Abstract:
The present disclosure relates to an apparatus for refilling a replaceable ink container. The ink container has a top and bottom portion relative to a gravitational frame of reference. The replaceable ink container further has a capillary storage member disposed therein and a fluid outlet disposed on the bottom portion. The apparatus for refilling includes a fluid interconnect configured for insertion into the bottom portion to compress the capillary storage member. Included is a back pressure measuring device for determining an amount of ink to fill the replaceable ink container. Also included is an ink delivery device for providing the determined quantity of ink to the replaceable ink container through the fluid interconnect. The ink delivery device is configured to deliver ink to the ink container positioned in a bottom down orientation relative to the gravitational frame of reference to provide ink to the capillary storage member proximate the fluid outlet.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to ink containers for providing ink to inkjet printers. More specifically, the present invention relates to a method and apparatus for refilling a replaceable ink container having a capillary storage member for retaining and providing the controlled release of ink from the ink container. 
     Inkjet printers frequently make use of an inkjet printhead mounted within a carriage that is moved back and forth across print media, such as paper. As the printhead is moved across the print media, a control system activates the printhead to deposit or eject ink droplets onto the print media to form images and text. Ink is provided to the printhead by a supply of ink that is either carried by the carriage or mounted to the printing system not to move with the carriage. 
     For the case where the ink supply is not carried with the carriage, the ink supply can be in continuous fluid communication with the printhead by the use of a conduit to replenish the printhead continuously. Alternatively, the printhead can be intermittently connected with the ink supply by positioning the printhead proximate to a filling station that facilitates connection of the printhead to the ink supply. 
     For the case where the ink supply is carried with the carriage, ink supply may be integral with the printhead, whereupon the entire printhead and ink supply is replaced when ink is exhausted. Alternatively, the ink supply can be carried with the carriage and be separately replaceable from the printhead. For the case where the ink supply is separately replaceable, the ink supply is replaced when exhausted, and the printhead is replaced at the end of printhead life. Regardless of where the ink supply is located within the printing system, it is critical that the ink supply provides a reliable supply of ink to the inkjet printhead. 
     In addition to providing ink to the inkjet printhead, the ink supply frequently provides additional functions within the printing system, such as maintaining a negative gauge pressure, frequently referred to as a back pressure, within the ink supply and inkjet printhead. Gauge pressure a pressure within the inkjet printhead relative to an atmospheric pressure. This negative gauge pressure must be sufficient so that a head pressure associated with the ink supply is kept at a value that is lower than the atmospheric pressure to prevent leakage of ink from either the ink supply or the inkjet printhead frequently referred to as drooling. The ink supply is required to provide a negative gauge pressure or back pressure over a wide range of temperatures and atmospheric pressures in which the inkjet printer experiences in storage and operation. 
     There is an ever-present need for ink containers for supplying ink to the inkjet printhead in a reliable manner. These ink containers should provide sufficient back pressure to prevent ink leakage during normal handling and temperature and pressure variations the ink container experiences during normal use and storage. In addition, these ink containers should have relatively low manufacturing costs to reduce the per page printing costs. 
     SUMMARY OF THE INVENTION 
     One aspect of the present invention is an apparatus for refilling a replaceable ink container. The ink container has a top and bottom portion relative to a gravitational frame of reference. The replaceable ink container further has a capillary storage member disposed therein and a fluid outlet disposed on the bottom portion. The apparatus for refilling includes a fluid interconnect configured for insertion into the bottom portion to compress the capillary storage member. Included is means for determining an amount of ink to fill the replaceable ink container. Also included is an ink delivery device for providing the determined quantity of ink to the replaceable ink container through the fluid interconnect. The ink delivery device is configured to deliver ink to the ink container positioned in a bottom down orientation relative to the gravitational frame of reference to provide ink to the capillary storage member proximate the fluid outlet. 
