Patent Publication Number: US-8118415-B2

Title: Ink cartridges and ink supply systems

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims priority from Japanese Patent Application No. JP-2007-268351, which was filed on Oct. 15, 2007, the disclosure of which is incorporated herein by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to ink cartridges and ink supply systems. In particular, the present invention is directed toward ink cartridges and ink supply systems in which a pump is used to cause ink flow. 
     2. Description of Related Art 
     A known inkjet printer has a print head configured to selectively eject ink from nozzles formed in the print head toward a sheet of paper to form an image on the sheet. 
     This known inkjet printer uses a replaceable ink cartridge having an ink tank configured to store ink therein, and ink is supplied from the ink tank to the print head via an ink path formed between the ink tank and the print head. 
     The ink cartridge has an ink supply opening for supplying ink from the interior of the ink tank to the exterior of the ink tank. The ink supply opening is sealed with a sealing member, such as rubber. When the ink cartridge is inserted into a mounting portion of the inkjet printer, an ink needle positioned at the mounting portion penetrates through the sealing member, and ink stored in the ink tank is supplied to the ink path via the ink needle. 
     When the ink cartridge is replaced with a new ink cartridge, air bubbles may enter the ink tank and the ink path. Moreover, when the ambient temperature varies, air dissolved in ink stored in the ink tank may transform into air bubbles. If such air bubbles enter the print head, the print head may fail to eject ink. Another known inkjet printer, such as the inkjet printer described in JP-A-2000-85141, has an ink supply system in which a sub ink tank, which is connected to a print head, and a main ink tank are in fluid communication with each other via an ink path, and a pump, which is configured to deliver ink in opposite directions, is provided in the ink path. The pump is driven for returning ink in the sub ink tank to the main ink tank, and for supplying ink in the main ink tank to the sub ink tank. This system allows air bubbles to be separated from ink in the main ink tank, and then ink without air bubbles is supplied to the sub ink tank. 
     When the ink cartridge is manufactured, minute impurities, such as dust, may enter the ink tank. When the impurities contained in ink reach the print head, the impurities may clog the nozzles and the print head may fail to eject ink. Impurities, such as dust, may be more difficult to remove from ink than air bubbles because some of impurities float on ink, some impurities settle at the bottom of the ink, and other impurities suspend in ink. In recent yeas, because consumer demands for higher resolution of printed images has risen, the diameter of nozzles has decreased. Consequently, the desirability to remove impurities of sizes which previously could be ignored is increasing. 
     SUMMARY OF THE INVENTION 
     Therefore, a need has arisen for ink cartridges and ink supply systems which overcome these and other shortcomings of the related art. A technical advantage of the present invention is that minute impurities are separated from ink stored in an ink tank. 
     According to an embodiment of the present invention, An ink cartridge comprises an ink tank which comprises an ink chamber formed in an interior of the ink tank, and a first wall separating the interior of the ink tank and an exterior of the ink tank, in which the first wall has a first opening formed therethrough. The ink tank also comprises a partition wall connected to the first wall. The partition wall defines a first chamber formed therein, and the first chamber is continuous with the first opening. Moreover, the ink tank comprises a divider. The first chamber and the ink chamber are in fluid communication via the divider, and when ink flows through the divider from the first chamber to the ink chamber, the divider is configured to divide a first air bubble contained in the ink into a plurality of second air bubbles. Specifically, a size of the first air bubble is greater than a size of each of the plurality of second air bubbles. The ink cartridge also comprises a pump configured to selectively force ink into and out of the interior of the ink tank. 
     According to another embodiment of the present invention, an ink supply system comprises an ink tank which comprises an ink chamber formed in an interior of the ink tank, and a first wall separating the interior of the ink tank and an exterior of the ink tank, in which the first wall has a first opening formed therethrough. The ink tank also comprises a partition wall connected to the first wall. The partition wall defines a first chamber formed therein, and the first chamber is continuous with the first opening. Moreover, the ink tank comprises a divider. The first chamber and the ink chamber are in fluid communication via the divider, and when ink flows through the divider from the first chamber to the ink chamber, the divider is configured to divide a first air bubble contained in the ink into a plurality of second air bubbles. Specifically, a size of the first air bubble is greater than a size of each of the plurality of second air bubbles. The ink cartridge also comprises a pump configured to selectively force ink into and out of the interior of the ink tank, and a tube configured to be in fluid communication with the first chamber via the first opening. 
     Other objects, features, and advantages of embodiments of the present invention will be apparent to persons of ordinary skill in the art from the following description of preferred embodiments with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       For a more complete understanding of the present invention, the 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. 
         FIG. 1  is a cross-sectional, pattern diagram of an inkjet printer, according to an embodiment of the present invention. 
         FIG. 2(A)  is a perspective view of an ink cartridge, according to an embodiment of the present invention, in which a case of the ink cartridge is assembled; and  FIG. 2(B)  is a perspective view of the ink cartridge in which the ink cartridge is not assembled. 
         FIG. 3  is a perspective view of the ink cartridge of  FIG. 2(A) , in which the ink cartridge is shown at an angle different than the angle at which the ink cartridge is shown in  FIG. 2(A) . 
         FIG. 4  is a perspective view of the ink cartridge of  FIG. 2(A) , in which a second case member of the ink cartridge is depicted by a double-dashed line in order to show the interior of the ink cartridge. 
         FIG. 5  is a side view of the ink cartridge of  FIG. 4  viewed in a direction indicated by an arrow V in  FIG. 4 , in which the case is depicted by a double-dashed line in order to show the interior of the ink cartridge. 
         FIG. 6  is a cross-sectional view of the ink cartridge of  FIG. 4  taken along a line VI-VI. 
         FIG. 7  is an exploded, cross-sectional view of the ink cartridge of  FIG. 6  in which the case is omitted. 
         FIG. 8  is a partial, cross-sectional view of the ink cartridge of  FIG. 7  taken along a line VIII-VIII of. 
         FIG. 9  is an exploded, perspective view of a check valve. 
         FIG. 10(A)  is a cross-sectional view of the check valve of  FIG. 9  taken along a line X-X; and  FIG. 10(B)  is a cross-sectional view of another check valve in which the cross section of  FIG. 10(B)  corresponds to the cross section of  FIG. 10(A) . 
         FIG. 11  is a cross-sectional view of the ink cartridge of  FIG. 6 , in which a predetermined amount of ink is stored in an ink chamber. 
         FIG. 12  is an exploded, perspective view of an air communication valve mechanism. 
         FIG. 13(A)  is a partial, enlarged, cross-sectional view of the air communication valve mechanism of  FIG. 12 , in which a piston is positioned at a position P 1 ; and  FIG. 13(B)  is a partial, enlarged, cross-sectional view of the air communication valve mechanism of  FIG. 12 , in which the piston is positioned at a position P 2 . 
         FIG. 14  is a partial, enlarged, cross-sectional view of a pump. 
         FIG. 15  is an exploded, perspective view of an ink supply valve mechanism. 
         FIG. 16  is a partial, enlarged, cross-sectional view of the ink supply valve mechanism of  FIG. 15 . 
         FIG. 17  is a perspective view of a cartridge mounting portion, in which the ink cartridges are not mounted to the cartridge mounting portion. 
         FIG. 18  is a perspective view of the cartridge mounting portion of  FIG. 17 , in which the ink cartridges are mounted to the cartridge mounting portion. 
