Patent Publication Number: US-11020979-B2

Title: Liquid discharge device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority from Japanese Patent Application No. 2018-185954 filed on Sep. 28, 2018, the content of which is incorporated herein by reference in its entirety. 
     TECHNICAL FIELD 
     The present disclosure relates to a liquid discharge device for discharging liquid. 
     BACKGROUND 
     A known inkjet printer includes a removable main tank, a subtank storing ink fed from the main tank that has been installed, and an image recording unit that discharges ink from the subtank to print an image (e.g., JP-A-2008-213162). The main tank and the subtank each have the internal space open to the air. When the main tank is installed in the inkjet printer, the liquid height difference between the internal spaces of the main tank and the subtank (hereinafter, the water head difference) causes ink transfer between the tanks toward the same liquid level. The inkjet printer then displays, on a display, a message urging replacement of the main tank, or disables the ink discharge through the image recording unit when the residual amount of the ink detected by a residual amount sensor decreases below a threshold. 
     SUMMARY 
     As the image recording unit discharges ink, the amount of liquid stored in each of the main tank and the subtank changes. For example, when the amount of ink stored in the cartridge decreases to near zero, the user may be urged to replace the cartridge. When the amount of ink stored in the subtank decreases to near zero, the user may be notified or the image recording may be disabled to prevent entry of air from the subtank into the image recording unit. The ink amounts of the main tank and the subtank are thus to be determined. 
     After the main tank is replaced, ink flows from the main tank into the subtank, thus increasing the residual ink amount in the subtank. In response to the main tank replacement, the message indicating the empty cartridge may be deleted from the display or the disabled ink discharge may be enabled. However, the determination as to whether the ink is flowing into the subtank cannot be performed until the signal output from the residual amount sensor changes. When, for example, the newly installed main tank stores a small amount of ink, the ink flow from the main tank into the subtank stops after the small amount of ink flows into the subtank. When the message indicating the empty cartridge is deleted in response to the main tank replacement, the empty state can actually continue although the message has been deleted. When the disabled ink discharge is enabled in response to the main tank replacement, the image recording may cause air entrapment or specifically the entry of air into an ink flow path from the subtank to the image recording unit. 
     In response to the above issue, one aspect of the present disclosure is directed to a liquid discharge device that determines the amount of liquid stored in each of a first liquid chamber and a second liquid chamber. 
     Another aspect of the present disclosure is directed to a liquid discharge device that deactivates an alarm or enables previously disabled printing after the cartridge is replaced and then the liquid is reliably determined to have flown into the second liquid chamber of the tank. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is an external perspective view of a multifunction peripheral  10  according to a first embodiment with a cover  48  at a closed position;  FIG. 1B  is an external perspective view of the multifunction peripheral  10  with the cover  48  at an open position; 
         FIG. 2  is a sectional view of a printer unit  11  schematically showing the internal structure; 
         FIG. 3  is a plan view of a carriage  23  and an ink feeder  15  showing their arrangement; 
         FIG. 4  is a perspective view of the ink feeder  15  viewed from the front left; 
         FIG. 5  is a cross-sectional view taken in the arrow direction of line V-V in  FIG. 4 ; 
         FIG. 6  is a cross-sectional view taken in the arrow direction of line V-V in  FIG. 4  with an ink cartridge  50  removed; 
         FIG. 7  is a cross-sectional view taken in the arrow direction of line V-V in  FIG. 4  showing a part around a subtank  100 ; 
         FIG. 8  is a cross-sectional view taken in the arrow direction of line VIII-VIII in  FIG. 4 ; 
         FIG. 9  is a cross-sectional view taken in the arrow direction of line IX-IX in  FIG. 4 ; 
         FIG. 10  is a cross-sectional view taken in the arrow direction of line IX-IX in  FIG. 4  showing a part around the subtank  100 ; 
         FIG. 11  is a perspective view of the subtank  100  and a buffer tank  90  viewed from the front left; 
         FIG. 12A  is a cross-sectional view taken in the arrow direction of line XIIA-XIIA in  FIG. 10 ;  FIG. 12B  is a cross-sectional view taken in the arrow direction of line XIIB-XIIB in  FIG. 11 ; 
         FIG. 13  is a block diagram of the multifunction peripheral  10 ; 
         FIG. 14  is a flowchart of an image recording process; 
         FIG. 15  is a flowchart of a counting process; 
         FIG. 16  is a schematic diagram of the ink cartridge  50  and the subtank  100  communicating with each other in which the cartridge is empty; 
         FIG. 17  is a block diagram of a multifunction peripheral  10  according to a second embodiment; 
         FIGS. 18A and 18B  are flowcharts of an image recording process according to the second embodiment; 
         FIG. 19  is a flowchart of a counting process according to the second embodiment; and 
         FIG. 20A  is a diagram showing a notification screen S_Empty;  FIG. 20B  is a diagram showing an ink in-flow screen; and  FIG. 20C  is a diagram showing a notification screen C_Empty. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present disclosure will be described below. The embodiments described below are merely examples and can be appropriately modified without departing from the spirit and scope of the present disclosure. An up-down direction  7  is defined based on the posture of a multifunction peripheral  10  placed on a horizontal plane with ink cartridges  50  installed for use (posture in  FIG. 1 , hereinafter referred to as a use posture), a front-back direction  8  is defined using a surface of the multifunction peripheral  10  with an opening  13  as a front surface, and a left-right direction  9  is defined for the multifunction peripheral  10  viewed from the front surface. In the present embodiment, the up-down direction  7  in the use posture corresponds to a vertical direction, and the front-back direction  8  and the left-right direction  9  correspond to a horizontal direction. 
     First Embodiment 
     The multifunction peripheral  10  and an ink feeder  15  according to a first embodiment will now be described. 
     Overall Structure of Multifunction Peripheral  10   
     As shown in  FIGS. 1A and 1B , the multifunction peripheral  10  (an example of a liquid discharge device) is in the shape of a substantially rectangular parallelepiped. The multifunction peripheral  10  includes a printer unit  11 , a scanner unit  12 , and an operation panel  22 . The printer unit  11 , which is a lower part of the multifunction peripheral  10 , records an image on a sheet of paper (sheet  28 ) with an inkjet recording method (see  FIG. 2 ). The scanner unit  12  with a scanning function is located above the printer unit  11 . The printer unit  11  includes a housing  14  having a front opening  13 , and the ink feeder  15  on the right of the opening  13  in the housing  14 . 
     The operation panel  22  is located in front of the scanner unit  12 . The operation panel  22  is operated by a user to cause the multifunction peripheral  10  to perform image recording by the printer unit  11  or image reading by the scanner unit  12 . The operation panel  22  includes a display  17 . The display  17  may be, for example, a liquid crystal display or an organic electroluminescence (EL) display, and has a display screen on which various items of information appear. The display  17  is an example of an alarm. However, the alarm is not limited to the display  17 , and may be a speaker, a light-emitting diode (LED) lamp, or a combination of these devices. The operation panel  22  outputs an operation signal corresponding to a user&#39;s operation to a controller  230 . For example, the operation panel  22  may include a push button, or may include a touch sensor overlaid on the display. 
     As shown in  FIG. 2 , the housing  14  contains a feeder  16 , a feed tray  20 , a discharge tray  21 , a conveyance roller pair  45 , a recorder  24 , a discharge roller pair  46 , and a platen  42 . 
     Feed Tray  20  and Discharge Tray  21   
     As shown in  FIGS. 1A and 1B , the feed tray  20  is insertable into and removable from the housing  14  in the front-back direction  8  through the opening  13 . The opening  13  is located in the front surface of the multifunction peripheral  10  in the middle in the left-right direction  9 . As shown in  FIG. 2 , the feed tray  20  can support a plurality of sheets  28  stacked on one another. The discharge tray  21  is located above the feed tray  20 , and is inserted or removed in the front-back direction  8  together with the feed tray  20 . The discharge tray  21  supports sheets  28  discharged from the discharge roller pair  46 . 
     Feeder  16   
     The feeder  16  feeds a sheet  28  supported on the feed tray  20  to a conveyance path  38 . As shown in  FIG. 2 , the feeder  16  includes a feed roller  25 , a feed arm  26 , and a shaft  27 . The feed roller  25  is rotatably supported at an end of the feed arm  26 . The feed roller  25  is driven by a feed motor (not shown). The feed arm  26  is rotatably supported by the shaft  27  that is supported by a frame of the printer unit  11 . The feed arm  26  is rotationally urged toward the feed tray  20  by its weight or by an elastic force from a spring or another member. 
     Hereafter, the rotation of the feed roller  25 , a conveyance roller  34 , and a discharge roller  36  for conveyance of the sheet  28  in a conveyance direction  38 A of the sheet  28  will be referred to as normal rotation. 
     Conveyance Path  38   
     As shown in  FIG. 2 , the conveyance path  38  is a space partially defined by an outer guide  18  and an inner guide  19  facing each other at a predetermined distance in the printer unit  11 . The conveyance path  38  extends rearward from the rear end of the feed tray  20 . The conveyance path  38  extends upward at the rear of the printer unit  11 , U-turns, and extends forward through a space between the recorder  24  and the platen  42  into the discharge tray  21 . As shown in  FIGS. 2 and 3 , a part of the conveyance path  38  between the conveyance roller pair  45  and the discharge roller pair  46  is located substantially in the middle of the multifunction peripheral  10  in the left-right direction  9 , and extends in the front-back direction  8 . The conveyance direction  38 A of the sheet  28  on the conveyance path  38  is indicated by an arrow in  FIG. 2 . 
     Conveyance Roller Pair  45   
     As shown in  FIG. 2 , the conveyance roller pair  45  is located upstream from the recorder  24  in the conveyance direction  38 A. The conveyance roller pair  45  includes the conveyance roller  34  and a pinch roller  35  facing each other. The conveyance roller  34  is driven by a conveyance motor (not shown) to rotate in normal or reverse direction. The pinch roller  35  rotates in accordance with the rotation of the conveyance roller  34 . The sheet  28  is conveyed in the conveyance direction  38 A between the conveyance roller  34  and the pinch roller  35  that are rotating in normal direction. 
     Discharge Roller Pair  46   
     As shown in  FIG. 2 , the discharge roller pair  46  is located downstream from the recorder  24  in the conveyance direction  38 A. The discharge roller pair  46  includes the discharge roller  36  and a spur  37  facing each other. The discharge roller  36  is driven by the conveyance motor (not shown) to rotate in normal or reverse direction. The spur  37  rotates in accordance with the rotation of the discharge roller  36 . The sheet  28  is conveyed in the conveyance direction  38 A between the discharge roller  36  and the spur  37  that are rotating in normal direction. 
     Recorder  24   
     As shown in  FIG. 2 , the recorder  24  is located between the conveyance roller pair  45  and the discharge roller pair  46  in the conveyance direction  38 A. The recorder  24  faces the platen  42  in the up-down direction  7  across the conveyance path  38 . The recorder  24  includes a carriage  23  and a printhead  39  included in the carriage  23 . 
     As shown in  FIG. 3 , the carriage  23  is supported by guide rails  43  and  44  spaced from each other in the front-back direction  8  and each extending in the left-right direction  9 . The guide rails  43  and  44  are supported by a frame (not shown). The carriage  23  is connected to a known belt mechanism included in the guide rail  44 . The belt mechanism is driven by a carriage drive motor (not shown) to rotate. As the belt mechanism rotates, the carriage  23  is guided by the guide rails  43  and  44  to reciprocate in the left-right direction  9 . The carriage  23  moves beyond the right and left ends of a width  38 B of the conveyance path  38 , as indicated by dash-dot lines in  FIG. 3 . 
     The printhead  39  and four subtanks  100  included in the ink feeder  15  are connected to each other with four ink tubes  32 . The printhead  39  is connected to a control board (not shown) with a flexible flat cable  33 . 
     The four subtanks  100  include a magenta subtank  100 M, a cyan subtank  100 C, a yellow subtank  100 Y, and a black subtank  100 B. The magenta subtank  100 M, the cyan subtank  100 C, the yellow subtank  100 Y, and the black subtank  100 B are herein collectively referred to as the subtanks  100 , unless they are distinguished. 
     The four ink tubes  32  include a yellow ink tube  32 Y, a cyan ink tube  32 C, a magenta ink tube  32 M, and a black ink tube  32 B. The yellow ink tube  32 Y, the cyan ink tube  32 C, the magenta ink tube  32 M, and the black ink tube  32 B are herein collectively referred to as the ink tubes  32 , unless they are distinguished. The four ink tubes  32  are bundled together. 
     The flexible flat cable  33  electrically connects the control board including a control unit to the printhead  39 . The flexible flat cable  33  transfers a control signal output from the control unit to the printhead  39 . 
