Patent Publication Number: US-2002005882-A1

Title: Ink cartridge with spillover dam

Description:
BACKGROUND OF THE INVENTION  
       [0001] The present invention relates to cartridges used in supplying liquid ink to a printhead in a thermal ink jet printing apparatus.  
       [0002] Thermal ink jet printing is well understood in the art. U.S. Pat. No. 5,997,121 describes several aspects of such printing.  
       [0003] 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. In current practical embodiments of drop on demand thermal ink jet printers, it has been found that the printers work most effectively when the pressure of the ink in the printhead nozzle is kept 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, it is important that a certain negative pressure, or “back pressure”, exist in each of the nozzles and, by extension, within the ink supply manifold of the printhead. The attributes of creating and maintaining such back pressure are described in the U.S. Pat. No. 5,289,212, the contents of which are incorporated herein by reference.  
       [0004] The 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 required negative pressure. The ink cartridge is typically a user-replaceable unit that mates with the printhead of the printing apparatus.  
       [0005] Ink tank cartridges for supplying liquid ink to a “drop on demand” thermal ink jet printhead are well known. Such cartridges are typically formed of molded plastic material, and include an outlet opening through which the liquid ink is supplied to the printhead of the printing apparatus.  
       SUMMARY OF THE INVENTION  
       [0006] The present invention is a fluid cartridge for supplying fluid on demand, such as an ink cartridge for an ink jet printhead. The cartridge includes a housing having a top wall and side walls to define an interior chamber. A vent opening through the top wall provides fluid communication into the interior chamber. A fluid conduit extends from the vent opening to another point on the exterior of the housing. A fluid dam is placed in the fluid conduit. The fluid dam does not completely obstruct the fluid conduit. 
     
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING  
     [0007]FIG. 1 is a perspective view of an exemplary ink tank incorporating a particular embodiment of the present invention showing the internal structure thereof in phantom.  
     [0008]FIG. 2 is a side cross-sectional view of an ink cartridge incorporating the present invention.  
     [0009]FIG. 3 is a perspective view of an ink cartridge incorporating the present invention.  
    
    
     DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT  
     [0010] Referring to FIGS. 1 and 2, a fluid cartridge  10 , specifically an ink cartridge for use with a thermal ink jet printhead, includes a housing  12 . In FIG. 1, the internal structure of the cartridge is shown in phantom lines. FIG. 2 is a side view in cross section. The housing  12  is formed of a top wall  14  for one portion, a top wall  15  for another portion, a plurality of side walls  16  (in the illustrated embodiment, four side walls), and a bottom wall to enclose an interior chamber. The top wall  14  of the illustrated embodiment is rectangular, having a long dimension and a shorter dimension. The size of the cartridge is determined by the fluid capacity desired for the interior. Although a rectangular shape is shown, other shapes may be used, as dictated by the printhead into which the cartridge is to fit.  
     [0011] In the illustrated embodiment, a divider  20  extending from the top wall  14  toward the bottom wall  18  divides the interior chamber into a wick chamber  22  and a free ink chamber  24 . A fluid conduit  30  connects the wick chamber  22  and the free ink chamber  24 . In the illustrated embodiment, the fluid conduit  30  is formed of a gap between the bottom wall  18  of the housing and the bottom edge of the divider wall  20 .  
     [0012] The housing walls  15 ,  16 ,  18  forming the fluid or ink chamber are integrally formed or sealed so that there is no fluid communication between the fluid chamber  24  and the ambient environment, except through the fluid conduit  30  and the wick chamber  22 . In the preferred embodiment, the top and side walls  14 ,  15 ,  16  of the housing are integrally formed with no openings except for a single vent opening  60  through the top wall  14  of the wick chamber  22 . The top and side walls may be molded of a plastic material such as polypropylene, using injection molding techniques. However, those skilled in the art will recognize that other materials and manufacturing techniques may be used to form the housing.  
     [0013] An outlet opening  40  is formed through one of the walls forming the housing for the wick chamber  22 . The outlet opening provides the point at which the cartridge interacts with the remainder of the printhead, and through which ink is supplied from the cartridge to the ink jet printhead. The outlet opening  40  may be through the bottom wall  18  of the wick chamber, which is substantially opposed to the top wall  14 . However, the outlet opening may also be provided through one of the side walls  16  of the housing. An outlet opening in one of the side walls is best located in the lower portion of the side wall, near the bottom of the cartridge.  
     [0014] A seal  50  covers the outlet opening until the cartridge is installed in the printhead of the printing apparatus. For example, metallic tape, foil, or other material that the ink cannot penetrate is placed on the outer surface of the wall  18  having the outlet opening  40 , to cover the outlet opening, and sealed to the outer surface of the bottom wall. The seal  50  is removable, so that the user can remove it before inserting the cartridge into the printhead. An extended end of the seal  50  extends beyond the end of the bottom wall  18 . The user can grasp this extended end to remove the tape from the bottom wall  18  when the user is ready to install the cartridge in the printhead. However, in certain configurations, the seal may remain in place, and be punctured or otherwise penetrated by the printhead when the cartridge is installed for use in the printing apparatus.  