         FIG. 19  is a side view of the cartridge mounting portion of  FIG. 18  as viewed from a direction indicated by an arrow XIX. 
         FIG. 20  is a cross-sectional view of the cartridge mounting portion of  FIG. 17  taken along a line XX-XX. 
       FIGS.  21 (A)-(C) are schematic diagrams of an ink supply operation. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Embodiments of the present invention and their features and technical advantages may be understood by referring to  FIGS. 1-21(C) , like numerals being used for like corresponding portions in the various drawings. 
     Referring to  FIG. 1 , an inkjet recording device  10  may be configured to record images, e.g., color images or monochrome images, on a recording medium e.g., a sheet of paper, using black ink or a plurality of, e.g., five, colors of inks, e.g. cyan ink, magenta ink, yellow ink, dye-based black ink, and pigment-based black ink. Inkjet recording device  10  may comprise a paper feed device  12 , a convey device  13 , a recording unit  14 , an ink supply system  11 , a paper tray  16 , and a discharge tray  17 . Paper tray  16  may be configured to accommodate recording media, e.g., sheets of paper, and the recording media may be fed by paper feed device  12  to a paper path  18 . Paper path  18  may have a sideways “U” shape, and convey device  13  may be provided along paper path  18 . Convey device  13  may comprise a pair of convey rollers  13 A, a pair of discharge rollers  13 B, and a platen  19 . Convey rollers  13 A may be positioned on the upstream side of recording unit  14  in paper path  18 , and discharge rollers  13 B may be positioned on the downstream side of recording unit  14  in paper path  18 . 
     Convey rollers  13 A may be configured to convey the sheet fed by paper feed device  12  to platen  19 . Recording unit  14  may be positioned directly above platen  19 , and may be configured to record images on the sheet passing over platen  19 . Discharge rollers  13 B may be configured to contact, position, and start conveying the sheet when the leading edge of the sheet reaches discharge rollers  13 B. Both convey rollers  13 A and discharge rollers  13 B may be configured to convey the sheet until the trailing edge of the sheet passes between convey rollers  13 A. After the sheet has passed between convey rollers  13 A, the sheet may be conveyed by discharge rollers  13 B but not convey rollers  13 A. Discharge tray  17  may be positioned at the downstream end of paper path  18 . Discharge rollers  13 B may be configured to discharge the sheet, on which the image has been recorded, to discharge tray  17 . 
     Recording unit  14  may comprise a carriage  30 , at least one sub ink tank  21 , a head control board  27 , and a recording head  26 . Carriage  30  may be supported by rails configured to allow carriage  30  to slide, and may be configured to slide in a back-and-forth direction when inkjet recording device  10  is positioned, as shown in  FIG. 1 . Sub ink tank  21  may be configured to store ink to be supplied to recording head  26 . A plurality of, e.g., five, sub ink tanks  21  may be provided, corresponding to the five colors of inks, respectively. 
     Recording head  26  may comprise a plurality of nozzles  28 , through which ink may be ejected toward the sheet of paper based on image signals input to head control board  27 . Inkjet recording device  10  may comprise a main controller, which may be configured to control inkjet recording device  10 , and the main controller may output image signals to head control board  27 . 
     Carriage  30  may comprise a side face having at least one joint  33  provided thereon. At least one flexible tube  32  may be connected to the at least one joint  33 . A plurality of e.g., five, tubes  32 , and a plurality of, e.g., five, joints  33  may be provided, each corresponding to the five colors of inks, respectively. A path  34  may be provided in carriage  30 , and may extend from joint  33  to the bottom of sub ink tank  21 . 
     A valve mechanism  37  may be provided in carriage  30 , and valve mechanism  37  may comprise a cylinder  39 , which may be in fluid communication with one or more of sub ink tank  21 , a coil spring  41 , and a piston  40 . Coil spring  41  and piston  40  may be accommodated in cylinder  39 . Cylinder  39  may comprise a bottom wall, and an opening  42  may be formed through the bottom wall of cylinder  39 . Coil spring  41  may be compressed, and may bias piston  40  toward opening  42  to close opening  42 . A rod  43  may extend from piston  40  to the exterior of cylinder  39  via opening  42 . 
     When a force is applied to rod  43  in a direction opposite the direction of the biasing force of coil spring  41 , piston  40  may be configured to move within cylinder  39  against the biasing force of coil spring  41 , and opening  42  may be opened. The interior of sub ink tank  21  may be configured to be in fluid communication with the atmosphere via cylinder  39  and opening  42  when opening  42  is opened. When ink flows into or out of sub ink tank  21  via tube  32 , opening  42  may be opened. When inkjet recording device  10  is in a waiting or non-recording state, e.g., a state in which inkjet recording device  10  does not perform recording, opening  42  may be closed to prevent ink evaporation. 
     Ink supply system  11  may comprise a cartridge mounting portion  200 , at least one ink cartridge  50 , at least one flexible tube  32 , and at least one sub ink tank  21 . Cartridge mounting portion  200  may be configured to be detachably receive at least one ink cartridge  50  therein. 
     Ink cartridge  50  may comprise an ink tank for storing ink, e.g., main ink tank  70 . Main ink tank  70  and sub ink tank  21  may be configured to be in fluid communication via tube  32 . A plurality of, e.g., five, tubes  32 , may be connected to a plurality of, e.g., five, main ink tanks  70  of a plurality of, e.g., five, ink cartridges  50  and a plurality of, e.g., five, sub ink tanks  21 , respectively. Ink may flow between main ink tank  70  and sub ink tank  21  bi-directionally via tube  32 . Tube  32  may comprise at least one flexible synthetic resin, and may be configured to bend and to follow the movement of carriage  30  when carriage  30  reciprocates. 
     When ink in sub ink tank  21  and tube  32  is returned to main ink tank  70 , air bubbles, which may have been trapped in sub ink tank  21  and tube  32 , may be transferred to main ink tank  30  along with ink, and may be separated from ink inside main ink tank  30 . After that, ink from which air bubbles have been separated may be supplied from main ink tank  70  to sub ink tank  21 . Consequently, ink in sub ink tank  21  may be replaced with ink in main ink tank  70 , and ink in sub ink tank  21  and ink in main ink tank  70  may be mixed. Thus, the viscosity of ink may be equalized by the mixture. 
     Referring to  FIGS. 2(A)-3 , ink cartridge  50  may comprise a case  52 , which may have a rectangular parallelepiped shape, having a width in a Y-axis direction when positioned, as shown in  FIGS. 2(A)-3 , a height in a Z-axis direction when positioned, as shown in  FIGS. 2(A)-3 , and a depth in an X-axis direction when positioned, as shown in  FIGS. 2(A)-3 . The height may be greater than the width, and the depth may be greater than the height. An X-axis direction may be parallel with a direction in which ink cartridge  50  is mounted into cartridge mounting portion  200 . An X-Y plane which is defined by an X axis and a Y axis may be a horizontal plane. The X-axis, the Y-axis, and the Z-axis may be perpendicular to each other. 
     Case  52  may comprise a first case member  53  and a second case member  54 . Case  52  may be configured to be selectively disassembled into first case member  53  and second case member  54  along the X-axis direction and the Z-axis direction when case  52  is positioned, as shown in  FIG. 2(B) . The shape of first case member  53  may be substantially the same as the shape of second case member  54 . Each of first case member  53  and second case member  54  may comprise at least one synthetic resin, and may be manufactured by injection molding. 
