Patent Publication Number: US-2023150261-A1

Title: Liquid discharge apparatus

Description:
REFERENCE TO RELATED APPLICATIONS 
     This application claims priority from Japanese Patent Application No. 2021-187626 filed on Nov. 18, 2021. The entire content of the priority application is incorporated herein by reference. 
     BACKGROUND ART 
     There is known a liquid discharge apparatus including: a first supply manifold and first return manifold which are connected to a first individual channel; and a second supply manifold and second return manifold which are connected to a second individual channel. The first supply manifold and the second return manifold are connected by a first bypass route. The first individual channel has a first nozzle discharge port, and, due to pressure that has been applied from a piezoelectric body to liquid in the first individual channel, the liquid is discharged from the first nozzle discharge port. 
     DESCRIPTION 
     In this kind of liquid discharge apparatus, the first supply manifold is connected to the first return manifold by the first individual channel. A pressure wave that has been applied to the liquid in the first individual channel from the piezoelectric body will propagate to the first supply manifold and will propagate to the first return manifold. Supposing the first supply manifold and the first return manifold to be connected by a bypass route, a wave of large amplitude will be generated as a result that the pressure wave propagating to the first supply manifold and pressure wave propagating to the first return manifold are superimposed in phase via the bypass route. As a result, there will occur crosstalk whereby discharge of the liquid from nozzle discharge ports of surrounding individual channels will become unstable. In contrast, in the above-described liquid discharge apparatus, the first supply manifold is connected to the second return manifold by the first bypass route. As a result, the pressure wave propagating to the first supply manifold and pressure wave propagating to the first return manifold (that is in phase with the pressure wave propagating to the first supply manifold) will not merge, hence crosstalk will be reduced. 
     However, in the case of the above-described liquid discharge apparatus further including a third supply manifold and a third return manifold which are connected by a third individual channel, the first supply manifold will be connected by bypass routes to the second return manifold and the third return manifold. In contrast, each of the second supply manifold and the third supply manifold will be connected by a bypass route to the first return manifold. In this way, the number of the bypass routes of the first supply manifold will differ from other manifolds, and liquid flow rate in the first supply manifold will differ from in other manifolds. There is a risk that difference in flow rates among the manifolds will cause nonuniformity of head heat-dissipating performance and bubble discharge performance. 
     The present teaching, which was made in view of such circumstances, has an object of providing a liquid discharge apparatus enabling uniformity of flow rates of liquid in manifolds to be achieved, while crosstalk is reduced. 
    
    
     
       According to an aspect of the present teaching, there is provided a liquid discharge apparatus including: a plurality of liquid channels each including: an individual channel having a nozzle; a supply manifold connected to the individual channel to supply liquid to the individual channel; and a return manifold connected to the individual channel, the liquid that has not been discharged from the nozzle being flowed through the return manifold; and a plurality of bypasses each connected to the supply manifold and the return manifold to cause the liquid to flow therethrough, wherein the liquid channels include a first liquid channel, a second liquid channel, and a third liquid channel arranged in a first direction, the supply manifold included in the first liquid channel is connected only to the return manifold included in the second liquid channel, via a first bypass included in the bypasses, and the return manifold included in the first liquid channel is connected only to the supply manifold included in the third liquid channel, via a second bypass included in the bypasses. 
         FIG.  1    is a diagram in which a liquid discharge apparatus according to an embodiment of the present teaching is viewed from above. 
         FIG.  2    is a cross-sectional view depicting part of a head. 
         FIG.  3    is a diagram in which a channel unit in the head of  FIG.  2    is viewed from above. 
         FIG.  4    is an exploded view of the channel unit of  FIG.  2   . 
         FIG.  5    is a perspective view of the channel unit of  FIG.  2   . 
         FIGS.  6 A to  6 C  are diagrams in which a liquid discharge apparatus according to a second modification of the present teaching is viewed from the left. 
         FIG.  7    is a diagram in which a channel unit of a liquid discharge apparatus according to a fourth modification of the present teaching is viewed from above. 
         FIG.  8    is a perspective view of the channel unit of  FIG.  7   . 
         FIG.  9    is a perspective view of a channel unit of a liquid discharge apparatus according to a fifth modification of the present teaching. 
         FIGS.  10 A and  10 B  are diagrams in which the channel unit of  FIG.  9    is viewed from the left. 
         FIG.  11    is a perspective view of a channel unit of a liquid discharge apparatus according to a sixth modification of the present teaching. 
         FIG.  12    is a diagram in which a channel unit of a liquid discharge apparatus according to another modification of the present teaching is viewed from the left. 
         FIG.  13    is a diagram in which a channel unit of a liquid discharge apparatus according to still another modification of the present teaching is viewed from the left. 
     
    
    
     An embodiment of the present teaching will be specifically described below with reference to the drawings. Note that hereafter, identical or corresponding elements will be assigned with identical reference symbols in all of the drawings, and duplicated descriptions thereof omitted. 
     &lt;Liquid Discharge Apparatus&gt; 
     A liquid discharge apparatus  10  according to one embodiment of the present teaching is a device that discharges liquid such as ink, as depicted in  FIG.  1   . Although hereafter, there will be described an example of the liquid discharge apparatus  10  having been applied to an ink jet printer in which an image is formed by liquid being discharged onto a recorded medium A from a head  20 , the liquid discharge apparatus  10  is not limited to this. Moreover, a sheet material of the likes of paper and cloth may be employed as the recorded medium A. 
