Abstract:
A liquid supply system adapted to be mounted in a carriage unit having a first liquid introduction portion and a second liquid introduction portion is proposed. The liquid supply system comprises two liquid supply units each having liquid supply portion adapted to liquid to the first and second liquid introduction portions, respectively. The two liquid supply units are adapted to be attached to and detached from the carriage unit. The liquid supply system further comprises a holder unit adapted to be attached to and detached from the carriage unit and adapted to fix the two liquid supply units to the carriage unit. The two liquid supply units are located between the holder unit and the carriage unit.

Description:
BACKGROUND 
     1. Technical Field 
     The present invention relates to liquid supply systems equipped with liquid supply units that supply liquid to liquid ejection apparatuses. 
     2. Related Art 
     Printers are widely used as a kind of liquid ejection apparatuses, and ink cartridges are used as liquid supply units for the printers. Hitherto, with a printer that prints using ink of a plurality of colors, independent ink cartridges are prepared for respective ink colors and are independently attached to and detached from the printer. However, in the case of using independent ink cartridges for the respective ink colors, if the number of ink colors increases, the structure of a cartridge attaching portion becomes complicated as a result of enabling many ink cartridges to be attached, which is disadvantageous for a size reduction of the printer. In addition, the operation of replacing the ink cartridges takes time and effort. 
     A printer has been proposed to which an integrated ink cartridge that contains ink of a plurality of colors is attached to perform. For example, JP-A-2008-74100 discloses an ink tank (ink cartridge) in which the inside of a housing thereof is partitioned into a plurality of ink containing portions and an ink supply port is provided in each ink containing portion. The ink tank has a plurality of lock portions, and is attached to the printer by engaging these lock portions with lock portions on the printer side. 
     With an integrated ink cartridge such as the one disclosed in JP-A-2008-74100, time and effort in the operation of replacing the ink cartridge can be reduced since a plurality of ink cartridges are integrated. Furthermore, an integrated ink cartridge is more space-saving than a plurality of ink cartridges are, and allows the configuration of a cartridge attaching portion to be simplified. Accordingly, an integrated ink cartridge is advantageous for a size reduction of a printer. 
     However, although an integrated ink cartridge is advantageous in terms of a size reduction and time and effort in replacement, an entire ink cartridge needs to be replaced if the remaining amount of ink of only one of the plurality of ink colors becomes small. Accordingly, a problem arises in that the ink is wasted. For this reason, there has been a demand for an ink cartridge that is advantageous for a size reduction and time and effort in replacement and with less waste of ink. This problem is not limited to ink cartridges for printers, but is also a problem shared by liquid supply systems for other kinds of liquid ejection apparatuses. 
     SUMMARY 
     The invention has been made in order to solve at least a part of the above-described problem, and can be achieved as the following modes or application examples. 
     A mode of the invention is a liquid supply system adapted to be mounted in a carriage unit having a first liquid introduction portion and a second liquid introduction portion, including: a first liquid supply unit having a first liquid supply portion adapted to supply first liquid to the first liquid introduction portion and adapted to be attached to and detached from the carriage unit; a second liquid supply unit having a second liquid supply portion adapted to supply second liquid to the second liquid introduction portion and adapted to be attached to and detached from the carriage unit independently of the first liquid supply unit; and a holder unit adapted to be attached to and detached from the carriage unit and adapted to fix the first liquid supply unit and the second liquid supply unit to the carriage unit, wherein when a plane in which the first liquid supply portion abuts against the first liquid introduction portion in a state where the first liquid supply unit is attached to the carriage unit is defined as a reference plane, and a direction perpendicular to the reference plane is defined as an attaching direction, the first liquid supply unit is located between the holder unit and the carriage unit in the attaching direction, the second liquid supply unit is located between the holder unit and the carriage unit in the attaching direction, and the holder unit has a terminal portion adapted to be electrically connected to the carriage unit. 
     According to this mode, the first liquid supply unit and the second liquid supply unit can be independently replaced, whereas both the first liquid supply unit and the second liquid supply unit can be fixed to the carriage unit using the holder unit, which is a single member. Accordingly, it is possible to achieve both a reduction in time and effort in replacement and a reduction in waste of ink. In addition, the terminal portion can be arranged in the holder unit instead of arranging a terminal portion in each of the first liquid supply unit and the second liquid supply unit. Accordingly, the size of the liquid supply system can be reduced. 
     A mode of the invention is a liquid supply system adapted to be mounted in a carriage unit having a first liquid introduction portion and a second liquid introduction portion, including: a first liquid supply unit having a first liquid supply portion adapted to supply first liquid to the first liquid introduction portion and adapted to be attached to and detached from the carriage unit; a second liquid supply unit having a second liquid supply portion adapted to supply second liquid to the second liquid introduction portion and adapted to be attached to and detached from the carriage unit independently of the first liquid supply unit; and a holder unit adapted to be attached to and detached from the carriage unit and adapted to fix the first liquid supply unit and the second liquid supply unit to the carriage unit, wherein when a plane in which the first liquid supply portion abuts against the first liquid introduction portion in a state where the first liquid supply unit is attached to the carriage unit is defined as a reference plane, and a direction perpendicular to the reference plane is defined as an attaching direction, the first liquid supply unit is located between the holder unit and the carriage unit in the attaching direction, the second liquid supply unit is located between the holder unit and the carriage unit in the attaching direction, and the holder unit has a first engaging portion and a second engaging portion that can engage with the carriage unit. 
     According to this mode, the first liquid supply unit and the second liquid supply unit can be independently replaced, whereas both the first liquid supply unit and the second liquid supply unit can be fixed to the carriage unit using the holder unit, which is a single member. Accordingly, it is possible to achieve both a reduction in time and effort in replacement and a reduction in waste of ink. In addition, the engaging portion can be arranged in the holder unit instead of arranging an engaging portion in each of the first liquid supply unit and the second liquid supply unit. Accordingly, the size of the liquid supply system can be reduced. 
     In a mode of the invention, it is desirable that the first liquid supply unit has a first atmosphere communication hole, and the holder unit has a first atmosphere release opening adapted to be in communication with the first atmosphere communication hole. With this configuration, it is less likely that the first atmosphere communication hole of the first liquid supply unit is blocked by the holder unit. 
     In a mode of the invention, it is desirable that when a direction in which the carriage unit scans is defined as a main scanning direction, the first liquid supply unit has a first restriction portion adapted to restrict movement in the main scanning direction with respect to the holder unit when the first liquid supply unit is attached to the carriage unit. With this configuration, movement of the first liquid supply unit in the main scanning direction can be restricted when the first liquid supply unit is fixed to the carriage unit using the holder unit. 
