Patent Publication Number: US-8529033-B2

Title: Liquid supply systems

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application claims priority to and the benefit of Japanese Patent Application No. 2009-158405, which was filed on Jul. 3, 2009, 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 to liquid supply systems configured to supply liquid. 
     2. Description of the Related Art 
     A known liquid supply system has a liquid cartridge that stores liquid, and a cartridge mounting portion. The liquid cartridge is configured to be mounted to the cartridge mounting portion in a mounting direction. Liquid is supplied to a supply destination from the liquid cartridge positioned in a mounted position in the cartridge mounting portion. The cartridge mounting portion or the liquid cartridge has an urging member configured to urge the liquid cartridge in a demounting direction, which is opposite to the mounting direction. 
     For example, another known liquid cartridge has a supply portion having a supply path formed therethrough, and liquid stored in the liquid cartridge is supplied to the outside of the liquid cartridge through the supply path. If the supply path always communicates with the outside of the liquid cartridge, then the liquid flows out through the supply path even when it is not intended. Therefore, in order to allow the liquid to be supplied to the outside of the liquid cartridge only when the liquid cartridge is positioned in the mounted position in the cartridge mounting portion, the known supply portion has a valve mechanism including a valve capable of selectively opening and closing the supply path and a spring urging the valve in a direction for the valve to close the supply path. When the liquid cartridge is mounted to the cartridge mounting portion in the mounting direction, the valve is moved against the urging force applied by the spring of the valve mechanism, such that the spring contracts and the valve opens the supply path, the supply path is brought into communication with a liquid path formed in the cartridge mounting portion, and the liquid can be supplied from the supply path into the liquid path. Thus, when the liquid cartridge is in the mounted position of the cartridge mounting portion, the liquid cartridge is urged in the demounting direction, opposite to the mounting direction, by the force of the contracted spring. 
     Hence, the cartridge mounting portion has a locking mechanism configured to retain the liquid cartridge in the mounted position against the urging force of the spring. When the liquid cartridge retained by the locking mechanism is released, the liquid cartridge ejects out of the cartridge mounting portion due to a kinetic energy produced by the urging force of the spring and transferred to the liquid cartridge. If the liquid cartridge that has jumped out of the cartridge mounting portion falls over, liquid may splash out of the liquid cartridge. 
     In another known liquid supply system, to allow a user to readily remove a liquid cartridge from a cartridge mounting portion, an urging member configured to urge the liquid cartridge in the demounting direction is positioned in the cartridge mounting portion. When a plurality of liquid cartridges are placed side by side in the cartridge mounting portion, it may be difficult to demount only one of those liquid cartridges from the cartridge mounting portion because the presence of the cartridges adjacent thereto hinders the demounting. With the urging member urging the liquid cartridge in the demounting direction, however, only the liquid cartridge that the user intends to demount can be moved in the demounting direction, such that the liquid cartridge becomes offset from the other liquid cartridges in the demounting direction. Nevertheless, if the liquid cartridge is moved and completely comes out of the cartridge mounting portion, the liquid cartridge that has come out may fall over and liquid may splash out of the liquid cartridge and taint the environment. 
     In a known inkjet recording apparatus, e.g., the inkjet recording apparatus described in Patent Application Publication No. JP 2005-288866 A, an elastic member is provided in a bottom plate of a cartridge mounting portion. The elastic member has a hook and is bendable. During mounting of an ink cartridge to the cartridge mounting portion, the bottom surface of the ink cartridge comes into contact with the hook, and the elastic member bends. When the ink cartridge is locked or retained at a mounted position, the elastic member has returned to its original position from the bended position, and the hook is positioned in a recess provided in the bottom surface of the ink cartridge. When the demounting of the ink cartridge from the cartridge mounting portion is attempted, the ink cartridge moves to jump out of the cartridge mounting portion by being urged by an urging member in the demounting direction. Nevertheless, because the hook comes into contact with an end of the recess of the ink cartridge, the movement of the ink cartridge is restricted, which prevents the ink cartridge from jumping out of the cartridge mounting portion. 
     Nevertheless, when the ink cartridges are mounted to and demounted from the cartridge mounting portion repeatedly, the elastic member may become fatigued and may not return to its original position from the bended position. If the elastic member remains in the bended position, the hook may not be able to come into contact with the end of the recess of the ink cartridge even if the ink cartridge is moved in the demounting direction by the urging force of the urging member. Consequently, the movement of the ink cartridge may not be restricted, and the ink cartridge may jump out of the cartridge mounting portion. 
     In another known liquid supply system, e.g., the ink supply system described in Patent Application Publication No. US 2009/0135237 A1, a cartridge mounting portion has a locking arm configured to retain an ink cartridge by coming into contact with the ink cartridge placed in a mounted position in the cartridge mounting portion. When a user presses down an operation lever of the locking arm, the locking arm pivots in a direction, such that the ink cartridge becomes released, and a stopper of the locking arm is moved to such a position as to come into contact with the ink cartridge moved by an urging member and thus to restrict the movement of the ink cartridge. Nevertheless, if the lever of the locking arm is not sufficiently pressed down by the user, the locked ink cartridge may be released, but the stopper of the locking arm may not reach such a position as to contact the ink cartridge being moved by the urging member. In such a case, the movement of the ink cartridge may not be restricted, and the ink cartridge may jump out of the cartridge mounting portion. 
