosures of these co-pending patent/applications are incorporated herein by reference. 


   BACKGROUND OF THE INVENTION 
   The following invention relates to a printhead assembly capping device for a printer. 
   More particularly, though not exclusively, the invention relates to a capping device for a printhead assembly of an A4 pagewidth drop on demand printer capable of printing up to 1600 dpi photographic quality at up to 160 pages per minute. 
   The overall design of a printer in which the capping can be utilized revolves around the use of replaceable printhead modules in an array approximately 8½ inches (21 cm) long. An advantage of such a system is the ability to easily remove and replace any defective modules in a printhead array. This would eliminate having to scrap an entire printhead if only one chip is defective. 
   A printhead module in such a printer can be comprised of a “Memjet” chip, being a chip having mounted thereon a vast number of thermo-actuators in micro-mechanics and micro-electromechanical systems (MEMS). Such actuators might be those as disclosed in U.S. Pat. No. 6,044,646 to the present applicant, however, might be other MEMS print chips. 
   In a typical embodiment, eleven “Memjet” tiles can butt together in a metal channel to form a complete 8½ inch printhead assembly. 
   The printhead, being the environment within which the capping device of the present invention is to be situated, might typically have six ink chambers and be capable of printing four color process (CMYK) as well as infra-red ink and fixative. An air pump would supply filtered air through a seventh chamber to the printhead, which could be used to keep foreign particles away from its ink nozzles. 
   Each printhead module receives ink via an elastomeric extrusion that transfers the ink. Typically, the printhead assembly is suitable for printing A4 paper without the need for scanning movement of the printhead across the paper width. 
   The printheads themselves are modular, so printhead arrays can be configured to form printheads of arbitrary width. 
   Additionally, a second printhead assembly can be mounted on the opposite side of a paper feed path to enable double-sided high speed printing. 
   OBJECTS OF THE INVENTION 
   It is an object of the present invention to provide a printhead assembly capping device. 
   Another object of the present invention is to provide a printhead assembly including a capping device providing an air flow path during operation of the printer and serving to prevent ingress of foreign particles to printhead nozzles during non-operational period of the printer. 
   SUMMARY OF THE INVENTION 
   The present invention provides a printhead assembly for a drop on demand ink jet printer, comprising: 
   a printhead module having a printhead including ink jet nozzles, the module being affixed to the assembly, 
   a capping device affixed to the assembly and movable linearly with respect thereto, the capping device at least partially surrounding the printhead module and movable between a capped position whereby the nozzles are capped by the capping device and an uncapped position whereby the nozzles are uncapped. 
   Preferably a plurality of printhead modules are situated along a channel, the modules and channel extending substantially across a pagewidth. 
   Preferably the capping device partly surrounds the channel. 
   Preferably the capping device has an onsert molded elastomeric pad which bears onto one or more of the printhead modules. 
   Preferably each printhead module includes a nozzle guard to protect the nozzles and wherein the elastomeric pad clamps against the nozzle guard in the capped position. 
   Preferably the elastomeric pad includes air ducts via which air is pumped to the printhead modules when the capping device is in the uncapped position. 
   Preferably a camshaft bears against the capping device and serves to move the capping device between said capped and uncapped positions. 
   Preferably the capping device includes a spring to bias the device with respect to the printhead modules against the camshaft. 
   Preferably the capping device is formed of stainless spring steel. 
   Preferably each printhead module includes a ramp and wherein the capping device includes a boss that rides over the ramp when the capping device is moved between the capped and uncapped positions, the ramp serving to elastically distort the capping device as it is moved between said capped and uncapped positions so as to prevent scraping of the device against the nozzle guard. 
   Preferably each printhead module has alternating air inlets and outlets cooperating with the elastomeric pad so as to be either sealed off or grouped into air inlet/outlet chambers depending on the position of the capping device, the chambers serving to duct air to the printhead when the capping device is uncapped. 
   Preferably the capping device applies a compressive force to each printhead module and an underside of the channel. 
   Preferably rotation of the camshaft is reversible. 
