Abstract:
Described is an ink delivery system is that utilizes a filter carrier to simplify the process of attaching the filter. The filter carrier is an element that has a conduit that is substantially surrounded by a filter attach surface. The filter is attached to this surface, such that substantially all fluid passing through the conduit is filtered. The filter carrier is installed into a housing upon which a printhead is mounted. The filter then divides the ink delivery portion of the housing into upstream and downstream sections such that ink flows from the upstream portion through the filter to the downstream portion and to the printhead. The separation of the filter sing from the cartridge housing provides more freedom of material selection for both the cartridge housing and a good heat staking material for the filter carrier. The separation also greatly simplifies the molding of the rigid cartridge housing. Also, the filter staking process is greatly simplified when it is performed external to the cartridge housing. Also provided is the ability to have an adjustable air warehouse volume to accommodate various out-gassing rates of different print usages cartridge usages.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is related to U.S. patent application Ser. No. 08/748,726, filed Nov. 13, 1996, now U.S. Pat. No. 5,815,185 entitled “Ink Flow Heat Exchanger for Inkjet Printhead” and U.S. patent application Ser. No. 08/706,121, filed Aug. 30, 1996, now U.S. Pat. No. 5,966,155 entitled “Inkjet Printing System with Off-Axis Ink Supply Having Ink Path Which Does Not Extend above Print Cartridge.” The foregoing commonly assigned patent applications are herein incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to inkjet printers and, more particularly, to an inkjet printer having a scanning printhead with an ink delivery system is provided that utilizes a filter carrier to simplify the process of attaching the filter. 
     BACKGROUND OF THE INVENTION 
     Thermal inkjet hardcopy devices such as printers, graphics plotters, facsimile machines and copiers have gained wide acceptance. These hardcopy devices are described by W. J. Lloyd and H. T. Taub in “Ink Jet Devices,” Chapter 13 of  Output Hardcopy Devices  (Ed. R. C. Durbeck and S. Sherr, San Diego: Academic Press, 1988) and U.S. Pat. Nos. 4,490,728 and 4,313,684. The basics of this technology are further disclosed in various articles in several editions of the  Hewlett - Packard Journal  [Vol. 36, No. 5 (May 1985), Vol. 39, No. 4 (August 1988), Vol. 39, No. 5 (October 1988), Vol. 43, No. 4 (August 1992), Vol. 43, No. 6 (December 1992) and Vol. 45, No. 1 February 1994)], incorporated herein by reference. Inlet hardcopy devices produce high quality print, are compact and portable, and print quickly and quietly because only ink strikes the paper. 
     An inkjet printer forms a printed image by printing a pattern of individual dots at particular locations of an array defined for the printing medium. The locations are conveniently visualized as being small dots in a rectilinear array. The locations are sometimes “dot locations”, “dot positions”, or pixels”. Thus, the printing operation can be viewed as the filing of a pattern of dot locations with dots of ink. 
     Inkjet hardcopy devices print dots by ejecting very small drops of ink onto the print medium and typically include a movable carriage that supports one or more printheads each having ink ejecting nozzles. The carriage traverses over the surface of the print medium, and the nozzles are controlled to eject drops of ink at appropriate times pursuant to command of a microcomputer or other controller, wherein the timing of the application of the ink drops is intended to correspond to the pattern of pixels of the image being printed. 
     The typical inkjet printhead (i.e., the silicon substrate, structures built on the substrate, and connections to the substrate) uses liquid ink (i.e., dissolved colorants or pigments dispersed in a solvent). It has an array of precisely formed orifices or nozzles attached to a printhead substrate that incorporates an array of ink ejection chambers which receive liquid ink from the ink reservoir. Each chamber is located opposite the nozzle so ink can collect between it and the nozzle. The ejection of ink droplets is typically under the control of a microprocessor, the signals of which are conveyed by electrical traces to the resistor elements. When electric printing pulses heat the inkjet firing chamber resistor, a small portion of the ink next to it vaporizes and ejects a drop of ink from the printhead. Properly arranged nozzles form a dot matrix pattern. Properly sequencing the operation of each nozzle causes characters or images to be printed upon the paper as the printhead moves past the paper. 
