Patent Publication Number: US-9902165-B2

Title: Ink supply system and inkjet printer

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of priority to Japanese Patent Application No. 2016-056564 filed on Mar. 22, 2016. The entire contents of this application are hereby incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an ink supply system and an inkjet printer. 
     2. Description of the Related Art 
     There are conventional inkjet printers using additional ink tanks, in addition to ink cartridges that supply ink to ink heads for discharging ink, in order to increase the amount of ink available (see, for example, Japanese Laid-Open Patent Publication No. 2010-94847). 
     With inkjet printers of this type, an ink head and an ink cartridge are connected together via a main supply channel. Another ink tank is connected to a middle portion of the main supply channel via a sub-supply channel. A solenoid valve is provided at a downstream portion of the main supply channel. When printing, the solenoid valve is opened so that ink stored in the ink cartridge and/or the other ink tank is supplied to the ink head. During standby, the solenoid valve is closed so that ink stored in the ink cartridge and the other ink tank is not supplied to the ink head. 
     With the inkjet printer described above, however, the solenoid valve is closed during standby. Therefore, when the temperature around the inkjet printer increases, ink in a section of the main supply channel between the solenoid valve and the ink head may possibly swell. During standby, ink in a section of the main supply channel between the solenoid valve and the ink head may possibly swell, resulting in ink leakage from the ink head. 
     SUMMARY OF THE INVENTION 
     Preferred embodiments of the present invention, which has been developed in view of the problem set forth above, provide an ink supply system and an inkjet printer, with which it is possible to prevent ink from swelling and leaking from the ink head during standby. 
     An ink supply system according to a preferred embodiment of the present invention includes a first ink head, a first main ink tank, a first sub-ink tank, a first main supply channel, a first sub-supply channel, a first upstream-side valve and a controller. 
     The first ink head includes a first nozzle that discharges ink. The first main ink tank and the first sub-ink tank store ink. The first main supply channel includes a first main upstream portion connected to the first main ink tank, a first main downstream portion connected to the first ink head, and a first middle portion located between the first main upstream portion and the first main downstream portion. The first sub-supply channel includes a first sub-upstream portion connected to the first sub-ink tank, and a first sub-downstream portion connected to the first middle portion of the first main supply channel. The upstream-side valve is provided on the first main upstream portion of the first main supply channel, the upstream-side valve being able to be opened and closed. The controller controls an open/closed state of the first upstream-side valve. The controller includes a first standby setting processor, a second standby setting processor, a standby state determination processor and a standby state switching processor. The first standby setting processor sets a first standby state in which the first upstream-side valve is open during standby. The second standby setting processor sets a second standby state in which the first upstream-side valve is closed during standby. The standby state determination processor determines whether or not an amount of time elapsed from when a setting operation was done by the first standby setting processor or the second standby setting processor is greater than or equal to a first amount of time. The standby state switching processor either switches from the first standby state to the second standby state or switches from the second standby state to the first standby state when it is determined by the standby state determination processor that the elapsed time is greater than or equal to the first amount of time. 
     With the ink supply system, the open/closed state of the valves is switched from the first standby state to the second standby state or from the second standby state to the first standby state, during standby, after every passage of an amount of time that is greater than or equal to the first amount of time. Therefore, for example, during standby, since the first upstream-side valve is open in the first standby state, the pressure in the main supply channel is released toward the first ink cartridge. Therefore, during standby, it is possible to prevent ink from swelling and leaking from the ink head. 
     Another ink supply system according to a preferred embodiment of the present invention includes a first ink head, a first main ink tank, a first sub-ink tank, a first main supply channel, a first sub-supply channel, a first downstream-side valve and a controller. The first ink head discharges ink. The first main ink tank and the first sub-ink tank store ink. The first main supply channel includes a first main upstream portion connected to the first main ink tank, a first main downstream portion connected to the first ink head, and a first middle portion located between the first main upstream portion and the first main downstream portion. The first sub-supply channel includes a first sub-upstream portion connected to the first sub-ink tank, and a first sub-downstream portion connected to the first middle portion of the first main supply channel. The first downstream-side valve is provided between the first middle portion and the first main downstream portion of the first main supply channel, the first downstream-side valve being able to open and close the first main downstream portion. The controller controls an open/closed state of the first downstream-side valve. The controller includes a first standby setting processor, a second standby setting processor, a standby state determination processor and a standby state switching processor. The first standby setting processor sets a first standby state in which the first downstream-side valve is open. The second standby setting processor sets a second standby state in which the first downstream-side valve is closed. The standby state determination processor determines whether or not an amount of time elapsed from when a setting operation was done by the first standby setting processor or the second standby setting processor is greater than or equal to a first amount of time. The standby state switching processor either switches from the first standby state to the second standby state or switches from the second standby state to the first standby state when it is determined by the standby state determination processor that the elapsed time is greater than or equal to the first amount of time, during standby. 
     With the ink supply system, the open/closed state of the valves is switched from the first standby state to the second standby state or from the second standby state to the first standby state, during standby, after every passage of an amount of time that is greater than or equal to the first amount of time. Therefore, for example, during standby, since the first downstream-side valve is open in the first standby state, the pressure in the main supply channel is released toward the first ink cartridge. Therefore, during standby, it is possible to prevent ink from leaking from the ink head. 
     According to various preferred embodiments of the present invention, it is possible to prevent ink from swelling and leaking from an ink head during standby. 
     The above and other elements, features, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a printer according to a first preferred embodiment of the present invention. 
         FIG. 2  is a conceptual diagram showing an ink supply system. 
         FIG. 3  is a schematic diagram showing the ink supply system. 
         FIG. 4  is a block diagram of the ink supply system. 
         FIG. 5  is a schematic diagram showing a first ink supply mechanism and a second ink supply mechanism in a first standby state and a first printing state. 
         FIG. 6  is a schematic diagram showing the first ink supply mechanism and the second ink supply mechanism in a second standby state and a second printing state. 
         FIG. 7  is a flow chart showing a control procedure by the ink supply system when printing. 
         FIG. 8  is a flow chart showing a control procedure by the ink supply system during standby. 
         FIG. 9  is a schematic diagram showing the first ink supply mechanism and the second ink supply mechanism in the first standby state according to a second preferred embodiment of the present invention. 
         FIG. 10  is a schematic diagram showing the first ink supply mechanism and the second ink supply mechanism in the second standby state according to the second preferred embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Ink supply systems according to preferred embodiments of the present invention and inkjet printers including the same (hereinafter referred to simply as a “printer”) will now be described with reference to the drawings. Note that the preferred embodiments to be described hereinbelow are not intended to limit the scope of the present invention. Elements or features with the same or similar function will be denoted by the same reference signs, and redundant descriptions will be omitted or simplified. 