   As used herein, the term “ink” is intended to mean any fluid which flows through the printhead to be delivered to print media. The fluid may be one of many different colored inks, infra-red ink, a fixative or the like. 


   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A preferred form of the present invention will now be described by way of example with reference to the accompanying drawings wherein: 
       FIG. 1  is a schematic overall view of a printhead; 
       FIG. 2  is a schematic exploded view of the printhead of  FIG. 1 ; 
       FIG. 3  is a schematic exploded view of an ink jet module; 
       FIG. 3   a  is a schematic exploded inverted illustration of the ink jet module of  FIG. 3 ; 
       FIG. 4  is a schematic illustration of an assembled ink jet module; 
       FIG. 5  is a schematic inverted illustration of the module of  FIG. 4 ; 
       FIG. 6  is a schematic close-up illustration of the module of  FIG. 4 ; 
       FIG. 7  is a schematic illustration of a chip sub-assembly; 
       FIG. 8   a  is a schematic side elevational view of the printhead of  FIG. 1 ; 
       FIG. 8   b  is a schematic plan view of the printhead of  FIG. 8   a;    
       FIG. 8   c  is a schematic side view (other side) of the printhead of  FIG. 8   a;    
       FIG. 8   d  is a schematic inverted plan view of the printhead of  FIG. 8   b;    
       FIG. 9  is a schematic cross-sectional end elevational view of the printhead of  FIG. 1 ; 
       FIG. 10  is a schematic illustration of the printhead of  FIG. 1  in an uncapped configuration; 
       FIG. 11  is a schematic illustration of the printhead of  FIG. 10  in a capped configuration; 
       FIG. 12   a  is a schematic illustration of a capping device; 
       FIG. 12   b  is a schematic illustration of the capping device of  FIG. 12   a , viewed from a different angle; 
       FIG. 13  is a schematic illustration showing the loading of an ink jet module into a printhead; 
       FIG. 14  is a schematic end elevational view of the printhead illustrating the printhead module loading method; 
       FIG. 15  is a schematic cut-away illustration of the printhead assembly of  FIG. 1 ; 
       FIG. 16  is a schematic close-up illustration of a portion of the printhead of  FIG. 15  showing greater detail in the area of the “Memjet” chip; 
       FIG. 17  is a schematic illustration of the end portion of a metal channel and a printhead location molding; 
       FIG. 18   a  is a schematic illustration of an end portion of an elastomeric ink delivery extrusion and a molded end cap; and 
       FIG. 18   b  is a schematic illustration of the end cap of  FIG. 18   a  in an out-folded configuration. 
   


   DETAILED DESCRIPTION OF THE INVENTION 
   In  FIG. 1  of the accompanying drawings there is schematically depicted an overall view of a printhead assembly.  FIG. 2  shows the core components of the assembly in an exploded configuration. The printhead assembly  10  of the preferred embodiment comprises eleven printhead modules  11  situated along a metal “Invar” channel  16 . At the heart of each printhead module  11  is a “Memjet” chip  23  ( FIG. 3 ). The particular chip chosen in the preferred embodiment being a six-color configuration. 
   The “Memjet” printhead modules  11  are comprised of the “Memjet” chip  23 , a fine pitch flex PCB  26  and two micro-moldings  28  and  34  sandwiching a mid-package film  35 . Each module  11  forms a sealed unit with independent ink chambers  63  ( FIG. 9 ) which feed the chip  23 . The modules  11  plug directly onto a flexible elastomeric extrusion  15  which carries air, ink and fixative in channels  49  to  55  ( FIG. 9 ). The upper surface of the extrusion  15  has repeated patterns of holes  21  which align with ink inlets  32  ( FIG. 3   a ) on the underside of each module  11 . The extrusion  15  is bonded onto a flex PCB (flexible printed circuit board). 
