Patent Publication Number: US-10773524-B2

Title: Liquid discharge apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application claims priority from Japanese Patent Application No. 2018-182380, filed on Sep. 27, 2018, the disclosure of which is incorporated herein by reference in its entirety. 
     BACKGROUND 
     Field of the Invention 
     The present disclosure relates to a liquid discharge apparatus having a supply channel and a return channel. 
     Description of the Related Art 
     Conventionally, there is a publicly known technique for circulating an ink in a direction which is reverse to a direction adopted during printing, in an ink-jet recording head of a circulation type during maintenance performed therefor. 
     However, only by circulating the ink in the reverse direction, it is not possible to remove any air bubble inside the channel (in particular, an air bubble in the vicinity of a nozzle in an individual channel), in some cases. 
     An object of the present disclosure is to provide a liquid discharge apparatus capable of removing the air bubble more assuredly. 
     According to an aspect of the present disclosure, there is provided a liquid discharge apparatus including: a plurality of individual channels in which a plurality of nozzles are opened, respectively; a supply channel communicating with an outlet port of a storage chamber storing a liquid and with an inlet port of each of the plurality of individual channels; a return channel communicating with an outlet port of each of the plurality of individual channels and with an inlet port of the storage chamber; an open/close valve which is provided on the supply channel and which is switchable between an open position allowing communication between the storing chamber and the plurality of individual channels via the supply channel and a close position suppressing the communication; a pump provided on the return channel; and a controller. In a case that an air bubble is removed, the controller is configured to control the open/close valve and the pump so as to execute: circulation of the liquid along a circulation route starting from, and returning to, the storing chamber via the supply channel, the plurality of individual channels and the return channel by maintaining the open/close valve at the open position and driving the pump; and then moving of the liquid from the storing chamber to the plurality of individual channels via the return channel and exhausting of the liquid from the plurality of nozzles of the plurality of individual channels, respectively, by maintaining the open/close valve at the close position and driving the pump. 
     According to another aspect of the present disclosure, there is provided a liquid discharge apparatus including: a plurality of individual channels which include a plurality of nozzles, respectively; a supply channel communicating with an outlet port of a storage chamber storing a liquid and with an inlet port of each of the plurality of individual channels; a return channel communicating with an outlet port of each of the plurality of individual channels and an inlet port of the storage chamber; a check valve which is provided on the supply channel and which is configured to allow a flow of the liquid from the storing chamber to the plurality of individual channels via the supply channel and to suppress a flow of the liquid from the plurality of individual channels to the storing chamber via the supply channel; a pump provided on the return channel; and a controller. In a case that the controller removes an air bubble, the controller is configured to control the pump so as to execute: circulation of the liquid along a circulation route starting from, and returning to, the storing chamber via the supply channel, the plurality of individual channels and the return channel, by driving the pump; and then moving of the liquid from the storing chamber to the plurality of individual channels via the return channel and exhausting of the liquid from the plurality of nozzles of the plurality of individual channels, respectively, by driving the pump. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a plan view of a printer  100 . 
         FIG. 2  is a plan view of a head  1  included in the printer  100 . 
         FIG. 3  is a cross-sectional view of the head  1  along a line in  FIG. 2 . 
         FIG. 4  is a block diagram depicting the electrical configuration of the printer  100 . 
         FIG. 5  is a flow chart depicting an air-bubble removing processing executed by a controller  10  of the printer  100 . 
         FIG. 6A  is a view corresponding to  FIG. 3  and depicting a situation during a purge step, and  FIG. 6B  is a view corresponding to  FIG. 3  and depicting a situation during a return purge step. 
         FIG. 7  is a view corresponding to  FIG. 3  and according to a second embodiment. 
         FIG. 8  is a flow chart depicting an air-bubble removing processing according to the second embodiment. 
         FIG. 9  is a flow chart depicting an air-bubble removing processing according to a third embodiment. 
     
    
    
     DESCRIPTION OF THE EMBODIMENT 
     First Embodiment 
     Firstly, the configuration of a printer  100  according to a first embodiment will be explained, with reference to  FIG. 1 . 
     The printer  100  has a head unit  1   x  which includes four heads  1 ; a platen  3 ; a conveying mechanism  4 ; a cap unit  6   x ; and a controller  10 . 
     The conveying mechanism  4  has two pairs of rollers  4   a  and  4   b  which are arranged in a conveyance direction (direction orthogonal to the vertical direction) with the platen  3  intervened therebetween. In a case that a conveyance motor  4   m  (see  FIG. 4 ) is driven, the pairs of rollers  4   a  and  4   b  are thereby rotated in a state that each of the pairs of rollers  4   a  and  4   b  hold a paper sheet  9  (paper  9 ) therebetween so as to convey the paper sheet  9  in the conveyance direction. 
     The head unit  1   x  is an ink-jet head of a line system, and is elongated in a paper width direction which is a direction orthogonal to the vertical direction and the conveyance direction. Note that the term “ink-jet head of the line system” means an ink-jet head of such a system wherein an ink is discharged or jetted toward the paper sheet  9  from a plurality of nozzles  33   d  (see  FIGS. 2 and 3 ) in a state that the position of the ink-jet head is fixed. The four heads  1  are arranged in a staggered manner in the paper width direction. The lower surface of each of the heads  1  is a nozzle surface  25   a  formed with the plurality of nozzles  33   d  (see  FIG. 3 ). 
     Further, the head unit  1   x  is driven by a head moving motor  1   m  (see  FIG. 4 ) to be movable in the paper width direction between a position at which the four heads  1  overlap, in the vertical direction, with the platen  3  (recording position: see  FIG. 1 ) and a position at which the four heads  1  overlap, in the vertical direction, with the four caps  6 , respectively (stand-by position). 
     The platen  3  is a member having a shape of a flat plate, and is arranged at a position below the head unit  1   x  which is at the recording position, and between the two pairs of rollers  4   a  and  4   b  in the conveyance direction. The paper sheet  9  is placed on the upper surface of the platen  3 . 
     The cap unit  6   x  is located on a side opposite to the head unit  1   x , with respect to the platen  3 , in the paper width direction; the cap unit  6   x  includes the four caps  6  corresponding to the four heads  1 , respectively, of the head unit  1   x . Each of the caps  6  has an annular-shaped lip part  6   a  which is formed of an elastic body. Further, a suction pump P 3  (see  FIG. 4 ) is connected to the four caps  6 . The four caps  6  are communicated with a waste ink tank (not depicted in the drawings) via the suction pump P 3 . 