     The ink cartridge containing the nozzles is moved repeatedly across the width of the medium to be printed upon. At each of a designated number of increments of this movement across the medium, each of the nozzles is caused either to eject ink or to refrain from ejecting ink according to the program output of the controlling microprocessor. Each completed movement across the medium can print a swath approximately as wide as the number of nozzles arranged in a column of the ink cartridge multiplied times the distance between nozzle centers. After each such completed movement or swath the medium is moved forward the width of the swath, and the ink cartridge begins the next swath. By proper selection and timing of the signals, the desired print is obtained on the medium. 
     A concern with inkjet printing is the sufficiency of ink flow to the paper or other print media. Print quality is a function of ink flow through the printhead. Too little ink on the paper or other media to be printed upon produces faded and hard-to-read documents. 
     In an inkjet printhead ink is fed from an ink reservoir integral to the printhead or an “off-axis” ink reservoir which feeds ink to the printhead via tubes connecting the printhead and reservoir. Ink is then fed to the various vaporization chambers either through an elongated hole formed in the center of the bottom of the substrate, “center feed”, or around the outer edges of the substrate, “edge feed”. In center feed the ink then flows through a central slot in the substrate into a central manifold area formed in a barrier layer between the substrate and a nozzle member, then into a plurality of ink channels, and finally into the various vaporization chambers. In edge feed ink from the ink reservoir flows around the outer edges of the substrate into the ink channels and finally into the vaporization chambers. In either center feed or edge feed, the flow path from the ink reservoir and the manifold inherently provides restrictions on ink flow to the firing chambers. 
     Air and other gas bubbles and particulate matter can cause major problems in ink delivery systems. Ink delivery systems are capable of releasing gasses and generating bubbles, thereby causing systems to get clogged and degraded by bubbles. In the design of a good ink delivery system, it is important that techniques for eliminating or reducing bubble problems be considered. 
     Inkjet printheads are typically attached to a housing or body pf a print cartridge which contains an ink reservoir. The housing has a conduit for supplying ink from the ink reservoir to the printhead. Inkjet printheads are very sensitive to particulate contamination. To deal with this problem, a filter is typically disposed between the reservoir of ink and the printhead. A filter is attached to the inside of the housing, separating the ink conduit of the housing into two regions—one upstream and one downstream of the filter. This type of design has a number of drawbacks. 
     First, the housing material tends to be selected for structural rigidity and high heat deflection. Fillers (such as glass fibers) are typically included to enhance these properties. Such materials tend to be difficult surfaces to which to attach a filter and effect a complete seal around the perimeter of the filter. If the seal is not complete, bubbles or particulates may slip past the filter and block the ink channels or nozzles. 
     One method to improve upon this is to provide a second plastic material by insert molding to rigid outer housing. However insert molding is very expensive and the outer rigid housing must be adapted to be compatible with insert molding. The separation the filter staking from the cartridge housing would provide more freedom of material selection for both the cartridge housing and a good heat staking material for the filter carrier. Moreover, the filter staking process is greatly simplified when it can be performed external to the cartridge housing is done outside a pen body. All of these difficulties are even further compounded by the advent of a new design that provides a jet impinging flow of ink to cool the printhead. This design makes the molding of the rigid housing very difficult. 
     Another problem that occurs during the life of the print element is air out gassing. Air builds up between the filter and the printhead during operation of the printhead. For printers that have a high use model, it would be preferable to have a larger volume between the filter and the printhead for the storage of air. For low use rate printers, this volume would be reduced. 
     Accordingly, there is a need to provide a way to reduce dependency of the filter attach properties upon the selection of exterior housing properties without adding a costly insertion molding process. Further, there is a need to provide a housing and filter design that makes the jet impinging flow design easier to mold. There is also a need for a way to provide a variable volume for the storage of out gassed air for the same print cartridge housing. 