   The fine pitch flex PCB  26  wraps down the side of each printhead module  11  and makes contact with the flex PCB  17  ( FIG. 9 ). The flex PCB  17  carries two busbars  19  (positive) and  20  (negative) for powering each module  11 , as well as all data connections. The flex PCB  17  is bonded onto the continuous metal “Invar” channel  16 . The metal channel  16  serves to hold the modules  11  in place and is designed to have a similar coefficient of thermal expansion to that of silicon used in the modules. 
   A capping device  12  is used to cover the “Memjet” chips  23  when not in use. The capping device is typically made of spring steel with an onsert molded elastomeric pad  47  ( FIG. 12   a ). The pad  47  serves to duct air into the “Memjet” chip  23  when uncapped and cut off air and cover a nozzle guard  24  ( FIG. 9 ) when capped. The capping device  12  is actuated by a camshaft  13  that typically rotates throughout 180°. 
   The overall thickness of the “Memjet” chip is typically 0.6 mm which includes a 150 micron inlet backing layer  27  and a nozzle guard  24  of 150 micron thickness. These elements are assembled at the wafer scale. 
   The nozzle guard  24  allows filtered air into an 80 micron cavity  64  ( FIG. 16 ) above the “Memjet” ink nozzles  62 . The pressurized air flows through microdroplet holes  45  in the nozzle guard  24  (with the ink during a printing operation) and serves to protect the delicate “Memjet” nozzles  62  by repelling foreign particles. 
   A silicon chip backing layer  27  ducts ink from the printhead module packaging directly into the rows of “Memjet” nozzles  62 . The “Memjet” chip  23  is wire bonded  25  from bond pads on the chip at 116 positions to the fine pitch flex PCB  26 . The wire bonds are on a 120 micron pitch and are cut as they are bonded onto the fine pitch flex PCB pads ( FIG. 3 ). The fine pitch flex PCB  26  carries data and power from the flex PCB  17  via a series of gold contact pads  69  along the edge of the flex PCB. 
   The wire bonding operation between chip and fine pitch flex PCB  26  may be done remotely, before transporting, placing and adhering the chip assembly into the printhead module assembly. Alternatively, the “Memjet” chips  23  can be adhered into the upper micro-molding  28  first and then the fine pitch flex PCB  26  can be adhered into place. The wire bonding operation could then take place in situ, with no danger of distorting the moldings  28  and  34 . The upper micro-molding  28  can be made of a Liquid Crystal Polymer (LCP) blend. Since the crystal structure of the upper micro-molding  28  is minute, the heat distortion temperature (180° C.–260° C.), the continuous usage temperature (200° C.–240° C.) and soldering heat durability (260° C. for 10 seconds to 310° C. for 10 seconds) are high, regardless of the relatively low melting point. 
   Each printhead module  11  includes an upper micro-molding  28  and a lower micro-molding  34  separated by a mid-package film layer  35  shown in  FIG. 3 . 
   The mid-package film layer  35  can be an inert polymer such as polyimide, which has good chemical resistance and dimensional stability. The mid-package film layer  35  can have laser ablated holes  65  and can comprise a double-sided adhesive (ie. an adhesive layer on both faces) providing adhesion between the upper micro-molding, the mid-package film layer and the lower micro-molding. 
   The upper micro-molding  28  has a pair of alignment pins  29  passing through corresponding apertures in the mid-package film layer  35  to be received within corresponding recesses  66  in the lower micro-molding  34 . This serves to align the components when they are bonded together. Once bonded together, the upper and lower micro-moldings form a tortuous ink and air path in the complete “Memjet” printhead module  11 . 
   There are annular ink inlets  32  in the underside of the lower micro-molding  34 . In a preferred embodiment, there are six such inlets  32  for various inks (black, yellow, magenta, cyan, fixitive and infrared). There is also provided an air inlet slot  67 . The air inlet slot  67  extends across the lower micro-molding  34  to a secondary inlet which expels air through an exhaust hole  33 , through an aligned hole  68  in fine pitch flex PCB  26 . This serves to repel the print media from the printhead during printing. The ink inlets  32  continue in the undersurface of the upper micro-molding  28  as does a path from the air inlet slot  67 . The ink inlets lead to 200 micron exit holes also indicated at  32  in  FIG. 3 . These holes correspond to the inlets on the silicon backing layer  27  of the “Memjet” chip  23 . 
