Patent Publication Number: US-8113635-B2

Title: Liquid discharge apparatus and check method of the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This Non-provisional application claims priority under 35 U.S.C. §119(a) on Patent Application No. 2007-006797 filed in Japan on Jan. 16, 2007 and Patent Application No. 2007-056632 filed in Japan on Mar. 7, 2007, the entire contents of which are hereby incorporated by reference. 
     TECHNICAL FIELD 
     The present invention relates to a liquid discharge apparatus, in particular, a liquid discharge apparatus in which a piezoelectric actuator applies discharge pressure to liquid filled into a pressure chamber of a cavity unit, and a check method of the apparatus. 
     BACKGROUND 
     Conventionally, in a liquid discharge apparatus, for example, an ink jet head disclosed in Japanese Patent Application Laid-Open No. 2002-59547, a piezoelectric actuator is disposed as opposed to a pressure chamber of a cavity unit and capacity of the pressure chamber is changed by displacement of the piezoelectric actuator, thereby discharging ink. 
       FIG. 1  schematically shows an ink jet head  910 . In a piezoelectric actuator  921 , a plurality of ceramic layers  962  are stacked with individual electrodes  952  and common electrodes  953  interposed alternately, and a region of the ceramic layer  962  sandwiched between the individual electrode  952  and the common electrode  953  in the vertical direction is an activated part. By grounding the common electrode  953  and selectively applying voltage to the individual electrode  952 , the corresponding activated part is displaced, thereby applying discharge pressure to liquid in a pressure chamber  924 . 
     Since the piezoelectric actuator  921  is generally formed by laminating green sheets made of ceramics such as PZT and sintering them, a minute defect (crack)  960  is easy to occur in the ceramic layer  962  as a sintered body. When, in a lowermost ceramic layer  962   a  which covers an opening of the pressure chamber  924 , the defect  960  extends from the surface of the pressure chamber  924  to the electrode as shown in  FIG. 1 , disadvantageously, ink penetrates into the lowermost ceramic layer  962   a  from the pressure chamber  924  through the defect  960 , causing electrical short circuit between the electrodes. 
     Thus, in Japanese Patent Application Laid-Open No. 2002-59547, an ink impermeable adhesive sheet is used to adhere a cavity unit  920  to the piezoelectric actuator  921  and the adhesive sheet covers the whole surface of the piezoelectric actuator  921  opposed to the cavity unit  920 . Thus, the ceramic layers  962  of the piezoelectric actuator  921  do not directly contact ink. 
     SUMMARY 
     In the cavity unit  920 , electric charges may accumulate in ink due to static electricity and the like. Generally, ink is positively charged and a potential difference between an ink  970  filled into the pressure chamber  924  and the grounded common electrode  953  of the piezoelectric actuator  921  occurs across the lowermost ceramic layer  962   a . Since such potential difference generates electroendosmosis which moves the positively charged ink  970  toward the cathode (common electrode  953 ), a positive force of penetrating into the ceramic layer  962  is applied to the ink. 
     In the above-mentioned Japanese Patent Application Laid-Open No. 2002-59547, although the adhesive sheet covers the ceramic layer  962  of the piezoelectric actuator  921 , microscopically, a lot of minute holes exist in the adhesive sheet. Thus, when the above-mentioned force of positively guiding the ink toward the ceramic layer is applied, the ink passes through the adhesive sheet. As a result, when the defect  960  as shown in  FIG. 1  exists in the ceramic layer  962 , the ink penetrates into the defect, causing electrical short circuit as conventional. 
     In addition, the defect in the ceramic layer  962  occurs at a step of sintering the ceramic layer  962  as well as a step of adhering the piezoelectric actuator  921  to the cavity unit  920  and a step of stacking the other member such as a flexible wiring substrate on the piezoelectric actuator  921  due to a force of pressing the piezoelectric actuator  921  toward the cavity unit  920 . For this reason, it is difficult to visually confirm the defect  960  existing in the ceramic layer  962  in an assembled state. 
     To solve the above-mentioned problem, an object is to provide a liquid discharge apparatus and a check method of the apparatus which can detect the existence of the defect (crack) in the ceramic layer covering the opening of the pressure chamber with high accuracy. 
     To achieve the above-mentioned object, the liquid discharge apparatus according to a first aspect is a liquid discharge apparatus, comprising: a cavity unit including a nozzle for discharging liquid and a pressure chamber which communicates with the nozzle and has an opening; and a piezoelectric actuator which includes a first ceramic layer covering the opening of the pressure chamber, second and third ceramic layers sequentially stacked on the side opposite to the side on which the first ceramic layer covers the opening, a first electrode disposed between the first ceramic layer and the second ceramic layer, a second electrode disposed between the second ceramic layer and the third ceramic layer and a third electrode sandwiching the third ceramic layer with the second electrode, and said piezoelectric actuator being fixed to the cavity unit, wherein the piezoelectric actuator is displaced by applying voltage between the first electrode and the second electrode and between the second electrode and the third electrode, thereby applying discharge pressure to liquid filled in the pressure chamber, the first electrode and the third electrode are connected to at least two terminals which are provided on the piezoelectric actuator, and independent of each other on the piezoelectric actuator electrically, respectively. 
