Patent Publication Number: US-7581825-B2

Title: Inkjet head and a method of manufacturing thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to Japanese Patent Application No. 2004-360759 filed on Dec. 14, 2004, the contents of which are hereby incorporated by reference into the present application. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an inkjet head that performs printing operation by discharging ink onto a recording medium such as a printing sheet. The present invention also relates to a method of manufacturing the inkjet head. 
     2. Description of the Related Art 
     An inkjet head of an inkjet printer includes a flow channel unit and an actuator unit. The flow channel unit includes a plurality of nozzles and a plurality of pressure chambers. Each pressure chamber is connected to a uniquely corresponding nozzle, and ink is discharged from the nozzle when a pressure within the pressure chamber corresponding to the nozzle is increased. The actuator unit includes a plurality of actuators. Each actuator faces a uniquely corresponding pressure chamber when the actuator unit is attached to the flow channel unit. When one of the actuator is selected and activated, the pressure within the pressure chamber uniquely corresponding to the activated actuator is increased and ink is discharged from the nozzle uniquely corresponding to the activated actuator and the pressure chamber. 
     Japanese Laid-Open Patent Application Publication No. 2003-80709 discloses an actuator unit having a piezoelectric sheet, a common electrode and a plurality of individual electrodes. The piezoelectric sheet is interposed between the common electrode and the plurality of individual electrodes. The common electrode is formed over a plurality of pressure chambers when the actuator unit is attached to the flow channel unit. Each of the plurality of individual electrodes is disposed to face the uniquely corresponding pressure chamber. 
     In this inkjet head, a conductive adhesive is applied on a side end face of the actuator unit from an upper surface of the flow channel unit. Because the common electrode (internal electrode) of the actuator unit extends to a peripheral border of the piezoelectric sheet, the common electrode is electrically connected to the flow channel unit via the conductive adhesive applied on the side end face of the actuator unit. 
     When a potential difference exists between the flow channel unit and the common electrode of the actuator unit, moisture from the ink within the flow channel unit is electrolyzed, and hydrogen ions (H + ) are consequently generated. If the common electrode of the actuator unit is on the negative side, the generated hydrogen ions move to the common electrode, and the common electrode occludes the hydrogen ions and expands. In this way, when a potential difference arises between the flow channel unit and the common electrode of the actuator unit, the actuator unit can be damaged by the expansion of the common electrode (internal electrode). 
     In the inkjet head disclosed in Japanese Laid-Open Patent Application Publication No. 2003-80709, because the flow channel unit and the common electrode (internal electrode) of the actuator unit are electrically connected via the conductive adhesive applied on the side end face of the actuator unit, the difference in electrical potential between the flow channel unit and the common electrode of the actuator unit becomes zero. Accordingly, it becomes possible to prevent the actuator unit from being damaged due to migration in the common electrode of the actuator unit. 
     BRIEF SUMMARY OF THE INVENTION 
     However, in the inkjet head described in Japanese Laid-Open Patent Application Publication No. 2003-80709, because the actuator unit and the flow channel unit are fixed together with an adhesive, the adhesive can leak onto the upper surface of the flow channel unit to which the actuator unit is attached. When the leaked adhesive covers the upper surface of the flow channel unit, the flow channel unit and the common electrode of the actuator unit cannot be electrically connected, even if conductive adhesive is applied on the side end face of the actuator unit. 
     It may be possible to scrape off the adhesive to expose a spotless area on the upper surface of the flow channel unit, and then apply the conductive adhesive to the spotless area to electrically connect the common electrode of the actuator unit to the spotless area. However, not only is it troublesome to scrape off the adhesive, but the scum from the scraped adhesive can infiltrate a channel within the flow channel unit and cause the channel to clog up. 
     Hence, an objective of the present invention is to provide an inkjet head that maintains a reliable connection between a flow channel unit and a common electrode of an actuator unit without producing any dross or scum during its process of manufacturing. 
     Another objective of the present invention is to provide a method of manufacturing such an inkjet head. 
     The inkjet head of the present invention includes a flow channel unit and an actuator unit attached to the flow channel unit. The flow channel unit includes a plurality of nozzles, and a plurality of pressure chambers. Each pressure chamber is connected to a uniquely corresponding nozzle. The actuator unit includes a piezoelectric sheet, a plurality of individual electrodes and a common electrode. The plurality of individual electrodes and the common electrode sandwich the piezoelectric sheet. Each individual electrode faces a uniquely corresponding pressure chamber when the flow channel unit is attached to the actuator unit. A contact terminal is exposed on an attachment surface of the actuator unit. The flow channel unit is attached to the attachment surface of the actuator unit. The contact terminal is electrically connected to the common electrode. A cavity is formed on an attachment surface of the flow channel unit. The actuator unit is attached to the attachment surface of the flow channel unit. The cavity faces the contact terminal when the flow channel unit is attached to the actuator unit. The cavity is filled with a conductive material, and the conductive material electrically connects the contact terminal of the actuator unit with the flow channel unit. 
     According to this configuration, when the flow channel unit and the actuator unit are attached, the flow channel unit and the common electrode of the actuator unit can be electrically connected without having to scrape off the adhesive that covers the flow channel unit. Accordingly, it becomes possible to electrically connect the flow channel unit and the common electrode of the actuator unit with high reliability, without clogging an ink channel within the flow channel unit. As a result, the difference in electrical potential between the flow channel unit and the common electrode of the actuator unit becomes zero, and migration becomes improbable. 
     A method of manufacturing an inkjet head according to the invention includes a step of fabricating a flow channel unit having a cavity on a flat surface, a step of applying an adhesive on the flat surface of the flow channel unit, a step of filling a conductive material within the cavity of the flow channel unit, a step of fabricating an actuator unit, and a step of attaching the actuator unit to the flow channel. The flow channel unit to be fabricated includes a plurality of nozzles, a plurality of pressure chambers, each pressure chamber being connected to a uniquely corresponding nozzle; and the cavity formed on the flat surface of the flow channel unit. The actuator unit to be fabricated includes a piezoelectric sheet; a plurality of individual electrodes; a common electrode which, with the plurality of individual electrodes, sandwiches the piezoelectric sheet; and a contact terminal electrically connected to the common electrode and exposed on an attachment surface of the actuator unit. The flat surface of the flow channel unit is attached to the attachment surface of the actuator unit. The flow channel unit and the actuator unit are attached each other so that each of the plurality of individual electrodes faces a uniquely corresponding pressure chamber and so that the contact terminal contacts the conductive material filled in the cavity. 
     According to this method, when attaching the flow channel unit to the actuator unit, the flow channel unit and the common electrode of the actuator unit can be electrically connected without having to scrape off the adhesive that covers the flow channel unit. Accordingly, it becomes possible to electrically connect the flow channel unit and the common electrode of the actuator unit with high reliability, without clogging an ink channel within the flow channel unit. As a result, the difference in electrical potential between the flow channel unit and the common electrode of the actuator unit becomes zero, and migration becomes improbable. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an external perspective diagram of an inkjet head assembly according to a first embodiment of the present invention. 
         FIG. 2  is a cross-sectional diagram along the line II-II shown in  FIG. 1 . 
         FIG. 3  is a planar diagram viewed from an upper surface of an inkjet head shown in  FIG. 2 . 
         FIG. 4  is an enlarged planar diagram of a region framed by the dashed lines shown in  FIG. 3 . 
         FIG. 5  is a cross-sectional diagram along the line V-V shown in  FIG. 4 . 
         FIG. 6(   a ) is an enlarged cross-sectional diagram of a portion of a region framed by the dotted lines shown in  FIG. 5 , and  FIG. 6(   b ) is an enlarged planar diagram of a portion of an actuator unit. 
         FIG. 7  is a flow chart of the manufacturing steps of the inkjet head. 
         FIG. 8(   a ) is an enlarged cross-sectional diagram of an inkjet head according to a second embodiment of the present invention, and  FIG. 8(   b ) is an enlarged planar diagram of a portion of an actuator unit. 
         FIG. 9(   a ) is an enlarged cross-sectional diagram of an inkjet head according to a third embodiment of the present invention, and  FIG. 9(   b ) is an enlarged planar diagram of a portion of an actuator unit. 
         FIG. 10(   a ) is an enlarged cross-sectional diagram of an inkjet head according to a fourth embodiment of the present invention, and  FIG. 10(   b ) is an enlarged planar diagram of a portion of an actuator unit. 
         FIG. 11(   a ) is a diagram showing a condition before a conductive wiring is formed on an actuator unit, and  FIG. 11  ( b ) is a diagram showing a condition after the conductive wiring has been formed on the actuator unit. 
         FIG. 12  ( a ) is an enlarged cross-sectional diagram of an inkjet head according to a fifth embodiment of the present invention, and  FIG. 12  ( b ) is an enlarged planar diagram of a portion of an actuator unit. 
         FIG. 13  ( a ) is an enlarged cross-sectional diagram of an inkjet according to a transfiguration example based on the third embodiment of the present invention, and  FIG. 13  ( b ) is an enlarged planar diagram of an actuator unit. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Preferred embodiments of the present invention will be described below with reference to the figures. 
