Abstract:
A printer has an inkjet head, which has a passage composite. The passage composite has a main body, having a surface and a projection portion that extends outward from the surface. The projection portion has an opening formed through it, and the projection portion also has an end, and an edge opposite the end. The main body also has at least one rib positioned outside the projection portion. The at least one rib extends away from the surface, and is separated by a predetermined nonzero distance from the edge of the projection portion.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present application claims priority from Japanese Patent Application No. 2007-038366, which was filed on Feb. 19, 2007, the disclosure of which is herein incorporated in its entirety by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a passage composite, and the use of a passage composite in an ink jet head and in a printer. 
         [0004]    2. Description of the Related Art 
         [0005]    Known ink jet heads for ejecting ink from nozzles to a sheet of paper each include a passage unit having a plurality of individual ink passages extending to nozzles arranged on the bottom surface of the ink jet head, and a reservoir unit that temporarily stores ink and supplies the ink to the passage unit. 
         [0006]    In the known ink jet heads, the reservoir unit has a laminate structure including a passage block and three metal plates. The passage block is long in the main scanning direction and is made of a thermoplastic resin. Each metal plate has a rectangular planar surface that is long in the main scanning direction. The reservoir unit has an ink passage therein. The passage block has a loop projection and defines at least part of a passage opening closed by a film. The passage block has ribs projecting perpendicular to the first surface. Some of the ribs are connected to the outer surface of the loop projection. 
       SUMMARY OF THE INVENTION 
       [0007]    Accordingly, it is an object of the present invention to provide a passage composite in which an operation of arranging a film can easily and efficiently be performed and which ensures improvement of yield. In an embodiment of the invention, a passage composite comprises a main body comprising, the main body comprising a particular surface, a passage projection portion extending away from the particular surface and comprising a particular end, an edge opposite the particular end, and an opening formed therethrough, and at least one rib positioned outside the passage projection portion, and extending away from the particular surface, wherein at least a portion of the at least one rib is positioned a predetermined nonzero distance from the edge of the passage projection portion. 
         [0008]    In another embodiment of the invention, an ink jet head comprises a passage composite. The passage composite comprises a main body, which comprises a particular surface, a passage projection portion extending away from the particular surface and comprising a particular end, an edge opposite the particular end, and an opening formed therethrough, and at least one rib positioned outside the passage projection portion, and extending away from the particular surface, wherein at least a portion of the at least one rib is positioned a predetermined nonzero distance from the edge of the passage projection portion. 
         [0009]    In yet another embodiment of the invention, a printer comprises an ink cartridge configured to supply ink, and an ink jet head comprising a passage composite, the passage composite comprising a main body. The main body comprises a particular surface, a passage projection portion extending away from the particular surface and comprising a particular end, an edge opposite the particular end, and an opening formed therethrough, and at least one rib positioned outside the passage projection portion, and extending away from the particular surface, wherein at least a portion of the at least one rib is positioned a predetermined nonzero distance from the edge of the passage projection portion. 
         [0010]    Other objects, features, and advantages will be apparent to persons of ordinary skill in the art from the following detailed description of the invention and the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    For a more complete understanding of the present invention, needs satisfied thereby, and the objects, features, and advantages thereof, reference now is made to the following description taken in connection with the accompanying drawing. 
           [0012]      FIG. 1  is a perspective view of an ink jet head according to an embodiment of the invention. 
           [0013]      FIG. 2  is a longitudinal sectional view of a reservoir unit shown in  FIG. 1  according to an embodiment of the invention. 
           [0014]      FIG. 3A  is a top view of a main body of an upper reservoir block shown in  FIG. 2 , according to an embodiment of the present invention. 
           [0015]      FIG. 3B  is a bottom view of the main body shown in  FIG. 3A . 
           [0016]      FIG. 4  is a perspective view of the main body of the upper reservoir block in  FIG. 2 , when viewed from above. 
           [0017]      FIG. 5  is a perspective view of the main body of the upper reservoir block in  FIG. 2 , when viewed from below. 