   There is a pair of elastomeric pads  36  on an edge of the lower micro-molding  34 . These serve to take up tolerance and positively located the printhead modules  11  into the metal channel  16  when the modules are micro-placed during assembly. 
   A preferred material for the “Memjet” micro-moldings is a LCP. This has suitable flow characteristics for the fine detail in the moldings and has a relatively low coefficient of thermal expansion. 
   Robot picker details are included in the upper micro-molding  28  to enable accurate placement of the printhead modules  11  during assembly. 
   The upper surface of the upper micro-molding  28  as shown in  FIG. 3  has a series of alternating air inlets and outlets  31 . These act in conjunction with the capping device  12  and are either sealed off or grouped into air inlet/outlet chambers, depending upon the position of the capping device  12 . They connect air diverted from the inlet slot  67  to the chip  23  depending upon whether the unit is capped or uncapped. 
   A capper cam detail  40  including a ramp for the capping device is shown at two locations in the upper surface of the upper micro-molding  28 . This facilitates a desirable movement of the capping device  12  to cap or uncap the chip and the air chambers. That is, as the capping device is caused to move laterally across the print chip during a capping or uncapping operation, the ramp of the capper cam detail  40  serves to elastically distort and capping device as it is moved by operation of the camshaft  13  so as to prevent scraping of the device against the nozzle guard  24 . 
   The “Memjet” chip assembly  23  is picked and bonded into the upper micro-molding  28  on the printhead module  11 . The fine pitch flex PCB  26  is bonded and wrapped around the side of the assembled printhead module  11  as shown in  FIG. 4 . After this initial bonding operation, the chip  23  has more sealant or adhesive  46  applied to its long edges. This serves to “pot” the bond wires  25  ( FIG. 6 ), seal the “Memjet” chip  23  to the molding  28  and form a sealed gallery into which filtered air can flow and exhaust through the nozzle guard  24 . 
   The flex PCB  17  carries all data and power connections from the main PCB (not shown) to each “Memjet” printhead module  11 . The flex PCB  17  has a series of gold plated, domed contacts  69  ( FIG. 2 ) which interface with contact pads  41 ,  42  and  43  on the fine pitch flex PCB  26  of each “Memjet” printhead module  11 . 
   Two copper busbar strips  19  and  20 , typically of 200 micron thickness, are jigged and soldered into place on the flex PCB  17 . The busbars  19  and  20  connect to a flex termination which also carries data. 
   The flex PCB  17  is approximately 340 mm in length and is formed from a 14 mm wide strip. It is bonded into the metal channel  16  during assembly and exits from one end of the printhead assembly only. 
   The metal U-channel  16  into which the main components are place is of a special alloy called “Invar 36”. It is a 36% nickel iron alloy possessing a coefficient of thermal expansion of 1/10 th  that of carbon steel at temperatures up to 400° F. The Invar is annealed for optimal dimensional stability. 
   Additionally, the Invar is nickel plated to a 0.056% thickness of the wall section. This helps to further match it to the coefficient of thermal expansion of silicon which is 2×10 −6  per ° C. 
   The Invar channel  16  functions to capture the “Memjet” printhead modules  11  in a precise alignment relative to each other and to impart enough force on the modules  11  so as to form a seal between the ink inlets  32  on each printhead module and the outlet holes  21  that are laser ablated into the elastomeric ink delivery extrusion  15 . 
   The similar coefficient of thermal expansion of the Invar channel to the silicon chips allows similar relative movement during temperature changes. The elastomeric pads  36  on one side of each printhead module  11  serve to “lubricate” them within the channel  16  to take up any further lateral coefficient of thermal expansion tolerances without losing alignment. The Invar channel is a cold rolled, annealed and nickel plated strip. Apart from two bends that are required in its formation, the channel has two square cutouts  80  at each end. These mate with snap fittings  81  on the printhead location moldings  14  ( FIG. 17 ). 
