Abstract:
A porous foam based ink containment system is provided with grooves defined in the exterior portion thereof, for storing ink, while preventing ink leakage from the ink-jet pen. The grooves provide passageways to allow air diffused throughout the ink and trapped air bubbles within the foam to expand and move to the atmosphere. An atmospheric vent is in fluid communication with at least one of the grooves.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This is a continuation of application Ser. No. 08/548,568 filed on Oct. 26, 1995, now abandoned which is hereby incorporated by reference herein. 
    
    
     TECHNICAL FIELD 
     The present invention is directed to a foam-based ink containment system for an ink-jet printer. 
     BACKGROUND AND SUMMARY OF THE INVENTION 
     An ink-jet printer includes a pen in which small droplets of ink are formed and ejected from the printer pen toward a printing medium. Such pens include printheads with orifice plates with several very small nozzles through which the ink droplets are ejected. Adjacent to the nozzles are ink chambers, where ink is stored prior to ejection through the nozzle. Ink is delivered to the ink chambers through ink channels in fluid communication with an ink supply. The ink supply may be, for example, contained in a reservoir part of the pen. 
     For color printing, multiple colors are made available to the printer. For each color of ink there is a separate ink reservoir and ink delivery system coupled to a separate group of ink chambers and nozzles. In order to achieve high quality, high-resolution printing, these groups of nozzles are placed relatively close together on the printhead. Control of ink flow is required to prevent excess ink from being delivered to the printhead. Excess ink delivery leads to leakage, or drooling from the nozzles. 
     Ink-jet printer systems are affected by changes in ambient conditions, such as temperature and pressure. When the ambient temperature increases or ambient pressure decreases, air diffused throughout the ink and air bubbles present within the ink reservoir expand to cause displacement of ink. Unless this expansion is managed, the displaced ink is forced out the printhead nozzles resulting in undesired drool. 
     When an inkjet pen drools, one color of ink may migrate across the surface of the printhead to another color group. When ambient temperature or pressure changes, the migrated ink may be sucked back into the nozzles of another color ink. The mixing of these two ink colors causes contamination, producing poor quality printing. 
     Open cell foam is often used to store ink within a reservoir of an ink jet pen. In conventional foam ink storage systems, the top of the reservoir may be vented to ambient to allow equalization of pressure within the ink container to the outside air pressure. However, substantially all of the exterior surfaces of conventional foam ink storage members are in contact with the walls of the pen reservoir. Such contact between ink saturated foam and the reservoir walls creates a seal through which air is unable to pass for venting to atmosphere. When changes in ambient conditions occur to expand air in the reservoir, the expanded trapped air displaces ink and causes drool through the nozzles. 
     To control leakage, extra felting of the foam member has been employed. Felting is a measure of the extent to which foam is compressed. Compressing the foam decreases the pore dimensions. By increasing the felting of the foam (i.e., the amount of compression of the foam), pore size decreases and capillary force increases. A greater capillary force increases back pressure within the reservoir. An increase in back pressure within the reservoir helps to prevent drool. However, extra felting of the foam does not aid removal of air trapped within the foam. Extra felting also reduces the foam&#39;s ink storage capacity. Moreover, extra felting makes manufacturing difficult, as the foam is difficult to insert in the necessarily small reservoir. 
     Grooved reservoir walls have been used to prevent ink drool. The grooves create a series of interconnected channels between the foam member and the reservoir walls. Expanding air from the foam&#39;s interior diffuses into these channels and is vented out of the reservoir. However, the grooved reservoir walls can be difficult to manufacture. Additionally, grooved reservoir walls can make the walls more flexible, and the pressure exerted by the compressed foam can deform the flexible reservoir walls so that the ink-jet pen does not fit properly within the printer. 
     The present invention is directed to a system for storing ink in a pen reservoir, while preventing ink leakage due to a change in ambient temperature or pressure. The system comprises porous grooved foam. The porous foam is grooved on the exterior portion to provide paths for air to move to the atmosphere. Thus, air within the interior portion of the foam may expand to the grooves on the exterior portion. An atmospheric vent is in fluid communication with at least one of the grooves, thereby to vent excess air within the reservoir. The grooved foam may be used in any of a variety of ink-jet pen reservoirs and may be implemented with any foam-based pen. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an ink-jet printer pen constructed in accordance with the invention. 
         FIG. 2  is cross-sectional side view of the apparatus in  FIG. 1  taken along line  2 — 2 . 
         FIG. 3  is an end view of the foam member of the present invention. 
         FIG. 4  is an enlarged partial side view of the foam constructed in accordance with a preferred embodiment of the present invention. 
         FIG. 5  is an enlarged cross-sectional side view of the foam in  FIG. 4  taken along line  5 — 5 . 