     Case  52  may comprise a top face  59  and a front face  60 . Front face  60  has a first end and a second end, and top face  59  may be connected to the first end of front face  60 . Opening  56  may be formed through top face  59 , may extend to front face  60 , and may be defined by cut-out portions  61  formed in first case member  53  and second case member  54 , respectively. A portion of a rod  182  may be positioned in opening  56 , and rod  182  may be configured to extend from front face  60 . Opening  57  may be formed through front face  60 , adjacent to the second end of front face  60 . Opening  57  may be defined by a pair of semicircular cut-out portions formed in first case member  53  and second case member  54 , respectively. An ink supply valve mechanism  130  may extend from the interior of case  52  to the exterior of case  52  through opening  57 . Opening  58  may be formed through front face  60  between opening  56  and opening  57 , and may be defined by rectangular cut-out portions  62  formed in first case member  53  and second case member  54 , respectively. A detection portion  75  may be positioned in the interior of case  52 , and may be exposed to the exterior of case  52  through opening  58 . 
     Referring to  FIGS. 4-6 , ink cartridge  50  may comprise main ink tank  70 , a pump  170 , an air communication valve mechanism  110 , and ink supply valve mechanism  130 . At least a portion of each of main ink tank  70 , pump  170 , air communication valve mechanism  110 , and ink supply valve mechanism  130  may be positioned in case  52 . Each of main ink tank  70 , pump  170 , air communication valve mechanism  110 , and ink supply valve mechanism  130  may comprise at least one synthetic resin. 
     Main ink tank  70  may be substantially enclosed in case  52  and may have a width in the Y-axis direction, a height in the Z-axis direction, a depth in the X-axis direction, when main ink tank  70  is positioned, as shown in  FIG. 4 . The height of main ink tank  70  may be greater than the width of main ink tank  70 , and the depth of main ink tank  70  may be greater than the height of main ink tank  70 . Main ink tank  70  may comprise a translucent, e.g., transparent or semi-transparent, frame  71 , and a pair of translucent, e.g., transparent or semi-transparent, films  81 , as shown in  FIG. 8 , welded to both side faces of frame  71 , respectively. Frame  71  and films  81  may define an ink chamber  73  therein for storing ink. Films  81  are not shown in  FIGS. 4-6   
     Referring to  FIGS. 4-7 , main tank  70  may comprise a cylindrical ink fill portion  72 , and ink fill portion  72  may be integrally formed with frame  71 . An ink fill opening  82  may be formed through a rear face  80  of main tank  70 . Ink fill portion  72  may extend from ink fill opening  82  toward ink chamber  73  in the X-axis direction when main ink tank  70  is positioned, as shown in  FIGS. 4-7 . Ink chamber  73  may be configured to be filled with a predetermined amount of ink via ink fill opening  82  and ink fill portion  72 . The predetermined amount of ink may be about 80% of a maximum capacity of ink chamber  73 . Ink chamber  73  may comprise an upper portion positioned closer to air communication valve mechanism  110  than to ink supply valve mechanism  130 , and a lower portion positioned closer to ink supply valve mechanism  130  than to air communication valve mechanism  110 . After ink chamber  73  is filled with ink, a rubber plug may be press-fitted in ink fill portion  72  from ink fill opening  82 . Ink chamber  73  may be hermetically closed after ink chamber  73  is filled with ink because ink supply valve mechanism  130  and air communication valve mechanism  110  also may be closed. Referring to  FIG. 11 , an air layer  83 , which contacts ink in ink chamber  73 , may be formed at the upper portion of ink chamber  73  after ink chamber  73  is filled with ink 
     Referring to  FIGS. 6 ,  7 ,  11 , and  12 , rear face  80  may comprise an upper end and a lower end, and a circular opening  84  may be formed through rear face  80  of main ink tank  70 , adjacent to the upper end of rear face  80 . A cylindrical valve accommodating chamber  85  may be formed in main ink tank  70 , and valve accommodating chamber  85  may extend from opening  84  in the X-axis direction when main ink tank  70  is positioned, as shown in  FIGS. 6 ,  7 ,  11 , and  12 . A piston  116  of a valve  113 , a coil spring  112 , and a valve seat  114  may be accommodated within valve accommodating chamber  85 . Valve accommodating chamber  85  may comprise an end opposite opening  84  in the X-axis direction when main ink tank  70  is positioned, as shown in  FIGS. 6 ,  7 , and  11 . An opening  100  may be formed at the end of valve accommodating chamber  85 , and opening  100  may be in fluid communication with the upper portion of ink chamber  73 . In particular, opening  100  may be in fluid communication with air layer  83  formed at the upper portion of ink chamber  73 . A portion of a rod  117  of valve  113  may be positioned in opening  100 . The diameter of opening  100  may be greater than the outer diameter of rod  117 . Therefore, rod  117  may not close opening  100 , and air communication between valve accommodating chamber  85  and ink chamber  73  may not be prevented. A cross section of rod  117  taken along a plane perpendicular to the X-axis direction may have a cross shape. Valley portions  117 B of rod  117  may be configured to allow air to pass therethrough. Valve accommodating chamber  85  may comprise a cylindrical wall surface extending from opening  84  to the end of valve accommodating chamber  85 . An opening  101  may be formed in the wall surface of valve accommodating chamber  85 , and may be in fluid communication with the atmosphere. Air communication valve mechanism  110  may be configured to alternately allow and prevent fluid communication between opening  100  and opening  101 . 
     Referring to  FIGS. 6-8 , and  15 , main ink tank  70  may comprise side wall  71 A defining a front face  79  of main ink tank  70 , and separating the interior of main ink tank  70  and the exterior of main ink tank  70 . Side wall  71 A may comprise an upper end and a lower end, and a circular opening  87  may be formed through side wall  71 A adjacent to the lower end of side wall  71 A. 
     Main ink tank  70  may comprise a partition wall connected to side wall  71 A, and the partition wall defines a first chamber formed therein. The first chamber is continuous with opening  87 . The partition wall may comprise a cylindrical wall  71 B extending from side wall  71 A, and the first chamber may comprise a cylindrical valve accommodating chamber  88  defined by cylindrical wall  71 B. Valve accommodating chamber  88  may extend from opening  87  in the X-axis direction when main ink tank  70  is positioned, as shown in  FIGS. 6-8 , toward ink chamber  73 . A valve  133  and a biasing member, e.g., a spring unit  134  shown in  FIG. 15 , may be accommodated within valve accommodating chamber  88 . 
     Cylindrical wall  71 B also may comprise an end wall  105 , which may define an end of valve accommodating chamber  88  opposite opening  87  in the X-axis direction when main ink tank  70  is positioned, as shown in  FIGS. 6-8 . An opening  89  may be formed through end wall  105 , and opening  89  may be continuous with ink chamber  73 . 
     An opening  104  may be formed through cylindrical wall  71 B above valve accommodating chamber  88  and adjacent to side wall  71 A, and may be positioned above opening  89  and opening  87 . 
