Abstract:
A fluid ejection apparatus includes a fluid ejection head comprising a nozzle through which fluid is ejected, a fluid supply passage through which fluid is supplied to the fluid ejection head, a suction device configured to draw fluid from the nozzle, and a movable member positioned within a predetermined portion of the fluid supply passage. The movable member has openings formed therethrough, and is configured to hold air bubbles therein. The movable member is further configured to move between a first position and a second position downstream of the first position in a fluid flowing direction. When the movable member is in the second position, the movable member partitions the predetermined portion of the fluid supply passage into a first space upstream of the movable member and a second space downstream of the movable member. Moreover, when the suction device transitions from an inactive state to an active state to draw fluid from the nozzle, the movable member moves from the first position to the second position and remains in the second position until the suction device transitions from the active state to the inactive state.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    The present application claims priority from Japanese Patent Application No. 2007-248323, filed on Sep. 26, 2007, the disclosure of which is incorporated herein by reference in its entirety. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates generally to fluid ejection apparatus configured to eject droplets of fluid. 
         [0004]    2. Description of Related Art 
         [0005]    Known fluid recording apparatus, such as inkjet recording apparatus, eject ink droplets from nozzles to recording mediums, such as recording sheets, to form images, such as text images, on the recording mediums. An inkjet recording apparatus includes a fluid ejection head, e.g., an inkjet head, having nozzles, and an ink cartridge which stores ink therein and is connected to the inkjet head. When ink is consumed as ink droplets are ejected from the nozzles of the inkjet head, ink is supplied from the ink cartridge to the inkjet head. 
         [0006]    Air may enter a passage, e.g., a fluid supply passage, which connects the inkjet head to the ink cartridge, e.g., when the cartridge is replaced. If air in the fluid supply passage flows into the inkjet head together with ink, ink may not be properly ejected from the nozzles. Ink is suctioned from the nozzles of the inkjet head using a suction pump in order to discharge air that is present in a portion of the fluid supply passage upstream of the inkjet head in an ink flow direction together with ink. 
         [0007]    For example, in one inkjet recording apparatus, such as the inkjet recording apparatus described in Japanese Laid-Open Patent Publication No. 2005-199600, the inkjet recording apparatus includes a damper configured to absorb fluctuations in ink pressures. The damper is positioned at a portion of a fluid supply passage between an inkjet head and an ink cartridge, and is positioned upstream of the inkjet head. When a predetermined amount of air is accumulated in the damper, ink is suctioned from the nozzles using a suction pump to discharge air in the damper via the nozzles. 
         [0008]    Nevertheless, the inkjet recording apparatus has to suction ink using a relatively large suction force to discharge air attached to a corner portion of the fluid supply passage upstream of the inkjet head from the nozzles of the inkjet head. Consequently, in the known inkjet recording apparatus, a significant amount of ink is discharged via the nozzles when air is discharged via the nozzles. 
       SUMMARY OF THE INVENTION 
       [0009]    Therefore, a need has arisen for fluid ejection apparatus which overcome these and other shortcomings of the related art. A technical advantage of the present invention is that when air is discharged from the fluid supply passage via the nozzles, the amount of ink also discharged via the nozzles is reduced. 
         [0010]    According to an embodiment of the present invention, a fluid ejection apparatus comprises a fluid ejection head comprising a nozzle through which fluid is ejected, a fluid supply passage through which fluid is supplied to the fluid ejection head, a suction device configured to draw fluid from the nozzle, and a movable member positioned within a predetermined portion of the fluid supply passage. The movable member has at least one opening formed therethrough, and is configured to hold at least one air bubble therein. The movable member is further configured to move between a first position and a second position downstream of the first position in a fluid flowing direction. When the movable member is in the second position, the movable member partitions the predetermined portion of the fluid supply passage into a first space upstream of the movable member and a second space downstream of the movable member. Moreover, when the suction device transitions from an inactive state to an active state to draw ink from the nozzle, the movable member moves from the first position to the second position and remains in the second position until the suction device transitions from the active state to the inactive state. 
         [0011]    Other objects, features, and advantages will be apparent to persons of ordinary skill in the art from the following detailed description of the invention and the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0012]    For a more complete understanding of the invention, needs satisfied thereby, and the objects, features, and advantages thereof, reference now is made to the following description taken in connection with the accompanying drawings. 
