Abstract:
A method of making an ink cartridge by forming the ink cartridge with an ink chamber and an air accumulation chamber, forming a vent hole at a first end of the air accumulation chamber, and disposing a one way valve at the vent hole for preventing gas from entering the air accumulation chamber through the vent hole. A mass is placed within the air accumulation chamber, the mass having a dimension smaller than an interior dimension of the air accumulation chamber such that the mass is movable between the first end and a second end of the air accumulation chamber.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
       [0001]    U.S. patent application Ser. No. 13/______, entitled “Air Extraction Momentum Method,” filed concurrently herewith, and U.S. patent application Ser. No. 13/______, entitled “Air Extraction Momentum Pump for Inkjet Printhead,” filed concurrently herewith are assigned to the same assignee hereof, Eastman Kodak Company of Rochester, N.Y., and contain subject matter related, in certain respect, to the subject matter of the present application. The above-identified patent applications are incorporated herein by reference in their entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates generally to the field of inkjet printing, and in particular to an air extraction device for removing air from the printhead while in the printer. 
       BACKGROUND OF THE INVENTION 
       [0003]    An inkjet printing system typically includes one or more printheads and their corresponding ink supplies. A printhead includes an ink inlet that is connected to its ink supply and an array of drop ejectors, each ejector including an ink pressurization chamber, an ejecting actuator and a nozzle through which droplets of ink are ejected. The ejecting actuator may be one of various types, including a heater that vaporizes some of the ink in the chamber in order to propel a droplet out of the nozzle, or a piezoelectric device that changes the wall geometry of the ink pressurization chamber in order to generate a pressure wave that ejects a droplet. The droplets are typically directed toward paper or other print medium (sometimes generically referred to as recording medium or paper herein) in order to produce an image according to image data that is converted into electronic firing pulses for the drop ejectors as the print medium is moved relative to the printhead. 
         [0004]    Motion of the print medium relative to the printhead can include keeping the printhead stationary and advancing the print medium past the printhead while the drops are ejected. This architecture is appropriate if the nozzle array on the printhead can address the entire region of interest across the width of the print medium. Such printheads are sometimes called pagewidth printheads. A second type of printer architecture is the carriage printer, where the printhead nozzle array is somewhat smaller than the extent of the region of interest for printing on the print medium and the printhead is mounted on a carriage. In a carriage printer, the print medium is advanced a given distance along a print medium advance direction and then stopped. While the print medium is stopped, the printhead carriage is moved in a carriage scan direction that is substantially perpendicular to the print medium advance direction as the drops are ejected from the nozzles. After the carriage has printed a swath of the image while traversing the print medium, the print medium is advanced, the carriage direction of motion is reversed, and the image is formed swath by swath. 
         [0005]    Inkjet ink includes a variety of volatile and nonvolatile components including pigments or dyes, humectants, image durability enhancers, and carriers or solvents. A key consideration in ink formulation and ink delivery is the ability to produce high quality images on the print medium. Image quality can be degraded if air bubbles block the small ink passageways from the ink supply to the array of drop ejectors. Such air bubbles can cause ejected drops to be misdirected from their intended flight paths, or to have a smaller drop volume than intended, or to fail to eject. Air bubbles can arise from a variety of sources. Air that enters the ink supply through a non-airtight enclosure can be dissolved in the ink, and subsequently be exsolved (i.e. come out of solution) from the ink in the printhead at an elevated operating temperature, for example. Air can also be ingested through the printhead nozzles. For a printhead having replaceable ink supplies, such as ink tanks, air can also enter the printhead when an ink tank is changed. 