     The partition wall also may comprise a substantially cylindrical side wall  108  and an end wall  107 , both of which may be continuous with side wall  71 A. The first chamber also may comprise a buffer chamber  90  defined by side wall  108  and end wall  107 . Buffer chamber  90  may be positioned above valve accommodating chamber  88 , e.g., directly above opening  104 . Buffer chamber  90  may extend in the widthwise direction of main ink tank  70 , i.e., in the Y-axis direction in  FIG. 8 . Side wall  108  may extend from a widthwise end of frame  71  to the widthwise center of frame  71 . An end of side wall  108  at the widthwise center of frame  71  may be connected to end wall  107 . 
     Opening  104  may be continuous with buffer chamber  90 . Valve accommodating chamber  88  may be in fluid communication with ink chamber  73  via opening  104  and buffer chamber  90 . The fluctuation of ink flow from opening  87  into main ink tank  70  may be buffered in buffer chamber  90 , and air bubbles flowing into main ink tank  70  with ink and air bubbles remaining in valve accommodating chamber  88  may be temporarily collected in buffer chamber  90 . 
     A recessed portion  105 A may be formed in a face of end wall  105 , and may face valve accommodating chamber  88 . A check valve  95  may be positioned in recessed portion  105 A. Opening  89  may be continuous with recessed portion  105 A. 
     Check valve  95  may be configured to selectively open opening  89 , such that check valve  95  allows ink to flow from ink chamber  73  to the valve accommodating chamber  88  through opening  89  when the pressure in ink chamber  73  is greater than the pressure in valve accommodating chamber  88 , and to selectively close opening  89  when the pressure in ink chamber  73  is less than the pressure in valve accommodating chamber  88 . A flow path  91  may be formed from ink chamber  73  to valve accommodating chamber  88  in main ink tank  70 , as shown in  FIG. 7 . Flow path  91  may extend from the lower portion of the chamber  73  via the opening  89  to valve accommodating chamber  88 . 
     Referring to  FIG. 8 , a recessed portion  107 A may be formed in a face of end wall  107 , and may face ink chamber  73 . A check valve  93  may be positioned in recessed portion  107 A. An opening  106  may be formed through end wall  107  in the widthwise direction, and may be continuous with recessed portion  107 A. 
     Check valve  93  may be configured to selectively open opening  106 , such that check valve  93  allows ink to flow from buffer chamber  90  to ink chamber  73  through opening  106  when the pressure in ink chamber  73  is less than the pressure in valve accommodating chamber  88 , and to selectively close opening  106  when the pressure in ink chamber  73  is greater than the pressure in valve accommodating chamber  88 . A flow path  92  may be formed from valve accommodating chamber  88  to ink chamber  73  via buffer chamber  90  in main ink tank  70 . 
     Referring to  FIG. 7 , main tank  70  may comprise an upper face  78 , and a space  96  may be formed at upper face  78  to position pump  170  therein. A pump seat  98  may be positioned on a wall defining the end of valve accommodating chamber  85 . A pump seat  99  may be positioned on upper face  78  adjacent to front face  79 . Pump seats  98  and  99  may be formed integrally with frame  71 . 
     Pump  170  may be attached to main ink tank  70  at pump seats  98  and  99 . Pump  170  may comprise a cylindrical tube  171 . A cylindrical opening  102  may be formed through pump seat  99  in the X-axis direction, as shown in  FIG. 7 . The diameter of an opening  102  may be slightly greater than the outer diameter of cylindrical tube  171 . Cylindrical tube  171  may comprise a front end  176  and a rear end  175  opposite front end  176 . Cylindrical tube  171  may be inserted through opening  102 , and rear end  175  may be attached to pump seat  98 . Front end  176  of cylindrical tube  171  may be attached to pump seat  99 . Cylindrical tube  171  may have an inner surface defining an inner space  171 A. Pump seat  98  may have an opening  103  formed therethrough, and inner space  171 A and ink chamber  73  may be in fluid communication via opening  103 . In another embodiment, pump  170  may comprise a square-pillar tube instead of cylindrical tube  171 . In yet another embodiment, pump  170  may comprise a tube having any other shape, as long as the tube comprises a hollow body with two ends opposite each other. 
     Referring to  FIGS. 5-7 , main ink tank  70  may comprise detection portion  75  extending from front face  79  of main ink tank  70  away from ink chamber  73  in the X-axis direction. Detection portion  75  may be integrally formed with frame  71 , and detection portion  75  may comprise the same material as frame  71 , e.g., at least one translucent, e.g., transparent or semi-transparent, synthetic resin. Detection portion  75  may be configured to allow light emitted from an optical sensor  203  to pass through. 
     Referring again to  FIGS. 6-8 , detection portion  75  may have an inner space  76  formed therein. Inner space  76  may be in fluid communication with ink chamber  73 . A sensor arm  150  may comprise a light blocking portion  157 , at least a portion of which may be configured to move in and out of inner space  76  based on an amount of ink in ink chamber  73 . At least a portion of light blocking portion  157  may be configured to contact a support wall  74 , which bounds the bottom of inner space  76 , when a portion of light blocking portion  157  enters inner space  76 , thus holding light blocking portion  157  at the position. At least a portion of light blocking portion  157  may be configured to be positioned at a particular position once it exits inner space  76 , as shown in  FIG. 6 . 
     Main ink tank  70  may comprise a support portion  97  which may be formed integrally with frame  71  and may be configured to pivotally support sensor arm  150  and to grasp a shaft  158  of sensor arm  150 . 
     Referring to  FIGS. 9 and 10 , check valve  93  is described. Check valve  93  may have substantially the same structure as check valve  95 , except that the size and the number of openings  244  formed through a valve seat  241  may be different. 
     Check valve  93  may comprise a valve member  231  and valve seat  241  for accommodating valve member  231 . Valve member  231  may be manufactured by injection-molding silicon rubber, and valve seat  241  may be manufactured by injection-molding polypropylene. 
     Valve member  231  may have an umbrella shape, and may comprise a disc portion  233 , and a cylindrical shaft portion  234  extending from disc portion  233 . Disc portion  233  may have a thin, round shape. Shaft portion  234  may extend from a substantially center of disc portion  233  in a direction perpendicular to a surface of disc portion  233 . Shaft portion  234  may comprise a thick portion  235 , the diameter of which is greater than the diameter of the remaining portions of shaft portion  234 . Thick portion  235  may be separated from disc portion  233  by a predetermined distance. Thick portion  235  may function as a stopper for limiting the stroke of valve member  231  when valve member  231  is assembled to valve seat  241 . 
     Valve seat  241  may comprise a divider, e.g., a circular bottom wall  243  and a cylindrical side wall  246  extending from the outer edge of bottom wall  243  in a direction perpendicular to bottom wall  243 . Side wall  246  may have a cylindrical inner opening  246 A formed therein, and the diameter of inner opening  246 A is greater than the outer diameter of disc portion  233  of valve member  231 . Therefore, valve seat  241  may be configured to accommodate disc portion  233 . Referring to  FIG. 8 , valve seat  241  may be fitted into recessed portion  107 A while bottom wall  243  contacts the bottom of recessed portion  107 A. Referring to  FIG. 10(A) , bottom wall  243  may have at least one opening, e.g., a plurality of openings  244 , and an opening  245  formed therethrough. Ink may pass through openings  244 , and shaft portion  234  of valve member  231  may be inserted through opening  245 . In this embodiment, opening  245  may be formed through the center of bottom wall  243 , and openings  244  may be positioned on concentric circles around opening  245 . The position or the number of openings  244  may be changed based on the flow rate of ink through openings  244 . 