     In a mode of the invention, it is desirable that when a direction in which the carriage unit scans is defined as a main scanning direction, the first liquid supply unit has a first restriction portion adapted to restrict movement in a direction intersecting the attaching direction and the main scanning direction with respect to the holder unit when the first liquid supply unit is attached to the carriage unit. With this configuration, movement of the first liquid supply unit in the direction intersecting the main scanning direction and the attaching direction can be restricted when the first liquid supply unit is fixed to the carriage unit using the holder unit. 
     In a mode of the invention, it is desirable that when a direction in which the carriage unit scans is defined as a main scanning direction, the first liquid supply unit and the second liquid supply unit are configured to be arranged side-by-side in a direction orthogonal to the main scanning direction when the first liquid supply unit and the second liquid supply unit are attached to the carriage unit, the first liquid supply unit has a first restriction portion adapted to restrict movement in the main scanning direction with respect to the holder unit when the first liquid supply unit is attached to the carriage unit, the second liquid supply unit has a second restriction portion adapted to restrict movement in the main scanning direction with respect to the first liquid supply unit when the second liquid supply unit is attached to the carriage unit, and the holder unit has a third restriction portion adapted to restrict movement in the main scanning direction with respect to the second liquid supply unit when the second liquid supply unit is attached to the carriage unit. With this configuration, when the first liquid supply unit and the second liquid supply unit are arranged side-by-side in the direction orthogonal to the main scanning direction when the first and second liquid supply units are attached to the carriage unit, even if the force exerted in the main scanning direction is applied by sliding of the carriage unit, it is less likely that the positions of the first liquid supply unit and the second liquid supply unit move in the main scanning direction. In addition, since the liquid supply units can restrict movement thereof among them, the configuration of the holder unit can be simplified. Accordingly, this mode is advantageous for a size reduction. 
     In a mode of the invention, it is desirable that when the first restriction portion and the second restriction portion are viewed in a plan view in the attaching direction in a state where the first liquid supply unit and the second liquid supply unit are attached to the carriage unit, positions of the first restriction portion and the second restriction portion in the main scanning direction are different from each other. With this configuration, the first liquid supply unit and the second liquid supply unit can be prevented from being incorrectly attached. 
     In a mode of the invention, it is desirable that a third liquid supply unit is further included that has a third liquid supply portion adapted to supply third liquid to the carriage unit and adapted to be attached to and detached from the carriage unit independently of the first liquid supply unit and the second liquid supply unit, wherein when a direction in which the carriage unit scans is defined as a main scanning direction, the first liquid supply unit and the second liquid supply unit are configured to be arranged side-by-side in a direction orthogonal to the main scanning direction when the first liquid supply unit and the second liquid supply unit are attached to the carriage unit, the first liquid supply unit and the third liquid supply unit are configured to be arranged side-by-side in the direction orthogonal to the main scanning direction when the first liquid supply unit and the third liquid supply unit are attached to the carriage unit, and the second liquid supply unit and the third liquid supply unit are configured to be arranged side-by-side in the main scanning direction when the second liquid supply unit and the third liquid supply unit are attached to the carriage unit. With this configuration, the three liquid supply units can be efficiently arranged. In addition, since the liquid supply units can restrict movement thereof among them, the configuration of the holder unit can be simplified. Accordingly, this mode is advantageous for a size reduction. 
     A mode of the invention is any of the above-described liquid supply systems further including: a liquid container; and a first liquid supply tube that connects the first liquid supply unit to the liquid container. The liquid supply system in this mode can supply liquid from the liquid container to the first liquid supply unit. Accordingly, the size of the first liquid supply unit can be reduced. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described with reference to the accompanying drawings, wherein like numbers reference like elements. 
         FIG. 1  is a perspective view of a printer to which ink cartridges according to Embodiment 1 of the invention is attached. 
         FIGS. 2A and 2B  are perspective views schematically showing an ink cartridge. 
         FIGS. 3A and 3B  are perspective views schematically showing a holder unit. 
         FIGS. 4A to 4D  are illustrative diagrams schematically showing a cross-sectional configuration of a carriage unit and an ink supply system. 
         FIGS. 5A to 5C  are illustrative diagrams schematically showing a plan configuration of the carriage unit and the ink supply system. 
         FIGS. 6A to 6C  are illustrative diagrams schematically showing an ink supply system according to Embodiment 2. 
         FIGS. 7A to 7C  are illustrative diagrams schematically showing an ink supply system according to Embodiment 3. 
         FIGS. 8A to 8C  are illustrative diagrams schematically showing an ink supply system according to Embodiment 4. 
         FIG. 9  is an illustrative diagram schematically showing an ink supply system according to Embodiment 5. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Hereinafter, embodiments of a liquid supply unit and a liquid supply system to which the invention is applied will be described with reference to the drawings. 
     Embodiment 1 
     Overall Configuration 
       FIG. 1  is a perspective view of a printer to which ink cartridges according to Embodiment 1 of the invention are attached. A printer  500 , which serves as a liquid ejection apparatus, includes a control unit  510  that controls each part of the printer  500 , a carriage unit  520 , a main scanning feed mechanism that moves the carriage unit  520  back and forth in a main scanning direction, and a sub-scanning feed mechanism that conveys a print medium P in a sub-scanning direction orthogonal to the main scanning direction. As will be described later, ink cartridges  20 , each serving as a liquid supply unit, are attached to the carriage unit  520  so as to be held by a holder unit  30 . 
     In this specification, an X direction, a Y direction, and a Z direction are three directions orthogonal to one another. Regarding each of the three, namely XYZ directions shown in  FIG. 1 , the orientation of the arrow indicates a + direction (positive direction), and the orientation opposite to the arrow orientation indicates a − direction (negative direction). The printer  500 , when in use, is arranged on an XY plane, which is a horizontal plane. At this time, the X direction is a direction parallel with the main scanning direction (the left-right direction of the printer  500 ) in which the carriage unit  520  is moved back and forth, and the Y direction is a direction parallel with the sub-scanning direction (the front-rear direction of the printer  500 ) in which the print medium P is conveyed. The +Y direction indicates forward, and the −Y direction indicates rearward. The Z direction is the vertical direction (the up-down direction of the printer  500 ), and the −Z direction is the vertically downward direction. 