     SUMMARY OF THE INVENTION 
     An ink delivery system is provided that utilizes a filter carrier to simplify the process of attaching the filter. The filter carrier is an element that has a conduit therethrough that is substantially surrounded by a filter attach surface. The filter is attached to this surface, such that substantially all fluid passing through the conduit is filtered. The filter carrier is installed into a housing upon which a printhead is mounted. The filter then divides the ink conduit of the housing into upstream and downstream sections such that ink flows from the upstream portion through the filter to the downstream portion and to the printhead. The separation of the filter staking from the cartridge housing provides more freedom of material selection for both the cartridge housing and a good heat staking material for the filter carrier. The separation also greatly simplifies the molding of the rigid cartridge housing. Also, the filter staking process is greatly simplified when it is performed external to the cartridge housing. The present invention also provides the ability to have an adjustable air warehouse volume to accommodate various out-gassing rates of different print usages cartridge usages. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of one embodiment of an inkjet printer incorporating the present invention. 
     FIG. 2 is a simplified, partial top view of another embodiment of an inkjet printer incorporating the present invention, but illustrating a different routing of the ink supply tubes from the off-axis ink reservoirs to the carriage-mounted ink cartridges. 
     FIG. 3 is a perspective view of a single print cartridge and also showing the fluid interconnect portion of the carriage. 
     FIG. 4 is another perspective view a single print cartridge and the fluid interconnect portion of the carriage. 
     FIG. 5 is a cross-sectional, perspective view along line A—A of the print cartridge of FIG. 3 shown connected to the fluid interconnect on the carriage. 
     FIG. 6 is a perspective view of the back side of the printhead assembly. 
     FIG. 7 is a cross-sectional view along line B—B of FIG. 3 illustrating the portion of the printhead assembly showing the flow of ink to the ink ejection chambers in the printhead. 
     FIG. 8 is a perspective view the of print cartridge of FIG. 3 showing the headland area where the substrate and flex tape is attached. 
     FIG. 9 is a cross-sectional, perspective view along line B—B of FIG. 3 illustrating an ink chamber for containing a pressure regulator, the filter carrier of the present invention and the ink conduit leading to the back surface of the substrate. 
     FIG. 10 is a cross-sectional view along line A—A of FIG. 5 illustrating the location of the filter carrier of the present invention in the print cartridge. 
     FIG. 11 is a side elevational view of the filter carrier of the present invention. 
     FIG. 11A is a cross-sectional view along line A—A of FIG.  11 . 
     FIG. 12 is a perspective view looking at the top of the filter carrier of the present invention. 
     FIG. 13 is a perspective view looking at the bottom of the filter carrier of the present invention. 
     FIG. 14 is a perspective view looking down on the carriage of the printer shown in FIG. 2 with one print cartridge installed. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     While the filter carrier assembly of the present invention will be described below in the context of an off-axis printer having an external ink source, it should be apparent that the present invention is equally useful in an inkjet printer which uses inkjet print cartridges having an ink reservoir integral with the print cartridge. FIG. 1 is a perspective view of one embodiment of an inkjet printer  10  suitable for utilizing the filter carrier assembly of the present invention, with its cover removed. Generally, printer  10  includes a tray  12 A for holding virgin paper. When a printing operation is initiated, a sheet of paper from tray  12 A is fed into printer  10  using a sheet feeder, then brought around in a U direction to now travel in the opposite direction toward tray  12 B. The sheet is stopped in a print zone  14 , and a scanning carriage  16 , supporting one or more print cartridges  18 , is then scanned across the sheet for printing a swath of ink thereon. After a single scan or multiple scans, the sheet is then incrementally shifted using a conventional stepper motor and feed rollers to a next position within the print zone  14 , and carriage  16  again scans across the sheet for printing a next swath of ink. When the printing on the sheet is complete, the sheet is forwarded to a position above tray  12 B, held in that position to ensure the ink is dry, and then released. 
     The carriage  16  scanning mechanism may be conventional and generally includes a slide rod  22 , along which carriage  16  slides, a flexible circuit (not shown in FIG. 1) for transmitting electrical signals from the printer&#39;s microprocesser to the carriage  16  and print cartridges  18  and a coded strip  24  which is optically detected by a photodetector in carriage  16  for precisely positioning carriage  16 . A stepper motor (not shown), connected to carriage  16  using a conventional drive belt and pulley arrangement, is used for transporting carriage  16  across print zone  14 . 
