Patent Publication Number: US-2022227132-A1

Title: Liquid ejection head

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2021-007372, filed Jan. 20, 2021, the entire contents of which are incorporated herein by reference. 
     FIELD 
     Embodiments described herein relate generally to a liquid ejection head. 
     BACKGROUND 
     A liquid ejection head, such as an inkjet head or an inkjet printer head, can include a nozzle plate and a base plate. The nozzle plate includes a plurality of nozzles. The base plate is provided facing the nozzle plate and forms or includes a plurality of pressure chambers that are fluidly connected to the nozzles and a common chamber. A voltage can be applied to a drive element provided for the pressure chambers so as to cause a pressure change in the pressure chambers so that liquid is ejected from a nozzle. A liquid tank is connected to the liquid ejection head, and the liquid from the tank circulates in a circulation path that passes through the liquid ejection head back to the liquid tank. 
     In an inkjet printer head of shear-mode shared wall type, dummy chambers which are not utilized to eject ink may be provided alternately with actual (non-dummy) pressure chambers that are used to eject ink. The nozzles are fluidly connected a non-dummy pressure chamber, but the dummy chambers are not connected to any nozzle. Any nozzle adjacent to a dummy chamber is blocked off from the dummy chamber by the nozzle plate or the like. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts an inkjet head in a perspective view according to a first embodiment. 
         FIG. 2  depicts aspects of an inkjet head in an exploded perspective view. 
         FIG. 3  depicts aspects of an inkjet head in a cross-sectional view according to a first embodiment. 
         FIG. 4  depicts aspects of an inkjet head in a cross-sectional view according to a first embodiment. 
         FIG. 5  depicts aspects of an inkjet head in an enlarged perspective view according to a first embodiment. 
         FIG. 6  is a graph illustrating an example of an acoustic resonance period of a drive flow path and a dummy flow path in an inkjet head according to a first embodiment. 
         FIG. 7  depicts a configuration example of an inkjet recording device according to a second embodiment. 
         FIG. 8  depicts aspects of a liquid ejection head according to another embodiment. 
         FIG. 9  depicts aspects of a liquid ejection head according to a modified embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     At least one embodiment of the present disclosure provides a liquid ejection head having lower crosstalk between adjacent pressure chambers. 
     According to an embodiment, a liquid ejection head includes a plurality of drive flow paths, a plurality of dummy flow paths, and a plurality of side walls. The drive flow paths connect to liquid ejection nozzles. The dummy flow paths connect to dummy nozzles. The dummy flow paths are adjacent the drive flow paths. The side walls are between the drive flow paths and the dummy flow paths and configured to simultaneously change volumes of both the drive flow paths and the dummy flow paths in response to a drive signal. A first acoustic resonance period of liquid in the dummy flow paths is shorter than a second acoustic resonance period of the liquid in the drive flow paths. 
     First Embodiment 
     A configuration of an inkjet head  10  that is one example of a liquid ejection head according to a first embodiment will be described with reference to  FIGS. 1 to 5 .  FIG. 1  is a perspective view illustrating an inkjet head of the first embodiment.  FIG. 2  is an exploded perspective view illustrating a portion of the inkjet head.  FIGS. 3 and 4  are cross-sectional views, and  FIG. 5  is a perspective view illustrating a portion of the inkjet head in an enlarged manner. In the example embodiments, the parallel arrangement direction for ejection nozzles  28  and for drive flow paths  31  of the inkjet head  10  is along or parallel to the X axis, which may be referred to as along or in the X direction, the extension direction of each of the drive flow paths  31  is along or parallel to the Y axis, which may be referred to as along or in the Y direction, and the ejection direction for liquid from the ejection nozzles  28  is along or parallel to the Z axis, which may be referred to as along or in the Z direction. In general, unless otherwise stated, references to these directions are intended to be descriptive of the relative orientation and/or positions amongst the described device elements themselves rather than to any other fixed or absolute coordinate system (such as the direction of gravity or the like). 