           [0013]      FIG. 1  is a plan view of a printer, according to an embodiment of the present invention. 
           [0014]      FIG. 2  is a vertical, sectional view of a portion of an inkjet head of the printer of  FIG. 1 , according to an embodiment of the present invention. 
           [0015]      FIG. 3  is a vertical, sectional view of a sub-tank of the printer of  FIG. 1 , according to an embodiment of the present invention. 
           [0016]      FIG. 4  is a sectional view of the sub-tank of  FIG. 3  taken along line X-X. 
           [0017]      FIG. 5  is a block diagram showing a configuration of the printer of  FIG. 1 . 
           [0018]      FIGS. 6A-6C  are sectional views of a portion of the sub-tank of  FIG. 3  showing the movements of a movable member during a suction operation with a suction pump. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0019]    Embodiments of the present invention and their features and technical advantages may be understood by referring to  FIGS. 1-6C , like numerals being used for like corresponding portions in the various drawings. 
         [0020]    Referring to  FIG. 1 , a fluid ejection device, e.g., a printer  1 , according to an embodiment of the present invention, may form, e.g., print, a desired image, e.g., text, on recording mediums, e.g., recording sheets P, by ejecting droplets of fluid, e.g., ink, from a fluid ejection head, e.g., inkjet head  3 , toward the recording sheets P. 
         [0021]    Printer  1  may comprise a carriage  2 , inkjet head  3 , sub-tanks  4   a - 4   d , which herein after collectively are referred to as sub-tank  4 , ink cartridges  6   a - 6   d , which herein after collectively are referred to as ink cartridge  6 , a suction cap  13 , and a suction device, e.g., a suction pump  14 . Carriage  2  may be configured to reciprocate along one direction. Inkjet head  3  and sub-tank  4  may be mounted to carriage  2 . Ink cartridge  6  may store ink therein. Suction cap  13  may be attached to a fluid ejection surface of inkjet head  3 . Suction pump  14  may be connected to suction cap  13 . 
         [0022]    Carriage  2  may be configured to reciprocate along guide shafts  17  extending parallel to a scanning direction, e.g., a right-left direction in  FIG. 1 . Carriage  2  may be connected to an endless belt  18 . When a carriage drive motor  19  drives endless belt  18 , endless belt  18  may move carriage  2  in the right-left direction in  FIG. 1 . 
         [0023]    Inkjet head  3  and sub-tanks  4   a - 4   d  may be mounted on carriage  2 . Inkjet head  3  may reciprocate in the scanning direction together with carriage  2 . Inkjet head  3  may be configured to eject ink droplets from nozzles  40 , as shown in  FIG. 2 , formed on a lower side of inkjet head  3  when inkjet head  3  is mounted on carriage  2 . Recording sheets may be conveyed by a sheet feeding mechanism (not shown) in a sheet feeding direction, as indicated by the downwardly pointed arrow in  FIG. 1 . A desired text or an image or both may be formed on recording sheet P. 
         [0024]    Sub-tanks  4   a - 4   d  may be positioned in a row in the scanning direction. A tube joint  20  may be integrally formed with sub-tanks  4   a - 4   d . Each sub-tank  4   a - 4   d  may be coupled to a corresponding one of ink cartridges  6   a - 6   d , respectively, via flexible tubes  5   a - 5   d , respectively, connected to tube joint  20 . Flexible tubes  5   a - 5   d  hereinafter collectively may be referred to as tube  5 . 
         [0025]    Each of ink cartridges  6   a - 6   d  may store ink of a different color, such as black, cyan, magenta, and yellow. Ink cartridges  6   a - 6   d  may be removably mounted to a holder  7 . Holder  7  may comprise a cartridge detection sensor  85 , as shown in  FIG. 5 , configured to detect whether ink cartridges  6   a - 6   d  are mounted to holder  7 . Cartridge detection sensor  85  may comprise an optical sensor comprising a light-emitting device and a light-receiving device or a contact sensor. The optical sensor may detect ink cartridges  6   a - 6   d  when ink cartridges  6   a - 6   d  mounted to holder  7  interrupt the light emitted from the light-emitting device toward the light-receiving device. The contact sensor may detect ink cartridges  6   a - 6   d  when a contact portion positioned on holder  7  contacts a contact portion positioned on ink cartridges  6   a - 6   d  to have continuity therebetween. 