     First Preferred Embodiment 
       FIG. 1  is a perspective view of a printer  10  according to a first preferred embodiment of the present invention. In  FIG. 1 , when the printer  10  is seen from the front side, the direction away from the printer  10  will be referred to as “front”, and the direction toward the printer  10  as “rear”. The terms “left”, “right”, “up” and “down” refer to these directions when the printer  10  is seen from the front side. The designations F, Rr, L, R, U and D, as used in the figures, refer to front, rear, left, right, up and down, respectively. Note however that these designations of direction are used merely for the purpose of illustration, and do not in any way limit how the printer  10  is installed and do not in any way limit the present invention. The character “X” in the figures denotes the main scanning direction. Herein, the main scanning direction X is the left-right direction, for example. The character “Y” in the figures denotes the sub scanning direction. Herein, the sub scanning direction Y is the front-rear direction, for example. The main scanning direction X and the sub scanning direction Y are perpendicular to each other as seen from above. Note however that there is no particular limitation on the main scanning direction X and the sub scanning direction Y, and these directions may be set appropriately in accordance with each preferred embodiment of the printer  10 . 
     The printer  10  of the present preferred embodiment preferably is an inkjet printer. The term “inkjet” as used in the present preferred embodiment refers to inkjet printing of any of various methods known in the art, e.g., continuous printing such as binary deflection printing or continuous deflection printing, and on-demand printing such as thermal printing or piezoelectric printing, for example. The printer  10  prints on a recording medium  5 . 
     The recording medium  5  is recording paper, for example. Note however that the recording medium  5  is not limited to recording paper. For example, the recording medium  5  may be a sheet recording medium, e.g., a sheet made of a resin such as PVC or polyester. The recording medium  5  may include aluminum, iron, wood, leather, etc. There is no particular limitation on the flexibility and the thickness of the recording medium  5 . That is, the recording medium  5  may be a hard medium such as a glass substrate. The recording medium  5  may also be a thick medium such as a cardboard. 
     In the present preferred embodiment, the printer  10  includes a platen  14 , a guide rail  18  and an ink supply system  30  (see  FIG. 2 ). The recording medium  5  is placed on the platen  14 . Although not shown in the figures, a cylindrical grit roller is provided on the platen  14 . The grit roller is buried in the platen  14  with the upper surface thereof exposed. 
     The guide rail  18  is located above the platen  14 . The guide rail  18  is parallel or substantially parallel to the platen  14 . The platen  14  extends in the main scanning direction X. Although not shown in the figures, a plurality of pinch rollers are arranged generally at equal or substantially equal intervals below the guide rail  18 . These pinch rollers oppose the grit roller. The pinch rollers are structured so that the positions thereof in the up-down direction are able to be set depending on the thickness of the recording medium  5 . The recording medium  5  is sandwiched between the grit roller and the pinch rollers. The grit roller and the pinch rollers carry the recording medium  5 , sandwiched therebetween, in the sub scanning direction Y. 
     Next, the ink supply system  30  will be described.  FIG. 2  is a conceptual diagram showing the ink supply system  30 .  FIG. 3  is a schematic diagram showing the ink supply system  30 . In the present preferred embodiment, as shown in  FIG. 2 , the ink supply system  30  includes a plurality of ink supply mechanisms  31  and a controller  28  (see  FIG. 1 ). As shown in  FIG. 3 , the ink supply mechanism  31  supplies ink from an ink cartridge  100  and/or a sub-tank  34  to be described below to an ink head  20 . The ink supply system  30  preferably includes the same number of ink supply mechanisms  31  as the number of ink heads  20 , for example. In the present preferred embodiment, preferably the number of ink heads  20  is “8”, and the number of ink supply mechanisms  31  is “8”, for example. Note however that there is no particular limitation on the number of ink heads  20  and the number of ink supply mechanisms  31 . Note that the ink supply mechanisms  31  have the same structure. 
     The ink supply mechanism  31  of the ink supply system  30  includes the ink head  20 , the ink cartridge  100 , the sub-tank  34 , a main supply channel  32 , an upstream-side valve  48 , a sub-supply channel  38  and the downstream-side valve  50 . 
     The ink head  20  discharges ink onto the recording medium  5  (see  FIG. 1 ) placed on the platen  14  (see  FIG. 1 ). The ink head  20  includes a nozzle  21  that discharges ink. Although not shown in the figures, the ink head  20  is mounted on a carriage  25  (see  FIG. 1 ). The carriage  25  is in engagement with the guide rail  18 . The carriage  25  is slidable on the guide rail  18 . The carriage  25  is movable in the main scanning direction X. The ink heads  20  are movable in the main scanning direction X along the guide rail  18  via the carriage  25 . Although not shown in the figures, a portion of a drive belt extending in the left-right direction is secured on an upper portion on the back of the carriage  25 . The drive belt is electrically connected to a scan motor. As the scan motor is driven, the ink heads  20  move in the main scanning direction X. 
     The ink cartridge  100  stores ink. In the present preferred embodiment, the number of ink cartridges  100  preferably is the same as the number of ink heads  20 , for example. One ink head  20  is connected to one ink cartridge  100 . There is no particular limitation on the type of an ink to be stored in each of the ink cartridges  100 . For example, an ink to be stored in each of the ink cartridges  100  may be any of a process color ink such as a cyan ink, a magenta ink, a yellow ink, a black ink, a light cyan ink, a light magenta ink and a light black ink, or a special color ink such as a white ink, a metallic ink and a clear ink. In the present preferred embodiment, a magenta ink is preferably stored, as a “dummy ink”, in one of the ink cartridges  100 , for example. Inks of different colors are stored in the other ink cartridges  100 . Note that the ink to be used as the dummy ink is not limited to a magenta ink. The ink head  20  connected to the ink cartridge  100  storing a magenta ink as a dummy ink therein is not used when printing. Note however that all of the ink heads  20  may be used when printing. In such a case, the ink cartridges  100  store inks of different colors, each storing any of the process color inks and the special color inks. 
     In the present preferred embodiment, the amount of ink that is able to be stored in one ink cartridge  100  is referred to as the “first amount”. There is no particular limitation on where the ink cartridges  100  are arranged. In the present preferred embodiment, as shown in  FIG. 1 , an ink cartridge accommodating section  22  is provided on an upper-left portion of the printer  10 . The ink cartridges  100  are accommodated in the ink cartridge accommodating section  22 . Herein, the ink cartridges  100  are secured on the main body of the printer  10 . Note however that the ink cartridges  100  may be secured on the ink heads  20 . Alternatively, the ink cartridges  100  may be provided at a position away from the printer  10 . As shown in  FIG. 3 , ink stored the ink cartridge  100  is supplied to the sub-tank  34  and the ink head  20 . 
     The sub-tank  34  stores ink. In the present preferred embodiment, the amount of ink that is able to be stored in the sub-tank  34  is referred to as the “second amount”. The second amount is smaller than the first amount representing the amount of ink that can be stored in the ink cartridge  100 . That is, the sub-tank  34  is capable of storing an amount of ink that is smaller than that of the ink cartridge  100 . In the present preferred embodiment, the first amount preferably is about 5 to about 20 times larger than the second amount. For example, the first amount preferably is about 1000 ml. The second amount preferably is about 100 ml. However, as long as the first amount is larger than the second amount, there is no particular limitation on the ratio between the first amount and the second amount, the specific value of the first amount and the specific value of the second amount. 
