Patent Publication Number: US-6905202-B2

Title: Ink-jet head and recording apparatus

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an ink-jet head and a recording apparatus. 
     One of conventionally known inkjet heads includes a pressure chamber charged with an ink, an ink supplying passage communicated with the pressure chamber for supplying the ink to the pressure chamber, a nozzle communicated with the pressure chamber through an ink discharging passage, and pressure applying means (an actuator) for applying a pressure to the pressure chamber. In such an ink-jet head, the pressure is applied to the pressure chamber by the pressure applying means, so as to discharge the ink charged in the pressure chamber from the nozzle. 
     In this ink-jet head, meniscus vibration is caused at the tip opening of the nozzle when the ink is discharged. Pressure waves caused by the vibration are propagated from the pressure chamber to the ink supplying passage. The pressure waves propagated to the ink supplying passage are also propagated to another pressure chamber communicated with this ink supplying passage, so that the ink may be discharged from another nozzle communicated with this other pressure chamber. 
     As a countermeasure, for example, Japanese Laid-Open Patent Publication No. 9-314836 discloses an ink-jet head including a damper wall as a top wall of an ink supplying passage. In this ink-jet head, an air chamber is provided in a position opposing an ink supplying passage, and a partition wall between the ink supplying passage and the air chamber is made from a flexible damper wall. Thus, when the pressure waves caused as described above are propagated to the ink supplying passage, the damper wall absorbs and eliminates the pressure waves. Therefore, the propagation of the pressure waves to another pressure chamber is avoided, so that an ink can be prevented from being discharged from another nozzle. 
     Such an ink-jet head is fabricated by jointing a plurality of stacked plate materials with one another. Also, the air chamber is a space enclosed with the damper wall. Therefore, the pressure within the air chamber is increased through heating performed in fabricating the ink-jet head and is lowered thereafter due to decrease of the temperature. As a result, in a completed ink-jet head, the damper wall remains to be deformed due to the pressure difference between the ink supplying passage and the air chamber. When the damper wall is thus deformed, the pressure waves propagated through the ink cannot be absorbed. 
     Furthermore, since the air chamber is an enclosed space, the air within the air chamber is expanded and shrunk in accordance with the ambient temperature change during the operation of the inkjet head. Therefore, the pressure within the air chamber is varied. As a result, the characteristic of the damper wall is varied, so that the pressure waves propagated through the ink supplying passage may not be definitely absorbed by the damper wall. 
     SUMMARY OF THE INVENTION 
     The present invention was devised in consideration of the aforementioned problems, and an object is improving the reliability of an ink-jet head and improving recording quality of a recording apparatus by improving the structure of an ink-jet head so as to prevent a damper wall from remaining to be deformed and prevent a pressure within an air chamber from varying in accordance with the ambient temperature change. 
     In order to achieve the object, according to the present invention, an air chamber is communicated with the atmospheric air. 
     Specifically, the ink-jet head of this invention includes a pressure chamber part in which a pressure chamber charged with an ink is formed; a nozzle plate in which a nozzle for discharging the ink is formed; an ink passage part disposed between the pressure chamber part and the nozzle plate in which an ink supplying passage communicated with the pressure chamber for supplying the ink to the pressure chamber and an ink discharging passage for communicating the pressure chamber with the nozzle are respectively formed; an actuator, stacked on the pressure chamber part, for applying a pressure to the pressure chamber for discharging the ink charged in the pressure chamber from the nozzle; an air chamber provided in the ink passage part in a position opposing the ink supplying passage; a damper wall with flexibility for separating the ink supplying passage from the air chamber; and a communicating hole for communicating the air chamber with the atmospheric air. 
     In the ink-jet head having the aforementioned structure, the air chamber is communicated with the atmospheric air through the communicating hole. Therefore, even when the temperature is changed during the fabrication of the ink-jet head, the pressure within this air chamber is always the atmospheric pressure. Accordingly, in the fabricated ink-jet head, the damper wall can be prevented from remaining to be deformed. 
     Also, even when the air within the air chamber is expanded/shrunk during the operation of the ink-jet head due to the ambient temperature change, since the air chamber is communicated with the atmospheric air, the pressure within the air chamber is always the atmospheric pressure. Accordingly, the characteristic of the damper wall can be always kept constant. 
     Therefore, pressure waves propagated to the ink supplying passage are definitely absorbed by the damper effect provided by the damper wall. As a result, the ink can be prevented from being discharged by the propagated pressure waves, so as to improve the reliability of the ink-jet head. 
     In this ink-jet head, the ink passage part may include a plurality of plate materials stacked between the nozzle plate and the pressure chamber part. In this case, the communicating hole may extend within the ink passage part in a direction perpendicular to a stacking direction and be opened on a side face of the ink passage part. 
     The communicating hole may consist of a plurality of long holes that are respectively formed to penetrate, in a thickness direction, given two adjacent plate materials out of the plurality of plate materials and are arranged in a line at substantially equal intervals. In this case, the long holes formed in one of the two plate materials are preferably shifted in positions thereof in a lining direction from the long holes formed in the other of the two plate materials in such a manner that an end of one long hole formed in one plate material is communicated with an end of another long hole formed in the other plate material when the two plate materials are stacked. 