     The liquid discharge apparatus  10 , in which a line head system is adopted, comprises a platen  11 , a head unit  12 , a storage tank  13 , a conveying device  17 , and a control unit  14 . Note that a designated first direction will be referred to as a front-rear direction, a second direction intersecting with (for example, orthogonal to) the first direction will be referred to as a left-right direction, and a third direction intersecting with (for example, orthogonal to) the first direction and the second direction will be referred to as an up-down direction. However, disposition of the liquid discharge apparatus  10  is not limited to this. 
     The platen  11 , which is of a rectangular flat plate-like shape, for example, has a flat upper surface on which the recorded medium A is placed, and determines a distance between the recorded medium A and the head  20  in the up-down direction. The head  20 , which extends longways in the left-right direction, has a length in the left-right direction not less than that of the recorded medium A. The head unit  12  is provided with one or a plurality of the heads  20 . The head  20  is provided with a discharge surface  21  ( FIG.  2   ) facing the upper surface of the platen  11 , and a plurality of nozzles  31  that open onto the discharge surface  21 . Note that details of the head  20  will be mentioned later. 
     The storage tank  13  is provided for each kind of liquid. For example, four storage tanks  13  have respectively stored therein black, yellow, cyan, and magenta liquids. The storage tanks  13  are corresponded to the plurality of nozzles  31  of the head  20 , and supply liquid to the corresponding nozzles  31 . 
     The conveying device  17  has a pair of conveying rollers  18  and conveying motors  19 , for example. The pair of conveying rollers  18  are disposed sandwiching the platen  11  between each other in the front-rear direction with their axes extending in the left-right direction. The conveying roller  18 , which is coupled to the conveying motor  19 , rotates around its axis due to the conveying motor  19 . As a result, the recorded medium A is conveyed in the front-rear direction on the platen  11 . 
     The control unit  14 , which is a computer, comprises an arithmetic circuit such as a CPU, and a memory of the likes of RAM and ROM. In the control unit  14 , an arithmetic unit controls operation of the conveying motor  19  of the conveying device  17  and drive element  23  of the head  20 , based on a program stored in a storage unit. For example, the control unit  14  executes a discharging operation causing liquid to be discharged onto the recorded medium A from the head  20  by the drive element  23 , and a conveying operation causing the recorded medium A to be conveyed by the conveying device  17 . As a result, there proceeds a print processing in which an image is formed on the recorded medium A by liquid, without the head  20  moving. 
     &lt;Head&gt; 
     As depicted in  FIGS.  2  and  3   , the head  20  comprises a channel forming body  22  and the drive element  23 , and is installed with a sub-tank  15 . The channel forming body  22  is a laminated body having laminated therein a plurality of plates, and includes a nozzle plate  24 , a plurality of (for example, eight) channel plates  25 , and a vibrating plate  26 , for example. These plates, which are of rectangular plate-like shape, are laminated in the up-down direction in this order, and are bonded to each other by an adhesive agent, or the like. 
     Each plate has formed therein a through-hole penetrating the plate, and a recess recessing from a lower surface or upper surface of the plate. For example, the plate comprises a resin or metal, and has its through-hole and recess formed by etching. Inside the channel forming body  22  where each of the plates are laminated, the through-holes and recesses are combined to form a channel unit  27 , for example. The channel unit  27  includes a plurality of liquid channels  28  and a plurality of bypasses  60 . The liquid channel  28  includes a plurality of individual channels  30 , a supply manifold  40 , and a return manifold  50 . The bypass  60  connects the supply manifold  40  and the return manifold  50 , and has liquid flowing therethrough. Note that details of the manifolds and bypasses  60  will be mentioned later. 
     As depicted in  FIG.  2   , the individual channel  30  includes the nozzle  31 , a supply throttle  32 , a pressure chamber  33 , a descender  34 , and a return throttle  35 . The nozzle  31  penetrates the nozzle plate  24  in the up-down direction, and opens onto the discharge surface  21  being the lower surface of the nozzle plate  24 . The supply throttle  32  is connected to the supply manifold  40  and pressure chamber  33 . Cross-sectional area orthogonal to a flow-through direction that liquid flows in these is smaller in the supply throttle  32  than in the supply manifold  40  and the pressure chamber  33 . The pressure chamber  33  has its upper end opening covered by the vibrating plate  26 . The descender  34  is connected to the pressure chamber  33  and the nozzle  31 . The return throttle  35  is connected to the descender  34  and return manifold  50 , and cross-sectional area orthogonal to a flow-through direction that liquid flows is smaller in the return throttle  35  than in the descender  34  and the return manifold  50 . 
     The drive element  23 , which is an element applying a discharge pressure to liquid of the pressure chamber  33 , is, for example, a piezoelectric element. The drive element  23  expands/contracts on receiving a control signal from the control unit  14  ( FIG.  1   ). The vibrating plate  26  between the drive element  23  and the pressure chamber  33  deforms cooperatively with the drive element  23 , and undergoes change in a direction that will increase/decrease volume of the pressure chamber  33 . Hence, liquid of the pressure chamber  33  is applied with a discharge pressure discharging it from the nozzle  31 , and liquid is discharged from the nozzle  31  communicating with the pressure chamber  33 . 
     &lt;Manifolds and Bypasses&gt; 
     As depicted in  FIG.  3   , the supply manifold  40  and the return manifold  50 , which extend longways in the left-right direction, are connected to a plurality of the individual channels  30 . For example, the supply manifold  40  has a supply port  41  at its right end, and an outflow port  42  at its left end. The return manifold  50  has a return port  51  at its right end, and an inflow port  52  at its left end. The supply port  41  is connected to the sub-tank  15  by a supply pipe  43 , and the return port  51  is connected to the sub-tank  15  by a return pipe  44 . Moreover, the outflow port  42  and the inflow port  52  are connected by the bypass  60 . The sub-tank  15  is connected by a tube  13   a  ( FIG.  1   ) to the storage tank  13 . 