   The elastomeric ink delivery extrusion  15  is a non-hydrophobic, precision component. Its function is to transport ink and air to the “Memjet” printhead modules  11 . The extrusion is bonded onto the top of the flex PCB  17  during assembly and it has two types of molded end caps. One of these end caps is shown at  70  in  FIG. 18   a.    
   A series of patterned holes  21  are present on the upper surface of the extrusion  15 . These are laser ablated into the upper surface. To this end, a mask is made and placed on the surface of the extrusion, which then has focused laser light applied to it. The holes  21  are evaporated from the upper surface, but the laser does not cut into the lower surface of extrusion  15  due to the focal length of the laser light. 
   Eleven repeated patterns of the laser ablated holes  21  form the ink and air outlets  21  of the extrusion  15 . These interface with the annular ring inlets  32  on the underside of the “Memjet” printhead module lower micro-molding  34 . A different pattern of larger holes (not shown but concealed beneath the upper plate  71  of end cap  70  in  FIG. 18   a ) is ablated into one end of the extrusion  15 . These mate with apertures  75  having annular ribs formed in the same way as those on the underside of each lower micro-molding  34  described earlier. Ink and air delivery hoses  78  are connected to respective connectors  76  that extend from the upper plate  71 . 
   Due to the inherent flexibility of the extrusion  15 , it can contort into many ink connection mounting configurations without restricting ink and air flow. The molded end cap  70  has a spine  73  from which the upper and lower plates are integrally hinged. The spine  73  includes a row of plugs  74  that are received within the ends of the respective flow passages or channels  49  to  55  of the extrusion  15 . 
   The other end of the extrusion  15  is capped with simple plugs which block the channels  49  to  55  in a similar way as the plugs  74  on spine  17 . 
   The end cap  70  clamps onto the ink extrusion  15  by way of snap engagement tabs  77 . Once assembled with the delivery hoses  78 , ink and air can be received from ink reservoirs and an air pump, possibly with filtration means. The end cap  70  can be connected to either end of the extrusion, ie. at either end of the printhead. 
   The plugs  74  are pushed into the channels  49  to  55  of the extrusion  15  and the plates  71  and  72  are folded over. The snap engagement tabs  77  clamp the molding and prevent it from slipping off the extrusion. As the plates are snapped together, they form a sealed collar arrangement around the end of the extrusion. Instead of providing individual hoses  78  pushed onto the connectors  76 , the molding  70  might interface directly with an ink cartridge. A sealing pin arrangement can also be applied to this molding  70 . For example, a perforated, hollow metal pin with an elastomeric collar can be fitted to the top of the inlet connectors  76 . This would allow the inlets to automatically seal with an ink cartridge when the cartridge is inserted. The air inlet and hose might be smaller than the other inlets in order to avoid accidental charging of the airways with ink. 
   The capping device  12  for the “Memjet” printhead would typically be formed of stainless spring steel. An elastomeric seal or onsert molding  47  is attached to the capping device as shown in  FIGS. 12   a  and  12   b . The metal part from which the capping device is made is punched as a blank and then inserted into an injection molding tool ready for the elastomeric onsert to be shot onto its underside. Small holes  79  ( FIG. 13   b ) are present on the upper surface of the metal capping device  12  and can be formed as burst holes. They serve to key the onsert molding  47  to the metal. After the molding  47  is applied, the blank is inserted into a press tool, where additional bending operations and forming of integral springs  48  takes place. 
   The elastomeric onsert molding  47  has a series of rectangular recesses or air chambers  56 . These create chambers when uncapped. The chambers  56  are positioned over the air inlet and exhaust holes  30  of the upper micro-molding  28  in the “Memjet” printhead module  11 . These allow the air to flow from one inlet to the next outlet. When the capping device  12  is moved forward to the “home” capped position as depicted in  FIG. 11 , these airways  32  are sealed off with a blank section of the onsert molding  47  cutting off airflow to the “Memjet” chip  23 . This prevents the filtered air from drying out and therefore blocking the delicate “Memjet” nozzles. 
