Patent Publication Number: US-7896478-B2

Title: Fluid path unit for fluid ejection device

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present disclosure relates to the subject matter contained in Japanese patent application No. 2007-049913 filed on Feb. 28, 2007, which is expressly incorporated herein by reference in its entirety. 
     TECHNICAL FIELD 
     The present invention relates to a fluid ejection device, and in particular to a fluid path unit for the fluid ejection device. 
     BACKGROUND ART 
     JP-A-2004-25636 (U.S. Pat. No. 6,955,418) discloses an inkjet head as an example of a fluid ejection device for ejecting fluid from a nozzle. The inkjet head is designed to eject ink droplets from plural nozzles toward a recording sheet. The inkjet head has a fluid path unit and a piezoelectric actuator that is stacked on the fluid path unit. The fluid path unit has a common fluid reservoir connected to an ink supply port, and plural pressure chambers that corresponds to respective nozzles and that are disposed in fluid paths extending from the common fluid reservoir to the. The piezoelectric actuator selectively varies the volume of the pressure chambers to impart ejection pressure to ink in the pressure chambers, to thereby eject ink droplets from the nozzles. 
     When the actuator varies the volume of a pressure chamber, a pressure wave is caused in the pressure chamber, which includes not only an advancing component traveling toward the nozzle as the ejection pressure but also a receding component traveling toward the common fluid reservoir. If the receding component of the pressure wave propagates to another adjacent pressure chamber through the common fluid reservoir, so-called crosstalk problem arises. Therefore, the a damper wall for absorbing the receding component of the pressure wave is provided to face the common fluid reservoir. 
     Recent tendency of development in the field of a fluid ejection device is directed toward a higher density at which nozzles are arranged. In particular, in case of an inkjet head, the nozzles are desirably arranged at a higher density to make the head smaller in size and obtain an image at a higher resolution. Since there is a limit on the number of the nozzles arrayed into one row, nozzles for one color are likely to be arrayed into multiple rows. However, because the common fluid reservoir in the fluid path unit disclosed in JP-A-2004-25636 is elongated to overlap with a row of pressure chambers communicating therewith when viewed in a plan view, if the pressure chambers are arranged at a higher density and in multiple rows to accommodate the higher density and multiple row arrangement of the nozzles, the width of the common fluid reservoir is reduced. The reduced width of the common fluid reservoir undesirably deteriorates damping effect for the pressure wave occurring in the fluid stored in the common fluid reservoir. 
     SUMMARY 
     The present invention can provide, as an illustrative, non-limiting embodiment, a fluid path unit for a fluid ejection device, which includes: first pressure chambers arrayed in a first pressure chamber row; second pressure chambers arrayed in a second pressure chamber row adjacent to the first pressure chamber row; first outlet paths, through which the first pressure chambers respectively communicate with first nozzles, the first outlet paths arrayed in a first outlet path row; second outlet paths, through which the second pressure chambers respectively communicate with second nozzles, the second outlet paths arrayed in a second outlet path row; a common fluid reservoir; and first connection paths, though which the first pressure chambers communicate with the common fluid reservoir. Each of the first connection paths extends across the second outlet path row. 
     Accordingly, as one of advantages, the present invention can enhance the degree of freedom of layout of a common fluid reservoir. As another one of the advantages, the present invention can arrange nozzles at higher density. As yet another one of the advantages, the present invention can ensure a sufficiently long width of the common liquid chamber. As still another one of the advantages, the present invention can enhance damping performance of the common liquid chamber. 
     These and other advantages of the present invention will be described in detail with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded perspective view showing an inkjet head. 
         FIG. 2  is a plan view of a fluid path unit shown in  FIG. 1 . 
         FIG. 3  is a cross-sectional view taken along line III-III shown in  FIG. 2  to illustrate a piezoelectric actuator. 
         FIG. 4  is a cross-sectional view taken along line IV-IV shown in  FIG. 3 . 
         FIG. 5  is an exploded perspective view of a part of the fluid path unit shown in  FIG. 1 . 
         FIG. 6  is a drawing showing the layout of nozzles arranged on a nozzle surface of the fluid path unit shown in  FIG. 1 . 
         FIG. 7  is a plan view of another fluid path unit. 
         FIG. 8  is a cross-sectional view taken along line VIII-VIII shown in  FIG. 7 . 
         FIG. 9  is a cross-sectional view taken along line IX-IX shown in  FIG. 8 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Illustrative, non-limiting Embodiments of the present invention will be described hereunder with reference to the drawings. 
       FIG. 1  is an exploded perspective view showing an inkjet head  1 . As shown in  FIG. 1 , the inkjet head  1  has a fluid path unit  2  made up of plural plates stacked one on another, and a piezoelectric actuator  3  overlaid on and bonded to the fluid path unit  2 . The fluid path unit  2  is configured so that ink is downwardly ejected from nozzles  25  (see  FIG. 3 ) opened at a lower surface of the lowermost plate. A flexible flat cable  4  for establishing an electrical connection with an external device is superimposed on an upper surface of the piezoelectric actuator  3 . Exposed terminals (not shown) on a lower surface of the flexible flat cable  4  are connected to surface electrodes (not shown) formed on the upper surface of the piezoelectric actuator  3 . In relation to the concept of a direction used in the following descriptions, explanations are provided while a side of the fluid path unit  2  on which the piezoelectric actuator  3  is provided is taken as an upward direction and while a direction opposite to the side is taken as a downward direction. 