     SUMMARY OF THE INVENTION 
     Therefore, a need has arisen for liquid supply systems which overcome these and other shortcomings of the related art. A technical advantage of the present invention is that chances of a liquid cartridge jumping out of a cartridge mounting portion are reduced. 
     In an embodiment of the invention, a liquid supply system comprises a liquid cartridge comprising a liquid chamber configured to store liquid therein, a cartridge mounting portion, wherein the liquid cartridge is configured to be removably mounted to the cartridge mounting portion in a mounting direction, and an urging member positioned in one of the liquid cartridge and the cartridge mounting portion and configured to urge the liquid cartridge in a demounting direction opposite to the mounting direction when the liquid cartridge is positioned in a mounted position in the cartridge mounting portion, wherein the liquid cartridge is configured to supply liquid stored in the liquid chamber to the cartridge mounting portion in the mounted position. The cartridge mounting portion comprises a bottom plate comprising a first surface extending from a front end of the first surface to a rear end of the first surface, in the mounting direction, of the first surface in a first direction parallel to the demounting direction, wherein the first surface is configured to support the liquid cartridge and a second surface that borders the first surface and extends from the second end of the first surface in a second direction, wherein an angle formed between the second direction and a downward vertical direction is less than an angle formed between the first direction and the downward vertical direction. 
     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 
       For a more complete understanding of the present 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 drawing. 
         FIG. 1  is a schematic top view of a printer according to an embodiment of the invention. 
         FIG. 2  is a cross-sectional view of an ink supply system taken along a plane that is parallel to a mounting direction and perpendicular to a horizontal plane according to an embodiment of the invention. 
         FIG. 3  is a cross-sectional view of an ink cartridge taken along a plane that is parallel to the mounting direction and perpendicular to the horizontal plane according to an embodiment of the invention. 
         FIG. 4  is a cross-sectional view of a cartridge mounting portion of a holder taken along a plane that is parallel to the mounting direction and perpendicular to the horizontal plane according to an embodiment of the invention. 
         FIG. 5A  is a cross-sectional view of the ink supply system taken along a plane that is parallel to the mounting direction and perpendicular to the horizontal plane, during mounting of the ink cartridge to the cartridge mounting portion. 
         FIG. 5B  is another cross-sectional view of the ink supply system taken along a plane that is parallel to the mounting direction and perpendicular to the horizontal plane, in which the ink cartridge is positioned in a mounted position. 
         FIG. 6A  is a cross-sectional view of the ink supply system taken along a plane that is parallel to the mounting direction and perpendicular to the horizontal plane immediately after a locked ink cartridge is released. 
         FIG. 6B  is another cross-sectional view of the ink supply system taken along a plane that is parallel to the mounting direction and perpendicular to the horizontal plane some time after the locked ink cartridge is released. 
         FIG. 7  is a cross-sectional view of an ink supply system taken along a plane that is parallel to the mounting direction and perpendicular to the horizontal plane, according to another embodiment of the invention. 
         FIG. 8A  is a cross-sectional view of the ink supply system taken along a plane that is parallel to the mounting direction and perpendicular to the horizontal plane immediately after a locked ink cartridge is released, according to yet another embodiment of the invention. 
         FIG. 8B  is another cross-sectional view of the ink supply system taken along a plane that is parallel to the mounting direction and perpendicular to the horizontal plane some time after the locked ink cartridge is released, according to yet another embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION 
     Embodiments of the present invention, and their features and advantages, may be understood by referring to  FIGS. 1-8B , like numerals being used for like corresponding parts in the various drawings. 
     Referring to  FIG. 1 , a printer  1  comprises a carriage  2  configured to reciprocate in a scanning direction, e.g., the lateral direction when the printer is positioned as shown in  FIG. 1 , an inkjet head  3  and sub-tanks  4   a  to  4   d  mounted on the carriage  2 , an ink supply system  21 , as an example of a liquid supply system, comprising cartridge mounting portions  7  and ink cartridges  5 , as an example of liquid cartridges, storing different color inks, respectively, and configured to be demountably mounted to cartridge mounting portions  7 , respectively, a conveyance mechanism  6  configured to convey a recording sheet P in a conveying direction that is perpendicular to the scanning direction. 
     The carriage  2  may be configured to reciprocate along two guide shafts  17  extending substantially parallel to the scanning direction. An endless belt  18  may be connected to the carriage  2 . When the endless belt  18  is driven to run by a carriage drive motor  19 , the carriage  2  may move in the scanning direction with the running of the endless belt  18 . 
     The carriage  2  may carry the inkjet head  3  and the four sub-tanks  4   a  to  4   d . The inkjet head  3  may have a number of liquid ejection nozzles formed in the bottom face thereof, e.g., the face hidden behind in  FIG. 1 . The four sub-tanks  4   a  to  4   d  may be arranged side by side in the scanning direction. A tube joint  20  may be integrally positioned with the four sub-tanks  4   a  to  4   d . The four sub-tanks  4   a  to  4   d  may be in fluid communication with the four ink cartridges  5 , respectively, via flexible tubes  11  connected to the tube joint  20 . 
