Patent Publication Number: US-2023139735-A1

Title: Liquid supply device, method of supplying liquid, and image recording device

Description:
REFERENCE TO RELATED APPLICATIONS 
     This application claims priority from Japanese Patent Application No. 2021-177150 filed on Oct. 29, 2021. The entire content of the priority application is incorporated herein by reference. 
     BACKGROUND ART 
     There is known an image recording device comprising a head and a carriage mounted with the head, that discharges ink from nozzles of the head when the carriage moves in a predetermined direction. The image recording device has an ink supply device that supplies ink to the head from a reservoir of the ink. In the case of a plurality of kinds of inks is supplied, the ink supply device has a plurality of ink channels provided between a plurality of the reservoirs and the head. 
     There is a printer comprising: a head having four kinds of nozzles respectively discharging four colors of inks; and a cap collectively covering the four kinds of nozzles. In this printer, the four colors of inks are respectively supplied to four sub-tanks from four cartridges, and four ink channels are employed to respectively supply the four colors of inks to the head from the four sub-tanks. 
     DESCRIPTION 
     In the printer described in Japanese Patent Publication Laid Open No. 2020-011485, there is performed a so-called initial introduction where the four colors of inks are respectively initially introduced into the four ink channels by a suction pressure being applied from the head side. In this printer, ink is supplied employing a water head difference between the cartridge and the sub-tank. Therefore, as much ink will flow into the sub-tank from the cartridge as an amount of ink in the sub-tank that has flowed to the head side due to the suction pressure. 
     Sometimes, there is a difference in resistance between the four ink channels connecting the four sub-tanks and the head. In such a case, when the previously-mentioned initial introduction is performed, an amount of ink flowing to the head side from the sub-tank through a channel having a small channel resistance will increase, and an amount of ink flowing to the head side from the sub-tank through a channel having a large channel resistance will decrease. There will thus occur a difference in ink introduction amounts between the plurality of ink channels. This will result in that when, for example, suction time is set so that a sufficient amount of ink will flow to the head side through the channel having a large channel resistance, an excessive amount of ink will flow to the head side through the channel having a small channel resistance. 
     The present disclosure, which was made in view of the above-described circumstances, has an object of providing a means by which difference in liquid amounts flowing into a head through a plurality of channels by suction becomes smaller. 
     (1) A liquid supply device according to an aspect of the present disclosure includes: a first reservoir configured to store a first liquid;
         a second reservoir configured to store a second liquid;   a first tank having flexibility, the first tank being positioned lower than the first reservoir;   a second tank having a flexibility, the second tank being positioned lower than the second reservoir;   a first valve configured to open and close a channel connecting the first reservoir and the first tank;   a second valve configured to open and close a channel connecting the second reservoir and the second tank;   a head, the first liquid being capable of flowing into the head from the first tank through a first channel, the second liquid being capable of flowing into the head from the second tank through a second channel;   a suction mechanism configured to drive so that a suction pressure is applied to the first channel and the second channel from a head side, of the first channel and the second channel, at which the head is positioned;   a first sensor;   a second sensor; and   a controller.       

     The controller is configured to:
         execute a valve-opening operation of opening the first valve and the second valve, in response to receiving of a suction instruction;   execute, after executing the valve-opening operation, a valve-closing operation of closing the first valve depending on output of a first signal from the first sensor, and closing the second valve depending on output of a second signal from the second sensor, the first signal being a signal indicating that an amount of the first liquid in the first tank is a first threshold value or more, the second signal being a signal indicating that an amount of the second liquid in the second tank is a second threshold value or more; and   execute, after executing the valve-closing operation, a suction operation of driving the suction mechanism for a predetermined time period.       

     According to the liquid supply device described above, in the liquid supply device configured to perform suction to introduce the liquid into the plurality of channels connecting the plurality of reservoirs and the head, the suction mechanism is driven in a state where the liquid of not less than the predetermined amount has been supplied to each of the tanks, and supply of the liquid to each of the tanks from each of the reservoirs then has been stopped. Therefore, difference in liquid amounts flowing into the head through the plurality of channels by suction becomes smaller. 
     (2) According to another aspect of the present disclosure, the controller may be configured to execute, after executing the suction operation, the valve-opening operation again. 
     (3) According to another aspect of the present disclosure, the controller may be configured to open the first valve depending on output of a third signal from the first sensor, and open the second valve depending on output of a fourth signal from the second sensor, the third signal being a signal indicating that the amount of the first liquid in the first tank is less than a third threshold value smaller than the first threshold value, the fourth signal being a signal indicating that the amount of the second liquid in the second tank is less than a fourth threshold value smaller than the second threshold value. 
     (4) According to another aspect of the present disclosure, the first sensor may include a first signal outputting sensor configured to output the first signal and a third signal outputting sensor configured to output the third signal, and the second sensor may include a second signal outputting sensor configured to output the second signal and a fourth signal outputting sensor configured to output the fourth signal. 
     (5) According to another aspect of the present disclosure, the controller may be configured to repeatedly execute the valve-opening operation, the valve-closing operation, and the suction operation a predetermined number of times, in response to the suction instruction. 
     (6) According to another aspect of the present disclosure, the controller may be configured to keep the first valve in a closed state in the valve-opening operation, after executing the valve-opening operation, the valve-closing operation, and the suction operation a certain number of times fewer than the predetermined number of times. 
     (7) According to another aspect of the present disclosure, the controller may be configured to execute the valve-opening operation again, after having repeatedly executed the valve-opening operation, the valve-closing operation, and the suction operation the predetermined number of times. 
     (8) According to another aspect of the present disclosure, the suction device may suck each of the first liquid and the second liquid as much as a predetermined amount by being driven for the predetermined time period, and the predetermined amount is larger than a volume of the first tank and a volume of the second tank. 
     (9) According to another aspect of the present disclosure, the controller may be configured to: execute a recording operation of discharging the first liquid and the second liquid from the head, in a state that the first valve and the second valve are closed; execute a first valve opening and closing operation of opening the first valve depending on output of a third signal from the first sensor, and closing the first valve depending on output of the first signal from the first sensor after the outputting of the third signal, the third signal being a signal indicating that the amount of the first liquid in the first tank is less than a third threshold value smaller than the first threshold value; execute a second valve opening and closing operation of opening the second valve depending on output of a fourth signal from the second sensor, and closing the second valve depending on output of the second signal from the second sensor after the outputting of the fourth signal, the fourth signal being a signal indicating that the amount of the second liquid in the second tank is less than a fourth threshold value smaller than the second threshold value; and stop the first valve opening and closing operation and the second valve opening and closing operation in response to the receiving of the suction instruction until completion of the executing of the suction operation. 
     (10) According to another aspect of the present disclosure, the first sensor may include a first signal outputting sensor configured to output the first signal and a third signal outputting sensor configured to output the third signal, and the second sensor may include a second signal outputting sensor configured to output the second signal and a fourth signal outputting sensor configured to output the fourth signal. 
     (11) An image recording device according to another aspect of the present disclosure includes: the liquid supply device as described in any one of (1) to (10); and
         a conveyer configured to convey a recording medium to which the first liquid and the second liquid are to be discharged from the head.       

     (12) A method of supplying liquid according to another aspect of the present disclosure is a method of supplying liquid using a first reservoir configured to store a first liquid; a second reservoir configured to store a second liquid; a first tank which has a flexibility and which is positioned lower than the first reservoir; a second tank which has a flexibility and which is positioned lower than the second reservoir; and a head, the first liquid being capable of flowing into the head from the first tank through a first channel, the second liquid being capable of flowing into the head from the second tank through a second channel. 