     Further, the cap unit  6   x  is movable in the vertical direction by being driven by a cap moving motor  6   m  (see  FIG. 4 ). In a case that the head unit  1   x  is at the stand-by position, the cap unit  6   x  is moved in the vertical direction to thereby allow each of the caps  6  to assume (to be arranged at) a position at which the lip part  6   a  is located at a position below the nozzle surface  25   a  and does not cover the nozzle surface  25   a  (uncapping position), and a position at which the lip part  6   a  makes contact with the nozzle surface  25   a  and covers the nozzle surface  25   a  (capping position). In a case that the each of the caps  6  is at the capping position, each of the caps  6  covers all the plurality of nozzles  33   d  of one of the heads  1 . In a case that the suction pump P 3  (see  FIG. 4 ) is driven in this situation, suction force is generated in the inside of each of the caps  6 , which in turn causes the ink inside all the plurality of nozzles  33   d  in the inside of one of the heads  1  to be exhausted (discharged) to the waste ink tank (not depicted in the drawings). 
     The controller  10  has a ROM (Read Only Memory), a RAM (Random Access Memory), and an ASIC (Application Specific Integrated Circuit). The ASIC performs a recording processing, an air-bubble removing processing, etc., in accordance with programs stored in the ROM. In the recording processing, the controller  10  controls a driver IC  1   d  of each of the heads  1  and the conveyance motor  4   m  (for both of which, see  FIG. 4 ) based on a recording instruction, image data, etc., inputted to the controller  10  from an external apparatus or device such as a PC (Personal Computer) to thereby record an image, etc., on the paper sheet  9 . Note that there is such a case that the recording instruction and the image data are inputted separately from each other, and there is also such a case that the image data is included in the recording instruction. 
     Next, the configuration of each of the heads  1  will be explained. 
     As depicted in  FIG. 3 , each of the heads  1  has a channel unit  20  including four plates  21 ,  23 ,  24  and  25  and a plate unit  22 , and four actuators  40 . The four plates  21  and  23  to  25  and the plate unit  22  are adhered to one another in a state that the four plates  21  and  23  to  25  and the plate unit  22  are stacked on one another in the vertical direction. 
     The plate  25  is located on the lowermost side among the four plates  21  and  23  to  25  and the plate unit  22 . The plate  25  has a plurality of through holes constructing the plurality of nozzles  33   d , respectively. The lower surface of the plate  25  corresponds to the nozzle surface  25   a.    
     The plate  24  is arranged on the upper surface of the plate  25 . The plate  24  has a plurality of through holes constructing a plurality of pressure chambers  33   c , respectively. Each of the pressure chambers  33   c  are formed for one of the nozzles  33   d . Each of the nozzles  33   d  is overlapped, in the vertical direction, with a central part or portion in the paper width direction and of the conveyance direction of one of the pressure chambers  33   c.    
     Sets or pairs each of which constructed of one piece of the nozzles  33   d  and one piece of the pressure chambers  33   c  are aligned in the paper width direction, as depicted in  FIG. 2 , so as to form four rows R 1  to R 4 . The four rows R 1  to R 4  are arranged side by side to one another in the conveyance direction. The four actuators  40  are provided to correspond to these four rows R 1  to R 4 , respectively. A black ink is discharged from nozzles  33   d  included in the plurality of nozzles  33   d  and belonging to the row R 1  which is the first row, among the four rows R 1  to R 4 , from the upstream side in the conveyance direction. A yellow ink is discharged from nozzles  33   d  included in the plurality of nozzles  33   d  and belonging to the row R 2  which is the second row, among the four rows R 1  to R 4 , from the upstream side in the conveyance direction. A cyan ink is discharged from nozzles  33   d  included in the plurality of nozzles  33   d  and belonging to the row R 3  which is the third row, among the four rows R 1  to R 4 , from the upstream side in the conveyance direction. A magenta ink is discharged from nozzles  33   d  included in the plurality of nozzles  33   d  and belonging to the row R 4  which is the fourth row, among the four rows R 1  to R 4 , from the upstream side in the conveyance direction. 
     A vibration film  26  is arranged on the upper surface of the plate  24 , as depicted in  FIG. 3 . The vibration film  26  covers the plurality of pressure chambers  33   c . Through holes constructing inflow paths  33   b , respectively, are formed in the vibration film  26  at parts thereof which overlap, in the vertical direction, with downstream-side end parts in the conveyance direction of the pressure chambers  33   c  belonging to the rows R 1  and R 2 , respectively (see  FIG. 2 ); further, through holes constructing the inflow paths  33   b , respectively, are formed in the vibration film  26  at parts thereof which overlap, in the vertical direction, with upstream-side end parts in the conveyance direction of the pressure chambers  33   c  belonging to the rows R 3  and R 4 , respectively (see  FIG. 2 ). Furthermore, through holes constructing outflow paths  33   e , respectively, are formed in the vibration film  26  at parts thereof which overlap, in the vertical direction, with upstream-side end parts in the conveyance direction of the pressure chambers  33   c  belonging to the rows R 1  and R 2 , respectively (see  FIG. 2 ); further, through holes constructing the outflow paths  33   e , respectively are formed in the vibration film  26  at parts thereof which overlap, in the vertical direction, with downstream-side end parts in the conveyance direction of the pressure chambers  33   c  belonging to the rows R 3  and R 4 , respectively (see  FIG. 2 ). The vibration film  26  is formed, for example, by oxidizing the upper surface of the plate  24 . For example, the vibration film  26  can be composed of silicon dioxide (SiO 2 ). 
     The plate  23  is arranged on the upper surface of the vibration film  26 . As depicted in  FIGS. 2 and 3 , through holes constructing inflow paths  33   a , respectively, are formed in the plate  23  at parts thereof which overlap, in the vertical direction, with the inflow paths  33   b , respectively; and through holes constructing outflow paths  33   f , respectively, are formed in the plate  23  at parts thereof which overlap, in the vertical direction, with the outflow paths  33   e , respectively. As depicted in  FIG. 3 , the lower surface of the plate  23  is formed with four recessed parts  23   x  accommodating the four actuators  40 , respectively. Each of the actuators  40  is arranged in a space defined by the vibration film  26  and one of the recessed parts  23   x.    
     Each of the actuators  40  has a common electrode  42  arranged on the upper surface of the vibration film  26 , a piezoelectric body  41  arranged on the upper surface of the common electrode  42 , and a plurality of individual electrodes  43  arranged on the upper surface of the piezoelectric body  41 . The piezoelectric body  41  and the common electrode  42  extend in the paper width direction so as to straddle over (cover) the pressure chambers  33   c  belonging to each of the rows R 1  to R 4 . Each of the individual electrodes  43  is provided with respect to one of the pressure chambers  33   c , and overlaps with one of the pressure chambers  33   c  in the vertical direction. 