     A check method of the liquid discharge apparatus according to a second aspect is a check method of a liquid discharge apparatus comprising a cavity unit including a nozzle for discharging liquid and a pressure chamber which communicates with the nozzle and has an opening; and a piezoelectric actuator which includes a first ceramic layer covering the opening of the pressure chamber, second and third ceramic layers sequentially stacked on the side opposite to the side on which the first ceramic layer covers the opening, a first electrode disposed between the first ceramic layer and the second ceramic layer, a second electrode disposed between the second ceramic layer and the third ceramic layer and a third electrode sandwiching the third ceramic layer with the second electrode, and said piezoelectric actuator being fixed to the cavity unit, wherein the piezoelectric actuator is displaced by applying voltage between the first electrode and the second electrode and between the second electrode and the third electrode, thereby applying discharge pressure to liquid filled in the pressure chamber, comprising the steps of: connecting the first electrode and the third electrode to at least two terminals which are provided on the piezoelectric actuator, and independent of each other on the piezoelectric actuator electrically, respectively; filling liquid into the pressure chamber; and measuring an electrical characteristic between the first electrode and the cavity unit. 
     According to the first aspect and the second aspect, the first ceramic layer, the first electrode, the second ceramic layer, the second electrode, the piezoelectric actuator is disposed from the side of the pressure chamber. By applying voltage between the first electrode and the second electrode and between the second electrode and the third electrode, the second ceramic layer and the third ceramic layer are displaced, thereby applying discharge pressure to liquid filled in the pressure chamber. With such configuration, the existence of a defect in the first ceramic layer can be detected by using the first electrode. That is, the electrical characteristic between the first electrode and the cavity unit changes due to penetration of liquid into the defect developed in the first ceramic layer. Thus, in the state where the first electrode and the third electrode are connected to at least two terminals which are provided on the piezoelectric actuator, and independent of each other on the piezoelectric actuator electrically, respectively, the existence of the defect in the first ceramic layer can be detected by filling liquid into the pressure chamber and measuring the electrical characteristic between the first electrode and the cavity unit. 
     The above and further objects and features will more fully be apparent from the following detailed description with accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is a vertical sectional view showing a conventional ink jet head; 
         FIG. 2  is an exploded perspective view of a cavity unit and a piezoelectric actuator in an ink jet head according to a first embodiment; 
         FIG. 3  is an exploded perspective view of the piezoelectric actuator and a wiring substrate in the ink jet head according to the first embodiment; 
         FIG. 4  is a plan view of the wiring substrate in the ink jet head according to the first embodiment; 
         FIG. 5  is a sectional view of the ink jet head taken along a line IV-IV in  FIG. 2 ; 
         FIG. 6  is a sectional view of the ink jet head taken along a line V-V in  FIG. 3 ; 
         FIG. 7  is a sectional view of the ink jet head taken along a line VI-VI in  FIG. 3 ; 
         FIG. 8  is a sectional view showing a connection between the wiring substrate and the piezoelectric actuator in the ink jet head according to the first embodiment; 
         FIG. 9  is an exploded perspective view of a piezoelectric actuator and a wiring substrate in an ink jet head according to a second embodiment; 
         FIG. 10  is a sectional view of the ink jet head taken along a line IX-IX in  FIG. 9 ; 
         FIG. 11  is a plan view of a piezoelectric actuator in an ink jet head according to a third embodiment; 
         FIG. 12  is a plan view of a wiring substrate in the ink jet head according to the third embodiment; 
         FIG. 13  is a plan view of a piezoelectric actuator in an ink jet head according to a fourth embodiment; 
         FIG. 14  is a plan view of a wiring substrate in the ink jet head according to the fourth embodiment; 
         FIGS. 15A and 15B  are plan views showing modified configuration examples of the piezoelectric actuator in the ink jet head according to the fourth embodiment; 
         FIG. 16  is a plan view of a piezoelectric actuator in an ink jet head according to a fifth embodiment; and 
         FIG. 17  is a plan view of a wiring substrate in the ink jet head according to the fifth embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     An ink jet head embodied as a liquid discharge apparatus in this embodiment will be described below with reference to the drawings. Terms “upper” and “lower” in the following description means relative position in the drawings. First, with reference to  FIGS. 2 to 8 , an ink jet head  10  according to a first embodiment will be described. As shown in  FIG. 2 , the ink jet head  10  has a cavity unit  20  made of a plurality of plates, a piezoelectric actuator  21  joined to an upper surface of the cavity unit and a flexible wiring substrate  22  ( FIG. 3 ) joined to an upper surface of the piezoelectric actuator  21 . 
     The cavity unit  20  is formed by stacking a nozzle plate  30 , a spacer plate  31 , a damper plate  32 , two manifold plates  33   a ,  33   b , a supply plate  34 , a base plate  35  and a cavity plate  36  which are thin plates and integrating them into one unit by use of an adhesive. Each of the plates  30  to  36  has the thickness of about 50 to 150 μm. The nozzle plate  30  is made of synthetic resin such as polyimide and the other plates  31  to  36  are made of 42% nickel alloy steel plate. A number of ink discharge nozzles  23  each having a minute diameter (about 20 μm) are drilled in the nozzle plate  30  at minute intervals. The nozzles  23  are arranged in five rows in the long side direction (X direction) of the nozzle plate  30 . 
     A plurality of pressure chambers  24  corresponding to the nozzles  23  are arranged on the cavity plate  36  in five rows. Each of the pressure chambers  24  passes through the cavity plate  36  and is shaped to be elongate when viewed in a plan view so that the longitudinal direction may be the short side direction (Y direction) of the cavity plate  36 . That is, an upper surface of each pressure chamber  24  is opened, and upper and lower sides of each pressure chamber  24  are defined by covering the opening with the piezoelectric actuator  21  and a lower surface of each pressure chamber  24  with the base plate  35 . One end of the pressure chamber  24  in the longitudinal direction communicates with the nozzles  23  and the other end communicates with a common ink chamber  25  described later. 
