Abstract:
In one embodiment, a foam ink supply includes: a chamber defined by a ceiling, a floor, and a wall between the ceiling and the floor; an outlet from the chamber; and a block of foam only partially filling the chamber, the block of foam positioned adjacent to the outlet and spaced apart from at least part of the wall.

Description:
BACKGROUND 
   Ink cartridges used in inkjet printers include a printhead and one or more chambers that hold the ink. The printhead is a micro-electromechanical part that contains an array of miniature thermal resistors or piezoelectric transducers that are energized to eject small droplets of ink out of an associated array of orifices. The cartridge is mounted in a carriage in the printer and electrically connected to the printer controller. Under the direction of the controller, the cartridge is scanned back and forth across the print medium (usually paper) as resistors or transducers are energized to eject droplets of ink through the orifices on to the medium in the desired pattern. 
   In many conventional ink cartridges, each ink chamber is filled with a block of foam to hold the ink and to generate backpressure that helps regulate the flow of ink to the printhead. The ink-holding capacity of full blocks of foam that fill the ink chamber, however, is not always fully utilized. Full blocks of foam can also generate too much backpressure, stranding ink in the cartridge. The cost of the foam is a significant part of the overall cost of the ink cartridge. 

   
     DRAWINGS 
       FIG. 1  is a perspective view illustrating an ink cartridge according to an embodiment of the invention. 
       FIGS. 2 and 3  are front and side elevation section views illustrating internal features of the ink cartridge of  FIG. 1 . 
       FIGS. 4-6  are front and side elevation and plan section views, respectively, of the ink cartridge of  FIG. 1  with the ink holding foam omitted to more clearly illustrate some of the internal features of the ink cartridge. 
       FIG. 7  is an elevation section view of the cartridge of  FIG. 1  showing the printhead area of the cartridge. 
       FIG. 8  is a bottom plan view of the cartridge of  FIG. 1  showing the ink ejection orifices. 
       FIG. 9  is a detail section view of a portion of the printhead in the cartridge of  FIG. 1 . 
       FIG. 10  is an elevation section view of the cartridge of  FIG. 1  showing one example of a conventional feature that may be used to help retain a new smaller foam block. 
       FIG. 11  is a perspective view illustrating an ink cartridge according to another embodiment of the invention. 
       FIGS. 12 and 13  are elevation section views illustrating an ink cartridge according to another embodiment of the invention. 
       FIG. 14  is an elevation section view illustrating an ink cartridge according to another embodiment of the invention. 
   