     In one preferred embodiment the means for determining an amount of ink is a back pressure measuring device for measuring back pressure tending to draw ink toward the capillary storage material. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exemplary embodiment of an inkjet printer that incorporates the ink container that is suitable for refilling using the method and apparatus of the present invention. 
     FIG. 2 is a schematic representation of the ink container and an inkjet printhead that receives ink from the ink container to accomplish printing. 
     FIG. 3 is an exploded view of the ink container showing an ink reservoir, a network of fused fibers for insertion into the reservoir, and a reservoir cover for enclosing the reservoir. 
     FIG. 4A is represents the network of fused fibers shown in FIG.  3 . 
     FIG. 4B is a greatly enlarged perspective view taken across lines  4 B— 4 B of the network of fused fibers shown in FIG. 4A that are inserted into the ink reservoir shown in FIG.  3 . 
     FIG. 5A is a cross section of a single fiber taken across lines  5 — 5  of FIG.  4 . 
     FIG. 5B is an alternative embodiment of a fiber shown in FIG. 4 having a crossshaped or x-shaped core portion. 
     FIG. 6 is a cross section of a pair of fibers that are fused at a contact point taken across lines  6 — 6  shown in FIG.  4 . 
     FIG. 7 is a simplified representation of the apparatus of the present invention for filling the ink container shown in FIG.  3 . 
     FIG. 8 is a simplified representation of the method of the present invention for filling the ink container. 
     FIG. 9 is a simplified representation of the apparatus of the present invention for determining an amount of ink required to fill the ink container. 
     FIG. 10 is a schematic representation of a method of the present invention for determining an amount of ink required to fill the ink container. 
     FIG. 11 is schematic representation of an inkjet printing system that includes an ink container that is refilled using the method and apparatus of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 is a perspective view of one exemplary embodiment of a printing system  10 , shown with its cover open, that includes at least one ink container  12  that is suitable for refilling using the method and apparatus of the present invention. The printing system  10  further includes at least one inkjet printhead (not shown) installed in the printer portion  14 . The inkjet printhead is responsive to activation signal from the printer portion  14  to eject ink. The inkjet printhead is replenished with ink by the ink container  12 . 
     Before discussing the details of the method and apparatus of the present invention for refilling ink container  12 , it will be helpful to first discuss further detail of the ink container  12 . The method and apparatus of the present invention will then be discussed with respect to FIGS. 7-10. 
     The inkjet printhead is preferably installed in a scanning carriage  18  and moved relative to a print media as shown in FIG.  1 . Alternatively, the inkjet printhead is fixed and the print media is moved past the printhead to accomplish printing. The inkjet printer portion  14  includes a media tray  20  for receiving print media  22 . As print media  22  is stepped through the print zone, the scanning carriage moves the printhead relative to the print media  22 . The printer portion  14  selectively activates the printhead to deposit ink on print media to thereby accomplish printing. 
     The printing system  10  shown in FIG. 1 is shown with two replaceable ink containers  12  representing an ink container  12  for black ink and a three-color partitioned ink container  12  containing cyan, magenta, and yellow inks, allowing for printing with four colorants. The ink container  12  is suitable for printing systems  10  that make use of fewer or greater numbers of ink colors such as printing systems that use greater or less than  4 -ink colors, such as in high fidelity printing which typically uses 6 or more colors. 
     FIG. 2 is a schematic representation of the printing system  10  which includes the ink supply or ink container  12 , an inkjet printhead  24 , and a fluid interconnect  26  for fluidically interconnecting the ink container  12  and the printhead  24 . 
     The printhead  24  includes a housing  28  and an ink ejection portion  30 . The ink ejection portion  30  is responsive to activation signals by the printer portion  14  for ejecting ink to accomplish printing. The housing  28  defines a small ink reservoir for containing ink  32  that is used by the ejection portion  30  for ejecting ink. As the inkjet printhead  24  ejects ink or depletes the ink  32  stored in the housing  28 , the ink container  12  replenishes the printhead  24 . A volume of ink contained in the ink supply  12  is typically significantly larger than a volume of ink container within the housing  28 . Therefore, the ink container  12  is a primary supply of ink for the printhead  24 . 
