Abstract:
A head chip has a substrate, a chamber formed in the substrate for containing ink and an end portion communicating with a nozzle opening, and an electrode disposed on a sidewall of the chamber. The chamber has an end portion communicating with a nozzle opening. When a driving voltage is applied to the electrode, a capacity within the chamber is varied to discharge ink contained in the chamber from the nozzle opening. An ink chamber plate is connected to the substrate and defines a common ink chamber communicating with the chamber. The common ink chamber has a partitioning portion for partitioning the chamber and the common ink chamber. The partitioning portion has communicating holes that evenly divide a chamber longitudinal direction of the partitioning portion using a distance between the nozzle opening and a communicating hole establishing communication between the common ink chamber and the chamber.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a head chip that is mounted on an ink jet recording device applied to, for example, a printer or a facsimile. 
     2. Description of the Related Art 
     Conventionally, there is known an ink jet recording device that records characters and images on a medium to be recorded using an ink jet head having a plurality of nozzles for discharging ink. In such an ink jet recording device, the nozzles of the ink jet head are provided in a head holder so as to oppose the medium to be recorded, and this head holder is mounted on a carriage to be scanned in a direction perpendicular to a conveying direction of the medium to be recorded. 
     A sectional view in the longitudinal direction of an example of a head chip of such an ink jet head is shown in FIG. 16A and a sectional view of a main portion of the same is shown in FIG.  16 B. As shown in FIGS. 16A and 16B, a plurality of grooves  102  are provided in parallel with each other in a piezoelectric ceramic plate  101 , and each groove  102  is separated by sidewalls  103 . An end portion in the longitudinal direction of each groove  102  is extended to an end surface of the piezoelectric ceramic plate  101  and the other end portion is not extended to the other end surface, making the groove  102  to be gradually shallow. In addition, electrodes  105  for applying a driving electric field are formed on surfaces on opening side of both sidewalls  103  in each groove  102  throughout its longitudinal direction. 
     In addition, a cover plate  107  is joined on the opening side of the grooves  102  of the piezoelectric ceramic plate  101  via a partitioning portion using an adhesive  109 . The cover plate  107  includes a common ink chamber  111  in the form of a recessed portion communicating with each groove  102  via communication holes provided in the partitioning portion in the longitudinal direction of the respective grooves  102  and an ink supply port  112  that is bored from the bottom portion of the common ink chamber  111  in the direction opposite to the grooves  102 . 
     In addition, a nozzle plate  115  is joined to an end surface of the joined body of the piezoelectric ceramic plate  101 , the partitioning portion and the cover plate  107  in which the grooves  102  are opened, and nozzle openings  117  are formed in the nozzle plate  115  at positions opposing the respective grooves  102 . 
     Further, a wiring substrate is fixed to the surface of the piezoelectric ceramic plate  101  on the opposite side of the nozzle plate  115  and on the opposite side of the cover plate  107 . Wiring connected to each electrode  105  via bonding wires  121  or the like is formed on the wiring substrate, and a driving voltage can be applied to the electrodes  105  via the wiring. 
     In a head chip configured in this way, when each groove  102  is filled with ink from the ink supply port  112  and a predetermined driving electric field is caused to act on the sidewalls  103  on both sides of the predetermined groove  102  via the electrode  105 , the sidewalls  103  are deformed to change the capacity inside the predetermined groove  102 , whereby the ink in the groove  102  is discharged from the nozzle opening  117 . 
     For example, as shown in FIG. 17, if ink is discharged from the nozzle opening  117  corresponding to a groove  102   a , a positive driving voltage is applied to electrodes  105   a  and  105   b  in the groove  102   a  and, at the same time, opposing electrodes  105   c  and  105   d  to the respective electrodes are grounded. Consequently, a driving electric field in the direction toward the groove  102   a  acts on sidewalls  103   a  and  103   b  and, if the driving electric field is perpendicular to a direction of polarization of the piezoelectric ceramic plate  101 , the sidewalls  103   a  and  103   b  are deformed in the direction of the groove  102   a  by a piezoelectric thickness slip effect and the capacity inside the groove  102   a  decreases to increase pressure, whereby the ink is discharged from the nozzle opening  117 . 
     As a measure for solving a problem that it is difficult to achieve high speed consecutive discharging, that is, to achieve high speed printing in a head chip like this, the degree of sealing of a chamber is increased for the sake of shortening a time from the stoppage of vibration of the sidewalls caused by ink discharging to the obtainment of a situation where pressure of ink in the chamber corresponding to the groove becomes zero to perform the next ink discharging, although this time varies depending on the length of the chamber, the shape of the nozzle opening, and the like. However, if the opening area of the communicating hole is narrowed too much for the sake of enhancing the degree of sealing of the chamber, there occurs a problem that ink necessary for discharging is not sufficiently supplied from the common ink chamber to the chamber and printing is not normally performed. 