     The features of inkjet printer  10  include an ink delivery system for providing ink to the print cartridges  18  and ultimately to the ink ejection chambers in the printheads from an off-axis ink supply station  30  containing replaceable ink supply cartridges  31 ,  32 ,  33 , and  34 , which may be pressurized or at atmospheric pressure. For color printers, there will typically be a separate ink supply cartridge for black ink, yellow ink, magenta ink, and cyan ink. Four tubes  36  carry ink from the four replaceable ink supply cartridges  31 - 34  to the print cartridges  18 . 
     FIG. 3 is a perspective view of one embodiment of a print cartridge  18 . A shroud  76  (also shown in FIG. 10) surrounds needle  60  (obscured by shroud  76 ) to prevent inadvertent contact with needle  60  and also to help align septum  52  (FIG. 10) with needle  60  when installing print cartridge  18  in carriage  16 . A flexible tape  80  containing contact pads  86  leading to the printhead substrate is secured to print cartridge  18 . These contact pads  86  align with and electrically contact electrodes  49  (FIG. 3A) on carriage  16 . Preferably, the electrodes on carriage  16  are resiliently biased toward print cartridge  18  to ensure a reliable contact. Such carriage electrodes are found in U.S. Pat. No. 5,408,746, entitled Datum Formation for Improved Alignment of Multiple Nozzle Members in a Printer, by Jeffrey Thoman et al., assigned to the present assignee and incorporated herein by reference. 
     The printhead nozzle array is at location  58 . An integrated circuit chip  78  provides feedback to the printer regarding certain parameters of print cartridge  18 . 
     FIG. 4 illustrates the bottom side of print cartridge  18 . Two parallel rows of offset nozzles  82  are shown laser ablated through tape  80 . 
     FIG. 5 is a cross-sectional view of print cartridge  18 , without tape  80 , taken along line  5 A— 5 A in FIG.  3 . Shroud  76  is shown having an inner conical or tapered portion  75  to receive septum  52  and center septum  52  with respect to needle  60 . In an alternative embodiment, needle  60  is part of a separate subassembly, and shroud  76  is a separate subassembly, for manufacturing ease. 
     A regulator valve (not shown) within print cartridges  18  regulates pressure by opening and closing an inlet hole  65  to ink chamber  61  internal to print cartridges  18 . For a description of the design and operation of the regulator see U.S. patent application Ser. No. 08/706,121, filed Aug. 30, 1996, now U.S. Pat. No. 5,966,155 entitled “Inkjet Printing System with Off-Axis Ink Supply Having Ink Path Which Does Not Extend above Print Cartridge,” which is herein incorporated by reference. 
     When the regulator valve is opened, a hollow needle  60  is in fluid communication with an ink chamber  61  internal to the cartridge  18 . The needle  60  extends through a self-sealing hole formed in through the center of the septum  52 . The hole is automatically sealed by the resiliency of the rubber septum  52  when the needle is removed. A plastic conduit  62  leads from the needle  60  to chamber  61  via hole  65 . The conduit may be glued, heat-staked, ultrasonically welded or otherwise secured to the print cartridge body. The conduit may also be integral to the print cartridge body. Surfaces  190 ,  192  support the filter carrier  200  which will be described in detail below with respect to FIGS. 9-13. 
     A septum elbow  71  routes ink from the manifold  66  to the septum  52 , and supports the septum. The septum is affixed to the elbow using a crimp cap  73 . The coupler  67  in this exemplary embodiment is a flexible bellows for allowing a degree of x, y and z movement of the septum  52  when the needle  60  is inserted into the septum to minimize the load on the needle and ensure a fluid-tight and air-tight seal around the needle. The bellows may be formed of butyl rubber or other flexible material having low vapor and air transmission properties. Alternatively, the bellows can be replaced with a U-shaped or circular flexible tube. A spring  70  urges the septum  52  upwardly, allowing the septum to take up z tolerances, minimizes the load on the needle  60  and ensures a tight seal around the needle  60 . 