     The ink container  12  includes a reservoir  34  having a fluid outlet  36  and an air inlet  38 . Disposed within the reservoir  34  is a network of fibers that are heat fused at points of contact to define a capillary storage member  40 . The capillary storage member  40  performs several important functions within the inkjet printing system  10 . The capillary storage member  40  must have sufficient capillarity to retain ink to prevent ink leakage from the reservoir  34  during insertion and removal of the ink container  12  from the printing system  10 . This capillary force must be sufficiently great to prevent ink leakage from the ink reservoir  34  over a wide variety of environmental conditions such as temperature and pressure changes. The capillary should be sufficient to retain ink within the ink container  12  for all orientations of the reservoir  34  as well as undergoing shock and vibration that the ink container  12  may undergo during handling. 
     Once the ink container  12  is installed into the printing system  10  and fluidically coupled to the printhead by way of fluid interconnect  26 , the capillary storage member  40  should allow ink to flow from the ink container  12  to the inkjet printhead  24 . As the inkjet printhead  24  ejects ink from the ejection portion  30 , a negative gauge pressure, sometimes referred to as a back pressure, is created in the printhead  24 . This negative gauge pressure within the printhead  24  should be sufficient to overcome the capillary force retaining ink within the capillary member  40 , thereby allowing ink to flow from the ink container  12  into the printhead  24  until equilibrium is reached. Once equilibrium is reached and the gauge pressure within the printhead  24  is equal to the capillary force retaining ink within the ink container  12 , ink no longer flows from the ink container  12  to the printhead  24 . The gauge pressure in the printhead  24  will generally depend on the rate of ink ejection from the ink ejection portion  30 . As the printing rate or ink ejection rate increases, the gauge pressure within the printhead will become more negative causing ink to flow at a higher rate to the printhead  24  from the ink container  12 . In one preferred inkjet printing system  10  the printhead  24  produces a maximum back pressure that is equal to 10 inches of water or a negative gauge pressure that is equal to 10 inches of water. 
     The printhead  24  can have a regulation device included therein for compensation for environmental changes such as temperature and pressure variations. If these variations are not compensated for, then uncontrolled leaking of ink from the printhead ejection portion  30  can occur. In some configurations of the printing system  10  the printhead  24  does not include a regulation device, instead the capillary member  40  is used to maintain a negative back pressure in the printhead  24  over normal pressure and temperature excursions. The capillary force of the capillary member  40  tends to pull ink back to the capillary member, thereby creating a slight negative back pressure within the printhead  24 . This slightly negative back pressure tends to prevent ink from leaking or drooling from the ejection portion  30  during changes in atmospheric conditions such as pressure changes and temperature changes. The capillary member  40  should provide sufficient back pressure or negative gauge pressure in the printhead  24  to prevent drooling during normal storage and operating conditions. 
     The embodiment in FIG. 2 depicts an ink container  12  and a printhead  24  that are each separately replaceable. The ink container  12  is replaced when exhausted and the printhead  24  is replaced at end of life. The method and apparatus of the present invention is applicable to inkjet printing systems  10  having other configurations than those shown in FIG.  2 . For example, the ink container  12  and the printhead  24  can be integrated into a single print cartridge. The print cartridge which includes the ink container  12  and the printhead  24  is then replaced when ink within the cartridge is exhausted. 
     The ink container  12  and printhead  24  shown in FIG. 2 contain a single color ink. Alternatively, the ink container  12  can be partitioned into three separate chambers with each chamber containing a different color ink. In this case, three printheads  24  are required with each printhead in fluid communication with a different chamber within the ink container  12 . Other configurations are also possible, such as more or less chambers associated with the ink container  12  as well as partitioning the printhead and providing separate ink colors to different partitions of the printhead or ejection portion  30 . 