     The common electrode  42  and the plurality of individual electrodes  43  are electrically connected to the driver IC  1   d  (see  FIG. 4 ). The driver IC  1   d  is controlled by the controller  10  such that the driver IC  1   d  maintains the potential of the common electrode  42  to the ground potential while changing the potential of the individual electrodes  43 . Specifically, the driver IC  1   d  generates a driving signal based on a control signal from the controller  10 , and applies the driving signal to a certain individual electrode  43  included in the plurality of individual electrodes  43 . With this, the potential of the certain individual electrode  43  is changed between a predetermined driving potential and the ground potential. In this situation, parts or portions of the vibration plate and the piezoelectric body  41 , respectively, which are sandwiched between the certain individual electrode  43  and a certain pressure chamber  33   c  included in the plurality of pressure chambers  33   c  and corresponding to the certain individual electrode  43  are deformed to project toward the certain pressure chamber  33   c , thereby changing the volume of the certain pressure chamber  33   c  and imparting the pressure to the ink inside the certain pressure chamber  33   c , which in turn cause the ink to be discharged from a nozzle  33   d  included in the plurality of nozzles  33   d  and corresponding to the certain pressure chamber  33   c.    
     The plates  23  to  25  and the vibration film  26  are formed with a plurality of individual channels  33  each of which is constructed of the inflow paths  33   a ,  33   b , the pressure chamber  33   c , the nozzle  33   d  and the outflow paths  33   e  and  33   g . Each of the individual channels  33  has a shape which is symmetric in the conveyance direction with respect to a straight line along the vertical direction and passing through the nozzle  33   d.    
     The plate unit  22  is arranged on the upper surface of the plate  23 . The plate unit  22  is formed with four supply common channels  31   d  and four return common channels  32   d . As depicted in  FIG. 2 , a pair or set constructed of one supply common channel  31   d  and one return common channel  32   d  is provided on each of the four rows R 1  to R 4 . The supply common channel  31   d  and the return common channel  32   d  belonging to one set are arranged side by side to each other in the conveyance direction. Between the rows R 1  and R 2  and the rows R 3  and R 4 , the arrangement of the supply common channel  31   d  and the return common channel  32   d  is opposite. Namely, in the rows R 1  and R 2 , the return common channel  32   d  is arranged on the upstream side in the conveyance direction and the supply common channel  31   d  is arranged on the downstream side in the conveyance direction; in the rows R 3  and R 4 , the supply common channel  31   d  is arranged on the upstream side in the conveyance direction and the return common channel  32   d  is arranged on the downstream side in the conveyance direction. Each of the supply common channels  31   d  extends in the paper width direction, and overlaps, in the vertical direction, with the inflow paths  33   a  communicating with the pressure chambers  33   c , respectively, belonging to one of the rows R 1  to R 4 . Each of the return common channels  32   d  extends in the paper width direction, and overlaps, in the vertical direction, with the outflow paths  33   f  communicating with the pressure chambers  33   c , respectively, belonging to one of the rows R 1  to R 4 . 
     As described above, channel groups corresponding to the four color inks, respectively, are formed in the channel unit  20  so as to correspond to the four rows R 1  to R 4 , respectively. Each of the channel groups includes the plurality of individual channels  33 , the supply common channel  31   d  and the return common channel  32   d.    
     As depicted in  FIG. 3 , the plate unit  22  is constructed of three plates  22   a  to  22   c  which are stacked on top of one another in the vertical direction and adhered to one another. The supply and return common channels  31   d  and  32   d  are formed across and through the three plates  22   a  to  22   d . The plate  22   b  included in the three plates  22   a  to  22   d  and located in the center in the vertical direction is provided with filters F 1  and F 2  which are disposed in through holes constructing the supply and return common channels  31   d  and  32   d , respectively. 
     Each of the filters F 1  and F 2  is, for example, an electroformed filer, a mesh filter, etc., and a plurality of fine through holes are formed in the entire area of each of the filters F 1  and F 2 . As compared with the mesh filter, the electroformed filter can be produced highly precisely, and has finely formed holes, and has a high filtration performance. For example, each of the through holes in the electroformed filter has a diameter which is approximately 10 μm, whereas each of the through holes in the mesh filter has a diameter which is approximately 20 μm. 
     The plate  21  is arranged on the upper surface of the plate unit  22 . Supply holes  31   x  are formed in the plate  21  at parts or portions thereof each of which overlaps, in the vertical direction, with one end in the paper width direction of one of the supply common channels  31   d ; and return holes  32   x  are formed in the plate  21  at parts or portions thereof each of which overlaps, in the vertical direction, with one end in the paper width direction of one of the return common channels  32   d.    
     The plurality of individual channels  33 , the supply common channel  31   d  and the return common channel  32   d  belonging to each of the rows R 1  to R 4  are communicated with a storing chamber  7   a  of a sub tank  7 , via one of the supply holes  31   x  and one of the return holes  32   x . The sub tank  7  is provided as sub tanks  7  which are provided on the rows R 1  to R 4 , respectively, and store the respective color inks in the storing chambers  7   a  thereof, respectively. Specifically, a sub tank  7  storing the black ink is provided with respect to the row R 1 ; a sub tank  7  storing the yellow ink is provided with respect to the row R 2 ; a sub tank  7  storing the cyan ink is provided with respect to the row R 3 ; and a sub tank  7  storing the magenta ink is provided with respect to the row R 4 . 
     Four main tanks (not depicted in the drawings) configured to store the black, yellow, cyan and magenta inks, respectively, are installed in the printer  100 . The sub tank  7  provided with respect to the row R 1  communicates with the main tank storing the black ink, and stores the black ink supplied from the main tank in the storing chamber  7   a ; the sub tank  7  provided with respect to the row R 2  communicates with the main tank storing the yellow ink, and stores the yellow ink supplied from the main tank in the storing chamber  7   a ; the sub tank  7  provided with respect to the row R 3  communicates with the main tank storing the cyan ink, and stores the cyan ink supplied from the main tank in the storing chamber  7   a ; and the sub tank  7  provided with respect to the row R 4  communicates with the main tank storing the magenta ink, and stores the magenta ink supplied from the main tank in the storing chamber  7   a.    
     In the following, the relationship between the sub tanks  7  belonging to the row R 1  to R 4 , respectively, and the plurality of individual channels  33 , etc., will be explained. 