     When shaft portion  234  of valve member  231  is inserted into opening  245 , thick portion  235  may come into contact with a portion of bottom wall  243  defining opening  245 . When shaft portion  234  is further inserted, thick portion  235  may pass through opening  245  while bending and deforming the portion of bottom wall  243  defining opening  245 . As such, check valve  93  may be assembled. Disc portion  233  may selectively come into contact with bottom wall  243  to close openings  244 , and separate from bottom wall  243  to open openings  244 , based on the pressure differential between ink chamber  73  and buffer chamber  90 . More specifically, check valve  93  may selectively allow ink to flow from buffer chamber  90  to ink chamber  73  through openings  244  while disc portion  233  is separated from bottom wall  243 , and prevent ink from flowing from ink chamber  73  to buffer chamber  90  while disc portion  233  contacts bottom wall  243 . 
     Check valve  95  may have substantially the same structure as check valve  93  except that check valve  95  may have openings  254  formed therethrough instead of opening  244 . Therefore, only the differences between check valve  95  and check valve  93  are discussed with respect to check valve  95 . 
     Referring to  FIG. 10(B) , bottom wall  243  of valve seat  251  of check valve  95  may have at least one opening, e.g., a plurality of openings  254 , formed therethrough. Openings  254  may be positioned on a circle around opening  245 . In this embodiment, the diameter of each of openings  254  may be greater than the diameter of each of openings  244  of valve seat  241 . Therefore, the flow resistance of openings  254  may be less than the flow resistance of openings  244 . Disc portion  233  selectively may come into contact with bottom wall  243  to close openings  254 , and separate from bottom wall  243  to open openings  254 , based on the pressure differential between ink chamber  73  and valve accommodating chamber  88 . More specifically, check valve  95  may selectively allow ink to flow from ink chamber  73  to valve accommodating chamber  88  through openings  254  while disc portion  233  is separated from bottom wall  243 , and prevent ink from flowing from valve accommodating chamber  88  to ink chamber  73  while disc portion  233  contacts bottom wall  243 . 
     The diameter of each of openings  244  is less than the diameter of an opening  149 A of an ink supply tube  149 , as shown in  FIG. 16 . The diameter of each of openings  244  may between 0.30 mm and 0.55 mm. When ink passes through openings  244 , air bubbles contained in ink which are larger than the openings  244  may be divided by openings  244  into minute air bubbles having substantially the same diameter as that of openings  244 . 
     Referring to  FIG. 7 , when air is supplied into ink chamber  73  by pump  170  while opening  87  is open, the pressure in ink chamber  73  increases until it is greater than the pressure in valve accommodating chamber  88 , at which time opening  89  is opened by check valve  95  and opening  106  is closed by check valve  93 . When this occurs, ink stored in ink chamber  73  may flow into valve accommodating chamber  88  via flow path  91 , and flow out of main ink tank  70  via opening  87 . In contrast, when air is drawn from ink chamber  73  by pump  170 , the pressure in ink chamber  73  decreases until it is less than the pressure in valve accommodating chamber  88 , at which time opening  89  is closed by check valve  95  and opening  106  is opened by check valve  93 . When this occurs, ink may flow from flexible tube  32  into valve accommodating chamber  88 , and then into ink chamber  73  via flow path  92 . 
     In this embodiment, when ink flows into valve accommodating chamber  88  via opening  87 , ink may flow from valve accommodating chamber  88  to ink chamber  73  via flow path  92 . When ink flows out to the exterior of main ink tank  70  via opening  87 , ink may flow from ink chamber  73  to the exterior of main ink tank  70  via flow path  91 . Because check valve  93  is positioned in flow path  92  and check valve  95  is positioned in flow path  91 , a circulating flow path along which ink circulates uni-directionally is formed in main ink tank  70 , as shown in  FIG. 7 . 
     Referring to  FIG. 7 , sensor arm  150  may comprise at least one resin, e.g., a synthetic resin, and may be manufactured by injection molding. Sensor arm  150  may comprise a float portion  152 , a connection portion  153  comprising shaft  158 , and an arm portion  154 . Float portion  152  may extend from connection portion  153  in a direction perpendicular to a direction in which shaft  158  extends. The specific gravity of float portion  152  may be less than the specific gravity of ink stored in ink chamber  73 . Therefore, float portion  152  may be configured to float on ink if the movement of float portion  152  is not restricted. Float portion  152  may have a hollow space formed therein, or may comprise a solid material having a specific gravity which is less than the specific gravity of ink. 
     Arm portion  154  may comprise a first arm  155 , a second arm  156 , and light blocking portion  157 . First arm  155  may extend from connection portion  153  in a direction perpendicular to the direction in which float portion  152  extends. Second arm  156  may extend from first arm  155  in a direction away from float portion  152 . Light blocking portion  157  may be connected to an end of second arm  156 . 
     Arm portion  154  may have less mass than float portion  152 . As shown in  FIG. 6 , because the float portion  152  may be heavier than the arm portion  154 , sensor arm  150  may be configured to pivot about shaft  158  in a counterclockwise direction  162 , and at least a portion of light blocking member  157  may be configured to move out of inner space  76  of detection portion  75 , when ink chamber  76  does not store ink therein. Float portion  152  may comprise a bottom end, and ink chamber  73  may comprise a bottom inner wall surface. When the bottom end of float portion  152  contacts the bottom inner wall surface of ink chamber  73 , sensor arm  150  may be configured to stop pivoting, and light blocking portion  157  may be positioned, as shown in  FIG. 6 . 
     Referring to  FIG. 11 , when ink tank  76  is filled with the predetermined amount of ink, the entirety of sensor arm  150  may be submerged in ink. In this state, the buoyancy force acting on float portion  152  may be greater than the buoyancy force acting on arm portion  154 , and the buoyancy force acting on float portion  152  may be sufficient enough to pivot sensor arm  150  around shaft  158  in a clockwise direction  163 , as shown in  FIG. 11 , even when float portion  152  has a greater mass than the arm portion  154 . Light blocking portion  157  may be configured to move into inner space  76  of detection portion  75 , in accordance with the pivot of sensor arm  150 . Sensor arm  150  may be configured to stop pivoting when light blocking portion  157  contacts support wall  74 . 
     Referring to  FIGS. 12-13(B) , air communication valve mechanism  110  may be configured to allow fluid communication between the atmosphere and air layer  83  via opening  101 . Air communication valve mechanism  110  may comprise a cap  111 , coil spring  112 , valve  113 , and valve seat  114 . Cap  111 , coil spring  112 , valve  113 , and valve seat  114  may be aligned in this order in the X-axis direction, as shown in  FIG. 12 . Coil spring  112 , valve  113 , and vale seat  114  may be accommodated in valve accommodating chamber  85 , and cap  111  may be attached to the surrounding area of opening  84 . 
     Coil spring  112  may bias valve  113  towards valve seat  114  in the X-axis direction. Coil spring  112  may comprise a metal material or a resin material. Coil spring  112  may be accommodated in valve accommodating chamber  85  in a compressed state, and may generate a force in a direction in which coil spring  112  expands. Coil spring  112  may be replaced with any urging member, e.g., a leaf spring, which urges valve  113  towards valve seat  114 . 