     The print cartridges and ink supply connections described above are down-connect types where the ink connection is made when pressing the print cartridge down into the carriage. This enables a resulting printer to have a very low profile since the ink path does not extend above the print cartridge. In the embodiments shown having the needle extending from the print cartridge, the needle may be replaced with a septum, and the septum on the scanning carriage replaced with a hollow needle. When in use in the printer  10 , the print cartridges  18  are in fluid communication with an off carriage ink supply  31 - 34  that is releasably mounted in an ink supply station  30 . Without this fluid communication, the new off-axis design print cartridges have very little internal ink capacity in their reservoirs and these print cartridges  18  can expel only approximately 1 cc of ink. 
     Referring to FIGS. 4 and 6, printhead assembly  83  is preferably a flexible polymer tape  80  having nozzles  82  formed therein by laser ablation. Conductors  84  are formed on the back of tape  80  and terminate in contact pads  86  for contacting electrodes on carriage  16 . The other ends of conductors  84  are bonded through windows  87  to terminals of a substrate  88  on which are formed the various ink ejection chambers and ink ejection elements. The ink ejection elements may be heater resistors or piezoelectric elements. 
     A demultiplexer on substrate  88  demultiplexes the incoming electrical signals applied to contact pads  86  and selectively energizes the various ink ejection elements to eject droplets of ink from nozzles  82  as printhead  58  scans across the print zone. In one embodiment, the dots per inch (dpi) resolution is 300 dpi, and there are 300 nozzles  82 . In another embodiment, at least the black ink cartridge prints at a resolution of 600 dpi. 
     The printhead assembly may be similar to that described in U.S. Pat. No. 5,278,584, by Brian Keefe, et al., entitled “Ink Delivery System for an Inkjet Printhead,” assigned to the present assignee and incorporated herein by reference. In such a printhead assembly, ink within print cartridge  18  flows around the edges of the rectangular substrate  88  and into ink channels  90  leading to each of the ink ejection chambers. 
     FIG. 7 is a cross-sectional view along line B—B of FIG.  3 . Elements identified with the same numerals as in other figures may be identical and will not be redundantly described. FIG. 7 illustrates the flow of ink  92  from the ink chamber  61  within print cartridge  18  to ink ejection chambers  94 . Energization of the ink ejection elements  96  and  98  cause a droplet of ink  101 ,  102  to be ejected through the associated nozzles  82 . A photoresist barrier layer  104 , the flexible tape  80  and substrate  88  define the ink channels  90  and chambers  94 . The conductor portion of the flexible tape  80  is glued with adhesive  108  to the plastic print cartridge body  110 . Filter carrier  200  and filter  202  will be described in detail below with respect to FIGS. 9-13. 
     The plastic print cartridge body  110  is formed such that the ink conduit  63  directs the flow of ink from an ink chamber within the print cartridge  10  towards the back of the substrate  88  and through a narrow gap that exists between the back of the substrate  88  and the walls  162  and  163 . The gap at the end of ink conduit  63  is much narrower than the gap between the ink conduit  54  and substrate  88  in prior print cartridges. The filter carrier  200  and the walls  162  and  163  direct the flow of ink  92  through the ink conduit  63 . The walls  162  and  163  of the ink conduit  63  terminate approximately 0.127 mm (5 mils) from the back of the substrate  88 , thereby forming the narrow gap. An acceptable range for this gap is from about 3 mils to about 12 mils, depending on the ink viscosity and flow rates. The distance, in the preferred embodiment, between walls  162  and  163  is approximately 1 mm. The distance between walls  162  and  163  may be anywhere between about 1 mm and 5 mm. Other distances may also be suitable depending upon the size of substrate  88 , ink viscosity, and flow rates. The thickness of walls  162  and  163  is about 0.5 mm, but thinner walls will also work. The lower limit is dependent more on manufacturing tolerances than on thermal performance of the device. Walls thicker than 0.5 mm will also work. Thicker walls will have better thermal performance, but also worse pressure drop and bubble tolerance. 