     SUMMARY OF THE INVENTION 
     In view of such circumstances, it is an object of the present invention is to provide a head chip in which the minimum size of the communicating hole, with which it is possible to sufficiently supply ink necessary for discharging and, at the same time, to enhance the degree of sealing of the chamber to a limit, is defined with reference to the length in the longitudinal direction of the chamber. 
     In order to solve the above-mentioned object, according to a first aspect of the present invention, a head chip includes: a chamber that is defined on a substrate and has an end portion in a longitudinal direction that communicates with a nozzle opening; and an electrode provided on a sidewall of the chamber, in which a driving voltage is applied to the electrode so that a capacity within the chamber is changed to discharge ink filled therein from the nozzle opening. The head chip is characterized in that: an ink chamber plate defining a common ink chamber communicating with the chamber is joined on the substrate; the common ink chamber is provided with a partitioning portion for partitioning the chamber and the common ink chamber; the partitioning portion is provided with a plurality of communicating holes that evenly divide a chamber longitudinal direction of the partitioning portion using a distance between the nozzle opening and a communicating hole establishing communication between the common ink chamber and the chamber and which is provided in the partitioning portion at a position close to the nozzle opening, and each of the plurality of communicating holes has the same opening ratio to an area of the partitioning portion; and if a length in the longitudinal direction of the chamber is referred to as Y (mm) and an opening ratio of each communicating hole to the area of the partitioning portion is referred to as X (%), when a size of the communicating hole satisfying a relation of “Y=−4.5X+15.8” is referred to as S min  and a size of a communicating hole obtained by coupling the plurality of communicating holes to each other is referred to as S max , there is obtained a relation of S min  size of communicating hole&lt;S max . 
     According to a second aspect of the present invention, in the first aspect of the invention, a head chip is characterized in that the partitioning portion is formed of a separate member. 
     According to a third aspect of the present invention, in the first or the second aspect of the invention, a head chip is characterized in that the substrate is formed of a piezoelectric ceramic plate, and the chamber is defined by forming a groove in the piezoelectric ceramic plate. 
     According to a fourth aspect of the present invention, in the first or the second aspect of the invention, a head chip is characterized in that the sidewalls are made of piezoelectric ceramic and are arranged on the substrate at a predetermined interval, and the chamber is defined between the sidewalls. 
     According to a fifth aspect of the present invention, in the fourth aspect of the invention, a head chip is characterized in that the sidewalls are made of piezoelectric ceramic and are arranged on the substrate at a predetermined interval, and the chamber is defined between the sidewalls, and that the common ink chamber is defined on the substrate, and the chamber and the common ink chamber communicate with each other at one end in the longitudinal direction of the chamber. 
     In the present invention, the minimum size of the communicating hole, with which it is possible to sufficiently supply ink necessary for discharging and, at the same time, to enhance the degree of sealing of the chamber to a limit, is defined with reference to the length in the longitudinal direction of the chamber. Therefore, it becomes possible to shorten the converging time, during which pressure in the chamber attenuates, without causing the deterioration of an ink supply property and an ink discharging property. As a result, it becomes possible to achieve high speed printing by consecutively discharging ink at high speed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more better understanding of the present invention, reference is made of a detailed description to be read in conjunction with the accompanying drawings, in which: 
     FIG. 1 is a sectional view in the longitudinal direction of a head chip according to first or third embodiment of the present invention; 
     FIG. 2 is a sectional view cut along the line  2 — 2  of FIG. 1; 
     FIG. 3 is a sectional view in the longitudinal direction of a head chip according to second or third embodiment of the present invention; 
     FIG. 4 is a sectional view cut along the line  4 — 4  of FIG. 3; 
     FIG. 5 is a sectional view in the longitudinal direction of a head chip according to one aspect of a fourth embodiment mode of the present invention; 
     FIG. 6 is a sectional view cut along the line  6 — 6  of FIG. 5; 
     FIG. 7 is a sectional view in the longitudinal direction of a head chip according to one aspect of a fifth embodiment mode of the present invention; 