         [0026]    Four colors of ink stored in ink cartridges  6   a - 6   d  may be temporarily stored in corresponding sub-tanks  4   a - 4   d  and then may be supplied to inkjet head  3 . Sub-tanks  4   a - 4   d  and tubes  5   a - 5   d  connecting four sub-tanks  4   a - 4   d  to ink cartridges  6   a - 6   d  may comprise a fluid supply passage through which ink is supplied to inkjet head  3 . 
         [0027]    Suction cap  13  may be positioned at a maintenance position, which corresponds to a portion (right side in  FIG. 1 ) of a carriage  2  movement area in the scanning direction outside a print area where carriage  2  faces recording sheet P. When carriage  2  moves to the maintenance position, suction cap  13  may face a lower surface of inkjet head  3 , i.e., a fluid ejection surface having a plurality of nozzles  40  formed therein. A cap drive motor  84 , as shown in  FIG. 5 , may drive suction cap  13  upward to cover nozzles  40  of inkjet head  3 . 
         [0028]    Suction cap  13  may be coupled to a suction pump  14  via a switching unit  15 . When suction pump  14  is driven with suction cap  13  covering nozzles  40 , ink may be suctioned or purged from nozzles  40 . Thus, ink in nozzles  40  thickened due to drying may be purged or air in an ink passage in inkjet head  3  or in sub-tank  4 , which is positioned upstream of the inkjet head  3  in an ink flow direction, may be purged from nozzles  40  together with ink. Consequently, fluid ejection performances of inkjet head  3  may be recovered. 
         [0029]    Suction cap  13  may comprise a first cap  13   a  configured to cover nozzles  40  corresponding to black ink, and a second cap  13   b  configured to cover nozzles  40  corresponding to cyan ink, magenta ink, and yellow ink. First cap  13   a  and second cap  13   b  may be separated from each other. First cap  13   a  and second cap  13   b  may be coupled to switching unit  15  via tubes  11   a  and  11   b , respectively. Switching unit  15  may be coupled to suction pump  14 . Switching unit  15  may switch between first cap  13   a  and second cap  13   b  to selectively suction ink from nozzles  40  that eject black ink therethrough and nozzles  40  that eject cyan ink, magenta ink, and yellow ink therethrough. 
         [0030]    Referring to  FIG. 2 , inkjet head  3  may comprise a passage unit  22  and a piezoelectric actuator  23 . Passage unit  22  may comprise an ink flow path comprising nozzles  40  and pressure chambers  34 . Piezoelectric actuator  23  may apply pressure to ink in pressure chambers  34  to eject ink from nozzles  40  of passage unit  22 . 
         [0031]    Passage unit  22  may comprise a cavity plate  30 , a base plate  31 , a manifold plate  32  comprising a metal material, such as stainless steel, and a nozzle plate  33  comprising insulating material, such as high polymer synthetic resin material, e.g., polyimide. Plates  30 - 33  may be laminated and bonded to each other. 
         [0032]    Cavity plate  30  may have pressure chambers  34  formed therein. Pressure chambers  34  may be arranged in a direction perpendicular to the sheet of  FIG. 2 . Base plate  31  may have communication openings  35  and  36  which communicate with respective pressure chambers  34 . Manifold plate  32  may have manifold  37  which communicates with pressure chambers  34  via communication openings  35 , and communication openings  39  which communicate with respective communication openings  36 . Nozzle plate  33  may have nozzles  40  formed therein. Nozzles  40  may be positioned in correspondence with pressure chambers  34  in a direction perpendicular to the sheet of  FIG. 2 . Passage unit  22  may comprise a plurality of individual ink passages  41  leading from manifold  37  to each nozzle  40  via corresponding pressure chamber  34 . 
         [0033]    Piezoelectric actuator  23  may comprise a metal vibration plate  50  bonded to the upper surface of passage unit  22  to cover pressure chambers  34 , a piezoelectric layer  51  positioned on the upper surface of vibration plate  50 , and a plurality of individual electrodes  52  formed on the upper surface of piezoelectric layer  51 . 
         [0034]    Metal vibration plate  50  may be maintained at ground potential by a head driver  53 . Piezoelectric layer  51  may comprise a piezoelectric material having a main component of lead zirconate titanate (PZT), which is a ferroelectric substance and is a solid solution of lead titanate and lead zirconate. Piezoelectric layer  51  may extend over the plurality of pressure chambers  34  on the upper surface of vibration plate  50 . Individual electrodes  52  may be positioned at locations opposed to the middle portion of corresponding pressure chambers  34  on the upper surface of the piezoelectric layer  51 . Head driver  53  may selectively apply the ground potential or a predetermined drive potential different from the ground potential to individual electrodes  52 . 