     Note that there is no particular limitation on where the sub-tanks  34  are arranged. In the present preferred embodiment, as shown in  FIG. 1 , a sub-tank accommodating section  26  is provided on an upper-left portion of the printer  10  and below the ink cartridge accommodating section  22 . Although not shown in the figures, the sub-tanks  34  are accommodated in the sub-tank accommodating section  26 . Herein, the sub-tanks  34  are secured on the main body of the printer  10 , as are the ink cartridges  100 . Note however that the sub-tanks  34  may be secured on the ink heads  20 . Alternatively, the sub-tanks  34  may be provided at a position spaced away from the printer  10 . Herein, the sub-tanks  34  are arranged at a position below the ink cartridges  100 . 
     Note that as shown in  FIG. 3 , the sub-tank  34  may be provided with a detection sensor  56  to detect the amount of ink stored in the sub-tank  34 . The detection sensor  56  detects the amount of ink stored in the sub-tank  34  being less than or equal to a predetermined amount that is smaller than the second amount. The predetermined amount is pre-stored in a storage processor  61  (see  FIG. 4 ) of the controller  28  to be described below. Note that there is no particular limitation on the type of the detection sensor  56 . For example, the detection sensor  56  may include a photosensor. 
     Note that ink stored in the ink cartridge  100  and the sub-tank  34  is preferably deaerated. 
     As shown in  FIG. 3 , the main supply channel  32  is a channel used to supply ink stored in the ink cartridge  100  and ink stored in the sub-tank  34  to the ink head  20 . The main supply channel  32  is a flexible tube, for example. However, there is no particular limitation on the material of the main supply channel  32 . 
     In the description below, one side that is closer to the ink cartridge  100 , between the ink cartridge  100  and the ink head  20 , will be referred to as the upstream side. The other side that is closer to the ink head  20  will be referred to as the downstream side. The main supply channel  32  includes a main upstream portion  36   a , a main downstream portion  36   b  and a middle portion  36   c . The main upstream portion  36   a  is an upstream portion of the main supply channel  32 . The main upstream portion  36   a  is removably connected to the ink cartridge  100 . In the present preferred embodiment, an ink extraction member  30   a  is provided at the upstream end of the main upstream portion  36   a . The ink extraction member  30   a  is removably inserted into the ink cartridge  100 . Thus, it is possible to prevent ink leakage from the connection between the main upstream portion  36   a  and the ink cartridge  100 . Note that the main upstream portion  36   a  may be un-removably connected to the ink cartridge  100 . 
     The main downstream portion  36   b  is a downstream portion of the main supply channel  32 . The main downstream portion  36   b  is connected to the ink head  20 . The middle portion  36   c  is a middle portion of the main supply channel  32 . Herein, the middle portion  36   c  is located between the main upstream portion  36   a  and the main downstream portion  36   b . Specifically, a three-way valve  46  is provided at the upstream end of the middle portion  36   c . The downstream end of the main upstream portion  36   a  is connected to the upstream end of the middle portion  36   c  via the three-way valve  46 . The downstream-side valve  50  is connected to the downstream end of the middle portion  36   c . The upstream end of the main downstream portion  36   b  is connected to the downstream end of the middle portion  36   c  via the downstream-side valve  50 . 
     The upstream-side valve  48  opens and closes the main supply channel  32 . The upstream-side valve  48  adjusts the amount of ink flowing from the ink cartridge  100  to the ink head  20 . The upstream-side valve  48  is provided on the main supply channel  32 . Specifically, the upstream-side valve  48  is provided on the main upstream portion  36   a  of the main supply channel  32 . There is no particular limitation on the type of the upstream-side valve  48 . For example, the upstream-side valve  48  is a solenoid valve. The upstream-side valve  48  is controlled by a driving signal sent from the controller  28  (see  FIG. 1 ). 
     The sub-supply channel  38  is a channel used to supply ink stored in the sub-tank  34  to the ink head  20  via the main supply channel  32 . The sub-supply channel  38  is a channel used to supply ink stored in the ink cartridge  100  to the sub-tank  34 . Herein, the sub-supply channel  38  is a flexible tube, as is the main supply channel  32 . However, there is no particular limitation on the material of the sub-supply channel  38 . 
     In the present preferred embodiment, the sub-supply channel  38  includes a sub-upstream portion  39   a  and a sub-downstream portion  39   b . The sub-upstream portion  39   a  is an upstream portion of the sub-supply channel  38 . The sub-tank  34  is removably connected to the sub-upstream portion  39   a . In the present preferred embodiment, an ink extraction member  40  is provided at the upstream end of the sub-upstream portion  39   a . The ink extraction member  40  is removably inserted into the sub-tank  34 . Note that the sub-upstream portion  39   a  may be un-removably connected to the sub-tank  34 . The sub-downstream portion  39   b  is a downstream portion of the sub-supply channel  38 . The sub-downstream portion  39   b  is connected to the main upstream portion  36   a  and the middle portion  36   c  of the main supply channel  32 . Specifically, the upstream end of the sub-downstream portion  39   b  is connected to the downstream end of the sub-upstream portion  39   a . The three-way valve  46 , to which the downstream end of the main upstream portion  36   a  and the upstream end of the middle portion  36   c  are connected, is connected to the downstream end of the sub-downstream portion  39   b.    
     The downstream-side valve  50  opens and closes the main downstream portion  36   b  of the main supply channel  32 . The downstream-side valve  50  adjusts the amount of ink flowing from the ink cartridge  100  to the ink head  20  and the amount of ink flowing from the sub-tank  34  to the ink head  20 . The downstream-side valve  50  is connected between the middle portion  36   c  and the main downstream portion  36   b  of the main supply channel  32 . There is no particular limitation on the type of the downstream-side valve  50 . For example, the downstream-side valve  50  is a solenoid valve, as is the upstream-side valve  48 . The downstream-side valve  50  is controlled by a driving signal sent from the controller  28  (see  FIG. 1 ). 
     Note that the ink supply mechanism  31  may include a damper and a supply pump  47 . The damper  44  dampens ink pressure fluctuations to stabilize the ink discharge operation of the ink head  20 . In the present preferred embodiment, the damper  44  is provided on a middle portion of the main downstream portion  36   b  of the main supply channel  32 , on the downstream side of the downstream-side valve  50 . The damper  44  is located between the downstream-side valve  50  and the ink head  20 . 
     The supply pump  47  supplies ink stored in the ink cartridge  100  and ink stored in the sub-tank  34  to the ink head  20 , and to pump the ink to be discharged from the ink head  20 . A drive motor  57  is electrically connected to the supply pump  47 . As the drive motor  57  is driven to actuate the supply pump  47 , ink stored in the ink cartridge  100  and ink stored in the sub-tank  34  are supplied to the ink head  20 . In the present preferred embodiment, the supply pump  47  is provided on a middle portion of the main downstream portion  36   b  of the main supply channel  32 , on the downstream side of the downstream-side valve  50  and the damper  44 . The supply pump  47  is located between the damper  44  and the ink head  20 . 