     As shown in  FIG. 2 , the printhead  39  includes a plurality of nozzles  40  on its bottom surface. The nozzles  40  have ends exposed at the bottom surface of the printhead  39 . The printhead  39  discharges ink through the nozzles  40  as fine droplets. While the carriage  23  is moving, the printhead  39  discharges ink droplets toward the sheet  28  supported on the platen  42 . This records an image on the sheet  28 . In this process, the ink stored in the four subtanks  100  is used. 
     Platen  42   
     As shown in  FIGS. 2 and 3 , the platen  42  is located between the conveyance roller pair  45  and the discharge roller pair  46  on the conveyance path  38 . The platen  42  faces the recorder  24  in the up-down direction  7  across the conveyance path  38 . The platen  42  supports the sheet  28  from below when the conveyance roller pair  45  conveys the sheet  28 . 
     Cover  48   
     As shown in  FIG. 1B , the housing  14  has a front right opening  47 . The housing  14  contains the ink feeder  15  with a front surface exposed at the opening  47 . The housing  14  has a cover  48  attached to open and close the opening  47 . The cover  48  has a lower end under the opening  47 , which is pivotably supported by the housing  14  about an axis in the left-right direction  9 . The cover  48  is pivotable between a closed position (shown in  FIG. 1A ) at which the opening  47  is closed and an open position (shown in  FIG. 1B ) at which the opening  47  is open. 
     As shown in  FIG. 1A , the cover  48  has a translucent part  49 . The translucent part  49  is translucent to allow the interior to be viewable from outside the cover  48 . With the cover  48  at the closed position, the translucent part  49  allows viewing of the front surfaces of the ink cartridges  50  installed in the ink feeder  15 . 
     Cover Sensor  88   
     The multifunction peripheral  10  includes a cover sensor  88  (see  FIG. 13 ). The cover sensor  88  may be, for example, a mechanical sensor such as a switch with and from which the cover  48  contacts and separates, or an optical sensor for which light is blocked or transmitted depending on the position of the cover  48 . The cover sensor  88  outputs a signal corresponding to the position of the cover  48  to the controller  230 . More specifically, the cover sensor  88  outputs a low-level signal to the controller  230  when the cover  48  is at the closed position. The cover sensor  88  outputs a high-level signal having a higher signal intensity than the low-level signal to the controller  230  when the cover  48  is at a position different from the closed position. In other words, the cover sensor  88  outputs a high-level signal to the controller  230  when the cover  48  is at the open position. 
     Ink Feeder  15   
     As shown in  FIG. 4 , the ink feeder  15  includes the four ink cartridges  50 , an installation case  71 , the four subtanks  100 , and an air communication portion  70  (see  FIGS. 5 and 11 ). 
     Ink Cartridge  50   
     As shown in  FIGS. 1A, 1B, and 3 , the four ink cartridges  50  (examples of cartridges) include a magenta ink cartridge  50 M, a cyan ink cartridge  50 C, a yellow ink cartridge  50 Y, and a black ink cartridge  50 B. The magenta ink cartridge  50 M, the cyan ink cartridge  50 C, the yellow ink cartridge  50 Y, and the black ink cartridge  50 B are herein collectively referred to as the ink cartridges  50 , unless they are distinguished. 
     In  FIG. 4 , the magenta ink cartridge  50 M, which is the leftmost one of the four ink cartridges  50  in the left-right direction  9 , alone is installed in the installation case  71 . 
     As shown in  FIGS. 5 and 6 , an ink cartridge  50  includes a cartridge body  51  and a joint receiver  52 . The cartridge body  51  includes a first reservoir  53  (an example of a first liquid chamber) storing ink (an example of liquid). 
     The cartridge body  51  is in the shape of a substantially rectangular parallelepiped box. The cartridge body  51  is substantially rectangular as viewed in the up-down direction  7  and the front-back direction  8 . The cartridge body  51  has a downward protrusion  65  on its front end. The cartridge body  51  has an upper wall  54 , a lower subwall  55 , a right wall  56  (see  FIG. 4 ), a left wall  57  (see  FIG. 4 ), a rear wall  58 , a front wall  59 , and a lower wall  60 . The lower wall  60  is located at the front part and the lower end of the cartridge body  51 , and below the lower subwall  55 . The lower subwall  55  is located behind the lower wall  60 . The cartridge body  51  has a communication port  61  that is open rearward (an example of a horizontal direction) in the protrusion  65 . The communication port  61  is an opening defined by the lower subwall  55 , the lower wall  60 , the right wall  56 , and the left wall  57 . 
     The upper wall  54  has a contact part  64  protruding upward in the middle in the front-back direction  8 . The contact part  64  comes into contact with a lock lever  79  (described later) on the installation case  71 . 
     The contact part  64  receives an integrated circuit (IC) chip  66  (an example of a cartridge memory) on its upper surface. The IC chip  66  includes an IC chip. The IC chip  66  also includes a memory (not shown). In the IC chip  66 , the IC chip is electrically connected to the memory. The IC chip  66  is exposed on its upper surface for electrical connection with a contact  152 . More specifically, the IC chip  66  is electrically connected to the contact  152  when the ink cartridge  50  is installed in the installation case  71 . The controller  230  can read information from the memory of the IC chip  66  through the contact  152  and the IC chip  66 , and can write information to the memory of the IC chip  66  through the contact  152  and the IC chip  66 . 
     The memory of the IC chip  66  stores an ink amount Vc and identification information for identifying each ink cartridge  50 . For a fresh ink cartridge  50 , the memory of the IC chip  66  stores an initial ink amount Vc 0  as the ink amount Vc. The initial ink amount Vc 0  is an example of a maximum liquid amount indicating a maximum amount of ink that can be stored in the ink cartridge  50 . In other words, the initial ink amount Vc 0  indicates the amount of ink stored in a fresh ink cartridge  50 . Hereafter, information stored in the memory of the IC chip  66  may be collectively referred to as cartridge (CTG) information. A fresh ink cartridge herein refers to an unused ink cartridge  50  from which ink has yet to flow out after manufactured and sold. 
     The memory of the IC chip  66  includes, for example, a non-writable storage area in which no information is overwritten by the controller  230  and a writable storage area in which information can be overwritten by the controller  230 . For example, identification information is stored in the non-writable area, and the ink amount Vc is stored in the writable area. 
     The upper surface of the lower subwall  55 , which defines the bottom surface of the first reservoir  53 , is inclined downward to the protrusion  65  in the front-back direction  8 . 
     The joint receiver  52  is cylindrical and extends rearward from a part of the cartridge body  51  surrounding the communication port  61 . The joint receiver  52  receives a joint  102  (described later) included in a subtank  100 . 
       FIG. 5  shows the ink cartridge  50  installed in the subtank  100 .  FIG. 6  shows the ink cartridge  50  separate from the subtank  100 . The installed state will be detailed later. 
     The joint receiver  52  includes a plug  62  that can close the communication port  61  and a spring  63  that urges the plug  62  rearward. As shown in  FIG. 6 , under no external force applied to the ink cartridge  50 , the plug  62  is located to close the communication port  61 . The spring  63  extends in the front-back direction  8  between the plug  62  and the front wall  59 , and can be compressed in the front-back direction  8 . As shown in  FIG. 5 , when receiving a forward external force greater than the elastic force of the spring  63  from the joint  102 , the plug  62  moves forward to leave the communication port  61 . 
     Installation Case  71   
     The installation case  71  is in the shape of a substantially rectangular parallelepiped box that is open forward. The installation case  71  has an upper wall  72 , a lower wall  73 , a right wall  74 , a left wall  75 , a rear wall  76 , and three partition walls  77 . The upper wall  72 , the lower wall  73 , the right wall  74 , the left wall  75 , and the rear wall  76  define an internal space  78  opening forward. The three partition walls  77  are parallel with the right wall  74  and the left wall  75 , and partition the internal space  78  into four spaces. Each of the four partition spaces receives the corresponding one of the four ink cartridges  50 . 
     Lock Lever  79   
     As shown in  FIGS. 4, 5, and 6 , the installation case  71  includes lock levers  79  that hold the ink cartridges  50  inside the internal space  78 . The lock levers  79  are plate-like members extending in the front-back direction. Each lock lever  79  is pivotably attached, at the center, to the upper wall  72  about an axis in the left-right direction  9 . The lock lever  79  pivots between a locked position inclined rearward and an unlocked position inclined forward. Under no external force applied, the lock lever  79  is inclined rearward to the locked position with its weight. The lock lever  79  at the locked position has the rear end in contact with the front surface of the contact part  64  of the ink cartridge  50  inside the internal space  78  to prevent the ink cartridge  50  from moving forward in the front-back direction  8 . When the front end of the lock lever  79  at the locked position is depressed with, for example, a finger of the user, the lock lever  79  pivots from the locked position to the unlocked position. The lock lever  79  at the unlocked position has the rear end located above the front surface of the contact part  64 . The lock lever  79  at the unlocked position is not in contact with the contact part  64  of the ink cartridge  50  moving forward in the front-back direction  8 , thus allowing the ink cartridge  50  to be removable from the installation case  71 . 
     Contact  152   
     The contact  152  (an example of an interface) is located on the upper wall  72  of the installation case  71 . The contact  152  protrudes downward toward the internal space  78  of the installation case  71  from the upper wall  72 . The contact  152  is located to be in contact with the IC chip  66  (described below) of the ink cartridge  50  when the ink cartridge  50  is installed in the installation case  71 . The contact  152  is conductive and elastically deformable in the up-down direction  7 . The contact  152  is electrically connected to the controller  230 . 
     Installation Sensor  154   
     The installation sensor  154  is located on the upper wall  72  of the installation case  71 . The installation sensor  154  detects the ink cartridge  50  installed in the installation case  71 . The installation sensor  154  includes a light emitter and a light receiver located at a distance from each other in the left-right direction  9 . When the ink cartridge  50  is installed in the installation case  71 , a detectable unit (not shown) of the ink cartridge  50  is located between the light emitter and the light receiver of the installation sensor  154 . In other words, the light emitter and the light receiver of the installation sensor  154  are located opposite to each other across the detectable unit of the ink cartridge  50  installed in the installation case  71 . 
     The installation sensor  154  outputs different signals (installation signals in the drawings) depending on whether light emitted from the light emitter in the left-right direction  9  is received by the light receiver. The installation sensor  154  outputs a low-level signal to the controller  230  when, for example, the intensity of the light received by the light receiver is lower than a threshold intensity. In contrast, the installation sensor  154  outputs a high-level signal having a higher signal intensity than the low-level signal to the controller  230  when the intensity of the light received by the light receiver is equal to or higher than the threshold intensity. The high-level signal is an example of a third signal, and the low-level signal is an example of a fourth signal. 
     Subtank  100   
       FIGS. 4 to 11  show the subtanks  100  (examples of tanks). The subtanks  100  are located under the lower wall  73  of the installation case  71 . 
     As shown in  FIG. 7 , each subtank  100  includes a tank body  101  and the joint  102 . The tank body  101  includes an internal second reservoir  105  (an example of a second liquid chamber) to store ink. The subtank  100  includes a liquid flow path  103  and a gas flow path  104  that communicate with the second reservoir  105 . The liquid flow path  103  and the gas flow path  104  are defined inside the tank body  101  and the joint  102 . The subtank  100  also includes an air communication port  106  (see  FIGS. 9, 10, and 12A ) that allows the second reservoir  105  to communicate with the outside. 
     Liquid Flow Path  103  and Gas Flow Path  104   
     As shown in  FIG. 7 , the liquid flow path  103  and the gas flow path  104  are located in parallel. 
     The liquid flow path  103  has a first opening  131 , a second opening  132 , a vertical part  133 , and a horizontal part  134 . The first opening  131  is formed in one end (rear end) of the liquid flow path  103  and communicates with the second reservoir  105 . The first opening  131  is open in the up-down direction  7 . The second opening  132  is formed in the opposite end (front end) of the liquid flow path  103  and is open to the outside. The second opening  132  is open in the front-back direction  8 . With the ink cartridge  50  installed, the second opening  132  is located in the first reservoir  53  of the ink cartridge  50 . The vertical part  133  is a part of the liquid flow path  103  extending upward from the first opening  131 . The horizontal part  134  is a part of the liquid flow path  103  extending rearward from the second opening  132 . The upper end of the vertical part  133  is connected to the rear end of the horizontal part  134 . 
     The gas flow path  104  has a third opening  141 , a fourth opening  142 , a vertical part  143 , and a horizontal part  144 . The third opening  141  is formed in one end (rear end) of the gas flow path  104  and communicates with the second reservoir  105 . The third opening  141  is open in the up-down direction  7 . The fourth opening  142  is formed in the opposite end (front end) of the gas flow path  104  and is open to the outside. The fourth opening  142  is open in the front-back direction  8 . With the ink cartridge  50  installed, the fourth opening  142  communicates with the first reservoir  53  of the ink cartridge  50 . The vertical part  143  is a part of the gas flow path  104  extending upward from the third opening  141 . The horizontal part  144  is a part of the gas flow path  104  extending rearward from the fourth opening  142 . The upper end of the vertical part  143  is connected to the rear end of the horizontal part  144 . 