     FIG. 3 is an exploded view of the ink container  12  shown in FIG.  2 . The ink container  12  includes an ink reservoir portion  34 , the capillary member  40  and a lid  42  having an air inlet  38  for allowing entry of air into the ink reservoir  34 . The capillary member  40  is inserted into the ink reservoir  34 . The reservoir  34  is filled with ink as will be discussed in more detail with respect to FIG.  7 . In the preferred embodiment, each of the height, width, and length dimensions indicated by H, W, and L, respectively are all greater than one inch to provide a high capacity ink container  12 . 
     In the preferred embodiment, the capillary member  40  is formed from a network of fibers that are heat fused at points of contact. These fibers are preferably formed of a bi-component fiber having a sheath formed of polyester such as polyethylene terephthalate (PET) or a co-polymer thereof and a core material that is formed of a low cost, low shrinkage, high strength thermoplastic polymer, preferably polypropylene or polybutylene terephthalate. 
     The network of fibers are preferably formed using a melt blown fiber process. For such a melt blow fiber process, it may be desirable to select a core material of a melt index similar to the melt index of the sheath polymer. Using such a melt blown fiber process, the main requirement of the core material is that it is crystallized when extruded or crystallizable during the melt blowing process. Therefore, other highly crystalline thermoplastic polymers such as high density polyethylene terephthalate, as well as polyamides such as nylon and nylon 66 can also be used. Polypropylene is a preferred core material due to its low price and ease of processibility. In addition, the use of a polypropylene core material provides core strength allowing the production of fine fibers using various melt blowing techniques. The core material should be capable of forming a bond to the sheath material as well. 
     FIG. 4B is a greatly simplified representation of the network of fibers which form the capillary member  40 , shown greatly enlarged in break away taken across lines  4 A— 4 A of the capillary member  40  shown in FIG.  4 A. The capillary member  40  is made up of a network of fibers with each individual fiber  46  being heat bonded or heat fused to other fibers at points of contact. The network of fibers  46  which make up the capillary member  40  can be formed of a single fiber  46  that is wrapped back upon itself, or formed of a plurality of fibers  46 . The network of fibers form a self-sustaining structure having a general fiber orientation represented by arrow  44 . The self-sustaining structure defined by the network of fibers  46  defines spacings or gaps between the fibers  46  which form a tortuous interstitial path. This interstitial path is formed to have excellent capillary properties for retaining ink within the capillary member  40 . 
     In one preferred embodiment, the capillary member  40  is formed using a melt blowing process whereby the individual fibers  46  are heat bonded or melt together to fuse at various points of contact throughout the network of fibers. This network of fibers, when fed through a die and cooled, hardens to form a self-sustaining three dimensional structure. 
     FIG. 5A represents a cross section taken across lines  5 A— 5 A in FIG. 4 to illustrate a cross section of an individual fiber  46 . Each individual fiber  46  is a bi-component fiber, having a core  50  and a sheath  52 . The size of the fiber  46  and relative portion of the sheath  52  and core  50  have been greatly exaggerated for illustrative clarity. The core material preferably comprises at least 30 percent and up to 90 percent by weight of the overall fiber content. In the preferred embodiment, each individual fiber  46  has, on average, a diameter of 12 microns or less. 
     FIG. 5B represents an alternative fiber  46  that is similar to the fiber  46  shown in FIG. 5A, except fiber  46  in FIG. 5B has a cross or x-shaped cross section instead of a circular cross section. The fiber  46  shown in FIG. 5B has a non-round or cross-shaped core  50  and a sheath  52  that completely covers the core material  50 . Various other alternative cross sections can also be used, such as a tri-lobal or y-shaped fiber, or an h-shaped cross-section fiber, just to name a few. The use of non-round fibers results in an increased surface area at the fibrous surface. The capillary pressure and absorbency of the network of fibers  40  is increased in direct proportion to the wettable fiber surface. Therefore, the use of nonround fibers tends to improve the capillary pressure and absorbency of the capillary member  40 . 