     In the present preferred embodiment, the ink supply mechanism  31  may include a cap  52  and a suction pump  54 . Although not shown in the figures, the cap  52  and the suction pump  54  are located at the home position, which is located on the right end of the guide rail  18 . The home position refers to the position where the ink head  20  stands by during standby. The cap  52  prevents ink on the nozzle  21  of the ink head  20  from hardening and clogging the nozzle  21 . The cap  52  is attached to the ink head  20  so as to cover the nozzle  21  of the ink head  20  during standby, other than when printing. The suction pump  54  sucks ink and air in the cap  52 . Herein, the suction pump  54  is connected to the cap  52 . A drive motor  55  is electrically connected to the suction pump  54 . With the cap  52  attached to the ink head  20 , the drive motor  55  is driven to appropriately actuate the suction pump  54 , thus sucking air in the cap  52 , the ink head  20 , the main supply channel  32  and the sub-supply channel  38 . 
     The ink supply mechanism  31  according to the present preferred embodiment has been described above. Next, the controller  28  will be described.  FIG. 4  is a block diagram of the ink supply system  30 . As shown in  FIG. 4 , the controller  28  is configured or programmed to control a printing operation and to control ink supply to the ink head  20 . There is no particular limitation on the configuration of the controller  28 . For example, the controller  28  may be a computer and may include a central processing unit (hereinafter referred to as a “CPU”), a ROM storing a program, or the like, to be executed by the CPU, and a RAM, etc. 
     The controller  28  controls the upstream-side valve  48 , the downstream-side valve  50 , the detection sensor  56  provided in the sub-tank  34 , the drive motor  57  electrically connected to the supply pump  47 , and the drive motor  55  electrically connected to the suction pump  54 . The controller  28  controls opening and closing of the main upstream portion  36   a  of the main supply channel  32  by controlling the open/closed state of the upstream-side valve  48 . The controller  28  controls the opening and closing of the main downstream portion  36   b  of the main supply channel  32  by controlling the open/closed state of the downstream-side valve  50 . In the present preferred embodiment, the controller  28  controls the open/closed state of the upstream-side valve  48  and the downstream-side valve  50  of the ink supply mechanism  31  so as to control the timing to supply ink stored in the ink cartridge  100  to the ink head  20  and the sub-tank  34  and the timing to supply ink stored in the sub-tank  34  to the ink head  20 . 
     The controller  28  detects the amount of ink stored in the sub-tank  34  by receiving a signal sent from the detection sensor  56 . The controller  28  controls the actuation of the supply pump  47  by controlling the driving of the drive motor  57 . The controller  28  controls the actuation of the suction pump  54  by controlling the driving of the drive motor  55 . 
     In the present preferred embodiment, the controller  28  includes the storage processor  61 , a first standby setting processor  62 , a second standby setting processor  63 , a first printing setting processor  64 , a second printing setting processor  65 , a standby state determination processor  66 , a printing state determination processor  67 , a standby state switching processor  68 , and a printing state switching processor  69 . Note that the storage processor  61 , the first standby setting processor  62 , the second standby setting processor  63 , the first printing setting processor  64 , the second printing setting processor  65 , the standby state determination processor  66 , the printing state determination processor  67 , the standby state switching processor  68  and the printing state switching processor  69  maybe implemented as software or hardware, and may be one processor or a plurality of processors. 
     In the present preferred embodiment, as shown in  FIG. 2 , the controller  28  performs the same control on four of the eight ink supply mechanisms  31  and performs the same control on the other four ink supply mechanisms  31 . Now, one group of four of the eight ink supply mechanisms  31  will be referred to as a first group  71 , and the other group of four ink supply mechanisms  31  as a second group  72 , for example. Note however that there is no particular limitation on the number of ink supply mechanisms  31  included in the first group  71 , and the number of ink supply mechanisms  31  included in the second group  72 . The number of ink supply mechanisms  31  included in the first group  71  may be the same as, or different from, the number of ink supply mechanisms  31  included in the second group  72 . 
       FIG. 5  is a schematic diagram showing a first ink supply mechanism  31   a  and a second ink supply mechanism  31   b  in a first standby state and a first printing state.  FIG. 6  is a schematic diagram showing the first ink supply mechanism  31   a  and the second ink supply mechanism  31   b  in a second standby state and a second printing state. Note that in  FIG. 5  and  FIG. 6 , arrows A 1  to A 3  and arrows B 1  to B 3  show the flow of ink. For each of valves  48   a ,  48   b ,  50   a  and  50   b  in  FIG. 5  and  FIG. 6 , “x” indicates that the valve is closed. In the description below, as shown in  FIG. 5 , the ink supply mechanism  31  of the first group  71  will be referred to as the first ink supply mechanism  31   a . The ink head  20 , the ink cartridge  100 , the sub-tank  34 , the main supply channel  32 , the upstream-side valve  48 , the sub-supply channel  38 , the downstream-side valve  50 , the damper  44  and the supply pump  47  of the first ink supply mechanism  31   a  will be referred to as a first ink head  20   a , a first ink cartridge  100   a , a first sub-tank  34   a , a first main supply channel  32   a , a first upstream-side valve  48   a , a first sub-supply channel  38   a , a first downstream-side valve  50   a , a first damper  44   a  and a first supply pump  47   a , respectively. The main upstream portion  36   a , the main downstream portion  36   b  and the middle portion  36   c  of the first main supply channel  32   a  will be referred to as a first main upstream portion  36   aa , a first main downstream portion  36   ba  and a first middle portion  36   ca , respectively. The sub-upstream portion  39   a  and the sub-downstream portion  39   b  of the first sub-supply channel  38   a  will be referred to as a first sub-upstream portion  39   aa  and a first sub-downstream portion  39   ba , respectively. In the present preferred embodiment, the first ink cartridge  100   a  is an example of the “first main ink tank”. The first sub-tank  34   a  is an example of the “first sub-ink tank”. 
     The ink supply mechanism  31  of the second group  72  will be referred to as the second ink supply mechanism  31   b . The ink head  20 , the ink cartridge  100 , the sub-tank  34 , the main supply channel  32 , the upstream-side valve  48 , the sub-supply channel  38 , the downstream-side valve  50 , the damper  44  and the supply pump  47  of the second ink supply mechanism  31   b  will be referred to as a second ink head  20   b , a second ink cartridge  100   b , a second sub-tank  34   b , a second main supply channel  32   b , a second upstream-side valve  48   b , a second sub-supply channel  38   b , a second downstream-side valve  50   b , a second damper  44   b  and a second supply pump  47   b , respectively. The main upstream portion  36   a , the main downstream portion  36   b  and the middle portion  36   c  of the second main supply channel  32   b  will be referred to as a second main upstream portion  36   ab , a second main downstream portion  36   bb  and a second middle portion  36   cb , respectively. The sub-upstream portion  39   a  and the sub-downstream portion  39   b  of the second sub-supply channel  38   b  will be referred to as a second sub-upstream. portion  39   ab  and a second sub-downstream portion  39 b b , respectively. In the present preferred embodiment, the second ink cartridge  100   b  is an example of the “second main ink tank”. The second sub-tank  34   b  is an example of the “second sub-ink tank”. 
     In the present preferred embodiment, the open/closed states of the valves of the ink supply system  30  include the first standby state, the second standby state, the first printing state and the second printing state, as shown in  FIG. 5  and  FIG. 6 . The first standby state and the second standby state are each an open/closed state of the valves during standby. The first printing state and the second printing state are each an open/closed state of the valves when printing. In the present preferred embodiment, as shown in  FIG. 5 , the open/closed state of the valves in the first standby state is the same as that in the first printing state. As shown in  FIG. 6 , the open/closed state of the valves in the second standby state is the same as that in the second printing state. 