     As illustrated in  FIG. 1 , the inkjet head  10  is of a shear-mode shared wall type having a so-called side shooter design. The inkjet head  10  is configured to eject ink and is provided, for example, in an inkjet printer. 
     The inkjet head  10  includes a base plate  11 , a nozzle plate  12 , and a frame member  13 . The base plate  11  is one example of a base or a base member. An ink chamber  16  (see FIG.  3 ) is formed inside the inkjet head  10 . The ink chamber  16  holds ink that can be supplied from an ink tank or the like. The ink is one example of a liquid to be ejected from the inkjet head  10 . 
     Other components, such as a circuit board  17  and a manifold  18 , are attached to the inkjet head  10 . The circuit board  17  controls the inkjet head  10 . The manifold  18  forms a portion of an ink circulation path between the inkjet head  10  and the ink tank. 
     The base plate  11  has, for example, a rectangular plate shape formed using ceramics, such as alumina. The base plate  11  includes a flat installation surface  21  (also referred to as mounting surface  21 ). As shown in  FIG. 2 , a plurality of supply holes  25 , a pair of actuators  14 , a plurality of discharge holes  26  are provided on the installation surface  21 . 
     The supply holes  25  are provided next to each other in a row along the longitudinal direction (a first direction/X direction) of the base plate  11 . The row of the supply holes  25  is positioned at a central portion or on a center line of the base plate  11  with respect to the width direction (a second direction/Y direction) of the base plate  11 . As shown in  FIG. 3 , each supply hole  25  communicates with an ink supply unit  181  of the manifold  18 . Each supply hole  25  is connected to the ink tank via the ink supply unit  181 . The ink of the ink tank is supplied to the ink chamber  16  from the respective supply holes  25 . 
     As illustrated in  FIG. 2 , the discharge holes  26  are provided side by side in two rows parallel to the row of the supply holes  25 , with the row of supply holes being therebetween. Each discharge hole  26  communicates with an ink discharge unit  182  of the manifold  18  (see  FIG. 3 ). Each discharge hole  26  is connected to the ink tank via the ink discharge unit  182 . The ink of the ink chamber  16  is discharged from the respective discharge holes  26  to the ink tank. In this manner, the ink circulates between the ink tank and the ink chamber  16 . 
     The pair of actuators  14  are adhered to the installation surface  21  of the base plate  11 . The actuators  14  are in two rows parallel to the row of the supply holes  25  with one of the actuators  14  on each side of the row of supply holes. Each actuator  14  comprises, for example, two plate-shaped piezoelectric bodies formed of lead zirconate titanate (PZT). The two piezoelectric bodies are bonded together so that the polarization directions are opposite to each other in its thickness direction. Each actuator  14  is adhered to the installation surface  21  with, for example, a thermosetting epoxy-based adhesive. The two rows of the actuators  14  are disposed corresponding to, respectively, two rows of ejection nozzles  28  provided in the longitudinal direction of the nozzle plate  12  (see  FIG. 2 ). The two rows of the actuators  14  are also positioned in parallel inside the ink chamber  16 . As illustrated in  FIG. 3 , the actuators  14  divide the ink chamber into at least one supply chamber  161  and two discharge chambers  162 . The supply chamber  161  are formed between the two rows of the actuators  14 , and the supply holes  25  of the base plate  11  communicate with the supply chamber  161  through the installation surface  21 . The two discharge chambers  162  are formed on the other side of the actuators  14  from the supply chamber  161  in the width direction (Y direction in  FIG. 3 ), and the discharge holes  26  of the base plate  11  communicate with the discharge chambers  162  through the installation surface  21 . 
     Each actuator  14  is formed into a trapezoidal cross section shape. The top of the actuator  14  adheres to the nozzle plate  12 . The actuator  14  includes a plurality of drive flow paths  31  and a plurality of dummy flow paths  32 . The drive flow paths  31  and the dummy flow paths  32  are pressure chambers formed by grooves, which have the same shape with each other, at the top of the actuator  14 , and side walls  33  are formed between the grooves as drive elements. The shape of each drive flow path  31  may be different from that of each dummy flow path  32 . As shown in  FIGS. 3 and 4 , at least one side wall  33  is formed between the neighboring drive flow path  31  and dummy flow path  32 , and configured to simultaneously change the volumes of both the drive flow path  31  and the dummy flow path  32  in response to one or more drive signals. 
     As shown in  FIGS. 4 and 5 , the drive flow paths  31  and the dummy flow paths  32  are alternately disposed and separated from each other by the side walls  33 . The drive flow paths  31  and the dummy flow paths  32  each extend in the direction (a second direction/Y direction) intersecting the longitudinal direction (a first direction/X direction) of the actuators  14  and are in parallel with each other in the longitudinal direction (a first direction/X direction) of the actuators  14 . 
     The plurality of ejection nozzles  28  of the nozzle plate  12  are open in the plurality of drive flow paths  31 . One end portion of the drive flow path  31  is open to the supply chamber  161  of the ink chamber  16 . The other end portion of the drive flow path  31  is open to the discharge chamber  162  of the ink chamber  16 . That is, both ends of the drive flow paths  31  are open to the ink chamber  16 . Therefore, the ink flows in from one end portion of the drive flow path  31  and then out from the other end portion. 
     The nozzle plate  12  also includes a plurality of dummy nozzles  29  open to the dummy flow paths  32 . One end of the dummy flow path  32  is open to the supply chamber  161 . The other end of the dummy flow path  32  is open to discharge chambers  162 . That is, both ends of the dummy flow paths  32  connect to the ink chamber  16 . Therefore, the ink flows in from the one end of the dummy flow path  32  and out from the other end. 
     Electrodes  34  are provided for each of the drive flow paths  31  and the dummy flow paths  32 . The electrodes  34  are formed by, for example, a nickel thin film. The electrodes  34  cover inner surfaces of the drive flow paths  31  and the dummy flow paths  32 . 
     The ink chamber  16  is formed by the surrounding base plate  11 , nozzle plate  12 , and frame member  13 . The ink chamber  16  is a region formed between the base plate  11  and the nozzle plate  12 . 
     As illustrated in  FIG. 2 , pattern wirings  35  are formed on the installation surface  21  of the base plate  11 . The pattern wirings  35  are, for example, formed from a nickel thin film. Each pattern wiring  35  has a common pattern portion and an individual pattern portion, and reaches a particular one of the electrodes  34  of an actuator  14 . 
     The nozzle plate  12  is, for example, a rectangular film made of polyimide. The nozzle plate  12  faces the installation surface  21  of the base plate  11 . The nozzle plate  12  has the ejection nozzles  28  and the dummy nozzles  29  penetrating therethrough in the thickness direction. 
     The plurality of ejection nozzles  28  are provided in the same number as the drive flow paths  31  in the longitudinal direction (first direction/X direction) of the nozzle plate  12 , and each of the ejection nozzles  28  connects with a corresponding one of the drive flow paths  31 . The ejection nozzles  28  are arranged in two rows parallel to each other in the width direction (second direction/Y direction) of the nozzle plate  21 . Each of the rows corresponds to one of the pair of actuators  14 . Each ejection nozzle  28  has a generally cylindrical shape. In some examples, the ejection nozzle  28  may have a constant diameter or a changing diameter that decreases at some point along the length of the generally cylindrical shape, such as at the central portion or towards an end of the cylindrical shape. If some portion of the ejection nozzle  28  is reduced in diameter, the diameter of the smallest portion is regarded as the diameter of the ejection nozzle  28 . The ejection nozzles  28  overlap the drive flow paths  31  formed by the pair of actuators  14  and fluidly connect to one of the drive flow path  31 . Each of the ejection nozzles  28  is positioned near the central portion of one of the drive flow paths  31 . 
     As illustrated in  FIG. 2 , dummy nozzles  29  are also arranged in two rows spaced from each other in the width direction (Y direction). The two rows of dummy nozzles  29  correspond in general to the pair of actuators  14  and thus run in the longitudinal direction (X direction) like the two rows of the ejection nozzles  28 . These two rows each include subgroups (or subsets) of the dummy nozzles  29 . Each subgroup includes multiple dummy nozzles  29  aligned with each other along the width direction (Y direction) of the nozzle plate  12 . Each of these subgroups of each row of the dummy nozzles  29  is aligned to a subgroup in the opposite row. Each dummy nozzle  29  in the same subgroup of dummy nozzles  29  faces the same one of the dummy flow paths  32  (see also  FIG. 5 ). 
     The summed total opening area of the dummy nozzles  29  on each dummy flow path  32  can be set such that ink will not be ejected from the dummy flow path  32  and the acoustic resonance period of ink inside the dummy flow path  32  will be shorter than an acoustic resonance period of ink inside a drive flow path  31 . For example, the total nozzle opening area of the dummy nozzles  29  is set to be greater than that of the nozzle opening area of the single ejection nozzle  28  on a drive flow path  31 . In one instance, the acoustic resonance period of the dummy flow path  32  may be set to be equal to or shorter than one-half (½) of the acoustic resonance period of the drive flow path  31 . In another instance, the acoustic resonance period of the dummy flow path  32  may be one-half (½) of the acoustic resonance period of the drive flow path  31 . As one example, a half cycle (AL) of the acoustic resonance period of the drive flow path  31  may be set to satisfy the following relationship: 
         AL= 2π/{ c √( Sn/Vd/Ln )}.
 
     In this context, the value c is the pressure propagation velocity of the ink in the dummy flow path  32 , the value Sn is the opening area of a dummy nozzle  29  on the dummy flow path  32 , the value Ln is the length of an ejection nozzle  28  and a dummy nozzle  29  and the length Ln is equal to the thickness of the nozzle plate  12 , and the value Vd is a volume of the dummy flow path  32  for each dummy nozzle  29  (dummy flow path volume per dummy nozzle on the dummy flow path). 
     In the present embodiment, each of the dummy nozzles  29  has the same or substantially the same shape as each of the ejection nozzles  28 . Each subgroup of the dummy nozzles  29  in each of the two rows extends over the entire length or substantially the entire length of the corresponding one of the dummy flow paths  32  in the width direction (second direction/Y direction) of the nozzle plate  12  or the base plate  11 , that is the lengthwise direction of the dummy flow path  32  (see  FIG. 5 ). In this case, for example, dummy nozzles  29  at both ends of the dummy nozzle subgroup are positioned at or near the lengthwise ends of the corresponding dummy flow path  32 . 
     Each dummy nozzle  29  may have a diameter that is constant or that changes in the thickness direction (third direction/Z direction) of the nozzle plate  12 . In the latter case, for example, the diameter of the dummy nozzle  29  may decreases at a nozzle central portion in the ink ejecting direction or gradually decreases, towards an end of the nozzle. In general, the narrowest (smallest) diameter along the length of the dummy nozzle  29  is taken as a diameter of the dummy nozzle  29 . 
     In one example where: 
     the thickness Ln of the nozzle plate  12 =50 μm; 
     the diameter of the ejection nozzle  28 =Φ 20 μm; 
     the diameter of the dummy nozzle  29 =Φ 20 μm; 
     the number of dummy nozzles  29  arranged in one dummy flow path  32 =20; 
     the size of the drive flow path  31 =(40 μm×150 μm×2 mm); and 
     the size of the dummy flow path  32 =(40 μm×150 μm×2 mm); 
     ink density ρ=1000 kg/m 3 ; 
     pressure propagation velocity c of ink in the flow paths  31  and  32 =920 m/s; 
     groove width Wc=40 μm; 
     groove depth Hc=150 μm; 
     flow path length Lc=2 mm; 
     diameter Dn of each dummy nozzle  29 =20 μm; 
     nozzle length Ln=50 μm; 
     dummy nozzle interval Ld=0.1 mm (20 dummy nozzles); and 
     nozzle cross-sectional area Sn=πDn 2 /4, 
     the volume Vd of the dummy flow path  32  per dummy nozzle  29  satisfies the following relationship: 
     
       
      
       Vd=Wc·Hc·Ld.  
      
     
     Therefore, the acoustic resonance period T of the dummy flow path  32  is equal to 2π/{c√(Sn/Vd/Ln)}, and T will be 2.11 μs (Helmholtz resonance frequency). 
     The acoustic resonance period of the drive flow path  31  is: 
       2 Lc/c= 4.35 μs.
 
     Hence, the acoustic resonance period of the dummy flow path  32  will be equal to or less than one-half (½) of the acoustic resonance period of the drive flow path  31 . 
     Referring back to  FIGS. 1 and 2 , the frame member  13  has a rectangular frame shape formed using, for example, a nickel alloy. The frame member  13  is interposed between the installation surface  21  of the base plate  11  and the nozzle plate  12 . The frame member  13  adheres to the installation surface  21  and the nozzle plate  12 . The nozzle plate  12  is attached to the base plate  11  via the frame member  13 . 
     The manifold  18  is joined to the base plate  11  on the opposite side from the nozzle plate  12 . The ink supply unit  181  constitutes part of a flow path connecting to the supply hole  25 , and the ink discharge unit  182  constitutes part of a flow path connecting to the discharge hole  26 . The ink supply unit  181  and the ink discharge unit are formed inside the manifold  18  (see  FIG. 3 ). 
     The circuit board  17  is a film carrier package (FCP) and includes a film  51  and one or more ICs  52 . The film  51  is a resin on which a plurality of wirings are formed. The film  51  has flexibility. The ICs  52  are connected to the wirings on the film  51 . The FCP is also referred to as a tape carrier package (TCP). The film  51  is tape automated bonding (TAB), for example. One end portion of the film  51  is connected to the pattern wirings  35  on the installation surface  21  by thermocompression using an anisotropic conductive film (ACF)  53 . The ICs  52  apply voltages to the electrodes  34 . The ICs  52  are fixed to the film  51  by, for example, a resin. The ICs  52  are electrically connected to the electrodes  34  via the wirings of the film  51  or the pattern wirings  35  of the base plate  11 . 
     In the inkjet head  10  according to the present embodiment, the ICs  52  apply drive voltages to the electrodes  34  of the drive flow paths  31  via the wirings of the film  51  by a signal from a control unit of an inkjet printer in which the inkjet head  10  is installed. The application of the drive voltages causes a difference in potential between the electrode  34  of each of the drive flow paths  31  and the electrode  34  of each of the dummy flow  32  so that a side wall  33  is selectively deformed in shear mode. The side wall  33  between a drive flow path  31  and a dummy flow path  32  deforms in response to the drive signals so that the volumes of the drive flow path  31  and the dummy flow path  32  are both simultaneously changed. 
     By deforming the side wall  33  in shear mode, the volume of the drive flow path  31  provided with the corresponding electrode  34  increases, and the pressure decreases. This causes the ink in the ink chamber  16  to flow into the corresponding drive flow path  31 . Simultaneously, the volume of the dummy flow path  32  adjacent the corresponding drive flow path  31  decreases, and the pressure increases. This increase in the pressure of the dummy flow path  32  pushes the ink of the dummy flow path  32  out from both ends of the dummy flow path  32  to the ink chamber  16 , and the pressure change in the dummy flow path  32  is reduced. 
     When the volume of the drive flow path  31  is to be increased, the IC  52  applies a drive voltage of a reverse potential to the electrode  34  of the drive flow path  31 . As a result, the side wall  33  deforms, the volume of the drive flow path  31  provided with the corresponding electrodes  34  decreases, and the pressure increases. This pressurizes the ink in the drive flow path  31 , and the ink can be ejected from the nozzle  28 . 
     With the liquid ejection head, such as the inkjet head  10 , according to the present embodiment, crosstalk between adjacent nozzles can be suppressed. In the inkjet head  10 , the dummy flow paths  32  includes the dummy nozzles  29  and is formed between the two neighboring drive flow paths  31  that form the pressure chambers communicating with the ejection nozzles  28 , and the acoustic resonance periods of the drive flow path  31  and the dummy flow path  32  are set to be different from each other by inclusion of the dummy nozzles  29 . This mitigates or suppresses the crosstalk between the adjacent ejection nozzles  28 . 
     For example, when ink is to be simultaneously ejected from three adjacent ejection nozzles  28  having dummy flow paths  32  sandwiched therebetween, at the time of ejection of the ink from the middle nozzle of the three nozzles  28 , the corresponding side walls  31  acting as a drive element can be selectively deformed to pressurize the middle drive flow path  31 , the pressures in the adjacent dummy flow paths  32  will be correspondingly reduced, and the thus the deformation amounts that will be caused the adjacent drive elements can decrease. Therefore, the pressurization amount for the adjacent drive flow paths is reduced. 
     When there are no dummy nozzles  29  on the dummy flow path  32 , if the multiple adjacent ejection nozzles  28  are to be simultaneously driven, speed and volume of an ink droplet from adjacent ejection nozzles  28  can be reduced and printing quality may be deteriorated as compared with the case in which only a single ejection nozzle  28  at a time is driven to eject the ink. In such a case, liquid ejection performance cannot be maintained at an expected or a desired level. On the other hand, in the present embodiment, as shown in  FIG. 6 , if the acoustic resonance period of the dummy flow path  32 , with which the dummy nozzles  29  communicate, is set to one-half (½) of the acoustic resonance period of the drive flow path  31 , the influence of the pressure variation in the dummy flow paths  32  will be offsetting with respect to each other during the period of the half cycle of the pressure vibration of the drive flow path  31 . Accordingly, the influence of pressure vibrations of the dummy flow paths  32  will be reduced. Therefore, the crosstalk between the adjacent ejection nozzles  28  will be mitigated or suppressed, and the liquid ejection performance can be maintained at a desired level and/or a greater liquid ejection performance can be achieved. 
     In the inkjet head  10 , the drive flow paths  31  and the dummy flow paths  32  are alternately disposed, and ink can be simultaneously ejected from each of the drive flow paths  31 . Thus, the drive frequency of the inkjet head  10  can be further increased. Since both ends of each of the dummy flow paths  32  are open to the ink chamber  16 , each dummy flow path  32  can be easily filled with the ink, and accumulation of air in the dummy flow path  32  can be suppressed. Further, since the ink of each dummy flow path  32  flows from the supply chamber  161  of the ink chamber  16  to the discharge chamber  162 , increase in liquid temperature of the ink in the dummy flow path  32  can be suppressed. Accordingly, even if the inkjet head  10  has the dummy flow path  32  provided in addition to the drive flow path  31 , the influence on the ink ejection due to a different crosstalk amount of the drive flow path  31  or the increase in the temperature of the ink of the dummy flow path  32  can be effectively suppressed. 
     Second Embodiment 
     An example of an inkjet recording device  100  including the inkjet head  10  will be described as a second embodiment with reference to  FIG. 7 . The inkjet recording device  100  includes a housing  111 , a medium supply unit  112 , an image forming unit  113 , a medium discharge unit  114 , a conveyance device  115 , and a control unit  116 . 
     The inkjet recording device  100  is one example of a liquid ejection device. The inkjet recording device  100  performs an image forming process on a sheet of paper P that serves as a recording medium. The inkjet recording device  100  ejects liquid (e.g., ink) on to an ejection target (e.g., a sheet of paper). By ejecting a liquid while conveying the ejection target along a predetermined conveyance path A from the medium supply unit  112  to the medium discharge unit  114  via the image forming unit  113  and image can be formed on the ejection target (paper P). 
     The housing  111  includes an outer frame of the inkjet recording device  100 . A discharge port for discharging the sheet P to the outside is provided in the housing  111 . 
     The medium supply unit  112  includes a plurality of paper feed cassettes and is configured to hold a plurality of sheets P of various sizes. 
     The medium discharge unit  114  includes a sheet discharge tray configured to hold the sheet P after discharge from the discharge port. 
     The image forming unit  113  includes a supporting unit  117  that supports the sheet P and a plurality of head units  130  that face the supporting unit  117  at a position above the supporting unit  117 . 
     The supporting unit  117  includes a conveyance belt  118  provided in a loop shape, a support plate  119  that supports the conveyance belt  118  from the back side, and a plurality of belt rollers  120  provided on the back side of the conveyance belt  118 . 
     At the time of forming an image, the supporting unit  117  supports the sheet P on its sheet holding surface that is an upper surface of the conveyance belt  118  and conveys the sheet P downstream by rotating the belt rollers  120  and sending forward the conveyance belt  118  at a predetermined timing. 
     The head units  130  are for ejecting different colors, such as four colors, respectively. Each head unit  130  includes an inkjet head  10  for one corresponding color (there are four inkjet heads  10  for four colors in the example shown in  FIG. 7 ), an ink tank  132  as a liquid tank of the corresponding color mounted on the inkjet head  10 , a connection flow path  133  that connect the inkjet head  10  to the ink tank  132 , and a circulation pump  134  that is one example of a circulation unit. Each head unit  130  is a circulation-type head unit that constantly circulates the liquid or the ink in the ink tank  132  as well as in the drive flow paths  31 , the dummy flow paths  32  and the ink chamber  16  which are provided inside the inkjet head  10 . 
     In the present example, the inkjet heads  10  are for four colors (cyan, magenta, yellow, and black), and ink tanks  132  for respectively containing inks of these four colors are provided. Each ink tank  132  is connected to the corresponding inkjet head  10  by a connection flow path  133 . The connection flow path  133  includes a supply flow path connected to a liquid supply port of the inkjet head  10  and a collection flow path that is connected to a liquid discharge port of the inkjet head  10 . 
     A negative pressure control device, such as a pump, is also connected to the ink tank  132 . The negative pressure control device controls pressure inside the ink tank  132  according to head pressure values of both the inkjet head  10  and the ink tank  132  to form a meniscus of ink within each ejection nozzle  28 . 
     The circulation pump  134  is, for example, a liquid feed pump comprising a piezoelectric pump. The circulation pump  134  is provided on the supply flow path of the connection flow path  133 . The circulation pump  134  is connected to a drive circuit of the control unit  116  by wiring and is controlled by a Central Processing Unit (CPU). The circulation pump  134  circulates the liquid in a circulation flow path including the inkjet head  10  and the ink tank  132 . 
     The conveyance device  115  conveys the sheet P along the conveyance path A from the medium supply unit  112  to the medium discharge unit  114  via the image forming unit  113 . The conveyance device  115  includes a plurality of guide plate pairs  121  disposed along the conveyance path A and a plurality of conveyance rollers  122 . 
     Each of the guide plate pairs  121  includes a pair of plate members arranged to face each other sandwiching the sheet P therebetween and is configured to guide the sheet P along the conveyance path A. 
     The conveyance rollers  122  are driven and rotate by the control of the control unit  116  to send the sheet P downstream along the conveyance path A. On the conveyance path A, sensors for detecting a conveyance circumstance or condition of the sheet P are provided in various appropriate places or at predetermined positions within the inkjet recording device  100 . 
     The control unit  116  includes a control circuit as a controller, such as a CPU, a Read Only Memory (ROM) that stores various programs, a Random Access Memory (RAM) that temporarily stores various variable data and image data, and an interface unit that receives data from outside of the inkjet recording device  100 , such as a separate unit, an external device and a network, and outputs data to the outside. 
     In the inkjet recording device  100 , upon detection of a print instruction from a user who operates an operation input unit of an operation interface provided to the inkjet recording device  100 , the control unit  116  drives the conveyance device  115  to convey the sheet P along the conveyance path A and outputs one or more print signals to the head units  130  at a predetermined timing to drive the inkjet heads  10 . 
     As part of liquid ejection operation, the inkjet heads  10  send one or more drive signals to the ICs  52  by one or more image signals in response to the image data temporarily stored in the RAM, apply the drive voltages to the electrodes  34  of the drive flow paths  31  via the wirings, selectively drive the side walls  33  of the actuators  14 , eject the ink from the ejection nozzles  28 , and form images on the sheet P held on the conveyance belt  118 . 
     Also, as part of the liquid ejection operation, the control unit  116  drives the circulation pumps  134  to circulate the liquid or the ink in the circulation flow paths via the ink tanks  132  and the inkjet heads  10 . By this circulation operation, the circulation pump  134  is driven to supply the ink in the ink tanks  132  from the supply holes  25  to the supply chambers  161  of the ink chamber  16  via the ink supply unit  181  of the manifold  18 . Ink is supplied to both the drive flow paths  31  and the dummy flow paths  32 . The ink flows into the discharge chambers  162  of the ink chamber  16  via the drive flow paths  31  and the dummy flow paths  32 . The ink is discharged from the discharge holes  26  to the ink tanks  132  via the ink discharge units  182  of the manifolds  18 . 
     [Modifications] 
     The disclosure is not limited to the above-described first and second embodiments. Components, elements, configurations, and the like can be modified by those of ordinary skill in the art without departing from the scope of the present disclosure. 
     For example, while in the first embodiment, each of the dummy nozzles  29  has the same shape as the ejection nozzles  28 , embodiments are not limited thereto. For example, the total number of dummy nozzles  29  may be reduced by increasing the opening area of the dummy nozzles  29  relative to the ejection nozzles  28 , or conversely, a more dummy nozzles  29  may be incorporated by decreasing the opening area of the dummy nozzles  29  relative to the ejection nozzles  28 . 
     While in the first embodiment, as illustrated in  FIG. 2 , each widthwise (Y direction) subgroup or subset of the dummy nozzles  29  in each of the two lengthwise (X direction) rows extends along the entire or substantially entire length of the corresponding one of the dummy flow paths  32  in the second direction/Y direction (that is the lengthwise direction of the dummy flow path  32 ), embodiments are not limited thereto. In one modified embodiment, as illustrated in  FIG. 8 , an inkjet head  110  may have a subgroup of dummy nozzles  29  formed only in a central portion along the length of a dummy flow path  32  rather than substantially the end-to-end length of the dummy flow path  32 . The subgroup may be centered between the adjacent ejection nozzles  28 . Alternatively, in another embodiment, as illustrated in  FIG. 9 , an inkjet head  210  comprises a dummy nozzle  290  having a slit or slot shape extending along the second direction/Y direction rather than round (cylindrical). 
     In the above examples, a liquid ejection head is incorporated into an inkjet printer, such as the inkjet recording device  100 , for forming a two-dimensional image with the ink on a sheet P or the like, but the present disclosure is not limited thereto. In other examples, the described liquid ejection heads can be incorporated in, or utilized as, an inkjet recording device  100  such as a 3D printer, an industrial manufacturing machine, or a medical machine dispensing liquids. In the case of the 3D printer, a three-dimensional object can be formed by ejecting a substance such as a binder for solidifying a material or the like from the inkjet head. 
     The number of inkjet heads  10  or colors and characteristics of the ink or liquid to be used for image forming can be varied as appropriate. Transparent glossy ink, ink that develops colors upon being irradiated with infrared or ultraviolet rays, or other specialty inks can be ejected. 
     As still another embodiment, the inkjet head  10  may be used for ejecting a liquid other than ink. For example, a dispersion liquid, such as a suspension or solution, may be ejected. Examples of a liquid other than the ink that can be ejected by the inkjet head  10  include, but are not limited to, a liquid such as a resist type material for forming a wiring pattern on a printed wiring board, a liquid including cells therein for artificially forming a tissue or an organ, binders such as an adhesive, wax, or a liquid resin. 
     With a liquid ejection head, such as the inkjet head  10 , and a liquid ejection device, such as the inkjet recording device  100 , according to at least one of the present embodiments, crosstalk between adjacent nozzles can be effectively suppressed. 
     While certain embodiments have been described, these embodiments have been presented by way of example only and are not intended to limit the scope of the disclosure. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the disclosure. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the disclosure.