     An inkjet head according to a first embodiment of the present invention will be described.  FIG. 1  is an external perspective view of an inkjet head assembly  1  of the first embodiment of the present invention.  FIG. 2  is a cross-sectional diagram along the line II-II shown in  FIG. 1 . As shown in  FIG. 1 , inkjet head assembly  1  includes inkjet head  70 , having a planar shape of a rectangle long in the main scanning direction X, for discharging ink on a printing sheet. Inkjet head assembly  1  also includes base block  71  and holder  72 . Base block  71  includes ink storage  3  and is disposed on an upper surface of inkjet head  70 , and holder  72  supports inkjet head  70  and base block  71 . 
     As shown in  FIG. 2  and  FIG. 3 , inkjet head  70  includes flow channel unit  4 , which has a plurality of ink flow channels, and four actuator units  21 , which are attached to the upper surface of flow channel unit  4  by epoxy-based thermosetting adhesive  6  (refer to  FIG. 5 ). Actuator unit  21  is constructed by stacking a plurality of thin boards on top of one another. Further, a bottom surface of inkjet head  70  is ink discharging surface  70   a , which has a plurality of nozzles  8  (refer to  FIG. 5 ) of minute diameter. Further, as shown in  FIG. 2 , FPC (Flexible Printed Circuit)  50 , which is a feeding member, is attached on an upper surface of actuator unit  21  by soldering, and extends out to the left or to the right. 
       FIG. 3  is a planar diagram of inkjet head  70  viewed from the top. As shown in  FIG. 3 , flow channel unit  4  has a planar shape of a rectangle, long in the main scanning direction X. In  FIG. 3 , manifold flow channel  5 , which is a common ink chamber built within flow channel unit  4 , is drawn with broken lines. Ink stored in ink storage  3  of base block  71  is supplied to manifold flow channel  5  through a plurality of openings  3   a . Manifold flow channel  5  diverges into a plurality of sub-manifold flow channels  5   a  extending parallel to the longitudinal direction (main scanning direction X) of flow channel unit  4 . 
     Four actuator units  21 , each having a planar shape of a trapezoid, are arranged in two rows and attached on the upper surface of flow channel unit  4  in a zigzag pattern so as not overlap with openings  3   a . Each actuator unit  21  is disposed so that parallel sides (top side and bottom side) of each actuator unit  21  lie along a longitudinal direction X of flow channel  4 . The plurality of openings  3   a  is also arranged in two rows, each row having five openings, along the longitudinal direction X of flow channel unit  4 . In total, there are 10 openings  3   a , all formed at positions where openings  3   a  will not interfere with actuator unit  21 . Further, slanted sides of adjacent actuator units  21  partially overlap along a width direction (sub-scanning direction Y) of flow channel unit  4 . 
     As shown in  FIG. 5 , a bottom surface of flow channel unit  4  is ink discharging surface  70   a . A plurality of nozzles  8  is arranged in a matrix pattern in an ink discharging region that corresponds a region where four actuator units  21  are attached to the top surface of flow channel unit  4 . As shown in  FIG. 3 , pressure chamber group  9 , comprising a plurality of pressure chambers  10  (refer to  FIG. 5 ) is also arranged in a matrix pattern in the ink discharging region that corresponds the region where four actuator units  21  are attached to the top surface of flow channel unit  4 . In other words, each actuator unit  21  is configured to span over the plurality of pressure chambers  10  which compose pressure chamber group  9 . 
     Referring back to  FIG. 2 , base block  71  is made of metallic material such as stainless steel. Ink storage  3  within base block  71  is a hollow region having an approximate shape of a rectangle extending in the longitudinal direction X of base block  71 . Through an opening (not shown) formed on one end of ink storage  3 , ink is supplied to ink storage  3  from an ink tank (not shown) installed on the exterior of inkjet head assembly  1 , and ink storage  3  is always filled with ink. A total of 10 openings  3   b  through which the ink flows is formed on ink storage  3  in two rows, along the extended direction. These openings  3   b  are formed in a zigzag pattern so as to communicate with openings  3   a  of flow channel unit  4 . In other words, 10 openings  3   b  on ink storage  3  and 10 openings  3   a  on flow channel unit  4  are formed with the same positional relationship. 
     Bottom surface  73  of base block  71  protrudes downward at proximity sections  73   a  of openings  3   b . Further, base block  71  contacts proximity sections of openings  3   a  on the upper surface of flow channel unit  4  only at proximity sections  73   a  of openings  3   b  on bottom surface  73 . Therefore, except for proximity sections  73   a  of openings  3   b  on bottom surface  73  of base block  73 , a region of bottom surface  73  is separated from inkjet head  70 , and actuator units  21  are disposed in that separated region. 
     Holder  72  includes gripper  72   a , which grips base block  71 , and a pair of protrusions  72   b , which protrudes upward from an upper surface of gripper  72   a . The pair of protrusions  72   b  is formed with a distance between them in the sub scanning direction. Base block  71  is attached and fixed at a cavity formed on a bottom surface of gripper  72   a  of holder  72 . FPCs  50 , connected to the top surfaces of actuator units  21 , are each disposed along a surface of protrusion  72   b  of holder  72  via elastic member  83  such as a sponge. Further, driver IC  80  is installed on FPC  50  disposed on the surface of protrusion  72   b  of holder  72 . In other words, FPC  50  transmits a driving signal outputted from driver IC  80  to actuator unit  21  of inkjet head  70 . FPC  50  electrically connects actuator unit  21  and driver IC  80 . 
     Heat generated from driver IC  80  can be efficiently dissipated because heat sink  82 , shaped approximately as a rectangular parallelepiped, is attached to an outer surface of driver IC  80 . Board  81 , connected to an outer side of FPC  50 , is disposed above driver IC  80  and heat sink  82 . Sealing member  84  is attached between an upper surface of heat sink  82  and board  81 , and also between a bottom surface of heat sink  82  and FPC  50 . This can prevent dust and ink from entering inkjet head assembly  1 . 
       FIG. 4  is an enlarged planar diagram of the region framed by the dashed lines illustrated in  FIG. 3 . As shown in  FIG. 4 , in a region within flow channel unit  4  that faces actuator unit  21 , four sub-manifold flow channel  5   a  extend parallel to the longitudinal direction X of flow channel unit  4 . A plurality of individual ink flow channels  7  (refer to  FIG. 5 ) is connected to sub-manifold flow channel  5   a , wherein each individual ink flow channel  7  is connected to one nozzle  8 . 
     Pressure chamber group  9  comprising a plurality of pressure chambers  10  is formed on a region on the upper surface of flow channel unit  4  that faces actuator unit  21 . Pressure chambers  10  are arranged in a matrix pattern that has the similar pattern as of the matrix pattern of nozzles  8 . Pressure chamber  10  has a planar shape of approximately a rhombus, and pressure chamber group  9  is shaped as a trapezoid with approximately the same size dimension as the outer shape of actuator unit  21 . One pressure chamber group  9  is formed for each actuator unit  21 . An acute-angle section of each pressure chamber  10  of pressure chamber group  9  is connected to one corresponding nozzle  8 , via one corresponding ink flow channel  7  (see  FIG. 5 ). Further, the other acute-angle section of each pressure chamber  10  is connected to sub-manifold flow channel  5   a , via aperture  13 . As will be described below, individual electrodes  35  (refer to  FIG. 6 ), each being slightly smaller than pressure chamber  10 , are arranged in a matrix pattern on actuator unit  21  so as to face pressure chambers  10 . The matrix pattern of individual electrodes  35  has the same pattern as of the matrix pattern of pressure chambers. 
     Further, cavity  30  is formed on the upper surface of flow channel unit  4  which faces actuator unit  21  at a position outside of pressure chamber group  9 . Referring to  FIG. 4 , aperture  13 , nozzles  8 , and pressure chambers  10  (pressure chamber group  9 ) disposed below actuator unit  21  should have been drawn with broken lines, but they were instead drawn with solid lines to render the diagram easier to understand. 
     Next, a cross-sectional structure of inkjet head  70  will be explained.  FIG. 5  is a cross-sectional diagram along line V-V shown in  FIG. 4 , and illustrates individual ink flow channel  7 . As shown in  FIG. 5 , nozzle  8  is connected to sub-manifold flow channel  5   a  via pressure chamber  10  and aperture  13 . Accordingly, individual ink flow channel  7 , which reaches nozzle  8  from an outlet of sub-manifold flow channel  5   a  through aperture  13  and pressure chamber  10 , is formed within inkjet head  70  for each pressure chamber  10 . 
     As shown in  FIG. 5 , inkjet head  70  has a laminated structure with a total of eight plates stacked on top of one another. From top to bottom, the stacked plates consist of actuator unit  21 , cavity plate  22 , base plate  23 , aperture plate  24 , supply plate  25 , manifold plates  26  and  27 , and nozzle plate  28 . Flow channel unit  4  is constructed by seven of these plates, excluding actuator unit  21 . 
