Patent Publication Number: US-11390078-B2

Title: Inkjet head and inkjet recording apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present invention claims priority under 35 U.S.C. § 119 to International Patent Application No. PCT/JP2018/031928, filed on Aug. 29, 2018, the entire contents of which are incorporated herein by reference. 
     TECHNOLOGICAL FIELD 
     The present invention relates to an inkjet head and an inkjet recording apparatus. 
     BACKGROUND ART 
     There is known an inkjet recording apparatus which forms an image with ink discharged from nozzles on inkjet heads and landed on desired positions. An inkjet head of an inkjet recording apparatus includes ink storages for storing ink and pressure changers for changing pressure in ink in the ink storages corresponding to nozzles, and discharges ink from the nozzles communicating to the ink storages according to change in the pressure in ink in the ink storages. 
     In an inkjet head, as air bubbles and foreign substances enter the ink storage, pressure is not normally applied to ink, and an error occurs in ink discharge from the nozzle, degrading image quality. Therefore, conventionally, there is a technique in which multiple ink storages respectively corresponding to nozzles communicate to a common ejection flow path and part of ink supplied to each ink storage is ejected outside an inkjet head via the common ejection flow path with air bubbles and foreign substances. There is also a technique in which ink is ejected from ink storages to two common ejection flow paths to make it easier to eject air bubbles and foreign substances (for example, Patent Document 1). 
     CITATION LIST 
     Patent Literature 
     Patent Document 1: Japanese Patent Application Laid-Open Publication No. 2009-056766A 
     SUMMARY OF INVENTION 
     Technical Problem 
     However, in an inkjet head with a common ejection flow path, a pressure wave with characteristics corresponding to the shape of the common ejection flow path is generated as a standing wave in the common ejection flow path, caused by changes in pressure in ink in ink storages. A pressure wave generated in the ink storage by the standing wave further causes pressure in ink in the ink storage to deviate from the desirable pressure in ink discharge, and the characteristics of ink discharge from the nozzles to fluctuate, leading to deterioration of the quality of the recorded image. Especially in a configuration with two common ejection flow paths as in the above conventional technique, the image quality significantly deteriorates, problematically, as pressure waves caused by standing waves generated in the common ejection flow paths are superposed. 
     An object of the present invention is to provide an inkjet head and an inkjet recording apparatus that effectively suppress deterioration of image quality. 
     Solution to Problem 
     To achieve at least one of the above-mentioned objects, the invention recited in claim  1  is an inkjet head including: 
     a plurality of ink dischargers, each including:
         an ink storage for storing ink;   a pressure changer that changes pressure in ink stored in the ink storage;   a nozzle which communicates to the ink storage and through which ink is discharged according to change in the pressure in ink in the ink storage; and   a first individual ejection flow path and a second individual ejection flow path which communicate to the ink storage and through which ink is ejected from the ink storage but not supplied to the nozzle;       

     a first common ejection flow path that communicates to a plurality of first individual ejection flow paths of the respective plurality of the ink dischargers; and 
     a second common ejection flow path that communicates to a plurality of second individual ejection flow paths of the respective plurality of the ink dischargers; 
     wherein a shape of a first section of the first common ejection flow path into which ink flows from the plurality of first individual ejection flow paths is different from a shape of a second section of the second common ejection flow path into which ink flows from the plurality of second individual ejection flow paths. 
     The invention recited in claim  2  is the inkjet head according to claim  1 , wherein a volume of the first section of the first common ejection flow path is different from a volume of the second section of the second common ejection flow path. 
     The invention recited in claim  3  is the inkjet head according to claim  2 , wherein the volume of the second section of the second common ejection flow path is 1.1 times or more the volume of the first section of the first common ejection flow path. 
     The invention recited in claim  4  is the inkjet head according to claim  3 , 
     wherein in the first section of the first common ejection flow path, a cross section perpendicular to a direction of ink ejection has a rectangular shape with a first area throughout in the direction of ink ejection; 
     wherein in the second section of the second common ejection flow path, a cross section perpendicular to a direction of ink ejection is a rectangular shape with a second area throughout in the direction of ink ejection; and 
     wherein the second area is 1.1 times or more the first area. 
     The invention recited in claim  5  is the inkjet head according to any one of claims  2  to  4 , 
     wherein the volume of the second section of the second common ejection flow path is 10 times or less the volume of the first section of the first common ejection flow path. 
     The invention recited in claim  6  is the inkjet head according to any one of claims  1  to  5 , 
     wherein a length of the first section in a direction of ink ejection in the first section is different from a length of the second section in a direction of ink ejection in the second section. 
     The invention recited in claim  7  is the inkjet head according to any one of claims  1  to  6 , 
     wherein a surface roughness of an inner wall of the first section of the first common ejection flow path is different from a surface roughness of an inner wall of the second section of the second common ejection flow path. 
     The invention recited in claim  8  is the inkjet head according to any one of claims  1  to  7 , 
     wherein a length of the first individual ejection flow path communicating to the ink storage in a direction of ink ejection in the first individual ejection flow path is different from a length of the second individual ejection flow path communicating to the ink storage in a direction of ink ejection in the second individual ejection flow path. 
     The invention recited in claim  9  is the inkjet head according to any one of claims  1  to  8 , 
     wherein the first individual ejection flow path communicating to the ink storage includes two or more first individual ejection flow paths, and the second individual ejection flow path communicating to the ink storage includes two or more second individual flow paths. 
     The invention recited in claim  10  is the inkjet head according to any one of claims  1  to  9 , including: 
     an ink ejection opening through which ink is ejected outside, 
     wherein the first common ejection flow path and the second common ejection flow path communicate to the ink ejection opening. 
     The invention recited in claim  11  is an inkjet recording apparatus including the inkjet head according to any one of claims  1  to  10 . 
     Advantageous Effects of Invention 
     With the present invention, it is possible to effectively suppress deterioration of image quality. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  shows a schematic configuration of an inkjet recording apparatus according to an embodiment of the present invention. 
         FIG. 2  is a schematic drawing of a configuration of a head unit. 
         FIG. 3  shows a perspective view of an inkjet head. 
         FIG. 4  shows an exploded perspective view of main components of the inkjet head. 
         FIG. 5  is an enlarged plan view of a lower surface of a pressure chamber substrate. 
         FIG. 6  is a plan view of an upper surface of a flow path spacer substrate. 
         FIG. 7  shows a cross-section of ahead chip perpendicular to an X direction along a line A-A in  FIGS. 4 and 6 . 
         FIG. 8  schematically shows a configuration of an ink circulation mechanism. 
         FIG. 9  is a diagram for describing problems in a conventional configuration. 
         FIG. 10  is a diagram for describing effects to be expected in a configuration of this embodiment. 
         FIG. 11  is a diagram for describing effects to be expected in another configuration of this embodiment. 
         FIG. 12  shows shapes of samples used in an experiment and evaluation results. 
         FIG. 13  is a plan view of an upper surface of the flow path spacer substrate in Variation 1. 
         FIG. 14  is a plan view of an upper surface of the flow path spacer substrate in Variation 3. 
         FIG. 15  is a plan view of an upper surface of the flow path spacer substrate in Variation 4. 