     The method includes:
         opening a first valve configured to open and close a channel connecting the first reservoir and first tank, and opening a second valve configured to open and close a channel connecting the second reservoir and the second tank, in response to receiving of a suction instruction;   after the opening of the first valve and the second valve, closing the first valve depending on output of a first signal from a first sensor, and closing the second valve depending on output of a second signal from a second sensor, the first signal being a signal indicating that an amount of the first liquid in the first tank is a first threshold value or more, the second signal being a signal indicating that an amount of the second liquid in the second tank is a second threshold value or more; and   after the closing of the first valve and the second valve, driving a suction mechanism for a predetermined time period, the suction mechanism being configured to drive so that a suction pressure is applied to the first channel and the second channel from a head side, of the first channel and the second channel, at which the head is positioned.       

    
    
     
       The present disclosure results in difference in liquid amounts flowing into a head through a plurality of channels by suction becoming smaller. 
         FIG.  1    is a schematic view depicting internal configuration of a printer  10 . 
         FIG.  2    is a diagram depicting a moving range of a carriage  41 . 
         FIG.  3    is a block diagram depicting configuration of a controller  60  and elements connected to the controller  60 . 
         FIG.  4    is a schematic view depicting configuration of an ink supply unit  50 . 
         FIGS.  5 A and  5 B  are diagrams each depicting configuration of a head  42  and its periphery.  FIG.  5 A  is a perspective view of the head  42  and its periphery.  FIG.  5 B  is a cross-sectional view of an exhaust portion  45 . 
         FIG.  6    is a flowchart of ink automatic supply processing by the controller  60 . 
         FIG.  7    is a flowchart of image recording processing by the controller  60 . 
         FIG.  8    is a flowchart of initial introduction processing by the controller  60 . 
         FIG.  9    is a flowchart of initial introduction processing by a controller  60 . 
     
    
    
     A printer  10  (one example of an image recording device) and ink supply unit  50  (one example of a liquid supply device) according to an embodiment of the present disclosure will be described below. Note that the embodiment described below is merely one example of the present disclosure, and it goes without saying that the embodiment of the present disclosure can be appropriately altered in a range not altering the gist of the present disclosure. In the description below, progression from a start point to an end point of an arrow will be expressed as orientation, and coming and going on a line connecting a start point and an end point of an arrow will be expressed as direction. Moreover, an up-down direction  7  is defined with reference to a state of the printer  10  having been usably installed (the state of  FIG.  1   ), a front-rear direction  8  is defined assuming a surface provided with a discharge port  13  to be a front surface, and a left-right direction  9  is defined looking at the printer  10  from the front. The up-down direction  7 , the front-rear direction  8 , and the left-right direction  9  are orthogonal to each other. 
     [Overall Configuration of Printer  10 ] 
     The printer  10  depicted in  FIG.  1    is an image recording device that records an image on a sheet S (one example of a recording medium) by an ink jet recording system. The sheet S is a long paper sheet that has been wound into a roll shape. In order for the sheet S to be mounted in the printer  10 , a winding center of the sheet S has a through-hole formed therein. A recording objective medium may be the likes of a seal paper, fan-fold paper, cut paper, or a fabric. 
     The printer  10  comprises a housing  11  of substantially rectangular parallelepiped shape. The housing  11  has a size enabling it to be mounted on a tabletop, on a floor, or in a rack, and so on. Located in a front wall  12  of the housing  11  is the discharge port  13  which is slit-like and extends in the left-right direction  9 . The sheet S that has been recorded with an image by the printer  10  is discharged from the discharge port  13 . The discharged sheet S is wound by a winding device (not depicted) fitted to the printer  10 , for example. 
     As depicted in  FIG.  1   , the printer  10  comprises the following within the housing  11 , namely, a holder  21 , a tensioner  22 , a conveying roller pair  23 , a discharging roller pair  24 , a platen  25 , a cartridge holder  26 , a carriage  41 , a head  42 , and the ink supply unit  50  (see  FIG.  4   ). The head  42  is installed in the carriage  41 . The cartridge holder  26  is fitted with a cartridge  51  that stores ink (one example of a liquid). As depicted in  FIG.  2   , the printer  10  further comprises the following within the housing  11 , namely, two guide rails  37 ,  38  and a cap  81 . As depicted in  FIG.  3   , the printer  10  further comprises the following within the housing  11 , namely, a controller  60 , a motor for holder drive  71 , a motor for conveyance  72 , a motor for carriage drive  73 , and a motor for cap drive  74 . The printer  10  may further comprise a wipe unit, various kinds of motors, various kinds of sensors, and so on, besides the above-mentioned elements. 
     [Conveying Mechanism of Sheet S] 
     Located inside the housing  11  are a pair of side frames (not depicted) that extend in the up-down direction  7  and the front-rear direction  8 . The holder  21  has a rotating shaft  31  that supports the sheet S. The rotating shaft  31  extends in the left-right direction  9  and has its two ends fixed to the side frames. Motive power of the motor for holder drive  71  (see  FIG.  3   ) is transmitted to the rotating shaft  31 . This motive power causes the holder  21  to rotate in a circumferential direction of the rotating shaft  31 . In  FIG.  1   , a rotating direction of the holder  21  is counter-clockwise. Rotation of the holder  21  causes a roll body supported by the holder  21  to rotate too. The sheet S is led out upwardly from a rear end of the roll body and guided to the tensioner  22  as a result of the conveying roller pair  23  and discharge roller pair  24  rotating. 
     The tensioner  22 , the conveying roller pair  23 , and the discharge roller pair  24  each extend in the left-right direction  9  between the side frames and are installed in a manner enabling them to rotate in a circumferential direction of their rotational axes parallel to the left-right direction  9 . The tensioner  22  is applied with a biasing force in a rearward orientation by a biasing member such as a spring. The tensioner  22  abuts on the sheet S led out from the roll body and thereby guides the sheet S in such a manner that the sheet S curves frontwards. 
     The conveying roller pair  23  include a drive roller  32  and a pinch roller  33 , and are located forward of the tensioner  22 . The discharge roller pair  24  include a drive roller  34  and a pinch roller  35 , and are located further forward than the conveying roller pair  23 . Lower end positions of the drive rollers  32 ,  34  substantially coincide with an upper end position of the tensioner  22  in the up-down direction  7 . The pinch roller  33  abuts from below on the drive roller  32 . The pinch roller  35  abuts from below on the drive roller  34 . 
     Motive power of the motor for conveyance  72  (see  FIG.  3   ) is transmitted to the drive rollers  32 ,  34 . This motive power causes the drive rollers  32 ,  34  to rotate. As a result, the drive rollers  32 ,  34  convey the sheet S in a conveying orientation  6  while nipping the sheet S between the drive roller  32  and the pinch roller  33  as well as between the drive roller  34  and the pinch roller  35 . In the present embodiment, the conveying orientation  6  is a frontward orientation. The motor for conveyance  72 , the conveying roller pair  23 , and the discharge roller pair  24  function as a conveyer (conveying unit) that conveys the sheet S to which ink discharged from the head  42  lands. 