     As shown in  FIG. 5 , in the first ink supply mechanism  31   a  of the first group  71  in the first standby state and the first printing state, the first upstream-side valve  48   a  and the first downstream-side valve  50   a  are open. That is, in the first ink supply mechanism  31   a  in the first standby state and the first printing state, the first main upstream portion  36   aa  and the first main downstream portion  36   ba  of the first main supply channel  32   a  are open. In the second ink supply mechanism  31   b  in the first standby state and the first printing state, the second upstream-side valve  48   b  is closed and the second downstream-side valve  50   b  is open. 
     Therefore, in the first ink supply mechanism  31   a  in the first standby state and the first printing state, ink stored in the first ink cartridge  100   a  flows as indicated by arrows Al and A 2  to be supplied to the first ink head  20   a  and the first sub-tank  34   a . Specifically, ink stored in the first ink cartridge  100   a  is supplied to the first ink head  20   a  via the first main upstream portion  36   aa , the first middle portion  36   ca  and the first main downstream portion  36   ba  of the first main supply channel  32   a , as indicated by arrow A 2 . At the same time, ink stored in the first ink cartridge  100   a  is supplied to the first sub-tank  34   a  via the first main upstream portion  36   aa  and the first sub-downstream portion  39   ba  and the first sub-upstream portion  39   aa  of the first sub-supply channel  38   a , as indicated by arrow A 1 . 
     On the other hand, in the second ink supply mechanism  31   b  in the first standby state and the first printing state, the second main upstream portion  36   ab  of the second main supply channel  32   b  is closed and the second main downstream portion  36   bb  is open. Therefore, in the second ink supply mechanism  31   b  in the first standby state and the first printing state, since the second main upstream portion  36   ab  is closed, ink stored in the second ink cartridge  100   b  is not supplied to the second ink head  20   b  and the second sub-tank  34   b . Herein, ink stored in the second sub-tank  34   b  is supplied to the second ink head  20   b . Specifically, in the second ink supply mechanism  31   b  in the first standby state and the first printing state, ink stored in the second sub-tank  34   b  is supplied to the second ink head  20   b  via the second sub-upstream portion  39   ab  and the second sub-downstream portion  39   bb  of the second sub-supply channel  38   b  and the second middle portion  36   cb  and the second main downstream portion  36   bb  of the second main supply channel  32   b , as indicated by arrow A 3 . 
     As shown in  FIG. 5  and  FIG. 6 , the second standby state and the second printing state are states that are achieved by switching around the open/closed state of the valves in the first ink supply mechanism  31   a  in the first standby state and the first printing state and that in the second ink supply mechanism  31   b . That is, in the second standby state and the second printing state, the open/closed state of the valves of the first ink supply mechanism  31   a  is the same as that of the valves of the second ink supply mechanism  31   b  in the first standby state and the first printing state. Specifically, in the first ink supply mechanism  31   a  in the second standby state and the second printing state, the first upstream-side valve  48   a  is closed and the first downstream-side valve  50   a  is open. In the first ink supply mechanism  31   a  in the second standby state and the second printing state, ink flows as indicated by arrow B 1 . 
     The open/closed state of the valves of the second ink supply mechanism  31   b  in the second standby state and the second printing state is the same as that of the valves of the first ink supply mechanism  31   a  in the first standby state and the first printing state. Specifically, in the second ink supply mechanism  31   b  in the second standby state and the second printing state, the second upstream-side valve  48   b  and the second downstream-side valve  50   b  are open. Therefore, in the second ink supply mechanism  31   b  in the second standby state and the second printing state, ink flows as indicated by arrows B 2  and B 3 . 
       FIG. 7  is a flow chart showing a control procedure by the ink supply system  30  when printing. Next, transitions of the open/closed state of the valves of the ink supply mechanism  31  when printing will be described with reference to the flow chart of  FIG. 7 . When printing, the open/closed state of the valves in the first ink supply mechanism  31   a  included in the first group  71  is different from that in the second ink supply mechanism  31   b  included in the second group  72 , and they are switched around after every passage of a predetermined amount of time (herein, the second amount of time). 
     First, in step S 101 , a printing operation by the printer  10  is started. At this point, the ink head  20  moves in the main scanning direction X along the guide rail  18 . Then, when the ink head  20  is positioned above the recording medium  5  placed on the platen  14 , ink is discharged onto the recording medium  5  to perform printing. Note that when printing, the supply pump  47  is operative. 
     As described above, after a printing operation is started, in step S 103 , a setting operation is performed to open and close the valves by the ink supply system  30 . Herein, as shown in  FIG. 5 , the first printing setting processor  64  of the controller  28  sets the open/closed state of the valves to the first printing state. Thus, in the first ink supply mechanism  31   a , ink to be discharged from the first ink head  20   a  is supplied from the first ink cartridge  100   a  as indicated by arrow A 2 . On the other hand, in the second ink supply mechanism  31   b , the second upstream-side valve  48   b  is closed. 
     Therefore, ink to be discharged from the second ink head  20   b  is supplied from the second sub-tank  34   b  as indicated by arrow A 3 . 
     Note however that in step S 103 , the second printing setting processor  65  may set the open/closed state of the valves to the second printing state as shown in  FIG. 6 . In this case, in the first ink supply mechanism  31   a , the first upstream-side valve  48   a  is closed. Therefore, ink to be discharged from the first ink head  20   a  is supplied from the first sub-tank  34   a  as indicted by arrow B 1 . On the other hand, in the second ink supply mechanism  3  l b , the second upstream-side valve  48   b  and the second downstream-side valve  50   b  are open. Therefore, ink to be discharged from the second ink head  20   b  is supplied from the second ink cartridge  100   b  as indicated by arrow B 3 . 
     Next, in step S 105  of  FIG. 7 , the printing state determination processor  67  calculates the amount of time elapsed from when the open/closed state of the valves was set to the first printing state or the second printing state. Then, the printing state determination processor  67  determines whether or not the elapsed time is greater than or equal to the second amount of time. Note that the second amount of time is a value pre-stored in the storage processor  61 . There is no particular limitation on the second amount of time. For example, the second amount of time is preferably such an amount of time that the first sub-tank  34   a  and the second sub-tank  34   b  will not be exhausted. The second amount of time preferably is about 1 to about 10 minutes, for example. The second amount of time preferably is about 5 minutes, for example. 
     In step S 105 , if it is determined by the printing state determination processor  67  that the amount of time elapsed from when the open/closed state of the valves was set to the first printing state or the second printing state is greater than or equal to the second amount of time, step S 107  is performed next. In step S 107 , the printing state switching processor  69  switches the open/closed state of the valves. For example, as shown in  FIG. 5 , when the open/closed state of the valves is the first printing state, the printing state switching processor  69  switches the open/closed state of the valves from the first printing state to the second printing state as shown in  FIG. 6 . On the other hand, when the open/closed state of the valves is the second printing state, the printing state switching processor  69  switches the open/closed state of the valves from the second printing state to the first printing state as shown in  FIG. 5 . After the switching of the open/closed state of the valves in step S 107 , step S 105  is performed again. 
