Abstract:
In one embodiment, a printhead assembly includes: an ink reservoir; a printhead; a passage for carrying ink from the ink reservoir to the printhead; and a port from the passage to a source of air pressure. The port is operable between a closed position in which the passage is not pressurized with air and an open position in which the passage is exposed to pressurized air. In another embodiment, an ink supply includes: a reservoir for holding ink; a printhead; a standpipe connecting the reservoir and the printhead such that ink may flow from the reservoir to the printhead through the standpipe; and a valve operatively connected to the standpipe. The valve is operative between a first position in which the standpipe is pressurized with air and a second position in which of the standpipe is not pressurized with air.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This is a continuation of application Ser. No. 11/040,601 filed Jan. 21, 2005 now U.S. Pat. No. 7,296,881, titled Printhead Evacuation Mechanism And Method. Priority is claimed under 35 U.S.C. §120. 

   TECHNICAL FIELD 
   The present invention relates generally to methods and mechanisms for preventing failures in an inkjet print cartridge. More specifically, the present invention relates to a venting mechanism used to prepare inkjet print cartridges for periods of inactivity. 
   BACKGROUND 
   Inkjet print cartridges typically use inks that include a volatile solvent such as alcohol and/or water. Where inkjet print cartridges remain inactive for long periods, as when the print cartridge is in transit to an end user, is in storage, or where the printer in which the print cartridge is installed is not used for long periods, the solvents in the inks will begin to evaporate. This evaporation is especially problematic in the area of the nozzles of the print cartridge as the evaporating solvents leave behind solid deposits of pigments and the like that can occlude the nozzles, thereby rending the print cartridge inoperative and/or can reduce the print quality thereof. 
   Many steps have been taken to prevent the evaporation of ink solvents from a print cartridge, with the aim of preventing occlusions of the print cartridge nozzle. One solution has been to apply tape over the print cartridge nozzles. While this solution does reduce evaporation of solvents from the ink in the print cartridge, it does not prevent all such evaporation. Furthermore, the use of tape over the nozzles of the printhead is typically useful only prior to the installation of the print cartridge in a printer; a user cannot easily reapply tape over the nozzles of the print cartridge. 
   Another solution is to provide a pumping mechanism that can remove ink from the print cartridge, or at least from the region of the print cartridge adjacent the nozzles thereof; the idea being that where there is no ink, there can be no evaporation and the incidence of occlusions will decrease. However, such systems are complicated and in any case, it has been difficult to remove all ink from the region of the print cartridge adjacent to the nozzles thereof. 
   Accordingly, there is a need for a method and a mechanism that will facilitate the removal of ink from the region of a print cartridge adjacent to the nozzles thereof where the print cartridge will remain inactive for a time. In addition, there is a need for a mechanism that can prime a print cartridge in which ink has been removed from the region of the print cartridge adjacent the nozzles so that the print cartridge may begin or resume printing. 

   
     DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic cross section view of a print cartridge that incorporates one embodiment of a venting mechanism and an embodiment of an ink supply system; 
       FIG. 2  is a schematic cross section view of a print cartridge that has associated therewith an ink supply system and a vent according to an embodiment of the present invention; 
       FIG. 3  is a flow chart illustrating exemplary steps in a de-priming process according to one embodiment; 
       FIG. 4  is a flow chart illustrating exemplary steps in a de-priming process according to another embodiment; and, 
       FIG. 5  is a flow chart illustrating exemplary steps in a priming process used to prepare a de-primed print cartridge for printing according to an embodiment of the present invention. 
   

   DETAILED DESCRIPTION 
   In the following detailed description of the invention, reference is made to the accompanying drawings that form a part hereof and in which is shown, by way of illustration, specific embodiments in which the invention may be practiced. In the drawings, like numerals describe substantially similar components throughout the several views. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. Other embodiments may be utilized and structural, logical, and electrical changes may be made without departing from the scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims and equivalents thereof. 