     [Platen  25 ] 
     The platen  25  is fitted to the side frames at a position between the conveying roller pair  23  and discharge roller pair  24  in the front-rear direction  8 . The platen  25  extends in the left-right direction  9  between the side frames, and includes a supporting surface  36  for the sheet S, that extends in the front-rear direction  8  and the left-right direction  9 . The supporting surface  36  is an upper end surface of the platen  25 . A position in the up-down direction  7  of the supporting surface  36  substantially coincides with the upper end position of the tensioner  22 . The platen  25  may be a sucking platen that sucks the sheet S onto the supporting surface  36 . 
     [Carriage  41  and Head  42 ] 
     As depicted in  FIG.  2   , the guide rails  37 ,  38  extend in the left-right direction  9  parallelly to each other. Positions in the up-down direction  7  of the guide rails  37 ,  38  are the same. The guide rail  38  is located rearward of the guide rail  37  in the front-rear direction  8 . Both ends of the guide rails  37 ,  38  are fixed to the side frames. The carriage  41  is supported by the guide rails  37 ,  38 . Motive power of the motor for carriage drive  73  (see  FIG.  3   ) is transmitted to a carriage drive mechanism (not depicted). The carriage  41  moves in the left-right direction  9  due to action of the carriage drive mechanism, in a state of being supported by the guide rails  37 ,  38 . 
     As depicted in  FIG.  1   , the head  42  is installed in the carriage  41 . A lower surface of the head  42  is referred to as a nozzle surface  43 . A plurality of nozzles  44  each configured to discharge ink is located in the nozzle surface  43 . The cartridge  51  fitted to the cartridge holder  26 , and the head  42  are connected via the ink supply unit  50  (see  FIG.  4   ). Ink stored in the cartridge  51  is supplied to the head  42  via the ink supply unit  50 . While the carriage  41  is moving in the left-right direction  9 , ink that has been supplied to the head  42  is discharged from the nozzles  44 . As a result, image recording is performed on the sheet S. 
     [Controller  60 ] 
     As depicted in  FIG.  3   , the controller  60  has a CPU  61 , a ROM  62 , a RAM  63 , an EEPROM  64 , and an ASIC  65 . The ROM  62  stores the likes of various kinds of data required in operation of the controller  60 . The RAM  63  is a working memory of the CPU  61 . The EEPROM  64  stores the likes of a control program executed by the CPU  61 . Prior to image recording being executed by the printer  10 , the control program stored in the EEPROM  64  is copied to the RAM  63 . The CPU  61  executes the control program stored in the RAM  63 . As a result, the controller  60  executes ink automatic supply processing, image recording processing, and initial introduction processing that will be described later. The controller  60  is one example of a controller. 
     The controller  60  is electrically connected to the motor for holder drive  71 , the motor for conveyance  72 , the motor for carriage drive  73 , the motor for cap drive  74 , a motor for elevator member drive  75 , a motor for pump drive  76 , and the head  42 , via the ASIC  65 . The motor for holder drive  71 , the motor for conveyance  72 , the motor for carriage drive  73 , the motor for cap drive  74 , the motor for elevator member drive  75 , and the motor for pump drive  76  rotate according to control from the controller  60 , and generate motive power. The head  42  discharges ink onto the sheet S conveyed on the platen  25 , according to control from the controller  60 . 
     The holder  21  rotates due to motive power from the motor for holder drive  71 . The drive rollers  32 ,  34  rotate due to motive power from the motor for conveyance  72 . The sheet S is conveyed in the conveying orientation  6  due to motive power from the motor for conveyance  72 . The carriage  41  moves in the left-right direction  9  due to motive power from the motor for carriage drive  73 . The cap  81  moves in the up-down direction  7  between a relatively high covering position and a relatively low separated position, due to motive power from the motor for cap drive  74 . An elevator member  106  (see  FIG.  5 B ; details described later) moves in the up-down direction  7  between a relatively high abutting position and a relatively low non-abutting position, due to motive power from the motor for elevator member drive  75 . A pump  85  (see  FIG.  4   ), which is driven by motive power from the motor for pump drive  76 , provides a suction pressure to a channel connected to the pump  85 . Note that some of the motor for holder drive  71 , the motor for conveyance  72 , the motor for carriage drive  73 , the motor for cap drive  74 , the motor for elevator member drive  75 , and the motor for pump drive  76  may be realized by a common motor. 
     [Moving Range of Carriage  41 , and Cap  81 ] 
     As depicted in  FIG.  2   , the platen  25 , which has a shape long in the left-right direction  9 , is located below the carriage  41  in the up-down direction  7  (see  FIG.  1   ). A left end of the platen  25  is located close to left ends of the guide rails  37 ,  38  in the left-right direction  9 . A right end of the platen  25  is located further to the right than centers of the guide rails  37 ,  38  in the left-right direction  9 . The cap  81  is located to the right of the platen  25  in the left-right direction  9 . While image recording is being executed by the printer  10 , the carriage  41  moves in the left-right direction  9  within a range of the platen  25 . While image recording is not being executed by the printer  10 , the carriage  41  is located in a position where the head  42  faces the cap  81  (hereafter, referred to as a standby position). 
     As depicted in  FIG.  4   , the cap  81  includes: a nozzle cap  82  configured to cover the nozzle surface  43  of the head  42 ; and an exhaust cap  83  configured to cover an exhaust port surface  46  of an exhaust portion  45  (details of which will be described later). When the carriage  41  is located in the standby position, the cap  81  is located in the covering position. At this time, the nozzle cap  82  covers the nozzle surface  43  of the head  42 , and the exhaust cap  83  covers the exhaust port surface  46  of the exhaust portion  45 . When the carriage  41  is located in a position other than the standby position, the cap  81  is located in the separated position. At this time, the nozzle cap  82  does not cover the nozzle surface  43 , and the exhaust cap  83  does not cover the exhaust port surface  46 . In this way, the cap  81  has a function of covering the nozzle surface  43  and the exhaust port surface  46  in a time period in which image recording is not executed. 
     [Ink Supply Unit  50 ] 
     The ink supply unit  50  of the printer  10  will be described with reference to  FIG.  4   . The cartridge holder  26  (see  FIG.  1   ) is installed with four cartridges  51   b,    51   c,    51   m,    51   y  that respectively store black, cyan, magenta, and yellow inks. The ink supply unit  50  comprises the cartridges  51   b,    51   c,    51   m,    51   y,  four valves  52   b,    52   c,    52   m,    52   y,  four sub-tanks  53   b,    53   c,    53   m ,  53   y,  eight sensors  54   b,    54   c,    54   m,    54   y,    55   b,    55   c,    55   m,    55   y,  the head  42 , the pump  85 , and the controller  60 . 
     The inks stored in the cartridges  51   b,    51   c,    51   m,    51   y,  which are so-called latex inks, contain a pigment, resin fine particles, and an additive. The ink has a viscosity suitable for evenly dispersing the pigment and the resin fine particles. The pigment represents the color of the ink. The resin fine particles, which are for causing the pigment to adhere to the sheet S, are of a synthetic resin whose glass transition temperature is exceeded by heating of a heater (not depicted), for example. Note that the printer  10  may be installable with at least two cartridges, and may have at least two sub-tanks. 
     An ink channel  56   b  connects the cartridge  51   b  and the sub-tank  53   b.  An ink channel  56   c  connects the cartridge  51   c  and the sub-tank  53   c.  An ink channel  56   m  connects the cartridge  51   m  and the sub-tank  53   m.  An ink channel  56   y  connects the cartridge  51   y  and the sub-tank  53   y . An ink channel  57   b  connects the sub-tank  53   b  and the head  42 . An ink channel  57   c  connects the sub-tank  53   c  and the head  42 . An ink channel  57   m  connects the sub-tank  53   m  and the head  42 . An ink channel  57   y  connects the sub-tank  53   y  and the head  42 . 