         [0006]    In a conventional inkjet printer, a part of the printhead maintenance station is a cap that is connected to a suction pump, such as a peristaltic or tube pump. The cap surrounds the printhead nozzle face during periods of nonprinting in order to inhibit evaporation of the volatile components of the ink. Periodically, the suction pump is activated to remove ink and unwanted air bubbles from the nozzles. This pumping of ink through the nozzles is not a very efficient process and wastes a significant amount of ink over the life of the printer. Not only is ink wasted, but in addition, a waste pad must be provided in the printer to absorb the ink removed by suction. The waste ink and the waste pad are undesirable expenses. In addition, the waste pad takes up space in the printer, requiring a larger printer volume. Furthermore the waste ink and the waste pad must be subsequently disposed. Also, the suction operation can delay the printing operation 
         [0007]    Co-pending US Patent Application Publication No. 2011/0209706 entitled “Air Extraction Device for Inkjet Printhead” discloses an inkjet printhead including an air extraction chamber having a compressible member for forcing air to be vented from an air chamber through a one-way relief valve in its open position, and for applying a reduced air pressure to a membrane while the one-way relief valve is in its closed position. The compressible member, for example a bellows, is compressed by a projection from a wall of the printer when the carriage moves to an end of travel. Co-pending U.S. patent application Ser. No. 13/095,998 filed on Apr. 28, 2011, is a related design that uses a piston assembly rather than a compressible member, the piston being moved to a first position by a projection from a wall of the printer when the carriage moves to an end of travel. Both of these air extraction devices are actuated by moving the carriage to an end of travel. Both of these copending patent applications are incorporated by reference herein in their entireties. 
         [0008]    U.S. Pat. No. 6,116,726, entitled “Ink Jet Printer Cartridge with Inertially-Driven Air Evacuation Apparatus and Method”, discloses an inkjet printhead (or pen) including a movable inertia element connected to the body of the printhead. The body defines an ink chamber and an air outlet. A compressor element is connected to the inertia element and the air outlet. When the printhead is accelerated along the carriage path during printing, the resulting motion of the inertia element operates the compressor to pump a small amount of air from the chamber. Such a pump is actuated as the carriage moves back and forth during the normal printing process and does not require the carriage to move to an end of travel in order to encounter a projection from a carriage wall. However, the design of the compressor element is somewhat complex. 
         [0009]    What is needed is an air extraction device for an inkjet printhead that is actuated as the carriage moves back and forth during the normal printing process, but has a simpler design. 
       SUMMARY OF THE INVENTION 
       [0010]    A preferred embodiment of the present invention comprises a method of making an ink cartridge by forming the ink cartridge with an ink chamber and an air accumulation chamber, forming a vent hole at a first end of the air accumulation chamber, and disposing a one way valve at the vent hole for preventing gas from entering the air accumulation chamber through the vent hole. A narrower a neck region fluidically connects the ink chamber and the air accumulation chamber within the ink cartridge. A mass is placed within the air accumulation chamber, the mass having a dimension smaller than an interior dimension of the air accumulation chamber such that the mass is movable between the first end and a second end of the air accumulation chamber. The mass has a dimension greater than the neck region for preventing the mass from entering the ink chamber. The mass comprises an average density of less than two grams per cubic centimeter and has a through-hole such that a first end of the through-hole faces the first end of the air accumulation chamber and a second end of the through-hole faces the second end of the air accumulation chamber. A one way valve at the first end of the through-hole prevents gas from entering the through-hole through the first end of the through hole. 
         [0011]    Another preferred embodiment of the present invention comprises a method of making an ink cartridge by forming an ink cartridge having a first chamber for holding ink and a second chamber smaller than the first chamber for holding a smaller portion of the ink and for holding air, including forming a neck region for fluidically connecting the first chamber and the second chamber. A vent hole is formed at a first end of the first chamber for evacuating a portion of the air. 
         [0012]    A mass is disposed within the first chamber and has a dimension smaller than an interior dimension of the first chamber such that the mass is movable between the first end and a second end of the first chamber. It is also large enough such that air is forced out of the vent hole when the mass moves in a direction toward the first end of the first chamber. The neck region is formed proximate the second end of the first chamber so that there is enough air space in the first chamber between the first end of the mass and the vent hole to capture air to be forced out of the vent hole when the mass moves toward the vent hole. The mass has a through hole and a one way valve at a first end of the through-hole for preventing gas from entering the through-hole through the first end of the through hole. The vent hole also has a one way valve for preventing air from entering the first chamber through the vent hole. A density of the ink and the mass has the following relationship: if the ink comprises a density d i  grams/cm 3 , then the mass is formed such that the mass has an effective density d m  grams/cm 3 , wherein 0.8 d i &lt;d m &lt;1.2 d i . 