     An outlet port  7   ay  of the storing chamber  7   a  is connected to inlet ports  33   x  of the plurality of individual channels  33 , via the supply channel  31 . The inlet ports  33   x  correspond to an upper end of the inflow channel  33   a . The supply channel  31  has a channel  31   a  having one end connected to the outlet port  7   ay  and the other end connected to a supply pump P 1 ; a channel  31   b  having one end connected to the supply pump P 1  and the other end connected to an open/close valve V 1 ; a channel  31   c  having one end connected to the open/close valve V 1  and the other end connected to the supply common channel  31   d  via the supply port  31   x ; and the supply common channel  31   d.    
     An inlet port  7   ax  of the storing chamber  7   a  is connected to outlet ports  33   y  of the plurality of individual channels  33 , via the return channel  32 . The outlet ports  33   y  correspond to an upper end of the outflow path  33   f . The return channel  32  has a channel  32   a  having one end connected to the inlet port  7   ax  and the other end connected to a return pump P 2 ; a channel  32   c  having one end connected to the return pump P 2  and the other end connected to the return common channel  32   d  via the return hole  32   x ; and the return common channel  32   d.    
     The channels  31   a ,  31   b ,  31   c ,  32   a  and  32   c  are defined by tubes, etc., respectively. 
     The open/close valve V 1  is controlled by the controller  10  to be thereby switched between an open position in which the open/close valve V 1  allows communication between the storing chamber  7   a  and the plurality of individual channels via the supply channel  31 , and a close position in which the open/close valve V 1  suppresses the above-described communication. The supply pump P 1  is driven by being controlled by the controller  10 , and applies pressure in a direction from the outlet port  7   ay  of the storing chamber  7   a  toward the supply hole  31   x  to the ink to thereby move the ink from the storing chamber  7   a  to each of the plurality of individual channels  33  via the supply channel  31 . The return pump P 2  is driven by being controlled by the controller  10 , and applies pressure in a direction from the inlet port lax of the storing chamber  7   a  toward the return hole  32   x  to the ink to thereby move the ink from the storing chamber  7   a  to each of the plurality of individual channels  33  via the return channel  32 . It is possible to adopt pumps, in which any pulsatory motion hardly occurs (for example, pumps provided with regulators configured to adjust the pressure), in view of applying a desired pressure, as the supply pump P 1  and the return pump P 2 , respectively. 
     The open/close valve V 1 , the supply pump P 1  and the return pump P 2  are provided with respect to each of the rows R 1  to R 4 , similarly to the sub tank  7 . 
     Arrows in  FIG. 3  indicate flow of the ink in a case that the open/close valve  1  is at the open position, that the supply pump P 1  is driven, and that the driving of the return pump P 2  is stopped. In this situation, the ink inside the storing chamber  7   a  flows out of the outflow port  7   ay , passes through the channels  31   a  to  31   c , further flows through the supply common channel  31   d , and reaches each of the individual channels  33 . The ink inflowed from the inlet port  33   x  into each of the individual channels  33  passes through the inflow paths  33   a  and  33   b , enters into each of the pressure chambers  33   c , a part of the ink is exhausted (discharged) from one of the nozzles  33   d , remainder of the ink passes through the outflow paths  33   e  and  33   f  and flows out from the outlet port  33   y . The ink flowed out from each of the individual channels  33  via the outlet port  33   y  passes through the return common channel  32   d , further passes through the channels  32   c  and  32   a , and returns to the storing chamber  7   a  from the inlet port lax. By allowing the ink to circulate along a circulation route starting from and returning to the storing chamber  7   a  via the supply channel  31 , the plurality of individual channels  33  and the return channel  32  in the above-described manner, it is possible to exhaust any air bubbles inside each of the individual channels  33  and to prevent any increase in the viscosity of the ink. Further, in a case that the ink contains a sediment component (a component which might sediment or settle; a pigment, etc.), such a sediment component is agitated, which in turn prevents any sedimentation thereof from occurring. 
     Next, referring to  FIG. 5 , an explanation will be given about an air-bubble removing processing of removing air bubbles executed by the controller  10 . In a case that the power source of the printer  100  is switched ON, the controller  10  executes the air-bubble removing processing as described below, before executing a recording processing. 
     At a time of starting the air-bubble removing processing, the head unit  1   x  is arranged at a position (stand-by position) at which the four heads  1  overlap, in the vertical direction, with four caps  6  (see  FIG. 1 ), respectively. It is allowable that each of the cap units  6   x  is arranged at the capping position, or that each of the cap units  6   x  is not arranged at the capping position. Namely, it is allowable that the lip part  6   a  makes contact with the nozzle surface  25   a , or that the rip part  6   a  does not make contact with the nozzle surface  25   a . In the air-bubble removing processing, the ink exhausted from the nozzles  33   d  in the air-bubble removing processing is received by each of the caps  6 . 
     Further, at the time of starting the air-bubble removing processing, the open/close valve V 1  is at the close position. 
     The air-bubble removing processing is executed regarding a color (color ink) selected among the four colors (four color inks) which are the black, yellow, cyan and magenta (inks). For example, it is allowable that the frequency at which the air-bubble removing processing is performed is allowed to be different between the black ink and color inks (yellow, cyan and magenta inks). In such a case, it is allowable that time intervals at which the air-bubble removing processing is executed with respect to the colors (color inks), respectively, are previously stored in the ROM, and that the color (color ink) for which the air-bubble removing processing is to be executed is selected based on the time intervals stored in the ROM. In this situation, it is allowable that all the four colors (four color inks) are selected, or that one to three color(s) (one to three color ink(s)) are/is selected among the four color inks. The controller  10  controls the open/close valve V 1  and the supply pump P 1  and the return pump P 2  corresponding to a selected color (color ink) in the following manner, and to execute the air-bubble removing processing. 
     Firstly, the controller  10  performs a pre-purge step. In the pre-purge step, the controller  10  drives both of the supply pump P 1  and the return pump P 2  (step S 1 ), immediately thereafter switches the open/close valve V 1  from the close position to the open position (step S 2 ). With this, as depicted in  FIG. 6A , the ink is moved from the storing chamber  7   a  to each of the plurality of individual channels  33  via the supply channel  31 , and the ink is moved from the storing chamber  7   a  to each of the individual channels  3  via the return channel  32 , thereby exhausting ink I from the nozzle  33   d  of each of the plurality of individual channels  33 . 
     The pressure of each of the supply pump P 1  and the return pump P 2  in step S 1  is, for example, about 80 kPa. 