   DESCRIPTION 
   Embodiments of the present invention were developed in an effort to effectively utilize a reduced size foam block in a conventional ink cartridge—reducing the size of the block of foam for holding ink in the ink chamber without changing the size or other characteristics of the molded plastic cartridge housing. Reducing the size of the block of foam helps in lowering the cost of the cartridge and, in some cases, reducing backpressure and allowing better utilization of the ink-holding capacity of the foam. An ink cartridge is also commonly referred to as an ink pen, a print cartridge or an inkjet print head assembly. The exemplary embodiments shown in the figures and described below illustrate but do not limit the invention. Other forms, details, and embodiments may be made and implemented. Hence, the following description should not be construed to limit the scope of the invention, which is defined in the claims that follow the description. 
     FIGS. 1-9  illustrate an ink cartridge  10  for a thermal inkjet printer. Embodiments of the invention might also be implemented in an ink cartridge for a piezoelectric inkjet printer or any other inkjet printer in which it might be desirable to use foam or another suitable ink holding material in the ink supply.  FIG. 1  is a perspective view of cartridge  10 .  FIGS. 2-6  are section views of ink cartridge  10 . The ink holding foam is omitted from the section views of  FIGS. 4-6  to more clearly illustrate some of the internal features of ink cartridge  10 .  FIG. 7  is an elevation section view showing the printhead area of cartridge  10 .  FIG. 8  is a bottom plan view of cartridge  10  showing the ink ejection orifices.  FIG. 9  is a detail section view of a portion of the printhead in cartridge  10 . 
   Referring first to FIGS.  1  and  7 - 9 , cartridge  10  includes a printhead  12  located at the bottom of cartridge  10  below ink chamber  14 . Printhead  12  includes an orifice plate  16  with two arrays  18 ,  20  of ink ejection orifices  22 . In the embodiment shown, each array  18 ,  20  is a single row of orifices  22 . As shown in the detail view of  FIG. 9 , firing resistors  24  formed on an integrated circuit chip  26  are positioned behind ink ejection orifices  22 . A flexible circuit  28  carries electrical traces from external contact pads  30  to firing resistors  24 . 
   When ink cartridge  10  is installed in a printer, cartridge  10  is electrically connected to the printer controller through contact pads  30 . In operation, the printer controller selectively energizes firing resistors  24  through the signal traces in flexible circuit  28 . When a firing resistor  24  is energized, ink in a vaporization chamber  32  ( FIG. 9 ) next to a resistor  24  is vaporized, ejecting a droplet of ink through an orifice  22  on to the print media. The low pressure created by ejection of the ink droplet and cooling of chamber  32  then draws ink from an ink supply to refill vaporization chamber  32  in preparation for the next ejection. The flow of ink through printhead  12  is illustrated by arrows  34  in  FIG. 9 . 
   Referring now also to  FIGS. 2-6 , ink is held in a foam block  36  in ink chamber  14  formed within a cartridge housing  38 . Housing  38 , which is typically molded plastic, may be molded as a single unit, molded as two parts (e.g., a lid  40  and a body  42 ) or constructed of any number of separate parts fastened to one another in the desired configuration. An outlet  44  to printhead  12  is located near the bottom of ink chamber  14 . A filter  46  covering outlet  44  may be used to keep contaminants, air bubbles and ink flow surges from entering printhead  12 . Ink is held in foam  36  or another suitable porous material to retain the ink at an appropriate backpressure through capillary action. Foam  36  is usually compressed around filter  46  and outlet  44  to increase its capillarity in the region of outlet  44 . As ink is depleted from foam  36 , the increased capillarity near outlet  44  tends to draw ink from all other portions of foam  36  to maximize the amount of ink drawn from chamber  14 . 
   In the embodiment shown in the figures, foam  36  does not fill chamber  14 . This “partial-fill” foam configuration may be desirable, for example, to reduce the size of a conventional foam block without also changing the size or other characteristics of the molded plastic cartridge housing, such as housing  38 . Although a single color cartridge  10  with only one ink chamber  14  is shown and described, embodiments of the invention are also applicable to tri-color and other multi-chambered cartridges in which a “partial-fill” foam configuration may be used in one or more of the multiple ink chambers. Referring now to  FIGS. 4-6 , housing body  42  includes a front wall  48 , side walls  50 ,  52 , back wall  54  and a floor  56 . Printhead  12  is positioned below outlet  44  in a depression  58  in a front part  60  of floor  56 . Depression  58  is formed by a step  62  in floor  56 . Filter  46  is affixed to the top of outlet  44  and contained by guides  64  that project up from floor front part  62  at depression  58 . In the embodiment shown, outlet  44  projects a short distance into ink chamber  14  so that filter  46  is elevated above a rear part  66  of floor  56 . An elevated filter  46  allows the compression of foam  36  around filter  46  to increase the capillarity of foam  36  in the region of outlet  44 . 
   Ribs  68  and posts  69  are formed across floor  56  at step  62 . Ribs  68  help wick ink from the area between posts  69  and from floor  56 . Posts  69  are ejector pins used in the fabrication of conventional inkjet cartridge housings to remove the housing body from the mold. Foam block  36  is sized and shaped to fit tightly within a space bounded by ejector pin posts  68 , front wall  48 , sidewalls  50 ,  52 , lid/ceiling  40  and filter  46 .  FIG. 10  is a detailed view showing foam  36  compressed behind ejector pin posts  68  to create added friction that helps retain foam  36  behind posts  68 . The added friction created by a rough surface texture  70  on the bottom on ceiling  40  also helps retain foam  36 . Wicking ribs  68  and ejector pin posts  69  illustrate one example of an existing feature that may be used to help retain a new smaller foam block  36  in an otherwise conventional inkjet cartridge  10 . In the embodiment shown in  FIGS. 2-3  and  10 , foam block  36  is held in place by a combination of factors and structural features—foam  36  is tucked behind posts  69 , covers ribs  68 , and presses against front wall  48 , sidewalls  50 ,  52 , ceiling  40 , ribs  68  and posts  69 . 
   Other configurations are possible. For example, in the embodiment shown in  FIG. 11 , ejector pin posts are omitted or ignored and rough surface texture  70  on ceiling  40  or on the inside of walls  48 ,  50  and  52  (not shown), or both, retains foam  36  compressed between lid  40  and filter  46 . In the embodiment shown in  FIGS. 12 and 13 , a shorter foam block  72  is retained on just two sides, compressed between spikes  74  protruding from sidewalls  50  and  52 . In the embodiment shown in  FIG. 14 , step  62  in floor  56  is extended to help retain foam  36 . A combination of pressure/compression and surface features (steps, bumps, posts, spikes and textures, for example) are used in the various embodiments to retain the foam. The less the walls are involved in holding the foam in place, the more the floor and lid/ceiling will be involved in holding the foam in place, and vice versa. 
   As noted at the beginning of this Description, the exemplary embodiments shown in the figures and described above illustrate but do not limit the invention. Other forms, details, and embodiments may be made and implemented. Therefore, the foregoing description should not be construed to limit the scope of the invention, which is defined in the following claims.