       FIG. 2  is a plan view of the fluid path unit  2  shown in  FIG. 1 .  FIG. 3  is a cross-sectional view taken along line III-III shown in  FIG. 2 , showing the piezoelectric actuator  3  ( FIGS. 2 and 3  are enlarged partial views focusing on four left rows of pressure chambers  23  provided for black ink). As shown in  FIG. 3 , the piezoelectric actuator  3  includes plural piezoelectric sheets  30  stacked one on another, each of which is formed from a ceramics material of lead zirconate titanate (PZT) having a thickness of about 30 μm. The actuator  3  further includes discrete electrodes  31  and common electrodes  32  so that the piezoelectric sheet  30  is vertically interposed between the discrete electrodes  31  and the common electrodes  32 . The discrete electrodes  31  are individually arranged to correspond to respective pressure chambers  23  to be described later, whilst the common electrodes  32  are continually arranged to correspond to the plural pressure chambers  23 . The discrete electrodes  31  and the common electrodes  32  are electrically connected to the surface electrodes (not shown) on an upper surface of the top sheet, i.e. the highest layer, by way of side end faces or through holes of the piezoelectric sheets  30 . 
     As shown in  FIG. 3 , the fluid path unit  2  includes a pressure chamber plate  11 , a first spacer plate  12 , a connection path plate  13 , a second spacer plate  14 , a first manifold plate  15 , a second manifold plate  16 , a damper plate  17 , a cover plate  18 , and a nozzle plate  19 , which are arranged in this order from top and bonded together. The nozzle plate  19  is a resin plate such as polyimide, and the other plates  11  to  18  are a metal plate such as a 42% nickel alloy steel plate. Openings constituting fluid paths are formed in the plates  11  through  19  by means of electrolytic etching, laser machining, plasma jet machining, or the like. 
     First, the structure of the respective plates  11  through  19  is generally described. As shown in  FIGS. 2 and 3 , the pressure chamber plate  11  has pressure chamber holes  11   a , which are arranged in four rows for each of four colors of ink. In  FIGS. 2 and 3 , four rows of the pressure chamber holes  11   a  for black ink and one of four rows of the pressure chamber holes  11   a  for yellow ink are shown, while illustration for other rows of the pressure chamber holes  11   a  for yellow, cyan and magenta ink is omitted. The pressure chamber plate  11  also has ink supply ports  11   b  as fluid inlet ports. In  FIG. 3 , one ink supply port  11   b  for black ink is shown, while illustration for other ink supply ports  11   b  for other colors is omitted. Hereafter, the discussion will be focused on a fluid path arrangement for black ink because each of fluid path arrangements for ink of other colors are substantively the same as the fluid path arrangement for black ink. As best shown in  FIG. 3 , each of the pressure chamber holes  11   a  is elongated in a direction orthogonal to an array direction when viewed in a plan view, and has a shape gradually tapered toward an outlet path  24  to be described later. The ink supply port  11   b  of the pressure chamber plate  11  is covered with a filter  20  (see  FIG. 1 ) for eliminating dust that might be mixed in ink supplied from an ink tank (not shown). 
     As shown in  FIGS. 3 and 5 , the first spacer plate  12  has: communication holes  12   a , each in fluid communication with an end of a respective pressure chamber hole  11   a ; outlet through holes  12   b , each in fluid communication with an opposite end of the respective pressure chamber hole  11   a ; and an ink supply hole (not shown) that has the same shape as that of the ink supply port  11   b  and that is in fluid communication with the ink supply port  11   b . As best shown in  FIG. 5 , the connection path plate  13  has: elongated connection path holes  13   a  having one ends respectively in fluid communication with the communication holes  12   a ; outlet through holes  13   b  respectively in fluid communication with the outlet through holes  12   b , and an ink supply port (not shown) that has the same shape as that of the ink supply port  11   b  and that is in fluid communication with the ink supply ports  11   b . The second spacer plate  14  has communication holes  14   a  in fluid communication with the other ends of a respective connection path holes  13   a ; outlet through holes  14   b  in fluid communication with the respective outlet through holes  13   b ; and an ink supply hole (not shown) that has the same shape as that of the ink supply port  11   b  and that is in fluid communication with the ink supply port  11   b . Connection paths  22  ( 22 A,  22 B, . . . as best shown in  FIGS. 4 and 5 ), which will be described later, are defined by the first spacer plate  12 , the connection path plate  13 , and the second spacer plate  14 . 
