Patent Abstract:
An inkjet assembly comprising a vented ink reservoir for containing a liquid ink therein, the vented ink reservoir defining an internal volume occupied at least in part by a semipermeable membrane in fluid communication with a vent that automatically adjusts for pressure differentials by enabling gaseous diffusion between an environment external to the vented ink reservoir and the internal volume of the vented ink reservoir, while inhibiting liquid diffusion therethrough. A method is also disclosed for mounting the semipermeable membrane to at least one of an ink reservoir cap and an ink tank.

Full Description:
BACKGROUND 
   1. Field of the Invention 
   The present invention is directed to a vented ink reservoir for facilitating gaseous communication between an interior of an ink reservoir and an external environment; and, more particularly to a vented ink reservoir utilizing a semipermeable membrane to enable the ingress and/or egress of gas with respect to an interior volume of the ink reservoir, where the ink reservoir includes a backpressure regulator housed therein that prevents weeping from one or more printhead nozzles in fluid communication therewith. 
   2. Background of the Invention 
   Inkjet pens consist of a jetting structure and an ink containing structure. These structures can be combined into a single integrated cartridge, or separated into tanks and printheads. In either situation, the ink that is fed to the jetting structure must be kept at a negative pressure with respect to pressure outside the pen to prevent the ink from running out of the pen due to gravity, also known as weeping. 
   Several methods are known for the control of this negative pressure, also known as “backpressure”. In some inkjet structures the backpressure is provided by capillary action from a foam sponge, while other structures seal up the system and use a regulation device or a bubble-generating device to allow air to replace spent ink within the system while maintaining a reasonable range of backpressures. Still further systems are sealed off and start at a moderate backpressure and increase in backpressure until the jetting device can no longer pull ink from the reservoir. 
   Prior art techniques have attempted to control backpressure by providing a collapsible bag acting as the reservoir. The volume of the bag decreases in proportion to the volume of ink leaving the reservoir. However, these collapsible bags require multiple seals and have been found to be problematic to fabricate. 
   SUMMARY OF THE INVENTION 
   The present invention is directed to a semipermeable membrane operatively coupled to an ink reservoir vent that allows gaseous communication between an external atmosphere and an interior of the ink reservoir. The semipermeable membrane inhibits liquid ink from passing therethrough, but enables the ingress or egress of gas to provide a venting function. 
   In an exemplary embodiment, the present invention is teamed with an internal backpressure regulator. The backpressure regulator is submerged within the reservoir and relies, at least in part, upon the pressure differential between the exterior and interior of the regulator for normal operation. The invention allows the ingress of gas into and the egress of gas out of the ink reservoir to approximate equalization of the pressure between the interior of the reservoir and the exterior environment to maintain a sufficient gradient between the inside and outside of the regulator. A more detailed explanation of the backpressure regulator can be found in co-pending U.S. patent application Ser. No. 10/465,403, the disclosure of which is hereby incorporated by reference. 
   It is a first aspect of the present invention to provide an inkjet assembly that includes a vented ink reservoir for containing a liquid ink therein, where the vented ink reservoir defines an internal volume occupied at least in part by a semipermeable membrane in fluid communication with a vent that automatically adjusts for pressure differentials by enabling gaseous diffusion between an environment external to the vented ink reservoir and the internal volume of the vented ink reservoir, while inhibiting liquid diffusion therethrough. 
   In a more detailed embodiment of the first aspect, at least a portion of the semipermeable membrane is adapted to be above a highest level of the liquid ink within the internal volume of the vented ink reservoir. In another more detailed embodiment, the semipermeable membrane is operatively coupled to the ink reservoir by impulse sealing. In yet another more detailed embodiment, the semipermeable membrane includes polytetrafluoroethylene. In a further detailed embodiment, the semipermeable membrane defines a non-circular gaseous throughput. In yet a further more detailed embodiment, the semipermeable membrane is angled with respect to a level of ink within the ink reservoir. In another detailed embodiment, the semipermeable membrane includes a cross-sectional area for gaseous throughput ranging from between about 0.5 cm 2  to about 6 cm 2 . In yet another more detailed embodiment, the vented ink reservoir includes a cap mounted to a tank, and the semipermeable membrane is mounted to the cap. In still a further more detailed embodiment, the cap includes a raised hump providing a space adapted to trap gas therein above a highest level of liquid ink within the vented ink reservoir, and at least a portion of the semipermeable membrane extends into the space provided by the raised hump. 