     Tank Body  101   
     The tank body  101  has outer walls defining the shape of a substantial rectangular parallelepiped. The tank body  101  is substantially T-shaped as viewed in the up-down direction  7  (see  FIGS. 9 and 10 ), substantially rectangular as viewed in the front-back direction  8  (see  FIG. 8 ), and L-shaped as viewed in the left-right direction  9  (see  FIGS. 4 to 7 ). 
     As shown in  FIGS. 4 to 11 , the outer walls of the tank body  101  include a rear upper wall  107 , a curved upper wall  130 , a front upper wall  108 , a lower wall  109 , two rear side walls  110 , two front curved side walls  111 , a rear wall  112 , and a front wall  113 . The rear upper wall  107  extends forward from the rear end and is inclined upward with respect to the horizontal plane. The curved upper wall  130  extends from the front end of the rear upper wall  107  and curves upward as it extends forward. The front upper wall  108  extends from the upper end of the curved upper wall  130  forward in parallel with the horizontal plane. The lower wall  109  extends in the front-back direction  8  in parallel with the horizontal plane. The lower wall  109  is T-shaped as viewed in the up-down direction  7 . The rear side walls  110  connect the rear upper wall  107  and the lower wall  109  in the up-down direction  7 . The rear side walls  110  are substantially rectangular as viewed in the left-right direction  9 . As shown in  FIG. 9 , adjacent tank bodies  101  for different inks share one rear side wall  110 . The front curved side walls  111  connect the curved upper wall  130  and the front upper wall  108  to the lower wall  109  in the up-down direction  7 . The front curved side walls  111  are substantially rectangular as viewed in the left-right direction  9 , and L-shaped with a round corner as viewed in the up-down direction  7 . The rear wall  112  extends upward from the rear end of the lower wall  109 , and is connected to the two right and left rear side walls  110  and the rear upper wall  107 . The front wall  113  extends upward from the front end of the lower wall  109 , and is connected to the two right and left front curved side walls  111 . 
     As shown in  FIGS. 7 and 11 , the lower wall  109  has a communication port  129  that communicates with the second reservoir  105 . The communication port  129  is connected to one end of the ink tube  32 , and the ink tube  32  connects the second reservoir  105  and the printhead  39 . 
     The tank body  101  includes an inner cylinder  114  extending in the front-back direction  8  at the front end and the upper part of the tank body  101 . The inside of the inner cylinder  114  communicates with the opening defined by the front wall  113 , the two right and left front curved side walls  111 , and the front upper wall  108 . The rear end of the joint  102  is attachable to the inner cylinder  114 . In the installed state with the joint  102  attached to the inner cylinder  114 , the inside of the inner cylinder  114  communicates with the inside of the joint  102 . 
     Wide Part  150  and Narrow Part  151   
     As shown in  FIG. 10 , the tank body  101  has a wide part  150  and a narrow part  151  aligned with each other in the front-back direction  8 . The wide part  150  is a rear part in the tank body  101  in the front-back direction  8  and includes the two rear side walls  110  and the rear wall  112 . The narrow part  151  is located at the front end in the front-back direction  8  (an example of an end in a first direction) in the tank body  101  and includes the two front curved side walls  111  and the front wall  113 . The narrow part  151  has a width in the left-right direction  9  (an example of a second direction orthogonal to the first direction) smaller than the width of the wide part  150  in the left-right direction  9 . The second reservoir  105  extends across the wide part  150  and the narrow part  151 . 
     As shown in  FIG. 8 , the width of the wide part  150  in the left-right direction  9  is substantially the same as the width of the ink cartridge  50  in the left-right direction  9 . Thus, the width of the narrow part  151  in the left-right direction  9  is smaller than the width of the ink cartridge  50  in the left-right direction  9 . 
     Vertical Wall  115  and Horizontal Wall  116   
     As shown in  FIGS. 7 and 11 , the tank body  101  includes a vertical wall  115  and a horizontal wall  116  in the upper front part of the tank body  101 . 
     The vertical wall  115  extends in the up-down direction  7  and is located between the front wall  113  and the curved upper wall  130  in the front-back direction  8 . The vertical wall  115  connects the two right and left front curved side walls  111 , and partitions the space defined by the front wall  113 , the front upper wall  108 , and the two front curved side walls  111  into front and rear parts. The lower end position of the vertical wall  115  is a position at the first opening  131  of the liquid flow path  103  in the up-down direction  7 , and also a position at the third opening  141  of the gas flow path  104  in the up-down direction  7 . The lower end position of the vertical wall  115  is equal to the lower end position of the front end of the rear upper wall  107 . More specifically, the upper surface of the second reservoir  105  is defined by an imaginary plane on the lower end position of the vertical wall  115  and parallel with the horizontal plane, and the bottom surface of the rear upper wall  107 . 
     The horizontal wall  116  extends forward from the upper end of the vertical wall  115 . The horizontal wall  116  extends into the inner cylinder  114 . The horizontal wall  116  connects the two right and left front curved side walls  111 , and also connects the facing inner surfaces inside the inner cylinder  114  in the left-right direction  9 . The horizontal wall  116  partitions the space defined by the front upper wall  108  and the two front curved side walls  111  into upper and lower parts, and also partitions the space defined by the inner cylinder  114  into upper and lower parts. 
     As shown in  FIG. 10 , the vertical part  133  of the liquid flow path  103  is defined by the vertical wall  115 , the front wall  113 , and the two front curved side walls  111 . The vertical part  133  of the liquid flow path  103  has a rectangular cross section orthogonal to the up-down direction  7 . The vertical part  133  of the liquid flow path  103  is flush with the two front curved side walls  111  defining the second reservoir  105 . Thus, the vertical part  133  of the liquid flow path  103  has a width in the left-right direction  9  equal to the width of the second reservoir  105  defined by the narrow part  151  in the left-right direction  9 . 
     As shown in  FIG. 10 , the vertical part  143  of the gas flow path  104  is defined by the curved upper wall  130 , the vertical wall  115 , and the two front curved side walls  111 . The vertical part  143  of the gas flow path  104  has a rectangular cross section orthogonal to the up-down direction  7 . The vertical part  143  of the gas flow path  104  is flush with the two front curved side walls  111  defining the second reservoir  105 . Thus, the vertical part  143  of the gas flow path  104  has a width in the left-right direction  9  equal to the width of the second reservoir  105  defined by the narrow part  151  in the left-right direction  9 . 
     As shown in  FIG. 10 , the third opening  141  of the gas flow path  104  has a length  149  in the front-back direction  8  (an example of the horizontal direction), and the first opening  131  of the liquid flow path  103  has a length  148  in the front-back direction  8  (an example of the horizontal direction). The length  149  is greater than the length  148 . The third opening  141  of the gas flow path  104  has a length in the left-right direction  9  equal to the length of the first opening  131  of the liquid flow path  103  in the left-right direction  9 . Thus, the third opening  141  of the gas flow path  104  has a larger opening area than the first opening  131  of the liquid flow path  103 . 
     As shown in  FIG. 7 , the opening area of the gas flow path  104  in the vertical part  143  of the gas flow path  104  increases toward the third opening  141  of the gas flow path  104 . In the vertical part  133  of the liquid flow path  103 , the opening area of the liquid flow path  103  remains constant in the up-down direction  7 . 
     As shown in  FIG. 7 , the horizontal part  134  of the liquid flow path  103  in the tank body  101  is defined by the front upper wall  108 , the horizontal wall  116 , the two front curved side walls  111 , and the inner cylinder  114 . The horizontal part  144  of the gas flow path  104  in the tank body  101  is defined by the horizontal wall  116 , the two front curved side walls  111 , and the inner cylinder  114 . 
     First Rib  117   
     As shown in  FIGS. 7 and 11 , the tank body  101  includes a first rib  117  connected to the vertical wall  115 . The first rib  117  protrudes from a front curved side wall  111  and extends downward from the vertical wall  115 . The first rib  117  is separate from the lower wall  109 . Each of the two right and left front curved side walls  111  has the first rib  117 . The single second reservoir  105  includes the two first ribs  117  separate from each other in the left-right direction  9 . 
     Liquid Level Sensor  155   
     As shown in  FIG. 7 , a liquid level sensor  155  detects the liquid level of the second reservoir  105  of the tank body  101  equal to or higher than a predetermined level B. The predetermined level B is lower than an imaginary line L extending through the third opening  141  of the gas flow path  104  in the horizontal direction. The liquid level sensor  155  optically detects the liquid level of the ink in the second reservoir  105  at the predetermined level B using a prism with different reflectance values depending on whether the ink is in contact with the rear wall  112  of the tank body  101  at the predetermined level B. 
     The liquid level sensor  155  includes a light emitter and a light receiver located at a distance from each other in the left-right direction  9 . The liquid level sensor  155  outputs different signals (liquid level signals in the drawings) depending on whether light output from the light emitter is received by the light receiver. In the present embodiment, when the second reservoir  105  of the tank body  101  has a liquid level equal to or higher than the predetermined level B, the liquid level sensor  155  outputs a low-level signal. When the second reservoir  105  of the tank body  101  has a liquid level lower than the predetermined level B, the liquid level sensor  155  outputs a high-level signal. The low-level signal is an example of a first signal. The high-level signal is an example of a second signal. 
     Joint  102   
     As shown in  FIGS. 4 to 9 and 11 , the joint  102  includes a joint body  118 , an inner wall  119 , a plug  120  (see  FIGS. 6 and 7 ), and a spring  121  (see  FIGS. 6 and 7 ). 
     Joint Body  118   
     As shown in  FIG. 7 , the joint body  118  includes an external cylinder  122  at its rear end, a front end  123 , and a main body  124  connecting the external cylinder  122  and the front end  123 . The external cylinder  122  is cylindrical and extends in the front-back direction  8 . The external cylinder  122  is fitted in the inner cylinder  114  of the tank body  101 . This fixes the joint body  118  to the tank body  101 . The front end  123  is disc-shaped with the center at an axis in the front-back direction  8 . The main body  124  is cylindrical and extends in the front-back direction  8 . The main body  124  has an upper opening  125  facing upward and a lower opening  126  facing downward at the front end of the main body  124 . 
     Partition Wall  127  and Second Rib  128   
     As shown in  FIGS. 7 and 8 , the inner wall  119  is located inside the joint body  118 . The inner wall  119  extends rearward from the front end  123  beyond the external cylinder  122 . The inner wall  119  has a partition wall  127  and a second rib  128 . As shown in  FIG. 8 , the inner wall  119  is T-shaped as viewed in the front-back direction  8 . The partition wall  127  has a rear end surface in contact with the front end surface of the horizontal wall  116  in the tank body  101 . The partition wall  127  and the horizontal wall  116  partition the internal space of the connection part between the joint body  118  and the tank body  101  into the liquid flow path  103  and the gas flow path  104 . 
     The partition wall  127  extends across the inside of the joint body  118  in the left-right direction  9 . The partition wall  127  extends rearward from the front end  123 . The joint body  118  has an internal space partitioned by the partition wall  127  into upper and lower parts. 
     The second rib  128  protrudes downward from the middle of the partition wall  127  in the left-right direction  9 . The second rib  128  extends rearward from the front end  123 . The second rib  128  and the joint body  118  have a gap between them. 
     The horizontal part  134  of the liquid flow path  103  in the joint  102  is defined by the inner surface of the joint body  118  and the bottom surface of the inner wall  119 . The horizontal part  134  of the liquid flow path  103  in the joint  102  has a substantially semicircular cross section. More specifically, the cross section of the horizontal part  134  has a semicircular shape with an upper part divided by the second rib  128  into right and left areas, and a continuous lower part that is not divided into right and left areas. The horizontal part  144  of the gas flow path  104  in the joint  102  is defined by the inner surface of the joint body  118  and the upper surface of the inner wall  119 . The horizontal part  144  of the gas flow path  104  in the joint  102  has a semicircular cross section. 
     Plug  120  and Spring  121   
     The plug  120  is a cylindrical member and located outside the main body  124  of the joint body  118 . The plug  120  is movable in the front-back direction  8  along the main body  124 . The spring  121  has a front end fixed to the rear end of the plug  120 , and a rear end in contact with a buffer tank  90  in the air communication portion  70  and the external cylinder  122  of the joint body  118 . The spring  121  urges the plug  120  forward. Under no external force applied, the plug  120  is located at the front end of the joint body  118  and closes the upper opening  125  and the lower opening  126 . Under a rearward external force greater than the elastic force of the spring  121  applied, the plug  120  moves rearward to open the upper opening  125  and the lower opening  126 . When the ink cartridge  50  is installed, the joint receiver  52  of the ink cartridge  50  comes into contact with the plug  120 . Under the external force applied during the installation of the ink cartridge  50 , the plug  120  in contact with the joint receiver  52  moves rearward. 