         FIG. 16  is a plan view of an upper surface of the flow path spacer substrate in Variation 5. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, an inkjet head and an inkjet recording apparatus according to an embodiment are described with reference to the drawings. 
       FIG. 1  shows a schematic configuration of an inkjet recording apparatus  1  according to the embodiment of the present invention. 
     The inkjet recording apparatus  1  includes a conveyor  2 , head units  3 . 
     The conveyor  2  includes a conveyance belt  2   c  which is supported inside by two conveying rollers  2   a ,  2   b  rotating around a rotation axis extending in the X direction in  FIG. 1 . The conveyance belt  2   c , with the recording medium M being placed on a conveyance surface of the conveyance belt  2   c , circularly moves according to the rotation of the conveying roller  2   a  with the motion of the conveyance motor, and thereby the conveyor  2  conveys a recording medium M in a moving direction of the conveyance belt  2   c  (conveyance direction; Y direction in  FIG. 1 ). 
     The recording medium M may be a sheet of paper cut in a certain size. The recording medium M is supplied onto the conveyance belt  2   c  by a sheet feeding device not shown in the drawings, and discharged to a predetermined sheet ejector from the conveyance belt  2   c  after an image is recorded thereon by discharge of ink from the head unit  3 . The recording medium M may be roll paper. The recording medium M may be, besides paper such as plain paper and coated paper, various media on which ink landed on the surface may be fixed, such as fabric and sheet-shaped resin. 
     The head unit  3  discharges ink onto the recording medium M conveyed by the conveyor  2  at predetermined timings according to image data, thereby recording an image. In the inkjet recording apparatus  1  in this embodiment, four head units corresponding respectively to four color ink of yellow (Y), magenta (M), cyan (C), and black (K), are aligned at predetermined intervals in the order of Y, M, C, K from the upstream in the conveyance direction of the recording medium M. The number of the head units  3  may be three or less or five or more. 
       FIG. 2  is a schematic drawing of a configuration of the head unit  3 , showing a plan view of the head unit  3  viewed from the side opposite to the conveyance face of the conveyance belt  2   c . The head unit  3  includes a plate-like base and multiple (eight, in this embodiment) inkjet heads  100  fixed to the base  3   a  by mating with a through hole provided on the base  3   a . Each of the inkjet heads  100  is fixed to the base  3   a  with the nozzle opening face  112 , on which openings of nozzles  111  are disposed, being exposed in the −Z direction from the through hole of the base  3   a.    
     In the inkjet head  100 , multiple nozzles  111  are aligned at equal intervals in a direction crossing to the conveyance direction of the recording medium (width direction orthogonal to the conveyance direction, that is, X direction in this embodiment). That is, each of the inkjet heads  100  includes a row of nozzles  111  (nozzle row) arranged one-dimensionally at equal intervals in the X direction. 
     The inkjet head  100  may include multiple nozzle rows. In that case, multiple nozzle rows are arranged alternately in the X direction so that the positions of the nozzles  111  in the X direction do not overlap each other. 
     The eight inkjet heads  100  of the head unit  3  are arranged in a staggered pattern such that the arrangement range of the nozzles  111  in the X direction is continuous. The arrangement range of the nozzles  111  included in the head unit  3  in the X direction covers the width in the X direction of the area in which an image can be recorded on the recording medium M conveyed by the conveyance belt  2   c . The head unit  3 , which is employed at a fixed position in image recording, discharges ink from the nozzles  111  to the positions at predetermined intervals in the conveyance direction of the recording medium M (conveyance direction intervals), thereby recording an image by a single-pass method. 
       FIG. 3  shows a perspective view of the inkjet head  100 . 
     The inkjet head  100 , which includes a case  101 , and an exterior member  102  mating with the case  101  at the lower end of the case  101 , houses main components inside the case  101  and the exterior member  102 . The exterior member  102  includes an inlet  103   a  through which ink is supplied from the outside, and outlets  103   b ,  103   c  (ink ejection outlets) through which ink is ejected to the outside. The exterior member  102  includes multiple attachment holes  104  for attaching the inkjet head  100  to the base  3   a  of the head unit  3 . 
       FIG. 4  shows an exploded perspective view of the main components of the inkjet head  100 . 
     In  FIG. 4 , the main components housed inside the exterior member  102  among the components of the inkjet head  100 . Specifically, shown in  FIG. 4  are a head chip  10  including a nozzle substrate  11 , a flow path spacer substrate  12 , and a pressure chamber substrate  13 , a wiring substrate  15  fixed to the head chip  10 , and an FPC  20  (Flexible Printed Circuit) electrically connected to the wiring substrate  15 . 
     In  FIG. 4 , the components are shown such that the nozzle opening face  112  of the inkjet head  100  is upward, that is, upside down in comparison to  FIG. 3 . Hereinafter, the −Z direction side of each substrate is referred to as the upper side, and the +Z direction side as the lower side. 
     The head chip  10  includes a layered structure of the nozzle substrate  11  with the nozzles  111 , the flow path spacer substrate  12  with the through flow paths  121  communicating to the nozzles  111 , etc., and the pressure chamber substrate  13  with the pressure chambers  131  communicating to the nozzles  111  through the penetrating flow paths  121 . Hereinafter, a substrate composed of the flow path spacer substrate  12  and the pressure chamber substrate  13  is referred to as a flow path substrate  14 . 
     The nozzle substrate  11 , the flow path spacer substrate  12 , the pressure chamber substrate  13 , and the wiring substrate  15  are each a plate-like member in a rectangular parallelepiped pillar longer in the X direction. 
     The nozzle substrate  11  is a substrate of polyimide on which the nozzles  111 , the holes penetrating the nozzle substrate  11  in the thickness direction (Z direction) are aligned in the X direction to form a row. The upper surface of the nozzle substrate  11  is the nozzle opening face  112  of the inkjet head  100 . The thickness of the nozzle substrate  11  (the length of the nozzles  111  in the ink discharge direction) is, for example, several tens of μm to several hundreds of μm. 
     The inner wall of each of the nozzles  111  may be in a tapered shape whose cross sectional area perpendicular to the Z direction is smaller toward the opening on the ink discharge side. A substrate of resin other than polyimide, a silicon substrate, a metal substrate such as SUS, etc. may be used as the nozzle substrate  11 . 
     A water-repellent film containing liquid-repellent substance such as fluororesin particles is formed on the nozzle opening face  112  of the nozzle substrate  11 , With the water-repellent film, it is possible to suppress adhesion of ink or foreign substances onto the nozzle opening face  112 , suppressing occurrence of ink discharge failures due to the adhesion of ink or foreign materials. 
     The flow path spacer substrate  12  includes the penetrating flow paths  121  communicating to the nozzles  111 , the first individual ejection flow paths  122   a  and the second individual ejection flow paths  122   b  branching from the penetrating flow paths  121 , and the first belt-like penetrating flow path  123   a  communicating to the first individual ejection flow paths  122   a , and the first belt-like penetrating flow path  123   b  communicating to the second individual ejection flow paths  122   b . The penetrating flow paths  121 , the first individual ejection flow paths  122   a , and the second individual ejection flow paths  122   b  among the above are disposed corresponding to the nozzles  111 . 