     The four ink cartridges  5  may be configured to store inks of four colors, for example, black; yellow; cyan; and magenta, respectively. The four ink cartridges  5  may be configured to be mounted to the four cartridge mounting portions  7  positioned in a holder  10  of the ink supply system  21 , respectively. The inks of the four colors stored in the four ink cartridges  5  may be supplied to the four sub-tanks  4   a  to  4   d  via the four tubes  11 , may be temporarily stored in the sub-tanks  4   a  to  4   d , and subsequently may be supplied to the inkjet head  3 . While the inkjet head  3  reciprocates in the scanning direction together with the carriage  2 , the inkjet head  3  may eject inks from a number of the nozzles positioned in the bottom face thereof onto the recording sheet P, conveyed by the conveyance mechanism  6  in the conveying direction. 
     The conveyance mechanism  6  may comprise a paper feed roller  25  positioned on the upstream side in the conveying direction with respect to the inkjet head  3 , and a paper discharge roller  26  positioned on the downstream side in the conveying direction with respect to the inkjet head  3 . The paper feed roller  25  and the paper discharge roller  26  may be driven to rotate by a paper feed motor  27  and a paper discharge motor  28 , respectively. The conveyance mechanism  6  may be configured to feed the recording sheet P to the inkjet head  3  from the upper side in  FIG. 1  by using the paper feed roller  25 , and to discharge the recording paper P having an image, characters, and the like recorded thereon by the inkjet head  3  toward the lower side in  FIG. 1  by using the paper discharge roller  26 . 
       FIGS. 2 to 4  illustrate the ink supply system  21  comprising the ink cartridges  5  and the holder  10  comprising the cartridge mounting portions  7 , according to an embodiment of the invention. The ink cartridge  5  may be configured to be mounted to the cartridge mounting portion  7  of the holder  10  in a mounting direction, and to be demounted from the cartridge mounting portion  7  in a demounting direction which is opposite to the mounting direction. In an embodiment, each of the mounting direction and the demounting direction is a substantially horizontal direction, and therefore, the mounting direction and the demounting direction are substantially parallel to a horizontal plane. 
     Referring to  FIGS. 2 and 3 , the ink cartridge  5  may comprise a cartridge body  30  storing ink, and a sensor arm  40  used for determining the amount of ink stored in the cartridge body  30 . The cartridge body  30  may be a substantially rectangular-parallelepiped hollow body made of a translucent, e.g., transparent or semi-transparent, material such as a synthetic resin material. The ink cartridge  5  may comprise a projection  38 . The projection may extend in the mounting direction from the upper end of the front-end face, in the mounting direction, of the cartridge body  30  when the ink cartridge  5  is positioned in a mounted position in the cartridge mounting portion  7 . The projection  38  may comprise a synthetic resin material that does not allow light, e.g., visible or infrared light, to pass therethrough. When the ink cartridge  5  is positioned in the mounted position, the projection  38  may be positioned between a light emitter  65   a  and a light receiver  65   b  of an optical sensor  65  described below. The projection  38  may be configured to block light, e.g., visible or infrared light, emitted from the light emitter  65   a  of the optical sensor  65  toward the light receiver  65   b . The ink cartridge  5  may be configured to supply ink stored in an ink chamber  31 , described in more detail herein, to an ink supply path  82 , described in more detail herein, of the cartridge mounting portion  7  when the ink cartridge  5  is positioned in the mounted position. 
     The ink cartridge  5  may comprise a projection  39 . The projection  39  may project upward from a top face  30   a  of the cartridge body  30  near the center of the top face  30   a  in the horizontal direction when the ink cartridge  5  is positioned in the cartridge mounting portion  7 . A side face  39   a  of the projection  39  facing in the demounting direction and the top face  30   a  of the cartridge body  30  may form substantially a right angle. The ink cartridge  5  also may comprise a grip  42 . The grip  42  may extend in the demounting direction from the upper end of the rear-end face, in the mounting direction, of the cartridge body  30 , e.g., from the upper end of the front-end face, in the demounting direction, of the cartridge body  30 , when the ink cartridge  5  is positioned in the mounted position in the cartridge mounting portion  7 . 
     The grip  42  may comprise a plurality of ribs  42   a  positioned therein in the form of a lattice. With the ribs  42   a  positioned in the grip  42 , deformation of the grip  42  may be suppressed when a user holds the grip  42  with a certain force, e.g., when replacing the ink cartridge  5 . The projection  39  and the grip  42  may be formed integrally with the cartridge body  30  by injection molding or the like, or may be formed separately and then may be bonded to the cartridge body  30 , e.g., with adhesive or the like. The projection  38  also may be formed integrally with the cartridge body  30 . In that case, however, the projection  38  may be made of a translucent material, and the surface of the projection  38  may be covered with a film or the like that does not allow light to pass therethrough. 
     The ink cartridge  5  may comprise the ink chamber  31  configured to store ink, an ink supply portion  32  configured to supply ink stored in the ink chamber  31  to the outside of the ink cartridge  5 , and an air communication portion  33  configured to establish fluid communication between the ink chamber  21  and the outside of the ink cartridge  5 , such that air may be introduced into the ink chamber  31 . The ink supply portion  32  and the air communication portion  33  may be positioned at the front-end face, in the mounting direction, of the cartridge body  30 , and the air communication portion  33  may be positioned above the ink supply portion  32  when the ink cartridge  5  is positioned in the mounted position. 