   Another function of the onsert molding  47  is to cover and clamp against the nozzle guard  24  on the “Memjet” chip  23 . This protects against drying out, but primarily keeps foreign particles such as paper dust from entering the chip and damaging the nozzles. The chip is only exposed during a printing operation, when filtered air is also exiting along with the ink drops through the nozzle guard  24 . This positive air pressure repels foreign particles during the printing process and the capping device protects the chip in times of inactivity. 
   The integral springs  48  bias the capping device  12  away from the side of the metal channel  16 . The capping device  12  applies a compressive force to the top of the printhead module  11  and the underside of the metal channel  16 . The lateral capping motion of the capping device  12  is governed by an eccentric camshaft  13  mounted against the side of the capping device. It pushes the device  12  against the metal channel  16 . During this movement, the bosses  57  beneath the upper surface of the capping device  12  ride over the respective ramps  40  formed in the upper micro-molding  28 . This action flexes the capping device and raises its top surface to raise the onsert molding  47  as it is moved laterally into position onto the top of the nozzle guard  24 . 
   The camshaft  13 , which is reversible, is held in position by two printhead location moldings  14 . The camshaft  11  can have a flat surface built in one end or be otherwise provided with a spline or keyway to accept gear  22  or another type of motion controller. 
   The “Memjet” chip and printhead module are assembled as follows:
         1. The “Memjet” chip  23  is dry tested in flight by a pick and place robot, which also dices the wafer and transports individual chips to a fine pitch flex PCB bonding area.   2. When accepted, the “Memjet” chip  23  is placed 530 microns apart from the fine pitch flex PCB  26  and has wire bonds  25  applied between the bond pads on the chip and the conductive pads on the fine pitch flex PCB. This constitutes the “Memjet” chip assembly.   3. An alternative to step  2  is to apply adhesive to the internal walls of the chip cavity in the upper micro-molding  28  of the printhead module and bond the chip into place first. The fine pitch flex PCB  26  can then be applied to the upper surface of the micro-molding and wrapped over the side. Wire bonds  25  are then applied between the bond pads on the chip and the fine pitch flex PCB.   4. The “Memjet” chip assembly is vacuum transported to a bonding area where the printhead modules are stored.   5. Adhesive is applied to the lower internal walls of the chip cavity and to the area where the fine pitch flex PCB is going to be located in the upper micro-molding of the printhead module.   6. The chip assembly (and fine pitch flex PCB) are bonded into place. The fine pitch flex PCB is carefully wrapped around the side of the upper micro-molding so as not to strain the wire bonds. This may be considered as a two step gluing operation if it is deemed that the fine pitch flex PCB might stress the wire bonds. A line of adhesive running parallel to the chip can be applied at the same time as the internal chip cavity walls are coated. This allows the chip assembly and fine pitch flex PCB to be seated into the chip cavity and the fine pitch flex PCB allowed to bond to the micro-molding without additional stress. After curing, a secondary gluing operation could apply adhesive to the short side wall of the upper micro-molding in the fine pitch flex PCB area. This allows the fine pitch flex PCB to be wrapped around the micro-molding and secured, while still being firmly bonded in place along on the top edge under the wire bonds.   7. In the final bonding operation, the upper part of the nozzle guard is adhered to the upper micro-molding, forming a sealed air chamber. Adhesive is also applied to the opposite long edge of the “Memjet” chip, where the bond wires become ‘potted’ during the process.   8. The modules are ‘wet’ tested with pure water to ensure reliable performance and then dried out.   9. The modules are transported to a clean storage area, prior to inclusion into a printhead assembly, or packaged as individual units. The completes the assembly of the “Memjet” printhead module assembly.   10. The metal Invar channel  16  is picked and placed in a jig.   11. The flex PCB  17  is picked and primed with adhesive on the busbar side, positioned and bonded into place on the floor and one side of the metal channel.   12. The flexible ink extrusion  15  is picked and has adhesive applied to the underside. It is then positioned and bonded into place on top of the flex PCB  17 . One of the printhead location end caps is also fitted to the extrusion exit end. This constitutes the channel assembly.       