     The pressure chamber substrate  13  includes the pressure chambers  131  communicating to the penetrating flow paths  121 , the first ditch-like flow path  132   a  communicating to the first belt-like penetrating flow path  123   a , the first vertical ejection flow path  133   a  communicating to the first ditch-like flow path  132   a , the second ditch-like flow path  132   b  communicating to the second belt-like penetrating flow path  123   b , and the second vertical ejection flow path  133   b  communicating to the second ditch-like flow path  132   b . The pressure chambers  131  are disposed corresponding to the nozzles  111  respectively. 
     The flow path spacer substrate  12  and the pressure chamber substrate  13  are each a plate-like member whose shape viewed in the Z direction is substantially the same as the nozzle substrate  11 . 
     The flow path spacer substrate  12  in this embodiment is made of a silicon substrate. The thickness of the flow path spacer substrate  12  is not particularly limited, but is several hundreds of μm. The nozzle substrate  11  is attached (fixed) to the upper surface of the flow path spacer substrate  12 , and the pressure chamber substrate  13  to the lower surface  13 , both with an adhesive agent. 
     The material of the pressure chamber substrate  13  is a ceramic piezoelectric body (a member that deforms in response to voltage application). PZT (lead zirconate titanate), lithium niobate, barium titanate, lead titanate, lead metaniobate, etc. are examples of the piezoelectric body. PZT is used for the pressure chamber substrate  13  in this embodiment. 
     The penetrating flow paths  121  of the flow path spacer substrate  12  are through holes penetrating the flow path spacer substrate  12  in the Z direction, whose cross-section perpendicular to the Z direction is in a rectangular shape longer in the Y direction. The pressure chambers  131  of the pressure chamber substrate  13  are through holes penetrating the pressure chamber substrate  13  in the Z direction, and have a cross section perpendicular to the Z direction in a shape identical to that of the penetrating flow paths  121 . In the state where the flow path spacer substrate  12  and the pressure chamber substrate  13  are joined, the penetrating flow paths  121  and the pressure chambers  131  are connected to form channels  141  (ink storages). The channels  141  are disposed at positions overlapping the nozzles  111  and communicate to the nozzles  111 . Ink is supplied via the ink supply openings  151  on the wiring substrate  15  and is stored in each of the channels  141 . 
       FIG. 5  is an enlarged plan view of the lower surface of the pressure chamber substrate  13 . As shown in  FIG. 5 , each of the pressure chambers  131  is partitioned from the pressure chambers  131  next to each other in the X direction by the partitions  134  of a piezoelectric body. A metal drive electrode  136  (pressure changer) is disposed on each of the inner walls of the partitions  134  of the pressure chambers  131 . Connection electrodes  135  electrically connected to the drive electrodes  136  are disposed in an area near the openings of the pressure chambers  131  on the −Y direction side on the surface of the pressure chamber substrate  13 . The connection electrodes  135  are electrically connected to an external drive circuit via the wiring  153  of the wiring substrate  15  and the wiring  21  of the FPC  20  shown in  FIG. 4 . 
     In the pressure chamber substrate  13 , as the partitions  134  repeat shear mode displacement according to the drive signals applied to the drive electrodes  136  via the connection electrodes  135 , pressures in ink in the pressure chambers  131  (channels  141 , accordingly) change. The changes in pressure causes ink in the channels  141  to be discharged from the nozzles  111 . Thus, the head chip  10  of this embodiment is a head chip that discharges ink in the shear mode. 
     An air chamber without an ink flow-in path may be disposed instead of the channel  141  alternately at a position of every other channel  141  in the X direction in  FIGS. 4 and 5 . Such a configuration can prevent deformation of the partition  134  next to the pressure chamber  131  in the channel  141  from affecting the other channels  141 . 
     As shown in  FIG. 4 , the flow path spacer substrate  12  extends in the arrangement direction of the channels  141  (X direction), and includes the first belt-like penetrating path  123   a  and the second belt-like penetrating flow path  123   b  penetrating the flow path spacer substrate  12  in the Z direction. The first belt-like penetrating flow path  123   a  is disposed on the +Y direction side of the row of the channels  141 , and the second belt-like penetrating flow path  123   b  is disposed on the −Y direction side of the row of the channels  141 . The first ditch-like flow path  132   a  is disposed in an area overlapping the first belt-like penetrating flow path  123   a  in the Z direction on the joint face of the pressure chamber substrate  13  with the flow path spacer substrate  12 . The second ditch-like flow path  132   b  is disposed in an area overlapping the second belt-like penetrating flow path  123   b  in the Z direction. 
     The first belt-like penetrating flow path  123   a  and the first ditch-like flow path  132   a  form the first common ejection flow path  142   a  extending in the X direction in the state where the flow path spacer substrate  12  and the pressure chamber substrate  13  are joined. The first belt-like penetrating flow path  123   b  and the second ditch-like flow path  132   b  form the second common ejection flow path  142   b  extending in the X direction in the state where the flow path spacer substrate  12  and the pressure chamber substrate  13  are joined. The first common ejection flow path  142   a  and the second common ejection flow path  142   b  configured as described above extend along the joint face of the flow path spacer substrate  12  and the nozzle substrate  11  (that is, the joint face of the flow path substrate  14  and the nozzle substrate  11 ), and part of the inner wall thereof is formed of the nozzle substrate  11 . Hereinafter, the first common ejection flow path  142   a  and the second common ejection flow path  142   b  when indistinct are simply referred to as the common ejection flow path(s)  142 . 
     The first vertical ejection flow path  133   a  penetrating the pressure chamber substrate  13  in the Z direction is connected to the end in the +X direction of the first common ejection flow path  142   a . The second vertical ejection flow path  133   b  penetrating the pressure chamber substrate  13  in the Z direction is connected to the end in the X direction of the second common ejection flow path  142   b . Hereinafter, the first vertical ejection flow path  133   a  and the second vertical ejection flow path  133   b  when indistinct are simply referred to as the vertical ejection flow path(s)  133 . 
     As described above, in the flow path spacer substrate  12 , the first individual ejection flow paths  122   a  connected to the first belt-like penetrating flow path  123   a  (first common ejection flow path  142   a ) and the second individual ejection flow paths  122   b  connected to the second belt-like penetrating flow path  123   b  (second common ejection flow path  142   b ) are branched from each of the penetrating flow paths  121  (channels  141 ). The first individual ejection flow paths  122   a  are each a ditch-like flow path extending in the +Y direction from an opening of the penetrating flow path  121  on the nozzle substrate  11  side along the surface of the flow path spacer substrate  12 , and part of the inner wall thereof is formed of the nozzle substrate  11 . The second individual ejection flow paths  122   b  are each a ditch-like flow path extending in the −Y direction from an opening of the penetrating flow path  121  on the nozzle substrate  11  side along the surface of the flow path spacer substrate  12 , and part of the inner wall thereof is formed of the nozzle substrate  11 . That is, the first individual ejection flow paths  122   a  and the second individual ejection flow paths  122   b  extend in the opposite directions from the penetrating flow paths  121  (channels  141 ). Hereinafter, the first individual ejection flow path  122   a  and the second individual ejection flow path  122   b  when indistinct are simply referred to as the individual ejection flow path(s)  122 . 
       FIG. 6  is a plan view of the upper surface of the flow path spacer substrate  12 . 