         [0013]    These, and other, aspects and objects of the present invention will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following description, while indicating preferred embodiments of the present invention and numerous specific details thereof, is given by way of illustration and not of limitation. For example, the summary descriptions above are not meant to describe individual separate embodiments whose elements are not interchangeable. In fact, many of the elements described as related to a particular embodiment can be used together with, and possibly interchanged with, elements of other described embodiments. Many changes and modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications. It is to be understood that the attached drawings are for purposes of illustrating the concepts of the invention. The figures below are intended to be drawn neither to any precise scale with respect to relative size, angular relationship, or relative position nor to any combinational relationship with respect to interchangeability, substitution, or representation of an actual implementation. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  is a schematic representation of an inkjet printer system; 
           [0015]      FIG. 2  is a schematic perspective of a portion of a carriage printer according to an embodiment of the invention; 
           [0016]      FIG. 3  shows a cross-section of a printhead according to an embodiment of the invention; 
           [0017]      FIG. 4  shows a cross-section of the printhead of  FIG. 3  with the one-way valve open over the air vent opening; 
           [0018]      FIG. 5  shows a cross-section of a printhead according to another embodiment of the invention; 
           [0019]      FIG. 6  shows a cross-section of a printhead according to yet another embodiment of the invention; 
           [0020]      FIG. 7  shows a bottom view of a printhead die; 
           [0021]      FIG. 8  shows a schematic top view of a configuration of ink tanks and a printhead having chambers having noncollinear chamber axes; and 
           [0022]      FIG. 9  shows a schematic top view of a configuration of ink tanks and a printhead having chambers having collinear chamber axes. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0023]    Referring to  FIG. 1 , a schematic representation of an inkjet printer system  10  is shown, for its usefulness with the present invention and is fully described in U.S. Pat. No. 7,350,902, which is incorporated by reference herein in its entirety. Inkjet printer system  10  includes an image data source  12 , which provides data signals that are interpreted by a controller  14  as being commands to eject drops. Controller  14  includes an image processing unit  15  for rendering images for printing, and outputs signals to an electrical pulse source  16  of electrical energy pulses that are inputted to an inkjet printhead  100 , which includes at least one inkjet printhead die  110 . Inkjet printhead die  110  are sometimes interchangeably called ejector die herein. 
         [0024]    In the example shown in  FIG. 1 , there are two nozzle arrays. Nozzles  121  in the first nozzle array  120  have a larger opening area than nozzles  131  in the second nozzle array  130 . In this example, each of the two nozzle arrays has two staggered rows of nozzles, each row having a nozzle density of 600 per inch. The effective nozzle density then in each array is 1200 per inch (i.e. d= 1/1200 inch in  FIG. 1 ). If pixels on the recording medium  20  were sequentially numbered along the paper advance direction, the nozzles from one row of an array would print the odd numbered pixels, while the nozzles from the other row of the array would print the even numbered pixels. 
         [0025]    In fluid communication with each nozzle array is a corresponding ink delivery pathway. Ink delivery pathway  122  is in fluid communication with the first nozzle array  120 , and ink delivery pathway  132  is in fluid communication with the second nozzle array  130 . Portions of ink delivery pathways  122  and  132  are shown in  FIG. 1  as openings through printhead die substrate  111 . One or more inkjet printhead die  110  will be included in inkjet printhead  100 , but for greater clarity only one inkjet printhead die  110  is shown in  FIG. 1 . In  FIG. 1 , first fluid source  18  supplies ink to first nozzle array  120  via ink delivery pathway  122 , and second fluid source  19  supplies ink to second nozzle array  130  via ink delivery pathway  132 . Although distinct fluid sources  18  and  19  are shown, in some applications it may be beneficial to have a single fluid source supplying ink to both the first nozzle array  120  and the second nozzle array  130  via ink delivery pathways  122  and  132  respectively. Also, in some embodiments, fewer than two or more than two nozzle arrays can be included on printhead die  110 . In some embodiments, all nozzles on inkjet printhead die  110  can be the same size, rather than having multiple sized nozzles on inkjet printhead die  110 . 