     As shown in  FIG. 6 , actuator unit  21  comprises three piezoelectric sheets  41 - 43 . As will be explained below, by stacking three piezoelectric sheets  41 - 43  and disposing common electrode between the uppermost layer  41  and second layer  42 , only the uppermost layer  41  becomes an active layer to which an electric field is applied. The remaining two layers  42 ,  43  become inactive layers and do not have active portions. 
     As shown in  FIG. 5 , cavity plate  22  is a metallic plate with a large number of approximately rhomboid-shaped holes formed within the ink discharging region that corresponds the region where four actuator units  21  are attached to cavity plate  22 . Actuator unit  21  caps each rhomboid-shaped hole, and the capped rhomboid-shaped hole forms pressure chamber  10 . Besides the rhomboid-shaped hole, hole  22   a  is formed on cavity plate  22 . Hole  22   a  is formed at a location where actuator unit  21  is attached but outside of pressure chamber group  9 . Hole  22   a  penetrates cavity plate  22 . 
     Base plate  23  is a metallic plate, and for each pressure chamber  10  of cavity plate  22 , base plate  23  has connecting hole  23   a , which connects pressure chamber  10  and aperture  13 , and connecting hole  23   b , which connects pressure chamber  10  to nozzle  8 . Notch  29  extending along a sub scanning direction Y from a position that faces hole  22   a  of cavity plate  22  is formed on base plate  23 . Notch  29  is formed to penetrate base plate  23  in a thick direction. According to this configuration, cavity  30  and a connection passage are formed on flow channel unit  4  by stacking cavity plate  22 , base plate  23 , and aperture plate  24 . Cavity  30  is formed by hole  22   a , and the connection passage is formed by notch  29 , a bottom surface of cavity plate  22 , and an upper surface of aperture plate  24 . Cavity  30  opens up toward actuator unit  21  (in actuality, the opening is covered by actuator unit  21 ). 
     As will be explained below, the connection passage enables cavity  30  to connect to the outside when manufacturing inkjet head  70 , and is sealed by disposing a sealing material (not shown) on an outlet (opening) of the connection passage once the manufacturing of inkjet head  70  is completed. Conductive member (conductive material)  31  to be used as conductive paste is filled within cavity  30 , and contacts terminal (contact terminal)  46  of actuator unit  21 , to be described hereinafter. As a result, flow channel unit  4  and contact terminal  46  become electrically connected. 
     Aperture plate  24  is a metallic plate that has, for each pressure chamber  10  of cavity plate  22 , a hole to become aperture  13  and a connecting hole to connect pressure chamber  10  to nozzle  8 . Supply plate  25  is a metallic plate that has, for each pressure chamber  10  of cavity plate  22 , a connecting hole that connects aperture  13  to sub-manifold flow channel  5   a  and another connecting hole that connects pressure chamber  10  to nozzle  8 . Manifold plates  26  and  27  are metallic plates that have, for each pressure chamber  10  of cavity plate  22 , sub-manifold flow channel  5   a  and a connecting hole to connect pressure chamber  10  to nozzle  8 . Nozzle plate  28  is a metallic plate that has nozzle  8  for each pressure chamber  10  of cavity plate  22 . 
     Seven metallic plates  22  to  28  are bonded by electro conductive adhesive so that the whole flow channel unit  4  becomes a block of conductive material. 
     These eight plates  21 - 28  are each stacked in a certain alignment so as to form individual ink flow channel  7 , as shown in  FIG. 5 . Individual ink flow channel  7  first proceeds upward from sub-manifold flow channel Sa, extends horizontally at aperture  13 , proceeds further upward, extends horizontally at pressure chamber  10 , proceeds downward in a slightly slanted direction away from aperture  13 , and then proceeds vertically downward toward nozzle  8 . 
     As is obvious from  FIG. 5 , pressure chamber  10  and aperture  13  are formed at different levels with respect to the stacked direction of each plate. Accordingly, within flow channel unit  4  facing actuator unit  21 , it is possible to dispose aperture  13 , which is connected to pressure chamber  10 , at a same planar-view position as a neighboring pressure chamber  10 , as shown in  FIG. 4 . As a result, since pressure chambers  10  are very tightly and densely disposed with respect to one another, high-resolution image printing can be performed by inkjet head assembly  1 , which has a relatively small area. In addition, by the connection passage created by notch  29  formed on base plate  23 , a bottom section of cavity  30  formed on cavity plate  22  can be connected to the outside. Accordingly, when heat processing is applied to the conductive paste that is to fill cavity  30 , solvent gas generated from the conductive paste can be released to the outside through the connection passage. This can prevent unwanted pressure from building inside cavity  30 , and an optimal attachment can be made at least between each of the plates that make up cavity  30 . 
     Next, a configuration of actuator unit  21  will be explained.  FIG. 6  ( a ) is an enlarged cross-sectional diagram of the region framed by the dashed lines in  FIG. 5 , and  FIG. 6  ( b ) is an enlarged planar diagram of a portion of actuator unit  21 . 
     As shown in  FIG. 6  ( a ), actuator unit  21  consists of three piezoelectric sheets  41 ,  42 , and  43 , each sheet being approximately 15 μm thick and each having the same construction. Piezoelectric sheets  41 - 43  are flat-plates stacked on top of one another and disposed to straddle the large number of pressure chambers  10 , which compose pressure chamber group  9 . With piezoelectric sheets  41 - 43  being disposed as stacked flat-plates that span across the large number of pressure chambers  10 , it becomes possible to dispose individual electrodes  35  very densely on piezoelectric sheet  41  using, for example, screen printing technology. Therefore, it also becomes possible to densely dispose pressure chambers  10 , which are formed to have the same positional relationship as individual electrodes  35 . As a result, high-resolution images can be printed. Piezoelectric sheets  41 - 43  are made of ceramic material such as titanic acid lead zirconate (PZT), which has ferroelectric properties. 
     Individual electrodes  35  are formed on a top surface of the uppermost layer, piezoelectric sheet  41 . Common electrode  34 , formed over an entire surface and having an approximate thickness of 2 μm, is interposed between piezoelectric sheet  41  and piezoelectric sheet  42  disposed below. Similar to common electrode  34 , reinforcement electrode  33 , formed over an entire surface and having an approximate thickness of 2 μm, is interposed between piezoelectric sheet  42  and the bottommost layer, piezoelectric sheet  43 . Individual electrodes  35 , common electrode  34 , and reinforcement electrode  33  are all made from metallic materials such as Ag-Pd. Further, a side end surface on one side of common electrode  34  and reinforcement electrode  33  becomes exposed when each sheet is stacked. This is because common electrode  34  and reinforcement electrode  33  are formed over an entire surface of piezoelectric sheets  42  and  43 , respectively. 
     As shown in  FIG. 6  ( b ), individual electrode  35  comprises main electrode region  35   a  and auxiliary electrode region  35   b . Main electrode  35   a  is disposed at a position that faces pressure chamber  10 , and auxiliary electrode region  35   b  is connected to main electrode  35   a  and is disposed at a position that does not face pressure chamber  10 . Main electrode  35   a  has a planar shape of approximately a rhombus that is approximately congruent to pressure chamber  10 . An acute angle section of the rhomboid-shaped main electrode  35   a  extends outward and is connected to auxiliary electrode region  35   b . Land  36 , which is circular, is installed on a leading surface of auxiliary electrode region  35   b . As shown in  FIG. 6  ( b ), land  36  faces a region where pressure chamber  10  is not formed on cavity plate  22 . Land  36  is made of, for example, metal including glass flit, and is attached and electrically connected to auxiliary electrode region  35   b .  FIG. 6  ( a ) simplifies the illustration of FPC  50 , but land  36  is electrically coupled to each of a plurality of contact points on FPC  50 . 
     Holes  47   a - 49   a  are formed on each of piezoelectric sheets  41 - 43 , each hole penetrating one of the sheets in a thick direction so as not to overlap with one another. Conductive wirings  47   b - 49   b  made of conductive material are disposed within holes  47   a - 49   a . An upper surface of conductive wiring  47   b  is exposed at the upper surface of actuator unit  21  and is connected by soldering to an independent contact point on FPC  50 . Conductive wiring  47   b  is connected to ground through FPC  50 . On the other hand, a bottom surface of conductive wiring  47   b  is electrically connected to common electrode  34 . An upper surface of conductive wiring  48   b  is electrically connected to common electrode  34  and a bottom surface of conductive wiring  48   b  is electrically connected to reinforcement electrode  33 . An upper surface of conductive wiring  49   b  is electrically connected to reinforcement electrode  33 , and a bottom surface of conductive wiring  49   b  is exposed at the bottom surface of actuator unit  21 . That exposed portion of conductive wiring  49   b  is contact terminal  46 , which was described above. According to this configuration, flow channel unit  4  is maintained at ground potential because flow channel unit  4  is connected to ground through contact terminal  46 , conductive wiring  49   b , reinforcement electrode  33 , conductive wiring  48   b , common electrode  34 , conductive wiring  47   b , and FPC  50 . Also, common electrode  34  and reinforcement electrode  33  are equally maintained at ground potential. In other words, this configuration is such that it produces no difference in electrical potential between flow channel unit  4  and actuator unit  21 . 