     FIG. 1  illustrates schematically one embodiment of a print cartridge  10 . Print cartridge  10  has one or more reservoirs  12  that are fluidically coupled to a standpipe  14  by coupling  16 . Standpipe  14  has a printhead  18  that is adapted for dispensing ink from the standpipe  14  in an inkjet printing process of a type known in the art. As ink is expelled from one or more nozzles  17  the printhead  18 , a vacuum is generated in the standpipe  14  that acts to draw ink from reservoir  12  into the standpipe  14  through coupling  16 . As used herein, the term vacuum pressure is used to designate a reduced pressure that is generally lower than a reference pressure, which in one embodiment is atmospheric pressure, and in another embodiment is a source of pressurized air or other fluids. 
   In one embodiment, coupling  16  is a passage or conduit having a check valve or filter installed therein for controlling the flow of ink from reservoir  12  to standpipe  14 . That is, a vacuum within the standpipe  14  will act to draw ink through the coupling  16 . However, absent a sufficiently large pressure differential, ink will not generally flow freely through the coupling  16  from the reservoir to the standpipe  14 , though a nominal amount of ink may continue to flow. In one embodiment, the check valve will be selected such that the surface tension of ink and its solvents on the check valve will prevent the flow of ink therethrough where there is air or another similar fluid present on one side of the check valve, such as where all ink has been removed from the standpipe  14  and the standpipe  14  contains only air. 
   As ink is drawn from the reservoir  12  and into standpipe  14 , a vacuum is generated within the reservoir  12 . In one embodiment, the vacuum in reservoir  12  acts to draw additional ink from an auxiliary or supplemental reservoir  24  that is fluidically connected to the reservoir  12  by conduit  22 . In another embodiment, a pumping mechanism  20  actively pumps ink from reservoir  24  into reservoir  12  to replenish the ink ejected by the printhead  18 . Pumping mechanism  20  includes a motor  26  that is coupled to a pump  28 . The pumping mechanism  20  may be manually actuated when the print cartridge  10  is determined to be out of ink or when it is determined that the level of ink in the reservoir  12  is below a predetermined minimum. Alternatively, the vacuum in the reservoir  12  may be sensed by a sensor (not shown) whose output actuates the pumping mechanism  20 . 
   Where a print cartridge  10  is to remain unused for an extended period of time, the print cartridge  10  may be de-primed, i.e. ink may be removed from the standpipe  14  and the printhead  18  to prevent the clogging of the nozzles  17  of the printhead  18  and subsequent malfunctions of the print cartridge  10  that may arise therefrom. The print cartridge  10  is de-primed by coupling the standpipe  14  to pressures higher than those present in the reservoir  12 . In one embodiment, a snorkel  30  is fluidically coupled to standpipe  14  by a conduit  32 . Snorkel  30  is in turn fluidically coupled to a valve mechanism  34  by conduit  36 . The valve mechanism  34  is adapted to selectively connect the snorkel  30  to atmospheric air, which is at a generally higher pressure than the vacuum within the reservoir  12  and standpipe  14 . Alternatively, the valve mechanism  34  may connect the snorkel  30  to a source of high-pressure air  13 . 
   As described above, the act of ejecting ink from the printhead  18  during printing generates a vacuum within the volume of the standpipe  14 . This vacuum in turn draws ink from the reservoir  12  into the standpipe  14 , thereby giving rise to a vacuum within the reservoir  12 . Introducing to the standpipe  14  a higher pressure by coupling the snorkel  30  to the atmosphere or to a source of higher pressure creates a pressure differential that acts to force ink from the standpipe  14  through the conduit  16  and back into the reservoir  12 . When the air or other gas introduced into the standpipe  14  contacts the check valve or filter, ink is substantially prevented from flowing into the standpipe  14  from the reservoir  12 . 
   In one embodiment, a wiper  36  may be simultaneously employed to prevent clogging of the nozzles  17  of the printhead  18 . Wiper  36  moves laterally with respect to the print cartridge  10  such that the tips  38  of the wiper  36  are drawn across the surface of the printhead  18 . The wiping action of the tips  38  against the printhead  18  acts to remove excess liquid ink and/or accretions formed around or in the nozzles  17  of the printhead  18 . In another embodiment, the wiper  36  may be provided with a wick  40  that dispenses a non-volatile material that, when applied to the printhead  18 , prevents ink in the nozzles  17  from drying out and also prevents the ingress of air into the print cartridge  10  through the printhead  18 . As wiper  36  moves laterally, the tips  38  of the wiper  36  are drawn across the wick  40  and a small amount of the non-volatile material is deposited thereon. The non-volatile material is then applied to the printhead  18  by the tips  38  of the wiper  36 . In one embodiment, the non-volatile material remains relatively viscous and does not cure or harden to any significant degree. In this manner, re-priming of the print cartridge  10  is not impeded by accretions of the non-volatile material within the nozzles  17  of the printhead. 
   Re-priming of the print cartridge  10  in preparation for printing operations after a period of inactivity involves filling the standpipe  14  with ink. In one embodiment, the pumping mechanism  20  is activated to pump ink into the reservoir  12  under sufficient pressure to force ink through conduit  16  and into the standpipe  14 . Alternatively, the valve mechanism  34  may be actuated to couple the supplemental reservoir  24  directly to the standpipe  14  such that the pumping mechanism  20  can pump ink directly into the standpipe  14  as through conduit  36 . In another embodiment, the pumping mechanism  20  may be coupled to the snorkel  30 . Thereafter, ink and/or air within the snorkel  30  and standpipe  14  is withdrawn by the pumping mechanism  20  to generate a vacuum therein, thereby drawing ink into the standpipe  14  from the reservoir  12  for printing. 
   In addition to priming and de-priming the print cartridge, the supplemental reservoir  24  and pumping mechanism  20 , may also be used to supply ink to one or more print cartridges  10  to replenish the reservoir  12  during printing. 
     FIG. 2  illustrates a close-up cross-sectional view of an exemplary printhead assembly  100  according to the present invention.  FIG. 2  shows only the components corresponding to a single reservoir  102  for a single color, though it is understood that printhead assembly  100  may be adapted to include multiple reservoirs, one for each color printable by a printing system. Conduit  104  is connected to printhead inlet port  106  to provide fluid communication between the off-axis ink supply container  108  and the printhead assembly  100 . Inlet port  106  may have a valve mechanism (not shown) associated therewith to control the flow of ink from an off-axis ink supply container  108  to the reservoir  102 . Ink flows into reservoir  102  through fluid channel  110  from conduit  104 . 
   In one embodiment, reservoir  102  includes an accumulator bag  112  and spring  114  along with a bubbler  116  to maintain a slight negative pressure in the reservoir  102 , as is known in the art. Where ink and/or air is withdrawn from the reservoir  102  through port  106 , the accumulator bag  112  expands by drawing air through port  111 . Spring  114  and bubbler  116  cooperate to ensure that as ink and/or air is withdrawn from reservoir  102 , the accumulator bag  112  does not over inflate. Spring  114  resists pressure from the accumulator bag  112  as it inflates. Bubbler  116  includes a diaphragm or valve element that allows air to enter the reservoir  102  from the exterior, thereby limiting the reduction of pressure within the reservoir  102  to a predetermined level. 
   A particle filter  118  separates the reservoir  102  from the lower body portion  120  of the print head assembly  100 . As needed, ink may flow through particle filter  118  into inlet channel  122  and ultimately into plenum or standpipe  124 , which resides directly above a slot (not shown). The slot ultimately feeds a thermal printing device (not shown), which ejects ink through nozzles  125  disposed in the bottom side  126  of the lower body portion  120  of the printhead assembly  100 , according to methods known in the art. The standpipe  124  is also fluidically connected to a port  128  via a flow path, which is shown in  FIG. 2  as having a channel  130 , a conduit  132  and an outlet  134 . Channel  130 , conduit  132  and outlet  134  may all be generically and collectively referred to herein as a snorkel. 