     The plurality of liquid channels  28  include a first liquid channel  28   a , a second liquid channel  28   b , and a third liquid channel  28   c  that are arranged in the front-rear direction. The first liquid channel  28   a  includes a first supply manifold  40   a  being the supply manifold  40  and first return manifold  50   a  being the return manifold  50 , and a plurality of first individual channels  30   a  being the individual channels  30  connected to these first supply manifold  40   a  and first return manifold  50   a . The second liquid channel  28   b  includes a second supply manifold  40   b  being the supply manifold  40  and second return manifold  50   b  being the return manifold  50 , and a plurality of second individual channels  30   b  being the individual channels  30  connected to these second supply manifold  40   b  and second return manifold  50   b . The third liquid channel  28   c  includes a third supply manifold  40   c  being the supply manifold  40  and third return manifold  50   c  being the return manifold  50 , and a plurality of third individual channels  30   c  being the individual channels  30  connected to these third supply manifold  40   c  and third return manifold  50   c.    
     The first supply manifold  40   a , the second supply manifold  40   b , and the third supply manifold  40   c  are arranged in this order from the rear. The first return manifold  50   a , the second return manifold  50   b , and the third return manifold  50   c  are arranged in this order from the rear. The first supply manifold  40   a  is disposed above the first return manifold  50   a  so as to overlap the first return manifold  50   a  viewing along the up-down direction. The second supply manifold  40   b  is disposed above the second return manifold  50   b  so as to overlap the second return manifold  50   b  viewing along the up-down direction. The third supply manifold  40   c  is disposed above the third return manifold  50   c  so as to overlap the third return manifold  50   c  viewing along the up-down direction. 
     The bypass  60  includes a first bypass  61 , a second bypass  62 , and a third bypass  63 . The first bypass  61  is connected to the outflow port  42  of the first supply manifold  40   a  and the inflow port  52  of the second return manifold  50   b . The second bypass  62  is connected to the outflow port  42  of the third supply manifold  40   c  and the inflow port  52  of the first return manifold  50   a . The third bypass  63  is connected to the outflow port  42  of the second supply manifold  40   b  and the inflow port  52  of the third return manifold  50   c.    
     As depicted in  FIG.  4   , the plurality of channel plates  25  in the channel forming body  22  include a first channel plate  25   a , a second channel plate  25   b , a third channel plate  25   c , and a fourth channel plate  25   d . The first channel plate  25   a , the second channel plate  25   b , the third channel plate  25   c , and the fourth channel plate  25   d  are laminated from above in this order. For example, in the up-down direction, dimensions of the first channel plate  25   a  and fourth channel plate  25   d  are larger than dimensions of the second channel plate  25   b  and third channel plate  25   c . Note that in  FIG.  4   , the individual channel  30  is not illustrated. 
     The first supply manifold  40   a , the second supply manifold  40   b , and the third supply manifold  40   c  are formed as through-holes penetrating the first channel plate  25   a  in the up-down direction, and extend in the left-right direction. The first return manifold  50   a , the second return manifold  50   b , and the third return manifold  50   c  are formed as through-holes penetrating the fourth channel plate  25   d  in the up-down direction, and extend in the left-right direction. 
     The first bypass  61  includes a first upper portion  61   a , a first middle portion  61   b , and a first lower portion  61   c , these being connected in this order. The first upper portion  61   a  penetrates the second channel plate  25   b  in the up-down direction. In the front-rear direction, a dimension of the first upper portion  61   a  is larger than a dimension of the first supply manifold  40   a , and the first upper portion  61   a  extends further to the front than the first supply manifold  40   a . The first upper portion  61   a  overlaps the first supply manifold  40   a  viewing along the up-down direction, and an upper end of the first upper portion  61   a  is connected to the outflow port  42  at a lower end of the first supply manifold  40   a . The first middle portion  61   b  penetrates the third channel plate  25   c  in the up-down direction. The first lower portion  61   c  penetrates the fourth channel plate  25   d  in the up-down direction. In the front-rear direction, a dimension of the first lower portion  61   c  is larger than a dimension of the second return manifold  50   b , and the first lower portion  61   c  extends further to the rear than the second return manifold  50   b . In a portion where the first upper portion  61   a  and the first lower portion  61   c  overlap when viewed along the up-down direction, an upper end of the first middle portion  61   b  is connected to a lower end of the first upper portion  61   a , and a lower end of the first middle portion  61   b  is connected to an upper end of the first lower portion  61   c . A front end of the first lower portion  61   c  is connected to the inflow port  52  being a rear end of the second return manifold  50   b.    
     The second bypass  62  includes a second upper portion  62   a , a second middle portion  62   b , and a second lower portion  62   c , these being connected in this order. The second upper portion  62   a  penetrates the second channel plate  25   b  in the up-down direction. In the front-rear direction, a dimension of the second upper portion  62   a  is larger than a dimension of the third supply manifold  40   c , and the second upper portion  62   a  extends further to the rear than the third supply manifold  40   c . The second upper portion  62   a  overlaps the third supply manifold  40   c  viewing along the up-down direction, and an upper end of the second upper portion  62   a  is connected to the outflow port  42  at a lower end of the third supply manifold  40   c . The second middle portion  62   b  penetrates the third channel plate  25   c  in the up-down direction. The second lower portion  62   c  penetrates the fourth channel plate  25   d  in the up-down direction. In the front-rear direction, a dimension of the second lower portion  62   c  is larger than a dimension of the first return manifold  50   a , and the second lower portion  62   c  extends further to the front than the first return manifold  50   a . In a portion where the second upper portion  62   a  and the second lower portion  62   c  overlap when viewed along the up-down direction, an upper end of the second middle portion  62   b  is connected to a lower end of the second upper portion  62   a , and a lower end of the second middle portion  62   b  is connected to an upper end of the second lower portion  62   c . A rear end of the second lower portion  62   c  is connected to the inflow port  52  being a front end of the first return manifold  50   a.    