     Cap  111  may comprise a circular end wall  119  and a cylindrical side wall  118  extending from the outer edge of end wall  119 . End wall  119  may contact coil spring  112 . Two slots  120  may be formed through side wall  118 , and two ribs may be formed on the surrounding area of opening  84  and inserted into slots  120 . Cap  111  may be attached to the surrounding area of opening  84 . 
     Valve  113  may comprise piston  116 , and rod  117  extending from piston  116 . Piston  116  may contact coil spring  112 . Piston  116  may be biased toward valve seat  114  in the X-axis direction. A circular groove  122  may be formed in the peripheral wall of piston  116 , and an elastic O-ring  121  may be fitted in groove  122 . The outer diameter of O-ring  121  may be greater than the outer diameter of the peripheral wall of piston  116 . Valve  113  may be configured to slide inside valve accommodating chamber  85 , with O-ring  121  contacting the wall surface of valve accommodating chamber  85 , while preventing fluid communication between the coil spring  112  side of piston  116  and the rod  117  side of piston  116 . 
     Valve seat  114  may be configured to contact piston  116 , which is biased by coil spring  112  in the X-axis direction, and may be positioned at the end of valve accommodating chamber  85 . Valve seat  114  may have an annular shape with an opening  115  formed through the center thereof. The center of opening  115  may be aligned with the center of opening  100 , which is formed at the end of valve accommodating chamber  85 . A portion of rod  117  may be positioned in opening  115 . Valve seat  114  may comprise an elastic material, e.g. rubber, allowing valve seat  114  and piston  116  urged by coil spring  112  to contact tightly without a gap therebetween. 
     Referring to  FIG. 13(A) , when an external force is not applied to rod  117 , valve  113  may be biased by coil spring  112 , and may be positioned at a position P 1 , at which piston  116  contacts valve seat  114 . Piston  116  and valve seat  114  may contact tightly, and valve seat  114  and the end of valve accommodating chamber  85  may contact tightly. Fluid communication between ink chamber  73  and valve accommodating chamber  85  via openings  100  and  115  may be prevented. 
     Referring to  FIG. 13(B) , when an external force, which may be greater than the biasing force of coil spring  112 , is applied to rod  117  in a direction  123 , valve  113  may move against the biasing force of coil spring  112  in direction  123 , and piston  116  may separate from valve seat  114 . Valve  113  may move to a position P 2 , at which position piston  116  may contact end wall  119  of cap  111 . When this occurs, fluid communication between the atmosphere and ink chamber  73  may be established via opening  100 , opening  115 , valve accommodating chamber  85 , and opening  101 , as indicated by arrows  124 . The external force may be applied by a piston  181  when a plunger  172  is pushed into an end of cylindrical tube  171 , and piston  181  may push rod  117 , as described below. 
     Referring to  FIG. 14 , pump  170  may be configured to selectively supply air to air layer  83  formed in ink chamber  73 , and to draw air from air layer  83 . When air is supplied to air layer  83 , the air pressure of air layer  83  may increase, which may cause ink stored in ink chamber  73  to flow out of ink chamber  73 . As a result, the volume of air layer  83  may increase. When air is drawn from air layer  83 , the air pressure of air layer  83  decreases, which may cause ink to flow into ink chamber  73 . As a result, the volume of air layer  83  may decrease. 
     Pump  170  may comprise cylindrical tube  171  and plunger  172 , each of which may comprise at least one synthetic resin, and may be manufactured by injection molding. 
     Cylindrical tube  171  may be attached to upper face  78  of main ink tank  70 . Cylindrical tube  171  may have a central axis extending between front end  176  and rear end  175 , and the central axis of cylindrical tube  171  may be parallel with the X-axis direction. Cylindrical tube  171  may have an opening  174  at front end  176  thereof adjacent to front face  79  of main ink tank  70 . Plunger  172  may be inserted into inner space  171 A of cylindrical tube  171  through opening  174 . Cylindrical tube  171  may comprise an end wall  179  at rear end  175  thereof, which contacts pump seat  98 . An opening  173  may be formed through end wall  179 . Air in inner space  171 A may flow into and out of ink chamber  73  via opening  173 . 
     An annular attachment member  177  may be provided at rear end  175 . A portion of attachment member  177  may be buried in end wall  179 , and the other portion of attachment member  177  may extend from rear end  175  in the axial direction of cylindrical tube  171 . Pump seat  98  may have an annular groove formed therein, and the extending portion of attachment member  177  may be fitted in the groove of pump seat  98 . Rear end  175  of cylindrical tube  171  may thus be attached to pump seat  98 . Attachment member  177  may be coated with a rubber material, and therefore, attachment member  177  and pump seat  98  may contact tightly without a gap therebetween. As a result, an air path between inner space  171 A of cylindrical tube  171  and ink chamber  73  may be air-tightly sealed, such that air may not leak from the air path and air may not enter into the air path from the atmosphere. 
     Cylindrical tube  171  may comprise a flange  178  at front end  176 , and flange  178  may extend from cylindrical tube  171  in the radial direction of cylindrical tube  171 . Rear end  175  of cylindrical tube  171  may be inserted into opening  102  of pump seat  99 , and when front end  176  of cylindrical tube  171  reaches pump seat  99 , flange  178  may contact the surrounding area of opening  102 . 
     Plunger  172  may comprise piston  181  and rod  182 , which may be integrally formed. A circular groove  184  may be formed in the peripheral wall of piston  181 , and an elastic O-ring  183  may be fitted in groove  184 . The outer diameter of O-ring  184  may be greater than the outer diameter of the peripheral surface of piston  181 . Piston  181  may be configured to slide within inner space  171 A with O-ring  184  contacting the inner surface of cylindrical tube  171 , while preventing air communication between the front-end  176  side of piston  181  and the rear-end  175  side of piston  181 . In another embodiment, O-ring  183  may be omitted, and the peripheral surface of piston  181  may be coated with an elastic material, and piston  181  may be configured to slide on the inner surface of cylindrical tube  171  with the peripheral surface of piston  181  contacting the inner surface of cylindrical tube  171  while preventing fluid communication between the front-end  176  side of piston  181  and the rear-end  175  side of piston  181 . 
     A rack gear  185  may be formed on the upper surface of rod  182 . Rack gear  185  may be configured to engage a pinion gear  221 . A driving force thus may be transferred to piston  181  via rod  182 , to slide piston  181  in the axial direction of cylindrical tube  171 . When piston  181  slides towards rear face  80  of main ink tank  70  in the X-axis direction, the volume of inner space  171 A of cylindrical tube  171  may decrease. Air corresponding to the decrease of the volume of inner space  171 A may be supplied to air layer  83  formed in ink chamber  73  via openings  173  and  103 . When piston  181  slides towards front face  79  of main ink tank  70  in the X-axis direction, the volume of inner space  171 A of cylindrical tube  171  may increase. Air may be drawn from air layer  83  into inner space  171 A via openings  173  and  103 . 
     The capacity of pump  170  may be greater than or equal to the capacity of sub ink tank  21  and the capacity of tube  32 . The capacity of pump  170  may be determined based on the cross sectional area of inner space  171 A of cylindrical tube  171  and the moving range of piston  181 . Cylindrical tube  171  may have a cross sectional area and a length which allows the capacity of pump  170  to be greater than or equal to the capacity of sub ink tank  21  and the capacity of tube  32 . The moving range of piston  181  may be predetermined by a driving mechanism  220 . Pump  170  may be configured to supply a predetermined amount of air into ink chamber  73 , and may draw the predetermined amount of air from ink chamber  73 . 