     In the supply channel  31 , the open/close valve V 1  is switched from the close position to the open position in a state that the pressure generated by the supply pump P 1  acts on the supply channel  31  in step S 1 . With this, a large pressure acts on the supply channel  31  at once. With this, it is possible to exhaust any foreign matter (air bubble, dust, etc.) together with the ink I from the nozzle  33   d , in a small waste liquid amount as compared with a case of allowing the pressure to act on the supply channel  31  gradually. 
     After the pre-purge step, the controller  10  performs a circulating step. In the circulating step, the controller  10  maintains the open position of the open/close valve V 1  and the driving of the supply pump P 1 , and stops the driving of the return pump P 2  (step S 3 ). With this, as depicted in  FIG. 3 , the ink is circulated along the circulation route starting from and returning to the storing chamber  7   a  via the supply channel  31 , the plurality of individual channels  33  and the return channel  32 . 
     The circulating step is performed not only during the air-bubble removing processing but also during the recording processing. The controller  10  makes the pressure of the supply pump P 1  in the circulating step (step S 3 ) during the air-bubble removing processing to be greater than the pressure of the supply pump P 1  (for example, approximately in a range of 10 Pa to 20 Pa) in the circulating step during the recording processing. Specifically, the controller  10  makes the pressure of the supply pump P 1  in the circulating step (step S 3 ) during the air-bubble removing processing to be greater, for example, than withstanding pressure of meniscus in the nozzle  33   d  (for example, approximately in a range of 4 kPa to 5 kPa). The pressure of the pump P 1  in step S 3  is, for example, about 80 kPa. 
     In the circulating step, the air bubbles flow together with the ink along the circulation route, and an air bubble A might remain in the inside of the return channel  32  (see  FIG. 3 ). In particular, the air bubble A cannot pass through the filter F 2  at the upstream side of the filter F 2  in the return common channel  32   d , and the remaining air bubble A is likely to become large-sized. 
     After the circulating step, the controller  10  performs a return purge step. In the return purge step, the controller  10  stops the driving of the supply pump P 1 , and switches the open/close valve V 1  from the open position to the close position (step S 4 ). After step S 4 , the controller  10  maintains the stopping of driving of the supply pump P 1  and the close position of the open/close valve V 1 , and drives the return pump P 2  (step S 5 ). With this, as depicted in  FIG. 6B , the ink is moved from the storing chamber  7   a  to the plurality of individual channels  33  via the return channel  32 . With this, the ink I is exhausted (discharged) from the nozzles  33   d  of the plurality of individual channels  33 . 
     Note that the open/close valve V 1  is made to be at the close position in steps S 4  and S 5  for the following reason: namely, in a case that the return pump P 2  is driven while allowing the open/close valve V 1  to be at the open position, there is such a possibility that the air bubble A might flow to the supply channel  31 ; the open/close valve V 1  is made to be at the close position for avoiding such a possibility. 
     The pressure of the return pump P 2  in step S 5  is, for example, about 80 kPa. 
     In the return purge step, the air bubble A remaining inside the return channel  32  is moved together with the ink, and is moved toward the nozzle  33   d . This air bubble A is exhausted (discharged) from the nozzle  33   d  together with the ink I (see  FIG. 6B ). 
     After the return purge step, the controller  10  performs a post-purge step. In the post-purge step, the controller  10  drives both of the supply pump P 1  and the return pump P 2  (step S 6 ), and immediately thereafter switches the open/close valve V 1  from the close position to the open position (step S 7 ). With this, similarly to the pre-purge step, as depicted in  FIG. 6A , the ink is moved from the storing chamber  7   a  to each of the plurality of individual channels  33  via the supply channel  31 , and the ink is moved from the storing chamber  7   a  to each of the individual channels  3  via the return channel  32 , thereby exhausting ink I from the nozzle  33   d  of each of the plurality of individual channels  33 . 
     In the pre-purge step, the pressures of the supply pump P 1  and the return pump P 2  are both made to be approximately 80 kPa, whereas in the post-purge step, the pressure of the supply pump P 1  and the pressure of the return pump P 2  are made to be mutually different. Specifically, in step S 6 , the controller  10  makes the pressure of the supply pump P 1  to be greater than the pressure of the return pump P 2 . For example, it is allowable that the pressure of the supply pump P 1  is made to be approximately 96 kPa, and the pressure of the return pump P 2  is made to be approximately 64 kPa. 
     The driving time of the pump in each of the pre-purge step, the circulating step, the return purge step and the post-purge step is approximately 15 seconds in a case that a predetermined time has not elapsed since the air-bubble removing processing executed the last time. The controller  10  causes the RAM to store the timing at which the air-bubble removing processing has been executed and in the air-bubble removing processing which is to be executed in a case that the predetermined time has elapsed since the air-bubble removing processing executed the last time, the controller  10  makes the driving time of the pump in each of the pre-purge step, the circulating step, the return purge step and the post-purge step to be longer than 15 seconds (for example, approximately 30 seconds). The predetermined time is, for example, approximately 1 (one) hour. In such a case that the power source of the printer  100  has been switched OFF, and then the power source of the printer  100  is switched ON after a time period which is not less than one hour thereafter has elapsed, each of the pre-purge step, the circulating step, the return purge step and the post-purge step is performed for a period of time longer than the usual period of time. 
     After performing the post-purge step, the controller  10  ends this routine. 
     As described above, according to the present embodiment, in a case that the controller  10  executes the air-bubble removing processing, the controller  10  firstly performs the circulating step and then performs the return purge step (see  FIG. 5 ). In the circulating step ( FIG. 3 ), the air bubbles A might gather in the return channel  32 , might combine with each other and might become large-sized. Then, in the return purge step (see  FIG. 6B ), the large-sized air bubble A is exhausted from the nozzle  33   d  together with the ink. In a case that the air bubble is small-sized, since the surface area of the air bubble A is small and thus the pressure toward the nozzle  33   d  is less likely to act on the air bubble A, the floating forces of the air bubble A is dominant, which in turn requires a large pressure for exhausting the air bubble A. In view of this situation, in the present embodiment, the large-sized air bubble A can be efficiently exhausted with a small pressure. Namely, the air bubble A can be removed efficiently. 