     The ink cartridge  5  also may comprise a detection portion  34 . The detection portion  34  may project from the front end, in the mounting direction, of the ink chamber  31 , and may be positioned between the ink supply portion  32  and the air communication portion  33  when the ink cartridge  5  is positioned in the mounted position in the cartridge mounting portion  7 . A light-blocking plate  40   c  of the sensor arm  40  may be positioned in the ink chamber  31 , and may be configured to move up and down in the detection portion  34 . When the ink cartridge  5  is in the mounted position in the cartridge mounting portion  7 , a lower portion of the detection portion  34  may be positioned between a light emitter  66   a  and a light receiver  66   b  of an optical sensor  66 , which is described in more detail herein. 
     The sensor arm  40  may comprise an arm portion  40   a  positioned in the ink chamber  31  and pivotally supported by the cartridge body  30 , a float  40   b  positioned at one end of the arm portion  40   a  and configured to move up and down according to the movement of the ink surface in the ink chamber  31 , and the light-blocking plate  40   c  positioned at the other end of the arm portion  40   a . The light-blocking plate  40   c  may be positioned in the detection portion  34  and may be configured to block light, e.g., visible or infrared light, emitted from the light emitter  66   a  toward the light receiver  66   b  of the optical sensor  66  positioned in the cartridge mounting portion  7  when the ink cartridge  5  is positioned in the mounted position in the cartridge mounting portion  7 . 
     The sensor arm  40  may be configured such that, when the float  40   b  moves up and down according to the movement of the ink surface in the ink chamber  31 , the light-blocking plate  40   c  connected to the float  40   b  via the arm portion  40   a  may move up and down in the detection portion  34  relative to the cartridge body  30 . More specifically, when there is a sufficient amount of ink stored in the ink chamber  31 , a large buoyancy acts on the float  40   b , and a moment in the counterclockwise direction in  FIG. 3  acts on the arm portion  40   a . Accordingly, as shown by the solid line in  FIG. 3 , the light-blocking plate  40   c  is in contact with the bottom surface of the detection portion  34 . In contrast, when the amount of ink remaining in the ink chamber  31  becomes small and part of the float  40   b  is exposed above the ink surface, the buoyancy acting on the float  40   b  becomes small and, as shown by the chain double-dashed line in  FIG. 3 , the arm portion  40   a  pivots clockwise in  FIG. 3 , whereby the light-blocking plate  40   c  comes into contact with the top surface of the detection portion  34 . 
     When the ink surface in the ink chamber  31  moves, the light-blocking plate  40   c  may move with the movement of the float  40   b , relative to the cartridge body  30 . The up-and-down movement of the light-blocking plate  40   c  may be limited by the bottom and top surfaces of the detection portion  34 . The ink supply portion  32  and the air communication portion  33  may extend in the mounting direction from portions adjacent to the upper and lower ends of the front-end face, in the mounting direction, of the cartridge body  30 , respectively, with the detection portion  34  positioned therebetween, when the ink cartridge  5  is positioned in the mounted position in the cartridge mounting portion  7 . The ink supply portion  32  and the air communication portion  33  may be configured such that ink stored in the ink chamber  31  is supplied in the mounting direction through an ink supply path  37  formed through the ink supply portion  32  while air is introduced from the front side, in the mounting direction, of the cartridge body  30 . The air may be introduced through an air communication path  36  formed through the air communication portion  33  into the ink chamber  31 . 
     When the ink cartridge  5  is in positioned in the mounted position in the cartridge mounting portion  7  and the ink is being supplied to the outside of the ink cartridge  5 , the air communication portion  33  is positioned adjacent to the upper end of the ink chamber  31  and the ink supply portion  32  is positioned adjacent to the lower end of the ink chamber  31 . Therefore, air may be introduced smoothly from the air communication portion  33  into an upper space of the ink chamber  31 , and ink remaining in a lower space of the ink chamber  31  may be fully supplied. 
     The ink supply portion  32  may comprise a valve-mechanism-housing chamber  52  configured to house a valve mechanism  50 . The valve-mechanism-housing chamber  52  may be configured to communicate with the outside of the ink cartridge  5  through the ink supply path  37 . Ink supply path  37  may be formed through a wall defining front end, in the mounting direction, of the valve-mechanism-housing chamber  52 . The valve-mechanism-housing chamber  52  may be in fluid communication with the ink chamber  31  and may house the valve mechanism  50  comprising a valve  53 , a spring  54 , and a sealing member  55 . The sealing member  55  may have a substantially annular shape and may be positioned on the inner wall of the valve-mechanism-housing chamber  52  at the front end of the valve-mechanism-housing chamber  52  in such a manner as to surround the ink supply path  37 . 
     The valve  53  may be urged by the spring  54  toward the sealing member  55 , such that the valve  53  may contact the sealing member  55 , thereby closing the ink supply path  37 . When the valve  53  urged by the spring  54  contacts the sealing member  55  and the ink supply path  37  is closed, ink stored in the ink chamber  31  may not be supplied from the ink supply path  37  to the outside of the ink cartridge  5 . When the ink cartridge  5  is positioned in the mounted position in the cartridge mounting portion  7 , an ink supply tube  70  of the cartridge mounting portion  7  comes into the ink supply path  37  and contacts and pushes the valve  53  against the urging force of the spring  54 . When this occurs, the spring  54  may urge the valve  53  in the mounting direction. 