           [0018]      FIGS. 6A to 6C  are diagrams illustrating a procedure for welding a filter shown in  FIG. 2  to the main body, according to an embodiment of the invention. 
           [0019]      FIG. 7  is a plan view of a passage unit shown in  FIG. 1 , according to an embodiment of the invention. 
           [0020]      FIG. 8  is an enlarged view of part surrounded by an alternate long and short dash line in  FIG. 7 . 
           [0021]      FIG. 9  is a partially cross-sectional view taken along the line IX-IX in  FIG. 8 . 
           [0022]      FIG. 10A  is an enlarged cross-sectional view of an actuator unit shown in  FIG. 9 . 
           [0023]      FIG. 10B  is a plan view of an individual electrode arranged on one surface of the actuator unit in  FIG. 10A . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0024]    Embodiments of the present invention, and their features and advantages, are understood by referring to  FIGS. 1-10B , with like numerals being used for like corresponding parts in the various drawings. 
         [0025]      FIG. 1  may be an external perspective view of an ink jet head according to an embodiment. Referring to  FIG. 1 , an ink jet head  1 , may have a substantially rectangular shape, and the longer sides of ink jet head  1  may extend in the main scanning direction. Ink jet head  1  may include, in order from the bottom, a passage unit  5 , a reservoir unit  3 , and a substrate  2 . Referring to  FIG. 9 , passage unit  5  may include a plurality of individual ink passages  60 , which may be in fluid communication with a plurality of nozzles  8 . Referring back to  FIG. 1 , reservoir unit  3  temporarily may store ink and may supply the ink to passage unit  5 . The substrate  2  may be mounted with electronic components, such as connectors  2   a  and capacitors  2   b.  With reference to the following description and the associated drawings, one side of the ink jet head  1 , e.g., the side in which the passage unit  5  may be arranged, will be interchangeably referred to as a “lower side.” Another side, e.g., the side in which the substrate  2  may be arranged will be interchangeably referred to as an “upper side.” 
         [0026]    Referring now to  FIG. 7 , a plurality of, e.g., four, actuator units  7  may be fixed to an upper surface  5   a  of the passage unit  5 . Flexible printed circuits (FPCs)  6 , which may function as interconnecting members attached to the respective actuator units  7 , may extend from between the passage unit  5  and the reservoir unit  3 , in an upward direction along the side surfaces of the reservoir unit  3 . FPCs  6  may be connected to the respective connectors  2   a  on the substrate  2 . Each FPC  6  may be mounted with a driver IC  6   a . Driver IC  6   a  may be positioned between the corresponding actuator unit  7  and the substrate  2 . In other words, each FPC  6  may be electrically connected to both of the substrate  2  and the driver IC  6   a.  Accordingly, the FPC  6  may transmit an image signal output from the substrate  2  to the corresponding driver IC  6   a,  and may supply a drive signal output from the driver IC  6   a  to the actuator unit  7 . Referring to  FIG. 2 , the the ink jet head is enlarged in the vertical direction, and passages which may not appear in the plane shown in the sectional view of  FIG. 2 , are shown in  FIG. 2 . 
         [0027]    Reservoir unit  3  may have a laminate structure containing the upper reservoir block  11  extending in the main scanning direction, and a plurality, e.g., three, plates  16 ,  17 , and  18  extending in the main scanning direction. The plates  16  to  18  may be plates made of metal, e.g., stainless steel. The laminated plates  16  to  18  may constitute a lower reservoir block  15  of the reservoir unit  3 . 
         [0028]    The upper reservoir block  11  may be made of a thermoplastic resin, e.g., polyacetal or polypropylene. Upper reservoir block  11  may includes the main body  12  extending in the main scanning direction, and films  13  and  14 , which may be welded to the main body  12 . Upper reservoir block  11  may have an inlet port  21 , an outlet port  22 , and an upper reservoir passage  25 . Outlet port  22  may be arranged substantially in the center of the main body  12  in the lengthwise direction thereof The inlet port  21  may be in fluid communication with a space over the main body  12 . The outlet port  22  may be in fluid communication with a space under the main body  12 . The upper reservoir passage  25  may connect the inlet port  21  to the outlet port  22 . In other words, the upper reservoir passage  25  may be arranged between the center and one end of the upper reservoir block  11  in the lengthwise direction thereof. 