     As shown in  FIG. 3 , the first manifold plate  15  has: a first manifold hole  15   a  that is in fluid communication with the pressure chamber holes  11   a  of the corresponding rows (the four rows in this example) through the communication holes  12   a , the connection path holes  13   a  and the communication holes  14   a  (see  FIG. 5 ); and outlet through holes  15   b  in fluid communication with the respective outlet through holes  14   b . The second manifold plate  16  has: a second manifold hole  16   a  that has the same shape as that of the first manifold hole  15   a  and that is in fluid communication with the first manifold hole  15   a ; and outlet through holes  16   b  in fluid communication with the respective outlet through holes  15   b . A common fluid reservoir  21  (see  FIG. 2 ), which is elongated in the array direction and which has a substantially U-shape, is mainly defined by the first and second manifold holes  15   a  and  16   a  of the first and second manifold plates  15  and  16 . 
     As shown in  FIG. 3 , the damper plate  17  has: damper walls  17   a ; and outlet through holes  17   b  in fluid communication with the respective outlet through holes  16   b . Each of the damper walls  17   a  is provided such that a recess is formed in the damper plate  17  to reduce the thickness of the wall portion of the damper plate and to be located in an opposite side of the first and second manifold holes  15   a  and  16   a . The common fluid reservoir  21  partially defined by the damper wall  17   a . A gap is formed between the damper wall  17   a  and the cover plate  18 . The cover plate  18  has outlet through holes  18   a  in fluid communication with the respective outlet through holes  17   b . The nozzle plate  19  has nozzle holes  19   a  that are in fluid communication with the respective outlet through holes  18   a . Each of the nozzle holes  19   a  is reduced in diameter toward a downward end, and serves as the nozzle  25 , from which ink can be ejected. 
     Fluid paths in the fluid path unit  2  will now be generally described. As shown in  FIGS. 2 and 3 , the first and second manifold holes  15   a  and  16   a  are vertically sandwiched between the second spacer plate  14  and the damper plate  17 , thereby defining the common fluid reservoir  21 . The common fluid reservoir  21  has the substantially U-shape as viewed in a plan view and extends in the array direction so as to overlap with the pressure chambers  23  to be described later. The common fluid reservoir  21  has a fluid introducing section  21   a  that is in fluid communication with the ink supply port  11   b ; a first common chamber  21   b  that extends in the array direction continuously from the left end of the fluid introducing section  21   a ; and a second common chamber  21   c  that extends in the array direction continuously from the right end of the base section  21   a . A lower surface of the common fluid reservoir  21  is defined by the damper wall  17   a  that is substantially identical in shape and size to the common fluid reservoir  21 . A lower side of a space situated along the side of the damper wall  17   a  opposite the common fluid reservoir  23  is closed by the cover plate  18 . Although the first common chamber  21   b  and the second common chamber  21   c  are continuous to each other through the fluid introducing section  21   a  in this example, the first common chamber  21   b  and the second common chamber  21   c  can be separated from each other. In this case, two fluid paths are provided so that fluid can be supplied from the supply port  11   b  through the two fluid paths independently to the first common chamber  21   b  and the second common chamber  21   c.    
     The common fluid reservoir  21  is in fluid communication with the plural pressure chambers  23  via the plural crank-shaped connection paths  22  ( 22 A,  22 B, see, for example,  FIGS. 4 and 5 ). Each of the connection path  22  is formed by the communication hole  12   a  of the first spacer plate  12 , the connection path hole  13   a  of the connection path plate  13  and the communication hole  14   a  of the second spacer plate  14 . Fluid path resistance of the connection path  22  is greater than that of the outlet path  24  ( 24 A,  24 B, . . . , see, for example,  FIG. 3 ) to be described later, thereby inhibiting backflow of fluid from the pressure chamber  23  to the connection path  22 . To this end, the cross-sectional area of the connection path  22  is set smaller than the cross-sectional area of the outlet path  24  in this example. 
     The pressure chambers  23  are formed such that the pressure chamber holes  11   a  are vertically sandwiched between the piezoelectric actuator  3  and the first spacer plate  12 . The connection path  22  is in fluid communication with one end of a respective pressure chamber  23 , and the outlet path  24  is in fluid communication with the other end of the respective pressure chamber  23 . Each of the outlet paths  24  is formed by the outlet through holes  12   b ,  13   b ,  14   b ,  15   b ,  16   b ,  17   b , and  18   a  (see  FIGS. 5 and 3 ). The outlet path  24  extends vertically such that the axis of the outlet path is parallel to a stacking direction of the plates (a direction orthogonal to the plate surface). The outlet path is in fluid communication with the nozzle  25 . 
     The layout of the connection paths  22  will now be described in detail by reference to  FIGS. 2 through 5 .  FIG. 4  is a cross-sectional view taken along line IV-IV shown in  FIG. 3 .  FIG. 5  is an exploded perspective view of the part of the fluid path unit  2  shown in  FIG. 1 . The pressure chambers  23 A to  23 D arranged in the first to fourth rows from the left in  FIG. 2  are for use with black ink. The pressure chambers  23 A arrayed in the first row and the pressure chambers  23 B arrayed in the second row are in fluid communication with the first chamber  21   b  of the common fluid reservoir  21  through the connection paths  22 A and  22 B (see  FIG. 4 ). The pressure chambers  23 C arrayed in the third row and the pressure chambers  23 D arrayed in the fourth row are in fluid communication with the second chamber  21   c  of the common fluid reservoir  21  through the connection paths  22 C and  22 D (see  FIG. 4 ). 