     The air communication portion  33  may comprise a valve-mechanism-housing chamber  62  configured to house a valve mechanism  60 . The valve-mechanism-housing chamber  62  may be configured to communicate with the outside of the ink cartridge  5  through the air communication path  36 . Air communication path  36  may be formed through a wall defining a front end, in the mounting direction, of the valve-mechanism-housing chamber  62 . The valve-mechanism-housing chamber  62  may be in fluid communication with the ink chamber  31  and may house the valve mechanism  60  comprising a valve  63 , a spring  64 , and a sealing member  61 . The sealing member  61  may have a substantially annular shape and may be positioned on the inner wall of the valve-mechanism-housing chamber  62  at the front end of the valve-mechanism-housing chamber  62  in such a manner as to surround the air communication path  36 . 
     The valve  63  may comprise a projection  63   a  projecting frontward and may be urged by the spring  64  toward the sealing member  61 , such that the valve  63  may contact the sealing member  61  with the projection  63   a  positioned in the air communication path  36 , thereby closing the air communication path  36 . When the valve  63  urged by the spring  64  contacts the sealing member  61  and the air communication path  36  is closed, air may not be introduced from the air communication path  36  into the ink chamber  31 . When the ink cartridge  5  is positioned in the mounted position in the cartridge mounting portion  7 , a rod  71  of the cartridge mounting portion  7  contacts and pushes the projection  63   a  against the urging force of the spring  64 . When this occurs, the spring  64  may urge the valve  63  in the mounting direction. 
     When the ink cartridge  5  is positioned in the mounted position in the cartridge mounting portion  7  of the holder  10 , the ink supply tube  70  is inserted into the ink supply path  37  and pushes the valve  53  in the demounting direction against the urging force of the spring  54 . Meanwhile, the rod  71  may push the projection  63   a  of the valve  63 , which extends through the air communication path  36 , in the demounting direction against the urging force of the spring  64 . Then, the valves  53  and  63  may move away from the sealing members  55  and  61 , respectively, which may allow ink stored in the ink chamber  31  to be supplied through the ink supply path  37  to the cartridge mounting portion  7 , and air to be introduced through the air communication path  36  into the ink chamber  31 . When the ink cartridge  5  is positioned in the mounted position in the cartridge mounting portion  7  of the holder  10 , the force exerted by the spring  64  in the air communication portion  33  may be greater than the force exerted by the spring  54  in the ink supply portion  32 . 
     Because of the provision of the grip  42  at an upper rear portion, in the mounting direction, of the cartridge body  30  and the provisions of ribs (not shown) positioned in the ink chamber  31 , the ink cartridge  5  in the mounted position in the cartridge mounting portion  7  has its center of gravity, shown as Point A in  FIG. 3 , at a position in rear, in the mounting direction, of a first center line, e.g., the vertical broken line in  FIG. 3 , of the ink cartridge  5  and above a second center line, e.g., the lateral broken line in  FIG. 3  of the ink cartridge  5 . The first center line is substantially perpendicular to the mounting and demounting directions and intersects the center of the dimension, e.g., depth, of the ink cartridge  5  in the mounting and demounting directions. The second center line is substantially perpendicular to the vertical direction and intersects the center of dimension, e.g., height of the ink cartridge  5  in the vertical direction. 
     Moreover, the center of gravity of the ink cartridge  5  may be positioned at a position in rear, in the mounting direction, of a theoretical center of gravity, shown as Point B in  FIG. 3 , only for the sake of explanation of the ink cartridge  5 , which is calculated based on the assumption that the ink cartridge  5  has a homogeneous density over the entirety of the ink cartridge  5 . Such a position of the center of gravity of the ink cartridge  5  would apply when the ink cartridge  5  is empty, that is, when there is no ink in the ink cartridge  5 . Nevertheless, even in a case where there is some ink stored in the ink cartridge  5 , the center of gravity, also taking the weight of the ink into account, is preferably positioned as described above. 
     Referring again to  FIG. 1 , the holder  10  may comprise the four cartridge mounting portions  7  aligned in the scanning direction and to which the four ink cartridges  5  are to be mounted. Referring to  FIGS. 2 and 4 , the cartridge mounting portion  7  of the holder  10  may comprise a front plate  81 , a top plate  83  extending from the upper end of the front plate  81  substantially in the demounting direction, and a bottom plate  84  positioned opposite the top plate  83  and extending from the lower end of the front plate  81  substantially in the demounting direction. A cartridge-housing chamber  80  may be defined by the front plate  81 , the top plate  83 , and the bottom plate  84 , and may be formed in the cartridge mounting portion  7 . The cartridge mounting portion  7  may have an opening opposite the front plate  81 . The ink cartridge  5  may be inserted into the cartridge-housing chamber  80  through the opening toward the front plate  81 , in the mounting direction. 
     The cartridge mounting portion  7  may comprise the optical sensors  65  and  66 , the ink supply tube  70 , the rod  71 , and a locking mechanism  90 . The ink supply tube  70  may be positioned adjacent to the lower end of the front plate  81  and extends therefrom in the demounting direction. The ink supply tube  70  may comprise the ink supply path  82  formed therein and extending horizontally. The ink supply path  82  may be in fluid communication with the inkjet head  3  via the flexible tube  11  shown in  FIG. 1 . The rod  71  may be positioned adjacent to the upper end of the front plate  81  and may extend therefrom in the demounting direction. The optical sensor  66  may be positioned at a vertically center portion of the front plate  81  and may comprise the light emitter  66   a  and the light receiver  66   b . Light emitter  66   a  and light receiver  66   b  may face each other at a specific predetermined distance in a direction perpendicular to the sheet of  FIG. 3 . The optical sensor  65  may be positioned at the front plate  81  above the rod  71  and may comprise the light emitter  65   a  and the light receiver  65   b  facing each other at a specific predetermined distance in the direction perpendicular to the sheet of  FIG. 3 . 