     Five common ink chambers  25  long in the long side direction (X direction) are formed on the two manifold plates  33   a ,  33   b  so as to pass through the plates and extend along each row of the pressure chambers  24 . That is, upper and lower sides of each common ink chamber (manifold chamber)  25  are defined by stacking the two manifold plates  33   a ,  33   b  and covering upper surfaces thereof with the supply plate  34  and lower surfaces thereof with the damper plate  32 . 
     Connection channels  29  and through holes  28  for supplying ink from the common ink chambers  25  to the pressure chambers  24  are provided on the base plate  35  and the supply plate  34 , respectively, which are located between the cavity plate  36  and the manifold plate  33   b . Each of connection channels  29  on the supply plate  34  has a narrowed part having a small cross-sectional area so as to have a large channel resistance and is connected to one end of each pressure chamber  24  through the through hole  28  on the base plate  35 . 
     Four ink supply ports  40  are drilled in an end of one of short sides of each the cavity plate  36 , base plate  35  and supply plate  34  at corresponding positions. These ink supply ports  40  communicate with one ends of common ink chambers  25  respectively and ink is supplied from an ink source to the common ink chambers  25  through the ink supply ports  40 . To supply frequently-used ink, for example, black ink, one ink supply port  40  is larger than the remaining ink supply ports  40 . A filter  40   a  is adhered to each ink supply port  40  by use of an adhesive or the like. 
     The damper plate  32  has thinned parts  32   a  at positions corresponding to the common ink chambers  25 . When discharge pressure is applied to ink in the pressure chambers  24 , the pressure transmitted to the common ink chambers  25  is absorbed due to elastic deformation of the thinned parts  32   a.    
     Front ends of the pressure chambers  24  communicate with the nozzles  23  on the nozzle plate  30  through communicating holes  26  drilled in the base plate  35 , the supply plate  34 , the two manifold plates  33   a ,  33   b , the damper plate  32  and the spacer plate  31 . 
     Ink is supplied from the ink supply ports  40  to the common ink chambers  25  and then, distributed into the pressure chambers  24  through the connection channels  29  on the supply plate  34  and the through holes  28  on the base plate  35 . Then, the ink reaches the nozzles  23  corresponding to the pressure chambers  24  from the pressure chambers  24  through the communicating holes  26 . 
     The piezoelectric actuator  21  is shaped like a flat plate over the plurality of pressure chamber  24  and has a plurality of ceramic layers stacked in the same direction as the stacking direction of the plurality of plates  30  to  36  and a plurality of electrodes disposed in the direction perpendicular to the stacking direction of the plurality of ceramic layers. A mix containing ceramic particles, binder and solvent is shaped to a thin plate having a thickness of about 30 μm to form a green sheet. Electrodes are appropriately patterned on an upper surface of the green sheet using conductive paste. The piezoelectric actuator  21  is formed by stacking the plurality of green sheets and integrating them by means of sintering. Thus, each green sheet becomes a ceramic layer of sintered body. The ceramic layers thus formed include a lowermost first ceramic layer  41  which directly covers openings of the pressure chambers (on the side of the cavity unit  20 ), a second ceramic layer  42  stacked on an upper surface of the first ceramic layer  41 , a third ceramic layer  43  stacked on an upper surface of the second ceramic layer  42 , an uppermost fourth ceramic layer  44  (insulating film) and a fifth ceramic layer  45  located immediately below the uppermost fourth ceramic layer  44 . The plurality of second and third ceramic layers  42 ,  43  are alternately stacked. 
     The electrodes include a first electrode  51  disposed between the first ceramic layer  41  and the second ceramic layer  42 , a second electrode  52  disposed between the second ceramic layer  42  and the third ceramic layer  43  and a third electrode  53  disposed between the third ceramic layer  43  and the second ceramic layer  42  above the upper surface of the third ceramic layer  43  (sandwiching the third ceramic layer  43  with the second electrode  52 ). 
     In this embodiment, the material of the fourth and fifth ceramics layers  44 ,  45  may not be different from that of the first, second and third ceramics layers  41 ,  42 ,  43 . For example, the material thereof may be a film made of polyimide or the like, or insulating material such as insulating resin coat. 
     In  FIG. 3 , the first electrode  51  is provided over the upper surface of the first ceramic layer  41 . However, the first electrode  51  only needs to be formed corresponding to all of the pressure chambers  24  so as to communicate with each other. 
     The second electrodes  52  are provided on the second ceramic layer  42  and correspond to the respective pressure chambers  24 . The third electrode  53  is formed corresponding to all of the pressure chambers  24  so as to communicate with each other. The third electrode  53  may be formed over the upper surface of the third ceramic layer  43 . In this embodiment, as described later, the third electrode  53  is formed on the third ceramic layer  43  to be shaped like a band for each row of pressure chamber  24  while keeping a region for conductive materials  52   b  for connecting the second electrodes  52  to second terminals  52   c  provided on the fourth ceramic layer  44 . The plurality of second ceramic layers  42  having the second electrodes  52  and the plurality of third ceramic layers  43  having the third electrode  53  are alternately stacked. 