     The filters F 1  and F 2  are provided on the supply channel  31  and the return channel  32 , respectively (see  FIG. 3 ). In this case, it is possible to prevent any foreign matter from entering into the individual channel  33  from each of the supply channel  31  and the return channel  32 . However, in such a configuration provided with the filters F 1  and F 2 , since the air bubble A hardly passes through the filters F 1  and F 2 , and thus the air bubble A might remain between the filters F 1  and F 2  and the individual channel  33 , which in turn might cause any clogging of the filters F 1  and F 2 . This consequently might increase the resistance in channel and might lead to any shortage in the supply of the ink to the individual channel  33 . In view of this situation, in the circulating step (see  FIG. 3 ) of the present embodiment, the air bubbles A might gather in the vicinity of the filter F 2  of the return channel  32 , might combine with each other and might become large-sized. Then, in the return purge step (see  FIG. 6B ), the large-sized air bubble A is exhausted from the nozzle  33   d  together with the ink I. With this, the air bubble A can be efficiently exhausted, thereby making it possible to suppress any clogging of the filters F 1  and F 2  and any problem associated therewith. Namely, the present disclosure is particularly effective in the configuration provided with the filters F 1  and F 2 . 
     In a case that the controller  10  executes the air-bubble removing processing, the controller  10  performs the post-purge step after performing the return purge step (see  FIG. 5 ). In such a case, the air bubble A can be removed more assuredly, by performing the post-purge step (see  FIG. 6A ). 
     In the post-purge step, the controller  10  drives both of the supply pump P 1  and the return pump P 2  (see step S 6  in  FIG. 5 ). In the head  1  of the circulating type as in the present embodiment, the supply pump P 1  and the return pump P 2  are generally provided. In a case that the post-purge step is performed by using another mechanism, the number of parts is increased, whereas in the present embodiment, the post-purge step is performed by using the supply pump P 1  and the return pump P 2 , thereby making it possible to suppress the increase in the number of parts. 
     The controller  10  makes the pressure of the supply pump P 1  and the pressure of the return pump P 2  to be mutually different in the post-purge step. In a case that the pressure of the supply pump P 1  and the pressure of the return pump P 2  are made to be same with each other, the air bubbles A (see  FIG. 3 ) in the ink flowing from the both sides, namely from the supply channel  31  and the return channel  32  might remain at a location immediately below the actuator  40 . In such a case, the deformation of the actuator  40  might be hindered by the air bubble A. According to the above-described configuration, by making the pressure of the supply pump P 1  and the pressure of the return pump P 2  to be mutually different in the post-purge step, the air bubble A is moved to a location away from the actuator  40 , thereby making it possible to prevent the air bubble A from remaining in the location immediately below the actuator  40 . Thus, the problem that the deformation of the actuator  40  is hindered by the air bubble A can be suppressed. 
     In the post-purge step, the controller  10  makes the pressure of the supply pump P 1  to be greater than the pressure of the return pump P 2 . In a case that the pressure of the return pump P 2  is made to be greater than the pressure of the supply pump P 1 , the air bubble A might remain at a location on the side of the supply channel  31  than at the location immediately below the actuator  40 . In such a case, in the circulating step during the recording processing, the air bubble A might be moved from the side of the supply channel  31  toward the location immediately below the actuator  40 , and the deformation of the actuator  40  might be hindered by the air bubble A. According to the above-described configuration, this problem can be suppressed. 
     In a case that the controller  10  executes the air-bubble removing processing, the controller  10  performs the pre-purge step before performing the circulating step (see  FIG. 5 ). In this case, the air bubble A can be removed more assuredly by performing the pre-purge step (see  FIG. 6A ). 
     The controller  10  makes the pressure of the supply pump P 1  in the circulating step during the air-bubble removing processing to be greater than the pressure of the supply pump P 1  in the circulating step during the recording processing. Specifically, the controller  10  makes the pressure of the supply pump P 1  in the circulating step during the air-bubble removing processing to be greater than the withstanding pressure of meniscus in the nozzles  33   d . In this case, in the circulating step during the air-bubble removing processing, it is possible to destroy the meniscus of each of the nozzles  33   d  and to exhaust (discharge) the air bubble A, together with the ink I, from each of the nozzles  33   d.    
     In the case that the power source of the printer  100  is switched ON, the controller  10  executes the air-bubble removing processing. In this case, by removing the air bubble A before the recording processing, it is possible to suppress occurrence of a various kinds of problems during the recording processing due to the air bubble A (any unsatisfactory discharge of the ink from the nozzles  33   d , any shortage in the supply of the ink to the individual channel  33 , etc.). 
     In the air-bubble removing processing to be executed in a case that the predetermined time has elapsed since the air-bubble removing processing executed the last time, the controller  10  performs each of the circulation step and the return purge step for a longer period of time than in a case that the predetermined time has not elapsed since the air-bubble removing processing executed the last time. With this, it is possible to exhaust any air bubbles inside each of the individual channels  33  and to prevent any increase in the viscosity of the ink, more assuredly. 
     In the channel unit  20  of the head  1 , the plurality of individual channels  33 , the supply channel and the return channel  32  for each of the plurality of different kinds of liquids (four color inks) are formed while being arranged side by side to one another (see  FIG. 2 ). In this configuration, the widths of the respective channels  31  to  33  have to be narrow, and the various kinds of problems due to the air bubble A might be conspicuous. In view of this, the present embodiment is capable of efficiently removing the air bubble A, and thus is particularly effective in the above-described configuration. 
     The printer  100  is provided with the supply pump P 1  and the return pump P 2  corresponding to each of the plurality of different kinds of liquids (four color inks). In a case that the controller  10  executes the air-bubble removing processing regarding a selected color (color ink) which is selected among the four colors (four color inks), the controller  10  uses a pump P 1  and a pump P 2  which are included in the pumps P 1  the pumps P 2  and which correspond to the selected color, rather than using all the pumps P 1  and all the pumps P 2 . With this, it is possible to suppress any wasteful exhaust (discharge) of the ink, and thus to suppress the amount of waste liquid. 
     Second Embodiment 
     Next, a printer according to a second embodiment of the present disclosure will be explained, with reference to  FIGS. 7 and 8 . With respect to a part or portion, of the configuration of the second embodiment, which is same as that of the first embodiment, a same reference number or symbol is assigned, and any detailed explanation for such a part or portion will be omitted in some cases. 
     The second embodiment is different from the first embodiment in having a configuration wherein a check valve V 2  is provided, rather than the open/close valve V 1 , and in the content of the air-bubble removing processing. 
     The check valve V 2  allows a flow of the ink from the storing chamber  7   a  to the plurality of individual channels  33  via the supply channel  31  (flow of the ink indicated by arrows in  FIG. 7 ), and suppresses a flow of the ink from the plurality of individual channels  33  to the storing chamber  7   a  via the supply channel  31  (flow in a direction reverse to the direction of the flow of the ink indicated by arrows in  FIG. 7 ). Specifically, the check valve V 2  is configured to open the channel in a case that the pressure on the side of the storing chamber  7   a  is greater by a predetermined pressure (for example, 1 kPa to 2 kPa) than the pressure on the side of the individual channels  33 , and to close the channel in a case different from the above case. 