         FIG. 6  is an enlarged cross-sectional view of the foam in  FIG. 4  taken along line  6 — 6 . 
         FIG. 7  is a side view of the foam constructed in accordance with another preferred embodiment of the present invention. 
         FIG. 8  is an enlarged cross-sectional view of the foam of  FIG. 7  taken along line  8 — 8 . 
         FIG. 9  is an enlarged cross-sectional view of the foam of  FIG. 7  taken along line  9 — 9 . 
         FIG. 10  is an end view of an alternative version of the foam member of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       FIG. 1  shows a three-color ink-jet cartridge  10  having a box shaped body  12 . A printhead  20  is attached to the bottom of the pen body  12  (FIG.  2 ). The printhead  20  defines three separate sets of print orifices (not shown) that provide apertures for expelling ink in a controlled pattern during printing. The printhead  20  is electronically controlled through a connector circuit  24  mounted on the body  12 . 
     Referring to  FIG. 2 , the body  12  defines three similar sized adjacent ink chambers  26   a ,  26   b ,  26   c , (also referred to herein as reservoirs). On each side of the cartridge  10  there is a side cover  32 ,  34  each of which forms a respective wall of ink chambers  26   a  and  26   c . The pen body  12  includes interior walls  36  and  38 , which partially define ink chamber  26   b  and serve as the interior walls for ink chambers  26   a  and  26   c.    
     Each ink chamber  26   a ,  26   b ,  26   c  is connected to ink outlets  40 ,  42 ,  44 , respectively (FIG.  2 ). Each ink outlet is fluidly coupled to its associated set of print orifices of the printhead  20 . 
     During manufacture, ink is introduced to the ink chambers by way of ink supply apertures  22  ( FIG. 1 ) at the top  28  of the pen body  12 . The supply apertures are plugged after completion of the ink filling process, but not entirely cut-off from atmospheric pressure. An atmospheric vent plug having a small or serpentine opening in it plugs each ink supply aperture to prevent the escape of ink. This type of atmospheric vent allows equalization of air pressure within the ink container to the outside air pressure as ink is ejected from the respective ink chamber. The vent also reduces pressure disequilibrium caused by changes in temperature or air pressure such as might be experienced with weather systems or changes in altitude of the printer itself. 
     Each chamber  26   a ,  26   b ,  26   c , contains a different color ink, for instance, cyan, yellow and magenta. Each chamber is filled with a porous foam sponge  30   a ,  30   b ,  30   c  formed of open cell foam. The porous foam is capable of absorbing and storing liquid ink. In a preferred embodiment, each porous foam member  30   a ,  30   b ,  30   c  extends from the top end  48  of the ink chambers, at which the atmospheric vents (not shown) are located, to the bottom end  50  of the ink chambers (see FIG.  2 ). The foam member  30   a ,  30   b ,  30   c  additionally extends from a front side  16  of the pen body  12  (also referred to as a first end), to a back side  18  of the pen body (also referred to as a second end). 
     The foam members are substantially rectangular in shape (FIG.  7 ). The foam member  30  is oriented within an ink chamber such that a first end  260  is placed at the front side  16  of the ink-jet cartridge  10  and a second end  262  is placed at the back side  18  of the cartridge (FIG.  1 ). 
     The foam is a porous material having an extensive network of pores and capillaries. Ink for use by the printer is stored in the pores and capillaries. The porous foam members  30   a ,  30   b ,  30   c  are placed within the ink chambers  26   a ,  26   b ,  26   c , respectively, and compressed between the walls of the chambers. That is, foam member  30   a  is compressed between the interior of walls  32  and  36 , foam member  30   b  is compressed between the interior of walls  36  and  38  and foam member  30   c  is compressed between the interior of walls  38  and  34 . The foam is compressed to ensure a compact fit (i.e. avoid unintentional air gaps between the foam member and the chamber walls). Additionally, compression of the foam member reduces pore size, which increases the capillary force within the foam. An increase in capillary force within the foam enhances the back pressure within the ink chamber. As used herein, the term “back pressure” means the capillary force within the pen chamber, which resists gravitational force and, hence, resists the flow of ink through the printhead. The back pressure within the ink reservoir or chamber helps to prevent ink leakage from the printhead. 
     Air is present throughout the ink that is stored in the porous foam members  30   a-c . The air is often in the form of bubbles throughout the foam. Increasing ambient temperature or decreasing ambient pressure causes air diffusion from the ink, forming more air bubbles. These air bubbles are typically small and distributed generally uniformly throughout the foam member  30 . However, the overall effect of a large number of such bubbles, especially when subjected to severe variations in ambient temperature or pressure, is for the bubbles to expand and displace an equivalent volume of ink. 