         [0029]    A cylindrical joint  20  surrounding the inlet port  21  and extending upward may be arranged on an upper reference surface  12   a , e.g., a first surface of the main body  12 , and may face upward. The joint  20  may be connected to a connecting member coupled to one end of an ink supply tube (not shown) connected to an ink tank (not shown). With the above-described arrangement, ink may be supplied from the ink tank to the upper reservoir passage  25  via the joint  20 . 
         [0030]    Part of the main body  12  may serve as the wall surface of the upper reservoir passage  25 , and may constitute a protuberance  31  raised upward from the upper reference surface  12   a . A side wall  33  of the protuberance  31  may be a loop projection projecting upward from the upper reference surface  12   a . More specifically, the protuberance  31  may be arranged between the outlet port  22  and the vicinity of the center of the upper reservoir passage  25 . Proturberance  31  may extend in the lengthwise direction of the upper reservoir block  11 , e.g., the main scanning direction. 
         [0031]    Referring to  FIGS. 3A and 4 , the protuberance  31 , when viewed in a plan view, may have a wide portion  32   a , which may be substantially oval shaped, and a narrow portion  32   b . The width, e.g., the portion extending in the sub-scanning direction, of the wide portion  32   a , may spread close to both ends of the main body  12 , in the widthwise direction of the main body  12 . The narrow portion  32   b  may be located in the vicinity of one end of the protuberance  31 , facing the outlet port  22 . The width of the narrow portion  32   b  may be narrower than that of the wide portion  32   a.    
         [0032]    In the protuberance  31 , the narrow portion  32   b  may have a passage opening  34 , which may extend in a first direction perpendicular to the upper reference surface  12   a , and which may be elongated in the main scanning direction. The edge of the side wall  33 , which may extend perpendicular to the upper reference surface  12   a  of the protuberance  31 , may partially define the passage opening  34 . Referring back to  FIG. 2 , the passage opening  34  may be closed by the film  13 . In other words, the space surrounded by the film  13  and the inner surface  33   c  of the loop side wall  33  may serve as part of the upper reservoir passage  25 . 
         [0033]    The protuberance  31  may allow the depth, e.g., the height in the vertical direction in  FIG. 2 , of the upper reservoir passage  25  to be increased, in a portion between the vicinity of the outlet port  22  and the vicinity of the center of the upper reservoir passage  25 , in the lengthwise direction thereof A filter  10  may be positioned in such a deep portion, perpendicularly to the vertical direction in  FIG. 2 . Ink, which may be supplied from the inlet port  21  into the upper reservoir passage  25 , may flow upward in the deep portion, while passing through the filter  10 , and then may flow out of the outlet port  22 . 
         [0034]    Part of the main body  12  may constitute a loop projection  41 . Loop projection  41  may project downward from a lower reference surface  12   b . Specifically, the loop projection  41  may surround a region extending from the inlet port  21  of the upper reservoir passage  25  to the vicinity of the outlet port  22 . Referring now to  FIGS. 3B and 5 , the loop projection  41 , when viewed in a plan view, may have a substantially oval-shaped wide portion  42   a , and a narrow portion  42   b . An area of wide portion  42   a  may be larger than an area of wide portion  32   a  of the protuberance  31  on the opposite side. The narrow portion  42   b  may extend from a first end of the loop projection  41  facing the inlet port  21  to one end of the wide portion  42   a  adjacent to the first end of the loop projection  41 . The width of the narrow portion  42   b  may be narrower than the width of the wide portion  42   a . The edge of the loop projection  41  may define a passage opening  44 , which may extend in the first direction, perpendicular to the lower reference surface  12   b . Referring back to  FIG. 2 , the passage opening  44  may be closed by the film  14 . In other words, the space formed by the film  14  and the inner surface  41   c  of the loop projection  41  may serve as part of the upper reservoir passage  25 . 