         [0035]    When ink is ejected from nozzle  40 , head driver  53  may apply drive potential to individual electrode  52  corresponding to pressure chamber  43  communicating with nozzle  40 . A potential difference may occur between individual electrode  52  to which drive potential is applied and vibration plate  50  maintained at ground potential. An electric filed may be generated in a portion of piezoelectric layer  51  interposed between individual electrode  52  and vibration plate  50 . The electric filed may be generated in a direction parallel to the thickness direction of piezoelectric layer  51 . When the polarization direction of piezoelectric layer  51  is the same direction as the direction in which the electric field is generated, piezoelectric layer  51  may expand in its thickness direction and may contract in its plane direction perpendicular to the thickness direction of piezoelectric layer  51 . Unimorph deformation may occur, due to deformation of piezoelectric layer  51 , such that a portion of vibration plate  50  opposing pressure chamber  34  deforms in a convex shape curving toward pressure chamber  34 . At this time, a volumetric capacity of pressure chamber  34  may decrease, such that the ink pressure in pressure chamber  34  may increase. Thus, ink may be ejected from nozzle  40  communicating with pressure chamber  34 . 
         [0036]    Referring to  FIGS. 3 and 4 , sub-tanks  4   a - 4   d  are configured to supply ink to inkjet head  3 , and sub-tanks  4   a - 4   d  may have substantially the same structure. Referring to  FIG. 3 , sub-tank  4  may comprise a synthetic resin material. Sub-tank  4  may comprise an ink storage chamber  60  extending in a horizontal direction, and a vertical passage  61  extending in a vertical, e.g., up-down, direction. Vertical passage  61  may communicate with ink storage chamber  60  and inkjet head  3 . 
         [0037]    Ink storage chamber  60  may communicate with ink cartridge  6  via tube  5  coupled to tube joint  20 , and temporarily may store ink supplied from ink cartridge  6 . An outlet of ink storage chamber  60  may be positioned slightly lower than an upper end  76  of vertical passage  61 , and may communicate with vertical passage  61  via horizontal communication passage  62 . A space adjacent to upper end  76  of vertical passage  61 , which is positioned at a portion of the fluid supply passage, may function as a corner portion when the direction of the ink flow bends from the horizontal direction from the ink storage chamber  60  toward vertical passage  61  via communication passage  62 , to the downward direction in the vertical passage  61 . Upper end  76  of vertical passage  61  may function as a wall surface defining the space of the corner portion. 
         [0038]    A connection  66  may be positioned below vertical passage  61 . Connection  66  may be connected at its lower end to inkjet head  3 . A filter  63  configured to remove dust from the ink flowing from sub-tank  4  toward inkjet head  3  may be positioned at the joint between the inkjet head  3  and sub-tank  4 , i.e., connection  66 . 
         [0039]    A recess  67  may be formed in a wall which partitions vertical passage  61  and ink storage chamber  60 . A space in recess  67  may communicate with vertical passage  61 . 
         [0040]    Ink supplied from ink cartridge  6  to sub-tank  4  via tube  5  may be temporarily stored in ink storage chamber  60 . Thereafter, ink may flow in the horizontal direction from the outlet of ink storage chamber  60  toward vertical passage  61 . Then, ink may flow downward in vertical passage  61  and pass through filter  63 . Thus, ink may be supplied to inkjet head  3 . 
         [0041]    A movable member  70  and a coil spring  75  may be positioned in vertical passage  61 . 
         [0042]    Printer  1  may be configured to draw ink from nozzles  40  formed on the lower surface of inkjet head  3  using suction pump  14 , with nozzles  40  covered with suction cap  13 , to discharge air present in sub-tank  4  together with ink from nozzles  40 . 
         [0043]    When ink is drawn using suction pump  14 , movable member  70  may separate air from upper end  76  of vertical passage  61 , and then may move to the downstream side of vertical passage  61  in the ink flow direction due to the suction force, while holding the air. Coil spring  75  may be positioned below movable member  70  to urge movable member  70  upward. Movable member  70  may be placed in a standby position e.g., a position corresponding to the corner portion, while being pressed against upper end  76  due to buoyancy, when suction pump  14  does not perform the suctioning operation. 
