Patent Publication Number: US-6663234-B2

Title: Ink cartridge providing improved ink supply

Description:
This application is based on a provisional application No. 60/297,365, filed Jun. 11, 2001. 
    
    
     BACKGROUND 
     The present invention relates to ink cartridges used for supplying liquid ink to a printhead in a thermal ink jet printing apparatus. Specifically, the present invention relates to structure and method for improving the flow of ink and air through an ink cartridge to provide improved ink delivery to the ink jet printing apparatus. 
     The principles of thermal ink jet printing are well understood in the art. U.S. Pat. No. 5,997,121 describes several aspects of such printing. In existing thermal ink jet printing, the printhead comprises one or more ink filled channels communicating with a relatively small supply chamber, or manifold, at one end, and having an opening at the opposite end, referred to as a nozzle. Current practical embodiments of drop on demand thermal ink jet printers work most effectively when the pressure of the ink in the printhead nozzle remains within a predetermined range of gauge pressures. Specifically, at those times during operation in which an individual nozzle or an entire printhead is not actively emitting a droplet of ink, a certain negative pressure, or “back pressure”, in each of the nozzles, and by extension, within the ink supply manifold of the printhead keeps the ink from dribbling out the nozzles. The attributes of creating and maintaining such back pressure are described in U.S. Pat. No. 5,289,212, the contents of which are hereby incorporated herein by reference. 
     The liquid ink is supplied to the printhead from an ink cartridge. The ink cartridge contains a supply of ink, and is typically configured to maintain the appropriate negative pressure in the printhead ink channels. The ink cartridge is typically a user replaceable unit that mates with the printhead of the printing apparatus. In certain embodiments, the printhead and the ink cartridge are formed as a single integrated unit. In other embodiments, the ink cartridge or container is manufactured and sold separately from the printhead. The printhead may be permanently installed in the printer, or may be separately replaceable. 
     SUMMARY 
     A fluid cartridge for dispensing fluid, such as liquid ink in a drop on demand ink jet printer, includes a housing that encloses a foam chamber, and has an outlet port through one wall of the housing into the foam chamber. Foam material is contained within the foam chamber. The foam material has a higher density adjacent the outlet port than away from the port. 
     An ink cartridge for dispensing liquid ink to a drop on demand ink jet printer comprises a housing having a top wall, a plurality of sidewalls, and a cover wall, all enclosing an interior space. The top wall and the cover wall oppose one another across the interior space. A divider separates the interior space into a foam chamber and a free ink chamber. A fluid conduit connects the free ink chamber and the foam chamber. Ink-retaining foam material is contained in the foam chamber. An outlet port through the cover wall extends into the foam chamber. First and second structural projections extend from the top wall of the housing into the foam chamber. The first and second structural projections abut the foam material in the foam chamber. The first structural projection is approximately opposite the outlet port through the cover wall, and extends farther into the foam chamber than does the second structural projection. 
     A method of assembling an ink cartridge for a drop on demand ink jet printer includes supplying a housing having a plurality of walls defining an interior space, and having one side of the housing open to provide access to the interior space. The method further includes compressing ink retaining foam, and inserting the compressed ink retaining foam through the open side of the housing into the interior space of the housing, so that a first portion of the foam in the interior space of the housing is more compressed than a second portion of the foam in the interior space of the housing. A cover wall is applied over the open side of the housing to enclose the foam in the interior space of the housing. In a particular implementation, the cover wall has a port through it, and the step of applying the cover wall over the open side of the housing comprises applying the cover wall so that the port is approximately adjacent the first portion of the foam in the interior space of the housing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a perspective view of an exemplary ink cartridge incorporating a particular embodiment of the present invention, showing the internal structure thereof in phantom. 
     FIG. 2 is a side cross-sectional view of the ink cartridge of FIG.  1 . 
     FIG. 3 is a side cross-sectional view of a portion of the ink cartridge shown in FIG. 2, showing different levels of compression of the capillary material in the ink cartridge. 
     FIG. 4 is a side cross-sectional view of the ink cartridge of FIGS. 1 and 2 before insertion of the capillary material. 
     FIG. 5 is an end view of the capillary material and a compression fixture, taken along line  5 — 5  of FIG.  4 . 
     FIG. 6 is a cross-sectional view of the ink jet cartridge shown in FIG. 4 showing the cartridge partially assembled. 