       FIG. 7  shows a cross-section of the head chip  10  perpendicular to the X direction along a line A-A in  FIGS. 4 and 6 . 
     Hereinafter, a section of the first common ejection flow path  142   a  into which ink flows from the first individual ejection flow paths  122   a  is the first section S 1 , and a section of the second common ejection flow path  142   b  into which ink flows from the second individual ejection flow path  122   b  is the second section S 2 . Specifically, the first section S 1  is a section between the most upstream connection point and the most downstream connection point in the ink ejection direction (X direction) of the connection points of the first individual ejection flow paths  122   a  to the first common ejection flow path  142   a . The second section S 2  is a section between the most upstream connection point and the most downstream connection point in the ink ejection direction (X direction) of the connection points of the second individual ejection flow paths  122   b  to the second common ejection flow path  142   a.    
     In this embodiment, the length in the X direction and the depth in the Z direction are equal between the first section S 1  and the second section S 2 . 
     However, the width Wa of the first section S 1  in the Y direction is smaller than the width Wb of the second section in the Y direction. Thus, as shown in  FIG. 7 , the rectangular area (first area) of the cross-section perpendicular to the X direction (direction of ink ejection) in the first section S 1  in the first common ejection flow path  142   a  is smaller than the rectangular area (second area) of the cross-section perpendicular to the X direction in the second section S 2  in the second common ejection flow path  142   a . More specifically, the length of the side parallel to the Z direction is equal between the rectangle of the first cross-section and the rectangle of the second cross-section, but the length of the side parallel to the Y direction is smaller in the rectangle of the first cross-section. As a result, the volume of the first common ejection flow path  142   a  in the first section S 1  is smaller than that of the second common ejection flow path  142   b  in the second section S 2 . 
     The effects and advantages of differentiation of the shapes and volumes between the first common ejection flow path  142   a  and the second common ejection flow path  142   b  are described in detail later. 
     As shown in  FIG. 7 , a part of the nozzle substrate  11  that forms the inner wall of the common ejection flow path  142  functions as a damper plate  11 D with flexibility. 
     As a pressure wave caused by a change in the pressure in ink in the channel  141  propagates to the common ejection flow path  142  via the individual ejection flow path  122 , a change in the pressure in ink may be caused inside the common ejection flow path  142 . As the damper plate  11 D deforms (bends) according to the change in the pressure in ink in the common ejection flow path  142  in that case, the pressure change may be absorbed. 
     The opposite side of the damper plate  11 D from the common ejection flow path  142  is open air, and air does not prevent the damper plate  11 D from deforming with the elasticity. Thus, the change in the pressure in ink inside the common ejection flow path  142  may be effectively absorbed. 
     The channel  141 , the first individual ejection flow path  122   a , the second individual ejection flow path  122   b , and the nozzle  111  shown in  FIG. 7  and the drive electrode  136  as a pressure changer shown in  FIG. 5  form an ink discharger  10   a . Thus, the head chip  10  includes as many ink discharger  10   a  as the nozzles  111 . 
     In the head chip  10  configured as described above, part of ink supplied to the channel  141  and not discharged from the nozzle  111  is ejected to the outside via the first individual ejection flow path  122   a  and the first common ejection flow path  142   a , and via the second individual ejection flow path  122   b  and the second common ejection flow path  142   b . Specifically, ink having passed through the first individual ejection flow path  122   a  and the first common ejection flow path  142   a  is ejected to the outside of the inkjet head  100  through the outlet  103   b  (or the outlet  103   c ) via the first vertical ejection flow path  133   a  and the first ejection hole  152   a  disposed on the wiring substrate  15 . Similarly, ink having passed through the second individual ejection flow path  122   b  and the second common ejection flow path  142   b  is ejected to the outside of the inkjet head  100  through the outlet  103   b  (or the outlet  103   c ) via the second vertical ejection flow path  133   b  and the second ejection hole  152   b  disposed on the wiring substrate  15 . The first common ejection flow path  142   a  and the second common ejection flow path  142   b  may communicate to a common outlet, or respectively to individual outlets. 
     Such a configuration as described above makes it possible to eject air bubbles and foreign substances that have entered the channels  141  may be ejected outside with ink. 
     Flow of ink supplied through the ink supply holes  151  to the channels  141  and flow of ink ejected from the channels  141  through the first common ejection flow path  142   a  or the second common ejection flow path  142   b  may be generated by an ink circulation mechanism  9  (see  FIG. 8 ) of the inkjet recording apparatus  1 . 
     The wiring substrate  15  shown in  FIG. 4  is preferably a plate-like substrate with an area larger than that of the pressure chamber substrate  13  for securing the connecting region with the pressure chamber substrate  13 , and is attached to the lower surface of the pressure chamber  13  with an adhesive agent. Glass, ceramics, silicone, plastics, and the like may be used for the wiring substrate  15 , for example. 
     The wiring substrate  15  includes multiple ink supply openings  151  at positions overlapping the channels  141  in the Z direction, and the first ejection outlet  152   a  and the second ejection outlet  152   b  at positions overlapping the first vertical ejection flow path  133   a  and the second vertical ejection flow path  133   b . Hereinafter, the first ejection outlet  152   a  and the second ejection outlet  152   b  when indistinct are simply referred to as the ejection outlet(s)  152 . Wires  153  extending from each of ends of the ink supply openings  151  toward the end of the wiring substrate  15  are provided on the face of the wiring substrate  15  attached to the pressure chamber substrate  13 . 
     An ink manifold (common ink chamber) not shown in the drawings is connected to the lower face of the wiring substrate  15 , and ink is supplied from the ink manifold to the ink supply openings  151 . 
     The pressure chamber substrate  13  and the wiring substrate  15  are attached by a conductive adhesive agent including conductive particles. Thus, the connection electrodes  135  on the pressure chamber substrate  13  and the wires  153  on the wiring substrate  15  are electrically connected via the conductive particles. 
     The FPC  20  is connected to the end of the wiring substrate  15  with wires  153  via an ACF (anisotropic conductive film), for example. The wires  153  on the wiring substrate  15  are electrically connected respectively to the wires  21  on the FPC  20  by this connection. 
     Next, a configuration of an ink circulation mechanism  9  for circulating and ejecting ink in the inkjet head  100  is described. 
       FIG. 8  schematically shows a configuration of the ink circulation mechanism  9 . 
     The ink circulation mechanism  9  includes a supply subtank  91 , reflux subtank  92 , and a main tank  93 . 
     The supply subtank  91  stores ink supplied to the ink manifold in the inkjet head  100 . The supply subtank  91  is connected to the inlet  103   a  with an ink flow path  94 . 
     The reflux subtank  92  is connected to the outlets  103   b  and  103   c  with an ink flow path  95 , and stores ink passing through the above-described ink ejection flow path including the individual ejection flow paths  122  and the common ink ejection flow paths  142  and ejected to the outlet  103   b  or the outlet  103   c.    
     The supply subtank  91  and the reflux subtank  92  are connected via the ink flow path  96 . Ink may be returned from the reflux subtank  92  to the supply subtank  91  by a pump  98  provided on the ink flow path  96 . 