     The third bypass  63  includes a third upper portion  63   a , a third middle portion  63   b , and a third lower portion  63   c , these being connected in this order. The third upper portion  63   a  penetrates the second channel plate  25   b  in the up-down direction. In the front-rear direction, a dimension of the third upper portion  63   a  is larger than a dimension of the second supply manifold  40   b , and the third upper portion  63   a  extends further to the front than the second supply manifold  40   b . The third upper portion  63   a  overlaps the second supply manifold  40   b  viewing along the up-down direction, and an upper end of the third upper portion  63   a  is connected to the outflow port  42  at a lower end of the second supply manifold  40   b . The third middle portion  63   b  penetrates the third channel plate  25   c  in the up-down direction. The third lower portion  63   c  penetrates the fourth channel plate  25   d  in the up-down direction. In the front-rear direction, a dimension of the third lower portion  63   c  is larger than a dimension of the third return manifold  50   c , and the third lower portion  63   c  extends further to the rear than the third return manifold  50   c . In a portion where the third upper portion  63   a  and the third lower portion  63   c  overlap when viewed along the up-down direction, an upper end of the third middle portion  63   b  is connected to a lower end of the third upper portion  63   a , and a lower end of the third middle portion  63   b  is connected to an upper end of the third lower portion  63   c . A front end of the third lower portion  63   c  is connected to the inflow port  52  being a rear end of the third return manifold  50   c.    
     As depicted in  FIG.  5   , the first supply manifold  40   a  included in the first liquid channel  28   a  is connected via the first bypass  61  included in the bypass  60 , only to the second return manifold  50   b  included in the second liquid channel  28   b . The first return manifold  50   a  included in the first liquid channel  28   a  is connected via the second bypass  62  included in the bypass  60 , only to the third supply manifold  40   c  included in the third liquid channel  28   c . The second supply manifold  40   b  included in the second liquid channel  28   b  is connected via the third bypass  63  included in the bypass  60 , only to the third return manifold  50   c  included in the third liquid channel  28   c . Note that in  FIG.  5   , the individual channel  30  is not illustrated. 
     &lt;Flow of Liquid&gt; 
     Liquid is supplied to the sub-tank  15  from the storage tank  13 , passes along the supply pipe  43  from the sub-tank  15 , and flows into the first supply manifold  40   a  via the supply port  41 . Then, the liquid flows to the left along the first supply manifold  40   a , and, while doing so, is supplied to each of the plurality of first individual channels  30   a  connected to the first supply manifold  40   a . In the first individual channel  30   a , the liquid flows through the supply throttle  32 , the pressure chamber  33 , and the descender  34 , and is supplied to the nozzle  31 . Now, the liquid is discharged from the nozzle  31  upon being applied with a pressure by the drive element  23 . On the other hand, liquid that has not been discharged from the nozzle  31  passes through the return throttle  35  and flows into the first return manifold  50   a . The liquid flows to the right along the first return manifold  50   a , passes along the return pipe  44  from the return port  51  of the first return manifold  50   a , and returns to the sub-tank  15 . Thus, as a nozzle circulation, the liquid circulates from the sub-tank  15 , through the first supply manifold  40   a , first individual channels  30   a , and first return manifold  50   a , back to the sub-tank  15 . 
     Moreover, liquid that has not flowed into the first individual channels  30   a  from the first supply manifold  40   a  while flowing to the left along the first supply manifold  40   a  passes through the first bypass  61  from the outflow port  42  of the first supply manifold  40   a , and flows via the inflow port  52  into the second return manifold  50   b . The liquid flows to the right along the second return manifold  50   b , passes through the return pipe  44  from the return port  51  of the second return manifold  50   b , and returns to the sub-tank  15 . Thus, as a manifold circulation, the liquid circulates from the sub-tank  15 , through the first supply manifold  40   a , first bypass  61 , and second return manifold  50   b , back to the sub-tank  15 . 
     Similarly to in the first supply manifold  40   a , liquid flows into the second supply manifold  40   b  from the sub-tank  15 , and, while flowing along the second supply manifold  40   b , is supplied to each of the plurality of second individual channels  30   b . In the second individual channel  30   b , the liquid is discharged from the nozzle  31  upon being applied with a pressure by the drive element  23 . On the other hand, liquid that has not been discharged from the nozzle  31  passes along the second return manifold  50   b  from the second individual channels  30   b , and returns to the sub-tank  15 . Thus, as a nozzle circulation, the liquid circulates from the sub-tank  15 , through the second supply manifold  40   b , second individual channels  30   b , and second return manifold  50   b , back to the sub-tank  15 . 
     Moreover, liquid that has not flowed into the second individual channels  30   b  from the second supply manifold  40   b  passes through the third bypass  63  from the second supply manifold  40   b , flows into the third return manifold  50   c , and returns to the sub-tank  15  from the third return manifold  50   c . Thus, as a manifold circulation, the liquid circulates from the sub-tank  15 , through the second supply manifold  40   b , third bypass  63 , and third return manifold  50   c , back to the sub-tank  15 . 