   In a more detailed embodiment of the first aspect, a bottom surface of the cap partially defining the internal volume includes a downwardly extending closed wall seating the semipermeable membrane thereto to define a gaseous cavity within the internal volume. In a further detailed embodiment, a bottom surface of the cap includes a downwardly extending closed wall to which the semipermeable membrane is mounted thereto to define a gaseous cavity within the internal volume, and a top surface of the cap includes a humped portion corresponding to a raised space within the bottom surface of the cap adapted to be occupied by a trapped gas, where at least a portion of the semipermeable membrane is in gaseous communication with the trapped gas. In yet a further detailed embodiment, the gaseous cavity formed by the downwardly extending closed wall occupies a portion of the raised space. In a more detailed embodiment, the cap includes an ink inlet adapted to be in fluid communication with the internal volume of the vented ink reservoir. In another more detailed embodiment, the cap includes a serpentine tunnel extending therealong in fluid communication with the vent. 
   It is a second aspect of the present invention to provide a method of regulating the pressure between an interior volume of an ink container and an external environment, where the method includes the steps of: (a) positioning a semipermeable membrane within an ink container, where the semipermeable membrane includes a first surface in fluid communication with an interior volume of the ink container and an opposing surface in fluid communication with an external environment; (b) mounting the semipermeable membrane to the ink container; and (c) regulating a pressure differential between the interior volume and the external environment automatically and concurrently by facilitating gaseous diffusion and inhibiting liquid diffusion across the semipermeable membrane. 
   In a more detailed embodiment of the second aspect, the interior volume is occupied by, at least in part, a liquid ink, and at least a portion of the semipermeable membrane is positioned above a highest level of the liquid ink within the interior volume. In another more detailed embodiment, the interior volume is occupied by, at least in part, a liquid ink, and the semipermeable membrane is angled with respect to a level of the liquid ink within the interior volume. In yet another more detailed embodiment, the semipermeable membrane is operative to facilitate gaseous diffusion while the first surface is in concurrent fluid communication with a liquid ink and a gas. In a more detailed embodiment, a surface area available for gaseous diffusion through the semipermeable membrane is non-circular. In a further detailed embodiment, an additional step of reducing an amount of ink vapor leaving the interior volume of the ink container by reducing a volumetric flow of gas passing in proximity to the opposing surface of the semipermeable membrane is provided. In still a further more detailed embodiment, the regulating step includes providing a serpentine passageway for gaseous travel, wherein the serpentine passageway includes a first end terminating approximate the opposing surface of the semipermeable membrane and a second end terminating approximate the external environment. In yet a further more detailed embodiment, the semipermeable membrane includes polytetrafluoroethylene. In yet another detailed embodiment, the semipermeable membrane includes a cross sectional area for gaseous exchange ranging from about 0.5 cm 2  to about 6 cm 2 . In even a further detailed embodiment, the mounting step includes the step of sealing the semipermeable membrane to the ink container by impulse sealing. 
   It is a third aspect of the present invention to provide a method of mounting a porous substrate, concurrently inhibiting liquid diffusion therethrough and enabling gaseous diffusion therethrough, to a nonporous substrate concurrently inhibiting gaseous and liquid diffusion therethrough, where the method includes the steps of: (a) positioning a porous substrate adjacent to a nonporous substrate; (b) moving a pressure source adjacent to the porous substrate to sandwich the porous substrate between the pressure source and the nonporous substrate; (c) applying thermal energy in a pulse adjacent to the porous substrate to melt a portion of the nonporous substrate; and (d) removing the thermal energy source to solidify the portion of the nonporous substrate, interlocking the porous substrate and nonporous substrate to inhibit fluid communication therebetween, where the porous substrate facilitates gaseous diffusion therethrough, but inhibits liquid diffusion therethrough. 
   It is a fourth aspect of the present invention to provide an ink reservoir cap adapted to be mounted to an ink tank to provide a vented ink reservoir automatically regulating the internal pressure therein, where the ink reservoir cap includes a cap body adapted to be mounted to an ink tank to provide a vented ink reservoir, the cap body and ink tank define an interior volume available for ink occupation with the cap body seating a semipermeable membrane over a vent extending therethrough, where the membrane is housed within the interior volume to provide gaseous communication, but restrict liquid communication, between an external environment and the interior volume of the vented ink reservoir. 