     Further, land  36  of individual electrode  35  is joined independently to a contact point on FPC  50 , and each land  36  is connected to driver IC  80  independently from other lands. As a result, electrical potential can be controlled independently for each actuator that corresponds to each pressure chamber  10 . 
     Next, a method of driving actuator unit  21  will be explained. The polarization direction of piezoelectric sheet  41  of actuator unit  21  is in the thick direction. In other words, actuator unit  21  is of a so-called unimorph construction having one top side (that is, away from pressure chamber  10 ) piezoelectric sheet  41  as an active layer and two bottom side (that is, cross to pressure chamber  10 ) piezoelectric sheets  42  and  43  as inactive layers. Therefore, if an individual electrode  35  is activated and given a predetermined potential of either positive or negative, electric field is grown along the polarization direction of the active piezoelectric sheet  41  at a portion interposed between the activated individual electrode  35  and common electrode  34 . That portion shrinks in a direction perpendicular to the polarization direction, due to the piezoelectric transversal effect. On the other hand, piezoelectric sheets  42  and  43  do not shrink on their own because they are not influenced by the electric field. Therefore, a difference in distortion arises in the direction perpendicular to the polarization direction between the uppermost layer (piezoelectric sheet  41 ), and the lower layers (piezoelectric sheets  42  and  43 ). As a result, piezoelectric sheets  41 - 43  transform so as to protrude toward the inactive side (unimorph transformation). At this time, as shown in  FIG. 6  ( a ), since a bottom surface of piezoelectric sheets  41 - 43  are fixed on a top surface of cavity plate  22  which separates pressure chambers  10 , piezoelectric sheets  41 - 43  transform to protrude toward a corresponding pressure chamber  10 . As a result, the volume of the corresponding pressure chamber  10  decreases, the pressure on the ink increases, and ink is discharged from the corresponding nozzle  8 . Then, when individual electrode  35  and common electrode  34  are brought back to equal electrical potential, piezoelectric sheets  41 - 43  suction ink from the manifold  5  because piezoelectric sheets  41 - 43  return to their original shapes and the volume of pressure chamber  10  return to the original volume. 
     In addition, as another method of driving actuator unit  21 , individual electrodes  35  and common electrode  34  are initially held at different electrical potentials. Then, every time a discharge request is made, an the individual electrode  35  and common electrode  34  are brought to equal electrical potential, and at a predetermined timing, individual electrode  35  and common electrode  34  are placed back at different electrical potentials. In this case, because piezoelectric sheets  41 - 43  move back to their original shapes when the individual electrode  35  and common electrode  34  are brought to equal electrical potential, the volume of pressure chamber  10  increases from their original volume (at condition where both electrodes have different electrical potentials), and ink is suctioned into the pressure chambers  10  from the sub-manifold flow channel  5   a . Then, at the timing when the individual electrode  35  and common electrode  34  are placed back at different electrical potentials, piezoelectric sheets  41 - 43  transform and protrude towards the pressure chamber  10  side, the pressure on the ink increases due to decreasing volumes of pressure chamber  10 , and ink is discharged from nozzle  8 . 
     &lt;A Method of Manufacturing an Inkjet Head&gt; 
     Next, a method of manufacturing inkjet head will be explained with reference to  FIG. 7 .  FIG. 7  is a flow chart of manufacturing steps of inkjet head. 
     In order to manufacture inkjet head, components such as flow channel unit  4  and actuator unit  21  are fabricated separately and subsequently combined. First, in step  1  (S 1 ), flow channel unit  4  is fabricated. In order to fabricate flow channel unit  4 , holes as shown in  FIG. 5  are formed on plates  22 - 28  by applying etching. The etching has photoresist as a mask, patterned on each of plates  22 - 28  which compose flow channel unit  4 . At this time, hole  22   a  to become cavity  30  is also formed on cavity plate  22 . Further, notch  29  is formed on base plate  23 . Then, the seven plates  22 - 28  are layered on top of one another via an epoxy-based electro conductive thermosetting adhesive so that the plates  22 - 28  align to form a plurality of individual ink flow channels  7  within the flow channel unit  4  and cavity  30  on a flat surface of the flow channel unit  4  to which actuator unit  21  will be attached. Next, pressure and heat are applied to the seven plates  22 - 28  and the temperature of the plates is raised above a hardening temperature of the thermosetting adhesive. As a result, the thermosetting adhesive hardens, the seven plates  22 - 28  become fixed to one another, and flow channel unit  4  as shown in  FIG. 5  can be attained. In order to avoid interference among flow channel unit  4 , actuator unit  21 , and contact terminal  46 , it is preferable to form hole  22   a  so that an opening area at the top surface of cavity plate  22  is larger than an opening area at the bottom surface. It is also preferable that the opening area of hole  22   a  at the top surface of cavity plate  22  is larger than the contact terminal  46 . As a result, when attaching actuator unit  21  with flow channel unit  4 , damages or cracks on actuator unit  21  can be prevented. 
     On the other hand, when fabricating actuator unit  21 , three green sheets made of piezoelectric ceramics are prepared in step  2  (S 2 ). The green sheets are formed beforehand with consideration to shrinking that will result from subsequent heating. On the green sheet to become piezoelectric sheet  42 , conductive paste is screen printed in a pattern corresponding to common electrode  34 . On the green sheet to become piezoelectric sheet  43 , conductive paste is screen printed in a pattern corresponding to reinforcement electrode  33 . Further, holes  47   a - 49   a  are formed on each of the three green sheets, and conductive paste is filled in each of holes  47   a - 49   a . Then, while aligning the green sheets with a jig so that holes  47   a - 49   a  do not overlap. The green sheet with the conductive paste screen printed in a pattern corresponding to common electrode  34  is disposed directly below the green sheet without the conductive paste. Further, the green sheet with the conductive paste screen printed in a pattern corresponding to reinforcement electrode  33  is disposed directly below the green sheet with the conductive paste screen printed in the pattern corresponding to common electrode  34 . 
     Then, in step  3  (S 3 ), the laminated body attained in step  2  is degreased in the same way as heretofore known ceramics, and is heated at a predefined temperature. As a result, the three green sheets become piezoelectric sheets  41 - 43 , and the conductive paste becomes common electrode  34 , reinforcement electrode  33 , and conductive wirings  47   b - 49   b . Among these, conductive wiring  47   b  becomes a contact terminal, which protrudes from a top surface of piezoelectric sheet  41  and to which FPC  50  is connected. On the other hand, conductive wiring  49   b  becomes contact terminal  46  which protrudes from a bottom surface of piezoelectric sheet  43  to which conductive member  31  contacts. Then, conductive paste is screen printed on top of the uppermost layer, piezoelectric sheet  41 , in a pattern corresponding to the plurality of individual electrodes  35 . Then, the conductive paste is heated by performing a heating process on the laminated body, and individual electrodes  35  are formed on piezoelectric sheet  41 . Land  36  is subsequently formed by printing metal including glass flits on auxiliary electrode region  35   b  of individual electrode  35 . At this time, a land identical to land  36  may be formed to electrically connect to the exposed portion of conductive wiring  47   b . This will enable a more reliable connection between FPC  50  and conductive wiring  47   b . In this way, actuator unit  21  as shown in  FIG. 6  ( a ) can be manufactured. 
     Step  1  to fabricate flow channel unit  4  and steps  2 - 3  to fabricate actuator unit  21  are independent of one another. Therefore, either one of step  1  or steps  2 - 3  can be performed before the other, or they can be carried out simultaneously. 
     In step  4  (S 4 ), using a bar coater, epoxy-based thermosetting adhesive  6  is applied on a top surface of flow channel unit  4 . The top surface of flow channel unit  4  has a plurality of holes for forming pressure chambers and hole  22   a  for forming cavity  30 . The adhesive  6  is applied on the top surface of flow channel unit  4  except holes for forming pressure chambers and hole  22   a  for forming cavity  30 . A two-component epoxy type, for example, is used as epoxy-based thermosetting adhesive  6 . 
     Next, in step  5  (S 5 ), conductive paste to become conductive member  31  is filled in cavity  30  of flow channel unit  4 , which was obtained in step  1 . At this time, since a diameter of a bottom side of cavity  30  is smaller than a diameter of an opening at the top side of cavity  30 , the conductive paste filled in cavity  30  protrudes above the surface of cavity plate  22 , even if with a small amount of the conductive paste. As a result, the conductive paste  31  and contact terminal  46  easily come in contact with one another. In addition, it becomes difficult for epoxy-based thermosetting adhesive  6  to enter between contact terminal  46  and the conductive paste. Therefore, secure contact can be obtained between contact terminal  46  and the conductive paste that will become conductive member  31 . This also leads to cost reduction because only a small amount of conductive paste is necessary. Further, in order to avoid an insecure attachment between actuator unit  21  and flow channel unit  4  caused by an excessive amount of conductive paste, it is preferable that the filling amount of the conductive paste be held between 50%-95% of the inside volume of cavity  30 . 