     In step S 105  of  FIG. 7 , if it is determined by the printing state determination processor  67  that the amount of time elapsed from when the open/closed state of the valves was set to the first printing state or the second printing state is less than the second amount of time, step S 109  is performed next. Next, in step S 109 , it is determined if a printing operation has been completed. For example, it is determined if a printing operation has been completed based on whether or not the controller  28  has received a print-end signal from the printer  10 . When the controller  28  receives a print-end signal and determines that a printing operation by the printer  10  has been completed, the printing process is ended. On the other hand, when the controller  28  determines that a printing operation by the printer  10  has not been completed, step S 105  is again performed next. As described above, in the present preferred embodiment, the open/closed state of the valves in the ink supply system  30  is switched from the first printing state to the second printing state or from the second printing state to the first printing state after every passage of the second amount of time. 
       FIG. 8  is a flow chart showing a control procedure by the ink supply system  30  during standby. Next, transitions of the open/closed state of the valves of the ink supply mechanism.  31  during standby will be described with reference to the flow chart of  FIG. 8 . Herein, “during standby” refers to a period of time when the printer  10  is not printing. Also, “during standby” refers to a state where the ink head  20  is located at the home position. In the present preferred embodiment, the downstream-side valve  50  is open even during standby. Even during standby, as when printing, the open/closed state of the valves in the first ink supply mechanism  31   a  included in the first group  71  is different from that in the second ink supply mechanism  31   b  included in the second group  72 , and they are switched around after every passage of a predetermined amount of time (herein, the first amount of time). 
     First, in step S 201 , the printer  10  which is printing stops printing. For example, a printing operation ends when the controller  28  receives a print-end signal. Then, the ink head  20  moves to the home position located at the right end of the guide rail  18 . Then, at the home position, the cap  52  is attached to the ink head  20 . Note that the supply pumps  47   a  and  47   b  are stopped during standby. Therefore, it is unlikely that ink leaks from the ink head  20  unless the suction pump  54  connected to the cap  52  is operative. 
     After a printing operation ends and the system is on standby, in step S 203 , a setting operation is performed for the open/closed state of the valves by the ink supply system  30 . In step S 203 , the first standby setting processor  62  of the controller  28  sets the open/closed state of the valves in each ink supply mechanism  31  to the first standby state as shown in  FIG. 5 . In the first ink supply mechanism  31   a  in the first standby state, the first upstream-side valve  48   a  and the first downstream-side valve  50   a  are open. In the second ink supply mechanism  31   b  in the first standby state, the second upstream-side valve  48   b  is closed. The second downstream-side valve  50   b  is open. In the present preferred embodiment, the supply pumps  47   a  and  47   b  are stopped during standby, as described above. Therefore, even when the downstream-side valve  50  is not closed, ink in the main supply channel  32  and the sub-supply channel  38  is not discharged from the ink head  20  but the ink is slightly flowing through the main supply channel  32  and the sub-supply channel  38 , unless the suction pump  54  is operative. 
     Note that instep S 203 , the second standby setting processor  63  may set the open/closed state of the valves to the second standby state as shown in  FIG. 6 . In the first ink supply mechanism  31   a  in the second standby state, the first upstream-side valve  48   a  is closed and the first downstream-side valve  50   a  is open. In the second ink supply mechanism  31   b  in the second standby state, the second upstream-side valve  48   b  and the second downstream-side valve  50   b  are open. 
     Next, in step S 205  of  FIG. 8 , the standby state determination processor  66  calculates the amount of time elapsed from when the open/closed state of the valves was set to the first standby state or the second standby state. Then, the standby state determination processor  66  determines whether or not the elapsed time is greater than or equal to the first amount of time. Note that the first amount of time is a value pre-stored in the storage processor  61 . In the present preferred embodiment, the first amount of time is longer than the second amount of time, which is used when printing. That is, the second amount of time is shorter than the first amount of time. There is no particular limitation on the specific value of the first amount of time. For example, the first amount of time is preferably such an amount of time that the operator will not feel stressed by the switching of the open/closed state of the valves during standby. The upper limit value of the first amount of time is preferably determined taking into consideration the temperature characteristics and the swelling characteristics of the ink. Thus, the first amount of time is preferably from about  20  minutes to about  60  minutes, for example. The first amount of time is preferably about  30  minutes, for example. 
     In step S 205 , if it is determined by the standby state determination processor  66  that the amount of time elapsed from when the open/closed state of the valves was set to the first standby state or the second standby state is greater than or equal to the first amount of time, step S 207  is performed next. In step S 207 , the standby state switching processor  68  switches the open/closed state of the valves. For example, when the open/closed state of the valves is the first standby state, the standby state switching processor  68  switches the open/closed state of the valves from the first standby state to the second standby state as shown in  FIG. 6 . On the other hand, when the open/closed state of the valves is the second standby state, the standby state switching processor  68  switches the open/closed state of the valves from the second standby state to the first standby state as shown in  FIG. 5 . After the switching of the open/closed state of the valves in step S 207 , step S 205  is performed again. 
     In step S 205  of  FIG. 8 , if it is determined by the standby state determination processor  66  that the amount of time elapsed from when the open/closed state of the valves was set to the first standby state or the second standby state is less than the first amount of time, step S 209  is performed next. Next, in step S 209 , it is determined whether or not to start a printing operation. For example, it is determined whether or not to start a printing operation based on whether or not the controller  28  has received a print-start signal. When the controller  28  receives a print-start signal, the standby process is ended. On the other hand, when the controller  28  determines that the system is on standby, step S 205  is again performed next. As described above, in the present preferred embodiment, the open/closed state of the valves in the ink supply system  30  is switched from the first standby state to the second standby state or from the second standby state to the first standby state after every passage of the first amount of time, which is longer than the second amount of time, during standby. 
     As described above, in the present preferred embodiment, the open/closed state of the valves  48  and  50  is switched from the first standby state to the second standby state or from the second standby state to the first standby state by the standby state switching processor  68  after every passage of the first amount of time, as shown in  FIG. 5  and  FIG. 6 , during standby. Therefore, during standby, since the first upstream-side valve  48   a  is open in the first standby state, the pressure in the main supply channel  32   a  is released toward the first ink cartridge  100   a . Therefore, it is possible to prevent ink from swelling and leaking from the first ink head  20   a  during standby. 
     Note that in order to prevent ink from swelling during standby, one may consider leaving all of the upstream-side valve  48  and the downstream-side valve  50  open at all times. However, if all the valves  48  and  50  are left open at all times, ink may possibly leak from the ink head  20  because of the valves being open for a long time. In view of this, in the present preferred embodiment, the open/closed state of the upstream-side valve  48  is switched after every passage of an amount of time that is greater than or equal to the first amount of time during standby, thus shortening the state in which all the valves  48  and  50  are left open at all times. Therefore, it is possible to better prevent ink from leaking from the ink head  20 . 