     Another method for improving the capillary pressure and absorbency is to reduce a diameter of the fiber  46 . With a constant fiber bulk density or weight, the use of smaller fibers  46  improves the surface area of the fiber. Smaller fibers  46  tend to provide a more uniform retention. Therefore, by changing the diameter of the fiber  46  as well as by changing the shape of the fiber  46 , the desired capillary pressure for the printing system  10  can be achieved. 
     FIG. 6 illustrates the heat melding or heat fusing of individual fibers  46 . FIG. 6 is a cross section taken across lines  66  at a point of contact between two individual fibers. Each individual fiber  46  has a core  50  and a sheath  52 . At a point of contact between the two fibers  46 , the sheath material  52  is melted together or fused with the sheath material of the adjacent fiber  46 . The fusing of individual fibers is accomplished without the use of adhesives or binding agents. Furthermore, individual fibers  46  are held together without requiring any retaining means, thereby forming a self-sustaining structure. 
     FIG. 7 is a schematic illustration of the filling apparatus  54  of the present invention for filling ink into the ink container  12 . The filling apparatus  54  of the present invention includes a source of ink  56 , a pressurizing device  58  coupled to the source of ink  56  and a fluid interconnect  60  for coupling pressurized ink to the ink container  12 . The pressurizing device  58  provides sufficient pressurization to provide ink from the source of ink  56  to the ink container  12 . The pressurization required will in general be related an ink column height or ink head that must be overcome to provide ink to the fluid outlet  36  of the ink container  12 . The pressurization device  58  can be a wide variety of devices sufficient to deliver a controlled amount of ink to the fluid outlet  36  of the ink container  12 . For example, the pressurization device  58  can be a pump or can make us of the positioning of the source of ink  56  above the ink container  12  such that the ink head is. sufficient to deliver ink to the fluid outlet  36  of the ink container  12 . 
     Ink is delivered to the fluid outlet  36  of the ink container  12  by the filling apparatus  54  of the present invention. As ink is delivered to the fluid outlet  36  ink is provided to a portion of the capillary storage member or network of fibers  40  adjacent the fluid outlet  36 . This delivered ink is drawn into the interstitial spaces  48  between fibers  46  of the network of fibers  40  by the capillarity of this network of fibers. As ink is drawn into the interstitial spaces  48  of the network of fibers  40  air within the interstitial spaces is displaced defining an ink front  62 . As ink is further delivered to the ink container  12  this ink front  62  expands outwardly into the capillary material  40  as represented by ink front  64 . This expanding ink front  62 ,  64  tends to expand from the region proximate the fluid outlet  36  into filling interstitial spaces  48  displacing air from the network of fibers  40  in a region surrounding the fluid outlet  36 . As air is displaced from the network of fibers  40  and vented through the air inlet  38  to atmosphere to prevent pressurization of the ink container  12  as ink is added. Once the proper amount of ink required to fill the ink container  12  the flow of ink from the ink container  56  is ceased. 
     It is preferable that the fluid interconnect  60  at least slightly compress the network of fibers  40  to create a region of increased capillary to aid in drawing ink into the capillary material  40 . In one preferred embodiment, the fluid interconnect  60  is a hollow ink conduit that is inserted into the fluid outlet  36  sufficiently to compress the network of fibers  40 . 
     It is preferable that the capillary material  40  is formed from at least one bi-component fiber having polypropylene core and a polyethylene terephthalate sheath to greatly simplify the process of filling the ink container  12 . This capillary material  40  is more hydrophilic than the polyurethane foam that has been used previously as an absorbent material in thermal inkjet pens such as those disclosed in U.S. Pat. No. 4,771,295, to Baker, et al., entitled “Thermal Inkjet Pen Body Construction Having Improved Ink Storage and Feed Capability” issued Sep. 13, 1988, and assigned to the assignee of the present invention. Polyurethane foam, in its untreated state, has a large ink contact angle, therefore making it difficult to fill ink containers having polyurethane foam contained therein without using expensive and time consuming steps such as vacuum filling in order to wet the foam. Polyurethane foam can be treated to improve or reduce the ink contact angle; however, this treatment, in addition to increasing manufacturing cost and complexity, tends to add impurities into the ink which tend to reduce printhead life or reduce printhead quality. The use of the capillary member  40  of the present invention has a relatively low ink contact angle, allowing ink to be readily absorbed into the capillary member  40  without requiring treatment of the capillary member  40 . 