         [0044]    Referring to  FIGS. 3 and 4 , movable member  70  may comprise a synthetic resin material, and may have a substantially rectangular shape in horizontal cross-sectional, similar to vertical passage  61 . Alternatively, movable member  70  may have a multi-angular shape. Movable member  70  may comprise a tubular portion  71  configured to slide along the inner wall of vertical passage  61 , and a ceiling portion  72  positioned at an upstream end of tubular portion  71  in the ink flow direction. Movable member  70  may be slidably moved upward or downward in vertical passage  61 . When movable member  70  is in the standby position, tubular portion  71  may extend in the vertical direction from upper end  76  to the position of communication passage  62 . Ceiling portion  72  may have a plurality of holes  74  that pass through ceiling portion  72  in its thickness, i.e., vertical, direction. Holes  74  may be uniformly formed on a surface of ceiling portion  72  up to a portion adjacent to the outer edges of ceiling portion  74 . The diameter of each hole  74  may correspond to a size which allows ink to pass therethrough and to prevent a gas meniscus from being damaged i.e., prevent gas from passing through holes  74 . 
         [0045]    Movable member  70  may comprise a switching portion, e.g., a rib  73 , which extends from the lower end of tubular portion  71  and is configured to be received recess  67 . The width of rib  73  may be substantially the same as the distance between the inner walls of recess  67 . Rib  73  may be configured to slidably move along the inner walls of recess  67 . When movable member  70  is positioned adjacent to upper end  76 , rib  73  may be positioned above communication passage  62 . When rib  73  is positioned above communication passage  62 , ink flowing in the horizontal direction from ink storage chamber  60  toward vertical passage  61  via communication passage  62  may enter a downstream-side space of vertical passage  61  in the ink flow direction, e.g., a second space  69 , as shown in  FIG. 6A . 
         [0046]    When movable member  70  moves away from upper end  76  to the downstream side in the ink flow direction and rib  73  is positioned below communication passage  62 , ink flowing in the horizontal direction from ink storage chamber  60  to vertical passage  61  via communication passage  62  may enter a space of vertical passage  61  positioned between upper end  76  and an upstream end of movable member  70  in the ink flow direction, e.g., a first space  68 , as shown in  FIGS. 6B and 6C . 
         [0047]    Movable member  70  may be configured to partition vertical passage  61  into first space  68  and second space  69 . First space  68  and second space  69  may communicate with each other via holes  74 . When movable member  70  positioned at the standby position, e.g., at the corner portion of vertical passage  61 , adjacent to upper end  76 , rib  73  may close a portion of the fluid supply passage from ink storage chamber  60  to first space  68 , to lead ink toward second space  69 . As shown in  FIG. 3 , first space  68  substantially may not exist in vertical passage  61  when movable member  70  is positioned at the corner portion of vertical passage  61 . When rib  73  is positioned below communication passage  62  as movable member  70  moves away from upper end  76 , rib  73  may close a portion of the fluid supply passage from ink storage chamber  60  to second space  69 , to lead ink toward first space  68 . 
         [0048]    Referring to  FIG. 5 , a controller  8  configured to perform overall control of printer  1  is depicted. Controller  8  may comprise a central processing unit (CPU), a read only memory (ROM) that stores programs and data to control overall operations of printer  1 , and a random access memory (RAM) which temporarily stores data that the CPU processes. 
         [0049]    Controller  8  further may comprise a recording control unit  81  and a suction control device, e.g., a suction control unit  82 . Recording control unit  81  may control e.g., a carriage drive motor  19  which drives carriage  2  to reciprocatingly move, head driver  53  for inkjet head  3 , and a feed motor  83  of the sheet conveying mechanism (not shown) which conveys recording sheets P, to form an image, e.g., text, on recording sheets P, based on data input from an input device  80 , e.g., a personal computer. Suction control unit  82  may control e.g., a cap drive motor  84  which drives suction cap  13  to move up and down and suction pump  14  to perform an ink suction operation to draw or purge ink from nozzles  40  of inkjet head  3 . 
