Abstract:
A cartridge for an inkjet printing apparatus. A case of molded plastic includes a downwardly-projecting nose section. An opening in the bottom of the nose section is surrounded by an upstanding stand pipe internal to the cartridge. An insert holds a filter and includes a tube section and an upper flange. The insert is selectively removably fixed to the stand pipe to permit ready filter replacement and thereby facilitate reliable recharging of the cartridge.

Description:
REFERENCE TO RELATED APPLICATION 
   The Present application claims priority of Provisional Patent Application 60/614,188 of Raymond Shaw covering “Press in #82” filed Sep. 29, 2004 in the United States Patent and Trademark Office. 

   BACKGROUND 
   1. Field of the Invention 
   The present invention relates to cartridges for storing ink. More particularly, this invention pertains to a reusable cartridge that is suitable for use with non-water soluble printer ink. 
   2. Description of the Prior Art 
   Inkjet technology provides a more-or-less ubiquitous alternative to other commonly employed technologies (e.g. laser) over a broad spectrum of document imprinting applications. Common and well-recognized applications of this technology include computer printers and facsimile machines. Inkjet printing advantageously produces documents that are not subject to the fading observed with other technologies such as laser printers. 
   Such technology involves the selective, patterned heating of ink contained within a cassette for controlled dispersion onto a sheet of paper. A representative cartridge for an inkjet printer is disclosed, for example, in U.S. Pat. No. 6,328,424 of Gary Allen Denton et al. titled “Inkjet Cartridge With Simultaneous Electrical and Fluid Connections”. Such patent teaches a refillable cartridge that includes a foam-filled ink reservoir. A filter of mesh-like composition is provided between the foam-filled reservoir and a standpipe that forms a lower reservoir. The filter eliminates air bubbles that would otherwise degrade the printing process. The ink moves from the foam-filled reservoir through the standpipe into a chamber or “lower reservoir” wherein it may be selectively heated by an arrangement of heaters to cause the ink to be selectively thinned to permit passage, by capillary action, to a paper surface. 
   Recycling of inkjet cartridges is complicated by the necessary presence of the mesh-like filter. This is especially the case in the event that the ink stored in the cartridge is oil-based. Commonly, such a filter is either glued or laser welded to the open top of the stand pipe and the empty cartridge must be recharged with ink without its removal and replacement as such a process would be difficult and prohibitively expensive. As a result, the filter, often clogged with particles of contaminants and dried ink, is generally the cause of the abysmally low rate of success (generally about 40 per cent) of conventional cartridge recycling processes. 
   SUMMARY OF THE INVENTION 
   The preceding and other shortcomings of the prior art by providing a reusable cartridge for an ink jet printing apparatus. Such cartridge includes a case. The case has mutually orthogonal pairs of parallel planar walls defining the sides of an ink reservoir. A substantially planar cover is arranged to form the top of the case. 
   The bottom of the case comprises a planar floor and a downwardly-projecting nose section. An aperture is provided in the bottom of the nose section. An upright stand pipe interior to the nose section surrounds the opening. A removable insert is provided for selective affixation to the standpipe. The insert includes a tube section for insertion into the stand pipe and an upper flange. A filter is located interior to the flange. 
   In a second aspect, the invention provides an insert for an inkjet cartridge case of the type that includes a downwardly-projecting nose section having an aperture with an upright stand pipe surrounding the aperture. Such insert includes a tube. An upper peripheral flange is provided. A filter is fixed within the peripheral flange. 
   In a third aspect, the invention provides a cartridge for an ink jet printing apparatus. Such cartridge includes a case that comprises mutually orthogonal pairs of parallel planar walls defining the sides of an ink reservoir. 
   A substantially planar cover forms the top of the case. A planar floor and a downwardly-projecting nose section comprise the bottom of the case. An aperture exists in the bottom of the nose section and an upright stand pipe is interior to the nose section surrounding the aperture. 
   A planar filter is fixed to the top of the stand pipe. The dimensions of the planar filter exceed those of the underlying stand pipe. 
   The preceding and other features of the invention will become further apparent from the detailed description that follows. Such description is accompanied by a set of drawing figures. Numerals of the drawing figures, corresponding to those of the written description, point to the features of the invention. Like numerals refer to like features throughout both the drawing figures and the written description. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a cross-sectional view of a reusable inkjet cartridge in accordance with the invention; 
       FIG. 2  is a perspective view of a filter insert in accordance with the invention; 
       FIG. 3  is a perspective view of a filter insert in accordance with an alternative embodiment of the invention; and 
       FIG. 4  is a side elevation view of an inkjet cartridge in accordance with a further embodiment of the invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1  is a cross-sectional view of a reusable inkjet cartridge  10  in accordance with the invention. It includes a molded plastic body  12  of substantially hollow interior having a lid-like cover  14 . The body  12  includes a downwardly-extending nose portion  16 . A stand pipe  18  extends upwardly from the bottom of the nose portion  16 . 
   A first aperture  20  extends through the bottom of the nose portion  16  of the molded plastic body  12 . It provides a passageway for ink from the bottom of the stand pipe  18  to capillary ink passages within a heater chip  22  that is fixed to the bottom of the nose portion  16 . A tab circuit  24  is fixed to the outer surface  26  of a cartridge body wall and extends underneath the nose portion  16  to make electrical contact with, and thereby control, the heater chip  22 . 
   The tab circuit  24  comprises printed circuits whereby the heaters of the heater chip  22  are selectively connected to a source of energizing signals when the cartridge  10  is mounted on a cartridge carrier (not shown). As such heaters are selectively energized, ink, which is fast-drying, is ejected from the capillary passages within the heater chip  22  through apertures in a nozzle plate  28 , thereby imprinting an underlying document. 