     Although the same volume of ink is ejected from nozzles  82  as previous print cartridges, the ink velocity across the back of substrate  88  is much higher due to the narrower gap that exits at the end of ink conduit  63  relative to the large area available for flow everywhere in ink conduit  63 . The increased ink velocity caused by the proximity of the ends of walls  162  and  163  to the back of substrate  88  cause a relatively large transfer of heat from the back of substrate  88  to the moving ink. The heated ink flows around the edges of substrate  88  and into the ink ejection chambers  94 . 
     As the ink heats up, the solubility of air in the ink decreases, and air defuses out of the ink in the form of bubbles  112 . In order for these bubbles  112  to not restrict the flow of ink, bubble accumulation chambers  168  and  170  are formed in the print cartridge body to accumulate these bubbles. Bubble accumulation chambers  168  and  170  are defined and formed both by the filter carrier  200  and the walls  162 ,  163 . Hence, bubbles  112  will not interfere with the flow of ink through ink conduit  63  and around the edges of substrate  88  to the ink ejection chambers  94 . In the preferred embodiment, these chambers  168  and  170  each have a capacity of 2 to 3 cubic centimeters; however, the capacity can be greater than or less than this preferred volume depending on the anticipated out gassing. An acceptable range is approximately 1 to 5 cubic centimeters. Chambers  168  and  170  extend along the length of substrate  88  to be in fluid communication with all the ink channels  90  formed in barrier layer  104  on substrate  88 . 
     FIG. 8 is perspective view of the print cartridge  18  with the tape  80  removed along with substrate  88  to reveal walls  162  and  163 , ink conduit  63 , and chambers  168  and  170 . In one embodiment, the preferred length of substrate  88  is approximately one-half inch so that the lengths of walls  162  and  163  are slightly less than one-half inch. 
     An adhesive/sealant is applied to headland areas  174  and  176 , and the assembly of FIG. 7 is then secured to the print cartridge  18  as shown in FIG.  3 . The adhesive/sealant at areas  174  and  176  squishes upward to secure the ends of the substrate  881  to the print cartridge body and insulate the conductive traces on the back of tape  80  so that they will not be shorted by any ink in the vicinity of the conductors. An adhesive/sealant along the top of headland walls  178  and  179  secures the tape  80  to the print cartridge body. 
     FIG. 9 is a cross-sectional, perspective view of the print cartridge of FIG. 3 with tape  80  removed along line B—B of FIG. 3 illustrating an ink chamber  61  for containing ink and a pressure regulator, the filter carrier  200  (with filter screen  202  removed) described in detail below, walls  162  and  163 , the ink conduit  63  (defined by the filter carrier  200  and walls  162 ,  163 ) leading to the back surface of the substrate  88  and bubble accumulation chambers  168  and  170  defined and formed both by the filter carrier  200  and the walls  162 ,  163 . 
     Inkjet printheads are very sensitive to particulate contamination. To deal with this problem, a filter is required between the reservoir of ink  61  and the printhead  58 . The filter prevents particulate contaminates from flowing from the ink reservoir  61  to the printhead  58  and clogging the printhead nozzles  82 . Also, the filter prevents air bubbles from traveling from the printhead  58  into the reservoir  61 . The filter separates the ink conduit  63  of the housing into two regions: (1) one upstream and in fluid communication with the reservoir  61  and (2) one downstream of the filter and in fluid communication with the printhead. 
     The external body  110  tends to be selected and molded from a relatively rigid engineering plastic for structural rigidity and high heat deflection. Fillers (such as glass fibers) are typically included to enhance these properties. Such materials tend to be difficult surfaces to which to attach a filter and effect a complete seal around the perimeter of the filter. If the seal is not complete, bubbles or particulates may slip past the filter and block the ink channels or nozzles. The separation of the filter staking from the cartridge housing provides more freedom of material selection for both the cartridge housing material and a good heat staking material for the filter carrier. Moreover, the filter staking process is greatly simplified when it can be performed external to the cartridge housing. These difficulties are further compounded by the new design described above which provides a jet impinging flow of ink to cool the printhead. This design makes the molding of the rigid housing with walls  162 ,  163  very difficult. 