     Next, in step  6  (S 6 ), actuator unit  21  is mounted on flow channel unit  4 , which is coated with thermosetting adhesive  6 . At this time, each actuator unit  21  is placed in a position on flow channel unit  4  so that each of individual electrode  35  of actuator unit  21  faces a corresponding pressure chamber  10  of flow channel unit  4 , and so that contact terminal  46  of actuator unit  21  faces the conductive paste filled in cavity  30  of flow channel unit  4 . This position placement is based on a position marker (not shown) formed on flow channel unit  4  and actuator unit  21  during the fabrication steps (steps  1 - 3 ). 
     Next, in step  7  (S 7 ), the laminated body consisting of flow channel unit  4 , thermosetting adhesive  6  fixed between flow channel unit  4  and actuator unit  21 , and actuator unit  21  is heated with a heating/pressurizing device (not shown) to a temperature no higher than the hardening temperature of thermosetting adhesive  6 . By heating the laminated body this way, a part of the solvent of the conductive paste within cavity  30  evaporates. Then, the evaporated gas is released to the outside through a connection passage created by notch  29 , which connects cavity  30  to the outside. This can prevent unwanted pressure from building inside cavity  30 . Therefore, it becomes possible to attach flow channel unit  4  and actuator unit  21  securely. 
     Next, in step  8  (S 8 ), pressure is applied to the laminated body as the body is heated above the hardening temperature of thermosetting adhesive  6 . In this way, thermosetting adhesive  6  hardens, causing flow channel  4  and actuator unit  21  to become attached. Further, contact terminal  46  and conductive member  31  make secure electrical contact. Then, in step  9  (S 9 ), the laminated body is taken out of the heating/pressurizing device and naturally cooled. Next, in step  10  (S 10 ), an outlet of the connection passage is sealed with a sealing material (not shown), which can prevent ink spew or dust from entering cavity  30  through the connection passage. In this way, inkjet head  70  composed of flow channel unit  4  and actuator unit  21  is manufactured. 
     Then, after carrying out a connecting step of FPC  50 , inkjet head assembly  1  as described above is completed by finishing an attaching step of base block  71 . 
     According to inkjet head assembly  1  of the first embodiment described above, when flow channel unit  4  and actuator unit  21  are attached, the inside of cavity  30  where conductive member  31  is installed does not get covered by thermosetting adhesive  6 . Further, since conductive member  31  and contact terminal  46  contact one another, flow channel unit  4  and common electrode  34  of actuator unit  21  can be electrically connected without having to scrape off thermosetting adhesive  6 , which covers flow channel unit  4 . As a result, a reliable connection between flow channel unit  4  and common electrode  34  of actuator unit  21  can be attained without clogging the ink channel within the flow channel unit  4 . Therefore, the potential difference between flow channel unit  4  and common electrode  34  of actuator unit  21  becomes zero, and migration becomes improbable. Further, since a large proportion of conductive wirings  47   b - 49   b  of actuator unit  21  is unexposed to the outside, conductive wirings  47   b - 49   b  can be protected from ink spew and dust. Further, since conductive wirings  47   b - 49   b  are not disposed to overlap with one another, conductive wirings  47   b - 49   b  will not easily come off actuator unit  21  when pressure is applied to actuator unit  21 . This is because holes  47   a - 49   a , in which conductive wirings  47   b - 49   b  are disposed, do not continuously penetrate actuator unit  21  in a direction perpendicular to the attachment surface between actuator unit  21  and flow channel unit  4 . Accordingly, even if pressure generated by the contact made between contact terminal  46  and conductive member  31  is applied to conductive wiring  49   b , piezoelectric sheet  42  is positioned on an upper side of conductive wiring  49   b  so that pressure can be absorbed not only by the force of attachment between conductive wiring  49   b  and hole  49   a , but also by piezoelectric sheet  42 . 
     In the above embodiment, epoxy-based thermosetting adhesive  6  is not electric conductive. However, flow channel unit  4  and common electrode  34  of actuator unit  21  is securely connected via conductive member  31  and contact terminal  46  and maintained at the same electrical potential. Even if adhesive  6  is electric conductive, still conductive member  31  and contact terminal  46  are useful in making flow channel unit  4  and common electrode  34  of actuator unit  21  at the same electrical potential. When conductive member  31  and contact terminal  46  are not used, it may be possible that flow channel unit  4  and common electrode  34  of actuator unit  21  have different electrical potential due to resistance of adhesive  6 . Conductive member  31  and contact terminal  46  have very low resistance, therefore, flow channel unit  4  and common electrode  34  of actuator unit  21  are maintained at the same level accurately. 
     In the above embodiment, seven plates  22 - 28  are adhered by electro conductive adhesive to fabricate flow channel unit  4 . However, in a case that conductive member  31  is deep enough to connect seven plates  22 - 28 , plates  22 - 28  may be adhered by non-electro conductive adhesive. 
     Next, an inkjet head  170  according to a second embodiment of the present invention will be described.  FIG. 8  ( a ) is an enlarged cross-sectional diagram of a portion of inkjet head  170  according to the second embodiment of the present invention, and  FIG. 8  ( b ) is an enlarged planar diagram of a portion of inkjet head  170 . Components identical to inkjet head assembly  1  of the first embodiment will be represented with the same notations, and their explanation will be shortened. 
     Actuator unit  121  of inkjet head  170  according to the present embodiment has hole  112  that continuously penetrates piezoelectric sheets  41 - 43  in the thick direction, as shown in  FIG. 8  ( a ). Hole  112  is formed at a position that faces conductive member  131 , and conductive wiring  113  made of conductive material is disposed inside hole  112 . Conductive wiring  113  is electrically connected to common electrode  34  and reinforcement electrode  33 . An upper surface of conductive wiring  113  is exposed on an upper surface of actuator unit  121 , and is connected by soldering to independent connection point (not shown) on FPC  50 . Conductive wiring  113  is also connected to ground at the upper surface of conductive wiring  113  via FPC  50 . On the other hand, a bottom surface of conductive wiring  113  is exposed at a bottom surface of actuator unit  121 , and the exposed section is contact terminal  146 . According to this configuration, as was the case with the first embodiment, flow channel unit  104  is maintained at ground potential because common electrode  34  and reinforcement electrode  33  are maintained at ground in a region that corresponds to all pressure chambers  10 , and also because contact terminal  146  contacts conductive member  131 . In other words, according to this configuration, a difference in electrical potential between flow channel unit  104  and actuator unit  121  does not arise. 
     Flow channel unit  104  is composed of seven metallic plates stacked on top of one another, as was the case with flow channel unit  4  mentioned above, but cavity plate  22 , base plate  23 , and aperture plate  24  have slightly different configurations as those of the above-mentioned embodiment. As shown in  FIGS. 8  ( a ) and ( b ), in addition to holes to become pressure chambers  10 , holes  122   a  and cavity  122   b  are formed on cavity plate  22  of flow channel unit  104 . Hole  122   a  penetrates cavity plate  22  in a thick direction at a position that faces contact terminal  146 . Cavity  122   b  extends parallel to a sub-scanning direction on a bottom surface that faces base plate  23 . Other than connecting holes  23   a  and  23   b , hole  123  that penetrates base plate  23  in the thick direction is also formed on base plate  23 . In addition to aperture  13  and a connecting hole that connects pressure chamber  10  with nozzle  8 , hole  124 , which penetrates aperture plate  24  in the thick direction at a region that faces cavity  122   b , is formed on aperture plate  24 . By stacking these plates  22 - 24  and supply plate  25 , first spare chamber  126 , second spare chamber  127 , and cavity  130  are formed within flow channel unit  104 . First spare chamber  126  is framed by cavity  122   b  and an upper surface of base plate  23 , and second spare chamber  127  is framed by hole  124 , a bottom surface of base plate  23 , and an upper surface of supply plate  25 . 
     Cavity  130  connects the first and second spare chambers  126  and  127 . A conductive paste to become conductive member  131  is filled in cavity  130 . Then, as was the case in the first embodiment described above, flow channel unit  104  and actuator unit  121  are attached with thermosetting adhesive  6 , and contact terminal  146  of actuator unit  121  contacts conductive member  131 . As a result, flow channel unit  104  and contact terminal  146  of actuator unit  121  become electrically connected. 
     &lt;A Method of Manufacturing an Inkjet Head&gt; 
     A method of manufacturing inkjet head  170  of the second embodiment described above is nearly equivalent to the method of manufacturing the first embodiment. First, flow channel unit  104  is fabricated. At this time, the method of manufacturing the second embodiment differs in that hole  122   a  and cavity  122   b  are formed on cavity plate  22 , hole  123  is formed on base plate  23 , and hole  124  is formed on aperture plate  24 . These holes  122   a ,  123 , and  124  are formed by etching, and cavity  122   b  is formed by half-etching. Then, each plate is stacked on top of one another via the thermosetting adhesive, and the plates are pressurized and heated above a hardening temperature of the thermosetting adhesive. As a result, the thermosetting adhesive hardens, and flow channel unit  104  comprising cavity  130 , first spare chamber  126 , and second spare chamber  127  can be attained. 