     A main scan mechanism of the printer  500  includes a carriage motor  522  and a drive belt  524  that is looped in the main scanning direction, and the power of the carriage motor  522  is transmitted to the carriage unit  520  via the drive belt  524 . A sub-scan mechanism includes a conveyance motor  532  and a platen roller  534 , and the print medium P is conveyed using the power of the conveyance motor  532  via the platen roller  534 . The carriage motor  522  and the conveyance motor  532  operate based on a control signal from the control unit  510 . 
     The control unit  510  and the carriage unit  520  are electrically connected via a flexible cable  517 . The carriage unit  520  includes a cartridge attaching portion  60  to which the holder unit  30  and a plurality of ink cartridges  20  are attached, and a print head  540  arranged below the cartridge attaching portion  60 . The print head  540  operates based on a control signal from the control unit  510 , and discharges ink toward the print medium P. The print medium P is thereby printed. 
     Ink Supply System 
     As shown in  FIG. 1 , the carriage unit  520  includes a bottom wall portion  61  that constitutes a bottom portion of the cartridge attaching portion  60 , a first side wall portion  62  that constitutes a wall surface of the cartridge attaching portion  60  in the +Y direction, a second side wall portion  63  that constitutes a wall surface of the cartridge attaching portion  60  in the −Y direction, a third side wall portion  64  that constitutes a wall surface of the cartridge attaching portion  60  in the −X direction, and a fourth side wall portion  65  that constitutes a wall surface of the cartridge attaching portion  60  in the +X direction. The print head  540  is provided below the bottom wall portion  61 . The cartridge attaching portion  60  is provided with a recessed space surrounded by these five wall portions, and the plurality of ink cartridges  20  and the holder unit  30  can be attached in this recessed space from above (+Z direction). 
     Hereinafter, in this specification, a multiple unit constituted by the holder unit  30  holding the plurality of ink cartridges  20  will be called an ink supply system  10  (liquid supply system). In the ink supply system  10 , the holder unit  30  that is arranged so as to cover the plurality of ink cartridges  20  is engaged with the cartridge attaching portion  60 , thereby fixing the plurality of ink cartridges  20  to the carriage unit  520 . Ink can thereby be supplied from the ink cartridges  20  each serving as an ink supply unit (liquid supply unit) to the print head  540 . Note that the XYZ directions shown in the drawings in this specification indicate the XYZ directions in a state where the ink supply system  10  is attached to the carriage unit  520  of the printer  500  installed on an XY plane as shown in  FIG. 1 . 
     Ink Cartridge 
     Each ink cartridge  20  contains ink, which serves as a printing material. The printer  500  according to Embodiment 1 discharges, from the print head  540 , ink of six colors, namely black, yellow, magenta, light magenta, cyan, and light cyan. Accordingly, six ink cartridges  20  can be attached to the cartridge attaching portion  60 . Each of six ink cartridges  20  stores ink of a corresponding one of the aforementioned six colors. Note that the number and the type of ink cartridges that can be attached to the cartridge attaching portion  60  are not limited to the aforementioned number and type, and can be changed as appropriate. 
       FIGS. 2A and 2B  are perspective views schematically showing the ink cartridge  20 .  FIG. 2A  is a perspective view as viewed obliquely from above, and  FIG. 2B  is a perspective view as viewed obliquely from below. The ink cartridge  20  includes a rectangular parallelepiped housing  21 , an ink supply portion  280 , an atmosphere communication port  22 , a front projection portion  23 , and a rear projection portion  24 . An ink containing portion that contains ink is provided within the housing  21 , and a porous ink holding member  284  (see  FIG. 4D ) is arranged therein. The ink supply portion  280  is provided in a bottom portion of the housing  21 , and the atmosphere communication port  22  is open in an upper face of the housing  21 . The ink supply portion  280  and the atmosphere communication port  22  are in communication with the ink containing portion. 
     The front projection portion  23  projects in the +Y direction from a side face (front face) of the housing that is oriented in the +Y direction. The rear projection portion  24  projects in the −Y direction from a side face (back face) of the housing  21  that is oriented in the −Y direction. The front projection portion  23  and the rear projection portion  24  each have a rib-like form extending in the Z direction along a side face of the housing  21 , and have a fixed dimension of projection from the side face of the housing  21  and a fixed width in the X direction. 
     Holder Unit 
       FIGS. 3A and 3B  are perspective views schematically showing the holder unit  30 .  FIG. 3A  is a perspective view as viewed obliquely from below, and  FIG. 3B  is a perspective view as viewed obliquely from above. As mentioned above, Embodiment 1 provides the configuration in which the six ink cartridges  20  are held by a single holder unit  30  and fixed to the carriage unit  520 , but  FIGS. 3A and 3B  show a simplified configuration in which two ink cartridges  20  are held for the purpose of simplification of the description. 
     The holder unit  30  includes an upper wall portion  31  that covers, from the side in the +Z direction, the two ink cartridges  20  arranged side-by-side in the X direction serving as the main scanning direction, a front wall portion  32  that is continuous with an end portion of the upper wall portion  31  in the +Y direction, and a rear wall portion  33  that is continuous with an end portion of the upper wall portion  31  in the −Y direction. The holder unit  30  houses and holds the two ink cartridges  20  in a space surrounded by these three wall portions. The holder unit  30  also includes a first engaging projection portion  34 , two second engaging projection portions  35 , two atmosphere release openings  36 , two front recess portions  37 , two rear recess portions  38 , and a terminal portion  40 . 
     The first engaging projection portion  34  projects in the +Y direction from the front wall portion  32  of the holder unit  30 . The two second engaging projection portions  35  are arranged side-by-side in the X direction, while projecting in the −Y direction from the rear wall portion  33 . The terminal portion  40  includes a circuit board  41  arranged obliquely between a leading end of the first engaging projection portion  34  and a lower end of the front wall portion  32 , and a terminal group  42  placed on the circuit board  41 . The terminal group  42  includes contact portions arrayed on a surface of the circuit board  41 . A storage element is provided on the back side of the circuit board  41 . Information regarding the ink in the ink cartridges  20  (amount of ink, ink color, etc.) is stored in the storage element. The terminal group  42  is electrically connected to the storage element. 
     Atmosphere release openings  36  are formed in the upper wall portion  31 . The two atmosphere release openings  36 , which are arranged side-by-side in the X direction, are through holes penetrating the upper wall portion  31 . The front wall portion  32  and the rear wall portion  33  are opposed to each other in the Y direction, and two pairs of recess portions are formed in opposing faces of these wall portions. That is to say, the two front recess portions  37  are formed in the front wall portion  32  while being arranged side-by-side in the X direction, and the two rear recess portions  38  are formed in the rear wall portion  33  while being arranged side-by-side in the X direction. These four recess portions each have a groove shape having a fixed width and a fixed depth, and extend in the Z direction. The two front recess portions  37  are opposed to the rear recess portions  38  in the Y direction. 