     Installed State of Ink Cartridge  50   
     In the installed state of the ink cartridge  50  installed in the subtank  100  as shown in  FIGS. 5 and 7 , the joint body  118  of the subtank  100  is inserted in the joint receiver  52  of the ink cartridge  50  in the front-back direction  8  and further in the communication port  61 . In this installed state, the second opening  132  of the liquid flow path  103  and the fourth opening  142  of the gas flow path  104  in the subtank  100  enter the first reservoir  53  of the ink cartridge  50 . As shown in  FIGS. 4 and 5 , the ink cartridge  50  can be removed from and installed in the subtank  100  in the front-back direction  8 . 
     Layout of Ink Cartridge  50  and Subtank  100   
     The layout of the ink cartridge  50  and the subtank  100  will now be described. In the layout described below, the ink cartridge  50  is installed in the installation case  71 , and the ink cartridge  50  and the subtank  100  are in the use posture shown in  FIG. 5 . 
     As shown in  FIG. 5 , the protrusion  65  of the ink cartridge  50  is located at substantially the same position as the joint  102  in the up-down direction  7 , whereas the part of the ink cartridge  50  above the protrusion  65  is located higher than the joint  102 . Thus, a most part of the first reservoir  53  of the ink cartridge  50  is located higher than the second opening  132 . The upper part of the subtank  100 , or the part at and above the curved upper wall  130 , is located at substantially the same position as the joint  102 , whereas the part of the subtank  100  below the curved upper wall  130  is located lower than the joint  102 . Thus, a most part of the second reservoir  105  of the subtank  100  is located lower than the third opening  141 . 
     The part of the first reservoir  53  above the protrusion  65  is located higher than the horizontal part  134  of the liquid flow path  103  and the horizontal part  144  of the gas flow path  104 . The second reservoir  105  is located lower than the horizontal part  134  of the liquid flow path  103  and the horizontal part  144  of the gas flow path  104 . The lower part of the first reservoir  53  and the upper part of the second reservoir  105  are arranged coaxially in the front-back direction  8 . The first reservoir  53  has a larger volume than the second reservoir  105 . 
     The horizontal part  144  of the gas flow path  104  is located higher than the horizontal part  134  of the liquid flow path  103 . 
     As shown in  FIG. 7 , the first opening  131  of the liquid flow path  103 , the third opening  141  of the gas flow path  104 , and the air communication port  106  are located rearward in the stated order from the communication port  61  of the first reservoir  53 . The position of the communication port  61  of the first reservoir  53  in the up-down direction  7  corresponds to the position in the up-down direction  7  at which the first reservoir  53  and the liquid flow path  103  communicate with each other. The rearward direction from the communication port  61  at this position in the up-down direction  7  is a direction away from the first reservoir  53 . 
     Air Communication Portion  70   
     As shown in  FIGS. 5, 11, 12A, and 12B , the air communication portion  70  includes a buffer tank  90 , communication flow paths  145 , and an air communication path  147 . 
     Buffer Tank  90   
     As shown in  FIGS. 5 and 11 , the buffer tank  90  is located under the installation case  71  and above the subtank  100 . 
     As shown in  FIGS. 5 and 11 , the buffer tank  90  includes an upper wall  91 , a lower wall  92 , two side walls  93 , three partition walls  94 , a rear wall  95 , and an upright wall  96 . The upper wall  91  extends along a plane inclined with respect to the horizontal plane. The lower wall  92  extends in parallel with the horizontal plane in the rear part and curves upward as it extends forward. The lower wall  92  has a front end connected to the front end of the upper wall  91 . The two side walls  93  connect the upper wall  91  and the lower wall  92  in the up-down direction  7  at both ends of the upper and lower walls in the left-right direction  9 . The three partition walls  94  are arranged in the left-right direction  9  in parallel with the two side walls  93 . The rear wall  95  connects the rear end of the upper wall  91  and the rear end of the lower wall  92 . The upright wall  96  extends upward from the rear end of the upper wall  91 . The rear wall  95  and the upright wall  96  have a gap between them in the front-back direction  8 . 
     The upper wall  91  of the buffer tank  90  is located below the lower wall  73  of the installation case  71 . The upper wall  91  of the buffer tank  90  supports the lower wall  73  of the installation case  71 . Thus, the upper wall  91  of the buffer tank  90  can support the ink cartridge  50  housed in the installation case  71  with the lower wall  73  of the installation case  71 . 
     Buffer Chamber  97   
     The internal space defined by the upper wall  91 , the lower wall  92 , the two side walls  93 , and the rear wall  95  is partitioned by the three partition walls  94  into four buffer chambers  97 . The four buffer chambers  97  are each connected to and communicate with the corresponding one of the four subtanks  100 . Each of the four buffer chambers  97  is a storage space for air delivered to the first reservoir  53  as the ink in the first reservoir  53  is fed to the second reservoir  105  by gas-liquid displacement. The four buffer chambers  97  are located above the recorder  24 . 
     As shown in  FIG. 5 , the first reservoir  53  is located above the buffer chamber  97 , and the buffer chamber  97  is located above the second reservoir  105 . The part of the first reservoir  53  formed in the protrusion  65  and a part of the buffer chamber  97  are arranged coaxially in the front-back direction  8  (an example of the horizontal direction). In addition, a part of the protrusion  65 , a part of the joint  102 , and a part of the buffer tank  90  are arranged coaxially in the front-back direction  8  (an example of the horizontal direction). Additionally, a part of the first reservoir  53  and a part of the buffer chamber  97  are arranged coaxially in the up-down direction  7 . 
     Communication Flow Path  145   
     As shown in  FIG. 12A , the lower wall  92  of the buffer tank  90  has openings  98  communicating with the buffer chambers  97 . The ink feeder  15  includes connection pipes  99  connecting the air communication ports  106  in the tank bodies  101  and the openings  98  in the buffer tank  90 . The connection pipes  99  are cylindrical. The inner surface of each connection pipe  99  defines a communication flow path  145  connecting the second reservoir  105  and the buffer chamber  97 . The communication flow path  145  extends in the up-down direction  7 . 
     Air Communication Path  147   
     As shown in  FIG. 12B , the upper wall  91  has an opening  146  at its rear end in each buffer chamber  97 . The upper wall  91  has four openings  146  behind the upright wall  96 . The bottom surface of the upper wall  91  is inclined upward in the front-back direction  8  (an example of the horizontal direction) away from the openings  98  (rearward). The openings  146  are formed in the upper wall  91  at the highest position of the bottom surface of the upper wall  91  in the up-down direction  7 . The front surface of the rear wall  95  and the rear surface of the upright wall  96  define an air communication path  147  extending in the up-down direction  7 . The air communication path  147  extends through the opening  146  upward from the buffer chamber  97 , and communicates with the outside of the housing  14  of the multifunction peripheral  10 . 
     Operation in Present Embodiment 
     The flow of ink and air at the initial loading of an ink cartridge  50  into an empty subtank  100  will now be described. 
     Before initially loaded (or in an unloaded state) as shown in  FIG. 6 , the ink cartridge  50  is separate from the subtank  100 . In the unloaded state, the communication port  61  of the ink cartridge  50  is closed by the plug  62 , and the first reservoir  53  is sealed in the ink cartridge  50 . Thus, ink filling the first reservoir  53  does not flow outside. In the unloaded state, the upper opening  125  and the lower opening  126  (see  FIG. 7 ) of the subtank  100  are closed by the plug  120 . Thus, the second opening  132  of the liquid flow path  103  and the fourth opening  142  of the gas flow path  104  communicating with the second reservoir  105  are closed to the outside. The second reservoir  105  includes, in addition to the liquid flow path  103  and the gas flow path  104 , the air communication port  106  (see  FIG. 7 ) and the communication port  129  (see  FIG. 7 ) for communicating with the outside. The air communication port  106  communicates with the air outside the multifunction peripheral  10  through the buffer chamber  97 . The communication port  129  communicates with the printhead  39  through the ink tube  32 . However, when the printhead  39  is idle, no ink flows out through the communication port  129 . In this state, the second reservoir  105  contains no ink and is empty. 
     As shown in  FIGS. 5 and 7 , when the ink cartridge  50  is installed in the subtank  100 , the plug  62  closing the communication port  61  moves forward against the urging force of the spring  63 , and the plug  120  closing the upper opening  125  and the lower opening  126  moves rearward against the urging force of the spring  121 . As a result, the first reservoir  53  communicates with the second reservoir  105  through the liquid flow path  103  and the gas flow path  104 . In this state, the ink in the first reservoir  53  of the ink cartridge  50  falls freely through the liquid flow path  103  and enters the second reservoir  105  of the subtank  100 . With the air communication port  106  open to the outside air, air with the same volume as the ink entering the second reservoir  105  flows into the first reservoir  53  through the air communication port  106  and the gas flow path  104 . In this manner, the ink in the first reservoir  53  is fed to the second reservoir  105  as the ink in the first reservoir  53  is replaced by air (gas-liquid displacement). 
     As the gas-liquid displacement proceeds, the liquid level of the ink in the second reservoir  105  increases. When the liquid level of the ink increases and reaches the lower end position of the vertical wall  115 , the third opening  141  of the gas flow path  104  is closed. In this state, the gas-liquid displacement no longer proceeds, thus stopping the ink feeding from the first reservoir  53  to the second reservoir  105 . The ink is fed in this manner at the initial loading. 
     The flow of ink and air during a recording operation performed by the printer unit  11  with the ink cartridge  50  in the installed state will now be described. 
     When the printhead  39  discharges ink during the recording operation, the ink in the second reservoir  105  is drawn to the printhead  39  through the communication port  129 . The liquid level of the ink in the second reservoir  105  lowers as the ink decreases, thus opening the closed third opening  141  of the gas flow path  104 . When the third opening  141  of the gas flow path  104  is open, the gas-liquid displacement is performed in the manner described above to feed ink from the first reservoir  53  to the second reservoir  105 . To supplement ink used in the printhead  39 , ink is fed from the first reservoir  53  to the second reservoir  105 . The liquid level of the ink in the second reservoir  105  remains at the position of the third opening  141  of the gas flow path  104 . 
     When the ink in the first reservoir  53  is used up, the empty ink cartridge  50  can be replaced with another ink cartridge  50  filled with ink to allow the multifunction peripheral  10  to continue the recording operation. 
     Controller  230   
     As shown in  FIG. 13 , the controller  230  includes a central processing unit (CPU)  231 , a read-only memory (ROM)  232 , a random-access memory (RAM)  233 , an electrically programmable read-only memory (EEPROM)  234 , and an application-specific integrated circuit (ASIC)  235 . The ROM  232  stores various programs to be executed by the CPU  231  to control various operations. The RAM  233  provides a storage area for temporarily storing data or signals used by the CPU  231  executing the programs or a work area used for processing data. The EEPROM  234  stores setting information to be retained after the power is shut off. The ROM  232 , the RAM  233 , and the EEPROM  234  are examples of a device memory. 
     The ASIC  235  is used to operate the feed roller  25 , the conveyance roller  34 , the discharge roller  36 , and the printhead  39 . The controller  230  rotates the feed roller  25 , the conveyance roller  34 , and the discharge roller  36  by driving a motor (not shown) through the ASIC  235 . The controller  230  further outputs a driving signal to a driving element of the printhead  39  through the ASIC  235  to cause the printhead  39  to discharge ink through the nozzles  40 . The ASIC  235  can output different driving signals depending on the amount of ink to be discharged through the nozzles  40 . 
     The display  17  and the operation panel  22  are connected to the ASIC  235 . 
     The contact  152 , the cover sensor  88 , the installation sensor  154 , and the liquid level sensor  155  are also electrically connected to the ASIC  235 . The controller  230  accesses the memory of the IC chip  66  of the ink cartridge  50  installed in the installation case  71  through the contact  152 . The controller  230  detects the position of the cover  48  with the cover sensor  88 . The controller  230  also detects the ink cartridge  50  installed in the installation case  71  based on a detection signal from the installation sensor  154 . The controller  230  further detects the liquid level of the ink stored in the second reservoir  105  equal to or higher than the predetermined level B with the liquid level sensor  155 . 
     When the liquid level sensor  155  outputs a high-level signal, the ROM  232  stores a predetermined ink amount Vsc (an example of a fixed value A) stored in the second reservoir  105  of the subtank  100  and a predetermined ink amount Vcc stored in the first reservoir  53  of the ink cartridge  50 . The predetermined ink amount Vcc is zero in the present embodiment. 
     The EEPROM  234  stores various items of information associated with the four ink cartridges  50  installed in the installation case  71 , in other words, associated with the subtanks  100  communicating with the ink cartridges  50 . The various items of information include, for example, ink amounts Vc and Vs, which are examples of the liquid amount, a volume V th , a flag C_Empty, a flag S_Empty, a count value SN, a count value TN, and a threshold value N th . 