     FIG. 7 is a cross-sectional view of an alternative embodiment of an ink cartridge incorporating an aspect of the present invention. 
    
    
     DETAILED DESCRIPTION 
     Referring to FIGS. 1 and 2, a fluid cartridge  10  includes a housing  12  formed of a plurality of walls  14 ,  15 ,  16 , and a cover wall  18 . In the particular embodiment illustrated, the walls of the housing include a top wall  14 ,  15 , and side walls  16  enclosing an interior space. The cover wall  18  encloses the interior space by closing off the open side of the housing body. The cover wall  18  substantially opposes the top wall  14  across the interior space. 
     The top wall  14  and the side walls  16  of the housing may be a single integral unit of molded plastic. The cover wall  18  may be attached to the housing body by glue, ultrasonic welding, or other appropriate attachment techniques. FIG. 1 shows the internal structure of the cartridge in phantom lines. FIG. 2 is a side cross-sectional view of the ink cartridge of FIG.  1 . 
     The interior of the housing contains a capillary chamber  22  and a free fluid or ink chamber  24 . A divider  20  extends from the top wall  14  toward the cover wall  18 , and also extends between two opposing side walls  16 , to divide the housing interior into the capillary chamber  22  and the ink chamber  24 . A fluid conduit  30  provides fluid communication between the ink chamber  24  and the capillary chamber  22 . In the embodiment particularly described and shown, the fluid conduit  30  is adjacent the cover wall  18  of the housing, and is formed as a gap in the divider  20  adjacent the cover wall. 
     An outlet port  40  is formed through one of the walls forming the housing of the capillary chamber. When the ink cartridge is mated with an ink jet printhead, the outlet port  40  provides fluid communication from the ink cartridge capillary chamber  22  to a manifold of the printhead that in turn leads to the channels that form the printhead nozzles. In the particular embodiment illustrated, the outlet port  40  is formed through the cover wall  18 . The outlet port  40  is positioned toward the side of the capillary chamber away from the fluid conduit  30  that extends between the free ink chamber  24  and the capillary chamber  22 . In certain embodiments, the outlet port may alternatively be formed through one of the side walls  16  of the capillary chamber, generally near the bottom portion of the capillary chamber. The top wall  15  of the ink chamber  24  may be lower than the top wall  14  of the capillary chamber, so that the ink chamber has a smaller volume than the capillary chamber. However, the top wall  15  of the ink chamber may be at the same height as, or in some implementations, higher than the top wall  14  of the capillary chamber  22 . 
     A seal  50  covers the outlet port  40 . For example, metallic tape, foil, or other material that ink cannot penetrate is placed on the outer surface of the cover wall  18  to cover the outlet port  40 , and is sealed to the outer surface of the cover wall. The seal  50  is removable, so that the user can remove it before inserting the cartridge into the printhead. However, in certain printing devices, the seal may remain in place, and be punctured or otherwise penetrated by the printhead element when the cartridge is installed for use in the printing device. 
     An ink-retaining member, such as ink-retaining capillary material  62 , is contained in the interior of the capillary chamber  22 . The capillary material  62  may be a polyether foam material, which material is well understood by those familiar with the art. A particular implementation is described using foam for the capillary material. However, other materials that provide a capillary force can be used without departing from the concepts described. When saturated with liquid (such as ink), the foam material  62  facilitates maintaining a negative pressure in the ink supply manifold and ink jet nozzles of the printhead for proper operation of the printhead. Therefore, the specific material may be different for different print apparatus configurations. The negative pressure is supplied through the action of the pores within the foam that act as tiny capillary tubes. The capillary force supplied by a particular tube within the foam is proportional to the diameter of the tube. Pores per inch is used as a measure of the capillary size of the foam. Thus, as the number of pores per inch increases within the foam, so does the capillary force supplied by the foam. 