     As shown in  FIG. 2 , the pressure chambers  23 A of the first row are disposed at positions spaced leftwardly away from the common fluid reservoir  21  as viewed in a plan view (as viewed in a direction in which the pressure chambers are deformable). The pressure chambers  23 B of the second row are arranged at positions where the pressure chambers  23 B overlap with the first chamber  21   b  of the common fluid reservoir  21  as viewed in the plan view (as viewed in the direction in which the pressure chambers are deformable). The pressure chambers  23 A of the first row and the pressure chambers  23 B of the second row are arranged in such a manner that sides of the pressure chambers  23 A to be brought in fluid communication with the outlet paths  24 A and sides of the pressure chambers  23 B to be brought into fluid communication with the outlet paths  24 B are made close to each other; and that sides of the pressure chambers  23 A to be brought in fluid communication with the connection paths  22 A and sides of the pressure chambers  23 B to be brought into fluid communication with the connection paths  22 B are spaced apart from each other. 
     Two rows  24 AR and  24 BR of the outlet paths  24 A and  24 B are interposed between the first row of the pressure chambers  23 A and the common fluid reservoir  21  as viewed in a plan view. Given that an aggregation of the outlet paths  24 A and  24 B of the two rows is taken as an outlet path group  240 , axes of outlet paths of the outlet path group  240  are arranged at uneven intervals in the array direction when viewed from a direction A ( FIG. 2 ) orthogonal to both the array direction of the outlet paths  24 A and  24 B and the direction of the axes of the respective outlet paths. Specifically, the outlet path group  240  has large spacing sections L where the distance between the axes of the adjacent outlet paths  24 A and  24 B is large and small spacing sections S where the distance between the axes of the adjacent outlet paths  24 B and  24 A is small. The large spacing sections L and the small spacing sections S are alternately arranged with respect to the array direction. 
     As shown in  FIGS. 4 and 5 , the connection paths  22 A in fluid communication with the pressure chambers  23 A of the first row serve as cross-paths  22 A (the connection paths  22 A are hereinafter referred to also as the cross-paths  22 A). That is, the connection paths  22 A extends across the rows  24 AR and  24 BR of the outlet paths  24 A and  24 B to connect the first chamber  21   b  of the common fluid reservoir  21  to the pressure chambers  23 A of the first row. Further, the cross-paths  22 A pass through the large spacing sections L of the outlet path group  240 , and are arranged obliquely with respect to the array direction when viewed in a plan view. A dummy space  27  is provided below the pressure chambers  23 A of the first row. The dummy space  27  is provided by forming dummy holes in the first and second manifold plates  15  and  16  (see  FIG. 3 ), and the dummy space  27  is substantially identical with the common fluid reservoir  21  in terms of a height in the vertical direction and a length in the array direction. 
     The connection paths  22 B in fluid communication with the pressure chambers  23 B of the second row serve as noncross-paths  22 B (the connection paths  22 B are hereinafter referred to also as the noncross-paths  22 B). That is, the connection paths  22 B does not extend across the rows  24 AR and  24 BR of the outlet paths  24 A and  24 B to connect the first chamber  21   b  of the common fluid reservoir  21  to the pressure chambers  23 B. As best shown in  FIG. 4 , the noncross-paths  22 B are entirely located opposite from the pressure chambers  23 A of the first row with respect to the row  24 BR of the outlet paths  24 B. The noncross-paths  22 B and the cross-paths  22 A have substantially the same fluid path cross-sectional area and fluid path length to provide substantially the same fluid path resistance. Consequently, the nozzles  25 A (see  FIG. 3 ) in fluid communication with the cross-paths  22 A and the nozzles  25 B (see  FIG. 3 ) in fluid communication with the noncross-paths  22 B can exhibit a similar ejection characteristic. In order to make the noncross-path  22 B substantially identical in length to the cross-path  22 A, the inclination of the noncross-path  22 B is greater than that of the cross-paths  22 A with respect to the scanning direction when viewed in a plan view. 
     The first chamber  21   b  of the common fluid reservoir  21  is sufficiently wide in the scanning direction and long in the array direction to overlap with the pressure chambers  23 B of the second row and the pressure chambers  23 C of the third row when viewed in a plan view. 
     As shown in  FIG. 2 , the pressure chambers  23 C of the third row are laid above the first chamber  21   b  of the common fluid reservoir  21  when viewed in a plan view. The pressure chambers  23 D of the fourth row are disposed at positions where the pressure chambers  23 D overlap with the second chamber  21   c  of the common fluid reservoir  21  when viewed in a plan view. The pressure chambers  23 C of the third row and the pressure chambers  23 D of the fourth row are arranged in such a manner that sides of the pressure chambers  23 C to be brought in fluid communication with the outlet paths  24 C (see  FIG. 4 ) and sides of the pressure chambers  23 D to be brought into fluid communication with the outlet paths  24 D (see  FIG. 4 ) are made close to each other; and that sides of the pressure chambers  23 C to be brought in fluid communication with the connection paths  22 C (see  FIG. 4 ) and sides of the pressure chambers  23 D to be brought into fluid communication with the connection paths  22 D (see  FIG. 4 ) are spaced apart from each other. 