     The ink amount Vc and the identification information are read by the controller  230  from the memory of the IC chip  66  through the contact  152  while the ink cartridge  50  is installed in the installation case  71 . The volume V th  may be stored in the ROM  232  instead of the EEPROM  234 . 
     The ink amount Vc indicates the amount of ink stored in the first reservoir  53  of the ink cartridge  50 . The ink amount Vs indicates the amount of ink stored in the second reservoir  105  of the subtank  100 . The ink amounts Vc and Vs are calculated based on, for example, the volume V th . When the first reservoir  53  of the ink cartridge  50  contains ink that can flow into the subtank  100 , the liquid level of the ink in the second reservoir  105  of the subtank  100  is at the position of the imaginary line L including the third opening  141  of the gas flow path  104 . This state is referred to as the equilibrium state. More specifically, in the equilibrium state, ink transfer stops between the first reservoir  53  and the second reservoir  105 . The ink amount Vs in the equilibrium state is the volume V th  of the second reservoir  105  lower than the imaginary line L. Thus, once the total amount Vt of ink is calculated, the ink amount Vs and the ink amount Vc can be calculated. More specifically, when the total amount Vt is equal to or greater than the volume V th , the ink amount Vs is the volume Vth, and the ink amount Vc is obtained by subtracting the volume V th  from the total amount Vt. When the total amount Vt is smaller than the volume Vth, the ink amount Vs is equal to the total amount Vt, and the ink amount Vc is zero. The ink amounts Vc and Vs may be determined by referring to a table storing the correspondence between the ink amounts and the total amount Vt without using the volume Vth. 
     The count value SN is equivalent to an ink discharge amount Dh (an ink amount indicated by a driving signal) instructed to discharge through the printhead  39  after the signal output from the liquid level sensor  155  changes from a low level to a high level and is updated toward the threshold value N th . The count value SN is counted up from an initial value of 0. The threshold value N th  is equivalent to the volume of a part of the second reservoir  105  between the position near the upper end of the communication port  129  and the predetermined level B. However, the count value SN may be counted down from an initial value equivalent to the volume. In this case, the threshold value N th  is zero (0). The count value SN is an example of a second count value. 
     The count value TN is equivalent to an ink discharge amount Dh (an ink amount indicated by a driving signal) instructed to discharge through the printhead  39  after the signal output from the cover sensor  88  changes from a high level to a low level, and is counted up from an initial value of 0. The count value TN may be counted down from an initial value equivalent to the total amount Vt of ink. The count value TN is an example of a first count value as well. 
     The flag C_Empty is information indicating whether the ink cartridge  50  is in a cartridge empty state. The flag C_Empty is set either ON corresponding to the cartridge empty state or OFF corresponding to a non-cartridge empty state. The cartridge empty state refers to the state of the ink cartridge  50  (more specifically, the first reservoir  53 ) storing substantially no ink. In other words, the cartridge empty state refers to the state of no ink transferred from the first reservoir  53  to the second reservoir  105  communicating with each other. More specifically, the cartridge empty state refers to the state in which the liquid level of the subtank  100  communicating with the ink cartridge  50  is lower than the predetermined level B. 
     The flag S_Empty is information indicating whether the subtank  100  is in the empty ink state. The flag S_Empty is set either ON corresponding to the empty ink state or OFF corresponding to a non-empty ink state. The empty ink state refers to, for example, the state of the liquid level of the ink stored in the subtank  100  (more specifically, the second reservoir  105 ) reaching the position near the upper end of the communication port  129 . In other words, the empty ink state refers to the state of the count value SN 1  equal to or greater than the threshold value Nthl. When the ink continues to be discharged through the printhead  39  in the empty ink state, the liquid level of the ink in the subtank  100  may fall below the upper end of the communication port  129 , and air may mix in an ink flow path from the subtank  100  to the printhead  39  or in the printhead  39  (air entrapment). The nozzles  40  may not be filled with the ink, and the ink may not be discharged. 
     Operation of Multifunction Peripheral  10   
     The operation of the multifunction peripheral  10  according to the present embodiment will be described with reference to  FIGS. 14 and 15 . Each of the processes shown in  FIGS. 14 and 15  is performed by the CPU  231  of the controller  230 . Each of the processes described below may be performed by the CPU  231  reading programs stored in the ROM  232 , or may be implemented by a hardware circuit installed in the controller  230 . Further, the processes described below can be performed in an order changed appropriately without departing from the spirit and scope of the present disclosure. 
     Image Recording Process 
     The controller  230  performs an image recording process shown in  FIG. 14  in response to a recording instruction input to the multifunction peripheral  10 . The recording instruction is an example of first and second discharge instructions for causing the multifunction peripheral  10  to record an image represented by image data on a sheet. The recording instruction may be received in any manner, but may be received as a corresponding user operation performed through the operation panel  22  or may be received from an external device through a communication interface (not shown). 
     First, the controller  230  determines the set values for the four flags S_Empty (S 11 ). When determining that at least one of the four flags S_Empty is set ON (S 11 : ON), the controller  230  displays a notification screen S_Empty on the display  17  (S 12 ). The notification screen S_Empty notifies the user that the corresponding subtank  100  is in the empty ink state and the ink cannot be discharged through the printhead  39 . For example, the notification screen S_Empty may include information indicating the color and the ink amounts Vc and Vs of the ink stored in the subtank  100  in the empty ink state. In step S 12 , the controller  230  may display the notification screen C_Empty on the display  17  together with the notification screen S_Empty when determining that at least one of the four flags C_Empty is set ON. 
     The controller  230  also performs the processing in steps S 13  to S 19  for each ink cartridge  50  corresponding to the flag S_Empty set ON. More specifically, the processing in steps S 13  to S 19  is performed for each ink cartridge  50  for which the flag S_Empty is set ON, among the four ink cartridges  50 . The processing in steps S 13  to S 19  is common to the ink cartridges  50 . The processing in steps S 13  to S 19  for one ink cartridge  50  will be described. 
     The controller  230  first obtains a signal output from the installation sensor  154  (S 13 ). The controller  230  then determines whether the signal obtained from the installation sensor  154  is a high-level signal or a low-level signal (S 14 ). Then, the controller  230  repeatedly performs the processing in steps S 13  and S 14  at predetermined time intervals until the signal output from the installation sensor  154  changes from a low level to a high level and then from a high level to a low level again (S 14 : No). In other words, the controller  230  repeatedly performs the processing in steps S 13  and S 14  until the ink cartridge  50  is removed from the installation case  71  and an ink cartridge  50  is newly installed in the installation case  71 . 
     In response to a low-level signal, a high-level signal, and then a low-level signal obtained in the stated order from the installation sensor  154  (S 14 : Yes), the controller  230  performs the processing in step S 15 . More specifically, the controller  230  reads identification information and an ink amount Vc from the IC chip  66  of the ink cartridge  50  through the contact  152 , and stores the identification information and the ink amount Vc into the EEPROM  234  (S 15 ). At this time, the controller  230  updates the ink amount Vc stored in the EEPROM  234  to the ink amount Vc read from the IC chip  66 . 
     The controller  230  also calculates the total amount Vt after the cartridge replacement (S 16 ). In detail, the controller  230  calculates the ink amount Vs before the cartridge replacement based on the count value SN before the cartridge replacement stored in the EEPROM  234  and the ink amount Vsc stored in the ROM  232  (Vs=Vsc−SN), and stores the ink amount Vs into the EEPROM  234 . The ink amount Vs before the cartridge replacement is equal to the total amount Vt before the cartridge replacement. Based on the calculated ink amount Vs and the ink amount Vc read from the memory of the IC chip  66  of the replaced ink cartridge  50 , the total amount Vt after the cartridge replacement is calculated. More specifically, once the ink cartridge  50  is replaced, the ink amount Vc stored in the first reservoir  53  of the newly installed ink cartridge  50  is added to the ink amount Vs (=Vsc−SN) stored in the second reservoir  105  of the subtank  100  immediately before the ink cartridge  50  is replaced. The controller  230  thus calculates the sum of the ink amount Vc read from the IC chip  66  of the replaced ink cartridge  50  and the ink amount Vs before the cartridge replacement stored in the EEPROM  234  as the total amount Vt (Vt=Vs+Vc). 
     The controller  230  calculates the ink amount Vc and the ink amount Vs when the liquid level of the ink in the second reservoir  105  reaches the imaginary line L based on the calculated total amount Vt and the volume V th  read from the EEPROM  234  (S 16 ). When the ink cartridge is replaced, the ink stored in the first reservoir  53  of the newly installed ink cartridge  50  flows into the second reservoir  105  of the subtank  100  through the liquid flow path  103 . As a result, the ink amount Vc of the first reservoir  53  decreases, and the ink amount Vs of the second reservoir  105  increases. The liquid level of the ink in the second reservoir  105  of the subtank  100  then reaches the imaginary line L, and the equilibrium state is entered. 
     The controller  230  determines whether the calculated total amount Vt is equal to or greater than the volume V th . For example, when a fresh ink cartridge  50  is installed in the installation case  71 , the total amount Vt is equal to or greater than the volume V th . For the total amount Vt equal to or greater than the volume V th , the controller  230  determines the volume V th  to be the ink amount Vs. Then, the controller  230  stores the calculated ink amount Vc into the EEPROM  234  (S 17 ). At this time, the controller  230  updates the ink amount Vs stored in the EEPROM  234  to the determined ink amount Vs. The controller  230  also stores the calculated ink amount Vc into the memory of the IC chip  66  through the contact  152  (S 17 ). At this time, the controller  230  updates the ink amount Vc stored in the memory of the IC chip  66  to the calculated ink amount Vc. 
     The controller  230  then determines whether the signal received from the liquid level sensor  155  has changed from a high level to a low level (S 18 ). When an ink cartridge  50  is newly installed in the installation case  71 , ink flows from the first reservoir  53  of the ink cartridge  50  into the second reservoir  105  of the subtank  100 . When the liquid level of the ink in the second reservoir  105  reaches the predetermined level B, the signal output from the liquid level sensor  155  changes from a high-level signal to a low-level signal. When the signal received from the liquid level sensor  155  remains at a high level (S 18 : No), the controller  230  repeats the determination in step S 18  until receiving a low-level signal. More specifically, the controller  230  waits until the liquid level of the ink in the second reservoir  105  is raised to the predetermined level B. 
     When determining that the signal received from the liquid level sensor  155  has changed from a high level to a low level (S 18 : Yes), the controller  230  sets each of the flag S_Empty and the flag C_Empty OFF. The controller  230  also deletes either the notification screen S_Empty or the notification screen C_Empty appearing on the display  17  (S 19 ). Further, the controller  230  displays the calculated ink amounts Vc and Vs on the display  17 . The controller  230  may display the calculated total amount Vt on the display  17 . The total amount Vt and the ink amounts Vc and Vs may be numerically indicated, or may be indicated using an image, such as an index bar. Not both the ink amount Vc and the ink amount Vs may be indicated, and at least one of the ink amounts, or for example, the ink amount Vc alone, may be indicated. The controller  230  then performs the processing in step S 11  and subsequent steps again. 
     When the flags S_Empty corresponding to all the ink cartridges  50  are all not ON, or in other words, are all OFF, the controller  230  obtains signals output from the four liquid level sensors  155  at the current time (S 20 ). In step S 20 , the controller  230  further causes the RAM  233  to store information indicating whether the signal obtained from each liquid level sensor  155  is a high-level signal or a low-level signal. 
     The controller  230  then records the image represented by the image data included in the recording instruction on one sheet (S 21 ). More specifically, the controller  230  causes the sheet on the feed tray  20  to be conveyed by the feed roller  25  and the conveyance roller  34 , the printhead  39  to discharge the ink, and the sheet having the recorded image to be discharged to the discharge tray  21  with the discharge roller  36 . More specifically, the controller  230  enables the ink discharge through the printhead  39  when all the four flags S_Empty are set OFF. In contrast, the controller  230  disables the ink discharge through the printhead  39  when at least one of the four flags S_Empty is set ON. 
     The controller  230  then obtains signals output from the four liquid level sensors  155  at the current time upon recording the image on one sheet in response to the recording instruction (S 22 ). Similarly to step S 20 , the controller  230  causes the RAM  233  to store information indicating whether the signal obtained from each liquid level sensor  155  is a high-level signal or a low-level signal (S 22 ). The controller  230  then performs a counting process (S 23 ). The counting process is to update the count values TN, SN, the flag C_Empty, and the flag S_Empty based on the signals obtained from each liquid level sensor  155  in steps S 20  and S 22 . The counting process will be described in detail below with reference to  FIG. 8 . 
     The controller  230  then repeatedly performs the processing in steps S 11  to S 24  until all the images indicated by the recording instruction are recorded on one sheet (S 24 : Yes). After recording all the images indicated by the recording instruction on one sheet (S 24 : No), the controller  230  determines the set values for the four flags S_Empty and the set values for the four flags C_Empty (S 25  and S 26 ). 