     The locking mechanism  90  may be positioned at the top plate  83  and may comprise a locking lever  91  extending in one direction and a spring  92 . The locking lever  91  may be pivotally supported by the top plate  83  at a position between the front and rear ends of the locking lever  91  in mounting direction. Although the locking lever  91  may be urged by the contracting force of the spring  92  so as to pivot counterclockwise in  FIGS. 2 and 4  before the ink cartridge  5  is mounted to the cartridge mounting portion  7 , the locking lever  91  may be stopped in a specific position by a stopper (not shown). When the ink cartridge  5  is positioned in the mounted position in the cartridge-housing chamber  80 , the locking lever  91  is positioned in a locking position where the locking lever  91  may contact the side face  39   a  of the projection  39  of the ink cartridge  5 . The locking lever  91  may comprise an operation portion  91   a  at the rear end, in the mounting direction, of the locking lever  91 . The locking lever  91  may be configured to pivot clockwise in  FIGS. 2 and 4  when the operation portion  91   a  is pressed downward, whereby the locking lever  91  may be moved to a release position where the locking lever  91  is separated from the side face  39   a  of the projection  39 . 
     Referring to  FIG. 4 , as shown in a cross-section taken along a plane that is parallel to the mounting direction and perpendicular to a horizontal plane, the top surface of the bottom plate  84  of the cartridge mounting portion  7  may comprise a first surface  84   a  extending from the front end, in the mounting direction, of the first surface  84   a  to the rear end, in a first direction parallel to the demounting direction. The top surface of the bottom plate  84  also may comprise a second surface  84   b  contiguous with the first surface  84   a  and extending from the rear end of the first surface  84   a  in a second direction. An angle θ 1  formed between the second direction and the downward vertical direction, e.g., the direction of the gravitational force, is less than an angle θ 2  formed between the first direction and the downward vertical direction. In addition, the length of the first surface  84   a  in the first direction is greater than the length of the second surface  84   b  in the second direction. 
       FIGS. 5A and 5B , illustrate how the ink cartridge  5  is mounted to the cartridge mounting portion  7  of the holder  10 , according to an embodiment of the invention. Referring to  FIG. 5A , a user may hold the grip  42  of the ink cartridge  5  and insert the ink cartridge  5  from the opening of the cartridge mounting portion  7  into the cartridge-housing chamber  80 . The ink cartridge  5  may be mounted to the cartridge mounting portion  7  in the mounting direction while being supported by the first surface  84   a  of the bottom plate  84  of the cartridge mounting portion  7 . During the mounting of the ink cartridge  5  into the cartridge mounting portion, the front end, in the mounting direction, of the locking lever  91  may slide on the top face  30   a  of the ink cartridge  5  and may climb over the projection  39 . Because the length of the first surface  84   a  in the first direction of the bottom plate  84  is greater than the length the second surface  84   b  in the second direction, the ink cartridge  5  readily may be mounted in the mounting direction. 
     Referring to  FIG. 5B , when the ink cartridge  5  reaches the mounted position, the front end, in the mounting direction, of the locking lever  91  may contact the side face  39   a  of the projection  39  of the ink cartridge  5 , whereby the locking lever  91  locks the ink cartridge  5 . That is, the ink cartridge  5  may become unmovable in the demounting direction. 
     At the same time, the ink supply tube  70  may contact the valve  53  of the ink supply portion  32 , and the rod  71  may contact the projection  63   a  of the valve  63  of the air communication portion  33 . Then, the valves  53  and  63  may be pushed by the ink supply tube  70  and the rod  71 , respectively, causing the springs  54  and  64  to contract, whereby the ink supply path  82  in the cartridge mounting portion  7  may be placed in fluid communication with the valve-mechanism-housing chamber  52 , and the air communication path  36  is opened. Consequently, air may be introduced into the ink chamber  31  through the air communication path  36 , and the ink stored in the ink chamber  31  may be supplied via the ink supply path  37  of the ink cartridge  5  to the ink supply path  82  in the cartridge mounting portion  7 . 
     Moreover, the projection  38  projecting from the cartridge body  30  may be positioned between the light emitter  65   a  and the light receiver  65   b  of the optical sensor  65 . Light emitted from the light emitter  65   a  of the optical sensor  65  may be blocked by the projection  38  and may not be received by the light receiver  65   b . In contrast, when the ink cartridge  5  is not mounted to the cartridge mounting portion  7 , light emitted from the light emitter  65   a  of the optical sensor  65  is received by the light receiver  65   b . That is, it may be determined whether the ink cartridge  5  has been mounted to the cartridge mounting portion  7  based on whether light emitted from the light emitter  65   a  is received by the light receiver  65   b.    