     Attaching of ink supply system to cartridge attaching portion 
       FIGS. 4A to 4D  are illustrative diagrams schematically showing a cross-sectional configuration of the carriage unit  520  and the ink supply system  10 , and  FIGS. 5A to 5C  are illustrative diagrams schematically showing a plan configuration of the carriage unit  520  and the ink supply system  10 . Note that  FIGS. 5A to 5C  show a simplified configuration in which not six, but two ink cartridges  20  containing different ink are held by a single holder unit  30 , as in  FIGS. 3A and 3B . 
       FIGS. 4A and 5A  are a cross-sectional view and a plan view, respectively, that schematically show the carriage unit  520 . The cartridge attaching portion  60  in the carriage unit  520  is provided with a plurality of ink introduction portions  640 , a contact point mechanism  70 , a first engaging portion  66 , and two second engaging portions  68 . The ink introduction portions  640  project in the +Z direction from the bottom wall portion  61 , as shown in  FIG. 4A . The same number of ink introduction portions  640  as the number of ink cartridges  20  to be attached to the cartridge attaching portion  60  are arranged on the bottom wall portion  61  side-by-side in the X direction. The adjacent ink introduction portions  640  are partitioned by a rib (not shown). Regions demarcated in the X direction by the rib are each a cartridge attachment slot that includes a single ink introduction portion  640 . 
     The contact point mechanism  70  includes a terminal group  71  in which a plurality of terminals are arranged, and a terminal base  72  that holds the terminal group  71 . The terminal base  72  has an inclined face that inclines relative to the bottom wall portion  61  and the first side wall portion  62 , and contact portions of the terminals constituting the terminal group  71  are arranged on the inclined face. The terminal group  71  is biased in the direction in which the contact portions of the terminals project from the inclined face  73 . When the holder unit  30  is engaged with the cartridge attaching portion  60 , the contact portions of the terminal group  71  elastically come into contact with the contact portions of the terminal group  42  provided in the holder unit  30 . 
     The first engaging portion  66 , which can move relative to the first side wall portion  62 , is provided in the first side wall portion  62 . The first engaging portion  66  according to Embodiment 1 is a rotary lever, and can rotate around an axis extending in the X direction with a rotation fulcrum  67  provided in an upper part of the first side wall portion  62  as the center. This first engaging portion  66  is a portion that is to engage with the first engaging projection portion  34  of the above-described holder unit  30 . Meanwhile, the two engaging portions  68  are formed in the second side wall portion  63 . The second engaging portions  68  are pass-through portions that passes through the second side wall portion  63  in the Y direction, and are arranged side-by-side in the X direction. The second engaging portions  68  can engage with the second engaging projection portions  35  of the above-described holder unit  30 . Note that the second engaging portions  68  do not need to be pass-through portions. For example, the second engaging portions  68  may be recess portions. 
       FIG. 5B  is a plan view of the ink supply system  10  as viewed from above. In the ink supply system  10 , the two ink cartridges  20  arranged side-by-side in the X direction are held by the holder unit  30 . Of each of the two ink cartridges  20 , the front projection portion  23  engages with the corresponding front recess portion  37  of the holder unit  30 , and the rear projection portion  24  engages with the corresponding rear recess portion  38  of the holder unit  30 . The front projection portion  23  and the rear projection portion  24  each function as a first restriction portion that restricts movement of the ink cartridge  20  in the X direction, which is the main scanning direction, by engaging with the holder unit  30 . In addition, the atmosphere communication ports  22  of the two ink cartridges  20  overlap, in the Z direction, the two atmosphere release openings  36  on the side of the holder unit  30 . Note that the number and the shape of the first restriction portions (front projection portion  23 , rear projection portion  24 ) are not limited to the aforementioned number and shape. For example, the projections may be replaced with recesses. 
       FIG. 4B  shows a state in the middle of attaching the ink supply system  10  to the cartridge attaching portion  60 . When attaching the ink supply system  10  to the cartridge attaching portion  60 , a rear end portion (end portion in the −Y direction) of the holder unit  30  is lowered in the −Z direction relative to a front end portion (end portion in the +Y direction) of the holder unit  30 , and the two second engaging projection portions  35  are inserted into the second engaging portions  68  of the cartridge attaching portion  60  to engage therewith. Thereafter, the front end portion (end portion in the +Y direction) of the holder unit  30  is lowered, the first engaging portion  66  of a rotary type is rotated, and the first engaging projection portion  34  is engaged with the first engaging portion  66 . Thereby, the attaching of the ink supply system  10  to the cartridge attaching portion  60  is complete as shown in  FIGS. 4C and 5C . 
     In the state where the attaching is complete as shown in  FIGS. 4C and 5C , movement of the ink cartridges  20  in the +Z direction is restricted by the holder unit  30 , and the ink cartridges  20  are fixed to the cartridge attachment slots. The first engaging portion  66  is biased in the −Z direction by a biasing portion (not shown). Otherwise, the ink cartridge  20  is biased in the +Z direction from the bottom wall portion  61  of the cartridge attaching portion  60  by a biasing portion (not shown), and the first engaging projection portion  34  of the holder unit  30  is biased in the +Z direction toward the first engaging portion  66 . For this reason, the engaging state between the first engaging projection portion  34  and the first engaging portion  66  is stable. Accordingly, the state of the holder unit  30  fixing the ink cartridges  20  in the Z direction is stable. In addition, as mentioned above, the front projection portion  23  and the rear projection portion (first restriction portion) of each ink cartridge  20  engage with the recess portions (front recess portion  37 , rear recess portion  38 ) of the holder unit  30  to position the ink cartridge  20  in the X direction (main scanning direction). Furthermore, the front wall portion  32  and the rear wall portion  33  of the holder unit  30  position the ink cartridge  20  in the Y direction (direction orthogonal to the main scanning direction). 
     As shown in  FIG. 4C , in a state where the ink supply system  10  is attached to the cartridge attaching portion  60 , the ink supply portion  280  of each ink cartridge  20  is opposed, in the Z direction, to the corresponding ink introduction portion  640  of the cartridge attaching portion  60 , and the ink supply portion  280  is connected to the ink introduction portion  640 . The ink in the ink cartridge  20  can thereby be introduced to the ink introduction portion  640  via the ink supply portion  280 . In this state, the contact portions of the terminal group  71  provided in the contact point mechanism  70  elastically come into contact with the contact portions of the terminal group  42  provided in the terminal portion  40  on the side of the ink cartridge  20 . Thereby, the terminal portion  40  on the side of the ink supply system  10  is electrically connected to the contact point mechanism  70  on the side of the carriage unit  520 . 