     Similarly to in the first supply manifold  40   a , liquid flows into the third supply manifold  40   c  from the sub-tank  15 , and, while flowing along the third supply manifold  40   c , is supplied to each of the plurality of third individual channels  30   c . In the third individual channel  30   c , the liquid is discharged from the nozzle  31  upon being applied with a pressure by the drive element  23 . On the other hand, liquid that has not been discharged from the nozzle  31  passes along the third return manifold  50   c  from the third individual channels  30   c , and returns to the sub-tank  15 . Thus, as a nozzle circulation, the liquid circulates from the sub-tank  15 , through the third supply manifold  40   c , third individual channels  30   c , and third return manifold  50   c , back to the sub-tank  15 . 
     Moreover, liquid that has not flowed into the third individual channels  30   c  from the third supply manifold  40   c  passes through the second bypass  62  from the third supply manifold  40   c , flows into the first return manifold  50   a , and returns to the sub-tank  15  from the first return manifold  50   a . Thus, as a manifold circulation, the liquid circulates from the sub-tank  15 , through the third supply manifold  40   c , second bypass  62 , and first return manifold  50   a , back to the sub-tank  15 . 
     Thus, the first supply manifold  40   a  and the first return manifold  50   a  of the first liquid channel  28   a  are connected by bypasses  60  to liquid channels  28  that differ from each other. The second supply manifold  40   b  and the second return manifold  50   b  of the second liquid channel  28   b  are connected by bypasses  60  to liquid channels  28  that differ from each other. The third supply manifold  40   c  and the third return manifold  50   c  of the third liquid channel  28   c  are connected by bypasses  60  to liquid channels  28  that differ from each other. Moreover, the first supply manifold  40   a  is connected by the first bypass  61  one-on-one to the second return manifold  50   b , the second supply manifold  40   b  is connected by the third bypass  63  one-on-one to the third return manifold  50   c , and the third supply manifold  40   c  is connected by the second bypass  62  one-on-one to the first return manifold  50   a . Hence, uniformity of flow rates of liquid in the manifolds  40 ,  50  can be achieved, while crosstalk is reduced. 
     &lt;First Modification&gt; 
     In a liquid discharge apparatus  10  according to a first modification, in the above-described embodiment, cross-sectional area through which liquid passes, of the second bypass  62  is larger than in the first bypass  61  and the third bypass  63 . For example, cross-sectional area of the second bypass  62  is area orthogonal to a flow-through direction that liquid flows to the first return manifold  50   a  from the third supply manifold  40   c . Cross-sectional area of the first bypass  61  is area orthogonal to a flow-through direction that liquid flows to the second return manifold  50   b  from the first supply manifold  40   a . Cross-sectional area of the third bypass  63  is area orthogonal to a flow-through direction that liquid flows to the third return manifold  50   c  from the second supply manifold  40   b.    
     In the example of  FIGS.  4  and  5   , cross-sectional area of the bypass  60  differs in its upper portion, middle portion, and lower portion. In such a case, fellow corresponding portions in the first bypass  61 , the second bypass  62 , and the third bypass  63  may be compared. In this case, cross-sectional area of the second upper portion  62   a  is larger than cross-sectional area of the first upper portion  61   a  and cross-sectional area of the third upper portion  63   a . Cross-sectional area of the second middle portion  62   b  is larger than cross-sectional area of the first middle portion  61   b  and cross-sectional area of the third middle portion  63   b . Cross-sectional area of the second lower portion  62   c  is larger than cross-sectional area of the first lower portion  61   c  and cross-sectional area of the third lower portion  63   c . Now, for example, cross-sectional area of the upper portions  61   a ,  62   a ,  63   a  is cross-sectional area orthogonal to the front-rear direction, cross-sectional area of the middle portions  61   b ,  62   b ,  63   b  is cross-sectional area orthogonal to the up-down direction, and cross-sectional area of the lower portions  61   c ,  62   c ,  63   c  is cross-sectional area orthogonal to the front-rear direction. 
     If length along a flow-through direction in the second bypass  62  is longer than in the first bypass  61  and the third bypass  63 , then channel resistance in the second bypass  62  will become larger than in the first bypass  61  and the third bypass  63 . In contrast, cross-sectional area with respect to a direction that liquid flows through the second bypass  62  is larger than in the first bypass  61  and the third bypass  63 . As a result, channel resistance in the second bypass  62  will become smaller than in the first bypass  61  and the third bypass  63 . Hence, in the first bypass  61 , the second bypass  62 , and the third bypass  63 , channel resistances can be made equal to each other or have their differences with each other reduced to no more than a designated value, and flowrates can be made uniform with each other. For example, in the case of a viscosity region of liquid such as ink being not less than 2 (mPa·s) and not more than 10 (mPa·s), channel resistance of the bypass  60  will be about not less than  200  (kPa/(cc/s)) and not more than 2000 (kPa/(cc/s)). 
     Note that the bypass  60  may have each of cross-sectional areas of its upper portion, middle portion, and lower portion equal to each other, and may have said cross-sectional areas fixed. Moreover, regarding at least one portion from among the upper portion, the middle portion, and the lower portion, cross-sectional area may be larger in the second bypass  62  than in the first bypass  61  and the third bypass  63 , whereas for the other portions, cross-sectional area in the second bypass  62  may be the same as in the first bypass  61  and the third bypass  63 . 
     &lt;Second Modification&gt; 
     In a liquid discharge apparatus  10  according to a second modification, in the above-described embodiment and first modification, the supply manifold  40  and return manifold  50  extend in the left-right direction. A dimension in the up-down direction of the second bypass  62  is larger than in the first bypass  61  and the third bypass  63 . 