     The main tank  93  stores ink supplied to the supply subtank  91 . The main tank  93  is connected to the supply subtank  91  with the ink flow path  97 . Ink is supplied from the main tank  93  to the supply subtank  91  by the pump  99  provided on the ink flow path  97 . 
     The liquid level of the supply subtank  91  is provided at a position higher than the ink discharge level of the head chip  10  (hereinafter also referred to as a “position reference level”), and the liquid level of the reflux subtank  92  is provided at a position lower than the position reference level. A pressure P 1  caused by a water head difference between the position reference level and the supply subtank  91  and a pressure P 2  caused by a water head difference between the position reference level and the reflux subtank  92  are generated. As a result, a pressure in ink at the inlet  103   a  is higher than pressures in ink at the outlets  103   b ,  103   c . The difference in pressure generates ink flow from the inlet  103   a  through the ink manifold, the ink supply openings  151 , the channels  141 , the penetrating flow paths  121 , the individual ejection flow paths  122 , the common ejection flow paths  142 , the vertical ejection flow paths  133 , the ejection holes  152  to the outlets  103   b  and  103   c , and ink is supplied to the ink discharger  10   a  and ejected (refluxed) from the ink discharger  10   a . The pressure P 1  and the pressure P 2  may be adjusted and the ink flow speed may be thereby adjusted, as the amounts of ink in the subtanks and the positions of the subtanks in the vertical direction are changed. 
     Next, functions and effects of the above-described configuration of the first common ejection flow path  142   a  and the second common ejection flow path  142   b  are described. 
     As described above, the change in the pressure in ink in the common ejection flow path  142  caused by the pressure wave propagating from the channels  141  to the common ejection flow path  142  is absorbed as part of the nozzle substrate  11  functions as the damper plate  11 D. However, it is difficult that the change in the pressure in ink in the common ejection flow path  142  is completely absorbed by the damper plate  11 D. 
     The pressure change that is not absorbed causes a standing wave in the common ejection flow path  142 . The standing wave is generated by interference of pressure waves propagating from the multiple channels  141  inside the common ejection flow path  142 , and the characteristics (wavelength, period, amplitude, phase, etc.) are influenced by the shape of the common ejection flow path  142  (especially the shapes of the above-described first section S 1  and second section S 2 ). 
     As the pressure wave caused by the standing wave inside the common ejection flow path  142  propagates to the channels  141  via the individual ejection flow path  1122 , the ink pressure in the channel  141  deviates from the desired pressure in ink discharge. As a result, a fluctuation in the characteristics of ink discharge from the nozzle  111  (crosstalk) is generated, resulting in deterioration of the image quality of recorded images. 
     Especially, in a conventional configuration with two common ejection flow paths  142  in the same shape, the pressure waves caused by the standing waves in the two common ejection flow paths  142  are superposed and increased in the channels  141 , and thereby the deterioration of the image quality due to crosstalk is significant, problematically. 
       FIG. 9  is a diagram for describing problems in a conventional configuration. 
     As shown on the left of  FIG. 9 , in a conventional configuration, two common ejection flow paths  142   c  having the same shape and an equal width (Wc) are provided on the upper and lower sides of the channels  141 . In such a conventional configuration, the positions and shapes of the two common ejection flow paths  142   c  are symmetrical to the channels  141 . Thus, a standing wave with almost the same characteristics is generated in each of the common ejection flow paths  142   c , because of the pressure waves propagating from the channels  141  to the common ejection flow paths  142   c.    
     A graph G 1 - 1  on the upper right of  FIG. 9  shows a density distribution (pressure distribution) in the X direction of standing waves generated in the (first) common ejection flow path  142   c  on the upper side. A graph G 1 - 2  on the lower right of  FIG. 9  shows a density distribution (pressure distribution) in the X direction of standing waves generated in the (second) common ejection flow path  142   c  on the lower side. As can be seen in these graphs, the standing waves generated in the two common ejection flow paths  142   c  have the almost same characteristics (wavelength, period, amplitude, and phase). 
     A graph G 1 - 3  in the center right of  FIG. 9  shows a magnitude of the pressure change caused by the pressure waves propagating from the two common ejection flow paths  142   c  in the channels  141  throughout in the X direction. That is, the graph G 1 - 3  shows a magnitude of the influence of the standing waves generated in the two common ejection flow paths  142   c  to the channels  141 . As shown in the graph G 1 - 3 , the distribution of the pressure change in the channels  141  has a profile of superposed density distributions of the standing waves in the two common ejection flow paths  142   c . That is, in the conventional configuration in  FIG. 9 , as the phases of the standing waves of the two common ejection flow paths  142   c  are aligned, the pressure change in the channels  141  is superimposed pressures with the same phases of the standing waves in the two common ejection flow paths  142   c . As a result, the fluctuation of the ink discharge characteristics (crosstalk) is increased, resulting in significant deterioration of the image quality. 
     On contrary, in the inkjet head  100  in this embodiment, the characteristics of the standing waves in the common ejection flow paths  142  do not correspond to each other, as the shape of the first section S 1  of the first common ejection flow path  142   a  and the shape of the second section S 2  of the second common ejection flow path  142   b  are different from each other. 
       FIG. 10  is a diagram for describing effects to be expected in a configuration in this embodiment. 
     A graph G 2 - 1  on the upper right of  FIG. 10  shows a density distribution (pressure distribution) of standing waves generated in the first section S 1  of the first common ejection flow path  142   a  of this embodiment. A graph G 2 - 2  on the lower right shows a density distribution of standing waves generated in the second section S 2  of the second common ejection flow path  142   b . As can be seen in these graphs, in this embodiment, as the shapes of the first section S 1  and the second section S 2  are different from each other, the phases of the standing waves generated in the first section S 1  and the second section S 2  are misaligned by 180 degrees. 
     As a result, as shown in the graph G 2 - 3  on the center right of  FIG. 10 , the pressure changes in the channels  141  caused by the standing waves are zero, as the pressures of the opposite phases in the first common ejection flow path  142   a  and the second common ejection flow path  142   b  are set off against each other. That is, the standing waves do not affect the channels  141  at any positions. As a result, the fluctuation of the ink discharge characteristics (crosstalk) caused by the standing waves in the common ejection flow paths  142  is suppressed to be extremely low, and thus the deterioration of the image quality due to the standing waves is effectively suppressed. 
       FIG. 11  is a diagram for describing effects to be expected in another configuration of this embodiment. 
     As the shapes of the first section S 1  and the second section S 2  are adjusted, the wavelength of the standing wave generated in the second section S 2  may be twice the wavelength of the standing wave created in the first section S 1 , as shown in the graph G 3 - 2  on the lower right of  FIG. 11 . In that case, the influence of the standing waves generated in the two common ejection flow paths  142  is not completely canceled, but the pressure change of the standing waves (compression and rarefaction) at many positions. Thus, the pressure change caused by the standing waves in the channels  141  is suppressed compared to the conventional configuration shown in  FIG. 9 , as shown in the graph G 3 - 3  on the center right of  FIG. 11 . 