     FIG. 8 is a sectional view cut along the line  8 — 8  of FIG. 7; 
     FIG. 9 is a plain view of a partitioning portion corresponding to one chamber of the head chip according to every embodiment mode of the present invention; 
     FIG. 10 is a plain view of a partitioning portion corresponding to one chamber of the head chip according to the first embodiment of the present invention; 
     FIG. 11 is a plain view of a partitioning portion corresponding to one chamber of the head chip according to the second embodiment of the present invention; 
     FIG. 12 is a plain view of a partitioning portion corresponding to one chamber of the head chip according to the third embodiment of the present invention; 
     FIG. 13 is a graph in which pressure values obtained in the case of the first embodiment for respective communicating hole opening ratios after one AP has elapsed are distributed with reference to respective nozzle resistance values; 
     FIG. 14 is a graph in which pressure values obtained in the case of the second embodiment for respective communicating hole opening ratios after one AP has elapsed are distributed with reference to respective nozzle resistance values; 
     FIG. 15 is a graph in which pressure values obtained in the case of the third embodiment for respective communicating hole opening ratios after one AP has elapsed are distributed with reference to respective nozzle resistance values; 
     FIG. 16A is a sectional view in the longitudinal direction showing an outline of a head chip according to the prior art; 
     FIG. 16B is a sectional view showing an outline of a main portion of the head chip according to the prior art; and 
     FIG. 17 is a sectional view showing the outline of the head chip according to the prior art. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention will be described in detail below based on embodiment modes of the present invention. 
     FIG. 1 is a sectional view in the longitudinal direction of a chamber of a head chip, while FIG. 2 is sectional view cut along a line  2 — 2  of FIG.  1 . These drawings show a first or third embodiment mode. 
     First, the head chip  11  will be described in detail. As shown in FIGS. 1 and 2, chambers  17  consisting of a plurality of grooves or channels are provided in parallel with each other in a piezoelectric ceramic plate  16  constituting the head chip  11 , and each chamber  17  is separated by sidewalls  18 . One end portion in the longitudinal direction of each chamber  17  extends to one end surface of the piezoelectric ceramic plate  16  and the other end portion does not extend to the other end surface, making the groove to be gradually shallow. In addition, electrodes  19  for applying a driving electric field are formed on surfaces on opening side of both the sidewalls  18  in each chamber  17  throughout its longitudinal direction. 
     Here, each chamber  17  formed on the piezoelectric ceramic plate  16  is formed by, for example, a dice cutter of a disk shape, and the portion where the groove is made to be gradually shallow is formed according to a shape of the dice cutter. In addition, the electrodes  19  formed in each chamber  17  are formed by, for example, publicly-known evaporation from a diagonal direction. 
     An ink chamber plate  20  is joined to the opening side of the chamber  17  of the piezoelectric ceramic plate  16  via adhesive  35 . This ink chamber plate  20  includes a common ink chamber  21  to be a recessed portion communicating with each chamber  17  and the common ink chamber  21  is sealed with a common ink chamber lid  33  having an ink supply port  22  communicating with this common ink chamber. It is possible to form the ink chamber plate  20  using a ceramic plate, a metallic plate, or the like, although it is preferable to use a ceramic plate having a close coefficient of thermal expansion if consideration is given to deformation and the like after the joining with the piezoelectric ceramic plate  16 . 
     The ink chamber plate  20  like this is provided with a partitioning portion  30  that is provided with a plurality of communicating holes  32  that establish communication between the chamber  17  and the common ink chamber  21  and are arranged in the longitudinal direction of the chamber  17  at regular intervals so as to pass through the partitioning portion in the thickness direction. 
     With this construction, the intervals between respective communicating holes  32 , that is, a distance from the communicating hole  32  positioned close to the nozzle opening  24  to the nozzle opening  24  is set as a pump portion  17   a  and a length thereof becomes a pump length of the head chip  11 . Converging time, during which pressure attenuates, is determined by the pump length. Here, the pressure is generated by the repetitive reflection of sound pressure in the chamber  17  when vibration of sidewalls  18  stops after ink discharging. Consequently, it becomes possible to easily define the length of the pump portion  17   a  by the position (number) of the communicating hole  32  and to shorten the converging time. 
     It should be noted here that no specific limitation is imposed on the number of such communicating holes  32  and it is possible to arrange communicating holes whose number is within a range in which there is exerted no influence on a discharging capability. Further, in order to prevent a bubble from staying in an end portion where the chamber  17  is made shallow, the communicating hole  32  is provided at a position opposing the end portion. 