     That is, the second ceramic layer  42  is sandwiched between the first electrode  51  and the second electrodes  52 , the third ceramic layer  43  is sandwiched between the second electrodes  52  and the third electrode  53  and the second ceramic layer  42  above the third ceramic layer  43  is sandwiched between the third electrode  53  and the second electrodes  52 . By connecting the first and third electrodes  51 ,  53  to a common low voltage area and connecting the second electrodes  52  to a high voltage area, regions of the ceramic layers sandwiched by each electrode are polarized symmetrically with respect to the second electrodes  52  (the direction from the second electrodes  52  toward the first electrode  51  and the direction from the second electrodes  52  toward the third electrode  53 ) to form activated parts. For discharge of ink, the first and third electrodes  51 ,  53  are connected to a common low voltage area (for, example, grounded) and the second electrodes  52  are connected to a high voltage area. That is, when voltage in the polarizing direction is applied, the activated parts extend in the stacking direction. 
     No electrode is provided between the fourth ceramic layer  44  and the fifth ceramic layer  45 . This prevents displacement of the above-mentioned activated parts from appearing on the side of the upper surface of the piezoelectric actuator  21  and allows the displacement to remarkably appear on the side of the pressure chambers  24 . First, second and third terminals connected to the first, second and third electrodes  51 ,  52 ,  53 , respectively, are provided on the upper surface of the fourth ceramic layer  44  on the opposite side to the pressure chambers  24 . 
     A first terminal  51   c  is electrically connected to the first electrode  51  through the conductive materials  51   a  filled in through holes provided in the ceramic layers  42 ,  43 ,  44 ,  45  in the stacking direction. 
     The third electrode  53  has band-like conductive material  53   a  connecting both ends of each band-like parts along the row of the pressure chambers  24  to each other (only one end is shown in  FIG. 3 ). Conductive materials  53   b  are provided on the ceramic layers  42 ,  44 ,  45  at positions corresponding to the conductive material  53   a  in the stacking direction. A conductive material on the fourth ceramic layer  44  forms a third terminal  53   c . A through hole is provided on each of the ceramic layers  42 ,  43 ,  44 ,  45  in the stacking direction by passing through the region where the conductive material  53   a ,  53   b  or the third terminal  53   c  is provided. A conductive material  53   d  is filled in the through hole. The conductive material  53   d  electrically connects the band-like conductive materials  53   a ,  53   b  and the third terminal  53   c  to one another. Thus, the third terminal  53   c  is electrically connected to all the third electrodes  53 . 
     The conductive materials  53   a ,  53   b  and the third terminal  53   c  are each shaped like a band along both side edges of each ceramic layer  42 ,  43 ,  44 ,  45  in parallel with the pulling direction of the wiring substrate  22  described later. The first terminal  51   c  and the conductive material  51   a  which are connected to the first electrode  51  are shaped like an island at corners of the ceramic layers  42 ,  43 ,  44 ,  45  on the extension of the conductive materials  53   a ,  53   b  and the third terminal  53   c  in the longitudinal direction. The first terminal  51   c  and the third terminal  53   c  are independent of each other on the piezoelectric actuator electrically, at least when forming a pattern. The first terminal  51   c  is separated from the third terminal  53   c.    
     Each second electrode  52  has an extension conductive material  52   a  to be connected to the second terminal  52   c  on the fourth ceramic layer  44  at one end thereof. The extension conductive material  52   a  deviates from the extension of the second electrode  52  in the longitudinal direction so as to be located at a partition between the pressure chambers  24 . Conductive materials  52   b  are formed on the third ceramic layer  43  and the fifth ceramic layer  45  at positions corresponding to the extension conductive materials  52   a  in the vertical direction. A conductive material  52   d  is filled in through holes passing through regions where the conductive materials  52   b  are provided on the third and fifth ceramic layers  43 ,  45  in the stacking direction. The extension conductive materials  52   a  on the second ceramic layer  42 , the conductive materials  52   b  on the third ceramic layer  43  and the fifth ceramic layer  45  and the second terminals  52   c  on the fourth ceramic layer  44  are electrically connected to one another through the conductive materials  52   d . Thus, each second terminal  52   c  is electrically connected to all the second electrodes  52  in the stacking direction. 
     No through hole is provided on the regions of the conductive material  53   b  and the extension conductive materials  52   a  on the second ceramic layer  42  adjacent to the first electrode  51  so that the third electrodes  53  and the second electrodes  52  are electrically independent of the first electrode  51 . 
     The second terminal  52   c  connected to the second electrode  52  has a predetermined length in the direction perpendicular to the row of the pressure chambers  24  and has a connection terminal part  52   e  to be connected to the wiring substrate  22  described later at one end thereof in the length direction. Each connection terminal part  52   e  is located at one end of the each second terminal  52   c  and adjacent connection terminal parts  52   e  are located at the opposite ends of the second terminals  52   c . Thus, a distance between adjacent connection terminal parts  52   e  is large. Although  FIG. 3  does not show connection terminal parts such as the connection terminal parts  52   e  on the first terminal  51   c  and the third terminal  53   c , the connection terminal parts may be protrudingly provided on the terminals. 
     The flexible wiring substrate  22 , as shown in  FIG. 8 , has structure in which wiring is formed on an insulating film  64  made of polyimide or the like and the wiring is covered with an insulator  65 . A second wiring  62  is connected to the second terminal  52   c  by allowing a connection terminal  62   a  as an end of the second wiring  62  to be exposed from an opening of the insulating film  64 , providing a bump of a conductive brazing material  66  on the connection terminal  62   a  and welding the brazing material  66  to the second terminal  52   c . Similarly, a first wiring  61  connected to the first terminal  51   c  and a third wiring  63  connected to the third terminal  53   c  are exposed from openings of the insulating film  64  at positions corresponding to the first and third terminals  51   c ,  53   c  and connected to the first and third terminals  51   c ,  53   c  through conductive brazing material, respectively. 