     In conventional foam ink storage systems, substantially all of the exterior surfaces of the foam member are in contact with the interior of the walls of the chamber over substantially the entire area of the walls. The air is trapped because areal contact between the ink saturated foam member and the reservoir wall creates a seal through which air is unable to pass between the foam and walls and escape through the atmospheric vent. If the ink displaced due to increased pressure has no other path to follow, some ink is forced through the printhead orifices, causing undesired printhead drool. 
     Referring to  FIG. 2 , the foam member  30  is not completely filled to the top with ink. The region of foam saturated with ink is known as the “wet zone”  31 . There is a region of foam, nearest the ink supply aperture  22 , that is void of ink due to hydrophobic characteristics of dry foam and the capillary forces of the saturated wet zone. This area is known as a “dry zone”  35  (FIG.  2 ). Between the dry zone  35  and the wet zone  31  is a narrow “damp zone”  33  which is wetted with ink but is not saturated. The damp zone  33  attracts additional ink by capillarity and thus provides back pressure for the pen. 
     During a volumetric change within the pen reservoirs  26   a-c  caused by temperature or pressure changes, the expansion of air within the ink is first accommodated by ink moving into the damp zone  33  of each foam member  30   a-c . Once the damp zone  33  is saturated with ink, back pressure in the reservoir is reduced. Thus, the pen is unable to accommodate any additional air expansion without undesirable ink drool. 
     There are other, less significant damp zones or regions within the foam member but ink is unable to migrate into many of these regions due to air being trapped in such areas. 
     To facilitate the release of air bubbles in the ink, a multitude of channels are defined in the exterior portions of the porous foam member  30 . That is, the walls of the channels are defined by the porous foam member  30 . The foam member, as mentioned, has throughout its entire volume a multitude of pores and capillaries for storing ink. 
     Referring to  FIGS. 2-6 , in a preferred embodiment, a series of channels  154  extend linearly from the first end to the second end of the foam member  30 , also referred to as a first direction (that is, the ends corresponding to the ends  260 ,  262  of the embodiment of FIG.  7 ). When the foam member  30  is inserted in the cartridge, the channels  154  preferably extend at an angle substantially perpendicular to a line between the top  28  and bottom  29  of the cartridge (i.e. horizontally). An angle other than perpendicular is acceptable. For reasons explained next, however, it is preferred that the orientation of the channels  154  do not provide a substantially continuous series of linear passageways or gaps between the top  28  and bottom  29  of the cartridge  10 . 
     During the ink fill process, ink is forced into the porous foam member  30  at a relatively high rate. Approximately 20 grams of ink are forced into the foam member  30  within a period of 1 to 2 seconds. Referring to ink chamber  26   a , for example, any continuous passageway or gap extending to the top  28  of the cartridge  10 , (i.e. extending vertically) between the interior of walls  32  or  36  and the foam member  30   a , can result in ink flowing back through the relatively low fluid resistance of the gap. Thus, under the relatively high pressure exerted during the ink fill process, ink would flow back through these gaps to the top of the pen and out the ink supply apertures  22  rather than appropriately entering and saturating the foam member  30   a.    
     An enlarged cross-section of channels  154 , in a preferred embodiment of the present invention, is illustrated in FIG.  5 . Each channel  154  is semi-circular in shape, with width “w”, at the outermost edge of the channel (the cross-sectional width) being approximately 2.5 mm. A preferred cross-sectional depth “d”, for each channel  154 , is approximately 1.3 mm. In comparison to the channels, the pores and capillaries of the foam member  30  are much smaller in size. The pores and capillaries of the foam member  30  are approximately 0.2 mm in diameter. A preferred, felted, urethane foam has a porosity of approximately 5 pores/mm of foam. 
     Referring again to  FIG. 4 , in a preferred embodiment of the invention, the exterior of the foam member  30  also includes a plurality of grooves  156  which are contiguous communication with one or more channels  154 . The grooves in the embodiments represented by  FIGS. 2-6  are oriented substantially normal to the channels  154 , extending in a second direction. 
       FIG. 6  presents an enlarged cross-section of the grooves  156 . In a preferred embodiment, the groove  156  is semi-circular in shape (i.e. the same shape as channel  154  (FIG.  5 )). A preferred groove cross-sectional width “w 2 ” is approximately 2.3 mm and a preferred cross-sectional depth “d 2 ” is approximately 1.2 mm. 
     The grooves  156  and channels  154  are defined by the porous foam member  30  such that the portions of the foam member between pairs of grooves and channels form equidistantly spaced protuberances  158 . 