     Two rows  24 CR and  24 DR of the outlet paths  24 C and  24 D are interposed between the pressure chambers  23 C of the third row and the pressure chambers  23 D of the fourth row when viewed in a plan view. The two rows  24 CR and  24 DR of the outlet paths  24 C and  24 D are interposed between the first chamber  21   b  and the second chamber  21   c  when viewed in a plan view. Given that an aggregation of the outlet paths  24 C and  24 D of the two rows is taken as an outlet path group  241 , axes of outlet paths of the outlet path group  241  are arranged at uneven intervals in the array direction when viewed in the direction A ( FIG. 2 ) orthogonal to the array direction of the outlet paths  24 C and  24 D and the direction of the axes of the outlet paths  24 C and  24 D. Specifically, the outlet path group  241  has large spacing sections L where the distance between the axes of the adjacent outlet paths  24 C and  24 D is large and small spacing sections S where the distance between the axes of the adjacent outlet paths  24 C and  24 D is small. The large spacing sections L and the small spacing sections S are alternately arranged with respect to the array direction. 
     As shown in  FIGS. 4 and 5 , the connection paths  22 C in mutual communication with the pressure chambers  23 C of the third row serve as cross-paths  22 C (the connection paths  22 C are hereinafter referred to also as the cross-paths  22 C). That is, the connection paths  22 C extend across the rows  24 CR and  24 DR of the outlet paths  24 C and  24 D to connect the second chamber  21   c  of the common fluid reservoir  21  to the pressure chambers  23 C of the third row. Further, the cross-paths  22 C pass through the large spacing sections L of the outlet path group  241 , and are arranged obliquely with respect to the array direction when viewed in a plan view. 
     The connection paths  22 D in fluid communication with the pressure chambers  23 D of the fourth row serve as noncross-paths  22 D (the connection paths  22 D are hereinafter referred to also as the noncross-paths  22 D). That is, the connection paths  22 D do not extend across the rows  24 CR and  24 DR of the outlet paths  24 C and  24 D to connect the second chamber  21   c  of the common fluid reservoir  21  to the pressure chambers  23 D. As best shown in  FIG. 4 , the noncross-paths  22 D are entirely located opposite from the pressure chambers  23 C of the third row with respect to the row  24 DR of the outlet paths  24 D. The noncross-paths  22 D are made substantially identical to the cross-paths  22 A,  22 C and the noncross-paths  22 B in terms of flow path cross-sectional area and flow path length, thereby exhibiting substantially the same fluid path resistance as that of the other paths  22 A to  22 C. 
       FIG. 6  shows the layout of nozzles arranged on a nozzle surface of the fluid path unit  2  shown in  FIG. 1 . As shown in  FIG. 6 , four rows of nozzles  25 A to  25 D are assigned to each of colors of black BK, yellow Y, cyan C, and magenta M. When attention is paid to the nozzles for one of the four colors, positions of the nozzles are offset sequentially from the first row to the fourth row at uniform intervals in the array direction (the sheet feeding direction), and the nozzles in the first row to the fourth row are arranged, as a whole, at the same pitch as that of the small spacing section S in the array direction. As a result, positions of the outlet paths  24 A to  24 D assigned to the nozzles  25 A to  25 D are also offset sequentially from the first row to the fourth row at uniform intervals in the array direction, and the outlet paths  24 A to  24 D in the first row to the fourth row are arranged, as a whole, at the same pitch as that of the small spacing sections S in the array direction. Two of the outlet paths  24 A and  24 B of the first and second rows and two of the outlet paths  24 C and  24 D of the third and fourth rows are alternately arranged in the array direction when viewed from direction of arrow A. 
     Next, operation of the inkjet head  1  will be described. As shown in  FIG. 3 , a voltage is selectively applied to the discrete electrodes  31  of the piezoelectric actuator  3 , so that a potential difference arises between the discrete electrodes  31  and the common electrodes  32 . An electric field acts on an active section of the piezoelectric sheets located between the electrodes  31  and  32 , so that distortion deformation arises in the stacking direction. When pressure is imparted to ink in the pressure chamber  23  as a result of deformation of the active section, ink passes through the outlet path  24 , and is ejected from the nozzle  25 . A pressure wave acting on the pressure chambers  23  in this ejection process includes not only an advancing component traveling toward the nozzle  25  but also a receding component traveling toward the common fluid reservoir  21 . 
     The receding component of the pressure wave is interrupted to a certain extent by means of the connection paths  22 , but a portion of the receding component propagates to the common fluid reservoir  21 . The receding component of the pressure wave having propagated to the common fluid reservoir  21  is absorbed by elasticity of ink in the common fluid reservoir  21  and elastic deformation of the thin damper wall  17   a . Since each of the first and second chambers  21   b  and  21   c  of the common fluid reservoir  21  is sufficiently wide in the scanning direction, superior damping performance can be obtained. More specifically, acoustic capacity corresponding to a value expressing damping performance of the common fluid reservoir  21  is calculated from a sum of a term Cv, which is determined from the volume of the common fluid reservoir  21  and an elastic coefficient of ink, and a term Cd determined from elastic deformation of the damper wall  17   a . However, since the term Cd is far greater than the term Cv, the acoustic capacity is evaluated primarily by the term Cd expressed by the following expression. 
     