     As the shapes of the first section S 1  and the second section S 2  are adjusted, at least any of the wavelength, amplitude, period, and phase may be differentiated between the standing wave generated in the first section S 1  and the standing wave generated in the first section S 1 , in a way different from those in  FIGS. 10 and 11 . For example, the phase of the standing waves in the first section S 1  and the second section S 2  are shifted at 180 degrees in the example shown in  FIG. 10 , but the phase difference of the standing wave may be other than 180 degrees. The wavelength ratio of the first section S 1  to the second section S 2  is two in the example shown in  FIG. 11 , but the wavelength ratio may be other than two. 
     In many cases among those, the influence of the standing waves in the two common ejection flow paths  142  is not completely set off, but it is possible to suppress the fluctuation of the ink discharge characteristics (crosstalk) in the channels  141  by canceling part of the influence of the standing waves. This makes it possible to suppress the deterioration of the image quality caused by the standing waves. 
     Next, an experiment for checking the effects of the above-described embodiment is described. 
     In the experiment, samples of 19 types of inkjet heads  100 , “No. 1” to “No. 19,” which have different combinations of shapes of the first section S 1  in the first common ejection flow path  142   a  and the second section S 2  in the second common ejection flow path  142   b  were prepared, and the extent of crosstalk in each of the samples was evaluated. 
     Specifically, prepared as the samples were inkjet heads  100  each including: 256 channel  141  (nozzles  111 ) to each of which the first individual ejection flow path  122   a  and the second individual ejection flow path  122   b  communicate; the first common ejection flow path  142   a  to which the 256 first individual ejection flow paths  122   a  are connected; and the second common ejection flow path  142   b  to which the 256 second individual ejection flow paths  122   b  are connected. Hereinafter, regarding the size of the first section S 1  in the first common ejection flow path  142   a  in each sample, the length in the X direction is referred to as a “length La,” the width in the Y direction a “width Wa,” the depth in the Z direction a “depth Da,” and the volume a “volume Va.” Regarding the size of the second section S 2  in the second common ejection flow path  142   b  in each sample, the length in the X direction is referred to as a “length Lb,” the width in the Y direction a “width Wb,” the depth in the Z direction a “depth Db,” and the volume a “volume Vb.” 
       FIG. 12  shows shapes of the samples used in the experiment and evaluation results. 
     Shown in  FIG. 12  are the sizes of the first section S 1  and the second section S 2 , the ratios of the sizes (size ratios) of the second section S 2  to the first section S 1 , and evaluation results about the crosstalk, in the samples in 19 types. 
     The sample “No. 1,” in which the shape of the first section S 1  in the first common ejection flow path  142   a  and the shape of the second section S 2  in the second common ejection flow path  142   b  were identical, was a comparative example. In the sample “No. 1,” the lengths La and Lb were 72 mm, the widths Wa and Wb 1 mm, the depths Da and Db 1 mm, and the volumes Va and Vb 72 mm 3 . 
     In the samples “No. 2” to “No. 7,” the depth Db of the second section S 2  in the second common ejection flow path  142   b  was increased compared to the sample “No. 1.” Specifically, in the samples “No. 2” to “No. 7,” the depths Db were, respectively, 1.05 mm, 1.1 mm, 1.2 mm, 1.3 mm, 1.4 mm, and 1.5 mm. 
     In the samples “No. 8” to “No. 13,” the width Wb of the second section S 2  in the second common ejection flow path  142   b  was increased compared to the sample “No. 1.” Specifically, in the samples “No. 8” to “No. 13,” the widths Wb were, respectively, 1.05 mm, 1.1 mm, 1.2 mm, 1.3 mm, 1.4 mm, and 1.5 mm. 
     In the samples “No. 14” to “No. 19,” both the width Wb and the depth Db of the second section S 2  in the second common ejection flow path  142   b  were increased compared to the sample “No. 1.” Specifically, in the samples “No. 14” to “No. 19,” both the widths Wb and the depths Db were, respectively, 1.05 mm, 1.1 mm, 1.2 mm, 1.3 mm, 1.4 mm, and 1.5 mm. 
     The crosstalk was evaluated on two levels of “good” and “poor.” 
     Specifically, the 256 channels  141  were driven in two types of drive patterns at drive frequencies of 10 Hz and 10 kHz, the crosstalk was evaluated based on the maximum rate of change in the ink flight speed (maximum change rate) in the channel  141  among all the 256 channels  141 . Specifically, the samples with the maximum change rate of the flight speed less than 10% were evaluated as “good,” and those with the rate equal to or greater than 10% were evaluated as “poor.” “Good” indicates that the level of the crosstalk is in a normal range for obtaining the image quality without problems in actual use, and “poor” indicates that the level of the crosstalk is problematically out of an allowable range of deterioration in the image quality. 
     The evaluation result of the crosstalk “poor” was obtained in the samples “No. 1,” “No. 2,” and “No. 8,” in which the volume ratio of the second section S 2  to the first section S 1  (Vb/Va) is 1.05 or less, and the evaluation result “good” was obtained in the other samples in which the volume ratio (Vb/Va) is 1.1 or greater, as shown in  FIG. 12 . That is, it was confirmed that, with a configuration in which the volume of the second section S 2  in the second common ejection flow path  142   b  is 1.1 times the volume of the first section S 1  of the first common ejection flow path  142   a , it is possible to suppress the crosstalk caused by the standing waves in the common ejection flow paths  142  and obtain the image quality without problems in actual use. 
     However, as the volume of the second section S 2  was over 10 times the volume of the first section S 1 , ink was ejected from the channels  141  mainly to the common ejection flow path  142   b , and with difficulty to the first common ejection flow path  142   b . Thus, the volume ratio between the first section S 1  and the second section S 2  is preferably not over 10. 
     As described hereinbefore, the inkjet head  100  in this embodiment includes: the ink dischargers  10   a , each including: the channel  141  as an ink storage for storing ink; the drive electrode  136  as a pressure changer that changes pressure in ink stored in the channel  141 ; the nozzle  111  which communicates to the channel  141  and through which ink is discharged according to change in the pressure in ink in the channel  141 ; and the first individual ejection flow path  122   a  and the second individual ejection flow path  122   b  which communicate to the channel  141  and through which ink is ejected from the channel  141  but not supplied to the nozzle  111 ; the first common ejection flow path  142   a  that communicates to the first individual ejection flow paths  122   a  of the respective ink dischargers  10   a ; and the second common ejection flow path  142   b  that communicates to the second individual ejection flow paths  10   b  of the respective ink dischargers  10   a ; wherein the shape of the first section S 1  of the first common ejection flow path  142   a  into which ink flows from the first individual ejection flow paths  122   a  is different from the shape of the second section S 2  of the second common ejection flow path  122   b  into which ink flows from the second individual ejection flow paths  142   b.    
     With such a configuration, the characteristics of the standing waves generated in the first section S 2  and the second section S 2  (wavelength, period, amplitude, phase, etc.) may be different from each other. This makes it possible to set off at least part of the pressure wave caused by the standing waves propagating from the two common ejection flow paths  142  to the channels  141 . Therefore, it is possible to suppress the pressure change in the channels  141  caused by propagation of the pressure wave caused by the standing waves to the channels  141 , and thus suppress the fluctuation of the ink discharge characteristics (crosstalk) in the channels  141 . As a result of the above, the deterioration of the image quality due to the standing waves may be effectively suppressed. 