     Next, actuator unit  121  is fabricated. First, three green sheets made of piezoelectric ceramics are prepared. The green sheets are formed beforehand with consideration to the shrinking that will results from subsequent heating. On the green sheet to become piezoelectric sheet  42 , conductive paste is screen printed in a pattern corresponding to common electrode  34 . On the green sheet to become piezoelectric sheet  43 , conductive paste is screen printed in a pattern corresponding to reinforcement electrode  33 . Then, a hole is formed on each of the three green sheets, and each green sheet is positioned to overlap one another and is aligned so that the holes line up to form hole  112 . Hole  112  is then filled with conductive paste. Obviously, the hole on each of the three green sheets can be individually filled with the conductive paste prior to stacking the green sheets. Next, the laminated body is degreased in the same way as heretofore known ceramics, and is heated at a predefined temperature. As a result, the three green sheets become piezoelectric sheets  41 - 43 , and the conductive paste becomes common electrode  34 , reinforcement electrode  33 , and conductive wiring  113 . Then, conductive paste is screen printed on top of the uppermost layer, piezoelectric sheet  41 , in a pattern corresponding to individual electrodes  35 . Then, the conductive paste is heated by performing a heating process on the laminated body, and individual electrodes  35  are formed on piezoelectric sheet  41 . Land  36  is subsequently formed by printing metal including glass flits on auxiliary electrode region  35   b  of individual electrode  35 . In this way, actuator unit  121  as shown in  FIG. 8  ( a ) can be manufactured. 
     Parenthetically speaking, in order to prevent conductive wiring  113  from coming off actuator unit  121  when connecting conductive wiring  113  and FPC  50 , land  36  may be formed in an offset position from an exposed portion of conductive wiring  113 , while at the same time electrically connecting a similar land to conductive wiring  113  exposed on a surface of piezoelectric sheet  41 . This enables conductive wiring  113  to be placed at ground potential because conductive wiring  113  does not directly receive the pressure produced from connecting FPC  50 . 
     Next, using a bar coater, an epoxy-based thermosetting adhesive is applied on a top surface of flow channel unit  121 . Adhesive is applied to the top surface of flow channel unit other than cavity  130  and the plurality of cavities corresponding to the plurality of pressure chambers of flow channel unit  104 , as was done in the first embodiment. Then, cavity  130  of flow channel unit  104  is filled with conductive paste, which becomes conductive member  131 . At this time, since a diameter of a bottom side of hole  122   a  constituting a portion of cavity  130  is smaller than a diameter of an opening side of hole  122   a , the conductive paste protrudes above the surface of cavity plate  22 . 
     Next, each actuator unit  121  is mounted on flow channel unit  104 . At this time, each actuator unit  121  is placed in position on flow channel unit  104  so that the active layer faces pressure chambers  10  and so that the conductive paste filled in cavity  130  of flow channel unit  104  faces contact terminal  146  of actuator unit  121 . 
     Next, the laminated body consisting of flow channel unit  104 , thermosetting adhesive  6  fixed between flow channel unit  104  and actuator unit  121 , and actuator unit  121  is heated with a heating/pressurizing device (not shown) to a temperature no higher than the hardening temperature of thermosetting adhesive  6 . By heating the laminated body in this way, a part of a solvent of the conductive paste within cavity  130  evaporates, and the evaporated gas is released into the first and second spare chambers  126  and  127 . This allows the pressure within cavity  130  to. Therefore, flow channel unit  104  and actuator unit  121  can be securely attached to one another. Then, inkjet head  170  is manufactured by heating the laminated body above a hardening temperature of thermosetting adhesive  6  and then naturally cooling it, as was done in the first embodiment. Finally, after carrying out a connecting step of FPC  50 , the inkjet head as described above is completed by finishing an attachment step of base block  71 . With the present embodiment, since excess conductive paste can also be released into the first and second spare chambers  126  and  127 , the attachment between each plate does not get adversely affected even if the conductive paste overflows. 
     Not only is inkjet head  170  of the above-mentioned second embodiment able to attain all the effects attained by inkjet head assembly  1  of the first embodiment, but also inkjet head  170  of the second embodiment can also electrically connect common electrode  34 , reinforcement electrode  33 , and terminal  146  all at once. This is possible because the inkjet head  170  of the second embodiment bears conductive wiring  113  within hole  112 , which penetrates actuator unit  121 . Further, with respect to the method of manufacturing, conductive wiring  113 , which electrically connects contact terminal  146  to common electrode  34  and reinforcement electrode  33 , can be easily formed by filling hole  112  with the conductive paste to become conductive wiring  113  and heating the conductive paste. 
     Next, an inkjet head  270  according to a third embodiment of the present invention will be described.  FIG. 9  ( a ) is an enlarged cross-sectional diagram of inkjet head  270  according to the third embodiment of the present invention, and  FIG. 9  ( b ) is an enlarged planar diagram of a portion of inkjet head  270 . Components identical to the inkjet heads of the first and second embodiments will be represented with the same notations, and their explanation will be shortened. 
     The inkjet head of the present embodiment is similar to the inkjet head of the second embodiment with the exception that a configuration of flow channel unit  204  is slightly different than the configuration of flow channel unit  104 . As shown in  FIGS. 9  ( a ) and  FIGS. 9  ( b ), in addition to holes to become pressure chambers  10 , holes  222   a  and groove  222   b  are formed on cavity plate  22  of flow channel unit  204 . Hole  222   a  penetrates cavity plate  22  in a thick direction at a position that faces contact terminal  146 . Groove  222   b  extends parallel to a sub-scanning direction Y on a top surface of cavity plate  22  that faces actuator unit  121 . Groove  222   b  extends from hole  222   a  and reaches a region that does not face actuator unit  121 , and opens toward the actuator unit  121  side. Only connecting holes  23   a  and  23   b  are formed on base plate  23 . By stacking actuator unit  121 , cavity plate  22 , and base plate  23 , a connection passage and cavity  230  connecting to that connection passage are formed on flow channel unit  204 . The connection passage is framed by a bottom surface of actuator unit  121  and groove  222   b , and is connected to the outside. Sealing material  232  is disposed on an outlet of the connection passage, preventing ink spew and dust from entering cavity  230  through the connection passage. Cavity  230  is filled with conductive paste to become conductive member  231 . Then, similarly to the first and second embodiments described above, flow channel unit  204  and actuator unit  121  are attached with thermosetting adhesive  6 , and contact terminal  146  of actuator unit  121  contacts conductive member  231 . As a result, flow channel unit  204  and terminal  146  become electrically connected. 
     &lt;A Method of Manufacturing an Inkjet Head&gt; 
     In a method of manufacturing inkjet head  270  of the third embodiment mentioned above, flow channel unit  204  is first fabricated as was done in the first and second embodiments. At this time, the method of manufacturing the third embodiment differs in that hole  222   a  and groove  222   b  are formed on cavity plate  22 . The holes to become pressure chambers  10  and hole  222   a  are formed by etching, and groove  222   b  is formed by half-etching. Holes are also formed on the plates other than cavity plate  22 , by etching. Then, each plate is stacked on top of one another via a thermosetting adhesive, and pressure is applied to the laminated body while the body is heated above the hardening temperature of thermosetting adhesive  6 . As a result, the thermosetting adhesive hardens, and flow channel unit  204  can be attained with groove  222   b  and cavity  230  formed on a top surface that faces actuator unit  121  of flow channel unit  204 . 
     Next, actuator unit  121  is fabricated in a similar fashion as the second embodiment. Using a bar coater, an epoxy-based thermosetting adhesive is applied on the top surface of flow channel unit  204 , as was done with the above-mentioned embodiments. Then, cavity  230  of flow channel unit  204  is filled with conductive paste to become conductive member  231 . Then, each actuator unit  121  is mounted on flow channel unit  204 . At this time, each actuator unit  121  is positioned on flow channel unit  204  so that an active layer faces the pressure chambers region, and so that the conductive paste filled in cavity  230  of flow channel unit  204  faces contact terminal  146  of actuator unit  121 . 
     Next, the laminated body consisting of flow channel unit  204 , thermosetting adhesive  6  fixed between flow channel unit  204  and actuator unit  121 , and actuator unit  121  is heated with a heating/pressurizing device (not shown) to a temperature no higher than the hardening temperature of thermosetting adhesive  6 . By heating the laminated body in this way, a part of a solvent of the conductive paste within cavity  230  evaporates, and the evaporated gas is released to the outside through a connection passage framed by groove  222   b  and a bottom surface of actuator unit  121 . As was the case with the first embodiment, this enables secure attachment between flow channel  204  and actuator unit  121 . Then, as was done in the first embodiment, the laminated body is further heated and then naturally cooled. Then, an outlet of the connection passage is sealed with sealing material  232 . This can prevent ink spew and dust from entering cavity  230  through the connection passage. In this way, inkjet head  270  comprising flow channel unit  204  and actuator unit  121  is manufactured. Finally, after carrying out a connecting step of FPC  50 , the inkjet head as described above is completed by finishing an attachment step of base block  71 . 