     The ink stored in the cartridge  51   b  is supplied to the sub-tank  53   b  via the ink channel  56   b.  The sub-tank  53   b  stores the ink that has been supplied from the cartridge  51   b.  The ink stored in the sub-tank  53   b  is supplied to the head  42  via the ink channel  57   b.  Similarly, the ink stored in the cartridge  51   c  is supplied to the head  42  via the ink channel  56   c,  the sub-tank  53   c , and the ink channel  57   c.  The ink stored in the cartridge  51   m  is supplied to the head  42  via the ink channel  56   m,  the sub-tank  53   m,  and the ink channel  57   m.  The ink stored in the cartridge  51   y  is supplied to the head  42  via the ink channel  56   y,  the sub-tank  53   y,  and the ink channel  57   y.    
     The sub-tanks  53   b,    53   c,    53   m,    53   y  are flexible. Outer shapes of the sub-tanks  53   b ,  53   c,    53   m,    53   y  change between an expanded (swollen) state and a contracted (shrunken) state depending on an amount of ink stored therein. The sub-tank  53   b  is located in a lower position than the cartridge  51   b.  Supply of ink from the cartridge  51   b  to the sub-tank  53   b  is performed by water head difference. Supply of ink from the sub-tank  53   b  to the head  42  is initially performed by sucking the ink from the head  42  side by the pump  85 . Subsequently, the same amount of ink as ink that has been discharged from the head  42  is supplied to the head  42  from the sub-tank  53   b.  Supply of ink from the sub-tanks  53   c,    53   m,    53   y  to the head  42  is performed by a similar method too. 
     The black ink can flow into the head  42  through the ink channel  57   b  from the sub-tank  53   b,  the cyan ink can flow into the head  42  through the ink channel  57   c  from the sub-tank  53   c,  the magenta ink can flow into the head  42  through the ink channel  57   m  from the sub-tank  53   m,  and the yellow ink can flow into the head  42  through the ink channel  57   y  from the sub-tank  53   y.  The ink supply unit  50  has four ink channels (an ink channel for black ink, an ink channel for cyan ink, an ink channel for magenta ink, and an ink channel for yellow ink) between the cartridges  51   b,    51   c,    51   m,    51   y  and the head  42 . 
     The sensors  54   b,    55   b,  which are located on an inside or an outside of the sub-tank  53   b,  detect ink amount of the sub-tank  53   b.  The sensor  54   b  outputs a sensor signal Sb 1  indicating that ink amount of the sub-tank  53   b  (amount of the ink in the sub-tank  53   b ) is a threshold value TH 1  or more. The sensor  55   b  outputs a sensor signal Sb 2  indicating that ink amount of the sub-tank  53   b  is less than a threshold value TH 2 . Similarly, the sensors  54   c,    54   m ,  54   y  respectively output sensor signals Sc 1 , Sm 1 , Sy 1  indicating that ink amounts of the sub-tanks  53   c,    53   m,    53   y  are the threshold values TH 1  or more. The sensors  55   c,    55   m,    55   y  respectively output sensor signals Sc 2 , Sm 2 , Sy 2  indicating that ink amounts of the sub-tanks  53   c,    53   m,    53   y  are less than the threshold values TH 2 . 
     Each of sensors  54   b,    54   c,    54   m,    54   y,    55   b,    55   c,    55   m,    55   y  detects ink amount of one of sub-tanks  53   b,    53   c,    53   m,    53   y  corresponding thereto by an arbitrary method. Each sensor may detect ink amount of the one of the sub-tanks  53   b,    53   c,    53   m  , 53   y  corresponding thereto by optically detecting change in outer shape of the one of the sub-tanks  53   b,    53   c,    53   m,    53   y  corresponding thereto, for example. Each sensor may detect ink amount of the one of the sub-tanks  53   b,    53   c,    53   m,    53   y  corresponding thereto by a publicly known float system, prism system, or electrode system. The threshold values TH 2  employed in comparison with ink amounts by the sensors  55   b,    55   c,    55   m,    55   y  are respectively smaller than the threshold values TH 1  employed in comparison with ink amounts by the sensors  54   b,    54   c,    54   m,    54   y.  The threshold values employed in comparison with ink amounts by the sensors  54   b,    54   c,    54   m,    54   y  are not necessarily all the same value, and there may be threshold value(s) whose value(s) is different from a value of the other threshold value of the four threshold values. The threshold values employed in comparison with ink amounts by the sensors  55   b,    55   c,    55   m,    55   y  are not necessarily all the same value, and there may be threshold value(s) whose value(s) is different from a value of the other threshold value of the four threshold values. 
     The controller  60  is inputted with the sensor signals Sb 1 , Sc 1 , Sm 1 , Sy 1 , Sb 2 , Sc 2 , Sm 2 , Sy 2  that have been respectively outputted from the sensors  54   b,    54   c,    54   m,    54   y,    55   b,    55   c ,  55   m,    55   y.  The controller  60  outputs a control signal Vb of the valve  52   b,  a control signal Vc of the valve  52   c,  a control signal Vm of the valve  52   m,  and a control signal Vy of the valve  52   y , based on the sensor signals the controller has been inputted with. The control signals Vb, Vc, Vm, Vy are binary signals for switching states of the valves  52  between an open state and a closed state. 
     The valve  52   b,  which is located on the ink channel  56   b,  opens and closes the ink channel  56   b  according to the control signal Vb. The valve  52   c,  which is located on the ink channel  56   c,  opens and closes the ink channel  56   c  according to the control signal Vc. The valve  52   m,  which is located on the ink channel  56   m,  opens and closes the ink channel  56   m  according to the control signal Vm. The valve  52   y,  which is located on the ink channel  56   y,  opens and closes the ink channel  56   y  according to the control signal Vy. 
     The ink channel  57   b  branches on its head  42  side into a portion reaching the nozzle  44  of the head  42  and portion reaching an exhaust port  47  of the exhaust portion  45 . An inner space of the nozzle cap  82  is connected to a first end of a switching portion  84 . An inner space of the exhaust cap  83  is connected to a second end of the switching portion  84 . A third end of the switching portion  84  is connected to one end of the pump  85 . A waste liquid tank  86  is located on the other end side of the pump  85 . The switching portion  84  switches which of the inner space of the nozzle cap  82  and inner space of the exhaust cap  83  the pump  85  is to be connected to, by control from the controller  60 . The pump  85  is one example of a suction mechanism applying a suction pressure to the ink channels  57   c,    57   b,    57   m,    57   y  from the head  42  side. 
     [Exhaust Portion  45 ] 
     As depicted in  FIG.  5 A , a buffer  91  having an inner space (not depicted) configured to store a small amount of ink, is located in an upper portion of the head  42 . The buffer  91  and the head  42  are connected by a coupling portion  92  extending in the up-down direction  7 . The exhaust portion  45 , which is of rectangular parallelepiped shape, is located on a right side of the buffer  91 . The exhaust port surface  46 , which is a lower surface of the exhaust portion  45 , is located in a higher position than the nozzle surface  43  in the up-down direction  7 . Four exhaust ports  47  are located in the exhaust port surface  46 . The four exhaust ports  47  are aligned at a predetermined interval in the front-rear direction  8 . 