     As ink is ejected from the channels  141  via the two common ejection flow paths  142 , bubbles and foreign substances in the channels  141  may be effectively ejected, in comparison to a configuration with a single common ejection flow path  142 . 
     As the volume of the first section S 1  of the first common ejection flow path  142   a  is different from the volume of the second section S 2  of the second common ejection flow path.  142   b , it is is possible to more effectively differentiate the characteristics of the standing waves generated in the first section S 1  and the second section S 2 . 
     As the volume of the second section S 2  of the second common ejection flow path  142   b  is 1.1 times or more the volume of the first section S 1  of the first common ejection flow path  142   a , it is possible to effectively differentiate the characteristics of the standing waves generated in the first section S 1  and the second section S 2 , and suppress the extent of crosstalk to be in a range that can obtain the image quality without problems in actual use. 
     In the first section S 1  of the first common ejection flow path  142   a , a cross section perpendicular to the X direction (the direction of ink ejection) has a rectangular shape with the first area throughout in the X direction, and in the second section S 2  of the second common ejection flow path  142   b , a cross section perpendicular to the X direction (the direction of ink ejection) is a rectangular shape with the second area throughout in the X direction. The second area is 1.1 times or more the first area. With such a configuration, it is possible to effectively differentiate the characteristics of the standing waves generated in the first section S 1  and the second section S 2  by simply differentiating the lengths of the sides of the rectangular cross sections of the first section S 1  and the second section S 2 . 
     As the volume of the second section S 2  of the second common ejection flow path  142   b  is 10 times or less the volume of the first section S 1  of the first common ejection flow path  142   a , it is is possible to suppress occurrence of errors in which ink is not smoothly ejected from the channels  141  to the first common ejection flow path  142   a.    
     The inkjet head  100  in this embodiment includes the outlet  103   b  and the outlet  103   c  as an ink ejection opening through which ink is ejected outside, and the first common ejection flow path  142   a  and the second common ejection flow path  142   b  communicate to the outlet  103   b  or the outlet  103   c . This makes it possible to eject outside air bubbles and foreign substances in the channels  141 . 
     As the inkjet recording apparatus  1  in this embodiment includes the above-described inkjet head  100 , it is possible to form high-quality images with suppressed crosstalk. 
     Next, Variations 1 to 5 of the above-described embodiment are described. Each variation may be combined with other variations. 
     (Variation 1) 
       FIG. 13  is a plan view of an upper surface of the flow path spacer substrate  12  in Variation 1. 
     This variation is different from the above-described embodiment in that the first section S 1  of the first common ejection flow path  142   a  and the second section S 2  of the second common ejection flow path  142   b  are different from each other in length in the X direction, and is the same as the above-described embodiment in other respects. 
     As shown in  FIG. 13 , in this variation, the first individual ejection flow path  122   a  and the second individual ejection flow path  122   b  branched from each of the channels  141  extend in respective directions that are inclined in mutually opposite directions from the Y direction. Because of this, the length in the X direction (direction of ink ejection) of the first section S 1  of the first common ejection flow path  142   a  to which ink flows from the first individual ejection flow paths  122  is shorter than the length in the X direction of the second section S 2  of the second common ejection flow path  142   b  to which ink flows from the second individual ejection flow paths  142   b.    
     With the configuration in which the length of the first section S 1  along the ink ejection direction in the first section S 1  is different from the length of the second section S 2  along the ink ejection direction in the second section S 2 , the characteristics of the standing waves in the section S 1  and the section S 2  may be different from each other. 
     (Variation 2) 
     In the variation  2 , the shape of the first section S 1  of the first common ejection flow path  142   a  is different from the shape of the second section S 2  of the second ejection flow path  142   b , and in addition, the surface roughness of the inner wall of the first section S 1  is different from the surface roughness of the inner wall of the second section S 2 . Variation 2 is the same as the above-described embodiment in other respects. 
     In this variation, the surface roughness Ra of the inner wall of the first section S 1  (arithmetic average of roughness) is greater than the surface roughness Ra of the inner wall of the second section S 2 . With this configuration, in the first section S 1  of the first common ejection flow path  142   a  with a surface roughness Ra comparatively large, the pressure wave entering from the individual ejection flow path  122  is more easily absorbed with the unevenness of the surface of the inner wall. This makes it possible to effectively differentiate the characteristics of the standing waves generated in the first section S 1  and the second section S 2 . 
     The surface roughness Ra of part of the inner wall of the first section S 1  may be greater than the surface roughness Ra of corresponding part of the inner wall of the second section S 2 . For example, the surface roughness Ra may be different between the first section S 1  and the second section S 2  in the part formed by the nozzle substrate  11  only, and the surface roughness Ra may be the same in the rest of the inner wall. 
     The inequality relation of the surface roughness Ra may be inverse in the first section S 1  and the second section S 2 . That is, the surface roughness Ra (arithmetic average of roughness) of the inner wall of the first section S 1  may be smaller than the surface roughness Ra of the inner wall of the second section S 1 . 
     (Variation 3) 
       FIG. 14  is a plan view of an upper surface of the flow path spacer substrate  12  in Variation 3. 
     This variation is different from the above-described embodiment in that the first individual ejection flow paths  122   a  and the second individual ejection flow paths  122   b  branching from the channels  141  are different from each other in length, and is the same as the above-described embodiment in other respects. 
     As shown in  FIG. 14 , the channels  141  are arranged in a staggered pattern. That is, the channels  141  are arranged in two rows (channel rows) in the X direction, and the positions of the two channel rows are misaligned in the X direction so as to differentiate the positions of the channels  141 . 
     With this configuration, in the channels  141  odd-numbered in the X direction, the length in the Y direction (direction of ink ejection) of the first individual ejection flow paths  122   a  is shorter than that of the second individual ejection flow paths  122   b . On contrary, in the channels  141  even-numbered in the X direction, the length in the Y direction of the first individual ejection flow paths  122   a  is longer than that of the second individual ejection flow paths  122   b.    
     With the configuration in which the length in the direction of ink ejection of the first individual ejection flow path  122   a  communicating to one of the channels  141  is different from the length in the direction of ink ejection of the second individual ejection flow path  122   b  communicating to the concerning one of the channels  141  as in this variation, the characteristics of the pressure wave propagating from the channels  141  to the common ejection flow path  142   a  are different from the characteristics of the pressure wave propagating from the channels  141  to the second common ejection flow path  142   b . This makes it possible to effectively differentiate the characteristics of the standing waves generated in the first common ejection flow path  142   a  and the second common ejection flow path  142   b.    
     (Variation 4) 
       FIG. 15  is a plan view of an upper surface of the flow path spacer substrate  12  in Variation 4. 
     This variation is different from the above-described embodiment in that two of the first individual ejection flow paths  122   a  and two of the second individual ejection flow paths  122   b  communicate to each of the channels  141 , and is the same as the above-described embodiment in other respects. 
     As shown in  FIG. 15 , each of the channels  141  and the first common ejection flow path  142   a  are connected by two of the first individual ejection flow paths  122   a , and each of the channels  141  and the second common ejection flow path  142   b  are connected by two of the second individual ejection flow paths  122   b . In  FIG. 15 , the two of the first individual ejection flow paths  122   a  connected to one of the channels  141  are equal in length and width, and so are the two second individual ejection flow paths  122   b . However, the configuration is not limited to the above, and two of the first common individual ejection flow paths  122   a  communicating to one of the channels  141  may be different from each other in width and length, and two of the second individual ejection flow paths communicating to one of the channels  141  may be different from each other in length and width. 