     In addition, the detection portion  34  may be positioned between the light emitter  66   a  and the light receiver  66   b  of the optical sensor  66 . When there is more than sufficient amount of ink in the ink chamber  31  for operation, the light-blocking plate  40   c  housed in the detection portion  34  may be in the lowest position where the light-blocking plate  40   c  is in contact with the bottom surface of the detection portion  34 . Light emitted from the light emitter  66   a  may be blocked by the light-blocking plate  40   c  in this position and may not be received by the light receiver  66   b . In contrast, when the amount of ink remaining in the ink chamber  31  is small, the light-blocking plate  40   c  may be in the highest position where the light-blocking plate  40   c  is in contact with the top surface of the detection portion  34 . When light-blocking plate  40   c  is in this position, light-blocking plate  40   c  does not block light emitted from the light emitter  66   a , and light receiver  66   b  may receive the emitted light. That is, based on whether light emitted from the light emitter  66   a  is received by the light receiver  66   b , it may be determined whether the amount of ink remaining in the ink chamber  31  is larger or smaller than a predetermined specific amount. The specific amount may indicate a near-empty state of the ink cartridge  5  where the amount of ink remaining in the ink chamber  31  is small and the ink cartridge  5  will soon need to be replaced. 
       FIGS. 6A and 6B  illustrate how the ink cartridge  5  is demounted from the cartridge mounting portion  7 . In the following, the ink cartridge  5  in the near-empty state is demounted from the cartridge mounting portion  7 . When a user presses down the operation portion  91   a  of the locking lever  91 , the front end, in the mounting direction, of the locking lever  91  that has been in contact with the side face  39   a  of the projection  39  of the ink cartridge  5  may be moved upward, whereby the ink cartridge  5  locked by the locking lever  91  may be released, allowing the ink cartridge  5  to be moved in the demounting direction. 
     Referring to  FIG. 6A , when the user has operated operation portion  91   a  of the locking lever  91 , the ink cartridge  5  in the mounted position in the cartridge-housing chamber  80  may be pushed out in the demounting direction by the urging forces of the expanding springs  54  and  64 , whereby the ink cartridge  5  may move in the demounting direction along the first surface  84   a  of the cartridge mounting portion  7  due to a kinetic energy produced by the urging forces of the springs  54  and  64  and transferred to the ink cartridge  5 . 
     Referring to  FIG. 6B , when the center of gravity of the ink cartridge  5  reaches a position in rear, in the mounting direction, of the border between the first surface  84   a  and the second surface  84   b , the ink cartridge  5  tilts onto the second surface  84   b  due to the gravitational force operating on the cartridge at the center of gravity as shown in  FIG. 3 . That is, a portion of the ink cartridge  5  in rear, in the mounting direction, of the center of gravity moves toward the second surface  84   b  due to the gravitational force, while a portion of the ink cartridge  5  in front, in the mounting direction, of the center of gravity moves upward. When the ink cartridge  5  tilts, the projection  38  may contact the top plate  83  of the cartridge-housing chamber  80 . Then, a frictional force may be produced at the contact point between the projection  38  and the top plate  83 . This frictional force may absorb some of the kinetic energy of the ink cartridge  5  produced by the urging forces of the springs  54  and  64 , which may reduce movement of the ink cartridge  5  in the demounting direction. Ultimately, the kinetic energy becomes zero, whereby the ink cartridge  5  stops moving in the cartridge-housing chamber  80 . In this manner, chances of the ink cartridge  5  jumping out of the cartridge mounting portion  7  are reduced. 
     As described above, with respect to  FIG. 3 , because of the provision of the grip  42  at an upper rear portion, in the mounting direction, of the cartridge body  30 , the ink cartridge  5  positioned in the mounted position in the cartridge mounting portion  7  may have its center of gravity at a position in rear, in the mounting direction, of the first center line of the ink cartridge  5  and above the second center line of the ink cartridge  5 . Moreover, the center of gravity of the ink cartridge  5  may be positioned at a position in rear, in the mounting direction, of the theoretical center of gravity of the ink cartridge  5  as previously described. Therefore, even when the length of the second surface  84   b  in the second direction is short and the distance the ink cartridge  5  moves in the demounting direction is short, the ink cartridge  5  may tilt. Accordingly, the length of the first surface  84   a  of the bottom plate  84  in the first direction may be made relatively long. Therefore, when a user intends to mount the ink cartridge  5  to the cartridge mounting portion  7 , the user readily may mount the ink cartridge  5  in the mounting direction by moving the ink cartridge  5  along the first surface  84   a.    
     In most cases, the ink cartridge  5  may be demounted from the cartridge mounting portion  7  and is replaced with a new ink cartridge  5  when the amount of ink remaining in the ink chamber  31  becomes small. Therefore, it is acceptable that the center of gravity of the ink cartridge  5  be at the above-described position at least when the ink cartridge  5  is empty, that is, when there is no ink in the ink cartridge  5 . Nevertheless, considering a case where the ink cartridge  5  is demounted when a relatively large amount of ink is remaining in the ink chamber  31 , it is also acceptable that, even if the ink chamber  31  is filled with ink, the ink cartridge  5  have its center of gravity, also taking the weight of the ink into account, at the above-described position. 
     As described above, with the ink cartridge  5  having its center of gravity at a position as far toward the rear upper side as possible, the ink cartridge  5  easily may tilt even when the distance the ink cartridge  5  moves in the demounting direction is short. Thus, the chances of the ink cartridge  5  jumping out of the cartridge mounting portion  7  may be further reduced. In addition, because the projection  38  positioned far from the center of gravity of the ink cartridge  5  contacts the top plate  83 , a frictional force may be produced even when the tilt of the ink cartridge  5  is not too large. 