     For example, as depicted in  FIG.  6 A , the first upper portion  61   a  of the first bypass  61  and third upper portion  63   a  of the third bypass  63  are formed in the second channel plate  25   b . In contrast, as depicted in  FIG.  6 B , the second upper portion  62   a  of the second bypass  62  is formed in the first channel plate  25   a  and the second channel plate  25   b . Therefore, in the up-down direction, dimensions of the first upper portion  61   a  and third upper portion  63   a  are equal to a dimension hb of the second channel plate  25   b , whereas a dimension of the second upper portion  62   a  is equal to the sum of a dimension ha of the first channel plate  25   a  and the dimension hb of the second channel plate  25   b . Hence, the dimension of the second upper portion  62   a  is larger than the dimensions of the first upper portion  61   a  and third upper portion  63   a.    
     Moreover, as a separate example, as depicted in  FIG.  6 C , the second upper portion  62   a  of the second bypass  62  is formed in the first channel plate  25   a , and its second middle portion  62   b  is formed in the second channel plate  25   b  and third channel plate  25   c . In this case, in the up-down direction, the dimensions of the first upper portion  61   a  and third upper portion  63   a  are equal to the dimension hb of the second channel plate  25   b , and the dimension of the second upper portion  62   a  is equal to the dimension ha of the first channel plate  25   a . Now, the dimension ha of the first channel plate  25   a  is larger than the dimension hb of the second channel plate  25   b . Therefore, in the up-down direction, the dimension of the second upper portion  62   a  is larger than the dimensions of the first upper portion  61   a  and third upper portion  63   a.    
     In a cross-section of the upper portion orthogonal to the front-rear direction, a dimension in the up-down direction is smaller than a dimension in the left-right direction, for example. In this case, flow-through resistance of liquid along the front-rear direction can be kept smaller by increasing the dimension in the up-down direction than by increasing the dimension in the left-right direction. Hence, in the up-down direction, the dimension of the second upper portion  62   a  is made larger than the dimensions of the first upper portion  61   a  and third upper portion  63   a . As a result, even if length along a flow-through direction of liquid is longer in the second bypass  62  than in the first bypass  61  and third bypass  63 , channel resistance of the second bypass  62  can be kept small, and uniformity of flowrate in the first bypass  61 , second bypass  62 , and third bypass  63  can be achieved. 
     Note that as in the above-described examples of  FIGS.  6 B and  6 C , the dimension in the up-down direction has been made larger in the second bypass  62  than in the first bypass  61  and third bypass  63 , for one portion from among the upper portion, middle portion, and lower portion. However, dimensions of the whole of the second bypass  62  may be made larger than in the first bypass  61  and third bypass  63 . 
     &lt;Third Modification&gt; 
     In a liquid discharge apparatus  10  according to a third modification, in the above-described embodiment and the first and second modifications, the supply manifold  40  and return manifold  50  extend in the left-right direction. The first individual channel  30   a  included in the first liquid channel  28   a  is located further to one side in the left-right direction than the first bypass  61 . The second individual channel  30   b  included in the second liquid channel  28   b  is located further to one side in the left-right direction than the third bypass  63 . The second bypass  62  is located further to the other side in the left-right direction than both the first bypass  61  and the third bypass  63 . 
     In the example of  FIG.  3   , the first individual channel  30   a , second individual channel  30   b , and third individual channel  30   c  are disposed further to the right than the first bypass  61  and third bypass  63 , in the left-right direction. The second bypass  62  is disposed further to the left than the first bypass  61  and third bypass  63 , in the left-right direction. As a result, as depicted in  FIG.  4   , the first upper portion  61   a , second upper portion  62   a , and third upper portion  63   a  are formed in the same second channel plate  25   b  as each other. Therefore, increase in size of the head  20  in the up-down direction and increase in the number of components can be suppressed. 
     &lt;Fourth Modification&gt; 
     In a liquid discharge apparatus  10  according to a fourth modification, in the above-described embodiment and the first and second modifications, the supply manifold  40  and return manifold  50  extend in the left-right direction. The first individual channel  30   a  included in the first liquid channel  28   a  is located further to one side in the left-right direction than the first bypass  61 . The second individual channel  30   b  included in the second liquid channel  28   b  is located further to one side in the left-right direction than the third bypass  63 . The second bypass  62  is located between the first individual channel  30   a  included in the first liquid channel  28   a  and first bypass  61  and between the second individual channel  30   b  included in the second liquid channel  28   b  and third bypass  63 , in the left-right direction. 
     In the example of  FIGS.  7  and  8   , the first individual channel  30   a , second individual channel  30   b , and third individual channel  30   c  are disposed further to the right than the second bypass  62 , in the left-right direction. The first bypass  61  and third bypass  63  are disposed further to the left than the second bypass  62 , in the left-right direction. As a result, dimensions in the left-right direction of the third supply manifold  40   c  and first return manifold  50   a  connected to the second bypass  62  are shorter than in the first supply manifold  40   a  and second return manifold  50   b  connected to the first bypass  61  and in the second supply manifold  40   b  and third return manifold  50   c  connected to the third bypass  63 . As a result, even if the second bypass  62  is longer than the first bypass  61  and third bypass  63 , the third supply manifold  40   c  and first return manifold  50   a  will be shorter than the other manifolds. Hence, uniformity of flowrate in the supply manifolds  40  and return manifolds  50  can be achieved. 
     &lt;Fifth Modification&gt; 
     A liquid discharge apparatus  10  according to a fifth modification, in the above-described embodiment and the first to fourth modifications, comprises the drive element  23  that applies to liquid of the individual channel  30  a discharge pressure discharging the liquid from the nozzle  31 . The supply manifold  40  and return manifold  50  extend in the left-right direction. The drive element  23 , the supply manifold  40 , and the return manifold  50  are disposed in this order in the up-down direction. The bypass  60  is disposed in the same position as the supply manifold  40  in the up-down direction, or in a position closer to the supply manifold  40  than to the return manifold  50  in the up-down direction. 