     [0015] A vent opening  60  extends through the top wall  14  of the wick chamber so the pressure inside the wick chamber  22  can be the same as the atmospheric pressure of the surrounding ambient environment. Preferably, the ink chamber  24  has no fluid communication with the ambient environment, except through the fluid conduit  30  between the ink chamber and the wick chamber, and thus through the wick chamber. A vent tube  61  extends into the interior of the wick chamber from the vent opening  60 .  
     [0016] An ink retaining member, such as a wick  62  substantially fills the interior of the wick chamber. Wick material appropriate for use in fluid supply cartridges such as liquid ink cartridges is well understood by those familiar with the art. For example, polyether foam material may be used as the wick  62 . When saturated with liquid (such as ink), the wick material facilitates maintaining the negative pressure for proper operation of the printhead. Therefore, the specific material may be different for different print apparatus configurations.  
     [0017] The ink chamber  24  is substantially free of ink retaining material. Liquid ink, stored in the ink chamber  24 , is transferred from the ink chamber to the wick  62  through the fluid conduit  30 . The ink is released through the outlet opening  40  as necessary to supply the printhead with ink for printing.  
     [0018] Interior structure  64  in the housing prevents the wick material  62  from contacting the vent tube  61  and the opening  60 . Preventing contact between the wick material and the vent opening reduces potential leakage of ink through the vent opening. Such structure is described in copending patent application entitled LIQUID INK CARTRIDGE WITH RECESSED FILL HOLE AND INK TANK VENT, with inventors Dennis M. Lengyel and Hiep H. Nguyen, filed on the same date as the present application, assigned to the same assignee as the present application, and bearing Xerox Corporation Attorney Docket No. D/A0764, which application is hereby incorporated by reference. However, the structure described herein can be successfully used with various cartridge configurations other than the one described in the incorporated patent application.  
     [0019] A fluid conduit is formed in the outer surface of the housing leading from the vent opening to another point on the cartridge housing. As illustrated, a first portion of the fluid conduit is a recess  70  formed in the outer surface of the top wall  14  of the wick portion of the housing. The recess  70  is {fraction (1/16)} in (1 mm) in depth. The vent opening  60  extends through the top wall of the housing to provide fluid communication between the recess and the interior chamber, particularly with the wick chamber. Thus, the vent opening  60  through the top wall of the housing coincides with the recess  70 . In accordance with the illustrated embodiment, the recess  70  surrounds the vent opening and is elongate, substantially along the long dimension of the top wall  14  of the housing. In the embodiment illustrated in FIG. 1, the recess encompasses a substantial portion of the top wall  14  of the housing, and is approximately {fraction (7/8)} in (21 mm) long, and {fraction (7/16)} in (10 mm) wide. However, on large cartridges, the recess may encompass only a small fraction of the area of the top wall.  
     [0020] Baffles or islands  72  in the recess  70  have a height equal to the depth of the recess, so that the top of each island  72  is coplanar with the outer surface of the top wall  14  of the housing. Although oval islands are shown, other shapes may be used. Each island extends across only a portion Of the recess, so the island does not completely block fluid flow through the recess.  
     [0021] Metallic or foil tape  80  or other material that is impervious to the liquid ink covers the recess (see FIG. 3). The tape is attached with adhesive to the raised portions of the outer surface of the top wall  14  that surround the recess  70 . The islands  72  keep the tape from dropping into the recess. In some circumstances, the tape may also be attached to the top surfaces of the islands. Thus, the tape  80  does not seal or close off the vent opening.  
     [0022] One end of the recess communicates with a second portion of the fluid conduit, which is an overflow tube  82  that extends from the recess to another point on the exterior of the housing. A first end of the overflow tube  82  opens into the recess in the top wall of the housing at one end of the recess. The second end of the overflow tube is near the outlet opening  40  from the wick chamber of the housing. As previously noted, in the illustrated embodiment, the outlet opening  40  is through the bottom wall of the housing. The second end of the overflow tube is substantially coplanar with the outlet tube. The overflow tube  82  is a fluid conduit that extends along one of the side walls of the housing. The tape  50  that seals the outlet opening  40  from the wick chamber also seals the second end of the overflow tube  82 . Such sealing of the overflow tube prevents leakage or evaporation of ink while the cartridge is in transit before installation by the user. However, in certain circumstances, it may be desirable to use the tape to not seal the overflow tube. Additional details of the overflow tube are contained in copending patent application entitled INK CARTRIDGE WITH OVERFLOW CONDUIT, with inventors Edward Carrese, Dennis Lengyel, Eric Merz, and Hiep Nguyen, filed on the same date as the present application, assigned to the same assignee as the present application, and bearing Xerox Corporation Attorney Docket No. D/A0763Q, which application is hereby incorporated by reference.  