         [0035]    Referring again to  FIGS. 3A to 5 , each of which show a state in which the films  13  and  14  may be not arranged, the upper end of the protuberance  31  surrounding the passage opening  34  may be tapered to provide a tapered portion  33   a.  The downward projecting end of the loop projection  41  surrounding the passage opening  44  may be tapered to form a tapered portion  41   a.  The tapered portions  33   a  and  41   a  may be configured to be melted when the films  13  and  14 , for closing the passage openings  34  and  44 , are welded to the main body  12 . Referring to  FIG. 3A , a portion of main body  12 , e.g., the portion surrounding passage opening  34 , may be configured to be welded to the film  13 . Referring to  FIG. 3B , a portion of main body  12 , e.g., the portion surrounding passage opening  44 , which is a hatched portion of  FIG. 3B , may be configured to be welded to the film  14 . In this manner, the passage openings  34  and  44  may be closed by the films  13  and  14 , respectively. 
         [0036]    Referring to  FIG. 6A , a rolled film  90  may be unrolled, and may be pressed against the tapered portion  41   a , thus covering the passage opening  44  with the film  90 . Subsequently, the tapered portion  41   a  may be melted by heating through the film  90 . Referring to  FIG. 6B , the film  90  may be welded to the loop projection  41 . After that, the film  90  may be cut along the outer surface  41   b  of the loop projection  41  using a cutting tool, e.g., a cutter or a laser beam, to remove the excess film  90 . Consequently, referring to  FIG. 6C , the passage opening  44  may be covered with the film  14 .  6 C. Film  13  may be welded according to a similar procedure, thus an explanation of the procedure for welding film  13  is omitted. 
         [0037]    The films  13  and  14  each may comprise a flexible material having a gas barrier property, e.g., a polyethylene terephtharate (PET) film with a vapor-deposited silica (SiOx) or aluminum layer. Accordingly, a gas outside the ink jet head  1  may be substantially prevented from entering the upper reservoir passage  25  in the upper reservoir block  11  through the films  13  and  14 . 
         [0038]    As described above, the flexible films  13  and  14  may define portions of the upper reservoir passage  25 . Accordingly, films  13  and  14  may absorb abrupt variations in pressure exerted on ink in the upper reservoir passage  25 , by deforming in response to the abrupt variations in pressure exerted on the ink. In other words, the films  13  and  14  each may function as a damper. Consequently, ink may flow smoothly in the upper reservoir passage  25 , and the ink ejecting property may be stabilized. Referring back to  FIG. 2 , the film  14  may be positioned at a slight distance from the upper surface of the lower reservoir block  15 , or the plate  16 , so as not to impair the damper function of film  14 . 
         [0039]    The upper reference surface  12   a  may be provided with a plurality of ribs  35 , which may upwardly project perpendicular to the upper reference surface  12   a , and may extend in the main scanning and sub-scanning directions. In other words, the ribs  35  may be arranged substantially in a lattice. The lower reference surface  12   b  similarly may be provided with a plurality of ribs  45  arranged substantially in a lattice, the ribs  45  downwardly projecting perpendicular to the lower reference surface  12   b . The arrangement of the ribs  35  and  45  may increase the solidity of the upper reservoir block  11 , which may prevent the upper reservoir block  11  from deforming. 
         [0040]    Referring back to  FIGS. 6A to 6C , the level of each rib  45 , relative to the lower reference surface  12   b , hereinafter, interchangeably referred to as “the level of each rib  45 ” may be slightly lower than the level of the loop projection  41 , relative to the lower reference surface  12   b , hereinafter, interchangeably referred to as “the level of the loop projection  41 ”, after completion of melting the tapered portion  41   a . Each of the ribs  45  connected to the outer surface  41   b  of the loop projection  41 , hereinafter interchangeably referred to as the specific notched ribs, may have a notch  45   a  in its upper end, and may be positioned such that the notch  45   a  is next to the outer surface  41   b . Rib  45  may be divided into a first segment  46  and a second segment  47  in its extending direction, e.g., the sub-scanning direction as shown in  FIGS. 6A to 6C , such that the first segment  46  may connect to the outer surface  41   b  of the loop projection  41 . Notch  45   a  and the second segment  47  may be positioned on the opposite side of the first segment  46  relative to the loop projection  41 . Further, the level of the first segment  46  of the rib  45  may be lower than the level of the loop projection  41 . In other words, the rib  45  may be separated from the end of the loop projection  41 . In addition, the level of the second segment  47  of the rib  45  may be higher than that of the first segment  46 . 