     In other words, the communicating hole is preferably formed in the two plate materials alternately in the stacking direction (which herein means a direction for stacking components or plate materials included in an ink-jet head). Thus, through holes are merely formed to be arranged in a line in each plate material. Therefore, lowering of the strength of each plate material attained before stacking them can be suppressed. As a result, the plate materials can be easily dealt with in the fabrication of the ink-jet head. 
     Alternatively, the communicating hole may be an expanding slot that is formed in a given plate material out of the plurality of plate materials and is opened at an end of the given plate material. 
     In this case, the communicating hole is preferably formed in a zigzag manner from the air chamber to the side face of the ink passage part. Thus, the lowering of the strength of the plate material can be suppressed as compared with the case where the expanding slot is linearly formed. Therefore, the plate materials can be easily dealt with in the fabrication of the ink-jet head. 
     Also, the communicating hole may extends within the ink passage part in a stacking direction and be opened on an exposed face of the nozzle plate. Alternatively, the communicating hole may extend within the ink passage part in a stacking direction and be opened on an exposed face of the pressure chamber part. 
     In such a case, the communicating hole can be formed by forming through holes in the respective plate materials included in the ink passage part so as to communicate with each other when the plate materials are stacked. Therefore, the strength of the plate materials attained before stacking them is not lowered, and hence, the plate materials can be easily dealt with in the fabrication of the ink-jet head. 
     The ink supplying passage may includes a plurality of ink supplying passages for respectively supplying inks of different colors, the air chamber may include a plurality of air chambers, respectively corresponding to the plurality of ink supplying passages, separated by the damper wall, and the communicating hole may include a plurality of communicating holes respectively corresponding to the plurality of air chambers. 
     Furthermore, each of the plurality of ink supplying passages for the inks of different colors may further include a plurality of ink supplying passages, the air chamber may include a plurality of air chambers, respectively corresponding to the plurality of ink supplying passages for the inks of different colors, separated by the damper wall, and the communicating hole may include a plurality of communicating holes respectively corresponding to the plurality of air chambers. Specifically, the air chamber is provided correspondingly to each of the ink supplying passages, and the communicating hole is provided correspondingly to each of the air chambers. 
     Thus, the pressure within the air chamber provided correspondingly to each ink supplying passage can be always the atmospheric pressure. Therefore, the pressure waves propagated to each ink supplying passage can be definitely absorbed by the damper wall. 
     A port for communicating the communicating hole with the air chamber is preferably disposed to have an edge thereof in a position away from the damper wall in a stacking direction. 
     If the port is constructed from the damper wall, the port (opening space) is in contact with the damper wall in the stacking direction, and therefore, a part of the periphery of the damper wall cannot be fixed. When a part of the periphery of the damper wall is thus not fixed, strain is caused in deformation of the damper wall, and therefore, the pressure waves cannot be definitely absorbed. 
     Accordingly, the port is disposed to have the edge thereof in the position away from the damper wall in the stacking direction. Thus, the whole periphery of the damper wall can be fixed. As a result, the damper wall can be uniformly deformed, so that the pressure waves can be definitely absorbed. 
     A protection part is preferably disposed between the ink passage part and the nozzle plate for protecting the communicating hole. 
     The ink-jet head is fabricated by jointing the actuator, the pressure chamber part and the ink passage part to one another and then jointing the nozzle plate to the resultant. Since the ink-jet head of this invention includes the communicating hole, there is a space within the ink passage part. Therefore, the strength is lowered in this space. 
     Accordingly, the protection part is disposed between the ink passage part and the nozzle plate. Thus, the communicating hole (namely, the space) can be protected by the protection part, and hence, the components can be easily dealt with in jointing the nozzle plate. 
     A second air chamber and a second communicating hole for communicating the second air chamber with the atmospheric air may be formed in the protection part. 
     Assuming that the second air chamber and the second communicating hole are not formed in the protection part, the air present between the nozzle plate and the protection part expands in jointing the nozzle plate to the protection part. Therefore, an adhesive applied between the nozzle plate and the protection part flows out. As a result, a void is caused in a joint layer between the nozzle plate and the protection part after the adhesion, and nozzles of the nozzle plate may be communicated with each other through the void. 
     Therefore, the second air chamber and the second communicating hole are formed in the protection part. Thus, the air expanded between the nozzle plate and the protection part escapes to the outside from the second air chamber through the second communicating hole. As a result, a void can be prevented from being caused in the joint layer between the nozzle plate and the protection part. 
     The communicating hole and the second communicating hole are preferably shifted in positions thereof in a direction perpendicular to a stacking direction. 
     In the fabrication of the ink-jet head, the ink passage part and the protection part are stacked and jointed to each other by heating them under a pressure applied in the stacking direction. 
     If the communicating hole and the second communicating hole are formed in the same position in a direction perpendicular to the stacking direction, a space formed by the communicating hole and a space formed by the second communicating hole are adjacent to each other in the stacking direction. In this case, even when the pressure is applied to the ink passage part and the protection part stacked on each other, the pressure cannot be definitely transmitted in the stacking direction. As a result, a joint failure may be caused. 
     Therefore, the communicating hole and the second communicating hole are arranged to be shifted in their positions in the direction perpendicular to the stacking direction. Thus, the space formed by the communicating hole and the space formed by the second communicating hole are never adjacent to each other in the stacking direction. In this case, the pressure applied to the ink passage part and the protection part stacked on each other can be definitely transmitted in the stacking direction. As a result, these parts can be definitely jointed to each other. 