     Four ink inflow ports  93  are located in an upper surface of the buffer  91 . The four ink inflow ports  93  are respectively connected to ink tubes (not depicted) configuring parts of the ink channels  57   b,    57   c,    57   m,    57   y.  Four coupling channels  94  are located in a rear portion of the coupling portion  92 . The four coupling channels  94  extend in the up-down direction  7  and are aligned in the left-right direction  9 . Four connecting portions  95  are located in an upper portion of the exhaust portion  45 . The four ink inflow ports  93  are respectively connected to the four coupling channels  94  via four ink channels (not depicted) in the buffer  91 . Ink that has reached the ink inflow port  93  passes along the ink channels in the buffer  91  and coupling channels  94  to reach the head  42  and be discharged in a downward orientation from the nozzles  44  located in the nozzle surface  43 . 
     The four coupling channels  94  are respectively connected to the four connecting portions  95  too, via another four ink channels (not depicted) in the buffer  91 . The four connecting portions  95  are respectively connected to the four exhaust ports  47  via four channels along which mainly gas flows. As depicted in  FIG.  5 B , the channel connecting the connecting portion  95  and the exhaust port  47  has a diameter enlarged portion  101 . A spring  102  and valve body  103  are located in an inner space of the diameter enlarged portion  101 . The valve body  103  has a main body portion  104  and a projecting portion  105 . The main body portion  104 , which has an outer diameter substantially equal to an inner diameter of the diameter enlarged portion  101 , is located within the diameter enlarged portion  101 . The projecting portion  105 , which has an outer diameter smaller than the inner diameter of the diameter enlarged portion  101 , projects downwardly toward the exhaust port  47  from the diameter enlarged portion  101 . The spring  102 , which is located above the valve body  103 , biases the valve body  103  in a downward orientation. In a normal state, the main body portion  104  is pressed onto a bottom surface of the diameter enlarged portion  101  by action of the spring  102 , and the four exhaust ports  47  are in a closed state. 
     Located below the exhaust cap  83  is the elevator member  106 . The elevator member  106  has four abutting portions  107 . The four abutting portions  107 , which have shapes projecting in an upward orientation, are aligned at a predetermined interval in the front-rear direction  8 . Four through-holes are located in a bottom surface of the exhaust cap  83 . The four through-holes are aligned at a predetermined interval in the front-rear direction  8 . The interval of the four exhaust ports  47 , the interval of the four abutting portions  107 , and the interval of the four through-holes of the exhaust cap  83  are all the same. The four abutting portions  107  respectively penetrate the four through-holes of the exhaust cap  83 . 
     As described above, the elevator member  106  is capable of moving in the up-down direction  7  between the relatively high abutting position and the relatively low non-abutting position, due to motive power from the motor for elevator member drive  75 . The elevator member  106  is capable of moving in the up-down direction  7 , independently of the exhaust cap  83 . When the carriage  41  is located in the standby position and the elevator member  106  is located in the abutting position, the four abutting portions  107  respectively abut on the four projecting portions  105 . At this time, the four valve bodies  103  move in an upward orientation against a restoring force of the spring  102 , and separate from the bottom surface of the diameter enlarged portion  101 . Hence, the four exhaust ports  47  attain an open state. 
     When the carriage  41  is located in the standby position and the elevator member  106  is located in the non-abutting position, the exhaust ports  47  attain a closed state. By the inner space of the nozzle cap  82  and the pump  85  being connected by the switching portion  84 , and the pump  85  thereupon being driven under such condition, the ink channels  57   b,    57   c,    57   m,    57   y  are provided with a suction pressure from the head  42  side. As a result, ink and gas in the ink channels  57   b,    57   c,    57   m,    5 ′ 7   y  is discharged from the nozzles  44 . The ink that has been discharged from the nozzles  44  is stored in the waste liquid tank  86 . 
     When the carriage  41  is located in the standby position and the elevator member  106  is located in the abutting position, the exhaust ports  47  attain an open state. By the inner space of the exhaust cap  83  and the pump  85  being connected by the switching portion  84 , and the pump  85  thereupon being driven under such condition, the ink channels  57   b,    57   c,    57   m,    57   y  are provided with a suction pressure from the head  42  side (specifically, from the exhaust portion  54 ). As a result, ink and gas in the ink channels  57   b,    57   c,    57   m,    57   y  is discharged from the discharge ports  47 . Mainly gas is discharged from the discharge ports  47 . In an aspect of the present disclosure, “applying a suction pressure to channel(s) from a head side” includes applying the suction pressure to the channel(s) by using element(s) configured to apply the suction pressure to the channel(s) from a side, of the channel(s), at which the head  42  is connected to the channel(s). Such element includes, for example, the head  42 , the exhaust portion  45  and the like. 
     [Operation of Controller  60 ] 
     The controller  60  continuously or always executes the ink automatic supply processing depicted in  FIG.  6   . The controller  60  executes the initial introduction processing depicted in  FIG.  8    during initial setting of the printer  10 . The controller  60  executes the image recording processing depicted in  FIG.  7    after initial setting of the printer  10  has been completed. The controller  60  executes image recording processing and ink automatic supply processing in parallel (or time divisionally). The controller  60  stops ink automatic supply processing while initial introduction processing is being executed. 
     [Ink Automatic Supply Processing] 
     The controller  60  repeatedly executes steps S 11 -S 26  in the ink automatic supply processing depicted in  FIG.  6   . The controller  60  determines whether the sensor signal Sb 2  (the signal indicating that ink amount of the sub-tank  53   b  is less than the threshold value TH 2 ) has been received from the sensor  55   b  (step S 11 ). In response to having determined the sensor signal Sb 2  to have been received (step S 11 : Yes), the controller  60  opens the valve  52   b  (step S 12 ). Next, the controller  60  determines whether the sensor signal Sb 1  (the signal indicating that ink amount of the sub-tank  53   b  is the threshold value TH 1  or more) has been received from the sensor  54   b  (step S 13 ). In response to having determined the sensor signal Sb 1  to have been received (step S 13 : Yes), the controller  60  closes the valve  52   b  (step S 14 ). 
     Next, the controller  60  determines whether the sensor signal Sc 2  (the signal indicating that ink amount of the sub-tank  53   c  is less than the threshold value TH 2 ) has been received from the sensor  55   c  (step S 15 ). In response to having determined the sensor signal Sc 2  to have been received (step S 15 : Yes), the controller  60  opens the valve  52   c  (step S 16 ). Next, the controller  60  determines whether the sensor signal Sc 1  (the signal indicating that ink amount of the sub-tank  53   c  is the threshold value TH 1  or more) has been received from the sensor  54   c  (step S 17 ). In response to having determined the sensor signal Sc 1  to have been received (step S 17 : Yes), the controller  60  closes the valve  52   c  (step S 18 ). 
     Next, the controller  60  determines whether the sensor signal Sm 2  (the signal indicating that ink amount of the sub-tank  53   m  is less than the threshold value TH 2 ) has been received from the sensor  55   m  (step S 19 ). In response to having determined the sensor signal Sm 2  to have been received (step S 19 : Yes), the controller  60  opens the valve  52   m  (step S 20 ). Next, the controller  60  determines whether the sensor signal Sm 1  (the signal indicating that ink amount of the sub-tank  53   m  is the threshold value TH 1  or more) has been received from the sensor  54   m  (step S 21 ). In response to having determined the sensor signal Sm 1  to have been received (step S 21 : Yes), the controller  60  closes the valve  52   m  (step S 22 ). 