         [0041]    Referring again to  FIGS. 3A and 4 , the ribs  35  may be coupled to the side wall  33  of the protuberance  31 , and each rib  35  may have a similar notch  35   a.  Specifically, the notch  35   a,  in each of the ribs  35 , may be arranged in a first segment  36 , which may connect to the external surface  33   b.  External surface  33   b  may be a portion of the side wall  33  of the protuberance  31 , e.g., the portion defining the passage opening  34 . Consequently, each rib  35  may be separated from the end of the side wall  33  of the protuberance  31 . A second segment  37  may be disposed on the opposite side of the first segment  36  relative to the side wall  33 . In addition, the level of a second segment  37  of the rib  35 , relative to the upper reference surface  12   a , may be higher than that of the first segment  36 . The level of the rib  35  relative to the upper reference surface  12   a  hereinafter may be interchangeably referred to as “the level of the rib  35 .” 
         [0042]    Referring again to  FIG. 2 , among the plates  16  to  18 , the upper plate  16  may have a through hole located substantially at the center thereof, which may serve as a downward passage  16   a.  Downward passage  16   a  may be in fluid communication with the upper reservoir passage  25 , via the outlet port  22 . The lower plate  18  may have a plurality of, e.g., ten, through holes, which may serve as supply passages  18   a.  Referring to  FIG. 7 , supply passages  18   a  may be in fluid communication with respective ink supply ports  9 , which may be arranged in the passage unit  5 . Referring back to  FIG. 2 , the intermediate plate  17  may have a hole, which may serve as a reservoir  17   a . Reservoir  17   a  may be in fluid communication with the downward passage  16   a  and the plurality of supply passages  18   a . The downward passage  16   a , the reservoir  17   a , and the supply passages  18   a  may constitute a lower reservoir passage  27 . 
         [0043]    As indicated by the solid arrows in  FIG. 2 , which indicate the flow of ink in the reservoir unit  3 , ink supplied from the inlet port  21  into the upper reservoir passage  25  may flow downward, and then may flow in the main scanning direction. At that time, the ink flowing in the main scanning direction may travel upward while passing through the filter  10 , and again may flow downward in the center of the upper reservoir block  11 . Ink flowing in the main scanning direction then may flow outward from the outlet port  22  into the downward passage  16   a  constituting the lower reservoir passage  27 . In the lower reservoir passage  27 , the ink may flow from the outlet port  22  of the upper reservoir passage  25  into the reservoir  17   a  via the downward passage  16   a . In the reservoir  17   a , the ink may reach the respective supply passages  18   a . Referring now to  FIG. 7 , once ink reaches the respective supply passages  18   a , ink may be supplied to the passage unit  5  via the respective ink supply ports  9 . 
         [0044]    As described above, the reservoir unit  3  may have a series of ink passages, such as the upper reservoir passage  25  and the lower reservoir passage  27 . These ink passages may function as an ink reservoir for temporarily storing ink. 
         [0000]    In  FIG. 8 , pressure chambers  53 , apertures  55 , and the nozzles  8  should be drawn using dashed lines because they are located under the actuator units  7 . Nevertheless, in  FIG. 8 , the pressure chambers  53 , the apertures  55 , and the nozzles  8  are drawn using solid lines to facilitate understanding of the drawings. 
         [0045]    Referring to  FIG. 8 , the passage unit  5  may be a rectangular solid having substantially the same planar shape as that of the plate  18  in the reservoir unit  3 . The four actuator units  7  may have a trapezoidal planar shape, and may be arranged on the upper surface  5   a  facing the reservoir unit  3 . 