     In addition, a nozzle plate  23  is joined to an end surface of the joined body of the piezoelectric ceramic plate  16  and the ink chamber plate  20  in which the chambers  17  are opened, and a nozzle opening  24  is formed in the nozzle plate  23  at a position opposing each chamber  17 . 
     This nozzle plate  23  is produced by forming the nozzle opening  24  in a polyimide film or the like using, for instance, an excimer laser apparatus. Also, although not shown in the drawing, on a surface of the nozzle plate  23  opposing an object to be printed, there is provided a water-repellent film having water repellency in order to prevent the adhesion of ink or the like. 
     In addition, ink introduced from an unillustrated ink cartridge or ink pack passes through an unillustrated ink flow path, is filled into the common ink chamber  21  from the ink supply port  22 , passes through each communicating hole  32 , and is filled into each chamber  17 . 
     In this case, if the length of the chamber  17  in the longitudinal direction is referred to as Y (mm) and the opening ratio of one communicating hole  32  to the area of the partitioning portion  30  for one chamber is referred to as X (%), the minimum area of the communicating hole is determined using an expression of “Y=−4.5X+15.8”. In this manner, it becomes possible to circumvent the shortage of ink supply to the chamber. Here, in terms of the structure of the present head chip, needless to say, the maximum size of the communicating hole becomes a size where the plurality of communicating holes are coupled to each other. 
     It should be noted here that a head chip that uses insulating ink is described as an example in the embodiment mode described above, although a head chip that uses conductive ink, such as water ink, may be employed. 
     In the case where conductive ink, such as water ink, is used in a head chip in this manner, electrodes are subjected to conduction by the ink in the chambers  17 , so that there occurs electrolysis of the ink and, at the same time, it becomes impossible to perform normal driving. In view of this problem, a chamber for discharging ink to a piezoelectric ceramic plate and a dummy chamber that is not filled with ink are alternately arranged to have the conductive ink discharged. In this case, the dummy chamber may be prevented from being filled with ink by a partitioning portion. 
     Even with a head chip that uses conductive ink in this manner, it is possible to obtain the same effect by providing a plurality of communicating holes  32  like in the case of the head chip  11  using the insulating ink described above in the partitioning portion for each chamber that discharges the ink. 
     FIG. 3 is a sectional view in the longitudinal direction of a chamber of a head chip, while FIG. 4 is sectional view cut along the line  4 — 4  of FIG.  3 . These drawings show a second or third embodiment mode. 
     The second or third embodiment mode differs from the first embodiment only in that there is not used the common ink chamber lid  33  provided with the ink supply port  22  communicating with the common ink chamber  21 , the ink chamber plate  20  is not provided with the partitioning portion  30 , and the partitioning portion  30  having the communicating holes  32  is made of a separate member. All other aspects are the same as those in the first embodiment mode. 
     The head chip  11  having a construction like this is obtained by first joining the piezoelectric ceramic plate  16  to the ink chamber plate  20  so that the partitioning portion  30  is nipped between them and then joining the nozzle plate  23  to an end surface of the joined body. 
     Even in the case of the head chip  11  like this, if the length of the chamber  17  in the longitudinal direction is referred to as Y (mm) and the opening ratio of one communicating hole  32  to the area of the partitioning portion  30  for one chamber is referred to as X (%), the minimum area of the communicating hole is determined using an expression of “Y=−4.5X+5.8”. In this manner, it becomes possible to circumvent the shortage of ink supply to the chamber. Here, in terms of the structure of the present head chip, needless to say, the maximum size of the communicating hole becomes a size where the plurality of communicating holes are coupled to each other. 
     Also, it is possible to use conductive ink with the same method as in the first embodiment mode. 
     FIGS. 5 and 6 show a fourth embodiment mode of the present invention. FIG. 5 is a sectional view in the longitudinal direction of a head chip according to this embodiment mode, while FIG. 6 is a sectional view cut along the line  6 — 6  of FIG.  5 . 
     As shown in the drawings, the head chip  11 A has a construction where sidewalls  18 A made of a piezoelectric ceramic are arranged on a substrate  16 A at predetermined intervals and chambers  17 A are defined between respective sidewalls  18 A. 
     Also, a sealing plate  60 A is provided on the substrate  16 A and one end of the chamber  17 A in the longitudinal direction is sealed with the sealing plate. 
     Also, the partitioning portion  30 A exists between the chamber  17 A and the common ink chamber  21 A provided for the ink chamber plate  20 A and a plurality of communicating holes  32 A are established in the partitioning portion at predetermined regular intervals. 