     The wiring substrate  22  is pulled out from the upper surface of the piezoelectric actuator  21  in the direction perpendicular to the long side direction of the piezoelectric actuator (X direction) and connected to a driving circuit (not shown). The first and third wirings  61 ,  63  extend in parallel along both side edges of the wiring substrate  22  in the direction of pulling the wiring substrate  22 . When ink is discharged, the first and third wirings  61 ,  63  are grounded, that is, connected to a ground potential, and positive voltage is selectively applied to the second electrode  52  through the second wiring  62 . Since the number of third electrodes  53  is larger than that of the first electrodes  51 , to bring impedance into balance, the third wiring  63  has a smaller electrical resistance value than the first wiring  61 , for example, has a larger width when viewed in a plan view than the first wiring  61 . 
     Here, a manufacturing process of the ink jet head  10  will be briefly described. The cavity unit  20 , the piezoelectric actuator  21  and the wiring substrate  22  are previously configured as described above (first step). Next, the piezoelectric actuator  21  is adhered to the upper surface of the cavity unit  20  under pressure (second step). Next, the wiring substrate  22  provided with the brazing material  66  is disposed on the upper surface of the piezoelectric actuator  21  and the bump of the brazing material  66  is heated and welded to the first, second and third terminals  51   c ,  52   c ,  53   c  while pressing the wiring substrate  22  (third step). Thus, the wiring substrate  22  is fixed to the piezoelectric actuator  21  and the first, second and third terminals  51   c ,  52   c ,  53   c  are electrically connected to the corresponding first, second and third wiring  61 ,  62 ,  63 . Next, a conductive member  69  made of conductive paste is adhered to the side face of the piezoelectric actuator  21  over the third electrode  53  and the cavity unit  20  (fourth step). In this embodiment, the conductive member  69  is provided on the regions of the side face of the piezoelectric actuator  21  where the first electrode  51  and the third electrode  53  are exposed. The first electrode  51 , the third electrode  53  and the cavity unit  20  are electrically connected to one another via the conductive member  69 . This prevents voltage applied to the second electrodes  52  from leaking thereby making ink discharge in the other pressure chambers unstable or charging ink with static electricity as described in Japanese Patent Application Laid-Open No. 2003-80709. 
     Before or after the fourth step, the wiring substrate  22  is connected to an external substrate (not shown) coupled to a power source or the like (fifth step). A plurality of connection terminals connected to the first, second and third wirings  61 ,  62 ,  63  (connected to the second wiring  62  through a driving circuit) are arranged along one edge of the wiring substrate  22 . A receptacle connector engaged with the connection terminal of the wiring substrate  22  is installed on the external substrate. By engaging the wiring substrate  22  (connection terminal) with the receptacle connector, the wiring substrate  22  is electrically connected to the external substrate and the first, second and third wirings  61 ,  62 ,  63  on the wiring substrate  22  are connected to external wiring printed on the external substrate. Electric power or a control signal is supplied to the driving circuit through the external substrate, thereby enabling application of voltage to the second electrodes  52 . 
     Whether a defect (crack) occurs in the first ceramic layer  41  or not is checked as follows. Ink is filled into an ink flow path in the ink jet head including the pressure chamber  24  and an electrical characteristic such as a resistance value between the first electrode  51  and the cavity unit  20  is measured. Specifically, since the plates  31  to  36  of the cavity unit  20  are electrically conductive, an insulation resistance meter is connected to one of the plates and a member electrically connected to the first electrode  51  to measure a insulation resistance value. Ink can be filled into the cavity unit  20  (pressure chamber) at any time after completion of the second step. 
     When a defect (crack) extending from the pressure chamber  24  in the stacking direction occurs in the first ceramic layer  41 , ink in the pressure chamber  24  penetrates in the defect. Since the first electrode  51  is electrically independent of the cavity unit  20 , without the above-mentioned defect, the first electrode  51  is connected to the cavity unit  20  only through capacitance of the first ceramic layer  41  and a resistance value becomes infinite. However, when the ink penetrates into the defect, the resistance value is remarkably lowered. Accordingly, by measuring the resistance value, whether a defect exists in the first ceramic layer  41  or not can be checked. 
     The ink jet head with the first ceramic layer  41  determined to have a defect according to the above-mentioned check is eliminated from the manufacturing process as a defective product. Thus, since the ink jet head  10  having the piezoelectric actuator  21  without defect (crack) which leads to electrical short circuit can be selected as a non-defective product and connected to a main unit of an ink jet printer or the like, the manufacturing process can be made more efficient. As an electrical characteristic, in addition to a resistance value, capacitance between the first electrode  51  and the cavity unit  20  may be measured as necessary. 
     The above-mentioned check can be carried out between the second step and the third step (that is, before the wiring substrate  22  is connected to the piezoelectric actuator  21 ) by using the first terminal  51   c  connected to the first electrode  51 . For this reason, ink is filled after the second step and before the third step. In this case, when a defect occurs in the first ceramic layer  41  at the first step and the piezoelectric actuator  21  is adhered to the cavity unit  20  at the second step, the defect occurring in the first ceramic layer  41  can be detected by applying pressure. The above-mentioned check can be also carried out between the third step and the fourth step (after the piezoelectric actuator  21  is connected to the wiring substrate  22 ) by using the first wiring  61  on the wiring substrate  22 . For this reason, ink is filled after the second step and before the fourth step. In this case, in addition to a defect occurring at the first and second steps, when the wiring substrate  22  is connected to the piezoelectric actuator  21  at the third step, the defect occurring in the first ceramic layer  41  can be detected by applying pressure. 