     Specifically, in the example of  FIGS.  4  and  5   , the upper portions  61   a ,  62   a ,  63   a  were formed in the second channel plate  25   b . In contrast, in the example of  FIGS.  9 ,  10 A and  10 B , the upper portions  61   a ,  62   a ,  63   a  are each formed in the first channel plate  25   a . In this case, the channel forming body  22  does not include the second channel plate  25   b . However, the upper portions  61   a ,  62   a ,  63   a  may be formed in the first channel plate  25   a  and the second channel plate  25   b . Alternatively, the middle portions  61   b ,  62   b ,  63   b  may be formed in the second channel plate  25   b  and the third channel plate  25   c . In this case, the channel forming body  22  does include the second channel plate  25   b.    
     The first upper portion  61   a  of the first bypass  61 , which penetrates the first channel plate  25   a  in the up-down direction, extends frontwards from the first supply manifold  40   a . A rear end of the first upper portion  61   a  is connected to the outflow port  42  at the front end of the first supply manifold  40   a . The second upper portion  62   a  of the second bypass  62 , which penetrates the first channel plate  25   a  in the up-down direction, extends rearwards from the third supply manifold  40   c . A front end of the second upper portion  62   a  is connected to the outflow port  42  at the rear end of the third supply manifold  40   c . The third upper portion  63   a  of the third bypass  63 , which penetrates the first channel plate  25   a  in the up-down direction, extends frontwards from the second supply manifold  40   b . A rear end of the third upper portion  63   a  is connected to the outflow port  42  at the front end of the second supply manifold  40   b.    
     In this way, the bypass  60  is disposed in the same position as the supply manifold  40  in the up-down direction, or in a position closer to the supply manifold  40  than to the return manifold  50  in the up-down direction. The drive element  23  is closer to the supply manifold  40  than to the return manifold  50  in the up-down direction. Therefore, the bypass  60  is close to the drive element  23 , the drive element  23  can be cooled by liquid flowing along the bypass  60 , and thermal degradation of the drive element  23  can be reduced. 
     Note that in the case described above, the first bypass  61 , second bypass  62 , and third bypass  63  are all formed in the first channel plate  25   a . However, at least one bypass  60  of the first bypass  61 , second bypass  62 , and third bypass  63  may be formed in the first channel plate  25   a , and the other bypasses  60  formed in the second channel plate  25   b . Moreover, in the case described above, the bypass  60  was disposed in the same position in the up-down direction as the supply manifold  40 . However, the bypass  60  may be disposed in a position closer to the supply manifold  40  than a midway point between the supply manifold  40  and return manifold  50 , in the up-down direction. 
     &lt;Sixth Modification&gt; 
     A liquid discharge apparatus  10  according to a sixth modification, in the above-described embodiment and the first to fifth modifications, comprises a plurality of pairs of the channel units  27  configured including a plurality of the liquid channels  28  and the bypasses  60 , as depicted in  FIG.  11   . The supply manifold  40  included in one pair of the channel units  27  is provided with a first supply port  41   a  supplied with liquid from a first tank  15   a , and the supply manifold  40  included in another pair of the channel units  27  is provided with a second supply port  41   b  supplied with liquid from a second tank  15   b . Now, the bypasses  60  included in the plurality of channel units  27  may have the same layout as each other. Note that in  FIG.  11   , the individual channel  30  is not illustrated. 
     In the example of  FIG.  11   , the channel unit  27  includes a first channel unit  27   a  and a second channel unit  27   b  that differs from the first channel unit  27   a . Each of the channel units  27 , that is, the first channel unit  27   a  and the second channel unit  27   b  includes a plurality of the liquid channels  28  and a plurality of the bypasses  60 . The plurality of liquid channels  28  include the first liquid channel  28   a , the second liquid channel  28   b , and the third liquid channel  28   c . The first liquid channel  28   a  includes the first supply manifold  40   a  and the first return manifold  50   a . The second liquid channel  28   b  includes the second supply manifold  40   b  and the second return manifold  50   b . The third liquid channel  28   c  includes the third supply manifold  40   c  and the third return manifold  50   c.    
     The first supply port  41   a  of the first channel unit  27   a  includes the supply port  41  of the first supply manifold  40   a , supply port  41  of the second supply manifold  40   b , and supply port  41  of the third supply manifold  40   c  in the first channel unit  27   a . The second supply port  41   b  of the second channel unit  27   b  includes the supply port  41  of the first supply manifold  40   a , supply port  41  of the second supply manifold  40   b , and supply port  41  of the third supply manifold  40   c  in the second channel unit  27   b . A first return port  51   a  of the first channel unit  27   a  includes the return port  51  of the first return manifold  50   a , return port  51  of the second return manifold  50   b , and return port  51  of the third return manifold  50   c  in the first channel unit  27   a . A second return port  51   b  of the second channel unit  27   b  includes the return port  51  of the first return manifold  50   a , return port  51  of the second return manifold  50   b , and return port  51  of the third return manifold  50   c  in the second channel unit  27   b.    