   In a more detailed embodiment of the fourth aspect, the cap body further includes a filler conduit adapted provide fluid communication between an ink source and the interior volume of the vented ink reservoir. In another more detailed embodiment, the cap body further includes a raised space in fluid communication with the semipermeable membrane, the raised space adapted to trap a volume of gas above a highest level of liquid ink within the vented ink reservoir. In a more detailed embodiment, at least a portion of the semipermeable membrane is adapted to be in gaseous communication with gas within the raised space. In a further detailed embodiment, the cap body further includes a plurality of alignment pins adapted to align the cap body with respect to the ink tank prior to mounting the cap body onto the ink tank. In still a further more detailed embodiment, the cap body and the ink tank include a channel and a corresponding rib adapted to interact with the channel to provide an interface adapted to be fluidically sealed and provide a vented ink reservoir. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an exploded view of a vented ink reservoir in accordance with a first exemplary embodiment of the present invention; 
       FIG. 2  is a cross-sectional view of the vented ink reservoir of the first exemplary embodiment of the present invention; 
       FIG. 3  is an elevated, perspective view of the top of an ink reservoir cap in accordance with a second exemplary embodiment of the present invention; 
       FIG. 4  is a bottom view of the ink reservoir cap of  FIG. 3 ; and 
       FIG. 5  is a bottom, perspective view of the ink reservoir cap of  FIG. 3 . 
   

   DETAILED DESCRIPTION 
   The exemplary embodiments of the present invention are described and illustrated below as ink cartridges (reservoirs) utilizing at least one semipermeable membrane to regulate the volumetric flow of gas between an interior of an ink cartridge and an exterior environment. The various orientational, positional, and reference terms used to describe the elements of the inventions are therefore used according to this frame of reference. However, for clarity and precision, only a single orientational or positional reference will be utilized; and, therefore it will be understood that the positional and orientational terms used to describe the elements of the exemplary embodiments of the present invention are only used to describe the elements in relation to one another. 
   Referring to  FIGS. 1–2 , a first exemplary embodiment includes an ink reservoir cap  10  mounted to an ink tank  12  to provide a partially sealed ink reservoir  14  having an interior volume  16  available for holding liquid ink. A raised rib  18  running about the perimeter of a top surface  20  of the upper opening of the tank  12  is adapted to provide a seat for, and be received within, a complementary channel  22  extending along an underneath surface  24  of the cap  10 . An alignment pin  26  extending downwardly from the cap  10  is adapted to be received within a socket  28  concurrently as the raised rib  18  is received within the channel  22 . The cap  10  is mounted to the tank  12  by sealing an interface  30  between the rib  18  and the channel  22  using a conventional technique after the cap  10  has been aligned and seated upon the tank  12  as discussed above. Such conventional techniques are known by those of ordinary skill and include, without limitation, adhesive, laser welding, and vibration welding. 
   Referencing  FIG. 2 , a closed wall  32  extends from the underneath surface  24  of the cap  10  that partially defines a gaseous cavity  34  in gaseous communication with an external environment  36 . A bottom surface  38  of the closed wall  32 , opposite the surface  24 , is beveled uniformly along a plane to provide a planar surface onto which a semipermeable membrane  40  is mounted thereto. In the present exemplary embodiment, the semipermeable membrane  40  is a solid rectangle that overlies the oblong shaped, closed wall  32  completely covering over the entire exposed area to partially define the gaseous cavity  34 . To bond the membrane  40  thereto, an impulse sealing electrode is aligned with the bottom surface  38  of the closed wall  32  and sandwiches the membrane  40  therebetween. Thereafter, an electric current is applied for a fraction of a second to the impulse sealing electrode causing material at the bottom surface  38  to become viscous. In this viscous state, the material at the bottom surface  38  bonds to the membrane  40 , resulting in a liquid-tight seal between the closed wall  32  and the membrane  40 . Those of ordinary skill are familiar with other methods may be utilized to mount the membrane  40  to the closed wall  32  such as, without limitation, press fitting and insert molding. 