     Next, referring to  FIGS. 9 and 10 , an ink jet head  110  according to a second embodiment will be described. The ink jet head  110  is different from the ink jet head in the first embodiment, in the construction of a first electrode  151  and the check method related thereto. The same reference numerals are given to the same components and description of the components is omitted. 
     In the first embodiment, the first electrode  51  covers the whole upper surface of the first ceramic layer  41  and reaches each edge of the first ceramic layer  41 . Thus, the first electrode  51  is exposed from four side faces of the piezoelectric actuator  21  in which the ceramic layers  41  to  45  are stacked. On the contrary, as shown in  FIG. 9 , the first electrode  151  in the second embodiment is not formed on the whole surface of the first ceramic layer  41  and is partially cut out. The cutout region is provided in the vicinity of an edge and the cutout region of the upper surface of the first ceramic layer  41  is exposed. Thus, when the ceramic layers  41  to  45  are stacked, as shown in  FIG. 10 , a part of the first electrode  151  is not exposed from the side face of the piezoelectric actuator  121 . The cutout region deviates from the positions corresponding to the pressure chambers  24  and the first electrode  151  is ensured to be located below each second electrode  52  so that each activated part stably operates. Hereinafter, the unexposed region of the first electrode  151  on the side face of the piezoelectric actuator  121  is referred to as a contact prevention part  151   e.    
     A manufacturing process of the ink jet head  110  having the contact prevention part  151   e  will be briefly described. As in the first embodiment, through the first to third steps, the cavity unit  20 , the piezoelectric actuator  121  and the wiring substrate  22  are assembled. At the fourth step, the conductive member  69  is provided on the side face of the piezoelectric actuator  121 . At this time, the conductive member  69  is provided over the exposed region of the third electrode  53  and the contact prevention part  151   e  on the side face of the piezoelectric actuator  121  and the upper surface of the cavity unit  20 . Consequently, the cavity unit  20 , the third electrode  53 , the third terminal  53   c  and the third wiring  63  are grounded, while the first electrode  151 , the first terminal  51   c  and the first wiring  61  are not electrically connected to the cavity unit  20  and the third electrode  53 . 
     The above-mentioned check can be carried out after the fourth step by using the first wiring  61  connected to the first terminal  51   c  and the third wiring  63  connected to the third terminal  53   c . In this case, the defect occurring through the first to fourth steps can be detected. Since the check is performed downstream of the manufacturing process, reliability of eliminating a defective product from all products is improved. When an insulation resistance value is measured, in addition to the cavity unit  20 , the third wiring  63  disposed on the upper surface of the ink jet head  110  can be used, thereby improving workability and operability of check. 
     Further describing the manufacturing process, as in the first embodiment, at the fifth step before or after the fourth step, the wiring substrate  22  is connected to the external substrate. In the second embodiment, unlike First embodiment, the first electrode  151  is not connected to the third electrode  53  at the fourth step. Thus, a component for connecting the electrodes to each other is added. For example, following the above-mentioned check, for the conduction of the first and third wirings  61 ,  63 , a bridge part made of a conductive material paste such as solder may be formed on the wiring substrate  22 . Following the above-mentioned check and the fifth step, for the conduction of two external wirings connected to the first and third wirings  61 ,  63 , respectively, via a connector and electrical wiring, a bridge part made of a conductive material paste such as solder may be formed on the external substrate. Connection wiring for the conduction of two external wirings connected to the first and third wirings  61 ,  63  is previously printed on the external substrate. In this case, when the fifth step is performed after the fourth step and the above-mentioned check, at the fifth step, the wiring substrate  22  is connected to the external substrate and the first electrode  151  is electrically connected to the third electrode  53 . Accordingly, even with the above-mentioned configuration in which the first electrode  151  is not connected to the third electrode  53  via the conductive member  69 , it is unnecessary to add a step of connecting the electrodes to each other, and thus, the ink jet head  110  having the above-mentioned effect in checking can be manufactured without increasing manufacturing costs. 
     Next, a third embodiment will be described with reference to  FIGS. 11 and 12  and a fourth embodiment will be described with reference to  FIGS. 13 to 15A  and  15 B, and a fifth embodiment will be described with reference to  FIGS. 16 and 17 . The third to fifth embodiments each are different from the first and second embodiments in the arrangement of terminals on the piezoelectric actuator, but are the same as the first and second embodiments in structure of the first electrode, the manufacturing process of the ink jet head and the procedure of the above-mentioned check. Hereinafter, the third to fifth embodiments will be described as variants of the first embodiment for convenience. Same reference numerals are given to the same components as those in First embodiment and description of the components is omitted. 
     In the third embodiment, as shown in  FIG. 11 , a first terminal  251   c  of the first electrode  51  and third terminals  253   c  of the third electrode  53  are provided in the vicinity of short sides of the fourth ceramic layer  44  so as to be separated from each other in the short side direction. More specifically, the first terminal  251   c  is centrally located between the two third terminals  253   c  in the short side direction. As shown in  FIG. 12 , corresponding to the first and third terminals  251   c ,  253   c , first and third wirings  261 ,  263  connected to the first and third terminals  251   c ,  253   c  are arranged on the wiring substrate  222 . By changing layout of the first and third terminals  251   c ,  253   c , positions of through holes for connecting the terminals to the electrodes are changed as appropriate. 