     The number of the first individual ejection flow paths  122   a  and the second individual ejection flow paths  122   b  communicating to each of the channels  141  may be three or more. 
     With the configuration in which two or more of the first individual ejection flow paths  122   a  and two or more of the second individual ejection flow paths  122   b  communicate to one of the channels  141 , it is possible to effectively eject air bubbles and foreign substances from the channels  141 . 
     (Variation 5) 
       FIG. 16  is a plan view of an upper surface of the flow path spacer substrate  12  in Variation 5. 
     In this variation, the channels  141  are aligned in two rows (channel rows) in the X direction, and the first common ejection flow path  142   a  and the second common ejection flow path  142   b  are arranged on the both sides of the channels  141 . The second ejection flow path  142   b  is shared by the two channel rows. 
     In other words, the first common ejection flow path  142   a , the second common ejection flow path  142   b , and the first common ejection flow path  142   a  parallel to one another are arranged in the said order in the Y direction, and one channel row is aligned in the X direction between the second common ejection flow path  142  and one of the first common ejection flow paths  142   a , and another channel row is aligned in the X direction between the second common ejection flow path  142  and the other one of the first common ejection flow paths  142   a . The channels  141  in each channel row communicate to the first common ejection flow path  142   a  and the second common ejection flow path  142   b  on each side in the Y direction. 
     With the configuration in this variation, more ink flows into the second common ejection flow path  142   b  as the channels  141  twice as many in number as those connected to the first common ejection flow path  142   a  are connected thereto, but as the width Wb of the second common ejection flow path  142   b  is greater than the first common ejection flow path  142   b , it is possible to suppress occurrence of troubles of congestion of ink flow to the second common ejection flow path  142   b . The characteristics of the standing waves generated in the two first common ejection flow paths  141   a  may be different from the characteristics of the standing waves generated in the second common ejection flow path  142   b.    
     The present invention is not limited to the above embodiment and variations, and various changes can be made thereto. 
     For example, in the above embodiment and variations, the full widths, depths, and lengths of the first section S 1  and the second section S 2  are differentiated so that the shapes of the first section S 1  in the first common ejection flow path  142   a  and the second section S 2  in the second common ejection flow path  142   b  are different from each other. However, the invention is not limited to this. The first section S 1  and the second section S 2  may be in any shape under the condition that one does not coincide with the other even if rotated or moved in any way. 
     For example, the widths and depths of the first section S 1  and the second section S 2  may be changed by position. Alternatively, the cross-sectional areas of the first section S 1  and the second section S 2  may be gradually increased in the direction of ink ejection in the common ejection flow paths  142 . The first section S 1  and the second section S 2  may be different in shape but equal in volume. 
     The common ejection flow paths  142  and the individual ejection flow paths  122  are not necessarily in a linear shape, and may be in a shape bended at a point midway. 
     Ink is not necessarily ejected in the same direction in the first common ejection flow path  142   a  and the second common ejection flow path  142   b , and ink may be ejected in the opposite directions. 
     In the above embodiment and variations, part of the nozzle substrate  11  functions as the damper substrate  11 D, as an example. However, the present invention is not limited to this. For example, a sealed air chamber may be provided inside the head chip  10 , and the common ejection flow path  142  is provided at a position adjacent to the air chamber. A material between the common ejection flow path  142  and the air chamber may thereby function as a damper substrate. 
     The configuration may be without a damper substrate. 
     In the above embodiment, the common ejection flow path  142  includes the belt-like penetrating flow path  123  in the flow path spacer substrate  12  and the ditch-like flow path  132  in the pressure substrate  13 , as an example. However, the present invention is not limited to this. For example, the common ejection flow path  142  may be a ditch on the surface of the spacer substrate  12  on the nozzle substrate  11  side. 
     The head chip  10  may be with the pressure chamber substrate  13  and the nozzle substrate  11  but without the flow path spacer substrate  12 . In that case, the flow path substrate  14  is composed exclusively by the pressure chamber substrate  13 , and the individual ejection flow paths  122  and the common ejection flow paths  142  are provided in the pressure chamber substrate  13 . In that case, the individual ejection flow path  122  and the common ejection flow path  142  may be a ditch provided on the surface of the pressure chamber substrate  13  on the nozzle substrate  11  side. 
     In the above-described embodiment, the inkjet head  100  including the head chip  10  in the shear mode is described as an example. However, the present invention is not limited to this. For example, the present invention may be applied to an inkjet head with a head chip in a bent mode in which ink in the pressure chamber is changed by deforming a pressure element (pressure changer) fixed on the wall of the pressure chamber as the ink storage. 
     In the above-described embodiment and variations, the recording medium M is conveyed by the conveyor  2  with the conveyance belt  2   c , as an example. However, the present invention is not limited to this, and the conveyor  2  may convey the recording medium M by holding the recording medium M on the peripheral surface of the rotating conveyance drum, for example. 
     In the above-described embodiment and variations, the inkjet recording apparatus  1  in a single pass format is described as an example, but the present invention can be applied to the inkjet recording apparatus which records the image while scanning with the inkjet heads  100 . 
     While the present invention is described with some embodiments, the scope of the present invention is not limited to the above-described embodiments but encompasses the scope of the invention recited in the claims and the equivalent thereof. 
     INDUSTRIAL APPLICABILITY 
     The present invention can be used in an inkjet head and an inkjet recording apparatus. 
     REFERENCE SIGN LIST 
     
         
           1  Inkjet Recording Apparatus 
           2  Conveyor 
           2   a ,  2   b  Conveying Roller 
           2   c  Conveyance Belt 
           3  Head Unit 
           9  Ink Circulation Mechanism 
           10  Head Chip 
           10   a  Ink Discharger 
           11  Nozzle Substrate 
           11 D Damper Plate 
           111  Nozzle 
           112  Nozzle Opening Face 
           12  Flow Path Spacer Substrate 
           121  Penetrating Flow Path 
           122   a  First Individual Ejection Flow Path 
           122   b  Second Individual Ejection Flow Path 
           123   a  First Belt-like Penetrating Flow Path 
           123   b  Second Belt-like Penetrating Flow Path 
           13  Pressure Chamber Substrate 
           131  Pressure Chamber 
           132   a  First Ditch-like Flow Path 
           132   b  Second Ditch-like Flow Path 
           133   a  First Vertical Ejection Flow Path 
           133   b  Second Vertical Ejection Flow Path 
           134  Partition 
           135  Connection Electrode 
           136  Drive Electrode 
           14  Flow Path Substrate 
           141  Channel 
           142   a  First Common Ejection Flow Path 
           142   b  Second Common Ejection Flow Path 
           142   c  Common Ejection Flow Path 
           15  Wiring Substrate 
           151  Ink Supply Opening 
           152   a  First Ejection Hole 
           152   b  Second Ejection Hole 
           20  FPC 
           100  Inkjet Head 
           103   a  Inlet 
           103   b ,  103   c  Outlet 
         M Recording Medium 
         S 1  First Section 
         S 2  Second Section