         [0050]    Referring to  FIGS. 6A-6C , operations of movable member  70  are discussed. When the ink suction operation with suction pump  14  is not performed, movable member  70  may be pressed against upper end  76  by coil spring  78 , such that movable member  70  is positioned hi a space of vertical passage  61  at the corner portion, as shown in  FIG. 6A , in which movable member  70  is positioned above the outlet of ink from ink storage chamber  60 , i.e., communication passage  62 . Therefore, air  90  trapped in the fluid supply passage leading from ink cartridge  6  to inkjet head  3  may float due to buoyancy and may tend to accumulate at the underside of ceiling portion  72  of movable member  70  positioned at upper end  76 . When rib  73  is positioned above communication passage  62 , the fluid resistance in the fluid supply passage leading to second space  69  is less than the fluid resistance in the fluid supply passage leading to first space  68 . Therefore, ink flowing in the horizontal direction from ink storage chamber  60  toward vertical passage  61  via communication passage  62  may enter second space  69  and flow toward inkjet head  3 . 
         [0051]    When the ink suction operation is performed with suction pump  14 , pressures in a portion of vertical passage  61  downstream of movable member  70  in the ink flow direction may be reduced. Therefore, movable member  70  may move away from upper end  76  in the downstream side in the ink flow direction, as shown in  FIG. 6B . A condition in which movable member  70  moves away from upper end  76  in the downstream side in the ink flow direction may be (P×S&gt;F+C 1 +C 2 ), in which P is the drawing pressure applied by suction pump  14  to a portion of vertical passage  61  downstream of movable member  70  in the ink flow direction; S is the horizontal sectional area of ceiling portion  71 ; F is the urging force of coil spring  75 ; C 1  is the buoyancy applied to movable member  70 ; and C 2  is the buoyancy applied to air accumulated at the underside of ceiling portion  72 . In other words, when force P×S to move or pull movable member  70  downward or toward the downstream side in the ink flow direction becomes greater than the force F+C 1 +C 2  to move or push movable member  70  upward or toward the upstream side in the ink flow direction, movable member  70  may move away from upper end  76  in the downstream side in the ink flow direction. 
         [0052]    When movable member  70  moves away from upper end  76  toward the downstream side in the ink flow direction, movable member  70  may separate air  90  from upper end  76 . Further, movable member  70  may move in the downstream side in the ink flow direction while holding air  90  at the underside of ceiling portion  72 . Movable member  70  may comprise tubular portion  71  having a cylindrical shape, and ceiling portion  72  connected thereto. Therefore, when movable member  70  moves in the downstream side in the ink flow direction during the ink suction operation with suction pump  14 , movable member  70  reliably may hold air  90 . 
         [0053]    When movable member  70  moves in the downstream side in the ink flow direction while holding air  90  at the underside of ceiling portion  72 , rib  73  may be positioned below communication passage  62 . At this time, fluid resistance in the fluid supply passage leading to first space  68  may become less than the fluid resistance in the fluid supply passage leading to second space  69 . Therefore, ink flowing in the horizontal direction from ink storage chamber  60  toward vertical passage  61  via communication passage  62  may enter first space  68 . 
         [0054]    Ink flowing into first space  68  may push movable member  70  toward the downstream side in the ink flow direction, such that a force U to push movable member  70  toward the downstream side in the ink flow direction may be applied to movable member  70 . The relationship of the force to move movable member  70  in the upstream side in the ink flow direction to the force to move movable member  70  in the downstream side in the ink flow direction may be expressed as (P+U)×S&gt;F+C 1 +C 2 . 
         [0055]    While the ink suction operation continuously is performed, coil spring  75  may be compressed to its compression limit, and movable member  70  may stop on the upper end of connection  66  via coil spring  75 . If the ink suction operation is further continued with movable member  70  on the upper end of connection  66 , ink may flow into second space  69  from first space  68  via holes  74  formed on ceiling portion  72 . Ink thus flowing into second space  69  may move or push air  90  held at ceiling portion  72  toward the downstream side in the ink flow direction. Holes  74  may be formed on a surface of ceiling portion  72  up to a portion adjacent to its outer edges, such that ink flowing from first space  68  to second space  69  through holes  74  may separate and push air  90  clingingly adhered to a corner portion defined by tubular portion  71  and ceiling portion  72 , toward the downstream side in the ink flow direction. 
         [0056]    Air  90  moved to the downstream side in the ink flow direction may be pulled toward inkjet head  3 . Air  90  may pass through the ink passage in inkjet head  3  and may be discharged from nozzles  40 . Thus, movable member  70  may separate air  90  from upper end  76  during the ink suction operation. Then, air  90  may be moved smoothly in the downstream side in the ink flow direction and discharged from nozzles  40 . With this configuration, an amount of ink discharged from nozzles  40  to discharge air  90  may be reduced. 
         [0057]    When the ink suction operation is performed with suction pump  14  and with air being present in sub-tank  4 , air in sub-tank  4  may not reach inkjet head  3  if a volume of ink suctioned by suction pump  14  is relatively small, e.g., an amount of time during which ink is suctioned by suction pump  14  is relatively short. As the ink suction operation is completed, air that has not reached inkjet head  3  may move upward in the ink flow direction. Suction control unit  82  may change ink suction volumes by suction pump  14 , such that suction pump  14  performs the ink suction operation selectively in a first suction mode and in a second suction mode in which the ink suction volume is greater than the ink suction volume in the first mode. 
         [0058]    When ink droplets are not ejected from nozzles  40  for a relatively long period of time, ink in the ink passage, e.g., nozzles  40 , of inkjet head  3  may thicken due to drying. If ink thickens, ink may not properly be ejected from nozzles  40  to recording sheets P to form an image on recording sheets P. 
         [0059]    When ink droplets are not ejected from nozzles  40  for a predetermined period of time, suction control unit  82  may select the first suction mode to allow suction pump  14  perform the ink suction operation in the first suction mode to suction ink in the ink passage of inkjet head  3  from nozzles  40 . Thus, thickened ink may be discharged from nozzles  40 . More specifically, recording control unit  81  may control carriage drive motor  19  to move carriage  2  and inkjet head  3  to the maintenance position where inkjet head  3  faces suction cap  13 . Suction control unit  82  may control cap drive motor  84  to raise suction cap  13  and cover nozzles  40  of inkjet head  3  with suction cap  13 . Suction pump  14  may perform drawing of a relatively small ink volume, e.g., by performing the ink suction operation for relatively short period of time, to discharge only ink in inkjet head  3 . The ink suction volume in the first suction mode may be less than the volumetric capacity of the movable range of movable member  70  in vertical passage  61 , e.g., from upper end  76  to a position closest to the upper end of connection  66  via coil spring  75 , when coil spring  75  is compressed at its compression limit. Therefore, movable member  70  may not reach the most downstream portion in its movable range, e.g., a position closest to the upper end of connection  66  via coil spring  75 , during the ink suction operation. Air that is moved by movable member  70  in the downstream side in the ink flow direction may not enter inkjet head  3 . Only thickened ink in inkjet head  3  may be discharged or purged from nozzles  40 . 
         [0060]    Air may enter the fluid supply passage from ink cartridge  6  to inkjet head  3  including sub-tank  4 , due to various factors. For example, when ink cartridge  6  is replaced with a new ink cartridge  6 , air readily may enter the fluid supply passage from an end of tube  5  which is coupled to ink cartridge  6 . Air gradually may enter from a joint between sub-tank  4  and tube  5  over a relatively long period of time. Air thus entering the fluid supply passage may be accumulated at the upper end  76  due to buoyancy and increase its size. If air flows into inkjet head  3  together with ink from sub-tank  4 , ink droplets may not properly be ejected from inkjet head  3 . 
         [0061]    When cartridge detection sensor  85  detects that ink cartridge  6  is replaced with a new one, or it is determined that air is not discharged from sub-tank  4  for a relatively long period of time, suction control unit  82  may select the second section mode to allow suction pump  14  perform the ink suction operation in the second suction mode to discharge air and ink in sub-tank  4  from nozzles  40 . 
         [0062]    More specifically, suction control unit  82  may control cap drive motor  84  to raise suction cap  13  and cover nozzles  40  of inkjet head  3  with suction cap  13 , similar to the ink suction operation in the first suction mode. Suction pump  14  may perform the ink suction operation. At this time, the volume of ink suctioned from nozzles  40  may be greater than the volumetric capacity of the movable range of movable member  70  in vertical passage  61 . Movable member  70  may move to connection  66  and air may be moved toward inkjet head  3  in the downstream side in the ink flow direction while suction pump  14  performs the ink suction operation. Air may be drawn inside print head  3  together with ink as the ink suction operation is further continued. Air may be discharged from nozzles  40  through the ink passage in inkjet head  3 . 