     Each of the ink passage part and the protection part may include a plurality of plate materials stacked on one another. 
     In this case, the communicating hole may consist of a plurality of long holes that are respectively formed to penetrate, in a thickness direction, given two adjacent plate materials out of the plurality of plate materials included in the ink passage part and are arranged in a line at substantially equal intervals, the long holes formed in one of the two plate materials being shifted in positions thereof in a lining direction from the long holes formed in the other of the two plate materials in such a manner that an end of one long hole formed in one plate material is communicated with an end of another long hole formed in the other plate material when the two plate materials are stacked. Also, the second communicating hole may consist of a plurality of long holes that are respectively formed to penetrate, in the thickness direction, given two adjacent plate materials out of the plurality of plate materials included in the protection part and are arranged in a line at substantially equal intervals, the long holes formed in one of the two plate materials being shifted in positions thereof in the lining direction from the long holes formed in the other of the two plate materials in such a manner that an end of one long hole formed in one plate material is communicated with an end of another long hole formed in the other plate material when the two plate materials are stacked. 
     In this case, each long hole of the second communicating hole and each long hole of the communicating hole are preferably disposed in positions opposing each other in the stacking direction and shifted from each other in the lining direction. 
     In this case, the communicating hole and the second communicating hole are disposed to be adjacent to each other in the stacking direction. However, each long hole (space) of the communicating hole and each long hole (space) of the second communicating hole are never adjacent to each other in the stacking direction. Therefore, when the pressure is applied to the ink passage part and the protection part stacked on each other, the pressure can be definitely transmitted in the stacking direction. As a result, the ink passage part and the protection part can be definitely jointed to each other. 
     Another ink-jet head of this invention includes a pressure chamber charged with an ink; an ink supplying passage communicated with the pressure chamber for supplying the ink to the pressure chamber; a nozzle communicated with the pressure chamber through an ink discharging passage; an actuator for applying a pressure to the pressure chamber for discharging the ink charged in the pressure chamber from the nozzle; a damper wall with flexibility disposed as one of partition walls for separating the ink supplying passage; an air chamber provided on a side of the damper wall opposite to the ink supplying passage; and a communicating hole for communicating the air chamber with the atmospheric air. 
     Still another ink-jet head of this invention includes a nozzle; a pressure chamber communicated with the nozzle and charged with an ink; an ink supplying passage communicated with the pressure chamber for supplying the ink to the pressure chamber; pressure applying means for applying a pressure to the pressure chamber for discharging the ink from the nozzle; and pressure absorbing means including an air chamber for absorbing pressure variation of the ink within the ink supplying passage. The air chamber of the pressure absorbing means is communicated with the atmospheric air. 
     The recording apparatus of this invention includes an ink-jet head for performing recording by jetting ink drops onto a recording medium from a nozzle of the ink-jet head. 
     In this recording apparatus, the inkjet head includes a pressure chamber part in which a pressure chamber charged with an ink is formed; a nozzle plate in which the nozzle for discharging the ink is formed; an ink passage part disposed between the pressure chamber part and the nozzle plate, in which an ink supplying passage communicated with the pressure chamber for supplying the ink to the pressure chamber and an ink discharging passage for communicating the pressure chamber with the nozzle are respectively formed; an actuator, stacked on the pressure chamber part, for applying a pressure to the pressure chamber for discharging the ink charged in the pressure chamber from the nozzle; an air chamber provided in the ink passage part in a position opposing the ink supplying passage; a damper wall with flexibility for separating the ink supplying passage from the air chamber; and a communicating hole for communicating the air chamber with the atmospheric air. 
     In the recording apparatus having this structure, pressure waves propagated from the nozzle of the ink-jet head through the pressure chamber to the ink supplying passage can be definitely absorbed by the damper wall. Therefore, the ink can be prevented from being discharged by the propagated pressure waves. As a result, the recording apparatus can attain improved recording quality. 
     In another recording apparatus of this invention, the ink-jet head includes a pressure chamber charged with an ink; an ink supplying passage communicated with the pressure chamber for supplying the ink to the pressure chamber; the nozzle communicated with the pressure chamber through an ink discharging passage; an actuator for applying a pressure to the pressure chamber for discharging the ink charged in the pressure chamber from the nozzle; a damper wall with flexibility disposed as one of partition walls for separating the ink supplying passage; an air chamber provided on a side of the damper wall opposite to the ink supplying passage; and a communicating hole for communicating the air chamber with the atmospheric air. 