     Further, electrodes  19 A provided on both sidewalls  18 A of the chambers  17 A are provided over the entire surface of the sidewalls and the conduction between the electrodes and an unillustrated driving circuit is established by wiring  61 A. For instance, the wiring  61 A is extended along the chambers  17 A defined on both sides between the substrate  16 A and each sidewall  18 A and surely contacts the electrodes  19 A in both end portions in the width direction of the extended wiring  61 A, whereby the conduction between the electrodes and the wiring is realized. 
     Even in the case of the head chip  11 A like this, if the length of the chamber  17 A in the longitudinal direction is referred to as Y (mm) and the opening ratio of one communicating hole  32 A to the area of the partitioning portion  30 A for one chamber is referred to as X (%), the minimum area of the communicating hole is determined using an expression of “Y=−4.5X+15.8”. In this manner, it becomes possible to circumvent the shortage of ink supply to the chamber. Here, in terms of the structure of the present head chip, needless to say, the maximum size of the communicating hole becomes a size where the plurality of communicating holes are coupled to each other. 
     Also, it is possible to use conductive ink with the same method as in the first embodiment mode. 
     Further, the partitioning portion  30 A is a separate member in this embodiment mode. However, needless to say, there occurs no problem even if there is obtained a construction where the ink chamber plate  20 A is provided with the partition portion and the common ink chamber  21 A is formed using the common ink chamber lid that is a separate member and includes the ink supply port  22 A communicating with the common ink chamber. 
     FIGS. 7 and 8 show a fifth embodiment mode of the present invention. FIG. 7 is a sectional view in the longitudinal direction of a head chip according to an embodiment mode, while FIG. 8 is a sectional view cut along the line  8 — 8  of FIG.  7 . 
     The fifth embodiment mode differs from the fourth embodiment mode only in that a second sealing plate  60 B exists outside of the sealing plate  60 A, a communicating hole  32 B having the same size as the communicating hole  32 A is established in the sealing plate  60 A at a position opposing the chamber  17 A, the common ink chamber  21 A provided on the ink chamber plate  20 A is set as the first ink chamber  21   a , a second ink chamber  21   b  is defined between the sealing plate and the second sealing plate, the communicating hole  32 B establishes communication between the second ink chamber  21   b  and the chamber  17 A, an ink supply communicating hole  31 A for establishing communication between the first ink chamber  21   a  and the second ink chamber  21   b  is formed in the partitioning portion  30 A, and the communicating hole  32 A existing close to the sealing plate  60 A is eliminated from the partitioning portion  30 A. All other aspects are the same as those in the fourth embodiment mode. 
     Even in the case of the head chip  11 A like this, if the length of the chamber  17 A in the longitudinal direction is referred to as Y (mm) and the opening ratio of one communicating hole  32 A to the area of the partitioning portion  30 A for one chamber is referred to as X (%), the minimum area of the communicating hole is determined using an expression of “Y=−4.5X+15.8”. In this manner, it becomes possible to circumvent the shortage of ink supply to the chamber. Here, in terms of the structure of the present head chip, needless to say, the maximum size of the communicating hole becomes a size where the plurality of communicating holes are coupled to each other. 
     Also, it is possible to use conductive ink by sealing the dummy chambers using the sealing plate  60 A and concurrently using the same method as in the first embodiment mode. 
     Further, the partitioning portion  30 A is a separate member in this embodiment mode. However, needless to say, there occurs no problem even if there is obtained a construction where the ink chamber plate  20 A is provided with the partition portion and the common ink chamber  21 A is formed using the common ink chamber lid that is a separate member and includes the ink supply port  22 A communicating with the common ink chamber  21 A. 
     Finally, how to define the size of each communicating hole  32  or  32 A will be described with reference to FIG.  9 . FIG. 9 is a plain view of the partitioning portion  30  or  30 A positioned on one chamber  17  or  17 A and a plurality of communicating holes  32  or  32 A of the partitioning portion. 
     It is assumed that the length of the chamber  17  or  17 A in the longitudinal direction is referred to as Y (mm), the width of the chamber  17  or  17 A is referred to as Z (mm), the length of a long side of one communicating hole  32  or  32 A having a rectangular shape is referred to A (mm), and the length of a short side thereof is referred to as B (mm). Here, if the opening ratio of one communicating hole  32  or  32 A to the area of the partitioning portion  30  or  30 A provided for one chamber  17  or  17 A is referred to as X (%), there is obtained an equation of “X (%)=(A×B)×100/(Y×Z)”. Also, the communicating hole  32  or  32 A has a rectangular shape in this embodiment mode. However, needless to say, this hole may have any other shape such as an oval shape or a circular shape. 