       FIG. 4D  is an enlarged view of a connecting portion of the ink supply portion  280  and the ink introduction portion  640 . The ink supply portion  280  includes an ink supply port  281  and an outer wall  282  that surrounds the ink supply port  281 . The outer wall  282  includes an opening face  288  that is oriented in the −Z direction. An ink supply port constituting member  283  is arranged at the ink supply port  281 . The ink supply port constituting member  283  is a fibrous member formed by bundling polypropylene or the like that is drawn and made fibrous, or a porous member formed by a foam body such as polyurethane. The ink supply port constituting member  283  is in contact with the ink holding member  284  arranged in the +Z direction relative thereto. 
     The ink introduction portion  640  includes a tubular ink introduction port  641 , and a seal portion  648  that surrounds the ink introduction port  641 . The seal portion  648  can undergo elastic deformation in the Z direction. A mesh filter  642  is attached to a leading end in the +Z direction of the ink introduction port  641 . The opening face  288  of the ink supply portion  280  elastically comes into contact with the seal portion  648  and sticks thereto. Thereby, the periphery of the ink supply port  281  and the ink introduction port  641  is tightly closed, preventing leakage of the ink. At this time, the mesh filter  642  comes into surface contact with the ink supply port constituting member  283  while being pressed thereagainst. Thereby, the ink supply port constituting member  283  is connected to the ink introduction port  641 . 
     In this specification, assuming that a plane in which the ink supply portion  280  of each ink cartridge  20  abuts against the corresponding ink introduction portion  640  of the cartridge attaching portion  60  is a reference plane SP, and a direction in which the ink supply portion  280  abuts against the ink introduction portion  640  is an attaching direction SD, the attaching direction SD is a direction perpendicular to the reference plane SP. As mentioned above, since the opening face  288  of the ink supply portion  280  abuts against the seal portion  648  of the ink introduction portion  640 , the reference plane SP corresponds to the opening face  288 . When the printer  500  is in use, the opening face  288  corresponds to an XY plane, and accordingly, the reference plane SP is an XY plane and the attaching direction SD is the Z direction. 
     As mentioned above,  FIGS. 3A, 3B, and 5A to 5C  simplify the holder unit  30  and show the mode in which the two ink cartridges  20  are held thereby. However, in the case of holding four more ink cartridges  20  as shown in  FIG. 1 , the dimension of the upper wall portion  31  of the holder unit  30  in the X direction is set so as to be able to cover the six ink cartridges  20 , and six atmosphere release openings  36  are provided at positions overlapping six atmosphere communication ports  22  on the ink cartridge side. Then, six pairs of the front recess portion  37  and the rear recess portion  38 , which are opposed to each other, are provided respectively in the front wall portions  32  and the rear wall portions  33 . 
     Note that the number of ink cartridges  20  to be held by the holder unit  30  may be any number that is 2 or greater. For example, six ink cartridges  20  can be attached to the cartridge attaching portion  60  using three holder units  30  each of which holds two ink cartridges  20  as shown in  FIGS. 3A, 3B, and 5A to 5C , or using two holder units  30  each of which holds three ink cartridges  20 . 
     As described above, with the ink supply system  10  according to Embodiment 1, at least two ink cartridges  20  can be fixed to the cartridge attaching portion  60  using a single holder unit  30 . Accordingly, a plurality of ink cartridges  20  do not need to be individually engaged with the cartridge attaching portion  60 , and a replacement operation can be easily performed. In addition, an engagement structure does not need to be provided for each ink cartridge  20 , and furthermore, and a terminal portion does not need to be provided in each ink cartridge  20  since the holder unit  30  has the terminal portion  40 . Accordingly, the structure of the ink cartridges  20  and the cartridge attaching portion  60  can be simplified, which is advantageous for a size reduction. In addition, the plurality of ink cartridges  20 , which are separate bodies, can be independently replaced. Accordingly, the ink cartridges do not need to be replaced while some ink remains as in the case of an integrated ink cartridge, and waste of ink can be reduced. 
     In Embodiment 1, when the plurality of ink cartridges  20  are attached to the holder unit  30 , the atmosphere communication port  22  of each ink cartridge  20  overlaps the corresponding atmosphere release opening  36  of the holder unit  30 . Accordingly, the atmosphere communication port  22  is not blocked by the holder unit  30 , and a state where the ink cartridge  20  is in communication with the atmosphere can be maintained. 
     In Embodiment 1, the movement of the ink cartridges  20  in the X direction that is the main scanning direction can be restricted by engaging the recess portions (front recess portion  37 , rear recess portion  38 ) of the holder unit  30  with the projection portions (front projection portion  23 , rear projection portion  24 ) of the ink cartridges  20 . Accordingly, the ink cartridge  20  can be positioned in the X direction. Note that a similar effect can also be obtained with a configuration in which the holder unit  30  is provided with projection portions and each ink cartridge  20  is provided with recess portions. 
     Embodiment 2 
       FIGS. 6A to 6C  are illustrative diagrams schematically showing an ink supply system  10 A according to Embodiment 2.  FIG. 6A  is a cross-sectional view schematically showing a state where the ink supply system  10 A is attached to a carriage unit  520 ,  FIG. 6B  is a perspective view showing an ink cartridge  20 A as viewed obliquely from above, and  FIG. 6C  is a perspective view of the ink cartridge  20 A as viewed obliquely from below. Hereinafter, the same part as that of the already-described mode will be assigned the same signs and descriptions thereof will be omitted. Only different part will be assigned different signs and will be described. Embodiment is different from Embodiment 1 in the mode of the restriction portion for restricting movement of the ink cartridge  20 A when a plurality of ink cartridges  20 A are held by a holder unit  30 A. 
     The ink supply system  10 A according to Embodiment 2 includes a plurality of ink cartridges  20 A, and a holder unit  30 A that fixes the ink cartridges  20 A to a cartridge attaching portion  60 . As shown in  FIG. 6B , each ink cartridge  20 A does not have a front projection portion  23  and a rear projection portion  24  formed on side faces of a housing  21  as in Embodiment 1. Instead, two upper recess portions  25  and  26  are formed in a face (upper face) of the housing  21  that is oriented in the +Z direction. The two upper recess portions  25  are arranged on the sides of an atmosphere communication port  22  in the +Y direction and the −Y direction. 