     [0023] A fluid dam or barrier  90  partially blocks fluid flow between the first portion of the fluid conduit (the recess  70  in the top wall of the housing) and the overflow tube  82 . The dam  90  extends across the Width of the recess  70 , between the vent opening  60  and the overflow tube  82 . In the particular embodiment illustrated, the recess  70  narrows in width in the end having the opening into the overflow tube  82 . The dam  90  is placed across the narrow portion of the recess. The dam has a height less than the depth of the recess so that the top of the dam does not contact the tape  80 . For example, the height of the dam may be one-half to one-third the depth of the recess. The gap between the top of the dam and the tape  80  ensures that the dam does not completely obstruct the flow of spill over fluid into the overflow tube.  
     [0024] The recess  70  is in fluid communication with the overflow tube  82 . When the overflow tube is in fluid communication with the ambient environment, the vent hole  60  continues to provide atmospheric or fluid communication between the interior of the wick chamber  22  and the ambient environment.  
     [0025] Prior to filling with ink, the ink chamber  24  and wick chamber  22  are substantially evacuated of air or other gases, so that they contain a vacuum. However, as those familiar with the art will recognize, it is often impractical to obtain a perfect vacuum in a mass manufacturing operation. Therefore, it is almost inevitable that a small amount of air will remain in the ink chamber  24 , forming a bubble, and preventing the ink from completely filling the ink chamber. Ink is supplied to the cartridge through the vent opening  60  into the wick chamber. After saturating a substantial portion of the wick  62 , the ink flows into the ink chamber  24 . When the ink chamber is substantially full of ink, the tape seal  80  is placed over the recess  70  to seal the interior of the cartridge.  
     [0026] While the seals  50 ,  80  block fluid exchange between the interior and exterior of the cartridge, changes in the external environmental conditions change the relative pressure between the interior and exterior of the cartridge. These changes are principally due to the air bubble in the ink chamber  24 . For example, if the cartridge is heated, the air bubble with try to expand, increasing the relative pressure inside the cartridge. Also, placing the cartridge in an environment with a lower atmospheric pressure (such as by taking the cartridge to a high elevation) will cause the interior of the cartridge to have a higher pressure relative to the exterior.  
     [0027] If the fluid conduit to the vent opening  60  is opened (such as by removing the seal  50  from the overflow tube  82 ) when the internal pressure is higher than the external pressure, the air inside the chamber (particularly the air bubble in the ink chamber) expands.  
     [0028] When environmental changes increase the volume of air in the free ink chamber portion of the tank, ink flows through the fluid conduit  30  between the free ink chamber and the wick chamber. If the wick material  62  in the chamber becomes completely saturated, some of the ink may exit the housing interior through the vent outlet  60  into the recess. The recess  70  receives the ink that exits through the vent opening. The dam  90  contains the ink in the recess, so that it does not flow down the overflow tube  82  and exit the cartridge. This helps maintain the neatness of the outer surface of the cartridge for the user. However, should the environmental changes be extraordinarily large, enough ink may exit through the vent opening that ink may flow over the dam  90  and down the overflow tube.  
     [0029] The structure described above reduces the sudden ejection or squirting of ink when a seal is removed, if the opening of the vent tube  82  has been sealed and environmental changes have occurred to create a significant pressure differential between the interior and exterior of the housing. If the external pressure is significantly less than the internal pressure, the increased pressure in the overflow tube prevents the ink from entering the recess in the top wall, or the overflow tube. When the tape  50  covering the outlet of the overflow tube  82  and the outlet opening  40  from the wick chamber is removed, the overflow tube  82  is opened first, before the outlet opening  40 . The air in the overflow tube  82  and the recess  70  escapes first, before allowing ink to begin to flow into the recess (if the pressure differential is sufficient). The dam  90  contains ink that enters the recess, so that it does not flow into the overflow tube. In rare cases, sufficient ink may enter the recess that the depth of ink in the overflow tube exceeds the height of the dam, and the ink flows over the dam (through the gap between the top of the dam and the tape), to reach the overflow tube,  
     [0030] A specific embodiment of the present invention has been described. Those skilled in the art after reading the above description will identify various modifications that can be made to the embodiment described above without departing from the spirit of the invention. For example, other shapes of ink cartridges may incorporate the invention. Also, other shapes may be incorporated into the recess and the islands, or other structures may be used, as can different styles of fluid dams or barriers. In addition, the vent opening, the outlet opening, and other elements may be placed in different locations. Therefore, the above description is illustrative, and the scope of the invention is not to be limited to the embodiment described above.