         [0026]    Not shown in  FIG. 1 , are the drop forming mechanisms associated with the nozzles. Drop forming mechanisms can be of a variety of types, some of which include a heating element to vaporize a portion of ink and thereby cause ejection of a droplet, or a piezoelectric transducer to constrict the volume of a fluid chamber and thereby cause ejection, or an actuator which is made to move (for example, by heating a bi-layer element) and thereby cause ejection. In any case, electrical pulses from electrical pulse source  16  are sent to the various drop ejectors according to the desired deposition pattern. In the example of  FIG. 1 , droplets  181  ejected from the first nozzle array  120  are larger than droplets  182  ejected from the second nozzle array  130 , due to the larger nozzle opening area. Typically other aspects of the drop forming mechanisms (not shown) associated respectively with nozzle arrays  120  and  130  are also sized differently in order to optimize the drop ejection process for the different sized drops. During operation, droplets of ink are deposited on a recording medium  20 . As the nozzles are the most visible part of the drop ejector, the terms drop ejector array and nozzle array will sometimes be used interchangeably herein. 
         [0027]      FIG. 2  shows a schematic perspective of a portion of a desktop carriage printer according to an embodiment of the invention. Some of the parts of the printer have been hidden in the view shown in  FIG. 2  so that other parts can be more clearly seen. Printer chassis  300  has a print region  303  across which carriage  200  is moved back and forth in reciprocative fashion along carriage scan direction  305 , while drops of ink are ejected from printhead  250  that is mounted on carriage  200 . Near the end of each printing swath, carriage  220  is decelerated, stopped, and accelerated in the opposite direction to reach a printing velocity in the opposite direction. The magnitude of the carriage acceleration is typically between 1 g and 3 g, where g is the acceleration due to gravity. The letters ABCD indicate a portion of an image that has been printed in print region  303  on a piece  371  of paper or other recording medium. Carriage motor  380  moves belt  384  to move carriage  200  along carriage guide rod  382 . An encoder sensor (not shown) is mounted on carriage  200  and indicates carriage location relative to an encoder  383 . 
         [0028]    Printhead  250  is mounted on carriage  200 , and ink tanks  262  are mounted to supply ink to printhead  250 , and contain inks such as cyan, magenta, yellow and black, or other recording fluids. Optionally, several ink tanks can be bundled together as one multi-chamber ink supply, for example, cyan, magenta and yellow. Inks from the different ink tanks  262  are provided to different nozzle arrays, as described in more detail below. 
         [0029]    A variety of rollers are used to advance the recording medium through the printer. In the view of  FIG. 2 , feed roller  312  and passive roller(s)  323  advance piece  371  of recording medium along media advance direction  304 , which is substantially perpendicular to carriage scan direction  305  across print region  303  in order to position the recording medium for the next swath of the image to be printed. Discharge roller  324  continues to advance piece  371  of recording medium toward an output region where the printed medium can be retrieved. Star wheels (not shown) hold piece  371  of recording medium against discharge roller  324 . 
         [0030]    Typical lengths of recording media are 6 inches for photographic prints (4 inches by 6 inches) or 11 inches for paper (8.5 by 11 inches). Thus, in order to print a full image, a number of swaths are successively printed while moving printhead chassis  250  across the piece  371  of recording medium. Following the printing of a swath, the recording medium  20  is advanced along media advance direction  304 . Feed roller  312  can include a separate roller mounted on the feed roller shaft, or can include a thin high friction coating on the feed roller shaft. A rotary encoder (not shown) can be coaxially mounted on the feed roller shaft in order to monitor the angular rotation of the feed roller  312 . The motor that powers the paper advance rollers, including feed roller  312  and discharge roller  324 , is not shown in  FIG. 2 . For normal paper feeding feed roller  312  and discharge roller  324  are driven in forward rotation direction  313 . 