     During printing operations, the printhead draws ink from the ink cartridge through the outlet port  40 . As ink is drawn from the foam  62  through the outlet port  40 , the capillary force of the foam draws ink from the free ink chamber  24  through the fluid conduit  30  to replenish the ink supply in the foam  62 . As ink flows from the free ink chamber  24  into the foam  62  through the fluid conduit  30 , air bubbles migrate through the capillary material (foam)  62  to the fluid conduit  30  and into the free ink chamber  24 . Thus, the fluid conduit  30  may be referred to as the “bubbler.” Air enters the interior of the housing through the vent opening  60  in the top wall of the capillary chamber portion of the housing. The air travels through the foam  62  from the vent opening  60  to the fluid conduit  30 . Vertical grooves  66  extend upward along the capillary chamber side of the divider  20  from the fluid conduit opening  30  to assist in the exchange of air and ink through the conduit  30 . In addition, incomplete saturation of the foam  62  may cause the foam  62  to contain localized pockets of air that are surrounded by ink. 
     The cartridge is structured so that the capillary material (foam)  62  has increased density adjacent the outlet port  40  than it does above the fluid conduit opening  30  through the divider  20 . For example, the interior of the capillary chamber  22  is structured asymmetrically, so that the space in the capillary chamber for the capillary material above the port  40  is less than the space in the capillary chamber adjacent the divider. 
     As seen in FIG. 2, projections  64 ,  65  extend into the interior of the capillary chamber portion  22  of the housing. The projections  64 ,  65  abut the foam  62  to hold the foam in place in the capillary chamber. The first projection  64  projects farther into the interior of the capillary chamber  22  to provide greater compression to the portion of the foam between the first projection  64  and the cover wall  18 , while the second projection  65  provides a lesser amount of compression of the portion of the foam  62  between the second projection  65  and the cover wall  18 . The greater density of the foam between the first projection  64  and the cover wall  18  provides a higher number of pores per inch in that portion of the foam. Referring to FIG. 3, the approximate regions of higher and lower density of the foam are illustrated. These areas of higher and lower density are not exact, as the compression of the foam yields a probabilistic distribution of foam density in general accord with the diagram shown in FIG.  3 . 
     The first projection  64 , which may be called the port rib, is substantially aligned with the port opening  40 , so that the foam between the is port rib and the outlet port is more compressed than the foam away from the outlet port. In particular, the foam above the outlet port  40  is more compressed than the foam near the divider  20 . The second projection  65 , which may be called the bubbler rib because it is nearer the bubbler conduit  30 , projects less far into the interior of the capillary chamber  22  than does the port rib  64 . The bubbler rib  65  abuts the upper surface of the foam material  62  to help retain the foam material in place within the capillary chamber, and resist the tendency of the foam material to shift and change its density distribution. 
     In one particular embodiment, the projections  64 ,  65  are H shaped in cross-section. However, after reading the present description, those skilled in the art will recognize that numerous other shapes may be used. Among the other possible shapes are referring to their cross-sectional shape Z, I, curved, and other shapes. 
     The difference in the extent to which the projections  64 ,  65  extend into the interior of the capillary chamber depends on the size of the capillary chamber, and the desired extent of capillary force differentials. In one particular embodiment, the port rib  64  is approximately 2.0 mm longer than the bubbler rib  65 . The interior of the top wall  14  of the capillary chamber may alternatively be shaped in other ways to provide the asymmetrical space for the capillary foam material  62 . 
     Referring to the foam density distribution illustrated in FIG. 3, the increased foam density adjacent the outlet port  40  provides increased foam pores per inch, which in turn yields an increased capillary force near the outlet port  40 . In addition to the increased capillary force around the port  40  drawing ink toward the port the relative decreased density adjacent the divider  20  above the bubbler conduit  30  tends to encourage air to follow a path from the vent opening  60  to the fluid bubbler conduit  30 , away from the port  40 . Increasing the flow of ink toward the outlet opening  40  and reducing the migration of air toward the outlet opening reduces the possibility of “depriming” the manifold and ink channels in the printhead. Depriming occurs when the printhead prematurely ingests air from the outlet port  40  of the ink cartridge into the ink manifold and ink ejection channels. 
     A region of the foam adjacent and along the cover wall  18  also has a higher density than does the foam away from the cover wall. Increased density foam (with more pores per inch) along the cover wall between the bubbler conduit  30  and the outlet port  40 , with its higher capillary force, helps draw ink from the free ink chamber  24  toward the outlet port  40 . Such additional draw helps the printer more completely use the ink in the cartridge. This more complete usage of the ink leaves less residual ink in the cartridge when the printer is no longer able to draw ink from the cartridge. 