     The holder unit  30 A is not provided with front recess portions  37  in a front wall portion  32  as in Embodiment 1, and is not provided with rear recess portions  38  in a rear wall portion  33  as in Embodiment 1. Instead, the holder unit  30 A includes upper projection portions  39  that project downward (−Z direction) from the upper wall portion  31 . A total of four upper projecting portions  39  are provided. Namely, two upper projection portions  39  are provided on the sides of each of the two atmosphere release openings  36  in the +Y direction and the −Y direction. 
     Here, it is assumed, as in Embodiment 1, that a direction perpendicular to an abutting face (opening face  288 : XY plane) in which an ink supply portion  280  of each ink cartridge  20 A abuts against a corresponding ink introduction portion  640  of the holder unit  30 A is an attaching direction SD (Z direction), and, of the attaching direction SD, a direction that extends from the ink introduction portion  640  toward the ink supply portion  280  (i.e., the direction in which the ink cartridge  20 A is detached: +Z direction) is a first direction, and a direction that extends from the ink supply portion  280  toward the ink introduction portion  640  (i.e., the direction in which the ink cartridge  20 A is attached: −Z direction) is a second direction. At this time, the upper projection portions  39  project while being oriented in the second direction (−Z direction) from the upper wall portion  31  of the holder unit  30 A. 
     As shown in  FIG. 6A , when the plurality of ink cartridges  20 A are held by the holder unit  30 A, the upper projection portions  39  of the holder unit  30 A engage with the two upper recess portions  25  of each ink cartridge  20 A. Thereby, the ink cartridge  20 A can be positioned in the X direction and the Y direction. 
     As described above, with the ink supply system  10 A according to Embodiment 2, the configuration similar to that in Embodiment 1 achieves an effect similar to that of Embodiment 1. In addition, each ink cartridge  20 A includes recess portions (upper recess portions  25 ) each serving as a first restriction portion that restricts movement of the ink cartridge  20 A in the X direction that is the main scanning direction of the carriage unit  520 , and the direction (Y direction) that intersects the attaching direction SD (Z direction) when the ink cartridge  20 A is held by the holder unit  30 A to constitute the ink supply system  10 A. Accordingly, when the plurality of ink cartridges  20 A are fixed to the carriage unit  520  using the holder unit  30 A, movement of each ink cartridge  20 A in the main scanning direction (X direction) and the direction (Y direction) that intersects the attaching direction SD (Z direction) can be restricted, and the ink cartridge  20 A can be positioned in these directions. 
     Note that the number and the shape of first restriction portion according to Embodiment 2 are not limited to the aforementioned number and shape. For example, the recess of the first restriction portion according to Embodiment 2 may be replaced with projection. That is to say, recess portions may be formed in place of the upper projection portions  39 , and projection portions may be formed in place of the upper recess portions  25 . 
     Embodiment 3 
       FIGS. 7A to 7C  are illustrative diagrams schematically showing an ink supply system  110  according to Embodiment 3.  FIG. 7A  is a plan view of a carriage unit  520 ,  FIG. 7B  is a plan view of the ink supply system  110 , and  FIG. 7C  is a plan view showing a state where the ink supply system  110  is attached to a cartridge attaching portion  160  of the carriage unit  520 . The ink supply system  110  according to Embodiment 3 includes four ink cartridges  120 A,  120 B,  120 C, and  120 D, and a holder unit  130 . 
     The cartridge attaching portion  160  according to Embodiment 3 is provided with ink introduction portions  640 , a contact point mechanism  70 , a first engaging portion  66 , and two second engaging portions  68 . The cartridge attaching portion  160  is configured similarly to the cartridge attaching portion  60  according to Embodiment 1 except the arrangement of the ink introduction portions  640 . In the cartridge attaching portion  160 , four ink introduction portions  640  are arranged in 2×2 lines, and a total of four cartridge attachment slots are provided. 
     As shown in  FIG. 7B , the ink cartridges  120 A,  120 B,  120 C, and  120 D are arranged in 2×2 lines so as to correspond to the arrangement of the ink introduction portions  640 . The ink cartridges  120 A and  120 B constitute a line of the 2×2 lines on the side in the −X direction, and are located respectively on the sides in the +Y direction and the −Y direction. The ink cartridges  120 C and  120 D constitute a line of the 2×2 lines on the side in the +X direction, and are located respectively on the sides in the +Y direction and the −Y direction. The four ink cartridges  120 A,  120 B,  120 C, and  120 D each include a rectangular parallelepiped housing. An ink supply portion  280  is provided in a bottom portion of each housing, and an atmosphere communication port  22  is open in an upper face of each housing. A front recess portion  123  is formed in a side face of each housing in the +Y direction, and a rear projection portion  124  is formed in a side face of each housing in the −Y direction. 
     As shown in  FIG. 7B , the positions of the front recess portions  123  and the rear projection portions  124  in the X direction are different among the four ink cartridges  120 A,  120 B,  120 C, and  120 D. Regarding the ink cartridges that are adjacent in the Y direction (i.e., the ink cartridges  120 A and  120 B, and the ink cartridges  120 C and  120 D), the positions of the front recess portions  123  and the rear projection portions  124  are determined such that the rear projection portion  124  of the ink cartridge  120 A engages with the front recess portion  123  of the ink cartridge  120 B, and the rear projection portion  124  of the ink cartridge  120 C engages with the front recess portion  123  of the ink cartridge  120 D. 
     The holder unit  130  includes four atmosphere release openings  36 , two front projection portions  137 , two rear recess portions  138 , and a terminal portion  40 . The atmosphere release openings  36  are formed at positions overlapping the atmosphere communication ports  22  of the four ink cartridges  120 A,  120 B,  120 C, and  120 D. The front projection portions  137  are formed such that the position and the shape thereof enable the front projection portions  137  to engage with the front recess portions  123  of the ink cartridges  120 A and  120 C. The rear recess portions  138  are formed such that the position and the shape thereof enable the rear recess portions  138  to engage with the rear projection portions  124  of the ink cartridges  120 B and  120 D. 
     The holder unit  130  also includes a first engaging projection portion  34  and two second engaging projection portions  35 . These engaging projection portions are engaged with the first engaging portion  66  and the two second engaging portions  68  of the cartridge attaching portion  160 , and the attaching of the holder unit  130  is thereby complete as shown in  FIG. 7C . 