         [0031]    Toward the rear of the printer chassis  300 , in this example, is located the electronics board  390 , which includes cable connectors for communicating via cables (not shown) to the printhead carriage  200  and from there to the printhead  250 . Also on the electronics board are typically mounted motor controllers for the carriage motor  380  and for the paper advance motor, a processor and/or other control electronics (shown schematically as controller  14  and image processing unit  15  in  FIG. 1 ) for controlling the printing process, and an optional connector for a cable to a host computer. 
         [0032]    Toward the right side of the printer chassis  300 , in the example of  FIG. 2 , is the maintenance station  330 . Maintenance station  330  can include a wiper (not shown) to clean the nozzle face of printhead  250 , as well as a cap  332  to seal against the nozzle face in order to slow the evaporation of volatile components of the ink. Many conventional printers include a vacuum pump attached to the cap in order to suck ink and air out of the nozzles of printhead when they are malfunctioning. 
         [0033]    A different way to remove air from the printhead  250  is shown in  FIG. 2  and discussed in more detail below relative to embodiments of the present invention. Printhead  250  includes one or more air accumulation chambers  220  in which is disposed a movable mass  222 . An ink chamber  242  is connected to each air accumulation chamber  220 . Internal walls  241  (represented by dashed lines) provide separation between adjacent ink chambers  242 . Four ink chambers  242  are shown in the example of  FIG. 2 , corresponding to cyan, magenta, yellow and black inks. Similarly, four ink tanks  262  are shown. However, in other examples, there can be more than four ink chambers  242  or fewer than four ink chambers  242 . 
         [0034]      FIG. 3  shows a cross-section of a printhead  250  similar to the printhead  250  shown in  FIG. 2 , where the cross-section is through a plane parallel to an internal wall  241 . Inkjet printhead  250  includes a printhead body  240  and a printhead die  251  (that is, an ejector die). Printhead body includes an ink chamber  242  containing an ink  243 . Ink chamber  242  includes an ink inlet port  245  and an ink outlet  248  that is fluidically connected to printhead die  251 . Printhead body also includes an air accumulation chamber  220  having a chamber axis  221 . Preferably, chamber axis  221  is parallel to carriage scan direction  305  when printhead  250  is mounted on carriage  200  (see  FIG. 2 ). Near one end  227  of air accumulation chamber  220  is an air vent opening  228 . Inside air accumulation chamber is a mass  222  that is movable along chamber axis  221  toward and away from the end  227  that is near air vent opening  228 . A neck region  239  connects ink chamber  242  and air accumulation chamber  220 , so that ink  243  is typically in the ink chamber, the neck region  239  and the air accumulation chamber  220 . An air space  217  is located above the level of the ink  243  in the air accumulation chamber  220 . 
         [0035]    An ink source such as ink tank  262  is fluidically connected to printhead body  240  at ink inlet port  245  in order to replenish ink  243  in ink chamber  242  to replace ink that is used during printing. The ink source typically includes a pressure regulation mechanism (not shown) in order to keep ink  243  at a sufficiently negative pressure that it does not drool out the nozzles (not shown) in nozzle face  252 . As ink  243  exits ink chamber  243  through ink outlet  248 , the volume of air space  217  increases, thereby reducing the air pressure in air space  217 . This reduced air pressure draws ink  243  from the ink source (such as replaceable ink tank  262  that is mountable on printhead  250 ) through ink outlet port  263  that mates with ink inlet port  245  in order to replenish the ink  243  in ink chamber  242  and air accumulation chamber  220 . Typically a porous filter  247  is disposed at the entry to ink inlet port  245 . 
         [0036]    Although a replaceable ink tank  262  is one type of ink source, alternatively an off-axis ink source (not shown) that is stationarily mounted on the printer chassis  300  ( FIG. 2 ) can be fluidically connected to ink chamber  243  via flexible tubing (not shown). Also, although ink inlet port  245  is shown in  FIG. 3  as extending outwardly from printhead body  240  along carriage scan direction  305  near a lower region of printhead body  240  close to ink outlet  248 , in other examples, ink inlet port  245  can extend outwardly from printhead body  240  out of the plane of  FIG. 3 , or in other directions. In other examples, ink inlet port  245  can be located closer to air accumulation chamber  220  than to ink outlet  248 . In some examples, ink tank  262  can be mounted on top of air accumulation chamber  220 . 