     When at least one of the four flags S_Empty is set ON (S 25 : ON), the controller  230  displays the notification screen S_Empty on the display  17  (S 27 ). When all the four flags S_Empty are set OFF and at least one of the four flags C_Empty is set ON (S 25 : OFF and S 26 : ON), the controller  230  displays the notification screen C_Empty on the display  17  (S 28 ). The processing in steps S 25  and S 26  is an example of activating the alarm. 
     The notification screen S_Empty displayed in step S 27  may be the same as in step S 12 . The notification screen C_Empty notifies the user that the ink cartridge  50  corresponding to the flag C_Empty set ON is in the cartridge empty state. For example, the notification screen C_Empty may include information indicating the color and the ink amounts Vc and Vs of the ink stored in the ink cartridge  50  in the cartridge empty state. In contrast, when all the four flags S_Empty and the four flags C_Empty are set OFF (S 26 : OFF), the controller  230  completes the image recording process. 
     An example of the discharge instruction is not limited to the recording instruction, but may be a maintenance instruction instructing maintenance of the nozzles  40  such as a purge. For example, the controller  230  performs the same process as in  FIG. 14  in response to a maintenance instruction obtained through the operation panel  22 . The process in response to a maintenance instruction differs from the above process in the manner described below. First, the controller  230  drives a maintenance mechanism (not shown) in step S 21 , and discharges the ink through the nozzles  40 . The controller  230  also performs the processing in steps subsequent to step S 24  without performing the processing in step S 24  after the counting process. 
     Counting Process 
     The counting process performed by the controller  230  in step S 23  will be described in detail with reference to  FIG. 15 . The controller  230  performs the counting process independently for each of the four ink cartridges  50 . The counting process is common to the ink cartridges  50 . The counting process for one ink cartridge  50  will be described. 
     First, the controller  230  compares sets of information indicating the signals from the liquid level sensors  155  stored in the RAM  233  in steps S 20  and S 22  (S 31 ). More specifically, the controller  230  determines whether the signal from each of the four liquid level sensors  155  has changed before and after the processing in step S 21  immediately before the counting process (S 23 ). 
     When the sets of information stored in the RAM  233  in steps S 20  and S 22  both indicate a low-level signal (S 31 : L→L) (in other words, the output of each liquid level sensor  155  remains unchanged before and after the processing in step S 21 ), the controller  230  updates the count value TN (S 32 ). More specifically, the controller  230  counts up the count value TN to a value equivalent to the amount of ink instructed to discharge in the immediately preceding step S 21 . 
     The controller  230  also calculates the current total amount Vt (S 33 ). First, the controller  230  calculates the total amount Vt after the cartridge replacement that is the sum of the ink amount Vc and the ink amount Vs stored in the EEPROM  234  after the cartridge replacement. The controller  230  then calculates the current total amount Vt by subtracting the ink amount equivalent to the count value TN from the calculated total amount Vt (Vt=Vt−TN). The controller  230  then obtains the ink amounts Vc and Vs based on the calculated current total amount Vt and the volume V th  (S 33 ). 
     The controller  230  determines whether the calculated current total amount Vt is equal to or greater than the volume V th . For the current total amount Vt equal to or greater than the volume V th , the controller  230  determines the volume V th  to be the ink amount Vs. For the current total amount Vt smaller than the volume V th , the controller  230  determines the current total amount Vt to be the ink amount Vs. 
     Subsequently, the controller  230  displays the calculated ink amounts Vc and Vs and/or the calculated total amount Vt on the display  17  (S 34 ). The controller  230  also updates the ink amount Vc stored in the memory of the IC chip  66  of the ink cartridge  50  to the calculated ink amount Vc (S 35 ). 
     When the information stored in the RAM  233  in step S 20  indicates a low-level signal and the information stored in the RAM  233  in step S 22  indicates a high-level signal (S 31 : L→H) (in other words, the output of the liquid level sensor  155  is changed before and after the processing in step S 21 ), the controller  230  substitutes a value indicating ON into the flag C_Empty (S 36 ). The output from the liquid level sensors  155  changing from a low-level signal to a high-level signal corresponds to the liquid level of the second reservoir  105  reaching the predetermined level B during the processing in step S 21  as shown in  FIG. 16 . Subsequently, no ink transfer occurs between the ink cartridge  50  and the subtank  100 . 
     The controller  230  also reads a predetermined ink amount Vcc (=0) from the ROM  232 , and sets the ink amount Vc to the predetermined ink amount Vcc (S 37 ). Similarly, the controller  230  reads a predetermined ink amount Vsc (equivalent to the volume of a part of the second reservoir  105  lower than the predetermined level B) from the ROM  232 , and sets the ink amount Vs to the predetermined ink amount Vsc (S 37 ). The ink amounts Vc and Vs calculated in the residual amount updating process include errors. The controller  230  thus sets the ink amount Vc to the predetermined ink amount Vcc and the ink amount Vs to the predetermined ink amount Vsc at the time when the output from the liquid level sensor  155  changes from a low-level signal to a high-level signal, thus resetting the accumulated errors. Further, the controller  230  calculates the current total amount Vt as a value equal to the ink amount Vs (Vt=Vsc) (S 37 ). When the ink amount Vc is zero, the total amount Vt has the same value as the ink amount Vs. 
     The controller  230  then displays the current ink amounts Vc and Vs and/or the current total amount Vt on the display  17 . The controller  230  also overwrites the ink amount Vc stored in the memory of the IC chip  66  of the ink cartridge  50  with the above ink amount Vc (=0) (S 39 ). Information indicating the ink amount Vc= 0  stored in the memory of the IC chip  66  is an example of ink runout information. 
     The output of each liquid level sensor  155  changes during the processing in step S 21 . The predetermined ink amount Vsc read in step S 37  is thus not strictly the amount of ink stored in the subtank  100  at the moment when the output from the liquid level sensor  155  changes, but indicates the amount of ink immediately before the output from the liquid level sensor  155  changes. With the difference between the ink amounts being small, the predetermined ink amount Vsc read in step S 37  is approximately the ink amount Vs at the time when the output from the liquid level sensor  155  changes. 
     The controller  230  also counts up the count value SN stored in EEPROM  234  to the value equivalent to the amount of ink instructed to discharge in the immediately preceding step S 21  (S 40 ). In other words, the controller  230  starts updating the count value SN in response to the output from the liquid level sensors  155  changing from a low-level signal to a high-level signal. The controller  230  counts up the count value TN stored in the EEPROM  234  to a value equivalent to the amount of ink instructed to discharge in the immediately preceding step S 21 . 
     The controller  230  then calculates the ink amount Vs (S 41 ). The calculated ink amount Vs is obtained by subtracting the ink amount equivalent to the count value SN stored in the EEPROM  234  from the predetermined ink amount Vsc stored in the ROM  232 . As described above, after the output from the liquid level sensor  155  changes to a high-level signal, the ink amount Vs is the same value as the current total amount Vt. The ink amount Vc is zero. 
     The controller  230  then displays the calculated current ink amounts Vc and Vs and/or the calculated current total amount Vt on the display  17  (S 42 ). The ink amount Vc is zero after the output from the liquid level sensor  155  changes to a high-level signal, and thus the controller  230  does not update the ink amount Vc stored in the memory of the IC chip  66  of the ink cartridge  50 . 
     The controller  230  then compares the count value SN updated in step S 40  with the threshold value N th  (S 43 ). When determining that the count value SN updated in step S 40  is smaller than the threshold value N th  (S 43 : No), the controller  230  completes the counting process. In contrast, when determining that the count value SN updated in step S 40  is equal to or greater than the threshold value Nth (S 43 : Yes), the controller  230  substitutes the value indicating ON into the flag S_Empty (S 44 ). The controller  230  disables the ink discharge through the printhead  39  in response to the flag S_Empty set ON, and completes the counting process. 
     When the sets of information stored in the RAM  233  in steps S 20  and S 22  both indicate a high-level signal (S 31 : H→H), the controller  230  reads the count value SN stored in the EEPROM  234 . The controller  230  then counts up the read count value SN to a value equivalent to the amount of ink instructed to discharge in the immediately preceding step S 21  and stores the value into the EEPROM  234  again. More specifically, the controller  230  updates the count value SN (S 40 ). The controller  230  also updates the count value TN. The controller  230  then performs the processing from steps S 41  to S 44  described above using the count value SN updated in step S 40 . 
     Operational Effects of First Embodiment 
     The structure according to the first embodiment can obtain the ink amounts Vc and Vs from the current total amount Vt using the volume V th . Further, the total amount Vt is updated to the predetermined ink amount Vsc in response to a high-level signal output from the liquid level sensor  155 , and the total amount Vt can be corrected. The ink amounts Vc and Vs can then be determined from the corrected total amount Vt. The time at which ink is no longer fed from the first reservoir  53  of the ink cartridge  50  to the second reservoir  105  of the subtank  100  as well as the subsequent ink amount Vs can also be determined. The value updated to the predetermined ink amount Vsc may not be the total amount Vt but may be the ink amount Vs. When the liquid level sensor  155  outputs a high-level signal, ink is not transferred from the first reservoir  53  to the second reservoir  105 , and the total amount Vt is equal to the ink amount Vs. 
     The controller  230  displays, on the display  17 , the notification screen C_Empty with a message urging replacement of the ink cartridge to notify the user that the ink cartridge  50  is to be replaced. 
     With the ink amount Vc stored in the memory of the IC chip  66 , the ink amount Vc of the first reservoir  53  in the ink cartridge  50  can be read from the IC chip  66  after the ink in the ink cartridge  50  has been used and the ink cartridge  50  is removed from the installation case  71 . When the ink cartridge  50  in which the ink has run out is installed in the installation case  71 , the ink amount Vc is read from the IC chip  66 , and the total amount Vt is calculated. 
     With the memory of the IC chip  66  storing ink amount Vc=0, the ink cartridge  50  can be determined to contain no ink. 
     Second Embodiment 
     A second embodiment will now be described. The structure of a multifunction peripheral  10  according to the second embodiment is the same as in the first embodiment except that the multifunction peripheral  10  includes a temperature sensor  89  and the controller  230  receives a signal output from the temperature sensor  89  as shown in  FIG. 17 , and will not be described in detail. The operation of the multifunction peripheral  10  according to the second embodiment will now be described. 
     Image Recording Process 
     The controller  230  performs an image recording process shown in  FIGS. 18A and 18B  in response to a recording instruction input to the multifunction peripheral  10 . The recording instruction is an example of a discharge instruction for causing the multifunction peripheral  10  to record an image represented by image data on a sheet. The recording instruction may be received in any manner, but may be received as a corresponding user operation performed through the operation panel  22  or may be received from an external device through a communication interface (not shown). 
     First, the controller  230  determines the set values of the flags S_Empty for the four ink cartridges  50  (S 51 ). When determining that at least one of the flags S_Empty for the four ink cartridges  50  is set ON (S 51 : ON), the controller  230  displays a notification screen S_Empty on the display  17  (S 52 ). The notification screen S_Empty notifies the user that the corresponding subtank  100  is in the empty ink state and the ink cannot be discharged through the printhead  39 . For example, the notification screen S_Empty may include information indicating the color and the ink amounts Vc and Vs of the ink stored in the subtank  100  in the empty ink state. In step S 52 , the controller  230  may display the notification screen C_Empty on the display  17  together with the notification screen S_Empty when determining that at least one of the flags C_Empty for the four ink cartridges  50  is set ON. The notification screen S_Empty appearing on the display  17  in step S 52  is an example of activating a first notification of the alarm. 
       FIG. 20A  is a diagram displaying an example notification screen S_Empty. The example notification screen S_Empty includes objects  251 ,  252 , and  253 . The object  251  is a message urging replacement of the ink cartridge  50  and carries a text message: Replace the ink cartridge. The object  252  indicates the type of the ink cartridge  50  to be replaced. In the illustrated example, the object  252  includes letter M representing magenta. The object  253  represents an empty ink cartridge  50 . 
     The controller  230  also performs the processing in steps S 53  to S 62  for each ink cartridge  50  corresponding to the flag S_Empty set ON. More specifically, the processing in steps S 53  to S 62  is performed for each ink cartridge  50  for which the flag S_Empty is set ON, among the four ink cartridges  50 . The processing in steps S 53  to S 62  is common to the ink cartridges  50 . The processing in steps S 53  to S 62  for one ink cartridge  50  will be described. 
     The controller  230  first receives a signal output from the installation sensor  154  (S 53 ). The controller  230  then determines whether the signal received from the installation sensor  154  has changed from a high-level signal to a low-level signal (S 54 ). Then, the controller  230  repeatedly performs the processing in steps S 53  and S 54  at predetermined time intervals until the signal output from the installation sensor  154  changes from a low level to a high level and then from a high level to a low level again (S 54 : No). In other words, the controller  230  repeatedly performs the processing in steps S 53  and S 54  until the ink cartridge  50  is removed from the installation case  71  and an ink cartridge  50  is newly installed in the installation case  71 . 