     Even when the first and third terminals  251   c ,  253   c  are arranged in the similar manner as in the first embodiment, the region where the terminals are provided on the upper surface of the fourth ceramic layer  44  can be made compact in the long side direction. In providing three kinds of terminals on the upper surface of the piezoelectric actuator  221 , the piezoelectric actuator  221  is prevented from increasing in size. 
     In the fourth embodiment, as shown in  FIG. 13 , a first terminal  351   c  of the first electrode  51  and the third terminal  353   c  of the third electrode  53  are provided side by side in the vicinity of short sides of the upper surface of the fourth ceramic layer  44  so as to extend in the short side direction. The first terminal  351   c  has a plurality of protruding parts  351   f ,  351   f , . . . which are provided at substantially regular intervals in the extending direction of the first terminal  351   c  so as to protrude toward the third terminal  353   c . The third terminal  353   c  also has a plurality of protruding parts  353   f ,  353   f , . . . which are provided at substantially regular intervals in the extending direction of the third terminal  353   c  so as to protrude toward the first terminal  351   c . The protruding parts  351   f ,  351   f , . . . of the first terminal  351   c  are opposed to narrower parts  353   g  formed between adjacent protruding parts  353   f ,  353   f  of the third terminal  353   c . Similarly, the protruding parts  353   f ,  353   f  of the third terminal  353   c  are opposed to narrower parts  351   g  formed between adjacent protruding parts  351   f ,  351   f  of the first terminal  351   c . That is, the protruding parts  351   f ,  353   f  of the first and third terminals  351   c ,  353   c  are alternately formed in the extending direction of the first and third terminals  351   c ,  353   c.    
     As shown in  FIG. 14 , a first wiring  361  connected to the first terminal  351   c  and a third wiring  363  connected to the third terminal  353   c  are arranged in parallel to each other on the wiring substrate  322 . An opening formed on the first wiring  361  to provide the brazing material  66  welded to the first terminal  351   c  and an opening formed on the third wiring  363  in a similar manner are alternately disposed in the extending direction of the first and third wirings  361 ,  363 . The amount of the brazing material  66  welded to the first terminal  351   c  and the third terminal  353   c  is smaller than the amount of the brazing material  66  welded to the second terminal  52   c.    
     In the ink jet head having the first and third terminals  351   c ,  353   c , as in the first embodiment, at the third step, the brazing material  66  is welded to the protruding parts  351   f ,  353   f  of the first terminal  351   c  and the third terminal  353   c.    
     As described above, regions of the first and third terminals  351   c ,  353   c , to which the brazing material  66  is welded, are wider protruding parts  351   f ,  353   f . The protruding part of one terminal is opposed to a narrow region between the protruding parts of the other terminal. For this reason, a sufficient area where the brazing material  66  is welded is ensured in the first and third terminals  351   c ,  353   c . A region where the terminals are provided on the upper surface of the fourth ceramic layer  44  can be made compact in the long side direction and the piezoelectric actuator  321  is prevented from increasing in size. Furthermore, since the protruding parts to which the brazing material  66  is welded are alternately arranged as described above, there is a little possibility that the brazing materials  66  welded to the terminals are bridged to each other. 
     Since the amount of the brazing material  66  welded to the first terminal  351   c  of the first electrode  51  and the amount of the brazing material  66  welded to the third terminal  353   c  of the third electrode  53  are each smaller than the amount of the brazing material  66  welded to the second terminal  52   c  of the second electrode  52 , the bridging of the brazing material  66  between the first and third terminals  351   c ,  353   c  which are opposed can be prevented and the state where the first electrode  51  is electrically independent of the third electrode  53  can be kept. Thus, in the defect check performed later, detection of the existence of defect can be made more reliably. 
       FIGS. 15A and 15B  show variants of this embodiment in configuration. In the configuration example shown in  FIG. 15A , the first terminal  351   c ′ of the first electrode  51  and the third terminal  353   c ′ of the third electrode  53  are provided side by side in the vicinity of short sides of the upper surface of the fourth ceramic layer  44  so as to extend in the long side direction. In this modified configuration example, the first and third terminals  351   c ′,  353   c ′ have no protruding part, but as in the configuration example shown in  FIG. 13 , the brazing materials  66  are alternately arranged so as to shift to each other in the long side direction. This can prevent bridging of the brazing material  66 . In  FIG. 15B , as in the configuration example shown in  FIG. 15A , a first terminal  351   c ″ of the first electrode  51  and a third terminal  353   c ″ of the third electrode  53  are provided side by side in the vicinity of short sides of the upper surface of the fourth ceramic layer  44  so as to extend in the long side direction. In this modified configuration example, the brazing materials  66  welded to the first and third terminals  351   c ″,  353   c ″ are provided at the same position in the extending direction of the first and third terminals  351   c ″,  353   c ″. However, as in the configuration example shown in  FIG. 13 , since the amount of the brazing material  66  is smaller than the amount of the brazing material  66  welded to the second terminal of the second electrode  52 , even if the first and third terminals  351   c ″,  353   c ″ are arranged closely, bridging of the brazing material  66  can be prevented. 
     In the fifth embodiment, as shown in  FIG. 16 , a first terminal  451   c  of the first electrode  51  extends along a first short side  44 A of two short sides of the ceramic layer  44  and a third terminal  453   c  of the third electrode  53  extends along a second short side  44 B opposed to the first short side  44 A of the fourth ceramic layer  44 . In relation to this, as shown in  FIG. 17 , only a first wiring  461  connected to the first terminal  451   c  of the first electrode  51  is provided along one side of the wiring substrate  422  and only a third wiring  463  connected to the third terminal  453   c  of the third electrode  53  is provided along a side opposed to the side of the wiring substrate  422 . 