     Next, the controller  60  determines whether the sensor signal Sy 2  (the signal indicating that ink amount of the sub-tank  53   y  is less than the threshold value TH 2 ) has been received from the sensor  55   y  (step S 23 ). In response to having determined the sensor signal Sy 2  to have been received (step S 23 : Yes), the controller  60  opens the valve  52   y  (step S 24 ). Next, the controller  60  determines whether the sensor signal Sy 1  (the signal indicating that ink amount of the sub-tank  53   y  is the threshold value TH 1  or more) has been received from the sensor  54   y  (step S 25 ). In response to having determined the sensor signal Sy 1  to have been received (step S 25 : Yes), the controller  60  closes the valve  52   y  (step S 26 ). 
     [Image Recording Processing] 
     The controller  60  repeatedly executes steps S 31 -S 41  in the image recording processing depicted in  FIG.  7   . At a timepoint of the controller  60  executing the step S 31 , the carriage  41  is located in the standby position, and the cap  81  is located in the covering position. The nozzle surface  43  of the head  42  is covered by the nozzle cap  82 . 
     The controller  60  receives an image recording instruction from an operating unit (not depicted) (step S 31 ). Specifically, the controller  60  waits in the step S 31  until it receives the image recording instruction. Upon receiving the image recording instruction in the step S 31 , the controller  60  closes the four valves  52   b,    52   c,    52   m,    52   y  (step S 32 ). Next, the controller  60  moves the cap  81  in a downward orientation from the covering position to the separated position (step S 33 ). 
     Next, the controller  60  moves the carriage  41  in a leftward orientation to a recording start position (step S 34 ). The recording start position is a predetermined position that the carriage  41  faces the platen  25 . Next, the controller  60  conveys the sheet S to the recording start position (step S 35 ). Note that the controller  60  may execute a step S 35  in parallel with the steps S 32 -S 34 . At a timepoint of the controller  60  having completed processing up to the step S 35 , the printer  10  is in a state where image recording can be started. 
     Next, the controller  60  executes a predetermined amount of image recording on the sheet S (step S 36 ). Specifically, the controller  60  moves the carriage  41  in the left-right direction  9 . While the carriage  41  is moving in the left-right direction  9 , the controller  60  causes ink corresponding to image data to be discharged from the nozzles  44  of the head  42 . The step S 36  is one example of a recording operation. 
     Next, the controller  60  determines whether there is image data remaining (step S 37 ). In response to having determined there to be image data remaining in the step S 37  (step S 37 : Yes), the controller  60  proceeds to a step S 38 . In this case, the controller  60  conveys the sheet S the predetermined amount (step S 38 ), and proceeds to the step S 36 . 
     In response to having determined there to be no image data remaining in the step S 37  (step S 37 : No), the controller  60  proceeds to a step S 39 . In this case, the controller  60  discharges the sheet S to a predetermined position (step S 39 ). Next, the controller  60  moves the carriage  41  in a rightward orientation to the standby position (step S 40 ). Next, the controller  60  moves the cap  81  in an upward orientation from the separated position to the covering position (step S 41 ). After that, the controller  60  proceeds to the step S 31  in order to execute the next image recording. 
     [Initial Introduction Processing] 
     At a timepoint of the printer  10  having been shipped from a factory, ink does not exist in the ink channels  56   b,    56   c,    56   m,    56   y,    57   b,    57   c,    57   m,    57   y.  Accordingly, after the printer  10  has been set in place and the cartridge holder  26  installed with the cartridges  51   b,    51   c,    51   m ,  51   y,  the controller  60  executes the initial introduction processing depicted in  FIG.  8   . The initial introduction processing is a processing by which the four colors of inks are introduced into the head  42  from the cartridges  51   b,    51   c,    51   m,    51   y.  At a timepoint of the controller  60  executing a step S 51 , the carriage  41  is located in the standby position, and the cap  81  is located in the covering position. The valves  52   b,    52   c,    52   m,    52   y  are closed, and the sub-tanks  53   b,    53   c,    53   m ,  53   y  are empty. 
     After the cartridge holder  26  has been installed with the cartridges  51   b,    51   c,    51   m ,  51   y,  the controller  60  receives an initial introduction instruction from the operating unit (step S 51 ). Specifically, the controller  60  waits in the step S 51  until it receives the initial introduction instruction. Next, the controller  60  stops the ink automatic supply processing (step S 52 ). While executing from a step S 53  to a step S 60 , the controller  60  does not execute the ink automatic supply processing depicted in  FIG.  6   . Next, the controller  60  initializes to 1 a count value N for counting number-of-times-of-suction (step S 53 ). 
     Next, the controller  60  opens the four valves  52   b,    52   c,    52   m,    52   y  (step S 54 ). Thereafter, black ink is supplied from the cartridge  51   b  to the sub-tank  53   b,  cyan ink is supplied from the cartridge  51   c  to the sub-tank  53   c,  magenta ink is supplied from the cartridge  51   m  to the sub-tank  53   m,  and yellow ink is supplied from the cartridge  51   y  to the sub-tank  53   y.  Supply of these inks is performed using water head difference. 
     Next, the controller  60  waits until ink amounts of the four sub-tanks  53   b,    53   c,    53   m ,  53   y  all become the threshold values TH 1  or more (step S 55 ). Specifically, the controller  60  waits in the step S 55  until the controller  60  respectively receives the sensor signals Sb 1 , Sc 1 , Sm 1 , Sy 1  from the sensors  54   b,    54   c,    54   m,    54   y.    
     Next, the controller  60  closes the four valves  52   b,    52   c,    52   m,    52   y  (step S 56 ). Thereafter, supply of black ink from the cartridge  51   b  to the sub-tank  53   b,  supply of cyan ink from the cartridge  51   c  to the sub-tank  53   c,  supply of magenta ink from the cartridge  51   m  to the sub-tank  53   m,  and supply of yellow ink from the cartridge  51   y  to the sub-tank  53   y  stop. 
     Next, the controller  60  performs suction by driving the pump  85  for a predetermined time (step S 57 ). While the controller  60  is executing the step S 57 , the valves  52   b,    52   c,    52   m ,  52   y  are in a closed state. The elevator member  106  (see  FIGS.  5 A and  5 B ) is located in the abutting position, and the switching portion  84  (see  FIG.  4   ) connects the pump  85  to the inner space of the exhaust cap  83 . Therefore, the ink channels  57   b,    57   c,    57   m,    57   y  are provided with a suction pressure from the head  42  side (specifically, from the exhaust portion  45 ; that is from a side, of the ink channels  57   b,    57   c,    57   m,    57   y,  at which the head  42  is connected to the ink channels  57   b,    57   c,    57   m,    57   y ), and the inks that have been stored in the sub-tanks  53   b,    53   c,    53   m ,  53   y  are respectively introduced into the ink channels  57   b,    57   c,    57   m,    57   y.  Note that the switching portion  84  (see  FIG.  4   ) may connect the pump  85  to the inner space of the nozzle cap  82  so that the inks in the sub-tanks  53   b,    53   c,    53   m,    53   y  are respectively introduced into the ink channels  57   b,    57   c,    57   m,    57   y  by a suction pressure provided via the head  42 . Further, the switching portion  84  may firstly connect the pump  85  to the inner space of the exhaust cap  83  for performing suction of the inks via the exhaust portion  45 . And then, after performing the suction via the exhaust portion  45  several times, the elevator portion  106  is lowered to the non-abutting position and the switching portion  84  may connect the pump  85  to the inner space of the nozzle cap  82  for performing additional or finishing suction of the inks via the nozzle  44  of the head  42 . 