   The cap  10  includes a humped portion  41  adjacent to the cavity  34  to provide a raised space  42  within the interior volume  16  of the reservoir  14 . In the present embodiment, the gaseous cavity  34  extends partially within the space  42 . The cap  10  also includes an inlet orifice  46  to facilitate filling/refilling the reservoir with ink. The space  42 , as shown in  FIG. 2 , provides a step-up in height (with respect to the inlet orifice  46 ) that ensures that some gas will remain within the reservoir  14  and in communication with gas within the gaseous cavity  34  by way of the semipermeable membrane  40  when the ink is at its highest level. In the orientation shown in  FIG. 2 , ink would spill out of an inlet orifice  46  (presuming no plug was inserted therein) before displacing the volume of gas occupying the space  42 . Because the gaseous cavity  34  extends at least partially within the raised space  42 , at least a portion of the membrane  40  will be exposed to gas occupying the reservoir  14  even when the ink is “full”. As the level of ink within the reservoir  14  drops from usage, a larger and larger area of the membrane  40  becomes exposed for gaseous transfer between the interior  16  of the reservoir  14  and the gaseous cavity  34 . Eventually, the entire membrane  40  is exposed for gaseous transfer between the cavity  34  and the interior  16  of the reservoir  14 . 
   A cylindrical venting conduit  48  is provided through the cap  10  and includes an opening  50  in direct communication with the gaseous cavity  34  and in fluid communication with the external environment  36  by way of a tunnel  54 . The tunnel  54  comprises a trench  56  originating at the cylindrical conduit  48  and traveling in a serpentine pattern within a top surface  62  of the cap  10 . The trench  56  is covered by a secondary structure  52  that provides an outlet  58  to the external environment  36  opposite the cylindrical conduit  48 . Exemplary secondary structures  52  include flat panels, flat panels having a corresponding trench formed therein, and corresponding concave structures operatively coupled to the cap  10  by an amendable process known to those of ordinary skill in the art. 
   After the cap  10  is mounted to the tank  12 , the reservoir  14  is filled with ink via the inlet orifice  46 . The inlet orifice  46  is in fluid communication with a first cylindrical conduit  64  extending down from the cap  10  into the interior  16  of the reservoir  14 , which transitions into a second cylindrical orifice  70  in direct fluid communication with the interior  16  of the ink reservoir  14 . A plug (not shown) is positioned within the first cylindrical conduit  64  after an appropriate volume of ink has been added to the reservoir  14  to seal the inlet orifice  46 . An appropriate volume of ink includes an amount of ink raising the level of ink within the reservoir  14  to abut the orifice  70 . 
   The inflow of ink into the reservoir  14  submerges an internal backpressure regulator  74  in fluid communication with a printhead  76 . The backpressure regulator  74  regulates the volume of ink passing between the reservoir  14  and the printhead  76  to prevent weeping when printing operations are no longer desired. The regulator  74  includes an inlet  78  that provides selective fluid communication between an interior  80  of the regulator  74  and the reservoir  14 . The ink stream flows through the regulator  74 , through an ink filter cap  82 , through an ink filter  84 , and is eventually delivered to a plurality of nozzles  86  on the face of the printhead  76 . The exterior of the backpressure regulator  74  is fully submerged when the ink reservoir  14  is full, and becomes partially submerged as ink within the reservoir  14  is consumed below a certain point. For a more detailed discussion of the operation of the backpressure regulator  74 , see co-pending U.S. patent application Ser. No. 10/465,403. 
   In a completely sealed reservoir, ink leaving the reservoir would decrease the internal pressure of the reservoir, as the internal volume of the reservoir remains the same, but the volume of ink within the reservoir has decreased. This gradual decrease in internal pressure within the reservoir decreases the pressure differential between the exterior of the regulator  74  and the interior  80  of the regulator. It is preferred to maintain this pressure differential between the exterior of the regulator  74  and the interior  80  of the regulator by enabling gaseous diffusion between the interior volume  16  and the external environment  36 . 
   The membrane  40  in accordance with the present invention allows gas to flow between the exterior environment  36  and the interior  16  of the reservoir  14  by way of the cylindrical venting conduit  48 , but substantially inhibits liquid (ink) from passing therethrough. Accordingly, the semipermeable membrane  40  may be a material having very small pores selectively allowing gas to flow therethrough, but inhibiting a liquid from passing therethrough. At extremely high pressure levels a liquid might be forced through the pores of the membrane  40 , but such pressures are seldom seen during normal printhead operation. The semipermeable membrane  40  may comprise a single material or a composite material and may also include multiple layers of a unitary or composite material. An exemplary material comprising the semipermeable membrane  40  in accordance with the present invention is a single layer polytetrafluoroethylene (PTFE) membrane from W. L. Gore &amp; Associates (www.gore.com). 