     FIG. 8 is a flow chart illustrating a method of the present invention for refilling the replaceable ink container  12 . The method begins by determining an amount of ink required to, properly fill the replaceable ink container  12  as represented by step  66 . Fluid connection is than made to the replaceable ink container  12  so that ink can be provided to the ink container as represented by step  68 . In the preferred embodiment, fluid connection is accomplished by inserting a fluid interconnect  60  into the fluid outlet  36  of the replaceable ink connector  12 . The amount of ink required to fill the replaceable ink container  12  is then provided to the replaceable ink container as represented by step  70 . 
     The method and apparatus of the present invention determines the amount required to properly fill the replaceable ink container  12  and then delivers this amount to the ink container  12 . It is critical that the proper amount of ink be provided to the replaceable ink container  12 . If too much ink is provided to the replaceable ink container  12  and the capillary storage member  40  will have insufficient capillarity to retain this ink. If the ink container  12  cannot retain the ink, ink can leak from the reservoir  34  during handling of the ink container  12  such as during insertion and removable of the ink container  12  from the printing system  10 . Furthermore, too much ink placed in the ink container  12  can result in ink leakage during changes in environmental conditions such as temperature and pressure changes. Therefore, it is critical that the ink container  12  is not overfilled during the refilling process. 
     The case where the printing system  10  is capable of tracking ink usage for the replaceable ink container  12  it is important that the ink container  12  is not underfilled during the refilling process. Underfilling of the replaceable ink container  12  can result in the printing system  10  inferring that ink is remaining in the ink container  12  when, in fact, the ink container  12  is exhausted of ink. The printing system  10  for this case may continue to print even when the ink container is exhausted. If the ink container  12  is sufficiently underfilled during the refilling process and the printhead can be operated without ink sometimes referred to as “dry firing” which can result in catastrophic damage to the printhead. In addition, operation of the printhead once the ink container  12  is exhausted can result in air injestion into the printhead  24 . If a sufficient amount of air is injested into the printhead  24 , the printhead  24  maybe incapable of properly maintaining proper back pressure within the printhead  24  which can result in ink uncontrollably leaking from the printhead  24 . This ink leakage from the printhead  24  not only can reduce print quality but also damage the printing system  10 . 
     There are several problems with determining the proper amount of ink required to fill the replaceable ink container  12 . One problem is that it is difficult to determine the amount of ink remaining or stranded in the capillary storage member  40 . The ink. remaining in the capillary storage member  40  is retained within the interstitial spaces of the network of fibers. Therefore, it is difficult to measure this amount of stranded ink. 
     Another problem with determining the amount of ink required to properly fill the replaceable ink container  12  is that frequently the replaceable ink container  12  has more than one ink compartment. Each ink compartment typically contains a different ink color. 
     For example, a tri-color ink container  12  has three separate compartments contained therein. Each compartment contains a different ink color such as one of cyan, magenta, and yellow inks. The printing system  10  may have previously indicated that one of the three inks is exhausted, however, the remaining two inks may have varying ink levels depending on the particular items printed. To properly refill a tri-color replaceable ink container  12  is necessary to determine an amount of ink necessary to fill each of the compartments in the replaceable ink container  12 . In the case of a tri-color replaceable ink container, it is necessary to determine an amount of each of cyan, magenta, and yellow inks that are necessary for filling their respective compartments. 