     The pump  85  sucks a predetermined amount (that is, for example, a design value planned suction amount, each of which may be decided depending on a driving duration of the pump  85 , a viscosity of the ink, and the like) of ink by being driven for a predetermined time period. The predetermined amount is larger than volumes (capacities) of the sub-tanks  53   b,    53   c ,  53   m,    53   y  (each of which may be, for example, the difference between a volume in the expanded state and a volume in the contracted state), but smaller than volumes of the ink channels  57   b ,  57   c,    57   m,    57   y.  Specifically, the longer a moving distance in the left-right direction  9  of the carriage  41  is (in other words, the longer the width of the sheet S is), the longer lengths of the ink channels  57   b,    57   c,    57   m,    57   y  will become. Thus, the predetermined amount sucked by the pump  85  will become smaller compared to volumes of the ink channels  57   b,    57   c,    57   m,    57   y  more sufficiently. Therefore, the inks of each color that have been introduced into the ink channels  57   b,    57   c,    57   m,    57   y  will not reach the head  42  simply by the step S 57  having been executed once by the controller  60 . Accordingly, the controller  60  repeatedly executes the steps S 54 -S 57  a predetermined number-of-times-of-suctions (hereafter, referred to as M), as described below. 
     Next, the controller  60  determines whether the count value N is the predetermined number-of-times-of-suctions M or more (step S 58 ). In response to having determined the count value N is less than the number-of-times-of-suctions M in the step S 58  (S 58 : No), the controller  60  proceeds to a step S 59 . In this case, the controller  60  adds 1 to the count value N (step S 59 ), and proceeds to the step S 54  in order to execute the steps S 54 -S 57  again. 
     In response to having determined the count value N is the number-of-times-of-suctions M or more in the step S 58  step (S 58 : Yes), the controller  60  proceeds to a step S 60 . In this case, the controller  60  opens the four valves  52   b,    52   c,    52   m,    52   y  (step S 60 ). Next, the controller  60  resumes ink automatic supply that has been stopped in the step S 52  (step S 61 ), and finishes the initial introduction processing. 
     The number-of-times-of-suctions M in the step S 58  is determined such that the following expressions (1) and (2) are satisfied, for example. 
         M&gt;Q/v   (1)
 
       β×( m− 1)× V&lt;v&lt;α×m×V   (2)
 
     This is provided that, in expressions (1) and (2), Q is suction amount required during initial introduction, v is suction amount (total of suction amounts in all of the ink channels) when the pump  85  is driven once in the step S 57 , m is the number of ink channels in the ink supply unit  50 , V is volume of any one of the sub-tanks  53   b,    53   c,    53   m,    53   y,  and α and β indicate safety factors. The safety factors α and β take values greater than 0, but less than 1. 
     When the steps S 54 -S 56  are initially executed by the controller  60 , inks of amounts corresponding to the threshold values TH 1  respectively flow from the cartridges  51   b,    51   c,    51   m ,  51   y  into the sub-tanks  53   b,    53   c,    53   m,    53   y.  Subsequently, when the step S 57  is executed for the first time by the controller  60 , amounts of inks introduced into the ink channels  57   b,    57   c,    57   m ,  57   y  from the sub-tanks  53   b,    53   c,    53   m,    53   y  will differ depending on channel resistances of the ink channels  57   b,    57   c,    57   m,    57   y,  and so on. When the steps S 54 -S 56  are executed a second time and thereafter by the controller  60 , inks of amounts corresponding to the amounts of inks that were introduced into the ink channels  57   b,    57   c,    57   m,    57   y  from the sub-tanks  53   b,    53   c,    53   m ,  53   y  when the step S 57  was executed the previous time by the controller  60  will respectively flow from the cartridges  51   b,    51   c,    51   m,    51   y  into the sub-tanks  53   b,    53   c,    53   m,    53   y.    
     In the initial introduction processing, after having supplied each of the sub-tanks  53   b ,  53   c,    53   m,    53   y  with inks of not less than amounts corresponding to the threshold values TH 1 , the controller  60  drives the pump  85  in a state where supply of inks to each of the sub-tanks  53   b ,  53   c,    53   m,    53   y  from each of the cartridges  51  has been stopped. Hence, if there is a resistance difference between the ink channels  57   b,    57   c,    57   m,    57   y  and there is a difference in suction amounts between the ink channels  57   b,    57   c,    57   m,    57   y,  then, after one or more of the sub-tanks  53   b,    53   c,    53   m,    53   y  connected to one or more of the ink channels  57   b,    57   c,    57   m,    57   y  having a small channel resistance has become empty, the suction pressure of the pump  85  will be provided to the other of the ink channels  57   b,    57   c,    57   m,    57   y.  Therefore, a difference in ink amounts flowing into the head  42  through the plurality of ink channels  57   b,    57   c,    57   m,    57   y  by suction becomes smaller. 
     Let it be assumed that in the above-described embodiment, two colors differing from each other are selected from among black, cyan, magenta, and yellow, and the first letters of the English spellings of the selected two colors are set to p and q (p and q are any of b, c, m, and y). The cartridge  51   p  is one example of a first reservoir, and the cartridge  51   q  is one example of a second reservoir. The valve  52   p  is one example of a first valve, and the valve  52   q  is one example of a second valve. The sub-tank  53   p  is one example of a first tank, and the sub-tank  53   q  is one example of a second tank. The sensor  54   p  is one example of a first sensor and a first signal outputting sensor, and the sensor  54   q  is one example of a second sensor and a second signal outputting sensor. The sensor  55   p  is one example of the first senor and a third signal outputting sensor, and the sensor  55   q  is one example of the second sensor and a fourth signal outputting sensor. The sensors  54   p  and  55   p  may be single (or integrated) sensor, and the sensors  54   q  and  55   q  may be single (or integrated) sensor. The threshold value TH 1  relating to the sensor  54   p  is one example of a first threshold value, and the threshold value TH 1  relating to the sensor  54   q  is one example of a second threshold value. The threshold value TH 2  relating to the sensor  55   p  is one example of a third threshold value, and the threshold value TH 2  relating to the sensor  55   q  is one example of a fourth threshold value. The ink channel  56   p  is one example of a channel connecting the first reservoir and the first tank, and the ink channel  56   q  is one example of a channel connecting the second reservoir and the second tank. The ink channel  57   p  is one example of a first channel, and the ink channel  57   q  is one example of a second channel. 
     In  FIG.  6   , the controller  60  opens the valve  52   p  in response to receiving the sensor signal Sp 2  from the sensor  55   p,  and closes the valve  52   p  in response to receiving the sensor signal Sp 1  from the sensor  54   p  subsequently to having received the sensor signal Sp 2 . This operation is one example of a first valve opening and closing operation. The controller  60  opens the valve  52   q  in response to receiving the sensor signal Sq 2  from the sensor  55   q,  and closes the valve  52   q  in response to receiving the sensor signal Sq 1  from the sensor  54   q  subsequently to having received the sensor signal Sq 2 . This operation is one example of a second valve opening and closing operation. 