     As shown in  FIG. 4 , the protuberances  158  are substantially rectangular in shape, oriented with long axes extending horizontally from the front side  16  to back side  18  of the cartridge  12 . The protuberances  158  are configured in rows, each row offset from the adjacent row of protuberances. The offset row configuration of the embodiment represented in  FIG. 4  result in a linearly discontinuous passageway extending from the bottom  50  to the top  48  of the foam member  30  (FIGS.  1  and  4 ). Thus, there is no linearly continuous passageway or gap between the interior of the walls of the chamber and the foam member  30  when a foam member is inserted within an ink chamber. As discussed above, this is useful for an effective ink filling process. 
     In another preferred embodiment of the present invention, represented in  FIGS. 7-9 , the foam member  130  is substantially rectangular in shape, and includes channels  254 , grooves  256  and protuberances  278 . 
     A series of channels  254  extend linearly from the first end  260  to the second end  262  of the foam member  130  (also referred to as a first direction). When the foam member  130  is inserted in the cartridge, the channels  254  extend substantially normal to a line between the top  28  and bottom  29  of the cartridge (i.e. horizontally). An angle of less than 90° is acceptable. Preferably, however the channels  254  should not provide a substantially continuous series of linear passageways or gaps between the top  28  and bottom  29  of the cartridge  10 . 
       FIG. 8  presents an enlarged cross-section of channels  254 , defined within the foam member  130 . Each channel  254  is defined by a flat base  274  that is about 0.4 mm wide. The walls  270  of each channel  254  diverge from the base  274  at about a 45° angle. In a preferred embodiment, the outermost cross-sectional width “w 3 ” of each channel  254  is approximately 2.4 mm. 
     The foam member  130  includes vertical grooves  256 .  FIG. 9  presents an enlarged cross-section of the groove  256 . The grooves are substantially the same shape as channels  254  (FIG.  8 ). That is, each groove  256  is defined by a flat base  280  that is about 0.4 mm wide. The walls of each groove  256  diverge from the base  280  at approximately a 45° angle. The outermost cross-sectional width “w 4 ” of groove  256  is approximately 2.4 mm, and the cross-sectional depth “d 4 ” of the groove is preferably about 1.0 mm. 
     The foam member  130  also defines rows of protuberances  258 . The grooves  256  are arranged in spaced apart groups so that there are no linearly continuous vertical paths through the rows  258  from the bottom  50  to the top  48  of the foam member  230  (FIG.  7 ). 
     The liquid ink contained by the relatively small capillaries and pores of the foam member will remain within the ink-saturated foam rather than flowing into the relatively larger grooves and channels. In each of the above-described embodiments, the grooves and channels are coupled such that air may move between them. The grooves, which considered together with the channels, form tortuous, fluidly continuous air passageways or gaps which lead to the ink chamber atmospheric vent. 
     In each embodiment of the present invention, the cross-sectional depth and width of the channels and grooves are sufficiently deep and wide, respectively, such that there remain continuous passageways between the walls of the chamber and the foam member when the foam is compressed. The effect of this fluid communication allows trapped and expanding air within the ink-saturated foam and within the chamber itself to escape through, the passageways to the vent, when the ambient pressure or temperature change. 
     Another effect of the present invention is that the grooved surface portion of the foam member adjacent to the foam wet zone may serve as a “damp zone.” Thus, ink can move into this region when air within the foam expands since air that occupied the region is now able to escape through the fluidly continuous air passageways. This increased damp zone greatly enhances the cartridges ability to tolerate ambient condition changes of a severity such that the foams capillarity may be temporarily overcome. 
     In another preferred embodiment, three pieces of porous foam are laminated together in a sandwich-type configuration (FIG.  10 ). The interior portion of foam  310  possesses a substantially smaller porosity than the porosity of the exterior portions of foam  320 ,  330 . When the foam is saturated with ink, ink is drawn to the smaller pores and capillaries of the interior portion of foam. 
     Preferably, the pores (and capillaries) of the interior foam member are approximately 0.2 mm in diameter, while the pores of the two exterior foam members are about 1 mm in diameter. Stated another way, a preferred, felted, polyurethane interior foam member will have about 5 pores/mm of foam, and the exterior foam members have about 1 pores/mm. With a large foam pore size difference, ink will not occupy the exterior portion of the foam member  30   a-c  until the interior is saturated. 
     The unsaturated outer layers of foam provide at least one fluidly continuous air passageway. Thus, as the ambient temperature or pressure changes, trapped and expanding air within the ink saturated interior foam, and the chamber itself, can escape through these passages to atmosphere. Such a preferred embodiment also transforms the entire border of the inner and outer layers of foam into a “damp zone” in which ink can migrate during such volumetric challenges. 
     Having illustrated and described the principles of the invention, it should be apparent to those persons skilled in the art that the illustrated embodiments may be modified without departing from such principles. We claim as our invention all such embodiments that may come within the scope and spirit of the following claims and equivalents thereto.