     In still another recording apparatus of this invention, the inkjet head includes a pressure chamber communicated with the nozzle and charged with an ink; an ink supplying passage communicated with the pressure chamber for supplying the ink to the pressure chamber; pressure applying means for applying a pressure to the pressure chamber for discharging the ink from the nozzle; and pressure absorbing means including an air chamber for absorbing pressure variation of the ink within the ink supplying passage, and the air chamber of the pressure absorbing means is communicated with the atmospheric air. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic perspective view of an ink-jet type recording apparatus according to an embodiment of the invention; 
         FIG. 2  is a partial bottom view of an ink-jet head; 
         FIG. 3  is a cross-sectional view taken on line III—III of  FIG. 2 ; 
         FIG. 4  is a cross-sectional view taken on line IV—IV of  FIG. 2 ; 
         FIG. 5  is a bottom view of an ink-jet head according to Embodiment 1 of the invention; 
         FIG. 6  is a cross-sectional view taken on line V—V of  FIG. 5 ; 
         FIG. 7  is a perspective explanatory diagram for showing the structure of a communicating hole of Embodiment 1; 
         FIG. 8  is a plan view of an ink passage part in which long holes are formed; 
         FIG. 9  is a bottom view corresponding to  FIG. 5  of an ink-jet head according to Modification 1; 
         FIG. 10  is a cross-sectional view taken on line VI—VI of  FIG. 9 ; 
         FIG. 11  is a perspective explanatory diagram corresponding to  FIG. 7  for showing the structure of a communicating hole according to Modification 1; 
         FIG. 12  is a perspective explanatory diagram corresponding to  FIG. 7  for showing the structure of a communicating hole according to Modification 2; 
         FIG. 13  is a bottom view corresponding to  FIG. 5  of an ink-jet head according to Modification 3; 
         FIG. 14  is a cross-sectional view taken on line VII—VII of  FIG. 13 ; 
         FIG. 15  is a partial cross-sectional view corresponding to  FIG. 6  of an ink-jet head according to Embodiment 2 of the invention; and 
         FIG. 16  is a bottom view corresponding to  FIG. 5  of an ink-jet head according to a modification of Embodiment 2. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Preferred embodiments of the invention will now be described with reference to the accompanying drawings. 
     Embodiment 1 
       FIG. 1  shows the outline of an ink-jet type recording apparatus A according to an embodiment of the invention. This recording apparatus A includes an ink-jet head for jetting ink drops onto a recording paper  14 . On the ink-jet head  1 , four ink cartridges  13  respectively containing inks of four colors, that is, black, cyan, magenta and yellow, are mounted. The ink-jet head  1  is fixedly supported on a carriage  11 . The carriage  11  is provided with a carriage motor not shown. The ink-jet head  1  and the carriage  11  are guided by a carriage axis  12  extending along a primary scanning direction (namely, a direction X in  FIGS. 1 and 2 ) to be reciprocated along this direction by the carriage motor. 
     The recording paper  14  is sandwiched between two transfer rollers  15  driven to rotate by a transfer motor not shown. The recording paper  14  is transferred by the transfer motor and the transfer rollers  15  below the ink-jet head  1  in a secondary scanning direction (namely, a direction Y in  FIGS. 1 and 2 ) perpendicular to the primary scanning direction. 
     The ink jet head  1  includes, as shown in  FIGS. 2 through 6 , a head body  2  that has pressure chamber recesses  32  formed in an upper portion thereof (namely, on the upper side in  FIG. 3  or  4 ), nozzles  51  formed in a lower portion thereof (namely, on the lower side in  FIG. 3  or  4 ) and ink supplying passages  41  formed between the pressure chamber recesses  32  and the nozzles  51 . 
     The ink supplying passages  41  are communicated with the ink cartridges  13  of the respective colors so as to be supplied with the inks from the ink cartridges  13 . The ink supplying passages  41  include nine passages in total, that is, three passages for the black ink (referred to as  41 B) and two passages for each of the cyan, magenta and yellow inks (respectively referred to as  41 C,  41 M and  41 Y). The nine ink supplying passages  41  are provided so as to extend in the secondary scanning direction and to be spaced out from each other in the primary scanning direction. 
     Each ink supplying passage  41  is made from an ink passage part  4  including eleven stacked stainless steel thin plates (hereinafter sometimes referred to as plate materials). In the ink passage part  4 , orifices  3   c  and ink discharging passages  42  are formed. 
     The orifices  3   c  are arranged on the top wall of the ink supplying passage  41  at substantially equal intervals in the secondary scanning direction. Each orifice  3   c  is communicated with a supply port  3   a  for supplying the ink to the pressure chamber recess  32  (pressure chamber  31 ). Each orifice  3   c  is formed in the second stainless steel thin plate from the top having a smaller thickness than the other stainless steel thin plates, and has a diameter of approximately 38 μm. 
     The ink discharging passages  42  are disposed in positions on one side of the ink supplying passage  41  at substantially equal intervals in the secondary scanning direction. Each ink discharging passage  42  communicates a discharge port  3   b  for discharging the ink from the pressure chamber recess  32  (pressure chamber  31 ) with the nozzle  51 . Through holes formed in the respective plate materials for forming each ink discharging passage  42  are successively reduced in their diameters in the downward direction, so that steps can be formed on the inner side walls of each ink discharging passage  42 . 
     The ink passage part  4  also includes air chamber recesses  45  opening downward correspondingly to the ink supplying passages  41  ( 41 B,  41 C,  41 M and  41 Y). Each air chamber recess  45  is disposed in a position opposing the ink supplying passage  41  in a stacking direction so as to extend in the secondary scanning direction. Each air chamber recess  45  is closed by jointing a nozzle plate  5  described later to the bottom face of the ink passage part  4 , so as to form an air chamber  43 . 
     The ink supplying passage  41  and the air chamber  43  are separated by one stainless steel thin plate having a smaller thickness (of approximately 10 μm) than the other stainless steel thin plates. Thus, the bottom wall of the ink supplying passage  41  is constructed from a damper wall  44  with flexibility. 
     The ink passage part  4  further includes communicating holes  6  for communicating the air chambers  45  with the atmospheric air. Each communicating hole  6  extends from one end of the air chamber  43  (one end opposite to the end connected to the ink cartridge  13 ) in the secondary scanning direction so as to be opened on the side face of the ink passage part  4 . 