     In  FIG.  8   , the initial introduction instruction is one example of a suction instruction, the step S 54  is one example of a valve-opening operation, the step S 56  is one example of a valve-closing operation, and the step S 57  is one example of a suction operation. In response to having received the initial introduction instruction in the step S 51 , the controller  60  executes the valve-opening operation to open the valves  52   b,    52   c,    52   m,    52   y  in the step S 54 . Subsequently to having executed the valve-opening operation and in response to having received from the sensors  54   b,    54   c,    54   m,    54   y  a sensor signal indicating ink amount of the sub-tanks  53   b,    53   c ,  53   m,    53   y  to be the threshold value TH 1  or more, the controller  60  executes the valve-closing operation to close the valves  52   b,    52   c,    52   m,    52   y.  Subsequently to having executed the valve-closing operation, the controller  60  executes the suction operation to drive the pump  85  for the predetermined time period. 
     Effects of Embodiments 
     In the printer  10  and ink supply unit  50  according to the above-described embodiment, in the case that suction is performed to introduce ink into the plurality of ink channels  56   b,    56   c,    56   m,    56   y  and plurality of ink channels  57   b,    57   c,    57   m,    57   y  connecting the plurality of cartridges  51  and the head  42 , the pump  85  is driven in a state where the ink of not less than a predetermined amount has been supplied to each of the sub-tanks  53   b,    53   c,    53   m,    53   y  and supply of ink to each of the sub-tanks  53   b,    53   c,    53   m,    53   y  from each of the cartridges  51  then has been stopped. Therefore, difference in ink amounts flowing into the head  42  through the plurality of ink channels  57   b,    57   c,    57   m,    57   y  by suction becomes smaller. 
     The controller  60  executes the valve-opening operation after executing the suction operation. Hence, after the suction operation has been executed, ink will be supplied to each of the sub-tanks  53   b,    53   c,    53   m,    53   y.  The controller  60  opens the corresponding one of the valves  52   b,    52   c,    52   m,    52   y  in response to receiving from one of the sensors  55   b,    55   c,    55   m,    55   y  a sensor signal indicating ink amount of one of the sub-tanks  53   b,    55   c,    55   m,    55   y  is less than the threshold value TH 2 . Hence, when ink amount of each of the sub-tanks  53   b,    53   c,    53   m,    53   y  becomes less than a designated amount, ink will be supplied to each of the sub-tanks  53   b,    53   c ,  53   m,    53   y.    
     In response to receiving the initial introduction instruction, the controller  60  repeatedly executes the valve-opening operation, the valve-closing operation, and the suction operation the predetermined number-of-times-of-suctions M (one example of a predetermined number of times). Hence, a required amount of ink can be introduced into each of the ink channels  57 . After having repeatedly executed the valve-opening operation, the valve-closing operation, and the suction operation the number-of-times-of-suctions M, the controller  60  executes the valve-opening operation. Hence, after the valve-opening operation, the valve-closing operation, and the suction operation have been repeatedly executed, ink will be supplied to each of the sub-tanks  53 . 
     The controller  60  executes the image recording operation in a state of the valves  52   b ,  52   c,    52   m,    52   y  having been closed. The controller  60  executes the first valve opening and closing operation and the second valve opening and closing operation, and, in response to receiving the initial introduction instruction, does not execute (that is, stops) the first valve opening and closing operation and the second valve opening and closing operation until execution of the suction operation has been completed. Hence, even in the case of automatic supply of inks from each of the cartridges  51  to each of the sub-tanks  53   b,    53   c,    53   m,    53   y  being performed, automatic supply of the inks will be stopped and each of the valves  52   b,    52   c,    52   m ,  52   y  will be closed until execution of the suction operation is completed. 
     While the invention has been described in conjunction with various example structures outlined above and illustrated in the figures, various alternatives, modifications, variations, improvements, and/or substantial equivalents, whether known or that may be presently unforeseen, may become apparent to those having at least ordinary skill in the art. Accordingly, the example embodiments of the disclosure, as set forth above, are intended to be illustrative of the invention, and not limiting the invention. Various changes may be made without departing from the spirit and scope of the disclosure. Therefore, the disclosure is intended to embrace all known or later developed alternatives, modifications, variations, improvements, and/or substantial equivalents. Some specific examples of potential alternatives, modifications, or variations in the described invention are provided below: 
     Modified Example 
     Various kinds of modified examples may be configured for the printer  10  and controller  60  according to the above-described embodiment. In the above-described embodiment, controller  60  executes the initial introduction processing depicted in  FIG.  8   . In a modified example, a controller  60  executes an initial introduction processing depicted in  FIG.  9   . 
     The initial introduction processing depicted in  FIG.  9    is the initial introduction processing depicted in  FIG.  8    to which a step S 71  and a step S 74  have been added and in which the step S 54  and the step S 56  have been respectively replaced by a step S 72  and a step S 73 . The controller  60  according to the modified example uses four flags Fb, Fc, Fm, Fy respectively corresponding to black, cyan, magenta, and yellow to execute the initial introduction processing. Each of the flags Fb, Fc, Fm, Fy is cleared in a state where introduced amount of the ink of corresponding color is insufficient, and is set in a state where introduced amounts of the ink of corresponding color is sufficient. The flags Fb, Fc, Fm, Fy are stored in the RAM  63  (see  FIG.  3   ). 
     After executing the step S 51  and the step S 52 , the controller  60  clears the four flags Fb, Fc, Fm, Fy (step S 71 ). After executing the step S 53  or the step S 59 , the controller  60  opens valves corresponding to cleared flags, of the valves  52   b,    52   c,    52   m,    52   y  (step S 72 ). If, for example, the flags Fb, Fy are cleared and the flags Fc, Fm are set, then in the step S 72 , the controller  60  will open the valves  52   b,    52   y  and leave closed the valves  52   c,    52   m.    
     After executing the step S 55 , the controller  60  closes valves that are open, of the valves  52   b,    52   c,    52   m,    52   y  (step S 73 ). After executing the step S 57 , the controller  60  sets flags of colors whose ink introduction amounts are sufficient, of the flags Fb, Fc, Fm, Fy (step S 74 ). In the step S 74 , the controller  60  determines whether ink introduction amounts of each of the colors are sufficient, based on the sensor signals Sb 1 , Sc 1 , Sm 1 , Sy 1 , Sb 2 , Sc 2 , Sm 2 , Sy 2  respectively outputted from the sensors  54   b,    54   c,    54   m,    54   y,    55   b,    55   c,    55   m,    55   y.  For example, the controller  60  will set the flag Fb in response to a determination that introduction amount of black ink has become sufficient by the step S 57  executed immediately priorly. 
     In the controller  60  according to the modified example, after executing the valve-opening operation, the valve-closing operation, and the suction operation a certain number of times which is fewer than the predetermined number-of-times-of-suctions M, the controller  60  keeps at least one of the valves  52   b,    52   c,    52   m,    52   y  in a closed state in the valve-opening operation. Hence, this modified example results in that, for a channel where introduction of ink has been completed, supply of ink from the cartridge  51  to the corresponding one of the sub-tanks  53   b,    53   c,    53   m,    53   y  can be stopped and needless discharge of ink thereby prevented. 
     In the above-described embodiment, the printer  10  is configured to comprise one head  42 . However, the printer  10  may comprise two or more heads  42 . In the above-described embodiment, the ink supply unit  50  of the printer  10  is configured to comprise four ink channels. However, the printer  10  may comprise two, three, or five or more ink channels.