     The present invention provides a way to reduce the dependency of the filter attach properties upon the selection of exterior housing properties without adding a costly insertion molding process. Further, there is a need to provide a housing and filter design that makes the jet impinging flow design easier to mold. There is also a need for a way to provide a variable volume for the storage of out gassed air for the same print cartridge housing. 
     FIG. 10 is a cross-sectional view along line A—A of FIG. 5 illustrating the location of the filter carrier  200  of the present invention in the print cartridge  18 . Filter carrier  200  is supported in cartridge  18  by support surfaces  190 ,  192 . Filter carrier  200  is also supported walls  162 ,  163  which were described above. The position of the filter screen  202  is also shown. 
     Referring to FIGS. 11 through 13, filter screen  202  is attached to the top surface  204  of filter carrier  200  through heat staking (heat and pressure welding), adhesives or other bonding processes, to form a leak-proof seal between the filter screen  202  and filter carrier  200 . The filter carrier  200  is made of a plastic such polypropylene or high density polyethylene, or other suitable material. 
     Filter screen  202  is attached to the top surface  204  of filter carrier  200  through preferably heat staking (heat and pressure welding), or alternatively, adhesives or other bonding processes, to form a leak-proof seal between the filter screen  202  and filter carrier  200 . The filter screen  202  is formed of a material which is permeable to the ink to be stored within the ink reservoir, and compatible with the plastic of material from which the filter carrier  200  is fabricated. A preferred material for the filter screen  202  is a section of finely woven stainless steel mesh, the periphery edges of which are attached to the top surface  204  of filter carrier  200  by heat staking. The mesh has a nominal passage dimension of 15 microns between adjacent mesh strands, and has a typical thickness of less than 0.005 inches. 
     The filter carrier  200  is inserted into the cartridge body  110  such that the bottom surfaces  208 ,  210  of filter carrier  200  rest on cartridge body surfaces  190 ,  192 , respectively, and bottom surface  212  of the snout portion  214  of filter carrier  200  rests on the top surface cartridge body walls  162 ,  163 . The seal between the bottom surface  212  of the snout portion  214  of filter carrier  200  and the walls  162 ,  163  is a face seal. The inside of the filter carrier  200  has square corners for ink to wick up in the event that air fills the filter standpipe. The manufacture of the square corners is facilitated by slits  216 . Tabs  218  hold filter screen  202  in place during the heat staking process to filter carrier  200 . The sloping surface  220  of filter carrier  200  helps prevent trapping of air during the cartridge filling process. Grooves  222  are provided to prevent distortion during the molding process for filter carrier  200 . 
     The filter carrier  200  has a carrier seal  206  on all sides to engage a housing seal surface disposed on the inside walls of the housing  110  to define a seal zone that separates chamber  61  from the region in fluid communication with printhead and make a leak proof seal around the filter carrier  200  and the cartridge body  110 . The carrier seal  206  is adapted to deform upon installation of the filter carrier  200  in the housing  110  and provide a reliable seal. 
     Another problem that occurs during the life of the print element is air out gassing. Air builds up between the filter and the printhead during operation of the printhead. For printers that have a high use model, it would be preferable to have a larger volume between the filter and the printhead for the storage of air. For low use rate printers, this volume would be reduced. The present invention also addresses this problem. The filter carrier  200  height can be adjusted to readily provide varying volumes for chambers  168 ,  170  depending on the anticipated out-gassing. 
     The mesh passage size is sufficiently small that while ink may pass through the passages of the mesh, air bubbles under normal atmospheric pressure will not pass through the mesh passages which are wetted by the ink. The required air bubble pressure necessary to permit bubbles to pass through the mesh, in this embodiment, about 30 inches of water, is well above that experienced by the pen under any typical storage, handling or operational conditions. As a result, the mesh also serves the function of an air check valve for the print cartridge. 