     In response to a low-level signal, a high-level signal, and then a low-level signal received in the stated order from the installation sensor  154  (S 54 : Yes), the controller  230  reads the identification information, type information, and the ink amount Vc from the IC chip  66  of the ink cartridge  50  through the contact  152 , and stores the items of information into the EEPROM  234  (S 55 ). At this time, the controller  230  updates the ink amount Vc stored in the EEPROM  234  to the ink amount Vc read from the IC chip  66 . 
     The controller  230  then deletes the notification screen S_Empty from the display  17  and displays an ink in-flow screen on the display  17  (S 56 ). The ink in-flow screen notifies the user that ink is flowing from the ink cartridge  50  into the subtank  100 . The ink in-flow screen appearing on the display  17  is an example of activating a third notification of the alarm. 
       FIG. 20B  is a diagram showing an example ink in-flow screen. In the illustrate example, the ink in-flow screen includes objects  254  and  255 . The object  254  indicates that ink is flowing from the ink cartridge  50  into the subtank  100  and carries a text message: Ink in cartridge ( 1 ) is being transferred to body ( 2 ). The object  255  represents the ink cartridge  50  and the subtank  100  in the multifunction peripheral  10  in a schematic view. 
     The controller  230  then determines that the signal received from the liquid level sensor  155  has changed from a high-level signal to a low-level signal (S 57 ). When an ink cartridge  50  is newly installed in the installation case  71 , ink flows from the first reservoir  53  of the ink cartridge  50  into the second reservoir  105  of the subtank  100 . When the liquid level of the ink in the second reservoir  105  reaches the predetermined level B, the signal output from the liquid level sensor  155  changes from a high-level signal to a low-level signal. When the signal received from the liquid level sensor  155  remains at a high level (S 57 : No), the controller  230  performs a determination process for an elapsed time T (S 58 ). 
     The controller  230  selects and reads a predetermined time ST from the ROM  232  based on the type information read from the IC chip  66  of the ink cartridge  50  in step S 55 , and stores the predetermined time ST into the RAM  233 . The controller  230  then receives a signal from the temperature sensor  89  to correct the predetermined time ST stored in the RAM  233  based on the temperature t indicated by the received signal and temperature correction information stored in the ROM  232 . More specifically, the controller  230  calculates a correction amount Δ based on the temperature correction information (Δ=p×t+q, where p and q are constants), adds the correction amount A to the predetermined time ST to calculate a corrected predetermined time ST, and stores the corrected predetermined time ST into the RAM  233 . 
     The controller  230  then determines the current elapsed time T after receiving a low-level signal, a high-level signal, and then a low-level signal in the stated order from the installation sensor  154  (S 54 : Yes). For example, the controller  230  stores, into the RAM  233 , the time at which a low-level signal is received after a high-level signal is received from the installation sensor  154 , and determines the elapsed time T based on the stored time and the current time. The elapsed time T may be determined based on the time indicated by a timer activated upon receiving a low-level signal after receiving a high-level signal from the installation sensor  154 . 
     The controller  230  determines whether the determined elapsed time T exceeds the predetermined time ST (S 58 ). When the controller  230  determines that the elapsed time T does not exceed the predetermined time ST (S 58 : No), the controller  230  repeats the determination in steps S 57  and S 58  until a low-level signal is received or the elapsed time T exceeds the predetermined time ST. More specifically, the controller  230  waits until the liquid level of the ink in the second reservoir  105  increases to the predetermined level B or the predetermined time ST elapses after the ink cartridge  50  is installed. 
     When determining that the elapsed time T exceeds the predetermined time ST (S 58 : Yes), the controller  230  deletes the ink in-flow screen from the display  17 , and displays a notification screen S_Empty on the display  17  (S 59 ). The notification screen S_Empty displayed in step S 59  may be the same as or different from the screen displayed in step S 52 . The controller  230  then performs the processing in step S 51  and subsequent steps again. The notification screen S_Empty appearing on the display  17  in step S 59  is an example of activating a fourth notification of the alarm. 
     When determining that the signal received from the liquid level sensor  155  has changed from a high-level signal to a low-level signal (S 57 : Yes), the controller  230  calculates the total amount Vt after the cartridge replacement (S 60 ). In detail, the controller  230  calculates the ink amount Vs before the cartridge replacement based on the count value SN before the cartridge replacement stored in the EEPROM  234  and the ink amount Vsc stored in the ROM  232  (Vs=Vsc−SN), and stores the ink amount Vs into the EEPROM  234 . The ink amount Vs before the cartridge replacement is equal to the total amount Vt before the cartridge replacement. Based on the calculated ink amount Vs and the ink amount Vc read from the memory of the IC chip  66  of the replaced ink cartridge  50 , the total amount Vt after the cartridge replacement is calculated (Vt=Vs+Vc). Once the ink cartridge  50  is replaced, a portion of the ink amount Vc stored in the first reservoir  53  of the newly-installed ink cartridge  50  is added to the ink amount Vs (=Vsc−SN) stored in the second reservoir  105  of the subtank  100  immediately before the ink cartridge  50  is replaced. 
     The controller  230  calculates the ink amount Vc and the ink amount Vs obtained when ink transfer from the first reservoir  53  to the second reservoir  105  is complete based on the calculated total amount Vt and the volume V th  read from the EEPROM  234  (S 60 ). When the ink cartridge  50  is replaced, the ink stored in the first reservoir  53  of the newly installed ink cartridge  50  flows into the second reservoir  105  of the subtank  100  through the liquid flow path  103 . As a result, the ink amount Vc of the first reservoir  53  decreases, and the ink amount Vs of the second reservoir  105  increases. The liquid level of the ink in the second reservoir  105  of the subtank  100  then reaches the imaginary line L, and the equilibrium state is entered. 
     The controller  230  determines whether the calculated total amount Vt is equal to or greater than the volume V th . For example, when a fresh ink cartridge  50  is installed in the installation case  71 , the total amount Vt is equal to or greater than the volume V th . For the total amount Vt equal to or greater than the volume V th , the controller  230  determines the volume V th  to be the ink amount Vs. The controller  230  then stores the calculated ink amount Vc into the EEPROM  234  (S 61 ). At this time, the controller  230  updates the ink amount Vs stored in the EEPROM  234  to the calculated ink amount Vs. The controller  230  also stores the calculated ink amount Vc into the memory of the IC chip  66  through the contact  152  (S 61 ). At this time, the controller  230  updates the ink amount Vc stored in the memory of the IC chip  66  to the calculated ink amount Vc. 
     The controller  230  then sets each of the flag S Empty and the flag C_Empty OFF. The controller  230  also deletes the notification screen S_Empty and the notification screen C_Empty appearing on the display  17  (S 62 ). Further, the controller  230  displays the calculated ink amounts Vc and Vs on the display  17 . The controller  230  may display the calculated total amount Vt on the display  17 . The total amount Vt and the ink amounts Vc and Vs may be numerically indicated, or may be indicated using an image, such as an index bar. Not both the ink amount Vc and the ink amount Vs may be indicated, and at least one of the ink amounts, or for example, the ink amount Vc alone, may be indicated. The controller  230  then performs the processing in step S 51  and subsequent steps again. 
     When the flags S_Empty corresponding to all the ink cartridges  50  are all not ON, or in other words, are all OFF (S 51 : OFF), the controller  230  receives signals output from the four liquid level sensors  155  at the current time (S 63 ). In step S 63 , the controller  230  further causes the RAM  233  to store information indicating whether the signal received from each liquid level sensor  155  is a high-level signal or a low-level signal. 
     The controller  230  then records the image represented by the image data included in the recording instruction on one sheet (S 64 ). More specifically, the controller  230  causes the sheet on the feed tray  20  to be conveyed by the feed roller  25  and the conveyance roller  34 , the printhead  39  to discharge the ink, and the sheet having the recorded image to be discharged to the discharge tray  21  with the discharge roller  36 . More specifically, the controller  230  performs the processing in step S 64  when all the four flags S_Empty are set OFF (S 51 : OFF). More specifically, the controller  230  enables the ink discharge through the printhead  39 . In contrast, the controller  230  does not perform the processing in step S 64  when at least one of the four flags S_Empty is set ON (S 51 : ON). More specifically, the controller  230  disables the ink discharge through the printhead  39  for all the four subtanks  100 . 
     The controller  230  then receives signals output from the four liquid level sensors  155  at the current time upon recording the image on one sheet in response to the recording instruction (S 65 ). Similarly to step S 63 , the controller  230  causes the RAM  233  to store information indicating whether the signal received from the liquid level sensor  155  is a high-level signal or a low-level signal (S 65 ). The controller  230  then performs a counting process (S 66 ). The counting process is to update the count values TN, SN, the flag C_Empty, and the flag S_Empty based on the signals received from each liquid level sensor  155  in steps S 63  and S 65 . The counting process will be described in detail below with reference to  FIG. 19 . 
     The controller  230  then repeatedly performs the processing in steps S 51  to S 67  until all the images indicated by the recording instruction are recorded on one sheet until no next sheet is provided (S 67 : Yes). When all the images indicated by the recording instruction are recorded on one sheet and no next sheet is provided (S 67 : No), the controller  230  determines the set values for the four flags S_Empty and the set values for the four flags C_Empty (S 68  and S 69 ). 
     When at least one of the four flags S_Empty is set ON (S 68 : ON), the controller  230  displays the notification screen S_Empty on the display  17  (S 70 ). When all the four flags S_Empty are set OFF and at least one of the four flags C_Empty is set ON (S 68 : OFF and S 69 : ON), the controller  230  displays the notification screen C_Empty on the display  17  (S 71 ). The processing in steps S 68  and S 69  is an example of activating a first notification of the alarm. 
     The notification screen S_Empty displayed in step S 70  may be the same as in step S 52 . The notification screen C_Empty notifies the user that the ink cartridge  50  corresponding to the flag C_Empty set ON is in the cartridge empty state. For example, the notification screen C_Empty may include information indicating the color and the ink amounts Vc and Vs of the ink stored in the ink cartridge  50  in the cartridge empty state. 
       FIG. 20C  is a diagram showing an example notification screen C_Empty. In the illustrated example, the notification screen C_Empty includes objects  251 ,  252 , and  253 , in the same manner as the notification screen S_Empty in  FIG. 20A , and further includes an object  256 . The object  256  carries a text message: You can continue printing with ink remaining in the body. This notifies the user that printing can be continued. 
     In contrast, when all the four flags S_Empty and the four flags C_Empty are set OFF (S 69 : OFF), the controller  230  completes the image recording process. 
     An example of the discharge instruction is not limited to the recording instruction, but may be a maintenance instruction instructing maintenance of the nozzles  40  such as a purge. For example, the controller  230  performs the same process as in  FIGS. 18A and 18B  in response to a maintenance instruction received through the operation panel  22 . The process in response to a maintenance instruction differs from the above process in the manner described below. First, the controller  230  drives a maintenance mechanism (not shown) in step S 64 , and discharges the ink through the nozzles  40 . The controller  230  also performs the processing in steps subsequent to step S 67  without performing the processing in step S 67  after the counting process. 
     Counting Process 
     The counting process performed by the controller  230  in step S 66  will be described in detail with reference to  FIG. 19 . The controller  230  performs the counting process independently for each of the four ink cartridges  50 . The counting process is common to the ink cartridges  50 . The counting process for one ink cartridge  50  will be described. 
     First, the controller  230  compares sets of information indicating the signals from the liquid level sensors  155  stored in the RAM  233  in steps S 63  and S 65  (S 81 ). More specifically, the controller  230  determines whether the signal output from each of the four liquid level sensors  155  has changed before and after the processing in step S 64  immediately before the counting process (S 66 ). 
     When the sets of information stored in the RAM  233  in steps S 63  and S 65  both indicate a low-level signal (S 81 : L→L) (in other words, the signal output from each liquid level sensor  155  remains unchanged before and after the processing in step S 64 ), the controller  230  updates the count value TN (S 82 ). More specifically, the controller  230  counts up the count value TN to a value equivalent to the amount of ink instructed to discharge in the immediately preceding step S 64 . 
     The controller  230  also calculates the current total amount Vt (S 83 ). First, the controller  230  calculates the total amount Vt after the cartridge replacement that is the sum of the ink amount Vc and the ink amount Vs stored in the EEPROM  234  after the cartridge is replaced. The controller  230  then calculates the current total amount Vt by subtracting the ink amount equivalent to the count value TN from the calculated total amount Vt (Vt=Vt−TN). The controller  230  then obtains the ink amounts Vc and Vs based on the calculated current total amount Vt and the volume V th  (S 83 ). 
     The controller  230  determines whether the calculated current total amount Vt is equal to or greater than the volume V th . For the current total amount Vt equal to or greater than the volume V th , the controller  230  determines the volume V th  to be the ink amount Vs. For the current total amount Vt smaller than the volume V th , the controller  230  determines the current total amount Vt to be the ink amount Vs. 
     Subsequently, the controller  230  displays the calculated ink amounts Vc and Vs and/or the calculated total amount Vt on the display  17  (S 84 ). The controller  230  also updates the ink amount Vc stored in the memory of the IC chip  66  of the ink cartridge  50  to the calculated ink amount Vc (S 85 ). 
     When the information stored in the RAM  233  in step S 63  indicates a low-level signal and the information stored in the RAM  233  in step S 65  indicates a high-level signal (S 81 : L→) (in other words, the signal output from each liquid level sensor  155  is changed before and after the processing in step S 64 ), the controller  230  sets the flag C_Empty ON (S 86 ). The output from the liquid level sensors  155  changing from a low-level signal to a high-level signal corresponds to the liquid level of the second reservoir  105  reaching the predetermined level B during the processing in step S 64 . Subsequently, no ink transfer occurs between the ink cartridge  50  and the subtank  100 . 
     The controller  230  also reads a predetermined ink amount Vcc (=0) from the ROM  232 , and sets the ink amount Vc to the predetermined ink amount Vcc (S 87 ). Similarly, the controller  230  reads a predetermined ink amount Vsc (equivalent to the volume of a part of the second reservoir  105  lower than the predetermined level B) from the ROM  232 , and sets the ink amount Vs to the predetermined ink amount Vsc (S 87 ). The ink amounts Vc and Vs calculated in the counting process include errors. The controller  230  thus sets the ink amount Vc to the predetermined ink amount Vcc and sets the ink amount Vs to the predetermined ink amount Vsc at the time when the output from the liquid level sensor  155  changes from a low-level signal to a high-level signal, thus resetting the accumulated errors. Further, the controller  230  calculates the current total amount Vt as a value equal to the ink amount Vs (Vt=Vsc) (S 87 ). When the ink amount Vc is zero, the total amount Vt has the same value as the ink amount Vs. 
     The controller  230  then displays the current ink amounts Vc and Vs and/or the current total amount Vt on the display  17 . The controller  230  also overwrites the ink amount Vc stored in the memory of the IC chip  66  of the ink cartridge  50  with the above ink amount Vc (=0) (S 89 ). 
     The signal output from each liquid level sensor  155  changes during the processing in step S 64 , and thus the predetermined ink amount Vsc read in step S 87  is not strictly the amount of ink stored in the subtank  100  at the moment when the signal output from the liquid level sensor  155  changes, but indicates the amount of ink immediately before the signal output from the liquid level sensor  155  changes. With the difference between the ink amounts being small, the predetermined ink amount Vsc read in step S 87  is approximately the ink amount Vs at the time when the signal output from the liquid level sensor  155  changes. 
     The controller  230  also updates the count value SN stored in EEPROM  234  to the value equivalent to the amount of ink instructed to discharge in the immediately preceding step S 64  (S 90 ). In other words, the controller  230  starts updating and counting up the count value SN in response to the output from the liquid level sensors  155  changing from a low-level signal to a high-level signal. The controller  230  counts up the count value TN stored in the EEPROM  234  to a value equivalent to the amount of ink instructed to discharge in the immediately preceding step S 64 . 
     The controller  230  then calculates the ink amount Vs (S 91 ). The calculated ink amount Vs is obtained by subtracting the ink amount equivalent to the count value SN stored in the EEPROM  234  from the predetermined ink amount Vsc stored in the ROM  232 . As described above, after the output from the liquid level sensor  155  changes to a high-level signal, the ink amount Vs is the same value as the current total amount Vt. The ink amount Vc is zero. 
     The controller  230  then displays the calculated current ink amounts Vc and Vs and/or the calculated current total amount Vt on the display  17  (S 92 ). The ink amount Vc is zero after the output of liquid level sensor  155  changes to a high-level signal, and thus the controller  230  does not update the ink amount Vc stored in the memory of the IC chip  66  of the ink cartridge  50 . 
     The controller  230  then compares the count value SN updated in step S 90  with the threshold value Nth (S 93 ). When determining that the count value SN updated in step S 90  is smaller than the threshold value N th  (S 93 : No), the controller  230  completes the counting process. In contrast, when determining that the count value SN updated in step S 90  is equal to or greater than the threshold value Nth (S 93 : Yes), the controller  230  sets the flag S_Empty ON (S 94 ). The controller  230  disables the ink discharge through the printhead  39  in response to the flag S_Empty set ON, and completes the counting process. 
     When the sets of information stored in the RAM  233  in steps S 63  and S 65  both indicate a high-level signal (S 91 : H→H), the controller  230  reads the count value SN stored in the EEPROM  234 . The controller  230  then counts up the read count value SN to a value equivalent to the amount of ink instructed to discharge in the immediately preceding step S 64  and stores the value into the EEPROM  234  again. More specifically, the controller  230  updates the count value SN (S 90 ). The controller  230  also updates the count value TN. The controller  230  then performs the processing from steps S 91  to S 94  described above using the count value SN updated in step S 90 . 
     Operational Effects of Second Embodiment 
     The structure according to the second embodiment can delete the notification screen S_Empty from the display  17  in response to a low-level signal received from the liquid level sensor  155  after a low-level signal is received from installation sensor  154  and before the predetermined time ST elapses. 
     Further, the ink in-flow screen can appear on the display  17  in response to a low-level signal received from the installation sensor  154 , and the notification screen S_Empty can appear again on the display  17  when the elapsed time T exceeds the predetermined time ST. Additionally, the controller  230  uses, in determining whether the elapsed time T exceeds the predetermined time ST, a different predetermined time ST in accordance with the type information about the installed ink cartridge  50  or a signal from the temperature sensor  89 , thus allowing appropriate determination that ink is not flowing from the ink cartridge  50  into the subtank  100 . 
     Modification of Second Embodiment 
     In the second embodiment, the ink in-flow screen appears on the display  17  in response to a low-level signal received from the installation sensor  154 . The ink in-flow screen may not appear, and the notification screen S_Empty may remain appearing. Instead of displaying the ink in-flow screen, the notification screen S_Empty may be deleted. When the notification screen S_Empty continues to appear or is deleted without displaying the ink in-flow screen, the controller  230  may display the notification screen S_Empty on the display  17  when the elapsed time T from the installation of the ink cartridge  50  exceeds the predetermined time ST (S 58 : Yes). The notification screen S_Empty appearing on the display  17  in this case is an example of activating a second notification of the alarm. 
     In the second embodiment, when all the four flags S_Empty are set OFF, the controller  230  enables ink discharge through the printhead  39 . Thus, when the notification screen C_Empty appears with all the four flags S_Empty set OFF and the user replaces the ink cartridge  50 , ink discharge is enabled through the printhead  39 . When the ink cartridge  50  is replaced, or more specifically, in response to a low-level signal, a high-level signal, and then a low-level signal received in the stated order from the installation sensor  154 , the controller  230  may disable ink discharge through the printhead  39 . When ink flows from the ink cartridge  50  into the subtank  100  and in response to a low-level signal received from the liquid level sensor  155 , the controller  230  may enable ink discharge through the printhead  39 . 
     In the second embodiment, the controller  230  corrects the predetermined time ST based on the temperature t detected by the temperature sensor  89  (S 58 ). As the temperature increases, the viscosity of the ink decreases to increase the inflow rate of the ink from the ink cartridge  50  into the subtank  100 . As the inflow rate increases, less time is taken for the same volume of ink to flow in. Thus, the predetermined time ST may be corrected to shorten as the temperature t increases. 
     The predetermined time ST may also be corrected based on the viscosity of the ink. As the viscosity of the ink increases, the inflow rate of the ink from the ink cartridge  50  into the subtank  100  decreases. Thus, the predetermined time ST may be corrected to extend as the viscosity of the ink increases. For example, the controller  230  may correct the predetermined time ST stored in the RAM  233  based on the information indicating the viscosity of the ink stored in the memory of the IC chip  66  of the ink cartridge  50  (S 58 ). 
     The predetermined time ST may also be corrected based on the liquid level of the ink stored in the first reservoir  53  of the ink cartridge  50 . As the liquid level increases, the inflow rate of the ink from the ink cartridge  50  into the subtank  100  increases. Thus, the predetermined time ST may be corrected to shorten as the liquid level increases. For example, the controller  230  may correct the predetermined time ST stored in the RAM  233  based on the information stored in the memory of the IC chip  66  of the ink cartridge  50  and indicating the liquid level of the ink stored in the first reservoir  53  (S 58 ). 
     Other Modifications 
     In one or more of the above embodiments, the controller  230  performs the processing in step S 15  in response to a low-level signal, a high-level signal, and then a low-level signal received in the stated order from the installation sensor  154  (S 14 :Yes). The controller  230  performs the processing in step S 15  in response to the ink cartridge  50  installed in the installation case  71  previously containing no ink cartridge  50 . More specifically, the controller  230  may perform the processing in step S 15  when determining that the ink cartridge  50  is installed in the installation case  71 . The controller  230  receiving a low-level signal, a high-level signal, and then a low-level signal in the stated order from the installation sensor  154  is an example of the controller  230  determining that the cartridge is installed in the installation case  71 . Other examples of the controller  230  determining that the ink cartridge  50  is installed in the installation case  71  will be described below. 
     For example, the controller  230  receives a low-level signal after receiving a high-level signal from the cover sensor  88 . The controller  230  then reads identification information from the memory of the IC chip  66  and compares the read identification information with identification information for the ink cartridge  50  yet to be replaced stored in the EEPROM  234 . When determining that the identification information read from the memory of the IC chip  66  disagrees with the identification information stored in the EEPROM  234 , the controller  230  may perform the processing in step S 35 . More specifically, an example of the controller  230  determining that the ink cartridge  50  is installed in the installation case  71  includes the controller  230  reading identification information from the memory of the IC chip  66 , comparing the read identification information with identification information for the ink cartridge  50  yet to be replaced stored in the EEPROM  234 , and determining, as a result, that the identification information read from the memory of the IC chip  66  disagrees with the identification information stored in the EEPROM  234 . 
     For example, the controller  230  receives a low-level signal after receiving a high-level signal from the cover sensor  88 . The controller  230  then displays, to the user, a confirmation screen on the display  17  indicating whether an ink cartridge  50  is newly installed in the installation case  71 . The controller  230  receives an input corresponding to the confirmation screen through the operation panel  22  while the confirmation screen is on the display  17 . The controller  230  performs the processing in step S 35  when the received input corresponds to an ink cartridge  50  newly installed in the installation case  71 . More specifically, an example of the controller  230  determining that the ink cartridge  50  is installed in the installation case  71  includes the controller  230  receiving a low-level signal after receiving a high-level signal from the cover sensor  88 , displaying, to the user, a confirmation screen on the display  17  indicating whether an ink cartridge  50  is newly installed in the installation case  71 , and receiving an input corresponding to the confirmation screen through the operation panel  22  while the confirmation screen is on the display  17 , with the received input then corresponding to an ink cartridge  50  newly installed in the installation case  71 . 
     In the above embodiments, the liquid level sensor  155  optically detects the liquid level of the ink in the second reservoir  105  using a prism with different reflectance values depending on whether the ink is in contact with the rear wall  112  of the second reservoir  105 . However, the liquid level sensor  155  may have any structure to detect the liquid level of the ink in the second reservoir  105 . For example, the second reservoir  105  may contain an actuator that rotates depending on whether the liquid level in the second reservoir  105  is lower than a boundary position B, and the liquid level sensor  155  may detect a detection target portion included in the actuator located at a detection position. In some embodiments, the liquid level of the ink in the second reservoir  105  may be detected with an electrode. The liquid level sensor  155  may also output different signals for different liquid levels in the first reservoir  53  of the ink cartridge  50 , instead of outputting different signals for different liquid levels in the second reservoir  105  of the subtank  100 . 
     In the above embodiments, when at least one of the four flags S_Empty is set ON, all the four subtanks  100  are disabled from discharging ink through the printhead  39 . The subtank  100  for which the flag S_Empty is set ON may be selectively disabled from discharging ink through the printhead  39 . When at least one of the flags S_Empty associated with magenta, cyan, and yellow is set ON, and the flag S Empty associated with black is set OFF, the discharge of the magenta, cyan, and yellow inks may be disabled, and the discharge of the black ink may be enabled. 
     The IC chip  66  is electrically connectable to the contact  152  through contact. However, an information medium and an interface such as near field communication (NFC) or radio frequency identification (RFID) may be used for reading and writing data in a contactless manner using radio waves. 
     In the embodiments described above, the ink is an example of liquid. However, the liquid may be a pretreatment liquid discharged to a sheet or another substrate before ink is applied in image recording, or may be water for cleaning the printhead  39 .