     If the main supply channel  32  and the sub-supply channel  38  were broken and all the valves  48  and  50  were left open at all times, more ink would leak from the broken portions. However, in the present preferred embodiment, the open/closed state of the upstream-side valve  48  is switched after every passage of an amount of time that is greater than or equal to the first amount of time during standby. Therefore, even if the main supply channel  32  and the sub-supply channel  38  are broken during standby, it is possible to reduce the amount of ink that leaks from the broken portions, as compared with a case in which the valves  48  and  50  are left open at all times. 
     According to the present preferred embodiment, the printing state determination processor  67  determines whether or not the amount of time elapsed from when the state was set to the first printing state or the second printing state by the first printing setting processor  64  or the second printing setting processor  65  is greater than or equal to the second amount of time, which is shorter than the first amount of time. Then, if it is determined by the printing state determination processor  67  that the elapsed time is greater than or equal to the second amount of time, the printing state switching processor  69  switches either from the first printing state to the second printing state or from the second printing state to the first printing state. Thus, the only difference between when printing and during standby is the time elapsed based on which the open/closed state of the valves is switched, and the control is otherwise the same between when printing and during standby. Therefore, it is possible to ensure an ink flow when printing and during standby without complicated control. 
     According to the present preferred embodiment, as shown in  FIG. 2 , a plurality of ink supply mechanisms  31  are divided into the first group  71  and the second group  72  so that the first ink supply mechanism  31   a  of the first group  71  and the second ink supply mechanism  31   b  of the second group  72  are controlled differently. In the first standby state and the first printing state, in the first ink supply mechanism  31   a , the first upstream-side valve  48   a  and the first downstream-side valve  50   a  are open. In the first standby state and the first printing state, in the second ink supply mechanism  31   b , the second upstream-side valve  48   b  is closed and the second downstream-side valve  50   b  is open. In the second standby state and the second printing state, in the first ink supply mechanism  31   a , the first upstream-side valve  48   a  is closed and the first downstream-side valve  50   a  is open. In the second standby state and the second printing state, in the second ink supply mechanism  31   b , the second upstream-side valve  48   b  and the second downstream-side valve  50   b  are open. Thus, in the first printing state and the second printing state, the second downstream-side valve  50   b  is open. Therefore, when printing, whether in the first printing state or in the second printing state, ink stored in the ink cartridge  100  or the sub-tank  34  is supplied to the ink head  20 . Therefore, when printing, the open/closed state of the valves can be switched without stopping the printing operation. 
     In the present preferred embodiment, immediately after the switching of the open/closed state of the upstream-side valve  48 , ink pulsation is caused by the propagation of pressure waves in the main supply channel  32  and the sub-supply channel  38 . For example, the phase of the pulsation immediately after the upstream-side valve  48  is switched from the closed state to the open state is opposite to the phase of the pulsation immediately after the upstream-side valve  48  is switched from the open state to the closed state. If the upstream-side valve  48  were switched from closed to open or the upstream-side valve  48  were switched from open to closed in all of the first ink supply mechanisms  31   a  of the first group  71  and the second ink supply mechanisms  31   b  of the second group  72 , all of the ink supply mechanisms  31  would be in the same pulsation phase. Then, the pulsations would be superposed together to produce a significant vibration, affecting the printer  10 . However, in the present preferred embodiment, in the first ink supply mechanism  31   a  and the second ink supply mechanism  31   b , when the first upstream-side valve  48   a  is switched from open to closed, the second upstream-side valve  48   b  is switched from closed to open. On the other hand, when the first upstream-side valve  48   a  is switched from closed to open, the second upstream-side valve  48   b  is switched from open to closed. Therefore, immediately after the switching of the open/closed state of the upstream-side valve  48 , the phase of the pulsation in the first ink supply mechanism  31   a  is opposite to the phase of the pulsation in the second ink supply mechanism  31   b . Therefore, even immediately after the switching of the open/closed state of the upstream-side valve  48 , pulsations are canceled out with each other, thus controlling vibration caused by pulsation. 
     According to the present preferred embodiment, the amount of ink that is able to be stored in the first ink cartridge  100   a  and the second ink cartridge  100   b  is the first amount. The amount of ink that is able to be stored in the first sub-tank  34   a  and the second sub-tank  34   b  is the second amount, which is smaller than the first amount. Therefore, when the first sub-tank  34   a  and the second sub-tank  34   b  are exhausted, for example, they are able to be replenished with ink in the first ink cartridge  100   a  and ink in the second ink cartridge  100   b , respectively. Thus, it is possible to increase the amount of ink available as compared with printers in which the ink cartridge  100  is connected to the ink head  20  and no sub-tank  34  is connected to the ink head  20 . 
     According to the present preferred embodiment, the ink supply system  30  includes the first supply pump  47   a  provided on the first main downstream portion  36   ba  in the first ink supply mechanism  31   a  to discharge ink from the nozzle  21  of the first ink head  20   a , and the second supply pump  47   b  provided on the second main downstream portion  36   bb  in the second ink supply mechanism  31   b  to discharge ink from the nozzle  21  of the second ink head  20   b . During standby, the first supply pump  47   a  and the second supply pump  47   b  are stopped by the first standby setting processor  62  and the second standby setting processor  63 . Thus, even when the first downstream-side valve  50   a  and the second downstream-side valve  50   b  are opened during standby, it is possible to prevent ink from leaking from the first ink head  20   a  and the second ink head  20   b  because the first supply pump  47   a  and the second supply pump  47   b  are stopped. 
     The printer  10  including the ink supply system  30  according to the first preferred embodiment has been described above. The printer of the present invention is not limited to the printer  10  of the first preferred embodiment, but can be implemented in various other preferred embodiments. Next, another preferred embodiment of the present invention will be described briefly. Note that in the description below, like elements to those that have already been described above will be denoted by like reference signs and will not be further described below. 
     Second Preferred Embodiment 
     In the first preferred embodiment, the first standby state preferably is the same as the first printing state, and the second standby state is the second printing state. Specifically, as shown in  FIG. 5 , in the first ink supply mechanism  31   a  in the first standby state, the first upstream-side valve  48   a  and the first downstream-side valve  50   a  are open. In the second ink supply mechanism  31   b  in the first standby state, the second upstream-side valve  48   b  is closed and the second downstream-side valve  50   b  is open. As shown in  FIG. 6 , in the first ink supply mechanism  31   a  in the second standby state, the first upstream-side valve  48   a  is closed and the first downstream-side valve  50   a  is open. In the second ink supply mechanism  31   b  in the second standby state, the second upstream-side valve  48   b  and the second downstream-side valve  50   b  are open. However, the first standby state may be different from the first printing state. The second standby state may be different from the second printing state. 