   In one embodiment, ports  106  and  128  are fluidically connected to valve mechanism  140  by conduits  104  and  142 , respectively. Note that in other embodiments, ports  106  and  128  may be connected to separate valve mechanisms or the like. Valve mechanism  140  is adapted to selectively couple the off-axis ink supply container  108  to the reservoir  102 . In addition, the valve mechanism  140  may couple the snorkel to the atmosphere or to a supply of relatively high pressure air  141 . In another embodiment, valve mechanism  140  may include multiple valves connected to one another to effect the various connections described herein in a manner known to those skilled in the art. Coupled between the valve mechanism  140  and the off-axis ink supply container  108  is a pumping mechanism  146  that includes a pump  148  that is powered by motor  150 . In another embodiment, pumping mechanism  146  may be omitted in favor of a gravity flow or vacuum operated system. The printhead assembly  100  may optionally be provided with a wiper  160  and wick  162  that function as described in conjunction with  FIG. 1 . 
   Where there exists a vacuum within the reservoir  102 , inlet channel  122 , and standpipe  124 , or where there exists a source of pressure higher than that within the reservoir  102 , inlet channel  122 , and standpipe  124 , de-priming the printhead assembly  100  involves actuating valve mechanism  140  to couple the snorkel to atmospheric air or to a supply of air at a pressure greater than that present in the reservoir  102 , inlet channel  122  and standpipe  124 . This is shown in  FIG. 3  at  200 . The relatively higher pressure introduced into the snorkel through port  128  forces ink within the snorkel, standpipe  124 , and inlet channel  122  back into the reservoir  102  through particle filter  118 . When air contacts the particle filter  118 , the surface tension of ink in the particle filter  118  is sufficient to substantially prevent the flow of air therethrough and is further able to substantially prevent the flow of ink from the reservoir  102  back into the inlet channel  122 . 
   Where the pressure within the reservoir  102  and the lower body portion  120  is higher than or substantially the same as atmospheric pressure, the process of de-priming the printhead assembly  100  involves a first step of actuating the valve mechanism  140  to couple the reservoir  102  to the pumping mechanism  146  as shown at  300  in  FIG. 4 . Pumping mechanism  146  is then actuated to withdrawn ink and/or air from the reservoir  102 , thereby creating a relatively low pressure or vacuum within the reservoir  102  as at  302 . Once there is a relatively low pressure within the reservoir  102 , pumping mechanism  146  is shut down ( 304 ) and the valve mechanism  140  is actuated to break the connection between the reservoir  102  and the pumping mechanism ( 306 ). Finally, valve mechanism  140  is actuated to couple the snorkel to atmospheric air or to a supply of air at a pressure greater than that present in the reservoir  102 , inlet channel  122  and standpipe  124  ( 308 ). 
   Once ink has been removed from the region or volume adjacent the nozzles  125  of the printhead  100 , wiper  160  is drawn across the nozzles  125  of the printhead assembly  100  to remove external accretions and to apply a non-volatile material obtained from the wick  162  to the orifice plate in which the nozzles  125  of the printhead assembly  100  are formed, thereby preventing the formation of accretions within the nozzles  125 . 
   An exemplary embodiment of a method of priming the printhead assembly  100  in preparation for printing is described with reference to  FIG. 5 . In this embodiment, port  128  of the printhead assembly  100  is coupled to the pumping mechanism  146  by selectively actuating the valve mechanism  140  as at step  400 . Thereafter, pumping mechanism  146  is actuated to draw air, and if any remains, ink, from the snorkel (step  402 ). The withdrawal of air/ink from the snorkel reduces the pressure therein, which subsequently induces ink to flow from the reservoir  102  through particle filter  118  into inlet channel  122  and standpipe  124 . Once a sufficient pressure differential has been created as between the reservoir  102  and the lower body portion  120 , the pumping mechanism  146  is shut down (step  404 ) and the valve mechanism  140  is actuated to de-couple port  128  from the pumping mechanism  146  (step  406 ). Note that valve mechanism  140 , upon de-coupling port  128  from the pumping mechanism  146 , also seals port  128  and prevents the ingress or escape of air. An alternate embodiment of the method illustrated in  FIG. 5  involves coupling the off-axis reservoir  108  to the reservoir  102  through pumping mechanisms  146  and actuating pumping mechanism  146  to pump ink into the reservoir  102  at a pressure sufficient to force ink into the inlet channel  122  and standpipe  124 . 
   CONCLUSION 
   Although specific embodiments have been illustrated and described herein, it is manifestly intended that this invention be limited only by the following claims and equivalents thereof.