         [0037]    In  FIG. 3 , air bubbles  244  are shown as rising both from ink outlet  248  and from ink inlet port  245  of printhead  250 . Air bubbles  244  originating at ink outlet  248  can come, for example, from printhead die  251  due to air ingested through the nozzles or to air coming out of solution from the ink  243  at elevated temperatures. Air bubbles  244  originating at inlet ports  245  can enter, for example, during the changing of ink tanks  262 . As discussed below, the movable mass  222  in air accumulation chamber  220  is effective in removing air due to various sources in printhead  250 . The open vertical geometry of ink chamber  242 , leading to an air space  217  above ink  243  in air accumulation chamber  220 , facilitates the free rising of air bubbles  244  through ink  243 , due to their buoyancy, toward the air space  217 . With a porous filter  247  disposed at the ink inlet port  245 , no additional filter is typically required along an ink path between the air accumulation chamber  220  and the ink outlet  248  of the ink chamber  248 . Thus, the rising of air bubbles is not hindered as it would be by the fine mesh screen ( 42 ) in  FIG. 2  of U.S. Pat. No. 6,116,726, described in the Background section herein. 
         [0038]    Further details will now be provided in order to explain how excess air (from air bubbles  244 ) in air space  217  is removed from air accumulation chamber  220 . Air accumulation chamber  220  includes a first wall  225  located near neck region  239  and a second wall  226  located opposite first wall  225 . Air vent opening  228  is located in or near second wall  226 . A one-way valve  229  covers air vent opening  228 . In the example shown in  FIGS. 3 and 4 , one way valve  229  includes a flapper valve having a free end  230  that is located near the second wall  226  of the air accumulation chamber  220 , and is outside the air accumulation chamber  220 . Under normal conditions ( FIG. 3 ), elastomeric restoring forces keep the free end  230  sealed against air vent opening  228 , so that air does not enter or exit air vent opening  228 . As mass  222  moves in a direction from first wall  225  toward second wall  226 , the air pressure in the region between mass  222  and second wall  226  increases as the volume therein decreases. When the air pressure exceeds a cracking pressure of the one-way valve  229 , the free end  230  is forced away from air vent opening  228  as in  FIG. 4  and letting some air escape from air accumulation chamber  220 . Then elastomeric restoring forces close the one-way valve  229  again ( FIG. 3 ), so that air can no longer enter or exit air vent opening  228 . 
         [0039]    Mass  222  is moved back and forth along chamber axis  221  due to forces (inertia, momentum) arising from carriage acceleration and deceleration at least at both ends of carriage travel. The force on mass  222  will exceed the force on the ink  243  in air accumulation chamber  220 , if the density of mass  222  is greater than the average density of the ink  243  and the air in air space  217 . If the density of mass  222  is the same as the average density of ink  243  and air in air space  217 , there will be no differential force to move mass  222  along chamber axis  221 . Typically the density of mass  222  is on the order of the density of ink  243  that is on the order of 1 gram /cm 3 . To keep the mass  222  from moving too quickly in air accumulation chamber  220  (tending to force ink out of air vent opening  228 ), the density or average density of mass  222  is typically less than 2 grams/cm 3 . 
         [0040]    A dimension of mass  222  is preferably greater than a dimension of neck region  239 , thereby constraining the mass  222  from passing through neck region  239  and entering ink chamber  243 . In the example of  FIG. 3 , length dimensions are indicated as being parallel to chamber axis  221  and width dimensions are indicated as being perpendicular to chamber axis  221 . Length L N  of neck region  239  is less than length L C  of air accumulation chamber  220 . Length L M  of mass  222  is greater than length L N  of neck region  239 , but is less than length L C  of air accumulation chamber  220 . Width W M  of mass  222  is less than width W C  of air accumulation chamber  220 , thereby providing a gap. It is not required that the seals between mass  222  and the walls of air accumulation chamber  220  be airtight. An air gap between mass  222  and the walls of air accumulation chamber  220  allows free movement of mass  222  without excessive pressure build-up. 