         [0063]    When the ink suction operation with suction pump  14  is not performed, movable member  70  may remain at upper end  76 . At this time, ink flowing from ink storage chamber  60  may flow into second space  69  positioned downstream of movable member  70  in the ink flow direction. Even when gas is held by movable member  70 , the gas may not be caught in the ink flow from ink storage chamber  60  to second space  69 , and may not be moved in the downstream side in the ink flow direction. When the ink suction operation with suction pump  14  is performed, the pressure in a portion of vertical passage  61  downstream of movable member  70  may be reduced, such that movable member  70  may separate the gas from upper end  76  and move in the downstream side in the ink flow direction while holding the gas. 
         [0064]    Movable member  70  may have holes  74  which allow first space  68  and second space  69  to communicate with each other. Therefore, when movable member  70  moves in the downstream side in the ink flow direction, ink may flow from first space  68  to second space  69  through holes  74 . Ink flowing from first space  68  to second space  69  through holes  74  may push the gas held by movable member  70  in the downstream side in the ink flow direction. Thus, the gas smoothly may be moved in the downstream side in the ink flow direction and discharged from nozzles  40  during the ink suction operation. Accordingly, an amount of ink discharged may be reduced. 
         [0065]    In another embodiment of the present invention, movable member  70  may comprise a foaming synthetic resin material having a specific gravity which is less than the specific gravity of ink. In this case, movable member  70  may be pressed against upper end  76  due to buoyancy, such that coil spring  77  may be unnecessary. The condition to move movable member  70  away from upper end  76  in the downstream side in the ink flow direction may be (P×S&gt;C 1 +C 2 ). In other words, when force P×S to move or pull movable member  70  downward or toward the downstream side in the ink flow direction becomes greater than the force C 1 +C 2  to move or push movable member  70  upward or toward the upstream side in the ink flow direction, movable member  70  may move away from upper end  76  in the downstream side in the ink flow direction. 
         [0066]    Rib  73  may switch the space into which ink flowing from ink storage chamber  60  enters, between first space  68  and second space  69 . Nevertheless, in another embodiment of the present invention, movable member  70  may not comprise rib  73 . As movable member  70  is moved in the downstream side in the ink flow direction during the ink suction operation with suction pump  14 , fluid resistance in the fluid supply passage leading to first space  68  gradually may reduce, and fluid resistance in the fluid supply passage leading to second space  69  gradually may increase. Therefore, ink may tend to enter first space  68 . A space into which ink flowing out from ink storage chamber  60  enters smoothly may be switched from second space  69  to first space  68 . 
         [0067]    Further, in yet another embodiment of the present invention, movable member  70  may not comprise tubular portion  71 . For example, the lower surface (downstream surface in the ink flow direction) of movable member  70  may be convex and may curve more greatly toward the downstream side in the ink flow direction with respect to the horizontal plane perpendicular to the direction in which vertical passage  61  extends as the distance from a middle portion of movable member  70  toward its periphery increases. With this configuration, air positioned downstream of movable member  70  in the ink flow direction may float up due to buoyancy, and reliably may be held on the underside of moveable member  70 . 
         [0068]    Ceiling portion  72  may be positioned to cover the uppermost end of tubular portion  71 . Nevertheless, in yet another embodiment of the present invention, ceiling portion  72  may be positioned below the uppermost end of tubular portion  71 . In this configuration, movable member  70  may have a cross section of generally a H-shape in vertical sectional view of sub-tank  4 . When movable member  70  is placed in the standby position, e.g., the corner portion of vertical passage  61 , a space, e.g., first space  68 , may exist between upper end  76  and ceiling portion  72 . 
         [0069]    The above-described embodiments of the present invention may be applied to an inkjet printer configured to form, e.g., an image on recording sheet P by ejecting ink. Nevertheless, the above-described embodiment of the present invention also may be applied to other types of fluid ejection apparatus that eject fluid of various types to an ejection object according to usages. 
         [0070]    While the invention has been described in connection with various exemplary structures and illustrative embodiments, it will be understood by those skilled in the art that other variations and modifications of the structures and embodiments described above may be made without departing from the scope of the invention. Other structures and embodiments will be apparent to those skilled in the art from a consideration of the specification or practice of the invention disclosed herein. It is intended that the specification and the described examples are illustrative with the true scope of the invention being defined by the following claims.