       
         
           
             
               
                 
                   Cd 
                   = 
                   
                     
                       
                         IdW 
                         d 
                         s 
                       
                       ⁡ 
                       
                         ( 
                         
                           1 
                           - 
                           
                             v 
                             d 
                             2 
                           
                         
                         ) 
                       
                     
                     
                       60 
                       ⁢ 
                       
                         E 
                         d 
                       
                       ⁢ 
                       
                         t 
                         d 
                         s 
                       
                     
                   
                 
               
               
                 
                   Mathematical 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   Expression 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   1 
                 
               
             
           
         
       
     
     where Wd is the width (m) of the damper; td is the thickness (m) of the damper; ld is the length (m) of the damper; Ed is a modulus of elasticity (Pa) of the damper; and vd is a Poisson ratio of the damper. 
     The performance of damping the pressure wave obtained by the common fluid reservoir  21  becomes proportional to the fifth power of the width Wd of the damper. For this reason, since the common fluid reservoir  21  and the damper wall  17   a , in particular, the common chamber  21   b , 21   c  and a corresponding portion of the damper wall  17   a  are widely formed so as to cover the two rows of pressure chambers  23 , so-called crosstalk can be eliminated. 
     Each of the cross-paths  22 A extends across the rows  24 AR and  24 BR of the outlet paths  24 A and  24 B. Hence, the pressure chambers  23 A that do not overlap with the common fluid reservoir  21  can be connected to the wide first chamber  21   b  of the common fluid reservoir  21  through the cross-paths  22 A. Similarly, each of the cross-paths  22 C extends across the rows  24 CR and  24 DR of the outlet paths  24 C and  24 D. Hence, the pressure chambers  23 C that do not overlap with the second chamber  21 C can be connected to the wide second chamber  21   c  of the common fluid reservoir  21  through the cross-paths  22 C. Accordingly, even when the fluid path unit  2  is miniaturized as a result of arrangement of the nozzles  25  at a high density, the pressure chambers  23 A and  23 C can be connected to the wide common fluid reservoir  21 , and sufficient damping performance can be ensured. 
     Moreover, the cross-paths  22 A pass through the large spacing sections L where a large distance exists between the axes of the adjacent outlet paths  24 A and  24 B, and the cross-paths  22 C pass through the large spacing sections L where a large distance exists between the axes of the adjacent outlet paths  24 C and  24 D. Even when the nozzles  25  are made denser, it becomes possible to ensure a space where the cross-paths  22 A and  22 C are to be arranged. Further, the large spacing sections L and the small spacing sections S are alternately arranged in the array directions of the outlet paths  24 A to  24 D. The cross-paths  22 A and  22 C are arranged at uniform intervals in the array direction. Therefore, even when the nozzles are arranged at a higher density, the rigidity of the fluid path unit  2  can be maintained appropriately. Moreover, since the cross-paths  22 A and  22 C extend obliquely with respect to the array direction of the outlet paths  24 A to  24 D. Hence, the cross-paths  22 A and  22 C can pass through areas between the adjacent outlet paths  24 A to  24 D where the largest spacing is present. The rigidity of the fluid path unit  2  can be maintained more appropriately. 
     The pressure chambers  23 B of the second row and the pressure chambers  23 C of the third row are arranged to overlap with the first chamber  21   b  communicating with the pressure chambers  23 A of the first row and the pressure chambers  23 B of the second row. Hence, structural balance of the fluid path unit  2  becomes superior, and ejection characteristics can be made equal. Moreover, the dummy space  27  is formed at the position where the dummy space overlaps with the pressure chambers  23 A of the first row. Hence, the rigidity of the pressure chambers  23 A become equal to the rigidity of the other pressure chambers  23 B to  23 D that overlap with the common fluid reservoir  21 . The ejection characteristics of the pressure chambers can be made equal more effectively. 
       FIG. 7  is a plan view of a fluid path unit  102 .  FIG. 8  is a cross-sectional view taken along line VIII-VIII shown in  FIG. 7 .  FIG. 9  is a cross-sectional view taken along line IX-IX shown in  FIG. 8 . The configuration of the fluid path unit  102  similar to that of the fluid path unit  2  is assigned the same reference numeral, and its explanation is omitted. 
     Pressure chambers  123 A to  123 D of the first to fourth rows from the left in  FIG. 7  are for black ink use. Of these pressure chambers, the pressure chambers  123 A and  123 B of the first and second rows are in fluid communication with a common fluid reservoir  121  through connection paths  122 A and  122 B (see  FIG. 9 ). The pressure chambers  123 C and  123 D of the third and fourth rows are in fluid communication with the common fluid reservoir  121  through connection paths  122 C and  122 D (see  FIG. 9 ). Nozzles are arranged at uniform intervals, in a array direction when viewed in the direction of arrow A, in sequence of a nozzle assigned to the pressure chamber  123 A of the first row, a nozzle assigned to the pressure chamber  123 C of the third row, a nozzle assigned to the pressure chamber  123 B of the second row, and a nozzle assigned to the pressure chamber  123 D of the fourth row. 
     The pressure chambers  123 A of the first row are disposed on the left spaced apart from the common fluid reservoir  121  when viewed in a plan view. The pressure chambers  123 B of the second row are disposed at positions where the pressure chambers  123 B overlap with the common fluid reservoir  121  when viewed in the plan view. The pressure chambers  123 A of the first row and the pressure chambers  123 B of the second row are arranged such that sides of the pressure chambers  123 A that are in fluid communication with connection paths  122 A and sides of the pressure chambers  123 B that are in fluid communication with outlet paths  124 B are in close proximity to each other. One row  124 BR of the outlet paths  124 B is arranged between the pressure chambers  123 A of the first row and the common fluid reservoir  121  when viewed in the plan view. 