     As shown in  FIGS. 6 through 8 , each communicating hole  6  consists of a first communicating section  61  opened on the side wall of the air chamber  43  and extending in the secondary scanning direction, a second communicating section  62  connected to the end of the first communicating section  61  and extending in the upper direction in the ink passage part  4  and a main section  63  connected to the upper end of the second communicating section  62  and extending in the secondary scanning direction in the ink passage part  4  so as to be opened on the side face of the head body  2 . 
     The first communicating section  61  of the communicating hole  6  is constructed from a through hole formed in the lower plate material out of the two plate materials positioned below the plate material used as the damper wall  44 . Therefore, a port of the first communicating section  61  opened to the air chamber  43  is disposed to have an edge in a position away from the damper wall  44  in the stacking direction by a distance corresponding to the thickness of the plate material (shown as a distance t in FIG.  6 ). 
     The second communicating section  62  of the communicating hole  6  is constructed from through holes respectively formed, so as to be communicated with one another in the stacking direction, in the four plate materials, that is, the plate material used as the damper wall  44 , one plate material disposed on and two plate materials disposed below the plate material use as the damper wall  44 . 
     The main section  63  of the communicating hole  6  is constructed from through holes formed respectively in the two plate materials disposed above the plate material used as the damper wall  44 . Specifically, as shown in  FIG. 8 , each of these two plate materials is provided with a plurality of long holes  63   a  arranged in a line at substantially equal intervals and penetrating the plate material in the thickness direction.  FIG. 8  shows the lower plate material  46  out of the two plate materials. The respective long holes  63   a  are positioned to be shifted in the lining direction so that when the two plate materials are stacked, one long hole  63   a  formed in one plate material is communicated at the end thereof with the end of another long hole  63   a  formed in the other plate material. 
     The through holes of the communicating holes  6  and the long holes  63   a  may be in the shape of a circle, an ellipse or a polygon such as a triangle or a quadrangle. Alternatively, the long holes  63   a  may be in another random shape. These through holes and long holes  63   a  can be formed by etching or any other known method. 
     A pressure chamber part  3  made from a photosensitive glass with a thickness of approximately 200 μm is fixedly jointed onto the top face of the ink passage part  4 . This pressure chamber part  3  forms the side walls of the plural pressure chamber recesses  32  each having the supply port  3   a  communicated with the orifice  3   c  and the discharge port  3   b  communicated with the ink discharging passage  42 . The bottom walls of the recesses  32  are formed by the ink passage part  4 . 
     The recesses  32  are opened so as to extend in the primary scanning direction on the top face of the head body  2  and are arranged at substantially equal intervals in the secondary scanning direction. The length and the width of the opening of each recess  32  are set to approximately 1250 μm and approximately 130 μm, respectively. The both ends of each recess  32  are in a substantially semi-circular shape. 
     On the other hand, the nozzle plate  5  of a stainless steel is fixedly jointed onto the bottom face of the ink passage part  4 . 
     In the nozzle plate  5 , a plurality of nozzles  51  for jetting ink drops onto the recording paper  14  are formed. Each nozzle  51  is communicated with the discharge port  3   b  of each recess  32  through the ink discharging passage  42 . The plural nozzles  51  are arranged on the bottom face of the ink-jet head  1  in a line extending in the secondary scanning direction so as to form a nozzle line  51   a . One nozzle line  51   a  is provided correspondingly to each of all the ink supplying passages  41  excluding one ink supplying passage  41 B for the black ink. The one ink supplying passage  41 B for the black ink is provided with two nozzle lines  51   a  at both ends thereof in the primary scanning direction. In a pair of adjacent nozzle lines  51   a , the nozzles  51  of one nozzle line  51   a  are respectively disposed to be shifted from the nozzles  51  of the other nozzle line  51   a  by a half pitch in the secondary scanning direction (i.e., the lining direction of the nozzle line  51   a ). 
     Each nozzle  51  has a taper section in which the diameter of the nozzle is reduced toward the tip thereof and a straight section continued from the end of the taper section closer to the tip of the nozzle. The straight section has a diameter of approximately 20 μm. 
     The bottom face of the nozzle plate  5  is coated with a water repellent film (not shown). The water repellent film can be formed by any known method. 
     A piezoelectric actuator  21  is provided above each of the recesses  32  of the head body  2 . The piezoelectric actuator  21  has a vibration plate  22  of Cr that is fixedly jointed to the top face of the head body  2  so as to cover each recess  32  of the head body  2  and to form the pressure chamber  31  together with the recess  32 . One vibration plate  22  is shared by all the piezoelectric actuators  21  and also works as a common electrode shared by all piezoelectric devices  23  described later. The common electrode may be provided separately from the vibration plate  22 . 
     Each piezoelectric actuator  21  includes the piezoelectric device  23  of lead zirconate titanate (PZT) and an individual electrode  24  of Pt for applying a voltage (driving voltage) to the piezoelectric device  23  together with the vibration plate  22 . The piezoelectric device  23  is provided on a face of the vibration plate  22  opposite to the pressure chamber  31  (namely, on the upper face of the vibration plate  22 ) in a portion corresponding to the pressure chamber  31  (namely, in a portion opposing the opening of the recess  32 ) with an intermediate layer  25  of Cu sandwiched therebetween. The individual electrode  24  is jointed onto a face of each piezoelectric device  23  opposite to the vibration plate  22  (namely, on the upper face of the piezoelectric device  23 ). 