   Referring to additional details of the cartridge  10 , a conventional hydrophobic foam material  30  (e.g. unfelted polyurethane open cell foam) fills a portion of the interior of the cartridge  10 . Prior to placing the foam material  30  within the body  12 , a filter insert  32  comprising a fine mesh screen  34  that is held by a molded frame comprising a peripheral flange  36  and upstanding tube section  38  is fitted to the stand pipe  18 . The screen  34  prevents small particles of the foam material  30  form migrating through the stand pipe  18  and passage  20 . Such migration could cause blockage of ink flow through the capillary ink passages within the heater chip  22 . While the foam material  30  need not extend to the bottom of the stand pipe  18 , it must extend downwardly to a level below the top of the stand pipe  18 . Exemplary material for the screen  34  may comprise, but is not limited to, 316 stainless steel, 5 micron, 325×2300 twilled Dutch weave with wire size of 0.0014×0.0010 inch diameter. A screen  34  of round shape may be of 0.437 inch diameter. 
   The cartridge  10  is filled (and refilled) by insertion of a needle (not shown) into the foam material  30  (which is replaced and renewed when the cartridge is recycled) before the lid  14  is fixed to the cartridge body  12 . Ink is injected into the foam material  30  through the needle to saturate it and to cause the stand pipe  18  to be filled with ink from an ink supply (not shown). A slight negative pressure is applied to the nozzle plate  28  to prime the cartridge  10  by drawing into the capillary ink passages of the heater chip  22 . 
   In the prior art, the fine mesh screen  34  is fixed to the upper region of the stand pipe  18 . As a consequence, when a cartridge is recycled or refilled it cannot be changed. As a consequence, the refilled cartridge is likely to be inoperable or to have a useful lifetime that is limited by the existence of accumulated foam debris on the filter screen. Further, the screen prevents accessing of the interior of the stand pipe at the bottom of the nose portion of the case. In the case of oil-based inks, an accumulation of hardened ink is likely to exist in this area, further limiting the useful life of the recharged cartridge. 
   This shortcoming is addressed in the present invention by utilizing the insert  32 .  FIG. 2  is a perspective view of an insert in accordance with the invention. As can be seen, the filter screen  34  is secured by any of a number of processes and means including, but not limited to, gluing or laser welding, to the interior of the peripheral flange  36 . The upstanding tube section  38  is integral with the flange  36 , the insert  32  preferably comprising a single molded piece for holding the filter screen  34 . 
   A pair of ridges  40 ,  42  encircles and protrudes from the periphery of the cylindrical tube  38 . They enable the insert  32  to be securely press-fit against the inner surface of the stand pipe  18 . 
     FIG. 3  is a perspective view of a filter insert  44  in accordance with an alternative embodiment of the invention. The embodiment of  FIG. 3  differs from that of the preceding figures insofar as it is of generally-rectangular shape. In the case of the present embodiment and that of the preceding figures, the insert is shaped to conform to the shape of a stand pipe and accompanying filter-screen of a inkjet cartridge of standard design. That is, with the exception of the insert  32 , all elements of the cartridge  10  of  FIG. 1  are representative of a standard “off the shelf” device. In the event that an inkjet cartridge were to include a filter-screen that was conventionally directly fixed to the top of the stand pipe  18  (by, e.g., gluing or laser welding), such a cartridge may readily be converted to one in accordance with the invention by removal of the filter-screen and replacement with a filter insert in accordance with the invention. 
   Such replacement of a directly-affixed filter-screen with a filter insert is, in fact, contemplated in accordance with the invention. This enables and facilitates the recharging of such a conventional cartridge by enabling replacement of the filter-screen at the time of refilling of the cartridge. While appropriate tooling is contemplated for removal of a directly-fixed filter-screen, subsequent removals for replacement of the filter insert are much more routine. Thus, filter replacement may be accomplished through multiple refillings of an inkjet cartridge in accordance with the invention. Further, with each filter-screen insert removal, one obtains access to the interior of the stand pipe, allowing the clearance of dried ink before significant blockage can occur. 
     FIG. 4  is a side elevation view of an inkjet cartridge  46  in accordance with a further embodiment of the invention. Unlike the embodiments of the preceding figures, a removable filter insert is not employed. Rather, a filter-screen  48  is directly fixed to the top of the stand pipe  18 . The diameter of the circular filter-screen  48  is selected to exceed the outer diameter of the standpipe  18 . In the event that the stand pipe were to be of generally-rectangular shape, the dimensions of the filter-screen would be selected to overlap the corresponding dimensions of the stand pipe. Appropriate composition and dimensions for a filter-screen  48  in accordance with this embodiment of the invention may comprise, but are not limited to, type 316L stainless steel, 325×2300 twilled Dutch weave, wire diameter 0.001×0.0010 of diameter 0.437 or 0.453 inch (round filter). A rectangular filter in accordance with the teachings of this embodiment may be, for example, 0.460 or 0.470×0.840 inches with 0.050 inch corner radii. 
   Thus it is seen that the present invention facilitates the refilling of an inkjet cartridge. By employing a cartridge in accordance with the invention, one may greatly enhance the useful life of a given cartridge by assuring its reliable refilling. Further, by utilizing a filter insert in accordance with the invention, one may simply convert a conventional or standard inkjet cartridge into a readily refillable device. 
   While the invention has been described with reference to its presently-preferred embodiment, it is not limited thereto. Rather, this invention is limited only insofar as it is defined by the following set of patent claims and includes within its scope all equivalents thereof.