     The front recess portion  123  of the ink cartridge  120 A is a first restriction portion that engages with the corresponding front projection portion  137  of the holder unit  130  and restricts movement of the ink cartridge  120 A in the X direction that is the main scanning direction. The front recess portion  123  of the ink cartridge  120 B is a second restriction portion that engages with the rear projection portion  124  of the ink cartridge  120 A and restricts movement of the ink cartridge  120 B in the X direction that is the main scanning direction. The rear recess portions  138  of the holder unit  130  are third restriction portions, one of which engages with the rear projection portion  124  of the ink cartridge  120 B and restricts movement of the ink cartridge  120 B in the X direction that is the main scanning direction. Regarding the line of the ink cartridges  120 C and  120 D, similarly, the ink cartridge  120 C includes the front recess portion  123  serving as the first restriction portion, the ink cartridge  120 D includes the front recess portion  123  serving as the second restriction portion, and the holder unit  130  includes the corresponding rear recess portion  138  serving as the third restriction portion. 
     In the state where the attaching is complete as shown in  FIG. 7C , movement of the four ink cartridges  120 A to  120 D in the +Z direction is restricted by the holder unit  130 , and the ink cartridges  120 A to  120 D are fixed to the cartridge attaching portion  160 . The ink supply portions  280  of the four ink cartridges  120 A to  120 D are connected to the four ink introduction portions  640  in one-to-one correspondence. Furthermore, the terminal group  71  provided in the contact point mechanism  70  on the side of the cartridge attaching portion  160  comes into contact with the terminal group  42  provided in the terminal portion  40  on the side of the holder unit  130 . 
     As described above, in the ink supply system  110  according to Embodiment 3, the four ink cartridges  120 A to  120 D can be covered with the single holder unit  130  and fixed to the cartridge attaching portion  160  as in Embodiments 1 and 2. Accordingly, the ink cartridges  120 A to  120 D do not need to be individually engaged with the holder unit  130 , and a replacement operation can be easily performed. In addition, the structure of the ink cartridges  120 A to  120 D and the cartridge attaching portion  160  can be simplified, which is advantageous for a size reduction. Furthermore, the ink cartridges do not need to be replaced while some ink remains, and waste of ink can be reduced. In addition, in Embodiment 3, the ink cartridges can restrict movement thereof among them, and accordingly, the configuration of the holder unit  130  can be simplified. Accordingly, Embodiment 3 is more advantageous for a size reduction. 
     In the ink supply system  110  according to Embodiment 3, the ink cartridge  120 A and the ink cartridge  120 B are arranged side-by-side in the Y direction orthogonal to the X direction serving as the main scanning direction when these ink cartridges are attached to the carriage unit  520 , and the movement of the ink cartridges  120 A and  120 B in the X direction can be restricted by the above-described first to third restriction portions. Accordingly, even if the force exerted in the main scanning direction (X direction) is applied by sliding of the carriage unit  520 , it is unlikely that the positions of the ink cartridges  120 A and  120 B move in the main scanning direction (X direction). The same applies to the ink cartridges  120 C and  120 D. 
     In addition, in the ink supply system  110  according to Embodiment 3, when the front recess portions  123  of the ink cartridges  120 A and  120 B and the rear recess portion  138  of the holder unit  130  are viewed in a plan view in the Z direction (attaching direction SD), the positions of the front recess portion  123  of the ink cartridge  120 A and the front recess portion  123  of the ink cartridge  120 B in the main scanning direction (X direction) are different. Accordingly, it is possible to prevent the ink cartridges  120 A and  120 B from being incorrectly attached. In addition, the positions of the front recess portions  123  and the rear projection portions  124  of the four ink cartridges  120 A,  120 B,  120 C, and  120 D in the X direction are different, and accordingly, it is also possible to prevent the ink cartridges  120 C and  120 D from being incorrectly attached. 
     Embodiment 4 
       FIGS. 8A to 8C  are illustrative diagrams schematically showing an ink supply system  210  according to Embodiment 4.  FIG. 8A  is a plan view of a carriage unit  520 ,  FIG. 8B  is a plan view of the ink supply system  210 , and  FIG. 8C  is a plan view showing a state where the ink supply system  210  is attached to a cartridge attaching portion  260  of the carriage unit  520 . The ink supply system  210  according to Embodiment 4 includes three ink cartridges  220 A,  220 B, and  220 C, and a holder unit  230 . 
     The cartridge attaching portion  260  according to Embodiment 4 is provided with ink introduction portions  640 , a contact point mechanism  70 , a first engaging portion  66 , and two second engaging portion  68 . The cartridge attaching portion  260  is configured similarly to the cartridge attaching portion  60  according to Embodiment 1 except the arrangement of the ink introduction portions  640 . In the cartridge attaching portion  260 , one of the three ink introduction portions  640  is arranged on the side in the +Y direction, and the other two ink introduction portions  640  are arranged on the side in the −Y direction. 
     As shown in  FIG. 8B , the ink cartridges  220 A,  220 B, and  220 C are arranged so as to correspond to the arrangement of the ink introduction portions  640 . The ink cartridge  220 A is located on the side in the +Y direction, and the ink cartridges  220 B and  220 C are arranged on the side in the −Y direction relative to the ink cartridge  220 A, side-by-side in the X direction. That is to say, the ink cartridges  220 A and  220 B are arranged side-by-side in the Y direction orthogonal to the X direction (main scanning direction), the ink cartridges  220 A and  220 C are arranged side-by-side in the Y direction orthogonal to the X direction (main scanning direction), and the ink cartridges  220 B and  220 C are arranged side-by-side in the X direction (main scanning direction). The three ink cartridges  220 A,  220 B, and  220 C each include a rectangular parallelepiped housing. An ink supply portion  280  is provided in a bottom portion of each housing, and an atmosphere communication port  22  is open in an upper face of each housing. 
     The ink cartridge  220 A includes two front projection portions  223  formed in a side face of the housing in the +Y direction, and two rear projection portions  224  formed in a side face of the housing in the −Y direction. The ink cartridges  220 B and  220 C have the same shape, and each include a front recess portion  225  formed in a side face of the housing in the +Y direction, and a rear projection portion  226  formed in a side face of the housing in the −Y direction. The positions of the front recess portions  225  and the rear projection portions  226  in the X direction are different between the two ink cartridges  220 B and  220 C. The rear projection portions  224  of the ink cartridge  220 A are formed such that the position and the shape thereof enable the rear projection portions  224  to engage with the front recess portions  225  of the ink cartridges  220 B and  220 C. 