     The vibration plate  22 , the piezoelectric devices  23 , the individual electrodes  24  and the intermediate layers  25  are all made from thin films. The vibration plate  22  has a thickness of approximately 6 μm, each piezoelectric device  23  has a thickness of 8 μm or less (for example, approximately 3 μm), each individual electrode  24  has a thickness of approximately 0.2 μm, and each intermediate layer  25  has a thickness of approximately 3 μm. 
     Each piezoelectric actuator  21  applies the driving voltage to the corresponding piezoelectric device  23  via the vibration plate  22  and the corresponding individual electrode  24 , so as to deform a portion of the vibration plate  22  corresponding to the pressure chamber  31  (namely, the portion corresponding to the opening of the recess  32 ), and thus, the ink contained in the pressure chamber  31  is discharged from the discharge port  3   b  and the nozzle  51 . Specifically, when a pulse voltage is applied between the vibration plate  22  and the individual electrode  24 , the piezoelectric device  23  shrinks owing to the piezoelectric effect in the width direction perpendicular to the thickness direction at the rise of the pulse voltage but the vibration plate  22 , the individual electrode  24  and the intermediate layer  25  do not shrink. Therefore, the portion of the vibration plate  22  corresponding to the pressure chamber  31  is deformed into a convex shape protruding toward the pressure chamber  31  through what is called a bimetal effect. This deformation increases the pressure within the pressure chamber  31 , and the increased pressure pushes out the ink contained in the pressure chamber  31  through the discharge port  3   b  and the ink discharging passage  42  from the nozzle  51 . Then, the piezoelectric device  23  expands at the fall of the pulse voltage and the portion of the vibration plate  22  corresponding to the pressure chamber  31  is restored in its shape. At this point, the ink pushed out from the nozzle  51  is pulled off from the ink remaining in the ink passage  12  and jetted onto the recording paper  14  as ink drops (for example, 3 pl), so as to adhere onto the recording paper  14  in the form of dots. Also, when the vibration plate  22  restores from the deformed convex shape to the original shape, the ink is charged in the pressure chamber  31  from the ink cartridge  13  through the ink supplying passage  41  and the supply port  3   a . The pulse voltage to be applied to each piezoelectric device  23  is not limited to the aforementioned push-pull type pulse voltage but may be a pull-push type pulse voltage that falls from a first voltage to a second voltage lower than the first voltage and then rises to the first voltage. 
     The application of the driving voltage to the respective piezoelectric devices  23  is performed at predetermined time intervals (for example, every approximately 50 μs; with a driving frequency of 20 kHz) while the ink-jet head  1  and the carriage  11  are moved in the primary scanning direction from one end to the other end of the recording paper  14  at a substantially constant speed. However, when the ink-jet head  1  reaches a portion of the recording paper  14  where no ink drops are to be adhered, the voltage is not applied. Thus, ink drops are made to impact on desired portions of the recording paper  14 . When a recording operation for one scanning is completed, the recording paper  14  is transferred in the secondary scanning direction by a given amount by the transfer motor and the transfer rollers  15 . Thereafter, ink drops are jetted while moving the ink-jet head  1  and the carriage  11  in the primary scanning direction again for a recording operation for another scanning. Such operations are repeated, so as to form a desired image on the whole recording paper  14 . 
     When the ink is thus jetted from the nozzle  51  by driving the piezoelectric actuator  21 , the meniscus vibration is caused at the tip opening of the nozzle  51 . Due to the meniscus vibration, pressure waves are propagated through the ink discharging passage  42  and the pressure chamber  31  to the ink supplying passage  41 . When the pressure waves propagated to the ink supplying passage  41  reach the damper wall  44 , the damper wall  44  is deformed so as to absorb and eliminate the pressure waves. In this manner, the problem that an ink is jetted from another nozzle  51  due to the pressure waves propagated through the ink supplying passage  41  can be avoided. 
     In particular, since the port of the first communicating section  61  of the communicating hole  6  opened to the air chamber  43  is disposed away from the damper wall  44  in the stacking direction by the distance corresponding to the thickness of the plate material, the whole peripheral edge of the damper wall  44  is clipped and fixed by the plate materials included in the ink passage part  4 . Therefore, no strain is caused in the deformation of the damper wall  44  but the damper wall  44  is uniformly deformed. As a result, the pressure waves can be definitely absorbed. 
     This ink-jet head  1  is fabricated by jointing the ink passage part  4  including a plurality of stacked and jointed plate materials with a first block obtained by previously jointing the piezoelectric actuators  21  to the pressure chamber part  3 , and jointing the nozzle plate  5  to the resultant ink passage part  4 . 
     The ink passage part  4  is obtained by applying an adhesive on the faces of the respective plate materials and jointing them with one another by stacking them. Since the ink passage part  4  is heated at this point, the air within the air chambers  43  is expanded and then shrunk afterward due to the temperature decrease. If the air chamber  43  is an enclosed space, the damper wall  44  remains to be deformed due to the pressure difference caused between the ink supplying passage  41  and the air chamber  43  by the temperature change occurring in the fabrication of the ink-jet head  1 . However, the air chamber  43  of this embodiment is communicated with the atmospheric air through the communicating hole  6 , and therefore, the pressure within the air chamber  43  is always the atmospheric pressure. Accordingly, the damper wall  44  can be prevented from remaining to be deformed. Also, even when the ambient temperature is changed during the operation of the ink-jet head  1 , since the air chamber  43  is communicated with the atmospheric air, the pressure within the air chamber  43  is always the atmospheric pressure. 