     In a case of executing the air-bubble removing processing, the controller performs the pre-purge step, the circulating step, the return purge step and the post-purge step sequentially as depicted in  FIG. 8 , in a similar manner as in the first embodiment ( FIG. 5 ). In the first embodiment, the opening/closing control of the open/close valve V 1  is performed in each of the steps, whereas in the second embodiment, any opening/closing control of the valve is not performed, since the check valve V 2  is adopted, instead of adopting the open/close valve V 1 . Specifically, the air-bubble removing processing in the second embodiment is executed as follows. 
     In the pre-purge step, the controller drives both of the supply pump P 1  and the return pump P 2  (step S 21 ). In this situation, the flow of the ink is allowed in the check valve V 2 , and the ink is moved from the storing chamber  7   a  to the plurality of individual channels  33  via the supply channel  31 , and the ink is moved from the storing chamber  7   a  to the plurality of individual channels  33  via the return channel  32 , thereby causing the ink to be exhausted (discharged) from the nozzles  33   d  of the plurality of individual channels  33 . 
     In the circulating step, the controller maintains the driving of the supply pump P 1  and stops the driving of the return pump P 2  (step S 23 ). In this situation, the flow of the ink is allowed in the check valve V 2 , and the ink is circulated along a circulation route starting from, and returning to, the storing chamber  7   a  via the supply channel  31 , the plurality of individual channels  33  and the return channel  32 , as depicted in  FIG. 7 . 
     In the return purge step, the controller stops the driving of the supply pump P 1  (step S 24 ). After the step S 24 , the controller maintains the stopping of driving of the supply pump P 1 , and drives the return pump P 2  (step S 25 ). In this situation, the flow of the ink is suppressed in the check valve V 2 , and the ink is moved from the storing chamber  7   a  to the plurality of individual channels  33  via the return channel  32 . With this, the ink is exhausted (discharged) from the nozzles  33   d  of the plurality of individual channels  33 . 
     In the post-purge step, the controller drives both of the supply pump P 1  and the return pump P 2  (step S 26 ). In this situation, the flow of the ink is allowed in the check valve V 2 , and the ink is moved from the storing chamber  7   a  to the plurality of individual channels  33  via the supply channel  31 , and the ink is moved from the storing chamber  7   a  to the plurality of individual channels  33  via return channel  32 . With this, the ink is exhausted (discharged) from the nozzles  33   d  of the plurality of individual channels  33 . 
     As described above, according to the second embodiment wherein the check valve V 2  is adopted, rather than the open/close valve V 1 , in the case that the controller executes the air-bubble removing processing, the controller firstly performs the circulating step and then performs the return purge step (see  FIG. 8 ) in a similar manner to that in the first embodiment. Accordingly, it is possible to achieve such an effect that a large-sized air bubble can be exhausted efficiently with a small pressure by performing the return purge step after performing the circulating step, in a similar manner to that in the first embodiment. 
     Third Embodiment 
     Next, a printer according to a third embodiment of the present disclosure will be explained, with reference to  FIG. 9 . With respect to a part or portion, of the configuration of the third embodiment, which is same as those of the first and second embodiments, a same reference number or symbol is assigned, and any detailed explanation therefor will be omitted in some cases. 
     The third embodiment is different from the first embodiment in the content of the air-bubble removing processing. 
     In a case of executing the air-bubble removing processing, the controller performs the pre-purge step, the circulating step, the return purge step and the post-purge step sequentially, in a similar manner as in the first embodiment ( FIG. 5 ). In the first embodiment, the supply pump P 1  and the return pump P 2  are used in the pre-purge step and in the post-purge step, whereas in the third embodiment, a suction pump P 3  is used in the pre-purge step and in the post-purge step. 
     At a time of starting the air-bubble removing processing, the head unit  1   x  is arranged at a position at which the four heads  1  overlap, in the vertical direction, with the four caps  6  (see  FIG. 1 ), respectively (stand-by position). The cap unit  6   x  is arranged at the capping position (namely, the cap unit  6   x  is in a state that the lip part  6   a  makes contact with the nozzle surface  25 , and that all the nozzles  33   d  of each of the heads  1  are covered by one of the caps  6 ). Accordingly, in the third embodiment, the air-bubble removing processing is executed regarding all the four colors (four color inks) included in each of the head  1 , rather than being executing regarding a selected color (color ink) among the four colors (four color inks). 
     In the pre-purge step, the controller drives the suction pump P 3  in a state that the stopping of driving of the supply pump P 1  and the stopping of driving of the return pump P 2  are maintained (step S 31 ), immediately thereafter switches the open/close valve V 1  from the close position to the open position (step S 32 ). In this situation, a suction force is generated inside each of the caps  6 , and the ink is moved from the storing chamber  7   a  to each of the plurality of individual channels  33  via the supply channel  31 , and the ink is moved from the storing chamber  7   a  to each of the individual channels  3  via the return channel  32 , thereby exhausting ink from the nozzle  33   d  of each of the plurality of individual channels  33  of one of the heads  1 . The driving of the suction pump P 3  is stopped after a predetermined time elapses. 
     In the circulating step, the controller maintains the open position of the open/close valve V 1  and stopping of driving of the return pump P 2  and stopping of driving of the suction pump P 3 , and drives the supply pump P 1  (step S 33 ). In the return purge step, the controller performs steps S 34  and S 35  which are similar to steps S 4  and S 5  in the first embodiment. 
     In the post-purge step, the controller drives the suction pump P 3  in a state that the stopping of driving of the supply pump P 1  and the stopping of driving of the return pump P 2  are maintained (step S 36 ), immediately thereafter switches the open/lose valve V 1  from the close position to the open position (step S 37 ). In this situation, the suction force is generated in the inside of each of the caps  6 , similarly in the pre-purge step, and the ink is moved from the storing chamber  7  to the plurality of individual channels  33  via the supply channel  31  and the ink is moved from the storing chamber  7  to the plurality of individual channels  33  via the return channel  32 , thereby exhausting the ink from all the nozzles  33   d  of each of the heads  1 . The driving of the suction pump P 3  is stopped after a predetermined time elapses. 