         [0041]    Mass  222  can have a variety of shapes, but it is typically advantageous for low friction travel along chamber axis  221  if mass  222  includes a circular cross-section in a plane perpendicular to chamber axis  221 . In the example of  FIGS. 3 and 4 , it is advantageous if mass  222  has the shape of a right circular cylinder. In the example of printhead  250  in  FIG. 5 , mass  222  has the shape of a sphere. 
         [0042]    As described above relative to  FIGS. 3 and 4 , it is desirable to build up pressure in the region of air accumulation chamber  220  that is near air vent opening  228  in order to expel air through one way valve  229  as mass  222  moves toward the air vent opening  228 . However, in some embodiments it is not desirable to build up pressure on the other side of mass  222 , as mass  222  moves away from air vent opening  228 . Such a buildup of pressure can cause an undesirable pressure surge toward ink outlet  248  and ink inlet port  245 .  FIG. 6  shows a cross-sectional view in which mass  222  includes a through hole  223  extending from a first face  218 , which can be considered as a front face, that is proximate to air vent opening  228  (and distal to neck region  239 ) to a second face  219 , which can be considered as a rear face, that is distal to air vent opening  228 . Included on first face  218  is a one-way valve  224 , such as a flapper valve. As mass  222  moves along chamber axis  221  toward air vent opening  228 , one-way valve  224  is held in the closed position (e.g. by elastomeric forces) so that it seals against through hole  223 . As a result, air and ink cannot flow through the through hole  223  when mass  222  moves toward air vent opening  228 , so pressure can build up to open one-way valve  229  as in  FIG. 4 . However, as mass  222  moves along chamber axis  221  away from air vent opening  228 , pressure that is built up in the region of air accumulation chamber  220  between second face  219  and wall  225  is relieved when the increased pressure causes one-way valve  224  on first face  218  of mass  222  to open, as shown in  FIG. 6 . Although the through hole  223  is shown as parallel to air chamber axis  221  in  FIG. 6 , and front face  218  and rear face  219  is shown as perpendicular to air chamber axis  221  therein, the air gap between mass  222  and the walls of air accumulation chamber  220  allows a slight tilting of mass  222  with respect thereto, and so these parallel and perpendicular relationships remain “substantially parallel” and “substantially perpendicular”. 
         [0043]    A mass  222  having a through hole  223  has an effective density that is an average of the density of solid material that mass  222  is made of and the density of the air or ink in through hole  223 . If the ink has a density d i  grams/cm 3 , then for effective pumping, without over-pumping, it is desirable for the mass  222  to have an effective density of d m  grams/cm 3 , where 0.8 d i &lt;d m &lt;1.2 d i . 
         [0044]    In the examples shown in  FIG. 3 , near the air vent opening  228  is a cap assembly  237 . An inner cap  231  includes air vent opening  228  and one-way valve  229  covering the air vent opening  228 . Inner cap  231  is affixed to air accumulation chamber  220  at interface  234 . A second cap  232  is affixed over inner cap  231  and includes a breather membrane  233  through which air can readily pass, but through which ink cannot readily pass. Breather membrane  233  is outside air accumulation chamber  220 . If some ink  243  is inadvertently forced through air vent opening  228 , it can collect in the region between inner cap  231  and second cap  232 . Breather membrane  233  is in a vertical orientation, so that ink tends to run off it and not degrade its permeability to air. One way valve  229  is disposed between breather membrane  233  and the interface  234  between inner cap  231  and air accumulation chamber  220 . Outer cap  235  includes a tortuous vent path  236  that allows air to pass through to outside printhead  250 , but would inhibit accumulated ink from dripping out if the printhead  250  were removed from carriage  200  ( FIG. 2 ) and turned upside down. 