     By providing only one of the first terminal  451   c  and the third terminal  453   c  in the vicinity of one of short sides, as in the first to third embodiment, the piezoelectric actuator  421  is prevented from increasing in size. 
     Although these embodiments have been described above, the present invention is not limited to the above-mentioned configuration. For example, arrangement of the first terminal is not limited to that described in each embodiment. A plurality of first terminals may be disposed along the side edge of the piezoelectric actuator. In relation to this, the first wiring may be disposed along both side edges of the wiring substrate in the pulling direction of the wiring substrate or may be disposed along three sides of the wiring substrate in the shape of U. A brazing material such as solder may be used as the conductive material for electrically connecting each terminal to each wiring on the wiring substrate. 
     Although the plates  31  to  36  of the cavity unit  20  are made of conductive material, at least one plate which contacts ink only needs to be made of conductive material. 
     The liquid discharge apparatus can be applied to the ink jet head as well as apparatuses for discharging various liquid to form an electrical wiring pattern or color filter. 
     The piezoelectric actuator  21  is not limited to the above-mentioned embodiments, and the polarizing direction in the ceramics layers may be different from the direction in which voltage is applied to the electrodes. For example, shearing deformation may occur in the ceramics layers by applying voltage so that electric field slants with respect to the polarizing direction in the ceramics layers. 
     Although the piezoelectric actuator  21  and the ceramics layers  41  to  45  constructing the piezoelectric actuator  21  are rectangular sheets in the drawings, these are not limited to this. For example, these may have any shapes according to the design of the ink jet head, such as a trapezoid shape or a circular shape. 
     In these embodiments, pressure can be selectively applied to liquid in a plurality of pressure chambers, thereby discharging the liquid. Since the first electrode is provided over the plurality of pressure chambers, any defect in the plurality of pressure chambers on the first ceramic layer can be detected. 
     In these embodiments, through the first, second and third terminals provided on the insulating layer, it is possible to apply voltage for discharging liquid and detect the existence of the defect on the ceramic layer. 
     In these embodiments, through wiring substrate having the first, second and third wirings, it is possible to apply voltage for discharging liquid and detect the existence of the defect on the ceramic layer. 
     In these embodiments, by displacement of the plurality of second and third ceramic layers which are each sandwiched between the plurality of second and third electrodes, large discharge pressure can be obtained. Since the plurality of third wirings connected to the third terminal has a lower electric resistance value than the plurality of first wirings connected to the first terminal, the impedance can be kept in balance and the defect in the ceramic layer can be detected as described above without impairing the characteristic of the liquid discharge apparatus. 
     In these embodiments, since the conductive member does not contact the first electrode, with the configuration in which the cavity unit, the piezoelectric actuator and the wiring substrate are assembled and the conductive member is provided, by measuring electrical characteristic between the first wiring and the third wiring, the existence of the defect in the first ceramic layer can be detected. Thus, downstream of the manufacturing process, the existence of the defect occurring when the cavity unit, the piezoelectric actuator and the wiring substrate are assembled can be detected, resulting in improvement in reliability of selecting a defective product from all products. 
     In these embodiments, even after the conductive member is provided on sides of the plurality of ceramic layers and the cavity unit and the piezoelectric actuator are assembled, the third electrode can be easily connected to the cavity unit. Since the contact prevention part provided at the first electrode is a part partially cut out so as not to be exposed in the region where the conductive member is provided, the contact prevention part can be easily manufactured. 
     In these embodiments, since the amount of the first and third conductive bumps is small, when the bumps are welded to the first and third terminals, the possibility that the first and third bumps bridge to each other can be lowered. Thus, even after the wiring substrate is provided on the piezoelectric actuator, the first wiring and the third wiring are held individualy and the defect can be reliably measured by using the first and third wirings. 
     In these embodiments, since the first terminal and the third terminal are arranged along one edge of the piezoelectric actuator and the first and third conductive bumps are alternately provided in the extending direction of the first and third terminals, the possibility that the first and third conductive bumps bridge to each other can be further lowered. 
     In these embodiments, the protruding part of one terminal is opposed to a narrower part between adjacent protruding parts of the other terminal and the protruding parts of both terminals are alternately provided in the extending direction of the terminals. Thus, a sufficient area where the bumps are welded to the protruding parts can be ensured and a region in the piezoelectric actuator where the first terminal and the third terminal are provided can be made compact in the aligning direction of the first and third terminals, thereby preventing the piezoelectric actuator from increasing in size. 
     In these embodiments, the first terminal is provided along one edge of the insulating layer and the third terminal is provided along a edge opposite to the one edge. The first terminal and the third terminal are separately provided along one edge of the insulating layer. In each case, the region where the terminals are provided can be made compact in the direction perpendicular to the one edge, thereby preventing the piezoelectric actuator from increasing in size. 
     In these embodiments, an electrical characteristic between the first electrode and the cavity unit can be measured between the first wiring and the third wiring in the state where the cavity unit, the piezoelectric actuator and the wiring substrate are assembled. Accordingly, downstream of the manufacturing process, the defect occurring when the cavity unit, the piezoelectric actuator and the wiring substrate are assembled can be detected, resulting in improvement in reliability of selecting a defective product from all products. 
     As this description may be embodied in several forms without departing from the spirit of essential characteristics thereof, the present embodiment is therefore illustrative and not restrictive, since the scope is defined by the appended claims rather than by the description preceding them, and all changes that fall within metes and bounds of the claims, or equivalence of such metes and bounds thereof are therefore intended to be embraced by the claims.