     Next, a printer according to the second preferred embodiment of the present invention will be described.  FIG. 9  is a schematic diagram showing the first ink supply mechanism  31   a  and the second ink supply mechanism  31   b  in the first standby state according to the second preferred embodiment.  FIG. 10  is a schematic diagram showing the first ink supply mechanism  31   a  and the second ink supply mechanism  31   b  in the second standby state according to the second preferred embodiment. Note that in  FIG. 9  and  FIG. 10 , arrows C 1  to C 3  and arrows D 1  to D 3  show the flow of ink. For each of valves  48   a ,  48   b ,  50   a  and  50   b  in  FIG. 9  and  FIG. 10 , “x” indicates that the valve is closed. In the second preferred embodiment, as shown in  FIG. 9 , in the first ink supply mechanism  31   a  in the first standby state, the first upstream-side valve  48   a  and the first downstream-side valve  50   a  are open, as in the first preferred embodiment. In the second ink supply mechanism  31   b  in the first standby state, the second upstream-side valve  48   b  is open and the second downstream-side valve  50   b  is closed. Then, in the second preferred embodiment, as shown in  FIG. 10 , in the first ink supply mechanism  31   a  in the second standby state, the first upstream-side valve  48   a  is open and the first downstream-side valve  50   a  is closed. In the second ink supply mechanism  31   b  in the second standby state, the second upstream-side valve  48   b  and the second downstream-side valve  50   b  are open, as in the first preferred embodiment. In the present preferred embodiment, between the first standby state and the second standby state, the open/closed state of the first downstream-side valve  50   a  of the first ink supply mechanism.  31   a  and that of the second downstream-side valve  50   b  of the second ink supply mechanism  31   b  are switched around. 
     Note that in the present preferred embodiment, the first printing state and the second printing state preferably are the same as the first printing state and the second printing state of the first preferred embodiment. Transitions of the open/closed state of the valves of the ink supply mechanism  31  when printing preferably are the same as those when printing in the first preferred embodiment. Therefore, the first printing state, the second printing state, and the transitions of the open/closed state of the valves of the ink supply mechanism  31  when printing according to the present preferred embodiment will not be described below. 
     Next, transitions of the open/closed state of the valves of the ink supply mechanism  31  during standby according to the present preferred embodiment will be described. In the present preferred embodiment, since the control procedure by the ink supply system  30  during standby is the same as that of the flow chart of  FIG. 8 , transitions of the open/closed state of the valves of the ink supply mechanism  31  during standby will be described using the flow chart of  FIG. 8 . 
     First, in step S 201 , the printer  10  which is printing stops printing. During standby, the first supply pump  47   a  and the second supply pump  47   b  are stopped. Then, in step S 203 , the first standby setting processor  62  of the controller  28  sets the open/closed state of the valves in the ink supply mechanism  31  to the first standby state as shown in  FIG. 9 . Specifically, in the first printing state, the first upstream-side valve  48   a  and the first downstream-side valve  50   a  are open. In the second ink supply mechanism  31   b  in the first standby state, the second upstream-side valve  48   b  is open and the second downstream-side valve  50   b  is closed. Therefore, in the first standby state, ink stored in the first ink cartridge  100   a  flows through the first main supply channel  32   a  and the first sub-supply channel  38   a  as indicated by arrows C 1  and C 2 . Ink stored in the second ink cartridge  100   b  is supplied to the second sub-tank  34   b  through the second main upstream portion  36 ab of the second main supply channel  32   b  and the second sub-supply channel  38   b  as indicated by arrow C 3 . 
     Note that in step S 203  of  FIG. 8 , the second standby setting processor  63  may set the open/closed state of the valves to the second standby state as shown in  FIG. 10 . Then, in the first ink supply mechanism  31   a  in the second standby state, the first upstream-side valve  48   a  is open and the first downstream-side valve  50   a  is closed. Then, ink flows as indicated by arrow D 1 . In the second ink supply mechanism  31   b  in the second standby state, the second upstream-side valve  48   b  and the second downstream-side valve  50   b  are open. Then, ink flows as indicated by arrows D 2  and D 3 . 
     Next, in step S 205  of  FIG. 8 , the standby state determination processor  66  calculates the amount of time elapsed from when the open/closed state of the valves was set to the first standby state or the second standby state. Then, the standby state determination processor  66  determines whether or not the elapsed time is greater than or equal to the first amount of time, which is longer than the second amount of time. If it is determined by the standby state determination processor  66  that the amount of time elapsed from when the open/closed state of the valves was set to the first standby state or the second standby state is greater than or equal to the first amount of time, step S 207  is performed next. In step S 207 , the standby state switching processor  68  switches the open/closed state of the valves. For example, when the open/closed state of the valves is the first standby state, the standby state switching processor  68  switches the open/closed state of the valves from the first standby state to the second standby state as shown in  FIG. 10 . On the other hand, when the open/closed state of the valves is the second standby state, the standby state switching processor  68  switches the open/closed state of the valves from the second standby state to the first standby state as shown in  FIG. 9 . After the switching of the open/closed state of the valves in step S 207 , step S 205  is performed again. 
     In step S 205  of  FIG. 8 , if it is determined by the standby state determination processor  66  that the amount of time elapsed from when the open/closed state of the valves was set to the first standby state or the second standby state is less than the first amount of time, step S 209  is performed next. Next, in step S 209 , it is determined whether or not to start a printing operation. For example, when the controller  28  receives a print-start signal, the standby process is ended. On the other hand, when the controller  28  determines that the system is on standby, step S 205  is again performed next. 
     As described above, in the present preferred embodiment, during standby, the standby state switching processor  68  switches the open/closed state of the valves  48  and  50  from the first standby state to the second standby state or from the second standby state to the first standby state after every passage of the first amount of time. Therefore, during standby, since the first downstream-side valve  50   a  is open in the first standby state, the pressure in the main supply channel  32  is released toward the first ink cartridge  100   a . Therefore, it is possible to prevent ink from swelling and leaking from the first ink head  20   a  during standby. The present preferred embodiment achieves similar advantageous effects to those of the first preferred embodiment. 
     Note that the various processors of the controller  28 , i.e., the storage processor  61 , the first standby setting processor  62 , the second standby setting processor  63 , the first printing setting processor  64 , the second printing setting processor  65 , the standby state determination processor  66 , the printing state determination processor  67 , the standby state switching processor  68  and the printing state switching processor  69 , maybe implemented by software. 
     That is, the various processors may be implemented by a computer with a computer program loaded on the computer. The present invention encompasses a non-transitory computer readable medium including a computer program that instructs a computer to function as the various processors described above. The various processors may be implemented by a processor or processors executing a computer program stored in the controller  28 . In this case, the various processors may be implemented by a single processor or may be implemented by a plurality of processors. The present invention also encompasses a circuit that implements similar functions to those realized by programs executed by the various processors. 
     The terms and expressions used herein are used for explanation purposes and should not be construed as being restrictive. It should be appreciated that the terms and expressions used herein do not eliminate any equivalents of features illustrated and mentioned herein, but include various modifications falling within the claimed scope of the present invention. The present invention may be embodied in many different forms and preferred embodiments. The present disclosure is to be considered as providing non-limiting examples of the principles of the present invention. These non-limiting examples are described herein with the understanding that such examples are not intended to limit the present invention to preferred embodiments described herein and/or illustrated herein. Hence, the present invention is not limited to the preferred embodiments described herein. The present invention includes any and all preferred embodiments including equivalent elements, modifications, omissions, combinations, adaptations and/or alterations as would be appreciated by those skilled in the art on the basis of the present disclosure. The limitations in the claims are to be interpreted broadly based on the language included in the claims and not limited to examples described in the present specification or during the prosecution of the application. 
     While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims.