Patent Publication Number: US-8540354-B2

Title: Liquid ejection head

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority from Japanese Patent Application No. 2011-065428, filed on Mar. 24, 2011, the entire subject matter of which is incorporated herein by reference. 
     TECHNICAL FIELD 
     Aspects of the present invention relate to a liquid ejection head including a plurality of pressure chambers arranged in a matrix form. 
     BACKGROUND 
     There has been known a head which ejects liquid such as ink and includes a plurality of pressure chambers arranged in a matrix form in a two-dimensional area having a parallelogram shape. In such a head, a longitudinal direction of each pressure chamber is aligned in a shorter direction of the head. 
     If the longitudinal direction of the pressure chambers is arranged in the shorter direction of the head, the area in which the pressure chambers are arranged in the matrix form becomes larger, so that it is difficult to reduce the entire size of the head. 
     SUMMARY 
     Accordingly, an aspect of the present invention provides a liquid ejection head including a plurality of pressure chambers arranged such that the entire size of the head is compact. 
     According to an illustrative embodiment of the present invention, there is provided a liquid ejection head comprising: a flow path unit which includes: a plurality of liquid ejection ports arranged in a matrix form in a two-dimensional area of a parallelogram; and a plurality of pressure chambers communicating with the plurality of liquid ejection ports, respectively, and each pressure chamber being long in a first direction. The flow path unit is long in a second direction. Each of the pressure chambers has a length in the second direction larger than a length in a direction orthogonal to the second direction. The plurality of pressure chambers are arranged in a matrix form in a substantially same area as the two-dimensional area. 
     According to the above configuration, the plurality of pressure chambers are arranged in the matrix form such that each pressure chamber is long in the longitudinal direction (second direction) of the flow path unit. Thereby, a width of the area in which the pressure chambers are arranged is reduced in the shorter direction of the flow path unit, so that the entire size of the head can be compact. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects of the present invention will become more apparent and more readily appreciated from the following description of illustrative embodiments of the present invention taken in conjunction with the attached drawings, in which: 
         FIG. 1  is a schematic side view showing an internal structure of an inkjet printer including an inkjet head according to an illustrative embodiment of the present invention; 
         FIG. 2  is a plan view of a flow path unit configuring a lower structure of the inkjet head of  FIG. 1 ; 
         FIG. 3  is a plan view showing a positional relation between a supply flow path and ejection ports formed in the flow path unit of  FIG. 2 ; 
         FIG. 4  is a sectional view of the flow path unit taken along a line of IV-IV of  FIG. 3 ; 
         FIG. 5  is an enlarged plan view of driving signal lines provided in an actuator unit and an FPC, wherein the driving signal lines are shown partially; 
         FIG. 6  is an enlarged plan view of an actuator unit according to a first modified illustrative embodiment in an arrangement mode of pressure chambers; 
         FIG. 7A  is a plan view showing an arrangement relation of individual electrodes according to the first illustrative modified embodiment; 
         FIG. 7B  is a plan view showing an arrangement relation of individual electrodes according to the illustrative embodiment shown in  FIG. 5 ; 
         FIG. 8  is an enlarged plan view of an actuator unit according to a second modified illustrative embodiment in an arrangement mode of the pressure chambers. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, illustrative embodiments of the present invention will be described with reference to the accompanying drawings. 
     First, an overall configuration of an inkjet printer  1  including an inkjet head  100  according to an illustrative embodiment of the present invention is described with reference to  FIG. 1 . 
     The printer  1  has a rectangular parallelepiped housing  1   a . A top plate upper part of the housing  1   a  is provided with a sheet discharge part  31 . In the below descriptions, an internal space of the housing  1   a  is divided into spaces A, B and C in order from the upper. The spaces A, B accommodate a sheet conveyance path continuing to the sheet discharge part  31 . In the space A, a sheet P is conveyed and an image is recorded on the sheet P. In the space B, a sheet feeding operation is performed. The space C accommodates an ink cartridge  40  which is an ink supply source. 
     In the space A, four inkjet heads  100 , a conveyance unit  21  which conveys the sheet P, a guide unit (which will be described later) which guides the sheet P, and the like are provided. In the upper part of the space A, a controller  1   p  is arranged which controls operations of respective units of the printer  1  including the above mechanisms and controls he entire operation of the printer  1 . 
     The controller  1   p  controls a preparation operation relating to a recording, feed/convey/discharge operations of the sheet P, an ink ejection operation synchronous with the conveyance of the sheet P, a recovering and maintaining operation of ejection performance (maintenance operation) and the like such that an image is recorded on the sheet P, based on image data supplied from the outside. 
     The controller  1   p  has a ROM (Read Only Memory), a RAM (Random Access Memory: including non-volatile RAM), an ASIC (Application Specific Integrated Circuit), an I/F (Interface), an I/O (Input/Output Port) and the like, in addition to a CPU (Central Processing Unit) which is a calculation processing device. The ROM stores therein programs which are executed by the CPU, a variety of fixed data and the like. The RAM temporarily stores therein data (for example, image data) which is necessary when executing the programs. In the ASIC, rewriting of image data, rearrangement (signal processing and image processing) and the like are performed. The I/F transmits and receives data to and from a higher-level apparatus. The I/O inputs and outputs detection signals of various sensors. 
     Each of the heads  100  is a line-type head having a substantially rectangular parallelepiped shape which is long in a main scanning direction (second direction). The four heads  100  are arranged in a sub-scanning direction at a predetermined distance and are supported to the housing  1   a  via a head frame  3 . The head  100  includes a flow path unit  110  and four actuator units  120  (refer to  FIG. 2 ). When recording an image, magenta, cyan, yellow and black inks are ejected from lower surfaces (ejection surfaces  100   a ) of the four heads  100 , respectively. The detailed configuration of the head  100  will be described later. 
     As shown in  FIG. 1 , the conveyance unit  21  has belt rollers  6 ,  7 , an endless conveyance belt  8  which is wound around the belt rollers  6 ,  7 , a nip roller  4  and a separation plate  5 , which are arranged on an outer side of the conveyance belt  8 , a platen  9  which is arranged on an inner side of the conveyance belt  8 , and the like. 
     The belt roller  7  is a driving roller and is rotated in a clockwise direction of  FIG. 1  as a conveyance motor  19  is driven. As the belt roller  7  is rotated, the conveyance belt  8  travels in a thick arrow direction of  FIG. 1 . The belt roller  6  is a driven roller and is rotated in the clockwise direction of  FIG. 1  as the conveyance belt  8  travels. The nip roller  4  is arranged to face the belt roller  6  and presses the sheet P, which is fed from an upstream side guide unit (which will be described later), onto an outer peripheral surface  8   a  of the conveyance belt  8 . The separation plate  5  is arranged to face the belt roller  7 , separates the sheet P from the outer peripheral surface  8   a  and guides the same to a downstream side guide unit (which will be described later). The platen  9  is arranged to face the four heads  100  and supports a loop upper part of the conveyance belt  8  from the inner side thereof. Thereby, a predetermined gap suitable for the image recording is formed between the outer peripheral surface  8   a  and the ejection surfaces  100   a  of the heads  100 . 
     The guide unit includes the upstream side guide part and downstream side guide part that are arranged with the conveyance unit  21  being interposed therebetween. The upstream side guide part has two guides  27   a ,  27   b  and a pair of conveyance rollers  26 . The upstream side guide part is provided along a conveyance path from a sheet feeding unit  1   b  (which will be described later) to the conveyance unit  21 . The downstream side guide part has two guides  29   a ,  29   b  and two pairs of conveyance rollers  28 . The downstream side guide part is provided along a conveyance path from the conveyance unit  21  to the sheet discharge part  31 . 
     In the space B, the sheet feeding unit  1   b  is provided. The sheet feeding unit  1   b  has a sheet feeding tray  23  and a sheet feeding roller  25 . The sheet feeding tray  23  is detachably attached to the housing  1   a . The sheet feeding tray  23  is a box which is opened upward and accommodates therein the sheets P having a plurality of sizes. The sheet feeding roller  25  feeds an uppermost sheet P in the sheet feeding tray  23 , to the upstream side guide part. 
     In the spaces A and B, as described above, the sheet conveyance path from the sheet feeding unit  1   b  to the sheet discharge part  31  via the conveyance unit  21  is formed. When the controller  1   p  drives the sheet feeding roller  25 , the conveyance rollers  26 ,  28 , the conveyance motor  19  and the like, based on a recording instruction, the sheet P is first fed from the sheet feeding tray  23 . The sheet P is fed to the conveyance unit  21  by the conveyance rollers  26 . When the sheet P passes below the respective heads  100  in the sub-scanning direction, the inks are ejected from the respective ejection surfaces  100   a , so that a color image is formed on the sheet P. Then, the sheet P is separated by the separation plate  5  and is conveyed upward by the two conveyance rollers  28 . Also, the sheet P is discharged to the sheet discharge part  31  through an upper opening  30 . 
     In the meantime, the sub-scanning direction is a direction which is parallel with the conveyance direction of the sheet P by the conveyance unit  21  and the main scanning direction is a direction which is parallel with a horizontal surface and is orthogonal to the sub-scanning direction. 
     In the space C, an ink unit  1   c  is detachably attached to the housing  1   a . The ink unit  1   c  has a cartridge tray  35  and four cartridges  40  which are accommodated in line in the cartridge tray  35 . The respective cartridges  40  supply inks to the corresponding heads  100  through ink tubes. 
     In the below, the configuration of the head  100  is more specifically described with reference to  FIGS. 2 to 5 . The head  100  includes an upper structure and a lower structure of a flow path forming member. The upper structure communicates with the cartridge  40  and temporarily stores therein the ink. The lower structure includes the flow path unit  110  and communicates with the upper structure. A lower surface of the lower structure is the ejection surface  100   a  and the ink is ejected through ejection ports  109  (which will be described later). Four parallelogram-shaped actuator units  120  are attached on an upper surface of the flow path unit  110 . Each actuator unit  120  is electrically connected to a circuit substrate, which is arranged at the upper part of the upper structure, by a flexible printed circuit (FPC)  150 . In the circuit substrate, a control signal from the outside is processed, and a driving signal based on the control signal is supplied from a driver IC on the FPC  150  to the actuator unit  120 . In the meantime, the FPCs  150  are drawn out alternately with respect to the main scanning direction from the actuator units  120  to the outside of the flow path unit  110  toward the sub-scanning direction. 
     The respective actuator units  120  have the same size and have a congruent parallelogram. Each side of the actuator unit  120  is inclined to the main scanning direction. Specifically, one sides of the actuator unit  120  form an acute angle θ 1  with the main scanning direction and the other sides form an angle θ 2  (&lt;θ 1 ). Hereinafter, the former sides in the left and right directions of  FIG. 2  are respectively referred to as the ‘left side’ and the ‘right side’ and the latter sides in the upper and lower directions of  FIG. 2  are respectively referred to as the ‘upper side’ and the ‘lower side.’ In an illustrative embodiment, θ 1  and θ 2  may be selected to satisfy the relationships: tan θ 1 =unit distance of 50 dpi/unit distance of 1200 dpi=24; and tan θ 2 =unit distance of 100 dpi/unit distance of 25 dpi=0.25. 
     The flow path unit  110  has a substantially rectangular parallelepiped shape and has a laminated structure including a plurality of plates  111  to  115  adhered to each other. On an upper surface thereof, ink supply ports  131  and pressure chambers  141  are opened. In the flow path unit  110 , supply flow paths  132  are formed. The supply flow path  132  allows the supply ports  131  of the upper surface and the ejection ports  109  of the lower surface to communicate with each other and is configured by common flow paths  133 , branch flow paths  134  and individual ink flow paths  140  from the upstream side. The lower surface of the flow path unit is the ejection surface  100   a  through which the ink is ejected, and the plurality of ejection ports  109  are opened. 
     The supply ports  131   a ,  131   b  of the upper surface are supplied with the ink from the upper structure. The supply ports  131  are opened while avoiding the arrangement areas of the actuator units  120  and are provided by a pair for each of the actuator units  120 . The supply ports  131   a  are arranged near an area between the upper sides of the parallelogram areas and an upper end of the flow path unit  110  in  FIG. 2  with respect to the sub-scanning direction and near obtuse angle parts of the parallelogram areas. The supply ports  131   b  are positioned between a lower end of the flow path unit  110  and obtuse angle parts of the lower sides of the parallelogram areas, thereby configuring the same arrangement relation as the supply ports  131   a . As shown in  FIG. 2 , one pair of the supply ports  131   a ,  131   b  are arranged in vacant areas which are formed due to the inclination of the actuator unit  120  with respect to the main scanning direction, and is substantially symmetric about a center of the parallelogram area. 
     The pressure chamber  141  of the upper surface is a hole which penetrates the plate  111  and configures a middle part of the individual ink flow path  140 . As shown in  FIG. 5 , the pressure chamber  141  has a substantially rectangular shape having a longitudinal direction (first direction) in the main scanning direction (second direction) and curved corners. The pressure chambers  141  are arranged in a matrix form and configure four pressure chamber groups. Each pressure chamber group occupies the parallelogram area and vertically overlaps with the actuator unit  120 . In the pressure chamber groups, the plurality of pressure chambers  141  configure pressure chamber columns  141   x  along the left side of the parallelogram area, and the plurality of pressure chamber columns  141   x  are arranged at an equal interval in the main scanning direction. A pressure chamber  141  is positioned between two pressure chambers  141  adjacent to each other in an adjacent pressure chamber column  141   x , with respect to the direction along the pressure chamber column  141   x . In this illustrative embodiment, as shown in  FIG. 5 , d 1 =2×d 2 . The pressure chamber  141  is positioned at an equal distance (at the center of an interval) to the two pressure chambers  141  in the adjacent pressure chamber column  141   x . Thereby, an influence of crosstalk becomes uniform. 
     As shown in  FIGS. 2 and 3 , the internal supply flow path  132  communicates with the supply ports  131   a ,  131   b . As shown in  FIG. 3 , the supply flow path  132  has a common flow path  133   a  extending along the upper side of the actuator unit  120  and a common flow path  133   b  extending along the lower side thereof. The common flow paths  133   a ,  133   b  communicate with the supply ports  131   a ,  131   b  near the obtuse angle parts of the parallelogram area, respectively. The common flow path  133   a  and the common flow path  133   b  are connected by the plurality of branch flow paths  134 . The branch flow paths  134  linearly extend along the pressure chamber columns  141   x  and are arranged at an equal interval in the main scanning direction. The pressure chamber column  141   x  and an ejection port column (which will be described later)  109   x  are positioned in the main scanning direction between the two branch flow paths  134 . The branch flow paths  134  partially overlap with the pressure chambers  141  vertically while avoiding the ejection ports  109 . 
     As shown in  FIG. 4 , an exit port of the branch flow path  134  is connected with the plurality of individual ink flow paths  140 . In this illustrative embodiment, the one pressure chamber column  141   x  shares the one branch flow path  134  by the individual ink flow paths  140 . The individual ink flow paths  140  distribute the ink of the branch flow path  134  to the ejection ports  109 . The individual ink flow path  140  is configured by an upstream side half part and a downstream side half part with the pressure chamber  141  being interposed therebetween. The upstream side half part connects the exit port and one end of the pressure chamber  141  and is formed in the plate  112  and the plate  113 . The downstream side half part connects the other end of the pressure chamber  141  and the ejection port  109  and is formed in the plates  112  to  115 . 
     As shown in  FIG. 3 , the ejection ports  109  of the lower surface (ejection surface  100   a ) are arranged in a matrix form and configure four ejection port groups  109   g . Each ejection port group  109   g  occupies a similar area to the actuator unit  120  and is included within the actuator unit  120  when seen from a plan view. In the ejection port group  109   g , the plurality of ejection ports  109  configures ejection port columns  109   x  along the left side of the parallelogram area, and the plurality of ejection port columns  109   x  is arranged at an equal interval in the main scanning direction. In one ejection port column  109   x , the predetermined number of ejection ports  109  (for example, 48 ejection ports) is arranged at an equal interval. Meanwhile, although not shown, in an area a 1  of  FIG. 3 , the pressure chamber columns  141   x , the ejection port columns  109   x  and the branch flow paths  134  are arranged at an equal interval in the direction along the upper side of the parallelogram area, like the other areas. The ejection ports  109  are arranged at the same interval as the pressure chambers  141  in the main and sub-scanning directions. 
     Also, the ejection ports  109  are arranged at a predetermined interval corresponding to a printing resolution over an entire area of a printing width. In this illustrative embodiment, as shown in  FIG. 3 , the ejection ports  109  are arranged along the left side of the parallelogram from one end of the ejection port column  109   x  toward the other end with being shifted by a unit distance of the resolution in the main scanning direction (for example, by 21 μm when the resolution in the main scanning direction is 1200 dpi). The other end of the ejection port column  109   x  and one end of the adjacent ejection port column  109   x  are spaced by a unit distance in the main scanning direction. That is, an interval (for example, Δ 1  of  FIG. 3 ) between the ejection ports  109  in each ejection port column  109   x , an interval (Δ 2  of  FIG. 3 ) between the ejection ports  109  adjacent to each other over the two different ejection port columns  109   x  and an interval (Δ 3  of  FIG. 3 ) between the ejection ports  109  adjacent to each other over the two different ejection port groups  109   g  are the same. In the meantime, the pressure chambers  141  also have the same arrangement shape as the ejection ports  109 . 
     As shown in  FIG. 4 , the actuator unit  120  has a laminated structure mainly having three piezoelectric layers  123  to  125 . The piezoelectric layers are sheet-type members configured by PZT (piezoelectric zirconate titanate)-based ceramics having ferroelectricity. Only the piezoelectric layer  123  is a layer positioned vertically between electrodes and is polarized in the same direction as the laminating direction of the laminated structure. A piezoelectric layer  126  seals the pressure chambers  141  and defines ceiling surfaces of the pressure chambers  141 . The piezoelectric layers  123 ,  125 ,  126  define the parallelogram area of one actuator unit  120  and are provided over all the pressure chambers  141  facing the parallelogram area. 
     Individual electrodes  121  are formed to face the pressure chambers  141  on an upper surface of the piezoelectric layer  124 . The individual electrode  121  occupies the substantially same parallelogram area as the pressure chamber  141 , when seen from a plan view. As shown in  FIG. 5 , the individual electrode  121  is substantially similar to the pressure chamber  141  and has a smaller size than the pressure chamber. The individual electrode  121  has the same longitudinal direction as the pressure chamber  141  and shares a center with the pressure chamber. The individual electrode  121  has an extension end at an opposite side to the ejection port  109  and is connected to a land  122  (connection part) at a distal end thereof. The land  122  has a cylindrical shape. The lands  122  have the same arrangement shape as the ejection ports  109  and configure four land groups. In the land groups, the plurality of lands  122  are arranged at an equal interval along the left side of the parallelogram, thereby forming land columns  122   x . The plurality of land columns  122   x  is arranged in the main scanning direction. As a whole, the lands  122  are arranged in the same matrix form as the ejection ports  109 . Hereinafter, an area which is formed along the land column  122   x  and between the adjacent land columns  122   x  is referred to as a band-shaped area a 2  (refer to  FIG. 5 ). 
     As shown in  FIG. 4 , a common electrode  124  is formed between the piezoelectric layer  123  and the piezoelectric layer  125 . The common electrode  124  is integrally formed over the overall planar area of one actuator unit  120 . The common electrode  124  is grounded in an area which is not shown. 
     The individual electrode  121  and the common electrode  124  are made of Au (gold). The land  122  is made of conductive material such as Ag—Pd (silver/palladium), Au (gold), Ag (silver) and the like. For example, the land may be made of Ag—Pd. 
     A part of the piezoelectric layer  123  positioned between both electrodes  121 ,  124  is an active part, which is spontaneously deformed when an electric field is applied thereto. In the meantime, the piezoelectric layers  125 ,  126  which are not polarized are non-active parts, which are not spontaneously deformed by the applying of the electric field. Here, when the individual electrode  121  becomes a potential different from the ground, the active part grows in a thickness direction by the electric field and shrinks in a plane direction. Since the non-active parts are not spontaneously deformed, a distortion difference is caused between the active part and the non-active parts. At this time, a part positioned between the individual electrode  121  and the pressure chamber  141  is deformed (unimorph deformation) in a convex shape toward the pressure chamber  141 . The deformation is independent for each of the individual electrodes  121 . That is, the actuator unit  120  is formed with the plurality of actuators which can be individually driven. Here, when the actuator is deformed, the energy is applied to the ink in the pressure chamber  141 . When the energy has a predetermined level or higher, the ink is ejected from the ejection port  109 . That is, each actuator selectively applies the ejection energy to each pressure chamber  141 . 
     As shown in  FIG. 5 , each land  122  is connected with one driving signal line  151 . The driving signal line  151  electrically connects the land  122  to an output terminal of the driver IC by a wiring in the FPC  150 . Each driving signal line  151  is drawn out rightward from the land  122  in  FIG. 5 , is bent upward along the longitudinal direction of the band-shaped area a 2  and is drawn out toward one end of the band-shaped area a 2 . In one band-shaped area a 2 , the plurality of driving signal lines  151  from one land column  122   x  are arranged. The controller  1   p  outputs a control signal based on image data to the driver IC. The driver IC selectively supplies a driving signal based on the control signal to the driving signal lines  151 . When the driving signal is supplied to the individual electrodes  121 , the ejection energy is applied to the ink in the pressure chambers  141 , so that the ink is ejected from the ejection ports  109 . 
     According to this illustrative embodiment, the longitudinal directions of the pressure chambers  141  are aligned with the longitudinal direction (main scanning direction) of the flow path unit  110 . Therefore, since the flow path unit  110  can become compact in the sub-scanning direction, as a whole, the compact printer  1  is realized. 
     Also, as the longitudinal directions of the pressure chambers  141  are aligned with the longitudinal direction of the flow path unit  110 , the driving signal lines  151  can be appropriately arranged, as described below. Since the driving signal lines  151  are respectively connected to the lands  122 , the driving signal lines should pass to an area between the lands  122 , when seen from a plan view. 
     In the meantime, the land  122  is arranged near the pressure chamber  141 . Accordingly, when the longitudinal direction of the pressure chamber  141  is aligned with the longitudinal direction of the flow path unit  110 , the arrangement interval of the lands  122  in the main scanning direction can be correspondingly made to be larger than the arrangement interval in the sub-scanning direction. Thereby, as shown in the band-shaped area a 2  of  FIG. 5 , the area between the lands  122  can widen the width in the main scanning direction. Therefore, it is possible to arrange the plurality of driving signal lines  151  by drawing out the driving signal lines  151  in the longitudinal direction of the band-shaped area a 2 . 
     Further, the FPC  150  is also drawn out from the actuator unit  120  in the sub-scanning direction. In the meantime, if the FPC  150  is drawn out in the main scanning direction, since the FPC  150  interferes with the upper structure of the head  100  positioned at the upper part, it is not easy to perform an aligning operation for connection to the circuit substrate. In contrast, according to this illustrative embodiment, when drawing out the FPC  150 , it is possible to easily draw out the FPC  150  to the outside toward the sub-scanning direction while avoiding the upper structure, so that the aligning operation can be easy. 
     Also, the pressure chamber  141  is arranged such that the position thereof in the direction of the pressure chamber column  141   x  is located at the exact center of the interval between the adjacent pressure chambers  141  in the adjacent pressure chamber column  141   x . Therefore, the pressure chambers  141  are relatively uniformly distributed in the plane area and the influence of the crosstalk from the pressure chambers  141  arranged around the corresponding pressure chamber  141  is uniform. That is, since the influence applied from the surrounding is uniform when each pressure chamber  141  performs the ejection operation, the ejection operation becomes stable. 
     Meanwhile, in this illustrative embodiment, the upper side and lower side of the actuator unit  120  are inclined with respect to the main scanning direction. In contrast, if the upper and lower sides are aligned with the main scanning direction, the actuator units  120  are shifted little by little in the sub-scanning direction, so that the overall width in the sub-scanning direction is increased. In contrast, in this illustrative embodiment, the actuator units  120  are arranged as described above, so that it is possible to arrange the actuator units at the same position with respect to the sub-scanning direction. Thereby, it is possible to arrange the actuator units  120  along the main scanning direction while the interval of the ejection ports  109  does not break off, so that the space of the planar area can be effectively used. 
     In the below, modified illustrative embodiments in the arrangement mode of the pressure chambers  141  are described. In a first modified illustrative embodiment, as shown in  FIG. 6 , the longitudinal direction of the pressure chamber  141  is orthogonal to the direction of the left side of the parallelogram. At this time, a length h 1  of the pressure chamber  141  in the main scanning direction is larger than a length v 1  of the pressure chamber  141  in the sub-scanning direction. By arranging the pressure chambers as described above, the head  100  becomes compact, as a whole, like the above illustrative embodiment. The arrangement relation of the ejection ports  109  is the same as the above illustrative embodiment. Also, like the above illustrative embodiment, each pressure chamber  141  is arranged such that the position thereof in the direction of the pressure chamber column  141   x  is located at the exact center of the interval between the adjacent pressure chambers  141  in the adjacent pressure chamber column  141   x . That is, the pressure chambers are arranged such that a distance d 3  becomes the double of a distance d 4  in  FIG. 6 . 
     Therefore, in the first modified illustrative embodiment, as described below, the pressure chambers  141  are arranged more uniformly, compared to the above illustrative embodiment.  FIGS. 7A and 7B  show the first modified illustrative embodiment and the above illustrative embodiment, respectively. Regarding the distances of the pressure chamber  141  to the adjacent different pressure chambers  141  in the main scanning direction, a relation of about d 5 =d 6  is satisfied in the first modified illustrative embodiment. However, in the above illustrative embodiment, d 7 &gt;d 8 . Like this, when the distances between the pressure chambers  141  are different, the influence of the crosstalk occurring between the pressure chambers  141  becomes non-uniform, so that the ejection characteristics may be non-uniform. In contrast, according to the first modified illustrative embodiment, the pressure chambers are arranged such that distances between the pressure chambers  141  are uniform. Therefore, the influence of the crosstalk is also uniform, so that the ejection characteristics are uniform. 
     Also, when it is assumed that the arrangement shape of the lands  122  and the shapes and sizes of the pressure chambers  141  are not changed in the pressure chamber column  141   x , the distance between two adjacent pressure chambers  141  in the pressure chamber column  141   x  is largest in the first modified illustrative embodiment. For example, a distance d 9  between the pressure chambers  141  in  FIG. 7A  is larger than a distance d 10  between the pressure chambers  141  in  FIG. 7B . Accordingly, when it is assumed that the width of the pressure chamber  141  is constant, the distance between the pressure chambers  141  is largest in the first modified illustrative embodiment and the influence of the crosstalk in the direction of the left side of the parallelogram can be reduced. To the contrary, from a standpoint of suppressing the influence of the crosstalk, the distance between the pressure chambers  141  can be made to be a predetermined size even though the width of the pressure chamber  141  is changed. At this time, in the first modified illustrative embodiment, the width of the pressure chamber  141  can be made to be largest. The larger the width of the pressure chamber  141 , the higher the efficiency of the ejection operation. Hence, according to the first modified illustrative embodiment, it is possible to realize the more efficient pressure chamber  141 . 
     In a second modified illustrative embodiment, as shown in  FIG. 8 , the longitudinal direction of the pressure chamber  41  is aligned with the direction of the upper side of the parallelogram. The arrangement relation of the ejection ports  109  is the same as the above illustrative embodiment. At this time, a length h 2  of the pressure chamber  141  in the main scanning direction is larger than a length v 2  of the pressure chamber  141  in the sub-scanning direction. By arranging the pressure chambers as described above, the head  100  becomes compact, as a whole, like the above illustrative embodiment. 
     While the present invention has been shown and described with reference to certain illustrative embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. 
     For example, in the above illustrative embodiments, four actuator units  120  and four ejection port groups  109   g  corresponding to the actuator units are provided for each head  100 . However, the number thereof may be eight, for example. 
     In the above illustrative embodiments, each set of the land  122 , the pressure chamber  141  (individual electrode  121 ) and the ejection port  109  is arranged in same order of the land  122 , the pressure chamber  141  (individual electrode  121 ) and the ejection port  109 . However, a set in which the land, the pressure chamber and the ejection port are arranged in the reverse order may be included. 
     The liquid ejection head according to illustrative embodiments of the present invention can be applied to a liquid ejection apparatus such as facsimile and copier without limiting to the printer. Also, the number of the liquid ejection heads which are applied to the liquid ejection apparatus is not limited to four. That is, one or more liquid ejection heads may be provided. The liquid ejection head is not limited to the line type and may be a serial type. Furthermore, the liquid ejection head may eject liquid other than ink.