     Accordingly, the pressure waves can be definitely absorbed by the damper wall  44 . As a result, the ink can be stably jetted from the nozzle  51 , so as to improve the reliability of the ink-jet head  1  and improve the recording quality of the recording apparatus A. 
     Furthermore, the communicating hole  6  is constructed from the through holes (long holes  63   a ) provided in the plate materials included in the ink passage part  4  (as shown in FIG.  8 ). Therefore, lowering in the strength of the plate materials otherwise caused before stacking the plate materials can be suppressed. As a result, components can be easily dealt with in the fabrication of the ink-jet head. 
     In Embodiment 1, a plurality of ink supplying passages  41  and air chambers  43  are provided correspondingly to the colors of the ink and each air chamber  43  is provided with a plurality of communicating holes  6 , which does not limit the invention. Instead, one communicating hole  6  may be provided correspondingly to each color of the ink. In other words, one communicating hole  6  may be shared by a plurality of air chambers  43 . 
     Also, there is no need to dispose the air chamber  43  and the damper wall  44  in the positions opposing each ink supplying passage  41  in the stacking direction. The air chamber  43  and the damper wall  44  may be disposed in other positions, such as positions opposing the side wall of each ink supplying passage  41 . 
     Modification 1 
     In Modification 1 of Embodiment 1, a communicating hole  6  is constructed from an expanding slot  64  formed in a plate material included in an ink passage part  4  as shown in  FIGS. 9 through 11 . In an ink-jet head  1  according to this modification, like reference numerals are used to refer to like elements used in Embodiment 1 so as to omit the description. 
     The expanding slot  64  is formed in the lower plate material out of the two plate materials disposed below the plate material used as the damper wall  44 . The expanding slot  64  extends from the air chamber  43  in the secondary scanning direction to be opened at the end of the plate material. When respective components are stacked, the side wall of the communicating hole  6  is formed by the plate material having the expanding slot  64 , the top wall of the communicating hole  6  is formed by the plate material disposed above, and the bottom wall of the communicating hole  6  is formed by the nozzle plate  5 . 
     The expanding slot  64  is formed by communicating a plurality of long holes  64   a  with one another in the secondary scanning direction. Two long holes  64   a  adjacent to each other in the secondary scanning direction are disposed to be shifted from each other in the primary scanning direction. Thus, the expanding slot  64  is formed from the air chamber  43  to the side face of the ink passage part  4  in a zigzag manner. 
     When the ink-jet head  1  is provided with such a communicating hole  6 , the pressure within the air chamber  43  can be always the atmospheric pressure as in Embodiment 1. Therefore, the pressure waves can be definitely absorbed by the damper wall  44 . As a result, the ink can be stably jetted from the nozzle  51 , so as to improve the reliability of the ink-jet head  1  and improve the recording quality of the recording apparatus A. 
     Also, since the expanding slot  64  used as the communicating hole  6  is formed in a zigzag manner, the lowering of the strength of the plate material having the expanding slot  64  can be suppressed. As a result, the plate material can be easily dealt with in the fabrication of the ink-jet head  1 . 
     Modification 2 
     In Modification 2 of Embodiment 1, a communicating hole  6  is constructed from an expanding slot  65  formed in a predetermined one of plate materials included in an ink passage part  4  as shown in FIG.  12 . Differently from Modification 1, this expanding slot  65  is linearly formed. 
     Also when the communicating hole  6  is constructed from such a linear expanding slot  65 , an air chamber  43  is communicated with the atmospheric air so that the pressure within the air chamber  43  can be always the atmospheric pressure. As a result, the ink can be stably jetted from the nozzle  51 , so as to improve the reliability of an ink-jet head  1 . 
     However, since the expanding slot  65  is linearly formed, the strength of the plate material having the expanding slot  65  may be lowered. Therefore, from the viewpoint of easiness in dealing with the plate material, the zigzag expanding slot  64  of Modification 1 is preferred. 
     Modification 3 
     In Modification 3 of Embodiment 1, a communication hole  6  extends not in the secondary scanning direction but in the vertical direction. 
     Specifically, as shown in  FIGS. 13 and 14 , the communicating hole  6  of Modification 3 consists of a communicating section  61  and a main section  66 . The communicating section  61  is constructed from a long hole (penetrating in the thickness direction) formed, in the secondary scanning direction, in the lower plate material out of the two plate materials disposed below the plate material used as the damper wall  44 . The main section  66  is constructed from a through hole formed continuously from the end of the long hole in the nozzle plate  5 . 
     Also in this manner, the air chamber  43  is communicated with the atmospheric air through the communicating hole  6 , so that the pressure within the air chamber  43  can be always the atmospheric pressure. As a result, the pressure waves can be definitely absorbed by the damper wall  44 , and the ink can be stably jetted from the nozzle  51  so as to improve the reliability of the ink-jet head  1  and improve the recording quality of the recording apparatus A. 