     As described above, according to the third embodiment, the air bubble A in the vicinity of the nozzle  33   d  can be efficiently removed by performing each of the purge steps with the suction pump P 3 . Further, in a case of performing each of the purge steps by using the supply pump P 1  and the return pump P 2 , there might be such a problem that a swirl is generated immediately below the actuator  40  and that it might be difficult to exhaust the air bubble A. In the case of performing each of the purge steps by using the suction pump P 3  as in the third embodiment, however, the above-described problem caused due to the occurrence of swirl is hardly generated. 
     &lt;Modifications&gt; 
     Although the embodiments of the present disclosure have been explained in the foregoing, the present disclosure is not limited to or restricted by the above-described embodiments; it is allowable to make a various kind of changes to the present disclosure, within the scope described in the claims. 
     For example, in a case of performing the purge step with the supply pump and the return pump as in the first embodiment, the suction pump and/or the caps may be omitted. 
     The pump may be a bidirectional pump. For example, in the above-described embodiment, it is allowable that the return pump P 2  is a bidirectional pump (having a driving mode switchable between a forward driving by which pressure in a direction from the return hole  32   x  toward the inlet port  7   ax  of the storing chamber  7   a  is imparted to the ink, and a reverse driving by which pressure in a direction from the inlet port  7   ax  of the storing chamber  7   a  toward the return hole  32   x  is imparted to the ink), and that the return pump P 2  is driven in the forward direction in the circulating step and the return pump P 2  is driven in the reverse direction in each of the pre-purge step and the post-purge step. In a case of driving the return pump P 2  in the forward direction in the circulating step, if the pressure of the return pump P 2  is too great, there is a such a possibility that the air is drawn from the nozzle; thus, it is possible to make the pressure of the return pump P 2  to be smaller than the pressure of the supply pump P 1 . Further, in this case, it is allowable that the supply pump P 1  is omitted, that the circulating step is performed by driving the return pump P 2  in the forward direction, and that the return purge step is performed by driving the return pump P 2  in the reverse direction. 
     In the above-described embodiment, although each of the open/close valve and the check valve is arranged between the supply pump and the supply hole, each of the open/close valve and the check valve may be arranged between the storing chamber and the supply pump. Each of the open/close valve and the check valve may be provided on the return channel (for example, between the storing chamber and the return pump). 
     It is allowable to provide the filter on only one of the supply channel and the return channel, or on neither of the supply channel and the return channel. 
     In the circulating step, it is allowable that the liquid is exhausted from the nozzle, or the liquid is not exhausted from the nozzle. It is allowable to make the pressure of the pump in the circulating step during the air-bubble removing processing to be not more than the pressure of the pump in the circulating step during the recording processing, or not more than the withstanding pressure of the meniscus in the nozzle. 
     In the pre-purge step, it is allowable to make the pressure of the supply pump to be different from the pressure of the return pump, similarly in the post-purge step. It is allowable to omit the pre-purge step. 
     In the post-purge step, it is allowable to make the pressure of the supply pump to be smaller than the pressure of the return pump. Alternatively, in the post-purge step, it is allowable to make the pressure of the supply pump and the pressure of the return pump to be same with each other. It is allowable to omit the post-purge step. 
     The air-bubble removing processing may be executed not only when the power source of the liquid discharge apparatus is switched ON, but also at a timing designated by a user, or every predetermined period. Further, in the air-bubble removing processing performed every time, a period of time during which each of the steps, such as the circulating step, the return purge step, etc., may be uniform (in the air-bubble removing processing to be executed in a case that the predetermined time has elapsed since the air-bubble removing processing executed the last time, it is allowable that each of the steps is not performed for a long period of time). 
     It is allowable to execute the air-bubble removing processing regarding all a plurality of different kinds of liquids at a time, rather than regarding a selected liquid among the plurality of different kinds of liquids (see the third embodiment). 
     It is allowable to form individual channels, a supply channel and a return channel only for one kind of liquid (for example, black ink), in one piece of the liquid discharging head. 
     The number of each of the supply and return channels provided on one piece of the liquid discharging head are not limited to a plural, and may be 1 (one). For example, it is allowable that one supply channel and one return channel corresponding to one kind of liquid are provided on one piece of the liquid discharging head. 
     The position of the supply hole and the position of the return hole are not particularly limited. For example, in the first embodiment, it is allowable that in the first embodiment (see  FIG. 2 ), the supply hole  31   x  is provided on one end in the extending direction of the supply common channel  31   d , and the return hole  32   x  is provided on the other end in the extending direction of the return common channel  32   d . In this case, the flows of the ink are reverse to each other in one set of the supply and return common channels. 
     It is allowable to provide two or more pieces of the supply hole with respect to one piece of the supply common channel. In this case, in a plurality of individual channels communicating with one piece of the supply common channel, the pressure applied to the individual channels becomes greater as a distance therefrom to the supply hole is shorter; however, it is possible to suppress the variation (unevenness) in the applied pressure among the individual channels, as compared with a case of supplying the liquid in one piece of the supply common channel from one supply hole. 
     It is allowable to provide two or more pieces of the return hole with respect to one piece of the return common channel. In this case, in a plurality of individual channels communicating with one piece of the return common channel, the pressure applied to the individual channels becomes greater as a distance therefrom to the return hole is shorter; however, it is possible to suppress the variation (unevenness) in the applied pressure among the individual channels, as compared with a case of exhausting the liquid in one piece of the return common channel from one return hole. 
     The number of the nozzles and the number of the pressure chambers included in each of the individual channels are not particularly limited. For example, it is allowable that each of the individual channels includes one nozzle and two pressure chambers. It is allowable that each of the individual channels includes two or more nozzles. 
     The actuator is not limited to or restricted by being of the piezo system using the piezoelectric element, and may be of another system (for example, a thermal system using a heating element, an electrostatic system using the electrostatic force, etc.). 
     The liquid discharging head is not limited to being of the line system, and may be of the serial system (system for discharging the liquid(s) from the nozzles toward a discharge target while moving in a scanning direction parallel to a paper width direction). 
     The discharge target is not limited to a paper sheet (paper), and may be, for example, cloth, fabric, substrate, etc. 
     The liquid which is to be discharged from the nozzles is not limited to the ink, and may be any liquid (for example, a treatment solution for aggregating or depositing (precipitating) a component in an ink, a liquefied metal, a resin, etc.). 
     The present disclosure is not limited to or restricted by being applicable to a printer, and is applicable also to a facsimile machine, copying machine, a multi-functional peripheral, etc. Further, the present disclosure is applicable also to a liquid discharge apparatus usable in a variety of kinds of usage or application other than recording of an image, etc. For example, the present disclosure is applicable also to a liquid discharge apparatus configured to form a conductive pattern on a substrate by discharging or jetting a conductive liquid onto the substrate.