     As shown in  FIG. 9 , the connection paths  122 A in fluid communication with the pressure chambers  123 A of the first row serve as cross-paths  122 A (the connection paths  122 A are hereinafter referred to also as the cross-paths  122 A). That is, the connection paths  122 A extend across the row  124 BR of the outlet paths  124 B to connect the common fluid reservoir  121  to the pressure chambers  123 A of the first row. The cross-paths  122 A extend in a direction (the scanning direction) orthogonal to the array direction of the outlet paths  124 . That is, the cross-paths  122 A extend orthogonal to the array direction when viewed in the plan view. The array direction corresponds to the sheet feeding direction. Moreover, a dummy space  127  is provided below the pressure chambers  123 A communicating with the cross-paths  122 A. 
     The connection paths  122 B in fluid communication with the pressure chambers  123 B of the second row serve as noncross-paths  122 B (the connection paths  122 B are hereinafter referred to also as the noncross-paths  122 B). That is, the connection paths  122 B do not extend across the row  124 BR of the outlet paths  124 B to connect the common fluid reservoir  121  to the pressure chambers  123 B. Each of the connection paths  122 B is entirely located opposite from the pressure chamber  123 A of the first row with respect to the row  124 BR of the outlet paths  124 B. The noncross-paths  122 B are made substantially identical to the cross-paths  122 A in terms of fluid path cross-sectional area and fluid path length to have substantially the same fluid path resistance as that of the cross-paths  122 A. In order to make the noncross-paths  122 B substantially identical in length to the cross-paths  122 A, the noncross-paths  122 B are tilted with respect to the scanning direction when viewed in the plan view. 
     The common fluid reservoir  121  is sufficiently wide in the scanning direction to overlap with the pressure chambers  123 B of the second row and the pressure chambers  123 C of the third row when viewed in the plan view. Pressure chambers  123 C and  123 D of the third and fourth rows are symmetrically arranged to the pressure chambers  123 A and  123 B of the first and second rows with respect to a center line C of the common fluid reservoir  121  when viewed in the plan view, and hence their detailed explanations are omitted. 
     The cross-paths  122 A extend across the row  124 BR of the outlet paths  124 B. Hence, the pressure chambers  123 A that do not overlap with the common fluid reservoir  121  can be connected to the wide common fluid reservoir  121  through the cross-fluid paths  122 A. Similarly, the cross-paths  122 D extend across the row  124 CR of the outlet paths  124 C. Hence, the pressure chambers  123 D that do not overlap with the common fluid reservoir  121  can be connected to the wide common fluid reservoir  121  through the cross-paths  122 D. Accordingly, even when the fluid path unit  102  is miniaturized and constructed at a higher density, the pressure chambers  123 A and  123 D can be connected to the wide common fluid reservoir  121  to ensure sufficient damping performance. 
     The cross-paths  122 A in fluid communication with the pressure chambers  123 A of the first row and the outlet paths  124 B in fluid communication with the pressure chambers  123 B of the second row are alternately arranged in the array direction. The cross-paths  122 A can be shortened. Consequently, the path arrangement can be advantageously made simple, and thus manufacture can be made easy. Furthermore, the common fluid reservoir  121  is arranged to overlap with the pressure chambers  123 B of the second row and the pressure chambers  123 C of the third row. Hence, the sufficiently long width of the common fluid reservoir  121  can be ensured, and the path arrangement can be advantageously made simple, and thus manufacture can be made easy. 
     The present invention has been discussed with reference to a case in which the present invention is applied to the inkjet head. In stead, the present invention can be applied to other types of the fluid ejection device that can eject fluid other than ink, such as a device for ejecting coloring fluid to manufacture a color filter of a liquid-crystal display device and a device for ejecting electrically conductive fluid to form electrical wirings. 
     A piezoelectric actuator is used as pressure generation means for applying pressure to fluid in a pressure chamber. In stead, other types of pressure generation means, such as an actuator that can be displaced using static electricity, can be used. 
     The present invention can provide at least the following illustrative, non-limiting embodiments: 
     (1) A fluid ejection device including: a common fluid reservoir for storing fluid supplied from a fluid inlet port; plural connection paths through which the fluid from the common fluid reservoir flows while being divided; plural pressure chambers disposed in plural rows so as to come into fluid communication with the plural connection fluid paths respectively; pressure generation means for imparting ejection pressure to the fluid in the pressure chambers; and plural outlet path that correspond to the plural pressure chambers respectively and that guide the fluid in the pressure chambers to nozzles to eject the fluid from the nozzles, wherein pressure chambers of a first row among the pressure chambers of the plural rows are arranged, when viewed in a plan view, so as not to overlap with the common fluid reservoir that is in fluid communication with the pressure chambers of the first row, and at least one row of the outlet paths in fluid communication with pressure chambers of a second row adjacent to the pressure chambers of the first row is interposed between the first row of the pressure chambers and the common fluid reservoir; and connection paths in fluid communication with the pressure chambers of the first row are cross-paths that extend across the row of the outlet paths in fluid communication with the pressure chambers of the second row to connect the pressure chambers of the first row to the common fluid reservoir. 
     According to the device of (1), the cross-paths serving as connection paths in fluid communication with the pressure chambers of the first row are connected to the common fluid reservoir while extending across the row of the outlet paths in fluid communication with the pressure chambers of the second row. Hence, it is not necessary to provide the common fluid reservoir at a position where the common fluid reservoir overlaps with the pressure chambers of the first row when viewed in the plan view, and the degree of freedom of layout of the common fluid reservoir is significantly enhanced. When the degree of freedom of layout of the common fluid reservoir is enhanced as mentioned above, the sufficient width of the common fluid reservoir can be greatly ensured by effective utilization of the space even when the nozzles and corresponding pressure chambers are arranged at a higher density. Therefore, an attempt can be made to achieve higher integration of nozzles and enhanced damping performance of the common fluid reservoir. 
     (2) The device according to (1), wherein the pressure chambers of the second row overlap with the common fluid reservoir when viewed in the plan view, and the common fluid reservoir has such a width as to continuously overlap with the pressure chambers of at least the second row and a third row when viewed in the plan view. 