         [0045]      FIG. 7  shows a bottom view of printhead die  251  (i.e. ejector die). Nozzle arrays  257 , included in nozzle face  252 , are disposed along nozzle array direction  254  that is substantially parallel to media advance direction  304  (see  FIG. 2 ) when printhead  250  is installed in carriage  200 . Chamber axis  221  (see  FIG. 3 ) is substantially parallel to nozzle face  252  and substantially perpendicular to array direction  254 . Ink feed(s)  255  bring ink from mounting substrate ink passageway(s)  259  (see  FIG. 3 ) to nozzle arrays  257 . 
         [0046]    In  FIG. 2 , the ink connections between ink tanks  262  and ink chambers  242  are not visible.  FIGS. 8 and 9  schematically show top views of two different configurations of ink connections. Ink chambers (not shown) and air accumulation chambers  220 , are similar to those described above relative to  FIG. 3 , for example.  FIG. 8  shows a configuration similar to that of  FIG. 2  where there are a plurality of ink tanks  262  (designated K, C, M and Y for black, cyan, magenta and yellow inks) including air accumulation chambers  220 , such that the different air accumulation chambers  220  have chamber axes  221  that are not collinear. Ink connection lines  265  bring ink from ink tanks  262  to corresponding chambers in printhead  250 . By contrast, in the configuration shown in  FIG. 9  the chamber axes  221  of different air accumulation chambers  220  are collinear. 
         [0047]    Because embodiments of this invention extract air without extracting ink, less ink is wasted than in conventional printers. The waste ink pad used in conventional printers can be eliminated, or at least reduced in size to accommodate maintenance operations such as spitting from the jets. This allows the printer to be more economical to operate, more environmentally friendly and more compact. Furthermore, since the air extraction method of the present invention is done during printing, it is not necessary to delay printing operations to extract air from the printhead. 
         [0048]    The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention. 
       PARTS LIST 
       [0000]    
       
           10  Inkjet printer system 
           12  Image data source 
           14  Controller 
           15  Image processing unit 
           16  Electrical pulse source 
           18  First fluid source 
           19  Second fluid source 
           20  Recording medium 
           100  Inkjet printhead 
           110  Inkjet printhead die 
           111  Substrate 
           120  First nozzle array 
           121  Nozzle(s) 
           122  Ink delivery pathway (for first nozzle array) 
           130  Second nozzle array 
           131  Nozzle(s) 
           132  Ink delivery pathway (for second nozzle array) 
           181  Droplet(s) (ejected from first nozzle array) 
           182  Droplet(s) (ejected from second nozzle array) 
           200  Carriage 
           217  Air space 
           218  First face (of mass) 
           219  Second face (of mass) 
           220  Air accumulation chamber 
           221  Chamber axis 
           222  Mass 
           223  Through hole 
           224  One-way valve (on first face of mass) 
           225  First wall 
           226  Second wall 
           227  End (of air accumulation chamber) 
           228  Air vent opening 
           229  One-way valve 
           230  Free end 
           231  Inner cap 
           232  Second cap 
           233  Breather membrane 
           234  Interface 
           235  Outer cap 
           236  Tortuous vent path 
           237  Cap assembly 
           239  Neck region 
           240  Printhead body 
           241  Internal wall 
           242  Ink chamber 
           243  Ink 
           244  Air bubble(s) 
           245  Ink inlet port 
           246  Ink outlet 
           247  Porous filter 
           248  Ink outlet 
           250  Printhead 
           251  Printhead die 
           252  Nozzle face 
           253  Nozzle array 
           254  Nozzle array direction 
           255  Ink feed 
           257  Nozzle array(s) 
           258  Mounting substrate 
           259  Mounting substrate passageway 
           262  Ink tank 
           263  Ink outlet port 
           265  Ink connection lines 
           300  Printer chassis 
           303  Print region 
           304  Media advance direction 
           305  Carriage scan direction 
           306  Wall 
           312  Feed roller 
           313  Forward rotation direction (of feed roller) 
           323  Passive roller(s) 
           324  Discharge roller 
           330  Maintenance station 
           332  Cap 
           371  Piece of recording medium 
           380  Carriage motor 
           382  Carriage guide rod 
           383  Encoder 
           384  Belt 
           390  Electronics board