     Also, the communicating hole  6  can be formed merely by forming through holes respectively in the plate material of the ink passage part  4  and the nozzle plate  5 . Therefore, the lowering of the strength of the plate materials (the plate material and the nozzle plate  5 ) can be prevented, and hence, the respective plate materials can be easily dealt with in the fabrication of the ink-jet head  1 . 
     The communicating hole  6  may be opened on the top face of the ink-jet head  1  as shown with two-dot chain lines in FIG.  14 . Specifically, through holes are formed not only in the respective plate materials included in the ink passage part  4  but also in the pressure chamber part  6  and the vibration plate  22  of the piezoelectric actuator  21 . These through holes are formed so as to communicate with one another when the components are stacked. 
     Also in this manner, the communicating hole  6  can be formed by forming the through holes in the respective plate materials of the ink passage part  4 , the pressure chamber part  6  and the vibration plate  22 . Therefore, the lowering of the strength of the respective plate materials can be prevented, and hence, the respective plate materials can be easily dealt with in the fabrication of the ink-jet head  1 . 
     Embodiment 2 
     In Embodiment 2 of the invention, a protection part  7  is provided between an ink passage part  4  and a nozzle plate  5  as shown in FIG.  15 . Thus, a communicating hole  6  formed in the ink passage part  4  can be protected. 
     An ink-jet head  1  of this embodiment has a basic structure substantially the same as that of Embodiment 1, and therefore, like reference numerals are used to refer to like elements to omit the description, and a difference alone will be herein described. 
     The protection part  7  consists of two plate materials stacked between the ink passage part  4  and the nozzle plate  5 . The protection part  7  includes a second air chamber  71  and a second communicating hole  8 . 
     The second air chamber  71  is formed in a position opposing, in the stacking direction, the air chamber  43  of the ink supplying passage  41 . Also, the second communicating hole  8  is formed in a position opposing, in the stacking direction, the communicating hole  6  so as to extend in the secondary scanning direction. The second communicating hole  8  is formed for communicating the second air chamber  71  with the atmospheric air. 
     The second communicating hole  8  is constructed from through holes (long holes) formed in the two plate materials included in the protection part  7  in the same manner as the main section  63  of the communicating hole  6 . Specifically, a plurality of long holes  81  penetrating in the thickness direction are formed in each of the two plate materials so as to be arranged in a line at substantially equal intervals. The long holes  81  are formed in positions shifted in the lining direction so that one long hole  81  formed in one plate material can be communicated with another long hole  81  formed in the other plate material at the ends thereof when the plate materials are stacked. Also, the respective long holes  81  of the second communicating hole  8  are formed in positions shifted in the lining direction from the long holes  63   a  of the communicating hole  6  (main section  63 ). 
     In the fabrication of the ink-jet head  1 , the piezoelectric actuator  21 , the pressure chamber part  3  and the ink passage part  4  are jointed with one another, and the nozzle plate  5  is jointed to the resultant. Since spaces are formed by the communicating holes  6  within the ink passage part  4 , the strength is lowered in these spaces. 
     Therefore, the protection part  7  is disposed between the ink passage part  4  and the nozzle plate  5 . Thus, the communicating holes  6  (spaces) can be protected, so that the components can be easily dealt with in the fabrication of the ink-jet head  1 . 
     Furthermore, since the protection part  7  includes the second air chamber  71  and the second communicating hole  8 , when the nozzle plate  5  is jointed to the protection part  7 , the air expanding between the protection part  7  and the nozzle plate  5  can escape to the outside of the ink-jet head  1  through the second air chamber  71  and the second communicating hole  8 . Therefore, no void is formed in a joint layer between the protection part  7  and the nozzle plate  5 . As a result, the nozzles  51  of the nozzle plate  5  can be prevented from communicating with each other. 
     Moreover, in the fabrication of the ink-jet head  1 , the ink passage part  4  and the protection part  7  are stacked on and jointed with each other by heating these parts under a pressure applied in the stacking direction. At this point, if the long holes  63   a  of the communicating hole  6  (main section  63 ) are disposed in the same positions in the lining direction as the long holes  81  of the second communicating hole  8 , the space formed by each long hole  63   a  of the communicating hole  6  is adjacent to the space formed by each long hole  81  of the second communicating hole  8  in the stacking direction. Therefore, even when the pressure is applied in the stacking direction, it cannot be definitely transmitted in the stacking direction due to these spaces. As a result, a joint failure may be caused. 
     In contrast, when the long holes  81  of the second communicating hole  8  are shifted in the positions in the lining direction from the long holes  63   a  of the communicating hole  6  as in Embodiment 2, the space formed by each communicating hole  6  and the space formed by each second communicating hole  8  are never adjacent to each other in the stacking direction. Therefore, when the pressure is applied with these parts stacked, the pressure can be definitely transmitted in the stacking direction, so that the respective parts can be definitely jointed to each other. 
     The structures of the communicating hole  6  and the second communicating hole  8  are not limited to those described above. For example, each of the communicating hole  6  and the second communicating hole  8  can be formed in the structure described in any of Modifications 1 through 3 of Embodiment 1. 
     Furthermore, the communicating hole  6  and the second communicating hole  8  may be disposed, for example, in positions shifted from each other in a direction perpendicular to the stacking direction as shown in FIG.  16 . Thus, the space formed by the second communicating hole  8  and the space formed by the communicating hole  6  can be prevented from being adjacent to each other in the stacking direction. Therefore, the respective parts can be definitely jointed to each other in the fabrication of the ink-jet head  1 .