     Weighing the ink container to determine residual ink stranded in the capillary storage member  40  is suitable for determining an amount of ink required to fill a monochrome ink container  12  based on the weight of the ink container  12 . However, weighing the ink container  12  is not well suited for an ink container that has more than two compartments for storing ink. Even if one were to infer one of the ink compartments were exhausted, there is no way to determine how much ink is stranded in each of the remaining two compartments. The method and apparatus of the present invention, as well will be discussed with respect to FIGS. 9 and 10, provides a technique for determining an amount of ink required to fill a replaceable ink container  12  that has three more separate compartments, each of which contains a separate quantity of ink. In the case where the ink container  12  contains less than three compartments of ink then the weighing technique previously discussed is suitable. 
     FIG. 9 depicts an apparatus  72  for determining an amount of ink to fill an ink container  12 . The apparatus  72  includes a backpressure measurement device  74 , a negative pressure or vacuum device  76 , and a fluidic interconnect  78  for coupling the backpressure measurement device  74  to the capillary storage member  40  within the ink container  12 . The vacuum device  76  creates a negative pressure or vacuum sufficient to overcome the capillary force retaining ink within the capillary storage member  40 . The backpressure measurement device  74  then determines the backpressure or retaining force tending to retain the ink within the capillary storage member  40 . By characterizing the relationship between an amount of ink within the capillary storage member  40  and the backpressure or retaining force for the capillary material  40  then an amount of ink retained within the capillary storage member  40  for a given measured back pressure can be inferred. 
     FIG. 10 is a flow diagram depicting the method of the present invention for determining an amount of ink to fill an ink container  12 . A conduit or fluidic interconnect  78  is first inserted into the ink container  12  to engage the capillary storage member  40  as represented by step  80 . Ink is then drawn from the capillary storage member  40  by the vacuum device  76  as represented by step  82 . The static backpressure of the ink container  12  is then measured by the backpressure measurement device  74  as represented by step  84 . Finally, based on the measured static backpressure of the ink container  12 , an amount of ink stranded in the capillary storage member  40  can be inferred. The stranded ink is inferred based on the measured static backpressure and stranded ink versus backpressure of characteristics of the capillary storage member  40 . Once the amount of stranded ink is inferred then an amount of ink required to fill the ink container  12  is equal to the difference between an amount of ink in a filled ink container  12  contains minus the amount of ink stranded in the capillary storage member  40 . 
     FIG. 11 shows inkjet printing system  10  in operation. With the ink container  12  refilled using the method and apparatus of the present invention then properly installed into the inkjet printing system  10 , fluidic coupling is established between the ink container  12  and the inkjet printhead  24  by way of a fluid conduit  26 . The selective activation of the drop ejection portion  30  to eject ink produces a negative gauge pressure within the inkjet printhead  24 . This negative gauge pressure draws ink retained in the interstitial spaces between fibers  46  within the capillary storage member  40 . Ink that is provided by the ink container  12  to the inkjet printhead  24  replenishes the inkjet printhead  24 . As ink leaves the reservoir through fluid outlet  36 , air enters through a vent hole  38  to replace a volume of ink and exits the reservoir  34 , thereby preventing the build up of a negative pressure or negative gauge pressure within the reservoir  34 . 
     The method and apparatus of the present invention provides a technique for refilling a wide variety of ink containers  12  without over or under filling the ink container which can lead to a variety of problems previously discussed that can result one or more of the following problems, reduced print quality, damage or reduction in reliability of the printhead  24 , damage or reduction in reliability of the printing system  10 . In addition, the method and apparatus of the present invention fills the ink container  12  from the fluid outlet  36  thereby providing a uniform ink front  62 ,  64  that expands into the capillary storage member  40  displacing air from the fluid outlet  36 . Once the ink container  12  is installed into the printing system  10  ink drawn from the capillary material  40  will tend to have little, if any, air bubbles that are drawn in from the capillary storage material  40 . Filling the ink container  12  in this manner tends to reduce air ingestion by the printing system  10  that tends to increase the reliability of the printing system  10 .