     Referring to  FIGS. 15 and 16 , ink supply valve mechanism  130  may be configured to supply ink in ink chamber  73  to the exterior of ink cartridge  50 , and may be connected to tube  32 . Ink supply valve mechanism  130  may comprise a cap  131 , a valve seat  132 , valve  133 , and spring unit  134 . Cap  131 , valve seat  132 , valve  133 , and spring unit  134  may be aligned in this order in the X-axis direction. Valve  133  and spring unit  134  may be accommodated within valve accommodating chamber  88 . A portion of valve seat  132  may be fitted in opening  87  from the exterior of valve accommodating chamber  88 . Cap  131  may be attached to the surrounding area of opening  87  via valve seat  132 , which may comprise an elastic synthetic resin. Valve seat  132  may have an annular shape with an opening  137  formed through the center thereof. 
     Valve seat  132  may comprise a first cylindrical portion  135  and a second cylindrical portion  136 . First cylindrical portion  135  may be fitted in opening  87  and second cylindrical portion  136  may contact the surrounding portion of opening  87 . A rigid ink supply tube  149  may be connected to an end of tube  32 . Ink supply tube  149  may be configured to be in fluid communication with valve accommodating chamber  88  via opening  137  when ink cartridge  50  is mounted to cartridge mounting portion  200 . More specifically, ink supply tube  149  may be configured to be inserted through opening  137  when ink cartridge  50  is mounted to cartridge mounting portion  200 . The diameter of opening  137  may be slightly smaller than the outer diameter of ink supply tube  149 . Consequently, when ink supply tube  149  is inserted through opening  137 , the outer surface of ink supply tube  149  may press the inner surface of valve seat  132 , which defines opening  137 , and the outer surface of ink supply tube  149  and the inner surface of valve seat  132  may contact tightly, which may prevent ink leakage between ink supply tube  149  and valve seat  132 . 
     Cap  131  may comprise a circular end wall  129  and a side wall  139  extending from the outer edge of end wall  129 . End wall  129  may have an opening  138  formed therethrough. Two slots  140  may be formed through side wall  139 . Two ribs are formed on the surrounding area of opening  87 , and the ribs may be inserted into slots  140 . Cap  131  may be attached to the surrounding area of opening  87 . 
     Spring unit  134  may be configured to bias valve  133  towards valve seat  132  in the X-axis direction. Spring unit  134  may comprise a first spring  144 , a second spring  145 , and a slider  146 . Each of first spring  144  and second spring  145  may comprise an elastic resin material, and may have an indented, rounded shape, e.g., a bowl shape, or a hollow circular conic shape. When a load is applied to first spring  144  or second spring  145 , the side surface thereof may be elastically deformed. 
     First spring  144  and second spring  145  may have an opening  144 A and an opening  145 A formed therethrough, respectively. Ink may flow through the interior of first spring  144  and second spring  145  via openings  144 A and  145 A, respectively, as indicated by arrows  16  in  FIG. 16 . Slider  146  may comprise two accommodating chambers which accommodate first spring  144  and second spring  145  therein, respectively. 
     Spring unit  134  may be accommodated in valve accommodating chamber  88  in a compressed state, and may generate a force in a direction which causes spring unit  134  to expand. End wall  105  may contact and support spring unit  134 . 
     Slider  146  may comprise ribs  147  for coupling valve  133  and spring unit  134 . Valve  133  may comprise claws  143 , which may be configured to engage ribs  147 . Any member may be used instead of spring unit  134 , as long as the member urges valve  133  towards valve seat  132 . 
     Valve  133  may comprise a circular end wall  141  and a cylindrical side wall  142  extending from the outer edge of end wall  141 . End wall  141  may have a plurality of openings  141 A formed therethrough, and openings  141 A may be aligned in the circumferential direction of end wall  141 . End wall  141  contacts first spring  144 . Side wall  142  may comprise claws  143 . Valve  133  and spring unit  134  may be coupled by the engagement between claws  143  and ribs  147 . Valve accommodating chamber  88  may comprise a cylindrical wall surface extending from opening  87  to the end of the valve accommodating chamber  88 . Valve  133  may be configured to slide within valve accommodating chamber  88  in the X-axis direction, with a gap  148  between side wall  142  and the wall surface of valve accommodating chamber  85 , and ink may flow through gap  148 . 
     When ink supply tube  149  is inserted into valve accommodating chamber  88  via openings  138  and  137 , an end of ink supply tube  149  may contact end wall  141  of valve  133  and press valve  133  against the biasing force of spring unit  134 . Valve  133  may move toward ink chamber  73 , and end wall  141  may separate from valve seat  132 . Tube  149  may have opening  149 A formed therethrough, adjacent to the end of tube  149 . When end wall  141  separates from valve seat  132 , fluid communication between valve accommodating chamber  88  and the interior of tube  149 , via opening  149 A, may be established. 
     When ink is supplied from ink chamber  73  to sub ink tank  21 , ink may enter into valve accommodating chamber  88  via check valve  95 , and then the ink may flow through gap  148  or flow through spring unit  134  and openings  141 A, as indicated by arrows  164  in  FIG. 16 . When ink is drawn from sub ink tank  21  to ink chamber  73 , ink may flow into valve accommodating chamber  88  via opening  149 A, and then the ink may flow to air layer  83  via buffer chamber  90  and check valve  93 . 
     Referring to  FIGS. 17-20 , cartridge mounting portion  200  may be configured to receive at least one ink cartridge  50 . In an embodiment, cartridge mounting portion  200  may receive a plurality of, e.g., five, ink cartridges  50  storing cyan ink, magenta ink, yellow ink, dye-based black ink, and pigment-based black ink, respectively. Cartridge mounting portion  200  may comprise a cartridge case  201  having an opening  202  on one side, and a closed end opposite the opening  202 . Ink cartridge  50  may be inserted into cartridge case  201  through opening  202 . When ink cartridge  50  is inserted into cartridge case  201  and is pressed in the X-axis direction, ink supply tube  149 , provided at the closed end of cartridge case  201 , may enter into ink supply valve mechanism  130 . After ink stored in ink chamber  73  is consumed, ink cartridge  50  may be removed from cartridge case  201  and replaced with a new ink cartridge  50 . 
     At least one optical sensor  203 , e.g., a photo interrupter, may be positioned at the closed end of cartridge  201 . Optical sensor  203  may comprise a light emitting portion and a light receiving portion. Optical sensor  203  may be configured to output a predetermined signal to the main controller of inkjet recording device  10  based on the intensity of light received by the light receiving portion. A plurality of, e.g., five, optical sensors  203  may be provided for the plurality of, e.g., five, ink cartridges  50 , respectively. Optical sensor  203  may be positioned, such that detection portion  75  is positioned between the light emitting portion and the light receiving portion when the ink cartridge  50  is mounted to cartridge mounting portion  200 . 
     When light blocking portion  157  is positioned within detection portion  75 , light blocking portion  157  may block light emitted from the light emitting portion. When light blocking portion  157  is positioned outside of detection portion  75 , light emitted from the light emitting portion may reach the light receiving portion unhindered. Based on the intensity of light received by the light receiving portion, the amount of ink remaining in ink cartridge  50  may be determined. 