   The laser ablation process is as follows:
         13. The channel assembly is transported to an eximir laser ablation area.   14. The assembly is put into a jig, the extrusion positioned, masked and laser ablated. This forms the ink holes in the upper surface.   15. The ink extrusion  15  has the ink and air connector molding  70  applied. Pressurized air or pure water is flushed through the extrusion to clear any debris.   16. The end cap molding  70  is applied to the extrusion  15 . It is then dried with hot air.   17. The channel assembly is transported to the printhead module area for immediate module assembly. Alternatively, a thin film can be applied over the ablated holes and the channel assembly can be stored until required.       

   The printhead module to channel is assembled as follows:
         18. The channel assembly is picked, placed and clamped into place in a transverse stage in the printhead assembly area.   19. As shown in  FIG. 14 , a robot tool  58  grips the sides of the metal channel and pivots at pivot point against the underside face to effectively flex the channel apart by 200 to 300 microns. The forces applied are shown generally as force vectors F in  FIG. 14 . This allows the first “Memjet” printhead module to be robot picked and placed (relative to the first contact pads on the flex PCB  17  and ink extrusion holes) into the channel assembly.   20. The tool  58  is relaxed, the printhead module captured by the resilience of the Invar channel and the transverse stage moves the assembly forward by 19.81 mm.   21. The tool  58  grips the sides of the channel again and flexes it apart ready for the next printhead module.   22. A second printhead module  11  is picked and placed into the channel 50 microns from the previous module.   23. An adjustment actuator arm locates the end of the second printhead module. The arm is guided by the optical alignment of fiducials on each strip. As the adjustment arm pushes the printhead module over, the gap between the fiducials is closed until they reach an exact pitch of 19.812 mm.   24. The tool  58  is relaxed and the adjustment arm is removed, securing the second printhead module in place.   25. This process is repeated until the channel assembly has been fully loaded with printhead modules. The unit is removed from the transverse stage and transported to the capping assembly area. Alternatively, a thin film can be applied over the nozzle guards of the printhead modules to act as a cap and the unit can be stored as required.       

   The capping device is assembled as follows:
         26. The printhead assembly is transported to a capping area. The capping device  12  is picked, flexed apart slightly and pushed over the first module  11  and the metal channel  16  in the printhead assembly. It automatically seats itself into the assembly by virtue of the bosses  57  in the steel locating in the recesses  83  in the upper micro-molding in which a respective ramp  40  is located.   27. Subsequent capping devices are applied to all the printhead modules.   28. When completed, the camshaft  13  is seated into the printhead location molding  14  of the assembly. It has the second printhead location molding seated onto the free end and this molding is snapped over the end of the metal channel, holding the camshaft and capping devices captive.   29. A molded gear  22  or other motion control device can be added to either end of the camshaft  13  at this point.   30. The capping assembly is mechanically tested.       

   Print charging is as follows:
         31. The printhead assembly  10  is moved to the testing area. Inks are applied through the “Memjet” modular printhead under pressure. Air is expelled through the “Memjet” nozzles during priming. When charged, the printhead can be electrically connected and tested.   32. Electrical connections are made and tested as follows:   33. Power and data connections are made to the PCB. Final testing can commence, and when passed, the “Memjet” modular printhead is capped and has a plastic sealing film applied over the underside that protects the printhead until product installation.
The present invention relates to an end cap for capping an end of an extrusion of a printhead assembly. The extrusion defines a plurality of respective channels for each carrying a medium such as air or ink and each channel has an opening at the end. The end cap comprises a body and a plurality of protrusions which extend from the body. The protrusions are located so as to each correspond with a respective channel opening. During capping, the body is located so that each protrusion is inserted into a corresponding channel opening to thereby plug each channel and cap the end of the extrusion. A print head assembly comprising an extrusion which is capped at an end with the end cap is also provided.