   As with any porous material, there is a pressure drop associated with gas passing through the membrane  40 . Several factors may be considered to minimize the effect of this pressure drop on the backpressure regulator  74 . The area of the membrane  40  available for gaseous transfer is partially determinative of the volumetric flow of gas that can pass through the membrane  40  at a given pressure. To reduce production costs, however, it is desired that the area of the membrane  40  be relatively small. Thus, an optimization of this area accounts for productions costs versus the maximum potential volumetric flow rate of gas during normal operation of the printhead  76 . 
   An additional factor that may be considered is the shape of the membrane  40  exposed to the ink. The pressure drop may increase across the membrane  40  as the exposure to ink is increased. The shape of the membrane may determine, in part, how quickly the membrane  40  recovers from being directly exposed to ink and provides gaseous communication through those areas. A circular shaped membrane  40  may not be optimal as a single spherical bubble of ink might block the path of gas through the entire membrane  40 . The potential for the natural, spherical shape of the bubble to completely block the membrane becomes less likely as the shape of the membrane  40  deviates from being circular. 
   Referencing  FIGS. 3–5 , a second exemplary ink reservoir cap  90  is shown that is adapted to be mounted to a corresponding structure, such as an ink tank, to provide a vented ink reservoir (similar to the embodiment shown in  FIGS. 1 and 2 ). The ink reservoir cap  90  includes an ink inlet  92  and a serpentine channel  98 , adjacent to the ink inlet  92 , having a vent hole  100  at a first end, while a second end terminates on the top surface  94  of the cap  90 . The cap  90  is attached to the reservoir and includes a channel  98  adapted to be covered to create a serpentine tunnel venting to the external environment. A humped portion  106  of the cap  90  creates a space  108  that is above the top surface  94 . The humped portion  106  includes a planar, U-shaped top surface  110  being joined by eight side surfaces beveled at the adjoining ends. 
   Referencing  FIGS. 4 and 5 , the bottom surface  96  includes a plurality of alignment posts  112  that are utilized to align the ink reservoir cap  90  onto the corresponding structure to provide an ink reservoir. A lip  114  protrudes from the bottom surface  96  to form a rectangular rib surrounding and abutting the alignment posts  112  that is adapted to be received by an interior wall of the corresponding structure. 
   A nodule  116  inside of the lip  114  includes a cylindrical wall  118  transitioning into a domed shaped end  120  in fluid communication with the ink inlet  92 . Adjacent to the nodule  116  is a continuous oval shaped wall  122  defining a cavity  124  adapted to be fluidically sealed by a semipermeable membrane (not shown) and provide a gaseous area. The top surface  126  of the wall is angled uniformly to receive the semipermeable membrane mounted thereto to inhibit liquid from entering the cavity  124 . 
   A portion  128  of the cavity  124  opposite the nodule  116  is located within the elevated space  108 . The space  108  is adapted to trap a minimum amount of gas within the reservoir when the reservoir is filled with ink to ensure that at least the portion of the cavity  124  is in gaseous communication with such trapped gas. If the pressure within the vented reservoir were to increase above that of the external environment, a percentage of the trapped gas would pass through the semipermeable membrane, into the cavity  124 , through the vent hole  100 , through the serpentine tunnel and into gaseous communication with an external environment. An opposite process would take place if the pressure within the vented reservoir were to decrease with respect to the external environment. 
   Following from the above description and invention summaries, it should be apparent to those of ordinary skill in the art that, while the methods and apparatuses herein described constitute exemplary embodiments of the present invention, the inventions contained herein are not limited to these precise embodiments and that changes may be made to them without departing from the scope of the invention as defined by the claims. Additionally, it is to be understood that the invention is defined by the claims and it is not intended that any limitations or elements describing the exemplary embodiments set forth herein are to be incorporated into the meanings of the claims unless such limitations or elements are explicitly recited in the claims. Likewise, it is to be understood that it is not necessary to meet any or all of the identified advantages or objects of the invention disclosed herein in order to fall within the scope of any claim, since the invention is defined by the claims and since inherent and/or unforeseen advantages of the present invention may exist even though they may not have been explicitly discussed herein.

Technology Classification (CPC): 1