     Driving mechanism  220  may be positioned behind cartridge mounting portion  200 . Driving mechanism  200  may comprise at least one pinion gear  221 , a shaft  222 , a link rod  223 , a shaft  224 , a first gear  225 , and a second gear  226 . 
     A plurality of, e.g., five, pinion gears  221  may be provided, corresponding to the plurality of, e.g., five, ink cartridges  50 . Pinion gear  221  may be configured to engage rack gear  185  when ink cartridge  50  is mounted to cartridge mounting portion  200 . Pinion gear  221  may have a semi-circular shape, and the teeth may be formed on the arc portion of pinion gear  221 . 
     A plurality of, e.g., five, pinion gears  221  may be fixed to shaft  222 . When shaft  222  rotates, all of the pinion gears  221  may rotate in the same direction in which shaft  222  rotates, and at the same speed at which shaft  222  rotates. Link rod  223  may be coupled to one end of shaft  222  at one end thereof, and may be coupled to shaft  224  at the other end thereof. First gear  225  may be fixed to shaft  224 , and second gear  226  may engage first gear  225 . 
     Second gear  226  may be coupled to a driving source, e.g., a motor. Paper feed device  12  and convey device  13  may be coupled to the same driving source, which may be controlled by the main controller of inkjet recording device  10 . 
     When a driving force is transferred to second gear  226  from the driving source, the driving force also may be transferred to rack gear  185  via first gear  225 , shaft  224 , link rod  223 , shaft  222 , and pinion gear  221 . Thus, piston  181  may be configured to slide back and forth within cylindrical tube  171 . 
     Referring to  FIGS. 21(A)-21(C) , an ink supply process from main ink tank  70  to sub ink tank  21  by an ink supply system  11 , according to an embodiment of the present invention, is depicted. During the ink supply process, opening  42  formed at cylinder  39  of valve mechanism  37  may be opened as described above. 
     Referring to  FIG. 21(A) , when plunger  172  is moved toward rear face  80  of main ink tank  70  from a state in which plunger  172  is positioned as far out of cylindrical tube  171  as its range of motion may allow, air in cylindrical tube  171  may be supplied to air layer  83  formed in ink chamber  73 , via openings  173  and  103 . As a result, the pressure in ink chamber  73  may increase. Referring to  FIG. 21(B) , when the pressure in ink chamber  73  increases and becomes greater than the pressure in valve accommodating chamber  88 , check valve  95  may open opening  89 , and ink stored in ink chamber  73  may flow into valve accommodating chamber  88 , via opening  89  and openings  254  of valve seat  251 . Ink then may flow into tube  32  and may be supplied to sub ink tank  21 , as indicated by arrows  23 . More specifically, ink may flow from ink chamber  73  via openings  254  of valve seat  251  into valve accommodating chamber  88 . Ink then passes through and around spring unit  134 , and flows into the interior of tube  32  via opening  149 A of ink supply tube  149 . Ink then flows into sub ink tank  21  via the interior of tube  32 . As a result, the volume of air layer  83  may increase. Referring to  FIG. 21(C) , when plunger  172  is moved to the end of cylindrical tube  171 , sub ink tank  21  and tube  32  may be filled with ink. 
     Referring to  FIG. 21(C) , when plunger  172  is moved back towards front face  79  of main ink tank  70  from a state in which plunger  172  is pushed into cylindrical tube  171  as far as plunger  172 &#39;s range of motion may allow, air may be drawn from air layer  83  into cylindrical tube  171  via openings  103  and  173 . As a result, the pressure in ink chamber  73  may decrease. Referring to  FIG. 21(B) , when the pressure in ink chamber  73  decreases and becomes less than the pressure in valve accommodating chamber  88 , check valve  93  may open opening  106 , and ink stored in sub ink tank  21  and tube  32  may flow into main ink tank  70 , as indicated by arrows  24 . More specifically, ink in valve accommodating chamber  88  may flow into ink chamber  73  via opening  104  and openings  244  of valve seat  241 . This may cause ink in sub ink tank  21  to flow into valve accommodating chamber  88  via tube  32 , which may result in a decrease in the volume of air layer  83 . 
     Referring again to  FIG. 21(A) , when plunger  172  is positioned as far out of cylindrical tube  171  as its range of motion may allow, ink in tube  32  and sub ink tank  21  may be completely drawn into main ink tank  70 . During the process in which ink is drawn into ink chamber  73  of main ink tank  70 , air bubbles trapped in tube  32  or sub ink tank  21  also may be drawn into ink chamber  73  via ink path  92 . 
     When the ink passes through openings  244 , air bubbles contained in ink may be divided by openings  244  into minute air bubbles having substantially the same diameter as openings  244 . The minute air bubbles may enter the ink chamber  73 . The minute air bubbles in ink chamber  73  may rise toward air layer  83  by buoyancy acting thereon. The minute air bubbles may rise while capturing minute impurities, such as minute dusts, which are present around the minute air bubbles. When the minute air bubbles reach air layer  83 , the minute air bubbles may move to the inner wall surface of the main ink tank  70  and may adhere to the inner wall surface. When this occurs, the impurities captured by the minute air bubbles also may adhere to the inner wall surface. Even when the minute air bubbles adhering to the inner wall surface of main ink tank  70  are broken and disappear, the impurities may continue to adhere to the inner wall surface. Accordingly, the impurities contained in ink may be separated from ink and collected at positions adjacent to air layer  83 . Subsequently, as described above, by supplying ink from main ink tank  70  to sub ink tank  21 , ink free from impurities may be supplied to the sub ink tank  21  via the tube  32 . 
     In this embodiment, because the air bubbles contained in ink are divided into the minute air bubbles when the ink flows into the ink chamber  73  via flow path  92 , the minute impurities contained in ink stored in ink chamber  73  may be captured by the minute air bubbles and collected at positions adjacent to air layer  83 . Consequently, ink free from the impurities may be supplied to recording head  26 , and consequently, clogging of nozzles  28  of recording head  26  or ink ejection failure may be prevented. 
     Because of check valves  93  and  95 , when ink flows into main ink tank  70 , ink flows into ink chamber  73  via flow path  92 , and when ink flows out of main ink tank  70 , ink flows out via flow path  91 . Therefore, even when ink flows out of main ink tank  70  immediately after ink flows into main ink tank  70 , the minute air bubbles drifting in ink chamber  73  may not be supplied to recording head  26 . When ink flows from main ink tank  70  to recording head  26 , ink passes through openings  254 , which have less flow resistance than that of openings  244 , and therefore, ink may flow smoothly. 
     In this embodiment, minute openings  244  are formed through valve seat  241  of check valve  93 . Nevertheless, openings  244  alternatively may be formed through end wall  107 , and a valve may selectively open and close openings  244  formed through end wall  107 . 
     In this embodiment, pump  170  is mounted on the ink cartridges  50 . In another embodiment, pump  170  may be mounted on cartridge mounting unit  200 , or pump  170  may be mounted on the carriage  30 . Pump  170  also may be positioned at a position other than cartridge mounting unit  200  and carriage  30 . Another type of pump, such as a tube pump, may be used instead of pump  170 . 
     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.