     The sub-tank  15  includes the first sub-tank  15   a  and the second sub-tank  15   b  that differs from the first sub-tank  15   a . The first sub-tank  15   a  and the second sub-tank  15   b  are connected to storage tanks  13  ( FIG.  1   ) that differ from each other. The first sub-tank  15   a  is connected by the supply pipe  43  to the first supply port  41   a  of the first channel unit  27   a , and is connected by the return pipe  44  to the first return port  51   a  of the first channel unit  27   a . The second sub-tank  15   b  is connected by the supply pipe  43  to the second supply port  41   b  of the second channel unit  27   b , and is connected by the return pipe  44  to the second return port  51   b  of the second channel unit  27   b . As a result, the first channel unit  27   a  and second channel unit  27   b  through which liquids of storage tanks  13  differing from each other flow can be disposed in the same head  20  as each other. In this case, spacing of the nozzles  31  of the first channel unit  27   a  and nozzles  31  of the second channel unit  27   b  can be made smaller than when the first channel unit  27   a  and second channel unit  27   b  have been disposed in different heads  20  from each other. Hence, impact position of the liquid discharged by the nozzles  31  of the first channel unit  27   a  and impact position of the liquid discharged by the nozzles  31  of the second channel unit  27   b  can be adjusted with high precision. 
     The plurality of bypasses  60  include the first bypass  61 , the second bypass  62 , and the third bypass  63 . Layout of the first bypass  61 , second bypass  62 , and third bypass  63  of the first channel unit  27   a  and layout of the first bypass  61 , second bypass  62 , and third bypass  63  of the second channel unit  27   b  are the same as each other. For example, in the examples of  FIGS.  3  and  11   , in the first channel unit  27   a  and second channel unit  27   b , the first liquid channel  28   a , the second liquid channel  28   b , and the third liquid channel  28   c  are arranged from the rear in this order. Moreover, in the first channel unit  27   a  and second channel unit  27   b , the first bypass  61  is connected to the first supply manifold  40   a  and second return manifold  50   b , the second bypass  62  is connected to the third supply manifold  40   c  and first return manifold  50   a , and the third bypass  63  is connected to the second supply manifold  40   b  and third return manifold  50   c . Furthermore, in the first channel unit  27   a  and second channel unit  27   b , the individual channel  30  is disposed further to the right than the first bypass  61  and third bypass  63 , and the second bypass  62  is disposed further to the left than the first bypass  61  and third bypass  63 . As a result, the same components can be utilized in manufacture of the first channel unit  27   a  and second channel unit  27   b , and improvement in manufacturing efficiency and lowering of cost can be achieved. 
     &lt;Other Modifications&gt; 
     In the above-described embodiment and all of the modifications, the channel unit  27  included three liquid channels  28 . However, the number of liquid channels  28  in the channel unit  27  is not limited to this, and it may include more than three of the liquid channels  28 . For example, as depicted in  FIG.  12   , the channel unit  27  includes n liquid channels  28 . In this case, the channel unit  27  includes n bypasses  60 . Of the n bypasses  60 , (n- 1 ) of the bypasses  60  are connected to the following supply manifold  40  and prior return manifold  50 , of fellow mutually adjacent liquid channels  28 , for example. 
     Among the n bypasses  60 , the second bypass  62  being the one remaining bypass  60  is connected to the first return manifold  50   a  of the rearmost first liquid channel  28   a  and n th  supply manifold  40 n of the frontmost nth liquid channel  28 n, of the n liquid channels  28  arranged in the front-rear direction. In this way, the supply manifold  40  and return manifold  50  of a certain liquid channel  28  are connected by the bypasses  60  one-on-one to mutually differing liquid channels  28 . Therefore, uniformity of flowrate of liquid in the manifolds  40 ,  50  can be achieved while crosstalk is reduced. 
     In the above-described embodiment and all of the modifications, in the channel unit  27 , the first liquid channel  28   a , second liquid channel  28   b , and third liquid channel  28   c  were arranged from rear to front. However, an arrangement direction of the liquid channels  28  is not limited to this. For example, as depicted in  FIG.  13   , in the channel unit  27 , the first liquid channel  28   a , second liquid channel  28   b , and third liquid channel  28   c  may be arranged from front to rear. In this case too, the first supply manifold  40   a  is connected via the first bypass  61 , only to the second return manifold  50   b . The first return manifold  50   a  is connected via the second bypass  62 , only to the third supply manifold  40   c . As a result, the supply manifold  40  and return manifold  50  of a certain liquid channel  28  are connected by the bypasses  60  one-on-one to mutually differing liquid channels  28 . Therefore, uniformity of flowrate of liquid in the manifolds  40 ,  50  can be achieved while crosstalk is reduced. 
     In the above-described embodiment and all of the modifications, a line head system was adopted for the liquid discharge apparatus  10 . However, the system adopted is not limited to this system, and, for example, another system such as a serial head system may be adopted too. In this serial head system, the liquid discharge apparatus  10  comprises a carriage that is installed with the head  20  and moves the head  20  in the left-right direction. The liquid discharge apparatus  10  alternately executes a recording operation to discharge liquid from the head  20  while moving the carriage and a conveying operation to convey the recorded medium A by the conveying device  17 , and thereby executes print processing to print an image on the recorded medium A. 
     In the above-described embodiment and modifications, a system employing a piezoelectric element (a piezo system) was adopted for the head  20 . However, the system adopted is not limited to this system. For example, a thermal system employing a heating element or an electrostatic system employing a conductive vibrating plate and electrodes may be adopted for the head  20 . 
     The above-described embodiment and each of the modifications may be combined with each other unless mutually exclusive. Moreover, numerous improvements or other embodiments of the present teaching will be obvious to a person skilled in the art from the above description. Hence, the above description should be interpreted merely as an exemplification, and is provided with an object of teaching a person skilled in the art the best mode of carrying out the present teaching. Details of structure and/or function of the present teaching may be substantively changed in a range not departing from the spirit of the present teaching.