     (First Embodiment) 
     FIG. 10 is a plain view of the partitioning portion  30  for one chamber of the head chip according to a first embodiment of the present invention. 
     As shown in the drawing, the head chip of the first embodiment has three communicating holes  32  established in the partitioning portion  30 , with intervals between the communicating holes being set at 1.8 mm. The intervals between the communicating holes are set as the distances between the centers of respective communicating holes  32  and only the communicating hole  32  existing at one end on a side opposite to the nozzle opening in one end portion of the chamber in the longitudinal direction is set so as to have a size that is one-half the sizes of other communicating holes. 
     There are four head chips like this where the length of a chamber in the longitudinal direction is set as Y=5.4 mm and the sizes of the communicating holes are A×B=0.09 mm×0.06 mm, 0.18 mm×0.06 mm, 0.27 mm×0.06 mm, and 0.36 mm×0.06 mm, respectively. 
     (Second Embodiment) 
     FIG. 11 is a plain view of the partitioning portion  30  for one chamber of the head chip according to a second embodiment of the present invention. 
     As shown in the drawing, the head chip of the second embodiment has four communicating holes  32  established in the partitioning portion  30 , with intervals between the communicating holes being set at 1.8 mm. The intervals between the communicating holes are set as the distances between the centers of respective communicating holes  32  and only the communicating hole  32  existing at one end on a side opposite to the nozzle opening in one end portion of the chamber in the longitudinal direction is set so as to have a size that is one-half the sizes of other communicating holes. 
     There are four head chips like this where the length of a chamber in the longitudinal direction is set as Y=7.2 mm and the sizes of the communicating holes are A×B=0.09 mm×0.06 mm, 0.18 mm×0.06 mm, 0.27 mm×0.06 mm, and 0.36 mm×0.06 mm, respectively. 
     (Third Embodiment) 
     FIG. 12 is a plain view of the partitioning portion  30  for one chamber of the head chip according to a third embodiment of the present invention. 
     As shown in the drawing, the head chip of the third embodiment has five communicating holes  32  established in the partitioning portion  30 , with intervals between the communicating holes being set at 1.8 mm. The intervals between the communicating holes are set as the distances between the centers of respective communicating holes  32  and only the communicating hole  32  existing at one end on a side opposite to the nozzle opening in one end portion of the chamber in the longitudinal direction is set so as to have a size that is one-half the sizes of other communicating holes. 
     There are four head chips like this where the length of a chamber in the longitudinal direction is set as Y=9.0 mm and the sizes of the communicating holes are A×B=0.09 mm×0.06 mm, 0.18 mm×0.06 mm, 0.27 mm×0.06 mm, and 0.36 mm×0.06 mm, respectively. 
     EXPERIMENTAL EXAMPLE 
     The behavior of pressure in the nozzle opening  24  in the case where nozzle resistance is set at one of 40%, 60%, and 80% is measured for four kinds of head chips in the first embodiment, four kinds of head chips in the second embodiment, and four kinds of head chips in the third embodiment. During this measurement, a voltage is applied to the electrodes  19  so that a maximum displacement amount of both sidewalls  18  of the chamber  17  toward the outside with reference to the chamber becomes 0.01 μm and this state continues for 25μ second or longer. The width Z of the chamber  17  is set at 0.078 mm. 
     Further, there is extracted a pressure value after time AP, whose length is determined by the intervals between the communicating holes  32 , has elapsed, and an opening ratio X (%), with which there is obtained a positive pressure value, of one communicating hole  32  to the area of the partitioning portion  30  occupied by one chamber  17  is obtained from the varying trend of the pressure value with reference to each nozzle resistance value in each embodiment. Here, the length of the time AP is the same and becomes 2.1μ second because every interval between the communicating holes is 1.8 mm. Also, if the pressure value after the time AP has elapsed is positive, this indicates that ink is correctly supplied. 
     FIG. 13 shows a graph in which pressure values obtained for each communicating hole opening ratio in the case of the first embodiment after one AP has elapsed are distributed with reference to each nozzle resistance value. 
     FIG. 14 shows a graph in which pressure values obtained for each communicating hole opening ratio in the case of the second embodiment after one AP has elapsed are distributed with reference to each nozzle resistance value. 
     FIG. 15 shows a graph in which pressure values obtained for each communicating hole opening ratio in the case of the third embodiment after one AP has elapsed are distributed with reference to each nozzle resistance value. 
     Table 1 shows values of the opening ratio X (%) read from FIGS. 13 to  15  described above, at which a positive pressure value is obtained in the nozzle opening  24  after the time AP has elapsed for each combination of the length of the chamber in the longitudinal direction and the nozzle resistance value. 
     