     According to the inkjet head of the third embodiment described above, common electrode  34  and flow channel unit  204  can be electrically connected without having to scrape off thermosetting adhesive  6 , which covers flow channel unit  204 . This is because conductive member  231  and contact terminal  146  contact one another when flow channel unit  204  and actuator unit  121  are attached. As a result, a reliable connection can be made between common electrode  34  and flow channel unit  204  without clogging the ink channel within the head. Therefore, potential difference between common electrode  34  and flow channel unit  204  becomes zero, and migration becomes improbable. Further, since the connection passage that connects to the outside is formed on an attachment surface between actuator unit  121  and flow channel unit  204 , gas from the conductive paste, generated during the heating process, can be effectively released to the outside. Accordingly, not only does the attachment between actuator unit  121  and flow channel unit  204  become more secure, but the electrical contact between conductive member  231  and contact terminal  146  becomes more reliable. 
     Next, an inkjet head according to a fourth embodiment of the present invention will be described.  FIG. 10  ( a ) is an enlarged cross-sectional diagram of a portion of inkjet head  370  according to the fourth embodiment of the present invention, and  FIG. 10  ( b ) is an enlarged planar diagram of inkjet head  370 . Components identical to the above-mentioned embodiments will be represented with the same notations, and their explanation will be shortened. 
     Actuator unit  321  of the inkjet head of the present embodiment, as shown in  FIG. 10  ( a ), does not have holes or conductive wirings that penetrate piezoelectric sheets  41 - 43 . Formed instead is conductive wiring  345 , which electrically connects common electrode  34  and reinforcement electrode  33 . Common electrode  34  and reinforcement electrode  33  extends to a peripheral border of the piezoelectric sheet  41 ,  42 ,  43  so as to become exposed at a side end surface of the actuator unit  321 . As shown in  FIG. 10  ( a ), conductive wiring  345  has a cross-sectional shape of an “L,” and extends along a bottom surface of actuator unit  321  from one side end surface of actuator unit  321 . Conductive wiring  345  is connected to common electrode  34  and reinforcement electrode  33  at their exposed side ends. A portion of conductive wiring  345  that extends on the bottom surface of actuator unit  321  has a planar shape of a triangle. That portion is contact terminal  346 , wherein an acute-angle section contacts conductive member  31 . Common electrode  34  is electrically connected to a contact point on FPC  50  at a region not shown in the figure, and is connected to ground. According to this configuration, common electrode  34  and reinforcement electrode  33  are equally maintained at ground in a region that corresponds to all pressure chambers  10 , and contact terminal  346  and conductive member  31  contact one another. Therefore, as was the case with the first embodiment, flow channel unit  4  is maintained at ground potential. In other words, according to this configuration, there is no difference in electrical potential between flow channel unit  4  and actuator unit  321 . Further, flow channel unit  4  is of the same configuration as the flow channel unit in the first embodiment. 
     &lt;A Method of Manufacturing an Inkjet Head&gt; 
     Next, a method of manufacturing inkjet head  370  according to the fourth embodiment will be explained. Flow channel unit  4  is formed with the same method of manufacturing as presented in the first embodiment (step  1 ). Inkjet head  370  is manufactured by attaching the fabricated actuator unit  321  with flow channel unit  4 , according to steps  4 - 10  described above. In other words, the method of manufacturing inkjet head  370  of the fourth embodiment is the same as the first embodiment with the exception of steps  2  and  3 . Inkjet head  370  of the fourth embodiment is otherwise manufactured by completing the same steps of manufacturing. 
     In order to fabricate actuator unit  321 , three green sheets made of piezoelectric ceramics are prepared. The green sheets are formed beforehand with consideration to the shrinking that will result from the subsequent calcination. On the green sheet to become piezoelectric sheet  42 , conductive paste is screen printed in a pattern corresponding to common electrode  34 . On the green sheet to become piezoelectric sheet  43 , conductive paste is screen printed in a pattern corresponding to reinforcement electrode  33 . Then, using a jig, the green sheet with the conductive paste that was screen printed in a pattern corresponding to common electrode  34  is disposed directly below the green sheet without the conductive paste. Further, the green sheet with the conductive paste that was screen printed in a pattern corresponding to reinforcement electrode  33  is disposed directly below the conductive paste that was screen printed in a pattern corresponding to common electrode  34 . 
     Next, the laminated body is degreased in the same way as heretofore known ceramics, and is calcinated at a predefined temperature. As a result, the three green sheets become piezoelectric sheets  41 - 43 , and the conductive paste becomes common electrode  34 , reinforcement electrode  33 , and conductive wiring  113 . Then, conductive paste is screen printed on top of the uppermost layer, piezoelectric sheet  41 , in a pattern corresponding to individual electrodes  35 . Then, the conductive paste is calcinated by performing a heating process on the laminated body, and individual electrodes  35  are formed on piezoelectric sheet  41 . Land  36  is subsequently formed by printing metal that includes glass flits on auxiliary electrode region  35   b  of each individual electrode  35 . 
     Next, conductive wiring  345  is formed on one side end surface of the laminated body and on a bottom surface of the laminated body.  FIG. 11  ( a ) shows a condition before conductive wiring  345  is formed on actuator unit  321 , and  FIG. 11  ( b ) shows a condition after conductive wiring  345  has been formed on actuator unit  321 . As shown in  FIG. 11  ( a ), the laminated body is mounted on platform  351 , and mask  352  is applied over a region on the laminated body where conductive wiring  345  will not be formed. Then, the laminated body and platform  351  are tilted to a predetermined angle, and conductive particles to become conductive wiring  345  are deposited using PVD (Physical Vapor Deposition). In this way, as shown in figure  11  ( b ), conductive wiring  345  can be formed simultaneously on a part of an side end surface of the laminated body and a part of the bottom surface of the laminated body. Further, by changing the deposition direction, a thickness of conductive wiring  345  on the side end surface of actuator unit  321  and a thickness of conductive wiring  345  on the bottom surface of actuator unit  321  can be easily adjusted. In this way, actuator unit  321  as shown in  FIG. 10  ( a ) can be fabricated. 
     According to inkjet head  370  of the fourth embodiment described above, as was the case with the first embodiment, common electrode  34  and flow channel unit  4  can be electrically connected without having to scrape off thermosetting adhesive  6 , which covers flow channel unit  4 . This is because conductive member  31  and contact terminal  346  contact one another when flow channel unit  4  and actuator unit  321  are attached. Therefore, the potential difference between common electrode  34  and flow channel unit  4  becomes zero, and migration becomes improbable. Further, since conductive wiring  345  is formed on actuator unit  321  at the side end surface and at the attachment surface, to which flow channel unit  4  is attached, common electrode  34 , reinforcement electrode  33 , and contact terminal  146  can be electrically connected all at once. In addition, since conductive wiring  345  is formed on a surface of actuator unit  321 , the strength of actuator unit  321  increases relative to having the conductive wiring built inside the actuator unit. In other words, since there is no need to form holes on piezoelectric sheets  41 - 43  for the conductive wirings, the strength of piezoelectric sheets  41 - 43  does not decrease. Further, because conductive wiring  345  is formed with a thin-film method such as the PVD method, a reliable conductivity can be attained even if the wiring is submicron in thickness. Therefore, when attaching actuator unit  321  and flow channel unit  4 , the thickness of conductive wiring  345  does not obstruct the attachment. For example, the thickness may be 0.1 μm-0.5 μm, but it may also be approximately 2 μm. However, a thickness of 1 μm or greater is preferable for the most reliable connection. 
     Next, an inkjet head  470  according to a fifth embodiment of the present invention will be described.  FIG. 12  ( a ) is an enlarged cross-sectional diagram of inkjet head  470  according to the fifth embodiment of the present invention, and  FIG. 12  ( b ) is an enlarged planar diagram of a portion of inkjet head  470 . Components identical to the above-mentioned embodiments will be represented with the same notations, and their explanation will be shortened. 
     Inkjet head  470  of the present embodiment, as shown in  FIG. 12  ( a ), is a laminated structure that has actuator unit  321  of the fourth embodiment stacked on top of flow channel unit  404 , which is similar to flow channel unit  204  of the third embodiment. Flow channel unit  404  is equivalent to flow channel unit  204 , with the exception that groove  422 , formed on cavity plate  22 , has a planar shape that is slightly different from groove  222   b  of flow channel unit  204  described above. As shown in  FIG. 12  ( b ), groove  422  has a planar shape of a triangle, which is slightly bigger than but nearly equivalent to a planar shape of a section formed on a bottom surface of actuator unit  321  of conductive wiring  345 . Groove  422  extends from hole  222   a  to a region that does not face actuator unit  321 . When flow channel unit  404  and actuator unit  321  are fabricated and attached together with thermosetting adhesive  6 , a portion of conductive wiring  345  is placed inside groove  422 , enabling a higher degree of adhesion. In other words, forming groove  422  on flow channel unit  404  can prevent conductive wiring  345  from interfering with the attachment between flow channel unit  404  and actuator unit  321 . This enables secure contact between contact terminal  346  of actuator unit  321  and conductive member  231 . Therefore, as with the above-mentioned embodiments, there is no potential difference between flow channel unit  404  and actuator unit  321 . Further, an outlet of a connection passage framed by groove  422  and a bottom surface of actuator unit  321  is sealed with sealing material  423  after flow channel unit  404  and actuator unit  321  are attached. As with the previous embodiments, this can prevent ink spew or dust from entering cavity  230  through the connection passage. Further, depending on a depth of groove  422 , when forming conductive wiring  345 , there may be no need to use the thin-film method which was used in the previous embodiments, and the thickness of conductive wiring  345  can be controlled more freely. For example, printing methods that form thicker conductive wirings  345  can be used, which contributes to cost reduction. 