         [0046]    The upper surface  5   a  of the passage unit  5  may contain the plurality of ink supply ports  9 . Referring back to  FIG. 2 , the plurality of ink supply ports  9  correspond to the respective supply passages  18   a  of the reservoir unit  3 . Referring again to  FIG. 9 , the passage unit  5  may have manifold passages  51  in fluid communication with the ink supply ports  9 , and sub-manifold passages  51  a branching off from the manifold passages  51 . In the lower surface of the passage unit  5 , ink ejecting areas  5   b  may be arranged opposite to the respective actuator units  7 , with the passage unit  5  therebetween. Referring to  FIG. 8 , the plurality of nozzles  8  may be arranged in each ink ejecting area  5   b  in a matrix pattern. Referring again to  FIG. 9 , in the upper surface  5   a  of the passage unit  5 , the many pressure chambers  53  may be arranged in a matrix pattern in each of areas facing the respective actuator units  7 . 
         [0047]    In an embodiment of the invention, as shown in  FIG. 8 , a plurality of, e.g., sixteen, rows of the pressure chambers  53  may be substantially equally spaced in the lengthwise direction, e.g., the horizontal direction as shown in  FIG. 8 , or the main scanning direction, of the passage unit  5  may be arranged in parallel in the widthwise direction, e.g., the vertical direction in  FIG. 8 , or the sub-scanning direction, of the passage unit  5  in each of areas facing the respective actuator units  7 . The pressure chambers  53  may be disposed in each of the areas such that the number of pressure chambers  53  in each row may gradually decrease, and each row may correspond to the trapezoidal shape of the actuator unit  7 , e.g., as the rows become closer to the shorter side of the trapezoid. The adjacent actuator units  7  may be equally spaced, such that the opposed sides of the actuator units  7  may be parallel to each other and the actuator units  7  are staggered. In aligning parts of the adjacent actuator units  7 , the pressure chambers  53  may be arranged in complementary relationship, with respect to the lateral direction in  FIG. 8 . 
         [0048]    Referring to  FIG. 9 , the passage unit  5  may include a plurality of, e.g., nine, plates made of metal, e.g., stainless steel. Specifically, the passage unit  5  includes, in order from the top, a cavity plate  61 , a base plate  62 , an aperture plate  63 , a supply plate  64 , manifold plates  65 ,  66 , and  67 , a cover plate  68 , and a nozzle plate  69 . Plates  61  to  69  each may have a rectangular planar surface in which the longer sides of the rectangular planar surface extend in the main scanning direction. 
         [0049]    The cavity plate  61  may have a plurality of substantially rhomboid-shaped through holes, which may correspond to the respective pressure chambers  53 . The aperture plate  63  may include the apertures  55 , which may be in fluid communication with the respective pressure chambers  53  via connecting holes formed in the base plate  62 . The manifold plates  65 ,  66 , and  67  may have one or more through holes, which may be coupled to each other. The through holes in manifold plates  65 ,  66 , and  67  may provide the manifold passages  51  and the sub-manifold passages  51   a  when the manifold plates  65 ,  66 , and  67  are laminated. The sub-manifold passages  51   a  may be in fluid communication with the respective apertures  55  via connecting holes formed in the supply plate  64 . The nozzle plate  69  may have one or more holes corresponding to the respective nozzles  8  for the pressure chambers  53 . The plates  61  to  64  may have connecting holes (not shown) for connecting the ink supply ports  9  with the manifold passages  51 . Furthermore, the plates  62  to  68  may have connecting holes for connecting the pressure chambers  53  with the nozzles  8 . 
         [0050]    These plates  61  to  69  may be laminated while being aligned with respect to each other, such that the manifold passages  51 , the sub-manifold passages  51   a , and the many individual ink passages  60  may be formed to extend from the outlets of the sub-manifold passages  51   a  to the respective nozzles  8  through the apertures  55  and the pressure chambers  53 . Consequently, ink supplied from the reservoir unit  3  into the passage unit  5  via the ink supply ports  9  may flow into the manifold passages  51 , and further may flow into the sub-manifold passages  51   a  branching off from the manifold passages  51 . The supplied ink further may flow into the individual ink passages  60 , such that the ink reaches the respective nozzles  8 . 