       
         
               
               
               
               
             
               
               
               
               
             
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Embodiment 
                 Embodiment 
                 Embodiment 
               
               
                   
                 1 
                 2 
                 3 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Chamber length Y (mm) 
                 5.4 
                 7.2 
                 9.0 
               
             
          
           
               
                   
                 Opening ratio X (%) of one 
               
               
                   
                 communicating hole 
               
             
          
           
               
                 Nozzle 
                 40% 
                 2.20 
                 1.80 
                 1.45 
               
               
                 resistance 
                 60% 
                 2.25 
                 1.80 
                 1.45 
               
               
                   
                 80% 
                 2.30 
                 1.85 
                 1.50 
               
               
                   
               
             
          
         
       
     
     If a relational expression between the chamber length Y (mm) and the opening ratio X (%) of one communicating hole is obtained from Table 1, there is obtained a relational expression of “Y=−4.5X+15.8”. The value of X lead from the relational expression and the value of Y in all cases becomes larger than the opening ratio X (%) in Table 1 and the pressure in the chamber becomes positive at all times. 
     As can be seen from this, in the head chip of a model like the models shown in the first to third experimental examples, the expression described above determines the minimum area of one communicating hole where there occurs no shortage of ink supply. 
     As described above, with the technique of the present invention, in a head chip in which a plurality of communicating holes are provided in a partitioning portion so as to evenly divide the longitudinal direction of a chamber of the partitioning portion of a common ink chamber using a distance between a nozzle opening and the communicating hole that establishes communication between the common ink chamber and the chamber is provided in the partitioning portion at a position close to the nozzle opening, there is provided the communicating hole at one end on a side opposite to the nozzle opening in one end portion of the chamber in the longitudinal direction, and each of the plurality of communicating holes has the same opening ratio to the area of the partitioning portion, 
     where if the length of the chamber in the longitudinal direction is referred to as Y (mm) and the opening ratio of one communicating hole to the area of the partitioning portion is referred to as X (%), by defining a relation of “Y=−4.5X+15.8” as the minimum size of the communicating hole, it becomes possible to sufficiently supply ink for discharging and to enhance the degree of sealing of a groove to a limit. As a result, it becomes possible to shorten a converging time, during which pressure in the chamber attenuates, to achieve high speed consecutive discharging, that is, to achieve high speed printing, and to stabilize printing quality.