     Moreover, because the urging force of the spring  64  of the air communication portion  33  is greater than the urging force of the spring  54  of the ink supply portion  32  when the ink cartridge  5  is positioned in the mounted position in the cartridge mounting portion  7  of the holder  10 , the ink cartridge  5  readily may tilt. That is, because the urging force applied to an upper portion of the front end, in the mounting direction, of the ink cartridge  5  may be greater than the urging force applied to a lower portion of the front end, in the mounting direction, of the ink cartridge  5 , the ink cartridge  5  readily may tilt in such a manner that the front-side portion, in the mounting direction, of the ink cartridge  5  moves upward. Thus, chances of the ink cartridge  5  jumping out of the cartridge mounting portion  7  are further reduced. 
     If the tilt of the second surface  84   b  toward the downward vertical direction is relatively large, i.e., if the angle θ 1  formed between the second direction and the downward vertical direction is relatively small and the tilt of the ink cartridge  5  is therefore large, the ink cartridge  5  may stop moving only by the projection  38  coming into contact with the top plate  83 . 
     In an embodiment, the kinetic energy may be reduced by a frictional force produced at the contact point when the ink cartridge  5  is tilted due to energy produced by gravity. Therefore, this embodiment may be realized such that each of the mounting direction and the demounting direction is a substantially horizontal direction, such that the direction in which the ink cartridge  5  moves with the kinetic energy may be substantially perpendicular to the downward vertical direction in which the ink cartridge  5  moves due to the gravitational force. Nevertheless, in another embodiment, each of the mounting and demounting directions may not be a horizontal direction and may be angled with respect to a horizontal direction. 
     Various additional embodiments are described herein. Elements having configurations identical with those in the above-described embodiment will be denoted by the same reference numerals, and the description thereof is omitted. 
     In the above-described embodiment, the projection  38  at the upper end of the front-end face, in the mounting direction, of the cartridge body  30  of the ink cartridge  5  tilted onto the second surface  84   b  may contact the top plate  83  and may produce a frictional force. Nevertheless, in another embodiment, the projection  38  may be distant from the top plate  83  and may not contact the top plate  83 . For example, a contacting member, such as a stick, that is configured to be able to contact the projection  38  when the ink cartridge  5  tilts, may be positioned in the cartridge mounting portion  7 . 
     Referring to  FIG. 7 , in another embodiment, when the ink cartridge  5  tilted onto the second surface  84   b  moves along the second surface  84   b , the bottom of the rear-end face, in the mounting direction, of the cartridge body  30  may contact a surface  95 , e.g., of a table, on which the printer  1  may be placed. Accordingly, a frictional force may be produced at the contact point between the bottom of the rear-end face of the cartridge body  30  and the surface  95 . The frictional force may reduce the kinetic energy of the ink cartridge  5 . Thus, chances of the ink cartridge  5  jumping out of the cartridge mounting portion  7  are reduced. The surface  95  may not be limited to a surface of the table, and may be a surface of the printer  1  or any other suitable surface. 
     In the above-described embodiment, the projection  38  of the ink cartridge  5  may contact the top plate  83 . In another embodiment, however, projection  38  may be omitted, and the top face  30   a  of the cartridge body  30  may contact the top plate  83 . 
     In the above-described embodiment, the grip  42  of the ink cartridge  5  may comprise the plurality of ribs  42   a  with spaces between the ribs  42   a . In another embodiment, the grip  42  may be filled with resin with almost no spaces provided within. In such a case, deformation of the grip  42  may be further suppressed, and the center of gravity of the ink cartridge  5  may be further shifted toward the rear side in the mounting direction. 
     In the above-described embodiment, the ink cartridge  5  may have its center of gravity at an upper rear position of the ink cartridge  5  because of the weight of the grip  42 . In another embodiment, the ink cartridge  5  may not have the grip  42 , but may comprise more ribs positioned in an upper rear portion of the ink chamber  31 , such that the ink cartridge  5  may have the center of gravity at an upper rear position of the ink cartridge  5 . 
     The tilt of the second surface  84   b  is changeable, according to need, with the magnitudes of the urging forces applied by the springs  54  and  64 . For example, if the urging forces applied by the springs  54  and  64  increase, the kinetic energy of the ink cartridge  5  also may increase. Therefore, to increase the frictional force produced when the ink cartridge  5  tilts and comes into contact with the top plate  83 , the tilt of the second surface  84   b  may be designed to be angled more toward the downward vertical direction. 
     While the urging force of the spring  64  of the air communication portion  33  is greater than the urging force of the spring  54  of the ink supply portion  32  when the ink cartridge  5  is positioned in the mounted position in the cartridge mounting portion  7  of the holder  10 , in another embodiment, the urging force of the spring  64  may be substantially equal to the urging force of spring  54 . 
     In another embodiment, the urging member that may be configured to urge the ink cartridge  5  mounted in the mounted position in the cartridge mounting portion  7  in the demounting direction may be positioned in the cartridge mounting portion  7 , not in the ink cartridge  5 . For example, referring to  FIGS. 8A and 8B , in yet another embodiment, the cartridge mounting portion  7  may comprise a spring  100  configured to push out the ink cartridge  5 , such that that a user may easily remove the ink cartridge  5  from the cartridge mounting portion  7 . 
     The above embodiments describe an ink supply system that supplies ink to an inkjet head of an inkjet printer. Nevertheless, the invention also may be applied to liquid supply systems used in various technical fields that supply liquid to destination devices. 
     While the invention has been described in connection with various example 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.