         [0051]    Referring to  FIG. 7 , the plurality of actuator units  7  may have a trapezoidal planar shape, and may be staggered such that the actuator units  7  may avoid the ink supply ports  9  in the upper surface  5   a  of the passage unit  5 . The longer sides of the respective trapezoidal planar-shaped actuator units  7  may be arranged along the lengthwise direction of the passage unit  5 , such that the long sides of two actuator units  7 , which sandwich another one actuator unit  7 , may be flush with each other. 
         [0052]    Referring to  FIG. 10A , the actuator units  7  each may include a plurality of, e.g., three piezoelectric sheets  71 ,  72 , and  73  made of a ferroelectric ceramic material, e.g., titanate zirconate (PZT). The piezoelectric sheets  71 ,  72 , and  73  each may have a thickness of approximately 15 μm. The piezoelectric sheets  71 ,  72 , and  73  may be disposed over the many pressure chambers  53  arranged for each ink ejecting area  5   b.    
         [0053]    The individual electrode  76  may be arranged on the upper piezoelectric sheet  71 , and may correspond to each pressure chamber  53 . A common electrode  75  may be interposed between the upper piezoelectric sheet  71  and the underlying piezoelectric sheet  72 , and may be configured to cover the entire surface of each sheet. The common electrode  75  may have a thickness of approximately 2 μm, and may be held substantially at ground potential. The individual electrodes  76  and the common electrode  75  may be made of a metallic material, e.g., Ag—Pd. Piezoelectric sheets  72  and  73  may have no electrodes arranged between them. 
         [0054]    Each individual electrode  76  may have a thickness of approximately 1 μm. Referring to  FIG. 10B , the individual electrode  76  may have a substantially rhomboid planar shape, similar to the shape of the pressure chamber  53 . One of the acute portions of the substantially rhomboid individual electrode  76  may be extended. The extended portion of individual electrode  76  may be provided with a circular land  77 , which may have a diameter of approximately 160 μm, and which may be electrically connected to the individual electrode  76 . The land  77  may be made of a gold containing, e.g., glass frit. Referring to  FIG. 1 , the respective lands  77  may be connected to the driver ICs  6   a  through the FPCs  6 . Consequently, the potentials of the individual electrodes  76  may be selectively controlled. 
         [0055]    To drive the actuator units  7 , according to an embodiment of the invention, first, the piezoelectric sheet  71  may be polarized in the thickness direction. Accordingly, when the individual electrode  76  and the common electrode  75  are set to different potentials, and an electric field is applied to part of the upper piezoelectric sheet  71  between the individual electrode  76  and the common electrode  75  in the polarization direction, the electric-field-applied portion may function as an active portion that may deform due to a piezoelectric effect. The other two piezoelectric sheets  72  and  73  each may serve as an inactive layer having no region sandwiched between the individual electrode  76  and the common electrode  75 . Accordingly, the sheets  72  and  73  may not voluntarily deform. In other words, each actuator unit  7  may be a unimorph type, consisting of a layer containing active portions and an inactive layer. 
         [0056]    Referring to  FIG. 10A , the piezoelectric sheets  71  to  73  may be fixed to the upper surface of the cavity plate  61  including the pressure chambers  53 . Accordingly, when the deformation of the portion of the upper piezoelectric sheet  71  in which an electric field has been applied, differs from that of the underlying parts of the piezoelectric sheets  72  and  73  relative to the direction along the surfaces of the sheets thereto, all of the piezoelectric sheets  71  to  73  may deform toward the pressure chamber  53 , e.g., unimorph deformation may occur. At that time, the capacity of the pressure chamber  53  may decrease, such that the pressure in the pressure chamber  53  then may rise. Consequently, ink may be squeezed out of the pressure chamber  53 , to the corresponding nozzle  8 , which may cause ink droplets to be ejected from the nozzle  8 . After that, when the individual electrode  76  is set to the same potential as that of the common electrode  75 , the piezoelectric sheets  71  to  73  may return to their original states, e.g., their flattened states, such that the capacity of the pressure chamber  53  may return to its original capacity. Thus, the ink may be introduced from the manifold passage  51  to the pressure chamber  53 , such that the ink may be stored in the pressure chamber  53 . 