     According to the device of (1), since the common fluid reservoir has a great width so that the common fluid reservoir continuously overlaps with pressure chambers of at least two rows when viewed in the plan view, and hence damping performance of the common fluid reservoir is enhanced. Since the pressure chambers of the first row are connected to the common fluid reservoir through the cross-paths that extend across the outlet paths, a receding component, which travels toward the common fluid reservoir, of pressure waves acting on the pressure chambers of the first row can be effectively dampened. 
     (3) The device of (1) or (2), wherein connection paths that are in fluid communication with the pressure chambers of the second row are noncross-paths that do not extend across the row of the outlet paths; and the cross-paths and the noncross-paths have a substantially identical fluid path resistance. 
     According to the device of (3), even when cross-paths and noncross-paths are mixedly present as connection fluid paths in one fluid ejection device, nozzles in fluid communication with the cross-paths and nozzles in fluid communication with the noncross-paths can exhibit a substantially same ejection characteristic because the cross-paths and the noncross-paths are substantially identical to each other in terms of fluid path resistance. 
     (4) The device of (3), wherein the cross-paths and the noncross-path have a substantially identical fluid path cross-sectional area and a substantially identical fluid path length. 
     According to the device of (4), the fluid path resistance of the cross-paths and the fluid path resistance of the noncross-paths can be made substantially identical to each other by a simple configuration. 
     (5) The device of any one of (1) to (4), wherein the pressure chambers of the first row and the pressure chambers of the second row are arranged so that sides of the pressure chambers of the first and second rows in fluid communication with the outlet paths are in close proximity to each other and that sides of the pressure chambers of the first and second rows in fluid communication with the connection paths are separated from each other, and an aggregation of the outlet paths for both of the rows is taken as an outlet path group; axes of the outlet paths of the outlet path group are arranged at uneven intervals in a array direction when viewed in a direction orthogonal to both the array direction of the outlet paths and a direction of axes of the outlet paths; the outlet path group has large spacing sections where distance between axes of the adjacent outlet paths is large and small spacing sections where distance between axes of the adjacent outlet paths is small; and the cross-paths pass through the large spacing sections to extend across the outlet path group. 
     According to the device of (5), the cross-paths pass through the large spacing sections where the distance between axes of the adjacent outlet paths is large. Hence, even when nozzles are arranged at a higher density, space where the cross-paths are to be arranged can be ensured. 
     (6) The device of (5), wherein the large spacing sections and the small spacing sections are alternately arranged in the array direction of the outlet paths. 
     According to the device of (6), plural cross-paths can be arranged at uniform intervals in the array direction. Hence, even when rigid areas between fluid paths become narrow as a result of nozzle arrangement of higher density, structural balance of the ejection device becomes superior, and a drop in strength of the entire ejection device can be prevented. 
     (7) The device of (5) or (6), wherein the cross-paths pass through the large spacing sections of the outlet path group so as to be oblique with respect to the array direction of the outlet paths when viewed in the plan view. 
     According to the device of (7), the cross-paths obliquely extend across the rows of the outlet paths in fluid communication with the pressure chambers of both the first and second rows. Hence, the cross-paths can pass through areas where distance between adjacent outlet paths is great, and the strength can be enhanced to a much greater extent. 
     (8) The device of any one of (5) to (7), wherein plural sets, each having the pressure chambers of the first row and the pressure chambers of the second row, are arranged in a direction orthogonal to the array direction of the first and second rows, and the common fluid reservoir in fluid communication with the pressure chambers of the first and second rows of one set overlaps with the pressure chambers of the second row of the one set and the pressure chambers of the first row of another set when viewed in the plan view. 
     According to the device of (8), since the pressure chambers of adjacent sets overlap with the common fluid reservoir while being arranged side by side when viewed in the plan view, the width of the common fluid reservoir is greatly ensured. Moreover, the rigidities of the pressure chambers of these sets are made equal to each other, and therefore ejection characteristics can be made equal to each other. 
     (9) The device of any one of (1) to (4), wherein the pressure chambers of the first and second rows are arranged so that sides of the pressure chambers of the first row in fluid communication with the cross-paths and sides of the pressure chambers of the second row in fluid communication with the outlet paths are in close proximity to each other; and the cross-paths in fluid communication with the pressure chambers of the first row and the outlet paths in fluid communication with the pressure chambers of the second row are alternately arranged in the array direction. 
     According to the device of (8), wherein the cross-paths that bring the pressure chambers of the first row in fluid communication with the common fluid reservoir can be shortened. Hence, the configuration of fluid paths can be made simple and manufacture can be facilitated. 
     (10) The device of (9), wherein two sets, each having the pressure chambers of the first row and the pressure chambers of the second row, are arranged in parallel to each other so that sides of the pressure chambers of the first rows of the two sets, in fluid communication with the cross-paths, are made in close to each other; and the common fluid reservoir overlaps with the pressure chambers of both second rows of the two sets when viewed in the plan view. 
     According to the device of (10), since pressure chambers of four rows are in fluid communication with one common fluid reservoir, the width of the common fluid reservoirs can be greatly ensured. The configuration of fluid paths can be made simple, and manufacture can be facilitated. 
     (11) The device of any one of (1) to (10), further including a dummy space provided at a position where the dummy space overlaps with the pressure chambers in fluid communication with the cross-paths when viewed in the plan view. 
     According to the device of (11), since the dummy space is provided to overlap with the pressure chambers in fluid communication with the cross-paths when viewed in the plan view. Hence, the pressure chambers overlapping with the dummy space and the pressure chambers overlapping with the common fluid reservoir are made equal to each other in terms of rigidity, so that ejection characteristics of the pressure chambers can be made equal to each other. 
     (12) The device of any one of (1) to (11), further including an elastically deformable damper wall facing the common fluid reservoir. 
     According to the device of (12), the pressure waves propagating to the fluid in the common fluid reservoir can be absorbed by elastic deformation of the damper wall, and therefore crosstalk can be effectively eliminated.