     According to the fifth embodiment described above, as with the inkjet heads of the previous embodiments, common electrode  34  and flow channel unit  404  can be electrically connected without having to scrape off thermosetting adhesive  6 , which covers flow channel unit  404 . This is because conductive member  231  and contact terminal  346  contact one another when flow channel unit  404  and actuator unit  321  are attached. Therefore, the potential difference between common electrode  34  and flow channel unit  404  becomes zero, and migration becomes improbable. 
     Preferable embodiments of the present invention have been described above, but the present invention is not limited to such embodiments, and various modifications are possible within the scope of the claims. For example, a cavity that penetrates a cavity plate is formed on a flow channel unit of each of the above-mentioned embodiments, but the cavity does not need to penetrate the cavity plate. Further, a connection passage that connects a cavity to the outside is not a necessity. Further, a diameter of a cavity does not need to get smaller as the cavity extends away from an actuator unit. Further, a cavity may be of any planar shape. Further, an outlet of a connection passage does not need to be sealed with a sealing material. Further, the flow channel unit, common electrode, and reinforcement electrode can be directly grounded without using the connection points on an FPC, even though the actuator unit of each of the above-mentioned embodiments connects the common electrode, reinforcement electrode, and flow channel unit to ground via the connection points of the FPC. The actuator unit and the flow channel will still be maintained at ground potential, and the potential difference will still be zero. Further, a common electrode may be supplied with a predefined electrical potential. Even so, the potential difference between the actuator unit and the flow channel unit will be zero because the common electrode, reinforcement electrode, and flow channel unit are still electrically connected and are at the same electrical potential. Therefore, migration becomes improbable. 
     In order to increase reliability of the connection between a flow channel unit and a common electrode, conductive members  31 ,  131 , and  231  disposed on the flow channel units  4 ,  104 ,  204 , and  404  are connected to contact terminals  46 ,  146 , and  346  disposed on the actuator units  21 ,  121 , and  321  at the attachment surfaces to attach to flow channel units  4 ,  104 ,  204 , and  404 . To further increase reliability of the connection, a conductive film layer that is different from the contact terminal may be installed on at least a portion of the attachment surfaces of the actuator units  21 ,  121 , and  321 . In each of the above-mentioned embodiments, flow channel units  4 ,  104 ,  204 , and  404  are fixed to actuator units  21 ,  121 , and  321  with an adhesive. Though it depends on the amount and thickness of the applied adhesive, the attachment surfaces on both units are uneven and are not so-called mirrored surfaces. Therefore, there are parts within the contact region where both surfaces penetrate the adhesive layer and make direct contact with each other. At this time, if a conductive thin-film layer that conducts with the common electrode is formed on the actuator unit  21 ,  121 , and  321  sides, the flow channel unit and the common electrode become electrically connected via those contact sections, making the connection between the flow channel unit and the common electrode more reliable. 
     As one specific example related to this, a transfiguration example based on the above-mentioned third embodiment will be explained with reference to  FIG. 13 . In  FIG. 13 , components that are the same as those in the third embodiment will be referred to with the same notation, and their explanation will be shortened. In this transfiguration example, as shown in  FIG. 13 , nearly the entire region on the attachment surface side of actuator unit  121  is covered with conductive thin-film layer  500  so as to electrically connect to contact terminal  146 . Nickel is used as the material for thin-film layer  500 . The nickel layer is formed by an electrode-less plating method. According to this configuration, flow channel unit  204  and thin-film layer  500  can be expected to make direct contact within an attachment region. Further, as shown in  FIG. 13 , an upper-side opening of pressure chamber  10  is sealed by thin-film layer  500 . In other words, an inner wall of pressure chamber  10  is constructed on a wall surface that electrically connects to common electrode  34 , and flow channel unit  204  in its entirety, including the ink, can be connected to ground. Accordingly, damages to actuator unit  121  can be effectively prevented. With regards to thin-film layer  500 , any material can be used as the conductive material if the material does not dissolve or react and erode due to the ink. Besides nickel, usable materials may include mono-layer, multi-layers, or alloy-layers such as gold, titanium, palladium, platinum, and aluminum. Further, a suitable method of forming thin-film  500  may be selected based on the material. For example, instead of the plating method, a deposition method, sputter technique, and CVD method can also be used. 
     As described in preferred embodiments, it is preferable that an area of an opening section of the cavity is larger than an area of a bottom section thereof. In this case, it becomes easier for the conductive material filled in the cavity to pile up near the opening section. As a result, the conductive material protrudes upward and can be securely connected to the contact terminal. 
     In addition, it is preferable that the flow channel unit further has a connection passage that connects the cavity to the outside air. This can prevent unwanted pressure from building inside the cavity because solvent gas, which is generated from the conductive material when the conductive material is hardened, is released to the outside air through the connection passage. 
     Further, at this time, an opening of the connection passage to the outside air may be sealed. This can prevent ink spew or dust from entering the cavity through the connection passage. 
     In addition, it is also preferable that the flow channel unit is equipped with a spare chamber connected to the cavity. This enables solvent gas generated from the conductive material to be released to the spare chamber, which can prevent unwanted pressure from building inside the cavity. 
     Further, with regards to the present invention, it is preferable that the common electrode extends to a peripheral border of the piezoelectric sheet so as to become exposed at a side end surface of the actuator unit. In this case, it is preferred that the actuator unit further includes a conductive wiring. The conductive wiring is formed continuously from the side end surface of the actuator unit and the attachment surface of the actuator unit, and the conductive wiring electrically connects the common electrode and the contact terminal. This enables the conductive wiring to be formed without decreasing the strength of the actuator unit. 
     Further, the connection passage may be a groove formed on the attachment surface of the flow channel unit. The groove faces at least a portion of the conductive wiring formed on the attachment surface of the actuator unit. This enables the conductive wiring to be formed without decreasing the strength of the actuator unit, and prevents interference between the conductive wiring and the flow channel unit. As a result, a more secure attachment between the flow channel unit and the actuator unit can be obtained. 
     Further, with regards to the present invention, it is also preferable that the actuator unit comprises a conductive wiring that is formed within the actuator unit. The conductive wiring extends along a direction orthogonal to the attachment surface of the actuator unit and electrically connects the common electrode with the contact terminal. This protects the conductive wiring from ink spew or dust because the conductive wiring is not exposed to the outside. 
     In addition, at this time, the actuator unit may further has a reinforcement electrode, disposed parallel to the common electrode on an opposite side of where the plurality of individual electrodes is disposed with respect to the common electrode. The conductive wiring may be directly connected to the common electrode and the reinforcement electrode, and may penetrate the actuator unit. This enables the common electrode and the contact terminal to be electrically connected all at once. 
     In addition, at this time, the actuator unit may further has a reinforcement electrode electrically connected to the common electrode and disposed parallel to the common electrode on an opposite side of where the plurality of individual electrodes is disposed with respect to the common electrode. The conductive wiring may be directly connected to at least one of the common electrode and the reinforcement electrode. In addition, the conductive wiring does not need to penetrate the actuator unit. As a result, since the conductive wiring does not penetrate the actuator unit, the conductive wiring is unlikely to get unhooked from the actuator unit when the actuator unit is pressurized. 
     With regards to the method of manufacturing the inkjet head, it is preferable that the step of fabricating the flow channel unit further includes a step of forming a connection passage to connect the cavity to the outside air. Further, it is preferable that the method of manufacturing the inkjet head includes a step of sealing an opening of the connection passage to the outside air. This step may be performed after the actuator unit and the flow channel unit are attached. This can prevent unwanted pressure from building inside the cavity and protects the conductive material from ink spew or dust because the opening is sealed after the solvent gas is released to the outside air through the connection passage. 
     Further, after forming the common electrode, which extends to a peripheral border of the piezoelectric sheet so as to become exposed at a side end surface of the actuator unit, it is preferable that the step of fabricating the actuator unit further includes a step of forming a conductive wiring to electrically connect the contact terminal and the common electrode. This may done by covering the side end surface and the attachment surface of the actuator unit with a mask so that at least a portion of the side end surface and the attachment surface becomes exposed, and then depositing a conductive member by using a physical vapor deposition method on a region of the side end surface and the attachment surface exposed from the mask. This enables the conductive wiring to be formed on the side end surface and on the attachment surface of the actuator unit at the same time. In addition, by changing the deposition direction, the thickness of the conductive wiring on the side end surface and on the attachment surface of the actuator unit can be adjusted. 
     Further, with regards to the present invention, it is preferable that the step of fabricating the actuator unit further includes a step of forming a conductive wiring to electrically connect the contact terminal and the common electrode by stacking an insulating layer with a penetration hole formed perpendicularly to the attachment surface of the actuator unit, and filling the penetration hole with a conductive member. This enables the contact terminal and the conductive wiring to be formed with ease.