     The holder unit  230  includes three atmosphere release openings  36 , two front recess portions  237 , two rear recess portions  238 , and a terminal portion  40 . The atmosphere release openings  36  are formed at positions overlapping the atmosphere communication ports  22  of the three ink cartridges  220 A,  220 B, and  220 C. The front recess portions  237  are formed such that the position and the shape thereof enable the front recess portions  237  to engage with the front projection portions  223  of the ink cartridge  220 A. The rear recess portions  238  are formed such that the position and the shape thereof enable the rear recess portions  238  to engage with the rear projection portions  226  of the ink cartridges  220 B and  220 C. 
     The holder unit  230  also includes a first engaging projection portion  34  and two second engaging projection portions  35 . These engaging projection portions are engaged with the first engaging portion  66  and the two second engaging portions  68  of the cartridge attaching portion  260 , and the attaching of the holder unit  230  is thereby complete as shown in  FIG. 8C . 
     The front projection portions  223  of the ink cartridge  220 A are first restriction portions that engage with the front recess portions  237  of the holder unit  230  and restrict movement of the ink cartridge  220 A in the X direction that is the main scanning direction. The front recess portions  225  of the ink cartridges  220 B and  220 C are second restriction portions that engage with the rear projection portions  224  of the ink cartridge  220 A and restrict movement of the ink cartridges  220 B and  220 C in the X direction that is the main scanning direction. The rear recess portions  238  of the holder unit  230  are third restriction portions that engage with the rear projection portions  226  of the ink cartridges  220 B and  220 C and restrict movement of the ink cartridges  220 B and  220 C in the X direction that is the main scanning direction. 
     In the state where the attaching is complete as shown in  FIG. 8C , movement of the three ink cartridges  220 A to  220 C in the +Z direction is restricted by the holder unit  230 , and the ink cartridges  220 A to  220 C are fixed to the cartridge attaching portion  260 . The ink supply portions  280  of the three ink cartridges  220 A to  220 C are connected to the three ink introduction portions  640  in one-to-one correspondence. Furthermore, the terminal group  71  provided in the contact point mechanism  70  on the side of the cartridge attaching portion  260  comes into contact with the terminal group  42  provided in the terminal portion  40  on the side of the holder unit  130 . 
     As described above, in the ink supply system  210  according to Embodiment 4, the three ink cartridges  220 A to  220 C can be fixed to the cartridge attaching portion  260  using a single holder unit  230  as in Embodiments 1 to 3. Accordingly, the ink cartridges  220 A to  220 C do not need to be individually engaged with the cartridge attaching portion  260 , and a replacement operation can be easily performed. In addition, the structure of the ink cartridges  220 A to  220 C and the cartridge attaching portion  260  can be simplified, which is advantageous for a size reduction. Furthermore, the ink cartridges do not need to be replaced while some ink remains, and waste of ink can be reduced. 
     In the ink supply system  210  according to Embodiment 4, two of the three ink cartridges  220 A to  220 C are arranged adjacent to each other in the X direction, and the remaining one is laterally arranged on the side in the +Y direction. With this configuration, the three ink cartridges  220 A to  220 C can be arranged in a space-saving manner, and an efficient arrangement can be achieved. In addition, the ink cartridges can restrict movement thereof among them as in Embodiment 3, and accordingly, the configuration of the holder unit  230  can be simplified. Accordingly, Embodiment 4 is advantageous for a size reduction. 
     In the ink supply system  210  according to Embodiment 4, when forming recess portions and projection portions as the restriction portions in the ink cartridges  220 A to  220 C, in the case of forming recess portions as the restriction portions, these recess portions are formed in a side face on the short side, which is a face separate from the corresponding ink supply portion  280 . Specifically, the front recess portions  225  serving as the second restriction portions are formed in the faces of the ink cartridges  220 B and  220 C in the +Y direction that are the short sides, at a portion where the ink cartridges  220 A and  220 B engage with each other and at a portion where the ink cartridges  220 A and  220 C engage with each other, and the rear projection portions  224  that engage with the front recess portions  225  are formed in the face of the ink cartridge  220 A on the side in the −Y direction that is the long side. Thus forming the recesses and projections at positions separate from the ink supply portions  280  can reduce influence on an ink flow within the ink cartridges, which is also advantageous. 
     Embodiment 5 
       FIG. 9  is an illustrative diagram schematically showing an ink supply system  300  according to Embodiment 5. The ink supply system  300 , which serves as a liquid supply system, includes a plurality of ink cartridges  20 , a holder unit  330 , a plurality of external tanks  301  (liquid containers) that contain ink, and a plurality of flexible tubes  302  (first liquid supply tubes) connecting the plurality of ink cartridges  20  to the plurality of external tanks  301  in one-to-one correspondence. The external tanks  301  are installed outside the printer  500 . For example, a stationary tank holder may be installed outside the printer  500 , and the external tanks  301  may be set in this tank holder. The flexible tubes  302  are connected to the ink cartridges  20  through an opening  331  provided in an upper face of the holder unit  330 . 
     In the ink supply system  300 , ink in the external tanks  301  can be supplied to the corresponding ink cartridges  20  via the flexible tubes  302 . Accordingly, by fixing the ink cartridges  20  in the ink supply system  300  to the cartridge attaching portion  60  in the printer  500  using the holder unit  330 , it is possible to supply the ink in the external tanks  301  to the ink introduction portions  640  in the cartridge attaching portion  60  via the ink cartridges  20  and perform printing with the printer  500 . In this mode, the ink cartridges  20  do not need to be replaced when ink runs short, and the external tanks  301  need only be replaced, or the ink need only be supplied to the external tanks  301 . Accordingly, the size of the ink cartridges  20  can be reduced. Note that some of the plurality of ink cartridges  20  can be connected to the external tanks  301  using the flexible tubes  302 . 
     OTHER MODES 
     The configurations in the above-described modes may be combined as appropriate in accordance with the purpose or usage. The invention is applicable not only to inkjet printers and ink cartridges thereof, but also to various liquid ejection apparatuses that eject various kinds of liquid including ink and liquid supply systems to be attached to and detached from carriage units of the liquid ejection apparatuses. For example, the invention is applicable to image forming apparatuses such as facsimiles. Here, ink includes general water-based ink and oil-based ink, as well as various liquid compositions such as gel ink and hot melt-ink. The invention is also applicable to liquid supply systems used in apparatuses that eject color materials used in manufacturing of color filters, apparatuses that eject electrode materials, apparatuses that eject various samples, apparatuses that eject lubricating oil, apparatuses that eject resin liquid, apparatus that eject etching liquid, and the like. 
     The entire disclosure of Japanese Patent Application No. 2014-243732 filed on Dec. 2, 2014, is expressly incorporated by reference herein.