     FIG. 4 shows the foam compressed and prepared for insertion into the capillary chamber  22  of the ink cartridge. The foam, in an uncompressed state, is considerably larger than the interior of the capillary chamber  22 . The foam  62  is initially a rectangular block of the foam material. To insert the foam material into the capillary chamber  22 , the foam is compressed by a compression fixture  70  to a size smaller than the interior of the capillary chamber  22 . Referring now to FIG. 5, the compression fixture includes a corner element  72  and two side fingers  74 ,  76 . For the compression fixture to compress the foam for insertion into the capillary chamber, the foam material is placed near or against the corner element  72 , as seen in the view of FIG. 5, which is from above the foam. The side of the foam that is to be adjacent the divider  20  of the cartridge housing (see FIG. 2) is placed against one leg  72   a  of the corner element. The first finger  74  presses against the side of the foam to compress the foam material laterally between the first finger  74  and the leg  72   b  of the corner element. After the first finger  74  has laterally compressed the foam material, a second finger  76  presses against the foam, compressing the foam longitudinally against the first leg of the corner element  72 . Friction between the surface of the foam and the elements  72 ,  74  of the compression fixture cause the foam to be more compressed nearer the second finger  76  than near the first leg  72   a  of the corner element. Different mechanisms can be used to move the fingers  74 ,  76  to compress the foam, such as a screw drive, hydraulic drive, or pneumatic drive. For example, an air cylinder may drive the shaft of each finger. 
     The compression fixture inserts the compressed foam at least partway into the capillary chamber of the housing. For example, the compression fixture may insert the compressed foam (and the corner element  72  and the fingers  74 ,  76  of the compression fixture) about half-way into the capillary chamber. The air cylinders holding the fingers  74 ,  76  against the foam are released. The foam slightly expands, although the fingers do not completely release the foam, as the fingers are constrained within the interior of the capillary chamber. A plunger  78  then presses the foam the remainder of the way into the capillary chamber. The compression fixture withdraws the fingers  74 ,  76  from the interior of the capillary chamber while the plunger  78  holds the foam material in place in the capillary chamber. 
     The compression fixture then removes the plunger  78 , and the cover wall  18  is placed over the open side of the capillary chamber  22  (and the free ink chamber  24 ). In a particular implementation, to obtain increased foam density adjacent the cover wall, when the foam  62  is inserted into the capillary chamber  22 , a small portion (1.5-3.0 mm) of the foam material remains extending beyond the open end of the capillary chamber  22 . Then, when the cover wall  18  is applied over the open side of the housing, to enclose the interior space of the housing, the cover wall  18  completes the compression of the foam material adjacent the open side of the housing. Thus, after the cover wall is sealed to the housing body, the foam material adjacent the cover wall  18  has a higher density than does foam material away from the cover wall  18  and aligned with the bubbler rib  65 . As the cover is brought into place, it also further compresses the foam material between the cover wall  18  and the port rib  64 , so that the foam material in that region has a higher density than does the foam material between the cover wall  18  and the bubbler rib  65 . 
     Referring now to FIG. 7, an implementation is illustrated in which the top of the capillary chamber is symmetrical, in that the port rib  64  and the bubbler rib  65  are of equal length. The capillary material or foam  62 ′ is formed asymmetrically, with a greater amount of capillary material aligned with the port rib  64  than is aligned with the bubbler rib  65 . When the capillary material  62 ′ is compressed into the capillary chamber  22 , and the cover wall  18  is placed over the open end of the capillary chamber, the capillary material  62 ′ between the port rib  64  and the cover wall  18  is more compressed than is the capillary material between the bubbler rib  65  and the cover wall. 
     Those skilled in the art will recognize that various modifications can be made to the particular implementations described above and shown in the accompanying figures. For example, numerous modifications can be made to the shape of the ribs, as well as the interior shapes of the capillary chamber and the free ink chamber. In addition, other mechanisms can be employed in the housing to provide variable compression to the foam material in the capillary chamber, such as providing projections along the sides of the chamber, or differently shaped ribs, or other shapes to the capillary or foam material. Other types of materials may be used to provide the appropriate capillary forces to draw fluid. Furthermore, the outlet port and vent openings can be provided in different locations than the specific embodiment illustrated. In addition, although particular implementations have been described in connection with thermal ink jet printers, the principles can also be applied to implementations in connection with other types of ink printers, and in particular, with other types of liquid ink printers. Therefore, the present invention is not to be limited to the specific implementation described above.