         [0057]    In the manufacture of the upper reservoir block  11 , when the excess film  90  may be cut off from the edge of the side wall  33  of the protuberance  31 , and the excess film  90  may be cut off from the edge of the loop projection  41  using a cutter, there is no obstacle in each cutting path, because, as described above, the level of each rib  35  may be lower than that of the side wall  33  of the protuberance  31  and the level of each rib  45  may be lower than that of the loop projection  41 , the ribs  35  may be separated from the the ends of the side wall  33 , and the ribs  45  may be separated from the loop projection  41 . Thus, the cutting operation can easily be performed. Furthermore, the occurrence of a cutting mistake caused by hitting the blade of the cutter against the ribs  35  or  45  may be prevented, which may increase the manufacturing yield. 
         [0058]    When the excess film  90  is cut off using a laser beam, the excess film  90  may be prevented from being welded to the ribs  35  or  45 . Consequently, the step of removing the film  90  welded to the ribs  35  or  45  may be eliminated, which may improve efficiency of the cutting operation. 
         [0059]    In the ink jet head  1  according to the present embodiment, some of the ribs  35  may be connected to the external surface  33   b  of the side wall  33  of the protuberance  31 . Some of the ribs  45  may be connected to the outer surface  41   b  of the loop projection  41 . Accordingly, the reinforcing effect by the ribs  35  and  45  may be increased. 
         [0060]    As mentioned above, in each of the specific ribs  35 , therefore, the level of parts which may be located in the cutting path for cutting the film  90  may be lowered below the level of the side wall  33  of the protuberance  31  extending from the upper reference surface  12   a . Similarly, in each of the specific ribs  45 , the level of parts which may be located in the cutting path may be lowered than that of the loop projection  41 . In each of the specific ribs  35  and  45 , the level of a part not located in the cutting path may be higher than that of a part in the cutting path. Consequently, the reinforcing effect by the ribs  35  and  45  may be further improved, and the film  90  may be cut efficiently. Thus, the solidity of the upper reservoir block  11  may be held sufficiently. 
         [0061]    In the ink jet head  1  according to the present embodiment, the level of a portion in which the notch  35   a  is not arranged, of each specific rib  35  is at or below the level of the side wall  33  of the protuberance  31 . Similarly, the level of a portion in which the notch  45   a  is not arranged, of each specific rib  45  is at or below the level of the loop projection  41 . Therefore, during welding of the films  13  and  14  to the main body  12 , if the unrolled film  90  is pressed against each of the side wall  33  and the loop projection  41  so as to cover the passage openings  34  and  44 , the ribs  35  and  45  may not obstruct the operation. Furthermore, a tool that heats the films  13  and  14  for welding may not contact the ribs  35  and  45 . Accordingly, the ribs  35  and  45  may not obstruct the operation of welding the films  13  and  14 . 
         [0062]    In the foregoing embodiment, the ribs  35  may be connected to the external surface  33   b  of the side wall  33  of the protuberance  31 , and the ribs  45  may be connected to the outer surface  41   b  of the loop projection  41 . Nevertheless, in another embodiment, it may be unnecessary to connect the ribs  35  to the external surface  33   b  of the side wall  33 , and it also may be unnecessary to connect the ribs  45  to the outer surface  41   b  of the loop projection  41 . 
         [0063]    In the foregoing embodiment, the specific ribs  35  and  45  may have the notch  35   a  and  45   a,  respectively. Nevertheless, in another embodiment, when the ribs  35  are not connected to the external surface  33   b  of the side wall  33  and the ribs  45  are not connected to the outer surface  41   b  of the loop projection  41 , it may be unnecessary to form the notches  35   a  and  45   a.  The level of each of the ribs  35  and  45  may be made uniform. 
         [0064]    Having described the preferred embodiment of the present invention, it should be understood that the invention is not limited to the above-described embodiment and various changes and modifications thereof may be made without departing from the sprit or scope of the invention as defined in the appended claims.