     FIG. 13 is a perspective view of carriage  16  looking down on carriage  16 . Ink is provided to carriage  16  by tubes  36  which connect to a plastic manifold  66 . Tubes  36  may be formed of Polyvinylidene Chloride (PVDC), such as Saran™, or other suitable plastic. Manifold  66  provides several 90° redirections of ink flow. Such a manifold  66  may not be needed if tubes  36  are sufficiently slender and can be bent without buckling. 
     A septum elbow  71  routes ink from manifold  66  to septum  52  and supports septum  52 . A bellows  67  (shown in cross-section) is provided for each of the individual stalls  68  for allowing a degree of x, y, and z movement of septum  52  when needle  60  is inserted into septum  52  to minimize the x, y, and z load on needle  60  and ensure a fluid-tight and air-tight seal around needle  60 . Bellows  67  may be formed of butyl rubber, high acn nitrile, or other flexible material with low vapor and air transmission properties. Bellow  67  can be any length and can even be a flexible diaphragm. 
     A spring  70  urges septum  52  upward. This allows septum  52  to take up z tolerances, minimizes the load on needle  60 , and ensures a tight seal around needle  60 . Slots  72  formed on each of the stalls  68  in carriage  16  align with tabs on each print cartridge  18  to restrict movement of the print cartridge  18  within the stall  68 . An air vent  74  formed in the top of print cartridge  18  is used by a pressure regulator in print cartridge  18 , to be described later. In an alternative embodiment, a separate regulator may be connected between the off-axis ink supply and each print cartridge  18 . In other embodiments bellows  67  may replaced with a U-shaped, circular, or straight flexible tube. 
     An opening in the bottom of the carriage  16  exposes the printhead location  58  of each print cartridge  18 . Carriage electrodes (not shown) oppose contact pads  86  (shown in FIG. 3) located on print cartridges  18 . Carriage electrodes are connected via an electrical flex circuit (not shown) to the printer&#39;s microprocessor which sends signals to control ink ejection. In an alternative embodiment the electrical flex circuit is connected directly to the print cartridges  18  by either electrical connectors or by being permanent soldering thereby eliminating the need and complexity of providing make/break connections on the carriage  16 . 
     The print cartridges  18  can be secured within the scanning carriage  16 , by a latch, which may be manually operated or spring loaded, where the latch presses down on a tab or a corner of the print cartridge  18 . In another embodiment, a single latch, such as a hinged bar, secures the print cartridge  18  in place within the carriage  16 . 
     Other embodiments of scanning carriages and print cartridges are described in U.S. patent application Ser. No. 08/706,121, filed Aug. 30, 1996, now U.S. Pat. No. 5,966,155 entitled “Inkjet Printing System with Off-Axis ink Supply Having ink Path Which Does Not Extend above Print Cartridge,” Attorney Docket No. 10960734, which is herein incorporated by reference. 
     The ink within each of the off-axis ink supply cartridges  31 - 34  may be at atmospheric pressure, whereby ink is drawn into each of print cartridges  18  by a negative pressure within each print cartridge determined by a regulator internal to each print cartridge as discussed above. Alternatively, the off-axis ink supply cartridges may be pressurized. In either the unpressurized or pressurized ink supply embodiments, a pressure regulator is used within the print cartridge for regulating the pressure of the ink chamber within the print cartridge. One embodiment of a pressure regulator is described in U.S. patent application Ser. No. 08/706,121, filed Aug. 30, 1996, now U.S. Pat. No. 5,966,155 entitled “Inkjet Printing System with Off-Axis ink Supply Having ink Path Which Does Not Extend above Print Cartridge,” which is herein incorporated by reference. 
     As a result of these design options, the filter carrier assembly offers a wide range of product implementations other than those illustrated in FIGS. 1 and 2. For example, such printhead assembly systems may be incorporated into an inkjet printer used in a facsimile machine, a copying machine, which may also be a combined facsimile/copying machine and large-format printers which print on a wide, continuous paper roll. 
     While particular embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made within departing from this invention in its broader aspects and, therefore, the appended claims are to encompass within their scope all such changes and modifications as fall within the true spirit and scope of this invention.